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+<div style='text-align:center; font-size:1.2em; font-weight:bold;'>The Project Gutenberg eBook of The Student&rsquo;s Elements of Geology, by Sir Charles Lyell</div>
+<div style='display:block; margin:1em 0'>
+This eBook is for the use of anyone anywhere in the United States and
+most other parts of the world at no cost and with almost no restrictions
+whatsoever. You may copy it, give it away or re-use it under the terms
+of the Project Gutenberg License included with this eBook or online
+at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you
+are not located in the United States, you will have to check the laws of the
+country where you are located before using this eBook.
+</div>
+<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: The Student&rsquo;s Elements of Geology</div>
+<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Sir Charles Lyell</div>
+<div style='display:block;margin:1em 0'>Release Date: August 29, 2001 [eBook #3772]<br />
+[Most recently updated: February 22, 2021]</div>
+<div style='display:block;margin:1em 0'>Language: English</div>
+<div style='display:block;margin:1em 0'>Character set encoding: UTF-8</div>
+<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Sue Asscher</div>
+<div style='margin-top:2em;margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE STUDENTS&rsquo;S ELEMENTS OF GEOLOGY  ***</div>
+
+<h1>The Student&rsquo;s Elements of Geology</h1>
+
+<h2>By S<small>IR</small> CHARLES LYELL, B<small>ART</small>., F.R.S.</h2>
+
+<h4>AUTHOR OF<br/>
+&ldquo;THE PRINCIPLES OF GEOLOGY,&rdquo; &ldquo;THE ANTIQUITY OF MAN,&rdquo; ETC.</h4>
+
+<div class="fig" style="width:100%;">
+<img src="images/title.jpg" width="172" height="154" alt="Thecosmilia
+annularis" />
+</div>
+
+<h4>WITH MORE THAN 600 ILLUSTRATIONS ON WOOD.</h4>
+
+<h4>
+NEW YORK<br/>
+HARPER &amp; BROTHERS, PUBLISHERS<br/>
+1878
+</h4>
+
+<div class="fig" style="width:100%;">
+<img src="images/frontispiece.jpg" width="269" height="437" alt="Tertiary or
+Cainozoic, Secondary or Mesozoic, Primary or Paleozoic" />
+</div>
+
+<hr />
+
+<h2>CONTENTS.</h2>
+
+<p>
+<a href="#pref01"><b>PREFACE</b></a>
+</p>
+
+<p>
+<a href="#chap01"><b>Chapter I</b>&mdash;ON THE DIFFERENT CLASSES OF
+ROCKS.</a><br/>
+Geology defined. &mdash; Successive Formation of the Earth&rsquo;s Crust.
+&mdash; Classification of Rocks according to their Origin and Age. &mdash;
+Aqueous Rocks. &mdash; Their Stratification and imbedded Fossils. &mdash;
+Volcanic Rocks, with and without Cones and Craters. &mdash; Plutonic Rocks, and
+their Relation to the Volcanic. &mdash; Metamorphic Rocks, and their probable
+Origin. &mdash; The term Primitive, why erroneously applied to the Crystalline
+Formations. &mdash; Leading Division of the Work.
+</p>
+
+<p>
+<a href="#chap02"><b>Chapter II</b>&mdash;AQUEOUS ROCKS&mdash;THEIR
+COMPOSITION AND FORMS OF STRATIFICATION.</a><br/>
+Mineral Composition of Strata. &mdash; Siliceous Rocks. &mdash; Argillaceous.
+&mdash; Calcareous. &mdash; Gypsum. &mdash; Forms of Stratification. &mdash;
+Original Horizontality. &mdash; Thinning out. &mdash; Diagonal Arrangement.
+&mdash; Ripple-mark.
+</p>
+
+<p>
+<a href="#chap03"><b>Chapter III</b>&mdash;ARRANGEMENT OF FOSSILS IN
+STRATA&mdash;FRESH-WATER AND MARINE.</a><br/>
+Successive Deposition indicated by Fossils. &mdash; Limestones formed of Corals
+and Shells. &mdash; Proofs of gradual Increase of Strata derived from Fossils.
+&mdash; Serpula attached to Spatangus. &mdash; Wood bored by Teredina. &mdash;
+Tripoli formed of Infusoria. &mdash; Chalk derived principally from Organic
+Bodies. &mdash; Distinction of Fresh-water from Marine Formations. &mdash;
+Genera of Fresh-water and Land Shells. &mdash; Rules for recognising Marine
+Testacea. &mdash; Gyrogonite and Chara. &mdash; Fresh-water Fishes. &mdash;
+Alternation of Marine and Fresh-water Deposits. &mdash; Lym-Fiord.
+</p>
+
+<p>
+<a href="#chap04"><b>Chapter IV</b>&mdash;CONSOLIDATION OF STRATA AND
+PETRIFACTION OF FOSSILS.</a><br/>
+Chemical and Mechanical Deposits. &mdash; Cementing together of Particles.
+&mdash; Hardening by Exposure to Air. &mdash; Concretionary Nodules. &mdash;
+Consolidating Effects of Pressure. &mdash; Mineralization of Organic Remains.
+&mdash; Impressions and Casts: how formed. &mdash; Fossil Wood. &mdash;
+Goppert&rsquo;s Experiments. &mdash; Precipitation of Stony Matter most rapid
+where Putrefaction is going on. &mdash; Sources of Lime and Silex in Solution.
+</p>
+
+<p>
+<a href="#chap05"><b>Chapter V</b>&mdash;ELEVATION OF STRATA ABOVE THE
+SEA.&mdash;HORIZONTAL AND INCLINED STRATIFICATION.</a><br/>
+Why the Position of Marine Strata, above the Level of the Sea, should be
+referred to the rising up of the Land, not to the going down of the Sea.
+&mdash; Strata of Deep-sea and Shallow-water Origin alternate. &mdash; Also
+Marine and Fresh-water Beds and old Land Surfaces. &mdash; Vertical, inclined,
+and folded Strata. &mdash; Anticlinal and Synclinal Curves. &mdash; Theories to
+explain Lateral Movements. &mdash; Creeps in Coal-mines. &mdash; Dip and
+Strike. &mdash; Structure of the Jura. &mdash; Various Forms of Outcrop.
+&mdash; Synclinal Strata forming Ridges. &mdash; Connection of Fracture and
+Flexure of Rocks. &mdash; Inverted Strata. &mdash; Faults described. &mdash;
+Superficial Signs of the same obliterated by Denudation. &mdash; Great Faults
+the Result of repeated Movements. &mdash; Arrangement and Direction of parallel
+Folds of Strata. &mdash; Unconformability. &mdash; Overlapping Strata.
+</p>
+
+<p>
+<a href="#chap06"><b>Chapter VI</b>&mdash;DENUDATION.</a><br/>
+Denudation defined. &mdash; Its Amount more than equal to the entire Mass of
+Stratified Deposits in the Earth&rsquo;s Crust. &mdash; subaërial Denudation.
+&mdash; Action of the Wind. &mdash; Action of Running Water. &mdash; Alluvium
+defined. &mdash; Different Ages of Alluvium. &mdash; Denuding Power of Rivers
+affected by Rise or Fall of Land. &mdash; Littoral Denudation. &mdash; Inland
+Sea-Cliffs. &mdash; Escarpments. &mdash; Submarine Denudation. &mdash;
+Dogger-bank. &mdash; Newfoundland Bank. &mdash; Denuding Power of the Ocean
+during Emergence of Land.
+</p>
+
+<p>
+<a href="#chap07"><b>Chapter VII</b>&mdash;JOINT ACTION OF DENUDATION,
+UPHEAVAL, AND SUBSIDENCE IN REMODELLING THE EARTH&rsquo;S CRUST.</a><br/>
+How we obtain an Insight at the Surface, of the Arrangement of Rocks at great
+Depths. &mdash; Why the Height of the successive Strata in a given Region is so
+disproportionate to their Thickness. &mdash; Computation of the average annual
+Amount of subaërial Denudation. &mdash; Antagonism of Volcanic Force to the
+Levelling Power of running Water. &mdash; How far the Transfer of Sediment from
+the Land to a neighbouring Sea-bottom may affect Subterranean Movements.
+&mdash; Permanence of Continental and Oceanic Areas.
+</p>
+
+<p>
+<a href="#chap08"><b>Chapter VIII</b>&mdash;CHRONOLOGICAL CLASSIFICATION
+OF ROCKS.</a><br/>
+Aqueous, Plutonic, volcanic, and metamorphic Rocks considered chronologically.
+&mdash; Terms Primary, Secondary, and Tertiary; Palæozoic, Mesozoic, and
+Cainozoic explained. &mdash; On the different Ages of the aqueous Rocks.
+&mdash; Three principal Tests of relative Age: Superposition, Mineral
+Character, and Fossils. &mdash; Change of Mineral Character and Fossils in the
+same continuous Formation. &mdash; Proofs that distinct Species of Animals and
+Plants have lived at successive Periods. &mdash; Distinct Provinces of
+indigenous Species. &mdash; Great Extent of single Provinces. &mdash; Similar
+Laws prevailed at successive Geological Periods. &mdash; Relative Importance of
+mineral and palæontological Characters. &mdash; Test of Age by included
+Fragments. &mdash; Frequent Absence of Strata of intervening Periods. &mdash;
+Tabular Views of fossiliferous Strata.
+</p>
+
+<p>
+<a href="#chap09"><b>Chapter IX</b>&mdash;CLASSIFICATION OF TERTIARY
+FORMATIONS.</a><br/>
+Order of Succession of Sedimentary Formations. &mdash; Frequent
+Unconformability of Strata. &mdash; Imperfection of the Record. &mdash;
+Defectiveness of the Monuments greater in Proportion to their Antiquity.
+&mdash; Reasons for studying the newer Groups first. &mdash; Nomenclature of
+Formations. &mdash; Detached Tertiary Formations scattered over Europe. &mdash;
+Value of the Shell-bearing Mollusca in Classification. &mdash; Classification
+of Tertiary Strata. &mdash; Eocene, Miocene, and Pliocene Terms explained.
+</p>
+
+<p>
+<a href="#chap10"><b>Chapter X</b>&mdash;RECENT AND POST-PLIOCENE
+PERIODS.</a><br/>
+Recent and Post-pliocene Periods. &mdash; Terms defined. &mdash; Formations of
+the Recent Period. &mdash; Modern littoral Deposits containing Works of Art
+near Naples. &mdash; Danish Peat and Shell-mounds. &mdash; Swiss
+Lake-dwellings. &mdash; Periods of Stone, Bronze, and Iron. &mdash;
+Post-pliocene Formations. &mdash; Coexistence of Man with extinct Mammalia.
+&mdash; Reindeer Period of South of France. &mdash; Alluvial Deposits of
+Paleolithic Age. &mdash; Higher and Lower-level Valley-gravels. &mdash; Loess
+or Inundation-mud of the Nile, Rhine, etc. &mdash; Origin of Caverns. &mdash;
+Remains of Man and extinct Quadrupeds in Cavern Deposits. &mdash; Cave of
+Kirkdale. &mdash; Australian Cave-breccias. &mdash; Geographical Relationship
+of the Provinces of living Vertebrata and those of extinct Post-pliocene
+Species. &mdash; Extinct struthious Birds of New Zealand. &mdash; Climate of
+the Post-pliocene Period. &mdash; Comparative Longevity of Species in the
+Mammalia and Testacea. &mdash; Teeth of Recent and Post-pliocene Mammalia.
+</p>
+
+<p>
+<a href="#chap11"><b>Chapter XI</b>&mdash;POST-PLIOCENE PERIOD,
+continued.&mdash;GLACIAL CONDITIONS.</a><br/>
+Geographical Distribution, Form, and Characters of Glacial Drift. &mdash;
+Fundamental Rocks, polished, grooved, and scratched. &mdash; Abrading and
+striating Action of Glaciers. &mdash; Moraines, Erratic Blocks, and
+&ldquo;Roches Moutonnees&rdquo;. &mdash; Alpine Blocks on the Jura. &mdash;
+Continental Ice of Greenland. &mdash; Ancient Centres of the Dispersion of
+Erratics. &mdash; Transportation of Drift by floating Icebergs. &mdash; Bed of
+the Sea furrowed and polished by the running aground of floating Ice-islands.
+</p>
+
+<p>
+<a href="#chap12"><b>Chapter XII</b>&mdash;POST-PLIOCENE PERIOD,
+continued.&mdash;GLACIAL CONDITIONS, concluded.</a><br/>
+Glaciation of Scandinavia and Russia. &mdash; Glaciation of Scotland. &mdash;
+Mammoth in Scotch Till. &mdash; Marine Shells in Scotch Glacial Drift. &mdash;
+Their Arctic Character. &mdash; Rarity of Organic Remains in Glacial Deposits.
+&mdash; Contorted Strata in Drift. &mdash; Glaciation of Wales, England, and
+Ireland. &mdash; Marine Shells of Moel Tryfaen. &mdash; Erratics near
+Chichester. &mdash; Glacial Formations of North America. &mdash; Many Species
+of Testacea and Quadrupeds survived the Glacial Cold. &mdash; Connection of the
+Predominance of Lakes with Glacial Action. &mdash; Action of Ice in preventing
+the silting up of Lake-basins. &mdash; Absence of Lakes in the Caucasus.
+&mdash; Equatorial Lakes of Africa.
+</p>
+
+<p>
+<a href="#chap13"><b>Chapter XIII</b>&mdash;PLIOCENE PERIOD.</a><br/>
+Glacial Formations of Pliocene Age. &mdash; Bridlington Beds. &mdash; Glacial
+Drifts of Ireland. &mdash; Drift of Norfolk Cliffs. &mdash; Cromer Forest-bed.
+&mdash; Aldeby and Chillesford Beds. &mdash; Norwich Crag. &mdash; Older
+Pliocene Strata. &mdash; Red Crag of Suffolk. &mdash; Coprolitic Bed of Red
+Crag. &mdash; White or Coralline Crag. &mdash; Relative Age, Origin, and
+Climate of the Crag Deposits. &mdash; Antwerp Crag. &mdash; Newer Pliocene
+Strata of Sicily. &mdash; Newer Pliocene Strata of the Upper Val d&rsquo;Arno.
+&mdash; Older Pliocene of Italy. &mdash; Subapennine Strata. &mdash; Older
+Pliocene Flora of Italy.
+</p>
+
+<p>
+<a href="#chap14"><b>Chapter XIV</b>&mdash;MIOCENE PERIOD.&mdash;UPPER
+MIOCENE.</a><br/>
+Upper Miocene Strata of France. &mdash; Faluns of Touraine. &mdash; Tropical
+Climate implied by Testacea. &mdash; Proportion of recent Species of Shells.
+&mdash; faluns more ancient than the Suffolk Crag. &mdash; Upper Miocene of
+Bordeaux and the South of France. &mdash; Upper Miocene of Oeningen, in
+Switzerland. &mdash; Plants of the Upper Fresh-water Molasse. &mdash; Fossil
+Fruit and Flowers as well as Leaves. &mdash; Insects of the Upper Molasse.
+&mdash; Middle or Marine Molasse of Switzerland. &mdash; Upper Miocene Beds of
+the Bolderberg, in Belgium. &mdash; Vienna Basin. &mdash; Upper Miocene of
+Italy and Greece. &mdash; Upper Miocene of India; Siwalik Hills. &mdash; Older
+Pliocene and Miocene of the United States.
+</p>
+
+<p>
+<a href="#chap15"><b>Chapter XV</b>&mdash;LOWER MIOCENE.</a><br/>
+Lower Miocene Strata of France. &mdash; Line between Miocene and Eocene.
+&mdash; Lacustrine Strata of Auvergne. &mdash; Fossil Mammalia of the Limagne
+d&rsquo;Auvergne. &mdash; Lower Molasse of Switzerland. &mdash; Dense
+Conglomerates and Proofs of Subsidence. &mdash; Flora of the Lower Molasse.
+&mdash; American Character of the Flora. &mdash; Theory of a Miocene Atlantis.
+&mdash; Lower Miocene of Belgium. &mdash; Rupelian Clay of Hermsdorf near
+Berlin. &mdash; Mayence Basin. &mdash; Lower Miocene of Croatia. &mdash;
+Oligocene Strata of Beyrich. &mdash; Lower Miocene of Italy. &mdash; Lower
+Miocene of England. &mdash; Hempstead Beds. &mdash; Bovey Tracey Lignites in
+Devonshire. &mdash; Isle of Mull Leaf-Beds. &mdash; Arctic Miocene Flora.
+&mdash; Disco Island. &mdash; Lower Miocene of United States. &mdash; Fossils
+of Nebraska.
+</p>
+
+<p>
+<a href="#chap16"><b>Chapter XVI</b>&mdash;EOCENE FORMATIONS.</a><br/>
+Eocene Areas of North of Europe. &mdash; Table of English and French Eocene
+Strata. &mdash; Upper Eocene of England. &mdash; Bembridge Beds. &mdash;
+Osborne or St. Helen&rsquo;s Beds. &mdash; Headon Series. &mdash; Fossils of
+the Barton Sands and Clays. &mdash; Middle Eocene of England. &mdash; Shells,
+Nummulites, Fish and Reptiles of the Bracklesham Beds and Bagshot Sands.
+&mdash; Plants of Alum Bay and Bournemouth. &mdash; Lower Eocene of England.
+&mdash; London Clay Fossils. &mdash; Woolwich and Reading Beds formerly called
+&ldquo;Plastic Clay&rdquo;. &mdash; Fluviatile Beds underlying Deep-sea Strata.
+&mdash; Thanet Sands. &mdash; Upper Eocene Strata of France. &mdash; Gypseous
+Series of Montmartre and Extinct Quadrupeds. &mdash; Fossil Footprints in Paris
+Gypsum. &mdash; Imperfection of the Record. &mdash; Calcaire Silicieux. &mdash;
+Gres de Beauchamp. &mdash; Calcaire Grossier. &mdash; Miliolite Limestone.
+&mdash; Soissonnais Sands. &mdash; Lower Eocene of France. &mdash; Nummulitic
+Formations of Europe, Africa, and Asia. &mdash; Eocene Strata in the United
+States. &mdash; Gigantic Cetacean.
+</p>
+
+<p>
+<a href="#chap17"><b>Chapter XVII</b>&mdash;UPPER CRETACEOUS
+GROUP.</a><br/>
+Lapse of Time between Cretaceous and Eocene Periods. &mdash; Table of
+successive Cretaceous Formations. &mdash; Maestricht Beds. &mdash; Pisolitic
+Limestone of France. &mdash; Chalk of Faxoe. &mdash; Geographical Extent and
+Origin of the White Chalk. &mdash; Chalky Matter now forming in the Bed of the
+Atlantic. &mdash; Marked Difference between the Cretaceous and existing Fauna.
+&mdash; Chalk-flints. &mdash; Pot-stones of Horstead. &mdash; Vitreous Sponges
+in the Chalk. &mdash; Isolated Blocks of Foreign Rocks in the White Chalk
+supposed to be ice-borne. &mdash; Distinctness of Mineral Character in
+contemporaneous Rocks of the Cretaceous Epoch. &mdash; Fossils of the White
+Chalk. &mdash; Lower White Chalk without Flints. &mdash; Chalk Marl and its
+Fossils. &mdash; Chloritic Series or Upper Greensand. &mdash; Coprolite Bed
+near Cambridge. &mdash; Fossils of the Chloritic Series. &mdash; Gault. &mdash;
+Connection between Upper and Lower Cretaceous Strata. &mdash; Blackdown Beds.
+&mdash; Flora of the Upper Cretaceous Period. &mdash; Hippurite Limestone.
+&mdash; Cretaceous Rocks in the United States.
+</p>
+
+<p>
+<a href="#chap18"><b>Chapter XVIII</b>&mdash;LOWER CRETACEOUS OR
+NEOCOMIAN FORMATION.</a><br/>
+Classification of marine and fresh-water Strata. &mdash; Upper Neocomian.
+&mdash; Folkestone and Hythe Beds. &mdash; Atherfield Clay. &mdash; Similarity
+of Conditions causing Reappearance of Species after short Intervals. &mdash;
+Upper Speeton Clay. &mdash; Middle Neocomian. &mdash; Tealby Series. &mdash;
+Middle Speeton Clay. &mdash; Lower Neocomian. &mdash; Lower Speeton Clay.
+&mdash; Wealden Formation. &mdash; Fresh-water Character of the Wealden.
+&mdash; Weald Clay. &mdash; Hastings Sands. &mdash; Punfield Beds of Purbeck,
+Dorsetshire. &mdash; Fossil Shells and Fish of the Wealden. &mdash; Area of the
+Wealden. &mdash; Flora of the Wealden.
+</p>
+
+<p>
+<a href="#chap19"><b>Chapter XIX</b>&mdash;JURASSIC GROUP.&mdash;PURBECK
+BEDS AND OOLITE.</a><br/>
+The Purbeck Beds a Member of the Jurassic Group. &mdash; Subdivisions of that
+Group. &mdash; Physical Geography of the Oolite in England and France. &mdash;
+Upper Oolite. &mdash; Purbeck Beds. &mdash; New Genera of fossil Mammalia in
+the Middle Purbeck of Dorsetshire. &mdash; Dirt-bed or ancient Soil. &mdash;
+Fossils of the Purbeck Beds. &mdash; Portland Stone and Fossils. &mdash;
+Kimmeridge Clay. &mdash; Lithographic Stone of Solenhofen. &mdash;
+Archæopteryx. &mdash; Middle Oolite. &mdash; Coral Rag. &mdash; Nerinæa
+Limestone. &mdash; Oxford Clay, Ammonites and Belemnites. &mdash; Kelloway
+Rock. &mdash; Lower, or Bath, Oolite. &mdash; Great Plants of the Oolite.
+&mdash; Oolite and Bradford Clay. &mdash; Stonesfield Slate. &mdash; Fossil
+Mammalia. &mdash; Fuller&rsquo;s Earth. &mdash; Inferior Oolite and Fossils.
+&mdash; Northamptonshire Slates. &mdash; Yorkshire Oolitic Coal-field. &mdash;
+Brora Coal. &mdash; Palæontological Relations of the several Subdivisions of
+the Oolitic group.
+</p>
+
+<p>
+<a href="#chap20"><b>Chapter XX</b>&mdash;JURASSIC GROUP,
+CONTINUED.&mdash;LIAS.</a><br/>
+Mineral Character of Lias. &mdash; Numerous successive Zones in the Lias,
+marked by distinct Fossils, without Unconformity in the Stratification, or
+Change in the Mineral Character of the Deposits. &mdash; Gryphite Limestone.
+&mdash; Shells of the Lias. &mdash; Fish of the Lias. &mdash; Reptiles of the
+Lias. &mdash; Ichthyosaur and Plesiosaur. &mdash; Marine Reptile of the
+Galapagos Islands. &mdash; Sudden Destruction and Burial of Fossil Animals in
+Lias. &mdash; Fluvio-marine Beds in Gloucestershire, and Insect Limestone.
+&mdash; Fossil Plants. &mdash; The origin of the Oolite and Lias, and of
+alternating Calcareous and Argillaceous Formations.
+</p>
+
+<p>
+<a href="#chap21"><b>Chapter XXI</b>&mdash;TRIAS, OR NEW RED SANDSTONE
+GROUP.</a><br/>
+Beds of Passage between the Lias and Trias, Rhætic Beds. &mdash; Triassic
+Mammifer. &mdash; Triple Division of the Trias. &mdash; Keuper, or Upper Trias
+of England. &mdash; Reptiles of the Upper Trias. &mdash; Foot-prints in the
+Bunter formation in England. &mdash; Dolomitic Conglomerate of Bristol. &mdash;
+Origin of Red Sandstone and Rock-salt. &mdash; Precipitation of Salt from
+inland Lakes and Lagoons. &mdash; Trias of Germany. &mdash; Keuper. &mdash; St.
+Cassian and Hallstadt Beds. &mdash; Peculiarity of their Fauna. &mdash;
+Muschelkalk and its Fossils. &mdash; Trias of the United States. &mdash; Fossil
+Foot-prints of Birds and Reptiles in the Valley of the Connecticut. &mdash;
+Triassic Mammifer of North Carolina. &mdash; Triassic Coal-field of Richmond,
+Virginia. &mdash; Low Grade of early Mammals favourable to the Theory of
+Progressive Development.
+</p>
+
+<p>
+<a href="#chap22"><b>Chapter XXII</b>&mdash;PERMIAN OR MAGNESIAN
+LIMESTONE GROUP.</a><br/>
+Line of Separation between Mesozoic and Palæozoic Rocks. &mdash;
+Distinctness of Triassic and Permian Fossils. &mdash; Term Permian. &mdash;
+Thickness of calcareous and sedimentary Rocks in North of England. &mdash;
+Upper, Middle, and Lower Permian. &mdash; Marine Shells and Corals of the
+English Magnesian Limestone. &mdash; Reptiles and Fish of Permian Marl-slate.
+&mdash; Foot-prints of Reptiles. &mdash; Angular Breccias in Lower Permian.
+&mdash; Permian Rocks of the Continent. &mdash; Zechstein and Rothliegendes of
+Thuringia. &mdash; Permian Flora. &mdash; Its generic Affinity to the
+Carboniferous.
+</p>
+
+<p>
+<a href="#chap23"><b>Chapter XXIII</b>&mdash;THE COAL OR CARBONIFEROUS
+GROUP.</a><br/>
+Principal Subdivisions of the Carboniferous Group. &mdash; Different Thickness
+of the sedimentary and calcareous Members in Scotland and the South of England.
+&mdash; Coal-measures. &mdash; Terrestrial Nature of the Growth of Coal.
+&mdash; Erect fossil Trees. &mdash; Uniting of many Coal-seams into one thick
+Bed. &mdash; Purity of the Coal explained. &mdash; Conversion of Coal into
+Anthracite. &mdash; Origin of Clay-ironstone. &mdash; Marine and brackish-water
+Strata in Coal. &mdash; Fossil Insects. &mdash; Batrachian Reptiles. &mdash;
+Labyrinthodont Foot-prints in Coal-measures. &mdash; Nova Scotia Coal-measures
+with successive Growths of erect fossil Trees. &mdash; Similarity of American
+and European Coal. &mdash; Air-breathers of the American Coal. &mdash; Changes
+of Condition of Land and Sea indicated by the Carboniferous Strata of Nova
+Scotia.
+</p>
+
+<p>
+<a href="#chap24"><b>Chapter XXIV</b>&mdash;FLORA AND FAUNA OF THE
+CARBONIFEROUS PERIOD.</a><br/>
+Vegetation of the Coal Period. &mdash; Ferns, Lycopodiaceæ,
+Equisetaceæ, Sigillariæ, Stigmariæ, Coniferæ. &mdash;
+Angiosperms. &mdash; Climate of the Coal Period. &mdash; Mountain Limestone.
+&mdash; Marine Fauna of the Carboniferous Period. &mdash; Corals. &mdash;
+Bryozoa, Crinoidea. &mdash; Mollusca. &mdash; Great Number of fossil Fish.
+&mdash; Foraminifera.
+</p>
+
+<p>
+<a href="#chap25"><b>Chapter XXV</b>&mdash;DEVONIAN OR OLD RED SANDSTONE
+GROUP.</a><br/>
+Classification of the Old Red Sandstone in Scotland and in Devonshire. &mdash;
+Upper Old Red Sandstone in Scotland, with Fish and Plants. &mdash; Middle Old
+Red Sandstone. &mdash; Classification of the Ichthyolites of the Old Red, and
+their Relation to Living Types. &mdash; Lower Old Red Sandstone, with
+Cephalaspis and Pterygotus. &mdash; Marine or Devonian Type of Old Red
+Sandstone. &mdash; Table of Devonian Series. &mdash; Upper Devonian Rocks and
+Fossils. &mdash; Middle. &mdash; Lower. &mdash; Eifel Limestone of Germany.
+&mdash; Devonian of Russia. &mdash; Devonian Strata of the United States and
+Canada. &mdash; Devonian Plants and Insects of Canada.
+</p>
+
+<p>
+<a href="#chap26"><b>Chapter XXVI</b>&mdash;SILURIAN GROUP.</a><br/>
+Classification of the Silurian Rocks. &mdash; Ludlow Formation and Fossils.
+&mdash; Bone-bed of the Upper Ludlow. &mdash; Lower Ludlow Shales with
+Pentamerus. &mdash; Oldest known Remains of fossil Fish. &mdash; Table of the
+progressive Discovery of Vertebrata in older Rocks. &mdash; Wenlock Formation,
+Corals, Cystideans and Trilobites. &mdash; Llandovery Group or Beds of Passage.
+&mdash; Lower Silurian Rocks. &mdash; Caradoc and Bala Beds. &mdash;
+Brachiopoda. &mdash; Trilobites. &mdash; Cystideæ. &mdash; Graptolites.
+&mdash; Llandeilo Flags. &mdash; Arenig or Stiper-stones Group. &mdash; Foreign
+Silurian Equivalents in Europe. &mdash; Silurian Strata of the United States.
+&mdash; Canadian Equivalents. &mdash; Amount of specific Agreement of Fossils
+with those of Europe.
+</p>
+
+<p>
+<a href="#chap27"><b>Chapter XXVII</b>&mdash;CAMBRIAN AND LAURENTIAN
+GROUPS.</a><br/>
+Classification of the Cambrian Group, and its Equivalent in Bohemia. &mdash;
+Upper Cambrian Rocks. &mdash; Tremadoc Slates and their Fossils. &mdash;
+Lingula Flags. &mdash; Lower Cambrian Rocks. &mdash; Menevian Beds. &mdash;
+Longmynd Group. &mdash; Harlech Grits with large Trilobites. &mdash; Llanberis
+Slates. &mdash; Cambrian Rocks of Bohemia. &mdash; Primordial Zone of Barrande.
+&mdash; Metamorphosis of Trilobites. &mdash; Cambrian Rocks of Sweden and
+Norway. &mdash; Cambrian Rocks of the United States and Canada. &mdash; Potsdam
+Sandstone. &mdash; Huronian Series. &mdash; Laurentian Group, upper and lower.
+&mdash; Eozoon Canadense, oldest known Fossil. &mdash; Fundamental Gneiss of
+Scotland.
+</p>
+
+<p>
+<a href="#chap28"><b>Chapter XXVIII</b>&mdash;VOLCANIC ROCKS.</a><br/>
+External Form, Structure, and Origin of Volcanic Mountains. &mdash; Cones and
+Craters. &mdash; Hypothesis of &ldquo;Elevation Craters&rdquo; considered.
+&mdash; Trap Rocks. &mdash; Name whence derived. &mdash; Minerals most abundant
+in Volcanic Rocks. &mdash; Table of the Analysis of Minerals in the Volcanic
+and Hypogene Rocks. &mdash; Similar Minerals in Meteorites. &mdash; Theory of
+Isomorphism. &mdash; Basaltic Rocks. &mdash; Trachytic Rocks. &mdash; Special
+Forms of Structure. &mdash; The columnar and globular Forms. &mdash; Trap Dikes
+and Veins. &mdash; Alteration of Rocks by volcanic Dikes. &mdash; Conversion of
+Chalk into Marble. &mdash; Intrusion of Trap between Strata. &mdash; Relation
+of trappean Rocks to the Products of active Volcanoes.
+</p>
+
+<p>
+<a href="#chap29"><b>Chapter XXIX</b>&mdash;ON THE AGES OF VOLCANIC
+ROCKS.</a><br/>
+Tests of relative Age of Volcanic Rocks. &mdash; Why ancient and modern Rocks
+cannot be identical. &mdash; Tests by Superposition and intrusion. &mdash;
+Test by Alteration of Rocks in Contact. &mdash; Test by Organic Remains.
+&mdash; Test of Age by Mineral Character. &mdash; Test by Included Fragments.
+&mdash; Recent and Post-pliocene volcanic Rocks. &mdash; Vesuvius, Auvergne,
+Puy de Come, and Puy de Pariou. &mdash; Newer Pliocene volcanic Rocks. &mdash;
+Cyclopean Isles, Etna, Dikes of Palagonia, Madeira. &mdash; Older Pliocene
+volcanic Rocks. &mdash; Italy. &mdash; Pliocene Volcanoes of the Eifel. &mdash;
+Trass.
+</p>
+
+<p>
+<a href="#chap30"><b>Chapter XXX</b>&mdash;AGE OF VOLCANIC
+ROCKS&mdash;CONTINUED.</a><br/>
+Volcanic Rocks of the Upper Miocene Period. &mdash; Madeira. &mdash; Grand
+Canary. &mdash; Azores. &mdash; Lower Miocene Volcanic Rocks. &mdash; Isle of
+Mull. &mdash; Staffa and Antrim. &mdash; The Eifel. &mdash; Upper and Lower
+Miocene Volcanic Rocks of Auvergne. &mdash; Hill of Gergovia. &mdash; Eocene
+Volcanic Rocks of Monte Bolca. &mdash; Trap of Cretaceous Period. &mdash;
+Oolitic Period. &mdash; Triassic Period. &mdash; Permian Period. &mdash;
+Carboniferous Period. &mdash; Erect Trees buried in Volcanic Ash in the Island
+of Arran. &mdash; Old Red Sandstone Period. &mdash; Silurian Period. &mdash;
+Cambrian Period. &mdash; Laurentian Volcanic Rocks.
+</p>
+
+<p>
+<a href="#chap31"><b>Chapter XXXI</b>&mdash;PLUTONIC ROCKS.</a><br/>
+General Aspect of Plutonic Rocks. &mdash; Granite and its Varieties. &mdash;
+Decomposing into Spherical Masses. &mdash; Rude columnar Structure. &mdash;
+Graphic Granite. &mdash; Mutual Penetration of Crystals of Quartz and Feldspar.
+&mdash; Glass Cavities in Quartz of Granite. &mdash; Porphyritic, talcose, and
+syenitic Granite. &mdash; Schorlrock and Eurite. &mdash; Syenite. &mdash;
+Connection of the Granites and Syenites with the Volcanic Rocks. &mdash;
+Analogy in Composition of Trachyte and Granite. &mdash; Granite Veins in Glen
+Tilt, Cape of Good Hope, and Cornwall. &mdash; Metalliferous Veins in Strata
+near their Junction with Granite. &mdash; Quartz Veins. &mdash; Exposure of
+Plutonic Rocks at the surface due to Denudation.
+</p>
+
+<p>
+<a href="#chap32"><b>Chapter XXXII</b>&mdash;ON THE DIFFERENT AGES OF THE
+PLUTONIC ROCKS.</a><br/>
+Difficulty in ascertaining the precise Age of a Plutonic Rock. &mdash; Test of
+Age by Relative Position. &mdash; Test by Intrusion and Alteration. &mdash;
+Test by Mineral Composition. &mdash; Test by included Fragments. &mdash; Recent
+and Pliocene Plutonic Rocks, why invisible. &mdash; Miocene Syenite of the Isle
+of Skye. &mdash; Eocene Plutonic Rocks in the Andes. &mdash; Granite altering
+Cretaceous Rocks. &mdash; Granite altering Lias in the Alps and in Skye.
+&mdash; Granite of Dartmoor altering Carboniferous Strata. &mdash; Granite of
+the Old Red Sandstone Period. &mdash; Syenite altering Silurian Strata in
+Norway. &mdash; Blending of the same with Gneiss. &mdash; Most ancient Plutonic
+Rocks. &mdash; Granite protruded in a solid Form.
+</p>
+
+<p>
+<a href="#chap33"><b>Chapter XXXIII</b>&mdash;METAMORPHIC ROCKS.</a><br/>
+General Character of Metamorphic Rocks. &mdash; Gneiss. &mdash;
+Hornblende-schist. &mdash; Serpentine. &mdash; Mica-schist. &mdash; Clay-slate.
+&mdash; Quartzite. &mdash; Chlorite-schist. &mdash; Metamorphic Limestone.
+&mdash; Origin of the metamorphic Strata. &mdash; Their Stratification. &mdash;
+Fossiliferous Strata near intrusive Masses of Granite converted into Rocks
+identical with different Members of the metamorphic Series. &mdash; Arguments
+hence derived as to the Nature of Plutonic Action. &mdash; Hydrothermal Action,
+or the Influence of Steam and Gases in producing Metamorphism. &mdash;
+Objections to the metamorphic Theory considered.
+</p>
+
+<p>
+<a href="#chap34"><b>Chapter XXXIV</b>&mdash;METAMORPHIC
+ROCKS&mdash;continued.</a><br/>
+Definition of slaty Cleavage and Joints. &mdash; Supposed Causes of these
+Structures. &mdash; Crystalline Theory of Cleavage. &mdash; Mechanical Theory
+of Cleavage. &mdash; Condensation and Elongation of slate Rocks by lateral
+Pressure. &mdash; Lamination of some volcanic Rocks due to Motion. &mdash;
+Whether the Foliation of the crystalline Schists be usually parallel with the
+original Planes of Stratification. &mdash; Examples in Norway and Scotland.
+&mdash; Causes of Irregularity in the Planes of Foliation.
+</p>
+
+<p>
+<a href="#chap35"><b>Chapter XXXV</b>&mdash;ON THE DIFFERENT AGES OF THE
+METAMORPHIC ROCKS.</a><br/>
+Difficulty of ascertaining the Age of metamorphic Strata. &mdash; Metamorphic
+Strata of Eocene date in the Alps of Switzerland and Savoy. &mdash; Limestone
+and Shale of Carrara. &mdash; Metamorphic Strata of older date than the
+Silurian and Cambrian Rocks. &mdash; Order of Succession in metamorphic Rocks.
+&mdash; Uniformity of mineral Character. &mdash; Supposed Azoic Period. &mdash;
+Connection between the Absence of Organic Remains and the Scarcity of
+calcareous Matter in metamorphic Rocks.
+</p>
+
+<p>
+<a href="#chap36"><b>Chapter XXXVI</b>&mdash;MINERAL VEINS.</a><br/>
+Different Kinds of mineral Veins. &mdash; Ordinary metalliferous Veins or
+Lodes. &mdash; Their frequent Coincidence with Faults. &mdash; Proofs that they
+originated in Fissures in solid Rock. &mdash; Veins shifting other Veins.
+&mdash; Polishing of their Walls or &ldquo;Slicken sides&rdquo;. &mdash; Shells
+and Pebbles in Lodes. &mdash; Evidence of the successive Enlargement and
+Reopening of veins. &mdash; Examples in Cornwall and in Auvergne. &mdash;
+Dimensions of Veins. &mdash; Why some alternately swell out and contract.
+&mdash; Filling of Lodes by Sublimation from below. &mdash; Supposed relative
+Age of the precious Metals. &mdash; Copper and lead Veins in Ireland older than
+Cornish Tin. &mdash; Lead Vein in Lias, Glamorganshire. &mdash; Gold in Russia,
+California, and Australia. &mdash; Connection of hot Springs and mineral Veins.
+</p>
+
+<p>
+<a href="#chap37"><b>INDEX</b></a>
+</p>
+
+<hr />
+
+<div class="chapter">
+
+<h2><a name="pref01"></a><a name="pagexiii"></a>PREFACE.</h2>
+
+<p>
+T<small>HE LAST</small> or sixth <small>EDITION</small> of my &ldquo;Elements
+of Geology&rdquo; was already out of print before the end of 1868, in which
+year I brought out the tenth edition of my &ldquo;Principles of Geology.&rdquo;
+</p>
+
+<p>
+In writing the last-mentioned work I had been called upon to pass in review
+almost all the leading points of speculation and controversy to which the rapid
+advance of the science had given rise, and when I proposed to bring out a new
+edition of the &ldquo;Elements&rdquo; I was strongly urged by my friends not to
+repeat these theoretical discussions, but to confine myself in the new treatise
+to those parts of the &ldquo;Elements&rdquo; which were most indispensable to a
+beginner. This was to revert, to a certain extent, to the original plan of the
+first edition; but I found, after omitting a great number of subjects, that the
+necessity of bringing up to the day those which remained, and adverting,
+however briefly, to new discoveries, made it most difficult to confine the
+proposed abridgment within moderate limits. Some chapters had to be entirely
+recast, some additional illustrations to be introduced, and figures of some
+organic remains to be replaced by new ones from specimens more perfect than
+those which had been at my command on former occasions. By these changes the
+work assumed a form so different from the sixth edition of the
+&ldquo;Elements,&rdquo; that I resolved to give it a new title and call it the
+&ldquo;Student&rsquo;s Elements of Geology.&rdquo;
+</p>
+
+<p>
+In executing this task I have found it very difficult to meet the requirements
+of those who are entirely ignorant of the science. It is only the adept who has
+already overcome<a name="pagexiv"></a> the first steps as an observer, and is
+familiar with many of the technical terms, who can profit by a brief and
+concise manual. Beginners wish for a short and cheap book in which they may
+find a full explanation of the leading facts and principles of Geology. Their
+wants, I fear, somewhat resemble those of the old woman in New England, who
+asked a bookseller to supply her with &ldquo;the cheapest Bible in the largest
+possible print.&rdquo;
+</p>
+
+<p>But notwithstanding the difficulty of reconciling brevity with
+the copiousness of illustration demanded by those who have not yet
+mastered the rudiments of the science, I have endeavoured to
+abridge the work in the manner above hinted at, so as to place it
+within the reach of many to whom it was before inaccessible.</p>
+
+<p class="right">
+C<small>HARLES</small> L<small>YELL</small>.
+</p>
+
+<p>
+73 H<small>ARLEY</small> S<small>TREET</small>, L<small>ONDON</small>,<br/>
+<i>December</i>, 1870.
+</p>
+
+<hr />
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap01"></a><a name="page25"></a>CHAPTER I.<br/>
+ON THE DIFFERENT CLASSES OF ROCKS.</h2>
+
+<p class="letter">Geology defined. &mdash; Successive Formation of
+the Earth&rsquo;s Crust. &mdash; Classification of Rocks according to
+their Origin and Age. &mdash; Aqueous Rocks. &mdash; Their
+Stratification and imbedded Fossils. &mdash; Volcanic Rocks, with
+and without Cones and Craters. &mdash; Plutonic Rocks, and their
+Relation to the Volcanic. &mdash; Metamorphic Rocks, and their
+probable Origin. &mdash; The term Primitive, why erroneously
+applied to the Crystalline Formations. &mdash; Leading Division of
+the Work.</p>
+
+<p>Of what materials is the earth composed, and in what manner are
+these materials arranged? These are the first inquiries with which
+Geology is occupied, a science which derives its name from the
+Greek <i>ge</i>, the earth, and <i>logos</i>, a discourse.
+Previously to experience we might have imagined that investigations
+of this kind would relate exclusively to the mineral kingdom, and
+to the various rocks, soils, and metals, which occur upon the
+surface of the earth, or at various depths beneath it. But, in
+pursuing such researches, we soon find ourselves led on to consider
+the successive changes which have taken place in the former state
+of the earth&rsquo;s surface and interior, and the causes which have
+given rise to these changes; and, what is still more singular and
+unexpected, we soon become engaged in researches into the history
+of the animate creation, or of the various tribes of animals and
+plants which have, at different periods of the past, inhabited the
+globe.</p>
+
+<p>All are aware that the solid parts of the earth consist of
+distinct substances, such as clay, chalk, sand, limestone, coal,
+slate, granite, and the like; but previously to observation it is
+commonly imagined that all these had remained from the first in the
+state in which we now see them&mdash;that they were created in
+their present form, and in their present position. The geologist
+soon comes to a different conclusion, discovering<a name="page26"></a>
+proofs that the external parts of the earth were not all
+produced in the beginning of things in the state in which we now
+behold them, nor in an instant of time. On the contrary, he can
+show that they have acquired their actual configuration and
+condition gradually, under a great variety of circumstances, and at
+successive periods, during each of which distinct races of living
+beings have flourished on the land and in the waters, the remains
+of these creatures still lying buried in the crust of the
+earth.</p>
+
+<p>By the &ldquo;earth&rsquo;s crust,&rdquo; is meant that small portion of the
+exterior of our planet which is accessible to human observation. It
+comprises not merely all of which the structure is laid open in
+mountain precipices, or in cliffs overhanging a river or the sea,
+or whatever the miner may reveal in artificial excavations; but the
+whole of that outer covering of the planet on which we are enabled
+to reason by observations made at or near the surface. These
+reasonings may extend to a depth of several miles, perhaps ten
+miles; and even then it may be said, that such a thickness is no
+more than 1/400 part of the distance from the surface to the
+centre. The remark is just: but although the dimensions of such a
+crust are, in truth, insignificant when compared to the entire
+globe, yet they are vast, and of magnificent extent in relation to
+man, and to the organic beings which people our globe. Referring to
+this standard of magnitude, the geologist may admire the ample
+limits of his domain, and admit, at the same time, that not only
+the exterior of the planet, but the entire earth, is but an atom in
+the midst of the countless worlds surveyed by the astronomer.</p>
+
+<p>The materials of this crust are not thrown together confusedly;
+but distinct mineral masses, called rocks, are found to occupy
+definite spaces, and to exhibit a certain order of arrangement. The
+term <i>rock</i> is applied indifferently by geologists to all
+these substances, whether they be soft or stony, for clay and sand
+are included in the term, and some have even brought peat under
+this denomination. Our old writers endeavoured to avoid offering
+such violence to our language, by speaking of the component
+materials of the earth as consisting of rocks and <i>soils.</i> But
+there is often so insensible a passage from a soft and incoherent
+state to that of stone, that geologists of all countries have found
+it indispensable to have one technical term to include both, and in
+this sense we find <i>roche</i> applied in French, <i>rocca</i> in
+Italian, and <i>felsart</i> in German. The beginner, however, must
+constantly bear in mind that the term rock by no means implies that
+a mineral mass is in an indurated or stony condition.<a name="page27"></a></p>
+
+<p>The most natural and convenient mode of classifying the various
+rocks which compose the earth&rsquo;s crust, is to refer, in the first
+place, to their origin, and in the second to their relative age. I
+shall therefore begin by endeavouring briefly to explain to the
+student how all rocks may be divided into four great classes by
+reference to their different origin, or, in other words, by
+reference to the different circumstances and causes by which they
+have been produced.</p>
+
+<p>The first two divisions, which will at once be understood as
+natural, are the aqueous and volcanic, or the products of watery
+and those of igneous action at or near the surface.</p>
+
+<p><b>Aqueous Rocks.</b>&mdash;The aqueous rocks, sometimes called
+the sedimentary, or fossiliferous, cover a larger part of the
+earth&rsquo;s surface than any others. They consist chiefly of mechanical
+deposits (pebbles, sand, and mud), but are partly of chemical and
+some of them of organic origin, especially the limestones. These
+rocks are <i>stratified,</i> or divided into distinct layers, or
+strata. The term <i>stratum</i> means simply a bed, or any thing
+spread out or <i>strewed</i> over a given surface; and we infer
+that these strata have been generally spread out by the action of
+water, from what we daily see taking place near the mouths of
+rivers, or on the land during temporary inundations. For, whenever
+a running stream charged with mud or sand, has its velocity
+checked, as when it enters a lake or sea, or overflows a plain, the
+sediment, previously held in suspension by the motion of the water,
+sinks, by its own gravity to the bottom. In this manner layers of
+mud and sand are thrown down one upon another.</p>
+
+<p>If we drain a lake which has been fed by a small stream, we
+frequently find at the bottom a series of deposits, disposed with
+considerable regularity, one above the other; the uppermost,
+perhaps, may be a stratum of peat, next below a more dense and
+solid variety of the same material; still lower a bed of
+shell-marl, alternating with peat or sand, and then other beds of
+marl, divided by layers of clay. Now, if a second pit be sunk
+through the same continuous lacustrine <i>formation</i> at some
+distance from the first, nearly the same series of beds is commonly
+met with, yet with slight variations; some, for example, of the
+layers of sand, clay, or marl, may be wanting, one or more of them
+having thinned out and given place to others, or sometimes one of
+the masses first examined is observed to increase in thickness to
+the exclusion of other beds.</p>
+
+<p>The term <i>formation,</i> which I have used in the above
+explanation, expresses in geology any assemblage of rocks which
+have some character in common, whether of origin,<a name="page28"></a>
+age, or composition. Thus we speak of stratified and
+unstratified, fresh-water and marine, aqueous and volcanic, ancient
+and modern, metalliferous and non-metalliferous formations.</p>
+
+<p>In the estuaries of large rivers, such as the Ganges and the
+Mississippi, we may observe, at low water, phenomena analogous to
+those of the drained lakes above mentioned, but on a grander scale,
+and extending over areas several hundred miles in length and
+breadth. When the periodical inundations subside, the river hollows
+out a channel to the depth of many yards through horizontal beds of
+clay and sand, the ends of which are seen exposed in perpendicular
+cliffs. These beds vary in their mineral composition, or colour, or
+in the fineness or coarseness of their particles, and some of them
+are occasionally characterised by containing drift-wood. At the
+junction of the river and the sea, especially in lagoons nearly
+separated by sand-bars from the ocean, deposits are often formed in
+which brackish and salt-water shells are included.</p>
+
+<p>In Egypt, where the Nile is always adding to its delta by
+filling up part of the Mediterranean with mud, the newly deposited
+sediment is <i>stratified,</i> the thin layer thrown down in one
+season differing slightly in colour from that of a previous year,
+and being separable from it, as has been observed in excavations at
+Cairo and other places.<a href="#fn-1.1" name="fnref-1.1" id="fnref-1.1"><sup>[1]</sup></a></p>
+
+
+<p>When beds of sand, clay, and marl, containing shells and
+vegetable matter, are found arranged in a similar manner in the
+interior of the earth, we ascribe to them a similar origin; and the
+more we examine their characters in minute detail, the more exact
+do we find the resemblance. Thus, for example, at various heights
+and depths in the earth, and often far from seas, lakes, and
+rivers, we meet with layers of rounded pebbles composed of flint,
+limestone, granite, or other rocks, resembling the shingles of a
+sea-beach or the gravel in a torrent&rsquo;s bed. Such layers of pebbles
+frequently alternate with others formed of sand or fine sediment,
+just as we may see in the channel of a river descending from hills
+bordering a coast, where the current sweeps down at one season
+coarse sand and gravel, while at another, when the waters are low
+and less rapid, fine mud and sand alone are carried
+seaward.<a href="#fn-1.2" name="fnref-1.2" id="fnref-1.2"><sup>[2]</sup></a></p>
+
+<p>If a stratified arrangement, and the rounded form of pebbles,
+are alone sufficient to lead us to the conclusion that certain
+rocks originated under water, this opinion is farther confirmed by
+the distinct and independent evidence of<a name="page29"></a>
+<i>fossils,</i> so abundantly included in the earth&rsquo;s crust. By
+a <i>fossil</i> is meant any body, or the traces of the existence
+of any body, whether animal or vegetable, which has been buried in
+the earth by natural causes. Now the remains of animals, especially
+of aquatic species, are found almost everywhere imbedded in
+stratified rocks, and sometimes, in the case of limestone, they are
+in such abundance as to constitute the entire mass of the rock
+itself. Shells and corals are the most frequent, and with them are
+often associated the bones and teeth of fishes, fragments of wood,
+impressions of leaves, and other organic substances. Fossil shells,
+of forms such as now abound in the sea, are met with far inland,
+both near the surface, and at great depths below it. They occur at
+all heights above the level of the ocean, having been observed at
+elevations of more than 8000 feet in the Pyrenees, 10,000 in the
+Alps, 13,000 in the Andes, and above 18,000 feet in the
+Himalaya.<a href="#fn-1.3" name="fnref-1.3" id="fnref-1.3"><sup>[3]</sup></a></p>
+
+<p>These shells belong mostly to marine testacea, but in some
+places exclusively to forms characteristic of lakes and rivers.
+Hence it is concluded that some ancient strata were deposited at
+the bottom of the sea, and others in lakes and estuaries.</p>
+
+<p>We have now pointed out one great class of rocks, which, however
+they may vary in mineral composition, colour, grain, or other
+characters, external and internal, may nevertheless be grouped
+together as having a common origin. They have all been formed under
+water, in the same manner as modern accumulations of sand, mud,
+shingle, banks of shells, reefs of coral, and the like, and are all
+characterised by stratification or fossils, or by both.</p>
+
+<p><b>Volcanic Rocks.</b>&mdash;The division of rocks which we may
+next consider are the volcanic, or those which have been produced
+at or near the surface whether in ancient or modern times, not by
+water, but by the action of fire or subterranean heat. These rocks
+are for the most part unstratified, and are devoid of fossils. They
+are more partially distributed than aqueous formations, at least in
+respect to horizontal extension. Among those parts of Europe where
+they exhibit characters not to be mistaken, I may mention not only
+Sicily and the country round Naples, but Auvergne, Velay, and
+Vivarais, now the departments of Puy de Dome, Haute Loire, and
+Ardêche, towards the centre and south of France, in which are
+several hundred conical hills having the forms of modern volcanoes,
+with craters more or less perfect on many of their summits. These
+cones are composed moreover<a name="page30"></a>
+of lava, sand, and ashes, similar to those of active volcanoes.
+Streams of lava may sometimes be traced from the cones into the
+adjoining valleys, where they have choked up the ancient channels
+of rivers with solid rock, in the same manner as some modern flows
+of lava in Iceland have been known to do, the rivers either flowing
+beneath or cutting out a narrow passage on one side of the lava.
+Although none of these French volcanoes have been in activity
+within the period of history or tradition, their forms are often
+very perfect. Some, however, have been compared to the mere
+skeletons of volcanoes, the rains and torrents having washed their
+sides, and removed all the loose sand and scoriæ, leaving
+only the harder and more solid materials. By this erosion, and by
+earthquakes, their internal structure has occasionally been laid
+open to view, in fissures and ravines; and we then behold not only
+many successive beds and masses of porous lava, sand, and
+scoriæ, but also perpendicular walls, or <i>dikes,</i> as
+they are called, of volcanic rock, which have burst through the
+other materials. Such dikes are also observed in the structure of
+Vesuvius, Etna, and other active volcanoes. They have been formed
+by the pouring of melted matter, whether from above or below, into
+open fissures, and they commonly traverse deposits of <i>volcanic
+tuff,</i> a substance produced by the showering down from the air,
+or incumbent waters, of sand and cinders, first shot up from the
+interior of the earth by the explosions of volcanic gases.</p>
+
+<p>Besides the parts of France above alluded to, there are other
+countries, as the north of Spain, the south of Sicily, the Tuscan
+territory of Italy, the lower Rhenish provinces, and Hungary, where
+spent volcanoes may be seen, still preserving in many cases a
+conical form, and having craters and often lava-streams connected
+with them.</p>
+
+<p>There are also other rocks in England, Scotland, Ireland, and
+almost every country in Europe, which we infer to be of igneous
+origin, although they do not form hills with cones and craters.
+Thus, for example, we feel assured that the rock of Staffa, and
+that of the Giant&rsquo;s Causeway, called basalt, is volcanic, because
+it agrees in its columnar structure and mineral composition with
+streams of lava which we know to have flowed from the craters of
+volcanoes. We find also similar basaltic and other igneous rocks
+associated with beds of <i>tuff</i> in various parts of the British
+Isles, and forming <i>dikes,</i> such as have been spoken of; and
+some of the strata through which these dikes cut are occasionally
+altered at the point of contact, as if they had been exposed to the
+intense heat of melted matter.</p>
+
+<p><a name="page31"></a>The absence of cones and craters, and long narrow streams of
+superficial lava, in England and many other countries, is
+principally to be attributed to the eruptions having been
+submarine, just as a considerable proportion of volcanoes in our
+own times burst out beneath the sea. But this question must be
+enlarged upon more fully in the chapters on Igneous Rocks, in which
+it will also be shown, that as different sedimentary formations,
+containing each their characteristic fossils, have been deposited
+at successive periods, so also volcanic sand and scoriæ have
+been thrown out, and lavas have flowed over the land or bed of the
+sea, at many different epochs, or have been injected into fissures;
+so that the igneous as well as the aqueous rocks may be classed as
+a chronological series of monuments, throwing light on a succession
+of events in the history of the earth.</p>
+
+<p><b>Plutonic Rocks</b> (<i>Granite,</i> etc).&mdash;We have now
+pointed out the existence of two distinct orders of mineral masses,
+the aqueous and the volcanic: but if we examine a large portion of
+a continent, especially if it contain within it a lofty mountain
+range, we rarely fail to discover two other classes of rocks, very
+distinct from either of those above alluded to, and which we can
+neither assimilate to deposits such as are now accumulated in lakes
+or seas, nor to those generated by ordinary volcanic action. The
+members of both these divisions of rocks agree in being highly
+crystalline and destitute of organic remains. The rocks of one
+division have been called Plutonic, comprehending all the granites
+and certain porphyries, which are nearly allied in some of their
+characters to volcanic formations. The members of the other class
+are stratified and often slaty, and have been called by some the
+<i>crystalline schists,</i> in which group are included gneiss,
+micaceous-schist (or mica-slate), hornblende-schist, statuary
+marble, the finer kinds of roofing slate, and other rocks
+afterwards to be described.</p>
+
+<p>As it is admitted that nothing strictly analogous to these
+crystalline productions can now be seen in the progress of
+formation on the earth&rsquo;s surface, it will naturally be asked, on
+what data we can find a place for them in a system of
+classification founded on the origin of rocks. I cannot, in reply
+to this question, pretend to give the student, in a few words, an
+intelligible account of the long chain of facts and reasonings from
+which geologists have been led to infer the nature of the rocks in
+question. The result, however, may be briefly stated. All the
+various kinds of granites which constitute the Plutonic family are
+supposed to be of igneous or aqueo-igneous origin, and to have been
+formed<a name="page32"></a> under great pressure, at a considerable depth in the earth, or
+sometimes, perhaps, under a certain weight of incumbent ocean. Like
+the lava of volcanoes, they have been melted, and afterwards cooled
+and crystallised, but with extreme slowness, and under conditions
+very different from those of bodies cooling in the open air. Hence
+they differ from the volcanic rocks, not only by their more
+crystalline texture, but also by the absence of tuffs and breccias,
+which are the products of eruptions at the earth&rsquo;s surface, or
+beneath seas of inconsiderable depth. They differ also by the
+absence of pores or cellular cavities, to which the expansion of
+the entangled gases gives rise in ordinary lava.</p>
+
+<p><b>Metamorphic, or Stratified Crystalline Rocks.</b>&mdash;The
+fourth and last great division of rocks are the crystalline strata
+and slates, or schists, called gneiss, mica-schist, clay-slate,
+chlorite-schist, marble, and the like, the origin of which is more
+doubtful than that of the other three classes. They contain no
+pebbles, or sand, or scoriæ, or angular pieces of imbedded
+stone, and no traces of organic bodies, and they are often as
+crystalline as granite, yet are divided into beds, corresponding in
+form and arrangement to those of sedimentary formations, and are
+therefore said to be stratified. The beds sometimes consist of an
+alternation of substances varying in colour, composition, and
+thickness, precisely as we see in stratified fossiliferous
+deposits. According to the Huttonian theory, which I adopt as the
+most probable, and which will be afterwards more fully explained,
+the materials of these strata were originally deposited from water
+in the usual form of sediment, but they were subsequently so
+altered by subterranean heat, as to assume a new texture. It is
+demonstrable, in some cases at least, that such a complete
+conversion has actually taken place, fossiliferous strata having
+exchanged an earthy for a highly crystalline texture for a distance
+of a quarter of a mile from their contact with granite. In some
+cases, dark limestones, replete with shells and corals, have been
+turned into white statuary marble; and hard clays, containing
+vegetable or other remains, into slates called mica-schist or
+hornblende-schist, every vestige of the organic bodies having been
+obliterated.</p>
+
+<p>Although we are in a great degree ignorant of the precise nature
+of the influence exerted in these cases, yet it evidently bears
+some analogy to that which volcanic heat and gases are known to
+produce; and the action may be conveniently called Plutonic,
+because it appears to have been developed in those regions where
+Plutonic rocks are generated, and under similar circumstances of
+pressure and depth in the<a name="page33"></a> earth. Intensely heated water or steam permeating stratified
+masses under great pressure have no doubt played their part in
+producing the crystalline texture and other changes, and it is
+clear that the transforming influence has often pervaded entire
+mountain masses of strata.</p>
+
+<p>In accordance with the hypothesis above alluded to, I proposed
+in the first edition of the Principles of Geology (1833) the term
+&ldquo;Metamorphic&rdquo; for the altered strata, a term derived from meta, <i>
+trans,</i> and morphe, <i>forma.</i></p>
+
+<p>Hence there are four great classes of rocks considered in
+reference to their origin&mdash;the aqueous, the volcanic, the
+Plutonic, and the metamorphic. In the course of this work it will
+be shown that portions of each of these four distinct classes have
+originated at many successive periods. They have all been produced
+contemporaneously, and may even now be in the progress of formation
+on a large scale. It is not true, as was formerly supposed, that
+all granites, together with the crystalline or metamorphic strata,
+were first formed, and therefore entitled to be called &ldquo;primitive,&rdquo;
+and that the aqueous and volcanic rocks were afterwards
+superimposed, and should, therefore, rank as secondary in the order
+of time. This idea was adopted in the infancy of the science, when
+all formations, whether stratified or unstratified, earthy or
+crystalline, with or without fossils, were alike regarded as of
+aqueous origin. At that period it was naturally argued that the
+foundation must be older than the superstructure; but it was
+afterwards discovered that this opinion was by no means in every
+instance a legitimate deduction from facts; for the inferior parts
+of the earth&rsquo;s crust have often been modified, and even entirely
+changed, by the influence of volcanic and other subterranean
+causes, while superimposed formations have not been in the
+slightest degree altered. In other words, the destroying and
+renovating processes have given birth to new rocks below, while
+those above, whether crystalline or fossiliferous, have remained in
+their ancient condition. Even in cities, such as Venice and
+Amsterdam, it cannot be laid down as universally true that the
+upper parts of each edifice, whether of brick or marble, are more
+modern than the foundations on which they rest, for these often
+consist of wooden piles, which may have rotted and been replaced
+one after the other, without the least injury to the buildings
+above; meanwhile, these may have required scarcely any repair, and
+may have been constantly inhabited. So it is with the habitable
+surface of our globe, in its relation to large masses of rock
+immediately below; it may continue the same for ages, while
+subjacent materials, at<a name="page34"></a> a great depth, are passing from a solid to a fluid state, and
+then reconsolidating, so as to acquire a new texture.</p>
+
+<p>As all the crystalline rocks may, in some respects, be viewed as
+belonging to one great family, whether they be stratified or
+unstratified, metamorphic or Plutonic, it will often be convenient
+to speak of them by one common name. It being now ascertained, as
+above stated, that they are of very different ages, sometimes newer
+than the strata called secondary, the terms primitive and primary
+which were formerly used for the whole must be abandoned, as they
+would imply a manifest contradiction. It is indispensable,
+therefore, to find a new name, one which must not be of
+chronological import, and must express, on the one hand, some
+peculiarity equally attributable to granite and gneiss (to the
+Plutonic as well as the <i>altered</i> rocks), and, on the other,
+must have reference to characters in which those rocks differ, both
+from the volcanic and from the <i>unaltered</i> sedimentary strata.
+I proposed in the Principles of Geology (first edition, vol. iii)
+the term &ldquo;hypogene&rdquo; for this purpose, derived from upo, <i>
+under,</i> and ginomai, <i>to be,</i> or <i>to be born</i>; a word
+implying the theory that granite, gneiss, and the other crystalline
+formations are alike <i>netherformed</i> rocks, or rocks which have
+not assumed their present form and structure at the surface. They
+occupy the lowest place in the order of superposition. Even in
+regions such as the Alps, where some masses of granite and gneiss
+can be shown to be of comparatively modern date, belonging, for
+example, to the period hereafter to be described as tertiary, they
+are still <i>underlying</i> rocks. They never repose on the
+volcanic or trappean formations, nor on strata containing organic
+remains. They are <i>hypogene,</i> as &ldquo;being under&rdquo; all the
+rest.</p>
+
+<p>From what has now been said, the reader will understand that
+each of the four great classes of rocks may be studied under two
+distinct points of view; first, they may be studied simply as
+mineral masses deriving their origin from particular causes, and
+having a certain composition, form, and position in the earth&rsquo;s
+crust, or other characters both positive and negative, such as the
+presence or absence of organic remains. In the second place, the
+rocks of each class may be viewed as a grand chronological series
+of monuments, attesting a succession of events in the former
+history of the globe and its living inhabitants.</p>
+
+<p>I shall accordingly proceed to treat of each family of rocks;
+first, in reference to those characters which are not
+chronological, and then in particular relation to the several
+periods when they were formed.
+</p>
+
+<p class="footnote">
+<a name="fn-1.1" id="fn-1.1"></a> <a href="#fnref-1.1">[1]</a>
+See Principles of Geology, by the Author, Index, &ldquo;Nile,&rdquo;
+&ldquo;Rivers,&rdquo; etc.
+</p>
+
+<p class="footnote">
+<a name="fn-1.2" id="fn-1.2"></a> <a href="#fnref-1.2">[2]</a>
+See p. 44, Fig. 7.
+</p>
+
+<p class="footnote">
+<a name="fn-1.3" id="fn-1.3"></a> <a href="#fnref-1.3">[3]</a>
+Col. R. J. Strachey found oolitic fossils 18,400 feet high in the Himalaya.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap02"></a><a name="page35"></a>CHAPTER II.<br/>
+AQUEOUS ROCKS.&mdash;THEIR COMPOSITION AND FORMS OF STRATIFICATION.</h2>
+
+<p class="letter">
+Mineral Composition of Strata. &mdash; Siliceous Rocks. &mdash; Argillaceous.
+&mdash; Calcareous. &mdash; Gypsum. &mdash; Forms of Stratification. &mdash;
+Original Horizontality. &mdash; Thinning out. &mdash; Diagonal Arrangement.
+&mdash; Ripple-mark.
+</p>
+
+<p>In pursuance of the arrangement explained in the last chapter,
+we shall begin by examining the aqueous or sedimentary rocks, which
+are for the most part distinctly stratified, and contain fossils.
+We may first study them with reference to their mineral
+composition, external appearance, position, mode of origin, organic
+contents, and other characters which belong to them as aqueous
+formations, independently of their age, and we may afterwards
+consider them chronologically or with reference to the successive
+geological periods when they originated.</p>
+
+<p>I have already given an outline of the data which led to the
+belief that the stratified and fossiliferous rocks were originally
+deposited under water; but, before entering into a more detailed
+investigation, it will be desirable to say something of the
+ordinary materials of which such strata are composed. These may be
+said to belong principally to three divisions, the siliceous, the
+argillaceous, and the calcareous, which are formed respectively of
+flint, clay, and carbonate of lime. Of these, the siliceous are
+chiefly made up of sand or flinty grains; the argillaceous, or
+clayey, of a mixture of siliceous matter with a certain proportion,
+about a fourth in weight, of aluminous earth; and, lastly, the
+calcareous rocks, or limestones, of carbonic acid and lime.</p>
+
+<p>
+<b>Siliceous and Arenaceous
+Rocks.</b>&mdash;To speak first of the sandy division: beds
+of loose sand are frequently met with, of which the grains consist
+entirely of silex, which term comprehends all purely siliceous
+minerals, as quartz and common flint. Quartz is silex in its purest
+form. Flint usually contains some admixture of alumina and oxide of
+iron. The siliceous grains in sand are usually rounded, as if by
+the action of running water. Sandstone is an aggregate of such
+grains, which often cohere together without any visible cement, but
+more commonly are bound together <a name="page36"></a>by a slight quantity of siliceous or calcareous matter, or by
+oxide of iron or clay.</p>
+
+<p>Pure siliceous rocks may be known by not effervescing when a
+drop of nitric, sulphuric or other acid is applied to them, or by
+the grains not being readily scratched or broken by ordinary
+pressure. In nature there is every intermediate gradation, from
+perfectly loose sand to the hardest sandstone. In <i>micaceous
+sandstones</i> mica is very abundant; and the thin silvery plates
+into which that mineral divides are often arranged in layers
+parallel to the planes of stratification, giving a slaty or
+laminated texture to the rock.</p>
+
+<p>When sandstone is coarse-grained, it is usually called <i>
+grit.</i> If the grains are rounded, and large enough to be called
+pebbles, it becomes a <i>conglomerate</i> or <i>pudding-stone,</i>
+which may consist of pieces of one or of many different kinds of
+rock. A conglomerate, therefore, is simply gravel bound together by
+cement.</p>
+
+<p><b>Argillaceous Rocks.</b>&mdash;Clay,
+strictly speaking, is a mixture of silex or flint with a large
+proportion, usually about one fourth, of alumina, or argil; but in
+common language, any earth which possesses sufficient ductility,
+when kneaded up with water, to be fashioned like paste by the hand,
+or by the potter&rsquo;s lathe, is called a <i>clay</i>; and such clays
+vary greatly in their composition, and are, in general, nothing
+more than mud derived from the decomposition or wearing down of
+rocks. The purest clay found in nature is porcelain clay, or
+kaolin, which results from the decomposition of a rock composed of
+feldspar and quartz, and it is almost always mixed with quartz. The
+kaolin of China consists of 71&middot;15 parts of silex,
+15&middot;86 of alumine, 1&middot;92 of lime, and 6&middot;73 of
+water;<a href="#fn-2.1" name="fnref-2.1" id="fnref-2.1"><sup>[1]</sup></a> but other porcelain clays differ materially, that of
+Cornwall being composed, according to Boase, of nearly equal parts
+of silica and alumine, with 1 per cent of magnesia.<a href="#fn-2.2" name="fnref-2.2" id="fnref-2.2"><sup>[2]</sup></a> <i>
+Shale</i> has also the property, like clay, of becoming plastic in
+water: it is a more solid form of clay, or argillaceous matter,
+condensed by pressure. It always divides into laminæ more or
+less regular.</p>
+
+<p>One general character of all argillaceous rocks is to give out a
+peculiar, earthy odour when breathed upon, which is a test of the
+presence of alumine, although it does not belong to pure alumine,
+but, apparently, to the combination of that substance with oxide of
+iron.<a href="#fn-2.3" name="fnref-2.3" id="fnref-2.3"><sup>[3]</sup></a>
+</p>
+
+<p><b>Calcareous Rocks.</b>&mdash;This
+division comprehends those rocks which, like chalk, are composed
+chiefly of lime and carbonic <a name="page37"></a>acid. Shells and corals are also formed of the same elements,
+with the addition of animal matter. To obtain pure lime it is
+necessary to calcine these calcareous substances, that is to say,
+to expose them to heat of sufficient intensity to drive off the
+carbonic acid, and other volatile matter. White chalk is sometimes
+pure carbonate of lime; and this rock, although usually in a soft
+and earthy state, is occasionally sufficiently solid to be used for
+building, and even passes into a <i>compact</i> stone, or a stone
+of which the separate parts are so minute as not to be
+distinguishable from each other by the naked eye.</p>
+
+<p>Many limestones are made up entirely of minute fragments of
+shells and coral, or of calcareous sand cemented together. These
+last might be called &ldquo;calcareous sandstones;&rdquo; but that term is more
+properly applied to a rock in which the grains are partly
+calcareous and partly siliceous, or to quartzose sandstones, having
+a cement of carbonate of lime.</p>
+
+<p>The variety of limestone called <i>oolite</i> is composed of
+numerous small egg-like grains, resembling the roe of a fish, each
+of which has usually a small fragment of sand as a nucleus, around
+which concentric layers of calcareous matter have accumulated.</p>
+
+<p>Any limestone which is sufficiently hard to take a fine polish
+is called <i>marble.</i> Many of these are fossiliferous; but
+statuary marble, which is also called saccharoid limestone, as
+having a texture resembling that of loaf-sugar, is devoid of
+fossils, and is in many cases a member of the metamorphic
+series.</p>
+
+<p><i>Siliceous limestone</i> is an intimate mixture of carbonate
+of lime and flint, and is harder in proportion as the flinty matter
+predominates.</p>
+
+<p>The presence of carbonate of lime in a rock may be ascertained
+by applying to the surface a small drop of diluted sulphuric,
+nitric, or muriatic acid, or strong vinegar; for the lime, having a
+greater chemical affinity for any one of these acids than for the
+carbonic, unites immediately with them to form new compounds,
+thereby becoming a sulphate, nitrate or muriate of lime. The
+carbonic acid, when thus liberated from its union with the lime,
+escapes in a gaseous form, and froths up or effervesces as it makes
+its way in small bubbles through the drop of liquid. This
+effervescence is brisk or feeble in proportion as the limestone is
+pure or impure, or, in other words, according to the quantity of
+foreign matter mixed with the carbonate of lime. Without the aid of
+this test, the most experienced eye cannot always detect the
+presence of carbonate of lime in rocks.</p>
+
+<p><a name="page38"></a>The above-mentioned three classes of rocks, the siliceous,
+argillaceous, and calcareous, pass continually into each other, and
+rarely occur in a perfectly separate and pure form. Thus it is an
+exception to the general rule to meet with a limestone as pure as
+ordinary white chalk, or with clay as aluminous as that used in
+Cornwall for porcelain, or with sand so entirely composed of
+siliceous grains as the white sand of Alum Bay, in the Isle of
+Wight, employed in the manufacture of glass, or sandstone so pure
+as the grit of Fontainebleau, used for pavement in France. More
+commonly we find sand and clay, or clay and marl, intermixed in the
+same mass. When the sand and clay are each in considerable
+quantity, the mixture is called <i>loam.</i> If there is much
+calcareous matter in clay it is called <i>marl</i>; but this term
+has unfortunately been used so vaguely, as often to be very
+ambiguous. It has been applied to substances in which there is no
+lime; as, to that red loam usually called red marl in certain parts
+of England. Agriculturists were in the habit of calling any soil a
+marl which, like true marl, fell to pieces readily on exposure to
+the air. Hence arose the confusion of using this name for soils
+which, consisting of loam, were easily worked by the plough, though
+devoid of lime.</p>
+
+<p><i>Marl slate</i> bears the same relation to marl which shale
+bears to clay, being a calcareous shale. It is very abundant in
+some countries, as in the Swiss Alps. Argillaceous or marly
+limestone is also of common occurrence.</p>
+
+<p>There are few other kinds of rock which enter so largely into
+the composition of sedimentary strata as to make it necessary to
+dwell here on their characters. I may, however, mention two
+others&mdash;magnesian limestone or dolomite, and gypsum. <i>Magnesian
+limestone</i> is composed of carbonate of lime and carbonate of
+magnesia; the proportion of the latter amounting in some cases to
+nearly one half. It effervesces much more slowly and feebly with
+acids than common limestone. In England this rock is generally of a
+yellowish colour; but it varies greatly in mineralogical character,
+passing from an earthy state to a white compact stone of great
+hardness. <i>Dolomite,</i> so common in many parts of Germany and
+France, is also a variety of magnesian limestone, usually of a
+granular texture.</p>
+
+<p><i>Gypsum</i> is a rock composed of sulphuric acid, lime, and
+water. It is usually a soft whitish-yellow rock, with a texture
+resembling that of loaf-sugar, but sometimes it is entirely
+composed of lenticular crystals. It is insoluble in acids, and does
+not effervesce like chalk and dolomite, because it does not contain
+carbonic acid gas, or fixed air, the lime <a name="page39"></a>being
+already combined with sulphuric acid, for which it has a
+stronger affinity than for any other. Anhydrous gypsum is a rare
+variety, into which water does not enter as a component part. <i>
+Gypseous marl</i> is a mixture of gypsum and marl. <i>Alabaster</i>
+is a granular and compact variety of gypsum found in masses large
+enough to be used in sculpture and architecture. It is sometimes a
+pure snow-white substance, as that of Volterra in Tuscany, well
+known as being carved for works of art in Florence and Leghorn. It
+is a softer stone than marble, and more easily wrought.</p>
+
+<p><b>Forms of
+Stratification.</b>&mdash;A series of strata sometimes
+consists of one of the above rocks, sometimes of two or more in
+alternating beds.</p>
+
+<p>Thus, in the coal districts of England, for example, we often
+pass through several beds of sandstone, some of finer, others of
+coarser grain, some white, others of a dark colour, and below
+these, layers of shale and sandstone or beds of shale, divisible
+into leaf-like laminæ, and containing beautiful impressions
+of plants. Then again we meet with beds of pure and impure coal,
+alternating with shales and sandstones, and underneath the whole,
+perhaps, are calcareous strata, or beds of limestone, filled with
+corals and marine shells, each bed distinguishable from another by
+certain fossils, or by the abundance of particular species of
+shells or zoophytes.</p>
+
+<p>
+This alternation of different kinds of rock produces the most distinct
+stratification; and we often find beds of limestone and marl, conglomerate and
+sandstone, sand and clay, recurring again and again, in nearly regular order,
+throughout a series of many hundred strata. The causes which may produce these
+phenomena are various, and have been fully discussed in my treatise on the
+modern changes of the earth&rsquo;s surface.<a href="#fn-2.4" name="fnref-2.4"
+id="fnref-2.4"><sup>[4]</sup></a> It is there seen that rivers flowing into
+lakes and seas are charged with sediment, varying in quantity, composition,
+colour, and grain according to the seasons; the waters are sometimes flooded
+and rapid, at other periods low and feeble; different tributaries, also,
+draining peculiar countries and soils, and therefore charged with peculiar
+sediment, are swollen at distinct periods. It was also shown that the waves of
+the sea and currents undermine the cliffs during wintry storms, and sweep away
+the materials into the deep, after which a season of tranquillity succeeds,
+when nothing but the finest mud is spread by the movements of the ocean over
+the same submarine area.
+</p>
+
+<p>It is not the object of the present work to give a
+description <a name="page40"></a>of these operations, repeated as they are, year after year, and
+century after century; but I may suggest an explanation of the
+manner in which some micaceous sandstones have originated, namely,
+those in which we see innumerable thin layers of mica dividing
+layers of fine quartzose sand. I observed the same arrangement of
+materials in recent mud deposited in the estuary of Laroche St.
+Bernard in Brittany, at the mouth of the Loire. The surrounding
+rocks are of gneiss, which, by its waste, supplies the mud: when
+this dries at low water, it is found to consist of brown laminated
+clay, divided by thin seams of mica. The separation of the mica in
+this case, or in that of micaceous sandstones, may be thus
+understood. If we take a handful of quartzose sand, mixed with
+mica, and throw it into a clear running stream, we see the
+materials immediately sorted by the water, the grains of quartz
+falling almost directly to the bottom, while the plates of mica
+take a much longer time to reach the bottom, and are carried
+farther down the stream. At the first instant the water is turbid,
+but immediately after the flat surfaces of the plates of mica are
+seen all alone, reflecting a silvery light, as they descend slowly,
+to form a distinct micaceous lamina. The mica is the heavier
+mineral of the two; but it remains a longer time suspended in the
+fluid, owing to its greater extent of surface. It is easy,
+therefore, to perceive that where such mud is acted upon by a river
+or tidal current, the thin plates of mica will be carried farther,
+and not deposited in the same places as the grains of quartz; and
+since the force and velocity of the stream varies from time to
+time, layers of mica or of sand will be thrown down successively on
+the same area.</p>
+
+<p><b>Original
+Horizontality.</b>&mdash;It is said generally that the upper
+and under surfaces of strata, or the &ldquo;planes of stratification,&rdquo;
+are parallel. Although this is not strictly true, they make an
+approach to parallelism, for the same reason that sediment is
+usually deposited at first in nearly horizontal layers. Such an
+arrangement can by no means be attributed to an original evenness
+or horizontality in the bed of the sea: for it is ascertained that
+in those places where no matter has been recently deposited, the
+bottom of the ocean is often as uneven as that of the dry land,
+having in like manner its hills, valleys, and ravines. Yet if the
+sea should go down, or be removed from near the mouth of a large
+river where a delta has been forming, we should see extensive
+plains of mud and sand laid dry, which, to the eye, would appear
+perfectly level, although, in reality, they would slope gently from
+the land towards the sea.</p>
+
+<p><a name="page41"></a>This tendency in newly-formed strata to assume a horizontal
+position arises principally from the motion of the water, which
+forces along particles of sand or mud at the bottom, and causes
+them to settle in hollows or depressions where they are less
+exposed to the force of a current than when they are resting on
+elevated points. The velocity of the current and the motion of the
+superficial waves diminish from the surface downward, and are least
+in those depressions where the water is deepest.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig1.jpg" width="175" height="73" alt="" />
+</div>
+
+<p>A good illustration of the principle here alluded to may be
+sometimes seen in the neighbourhood of a volcano, when a section,
+whether natural or artificial, has laid open to view a succession
+of various-coloured layers of sand and ashes, which have fallen in
+showers upon uneven ground. Thus let A B (Fig. 1) be two ridges,
+with an intervening valley. These original inequalities of the
+surface have been gradually effaced by beds of sand and ashes <i>c,
+d, e,</i> the surface at <i>e</i> being quite level. It will be
+seen that, although the materials of the first layers have
+accommodated themselves in a great degree to the shape of the
+ground A B, yet each bed is thickest at the bottom. At first a
+great many particles would be carried by their own gravity down the
+steep sides of A and B, and others would afterwards be blown by the
+wind as they fell off the ridges, and would settle in the hollow,
+which would thus become more and more effaced as the strata
+accumulated from <i>c</i> to <i>e.</i> Now, water in motion can
+exert this levelling power on similar materials more easily than
+air, for almost all stones lose in water more than a third of the
+weight which they have in air, the specific gravity of rocks being
+in general as 2&frac12; when compared to that of water, which is
+estimated at 1. But the buoyancy of sand or mud would be still
+greater in the sea, as the density of salt-water exceeds that of
+fresh.</p>
+
+<p><img src="images/fig2.jpg" width="336" height="100" alt=
+"Fig. 2. Section of strata of sandtone, grit, and congolmerate." />
+</p>
+
+<p>
+Yet, however uniform and horizontal may be the surface of new
+deposits in general, there are still many disturbing causes, such
+as eddies in the water, and currents moving first in one and then
+in another direction, which frequently cause
+<a name="page42"></a>irregularities. We may sometimes follow a bed of limestone,
+shale, or sandstone, for a distance of many hundred yards
+continuously; but we generally find at length that each individual
+stratum thins out, and allows the beds which were previously above
+and below it to meet. If the materials are coarse, as in grits and
+conglomerates, the same beds can rarely be traced many yards
+without varying in size, and often coming to an end abruptly. (See
+Fig. 2.)</p>
+
+<p><img src="images/fig3.jpg" width="307" height="307" alt=
+"Fig. 3: Section of sand at Sandy Hill, near Biggleswade, Bedfordshire." />
+</p>
+
+<p><b>Diagonal or Cross
+Stratification.</b>&mdash;There is also another phenomenon
+of frequent occurrence. We find a series of larger strata, each of
+which is composed of a number of minor layers placed obliquely to
+the general planes of stratification. To this diagonal arrangement
+the name of &ldquo;false or cross bedding&rdquo; has been given. Thus in the
+section (Fig. 3) we see seven or eight large beds of loose sand,
+yellow and brown, and the lines <i>a, b, c</i> mark some of the
+principal planes of stratification, which are nearly horizontal.
+But the greater part of the subordinate laminæ do not conform
+to these planes, but have often a steep slope, the inclination
+being sometimes towards opposite points of the compass. When the
+sand is loose and incoherent, as in the case here represented, the
+deviation from parallelism of the slanting laminæ cannot
+possibly be accounted for by any rearrangement of the particles
+acquired during the consolidation of the rock. In what manner,
+then, can such irregularities be <a name="page43"></a>due to original
+deposition? We must suppose that at the bottom
+of the sea, as well as in the beds of rivers, the motions of waves,
+currents, and eddies often cause mud, sand, and gravel to be thrown
+down in heaps on particular spots, instead of being spread out
+uniformly over a wide area. Sometimes, when banks are thus formed,
+currents may cut passages through them, just as a river forms its
+bed.</p>
+
+<p><img src="images/fig4.jpg" width="338" height="114" alt=
+"Fig. 4" /><img src="images/fig5.jpg" width="329" height="93" alt=
+"Fig. 5" /></p>
+
+<p>Suppose the bank A (Fig. 4) to be thus formed with a steep
+sloping side, and, the water being in a tranquil state, the layer
+of sediment No. 1 is thrown down upon it, conforming nearly to its
+surface. Afterwards the other layers, 2, 3, 4, may be deposited in
+succession, so that the bank B C D is formed. If the current then
+increases in velocity, it may cut away the upper portion of this
+mass down to the dotted line e, and deposit the materials thus
+removed farther on, so as to form the layers 5, 6, 7, 8. We have
+now the bank B, C, D, E (Fig. 5), of which the surface is almost
+level, and on which the nearly horizontal layers, 9, 10, 11, may
+then accumulate. It was shown in Fig. 3 that the diagonal layers of
+successive strata may sometimes have an opposite slope. This is
+well seen in some cliffs of loose sand on the Suffolk coast. A
+portion of one of these is represented in Fig. 6, where the layers,
+of which there are about six in the thickness of an inch, are
+composed of quartzose grains. This arrangement may have been due to
+the altered direction of the tides and currents in the same
+place.</p>
+
+<p><img src="images/fig6.jpg" width="213" height="129" alt=
+"Fig. 6: Cliff between Mismer and Dunwich." /></p>
+
+<p><img src="images/fig7.jpg" width="367" height="206" alt=
+"Fig. 7: Section from Monte Calvo to the sea by the valley of the Magnan, near Nice." />
+</p>
+
+<p><a name="page44"></a>The description above given of the slanting position of the
+minor layers constituting a single stratum is in certain cases
+applicable on a much grander scale to masses several hundred feet
+thick, and many miles in extent. A fine example may be seen at the
+base of the Maritime Alps near Nice. The mountains here terminate
+abruptly in the sea, so that a depth of one hundred fathoms is
+often found within a stone&rsquo;s throw of the beach, and sometimes a
+depth of 3000 feet within half a mile. But at certain points,
+strata of sand, marl, or conglomerate intervene between the shore
+and the mountains, as in the section (Fig. 7), where a vast
+succession of slanting beds of gravel and sand may be traced from
+the sea to Monte Calvo, a distance of no less than nine miles in a
+straight line. The dip of these beds is remarkably uniform, being
+always southward or towards the Mediterranean, at an angle of about
+25&deg;. They are exposed to view in nearly vertical precipices,
+varying from 200 to 600 feet in height, which bound the valley
+through which the river Magnan flows. Although, in a general view,
+the strata appear to be parallel and uniform, they are nevertheless
+found, when examined closely, to be wedge-shaped, and to thin out
+when followed for a few hundred feet or yards, so that we may
+suppose them to have been thrown down originally upon the side of a
+steep bank where a river or Alpine torrent discharged itself into a
+deep and tranquil sea, and formed a delta, which advanced gradually
+from the base of Monte Calvo to a distance of nine miles from the
+original shore. If subsequently this part of the Alps and bed of
+the sea were raised 700 feet, the delta may have emerged, a deep
+channel may then have been cut through it by the river, and the
+coast may at the same time have acquired its present
+configuration.</p>
+
+<p>It is well known that the torrents and streams which now
+<a name="page45"></a>descend from the Alpine declivities to the shore, bring down
+annually, when the snow melts, vast quantities of shingle and sand,
+and then, as they subside, fine mud, while in summer they are
+nearly or entirely dry; so that it may be safely assumed that
+deposits like those of the valley of the Magnan, consisting of
+coarse gravel alternating with fine sediment, are still in progress
+at many points, as, for instance, at the mouth of the Var. They
+must advance upon the Mediterranean in the form of great shoals
+terminating in a steep talus; such being the original mode of
+accumulation of all coarse materials conveyed into deep water,
+especially where they are composed in great part of pebbles, which
+cannot be transported to indefinite distances by currents of
+moderate velocity. By inattention to facts and inferences of this
+kind, a very exaggerated estimate has sometimes been made of the
+supposed depth of the ancient ocean. There can be no doubt, for
+example, that the strata <i>a</i>, Fig. 7, or those nearest to
+Monte Calvo, are older than those indicated by <i>b</i>, and these
+again were formed before <i>c</i>; but the vertical depth of gravel
+and sand in any one place cannot be proved to amount even to 1000
+feet, although it may perhaps be much greater, yet probably never
+exceeding at any point 3000 or 4000 feet. But were we to assume
+that all the strata were once horizontal, and that their present
+dip or inclination was due to subsequent movements, we should then
+be forced to conclude that a sea several miles deep had been filled
+up with alternate layers of mud and pebbles thrown down one upon
+another.</p>
+
+<p><a name="page46"></a>In the locality now under consideration, situated a few miles to
+the west of Nice, there are many geological data, the details of
+which cannot be given in this place, all leading to the opinion
+that, when the deposit of the Magnan was formed, the shape and
+outline of the Alpine declivities and the shore greatly resembled
+what we now behold at many points in the neighbourhood. That the
+beds <i>a, b, c, d</i> are of comparatively modern date is proved
+by this fact, that in seams of loamy marl intervening between the
+pebbly beds are fossil shells, half of which belong to species now
+living in the Mediterranean.</p>
+
+<p><img src="images/fig8.jpg" width="295" height="261" alt=
+"Fig. 8: Slab of ripple-marked (New Red) sandstone from Cheshire." />
+</p>
+
+<p><b>Ripple-mark.</b>&mdash;The
+ripple-mark, so common on the surface of sandstones of all ages
+(see Fig. 8), and which is so often seen on the sea-shore at low
+tide, seems to originate in the drifting of materials along the
+bottom of the water, in a manner very similar to that which may
+explain the inclined layers above described. This ripple is not
+entirely confined to the beach between high and low water mark, but
+is also produced on sands which are constantly covered by water.
+Similar undulating ridges and furrows may also be sometimes seen on
+the surface of drift snow and blown sand.</p>
+
+<p>
+The ripple-mark is usually an indication of a sea-beach, or of water from six
+to ten feet deep, for the agitation caused by waves even during storms extends
+to a very slight depth. To this rule, however, there are some exceptions, and
+recent ripple-marks have been observed at the depth of 60 or 70 feet. It has
+also been ascertained that currents or large bodies of water in motion may
+disturb mud and sand at the depth of 300 or even 450 feet.<a href="#fn-2.5"
+name="fnref-2.5" id="fnref-2.5"><sup>[5]</sup></a> Beach ripple, however, may
+usually be distinguished from current ripple by frequent changes in its
+direction. In a slab of sandstone, not more than an inch thick, the furrows or
+ridges of an ancient ripple may often be seen in several successive laminæ to
+run towards different points of the compass.
+</p>
+
+<p class="footnote">
+<a name="fn-2.1" id="fn-2.1"></a> <a href="#fnref-2.1">[1]</a>
+W. Phillips, Mineralogy, p.33.
+</p>
+
+<p class="footnote">
+<a name="fn-2.2" id="fn-2.2"></a> <a href="#fnref-2.2">[2]</a>
+Phil. Mag., vol. x, 1837.
+</p>
+
+<p class="footnote">
+<a name="fn-2.3" id="fn-2.3"></a> <a href="#fnref-2.3">[3]</a>
+See W. Phillips&rsquo;s Mineralogy, &ldquo;Alumine.&rdquo;
+</p>
+
+<p class="footnote">
+<a name="fn-2.4" id="fn-2.4"></a> <a href="#fnref-2.4">[4]</a>
+Consult Index to Principles of Geology, &ldquo;Stratification,&rdquo;
+&ldquo;Currents,&rdquo; &ldquo;Deltas,&rdquo; &ldquo;Water,&rdquo; etc.
+</p>
+
+<p class="footnote">
+<a name="fn-2.5" id="fn-2.5"></a> <a href="#fnref-2.5">[5]</a>
+Darwin, Volcanic Islands, p. 134.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap03"></a><a name="page47"></a>CHAPTER III.<br/>
+ARRANGEMENT OF FOSSILS IN STRATA.&mdash;FRESH-WATER AND MARINE
+FOSSILS.</h2>
+
+<p class="letter">Successive Deposition indicated by
+Fossils. &mdash; Limestones formed of Corals and Shells. &mdash; Proofs
+of gradual Increase of Strata derived from Fossils. &mdash; Serpula
+attached to Spatangus. &mdash; Wood bored by Teredina. &mdash; Tripoli
+formed of Infusoria. &mdash; Chalk derived principally from Organic
+Bodies. &mdash; Distinction of Fresh-water from Marine
+Formations. &mdash; Genera of Fresh-water and Land
+Shells. &mdash; Rules for recognising Marine
+Testacea. &mdash; Gyrogonite and Chara. &mdash; Fresh-water
+Fishes. &mdash; Alternation of Marine and Fresh-water
+Deposits. &mdash; Lym-Fiord.</p>
+
+<p>Having in the last chapter considered the forms of
+stratification so far as they are determined by the arrangement of
+inorganic matter, we may now turn our attention to the manner in
+which organic remains are distributed through stratified deposits.
+We should often be unable to detect any signs of stratification or
+of successive deposition, if particular kinds of fossils did not
+occur here and there at certain depths in the mass. At one level,
+for example, univalve shells of some one or more species
+predominate; at another, bivalve shells; and at a third, corals;
+while in some formations we find layers of vegetable matter,
+commonly derived from land plants, separating strata.</p>
+
+<p>It may appear inconceivable to a beginner how mountains, several
+thousand feet thick, can have become full of fossils from top to
+bottom; but the difficulty is removed, when he reflects on the
+origin of stratification, as explained in the last chapter, and
+allows sufficient time for the accumulation of sediment. He must
+never lose sight of the fact that, during the process of
+deposition, each separate layer was once the uppermost, and
+immediately in contact with the water in which aquatic animals
+lived. Each stratum, in fact, however far it may now lie beneath
+the surface, was once in the state of shingle, or loose sand or
+soft mud at the bottom of the sea, in which shells and other bodies
+easily became enveloped.</p>
+
+<p><b>Rate of Deposition indicated by
+Fossils.</b>&mdash;By attending to the nature of these
+remains, we are often enabled to determine whether the deposition
+was slow or rapid, whether it took place in a deep or shallow sea,
+near the shore or far <a name="page48"></a>from land, and whether the water
+was salt, brackish, or fresh.
+Some limestones consist almost exclusively of corals, and in many
+cases it is evident that the present position of each fossil
+zoophyte has been determined by the manner in which it grew
+originally. The axis of the coral, for example, if its natural
+growth is erect, still remains at right angles to the plane of
+stratification. If the stratum be now horizontal, the round
+spherical heads of certain species continue uppermost, and their
+points of attachment are directed downward. This arrangement is
+sometimes repeated throughout a great succession of strata. From
+what we know of the growth of similar zoophytes in modern reefs, we
+infer that the rate of increase was extremely slow, and some of the
+fossils must have flourished for ages like forest-trees, before
+they attained so large a size. During these ages, the water must
+have been clear and transparent, for such corals cannot live in
+turbid water.</p>
+
+<img src="images/fig9.jpg" width="212" height="359" alt=
+"Fossil Gryphæ, covered both on the outside and inside with fossil serpulæ." />
+
+<p>In like manner, when we see thousands of full-grown shells
+dispersed everywhere throughout a long series of strata, we cannot
+doubt that time was required for the multiplication of successive
+generations; and the evidence of slow accumulation is rendered more
+striking from the proofs, so often discovered, of fossil bodies
+having lain for a time on the floor of the ocean after death before
+they were imbedded in sediment. Nothing, for example, is more
+common than to see fossil oysters in clay, with Serpulæ, or
+barnacles (acorn-shells), or corals, and other creatures, attached
+to the inside of the valves, so that the mollusk was certainly not
+buried in argillaceous mud the moment it died. There must have been
+an interval during which it was still surrounded with clear water,
+when the creatures whose remains now adhere to it grew from an
+embryonic to a mature state. Attached shells which are merely
+external, like some of the Serpulæ (<i>a</i>) in Fig. 9, may
+often have grown upon an <a name="page49"></a>oyster or other shell while the animal within was still living;
+but if they are found on the inside, it could only happen after the
+death of the inhabitant of the shell which affords the support.
+Thus, in Fig. 9, it will be seen that two Serpulæ have grown
+on the interior, one of them exactly on the place where the
+adductor muscle of the <i>Gryphæa</i> (a kind of oyster) was
+fixed.</p>
+
+<img src="images/fig10.jpg" width="168" height="342" alt=
+"Fig. 10: Serpula attached to a fossil. Fig. 11: Recent Spatangus with spines removed from one side." />
+
+<p>Some fossil shells, even if simply attached to the <i>
+outside</i> of others, bear full testimony to the conclusion above
+alluded to, namely, that an interval elapsed between the death of
+the creature to whose shell they adhere, and the burial of the same
+in mud or sand. The sea-urchins, or <i>Echini</i>, so abundant in
+white chalk, afford a good illustration. It is well known that
+these animals, when living, are invariably covered with spines
+supported by rows of tubercles. These last are only seen after the
+death of the sea-urchin, when the spines have dropped off. In Fig.
+11 a living species of <i>Spatangus</i>, common on our coast, is
+represented with one half of its shell stripped of the spines. In
+Fig. 10 a fossil of a similar and allied genus from the white chalk
+of England shows the naked surface which the individuals of this
+family exhibit when denuded of their bristles. The full-grown <i>
+Serpula</i>, therefore, which now adheres externally, could not
+have begun to grow till the <i>Micraster</i> had died, and the
+spines became detached.</p>
+
+<img src="images/fig12.jpg" width="120" height="190" alt=
+"Fig. 12: Ananchytes from the chalk." />
+
+<p>Now the series of events here attested by a single fossil may be
+carried a step farther. Thus, for example, we often meet with a
+sea-urchin (<i>Ananchytes</i>) in the chalk (see Fig. 12) which has
+fixed to it the lower valve of a <i>Crania</i>, a genus of bivalve
+mollusca. The upper valve (<i>b</i>, Fig. 12) is almost invariably
+wanting, though occasionally found in a perfect state of
+preservation in white chalk at some distance. In this case, we see
+clearly that the sea-urchin first <a name="page50"></a>lived from youth to age, then died and lost its spines, which
+were carried away. Then the young <i>Crania</i> adhered to the
+bared shell, grew and perished in its turn; after which the upper
+valve was separated from the lower before the <i>Ananchytes</i>
+became enveloped in chalky mud.</p>
+
+<p><img src="images/fig13.jpg" width="313" height="187" alt=
+"Fig. 13: Fossil wood bored by Teredina." /></p>
+
+<p><img src="images/fig14.jpg" width="351" height="184" alt=
+"Fig. 14: Recent wood bored by Teredo." /></p>
+
+<p>It may be well to mention one more illustration of the manner in
+which single fossils may sometimes throw light on a former state of
+things, both in the bed of the ocean and on some adjoining land. We
+meet with many fragments of wood bored by ship-worms at various
+depths in the clay on which London is built. Entire branches and
+stems of trees, several feet in length, are sometimes found drilled
+all over by the holes of these borers, the tubes and shells of the
+mollusk still remaining in the cylindrical hollows. In Fig. 14, <i>
+e</i>, a representation is given of a piece of recent wood pierced
+by the <i>Teredo navalis</i>, or common ship-worm, which destroys
+wooden piles and ships. When the cylindrical tube <i>d</i> has been
+extracted from the wood, the valves are seen at the larger or
+anterior extremity, as shown at <i>c.</i> In like manner, a piece
+of fossil wood (<i>a</i>, Fig. 13) has been perforated by a kindred
+but extinct genus, the <i>Teredina</i> of Lamarck. The calcareous
+tube of this mollusk was united and, as it were, soldered on to the
+valves of the shell (<i>b</i>), which therefore cannot be detached
+from the tube, like the valves of <a name="page51"></a>the recent <i>Teredo.</i> The wood in this fossil specimen is
+now converted into a stony mass, a mixture of clay and lime; but it
+must once have been buoyant and floating in the sea, when the <i>
+Teredinæ</i> lived upon, and perforated it. Again, before the
+infant colony settled upon the drift wood, part of a tree must have
+been floated down to the sea by a river, uprooted, perhaps, by a
+flood, or torn off and cast into the waves by the wind: and thus
+our thoughts are carried back to a prior period, when the tree grew
+for years on dry land, enjoying a fit soil and climate.</p>
+
+<p><b>Strata of Organic
+Origin.</b>&mdash;It has been already remarked that there
+are rocks in the interior of continents, at various depths in the
+earth, and at great heights above the sea, almost entirely made up
+of the remains of zoophytes and testacea. Such masses may be
+compared to modern oyster-beds and coral-reefs; and, like them, the
+rate of increase must have been extremely gradual. But there are a
+variety of stone deposits in the earth&rsquo;s crust, now proved to have
+been derived from plants and animals of which the organic origin
+was not suspected until of late years, even by naturalists. Great
+surprise was therefore created some years since by the discovery of
+Professor Ehrenberg, of Berlin, that a certain kind of siliceous
+stone, called tripoli, was entirely composed of millions of the
+remains of organic beings, which were formerly referred to
+microscopic Infusoria, but which are now admitted to be plants.
+They abound in rivulets, lakes, and ponds in England and other
+countries, and are termed Diatomaceæ by those naturalists who
+believe in their vegetable origin. The subject alluded to has long
+been well-known in the arts, under the name of infusorial earth or
+mountain meal, and is used in the form of powder for polishing
+stones and metals. It has been procured, among other places, from
+the mud of a lake at Dolgelly, in North Wales, and from Bilin, in
+Bohemia, in which latter place a single stratum, extending over a
+wide area, is no less than fourteen feet thick. This stone, when
+examined with a powerful microscope, is found to consist of the
+siliceous plates or frustules of the above-figured
+Diatomaceæ, united together without any visible cement. It is
+difficult to convey an idea of their extreme minuteness; but
+Ehrenberg estimates that in the Bilin tripoli there are 41,000
+millions of individuals of the <i>Gaillonella distans</i> (see Fig.
+16) in every cubic inch (which weighs about 220 grains), or about
+187 millions in a single grain. At every stroke, therefore, that we
+make with this polishing powder, several millions, perhaps tens of
+millions, of perfect fossils are crushed to atoms.<a name="page52"></a></p>
+
+<img src="images/fig15.jpg" width="135" height="267" alt=
+"Figs 15 and 16: Gaillonella; Fig. 17: Bacillaria parodoxa" />
+
+<p>A well-known substance, called bog-iron ore, often met with in
+peat-mosses, has often been shown by Ehrenberg to consist of
+innumerable articulated threads, of a yellow ochre colour, composed
+of silica, argillaceous matter, and peroxide of iron. These threads
+are the cases of a minute microscopic body, called <i>Gaillonella
+ferruginea</i> (Fig. 15), associated with the siliceous frustules
+of other fresh-water algæ. Layers of this iron ore occurring
+in Scotch peat bogs are often called &ldquo;the pan,&rdquo; and are sometimes
+of economical value.</p>
+
+<p>It is clear much time must have been required for the
+accumulation of strata to which countless generations of
+Diatomaceæ have contributed their remains; and these
+discoveries lead us naturally to suspect that other deposits, of
+which the materials have been supposed to be inorganic, may in
+reality be composed chiefly of microscopic organic bodies. That
+this is the case with the white chalk, has often been imagined, and
+is now proved to be the fact. It has, moreover, been lately
+discovered that the chambers into which these Foraminifera are
+divided are actually often filled with thousands of well-preserved
+organic bodies, which abound in every minute grain of chalk, and
+are especially apparent in the white coating of flints, often
+accompanied by innumerable needle-shaped spiculæ of sponges
+(see Chapter XVII).</p>
+
+<p class="poem">
+&ldquo;The dust we tread upon was once
+alive!&rdquo;&mdash;B<small>YRON.</small>
+</p>
+
+<p>How faint an idea does this exclamation of the poet convey of
+the real wonders of nature! for here we discover proofs that the
+calcareous and siliceous dust of which hills are composed has not
+only been once alive, but almost every particle, albeit invisible
+to the naked eye, still retains the organic structure which, at
+periods of time incalculably remote, was impressed upon it by the
+powers of life.</p>
+
+<p><b>Fresh-water and Marine
+Fossils.</b>&mdash;Strata, whether deposited in salt or
+fresh water, have the same forms; but the imbedded fossils are very
+different in the two cases, because the aquatic animals which
+frequent lakes and rivers are distinct from those inhabiting the
+sea. In the northern part of the Isle of Wight formations of marl
+and limestone, more than <a name="page53"></a>50 feet thick occur, in which the shells are of extinct species.
+Yet we recognise their fresh-water origin, because they are of the
+same genera as those now abounding in ponds, lakes, and rivers,
+either in our own country or in warmer latitudes.</p>
+
+<p>In many parts of France&mdash;in Auvergne, for
+example&mdash;strata occur of limestone, marl, and sandstone
+hundreds of feet thick, which contain exclusively fresh-water and
+land shells, together with the remains of terrestrial quadrupeds.
+The number of land-shells scattered through some of these
+fresh-water deposits is exceedingly great; and there are districts
+in Germany where the rocks scarcely contain any other fossils
+except snail-shells (<i>helices</i>); as, for instance, the
+limestone on the left bank of the Rhine, between Mayence and Worms,
+at Oppenheim, Findheim, Budenheim, and other places. In order to
+account for this phenomenon, the geologist has only to examine the
+small deltas of torrents which enter the Swiss lakes when the
+waters are low, such as the newly-formed plain where the Kander
+enters the Lake of Thun. He there sees sand and mud strewn over
+with innumerable dead land-shells, which have been brought down
+from the valleys in the Alps in the preceding spring, during the
+melting of the snows. Again, if we search the sands on the borders
+of the Rhine, in the lower part of its course, we find countless
+land-shells mixed with others of species belonging to lakes,
+stagnant pools, and marshes. These individuals have been washed
+away from the alluvial plains of the great river and its
+tributaries, some from mountainous regions, others from the low
+country.</p>
+
+<p>Although fresh-water formations are often of great thickness,
+yet they are usually very limited in area when compared to marine
+deposits, just as lakes and estuaries are of small dimensions in
+comparison with seas.</p>
+
+<p>
+The absence of many fossil forms usually met with in marine strata, affords a
+useful negative indication of the fresh-water origin of a formation. For
+example, there are no sea-urchins, no corals, no chambered shells, such as the
+nautilus, nor microscopic Foraminifera in lacustrine or fluviatile deposits. In
+distinguishing the latter from formations accumulated in the sea, we are
+chiefly guided by the forms of the mollusca. In a fresh-water deposit, the
+number of individual shells is often as great as in a marine stratum, if not
+greater; but there is a smaller variety of species and genera. This might be
+anticipated from the fact that the genera and species of recent fresh-water and
+land shells are few when contrasted with the marine. Thus, the genera of true
+mollusca according to Woodward&rsquo;s system, excluding those<a
+name="page54"></a> altogether extinct and those without shells, amount to 446
+in number, of which the terrestrial and fresh-water genera scarcely form more
+than a fifth.<a href="#fn-3.1" name="fnref-3.1"
+id="fnref-3.1"><sup>[1]</sup></a>
+</p>
+
+<p><img src="images/fig18.jpg" width="345" height="126" alt=
+"Fig. 18: Cyrena obovata. Fig. 19: Cyrena fluminatis." /></p>
+
+<p><img src="images/fig20.jpg" width="360" height="208" alt=
+"Fig. 20: Anodonta Cordierii. Fig. 21: Anodonta latimarginata. Fig. 22: Unio littoralis." />
+</p>
+
+<p>Almost all bivalve shells, or those of acephalous mollusca, are
+marine, about sixteen only out of 140 genera being fresh-water.
+Among these last, the four most common forms, both recent and
+fossil, are <i>Cyclas, Cyrena, Unio,</i> and <i>Anodonta</i> (see
+Figures); the two first and two last of which are so nearly allied
+as to pass into each other.</p>
+
+<img src="images/fig23.jpg" width="142" height="204" alt="Fig. 23:
+Gryphæa incurva." />
+
+<p>
+Lamarck divided the bivalve mollusca into the Dimyary, or those having two
+large muscular impressions in each valve, as <i>a b</i> in the Cyclas, Fig. 18,
+and Unio, Fig. 22, and the <i> Monomyary,</i> such as the oyster and scallop,
+in which there is only one of these impressions, as is seen in Fig. 23. Now, as
+none of these last, or the unimuscular bivalves, are fresh-water,<a
+href="#fn-3.2" name="fnref-3.2" id="fnref-3.2"><sup>[2]</sup></a> we may at
+once presume a deposit containing any of them to be marine.<a
+name="page55"></a>
+</p>
+
+<p><img src="images/fig24.jpg" width="413" height="486" alt=
+"Fig. 24: Planorbis enomphalus. Fig. 25: Limnæa longiscala. Fig. 26: Pauldina lenta. Fig. 27: Succinea amphibia. Fig. 28: Ancylus velletia. Fig. 29: Valvata piscinalis. Fig. 30: Physa hypnorum. Fig. 31: Auricula. Fig. 32: Melania inquinata. Fig. 33: Physa columnaris. Fig. 34: Melanopsis buccinoidea." />
+</p>
+
+<img src="images/fig35.jpg" width="159" height="202" alt=
+"Fig. 35: Neritina globulud. Fig. 36: Nerita granulosa." />
+
+<p>The univalve shells most characteristic of fresh-water deposits
+are, <i>Planorbis, Limnæa,</i> and <i>Paludina.</i> (See
+Figures.) But to these are occasionally added <i>Physa, Succinea,
+Ancylus, Valvata, Melanopsis, Melania, Potamides,</i> and <i>
+Neritina</i> (see Figures), the four last being usually found in
+estuaries.</p>
+
+<p>
+<img src="images/fig37.jpg" width="80" height="257" alt="Fig. 37:
+Potamides cinctus." />
+</p>
+
+<p>Some naturalists include <i>Neritina</i> (Fig. 35) and the
+marine <i>Nerita</i> (Fig. 36) in the same genus, it being scarcely
+possible to distinguish the two by good generic characters. But, as
+a general rule, the <a name="page56"></a>fluviatile species are smaller, smoother, and more globular than
+the marine; and they have never, like the <i>Neritæ,</i> the
+inner margin of the outer lip toothed or crenulated. (See Fig.
+36.)</p>
+
+<p>The Potamides inhabit the mouths of rivers in warm latitudes,
+and are distinguishable from the marine Cerithia by their orbicular
+and multispiral opercula. The genus Auricula (Fig. 31) is
+amphibious, frequenting swamps and marshes within the influence of
+the tide.</p>
+
+<p>The terrestrial shells are all univalves. The most important
+genera among these, both in a recent and fossil state, are <i>
+Helix</i> (Fig. 38), <i>Cyclostoma</i> (Fig. 39), <i>Pupa</i> (Fig.
+40), <i>Clausilia</i> (Fig. 41), <i>Bulimus</i> (Fig. 42), <i>
+Glandina</i> and <i>Achatina.</i></p>
+
+<p><img src="images/fig38.jpg" width="414" height="153" alt=
+"Fig. 38: Helix Turomensis. Fig. 39: Cyclostoma elegans. Fig. 40: Pupa tridens.
+Fig. 41: Clausilia bidens. Fig. 42: Bulimus lubricus." />
+</p>
+
+<p><i>Ampullaria</i> (Fig. 43) is another genus of shells
+inhabiting rivers and ponds in hot countries. Many fossil species
+formerly referred to this genus, and which have been met with
+chiefly in marine formations, are now considered by conchologists
+to belong to <i>Natica</i> and other marine genera.</p>
+
+<img src="images/fig43.jpg" width="111" height="154" alt="Fig. 43:
+Ampullaria glauca." />
+
+<p>All univalve shells of land and fresh-water species, with the
+exception of <i>Melanopsis</i> (Fig. 34), and <i>Achatina,</i>
+which has a slight indentation, have entire mouths; and this
+circumstance may often serve as a convenient rule for
+distinguishing fresh-water from marine strata; since, if any
+univalves occur of which the mouths are not entire, we may presume
+that the formation is marine. The aperture is said to be entire in
+such shells as the fresh-water <i>Ampullaria</i> and the
+land-shells (Figs 38-42), when its outline is not interrupted by an
+indentation or notch, such as that seen at <i>b</i> in <i>
+Ancillaria</i> (Fig. 45); or is not prolonged into a canal, as that
+seen at <i>a</i> in <i>Pleurotoma</i> (Fig. 44).<a name="page57"></a></p>
+
+<p><img src="images/fig44.jpg" width="319" height="218" alt=
+"Fig. 44: Pleurotoma exorta. Fig. 45: Ancillaria subulata." /></p>
+
+<p>The mouths of a large proportion of the marine univalves have
+these notches or canals, and almost all species are carnivorous;
+whereas nearly all testacea having entire mouths are plant-eaters,
+whether the species be marine, fresh-water, or terrestrial.</p>
+
+<p>There is, however, one genus which affords an occasional
+exception to one of the above rules. The <i>Potamides</i> (Fig.
+37), a subgenus of Cerithium, although provided with a short canal,
+comprises some species which inhabit salt, others brackish, and
+others fresh-water, and they are said to be all plant-eaters.</p>
+
+<p>
+Among the fossils very common in fresh-water deposits are the shells of
+<i>Cypris,</i> a minute bivalve crustaceous animal.<a href="#fn-3.3"
+name="fnref-3.3" id="fnref-3.3"><sup>[3]</sup></a> Many minute living species
+of this genus swarm in lakes and stagnant pools in Great Britain; but their
+shells are not, if considered separately, conclusive as to the fresh-water
+origin of a deposit, because the majority of species in another kindred genus
+of the same order, the <i>Cytherina</i> of Lamarck, inhabit salt-water; and,
+although the animal differs slightly, the shell is scarcely distinguishable
+from that of the Cypris.
+</p>
+
+<p><b>Fresh-water Fossil
+Plants.</b>&mdash;The seed-vessels and stems of <i>
+Chara,</i> a genus of aquatic plants, are very frequent in
+fresh-water strata. These seed-vessels were called, before their
+true nature was known, gyrogonites, and were supposed to be
+foraminiferous shells. (See Fig. 46, <i>a</i>.)</p>
+
+<p>The <i>Charæ</i> inhabit the bottom of lakes and ponds,
+and flourish mostly where the water is charged with carbonate of
+lime. Their seed-vessels are covered with a very tough integument,
+capable of resisting decomposition; to which circumstance we may
+attribute their abundance in a fossil <a name="page58"></a>state. The annexed
+figure (Fig. 47) represents a branch of one
+of many new species found by Professor Amici in the lakes of
+Northern Italy. The seed-vessel in this plant is more globular than
+in the British <i>Charæ,</i>) and therefore more nearly
+resembles in form the extinct fossil species found in England,
+France, and other countries. The stems, as well as the
+seed-vessels, of these plants occur both in modern shell-marl and
+in ancient fresh-water formations. They are generally composed of a
+large central tube surrounded by smaller ones; the whole stem being
+divided at certain intervals by transverse partitions or joints.
+(See <i>b,</i> Fig. 46.)</p>
+
+<p><img src="images/fig46.jpg" width="391" height="248" alt=
+"Fig. 46: Chara medicaginula. Fig. 47: Chara elastica." /></p>
+
+<p>It is not uncommon to meet with layers of vegetable matter,
+impressions of leaves, and branches of trees, in strata containing
+fresh-water shells; and we also find occasionally the teeth and
+bones of land quadrupeds, of species now unknown. The manner in
+which such remains are occasionally carried by rivers into lakes,
+especially during floods, has been fully treated of in the
+&ldquo;Principles of Geology.&rdquo;</p>
+
+<p><b>Fresh-water and Marine
+Fish.</b>&mdash;The remains of fish are occasionally useful
+in determining the fresh-water origin of strata. Certain genera,
+such as carp, perch, pike, and loach (<i>Cyprinus, Perca, Esox,</i>
+and <i>Cobitis</i>), as also <i>Lebias,</i> being peculiar to
+fresh-water. Other genera contain some fresh-water and some marine
+species, as <i>Cottus, Mugil,</i> and <i>Anguilla,</i> or eel. The
+rest are either common to rivers and the sea, as the salmon; or are
+exclusively characteristic of salt-water. The above observations
+respecting fossil fishes are applicable only to the more modern or
+tertiary deposits; <a name="page59"></a>for in the more ancient rocks the forms depart so widely from
+those of existing fishes, that it is very difficult, at least in
+the present state of science, to derive any positive information
+from ichthyolites respecting the element in which strata were
+deposited.</p>
+
+<p>The alternation of marine and fresh-water formations, both on a
+small and large scale, are facts well ascertained in geology. When
+it occurs on a small scale, it may have arisen from the alternate
+occupation of certain spaces by river-water and the sea; for in the
+flood season the river forces back the ocean and freshens it over a
+large area, depositing at the same time its sediment; after which
+the salt-water again returns, and, on resuming its former place,
+brings with it sand, mud, and marine shells.</p>
+
+<p>There are also lagoons at the mouth of many rivers, as the Nile
+and Mississippi, which are divided off by bars of sand from the
+sea, and which are filled with salt and fresh water by turns. They
+often communicate exclusively with the river for months, years, or
+even centuries; and then a breach being made in the bar of sand,
+they are for long periods filled with salt-water.</p>
+
+<p>
+<b>Lym-Fiord.</b>&mdash;The Lym-Fiord in Jutland offers an excellent
+illustration of analogous changes; for, in the course of the last thousand
+years, the western extremity of this long frith, which is 120 miles in length,
+including its windings, has been four times fresh and four times salt, a bar of
+sand between it and the ocean having been often formed and removed. The last
+irruption of salt water happened in 1824, when the North Sea entered, killing
+all the fresh-water shells, fish, and plants; and from that time to the
+present, the sea-weed <i>Fucus vesiculosus,</i> together with oysters and other
+marine mollusca, have succeeded the <i>Cyclas, Lymnæa, Paludina,</i> and
+<i>Charæ.</i><a href="#fn-3.4" name="fnref-3.4"
+id="fnref-3.4"><sup>[4]</sup></a>
+</p>
+
+<p>But changes like these in the Lym-Fiord, and those before
+mentioned as occurring at the mouths of great rivers, will only
+account for some cases of marine deposits of partial extent resting
+on fresh-water strata. When we find, as in the south-east of
+England (Chapter XVIII), a great series of fresh-water beds, 1000
+feet in thickness, resting upon marine formations and again covered
+by other rocks, such as the Cretaceous, more than 1000 feet thick,
+and of deep-sea origin, we shall find it necessary to seek for a
+different explanation of the phenomena.</p>
+
+<p class="footnote">
+<a name="fn-3.1" id="fn-3.1"></a> <a href="#fnref-3.1">[1]</a>
+See Woodward&rsquo;s Manual of Mollusca, 1856.
+</p>
+
+<p class="footnote">
+<a name="fn-3.2" id="fn-3.2"></a> <a href="#fnref-3.2">[2]</a>
+The fresh-water Mulleria, when young, forms a single exception to the rule, as
+it then has two muscular impressions, but it has only one in the adult state.
+</p>
+
+<p class="footnote">
+<a name="fn-3.3" id="fn-3.3"></a> <a href="#fnref-3.3">[3]</a>
+For figures of fossil species of Purbeck, see Chapter XIX
+</p>
+
+<p class="footnote">
+<a name="fn-3.4" id="fn-3.4"></a> <a href="#fnref-3.4">[4]</a>
+See Principles, Index, &ldquo;Lym-Fiord.&rdquo;
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap04"></a><a name="page60"></a>CHAPTER IV.<br/>
+CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.</h2>
+
+<p class="letter">Chemical and Mechanical Deposits. &mdash; Cementing
+together of Particles. &mdash; Hardening by Exposure to
+Air. &mdash; Concretionary Nodules. &mdash; Consolidating Effects of
+Pressure. &mdash; Mineralization of Organic
+Remains. &mdash; Impressions and Casts: how formed. &mdash; Fossil
+Wood. &mdash; Goppert&rsquo;s Experiments. &mdash; Precipitation of Stony
+Matter most rapid where Putrefaction is going on. &mdash; Sources of
+Lime and Silex in Solution.</p>
+
+<p>Having spoken in the preceding chapters of the characters of
+sedimentary formations, both as dependent on the deposition of
+inorganic matter and the distribution of fossils, I may next treat
+of the consolidation of stratified rocks, and the petrifaction of
+imbedded organic remains.</p>
+
+<p><b>Chemical and Mechanical
+Deposits.</b>&mdash; A distinction has been made by
+geologists between deposits of a mechanical, and those of a
+chemical, origin. By the name mechanical are designated beds of
+mud, sand, or pebbles produced by the action of running water, also
+accumulations of stones and scoriæ thrown out by a volcano,
+which have fallen into their present place by the force of
+gravitation. But the matter which forms a chemical deposit has not
+been mechanically suspended in water, but in a state of solution
+until separated by chemical action. In this manner carbonate of
+lime is occasionally precipitated upon the bottom of lakes in a
+solid form, as may be well seen in many parts of Italy, where
+mineral springs abound, and where the calcareous stone, called
+travertin, is deposited. In these springs the lime is usually held
+in solution by an excess of carbonic acid, or by heat if it be a
+hot spring, until the water, on issuing from the earth, cools or
+loses part of its acid. The calcareous matter then falls down in a
+solid state, incrusting shells, fragments of wood and leaves, and
+binding them together.</p>
+
+<p>That similar travertin is formed at some points in the bed of
+the sea where calcareous springs issue cannot be doubted, but as a
+general rule the quantity of lime, according to Bischoff, spread
+through the waters of the ocean is very small, the free carbonic
+acid gas in the same waters being five times as much as is
+necessary to keep the lime in a fluid state. Carbonate of lime,
+therefore, can rarely be precipitated at the bottom of the sea by
+chemical action alone, but <a name="page61"></a>must be produced by vital agency as in the case of coral
+reefs.</p>
+
+<p>In such reefs, large masses of limestone are formed by the stony
+skeletons of zoophytes; and these, together with shells, become
+cemented together by carbonate of lime, part of which is probably
+furnished to the sea-water by the decomposition of dead corals.
+Even shells, of which the animals are still living on these reefs,
+are very commonly found to be incrusted over with a hard coating of
+limestone.</p>
+
+<p>If sand and pebbles are carried by a river into the sea, and
+these are bound together immediately by carbonate of lime, the
+deposit may be described as of a mixed origin, partly chemical, and
+partly mechanical.</p>
+
+<p>Now, the remarks already made in Chapter II, on the original
+horizontality of strata are strictly applicable to mechanical
+deposits, and only partially to those of a mixed nature. Such as
+are purely chemical may be formed on a very steep slope, or may
+even incrust the vertical walls of a fissure, and be of equal
+thickness throughout; but such deposits are of small extent, and
+for the most part confined to vein-stones.</p>
+
+<p><b>Consolidation of Strata.</b>&mdash;It is chiefly in the case of calcareous rocks that solidification
+takes place at the time of deposition. But there are many deposits
+in which a cementing process comes into operation long afterwards.
+We may sometimes observe, where the water of ferruginous or
+calcareous springs has flowed through a bed of sand or gravel, that
+iron or carbonate of lime has been deposited in the interstices
+between the grains or pebbles, so that in certain places the whole
+has been bound together into a stone, the same set of strata
+remaining in other parts loose and incoherent.</p>
+
+<p>Proofs of a similar cementing action are seen in a rock at
+Kelloway, in Wiltshire. A peculiar band of sandy strata belonging
+to the group called Oolite by geologists may be traced through
+several counties, the sand being for the most part loose and
+unconsolidated, but becoming stony near Kelloway. In this district
+there are numerous fossil shells which have decomposed, having for
+the most part left only their casts. The calcareous matter hence
+derived has evidently served, at some former period, as a cement to
+the siliceous grains of sand, and thus a solid sandstone has been
+produced. If we take fragments of many other argillaceous grits,
+retaining the casts of shells, and plunge them into dilute muriatic
+or other acid, we see them immediately changed into common sand and
+mud; the cement of lime, derived from the shells, having been
+dissolved by the acid.</p>
+
+<p><a name="page62"></a>Traces of impressions and casts are often extremely faint. In
+some loose sands of recent date we meet with shells in so advanced
+a stage of decomposition as to crumble into powder when touched. It
+is clear that water percolating such strata may soon remove the
+calcareous matter of the shell; and unless circumstances cause the
+carbonate of lime to be again deposited, the grains of sand will
+not be cemented together; in which case no memorial of the fossil
+will remain.</p>
+
+<p>In what manner silex and carbonate of lime may become widely
+diffused in small quantities through the waters which permeate the
+earth&rsquo;s crust will be spoken of presently, when the petrifaction of
+fossil bodies is considered; but I may remark here that such waters
+are always passing in the case of thermal springs from hotter to
+colder parts of the interior of the earth; and, as often as the
+temperature of the solvent is lowered, mineral matter has a
+tendency to separate from it and solidify. Thus a stony cement is
+often supplied to sand, pebbles, or any fragmentary mixture. In
+some conglomerates, like the pudding-stone of Hertfordshire (a
+Lower Eocene deposit), pebbles of flint and grains of sand are
+united by a siliceous cement so firmly, that if a block be
+fractured, the rent passes as readily through the pebbles as
+through the cement.</p>
+
+<p>It is probable that many strata became solid at the time when
+they emerged from the waters in which they were deposited, and when
+they first formed a part of the dry land. A well-known fact seems
+to confirm this idea: by far the greater number of the stones used
+for building and road-making are much softer when first taken from
+the quarry than after they have been long exposed to the air; and
+these, when once dried, may afterwards be immersed for any length
+of time in water without becoming soft again. Hence it is found
+desirable to shape the stones which are to be used in architecture
+while they are yet soft and wet, and while they contain their
+&ldquo;quarry-water,&rdquo; as it is called; also to break up stone intended
+for roads when soft, and then leave it to dry in the air for months
+that it may harden. Such induration may perhaps be accounted for by
+supposing the water, which penetrates the minutest pores of rocks,
+to deposit, on evaporation, carbonate of lime, iron, silex, and
+other minerals previously held in solution, and thereby to fill up
+the pores partially. These particles, on crystallising, would not
+only be themselves deprived of freedom of motion, but would also
+bind together other portions of the rock which before were loosely
+aggregated. On the same principle wet sand and mud become as hard
+as stone when <a name="page63"></a>frozen; because one ingredient of the mass, namely, the water,
+has crystallised, so as to hold firmly together all the separate
+particles of which the loose mud and sand were composed.</p>
+
+<p>
+Dr. MacCulloch mentions a sandstone in Skye, which may be moulded like dough
+when first found; and some simple minerals, which are rigid and as hard as
+glass in our cabinets, are often flexible and soft in their native beds: this
+is the case with asbestos, sahlite, tremolite, and chalcedony, and it is
+reported also to happen in the case of the beryl.<a href="#fn-4.1"
+name="fnref-4.1" id="fnref-4.1"><sup>[1]</sup></a>
+</p>
+
+<p>The marl recently deposited at the bottom of Lake Superior, in
+North America, is soft, and often filled with fresh-water shells;
+but if a piece be taken up and dried, it becomes so hard that it
+can only be broken by a smart blow of the hammer. If the lake,
+therefore, was drained, such a deposit would be found to consist of
+strata of marlstone, like that observed in many ancient European
+formations, and, like them, containing fresh-water shells.</p>
+
+<img src="images/fig48.jpg" width="195" height="97" alt=
+"Fig. 48: Calcareous nodules in Lias." />
+
+<p><b>Concretionary
+Structure.</b>&mdash;It is probable that some of the
+heterogeneous materials which rivers transport to the sea may at
+once set under water, like the artificial mixture called pozzolana,
+which consists of fine volcanic sand charged with about twenty per
+cent of oxide of iron, and the addition of a small quantity of
+lime. This substance hardens, and becomes a solid stone in water,
+and was used by the Romans in constructing the foundations of
+buildings in the sea. Consolidation in such cases is brought about
+by the action of chemical affinity on finely comminuted matter
+previously suspended in water. After deposition similar particles
+seem often to exert a mutual attraction on each other, and
+congregate together in particular spots, forming lumps, nodules,
+and concretions. Thus in many argillaceous deposits there are
+calcareous balls, or spherical concretions, ranged in layers
+parallel to the general stratification; an arrangement which took
+place after the shale or marl had been thrown down in successive
+laminæ; for these laminæ are often traceable through
+the concretions, remaining parallel to those of the surrounding
+unconsolidated rock. (See Fig. 48.) Such nodules of limestone have
+often a shell or other foreign body in the centre.</p>
+
+<p>Among the most remarkable examples of concretionary structure
+are those described by Professor Sedgwick as
+<a name="page64"></a>abounding in the magnesian limestone of the north of England.
+The spherical balls are of various sizes, from that of a pea to a
+diameter of several feet, and they have both a concentric and
+radiated structure, while at the same time the laminæ of
+original deposition pass uninterruptedly through them. In some
+cliffs this limestone resembles a great irregular pile of
+cannon-balls. Some of the globular masses have their centre in one
+stratum, while a portion of their exterior passes through to the
+stratum above or below. Thus the larger spheroid in the section
+(Fig. 49) passes from the stratum <i>b</i> upward into <i>a.</i> In
+this instance we must suppose the deposition of a series of minor
+layers, first forming the stratum <i>b,</i> and afterwards the
+incumbent stratum <i>a</i>; then a movement of the particles took
+place, and the carbonates of lime and magnesia separated from the
+more impure and mixed matter forming the still unconsolidated parts
+of the stratum. Crystallisation, beginning at the centre, must have
+gone on forming concentric coats around the original nucleus
+without interfering with the laminated structure of the rock.</p>
+
+<img src="images/fig49.jpg" width="181" height="201" alt=
+"Fig. 49: Spheroidal concretions in magnesian limestone. Fig. 50: Section through strata of grit." />
+
+<p>When the particles of rocks have been thus rearranged by
+chemical forces, it is sometimes difficult or impossible to
+ascertain whether certain lines of division are due to original
+deposition or to the subsequent aggregation of several particles.
+Thus suppose three strata of grit, A, B, C, are charged unequally
+with calcareous matter, and that B is the most calcareous. If
+consolidation takes place in B, the concretionary action may spread
+upward into a part of A, where the carbonate of lime is more
+abundant than in the rest; so that a mass, <i>d e f,</i> forming a
+portion of the superior stratum, becomes united with B into one
+solid mass of stone. The original line of division, <i>d e,</i>
+being thus effaced, the line <i>d f</i> would generally be
+considered as the surface of the bed B, though not strictly a true
+plane of stratification.</p>
+
+<p><b>Pressure and Heat.</b>&mdash;When
+sand and mud sink to the bottom of a deep sea, the particles are
+not pressed down by the enormous weight of the incumbent ocean; for
+the water, which becomes mingled with the sand and mud, resists
+pressure with a force equal to that of the column of fluid above.
+The same happens in regard to organic remains which are
+<a name="page65"></a>filled with water under great pressure as they sink, otherwise
+they would be immediately crushed to pieces and flattened.
+Nevertheless, if the materials of a stratum remain in a yielding
+state, and do not set or solidify, they will be gradually squeezed
+down by the weight of other materials successively heaped upon
+them, just as soft clay or loose sand on which a house is built may
+give way. By such downward pressure particles of clay, sand, and
+marl may become packed into a smaller space, and be made to cohere
+together permanently.</p>
+
+<p>Analogous effects of condensation may arise when the solid parts
+of the earth&rsquo;s crust are forced in various directions by those
+mechanical movements hereafter to be described, by which strata
+have been bent, broken, and raised above the level of the sea.
+Rocks of more yielding materials must often have been forced
+against others previously consolidated, and may thus by compression
+have acquired a new structure. A recent discovery may help us to
+comprehend how fine sediment derived from the detritus of rocks may
+be solidified by mere pressure. The graphite or &ldquo;black lead&rdquo; of
+commerce having become very scarce, Mr. Brockedon contrived a
+method by which the dust of the purer portions of the mineral found
+in Borrowdale might be recomposed into a mass as dense and compact
+as native graphite. The powder of graphite is first carefully
+prepared and freed from air, and placed under a powerful press on a
+strong steel die, with air-tight fittings. It is then struck
+several blows, each of a power of 1000 tons; after which operation
+the powder is so perfectly solidified that it can be cut for
+pencils, and exhibits when broken the same texture as native
+graphite.</p>
+
+<p>But the action of heat at various depths in the earth is
+probably the most powerful of all causes in hardening sedimentary
+strata. To this subject I shall refer again when treating of the
+metamorphic rocks, and of the slaty and jointed structure.</p>
+
+<p><b>Mineralisation of Organic
+Remains.</b>&mdash;The changes which fossil organic bodies
+have undergone since they were first imbedded in rocks, throw much
+light on the consolidation of strata. Fossil shells in some modern
+deposits have been scarcely altered in the course of centuries,
+having simply lost a part of their animal matter. But in other
+cases the shell has disappeared, and left an impression only of its
+exterior, or, secondly, a cast of its interior form, or, thirdly, a
+cast of the shell itself, the original matter of which has been
+removed. These different forms of fossilisation may easily
+<a name="page66"></a>be understood if we examine the mud recently thrown out from a
+pond or canal in which there are shells. If the mud be
+argillaceous, it acquires consistency on drying, and on breaking
+open a portion of it we find that each shell has left impressions
+of its external form. If we then remove the shell itself, we find
+within a solid nucleus of clay, having the form of the interior of
+the shell. This form is often very different from that of the outer
+shell. Thus a cast such as <i>a,</i> Fig. 51, commonly called a
+fossil screw, would never be suspected by an inexperienced
+conchologist to be the internal shape of the fossil univalve, <i>
+b,</i> Fig. 51. Nor should we have imagined at first sight that the
+shell a and the cast <i>b,</i> Fig. 52, belong to one and the same
+fossil. The reader will observe, in the last-mentioned figure
+(<i>b,</i> Fig. 52), that an empty space shaded dark, which the <i>
+shell itself</i> once occupied, now intervenes between the
+enveloping stone and the cast of the smooth interior of the whorls.
+In such cases the shell has been dissolved and the component
+particles removed by water percolating the rock. If the nucleus
+were taken out, a hollow mould would remain, on which the external
+form of the shell with its tubercles and striæ, as seen in
+<i>a,</i> Fig. 52, would be seen embossed. Now if the space alluded
+to between the nucleus and the impression, instead of being left
+empty, has been filled up with calcareous spar, flint, pyrites, or
+other mineral, we then obtain from the mould an exact cast both of
+the external and internal form of the original shell. In this
+manner silicified casts of shells have been formed; and if the mud
+or sand of the nucleus happen to be incoherent, or soluble in acid,
+we can then procure in flint an empty shell, which in shape is the
+exact counterpart of the original. This cast may be compared to a
+bronze statue, representing merely the superficial form,
+<a name="page67"></a>and not the internal organisation; but there is another
+description of petrifaction by no means uncommon, and of a much
+more wonderful kind, which may be compared to certain anatomical
+models in wax, where not only the outward forms and features, but
+the nerves, blood-vessels, and other internal organs are also
+shown. Thus we find corals, originally calcareous, in which not
+only the general shape, but also the minute and complicated
+internal organisation is retained in flint.</p>
+
+<p><img src="images/fig51.jpg" width="314" height="197" alt=
+"Fig. 51: Phasianella Heddingtonensis. Fig. 52: Pleurotomaria Anglica." />
+</p>
+
+<p>
+<img src="images/fig53.jpg" width="137" height="167" alt="Fig. 53: Section of a tree from the coal-measures." />
+</p>
+
+<p>Such a process of petrifaction is still more remarkably
+exhibited in fossil wood, in which we often perceive not only the
+rings of annual growth, but all the minute vessels and medullary
+rays. Many of the minute cells and fibres of plants, and even those
+spiral vessels which in the living vegetable can only be discovered
+by the microscope, are preserved. Among many instances, I may
+mention a fossil tree, seventy-two feet in length, found at
+Gosforth, near Newcastle, in sandstone strata associated with coal.
+By cutting a transverse slice so thin as to transmit light, and
+magnifying it about fifty-five times, the texture, as seen in Fig.
+53, is exhibited. A texture equally minute and complicated has been
+observed in the wood of large trunks of fossil trees found in the
+Craigleith quarry near Edinburgh, where the stone was not in the
+slightest degree siliceous, but consisted chiefly of carbonate of
+lime, with oxide of iron, alumina, and carbon. The parallel rows of
+vessels here seen are the rings of annual growth, but in one part
+they are imperfectly preserved, the wood having probably decayed
+before the mineralising matter had penetrated to that portion of
+the tree.</p>
+
+<p>In attempting to explain the process of petrifaction in such
+cases, we may first assume that strata are very generally permeated
+by water charged with minute portions of calcareous, siliceous, and
+other earths in solution. In what manner they become so impregnated
+will be afterwards considered. If an organic substance is exposed
+in the open air to the action of the sun and rain, it will in time
+putrefy, or be dissolved into its component elements, consisting
+usually of oxygen, hydrogen, nitrogen, and carbon. These will
+readily be absorbed by the atmosphere or be washed away by rain, so
+that all vestiges of the dead animal or plant disappear. But if the
+same substances be submerged in water, they decompose more
+gradually; and if buried in earth, still more
+<a name="page68"></a>slowly; as in the familiar example of wooden piles or other
+buried timber. Now, if as fast as each particle is set free by
+putrefaction in a fluid or gaseous state, a particle equally minute
+of carbonate of lime, flint, or other mineral, is at hand ready to
+be precipitated, we may imagine this inorganic matter to take the
+place just before left unoccupied by the organic molecule. In this
+manner a cast of the interior of certain vessels may first be
+taken, and afterwards the more solid walls of the same may decay
+and suffer a like transmutation. Yet when the whole is lapidified,
+it may not form one homogeneous mass of stone or metal. Some of the
+original ligneous, osseous, or other organic elements may remain
+mingled in certain parts, or the lapidifying substance itself may
+be differently coloured at different times, or so crystallised as
+to reflect light differently, and thus the texture of the original
+body may be faithfully exhibited.</p>
+
+<p>The student may perhaps ask whether, on chemical principles, we
+have any ground to expect that mineral matter will be thrown down
+precisely in those spots where organic decomposition is in
+progress? The following curious experiments may serve to illustrate
+this point: Professor Goppert of Breslau, with a view of imitating
+the natural process of petrifaction, steeped a variety of animal
+and vegetable substances in waters, some holding siliceous, others
+calcareous, others metallic matter in solution. He found that in
+the period of a few weeks, or sometimes even days, the organic
+bodies thus immersed were mineralised to a certain extent. Thus,
+for example, thin vertical slices of deal, taken from the Scotch
+fir (<i>Pinus sylvestris</i>), were immersed in a moderately strong
+solution of sulphate of iron. When they had been thoroughly soaked
+in the liquid for several days they were dried and exposed to a
+red-heat until the vegetable matter was burnt up and nothing
+remained but an oxide of iron, which was found to have taken the
+form of the deal so exactly that casts even of the dotted vessels
+peculiar to this family of plants were distinctly visible under the
+microscope.</p>
+
+<p>The late Dr. Turner observes, that when mineral matter is in a
+&ldquo;nascent state,&rdquo; that is to say, just liberated from a previous
+state of chemical combination, it is most ready to unite with other
+matter, and form a new chemical compound. Probably the particles or
+atoms just set free are of extreme minuteness, and therefore move
+more freely, and are more ready to obey any impulse of chemical
+affinity. Whatever be the cause, it clearly follows, as before
+stated, that where organic matter newly imbedded in sediment is
+decomposing, there will chemical changes take place most
+actively.</p>
+
+<p>
+<a name="page69"></a>An analysis was lately made of the water which was flowing
+off from the rich mud deposited by the Hooghly River in the Delta of the Ganges
+after the annual inundation. This water was found to be highly charged with
+carbonic acid holding lime in solution.<a href="#fn-4.2" name="fnref-4.2"
+id="fnref-4.2"><sup>[2]</sup></a> Now if newly-deposited mud is thus proved to
+be permeated by mineral matter in a state of solution, it is not difficult to
+perceive that decomposing organic bodies, naturally imbedded in sediment, may
+as readily become petrified as the substances artificially immersed by
+Professor Goppert in various fluid mixtures.
+</p>
+
+<p>It is well known that the waters of all springs are more or less
+charged with earthy, alkaline, or metallic ingredients derived from
+the rocks and mineral veins through which they percolate. Silex is
+especially abundant in hot springs, and carbonate of lime is almost
+always present in greater or less quantity. The materials for the
+petrifaction of organic remains are, therefore, usually at hand in
+a state of chemical solution wherever organic remains are imbedded
+in new strata.</p>
+
+<p class="footnote">
+<a name="fn-4.1" id="fn-4.1"></a> <a href="#fnref-4.1">[1]</a>
+Dr. MacCulloch, Syst. of Geol., vol. i, p. 123.
+</p>
+
+
+<p class="footnote">
+<a name="fn-4.2" id="fn-4.2"></a> <a href="#fnref-4.2">[2]</a>
+Piddington, Asiat. Research., vol. xviii, p. 226.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap05"></a><a name="page70"></a>CHAPTER V.<br/>
+ELEVATION OF STRATA ABOVE THE SEA.&mdash;HORIZONTAL AND INCLINED
+STRATIFICATION.</h2>
+
+<p class="letter">Why the Position of Marine Strata, above the Level
+of the Sea, should be referred to the rising up of the Land, not to
+the going down of the Sea. &mdash; Strata of Deep-sea and
+Shallow-water Origin alternate. &mdash; Also Marine and Fresh-water
+Beds and old Land Surfaces. &mdash; Vertical, inclined, and folded
+Strata. &mdash; Anticlinal and Synclinal Curves. &mdash; Theories
+to explain Lateral Movements. &mdash; Creeps in Coal-mines. &mdash;
+Dip and Strike. &mdash; Structure of the Jura. &mdash; Various
+Forms of Outcrop. &mdash; Synclinal Strata forming Ridges. &mdash;
+Connection of Fracture and Flexure of Rocks. &mdash; Inverted
+Strata. &mdash; Faults described. &mdash; Superficial Signs of the
+same obliterated by Denudation. &mdash; Great Faults the Result of
+repeated Movements. &mdash; Arrangement and Direction of parallel
+Folds of Strata. &mdash; Unconformability. &mdash; Overlapping
+Strata.</p>
+
+<p><b>Land has been raised, not the Sea
+lowered.</b>&mdash;It has been already stated that the
+aqueous rocks containing marine fossils extend over wide
+continental tracts, and are seen in mountain chains rising to great
+heights above the level of the sea <a href="#page29">(p.
+29)</a>. Hence it follows, that what is now dry land was once under
+water. But if we admit this conclusion, we must imagine, either
+that there has been a general lowering of the waters of the ocean,
+or that the solid rocks, once covered by water, have been raised up
+bodily out of the sea, and have thus become dry land. The earlier
+geologists, finding themselves reduced to this alternative,
+embraced the former opinion, assuming that the ocean was originally
+universal, and had gradually sunk down to its actual level, so that
+the present islands and continents were left dry. It seemed to them
+far easier to conceive that the water had gone down, than that
+solid land had risen upward into its present position. It was,
+however, impossible to invent any satisfactory hypothesis to
+explain the disappearance of so enormous a body of water throughout
+the globe, it being necessary to infer that the ocean had once
+stood at whatever height marine shells might be detected. It
+moreover appeared clear, as the science of geology advanced, that
+certain spaces on the globe had been alternately sea, then land,
+then estuary, then sea again, and, lastly, once more habitable
+land, having remained in each of these states for considerable
+periods. In order to account for such phenomena
+<a name="page71"></a>without admitting any movement of the land itself, we are
+required to imagine several retreats and returns of the ocean; and
+even then our theory applies merely to cases where the marine
+strata composing the dry land are horizontal, leaving unexplained
+those more common instances where strata are inclined, curved, or
+placed on their edges, and evidently not in the position in which
+they were first deposited.</p>
+
+<p>Geologists, therefore, were at last compelled to have recourse
+to the doctrine that the solid land has been repeatedly moved
+upward or downward, so as permanently to change its position
+relatively to the sea. There are several distinct grounds for
+preferring this conclusion. First, it will account equally for the
+position of those elevated masses of marine origin in which the
+stratification remains horizontal, and for those in which the
+strata are disturbed, broken, inclined, or vertical. Secondly, it
+is consistent with human experience that land should rise gradually
+in some places and be depressed in others. Such changes have
+actually occurred in our own days, and are now in progress, having
+been accompanied in some cases by violent convulsions, while in
+others they have proceeded so insensibly as to have been
+ascertainable only by the most careful scientific observations,
+made at considerable intervals of time. On the other hand, there is
+no evidence from human experience of a rising or lowering of the
+sea&rsquo;s level in any region, and the ocean cannot be raised or
+depressed in one place without its level being changed all over the
+globe.</p>
+
+<p>These preliminary remarks will prepare the reader to understand
+the great theoretical interest attached to all facts connected with
+the position of strata, whether horizontal or inclined, curved or
+vertical.</p>
+
+<p>Now the first and most simple appearance is where strata of
+marine origin occur above the level of the sea in horizontal
+position. Such are the strata which we meet with in the south of
+Sicily, filled with shells for the most part of the same species as
+those now living in the Mediterranean. Some of these rocks rise to
+the height of more than 2000 feet above the sea. Other mountain
+masses might be mentioned, composed of horizontal strata of high
+antiquity, which contain fossil remains of animals wholly
+dissimilar from any now known to exist. In the south of Sweden, for
+example, near Lake Wener, the beds of some of the oldest
+fossiliferous deposits, called Silurian and Cambrian by geologists,
+occur in as level a position as if they had recently formed part of
+the delta of a great river, and been left dry
+<a name="page72"></a>on the retiring of the annual floods. Aqueous rocks of equal
+antiquity extend for hundreds of miles over the lake-district of
+North America, and exhibit in like manner a stratification nearly
+undisturbed. The Table Mountain at the Cape of Good Hope is another
+example of highly elevated yet perfectly horizontal strata, no less
+than 3500 feet in thickness, and consisting of sandstone of very
+ancient date.</p>
+
+<p>
+Instead of imagining that such fossiliferous rocks were always at their present
+level, and that the sea was once high enough to cover them, we suppose them to
+have constituted the ancient bed of the ocean, and to have been afterwards
+uplifted to their present height. This idea, however startling it may at first
+appear, is quite in accordance, as before stated, with the analogy of changes
+now going on in certain regions of the globe. Thus, in parts of Sweden, and the
+shores and islands of the Gulf of Bothnia, proofs have been obtained that the
+land is experiencing, and has experienced for centuries, a slow upheaving
+movement.<a href="#fn-5.1" name="fnref-5.1" id="fnref-5.1"><sup>[1]</sup></a>
+</p>
+
+<p>It appears from the observations of Mr. Darwin and others, that
+very extensive regions of the continent of South America have been
+undergoing slow and gradual upheaval, by which the level plains of
+Patagonia, covered with recent marine shells, and the Pampas of
+Buenos Ayres, have been raised above the level of the sea. On the
+other hand, the gradual sinking of the west coast of Greenland, for
+the space of more than 600 miles from north to south, during the
+last four centuries, has been established by the observations of a
+Danish naturalist, Dr. Pingel. And while these proofs of
+continental elevation and subsidence, by slow and insensible
+movements, have been recently brought to light, the evidence has
+been daily strengthened of continued changes of level effected by
+violent convulsions in countries where earthquakes are frequent.
+There the rocks are rent from time to time, and heaved up or thrown
+down several feet at once, and disturbed in such a manner as to
+show how entirely the original position of strata may be modified
+in the course of centuries.</p>
+
+<p>Mr. Darwin has also inferred that, in those seas where circular
+coral islands and barrier reefs abound, there is a slow and
+continued sinking of the submarine mountains on which the masses of
+coral are based; while there are other areas of the South Sea where
+the land is on the rise, and where coral has been upheaved far
+above the sea-level.</p>
+
+<p><b>Alternations of Marine and Fresh-water
+Strata.</b>&mdash;It has been shown in the third chapter
+that there is such a difference<a name="page73"></a>between land, fresh-water, and marine fossils as to enable the
+geologist to determine whether particular groups of strata were
+formed at the bottom of the ocean or in estuaries, rivers, or
+lakes. If surprise was at first created by the discovery of marine
+corals and shells at the height of several miles above the
+sea-level, the imagination was afterwards not less startled by
+observing that in the successive strata composing the earth&rsquo;s
+crust, especially if their total thickness amounted to thousands of
+feet, they comprised in some parts formations of shallow-sea as
+well as of deep-sea origin; also beds of brackish or even of purely
+fresh-water formation, as well as vegetable matter or coal
+accumulated on ancient land. In these cases we as frequently find
+fresh-water beds below a marine set or shallow-water under those of
+deep-sea origin as the reverse. Thus, if we bore an artesian well
+below London, we pass through a marine clay, and there reach, at
+the depth of several hundred feet, a shallow-water and fluviatile
+sand, beneath which comes the white chalk originally formed in a
+deep sea. Or if we bore vertically through the chalk of the North
+Downs, we come, after traversing marine chalky strata, upon a
+fresh-water formation many hundreds of feet thick, called the
+Wealden, such as is seen in Kent and Surrey, which is known in its
+turn to rest on purely marine beds. In like manner, in various
+parts of Great Britain we sink vertical shafts through marine
+deposits of great thickness, and come upon coal which was formed by
+the growth of plants on an ancient land-surface sometimes hundreds
+of square miles in extent.</p>
+
+<p><b>Vertical, Inclined, and Curved
+Strata.</b>&mdash;It has been stated that marine strata of
+different ages are sometimes found at a considerable height above
+the sea, yet retaining their original horizontality; but this state
+of things is quite exceptional. As a general rule, strata are
+inclined or bent in such a manner as to imply that their original
+position has been altered.</p>
+
+<img src="images/fig54.jpg" width="172" height="152" alt=
+"Fig. 54: Vertical conglomerate and sandstone." />
+
+<p>The most unequivocal evidence of such a change is afforded by
+their standing up vertically, showing their edges, which is by no
+means a rare phenomenon, especially in mountainous countries. Thus
+we find in Scotland, on the southern skirts of the Grampians, beds
+of pudding-stone alternating with thin layers of fine sand, all
+placed vertically to the horizon. When Saussure first observed
+certain conglomerates in a
+<a name="page74"></a>similar position in the Swiss Alps, he remarked that the
+pebbles, being for the most part of an oval shape, had their longer
+axes parallel to the planes of stratification (see Fig. 54 on
+preceding page). From this he inferred that such strata must, at
+first, have been horizontal, each oval pebble having settled at the
+bottom of the water, with its flatter side parallel to the horizon,
+for the same reason that an egg will not stand on either end if
+unsupported. Some few, indeed, of the rounded stones in a
+conglomerate occasionally afford an exception to the above rule,
+for the same reason that in a river&rsquo;s bed, or on a shingle beach,
+some pebbles rest on their ends or edges; these having been shoved
+against or between other stones by a wave or current, so as to
+assume this position.</p>
+
+<p><b>Anticlinal and Synclinal
+Curves.</b>&mdash;Vertical strata, when they can be traced
+continuously upward or downward for some depth, are almost
+invariably seen to be parts of great curves, which may have a
+diameter of a few yards, or of several miles. I shall first
+describe two curves of considerable regularity, which occur in
+Forfarshire, extending over a country twenty miles in breadth, from
+the foot of the Grampians to the sea near Arbroath.</p>
+
+<p><img src="images/fig55.jpg" width="597" height="197" alt=
+"Fig. 55: Section of Forfarshire, from N.W. to S.E." /></p>
+
+<p>The mass of strata here shown may be 2000 feet in thickness,
+consisting of red and white sandstone, and various coloured shales,
+the beds being distinguishable into four principal groups, namely,
+No. 1, red marl or shale; No. 2, red sandstone, used for building;
+No. 3, conglomerate; and No. 4, grey paving-stone, and tile-stone,
+with green and reddish shale, containing peculiar organic remains.
+A glance at the
+<a name="page75"></a>section will show that each of the formations 2, 3, 4 are
+repeated thrice at the surface, twice with a southerly, and once
+with a northerly inclination or <i>dip</i>, and the beds in No. 1,
+which are nearly horizontal, are still brought up twice by a slight
+curvature to the surface, once on each side of A. Beginning at the
+north-west extremity, the tile-stones and conglomerates, No. 4 and
+No. 3, are vertical, and they generally form a ridge parallel to
+the southern skirts of the Grampians. The superior strata, Nos. 2
+and 1, become less and less inclined on descending to the valley of
+Strathmore, where the strata, having a concave bend, are said by
+geologists to lie in a &ldquo;trough&rdquo; or&ldquo;basin.&rdquo; Through the centre of
+this valley runs an imaginary line A, called technically a
+&ldquo;synclinal line,&rdquo; where the beds, which are tilted in opposite
+directions, may be supposed to meet. It is most important for the
+observer to mark such lines, for he will perceive by the diagram
+that, in travelling from the north to the centre of the basin, he
+is always passing from older to newer beds; whereas, after crossing
+the line A, and pursuing his course in the same southerly
+direction, he is continually leaving the newer, and advancing upon
+older strata. All the deposits which he had before examined begin
+then to recur in reversed order, until he arrives at the central
+axis of the Sidlaw hills, where the strata are seen to form an
+arch, or <i>saddle</i>, having an <i>anticlinal</i> line, B, in the
+centre. On passing this line, and continuing towards the S.E., the
+formations 4, 3, and 2, are again repeated, in the same relative
+order of superposition, but with a southerly dip. At Whiteness (see
+Fig. 55) it will be seen that the inclined strata are covered by a
+newer deposit, <i>a</i>, in horizontal beds. These are composed of
+red conglomerate and sand, and are newer than any of the groups, 1,
+2, 3, 4, before described, and rest <i>unconformably</i> upon
+strata of the sandstone group, No. 2.</p>
+
+<p>
+An example of curved strata, in which the bends or convolutions of the rock are
+sharper and far more numerous within an equal space, has been well described by
+Sir James Hall.<a href="#fn-5.2" name="fnref-5.2"
+id="fnref-5.2"><sup>[2]</sup></a> It occurs near St. Abb&rsquo;s Head, on the
+east coast of Scotland, where the rocks consist principally of a bluish slate,
+having frequently a ripple-marked surface. The undulations of the beds reach
+from the top to the bottom of cliffs from 200 to 300 feet in height, and there
+are sixteen distinct bendings in the course of about six miles, the curvatures
+being alternately concave and convex upward.
+</p>
+
+<p><b>Folding by Lateral
+Movement.</b>&mdash;An experiment was made by Sir James
+Hall, with a view of illustrating the manner in
+<a name="page76"></a>which such strata, assuming them to have been originally
+horizontal, may have been forced into their present position. A set
+of layers of clay were placed under a weight, and their opposite
+ends pressed towards each other with such force as to cause them to
+approach more nearly together. On the removal of the weight, the
+layers of clay were found to be curved and folded, so as to bear a
+miniature resemblance to the strata in the cliffs. We must,
+however, bear in mind that in the natural section or sea-cliff we
+only see the foldings imperfectly, one part being invisible beneath
+the sea, and the other, or upper portion, being supposed to have
+been carried away by <i>denudation</i>, or that action of water
+which will be explained in the next chapter. The dark lines in the
+plan (Fig. 57) represent what is actually seen of the strata in
+the line of cliff alluded to; the fainter lines, that portion which
+is concealed beneath the sea-level, as also that which is supposed
+to have once existed above the present surface.</p>
+
+<p>
+<img src="images/fig56.jpg" width="347" height="221" alt=
+"Fig. 56: Curved strata of slate near St. Abb’s Head, Berwickshire." />
+</p>
+
+<p><img src="images/fig57.jpg" width="345" height="195" alt=
+"Fig. 57" /></p>
+
+<p>
+<a name="page77"></a>We may still more easily illustrate the effects which a lateral
+thrust might produce on flexible strata, by placing several pieces
+of differently coloured cloths upon a table, and when they are
+spread out horizontally, cover them with a book. Then apply other
+books to each end, and force them towards each other. The folding
+of the cloths (see Fig. 58) will imitate those of the bent strata;
+the incumbent book being slightly lifted up, and no longer touching
+the two volumes on which it rested before, because it is supported
+by the tops of the anticlinal ridges formed by the curved cloths.
+In like manner there can be no doubt that the squeezed strata,
+although laterally condensed and more closely packed, are yet
+elongated and made to rise upward, in a direction perpendicular to
+the pressure.</p>
+
+<p><img src="images/fig58.jpg" width="358" height="205" alt=
+"Fig. 58" /></p>
+
+<p>Whether the analogous flexures in stratified rocks have really
+been due to similar sideway movements is a question which we can
+not decide by reference to our own observation. Our inability to
+explain the nature of the process is, perhaps, not simply owing to
+the inaccessibility of the subterranean regions where the
+mechanical force is exerted, but to the extreme slowness of the
+movement. The changes may sometimes be due to variation in the
+temperature of mountain masses of rock causing them, while still
+solid, to expand or contract; or melting them, and then again
+cooling them and allowing them to crystallise. If such be the case,
+we have scarcely more reason to expect to witness the operation of
+the process within the limited periods of our scientific
+observation than to see the swelling of the roots of a tree, by
+which, in the course of years, a wall of solid masonry may be
+lifted up, rent or thrown down. In both instances the force may be
+irresistible, but though adequate, it need not be visible by us,
+provided the time required for its development be very great. The
+lateral pressure arising from the unequal expansion of rocks by
+heat may cause one mass lying in the same horizontal plane
+gradually to occupy
+<a name="page78"></a>a larger space, so as to press upon another rock, which, if
+flexible, may be squeezed into a bent and folded form. It will also
+appear, when the volcanic and granitic rocks are described, that
+some of them have, when melted in the interior of the earth&rsquo;s
+crust, been injected forcibly into fissures, and after the
+solidification of such intruded matter, other sets of rents,
+crossing the first, have been formed and in their turn filled by
+melted rock. Such repeated injections imply a stretching, and often
+upheaval, of the whole mass.</p>
+
+<p>We also know, especially by the study of regions liable to
+earthquakes, that there are causes at work in the interior of the
+earth capable of producing a sinking in of the ground, sometimes
+very local, but often extending over a wide area. The continuance
+of such a downward movement, especially if partial and confined to
+linear areas, may produce regular folds in the strata.</p>
+
+<p>
+<b>Creeps in Coal-mines.</b>&mdash;The &ldquo;creeps,&rdquo; as they are called
+in coal-mines, afford an excellent illustration of this fact.&mdash;First, it
+may be stated generally, that the excavation of coal at a considerable depth
+causes the mass of overlying strata to sink down bodily, even when props are
+left to support the roof of the mine. &ldquo;In Yorkshire,&rdquo; says Mr.
+Buddle, &ldquo;three distinct subsidences were perceptible at the surface,
+after the clearing out of three seams of coal below, and innumerable vertical
+cracks were caused in the incumbent mass of sandstone and shale which thus
+settled down.&rdquo;<a href="#fn-5.3" name="fnref-5.3"
+id="fnref-5.3"><sup>[3]</sup></a> The exact amount of depression in these cases
+can only be accurately measured where water accumulates on the surface, or a
+railway traverses a coal-field.
+</p>
+
+<p>When a bed of coal is worked out, pillars or rectangular masses
+of coal are left at intervals as props to support the roof, and
+protect the colliers. Thus in Fig. 59, representing a section at
+Wallsend, Newcastle, the galleries which have been excavated are
+represented by the white spaces <i>a, b,</i> while the adjoining
+dark portions are parts of the original coal seam left as props,
+beds of sandy clay or shale constituting the floor of the mine.
+When the props have been reduced in size, they are pressed down by
+the weight of overlying rocks (no less than 630 feet thick) upon
+the shale below, which is thereby squeezed and forced up into the
+open spaces.</p>
+
+<p>
+Now it might have been expected that, instead of the floor rising up, the
+ceiling would sink down, and this effect, called a &ldquo;thrust,&rdquo; does,
+in fact, take place where the pavement is more solid than the roof. But it
+usually happens, in <a name="page79"></a>coal-mines, that the roof is composed
+of hard shale, or occasionally of sandstone, more unyielding than the
+foundation, which often consists of clay. Even where the argillaceous substrata
+are hard at first, they soon become softened and reduced to a plastic state
+when exposed to the contact of air and water in the floor of a mine.
+</p>
+
+<p><img src="images/fig59.jpg" width="390" height="266" alt=
+"Fig. 59: Section of carboniferous strata at Wallsend showing ‘creeps’." />
+</p>
+
+<p>The first symptom of a &ldquo;creep,&rdquo; says Mr. Buddle, is a slight
+curvature at the bottom of each gallery, as at <i>a</i>, Fig. 59:
+then the pavement, continuing to rise, begins to open with a
+longitudinal crack, as at <i>b</i>; then the points of the
+fractured ridge reach the roof, as at <i>c</i>; and, lastly, the
+upraised beds close up the whole gallery, and the broken portions
+of the ridge are reunited and flattened at the top, exhibiting the
+flexure seen at <i>d.</i> Meanwhile the coal in the props has
+become crushed and cracked by pressure. It is also found that below
+the creeps <i>a, b, c, d,</i> an inferior stratum, called the
+&ldquo;metal coal,&rdquo; which is 3 feet thick, has been fractured at the
+points <i>e, f, g, h,</i> and has risen, so as to prove that the
+upward movement, caused by the working out of the &ldquo;main coal,&rdquo; has
+been propagated through a thickness of 54 feet of argillaceous
+beds, which intervene between the two coal-seams. This same
+displacement has also been traced downward more than 150 feet below
+the metal coal, but it grows continually less and less until it
+becomes imperceptible.</p>
+
+<p>No part of the process above described is more deserving of our
+notice than the slowness with which the change in the arrangement
+of the beds is brought about. Days,
+<a name="page80"></a>months, or even years, will sometimes elapse between the first
+bending of the pavement and the time of its reaching the roof.
+Where the movement has been most rapid, the curvature of the beds
+is most regular, and the reunion of the fractured ends most
+complete; whereas the signs of displacement or violence are
+greatest in those creeps which have required months or years for
+their entire accomplishment. Hence we may conclude that similar
+changes may have been wrought on a larger scale in the earth&rsquo;s
+crust by partial and gradual subsidences, especially where the
+ground has been undermined throughout long periods of time; and we
+must be on our guard against inferring sudden violence, simply
+because the distortion of the beds is excessive.</p>
+
+<p>Engineers are familiar with the fact that when they raise the
+level of a railway by heaping stone or gravel on a foundation of
+marsh, quicksand, or other yielding formation, the new mound often
+sinks for a time as fast as they attempt to elevate it; when they
+have persevered so as to overcome this difficulty, they frequently
+find that some of the adjoining flexible ground has risen up in one
+or more parallel arches or folds, showing that the vertical
+pressure of the sinking materials has given rise to a lateral
+folding movement.</p>
+
+<p>In like manner, in the interior of the earth, the solid parts of
+the earth&rsquo;s crust may sometimes, as before mentioned, be made to
+expand by heat, or may be pressed by the force of steam against
+flexible strata loaded with a great weight of incumbent rocks. In
+this case the yielding mass, squeezed, but unable to overcome the
+resistance which it meets with in a vertical direction, may be
+gradually relieved by lateral folding.</p>
+
+<img src="images/fig60.jpg" width="191" height="99" alt="Fig. 60" />
+
+<p><b>Dip and Strike.</b>&mdash;In
+describing the manner in which strata depart from their original
+horizontality, some technical terms, such as &ldquo;dip&rdquo; and &ldquo;strike,&rdquo;
+&ldquo;anticlinal&rdquo; and &ldquo;synclinal&rdquo; line or axis, are used by geologists.
+I shall now proceed to explain some of these to the student. If a
+stratum or bed of rock, instead of being quite level, be inclined
+to one side, it is said to <i>dip</i>; the point of the compass to
+which it is inclined is called the <i>point of dip</i>, and the
+degree of deviation from a level or horizontal line is called <i>
+the amount of dip</i>, or <i>the angle of dip.</i> Thus, in the
+annexed diagram (Fig. 60), a series of strata are inclined, and
+they dip to the north at an angle of forty-five
+<a name="page81"></a>degrees. The <i>strike</i>, or <i>line of bearing</i>, is the
+prolongation or extension of the strata in a direction <i>at right
+angles</i> to the dip; and hence it is sometimes called the <i>
+direction</i> of the strata. Thus, in the above instance of strata
+dipping to the north, their strike must necessarily be east and
+west. We have borrowed the word from the German geologists, <i>
+streichen</i> signifying to extend, to have a certain direction.
+Dip and strike may be aptly illustrated by a row of houses running
+east and west, the long ridge of the roof representing the strike
+of the stratum of slates, which dip on one side to the north, and
+on the other to the south.</p>
+
+<p>A stratum which is horizontal, or quite level in all directions,
+has neither dip nor strike.</p>
+
+<p>It is always important for the geologist, who is endeavouring to
+comprehend the structure of a country, to learn how the beds dip in
+every part of the district; but it requires some practice to avoid
+being occasionally deceived, both as to the point of dip and the
+amount of it.</p>
+
+<p><img src="images/fig61.jpg" width="333" height="192" alt=
+"Fig. 61: Apparent horizontality of inclined strata." /></p>
+
+<p>If the upper surface of a hard stony stratum be uncovered,
+whether artificially in a quarry, or by waves at the foot of a
+cliff, it is easy to determine towards what point of the compass
+the slope is steepest, or in what direction water would flow if
+poured upon it. This is the true dip. But the edges of highly
+inclined strata may give rise to perfectly horizontal lines in the
+face of a vertical cliff, if the observer see the strata in the
+line of the strike, the dip being inward from the face of the
+cliff. If, however, we come to a break in the cliff, which exhibits
+a section exactly at right angles to the line of the strike, we are
+then able to ascertain the true dip. In the drawing (Fig. 61), we
+may suppose a headland, one side of which faces to the north, where
+the beds would appear perfectly horizontal to a person in the boat;
+while in the other side facing the west, the true dip
+<a name="page82"></a>would be seen by the person on shore to be at an angle of
+40&deg;. If, therefore, our observations are confined to a vertical
+precipice facing in one direction, we must endeavour to find a
+ledge or portion of the plane of one of the beds projecting beyond
+the others, in order to ascertain the true dip.</p>
+
+<img src="images/fig62.jpg" width="174" height="188" alt=
+"Fig. 62: Two hands used to determine the inclination of strata." />
+
+<p>If not provided with a clinometer, a most useful instrument,
+when it is of consequence to determine with precision the
+inclination of the strata, the observer may measure the angle
+within a few degrees by standing exactly opposite to a cliff where
+the true dip is exhibited, holding the hands immediately before the
+eyes, and placing the fingers of one in a perpendicular, and of the
+other in a horizontal position, as in Fig. 62. It is thus easy to
+discover whether the lines of the inclined beds bisect the angle of
+90&deg;, formed by the meeting of the hands, so as to give an angle
+of 45&deg;, or whether it would divide the space into two equal or
+unequal portions. You have only to change hands to get the line of
+dip on the upper side of the horizontal hand.</p>
+
+<p><img src="images/fig63.jpg" width="334" height="179" alt=
+"Fig. 63: Section illustrating the structure of the Swiss Jura." />
+</p>
+
+<p>
+It has been already seen, in describing the curved strata on the east coast of
+Scotland, in Forfarshire and Berwickshire, that a series of concave and convex
+bendings are occasionally repeated several times. These usually form part of a
+series of parallel waves of strata, which are prolonged in the same direction,
+throughout a considerable extent of country. Thus, for example, in the Swiss
+Jura, that lofty chain of mountains has been proved to consist of many parallel
+ridges, with intervening longitudinal valleys, as in Fig. 63, the ridges being
+formed by curved fossiliferous strata, <a name="page83"></a>of which the nature
+and dip are occasionally displayed in deep transverse gorges, called
+&ldquo;cluses,&rdquo; caused by fractures at right angles to the direction of
+the chain.<a href="#fn-5.4" name="fnref-5.4" id="fnref-5.4"><sup>[4]</sup></a>
+Now let us suppose these ridges and parallel valleys to run north and south, we
+should then say that the <i>strike</i> of the beds is north and south, and the
+<i>dip</i> east and west. Lines drawn along the summits of the ridges, A, B,
+would be anticlinal lines, and one following the bottom of the adjoining
+valleys a synclinal line.
+</p>
+
+<p><img src="images/fig64.jpg" width="225" height="144" alt=
+"Fig. 64: Ground-plan of the denuded ridge C, Fig. 63. Fig. 65: Transverse section." /></p>
+
+<p><b>Outcrop of Strata.</b>&mdash;It
+will be observed that some of these ridges, A, B, are unbroken on
+the summit, whereas one of them, C, has been fractured along the
+line of strike, and a portion of it carried away by denudation, so
+that the ridges of the beds in the formations <i>a, b, c</i> come
+out to the day, or, as the miners say, <i>crop out</i>, on the
+sides of a valley. The ground-plan of such a denuded ridge as C, as
+given in a geological map, may be expressed by the diagram, Fig.
+64, and the cross-section of the same by Fig. 65. The line D E,
+Fig. 64, is the anticlinal line, on each side of which the dip is
+in opposite directions, as expressed by the arrows. The emergence
+of strata at the surface is called by miners their <i>outcrop</i>,
+or <i>basset.</i></p>
+
+<p>
+If, instead of being folded into parallel ridges, the beds form a boss or
+dome-shaped protuberance, and if we suppose the summit of the dome carried off,
+the ground-plan would exhibit the edges of the strata forming a succession of
+circles, or ellipses, round a common centre. These circles are the lines of
+strike, and the dip being always at right angles is inclined in the course of
+the circuit to every point of the compass, constituting what is termed a
+quâ-quâversal dip&mdash;that is, turning every way.
+</p>
+
+<p>There are endless variations in the figures described by the
+basset-edges of the strata, according to the different inclination
+of the beds, and the mode in which they happen to have been
+denuded. One of the simplest rules, with which every geologist
+should be acquainted, relates to the V-like form of the beds as
+they crop out in an ordinary valley. First, if the strata be
+horizontal, the V-like form will be also on a level, and the newest
+strata will appear at the greatest heights.</p>
+
+<img src="images/fig66.jpg" width="263" height="614" alt=
+"Fig. 66: Slope of valley 40&deg;, dip of strata 20&deg;. Fig. 67: Slope of
+valley 20&deg;, dip of strata 50&deg;. Fig. 68: Slope of valley 20&deg;, dip of
+strata 20&deg;, in opposite directions." />
+
+<p><a name="page84"></a>Secondly, if the beds be inclined and intersected by a valley
+sloping in the same direction, and the dip of the beds be less
+steep than the slope of the valley, then the V&rsquo;s, as they are often
+termed by miners, will point upward (see Fig. 66), those formed by
+the newer beds appearing in a superior position, and extending
+highest up the valley, as A is seen above B.</p>
+
+<p>Thirdly, if the dip of the beds be steeper than the slope of the
+valley, then the V&rsquo;s will point downward (see Fig. 67), and those
+formed of the older beds will now appear uppermost, as B appears
+above A.</p>
+
+<p>Fourthly, in every case where the strata dip in a contrary
+direction to the slope of the valley, whatever be the angle of
+inclination, the newer beds will appear the highest, as in the
+first and second cases. This is shown by the drawing (Fig. 68),
+which exhibits strata rising at an angle of 20&deg;, and crossed by
+a valley, which declines in an opposite direction at 20&deg;.</p>
+
+<p>
+These rules may often be of great practical utility; for the different degrees
+of dip occurring in the two cases represented in <a name="page85"></a>Figs. 66
+and 67 may occasionally be encountered in following the same line of flexure at
+points a few miles distant from each other. A miner unacquainted with the rule,
+who had first explored the valley Fig. 66, may have sunk a vertical shaft below
+the coal-seam A, until he reached the inferior bed, B. He might then pass to
+the valley, Fig. 67, and discovering there also the outcrop of two coal-seams,
+might begin his workings in the uppermost in the expectation of coming down to
+the other bed A, which would be observed cropping out lower down the valley.
+But a glance at the section will demonstrate the futility of such hopes.<a
+href="#fn-5.5" name="fnref-5.5" id="fnref-5.5"><sup>[5]</sup></a>
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig69.jpg" width="385" height="122" alt="Section of
+carboniferous rocks of Lancashire." />
+<p class="caption">Section of carboniferous rocks of Lancashire. (E.
+Hull.<a href="#fn-5.6" name="fnref-5.6" id="fnref-5.6"><sup>[6]</sup></a>)<br/></p>
+</div>
+
+<p><b>Synclinal Strata forming
+Ridges.</b>&mdash;Although in many cases an anticlinal axis
+forms a ridge, and a synclinal axis a valley, as in A B, Fig. 63,
+yet this can by no means be laid down as a general rule, as the
+beds very often slope inward from either side of a mountain, as at
+<i>a, b,</i> Fig. 69, while in the intervening valley, <i>c</i>,
+they slope upward, forming an arch.</p>
+
+<p>It would be natural to expect the fracture of solid rocks to
+take place chiefly where the bending of the strata has been
+sharpest, and such rending may produce ravines giving access to
+running water and exposing the surface to atmospheric waste. The
+entire absence, however, of such cracks at points where the strain
+must have been greatest, as at <i>a</i>, Fig. 63, is often very
+remarkable, and not always easy of explanation. We must imagine
+that many strata of limestone, chert, and other rocks which are now
+brittle, were pliant when bent into their present position. They
+may have owed their flexibility in part to the fluid matter which
+they contained in their minute pores, as before described <a href=
+"#page62">p. 62</a> and in part to the permeation of
+sea-water while they were yet submerged.</p>
+
+<p><img src="images/fig70.jpg" width="319" height="100" alt=
+"Fig. 70: Strata of chert, grit, and marl, near St. Jean de Luz." />
+</p>
+
+<p><a name="page86"></a>At the western extremity of the Pyrenees, great curvatures of
+the strata are seen in the sea-cliffs, where the rocks consist of
+marl, grit, and chert. At certain points, as at <i>a</i>, Fig. 70,
+some of the bendings of the flinty chert are so sharp that
+specimens might be broken off well fitted to serve as ridge-tiles
+on the roof of a house. Although this chert could not have been
+brittle as now, when first folded into this shape, it presents,
+nevertheless, here and there, at the points of greatest flexure,
+small cracks, which show that it was solid, and not wholly
+incapable of breaking at the period of its displacement. The
+numerous rents alluded to are not empty, but filled with chalcedony
+and quartz.</p>
+
+<img src="images/fig71.jpg" width="169" height="142" alt=
+"Fig. 71: Bent and undulating gypseous marl." />
+
+<p>Between San Caterina and Castrogiovanni, in Sicily, bent and
+undulating gypseous marls occur, with here and there thin beds of
+solid gypsum interstratified. Sometimes these solid layers have
+been broken into detached fragments, still preserving their sharp
+edges (<i>g, g,</i> Fig. 71), while the continuity of the more
+pliable and ductile marls, <i>m, m,</i> has not been
+interrupted.</p>
+
+<img src="images/fig72.jpg" width="179" height="67" alt=
+"Fig. 72: Folded strata." />
+
+<p>We have already explained, Fig. 69, that stratified rocks have
+usually their strata bent into parallel folds forming anticlinal
+and synclinal axes, a group of several of these folds having often
+been subjected to a common movement, and having acquired a uniform
+strike or direction. In some disturbed regions these folds have
+been doubled back upon themselves in such a manner that it is often
+difficult for an experienced geologist to determine correctly the
+relative age of the beds by superposition. Thus, if we meet with
+the strata seen in the section, Fig. 72, we should naturally
+suppose that there were twelve distinct beds, or sets of beds, No.
+1 being the newest, and No. 12 the oldest of the series. But this
+section may perhaps exhibit merely six
+<a name="page87"></a>beds, which have been folded in the manner seen in Fig. 73, so
+that each of them is twice repeated, the position of one half being
+reversed, and part of No. 1, originally the uppermost, having now
+become the lowest of the series.</p>
+
+<img src="images/fig73.jpg" width="235" height="158" alt="Fig. 73" />
+
+<p>These phenomena are observable on a magnificent scale in certain
+regions in Switzerland, in precipices often more than 2000 feet in
+perpendicular height, and there are flexures not inferior in
+dimensions in the Pyrenees. The upper part of the curves seen in
+this diagram, Fig. 73, and expressed in fainter lines, has been
+removed by what is called denudation, to be afterwards
+explained.</p>
+
+<p><b>Fractures of the Strata and
+Faults.</b>&mdash;Numerous rents may often be seen in rocks
+which appear to have been simply broken, the fractured parts still
+remaining in contact; but we often find a fissure, several inches
+or yards wide, intervening between the disunited portions. These
+fissures are usually filled with fine earth and sand, or with
+angular fragments of stone, evidently derived from the fracture of
+the contiguous rocks.</p>
+
+<p>The face of each wall of the fissure is often beautifully
+polished, as if glazed, striated, or scored with parallel furrows
+and ridges, such as would be produced by the continued rubbing
+together of surfaces of unequal hardness. These polished surfaces
+are called by miners &ldquo;slickensides.&rdquo; It is supposed that the lines
+of the striæ indicate the direction in which the rocks were
+moved. During one of the minor earthquakes in Chili, in 1840, the
+brick walls of a building were rent vertically in several places,
+and made to vibrate for several minutes during each shock, after
+which they remained uninjured, and without any opening, although
+the line of each crack was still visible. When all movement had
+ceased, there were seen on the floor of the house, at the bottom of
+each rent, small heaps of fine brick-dust, evidently produced by
+trituration.</p>
+
+<p>
+It is not uncommon to find the mass of rock on one side of a fissure thrown up
+above or down below the mass with which it was once in contact on the other
+side. &ldquo;This mode of displacement is called a fault, shift, slip, or
+throw.&rdquo; &ldquo;The miner,&rdquo; says Playfair, describing a fault,
+&ldquo;is often perplexed, <a name="page88"></a>in his subterranean journey, by
+a derangement in the strata, which changes at once all those lines and bearings
+which had hitherto directed his course. When his mine reaches a certain plane,
+which is sometimes perpendicular, as in A B, Fig. 74, sometimes oblique to the
+horizon (as in C D, ibid.), he finds the beds of rock broken asunder, those on
+the one side of the plane having changed their place, by sliding in a
+particular direction along the face of the others. In this motion they have
+sometimes preserved their parallelism, as in Fig. 74, so that the strata on
+each side of faults A B, C D, continue parallel to one another; in other cases,
+the strata on each side are inclined, as in <i>a, b, c, d</i> (Fig. 75), though
+their identity is still to be recognised by their possessing the same thickness
+and the same internal characters.&rdquo;<a href="#fn-5.7" name="fnref-5.7"
+id="fnref-5.7"><sup>[7]</sup></a>
+</p>
+
+<p><img src="images/fig74.jpg" width="350" height="153" alt=
+"Fig. 74: Faults." /></p>
+
+<p><img src="images/fig75.jpg" width="350" height="141" alt=
+"Fig. 75: E F, fault or fissure filled with rubbish, on each side of which the shifted strata are not parallel." />
+</p>
+
+<p>
+In Coalbrook Dale, says Mr. Prestwich<a href="#fn-5.8" name="fnref-5.8"
+id="fnref-5.8"><sup>[8]</sup></a>, deposits of sandstone, shale, and coal,
+several thousand feet thick, and occupying an area of many miles, have been
+shivered into fragments, and the broken remnants have been placed in very
+discordant positions, often at levels differing several hundred feet from each
+other. The sides of the faults, when perpendicular, are commonly several yards
+apart, and are sometimes as much as 50 yards asunder, the interval being filled
+with broken <i>débris</i> of the strata. In following the <a
+name="page89"></a>course of the same fault it is sometimes found to produce in
+different places very unequal changes of level, the amount of shift being in
+one place 300, and in another 700 feet, which arises from the union of two or
+more faults. In other words, the disjointed strata have in certain districts
+been subjected to renewed movements, which they have not suffered elsewhere.
+</p>
+
+<p>We may occasionally see exact counterparts of these slips, on a
+small scale, in pits of loose sand and gravel, many of which have
+doubtless been caused by the drying and shrinking of argillaceous
+and other beds, slight subsidences having taken place from failure
+of support. Sometimes, however, even these small slips may have
+been produced during earthquakes; for land has been moved, and its
+level, relatively to the sea, considerably altered, within the
+period when much of the alluvial sand and gravel now covering the
+surface of continents was deposited.</p>
+
+<p>I have already stated that a geologist must be on his guard, in
+a region of disturbed strata, against inferring repeated
+alternations of rocks, when, in fact, the same strata, once
+continuous, have been bent round so as to recur in the same
+section, and with the same dip. A similar mistake has often been
+occasioned by a series of faults.</p>
+
+<p><img src="images/fig76.jpg" width="329" height="200" alt=
+"Fig. 76: Apparent alternations of strata caused by vertical faults." />
+</p>
+
+<p>If, for example, the dark line A H (Fig. 76) represent the
+surface of a country on which the strata <i>a, b, c</i> frequently
+crop out, an observer who is proceeding from H to A might at first
+imagine that at every step he was approaching new strata, whereas
+the repetition of the same beds has been caused by vertical faults,
+or downthrows. Thus, suppose the original mass, A, B, C, D, to have
+been a set of uniformly inclined strata, and that the different
+masses under E F, F G, and G D sank down successively, so as to
+leave vacant
+<a name="page90"></a>the spaces marked in the diagram by dotted lines, and to occupy those marked by
+the continuous lines, then let denudation take place along the line A H, so
+that the protruding masses indicated by the fainter lines are swept
+away&mdash;a miner, who has not discovered the faults, finding the mass
+<i>a</i>, which we will suppose to be a bed of coal four times repeated, might
+hope to find four beds, workable to an indefinite depth, but first, on arriving
+at the fault G, he is stopped suddenly in his workings, for he comes partly
+upon the shale <i>b</i>, and partly on the sandstone <i> c</i>; the same result
+awaits him at the fault F, and on reaching E he is again stopped by a wall
+composed of the rock <i>d.</i>
+</p>
+
+<p>
+The very different levels at which the separated parts of the same strata are
+found on the different sides of the fissure, in some faults, is truly
+astonishing. One of the most celebrated in England is that called the
+&ldquo;ninety-fathom dike,&rdquo; in the coal-field of Newcastle. This name has
+been given to it, because the same beds are ninety fathoms (540 feet) lower on
+the northern than they are on the southern side. The fissure has been filled by
+a body of sand, which is now in the state of sandstone, and is called the dike,
+which is sometimes very narrow, but in other places more than twenty yards
+wide.<a href="#fn-5.9" name="fnref-5.9" id="fnref-5.9"><sup>[9]</sup></a> The
+walls of the fissure are scored by grooves, such as would have been produced if
+the broken ends of the rock had been rubbed along the plane of the fault.<a
+href="#fn-5.10" name="fnref-5.10" id="fnref-5.10"><sup>[10]</sup></a> In the
+Tynedale and Craven faults, in the north of England, the vertical displacement
+is still greater, and the fracture has extended in a horizontal direction for a
+distance of thirty miles or more.
+</p>
+
+<p><b>Great Faults the Result of Repeated
+Movements.</b>&mdash;It must not, however, be supposed that
+faults generally consist of single linear rents; there are usually
+a number of faults springing off from the main one, and sometimes a
+long strip of country seems broken up into fragments by sets of
+parallel and connecting transverse faults. Oftentimes a great line
+of fault has been repeated, or the movements have been continued
+through successive periods, so that, newer deposits having covered
+the old line of displacement, the strata both newer and older have
+given way along the old line of fracture. Some geologists have
+considered it necessary to imagine that the upward or downward
+movement in these cases was accomplished at a single stroke, and
+not by a series of sudden but interrupted movements. They appear to
+have derived this idea from a notion that the grooved walls
+<a name="page91"></a>have merely been rubbed in one direction, which is far from
+being a constant phenomenon. Not only are some sets of striæ
+not parallel to others, but the clay and rubbish between the walls,
+when squeezed or rubbed, have been streaked in different
+directions, the grooves which the harder minerals have impressed on
+the softer being frequently curved and irregular.</p>
+
+<p><img src="images/fig77.jpg" width="323" height="161" alt=
+"Fig. 77: Faults and denuded coal-strata, Ashby de la Zouch." />
+</p>
+
+<p>
+The usual absence of protruding masses of rock forming precipices or ridges
+along the lines of great faults has already been alluded to in explaining Fig.
+76, p. 89, and the same remarkable fact is well exemplified in every coal-field
+which has been extensively worked. It is in such districts that the former
+relation of the beds which have been shifted is determinable with great
+accuracy. Thus in the coal-field of Ashby de la Zouch, in Leicestershire (see
+Fig. 77), a fault occurs, on one side of which the coal-beds <i>a, b, c, d</i>
+must once have risen to the height of 500 feet above the corresponding beds on
+the other side. But the uplifted strata do not stand up 500 feet above the
+general surface; on the contrary, the outline of the country, as expressed by
+the line <i>z z</i>, is uniformly undulating, without any break, and the mass
+indicated by the dotted outline must have been washed away.<a href="#fn-5.11"
+name="fnref-5.11" id="fnref-5.11"><sup>[11]</sup></a>
+</p>
+
+<p>
+The student may refer to Mr. Hull&rsquo;s measurement of faults, observed in
+the Lancashire coal-field, where the vertical displacement has amounted to
+thousands of feet, and yet where all the superficial inequalities which must
+have resulted from such movements have been obliterated by subsequent
+denudation. In the same memoir proofs are afforded of there having been two
+periods of vertical movement in the same fault&mdash;one, for example, before,
+and another after, the Triassic epoch.<a href="#fn-5.12" name="fnref-5.12"
+id="fnref-5.12"><sup>[12]</sup></a>
+</p>
+
+<p>
+The shifting of the beds by faults is often intimately connected with those
+same foldings which constitute the <a name="page92"></a>anticlinal and
+synclinal axes before alluded to, and there is no doubt that the subterranean
+causes of both forms of disturbance are to a great extent the same. A fault in
+Virginia, believed to imply a displacement of several thousand feet, has been
+traced for more than eighty miles in the same direction as the foldings of the
+Appalachian chain.<a href="#fn-5.13" name="fnref-5.13"
+id="fnref-5.13"><sup>[13]</sup></a> An hypothesis which attributes such a
+change of position to a succession of movements, is far preferable to any
+theory which assumes each fault to have been accomplished by a single upcast or
+downthrow of several thousand feet. For we know that there are operations now
+in progress, at great depths in the interior of the earth, by which both large
+and small tracts of ground are made to rise above and sink below their former
+level, some slowly and insensibly, others suddenly and by starts, a few feet or
+yards at a time; whereas there are no grounds for believing that, during the
+last 3000 years at least, any regions have been either upheaved or depressed,
+at a single stroke, to the amount of several hundred, much less several
+thousand feet.
+</p>
+
+<p>It is certainly not easy to understand how in the subterranean
+regions one mass of solid rock should have been folded up by a
+continued series of movements, while another mass in contact, or
+only separated by a line of fissure, has remained stationary or has
+perhaps subsided. But every volcano, by the intermittent action of
+the steam, gases, and lava evolved during an eruption, helps us to
+form some idea of the manner in which such operations take place.
+For eruptions are repeated at uncertain intervals throughout the
+whole or a large part of a geological period, some of the
+surrounding and contiguous districts remaining quite undisturbed.
+And in most of the instances with which we are best acquainted the
+emission of lava, scoria, and steam is accompanied by the uplifting
+of the solid crust. Thus in Vesuvius, Etna, the Madeiras, the
+Canary Islands, and the Azores there is evidence of marine deposits
+of recent and tertiary date having been elevated to the height of a
+thousand feet, and sometimes more, since the commencement of the
+volcanic explosions. There is, moreover, a general tendency in
+contemporaneous volcanic vents to affect a linear arrangement,
+extending in some instances, as in the Andes or the Indian
+Archipelago, to distances equalling half the circumference of the
+globe. Where volcanic heat, therefore, operates at such a depth as
+not to obtain vent at the surface, in the form of an eruption, it
+may nevertheless be conceived to give rise to upheavals, foldings,
+and faults in
+<a name="page93"></a>certain linear tracts. And marine denudation, to be treated of
+in the next chapter, will help us to understand why that which
+should be the protruding portion of the faulted rocks is missing at
+the surface.</p>
+
+<p><b>Arrangement and Direction of Parallel
+Folds of Strata.</b>&mdash;The possible causes of the
+folding of strata by lateral movements have been considered in a
+former part of this chapter. No European chain of mountains affords
+so remarkable an illustration of the persistency of such flexures
+for a great distance as the Appalachians before alluded to, and
+none has been studied and described by many good observers with
+more accuracy. The chain extends from north to south, or rather
+N.N.E. to S.S.W., for nearly 1500 miles, with a breadth of 50
+miles, throughout which the Palæozoic strata have been so
+bent as to form a series of parallel anticlinal and synclinal
+ridges and troughs, comprising usually three or four principal and
+many smaller plications, some of them forming broad and gentle
+arches, others narrower and steeper ones, while some, where the
+bending has been greatest, have the position of their beds
+inverted, as before shown in Fig. 73, p. 87.</p>
+
+<p>The strike of the parallel ridges, after continuing in a
+straight line for many hundred miles, is then found to vary for a
+more limited distance as much as 30&deg;, the folds wheeling round
+together in the new direction and continuing to be parallel, as if
+they had all obeyed the same movement. The date of the movements by
+which the great flexures were brought about must, of course, be
+subsequent to the formation of the uppermost part of the coal or
+the newest of the bent rocks, but the disturbance must have ceased
+before the Triassic strata were deposited on the denuded edges of
+the folded beds.</p>
+
+<p>The manner in which the numerous parallel folds, all
+simultaneously formed, assume a new direction common to the whole
+of them, and sometimes varying at an angle of 30&deg; from the
+normal strike of the chain, shows what deviation from an otherwise
+uniform strike of the beds may be experienced when the geographical
+area through which they are traced is on so vast a scale.</p>
+
+<p>
+The disturbances in the case here adverted to occurred between the
+Carboniferous period and that of the Trias, and this interval is so vast that
+they may have occupied a great lapse of time, during which their parallelism
+was always preserved. But, as a rule, wherever after a long geological interval
+the recurrence of lateral movements gives rise to a new set of folds, the
+strike of these last is different. Thus, <a name="page94"></a>for example, Mr.
+Hull has pointed out that three principal lines of disturbance, all later than
+the Carboniferous period, have affected the stratified rocks of Lancashire. The
+first of these, having an E.N.E. direction, took place at the close of the
+Carboniferous period. The next, running north and south, at the close of the
+Permian, and the third, having a N.N.W. direction, at the close of the Jurassic
+period.<a href="#fn-5.14" name="fnref-5.14" id="fnref-5.14"><sup>[14]</sup></a>
+</p>
+
+<p><img src="images/fig78.jpg" width="327" height="149" alt=
+"Fig. 78: Unconformable junction of old red sandstone and Silurian schist at the Siccar Point, near St. Abb’s Head, Berwickshire." />
+</p>
+
+<p><b>Unconformability of
+Strata.</b>&mdash; Strata are said to be unconformable when
+one series is so placed over another that the planes of the
+superior repose on the edges of the inferior (see Fig. 78). In this
+case it is evident that a period had elapsed between the production
+of the two sets of strata, and that, during this interval, the
+older series had been tilted and disturbed. Afterwards the upper
+series was thrown down in horizontal strata upon it. If these
+superior beds, <i>d, d,</i> Fig. 78, are also inclined, it is plain
+that the lower strata <i>a, a,</i> have been twice displaced;
+first, before the deposition of the newer beds, <i>d, d,</i> and a
+second time when these same strata were upraised out of the sea,
+and thrown slightly out of the horizontal position.</p>
+
+<p><img src="images/fig79.jpg" width="346" height="122" alt=
+"Fig. 79: Junction of unconformable strata near Mons, in Belgium." />
+</p>
+
+<p>It often happens that in the interval between the deposition of
+two sets of unconformable strata, the inferior rock has not only
+been denuded, but drilled by perforating shells. Thus, for example,
+at Autreppe and Gusigny, near Mons, beds of an ancient (primary or
+palæozoic) limestone, highly inclined, and often bent, are
+covered with horizontal strata
+<a name="page95"></a>of greenish and whitish marls of the Cretaceous formation. The
+lowest, and therefore the oldest, bed of the horizontal series is
+usually the sand and conglomerate, <i>a</i>, in which are rounded
+fragments of stone, from an inch to two feet in diameter. These
+fragments have often adhering shells attached to them, and have
+been bored by perforating mollusca. The solid surface of the
+inferior limestone has also been bored, so as to exhibit
+cylindrical and pear-shaped cavities, as at <i>c</i>, the work of
+saxicavous mollusca; and many rents, as at <i>b</i>, which descend
+several feet or yards into the limestone, have been filled with
+sand and shells, similar to those in the stratum <i>a.</i></p>
+
+<p><b>Overlapping
+Strata.</b>&mdash;Strata are said to overlap when an upper
+bed extends beyond the limits of a lower one. This may be produced
+in various ways; as, for example, when alterations of physical
+geography cause the arms of a river or channels of discharge to
+vary, so that sediment brought down is deposited over a wider area
+than before, or when the sea-bottom has been raised up and again
+depressed without disturbing the horizontal position of the strata.
+In this case the newer strata may rest for the most part
+conformably on the older, but, extending farther, pass over their
+edges. Every intermediate state between unconformable and
+over-lapping beds may occur, because there may be every gradation
+between a slight derangement of position, and a considerable
+disturbance and denudation of the older formation before the newer
+beds come on.
+</p>
+
+<p class="footnote">
+<a name="fn-5.1" id="fn-5.1"></a> <a href="#fnref-5.1">[1]</a>
+See &ldquo;Principles of Geology,&rdquo; 1867, p. 314.
+</p>
+
+<p class="footnote">
+<a name="fn-5.2" id="fn-5.2"></a> <a href="#fnref-5.2">[2]</a>
+Edin. Trans., vol. vii, pl. 3.
+</p>
+
+<p class="footnote">
+<a name="fn-5.3" id="fn-5.3"></a> <a href="#fnref-5.3">[3]</a>
+Proceedings of Geol. Soc., vol. iii, p. 148.
+</p>
+
+<p class="footnote">
+<a name="fn-5.4" id="fn-5.4"></a> <a href="#fnref-5.4">[4]</a>
+Thurmann, &ldquo;Essai sur les Soulèvemens Jurassiques de Porrentruy,&rdquo;
+Paris, 1832.
+</p>
+
+<p class="footnote">
+<a name="fn-5.5" id="fn-5.5"></a> <a href="#fnref-5.5">[5]</a>
+I am indebted to the kindness of T. Sopwith, Esq., for three models which I
+have copied in the above diagrams; but the beginner may find it by no means
+easy to understand such copies, although, if he were to examine and handle the
+originals, turning them about in different ways, he would at once comprehend
+their meaning, as well as the import of others far more complicated, which the
+same engineer has constructed to illustrate <i>faults.</i>
+</p>
+
+<p class="footnote">
+<a name="fn-5.6" id="fn-5.6"></a> <a href="#fnref-5.6">[6]</a>
+Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 324, 1868.
+</p>
+
+<p class="footnote">
+<a name="fn-5.7" id="fn-5.7"></a> <a href="#fnref-5.7">[7]</a>
+Playfair, Illust. of Hutt. Theory, &sect; 42.
+</p>
+
+<p class="footnote">
+<a name="fn-5.8" id="fn-5.8"></a> <a href="#fnref-5.8">[8]</a>
+Geol. Trans., second series. vol. v, p. 452.
+</p>
+
+<p class="footnote">
+<a name="fn-5.9" id="fn-5.9"></a> <a href="#fnref-5.9">[9]</a>
+Conybeare and Phillips Outlines, etc., p. 376.
+</p>
+
+<p class="footnote">
+<a name="fn-5.10" id="fn-5.10"></a> <a href="#fnref-5.10">[10]</a>
+Phillips, Geology, Lardner&rsquo;s Cyclop., p. 41.
+</p>
+
+<p class="footnote">
+<a name="fn-5.11" id="fn-5.11"></a> <a href="#fnref-5.11">[11]</a>
+See Mammatt&rsquo;s Geological Facts, etc., p. 90 and plate.
+</p>
+
+<p class="footnote">
+<a name="fn-5.12" id="fn-5.12"></a> <a href="#fnref-5.12">[12]</a>
+Hull, Quart. Geol. Journ., vol. xxiv, p. 318, 1868.
+</p>
+
+<p class="footnote">
+<a name="fn-5.13" id="fn-5.13"></a> <a href="#fnref-5.13">[13]</a>
+H. D. Rogers, Geol. of Pennsylvania, p. 897.
+</p>
+
+<p class="footnote">
+<a name="fn-5.14" id="fn-5.14"></a> <a href="#fnref-5.14">[14]</a>
+Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 323.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap06"></a><a name="page96"></a>CHAPTER VI.<br/>
+DENUDATION</h2>
+
+<p class="letter">Denudation defined. &mdash; Its Amount more than
+equal to the entire Mass of Stratified Deposits in the Earth&rsquo;s
+Crust. &mdash; Subaërial Denudation. &mdash; Action of the
+Wind. &mdash; Action of Running Water. &mdash; Alluvium defined.
+&mdash; Different Ages of Alluvium. &mdash; Denuding Power of
+Rivers affected by Rise or Fall of Land. &mdash; Littoral
+Denudation. &mdash; Inland Sea-Cliffs. &mdash; Escarpments. &mdash;
+Submarine Denudation. &mdash; Dogger-bank. &mdash; Newfoundland
+Bank. &mdash; Denuding Power of the Ocean during Emergence of
+Land.</p>
+
+<p>Denudation, which has been occasionally spoken of in the
+preceding chapters, is the removal of solid matter by water in
+motion, whether of rivers or of the waves and currents of the sea,
+and the consequent laying bare of some inferior rock. This
+operation has exerted an influence on the structure of the earth&rsquo;s
+crust as universal and important as sedimentary deposition itself;
+for denudation is the necessary antecedent of the production of all
+new strata of mechanical origin. The formation of every new deposit
+by the transport of sediment and pebbles necessarily implies that
+there has been, somewhere else, a grinding down of rock into
+rounded fragments, sand, or mud, equal in quantity to the new
+strata. All deposition, therefore, except in the case of a shower
+of volcanic ashes, and the outflow of lava, and the growth of
+certain organic formations, is the sign of superficial waste going
+on contemporaneously, and to an equal amount, elsewhere. The gain
+at one point is no more than sufficient to balance the loss at some
+other. Here a lake has grown shallower, there a ravine has been
+deepened. Here the depth of the sea has been augmented by the
+removal of a sandbank during a storm, there its bottom has been
+raised and shallowed by the accumulation in its bed of the same
+sand transported from the bank.</p>
+
+<p>When we see a stone building, we know that somewhere, far or
+near, a quarry has been opened. The courses of stone in the
+building may be compared to successive strata, the quarry to a
+ravine or valley which has suffered denudation. As the strata, like
+the courses of hewn stone, have been laid one upon another
+gradually, so the excavation both of the valley and quarry have
+been gradual. To pursue the comparison still farther, the
+superficial heaps of mud, sand, and gravel, usually called
+alluvium, may be likened to the
+<a name="page97"></a>rubbish of a quarry which has been rejected as useless by the
+workmen, or has fallen upon the road between the quarry and the
+building, so as to lie scattered at random over the ground.</p>
+
+<p>But we occasionally find in a conglomerate large rounded pebbles
+of an older conglomerate, which had previously been derived from a
+variety of different rocks. In such cases we are reminded that, the
+same materials having been used over and over again, it is not
+enough to affirm that the entire mass of stratified deposits in the
+earth&rsquo;s crust affords a monument and measure of the denudation
+which has taken place, for in truth the quantity of matter now
+extant in the form of stratified rock represents but a fraction of
+the material removed by water and redeposited in past ages.</p>
+
+<p><b>Subaërial
+Denudation.</b>&mdash;Denudation may be divided into
+subaërial, or the action of wind, rain, and rivers; and
+submarine, or that effected by the waves of the sea, and its tides
+and currents. With the operation of the first of these we are best
+acquainted, and it may be well to give it our first attention.</p>
+
+<p><i>Action of the Wind.</i>&mdash;In desert regions where no rain
+falls, or where, as in parts of the Sahara, the soil is so salt as
+to be without any covering of vegetation, clouds of dust and sand
+attest the power of the wind to cause the shifting of the
+unconsolidated or disintegrated rock.</p>
+
+<p>In examining volcanic countries I have been much struck with the
+great superficial changes brought about by this power in the course
+of centuries. The highest peak of Madeira is about 6050 feet above
+the sea, and consists of the skeleton of a volcanic cone now 250
+feet high, the beds of which once dipped from a centre in all
+directions at an angle of more than 30&deg;. The summit is formed
+of a dike of basalt with much olivine, fifteen feet wide,
+apparently the remains of a column of lava which once rose to the
+crater. Nearly all the scoriæ of the upper part of the cone
+have been swept away, those portions only remaining which were
+hardened by the contact or proximity of the dike. While I was
+myself on this peak on January 25, 1854, I saw the wind, though it
+was not stormy weather, removing sand and dust derived from the
+decomposing scoriæ. There had been frost in the night, and
+some ice was still seen in the crevices of the rock.</p>
+
+<p>On the highest platform of the Grand Canary, at an elevation of
+6000 feet, there is a cylindrical column of hard lava, from which
+the softer matter has been carried away; and other similar remnants
+of the dikes of cones of eruption
+<a name="page98"></a>attest the denuding power of the wind at points where running
+water could never have exerted any influence. The waste effected by
+wind aided by frost and snow, may not be trifling, even in a single
+winter, and when multiplied by centuries may become indefinitely
+great.</p>
+
+<p><img src="images/fig80.jpg" width="367" height="126" alt=
+"Fig. 80: Section through several eroded formations." /></p>
+
+<p><i>Action of Running Water.</i>&mdash;There are different
+classes of phenomena which attest in a most striking manner the
+vast spaces left vacant by the erosive power of water. I may
+allude, first, to those valleys on both sides of which the same
+strata are seen following each other in the same order, and having
+the same mineral composition and fossil contents. We may observe,
+for example, several formations, as Nos. 1, 2, 3, 4, in the diagram
+(Fig. 80): No. 1, conglomerate, No. 2, clay, No. 3, grit, and No.
+4, limestone, each repeated in a series of hills separated by
+valleys varying in depth. When we examine the subordinate parts of
+these four formations, we find, in like manner, distinct beds in
+each, corresponding, on the opposite sides of the valleys, both in
+composition and order of position. No one can doubt that the strata
+were originally continuous, and that some cause has swept away the
+portions which once connected the whole series. A torrent on the
+side of a mountain produces similar interruptions; and when we make
+artificial cuts in lowering roads, we expose, in like manner,
+corresponding beds on either side. But in nature, these appearances
+occur in mountains several thousand feet high, and separated by
+intervals of many miles or leagues in extent.</p>
+
+<p>In the &ldquo;Memoirs of the Geological Survey of Great Britain&rdquo; (vol.
+i), Professor Ramsay has shown that the missing beds, removed from
+the summit of the Mendips, must have been nearly a mile in
+thickness; and he has pointed out considerable areas in South Wales
+and some of the adjacent counties of England, where a series of
+primary (or palæozoic) strata, no less than 11,000 feet in
+thickness, have been stripped off. All these materials have of
+course been transported to new regions, and have entered into the
+composition of more modern formations. On the other hand, it is
+shown by
+<a name="page99"></a>observations in the same &ldquo;Survey,&rdquo; that the Palæozoic
+strata are from 20,000 to 30,000 feet thick. It is clear that such
+rocks, formed of mud and sand, now for the most part consolidated,
+are the monuments of denuding operations, which took place on a
+grand scale at a very remote period in the earth&rsquo;s history. For,
+whatever has been given to one area must always have been borrowed
+from another; a truth which, obvious as it may seem when thus
+stated, must be repeatedly impressed on the student&rsquo;s mind, because
+in many geological speculations it is taken for granted that the
+external crust of the earth has been always growing thicker in
+consequence of the accumulation, period after period, of
+sedimentary matter, as if the new strata were not always produced
+at the expense of pre-existing rocks, stratified or unstratified.
+By duly reflecting on the fact that all deposits of mechanical
+origin imply the transportation from some other region, whether
+contiguous or remote, of an equal amount of solid matter, we
+perceive that the stony exterior of the planet must always have
+grown thinner in one place, whenever, by accessions of new strata,
+it was acquiring thickness in another.</p>
+
+<p>It is well known that generally at the mouths of large rivers,
+deltas are forming and the land is encroaching upon the sea; these
+deltas are monuments of recent denudation and deposition; and it is
+obvious that if the mud, sand, and gravel were taken from them and
+restored to the continents they would fill up a large part of the
+gullies and valleys which are due to the excavating and
+transporting power of torrents and rivers.</p>
+
+<p><b>Alluvium.</b>&mdash;Between the
+superficial covering of vegetable mould and the subjacent rock
+there usually intervenes in every district a deposit of loose
+gravel, sand, and mud, to which when it occurs in valleys the name
+of alluvium has been popularly applied. The term is derived from
+<i>alluvio</i>, an inundation, or <i>alluo</i>, to wash, because
+the pebbles and sand commonly resemble those of a river&rsquo;s bed or
+the mud and gravel washed over low lands by a flood.</p>
+
+<p>In the course of those changes in physical geography which may
+take place during the gradual emergence of the bottom of the sea
+and its conversion into dry land, any spot may either have been a
+sunken reef, or a bay, or estuary, or sea-shore, or the bed of a
+river. The drainage, moreover, may have been deranged again and
+again by earthquakes, during which temporary lakes are caused by
+landslips, and partial deluges occasioned by the bursting of the
+barriers of such lakes. For this reason it would be unreasonable
+to
+<a name="page100"></a>hope that we should ever be able to account for all the alluvial
+phenomena of each particular country, seeing that the causes of
+their origin are so various. Besides, the last operations of water
+have a tendency to disturb and confound together all pre-existing
+alluviums. Hence we are always in danger of regarding as the work
+of a single era, and the effect of one cause, what has in reality
+been the result of a variety of distinct agents, during a long
+succession of geological epochs. Much useful instruction may
+therefore be gained from the exploration of a country like
+Auvergne, where the superficial gravel of very different eras
+happens to have been preserved and kept separate by sheets of lava,
+which were poured out one after the other at periods when the
+denudation, and probably the upheaval, of rocks were in progress.
+That region had already acquired in some degree its present
+configuration before any volcanoes were in activity, and before any
+igneous matter was superimposed upon the granitic and fossiliferous
+formations. The pebbles therefore in the older gravels are
+exclusively constituted of granite and other aboriginal rocks; and
+afterwards, when volcanic vents burst forth into eruption, those
+earlier alluviums were covered by streams of lava, which protected
+them from intermixture with gravel of subsequent date. In the
+course of ages, a new system of valleys was excavated, so that the
+rivers ran at lower levels than those at which the first alluviums
+and sheets of lava were formed. When, therefore, fresh eruptions
+gave rise to new lava, the melted matter was poured out over lower
+grounds; and the gravel of these plains differed from the first or
+upland alluvium, by containing in it rounded fragments of various
+volcanic rocks, and often fossil bones belonging to species of land
+animals different from those which had previously flourished in the
+same country and been buried in older gravels.</p>
+
+<p><img src="images/fig81.jpg" width="372" height="125" alt=
+"Fig. 81: Lavas of Auvergne resting on alluviums of different ages." />
+</p>
+
+<p>The annexed drawing (Fig. 81) will explain the different heights
+at which beds of lava and gravel, each distinct from the other in
+composition and age, are observed, some on the flat tops of hills,
+700 or 800 feet high, others on the slope of
+<a name="page101"></a>the same hills, and the newest of all in the channel of the
+existing river where there is usually gravel alone, although in
+some cases a narrow strip of solid lava shares the bottom of the
+valley with the river.</p>
+
+<p>The proportion of extinct species of quadrupeds is more numerous
+in the fossil remains of the gravel No. 1 than in that indicated as
+No. 2; and in No. 3 they agree more closely, sometimes entirely,
+with those of the existing fauna. The usual absence or rarity of
+organic remains in beds of loose gravel and sand is partly owing to
+the friction which originally ground down the rocks into small
+fragments, and partly to the porous nature of alluvium, which
+allows the free percolation through it of rain-water, and promotes
+the decomposition and removal of fossil remains.</p>
+
+<p>The loose transported matter on the surface of a large part of
+the land now existing in the temperate and arctic regions of the
+northern hemisphere, must be regarded as being in a somewhat
+exceptional state, in consequence of the important part which ice
+has played in comparatively modern geological times. This subject
+will be more specially alluded to when we describe, in the eleventh
+chapter, the deposits called &ldquo;glacial.&rdquo;</p>
+
+<p><b>Denuding Power of Rivers affected by Rise
+or Fall of Land.</b>&mdash;It has long been a matter of
+common observation that most rivers are now cutting their channels
+through alluvial deposits of greater depth and extent than could
+ever have been formed by the present streams. From this fact it has
+been inferred that rivers in general have grown smaller, or become
+less liable to be flooded than formerly. It may be true that in the
+history of almost every country the rivers have been both larger
+and smaller than they are at the present moment. For the rainfall
+in particular regions varies according to climate and physical
+geography, and is especially governed by the elevation of the land
+above the sea, or its distance from it and other conditions equally
+fluctuating in the course of time. But the phenomenon alluded to
+may sometimes be accounted for by oscillations in the level of the
+land, experienced since the existing valleys originated, even where
+no marked diminution in the quantity of rain and in the size of the
+rivers has occurred.</p>
+
+<p>We know that many large areas of land are rising and others
+sinking, and unless it could be assumed that both the upward and
+downward movements are everywhere uniform, many of the existing
+hydrographical basins ought to have the appearance of having been
+temporary lakes first filled with fluviatile strata and then
+partially re-excavated.</p>
+
+<p>
+<a name="page102"></a>Suppose, for example, part of a continent, comprising
+within it a large hydrographical basin like that of the Mississippi, to subside
+several inches or feet in a century, as the west coast of Greenland, extending
+600 miles north and south, has been sinking for three or four centuries,
+between the latitudes 60&deg; and 69&deg; N.<a href="#fn-6.1" name="fnref-6.1"
+id="fnref-6.1"><sup>[1]</sup></a> It will rarely happen that the rate of
+subsidence will be everywhere equal, and in many cases the amount of depression
+in the interior will regularly exceed that of the region nearer the sea.
+Whenever this happens, the fall of the waters flowing from the upland country
+will be diminished, and each tributary stream will have less power to carry its
+sand and sediment into the main river, and the main river less power to convey
+its annual burden of transported matter to the sea. All the rivers, therefore,
+will proceed to fill up partially their ancient channels, and, during frequent
+inundations, will raise their alluvial plains by new deposits. If then the same
+area of land be again upheaved to its former height, the fall, and consequently
+the velocity, of every river will begin to augment. Each of them will be less
+given to overflow its alluvial plain; and their power of carrying earthy matter
+seaward, and of scouring out and deepening their channels, will be sustained
+till, after a lapse of many thousand years, each of them has eroded a new
+channel or valley through a fluviatile formation of comparatively modern date.
+The surface of what was once the river-plain at the period of greatest
+depression, will then remain fringing the valley-sides in the form of a terrace
+apparently flat, but in reality sloping down with the general inclination of
+the river. Everywhere this terrace will present cliffs of gravel and sand,
+facing the river. That such a series of movements has actually taken place in
+the main valley of the Mississippi and in its tributary valleys during
+oscillations of level, I have endeavoured to show in my description of that
+country;<a href="#fn-6.2" name="fnref-6.2" id="fnref-6.2"><sup>[2]</sup></a>
+and the fresh-water shells of existing species and bones of land quadrupeds,
+partly of extinct races, preserved in the terraces of fluviatile origin, attest
+the exclusion of the sea during the whole process of filling up and partial
+re-excavation.
+</p>
+
+<p><b>Littoral Denudation.</b>&mdash;Part
+of the action of the waves between high and low watermark must be
+included in subaërial denudation, more especially as the
+undermining of cliffs by the waves is facilitated by land-springs,
+and these often lead to the sliding down of great masses of land
+into the sea. Along our coasts we find numerous submerged
+forests,
+<a name="page103"></a>only visible at low water, having the trunks of the trees erect
+and their roots attached to them and still spreading through the
+ancient soil as when they were living. They occur in too many
+places, and sometimes at too great a depth, to be explained by a
+mere change in the level of the tides, although as the coasts waste
+away and alter in shape, the height to which the tides rise and
+fall is always varying, and the level of high tide at any given
+point may, in the course of many ages, differ by several feet or
+even fathoms. It is this fluctuation in the height of the tides,
+and the erosion and destruction of the sea-coast by the waves, that
+makes it exceedingly difficult for us in a few centuries, or even
+perhaps in a few thousand years, to determine whether there is a
+change by subterranean movement in the relative level of sea and
+land.</p>
+
+<p>We often behold, as on the coasts of Devonshire and
+Pembrokeshire, facts which appear to lead to opposite conclusions.
+In one place a raised beach with marine littoral shells, and in
+another immediately adjoining a submerged forest. These phenomena
+indicate oscillations of level, and as the movements are very
+gradual, they must give repeated opportunities to the breakers to
+denude the land which is thus again and again exposed to their
+fury, although it is evident that the submergence is sometimes
+effected in such a manner as to allow the trees which border the
+coast not to be carried away.</p>
+
+<p><b>Inland Sea-cliffs.</b>&mdash;In
+countries where hard limestone rocks abound, inland cliffs have
+often retained faithfully for ages the characters which they
+acquired when they constituted the boundary of land and sea. Thus,
+in the Morea, no less than three or even four ranges of cliffs are
+well-preserved, rising one above the other at different distances
+from the actual shore, the summit of the highest and oldest
+occasionally attaining 1000 feet in elevation. A consolidated beach
+with marine shells is usually found at the base of each cliff, and
+a line of littoral caverns. These ranges of cliff probably imply
+pauses in the process of upheaval when the waves and currents had
+time to undermine and clear away considerable masses of rock.</p>
+
+<p>But the beginner should be warned not to expect to find evidence
+of the former sojourn of the sea on all those lands which we are
+nevertheless sure have been submerged at periods comparatively
+modern; for notwithstanding the enduring nature of the marks left
+by littoral action on some rocks, especially limestones, we can by
+no means detect sea-beaches and inland cliffs everywhere. On the
+contrary, they
+<a name="page104"></a>are, upon the whole, extremely partial, and are often entirely
+wanting in districts composed of argillaceous and sandy formations,
+which must, nevertheless, have been upheaved at the same time, and
+by the same intermittent movements, as the adjoining harder
+rocks.</p>
+
+<p><b>Escarpments.</b>&mdash;Besides the
+inland cliffs above alluded to which mark the ancient limits of the
+sea, there are other abrupt terminations of rocks of various kinds
+which resemble sea-cliffs, but which have in reality been due to
+subaërial denudation. These have been called &ldquo;escarpments,&rdquo; a
+term which it is useful to confine to the outcrop of particular
+formations having a scarped outline, as distinct from cliffs due to
+marine action.</p>
+
+<p>
+I formerly supposed that the steep line of cliff-like slopes seen along the
+outcrop of the chalk, when we follow the edge of the North or South Downs, was
+due to marine action; but Professor Ramsay has shown<a href="#fn-6.3"
+name="fnref-6.3" id="fnref-6.3"><sup>[3]</sup></a> that the present outline of
+the physical geography is more in favour of the idea of the escarpments having
+been due to gradual waste since the rocks were exposed in the atmosphere to the
+action of rain and rivers.
+</p>
+
+<p>Mr. Whittaker has given a good summary of the grounds for
+ascribing these apparent sea-cliffs to waste in the open air. 1.
+There is an absence of all signs of ancient sea-beaches or littoral
+deposits at the base of the escarpment. 2. Great inequality is
+observed in the level of the base line. 3. The escarpments do not
+intersect, like sea-cliffs, a series of distinct rocks, but are
+always confined to the boundary-line of the same formation. 4.
+There are sometimes different contiguous and parallel
+escarpments&mdash;those, for example, of the greensand and
+chalk&mdash;which are so near each other, and occasionally so
+similar in altitude, that we cannot imagine any existing
+archipelago if converted into dry land to present a like
+outline.</p>
+
+<p>The above theory is by no means inconsistent with the opinion
+that the limits of the outcrop of the chalk and greensand which the
+escarpments now follow, were originally determined by marine
+denudation. When the south-east of England last emerged from
+beneath the level of the sea, it was acted upon, no doubt, by the
+tide, waves, and currents, and the chalk would form from the first
+a mass projecting above the more destructible clay called Gault.
+Still the present escarpments so much resembling sea-cliffs have no
+doubt, for reasons above stated, derived their most characteristic
+features subsequently to emergence from subaërial waste by
+rain and rivers.</p>
+
+<p><a name="page105"></a><b>Submarine
+Denudation.</b>&mdash;When we attempt to estimate the amount
+of submarine denudation, we become sensible of the disadvantage
+under which we labour from our habitual incapacity of observing the
+action of marine currents on the bed of the sea. We know that the
+agitation of the waves, even during storms, diminishes at a rapid
+rate, so as to become very insignificant at the depth of a few
+fathoms, and is quite imperceptible at the depth of about sixteen
+fathoms; but when large bodies of water are transferred by a
+current from one part of the ocean to another, they are known to
+maintain at great depths such a velocity as must enable them to
+remove the finer, and sometimes even the coarser, materials of the
+rocks over which they flow. As the Mississippi when more than 150
+feet deep can keep open its channel and even carry down gravel and
+sand to its delta, the surface velocity being not more than two or
+three miles an hour, so a gigantic current, like the Gulf Stream,
+equal in volume to many hundred Mississippis, and having in parts a
+surface velocity of more than three miles, may act as a propelling
+and abrading power at still greater depths. But the efficacy of the
+sea as a denuding agent, geologically considered, is not dependent
+on the power of currents to preserve at great depths a velocity
+sufficient to remove sand and mud, because, even where the
+deposition or removal of sediment is not in progress, the depth of
+water does not remain constant throughout geological time. Every
+page of the geological record proves to us that the relative levels
+of land and sea, and the position of the ocean and of continents
+and islands, has been always varying, and we may feel sure that
+some portions of the submarine area are now rising and others
+sinking. The force of tidal and other currents and of the waves
+during storms is sufficient to prevent the emergence of many lands,
+even though they may be undergoing continual upheaval. It is not an
+uncommon error to imagine that the waste of sea-cliffs affords the
+measure of the amount of marine denudation of which it probably
+constitutes an insignificant portion.</p>
+
+<p>
+<b>Dogger-bank.</b>&mdash;That great shoal called the Dogger-bank, about sixty
+miles east of the coast of Northumberland, and occupying an area about as large
+as Wales, has nowhere a depth of more than ninety feet, and in its shallower
+parts is less than forty feet under water. It might contribute towards the
+safety of the navigation of our seas to form an artificial island, and to erect
+a light-house on this bank; but no engineer would be rash enough to attempt it,
+as he would feel sure that the ocean in the first heavy gale would <a
+name="page106"></a>sweep it away as readily as it does every temporary shoal
+that accumulates from time to time around a sunk vessel on the same bank.<a
+href="#fn-6.4" name="fnref-6.4" id="fnref-6.4"><sup>[4]</sup></a>
+</p>
+
+<p>No observed geographical changes in historical times entitle us
+to assume that where upheaval may be in progress it proceeds at a
+rapid rate. Three or four feet rather than as many yards in a
+century may probably be as much as we can reckon upon in our
+speculations; and if such be the case, the continuance of the
+upward movement might easily be counteracted by the denuding force
+of such currents aided by such waves as, during a gale, are known
+to prevail in the German Ocean. What parts of the bed of the ocean
+are stationary at present, and what areas may be rising or sinking,
+is a matter of which we are very ignorant, as the taking of
+accurate soundings is but of recent date.</p>
+
+<p><i>Newfoundland Bank.</i>&mdash;The great bank of Newfoundland
+may be compared in size to the whole of England. This part of the
+bottom of the Atlantic is surrounded on three sides by a rapidly
+deepening ocean, the bank itself being from twenty to fifty fathoms
+(or from 120 to 300 feet) under water. We are unable to determine
+by the comparison of different charts made at distant periods,
+whether it is undergoing any change of level, but if it be
+gradually rising we cannot anticipate on that account that it will
+become land, because the breakers in an open sea would exercise a
+prodigious force even on solid rock brought up to within a few
+yards of the surface. We know, for example, that when a new
+volcanic island rose in the Mediterranean in 1831, the waves were
+capable in a few years of reducing it to a sunken rock.</p>
+
+<p>In the same way currents which flow over the Newfoundland bank a
+great part of the year at the rate of two miles an hour, and are
+known to retain a considerable velocity to near the bottom, may
+carry away all loose sand and mud, and make the emergence of the
+shoal impossible, in spite of the accessions of mud, sand, and
+boulders derived occasionally from melting icebergs which, coming
+from the northern glaciers, are frequently stranded on various
+parts of the bank. They must often leave at the bottom large
+erratic blocks which the marine currents may be incapable of
+moving, but the same rocky fragments may be made to sink by the
+undermining of beds consisting of finer matter on which the blocks
+and gravel repose. In this way gravel and boulders may continue to
+overspread a submarine bottom after the latter has been lowered for
+hundreds of feet, the
+<a name="page107"></a>surface never having been able to emerge and become land. It is
+by no means improbable that the annual removal of an average
+thickness of half an inch of rock might counteract the ordinary
+upheaval which large submarine areas are undergoing; and the real
+enigma which the geologist has to solve is not the extensive
+denudation of the white chalk or of our tertiary sands and clays,
+but the fact that such incoherent materials have ever succeeded in
+lifting up their heads above water in an open sea. Why were they
+not swept away during storms into some adjoining abysses, the
+highest parts of each shoal being always planed off down to the
+depth of a few fathoms? The hardness and toughness of some rocks
+already exposed to windward and acting as breakwaters may perhaps
+have assisted; nor must we forget the protection afforded by a
+dense and unbroken covering of barnacles, limpets, and other
+creatures which flourish most between high and low water and
+shelter some newly risen coasts from the waves.
+</p>
+
+<p class="footnote">
+<a name="fn-6.1" id="fn-6.1"></a> <a href="#fnref-6.1">[1]</a>
+Principles of Geology 7th ed., p. 506; 10th ed., vol. ii, p. 196.
+</p>
+
+<p class="footnote">
+<a name="fn-6.2" id="fn-6.2"></a> <a href="#fnref-6.2">[2]</a>
+Second Visit to the United States, vol. i, chap. xxxiv.
+</p>
+
+<p class="footnote">
+<a name="fn-6.3" id="fn-6.3"></a> <a href="#fnref-6.3">[3]</a>
+Physical Geography and Geology of Great Britain, p. 78, 1864.
+</p>
+
+<p class="footnote">
+<a name="fn-6.4" id="fn-6.4"></a> <a href="#fnref-6.4">[4]</a>
+Principles, 10th ed., vol. i, p. 569.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap07"></a><a name="page108"></a>CHAPTER VII.<br/>
+JOINT ACTION OF DENUDATION, UPHEAVAL, AND SUBSIDENCE IN REMODELLING THE
+EARTH&rsquo;S CRUST.
+</h2>
+
+<p class="letter">
+How we obtain an Insight at the Surface, of the Arrangement of Rocks at great
+Depths. &mdash; Why the Height of the successive Strata in a given Region is so
+disproportionate to their Thickness. &mdash; Computation of the average annual
+Amount of subaërial Denudation. &mdash; Antagonism of Volcanic Force to the
+Levelling Power of running Water. &mdash; How far the Transfer of Sediment from
+the Land to a neighbouring Sea-bottom may affect Subterranean Movements.
+&mdash; Permanence of Continental and Oceanic Areas.
+</p>
+
+<p>
+<b>How we obtain an Insight at the Surface, of the Arrangement of Rocks at
+Great Depths.</b>&mdash; The reader has been already informed that, in the
+structure of the earth&rsquo;s crust, we often find proofs of the direct
+superposition of marine to fresh-water strata, and also evidence of the
+alternation of deep-sea and shallow-water formations. In order to explain how
+such a series of rocks could be made to form our present continents and
+islands, we have not only to assume that there have been alternate upward and
+downward movements of great vertical extent, but that the upheaval in the areas
+which we at present inhabit has, in later geological times, sufficiently
+predominated over subsidence to cause these portions of the earth&rsquo;s crust
+to be land instead of sea. The sinking down of a delta beneath the sea-level
+may cause strata of fluviatile or even terrestrial origin, such as peat with
+trees proper to marshes, to be covered by deposits of deep-sea origin. There is
+also no end to the thickness of mud and sand which may accumulate in shallow
+water, provided that fresh sediment is brought down from the wasting land at a
+rate corresponding to that of the sinking of the bed of the sea. The latter,
+again, may sometimes sink so fast that the earthy matter, being intercepted in
+some new landward depression, may never reach its former resting-place, where,
+the water becoming clear may favour the growth of shells and corals, and
+calcareous rocks of organic origin may thus be superimposed on mechanical
+deposits.
+</p>
+
+<p>
+The succession of strata here alluded to would be consistent with the
+occurrence of gradual downward and upward movements of the land and bed of the
+sea without any disturbance of the horizontality of the several formations. But
+<a name="page109"></a>the arrangement of rocks composing the earth&rsquo;s crust
+differs materially from that which would result from a mere series of vertical
+movements. Had the volcanic forces been confined to such movements, and had the
+stratified rocks been first formed beneath the sea and then raised above it,
+without any lateral compression, the geologist would never have obtained an
+insight into the monuments of various ages, some of extremely remote
+antiquity.
+</p>
+
+<p>
+What we have said in Chapter V of dip and strike, of the folding and inversion
+of strata, of anticlinal and synclinal flexures, and in Chapter VI of
+denudation at different periods, whether subaërial or submarine, must be
+understood before the student can comprehend what may at first seem to him an
+anomaly, but which it is his business particularly to understand. I allude to
+the small height above the level of the sea attained by strata often many miles
+in thickness, and about the chronological succession of which, in one and the
+same region, there is no doubt whatever. Had stratified rocks in general
+remained horizontal, the waves of the sea would have been enabled during
+oscillations of level to plane off entirely the uppermost beds as they rose or
+sank during the emergence or submergence of the land. But the occurrence of a
+series of formations of widely different ages, all remaining horizontal and in
+conformable stratification, is exceptional, and for this reason the total
+annihilation of the uppermost strata has rarely taken place. We owe, indeed, to
+the side way movements of <i>lateral compression</i> those anticlinal and
+synclinal curves of the beds already described <a
+href="images/fig55.jpg">(Fig. 55)</a>, which, together with denudation,
+subaërial and submarine, enable us to investigate the structure of the
+earth&rsquo;s crust many miles below those points which the miner can reach. I
+have already shown in <a href="images/fig56.jpg">Fig. 56</a>, how, at St.
+Abb&rsquo;s Head, a series of strata of indefinite thickness may become
+vertical, and then denuded, so that the edges of the beds alone shall be
+exposed to view, the altitude of the upheaved ridges being reduced to a
+moderate height above the sea-level; and it may be observed that although the
+incumbent strata of Old Red Sandstone are in that place nearly horizontal, yet
+these same newer beds will in other places be found so folded as to present
+vertical strata, the edges of which are abruptly cut off, as in 2, 3, 4 on the
+right-hand side of the diagram, <a href="images/fig55.jpg">Fig. 55.</a>
+</p>
+
+<p>
+<b>Why the Height of the Successive Strata in a given Region is so
+Disproportionate to their Thickness.</b>&mdash;We cannot too distinctly bear
+in mind how dependent we are on the joint action of the volcanic and aqueous
+forces, the one in
+<a name="page110"></a>
+disturbing the original position of rocks, and the other in destroying large
+portions of them, for our power of consulting the different pages and volumes
+of those stony records of which the crust of the globe is composed. Why, it may
+be asked, if the ancient bed of the sea has been in many regions uplifted to
+the height of two or three miles, and sometimes twice that altitude, and if it
+can be proved that some single formations are of themselves two or three miles
+thick, do we so often find several important groups resting one upon the other,
+yet attaining only the height of a few hundred feet above the level of the sea?
+</p>
+
+<p>
+The American geologists, after carefully studying the Allegheny or Appalachian
+mountains, have ascertained that the older fossiliferous rocks of that chain
+(from the Silurian to the Carboniferous inclusive) are not less than 42,000
+feet thick, and if they were now superimposed on each other in the order in
+which they were thrown down, they ought to equal in height the Himalayas with
+the Alps piled upon them. Yet they rarely reach an altitude of 5000 feet, and
+their loftiest peaks are no more than 7000 feet high. The Carboniferous strata
+forming the highest member of the series, and containing beds of coal, can be
+shown to be of shallow-water origin, or even sometimes to have originated in
+swamps in the open air. But what is more surprising, the lowest part of this
+great Palæozoic series, instead of having been thrown down at the bottom of an
+abyss more than 40,000 feet deep, consists of sediment (the Potsdam sandstone),
+evidently spread out on the bottom of a shallow sea, on which ripple-marked
+sands were occasionally formed. This vast thickness of 40,000 feet is not
+obtained by adding together the maximum density attained by each formation in
+distant parts of the chain, but by measuring the successive groups as they are
+exposed in a very limited area, and where the denuded edges of the vertical
+strata forming the parallel folds alluded to at page 87 &ldquo;crop out&rdquo;
+at the surface. Our attention has been called by Mr. James Hall, Palæontologist
+of New York, to the fact that these Palæozoic rocks of the Appalachian chain,
+which are of such enormous density, where they are almost entirely of
+mechanical origin, thin out gradually as they are traced to the westward, where
+evidently the contemporaneous seas allowed organic rocks to be formed by
+corals, echinoderms, and encrinites in clearer water, and where, although the
+same successive periods are represented, the total mass of strata from the
+Silurian to the Carboniferous, instead of being 40,000 is only 4000 feet thick.
+</p>
+
+<p>
+<a name="page111"></a>A like phenomenon is exhibited in every mountainous
+country, as, for example, in the European Alps; but we need not go farther than
+the north of England for its illustration. Thus in Lancashire and central
+England the thickness of the Carboniferous formation, including the Millstone
+Grit and Yoredale beds, is computed to be more than 18,000 feet; to this we may
+add the Mountain Limestone, at least 2000 feet in thickness, and the overlying
+Permian and Triassic formations, 3000 or 4000 feet thick. How then does it
+happen that the loftiest hills of Yorkshire and Lancashire, instead of being
+24,000 feet high, never rise above 3000 feet? For here, as before pointed out
+in the Alleghenies, all the great thicknesses are sometimes found in close
+approximation and in a region only a few miles in diameter. It is true that
+these same sets of strata do not preserve their full force when followed for
+indefinite distances. Thus the 18,000 feet of Carboniferous grits and shales in
+Lancashire, before alluded to, gradually thin out, as Mr. Hull has shown, as
+they extend southward, by attenuation or original deficiency of sediment, and
+not in consequence of subsequent denudation, so that when we have followed them
+for about 100 miles into Leicestershire, they have dwindled away to a thickness
+of only 3000 feet. In the same region the Carboniferous limestone attains so
+unusual a thickness&mdash;namely, more than 4000 feet&mdash;as to appear to
+compensate in some measure for the deficiency of contemporaneous sedimentary
+rock.<a href="#fn-7.1" name="fnref-7.1" id="fnref-7.1"><sup>[1]</sup></a>
+</p>
+
+
+<p>
+It is admitted that when two formations are unconformable their fossil remains
+almost always differ considerably. The break in the continuity of the organic
+forms seems connected with a great lapse of time, and the same interval has
+allowed extensive disturbance of the strata, and removal of parts of them by
+denudation, to take place. The more we extend our investigations the more
+numerous do the proofs of these breaks become, and they extend to the most
+ancient rocks yet discovered. The oldest examples yet brought to light in the
+British Isles are on the borders of Rosshire and Sutherlandshire, and have been
+well described by Sir Roderick Murchison, by whom their chronological relations
+were admirably worked out, and proved to be very different from those which
+previous observers had imagined them to be. I had an opportunity in the autumn
+of 1869 of verifying the splendid section given in Fig. 82 by climbing in a few
+hours from the banks of Loch Assynt to the summit of the mountain called
+Queenaig, 2673 feet high.
+</p>
+
+<p>
+The formations 1, 2, 3, the Laurentian, Cambrian, and
+<a name="page112"></a>
+Silurian, to be explained in Chapters XXV and XXVI, not only occur in
+succession in this one mountain, but their unconformable junctions are
+distinctly exposed to view.
+</p>
+
+<p>
+<img src="images/fig82.jpg" width="405" height="162" alt="Fig. 82:
+Unconformable Palæozoic stata, Sutherlandshire (Murchison)." />
+</p>
+
+<p>
+To begin with the oldest set of rocks, No. 1; they consist chiefly of
+hornblendic gneiss, and in the neighbouring Hebrides form whole islands,
+attaining a thickness of thousands of feet, although they have suffered such
+contortions and denudation that they seldom rise more than a few hundred feet
+above the sea-level. In discordant stratification upon the edges of this gneiss
+reposes No. 2, a group of conglomerate and purple sandstone referable to the
+Cambrian (or Longmynd) formation, which can elsewhere be shown to be
+characterised by its peculiar organic remains. On this again rests No. 3, a
+lower member of the important group called Silurian, an outlier of which,
+3&#x2032;, caps the summit of Queenaig, attesting the removal by denudation of
+rocks of the same age, which once extended from the great mass 3 to 3&#x2032;.
+Although this rock now consists of solid quartz, it is clear that in its
+original state it was formed of fine sand, perforated by numerous lob-worms or
+annelids, which left their burrows in the shape of tubular hollows <a
+href="images/fig563.jpg">Fig. 563</a> of <i>Arenicolites</i>), hundreds,
+nay thousands, of which I saw as I ascended the mountain.
+</p>
+
+<p>
+<img src="images/fig83.jpg" width="402" height="166" alt="Fig. 83: Diagrammatic
+section of the same groups near Queenaig (Murchison)." />
+</p>
+
+<p>
+In Queenaig we only behold this single quartzose member of the Silurian series,
+but in the neighbouring country (see Fig. 83) it is seen to the eastward to be
+followed by <a name="page113"></a>limestones, 3<i>a</i>, and schists,
+3<i>b</i>, presenting numerous folds, and becoming more and more metamorphic
+and crystalline, until at length, although very different in age and strike,
+they much resemble in appearance the group No. 1. It is very seldom that in the
+same country one continuous formation, such as the Silurian, is, as in this
+case, more fossiliferous and less altered by volcanic heat in its older than in
+its newer strata, and still more rare to find an underlying and unconformable
+group like the Cambrian retaining its original condition of a conglomerate and
+sandstone more perfectly than the overlying formation. Here also we may remark
+in regard to the origin of these Cambrian rocks that they were evidently
+produced at the expense of the underlying Laurentian, for the rounded pebbles
+occurring in them are identical in composition and texture with that
+crystalline gneiss which constitutes the contorted beds of the inferior
+formation No. 1. When the reader has studied the chapter on metamorphism, and
+has become aware how much modification by heat, pressure, and chemical action
+is required before the conversion of sedimentary into crystalline strata can be
+brought about, he will appreciate the insight which we thus gain into the date
+of the changes which had already been effected in the Laurentian rocks long
+before the Cambrian pebbles of quartz and gneiss were derived from them. The
+Laurentian is estimated by Sir William Logan to amount in Canada to 30,000 feet
+in thickness. As to the Cambrian, it is supposed by Sir Roderick Murchison that
+the fragment left in Sutherlandshire is about 3500 feet thick, and in Wales and
+the borders of Shropshire this formation may equal 10,000 feet, while the
+Silurian strata No. 3, difficult as it may be to measure them in their various
+foldings to the eastward, where they have been invaded by intrusive masses of
+granite, are supposed many times to surpass the Cambrian in volume and density.
+</p>
+
+<p>
+But although we are dealing here with stratified rocks, each of which would be
+several miles in thickness, if they were fully represented, the whole of them
+do not attain the elevation of a single mile above the level of the sea.
+</p>
+
+<p>
+<b>Computation of the Average Annual Amount of Subaërial
+Denudation.</b>&mdash;The geology of the district above alluded to may assist
+our imagination in conceiving the extent to which groups of ancient rocks, each
+of which may in their turn have formed continents and oceanic basins, have been
+disturbed, folded, and denuded even in the course of a few out of many of those
+geological periods to which our imperfect records relate. It is not easy for us
+to overestimate <a name="page114"></a>the effects which causes in every day
+action must produce when the multiplying power of time is taken into account.
+</p>
+
+<p>
+Attempts were made by Manfredi in 1736, and afterwards by Playfair in 1802, to
+calculate the time which it would require to enable the rivers to deliver over
+the whole of the land into the basin of the ocean. The data were at first too
+imperfect and vague to allow them even to approximate to safe conclusions. But
+in our own time similar investigations have been renewed with more prospect of
+success, the amount brought down by many large rivers to the sea having been
+more accurately ascertained. Mr. Alfred Tylor, in 1850, inferred that the
+quantity of detritus now being distributed over the sea-bottom would, at the
+end of 10,000 years, cause an elevation of the sea-level to the extent of at
+least three inches.<a href="#fn-7.2" name="fnref-7.2"
+id="fnref-7.2"><sup>[2]</sup></a> Subsequently Mr. Croll, in 1867, and again,
+with more exactness, in 1868, deduced from the latest measurement of the
+sediment transported by European and American rivers the rate of subaërial
+denudation to which the surface of large continents is exposed, taking
+especially the hydrographical basin of the Mississippi as affording the best
+available measure of the average waste of the land. The conclusion arrived at
+in his able memoir,<a href="#fn-7.3" name="fnref-7.3"
+id="fnref-7.3"><sup>[3]</sup></a> was that the whole terrestrial surface is
+denuded at the rate of one foot in 6000 years and this opinion was
+simultaneously enforced by his fellow-labourer, Mr. Geikie, who, being jointly
+engaged in the same line of inquiry, published a luminous essay on the subject
+in 1868.
+</p>
+
+<p>
+The student, by referring to my &ldquo;Principles of Geology,&rdquo;<a
+href="#fn-7.4" name="fnref-7.4" id="fnref-7.4"><sup>[4]</sup></a> may see that
+Messrs. Humphrey and Abbot, during their survey of the Mississippi, attempted
+to make accurate measurements of the proportion of sediment carried down
+annually to the sea by that river, including not only the mud held in
+suspension, but also the sand and gravel forced along the bottom.
+</p>
+
+<p>
+It is evident that when we know the dimensions of the area which is drained,
+and the annual quantity of earthy matter taken from it and borne into the sea,
+we can affirm how much on an average has been removed from the general surface
+in one year, and there seems no danger of our overrating the mean rate of waste
+by selecting the Mississippi as our example, for that river drains a country
+equal to more than half the continent of Europe, extends through twenty degrees
+of latitude, and therefore through regions enjoying a great variety of climate,
+and some of its tributaries <a name="page115"></a>descend from mountains of
+great height. The Mississippi is also more likely to afford us a fair test of
+ordinary denudation, because, unlike the St. Lawrence and its tributaries,
+there are no great lakes in which the fluviatile sediment is thrown down and
+arrested in its way to the sea. In striking a general average we have to
+remember that there are large deserts in which there is scarcely any rainfall,
+and tracts which are as rainless as parts of Peru, and these must not be
+neglected as counterbalancing others, in the tropics, where the quantity of
+rain is in excess. If then, argues Mr. Geikie, we assume that the Mississippi
+is lowering the surface of the great basin which it drains at the rate of one
+foot in 6000 years, 10 feet in 60,000 years, 100 feet in 600,000 years, and
+1000 feet in 6,000,000 years, it would not require more than about 4,500,000
+years to wear away the whole of the North American continent if its mean height
+is correctly estimated by Humboldt at 748 feet. And if the mean height of all
+the land now above the sea throughout the globe is 1000 feet, as some
+geographers believe, it would only require six million years to subject a mass
+of rock equal in volume to the whole of the land to the action of subaërial
+denudation. It may be objected that the annual waste is partial, and not
+equally derived from the general surface of the country, inasmuch as plains,
+water-sheds, and level ground at all heights remain comparatively unaltered;
+but this, as Mr. Geikie has well pointed out, does not affect our estimate of
+the sum total of denudation. The amount remains the same, and if we allow too
+little for the loss from the surface of table-lands we only increase the
+proportion of the loss sustained by the sides and bottoms of the valleys, and
+<i>vice versa.</i><a href="#fn-7.5" name="fnref-7.5"
+id="fnref-7.5"><sup>[5]</sup></a>
+</p>
+
+<p>
+<b>Antagonism of Volcanic Force to the Levelling Power of Running
+Water.</b>&mdash;In all these estimates it is assumed that the entire quantity
+of land above the sea-level remains on an average undiminished in spite of
+annual waste. Were it otherwise the subaërial denudation would be continually
+lessened by the diminution of the height and dimensions of the land exposed to
+waste. Unfortunately we have as yet no accurate data enabling us to measure the
+action of that force by which the inequalities of the surface of the
+earth&rsquo;s crust may be restored, and the height of the continents and depth
+of the seas made to continue unimpaired. I stated in 1830 in the
+&ldquo;Principles of Geology,&rdquo;<a href="#fn-7.6" name="fnref-7.6"
+id="fnref-7.6"><sup>[6]</sup></a> that running water and volcanic action are
+two antagonistic forces; the one labouring <a name="page116"></a>continually to
+reduce the whole of the land to the level of the sea, the other to restore and
+maintain the inequalities of the crust on which the very existence of islands
+and continents depends. I stated, however, that when we endeavour to form some
+idea of the relation of these destroying and renovating forces, we must always
+bear in mind that it is not simply by upheaval that subterranean movements can
+counteract the levelling force of running water. For whereas the transportation
+of sediment from the land to the ocean would raise the general sea-level, the
+subsidence of the sea-bottom, by increasing its capacity, would check this rise
+and prevent the submergence of the land. I have, indeed, endeavoured to show
+that unless we assume that there is, on the whole, more subsidence than
+upheaval, we must suppose the diameter of the planet to be always increasing,
+by that quantity of volcanic matter which is annually poured out in the shape
+of lava or ashes, whether on the land or in the bed of the sea, and which is
+derived from the interior of the earth. The abstraction of this matter causes,
+no doubt, subterranean vacuities and a corresponding giving way of the surface;
+if it were not so, the average density of parts of the interior would be always
+lessening and the size of the planet increasing.<a href="#fn-7.7"
+name="fnref-7.7" id="fnref-7.7"><sup>[7]</sup></a>
+</p>
+
+<p>
+Our inability to estimate the amount or direction of the movements due to
+volcanic power by no means renders its efficacy as a land-preserving force in
+past times a mere matter of conjecture. The student will see in Chapter XXIV
+that we have proofs of Carboniferous forests hundreds of miles in extent which
+grew on the lowlands or deltas near the sea, and which subsided and gave place
+to other forests, until in some regions fluviatile and shallow-water strata
+with occasional seams of coal were piled one over the other, till they attained
+a thickness of many thousand feet. Such accumulations, observed in Great
+Britain and America on opposite sides of the Atlantic, imply the long-continued
+existence of land vegetation, and of rivers draining a former continent placed
+where there is now deep sea.
+</p>
+
+<p>
+It will be also seen in Chapter XXV that we have evidence of a rich terrestrial
+flora, the Devonian, even more ancient than the Carboniferous; while on the
+other hand, the later Triassic, Oolitic, Cretaceous, and successive Tertiary
+periods have all supplied us with fossil plants, insects, or terrestrial
+mammalia; showing that, in spite of great oscillations of level and continued
+changes in the position of land and sea, the volcanic forces have maintained a
+due <a name="page117"></a>proportion of dry land. We may appeal also to
+fresh-water formations, such as the Purbeck and Wealden, to prove that in the
+Oolitic and Neocomian eras there were rivers draining ancient lands in Europe
+in times when we know that other spaces, now above water, were submerged.
+</p>
+
+<p>
+<b>How far the Transfer of Sediment from the Land to a Neighbouring Sea-bottom
+may affect Subterranean Movements.</b>&mdash;Little as we understand at present
+the laws which govern the distribution of volcanic heat in the interior and
+crust of the globe, by which mountain chains, high table-lands, and the abysses
+of the ocean are formed, it seems clear that this heat is the prime mover on
+which all the grander features in the external configuration of the planet
+depend.
+</p>
+
+<p>
+It has been suggested that the stripping off by denudation of dense masses from
+one part of a continent and the delivery of the same into the bed of the ocean
+must have a decided effect in causing changes of temperature in the
+earth&rsquo;s crust below, or, in other words, in causing the subterranean
+isothermals to shift their position. If this be so, one part of the crust may
+be made to rise, and another to sink, by the expansion and contraction of the
+rocks, of which the temperature is altered.
+</p>
+
+<p>
+I cannot, at present, discuss this subject, of which I have treated more fully
+elsewhere,<a href="#fn-7.8" name="fnref-7.8" id="fnref-7.8"><sup>[8]</sup></a>
+but may state here that I believe this transfer of sediment to play a very
+subordinate part in modifying those movements on which the configuration of the
+earth&rsquo;s crust depends. In order that strata of shallow-water origin
+should be able to attain a thickness of several thousand feet, and so come to
+exert a considerable downward pressure, there must have been first some
+independent and antecedent causes at work which have given rise to the
+incipient shallow receptacle in which the sediment began to accumulate. The
+same causes there continuing to depress the sea-bottom, room would be made for
+fresh accessions of sediment, and it would only be by a long repetition of the
+depositing process that the new matter could acquire weight enough to affect
+the temperature of the rocks far below, so as to increase or diminish their
+volume.
+</p>
+
+<p>
+<b>Permanence of Continental and Oceanic Areas.</b>&mdash;If the thickness of
+more than 40,000 feet of sedimentary strata before alluded to in the
+Appalachians proves a preponderance of downward movements in Palæozoic times in
+a district now forming the eastern border of North America, it also proves, as
+before hinted, the continued existence and waste of some neighbouring
+continent, probably formed of Laurentian <a name="page118"></a>rocks, and
+situated where the Atlantic now prevails. Such an hypothesis would be in
+perfect harmony with the conclusions forced upon us by the study of the present
+configuration of our continents, and the relation of their height to the depth
+of the oceanic basins; also to the considerable elevation and extent sometimes
+reached by drift containing shells of recent species, and still more by the
+fact of sedimentary strata, several thousand feet thick, as those of central
+Sicily, or such as flank the Alps and Apennines, containing fossil Mollusca
+sometimes almost wholly identical with species still living.
+</p>
+
+<p>
+I have remarked elsewhere<a href="#fn-7.9" name="fnref-7.9"
+id="fnref-7.9"><sup>[9]</sup></a> that upward and downward movements of 1000
+feet or more would turn much land into sea and sea into land in the continental
+areas and their borders, whereas oscillations of equal magnitude would have no
+corresponding effect in the bed of the ocean generally, believed as it is to
+have a mean depth of 15,000 feet, and which, whether this estimate be correct
+or not, is certainly of great profundity. Subaërial denudation would not of
+itself lessen the area of the land, but would tend to fill up with sediment
+seas of moderate depth adjoining the coast. The coarser matter falls to the
+bottom near the shore in the first still water which it reaches, and whenever
+the sea-bottom on which this matter has been thrown is slightly elevated, it
+becomes land, and an upheaval of a thousand feet causes it to attain the mean
+elevation of continents in general.
+</p>
+
+<p>
+Suppose, therefore, we had ascertained that the triturating power of subaërial
+denudation might in a given time&mdash;in three, or six, or a greater number of
+millions of years&mdash;pulverise a volume of rock equal in dimensions to all
+the present land, we might yet find, could we revisit the earth at the end of
+such a period, that the continents occupied very much the same position which
+they held before; we should find the rivers employed in carrying down to the
+sea the very same mud, sand, and pebbles with which they had been charged in
+our own time, the superficial alluvial matter as well as a great thickness of
+sedimentary strata would inclose shells, all or a great part of which we should
+recognise as specifically identical with those already known to us as living.
+Every geologist is aware that great as have been the geographical changes in
+the northern hemisphere since the commencement of the Glacial Period, there
+having been submergence and re-emergence of land to the extent of 1000 feet
+vertically, and in the temperate latitudes great vicissitudes of climate, the
+marine mollusca have not changed, and the <a name="page119"></a>same drift
+which had been carried down to the sea at the beginning of the period is now
+undergoing a second transportation in the same direction.
+</p>
+
+<p>
+As when we have measured a fraction of time in an hour-glass we have only to
+reverse the position of our chronometer and we make the same sand measure over
+again the duration of a second equal period, so when the volcanic force has
+remoulded the form of a continent and the adjoining sea-bottom, the same
+materials are made to do duty a second time. It is true that at each
+oscillation of level the solid rocks composing the original continent suffer
+some fresh denudation, and do not remain unimpaired like the wooden and glass
+framework of the hour-glass, still the wear and tear suffered by the larger
+area exposed to subaërial denudation consists either of loose drift or of
+sedimentary strata, which were thrown down in seas near the land, and
+subsequently upraised, the same continents and oceanic basins remaining in
+existence all the while.
+</p>
+
+<p>
+From all that we know of the extreme slowness of the upward and downward
+movements which bring about even slight geographical changes, we may infer that
+it would require a long succession of geological periods to cause the submarine
+and supramarine areas to change places, even if the ascending movements in the
+one region and the descending in the other were continuously in one direction.
+But we have only to appeal to the structure of the Alps, where there are so
+many shallow and deep water formations of various ages crowded into a limited
+area, to convince ourselves that mountain chains are the result of great
+oscillations of level. High land is not produced simply by uniform upheaval,
+but by a predominance of elevatory over subsiding movements. Where the ocean is
+extremely deep it is because the sinking of the bottom has been in excess, in
+spite of interruptions by upheaval.
+</p>
+
+<p>
+Yet persistent as may be the leading features of land and sea on the globe,
+they are not immutable. Some of the finest mud is doubtless carried to
+indefinite distances from the coast by marine currents, and we are taught by
+deep-sea dredgings that in clear water at depths equalling the height of the
+Alps organic beings may flourish, and their spoils slowly accumulate on the
+bottom. We also occasionally obtain evidence that submarine volcanoes are
+pouring out ashes and streams of lava in mid-ocean as well as on land (see
+Principles, vol. ii, p. 64), and that wherever mountains like Etna, Vesuvius,
+and the Canary Islands are now the site of eruptions, there are signs of
+accompanying upheaval, by <a name="page120"></a>which beds of ashes full of
+recent marine shells have been uplifted many hundred feet. We need not be
+surprised, therefore, if we learn from geology that the continents and oceans
+were not always placed where they now are, although the imagination may well be
+overpowered when it endeavours to contemplate the quantity of time required for
+such revolutions.
+</p>
+
+<p>
+We shall have gained a great step if we can approximate to the number of
+millions of years in which the average aqueous denudation going on upon the
+land would convey seaward a quantity of matter equal to the average volume of
+our continents, and this might give us a gauge of the minimum of volcanic force
+necessary to counteract such levelling power of running water; but to discover
+a relation between these great agencies and the rate at which species of
+organic beings vary, is at present wholly beyond the reach of our computation,
+though perhaps it may not prove eventually to transcend the powers of man.
+</p>
+
+<p class="footnote">
+<a name="fn-7.1" id="fn-7.1"></a> <a href="#fnref-7.1">[1]</a>
+Hull, Quart. Geol. Journ., vol. xxiv, p. 322, 1868.
+</p>
+
+<p class="footnote">
+<a name="fn-7.2" id="fn-7.2"></a> <a href="#fnref-7.2">[2]</a>
+Tylor, Phil. Mag., 4th series, p. 268, 1850.
+</p>
+
+<p class="footnote">
+<a name="fn-7.3" id="fn-7.3"></a> <a href="#fnref-7.3">[3]</a>
+Croll, Phil. Mag., 1868, p. 381.
+</p>
+
+<p class="footnote">
+<a name="fn-7.4" id="fn-7.4"></a> <a href="#fnref-7.4">[4]</a>
+Vol. i, p. 442, 1867.
+</p>
+
+<p class="footnote">
+<a name="fn-7.5" id="fn-7.5"></a> <a href="#fnref-7.5">[5]</a>
+Trans. Geol. Soc. Glasgow, vol. iii, p. 169.
+</p>
+
+<p class="footnote">
+<a name="fn-7.6" id="fn-7.6"></a> <a href="#fnref-7.6">[6]</a>
+1st ed., chap. x, p. 167, 1830; see also 10th ed., vol. i, chap. xv, p. 327,
+1867.
+</p>
+
+<p class="footnote">
+<a name="fn-7.7" id="fn-7.7"></a> <a href="#fnref-7.7">[7]</a>
+Principles, vol. ii, p. 237; also 1st ed., p. 447, 1830.
+</p>
+
+<p class="footnote">
+<a name="fn-7.8" id="fn-7.8"></a> <a href="#fnref-7.8">[8]</a>
+Principles, vol. ii, p. 229, 1868.
+</p>
+
+<p class="footnote">
+<a name="fn-7.9" id="fn-7.9"></a> <a href="#fnref-7.9">[9]</a>
+Principles, vol. i, p. 265, 1867.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap08"></a><a name="page121"></a>CHAPTER VIII.<br/>
+CHRONOLOGICAL CLASSIFICATION OF ROCKS.</h2>
+
+<p class="letter">Aqueous, Plutonic, volcanic, and metamorphic
+Rocks considered chronologically. &mdash; Terms Primary,
+Secondary, and Tertiary; Palæozoic, Mesozoic, and Cainozoic
+explained. &mdash; On the different Ages of the aqueous Rocks.
+&mdash; Three principal Tests of relative Age: Superposition,
+Mineral Character, and Fossils. &mdash; Change of Mineral
+Character and Fossils in the same continuous Formation. &mdash;
+Proofs that distinct Species of Animals and Plants have lived at
+successive Periods. &mdash; Distinct Provinces of indigenous
+Species. &mdash; Great Extent of single Provinces. &mdash;
+Similar Laws prevailed at successive Geological Periods. &mdash;
+Relative Importance of mineral and palæontological
+Characters. &mdash; Test of Age by included Fragments. &mdash;
+Frequent Absence of Strata of intervening Periods. &mdash;
+Tabular Views of fossiliferous Strata.</p>
+
+<p><b>Chronology of Rocks.</b>&mdash; In the first chapter it was
+stated that the four great classes of rocks, the aqueous, the
+volcanic, the Plutonic, and the metamorphic, would each be
+considered not only in reference to their mineral characters, and
+mode of origin, but also to their relative age. In regard to the
+aqueous rocks, we have already seen that they are stratified,
+that some are calcareous, others argillaceous or siliceous, some
+made up of sand, others of pebbles; that some contain
+fresh-water, others marine fossils, and so forth; but the student
+has still to learn which rocks, exhibiting some or all of these
+characters, have originated at one period of the earth&rsquo;s
+history, and which at another.</p>
+
+<p>To determine this point in reference to the fossiliferous
+formations is more easy than in any other class, and it is
+therefore the most convenient and natural method to begin by
+establishing a chronology for these strata, and then to refer as
+far as possible to the same divisions, the several groups of
+Plutonic, volcanic, and metamorphic rocks. Such a system of
+classification is not only recommended by its greater clearness
+and facility of application, but is also best fitted to strike
+the imagination by bringing into one view the contemporaneous
+revolutions of the inorganic and organic creations of former
+times. For the sedimentary formations are most readily
+distinguished by the different species of fossil animals and
+plants which they inclose, and of which one assemblage after
+another has flourished and then disappeared from the earth in
+succession.</p>
+
+<p>
+<a name="page122"></a>In the present work, therefore, the four great classes of
+rocks, the aqueous, Plutonic, volcanic, and metamorphic, will
+form four parallel, or nearly parallel, columns in one
+chronological table. They will be considered as four sets of
+monuments relating to four contemporaneous, or nearly
+contemporaneous, series of events. I shall endeavour, in a
+subsequent chapter on the Plutonic rocks, to explain the manner
+in which certain masses belonging to each of the four classes of
+rocks may have originated simultaneously at every geological
+period, and how the earth&rsquo;s crust may have been continually
+remodelled, above and below, by aqueous and igneous causes, from
+times indefinitely remote. In the same manner as aqueous and
+fossiliferous strata are now formed in certain seas or lakes,
+while in other places volcanic rocks break out at the surface,
+and are connected with reservoirs of melted matter at vast depths
+in the bowels of the earth, so, at every era of the past,
+fossiliferous deposits and superficial igneous rocks were in
+progress contemporaneously with others of subterranean and
+Plutonic origin, and some sedimentary strata were exposed to
+heat, and made to assume a crystalline or metamorphic
+structure.</p>
+
+<p>It can by no means be taken for granted, that during all these
+changes the solid crust of the earth has been increasing in
+thickness. It has been shown, that so far as aqueous action is
+concerned, the gain by fresh deposits, and the loss by
+denudation, must at each period have been equal (see above, Chap.
+VI, p. 96); and in like manner, in the inferior portion of the
+earth&rsquo;s crust, the acquisition of new crystalline rocks, at
+each successive era, may merely have counterbalanced the loss
+sustained by the melting of materials previously consolidated. As
+to the relative antiquity of the crystalline foundations of the
+earth&rsquo;s crust, when compared to the fossiliferous and
+volcanic rocks which they support, I have already stated, in the
+first chapter, that to pronounce an opinion on this matter is as
+difficult as at once to decide which of the two, whether the
+foundations or superstructure of an ancient city built on wooden
+piles may be the oldest. We have seen that, to answer this
+question, we must first be prepared to say whether the work of
+decay and restoration had gone on most rapidly above or below;
+whether the average duration of the piles has exceeded that of
+the buildings, or the contrary. So also in regard to the relative
+age of the superior and inferior portions of the earth&rsquo;s
+crust; we cannot hazard even a conjecture on this point, until
+we know whether, upon an average, the power of water above, or
+that of heat below, is most efficacious in giving new forms to
+solid matter.</p>
+
+<p>
+<a name="page123"></a>The early geologists gave to all the crystalline and
+non-fossiliferous rocks the name of Primitive or Primary, under
+the idea that they were formed anterior to the appearance of life
+upon the earth, while the aqueous or fossiliferous strata were
+termed Secondary, and alluviums or other superficial deposits,
+Tertiary. The meaning of these terms, has, however, been
+gradually modified with advancing knowledge, and they are now
+used to designate three great chronological divisions under which
+all geological formations can be classed, each of them being
+characterised by the presence of distinctive groups of organic
+remains rather than by any mechanical peculiarities of the strata
+themselves. If, therefore, we retain the term
+&ldquo;primary,&rdquo; it must not be held to designate a set of
+crystalline rocks some of which have been proved to be even of
+Tertiary age, but must be applied to all rocks older than the
+secondary formations. Some geologists, to avoid misapprehension,
+have introduced the term Palæozoic for primary, from
+<i>palaion,</i> &ldquo;ancient,&rdquo; and <i>zoon,</i> &ldquo;an
+organic being,&rdquo; still retaining the terms secondary and
+tertiary; Mr. Phillips, for the sake of uniformity, has proposed
+Mesozoic, for secondary, from <i>mesos,</i> &ldquo;middle,&rdquo;
+etc.; and Cainozoic, for tertiary, from <i>kainos,</i>
+&ldquo;recent,&rdquo; etc.; but the terms primary, secondary, and
+tertiary have the claim of priority in their favour, and are of
+corresponding value.</p>
+
+<p>It may perhaps be suggested that some metamorphic strata, and
+some granites, may be anterior in date to the oldest of the
+primary fossiliferous rocks. This opinion is doubtless true, and
+will be discussed in future chapters; but I may here observe,
+that when we arrange the four classes of rocks in four parallel
+columns in one table of chronology, it is by no means assumed
+that these columns are all of equal length; one may begin at an
+earlier period than the rest, and another may come down to a
+later point of time, and we may not be yet acquainted with the
+most ancient of the primary fossiliferous beds, or with the
+newest of the hypogene.</p>
+
+<p>For reasons already stated, I proceed first to treat of the
+aqueous or fossiliferous formations considered in chronological
+order or in relation to the different periods at which they have
+been deposited.</p>
+
+<p>There are three principal tests by which we determine the age
+of a given set of strata; first, superposition; secondly, mineral
+character; and, thirdly, organic remains. Some aid can
+occasionally be derived from a fourth kind of proof, namely, the
+fact of one deposit including in it fragments of a pre-existing
+rock, by which the relative ages of the two may, even in the
+absence of all other evidence, be determined.</p>
+
+<p>
+<a name="page124"></a><b>Superposition.</b>&mdash;The first and principal test of
+the age of one aqueous deposit, as compared to another, is
+relative position. It has been already stated, that, where strata
+are horizontal, the bed which lies uppermost is the newest of the
+whole, and that which lies at the bottom the most ancient. So, of
+a series of sedimentary formations, they are like volumes of
+history, in which each writer has recorded the annals of his own
+times, and then laid down the book, with the last written page
+uppermost, upon the volume in which the events of the era
+immediately preceding were commemorated. In this manner a lofty
+pile of chronicles is at length accumulated; and they are so
+arranged as to indicate, by their position alone, the order in
+which the events recorded in them have occurred.</p>
+
+<p>In regard to the crust of the earth, however, there are some
+regions where, as the student has already been informed, the beds
+have been disturbed, and sometimes extensively thrown over and
+turned upside down. (See <a href="#page73">p. 73,</a> <a
+href="#page87">p. 87.</a>) But an experienced geologist
+can rarely be deceived by these exceptional cases. When he finds
+that the strata are fractured, curved, inclined, or vertical, he
+knows that the original order of superposition must be doubtful,
+and he then endeavours to find sections in some neighbouring
+district where the strata are horizontal, or only slightly
+inclined. Here, the true order of sequence of the entire series
+of deposits being ascertained, a key is furnished for settling
+the chronology of those strata where the displacement is
+extreme.</p>
+
+<p><b>Mineral Character.</b>&mdash;The same rocks may often be
+observed to retain for miles, or even hundreds of miles, the same
+mineral peculiarities, if we follow the planes of stratification,
+or trace the beds, if they be undisturbed, in a horizontal
+direction. But if we pursue them vertically, or in any direction
+transverse to the planes of stratification, this uniformity
+ceases almost immediately. In that case we can scarcely ever
+penetrate a stratified mass for a few hundred yards without
+beholding a succession of extremely dissimilar rocks, some of
+fine, others of coarse grain, some of mechanical, others of
+chemical origin; some calcareous, others argillaceous, and others
+siliceous. These phenomena lead to the conclusion that rivers and
+currents have dispersed the same sediment over wide areas at one
+period, but at successive periods have been charged, in the same
+region, with very different kinds of matter. The first observers
+were so astonished at the vast spaces over which they were able
+to follow the same homogeneous rocks in a horizontal direction,
+that they came hastily to the opinion, that the whole
+<a name="page125"></a>globe had been environed by a succession of distinct aqueous
+formations, disposed round the nucleus of the planet, like the
+concentric coats of an onion. But, although, in fact, some
+formations may be continuous over districts as large as half of
+Europe, or even more, yet most of them either terminate wholly
+within narrower limits, or soon change their lithological
+character. Sometimes they thin out gradually, as if the supply of
+sediment had failed in that direction, or they come abruptly to
+an end, as if we had arrived at the borders of the ancient sea or
+lake which served as their receptacle. It no less frequently
+happens that they vary in mineral aspect and composition, as we
+pursue them horizontally. For example, we trace a limestone for a
+hundred miles, until it becomes more arenaceous, and finally
+passes into sand, or sandstone. We may then follow this
+sandstone, already proved by its continuity to be of the same
+age, throughout another district a hundred miles or more in
+length.</p>
+
+<p><b>Organic Remains.</b>&mdash;This character must be used as a
+criterion of the age of a formation, or of the contemporaneous
+origin of two deposits in distant places, under very much the
+same restrictions as the test of mineral composition.</p>
+
+<p>First, the same fossils may be traced over wide regions, if we
+examine strata in the direction of their planes, although by no
+means for indefinite distances. Secondly, while the same fossils
+prevail in a particular set of strata for hundreds of miles in a
+horizontal direction, we seldom meet with the same remains for
+many fathoms, and very rarely for several hundred yards, in a
+vertical line, or a line transverse to the strata. This fact has
+now been verified in almost all parts of the globe, and has led
+to a conviction that at successive periods of the past, the same
+area of land and water has been inhabited by species of animals
+and plants even more distinct than those which now people the
+antipodes, or which now co-exist in the arctic, temperate, and
+tropical zones. It appears that from the remotest periods there
+has been ever a coming in of new organic forms, and an extinction
+of those which pre-existed on the earth; some species having
+endured for a longer, others for a shorter, time; while none have
+ever reappeared after once dying out. The law which has governed
+the succession of species, whether we adopt or reject the theory
+of transmutation, seems to be expressed in the verse of the
+poet:&mdash;</p>
+
+<p class="poem">
+                Natura il fece, e poi ruppe la stampa.
+    A<small>RIOSTO</small>.<br/>
+                Nature made him, and then broke the die.
+</p>
+
+<p class="noindent">
+<a name="page126"></a>
+And this circumstance it is, which confers on fossils their
+highest value as chronological tests, giving to each of them, in
+the eyes of the geologist, that authority which belongs to
+contemporary medals in history.</p>
+
+<p>The same cannot be said of each peculiar variety of rock; for
+some of these, as red marl and red sandstone, for example, may
+occur at once at the top, bottom, and middle of the entire
+sedimentary series; exhibiting in each position so perfect an
+identity of mineral aspect as to be undistinguishable. Such exact
+repetitions, however, of the same mixtures of sediment have not
+often been produced, at distant periods, in precisely the same
+parts of the globe; and even where this has happened, we are
+seldom in any danger of confounding together the monuments of
+remote eras, when we have studied their imbedded fossils and
+their relative position.</p>
+
+<p><b>Zoological Provinces.</b>&mdash;It was remarked that the
+same species of organic remains cannot be traced horizontally,
+or in the direction of the planes of stratifications for
+indefinite distances. This might have been expected from analogy;
+for when we inquire into the present distribution of living
+beings, we find that the habitable surface of the sea and land
+may be divided into a considerable number of distinct provinces,
+each peopled by a peculiar assemblage of animals and plants. In
+the &ldquo;Principles of Geology,&rdquo; I have endeavoured to
+point out the extent and probable origin of these separate
+divisions; and it was shown that climate is only one of many
+causes on which they depend, and that difference of longitude as
+well as latitude is generally accompanied by a dissimilarity of
+indigenous species.</p>
+
+<p>As different seas, therefore, and lakes are inhabited, at the
+same period, by different aquatic animals and plants, and as the
+lands adjoining these may be peopled by distinct terrestrial
+species, it follows that distinct fossils will be imbedded in
+contemporaneous deposits. If it were otherwise&mdash;if the same
+species abounded in every climate, or in every part of the globe
+where, so far as we can discover, a corresponding temperature and
+other conditions favourable to their existence are
+found&mdash;the identification of mineral masses of the same age,
+by means of their included organic contents, would be a matter of
+still greater certainty.</p>
+
+<p>Nevertheless, the extent of some single zoological provinces,
+especially those of marine animals, is very great; and our
+geological researches have proved that the same laws prevailed at
+remote periods; for the fossils are often identical throughout
+wide spaces, and in detached deposits, consisting of rocks
+varying entirely in their mineral nature.</p>
+
+<p>
+<a name="page127"></a>The doctrine here laid down will be more readily understood,
+if we reflect on what is now going on in the Mediterranean. That
+entire sea may be considered as one zoological province; for
+although certain species of testacea and zoophytes may be very
+local, and each region has probably some species peculiar to it,
+still a considerable number are common to the whole
+Mediterranean. If, therefore, at some future period, the bed of
+this inland sea should be converted into land, the geologist
+might be enabled, by reference to organic remains, to prove the
+contemporaneous origin of various mineral masses scattered over a
+space equal in area to half of Europe.</p>
+
+<p>Deposits, for example, are well known to be now in progress in
+this sea in the deltas of the Po, Rhone, Nile, and other rivers,
+which differ as greatly from each other in the nature of their
+sediment as does the composition of the mountains which their
+drain. There are also other quarters of the Mediterranean, as off
+the coast of Campania, or near the base of Etna, in Sicily, or in
+the Grecian Archipelago, where another class of rocks is now
+forming; where showers of volcanic ashes occasionally fall into
+the sea, and streams of lava overflow its bottom; and where, in
+the intervals between volcanic eruptions, beds of sand and clay
+are frequently derived from the waste of cliffs, or the turbid
+waters of rivers. Limestones, moreover, such as the Italian
+travertins, are here and there precipitated from the waters of
+mineral springs, some of which rise up from the bottom of the
+sea. In all these detached formations, so diversified in their
+lithological characters, the remains of the same shells, corals,
+crustacea, and fish are becoming inclosed; or, at least, a
+sufficient number must be common to the different localities to
+enable the zoologist to refer them all to one contemporaneous
+assemblage of species.</p>
+
+<p>There are, however, certain combinations of geographical
+circumstances which cause distinct provinces of animals and
+plants to be separated from each other by very narrow limits; and
+hence it must happen that strata will be sometimes formed in
+contiguous regions, differing widely both in mineral contents and
+organic remains. Thus, for example, the testacea, zoophytes, and
+fish of the Red Sea are, as a group, extremely distinct from
+those inhabiting the adjoining parts of the Mediterranean,
+although the two seas are separated only by the narrow isthmus of
+Suez. Calcareous formations have accumulated on a great scale in
+the Red Sea in modern times, and fossil shells of existing
+species are well preserved therein; and we know that at the mouth
+of the Nile large
+<a name="page128"></a>deposits of mud are amassed, including the remains of
+Mediterranean species. It follows, therefore, that if at some
+future period the bed of the Red Sea should be laid dry, the
+geologist might experience great difficulties in endeavouring to
+ascertain the relative age of these formations, which, although
+dissimilar both in organic and mineral characters, were of
+synchronous origin.</p>
+
+<p>But, on the other hand, we must not forget that the
+north-western shores of the Arabian Gulf, the plains of Egypt,
+and the Isthmus of Suez, are all parts of one province of
+<i>terrestrial</i> species. Small streams, therefore, occasional
+land- floods, and those winds which drift clouds of sand along
+the deserts, might carry down into the Red Sea the same shells of
+fluviatile and land testacea which the Nile is sweeping into its
+delta, together with some remains of terrestrial plants and the
+bones of quadrupeds, whereby the groups of strata before alluded
+to might, notwithstanding the discrepancy of their mineral
+composition and <i>marine</i> organic fossils, be shown to have
+belonged to the same epoch.</p>
+
+<p>Yet, while rivers may thus carry down the same fluviatile and
+terrestrial spoils into two or more seas inhabited by different
+marine species, it will much more frequently happen that the
+coexistence of terrestrial species of distinct zoological and
+botanical provinces will be proved by the identity of the marine
+beings which inhabited the intervening space. Thus, for example,
+the land quadrupeds and shells of the valley of the Mississippi,
+of central America, and of the West India islands differ very
+considerably, yet their remains are all washed down by rivers
+flowing from these three zoological provinces into the Gulf of
+Mexico.</p>
+
+<p>In some parts of the globe, at the present period, the line of
+demarkation between distinct provinces of animals and plants is
+not very strongly marked, especially where the change is
+determined by temperature, as it is in seas extending from the
+temperate to the tropical zone, or from the temperate to the
+arctic regions. Here a gradual passage takes place from one set
+of species to another. In like manner the geologist, in studying
+particular formations of remote periods, has sometimes been able
+to trace the gradation from one ancient province to another, by
+observing carefully the fossils of all the intermediate places.
+His success in thus acquiring a knowledge of the zoological or
+botanical geography of very distant eras has been mainly owing to
+this circumstance, that the mineral character has no tendency to
+be affected by climate. A large river may convey yellow or red
+mud into some part of the ocean, where
+<a name="page129"></a>it may be dispersed by a current over an area several hundred
+leagues in length, so as to pass from the tropics into the
+temperate zone. If the bottom of the sea be afterwards upraised,
+the organic remains imbedded in such yellow or red strata may
+indicate the different animals or plants which once inhabited at
+the same time the temperate and equatorial regions.</p>
+
+<p>It may be true, as a general rule, that groups of the same
+species of animals and plants may extend over wider areas than
+deposits of homogeneous composition; and if so,
+palæontological characters will be of more importance in
+geological classification than the test of mineral composition;
+but it is idle to discuss the relative value of these tests, as
+the aid of both is indispensable, and it fortunately happens,
+that where the one criterion fails, we can often avail ourselves
+of the other.</p>
+
+<p><b>Test by included Fragments of older Rocks.</b>&mdash;It was
+stated, that proof may sometimes be obtained of the relative date
+of two formations by fragments of an older rock being included in
+a newer one. This evidence may sometimes be of great use, where a
+geologist is at a loss to determine the relative age of two
+formations from want of clear sections exhibiting their true
+order of position, or because the strata of each group are
+vertical. In such cases we sometimes discover that the more
+modern rock has been in part derived from the degradation of the
+older. Thus, for example, we may find chalk in one part of a
+country, and in another strata of clay, sand, and pebbles. If
+some of these pebbles consist of that peculiar flint, of which
+layers more or less continuous are characteristic of the chalk,
+and which include fossil shells, sponges, and foraminifera of
+cretaceous species, we may confidently infer that the chalk was
+the oldest of the two formations.</p>
+
+<p><b>Chronological Groups.</b>&mdash;The number of groups into
+which the fossiliferous strata may be separated are more or less
+numerous, according to the views of classification which
+different geologists entertain; but when we have adopted a
+certain system of arrangement, we immediately find that a few
+only of the entire series of groups occur one upon the other in
+any single section or district.</p>
+
+<p>
+The thinning out of individual strata was before described (p. 42).But let the
+diagram (Fig. 84) represent seven fossiliferous groups, instead of as many
+strata. It will then be seen that in the middle all the superimposed formations
+are present; but in consequence of some of them thinning out, No. 2 and No. 5
+are absent at one extremity of the section, and No. 4 at the other.
+<a name="page130"></a>
+</p>
+
+<p><img src="images/fig84.jpg" width="356" height="89" alt=
+"Fig. 84: Seven fossiliferous groups." /></p>
+
+<p>In another diagram (Fig. 85), a real section of the geological
+formations in the neighbourhood of Bristol and the Mendip Hills
+is presented to the reader, as laid down on a true scale by
+Professor Ramsay, where the newer groups 1, 2, 3, 4 rest
+unconformably on the formations 5, 6, 7 and 8. At the southern
+end of the line of section we meet with the beds No. 3 (the New
+Red Sandstone) resting immediately on Nos. 7 and 8, while farther
+north as at Dundry Hill in Somersetshire, we behold eight groups
+superimposed one upon the other, comprising all the strata from
+the inferior Oolite, No. 1, to the coal and carboniferous
+limestone. The limited horizontal extension of the groups 1 and 2
+is owing to denudation, as these formations end abruptly, and
+have left outlying patches to attest the fact of their having
+originally covered a much wider area.</p>
+
+<p><img src="images/fig85.jpg" width="411" height="242" alt=
+"Section South of Bristol." /></p>
+
+<p>In order, therefore, to establish a chronological succession
+of fossiliferous groups, a geologist must begin with a single
+section in which several sets of strata lie one upon the other.
+He must then trace these formations, by attention to their
+mineral character and fossils, continuously, as far as possible,
+from the starting-point. As often as he meets with new groups, he
+must ascertain by superposition their age relatively to those
+first examined, and thus learn how to intercalate them in a
+tabular arrangement of the whole.</p>
+
+<p>
+By this means the German, French, and English geologists
+<a name="page131"></a>have determined the succession of strata throughout a great
+part of Europe, and have adopted pretty generally the following
+groups, almost all of which have their representatives in the
+British Islands.
+</p>
+
+<p><img src="images/table.jpg" width="411" height="603" alt=
+"Abridged General Table of Fossiliferous Strata." /></p>
+
+<p class="center">
+<a name="page132"></a>TABULAR VIEW OF THE FOSSILIFEROUS STRATA,<br/>
+<small>SHOWING THE ORDER OF SUPERPOSITION OR CHRONOLOGICAL
+SUCCESSION OF THE PRINCIPAL GROUPS DESCRIBED IN THIS
+WORK.</small></p>
+
+<hr />
+
+<p class="center">
+POST-TERTIARY<br/>
+<small>EXAMPLES</small>
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">POST-<br/>
+TERTIARY</td>
+<td valign="middle" align="center">1.<br/>
+RECENT<br/>
+Shells and mammals, all of living species.</td>
+<td ><b>British</b><br/>
+Clyde marine strata, with canoes (<a href="#page146">p.
+146</a>).<br/>
+<b>Foreign</b><br/>
+Danish kitchen middens (<a href="#page146">p.
+146</a>).<br/>
+Lacustrine mud, with remains of Swiss lake-dwellings (<a href=
+"#page148">p. 148</a>).<br/>
+Marine strata inclosing Temple of Serapis, at Puzzuoli (<a href=
+"#page146">p. 146</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">2.<br/>
+POST-<br/>
+PLIOCENE.<br/>
+Shells, recent mammalia in part extinct.</td>
+<td ><b>British</b><br/>
+Loam of Brixham cave, with flint implements and bones of extinct
+and living quadrupeds (<a href="#page157">p.
+157</a>)<br/>
+Drift near Salisbury, with bones of mammoth, Spermophilus, and
+stone implements (<a href="#page161">p. 161</a>).<br/>
+Glacial drift of Scotland, with marine shells and remains of
+mammoth (<a href="#page176">p. 176</a>.<br/>
+Erratics of Pagham and Selsey Bill (<a href=
+"#page182">p. 182</a>).<br/>
+Glacial drift of Wales, with marine fossil shells, about 1400
+feet high, on Moel Tryfaen (<a href="#page181">p.
+181</a>).<br/>
+<b>Foreign</b><br/>
+Dordogne caves of the reindeer period (<a href=
+"#page150">p. 150</a>).<br/>
+Older valley-gravels of Amiens, with flint implements and bones
+of extinct mammalia (<a href="#page152">p.
+152</a>).<br/>
+Loess of Rhine (<a href="#page154">p. 154</a>).<br/>
+Ancient Nile-mud forming river-terraces (<a href=
+"#page154">p. 154</a>).<br/>
+Loam and breccia of Liege caverns, with human remains (<a href=
+"#page156">pp. 156, 157</a>).<br/>
+Australian cave breccias, with bones of extinct marsupials (<a
+href="#page158">p. 158</a>).<br/>
+Glacial drift of Northern Europe (<a href="#page166">p.
+166</a>, <a href="#page174">p. 174</a>).</td>
+</tr>
+</table>
+
+<p class="center">
+TERTIARY OR CAINOZOIC
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">PLIOCENE</td>
+<td valign="middle" align="center">3.<br/>
+NEWER<br/>
+PLIOCENE.<br/>
+The shells almost all of living species.</td>
+<td ><b>British</b><br/>
+Bridlington beds, marine Arctic fauna (<a href=
+"#page189">p. 189</a>).<br/>
+Glacial boulder formation of Norfolk cliffs (<a href=
+"#page190">p. 190</a>).<br/>
+Forest-bed of Norfolk cliffs, with bones of <i>Elephas
+meridionalis,</i> etc. (<a href="#page191">p.
+191</a>).<br/>
+Chillesford and Aldeby beds, with marine shells, chiefly Arctic
+(<a href="#page192">p. 192</a>).<br/>
+Norwich crag (<a href="#page193">p. 193</a>).<br/>
+<b>Foreign</b><br/>
+Eastern base of Mount Etna, with marine shells (<a href=
+"#page204">p. 204</a>).<br/>
+Sicilian calcareous and tufaceous strata (<a href=
+"#page205">p. 205</a>, 206).<br/>
+Lacustrine strata of Upper Val d&rsquo;Arno (<a href=
+"#page207">p. 207</a>).<br/>
+Madeira leaf-bed and land-shells (<a href="#page532">p.
+532</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">4.<br/>
+OLDER<br/>
+PLIOCENE.<br/>
+Extinct species of<br/>
+shells forming a<br/>
+large minority.</td>
+<td ><b>British</b><br/>
+Red crag of Suffolk, marine shells, some of northern forms (<a
+href="#page194">p. 194, 195</a>).<br/>
+White or coralline crag of Suffolk (<a href=
+"#page197">p. 197</a>).<br/>
+<b>Foreign</b><br/>
+Antwerp crag (<a href="#page204">p. 204</a>).<br/>
+Subapennine marls and sands (<a href="#page208">p.
+208</a>).</td>
+</tr>
+</table>
+
+<p class="center">
+<a name="page133"></a><small>EXAMPLES</small></p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">MIOCENE</td>
+<td valign="middle" align="center">5.<br/>
+UPPER<br/>
+MIOCENE.<br/>
+Majority of the<br/>
+shells extinct.</td>
+<td ><b>British</b><br/>
+Wanting.<br/>
+<b>Foreign</b><br/>
+Faluns of Touraine (<a href="#page211">p. 211</a>).<br/>
+Faluns, proper, of Bordeaux (<a href="#page214">p.
+214</a>).<br/>
+Fresh-water strata of Gers (<a href="#page215">p.
+215</a>).<br/>
+Swiss Oeningen beds, rich in plants and insects (<a href=
+"#page215">pp. 215-23</a>).<br/>
+Marine Molasse, Switzerland (<a href="#page223">p.
+223</a>).<br/>
+Bolderberg beds of Belgium (<a href="#page224">p.
+224</a>).<br/>
+Vienna basin (<a href="#page224">p. 224</a>).<br/>
+Beds of the Superga, near Turin (<a href="#page226">p.
+226</a>).<br/>
+Deposit at Pikermé, near Athens (<a href=
+"#page226">p. 226</a>).<br/>
+Strata of the Siwâlik hills, India (<a href=
+"#page226">p. 226</a>).<br/>
+Marine strata of the Atlantic border in the United States (<a
+href="#page227">p. 227</a>).<br/>
+Volcanic tuff and limestone of Madeira, the Canaries, and the
+Azores (<a href="#page536">).</a></td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">6.<br/>
+LOWER<br/>
+MIOCENE.<br/>
+Nearly all the<br/>
+shells extinct.</td>
+<td ><b>British</b><br/>
+Hempstead beds, marine and fresh-water strata (<a href=
+"#page244">p. 244</a>).<br/>
+Lignites and clays of Bovey Tracey (<a href=
+"#page245">p. 245</a>).<br/>
+Isle of Mull leaf-bed, volcanic tuff (<a href=
+"#page247">p. 247</a>).<br/>
+<b>Foreign</b><br/>
+Calcaire de la Beauce, etc. (<a href="#page230">p.
+230</a>).<br/>
+Grès de Fontainebleau (<a href="#page230">p.
+230</a>).<br/>
+Lacustrine strata of the Limagne d&rsquo;Auvergne, and the Cantal
+(<a href="#page233">p. 233</a>).<br/>
+Mayence basin (<a href="#page242">p. 242</a>).<br/>
+Radaboj beds of Croatia (<a href="#page242">p.
+242</a>).<br/>
+Brown coal of Germany (<a href="#page244">p.
+244</a>).<br/>
+Lower Molasse of Switzerland, fresh-water and brackish (<a href=
+"#page235">p. 235-9</a>).<br/>
+Rupelmonde, Kleynspawen, and Tongrian beds of Belgium (<a href=
+"#page241">p. 241</a>, 242).<br/>
+Nebraska beds, United States (<a href="#page248">p.
+248</a>).<br/>
+Lower Miocene beds of Italy (<a href="#page244">p.
+244</a>).<br/>
+Miocene flora of North Greenland (<a href="#page239">p.
+239</a>).</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="3" align="center">EOCENE</td>
+<td align="center">7.<br/>
+UPPER<br/>
+EOCENE.</td>
+<td ><b>British</b><br/>
+Bembridge fluvio-marine strata (<a href="#page252">p.
+252</a>).<br/>
+Osborne or St. Helen&rsquo;s series (<a href=
+"#page255">p. 255</a>).<br/>
+Headon series, with marine and fresh-water shells (<a href=
+"#page255">p. 255</a>).<br/>
+Barton sands and clays (<a href="#page258">p.
+258</a>).<br/>
+<b>Foreign</b><br/>
+Gypsum of Montmartre, fresh-water with <i>Palæotherium</i>
+(<a href="#page270">p. 270</a>).<br/>
+Calcaire silicieux, or Travertin inférieur (<a href=
+"#page273">p. 273</a>),<br/>
+Grès de Beauchamp, or Sables moyens (<a href=
+"#page273">p. 273</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">8.<br/>
+MIDDLE<br/>
+EOCENE.</td>
+<td ><b>British</b><br/>
+Bracklesham beds and Bagshot sands (<a href=
+"#page259">p. 259</a>).<br/>
+White clays of Alum Bay and Bournemouth (<a href=
+"#page262">p. 262</a>).<br/>
+<b>Foreign</b><br/>
+Calcaire grossier, miliolitic limestone (<a href=
+"#page274">p. 274</a>).<br/>
+Soissonnais sands, or Lits coquilliers, with <i>Nummulites
+planulata</i> (<a href="#page275">p. 275</a>).<br/>
+Claiborne beds of the United States, with <i>Orbitoides</i> and
+<i>Zeuglodon</i> (<a href="#page279">p. 279</a>).<br/>
+Nummulitic formation of Europe, Asia, etc. (<a href=
+"#page277">p. 277</a>).</td>
+</tr>
+
+<tr>
+<td valign="middle" align="center">9.<br/>
+LOWER<br/>
+EOCENE.</td>
+<td ><b>British</b><br/>
+London clay proper (<a href="#page263">p. 263</a>).<br/>
+Woolwich and Reading series, fluvio-marine (<a href=
+"#page267">p. 267</a>).<br/>
+Thanet sands (<a href="#page269">p. 269</a>).<br/>
+<b>Foreign</b><br/>
+Argile de Londres, near Dunkirk (<a href="#page252">p.
+252</a>).<br/>
+Argile plastique (<a href="#page276">p. 276</a>).<br/>
+Sables de Bracheux (<a href="#page276">p.
+276</a>).</td>
+</tr>
+</table>
+
+<p class="center">
+SECONDARY OR MESOZOIC.
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">CRETACEOUS</td>
+<td valign="middle" align="center">10.<br/>
+UPPER<br/>
+CRETACEOUS.</td>
+<td ><b>British</b><br/>
+Upper white chalk, with flints (<a href="#page290">p.
+290</a>).<br/>
+Lower white chalk, without flints (<a href=
+"#page298">p. 298</a>).<br/>
+Chalk marl (<a href="#page298">p. 298</a>).<br/>
+Chloritic series (or Upper Greensand), fire-stone of Surrey (<a
+href="#page298">p. 298</a>).<br/>
+Gault (<a href="#page300">p. 300</a>).<br/>
+Blackdown beds (<a href="#page301">p. 301</a>).</td>
+</tr>
+</table>
+
+<p class="center">
+<a name="page134"></a><small>EXAMPLES</small>
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">CRETACEOUS</td>
+<td valign="middle" align="center">10.<br/>
+UPPER<br/>
+CRETACEOUS.</td>
+<td ><b>Foreign</b><br/>
+Maetricht beds and Faxoe chalk (<a href="#page233">p.
+233</a>).<br/>
+Pisolitic limestone of France (<a href="#page285">p.
+285</a>).<br/>
+White chalk of France, Sweden, and Russia (<a href=
+"#page286">p. 286, 287</a>).<br/>
+Planer-kalk of Saxony (<a href="#page293">p.
+293</a>).<br/>
+Sands and clays of Aix-la-Chapelle (<a href=
+"#page302">p. 302</a>).<br/>
+Hippurite limestone of South of France (<a href=
+"#page305">p. 305</a>).<br/>
+New Jersey, U.S., sands and marls (<a href=
+"#page307">p. 307</a>).</td>
+</tr>
+
+<tr>
+<td valign="middle" align="center">11.<br/>
+LOWER<br/>
+CRETACEOUS or<br/>
+NEOCOMIAN.</td>
+<td ><b>British</b><br/>
+Sands of Folkestone, Sandgate, and Hythe (<a href=
+"#page308">p. 308</a>).<br/>
+Atherfield clay, with <i>Perna mulleti</i> (<a href=
+"#page309">p. 309</a>).<br/>
+Punfield marine beds, with <i>Vicarya lujana</i> (<a href=
+"#page318">p. 318</a>).<br/>
+Speeton clay of Flamborough Head and Tealby (<a href=
+"#page311">p. 311</a>).<br/>
+Weald clay of Surrey, Kent, and Sussex, fresh-water, with
+<i>Cypris</i> (<a href="#page313">p. 313-5</a>).<br/>
+Hastings sands (<a href="#page316">p. 316-8</a>).<br/>
+<b>Foreign</b><br/>
+Neocomian of Neufchatel, and Hils conglomerate of North Germany
+(<a href="#page312">p. 312</a>).<br/>
+Wealden beds of Hanover (<a href="#page319">p.
+319</a>).</td>
+</tr>
+
+<tr>
+<td valign="middle" align="center" rowspan="3">OOLITE</td>
+<td align="center" valign="middle">12.<br/>
+UPPER OOLITE.</td>
+<td ><b>British</b><br/>
+Upper Purbeck beds, fresh-water (<a href="#page323">p.
+323</a>).<br/>
+Middle Purbeck, with numerous marsupial quadrupeds, etc. (<a
+href="#page324">p. 324</a>).<br/>
+Lower Purbeck, fresh-water, with intercalated dirt-bed (<a href=
+"#page330">p. 330</a>).<br/>
+Portland stone and sand. (<a href="#page334">p.
+334</a>).<br/>
+Kimmeridge clay (<a href="#page335">p. 335</a>).<br/>
+<b>Foreign</b><br/>
+Marnes à gryphées virgules of Argonne (<a href=
+"#page336">p. 336</a>).<br/>
+Lithographic-stone of Solenhofen, with <i>Archæopteryx</i>
+(<a href="#page337">p. 337</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">13.<br/>
+MIDDLE OOLITE.</td>
+<td ><b>British</b><br/>
+Coral rag of Berkshire, Wilts, and Yorkshire (<a href=
+"#page339">p. 339</a>).<br/>
+Oxford clay, with belemnites and Ammonite (<a href=
+"#page340">p. 340</a>).<br/>
+Kelloway rock of Wilts and Yorkshire (<a href=
+"#page341">p. 341</a>).<br/>
+<b>Foreign</b><br/>
+Nerinæan limestone of the Jura (<a href=
+"#page339">p. 339</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">14.<br/>
+LOWER OOLITE.</td>
+<td ><b>British</b><br/>
+Cornbrash and forest marble (<a href="#page341">p.
+341</a>).<br/>
+Great or Bath oolite of Bradford (<a href="#page342">p.
+342</a>).<br/>
+Stonesfield slate, with marsupials and <i>Araucaria</i> (<a href=
+"#page345">p. 345</a>).<br/>
+Fuller&rsquo;s earth of Bath (<a href="#page348">p.
+348</a>).<br/>
+Inferior oolite (<a href="#page349">p. 349</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">LIAS</td>
+<td align="center" valign="middle">15.<br/>
+LIAS.</td>
+<td >Upper Lias, argillaceous, with <i>Ammonites
+striatulus</i> (<a href="#page353">p. 353</a>).<br/>
+Shale and limestone, with <i>Ammonites bifrons</i> (<a href=
+"#page353">p. 353</a>).<br/>
+Middle Lias or Marlstone series, with zones containing
+characteristic Ammonites (<a href="#page353">p.
+353</a>).<br/>
+Lower Lias, also with zones characterised by peculiar Ammonites
+(<a href="#page356">p. 356</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle" rowspan="3">TRIAS</td>
+<td align="center" valign="middle">16.<br/>
+UPPER TRIAS.</td>
+<td ><b>British</b><br/>
+Rhætic, Penarth or <i>Avicula contorta</i> beds (beds of
+passage) (<a href="#page366">p. 366</a>).<br/>
+Keuper or Upper New Red sandstone, etc. (<a href=
+"#page369">p. 369</a>).<br/>
+Red shales of Cheshire and Lancashire, with rock-salt (<a href=
+"#page371">p. 371</a>).<br/>
+Dolomite conglomerate of Bristol (<a href="#page373">p.
+373</a>).<br/>
+<b>Foreign</b><br/>
+Keuper beds of Germany (<a href="#page375">p.
+375</a>).<br/>
+St. Cassian or Hallstadt beds, with rich marine fauna (<a href=
+"#page376">p. 376</a>).<br/>
+Coal-field of Richmond, Virginia (<a href="#page382">p.
+382</a>).<br/>
+Chatham coal-field, North Carolina (<a href=
+"#page383">p. 383</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">17.<br/>
+MIDDLE TRIAS.</td>
+<td ><b>British</b><br/>
+Wanting.<br/>
+<b>Foreign</b><br/>
+Muschelkalk of Germany (<a href="#page378">p.
+378</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">18.<br/>
+LOWER TRIAS.</td>
+<td ><b>British</b><br/>
+Bunter or Lower New Red sandstone of Lancashire and Cheshire (<a
+href="#page372">p. 372</a>).<br/>
+<b>Foreign</b><br/>
+Bunter-sandstein of Germany (<a href="#page380">p.
+380</a>).<br/>
+Red sandstone of Connecticut Valley, with footprints of birds and
+reptiles (<a href="#page381">p. 381</a>).</td>
+</tr>
+</table>
+
+<p class="center">
+<a name="page135"></a>PRIMARY OR PALÆOZOIC<br/>
+<small>EXAMPLES</small></p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle">PERMIAN</td>
+<td align="center" valign="middle">19.<br/>
+PERMIAN.</td>
+<td ><b>British</b><br/>
+Upper Permian of St. Bees&rsquo; Head, Cumberland (<a href=
+"#page386">p. 386</a>).<br/>
+Middle Permian, magnesian limestone, and marl-slate of Durham and
+Yorkshire, with <i>Protosaurus</i> (<a href=
+"#page387">p. 387</a>).<br/>
+Lower Permian sandstones and breccias of Penrith and
+Dumfriesshire, intercalated (<a href="#page390">p.
+390</a>).<br/>
+<b>Foreign</b><br/>
+Dark-coloured shales of Thuringia (<a href=
+"#page392">p. 392</a>).<br/>
+Zechstein or Dolomitic limestone (<a href="#page392">p.
+392</a>).<br/>
+Mergel-schiefer or Kupfer-schiefer (<a href=
+"#page392">p. 392</a>).<br/>
+Rothliegendes of Thuringia, with <i>Psaronius</i> (<a href=
+"#page392">p. 392</a>).<br/>
+Magnesian limestones, etc., of Russia (<a href=
+"#page393">p. 393</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle" rowspan="2">CARBONIFEROUS</td>
+<td align="center" valign="middle">20.<br/>
+UPPER CARBONIFEROUS.</td>
+<td ><b>British</b><br/>
+Coal-measures of South Wales, with underclays inclosing
+<i>Stigmaria</i> (<a href="#page397">p. 397</a>).<br/>
+Coal-measures of north and central England (<a href=
+"#page395">p. 395</a>).<br/>
+Millstone grit (<a href="#page395">p. 395</a>).<br/>
+Yoredale series of Yorkshire (<a href="#page395">p.
+395</a>).<br/>
+Coal-field of Kilkenny with <i>Labyrinthodont</i> (<a href=
+"#page407">p. 407</a>).<br/>
+<b>Foreign</b><br/>
+Coal-field of Saarbruck, with <i>Archegosaurus</i> (<a href=
+"#page406">p. 406</a>).<br/>
+Carboniferous strata of South Joggins, Nova Scotia (<a href=
+"#page409">p. 409</a>).<br/>
+Pennsylvania coal-field (<a href="#page403">p.
+403</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">21.<br/>
+LOWER CARBONIFEROUS.</td>
+<td ><b>British</b><br/>
+Mountain limestone of Wales and South of England (<a href=
+"#page430">p. 430</a>).<br/>
+Same in Ireland (<a href="#page437">p. 437</a>437).<br/>
+Carboniferous limestone of Scotland alternating with coal-bearing
+sandstones (<a href="#page396">p. 396</a>).<br/>
+Erect trees in volcanic ash in the Island of Arran (<a href=
+"#page546">p. 546</a>).<br/>
+<b>Foreign</b><br/>
+Mountain limestone of Belgium (<a href="#page436">p.
+436</a>).</td>
+</tr>
+
+<tr>
+<td valign="middle" align="center" rowspan="3">DEVONIAN or<br/>
+O<small>LD</small> R<small>ED</small>
+S<small>ANDSTONE</small></td>
+<td align="center" valign="middle">22.<br/>
+UPPER<br/>
+DEVONIAN.</td>
+<td ><b>British</b><br/>
+Yellow sandstone of Dura Den, with <i>Holoptychius</i>, etc. (<a
+href="#page440">p. 440</a>); and of Ireland with
+<i>Anodon Jukesii</i> (<a href="#page441">p.
+441</a>).<br/>
+Sandstones of Forfarshire and Perthshire, with
+<i>Holoptychius</i>, etc. (<a href="#page442">p.
+442</a>).<br/>
+Pilton group of North Devon (<a href="#page449">p.
+449</a>).<br/>
+Petherwyn group of Cornwall, with <i>Clymenia</i> and
+<i>Cypridina</i> (<a href="#page451">p. 451</a>).<br/>
+<b>Foreign</b><br/>
+Clymenien-kalk and Cypridinen-schiefer of Germany (<a href=
+"#page450">p. 450</a>)</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">23.<br/>
+MIDDLE<br/>
+DEVONIAN.</td>
+<td ><b>British</b><br/>
+Bituminous schists of Gamrie, Caithness, etc., with numerous fish
+(<a href="#page443">p. 443</a>).<br/>
+Ilfracombe beds with peculiar trilobites and corals (<a href=
+"#page450">p. 450</a>).<br/>
+Limestones of Torquay, with broad-winged Spirifers (<a href=
+"#page451">p. 451</a>).<br/>
+<b>Foreign</b><br/>
+Eifel limestone, with underlying schists containing
+<i>Calceola</i> (<a href="#page453">p. 453</a>).<br/>
+Devonian strata of Russia (<a href="#page454">p.
+454</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">24.<br/>
+LOWER<br/>
+DEVONIAN.</td>
+<td ><b>British</b><br/>
+Arbroath paving-stones, with <i>Cephalaspis</i> and
+<i>Pterygotus</i> (<a href="#page446">p. 446</a>).<br/>
+Lower sandstones of Forfarshire, with <i>Pterygotus</i> (<a href=
+"#page446">p. 446</a>).<br/>
+Sandstones and slates of the Foreland and Linton (<a href=
+"#page454">p. 454</a>).<br/>
+<b>Foreign</b><br/>
+Oriskany sandstone of Western Canada and New York (<a href=
+"#page456">p. 456</a>).<br/>
+Sandstones of Gaspe, with <i>Cephalaspis</i> (<a href=
+"#page455">p. 455</a> ).</td>
+</tr>
+</table>
+
+<p class="center">
+<a name="page136"></a><small>EXAMPLES</small>
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr>
+<td align="center" valign="middle" rowspan="2">SILURIAN</td>
+<td align="center" valign="middle">25.<br/>
+UPPER SILURIAN</td>
+<td ><b>British</b><br/>
+Upper Ludlow formation, Downton sandstone, with bone-bed (<a
+href="#page459">p. 459</a>).<br/>
+Lower Ludlow formation, with oldest known fish remains (<a href=
+"#page461">p. 461</a>).<br/>
+Wenlock limestone and shale (<a href="#page465">p.
+465</a>).<br/>
+Woolhope limestone and grit (<a href="#page467">p.
+467</a>).<br/>
+Tarannon shales (<a href="#page468">p. 468</a>).<br/>
+<i>Beds of passage between Upper and Lower Silurian:</i><br/>
+Upper Llandovery, or May-hill sandstone, with <i>Pentamerus
+oblongus</i>, etc. (<a href="#page468">p. 468</a>).<br/>
+Lower Llandovery slates (<a href="#page469">p.
+469</a>).<br/>
+<b>Foreign</b><br/>
+Niagara limestone, with <i>Calymene, Homalonotus</i>, etc. (<a
+href="#page479">p. 479</a>).<br/>
+Clinton group of America, with <i>Pentamerus oblongus</i>, etc.
+(<a href="#page479">p. 479</a>).<br/>
+Silurian strata of Russia, with <i>Pentamerus</i> (<a href=
+"#page477">p. 477</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">26.<br/>
+LOWER SILURIAN.</td>
+<td ><b>British</b><br/>
+Bala and Caradoc beds (<a href="#page470">p.
+470</a>).<br/>
+Llandeilo flags (<a href="#page473">p. 473</a>).<br/>
+Arenig or Stiper-stones group (Lower Llandeilo of Murchison) (<a
+href="#page475">p. 475</a>).<br/>
+<b>Foreign</b><br/>
+Ungulite or Obolus grit of Russia (<a href=
+"#page477">p. 477</a>).<br/>
+Trenton limestone, and other Lower Silurian groups of North
+America (<a href="#page479">p. 479</a>).<br/>
+Lower Silurian of Sweden (<a href="#page477">p.
+477</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle" rowspan="2">CAMBRIAN</td>
+<td align="center" valign="middle">27.<br/>
+UPPER CAMBRIAN.</td>
+<td ><b>British</b><br/>
+Tremadoc slates (<a href="#page483">p. 483</a>).<br/>
+Lingula flags, with <i>Lingula Davisii</i> (<a href=
+"#page484">p. 484</a>).<br/>
+<b>Foreign</b><br/>
+&ldquo;Primordial&rdquo; zone of Bohemia in part, with trilobites of the
+genera <i>Paradoxides</i>, etc. (<a href="#page487">p.
+487</a>).<br/>
+Alum schists of Sweden and Norway (<a href=
+"#page489">p. 489</a>).<br/>
+Potsdam sandstone, with <i>Dikelocephalus</i> and <i>Obolella</i>
+(<a href="#page489">p. 489</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">28.<br/>
+LOWER CAMBRIAN.</td>
+<td ><b>British</b><br/>
+Menevian beds of Wales, with <i>Paradoxides Davidis</i>, etc. (<a
+href="#page484">p. 484</a>).<br/>
+Longmynd group, comprising the Harlech grits and Llanberis slates
+(<a href="#page485">p. 485</a>).<br/>
+<b>Foreign</b><br/>
+Lower portion of Barrande&rsquo;s &ldquo;Primordial&rdquo; zone in Bohemia
+(<a href="#page486">p. 486</a>).<br/>
+Fucoid sandstones of Sweden (<a href="#page489">p.
+489</a>).<br/>
+Huronian series of Canada? (<a href="#page490">p.
+490</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle" rowspan="2">LAURENTIAN</td>
+<td align="center" valign="middle">29.<br/>
+UPPER LAURENTIAN.</td>
+<td ><b>British</b><br/>
+Fundamental gneiss of the Hebrides? (<a href=
+"#page493">p. 493</a>).<br/>
+Hypersthene rocks of Skye? (<a href="#page491">p.
+491</a>).<br/>
+<b>Foreign</b><br/>
+Labradorite series north of the river St. Lawrence in Canada (<a
+href="#page491">p. 491</a>).<br/>
+Adirondack mountains of New York (<a href="#page491">p.
+491</a>).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">30.<br/>
+LOWER LAURENTIAN.</td>
+<td ><b>British</b><br/>
+Wanting?<br/>
+<b>Foreign</b><br/>
+Beds of gneiss and quartzite, with interstratified limestones, in
+one of which, 1000 feet thick, occurs a foraminifer, <i>Eozoon
+Canadense</i>, the oldest known fossil (<a href=
+"#page491">p. 491</a>).</td>
+</tr>
+</table>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap09"></a>
+<a name="page137"></a>CHAPTER IX.<br/>
+CLASSIFICATION OF TERTIARY FORMATIONS.</h2>
+
+<p class="letter">Order of Succession of Sedimentary Formations.
+&mdash; Frequent Unconformability of Strata. &mdash; Imperfection
+of the Record. &mdash; Defectiveness of the Monuments greater in
+Proportion to their Antiquity. &mdash; Reasons for studying the
+newer Groups first. &mdash; Nomenclature of Formations. &mdash;
+Detached Tertiary Formations scattered over Europe. &mdash; Value
+of the Shell-bearing Mollusca in Classification. &mdash;
+Classification of Tertiary Strata. &mdash; Eocene, Miocene, and
+Pliocene Terms explained.</p>
+
+<p>By reference to the tables given at the end of the last chapter
+the reader will see that when the fossiliferous rocks are arranged
+chronologically, we have first to consider the Post-tertiary and
+then the Tertiary or Cainozoic formations, and afterwards to pass
+on to those of older date.</p>
+
+<p><img src="images/fig86.jpg" width="372" height="139" alt=
+"Fig. 86: Order of Superposition of Deposits" /></p>
+
+<p>
+<b>Order of Superposition.</b>&mdash;The diagram (Fig. 86) will show the order
+of superposition of these deposits, assuming them all to be visible in one
+continuous section. In nature, as before hinted <a href="#page107">(p.
+107)</a>, we have never an opportunity of seeing the whole of them so displayed
+in a single region; first, because sedimentary deposition is confined, during
+any one geological period, to limited areas; and secondly, because strata,
+after they have been formed, are liable to be utterly annihilated over wide
+areas by denudation. But wherever certain members of the series are present,
+they overlie one another in the order indicated in the diagram, though not
+always in the exact manner there represented, because some of them repose
+occasionally in unconformable stratification on others. This mode of
+superposition has been already explained <a href="#page94">(p. 94,</a> <a
+href="#page111">p. 111</a>), where I pointed out that the discordance which
+implies a considerable lapse of time between two <a
+name="page138"></a>formations in juxtaposition is almost invariably accompanied
+by a great dissimilarity in the species of organic remains.
+</p>
+
+<p><b>Frequent Unconformability of
+Strata.</b>&mdash;Where the widest gaps appear in the
+sequence of the fossil forms, as between the Permian and Triassic
+rocks, or between the Cretaceous and Eocene, examples of such
+unconformability are very frequent. But they are also met with in
+some part or other of the world at the junction of almost all the
+other principal formations, and sometimes the subordinate divisions
+of any one of the leading groups may be found lying unconformably
+on another subordinate member of the same&mdash;the Upper, for
+example, on the Lower Silurian, or the superior division of the Old
+Red Sandstone on a lower member of the same, and so forth.
+Instances of such irregularities in the mode of succession of the
+strata are the more intelligible the more we extend our survey of
+the fossiliferous formations, for we are continually bringing to
+light deposits of intermediate date, which have to be intercalated
+between those previously known, and which reveal to us a long
+series of events, of which antecedently to such discoveries we had
+no knowledge.</p>
+
+<p>But while unconformability invariably bears testimony to a lapse
+of unrepresented time, the conformability of two sets of strata in
+contact by no means implies that the newer formation immediately
+succeeded the older one. It simply implies that the ancient rocks
+were subjected to no movements of such a nature as to tilt, bend,
+or break them before the more modern formation was superimposed. It
+does not show that the earth&rsquo;s crust was motionless in the region
+in question, for there may have been a gradual sinking or rising,
+extending uniformly over a large surface, and yet, during such
+movement, the stratified rocks may have retained their original
+horizontality of position. There may have been a conversion of a
+wide area from sea into land and from land into sea, and during
+these changes of level some strata may have been slowly removed by
+aqueous action, and after this new strata may be superimposed,
+differing perhaps in date by thousands of years or centuries, and
+yet resting conformably on the older set. There may even be a
+blending of the materials constituting the older deposit with those
+of the newer, so as to give rise to a passage in the mineral
+character of the one rock into the other as if there had been no
+break or interruption in the depositing process.</p>
+
+<p><b>Imperfection of the
+Record.</b>&mdash;Although by the frequent discovery of new
+sets of intermediate strata the transition from one type of organic
+remains to another is becoming less and
+<a name="page139"></a>less abrupt, yet the entire series of records appears to the
+geologists now living far more fragmentary and defective than it
+seemed to their predecessors half a century ago. The earlier
+inquirers, as often as they encountered a break in the regular
+sequence of formations, connected it theoretically with a sudden
+and violent catastrophe, which had put an end to the regular course
+of events that had been going on uninterruptedly for ages,
+annihilating at the same time all or nearly all the organic beings
+which had previously flourished, after which, order being
+re-established, a new series of events was initiated. In proportion
+as our faith in these views grows weaker, and the phenomena of the
+organic or inorganic world presented to us by geology seem
+explicable on the hypothesis of gradual and insensible changes,
+varied only by occasional convulsions, on a scale comparable to
+that witnessed in historical times; and in proportion as it is
+thought possible that former fluctuations in the organic world may
+be due to the indefinite modifiability of species without the
+necessity of assuming new and independent acts of creation, the
+number and magnitude of the gaps which still remain, or the extreme
+imperfection of the record, become more and more striking, and what
+we possess of the ancient annals of the earth&rsquo;s history appears as
+nothing when contrasted with that which has been lost.</p>
+
+<p>When we examine a large area such as Europe, the average as well
+as the extreme height above the sea attained by the older
+formations is usually found to exceed that reached by the more
+modern ones, the primary or palaeozoic rising higher than the
+secondary, and these in their turn than the tertiary; while in
+reference to the three divisions of the tertiary, the lowest or
+Eocene group attains a higher summit-level than the Miocene, and
+these again a greater height than the Pliocene formations. Lastly,
+the post-tertiary deposits, such, at least, as are of marine
+origin, are most commonly restricted to much more moderate
+elevations above the sea-level than the tertiary strata.</p>
+
+<p>It is also observed that strata, in proportion as they are of
+newer date, bear the nearest resemblance in mineral character to
+those which are now in the progress of formation in seas or lakes,
+the newest of all consisting principally of soft mud or loose sand,
+in some places full of shells, corals, or other organic bodies,
+animal or vegetable, in others wholly devoid of such remains. The
+farther we recede from the present time, and the higher the
+antiquity of the formations which we examine, the greater are the
+changes which the sedimentary deposits have undergone. Time, as I
+have
+<a name="page140"></a>explained in Chapters V, VI, and VII, has multiplied the effects
+of condensation by pressure and cementation, and the modification
+produced by heat, fracture, contortion, upheaval, and denudation.
+The organic remains also have sometimes been obliterated entirely,
+or the mineral matter of which they were composed has been removed
+and replaced by other substances.</p>
+
+<p><b>Why newer Groups should be studied
+first.</b>&mdash;We likewise observe that the older the
+rocks the more widely do their organic remains depart from the
+types of the living creation. First, we find in the newer tertiary
+rocks a few species which no longer exist, mixed with many living
+ones, and then, as we go farther back, many genera and families at
+present unknown make their appearance, until we come to strata in
+which the fossil relics of existing species are nowhere to be
+detected, except a few of the lowest forms of invertebrate, while
+some orders of animals and plants wholly unrepresented in the
+living world begin to be conspicuous.</p>
+
+<p>When we study, therefore, the geological records of the earth
+and its inhabitants, we find, as in human history, the
+defectiveness and obscurity of the monuments always increasing the
+remoter the era to which we refer, and the difficulty of
+determining the true chronological relations of rocks is more and
+more enhanced, especially when we are comparing those which were
+formed simultaneously in very distant regions of the globe. Hence
+we advance with securer steps when we begin with the study of the
+geological records of later times, proceeding from the newer to the
+older, or from the more to the less known.</p>
+
+<p>In thus inverting what might at first seem to be the more
+natural order of historical research, we must bear in mind that
+each of the periods above enumerated, even the shortest, such as
+the Post-tertiary, or the Pliocene, Miocene, or Eocene, embrace a
+succession of events of vast extent, so that to give a satisfactory
+account of what we already know of any one of them would require
+many volumes. When, therefore, we approach one of the newer groups
+before endeavouring to decipher the monuments of an older one, it
+is like endeavouring to master the history of our own country and
+that of some contemporary nations, before we enter upon Roman
+History, or like investigating the annals of Ancient Italy and
+Greece before we approach those of Egypt and Assyria.</p>
+
+<p><b>Nomenclature.</b>&mdash;The origin
+of the terms Primary and Secondary, and the synonymous terms
+Palaeozoic, and Mesozoic, were explained in Chapter VIII, p.
+123.</p>
+
+<p>The Tertiary or Cainozoic strata (see <a href="#page123">p. 123</a>) were
+so called
+<a name="page141"></a>because they were all posterior in date to the Secondary series,
+of which last the Chalk of Cretaceous, No. 9, Fig. 86, constitutes
+the newest group. The whole of them were at first confounded with
+the superficial alluviums of Europe; and it was long before their
+real extent and thickness, and the various ages to which they
+belong, were fully recognised. They were observed to occur in
+patches, some of fresh-water, others of marine origin, their
+geographical area being usually small as compared to the secondary
+formations, and their position often suggesting the idea of their
+having been deposited in different bays, lakes, estuaries, or
+inland seas, after a large portion of the space now occupied by
+Europe had already been converted into dry land.</p>
+
+<p>The first deposits of this class, of which the characters were
+accurately determined, were those occurring in the neighbourhood of
+Paris, described in 1810 by MM. Cuvier and Brongniart. They were
+ascertained to consist of successive sets of strata, some of
+marine, others of fresh-water origin, lying one upon the other. The
+fossil shells and corals were perceived to be almost all of unknown
+species, and to have in general a near affinity to those now
+inhabiting warmer seas. The bones and skeletons of land animals,
+some of them of large size, and belonging to more than forty
+distinct species, were examined by Cuvier, and declared by him not
+to agree specifically, nor most of them even generically, with any
+hitherto observed in the living creation.</p>
+
+<p>Strata were soon afterwards brought to light in the vicinity of
+London, and in Hampshire, which, although dissimilar in mineral
+composition, were justly inferred by Mr. T. Webster to be of the
+same age as those of Paris, because the greater number of the
+fossil shells were specifically identical. For the same reason,
+rocks found on the Gironde, in the South of France, and at certain
+points in the North of Italy, were suspected to be of
+contemporaneous origin.</p>
+
+<p>Another important discovery was soon afterwards made by Brocchi
+in Italy, who investigated the argillaceous and sandy deposits,
+replete with shells, which form a low range of hills, flanking the
+Apennines on both sides, from the plains of the Po to Calabria.
+These lower hills were called by him the Subapennines, and were
+formed of strata chiefly marine, and newer than those of Paris and
+London.</p>
+
+<p>Another tertiary group occurring in the neighbourhood of
+Bordeaux and Dax, in the South of France, was examined by M. de
+Basterot in 1825, who described and figured several hundred species
+of shells, which differed for the most part both from the Parisian
+series and those of the Subapennine hills.
+<a name="page142"></a>It was soon, therefore, suspected that this fauna might belong
+to a period intermediate between that of the Parisian and
+Subapennine strata, and it was not long before the evidence of
+superposition was brought to bear in support of this opinion; for
+other strata, contemporaneous with those of Bordeaux, were observed
+in one district (the Valley of the Loire), to overlie the Parisian
+formation, and in another (in Piedmont) to underlie the Subapennine
+beds. The first example of these was pointed out in 1829 by M.
+Desnoyers, who ascertained that the sand and marl of marine origin
+called faluns, near Tours, in the basin of the Loire, full of
+sea-shells and corals, rested upon a lacustrine formation, which
+constitutes the uppermost subdivision of the Parisian group,
+extending continuously throughout a great table-land intervening
+between the basin of the Seine and that of the Loire. The other
+example occurs in Italy, where strata containing many fossils
+similar to those of Bordeaux were observed by Bonelli and others in
+the environs of Turin, subjacent to strata belonging to the
+Subapennine group of Brocchi.</p>
+
+<p><b>Value of Testacean Fossils in
+Classification.</b>&mdash;It will be observed that in the
+foregoing allusions to organic remains, the testacea or the
+shell-bearing mollusca are selected as the most useful and
+convenient class for the purposes of general classification. In the
+first place, they are more universally distributed through strata
+of every age than any other organic bodies. Those families of
+fossils which are of rare and casual occurrence are absolutely of
+no avail in establishing a chronological arrangement. If we have
+plants alone in one group of strata and the bones of mammalia in
+another, we can draw no conclusion respecting the affinity or
+discordance of the organic beings of the two epochs compared; and
+the same may be said if we have plants and vertebrated animals in
+one series and only shells in another. Although corals are more
+abundant, in a fossil state, than plants, reptiles, or fish, they
+are still rare when contrasted with shells, because they are more
+dependent for their well-being on the constant clearness of the
+water, and are, therefore, less likely to be included in rocks
+which endure in consequence of their thickness and the copiousness
+of sediment which prevailed when they originated. The utility of
+the testacea is, moreover, enhanced by the circumstance that some
+forms are proper to the sea, others to the land, and others to
+fresh water. Rivers scarcely ever fail to carry down into their
+deltas some land-shells, together with species which are at once
+fluviatile and lacustrine. By this means we learn what terrestrial,
+fresh-water, and marine
+<a name="page143"></a>species coexisted at particular eras of the past: and having
+thus identified strata formed in seas with others which originated
+contemporaneously in inland lakes, we are then enabled to advance a
+step farther, and show that certain quadrupeds or aquatic plants,
+found fossil in lacustrine formations, inhabited the globe at the
+same period when certain fish, reptiles, and zoophytes lived in the
+ocean.</p>
+
+<p>Among other characters of the molluscous animals, which render
+them extremely valuable in settling chronological questions in
+geology, may be mentioned, first, the wide geographical range of
+many species; and, secondly, what is probably a consequence of the
+former, the great duration of species in this class, for they
+appear to have surpassed in longevity the greater number of the
+mammalia and fish. Had each species inhabited a very limited space,
+it could never, when imbedded in strata, have enabled the geologist
+to identify deposits at distant points; or had they each lasted but
+for a brief period, they could have thrown no light on the
+connection of rocks placed far from each other in the
+chronological, or, as it is often termed, vertical series.</p>
+
+<p><b>Classification of Tertiary
+Strata.</b>&mdash;Many authors have divided the European
+Tertiary strata into three groups&mdash;lower, middle, and upper;
+the lower comprising the oldest formations of Paris and London
+before mentioned; the middle those of Bordeaux and Touraine; and
+the upper all those newer than the middle group.</p>
+
+<p>In the first edition of the Principles of Geology, I divided the
+whole of the Tertiary formations into four groups, characterised by
+the percentage of recent shells which they contained. The lower
+tertiary strata of London and Paris were thought by M. Deshayes to
+contain only 3&frac12; per cent of recent species, and were termed
+Eocene. The middle tertiary of the Loire and Gironde had, according
+to the specific determinations of the same conchologist, 17 per
+cent, and formed the Miocene division. The Subapennine beds
+contained 35 to 50 per cent, and were termed Older Pliocene, while
+still more recent beds in Sicily, which had from 90 to 95 per cent
+of species identical with those now living, were called Newer
+Pliocene. The first of the above terms, Eocene, is derived from
+eos, <i>dawn</i>, and cainos, <i>recent</i>, because the fossil
+shells of this period contain an extremely small proportion of
+living species, which may be looked upon as indicating the dawn of
+the existing state of the testaceous fauna, no recent species
+having been detected in the older or secondary rocks.</p>
+
+<p>The term Miocene (from meion, <i>less</i>, and cainos,
+<a name="page144"></a><i>recent</i>) is intended to express a minor proportion of
+recent species (of testacea), the term Pliocene (from pleion, <i>
+more</i>, and cainos, <i>recent</i>) a comparative plurality of the
+same. It may assist the memory of students to remind them, that the
+<i>Mi</i>ocene contain a <i>mi</i>nor proportion, and <i>
+Pl</i>iocene a comparative <i>pl</i>urality of recent species; and
+that the greater number of recent species always implies the more
+modern origin of the strata.</p>
+
+<p>It has sometimes been objected to this nomenclature that certain
+species of infusoria found in the chalk are still existing, and, on
+the other hand, the Miocene and Older Pliocene deposits often
+contain the remains of mammalia, reptiles, and fish, exclusively of
+extinct species. But the reader must bear in mind that the terms
+Eocene, Miocene, and Pliocene were originally invented with
+reference purely to conchological data, and in that sense have
+always been and are still used by me.</p>
+
+<p>Since the year 1830 the number of known shells, both recent and
+fossil, has largely increased, and their identification has been
+more accurately determined. Hence some modifications have been
+required in the classifications founded on less perfect materials.
+The Eocene, Miocene, and Pliocene periods have been made to
+comprehend certain sets of strata of which the fossils do not
+always conform strictly in the proportion of recent to extinct
+species with the definitions first given by me, or which are
+implied in the etymology of those terms.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap10"></a><a name="page145"></a>CHAPTER X.<br/>
+RECENT AND POST-PLIOCENE PERIODS.</h2>
+
+<p class="letter">
+Recent and Post-pliocene Periods. &mdash; Terms defined. &mdash; Formations of
+the Recent Period. &mdash; Modern littoral Deposits containing Works of Art
+near Naples. &mdash; Danish Peat and Shell-mounds. &mdash; Swiss
+Lake-dwellings. &mdash; Periods of Stone, Bronze, and Iron. &mdash;
+Post-pliocene Formations. &mdash; Coexistence of Man with extinct Mammalia.
+&mdash; Reindeer Period of South of France. &mdash; Alluvial Deposits of
+Paleolithic Age. &mdash; Higher and Lower-level Valley-gravels. &mdash; Loess
+or Inundation-mud of the Nile, Rhine, etc. &mdash; Origin of Caverns. &mdash;
+Remains of Man and extinct Quadrupeds in Cavern Deposits. &mdash; Cave of
+Kirkdale. &mdash; Australian Cave-breccias. &mdash; Geographical Relationship
+of the Provinces of living Vertebrata and those of extinct Post-pliocene
+Species. &mdash; Extinct struthious Birds of New Zealand. &mdash; Climate of
+the Post-pliocene Period. &mdash; Comparative Longevity of Species in the
+Mammalia and Testacea. &mdash; Teeth of Recent and Post-pliocene Mammalia.
+</p>
+
+<p>
+We have seen in the last chapter that the uppermost or newest strata are called
+Post-tertiary, as being more modern than the Tertiary. It will also be observed
+that the Post-tertiary formations are divided into two subordinate groups: the
+Recent, and Post-pliocene. In the former, or the Recent, the mammalia as well
+as the shells are identical with species now living: whereas in the
+Post-pliocene, the shells being all of living forms, a part, and often a
+considerable part, of the mammalia belonged to extinct species. To this
+nomenclature it may be objected that the term Post-pliocene should in
+strictness include all geological monuments posterior in date to the Pliocene;
+but when I have occasion to speak of the whole collectively, I shall call them
+Post-tertiary, and reserve the term Post-pliocene for the older Post-tertiary
+formations, while the Upper or newer ones will be called &ldquo;Recent.&rdquo;
+</p>
+
+<p>
+Cases will occur where it may be scarcely possible to draw the boundary line
+between the Recent and Post-pliocene deposits; and we must expect these
+difficulties to increase rather than diminish with every advance in our
+knowledge, and in proportion as gaps are filled up in the series of records.
+</p>
+
+<p class="center">
+RECENT PERIOD
+</p>
+
+<p>
+It was stated in the sixth chapter, when I treated of denudation, that the dry
+land, or that part of the earth&rsquo;s surface which is not covered by the
+waters of lakes or seas, is <a name="page146"></a>generally wasting away by the
+incessant action of rain and rivers, and in some cases by the undermining and
+removing power of waves and tides on the sea-coast. But the rate of waste is
+very unequal, since the level and gently sloping lands, where they are
+protected by a continuous covering of vegetation, escape nearly all wear and
+tear, so that they may remain for ages in a stationary condition, while the
+removal of matter is constantly widening and deepening the intervening ravines
+and valleys.
+</p>
+
+<p>
+The materials, both fine and coarse, carried down annually by rivers from the
+higher regions to the lower, and deposited in successive strata in the basins
+of seas and lakes, must be of enormous volume. We are always liable to
+underrate their magnitude, because the accumulation of strata is going on out
+of sight.
+</p>
+
+<p>
+There are, however, causes at work which, in the course of centuries, tend to
+render visible these modern formations, whether of marine or lacustrine origin.
+For a large portion of the earth&rsquo;s crust is always undergoing a change of
+level, some areas rising and others sinking at the rate of a few inches, or a
+few feet, perhaps sometimes yards, in a century; so that spaces which were once
+subaqueous are gradually converted into land, and others which were high and
+dry become submerged. In consequence of such movements we find in certain
+regions, as in Cashmere, for example, where the mountains are often shaken by
+earthquakes, deposits which were formed in lakes in the historical period, but
+through which rivers have now cut deep and wide channels. In lacustrine strata
+thus intersected, works of art and fresh-water shells are seen. In other
+districts on the borders of the sea, usually at very moderate elevations above
+its level, raised beaches occur, or marine littoral deposits, such as those in
+which, on the borders of the Bay of Baiæ, near Naples, the well-known temple of
+Serapis was imbedded. In that case the date of the monument buried in the
+marine strata is ascertainable, but in many other instances the exact age of
+the remains of human workmanship is uncertain, as in the estuary of the Clyde
+at Glasgow, where many canoes have been exhumed, with other works of art, all
+assignable to some part of the Recent Period.
+</p>
+
+<p>
+<b>Danish Peat and Shell-mounds or Kitchen-middens.</b>&mdash;Sometimes we
+obtain evidence, without the aid of a change of level, of events which took
+place in pre-historic times. The combined labours, for example, of the
+antiquary, zoologist, and botanist have brought to light many monuments of the
+early inhabitants buried in peat-mosses in Denmark. Their <a
+name="page147"></a>geological age is determined by the fact that, not only the
+contemporaneous fresh-water and land shells, but all the quadrupeds, found in
+the peat, agree specifically with those now inhabiting the same districts, or
+which are known to have been indigenous in Denmark within the memory of man. In
+the lower beds of peat (a deposit varying from 20 to 30 feet in thickness),
+weapons of stone accompany trunks of the Scotch fir, <i>Pinus sylvestris.</i>
+This peat may be referred to that part of the stone period for which Sir John
+Lubbock proposed the name of &ldquo;Neolithic&rdquo;<a href="#fn-10.1"
+name="fnref-10.1" id="fnref-10.1"><sup>[1]</sup></a> in contradistinction to a
+still older era, termed by him &ldquo;Paleolithic,&rdquo; and which will be
+described in the sequel. In the higher portions of the same Danish bogs, bronze
+implements are associated with trunks and acorns of the common oak. It appears
+that the pine has never been a native of Denmark in historical times, and it
+seems to have given place to the oak about the time when articles and
+instruments of bronze superseded those of stone. It also appears that, at a
+still later period, the oak itself became scarce, and was nearly supplanted by
+the beech, a tree which now flourishes luxuriantly in Denmark. Again, at the
+still later epoch when the beech-tree abounded, tools of iron were introduced,
+and were gradually substituted for those of bronze.
+</p>
+
+
+<p>
+On the coasts of the Danish islands in the Baltic, certain mounds, called in
+those countries &ldquo;Kjökken-mödding,&rdquo; or
+&ldquo;kitchen-middens,&rdquo; occur, consisting chiefly of the castaway shells
+of the oyster, cockle, periwinkle, and other eatable kinds of molluscs. The
+mounds are from three to ten feet high, and from 100 to 1000 feet in their
+longest diameter. They greatly resemble heaps of shells formed by the Red
+Indians of North America along the eastern shores of the United States. In the
+old refuse-heaps, recently studied by the Danish antiquaries and naturalists
+with great skill and diligence, no implements of metal have ever been detected.
+All the knives, hatchets, and other tools, are of stone, horn, bone, or wood.
+With them are often intermixed fragments of rude pottery, charcoal and cinders,
+and the bones of quadrupeds on which the rude people fed. These bones belong to
+wild species still living in Europe, though some of them, like the beaver, have
+long been extirpated in Denmark. The only animal which they seem to have
+domesticated was the dog.
+</p>
+
+<p>
+As there is an entire absence of metallic tools, these refuse-heaps are
+referred to the Neolithic division of the age of stone, which immediately
+preceded in Denmark the age of <a name="page148"></a>bronze. It appears that a
+race more advanced in civilisation, armed with weapons of that mixed metal,
+invaded Scandinavia, and ousted the aborigines.
+</p>
+
+<p>
+<b>Lacustrine Habitations of Switzerland.</b>&mdash;In Switzerland a different
+class of monuments, illustrating the successive ages of stone, bronze, and
+iron, has been of late years investigated with great success, and especially
+since 1854, in which year Dr. F. Keller explored near the shore at Meilen, in
+the bottom of the lake of Zurich, the ruins of an old village, originally built
+on numerous wooden piles, driven, at some unknown period, into the muddy bed of
+the lake. Since then a great many other localities, more than a hundred and
+fifty in all, have been detected of similar pile-dwellings, situated near the
+borders of the Swiss lakes, at points where the depth of water does not exceed
+15 feet.<a href="#fn-10.2" name="fnref-10.2" id="fnref-10.2"><sup>[2]</sup></a>
+The superficial mud in such cases is filled with various articles, many
+hundreds of them being often dredged up from a very limited area. Thousands of
+piles, decayed at their upper extremities, are often met with still firmly
+fixed in the mud.
+</p>
+
+
+<p>
+As the ages of stone, bronze, and iron merely indicate successive stages of
+civilisation, they may all have coexisted at once in different parts of the
+globe, and even in contiguous regions, among nations having little intercourse
+with each other. To make out, therefore, a distinct chronological series of
+monuments is only possible when our observations are confined to a limited
+district, such as Switzerland.
+</p>
+
+<p>
+The relative antiquity of the pile-dwellings, which belong respectively to the
+ages of stone and bronze, is clearly illustrated by the associations of the
+tools with certain groups of animal remains. Where the tools are of stone, the
+castaway bones which served for the food of the ancient people are those of
+deer, the wild boar, and wild ox, which abounded when society was in the hunter
+state. But the bones of the later or bronze epoch were chiefly those of the
+domestic ox, goat, and pig, indicating progress in civilisation. Some villages
+of the stone age are of later date than others, and exhibit signs of an
+improved state of the arts. Among their relics are discovered carbonised grains
+of wheat and barley, and pieces of bread, proving that the cultivation of
+cereals had begun. In the same settlements, also, cloth, made of woven flax and
+straw, has been detected.
+</p>
+
+<p>
+The pottery of the bronze age in Switzerland is of a finer texture, and more
+elegant in form, than that of the age of stone. At Nidau, on the lake of
+Bienne, articles of iron have <a name="page149"></a>also been discovered, so
+that this settlement was evidently not abandoned till that metal had come into
+use.
+</p>
+
+<p>
+At La Thène, in the northern angle of the lake of Neufchâtel, a great many
+articles of iron have been obtained, which in form and ornamentation are
+entirely different both from those of the bronze period and from those used by
+the Romans. Gaulish and Celtic coins have also been found there by MM. Schwab
+and Desor. They agree in character with remains, including many iron swords,
+which have been found at Tiefenau, near Berne, in ground supposed to have been
+a battle-field; and their date appears to have been anterior to the great Roman
+invasion of Northern Europe, though perhaps not long before that event.<a
+href="#fn-10.3" name="fnref-10.3" id="fnref-10.3"><sup>[3]</sup></a> Coins,
+which sometimes occur in deposits of the age of iron, have never yet been found
+in formations of the ages of bronze or stone.
+</p>
+
+<p>
+The period of bronze must have been one of foreign commerce, as tin, which
+enters into this metallic mixture in the proportion of about ten per cent to
+the copper, was obtained by the ancients chiefly from Cornwall.<a
+href="#fn-10.4" name="fnref-10.4" id="fnref-10.4"><sup>[4]</sup></a> Very few
+human bones of the bronze period have been met with in the Danish peat, or in
+the Swiss lake-dwellings, and this scarcity is generally attributed by
+archæologists to the custom of burning the dead, which prevailed in the age of
+bronze.
+</p>
+
+<p class="center">
+POST-PLIOCENE PERIOD
+</p>
+
+<p>
+From the foregoing observations we may infer that the ages of iron and bronze
+in Northern and Central Europe were preceded by a stone age, the Neolithic,
+referable to that division of the post-tertiary epoch which I have called
+Recent, when the mammalia as well as the other organic remains accompanying the
+stone implements were of living species. But memorials have of late been
+brought to light of a still older age of stone, for which, as above stated, the
+name Paleolithic has been proposed, when man was contemporary in Europe with
+the elephant and rhinoceros, and various other animals, of which many of the
+most conspicuous have long since died out.
+</p>
+
+<p>
+<b>Reindeer Period in South of France.</b>&mdash;In the larger number of the
+caves of Europe, as for example in those of England, Belgium, Germany, and many
+parts of France, the animal remains agree specifically with the fauna of this
+oldest division of the age of stone, or that to which belongs the drift of
+Amiens and Abbeville presently to be mentioned, containing <a
+name="page150"></a>flint implements of a very antique type. But there are some
+caves in the departments of Dordogne, Aude, and other parts of the south of
+France, which are believed by M. Lartet to be of intermediate date between the
+Paleolithic and Neolithic periods. To this intermediate era M. Lartet gave, in
+1863, the name of the &ldquo;reindeer period,&rdquo; because vast quantities of
+the bones and horns of that deer have been met with in the French caverns. In
+some cases separate plates of molars of the mammoth, and several teeth of the
+great Irish deer, <i>Cervus megaceros,</i> and of the cave-lion, <i>Felis
+spelæa,</i> have been found mixed up with cut and carved bones of reindeer. On
+one of these sculptured bones in the cave of Perigord, a rude representation of
+the mammoth, with its long curved tusks and covering of wool, occurs, which is
+regarded by M. Lartet as placing beyond all doubt the fact that the early
+inhabitants of these caves must have seen this species of elephant still living
+in France. The presence of the marmot, as well as the reindeer and some other
+northern animals, in these caverns seems to imply a colder climate than that of
+the Swiss lake-dwellings, in which no remains of reindeer have as yet been
+discovered. The absence of this last in the old lacustrine habitations of
+Switzerland is the more significant, because in a cave in the neighbourhood of
+the lake of Geneva, namely, that of Mont Saleve, bones of the reindeer occur
+with flint implements similar to those of the caverns of Dordogne and Perigord.
+</p>
+
+<p>
+The state of the arts, as exemplified by the instruments found in these caverns
+of the reindeer period, is somewhat more advanced than that which characterises
+the tools of the Amiens drift, but is nevertheless more rude than that of the
+Swiss lake-dwellings. No metallic articles occur, and the stone hatchets are
+not ground after the fashion of celts; the needles of bone are shaped in a
+workmanlike style, having their eyes drilled with consummate skill.
+</p>
+
+<p>
+The formations above alluded to, which are as yet but imperfectly known, may be
+classed as belonging to the close of the Paleolithic era, of the monuments of
+which I am now about to treat.
+</p>
+
+<p>
+<b>Alluvial Deposits of the Paleolithic Age.</b>&mdash;The alluvial and marine
+deposits of the Paleolithic age, the earliest to which any vestiges of man have
+yet been traced back, belong to a time when the physical geography of Europe
+differed in a marked degree from that now prevailing. In the Neolithic period,
+the valleys and rivers coincided almost entirely with those by which the
+present drainage of the land is effected, and the peat-mosses were the same as
+those now growing. <a name="page151"></a>The situation of the shell-mounds and
+lake-dwellings above alluded to is such as to imply that the topography of the
+districts where they are observed has not subsequently undergone any material
+alteration. Whereas we no sooner examine the Post-pliocene formations, in which
+the remains of so many extinct mammalia are found, than we at once perceive a
+more decided discrepancy between the former and present outline of the surface.
+Since those deposits originated, changes of considerable magnitude have been
+effected in the depth and width of many valleys, as also in the direction of
+the superficial and subterranean drainage, and, as is manifest near the
+sea-coast, in the relative position of land and water. In Fig. 87 an ideal
+section is given, illustrating the different position which the Recent and
+Post-pliocene alluvial deposits occupy in many European valleys.
+</p>
+
+<p>
+<img src="images/fig87.jpg" width="367" height="218" alt="Fig. 87: Recent
+and Post-pliocene alluvial deposits." />
+</p>
+
+<p>
+The peat, No. 1, has been formed in a low part of the modern alluvial plain, in
+parts of which gravel No. 2 of the recent period is seen. Over this gravel the
+loam or fine sediment 2&#x2032; has in many places been deposited by the river
+during floods which covered nearly the whole alluvial plain.
+</p>
+
+<p>
+No. 3 represents an older alluvium, composed of sand and gravel, formed before
+the valley had been excavated to its present depth. It contains the remains of
+fluviatile shells of living species associated with the bones of mammalia, in
+part of recent, and in part of extinct species. Among the latter, the mammoth
+(<i>E. primigenius</i>) and the Siberian rhinoceros (<i>R. tichorhinus</i>) are
+the most common in Europe. No. 3&#x2032; is a remnant of the loam or
+brick-earth by which No. 3 was overspread. No. 4 is a still older and more
+elevated terrace, similar in its composition and organic remains to No. 3, and
+covered in like manner with its inundation-mud,
+<a name="page152"></a>4&#x2032;. Sometimes the valley-gravels of older date are
+entirely missing, or there is only one, and occasionally there are more than
+two, marking as many successive stages in the excavation of the valley. They
+usually occur at heights varying from 10 to 100 feet, sometimes on the right
+and sometimes on the left side of the existing river-plain, but rarely in great
+strength on exactly opposite sides of the valley.
+</p>
+
+<p>
+Among the genera of extinct quadrupeds most frequently met with in England,
+France, Germany, and other parts of Europe, are the elephant, rhinoceros,
+hippopotamus, horse, great Irish deer, bear, tiger, and hyæna. In the peat, No.
+1 (Fig. 87), and in the more modern gravel and silt (No. 2), works of art of
+the ages of iron and bronze, and of the later or Neolithic stone period,
+already described, are met with. In the more ancient or Paleolithic gravels, 3
+and 4, there have been found of late years in several valleys in France and
+England&mdash;as, for example, in those of the Seine and Somme, and of the
+Thames and Ouse, near Bedford&mdash;stone implements of a rude type, showing
+that man coexisted in those districts with the mammoth and other extinct
+quadrupeds of the genera above enumerated. In 1847, M. Boucher de Perthes
+observed in an ancient alluvium at Abbeville, in Picardy, the bones of extinct
+mammalia associated in such a manner with flint implements of a rude type as to
+lead him to infer that both the organic remains and the works of art were
+referable to one and the same period. This inference was soon after confirmed
+by Mr. Prestwich, who found in 1859 a flint tool in situ in the same stratum at
+Amiens that contained the remains of extinct mammalia.
+</p>
+
+<p>
+The flint implements found at Abbeville and Amiens are most of them considered
+to be hatchets and spear-heads, and are different from those commonly called
+&ldquo;celts.&rdquo; These celts, so often found in the recent formations, have
+a more regular oblong shape, the result of grinding, by which also a sharp edge
+has been given to them. The Abbeville tools found in gravel at different
+levels, as in Nos. 3 and 4, Fig. 87, in which bones of the elephant,
+rhinoceros, and other extinct mammalia occur, are always unground, having
+evidently been brought into their present form simply by the chipping off of
+fragments of flint by repeated blows, such as could be given by a stone hammer.
+</p>
+
+<p>
+Some of them are oval, others of a spear-headed form, no two exactly alike, and
+yet the greater number of each kind are obviously fashioned after the same
+general pattern. Their outer surface is often white, the original black flint
+having been discoloured and bleached by exposure to the air, <a
+name="page153"></a>or by the action of acids, as they lay in the gravel. They
+are most commonly stained of the same ochreous colour as the flints of the
+gravel in which they are imbedded. Occasionally their antiquity is indicated
+not only by their colour but by superficial incrustations of carbonate of lime,
+or by dendrites formed of oxide of iron and manganese. The edges also of most
+of them are worn, sometimes by having been used as tools, or sometimes by
+having been rolled in the old river&rsquo;s bed. They are met with not only in
+the lower-level gravels, as in No. 3, Fig. 87, but also in No. 4, or the higher
+gravels, as at St. Acheul, in the suburbs of Amiens, where the old alluvium
+lies at an elevation of about 100 feet above the level of the river Somme. At
+both levels fluviatile and land-shells are met with in the loam as well as in
+the gravel, but there are no marine shells associated, except at Abbeville, in
+the lowest part of the gravel, near the sea, and a few feet only above the
+present high-water mark. Here with fossil shells of living species are mingled
+the bones of <i>Elephas primigenius</i> and <i>E. antiquus, Rhinoceros
+tichorhinus, Hippopotamus, Felis spelæa, Hyæna spelæa,</i> reindeer, and many
+others, the bones accompanying the flint implements in such a manner as to show
+that both were buried in the old alluvium at the same period.
+</p>
+
+<p>
+Nearly the entire skeleton of a rhinoceros was found at one point, namely, in
+the Menchecourt drift at Abbeville, the bones being in such juxtaposition as to
+show that the cartilage must have held them together at the time of their
+inhumation.
+</p>
+
+<p>
+The general absence here and elsewhere of human bones from gravel and sand in
+which flint tools are discovered, may in some degree be due to the present
+limited extent of our researches. But it may also be presumed that when a
+hunter population, always scanty in numbers, ranged over this region, they were
+too wary to allow themselves to be overtaken by the floods which swept away
+many herbivorous animals from the low river-plains where they may have been
+pasturing or sleeping. Beasts of prey prowling about the same alluvial flats in
+search of food may also have been surprised more readily than the human tenant
+of the same region, to whom the signs of a coming tempest were better known.
+</p>
+
+<p>
+<b>Inundation-mud of Rivers.&mdash;Brick-earth.&mdash;Fluviatile Loam, or
+Loess.</b>&mdash;As a general rule, the fluviatile alluvia of different ages
+(Nos. 2, 3, 4, Fig. 87) are severally made up of coarse materials in their
+lower portions, and of fine silt or loam in their upper parts. For rivers are
+constantly shifting their <a name="page154"></a>position in the valley-plain,
+encroaching gradually on one bank, near which there is deep water, and
+deserting the other or opposite side, where the channel is growing shallower,
+being destined eventually to be converted into land. Where the current runs
+strongest, coarse gravel is swept along, and where its velocity is slackened,
+first sand, and then only the finest mud, is thrown down. A thin film of this
+fine sediment is spread, during floods, over a wide area, on one, or sometimes
+on both sides, of the main stream, often reaching as far as the base of the
+bluffs or higher grounds which bound the valley. Of such a description are the
+well-known annual deposits of the Nile, to which Egypt owes its fertility. So
+thin are they, that the aggregate amount accumulated in a century is said
+rarely to exceed five inches, although in the course of thousands of years it
+has attained a vast thickness, the bottom not having been reached by borings
+extending to a depth of 60 feet towards the central parts of the valley.
+Everywhere it consists of the same homogeneous mud, destitute of
+stratification&mdash;the only signs of successive accumulation being where the
+Nile has silted up its channel, or where the blown sands of the Libyan desert
+have invaded the plain, and give rise to alternate layers of sand and mud.
+</p>
+
+<p>
+In European river-loams we occasionally observe isolated pebbles and angular
+pieces of stone which have been floated by ice to the places where they now
+occur; but no such coarse materials are met with in the plains of Egypt.
+</p>
+
+<p>
+In some parts of the valley of the Rhine the accumulation of similar loam,
+called in Germany &ldquo;loess,&rdquo; has taken place on an enormous scale.
+Its colour is yellowish-grey, and very homogeneous; and Professor Bischoff has
+ascertained, by analysis, that it agrees in composition with the mud of the
+Nile. Although for the most part unstratified, it betrays in some places marks
+of stratification, especially where it contains calcareous concretions, or in
+its lower part where it rests on subjacent gravel and sand which alternate with
+each other near the junction. About a sixth part of the whole mass is composed
+of carbonate of lime, and there is usually an intermixture of fine quartzose
+and micaceous sand.
+</p>
+
+<p>
+Although this loam of the Rhine is unsolidified, it usually terminates where it
+has been undermined by running water in a vertical cliff, from the face of
+which shells of terrestrial, fresh-water and amphibious mollusks project in
+relief. These shells do not imply the permanent sojourn of a body of fresh
+water on the spot, for the most aquatic of them, the <i>Succinea</i>, <a
+name="page155"></a>inhabits marshes and wet grassy meadows. The <i>Succinea
+elongata</i> (or <i>S. oblongata</i>), Fig. 88, is very characteristic both of
+the loess of the Rhine and of some other European river-loams.
+</p>
+
+<p>
+<img src="images/fig88.jpg" width="383" height="94" alt="Fig. 88: Succinea
+elongata; Fig. 89: Pupa muscorum (Linn.); Fig. 90: Helix hispida (Linn.)
+(plebia)." />
+</p>
+
+<p>
+Among the land-shells of the Rhenish loess, <i>Helix hispida</i>, Fig. 90, and
+<i>Pupa muscorum</i>, Fig. 89, are very common. Both the terrestrial and
+aquatic shells are of most fragile and delicate structure, and yet they are
+almost invariably perfect and uninjured. They must have been broken to pieces
+had they been swept along by a violent inundation. Even the colour of some of
+the land-shells, as that of <i>Helix nemoralis</i>, is occasionally preserved.
+</p>
+
+<p>
+In parts of the valley of the Rhine, between Bingen and Basle, the fluviatile
+loam or loess now under consideration is several hundred feet thick, and
+contains here and there throughout that thickness land and amphibious shells.
+As it is seen in masses fringing both sides of the great plain, and as
+occasionally remnants of it occur in the centre of the valley, forming hills
+several hundred feet in height, it seems necessary to suppose, first, a time
+when it slowly accumulated; and secondly, a later period, when large portions
+of it were removed, or when the original valley, which had been partially
+filled up with it, was re-excavated.
+</p>
+
+<p>
+Such changes may have been brought about by a great movement of oscillation,
+consisting first of a general depression of the land, and then of a gradual
+re-elevation of the same. The amount of continental depression which first took
+place in the interior, must be imagined to have exceeded that of the region
+near the sea, in which case the higher part of the great valley would have its
+alluvial plain gradually raised by an accumulation of sediment, which would
+only cease when the subsidence of the land was at an end. If the direction of
+the movement was then reversed, and, during the re-elevation of the continent,
+the inland region nearest the mountains should rise more rapidly than that near
+the coast, the river would acquire a denuding power sufficient to enable it to
+sweep away gradually nearly all the loam and gravel with which parts of its
+basin had been filled up. Terraces and hillocks of mud and sand would then
+alone remain to attest the various levels at which <a name="page156"></a>the
+river had thrown down and afterwards removed alluvial matter.
+</p>
+
+<p>
+<b>Cavern Deposits containing Human Remains and Bones of Extinct
+Animals.</b>&mdash;In England, and in almost all countries where limestone
+rocks abound, caverns are found, usually consisting of cavities of large
+dimensions, connected together by low, narrow, and sometimes torturous
+galleries or tunnels. These subterranean vaults are usually filled in part with
+mud, pebbles, and breccia, in which bones occur belonging to the same
+assemblage of animals as those characterising the Post-pliocene alluvia above
+described. Some of these bones are referable to extinct and others to living
+species, and they are occasionally intermingled, as in the valley-gravels, with
+implements of one or other of the great divisions of the stone age, and these
+are not unfrequently accompanied by human bones, which are much more common in
+cavern deposits than in valley-alluvium.
+</p>
+
+<p>
+Each suite of caverns, and the passages by which they communicate the one with
+the other, afford memorials to the geologist of successive phases through which
+they must have passed. First, there was a period when the carbonate of lime was
+carried out gradually by springs; secondly, an era when engulfed rivers or
+occasional floods swept organic and inorganic debris into the subterranean
+hollows previously formed; and thirdly, there were such changes in the
+configuration of the region as caused the engulfed rivers to be turned into new
+channels, and springs to be dried up, after which the cave-mud, breccia,
+gravel, and fossil bones would bear the same kind of relation to the existing
+drainage of the country as the older valley-drifts with their extinct mammalian
+remains and works of art bear to the present rivers and alluvial plains.
+</p>
+
+<p>
+The quarrying away of large masses of Carboniferous and Devonian limestone,
+near Liege, in Belgium, has afforded the geologist magnificent sections of some
+of these caverns, and the former communication of cavities in the interior of
+the rocks with the old surface of the country by means of vertical or oblique
+fissures, has been demonstrated in places where it would not otherwise have
+been suspected, so completely have the upper extremities of these fissures been
+concealed by superficial drift, while their lower ends, which extended into the
+roofs of the caves, are masked by stalactitic incrustations.
+</p>
+
+<p>
+The origin of the stalactite is thus explained by the eminent chemist Liebig.
+Mould or humus, being acted on by moisture and air, evolves carbonic acid,
+which is dissolved <a name="page157"></a>by rain. The rain-water, thus
+impregnated, permeates the porous limestone, dissolves a portion of it, and
+afterwards, when the excess of carbonic acid evaporates in the caverns, parts
+with the calcareous matter, and forms stalactite. Even while caverns are still
+liable to be occasionally flooded such calcareous incrustations accumulate, but
+it is generally when they are no longer in the line of drainage that a solid
+floor of hard stalagmite is formed on the bottom.
+</p>
+
+<p>
+The late Dr. Schmerling examined forty caves near Liege, and found in all of
+them the remains of the same fauna, comprising the mammoth, tichorhine
+rhinoceros, cave-bear, cave-hyæna, cave-lion, and many others, some of extinct
+and some of living species, and in all of them flint implements. In four or
+five caves only parts of human skeletons were met with, comprising sometimes
+skulls with a few other bones, sometimes nearly every part of the skeleton
+except the skull. In one of the caves, that of Engihoul, where Schmerling had
+found the remains of at least three human individuals, they were mingled in
+such a manner with bones of extinct mammalia, as to leave no doubt on his mind
+(in 1833) of man having co-existed with them.
+</p>
+
+<p>
+In 1860, Professor Malaise, of Liege, explored with me this same cave of
+Engihoul, and beneath a hard floor of stalagmite we found mud full of bones of
+extinct and recent animals, such as Schmerling had described, and my companion,
+persevering in his researches after I had returned to England, extracted from
+the same deposit two human lower jaw-bones retaining their teeth. The skulls
+from these Belgian caverns display no marked deviation from the normal European
+type of the present day.
+</p>
+
+<p>
+The careful investigations carried on by Dr. Falconer, Mr. Pengelly, and
+others, in the Brixham cave near Torquay, in 1858, demonstrated that flint
+knives were there imbedded in such a manner in loam underlying a floor of
+stalagmite as to prove that man had been an inhabitant of that region when the
+cave-bear and other members of the ancient post-pliocene fauna were also in
+existence.
+</p>
+
+<p>
+The absence of gnawed bones had led Dr. Schmerling to infer that none of the
+Belgian caves which he explored had served as the dens of wild beasts; but
+there are many caves in Germany and England which have certainly been so
+inhabited, especially by the extinct hyæna and bear.
+</p>
+
+<p>
+A fine example of a hyæna&rsquo;s den was afforded by the cave of Kirkdale, so
+well described by the late Dr. Buckland in his <i>Reliquiæ Diluvianæ.</i> In
+that cave, above twenty-five miles north-north-east of York, the remains of
+about 300 hyænas, <a name="page158"></a>belonging to individuals of every age,
+were detected. The species (<i>Hyæna spelæa</i>) has been considered by
+palæontologists as extinct; it was larger than the fierce <i>Hyæna crocuta</i>
+of South Africa, which it closely resembled, and of which it is regarded by Mr.
+Boyd Dawkins as a variety. Dr. Buckland, after carefully examining the spot,
+proved that the hyænas must have lived there; a fact attested by the quantity
+of their dung, which, as in the case of the living hyæna, is of nearly the same
+composition as bone, and almost as durable. In the cave were found the remains
+of the ox, young elephant, hippopotamus, rhinoceros, horse, bear, wolf, hare,
+water-rat, and several birds. All the bones have the appearance of having been
+broken and gnawed by the teeth of the hyænas; and they occur confusedly mixed
+in loam or mud, or dispersed through a crust of stalagmite which covers it. In
+these and many other cases it is supposed that portions of herbivorous
+quadrupeds have been dragged into caverns by beasts of prey, and have served as
+their food&mdash;an opinion quite consistent with the known habits of the
+living hyæna.
+</p>
+
+<p>
+<i>Australian Cave-breccias.</i>&mdash;Ossiferous breccias are not confined to
+Europe, but occur in all parts of the globe; and those discovered in fissures
+and caverns in Australia correspond closely in character with what has been
+called the bony breccia of the Mediterranean, in which the fragments of bone
+and rock are firmly bound together by a red ochreous cement.
+</p>
+
+<p>
+<img src="images/fig91.jpg" width="319" height="264" alt="Fig. 91: Part of a
+lower jaw of Macropus atlas." />
+</p>
+
+<p>
+Some of these caves were examined by the late Sir T. Mitchell in the Wellington
+Valley, about 210 miles west of <a name="page159"></a>Sidney, on the river
+Bell, one of the principal sources of the Macquarie, and on the Macquarie
+itself. The caverns often branch off in different directions through the rock,
+widening and contracting their dimensions, and the roofs and floors are covered
+with stalactite. The bones are often broken, but do not seem to be water-worn.
+In some places they lie imbedded in loose earth, but they are usually included
+in a breccia.
+</p>
+
+<p>
+The remains belong to marsupial animals. Among the most abundant are those of
+the kangaroo, of which there are four species, while others belong to the
+genera <i>Phascolomys</i>, the wombat; <i>Dasyurus</i>), the ursine opossum;
+<i>Phalangista</i>, the vulpine opossum; and <i>Hypsiprymnus</i>, the
+kangaroo-rat.
+</p>
+
+<p>
+<img src="images/fig92.jpg" width="322" height="185" alt="Fig. 92: Lower jaw of
+largest living species of kangaroo." />
+</p>
+
+<p>
+In the fossils above enumerated, several species are larger than the largest
+living ones of the same genera now known in Australia. Fig. 91 of the right
+side of a lower jaw of a kangaroo (<i>Macropus atlas</i>, Owen) will at once be
+seen to exceed in magnitude the corresponding part of the largest living
+kangaroo, which is represented in Fig. 92. In both these specimens part of the
+substance of the jaw has been broken open, so as to show the permanent false
+molar (<i>a</i>, Fig. 91), concealed in the socket. From the fact of this molar
+not having been cut, we learn that the individual was young, and had not shed
+its first teeth.
+</p>
+
+<p>
+The reader will observe that all these extinct quadrupeds of Australia belong
+to the marsupial family, or, in other words, that they are referable to the
+same peculiar type of organisation which now distinguishes the Australian
+mammalia from those of other parts of the globe. This fact is one of many
+pointing to a general law deducible from the fossil vertebrate and invertebrate
+animals of times immediately antecedent to our own, namely, that the present
+geographical distribution of organic <i>forms</i> dates back to a period
+anterior to the origin of existing <i>species</i>; in other words, <a
+name="page160"></a>the limitation of particular genera or families of
+quadrupeds, mollusca, etc., to certain existing provinces of land and sea,
+began before the larger part of the species now contemporary with man had been
+introduced into the earth.
+</p>
+
+<p>
+Professor Owen, in his excellent &ldquo;History of British Fossil
+Mammals,&rdquo; has called attention to this law, remarking that the fossil
+quadrupeds of Europe and Asia differ from those of Australia or South America.
+We do not find, for example, in the Europæo-Asiatic province fossil kangaroos,
+or armadillos, but the elephant, rhinoceros, horse, bear, hyæna, beaver, hare,
+mole, and others, which still characterise the same continent.
+</p>
+
+<p>
+In like manner, in the Pampas of South America the skeletons of Megatherium,
+Megalonyx, Glyptodon, Mylodon, Toxodon, Macrauchenia, and other extinct forms,
+are analogous to the living sloth, armadillo, cavy, capybara, and llama. The
+fossil quadrumana, also associated with some of these forms in the Brazilian
+caves, belong to the Platyrrhine family of monkeys, now peculiar to South
+America. That the extinct fauna of Buenos Ayres and Brazil was very modern has
+been shown by its relation to deposits of marine shells, agreeing with those
+now inhabiting the Atlantic.
+</p>
+
+<p>
+The law of geographical relationship above alluded to, between the living
+vertebrata of every great zoological province and the fossils of the period
+immediately antecedent, even where the fossil species are extinct, is by no
+means confined to the mammalia. New Zealand, when first examined by Europeans,
+was found to contain no indigenous land quadrupeds, no kangaroos, or opossums,
+like Australia; but a wingless bird abounded there, the smallest living
+representative of the ostrich family, called the Kiwi by the natives
+(<i>Apteryx</i>). In the fossils of the Post-pliocene period in this same
+island, there is the like absence of kangaroos, opossums, wombats, and the
+rest; but in their place a prodigious number of well-preserved specimens of
+gigantic birds of the struthious order, called by Owen <i>Dinornis</i> and
+<i>Palapteryx</i>, which are entombed in superficial deposits. These genera
+comprehended many species, some of which were four, some seven, others nine,
+and others eleven feet in height! It seems doubtful whether any contemporary
+mammalia shared the land with this population of gigantic feathered bipeds.
+</p>
+
+<p>
+Mr. Darwin, when describing the recent and fossil mammalia of South America,
+has dwelt much on the wonderful relationship of the extinct to the living types
+in that part of the world, inferring from such geographical phenomena that the
+existing species are all related to the extinct ones which preceded them by a
+bond of common descent.
+</p>
+
+<p>
+<a name="page161"></a><b>Climate of the Post-pliocene Period.</b>&mdash;The
+evidence as to the climate of Europe during this epoch is somewhat conflicting.
+The fluviatile and land-shells are all of existing species, but their
+geographical range has not always been the same as at present. Some, for
+example, which then lived in Britain are now only found in Norway and Finland,
+probably implying that the Post-pliocene climate of Britain was colder,
+especially in the winter. So also the reindeer and the musk-ox (<i>Ovibos
+moschatus</i>), now inhabitants of the Arctic regions, occur fossil in the
+valleys of the Thames and Avon, and also in France and Germany, accompanied in
+most places by the mammoth and the woolly rhinoceros. At Grays in Essex, on the
+other hand, another species both of elephant and rhinoceros occurs, together
+with a hippopotamus and the <i>Cyrena fluminalis</i>, a shell now extinct in
+Europe but still an inhabitant of the Nile and some Asiatic rivers. With it
+occurs the <i>Unio littoralis</i>, now living in the Seine and Loire. In the
+valley of the Somme flint tools have been found associated with <i>Hippopotamus
+major</i> and <i>Cyrena fluminalis</i> in the lower-level Post-pliocene
+gravels; while in the higher-level (and more ancient) gravels similar tools are
+more abundant, and are associated with the bones of the mammoth and other
+Post-pliocene quadrupeds indicative of a colder climate.
+</p>
+
+<p>
+It is possible that we may here have evidence of summer and winter migrations
+rather than of a general change of temperature. Instead of imagining that the
+hippopotamus lived all the year round with the musk-ox and lemming, we may
+rather suppose that the apparently conflicting evidence may be due to the place
+of our observations being near the boundary line of a northern and southern
+fauna, either of which may have advanced or receded during comparatively slight
+and temporary fluctuations of climate. There may then have been a continuous
+land communication between England and the North of Siberia, as well as in an
+opposite direction with Africa, then united to Southern Europe.
+</p>
+
+<p>
+In drift at Fisherton, near Salisbury, thirty feet above the river Wiley, the
+Greenland lemming and a new species of the Arctic genus <i>Spermophilus</i>
+have been found, along with the mammoth, reindeer, cave-hyæna, and other
+mammalia suited to a cold climate. A flint implement was taken out from beneath
+the bones of the mammoth. In a higher and older deposit in the vicinity, flint
+tools like those of Amiens have been discovered. Nearly all the known
+Post-pliocene quadrupeds have now been found accompanying flint knives or
+hatchets in such a way as to imply their coexistence with <a
+name="page162"></a>man; and we have thus the concurrent testimony of several
+classes of geological facts to the vast antiquity of the human race. In the
+first place, the disappearance of a great variety of species of wild animals
+from every part of a wide continent must have required a vast period for its
+accomplishment; yet this took place while man existed upon the earth, and was
+completed before that early period when the Danish shell-mounds were formed or
+the oldest of the Swiss lake-dwellings constructed. Secondly, the deepening and
+widening of valleys, indicated by the position of the river gravels at various
+heights, implies an amount of change of which that which has occurred during
+the historical period forms a scarcely perceptible part. Thirdly, the change in
+the course of rivers which once flowed through caves now removed from any line
+of drainage, and the formation of solid floors of stalagmite, must have
+required a great lapse of time. Lastly, ages must have been required to change
+the climate of wide regions to such an extent as completely to alter the
+geographical distribution of many mammalia as well as land and fresh-water
+shells. The 3000 or 4000 years of the historical period does not furnish us
+with any appreciable measure for calculating the number of centuries which
+would suffice for such a series of changes, which are by no means of a local
+character, but have operated over a considerable part of Europe.
+</p>
+
+<p>
+<b>Relative Longevity of Species in the Mammalia and Testacea.</b>&mdash;I
+called attention in 1830<a href="#fn-10.5" name="fnref-10.5"
+id="fnref-10.5"><sup>[5]</sup></a> to the fact, which had not at that time
+attracted notice, that the association in the Post-pliocene deposits of shells,
+exclusively of living species, with many extinct quadrupeds betokened a
+longevity of species in the testacea far exceeding that in the mammalia.
+Subsequent researches seem to show that this greater duration of the same
+specific forms in the class mollusca is dependent on a still more general law,
+namely, that the lower the grade of animals, or the greater the simplicity of
+their structure, the more persistent are they in general in their specific
+characters throughout vast periods of time. Not only have the invertebrata, as
+shown by geological data, altered at a less rapid rate than the vertebrata, but
+if we take one of the classes of the former, as for example the mollusca, we
+find those of more simple structure to have varied at a slower rate than those
+of a higher and more complex organisation; the Brachiopoda, for example, more
+slowly than the lamellibranchiate bivalves, while the latter have been more
+persistent than the univalves, whether gasteropoda or cephalopoda. In like
+manner the specific identity of the characters of the foraminifera, <a
+name="page163"></a>which are among the lowest types of the invertebrata, has
+outlasted that of the mollusca in an equally decided manner.
+</p>
+
+<p>
+<b>Teeth of Post-pliocene Mammalia.</b>&mdash;To those who have never studied
+comparative anatomy, it may seem scarcely credible that a single bone taken
+from any part of the skeleton may enable a skilful osteologist to distinguish,
+in many cases, the genus, and sometimes the species, of quadrupeds to which it
+belonged. Although few geologists can aspire to such knowledge, which must be
+the result of long practice and study, they will nevertheless derive great
+advantage from learning, what is comparatively an easy task, to distinguish the
+principal divisions of the mammalia by the forms and characters of their teeth.
+</p>
+
+<p>
+<img src="images/fig93.jpg" width="339" height="481" alt="Fig. 93: Elephas
+primigenius (or Mammoth) molar of upper jaw, right side. Post-pliocene; Fig.
+94: Elephas antiquus, Falconer. Penultimate molar. Post-pliocene and Pliocene." />
+</p>
+
+<p>
+Figures 93 through 105 represent the teeth of some of the more common species
+and genera found in alluvial and cavern deposits.<a name="page164"></a>
+<a name="page165"></a>
+</p>
+
+<p>
+<img src="images/fig95.jpg" width="405" height="733" alt="Figs. 95 to 100: Teeth
+of extinct mammalia." />
+</p>
+
+<p>
+<img src="images/fig101.jpg" width="465" height="592" alt="Figs. 101 to 105:
+Teeth of extinct mammalia." />
+</p>
+
+<p>
+On comparing the grinding surfaces of the corresponding molars of the three
+species of elephants, Figs. 93, 94, 95 it will be seen that the folds of enamel
+are most numerous in the mammoth, fewer and wider, or more open, in <i>E.
+antiquus</i>; and most open and fewest in <i>E. meridionalis.</i> It will be
+also seen that the enamel in the molar of the <i>Rhinoceros tichorhinus</i>
+(Fig. 97), is much thicker than in that of the <i>Rhinoceros leptorhinus</i>
+(Fig. 96).
+</p>
+
+<p class="footnote">
+<a name="fn-10.1" id="fn-10.1"></a> <a href="#fnref-10.1">[1]</a>
+Sir John Lubbock, Pre-historic Times, p. 3, 1865.
+</p>
+
+
+<p class="footnote">
+<a name="fn-10.2" id="fn-10.2"></a> <a href="#fnref-10.2">[2]</a>
+Bulletin de la Sociétié Vaudoise des Sci. Nat., tome vi, Lausanne 1860; and
+Antiquity of Man, by the author, chap. ii.
+</p>
+
+<p class="footnote">
+<a name="fn-10.3" id="fn-10.3"></a> <a href="#fnref-10.3">[3]</a>
+Sir J. Lubbock&rsquo;s Lecture, Royal Institution, Feb. 27th, 1863.
+</p>
+
+<p class="footnote">
+<a name="fn-10.4" id="fn-10.4"></a> <a href="#fnref-10.4">[4]</a>
+Diodorus, v, 21, 22 and Sir H. James Note on Block of Tin dredged up in
+Falmouth Harbour. Royal Institution of Cornwall, 1863.
+</p>
+
+
+<p class="footnote">
+<a name="fn-10.5" id="fn-10.5"></a> <a href="#fnref-10.5">[5]</a>
+Principles of Geology, 1st ed., vol. iii, p. 140.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap11"></a><a name="page166"></a>CHAPTER XI.<br/>
+POST-PLIOCENE PERIOD, continued&mdash;GLACIAL CONDITIONS.<a href="#fn-11.1"
+name="fnref-11.1" id="fnref-11.1"><sup>[1]</sup></a></h2>
+
+<p class="letter">Geographical Distribution, Form, and Characters of
+Glacial Drift. &mdash; Fundamental Rocks, polished, grooved, and
+scratched. &mdash; Abrading and striating Action of Glaciers.
+&mdash; Moraines, Erratic Blocks, and &ldquo;Roches Moutonnees.&rdquo; Alpine
+Blocks on the Jura. &mdash; Continental Ice of Greenland. &mdash;
+Ancient Centres of the Dispersion of Erratics. &mdash;
+Transportation of Drift by floating Icebergs. &mdash; Bed of the
+Sea furrowed and polished by the running aground of floating
+Ice-islands.</p>
+
+<p><b>Character and Distribution of Glacial
+Drift.</b>&mdash;In speaking of the loose transported matter
+commonly found on the surface of the land in all parts of the
+globe, I alluded to the exceptional character of what has been
+called the boulder formation in the temperate and Arctic latitudes
+of the northern hemisphere. The peculiarity of its form in Europe
+north of the 50th, and in North America north of the 40th parallel
+of latitude, is now universally attributed to the action of ice,
+and the difference of opinion respecting it is now chiefly
+restricted to the question whether land-ice or floating icebergs
+have played the chief part in its distribution. It is wanting in
+the warmer and equatorial regions, and reappears when we examine
+the lands which lie south of the 40th and 50th parallels in the
+southern hemisphere, as, for example, in Patagonia, Tierra del
+Fuego, and New Zealand. It consists of sand and clay, sometimes
+stratified, but often wholly devoid of stratification for a depth
+of 50, 100, or even a greater number of feet. To this unstratified
+form of the deposit the name of <i>till</i> has long been applied
+in Scotland. It generally contains a mixture of angular and rounded
+fragments of rock, some of large size, having occasionally one or
+more of their sides flattened and smoothed, or even highly
+polished. The smoothed surfaces usually exhibit many scratches
+parallel to each other, one set of which often crosses an older
+set. The till is almost everywhere wholly devoid of organic
+remains, except those washed into it from older formations, though
+in some places it contains marine shells, usually of northern
+or
+<a name="page167"></a>Arctic species, and frequently in a fragmentary state. The bulk
+of the till has usually been derived from the grinding down into
+mud of rocks in the immediate neighbourhood, so that it is red in a
+region of Red Sandstone, as in Strathmore in Forfarshire; grey or
+black in a district of coal and bituminous shale, as around
+Edinburgh; and white in a chalk country, as in parts of Norfolk and
+Denmark. The stony fragments dispersed irregularly through the till
+usually belong, especially in mountainous countries, to rocks found
+in some part of the same hydrographical basin; but there are
+regions where the whole of the boulder clay has come from a
+distance, and huge blocks, or &ldquo;erratics,&rdquo; as they have been called,
+many feet in diameter, have not unfrequently travelled hundreds of
+miles from their point of departure, or from the parent rocks from
+which they have evidently been detached. These are commonly
+angular, and have often one or more of their sides polished and
+furrowed.</p>
+
+<p>The rock on which the boulder formation reposes, if it consists
+of granite, gneiss, marble, or other hard stone, capable of
+permanently retaining any superficial markings which may have been
+imprinted upon it, is usually smoothed or polished, like the
+erratics above described, and exhibits parallel striæ and
+furrows having a determinate direction. This direction, both in
+Europe and North America, agrees generally in a marked manner with
+the course taken by the erratic blocks in the same district. The
+boulder clay, when it was first studied, seemed in many of its
+characters so singular and anomalous, that geologists despaired of
+ever being able to interpret the phenomena by reference to causes
+now in action. In those exceptional cases where marine shells of
+the same date as the boulder clay were found, nearly all of them
+were recognised as living species&mdash;a fact conspiring with the
+superficial position of the drift to indicate a comparatively
+modern origin.</p>
+
+<p>The term &ldquo;diluvium&rdquo; was for a time the most popular name of the
+boulder formation, because it was referred by many to the deluge of
+Noah, while others retained the name as expressive of their opinion
+that a series of diluvial waves raised by hurricanes and storms, or
+by earthquakes, or by the sudden upheaval of land from the bed of
+the sea, had swept over the continents, carrying with them vast
+masses of mud and heavy stones, and forcing these stones over rocky
+surfaces so as to polish and imprint upon them long furrows and
+striæ. But geologists were not long in seeing that the
+boulder formation was characteristic of high latitudes, and that on
+the whole the size and number of erratic blocks increases
+<a name="page168"></a>as we travel towards the Arctic regions. They could not fail to
+be struck with the contrast which the countries bordering the
+Baltic presented when compared with those surrounding the
+Mediterranean. The multitude of travelled blocks and striated rocks
+in the one region, and the absence of such appearances in the
+other, were too obvious to be overlooked. Even the great
+development of the boulder formation, with large erratics so far
+south as the Alps, offered an exception to the general rule
+favourable to the hypothesis that there was some intimate
+connection between it and accumulations of snow and ice.</p>
+
+<p><img src="images/fig106.jpg" width="405" height="370" alt=
+"Fig. 106: Limestone, polished, furrowed, and scratched by the glacier of
+Rosenlau in Switzerland." />
+</p>
+
+<p><b>Transporting and abrading Power of
+Glaciers.</b>&mdash;I have described elsewhere (&ldquo;Principles&rdquo;
+vol. i, chap. xvi, 1867) the manner in which the snow of the Alpine
+heights is prevented from accumulating indefinitely in thickness by
+the constant descent of a large portion of it by gravitation.
+Becoming converted into ice it forms what are termed glaciers,
+which glide down the principal valleys. On their surface are seen
+mounds of rubbish or large heaps of sand and mud, with angular
+fragments of rock which fall from the steep slopes or precipices
+bounding the glaciers. When a glacier,
+<a name="page169"></a>thus laden, descends so far as to reach a region about 3500 feet
+above the level of the sea, the warmth of the air is such that it
+melts rapidly in summer, and all the mud, sand, and pieces of rock
+are slowly deposited at its lower end, forming a confused heap of
+unstratified rubbish called a <i>moraine</i>, and resembling the
+<i>till</i> before described (p. 166).
+</p>
+
+<p>Besides the blocks thus carried down on the top of the glacier,
+many fall through fissures in the ice to the bottom, where some of
+them become firmly frozen into the mass, and are pushed along the
+base of the glacier, abrading, polishing, and grooving the rocky
+floor below, as a diamond cuts glass, or as emery-powder polishes
+steel. The striæ which are made, and the deep grooves which
+are scooped out by this action, are rectilinear and parallel to an
+extent never seen in those produced on loose stones or rocks, where
+shingle is hurried along by a torrent, or by the waves on a
+sea-beach. In addition to these polished, striated, and grooved
+surfaces of rock, another mark of the former action of a glacier is
+the &ldquo;roche moutonnee.&rdquo; Projecting eminences of rock so called have
+been smoothed and worn into the shape of flattened domes by the
+glacier as it passed over them. They have been traced in the Alps
+to great heights above the present glaciers, and to great
+horizontal distances beyond them.</p>
+
+<p><b>Alpine Blocks on the
+Jura.</b>&mdash;The moraines, erratics, polished surfaces,
+domes, and striæ, above described, are observed in the great
+valley of Switzerland, fifty miles broad; and almost everywhere on
+the Jura, a chain which lies to the north of this valley. The
+average height of the Jura is about one-third that of the Alps, and
+it is now entirely destitute of glaciers; yet it presents almost
+everywhere similar moraines, and the same polished and grooved
+surfaces. The erratics, moreover, which cover it, present a
+phenomenon which has astonished and perplexed the geologist for
+more than half a century. No conclusion can be more incontestable
+than that these angular blocks of granite, gneiss, and other
+crystalline formations came from the Alps, and that they have been
+brought for a distance of fifty miles and upward across one of the
+widest and deepest valleys in the world; so that they are now
+lodged on a chain composed of limestone and other formations,
+altogether distinct from those of the Alps. Their great size and
+angularity, after a journey of so many leagues, has justly excited
+wonder; for hundreds of them are as large as cottages; and one in
+particular, composed of gneiss, celebrated under the name of Pierre
+à Bot, rests on the side of a hill about 900 feet above the
+lake of Neufchâtel, and is no less than 40 feet in
+diameter.</p>
+
+<p>
+<a name="page170"></a>In the year 1821, M. Venetz first announced his opinion that the
+Alpine glaciers must formerly have extended far beyond their
+present limits, and the proofs appealed to by him in confirmation
+of this doctrine were acknowledged by all subsequent observers, and
+greatly strengthened by new observations and arguments. M.
+Charpentier supposed that when the glaciers extended continuously
+from the Alps to the Jura, the former mountains were 2000 or 3000
+feet higher than at present. Other writers, on the contrary,
+conjectured that the whole country had been submerged, and the
+moraines and erratic blocks transported on floating icebergs; but a
+careful study of the distribution of the travelled masses, and the
+total absence of marine shells from the old glacial drift of
+Switzerland, have entirely disproved this last hypothesis. In
+addition to the many evidences of the action of ice in the northern
+parts of Europe which we have already mentioned, there occur here
+and there in some of these countries, what are wanting in
+Switzerland, deposits of marine fossil shells, which exhibit so
+arctic a character that they must have led the geologist to infer
+the former prevalence of a much colder climate, even had he not
+encountered so many accompanying signs of ice-action. The same
+marine shells demonstrate the submergence of large areas in
+Scandinavia and the British Isles, during the glacial cold.</p>
+
+<p>A characteristic feature of the deposits under consideration in
+all these countries is the occurrence of large erratic blocks, and
+sometimes of moraine matter, in situations remote from lofty
+mountains, and separated from the nearest points where the parent
+rocks appear at the surface by great intervening valleys, or arms
+of the sea. We also often observe striæ and furrows, as in
+Norway, Sweden, and Scotland, which deviate from the direction
+which they ought to follow if they had been connected with the
+present line of drainage, and they, therefore, imply the prevalence
+of a very distinct condition of things at the time when the cold
+was most intense. The actual state of North Greenland seems to
+afford the best explanation of such abnormal glacial markings.</p>
+
+<p><b>Greenland Continental
+Ice.</b>&mdash;Greenland is a vast unexplored continent,
+buried under one continuous and colossal mass of ice that is always
+moving seaward, a very small part of it in an easterly direction,
+and all the rest westward, or towards Baffin&rsquo;s Bay. All the minor
+ridges and valleys are levelled and concealed under a general
+covering of snow, but here and there some steep mountains protrude
+abruptly
+<a name="page171"></a>from the icy slope, and a few superficial lines of stones or
+moraines are visible at certain seasons, when no snow has fallen
+for many months, and when evaporation, promoted by the wind and
+sun, has caused much of the upper snow to disappear. The height of
+this continent is unknown, but it must be very great, as the most
+elevated lands of the outskirts, which are described as
+comparatively low, attain altitudes of 4000 to 6000 feet. The icy
+slope gradually lowers itself towards the outskirts, and then
+terminates abruptly in a mass about 2000 feet in thickness, the
+great discharge of ice taking place through certain large friths,
+which, at their upper ends, are usually about four miles across.
+Down these friths the ice is protruded in huge masses, several
+miles wide, which continue their course&mdash;grating along the
+rocky bottom like ordinary glaciers long after they have reached
+the salt water. When at last they arrive at parts of Baffin&rsquo;s Bay
+deep enough to buoy up icebergs from 1000 to 1500 feet in vertical
+thickness, broken masses of them float off, carrying with them on
+their surface not only fine mud and sand but large stones. These
+fragments of rock are often polished and scored on one or more
+sides, and as the ice melts, they drop down to the bottom of the
+sea, where large quantities of mud are deposited, and this muddy
+bottom is inhabited by many mollusca.</p>
+
+<p>Although the direction of the ice-streams in Greenland may
+coincide in the main with that which separate glaciers would take
+if there were no more ice than there is now in the Swiss Alps, yet
+the striation of the surface of the rocks on an ice-clad continent
+would, on the whole, vary considerably in its minor details from
+that which would be imprinted on rocks constituting a region of
+separate glaciers. For where there is a universal covering of ice
+there will be a general outward movement from the higher and more
+central regions towards the circumference and lower country, and
+this movement will be, to a certain extent, independent of the
+minor inequalities of hill and valley, when these are all reduced
+to one level by the snow. The moving ice may sometimes cross even
+at right angles deep narrow ravines, or the crests of buried
+ridges, on which last it may afterwards seem strange to detect
+glacial striæ and polishing after the liquefaction of the
+snow and ice has taken place.</p>
+
+<p>Rink mentions that in North Greenland powerful springs of clayey
+water escape in winter from under the ice, where it descends to
+&ldquo;the outskirts,&rdquo; and where, as already stated, it is often 2000
+feet thick&mdash;a fact showing how much grinding action is going
+on upon the surface of the subjacent
+<a name="page172"></a>rocks. I also learn from Dr. Torell that there are large areas
+in the outskirts, now no longer covered with permanent snow or
+glaciers, which exhibit on their surface unmistakable signs of
+ancient ice-action, so that, vast as is the power now exerted by
+ice in Greenland, it must once have operated on a still grander
+scale. The land, though now very elevated, may perhaps have been
+formerly much higher. It is well-known that the south coast of
+Greenland, from latitude 60&deg; to about 70&deg; N., has for the
+last four centuries been sinking at the rate of several feet in a
+century. By this means a surface of rock, well scored and polished
+by ice, is now slowly subsiding beneath the sea, and is becoming
+strewed over, as the icebergs melt, with impalpable mud and
+smoothed and scratched stones. It is not precisely known how far
+north this downward movement extends.</p>
+
+<p><b>Drift carried by
+Icebergs.</b>&mdash;An account was given so long ago as the
+year 1822, by Scoresby, of icebergs seen by him in the Arctic seas
+drifting along in latitudes 69&deg; and 70&deg; N., which rose
+above the surface from 100 to 200 feet, and some of which measured
+a mile in circumference. Many of them were loaded with beds of
+earth and rock, of such thickness that the weight was conjectured
+to be from 50,000 to 100,000 tons. A similar transportation of
+rocks is known to be in progress in the southern hemisphere, where
+boulders included in ice are far more frequent than in the north.
+One of these icebergs was encountered in 1839, in mid-ocean, in the
+antarctic regions, many hundred miles from any known land, sailing
+northward, with a large erratic block firmly frozen into it. Many
+of them, carefully measured by the officers of the French exploring
+expedition of the Astrolabe, were between 100 and 225 feet high
+above water, and from two to five miles in length. Captain
+d&rsquo;Urville ascertained one of them which he saw floating in the
+Southern Ocean to be 13 miles long and 100 feet high, with walls
+perfectly vertical. The submerged portions of such islands must,
+according to the weight of ice relatively to sea-water, be from six
+to eight times more considerable than the part which is visible, so
+that when they are once fairly set in motion, the mechanical force
+which they might exert against any obstacle standing in their way
+would be prodigious.</p>
+
+<p>We learn, therefore, from a study both of the arctic and
+antarctic regions, that a great extent of land may be entirely
+covered throughout the whole year by snow and ice, from the summits
+of the loftiest mountains to the sea-coast, and may yet send down
+angular erratics to the ocean. We may also conclude that such land
+will become in the course of
+<a name="page173"></a>ages almost everywhere scored and polished like the rocks which
+underlie a glacier. The discharge of ice into the surrounding sea
+will take place principally through the main valleys, although
+these are hidden from our sight. Erratic blocks and moraine matter
+will be dispersed somewhat irregularly after reaching the sea, for
+not only will prevailing winds and marine currents govern the
+distribution of the drift, but the shape of the submerged area will
+have its influence; inasmuch as floating ice, laden with stones,
+will pass freely through deep water, while it will run a ground
+where there are reefs and shallows. Some icebergs in Baffin&rsquo;s Bay
+have been seen stranded on a bottom 1000 or even 1500 feet deep. In
+the course of ages such a sea-bed may become densely covered with
+transported matter, from which some of the adjoining greater depths
+may be free. If, as in West Greenland, the land is slowly sinking,
+a large extent of the bottom of the ocean will consist of rock
+polished and striated by land-ice, and then overspread by mud and
+boulders detached from melting bergs.</p>
+
+<p>The mud, sand, and boulders thus let fall in still water must be
+exactly like the moraines of terrestrial glaciers, devoid of
+stratification and organic remains. But occasionally, on the outer
+side of such packs of stranded bergs, the waves and currents may
+cause the detached earthy and stony materials to be sorted
+according to size and weight before they reach the bottom, and to
+acquire a stratified arrangement.</p>
+
+<p>I have already alluded (p. 172) to the large quantity of ice,
+containing great blocks of stone, which is sometimes seen floating
+far from land, in the southern or Antarctic seas. After the
+emergence, therefore, of such a submarine area, the superficial
+detritus will have no necessary relation to the hills, valleys, and
+river-plains over which it will be scattered. Many a water-shed may
+intervene between the starting-point of each erratic or pebble and
+its final resting-place, and the only means of discovering the
+country from which it took its departure will consist in a careful
+comparison of its mineral or fossil contents with those of the
+parent rocks.
+</p>
+
+<p class="footnote">
+<a name="fn-11.1" id="fn-11.1"></a> <a href="#fnref-11.1">[1]</a>
+As to the former excess of cold, whether brought about by modifications in the
+height and distribution of the land or by altered astronomical conditions, see
+Principles, vol. i, (10th ed., 1867), chaps. xii and xiii, &ldquo;Vicissitudes
+of Climate.&rdquo;
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap12"></a><a name="page174"></a>CHAPTER XII.<br/>
+POST-PLIOCENE PERIOD, continued.&mdash;GLACIAL CONDITIONS,
+concluded.</h2>
+
+<p class="letter">Glaciation of Scandinavia and Russia. &mdash;
+Glaciation of Scotland. &mdash; Mammoth in Scotch Till. &mdash;
+Marine Shells in Scotch Glacial Drift. &mdash; Their Arctic
+Character. &mdash; Rarity of Organic Remains in Glacial Deposits.
+&mdash; Contorted Strata in Drift. &mdash; Glaciation of Wales,
+England, and Ireland. &mdash; Marine Shells of Moel Tryfaen.
+&mdash; Erratics near Chichester. &mdash; Glacial Formations of
+North America. &mdash; Many Species of Testacea and Quadrupeds
+survived the Glacial Cold. &mdash; Connection of the Predominance
+of Lakes with Glacial Action. &mdash; Action of Ice in preventing
+the silting up of Lake-basins. &mdash; Absence of Lakes in the
+Caucasus. &mdash; Equatorial Lakes of Africa.</p>
+
+<p><b>Glaciation of Scandinavia and Russia.</b>&mdash;In large
+tracts of Norway and Sweden, where there have been no glaciers in
+historical times, the signs of ice-action have been traced as high
+as 6000 feet above the level of the sea. These signs consist
+chiefly of polished and furrowed rock-surfaces, of moraines and
+erratic blocks. The direction of the erratics, like that of the
+furrows, has usually been conformable to the course of the
+principal valleys; but the lines of both sometimes radiate outward
+in all directions from the highest land, in a manner which is only
+explicable by the hypothesis above alluded to of a general envelope
+of continental ice, like that of Greenland (<a href="#page170">page 170</a>). Some of
+the far-transported blocks have been carried from the central parts
+of Scandinavia towards the Polar regions; others southward to
+Denmark; some south-westward, to the coast of Norfolk in England;
+others south-eastward, to Germany, Poland, and Russia.</p>
+
+<p>In the immediate neighbourhood of Upsala, in Sweden, I had
+observed, in 1834, a ridge of stratified sand and gravel, in the
+midst of which occurs a layer of marl, evidently formed originally
+at the bottom of the Baltic, by the slow growth of the mussel,
+cockle, and other marine shells of living species, intermixed with
+some proper to fresh water. The marine shells are all of dwarfish
+size, like those now inhabiting the brackish waters of the Baltic;
+and the marl, in which many of them are imbedded, is now raised
+more than 100 feet above the level of the Gulf of Bothnia. Upon the
+top of this ridge repose several huge erratics, consisting of
+gneiss for the most part unrounded, from nine to sixteen feet in
+diameter,
+<a name="page175"></a>and which must have been brought into their present position
+since the time when the neighbouring gulf was already characterised
+by its peculiar fauna. Here, therefore, we have proof that the
+transport of erratics continued to take place, not merely when the
+sea was inhabited by the existing testacea, but when the north of
+Europe had already assumed that remarkable feature of its physical
+geography which separates the Baltic from the North Sea, and causes
+the Gulf of Bothnia to have only one-fourth of the saltness
+belonging to the ocean. In Denmark, also, recent shells have been
+found in stratified beds, closely associated with the boulder
+clay.</p>
+
+<p><b>Glaciation of Scotland.</b>&mdash;Mr. T. F. Jamieson, in
+1858, adduced a great body of facts to prove that the Grampians
+once sent down glaciers from the central regions in all directions
+towards the sea. &ldquo;The glacial grooves,&rdquo; he observed, &ldquo;radiate
+outward from the central heights towards all points of the compass,
+though they do not always strictly conform to the actual shape and
+contour of the minor valleys and ridges.&rdquo;</p>
+
+<p>
+These facts and other characteristics of the Scotch drift lead us to the
+inference that when the glacial cold first set in, Scotland stood higher above
+the sea than at present, and was covered for the most part with snow and ice,
+as Greenland is now. This sheet of land-ice sliding down to lower levels,
+ground down and polished the subjacent rocks, sweeping off nearly all
+superficial deposits of older date, and leaving only till and boulders in their
+place. To this continental state succeeded a period of depression and partial
+submergence. The sea advanced over the lower lands, and Scotland was converted
+into an archipelago, some marine sand with shells being spread over the bottom
+of the sea. On this sand a great mass of boulder clay usually quite devoid of
+fossils was accumulated. Lastly, the land re-emerged from the water, and,
+reaching a level somewhat above its present height, became connected with the
+continent of Europe, glaciers being formed once more in the higher regions,
+though the ice probably never regained its former extension.<a href="#fn-12.1"
+name="fnref-12.1" id="fnref-12.1"><sup>[1]</sup></a> After all these changes,
+there were some minor oscillations in the level of the land, on which, although
+they have had important geographical consequences, separating Ireland from
+England, for example, and England from the Continent, we need not here enlarge.
+</p>
+
+<p>
+<i>Mammoth in Scotch Till.</i>&mdash;Almost all remains of the terrestrial
+fauna of the Continent which preceded the period of <a
+name="page176"></a>submergence have been lost; but a few patches of estuarine
+and fresh-water formations escaped denudation by submergence. To these belong
+the peaty clay from which several mammoths&rsquo; tusks and horns of reindeer
+were obtained at Kilmaurs, in Ayrshire as long ago as 1816. Mr. Bryce in 1865
+ascertained that the fresh-water formation containing these fossils rests on
+carboniferous sandstone, and is covered, first by a bed of marine sand with
+arctic shells, and then with a great mass of till with glaciated boulders.<a
+href="#fn-12.2" name="fnref-12.2" id="fnref-12.2"><sup>[2]</sup></a> Still more
+recent explorations in the neighbourhood of Kilmaurs have shown that the
+fresh-water formation contains the seed of the pond-weed <i>Potamogeton</i> and
+the aquatic Ranunculus; and Mr. Young of the Glasgow Museum washed the mud
+adhering to the reindeer horns of Kilmaurs and that which filled the cracks of
+the associated elephants&rsquo; tusks, and detected in these fossils (which had
+been in the Glasgow Museum for half a century) abundance of the same seeds.
+</p>
+
+<p>All doubts, therefore, as to the true position of the remains of
+the mammoth, a fossil so rare in Scotland, have been set at rest,
+and it serves to prove that part of the ancient continent sank
+beneath the sea at a period of great cold, as the shells of the
+overlying sand attest. The incumbent till or boulder clay is about
+40 feet thick, but it often attains much greater thickness in the
+same part of Scotland.</p>
+
+<p><img src="images/fig107.jpg" width="395" height="307" alt=
+"Figs. 107-112: Northern shells common in the drift of the Clyde, in Scotland." />
+</p>
+
+<p><i>Marine Shells of Scotch Drift.</i>&mdash;The greatest height
+to which marine shells have yet been traced in this boulder
+<a name="page177"></a>clay is at Airdie, in Lanarkshire, ten miles east of Glasgow,
+524 feet above the level of the sea. At that spot they were found
+imbedded in stratified clays with till above and below them. There
+appears no doubt that the overlying deposit was true glacial till,
+as some boulders of granite were observed in it, which must have
+come from distances of sixty miles at the least.</p>
+
+<p><img src="images/fig113.jpg" width="410" height="155" alt=
+"Fig. 113: Leda truncata; Fig. 114: Tellina calcarea, Chem." />
+</p>
+
+<p>The shells figured in Figs. 107 to 112 are only a few out of a
+large assemblage of living species, which, taken as a whole, bear
+testimony to conditions far more arctic than those now prevailing
+in the Scottish seas. But a group of marine shells, indicating a
+still greater excess of cold, has been brought to light since 1860
+by the Reverend Thomas Brown, from glacial drift or clay on the
+borders of the estuaries of the Forth and Tay. This clay occurs at
+Elie, in Fife, and at Errol, in Perthshire; and has already
+afforded about 35 shells, all of living species, and now
+inhabitants of arctic regions, such as <i>Leda truncata, Tellina
+proxima</i> (see Figs. 113 and 114), <i>Pecten Grœnlandicus,
+Crenella lævigata, Crenella nigra,</i> and others, some of
+them first brought by Captain Sir E. Parry from the coast of
+Melville Island, latitude 76&deg; N. These were all identified in
+1863 by Dr. Torell, who had just returned from a survey of the seas
+around Spitzbergen, where he had collected no less than 150 species
+of mollusca, living chiefly on a bottom of fine mud derived from
+the moraines of melting glaciers which there protrude into the sea.
+He informed me that the fossil fauna of this Scotch glacial deposit
+exhibits not only the species but also the peculiar varieties of
+mollusca now characteristic of very high latitudes. Their large
+size implies that they formerly enjoyed a colder, or, what was to
+them a more genial climate, than that now prevailing in the
+latitude where the fossils occur. Marine shells have also been
+found in the glacial drift of Caithness and Aberdeenshire at
+heights of 250 feet, and in Banff of 350 feet, and stratified drift
+continuous with the above ascends to heights of 500 feet. Already
+75 species are enumerated
+<a name="page178"></a>from Caithness, and the same number from Aberdeenshire and
+Banff, and in both cases all but six are arctic species.</p>
+
+<p>I formerly suggested that the absence of all signs of organic
+life in the Scotch drift might be connected with the severity of
+the cold, and also in some places with the depth of the sea during
+the period of extreme submergence; but my faith in such an
+hypothesis has been shaken by modern investigations, an exuberance
+of life having been observed both in arctic and antarctic seas of
+great depth, and where floating ice abounds. The difficulty,
+moreover, of accounting for the entire dearth of marine shells in
+till is removed when once we have adopted the theory of this
+boulder clay being the product of land-ice. For glaciers coming
+down from a continental ice-sheet like that which covers Greenland
+may fill friths many hundred feet below the sea-level, and even
+invade parts of a bay a thousand feet deep, before they find water
+enough to float off their terminal portions in the form of
+icebergs. In such a case till without marine shells may first
+accumulate, and then, if the climate becomes warmer and the ice
+melts, a marine deposit may be superimposed on the till without any
+change of level being required.</p>
+
+<p>
+Another curious phenomenon bearing on this subject was styled by the late Hugh
+Miller the &ldquo;striated pavements&rdquo; of the boulder clay. Where portions
+of the till have been removed by the sea on the shores of the Forth, or in the
+interior by railway cuttings, the boulders imbedded in what remains of the
+drift are seen to have been all subjected to a process of abrasion and
+striation, the striæ and furrows being parallel and persistent across them all,
+exactly as if a glacier or iceberg had passed over them and scored them in a
+manner similar to that so often undergone by the solid rocks below the glacial
+drift. It is possible, as Mr. Geikie conjectures, that this second striation of
+the boulders may be referable to floating ice.<a href="#fn-12.3"
+name="fnref-12.3" id="fnref-12.3"><sup>[3]</sup></a>
+</p>
+
+<p><i>Contorted Strata in Drift.</i>&mdash;In Scotland the till is
+often covered with stratified gravel, sand, and clay, the beds of
+which are sometimes horizontal and sometimes contorted for a
+thickness of several feet. Such contortions are not uncommon in
+Forfarshire, where I observed them, among other places, in a
+vertical cutting made in 1840 near the left bank of the South Esk,
+east of the bridge of Cortachie. The convolutions of the beds of
+fine and coarse sand, gravel, and loam, extend through a thickness
+of no less than 25 feet vertical, or from <i>b</i> to <i>c</i>,
+Fig. 115, the horizontal stratification being resumed very abruptly
+at a short distance, as to the right
+<a name="page179"></a>of <i>f</i>, <i>g.</i> The overlying coarse gravel and sand, <i>
+a</i>, is in some places horizontal, in others it exhibits cross
+bedding, and does not partake of the disturbances which the strata
+<i>b</i>, <i>c</i>, have undergone. The underlying till is exposed
+for a depth of about 20 feet; and we may infer from sections in the
+neighbourhood that it is considerably thicker.</p>
+
+<p><img src="images/fig115.jpg" width="397" height="216" alt=
+"Fig. 15: Section of contorted drift overlying till, seen on left bank of South Esk, near Cortachie, in 1840." />
+</p>
+
+<p>In some cases I have seen fragments of stratified clays and
+sands, bent in like manner, in the middle of a great mass of till.
+Mr. Trimmer has suggested, in explanation of such phenomena, the
+intercalation in the glacial period of large irregular masses of
+snow or ice between layers of sand and gravel. Some of the cliffs
+near Behring&rsquo;s Straits, in which the remains of elephants occur,
+consist of ice mixed with mud and stones; and Middendorf describes
+the occurrence in Siberia of masses of ice, found at various depths
+from the surface after digging through drift. Whenever the
+intercalation of snow and ice with drift, whether stratified or
+unstratified, has taken place, the melting of the ice will cause
+such a failure of support as may give rise to flexures, and
+sometimes to the most complicated foldings. But in many cases the
+strata may have been bent and deranged by the mechanical pressure
+of an advancing glacier, or by the sideway thrust of huge islands
+of ice running aground against sandbanks; in which case, the
+position of the beds forming the foundation of the banks may not be
+at all disturbed by the shock.</p>
+
+<p>
+There are indeed many signs in Scotland of the action of floating ice, as might
+have been expected where proofs of submergence in the Glacial Period are not
+wanting. Among these are the occurrence of large erratic blocks, frequently in
+clusters at or near the tops of hills or ridges, places which may have formed
+islets or shallows in the sea where floating ice would mostly ground and
+discharge its cargo on <a name="page180"></a>melting. Glaciers or land-ice
+would, on the contrary, chiefly discharge their cargoes at the bottom of
+valleys. Traces of an earlier and independent glaciation have also been
+observed in some regions where the striation, apparently produced by ice
+proceeding from the north-west, is not explicable by the radiation of land-ice
+from a central mountainous region.<a href="#fn-12.4" name="fnref-12.4"
+id="fnref-12.4"><sup>[4]</sup></a>
+</p>
+
+<p><b>Glaciation of Wales and England.</b>&mdash;The mountains of
+North Wales were recognised, in 1842, by Dr. Buckland, as having
+been an independent centre of the dispersion of
+erratics&mdash;great glaciers, long since extinct, having radiated
+from the Snowdonian heights in Carnarvonshire, through seven
+principal valleys towards as many points of the compass, carrying
+with them large stony fragments, and grooving the subjacent rocks
+in as many directions.</p>
+
+<p>Besides this evidence of land-glaciers, Mr. Trimmer had
+previously, in 1831, detected the signs of a great submergence in
+Wales in the Post-pliocene period. He had observed stratified
+drift, from which he obtained about a dozen species of marine
+shells, near the summit of Moel Tryfaen, a hill 1400 feet high, on
+the south side of the Menai Straits. I had an opportunity of
+examining in the summer of 1863, together with the Reverend W. S.
+Symonds, a long and deep cutting made through this drift by the
+Alexandra Mining Company in search of slates. At the top of the
+hill above-mentioned we saw a stratified mass of incoherent sand
+and gravel 35 feet thick, from which no less than 54 species of
+mollusca, besides three characteristic arctic varieties&mdash;in
+all 57 forms&mdash;have been obtained by Mr. Darbishire. They
+belong without exception to species still living in British or more
+northern seas; eleven of them being exclusively arctic, four common
+to the arctic and British seas, and a large proportion of the
+remainder having a northward range, or, if found at all in the
+southern seas of Britain, being comparatively less abundant. In the
+lowest beds of the drift were large heavy boulders of
+far-transported rocks, glacially polished and scratched on more
+than one side. Underneath the whole we saw the edges of vertical
+slates exposed to view, which here, like the rocks in other parts
+of Wales, both at greater and less elevations, exhibit beneath the
+drift unequivocal marks of prolonged glaciation. The whole deposit
+has much the appearance of an accumulation in shallow water or on a
+beach, and it probably acquired its thickness during the gradual
+subsidence of the coast&mdash;an hypothesis which would require us
+to ascribe to it a high antiquity,
+<a name="page181"></a>since we must allow time, first for its sinking, and then for
+its re-elevation.</p>
+
+<p>The height reached by these fossil shells on Moel Tryfaen is no
+less than 1300 feet&mdash;a most important fact when we consider
+how very few instances we have on record beyond the limits of
+Wales, whether in Europe or North America, of marine shells having
+been found in glacial drift at half the height above indicated. A
+marine molluscous fauna, however, agreeing in character with that
+of Moel Tryfaen, and comprising as many species, has been found in
+drift at Macclesfield and other places in central England,
+sometimes reaching an elevation of 1200 feet.</p>
+
+<p>
+Professor Ramsay<a href="#fn-12.5" name="fnref-12.5"
+id="fnref-12.5"><sup>[5]</sup></a> estimated the probable amount of submergence
+during some part of the glacial period at about 2300 feet; for he was unable to
+distinguish the superficial sands and gravel which reached that high elevation
+from the drift which, at Moel Tryfaen and at lower points, contains shells of
+living species. The evidence of the marine origin of the highest drift is no
+doubt inconclusive in the absence of shells, so great is the resemblance of the
+gravel and sand of a sea beach and of a river&rsquo;s bed, when organic remains
+are wanting; but, on the other hand, when we consider the general rarity of
+shells in drift which we know to be of marine origin, we cannot suppose that,
+in the shelly sands of Moel Tryfaen, we have hit upon the exact uppermost limit
+of marine deposition, or, in other words, a precise measure of the submergence
+of the land beneath the sea since the glacial period.
+</p>
+
+<p>We are gradually obtaining proofs of the larger part of England,
+north of a line drawn from the mouth of the Thames to the Bristol
+Channel, having been under the sea and traversed by floating ice
+since the commencement of the glacial epoch. Among recent
+observations illustrative of this point, I may allude to the
+discovery, by Mr. J. F. Bateman, near Blackpool, in Lancashire,
+fifty miles from the sea, and at the height of 568 feet above its
+level, of till containing rounded and angular stones and marine
+shells, such as <i>Turritella communis, Purpura lapillus, Cardium
+edule,</i> and others, among which <i>Trophon clathratum</i>
+(=<i>Fusus Bamffius</i>), though still surviving in North British
+seas, indicates a cold climate.</p>
+
+<p><i>Erratics near Chichester.</i>&mdash;The most southern
+memorials of ice-action and of a Post-pliocene fauna in Great
+Britain is on the coast of the county of Sussex, about 25 miles
+west of Brighton, and 15 south of Chichester. A marine deposit
+exposed between high and low tide occurs on both sides of the
+<a name="page182"></a>promontory called Selsea Bill, in which Mr. Godwin-Austen found
+thirty-eight species of shells, and the number has since been
+raised to seventy.</p>
+
+<p>This assemblage is interesting because on the whole, while all
+the species are recent, they have a somewhat more southern aspect
+than those of the present British Channel. It is true that about
+forty of them range from British to high northern latitudes; but
+several of them, as, for example, <i>Lutraria rugosa</i> and <i>
+Pecten polymorphous</i>, which are abundant, are not known at
+present to range farther north than the coast of Portugal, and seem
+to indicate a warmer temperature than now prevails on the coast
+where we find them fossil. What renders this curious is the fact
+that the sandy loam in which they occur is overlaid by yellow
+clayey gravel with large erratic blocks which must have been
+drifted into their present position by ice when the climate had
+become much colder. These transported fragments of granite,
+syenite, and greenstone, as well as of Devonian and Silurian rocks,
+may have come from the coast of Normandy and Brittany, and are many
+of them of such large size that we must suppose them to have been
+drifted into their present site by coast-ice. I measured one of
+granite, at Pagham, 21 feet in circumference. In the gravel of this
+drift with erratics are a few littoral shells of living species,
+indicating an ancient coast-line.</p>
+
+<p><b>Glacial Formations of North America.</b>&mdash;In the western
+hemisphere, both in Canada and as far south as the 40th and even
+38th parallel of latitude in the United States, we meet with a
+repetition of all the peculiarities which distinguish the European
+boulder formation. Fragments of rock have travelled for great
+distances, especially from north to south: the surface of the
+subjacent rock is smoothed, striated, and fluted; unstratified mud
+or <i>till</i> containing boulders is associated with strata of
+loam, sand, and clay, usually devoid of fossils. Where shells are
+present, they are of species still living in northern seas, and not
+a few of them identical with those belonging to European drift,
+including most of those already given in Figs. 107 to 112, p. 176.
+The fauna also of the glacial epoch in North America is less rich
+in species than that now inhabiting the adjacent sea, whether in
+the Gulf of St. Lawrence, or off the shores of Maine, or in the Bay
+of Massachusetts.</p>
+
+<p>The extension on the American continent of the range of erratics
+during the Post-pliocene period to lower latitudes than they
+reached in Europe, agrees well with the present southward
+deflection of the isothermal lines, or rather the
+<a name="page183"></a>lines of equal winter temperature. It seems that formerly, as
+now, a more extreme climate and a more abundant supply of ice
+prevailed on the western side of the Atlantic. Another resemblance
+between the distribution of the drift fossils in Europe and North
+America has yet to be pointed out. In Canada and the United States,
+as in Europe, the marine shells are generally confined to very
+moderate elevations above the sea (between 100 and 700 feet), while
+the erratic blocks and the grooved and polished surfaces of rock
+extend to elevations of several thousand feet.</p>
+
+<p>I have already mentioned that in Europe several quadrupeds of
+living, as well as extinct, species were common to pre-glacial and
+post-glacial times. In like manner there is reason to suppose that
+in North America much of the ancient mammalian fauna, together with
+nearly all the invertebrata, lived through the ages of intense
+cold. That in the United States the <i>Mastodon giganteus</i> was
+very abundant after the drift period, is evident from the fact that
+entire skeletons of this animal are met with in bogs and lacustrine
+deposits occupying hollows in the glacial drift. They sometimes
+occur in the bottom even of small ponds recently drained by the
+agriculturist for the sake of the shell-marl. In 1845 no less than
+six skeletons of the same species of Mastodon were found in Warren
+county, New Jersey, six feet below the surface, by a farmer who was
+digging out the rich mud from a small pond which he had drained.
+Five of these skeletons were lying together, and a large part of
+the bones crumbled to pieces as soon as they were exposed to the
+air.</p>
+
+<p>It would be rash, however, to infer from such data that these
+quadrupeds were mired in <i>modern</i> times, unless we use that
+term strictly in a geological sense. I have shown that there is a
+fluviatile deposit in the valley of the Niagara, containing shells
+of the genera <i>Melania, Lymnea, Planorbis, Velvata, Cyclaz, Unio,
+Helix,</i> etc., all of recent species, from which the bones of the
+great Mastodon have been taken in a very perfect state. Yet the
+whole excavation of the ravine, for many miles below the Falls, has
+been slowly effected since that fluviatile deposit was thrown down.
+Other extinct animals accompany the <i>Mastodon giganteus</i> in
+the post-glacial deposits of the United States, and this, taken
+with the fact that so few of the mollusca, even of the commencement
+of the cold period, differ from species now living is important, as
+refuting the hypothesis, for which some have contended, that the
+intensity of the glacial cold annihilated all the species in
+temperate and arctic latitudes.
+</p>
+
+<p>
+<a name="page184"></a><b>Connection of the Predominance of Lakes with Glacial
+Action.</b>&mdash;It was first pointed out by Professor Ramsay in
+1862, that lakes are exceedingly numerous in those countries where
+erratics, striated blocks, and other signs of ice-action abound;
+and that they are comparatively rare in tropical and sub-tropical
+regions. Generally in countries where the winter cold is intense,
+such as Canada, Scandinavia, and Finland, even the plains and
+lowlands are thickly strewn with innumerable ponds and small lakes,
+together with some others of a larger size; while in more temperate
+regions, such as Great Britain, Central and Southern Europe, the
+United States, and New Zealand, lake districts occur in all such
+mountainous tracts as can be proved to have been glaciated in times
+comparatively modern or since the geographical configuration of the
+surface bore a considerable resemblance to that now prevailing. In
+the same countries, beyond the glaciated regions, lakes abruptly
+cease, and in warmer and tropical countries are either entirely
+absent, or consist, as in equatorial Africa, of large sheets of
+water unaccompanied so far as we yet know by numerous smaller ponds
+and tarns.
+</p>
+
+<p>The southern limits of the lake districts of the Northern
+Hemisphere are found at about 40&deg; N. latitude on the American
+continent, and about 50&deg; in Europe, or where the Alps intervene
+four degrees farther south. A large proportion of the smaller lakes
+are dammed up by barriers of unstratified drift, having the exact
+character of the moraines of glaciers, and are termed by geologists
+&ldquo;morainic,&rdquo; but some of them are true rock-basins, and would hold
+water even if all the loose drift now resting on their margins were
+removed.</p>
+
+<p>In a paper read before the Geological Society of London in 1862,
+Professor Ramsay maintained that the first formation of most
+existing lakes took place during the glacial epoch, and was due,
+not to elevation or subsidence, but to actual erosion of their
+basins by glaciers. M. Mortillet in the same year advanced the
+theory that after the Alpine lake-basins had been filled up with
+loose fluviatile deposits, they were re-excavated by the great
+glaciers which passed down the valleys at the time of the greatest
+cold, a doctrine which would attribute to moving ice almost as
+great a capacity of erosion as that which assumed that the original
+basins were scooped out of solid rock by glaciers. It is impossible
+to deny that the mere geographical distribution of lakes points to
+the intimate connection of their origin with the abundance of ice
+during a former excess of cold, but how far the erosive action of
+moving ice has been the sole or even the
+<a name="page185"></a>principal cause of lake-basins, is a question still open to
+discussion.</p>
+
+<p>The lakes of Switzerland and the north of Italy are some of them
+twenty and thirty miles in length, and so deep that their bottoms
+are in some cases from 1000 to 2000 feet beneath the level of the
+sea. It is admitted on all hands that they were once filled with
+ice, and as the existing glaciers polish and grind down, as before
+stated, the surface of the rocks, we are prepared to find that
+every lake-basin in countries once covered by ice should bear the
+marks of superficial glaciation, and also that the ice during its
+advance and retreat should have left behind it much transported
+matter as well as some evidence of its having enlarged the
+pre-existing cavity. But much more than this is demanded by the
+advocates of glacial erosion. They suggest that as the old extinct
+glaciers were several thousand feet thick, they were able in some
+places gradually to scoop out of the solid rock cavities twenty or
+thirty miles in length, and as in the case of Lago Maggiore from a
+thousand to two thousand six hundred feet below the previous level
+of the river-channel, and also that the ice had the power to remove
+from the cavity formed by its grinding action all the materials of
+the missing rocks. A constant supply, it is argued, of fine mud
+issues from the termination of every glacier in the stream which is
+produced by the melting of the ice, and this result of friction is
+exhibited both during winter and summer, affording evidence of the
+continual deepening and widening of the valleys through which
+glaciers pass. As the fine mud is carried away by a river from the
+deep pool which is formed from the base of every cataract, so it
+seems to be imagined that lake-basins may be gradually emptied of
+the mud formed by abrasion during the glacial period.</p>
+
+<p>I am by no means disposed to object to this theory on the ground
+of the insufficiency of the time during which the extreme cold
+endured, but we must carefully consider whether that same time is
+not so vast as to make it probable that other forces, besides the
+motion of glaciers, must have cooperated in converting some parts
+of the ancient valley courses into lake-basins. They who have
+formed the most exalted conceptions of the erosive energy of moving
+ice do not deny that during the period termed &ldquo;Glacial&rdquo; there have
+been movements of the earth&rsquo;s crust sufficient to produce
+oscillations of level in Europe amounting to 1000 feet or more in
+both directions. M. Charpentier, indeed, attributed some of the
+principal changes of climate in Switzerland, during the glacial
+period, to a depression of the central Alps to the
+<a name="page186"></a>extent of 3000 feet, and Swiss geologists have long been
+accustomed to attribute their lake basins, in part, to those
+convulsions by which the shape and course of the valleys may have
+been modified. Our experience, in the lifetime of the present
+generation, of the changes of level witnessed in New Zealand during
+great earthquakes is entirely opposed to the notion that the
+movements, whether upward or downward, are uniform in amount or
+direction throughout areas of indefinite extent. On the contrary,
+the land has been permanently raised in one region several feet or
+yards, and the rise has been found gradually to die out, so as to
+be imperceptible at a distance of twenty miles, and in some areas
+is even exchanged for a simultaneous downward movement of several
+feet.</p>
+
+<p>But, it is asked, if such inequality of movement can have
+contributed towards the production of lake basins, does it not
+leave unexplained the comparative rarity of lakes in tropical and
+subtropical countries. In reply to this question it may be observed
+that in our endeavour to estimate the effects of subterranean
+movements in modifying the superficial geography of a country we
+must remember that each convulsion effects a very slight change. If
+it interferes with the drainage, whether by raising the lower or
+sinking the higher portion of a hydrographical basin, the upheaval
+or depression will only amount to a few feet at a time, and there
+may be an interval of years or centuries before any further
+movement takes place in the same region. In the mean time an
+incipient lake if produced may be filled up with sediment, and the
+recently-formed barrier will then be cut through by the river,
+whereas in a country where glacial conditions prevail no such
+obliteration of the temporary lake-basin would take place; for
+however deep it became by repeated sinking of the upper or rising
+of the lower extremity, being always filled with ice it might
+remain, throughout the greater part of its extent, free from
+sediment or drift until the ice melted at the close of the glacial
+period.</p>
+
+<p>
+One of the most serious objections to the exclusive origin by ice-erosion of
+wide and deep lake-basins arises from their capricious distribution, as for
+example in Piedmont, both to the eastward and westward of Turin, where great
+lakes are wanting,<a href="#fn-12.6" name="fnref-12.6"
+id="fnref-12.6"><sup>[6]</sup></a> although some of the largest extinct
+glaciers descending from Mont Blanc and Monte Rosa came down from the Alps,
+leaving their gigantic moraines in the low country. Here, therefore, we might
+have expected to find lakes of the first magnitude rivalling the contiguous
+Lago Maggiore in importance.
+</p>
+
+<p>
+<a name="page187"></a>A still more striking illustration of the same absence of
+lakes where large glaciers abound is afforded by the Caucasus, a chain more
+than 300 miles long, and the loftiest peaks of which attain heights from 16,000
+to 18,000 feet. This greatest altitude is reached by Elbruz, a mountain in lat.
+43&deg; N. three degrees south of Mont Blanc, but on the other hand 3000 feet
+higher. The present Caucasian glaciers are equal or superior in dimensions to
+those of Switzerland, and like them give rise occasionally to temporary lakes
+by obstructing the course of rivers, and causing great floods when the icy
+barriers give way. Mr. Freshfield, a careful observer, writing in 1869, says:<a
+href="#fn-12.7" name="fnref-12.7" id="fnref-12.7"><sup>[7]</sup></a> &ldquo;A
+total absence of lakes on both sides of the chains is the most marked feature.
+Not only are there no great subalpine sheets of water, like Como or Geneva, but
+mountain tarns, such as the Dauben See on the Gemmi, or the Klonthal See near
+Glarus, are equally wanting.&rdquo; The same author states on the authority of
+the eminent Swiss geologist, Mons. E. Favre, who also explored the Caucasus in
+1868, that moraines of great height and huge erratics of granite and other
+rocks &ldquo;justify the assertion that the present glaciers of the Caucasus,
+like those of the Alps, are only the shadows of their former selves.&rdquo;
+</p>
+
+<p>It seems safe to assume that the chain of lakes, of which the
+Albert Nyanza forms one in equatorial Africa, was due to causes
+other than glacial. Yet if we could imagine a glacial period to
+visit that region filling the lakes with ice and scoring the rocks
+which form their sides and bottoms, we should be unable to decide
+how much the capacity of the basins had been enlarged and the
+surface modified by glacial erosion. The same may be true of the
+Lago Maggiore and Lake Superior, although the present basins of
+both of them afford abundant superficial markings due to
+ice-action.</p>
+
+<p>
+But to whatever combination of causes we attribute the great Alpine lakes one
+thing is clear, namely, that they are, geologically speaking, of modern origin.
+Every one must admit that the upper valley of the Rhone has been chiefly caused
+by fluviatile denudation, and it is obvious that the quantity of matter removed
+from that valley previous to the glacial period would have been amply
+sufficient to fill up with sediment the basin of the Lake of Geneva, supposing
+it to have been in existence, even if its capacity had been many times greater
+than it is now.<a href="#fn-12.8" name="fnref-12.8"
+id="fnref-12.8"><sup>[8]</sup></a>
+</p>
+
+<p>On the whole, it appears to me, in accordance with the views of
+Professor Ramsay, M. Mortillet, Mr. Geikie, and others,
+<a name="page188"></a>that the abrading action of ice has formed some mountain tarns
+and many morainic lakes; but when it is a question of the origin of
+larger and deeper lakes, like those of Switzerland or the north of
+Italy, or inland fresh-water seas, like those of Canada, it will
+probably be found that ice has played a subordinate part in
+comparison with those movements by which changes of level in the
+earth&rsquo;s crust are gradually brought about.
+</p>
+
+<p class="footnote">
+<a name="fn-12.1" id="fn-12.1"></a> <a href="#fnref-12.1">[1]</a>
+Jamieson, Quart. Geol. Journ., 1860, vol. xvi, p. 370.
+</p>
+
+<p class="footnote">
+<a name="fn-12.2" id="fn-12.2"></a> <a href="#fnref-12.2">[2]</a>
+Bryce, Quart. Geol. Journ., vol. xxi, p. 217, 1865.
+</p>
+
+<p class="footnote">
+<a name="fn-12.3" id="fn-12.3"></a> <a href="#fnref-12.3">[3]</a>
+Geikie, Trans. Geol. Soc. Glasgow, vol. i, part ii, p. 68, 1863.
+</p>
+
+<p class="footnote">
+<a name="fn-12.4" id="fn-12.4"></a> <a href="#fnref-12.4">[4]</a>
+Milne Home, Trans. Royal Soc. Edinburgh, vol. xxv, 1868-9.
+</p>
+
+
+<p class="footnote">
+<a name="fn-12.5" id="fn-12.5"></a> <a href="#fnref-12.5">[5]</a>
+Quart. Geol. Journ., 1852, vol. viii, p. 372.
+</p>
+
+<p class="footnote">
+<a name="fn-12.6" id="fn-12.6"></a> <a href="#fnref-12.6">[6]</a>
+Antiquity of Man, p. 313.
+</p>
+
+<p class="footnote">
+<a name="fn-12.7" id="fn-12.7"></a> <a href="#fnref-12.7">[7]</a>
+Travels in Central Caucasus, 1869, p. 452.
+</p>
+
+<p class="footnote">
+<a name="fn-12.8" id="fn-12.8"></a> <a href="#fnref-12.8">[8]</a>
+See Principles, vol. i, p. 420, 10th ed., 1867.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h3><a name="page189"></a>TERTIARY OR CAINOZOIC PERIOD</h3>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap13"></a>CHAPTER XIII.<br/>
+PLIOCENE PERIOD</h2>
+
+<p class="letter">Glacial Formations of Pliocene Age. &mdash;
+Bridlington Beds. &mdash; Glacial Drifts of Ireland. &mdash; Drift
+of Norfolk Cliffs. &mdash; Cromer Forest-bed. &mdash; Aldeby and
+Chillesford Beds. &mdash; Norwich Crag. &mdash; Older Pliocene
+Strata. &mdash; Red Crag of Suffolk. &mdash; Coprolitic Bed of Red
+Crag. &mdash; White or Coralline Crag. &mdash; Relative Age,
+Origin, and Climate of the Crag Deposits. &mdash; Antwerp Crag.
+&mdash; Newer Pliocene Strata of Sicily. &mdash; Newer Pliocene
+Strata of the Upper Val d&rsquo;Arno. &mdash; Older Pliocene of Italy.
+&mdash; Subapennine Strata. &mdash; Older Pliocene Flora of
+Italy.</p>
+
+<p>It will be seen in the description given in the last chapter of
+the Post-pliocene formations of the British Isles that they
+comprise a large proportion of those commonly termed glacial,
+characterised by shells which, although referable to living
+species, usually indicate a colder climate than that now belonging
+to the latitudes where they occur fossil. But in parts of England,
+more especially in Yorkshire, Norfolk, and Suffolk, there are
+superficial formations of clay with glaciated boulders, and of sand
+and pebbles, containing occasional, though rare, patches of shells,
+in which the marine fauna begins to depart from that now inhabiting
+the neighbouring sea, and comprises some species of mollusca not
+yet known as living, as well as extinct varieties of others,
+entitling us to class them as Newer Pliocene, although belonging to
+the close of that period and chronologically on the verge of the
+later or Post-pliocene epoch.</p>
+
+<p><b>Bridlington Drift.</b>&mdash;To this era belongs the
+well-known locality of Bridlington, near the mouth of the Humber,
+in Yorkshire, where about seventy species or well-marked varieties
+of shells have been found on the coast, near the sea-level, in a
+bed of sand several feet thick resting on glacial clay with much
+chalk débris, and covered by a deposit of purple clay with
+glaciated boulders. More than a third of the species in this drift
+are now inhabitants of arctic regions, none of them extending
+southward to the British seas; which is the more remarkable as
+Bridlington is situated in lat. 54&deg;
+<a name="page190"></a>north. Fifteen species are British and Arctic, a very few belong
+to those species which range south of our British seas. Five
+species or well-marked varieties are not known living, namely, the
+variety of <i>Astarte borealis</i> (called <i>A. Withami</i>); <i>
+A. mutabilis</i>; the sinistral form of <i>Tritonium carinatum,
+Cardita analis,</i> and <i>Tellina obliqua,</i> Fig. 120, p. 194.
+Mr. Searles Wood also inclines to consider <i>Nucula
+Cobboldiæ,</i> Fig. 119, p. 194, now absent from the European
+seas and the Atlantic, as specifically distinct from a
+closely-allied shell now living in the seas surrounding Vancouver&rsquo;s
+Island, which some conchologists regard as a variety. <i>Tellina
+obliqua</i> also approaches very near to a shell now living in
+Japan.</p>
+
+<p>
+<b>Glacial Drift of Ireland.</b>&mdash;Marine drift containing the
+last-mentioned Nucula and other glacial shells reaches a height of from 1000 to
+1200 feet in the county of Wexford, south of Dublin. More than eighty species
+have already been obtained from this formation, of which two, <i>Conovulus
+pyramidalis</i> and <i> Nassa monensis,</i> are not known as living; while
+<i>Turritella incrassata</i> and <i>Cypræa lucida</i> no longer inhabit the
+British seas, but occur in the Mediterranean. The great elevation of these
+shells, and the still greater height to which the surface of the rocks in the
+mountainous regions of Ireland have been smoothed and striated by ice-action,
+has led geologists to the opinion that that island, like the greater part of
+England and Scotland, after having been united with the continent of Europe,
+from whence it received the plants and animals now inhabiting it, was in great
+part submerged. The conversion of this and other parts of Great Britain into an
+archipelago was followed by a re-elevation of land and a second continental
+period. After all these changes the final separation of Ireland from Great
+Britain took place, and this event has been supposed to have preceded the
+opening of the straits of Dover.<a href="#fn-13.1" name="fnref-13.1"
+id="fnref-13.1"><sup>[1]</sup></a>
+</p>
+
+<img src="images/fig116.jpg" width="252" height="116" alt=
+"Fig. 116: Tellina balthica" />
+
+<p><b>Drift of Norfolk Cliffs.</b>&mdash;There are deposits of
+boulder clay and till in the Norfolk cliffs principally made up of
+the waste of white chalk and flints which, in the opinion of Mr.
+Searles Wood, jun., and others, are older than the Bridlington
+drift, and contain a larger proportion of shells common to the
+Norwich and Red Crag, including a certain number
+<a name="page191"></a>of extinct forms, but also abounding in <i>Tellina balthica</i>
+(<i>T. solidula,</i> Fig. 116), which is found fossil at
+Bridlington, and living in our British seas, but wanting in all the
+formations, even the newest, afterwards to be described as Crag. As
+the greater part of these drifts are barren of organic remains,
+their classification is at present a matter of great
+uncertainty.</p>
+
+<p>They can nowhere be so advantageously studied as on the coast
+between Happisburgh and Cromer. Here we may see vertical cliffs,
+sometimes 300 feet and more in height, exposed for a distance of
+fifty miles, at the base of which the chalk with flints crops out
+in nearly horizontal strata. Beds of gravel and sand repose on this
+undisturbed chalk. They are often strangely contorted, and envelop
+huge masses or erratics of chalk with layers of vertical flint. I
+measured one of these fragments in 1839 at Sherringham, and found
+it to be eighty feet in its longest diameter. It has been since
+entirely removed by the waves of the sea. In the floor of the chalk
+beneath it the layers of flint were horizontal. Such erratics have
+evidently been moved bodily from their original site, probably by
+the same glacial action which has polished and striated some of the
+accompanying granitic and other boulders, occasionally six feet in
+diameter, which are imbedded in the drift.</p>
+
+<p><b>Cromer Forest-bed.</b>&mdash;Intervening between these
+glacial formations and the subjacent chalk lies what has been
+called the Cromer Forest-bed. This buried forest has been traced
+from Cromer to near Kessingland, a distance of more than forty
+miles, being exposed at certain seasons between high and low water
+mark. It is the remains of an old land and estuarine deposit,
+containing the submerged stumps of trees standing erect with their
+roots in the ancient soil. Associated with the stumps and overlying
+them, are lignite beds with fresh-water shells of recent species,
+and laminated clay without fossils. Through the lignite and
+forest-bed are scattered cones of the Scotch and spruce firs with
+the seeds of recent plants, and the bones of at least twenty
+species of terrestrial mammalia. Among these are two species of
+elephant, <i>E. meridionalis,</i> Nesti, and <i>E. antiquus,</i>
+the former found in the Newer Pliocene beds of the Val d&rsquo;Arno, near
+Florence. In the same bed occur <i>Hippopotamus major, Rhinoceros
+etruscus,</i> both of them also Val d&rsquo;Arno species, many species of
+deer considered by Mr. Boyd Dawkins to be characteristic of warmer
+countries, and also a horse, beaver, and field-mouse. Half of these
+mammalia are extinct, and the rest still survive in Europe. The
+vegetation taken alone
+<a name="page192"></a>does not imply a temperature higher than that now prevailing in
+the British Isles. There must have been a subsidence of the forest
+to the amount of 400 or 500 feet, and a re-elevation of the same to
+an equal extent in order to allow the ancient surface of the chalk
+or covering of soil, on which the forest grew, to be first covered
+with several hundred feet of drift, and then upheaved so that the
+trees should reach their present level. Although the relative
+antiquity of the forest-bed to the overlying glacial till is clear,
+there is some difference of opinion as to its relation to the crag
+presently to be described.</p>
+
+<img src="images/fig117.jpg" width="89" height="133" alt=
+"Fig. 117: Natica helicoides" />
+
+<p><b>Chillesford and Aldeby Beds.</b>&mdash;It is in the counties
+of Norfolk, Suffolk, and Essex, that we obtain our most valuable
+information respecting the British Pliocene strata, whether newer
+or older. They have obtained in those counties the provincial name
+of &ldquo;Crag,&rdquo; applied particularly to masses of shelly sand which have
+long been used in agriculture to fertilise soils deficient in
+calcareous matter. At Chillesford, between Woodbridge and
+Aldborough in Suffolk, and Aldeby, near Beccles, in the same
+county, there occur stratified deposits, apparently older than any
+of the preceding drifts of Yorkshire, Norfolk, and Suffolk. They
+are composed at Chillesford of yellow sands and clays, with much
+mica, forming horizontal beds about twenty feet thick. Messrs.
+Prestwich and Searles Wood, senior, who first described these beds,
+point out that the shells indicate on the whole a colder climate
+than the Red Crag; two-thirds of them being characteristic of high
+latitudes. Among these are <i>Cardium Grœnlandicum, Leda
+limatula, Tritonium carinatum,</i> and <i>Scalaria
+Grœnlandica.</i> In the upper part of the laminated clays a
+skeleton of a whale was found associated with casts of the
+characteristic shells, <i>Nucula Cobboldiæ</i> and <i>Tellina
+obliqua,</i> already referred to as no longer inhabiting our seas,
+and as being extinct varieties if not species. The same shells
+occur in a perfect state in the lower part of the formation. <i>
+Natica helicoides</i> (Fig. 117) is an example of a species
+formerly known only as fossil, but which has now been found living
+in our seas.</p>
+
+<p>At Aldeby, where beds occur decidedly similar in mineral
+character as well as fossil remains, Messrs. Crowfoot and Dowson
+have now obtained sixty-six species of mollusca, comprising the
+Chillesford species and some others. Of these about nine-tenths are
+recent. They are in a perfect state, clearly indicating a cold
+climate; as two-thirds of them are now met with in arctic
+<a name="page193"></a>regions. As a rule, the lamellibranchiate molluscs have both
+valves united, and many of them, such as <i>Mya arenaria,</i> stand
+with the siphonal end upward, as when in a living state. <i>Tellina
+balthica,</i> before mentioned (Fig. 116) as so characteristic of
+the glacial beds, including the drift of Bridlington, has not yet
+been found in deposits of Chillesford and Aldeby age, whether at
+Sudbourn, East Bavent, Horstead, Coltishall, Burgh, or in the
+highest beds overlying the Norwich Crag proper at Bramerton and
+Thorpe.</p>
+
+<p><img src="images/fig118.jpg" width="374" height="259" alt=
+"Fig. 118: &lt;i&gt;Mastodon arvernensis,&lt;/i&gt; third milk molar, left
+side, upper jaw: grinding surface. Norwich Crag, Postwick, also found in Red
+Crag, see p. 197." />
+</p>
+
+<p><b>Norwich or Fluvio-marine Crag.</b>&mdash;The beds above
+alluded to ought, perhaps, to be regarded as beds of passage
+between the glacial formations and those called from a provincial
+name &ldquo;Crag,&rdquo; the newest member of which has been commonly called
+the &ldquo;Norwich Crag.&rdquo; It is chiefly seen in the neighbourhood of
+Norwich, and consists of beds of incoherent sand, loam, and gravel,
+which are exposed to view on both banks of the Yare, as at
+Bramerton and Thorpe. As they contain a mixture of marine, land,
+and fresh-water shells, with bones of fish and mammalia, it is
+clear that these beds have been accumulated at the bottom of a sea
+near the mouth of a river. They form patches rarely exceeding
+twenty feet in thickness, resting on white chalk. At their junction
+with the chalk there invariably intervenes a bed called the
+&ldquo;Stone-bed,&rdquo; composed of unrolled chalk-flints, commonly of large
+size, mingled with the remains of a land fauna comprising <i>
+Mastodon arvernensis, Elephas meridionalis,</i> and an extinct
+species of deer. The mastodon, which is a species characteristic of
+the Pliocene strata of Italy and France, is the most abundant
+fossil, and one not found in the
+<a name="page194"></a>Cromer forest before mentioned. When these flints, probably long
+exposed in the atmosphere, became submerged, they were covered with
+barnacles, and the surface of the chalk became perforated by the
+<i>Pholas crispata,</i> each fossil shell still remaining at the
+bottom of its cylindrical cavity, now filled up with loose sand
+from the incumbent crag. This species of Pholas still exists, and
+drills the rocks between high and low water on the British coast.
+The name of &ldquo;Fluvio-marine&rdquo; has often been given to this formation,
+as no less than twenty species of land and fresh-water shells have
+been found in it. They are all of living species; at least only one
+univalve, <i>Paludina lenta,</i> has any, and that a very doubtful,
+claim to be regarded as extinct.</p>
+
+<p><img src="images/fig119.jpg" width="335" height="123" alt=
+"Fig. 119: Nucula Cobboldiæ; Fig. 120: Tellina obliqua." />
+</p>
+
+<p>
+Of the marine shells, 124 in number, about 18 per cent are extinct, according
+to the latest estimate given me by Mr. Searles Wood; but, for reasons presently
+to be mentioned, this percentage must be only regarded as provisional. It must
+also be borne in mind that the proportion of recent shells would be augmented
+if the uppermost beds at Bramerton, near Norwich, which belong to the most
+modern or Chillesford division of the Crag, had been included, as they were
+formerly, by Mr. Woodward and myself, in the Norwich series. Arctic shells,
+which formed so large a proportion in the Chillesford and Aldeby beds, are more
+rare in the Norwich Crag, though many northern species&mdash;such as
+<i>Rhynchonella psittacea, Scalaria Grœnlandica, Astarte borealis, Panopæa
+Norvegia,</i> and others&mdash;still occur. The <i>Nucula Cobboldiæ</i> and
+<i>Tellina obliqua,</i> Figs. 119 and 120, before mentioned, p. 194, are
+frequent in these beds, as are also <i>Littorina littorea, Cardium edule,</i>
+and <i>Turritella communis,</i> of our seas, proving the littoral origin of the
+beds.
+</p>
+
+<p class="center">
+OLDER PLIOCENE STRATA.
+</p>
+
+<p><b>Red Crag.</b>&mdash;Among the English Pliocene beds the next
+in antiquity is the Red Crag, which often rests immediately on the
+London Clay, as in the county of Essex, illustrated in Fig.
+121.<a name="page195"></a></p>
+
+<p><img src="images/fig121.jpg" width="339" height="76" alt=
+" Fig. 121: Red Crag, London clay and chalk." /></p>
+
+<p>
+It is chiefly in the county of Suffolk that it is found, rarely exceeding
+twenty feet in thickness, and sometimes overlying another Pliocene deposit, the
+Coralline Crag, to be mentioned in the sequel. It has yielded&mdash;exclusive
+of 25 species regarded by Mr. Wood as derivative&mdash;256 species of mollusca,
+of which 65, or 25 per cent, are extinct. Thus, apart from its order of
+superposition, its greater antiquity than the Norwich and glacial beds, already
+described, is proved by the greater departure from the fauna of our seas. It
+may also be observed that in most of the deposits of this Red Crag, the
+northern forms of the Norwich Crag, and of such glacial formations as
+Bridlington, are less numerous, while those having a more southern aspect begin
+to make their appearance. Both the quartzose sand, of which it chiefly
+consists, and the included shells, are most commonly distinguished by a deep
+ferruginous or ochreous colour, whence its name. The shells are often rolled,
+sometimes comminuted, and the beds have much the appearance of having been
+shifting sand-banks, like those now forming on the Dogger-bank, in the sea,
+sixty miles east of the coast of Northumberland. Cross stratification is almost
+always present, the planes of the strata being sometimes directed towards one
+point of the compass, sometimes to the opposite, in beds immediately overlying.
+That such a structure is not deceptive or due to any subsequent concretionary
+rearrangement of particles, or to mere bands of colour produced by the iron, is
+proved by each bed being made up of flat pieces of shell which lie parallel to
+the planes of the smaller strata.
+</p>
+
+<p>
+It has long been suspected that the different patches of Red Crag are not all
+of the same age, although their chronological relation cannot be decided by
+superposition. Separate masses are characterised by shells specifically
+distinct or greatly varying in relative abundance, in a manner implying that
+the deposits containing them were separated by intervals of time. At Butley,
+Tunstall, Sudbourn, and in the Red Crag of Chillesford, the mollusca appear to
+assume their most modern aspect when the climate was colder than when the
+earliest deposits of the same period were formed. At Butley, <i>Nucula
+Cobboldiæ</i>, so common in the Norwich and certain glacial beds, is found, and
+<i>Purpura tetragona</i> (Fig. 122) is very abundant. On the other hand, at
+<a name="page196"></a>Walton-on-the-Naze, in Essex, we seem to have an
+exhibition of the oldest phase of the Red Crag; and a warmer climate seems
+indicated, not only by the absence of many northern forms, but also by the
+abundance of some now living in the British seas and the Mediterranean.
+<i>Voluta Lamberti</i> (see Figs. 123 and 124), an extinct form, which seems to
+have flourished chiefly in the antecedent Coralline Crag period, is still
+represented here by individuals of every age.
+</p>
+
+<img src="images/fig122.jpg" width="97" height="208" alt=
+"Fig. 122: Purpura tetragona." />
+
+<p>The reversed whelk (Fig. 125) is common at Walton, where the
+dextral form of that shell is unknown. Here also we find most
+frequently specimens of lamellibranchiate molluscs, with both the
+valves united, showing that they belonged to this sea of the Upper
+Crag, and were not washed in from an older bed, such as the
+Coralline, in which case the ligament would not have held together
+the valves in strata so often showing signs of the boisterous
+action of the waves. No less than forty species of
+lamellibranchiate molluscs, with double valves, have been collected
+by Mr. Bell from the various localities of the Red Crag.</p>
+
+<p><img src="images/fig123.jpg" width="353" height="329" alt=
+"Fig. 123: Voluta Lamberti; Fig. 124: Voluta Lamberti; Fig. 125: Trophon antiquum." />
+</p>
+
+<p>At and near the base of the Red Crag is a loose bed of
+<a name="page197"></a>brown nodules, first noticed by Professor Henslow as containing
+a large percentage of earthy phosphates. This bed of coprolites (as
+it is called, because they were originally supposed to be the
+fæces of animals) does not always occur at one level, but is
+generally in largest quantity at the junction of the Crag and the
+underlying formation. In thickness it usually varies from six to
+eighteen inches, and in some rare cases amounts to many feet. It
+has been much used in agriculture for manure, as not only the
+nodules, but many of the separate bones associated with them, are
+largely impregnated with phosphate of lime, of which there is
+sometimes as much as sixty per cent. They are not unfrequently
+covered with barnacles, showing that they were not formed as
+concretions in the stratum where they now lie buried, but had been
+previously consolidated. The phosphatic nodules often collect
+fossil crabs and fishes from the London Clay, together with the
+teeth of gigantic sharks. In the same bed have been found many
+ear-bones of whales, and the teeth of <i>Mastodon arvernensis,
+Rhinoceros Schleiermacheri, Tapirus priscus,</i> and Hipparion (a
+quadruped of the horse family), and antlers of a stag, <i>Cervus
+anoceros.</i> Organic remains also of the older chalk and Lias are
+met with, showing how great was the denudation of previous
+formations during the Pliocene period. As the older White Crag,
+presently to be mentioned, contains similar phosphatic nodules near
+its base, those of the Red Crag may be partly derived from this
+source.</p>
+
+<p>
+<b>White or Coralline Crag.</b>&mdash;The lower or Coralline Crag is of very
+limited extent, ranging over an area about twenty miles in length, and three or
+four in breadth, between the rivers Stour and Alde, in Suffolk. It is generally
+calcareous and marly&mdash;often a mass of comminuted shells, and the remains
+of bryozoa<a href="#fn-13.2" name="fnref-13.2"
+id="fnref-13.2"><sup>[2]</sup></a> (or polyzoa), passing occasionally into a
+soft building-stone. At Sudbourn and Gedgrave, near Orford, this building-stone
+has been largely quarried. At some places in the neighbourhood the softer mass
+is divided by thin flags of hard limestone, and bryozoa placed in the upright
+position in which they grew. From the abundance of these coralloid mollusca the
+lowest or White Crag obtained its popular name, but true corals, as now
+defined, or zoantharia, are very rare in this formation.
+</p>
+
+<p>
+<a name="page198"></a>The Coralline Crag rarely, if ever, attains a thickness of
+thirty feet in any one section. Mr. Prestwich imagines that if the
+beds found at different localities were united in the probable
+order of their succession, they might exceed eighty feet in
+thickness, but Mr. Searles Wood does not believe in the possibility
+of establishing such a chronological succession by aid of the
+organic remains, and questions whether proof could be obtained of
+more than forty feet. I was unable to come to any satisfactory
+opinion on the subject, although at Orford, especially at Gedgrave,
+in the neighbourhood of that place, I saw many sections in pits,
+where this crag is cut through. These pits are so unconnected, and
+of such limited extent, that no continuous section of any length
+can be obtained, so that speculations as to the thickness of the
+whole deposit must be very vague. At the base of the formation at
+Sutton a bed of phosphatic nodules, very similar to that before
+alluded to in the Red Crag, with remains of mammalia, has been met
+with.</p>
+
+<p><img src="images/fig126.jpg" width="336" height="107" alt=
+"Fig. 126: Section near Woodbridge, in Suffolk." /></p>
+
+<p>
+Whenever the Red and Coralline Crag occur in the same district,
+the Red Crag lies uppermost; and in some cases, as in the section
+represented in Fig. 126, which I had an opportunity of seeing
+exposed to view in 1839, it is clear that the older deposit, or
+Coralline Crag, <i>b</i>, had suffered denudation, before the newer
+formation, <i>a</i>, was thrown down upon it. At D there was not
+only seen a distinct cliff, eight or ten feet high, of Coralline
+Crag, running in a direction N.E. and S.W., against which the Red
+Crag abuts with its horizontal layers, but this cliff occasionally
+overhangs. The rock composing it is drilled everywhere by <i>
+Pholades</i>, the holes which they perforated having been
+afterwards filled with sand, and covered over when the newer beds
+were thrown down. The older formation is shown by its fossils to
+have accumulated in a deeper sea, and contains none of those
+littoral forms such as the limpet, <i>Patella</i>, found in the Red
+Crag. So great an amount of denudation could scarcely take place,
+in such incoherent materials, without some of the fossils of the
+inferior beds becoming mixed up with the overlying crag, so that
+considerable difficulty must be occasionally experienced by
+<a name="page199"></a>the palæontologist in deciding which species belong
+severally to each group.</p>
+
+<p><img src="images/fig127.jpg" width="403" height="440" alt=
+"Fig. 127: Fascicularia aurantium, from the inferior or Coralline Crag,
+Suffolk. Fig. 128: Astarte Omalii, species common to Upper and Lower Crag." />
+</p>
+
+<p>Mr. Searles Wood estimates the total number of marine testaceous
+mollusca of the Coralline Crag at 350, of which 110 are not known
+as living, being in the proportion of thirty-one per cent extinct.
+No less than 130 species of bryozoa have been found in the
+Coralline Crag, and some belong to genera unknown in the living
+creation, and of a very peculiar structure; as, for example, that
+represented in Fig. 127, which is one of several species having a
+globular form. Among the testacea the genus <i>Astarte</i> (see
+Fig. 128) is largely represented, no less than fourteen species
+being known, and many of these being rich in individuals. There is
+an absence of genera peculiar to hot climates, such as <i>Conus,
+Oliva, Fasciolaria, Crassatella</i>, and others. The absence also
+of large cowries (<i>Cyprea</i>), those found belonging
+<a name="page200"></a>exclusively to the section <i>Trivia</i>, is remarkable. The
+large volute, called <i>Voluta Lamberti</i> (Fig. 123, p. 196), may
+seem an exception; but it differs in form from the volutes of the
+torrid zone, and, like the living <i>Voluta Magellanica</i>, must
+have been fitted for an extra-tropical climate.</p>
+
+<p><img src="images/fig129.jpg" width="410" height="184" alt=
+"Fig. 129: Lingula Dumortieri. Fig. 130: Pyrula reticulata. Fig. 131:
+Temnechinus excavatus." />
+</p>
+
+<p>The occurrence of a species of <i>Lingula</i> at Sutton (see
+Fig. 129) is worthy of remark, as these <i>Brachiopoda</i> seem now
+confined to more equatorial latitudes; and the same may be said
+still more decidedly of a species of <i>Pyrula</i>, supposed by Mr.
+Wood to be identical with <i>P. reticulata</i> (Fig. 130), now
+living in the Indian Ocean. A genus also of echinoderms, called by
+Professor Forbes <i>Temnechinus</i> (Fig. 131), occurs in the Red
+and Coralline Crag of Suffolk, and until lately was unknown in a
+living state, but it has been brought to light as an existing form
+by the deep-sea dredgings, both of the United States survey, off
+Florida, at a depth of from 180 to 480 feet, and more recently
+(1869), in the British seas, during the explorations of the
+&ldquo;Porcupine.&rdquo;</p>
+
+<p>
+<b>Climate of the Crag Deposits.</b>&mdash;One of the most interesting
+conclusions deduced from a careful comparison of the shells of the British
+Pliocene strata and the fauna of our present seas has been pointed out by
+Professor E. Forbes. It appears that, during the Glacial period, a period
+intermediate, as we have seen, between that of the Crag and our own time, many
+shells, previously established in the temperate zone, retreated southward to
+avoid an uncongenial climate, and they have been found fossil in the Newer
+Pliocene strata of Sicily, Southern Italy, and the Grecian Archipelago, where
+they may have enjoyed, during the era of floating icebergs, a climate
+resembling that now prevailing in higher European latitudes.<a href="#fn-13.3"
+name="fnref-13.3" id="fnref-13.3"><sup>[3]</sup></a> The Professor gave a list
+of fifty shells which inhabited the British seas while the Coralline and Red
+Crag were forming, and which, though now living in our seas, <a
+name="page201"></a>were wanting, as far as was then known, in the glacial
+deposits. Some few of these species have subsequently been found in the glacial
+drift, but the general conclusion of Forbes remains unshaken.
+</p>
+
+<p>The transport of blocks by ice, when the Red Crag was being
+deposited, appears to me evident from the large size of some huge,
+irregular, quite unrounded chalk flints, retaining their white
+coating, and 2 feet long by 18 inches broad, in beds worked for
+phosphatic nodules at Foxhall, four miles south-east of Ipswich.
+These must have been tranquilly drifted to the spot by floating
+ice. Mr. Prestwich also mentions the occurrence of a large block of
+porphyry in the base of the Coralline Crag at Sutton, which would
+imply that the ice-action had begun in our seas even in this older
+period. The cold seems to have gone on increasing from the time of
+the Coralline to that of the Norwich Crag, and became more and more
+severe, not perhaps without some oscillations of temperature, until
+it reached its maximum in what has been called the Glacial period,
+or at the close of the Newer Pliocene, and in the Post-pliocene
+periods.</p>
+
+<p>
+<b>Relation of the Fauna of the Crag to that of the recent Seas.</b>&mdash;By
+far the greater number of the recent marine species occurring in the several
+Crag formations are still inhabitants of the British seas; but even these
+differ considerably in their relative abundance, some of the commonest of the
+Crag shells being now extremely scarce&mdash;as, for example, <i>Buccinum
+Dalei</i>&mdash;while others, rarely met with in a fossil state, are now very
+common, as <i>Murex erinaceus</i> and <i>Cardium echinatum.</i> Some of the
+species also, the identity of which with the living would not be disputed by
+any conchologist, are nevertheless distinguishable as varieties, whether by
+slight deviations in form or a difference in average dimensions. Since Mr.
+Searles Wood first described the marine testacea of the Crags, the additions
+made to that fossil fauna have not been considerable, whereas we have made in
+the same period immense progress in our knowledge of the living testacea of the
+British and arctic seas, and of the Mediterranean. By this means the naturalist
+has been enabled to identify with existing species many forms previously
+supposed to be extinct.
+</p>
+
+<p>In the forthcoming supplement to the invaluable monograph
+communicated by Mr. Wood to the Palæontographical Society, in
+which he has completed his figures and descriptions of the British
+crag shells of every age, list will be found of all the fossil
+shells, of which a summary is given in the table, p. 202.</p>
+
+<p>
+<a name="page202"></a>To begin with the uppermost or Chillesford beds, it will be seen
+that about 9 per cent only are extinct, or not known as living,
+whereas in the Norwich, which succeeds in the descending order,
+seventeen in a hundred are extinct. Formerly, when the Norwich or
+Fluvio-marine Crag was spoken of, both these formations were
+included under the same head, for both at Bramerton and Thorpe, the
+chief localities where the Norwich Crag was studied, an overlying
+deposit occurs referable to the Chillesford age. If now the two
+were fused together as of old, their shells would, according to Mr.
+Wood, yield a percentage of fifteen in a hundred of species extinct
+or not known as living.</p>
+
+<p class="center">
+NUMBER OF KNOWN SPECIES OF MARINE TESTACEA IN THE CRAG.
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" width="60%" summary="Column 2:
+Total number, Column 3: Not known as living, Column 4: Percentage of Shells not
+known as living">
+<tr>
+<td align="center" colspan="4"><small>CHILLESFORD AND ALDEBY
+BEDS</small></td>
+</tr>
+
+<tr>
+<td >&nbsp;</td>
+<td align="center" valign="bottom">Total<br/>
+number</td>
+<td align="center" valign="bottom">Not known<br/>
+as living</td>
+<td align="center" valign="bottom">Percentage of<br/>
+Shells not known<br/>
+as living</td>
+</tr>
+
+<tr>
+<td >Bivalves</td>
+<td align="center">&nbsp; 61</td>
+<td align="center">&nbsp; 4</td>
+<td align="center" valign="middle" rowspan="3">&nbsp;
+9&middot;5</td>
+</tr>
+
+<tr>
+<td >Univalves</td>
+<td align="center">&nbsp; 33</td>
+<td align="center">&nbsp; 5</td>
+</tr>
+
+<tr>
+<td >Brachiopods</td>
+<td align="center">&nbsp; &nbsp; 0</td>
+<td align="center">&nbsp; 0</td>
+</tr>
+
+<tr>
+<td align="center" colspan="4"><small>NORWICH OR FLUVIO-MARINE
+CRAG</small></td>
+</tr>
+
+<tr>
+<td >Bivalves</td>
+<td align="center">&nbsp; 61</td>
+<td align="center">10</td>
+<td align="center" valign="middle" rowspan="3">17&middot;5</td>
+</tr>
+
+<tr>
+<td >Univalves</td>
+<td align="center">&nbsp; 64</td>
+<td align="center">12</td>
+</tr>
+
+<tr>
+<td >Brachiopods</td>
+<td align="center">&nbsp; &nbsp; 1</td>
+<td align="center">&nbsp; 0</td>
+</tr>
+
+<tr>
+<td align="center" colspan="4"><small>RED CRAG<br/>
+<i>(Exclusive to many derivative shells)</i></small></td>
+</tr>
+
+<tr>
+<td >Bivalves</td>
+<td align="center">128</td>
+<td align="center">31</td>
+<td align="center" valign="middle" rowspan="3">25&middot;0</td>
+</tr>
+
+<tr>
+<td >Univalves</td>
+<td align="center">127</td>
+<td align="center">33</td>
+</tr>
+
+<tr>
+<td >Brachiopods</td>
+<td align="center">&nbsp; &nbsp; 1</td>
+<td align="center">&nbsp; 1</td>
+</tr>
+
+<tr>
+<td align="center" colspan="4"><small>CORALLINE CRAG</small></td>
+</tr>
+
+<tr>
+<td >Bivalves</td>
+<td align="center">161</td>
+<td align="center">47</td>
+<td align="center" valign="middle" rowspan="3">31&middot;5</td>
+</tr>
+
+<tr>
+<td >Univalves</td>
+<td align="center">184</td>
+<td align="center">60</td>
+</tr>
+
+<tr>
+<td >Brachiopods</td>
+<td align="center">&nbsp; &nbsp; 5</td>
+<td align="center">&nbsp; 3</td>
+</tr>
+</table>
+
+<p>To come next to the Red Crag, the reader will observe that a
+percentage of 25 is given of shells unknown as living, and this
+increases to 31 in the antecedent Coralline Crag. But the gap
+between these two stages of our Pliocene deposits is really wider
+than these numbers would indicate, for several reasons. In the
+first place, the Coralline Crag is more strictly the product of a
+single period, the Red Crag, as we have seen, consisting of
+separate and independent patches, slightly varying in age, of which
+the newest is probably not much anterior to the Norwich Crag.
+Secondly, there was a great change of conditions, both as to
+the
+<a name="page203"></a>depth of the sea and climate, between the periods of the
+Coralline and Red Crag, causing the fauna in each to differ far
+more widely than would appear from the above numerical results.</p>
+
+<p>The value of the analysis given in the above table of the shells
+of the Red and Coralline Crags is in no small degree enhanced by
+the fact that they were all either collected by Mr. Wood himself,
+or obtained by him direct from their discoverers, so that he was
+enabled in each case to test their authenticity, and as far as
+possible to avoid those errors which arise from confounding
+together shells belonging to the sea of a newer deposit, and those
+washed into it from a formation of older date. The danger of this
+confusion may be conceived when we remember that the number of
+species rejected from the Red Crag as derivative by Mr. Wood is no
+less than 25. Some geologists have held that on the same grounds it
+is necessary to exclude as spurious some of the species found in
+the Norwich Crag proper; but Mr. Wood does not entertain this view,
+believing that the spurious shells which have sometimes found their
+way into the lists of this crag have been introduced by want of
+care from strata of Red Crag.</p>
+
+<p>There can be no doubt, on the other hand, that conchologists
+have occasionally rejected from the Red and Norwich Crags, as
+derivative, shells which really belonged to the seas of those
+periods, because they were extinct or unknown as living, which in
+their eyes afforded sufficient ground for suspecting them to be
+intruders. The derivative origin of a species may sometimes be
+indicated by the extreme scarcity of the individuals, their colour,
+and worn condition; whereas an opposite conclusion may be arrived
+at by the integrity of the shells, especially when they are of
+delicate and tender structure, or their abundance, and, in the case
+of the lamellibranchiata, by their being held together by the
+ligament, which often happens when the shells have been so broken
+that little more than the hinges of the two valves are preserved.
+As to the univalves, I have seen from a pit of Red Crag, near
+Woodbridge, a large individual of the extinct <i>Voluta
+Lamberti</i>, seven inches in length, of which the lip, then
+perfect, had in former stages of its growth been frequently broken,
+and as often repaired. It had evidently lived in the sea of the Red
+Crag, where it had been exposed to rough usage, and sustained
+injuries like those which the reversed whelk, <i>Trophon
+antiquum</i>, so characteristic of the same formation, often
+exhibits. Additional proofs, however, have lately been obtained by
+Mr. Searles Wood that this
+<a name="page204"></a>shell had not died out in the era of the Red Crag by the
+discovery of the same fossil near Southwold, in beds of the later
+Norwich Crag.</p>
+
+<p><b>Antwerp Crag.</b>&mdash;Strata of the same age as the Red and
+Coralline Crag of Suffolk have been long known in the country round
+Antwerp, and on the banks of the Scheldt, below that city; and the
+lowest division, or Black Crag, there found, is shown by the shells
+to be somewhat more ancient than any of our British series, and
+probably forms the first links of a downward passage from the
+strata of the Pliocene to those of the Upper Miocene period.</p>
+
+<img src="images/fig132.jpg" width="90" height="213" alt=
+"Fig. 132: Murex vaginatus" />
+
+<p>
+<b>Newer Pliocene Strata of Sicily.</b>&mdash;At several points north of
+Catania, on the eastern sea-coast of Sicily&mdash;as at Aci-Castello, for
+example, Trezza, and Nizzeti&mdash;marine strata, associated with volcanic
+tuffs and basaltic lavas, are seen, which belong to a period when the first
+igneous eruptions of Mount Etna were taking place in a shallow bay of the
+Mediterranean. They contain numerous fossil shells, and out of 142 species that
+have been collected all but eleven are identical with species now living. Some
+few of these eleven shells may possibly still linger in the depths of the
+Mediterranean, like <i>Murex vaginatus</i>, see Fig. 132. The last-mentioned
+shell had already become rare when the associated marine and volcanic strata
+above alluded to were formed. On the whole, the modern character of the
+testaceous fauna under consideration is expressed not only by the small
+proportion of extinct species, but by the relative number of individuals by
+which most of the other species are represented, for the proportion agrees with
+that observed in the present fauna of the Mediterranean. The rarity of
+individuals in the extinct species is such as to imply that they were already
+on the point of dying out, having flourished chiefly in the earlier Pliocene
+times, when the Subapennine strata were in progress.
+</p>
+
+<p>
+Yet since the accumulation of these Newer Pliocene sands and clays, the whole
+cone of Etna, 11,000 feet in height and about 90 miles in circumference at its
+base, has been slowly built up; an operation requiring many tens of thousands
+of years for its accomplishment, and to estimate the magnitude of which it is
+necessary to study in detail the internal structure of the mountain, and to see
+the proofs of its double axis, or the evidence of the lavas of the present
+great centre of eruption having gradually overwhelmed and enveloped a <a
+name="page205"></a>more ancient cone, situated 3&frac12; miles to the east of
+the present one.<a href="#fn-13.4" name="fnref-13.4"
+id="fnref-13.4"><sup>[4]</sup></a>
+</p>
+
+<p>It appears that while Etna was increasing in bulk by a series of
+eruptions, its whole mass, comprising the foundations of subaqueous
+origin above alluded to, was undergoing a slow upheaval, by which
+those marine strata were raised to the height of 1200 feet above
+the sea, as seen at Catera, and perhaps to greater heights, for we
+cannot trace their extension westward, owing to the dense and
+continuous covering of modern lava under which they are buried.
+During the gradual rise of these Newer Pliocene formations
+(consisting of clays, sands, and basalts) other strata of
+Post-pliocene date, marine as well as fluviatile, accumulated round
+the base of the mountain, and these, in their turn, partook of the
+upward movement, so that several inland cliffs and terraces at low
+levels, due partly to the action of the sea and partly to the river
+Simeto, originated in succession. Fossil remains of the elephant,
+and other extinct quadrupeds, have been found in these
+Post-Pliocene strata, associated with recent shells.</p>
+
+<p>There is probably no part of Europe where the Newer Pliocene
+formations enter so largely into the structure of the earth&rsquo;s
+crust, or rise to such heights above the level of the sea, as
+Sicily. They cover nearly half the island, and near its centre, at
+Castrogiovanni, reach an elevation of 3000 feet. They consist
+principally of two divisions, the upper calcareous and the lower
+argillaceous, both of which may be seen at Syracuse, Girgenti, and
+Castrogiovanni. According to Philippi, to whom we are indebted for
+the best account of the tertiary shells of this island, thirty-five
+species out of one hundred and twenty-four obtained from the beds
+in central Sicily are extinct.</p>
+
+<p>A geologist, accustomed to see nearly all the Newer Pliocene
+formations in the north of Europe occupying low grounds and very
+incoherent in texture, is naturally surprised to behold formations
+of the same age so solid and stony, of such thickness, and
+attaining so great an elevation above the level of the sea. The
+upper or calcareous member of this group in Sicily consists in some
+places of a yellowish-white stone, like the Calcaire Grossier of
+Paris; in others, of a rock nearly as compact as marble. Its
+aggregate thickness amounts sometimes to 700 or 800 feet. It
+usually occurs in regular horizontal beds, and is occasionally
+intersected by deep valleys, such as those of Sortino and
+Pentalica,
+<a name="page206"></a>in which are numerous caverns. The fossils are in every stage of
+preservation, from shells retaining portions of their animal matter
+and colour to others which are mere casts. The limestone passes
+downward into a sandstone and conglomerate, below which is clay and
+blue marl, from which perfect shells and corals may be disengaged.
+The clay sometimes alternates with yellow sand.</p>
+
+<p>South of the plain of Catania is a region in which the tertiary
+beds are intermixed with volcanic matter, which has been for the
+most part the product of submarine eruptions. It appears that,
+while the clay, sand, and yellow limestone before mentioned were in
+course of deposition at the bottom of the sea, volcanoes burst out
+beneath the waters, like that of Graham Island, in 1831, and these
+explosions recurred again and again at distant intervals of time.
+Volcanic ashes and sand were showered down and spread by the waves
+and currents so as to form strata of tuff, which are found
+intercalated between beds of limestone and clay containing marine
+shells, the thickness of the whole mass exceeding 2000 feet. The
+fissures through which the lava rose may be seen in many places,
+forming what are called <i>dikes.</i></p>
+
+<p><img src="images/fig133.jpg" width="336" height="321" alt=
+"Fig. 133: Pecten jacobæus" /></p>
+
+<p>No shell is more conspicuous in these Sicilian strata than the
+great scallop, <i>Pecten jacobæus</i> (Fig. 133), now so
+common in the neighbouring seas. The more we reflect on the
+preponderating number of this and other recent shells, the more
+<a name="page207"></a>we are surprised at the great thickness, solidity, and height
+above the sea of the rocky masses in which they are entombed, and
+the vast amount of geographical change which has taken place since
+their origin. It must be remembered that, before they began to
+emerge, the uppermost strata of the whole must have been deposited
+under water. In order, therefore, to form a just conception of
+their antiquity, we must first examine singly the innumerable
+minute parts of which the whole is made up, the successive beds of
+shells, corals, volcanic ashes, conglomerates, and sheets of lava;
+and we must afterwards contemplate the time required for the
+gradual upheaval of the rocks, and the excavation of the valleys.
+The historical period seems scarcely to form an appreciable unit in
+this computation, for we find ancient Greek temples, like those of
+Girgenti (Agrigentum), built of the modern limestone of which we
+are speaking, and resting on a hill composed of the same; the site
+having remained to all appearances unaltered since the Greeks first
+colonised the island.</p>
+
+<p>It follows, from the modern geological date of these rocks, that
+the fauna and flora of a large part of Sicily are of higher
+antiquity than the country itself. The greater part of the island
+has been raised above the sea since the epoch of existing species,
+and the animals and plants now inhabiting it must have migrated
+from adjacent countries, with whose productions the species are now
+identical. The average duration of species would seem to be so
+great that they are destined to outlive many important changes in
+the configuration of the earth&rsquo;s surface, and hence the necessity
+for those innumerable contrivances by which they are enabled to
+extend their range to new lands as they are formed, and to escape
+from those which sink beneath the sea.</p>
+
+<p><b>Newer Pliocene Strata of the Upper Val D&rsquo;arno.</b>&mdash;When
+we ascend the Arno for about ten miles above Florence, we arrive at
+a deep narrow valley called the Upper Val d&rsquo;Arno, which appears
+once to have been a lake, at a time when the valley below Florence
+was an arm of the sea. The horizontal lacustrine strata of this
+upper basin are twelve miles long and two broad. The depression
+which they fill has been excavated out of Eocene and Cretaceous
+rocks, which form everywhere the sides of the valley in highly
+inclined stratification. The thickness of the more modern and
+unconformable beds is about 750 feet, of which the upper 200 feet
+consist of Newer Pliocene strata, while the lower are Older
+Pliocene. The newer series are made up of sands and a conglomerate
+called &ldquo;sansino.&rdquo; Among the imbedded fossil
+<a name="page208"></a>mammalia are <i>Mastodon arvernensis, Elephas meridionalis,
+Rhinoceros etruscus, Hippopotamus major,</i> and remains of the
+genera bear, hyæna, and felis, nearly all of which occur in
+the Cromer forest-bed (see Chap. 13, p. 191).</p>
+
+<p>In the same upper strata are found, according to M. Gaudin, the
+leaves and cones of <i>Glyptostrobus europæus</i>, a plant
+closely allied to <i>G. heterophyllus</i>, now inhabiting the north
+of China and Japan. This conifer had a wide range in time, having
+been traced back to the Lower Miocene strata of Switzerland, and
+being common at Œningen in the Upper Miocene, as we shall see
+in the sequel (p. 218).</p>
+
+<p><b>Older Pliocene of Italy.&mdash;Subapennine
+Strata.</b>&mdash;The Apennines, it is well-known, are composed
+chiefly of Secondary or Mesozoic rocks, forming a chain which
+branches off from the Ligurian Alps and passes down the middle of
+the Italian peninsula. At the foot of these mountains, on the side
+both of the Adriatic and the Mediterranean, are found a series of
+tertiary strata, which form, for the most part, a line of low hills
+occupying the space between the older chain and the sea. Brocchi
+was the first Italian geologist who described this newer group in
+detail, giving it the name of the Subapennine. Though chiefly
+composed of Older Pliocene strata, it belongs, nevertheless, in
+part, both to older and newer members of the tertiary series. The
+strata, for example, of the Superga, near Turin, are Miocene; those
+of Asti and Parma Older Pliocene, as is the blue marl of Sienna;
+while the shells of the incumbent yellow sand of the same territory
+approach more nearly to the recent fauna of the Mediterranean, and
+may be Newer Pliocene.</p>
+
+<p>We have seen that most of the fossil shells of the Older
+Pliocene strata of Suffolk which are of recent species are
+identical with testacea now living in British seas, yet some of
+them belong to Mediterranean species, and a few even of the genera
+are those of warmer climates. We might therefore expect, in
+studying the fossils of corresponding age in countries bordering
+the Mediterranean, to find among them some species and genera of
+warmer latitudes. Accordingly, in the marls belonging to this
+period at Asti, Parma, Sienna, and parts of the Tuscan and Roman
+territories, we observe the genera <i>Conus, Cypræa,
+Strombus, Pyrula, Mitra, Fasciolaria, Sigaretus, Delphinula,
+Ancillaria, Oliva, Terebellum, Terebra, Perna, Plicatula,</i> and
+<i>Corbis</i>, some characteristic of tropical seas, others
+represented by species more numerous or of larger size than those
+now proper to the Mediterranean.</p>
+
+<p><b>Older Pliocene Flora of Italy.</b>&mdash;I have already
+alluded to the Newer Pliocene deposits of the Upper Val d&rsquo;Arno
+above
+<a name="page209"></a>Florence, and stated that below those sands and conglomerates,
+containing the remains of the <i>Elephas meridionalis</i> and other
+associated quadrupeds, lie an older horizontal and conformable
+series of beds, which may be classed as Older Pliocene. They
+consist of blue clays with some subordinate layers of lignite, and
+exhibit a richer flora than the overlying Newer Pliocene beds, and
+one receding farther from the existing vegetation of Europe. They
+also comprise more species common to the antecedent Miocene period.
+Among the genera of flowering plants, M. Gaudin enumerates pine,
+oak, evergreen oak, plum, plane, alder, elm, fig, laurel, maple,
+walnut, birch, buckthorn, hickory, sumach, sarsaparilla, sassafras,
+cinnamon, Glyptostrobus, Taxodium, Sequoia, Persea, Oreodaphne
+(Fig. 134), Cassia, and Psoralea, and some others. This assemblage
+of plants indicates a warm climate, but not so subtropical an one
+as that of the Upper Miocene period, which will presently be
+considered.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig134.jpg" width="421" height="320" alt="Fig. 134: Creodaphne
+Heerii. Fig. 135: Liquidambar europæum, var. trilobatum" />
+<p class="caption">ig. 134: <i>Creodaphne Heerii</i>.<br/>
+Leaf<a href="#fn-13.5" name="fnref-13.5"
+id="fnref-13.5"><sup>[5]</sup></a><br/>
+Fig. 135: <i>Liquidambar europæum</i>, var. <i>trilobatum</i>, A. Br.
+(sometimes four-lobed, and more commonly five-lobed).<br/>
+<i>a.</i> Leaf. <i>b.</i> Part of same. <i>c.</i> Fruit. <i>d.</i> Seed
+Œningen.<br/></p>
+</div>
+
+<p>
+M. Gaudin, jointly with the Marquis Strozzi, has thrown much light on the
+botany of beds of the same age in another part of Tuscany, at a place called
+Montajone, between the rivers Elsa and Evola, where, among other plants, is
+found the <i>Oreodaphne Heerii</i>, Gaud. (see Fig. 134), which is probably
+only a variety of <i>Oreodaphne foetens</i>, or the laurel called <a
+name="page210"></a>the Til in Madeira, where, as in the Canaries, it
+constitutes a large portion of the native woods, but cannot now endure the
+climate of Europe. In the fossil specimens the same glands or protuberances are
+preserved<a href="#fn-13.6" name="fnref-13.6"
+id="fnref-13.6"><sup>[6]</sup></a> (see Fig. 134) as those which are seen in
+the axils of the primary veins of the leaves in the recent Til. Another plant
+also indicating a warmer climate is the <i> Liquidambar europæum</i>, Brong.
+(see Fig. 135), a species nearly allied to <i>L. styracifluum</i>, L., which
+flourishes in most places in the Southern States of North America, on the
+borders of the Gulf of Mexico.
+</p>
+
+<p class="footnote">
+<a name="fn-13.1" id="fn-13.1"></a> <a href="#fnref-13.1">[1]</a>
+See Antiquity of Man, chap. xiv.
+</p>
+
+<p class="footnote">
+<a name="fn-13.2" id="fn-13.2"></a> <a href="#fnref-13.2">[2]</a>
+Ehrenberg proposed in 1831 the term <i> Bryozoum</i>, or
+&ldquo;Moss-animal,&rdquo; for the molluscous or ascidian form of polyp,
+characterised by having two openings to the digestive sack, as in <i>Eschara,
+Flustra, Retepora,</i> and other zoophytes popularly included in the corals,
+but now classed by naturalists as mollusca. The term <i>Polyzoum,</i>
+synonymous with <i> Bryozoum,</i> was, it seems, proposed in 1830, or the year
+before, by Mr. J. O. Thompson.
+</p>
+
+<p class="footnote">
+<a name="fn-13.3" id="fn-13.3"></a> <a href="#fnref-13.3">[3]</a>
+E. Forbes Mem. Geol. Survey of Gt. Brit., vol. i, p. 386.
+</p>
+
+<p class="footnote">
+<a name="fn-13.4" id="fn-13.4"></a> <a href="#fnref-13.4">[4]</a>
+See a Memoir on the Lavas and Mode of Origin of Mount Etna by the Author in
+Phil. Trans., 1858.
+</p>
+
+<p class="footnote">
+<a name="fn-13.5" id="fn-13.5"></a> <a href="#fnref-13.5">[5]</a>
+Feuilles fossiles de la Toscane.
+</p>
+
+<p class="footnote">
+<a name="fn-13.6" id="fn-13.6"></a> <a href="#fnref-13.6">[6]</a>
+Contributions à la Flore fossile Italienne. Gaudin and Strozzi. Plate 11, Fig.
+3. Gaudin, p. 22.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap14"></a><a name="page211"></a>CHAPTER XIV.<br/>
+MIOCENE PERIOD&mdash;UPPER MIOCENE.</h2>
+
+<p class="letter">Upper Miocene Strata of France&mdash;Faluns of
+Touraine. &mdash; Tropical Climate implied by Testacea. &mdash;
+Proportion of recent Species of Shells. &mdash; faluns more ancient
+than the Suffolk Crag. &mdash; Upper Miocene of Bordeaux and the
+South of France. &mdash; Upper Miocene of Œningen, in
+Switzerland. &mdash; Plants of the Upper Fresh-water Molasse.
+&mdash; Fossil Fruit and Flowers as well as Leaves. &mdash; Insects
+of the Upper Molasse. &mdash; Middle or Marine Molasse of
+Switzerland. &mdash; Upper Miocene Beds of the Bolderberg, in
+Belgium. &mdash; Vienna Basin. &mdash; Upper Miocene of Italy and
+Greece. &mdash; Upper Miocene of India; Siwalik Hills. &mdash;
+Older Pliocene and Miocene of the United States.</p>
+
+<p><b>Upper Miocene Strata of France&mdash;Faluns of
+Touraine.</b>&mdash;The strata which we meet with next in the
+descending order are those called by many geologists &ldquo;Middle
+Tertiary,&rdquo; for which in 1833 I proposed the name of Miocene,
+selecting the &ldquo;faluns&rdquo; of the valley of the Loire, in
+France, as my example or type. I shall now call these falunian
+deposits Upper Miocene, to distinguish them from others to which
+the name of Lower Miocene will be given.</p>
+
+<p>No British strata have a distinct claim to be regarded as Upper
+Miocene, and as the Lower Miocene are also but feebly represented
+in the British Isles, we must refer to foreign examples in
+illustration of this important period in the earth&rsquo;s history.
+The term &ldquo;faluns&rdquo; is given provincially by French
+agriculturists to shelly sand and marl spread over the land in
+Touraine, just as similar shelly deposits were formerly much used
+in Suffolk to fertilise the soil, before the coprolitic or
+phosphatic nodules came into use. Isolated masses of such faluns
+occur from near the mouth of the Loire, in the neighbourhood of
+Nantes, to as far inland as a district south of Tours. They are
+also found at Pontlevoy, on the Cher, about seventy miles above the
+junction of that river with the Loire, and thirty miles south-east
+of Tours. Deposits of the same age also appear under new mineral
+conditions near the towns of Dinan and Rennes, in Brittany. I have
+visited all the localities above enumerated, and found the beds on
+the Loire to consist principally of sand and marl, in which are
+shells and corals, some entire, some rolled, and others in minute
+fragments. In certain districts, as at Doué, in the
+Department of Maine and Loire, ten miles south-west
+<a name="page212"></a>of Saumur, they form a soft building-stone, chiefly composed of
+an aggregate of broken shells, bryozoa, corals, and echinoderms,
+united by a calcareous cement; the whole mass being very like the
+Coralline Crag near Aldborough, and Sudbourn in Suffolk. The
+scattered patches of faluns are of slight thickness, rarely
+exceeding fifty feet; and between the district called Sologne and
+the sea they repose on a great variety of older rocks; being seen
+to rest successively upon gneiss, clay-slate, various secondary
+formations, including the chalk; and, lastly, upon the upper
+fresh-water limestone of the Parisian tertiary series, which, as
+before mentioned <a href="#page142">(p. 142)</a>,
+stretches continuously from the basin of the Seine to that of the
+Loire.</p>
+
+<img src="images/fig136.jpg" width="170" height="235" alt=
+"Fig. 136: Dinotherium giganteum." />
+
+<p>At some points, as at Louans, south of Tours, the shells are
+stained of a ferruginous colour, not unlike that of the Red Crag of
+Suffolk. The species are, for the most part, marine, but a few of
+them belong to land and fluviatile genera. Among the former, <i>
+Helix turonensis)</i> (<a href="images/fig38.jpg">Fig. 38</a>) is
+the most abundant. Remains of terrestrial quadrupeds are here and
+there intermixed, belonging to the genera Dinotherium (Fig. 136),
+Mastodon, Rhinoceros, Hippopotamus, Chæropotamus, Dichobune,
+Deer, and others, and these are accompanied by cetacea, such as the
+Lamantin, Morse, Sea-calf, and Dolphin, all of extinct species.</p>
+
+<p>The fossil testacea of the faluns of the Loire imply, according
+to the late Edward Forbes, that the beds were formed partly on the
+shore itself at the level of low water, and partly at very moderate
+depths, not exceeding ten fathoms below that level. The molluscan
+fauna is, on the whole, much more littoral than that of the
+Pliocene Red and Coralline Crag of Suffolk, and implies a shallower
+sea. It is, moreover, contrasted with the Suffolk Crag by the
+indications it affords of an extra-European climate. Thus it
+contains seven species of Cypræa, some larger than any
+existing cowry of the Mediterranean, several species of <i>Oliva,
+Ancillaria, Mitra, Terebra, Pyrula, Fasciolaria,</i> and <i>
+Conus.</i> Of the cones there are no less than eight species, some
+very large, whereas the only European cone now living is of
+diminutive size. The genus <i>Nerita,</i> and many others, are also
+represented by individuals
+<a name="page213"></a>of a type now characteristic of equatorial seas, and wholly
+unlike any Mediterranean forms. These proofs of a more elevated
+temperature seem to imply the higher antiquity of the faluns as
+compared with the Suffolk Crag, and are in perfect accordance with
+the fact of the smaller proportion of testacea of recent species
+found in the faluns.</p>
+
+<p>Out of 290 species of shells, collected by myself in 1840 at
+Pontlevoy, Louans, Bossée, and other villages twenty miles
+south of Tours, and at Savigné, about fifteen miles
+north-west of that place, seventy-two only could be identified with
+recent species, which is in the proportion of twenty-five per cent.
+A large number of the 290 species are common to all the localities,
+those peculiar to each not being more numerous than we might expect
+to find in different bays of the same sea.</p>
+
+<p>The total number of species of testaceous mollusca from the
+faluns in my possession is 302, of which forty-five only, or
+fourteen per cent, were found by Mr. Wood to be common to the
+Suffolk Crag. The number of corals, including bryozoa and
+zoantharia, obtained by me at Doué and other localities
+before adverted to, amounts to forty-three, as determined by Mr.
+Lonsdale, of which seven (one of them a zoantharian) agree
+specifically with those of the Suffolk Crag. Some of the genera
+occurring fossil in Touraine, as the corals Astrea and <i>
+Dendrophyllia</i>, and the bryozoan <i>Lunulites</i>, have not been
+found in European seas north of the Mediterranean; nevertheless,
+the zoantharia of the faluns do not seem to indicate, on the whole,
+so warm a climate as would be inferred from the shells.</p>
+
+<p>It was stated that, on comparing about 300 species of Touraine
+shells with about 450 from the Suffolk Crag, forty-five only were
+found to be common to both, which is in the proportion of only
+fifteen per cent. The same small amount of agreement is found in
+the corals also. I formerly endeavoured to reconcile this marked
+difference in species with the supposed co-existence of the two
+faunas, by imagining them to have severally belonged to distinct
+zoological provinces or two seas, the one opening to the north and
+the other to the south, with a barrier of land between them, like
+the Isthmus of Suez, now separating the Red Sea and the
+Mediterranean. But I now abandon that idea for several reasons;
+among others, because I succeeded in 1841 in tracing the Crag fauna
+southward in Normandy to within seventy miles of the Falunian type,
+near Dinan, yet found that both assemblages of fossils retained
+their distinctive characters, showing no signs of any blending of
+species or transition of climate.</p>
+
+<p>
+<a name="page214"></a>The principal grounds, however, for referring the English Crag
+to the older Pliocene and the French faluns to the Upper Miocene
+epochs, consist in the predominance of fossil shells in the British
+strata identifiable with species not only still living, but which
+are now inhabitants of neighbouring seas, while the accompanying
+extinct species are of genera such as characterise Europe. In the
+faluns, on the contrary, the recent species are in a decided
+minority; and most of them are now inhabitants of the
+Mediterranean, the coast of Africa, and the Indian Ocean; in a
+word, less northern in character, and pointing to the prevalence of
+a warmer climate. They indicate a state of things receding farther
+from the present condition of Central Europe in physical geography
+and climate, and doubtless, therefore, receding farther from our
+era in time.</p>
+
+<img src="images/fig137.jpg" width="134" height="300" alt=
+"Fig. 137: Voluta Lamberti." />
+
+<p>Among the conspicuous fossils common to the faluns of the Loire
+and the Suffolk Crag is a variety of the <i>Voluta Lamberti</i>, a
+shell already alluded to <a href="images/fig123.jpg">(Fig.
+123).</a> The specimens of this shell which I have myself collected
+in Touraine, or have seen in museums, are thicker and heavier than
+British individuals of the same species, and shorter in proportion
+to their width, and have the folds on the columella less oblique,
+as represented in Fig. 137.</p>
+
+<p><b>Upper Miocene of Bordeaux and the South of
+France.</b>&mdash;A great extent of country between the Pyrenees
+and the Gironde is overspread by tertiary deposits of various ages,
+and chiefly of Miocene date. Some of these, near Bordeaux, coincide
+in age with the faluns of Touraine, already mentioned, but many of
+the species of shells are peculiar to the south. The succession of
+beds in the basin of the Gironde implies several oscillations of
+level by which the same wide area was alternately converted into
+sea and land and into brackish-water lagoons, and finally into
+fresh-water ponds and lakes.</p>
+
+<p>Among the fresh-water strata of this age near the base of the
+Pyrenees are marls, limestones and sands, in which the eminent
+comparative anatomist, M. Lartet, has obtained a great number of
+fossil mammalia common to the faluns of the Loire and the Upper
+Miocene beds of Switzerland, such as <i>Dinotherium giganteum</i>
+and <i>Mastodon angustidens</i>; also
+<a name="page215"></a>the bones of quadrumana, or of the ape and monkey tribe, which were discovered
+in 1837, the first of that order of quadrupeds detected in Europe. They were
+found near Auch, in the Department of Gers, in latitude 43&deg; 39&#x2032; N.
+About forty miles west of Toulouse. They were referred by MM. Lartet and
+Blainville to a genus closely allied to the Gibbon, to which they gave the name
+of <i>Pliopithecus.</i> Subsequently, in 1856, M. Lartet described another
+species of the same family of long-armed apes (<i>Hylobates</i>), which he
+obtained from strata of the same age at Saint-Gaudens, in the Haute Garonne.
+The fossil remains of this animal consisted of a portion of a lower jaw with
+teeth and the shaft of a humerus. It is supposed to have been a tree-climbing
+frugivorous ape, equalling man in stature. As the trunks of oaks are common in
+the lignite beds in which it lay, it has received the generic name of
+<i>Dryopithecus.</i> The angle formed by the ascending ramus of the jaw and the
+alveolar border is less open, and therefore more like the human subject, than
+in the Chimpanzee, and what is still more remarkable, the fossil, a young but
+adult individual, had all its milk teeth replaced by the second set, while its
+last true molar (or wisdom-tooth) was still undeveloped, or only existed as a
+germ in the jaw-bone. In the mode, therefore, of the succession of its teeth
+(which, as in all the old-World apes, exactly agree in number with those in
+man) it differed from the Gorilla and Chimpanzee, and corresponded with the
+human species.
+</p>
+
+<p><b>Upper Miocene Beds of Œningen, in
+Switzerland.</b>&mdash;The faluns of the Loire first served, as
+already stated (p. 211), as the type of the Miocene formations in
+Europe. They yielded a plentiful harvest of marine fossil shells
+and corals, but were entirely barren of plants and insects. In
+Switzerland, on the other hand, deposits of the same age have been
+discovered, remarkable for their botanical and entomological
+treasures. We are indebted to Professor Heer, of Zurich, for the
+description, restoration, and classification of several hundred
+species and varieties of these fossil plants, the whole of which he
+has illustrated by excellent figures in his &ldquo;Flora Tertiaria
+Helvetiæ.&rdquo; This great work, and those of Adolphe
+Brongniart, Unger, Goppert and others, show that this class of
+fossils is beginning to play the same important part in the
+classification of the tertiary strata containing lignite or brown
+coal as an older flora has long played in enabling us to understand
+the ancient coal or carboniferous formation. No small skepticism
+has always prevailed among botanists as to whether the leaves alone
+and the wood of plants could
+<a name="page216"></a>ever afford sufficient data for determining even genera and
+families in the vegetable kingdom. In truth, before such remains
+could be rendered available a new science had to be created. It was
+necessary to study the outlines, nervation, and microscopic
+structure of the leaves, with a degree of care which had never been
+called for in the classification of living plants, where the flower
+and fruit afforded characters so much more definite and
+satisfactory. As geologists, we cannot be too grateful to those
+who, instead of despairing when so difficult a task was presented
+to them, or being discouraged when men of the highest scientific
+attainments treated the fossil leaves as worthless, entered with
+full faith and enthusiasm into this new and unexplored field. That
+they should frequently have fallen into errors was unavoidable, but
+it is remarkable, especially if we inquire into the history of
+Professor Heer&rsquo;s researches, how often early conjectures as
+to the genus and family founded on the leaves alone were afterwards
+confirmed when fuller information was obtained. As examples to be
+found on comparing Heer&rsquo;s earlier and later works, I may
+instance the chestnut, elm, maple, cinnamon, magnolia, buckbean or
+Menyanthes, vine, buckthorn (<i>Rhamnus</i>), <i>Andromeda</i> and
+<i>Myrica,</i> and among the conifers <i>Sequoia</i> and <i>
+Taxodium.</i> In all these cases the plants were first recognised
+by their leaves, and the accuracy of the determination was
+afterwards confirmed when the fruit, and in some instances both
+fruit and flower, were found attached to the same stem as the
+leaves.</p>
+
+<p>But let us suppose that no fruit, seed, or flower had ever been
+met with in a fossil state, we should still have been indebted to
+the persevering labours of botanical palæontologists for one
+of the grandest scientific discoveries for which the present
+century is remarkable&mdash;namely, the proofs now established of
+the prevalence of a mild climate and a rich arborescent flora in
+the arctic regions in that Miocene epoch on the history of which we
+are now entering. It may be useful if I endeavour to give the
+reader in a few words some idea of the nature of the evidence of
+these important conclusions, to show how far they may be safely
+based on fossil leaves alone. When we begin by studying the fossils
+of the Newer Pliocene deposits, such as those of the Upper Val
+d&rsquo;Arno, before alluded to, we perceive that the fossil
+foliage agrees almost entirely with the trees and shrubs of a
+modern European forest. In the plants of the Older Pliocene strata
+of the same region we observe a larger proportion of species and
+genera which, although they may agree with well-known Asiatic or
+other foreign types, are at present
+<a name="page217"></a>wanting in Italy. If we then examine the Miocene formations of
+the same country, exotic forms become more abundant, especially the
+palms, whether they belong to the European or American fan-palms,
+<i>Chamærops</i> and <i>Sabal</i>, or to the more tropical
+family of the date-palms or <i>Phœnicites</i>, which last are
+conspicuous in the Lower Miocene beds of Central Europe. Although
+we have not found the fruit or flower of these palms in a fossil
+state, the leaves are so characteristic that no one doubts the
+family to which they belong, or hesitates to accept them as
+indications of a warm and sub-tropical climate.</p>
+
+<p>
+When the Miocene formations are traced to the northward of the 50th degree of
+latitude, the fossil palms fail us, but the greater proportion of the leaves,
+whether identical with those of existing European trees or of forms now unknown
+in Europe, which had accompanied the Miocene palms, still continue to
+characterise rocks of the same age, until we meet with them not only in
+Iceland, but in Greenland, in latitude 70&deg; N., and in Spitzbergen, latitude
+78&deg; 56&#x2032;, or within about 11 degrees of the pole, and under
+circumstances which clearly show them to have been indigenous in those regions,
+and not to have been drifted from the south <a href="#page240">(see
+p. 240).</a> Not only, therefore, has the botanist afforded the geologist much
+palæontological assistance in identifying distinct tertiary formations in
+distant places by his power of accurately discriminating the forms, veining,
+and microscopic structure of leaves or wood, but, independently of that exact
+knowledge derivable from the organs of fructification, we are indebted to him
+for one of the most novel, unexpected results of modern scientific inquiry.
+</p>
+
+<p>The Miocene formations of Switzerland have been called <i>
+Molasse</i>, a term derived from the French <i>mol</i>, and applied
+to a <i>soft</i>, incoherent, greenish sandstone, occupying the
+country between the Alps and the Jura. This molasse comprises three
+divisions, of which the middle one is marine, and being closely
+related by its shells to the faluns of Touraine, may be classed as
+Upper Miocene. The two others are fresh-water, the upper of which
+may be also grouped with the faluns, while the lower must be
+referred to the Lower Miocene, as defined in the next chapter.</p>
+
+<p><b>Upper Fresh-water Molasse.</b>&mdash;This formation is best
+seen at Œningen, in the valley of the Rhine, between Constance
+and Schaffhausen, a locality celebrated for having produced in the
+year 1700 the supposed human skeleton called by Scheuchzer
+&ldquo;homo diluvii testis,&rdquo; a fossil afterwards demonstrated
+by Cuvier to be a reptile, or aquatic salamander,
+<a name="page218"></a>of larger dimensions than even its great living representative,
+the salamander of Japan.</p>
+
+<p>The Œningen strata consist of a series of marls and
+limestones, many of them thinly laminated, and which appear to have
+slowly accumulated in a lake probably fed by springs holding
+carbonate of lime in solution. The elliptical area over which this
+fresh-water formation has been traced extends, according to Sir
+Roderick Murchison, for a distance of ten miles east and west from
+Berlingen, on the right bank of the river to Wangen, and to
+Œningen, near Stein, on the left bank. The organic remains
+have been chiefly derived from two quarries, the lower of which is
+about 550 feet above the level of the Lake of Constance, while the
+upper quarry is 150 feet higher. In this last, a section thirty
+feet deep displays a great succession of beds, most of them
+splitting into slabs and some into very thin laminæ.
+Twenty-one beds are enumerated by Professor Heer, the uppermost a
+bluish-grey marl seven feet thick, with organic remains, resting on
+a limestone with fossil plants, including leaves of poplar,
+cinnamon, and pond-weed (<i>Potamogeton</i>), together with some
+insects; while in the bed No. 4, below, is a bituminous rock, in
+which the <i>Mastodon tapiroides</i>, a characteristic Upper
+Miocene quadruped, has been met with. The 5th bed, two or three
+inches thick, contains fossil fish, e.g., <i>Leuciscus</i> (roach),
+and the larvæ of dragon-flies, with plants such as the elm
+(<i>Ulmus</i>), and the aquatic Chara. Below this are other
+plant-beds; and then, in No. 9, the stone in which the great
+salamander (Andrias Scheuchzeri) and some fish were found. Below
+this other strata occur with fish, tortoises, the great salamander
+before alluded to, fresh-water mussels, and plants. In No. 16 the
+fossil fox of Œningen, <i>Galecynus Œningensis,</i> Owen,
+was obtained by Sir R. Murchison. To this succeed other beds with
+mammalia (<i>Lagomys</i>), reptiles, (<i>Emys</i>), fish, and
+plants, such as walnut, maple, and poplar. In the 19th bed are
+numerous fish, insects, and plants, below which are marls of a blue
+indigo colour.</p>
+
+<p>In the lower quarry eleven beds are mentioned, in which, as in
+the upper, both land and fresh-water plants and many insects occur.
+In the 6th, reckoning from the top, many plants have been obtained,
+such as <i>Liquidambar, Daphnogene, Podogonium,</i> and <i>
+Ulmus</i>, together with tortoises, besides the bones and teeth of
+a ruminant quadruped, named by H. von Meyer <i>Palæomeryx
+eminens.</i> No. 9 is called the insect-bed, a layer only a few
+inches thick, which, when exposed to the frost, splits into leaves
+as thin as paper. In these thin laminæ plants such as <i>
+Liquidambar, Daphnogene,</i> and <i>Glyptostrobus</i>,
+<a name="page219"></a>occur, with innumerable insects in a wonderful state of
+preservation, usually found singly. Below this is an indigo-blue
+marl, like that at the bottom of the higher quarry, resting on
+yellow marl ascertained to be at least thirty feet thick.</p>
+
+<img src="images/fig138.jpg" width="216" height="299" alt=
+"Fig. 138: Cinnamomum polymorphum." />
+
+<p>All the above fossil-bearing strata were evidently formed with
+extreme slowness. Although the fossiliferous beds are, in the
+aggregate, no more than a few yards in thickness, and have only
+been examined in the small area comprised in the two quarries just
+alluded to, they give us an insight into the state of animal and
+vegetable life in part of the Upper Miocene period, such as no
+other region in the world has elsewhere supplied. In the year 1859,
+Professor Heer had already determined no less than 475 species of
+plants and more than 800 insects from these Œningen beds. He
+supposes that a river entering a lake floated into it some of the
+leaves and land insects, together with the carcasses of quadrupeds,
+among others a great Mastodon. Occasionally, during tempests, twigs
+and even boughs of trees with their leaves were torn off and
+carried for some distance so as to reach the lake. Springs,
+containing carbonate of lime, seem at some points to have supplied
+calcareous matter in solution, giving origin locally to a kind of
+travertin, in which organic bodies sinking to the bottom became
+hermetically sealed up. The laminæ, says Heer, which
+immediately succeed each other were not all formed at the same
+season, for it can be shown that, when some of them originated,
+certain plants were in flower, whereas, when the next of these
+layers was produced, the same plants had ripened their fruit. This
+inference is confirmed by independent proofs derived from insects.
+The principal insect-bed is rarely two inches thick, and is
+composed, says Heer, of about 250 leaf-like laminæ, some of
+which were deposited in the spring, when the <i>Cinnamomum
+polymorphum</i> (Fig. 138) was in flower, others in summer, when
+winged ants were numerous, and when the poplar and willow had
+matured their seed; others, again, in autumn, when the same <i>
+Cinnamomum polymorphum</i> (Fig. 138) was in fruit, as well as the
+liquidambar, oak, clematis,
+<a name="page220"></a>and many other plants. The ancient lake seems to have had a belt
+of poplars and willows round its borders, countless leaves of which
+were imbedded in mud, and together with them, at some points, a
+species of reed, <i>Arundo</i>, which was very common.</p>
+
+<p>One of the most characteristic shrubs is a papilionaceous and
+leguminous plant of an extinct genus, called by Heer <i>
+Podogonium</i>, of which two species are known. Entire twigs have
+been found with flowers, and always without leaves, as the flowers
+evidently came out, as in the poplar and willow tribe, before any
+leaves made their appearance. Other specimens have been obtained
+with ripe fruits accompanied by leaves, which resemble those of the
+tamarind, to which it was evidently allied, being of the family
+Cæsalpineæ, now proper to warmer regions.</p>
+
+<img src="images/fig139.jpg" width="251" height="337" alt=
+"Fig. 138: Acer trilobatum." />
+
+<p>The Upper Miocene flora of Œningen is peculiarly important,
+in consequence of the number of genera of which not merely the
+leaves, but, as in the case of the <i>Podogonium</i> just
+mentioned, the fruit also and even the flower are known. Thus there
+are nineteen species of maple, ten of which have already been found
+with fruit. Although in no one region of the globe do so many
+maples now flourish, we need not suspect Professor Heer of having
+made too many species in this genus when we consider the manner in
+which he has dealt with one of them, <i>Acer trilobatum</i>, Figs.
+139 and 140. Of this plant the number of marked varieties figured
+and named is very great, and no less than three of them had been
+considered as distinct species by other botanists, while six of the
+others might have laid claim, with nearly equal propriety, to a
+like distinction. The common form, called <i>Acer trilobatum</i>,
+Fig. 139, may be taken as a normal representative of the
+Œningen fossil, and Fig. 140, as one of the most divergent
+varieties, having almost four lobes in the leaf instead of
+three.<a name="page221"></a>
+</p>
+
+<p><img src="images/fig140.jpg" width="285" height="233" alt=
+"Fig. 140: Acer trilobatum." /></p>
+
+<p>Among the conspicuous genera which abounded in the Miocene
+period in Europe is the plane-tree, <i>Platanus,</i> the fossil
+species being considered by Heer to come nearer to the American <i>
+P. occidentalis</i> than to <i>P. orientalis</i> of Greece and Asia
+Minor. In some of the fossil specimens the male flowers are
+preserved. Among other points of resemblance with the living
+plane-trees, as we see them in the parks and squares of London,
+fossil fragments of the trunk are met with, having pieces of their
+bark peeling off.</p>
+
+<img src="images/fig141.jpg" width="166" height="271" alt=
+"Platanus aceroides." />
+
+<p>The vine of Œningen, <i>Vitis teutonica</i>, Ad. Brong, is
+of a North American type. Both the leaves and seeds have been found
+at Œningen, and bunches of compressed grapes of the same
+species have been met with in the brown coal of Wetteravia in
+Germany. No less than eight species of smilax, a monocotyledonous
+genus, occur at Œningen and in other Upper Miocene localities,
+the flowers of some of them, as well as the leaves, being
+preserved; as in the case of the very common fossil, <i>S.
+sagittifera</i>, Fig. 142, <i>a.</i></p>
+
+<p>Leaves of plants supposed to belong to the order Proteaceæ
+have been obtained partly from Œningen and partly from the
+lacustrine formation of the same age at Locle in the Jura. They
+have been referred to the genera <i>Banksia, Grevillea, Hakea,</i>
+and <i>Persoonia.</i> Of Hakea there is the impression of a
+supposed seed-vessel, with its characteristic thick stalk and
+seeds, but as the fruit is without structure, and has not yet
+<a name="page222"></a>been found attached to the same stem as the leaf, the proof is
+incomplete.</p>
+
+<img src="images/fig142.jpg" width="208" height="291" alt=
+"Fig. 142: Smilax sagittifera." />
+
+<p>To whatever family the foliage hitherto regarded as proteaceous
+by many able palæontologists may eventually be shown to
+belong, we must be careful not to question their affinity to that
+order of plants on those geographical considerations which have
+influenced some botanists. The nearest living Proteaceæ now
+feel the in Abyssinia in lat. 20&deg; N., but the greatest number
+are confined to the Cape and Australia. The ancestors, however, of
+the Œningen fossils ought not to be looked for in such distant
+regions, but from that European land which in Lower Miocene times
+bore trees with similar foliage, and these had doubtless an Eocene
+source, for cones admitted by all botanists to be proteaceous have
+been met with in one division of that older Tertiary group <a href=
+"images/fig206.jpg">(see Fig. 206</a>). The source of these last,
+again, must not be sought in the antipodes, for in the white chalk
+of Aix-la-Chapelle leaves like those of Grevillea and other
+proteaceous genera have been found in abundance, and, as we shall
+see <a href="#page304">(p. 304)</a> in a most perfect
+state of preservation. All geologists agree that the distribution
+of the Cretaceous land and sea had scarcely any connection with the
+present geography of the globe.</p>
+
+<p><img src="images/fig143.jpg" width="490" height="157" alt=
+"Fig. 143: Fruit of the fossil and recent species of Hakea, a genus of Proteaceæ." />
+</p>
+
+<p>In the same beds with the supposed Proteaceæ there occurs
+at Locle a fan-palm of the American type Sabal (for genus see Fig.
+151), a genus which ranges throughout the low country near the sea
+from the Carolinas to Florida and
+<a name="page223"></a>Louisiana. Among the Coniferæ of Upper Miocene age is
+found a deciduous cypress nearly allied to the <i>Taxodium
+distichum</i> of North America, and a <i>Glyptostrobus</i> (Fig.
+144), very like the Japanese <i>G. heterophyllus,</i> now common in
+our shrubberies.</p>
+
+<img src="images/fig144.jpg" width="120" height="214" alt=
+"Fig. 144: Glyptostrobus Europæus." />
+
+<p>Before the appearance of Heer&rsquo;s work on the Miocene Flora
+of Switzerland, Unger and Goppert had already pointed out the large
+proportion of living North American genera which distinguished the
+vegetation of the Miocene period in Central Europe. Next in number,
+says Heer, to these American forms at Œningen the European
+genera preponderate, the Asiatic ranking in the third, the African
+in the fourth, and the Australian in the fifth degree. The American
+forms are more numerous than in the Italian Pliocene flora, and the
+whole vegetation indicates a warmer climate than the Pliocene,
+though not so high a temperature as that of the older or Lower
+Miocene period.</p>
+
+<p>The conclusions drawn from the insects are for the most part in
+perfect harmony with those derived from the plants, but they have a
+somewhat less tropical and less American aspect, the South European
+types being more numerous. On the whole, the insect fauna is richer
+than that now inhabiting any part of Europe. No less than 844
+species are reckoned by Heer from the Œningen beds alone, the
+number of specimens which he has examined being 5080. The entire
+list of Swiss species from the Upper and Lower Miocene together
+amount to 1322. Almost all the living families of Coleoptera are
+represented, but, as we might have anticipated from the
+preponderance of arborescent and ligneous plants, the wood-eating
+beetles play the most conspicuous part, the Buprestidæ and
+other long-horned beetles being particularly abundant.</p>
+
+<p>The patterns and some remains of the colours both of <i>
+Coleoptera</i> and <i>Hemiptera</i> are preserved at Œningen,
+as, for example in <i>Harpactor</i> (Fig. 145), in which the
+antennæ, one of the eyes, and the legs and wings are
+retained. The characters, indeed, of many of the insects are so
+well defined as to incline us to believe that if this class of the
+invertebrata were not so rare and local, they might be more useful
+than even the plants and shells in settling chronological points in
+geology.</p>
+
+<p><b>Middle or Marine Molasse (Upper Miocene) of
+Switzerland.</b>&mdash;It was before stated that the Miocene
+formation of Switzerland
+<a name="page224"></a>consisted of, first, the upper fresh-water molasse, comprising
+the lacustrine marls of Œningen; secondly, the marine molasse,
+corresponding in age to the faluns of Touraine; and thirdly, the
+lower fresh-water molasse. Some of the beds of the marine or middle
+series reach a height of 2470 feet above the sea. A large number of
+the shells are common to the faluns of Touraine, the Vienna basin,
+and other Upper Miocene localities. The terrestrial plants play a
+subordinate part in the fossiliferous beds, yet more than ninety of
+them are enumerated by Heer as belonging to this falunian division,
+and of these more than half are common to subjacent Lower Miocene
+beds, while a proportion of about forty-five in one hundred are
+common to the overlying Œningen flora. Twenty-six of the
+ninety-two species are peculiar.</p>
+
+<p>
+<img src="images/fig145.jpg" width="172" height="284" alt=
+"Fig. 145: Harpactor maculipes." />
+</p>
+
+<p>
+<img src="images/fig146.jpg" width="119" height="174" alt=
+"Fig. 146: Olica Dufresnii." />
+</p>
+
+<p><b>Upper Miocene of the Bolderberg, in Belgium.</b>&mdash;In a
+small hill or ridge called the Bolderberg, which I visited in 1851,
+situated near Hasselt, about forty miles E.N.E. of Brussels, strata
+of sand and gravel occur, to which M. Dumont first called attention
+as appearing to constitute a northern representative of the faluns
+of Touraine. On the whole, they are very distinct in their fossils
+from the two upper divisions of the Antwerp Crag before mentioned
+<a href="#page204">(p. 204)</a>, and contain shells of
+the genera <i>Oliva, Conus, Ancillaria, Pleurotoma,</i> and <i>
+Cancellaria</i> in abundance. The most common shell is an Olive
+(Fig. 146), called by Nyst <i>Oliva Dufresnii</i>; and
+constituting, as M. Bosquet observes, a smaller and shorter variety
+of the Bordeaux species.</p>
+
+<p>So far as the shells of the Bolderberg are known, the proportion
+of recent species agrees with that in the faluns of Touraine, and
+the climate must have been warmer than that of the Coralline Crag
+of England.</p>
+
+<p><b>Upper Miocene Beds of the Vienna Basin.</b>&mdash;In South
+Germany the general resemblance of the shells of the Vienna
+tertiary basin with those of the faluns of Touraine has long been
+acknowledged. In the late Dr. Hörnes&rsquo;s excellent
+work
+<a name="page225"></a>on the fossil mollusca of that formation, we see accurate
+figures of many shells, clearly of the same species as those found
+in the falunian sands of Touraine.</p>
+
+<p>
+According to Professor Suess, the most ancient and purely marine of the Miocene
+strata in this basin consist of sands, conglomerates, limestones, and clays,
+and they are inclined inward, or from the borders of the trough towards the
+centre, their outcropping edges rising much higher than the newer beds, whether
+Miocene or Pliocene, which overlie them, and which occupy a smaller area at an
+inferior elevation above the sea. M. Hornes has described no less than 500
+species of gasteropods, of which he identifies one-fifth with living species of
+the Mediterranean, Indian, or African seas, but the proportion of existing
+species among the lamellibranchiate bivalves exceeds this average. Among many
+univalves agreeing with those of Africa on the eastern side of the Atlantic are
+<i>Cypræa sanguinolenta, Buccinum lyratum,</i> and <i>Oliva flammulata.</i> In
+the lowest marine beds of the Vienna basin the remains of several mammalia have
+been found, and among them a species of <i>Dinotherium</i>, a Mastodon of the
+<i>Trilophodon</i> family, a Rhinoceros (allied to <i>R. megarhinus</i>,
+Christol), also an animal of the hog tribe, <i> Listriodon</i>, von Meyer, and
+a carnivorous animal of the canine family. The <i>Helix turonensis</i> <a
+href="images/fig38.jpg"> (Fig. 38)</a>, the most common land shell of the
+French faluns, accompanies the above land animals. In a higher member of the
+Vienna Miocene series are found <i>Dinotherium giganteum</i> <a
+href="images/fig136.jpg">(Fig. 136)</a>, <i>Mastodon longirostris,
+Rhinoceros Schleiermacheri, Acerotherium incisivum,</i> and <i> Hippotherium
+gracile,</i> all of them equally characteristic of an Upper Miocene deposit
+occurring at Eppelsheim, in Hesse Darmstadt; a locality also remarkable as
+having furnished in latitude 49&deg; 50&#x2032; N. the bone of a large ape of
+the Gibbon kind, the most northerly example yet discovered of a quadrumanous
+animal.
+</p>
+
+<img src="images/fig147.jpg" width="130" height="164" alt=
+"Fig. 147: Amphistegina Hauerina." />
+
+<p>M. Alcide d&rsquo;Orbigny has shown that the foraminifera of the
+Vienna basin differ alike from the Eocene and Pliocene species, and
+agree with those of the faluns, so far as the latter are known.
+Among the Vienna foraminifera, the genus <i>Amphistegina</i> (Fig.
+147) is very characteristic, and is supposed by d&rsquo;Archiac to
+take the same place among the Rhizopods of the Upper Miocene era
+which the Nummulites occupy in the Eocene period.</p>
+
+<p>The flora of the Vienna basin exhibits some species which
+<a name="page226"></a>have a general range through the whole Miocene period, such as
+<i>Cinnamomum polymorphum</i> <a href="images/fig138.jpg">(Fig.
+138)</a>, and <i>C. Scheuchzeri,</i> also Planera Richardi, Mich.,
+<i>Liquidambar europæum</i> <a href="images/fig134.jpg">
+(Fig. 135)</a> <i>Juglans bilinica, Cassia ambigua,</i> and <i>C.
+lignitum.</i> Among the plants common to the Upper Miocene beds of
+Œningen, in Switzerland, are <i>Platanus aceroides</i> <a
+href="images/fig141.jpg">(Fig. 141)</a>, <i>Myrica
+vindobonensis,</i> and others.</p>
+
+<p><b>Upper Miocene Strata of Italy.</b>&mdash;We are indebted to
+Signor Michelotti for a valuable work on the Miocene shells of
+Northern Italy. Those found in the hill called the Superga, near
+Turin, have long been known to correspond in age with the faluns of
+Touraine, and they contain so many species common to the Upper
+Miocene strata of Bordeaux as to lead to the conclusion that there
+was a free communication between the northern part of the
+Mediterranean and the Bay of Biscay in the Upper Miocene
+period.</p>
+
+<p><b>Upper Miocene Formations of Greece.</b>&mdash;At
+Pikermé, near Athens, MM. Wagner and Roth have described a
+deposit in which they found the remains of the genera <i>Mastodon,
+Dinotherium, Hipparion,</i> two species of <i>Giraffe,
+Antelope,</i> and others, some living and some extinct. With them
+were also associated fossil bones of the <i>Semnopithecus,</i>
+showing that here, as in the south of France, the quadrumana were
+characteristic of this period. The whole fauna attests the former
+extension of a vast expanse of grassy plains where we have now the
+broken and mountainous country of Greece; plains, which were
+probably united with Asia Minor, spreading over the area where the
+deep Ægean Sea and its numerous islands are now situated. We
+are indebted to M. Gaudry, who visited Pikermé, for a
+treatise on these fossil bones, showing how many data they
+contribute to the theory of a transition from the mammalia of the
+Upper Miocene through the Pliocene and Post-pliocene forms to those
+of living genera and species.</p>
+
+<p><b>Upper Miocene of India. Siwâlik Hills.</b>&mdash;The
+Siwâlik Hills lie at the southern foot of the Himalayan
+chain, rising to the height of 2000 and 3000 feet. Between the
+Jumna and the Ganges they consist of inclined strata of sandstone,
+shingle, clay, and marl. We are indebted to the indefatigable
+researches of Dr. Falconer and Sir Proby Cautley, continued for
+fifteen years, for the discovery in these marls and sandstones of a
+great variety of fossil mammalia and reptiles, together with many
+fresh-water shells. Out of fifteen species of shells of the genera
+<i>Paludina, Melania, Ampullaria,</i> and <i>Unio,</i> all are
+extinct or unknown species with the exception of four, which are
+still inhabitants of Indian rivers. Such a
+<a name="page227"></a>proportion of living to extinct mollusca agrees well with the
+usual character of an Upper Miocene or Falunian fauna, as observed
+in Touraine, or in the basin of Vienna and elsewhere.</p>
+
+<p>The genera of mammalia point in the same direction. One of them,
+of the genus <i>Chalicotherium</i> (or <i>Anisodon</i> of Lartet),
+is a pachyderm intermediate between the <i>Rhinoceros</i> and <i>
+Anoplothere,</i> and characteristic of the Upper Miocene strata of
+Eppelsheim, and of the south of France. With it occurs also an
+extinct form of Hippopotamus, called Hexaprotodon, and a species of
+Hippotherium and pig, also two species of <i>Mastodon</i>, two of
+elephant, and three other elephantine proboscidians; none of them
+agreeing with any fossil forms of Europe, and being intermediate
+between the genera Elephas and Mastodon, constituting the sub-genus
+<i>Stegodon</i> of Falconer. With these are associated a monkey,
+allied to the <i>Semnopithecus entellus</i>, now living in the
+Himalaya, and many ruminants. Among these last, besides the
+giraffe, camel, antelope, stag, and others, we find a remarkable
+new type, the <i>Sivatherium,</i> like a gigantic four-horned deer.
+There are also new forms of carnivora, both feline and canine, the
+<i>Machairodus</i> among the former, also hyænas, and a
+subursine form called the Hyænarctos, and a genus allied to
+the otter (<i>Enhydriodon</i>), of formidable size.</p>
+
+<p>The giraffe, camel, and a large ostrich may be cited as proofs
+that there were formerly extensive plains where now a steep chain
+of hills, with deep ravines, runs for many hundred miles east and
+west. Among the accompanying reptiles are several crocodiles, some
+of huge dimensions, and one not distinguishable, says Dr. Falconer,
+from a species now living in the Ganges (<i>C. Gangeticus</i>); and
+there is still another saurian which the same anatomist has
+identified with a species now inhabiting India. There was also an
+extinct species of tortoise of gigantic proportions
+(<i>Colossochelys Atlas</i>), the curved shell of which was twelve
+feet three inches long and eight feet in diameter, the entire
+length of the animal being estimated at eighteen feet, and its
+probable height seven feet.</p>
+
+<p>Numerous fossils of the Siwâlik type have also been found
+in Perim Island, in the Gulf of Cambay, and among these a species
+of <i>Dinotherium,</i> a genus so characteristic of the Upper
+Miocene period in Europe.</p>
+
+<p>
+<b>Older Pliocene and Miocene Formations in the United
+States.</b>&mdash;Between the Alleghany Mountains, formed of older rocks, and
+the Atlantic, there intervenes, in the United States, a low region occupied
+principally by beds of marl, clay, and sand, consisting of the cretaceous and
+tertiary formations, <a name="page228"></a>and chiefly of the latter. The
+general elevation of this plain bordering the Atlantic does not exceed 100
+feet, although it is sometimes several hundred feet high. Its width in the
+middle and southern states is very commonly from 100 to 150 miles. It consists,
+in the South, as in Georgia, Alabama, and South Carolina, almost exclusively of
+Eocene deposits; but in North Carolina, Maryland, Virginia, Delaware, more
+modern strata predominate, of the age of the English Crag and faluns of
+Touraine.<a href="#fn-14.1" name="fnref-14.1"
+id="fnref-14.1"><sup>[1]</sup></a>
+</p>
+
+<p><img src="images/fig148.jpg" width="399" height="221" alt=
+"Fig. 148: Fulgur canaliculatus. Fig. 149: Fusus quadricostatus." />
+</p>
+
+<p>In the Virginian sands, we find in great abundance a species of
+Astarte (<i>A. undulata,</i> Conrad), which resembles closely, and
+may possibly be a variety of, one of the commonest fossils of the
+Suffolk Crag (<i>A. Omalii</i>); the other shells also, of the
+genera <i>Natica, Fissurella, Artemis, Lucina, Chama,
+Pectunculus,</i> and <i>Pecten,</i> are analagous to shells both of
+the English Crag and French faluns, although the species are almost
+all distinct. Out of 147 of these American fossils I could only
+find thirteen species common to Europe, and these occur partly in
+the Suffolk Crag, and partly in the faluns of Touraine; but it is
+an important characteristic of the American group, that it not only
+contains many peculiar extinct forms, such as <i>Fusus
+quadricostatus,</i> Say (see Fig. 149), and <i>Venus
+tridacnoides,</i> abundant in these same formations, but also some
+shells which, like <i>Fulgur carica</i> of Say and <i>F.
+canaliculatus</i> (see Fig. 148), <i>Calyptræa costata, Venus
+mercenaria,</i> Lam., <i>Modiola glandula,</i> Totten, and <i>
+Pecten magellanicus,</i> Lam., are recent species, yet of forms now
+confined to the western side of the Atlantic&mdash;a fact implying
+that some traces of the beginning of the present geographical
+distribution of mollusca
+<a name="page229"></a>date back to a period as remote as that of the Miocene
+strata.</p>
+
+<img src="images/fig150.jpg" width="152" height="184" alt=
+"Fig. 150: Astrangia lineata." />
+
+<p>Of ten species of corals which I procured on the banks of the
+James River, one agrees generically with a coral now living on the
+coast of the United States. Mr. Lonsdale regarded these corals as
+indicating a temperature exceeding that of the Mediterranean, and
+the shells would lead to similar conclusions. Those occurring on
+the James River are in the 37th degree of N. latitude, while the
+French faluns are in the 47th; yet the forms of the American
+fossils would scarcely imply so warm a climate as must have
+prevailed in France when the Miocene strata of Touraine
+originated.</p>
+
+<p>Among the remains of fish in these post-eocene strata of the
+United States are several large teeth of the shark family, not
+distinguishable specifically from fossils of the faluns of
+Touraine.
+</p>
+
+<p class="footnote">
+<a name="fn-14.1" id="fn-14.1"></a> <a href="#fnref-14.1">[1]</a>
+Proceedings of the Geol. Soc., vol. iv, pt. iii, 1845, p. 547.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap15"></a><a name="page230"></a>CHAPTER XV.<br/>
+LOWER MIOCENE <small>(OLIGOCENE OF BEYRICH)</small>.</h2>
+
+<p class="letter">Lower Miocene Strata of France. &mdash; Line
+between Miocene and Eocene. &mdash; Lacustrine Strata of Auvergne.
+&mdash; Fossil mammalia of the Limagne d&rsquo;Auvergne. &mdash;
+Lower Molasse of Switzerland. &mdash; Dense Conglomerates and
+Proofs of Subsidence. &mdash; Flora of the Lower Molasse. &mdash;
+American Character of the Flora. &mdash; Theory of a Miocene
+Atlantis. &mdash; Lower Miocene of Belgium. &mdash; Rupelian Clay
+of Hermsdorf near Berlin. &mdash; Mayence Basin. &mdash; Lower
+Miocene of Croatia. &mdash; Oligocene Strata of Beyrich. &mdash;
+Lower Miocene of Italy. &mdash; Lower Miocene of England. &mdash;
+Hempstead Beds. &mdash; Bovey Tracey Lignites in Devonshire.
+&mdash; Isle of Mull Leaf-Beds. &mdash; Arctic Miocene Flora.
+&mdash; Disco Island. &mdash; Lower Miocene of United States.
+&mdash; Fossils of Nebraska.</p>
+
+<p>
+<b>Line between Miocene and Eocene Formations.</b>&mdash;The marine faluns of
+the valley of the Loire have been already described as resting in some places
+on a fresh-water tertiary limestone, fragments of which have been broken off
+and rolled on the shores and in the bed of the Miocene sea. Such pebbles are
+frequent at Pontlevoy on the Cher, with hollows drilled in them in which the
+perforating marine shells of the Falunian period still remain. Such a mode of
+superposition implies an interval of time between the origin of the fresh-water
+limestone and its submergence beneath the waters of the Upper Miocene sea. The
+limestone in question forms a part of the formation called the Calcaire de la
+Beauce, which constitutes a large table-land between the basins of the Loire
+and the Seine. It is associated with marls and other deposits, such as may have
+been formed in marshes and shallow lakes in the newest part of a great delta.
+Beds of flint, continuous or in nodules, accumulated in these lakes, and
+aquatic plants called Charae, left their stems and seed-vessels imbedded both
+in the marl and flint, together with fresh-water and land shells. Some of the
+siliceous rocks of this formation are used extensively for mill-stones. The
+flat summits or platforms of the hills round Paris, and large areas in the
+forest of Fontainebleau, as well as the Plateau de la Beauce, already alluded
+to, are chiefly composed of these fresh-water strata. Next to these in the
+descending order are marine sands and sandstone, commonly called the Gres de
+Fontainebleau, from which a considerable number of shells, very distinct from
+those of the faluns, have been obtained at Etampes, south of <a
+name="page231"></a>Paris, and at Montmartre and other hills in Paris itself, or
+in its suburbs. At the bottom of these sands a green clay occurs, containing a
+small oyster, <i>Ostrea cyathula,</i> Lam., which, although of slight
+thickness, is spread over a wide area. This clay rests immediately on the Paris
+gypsum, or that series of beds of gypsum and gypseous marl from which Cuvier
+first obtained several species of Palæotherium and other extinct mammalia.<a
+href="#fn-15.1" name="fnref-15.1" id="fnref-15.1"><sup>[1]</sup></a>
+</p>
+
+<p>At this junction of the clay and the gypsum the majority of
+French geologists have always drawn the line between the Middle and
+Lower Tertiary, or between the Miocene and Eocene formations,
+regarding the Fontainebleau sands and the <i>Ostrea cyathula</i>
+clay as the base of the Miocene, and the gypsum, with its mammalia,
+as the top of the Eocene group. I formerly dissented from this
+division, but I now find that I must admit it to be the only one
+which will agree with the distribution of the Miocene mammalia,
+while even the mollusca of the Fontainebleau sands, which were
+formerly supposed to present at preponderance of affinities to an
+Eocene fauna, have since been shown to agree more closely with the
+fossils of certain deposits always regarded as Middle Tertiary at
+Mayence and in Belgium. In fact, we are now arriving at that stage
+of progress when the line, wherever it be drawn between Miocene and
+Eocene, will be an arbitrary one, or one of mere convenience, as I
+shall have an opportunity of showing when the Upper Eocene
+formations in the Isle of Wight are described in the sixteenth
+chapter.</p>
+
+<p><b>Lower Miocene of Central France.</b>&mdash;Lacustrine strata,
+belonging, for the most part, to the same Miocene system as the
+Calcaire de la Beauce, are again met with farther south in
+Auvergne, Cantal, and Vélay. They appear to be the monuments
+of ancient lakes, which, like some of those now existing in
+Switzerland, once occupied the depressions in a mountainous region,
+and have been each fed by one or more rivers and torrents. The
+country where they occur is almost entirely composed of granite and
+different varieties of granitic schist, with here and there a few
+patches of Secondary strata, much dislocated, and which have
+suffered great denudation. There are also some vast piles of
+volcanic matter, the greater part of which is newer than the
+fresh-water strata, and is sometimes seen to rest upon them, while
+a small part has evidently been of contemporaneous origin. Of these
+igneous rocks I shall treat more particularly in the sequel.</p>
+
+<p>
+The study of these regions possesses a peculiar interest very
+distinct in kind from that derivable from the
+<a name="page232"></a>investigation
+either of the Parisian or English Tertiary areas. For we are
+presented in Auvergne with the evidence of a series of events of
+astonishing magnitude and grandeur, by which the original form and
+features of the country have been greatly changed, yet never so far
+obliterated but that they may still, in part at least, be restored
+in imagination. Great lakes have disappeared&mdash;lofty mountains have
+been formed, by the reiterated emission of lava, preceded and
+followed by showers of sand and scoriæ&mdash;deep valleys have
+been subsequently furrowed out through masses of lacustrine and
+volcanic origin&mdash;at a still later date, new cones have been thrown
+up in these valleys&mdash;new lakes have been formed by the damming up
+of rivers&mdash;and more than one assemblage of quadrupeds, birds, and
+plants, Eocene, Miocene, and Pliocene, have followed in succession;
+yet the region has preserved from first to last its geographical
+identity; and we can still recall to our thoughts its external
+condition and physical structure before these wonderful
+vicissitudes began, or while a part only of the whole had been
+completed. There was first a period when the spacious lakes, of
+which we still may trace the boundaries, lay at the foot of
+mountains of moderate elevation, unbroken by the bold peaks and
+precipices of Mont Dor, and unadorned by the picturesque outline of
+the Puy de Dome, or of the volcanic cones and craters now covering
+the granitic platform. During this earlier scene of repose deltas
+were slowly formed; beds of marl and sand, several hundred feet
+thick, deposited; siliceous and calcareous rocks precipitated from
+the waters of mineral springs; shells and insects imbedded,
+together with the remains of the crocodile and tortoise, the eggs
+and bones of water-birds, and the skeletons of quadrupeds, most of
+them of genera and species characteristic of the Miocene period. To
+this tranquil condition of the surface succeeded the era of
+volcanic eruptions, when the lakes were drained, and when the
+fertility of the mountainous district was probably enhanced by the
+igneous matter ejected from below, and poured down upon the more
+sterile granite. During these eruptions, which appear to have taken
+place towards the close of the Miocene epoch, and which continued
+during the Pliocene, various assemblages of quadrupeds successively
+inhabited the district, among which are found the genera mastodon,
+rhinoceros, elephant, tapir, hippopotamus, together with the ox,
+various kinds of deer, the bear, hyæna, and many beasts of
+prey which ranged the forest or pastured on the plain, and were
+occasionally overtaken by a fall of burning cinders, or buried in
+flows of mud, such as accompany volcanic <a name="page233"></a>eruptions.
+Lastly, these quadrupeds became extinct, and gave place in their
+turn to the species now existing. There are no signs, during the
+whole time required for this series of events, of the sea having
+intervened, nor of any denudation which may not have been
+accomplished by currents in the different lakes, or by rivers and
+floods accompanying repeated earthquakes, or subterranean
+movements, during which the levels of the district have in some
+places been materially modified, and perhaps the whole upraised
+relatively to the surrounding parts of France.</p>
+
+<p>
+<i>Auvergne.</i>&mdash;The most northern of the fresh-water groups is situated
+in the valley-plain of the Allier, which lies within the department of the Puy
+de Dome, being the tract which went formerly by the name of the Limagne
+d&rsquo;Auvergne. The average breadth of this tract is about twenty miles; and
+it is for the most part composed of nearly horizontal strata of sand,
+sandstone, calcareous marl, clay, and limestone, none of which observe a fixed
+and invariable order of superposition. The ancient borders of the lake wherein
+the fresh-water strata were accumulated may generally be traced with precision,
+the granite and other ancient rocks rising up boldly from the level country.
+The actual junction, however, of the lacustrine beds and the granite is rarely
+seen, as a small valley usually intervenes between them. The fresh-water strata
+may sometimes be seen to retain their horizontality within a very slight
+distance of the border-rocks, while in some places they are inclined, and in
+few instances vertical. The principal divisions into which the lacustrine
+series may be separated are the following:&mdash;first, Sandstone, grit, and
+conglomerate, including red marl and red sandstone; secondly, Green and white
+foliated marls; thirdly, Limestone, or travertin, often oolitic in structure;
+fourthly, Gypseous marls.
+</p>
+
+<p>The relations of these different groups cannot be learnt by the
+study of any one section; and the geologist who sets out with the
+expectation of finding a fixed order of succession may perhaps
+complain that the different parts of the basin give contradictory
+results. The arenaceous division, the marls, and the limestone may
+all be seen in some places to alternate with each other; yet it can
+by no means be affirmed that there is no order of arrangement. The
+sands, sandstone, and conglomerate constitute in general a littoral
+group; the foliated white and green marl, a contemporaneous central
+deposit more than 700 feet thick, and thinly foliated, a character
+which often arises from the innumerable thin shells or carapace
+valves shed by the small crustacean
+<a name="page234"></a>called <i>Cypris</i> in the ancient lakes of Auvergne; and
+lastly the limestone is for the most part subordinate to the newer
+portions of both the above formations.</p>
+
+<p>It seems that, when the ancient lake of the Limagne first began
+to be filled with sediment, no volcanic action had yet produced
+lava and scoriæ on any part of the surface of Auvergne. No
+pebbles, therefore, of lava were transported into the lake&mdash;no
+fragments of volcanic rocks imbedded in the conglomerate. But at a
+later period, when a considerable thickness of sandstone and marl
+had accumulated, eruptions broke out, and lava and tuff were
+deposited, at some spots, alternately with the lacustrine strata.
+It is not improbable that cold and thermal springs, holding
+different mineral ingredients in solution, became more numerous
+during the successive convulsions attending this development of
+volcanic agency, and thus deposits of carbonate and sulphate of
+lime, silex, and other minerals were produced. Hence these minerals
+predominate in the uppermost strata. The subterranean movements may
+then have continued until they altered the relative levels of the
+country, and caused the waters of the lakes to be drained off, and
+the further accumulation of regular fresh-water strata to
+cease.</p>
+
+<p><b>Lower Miocene Mammalia of the Limagne.</b>&mdash;It is
+scarcely possible to determine the age of the oldest part of the
+fresh-water series of the Limagne, large masses both of the sandy
+and marly strata being devoid of fossils. Some of the lowest beds
+may be of Upper Eocene date, although, according to M. Pomel, only
+one bone of a <i>Palæotherium</i> has been discovered in
+Auvergne. But in Vélay, in strata containing some species of
+fossil mammalia common to the Limagne, no less than four species of
+Palæothere have been found by M. Aymard, and one of these is
+generally supposed to be identical with <i>Palæotherium
+magnum,</i> an undoubted Upper Eocene fossil, of the Paris gypsum,
+the other three being peculiar.</p>
+
+<p>Not a few of the other mammalia of the Limagne belong
+undoubtedly to genera and species elsewhere proper to the Lower
+Miocene. Thus, for example, the Cainotherium of Bravard, a genus
+not far removed from the Anoplotherium, is represented by several
+species, one of which, as I learn from Mr. Waterhouse, agrees with
+<i>Microtherium Renggeri</i> of the Mayence basin. In like manner,
+the <i>Amphitragulus elegans</i> of Pomel, an Auvergne fossil, is
+identified by Waterhouse with <i>Dorcatherium nanum</i> of Kaup, a
+Rhenish species from Weissenau, near Mayence. A small species,
+also, of rodent, of the genus Titanomys of H. von Meyer, is common
+to the Lower Miocene of Mayence and the Limagne
+<a name="page235"></a>d&rsquo;Auvergne, and there are many other points of agreement
+which the discordance of nomenclature tends to conceal. A
+remarkable carnivorous genus, the Hyænodon of Laizer, is
+represented by more than one species. The same genus has also been
+found in the Upper Eocene marls of Hordwell Cliff, Hampshire, just
+below the level of the Bembridge Limestone, and therefore a
+formation older than the Gypsum of Paris. Several species of
+opossum (<i>Didelphis</i>) are met with in the same strata of the
+Limagne. The total number of mammalia enumerated by M. Pomel as
+appertaining to the Lower Miocene fauna of the Limagne and Velay
+falls little short of a hundred, and with them are associated some
+large crocodiles and tortoises, and some Ophidian and Batrachian
+reptiles.</p>
+
+<p><b>Lower Molasse of Switzerland.</b>&mdash;The two upper
+divisions of the Swiss Molasse&mdash;the one fresh-water, the other
+marine&mdash;have already been described in the preceding chapter. I
+shall now proceed to treat of the third division, which is of Lower
+Miocene age. Nearly the whole of this Lower Molasse is fresh-water,
+yet some of the inferior beds contain a mixture of marine and
+fluviatile shells, the <i>Cerithium margaritaceum,</i> a well-known
+Lower Miocene fossil, being one of the marine species.
+Notwithstanding, therefore, that some of these Lower Miocene strata
+consist of old shingle-beds several thousand feet in thickness, as
+in the Rigi, near Lucerne, and in the Speer, near Wesen, mountains
+5000 and 7000 feet above the sea, the deposition of the whole
+series must have begun at or below the sea-level.</p>
+
+<p>The conglomerates, as might be expected, are often very unequal
+in thickness, in closely adjoining districts, since in a littoral
+formation accumulations of pebbles would swell out in certain
+places where rivers entered the sea, and would thin out to
+comparatively small dimensions where no streams or only small ones
+came down to the coast. For ages, in spite of a gradual depression
+of the land and adjacent sea-bottom, the rivers continued to cover
+the sinking area with their deltas; until finally, the subsidence
+being in excess, the sea of the Middle Molasse gained upon the
+land, and marine beds were thrown down over the dense mass of
+fresh-water and brackish-water deposit, called the Lower Molasse,
+which had previously accumulated.</p>
+
+<p><b>Flora of the Lower Molasse.</b>&mdash;In part of the Swiss
+Molasse, which belongs exclusively to the Lower Miocene period, the
+number of plants has been estimated at more than 500 species,
+somewhat exceeding those which were before enumerated as occurring
+in the two upper divisions. The Swiss Lower
+<a name="page236"></a>Miocene may best be studied on the northern borders of the Lake
+of Geneva, between Lausanne and Vevay, where the contiguous
+villages of Monod and Rivaz are situated. The strata there, which I
+have myself examined, consist of alternations of conglomerate,
+sandstone, and finely laminated marls with fossil plants. A small
+stream falls in a succession of cascades over the harder beds of
+pudding-stone, which resist, while the sandstone and plant-bearing
+shales and marls give way. From the latter no less than 193 species
+of plants have been obtained by the exertions of MM. Heer and
+Gaudin, and they are considered to afford a true type of the
+vegetation of the Lower Miocene formations of Switzerland&mdash;a
+vegetation departing farther in its character from that now
+flourishing in Europe than any of the higher members of the series
+before alluded to, and yet displaying so much affinity to the flora
+of Œningen as to make it natural for the botanist to refer
+the whole to one and the same Miocene period. There are, indeed, no
+less than 81 species of these Older Miocene plants which pass up
+into the flora of Œningen.</p>
+
+<p>This fact is important as bearing on the propriety of classing
+the Lower Molasse of Switzerland as belonging to the Miocene rather
+than to the latter part of the Eocene period. There are, indeed, so
+many types among the fossils, both specific and generic, which have
+a wide range through the whole of the Molasse, that a unity of
+character is thereby stamped on the whole flora, in spite of the
+contrast between the plants of the uppermost and lowest formations,
+or between Oeningen and Monod. The proofs of a warmer climate, and
+the excess of arborescent over herbaceous plants, and of evergreen
+trees over deciduous species, are characters common to the whole
+flora, but which are intensified as we descend to the inferior
+deposits.</p>
+
+<p>Nearly all the plants at Monod are contained in three layers of
+marl separated by two of soft sandstone. The thickness of the marls
+is ten feet, and vegetable matter predominates so much in some
+layers as to form an imperfect lignite. One bed is filled with
+large leaves of a species of fig (<i>Ficus populina</i>), and of a
+hornbeam (<i>Carpinus grandis</i>), the strength of the wind having
+probably been great when they were blown into the lake; whereas
+another contiguous layer contains almost exclusively smaller
+leaves, indicating, apparently, a diminished strength in the wind.
+Some of the upper beds at Monod abound in leaves of
+Proteaceæ, Cyperaceæ, and ferns, while in some of the
+lower ones <i>Sequoia, Cinnamomum,</i> and <i>Sparganium</i> are
+common. In one bed of sandstone the trunk of a large palm-tree was
+found
+<a name="page237"></a>unaccompanied by other fossils, and near Vevay, in the same
+series of Lower Miocene strata, the leaves of a palm of the genus
+<i>Sabal</i> (Fig. 151), a genus now proper to America, were
+obtained.</p>
+
+<img src="images/fig151.jpg" width="174" height="226" alt=
+"Fig. 151: Sabal major" />
+
+<p>Among other genera of the same class is a <i>Flabellaria</i>
+occurring near Lausanne, and a magnificent <i>Phœnicites</i>
+allied to the date palm. When these plants flourished the climate
+must have been much hotter than now. The Alps were no doubt much
+lower, and the palms now found fossil in strata elevated 2000 feet
+above the sea grew nearly at the sea-level, as is demonstrated by
+the brackish-water character of some of the beds into which they
+were carried by winds or rivers from the adjoining coast.</p>
+
+<p>
+In the same plant-bearing deposits of the Lower Molasse in Switzerland leaves
+have been found which have been ascribed to the order Proteaceæ already spoken
+of as well represented in the Œningen beds (see p. 221). The Proteas and other
+plants of this family now flourish at the Cape of Good Hope; while the
+Banksias, and a set of genera distinct from those of Africa, grow most
+luxuriantly in the southern and temperate parts of Australia. They were
+probably inhabitants, says Heer, of dry hilly ground, and the stiff leathery
+character of their leaves must have been favourable to their preservation,
+allowing them to float on a river for great distances without being injured,
+and then to sink, when water-logged, to the bottom. It has been objected that
+the fruit of the Proteaceæ is of so tough and enduring a texture that it ought
+to have been more commonly met with; but in the first place we must not forget
+the numerous cones found in the Eocene strata of Sheppey, which all admit to be
+proteaceous and to belong to at least two species (see p. 222). Secondly,
+besides the fruit of Hakea before mentioned (p. 221), Heer found associated
+with fossil leaves, having the exact form and nervation of Banksia, fruit
+precisely such as may have come from a cone of that plant, and lately he has
+received another similar fruit from the Lower Miocene strata of Lucerne. They
+may have fallen out of a decayed cone in the same way as often happens to the
+seeds of the spruce fir, <i>Pinus abies,</i> found scattered over the ground in
+our woods. It is a known fact that
+<a name="page238"></a>among the living Proteaceæ the cones are very firmly
+attached to the branches, so that the seeds drop out without the
+cone itself falling to the ground, and this may perhaps be the
+reason why, in some instances in which fossil seeds have been
+found, no traces of the cone have been observed.
+</p>
+
+<p><img src="images/fig152.jpg" width="413" height="236" alt=
+"Fig. 152: Fruit of fossil Banksia and leaf of Banksia. Fig. 153: Sequoia Langsdorfii." />
+</p>
+
+<p>Among the Coniferæ the Sequoia here figured is common at
+Rivaz, and is one of the most universal plants in the Lowest
+Miocene of Switzerland, while it also characterises the Miocene
+Brown Coals of Germany and certain beds of the Val d&rsquo;Arno,
+which I have called Older Pliocene, <a href="#page208">p.
+208</a>.</p>
+
+<img src="images/fig154.jpg" width="237" height="282" alt=
+"Fig. 154: Lastræa stiriaca." />
+
+<p>Among the ferns met with in profusion at Monod is the <i>
+Lastræa stiriaca,</i> Unger, which has a wide range in the
+Miocene period from strata of the age of Œningen to the
+lowest part of the Swiss Molasse. In some specimens, as shown in
+Fig. 154, the fructification is distinctly seen.</p>
+
+<p>Among the laurels several species of <i>Cinnamomum</i> are very
+conspicuous. Besides the <i>C. polymorphum,</i> before figured, <a
+href="#page219">p. 219</a>, another species also ranges
+from the Lower to the Upper Molasse of Switzerland, and
+<a name="page239"></a>is very characteristic of different deposits of Brown Coal in
+Germany. It has been called <i>Cinnamomum Rossmässleri</i> by
+Heer (see Fig. 155). The leaves are easily recognised as having two
+side veins, which run up uninterruptedly to their point.</p>
+
+<img src="images/fig155.jpg" width="183" height="339" alt=
+"Fig. 155: Cinnamomum Rossmässleri." />
+
+<p><b>American Character of the Flora.</b>&mdash;If we consider not
+merely the number of species but those plants which constitute the
+mass of the Lower Miocene vegetation, we find the European part of
+the fossil flora very much less prominent than in the Œningen
+beds, while the foreground is occupied by American forms, by
+evergreen oaks, maples, poplars, planes, Liquidambar, Robinia,
+Sequoia, Taxodium, and ternate-leaved pines. There is also a much
+greater fusion of the characters now belonging to distinct
+botanical provinces than in the Upper Miocene flora, and we shall
+find this fusion still more strikingly exemplified as we go back to
+the antecedent Eocene and Cretaceous periods.</p>
+
+<p>Professor Heer has advocated the doctrine, first advanced by
+Unger to explain the large number of American genera in the Miocene
+flora of Europe, that the present basin of the Atlantic was
+occupied by land over which the Miocene flora could pass freely.
+But other able botanists have shown that it is far more probable
+that the American plants came from the east and not from the west,
+and instead of reaching Europe by the shortest route over an
+imaginary Atlantis, migrated in an opposite direction, crossing the
+whole of Asia.</p>
+
+<p>
+<b>Arctic Miocene Flora.</b>&mdash;But when we indulge in speculations as to
+the geographical origin of the Miocene plants of Central Europe, we must take
+into account the discoveries recently made of a rich terrestrial flora having
+flourished in the Arctic Regions in the Miocene period from which many species
+may have migrated from a common centre so as to reach the present continents of
+Europe, Asia, and America. Professor Heer has examined the various collections
+of fossil plants that have been obtained in North Greenland (lat. 70&deg;),
+Iceland, Spitzbergen, and other parts of the Arctic regions, <a
+name="page240"></a>and has determined that they are of Miocene age and indicate
+a temperate climate.<a href="#fn-15.2" name="fnref-15.2"
+id="fnref-15.2"><sup>[2]</sup></a> Including the collections recently brought
+from Greenland by Mr. Whymper, the Arctic Miocene flora now comprises 194
+species, and that of Greenland 137 species, of which 46, or exactly one-third,
+are identical with plants found in the Miocene beds of Central Europe.
+Considerably more than half the number are trees, which is the more remarkable
+since, at the present day, trees do not exist in any part of Greenland even 10
+degrees farther south.
+</p>
+
+<p>
+More than thirty species of Coniferæ have been found, including several
+Sequoias (allied to the gigantic Wellingtonia of California), with species of
+Thujopsis and Salisburia now peculiar to Japan. There are also beeches, oaks,
+planes, poplars, maples, walnuts, limes, and even a magnolia, two cones of
+which have recently been obtained, proving that this splendid evergreen not
+only lived but ripened its fruit within the Arctic circle. Many of the limes,
+planes, and oaks were large-leaved species, and both flowers and fruit, besides
+immense quantities of leaves, are in many cases preserved. Among the shrubs
+were many evergreens, as <i> Andromeda,</i> and two extinct genera,
+<i>Daphnogene</i> and <i> M&rsquo;Clintockia,</i> with fine leathery leaves,
+together with hazel, blackthorn, holly, logwood, and hawthorn. A species of
+Zamia (<i>Zamites</i>) grew in the swamps, with <i>Potamogeton, Sparganium,</i>
+and <i>Menyanthes,</i> while ivy and vines twined around the forest trees and
+broad-leaved ferns grew beneath their shade. Even in Spitzbergen, as far north
+as latitude 78&deg; 56&#x2032;, no less than ninety-five species of fossil
+plants have been obtained, including <i>Taxodium</i> of two species, hazel,
+poplar, alder, beech, plane-tree, and lime. Such a vigorous growth of trees
+within 12 degrees of the pole, where now a dwarf willow and a few herbaceous
+plants form the only vegetation, and where the ground is covered with almost
+perpetual snow and ice, is truly remarkable.
+</p>
+
+<p>The identity of so many of the fossils with Miocene species of
+Central Europe and Italy not only proves that the climate of
+Greenland was much warmer than it is now, but also renders it
+probable that a much more uniform climate prevailed over the entire
+northern hemisphere. This is also indicated by the whole character
+of the Upper Miocene flora of Central Europe, which does not
+necessitate a mean temperature very much greater than exists at
+present, if we suppose such absence of winter cold as is proper to
+insular climates. Professor Heer believes that the mean temperature
+of North Greenland must have been at least 30 degrees higher than
+at present,
+<a name="page241"></a>while an addition of 10 degrees to the mean temperature of
+Central Europe would probably be as much as was required. The chief
+locality where this wonderful flora is preserved is at Atanekerdluk
+in North Greenland (lat. 70&deg;), on a hill at an elevation of
+about 1200 feet above the sea. There is here a considerable
+succession of sedimentary strata pierced by volcanic rocks. Fossil
+plants occur in all the beds, and the erect trunks as thick as a
+man&rsquo;s body which are sometimes found, together with the
+abundance of specimens of flowers and fruit in good preservation,
+sufficiently prove that the plants grew where they are now found.
+At Disco island and other localities on the same part of the coast,
+good coal is abundant, interstratified with beds of sandstone, in
+some of which fossil plants have also been found, similar to those
+at Atanekerdluk.</p>
+
+<p><img src="images/fig156.jpg" width="270" height="120" alt=
+"Fig. 156: Leda (Nucula) Deshayesiana." /> <b>Lower
+Miocene, Belgium.</b>&mdash;The Upper Miocene Bolderberg beds,
+mentioned in <a href="#page224">p. 224</a>, rest on a
+Lower Miocene formation called the Rupelian of Dumont. This
+formation is best seen at the villages of Rupelmonde and Boom, ten
+miles south of Antwerp, on the banks of the Scheldt and near the
+junction with it of a small stream called the Rupel. A stiff clay
+abounding in fossils is extensively worked at the above localities
+for making tiles. It attains a thickness of about 100 feet, and
+though very different in age, much resembles in mineral character
+the &ldquo;London clay,&rdquo; containing, like it, septaria or
+concretions of argillaceous limestone traversed by cracks in the
+interior, which are filled with calc-spar. The shells, referable to
+about forty species, have been described by MM. Nyst and De
+Koninck. Among them <i>Leda</i> (or Nucula) <i>Deshayesiana</i>
+(see Fig. 156) is by far the most abundant; a fossil unknown as yet
+in the English tertiary strata, but when young much resembling Leda
+amygdaloides of the London Clay proper (see
+Fig. 213). Among other characteristic
+shells are <i>Pecten Hœninghausii,</i> and a species of <i>
+Cassidaria,</i> and several of the genus <i>Pleurotoma.</i> Not a
+few of these testacea agree with English Eocene species, such as
+<i>Actæon simulatus,</i> Sowb, <i>Cancellaria evulsa,</i>
+Brander, <i>Corbula pisum</i> (<a href="images/fig157.jpg">Fig.
+157</a>), and <i>Nautilus (Aturia) ziczac.</i> They are accompanied
+by many teeth of sharks, as <i>Lamna contortidens,</i> Ag., <i>
+Oxyrhinaxiphodon,</i> Ag., <i>Carcharodon angustidens</i> (see <a
+href="images/fig196.jpg">Fig. 196</a>),
+<a name="page242"></a>Ag., and other fish, some of them common to the Middle Eocene
+strata.</p>
+
+<p>
+
+<i>Kleyn Spawen beds.</i>&mdash;The succession of the Lower Miocene strata of
+Belgium can be best studied in the environs of Kleyn Spawen, a village situated
+about seven miles west of Maestricht, in the old province of Limburg in
+Belgium. In that region, about 200 species of testacea, marine and fresh-water,
+have been obtained, with many foraminifera and remains of fish. In none of the
+Belgian Lower Miocene strata could I find any nummulites; and M.
+d&rsquo;Archiac had previously observed that these foraminifera characterise
+his &ldquo;Lower Tertiary Series,&rdquo; as contrasted with the Middle, and
+they therefore serve as a good test of age between Eocene and Miocene, at least
+in Belgium and the North of France.<a href="#fn-15.3" name="fnref-15.3"
+id="fnref-15.3"><sup>[3]</sup></a> Between the Bolderberg beds and the Rupelian
+clay there is a great gap in Belgium, which seems, according to M. Beyrich, to
+be filled up in the North of Germany by what he calls the Sternberg beds, and
+which, had Dumont found them in Belgium, he might probably have termed Upper
+Rupelian.
+</p>
+
+<p>
+<b>Lower Miocene of Germany.&mdash;</b><i>Rupelian
+Clay of Hermsdorf, near Berlin.</i>&mdash;Professor Beyrich has
+described a mass of clay, used for making tiles, within seven miles
+of the gates of Berlin, near the village of Hermsdorf, rising up
+from beneath the sands with which that country is chiefly
+overspread. This clay is more than forty feet thick, of a dark
+bluish-grey colour, and, like that of Rupelmonde, contains
+septaria. Among other shells, the <i>Leda Deshayesiana,</i> before
+mentioned (Fig. 156), abounds, together with many species of <i>
+Pleurotoma, Voluta,</i> etc., a certain proportion of the fossils
+being identical in species with those of Rupelmonde.
+</p>
+
+<p>
+<i>Mayence Basin.</i>&mdash;An elaborate description
+has been published by Dr. F. Sandberger of the Mayence tertiary
+area, which occupies a tract from five to twelve miles in breadth,
+extending for a great distance along the left bank of the Rhine
+from Mayence to the neighbourhood of Manheim, and which is also
+found to the east, north, and south-west of Frankfort. M. De
+Koninck, of Liege, first pointed out to me that the purely marine
+portion of the deposit contained many species of shells common to
+the Kleyn Spawen beds, and to the clay of Rupelmonde, near Antwerp.
+Among these he mentioned <i>Cassidaria depressa, Tritonium
+argutum,</i> Brander (<i>T. flandricum,</i> De Koninck), <i>
+Tornatella simulata, Aporrhais Sowbyi, Leda Deshayesiana</i> (Fig.
+156), <i>Corbula pisum,</i> (Fig. 158) and others.
+</p>
+
+<p><b>Lower Miocene Beds of Croatia.</b>&mdash;The Brown Coal of
+Radaboj,
+<a name="page243"></a>near Angram in Croatia, not far from the borders of Styria, is
+covered, says Von Buch, by beds containing the marine shells of the
+Vienna basin, or, in other words, by Upper Miocene or Falunian
+strata. They appear to correspond in age to the Mayence basin, or
+to the Rupelian strata of Belgium. They have yielded more than 200
+species of fossil plants, described by the late Professor Unger.
+These plants are well preserved in a hard marlstone, and contain
+several palms; among them the Sabal, <a href="images/fig151.jpg">
+Fig. 151,</a> p. 237, and another genus allied to the date-palm <i>
+Phœnicites spectabilis.</i> The only abundant plant among the
+Radaboj fossils which is characteristic of the Upper Miocene period
+is the <i>Populus mutabilis,</i> whereas no less than fifty of the
+Radaboj species are common to the more ancient flora of the Lower
+Molasse of Switzerland.</p>
+
+<p><img src="images/fig157.jpg" width="317" height="214" alt=
+"Fig. 157: Vanessa Pluto." /></p>
+
+<p>The insect fauna is very rich, and, like the plants, indicates a
+more tropical climate than do the fossils of Œningen
+presently to be mentioned. There are ten species of Termites, or
+white ants, some of gigantic size, and large dragon-flies with
+speckled wings, like those of the Southern States in North America;
+there are also grasshoppers of considerable size, and even the
+Lepidoptera are not unrepresented. In one instance, the pattern of
+a butterfly&rsquo;s wing has escaped obliteration in the marl-stone
+of Radaboj; and when we reflect on the remoteness of the time from
+which it has been faithfully transmitted to us, this fact may
+inspire the reader with some confidence as to the reliable nature
+of the characters which other insects of a more durable texture,
+such as the beetles, may afford for specific determination. The
+Vanessa above figured retains, says Heer, some of its colours, and
+corresponds with <i>V. Hadena</i> of India.</p>
+
+<p>
+<a name="page244"></a>Professor Beyrich has made known to us the existence of a long
+succession of marine strata in North Germany, which lead by an
+almost gradual transition from beds of Upper Miocene age to others
+of the age of the base of the Lower Miocene. Although some of the
+German lignites called Brown Coal belong to the upper parts of this
+series, the most important of them are of Lower Miocene date, as,
+for example, those of the Siebengebirge, near Bonn, which are
+associated with volcanic rocks.</p>
+
+<p>Professor Beyrich confines the term &ldquo;Miocene&rdquo; to
+those strata which agree in age with the faluns of Touraine, and he
+has proposed the term &ldquo;Oligocene&rdquo; for those older
+formations called Lower Miocene in this work.</p>
+
+<p><b>Lower Miocene of Italy.</b>&mdash;In the hills of which the
+Superga forms a part there is a great series of Tertiary strata
+which pass downward into the Lower Miocene. Even in the Superga
+itself there are some fossil plants which, according to Heer, have
+never been found in Switzerland so high as the marine Molasse, such
+as <i>Banksia longifolia,</i> and <i>Carpinus grandis.</i> In
+several parts of the Ligurian Apennines, as at Dégo and
+Carcare, the Lower Miocene appears, containing some nummulites, and
+at Cadibona, north of Savona, fresh-water strata of the same age
+occur, with dense beds of lignite inclosing remains of the <i>
+Anthracotherium magnum</i> and <i>A. minimum,</i> besides other
+mammalia enumerated by Gastaldi. In these beds a great number of
+the Lower Miocene plants of Switzerland have been discovered.</p>
+
+<p><b>Lower Miocene of England&mdash;Hempstead Beds.</b>&mdash;We
+have already stated that the Upper Miocene formation is nowhere
+represented in the British Isles; but strata referable to the Lower
+Miocene period are found both in England, Scotland, and Ireland. In
+the Hampshire basin these occupy a very small superficial area,
+having been discovered by the late Edward Forbes at Hempstead near
+Yarmouth, in the northern part of the Isle of Wight, where they are
+170 feet thick, and rich in characteristic marine shells. They
+overlie the uppermost of an extensive series of Eocene deposits of
+marine, brackish, and fresh-water formations, which rest on the
+Chalk and terminate upward in strata corresponding in age to the
+Paris gypsum, and containing the same extinct genera of quadrupeds,
+<i>Palæotherium, Anoplotherium,</i> and others which Cuvier
+first described. The following is the succession of these Lower
+Miocene strata, most of them exposed in a cliff east of
+Yarmouth:</p>
+
+<p>
+1. The uppermost or Corbula beds, consisting of marine sands and clays, contain
+<i>Voluta Rathieri,</i> a characteristic <a name="page245"></a>Lower Miocene
+shell; <i>Corbula pisum</i> (Fig. 158), a species common to the Upper Eocene
+clay of Barton; Cyrena semistriata (Fig. 159), several Cerithia, and other
+shells peculiar to this series.
+</p>
+
+<p><img src="images/fig158.jpg" width="394" height="341" alt=
+"Fig. 158: Corbula pisum. Fig. 159: Cyrena semistriata. Fig. 160: Cerithium
+plicatum. Fig. 161: Cerithium elegans. Fig. 162: Rissoa Chastelii. Fig. 163:
+Paludina lenta." />
+</p>
+
+<p>2. Next are fresh-water and estuary marls and carbonaceous clays
+in the brackish-water portion of which are found abundantly <i>
+Cerithium plicatum,</i> Lam. (Fig. 160), <i>Cerithium elegans</i>
+(Fig. 161), and <i>Cerithium tricinctum</i>; also <i>Rissoa
+Chastelii</i> (Fig. 162), a very common Kleyn Spawen shell, and
+which occurs in each of the four subdivisions of the Hempstead
+series down to its base, where it passes into the Bembridge beds.
+In the fresh-water portion of the same beds <i>Paludina lenta</i>
+(Fig. 163) occurs; a shell identified by some conchologists with a
+species now living, <i>P. unicolor</i>; also several species of <i>
+Lymneus, Planorbis,</i> and <i>Unio.</i></p>
+
+<p>3. The next series, or middle fresh-water and estuary marls, are
+distinguished by the presence of <i>Melania fasciata, Paludina
+lenta,</i> and clays with <i>Cypris</i>; the lowest bed contains
+<i>Cyrena semistriata</i> (Fig. 159), mingled with Cerithia and a
+<i>panopæa.</i></p>
+
+<p>
+4. The lower fresh-water and estuary marls contain <i>Melania costata,</i>
+Sowerby, <i>Melanopsis,</i> etc. The bottom bed is carbonaceous, and called the
+&ldquo;Black band,&rdquo; in which <i> Rissoa Chastelii</i> (Fig. 162), before
+alluded to, is common. This bed contains a mixture of Hempstead shells with
+those of the underlying Upper Eocene or Bembridge series. The mammalia, <a
+name="page246"></a>among which is <i>Hyopotamus bovinus,</i> differ, so far as
+they are known, from those of the Bembridge beds. Among the plants, Professor
+Heer has recognised four species common to the lignite of Bovey Tracey, a Lower
+Miocene formation presently to be described: namely, <i>Sequoia Couttsiæ,</i>
+Heer; <i>Andromeda reticulata,</i> Ettings.; <i>Nelumbium (Nymphœa) doris,</i>
+Heer; and <i>Carpolithes Websteri,</i> Brong.<a href="#fn-15.4"
+name="fnref-15.4" id="fnref-15.4"><sup>[4]</sup></a> The seed-vessels of
+<i>Chara medicaginula,</i> Brong, and <i>C. helicteres</i> are characteristic
+of the Hempstead beds generally.
+</p>
+
+<p>The <i>Hyopotamus</i> belongs to the hog tribe, or the same
+family as the Anthracotherium, of which seven species, varying in
+size from the hippopotamus to the wild boar, have been found in
+Italy and other part of Europe associated with the lignites of the
+Lower Miocene period.</p>
+
+<p><b>Lignites and Clays of Bovey Tracey,
+Devonshire.</b>&mdash;Surrounded by the granite and other rocks of
+the Dartmoor hills in Devonshire, is a formation of clay, sand, and
+lignite, long known to geologists as the Bovey Coal formation,
+respecting the age of which, until the year 1861, opinions were
+very unsettled. This deposit is situated at Bovey Tracey, a village
+distant eleven miles from Exeter in a south-west, and about as far
+from Torquay in a north-west direction. The strata extend over a
+plain nine miles long, and they consist of the materials of
+decomposed and worn-down granite and vegetable matter, and have
+evidently filled up an ancient hollow or lake-like expansion of the
+valleys of the Bovey and Teign.</p>
+
+<p>
+The lignite is of bad quality for economical purposes, as there is a great
+admixture in it of iron pyrites, and it emits a sulphurous odour, but it has
+been successfully applied to the baking of pottery, for which some of the fine
+clays are well adapted. Mr. Pengelly has confirmed Sir H. De la Beche&rsquo;s
+opinion that much of the upper portion of this old lacustrine formation has
+been removed by denudation.<a href="#fn-15.5" name="fnref-15.5"
+id="fnref-15.5"><sup>[5]</sup></a>
+</p>
+
+<p>At the surface is a dense covering of clay and gravel with
+angular stones probably of the Post-pliocene period, for in the
+clay are three species of willow and the dwarf birch, <i>Betula
+nana,</i> indicating a climate colder than that of Devonshire at
+the present day.</p>
+
+<p>Below this are Lower Miocene strata about 300 feet in thickness,
+in the upper part of which are twenty-six beds of lignite, clay,
+and sand, and at their base a ferruginous quartzose sand, varying
+in thickness from two to twenty-seven
+<a name="page247"></a>feet. Below this sand are forty-five beds of alternating lignite
+and clay. No shells or bones of mammalia, and no insect, with the
+exception of one fragment of a beetle (<i>Buprestis</i>); in a
+word, no organic remains, except plants, have as yet been found.
+These plants occur in fourteen of the beds&mdash;namely, in two of the
+clays, and the rest in the lignites. One of the beds is a perfect
+mat of the debris of a coniferous tree, called by Heer <i>Sequoia
+Couttsiæ,</i> intermixed with leaves of ferns. The same
+Sequoia (before mentioned as a Hempstead fossil, p. 246) is spread
+through all parts of the formation, its cones, and seeds, and
+branches of every age being preserved. It is a species supplying a
+link between <i>Sequoia Langsdorfii</i> (see <a href=
+"images/fig152.jpg">Fig. 153,</a> p. 238) and <i>S.
+Sternbergi,</i> the widely spread fossil representatives of the two
+living trees <i>S. sempervirens</i> and <i>S. gigantea</i> (or
+Wellingtonia), both now confined to California. Another bed is full
+of the large rhizomes of ferns, while two others are rich in
+dicotyledonous leaves. In all, Professor Heer enumerates forty-nine
+species of plants, twenty of which are common to the Miocene beds
+of the Continent, a majority of them being characteristic of the
+Lower Miocene. The new species, also of Bovey, are allied to plants
+of the older Miocene deposits of Switzerland, Germany, and other
+Continental countries. The grape-stones of two species of vine
+occur in the clays, and leaves of the fig and seeds of a
+water-lily. The oak and laurel have supplied many leaves. Of the
+triple-nerved laurels several are referred to Cinnamomum. There are
+leaves also of a palm of which the genus is not determined. Leaves
+also of proteaceous forms, like some of the Continental fossils
+before mentioned, occur, and ferns like the well-known <i>
+Lastræa stiriaca</i> (<a href="images/fig154.jpg">Fig.
+154,</a> p. 238), displaying at Bovey, as in Switzerland, its
+fructification.</p>
+
+<p>The croziers of some of the young ferns are very perfect, and
+were at first mistaken by collectors for shells of the genus <i>
+Planorbis.</i> On the whole, the vegetation of Bovey implies the
+existence of a sub-tropical climate in Devonshire, in the Lower
+Miocene period.</p>
+
+<p>
+<b>Scotland: Isle of Mull.</b>&mdash;In the sea-cliffs forming the headland of
+Ardtun, on the west coast of Mull, in the Hebrides, several bands of tertiary
+strata containing leaves of dicotyledonous plants were discovered in 1851 by
+the Duke of Argyll.<a href="#fn-15.6" name="fnref-15.6"
+id="fnref-15.6"><sup>[6]</sup></a> From his description it appears that there
+are three leaf-beds, varying in thickness from 1&frac12; to 5&frac12; feet,
+which are interstratified with volcanic tuff and trap, the whole mass being
+about 130 feet in thickness. A sheet of basalt 40 feet <a
+name="page248"></a>thick covers the whole; and another columnar bed of the same
+rock, ten feet thick, is exposed at the bottom of the cliff. One of the
+leaf-beds consists of a compressed mass of leaves unaccompanied by any stems,
+as if they had been blown into a marsh where a species of <i>Equisetum</i>
+grew, of which the remains are plentifully imbedded in clay.
+</p>
+
+<p>
+It is supposed by the Duke of Argyll that this formation was accumulated in a
+shallow lake or marsh in the neighbourhood of a volcano, which emitted showers
+of ashes and streams of lava. The tufaceous envelope of the fossils may have
+fallen into the lake from the air as volcanic dust, or have been washed down
+into it as mud from the adjoining land. Even without the aid of organic remains
+we might have decided that the deposit was newer than the chalk, for
+chalk-flints containing cretaceous fossils were detected by the duke in the
+principal mass of volcanic ashes or tuff.<a href="#fn-15.7" name="fnref-15.7"
+id="fnref-15.7"><sup>[7]</sup></a>
+</p>
+
+<p>The late Edward Forbes observed that some of the plants of this
+formation resembled those of Croatia, described by Unger, and his
+opinion has been confirmed by Professor Heer, who found that the
+conifer most prevalent was the <i>Sequoia Langsdorfii</i> (<a href=
+"images/fig152.jpg">Fig. 153,</a> p. 238), also <i>Corylus
+grossedentata,</i> a Lower Miocene species of Switzerland and of
+Menat in Auvergne. There is likewise a plane-tree, the leaves of
+which seem to agree with those of <i>Platanus aceroides</i> (<a
+href="images/fig141.jpg">Fig. 141</a>), and a fern which is as yet
+peculiar to Mull, <i>Filicites hebridica,</i> Forbes.</p>
+
+<p>These interesting discoveries in Mull led geologists to suspect
+that the basalt of Antrim, in Ireland, and of the celebrated
+Giant&rsquo;s Causeway, might be of the same age. The volcanic
+rocks that overlie the chalk, and some of the strata associated
+with and interstratified between masses of basalt, contain leaves
+of dicotyledonous plants, somewhat imperfect, but resembling the
+beech, oak, and plane, and also some coniferæ of the genera
+pine and Sequoia. The general dearth of strata in the British
+Isles, intermediate in age between the formation of the Eocene and
+Pliocene periods, may arise, says Professor Forbes, from the extent
+of dry land which prevailed in that vast interval of time. If land
+predominated, the only monuments we are likely ever to find of
+Miocene date are those of lacustrine and volcanic origin, such as
+the Bovey Coal in Devonshire, the Ardtun beds in Mull, or the
+lignites and associated basalts in Antrim.</p>
+
+<p>
+<b>Lower Miocene, United states: Nebraska.</b>&mdash;In the territory of
+Nebraska, on the Upper Missouri, near the Platte River, lat. 42&deg; N., a
+tertiary formation occurs, consisting of white <a name="page249"></a>limestone,
+marls, and siliceous clay, described by Dr. D. Dale Owen,<a href="#fn-15.8"
+name="fnref-15.8" id="fnref-15.8"><sup>[8]</sup></a> in which many bones of
+extinct quadrupeds, and of chelonians of land or fresh-water forms, are met
+with. Among these, Dr. Leidy describes a gigantic quadruped, called by him
+<i>Titanotherium,</i> nearly allied to the <i>Palæotherium,</i> but larger than
+any of the species found in the Paris gypsum. With these are several species of
+the genus <i>Oreodon,</i> Leidy, uniting the characters of pachyderms and
+ruminants also; <i>Eucrotaphus,</i> another new genus of the same mixed
+character; two species of rhinoceros of the sub-genus <i>Acerotherium,</i> a
+Lower Miocene form of Europe before mentioned; two species of
+<i>Archæotherium,</i> a pachyderm allied to <i>Chæropotamus</i> and <i>
+Hyracotherium</i>; also <i>Pæbrotherium,</i> an extinct ruminant allied to
+<i>Dorcatherium,</i> Kaup; also <i> Agriochoerus,</i> of Leidy, a ruminant
+allied to <i> Merycopotamus</i> of Falconer and Cautley; and, lastly, a large
+carnivorous animal of the genus <i>Machairodus,</i> the most ancient example of
+which in Europe occurs in the Lower Miocene strata of Auvergne, but of which
+some species are found in Pliocene deposits. The turtles are referred to the
+genus <i>Testudo,</i> but have some affinity to <i>Emys.</i> On the whole, the
+Nebraska formation is probably newer than the Paris gypsum, and referable to
+the Lower Miocene period, as above defined.
+</p>
+
+<p class="footnote">
+<a name="fn-15.1" id="fn-15.1"></a> <a href="#fnref-15.1">[1]</a>
+Bulletin, 1856, Journ., vol. xii, p. 768.
+</p>
+
+<p class="footnote">
+<a name="fn-15.2" id="fn-15.2"></a> <a href="#fnref-15.2">[2]</a>
+Heer &ldquo;Miocene baltische Flora&rdquo; and &ldquo;Fossil-flora von
+Alaska&rdquo; 1869.
+</p>
+
+<p class="footnote">
+<a name="fn-15.3" id="fn-15.3"></a> <a href="#fnref-15.3">[3]</a>
+D&rsquo;Archiac Monogr., pp. 79, 100.
+</p>
+
+<p class="footnote">
+<a name="fn-15.4" id="fn-15.4"></a> <a href="#fnref-15.4">[4]</a>
+Pengelly, preface to The Lignite Formation of Bovey Tracey, p. xvii, London,
+1863.
+</p>
+
+<p class="footnote">
+<a name="fn-15.5" id="fn-15.5"></a> <a href="#fnref-15.5">[5]</a>
+Philos. Trans., 1863. Paper by W. Pengelly, F.R.S., and Dr. Oswald Heer.
+</p>
+
+<p class="footnote">
+<a name="fn-15.6" id="fn-15.6"></a> <a href="#fnref-15.6">[6]</a>
+Quart. Geol. Journal, 1851, p. 19.
+</p>
+
+<p class="footnote">
+<a name="fn-15.7" id="fn-15.7"></a> <a href="#fnref-15.7">[7]</a>
+Quart. Geol. Journal, 1851, p. 90.
+</p>
+
+<p class="footnote">
+<a name="fn-15.8" id="fn-15.8"></a> <a href="#fnref-15.8">[8]</a>
+David Dale Owen, Geol. Survey of Wisconsin, etc., Philad., 1852.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap16"></a><a name="page250"></a>CHAPTER XVI.<br/>
+EOCENE FORMATIONS.</h2>
+
+<p class="letter">Eocene Areas of North of Europe. &mdash; Table of
+English and French Eocene Strata. &mdash; Upper Eocene of England.
+&mdash; Bembridge Beds. &mdash; Osborne or St. Helen&rsquo;s Beds.
+&mdash; Headon Series. &mdash; Fossils of the Barton Sands and
+Clays. &mdash; Middle Eocene of England. &mdash; Shells,
+Nummulites, Fish and Reptiles of the Bracklesham Beds and Bagshot
+Sands. &mdash; Plants of Alum Bay and Bournemouth. &mdash; Lower
+Eocene of England. &mdash; London Clay Fossils. &mdash; Woolwich
+and Reading Beds formerly called &ldquo;Plastic Clay.&rdquo;
+Fluviatile Beds underlying Deep-sea Strata. &mdash; Thanet Sands.
+&mdash; Upper Eocene Strata of France. &mdash; Gypseous Series of
+Montmartre and Extinct Quadrupeds. &mdash; Fossil Footprints in
+Paris Gypsum. &mdash; Imperfection of the Record. &mdash; Calcaire
+Silicieux. &mdash; Gres de Beauchamp. &mdash; Calcaire Grossier.
+&mdash; Miliolite Limestone. &mdash; Soissonnais Sands. &mdash;
+Lower Eocene of France. &mdash; Nummulitic Formations of Europe,
+Africa, and Asia. &mdash; Eocene Strata in the United States.
+&mdash; Gigantic Cetacean.</p>
+
+<p><b>Eocene Areas of the North of Europe.</b>&mdash;The strata
+next in order in the descending series are those which I term
+Eocene.</p>
+
+<p><img src="images/fig164.jpg" width="348" height="306" alt=
+"Fig. 164: Map of the principal Eocene areas of North-western Europe." />
+</p>
+
+<p>In the map (Fig. 164) the position of several Eocene areas in
+the north of Europe is pointed out. When this map was constructed I
+classed as the newer part of the
+<a name="page251"></a>Eocene those Tertiary strata which have been described in the
+last chapter as Lower Miocene, and to which M. Beyrich has given
+the name of Oligocene. None of these occur in the London Basin, and
+they occupy in that of Hampshire, as we have seen at <a href=
+"#page244">p. 244</a>, too insignificant a superficial
+area to be noticed in a map on this scale. They fill a larger space
+in the Paris Basin between the Seine and the Loire, and constitute
+also part of the northern limits of the area of the Netherlands
+which are shaded in the map.</p>
+
+<p>
+It is in the northern part of the Isle of Wight that we have the uppermost beds
+of the true Eocene best exhibited&mdash;namely, those which correspond in their
+fossils with the celebrated gypsum of the Paris basin before alluded to, p. 231
+(see Table, p. 252). That gypsum has been selected by almost all Continental
+geologists as affording the best line of demarkation between the Middle and
+Lower Tertiary, or, in other words, between the Lower Miocene and Eocene
+formations.
+</p>
+
+<p>In reference to the Table I may observe, that the correlation of
+the French and English subdivisions here laid down is often a
+matter of great doubt and difficulty, notwithstanding their
+geographical proximity. This arises from various circumstances,
+partly from the former prevalence of marine conditions in one basin
+simultaneously with fluviatile or lacustrine in the other, and
+sometimes from the existence of land in one area causing a break or
+absence of all records during a period when deposits may have been
+in progress in the other basin. As bearing on this subject, it may
+be stated that we have unquestionable evidence of oscillations of
+level shown by the superposition of salt or brackish-water strata
+to fluviatile beds; and those of deep-sea origin to strata formed
+in shallow water. Even if the upward and downward movements were
+uniform in amount and direction, which is very improbable, their
+effect in producing the conversion of sea into land or land into
+sea would be different, according to the previous shape and varying
+elevation of the land and bottom of the sea. Lastly, denudation,
+marine and subaërial, has frequently caused the absence of
+deposits in one basin of corresponding age to those in the other,
+and this destructive agency has been more than ordinarily effective
+on account of the loose and unconsolidated nature of the sands and
+clays.</p>
+
+<p class="center">
+<a name="page252"></a>TABLE OF ENGLISH AND FRENCH EOCENE STRATA.<br/>
+<small>UPPER EOCENE</small></p>
+
+<table border="0" cellspacing="6" cellpadding="0" summary=
+"Upper, Middle, and Lower eocene strata: left side is English subdivisions,
+right side is French equivalents.">
+<tr>
+<td align="center">English subdivisions</td>
+<td align="center">French equivalents</td>
+</tr>
+
+<tr>
+<td valign="top">A.1. Bembridge series, Isle of Wight,
+p. 252.</td>
+<td valign="top">A.1. Gypseous series of Montmartre,
+<a href="#page270">p. 270.</a></td>
+</tr>
+
+<tr>
+<td valign="top">A.2. Osborne or St. Helen&rsquo;s series,
+Isle of Wight, <a href="#page255">p. 255.</a></td>
+<td valign="top">A.2 and 3. Calcaire siliceux, or
+Travertin Inférieur, <a href="#page273">p. 273.</a></td>
+</tr>
+
+<tr>
+<td valign="top">A.3. Headon series, Isle of Wight, <a
+href="#page255">p. 255.</a></td>
+<td >&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="top">A.4. Barton series. Sands and clays
+of Barton Cliff, Hants, <a href="#page258">p. 258.</a></td>
+<td valign="top">A.4. Grès de Beauchamp, or
+Sables Moyens, <a href="#page273">p. 273.</a></td>
+</tr>
+
+<tr>
+<td colspan="2" align="center"><small>MIDDLE EOCENE</small></td>
+</tr>
+
+<tr>
+<td valign="top">B.1. Bracklesham series, <a href=
+"#page259">p. 259.</a></td>
+<td valign="top">B.1. Calcaire Grossier <a href=
+"#page274">p. 274</a></td>
+</tr>
+
+<tr>
+<td valign="top">B.2. Alum Bay and Bournemouth beds,
+<a href="#page259">p. 259.</a></td>
+<td valign="top">B.2. Wanting in France?</td>
+</tr>
+
+<tr>
+<td valign="top">B.2. Wanting in England?</td>
+<td valign="top">B.2. Soissonnais Sands, or Lits
+Coquilliers, <a href="#page275">p. 275</a></td>
+</tr>
+
+<tr>
+<td colspan="2" align="center"><small>LOWER EOCENE</small></td>
+</tr>
+
+<tr>
+<td valign="top">C.1. London Clay, <a href="#page263">
+p. 263.</a></td>
+<td valign="top">C.1. Argile de Londres, Cassel, near
+Dunkirk.</td>
+</tr>
+
+<tr>
+<td valign="top">C.2. Woolwich and Reading series, <a
+href="#page267">p. 267.</a></td>
+<td valign="top">C.2. Argile plastique and lignite, <a
+href="#page276">p. 276</a></td>
+</tr>
+
+<tr>
+<td valign="top">C.3. Thanet sands, <a href=
+"#page269">p. 269.</a></td>
+<td valign="top">C.3. Sables de Bracheux, <a href=
+"#page276">p. 276</a></td>
+</tr>
+</table>
+
+<p><small>UPPER EOCENE, ENGLAND.</small></p>
+
+<p><b>Bembridge Series, A.1.</b>&mdash;These beds are about 120
+feet thick, and, as stated in <a href="#page245">p.
+245,</a> lie immediately under the Hempstead beds, near Yarmouth,
+in the Isle of Wight, being conformable with those Lower Miocene
+strata. They consist of marls, clays, and limestones of
+fresh-water, brackish, and marine origin. Some of the most abundant
+shells, as <i>Cyrena semistriata</i> var., and <i>Paludina
+lenta,</i> <a href="images/fig158.jpg">Fig. 163,</a> are common to
+this and to the overlying Hempstead series; but the majority of the
+species are distinct. The following are the subdivisions described
+by the late Professor Forbes:<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>a.</i> Upper marls, distinguished
+by the abundance of <i>Melania turritissima,</i> Forbes (<a href=
+"images/fig165.jpg">Fig. 165</a>).<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>b.</i> Lower marls, characterised
+by <i>Cerithium mutabile, Cyrena pulchra,</i> etc., and by the
+remains of <i>Trionyx</i> (see <a href="images/fig165.jpg">Fig.
+166</a>).<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>c.</i> Green marls, often
+abounding in a peculiar species of oyster, and accompanied by <i>
+Cerithium, Mytilus, Arca, nucula,</i> etc.<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>d.</i> Bembridge limestones,
+compact cream-coloured limestones alternating with shales and
+marls, in all of which land-shells are common, especially at
+Sconce, near Yarmouth,
+<a name="page253"></a>as described by Mr. F. Edwards. The <i>Bulimus ellipticus,</i>
+Fig. 167, and <i>Helix occlusa,</i> Fig. 168, are among its best
+known land-shells. <i>Paludina orbicularis,</i> Fig. 169, is also
+of frequent occurrence. One of the bands is filled with a little
+globular <i>Paludina.</i> Among the fresh-water pulmonifera, <i>
+Lymnea longiscata</i> (Fig. 171) and <i>Planorbis discus</i> (Fig.
+170)
+<a name="page254"></a>are the most generally distributed: the latter represents
+or takes the place of the <i>Planorbis euomphalus</i> (see Fig. 175) of the
+more ancient Headon series. <i>Chara tuberculata</i> (Fig. 172) is the
+characteristic Bembridge gyrogonite or seed-vessel.
+</p>
+
+<p><img src="images/fig165.jpg" width="418" height="584" alt=
+"Fig. 165: Melania turritissima, Fig. 166: Fragment of Carapace of Trionyx,
+Fig. 167: Bulimus ellipticus, Fig. 168: Helix occlusa, Fig. 169: Paludina
+orbicularis, Fig. 170: Planorbis discus, Fig. 171: Lymnea longiscata, Fig. 172:
+Chara tuberculata." />
+</p>
+
+<img src="images/fig173.jpg" width="126" height="176" alt=
+"Fig. 173: Lower molar tooth." />
+
+<p>From this formation on the shores of Whitecliff Bay, Dr. Mantell
+obtained a fine specimen of a fan palm, <i>Flabellaria
+Lamanonis,</i> Brong., a plant first obtained from beds of
+corresponding age in the suburbs of Paris. The well-known
+building-stone of Binstead, near Ryde, a limestone with numerous
+hollows caused by Cyrenæ which have disappeared and left the
+moulds of their shells, belongs to this subdivision of the
+Bembridge series. In the same Binstead stone Mr. Pratt and the
+Reverend Darwin Fox first discovered the remains of mammalia
+characteristic of the gypseous series of Paris, as <i>
+Palæotherium magnum</i> (Fig. 174), <i>P. medium, P. minus,
+P. minimum, P. curtum, P. crassum</i>; also <i>Anoplotherium
+commune</i> (Fig. 173), <i>A. secundarium, Dichobune cervinum,</i>
+and <i>Chæropotamus Cuvieri.</i> The Palæothere above
+alluded to resembled the living tapir in the form of the head, and
+in having a short proboscis, but its molar teeth were more like
+those of the rhinoceros. <i>Palæotherium magnum</i> was of
+the size of a horse, three or four feet high. The woodcut, Fig.
+174, is one of the restorations which Cuvier attempted of the
+outline of the living animal, derived from the study of the entire
+skeleton.
+<a name="page255"></a>As the vertical range of particular species of quadrupeds, so
+far as our knowledge extends, is far more limited than that of the
+testacea, the occurrence of so many species at Binstead, agreeing
+with fossils of the Paris gypsum, strengthens the evidence derived
+from shells and plants of the synchronism of the two
+formations.</p>
+
+<p><img src="images/fig174.jpg" width="392" height="246" alt=
+"Fig. 174: Palæotherium magnum." /></p>
+
+<p><b>Osborne or St. Helen&rsquo;s Series, A.2.</b>&mdash;This
+group is of fresh and brackish-water origin, and very variable in
+mineral character and thickness. Near Ryde, it supplies a freestone
+much used for building, and called by Professor Forbes the
+Nettlestone grit. In one part ripple-marked flagstones occur, and
+rocks with fucoidal markings. The Osborne beds are distinguished by
+peculiar species of <i>Paludina, Melania,</i> and <i>
+Melanopsis,</i> as also of <i>Cypris</i> and the seeds of <i>
+Chara.</i></p>
+
+<p><img src="images/fig175.jpg" width="403" height="165" alt=
+"Fig. 175: Planorbis euomphalus, Fig. 176: Helix labyrinthica." />
+</p>
+
+<p><b>Headon Series A.3.</b>&mdash;These beds are seen both in
+Whitecliff Bay, Headon Hill, and Alum Bay, or at the east and west
+extremities of the Isle of Wight. The upper and lower portions are
+fresh-water, and the middle of mixed origin, sometimes brackish and
+marine. Everywhere <i>Planorbis euomphalus,</i> Fig. 175,
+characterises the fresh-water deposits, just as the allied form, P.
+discus, <a href="images/fig165.jpg">Fig. 170,</a> does the
+Bembridge limestone. The brackish-water beds contain <i>Potamomya
+plana, Cerithium mutabile,</i> and <i>Potamides cinctus</i> (<a
+href="images/fig37.jpg">Fig. 37</a>), and the marine beds <i>
+Venus</i> (or <i>Cytherea</i>) <i>incrassata,</i> a species common
+to the Limburg beds and Grès de Fontainebleau, or the Lower
+Miocene series. The prevalence of salt-water remains is most
+conspicuous in some of the central parts of the formation.</p>
+
+<img src="images/fig177.jpg" width="102" height="91" alt=
+"Fig. 177: Neritina concava." />
+
+<p>
+Among the shells which are widely distributed through the Headon series are
+<i>Neritina concava</i> (Fig. 177), <i>Lymnea caudata</i> (Fig. 178), and <i>
+Cerithium concavum</i> (Fig. 179). <i>Helix labyrinthica,</i> Say (Fig. 176), a
+land-shell now inhabiting the United States, was discovered in this series by
+Mr. Searles Wood in Hordwell Cliff. It is also
+<a name="page256"></a>met with in Headon Hill, in the same beds. At Sconce, in
+the Isle of Wight, it occurs in the Bembridge series, and affords a rare
+example of an Eocene fossil of a species still living, though, as usual in such
+cases, having no local connection with the actual geographical range of the
+species. The lower and middle portion of the Headon series is also met with in
+Hordwell Cliff (or Hordle, as it is often spelt), near Lymington, Hants. Among
+the shells which abound in this cliff are <i>Paludina lenta</i> and various
+species of <i>Lymnea, Planorbis, Melania, Cyclas, Unio, Potamomya,
+Dreissena,</i> etc.
+</p>
+
+<img src="images/fig178.jpg" width="136" height="339" alt=
+"Fig. 178: Lymnea caudata, Fig. 179: Cerithium concavum." />
+
+<p>Among the chelonians we find a species of <i>Emys,</i> and no
+less than six species of <i>Trionyx</i>; among the saurians an
+alligator and a crocodile; among the ophidians two species of
+land-snakes (<i>Paleryx,</i> Owen); and among the fish Sir P.
+Egerton and Mr. Wood have found the jaws, teeth, and hard shining
+scales of the genus <i>Lepidosteus,</i> or bony pike of the
+American rivers. This same genus of fresh-water ganoids has also
+been met with in the Hempstead beds in the Isle of Wight. The bones
+of several birds have been obtained from Hordwell, and the remains
+of quadrupeds of the genera <i>Palæotherium (P. minus),
+Anoplotherium, Anthracotherium, Dichodon, Dichobune,
+Spalacodon,</i> and <i>Hyænodon.</i> The latter offers, I
+believe, the oldest known example of a true carnivorous animal in
+the series of British fossils, although I attach very little
+theoretical importance to the fact, because herbivorous species are
+those most easily met with in a fossil state in all save cavern
+deposits. In another point of view, however, this fauna deserves
+notice. Its geological position is considerably lower than that of
+the Bembridge or Montmartre beds, from which it differs almost as
+much in species as it does from the still more ancient fauna of the
+Lower Eocene beds to be mentioned in the sequel. It therefore
+teaches us what a grand succession of distinct assemblages of
+mammalia flourished on the earth during the Eocene period.</p>
+
+<p>
+Many of the marine shells of the brackish-water beds of the above series, both
+in the Isle of Wight and Hordwell Cliff, are common to the underlying Barton
+Clay: and, on the other hand, there are some fresh-water shells, such as
+<i>Cyrena obovata,</i> which are common to the Bembridge beds,
+<a name="page257"></a>notwithstanding the intervention of the St. Helen&rsquo;s
+series. The white and green marls of the Headon series, and some of the
+accompanying limestones, often resemble the Eocene strata of France in mineral
+character and colour in so striking a manner as to suggest the idea that the
+sediment was derived from the same region or produced contemporaneously under
+very similar geographical circumstances.
+</p>
+
+<p>At Brockenhurst, near Lyndhurst, in the New Forest, marine
+strata have recently been found containing fifty-nine shells, of
+which many have been described by Mr. Edwards. These beds rest on
+the Lower Headon, and are considered as the equivalent of the
+middle part of the Headon series, many of the shells being common
+to the brackish-water or Middle Headon beds of Colwell and
+Whitecliff Bays, such as <i>Cancellaria muricata,</i> Sowerby, <i>
+Fusus labiatus,</i> Sowerby, etc. In these beds at Brockenhurst,
+corals, ably described by Dr. Duncan, have recently been found in
+abundance and perfection; see Fig. 180, <i>Solenastræa
+cellulosa.</i></p>
+
+<img src="images/fig180.jpg" width="179" height="194" alt=
+"Fig. 180: Solenastræa cellulosa." />
+
+<p>
+Baron von Könen<a href="#fn-16.1" name="fnref-16.1"
+id="fnref-16.1"><sup>[1]</sup></a> has pointed out that no less than forty-six
+out of the fifty-nine Brockenhurst shells, or a proportion of 78 per cent,
+agree with species occurring in Dumont&rsquo;s Lower Tongrian formation in
+Belgium. This being the case, we might fairly expect that if we had a marine
+equivalent of the Bembridge series or of the contemporaneous Paris gypsum, we
+should find it to contain a still greater number of shells common to the
+Tongrian beds of Belgium, but the exact correlation of these fresh-water groups
+of France, Belgium, and Britain has not yet been fully made out. It is possible
+that the Tongrian of Dumont may be newer than the Bembridge series, and
+therefore referable to the Lower Miocene. If ever the whole series should be
+complete, we must be prepared to find the marine equivalent of the Bembridge
+beds, or the uppermost Eocene, passing by imperceptible shades into the
+inferior beds of the overlying Miocene strata.
+</p>
+
+<p>Among the fossils found in the Middle Headon are <i>Cytherea
+incrassata</i> and <i>Cerithium plicatum</i> <a href=
+"images/fig158.jpg">(Fig. 160).</a> These shells, especially the
+latter, are very characteristic of the Lower Miocene, and their
+occurrence in the Headon series has been cited as an objection to
+the line proposed to be
+<a name="page258"></a>drawn between Miocene and Eocene. But if we were to attach
+importance to such occasional passages, we should soon find that no
+lines of division could be drawn anywhere, for in the present state
+of our knowledge of the Tertiary series there will always be
+species common to beds above and below our boundary-lines.</p>
+
+<img src="images/fig181.jpg" width="99" height="142" alt=
+"Fig. 181: Chama squamosa." />
+
+<p><b>Barton Series</b> (<i>Sands and Clays</i>), <b>A.4</b> <a
+href="#page252">Table</a>&mdash;Both in the Isle of Wight, and in
+Hordwell Cliff, Hants, the Headon beds, above-mentioned, rest on
+white sands usually devoid of fossils, and used in the Isle of
+Wight for making glass. In one of these sands Dr. Wright found <i>
+Chama squamosa,</i> a Barton Clay shell, in great plenty, and
+certain impressions of marine shells have been found in sands
+supposed to be of the same age in Whitecliff Bay. These sands have
+been called Upper Bagshot in the maps of our Government Survey, but
+this identification of a fossiliferous series in the Isle of Wight
+with an unfossiliferous formation in the London Basin can scarcely
+be depended upon. The Barton Clay, which immediately underlies
+these sands, is seen vertical in Alum Bay, Isle of Wight, and
+nearly horizontal in the cliffs of the mainland near Lymington.
+This clay, together with the Bracklesham beds, presently to be
+described, has been termed Middle Bagshot by the Survey. In Barton
+Cliff, where it attains a thickness of about 300 feet, it is rich
+in marine fossils.</p>
+
+<p>It was formerly confounded with the London Clay, an older Eocene
+deposit of very similar mineral character, to be mentioned (<a
+href="#page263">p. 263</a>), which contains many shells in common,
+but not more than one-fourth of the whole. In other words, there
+are known at present 247 species in the London Clay and 321 in that
+of Barton, and only 70 common to the two formations. Fifty-six of
+these have been found in the intermediate Bracklesham beds, and the
+reappearance of the other 14 may imply a return of similar
+conditions, whether of temperature or depth or of a muddy
+argillaceous bottom, common to the two periods of the London and
+Barton Clays. According to M. Hebert, the most characteristic
+Barton Clay fossils correspond to those of the Gres de Beauchamp,
+or Sables Moyens, of the Paris Basin, but it also contains many
+common to the older Calcaire Grossier.</p>
+
+<p class="center">
+<small>SHELLS OF THE BARTON CLAY.</small>
+</p>
+
+<p>Certain foraminifera called Nummulites begin, when we study the
+Tertiary formations in a descending order, to make
+<a name="page259"></a>their first appearance in these beds. A small species called <i>
+Nummulites variolaria,</i> Fig. 190, is found both on the Hampshire
+coast and in beds of the same age in Whitecliff Bay, in the Isle of
+Wight. Several marine shells, such as <i>Corbula pisum</i> <a href=
+"images/fig158.jpg">(Fig. 158),</a> are common to the Barton beds
+and the Hempstead or Lower Miocene series, and a still greater
+number, as before stated, are common to the Headon series.</p>
+
+<p><img src="images/fig182.jpg" width="371" height="503" alt=
+"Fig. 182: Mitra scabra, Fig. 183: Voluta ambigua, Fig. 184: Typhis pungens,
+Fig. 185: Voluta athleta, Fig. 186: Terebellum fusiforme, Fig. 187: Terebellum
+sopita, Fig. 188: Cardita sulcata, Fig. 189: Crassatella sulcata, Fig. 190:
+Nummulites variolaria." />
+</p>
+
+<p class="center">
+<small>MIDDLE EOCENE, ENGLAND.</small>
+</p>
+
+<p><b>Bracklesham Beds and Bagshot Sands, B.1,</b> <a href=
+"#page252">Table</a>&mdash;Beneath the Barton Clay we find in the
+north of the Isle of Wight, both in Alum and Whitecliff Bays, a
+great series of various coloured sands and clays for the most part
+unfossiliferous,
+<a name="page260"></a>and probably of estuarine origin. As some of these beds contain
+<i>Cardita planicosta</i> (Fig. 191) they have been identified with
+the marine beds much richer in fossils seen in the coast section in
+Bracklesham Bay near Chichester in Sussex, where the strata consist
+chiefly of green clayey sands with some lignite. Among the
+Bracklesham fossils besides the Cardita, the huge <i>Cerithium
+giganteum</i> is seen, so conspicuous in the Calcaire Grossier of
+Paris, where it is sometimes two feet in length. The <i>Nummulites
+lævigata</i> (see Fig. 192), so characteristic of the lower
+beds of the Calcaire Grossier in France, where it sometimes forms
+stony layers, as near Compiègne, is very common in these
+beds, together with <i>N. scabra</i> and <i>N. variolaria.</i> Out
+of 193 species of testacea procured from the Bagshot and
+Bracklesham beds in England, 126 occur in the Calcaire Grossier in
+France. It was clearly, therefore, coeval with that part of the
+Parisian series more nearly than with any other.</p>
+
+<p><img src="images/fig191.jpg" width="318" height="401" alt=
+"Fig. 191: Cardita (Venericardia) planicosta, Fig. 192: Nummulites (Nummularia) lavigata." />
+</p>
+
+<p>
+According to tables compiled from the best authorities by Mr. Etheridge, the
+number of mollusca now known from the Bracklesham beds in Great Britain is 393,
+of which no less <a name="page261"></a>than 240 are peculiar to this
+subdivision of the British Eocene series, while 70 are common to the Older
+London Clay, and 140 to the Newer Barton Clay. The volutes and cowries of this
+formation, as well as the lunulites and corals, favour the idea of a warm
+climate having prevailed, which is borne out by the discovery of a serpent,
+<i>Palæophis typhœus</i> (see Fig. 193), exceeding, according to Professor
+Owen, twenty feet in length, and allied in its osteology to the Boa, Python,
+Coluber, and Hydrus. The compressed form and diminutive size of certain caudal
+vertebræ indicate so much analogy with Hydrus as to induce Professor Owen to
+pronounce this extinct ophidian to have been marine.<a href="#fn-16.2"
+name="fnref-16.2" id="fnref-16.2"><sup>[2]</sup></a> Among the companions of
+the sea-snake of Bracklesham was an extinct crocodile (<i>Gavialis Dixoni,</i>
+Owen), and numerous fish, such as now frequent the seas of warm latitudes, as
+the Ostracion of the family Balistidæ, of which a dorsal spine is figured (see
+Fig. 194), and gigantic rays of the genus <i> Myliobates</i> (see Fig. 195).
+</p>
+
+<p><img src="images/fig193.jpg" width="411" height="286" alt=
+"Fig. 193: Palæophis typhoeus, Owen; an Eocene sea-serpent, Fig. 194: Defensive
+spine of Ostracion." />
+</p>
+
+<img src="images/fig195.jpg" width="195" height="177" alt=
+"Fig. 195: Dental plates of Myliobates Edwardsi." />
+
+<p>The teeth of sharks also, of the genera <i>Carcharodon, Otodus,
+Lamna, Galeocerdo,</i> and others, are abundant. (See Figs. 196,
+197, 198, 199.)<a name="page262"></a></p>
+
+<p><img src="images/fig196.jpg" width="406" height="256" alt=
+"Fig. 196: Carcharodon angustidens, Fig. 197: Otodus obliquus, Fig. 198: Lamna
+elegans, Fig. 199: Galcocerdo latidens." />
+</p>
+
+<p class="center">
+<small>MARINE SHELLS OF BRACKLESHAM BEDS.</small>
+</p>
+
+<p><b>Alum Bay and Bournemouth Beds.</b> (<i>Lower Bagshot of
+English Survey</i>), <b>B.2,</b> <a href="#page252">
+Table</a>&mdash;To that great series of sands and clays which
+intervene between the equivalents of the Bracklesham Beds and the
+London Clay or Lower Eocene, our Government Survey has given the
+name of the Lower Bagshot sands, for they are supposed to agree in
+age with the inferior unfossiliferous sands of the country round
+Bagshot in the London Basin. This part of the series is finely
+exposed in the vertical beds of Alum bay, in the Isle of Wight, and
+east and west of Bournemouth, on the south coast of Hampshire. In
+some of the close and white compact clays of this locality, there
+are not only dicotyledonous leaves, but numerous fronds of ferns
+allied to Gleichenia which are well preserved with their fruit.</p>
+
+<p><img src="images/fig200.jpg" width="411" height="185" alt=
+"Fig. 200: Pleurotoma attenuata, Fig. 201: Voluta Selseïensis, Fig. 202:
+Turritella multisulcata, Fig. 203: Lucina serrata, Fig. 204: Conus deperditus." />
+</p>
+
+<p>
+None of the beds are of great horizontal extent, and there is much
+cross-stratification in the sands, and in some places
+<a name="page263"></a>black carbonaceous seams and lignite. In the midst of these
+leaf-beds in Studland Bay, Purbeck shells of the genus Unio attest
+the fresh-water origin of the white clay.</p>
+
+<p>
+No less than forty species of plants are mentioned by MM. de la Harpe and
+Gaudin from this formation in Hampshire, among which the Proteaceæ
+(<i>Dryandra,</i> etc.) and the fig tribe are abundant, as well as the cinnamon
+and several other laurineæ, with some papilionaceous plants. On the whole, they
+remind the botanist of the types of subtropical India and Australia.<a
+href="#fn-16.3" name="fnref-16.3" id="fnref-16.3"><sup>[3]</sup></a>
+</p>
+
+<p>Heer has mentioned several species which are common to this Alum
+Bay flora and that of Monte Bolca, near Verona, so celebrated for
+its fossil fish, and where the strata contain nummulites and other
+Middle Eocene fossils. He has particularly alluded to <i>Aralia
+primigenia</i> (of which genus a fruit has since been found by Mr.
+Mitchell at Bournemouth), <i>Daphnogene Veronensis,</i> and <i>
+Ficus granadilla,</i> as among the species common to and
+characteristic of the Isle of Wight and Italian Eocene beds; and he
+observes that in the flora of this period these forms of a
+temperate climate which constitute a marked feature in the European
+Miocene formations, such as the willow, poplar, birch, alder, elm,
+hornbeam, oak, fir, and pine, are wanting. The American types are
+also absent, or much more feebly represented than in the Miocene
+period, although fine specimens of the fan-palm (<i>Sabal</i>) have
+been found in these Eocene clays at Studland. The number of exotic
+forms which are common to the Eocene and Miocene strata of Europe,
+like those to be alluded to in the sequel which are common to the
+Eocene and Cretaceous fauna, demonstrate the remoteness of the
+times in which the geographical distribution of living plants
+originated. A great majority of the Eocene genera have disappeared
+from our temperate climates, but not the whole of them; and they
+must all have exerted some influence on the assemblages of species
+which succeeded them. Many of these last occurring in the Upper
+Miocene are indeed so closely allied to the flora now surviving as
+to make it questionable, even in the opinion of naturalists opposed
+to the doctrine of transmutation, whether they are not
+genealogically related the one to the other.</p>
+
+<p class="center">
+<small>LOWER EOCENE FORMATIONS, ENGLAND.</small>
+</p>
+
+<p>London Clay, C.1, <a href="#page252">Table</a>&mdash;This
+formation underlies the preceding, and sometimes attains a
+thickness of 500 feet. It consists of tenacious brown and
+bluish-grey clay,
+<a name="page264"></a>with layers of concretions called septaria, which abound chiefly
+in the brown clay, and are obtained in sufficient numbers from
+sea-cliffs near Harwich, and from shoals off the coast of Essex and
+the Isle of Sheppey, to be used for making Roman cement. The total
+number of British fossil mollusca known at present (January, 1870)
+in this formation are 254, of which 166 are peculiar, or not found
+in other Eocene beds in this country. The principal localities of
+fossils in the London clay are Highgate Hill, near London, the
+Island of Sheppey at the mouth of the Thames, and Bognor on the
+Sussex coast. Out of 133 fossil shells, Mr. Prestwich found only 20
+to be common to the Calcaire Grossier (from which 600 species have
+been obtained), while 33 are common to the &ldquo;Lits
+Coquilliers&rdquo; (<a href="#page275">p. 275</a>), in which 200
+species are known in France.</p>
+
+<p>In the Island of Sheppey near the mouth of the Thames, the
+thickness of the London Clay is estimated by Mr. Prestwich to be
+more than 500 feet, and it is in the uppermost 50 feet that a great
+number of fossil fruits were obtained, being chiefly found on the
+beach when the sea has washed away the clay of the rapidly wasting
+cliffs.</p>
+
+<img src="images/fig205.jpg" width="168" height="219" alt=
+"Fig. 205: Nipadites ellipticus." />
+
+<p>Mr. Bowerbank, in a valuable publication on these fossil fruits
+and seeds, has described no less than thirteen fruits of palms of
+the recent type <i>Nipa,</i> now only found in the Molucca and
+Philippine Islands, and in Bengal (see Fig. 205). In the delta of
+the Ganges, Dr. Hooker observed the large nuts of <i>Nipa
+fruticans</i> floating in such numbers in the various arms of that
+great river, as to obstruct the paddle-wheels of steamboats. These
+plants are allied to the cocoanut tribe on the one side, and on the
+other to the <i>Pandanus,</i> or screw-pine. There are also met
+with three species of <i>Anona,</i> or custard-apple; and
+cucurbitaceous fruits (of the gourd and melon family), and fruits
+of various species of <i>Acacia.</i></p>
+
+<p>Besides fir-cones or fruit of true Coniferæ there are
+cones of Proteaceæ in abundance, and the celebrated botanist
+the late Robert Brown pointed out the affinity of these to the New
+Holland types <i>Petrophila</i> and <i>Isopogon.</i> Of the first
+there are about fifty, and of the second thirty described species
+now living in Australia.</p>
+
+<p>
+<a name="page265"></a>Ettingshausen remarked in 1851 that five of the fossil
+species from Sheppey, named by Bowerbank<a href="#fn-16.4" name="fnref-16.4"
+id="fnref-16.4"><sup>[4]</sup></a> were specimens of the same fruit (see Fig.
+206), in different states of preservation; and Mr. Carruthers, having examined
+the original specimens now in the British Museum, tells me that all these cones
+from Sheppey may be reduced to two species, which have an undoubted affinity to
+the two existing Australian genera above mentioned, although their perfect
+identity in structure cannot be made out.
+</p>
+
+<p>
+<img src="images/fig206.jpg" width="182" height="228" alt=
+"Fig. 206: Eocene Proteaceous Fruit (Petrophiloides Richardsoni." />
+</p>
+
+<p>The contiguity of land may be inferred not only from these
+vegetable productions, but also from the teeth and bones of
+crocodiles and turtles, since these creatures, as Dean Conybeare
+remarked, must have resorted to some shore to lay their eggs. Of
+turtles there were numerous species referred to extinct genera.
+These are, for the most part, not equal in size to the largest
+living tropical turtles. A sea-snake, which must have been thirteen
+feet long, of the genus <i>Palæophis</i> before mentioned (p.
+261) has also been described by Professor Owen from Sheppey, of a
+different species from that of Bracklesham, and called <i>P.
+toliapicus.</i> A true crocodile, also, <i>Crocodilus
+toliapicus,</i> and another saurian more nearly allied to the
+gavial, accompany the above fossils; also the relics of several
+birds and quadrupeds. One of these last belongs to the new genus
+<i>Hyracotherium</i> of Owen, of the hog tribe, allied to
+Chæropotamus, another is a <i>Lophiodon</i>; a third a
+pachyderm called <i>Coryphodon eocænus</i> by Owen, larger
+than any existing tapir. All these animals seem to have inhabited
+the banks of the great river which floated down the Sheppey fruits.
+They imply the existence of a mammiferous fauna antecedent to the
+period when nummulites flourished in Europe and Asia, and therefore
+before the Alps, Pyrenees, and other mountain-chains now forming
+the backbones of great continents, were raised from the deep; nay,
+even before a part of the constituent rocky masses now entering
+into the central ridges of these chains had been deposited in the
+sea.</p>
+
+<p>
+The marine shells of the London Clay confirm the inference derivable from the
+plants and reptiles in favour of a high temperature. Thus many species of
+<i>Conus</i> and <i> Voluta</i>
+<a name="page266"></a>occur, a large <i>Cypræa, C. oviformis,</i> a very large
+<i>Rostellaria</i> (Fig. 209), a species of <i>Cancellaria,</i> six species of
+<i>Nautilus</i> (Fig. 211), besides other Cephalopoda of extinct genera, one of
+the most remarkable of which is the <i> Belosepia</i> (Fig. 212).
+<a name="page267"></a>Among many characteristic bivalve shells are <i>Leda
+amygdaloides</i> (Fig. 213) and <i>Cryptodon angulatum</i> (Fig. 214), and
+among the Radiata a star-fish, <i>Astropecten</i> (Fig. 215.)
+</p>
+
+<p>
+<img src="images/fig207.jpg" width="419" height="632" alt=
+"Fig. 207: Voluta nodosa, Fig. 208: Phorus extensus, Fig. 209: Rostellaria
+(Hippocrenes) ampla, Fig. 210: Nautilus centralis, Fig. 211: Aturia ziczac,
+Fig. 212: Belosepia sepioidea, Fig. 213: Leda amygdaloides, Fig. 214: Cyptodon
+(Axinus) angulatum, Fig. 215: Astropecten crispatus." />
+</p>
+
+<p>
+These fossils are accompanied by a sword-fish (<i>Tetrapterus priscus,</i>
+Agassiz), about eight feet long, and a saw-fish (<i>Pristis bisulcatus,</i>
+Agassiz), about ten feet in length; genera now foreign to the British seas. On
+the whole, about eighty species of fish have been described by M. Agassiz from
+these beds of Sheppey, and they indicate, in his opinion, a warm climate.
+</p>
+
+<p>In the lower part of the London clay at Kyson, a few miles east
+of Woodbridge, the remains of mammalia have been detected. Some of
+these have been referred by Professor Owen to an opossum, and
+others to the genus <i>Hyracotherium.</i> The teeth of this
+last-mentioned pachyderm were at first, in 1840, supposed to belong
+to a monkey, an opinion afterwards abandoned by Owen when more
+ample materials for comparison were obtained.</p>
+
+<p>
+<b>Woolwich and Reading Series, C.2,</b> <a href="#page252">
+Table</a>&mdash;This formation was formerly called the Plastic Clay, as it
+agrees with a similar clay used in pottery which occupies the same position in
+the French series, and it has been used for the like purposes in England.<a
+href="#fn-16.5" name="fnref-16.5" id="fnref-16.5"><sup>[5]</sup></a>
+</p>
+
+<p>No formations can be more dissimilar, on the whole, in mineral
+character than the Eocene deposits of England and Paris; those of
+our own island being almost exclusively of mechanical
+origin&mdash;accumulations of mud, sand, and pebbles; while in the
+neighbourhood of Paris we find a great succession of strata
+composed of limestones, some of them siliceous, and of crystalline
+gypsum and siliceous sandstone, and sometimes of pure flint used
+for millstones. Hence it is often impossible, as before stated, to
+institute an exact comparison between the various members of the
+English and French series, and to settle their respective ages. But
+in regard to the division which we have now under consideration,
+whether we study it in the basins of London, Hampshire, or Paris,
+we recognise as a general rule the same mineral character, the beds
+consisting over a large area of mottled clays and sand, with
+lignite, and with some strata of well-rolled flint pebbles, derived
+from the chalk, varying in size, but occasionally several inches in
+diameter. These strata may be seen in the Isle of Wight in contact
+with the chalk, or in the London basin, at Reading, Blackheath, and
+Woolwich. In some of the lowest of them, banks of oysters are
+observed, consisting of <i>Ostrea bellovacina,</i> so common in
+France in the
+<a name="page268"></a>same relative position. In these beds at Bromley, Dr. Buckland
+found a large pebble to which five full-grown oysters were affixed,
+in such a manner as to show that they had commenced their first
+growth upon it, and remained attached to it through life.</p>
+
+<p><img src="images/fig216.jpg" width="382" height="238" alt=
+"Fig. 216: Cyrena cuneiformis, Fig. 217: Melania (Melanatria) inquinata." />
+</p>
+
+<p>
+In several places, as at Woolwich on the Thames, at Newhaven in Sussex, and
+elsewhere, a mixture of marine and fresh-water testacea distinguishes this
+member of the series. Among the latter, <i> Cyrena cuneiformis</i> (see Fig.
+216) and <i>Melania inquinata</i> (see Fig. 217) are very common, as in beds of
+corresponding age in France. They clearly indicate points where rivers entered
+the Eocene sea. Usually there is a mixture of brackish, fresh-water, and marine
+shells, and sometimes, as at Woolwich, proofs of the river and the sea having
+successively prevailed on the same spot. At New Charlton, in the suburbs of
+Woolwich, Mr. de la Condamine discovered in 1849, and pointed out to me, a
+layer of sand associated with well-rounded flint pebbles in which numerous
+individuals of the <i>Cyrena tellinella</i> were seen standing endwise with
+both their valves united, the siphonal extremity of each shell being uppermost,
+as would happen if the mollusks had died in their natural position. I have
+described<a href="#fn-16.6" name="fnref-16.6"
+id="fnref-16.6"><sup>[6]</sup></a> a bank of sandy mud, in the delta of the
+Alabama River at Mobile, on the borders of the Gulf of Mexico, where in 1846 I
+dug out at low tide specimens of living species of <i>Cyrena</i> and of a <i>
+Gnathodon,</i> which were similarly placed with their shells erect, or in a
+posture which enables the animal to protrude its siphon upward, and draw in or
+reject water at pleasure. The water at Mobile is usually fresh, <a
+name="page269"></a>but sometimes brackish. At Woolwich a body of river-water
+must have flowed permanently into the sea where the <i>Cyrenæ</i> lived, and
+they may have been killed suddenly by an influx of pure salt-water, which
+invaded the spot when the river was low, or when a subsidence of land took
+place. Traced in one direction, or eastward towards Herne Bay, the Woolwich
+beds assume more and more of a marine character; while in an opposite, or
+south-western direction, they become, as near Chelsea and other places, more
+fresh-water, and contain <i>Unio, Paludina,</i> and layers of lignite, so that
+the land drained by the ancient river seems clearly to have been to the
+south-west of the present site of the metropolis.
+</p>
+
+<p><i>Fluviatile Beds underlying Deep-sea Strata.</i>&mdash;Before
+the minds of geologists had become familiar with the theory of the
+gradual sinking of land, and its conversion into sea at different
+periods, and the consequent change from shallow to deep water, the
+fluviatile and littoral character of this inferior group appeared
+strange and anomalous. After passing through hundreds of feet of
+London clay, proved by its fossils to have been deposited in deep
+salt-water, we arrive at beds of fluviatile origin, and associated
+with them masses of shingle, attaining at Blackheath, near London,
+a thickness of 50 feet. These shingle banks are probably of marine
+origin, but they indicate the proximity of land, and the existence
+of a shore where the flints of the chalk were rolled into sand and
+pebbles, and spread over a wide space. We have, therefore, first,
+as before stated (p. 268), evidence of oscillations of level during
+the accumulation of the Woolwich series, then of a great
+submergence, which allowed a marine deposit 500 thick to be laid
+over the antecedent beds of fresh and brackish water origin.</p>
+
+<p><b>Thanet Sands, C.3,</b> <a href="#page252">
+Table</a>&mdash;The Woolwich or plastic clay above described may
+often be seen in the Hampshire basin in actual contact with the
+chalk, constituting in such places the lowest member of the British
+Eocene series. But at other points another formation of marine
+origin, characterised by a somewhat different assemblage of organic
+remains, has been shown by Mr. Prestwich to intervene between the
+chalk and the Woolwich series. For these beds he has proposed the
+name of &ldquo;Thanet Sands,&rdquo; because they are well seen in
+the Isle of Thanet, in the northern part of Kent, and on the
+sea-coast between Herne Bay and the Reculvers, where they consist
+of sands with a few concretionary masses of sandstone, and contain,
+among other fossils, <i>Pholadomya cuneata, Cyprina morrisii,
+Corbula longirostris, Scalaria Bowerbankii,</i> etc. The greatest
+thickness of these beds is 90 feet.</p>
+
+<p class="center">
+<a name="page270"></a><small>UPPER EOCENE FORMATIONS OF FRANCE.</small>
+</p>
+
+<p>The tertiary formations in the neighbourhood of Paris consist of
+a series of marine and fresh-water strata, alternating with each
+other, and filling up a depression in the chalk. The area which
+they occupy has been called the Paris Basin, and is about 180 miles
+in its greatest length from north to south, and about 90 miles in
+breadth from east to west. MM. Cuvier and Brongniart attempted, in
+1810, to distinguish five different groups, comprising three
+fresh-water and two marine, which were supposed to imply that the
+waters of the ocean, and of rivers and lakes, had been by turns
+admitted into and excluded from the same area. Investigations since
+made in the Hampshire and London basins have rather tended to
+confirm these views, at least so far as to show that since the
+commencement of the Eocene period there have been great movements
+of the bed of the sea, and of the adjoining lands, and that the
+superposition of deep-sea to shallow-water deposits (the London
+Clay, for example, to the Woolwich beds) can only be explained by
+referring to such movements. It appears, notwithstanding, from the
+researches of M. Constant Prevost, that some of the minor
+alternations and intermixtures of fresh-water and marine deposits,
+in the Paris basin, may be accounted for without such changes of
+level, by imagining both to have been simultaneously in progress,
+in the same bay of the same sea, or a gulf into which many rivers
+entered.</p>
+
+<p><b>Gypseous Series of Montmartre, A.1,</b> <a href="#page252">
+Table</a>&mdash;To enlarge on the numerous subdivisions of the
+Parisian strata would lead me beyond my present limits; I shall
+therefore give some examples only of the most important formations.
+Beneath the Grès de Fontainebleau, belonging to the Lower
+Miocene period, as before stated, we find, in the neighbourhood of
+Paris, a series of white and green marls, with subordinate beds of
+gypsum. These are most largely developed in the central parts of
+the Paris basin, and, among other places, in the hill of
+Montmartre, where its fossils were first studied by Cuvier.</p>
+
+<p>The gypsum quarried there for the manufacture of plaster of
+Paris occurs as a granular crystalline rock, and, together with the
+associated marls, contains land and fluviatile shells, together
+with the bones and skeletons of birds and quadrupeds. Several
+land-plants are also met with, among which are fine specimens of
+the fan-palm or palmetto tribe (<i>Flabellaria</i>). The remains
+also of fresh-water fish, and of crocodiles and other reptiles,
+occur in the gypsum. The skeletons of
+<a name="page271"></a>mammalia are usually isolated, often entire, the most delicate
+extremities being preserved; as if the carcasses, clothed with
+their flesh and skin, had been floated down soon after death, and
+while they were still swollen by the gases generated by their first
+decomposition. The few accompanying shells are of those light kinds
+which frequently float on the surface of rivers, together with
+wood.</p>
+
+<p>In this formation the relics of about fifty species of
+quadrupeds, including the genera <i>Palæotherium</i> (see <a
+href="images/fig174.jpg">Fig. 174</a>), <i>Anoplotherium</i> (see
+Fig. 218), and others, have been found, all extinct, and nearly
+four-fifths of them belonging to the Perissodactyle or odd-toed
+division of the order <i>Pachydermata,</i> which now contains only
+four living genera, namely, rhinoceros, tapir, horse, and hyrax.
+With them a few carnivorous animals are associated, among which are
+the <i>Hyænodon dasyuroides,</i> a species of dog, <i>Canis
+Parisiensis,</i> and a weasel, <i>Cynodon Parisiensis.</i> Of the
+<i>Rodentia</i> are found a squirrel; of the <i>Cheiroptera,</i> a
+bat; while the <i>Marsupalia</i> (an order now confined to America,
+Australia, and some contiguous islands) are represented by an
+opossum.</p>
+
+<p>
+Of birds, about ten species have been ascertained, the skeletons of some of
+which are entire. None of them are referable to existing species.<a
+href="#fn-16.7" name="fnref-16.7" id="fnref-16.7"><sup>[7]</sup></a> The same
+remark, according to MM. Cuvier and Agassiz, applies both to the reptiles and
+fish. Among the last are crocodiles and tortoises of the genera <i>Emys</i> and
+<i> Trionyx.</i>
+</p>
+
+<p><img src="images/fig218.jpg" width="256" height="237" alt=
+"Fig. 218: Xiphodon gracile, or Anoplotherium gracile." /></p>
+
+<p>The tribe of land quadrupeds most abundant in this formation is
+such as now inhabits alluvial plains and marshes, and the banks of
+rivers and lakes, a class most exposed to suffer by river
+inundations. Among these were several species of <i>
+Palæotherium,</i> a genus before alluded to. These were
+associated with the Anoplotherium, a tribe intermediate between
+pachyderms and ruminants. One of the three divisions of this family
+was called by Cuvier <i>Xiphodon.</i> Their forms were slender
+and
+<a name="page272"></a>elegant, and one, named <i>Xiphodon gracile</i> (Fig. 218), was
+about the size of the chamois; and Cuvier inferred from the
+skeleton that it was as light, graceful, and agile as the
+gazelle.</p>
+
+<p>
+<i>Fossil Footprints.</i>&mdash;There are three superimposed masses of gypsum
+in the neighbourhood of Paris, separated by intervening deposits of laminated
+marl. In the uppermost of the three, in the valley of Montmorency, M. Desnoyers
+discovered in 1859 many footprints of animals occurring at no less than six
+different levels.<a href="#fn-16.8" name="fnref-16.8"
+id="fnref-16.8"><sup>[8]</sup></a> The gypsum to which they belong varies from
+thirty to fifty feet in thickness, and is that which has yielded to the
+naturalist the largest number of bones and skeletons of mammalia, birds, and
+reptiles. I visited the quarries, soon after the discovery was made known, with
+M. Desnoyers, who also showed me large slabs in the Museum at Paris, where, on
+the upper planes of stratification, the indented foot-marks were seen, while
+corresponding casts in relief appeared on the lower surfaces of the strata of
+gypsum which were immediately superimposed. A thin film of marl, which before
+it was dried and condensed by pressure must have represented a much thicker
+layer of soft mud, intervened between the beds of solid gypsum. On this mud the
+animals had trodden, and made impressions which had penetrated to the gypseous
+mass below, then evidently unconsolidated. Tracks of the <i> Anoplotherium</i>
+with its bisulcate hoof, and the trilobed footprints of <i>Palæotherium,</i>
+were seen of different sizes, corresponding to those of several species of
+these genera which Cuvier had reconstructed, while in the same beds were
+foot-marks of carnivorous mammalia. The tracks also of fluviatile, lacustrine,
+and terrestrial tortoises (<i>Emys, Trionyx,</i> etc.) were discovered, also
+those of crocodiles, iguanas, geckos, and great batrachians, and the footprints
+of a huge bird, apparently a wader, of the size of the gastornis, to be
+mentioned in the sequel. There were likewise the impressions of the feet of
+other creatures, some of them clearly distinguishable from any of the fifty
+extinct types of mammalia of which the bones have been found in the Paris
+gypsum. The whole assemblage, says Desnoyers, indicate the shores of a lake, or
+several small lakes communicating with each other, on the borders of which many
+species of pachyderms wandered, and beasts of prey which occasionally devoured
+them. The tooth-marks of these last had been detected by palæontologists long
+before on the bones and skulls of Paleotheres entombed in the gypsum.
+</p>
+
+<p>
+<a name="page273"></a><i>Imperfection of the Record.</i>&mdash;These foot-marks have
+revealed to us new and unexpected proofs that the air-breathing
+fauna of the Upper Eocene period in Europe far surpassed in the
+number and variety of its species the largest estimate which had
+previously been formed of it. We may now feel sure that the
+mammalia, reptiles, and birds which have left portions of their
+skeletons as memorials of their existence in the solid gypsum
+constituted but a part of the then living creation. Similar
+inferences may be drawn from the study of the whole succession of
+geological records. In each district the monuments of periods
+embracing thousands, and probably in some instances hundreds of
+thousands of years, are totally wanting. Even in the volumes which
+are extant the greater number of the pages are missing in any given
+region, and where they are found they contain but few and casual
+entries of the physical events or living beings of the times to
+which they relate. It may also be remarked that the subordinate
+formations met with in two neighbouring countries, such as France
+and England (the minor Tertiary groups above enumerated), commonly
+classed as equivalents and referred to corresponding periods, may
+nevertheless have been by no means strictly coincident in date.
+Though called contemporaneous, it is probable that they were often
+separated by intervals of many thousands of years. We may compare
+them to double stars, which appear single to the naked eye because
+seen from a vast distance in space, and which really belong to one
+and the same stellar system, though occupying places in space
+extremely remote if estimated by our ordinary standard of
+terrestrial measurements.</p>
+
+<p><b>Calcaire silicieux, or Travertin inférieur, A.2 and
+3,</b> <a href="#page252">Table</a>&mdash;This compact siliceous
+limestone extends over a wide area. It resembles a precipitate from
+the waters of mineral springs, and is often traversed by small
+empty sinuous cavities. It is, for the most part, devoid of organic
+remains, but in some places contains fresh-water and land species,
+and never any marine fossils. The calcaire siliceux and the
+calcaire grossier usually occupy distinct parts of the Paris basin,
+the one attaining its fullest development in those places where the
+other is of slight thickness. They are described by some writers as
+alternating with each other towards the centre of the basin, as at
+Sergy and Osny.</p>
+
+<p>The gypsum, with its associated marls before described, is in
+greatest force towards the centre of the basin, where the calcaire
+grossier and calcaire silicieux are less fully developed.</p>
+
+<p><b>Grès de Beauchamp, or Sables Moyens, A.4,</b> <a href=
+"#page252">Table</a>&mdash;In some parts of the Paris basin, sands
+and marls, called the
+<a name="page274"></a>Grès de Beauchamp, or Sables moyens, divide the gypseous
+beds from the calcaire grossier proper. These sands, in which a
+small nummulite (N. variolaria) is very abundant, contain more than
+300 species of marine shells, many of them peculiar, but others
+common to the next division.</p>
+
+<p class="center">
+<small>MIDDLE EOCENE FORMATIONS OF FRANCE.</small>
+</p>
+
+<p><b>Calcaire Grossier, upper and middle, B.1,</b> <a href=
+"#page252">Table</a>&mdash;The upper division of this group
+consists in great part of beds of compact, fragile limestone, with
+some intercalated green marls. The shells in some parts are a
+mixture of <i>Cerithium, Cyclostoma,</i> and <i>Corbula</i>; in
+others <i>Limnea, Cerithium, Paludina,</i> etc. In the latter, the
+bones of reptiles and mammalia, <i>Palæotherium</i> and <i>
+Lophiodon,</i> have been found. The middle division, or calcaire
+grossier proper, consists of a coarse limestone, often passing into
+sand. It contains the greater number of the fossil shells which
+characterise the Paris basin. No less than 400 distinct species
+have been procured from a single spot near Grignon, where they are
+imbedded in a calcareous sand, chiefly formed of comminuted shells,
+in which, nevertheless, individuals in a perfect state of
+preservation, both of marine, terrestrial, and fresh-water species,
+are mingled together. Some of the marine shells may have lived on
+the spot; but the <i>Cyclostoma</i> and <i>Limnea,</i> being land
+and fresh-water shells, must have been brought thither by rivers
+and currents, and the quantity of triturated shells implies
+considerable movement in the waters.</p>
+
+<p>Nothing is more striking in this assemblage of fossil testacea
+than the great proportion of species referable to the genus <i>
+Cerithium</i> (see <a href="images/fig158.jpg">p. 245</a>). There
+occur no less than 137 species of this genus in the Paris basin,
+and almost all of them in the calcaire grossier. Most of the living
+<i>Cerithia</i> inhabit the sea near the mouths of rivers, where
+the waters are brackish; so that their abundance in the marine
+strata now under consideration is in harmony with the hypothesis
+that the Paris basin formed a gulf into which several rivers
+flowed.</p>
+
+<p>In some parts of the calcaire grossier round Paris, certain beds
+occur of a stone used in building, and called by the French
+geologists &ldquo;Miliolite limestone.&rdquo; It is almost entirely
+made up of millions of microscopic shells, of the size of minute
+grains of sand, which all belong to the class Foraminifera.
+Examples of some of these are given in Figs. 219 to 221. As this
+miliolitic stone never occurs in the Faluns, or Upper Miocene
+strata of Brittany and Touraine, it often furnishes the geologist
+with a useful criterion for
+<a name="page275"></a>distinguishing the detached Eocene and Upper Miocene formations
+scattered over those and other adjoining provinces. The discovery
+of the remains of Palæotherium and other mammalia in some of
+the upper beds of the calcaire grossier shows that these land
+animals began to exist before the deposition of the overlying
+gypseous series had commenced.</p>
+
+<p><img src="images/fig219.jpg" width="323" height="197" alt=
+"Fig. 219: Calcarina rarispina, Fig. 220: Spirolina stenostoma, Fig. 221:
+Triloculina inflata." />
+</p>
+
+<p><b>Lower Calcaire grossier, or Glauconie grossiere, B.1,</b> <a
+href="#page252">Table</a>&mdash;The lower part of the calcaire
+grossier, which often contains much green earth, is characterised
+at Auvers, near Pontoise, to the north of Paris, and still more in
+the environs of Compiègne, by the abundance of nummulites,
+consisting chiefly of <i>N. lævigata, N. scabra,</i> and <i>
+N. Lamarcki,</i> which constitute a large proportion of some of the
+stony strata, though these same foraminifera are wanting in beds of
+similar age in the immediate environs of Paris.</p>
+
+<img src="images/fig222.jpg" width="179" height="100" alt=
+"Fig. 222: Nerita conoidea." />
+
+<p>
+<b>Soissonnais sands, or Lits coquilliers, B.2,</b> <a href=
+"#page252">Table</a>&mdash;Below the preceding formation, shelly sands are
+seen, of considerable thickness, especially at Cuisse-Lamotte, near Compiègne,
+and other localities in the Soissonnais, about fifty miles N.E. of Paris, from
+which about 300 species of shells have been obtained, many of them common to
+the calcaire grossier and the Bracklesham beds of England, and many peculiar.
+The <i>Nummulites planulata</i> is very abundant, and the most characteristic
+shell is the <i>Nerita conoidea,</i> Lam., a fossil which has a very wide
+geographical range; for, as M. d&rsquo;Archiac remarks, it accompanies the
+nummulitic formation from Europe to India, having been found in Cutch, near the
+mouths of the Indus, associated with <i>Nummulites scabra.</i> No less than 33
+shells of this group are said to be identical with shells of the London clay
+proper, yet, after visiting Cuisse-Lamotte and <a name="page276"></a>other
+localities of the &ldquo;Sables inférieurs&rdquo; of Archiac, I agree with Mr.
+Prestwich, that the latter are probably newer than the London clay, and perhaps
+older than the Bracklesham beds of England. The London clay seems to be
+unrepresented in the Paris basin, unless partially so, by these sands.<a
+href="#fn-16.9" name="fnref-16.9" id="fnref-16.9"><sup>[9]</sup></a>
+</p>
+
+<p class="center">
+<small>LOWER EOCENE FORMATIONS OF FRANCE.</small>
+</p>
+
+<p><b>Argile Plastique, C.2,</b> <a href="#page252">
+Table</a>&mdash;At the base of the tertiary system in France are
+extensive deposits of sands, with occasional beds of clay used for
+pottery, and called &ldquo;argile plastique.&rdquo; Fossil oysters
+(<i>Ostrea bellovacina</i>) abound in some places, and in others
+there is a mixture of fluviatile shells, such as <i>Cyrena
+cuneiformis</i> (<a href="images/fig216.jpg">Fig. 216</a>), <i>
+Melania inquinata</i> (<a href="images/fig216.jpg">Fig. 216</a>),
+and others, frequently met with in beds occupying the same position
+in the London Basin. Layers of lignite also accompany the inferior
+clays and sands.</p>
+
+<p>
+Immediately upon the chalk at the bottom of all the tertiary strata in France
+there generally is a conglomerate or breccia of rolled and angular
+chalk-flints, cemented by siliceous sand. These beds appear to be of littoral
+origin, and imply the previous emergence of the chalk, and its waste by
+denudation. In the year 1855, the tibia and femur of a large bird equalling at
+least the ostrich in size were found at Meudon, near Paris, at the base of the
+Plastic clay. This bird, to which the name of <i>Gastornis Parisiensis</i> has
+been assigned, appears, from the Memoirs of MM. Hébert, Lartet, and Owen, to
+belong to an extinct genus. Professor Owen refers it to the class of wading
+land birds rather than to an aquatic species.<a href="#fn-16.10"
+name="fnref-16.10" id="fnref-16.10"><sup>[10]</sup></a>
+</p>
+
+<p>That a formation so much explored for economical purposes as the
+Argile plastique around Paris, and the clays and sands of
+corresponding age near London, should never have afforded any
+vestige of a feathered biped previously to the year 1855, shows
+what diligent search and what skill in osteological interpretation
+are required before the existence of birds of remote ages can be
+established.</p>
+
+<p><b>Sables de Bracheux, C.3,</b> <a href="#page252">
+Table</a>&mdash;The marine sands called the Sables de Bracheux (a
+place near Beauvais), are considered by M. Hébert to be
+older than the Lignites and Plastic clay, and to coincide in age
+with the Thanet Sands of England. At La Fère, in the
+Department of Aisne, in a deposit of this age, a fossil skull has
+been found of a quadruped called by Blainville <i>Arctocyon
+primævus,</i> and
+<a name="page277"></a>supposed by him to be related both to the bear and to the
+Kinkajou (<i>Cercoleptes</i>). This creature appears to be the
+oldest known tertiary mammifer.</p>
+
+<p><b>Nummulitic Formations of Europe, Asia, etc.</b>&mdash;Of all
+the rocks of the Eocene period, no formations are of such great
+geographical importance as the Upper and Middle Eocene, as above
+defined, assuming that the older tertiary formation, commonly
+called nummulitic, is correctly ascribed to this group. It appears
+that of more than fifty species of these foraminifera described by
+D&rsquo;Archiac, one or two species only are found in other
+tertiary formations whether of older or newer date. <i>Nummulites
+intermedia,</i> a Middle Eocene form, ascends into the Lower
+Miocene, but it seems doubtful whether any species descends to the
+level of the London clay, still less to the Argile plastique or
+Woolwich beds. Separate groups of strata are often characterised by
+distinct species of nummulite; thus the beds between the lower
+Miocene and the lower Eocene may be divided into three sections,
+distinguished by three different species of nummulites, <i>N.
+variolaria</i> in the upper, <i>N. lævigata</i> in the
+middle, and <i>N. planulata</i> in the lower beds. The nummulitic
+limestone of the Swiss Alps rises to more than 10,000 feet above
+the level of the sea, and attains here and in other mountain chains
+a thickness of several thousand feet. It may be said to play a far
+more conspicuous part than any other tertiary group in the solid
+framework of the earth&rsquo;s crust, whether in Europe, Asia, or
+Africa. It occurs in Algeria and Morocco, and has been traced from
+Egypt, where it was largely quarried of old for the building of the
+Pyramids, into Asia Minor, and across Persia by Bagdad to the
+mouths of the Indus. It has been observed not only in Cutch, but in
+the mountain ranges which separate Scinde from Persia, and which
+form the passes leading to Caboul; and it has been followed still
+farther eastward into India, as far as eastern Bengal and the
+frontiers of China.</p>
+
+<p>Dr. T. Thompson found nummulites at an elevation of no less than
+16,500 feet above the level of the sea, in Western Thibet. One of
+the species, which I myself found very abundant on the flanks of
+the Pyrenees, in a compact crystalline marble (<a href=
+"images/fig223.jpg">Fig. 223</a>) is called by M. d&rsquo;Archiac
+<i>Nummulites Puschi.</i> The same is also very common in rocks of
+the same age in the Carpathians. In many distant countries, in
+Cutch, for example, some of the same shells, such as <i>Nerita
+conoidea</i> (<a href="images/fig222.jpg">Fig. 222</a>), accompany
+the nummulites, as in France. The opinion of many observers, that
+the Nummulitic formation belongs partly to the cretaceous era,
+seems chiefly to
+<a name="page278"></a>have arisen from confounding an allied genus, Orbitoides, with
+the true Nummulite.</p>
+
+<p><img src="images/fig223.jpg" width="326" height="202" alt=
+"Fig. 223: Nummulites Puschi." /></p>
+
+<p>When we have once arrived at the conviction that the nummulitic
+formation occupies a middle and upper place in the Eocene series,
+we are struck with the comparatively modern date to which some of
+the greatest revolutions in the physical geography of Europe, Asia,
+and Northern Africa must be referred. All the mountain-chains, such
+as the Alps, Pyrenees, Carpathians, and Himalayas, into the
+composition of whose central and loftiest parts the nummulitic
+strata enter bodily, could have had no existence till after the
+Middle Eocene period. During that period the sea prevailed where
+these chains now rise, for nummulites and their accompanying
+testacea were unquestionably inhabitants of salt water. Before
+these events, comprising the conversion of a wide area from a sea
+to a continent, England had been peopled, as I before pointed out
+(p. 267), by various quadrupeds, by herbivorous pachyderms, by
+insectivorous bats, and by opossums.</p>
+
+<p>
+Almost all the volcanoes which preserve any remains of their original form, or
+from the craters of which lava streams can be traced, are more modern than the
+Eocene fauna now under consideration; and besides these superficial monuments
+of the action of heat, Plutonic influences have worked vast changes in the
+texture of rocks within the same period. Some members of the nummulitic and
+overlying tertiary strata called <i>flysch</i> have actually been converted in
+the central Alps into crystalline rocks, and transformed into marble,
+quartz-rock, micha-schist, and gneiss.<a href="#fn-16.11" name="fnref-16.11"
+id="fnref-16.11"><sup>[11]</sup></a>
+</p>
+
+<p>
+<b>Eocene Strata in the United States.</b>&mdash;In North America the Eocene
+formations occupy a large area bordering the <a name="page279"></a>Atlantic,
+which increases in breadth and importance as it is traced southward from
+Delaware and Maryland to Georgia and Alabama. They also occur in Louisiana and
+other States both east and west of the valley of the Mississippi. At Claiborne,
+in Alabama, no less than 400 species of marine shells, with many echinoderms
+and teeth of fish, characterise one member of this system. Among the shells,
+the <i>Cardita planicosta,</i> before mentioned (<a href=
+"images/fig191.jpg">Fig. 191</a>), is in abundance; and this fossil and some
+others identical with European species, or very nearly allied to them, make it
+highly probable that the Claiborne beds agree in age with the central or
+Bracklesham group of England, and with the calcaire grossiere of Paris.<a
+href="#fn-16.12" name="fnref-16.12" id="fnref-16.12"><sup>[12]</sup></a>
+</p>
+
+<p>
+Higher in the series is a remarkable calcareous rock, formerly called
+&ldquo;the nummulite limestone,&rdquo; from the great number of discoid bodies
+resembling nummulites which it contains, fossils now referred by A.
+d&rsquo;Orbigny to the genus <i>Orbitoides,</i> which has been demonstrated by
+Dr. Carpenter to belong to the foraminifera.<a href="#fn-16.13"
+name="fnref-16.13" id="fnref-16.13"><sup>[13]</sup></a> That naturalist,
+moreover, is of opinion that the Orbitoides alluded to (<i>O. Mantelli</i>) is
+of the same species as one found in Cutch, in the Middle Eocene or nummulitic
+formation of India.
+</p>
+
+<p>
+Above the orbitoidal limestone is a white limestone, sometimes soft and
+argillaceous, but in parts very compact and calcareous. It contains several
+peculiar corals, and a large Nautilus allied to <i>N. ziczac</i>; also in its
+upper bed a gigantic cetacean, called <i>Zeuglodon</i> by Owen.<a
+href="#fn-16.14" name="fnref-16.14" id="fnref-16.14"><sup>[14]</sup></a>
+</p>
+
+<p>The colossal bones of this cetacean are so plentiful in the
+interior of Clarke County, Alabama, as to be characteristic of the
+formation. The vertebral column of one skeleton found by Dr.
+Buckley at a spot visited by me, extended to the length of nearly
+seventy feet, and not far off part of another backbone nearly fifty
+feet long was dug up. I obtained evidence, during a short
+excursion, of so many localities of this fossil animal within a
+distance of ten miles, as to lead me to conclude that they must
+have belonged to at least forty distinct individuals.</p>
+
+<p>Professor Owen first pointed out that this huge animal was not
+reptilian, since each tooth was furnished with double roots (<a
+href="images/fig224.jpg">Fig. 224</a>), implanted in corresponding
+double sockets; and his opinion of the cetacean nature of the
+fossil was afterwards
+<a name="page280"></a>confirmed by Dr. Wyman and Dr. R. W. Gibbes. That it was an
+extinct mammal of the whale tribe has since been placed beyond all
+doubt by discovery of the entire skull of another fossil species of
+the same family, having the double occipital condyles only met with
+in mammals, and the convoluted tympanic bones which are
+characteristic of cetaceans.
+</p>
+
+<p><img src="images/fig224.jpg" width="411" height="227" alt=
+"Fig. 224: Zeuglodon cetoides, Fig 225: Basilosaurus." /></p>
+
+<p class="footnote">
+<a name="fn-16.1" id="fn-16.1"></a> <a href="#fnref-16.1">[1]</a>
+Quart. Geol. Journal, vol. xx, p. 97, 1864.
+</p>
+
+<p class="footnote">
+<a name="fn-16.2" id="fn-16.2"></a> <a href="#fnref-16.2">[2]</a>
+Palæont. Soc. Monograph, Rept., pt. ii, p. 61.
+</p>
+
+<p class="footnote">
+<a name="fn-16.3" id="fn-16.3"></a> <a href="#fnref-16.3">[3]</a>
+Heer, Climat et Végétation du Pays Tertiaire, p. 172.
+</p>
+
+<p class="footnote">
+<a name="fn-16.4" id="fn-16.4"></a> <a href="#fnref-16.4">[4]</a>
+Bowerbank, Fossil Fruits and Seeds of London Clay, Plates ix and x.
+</p>
+
+<p class="footnote">
+<a name="fn-16.5" id="fn-16.5"></a> <a href="#fnref-16.5">[5]</a>
+Prestwich, Quart. Geol. Journ., vol. x.
+</p>
+
+<p class="footnote">
+<a name="fn-16.6" id="fn-16.6"></a> <a href="#fnref-16.6">[6]</a>
+Second Visit to the United States, vol. ii, p. 104.
+</p>
+
+<p class="footnote">
+<a name="fn-16.7" id="fn-16.7"></a> <a href="#fnref-16.7">[7]</a>
+Cuvier, Oss. Foss., tome iii, p. 255.
+</p>
+
+<p class="footnote">
+<a name="fn-16.8" id="fn-16.8"></a> <a href="#fnref-16.8">[8]</a>
+Sur des Empreintes de Pas d&rsquo;Animaux par M. J. Desnoyers. Compte rendu de
+l&rsquo;Institut, 1859.
+</p>
+
+<p class="footnote">
+<a name="fn-16.9" id="fn-16.9"></a> <a href="#fnref-16.9">[9]</a>
+D&rsquo;Archiac, Bulletin, tome x; and Prestwich, Quart. Geol. Journ., 1847, p.
+377.
+</p>
+
+<p class="footnote">
+<a name="fn-16.10" id="fn-16.10"></a> <a href="#fnref-16.10">[10]</a>
+Quart. Geol. Journ., vol. xii, p. 204, 1856.
+</p>
+
+<p class="footnote">
+<a name="fn-16.11" id="fn-16.11"></a> <a href="#fnref-16.11">[11]</a>
+Murchison, Quart. Journ. of Geol. Soc., vol. v, and Lyell, vol. vi, 1850.
+Anniversary Address.
+</p>
+
+<p class="footnote">
+<a name="fn-16.12" id="fn-16.12"></a> <a href="#fnref-16.12">[12]</a>
+See paper by the Author, Quart. Journ. of Geol. Soc., vol. iv, p. 12; and
+Second Visit to the United States, vol. ii, p. 59.
+</p>
+
+<p class="footnote">
+<a name="fn-16.13" id="fn-16.13"></a> <a href="#fnref-16.13">[13]</a>
+Quart. Journ. of Geol. Soc., vol. vi, p. 32.
+</p>
+
+<p class="footnote">
+<a name="fn-16.14" id="fn-16.14"></a> <a href="#fnref-16.14">[14]</a>
+See Memoir by R. W. Gibbes, Journ. of Acad. Nat. Sci. Philad., vol. i, 1847.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap17"></a><a name="page281"></a>CHAPTER XVII.<br/>
+UPPER CRETACEOUS GROUP.</h2>
+
+<p class="letter">Lapse of Time between Cretaceous and Eocene
+Periods. &mdash; Table of successive Cretaceous Formations. &mdash;
+Maestricht Beds. &mdash; Pisolitic Limestone of France. &mdash;
+Chalk of Faxoe. &mdash; Geographical Extent and Origin of the White
+Chalk. &mdash; Chalky Matter now forming in the Bed of the
+Atlantic. &mdash; Marked Difference between the Cretaceous and
+existing Fauna. &mdash; Chalk-flints. &mdash; Pot-stones of
+Horstead. &mdash; Vitreous Sponges in the Chalk. &mdash; Isolated
+Blocks of Foreign Rocks in the White Chalk supposed to be
+ice-borne. &mdash; Distinctness of Mineral Character in
+contemporaneous Rocks of the Cretaceous Epoch. &mdash; Fossils of
+the White Chalk. &mdash; Lower White Chalk without Flints. &mdash;
+Chalk Marl and its Fossils. &mdash; Chloritic Series or Upper
+Greensand. &mdash; Coprolite Bed near Cambridge. &mdash; Fossils of
+the Chloritic Series. &mdash; Gault. &mdash; Connection between
+Upper and Lower Cretaceous Strata. &mdash; Blackdown Beds. &mdash;
+Flora of the Upper Cretaceous Period. &mdash; Hippurite Limestone.
+&mdash; Cretaceous Rocks in the United States.</p>
+
+<p>We have treated in the preceding chapters of the Tertiary or
+Cainozoic strata, and have next to speak of the Secondary or
+Mesozoic formations. The uppermost of these last is commonly called
+the chalk or the cretaceous formation, from creta, the latin name
+for that remarkable white earthy limestone, which constitutes an
+upper member of the group in those parts of Europe where it was
+first studied. The marked discordance in the fossils of the
+tertiary, as compared with the cretaceous formations, has long
+induced many geologists to suspect that an indefinite series of
+ages elapsed between the respective periods of their origin.
+Measured, indeed, by such a standard, that is to say, by the amount
+of change in the Fauna and Flora of the earth effected in the
+interval, the time between the Cretaceous and Eocene may have been
+as great as that between the Eocene and Recent periods, to the
+history of which the last seven chapters have been devoted. Several
+deposits have been met with here and there, in the course of the
+last half century, of an age intermediate between the white chalk
+and the plastic clays and sands of the Paris and London districts,
+monuments
+<a name="page282"></a>which have the same kind of interest to a geologist which
+certain medieval records excite when we study the history of
+nations. For both of them throw light on ages of darkness, preceded
+and followed by others of which the annals are comparatively
+well-known to us. But these newly-discovered records do not fill up
+the wide gap, some of them being closely allied to the Eocene, and
+others to the Cretaceous type, while none appear as yet to possess
+so distinct and characteristic a fauna as may entitle them to hold
+an independent place in the great chronological series.</p>
+
+<p>Among the formations alluded to, the Thanet Sands of Prestwich
+have been sufficiently described in the last chapter, and classed
+as Lower Eocene. To the same tertiary series belong the Belgian
+formations, called by Professor Dumont, Landenian. On the other
+hand, the Maestricht and Faxoe limestones are very closely
+connected with the chalk, to which also the Pisolitic limestone of
+France is referable.</p>
+
+<p><b>Classification of the Cretaceous Rocks.</b>&mdash;The
+cretaceous group has generally been divided into an Upper and a
+Lower series, the Upper called familiarly <i>the chalk,</i> and the
+Lower <i>the greensand</i>; the one deriving its name from the
+predominance of white earthy limestone and marl, of which it
+consists in a great part of France and England, the other or lower
+series from the plentiful mixture of green or chloritic grains
+contained in some of the sands and cherts of which it largely
+consists in the same countries. But these mineral characters often
+fail, even when we attempt to follow out the same continuous
+subdivisions throughout a small portion of the north of Europe, and
+are worse than valueless when we desire to apply them to more
+distant regions. It is only by aid of the organic remains which
+characterise the successive marine subdivisions of the formation
+that we are able to recognise in remote countries, such as the
+south of Europe or North America, the formations which were there
+contemporaneously in progress. To the English student of geology it
+will be sufficient to begin by enumerating those groups which
+characterise the series in this country and others immediately
+contiguous, alluding but slightly to those of more distant regions.
+In the table (p. 283) it will be seen that I have used the term
+Neocomian for that commonly called &ldquo;Lower Greensand;&rdquo;
+as this latter term is peculiarly objectionable, since the green
+grains are an exception to the rule in many of the members of this
+group even in districts where it was first studied and named.
+<a name="page283"></a></p>
+
+<table border="1" cellpadding="2" width="80%">
+<tr>
+<td colspan="2" align="center">UPPER CRETACEOUS OR CHALK
+PERIOD.</td>
+</tr>
+
+<tr>
+<td colspan="2">
+<ol>
+<li>Maestricht Beds and Faxoe Limestone.</li>
+
+<li>Upper White Chalk, with flints.</li>
+
+<li>Lower White Chalk, without flints.</li>
+
+<li>Chalk Marl.</li>
+
+<li>Chloritic series (or Upper Greensand).</li>
+
+<li>Gault.</li>
+</ol>
+</td>
+</tr>
+
+<tr>
+<td colspan="2" align="center">LOWER CRETACEOUS OR NEOCOMIAN.</td>
+</tr>
+
+<tr>
+<td align="center">Marine</td>
+<td align="center">Fresh-water</td>
+</tr>
+
+<tr>
+<td >
+<ol>
+<li>Marine: Upper Neocomian, see <a href="#page308">
+p.308</a></li>
+
+<li>Marine: Middle Neocomian, see <a href="#page312">
+p.312</a></li>
+
+<li>Marine: Lower Neocomian, see <a href="#page312">
+p.312</a></li>
+</ol>
+</td>
+<td valign="middle">Wealden Beds (upper part).</td>
+</tr>
+</table>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig226.jpg" width="144" height="279" alt="Belemnitella mucronata." />
+<p class="caption">Belemnitella mucronata,<br/>
+Maestricht, Faxoe, and White Chalk.<br/>
+<i>a/</i> Entire specimen, showing vascular impression on outer surface, and
+characteristic slit. <i>b.</i> Section of same, showing place of phragmocone.<a
+href="#fn-17.1" name="fnref-17.1" id="fnref-17.1"><sup>[1]</sup></a><br/></p>
+</div>
+
+<p><i>Maestricht Beds.</i>&mdash;On the banks of the Meuse, at
+Maestricht, reposing on ordinary white chalk with flints, we find
+an upper calcareous formation about 100 feet thick, the fossils of
+which are, on the whole, very peculiar, and all distinct from
+tertiary species. Some few are of species common to the inferior
+white chalk, among which may be mentioned <i>Belemnitella
+mucronata</i> (Fig. 226) and <i>Pecten quadricostatus,</i> a shell
+regarded by many as a mere variety of <i>P. quinquecostatus</i>
+(see Fig. 270). Besides the
+Belemnite there are other <i>genera,</i> such as <i>Baculites</i>
+and <i>Hamites,</i> never found in strata newer than the
+cretaceous, but frequently met with in these Maestricht beds. On
+the other hand, <i>Voluta, Fasciolaria,</i> and other genera of
+univalve shells, usually met with only in tertiary strata,
+occur.</p>
+
+<p>The upper part of the rock, about 20 feet thick, as seen in St.
+Peter&rsquo;s Mount, in the suburbs of Maestricht, abounds in
+corals and Bryozoa, often detachable from the matrix; and these
+beds are succeeded by a soft yellowish limestone 50 feet thick,
+extensively quarried from time immemorial for building. The stone
+below is whiter, and contains occasional nodules of grey chert or
+chalcedony.</p>
+
+<p>M. Bosquet, with whom I examined this formation (August, 1850),
+pointed out to me a layer of chalk from two to four inches thick,
+containing green earth and numerous encrinital stems, which forms
+the line of demarkation between the strata containing the fossils
+peculiar to Maestricht and
+<a name="page284"></a>the white chalk below. The latter is distinguished by regular
+layers of black flint in nodules, and by several shells, such as
+<i>Terebratula carnea</i> (see <a href="images/fig240.jpg">Fig.
+246</a>), wholly wanting in beds higher than the green band. Some
+of the organic remains, however, for which St. Peter&rsquo;s Mount
+is celebrated, occur both above and below that parting layer, and,
+among others, the great marine reptile called <i>Mosasaurus</i>
+(see Fig. 227), a saurian supposed to have been 24 feet in length,
+of which the entire skull and a great part of the skeleton have
+been found. Such remains are chiefly met with in the soft
+freestone, the principal member of the Maestricht beds. Among the
+fossils common to the Maestricht and white chalk may be instanced
+the echinoderm, Fig. 228.</p>
+
+<p><img src="images/fig227.jpg" width="379" height="254" alt=
+"Mosasaurus Camperi." /></p>
+
+<img src="images/fig228.jpg" width="164" height="180" alt=
+"Hemipneustes radiatus." />
+
+<p>I saw proofs of the previous denudation of the white chalk
+exhibited in the lower bed of the Maestricht formation in Belgium,
+about 30 miles S.W. of Maestricht, at the village of Jendrain,
+where the base of the newer deposit consisted chiefly of a layer of
+well-rolled, black chalk-flint pebbles, in the midst of which
+perfect specimens of <i>Thecidea papillata</i> and <i>Belemnitella
+mucronata</i> are imbedded. To a geologist accustomed in England to
+regard rolled pebbles of chalk-flint as a common and distinctive
+feature of tertiary beds of different ages, it is a new and
+surprising phenomenon to behold strata made up of such materials,
+and yet to feel no doubt that they were
+<a name="page285"></a>accumulated in a sea in which the belemnite and other cretaceous
+mollusca flourished.</p>
+
+<p><b>Pisolitic Limestone of France.</b>&mdash;Geologists were for
+many years at variance respecting the chronological relations of
+this rock, which is met with in the neighbourhood of Paris, and at
+places north, south, east, and west of that metropolis, as between
+Vertus and Laversines, Meudon and Montereau. By many able
+palæontologists the species of fossils, more than fifty in
+number, were declared to be more Eocene in their appearance than
+Cretaceous. But M. Hébert found in this formation at
+Montereau, near Paris, the <i>Pecten quadricostatus,</i> a
+well-known Cretaceous species, together with some other fossils
+common to the Maestricht chalk and to the Baculite limestone of the
+Cotentin, in Normandy. He therefore, as well as M. Alcide
+d&rsquo;Orbigny, who had carefully studied the fossils, came to the
+opinion that it was an upper member of the Cretaceous group. It is
+usually in the form of a coarse yellowish or whitish limestone, and
+the total thickness of the series of beds already known is about
+100 feet. Its geographical range, according to M. Hébert, is
+not less than 45 leagues from east to west, and 35 from north to
+south. Within these limits it occurs in small patches only, resting
+unconformably on the white chalk.</p>
+
+<p>The <i>Nautilus Danicus,</i> <a href="images/fig229.jpg">Fig.
+230,</a> and two or three other species found in this rock, are
+frequent in that of Faxoe, in Denmark, but as yet no Ammonites,
+Hamites, Scaphites, Turrilites, Baculites, or Hippurites have been
+met with. The proportion of peculiar species, many of them of
+tertiary aspect, is confessedly large; and great aqueous erosion
+suffered by the white chalk, before the pisolitic limestone was
+formed, affords an additional indication of the two deposits being
+widely separated in time. The pisolitic formation, therefore, may
+eventually prove to be somewhat more intermediate in date between
+the secondary and tertiary epochs than the Maestricht rock.</p>
+
+<p><b>Chalk of Faxoe.</b>&mdash; In the island of Seeland, in
+Denmark, the newest member of the chalk series, seen in the
+sea-cliffs at Stevensklint resting on white chalk with flints, is a
+yellow limestone, a portion of which, at Faxoe, where it is used as
+a building stone, is composed of corals, even more conspicuously
+than is usually observed in recent coral reefs. It has been
+quarried to the depth of more than 40 feet, but its thickness is
+unknown. The imbedded shells are chiefly casts, many of them of
+univalve mollusca, which are usually very rare in the white chalk
+of Europe. Thus, there are two species of <i>Cypræa,</i> one
+of <i>Oliva,</i> two of <i>Mitra,</i> four of the genus
+<a name="page286"></a><i>Cerithium,</i> six of <i>Fusus,</i> two of <i>Trochus,</i>
+one of <i>Patella,</i> one of <i>Emarginula,</i> etc.; on the
+whole, more than thirty univalves, spiral or patelliform. At the
+same time, some of the accompanying bivalve shells, echinoderms,
+and zoophytes, are specifically identical with fossils of the true
+Cretaceous series. Among the cephalopoda of Faxoe may be mentioned
+<i>Baculites Faujasii</i> (Fig. 229), and <i>Belemnitella
+mucronata</i> (<a href="images/fig226.jpg">Fig. 226</a>), shells
+of the white chalk. The <i>Nautilus Danicus</i> (see Fig. 230) is
+characteristic of this formation; and it also occurs in France in
+the calcaire pisolitique of Laversin (Department of Oise). The
+claws and entire skull of a small crab, <i>Brachyurus rugosus</i>
+(Schlott.), are scattered through the Faxoe stone, reminding us of
+similar crustaceans inclosed in the rocks of modern coral reefs.
+Some small portions of this coralline formation consist of white
+earthy chalk.</p>
+
+<p><img src="images/fig229.jpg" width="420" height="208" alt=
+"Fig. 229: Portion of Baculites Faujasii, Fig. 230: Nautilus Danicus." />
+</p>
+
+<p><b>Composition, Extent and Origin of the White
+Chalk.</b>&mdash;The highest beds of chalk in England and France
+consist of a pure, white, calcareous mass, usually too soft for a
+building-stone, but sometimes passing into a more solid state. It
+consists, almost purely, of carbonate of lime; the stratification
+is often obscure, except where rendered distinct by interstratified
+layers of flint, a few inches thick, occasionally in continuous
+beds, but oftener in nodules, and recurring at intervals generally
+from two to four feet distant from each other. This upper chalk is
+usually succeeded, in the descending order, by a great mass of
+white chalk without flints, below which comes the chalk marl, in
+which there is a slight admixture of argillaceous matter. The
+united thickness of the three divisions in the south of England
+equals, in some places, 1000 feet. The section in <a href=
+"images/fig231.jpg">Fig. 231</a> will show the manner in which the
+white chalk extends from England into France, covered by the
+tertiary strata described in former chapters, and reposing on lower
+cretaceous beds.</p>
+
+<p>
+<a name="page287"></a>The area over which the white chalk preserves a nearly
+homogeneous aspect is so vast, that the earlier geologists
+despaired of discovering any analogous deposits of recent date.
+Pure chalk, of nearly uniform aspect and composition, is met with
+in a north-west and south-east direction, from the north of Ireland
+to the Crimea, a distance of about 1140 geographical miles, and in
+an opposite direction it extends from the south of Sweden to the
+south of Bordeaux, a distance of about 840 geographical miles. In
+Southern Russia, according to Sir R. Murchison, it is sometimes 600
+feet thick, and retains the same mineral character as in France and
+England, with the same fossils, including <i>Inoceramus Cuvieri,
+Belemnitella mucronata,</i> and <i>Ostrea vesicularis</i> (<a href=
+"images/fig251.jpg">Fig. 251).</a></p>
+
+<p><img src="images/fig231.jpg" width="609" height="100" alt=
+"Diagrammatic section from Hertfordshire, in England, to Sens, in France." />
+</p>
+
+<p>Great light has recently been thrown upon the origin of the
+unconsolidated white chalk by the deep soundings made in the North
+Atlantic, previous to laying down, in 1858, the electric telegraph
+between Ireland and Newfoundland. At depths sometimes exceeding two
+miles, the mud forming the floor of the ocean was found, by
+Professor Huxley, to be almost entirely composed (more than
+nineteen-twentieths of the whole) of minute Rhizopods, or
+foraminiferous shells of the genus Globigerina, especially the
+species <i>Globigerina bulloides</i> (see <a href=
+"images/fig232.jpg">Fig. 232.</a>) the organic bodies next in
+quantity were the siliceous shells called <i>
+Polycystineæ,</i> and next to them the siliceous skeletons of
+plants called <i>Diatomaceæ</i> (<a href=
+"images/fig232.jpg">Figs. 233, 234, 235</a>), and occasionally
+some siliceous spiculæ of sponges (<a href=
+"images/fig232.jpg">Fig. 236</a>) were intermixed. These were
+connected by a mass of living gelatinous matter to which he has
+given the name of <i>Bathybius,</i> and which contains abundance of
+very minute bodies termed Coccoliths and Coccospheres, which have
+also been detected fossil in chalk.</p>
+
+<p>Sir Leopold MacClintock and Dr. Wallich have ascertained that 95
+per cent of the mud of a large part of the North Atlantic consists
+of Globigerina shells. But Captain Bullock, <small>R.N.</small>,
+lately brought up from the enormous depth of 16,860 feet a
+white,
+<a name="page288"></a>viscid, chalky mud, wholly devoid of Globigerinæ. This mud was perfectly
+homogeneous in composition, and contained no organic remains visible to the
+naked eye. Mr. Etheridge, however, has ascertained by microscopical examination
+that it is made up of <i> Coccoliths, Discoliths,</i> and other minute fossils
+like those of the Chalk classed by Huxley as <i>Bathybius,</i> when this term
+is used in its widest sense. This mud, more than three miles deep, was dredged
+up in latitude 20&deg; 19&#x2032; N., longitude 4&deg; 36&#x2032; E., or about
+midway between Madeira and the Cape of Good Hope.
+</p>
+
+<p><img src="images/fig232.jpg" width="348" height="185" alt=
+"Fig. 232: Globigerina bulloides, Calcareous Rhizopod. Fig. 233: Actinocyclus,
+Fig. 234: Pinnularia, Fig. 235: Eunotia bidens, Siliceous Diatomaceæ. Fig.
+236: Spicula of sponge, Siliceous sponge." />
+</p>
+
+<p>The recent deep-sea dredgings in the Atlantic conducted by Dr.
+Wyville Thomson, Dr. Carpenter, Mr. Gwyn Jeffreys, and others, have
+shown that on the same white mud there sometimes flourish Mollusca,
+Crustacea, and Echinoderms, besides abundance of siliceous sponges,
+forming, on the whole, a marine fauna bearing a striking
+resemblance in its general character to that of the ancient
+chalk.</p>
+
+<p><b>Popular Error as to the Geological Continuity of the
+Cretaceous Period.</b>&mdash;We must be careful, however, not to
+overrate the points of resemblance which the deep-sea
+investigations have placed in a strong light. They have been
+supposed by some naturalists to warrant a conclusion expressed in
+these words: &ldquo;We are still living in the Cretaceous
+epoch;&rdquo; a doctrine which has led to much popular delusion as
+to the bearing of the new facts on geological reasoning and
+classification. The reader should be reminded that in geology we
+have been in the habit of founding our great chronological
+divisions, not on foraminifera and sponges, nor even on echinoderms
+and corals, but on the remains of the most highly organised beings
+available to us, such as the mollusca; these being met with, as
+explained (<a href="#page142">p. 142</a>), in stratified
+rocks of almost every age. In dealing with the mollusca, it is
+those of the highest or most specialised organisation, which afford
+us the best characters in proportion as their vertical range is the
+most limited. Thus the Cephalopoda
+<a name="page289"></a>are the most valuable, as having a more restricted range in time
+than the Gasteropoda; and these, again, are more characteristic of
+the particular stratigraphical subdivisions than are the
+Lamellibranchiate Bivalves, while these last, again, are more
+serviceable in classification than the Brachiopoda, a still lower
+class of shell-fish, which are the most enduring of all.</p>
+
+<p>When told that the new dredgings prove that &ldquo;we are still
+living in the Chalk Period,&rdquo; we naturally ask whether some
+cuttle-fish has been found with a Belemnite forming part of its
+internal framework; or have Ammonites, Baculites, Hamites,
+Turrilites, with four or five other Cephalopodous genera
+characteristic of the chalk and unknown as tertiary, been met with
+in the abysses of the ocean? Or, in the absence of these
+long-extinct forms, has a single spiral univalve, or species of
+Cretaceous Gasteropod, been found living? Or, to descend still
+lower in the scale, has some characteristic Cretaceous genus of
+Lamellibranchiate Bivalve, such as the Inoceramus, or Hippurite,
+foreign to the Tertiary seas, been proved to have survived down to
+our time? Or, of the numerous genera of lamellibranchiates common
+to the Cretaceous and Recent seas, has one species been found
+living? The answer to all these questions is&mdash;not one has been
+found. Even of the humblest shell-fish, the Brachiopods, no new
+species common to the Cretaceous and recent seas has yet been met
+with. It has been very generally admitted by conchologists that out
+of a hundred species of this tribe occurring fossil in the Upper
+Chalk&mdash;one, and one only, <i>Terebratulina striata,</i> is still
+living, being thought to be identical with <i>Terebratula
+caput-serpentis.</i> Although this identity is still questioned by
+some naturalists of authority, it would certainly not surprise us
+if another lamp-shell of equal antiquity should be met with in the
+deep sea.</p>
+
+<p>Had it been declared that we are living in the Eocene epoch, the
+idea would not be so extravagant, for the great reptiles of the
+Upper Chalk, the Mosasaurus, Pliosaurus, and Pterodactyle, and many
+others, as well as so many genera of chambered univalves, had
+already disappeared from the earth, and the marine fauna had made a
+greater approach to our own by nearly the entire difference which
+separates it from the fauna of the Cretaceous seas. The Eocene
+nummulitic limestone of Egypt is a rock mainly composed, like the
+more ancient white chalk, of globigerine mud; and if the reader
+will refer to what we have said of the extent to which the
+nummulitic marine strata, formed originally at the bottom of the
+sea, now enter into the frame-work of
+<a name="page290"></a>mountain chains of the principal continents, he will at once
+perceive that the present Atlantic, Pacific, and Indian Oceans are
+geographical terms, which must be wholly without meaning when
+applied to the Eocene, and still more to the Cretaceous Period; so
+that to talk of the chalk having been uninterruptedly forming in
+the Atlantic from the Cretaceous Period to our own, is as
+inadmissible in a geographical as in a geological sense.</p>
+
+<p><b>Chalk-flints.</b>&mdash;The origin of the layers of flint,
+whether in the form of nodules, or continuous sheets, or in veins
+or cracks not parallel to the stratification, has always been more
+difficult to explain than that of the white chalk. But here, again,
+the late deep-sea soundings have suggested a possible source of
+such mineral matter. During the cruise of the
+&ldquo;Bulldog,&rdquo; already alluded to, it was ascertained that
+while the calcareous <i>Globigerinæ</i> had almost exclusive
+possession of certain tracts of the sea-bottom, they were wholly
+wanting in others, as between Greenland and Labrador. According to
+Dr. Wallich, they may flourish in those spaces where they derive
+nutriment from organic and other matter, brought from the south by
+the warm waters of the Gulf Stream, and they may be absent where
+the effects of that great current are not felt. Now, in several of
+the spaces where the calcareous Rhizopods are wanting, certain
+microscopic plants, called <i>Diatomaceæ,</i> above mentioned
+(<a href="images/fig232.jpg">Figs. 233-235</a>), the solid parts
+of which are siliceous, monopolise the ground at a depth of nearly
+400 fathoms, or 2400 feet.</p>
+
+<p>The large quantities of silex in solution required for the
+formation of these plants may probably arise from the
+disintegration of feldspathic rocks, which are universally
+distributed. As more than half of their bulk is formed of siliceous
+earth, they may afford an endless supply of silica to all the great
+rivers which flow into the ocean. We may imagine that, after a
+lapse of many years or centuries, changes took place in the
+direction of the marine currents, favouring at one time a supply in
+the same area of siliceous, and at another of calcareous matter in
+excess, giving rise in the one case to a preponderance of
+Globigerinæ, and in the other of Diatomaceæ. These
+last, and certain sponges, may by their decomposition have
+furnished the silex, which, separating from the chalky mud,
+collected round organic bodies, or formed nodules, or filled
+shrinkage cracks.</p>
+
+<p>
+<b>Pot-stones.</b>&mdash;A more difficult enigma is presented by the occurrence
+of certain huge flints, or pot-stones, as they are called in Norfolk, occurring
+singly, or arranged in nearly continuous columns at right angles to the
+ordinary and <a name="page291"></a>horizontal layers of small flints. I visited
+in the year 1825 an extensive range of quarries then open on the river Bure,
+near Horstead, about six miles from Norwich, which afforded a continuous
+section, a quarter of a mile in length, of white chalk, exposed to the depth of
+about twenty-six feet, and covered by a bed of gravel. The pot-stones, many of
+them pear-shaped, were usually about three feet in height and one foot in their
+transverse diameter, placed in vertical rows, like pillars, at irregular
+distances from each other, but usually from twenty to thirty feet apart, though
+sometimes nearer together, as in Figure 237. These rows did not terminate
+downward in any instance which I could examine, nor upward, except at the point
+where they were cut off abruptly by the bed of gravel. On breaking open the
+pot-stones, I found an internal cylindrical nucleus of pure chalk, much harder
+than the ordinary surrounding chalk, and not crumbling to pieces like it, when
+exposed to the winter&rsquo;s frost. At the distance of half a mile, the
+vertical piles of pot-stones were much farther apart from each other. Dr.
+Buckland has described very similar phenomena as characterising the white chalk
+on the north coast of Antrim, in Ireland.<a href="#fn-17.2" name="fnref-17.2"
+id="fnref-17.2"><sup>[2]</sup></a>
+</p>
+
+<p><img src="images/fig237.jpg" width="390" height="307" alt=
+"View of a chalk-pit at Horstead, near Norwich, showing the position of the pot-stones." />
+</p>
+
+<p><b>Vitreous Sponges of the Chalk.</b>&mdash;These pear-shaped
+masses of flint often resemble in shape and size the large
+sponges
+<a name="page292"></a>called Neptune&rsquo;s Cups (<i>Spongia patera,</i> Hardw.),
+which grow in the seas of Sumatra; and if we could suppose a series
+of such gigantic sponges to be separated from each other, like
+trees in a forest, and the individuals of each successive
+generation to grow on the exact spot where the parent sponge died
+and was enveloped in calcareous mud, so that they should become
+piled one above the other in a vertical column, their growth
+keeping pace with the accumulation of the enveloping calcareous
+mud, a counterpart of the phenomena of the Horstead pot-stones
+might be obtained.</p>
+
+<img src="images/fig238.jpg" width="123" height="281" alt=
+"Fig. 238: Ventriculites radiatus. White chalk." />
+
+<p>Professor Wyville Thomson, describing the modern soundings in
+1869 off the north coast of Scotland, speaks of the ooze or chalk
+mud brought from a depth of about 3000 feet, and states that at one
+haul they obtained forty specimens of vitreous sponges buried in
+the mud. He suggests that the Ventriculites of the chalk were
+nearly allied to these sponges, and that when the silica of their
+spicules was removed, and was dissolved out of the calcareous
+matrix, it set into flint.</p>
+
+<p><b>Boulders and Groups of Pebbles in Chalk.</b>&mdash;The
+occurrence here and there, in the white chalk of the south of
+England, of isolated pebbles of quartz and green schist has justly
+excited much wonder. It was at first supposed that they had been
+dropped from the roots of some floating tree, by which means stones
+are carried to some of the small coral islands of the Pacific. But
+the discovery in 1857 of a group of stones in the white chalk near
+Croydon, the largest of which was syenite and weighed about forty
+pounds, accompanied by pebbles and fine sand like that of a beach,
+has been shown by Mr. Godwin Austen to be inexplicable except by
+the agency of floating ice. If we consider that icebergs now reach
+40 degrees north latitude in the Atlantic, and several degrees
+nearer the equator in the southern hemisphere, we can the more
+easily believe that even during the Cretaceous epoch, assuming that
+the climate was milder, fragments of coast ice may have floated
+occasionally as far as the south of England.</p>
+
+<p><b>Distinctness of Mineral Character in Contemporaneous Rocks of
+the Cretaceous Period.</b>&mdash;But we must not imagine that
+because pebbles are so rare in the white chalk of England and
+France there are no proofs of sand, shingle, and clay having
+<a name="page293"></a>been accumulated contemporaneously even in European seas. The
+siliceous sandstone called &ldquo;upper quader&rdquo; by the
+Germans overlies white argillaceous chalk or
+&ldquo;pläner-kalk,&rdquo; a deposit resembling in composition
+and organic remains the chalk marl of the English series. This
+sandstone contains as many fossil shells common to our white chalk
+as could be expected in a sea-bottom formed of such different
+materials. It sometimes attains a thickness of 600 feet, and, by
+its jointed structure and vertical precipices, plays a conspicuous
+part in the picturesque scenery of Saxon Switzerland, near Dresden.
+It demonstrates that in the Cretaceous sea, as in our own, distinct
+mineral deposits were simultaneously in progress. The quartzose
+sandstone alluded to, derived from the detritus of the neighbouring
+granite, is absolutely devoid of carbonate of lime, yet it was
+formed at the distance only of four hundred miles from a sea-bottom
+now constituting part of France, where the purely calcareous white
+chalk was forming. In the North American continent, on the other
+hand, where the Upper Cretaceous formations are so widely
+developed, true white chalk, in the ordinary sense of that term,
+does not exist.</p>
+
+<p><img src="images/fig239.jpg" width="321" height="189" alt=
+"Fig. 239: Ananchytes ovatus. White chalk, upper and lower." />
+</p>
+
+<p><b>Fossils of the White Chalk.</b>&mdash;Among the fossils of
+the white chalk, echinoderms are very numerous; and some of the
+genera, like <i>Ananchytes</i> (see Fig. 239), are exclusively
+cretaceous. Among the Crinoidea, the <i>Marsupites</i> (<a href=
+"images/fig240.jpg">Fig. 242</a>) is a characteristic genus. Among
+the mollusca, the cephalopoda are represented by Ammonites,
+Baculites (<a href="images/fig229.jpg">Fig. 229</a>), and
+Belemnites (<a href="images/fig226.jpg">Fig. 226</a>). Although
+there are eight or more species of Ammonites and six of them
+peculiar to it, this genus is much less fully represented than in
+each of the other subdivisions of the Upper Cretaceous group.</p>
+
+<p>Among the brachiopoda in the white chalk, the <i>
+Terebratulæ</i> are very abundant (see <a href=
+"images/fig240.jpg">Figs. 243-247</a>). With these
+<a name="page294"></a>are associated some forms of oyster (see <a href=
+"images/fig251.jpg">Fig. 251</a>), and other bivalves (Figs. 249,
+250).</p>
+
+<p><img src="images/fig240.jpg" width="432" height="519" alt=
+"Fig. 240: Micraster cor-angumum. White chalk. Fig. 241: Galerites albogalerus.
+White chalk. Fig. 242: Marsupites Milleri. White chalk. Fig. 243: Terebratulina
+striata. Upper white chalk. Fig. 244: Rhynchonella octoplicata. Upper white
+chalk. Fig. 245: Magas pumila. Upper white chalk. Fig. 246: Terebratula carnea.
+Upper white chalk. Fig. 247: Terebratula biplicata. Upper cretaceous. Fig. 248:
+Crania Parisiensis. Inferior or attached valve. Upper white chalk. Fig. 249:
+Peten Beaveri. Lower white chalk and chalk marl. Fig. 250: Lima spinosa. Upper
+white chalk." />
+</p>
+
+<p>Among the bivalve mollusca, no form marks the Cretaceous era in
+Europe, America, and India in a more striking manner than the
+extinct genus <i>Inoceramus</i> (<i>Catillus</i> of Lam.; see <a
+href="images/fig251.jpg">Fig. 252</a>), the shells of which are
+distinguished by a fibrous texture, and are often met with in
+fragments, having probably been extremely friable.</p>
+
+<p>Of the singular family called <i>Rudistes</i> by Lamarck,
+hereafter to be mentioned as extremely characteristic of the
+chalk
+<a name="page295"></a>of southern Europe, a single representative only (Fig. 253) has
+been discovered in the white chalk of England.</p>
+
+<p><img src="images/fig251.jpg" width="368" height="300" alt=
+"Fig. 251: Ostrea vesicularis. Upper chalk and upper greensand.
+Fig. 252: Inoceramus Lamarckii. White chalk." />
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig253.jpg" width="366" height="219" alt="[Illustration]" />
+<p class="caption"><i>Radiolites Mortoni</i>, Mantell. Houghton, Sussex. White
+chalk.<br/>
+Diameter one-seventh nat. size.<br/>
+Fig. 253. Two individuals deprived of their upper valves, adhering together.<br/>
+Fig. 254. Same seen from above.<br/>
+Fig. 255. Transverse section of part of the wall of the shell, magnified to
+show the structure.<br/>
+Fig. 256. Vertical section of the same.<br/>
+On the side where the shell is thinnest, there is one external furrow and
+corresponding internal ridge, <i>a</i>, <i>b</i>, figs. 255, 256; but they
+are usually less prominent than in these figures. The upper or opercular valve
+is wanting.</p>
+</div>
+
+<p>
+The general absence of univalve mollusca in the white chalk is very marked. Of
+bryozoa there is an abundance, such as <i>Eschara</i> and <i>Escharina</i>
+(Figs. 257, 258). These and other organic bodies, especially sponges, such as
+<i>Ventriculites</i>
+<a name="page296"></a>(Fig. 238), are dispersed indifferently through the soft
+chalk and hard flint, and some of the flinty nodules owe their irregular forms
+to inclosed sponges, such as Fig. 259, <i>a,</i> where the hollows in the
+exterior are caused by the branches of a sponge (Fig. 259, <i>b</i>), seen on
+breaking open the flint.
+</p>
+
+<p><img src="images/fig257.jpg" width="441" height="368" alt=
+"Fig. 257: Eschara disticha. White chalk. Fig. 258: Escharina oceani. White
+chalk. Fig. 259: A branching sponge in a flint, from the white chalk." />
+</p>
+
+<p>The remains of fishes of the Upper Cretaceous formations consist
+chiefly of teeth belonging to the shark family. Some of the genera
+are common to the Tertiary formations, and some are distinct. To
+the latter belongs the genus <i>Ptychodus</i> (<a href=
+"images/fig260.jpg">Fig. 260</a>), which is allied to the living
+Port Jackson shark, <i>Cestracion Phillippi,</i> the anterior teeth
+of which (see <a href="images/fig261.jpg">Fig. 261,</a> <i>a</i>)
+are sharp and cutting, while the posterior or palatal teeth
+(<i>b</i>) are flat (<a href="images/fig260.jpg">Fig. 260</a>).
+But we meet with no bones of land-animals, nor any terrestrial or
+fluviatile shells, nor any plants, except sea-weeds, and here and
+there a piece of drift-wood. All the appearances concur
+<a name="page297"></a>in leading us to conclude that the white chalk was the product
+of an open sea of considerable depth.</p>
+
+<img src="images/fig260.jpg" width="124" height="147" alt=
+"Fig. 260: Palatal tooth of Ptychodus decurrens. Lower white chalk." />
+
+<p>
+The existence of turtles and oviparous saurians, and of a Pterodactyl or winged
+lizard, found in the white chalk of Maidstone, implies, no doubt, some
+neighbouring land; but a few small islets in mid-ocean, like Ascension,
+formerly so much frequented by migratory droves of turtle, might perhaps have
+afforded the required retreat where these creatures laid their eggs in the
+sand, or from which the flying species may have been blown out to sea. Of the
+vegetation of such islands we have scarcely any indication, but it consisted
+partly of cycadaceous plants; for a fragment of one of these was found by
+Captain Ibbetson in the Chalk Marl of the Isle of Wight, and is referred by A.
+Brongniart to <i> Clathraria Lyellii,</i> Mantell, a species common to the
+antecedent Wealden period. The fossil plants, however, of beds corresponding in
+age to the white chalk at Aix-la-Chapelle, presently to be described, like the
+sandy beds of Saxony, before alluded to (p. 293), afford such evidence of land
+as to prove how vague must be any efforts of ours to restore the geography of
+that period.
+</p>
+
+<img src="images/fig261.jpg" width="275" height="267" alt=
+"Fig. 261: Cestracion Phillipi; recent." />
+
+<p>The Pterodactyl of the Kentish chalk, above alluded to, was of
+gigantic dimensions, measuring 16 feet 6 inches from tip to tip of
+its outstretched wings. Some of its elongated bones were at first
+mistaken by able anatomists for those of birds; of which class no
+osseous remains have as yet been derived from the white chalk,
+although they have been found (as will be seen on page 299) in the
+Chloritic sand.</p>
+
+<p>The collector of fossils from the white chalk was formerly
+puzzled by meeting with certain bodies which they call larch-cones,
+which were afterwards recognised by Dr. Buckland
+<a name="page298"></a>to be the excrement of fish (see Fig. 262). They are composed in
+great part of phosphate of lime.</p>
+
+<p><img src="images/fig262.jpg" width="398" height="258" alt=
+"Fig. 262: Coprolites of fish, from the chalk. Fig. 263: Baculites anceps.
+Lower chalk. Fig. 264: Ammonites Rhotomagensis. Chalk marl." />
+</p>
+
+<p><b>Lower White Chalk.</b>&mdash;The Lower White Chalk, which is
+several hundred feet thick, without flints, has yielded 25 species
+of Ammonites, of which half are peculiar to it. The genera
+Baculite, Hamite, Scaphite, Turrilite, Nautilus, Belemnite, and
+Belemnitella, are also represented.</p>
+
+<p><b>Chalk Marl.</b>&mdash;The lower chalk without flints passes
+gradually downward, in the south of England, into an argillaceous
+limestone, &ldquo;the chalk marl,&rdquo; already alluded to. It
+contains 32 species of Ammonites, seven of which are peculiar to
+it, while eleven pass up into the overlying lower white chalk. <i>
+A. Rhotomagensis</i> is characteristic of this formation. Among the
+British cephalopods of other genera may be mentioned <i>Scaphites
+æqualis</i> (<a href="images/fig265.jpg">Fig. 266</a>) and
+<i>Turrilites costatus</i> (<a href="images/fig265.jpg">Fig.
+265</a>).</p>
+
+<p><b>Chloritic Series (or Upper Greensand).</b>&mdash;According to
+the old nomenclature, this subdivision of the chalk was called
+Upper Greensand, in order to distinguish it from those members of
+the Neocomian or Lower Cretaceous series below the Gault to which
+the name of Greensand had been applied. Besides the reasons before
+given (<a href="#page282">p. 282</a>) for abandoning this
+nomenclature, it is objectionable in this instance as leading the
+uninitiated to suppose that the divisions thus named Upper and
+Lower Greensand are of co-ordinate value, instead of which the
+chloritic sand is quite a subordinate member of the Upper
+Cretaceous group, and the term Greensand has very commonly been
+used for the whole of the Lower Cretaceous rocks, which are almost
+comparable in importance to
+<a name="page299"></a>the entire Upper Cretaceous series. The higher portion of the
+Chloritic series in some districts has been called chloritic marl,
+from its consisting of a chalky marl with chloritic grains. In
+parts of Surrey, where calcareous matter is largely intermixed with
+sand, it forms a stone called malm-rock or firestone. In the cliffs
+of the southern coast of the Isle of Wight it contains bands of
+calcareous limestone with nodules of chert.</p>
+
+<img src="images/fig265.jpg" width="278" height="299" alt=
+"Fig. 265: Turrilites costatus. Lower chalk and chalk marl. Fig. 266: Scaphites
+æqualis. Chloritic marl and sand, Dorsetshire." />
+
+<p><i>Coprolite Bed.</i>&mdash;The so-called coprolite bed, found
+near Farnham, in Surrey, and near Cambridge, contains nodules of
+phosphate of lime in such abundance as to be largely worked for the
+manufacture of artificial manure. It belongs to the upper part of
+the Chloritic series, and is doubtless chiefly of animal origin,
+and may perhaps be partly coprolitic, derived from the excrement of
+fish and reptiles. The late Mr. Barrett discovered in it, near
+Cambridge, in 1858, the remains of a bird, which was rather larger
+than the common pigeon, and probably of the order Natatores, and
+which, like most of the Gull tribe, had well-developed wings.
+Portions of the metacarpus, metatarsus, tibia, and femur have been
+detected, and the determinations of Mr. Barrett have been confirmed
+by Professor Owen.</p>
+
+<p>This phosphatic bed in the suburbs of Cambridge must have been
+formed partly by the denudation of pre-existing rocks, mostly of
+Cretaceous age. The fossil shells and bones of animals washed out
+of these denuded strata, now forming a layer only a few feet thick,
+have yielded a rich harvest to the collector. A large Rudist of the
+genus Radiolite, no less than two feet in height, may be seen in
+the Cambridge Museum, obtained from this bed. The number of
+reptilian remains, all apparently of Cretaceous age, is truly
+surprising; more than ten species of Pterodactyl, five or six of
+Ichthyosaurus, one of Pliosaurus, one of Dinosaurus, eight of
+Chelonians, besides other forms, having been recognised.</p>
+
+<p>
+<a name="page300"></a>The chloritic sand is regarded by many geologists as a littoral
+deposit of the Chalk Ocean, and therefore contemporaneous with part
+of the chalk marl, and even, perhaps, with some part of the white
+chalk. For, as the land went on sinking, and the cretaceous sea
+widened its area, white mud and chloritic sand were always forming
+somewhere, but the line of sea-shore was perpetually shifting its
+position. Hence, though both sand and mud originated
+simultaneously, the one near the land, the other far from it, the
+sands in every locality where a shore became submerged might
+constitute the underlying deposit.</p>
+
+<p><img src="images/fig267.jpg" width="388" height="169" alt=
+"Fig. 267: Ostrea columba. Chloritic sand. Fig. 268: Ostrea carinata. Chalk
+marl and chloritic sand." />
+</p>
+
+<p>Among the characteristic mollusca of the chloritic sand may be
+mentioned <i>Terebrirostra lyra</i> (Fig. 269), <i>Plagiostoma
+Hoperi</i> (Fig. 271), <i>Pecten quinque-costatus</i> (Fig. 270),
+and <i>Ostrea columba</i> (Fig. 267).</p>
+
+<p><img src="images/fig269.jpg" width="375" height="194" alt=
+"Fig. 269: Terebrirostra lyra. Chloritic sand. Fig. 270: Pecten 5-costatus.
+White chalk and chloritic sand. Fig. 271: Plagiostoma Hoperi. White chalk and chloritic sand." />
+</p>
+
+<p>The Cephalopoda are abundant, among which 40 species of
+Ammonites are now known, 10 being peculiar to this subdivision, and
+the rest common to the beds immediately above or below.</p>
+
+<p><b>Gault.</b>&mdash;The lowest member of the Upper Cretaceous
+group,
+<a name="page301"></a>usually about 100 feet thick in the S.E. of England, is
+provincially termed Gault. It consists of a dark blue marl,
+sometimes intermixed with green sand. Many peculiar forms of
+cephalopoda, such as the <i>Hamite</i> (Fig. 272), and <i>
+Scaphite,</i> with other fossils, characterise this formation,
+which, small as is its thickness, can be traced by its organic
+remains to distant parts of Europe, as, for example, to the
+Alps.</p>
+
+<img src="images/fig272.jpg" width="242" height="196" alt=
+"Fig. 272: Ancyloceras spinigerum. Near Folkestone." />
+
+<p>Twenty-one species of British Ammonites are recorded as found in
+the Gault, of which only eight are peculiar to it, ten being common
+to the overlying Chloritic series.</p>
+
+<p><b>Connection between Upper and Lower Cretaceous
+Strata.&mdash;Blackdown Beds.</b>&mdash;The break between the Upper
+and Lower Cretaceous formations will be appreciated when it is
+stated that, although the Neocomian contains 31 species of
+Ammonite, and the Gault, as we have seen, 21, there are only three
+of those common to both divisions. Nevertheless, we may expect the
+discovery in England, and still more when we extend our survey to
+the Continent, of beds of passage intermediate between the Upper
+and Lower Cretaceous. Even now the Blackdown beds in Devonshire,
+which rest immediately on Triassic strata, and which evidently
+belong to some part of the Cretaceous series, have been referred by
+some geologists to the Upper group, by others to the Lower or
+Neocomian. They resemble the Folkestone beds of the latter series
+in mineral character, and 59 out of 156 of their fossil mollusca
+are common to them; but they have also 16 species common to the
+Gault, and 20 to the overlying Chloritic series; and what is very
+important, out of seven Ammonites six are found also in the Gault
+and Chloritic series, only one being peculiar to the Blackdown
+beds.</p>
+
+<p>Professor Ramsay has remarked that there is a stratigraphical
+break; for in Kent, Surrey, and Sussex, at those few points where
+there are exposures of junctions of the Gault and Neocomian, the
+surface of the latter has been much eroded or denuded, while to the
+westward of the great chalk escarpment the unconformability of the
+two groups is equally striking. At Blackdown this unconformability
+is still more marked, for though distant only 100 miles from
+<a name="page302"></a>Kent and Surrey, no formation intervenes between these beds and
+the Trias; all intermediate groups, such as the Lower Neocomian and
+Oolite, having either not been deposited or destroyed by
+denudation.</p>
+
+<p><b>Flora of the Upper Cretaceous Period.</b>&mdash;As the Upper
+Cretaceous rocks of Europe are, for the most part, of purely marine
+origin, and formed in deep water usually far from the nearest
+shore, land-plants of this period, as we might naturally have
+anticipated, are very rarely met with. In the neighbourhood of
+Aix-la-Chapelle, however, an important exception occurs, for there
+certain white sands and laminated clays, 400 feet in thickness,
+contain the remains of terrestrial plants in a beautiful state of
+preservation. These beds are the equivalents of the white chalk and
+chalk marl of England, or Senonien of d&rsquo;Orbigny, although the
+white siliceous sands of the lower beds, and the green grains in
+the upper part of the formation, cause it to differ in mineral
+character from our white chalk.</p>
+
+<p>Beds of fine clay, with fossil plants, and with seams of
+lignite, and even perfect coal, are intercalated. Floating wood,
+containing perforating shells, such as Pholas and Gastrochoena,
+occur. There are likewise a few beds of a yellowish-brown
+limestone, with marine shells, which enable us to prove that the
+lowest and highest plant-beds belong to one group. Among these
+shells are <i>Pecten quadricostatus,</i> and several others which
+are common to the upper and lower part of the series, and <i>
+Trigonia limbata,</i> D&rsquo;Orbigny, a shell of the white chalk.
+On the whole, the organic remains and the geological position of
+the strata prove distinctly that in the neighbourhood of
+Aix-la-Chapelle a gulf of the ancient Cretaceous sea was bounded by
+land composed of Devonian rocks. These rocks consisted of quartzose
+and schistose beds, the first of which supplied white sand and the
+other argillaceous mud to a river which entered the sea at this
+point, carrying down in its turbid waters much drift-wood and the
+leaves of plants. Occasionally, when the force of the river abated,
+marine shells of the genera <i>Trigonia, Turritella, Pecten,</i>
+etc., established themselves in the same area, and plants allied to
+<i>Zostera</i> and <i>Fucus</i> grew on the bottom.</p>
+
+<p>
+The fossil plants of this member of the upper chalk at Aix have been diligently
+collected and studied by Dr. Debey, and as they afford the only example yet
+known of a terrestrial flora older than the Eocene, in which the great
+divisions of the vegetable kingdom are represented in nearly the same
+proportions as in our own times, they deserve particular attention. Dr. Debey
+estimates the number of species <a name="page303"></a>as amounting to more than
+two hundred, of which sixty-seven are cryptogamous, chiefly ferns, twenty
+species of which can be well determined, most of them being in fructification.
+The scars on the bark of one or two are supposed to indicate tree-ferns. Of
+thirteen genera three are still existing, namely, <i>Gleichenia,</i> now
+inhabiting the Cape of Good Hope, and New Holland; Lygodium, now spread
+extensively through tropical regions, but having some species which live in
+Japan and North America; and <i> Asplenium,</i> a cosmopolite form. Among the
+phænogamous plants, the Conifers are abundant, the most common belonging to a
+genus called Cycadopteris by Debey, and hardly separable from Sequoia (or
+Wellingtonia), of which both the cones and branches are preserved. When I
+visited Aix, I found the silicified wood of this plant very plentifully
+dispersed through the white sands in the pits near that city. In one silicified
+trunk 200 rings of annual growth could be counted. Species of Araucaria like
+those of Australia are also found. Cycads are extremely rare, and of
+Monocotyledons there are but few. No palms have been recognised with certainty,
+but the genus Pandanus, or screw pine, has been distinctly made out. The number
+of the Dicotyledonous Angiosperms is the most striking feature in so ancient a
+flora.<a href="#fn-17.3" name="fnref-17.3" id="fnref-17.3"><sup>[3]</sup></a>
+</p>
+
+<p>
+Among them we find the familiar forms of the Oak, Fig, and Walnut (Quercus,
+Ficus, and Juglans), of the last both the nuts and leaves; also several genera
+of the Myrtaceæ. But the predominant order is the Proteaceæ, of which there are
+between sixty and seventy supposed species, many of extinct genera, but some
+referred to the following living forms&mdash;Dryandra, Grevillea, Hakea,
+Banksia, Persoonia&mdash;all <a name="page304"></a>now belonging to Australia,
+and Leucospermum, species of which form small bushes at the Cape.
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary="Table explaining the
+corresponding names of groups so much spoken of in palæontology.">
+<tr>
+<td>&nbsp;</td>
+<td align="center">Brongniart.</td>
+<td align="center">Lindley.</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="2">Cryptogamic.</td>
+<td >1. Cryptogamous amphigens, or cellular
+cryptogamic.</td>
+<td valign="top">Thallogens.</td>
+<td valign="top">Lichens, sea-weeds, fungi.</td>
+</tr>
+
+<tr>
+<td >2. Cryptogamous acrogens.</td>
+<td >Acrogens.</td>
+<td >Mosses, equisetums, ferns,
+lycopodiums,&mdash;Lepidodendra.</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="3">
+Phænerogamic.</td>
+<td >3. Dicotyledonous gymnosperms.</td>
+<td valign="top">Gymnogens.</td>
+<td valign="top">Conifers and Cycads.</td>
+</tr>
+
+<tr>
+<td valign="top">4. Dicot. angiosperms.</td>
+<td valign="top">Exogens.</td>
+<td valign="top">Compositæ, leguminosæ,
+cruciferæ, healths, etc. All native European trees except
+conifers.</td>
+</tr>
+
+<tr>
+<td valign="top">5. Monocotyledons.</td>
+<td valign="top">Endogens.</td>
+<td valign="top">Palms, lilies, aloes, rushes,
+grasses, etc.</td>
+</tr>
+</table>
+
+<p>The epidermis of the leaves of many of these Aix plants,
+especially of the Proteaceæ, is so perfectly preserved in an
+envelope of fine clay, that under the microscope the stomata, or
+polygonal cellules, can be detected, and their peculiar arrangement
+is identical with that known to characterise some living
+Proteaceæ (Grevillea, for example). Although this peculiarity
+of the structure of stomata is also found in plants of widely
+distant orders, it is, on the whole, but rarely met with, and being
+thus observed to characterise a foliage previously suspected to be
+proteaceous, it adds to the probability that the botanical evidence
+had been correctly interpreted.</p>
+
+<p>An occasional admixture at Aix-la-Chapelle of Fucoids and
+Zosterites attests, like the shells, the presence of salt-water. Of
+insects, Dr. Debey has obtained about ten species of the families
+Curculionidæ and Carabidæ.</p>
+
+<p>The resemblance of the flora of Aix-la-Chapelle to the tertiary
+and living floras in the proportional number of dicotyledonous
+angiosperms as compared to the gymnogens, is a subject of no small
+theoretical interest, because we can now affirm that these Aix
+plants flourished before the rich reptilian fauna of the secondary
+rocks had ceased to exist. The Ichthyosaurus, Pterodactyl, and
+Mosasaurus were of coeval date with the oak, the walnut, and the
+fig. Speculations have often been hazarded respecting a connection
+between the rarity of Exogens in the older rocks and a peculiar
+state of the atmosphere. A denser air, it was suggested, had in
+earlier times been alike adverse to the well-being of the higher
+order of flowering plants, and of the quick-breathing animals, such
+as mammalia and birds, while it was favourable to a cryptogamic and
+gymnospermous flora, and to a predominance of reptile life. But we
+now learn that there is no incompatibility in the co-existence of a
+vegetation like that of the present globe, and some of the most
+remarkable forms of the extinct reptiles of the age of
+gymnosperms.</p>
+
+<p>If the passage seem at present to be somewhat sudden from the
+flora of the Lower or Neocomian to that of the Upper Cretaceous
+period, the abruptness of the change will probably disappear when
+we are better acquainted with the fossil vegetation of the
+uppermost beds of the Neocomian and that of the lowest strata of
+the Gault or true Cretaceous series.</p>
+
+<p><b>Hippurite limestone.</b>&mdash;<i>Difference between the
+Chalk of the North and South of Europe.</i>&mdash;By the aid of the
+three tests,
+<a name="page305"></a>superposition, mineral character, and fossils, the geologist has
+been enabled to refer to the same Cretaceous period certain rocks
+in the north and south of Europe, which differ greatly both in
+their fossil contents and in their mineral composition and
+structure.</p>
+
+<img src="images/fig273.jpg" width="178" height="319" alt=
+"Fig. 273: Map." />
+
+<p>If we attempt to trace the cretaceous deposits from England and
+France to the countries bordering the Mediterranean, we perceive,
+in the first place, that in the neighbourhood of London and Paris
+they form one great continuous mass, the Straits of Dover being a
+trifling interruption, a mere valley with chalk cliffs on both
+sides. We then observe that the main body of the chalk which
+surrounds Paris stretches from Tours to near Poitiers (see Fig.
+273, in which the shaded part represents chalk).</p>
+
+<p>
+Between Poitiers and La Rochelle, the space marked A on the map separates two
+regions of chalk. This space is occupied by the Oolite and certain other
+formations older than the Chalk and Neocomian, and has been supposed by M. E.
+de Beaumont to have formed an island in the Cretaceous sea. South of this space
+we again meet with rocks which we at once recognise to be cretaceous, partly
+from the chalky matrix and partly from the fossils being very similar to those
+of the white chalk of the north: especially certain species of the genera
+<i>Spatangus, Ananchytes, Cidarites, Nucula, Ostrea,</i> <a
+name="page306"></a><i>Gryphæa (Exogyra), Pecten, Plagiostoma (Lima), Trigonia,
+Catillus (Inoceramus),</i> and <i>Terebratula.</i><a href="#fn-17.4"
+name="fnref-17.4" id="fnref-17.4"><sup>[4]</sup></a> But Ammonites, as M.
+d&rsquo;Archiac observes, of which so many species are met with in the chalk of
+the north of France, are scarcely ever found in the southern region; while the
+genera <i>Hamite, Turrilite,</i> and <i>Scaphite,</i> and perhaps
+<i>Belemnite,</i> are entirely wanting.
+</p>
+
+<p><img src="images/fig274.jpg" width="373" height="177" alt=
+"Fig. 274: Radiolites. White chalk of France. Fig. 275: Radiolites foliaceus.
+White chalk of France." />
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig276.jpg" width="254" height="443" alt="Fig. 276: Hippurites
+organisans. Upper chalk:&mdash;chalk marl of Pyrenees?" />
+<p class="caption">Fig. 276: Hippurites organisans. Upper chalk:&mdash;chalk
+marl of Pyrenees?<a href="#fn-17.5" name="fnref-17.5"
+id="fnref-17.5"><sup>[5]</sup></a><br/></p>
+</div>
+
+<p>On the other hand, certain forms are common in the south which
+are rare or wholly unknown in the north of France. Among these may
+be mentioned many <i>Hippurites, Sphærulites,</i> and other
+members of that great family of mollusca called <i>Rudistes</i> by
+Lamarck, to which nothing analogous has been discovered in the
+living creation, but which is quite characteristic of rocks of the
+Cretaceous era in the south of France, Spain, Sicily, Greece, and
+other countries bordering the Mediterranean. The species called <i>
+Hippurites organisans</i> (Fig. 276) is more abundant than any
+other in the south of Europe; and the geologist should make himself
+well acquainted with the cast of the interior, <i>d,</i> which is
+often the only part preserved in many compact marbles of the Upper
+Cretaceous period. The flutings on the interior of the Hippurite,
+which are represented on the cast by smooth, rounded longitudinal
+ribs, and in some individuals attain a great size and length, are
+wholly unlike the markings on the exterior of the shell.</p>
+
+<p>
+<a name="page307"></a><b>Cretaceous Rocks in the United States.</b>&mdash;If we pass
+to the American continent, we find in the State of New Jersey a
+series of sandy and argillaceous beds wholly unlike in mineral
+character to our Upper Cretaceous system; which we can,
+nevertheless, recognise as referable, palæontologically, to
+the same division.</p>
+
+<p>That they were about the same age generally as the European
+chalk and Neocomian, was the conclusion to which Dr. Morton and Mr.
+Conrad came after their investigation of the fossils in 1834. The
+strata consist chiefly of green sand and green marl, with an
+overlying coralline limestone of a pale yellow colour, and the
+fossils, on the whole, agree most nearly with those of the Upper
+European series, from the Maestricht beds to the Gault inclusive. I
+collected sixty shells from the New Jersey deposits in 1841, five
+of which were identical with European species&mdash;<i>Ostrea larva, O.
+vesicularis, Gryphæa costata, Pecten quinque-costatus,
+Belemnitella mucronata.</i> As some of these have the greatest
+vertical range in Europe, they might be expected more than any
+others to recur in distant parts of the globe. Even where the
+species were different, the generic forms, such as the Baculite and
+certain sections of Ammonites, as also the <i>Inoceramus</i> (see
+<a href="images/fig251.jpg">Fig. 252</a>) and other bivalves, have
+a decidedly cretaceous aspect. Fifteen out of the sixty shells
+above alluded to were regarded by Professor Forbes as good
+geographical representatives of well-known cretaceous fossils of
+Europe. The correspondence, therefore, is not small, when we
+reflect that the part of the United States where these strata occur
+is between 3000 and 4000 miles distant from the chalk of Central
+and Northern Europe, and that there is a difference of ten degrees
+in the latitude of the places compared on opposite sides of the
+Atlantic. Fish of the genera <i>Lamna, Galeus,</i> and <i>
+Carcharodon</i> are common to New Jersey and the European
+cretaceous rocks. So also is the genus <i>Mosasaurus</i> among
+reptiles.</p>
+
+<p>It appears from the labours of Dr. Newberry and others, that the
+Cretaceous strata of the United States east and west of the
+Appalachians are characterised by a flora decidedly analogous to
+that of Aix-la-Chapelle above-mentioned, and therefore having
+considerable resemblance to the vegetation of the Tertiary and
+Recent Periods.
+</p>
+
+<p class="footnote">
+<a name="fn-17.1" id="fn-17.1"></a> <a href="#fnref-17.1">[1]</a>
+For particulars of structure see <a href="#page318">p. 318.</a>
+</p>
+
+<p class="footnote">
+<a name="fn-17.2" id="fn-17.2"></a> <a href="#fnref-17.2">[2]</a>
+Geol. Trans., 1st Series, vol. iv, p. 413.
+</p>
+
+<p class="footnote">
+<a name="fn-17.3" id="fn-17.3"></a> <a href="#fnref-17.3">[3]</a>
+In this and subsequent remarks on fossil plants I shall often use Dr.
+Lindley&rsquo;s terms, as most familiar in this country; but as those of M. A.
+Brongniart are much cited, it may be useful to geologists to give a table
+explaining the corresponding names of groups so much spoken of in palæontology.
+</p>
+
+<p class="footnote">
+<a name="fn-17.4" id="fn-17.4"></a> <a href="#fnref-17.4">[4]</a>
+D&rsquo;Archiac, Sur la form. Crétacée du S.-O. de la France Mém. de la Soc.
+Géol. de France, tome ii.
+</p>
+
+<p class="footnote">
+<a name="fn-17.5" id="fn-17.5"></a> <a href="#fnref-17.5">[5]</a>
+D&rsquo;Orbigny&rsquo;s Paléontologie français, pl. 533.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap18"></a><a name="page308"></a>CHAPTER XVIII.<br/>
+LOWER CRETACEOUS OR NEOCOMIAN FORMATION.</h2>
+
+<p class="letter">Classification of marine and fresh-water Strata.
+&mdash; Upper Neocomian. &mdash; Folkestone and Hythe Beds. &mdash;
+Atherfield Clay. &mdash; Similarity of Conditions causing
+Reappearance of Species after short Intervals. &mdash; Upper
+Speeton Clay. &mdash; Middle Neocomian. &mdash; Tealby Series.
+&mdash; Middle Speeton Clay. &mdash; Lower Neocomian. &mdash; Lower
+Speeton Clay. &mdash; Wealden Formation. &mdash; Fresh-water
+Character of the Wealden. &mdash; Weald Clay. &mdash; Hastings
+Sands. &mdash; Punfield Beds of Purbeck, Dorsetshire. &mdash;
+Fossil Shells and Fish of the Wealden. &mdash; Area of the Wealden.
+&mdash; Flora of the Wealden.</p>
+
+<p>We now come to the Lower Cretaceous Formation which was formerly
+called Lower Greensand, and for which it will be useful for reasons
+before explained (p. 282) to use the term &ldquo;Neocomian.&rdquo;
+</p>
+
+<p class="center">
+<small>LOWER CRETACEOUS OR NEOCOMIAN GROUP.</small>
+</p>
+
+<table border="1" cellspacing="0" cellpadding="4" summary=
+"Column 1: Marine; column 2: Fresh-water.">
+<tr>
+<td align="center">Marine</td>
+<td align="center">Fresh-water</td>
+</tr>
+
+<tr>
+<td >
+<ol>
+<li>Upper Neocomian&mdash;Greensand of Folkestone, Sandgate, and Hythe,
+Atherfield clay, upper part of Speeton clay.</li>
+
+<li>Middle Neocomian&mdash;Punfield Marine bed, Tealby beds, middle part
+of Speeton clay.</li>
+
+<li>Lower Neocomian&mdash;Lower part of Speeton clay.</li>
+</ol>
+</td>
+<td valign="middle">Part of Wealden beds of Kent,
+Surrey, Sussex, Hants, and Dorset.</td>
+</tr>
+</table>
+
+<p>In Western France, the Alps, the Carpathians, Northern Italy,
+and the Apennines, an extensive series of rocks has been described
+by Continental geologists under the name of Tithonian. These beds,
+which are without any marine equivalent in this country, appear
+completely to bridge over the interval between the Neocomian and
+the Oolites. They may, perhaps, as suggested by Mr. Judd, be of the
+same age as part of the Wealden series.</p>
+
+<p class="center">
+<small>UPPER NEOCOMIAN.</small>
+</p>
+
+<p><b>Folkstone and Hythe Beds.</b>&mdash;The sands which crop out
+beneath the Gault in Wiltshire, Surrey, and Sussex are sometimes in
+the uppermost part pure white, at others of a yellow and
+ferruginous colour, and some of the beds contain much green matter.
+At Folkestone they contain layers of calcareous matter and chert,
+and at Hythe, in the neighbourhood, as also at Maidstone and other
+parts of Kent, the limestone called Kentish Rag is intercalated.
+This somewhat clayey
+<a name="page309"></a>and calcareous stone forms strata two feet thick, alternating
+with quartzose sand. The total thickness of these Folkestone and
+Hythe beds is less than 300 feet, and they are seen to rest
+immediately on a grey clay, to which we shall presently allude as
+the Atherfield clay. Among the fossils of the Folkestone and Hythe
+beds we may mention <i>Nautilus plicatus</i> (Fig. 277), <i>
+Ancyloceras (Scaphites) gigas</i> (Fig. 278), which has been aptly
+described as an Ammonite more or less uncoiled; <i>Trigonia
+caudata</i> (Fig. 280), <i>Gervillia anceps</i> (Fig. 279), a
+bivalve genus allied to Avicula, and <i>Terebratula sella</i> (<a
+href="images/fig281.jpg">Fig. 281</a>). In ferruginous beds of the
+same age in Wiltshire is found a remarkable shell called <i>Diceras
+Lonsdalii</i> (<a href="images/fig281.jpg">Fig. 282</a>), which
+abounds in the Upper and Middle Neocomian of Southern Europe. This
+genus is closely allied to Chama, and the cast of the interior has
+been compared to the horns of a goat.</p>
+
+<p><img src="images/fig277.jpg" width="433" height="350" alt=
+"Fig. 277: Nautilus licatus. Fig. 278: Ancyloceras gigas. Fig. 279: Gervillia
+anceps. Fig. 280: Trigonia caudata." />
+</p>
+
+<p><b>Atherfield Clay.</b>&mdash;We mentioned before that the
+Folkstone and Hythe series rest on a grey clay. This clay is only
+of slight thickness in Kent and Surrey, but acquires great
+dimensions at Atherfield, in the Isle of Wight. The difference,
+indeed, in mineral character and thickness of the Upper Neocomian
+formation near Folkestone, and the corresponding beds in the south
+of the Isle of Wight, about
+<a name="page310"></a>100 miles distant, is truly remarkable. In the latter place we
+find no limestone answering to the Kentish Rag, and the entire
+thickness from the bottom of the Atherfield clay to the top of the
+Neocomian, instead of being less than 300 feet as in Kent, is given
+by the late Professor E. Forbes as 843 feet, which he divides into
+sixty-three strata, forming three groups. The uppermost of these
+consists of ferruginous sands, the second of sands and clay, and
+the third or lowest of a brown clay, abounding in fossils.</p>
+
+<p><img src="images/fig281.jpg" width="394" height="196" alt=
+"Fig. 281: Terebratula sella. Fig. 282: Diceras Lonsdalii. a. The bivavle
+shell, b. Cast of one of the valves enlarged." />
+</p>
+
+<p>Pebbles of quartzose sandstone, jasper, and flinty slate,
+together with grains of chlorite and mica, and, as Mr.
+Godwin-Austen has shown, fragments and water-worn fossils of the
+oolitic rocks, speak plainly of the nature of the pre-existing
+formations, by the wearing down of which the Neocomian beds were
+formed. The land, consisting of such rocks, was doubtless submerged
+before the origin of the white chalk, a deposit which was formed in
+a more open sea, and in clearer waters.</p>
+
+<img src="images/fig283.jpg" width="234" height="206" alt=
+"Fig. 283: Perna mulleti." />
+
+<p>Among the shells of the Atherfield clay the biggest and most
+abundant shell is the large <i>Perna Mulleti,</i> of which a
+reduced figure is given in Fig. 283.</p>
+
+<p><i>Similarity of Conditions causing Reappearance of
+Species.</i>&mdash;Some species of mollusca and other fossils range
+through the whole series, while others are confined to particular
+subdivisions, and Forbes laid down a law which has since been found
+of very general application in regard to estimating the
+chronological relations of consecutive
+<a name="page311"></a>strata. Whenever similar conditions, he says, are repeated, the
+same species reappear, provided too great a lapse of time has not
+intervened; whereas if the length of the interval has been
+geologically great, the same genera will reappear represented by
+distinct species. Changes of depth, or of the mineral nature of the
+sea-bottom, the presence or absence of lime or of peroxide of iron,
+the occurrence of a muddy, or a sandy, or a gravelly bottom, are
+marked by the banishment of certain species and the predominance of
+others. But these differences of conditions being mineral,
+chemical, and local in their nature, have no necessary connection
+with the extinction, throughout a large area, of certain animals or
+plants. When the forms proper to loose sand or soft clay, or to
+perfectly clear water, or to a sea of moderate or great depth,
+recur with all the same species, we may infer that the interval of
+time has been, geologically speaking, small, however dense the mass
+of matter accumulated. But if, the genera remaining the same, the
+species are changed, we have entered upon a new period; and no
+similarity of climate, or of geographical and local conditions, can
+then recall the old species which a long series of destructive
+causes in the animate and inanimate world has gradually
+annihilated.</p>
+
+<img src="images/fig284.jpg" width="160" height="167" alt=
+"Fig. 284: Ammonites Deshayesii." />
+
+<p>
+<b>Speeton Clay, Upper Division.</b>&mdash;On the coast, beneath the white
+chalk of Flamborough Head, in Yorkshire, an argillaceous formation crops out,
+called the Speeton clay, several hundred feet in thickness, the palæontological
+relations of which have been ably worked out by Mr. John W. Judd,<a
+href="#fn-18.1" name="fnref-18.1" id="fnref-18.1"><sup>[1]</sup></a> and he has
+shown that it is separable into three divisions, the uppermost of which, 150
+feet thick, and containing 87 species of mollusca, decidedly belongs to the
+Atherfield clay and associated strata of Hythe and Folkestone, already
+described. It is characterised by the <i>Perna Mulleti</i> (<a
+href="images/fig283.jpg">Fig. 283</a>) and <i>Terebratula sella</i> (<a
+href="images/fig281.jpg">Fig. 281</a>), and by <i> Ammonites Deshayesii</i>
+(Fig. 284), a well-known Hythe fossil. Fine skeletons of reptiles of the genera
+Pliosaurus and Teleosaurus have been obtained from this clay. At the base of
+this upper division of the Speeton clay there occurs a layer of large Septaria,
+formerly worked for the manufacture of cement. This bed is crowded with
+fossils, especially Ammonites, one species of which, three feet in diameter,
+was observed by Mr. Judd.
+</p>
+
+<p class="center">
+<a name="page312"></a><small>MIDDLE NEOCOMIAN.</small>
+</p>
+
+<p>
+<b>Tealby Series.</b>&mdash;At Tealby, a village in the Lincolnshire Wolds,
+there crop out beneath the white chalk some non-fossiliferous ferruginous sands
+about twenty-feet thick, beneath which are beds of clay and limestone, about
+fifty feet thick, with an interesting suite of fossils, among which are <i>
+Pecten cinctus</i> (Fig. 285), from 9 to 12 inches in diameter, <i> Ancyloceras
+Duvallei</i> (Fig. 286), and some forty other shells, many of them common to
+the Middle Speeton clay, about to be mentioned. Mr. Judd remarks that as
+<i>Ammonites clypeiformis</i> and <i>Terebratula hippopus</i> characterise the
+Middle Neocomian of the Continent, it is to this stage that the Tealby series
+containing the same fossils may be assigned.<a href="#fn-18.2"
+name="fnref-18.2" id="fnref-18.2"><sup>[2]</sup></a>
+</p>
+
+<p><img src="images/fig285.jpg" width="394" height="229" alt=
+"Fig. 285: Pecten cinctus. Fig. 286: Ancyloceras (Crioceras) Duvallei." />
+</p>
+
+<p>The middle division of the Speeton clay, occurring at Speeton
+below the cement-bed, before alluded to, is 150 feet thick, and
+contains about 39 species of mollusca, half of which are common to
+the overlying clay. Among the peculiar shells, <i>Pecten
+cinctus</i> (Fig. 285) and <i>Ancyloceras (Crioceras) Duvallei</i>
+(Fig. 286) occur.</p>
+
+<p class="center">
+<small>LOWER NEOCOMIAN.</small>
+</p>
+
+<p>In the lower division of the Speeton clay, 200 feet thick, 46
+species of mollusca have been found, and three divisions, each
+characterised by its peculiar ammonite, have been noticed by Mr.
+Judd. The central zone is marked by <i>Ammonites Noricus</i> (see
+Fig. 287). On the Continent these beds are well-known by their
+corresponding fossils, the Hils clay and conglomerate of the north
+of Germany agreeing with
+<a name="page313"></a>the Middle and Lower Speeton, the latter of which, with the same
+mineral characters and fossils as in Yorkshire, is also found in
+the little island of Heligoland. Yellow limestone, which I have
+myself seen near Neuchatel, in Switzerland, represents the Lower
+Neocomian at Speeton.</p>
+
+<img src="images/fig287.jpg" width="155" height="174" alt=
+"Fig. 287: Ammonites Noricus." />
+
+<p class="center">
+<small>WEALDEN FORMATION.</small>
+</p>
+
+<p>Beneath the Atherfield clay or Upper Neocomian of the S.E. of
+England, a fresh-water formation is found, called the Wealden,
+which, although it occupies a small horizontal area in Europe, as
+compared to the White Chalk and the marine Neocomian beds, is
+nevertheless of great geological interest, since the imbedded
+remains give us some insight into the nature of the terrestrial
+fauna and flora of the Lower Cretaceous epoch. The name of Wealden
+was given to this group because it was first studied in parts of
+Kent, Surrey, and Sussex, called the Weald; and we are indebted to
+Dr. Mantell for having shown, in 1822, in his &ldquo;Geology of
+Sussex,&rdquo; that the whole group was of fluviatile origin. In
+proof of this he called attention to the entire absence of
+Ammonites, Belemnites, Brachiopoda, Echinodermata, Corals, and
+other marine fossils, so characteristic of the Cretaceous rocks
+above, and of the Oolitic strata below, and to the presence in the
+Weald of Paludinæ, Melaniæ, Cyrenæ, and various
+fluviatile shells, as well as the bones of terrestrial reptiles and
+the trunks and leaves of land-plants.</p>
+
+<p>The evidence of so unexpected a fact as that of a dense mass of
+purely fresh-water origin underlying a deep-sea deposit (a
+phenomenon with which we have since become familiar) was received,
+at first, with no small doubt and incredulity. But the relative
+position of the beds is unequivocal; the Weald Clay being
+distinctly seen to pass beneath the Atherfield Clay in various
+parts of Surrey, Kent, and Sussex, and to reappear in the Isle of
+Wight at the base of the Cretaceous series, being, no doubt,
+continuous far beneath the surface, as indicated by the dotted
+lines in <a href="images/fig288.jpg">Fig. 288.</a> They are also
+found occupying the same relative position below the chalk in the
+peninsula of Purbeck, Dorsetshire, where, as we shall see in the
+sequel, they repose on strata referable to the Upper Oolite.</p>
+
+<p><i>Weald Clay.</i>&mdash;The Upper division, or Weald Clay, is,
+in great part, of fresh-water origin, but in its highest
+portion
+<a name="page314"></a>contains beds of oysters and other marine shells which indicate
+fluvio-marine conditions. The uppermost beds are not only
+conformable, as Dr. Fitton observes, to the inferior strata of the
+overlying Neocomian, but of similar mineral composition. To explain
+this, we may suppose that, as the delta of a great river was
+tranquilly subsiding, so as to allow the sea to encroach upon the
+space previously occupied by fresh-water, the river still continued
+to carry down the same sediment into the sea. In confirmation of
+this view it may be stated that the remains of the <i>Iguanodon
+Mantelli,</i> a gigantic terrestrial reptile, very characteristic
+of the Wealden, has been discovered near Maidstone, in the
+overlying Kentish Rag, or marine limestone of the Upper Neocomian.
+Hence we may infer that some of the saurians which inhabited the
+country of the great river continued to live when part of the
+district had become submerged beneath the sea. Thus, in our own
+times, we may suppose the bones of large alligators to be
+frequently entombed in recent fresh-water strata in the delta of
+the Ganges. But if part of that delta should sink down so as to be
+covered by the sea, marine formations might begin to accumulate in
+the same space where fresh-water beds had previously been formed;
+and yet the Ganges might still pour down its turbid waters in the
+same direction, and carry seaward the carcasses of the same species
+of alligator, in which case their bones might be included in marine
+as well as in subjacent fresh-water strata.
+</p>
+
+<p><img src="images/fig288.jpg" width="410" height="159" alt=
+"Fig. 288" /></p>
+
+<p>The Iguanodon, first discovered by Dr. Mantell, was an
+herbivorous reptile, of which the teeth, though bearing a great
+analogy, in their general form and crenated edges (see <a href=
+"images/fig289.jpg">Figs. 289</a> <i>a</i> and <i>b</i>), to the
+modern Iguanas which now frequent the tropical woods of America and
+the West Indies, exhibit many important differences. It appears
+that they have often been worn by the process of mastication;
+whereas the existing herbivorous reptiles clip and gnaw off the
+vegetable productions on which they feed, but do not chew them.
+Their teeth frequently present an appearance
+<a name="page315"></a>of having been chipped off, but never, like the fossil teeth of
+the Iguanodon, have a flat ground surface (see Fig. 290, <i>b</i>)
+resembling the grinders of herbivorous mammalia. Dr. Mantell
+computes that the teeth and bones of this species which passed
+under his examination during twenty years must have belonged to no
+less than seventy-one distinct individuals, varying in age and
+magnitude from the reptile just burst from the egg, to one of which
+the femur measured twenty-four inches in circumference. Yet,
+notwithstanding that the teeth were more numerous than any other
+bones, it is remarkable that it was not until the relics of all
+these individuals had been found, that a solitary example of part
+of a jaw-bone was obtained. Soon afterwards remains both of the
+upper and lower jaw were met with in the Hastings beds in Tilgate
+Forest, near Cuckfield. In the same sands at Hastings, Mr. Beckles
+found large tridactyle impressions which it is conjectured were
+made by the hind feet of this animal, on which it is ascertained
+that there were only three well-developed toes.</p>
+
+<p><img src="images/fig289.jpg" width="388" height="318" alt=
+"Fig. 289 a, b: Tooth of Iguanodon Mantelli. Fig. 290: a. Partially worn tooth
+of young individual of the same; &lt;i&gt;b.&lt;/i&gt; Crown of tooth in adult worn down." />
+</p>
+
+<img src="images/fig291.jpg" width="86" height="125" alt=
+"Fig. 291: Cypris spinigera." />
+
+<p>Occasionally bands of limestone, called Sussex Marble, occur in
+the Weald Clay, almost entirely composed of a species of <i>
+Paludina,</i> closely resembling the common <i>P. vivipara</i> of
+English rivers. Shells of the <i>Cypris,</i> a genus of Crustaceans
+mentioned (<a href="#page57">p. 57</a>) as abounding in
+lakes and ponds, are also plentifully scattered through the clays
+of the Wealden,
+<a name="page316"></a>sometimes producing, like plates of mica, a thin lamination (see
+Fig. 292).</p>
+
+<img src="images/fig292.jpg" width="141" height="117" alt=
+"Fig. 292: Weald clay with Cyprides." />
+
+<p><b>Hastings Sands.</b>&mdash;This lower division of the Wealden
+consists of sand, sandstone, calciferous grit, clay, and shale; the
+argillaceous strata, notwithstanding the name, predominating
+somewhat over the arenaceous, as will be seen by reference to the
+following table, drawn up by Messrs. Drew and Foster, of the
+Geological Survey of Great Britain:</p>
+
+<table border="1" cellpadding="4" cellspacing="0" summary=
+"Names of subordinate formations, Mineral composition of the strata, and
+Thickness in feet of the Hastings Sand.">
+<tr>
+<td>&nbsp;</td>
+<td align="center">Names of Subordinate<br/>
+Formations.</td>
+<td align="center">Mineral Composition<br/>
+of the Strata.</td>
+<td align="center">Thickness<br/>
+in feet.</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="4">Hastings Sand</td>
+<td valign="top">Tunbridge Wells Sand</td>
+<td valign="top">Sandstone and loam</td>
+<td align="center" valign="top">150</td>
+</tr>
+
+<tr>
+<td valign="top">Wadhurst Clay</td>
+<td valign="top">Blue and brown shale and clay,
+with<br/>
+a little calc-grit</td>
+<td align="center" valign="top">100</td>
+</tr>
+
+<tr>
+<td valign="top">Ashdown Sand</td>
+<td valign="top">Hard sand, with some beds of
+calc-grit</td>
+<td align="center" valign="top">160</td>
+</tr>
+
+<tr>
+<td valign="top">Ashburnham Beds</td>
+<td valign="top">Mottled white and red clay, with<br/>
+some sandstone</td>
+<td align="center" valign="top">330</td>
+</tr>
+</table>
+
+<p>The picturesque scenery of the &ldquo;High Rocks&rdquo; and
+other places in the neighbourhood of Tunbridge Wells is caused by
+the steep natural cliffs, to which a hard bed of white sand,
+occurring in the upper part of the Tunbridge Wells Sand, mentioned
+in the above table, gives rise. This bed of &ldquo;rock-sand&rdquo;
+varies in thickness from 25 to 48 feet. Large masses of it, which
+were by no means hard or capable of making a good building-stone,
+form, nevertheless, projecting rocks with perpendicular faces, and
+resist the degrading action of the river because, says Mr. Drew,
+they present a solid mass without planes of division. The
+calcareous sandstone and grit of Tilgate Forest, near Cuckfield, in
+which the remains of the Iguanodon and Hylæosaurus were first
+found by Dr. Mantell, constitute an upper member of the Tunbridge
+Wells Sand, while the &ldquo;sand-rock&rdquo; of the Hastings
+cliffs, about 100 feet thick, is one of the lower members of the
+same. The reptiles, which are very abundant in this division,
+consist partly of saurians, referred by Owen and Mantell to eight
+genera, among which, besides those already enumerated, we find the
+Megalosaurus and Plesiosaurus. The Pterodactyl also, a flying
+reptile, is met with in the same strata, and many remains of
+Chelonians of the genera <i>Trionyx</i> and <i>Emys,</i> now
+confined to tropical regions.</p>
+
+<p>The fishes of the Wealden are chiefly referable to the Ganoid
+and Placoid orders. Among them the teeth and scales of <i>
+Lepidotus</i> are most widely diffused (see Fig. 293, next page).
+These
+<a name="page317"></a>ganoids were allied to the <i>Lepidosteus,</i> or Gar-pike, of
+the American rivers. The whole body was covered with large
+rhomboidal scales, very thick, and having the exposed part coated
+with enamel. Most of the species of this genus are supposed to have
+been either river-fish, or inhabitants of the sea at the mouth of
+estuaries.</p>
+
+<p><img src="images/fig293.jpg" width="331" height="172" alt=
+"Fig. 293: Lepidotus Mantelli, a. Palate and teeth, b. Side view of teeth, c. Scale." />
+</p>
+
+<img src="images/fig294.jpg" width="257" height="460" alt=
+"Fig. 294: Unio Valdensis. Fig. 295: Under side of slab of sandstone about one yard in diameter." />
+
+<p>At different heights in the Hastings Sands, we find again and
+again slabs of sandstone with a strong ripple-mark, and between
+these slabs beds of clay many yards thick. In some places, as at
+Stammerham, Horsham, near there, are indications of this clay
+having been exposed so as to dry and crack before the next layer
+was thrown down upon it. The open cracks in the clay have served as
+moulds, of which casts have been taken in relief, and which are,
+therefore, seen on the lower surface of the sandstone (see Fig.
+295).</p>
+
+<p>
+Near the same place a reddish sandstone occurs in which <a
+name="page318"></a>are innumerable traces of a fossil vegetable, apparently <i>
+Sphenopteris,</i> the stems and branches of which are disposed as if the plants
+were standing erect on the spot where they originally grew, the sand having
+been gently deposited upon and around them; and similar appearances have been
+remarked in other places in this formation.<a href="#fn-18.3" name="fnref-18.3"
+id="fnref-18.3"><sup>[3]</sup></a> In the same division also of the Wealden, at
+Cuckfield, is a bed of gravel or conglomerate, consisting of water-worn pebbles
+of quartz and jasper, with rolled bones of reptiles. These must have been
+drifted by a current, probably in water of no great depth.
+</p>
+
+<img src="images/fig296.jpg" width="185" height="203" alt=
+"Fig. 296: Sphenopteris gracilis." />
+
+<p>From such facts we may infer that, notwithstanding the great
+thickness of this division of the Wealden, the whole of it was a
+deposit in water of a moderate depth, and often extremely shallow.
+This idea may seem startling at first, yet such would be the
+natural consequence of a gradual and continuous sinking of the
+ground in an estuary or bay, into which a great river discharged
+its turbid waters. By each foot of subsidence, the fundamental rock
+would be depressed one foot farther from the surface; but the bay
+would not be deepened, if newly-deposited mud and sand should raise
+the bottom one foot. On the contrary, such new strata of sand and
+mud might be frequently laid dry at low water, or overgrown for a
+season by a vegetation proper to marshes.</p>
+
+<p><b>Punfield Beds, Brackish and Marine.</b>&mdash;The shells of
+the Wealden beds belong to the genera <i>Melanopsis, Melania,
+Paludina, Cyrena, Cyclas, Unio</i> (see <a href=
+"images/fig294.jpg">Fig. 294</a>), and others, which inhabit
+rivers or lakes; but one band has been found at Punfield, in
+Dorsetshire, indicating a brackish state of the water, where the
+genera <i>Corbula, Mytilus,</i> and <i>Ostrea</i> occur; and in
+some places this bed becomes purely marine, containing some
+well-known Neocomian fossils, among which <i>Ammonites
+Deshayesii</i> (<a href="images/fig284.jpg">Fig. 284</a>) may be
+mentioned. Others are peculiar as British, but very characteristic
+of the Upper and Middle Neocomian of Spain, and among these the <i>
+Vicarya Lujani</i> (<a href="images/fig297.jpg">Fig. 297</a>), a
+shell allied to Nerinea, is conspicuous.</p>
+
+<p>By reference to table (<a href="#page308">p. 308</a>) it will
+be seen that the
+<a name="page319"></a>Wealden beds are given as the fresh-water equivalents of the
+Marine Neocomian. The highest part of them in England may, for
+reasons just given, be regarded as Upper Neocomian, while some of
+the inferior portions may correspond in age to the Middle and Lower
+divisions of that group. In favour of this latter view, M. Marcou
+mentions that a fish called <i>Asteracanthus granulosus,</i>
+occurring in the Tilgate beds, is characteristic of the lowest beds
+of the Neocomian of the Jura, and it is well known that <i>Corbula
+alata,</i> common in the Ashburnham beds, is found also at the base
+of the Neocomian of the Continent.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig297.jpg" width="160" height="237" alt="Fig. 297: Vicarya
+Lujani." />
+<p class="caption">Fig. 297: <i>Vicarya Lujani</i>, De
+Verneuil.<a href="#fn-18.4" name="fnref-18.4" id="fnref-18.4"><sup>[4]</sup></a><br/>
+Wealden, Punfield.<br/></p>
+</div>
+
+<p>
+<i>Area of the Wealden.</i>&mdash;In regard to the geographical extent of the
+Wealden, it cannot be accurately laid down, because so much of it is concealed
+beneath the newer marine formations. It has been traced about 320 English miles
+from west to east, from the coast of Dorsetshire to near Boulogne, in France;
+and nearly 200 miles from north-west to south-east, from Surrey and Hampshire
+to Vassy, in France. If the formation be continuous throughout this space,
+which is very doubtful, it does not follow that the whole was contemporaneous;
+because, in all likelihood, the physical geography of the region underwent
+frequent changes throughout the whole period, and the estuary may have altered
+its form, and even shifted its place. Dr. Dunker, of Cassel, and H. von Meyer,
+in an excellent monograph on the Wealdens of Hanover and Westphalia, have shown
+that they correspond so closely, not only in their fossils, but also in their
+mineral characters, with the English series, that we can scarcely hesitate to
+refer the whole to one great delta. Even then, the magnitude of the deposit may
+not exceed that of many modern rivers. Thus, the delta of the Quorra or Niger,
+in Africa, stretches into the interior for more than 170 miles, and occupies,
+it is supposed, a space of more than 300 miles along the coast, thus forming a
+surface of more than 25,000 square miles, or equal to about one-half of
+England.<a href="#fn-18.5" name="fnref-18.5" id="fnref-18.5"><sup>[5]</sup></a>
+Besides, we know not, in such cases, how far the fluviatile sediment and
+organic remains of the river and the land may be carried out from the coast,
+and spread over the bed of the sea. I have <a name="page320"></a>shown, when
+treating of the Mississippi, that a more ancient delta, including species of
+shells such as now inhabit Louisiana, has been upraised, and made to occupy a
+wide geographical area, while a newer delta is forming;<a href="#fn-18.6"
+name="fnref-18.6" id="fnref-18.6"><sup>[6]</sup></a> and the possibility of
+such movements and their effects must not be lost sight of when we speculate on
+the origin of the Wealden.
+</p>
+
+<p>It may be asked where the continent was placed, from the ruins
+of which the Wealden strata were derived, and by the drainage of
+which a great river was fed. If the Wealden was gradually going
+downward 1000 feet or more perpendicularly, a large body of
+fresh-water would not continue to be poured into the sea at the
+same point. The adjoining land, if it participated in the movement,
+could not escape being submerged. But we may suppose such land to
+have been stationary, or even undergoing contemporaneous slow
+upheaval. There may have been an ascending movement in one region,
+and a descending one in a contiguous parallel zone of country. But
+even if that were the case, it is clear that finally an extensive
+depression took place in that part of Europe where the deep sea of
+the Cretaceous period was afterwards brought in.</p>
+
+<p><i>Thickness of the Wealden.</i>&mdash;In the Weald area itself,
+between the North and South Downs, fresh-water beds to the
+thickness of 1600 feet are known, the base not being reached.
+Probably the thickness of the whole Wealden series, as seen in
+Swanage Bay, cannot be estimated as less than 2000 feet.</p>
+
+<p><i>Wealden Flora.</i>&mdash;The flora of the Wealden is
+characterised by a great abundance of Coniferæ,
+Cycadeæ, and Ferns, and by the absence of leaves and fruits
+of Dicotyledonous Angiosperms. The discovery in 1855, in the
+Hastings beds of the Isle of Wight, of Gyrogonites, or
+spore-vessels of the Chara, was the first example of that genus of
+plants, so common in the tertiary strata, being found in a
+Secondary or Mesozoic rock.</p>
+
+<p class="footnote">
+<a name="fn-18.1" id="fn-18.1"></a> <a href="#fnref-18.1">[1]</a>
+Judd, Speeton clay, Quart. Geol. Journ., vol. xxiv, 1868, p. 218.
+</p>
+
+<p class="footnote">
+<a name="fn-18.2" id="fn-18.2"></a> <a href="#fnref-18.2">[2]</a>
+Judd, Quart. Geol. Journ., 1867, vol. xxiii, p. 249.
+</p>
+
+<p class="footnote">
+<a name="fn-18.3" id="fn-18.3"></a> <a href="#fnref-18.3">[3]</a>
+Mantell, Geol. of S.E. of England, p. 244.
+</p>
+
+<p class="footnote">
+<a name="fn-18.4" id="fn-18.4"></a> <a href="#fnref-18.4">[4]</a>
+Foss. de Utrillas.
+</p>
+
+<p class="footnote">
+<a name="fn-18.5" id="fn-18.5"></a> <a href="#fnref-18.5">[5]</a>
+Fitton, Geol. of Hastings, p. 58, who cites Lander&rsquo;s Travels.
+</p>
+
+<p class="footnote">
+<a name="fn-18.6" id="fn-18.6"></a> <a href="#fnref-18.6">[6]</a>
+See <a href="#page102">p. 102</a> and Second Visit to the United States, vol.
+ii, chap. xxxiv.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap19"></a><a name="page321"></a>CHAPTER XIX.<br/>
+JURASSIC GROUP.&mdash;PURBECK BEDS AND OOLITE.</h2>
+
+<p class="letter">The Purbeck Beds a Member of the Jurassic Group.
+&mdash; Subdivisions of that Group. &mdash; Physical Geography of
+the Oolite in England and France. &mdash; Upper Oolite. &mdash;
+Purbeck Beds. &mdash; New Genera of fossil Mammalia in the Middle
+Purbeck of Dorsetshire. &mdash; Dirt-bed or ancient Soil. &mdash;
+Fossils of the Purbeck Beds. &mdash; Portland Stone and Fossils.
+&mdash; Kimmeridge Clay. &mdash; Lithographic Stone of Solenhofen.
+&mdash; Archæopteryx. &mdash; Middle Oolite. &mdash; Coral
+Rag. &mdash; Nerinæa Limestone. &mdash; Oxford Clay,
+Ammonites and Belemnites. &mdash; Kelloway Rock. &mdash; Lower, or
+Bath, Oolite. &mdash; Great Plants of the Oolite. &mdash; Oolite
+and Bradford Clay. &mdash; Stonesfield Slate. &mdash; Fossil
+Mammalia. &mdash; Fuller&rsquo;s Earth. &mdash; Inferior Oolite and
+Fossils. &mdash; Northamptonshire Slates. &mdash; Yorkshire Oolitic
+Coal-field. &mdash; Brora Coal. &mdash; Palæontological
+Relations of the several Subdivisions of the Oolitic group.</p>
+
+<p><b>Classification of the Oolite.</b>&mdash;Immediately below the
+Hastings Sands we find in Dorsetshire another remarkable
+fresh-water formation, called <i>the Purbeck,</i> because it was
+first studied in the sea-cliffs of the peninsula of Purbeck in that
+county. These beds are for the most part of fresh-water origin, but
+the organic remains of some few intercalated beds are marine, and
+show that the Purbeck series has a closer affinity to the Oolitic
+group, of which it may be considered as the newest or uppermost
+member.</p>
+
+<p>In England generally, and in the greater part of Europe, both
+the Wealden and Purbeck beds are wanting, and the marine cretaceous
+group is followed immediately, in the descending order, by another
+series called the Jurassic. In this term, the formations commonly
+designated as &ldquo;the Oolite and Lias&rdquo; are included, both
+being found in the Jura Mountains. The Oolite was so named because
+in the countries where it was first examined the limestones
+belonging to it had an Oolitic structure (see <a href=
+"#page37">p. 37</a>). These rocks occupy in England a zone
+nearly thirty miles in average breadth, which extends across the
+island, from Yorkshire in the north-east, to Dorsetshire in the
+south-west. Their mineral characters are not uniform throughout
+this region; but the following are the names of the principal
+subdivisions observed in the central and south-eastern parts of
+England.</p>
+
+<p class="center">
+<a name="page322"></a>OOLITE
+</p>
+
+<table border="1" cellspacing="0" cellpadding="4" width="60%"
+summary="Upper, Middle and Lower Oolite systems.">
+<tr>
+<td valign="middle">Upper</td>
+<td ><i>a.</i> &nbsp;Purbeck beds.<br/>
+<i>b.</i> &nbsp;Portland stone and sand.<br/>
+<i>c.</i> &nbsp;Kimmeridge clay.</td>
+</tr>
+
+<tr>
+<td valign="middle">Middle</td>
+<td ><i>d.</i> &nbsp;Coral rag.<br/>
+<i>e.</i> &nbsp;Oxford clay, and Kelloway rock.</td>
+</tr>
+
+<tr>
+<td valign="middle">Lower</td>
+<td ><i>f.</i> &nbsp; Cornbrash and Forest marble.<br/>
+<i>g.</i> &nbsp;Great Oolite and Stonesfield slate.<br/>
+<i>h.</i> &nbsp;Fuller&rsquo;s earth.<br/>
+<i>i.</i>&nbsp; &nbsp;Inferior Oolite.</td>
+</tr>
+</table>
+
+<p>The Upper Oolitic system of the above table has usually the
+Kimmeridge clay for its base; the Middle Oolitic system, the Oxford
+clay. The Lower system reposes on the Lias, an argillo-calcareous
+formation, which some include in the Lower Oolite, but which will
+be treated of separately in the next chapter. Many of these
+subdivisions are distinguished by peculiar organic remains; and,
+though varying in thickness, may be traced in certain directions
+for great distances, especially if we compare the part of England
+to which the above-mentioned type refers with the north-east of
+France and the Jura Mountains adjoining. In that country, distant
+above 400 geographical miles, the analogy to the accepted English
+type, notwithstanding the thinness or occasional absence of the
+clays, is more perfect than in Yorkshire or Normandy.</p>
+
+<p><b>Physical Geography.</b>&mdash;The alternation, on a grand
+scale, of distinct formations of clay and limestone has caused the
+oolitic and liassic series to give rise to some marked features in
+the physical outline of parts of England and France. Wide valleys
+can usually be traced throughout the long bands of country where
+the argillaceous strata crop out; and between these valleys the
+limestones are observed, forming ranges of hills or more elevated
+grounds. These ranges terminate abruptly on the side on which the
+several clays rise up from beneath the calcareous strata.</p>
+
+<p><img src="images/fig298.jpg" width="368" height="106" alt=
+"Fig. 298: Configuration of surface." /></p>
+
+<p>Fig. 298 will give the reader an idea of the configuration of
+the surface now alluded to, such as may be seen in passing from
+London to Cheltenham, or in other parallel lines, from east to
+west, in the southern part of England. It has been necessary,
+however, in this drawing, greatly to exaggerate the inclination of
+the beds, and the height of the several formations, as compared to
+their horizontal extent.
+<a name="page323"></a>It will be remarked, that the lines of steep slope, or
+escarpment, face towards the west in the great calcareous eminences
+formed by the chalk and the Upper, Middle, and Lower Oolites; and
+at the base of which we have respectively the Gault, Kimmeridge
+clay, Oxford clay, and Lias. This last forms, generally, a broad
+vale at the foot of the escarpment of inferior Oolite, but where it
+acquires considerable thickness, and contains solid beds of
+marlstone, it occupies the lower part of the escarpment.</p>
+
+<p>The external outline of the country which the geologist observes
+in travelling eastward from Paris to Metz, is precisely analogous,
+and is caused by a similar succession of rocks intervening between
+the tertiary strata and the Lias; with this difference, however,
+that the escarpments of Chalk, Upper, Middle, and Lower Oolites
+face towards the east instead of the west. It is evident,
+therefore, that the denuding causes (see <a href=
+"#page105">p. 105</a>) have acted similarly over an area
+several hundred miles in diameter, removing the softer clays more
+extensively than the limestones, and causing these last to form
+steep slopes or escarpments wherever the harder calcareous rock was
+based upon a more yielding and destructible formation.</p>
+
+<p class="center">
+<small>UPPER OOLITE.</small>
+</p>
+
+<p><b>Purbeck Beds.</b>&mdash;These strata, which we class as the
+uppermost member of the Oolite, are of limited geographical extent
+in Europe, as already stated, but they acquire importance when we
+consider the succession of three distinct sets of fossil remains
+which they contain. Such repeated changes in organic life must have
+reference to the history of a vast lapse of ages. The Purbeck beds
+are finely exposed to view in Durdlestone Bay, near Swanage,
+Dorsetshire, and at Lulworth Cove and the neighbouring bays between
+Weymouth and Swanage. At Meup&rsquo;s Bay, in particular, Professor
+E. Forbes examined minutely, in 1850, the organic remains of this
+group, displayed in a continuous sea-cliff section, and it appears
+from his researches that the Upper, Middle, and Lower Purbecks are
+each marked by peculiar species of organic remains, these again
+being different, so far as a comparison has yet been instituted,
+from the fossils of the overlying Hastings Sands and Weald
+Clay.</p>
+
+<p><i>Upper Purbeck.</i>&mdash;The highest of the three divisions
+is purely fresh-water, the strata, about fifty feet in thickness,
+containing shells of the genera <i>Paludina, Physa, Limnæa,
+Planorbis, Valvata, Cyclas,</i> and <i>Unio,</i> with <i>
+Cyprides</i> and fish. All the species seem peculiar, and among
+these the <i>Cyprides</i>
+<a name="page324"></a>are very abundant and characteristic (see Fig. 299, <i>a, b,
+c.</i>)</p>
+
+<p>The stone called &ldquo;Purbeck Marble,&rdquo; formerly much
+used in ornamental architecture in the old English cathedrals of
+the southern counties, is exclusively procured from this
+division.</p>
+
+<p><img src="images/fig299.jpg" width="410" height="171" alt=
+"Fig. 299: Cyprides from the Upper Purbecks." /></p>
+
+<p><i>Middle Purbeck.</i>&mdash;Next in succession is the Middle
+Purbeck, about thirty feet thick, the uppermost part of which
+consists of fresh-water limestone, with cyprides, turtles, and
+fish, of different species from those in the preceding strata.
+Below the limestone are brackish-water beds full of <i>Cyrena,</i>
+and traversed by bands abounding in <i>Corbula</i> and <i>
+Melania.</i> These are based on a purely marine deposit, with <i>
+Pecten, Modiola, Avicula,</i> and <i>Thracia.</i> Below this,
+again, come limestones and shales, partly of brackish and partly of
+fresh-water origin, in which many fish, especially species of <i>
+Lepidotus</i> and <i>Microdon radiatus,</i> are found, and a
+crocodilian reptile named <i>Macrorhynchus.</i> Among the mollusks,
+a remarkable ribbed <i>Melania,</i> of the section <i>Chilina,</i>
+occurs.</p>
+
+<p><img src="images/fig300.jpg" width="358" height="190" alt=
+"Fig. 300: Ostrea distorta. Fig. 301: Hemicidaris Purbeckensis." />
+</p>
+
+<p>Immediately below is a great and conspicuous stratum, twelve
+feet thick, formed of a vast accumulation of shells of <i>Ostrea
+distorta</i> (Fig. 300), long familiar to geologists under the
+local name of &ldquo;Cinder-bed.&rdquo; In the uppermost part
+of
+<a name="page325"></a>this bed Professor Forbes discovered the first echinoderm (Fig.
+301) as yet known in the Purbeck series, a species of <i>
+Hemicidaris,</i> a genus characteristic of the Oolitic period, and
+scarcely, if at all, distinguishable from a previously known
+Oolitic fossil. It was accompanied by a species of <i>Perna.</i>
+Below the Cinder-bed fresh-water strata are again seen, filled in
+many places with species of <i>Cypris</i> (Fig. 302, <i>a, b,
+c</i>), and with <i>Valvata, Paludina, Planorbis, Limnæa,
+Physa</i> (Fig. 303), and <i>Cyclas,</i> all different from any
+occurring higher in the series. It will be seen that <i>Cypris
+fasciculata</i> (Fig. 302, <i>b</i>) has tubercles at the end only
+of each valve, a character by which it can be immediately
+recognised. In fact, these minute crustaceans, almost as frequent
+in some of the shales as plates of mica in a micaceous sandstone,
+enable geologists at once to identify the Middle Purbeck in places
+far from the Dorsetshire cliffs, as, for example, in the Vale of
+Wardour in Wiltshire. Thick beds of chert occur in the Middle
+Purbeck filled with mollusca and cyprides of the genera already
+enumerated, in a beautiful state of preservation, often converted
+into chalcedony. Among these Professor Forbes met with gyrogonites
+(the spore-vessels of <i>Chara</i>), plants never until 1851
+discovered in rocks older than the Eocene. About twenty feet below
+the &ldquo;Cinder-bed&rdquo; is a stratum two or three inches
+thick, in which fossil mammalia presently to be mentioned occur,
+and beneath this a thin band of greenish shales, with marine shells
+and impressions of leaves like those of a large <i>Zostera,</i>
+forming the base of the Middle Purbeck.</p>
+
+<p><img src="images/fig302.jpg" width="411" height="171" alt=
+"Fig. 302: Cyprides from the Middle Purbecks." /></p>
+
+<img src="images/fig303.jpg" width="130" height="125" alt=
+"Fig. 303: Physa Bristovii" />
+
+<p>
+<i>Fossil Mammalia of the Middle Purbeck.</i>&mdash;In 1852,<a href="#fn-19.1"
+name="fnref-19.1" id="fnref-19.1"><sup>[1]</sup></a> after alluding to the
+discovery of numerous insects and air-breathing mollusca in the Purbeck strata,
+I remarked that, although no mammalia had then been found, &ldquo;it was too
+soon to infer <a name="page326"></a>their non-existence on mere negative
+evidence.&rdquo; Only two years after this remark was in print, Mr. W. R.
+Brodie found in the Middle Purbeck, about twenty feet below the
+&ldquo;Cinder-bed&rdquo; above alluded to, in Durdlestone Bay, portions of
+several small jaws with teeth, which Professor Owen recognised as belonging to
+a small mammifer of the insectivorous class, more closely allied in its
+dentition to the <i> Amphitherium</i> (or <i>Thylacotherium</i>) than to any
+existing type.
+</p>
+
+<p>Four years later (in 1856) the remains of several other species
+of warm-blooded quadrupeds were exhumed by Mr. S. H. Beckles,
+<small>F.R.S.</small>, from the same thin bed of marl near the base
+of the Middle Purbeck. In this marly stratum many reptiles, several
+insects, and some fresh-water shells of the genera <i>Paludina,
+Planorbis,</i> and <i>Cyclas,</i> were found.</p>
+
+<p>Mr. Beckles had determined thoroughly to explore the thin layer
+of calcareous mud from which in the suburbs of Swanage the bones of
+the Spalacotherium had already been obtained, and in three weeks he
+brought to light from an area forty feet long and ten wide, and
+from a layer the average thickness of which was only five inches,
+portions of the skeletons of six new species of mammalia, as
+interpreted by Dr. Falconer, who first examined them. Before these
+interesting inquiries were brought to a close, the joint labours of
+Professor Owen and Dr. Falconer had made it clear that twelve or
+more species of mammalia characterised this portion of the Middle
+Purbeck, most of them insectivorous or predaceous, varying in size
+from that of a mole to that of the common polecat, <i>Mustela
+putorius.</i> While the majority had the character of insectivorous
+marsupials, Dr. Falconer selected one as differing widely from the
+rest, and pointed out that in certain characters it was allied to
+the living Kangaroo-rat, or <i>Hypsiprymnus,</i> ten species of
+which now inhabit the prairies and scrub-jungle of Australia,
+feeding on plants, and gnawing scratched-up roots. A striking
+peculiarity of their dentition, one in which they differ from all
+other quadrupeds, consists in their having a single large
+pre-molar, the enamel of which is furrowed with vertical grooves,
+usually seven in number.</p>
+
+<p>The largest pre-molar (see <a href="images/fig304.jpg">Fig.
+305</a>) in the fossil genus exhibits in like manner seven parallel
+grooves, producing by their termination a similar serrated edge in
+the crown; but their direction is diagonal&mdash;a distinction, says Dr.
+Falconer, which is &ldquo;trivial, not typical.&rdquo; As these
+oblique furrows form so marked a character of the majority of the
+teeth, Dr. Falconer gave to the fossil the generic name of <i>
+Plagiaulax.</i> The shape and relative size of the incisor, <i>
+a,</i> <a href="images/fig306.jpg">Fig. 306,</a> exhibit
+<a name="page327"></a>a no less striking similarity to Hypsiprymnus. Nevertheless, the
+more sudden upward curve of this incisor, as well as other
+characters of the jaw, indicate a great deviation in the form of
+Plagiaulax from that of the living kangaroo-rats.</p>
+
+<p><img src="images/fig304.jpg" width="374" height="162" alt=
+"Fig. 304: Pre-molar of the recent Australian Hypsiprymnus Gaimardi, showing 7
+grooves at right angles to the length of the jaw. Fig. 305: Third and largest
+pre-molar (lower jaw) of Plagiaulax Becklesii, showing 7 diagonal grooves." />
+</p>
+
+<img src="images/fig306.jpg" width="280" height="247" alt=
+"Fig. 306: Plagiaulax Becklessi. Right ramus of lower jaw." />
+
+<p>There are two fossil specimens of lower jaws of this genus
+evidently referable to two distinct species extremely unequal in
+size and otherwise distinguishable. The <i>Plagiaulax Becklesii</i>
+(Fig. 306) was about as big as the English squirrel or the flying
+phalanger of Australia (<i>Petaurus Australis,</i> Waterhouse). The
+smaller fossil, having only half the linear dimensions of the
+other, was probably only one-twelfth of its bulk. It is of peculiar
+geological interest, because, as shown by Dr. Falconer, its two
+back molars bear a decided resemblance to those of the Triassic <i>
+Microlestes</i> (<a href="images/fig389.jpg">Fig. 389</a>), the
+most ancient of known mammalia, of which an account will be given
+in Chapter XXI.</p>
+
+<p>Up to 1857 all the mammalian remains discovered in secondary
+rocks had consisted solely of single branches of the lower jaw, but
+in that year Mr. Beckles obtained the upper portion of a skull, and
+on the same slab the lower jaw of another quadruped with eight
+molars, a large canine, and a broad and thick incisor. It has been
+named Triconodon from its bicuspid teeth, and is supposed to have
+been a small insectivorous marsupial, about the size of a hedgehog.
+Other jaws have since been found indicating a larger species of the
+same genus.</p>
+
+<p>
+<a name="page328"></a>Professor Owen has proposed the name of <i>Galestes</i> for the
+largest of the mammalia discovered in 1858 in Purbeck, equalling
+the polecat (<i>Mustela putorius</i>) in size. It is supposed to
+have been predaceous and marsupial.</p>
+
+<p>Between forty and fifty pieces or sides of lower jaws with teeth
+have been found in oolitic strata in Purbeck; only five upper
+maxillaries, together with one portion of a separate cranium, occur
+at Stonesfield, and it is remarkable that with these there were no
+examples in Purbeck of an entire skeleton, nor of any considerable
+number of bones in juxtaposition. In several portions of the matrix
+there were detached bones, often much decomposed, and fragments of
+others apparently mammalian; but if all of them were restored, they
+would scarcely suffice to complete the five skeletons to which the
+five upper maxillaries above alluded to belonged. As the average
+number of pieces in each mammalian skeleton is about 250, there
+must be many thousands of missing bones; and when we endeavour to
+account for their absence, we are almost tempted to indulge in
+speculations like those once suggested to me by Dr. Buckland, when
+he tried to solve the enigma in reference to Stonesfield;
+&ldquo;The corpses,&rdquo; he said, &ldquo;of drowned animals, when
+they float in a river, distended by gases during putrefaction, have
+often their lower jaw hanging loose, and sometimes it has dropped
+off. The rest of the body may then be drifted elsewhere, and
+sometimes may be swallowed entire by a predaceous reptile or fish,
+such as an ichthyosaur or a shark.&rdquo;</p>
+
+<p>As all the above-mentioned Purbeck marsupials, belonging to
+eight or nine genera and to about fourteen species, insectivorous,
+predaceous, and herbivorous, have been obtained from an area less
+than 500 square yards in extent, and from a single stratum no more
+than a few inches thick, we may safely conclude that the whole
+lived together in the same region, and in all likelihood they
+constituted a mere fraction of the mammalia which inhabited the
+lands drained by one river and its tributaries. They afford the
+first positive proof as yet obtained of the co-existence of a
+varied fauna of the highest class of vertebrata with that ample
+development of reptile life which marks all the periods from the
+Trias to the Lower Cretaceous inclusive, and with a gymnospermous
+flora, or that state of the vegetable kingdom when cycads and
+conifers predominated over all kinds of plants, except the ferns,
+so far, at least, as our present imperfect knowledge of fossil
+botany entitles us to speak.</p>
+
+<p>The following table will enable the reader to see at a glance
+how conspicuous a part, numerically considered, the mammalian
+species of the Middle Purbeck now play when compared
+<a name="page329"></a>with those of other formations more ancient than the Paris
+gypsum, and, at the same time, it will help him to appreciate the
+enormous hiatus in the history of fossil mammalia which at present
+occurs between the Eocene and Purbeck periods, and between the
+latter and the Stonesfield Oolite, and between this again and the
+Trias.</p>
+
+<p><i>Number and Distribution of all the known Species of
+Fossil Mammalia from Strata older than the Paris Gypsum, or than
+the Bembridge Series of the Isle of Wight.</i></p>
+
+<table border="1" cellspacing="0" cellpadding="4" summary=
+"Number and Distribution of all the known Species of Fossil Mammalia from
+Strata older than the Paris Gypsum, or than the Bembridge Series of the Isle of Wight.">
+<tr>
+<td valign="middle" rowspan="7">
+T<small>ERTIARY</small></td>
+<td >Headon Series and beds between the Paris Gypsum
+and the Grès de Beauchamp</td>
+<td valign="top">14</td>
+<td >10&nbsp;English<br/>
+&nbsp;&nbsp; 4&nbsp;French</td>
+</tr>
+
+<tr>
+<td >Barton Clay and Sables de Beauchamp</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="top">Bagshot Beds, Calcaire Grossier, and
+Upper Soissonnais of Cuisse-Lamotte</td>
+<td valign="top">20</td>
+<td valign="top">16&nbsp;French<br/>
+&nbsp;&nbsp;&nbsp;1&nbsp;English<br/>
+&nbsp;&nbsp;&nbsp;3&nbsp;U.&nbsp;States<a href="#fn-19.2" name="fnref-19.2"
+id="fnref-19.2"><sup>[2]</sup></a></td>
+</tr>
+
+<tr>
+<td >London Clay, including the Kyson Sand</td>
+<td >7</td>
+<td>English</td>
+</tr>
+
+<tr>
+<td valign="top">Plastic Clay and Lignite</td>
+<td valign="top">9</td>
+<td>7 French<br/>
+2 English</td>
+</tr>
+
+<tr>
+<td >Sables de Bracheux</td>
+<td >1</td>
+<td>French</td>
+</tr>
+
+<tr>
+<td >Thanet Sands and Lower Landenian of Belgium</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="20">
+S<small>ECONDARY</small></td>
+<td >Maestricht Chalk</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >White Chalk</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Chalk Marl</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Chloritic Series (Upper Greensand)</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Gault</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Neocomian (Lower Greensand)</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Wealden</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Upper Purbeck Oolite</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Middle Purbeck Oolite</td>
+<td >14</td>
+<td >Swanage</td>
+</tr>
+
+<tr>
+<td >Lower Purbeck Oolite</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Portland Oolite</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Kimmeridge Clay</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Coral Rag</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Oxford Clay</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Great Oolite</td>
+<td >4</td>
+<td >Stonesfield</td>
+</tr>
+
+<tr>
+<td >Inferior Oolite</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Lias</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="top">Upper Trias</td>
+<td valign="top">4</td>
+<td >Wurtemberg<br/>
+Somersetshire<br/>
+N. Carolina</td>
+</tr>
+
+<tr>
+<td >Middle Trias</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Lower Trias</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="6">
+P<small>RIMARY</small></td>
+<td >Permian</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Carboniferous</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Devonian</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Silurian</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Cambrian</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td >Laurentian</td>
+<td >0</td>
+<td>&nbsp;</td>
+</tr>
+</table>
+
+<p>
+<a name="page330"></a>The Sables de Bracheux, enumerated in the Tertiary division of
+the table, supposed by Mr. Prestwich to be somewhat newer than the
+Thanet Sands, and by M. Hébert to be of about that age, have
+yielded at La Fere the <i>Arctocyon (Palæocyon)
+primævus,</i> the oldest known tertiary mammal.</p>
+
+<p>It is worthy of notice, that in the Hastings Sands there are
+certain layers of clay and sandstone in which numerous footprints
+of quadrupeds have been found by Mr. Beckles, and traced by him in
+the same set of rocks through Sussex and the Isle of Wight. They
+appear to belong to three or four species of reptiles, and no one
+of them to any warm-blooded quadruped. They ought, therefore, to
+serve as a warning to us, when we fail in like manner to detect
+mammalian footprints in older rocks (such as the New Red
+Sandstone), to refrain from inferring that quadrupeds, other than
+reptilian, did not exist or pre-exist.</p>
+
+<p>But the most instructive lesson read to us by the Purbeck strata
+consists in this: They are all, with the exception of a few
+intercalated brackish and marine layers, of fresh-water origin;
+they are 160 feet in thickness, have been well searched by skillful
+collectors, and by the late Edward Forbes in particular, who
+studied them for months consecutively. They have been numbered, and
+the contents of each stratum recorded separately, by the officers
+of the Geological Survey of Great Britain. They have been divided
+into three distinct groups by Forbes, each characterised by the
+same genera of pulmoniferous mollusca and cyprides, these genera
+being represented in each group by different species; they have
+yielded insects of many orders, and the fruits of several plants;
+and lastly, they contain &ldquo;dirt-beds,&rdquo; or old
+terrestrial surfaces and vegetable soils at different levels, in
+some of which erect trunks and stumps of cycads and conifers, with
+their roots still attached to them, are preserved. Yet when the
+geologist inquires if any land-animals of a higher grade than
+reptiles lived during any one of these three periods, the rocks are
+all silent, save one thin layer a few inches in thickness; and this
+single page of the earth&rsquo;s history has suddenly revealed to
+us in a few weeks the memorials of so many species of fossil
+mammalia, that they already outnumber those of many a subdivision
+of the tertiary series, and far surpass those of all the other
+secondary rocks put together!</p>
+
+<p><i>Lower Purbeck.</i>&mdash;Beneath the thin marine band
+mentioned at <a href="#page324">p. 324</a> as the base of the
+Middle Purbeck, some purely fresh-water marls occur, containing
+species of <i>Cypris</i> (Fig. 307 <i>a, c</i>), <i>Valvata,</i>
+and <i>Limnæa,</i> different from those of the
+<a name="page331"></a>Middle Purbeck. This is the beginning of the inferior division,
+which is about 80 feet thick. Below the marls are seen, at
+Meup&rsquo;s Bay, more than thirty feet of brackish-water strata,
+abounding in a species of <i>Serpula,</i> allied to, if not
+identical with, <i>Serpula coacervites,</i> found in beds of the
+same age in Hanover. There are also shells of the genus <i>
+Rissoa</i> (of the subgenus <i>Hydrobia</i>), and a little <i>
+Cardium</i> of the subgenus <i>Protocardium,</i> in these marine
+beds, together with <i>Cypris.</i> Some of the cypris-bearing
+shales are strangely contorted and broken up, at the west end of
+the Isle of Purbeck. The great dirt-bed or vegetable soil
+containing the roots and stools of <i>Cycadeæ,</i> which I
+shall presently describe, underlies these marls, and rests upon the
+lowest fresh-water limestone, a rock about eight feet thick,
+containing <i>Cyclas, Valvata,</i> and <i>Limnæa,</i> of the
+same species as those of the uppermost part of the Lower Purbeck,
+or above the dirt-bed. The fresh-water limestone in its turn rests
+upon the top beds of the Portland stone, which, although it
+contains purely marine remains, often consists of a rock
+undistinguishable in mineral character from the Lowest Purbeck
+limestone.</p>
+
+<img src="images/fig307.jpg" width="185" height="151" alt=
+"Fig. 307: Cyprides from the Lower Purbeck." />
+
+<img src="images/fig308.jpg" width="166" height="235" alt=
+"Fig. 308: Mantellia nidiformis." />
+
+<p><i>Dirt-bed or ancient Surface-soil.</i>&mdash;The most
+remarkable of all the varied succession of beds enumerated in the
+above list is that called by the quarrymen &ldquo;the dirt,&rdquo;
+or &ldquo;black dirt,&rdquo; which was evidently an ancient
+vegetable soil. It is from 12 to 18 inches thick, is of a dark
+brown or black colour, and contains a large proportion of earthy
+lignite. Through it are dispersed rounded and sub-angular fragments
+of stone, from 3 to 9 inches in diameter, in such numbers that it
+almost deserves the name of gravel. I also saw in 1866, in
+Portland, a smaller dirt-bed six feet below the principal one, six
+inches thick, consisting of brown earth with upright <i>Cycads</i>
+of the same species, <i>Mantellia nidiformis,</i> as those found in
+the upper bed, but no <i>Coniferæ.</i> The weight of the
+incumbent strata squeezing down the compressible dirt-bed has
+caused the <i>Cycads</i> to assume that form which has
+<a name="page332"></a>led the quarrymen to call them &ldquo;petrified birds&rsquo;
+nests,&rdquo; which suggested to Brongniart the specific name of
+<i>nidiformis.</i> I am indebted to Mr. Carruthers for Figure 308
+of one of these Purbeck specimens, in which the original
+cylindrical figure has been less distorted than usual by
+pressure.</p>
+
+<p>Many silicified trunks of coniferous trees, and the remains of
+plants allied to <i>Zamia</i> and <i>Cycas,</i> are buried in this
+dirt-bed, and must have become fossil on the spots where they grew.
+The stumps of the trees stand erect for a height of from one to
+three feet, and even in one instance to six feet, with their roots
+attached to the soil at about the same distances from one another
+as the trees in a modern forest. The carbonaceous matter is most
+abundant immediately around the stumps, and round the remains of
+fossil <i>Cycadeæ.</i></p>
+
+<p>Besides the upright stumps above mentioned, the dirt-bed
+contains the stems of silicified trees laid prostrate. These are
+partly sunk into the black earth, and partly enveloped by a
+calcareous slate which covers the dirt-bed. The fragments of the
+prostrate trees are rarely more than three or four feet in length;
+but by joining many of them together, trunks have been restored,
+having a length from the root to the branches of from 20 to 23
+feet, the stems being undivided for 17 or 20 feet, and then forked.
+The diameter of these near the root is about one foot; but I
+measured one myself, in 1866, which was 3&frac12; feet in diameter,
+said by the quarrymen to be unusually large. Root-shaped cavities
+were observed by Professor Henslow to descend from the bottom of
+the dirt-bed into the subjacent fresh-water stone, which, though
+now solid, must have been in a soft and penetrable state when the
+trees grew. The thin layers of calcareous slate (Fig. 309) were
+evidently deposited tranquilly, and would have been horizontal but
+for the protrusion of the stumps of the trees, around the top of
+each of which they form hemispherical concretions.</p>
+
+<p><img src="images/fig309.jpg" width="391" height="144" alt=
+"Fig. 309: Section in Isle of Portland, Dorset." /></p>
+
+<p>The dirt-bed is by no means confined to the island of Portland,
+where it has been most carefully studied, but is seen
+<a name="page333"></a>in the same relative position in the cliffs east of Lulworth
+Cove, in Dorsetshire, where, as the strata have been disturbed, and
+are now inclined at an angle of 45&deg;, the stumps of the trees
+are also inclined at the same angle in an opposite direction&mdash;a
+beautiful illustration of a change in the position of beds
+originally horizontal (see Fig. 310).</p>
+
+<p><img src="images/fig310.jpg" width="384" height="189" alt=
+"Fig. 310: Section of cliff east of Lulworth Cove." /></p>
+
+<p>From the facts above described we may infer, first, that those
+beds of the Upper Oolite, called &ldquo;the Portland,&rdquo; which
+are full of marine shells, were overspread with fluviatile mud,
+which became dry land, and covered by a forest, throughout a
+portion of the space now occupied by the south of England, the
+climate being such as to permit the growth of the <i>Zamia</i> and
+<i>Cycas.</i> Secondly. This land at length sank down and was
+submerged with its forests beneath a body of fresh-water, from
+which sediment was thrown down enveloping fluviatile shells.
+Thirdly. The regular and uniform preservation of this thin bed of
+black earth over a distance of many miles, shows that the change
+from dry land to the state of a fresh-water lake or estuary, was
+not accompanied by any violent denudation, or rush of water, since
+the loose black earth, together with the trees which lay prostrate
+on its surface, must inevitably have been swept away had any such
+violent catastrophe taken place.</p>
+
+<p>The forest of the dirt-bed, as before hinted, was not everywhere
+the first vegetation which grew in this region. Besides the lower
+bed containing upright <i>Cycadeæ,</i> before mentioned,
+another has sometimes been found above it, which implies
+oscillations in the level of the same ground, and its alternate
+occupation by land and water more than once.</p>
+
+<p><i>Subdivisions of the Purbeck.</i>&mdash;It will be observed
+that the division of the Purbecks into upper, middle, and lower,
+was made by Professor Forbes strictly on the principle of the
+<a name="page334"></a>entire distinctness of the species of organic remains which they
+include. The lines of demarkation are not lines of disturbance, nor
+indicated by any striking physical characters or mineral changes.
+The features which attract the eye in the Purbecks, such as the
+dirt-beds, the dislocated strata at Lulworth, and the Cinder-bed,
+do not indicate any breaks in the distribution of organised beings.
+&ldquo;The causes which led to a complete change of life three
+times during the deposition of the fresh-water and brackish strata
+must,&rdquo; says this naturalist, &ldquo;be sought for, not simply
+in either a rapid or a sudden change of their area into land or
+sea, but in the great lapse of time which intervened between the
+epochs of deposition at certain periods during their
+formation.&rdquo;</p>
+
+<p>Each dirt-bed may, no doubt, be the memorial of many thousand
+years or centuries, because we find that two or three feet of
+vegetable soil is the only monument which many a tropical forest
+has left of its existence ever since the ground on which it now
+stands was first covered with its shade. Yet, even if we imagine
+the fossil soils of the Lower Purbeck to represent as many ages, we
+need not be surprised to find that they do not constitute lines of
+separation between strata characterised by different zoological
+types. The preservation of a layer of vegetable soil, when in the
+act of being submerged, must be regarded as a rare exception to a
+general rule. It is of so perishable a nature, that it must usually
+be carried away by the denuding waves or currents of the sea, or by
+a river; and many Purbeck dirt-beds were probably formed in
+succession and annihilated, besides those few which now remain.</p>
+
+<p>The plants of the Purbeck beds, so far as our knowledge extends
+at present, consist chiefly of Ferns, Coniferæ, and
+Cycadeæ (<a href="images/fig308.jpg">Fig. 308</a>), without
+any angiosperms; the whole more allied to the Oolitic than to the
+Cretaceous vegetation. The same affinity is indicated by the
+vertebrate and invertebrate animals. Mr. Brodie has found the
+remains of beetles and several insects of the homopterous and
+trichopterous orders, some of which now live on plants, while
+others are of such forms as hover over the surface of our present
+rivers.</p>
+
+<p><b>Portland Oolite and Sand</b> (<i>b,</i> Table <a href=
+"#page321">p. 321</a>).&mdash;The Portland Oolite has already been
+mentioned as forming in Dorsetshire the foundation on which the
+fresh-water limestone of the Lower Purbeck reposes (see <a href=
+"#page331">p. 331</a>). It supplies the well-known building-stone
+of which St. Paul&rsquo;s and so many of the principal edifices of
+London are constructed. About fifty species of mollusca occur in
+this formation, among which are some ammonites of large size. The
+cast of a spiral univalve
+<a name="page335"></a>called by the quarrymen the &ldquo;Portland screw&rdquo;
+(<i>a,</i> Figure 311), is common; the shell of the same (<i>b</i>)
+being rarely met with. Also <i>Trigonia gibbosa</i> (Fig. 313) and
+<i>Cardium dissimile</i> (<a href="images/fig314.jpg">Fig.
+314</a>). This upper member rests on a dense bed of sand, called
+the Portland Sand, containing similar marine fossils, below which
+is the Kimmeridge Clay. In England these Upper Oolite formations
+are almost wholly confined to the southern counties. But some
+fragments of them occur beneath the Neocomian or Speeton Clay on
+the coast of Yorkshire, containing many more fossils common to the
+Portlandian of the Continent than does the same formation in
+Dorsetshire. Corals are rare in this formation, although one
+species is found plentifully at Tisbury, Wiltshire, in the Portland
+Sand, converted into flint and chert, the original calcareous
+matter being replaced by silex (Fig. 312).</p>
+
+<img src="images/fig311.jpg" width="159" height="277" alt=
+"Fig. 311: Cerithium Portlandicum." />
+
+<p><img src="images/fig312.jpg" width="351" height="235" alt=
+"Fig. 312: Isastræa oblonga. Fig. 313: Trigonia gibbosa." />
+</p>
+
+<p><b>Kimmeridge Clay.</b>&mdash;The <i>Kimmeridge Clay</i>
+consists, in great part, of a bituminous shale, sometimes forming
+an impure coal, several hundred feet in thickness. In some places
+in Wiltshire it much resembles peat; and the bituminous matter may
+have been, in part at least, derived from the decomposition of
+vegetables. But as impressions of plants are rare in these shales,
+which contain ammonites, oysters, and other marine shells, with
+skeletons of fish and saurians, the bitumen
+<a name="page336"></a>may perhaps be of animal origin. Some of the saurians
+(Pliosaurus) in Dorsetshire are among the most gigantic of their
+kind.</p>
+
+<p><img src="images/fig314.jpg" width="375" height="346" alt=
+"Fig. 314: Cardium dissimile. Fig. 315: Ostrea expansa. Fig. 316: Cardium
+striatulum. Fig. 317: Ostrea deltoidea. Fig. 318: Gryphæa (Exogyra) virgula." />
+</p>
+
+<p>Among the fossils, amounting to nearly 100 species, may be
+mentioned <i>Cardium striatulum</i> (Fig. 316) and <i>Ostrea
+deltoidea</i> (Fig. 317), the latter found in the Kimmeridge Clay
+throughout England and the north of France, and also in Scotland,
+near Brora. The <i>Gryphæa virgula</i> (Fig. 318), also met
+with in the Kimmeridge Clay near Oxford, is so abundant in the
+Upper Oolite of parts of France as to have caused the deposit to be
+termed &ldquo;marnes à gryphées virgules.&rdquo; Near
+Clermont, in Argonne, a few leagues from St. Menehould, where these
+indurated marls crop out from beneath the Gault, I have seen them,
+on decomposing, leave the surface of every ploughed field literally
+strewed over with this fossil oyster.</p>
+
+<img src="images/fig319.jpg" width="98" height="120" alt=
+"Fig. 319: Trigonellites latus." />
+
+<p>The <i>Trigonellites latus</i> (<i>Aptychus</i> of some authors)
+(Fig. 319) is also widely dispersed through this clay. The real
+nature of the shell, of which there are many species in oolitic
+rocks, is still a matter of conjecture. Some are of opinion that
+the two plates have been the gizzard of a cephalopod; others, that
+it may have formed a bivalve operculum of the same.</p>
+
+<p>
+<a name="page337"></a><b>Solenhofen Stone.</b>&mdash;The celebrated lithographic stone
+of Solenhofen in Bavaria, appears to be of intermediate age between
+the Kimmeridge clay and the Coral Rag, presently to be described.
+It affords a remarkable example of the variety of fossils which may
+be preserved under favourable circumstances, and what delicate
+impressions of the tender parts of certain animals and plants may
+be retained where the sediment is of extreme fineness. Although the
+number of testacea in this slate is small, and the plants few, and
+those all marine, count Munster had determined no less than 237
+species of fossils when I saw his collection in 1833; and among
+them no less than seven <i>species</i> of flying reptiles or
+pterodactyls (see Fig. 320), six saurians, three tortoises, sixty
+species of fish, forty-six of crustacea, and twenty-six of insects.
+These insects, among which is a libellula, or dragon-fly, must have
+been blown out to sea, probably from the same land to which the
+pterodactyls, and other contemporaneous air-breathers,
+resorted.</p>
+
+<img src="images/fig320.jpg" width="152" height="284" alt=
+"Fig. 320: Skeleton of Pterodactylus crassirostris." />
+
+<p>
+In the same slate of Solenhofen a fine example was met with in 1862 of the
+skeleton of a bird almost entire, and retaining even its feathers so perfect
+that the vanes as well as the shaft are preserved. The head was at first
+supposed to be wanting, but Mr. Evans detected on the slab what seems to be the
+impression of the cranium and beak, much resembling in size and shape that of
+the jay or woodcock. This valuable specimen is now in the British Museum, and
+has been called by Professor Owen <i>Archæopteryx macrura.</i> Although
+anatomists agree that it is a true bird, yet they also find that in the length
+of the bones of the tail, and some other minor points of its anatomy, it
+approaches more nearly to reptiles than any known living bird. In the living
+representatives of the class Aves, the tail-feathers are attached to a
+coccygian bone, consisting of several vertebræ united together, whereas in the
+Archæopteryx the tail is composed of twenty vertebræ, each of which supports a
+pair of quill-feathers. The first five only of the vertebræ, as seen in A, have
+transverse processes, the fifteen remaining ones become gradually longer and
+more tapering. The feathers diverge outward from them at an angle of 45&deg;.
+<a name="page338"></a>
+</p>
+
+<p><img src="images/fig321.jpg" width="422" height="440" alt=
+"Fig. 321: Tail and feather of Archæopteryx, from Solenhofen, and tail of living bird for comparison." />
+</p>
+
+<p>Professor Huxley in his late memoirs on the order of reptiles
+called Dinosaurians, which are largely represented in all the
+formations, from the Neocomian to the Trias inclusive, has shown
+that they present in their structure many remarkable affinities to
+birds. But a reptile about two feet long, called Compsognathus,
+lately found in the Stonesfield slate, makes a much greater
+approximation to the class Aves than any Dinosaur, and therefore
+forms a closer link between the classes Aves and Reptilia than does
+the Archæopteryx.</p>
+
+<p>It appears doubtful whether any species of British fossil,
+whether of the vertebrate or invertebrate class, is common to the
+Oolite and Chalk. But there is no similar break or discordance as
+we proceed downward, and pass from one to another of the several
+leading members of the Jurassic group, the Upper, Middle, and Lower
+Oolite, and the Lias, there being often a considerable proportion
+of the mollusca, sometimes as much as a fourth, common to such
+divisions as the Upper and Middle Oolite.</p>
+
+<p class="center">
+<a name="page339"></a><small>MIDDLE OOLITE.</small>
+</p>
+
+<p><b>Coral Rag.</b>&mdash;One of the limestones of the Middle
+Oolite has been called the &ldquo;Coral Rag,&rdquo; because it
+consists, in part, of continuous beds of petrified corals, most of
+them retaining the position in which they grew at the bottom of the
+sea. In their forms they more frequently resemble the reef-building
+polyparia of the Pacific than do the corals of any other member of
+the Oolite. They belong chiefly to the genera <i>Thecosmilia</i>
+(Fig. 322), <i>Protoseris,</i> and <i>Thamnastræa,</i> and
+sometimes form masses of coral fifteen feet thick.</p>
+
+<p><img src="images/fig322.jpg" width="369" height="192" alt=
+"Fig. 322: Thecosmilia annularis. Fig. 323: Thamnastræa." />
+</p>
+
+<img src="images/fig324.jpg" width="166" height="365" alt=
+"Fig. 324: Ostrea gregaria. Fig. 325: Nerinæa Goodhallii." />
+
+<p>In Fig. 323 of a <i>Thamnastræa</i> from this formation,
+it will be seen that the cup-shaped cavities are deepest on the
+right-hand side, and that they grow more and more shallow, until
+those on the left side are nearly filled up. The last-mentioned
+stars are supposed to represent a perfected condition, and the
+others an immature state. These coralline strata extend through the
+calcareous hills of the north-west of Berkshire, and north of
+Wilts, and again recur in Yorkshire, near Scarborough. The <i>
+Ostrea gregarea</i> (Fig. 324) is very characteristic of the
+formation in England and on the Continent.</p>
+
+<p>One of the limestones of the Jura, referred to the age of the
+English Coral Rag, has been called &ldquo;Nerinæan
+limestone&rdquo; (Calcaire à Nérinées) by M.
+Thirria;
+<a name="page340"></a><i>Nerinæa</i> being an extinct genus of univalve shells
+(Fig. 325) much resembling the <i>Cerithium</i> in external form.
+The section shows the curious and continuous ridges on the
+columnella and whorls.</p>
+
+<p><b>Oxford Clay.</b>&mdash;The coralline limestone, or
+&ldquo;Coral Rag,&rdquo; above described, and the accompanying
+sandy beds, called &ldquo;calcareous grits,&rdquo; of the Middle
+Oolite, rest on a thick bed of clay, called the &ldquo;Oxford
+Clay,&rdquo; sometimes not less than 600 feet thick. In this there
+are no corals, but great abundance of cephalopoda, of the genera
+Ammonite and Belemnite (Figs. 326 and 327). In some of the finely
+laminated clays ammonites are very perfect, although somewhat
+compressed, and are frequently found with the lateral lobe extended
+on each side of the opening of the mouth into a horn-like
+projection (Figure 327). These were discovered in the cuttings of
+the Great Western Railway, near Chippenham, in 1841, and have been
+described by Mr. Pratt (<i>An. Nat. Hist.,</i> Nov., 1841).</p>
+
+<p><img src="images/fig326.jpg" width="418" height="322" alt=
+"Fig. 326: Belemnites hastatus. Fig. 327: Ammonites Jason." />
+</p>
+
+<p>
+Similar elongated processes have been also observed to extend from the shells
+of some Belemnites discovered by Dr. Mantell in the same clay (see Figure 328),
+who, by the aid of this and other specimens, has been able to throw much light
+on the structure of singular extinct forms of cuttle-fish.<a href="#fn-19.3"
+name="fnref-19.3" id="fnref-19.3"><sup>[3]</sup></a>
+</p>
+
+<p>
+<a name="page341"></a><b>Kelloway Rock.</b>&mdash;The arenaceous limestone which
+passes under this name is generally grouped as a member of the
+Oxford clay, in which it forms, in the south-west of England,
+lenticular masses, 8 or 10 feet thick, containing at Kelloway, in
+Wiltshire, numerous casts of ammonites and other shells. But in
+Yorkshire this calcareo-arenaceous formation thickens to about 30
+feet, and constitutes the lower part of the Middle Oolite,
+extending inland from Scarborough in a southerly direction. The
+number of mollusca which it contains is, according to Mr.
+Etheridge, 143, of which only 34, or 23&frac12; per cent, are
+common to the Oxford clay proper. Of the 52 Cephalopoda, 15 (namely
+13 species of ammonite, the <i>Ancyloceras Calloviense</i> and one
+Belemnite) are common to the Oxford Clay, giving a proportion of
+nearly 30 per cent.</p>
+
+<img src="images/fig328.jpg" width="137" height="573" alt=
+"Fig. 328: Belemnites Puzosianus." />
+
+<p class="center">
+<small>LOWER OOLITE.</small>
+</p>
+
+<p>
+<b>Cornbrash and Forest Marble.</b>&mdash;The upper division of this series,
+which is more extensive than the preceding or Middle Oolite, is called in
+England the Cornbrash, as being a brashy, easily broken rock, good for corn
+land. It consists of clays and calcareous sandstones, which pass downward into
+the Forest Marble, an argillaceous limestone, abounding in marine fossils. In
+some places, as at Bradford, this limestone is replaced by a mass of clay. The
+sandstones of the Forest Marble of Wiltshire are often ripple-marked and filled
+with fragments of broken shells and pieces of drift-wood, having evidently been
+formed on a coast. Rippled slabs of fissile oolite are used for roofing, and
+have been traced over a broad band of country from Bradford in Wilts, to
+Tetbury in Gloucestershire. These calcareous tile-stones are separated from
+each other by thin seams of clay, which have been deposited upon them, and have
+taken their form, preserving the undulating ridges and furrows of the sand in
+such complete integrity, that the impressions of small footsteps, apparently of
+crustaceans, which walked over the soft wet sands, are still visible. In the
+same stone the claws of crabs, fragments <a name="page342"></a>of echini, and
+other signs of a neighbouring beach, are observed.<a href="#fn-19.4"
+name="fnref-19.4" id="fnref-19.4"><sup>[4]</sup></a>
+</p>
+
+<p><b>Great (or Bath) Oolite.</b>&mdash;Although the name of Coral
+Rag has been appropriated, as we have seen, to a member of the
+Middle Oolite before described, some portions of the Lower Oolite
+are equally entitled in many places to be called coralline
+limestones. Thus the Great Oolite near Bath contains various
+corals, among which the <i>Eunomia radiata</i> (Fig. 329) is very
+conspicuous, single individuals forming masses several feet in
+diameter; and having probably required, like the large existing
+brain-coral (<i>Meandrina</i>) of the tropics, many centuries
+before their growth was completed.</p>
+
+<p><img src="images/fig329.jpg" width="337" height="221" alt=
+"Fig. 329: Eunomia radiata." /></p>
+
+<p>Different species of crinoids, or stone-lilies, are also common
+in the same rocks with corals; and, like them, must have enjoyed a
+firm bottom, where their base of attachment remained undisturbed
+for years (<i>c,</i> Fig. 330). Such fossils, therefore, are almost
+confined to the limestones; but an exception occurs at Bradford,
+near Bath, where they are enveloped in clay sometimes 60 feet
+thick. In this case, however, it appears that the solid upper
+surface of the &ldquo;Great Oolite&rdquo; had supported, for a
+time, a thick submarine forest of these beautiful zoophytes, until
+the clear and still water was invaded by a current charged with
+mud, which threw down the stone-lilies, and broke most of their
+stems short off near the point of attachment. The stumps still
+remain in their original position; but the numerous articulations,
+once composing the stem, arms, and body of the encrinite, were
+scattered at random through the argillaceous deposit in which some
+now lie prostrate. These appearances are represented in the section
+<i>b,</i> Fig. 330, where the darker strata represent the Bradford
+clay, which is however a formation
+<a name="page343"></a>of such local development that in many places it cannot easily
+be separated from the clays of the overlying
+&ldquo;forest-marble&rdquo; and underlying &ldquo;fuller&rsquo;s
+earth.&rdquo; The upper surface of the calcareous stone below is
+completely incrusted over with a continuous pavement, formed by the
+stony roots or attachments of the Crinoidea; and besides this
+evidence of the length of time they had lived on the spot, we find
+great numbers of single joints, or circular plates of the stem and
+body of the encrinite, covered over with <i>serpulæ.</i> Now
+these <i>serpulæ</i> could only have begun to grow after the
+death of some of the stone-lilies, parts of whose skeletons had
+been strewed over the floor of the ocean before the irruption of
+argillaceous mud. In some instances we find that, after the
+parasitic <i>serpulæ</i> were full grown, they had become
+incrusted over with a bryozoan, called <i>Diastopora diluviana</i>
+(see <i>b,</i> Fig. 331);
+<a name="page344"></a>and many generations of these molluscoids had succeeded each
+other in the pure water before they became fossil.</p>
+
+<p><img src="images/fig330.jpg" width="356" height="288" alt=
+"Fig. 330: Apiocrinites rotundus, or Pear Eucrinite." /></p>
+
+<p><img src="images/fig331.jpg" width="362" height="241" alt=
+"Fig. 331: a. Aingle plate of body of Apiocrinus, overgrown with serpulæ and
+bryozoa; b. Portion of same magnified, showing the bryozoan Diastopora
+diluviana covering one of the serpulæ." />
+</p>
+
+<p>We may, therefore, perceive distinctly that, as the pines and
+cycadeous plants of the ancient &ldquo;dirt-bed,&rdquo; or fossil
+forest, of the Lower Purbeck were killed by submergence under fresh
+water, and soon buried beneath muddy sediment, so an invasion of
+argillaceous matter put a sudden stop to the growth of the Bradford
+Encrinites, and led to their preservation in marine strata.</p>
+
+<p>Such differences in the fossils as distinguish the calcareous
+and argillaceous deposits from each other, would be described by
+naturalists as arising out of a difference in the <i>stations</i>
+of species; but besides these, there are variations in the fossils
+of the higher, middle, and lower part of the oolitic series, which
+must be ascribed to that great law of change in organic life by
+which distinct assemblages of species have been adapted, at
+successive geological periods, to the varying conditions of the
+habitable surface. In a single district it is difficult to decide
+how far the limitation of species to certain minor formations has
+been due to the local influence of <i>stations,</i> or how far it
+has been caused by time or the law of variation above alluded to.
+But we recognise the reality of the last-mentioned influence, when
+we contrast the whole oolitic series of England with that of parts
+of the Jura, Alps, and other distant regions, where, although there
+is scarcely any lithological resemblance, yet some of the same
+fossils remain peculiar in each country to the Upper, Middle, and
+Lower Oolite formations respectively. Mr. Thurmann has shown how
+remarkably this fact holds true in the Bernese Jura, although the
+argillaceous divisions, so conspicuous in England, are feebly
+represented there, and some entirely wanting.</p>
+
+<p>The calcareous portion of the Great Oolite consists of several
+shelly limestones, one of which, called the Bath Oolite, is much
+celebrated as a building-stone. In parts of Gloucestershire,
+especially near Minchinhampton, the Great Oolite, says Mr. Lycett,
+&ldquo;must have been deposited in a shallow sea, where strong
+currents prevailed, for there are frequent changes in the mineral
+character of the deposit, and some beds exhibit false
+stratification. In others, heaps of broken shells are mingled with
+pebbles of rocks foreign to the neighbourhood, and with fragments
+of abraded madrepores, dicotyledonous wood, and crabs&rsquo; claws.
+The shelly strata, also, have occasionally suffered denudation, and
+the removed portions have been replaced by clay.&rdquo; In such
+shallow-water
+<a name="page345"></a>beds shells of the genera <i>Patella, Nerita, Rimula,
+Cylindrites</i> are common (see Figs. 334 to 337); while
+cephalopods are rare, and instead of ammonites and belemnites,
+numerous genera of carnivorous trachelipods appear. Out of 224
+species of univalves obtained from the Minchinhampton beds, Mr.
+Lycett found no less than 50 to be carnivorous. They belong
+principally to the genera <i>Buccinum, Pleurotoma, Rostellaria,
+Murex, Purpuroidea</i> (Fig. 333), and Fusus, and exhibit a
+proportion of zoophagous species not very different from that which
+obtains in seas of the Recent period. These zoological results are
+curious and unexpected, since it was imagined that we might look in
+vain for the carnivorous trachelipods in rocks of such high
+antiquity as the Great Oolite, and it was a received doctrine that
+they did not begin to appear in considerable numbers till the
+Eocene period, when those two great families of cephalopoda, the
+ammonites and belemnites, and a great number of other
+representatives of the same class of chambered shells, had become
+extinct.</p>
+
+<p><img src="images/fig332.jpg" width="397" height="341" alt=
+"Fig. 332: Terebratula digona. Fig. 333: Purpuroidea nodulata. Fig. 334:
+Cylindrites acutus. Fig. 335: Patella rugosa. Fig. 336: Nerita costulata.
+Fig. 337: Rimula (Emarginula) clathrata." />
+</p>
+
+<p>
+<b>Stonesfield Slate: Mammalia.</b>&mdash;The slate of Stonesfield has been
+shown by Mr. Lonsdale to lie at the base of the Great Oolite.<a href="#fn-19.5"
+name="fnref-19.5" id="fnref-19.5"><sup>[5]</sup></a> It is a slightly oolitic
+shelly limestone, forming large lenticular masses imbedded in sand only six
+feet thick, <a name="page346"></a>but very rich in organic remains. It contains
+some pebbles of a rock very similar to itself, and which may be portions of the
+deposit, broken up on a shore at low water or during storms, and redeposited.
+The remains of belemnites, trigoniæ, and other marine shells, with fragments of
+wood, are common, and impressions of ferns, cycadeæ, and other plants. Several
+insects, also, and, among the rest, the elytra or wing-covers of beetles, are
+perfectly preserved (see Fig. 338), some of them approaching nearly to the
+genus Buprestis. The remains, also, of many genera of reptiles, such as
+<i>Plesiosaur, Crocodile,</i> and <i> Pterodactyl,</i> have been discovered in
+the same limestone.
+</p>
+
+<img src="images/fig338.jpg" width="84" height="190" alt=
+"Fig. 338: Elytron of Buprestis?" />
+
+<p>But the remarkable fossils for which the Stonesfield slate is
+most celebrated are those referred to the mammiferous class. The
+student should be reminded that in all the rocks described in the
+preceding chapters as older than the Eocene, no bones of any
+land-quadruped, or of any cetacean, had been discovered until the
+<i>Spalacotherium</i> of the Purbeck beds came to light in 1854.
+Yet we have seen that terrestrial plants were not wanting in the
+Upper Cretaceous formation (see <a href="#page302">p.
+302</a>), and that in the Wealden there was evidence of fresh-water
+sediment on a large scale, containing various plants, and even
+ancient vegetable soils. We had also in the same Wealden many
+land-reptiles and winged insects, which render the absence of
+terrestrial quadrupeds the more striking. The want, however, of any
+bones of whales, seals, dolphins, and other aquatic mammalia,
+whether in the chalk or in the upper or middle oolite, is certainly
+still more remarkable.</p>
+
+<p>These observations are made to prepare the reader to appreciate
+more justly the interest felt by every geologist in the discovery
+in the Stonesfield slate of no less than ten specimens of lower
+jaws of mammiferous quadrupeds, belonging to four different species
+and to three distinct genera, for which the names of <i>
+Amphitherium, Phascolotherium,</i> and <i>Stereognathus</i> have
+been adopted.</p>
+
+<img src="images/fig339.jpg" width="218" height="122" alt=
+"Fig. 339: Tupaia Tana. Right ramus of lower jaw." />
+
+<p>
+It is now generally admitted that these or really the remains of mammalia
+(although it was at first suggested that they might be reptiles), and the only
+question open to controversy is limited to this point, whether the fossil
+mammalia found in the Lower Oolite <a name="page347"></a>of Oxfordshire ought
+to be referred to the marsupial quadrupeds, or to the ordinary placental
+series. Cuvier had long ago pointed out a peculiarity in the form of the
+angular process (<i>c,</i> Figs. 342 and 343) of the lower jaw, as a character
+of the genus <i>Didelphys</i>; and Professor Owen has since confirmed the
+doctrine of its generality in the entire marsupial series. In all these pouched
+quadrupeds this process is turned inward, as at <i>c, d,</i> Fig. 342, in the
+Brazilian opossum, whereas in the placental series, as at <i>c,</i> Figs. 340
+and 341, there is an almost entire absence of such inflection. The <i>Tupaia
+Tana</i> of Sumatra has been selected by Mr. Waterhouse for this illustration,
+because the jaws of that small insectivorous quadruped bear a great resemblance
+to those of the Stonesfield <i>Amphitherium.</i> By clearing away the matrix
+from the specimen of <i>Amphitherium Prevostii</i> here represented (Fig. 344),
+Professor Owen ascertained that the angular process (<i>c</i>) bent inward in a
+slighter degree than in any of the known marsupialia; in short, the inflection
+does not exceed that of the mole or hedgehog. This fact made him doubt whether
+<a name="page348"></a>the <i>Amphitherium</i> might not be an insectivorous
+placental, although it offered some points of approximation in its osteology to
+the marsupials, especially to the <i>Myrmecobius,</i> a small insectivorous
+quadruped of Australia, which has nine molars on each side of the lower jaw,
+besides a canine and three incisors.<a href="#fn-19.6" name="fnref-19.6"
+id="fnref-19.6"><sup>[6]</sup></a> Another species of <i>Amphitherium</i> has
+been found at Stonesfield (Fig. 345), which differs from the former (Fig. 344)
+principally in being larger.
+</p>
+
+<p><img src="images/fig340.jpg" width="408" height="231" alt=
+"Fig. 340: Part of lower jaw of Tupaia Tana. Fig. 341: Side view of same. Fig.
+342: Part of lower jaw of Didelphys Azaræ. Fig. 343: Side view of same. Fig.
+344: Amphitherium Prevostii." />
+</p>
+
+<p><img src="images/fig344.jpg" width="374" height="179" alt=
+"Fig. 344: Amphitherium Prevostii." /></p>
+
+<p><img src="images/fig345.jpg" width="375" height="126" alt=
+"Fig. 345: Amphitherium Broderipii. Fig. 346: Phascolotherium Bucklandii." />
+</p>
+
+<p>
+The second mammiferous genus discovered in the same slates was named originally
+by Mr. Broderip <i>Didelphys Bucklandi</i> (see Fig. 346), and has since been
+called <i>Phascolotherium</i> by Owen. It manifests a much stronger likeness to
+the marsupials in the general form of the jaw, and in the extent and position
+of its inflected angle, while the agreement with the living genus Didelphys in
+the number of the pre-molar and molar teeth is complete.<a href="#fn-19.7"
+name="fnref-19.7" id="fnref-19.7"><sup>[7]</sup></a>
+</p>
+
+<p>In 1854 the remains of another mammifer, small in size, but
+larger than any of those previously known, was brought to light.
+The generic name of <i>Stereognathus</i> was given to it, and, as
+is usually the case in these old rocks (see <a href="#page328">p.
+328</a>), it consisted of part of a lower jaw, in which were
+implanted three double-fanged teeth, differing in structure from
+those of all other known recent or extinct mammals.</p>
+
+<p><b>Plants of the Oolite.</b>&mdash;The Araucarian pines, which
+are now abundant in Australia and its islands, together with
+marsupial quadrupeds, are found in like manner to have accompanied
+the marsupials in Europe during the Oolitic period (see <a href=
+"images/fig347.jpg">Fig. 348</a>). In the same rock endogens of
+the most perfect structure are met with, as, for example, fruits
+allied to the Pandanus, such as the <i>Kaidacarpum ooliticum</i> of
+Carruthers in the Great Oolite, and the <i>Podocarya</i> of
+Buckland (see <a href="images/fig347.jpg">Fig. 347</a>) in the
+Inferior Oolite.</p>
+
+<p><b>Fuller&rsquo;s Earth.</b>&mdash;Between the Great and
+Inferior Oolite near Bath, an argillaceous deposit, called
+&ldquo;the fuller&rsquo;s earth,&rdquo;
+<a name="page349"></a>occurs; but it is wanting in the north of England. It abounds in
+the small oyster represented in Fig. 349. The number of mollusca
+known in this deposit is about seventy; namely, fifty
+Lamellibranchiate Bivalves, ten Brachiopods, three Gasteropods, and
+seven or eight Cephalopods.</p>
+
+<p><img src="images/fig347.jpg" width="410" height="272" alt=
+"Fig. 347: Portion of a fossil fruit of Podocarya Bucklandii. Fig. 348: Cone of
+fossil Araucaria sphærocarpa." />
+</p>
+
+<img src="images/fig349.jpg" width="97" height="114" alt=
+"Fig. 349: Ostrea acuminata." />
+
+<p><b>Inferior Oolite.</b>&mdash;This formation consists of a
+calcareous freestone, usually of small thickness, but attaining in
+some places, as in the typical area of Cheltenham and the Western
+Cotswolds, a thickness of 250 feet. It sometimes rests upon yellow
+sands, formerly classed as the sands of the Inferior Oolite, but
+now regarded as a member of the Upper Lias. These sands repose upon
+the Upper Lias clays in the south and west of England. The
+Collyweston slate, formerly classed with the Great Oolite, and
+supposed to represent in Northamptonshire the Stonesfield slate, is
+now found to belong to the Inferior Oolite, both by community of
+species and position in the series. The Collyweston beds, on the
+whole, assume a much more marine character than the Stonesfield
+slate. Nevertheless, one of the fossil plants <i>Aroides
+Stutterdi,</i> Carruthers, remarkable, like the Pandanaceous
+species before mentioned (Fig. 347) as a representative of the
+monocotyledonous class, is common to the Stonesfield beds in
+Oxfordshire.</p>
+
+<p>The Inferior Oolite of Yorkshire consists largely of shales and
+sandstones, which assume much the aspect of a true
+<a name="page350"></a>coal-field, thin seams of coal having actually been worked in
+them for more than a century. A rich harvest of fossil ferns has
+been obtained from them, as at Gristhorpe, near Scarborough (Fig.
+350). They contain also Cycadeæ, of which family a
+magnificent specimen has been described by Mr. Williamson under the
+name Zamia gigas, and a fossil called <i>Equisetum Columnare</i>
+(see <a href="images/fig397.jpg">Fig. 397</a>), which maintains an
+upright position in sandstone strata over a wide area. Shells of
+<i>Estheria</i> and <i>Unio,</i> collected by Mr. Bean from these
+Yorkshire coal-bearing beds, point to the estuary or fluviatile
+origin of the deposit.</p>
+
+<img src="images/fig350.jpg" width="258" height="186" alt=
+"Fig. 350: Hemitelites Brownii." />
+
+<p>At Brora, in Sutherlandshire, a coal formation, probably coeval
+with the above, or at least belonging to some of the lower
+divisions of the Oolitic period, has been mined extensively for a
+century or more. It affords the thickest stratum of pure vegetable
+matter hitherto detected in any secondary rock in England. One seam
+of coal of good quality has been worked three and a half feet
+thick, and there are several feet more of pyritous coal resting
+upon it.</p>
+
+<p><img src="images/fig351.jpg" width="396" height="167" alt=
+"Fig. 351: Terebratula fimbria. Fig. 352: Rhynchonella spinosa. Fig. 353: Pholadomya fidicula." />
+</p>
+
+<p>Among the characteristic shells of the Inferior Oolite, I may
+instance <i>Terebratula fimbria</i> (Fig. 351), <i>Rhynchonella
+spinosa</i> (Fig. 352), and <i>Pholadomya fidicula</i> (Fig. 353).
+The extinct genus <i>Pleurotomaria</i> is also a form very common
+in this division as well as in the Oolitic system generally. It
+resembles the <i>Trochus</i> in form, but is marked by a deep cleft
+(<i>a,</i> Figs. 354, 355) on one side of the mouth. The
+<a name="page351"></a><i>Collyrites (Dysaster) ringens</i> (Fig. 356) is an Echinoderm
+common to the Inferior Oolite of England and France, as are the two
+Ammonites (Figs. 357, 358).</p>
+
+<p><img src="images/fig354.jpg" width="428" height="604" alt=
+"Fig. 354: Pleurotomaria granulata. Fig. 355: Pleurotomaria ornata. Fig. 356:
+Collyrites (Dysaster) ringens. Fig. 357: Ammonites Humphresianus. Fig. 358:
+Ammonites Braikenridgii. Fig. 359: Ostrea Marshii." />
+</p>
+
+<p><b>Palæontological Relations of the Oolitic
+Strata.</b>&mdash;Observations have already been made on the
+distinctness of the organic remains of the Oolitic and Cretaceous
+strata, and
+<a name="page352"></a>the proportion of species common to the different members of the
+Oolite. Between the Lower Oolite and the Lias there is a somewhat
+greater break, for out of 256 mollusca of the Upper Lias,
+thirty-seven species only pass up into the Inferior Oolite.</p>
+
+<img src="images/fig360.jpg" width="144" height="163" alt=
+"Fig. 360: Ammonites macrocephalus." />
+
+<p>In illustration of shells having a great vertical range, it may
+be stated that in England some few species pass up from the Lower
+to the Upper Oolite, as, for example, <i>Rhynchonella obsoleta,
+Lithodomus inclusus, Pholadomya ovalis,</i> and <i>Trigonia
+costata.</i></p>
+
+<p>Of all the Jurassic Ammonites of Great Britain, <i>A.
+macrocephalus</i> (Fig. 360), which is common to the Great Oolite
+and Oxford Clay, has the widest range.</p>
+
+<p>We have every reason to conclude that the gaps which occur, both
+between the larger and smaller sections of the English Oolites,
+imply intervals of time, elsewhere represented by fossiliferous
+strata, although no deposit may have taken place in the British
+area. This conclusion is warranted by the partial extent of many of
+the minor and some of the larger divisions even in England.
+</p>
+
+<p class="footnote">
+<a name="fn-19.1" id="fn-19.1"></a> <a href="#fnref-19.1">[1]</a>
+Elements of Geology, 4th edition.
+</p>
+
+<p class="footnote">
+<a name="fn-19.2" id="fn-19.2"></a> <a href="#fnref-19.2">[2]</a>
+I allude to several Zeuglodons found in Alabama, and referred by some
+zoologists to three species.
+</p>
+
+<p class="footnote">
+<a name="fn-19.3" id="fn-19.3"></a> <a href="#fnref-19.3">[3]</a>
+See Phil. Trans. 1850, p. 363; also Huxley, Memoirs of Geol. Survey, 1864;
+Phillips, Palæont. Soc.
+</p>
+
+<p class="footnote">
+<a name="fn-19.4" id="fn-19.4"></a> <a href="#fnref-19.4">[4]</a>
+P. Scrope, Proc. Geol. Soc., March, 1831.
+</p>
+
+<p class="footnote">
+<a name="fn-19.5" id="fn-19.5"></a> <a href="#fnref-19.5">[5]</a>
+Proceedings Geol. Soc., vol. i, p. 414.
+</p>
+
+<p class="footnote">
+<a name="fn-19.6" id="fn-19.6"></a> <a href="#fnref-19.6">[6]</a>
+A figure of this recent <i>Myrmecobius</i> will be found in my Principles of
+Geology, chap. ix.
+</p>
+
+<p class="footnote">
+<a name="fn-19.7" id="fn-19.7"></a> <a href="#fnref-19.7">[7]</a>
+Owen&rsquo;s British Fossil Mammals, p. 62.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap20"></a><a name="page353"></a>CHAPTER XX.<br/>
+JURASSIC GROUP&mdash;<i>continued</i>&mdash;LIAS.</h2>
+
+<p class="letter">Mineral Character of Lias. &mdash; Numerous
+successive Zones in the Lias, marked by distinct Fossils, without
+Unconformity in the Stratification, or Change in the Mineral
+Character of the Deposits. &mdash; Gryphite Limestone. &mdash;
+Shells of the Lias. &mdash; Fish of the Lias. &mdash; Reptiles of
+the Lias. &mdash; Ichthyosaur and Plesiosaur. &mdash; Marine
+Reptile of the Galapagos Islands. &mdash; Sudden Destruction and
+Burial of Fossil Animals in Lias. &mdash; Fluvio-marine Beds in
+Gloucestershire, and Insect Limestone. &mdash; Fossil Plants.
+&mdash; The origin of the Oolite and Lias, and of alternating
+Calcareous and Argillaceous Formations.</p>
+
+<p><b>Lias.</b>&mdash;The English provincial name of Lias has been
+very generally adopted for a formation of argillaceous limestone,
+marl, and clay, which forms the base of the Oolite, and is classed
+by many geologists as part of that group. The peculiar aspect which
+is most characteristic of the Lias in England, France, and Germany,
+is an alternation of thin beds of blue or grey limestone, having a
+surface which becomes light-brown when weathered, these beds being
+separated by dark-coloured, narrow argillaceous partings, so that
+the quarries of this rock, at a distance, assume a striped and
+ribbon-like appearance.</p>
+
+<p>The Lias has been divided in England into three groups, the
+Upper, Middle, and Lower. The Upper Lias consists first of sands,
+which were formerly regarded as the base of the Oolite, but which,
+according to Dr. Wright, are by their fossils more properly
+referable to the Lias; secondly, of clay shale and thin beds of
+limestone. The Middle Lias, or marl-stone series, has been divided
+into three zones; and the Lower Lias, according to the labours of
+Quenstedt, Oppel, Strickland, Wright, and others, into seven zones,
+each marked by its own group of fossils. This Lower Lias averages
+from 600 to 900 feet in thickness.</p>
+
+<p>From Devon and Dorsetshire to Yorkshire all these divisions,
+observes Professor Ramsay, are constant; and from top to bottom we
+cannot assert that anywhere there is actual unconformity between
+any two subdivisions, whether of the larger or smaller kind.</p>
+
+<p>In the whole of the English Lias there are at present known
+about 937 species of mollusca, and of these 267 are Cephalopods, of
+which class more than two-thirds are Ammonites,
+<a name="page354"></a>the Nautilus and Belemnite also abounding. The whole series has
+been divided by zones characterised by particular Ammonites; for
+while other families of shells pass from one division to another in
+numbers varying from about 20 to 50 per cent, these cephalopods are
+almost always limited to single zones, as Quenstedt and Oppel have
+shown for Germany, and Dr. Wright and others for England.</p>
+
+<p>As no actual unconformity is known from the top of the Upper to
+the bottom of the Lower Lias, and as there is a marked uniformity
+in the mineral character of almost all the strata, it is somewhat
+difficult to account even for such partial breaks as have been
+alluded to in the succession of species, if we reject the
+hypothesis that the old species were in each case destroyed at the
+close of the deposition of the rocks containing them, and replaced
+by the creation of new forms when the succeeding formation began. I
+agree with Professor Ramsay in not accepting this hypothesis. No
+doubt some of the old species occasionally died out, and left no
+representatives in Europe or elsewhere; others were locally
+exterminated in the struggle for life by species which invaded
+their ancient domain, or by varieties better fitted for a new state
+of things. Pauses also of vast duration may have occurred in the
+deposition of strata, allowing time for the modification of organic
+life throughout the globe, slowly brought about by variation
+accompanied by extinction of the original forms.</p>
+
+<p><img src="images/fig361.jpg" width="412" height="251" alt=
+"Fig. 361: Plagiostoma (Lima) giganteum. Fig. 362: Gryphæa incurva." />
+</p>
+
+<p><b>Fossils of the Lias.</b>&mdash;The name of Gryphite limestone
+has sometimes been applied to the Lias, in consequence of the great
+number of shells which it contains of a species of oyster, or <i>
+Gryphæa</i> (Fig. 362). A large heavy shell called
+<a name="page355"></a><i>Hippopodium</i> (Fig. 365), allied to <i>Cypricardia,</i> is
+also characteristic of the upper part of the Lower Lias. In this
+formation occur also the Aviculas, Figs. 363 and 364. The Lias
+formation is also remarkable for being the newest of the secondary
+rocks in which brachiopoda of the genera <i>Spirifer</i> and <i>
+Leptæna</i> (Figs. 366, 367) occur, although the former is
+slightly modified in structure so as to constitute the subgenus
+Spiriferina, Davidson, and the Leptæna has dwindled to a
+shell smaller in size than a pea. No less than eight or nine
+species of Spiriferina are enumerated by Mr. Davidson as belonging
+to the Lias. Palliobranchiate mollusca predominate greatly in
+<a name="page356"></a>strata older than the Trias; but, so far as we yet know, they
+did not survive the Liassic epoch.</p>
+
+<p><img src="images/fig363.jpg" width="433" height="495" alt=
+"Fig. 363: Avicula inæquivalvis. Fig. 364: Avicula cygnipes. Fig. 365:
+Hippopodium ponderosum. Fig. 366: Spiriferina (Spirifera). Fig. 367: Leptæna Moorei." />
+</p>
+
+<p><img src="images/fig368.jpg" width="412" height="492" alt=
+"Fig. 368: Ammonites Bucklandi. Fig. 369: Ammonites planorbis. Fig. 370:
+Nautilus truncatus. Fig. 371: Ammonites bifrons." />
+</p>
+
+<p>
+Allusion has already been made, p. 354, to numerous zones in the Lias having
+each their peculiar Ammonites. Two of these occur near the base of the Lower
+Lias, having a united thickness, varying from 40 to 80 feet. The upper of these
+is characterised by <i>Ammonites Bucklandi,</i> and the lower by <i>Ammonites
+planorbis</i> (see Figs. 368, 369).<a href="#fn-20.1" name="fnref-20.1"
+id="fnref-20.1"><sup>[1]</sup></a> Sometimes, however, there is a third
+intermediate zone, that of <i>Ammonites angulatus,</i> which is the equivalent
+of the zone called the infra-lias on the Continent, the species of which are
+for the <a name="page357"></a>most part common to the superior group marked by
+<i>Ammonites Bucklandi.</i>
+</p>
+
+<img src="images/fig372.jpg" width="238" height="194" alt=
+"Fig. 372: Ammonites margaritatus." />
+
+<p>Among the Crinoids or Stone-lilies of the Lias, the
+Pentacrinites are conspicuous. (See Fig. 373.) Of <i>
+Palæocoma (Ophioderma) Egertoni</i> (Fig. 374), referable to
+the <i>Ophiuridæ</i> of Muller, perfect specimens have been
+met with in the Middle Lias beds of Dorset and Yorkshire.
+</p>
+
+<p><img src="images/fig373.jpg" width="407" height="350" alt=
+"Fig. 373: Extracrinus (Pentacrinus) Briareus. Fig. 374: Palæocoma (Ophioderma) tenuibrachiata." />
+</p>
+
+<p>The <i>Extracrinus Briareus</i> (removed by Major Austin from
+Pentacrinus on account of generic differences) occurs in tangled
+masses, forming thin beds of considerable extent, in the Lower Lias
+of Dorset, Gloucestershire, and Yorkshire. The remains are often
+highly charged with pyrites. This Crinoid, with its innumerable
+tentacular arms, appears to have been frequently attached to the
+driftwood of the liassic sea, in the same manner as Barnacles float
+about on wood at the present day. There is another species of <i>
+Extracrinus</i> and several of
+<a name="page358"></a><i>Pentacrinus</i> in the Lias; and the latter genus is found in
+nearly all the formations from the Lias to the London Clay
+inclusive. It is represented in the present seas by the delicate
+and rare <i>Pentacrinus caput-medusæ</i> of the Antilles,
+which, with Comatula, is one of the few surviving members of the
+ancient family of the Crinoids, represented by so many extinct
+genera in the older formations.</p>
+
+<p><img src="images/fig375.jpg" width="434" height="366" alt=
+"Fig. 375: Scales of Lepidotus gigas. Fig. 376: a. Scales of Æchmodus Leachii,
+b. Æchmodus (restored outline), c. Scales of Dapedius monilifer." />
+</p>
+
+<p>
+<b>Fishes of the Lias.</b>&mdash;The fossil fish, of which there are no less
+than 117 species known as British, resemble generically those of the Oolite,
+but differ, according to M. Agassiz, from those of the Cretaceous period. Among
+them is a species of <i> Lepidotus</i> (<i>L. gigas,</i> Agassiz), Fig. 375,
+which is found in the Lias of England, France, and Germany.<a href="#fn-20.2"
+name="fnref-20.2" id="fnref-20.2"><sup>[2]</sup></a> This genus was before
+mentioned (<a href="#page316">p. 316</a>) as occurring in the Wealden, and is
+supposed to have frequented both rivers and sea-coasts. Another genus of
+Ganoids (or fish with hard, shining, and enamelled scales), called
+<i>Æchmodus</i> (Fig. 376), is almost exclusively Liassic. The teeth of a
+species of <i> Acrodus,</i> also, are very abundant in the Lias (Fig. 377). <a
+name="page359"></a>
+</p>
+
+<p><img src="images/fig377.jpg" width="353" height="310" alt=
+"Fig. 377: Acrodus nobilis. Fig. 378: Hybodus reticulatus, a. Part of fin,
+commonly called Ichthyodorylite, b. Tooth." />
+</p>
+
+<p>But the remains of fish which have excited more attention than
+any others are those large bony spines called ichthyodorulites (a,
+Figure 378), which were once supposed by some naturalists to be
+jaws, and by others weapons, resembling those of the living
+Balistes and Silurus; but which M. Agassiz has shown to be neither
+the one nor the other. The spines, in the genera last mentioned,
+articulate with the backbone, whereas there are no signs of any
+such articulation in the ichthyodorulites.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig379.jpg" width="248" height="175" alt="Fig. 379: Chimæra
+monstrosa." />
+<p class="caption">Fig. 379: Chimæra monstrosa.<a href="#fn-20.3"
+name="fnref-20.3" id="fnref-20.3"><sup>[3]</sup></a><br/></p>
+</div>
+
+<p>
+These last appear to have been bony spines which formed the anterior part of
+the dorsal fin, like that of the living genera <i> Cestracion</i> and
+<i>Chimæra</i> (see <i>a,</i> Figure 379). In both of these genera, the
+posterior concave face is armed with small spines, as in that of the fossil
+<i>Hybodus</i> (Fig. 378), a placoid fish of the shark family found fossil at
+Lyme Regis. Such spines are simply imbedded in the flesh, and attached to
+strong muscles. &ldquo;They serve,&rdquo; says Dr. Buckland, &ldquo;as in the
+<i>Chimæra</i> (Fig. 379), to raise and depress the fin, their action <a
+name="page360"></a>resembling that of a movable mast, raising and lowering
+backward the sail of a barge.&rdquo;<a href="#fn-20.4" name="fnref-20.4"
+id="fnref-20.4"><sup>[4]</sup></a>
+</p>
+
+<p><b>Reptiles of the Lias.</b>&mdash;It is not, however, the
+fossil fish which form the most striking feature in the organic
+remains of the Lias; but the <i>Enaliosaurian</i> reptiles, which
+are extraordinary for their number, size, and structure. Among the
+most singular of these are several species of <i>Ichthyosaurus</i>
+and <i>Plesiosaurus</i> (Figs. 380, 381). The genus <i>
+Ichthyosaurus,</i> or fish-lizard, is not confined to this
+formation, but has been found in strata as high as the White Chalk
+of England, and as low as the Trias of Germany, a formation which
+immediately succeeds the Lias in the descending order. It is
+evident from their fish-like vertebræ, their paddles,
+resembling those of a porpoise or whale, the length of their tail,
+and other parts of their structure, that the Ichthyosaurs were
+aquatic. Their jaws and teeth show that they were carnivorous; and
+the half-digested remains of fishes and reptiles, found within
+their skeletons, indicate the precise nature of their food.</p>
+
+<p>
+Mr. Conybeare was enabled, in 1824, after examining many skeletons nearly
+perfect, to give an ideal restoration of the osteology of this genus, and of
+that of the <i> Plesiosaurus.</i><a href="#fn-20.5" name="fnref-20.5"
+id="fnref-20.5"><sup>[5]</sup></a> (See Figs. 380, 381.) The latter animal had
+an extremely long neck and small head, with teeth like those of the crocodile,
+and paddles analogous to those of the <i> Ichthyosaurus,</i> but larger. It is
+supposed to have lived in shallow seas and estuaries, and to have breathed air
+like the Ichthyosaur and our modern cetacea.<a href="#fn-20.6"
+name="fnref-20.6" id="fnref-20.6"><sup>[6]</sup></a> Some of the reptiles above
+mentioned were of formidable dimensions. One specimen of <i> Ichthyosaurus
+platydon,</i> from the Lias at Lyme, now in the British Museum, must have
+belonged to an animal more than 24 feet in length; and there are species of
+<i>Plesiosaurus</i> which measure from 18 to 20 feet in length. The form of the
+<i> Ichthyosaurus</i> may have fitted it to cut through the waves like the
+porpoise; as it was furnished besides its paddles with a tail-fin so
+constructed as to be a powerful organ of motion; but it is supposed that the
+<i>Plesiosaurus,</i> at least the long-necked species (Fig. 381), was better
+suited to fish in shallow creeks and bays defended from heavy breakers.
+</p>
+
+<p>
+It is now very generally agreed that these extinct saurians must have inhabited
+the sea; and it was urged that as there are now chelonians, like the tortoise,
+living in fresh water, <a name="page361"></a>and others, as the turtle,
+frequenting the ocean, so there may have been formerly some saurians proper to
+salt, others to fresh water. The common crocodile of the Ganges is well-known
+to frequent equally that river and the brackish and salt water near its mouth;
+and crocodiles are said in like manner to be abundant both in the rivers of the
+Isla de <a name="page362"></a>Pinos (Isle of Pines), south of Cuba, and in the
+open sea round the coast. In 1835 a curious lizard (<i>Amblyrhynchus
+cristatus</i>) was discovered by Mr. Darwin in the Galapagos Islands.<a
+href="#fn-20.7" name="fnref-20.7" id="fnref-20.7"><sup>[7]</sup></a> It was
+found to be exclusively marine, swimming easily by means of its flattened tail,
+and subsisting chiefly on seaweed. One of them was sunk from the ship by a
+heavy weight, and on being drawn up after an hour was quite unharmed.
+</p>
+
+<p><img src="images/fig380.jpg" width="593" height="371" alt=
+"Fig. 380: Skeleton of Ichthyosaurus communis, restored by Conybeare and
+Cuvier. Fig. 381: Skeleton of Plesiosaurus dolichodeirus, restored by Rev.
+W. D. Conybeare." />
+</p>
+
+<p>The families of Dinosauria, crocodiles, and Pterosauria or
+winged reptiles, are also represented in the Lias.</p>
+
+<p><b>Sudden Destruction of Saurians.</b>&mdash;It has been
+remarked, and truly, that many of the fish and saurians, found
+fossil in the Lias, must have met with sudden death and immediate
+burial; and that the destructive operation, whatever may have been
+its nature, was often repeated.</p>
+
+<p>
+&ldquo;Sometimes,&rdquo; says Dr. Buckland, &ldquo;scarcely a single bone or
+scale has been removed from the place it occupied during life; which could not
+have happened had the uncovered bodies of these saurians been left, even for a
+few hours, exposed to putrefaction, and to the attacks of fishes and other
+smaller animals at the bottom of the sea.&rdquo;<a href="#fn-20.8"
+name="fnref-20.8" id="fnref-20.8"><sup>[8]</sup></a> Not only are the skeletons
+of the Ichthyosaurs entire, but sometimes the contents of their stomachs still
+remain between their ribs, as before remarked, so that we can discover the
+particular species of fish on which they lived, and the form of their
+excrements. Not unfrequently there are layers of these coprolites, at different
+depths in the Lias, at a distance from any entire skeletons of the marine
+lizards from which they were derived; &ldquo;as if,&rdquo; says Sir H. De la
+Beche, &ldquo;the muddy bottom of the sea received small sudden accessions of
+matter from time to time, covering up the coprolites and other exuviæ which had
+accumulated during the intervals.&rdquo;<a href="#fn-20.9" name="fnref-20.9"
+id="fnref-20.9"><sup>[9]</sup></a> It is further stated that, at Lyme Regis,
+those surfaces only of the coprolites which lay uppermost at the bottom of the
+sea have suffered partial decay, from the action of water before they were
+covered and protected by the muddy sediment that has afterwards permanently
+enveloped them.
+</p>
+
+<p>
+Numerous specimens of the Calamary or pen-and-ink fish, (<i>Geoteuthis
+bollensis</i>) have also been met with in the Lias at Lyme, with the ink-bags
+still distended, containing the ink in a dried state, chiefly composed of
+carbon, and but slightly impregnated with carbonate of lime. These Cephalopoda,
+therefore, must, like the saurians, have been soon buried in <a
+name="page363"></a>sediment; for, if long exposed after death, the membrane
+containing the ink would have decayed.<a href="#fn-20.10" name="fnref-20.10"
+id="fnref-20.10"><sup>[10]</sup></a>
+</p>
+
+<p>As we know that river-fish are sometimes stifled, even in their
+own element, by muddy water during floods, it cannot be doubted
+that the periodical discharge of large bodies of turbid fresh water
+in the sea may be still more fatal to marine tribes. In the
+&ldquo;Principles of Geology&rdquo; I have shown that large
+quantities of mud and drowned animals have been swept down into the
+sea by rivers during earthquakes, as in Java in 1699; and that
+indescribable multitudes of dead fishes have been seen floating on
+the sea after a discharge of noxious vapours during similar
+convulsions. But in the intervals between such catastrophes, strata
+may have accumulated slowly in the sea of the Lias, some being
+formed chiefly of one description of shell, such as ammonites,
+others of gryphites.</p>
+
+<img src="images/fig382.jpg" width="181" height="124" alt=
+"Fig. 382: Wing of a neuropterous insect." />
+
+<p>
+<b>Fresh-water Deposits.&mdash;Insect-beds.</b>&mdash;From the above remarks
+the reader will infer that the Lias is for the most part a marine deposit. Some
+members, however, of the series have an estuarine character, and must have been
+formed within the influence of rivers. At the base of the Upper and Lower Lias
+respectively, insect-beds appear to be almost everywhere present throughout the
+Midland and South-western districts of England. These beds are crowded with the
+remains of insects, small fish, and crustaceans, with occasional marine shells.
+One band in Gloucestershire, rarely exceeding a foot in thickness, has been
+named the &ldquo;insect limestone.&rdquo; It passes upward, says the Reverend
+P. B. Brodie,<a href="#fn-20.11" name="fnref-20.11"
+id="fnref-20.11"><sup>[11]</sup></a> into a shale containing <i>Cypris</i> and
+<i> Estheria,</i> and is full of the wing-cases of several genera of
+Coleoptera, with some nearly entire beetles, of which the eyes are preserved.
+The nervures of the wings of neuropterous insects (Figure 382) are beautifully
+perfect in this bed. Ferns, with Cycads and leaves of monocotyledonous plants,
+and some apparently brackish and fresh-water shells, accompany the insects in
+several places, while in others marine shells predominate, the fossils varying
+apparently as we examine the bed nearer or farther from the ancient land, or
+the source whence the fresh water was derived. After studying 300 specimens of
+these insects from the Lias, Mr. Westwood declares that they comprise both <a
+name="page364"></a>wood-eating and herb-devouring beetles, of the Linnean
+genera <i>Elater, Carabus,</i> etc., besides grasshoppers (<i>Gryllus</i>), and
+detached wings of dragon-flies and may-flies, or insects referable to the
+Linnean genera <i>Libellula, Ephemera, Hemerobius,</i> and <i>Panorpa,</i> in
+all belonging to no less than twenty-four families. The size of the species is
+usually small, and such as taken alone would imply a temperate climate; but
+many of the associated organic remains of other classes must lead to a
+different conclusion.
+</p>
+
+<p>
+<b>Fossil Plants.</b>&mdash;Among the vegetable remains of the Lias, several
+species of <i>Zamia</i> have been found at Lyme Regis, and the remains of
+coniferous plants at Whitby. M. Ad. Brongniart enumerates forty-seven liassic
+acrogens, most of them ferns; and fifty gymnosperms, of which thirty-nine are
+cycads, and eleven conifers. Among the cycads the predominance of <i>
+Zamites,</i> and among the ferns the numerous genera with leaves having
+reticulated veins (as in <a href="images/fig349.jpg">Fig. 349</a>), are
+mentioned as botanical characteristics of this era.<a href="#fn-20.12"
+name="fnref-20.12" id="fnref-20.12"><sup>[12]</sup></a> The absence as yet from
+the Lias and Oolite of all signs of dicotyledonous angiosperms is worthy of
+notice. The leaves of such plants are frequent in tertiary strata, and occur in
+the Cretaceous, though less plentifully (see <a href= "#page303">p. 303</a>).
+The angiosperms seem, therefore, to have been at the least comparatively rare
+in these older secondary periods, when more space was occupied by the Cycads
+and Conifers.
+</p>
+
+<p>
+<b>Origin of the Oolite and Lias.</b>&mdash;The entire group of Oolite and Lias
+consists of repeated alternations of clay, sandstone, and limestone, following
+each other in the same order. Thus the clays of the Lias are followed by the
+sands now considered (see <a href="#page353">p. 353</a>) as belonging to the
+same formation, though formerly referred to the Inferior Oolite, and these
+sands again by the shelly and coralline limestone called the Great or Bath
+Oolite. So, in the Middle Oolite, the Oxford Clay is followed by calcareous
+grit and coral rag; lastly, in the Upper Oolite, the Kimmeridge Clay is
+followed by the Portland Sand and limestone (see <a
+href="images/fig298.jpg">Fig. 298</a>).<a href="#fn-20.13" name="fnref-20.13"
+id="fnref-20.13"><sup>[13]</sup></a> The clay beds, however, as Sir H. de la
+Beche remarks, can be followed over larger areas than the sand or sandstones.<a
+href="#fn-20.14" name="fnref-20.14" id="fnref-20.14"><sup>[14]</sup></a> It
+should also be remembered that while the Oolite system becomes arenaceous and
+resembles a coal-field in Yorkshire, it assumes in the Alps an almost purely
+calcareous form, the sands and clays being omitted; and even in the intervening
+tracts it is more complicated and variable than appears in ordinary
+descriptions. <a name="page365"></a>Nevertheless, some of the clays and
+intervening limestones do retain, in reality, a pretty uniform character for
+distances of from 400 to 600 miles from east to west and north to south.
+</p>
+
+<p>In order to account for such a succession of events, we may
+imagine, first, the bed of the ocean to be the receptacle for ages
+of fine argillaceous sediment, brought by oceanic currents, which
+may have communicated with rivers, or with part of the sea near a
+wasting coast. This mud ceases, at length, to be conveyed to the
+same region, either because the land which had previously suffered
+denudation is depressed and submerged, or because the current is
+deflected in another direction by the altered shape of the bed of
+the ocean and neighbouring dry land. By such changes the water
+becomes once more clear and fit for the growth of stony zoophytes.
+Calcareous sand is then formed from comminuted shell and coral, or,
+in some cases, arenaceous matter replaces the clay; because it
+commonly happens that the finer sediment, being first drifted
+farthest from coasts, is subsequently overspread by coarse sand,
+after the sea has grown shallower, or when the land, increasing in
+extent, whether by upheaval or by sediment filling up parts of the
+sea, has approached nearer to the spots first occupied by fine
+mud.</p>
+
+<p>The increased thickness of the limestones in those regions, as
+in the Alps and Jura, where the clays are comparatively thin,
+arises from the calcareous matter having been derived from species
+of corals and other organic beings which live in clear water, far
+from land, to the growth of which the influx of mud would be
+unfavourable. Portions therefore of these clays and limestones have
+probably been formed contemporaneously to a greater extent than we
+can generally prove, for the distinctness of the species of organic
+beings would be caused by the difference of conditions between the
+more littoral and the more pelagic areas and the different depths
+and nature of the sea-bottom. Independently of those ascending and
+descending movements which have given rise to the superposition of
+the limestones and clays, and by which the position of land and sea
+are made in the course of ages to vary, the geologist has the
+difficult task of allowing for the contemporaneous thinning out in
+one direction and thickening in another, of the successive organic
+and inorganic deposits of the same era.
+</p>
+
+<p class="footnote">
+<a name="fn-20.1" id="fn-20.1"></a> <a href="#fnref-20.1">[1]</a>
+Quart. Journ., vol. xvi, p. 376.
+</p>
+
+<p class="footnote">
+<a name="fn-20.2" id="fn-20.2"></a> <a href="#fnref-20.2">[2]</a>
+Agassiz, Poissons Fossiles, vol. ii, tab. 28, 29.
+</p>
+
+<p class="footnote">
+<a name="fn-20.3" id="fn-20.3"></a> <a href="#fnref-20.3">[3]</a>
+Agassiz, Poissons Fossiles, vol. iii, tab. C, Fig. 1.
+</p>
+
+<p class="footnote">
+<a name="fn-20.4" id="fn-20.4"></a> <a href="#fnref-20.4">[4]</a>
+Bridgewater Treatise, p. 290.
+</p>
+
+<p class="footnote">
+<a name="fn-20.5" id="fn-20.5"></a> <a href="#fnref-20.5">[5]</a>
+Geol. Soc. Transactions, Second Series, vol. i, p. 49.
+</p>
+
+<p class="footnote">
+<a name="fn-20.6" id="fn-20.6"></a> <a href="#fnref-20.6">[6]</a>
+Conybeare and De la Beche, Geol. Trans., First Series, vol. v, p. 559; and
+Buckland, Bridgewater Treatise, p. 203.
+</p>
+
+<p class="footnote">
+<a name="fn-20.7" id="fn-20.7"></a> <a href="#fnref-20.7">[7]</a>
+See Darwin, Naturalist&rsquo;s Voyage, p. 385. Murray.
+</p>
+
+<p class="footnote">
+<a name="fn-20.8" id="fn-20.8"></a> <a href="#fnref-20.8">[8]</a>
+Bridgewater Treatise, p. 115.
+</p>
+
+<p class="footnote">
+<a name="fn-20.9" id="fn-20.9"></a> <a href="#fnref-20.9">[9]</a>
+Geological Researches, p. 334.
+</p>
+
+<p class="footnote">
+<a name="fn-20.10" id="fn-20.10"></a> <a href="#fnref-20.10">[10]</a>
+Buckland, Bridgewater Treatise, p. 307.
+</p>
+
+<p class="footnote">
+<a name="fn-20.11" id="fn-20.11"></a> <a href="#fnref-20.11">[11]</a>
+A History of Fossil Insects, etc., 1846. London.
+</p>
+
+<p class="footnote">
+<a name="fn-20.12" id="fn-20.12"></a> <a href="#fnref-20.12">[12]</a>
+Tableau des Vég. Foss., 1849, p. 105.
+</p>
+
+<p class="footnote">
+<a name="fn-20.13" id="fn-20.13"></a> <a href="#fnref-20.13">[13]</a>
+Conybeare and Philips&rsquo;s Outlines, etc., p. 166.
+</p>
+
+<p class="footnote">
+<a name="fn-20.14" id="fn-20.14"></a> <a href="#fnref-20.14">[14]</a>
+Geological Researches, p. 337.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap21"></a><a name="page366"></a>CHAPTER XXI.<br/>
+TRIAS, OR NEW RED SANDSTONE GROUP.</h2>
+
+<p class="letter">Beds of Passage between the Lias and Trias,
+Rhætic Beds. &mdash; Triassic Mammifer. &mdash; Triple
+Division of the Trias. &mdash; Keuper, or Upper Trias of England.
+&mdash; Reptiles of the Upper Trias. &mdash; Foot-prints in the
+Bunter formation in England. &mdash; Dolomitic Conglomerate of
+Bristol. &mdash; Origin of Red Sandstone and Rock-salt. &mdash;
+Precipitation of Salt from inland Lakes and Lagoons. &mdash; Trias
+of Germany. &mdash; Keuper. &mdash; St. Cassian and Hallstadt Beds.
+&mdash; Peculiarity of their Fauna. &mdash; Muschelkalk and its
+Fossils. &mdash; Trias of the United States. &mdash; Fossil
+Foot-prints of Birds and Reptiles in the Valley of the Connecticut.
+&mdash; Triassic Mammifer of North Carolina. &mdash; Triassic
+Coal-field of Richmond, Virginia. &mdash; Low Grade of early
+Mammals favourable to the Theory of Progressive Development.</p>
+
+<p><b>Beds of Passage between the Lias and Trias&mdash;Rhætic
+Beds.</b>&mdash;We have mentioned in the last chapter (<a href=
+"#page356">p. 356</a>) that the base of the Lower Lias is
+characterised, both in England and Germany, by beds containing
+distinct species of Ammonites, the lowest subdivision having been
+called the zone of <i>Ammonites planorbis.</i> Below this zone, on
+the boundary line between the Lias and the strata of which we are
+about to treat, called &ldquo;Trias,&rdquo; certain cream-coloured
+limestones devoid of fossils are usually found. These white beds
+were called by William Smith the White Lias, and they have been
+shown by Mr. Charles Moore to belong to a formation similar to one
+in the Rhætian Alps of Bavaria, to which Mr. Gumbel has
+applied the name of Rhætic. They have also long been known as
+the Koessen beds in Germany, and may be regarded as beds of passage
+between the Lias and Trias. They are named the Penarth beds by the
+Government surveyors of Great Britain, from Penarth, near Cardiff,
+in Glamorganshire, where they sometimes attain a thickness of fifty
+feet.</p>
+
+<p>
+The principal member of this group has been called by Dr. Wright the <i>Avicula
+contorta</i> bed,<a href="#fn-21.1" name="fnref-21.1"
+id="fnref-21.1"><sup>[1]</sup></a> as this shell is very abundant, and has a
+wide range in Europe. General Portlock first described the formation as it
+occurs at Portrush, in Antrim, where the <i> Avicula contorta</i> is
+accompanied by <i>Pecten Valoniensis,</i> as in Germany.
+</p>
+
+<p>The best known member of the group, a thin band or bone-breccia,
+is conspicuous among the black shales in the neighbourhood
+<a name="page367"></a>of Axmouth in Devonshire, and in the cliffs of
+Westbury-on-Severn, as well as at Aust and other places on the
+borders of the Bristol Channel. It abounds in the remains of
+saurians and fish, and was formerly classed as the lowest bed of
+the Lias; but Sir P. Egerton first pointed out, in 1841, that it
+should be referred to the Upper New Red Sandstone, because it
+contained an assemblage of fossil fish which are either peculiar to
+this stratum, or belong to species well-known in the Muschelkalk of
+Germany. These fish belong to the genera <i>Acrodus, Hybodus,
+Gyrolepis,</i> and <i>Saurichthys.</i></p>
+
+<p><img src="images/fig383.jpg" width="407" height="410" alt=
+"Fig. 383: Cardium rhæticum. Fig. 384: Pecten Valoniensis. Fig. 385: Avicula
+contorta. Fig. 386: Hybodus plica ilis. Fig. 387: Saurichthys apicalis. Fig.
+388: Gyrolepsis tenuistriatus." />
+</p>
+
+<p>Among those common to the English bone-bed and the Muschelkalk
+of Germany are <i>Hybodus plicatilis</i> (Fig. 386), <i>Saurychthys
+apicalis</i> (Fig. 387), <i>Gyrolepis tenuistriatus</i> (Fig. 388),
+and <i>G. Albertii.</i> Remains of saurians, <i>Plesiosaurus</i>
+among others, have also been found in the bone-bed, and plates of
+an <i>Encrinus.</i> It may be questioned whether some of those
+fossils which have the most Triassic character may
+<a name="page368"></a>not have been derived from the destruction of older strata,
+since in bone-beds, in general, many of the organic remains are
+undoubtedly derivative.</p>
+
+<img src="images/fig389.jpg" width="246" height="158" alt=
+"Fig. 389: Microlestes antiquus, molar tooth." />
+
+<p><i>Triassic Mammifer.</i>&mdash;In North-western Germany, as in
+England, there occurs beneath the Lias a remarkable bone breccia.
+It is filled with shells and with the remains of fishes and
+reptiles, almost all the genera of which, and some even of the
+species, agree with those of the subjacent Trias. This breccia has
+accordingly been considered by Professor Quenstedt, and other
+German geologists of high authority, as the newest or uppermost
+part of the Trias. Professor Plieninger found in it, in 1847, the
+molar tooth of a small Triassic mammifer, called by him <i>
+Microlestes antiquus.</i> He inferred its true nature from its
+double fangs, and from the form and number of the protuberances or
+cusps on the flat crown; and considering it as predaceous, probably
+insectivorous, he called it <i>Microlestes</i> from micros, little,
+and lestes, a beast of prey. Soon afterwards he found a second
+tooth, also at the same locality, Diegerloch, about two miles to
+the south-east of Stuttgart.</p>
+
+<p>No anatomist had been able to give any feasible conjecture as to
+the affinities of this minute quadruped until Dr. Falconer, in
+1857, recognised an unmistakable resemblance between its teeth and
+the two back molars of his new genus <i>Plagiaulax</i> (<a href=
+"images/fig306.jpg">Fig. 306</a>), from the Purbeck strata. This
+would lead us to the conclusion that Microlestes was marsupial and
+plant-eating.</p>
+
+<p>In Würtemberg there are two bone-beds, namely, that
+containing the Microlestes, which has just been described, which
+constitutes, as we have seen, the uppermost member of the Trias,
+and another of still greater extent, and still more rich in the
+remains of fish and reptiles, which is of older date, intervening
+between the Keuper and Muschelkalk.</p>
+
+<p>The genera <i>Saurichthys, Hybodus,</i> and <i>Gyrolepis</i> are
+found in both these breccias, and one of the species, <i>
+Saurichthys Mongeoti,</i> is common to both bone-beds, as is also a
+remarkable reptile called <i>Nothosaurus mirabilis.</i> The saurian
+called <i>Belodon</i> by H. von Meyer, of the Thecodont family, is
+another Triassic form, associated at Diegerloch with
+Microlestes.</p>
+
+<p class="center">
+<a name="page369"></a><small>TRIAS OF ENGLAND.</small>
+</p>
+
+<p>Between the Lias and the Coal (or Carboniferous group) there is
+interposed, in the midland and western counties of England, a great
+series of red loams, shales, and sandstones, to which the name of
+the &ldquo;New Red Sandstone formation&rdquo; was first given, to
+distinguish it from other shales and sandstones called the
+&ldquo;Old Red,&rdquo; often identical in mineral character, which
+lie immediately beneath the coal. The name of &ldquo;Red
+Marl&rdquo; has been incorrectly applied to the red clays of this
+formation, as before explained (<a href="#page38">p.
+38</a>), for they are remarkably free from calcareous matter. The
+absence, indeed, of carbonate of lime, as well as the scarcity of
+organic remains, together with the bright red colour of most of the
+rocks of this group, causes a strong contrast between it and the
+Jurassic formations before described.</p>
+
+<p>The group in question is more fully developed in Germany than in
+England or France. It has been called the Trias by German writers,
+or the Triple Group, because it is separable into three distinct
+formations, called the &ldquo;Keuper,&rdquo; the
+&ldquo;Muschelkalk,&rdquo; and the &ldquo;Bunter-sandstein.&rdquo;
+Of these the middle division, or the Muschelkalk, is wholly wanting
+in England, and the uppermost (Keuper) and lowest (Bunter) members
+of the series are not rich in fossils.</p>
+
+<p><b>Upper Trias or Keuper.</b>&mdash;In certain grey indurated
+marls below the bone-bed Mr. Boyd Dawkins has found at Watchet, on
+the coast of Somersetshire, a molar tooth of Microlestes, enabling
+him to refer to the Trias strata formerly supposed to be Liassic.
+Mr. Charles Moore had previously discovered many teeth of mammalia
+of the same family near Frome, in Somersetshire, in the contents of
+a vertical fissure traversing a mass of carboniferous limestone.
+The top of this fissure must have communicated with the bed of the
+Triassic sea, and probably at a point not far from the ancient
+shore on which the small marsupials of that era abounded.</p>
+
+<p>This upper division of the Trias called the Keuper is of great
+thickness in the central counties of England, attaining, according
+to Mr. Hull&rsquo;s estimate, no less than 3450 feet in Cheshire,
+and it covers a large extent of country between Lancashire and
+Devonshire.</p>
+
+<p>In Worcestershire and Warwickshire in sandstone belonging to the
+uppermost part of the Keuper the bivalve crustacean <i>Estheria
+minuta</i> occurs. The member of the English &ldquo;New Red&rdquo;
+containing this shell, in those parts of England, is, according to
+Sir Roderick Murchison and Mr. Strickland, 600 feet thick, and
+consists chiefly of red marl or slate, with
+<a name="page370"></a>a band of sandstone. Ichthyodorulites, or spines of <i>
+Hybodus,</i> teeth of fishes, and footprints of reptiles were
+observed by the same geologists in these strata.</p>
+
+<img src="images/fig390.jpg" width="95" height="105" alt=
+"Fig. 390: Estheria minuta." />
+
+<img src="images/fig391.jpg" width="276" height="260" alt=
+"Fig. 391: Hyperodapedon Gordoni. Left Plate, Maxillary." />
+
+<p>In the Upper Trias or Keuper the remains of two saurians of the
+order Lacertilia have been found. The one called <i>
+Rhynchosaurus</i> occurred at Grinsell near Shrewsbury, and is
+characterised by having a small bird-like skull and jaws without
+teeth. The other <i>Hyperodapedon</i> (Fig. 391) was first noticed
+in 1858, near Elgin, in strata now recognised as Upper Triassic,
+and afterwards in beds of about the same age in the neighbourhood
+of Warwick. Remains of the same genus have been found both in
+Central India and Southern Africa in rocks believed to be of
+Triassic age. The Hyperodapedon has been shown by Professor Huxley
+to be a terrestrial reptile having numerous palatal teeth, and
+closely allied to the living Sphenodon of New Zealand.</p>
+
+<p>The recent discoveries of a living saurian in New Zealand so
+closely allied to this supposed extinct division of the Lacertilia
+seems to afford an illustration of a principle pointed out by Mr.
+Darwin of the survival in insulated tracts, after many changes in
+physical geography, of orders of which the congeners have become
+extinct on continents where they have been exposed to the severer
+competition of a larger progressive fauna.</p>
+
+<img src="images/fig392.jpg" width="85" height="138" alt=
+"Fig. 392: Tooth of Labyrinthodon." />
+
+<p>Teeth of Labyrinthodon (Fig. 392) found in the Keuper in
+Warwickshire were examined microscopically by Professor Owen, and
+compared with other teeth from the German Keuper. He found after
+careful investigation that neither of them could be referred to
+true saurians, although they had been named <i>Mastodonsaurus</i>
+and <i>Phytosaurus</i> by Jäger. It appeared that they were of
+the <i>Batrachian</i> order, and of gigantic
+<a name="page371"></a>dimensions in comparison with any representatives of that order
+now living. Both the Continental and English fossil teeth exhibited
+a most complicated texture, differing from that previously observed
+in any reptile, whether recent or extinct, but most nearly
+analogous to the <i>Ichthyosaurus.</i> A section of one of these
+teeth exhibits a series of irregular folds, resembling the
+labyrinthic windings of the surface of the brain; and from this
+character Professor Owen has proposed the name Labyrinthodon for
+the new genus. Fig. 393 of part of one is given from his
+&ldquo;Odontography,&rdquo; plate 64, A. The entire length of this
+tooth is supposed to have been about three inches and a half, and
+the breadth at the base one inch and a half.</p>
+
+<p><img src="images/fig393.jpg" width="354" height="336" alt=
+"Fig. 393: Transverse section of upper part of tooth of Labyrinthodon Jaegeri." />
+</p>
+
+<p><i>Rock-salt.</i>&mdash;In Cheshire and Lancashire there are red
+clays containing gypsum and salt of the age of the Trias which are
+between 1000 and 1500 feet thick. In some places lenticular masses
+of pure rock-salt nearly 100 feet thick are interpolated between
+the argillaceous beds. At the base of the formation beneath the
+rock-salt occur the Lower Sandstones and Marl, called provincially
+in Cheshire &ldquo;water-stones,&rdquo; which are largely quarried
+for building. They are often ripple-marked, and are impressed with
+numerous footprints of reptiles.</p>
+
+<p>The basement beds of the Keuper rest with a slight
+<a name="page372"></a>unconformability upon an eroded surface of the
+&ldquo;Bunter&rdquo; next to be described.</p>
+
+<img src="images/fig394.jpg" width="170" height="192" alt=
+"Fig. 394: Single footstep of Cheirotherium." />
+
+<p>
+<b>Lower Trias or Bunter.</b>&mdash;The lower division or English
+representative of the &ldquo;Bunter&rdquo; attains a thickness of 1500 feet in
+the counties last mentioned, according to Professor Ramsay. Besides red and
+green shales and red sandstones, it comprises much soft white quartzose
+sandstone, in which the trunks of silicified trees have been met with at
+Allesley Hill, near Coventry. Several of them were a foot and a half in
+diameter, and some yards in length, decidedly of coniferous wood, and showing
+rings of annual growth.<a href="#fn-21.2" name="fnref-21.2"
+id="fnref-21.2"><sup>[2]</sup></a> Impressions, also, of the footsteps of
+animals have been detected in Lancashire and Cheshire in this formation. Some
+of the most remarkable occur a few miles from Liverpool, in the whitish
+quartzose sandstone of Storton Hill, on the west side of the Mersey. They bear
+a close resemblance to tracks first observed in this member of the Upper New
+Red Sandstone, at the village of Hesseberg, near Hildburghausen, in Saxony. For
+many years these footprints have been referred to a large unknown quadruped,
+provisionally named <i>Cheirotherium</i> by Professor Kaup, because the marks
+both of the fore and hind feet resembled impressions made by a human hand. (See
+Fig. 394.) The foot-marks at Hesseberg are partly concave, and partly in
+relief, the former, or the depressions, are seen upon the upper surface of the
+sandstone slabs, but those in relief are only upon the lower surfaces, being,
+in fact, natural casts, formed in the subjacent footprints as in moulds. The
+larger impressions, which seem to be those of the hind foot, are generally
+eight inches in length, and five in width, and one was twelve inches long. Near
+each large footstep, and at a regular distance (about an inch and a half)
+before it, a smaller print of a fore foot, four inches long and three inches
+wide, occurs. The footsteps follow each other <a name="page373"></a>in pairs,
+each pair in the same line, at intervals of fourteen inches from pair to pair.
+The large as well as the small steps show the great toes alternately on the
+right and left side; each step makes the print of five toes, the first, or
+great toe, being bent inward like a thumb. Though the fore and hind foot differ
+so much in size, they are nearly similar in form.
+</p>
+
+<p><img src="images/fig395.jpg" width="367" height="82" alt=
+"Fig. 395: Line of footsteps on slab of sandstone." /></p>
+
+<p>As neither in Germany nor in England had any bones or teeth been
+met with in the same identical strata as the footsteps, anatomists
+indulged, for several years, in various conjectures respecting the
+mysterious animals from which they might have been derived.
+Professor Kaup suggested that the unknown quadruped might have been
+allied to the <i>Marsupialia</i>; for in the kangaroo the first toe
+of the fore foot is in a similar manner set obliquely to the
+others, like a thumb, and the disproportion between the fore and
+hind feet is also very great. But M. Link conceived that some of
+the four species of animals of which the tracks had been found in
+Saxony might have been gigantic <i>Batrachians,</i> and when it was
+afterwards inferred that the Labyrinthodon was an air-breathing
+reptile, it was conjectured by Professor Owen that it might be one
+and the same as the Cheirotherium.</p>
+
+<p><b>Dolomitic Conglomerate of Bristol.</b>&mdash;Near Bristol, in
+Somersetshire, and in other counties bordering the Severn, the
+lowest strata belonging to the Triassic series consist of a
+conglomerate or breccia resting unconformably upon the Old Red
+Sandstone, and on different members of the Carboniferous rocks,
+such as the Coal Measures, Millstone Grit, and Mountain Limestone.
+This mode of superposition will be understood by reference to the
+section below Dundry Hill (<a href="images/fig85.jpg">Fig. 85</a>),
+where No. 4 is the dolomitic conglomerate. Such breccias may have
+been partly the result of the subÆrial waste of an old
+land-surface which gradually sank down and suffered littoral
+denudation in proportion as it became submerged. The pebbles and
+fragments of older rocks which constitute the conglomerate are
+cemented together by a red or yellow base of dolomite, and in some
+places the encrinites and other fossils derived from the Mountain
+Limestone are so detached from the parent rocks that they have the
+deceptive appearance of belonging to a fauna contemporaneous with
+the dolomitic beds in which they occur. The imbedded fragments are
+both rounded and angular, some consisting of sandstone from the
+coal-measures, being of vast size, and weighing nearly a ton.
+Fractured bones and teeth of saurians which are truly of
+contemporaneous origin are dispersed through some parts of the
+breccia, and two of these reptiles called Thecodont saurians, named
+from the
+<a name="page374"></a>manner in which the teeth were implanted in the jawbone,
+obtained great celebrity because the patches of red conglomerate in
+which they were found, near Bristol, were originally supposed to be
+of Permian or Palæozoic age, and therefore the only
+representatives in England of vertebrate animals of so high a grade
+in rocks of such antiquity. The teeth of these saurians are
+conical, compressed, and with finely serrated edges (see Fig. 396);
+they are referred by Professor Huxley to the Dinosaurian order.</p>
+
+<img src="images/fig396.jpg" width="133" height="204" alt=
+"Fig. 396: Tooth of Thecodontosaurus." />
+
+<p><b>Origin of Red Sandstone and Rock-salt.</b>&mdash;In various
+parts of the world, red and mottled clays and sandstones, of
+several distinct geological epochs, are found associated with salt,
+gypsum, and magnesian limestone, or with one or all of these
+substances. There is, therefore, in all likelihood, a general cause
+for such a coincidence. Nevertheless, we must not forget that there
+are dense masses of red and variegated sandstones and clays,
+thousands of feet in thickness, and of vast horizontal extent,
+wholly devoid of saliferous or gypseous matter. There are also
+deposits of gypsum and of common salt, as in the blue-clay
+formation of Sicily, without any accompanying red sandstone or red
+clay.</p>
+
+<p>These red deposits may be accounted for by the decomposition of
+gneiss and mica schist, which in the eastern Grampians of Scotland
+has produced a mass of detritus of precisely the same colour as the
+Old Red Sandstone.</p>
+
+<p>It is a general fact, and one not yet accounted for, that
+scarcely any fossil remains are ever preserved in stratified rocks
+in which this oxide of iron abounds; and when we find fossils in
+the New or Old Red Sandstone in England, it is in the grey, and
+usually calcareous beds, that they occur. The saline or gypseous
+interstratified beds may have been produced by submarine gaseous
+emanations, or hot mineral springs, which often continue to flow in
+the same spots for ages. Beds of rock-salt are, however, more
+generally attributed to the evaporation of lakes or lagoons
+communicating at intervals with the ocean. In Cheshire two beds of
+salt occur of the extraordinary thickness of 90 or even 100 feet,
+and extending over an area supposed to be 150 miles in diameter.
+The adjacent beds present ripple-marked sandstones and footprints
+of animals at so many levels as to imply that the whole area
+underwent a slow and gradual depression during the formation of the
+red sandstone.</p>
+
+<p>Major Harris, in his &ldquo;Highlands of Ethiopia,&rdquo;
+describes a
+<a name="page375"></a>salt lake, called the Bahr Assal, near the Abyssinian frontier,
+which once formed the prolongation of the Gulf of Tadjara, but was
+afterwards cut off from the gulf by a broad bar of lava or of land
+upraised by an earthquake. &ldquo;Fed by no rivers, and exposed in
+a burning climate to the unmitigated rays of the sun, it has shrunk
+into an elliptical basin, seven miles in its transverse axis, half
+filled with smooth water of the deepest cærulean hue, and
+half with a solid sheet of glittering snow-white salt, the
+offspring of evaporation.&rdquo; &ldquo;If,&rdquo; says Mr. Hugh
+Miller, &ldquo;we suppose, instead of a barrier of lava, that
+sand-bars were raised by the surf on a flat arenaceous coast during
+a slow and equable sinking of the surface, the waters of the outer
+gulf might occasionally topple over the bar, and supply fresh brine
+when the first stock had been exhausted by evaporation.&rdquo;</p>
+
+<p>
+The Runn of Cutch, as I have shown elsewhere,<a href="#fn-21.3"
+name="fnref-21.3" id="fnref-21.3"><sup>[3]</sup></a> is a low region near the
+delta of the Indus, equal in extent to about a quarter of Ireland, which is
+neither land nor sea, being dry during part of every year, and covered by salt
+water during the monsoons. Here and there its surface is incrusted over with a
+layer of salt caused by the evaporation of sea-water. A subsiding movement has
+been witnessed in this country during earthquakes, so that a great thickness of
+pure salt might result from a continuation of such sinking.
+</p>
+
+<p class="center">
+<small>TRIAS OF GERMANY.</small>
+</p>
+
+<p>In Germany, as before hinted, chapter 21, the Trias first
+received its name as a Triple Group, consisting of two sandstones
+with an intermediate marine calcareous formation, which last is
+wanting in England.</p>
+
+<p class="center">
+<small>NOMENCLATURE OF TRIAS.</small>
+</p>
+
+<table border="1" cellspacing="0" cellpadding="4" width="80%"
+summary="German, French and English nomenclature.">
+<tr>
+<td align="center">German</td>
+<td align="center">French</td>
+<td align="center">English</td>
+</tr>
+
+<tr>
+<td valign="top">Keuper</td>
+<td valign="top">Marnes irisées</td>
+<td >Saliferous and gypseous<br/>
+shales and sandstone.</td>
+</tr>
+
+<tr>
+<td valign="top">Muschelkalk</td>
+<td >Muschelkalk, on calcaire coquillier</td>
+<td valign="top">Wanting in England.</td>
+</tr>
+
+<tr>
+<td valign="top">Bunter-sandstein</td>
+<td valign="top">Grès bigarré</td>
+<td >Sandtone and quartzose conglomerate.</td>
+</tr>
+</table>
+
+<p>
+<b>Keuper.</b>&mdash;The first of these, or the Keuper, underlying the beds
+before described as Rhætic, attains in Würtemberg a thickness of about 1000
+feet. It is divided by Alberti into sandstone, gypsum, and carbonaceous
+clay-slate.<a href="#fn-21.4" name="fnref-21.4"
+id="fnref-21.4"><sup>[4]</sup></a> Remains of reptiles called
+<i>Nothosaurus</i> and <i>Phytosaurus,</i> have been found in it with
+Labyrinthodon; the detached teeth, also, of <a name="page376"></a>placoid fish
+and of Rays, and of the genera <i>Saurichthys</i> and <i>Gyrolepis</i> (<a
+href="images/fig383.jpg">Figs. 387, 388</a>). The plants of the Keuper are
+generically very analogous to those of the oolite and lias, consisting of
+ferns, equisetaceous plants, cycads, and conifers, with a few doubtful
+monocotyledons. A few species such as <i>Equisetites columnaris,</i> are common
+to this group and the oolite.
+</p>
+
+<img src="images/fig397.jpg" width="179" height="207" alt=
+"Fig. 397: Equisetites columnaris." />
+
+<p><i>St. Cassian and Hallstadt Beds</i> (see Map, Fig.
+398).&mdash; The sandstones and clay of the Keuper resemble the
+deposits of estuaries and a shallow sea near the land, and afford,
+in the N.W. of Germany, as in France and England, but a scanty
+representation of the marine life of that period. We might,
+however, have anticipated, from its rich reptilian fauna, that the
+contemporaneous inhabitants of the sea of the Keuper period would
+be very numerous, should we ever have an opportunity of bringing
+their remains to light. This, it is believed, has at length been
+accomplished, by the position now assigned to certain Alpine rocks
+called the &ldquo;St. Cassian beds,&rdquo; the true place of which
+in the series was until lately a subject of much doubt and
+discussion. It has been proved that the Hallstadt beds on the
+northern flanks of the Austrian Alps correspond in age with the St.
+Cassian beds on their southern declivity, and the Austrian
+geologists, M. Suess of Vienna and others, have satisfied
+themselves that the Hallstadt formation is referable to the period
+of the Upper Trias.
+<a name="page377"></a>Assuming this conclusion to be correct, we become acquainted
+suddenly and unexpectedly with a rich marine fauna belonging to a
+period previously believed to be very barren of organic remains,
+because in England, France, and Northern Germany the upper Trias is
+chiefly represented by beds of fresh or brackish water origin.</p>
+
+<p><img src="images/fig398.jpg" width="389" height="237" alt=
+"Fig. 398: Map of Tyrol and Styria showing St. Cassian and Hallstadt Beds." />
+</p>
+
+<img src="images/fig399.jpg" width="137" height="274" alt=
+"Fig. 399: Scoliotoma. Fig. 400: Koninckia Leonhardi." />
+
+<p>About 600 species of invertebrate fossils occur in the Hallstadt
+and St. Cassian beds, many of which are still undescribed; some of
+the Mollusca are of new and peculiar genera, as <i>Scoliostoma,</i>
+Fig. 399, and <i>Platystoma,</i> Fig. 400, among the Gasteropoda;
+and <i>Koninckia,</i> Fig. 401, among the Brachiopoda.</p>
+
+<img src="images/fig401.jpg" width="246" height="238" alt=
+"Fig. 401: Koninckia Leonhardi." />
+
+<p>The following table of genera of marine shells from the
+Hallstadt and St. Cassian beds, drawn up first on the joint
+authority of M. Suess and the late Dr. Woodward, and since
+corrected by Messrs. Etheridge and Tate, shows how many connecting
+links between the fauna of primary and secondary Palæozoic
+and Mesozoic rocks are supplied by the St. Cassian and Hallstadt
+beds.</p>
+
+<p class="center">
+<small>GENERA OF FOSSIL MOLLUSCA IN THE ST. CASSIAN AND HALLSTADT BEDS.</small>
+</p>
+
+<table border="0" cellpadding="4" cellspacing="0" width="100%"
+summary=
+"Column 1: Common to Older Rocks. Column 2: Characteristic Triassic Genera.
+Column 3: Common to Newer Rocks.">
+<tr>
+<td colspan="2" align="center"><small>Common to Older
+Rocks</small></td>
+<td colspan="2" align="center"><small>Characteristic Triassic
+Genera</small></td>
+<td colspan="2" align="center"><small>Common to Newer
+Rocks</small></td>
+</tr>
+
+<tr>
+<td></td>
+<td valign="top">Orthoceras<br/>
+Bactrites<br/>
+Macrocheilus<br/>
+Loxonema<br/>
+Holopella<br/>
+Murchisonia<br/>
+Porcellia<br/>
+Athyris<br/>
+Retzia<br/>
+Cyrtina<br/>
+Euomphalus</td>
+<td></td>
+<td valign="top">Ceratites<br/>
+Cochloceras<br/>
+Choristoceras<br/>
+Rhabdoceras<br/>
+Aulacoceras<br/>
+Scoliostoma <a href="#fn-21.5" name="fnref-21.5" id="fnref-21.5"><sup>[5]</sup></a><br/>
+Naticella<br/>
+Platystoma<br/>
+Ptychostoma<br/>
+Euchrysalis<br/>
+Halobia<br/>
+Hornesia<br/>
+Amphiclina<br/>
+Koninckia<br/>
+Cassianella <a href="#fn-21.6" name="fnref-21.6" id="fnref-21.6"><sup>[6]</sup></a><br/>
+Myophoria <a href="#fn-21.6a" name="fnref-21.6a" id="fnref-21.6a"><sup>[6]</sup></a></td>
+<td></td>
+<td valign="top">Ammonites<br/>
+Chemnitzia<br/>
+Cerithium<br/>
+Monodonta<br/>
+Opis<br/>
+Sphoera<br/>
+Cardita<br/>
+Myoconcha<br/>
+Hinnites<br/>
+Monotis<br/>
+Plicatula<br/>
+Pachyrisma<br/>
+Thecidium</td>
+</tr>
+</table>
+
+<p>
+<a name="page378"></a>The first column marks the last appearance of several genera
+which are characteristic of Palæozoic strata. The second
+shows those genera which are characteristic of the Upper Trias,
+either as peculiar to it, or, as in the three cases marked by
+asterisks, reaching their maximum of development at this era. The
+third column marks the first appearance in Triassic rocks of genera
+destined to become more abundant in later ages.</p>
+
+<p>It is only, however, when we contemplate the number of species
+by which each of the above-mentioned genera are represented that we
+comprehend the peculiarities of what is commonly called the St.
+Cassian fauna. Thus, for example, the Ammonite, which is not common
+to older rocks, is represented by no less than seventy-three
+species; whereas Loxonema, which is only known as common to older
+rocks, furnishes fifteen Triassic species. Cerithium, so abundant
+in tertiary strata, and which still lives, is represented by no
+less than fourteen species. As the Orthoceras had never been met
+with in the marine Muschelkalk, much surprise was naturally felt
+that seven or eight species of the genus should appear in the
+Hallstadt beds, assuming these last to belong to the Upper Trias.
+Among these species are some of large dimensions, associated with
+large Ammonites with foliated lobes, a form never seen before so
+low in the series, while the Orthoceras had never been seen so
+high.</p>
+
+<p>On the whole, the rich marine fauna of Hallstadt and St.
+Cassian, now generally assigned to the lowest members of the Upper
+Trias or Keuper, leads us to suspect that when the strata of the
+Triassic age are better known, especially those belonging to the
+period of the Bunter sandstone, the break between the
+Palæozoic and Mesozoic Periods may be almost effaced. Indeed
+some geologists are not yet satisfied that the true position of the
+St. Cassian beds (containing so great an admixture of types, having
+at once both Mesozoic and Palæozoic affinities) is made out,
+and doubt whether they have yet been clearly proved to be newer
+than the Muschelkalk.</p>
+
+<p><b>Muschelkalk.</b>&mdash;The next member of the Trias in
+Germany, the <i>Muschelkalk,</i> which underlies the <i>Keuper</i>
+before described, consists chiefly of a compact greyish limestone,
+but includes beds of dolomite in many places, together with gypsum
+and rock-salt. This limestone, a formation wholly unrepresented in
+England, abounds in fossil shells, as the name implies. Among the
+Cephalopoda there are no belemnites, and no ammonites with foliated
+sutures, as in the Lias, and Oolite, and the Hallstadt beds; but we
+find instead a genus allied to
+<a name="page379"></a>the Ammonite, called <i>Ceratites</i> by de Haan, in which the
+descending lobes (Fig. 402) terminate in a few small denticulations
+pointing inward. Among the bivalve crustacea, the <i>Estheria
+minuta,</i> Bronn (see <a href="images/fig390.jpg">Fig. 390</a>),
+is abundant, ranging through the Keuper, Muschelkalk, and
+Bunter-sandstein; and <i>Gervillia socialis</i> (Fig. 403), having
+a similar range, is found in great numbers in the Muschelkalk of
+Germany, France, and Poland.</p>
+
+<p><img src="images/fig402.jpg" width="399" height="562" alt=
+"Fig. 402: Ceratites nodosus. Fig. 403: Gervillia (Avicula) socialis. Fig. 404:
+Enerinus liliiformis. Fig. 405: Aspidura loricata." />
+</p>
+
+<p>
+<a name="page380"></a>The abundance of the heads and stems of lily encrinites, <i>
+Encrinus liliiformis</i> (Fig. 404), (or <i>Encrinites
+moniliformis</i>), shows the slow manner in which some beds of this
+limestone have been formed in clear sea-water. The star-fish called
+<i>Aspidura loricata</i> (Fig. 405) is as yet peculiar to the
+Muschelkalk. In the same formation are found the skull and teeth of
+a reptile of the genus <i>Placodus</i> (see Fig. 406), which was
+referred originally by Munster, and afterwards by Agassiz, to the
+class of fishes. But more perfect specimens enabled Professor Owen,
+in 1858, to show that this fossil animal was a Saurian reptile,
+which probably fed on shell-bearing mollusks, and used its short
+and flat teeth, so thickly coated with enamel, for pounding and
+crushing the shells.</p>
+
+<img src="images/fig406.jpg" width="161" height="226" alt=
+"Fig. 406: Palatal teeth of Placodus gigas." />
+
+<img src="images/fig407.jpg" width="180" height="211" alt=
+"Fig. 407: Voltzia heterophylla." />
+
+<p><b>Bunter-sandstein.</b>&mdash;The <i>Bunter-sandstein</i>
+consists of various-coloured sandstones, dolomites, and red clays,
+with some beds, especially in the Hartz, of calcareous pisolite or
+roe-stone, the whole sometimes attaining a thickness of more than
+1000 feet. The sandstone of the Vosges is proved, by its fossils,
+to belong to this lowest member of the Triassic group. At Sulzbad
+(or Soultz-les-bains), near Strasburg, on the flanks of the Vosges,
+many plants have been obtained from the &ldquo;bunter,&rdquo;
+especially conifers of the extinct genus <i>Voltzia,</i> of which
+the fructification has been preserved. (See Fig. 407.) Out of
+thirty species of ferns, cycads, conifers, and other plants,
+enumerated by M. Ad. Brongniart, in 1849, as coming from the
+&ldquo;Grès bigarré,&rdquo; or Bunter, not one is
+common to the Keuper.</p>
+
+<p>The footprints of Labyrinthodon observed in the clays of this
+formation at Hildburghausen, in Saxony, have already been
+mentioned. Some idea of the variety and importance of the
+terrestrial vertebrate fauna of the three members of the Trias in
+Northern Germany may be derived from the fact that in the great
+monograph by the late Hermann von Meyer on the reptiles
+<a name="page381"></a>of the Trias, the remains of no less than eighty distinct
+species are described and figured.</p>
+
+<p class="center">
+<small>TRIAS OF THE UNITED STATES.</small>
+</p>
+
+<p><b>New Red Sandstone of the Valley of the Connecticut
+River.</b>&mdash;In a depression of the granitic or hypogene rocks
+in the States of Massachusetts and Connecticut strata of red
+sandstone, shale, and conglomerate are found, occupying an area
+more than 150 miles in length from north to south, and about five
+to ten miles in breadth, the beds dipping to the eastward at angles
+varying from 5 to 50 degrees. The extreme inclination of 50 degrees
+is rare, and only observed in the neighbourhood of masses of trap
+which have been intruded into the red sandstone while it was
+forming, or before the newer parts of the deposit had been
+completed. Having examined this series of rocks in many places, I
+feel satisfied that they were formed in shallow water, and for the
+most part near the shore, and that some of the beds were from time
+to time raised above the level of the water, and laid dry, while a
+newer series, composed of similar sediment, was forming.</p>
+
+<p>
+<img src="images/fig408.jpg" width="108" height="437" alt=
+"Fig. 408: Foot-prints of a bird, Turner’s Falls, Valley of the Connecticut." />
+</p>
+
+<p>
+According to Professor Hitchcock, the footprints of no less than thirty-two
+species of bipeds, and twelve of quadrupeds, have been already detected in
+these rocks. Thirty of these are believed to be those of birds, four of
+lizards, two of chelonians, and six of batrachians. The tracks have been found
+in more than twenty places, scattered through an extent of nearly 80 miles from
+north to south, and they are repeated through a succession of beds attaining at
+some points a thickness of more than 1000 feet.<a href="#fn-21.7"
+name="fnref-21.7" id="fnref-21.7"><sup>[7]</sup></a>
+</p>
+
+<p>The bipedal impressions are, for the most part, trifid, and show
+the same number of joints as exist in the feet of living
+tridactylous birds. Now, such birds have three phalangeal bones for
+the inner toe, four for the middle, and five for the outer one (see
+Fig. 408); but the impression of the terminal joint is that of the
+nail only. The fossil footprints exhibit regularly, where the
+joints are seen, the same number; and we see in each continuous
+line of tracks
+<a name="page382"></a>the three-jointed and five-jointed toes placed alternately
+outward, first on the one side, and then on the other. In some
+specimens, besides impressions of the three toes in front, the
+rudiment is seen of the fourth toe behind. It is not often that the
+matrix has been fine enough to retain impressions of the integument
+or skin of the foot; but in one fine specimen found at
+Turner&rsquo;s Falls, on the Connecticut, by Dr. Deane, these
+markings are well preserved, and have been recognised by Professor
+Owen as resembling the skin of the ostrich, and not that of
+reptiles.</p>
+
+<p>The casts of the footprints show that some of the fossil bipeds
+of the red sandstone of Connecticut had feet four times as large as
+the living ostrich, but scarcely, perhaps, larger than the Dinornis
+of New Zealand, a lost genus of feathered giants related to the
+Apteryx, of which there were many species which have left their
+bones and almost entire skeletons in the superficial alluvium of
+that island. By referring to what was said of the Iguanodon of the
+Wealden, the reader will perceive that the Dinosaur was somewhat
+intermediate between reptiles and birds, and left a series of
+tridactylous impressions on the sand.</p>
+
+<p>To determine the exact age of the red sandstone and shale
+containing these ancient footprints, in the United States, is not
+possible at present. No fossil shells have yet been found in the
+deposit, nor plants in a determinable state. The fossil fish are
+numerous and very perfect; but they are of a peculiar type, called
+<i>Ischypterus,</i> by Sir Philip Egerton, from the great size and
+strength of the fulcral rays of the dorsal fin, from ischus,
+strength, and pteron, a fin.</p>
+
+<p>The age of the Connecticut beds cannot be proved by direct
+superposition, but may be presumed from the general structure of
+the country. That structure proves them to be newer than the
+movements to which the Appalachian or Allegheny chain owes its
+flexures, and this chain includes the ancient or palæozoic
+coal-formation among its contorted rocks.</p>
+
+<p><b>Coal-field of Richmond, Virginia.</b>&mdash;In the State of
+Virginia, at the distance of about 13 miles eastward of Richmond,
+the capital of that State, there is a coal-field occurring in a
+depression of the granite rocks, and occupying a geological
+position analogous to that of the New Red Sandstone,
+above-mentioned, of the Connecticut valley. It extends 26 miles
+from north to south, and from four to twelve from east to west.</p>
+
+<p>The plants consist chiefly of zamites, calamites, equiseta, and
+ferns, and, upon the whole, are considered by Professor
+<a name="page383"></a>Heer to have the nearest affinity to those of the European
+Keuper.</p>
+
+<p>The equiseta are very commonly met with in a vertical position
+more or less compressed perpendicularly. It is clear that they grew
+in the places where they are now buried in strata of hardened sand
+and mud. I found them maintaining their erect attitude, at points
+many miles apart, in beds both above and between the seams of coal.
+In order to explain this fact, we must suppose such shales and
+sandstones to have been gradually accumulated during the slow and
+repeated subsidence of the whole region.</p>
+
+<img src="images/fig409.jpg" width="230" height="164" alt=
+"Fig. 409: Triassic coal-shale, Richmond, Virginia." />
+
+<p>The fossil fish are Ganoids, some of them of the genus <i>
+Catopterus,</i> others belonging to the liassic genus <i>
+Tetragonolepis (Æchmodus),</i> see <a href=
+"images/fig375.jpg">Fig. 376.</a> Two species of <i>
+Entomostraca</i> called <i>Estheria</i> are in such profusion in
+some shaly beds as to divide them like the plates of mica in
+micaceous shales (see Fig. 409).</p>
+
+<p>These Virginian coal-measures are composed of grits, sandstones,
+and shales, exactly resembling those of older or primary date in
+America and Europe, and they rival, or even surpass, the latter in
+the richness and thickness of the coal-seams. One of these, the
+main seam, is in some places from 30 to 40 feet thick, composed of
+pure bituminous coal. The coal is like the finest kinds shipped at
+Newcastle, and when analysed yields the same proportions of carbon
+and hydrogen&mdash;a fact worthy of notice, when we consider that
+this fuel has been derived from an assemblage of plants very
+distinct specifically, and in part generically, from those which
+have contributed to the formation of the ancient or palæozoic
+coal.</p>
+
+<p><b>Triassic Mammifer.</b>&mdash;In North Carolina, the late
+Professor Emmons has described the strata of the Chatham
+coal-field, which correspond in age to those near Richmond, in
+Virginia. In beds underlying them he has met with three jaws of a
+small insectivorous mammal which he has called <i>Dromatherium
+sylvestre,</i> closely allied to <i>Spalacotherium.</i> Its nearest
+living analogue, says Professor Owen, &ldquo;is found in
+Myrmecobius; for each ramus of the lower jaw contained ten small
+molars in a continuous series, one canine, and three
+<a name="page384"></a>conical incisors&mdash;the latter being divided by short
+intervals.&rdquo;</p>
+
+<p><b>Low Grade of Early Mammals favourable to the Theory of
+Progressive Development.</b>&mdash;There is every reason to believe
+that this fossil quadruped is at least as ancient as the
+Microlestes of the European Trias described in <a href=
+"#page368">p. 368</a>; and the fact is highly important,
+as proving that a certain low grade of marsupials had not only a
+wide range in time, from the Trias to the Purbeck, or uppermost
+oolitic strata of Europe, but had also a wide range in space,
+namely, from Europe to North America, in an east and west
+direction, and, in regard to latitude, from Stonesfield, in 52&deg;
+N., to that of North Carolina, 35&deg; N.</p>
+
+<p>If the three localities in Europe where the most ancient
+mammalia have been found&mdash;Purbeck, Stonesfield, and
+Stuttgart&mdash;had belonged all of them to formations of the same
+age, we might well have imagined so limited an area to have been
+peopled exclusively with pouched quadrupeds, just as Australia now
+is, while other parts of the globe were inhabited by placentals;
+for Australia now supports one hundred and sixty species of
+marsupials, while the rest of the continents and islands are
+tenanted by about seventeen hundred species of mammalia, of which
+only forty-six are marsupial, namely, the opossums of North and
+South America. But the great difference of age of the strata in
+each of these three localities seems to indicate the predominance
+throughout a vast lapse of time (from the era of the Upper Trias to
+that of the Purbeck beds) of a low grade of quadrupeds; and this
+persistency of similar generic and ordinal types in Europe while
+the species were changing, and while the fish, reptiles, and
+mollusca were undergoing great modifications, would naturally lead
+us to suspect that there must also have been a vast extension in
+space of the same marsupial forms during that portion of the
+Secondary or Mesozoic epoch which has been termed &ldquo;the age of
+reptiles.&rdquo; Such an inference as to the wide geographical
+range of the ancient marsupials has been confirmed by the discovery
+in the Trias of North America of the above-mentioned Dromatherium.
+The predominance in earlier ages of these mammalia of a low grade,
+and the absence, so far as our investigations have yet gone, of
+species of higher organisation, whether aquatic or terrestrial, is
+certainly in favour of the theory of progressive development.
+</p>
+
+<p class="footnote">
+<a name="fn-21.1" id="fn-21.1"></a> <a href="#fnref-21.1">[1]</a>
+Dr. Wright, on Lias and Bone Bed, Quart. Geol. Journ., 1860, vol. xvi.
+</p>
+
+<p class="footnote">
+<a name="fn-21.2" id="fn-21.2"></a> <a href="#fnref-21.2">[2]</a>
+Buckland, Proc. Geol. Soc., vol. ii, p. 439; and Murchison and Strickland,
+Geol. Trans., Second Series., vol. v, p. 347.
+</p>
+
+<p class="footnote">
+<a name="fn-21.3" id="fn-21.3"></a> <a href="#fnref-21.3">[3]</a>
+Principles of Geology, chap. xxvii.
+</p>
+
+<p class="footnote">
+<a name="fn-21.4" id="fn-21.4"></a> <a href="#fnref-21.4">[4]</a>
+Monog. des Bunter-Sandsteins.
+</p>
+
+<p class="footnote">
+<a name="fn-21.5" id="fn-21.5"></a> <a href="#fnref-21.5">[5]</a>
+Reaches its maximum in the Trias, but passes down to older rocks.
+</p>
+
+<p class="footnote">
+<a name="fn-21.6" id="fn-21.6"></a> <a href="#fnref-21.6">[6]</a>
+<a name="fn-21.6a" id="fn-21.6a"></a> <a href="#fnref-21.6a"></a>
+Reach their maximum in the Trias, but pass up to newer rocks.
+</p>
+
+<p class="footnote">
+<a name="fn-21.7" id="fn-21.7"></a> <a href="#fnref-21.7">[7]</a>
+Hitchcock, Mem. of Amer. Acad., New Series, vol. iii, p. 129, 1848.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h3>PRIMARY OR PALÆOZOIC SERIES</h3>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap22"></a><a name="page385"></a>CHAPTER XXII.<br/>
+PERMIAN OR MAGNESIAN LIMESTONE GROUP.</h2>
+
+<p class="letter">Line of Separation between Mesozoic and
+Palæozoic Rocks. &mdash; Distinctness of Triassic and Permian
+Fossils. &mdash; Term Permian. &mdash; Thickness of calcareous and
+sedimentary Rocks in North of England. &mdash; Upper, Middle, and
+Lower Permian. &mdash; Marine Shells and Corals of the English
+Magnesian Limestone. &mdash; Reptiles and Fish of Permian
+Marl-slate. &mdash; Foot-prints of Reptiles. &mdash; Angular
+Breccias in Lower Permian. &mdash; Permian Rocks of the Continent.
+&mdash; Zechstein and Rothliegendes of Thuringia. &mdash; Permian
+Flora. &mdash; Its generic Affinity to the Carboniferous.</p>
+
+<p>In pursuing our examination of the strata in descending order,
+we have next to pass from the base of the Secondary or Mesozoic to
+the uppermost or newest of the Primary or Palæozoic
+formations. As this point has been selected as a line of
+demarkation for one of the three great divisions of the
+fossiliferous series, the student might naturally expect that by
+aid of lithological and palæontological characters he would
+be able to recognise without difficulty a distinct break between
+the newer and older group. But so far is this from being the case
+in Great Britain, that nowhere have geologists found more
+difficulty in drawing the line of separation than between the
+Secondary and Primary series. The obscurity has arisen from the
+great resemblance in colour and mineral character of the Triassic
+and Permian red marls and sandstones, and the scarcity and often
+total absence in them of organic remains. The thickness of the
+strata belonging to each group amounts in some places to several
+thousand feet; and by dint of a careful examination of their
+geological position, and of those fossil, animal, and vegetable
+forms which are occasionally met with in some members of each
+series, it has at length been made clear that the older or Permian
+rocks are more connected with the Primary or Palæozoic than
+with the Secondary or Mesozoic strata already described.</p>
+
+<p>
+The term Permian has been proposed for this group by <a name="page386"></a>Sir
+R. Murchison, from Perm, a Russian province, where it occupies an area twice
+the size of France, and contains a great abundance and variety of fossils, both
+vertebrate and invertebrate. Professor Sedgwick in 1832<a href="#fn-22.1"
+name="fnref-22.1" id="fnref-22.1"><sup>[1]</sup></a> described what is now
+recognised as the central member of this group, the Magnesian limestone,
+showing that it attained a thickness of 600 feet along the north-east of
+England, in the counties of Durham, Yorkshire, and Nottinghamshire, its lower
+part often passing into a fossiliferous marl-slate and resting on an inferior
+Red Sandstone, the equivalent of the Rothliegendes of Germany. It has since
+been shown that some of the Red Sandstones of newer date also belong to the
+Permian group; and it appears from the observations of Mr. Binney, Sir R.
+Murchison, Mr. Harkness, and others, that it is in the region where the
+limestone is most largely developed, as, for example, in the county of Durham,
+that the associated red sandstones or sedimentary rocks are thinnest, whereas
+in the country where the latter are thickest the calcareous member is reduced
+to thirty, or even sometimes to ten feet. It is clear, therefore, says Mr.
+Hull, that the sedimentary region in the north of England area has been to the
+westward, and the calcareous area to the eastward; and that in this group there
+has been a development from opposite directions of the two types of strata.
+</p>
+
+<p>In illustration of this he has given us the following table:</p>
+
+<p class="center">
+<small>THICKNESS OF PERMIAN STRATA IN NORTH OF ENGLAND.</small>
+</p>
+
+<table border="0" cellspacing="4" cellpadding="0" summary=
+"Upper, middle, and lower Permian in N.W. and N.E. of England."
+width="80%">
+<tr>
+<td>&nbsp;</td>
+<td align="center"><small>N.W. of England</small></td>
+<td align="center"><small>N.E. of England</small></td>
+</tr>
+
+<tr>
+<td></td>
+<td align="center"><small>Feet</small></td>
+<td align="center"><small>Feet</small></td>
+</tr>
+
+<tr>
+<td >Upper Permian (Sedimentary)</td>
+<td align="center">600</td>
+<td align="center">50&ndash;100</td>
+</tr>
+
+<tr>
+<td >Middle Permian (Calcareous)</td>
+<td align="center">10&ndash;30</td>
+<td align="center">600</td>
+</tr>
+
+<tr>
+<td >Lower Permian (Sedimentary)</td>
+<td align="center">3000</td>
+<td align="center">100&ndash;250<a href="#fn-22.2" name="fnref-22.2"
+id="fnref-22.2"><sup>[2]</sup></a></td>
+</tr>
+</table>
+
+<p><b>Upper Permian.</b>&mdash;What is called in this table the
+Upper Permian will be seen to attain its chief thickness in the
+north-west, or on the coast of Cumberland, as at St. Bee&rsquo;s
+Head, where it is described by Sir Roderick Murchison as consisting
+of massive red sandstones with gypsum resting on a thin course of
+Magnesian Limestone with fossils, which again is connected with the
+Lower Red Sandstone, resembling the upper one in such a manner that
+the whole forms a continuous series. No fossil footprints have been
+found in this Upper as in the Lower Red Sandstone.</p>
+
+<p>
+<a name="page387"></a><b>Middle Permian&mdash;Magnesian Limestone and
+Marl-slate.</b>&mdash;This formation is seen upon the coast of
+Durham and Yorkshire, between the Wear and the Tees. Among its
+characteristic fossils are <i>Schizodus Schlotheimi</i> (Fig. 410)
+and <i>Mytilus septifer</i> (Fig. 412). These shells occur at
+Hartlepool and Sunderland, where the rock assumes an oolitic and
+botryoidal character. Some of the beds in this division are
+ripple-marked. In some parts of the coast of Durham, where the rock
+is not crystalline, it contains as much as 44 per cent of carbonate
+of magnesia, mixed with carbonate of lime. In other places&mdash;for it
+is extremely variable in structure&mdash;it consists chiefly of
+carbonate of lime, and has concreted into globular and
+hemispherical masses, varying from the size of a marble to that of
+a cannon-ball, and radiating from the centre. Occasionally earthy
+and pulverulent beds pass into compact limestone or hard granular
+dolomite. Sometimes the limestone appears in a brecciated form, the
+fragments which are united together not consisting of foreign rocks
+but seemingly composed of the breaking-up of the Permian limestone
+itself, about the time of its consolidation. Some of the angular
+masses in Tynemouth cliff are two feet in diameter.</p>
+
+<p><img src="images/fig410.jpg" width="439" height="153" alt=
+"Fig. 410: Schidozus Schlotheimi, Permian crystalline limestone. Fig. 411: The
+hinge of Schizodus truncatus, Permian. Fig. 412: Mytilus septifer, Permian
+crystalline limestone." />
+</p>
+
+<p>The magnesian limestone sometimes becomes very fossiliferous and
+includes in it delicate bryozoa, one of which, <i>Fenestella
+retiformis</i> (Fig. 413), is a very variable species, and has
+received many different names. It sometimes attains a large size,
+single specimens measuring eight inches in width. The same
+bryozoan, with several other British species, is also found
+abundantly in the Permian of Germany.</p>
+
+<p>The total known fauna of the Permian series of Great Britain at
+present numbers 147 species, of which 77, or more than half, are
+mollusca. Not one of these is common to rocks newer than the
+Palæozoic, and the brachiopods are the only group which have
+furnished species common to the more ancient or Carboniferous
+rocks. Of these <i>Lingula Crednerii</i>
+<a name="page388"></a>(Fig. 415) is an example. There are 25 Gasteropods and only one
+cephalopod, <i>Nautilus Freieslebeni,</i> which is also found in
+the German Zechstein.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig413.jpg" width="380" height="230" alt="Fig. 413: Magnesian
+Limestone." />
+<p class="caption">Fig. 413: Magnesian Limestone, Humbleton Hill, near
+Sunderland.<a href="#fn-22.3" name="fnref-22.3" id="fnref-22.3"><sup>[3]</sup></a><br/></p>
+</div>
+
+<p>Shells of the genera <i>Productus</i> (Fig. 414) and <i>
+Strophalosia</i> (the latter of allied form with hinge teeth),
+which do not occur in strata newer than the Permian, are abundant
+in the ordinary yellow magnesian limestone, as will be seen in the
+valuable memoirs of Messrs. King and Howse. They are accompanied by
+certain species of <i>Spirifera</i> (Fig. 416), <i>Lingula
+Crednerii</i> (Fig. 415), and other brachiopoda of the true primary
+or palæozoic type. Some of this same tribe of shells, such as
+Camarophoria, allied to Rhynchonella, Spiriferina, and two species
+of <i>Lingula,</i> are specifically the same as fossils of the
+carboniferous rocks. <i>Avicula, Arca,</i> and <i>Schizodus</i>
+(Fig. 410), and other lamellibranchiate bivalves, are abundant, but
+spiral univalves are very rare.</p>
+
+<p><img src="images/fig414.jpg" width="399" height="169" alt=
+"Fig. 414: Productus horridus. Fig. 415: Lingula Crednerii. Fig. 416: Spirifera alata." />
+</p>
+
+<p>Beneath the limestone lies a formation termed the marl-stone,
+which consists of hard calcareous shales, marl-slate, and
+thin-bedded limestones. At East Thickley, in Durham, where
+<a name="page389"></a>it is thirty feet thick, this slate has yielded many fine
+specimens of fossil fish&mdash;of the genera <i>Palæoniscus</i>
+ten species, <i>Pygopterus</i> two species, <i>Coelacanthus</i> two
+species, and <i>Platysomus</i> two species, which as genera are
+common to the older Carboniferous formation, but the Permian
+species are peculiar, and, for the most part, identical with those
+found in the marl-slate or copper-slate of Thuringia.</p>
+
+<p><img src="images/fig417.jpg" width="366" height="322" alt=
+"Fig. 417: Restored outline of a fish of the genus Palæoniscus. Fig. 418:
+Shark, Heterocercal. Fig. 419: Shad. (Clupea. Herring tribe.) Homocereal." />
+</p>
+
+<p>The <i>Palæoniscus</i> above mentioned belongs to that
+division of fishes which M. Agassiz has called
+&ldquo;Heterocercal,&rdquo; which have their tails unequally
+bilobate, like the recent shark and sturgeon, and the vertebral
+column running along the upper caudal lobe. (See Fig. 418.) The
+&ldquo;Homocercal&rdquo; fish, which comprise almost all the 9000
+species at present known in the living creation, have the tail-fin
+either single or equally divided; and the vertebral column stops
+short, and is not prolonged into either lobe. (See Fig. 419.) Now
+it is a singular fact, first pointed out by Agassiz, that the
+heterocercal form, which is confined to a small number of genera in
+the existing creation, is universal in the magnesian limestone, and
+all the more ancient formations. It characterises the earlier
+periods of the earth&rsquo;s history, whereas in the secondary
+strata, or those newer than the Permian, the homocercal tail
+predominates.</p>
+
+<p>A full description has been given by Sir Philip Egerton of the
+species of fish characteristic of the marl-slate, in Professor
+King&rsquo;s monograph before referred to, where figures of the
+<a name="page390"></a>ichthyolites, which are very entire and well preserved, will be
+found. Even a single scale is usually so characteristically marked
+as to indicate the genus, and sometimes even the particular
+species. They are often scattered through the beds singly, and may
+be useful to a geologist in determining the age of the rock.</p>
+
+<p><img src="images/fig420.jpg" width="429" height="356" alt=
+"Fig. 420: Palæoniscus comptus. Fig. 421: Palæoniscus elegans. Fig. 422:
+Palæoniscus glaphyrus. Fig. 423: Cœlacanthus granulatus. Fig. 424: Pygopterus
+mandibularis. Fig. 425: Acrolepis Sedgwickii." />
+</p>
+
+<p>We are indebted to Messrs. Hancock and Howse for the discovery
+in this marl-slate at Midderidge, Durham, of two species of <i>
+Protosaurus,</i> a genus of reptiles, one representative of which,
+<i>P. Speneri,</i> has been celebrated ever since the year 1810 as
+characteristic of the Kupfer-schiefer or Permian of Thuringia.
+Professor Huxley informs us that the agreement of the Durham fossil
+with Hermann von Meyer&rsquo;s figure of the German specimen is
+most striking. Although the head is wanting in all the examples yet
+found, they clearly belong to the Lacertian order, and are
+therefore of a higher grade than any other vertebrate animal
+hitherto found fossil in a Palæozoic rock. Remains of
+Labyrinthodont reptiles have also been met with in the same slate
+near Durham.</p>
+
+<p><b>Lower Permian.</b>&mdash;The inferior sandstones which lie
+beneath the marl-slate consist of sandstone and sand, separating
+the Magnesian Limestone from the coal, in Yorkshire and Durham. In
+some instances, red marl and gypsum have been found associated with
+these beds. They have been classed
+<a name="page391"></a>with the Magnesian Limestone by Professor Sedgwick, as being
+nearly co-extensive with it in geographical range, though their
+relations are very obscure. But the principal development of Lower
+Permian is, as we have seen by Mr. Hull&rsquo;s table <a href=
+"#page386">p. 386</a>, in the northwest, where the Penrith
+sandstone, as it has been called, and the associated breccias and
+purple shales are estimated by Professor Harkness to attain a
+thickness of 3000 feet. Organic remains are generally wanting, but
+the leaves and wood of coniferous plants, and in one case a cone,
+have been found. Also in the purple marls of Corncockle Muir near
+Dumfries, very distinct footprints of reptiles occur, originally
+referred to the Trias, but shown by Mr. Binney in 1856 to be
+Permian. No bones of the animals which they represent have yet been
+discovered.</p>
+
+<p><i>Angular Breccias in Lower Permian.</i>&mdash;A striking
+feature in these beds is the occasional occurrence, especially at
+the base of the formation, of angular and sometimes rounded
+fragments of Carboniferous and older rocks of the adjoining
+districts being included in a paste of red marl. Some of the
+angular masses are of huge size.</p>
+
+<p>In the central and southern counties, where the Middle Permian
+or Magnesian Limestone is wanting, it is difficult to separate the
+upper and lower sandstones, and Mr. Hull is of opinion that the
+patches of this formation found here and there in Worcestershire,
+Shropshire, and other counties may have been deposited in a sea
+separated from the northern basin by a barrier of Carboniferous
+rocks running east and west, and now concealed under the Triassic
+strata of Cheshire. Similar breccias to those before described are
+found in the more southern counties last mentioned, where their
+appearance is rendered more striking by the marked contrast they
+present to the beds of well-rolled and rounded pebbles of the Trias
+occupying a large area in the same region.</p>
+
+<p>
+Professor Ramsay refers the angular form and large size of the fragments
+composing these breccias to the action of floating ice in the sea. These masses
+of angular rock, some of them weighing more than half a ton, and lying
+confusedly in a red, unstratified marl, like stones in boulder-drift, are in
+some cases polished, striated, and furrowed like erratic blocks in the moraine
+of a glacier. They can be shown in some cases to have travelled from the parent
+rocks, thirty or more miles distant, and yet not to have lost their angular
+shape.<a href="#fn-22.4" name="fnref-22.4" id="fnref-22.4"><sup>[4]</sup></a>
+</p>
+
+<p><b>Permian Rocks of the Continent.</b>&mdash;Germany is the
+classic ground of the Magnesian Limestone now called Permian.
+<a name="page392"></a>The formation was well studied by the miners of that country a
+century ago as containing a thin band of dark-coloured cupriferous
+shale, characterised at Mansfield in Thuringia by numerous fossil
+fish. Beneath some variegated sandstones (not belonging to the
+Trias, though often confounded with it) they came down first upon a
+dolomitic limestone corresponding to the upper part of our Middle
+Permian, and then upon a marl-slate richly impregnated with copper
+pyrites, and containing fish and reptiles (Protosaurus) identical
+in species with those of the corresponding marl-slate of Durham. To
+the limestone they gave the name of Zechstein, and to the
+marl-slate that of Mergel-schiefer or Kupfer-schiefer. Beneath the
+fossiliferous group lies the Rothliegendes or Rothtodt-liegendes,
+meaning the red-lyer or red-dead-lyer, so-called by the German
+miners from its colour, and because the copper had <i>died out</i>
+when they reached this underlying non-metalliferous member of the
+series. This red under-lyer is, in fact, a great deposit of red
+sandstone, breccia, and conglomerate with associated porphyry,
+basalt, and amygdaloid.</p>
+
+<p>According to Sir R. Murchison, the Permian rocks are composed,
+in Russia, of white limestone, with gypsum and white salt; and of
+red and green grits, occasionally with copper ore; also magnesian
+limestones, marl-stones, and conglomerates.</p>
+
+<p><img src="images/fig426.jpg" width="421" height="245" alt=
+"Fig. 426: Walchia piniformis." /></p>
+
+<p><b>Permian Flora.</b>&mdash;About 18 or 20 species of plants are
+known in the Permian rocks of England. None of them pass down into
+the Carboniferous series, but several genera, such as <i>
+Alethopteris, Neuropteris, Walchia,</i> and <i>Ullmania,</i> are
+common to the two groups. The Permian flora on the Continent
+appears, from the researches of MM. Murchison and de Verneuil
+<a name="page393"></a>in Russia, and of MM. Geinitz and von Gutbier in Saxony, to be,
+with a few exceptions, distinct from that of the coal.</p>
+
+<p>
+<img src="images/fig427.jpg" width="87" height="145" alt=
+"Fig. 27: Cardiocarpon Ottonis." />
+</p>
+
+<p>In the Permian rocks of Saxony no less than 60 species of fossil
+plants have been met with. Two or three of these, as <i>Calamites
+gigas, Sphenopteris erosa,</i> and <i>S. lobata,</i> are also met
+with in the government of Perm in Russia. Seven others, and among
+them <i>Neuropteris Loshii, Pecopteris arborescens,</i> and <i>P.
+similis,</i> and several species of <i>Walchia</i> (see Fig. 426),
+a genus of Conifers, called <i>Lycopodites</i> by some authors, are
+said by Geinitz to be common to the coal-measures.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig428.jpg" width="134" height="336" alt="Fig. 428:
+Noeggerathia cuneifolia." />
+<p class="caption">Fig. 428: Noeggerathia cuneifolia.<br/>
+Brongniart.<a href="#fn-22.5" name="fnref-22.5"
+id="fnref-22.5"><sup>[5]</sup></a><br/></p>
+</div>
+
+<p>Among the genera also enumerated by Colonel Gutbier are the
+fruit called <i>Cardiocarpon</i> (see Fig. 427), <i>
+Asterophyllites,</i> and Annularia, so characteristic of the
+Carboniferous period; also <i>Lepidodendron,</i> which is common to
+the Permian of Saxony, Thuringia, and Russia, although not
+abundant. <i>Neoggerathia</i> (see Fig. 428), the leaves of which
+have parallel veins without a midrib, and to which various generic
+synonyms, such as <i>Cordaites, Flabellaria,</i> and <i>
+Poacites,</i> have been given, is another link between the Permian
+and Carboniferous vegetation. Coniferæ, of the Araucarian
+division, also occur; but these are likewise met with both in older
+and newer rocks. The plants called <i>Sigillaria</i> and <i>
+Stigmaria,</i> so marked a feature in the Carboniferous period, are
+as yet wanting in the true Permian.</p>
+
+<p>Among the remarkable fossils of the Rothliegendes, or lowest
+part of the Permian in Saxony and Bohemia, are the silicified
+trunks of tree-ferns called generically <i>Psaronius.</i> Their
+bark was surrounded by a dense mass of air-roots, which often
+constituted a great addition to the original stem, so as to double
+or quadruple its diameter. The same remark holds good in regard to
+certain living extra-tropical arborescent ferns, particularly those
+of New Zealand.</p>
+
+<p>Upon the whole, it is evident that the Permian plants approach
+much nearer to the Carboniferous flora than to the Triassic; and
+the same may be said of the Permian fauna.</p>
+
+<p class="footnote">
+<a name="fn-22.1" id="fn-22.1"></a> <a href="#fnref-22.1">[1]</a>
+Trans. Geol. Soc. Lond., Second Series, vol. iii, p. 37.
+</p>
+
+<p class="footnote">
+<a name="fn-22.2" id="fn-22.2"></a> <a href="#fnref-22.2">[2]</a>
+Edward Hull, Ternary Classification, Quart. Journ. Science, No. xxiii, 1869.
+</p>
+
+<p class="footnote">
+<a name="fn-22.3" id="fn-22.3"></a> <a href="#fnref-22.3">[3]</a>
+King&rsquo;s Monograph, pl. 2.
+</p>
+
+<p class="footnote">
+<a name="fn-22.4" id="fn-22.4"></a> <a href="#fnref-22.4">[4]</a>
+Ramsay, Quart. Geol. Journ., 1855; and Lyell, Principles of Geology, vol. i, p.
+223, 10th edit.
+</p>
+
+<p class="footnote">
+<a name="fn-22.5" id="fn-22.5"></a> <a href="#fnref-22.5">[5]</a>
+Murchison&rsquo;s Russia, vol. ii, pl. A, fig. 3.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap23"></a><a name="page394"></a>CHAPTER XXIII.<br/>
+THE COAL OR CARBONIFEROUS GROUP.</h2>
+
+<p class="letter">Principal Subdivisions of the Carboniferous Group.
+&mdash; Different Thickness of the sedimentary and calcareous
+Members in Scotland and the South of England. &mdash;
+Coal-measures. &mdash; Terrestrial Nature of the Growth of Coal.
+&mdash; Erect fossil Trees. &mdash; Uniting of many Coal-seams into
+one thick Bed. &mdash; Purity of the Coal explained. &mdash;
+Conversion of Coal into Anthracite. &mdash; Origin of
+Clay-ironstone. &mdash; Marine and brackish-water Strata in Coal.
+&mdash; Fossil Insects. &mdash; Batrachian Reptiles. &mdash;
+Labyrinthodont Foot-prints in Coal-measures. &mdash; Nova Scotia
+Coal-measures with successive Growths of erect fossil Trees.
+&mdash; Similarity of American and European Coal. &mdash;
+Air-breathers of the American Coal. &mdash; Changes of Condition of
+Land and Sea indicated by the Carboniferous Strata of Nova
+Scotia.</p>
+
+<p><b>Principal Subdivisions of the Carboniferous
+Group.</b>&mdash;The next group which we meet with in the
+descending order is the Carboniferous, commonly called &ldquo;The
+Coal,&rdquo; because it contains many beds of that mineral, in a
+more or less pure state, interstratified with sandstones, shales,
+and limestones. The coal itself, even in Great Britain and Belgium,
+where it is most abundant, constitutes but an insignificant portion
+of the whole mass. In South Wales, for example, the thickness of
+the coal-bearing strata has been estimated at between 11,000 and
+12,000 feet, while the various coal seams, about 80 in number, do
+not, according to Professor Phillips, exceed in the aggregate 120
+feet.</p>
+
+<p>The Carboniferous formation assumes various characters in
+different parts even of the British Islands. It usually comprises
+two very distinct members: first, the sedimentary beds, usually
+called the Coal-measures, of mixed fresh-water, terrestrial, and
+marine origin, often including seams of coal; second, that named in
+England the Mountain or Carboniferous Limestone, of purely marine
+origin, and made up chiefly of corals, shells, and encrinites, and
+resting on shales called the shales of the Mountain Limestone.</p>
+
+<p>In the south-western part of our island, in Somersetshire and
+South Wales, the three divisions usually spoken of are:</p>
+
+<ol>
+<li>Coal-measures: Strata of shale, sandstone, and grit, from 600
+to 12,000 feet thick, with occasional seams of coal.</li>
+
+<li>Millstone grit: A coarse quartzose sandstone passing into a
+conglomerate, sometimes used for millstones, with beds of shale;
+usually devoid of coal; occasionally above 600 feet thick.</li>
+
+<li>Mountain or Carboniferous Limestone: A calcareous rock
+containing marine shells, corals, and encrinites; devoid of coal;
+thickness variable, sometimes more than 1500 feet.</li>
+</ol>
+
+<p>
+<a name="page395"></a>If the reader will refer to the section in <a href=
+"images/fig85.jpg">Fig. 85,</a> he will see that the Upper and
+Lower Coal-measures of the coal-field near Bristol are divided by a
+micaceous flaggy sandstone called the Pennant Rock. The Lower
+Coal-measures of the same section rest sometimes, especially in the
+north part of the basin, on a base of coarse grit called the
+Millstone Grit (No. 2 on the previous page).</p>
+
+<p>In the South Welsh coal-field Millstone Grit occurs in like
+manner at the base of the productive coal. It is called by the
+miners the &ldquo;Farewell Rock,&rdquo; as when they reach it they
+have no longer any hopes of obtaining coal at a greater depth in
+the same district. In the central and northern coal-fields of
+England this same grit, including quartz pebbles, with some
+accompanying sandstones and shales containing coal plants, acquires
+a thickness of several thousand feet, lying beneath the productive
+coal-measures, which are nearly 10,000 feet thick.</p>
+
+<p>Below the Millstone Grit is a continuation of similar sandstones
+and shales called by Professor Phillips the Yoredale series, from
+Yoredale, in Yorkshire, where they attain a thickness of from 800
+to 1000 feet. At several intervals bands of limestone divide this
+part of the series, one of which, called the Main Limestone or
+Upper Scar Limestone, composed in great part of encrinites, is 70
+feet thick. Thin seams of coal also occur in these lower Yoredale
+beds in Yorkshire, showing that in the same region there were great
+alternations in the state of the surface. For at successive periods
+in the same area there prevailed first terrestrial conditions
+favourable to the growth of pure coal, secondly, a sea of some
+depth suited to the formation of Carboniferous Limestone, and,
+thirdly, a supply of muddy sediment and sand, furnishing the
+materials for sandstone and shale. There is no clear line of
+demarkation between the Coal-measures and the Millstone Grit, nor
+between the Millstone Grit and underlying Yoredale rocks.</p>
+
+<p>On comparing a series of vertical sections in a north-westerly
+direction from Leicestershire and Warwickshire into North
+Lancashire, we find, says Mr. Hull, within a distance of 120 miles
+an augmentation of the sedimentary materials to the extent of
+16,000 feet.</p>
+
+<table border="0" cellpadding="0" cellspacing="0" width="60%"
+summary="Augmentation of sedimentary materials">
+<tr>
+<td >Leicestershire and Warwickshire</td>
+<td >2,600 feet</td>
+</tr>
+
+<tr>
+<td >North Staffordshire</td>
+<td >9,000 feet</td>
+</tr>
+
+<tr>
+<td >South Lancashire</td>
+<td >12,130 feet</td>
+</tr>
+
+<tr>
+<td >North Lancashire</td>
+<td >18,700 feet</td>
+</tr>
+</table>
+
+<p>
+<a name="page396"></a>In central England, where the sedimentary beds are reduced to
+about 3000 feet in all, the Carboniferous Limestone attains an
+enormous thickness, as much as 4000 feet at Ashbourne, near Derby,
+according to Mr. Hull&rsquo;s estimate. To a certain extent,
+therefore, we may consider the calcareous member of the formation
+as having originated simultaneously with the accumulation of the
+materials of grit, sandstone, and shale, with seams of coal; just
+as strata of mud, sand, and pebbles, several thousand feet thick,
+with layers of vegetable matter, are now in the process of
+formation in the cypress swamps and delta of the Mississippi, while
+coral reefs are forming on the coast of Florida and in the sea of
+the Bermuda islands. For we may safely conclude that in the ancient
+Carboniferous ocean those marine animals which were limestone
+builders were never freely developed in areas where the rivers
+poured in fresh water charged with sand or clay; and the limestone
+could only become several thousand feet thick in parts of the ocean
+which remained perfectly clear for ages.</p>
+
+<p>The calcareous strata of the Scotch coal-fields, those of
+Lanarkshire, the Lothians, and Fife, for example, are very
+insignificant in thickness when compared to those of England. They
+consist of a few beds intercalated between the sandstones and
+shales containing coal and ironstone, the combined thickness of all
+the limestones amounting to no more than 150 feet. The vegetation
+of some of these northern sedimentary beds containing coal may be
+older than any of the coal-measures of central and southern
+England, as being coeval with the Mountain Limestone of the south.
+In Ireland the limestone predominates over the coal-bearing sands
+and shales. We may infer the former continuity of several of the
+coal-fields in northern and central England, not only from the
+abrupt manner in which they are cut off at their outcrop, but from
+their remarkable correspondence in the succession and character of
+particular beds. But the limited extent to which these strata are
+exposed at the surface is not merely owing to their former
+denudation, but even in a still greater degree to their having been
+largely covered by the New Red Sandstone, as in Cheshire, and here
+and there by the Permian strata, as in Durham.</p>
+
+<p>
+It has long been the opinion of the most eminent geologists that the
+coal-fields of Yorkshire and Lancashire were once united, the upper
+Coal-measures and the overlying Millstone Grit and Yoredale rocks having been
+subsequently removed; but what is remarkable, is the ancient date now assigned
+to this denudation, for it seems that a thickness of no less than <a
+name="page397"></a>10,000 feet of the coal-measures had been carried away
+before the deposition even of the lower Permian rocks which were thrown down
+upon the already disturbed truncated edges of the coal-strata.<a
+href="#fn-23.1" name="fnref-23.1" id="fnref-23.1"><sup>[1]</sup></a> The
+carboniferous strata most productive of workable coal have so often a
+basin-shaped arrangement that these troughs have sometimes been supposed to be
+connected with the original conformation of the surface upon which the beds
+were deposited. But it is now admitted that this structure has been owing to
+movements of the earth&rsquo;s crust of upheaval and subsidence, and that the
+flexure and inclination of the beds has no connection with the original
+geographical configuration of the district.
+</p>
+
+<p class="center">
+<small>COAL-MEASURES.</small>
+</p>
+
+<p>I shall now treat more particularly of the productive
+coal-measures, and their mode of origin and organic remains.</p>
+
+<p><b>Coal formed on Land.</b>&mdash;In South Wales, already
+alluded to, where the coal-measures attain a thickness of 12,000
+feet, the beds throughout appear to have been formed in water of
+moderate depth, during a slow, but perhaps intermittent, depression
+of the ground, in a region to which rivers were bringing a
+never-failing supply of muddy sediment and sand. The same area was
+sometimes covered with vast forests, such as we see in the deltas
+of great rivers in warm climates, which are liable to be submerged
+beneath fresh or salt water should the ground sink vertically a few
+feet.</p>
+
+<p>In one section near Swansea, in South Wales, where the total
+thickness of strata is 3246 feet, we learn from Sir H. De la Beche
+that there are ten principal masses of sandstone. One of these is
+500 feet thick, and the whole of them make together a thickness of
+2125 feet. They are separated by masses of shale, varying in
+thickness from 10 to 50 feet. The intercalated coal-beds, sixteen
+in number, are generally from one to five feet thick, one of them,
+which has two or three layers of clay interposed, attaining nine
+feet. At other points in the same coal-field the shales predominate
+over the sandstones. Great as is the diversity in the horizontal
+extent of individual coal-seams, they all present one
+characteristic feature, in having, each of them, what is called its
+<i>underclay.</i> These underclays, co-extensive with every layer
+of coal, consist of arenaceous shale, sometimes called fire-stone,
+because it can be made into bricks which stand the fire of a
+furnace. They vary in thickness from six inches to more than ten
+feet; and Sir William Logan first announced to the scientific world
+in 1841 that they were regarded by the colliers in South
+<a name="page398"></a>Wales as an essential accompaniment of each of the eighty or
+more seams of coal met with in their coal-field. They are said to
+form the <i>floor</i> on which the coal rests; and some of them
+have a slight admixture of carbonaceous matter, while others are
+quite blackened by it.</p>
+
+<p>All of them, as Sir William Logan pointed out, are characterised
+by inclosing a peculiar species of fossil vegetable called <i>
+Stigmaria,</i> to the exclusion of other plants. It was also
+observed that, while in the overlying shales, or &ldquo;roof&rdquo;
+of the coal, ferns and trunks of trees abound without any <i>
+Stigmariæ,</i> and are flattened and compressed, those
+singular plants of the underclay most commonly retain their natural
+forms, unflattened and branching freely, and sending out their
+slender rootlets, formerly thought to be leaves, through the mud in
+all directions. Several species of <i>Stigmaria</i> had long been
+known to botanists, and described by them, before their position
+under each seam of coal was pointed out, and before their true
+nature as the roots of trees (some having been actually found
+attached to the base of <i>Sigillaria</i> stumps) was recognised.
+It was conjectured that they might be aquatic, perhaps floating
+plants, which sometimes extended their branches and leaves freely
+in fluid mud, in which they were finally enveloped.</p>
+
+<p>
+Now that all agree that these underclays are ancient soils, it follows that in
+every instance where we find them they attest the terrestrial nature of the
+plants which formed the overlying coal, which consists of the trunks, branches,
+and leaves of the same plants. The trunks have generally fallen prostrate in
+the coal, but some of them still remain at right angles to the ancient soils
+(see Fig. 440). Professor Goppert, after
+examining the fossil vegetables of the coal-fields of Germany, has detected, in
+beds of pure coal, remains of plants of every family hitherto known to occur
+fossil in the carboniferous rocks. Many seams, he remarks, are rich in
+<i>Sigillariæ, Lepidodendra,</i> and <i>Stigmariæ,</i> the latter in such
+abundance as to appear to form the bulk of the coal. In some places, almost all
+the plants were calamites, in others ferns.<a href="#fn-23.2" name="fnref-23.2"
+id="fnref-23.2"><sup>[2]</sup></a>
+</p>
+
+<p>Between the years 1837 and 1840, six fossil trees were
+discovered in the coal-fields of Lancashire, where it is
+intersected by the Bolton railway. They were all at right angles to
+the plane of the bed, which dips about 15 degrees to the south. The
+distance between the first and the last was more than 100 feet, and
+the roots of all were imbedded in a soft argillaceous shale. In the
+same plane with the roots is a bed of
+<a name="page399"></a>coal, eight or ten inches thick, which has been found to extend
+across the railway, or to the distance of at least ten yards. Just
+above the covering of the roots, yet beneath the coal-seam, so
+large a quantity of the <i>Lepidostrobus variabilis</i> was
+discovered inclosed in nodules of hard clay, that more than a
+bushel was collected from the small openings around the base of
+some of the trees (see <a href="images/fig457.jpg">Fig. 457</a> of
+this genus). The exterior trunk of each was marked by a coating of
+friable coal, varying from one-quarter to three-quarters of an inch
+in thickness; but it crumbled away on removing the matrix. The
+dimensions of one of the trees is 15&frac12; feet in circumference
+at the base, 7&frac12; feet at the top, its height being eleven
+feet. All the trees have large spreading roots, solid and strong,
+sometimes branching, and traced to a distance of several feet, and
+presumed to extend much farther.</p>
+
+<p>In a colliery near Newcastle a great number of <i>
+Sigillariæ</i> occur in the rock as if they had retained the
+position in which they grew. No less than thirty, some of them four
+or five feet in diameter, were visible within an area of 50 yards
+square, the interior being sandstone, and the bark having been
+converted into coal. Such vertical stems are familiar to our
+coal-miners, under the name of coal-pipes. They are much dreaded,
+for almost every year in the Bristol, Newcastle, and other
+coal-fields, they are the cause of fatal accidents. Each
+cylindrical cast of a tree, formed of solid sandstone, and
+increasing gradually in size towards the base, and being without
+branches, has its whole weight thrown downward, and receives no
+support from the coating of friable coal which has replaced the
+bark. As soon, therefore, as the cohesion of this external layer is
+overcome, the heavy column falls suddenly in a perpendicular or
+oblique direction from the roof of the gallery whence coal has been
+extracted, wounding or killing the workman who stands below. It is
+strange to reflect how many thousands of these trees fell
+originally in their native forests in obedience to the law of
+gravity; and how the few which continued to stand erect, obeying,
+after myriads of ages, the same force, are cast down to immolate
+their human victims.</p>
+
+<p>It has been remarked that if, instead of working in the dark,
+the miner was accustomed to remove the upper covering of rock from
+each seam of coal, and to expose to the day the soils on which
+ancient forests grew, the evidence of their former growth would be
+obvious. Thus in South Staffordshire a seam of coal was laid bare
+in the year 1844, in what is called an open work at Parkfield
+colliery, near Wolverhampton. In the space of about a quarter of an
+acre the
+<a name="page400"></a>stumps of no less than 73 trees with their roots attached
+appeared, as shown in Fig. 429, some of them more than eight feet
+in circumference. The trunks, broken off close to the root, were
+lying prostrate in every direction, often crossing each other. One
+of them measured 15, another 30 feet in length, and others less.
+They were invariably flattened to the thickness of one or two
+inches, and converted into coal. Their roots formed part of a
+stratum of coal ten inches thick, which rested on a layer of clay
+two inches thick, below which was a second forest resting on a
+two-foot seam of coal. Five feet below this, again, was a third
+forest with large stumps of <i>Lepidodendra, Calamites,</i> and
+other trees.</p>
+
+<img src="images/fig429.jpg" width="279" height="274" alt=
+"Fig. 429: Ground plan of fossil forest, Parkfield Colliery, near
+Wolverhampton, showing the position of 73 trees in a quarter of an ace." />
+
+<p><b>Blending of Coal-seams.</b>&mdash;Both in England and North
+America seams of coal are occasionally observed to be parted from
+each other by layers of clay and sand, and, after they have been
+persistent for miles, to come together and blend in one single bed,
+which is then found to be equal in the aggregate to the thickness
+of the several seams. I was shown by Mr. H. D. Rogers a remarkable
+example of this in Pennsylvania. In the Shark Mountain, near
+Pottsville, in that State, there are thirteen seams of anthracite
+coal, some of them more than six feet thick, separated by beds of
+white quartzose grit and a conglomerate of quartz pebbles, often of
+the size of a hen&rsquo;s egg. Between Pottsville and the Lehigh
+Summit Mine, seven of these seams of coal, at first widely
+separated, are, in the course of several miles, brought nearer and
+nearer together by the gradual thinning out of the intervening
+coarse-grained strata and their accompanying shales, until at
+length they successively unite and form one mass of coal between
+forty and fifty feet thick, very pure on the whole, though with a
+few thin partings of clay. This mass of coal I saw quarried in the
+open air at Mauch
+<a name="page401"></a>Chunk, on the Bear Mountain. The origin of such a vast thickness
+of vegetable remains, so unmixed, on the whole, with earthy
+ingredients, can be accounted for in no other way than by the
+growth, during thousands of years, of trees and ferns in the manner
+of peat&mdash;a theory which the presence of the Stigmaria <i>in
+situ</i> under each of the seven layers of anthracite fully bears
+out. The rival hypothesis, of the drifting of plants into a sea or
+estuary, leaves the non-intermixture of sediment, or of clay, sand,
+and pebbles, with the pure coal wholly unexplained.</p>
+
+<p>The late Mr. Bowman was the first who gave a satisfactory
+explanation of the manner in which distinct coal-seams, after
+maintaining their independence for miles, may at length unite, and
+then persist throughout another wide area with a thickness equal to
+that which the separate seams had previously maintained.</p>
+
+<p><img src="images/fig430.jpg" width="396" height="97" alt=
+"Fig. 430: Uniting of distinct coal-seams." /></p>
+
+<p>Let A C (Fig. 430) be a three-foot seam of coal originally laid
+down as a mass of vegetable matter on the level area of an
+extensive swamp, having an under-clay, <i>f g,</i> through which
+the Stigmariæ or roots of the trees penetrate as usual. One
+portion, B C, of this seam of coal is now inclined; the area of the
+swamp having subsided as much as 25 feet at E C, and become for a
+time submerged under salt, fresh, or brackish water. Some of the
+trees of the original forest A B C fell down, others continued to
+stand erect in the new lagoon, their stumps and part of their
+trunks becoming gradually enveloped in layers of sand and mud,
+which at length filled up the new piece of water C E.</p>
+
+<p>When this lagoon has been entirely silted up and converted into
+land, the forest-covered surface A B will extend once more over the
+whole area A B E, and a second mass of vegetable matter, D E,
+forming three feet more of coal, will accumulate. We then find in
+the region E C two seams of coals, each three feet thick, with
+their respective under-clays, with erect buried trees based upon
+the surface of the lower coal, the two seams being separated by 25
+feet of intervening shale and sandstone. Whereas in the region A B,
+where the growth of the forest has never been interrupted by
+submergence, there will simply be one seam, two yards thick,
+corresponding to the united thickness of the beds B E and
+<a name="page402"></a>B C. It may be objected that the uninterrupted growth of plants
+during the interval of time required for the filling up of the
+lagoon will have caused the vegetable matter in the region D A B to
+be thicker than the two distinct seams E and C, and no doubt there
+would actually be a slight excess representing one or more
+generation of trees and plants forming the undergrowth; but this
+excess of vegetable matter, when compressed into coal, would be so
+insignificant in thickness that the miner might still affirm that
+the seam D A throughout the area D A B was equal to the two seams C
+and E.</p>
+
+<p><b>Cause of the Purity of Coal.</b>&mdash;The purity of the coal
+itself, or the absence in it of earthy particles and sand,
+throughout areas of vast extent, is a fact which appears very
+difficult to explain when we attribute each coal-seam to a
+vegetation growing in swamps. It has been asked how, during river
+inundations capable of sweeping away the leaves of ferns and the
+stems and roots of <i>Sigillariæ</i> and other trees, could
+the waters fail to transport some fine mud into the swamps? One
+generation after another of tall trees grew with their roots in
+mud, and their leaves and prostrate trunks formed layers of
+vegetable matter, which was afterwards covered with mud since
+turned to shale. Yet the coal itself, or altered vegetable matter,
+remained all the while unsoiled by earthy particles. This enigma,
+however perplexing at first sight, may, I think, be solved by
+attending to what is now taking place in deltas. The dense growth
+of reeds and herbage which encompasses the margins of
+forest-covered swamps in the valley and delta of the Mississippi is
+such that the fluviatile waters, in passing through them, are
+filtered and made to clear themselves entirely before they reach
+the areas in which vegetable matter may accumulate for centuries,
+forming coal if the climate be favourable. There is no possibility
+of the least intermixture of earthy matter in such cases. Thus in
+the large submerged tract called the &ldquo;Sunk Country,&rdquo;
+near New Madrid, forming part of the western side of the valley of
+the Mississippi, erect trees have been standing ever since the year
+1811-12, killed by the great earthquake of that date; lacustrine
+and swamp plants have been growing there in the shallows, and
+several rivers have annually inundated the whole space, and yet
+have been unable to carry in any sediment within the outer
+boundaries of the morass, so dense is the marginal belt of reeds
+and brush-wood. It may be affirmed that generally, in the
+&ldquo;cypress swamps&rdquo; of the Mississippi, no sediment
+mingles with the vegetable matter accumulated there from the decay
+of trees and semi-aquatic plants. As a singular proof of this
+<a name="page403"></a>fact, I may mention that whenever any part of a swamp in
+Louisiana is dried up, during an unusually hot season, and the wood
+set on fire, pits are burnt into the ground many feet deep, or as
+far down as the fire can descend without meeting with water, and it
+is then found that scarcely any residuum or earthy matter is left.
+At the bottom of all these &ldquo;cypress swamps&rdquo; a bed of
+clay is found, with roots of the tall cypress (<i>Taxodium
+distichum</i>), just as the under-clays of the coal are filled with
+<i>Stigmaria.</i></p>
+
+<p><b>Conversion of Coal into Anthracite.</b>&mdash;It appears from
+the researches of Liebig and other eminent chemists, that when wood
+and vegetable matter are buried in the earth exposed to moisture,
+and partially or entirely excluded from the air, they decompose
+slowly and evolve carbonic acid gas, thus parting with a portion of
+their original oxygen. By this means they become gradually
+converted into lignite or wood-coal, which contains a larger
+proportion of hydrogen than wood does. A continuance of
+decomposition changes this lignite into common or bituminous coal,
+chiefly by the discharge of carbureted hydrogen, or the gas by
+which we illuminate our streets and houses. According to Bischoff,
+the inflammable gases which are always escaping from mineral coal,
+and are so often the cause of fatal accidents in mines, always
+contain carbonic acid, carbureted hydrogen, nitrogen, and olefiant
+gas. The disengagement of all these gradually transforms ordinary
+or bituminous coal into anthracite, to which the various names of
+glance-coal, coke, hard-coal, culm, and many others, have been
+given.</p>
+
+<p>There is an intimate connection between the extent to which the
+coal has in different regions parted with its gaseous contents, and
+the amount of disturbance which the strata have undergone. The
+coincidence of these phenomena may be attributed partly to the
+greater facility afforded for the escape of volatile matter, when
+the fracturing of the rocks has produced an infinite number of
+cracks and crevices. The gases and water which are made to
+penetrate these cracks are probably rendered the more effective as
+metamorphic agents by increased temperature derived from the
+interior. It is well known that, at the present period, thermal
+waters and hot vapours burst out from the earth during earthquakes,
+and these would not fail to promote the disengagement of volatile
+matter from the Carboniferous rocks.</p>
+
+<p>In Pennsylvania the strata of coal are horizontal to the
+westward of the Alleghany Mountains, where the late Professor H. D.
+Rogers pointed out that they were most
+<a name="page404"></a>bituminous; but as we travel south-eastward, where they no
+longer remain level and unbroken, the same seams become
+progressively debitumenized in proportion as the rocks become more
+bent and distorted. At first, on the Ohio River, the proportion of
+hydrogen, oxygen, and other volatile matters ranges from forty to
+fifty per cent. Eastward of this line, on the Monongahela, it still
+approaches forty per cent, where the strata begin to experience
+some gentle flexures. On entering the Alleghany Mountains, where
+the distinct anticlinal axes begin to show themselves, but before
+the dislocations are considerable, the volatile matter is generally
+in the proportion of eighteen or twenty per cent. At length, when
+we arrive at some insulated coal-fields associated with the boldest
+flexures of the Appalachian chain, where the strata have been
+actually turned over, as near Pottsville, we find the coal to
+contain only from six per cent of volatile matter, thus becoming a
+genuine anthracite.</p>
+
+<p>
+<b>Clay-ironstone.</b>&mdash;Bands and nodules of clay-ironstone are common in
+coal-measures, and are formed, says Sir H. De la Beche, of carbonate of iron
+mingled mechanically with earthy matter, like that constituting the shales. Mr.
+Hunt, of the Museum of Practical Geology, instituted a series of experiments to
+illustrate the production of this substance, and found that decomposing
+vegetable matter, such as would be distributed through all coal strata,
+prevented the further oxidation of the proto-salts of iron, and converted the
+peroxide into protoxide by taking a portion of its oxygen to form carbonic
+acid. Such carbonic acid, meeting with the protoxide of iron in solution, would
+unite with it and form a carbonate of iron; and this mingling with fine mud,
+when the excess of carbonic acid was removed, might form beds or nodules of
+argillaceous ironstone.<a href="#fn-23.3" name="fnref-23.3"
+id="fnref-23.3"><sup>[3]</sup></a>
+</p>
+
+<p><b>Intercalated Marine Beds in Coal.</b>&mdash;Both in the
+coal-fields of Europe and America the association of fresh,
+brackish-water, and marine strata with coal-seams of terrestrial
+origin is frequently recognised. Thus, for example, a deposit near
+Shrewsbury, probably formed in brackish water, has been described
+by Sir R. Murchison as the youngest member of the coal-measures of
+that district, at the point where they are in contact with the
+overlying Permian group. It consists of shales and sandstones about
+150 feet thick, with coal and traces of plants; including a bed of
+limestone varying from two to nine feet in thickness, which is
+cellular, and resembles some lacustrine limestones of France and
+Germany. It has been traced for 30 miles in a straight line, and
+can be recognised
+<a name="page405"></a>at still more distant points. The characteristic fossils are a
+small bivalve, having the form of a <i>Cyclas</i> or <i>Cyrena,</i>
+also a small entomostracan, <i>Cythere inflata</i> (Fig. 432), and
+the microscopic shell of an annelid of an extinct genus called <i>
+Microconchus</i> (Fig. 431), allied to <i>Spirorbis.</i> In the
+coal-field of Yorkshire there are fresh-water strata, some of which
+contain shells referred to the family Unionidæ; but in the
+midst of the series there is one thin but very widely-spread
+stratum, abounding in fishes and marine shells, such as <i>
+Goniatites Listeri</i> (Fig. 433), <i>Orthoceras,</i> and <i>
+Aviculopecten papyraceus,</i> Goldf. (Fig. 434).</p>
+
+<img src="images/fig431.jpg" width="241" height="420" alt=
+"Fig. 431: Microconchus (Spirorbis) carbonarius. Fig. 432: Cythere (Leperditia)
+inflata. Fig. 433: Goniatites Listeri. Fig. 434: Aviculopecten papyraceus." />
+
+<p><b>Insects in European Coal.</b>&mdash;Articulate animals of the
+genus Scorpion were found by Count Sternberg in 1835 in the
+coal-measures of Bohemia, and about the same time in those of
+Coalbrook Dale by Mr. Prestwich, were also true insects, such as
+beetles of the family <i>Curculionidæ,</i> a neuropterous
+insect of the genus <i>Corydalis,</i> and another related to the
+<i>Phasmidæ,</i> have been found.</p>
+
+<p>
+From the coal of Wetting, in Westphalia, several specimens <a
+name="page406"></a>of the cockroach or <i>Blatta</i> family, and the wing of a
+cricket (<i>Acridites</i>) have been described by Germar. Professor Goldenberg
+published, in 1854, descriptions of no less than twelve species of insects from
+the nodular clay-ironstone of Saarbrück, near Trèves.<a href="#fn-23.4"
+name="fnref-23.4" id="fnref-23.4"><sup>[4]</sup></a> Among them are several <i>
+Blattinæ,</i> three species of <i>Neuroptera,</i> one beetle of the
+<i>Scarabæus</i> family, a grasshopper or locust, <i> Gryllacris</i> (see Fig.
+435), and several white ants or Termites. Professor Goldenberg showed me, in
+1864, the wing of a white ant, found low down in the productive coal-measures
+of Saarbrück, in the interior of a flattened Lepidodendron. It is much larger
+than that of any known living species of the same genus.
+</p>
+
+<p><img src="images/fig435.jpg" width="345" height="186" alt=
+"Fig. 435: Wing of a Grasshopper. Gryllacris lithanthraca." />
+</p>
+
+<img src="images/fig436.jpg" width="257" height="432" alt=
+"Fig. 436: Archegosaurus minor. Fossil reptile from the coal-measures, Saarbrück." />
+
+<p><b>Batrachian Reptiles in Coal.</b>&mdash;No vertebrated animals
+more highly organised than fish were known in rocks of higher
+antiquity than the Permian until the year 1844, when the <i>Apateon
+pedestris,</i> Meyer, was discovered in the coal-measures of
+Munster-Appel in Rhenish Bavaria, and three years later, in 1847,
+Professor von Dechen found three other distinct species of the same
+family of Amphibia in the Saarbruck coal-field above alluded to.
+These were described by the late Professor Goldfuss under the
+generic name of <i>Archegosaurus.</i> The skulls, teeth, and the
+greater portions of the skeleton, nay, even a large part of the
+skin, of two of these reptiles have been faithfully preserved in
+the centre of spheroidal concretions of clay-ironstone. The largest
+of these, <i>Archegosaurus Decheni,</i> must
+<a name="page407"></a>have been three feet six inches long. Figure 436 represents the
+skull and neck bones of the smallest of the three, of the natural
+size. They were considered by Goldfuss as saurians, but by Herman
+von Meyer as most nearly allied to the <i>Labyrinthodon</i> before
+mentioned (<a href="#page371">p. 371</a>), and the
+remains of the extremities leave no doubt they were quadrupeds,
+&ldquo;provided,&rdquo; says Von Meyer, &ldquo;with hands and feet
+terminating in distinct toes; but these limbs were weak, serving
+only for swimming or creeping.&rdquo; The same anatomist has
+pointed out certain points of analogy between their bones and those
+of the <i>Proteus anguinus</i>; and Professor Owen has observed
+that they make an approach to the <i>Proteus</i> in the shortness
+of their ribs. Two specimens of these ancient reptiles retain a
+large part of the outer skin, which consisted of long, narrow,
+wedge-shaped, tile-like, and horny scales, arranged in rows (see
+Fig. 437).</p>
+
+<img src="images/fig437.jpg" width="182" height="123" alt=
+"Fig. 437: Imbricated covering of skin of Archegosaurus medius." />
+
+<p>In 1865, several species belonging to three different genera of
+the same family of perennibranchiate Batrachians were found in the
+coal-field of Kilkenny in bituminous shale at the junction of the
+coal with the underlying Stigmaria-bearing clay. They were,
+probably, inhabitants of a marsh, and the large processes
+projecting from the vertebræ of their tail imply, according
+to Professor Huxley, great powers of swimming. They were of the
+Labyrinthodont family, and their association with the fish of the
+coal, of which so large a proportion are ganoids, reminds us that
+the living perennibranchiate amphibia of America frequent the same
+rivers as the ganoid Lepidostei or bony pikes.</p>
+
+<p>
+<i>Labyrinthodont footprints in coal-measures.</i>&mdash;In 1844, the very year
+when the Apateon, before mentioned, of the coal was first met with in the
+country between the Moselle and the Rhine, Dr. King published an account of the
+footprints of a large reptile discovered by him in North America. These occur
+in the coal-strata of Greensburg, in Westmoreland County, Pennsylvania; and I
+had an opportunity of examining them when in that country in 1846. The
+footmarks were first observed standing out in relief from the lower surface of
+slabs of sandstone, resting on thin layers of fine unctuous clay. I brought
+away one of these masses, which is represented in Fig. 438. It displays,
+together with footprints, the casts of cracks (<i>a, a&#x2032;</i>) of various
+sizes. The origin of such cracks in
+<a name="page408"></a>clay, and casts of the same, has before been explained, and
+referred to the drying and shrinking of mud, and the subsequent
+pouring of sand into open crevices. It will be seen that some of
+the cracks, as at <i>b, c,</i> traverse the footprints, and produce
+distortion in them, as might have been expected, for the mud must
+have been soft when the animal walked over it and left the
+impressions; whereas, when it afterwards dried up and shrank, it
+would be too hard to receive such indentations.</p>
+
+<p><img src="images/fig438.jpg" width="404" height="528" alt=
+"Fig. 438: Slab of sandstone from the coal-measures of Pennsylvania, with
+foot-prints of air-breathing reptile and casts of cracks." />
+</p>
+
+<p>We may assume that the reptile which left these prints
+<a name="page409"></a>on the ancient sands of the coal-measures was an air-breather,
+because its weight would not have been sufficient under water to
+have made impressions so deep and distinct. The same conclusion is
+also borne out by the casts of the cracks above described, for they
+show that the clay had been exposed to the air and sun, so as to
+have dried and shrunk.</p>
+
+<p>
+<b>Nova Scotia Coal-measures.</b>&mdash;The sedimentary strata in which thin
+seams of coal occur attain a thickness, as we have seen, of 18,000 feet in the
+north of England exclusive of the Mountain Limestone, and are estimated by Von
+Dechen at over 20,000 feet in Rhenish Prussia. But the finest example in the
+world of a natural exposure in a continuous section ten miles long, occurs in
+the sea-cliffs bordering a branch of the Bay of Fundy, in Nova Scotia. These
+cliffs, called the &ldquo;South Joggins,&rdquo; which I first examined in 1842,
+and afterwards with Dr. Dawson in 1845, have lately been admirably described by
+the last-mentioned geologist<a href="#fn-23.5" name="fnref-23.5"
+id="fnref-23.5"><sup>[5]</sup></a> in detail, and his evidence is most valuable
+as showing how large a portion of this dense mass was formed on land, or in
+swamps where terrestrial vegetation flourished, or in fresh-water lagoons. His
+computation of the thickness of the whole series of carboniferous strata as
+exceeding three miles, agrees with the measurement made independently by Sir
+William Logan in his survey of this coast.
+</p>
+
+<p>There is no reason to believe that in this vast succession of
+strata, comprising some marine as well as many fresh-water and
+terrestrial formations, there is any repetition of the same beds.
+There are no faults to mislead the geologist, and cause him to
+count the same beds over more than once, while some of the same
+plants have been traced from the top to the bottom of the whole
+series, and are distinct from the flora of the antecedent Devonian
+formation of Canada. Eighty-one seams of coal, varying in thickness
+from an inch to about five feet, have been discovered, and no less
+than seventy-one of these have been actually exposed in the
+sea-cliffs.</p>
+
+<p>In the section (Fig. 439), which I examined in 1842, the beds
+from <i>c</i> to <i>i</i> are seen all dipping the same way, their
+average inclination being at an angle of 24&deg; S.S.W. The
+vertical height of the cliffs is from 150 to 200 feet; and between
+<i>d</i> and <i>g</i>&mdash;in which space I observed seventeen
+trees in an upright position, or, to speak more correctly, at right
+angles to the planes of stratification&mdash;I counted nineteen
+seams of coal, varying in thickness from two inches to four feet.
+At low tide a fine horizontal section of the same beds is exposed
+to view on the beach, which at low tide extends sometimes 200
+<a name="page410"></a>yards from the base of the cliff. The thickness of the beds
+alluded to, between <i>d</i> and <i>g,</i> is about 2500 feet, the
+erect trees consisting chiefly of large <i>Sigillariæ,</i>
+occurring at ten distinct levels, one above the other. The usual
+height of the buried trees seen by me was from six to eight feet;
+but one trunk was about 25 feet high and four feet in diameter,
+with a considerable bulge at the base. In no instance could I
+detect any trunk intersecting a layer of coal, however thin; and
+most of the trees terminated downward in seams of coal. Some few
+only were based on clay and shale; none of them, except <i>
+Calamites,</i> on sandstone. The erect trees, therefore, appeared
+in general to have grown on beds of vegetable matter. In the
+underclays <i>Stigmaria</i> abounds.</p>
+
+<p><img src="images/fig439.jpg" width="394" height="142" alt=
+"Fig. 439: Section of the cliffs of the South Joggins, near Minudie, Nova Scotia." />
+</p>
+
+<p>These root-bearing beds have been found under all the
+coal-seams, and such old soils are at present the most destructible
+masses in the whole cliff, the sandstones and laminated shales
+being harder and more capable of resisting the action of the waves
+and the weather. Originally the reverse was doubtless true, for in
+the existing delta of the Mississippi those clays in which the
+innumerable roots of the deciduous cypress and other swamp trees
+ramify in all directions are seen to withstand far more effectually
+the undermining power of the river, or of the sea at the base of
+the delta, than do beds of loose sand or layers of mud not
+supporting trees. It is obvious that if this sand or mud be
+afterwards consolidated and turned to sandstone and hard shale, it
+would be the least destructible.</p>
+
+<p>In regard to the plants, they belonged to the same genera, and
+most of them to the same species, as those met with in the distant
+coal-fields of Europe. Dr. Dawson has enumerated more than 150
+species, two-thirds of which are European, a greater agreement than
+can be said to exist between the same Nova Scotia flora and that of
+the coal-fields of the United States. By referring to the section,
+Fig. 439, the position of the four-foot coal will be perceived, and
+in Fig. 440 (a section made by me in 1842 of a small portion) that
+from <i>e</i> to <i>f</i>
+<a name="page411"></a>of the same cliff is exhibited, in order to show the manner of
+occurrence of erect fossil trees at right angles to the planes of
+the inclined strata.</p>
+
+<img src="images/fig440.jpg" width="284" height="207" alt=
+"Fig. 440: Erect fossil trees, Coal-measures, Nova Scotia." />
+
+<p>In the sandstone which filled their interiors, I frequently
+observed fern-leaves, and sometimes fragments of <i>Stigmaria,</i>
+which had evidently entered together with sediment after the trunk
+had decayed and become hollow, and while it was still standing
+under water. Thus the tree, <i>a,</i> Fig. 440, represented in the
+bed <i>e</i> in the section, Fig. 439, is a hollow trunk five feet
+eight inches in length, traversing various strata, and cut off at
+the top by a layer of clay two feet thick, on which rests a seam of
+coal (<i>b,</i> Fig. 440) one foot thick. On this coal again stood
+two large trees (<i>c</i> and <i>d</i>), while at a greater height
+the trees <i>f</i> and <i>g</i> rest upon a thin seam of coal
+(<i>e</i>), and above them is an underclay, supporting the
+four-foot coal.</p>
+
+<p>Occasionally the layers of matter in the inside of the tree are
+more numerous than those without; but it is more common in the
+coal-measures of all countries to find a cylinder of pure
+sandstone&mdash;the cast of the interior of a
+tree&mdash;intersecting a great many alternating beds of shale and
+sandstone, which originally enveloped the trunk as it stood erect
+in the water. Such a want of correspondence in the materials
+outside and inside, is just what we might expect if we reflect on
+the difference of time at which the deposition of sediment will
+take place in the two cases; the imbedding of the tree having gone
+on for many years before its decay had made much progress. In many
+places distinct proof is seen that the enveloping strata took years
+to accumulate, for some of the sandstones surrounding erect
+sigillarian trunks support at different levels roots and stems of
+<i>Calamites</i>; the <i>Calamites</i> having begun to grow after
+the older <i>Sigillariæ</i> had been partially buried.</p>
+
+<p>The general absence of structure in the interior of the large
+fossil trees of the Coal implies the very durable nature of their
+bark, as compared with their woody portion. The
+<a name="page412"></a>same difference of durability of bark and wood exists in modern
+trees, and was first pointed out to me by Dr. Dawson, in the
+forests of Nova Scotia, where the Canoe Birch (<i>Betula
+papyracea</i>) has such tough bark that it may sometimes be seen in
+the swamps looking externally sound and fresh, although consisting
+simply of a hollow cylinder with all the wood decayed and gone.
+When portions of such trunks have become submerged in the swamps
+they are sometimes found filled with mud. One of the erect fossil
+trees of the South Joggins fifteen feet in height, occurring at a
+higher level than the main coal, has been shown by Dr. Dawson to
+have a coniferous structure, so that some <i>Coniferæ</i> of
+the Coal period grew in the same swamps as <i>Sigillariæ,</i>
+just as now the deciduous Cypress (<i>Taxodium distichum</i>)
+abounds in the marshes of Louisiana even to the edge of the
+sea.</p>
+
+<p>When the carboniferous forests sank below high-water mark, a
+species of <i>Spirorbis</i> or <i>Serpula</i> (<a href=
+"images/fig431.jpg">Fig. 431</a>), attached itself to the outside
+of the stumps and stems of the erect trees, adhering occasionally
+even to the interior of the bark&mdash;another proof that the
+process of envelopment was very gradual. These hollow upright
+trees, covered with innumerable marine annelids, reminded me of a
+&ldquo;cane-brake,&rdquo; as it is commonly called, consisting of
+tall reeds, <i>Arundinaria macrosperma,</i> which I saw in 1846, at
+the Balize, or extremity of the delta of the Mississippi. Although
+these reeds are fresh-water plants, they were covered with
+barnacles, having been killed by an incursion of salt-water over an
+extent of many acres, where the sea had for a season usurped a
+space previously gained from it by the river. Yet the dead reeds,
+in spite of this change, remained standing in the soft mud,
+enabling us to conceive how easily the larger <i>
+Sigillariæ,</i> hollow as they were but supported by strong
+roots, may have resisted an incursion of the sea.</p>
+
+<p>The high tides of the Bay of Fundy, rising more than 60 feet,
+are so destructive as to undermine and sweep away continually the
+whole face of the cliffs, and thus a new crop of erect fossil trees
+is brought into view every three or four years. They are known to
+extend over a space between two and three miles from north to
+south, and more than twice that distance from east to west, being
+seen in the banks of streams intersecting the coal-field.</p>
+
+<p><i>Structure of Coal.</i>&mdash;The bituminous coal of Nova
+Scotia is similar in composition and structure to that of Great
+Britain, being chiefly derived from sigillarioid trees mixed with
+leaves of ferns and of a Lycopodiaceous tree called <i>
+Cordaites</i>
+<a name="page413"></a>(<i>Noeggerathia,</i> etc., for genus, see <a href=
+"images/fig428.jpg">Fig. 428</a>), supposed by Dawson to have been
+deciduous, and which had broad parallel veined leaves without a
+mid-rib. On the surface of the seams of coal are large quantities
+of mineral charcoal, which doubtless consist, as Dr. Dawson
+suggests, of fragments of wood which decayed in the open air, as
+would naturally be expected in swamps where so many erect trees
+were preserved. Beds of cannel-coal display, says Dr. Dawson, such
+a microscopical structure and chemical composition as shows them to
+have been of the nature of fine vegetable mud such as accumulates
+in the shallow ponds of modern swamps. The underclays are loamy
+soils, which must have been sufficiently above water to admit of
+drainage, and the absence of sulphurets, and the occurrence of
+carbonate of iron in them, prove that when they existed as soils,
+rain-water, and not sea-water, percolated them. With the exception,
+perhaps, of <i>Asterophyllites</i> (see <a href=
+"images/fig460.jpg">Fig. 461</a>), there is a remarkable absence
+from the coal-measures of any form of vegetation properly aquatic,
+the true coal being a sub-aërial accumulation in soil that was
+wet and swampy but not permanently submerged.</p>
+
+<p>
+<b>Air-breathers of the Coal.</b>&mdash;If we have rightly interpreted the
+evidence of the former existence at more than eighty different levels of
+forests of trees, some of them of vast extent, and which lasted for ages,
+giving rise to a great accumulation of vegetable matter, it is natural to ask
+whether there were not many air-breathing inhabitants of these same regions. As
+yet no remains of mammalia or birds have been found, a negative character
+common at present to all the Palæozoic formations; but in 1852 the osseous
+remains of a reptile, the first ever met with in the carboniferous strata of
+the American continent, were found by Dr. Dawson and myself. We detected them
+in the interior of one of the erect Sigillariæ before alluded to as of such
+frequent occurrence in Nova Scotia. The tree was about two feet in diameter,
+and consisted of an external cylinder of bark, converted into coal, and an
+internal stony axis of black sandstone, or rather mud and sand stained black by
+carbonaceous matter, and cemented together with fragments of wood into a rock.
+These fragments were in the state of charcoal, and seem to have fallen to the
+bottom of the hollow tree while it was rotting away. The skull, jaws, and
+vertebræ of a reptile, probably about 2&frac12; feet in length (<i>Dendrerpeton
+Acadianum,</i> Owen), were scattered through this stony matrix. The shell,
+also, of a <i> Pupa</i> (see <a href="images/fig442.jpg">Fig. 442</a>), the
+first land-shell ever met with in the coal or in beds older than the tertiary,
+was observed in the <a name="page414"></a>same stony mass. Dr. Wyman of Boston
+pronounced the reptile to be allied in structure to <i>Menobranchus</i> and
+<i>Menopoma,</i> species of batrachians, now inhabiting the North American
+rivers. The same view was afterwards confirmed by Professor Owen, who also
+pointed out the resemblance of the cranial plates to those seen in the skull of
+<i>Archegosaurus</i> and <i>Labyrinthodon.</i><a href="#fn-23.6"
+name="fnref-23.6" id="fnref-23.6"><sup>[6]</sup></a> Whether the creature had
+crept into the hollow tree while its top was still open to the air, or whether
+it was washed in with mud during a flood, or in whatever other manner it
+entered, must be matter of conjecture.
+</p>
+
+<p>
+Footprints of two reptiles of different sizes had previously been observed by
+Dr. Harding and Dr. Gesner on ripple-marked flags of the lower coal-measures in
+Nova Scotia (No. 2, <a href= "images/fig447.jpg">Fig. 447</a>), evidently made
+by quadrupeds walking on the ancient beach, or out of the water, just as the
+recent Menopoma is sometimes observed to do. The remains of a second and
+smaller species of Dendrerpeton, <i>D. Oweni,</i> were also found accompanying
+the larger one, and still retaining some of its dermal appendages; and in the
+same tree were the bones of a third small lizard-like reptile, <i>Hylonomus
+Lyelli,</i> seven inches long, with stout hind limbs, and fore limbs
+comparatively slender, supposed by Dr. Dawson to be capable of walking and
+running on land.<a href="#fn-23.7" name="fnref-23.7"
+id="fnref-23.7"><sup>[7]</sup></a>
+</p>
+
+<p><img src="images/fig441.jpg" width="386" height="160" alt=
+"Fig. 441: Xylobius Sigillariæ. Coal, Nova Scotia." /></p>
+
+<p>In a second specimen of an erect stump of a hollow tree 15
+inches in diameter, the ribbed bark of which showed that it was a
+Sigillaria, and which belonged to the same forest as the specimen
+examined by us in 1852, Dr. Dawson obtained not only fifty
+specimens of Pupa vetusta (Fig. 442), and nine skeletons of
+reptiles belonging to four species, but also several examples of an
+articulated animal resembling the recent centipede or gally-worm, a
+creature which feeds on decayed vegetable matter (see Fig. 441).
+Under the microscope, the
+<a name="page415"></a>head, with the eyes, mandible, and labrum, are well seen. It is
+interesting, as being the earliest known representative of the
+myriapods, none of which had previously been met with in rocks
+older than the oolite or lithographic slate of Germany.</p>
+
+<img src="images/fig442.jpg" width="118" height="255" alt=
+"Fig. 442: Pupa vetusta." />
+
+<p>Some years after the discovery of the first Pupa, Dr. Dawson,
+carefully examining the same great section containing so many
+buried forests in the cliffs of Nova Scotia, discovered another
+bed, separated from the tree containing Dendrerpeton by a mass of
+strata more than 1200 feet thick. As there were 21 seams of coal in
+this intervening mass, the length of time comprised in the interval
+is not to be measured by the mere thickness of the sandstones and
+shales. This lower bed is an underclay seven feet thick, with
+stigmarian rootlets, and the small land-shells occurring in it are
+in all stages of growth. They are chiefly confined to a layer about
+two inches thick, and are unmixed with any aquatic shells. They
+were all originally entire when imbedded, but are most of them now
+crushed, flattened, and distorted by pressure; they must have been
+accumulated, says Dr. Dawson, in mud deposited in a pond or
+creek.</p>
+
+<img src="images/fig443.jpg" width="126" height="134" alt=
+"Fig. 443: Zonites (Conulus) priseus." />
+
+<p>
+The surface striæ of <i>Pupa vetusta,</i> when magnified 50 diameters, present
+exactly the same appearance as a portion corresponding in size of the common
+English <i>Pupa juniperi,</i> and the internal hexagonal cells, magnified 500
+diameters, show the internal structure of the fossil and recent Pupa to be
+identical. In 1866<a href="#fn-23.8" name="fnref-23.8"
+id="fnref-23.8"><sup>[8]</sup></a> Dr. Dawson discovered in this lower bed, so
+full of the Pupa, another land-shell of the genus Helix (sub-genus Zonites),
+see Fig. 443.
+</p>
+
+<p>None of the reptiles obtained from the coal-measures of the
+South Joggins are of a higher grade than the Labyrinthodonts, but
+some of these were of very great size, two caudal vertebræ
+found by Mr. Marsh in 1862 measuring two and a half inches in
+diameter, and implying a gigantic aquatic reptile with a powerful
+swimming tail.</p>
+
+<p>Except some obscure traces of an insect found by Dr.
+<a name="page416"></a>Dawson in a coprolite of a terrestrial reptile occurring in a
+fossil tree, no specimen of this class has been brought to light in
+the Joggins. But Mr. James Barnes found in a bed of shale at Little
+Grace Bay, Cape Breton, the wing of an Ephemera, which must have
+measured seven inches from tip to tip of the expanded
+wings&mdash;larger than any known living insect of the Neuropterous
+family.</p>
+
+<p>That we should have made so little progress in obtaining a
+knowledge of the terrestrial fauna of the Coal is certainly a
+mystery, but we have no reason to wonder at the extreme rarity of
+insects, seeing how few are known in the carboniferous rocks of
+Europe, worked for centuries before America was discovered, and now
+quarried on so enormous a scale. These European rocks have not yet
+produced a single land-shell, in spite of the millions of tons of
+coal annually extracted, and the many hundreds of soils replete
+with the fossil roots of trees, and the erect trunks and stumps
+preserved in the position in which they grew. In many large
+coal-fields we continue as much in the dark respecting the
+invertebrate air-breathers then living, as if the coal had been
+thrown down in mid-ocean. The early date of the carboniferous
+strata cannot explain the enigma, because we know that while the
+land supported a luxuriant vegetation, the contemporaneous seas
+swarmed with life&mdash;with Articulata, Mollusca, Radiata, and
+Fishes. The perplexity in which we are involved when we attempt to
+solve this problem may be owing partly to our want of diligence as
+collectors, but still more perhaps to ignorance of the laws which
+govern the fossilisation of land-animals, whether of high or low
+degree.</p>
+
+<p><b>Carboniferous Rain-prints.</b>&mdash;At various levels in the
+coal measures of Nova Scotia, ripple-marked sandstones, and shales
+with rain-prints, were seen by Dr. Dawson and myself, but still
+more perfect impressions of rain were discovered by Mr. Brown, near
+Sydney, in the adjoining island of cape Breton. They consist of
+very delicate markings on greenish slates, accompanied by
+worm-tracks (<i>a, b,</i> Fig. 444), such as are often seen between
+high and low water mark on the recent mud of the Bay of Fundy.</p>
+
+<p>The great humidity of the climate of the Coal period had been
+previously inferred from the number of its ferns and the continuity
+of its forests for hundreds of miles; but it is satisfactory to
+have at length obtained such positive proofs of showers of rain,
+the drops of which resembled in their average size those which now
+fall from the clouds. From such data we may presume that the
+atmosphere of the Carboniferous period corresponded in density with
+that now investing
+<a name="page417"></a>the globe, and that different currents of air varied then as now
+in temperature, so as to give rise, by their mixture, to the
+condensation of aqueous vapour.</p>
+
+<p><img src="images/fig444.jpg" width="411" height="306" alt=
+"Fig. 444: Carboniferous rain-prints with worm tracks on green shale, from Cape
+Breton, Nova Scotia. Fig. 445: Casts of rain-prints on a portion of the same
+slab (Fig. 444), seen to project on the underside of an incumbent layer of
+arenaceous shale." />
+</p>
+
+<p><b>Folding and Denudation of the Beds indicated by the Nova
+Scotia Coal-strata.</b>&mdash;The series of events which are
+indicated by the great section of the coal-strata in Nova Scotia
+consist of a gradual and long-continued subsidence of a tract which
+throughout most of the period was in the state of a delta, though
+occasionally submerged beneath a sea of moderate depth. Deposits of
+mud and sand were first carried down into a shallow sea on the low
+shores of which the footprints of reptiles were sometimes impressed
+(see <a href="#page407">p. 407</a>).</p>
+
+<img src="images/fig446.jpg" width="149" height="216" alt=
+"Fig. 446: Cone and branch of Lepidodendron corrugatum." />
+
+<p>Though no regular seams of coal were formed, the characteristic
+imbedded coal-plants are of the genera <i>Cyclopteris</i> and <i>
+Alethopteris,</i> agreeing with species occurring at much higher
+levels, and distinct from those of the antecedent Devonian group.
+The <i>Lepidodendron corrugatum</i> (see Fig. 446), a plant
+predominating in the Lower Carboniferous group of Europe, is also
+conspicuous in these shallow-water beds, together with many fishes
+and entomostracans. A more rapid rate of subsidence sometimes
+converted part of the sea into deep clear water, in which there
+<a name="page418"></a>was a growth of coral which was afterwards turned into
+crystalline limestone, and parts of it, apparently by the action of
+sulphuric acid, into gypsum. In spite of continued sinking,
+amounting to several thousand feet, the sea might in time have been
+rendered shallow by the growth of coral, had not its conversion
+into land or swampy ground been accelerated by the pouring in of
+sand and the advance of the delta accompanied with such fluviatile
+and brackish-water formations as are common in lagoons.</p>
+
+<p>The amount to which the bed of the sea sank down in order to
+allow of the formation of so vast a thickness of rock of
+sedimentary and organic origin is expressed by the total thickness
+of the Carboniferous strata, including the coal-measures, No. 1,
+and the rocks which underlie them, No. 2, Fig. 447.</p>
+
+<p><img src="images/fig447.jpg" width="400" height="187" alt=
+"Fig. 447: Diagram showing the curvature and supposed denudation of the
+Carboniferous strata in Nova Scotia." />
+</p>
+
+<p>After the strata No. 2 had been elaborated, the conditions
+proper to a great delta exclusively prevailed, the subsidence still
+continuing so that one forest after another grew and was submerged
+until their under-clays with roots, and usually seams of coal, were
+left at more than eighty distinct levels. Here and there, also,
+deposits bearing testimony to the existence of fresh or
+brackish-water lagoons, filled with calcareo-bituminous mud, were
+formed. In these beds (<i>h</i> and <i>i,</i> <a href=
+"images/fig439.jpg">Fig. 439</a>) are found fresh-water bivalves
+or mussels allied to Anodon, though not identical with that or any
+living genus, and called <i>Naiadites carbonarius</i> by Dawson.
+They are associated with small entomostracous crustaceans of the
+genus Cythere, and scales of small fishes. Occasionally some of the
+calamite brakes and forests of Sigillariæ and Coniferæ
+were exposed in the flood season, or sometimes, perhaps, by slight
+elevatory movements to the denuding action of the river or the
+sea.</p>
+
+<p>In order to interpret the great coast section exposed to view on
+the shores of the Bay of Fundy, the student must,
+<a name="page419"></a>in the first place, understand that the newest or last-mentioned
+coal formations would have been the only ones known to us (for they
+would have covered all the others), had there not been two great
+movements in opposite directions, the first consisting of a general
+sinking of three miles, which took place during the Carboniferous
+Period, and the second an upheaval of more limited horizontal
+extent, by which the anticlinal axis A was formed. That the first
+great change of level was one of subsidence is proved by the fact
+that there are shallow-water deposits at the base of the
+Carboniferous series, or in the lowest beds of No. 2.</p>
+
+<p>Subsequent movements produced in the Nova Scotia and the
+adjoining New Brunswick coal-fields the usual anticlinal and
+synclinal flexures. In order to follow these, we must survey the
+country for about thirty miles round the South Joggins, or the
+region where the erect trees described in the foregoing pages are
+seen. As we pass along the cliffs for miles in a southerly
+direction, the beds containing these fossil trees, which were
+mentioned as dipping about 18&deg; south, are less and less
+inclined, until they become nearly horizontal in the valley of a
+small river called the Shoulie, as ascertained by Dr. Dawson. After
+passing this synclinal line the beds begin to dip in an opposite or
+north-easterly direction, acquiring a steep dip where they rest
+unconformably on the edges of the Upper Silurian strata of the
+Cobequid Hills, as shown in Fig. 447. But if we travel northward
+towards Minudie from the region of the coal-seams and buried
+forests, we find the dip of the coal-strata increasing from an
+angle of 18&deg; to one of more than 40&deg;, lower beds being
+continually exposed to view until we reach the anticlinal axis A
+and see the lower Carboniferous formation, No. 2, at the surface.
+The missing rocks removed by denudation are expressed by the faint
+lines at A, and thus the student will see that, according to the
+principles laid down in the seventh chapter, we are enabled, by the
+joint operations of upheaval and denudation, to look, as it were,
+about three miles into the interior of the earth without passing
+beyond the limits of a single formation.
+</p>
+
+<p class="footnote">
+<a name="fn-23.1" id="fn-23.1"></a> <a href="#fnref-23.1">[1]</a>
+Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 327.
+</p>
+
+<p class="footnote">
+<a name="fn-23.2" id="fn-23.2"></a> <a href="#fnref-23.2">[2]</a>
+Quart. Geol. Journ., vol. v, Mem., p. 17.
+</p>
+
+<p class="footnote">
+<a name="fn-23.3" id="fn-23.3"></a> <a href="#fnref-23.3">[3]</a>
+Memoirs of the Geol. Survey, pp. 51, 255, etc.
+</p>
+
+<p class="footnote">
+<a name="fn-23.4" id="fn-23.4"></a> <a href="#fnref-23.4">[4]</a>
+Dunker and V. Meyer, Palæont., vol. iv, p. 17.
+</p>
+
+<p class="footnote">
+<a name="fn-23.5" id="fn-23.5"></a> <a href="#fnref-23.5">[5]</a>
+Acadian Geology, 2nd edit., 1868.
+</p>
+
+<p class="footnote">
+<a name="fn-23.6" id="fn-23.6"></a> <a href="#fnref-23.6">[6]</a>
+Quart. Geol. Journ., vol. ix, p. 58.
+</p>
+
+<p class="footnote">
+<a name="fn-23.7" id="fn-23.7"></a> <a href="#fnref-23.7">[7]</a>
+Dawson, Air-Breathers of the Coal in Nova Scotia, Montreal, 1863.
+</p>
+
+<p class="footnote">
+<a name="fn-23.8" id="fn-23.8"></a> <a href="#fnref-23.8">[8]</a>
+Dawson, Acadian Geology, 1868, p. 385.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap24"></a><a name="page420"></a>CHAPTER XXIV.<br/>
+FLORA AND FAUNA OF THE CARBONIFEROUS PERIOD.</h2>
+
+<p class="letter">Vegetation of the Coal Period. &mdash; Ferns,
+Lycopodiaceæ, Equisetaceæ, Sigillariæ,
+Stigmariæ, Coniferæ. &mdash; Angiosperms. &mdash;
+Climate of the Coal Period. &mdash; Mountain Limestone. &mdash;
+Marine Fauna of the Carboniferous Period. &mdash; Corals. &mdash;
+Bryozoa, Crinoidea. &mdash; Mollusca. &mdash; Great Number of
+fossil Fish. &mdash; Foraminifera.</p>
+
+<p><b>Vegetation of the Coal Period.</b>&mdash;In the last chapter
+we have seen that the seams of coal, whether bituminous or
+anthracitic, are derived from the same species of plants, and
+Goppert has ascertained that the remains of every family of plants
+scattered through the shales and sandstones of the coal-measures
+are sometimes met with in the pure coal itself&mdash;a fact which adds
+greatly to the geological interest of this flora.</p>
+
+<p>
+The coal-period was called by Adolphe Brongniart the age of Acrogens,<a
+href="#fn-24.1" name="fnref-24.1" id="fnref-24.1"><sup>[1]</sup></a> so great
+appears to have been the numerical preponderance of flowerless or cryptogamic
+plants of the families of ferns, club-mosses, and horse-tails. He reckoned the
+known species in 1849 at 500, and the number has been largely increased by
+recent research in spite of reductions owing to the discovery that different
+parts of even the same plants had been taken for distinct species.
+Notwithstanding these changes, Brongniart&rsquo;s generalisation concerning
+this flora still holds true, namely, that the state of the vegetable world was
+then extremely different from that now prevailing, not only because the
+cryptogamous plants constituted nearly the whole flora, but also because they
+were, on the whole, more highly developed than any belonging to the same class
+now existing, and united some forms of structure now only found separately and
+in distinct orders. The only phænogamous plants were constitute any feature in
+the coal are the coniferæ; monocotyledonous angiosperms appear to have been
+very rare, and the dicotyledonous, with one or two doubtful exceptions, were
+wanting. For this we are in some measure prepared by what we have seen of the
+Secondary or Mesozoic floras if, consistently with the belief in the theory of
+evolution, we expect to find the prevalence of simpler and less specialised
+organisms in older rocks.
+</p>
+
+
+<p>
+<a name="page421"></a><b>Ferns.</b>&mdash;We are struck at the first glance with the
+similarity of the ferns to those now living. In the fossil genus
+<i>Pecopteris,</i> for example (Fig. 448), it is not easy to decide
+whether the fossils might not be referred to the same genera as
+those established for living ferns; whereas, in regard to some of
+the other contemporary families of plants, with the exception of
+the fir tribe, it is not easy to guess even the class to which they
+belong. The ferns of the Carboniferous period are generally without
+organs of fructification, but in the few instances in which these
+do occur in a fit state for microscopical investigations they agree
+with those of the living ferns.</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig448.jpg" width="386" height="291" alt="Fig. 448: Pecopteris
+elliptica. Fig. 449: Caulopteris primæva." />
+<p class="caption">Fig. 448: <i>Pecopteris elliptica</i>,
+Bunbury.<a href="#fn-24.2" name="fnref-24.2" id="fnref-24.2"><sup>[2]</sup></a> Frostburg.<br/>
+Fig. 449: <i>Caulopteris primæva</i>, Lindley.<br/></p>
+</div>
+
+<p>When collecting fossil specimens from the coal-measures of
+Frostburg, in Maryland, I found in the iron-shales several species
+with well-preserved rounded spots or marks of the sori (see Fig.
+448). In the general absence of such characters they have been
+divided into genera distinguished chiefly by the branching of the
+fronds and the way in which the veins of the leaves are disposed.
+The larger portion are supposed to have been of the size of
+ordinary European ferns, but some were decidedly arborescent,
+especially the group called <i>Caulopteris</i> (see Fig. 449) by
+Lindley, and the <i>Psaronius</i> of the upper or newest
+coal-measures, before alluded to (<a href="#page393">p.
+393</a>). All the recent tree-ferns belong to one tribe
+(<i>Polypodiaceæ</i>), and to a small number only of genera
+in that tribe, in which the surface of the trunk is marked with
+scars,
+<a name="page422"></a>or cicatrices, left after the fall of the fronds. These scars
+resemble those of <i>Caulopteris.</i></p>
+
+<p>No less than 130 species of ferns are enumerated as having been
+obtained from the British coal-strata, and this number is more than
+doubled if we include the Continental and American species. Even if
+we make some reduction on the ground of varieties which have been
+mistaken, in the absence of their fructification, for species,
+still the result is singular, because the whole of Europe affords
+at present no more than sixty-seven indigenous species.</p>
+
+<p><img src="images/fig450.jpg" width="315" height="346" alt=
+"Living tree-ferns of different genera. Fig. 450: Tree-fern from Isle of
+Bourbon. Fig. 451: Cyathea glauca, Mauritius. Fig. 452: Tree-fern from Brazil." />
+</p>
+
+<p><b>
+Lycopodiaceæ</b>&mdash;<i>Lepidodendron.</i>&mdash;About
+forty species of fossil plants of the Coal have been referred to
+this genus, more than half of which are found in the British
+coal-measures. They consist of cylindrical stems or trunks, covered
+with leaf-scars. In their mode of branching, they are always
+dichotomous (see <a href="images/fig453.jpg">Fig. 454</a>). They
+belong to the <i>Lycopodiaceæ,</i> bearing sporangia and
+spores similar to those of the living representatives of this
+family (<a href="images/fig457.jpg">Fig. 457</a>); and although
+most of the Carboniferous species grew to the size of large trees,
+Mr. Carruthers has found by careful measurement that the volume of
+the fossil spores did not exceed that of the recent club-moss, a
+fact of some geological importance, as it may help to explain the
+facility with which these seeds may
+<a name="page423"></a>have been transported by the wind, causing the same wide
+distribution of the species of the fossil forests in Europe and
+America which we now observe in the geographical distribution of so
+many living families of cryptogamous plants.</p>
+
+<p><img src="images/fig453.jpg" width="344" height="310" alt=
+"Lepidodendrum Sternbergii. Coal-measures, near Newcastle. Fig. 453: Branching
+trunk, 49 feet long, supposed to have belonged to L. Sternbergii. Fig. 454:
+Branching stem with bark and leaves of L. Sternbergii. Fig. 455: Portion of
+same, nearer the root." />
+</p>
+
+<img src="images/fig456.jpg" width="293" height="244" alt=
+"Fig. 456: a. Lycopodium densum. Living species, New Zealand; b. Branch; c.
+Part of same, magnified." />
+
+<p>The Figs. 453&ndash;455 represent a fossil <i>Lepidodendron,</i>
+49 feet long, found in Jarrow Colliery, near Newcastle, lying in
+shale parallel to the planes of stratification. Fragments of
+others, found in the same shale, indicate, by the size of the
+rhomboidal scars which cover them, a still greater magnitude.</p>
+
+<p>The living club-mosses, of which there are about 200 species,
+are most abundant in tropical climates. They usually creep on the
+ground, but some stand erect, as the <i>Lycopodium densum</i> from
+New Zealand (see Fig. 456), which attains a height of three
+feet.</p>
+
+<p>
+<a name="page424"></a>In the Carboniferous strata of Coalbrook Dale, and in many other
+coal-fields, elongated cylindrical bodies, called fossil cones,
+named <i>Lepidostrobus</i> by M. Adolphe Brongniart, are met with.
+(See Fig. 457.) They often form the nucleus of concretionary balls
+of clay-ironstone, and are well preserved, exhibiting a conical
+axis, around which a great quantity of scales were compactly
+imbricated. The opinion of M. Brongniart that the <i>
+Lepidostrobus</i> is the fruit of <i>Lepidodendron</i> has been
+confirmed, for these <i>strobili</i> or fruits have been found
+terminating the tip of a branch of a well-characterised <i>
+Lepidodendron</i> in Coalbrook Dale and elsewhere.</p>
+
+<p><img src="images/fig457.jpg" width="421" height="161" alt=
+"Fig. 457: a. Lepidostrobus ornatus; b. Portion of a section, showing the large
+sporangia in their natural position, and each supported by its bract or scale;
+c. Spores in these sporangia, highly magnified." />
+</p>
+
+<p><img src="images/fig458.jpg" width="369" height="262" alt=
+"Fig. 458: Calamites Sucowii, common throughout Europe. Fig. 459: Stem of Fig.
+458, as retored by Dr. Dawson." />
+</p>
+
+<p><b>Equisetaceæ.</b>&mdash;To this family belong two fossil
+genera of the coal, <i>Equisetites</i> and <i>Calamites.</i> The
+Calamites were evidently closely related to the modern horse-tails
+(Equiseta) differing principally in their great size, the want of
+sheaths at the joints, and some details of fructification. They
+grew in dense brakes on sandy and muddy flats in the manner of
+modern Equisetaceæ, and their remains are frequent in the
+<a name="page425"></a>coal. Seven species of this plant occur in the great Nova Scotia
+section before described, where the stems of some of them five
+inches in diameter, and sometimes eight feet high, may be seen
+terminating downward in a tapering root (see Fig. 460).</p>
+
+<p><img src="images/fig460.jpg" width="408" height="233" alt=
+"Fig. 460: Radical termination of a Calamite. Fig. 461: Asterophyllites
+foliosus, Coal-measures, Newcastle." />
+</p>
+
+<p>Botanists are not yet agreed whether the <i>Asterophyllites,</i>
+a species of which is represented in Fig. 461, can form a separate
+genus from the Calamite, from which, however, according to Dr.
+Dawson, its foliage is distinguished by a true mid-rib, which is
+wanting in the leaves known to belong to some Calamites.</p>
+
+<img src="images/fig462.jpg" width="95" height="176" alt=
+"Fig. 462: Annularia sphenophylloides." /><img src=
+"images/fig463.jpg" width="92" height="166" alt=
+"Fig. 463: Sphenophyllum erosum." />
+
+<p>Figs. 462 and 463 represent leaves of <i>Annularia</i> and <i>
+Sphenophyllum,</i> common in the coal, and believed by Mr.
+Carruthers to be leaves of Calamites. Dr. Williamson, who has
+carefully studied the Calamites, thinks that they had a fistular
+pith, exogenous woody stem, and thick smooth bark, which last
+having always disappeared, leaves a fluted stem, as represented in
+Fig. 459.</p>
+
+<p><b>Sigillaria.</b>&mdash;A large portion of the trees of the
+Carboniferous period belonged to this genus, of which as many as 28
+species are enumerated as British. The structure, both internal and
+external, was very peculiar, and, with reference to existing types,
+very anomalous. They were formerly referred, by M. Ad. Brongniart,
+to ferns, which they resemble in the scalariform texture of their
+vessels and, in
+<a name="page426"></a>some degree, in the form of the cicatrices left by the base of
+the leaf-stalks which have fallen off (see Fig. 464). But some of
+them are ascertained to have had long linear leaves, quite unlike
+those of ferns. They grew to a great height, from 30 to 60, or even
+70 feet, with regular cylindrical stems, and without branches,
+although some species were dichotomous towards the top. Their
+fluted trunks, from one to five feet in diameter, appear to have
+decayed more rapidly in the interior than externally, so that they
+became hollow when standing; and when thrown prostrate, they were
+squeezed down and flattened. Hence, we find the bark of the two
+opposite sides (now converted into bright shining coal) constitute
+two horizontal layers, one upon the other, half an inch, or an
+inch, in their united thickness. These same trunks, when they are
+placed obliquely or vertically to the planes of stratification,
+retain their original rounded form, and are uncompressed, the
+cylinder of bark having been filled with sand, which now affords a
+cast of the interior.</p>
+
+<img src="images/fig464.jpg" width="158" height="275" alt=
+"Fig. 464: Sigillaria lævigata." />
+
+<p>Dr. Hooker inclined to the belief that the <i>
+Sigillariæ</i> may have been cryptogamous, though more highly
+developed than any flowerless plants now living. Dr. Dawson having
+found in some species what he regards as medullary rays, thinks
+with Brongniart that they have some relation to gymnogens, while
+Mr. Carruthers leans to the opinion that they belong to the
+Lycopodiaceæ.</p>
+
+<p><i>Stigmaria.</i>&mdash;This fossil, the importance of which has
+already been pointed out in <a href="#page398">p.
+398</a>, was originally conjectured to be an aquatic plant. It is
+now ascertained to be the root of <i>Sigillaria.</i> The connection
+of the roots with the stem, previously suspected, on botanical
+grounds, by Brongniart, was first proved, by actual contact, in the
+Lancashire coal-field, by Mr. Binney. The fact has lately been
+shown, even more distinctly, by Mr. Richard Brown, in his
+description of the <i>Stigmariæ</i> occurring in the
+under-clays of the coal-seams of the Island of Cape Breton, in Nova
+Scotia. In a specimen of one of these, represented in Fig. 465, the
+spread of the roots was sixteen feet, and some of them sent out
+rootlets, in all directions, into the surrounding clay.
+<a name="page427"></a></p>
+
+<p><img src="images/fig465.jpg" width="365" height="176" alt=
+"Fig. 465: Stigmaria attached to a trunk of Sigillaria." /></p>
+
+<p>In the sea-cliffs of the South Joggins in Nova Scotia, I
+examined several erect <i>Sigillariæ,</i> in company with Dr.
+Dawson, and we found that from the lower extremities of the trunk
+they sent out <i>Stigmariæ</i> as roots. All the stools of
+the fossil trees dug out by us divided into four parts, and these
+again bifurcated, forming eight roots, which were also dichotomous
+when traceable far enough. The cylindrical rootlets formerly
+regarded as leaves are now shown by more perfect specimens to have
+been attached to the root by fitting into deep cylindrical pits. In
+the fossil there is rarely any trace of the form of these cavities,
+in consequence of the shrinkage of the surrounding tissues. Where
+the rootlets are removed, nothing remains on the surface of the
+Stigmaria but rows of mammillated tubercles (see Figs. 466, 467),
+which have formed the base of each rootlet.</p>
+
+<p><img src="images/fig466.jpg" width="440" height="202" alt=
+"Fig. 466: Stigmaria ficoides. Fig. 467: Surface of another individual of same
+species, showing form of tubercles." />
+</p>
+
+<p>These protuberances may possibly indicate the place of a joint
+at the lower extremity of the rootlet. Rows of these tubercles are
+arranged spirally round each root, which have always a medullary
+axis and woody system much resembling that of <i>Sigillaria,</i>
+the structure of the vessels being, like it, scalariform.</p>
+
+<p><b>Coniferæ.</b>&mdash;The coniferous trees of this period
+are referred to five genera;
+<a name="page428"></a>the woody structure of some of them showing that they were
+allied to the Araucarian division of pines, more than to any of our
+common European firs. Some of their trunks exceeded forty-four feet
+in height. Many, if not all of them, seem to have differed from
+living <i>Coniferæ</i> in having large piths; for Professor
+Williamson has demonstrated the fossil of the coal-measures called
+<i>Sternbergia</i> to be the pith of these trees, or rather the
+cast of cavities formed by the shrinking or partial absorption of
+the original medullary axis (see Figs. 468, 469). This peculiar
+type of pith is observed in living plants of very different
+families, such as the common Walnut and the White Jasmine, in which
+the pith becomes so reduced as simply to form a thin lining of the
+medullary cavity, across which transverse plates of pith extend
+horizontally, so as to divide the cylindrical hollow into discoid
+interspaces. When these interspaces have been filled up with
+inorganic matter, they constitute an axis to which, before their
+true nature was known, the provisional name of <i>Sternbergia</i>
+(<i>d, d,</i> Fig. 468) was given. In the above specimen the
+structure of the wood (<i>b,</i> Figs. 468 and 469) is coniferous,
+and the fossil is referable to Endlicher&rsquo;s fossil genus <i>
+Dadoxylon.</i></p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig468.jpg" width="123" height="374" alt="Fig. 468: Fragment
+of coniferous wood." />
+<p class="caption">Fig. 468: Fragment of coniferous wood, <i>Dadoxylon</i>,
+of Endlicher, fractured longitudinally; from Coalbrook Dale.<br/>
+W.C. Williamson<a href="#fn-24.3" name="fnref-24.3"
+id="fnref-24.3"><sup>[3]</sup></a><br/></p>
+</div>
+
+<p><img src="images/fig469.jpg" width="317" height="162" alt=
+"Fig. 469: Magnified portion of Fig. 468; transverse section." />
+</p>
+
+<p>The fossil named <i>Trigonocarpon</i> (Figs. 470 and 471),
+formerly supposed to be the fruit of a palm, may now, according to
+Dr. Hooker, be referred, like the <i>Sternbergia,</i> to the <i>
+Coniferæ.</i> Its geological importance is great, for so
+abundant is it in the coal-measures, that in certain localities the
+fruit of
+<a name="page429"></a>some species may be procured by the bushel; nor is there any
+part of the formation where they do not occur, except the
+under-clays and limestone. The sandstone, ironstone, shales, and
+coal itself, all contain them. Mr. Binney has at length found in
+the clay-ironstone of Lancashire several specimens displaying
+structure, and from these, says Dr. Hooker, we learn that the <i>
+Trigonocarpon</i> belonged to that large section of existing
+coniferous plants which bear fleshy solitary fruits, and not cones.
+It resembled very closely the fruit of the Chinese genus <i>
+Salisburia,</i> one of the Yew tribe, or Taxoid conifers.</p>
+
+<img src="images/fig470.jpg" width="140" height="148" alt=
+"Fig. 470: Trigonocarpum ovatum." /><img src=
+"images/fig471.jpg" width="103" height="231" alt=
+"Fig. 471: Trigonocarpum olivæforme." />
+
+<img src="images/fig472.jpg" width="107" height="229" alt=
+"Fig. 472: Antholithes." />
+
+<p><b>Angiosperms.</b>&mdash;The curious fossils called <i>
+Antholithes</i> by Lindley have usually been considered to be
+flower spikes, having what seems a calyx and linear petals (see
+Fig. 472). Dr. Hooker, after seeing very perfect specimens, also
+thought that they resembled the spike of a highly-organised plant
+in full flower, such as one of the <i>Bromeliaceæ,</i> to
+which Professor Lindley had at first compared them. Mr. Carruthers,
+who has lately examined a large series in different museums,
+considers it to be a dicotyledonous angiosperm allied to <i>
+Orobanche</i> (broom-rape), which grew, not on the soil, but
+parasitically on the trees of the coal forests.</p>
+
+<p>
+In the coal-measures of Granton, near Edinburgh, a remarkable fossil (Fig. 473)
+was found and described in 1840,<a href="#fn-24.4" name="fnref-24.4"
+id="fnref-24.4"><sup>[4]</sup></a> by Dr. Robert Paterson. It was compressed
+between layers of bituminous shale, and consists of a stem bearing a
+cylindrical spike, <i>a,</i> which in the portion preserved in the slate
+exhibits two subdivisions and part of a third. The spike is covered on the
+exposed surface with the four-cleft calyces of the flowers arranged in parallel
+rows. The stem shows, at <i>b,</i> a little below the spike, remains of a
+lateral appendage, which is supposed to indicate the beginning of the spathe.
+The fossil has been referred to the <i> Aroidiæ,</i> and <a
+name="page430"></a>there is every probability that it is a true member of this
+order. There can at least be no doubt as to the high grade of its organisation,
+and that it belongs to the monocotyledonous angiosperms. Mr. Carruthers has
+carefully examined the original specimen in the Botanical Museum, Edinburgh,
+and thinks it may have been an epiphyte.
+</p>
+
+<img src="images/fig473.jpg" width="260" height="357" alt=
+"Fig. 473: Pothocites Grantonii." />
+
+<p><b>Climate of the Coal Period.</b>&mdash;As to the climate of
+the Coal, the Ferns and the Coniferæ are perhaps the two
+classes of plants which may be most relied upon as leading us to
+safe conclusions, as the genera are nearly allied to living types.
+All botanists admit that the abundance of ferns implies a moist
+atmosphere. But the coniferæ, says Hooker, are of more
+doubtful import, as they are found in hot and dry, and in cold and
+dry climates; in hot and moist, and in cold and moist regions. In
+New Zealand the coniferæ attain their maximum in numbers,
+constituting 1/62 part of all the flowering plants; whereas in a
+wide district around the Cape of Good Hope they do not form 1/1600
+of the phenogamic flora. Besides the conifers, many species of
+ferns flourish in New Zealand, some of them arborescent, together
+with many lycopodiums; so that a forest in that country may make a
+nearer approach to the carboniferous vegetation than any other now
+existing on the globe.</p>
+
+<p>
+<small>MARINE FAUNA OF THE CARBONIFEROUS PERIOD.</small>
+</p>
+
+<p>It has already been stated that the Carboniferous or Mountain
+Limestone underlies the coal-measures in the South of England and
+Wales, whereas in the North, and in Scotland, marine calcareous
+rocks partly of the age of the Mountain Limestone alternate with
+shales and sandstones, containing seams of coal. In its most
+calcareous form the Mountain Limestone is destitute of land-plants,
+and is loaded
+<a name="page431"></a>with marine remains&mdash;the greater part, indeed, of the rock being
+made up bodily of crinoids, corals, and bryozoa with interspersed
+mollusca.</p>
+
+<p><b>Corals.</b>&mdash;The corals deserve especial notice, as the
+cup-and-star corals, which have the most massive and stony
+skeletons, display peculiarities of structure by which they may be
+distinguished generally, as MM. Milne Edwards and Haime first
+pointed out, from all species found in strata newer than the
+Permian. There is, in short, an ancient or <i>Palæozoic,</i>
+and a modern or <i>Neozoic</i> type, if, by the latter term, we
+designate (as proposed by Professor E. Forbes) all strata from the
+triassic to the most modern, inclusive. The accompanying diagrams
+(Figs. 474, 475) may illustrate these types.</p>
+
+<table border="0" cellspacing="0" cellpadding="0"
+summary=
+"Fig. 474: Polæozoic type of lamelliferous cup-shaped Coral. Fig. 475: Neozole
+type of lamelliferous cup-shaped Coral.">
+<tr>
+<td valign="top"><img src="images/fig474.jpg" width=
+"162" height="226" alt=
+"Fig. 474: Palæozoic type of lamelliferous cup-shaped Coral." />
+</td>
+<td valign="top">
+<ol>
+<li>Vertical section of <i>Campophyllum flexuosum,</i>
+(<i>Cyathophyllum,</i> Goldfuss); from the Devonian of the Eifel.
+The lamellæ are seen around the inside of the cup; the walls
+consist of cellular tissue; and large transverse plates, called <i>
+tubulæ,</i> divide the interior into chambers.</li>
+
+<li>Arrangement of the <i>lamellæ</i> in <i>Polycoelia
+profunda,</i> Germar, sp.; from the Magnesian Limestone, Durham.
+This diagram shows the quadripartite arrangement of the primary
+septa, characteristic of palæozoic corals, there being four
+principal and eight intermediate lamellæ, the whole number in
+this type being always a multiple of four.</li>
+
+<li><i>Stauria astræiformis,</i> Milne Edwards. Young group,
+natural size. Upper Silurian, Gothland. The lamellæ or septal
+system in each cup are divided by four prominent ridges into four
+groups.</li>
+</ol>
+</td>
+</tr>
+
+<tr>
+<td valign="top"><img src="images/fig475.jpg" width=
+"162" height="204" alt=
+"Fig. 475: Neozoic type of lamelliferous cup-shaped Coral." /></td>
+<td valign="top">
+<ol>
+<li><i>Parasmilia centralis,</i> Mantell, sp. Vertical section.
+Upper Chalk, Gravesend. In this type the lamellæ are massive,
+and extend to the axis or columella composed of loose cellular
+tissue, without any transverse plates like those in Fig. 474, <i>
+a.</i></li>
+
+<li><i>Cyathina Bowerbankii,</i> Ed. and H. Transverse section,
+enlarged. Gault, Folkestone. In this coral the primary septa are a
+multiple of six. The twelve principal plates reach the columella,
+and between each pair there are three secondaries, in all
+forty-eight. The short intermediate plates which proceed from the
+columella are not counted. They are called <i>pali.</i></li>
+
+<li><i>Fungia patellaris,</i> Lamarck. Recent; very young state.
+Diagram of its six primary and six secondary septa, magnified. The
+sextuple arrangement is always more manifest in the young than in
+the adult state.</li>
+</ol>
+</td>
+</tr>
+</table>
+
+<p>
+<a name="page432"></a>It will be seen that the more ancient corals have what is called
+a quadripartite arrangement of the chief plates or <i>
+lamellæ</i>&mdash;parts of the skeleton which support the organs
+of reproduction. The number of these lamellæ in the
+Palæozoic type is 4, 8, 16, etc.; while in the Neozoic type
+the number is 6, 12, 24, or some other multiple of six; and this
+holds good, whether they be simple forms, as in Figs. 474, <i>
+a,</i> and 475, <i>a,</i> or aggregate clusters of corallites, as
+in 474, <i>c.</i> But further investigations have shown in this, as
+in all similar grand generalisations in natural history, that there
+are excepions to the rule. Thus in the Lower Greensand <i>
+Holocystis elegans</i> (Ed. and H.) and other forms have the
+Palæozoic type, and Dr. Duncan has shown to what extent the
+Neozoic forms penetrate downward into the Carboniferous and
+Devonian rocks.</p>
+
+<p><img src="images/fig476.jpg" width="396" height="313" alt=
+"Fig. 476: Lithostrotion basaltiforme. Fig. 477: Lonsdaleia floriformis." />
+</p>
+
+<p>
+From a great number of lamelliferous corals met with in the Mountain Limestone,
+two species (Figs. 476, 477) have been selected, as having a very wide range,
+extending from the eastern borders of Russia to the British Isles, and being
+found almost everywhere in each country. These fossils, together with numerous
+species of <i>Zaphrentis, Amplexus, Cyathophyllum, Clisiophyllum,
+Syringopora,</i> and <i>Michelinia,</i><a href="#fn-24.5" name="fnref-24.5"
+id="fnref-24.5"><sup>[5]</sup></a> form a group of rugose corals widely
+different from any that followed them.
+</p>
+
+<p>
+<a name="page433"></a><b>Bryozoa and Crinoidea.</b>&mdash;Of the <i>Bryozoa,</i> the
+prevailing forms are <i>Fenestella, Hemitrypa,</i> and <i>
+Polypora,</i> and these often form considerable beds. Their
+net-like fronds are easily recognised. <i>Crinoidea</i> are also
+numerous in the Mountain Limestone (see Figs. 478, 479), two
+genera, <i>Pentremites</i> and <i>Codonaster,</i> being peculiar to
+this formation in Europe and North America.</p>
+
+<p><img src="images/fig478.jpg" width="381" height="254" alt=
+"Fig. 478: Cyathocrinus planus. Fig. 479: Cyathocrinus caryocrinoides." />
+</p>
+
+<img src="images/fig480.jpg" width="166" height="146" alt=
+"Fig. 480: Palæchinus gigas." />
+
+<p>In the greater part of them, the cup or pelvis, Figure 479, <i>
+b,</i> is greatly developed in size in proportion to the arms,
+although this is not the case in Fig. 478. The genera <i>
+Poteriocrinus, Cyathocrinus, Pentremites, Actinocrinus,</i> and <i>
+Platycrinus,</i> are all of them characteristic of this formation.
+Other Echinoderms are rare, a few Sea-Urchins only being known:
+these have a complex structure, with many more plates on their
+surface than are seen in the modern genera of the same group. One
+genus, the <i>Palæchinus</i> (Fig. 480), is the analogue of
+the modern <i>Echinus,</i> but has four, five, or six rows of
+plates in the interambulacral region or area, whereas the modern
+genera have only two. The other, <i>Archæocidaris,</i>
+represents, in like manner, the <i>Cidaris</i> of the present
+seas.</p>
+
+<p>
+<b>Mollusca.</b>&mdash;The British Carboniferous mollusca enumerated by Mr.
+Etheridge<a href="#fn-24.6" name="fnref-24.6"
+id="fnref-24.6"><sup>[6]</sup></a> comprise 653 species referable to 86 genera,
+occurring chiefly in the Mountain Limestone. Of <a name="page434"></a>this
+large number only 40 species are common to the underlying Devonian rocks, 9 of
+them being Cephalopods, 7 Gasteropods, and the rest bivalves, chiefly
+Brachiopoda (or Palliobranchiates). This latter group constitutes the larger
+part of the Carboniferous Mollusca, 157 species being known in Great Britain
+alone, and it will be found to increase in importance in the fauna of the
+primary rocks the lower we descend in the series. Perhaps the most
+characteristic shells of the formation are large species of <i> Productus,</i>
+such as <i>P. giganteus, p. hemisphericus, P. semireticulatus</i> (Fig. 481),
+and <i>P. scabriculus.</i> Large plaited spirifers, as <i>Spirifera striata, S.
+rotundata,</i> and <i>S. trigonalis</i> (Fig. 482), also abound; and smooth
+species, such as <i>Spirifera glabra</i> (Fig. 483), with its numerous
+varieties.
+</p>
+
+<p><img src="images/fig481.jpg" width="411" height="212" alt=
+"Fig. 481: Productus semireticulatus. Fig. 482: Spirifera trigonalis." />
+</p>
+
+<img src="images/fig483.jpg" width="134" height="147" alt=
+"Fig. 483: Spirifera glabra." />
+
+<p><img src="images/fig484.jpg" width="393" height="197" alt=
+"Fig. 484: Terebratula hastata. Fig. 485: Aviculopecten sublobatus. Fig. 486:
+Pleurotomaria carinata." />
+</p>
+
+<p>Among the brachiopoda, <i>Terebratula hastata</i> (Fig. 484)
+deserves mention, not only for its wide range, but because it often
+retains the pattern of the original coloured
+<a name="page435"></a>stripes which ornamented the living shell. These coloured bands
+are also preserved in several lamellibranchiate bivalves, as in <i>
+Aviculopecten</i> (Fig. 485), in which dark stripes alternate with
+a light ground. In some also of the spiral univalves the pattern of
+the original painting is distinctly retained, as in <i>
+Pleurotomaria</i> (Fig. 486), which displays wavy blotches,
+resembling the colouring in many recent trochidæ.</p>
+
+<p><img src="images/fig487.jpg" width="393" height="340" alt=
+"Fig. 487: Euomphalus pentagulatus." /></p>
+
+<p>Some few of the carboniferous mollusca, such as Avicula, <i>
+Nucula</i> (sub-genus <i>Ctenodonta</i>), <i>Solemya,</i> and <i>
+Lithodomus,</i> belong no doubt to existing genera; but the
+majority, though often referred to as living types, such as <i>
+Isocardia, Turritella,</i> and <i>Buccinum,</i> belong really to
+forms which appear to have become extinct at the close of the
+Palæozoic epoch. <i>Euomphalus</i> is a characteristic
+univalve shell of this period. In the interior it is divided into
+chambers (Fig. 487, <i>d</i>), the septa or partitions not being
+perforated as in foraminiferous shells, or in those having
+siphuncles, like the Nautilus. The animal appears to have retreated
+at different periods of its growth from the internal cavity
+previously formed, and to have closed all communication with it by
+a septum. The number of chambers is irregular, and they are
+generally wanting in the innermost whorl. The animal of the recent
+<i>Turritella communis</i> partitions off in like manner as it
+advances in age a part of its spire, forming a shelly septum.</p>
+
+<p>
+<a name="page436"></a>More than twenty species of the genus <i>Bellerophon</i> (see
+Fig. 488), a shell like the living Argonaut without chambers, occur
+in the Mountain Limestone. The genus is not met with in strata of
+later date. It is most generally regarded as belonging to the
+pelagic Nucleobranchiata and the family Atlantidæ, partly
+allied to the Glass-Shell, <i>Carinaria</i>; but by some few it is
+thought to be a simple form of Cephalopod.</p>
+
+<img src="images/fig488.jpg" width="139" height="146" alt=
+"Fig. 488: Bellerophon costatus." />
+
+<img src="images/fig489.jpg" width="194" height="424" alt=
+"Fig. 489: Portion of Orthoxeras laterale. Fig. 490: Goniatites crenistra." />
+
+<p>The carboniferous Cephalopoda do not depart so widely from the
+living type (the Nautilus) as do the more ancient Silurian
+representatives of the same order; yet they offer some remarkable
+forms. Among these is <i>Orthoceras,</i> a siphuncled and chambered
+shell, like a Nautilus uncoiled and straightened (Fig. 489). Some
+species of this genus are several feet long. The <i>Goniatite</i>
+is another genus, nearly allied to the <i>Ammonite,</i> from which
+it differs in having the lobes of the septa free from lateral
+denticulations, or crenatures; so that the outline of these is
+angular, continuous, and uninterrupted. The species represented in
+Fig. 490 is found in most localities, and presents the zigzag
+character of the septal lobes in perfection. The dorsal position of
+the siphuncle, however, clearly distinguishes the Goniatite from
+the Nautilus, and proves it to have belonged to the family of the
+Ammonites, from which, indeed, some authors do not believe it to be
+generically distinct.</p>
+
+<p><b>Fossil Fish.</b>&mdash;The distribution of these is
+singularly partial; so much so, that M. De Koninck of Liége,
+the eminent palæontologist, once stated to me that, in making
+his extensive collection of the fossils of the Mountain Limestone
+of Belgium, he had found no more than four or five examples of the
+bones or teeth of fishes. Judging from Belgian data, he might have
+concluded that this class of vertebrata was of extreme rarity in
+the Carboniferous seas; whereas the
+<a name="page437"></a>investigation of other countries has led to quite a different
+result. Thus, near Clifton, on the Avon, as well as at numerous
+places around the Bristol basin from the Mendip Hills to Tortworth,
+there is a celebrated &ldquo;bone-bed,&rdquo; almost entirely made
+up of ichthyolites. It occurs at the base of the Lower Limestone
+shales immediately resting upon the passage beds of the Old Red
+Sandstone. Similar bone-beds occur in the Carboniferous Limestone
+of Armagh, in Ireland, where they are made up chiefly of the teeth
+of fishes of the Placoid order, nearly all of them rolled as if
+drifted from a distance. Some teeth are sharp and pointed, as in
+ordinary sharks, of which the genus <i>Cladodus</i> afford an
+illustration; but the majority, as in <i>Psammodus</i> and <i>
+Cochliodus,</i> are, like the teeth of the Cestracion of Port
+Jackson (see <a href="images/fig261.jpg">Fig. 261</a>), massive
+palatal teeth fitted for grinding. (See Figs. 491, 492.)</p>
+
+<img src="images/fig491.jpg" width="251" height="168" alt=
+"Fig. 491: Psammodus porosus." />
+
+<img src="images/fig492.jpg" width="200" height="186" alt=
+"Fig. 492: Cochliodus controtus." />
+
+<p>There are upward of seventy other species of fossil fish known
+in the Mountain Limestone of the British Islands. The defensive
+fin-bones of these creatures are not infrequent at Armagh and
+Bristol; those known as <i>Oracanthus, Ctenocanthus,</i> and <i>
+Onchus</i> are often of a very large size. Ganoid fish, such as <i>
+Holoptychius,</i> also occur; but these are far less numerous. The
+great <i>Megalichthys Hibberti</i> appears to range from the Upper
+Coal-measures to the lowest Carboniferous strata.</p>
+
+<p><b>Foraminifera.</b>&mdash;In the upper part of the Mountain
+Limestone group in the S.W. of England, near Bristol, limestones
+having a distinct oolitic structure alternate with shales. In these
+rocks the nucleus of every minute spherule is seen, under the
+microscope, to consist of a small rhizopod or foraminifer. This
+division of the lower animals, which is represented so fully at
+later epochs by the Nummulites and their numerous minute allies,
+appears in the Mountain Limestone to be restricted to a very few
+species, among which <i>Textularia, Nodosaria, Endothyra,</i> and
+<i>Fusulina</i> (Fig. 493), have been
+<a name="page438"></a>recognised. The first two genera are common to this and all the
+after periods; the third has been found in the Upper Silurian, but
+is not known above the Carboniferous strata; the fourth (Fig. 493)
+is characteristic of the Mountain Limestone in the United States,
+Arctic America, Russia, and Asia Minor, but is also known in the
+Permian.
+</p>
+
+<img src="images/fig493.jpg" width="115" height="110" alt=
+"Fig. 493: Fusulina cylindrica." />
+
+<p class="footnote">
+<a name="fn-24.1" id="fn-24.1"></a> <a href="#fnref-24.1">[1]</a>
+For botanical nomenclature see <a href="#page304">p. 304</a>.
+</p>
+
+<p class="footnote">
+<a name="fn-24.2" id="fn-24.2"></a> <a href="#fnref-24.2">[2]</a>
+Sir C. Bunbury, Quart. Geol. Journ., vol. ii, 1845.
+</p>
+
+<p class="footnote">
+<a name="fn-24.3" id="fn-24.3"></a> <a href="#fnref-24.3">[3]</a>
+Manchester Phil. Mem., vol. ix, 1851.
+</p>
+
+<p class="footnote">
+<a name="fn-24.4" id="fn-24.4"></a> <a href="#fnref-24.4">[4]</a>
+Trans. of Bot. Soc. of Edinburgh, vol. i, 1844.
+</p>
+
+<p class="footnote">
+<a name="fn-24.5" id="fn-24.5"></a> <a href="#fnref-24.5">[5]</a>
+For figures of these corals, see Palæontographical Society&rsquo;s Monographs,
+1852.
+</p>
+
+<p class="footnote">
+<a name="fn-24.6" id="fn-24.6"></a> <a href="#fnref-24.6">[6]</a>
+Quart. Geol. Journ., vol. xxiii, p. 674, 1867.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap25"></a><a name="page439"></a>CHAPTER XXV.<br/>
+DEVONIAN OR OLD RED SANDSTONE GROUP.</h2>
+
+<p class="letter">Classification of the Old Red Sandstone in
+Scotland and in Devonshire. &mdash; Upper Old Red Sandstone in
+Scotland, with Fish and Plants. &mdash; Middle Old Red Sandstone.
+&mdash; Classification of the Ichthyolites of the Old Red, and
+their Relation to Living Types. &mdash; Lower Old Red Sandstone,
+with Cephalaspis and Pterygotus. &mdash; Marine or Devonian Type of
+Old Red Sandstone. &mdash; Table of Devonian Series. &mdash; Upper
+Devonian Rocks and Fossils. &mdash; Middle. &mdash; Lower. &mdash;
+Eifel Limestone of Germany. &mdash; Devonian of Russia. &mdash;
+Devonian Strata of the United States and Canada. &mdash; Devonian
+Plants and Insects of Canada.</p>
+
+<p><b>Classification of the two Types of Old Red
+Sandstone.</b>&mdash;We have seen that the Carboniferous strata are
+surmounted by the Permian and Trias, both originally included in
+England under the name &ldquo;New Red Sandstone,&rdquo; from the
+prevailing red colour of the strata. Under the coal came other red
+sandstones and shales which were distinguished by the title of
+&ldquo;Old Red Sandstone.&rdquo; Afterwards the name of
+&ldquo;Devonian&rdquo; was given by Sir R. Murchison and Professor
+Sedgwick to marine fossiliferous strata which, in the south of
+England, occupy a similar position between the overlying coal and
+the underlying Silurian formations.</p>
+
+<p>It may be truly said that in the British Isles the rocks of this
+age present themselves in their mineral aspect, and even to some
+extent in their fossil contents, under two very different forms;
+the one as distinct from the other as are often lacustrine or
+fluviatile from marine strata. It has indeed been suggested that by
+far the greater part of the deposits belonging to what may be
+termed the Old Red Sandstone type are of fresh-water origin. The
+number of land-plants, the character of the fishes, and the fact
+that the only shell yet discovered belongs to the genus <i>
+Anodonta,</i> must be allowed to lend no small countenance to this
+opinion. In this case the difficulty of classification when the
+strata of this type are compared in different regions, even where
+they are contiguous, may arise partly from their having been formed
+in distinct hydrographical basins, or in the neighbourhood of the
+land in shallow parts of the sea into which large bodies of
+fresh-water entered, and where no marine mollusca or corals could
+flourish. Under such geographical conditions the limited extent of
+some kinds of sediment, as well as the
+<a name="page440"></a>absence of those marine forms by which we are able to identify
+or contrast marine formations, may be explained, while the great
+thickness of the rocks, which might seem at first sight to require
+a corresponding depth of water, can often be shown to have been due
+to the gradual sinking down of the bottom of the estuary or sea
+where the sediment was accumulated.</p>
+
+<p>Another active cause of local variation in Scotland was the
+frequency of contemporaneous volcanic eruptions; some of the rocks
+derived from this source, as between the Grampians and the Tay,
+having formed islands in the sea, and having been converted into
+shingle and conglomerate, before the upper portions of the red
+shales and sandstones were superimposed.</p>
+
+<p>The dearth of calcareous matter over wide areas is
+characteristic of the Old Red Sandstone. This is, no doubt, in
+great part due to the absence of shells and corals; but why should
+these be so generally wanting in all sedimentary rocks the colour
+of which is determined by the red oxide of iron? Some geologists
+are of opinion that the waters impregnated with this oxide were
+prejudicial to living beings, others that strata permeated with
+this oxide would not preserve such fossil remains.</p>
+
+<p>In regard to the two types, the Old Red Sandstone and the
+Devonian, I shall first treat of them separately, and then allude
+to the proofs of their having been to a great extent
+contemporaneous. That they constitute a series of rocks
+intermediate in date between the lowest Carboniferous and the
+uppermost Silurian is not disputed by the ablest geologists; and it
+can no longer be contended that the Upper, Middle, and Lower Old
+Red Sandstone preceded in date the three divisions to which, by aid
+of the marine shells, the Devonian rocks have been referred, while,
+on the other hand, we have not yet data for enabling us to affirm
+to what extent the subdivisions of the one series may be the
+equivalents in time of those of the other.</p>
+
+<p><b>Upper Old Red Sandstone.</b>&mdash;The highest beds of the
+series in Scotland, lying immediately below the coal in Fife, are
+composed of yellow sandstone well seen at Dura Den, near Coupar, in
+Fife, where, although the strata contain no mollusca, fish have
+been found abundantly, and have been referred to the genera <i>
+Holoptychius, Pamphractus, Glyptopomus,</i> and many others. In the
+county of Cork, in Ireland, a similar yellow sandstone occurs
+containing fish of genera characteristic of the Scotch Old Red
+Sandstone, as for example Coccosteus (a form represented by many
+species in the
+<a name="page441"></a>Old Red Sandstone and by one only in the Carboniferous group),
+and <i>Glytolepis</i> and <i>Asterolepis,</i> both exclusively
+confined to the &ldquo;Old Red.&rdquo; In the same Irish sandstone
+at Kiltorkan has been found an <i>Anodonta</i> or fresh-water
+mussel, the only shell hitherto discovered in the Old Red Sandstone
+of the British Isles (see Fig. 494).</p>
+
+<img src="images/fig494.jpg" width="212" height="150" alt=
+"Fig. 494: Anodonta Jukesii." />
+
+<img src="images/fig495.jpg" width="124" height="271" alt=
+"Fig. 495: Bifurcating branch of Lepidendron Griffithsii." />
+
+<img src="images/fig496.jpg" width="114" height="335" alt=
+"Fig. 496: Palæopteris Hibernia." />
+
+<p>In the same formation are found the fern (Fig. 496) and the <i>
+Lepidodendron</i> (Fig. 495), and other species of plants, some of
+which, Professor Heer remarks, agree specifically with species from
+the lower carboniferous beds. This induces him to lean to the
+opinion long ago advocated by Sir Richard Griffiths, that the
+yellow sandstone, in spite of its fish remains, should be classed
+as Lower Carboniferous, an opinion which I am not yet prepared to
+adopt. Between the Mountain Limestone and the yellow sandstone in
+the south-west of Ireland there intervenes a formation no less than
+5000 feet thick, called the &ldquo;Carboniferous slate,&rdquo; and
+at the base of this, in some places, are local deposits, such as
+the Glengariff Grits, which appear to be beds of passage between
+the Carboniferous and Old Red Sandstone groups.</p>
+
+<p>
+It is a remarkable result of the recent examination of the fossil flora of Bear
+Island, latitude 74&deg; 30&#x2032; N., that Professor Heer has described as
+occurring in that part of the Arctic region (nearly twenty-six degrees to the
+north of the Irish locality) a flora agreeing in several of its species with
+that of the yellow sandstones of Ireland. This Bear Island flora is believed by
+Professor Heer to comprise species of plants some of which ascend even to the
+higher stages of the European Carboniferous formation, or as high as the
+Mountain Limestone and Millstone Grit. Palæontologists have long maintained
+that
+<a name="page442"></a>the same species which have a wide range in space are also the
+most persistent in time, which may prepare us to find that some
+plants having a vast geographical range may also have endured from
+the period of the Upper Devonian to that of the Millstone Grit.</p>
+
+<img src="images/fig497.jpg" width="141" height="165" alt=
+"Fig. 497: Scale of Holoptychius nobilissimus." />
+
+<p>
+Outliers of the Upper &ldquo;Old Red&rdquo; occur unconformably on older
+members of the group, and the formation represented at Whiteness, near
+Arbroath, <i>a,</i> <a href="images/fig55.jpg">Fig. 55,</a> may probably be one
+of these outliers, though the want of organic remains renders this uncertain.
+It is not improbable that the beds given in this section as Nos. 1, 2, and 3,
+may all belong to the early part of the period of the Upper Old Red, as some
+scales of <i>Holoptychius nobilissimus</i> have been found scattered through
+these beds, No. 2, in Strathmore. Another nearly allied <i>Holoptychius</i>
+occurs in Dura Den, see Fig. 498 of this fish and also Fig. 497 of one of its
+scales, as these last are often the only parts met with; being scattered in
+Forfarshire through red-coloured shales and sandstones, as are scales of a
+large species of the same genus in a corresponding matrix in Herefordshire.<a
+href="#fn-25.1" name="fnref-25.1" id="fnref-25.1"><sup>[1]</sup></a> The number
+of fish obtained from the British Upper Old Red Sandstone amounts to fifteen
+species referred to eleven genera.
+</p>
+
+<p><img src="images/fig498.jpg" width="389" height="230" alt=
+"Fig. 498: Holoptychius, as restored by Professor Huxley." />
+</p>
+
+<p>Sir R. Murchison groups with this upper division of the Old Red
+of Scotland certain light-red and yellow sandstones and grits which
+occur in the northernmost part of the mainland, and extend also
+into the Orkney and Shetland Islands.
+<a name="page443"></a>They contain Calamites and other plants which agree generically
+with Carboniferous forms.</p>
+
+<p>
+<b>Middle Old Red Sandstone.</b>&mdash;In the northern part of Scotland there
+occur a great series of bituminous schists and flagstones, to the fossil fish
+of which attention was first called by the late Hugh Miller. They were
+afterwards described by Agassiz, and the rocks containing them were examined by
+Sir R. Murchison and Professor Sedgwick, in Caithness, Cromarty, Moray, Nairn,
+Gamrie in Banff, and the Orkneys and Shetlands, in which great numbers of
+fossil fish have been found. These were at first supposed to be the oldest
+known vertebrate animals, as in Cromarty the beds in which they occur seem to
+form the base of the Old Red system resting almost immediately on the
+crystalline or metamorphic rocks. But in fact these fish-bearing beds, when
+they are traced from north to south, or to the central parts of Scotland, thin
+out, so that their relative age to the Lower Old Red Sandstone, presently to be
+mentioned, was not at first detected, the two formations not appearing in
+superposition in the same district. In Caithness, however, many hundred feet
+below the fish-zone of the middle division, remains of <i>Pteraspis</i> were
+found by Mr. Peach in 1861. This genus has never yet been found in either of
+the two higher divisions of the Old Red Sandstone, and confirms Sir R.
+Murchison&rsquo;s previous suspicion that the rocks in which it occurs belong
+to the Lower &ldquo;Old Red,&rdquo; or agree in age with the Arbroath
+paving-stone.<a href="#fn-25.2" name="fnref-25.2"
+id="fnref-25.2"><sup>[2]</sup></a>
+</p>
+
+<p><i>Fossil Fish of the Middle Old Red Sandstone.</i>&mdash;The
+Devonian fish were referred by Agassiz to two of his great orders,
+namely, the Placoids and Ganoids. Of the first of these, which in
+the Recent period comprise the shark, the dog-fish, and the ray, no
+entire skeletons are preserved, but fin-spines, called
+ichthyodorulites, and teeth occur. On such remains the genera <i>
+Onchus, Odontacanthus,</i> and <i>Ctenodus,</i> a supposed
+cestraciont, and some others, have been established.</p>
+
+<p>
+By far the greater number of the Old Red Sandstone fishes belong to a sub-order
+of Ganoids instituted by Huxley in 1861, and for which he has proposed the name
+of <i> Crossopterygidæ</i>,<a href="#fn-25.3" name="fnref-25.3"
+id="fnref-25.3"><sup>[3]</sup></a> or the fringe-finned, in consideration of
+the peculiar manner in which the fin-rays of the paired fins are arranged so as
+to form a fringe round a central lobe, as in the Polypterus (see <i>a,</i> Fig.
+499), a genus of which there are several species now inhabiting the Nile and
+other African rivers. The reader will at once recognise in <i> Osteolepis</i>
+(Fig. 500), one of the common fishes of the Old Red Sandstone, many points of
+<a name="page444"></a>analogy with <i>Polypterus.</i> They not only agree in
+the structure of the fin, at first pointed out by Huxley, but also in the
+position of the pectoral, ventral, and anal fins, and in having an elongated
+body and rhomboidal scales. On the other hand, the tail is more symmetrical in
+the recent fish, which has also an apparatus of dorsal finlets of a very
+abnormal character, both as to number and structure. As to the dorsals of
+<i>Osteolepis,</i> they are regular in structure and position, having nothing
+remarkable about them, except that there are two of them, which is
+comparatively unusual in living fish.
+</p>
+
+<p><img src="images/fig499.jpg" width="408" height="159" alt=
+"Fig. 499: Polypterus. Living in the Nile and other rivers." />
+</p>
+
+<p><img src="images/fig500.jpg" width="373" height="144" alt=
+"Fig. 500: Restoration of Osteolepis." /></p>
+
+<p>Among the &ldquo;fringe-finned&rdquo; Ganoids we find some with
+rhomboidal scales, such as <i>Osteolepis,</i> Fig. 500; others with
+cycloidal scales, as <i>Holoptychius,</i> before mentioned (see
+Fig. 498). In the genera <i>Dipterus</i> and <i>Diplopterus,</i> as
+Hugh Miller pointed out, and in several other of the fringe-finned
+genera, as in <i>Gyroptychius</i> and <i>Glyptolepis,</i> the two
+dorsals are placed far backward, or directly over the ventral and
+anal fins. The <i>Asterolepis</i> was a ganoid fish of gigantic
+dimensions. <i>A. Asmusii,</i> Eichwald, a species characteristic
+of the Old Red Sandstone of Russia, as well as that of Scotland,
+attained the length of between twenty and thirty feet. It was
+clothed with strong bony armour, embossed with star-like tubercles,
+but it had only a cartilaginous skeleton. The mouth was furnished
+with two rows of teeth, the outer ones small and fish-like, the
+inner larger and with a reptilian character. The <i>Asterolepis</i>
+occurs also in the Devonian rocks of North America.</p>
+
+<p>
+<a name="page445"></a>If we except the Placoids already alluded to, and a few other
+families of doubtful affinities, all the Old Red Sandstone fishes
+are Ganoids, an order so named by Agassiz from the shining outer
+surface of their scales; but Professor Huxley has also called our
+attention to the fact that, while a few of the primary and the
+great majority of the secondary Ganoids resemble the living bony
+pike, <i>Lepidosteus,</i> or the <i>Amia,</i> genera now found in
+North American rivers, and one of them, <i>Lepidosteus,</i>
+extending as far south as Guatemala, the Crossopterygii, or
+fringe-finned Ichthyolites, of the Old Red are closely related to
+the African <i>Polypterus,</i> which is represented by five or six
+species now inhabiting the Nile and the rivers of Senegal. These
+North American and African Ganoids are quite exceptional in the
+living creation; they are entirely confined to the northern
+hemisphere, unless some species of <i>Polypterus</i> range to the
+south of the line in Africa; and, out of about 9000 living species
+of fish known to M. Günther, and of which more than 6000 are
+now preserved in the British Museum, they probably constitute no
+more than nine.</p>
+
+<img src="images/fig501.jpg" width="222" height="282" alt=
+"Fig. 501: Pterichthys. Upper side, showing mouth." />
+
+<p>If many circumstances favour the theory of the fresh-water
+origin of the Old Red Sandstone, this view of its nature is not a
+little confirmed by our finding that it is in Llake Superior and
+the other inland Canadian seas of fresh water, and in the
+Mississippi and African rivers, that we at present find those fish
+which have the nearest affinity to the fossil forms of this ancient
+formation.</p>
+
+<p>Among the anomalous forms of Old Red fishes not referable to
+Huxley&rsquo;s Crossopterygii is the <i>Pterichthys,</i> of which
+five species have been found in the middle division of the Old Red
+of Scotland. Some writers have compared their shelly covering to
+that of Crustaceans, with which, however, they have no real
+affinity. The wing-like appendages, whence the genus is named, were
+first supposed by Hugh Miller to be paddles, like those of the
+turtle; and there can now be no doubt that they do really
+correspond with the pectoral fins.</p>
+
+<p>
+<a name="page446"></a>The number of species of fish already obtained from the middle
+division of the Old Red Sandstone in Great Britain is about 70, and
+the principal genera, besides <i>Osteolepis</i> and <i>
+Pterichthys,</i> already mentioned, are <i>Glyptolepis,
+Diplacanthus, Dendrodus, Coccosteus, Cheirancanthus,</i> and <i>
+Acanthoides.</i></p>
+
+<p><img src="images/fig502.jpg" width="360" height="268" alt=
+"Fig. 502: Cephalapsis Lyellii." /></p>
+
+<p>
+<b>Lower Old Red Sandstone.</b>&mdash;The third or lowest division south of the
+Grampians consists of grey paving-stone and roofing-slate, with associated red
+and grey shales; these strata underlie a dense mass of conglomerate. In these
+grey beds several remarkable fish have been found of the genus named by Agassiz
+<i> Cephalaspis,</i> or &ldquo;buckler-headed,&rdquo; from the extraordinary
+shield which covers the head (see Fig. 502), and which has often been mistaken
+for that of a trilobite, such as <i> Asaphus.</i> A species of
+<i>Pteraspis,</i> of the same family, has also been found by the Reverend Hugh
+Mitchell in beds of corresponding age in Perthshire; and Mr. Powrie enumerates
+no less than five genera of the family Acanthodidæ, the spines, scales, and
+other remains of which have been detected in the grey flaggy sandstones.<a
+href="#fn-25.4" name="fnref-25.4" id="fnref-25.4"><sup>[4]</sup></a>
+</p>
+
+<img src="images/fig503.jpg" width="190" height="163" alt=
+"Fig. 503: Pteygotus anglicus." />
+
+<p>In the same formation at Carmylie, in Forfarshire, commonly
+known as the Arbroath paving-stone, fragments of a huge crustacean
+have been met with from time to time. They are called by the Scotch
+quarrymen the &ldquo;Seraphim,&rdquo; from the
+<a name="page447"></a>wing-like form and feather-like ornament of the thoracic
+appendage, the part most usually met with. Agassiz, having
+previously referred some of these fragments to the class of fishes,
+was the first to recognise their crustacean character, and,
+although at the time unable correctly to determine the true
+relation of the several parts, he figured the portions on which he
+founded his opinion, in the first plate of his &ldquo;Poissons
+Fossiles du Vieux Grès Rouge.&rdquo;</p>
+
+<table border="0" cellspacing="0" cellpadding="0"
+summary=
+"Fig. 504: Pterygotus anglicus. Ventral aspect. Restored by H. Woodward, F.G.S.">
+<tr>
+<td valign="top"><img src="images/fig504.jpg" width=
+"214" height="361" alt=
+"Fig. 504: Pterygotus anglicus. Ventral aspect." /></td>
+<td valign="bottom">
+<ol>
+<li>Carapace, showing the large sessile eyes at the anterior
+angles.</li>
+
+<li>The <i>metastoma</i> or post-oral plate (serving the office of
+a lower lip).</li>
+
+<li>Chelate appendages (antennules).</li>
+
+<li>First pair of simple palpi (antennæ).</li>
+
+<li>Second pair of simple palpi (mandibles).</li>
+
+<li>Third pair of simple palpi (first maxillæ).</li>
+
+<li>Pair of swimming feet with their broad basal joints, whose
+serrated edges serve the office of maxillæ.</li>
+
+<li>Thoracic plate covering the first two thoracic segments, which
+are indicated by the figures 1, 2, and a dotted line. 1-6. Thoracic
+segments. 7-12. Abdominal segments. 13. Telson, or
+tail-plate.)</li>
+</ol>
+</td>
+</tr>
+</table>
+
+<p>A restoration in correct proportion to the size of the fragments
+of <i>P. anglicus</i> (Fig. 504), from the Lower Old Red Sandstone
+of Perthshire and Forfarshire, would give us a creature measuring
+from five to six feet in length, and more than one foot across.</p>
+
+<p>The largest crustaceans living at the present day are the <i>
+Inachus Kaempferi,</i> of De Haan, from Japan (a brachyurous or
+short-tailed crab), chiefly remarkable for the extraordinary length
+of its limbs; the fore-arm measuring four feet in length, and the
+others in proportion, so that it covers about 25 square feet of
+ground; and the <i>Limulus Moluccanus,</i> the great King Crab of
+China and the Eastern seas, which, when adult, measures 1&frac12;
+foot across its carapace, and is three feet in length.</p>
+
+<p>Besides some species of <i>Pterygotus,</i> several of the allied
+genus <i>Eurypterus</i> occur in the Lower Old Red Sandstone, and
+with them the remains of grass-like plants so abundant in
+Forfarshire and Kincardineshire as to be useful to the geologist by
+enabling him to identify the inferior strata at distant points.
+Some botanists have suggested that these
+<a name="page448"></a>plants may be of the family <i>Fluviales,</i> and of fresh-water
+genera. They are accompanied by fossils, called
+&ldquo;berries&rdquo; by the quarrymen, which they compared to a
+compressed blackberry (see Figs. 505, 506), and which were called
+&ldquo;Parka&rdquo; by Dr. Fleming. They are now considered by Mr.
+Powrie to be the eggs of crustaceans, which is highly probable, for
+they have not only been found with <i>Pterygotus anglicus</i> in
+Forfarshire and Perthshire, but also in the Upper Silurian strata
+of England, in which species of the same genus, Pterygotus,
+occur.</p>
+
+<p>
+<img src="images/fig505.jpg" width="342" height="184" alt=
+"Fig. 505: Parka decipiens. In sandstone of lower beds of Old Red, Ley’s Mill,
+Forfarshire. Fig. 506: Parka decipiens. In shale of Lower Old Red, Park Hill,
+Fife." />
+</p>
+
+<img src="images/fig507.jpg" width="231" height="251" alt=
+"Fig. 507: Shale of Old Red Sandstone. Forfarshire. With impression of plants
+and eggs of Crustaceans." />
+
+<p>The grandest exhibitions, says Sir R. Murchison, of the Old Red
+Sandstone in England and Wales appear in the escarpments of the
+Black Mountains and in the Fans of Brecon and Carmarthen, the one
+2862, and the other 2590 feet above the sea. The mass of red and
+brown sandstone in these mountains is estimated at not less than
+10,000 feet, clearly intercalated between the Carboniferous and
+Silurian strata. No shells or corals have ever been found in the
+whole series, not even where the beds are calcareous, forming
+irregular courses of concretionary lumps called
+&ldquo;corn-stones,&rdquo; which may be described as mottled red
+and green earthy limestones. The fishes of this lowest English Old
+Red are <i>Cephalaspis</i> and <i>Pteraspis,</i> specifically
+different from species of the same genera which occur in the
+uppermost Ludlow or Silurian tilestones. Crustaceans also of the
+genus <i>Eurypterus</i> are met with.</p>
+
+<p>
+<a name="page449"></a><b>Marine or Devonian Type.</b>&mdash;We may now speak of the
+marine type of the British strata intermediate between the
+Carboniferous and Silurian, in treating of which we shall find it
+much more easy to identify the Upper, Middle, and Lower divisions
+with strata of the same age in other countries. It was not until
+the year 1836 that Sir R. Murchison and Professor Sedgwick
+discovered that the culmiferous or anthracitic shales and
+sandstones of North Devon, several thousand feet thick, belonged to
+the coal, and that the beds below them, which are of still greater
+thickness, and which, like the carboniferous strata, had been
+confounded under the general name &ldquo;graywacke,&rdquo; occupied
+a geological position corresponding to that of the Old Red
+Sandstone already described. In this reform they were aided by a
+suggestion of Mr. Lonsdale, who, after studying the Devonshire
+fossils, perceived that they belonged to a peculiar
+palæontological type of intermediate character between the
+Carboniferous and Silurian.</p>
+
+<p>It is in the north of Devon that these formations may best be
+studied, where they have been divided into an Upper, Middle, and
+Lower Group, and where, although much contorted and folded, they
+have for the most part escaped being altered by intrusive
+trap-rocks and by granite, which in Dartmoor and the more southern
+parts of the same county have often reduced them to a crystalline
+or metamorphic state.</p>
+
+<p class="center">
+<small>DEVONIAN SERIES IN NORTH DEVON.</small>
+</p>
+
+<table border="1" cellspacing="0" cellpadding="10" summary=
+"Left column &mdash; Upper, Middle and Lower Devonian Groups; right column
+&mdash; Types of strata found in each group.">
+<tr>
+<td align="center" valign="middle">U<small>PPER</small>
+D<small>EVONIAN OR</small> P<small>ILTON</small>
+G<small>ROUP</small></td>
+<td valign="top">
+<b>(a)</b> Sandy slates and
+schists with fossils, 36 species out of 110 common to the
+Carboniferous group (Pilton, Barnstaple, etc.), resting on soft
+schists in which fossils are very abundant (Croyde, etc.), and
+which pass down into<br/>
+<b>(b)</b> Yellow, brown, and red sandstone, with land
+plants (<i>Cyclopteris,</i> etc.) and marine shells. One zone,
+characterised by the abundance of cucullæa (Baggy Point,
+Marwood, Sloly, etc.) resting on hard grey and reddish sandstone
+and micaceous flags, no fossils yet found (Dulverton, Pickwell,
+Down, etc.)</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">M<small>IDDLE</small>
+D<small>EVONIAN OR</small> I<small>LFRACOMBE</small>
+G<small>ROUP.</small></td>
+<td ><b>(a)</b> Green glossy slates of
+considerable thickness, no fossils yet recorded from these beds
+(Mortenoe, Lee Bay, etc.).<br/>
+<b>(b)</b> Slates and schists, with several irregular
+courses of limestone containing shells and corals like those of the
+Plymouth Limestone (Combe Martin, Ilfracombe, etc.).</td>
+</tr>
+
+<tr>
+<td align="center" valign="middle">L<small>OWER</small>
+D<small>EVONIAN OR</small> L<small>YNTON</small>
+G<small>ROUP.</small></td>
+<td ><b>(a)</b> Hard, greenish, red, and purple
+sandstone&mdash;no fossils yet found (Hangman Hill, etc.).<br/>
+<b>(b)</b> Soft slates with subordinate
+sandstones&mdash;fossils numerous at various horizons&mdash;Orthis,
+Corals, Encrinites, etc. (Valley of Rocks, Lynmouth, etc.).</td>
+</tr>
+</table>
+
+<p>
+The above table exhibits the sequence of the strata or subdivisions as seen
+both on the sea-coast of the British Channel and in the interior of Devon. It
+will be seen that <a name="page450"></a>in all main points it agrees with the
+table drawn up in 1864 for the sixth edition of my &ldquo;Elements.&rdquo; Mr.
+Etheridge<a href="#fn-25.5" name="fnref-25.5"
+id="fnref-25.5"><sup>[5]</sup></a> has since published an excellent account of
+the different subdivisions of the rocks and their fossils, and has also pointed
+out their relation to the corresponding marine strata of the Continent. The
+slight modifications introduced in my table since 1864 are the result of a tour
+made in 1870 in company with Mr. T. Mck. Hughes, when we had the advantage of
+Mr. Etheridge&rsquo;s memoir as our guide.
+</p>
+
+<p>The place of the sandstones of the Foreland is not yet clearly
+made out, as they are cut off by a great fault and disturbance.</p>
+
+<img src="images/fig508.jpg" width="218" height="437" alt=
+"Fig. 508: Spirifera disjuncta. Fig. 509: Phacops latifrons." />
+
+<p><b>Upper Devonian Rocks.</b>&mdash;The slates and sandstones of
+Barnstaple (<i>a</i> and <i>b</i> of the preceding section) contain
+the shell <i>Spirifera disjuncta,</i> Sowerby (S. Verneuilii,
+Murch.), (see Fig. 508), which has a very wide range in Europe,
+Asia Minor, and even China; also <i>Strophalosia caperata,</i>
+together with the large trilobite <i>Phacops latifrons,</i> Bronn.
+(See Fig. 509), which is all but world-wide in its distribution.
+The fossils are numerous, and comprise about 150 species of
+mollusca, a fifth of which pass up into the overlying Carboniferous
+rocks. To this Upper Devonian belong a series of limestones and
+slates well developed at Petherwyn, in Cornwall, where they have
+yielded 75 species of fossils. The genus of Cephalopoda called <i>
+Clymenia</i> (Fig. 510) is represented by no less than eleven
+species, and strata occupying the same position in Germany are
+called Clymenien-Kalk, or sometimes Cypridinen-Schiefer, on account
+of the number of minute bivalve shells of the crustacean called <i>
+Cypridina serrato-striata</i> (Fig. 511), which is found in these
+beds, in the Rhenish provinces, the Harz, Saxony, and Silesia, as
+well as in Cornwall and Belgium.</p>
+
+<p><b>Middle Devonian Rocks.</b>&mdash;We come next to the most
+typical portion of the Devonian system, including the great
+limestones of Plymouth and Torbay, replete with
+<a name="page451"></a>shells, trilobites, and corals. Of the corals 51 species are
+enumerated by Mr. Etheridge, none of which pass into the
+Carboniferous formation. Among the genera we find <i>Favosites,
+Heliolites,</i> and <i>Cyathophyllum.</i> The two former genera are
+very frequent in Silurian rocks: some few even of the species are
+said to be common to the Devonian and Silurian groups, as, for
+example, <i>Favosites cervicornis</i> (Fig. 513), one of the
+commonest of all
+<a name="page452"></a>the Devonshire fossils. The <i>Cyathophyllum
+cæspitosum</i> (Fig. 514) and <i>Heliolites pyriformis</i>
+(Fig. 512) are species peculiar to this formation.</p>
+
+<p><img src="images/fig510.jpg" width="390" height="194" alt=
+"Fig. 510: Clymenia linearis. Fig. 511: Cypridina serrato-striata." />
+</p>
+
+<img src="images/fig512.jpg" width="203" height="165" alt=
+"Fig. 512: Heliolites porosa." />
+
+<p><img src="images/fig513.jpg" width="382" height="316" alt=
+"Fig. 513: Favosites cervicornis. Fig. 514: Cyathophyllum cæspitosum." />
+</p>
+
+<p><img src="images/fig515.jpg" width="359" height="207" alt=
+"Fig. 515: Stringocephalus Burtini. Fig. 516: Uncites Gryphus." />
+</p>
+
+<p>With the above are found no less than eleven genera of
+stone-lilies or crinoids, some of them, such as <i>
+Cupressocrinites,</i> distinct from any Carboniferous forms. The
+mollusks, also, are no less characteristic; of 68 species of
+Brachiopoda, ten only are common to the Carboniferous Limestone.
+The <i>Stringocephalus Burtini</i> (Fig. 515) and <i>Uncites
+Gryphus</i> (Fig. 516) may be mentioned as exclusively Middle
+Devonian genera, and extremely characteristic of the same division
+in Belgium. The <i>Stringocephalus</i> is also so abundant in the
+Middle Devonian of the banks of the Rhine as to have suggested the
+name of Stringocephalus Limestone.</p>
+
+<img src="images/fig517.jpg" width="262" height="213" alt=
+"Fig. 517: Megalodon cucullatus." />
+
+<p>The only two species of Brachiopoda common to the Silurian and
+Devonian formations are <i>Atrypa reticularis</i> (Fig. 532), which
+seems to have been a cosmopolite species, and <i>Strophomena
+rhomboidalis.</i></p>
+
+<p>Among the peculiar lamellibranchiate bivalves common to the
+Plymouth limestone of Devonshire and the Continent, we find the <i>
+Megalodon</i> (Fig. 517). There are also twelve genera of
+Gasteropods which have yielded 36 species, four of which pass to
+the Carboniferous group, namely <i>Macrocheilus,</i>
+<a name="page453"></a><i>Acroculia, Euomphalus,</i> and <i>Murchisonia.</i> Pteropods
+occur, such as <i>Conularia</i> (Fig. 518), and Cephalopods, such
+as <i>Cyrtoceras, Gyroceras, Orthoceras,</i> and others, nearly all
+of genera distinct from those prevailing in the Upper Devonian
+Limestone, or Clymenien-kalk of the Germans already mentioned.
+Although but few species of Trilobites occur, the characteristic
+<i>Bronteus flabellifer</i> (Fig. 519) is far from rare, and all
+collectors are familiar with its fan-like tail. In this same group,
+called, as before stated, the Stringocephalus, or Eifel Limestone,
+in Germany, several fish remains have been detected, and among
+others the remarkable genus Coccosteus, covered with its
+tuberculated bony armour; and these ichthyolites serve, as Sir R.
+Murchison observes (Siluria, p. 362), to identify this middle
+marine Devonian with the Old Red Sandstone of Britain and
+Russia.</p>
+
+<img src="images/fig518.jpg" width="132" height="280" alt=
+"Fig. 518: Conularia ornata." /><img src=
+"images/fig519.jpg" width="132" height="217" alt=
+"Fig. 519: Bronteus flabellifer." />
+
+<img src="images/fig520.jpg" width="252" height="145" alt=
+"Fig. 520: Calceola sandalina." />
+
+<p>Beneath the Eifel Limestone (the great central and typical
+member of &ldquo;the Devonian&rdquo; on the Continent) lie certain
+schists called by German writers &ldquo;Calceola-schiefer,&rdquo;
+because they contain in abundance a fossil body of very curious
+structure, <i>Calceola sandalina</i> (Fig. 520), which has been
+usually considered a brachiopod, but which some naturalists have
+lately referred to a Goniophyllum, supposing it to be an abnormal
+form of the order <i>Zoantharia rugosa</i> (see <a href=
+"images/fig474.jpg">Fig. 474</a>), differing from all other corals
+in being furnished with a strong operculum. This is by no means a
+rare fossil in the slaty limestone of South Devon, and, like the
+Eifel form, is confined to the middle group of this country.</p>
+
+<p><b>Lower Devonian Rocks.</b>&mdash;A great series of sandstones
+and glossy slates, with Crinoids, Brachiopods, and some corals,
+<a name="page454"></a>occurring on the coast at Lynmouth and the neighbourhood, and
+called the Lynton Group (see Table <a href="#page449">p. 449</a>,
+form the lowest member of the Devonian in North Devon. Among the 18
+species of all classes enumerated by Mr. Etheridge, two-thirds are
+common to the Middle Devonian, but only one, the ubiquitous <i>
+Atrypa reticularis,</i> can with certainty be identified with
+Silurian species. Among the characteristic forms are <i>Alveolites
+suborbicularis,</i> also common to this formation in the Rhine, and
+<i>Orthis arcuata,</i> very widely spread in the North Devon
+localities. But we may expect a large addition to the number of
+fossils whenever these strata shall have been carefully searched.
+The Spirifer Sandstone of Sandberger, as exhibited in the rocks
+bordering the Rhine between Coblentz and Caub, belong to this Lower
+division, and the same broad-winged Spirifers distinguish the
+Devonian strata of North America.</p>
+
+<img src="images/fig521.jpg" width="266" height="108" alt=
+"Fig. 521: Spirifora mucronata." />
+
+<img src="images/fig522.jpg" width="132" height="370" alt=
+"Fig. 522: Homalonotus armatus." />
+
+<p>Among the Trilobites of this era several large species of <i>
+Homalonotus</i> (Fig. 522) are conspicuous. The genus is still
+better known as a Silurian form, but the spinose species appear to
+belong exclusively to the &ldquo;Lower Devonian,&rdquo; and are
+found in Britain, Europe, and the Cape of Good Hope.</p>
+
+<p>
+<b>Devonian of Russia.</b>&mdash;The Devonian strata of Russia extend,
+according to Sir R. Murchison, over a region more spacious than the British
+Isles; and it is remarkable that, where they consist of sandstone like the
+&ldquo;Old Red&rdquo; of Scotland and Central England, they are tenanted by
+fossil fishes often of the same species and still oftener of the same genera as
+the British, whereas when they consist of limestone they contain shells similar
+to those of Devonshire, thus confirming, as Sir Roderick has pointed out, the
+contemporaneous origin which had been previously assigned to formations
+exhibiting two very distinct mineral types in different parts of Britain.<a
+href="#fn-25.6" name="fnref-25.6" id="fnref-25.6"><sup>[6]</sup></a> <a
+name="page455"></a>The calcareous and the arenaceous rocks of Russia above
+alluded to alternate in such a manner as to leave no doubt of their having been
+deposited in different parts of the same great period.
+</p>
+
+<img src="images/fig523.jpg" width="238" height="615" alt=
+"Fig. 523: Psilophyton princeps." />
+
+<p><b>Devonian Strata in the United States and
+Canada.</b>&mdash;Between the Carboniferous and Silurian strata
+there intervenes, in the United States and Canada, a great series
+of formations referable to the Devonian group, comprising some
+strata of marine origin abounding in shells and corals, and others
+of shallow-water and littoral origin in which terrestrial plants
+abound. The fossils, both of the deep and shallow water strata, are
+very analogous to those of Europe, the species being in some cases
+the same. In Eastern Canada Sir W. Logan has pointed out that in
+the peninsula of Gaspe, south of the estuary of St. Lawrence, a
+mass of sandstone, conglomerate, and shale referable to this period
+occurs, rich in vegetable remains, together with some fish-spines.
+Far down in the sandstones of Gaspe, Dr. Dawson found, in 1869, an
+entire specimen of the genus <i>Cephalaspis,</i> a form so
+characteristic, as we have already seen, of the Scotch Lower Old
+Red Sandstone. Some of the sandstones are ripple-marked, and
+towards the upper part of the whole series a thin seam of coal has
+been observed, measuring, together with some associated
+<a name="page456"></a>carbonaceous shale, about three inches in thickness. It rests on
+an under-clay in which are the roots of Psilophyton (see Fig. 523).
+At many other levels rootlets of this same plant have been shown by
+Principal Dawson to penetrate the clays, and to play the same part
+as do the rootlets of Stigmaria in the coal formation.</p>
+
+<p>
+We had already learnt from the works of Göppert, Unger, and Bronn that the
+European plants of the Devonian epoch resemble generically, with few
+exceptions, those already known as Carboniferous; and Dr. Dawson, in 1859,
+enumerated 32 genera and 69 species which he had then obtained from the State
+of New York and Canada. A perusal of his catalogue,<a href="#fn-25.7"
+name="fnref-25.7" id="fnref-25.7"><sup>[7]</sup></a> comprising <i>Coniferæ,
+Sigillariæ, Calamites, Asterophyllites, Lepidodendra,</i> and ferns of the
+genera <i>Cyclopteris, Neuropteris, Sphenopteris,</i> and others, together with
+fruits, such as <i>Cardiocarpum</i> and <i>Trigonocarpum,</i> might dispose
+geologists to believe that they were presented with a list of Carboniferous
+fossils, the difference of the species from those of the coal-measures, and
+even a slight admixture of genera unknown in Europe, being naturally ascribed
+to geographical distribution and the distance of the New from the Old World.
+But fortunately the coal formation is fully developed on the other side of the
+Atlantic, and is singularly like that of Europe, both lithologically and in the
+species of its fossil plants. There is also the most unequivocal evidence of
+relative age afforded by superposition, for the Devonian strata in the United
+States are seen to crop out from beneath the Carboniferous on the borders of
+Pennsylvania and New York, where both formations are of great thickness.
+</p>
+
+<p>The number of American Devonian plants has now been raised by
+Dr. Dawson to 120, to which we may add about 80 from the European
+flora of the same age, so that already the vegetation of this
+period is beginning to be nearly half as rich as that of the
+coal-measures which have been studied for so much longer a time and
+over so much wider an area. The Psilophyton above alluded to is
+believed by Dr. Dawson to be a lycopodiaceous plant, branching
+dichotomously (see <i>P. princeps,</i> Fig. 523), with stems
+springing from a rhizome, which last has circular areoles, much
+resembling those of Stigmaria, and like it sending forth
+cylindrical rootlets. The extreme points of some of the branchlets
+are rolled up so as to resemble the croziers or circinate vernation
+of ferns; the leaves or bracts, <i>a,</i> supposed to belong to the
+same plant, are described by Dawson as having inclosed the
+fructification. The remains of <i>Psilophyton princeps</i> have
+been traced through
+<a name="page457"></a>all the members of the Devonian series in America, and Dr.
+Dawson has lately recognised it in specimens of Old Red Sandstone
+from the north of Scotland.</p>
+
+<p>The monotonous character of the Carboniferous flora might be
+explained by imagining that we have only the vegetation handed down
+to us of one set of stations, consisting of wide swampy flats. But
+Dr. Dawson supposes that the geographical conditions under which
+the Devonian plants grew were more varied, and had more of an
+upland character. If so, the limitation of this more ancient flora,
+represented by so many genera and species, to the gymnospermous and
+cryptogamous orders, and the absence or extreme rarity of plants of
+higher grade, lead us naturally to speculate on the theory of
+progressive development, however difficult it may be to avail
+ourselves of this explanation, so long as we meet with even a few
+exceptional cases of what may seem to be monocotyledonous or
+dicotyledonous exogens.</p>
+
+<p><b>Devonian Insects of Canada.</b>&mdash;The earliest known
+insects were brought to light in 1865 in the Devonian strata of St.
+John&rsquo;s, New Brunswick, and are referred by Mr. Scudder to
+four species of <i>Neuroptera.</i> One of them is a gigantic
+Ephemera, and measured five inches in expanse of wing.</p>
+
+<p>Like many other ancient animals, says Dr. Dawson, they show a
+remarkable union of characters now found in distinct orders of
+insects, or constitute what have been named &ldquo;synthetic
+types.&rdquo; Of this kind is a stridulating or musical apparatus
+like that of the cricket in an insect otherwise allied to the <i>
+Neuroptera.</i> This structure, as Dr. Dawson observes, if rightly
+interpreted by Mr. Scudder, introduces us to the sounds of the
+Devonian woods, bringing before our imagination the trill and hum
+of insect life that enlivened the solitudes of these strange old
+forests.
+</p>
+
+<p class="footnote">
+<a name="fn-25.1" id="fn-25.1"></a> <a href="#fnref-25.1">[1]</a>
+Siluria, 4th ed., p. 265.
+</p>
+
+<p class="footnote">
+<a name="fn-25.2" id="fn-25.2"></a> <a href="#fnref-25.2">[2]</a>
+Siluria, 4th ed., p. 258.
+</p>
+
+<p class="footnote">
+<a name="fn-25.3" id="fn-25.3"></a> <a href="#fnref-25.3">[3]</a>
+Abridged from <i>crossotos,</i> a fringe, and <i> pteryx,</i> a fin.
+</p>
+
+<p class="footnote">
+<a name="fn-25.4" id="fn-25.4"></a> <a href="#fnref-25.4">[4]</a>
+Powrie, Geol. Quart. Journ., vol. xx, p. 417.
+</p>
+
+<p class="footnote">
+<a name="fn-25.5" id="fn-25.5"></a> <a href="#fnref-25.5">[5]</a>
+Quart. Geol. Journ., vol. xxiii., 1867.
+</p>
+
+<p class="footnote">
+<a name="fn-25.6" id="fn-25.6"></a> <a href="#fnref-25.6">[6]</a>
+Murchison&rsquo;s Siluria, p. 329.
+</p>
+
+<p class="footnote">
+<a name="fn-25.7" id="fn-25.7"></a> <a href="#fnref-25.7">[7]</a>
+Quart. Geol. Journ., vol. xv, p. 477, 1859; also vol. xviii, p. 296, 1862.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap26"></a><a name="page458"></a>CHAPTER XXVI.<br/>
+SILURIAN GROUP.</h2>
+
+<p class="letter">Classification of the Silurian Rocks. &mdash;
+Ludlow Formation and Fossils. &mdash; Bone-bed of the Upper Ludlow.
+&mdash; Lower Ludlow Shales with Pentamerus. &mdash; Oldest known
+Remains of fossil Fish. &mdash; Table of the progressive Discovery
+of Vertebrata in older Rocks. &mdash; Wenlock Formation, Corals,
+Cystideans and Trilobites. &mdash; Llandovery Group or Beds of
+Passage. &mdash; Lower Silurian Rocks. &mdash; Caradoc and Bala
+Beds. &mdash; Brachiopoda. &mdash; Trilobites. &mdash;
+Cystideæ. &mdash; Graptolites. &mdash; Llandeilo Flags.
+&mdash; Arenig or Stiper-stones Group. &mdash; Foreign Silurian
+Equivalents in Europe. &mdash; Silurian Strata of the United
+States. &mdash; Canadian Equivalents. &mdash; Amount of specific
+Agreement of Fossils with those of Europe.</p>
+
+<p><b>Classification of the Silurian Rocks.</b>&mdash;We come next
+in descending order to that division of Primary or Palæozoic
+rocks which immediately underlie the Devonian group or Old Red
+Sandstone. For these strata Sir Roderick Murchison first proposed
+the name of Silurian when he had studied and classified them in
+that part of Wales and some of the contiguous counties of England
+which once constituted the kingdom of the <i>Silures,</i> a tribe
+of ancient Britons. The following table will explain the two
+principal divisions, Upper and Lower, of the Silurian rocks, and
+the minor subdivisions usually adopted, comprehending all the
+strata originally embraced in the Silurian system by Sir Roderick
+Murchison. The formations below the Arenig or Stiper-stones group
+are treated of in the next chapter, when the
+&ldquo;Primordial&rdquo; or Cambrian group is described.</p>
+
+<table border="1" cellspacing="0" cellpadding="4" summary=
+"Principal divisions and subdivisions and thickness of each subdivision.">
+<tr>
+<td align="center" colspan="2">UPPER SILURIAN ROCKS.</td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td ><small>Thickness<br/>
+in feet</small></td>
+</tr>
+
+<tr>
+<td >1. L<small>UDLOW</small>
+F<small>ORMATION</small>:<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>a.</i> &nbsp;Upper Ludlow
+beds</td>
+<td >780</td>
+</tr>
+
+<tr>
+<td >&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>b.</i>
+&nbsp;Lower Ludlow beds:</td>
+<td >1,050</td>
+</tr>
+
+<tr>
+<td >2. W<small>ENLOCK</small>
+F<small>ORMATION</small>:<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>a.</i> &nbsp;Wenlock limestone and
+shale</td>
+<td valign="middle" rowspan="2">above 4,000</td>
+</tr>
+
+<tr>
+<td >&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>b.</i>
+&nbsp;Woolhope limestone and shale, and Denbighshire grits:</td>
+</tr>
+
+<tr>
+<td >3. L<small>LANDOVERY</small>
+F<small>ORMATION</small><br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(Beds of passage between Upper and
+Lower Silurian):<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>a.</i>&nbsp; Upper Llandovery
+(May-Hill beds):</td>
+<td >800</td>
+</tr>
+
+<tr>
+<td >&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>b.</i>&nbsp;
+Lower Llandovery:</td>
+<td >600&ndash;1,000</td>
+</tr>
+
+<tr>
+<td align="center" colspan="2">LOWER SILURIAN ROCKS.</td>
+</tr>
+
+<tr>
+<td >1. B<small>ALA AND</small> C<small>ARADOC</small>
+B<small>EDS</small>, including volcanic rocks:</td>
+<td >12,000</td>
+</tr>
+
+<tr>
+<td >2. L<small>LANDEILO</small> F<small>LAGS</small>,
+including volcanic rocks:</td>
+<td >4,500</td>
+</tr>
+
+<tr>
+<td >3. A<small>RENIG OR</small>
+S<small>TIPER-STONES</small> G<small>ROUP</small>, including
+volcanic rocks:</td>
+<td >above 10,000</td>
+</tr>
+</table>
+
+<p>
+<a name="page459"></a><small>UPPER SILURIAN ROCKS.</small></p>
+
+<p><b>1. Ludlow Formation.</b>&mdash;This member of the Upper
+Silurian group, as will be seen by above table, is of great
+thickness, and subdivided into two parts&mdash;the Upper Ludlow and the
+Lower Ludlow. Each of these may be distinguished near the town of
+Ludlow, and at other places in Shropshire and Herefordshire, by
+peculiar organic remains; but out of more than 500 species found in
+the Ludlow formation as a whole, not more than five species per
+hundred are common to the overlying Devonian. The student may refer
+to the excellent tables given in the last edition of Sir R.
+Murchison&rsquo;s Siluria for a list of the organic remains of all
+classes distributed through the different subdivisions of the Upper
+and Lower Silurian.</p>
+
+<p><i>a.</i> <b>Upper Ludlow:</b> <i>Downton
+Sandstone.</i>&mdash;At the top of this subdivision there occur
+beds of fine-grained yellowish sandstone and hard reddish grits
+which were formerly referred by Sir R. Murchison to the Old Red
+Sandstone, under the name of &ldquo;Tilestones.&rdquo; In mineral
+character this group forms a transition from the Silurian to the
+Old Red Sandstone, the strata of both being conformable; but it is
+now ascertained that the fossils agree in great part specifically,
+and in general character entirely, with those of the underlying
+Upper Ludlow rocks. Among these are <i>Orthoceras bullatum,
+Platyschisma helicites, Bellerophon trilobatus, Chonetes lata,</i>
+etc., with numerous defenses of fishes.</p>
+
+<p>These beds, therefore, now generally called the &ldquo;Downton
+Sandstone,&rdquo; are classed as the newest member of the Upper
+Silurian. They are well seen at Downton Castle, near Ludlow, where
+they are quarried for building, and at Kington, in Herefordshire.
+In the latter place, as well as at Ludlow, crustaceans of the
+genera Pterygotus (for genus see <a href="images/fig504.jpg">Fig.
+504</a>) and Eurypterus are met with.</p>
+
+<p>
+<i>Bone-bed of the Upper Ludlow.</i>&mdash;At the base of the Downton
+sandstones there occurs a bone-bed which deserves especial notice as affording
+the most ancient example of fossil fish occurring in any considerable quantity.
+It usually consists of one or two thin layers of brown bony fragments near the
+junction of the Old Red Sandstone and the Ludlow rocks, and was first observed
+by Sir R. Murchison near the town of Ludlow, where it is three or four inches
+thick. It has since been traced to a distance of 45 miles from that point into
+Gloucestershire and other counties, and is commonly not more than an inch
+thick, but varies to nearly a foot. Near Ludlow two bone-beds are observable,
+with 14 feet of <a name="page460"></a>intervening strata full of Upper Ludlow
+fossils.<a href="#fn-26.1" name="fnref-26.1" id="fnref-26.1"><sup>[1]</sup></a>
+At that point immediately above the upper fish-bed numerous small globular
+bodies have been found, which were determined by Dr. Hooker to be the sporangia
+of a cryptogamic land-plant, probably lycopodiaceous.
+</p>
+
+<p><img src="images/fig524.jpg" width="407" height="105" alt=
+"Fig. 524: Onchus tenuistriatus. Fig. 525: Shagreen-scales of a placoid fish, Thelodus parvidens." />
+</p>
+
+<p>Most of the fish have been referred by Agassiz to his placoid
+order, some of them to the genus Onchus, to which the spine (Fig.
+524) and the minute scales (Fig. 525) are supposed to belong. It
+has been suggested, however, that Onchus may be one of those
+Acanthodian fish referred by Agassiz to his Ganoid order, which are
+so characteristic of the base of the Old Red Sandstone in
+Forfarshire, although the species of the Old Red are all different
+from these of the Silurian beds now under consideration.</p>
+
+<img src="images/fig526.jpg" width="147" height="87" alt=
+"Fig. 526: Plectrodus mirabilis." />
+
+<p>The jaw and teeth of another predaceous genus (Fig. 526) have
+also been detected, together with some specimens of <i>Pteraspis
+Ludensis.</i> As usual in bone-beds, the teeth and bones are, for
+the most part, fragmentary and rolled.</p>
+
+<img src="images/fig527.jpg" width="133" height="123" alt=
+"Fig. 527: Orthis elegantula." /><img src=
+"images/fig528.jpg" width="119" height="104" alt=
+"Fig. 528: Rhynchonella navicula." />
+
+<p><i>Grey Sandstone and Mudstone, etc.</i>&mdash;The next
+subdivision of the Upper Ludlow consists of grey calcareous
+sandstone, or very commonly a micaceous stone, decomposing into
+soft mud, and contains, besides the shells mentioned aon page 459,
+<i>Lingula cornea, Orthis orbicularis,</i> a round variety of <i>O.
+elegantula, Modiolopsis platyphylla, Grammysia cingulata,</i> all
+characteristic of the Upper Ludlow. The lowest or mud-stone beds
+contain <i>Rhynchonella navicula</i> (Fig. 528), which is common to
+this bed and the Lower Ludlow. As usual in Palæozoic strata
+older than the coal, the brachiopodous mollusca greatly outnumber
+the lamellibranchiate (see <a href="#page470">p. 470</a>); but the
+latter are by no means unrepresented. Among other genera, for
+example, we observe <i>Avicula</i> and
+<a name="page461"></a><i>Pterinea, Cardiola, Ctenodonta</i> (sub-genus of <i>
+Nucula</i>), <i>Orthonota, Modiolopsis,</i> and <i>
+Palæarca.</i></p>
+
+<p>Some of the Upper Ludlow sandstones are ripple-marked, thus
+affording evidence of gradual deposition; and the same may be said
+of the accompanying fine argillaceous shales, which are of great
+thickness, and have been provincially named
+&ldquo;mud-stones.&rdquo; In some of these shales stems of
+crinoidea are found in an erect position, having evidently become
+fossil on the spots where they grew at the bottom of the sea. The
+facility with which these rocks, when exposed to the weather, are
+resolved into mud, proves that, notwithstanding their antiquity,
+they are nearly in the state in which they were first thrown
+down.</p>
+
+<p><img src="images/fig529.jpg" width="320" height="230" alt=
+"Fig. 529: Pentamerus Knightii." /></p>
+
+<p><i>b.</i> <b>Lower Ludlow Beds.</b>&mdash;The chief mass of this
+formation consists of a dark grey argillaceous shale with
+calcareous concretions, having a maximum thickness of 1000 feet. In
+some places, and especially at Aymestry, in Herefordshire, a
+subcrystalline and argillaceous limestone, sometimes 50 feet thick,
+overlies the shale. Sir R. Murchison therefore classes this
+Aymestry limestone as holding an intermediate position between the
+Upper and Lower Ludlow, but Mr. Lightbody remarks that at Mocktrie,
+near Leintwardine, the Lower Ludlow shales, with their
+characteristic fossils, occur both above and below a similar
+limestone. This limestone around Aymestry and Sedgeley is
+distinguished by the abundance of <i>Pentamerus Knightii,</i>
+Sowerby (Fig. 529), also found in the Lower Ludlow and Wenlock
+shale. This genus of brachiopoda was first found in Silurian
+strata, and is exclusively a palæozoic form. The name was
+derived from <i>pente,</i> five, and <i>meros,</i> a part, because
+both valves are divided by a central septum, making four chambers,
+and in one valve
+<a name="page462"></a>the septum itself contains a small chamber, making five. The
+size of these septa is enormous compared with those of any other
+brachiopod shell; and they must nearly have divided the animal into
+two equal halves; but they are, nevertheless, of the same nature as
+the septa or plates which are found in the interior of <i>
+Spirifera, Terebratula,</i> and many other shells of this order.
+Messrs. Murchison and De Verneuil discovered this species dispersed
+in myriads through a white limestone of Upper Silurian age, on the
+banks of the Is, on the eastern flank of the Urals in Russia, and a
+similar species is frequent in Sweden.</p>
+
+<img src="images/fig530.jpg" width="107" height="199" alt=
+"Fig. 530: Lingula Lewisii." />
+
+<p>Three other abundant shells in the Aymestry limestone are,
+first, <i>Lingula Lewisii</i> (Fig. 530); second, <i>Rhynchonella
+Wilsoni,</i> Sowerby (Fig. 531), which is also common to the Lower
+Ludlow and Wenlock limestone; third, <i>Atrypa reticularis,</i>
+Linn. (Fig. 532), which has a very wide range, being found in every
+part of the Upper Silurian system, and even ranging up into the
+Middle Devonian series.</p>
+
+<p><img src="images/fig531.jpg" width="279" height="109" alt=
+"Fig. 531: Rhynchonella (Terebratula) Wilsoni." /></p>
+
+<p>The Aymestry Limestone contains many shells, especially
+brachiopoda, corals, trilobites, and other fossils, amounting on
+the whole to 74 species, all except three or four being common to
+the beds either above or below.</p>
+
+<p>
+<img src="images/fig532.jpg" width="282" height="208" alt=
+"Fig. 532: Atrypa reticularis." /> The Lower Ludlow
+Shale contains, among other fossils, many large cephalopoda not
+known in newer rocks, as the <i>Phragmoceras</i> of Broderip, and
+the <i>Lituites</i> of Breynius (see Figs. 533, 534). The latter is
+partly straight and partly convoluted in a very flat spire. The
+<a name="page463"></a><i>Orthoceras Ludense</i> (Fig. 535), as well as the cephalopod
+last mentioned, occurs in this member of the species.</p>
+
+<p>
+<img src="images/fig533.jpg" width="157" height="244" alt=
+"Fig. 533: Phragmoceras ventricosum." />
+</p>
+
+<p>A species of Graptolite, <i>G. priodon,</i> Bronn (<a href=
+"images/fig545.jpg">Fig. 545</a>), occurs plentifully in the Lower
+Ludlow. This fossil, referred, though somewhat doubtfully, to a
+form of hydrozoid or sertularian polyp, has not yet been met with
+in strata above the Silurian.</p>
+
+<p>Star-fish, as Sir R. Murchison points out, are by no means rare
+in the Lower Ludlow rock. These fossils, of which six extinct
+genera are now known in the Ludlow series, represented by 18
+species, remind us of various living forms now found in our British
+seas, both of the families <i>Asteriadæ</i> and <i>
+Ophiuridæ.</i></p>
+
+<p><img src="images/fig534.jpg" width="396" height="177" alt=
+"Fig. 534: Lituites (Trochoceras) giganteus. Fig. 535: Fragment of Orthoceras Ludense." />
+</p>
+
+<p><b>Oldest known Fossil Fish.</b>&mdash;Until 1859 there was no
+example of a fossil fish older than the bone-bed of the Upper
+Ludlow, but in that year a specimen of Pteraspis was found at
+Church Hill, near Leintwardine, in Shropshire, by Mr. J. E. Lee of
+Caerleon, <small>F.G.S.</small>, in shale below the Aymestry
+limestone, associated with fossil shells of the Lower Ludlow
+formation&mdash;shells which differ considerably from those
+characterising the Upper Ludlow already described. This discovery
+is of no small interest as bearing on the theory of progressive
+development, because, according to Professor Huxley, the genus
+Pteraspis is allied to the sturgeon, and therefore by no means of
+low grade in the piscine class.</p>
+
+<p>It is a fact well worthy of notice that no remains of vertebrata
+have yet been met with in any strata older than the Lower
+Ludlow.</p>
+
+<p>When we reflect on the hundreds of Mollusks, Echinoderms,
+<a name="page464"></a>Trilobites, Corals, and other fossils already obtained from more
+ancient Silurian formations, Upper, Middle, and Lower, we may well
+ask whether any set of fossiliferous rocks newer in the series were
+ever studied with equal diligence, and over so vast an area,
+without yielding a single ichthyolite. Yet we must hesitate before
+we accept, even on such evidence, so sweeping a conclusion, as that
+the globe, for ages after it was inhabited by all the great classes
+of invertebrata, remained wholly untenanted by vertebrate
+animals.</p>
+
+<p class="center">
+<i>Dates of the Discovery of different Classes of Fossil Vertebrata; showing
+the gradual progress made in tracing them to rocks of higher antiquity.</i>
+</p>
+
+<table border="1" cellspacing="0" cellpadding="4"
+summary=
+"Column 1, Fossil; Column 2, Year; Column 3, Formations; Column 4, Geographical localities.">
+<tr>
+<td>&nbsp;</td>
+<td >Year</td>
+<td >Formations</td>
+<td >Geographical localities</td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="3">Mammalia</td>
+<td >1798</td>
+<td >Upper Eocene</td>
+<td >Paris (Gypsum of Montmartre).<sup>1</sup></td>
+</tr>
+
+<tr>
+<td >1818</td>
+<td >Lower Oolite</td>
+<td >Stonesfield.<sup>2</sup></td>
+</tr>
+
+<tr>
+<td >1847</td>
+<td >Upper Trias</td>
+<td >Stuttgart.<sup>3</sup></td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="6">Aves</td>
+<td >1782</td>
+<td >Upper Eocene</td>
+<td >Paris (Gypsum of Montmartre).<sup>4</sup></td>
+</tr>
+
+<tr>
+<td >1839</td>
+<td >Lower Eocene</td>
+<td >Isle of Sheppey (London Clay).<sup>5</sup></td>
+</tr>
+
+<tr>
+<td >1854</td>
+<td >Lower Eocene</td>
+<td >Woolwich Beds.<sup>6</sup></td>
+</tr>
+
+<tr>
+<td >1855</td>
+<td >Lower Eocene</td>
+<td >Mendon (Plastic Clay).<sup>7</sup></td>
+</tr>
+
+<tr>
+<td >1858</td>
+<td >Chloritic Series, or Upper Greensand</td>
+<td >Cambridge.<sup>8</sup></td>
+</tr>
+
+<tr>
+<td >1863</td>
+<td >Upper Oolite</td>
+<td >Solenhofen.<sup>9</sup></td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="2">Reptilia</td>
+<td >1710</td>
+<td >Permian (or Zechstein)</td>
+<td >Thuringia.<sup>10</sup></td>
+</tr>
+
+<tr>
+<td >1844</td>
+<td >Carboniferous</td>
+<td >Saarbrück, near
+Trèves.<sup>11</sup></td>
+</tr>
+
+<tr>
+<td valign="middle" rowspan="5">Pisces</td>
+<td >1709</td>
+<td >Permian (or Kupferschiefer)</td>
+<td >Thuringia.<sup>12</sup></td>
+</tr>
+
+<tr>
+<td >1793</td>
+<td >Carboniferous (Mountain Limestone)</td>
+<td >Glasgow.<sup>13</sup></td>
+</tr>
+
+<tr>
+<td >1828</td>
+<td >Devonian</td>
+<td >Caithness.<sup>14</sup></td>
+</tr>
+
+<tr>
+<td >1840</td>
+<td >Upper Ludlow</td>
+<td >Ludlow.<sup>15</sup></td>
+</tr>
+
+<tr>
+<td >1859</td>
+<td >Lower Ludlow</td>
+<td >Leintwardine.<sup>16</sup></td>
+</tr>
+</table>
+
+<p class="footnote">
+1. George Cuvier, Bulletin Soc. Philom. xx.<br/>
+2. In 1818, Cuvier, visiting the Museum of Oxford, decided on the
+mammalian character of a jaw from Stonesfield. See also <a href=
+"#page347">p. 347.</a><br/>
+3. Prof. Plieninger. See <a href="#page368">p.
+368.</a><br/>
+4. Cuvier, Ossemens Foss. Art. &ldquo;Oiseaux.&rdquo;<br/>
+5. Prof. Owen, Geol. Trans., 2nd series, vol. vi, p. 203, 1839.<br/>
+6. Upper part of the Woolwich beds. Prestwich, Quart. Geol. Journ.,
+vol. x, p. 157.<br/>
+7. <i>Gastornis Parisiensis.</i> Owen, Quart. Geol. Journ., vol.
+xii, p. 204, 1856.<br/>
+8. Coprolitic bed, in the Upper Greensand. See <a href=
+"#page299">p. 299.</a><br/>
+9. The <i>Archæopteryx macrura,</i> Owen. See <a href=
+"#page338">p. 338.</a><br/>
+10. The fossil monitor of Thuringia (<i>Protosaurus Speneri,</i> V.
+Meyer) was figured by Spener of Berlin in 1810. (Miscel.
+Berlin.)<br/>
+11. See <a href="#page406">p. 406.</a><br/>
+12. Memorabilia Saxoniæ Subterr., Leipsic, 1709.<br/>
+13. History of Rutherglen by Rev. David Ure, 1793.<br/>
+14. Sedgwick and Murchison, Geol. Trans., 2nd series, vol. ii, p.
+141, 1828.<br/>
+15. Sir R. Murchison. See <a href="#page459">p. 459.</a><br/>
+16. See <a href="#page461">p. 461.</a><br/>
+<br/>
+Obs.&mdash;The evidence derived from foot-prints, though often to be
+relied on, is omitted in the above table, as being less exact than
+that founded on bones and teeth.
+</p>
+
+<p>In the preceding Table a few dates are set before the reader of
+the discovery of different classes of animals in ancient rocks, to
+enable him to perceive at a glance how
+<a name="page465"></a>gradual has been our progress in tracing back the signs of
+vertebrata to formations of high antiquity. Such facts may be
+useful in warning us not to assume too hastily that the point which
+our retrospect may have reached at the present moment can be
+regarded as fixing the date of the first introduction of any one
+class of beings upon the earth.</p>
+
+<p><b>2. Wenlock Formation.</b>&mdash;We next come to the Wenlock
+formation, which has been divided (see Table, <a href="#page458">
+p. 458</a>) into Wenlock limestone, Wenlock shale, and Woolhope
+limestone and Denbighshire grits.</p>
+
+<img src="images/fig536.jpg" width="143" height="254" alt=
+"Fig. 536: Halysites catenularius." />
+
+<p>
+<i>a. Wenlock Limestone.</i>&mdash;This limestone, otherwise well known to
+collectors by the name of the Dudley Limestone, forms a continuous ridge in
+Shropshire, ranging for about 20 miles from S.W. to N.E., about a mile distant
+from the nearly parallel escarpment of the Aymestry limestone. This ridgy
+prominence is due to the solidity of the rock, and to the softness of the
+shales above and below it. Near Wenlock it consists of thick masses of grey
+subcrystalline limestone, replete with corals, encrinites, and trilobites. It
+is essentially of a concretionary nature; and the concretions, termed
+&ldquo;ball-stones&rdquo; in Shropshire, are often enormous, even 80 feet in
+diameter. They are of pure carbonate of lime, the surrounding rock being more
+or less argillaceous<a href="#fn-26.2" name="fnref-26.2"
+id="fnref-26.2"><sup>[2]</sup></a> Sometimes in the Malvern Hills this
+limestone, according to Professor Phillips, is oolitic.
+</p>
+
+<img src="images/fig537.jpg" width="113" height="283" alt=
+"Fig. 537: Favosites Gothlandica." />
+
+<p>Among the corals, in which this formation is so rich, 53 species
+being known, the &ldquo;chain-coral,&rdquo; <i>Halysites
+catenularius</i> (Fig. 536), may be pointed out as one very easily
+recognised, and widely spread in Europe, ranging through all parts
+of the Silurian group, from the Aymestry limestone to near the
+bottom of the Llandeilo rocks. Another coral, the <i>Favosites
+Gothlandica</i> (Fig. 537), is also met with in profusion in large
+hemispherical masses, which break up into columnar and prismatic
+fragments, like that here figured (Fig. 537, <i>b</i>). Another
+common form in the
+<a name="page466"></a>Wenlock limestone is the <i>Omphyma turbinatum</i> (Fig. 538),
+which, like many of its modern companions, reminds us of some
+cup-corals; but all the Silurian genera belong to the
+palæozoic type before mentioned (<a href=
+"#page432">p. 432</a>), exhibiting the quadripartite
+arrangement of the septalamellæ within the cup.</p>
+
+<img src="images/fig538.jpg" width="130" height="225" alt=
+"Fig. 538: Omphyma turbinatum." /><img src=
+"images/fig539.jpg" width="107" height="222" alt=
+"Fig. 539: Pseudocrinites bifasciatus." />
+
+<p>
+Among the numerous Crinoids, several peculiar species of <i> Cyathocrinus</i>
+(for genus see <a href="images/fig478.jpg">Figs. 478</a>, 479) contribute their
+calcareous stems, arms, and cups towards the composition of the Wenlock
+limestone. Of Cystideans there are a few very remarkable forms, most of them
+peculiar to the Upper Silurian formation, as, for example, the <i>
+Pseudocrinites,</i> which was furnished with pinnated fixed arms,<a
+href="#fn-26.3" name="fnref-26.3" id="fnref-26.3"><sup>[3]</sup></a> as
+represented in Fig. 539.
+</p>
+
+<img src="images/fig540.jpg" width="152" height="159" alt=
+"Fig. 540: Strophomena (Leptæna) depressa." />
+
+<p>The Brachiopoda are, many of them, of the same species as those
+of the Aymestry limestone; as, for example, <i>Atrypa
+reticularis</i> (Fig. <a href="images/fig532.jpg">532</a>), and
+<i>Strophomena depressa</i> (Fig. 540); but the latter species
+ranges also from the Ludlow rocks, through the Wenlock shale, to
+the Caradoc Sandstone.</p>
+
+<img src="images/fig541.jpg" width="124" height="138" alt=
+"Fig. 541: Calymene Blumenbachii." />
+
+<p>The crustaceans are represented almost exclusively by
+Trilobites, which are very conspicuous, 22 being peculiar. The <i>
+Calymene Blumenbachii</i> (Fig. 541), called the &rdquo;Dudley
+Trilobite,&rdquo; was known to collectors long before its true
+place in the animal kingdom was ascertained. It is often found
+coiled up like the common <i>Oniscus</i> or wood-louse, and this is
+so usual a circumstance among certain genera of trilobites as to
+lead us to conclude that they must have habitually resorted to this
+mode of protecting themselves when alarmed. The other common
+species is the <i>Phacops caudatus (Asaphus caudatus),</i> Brong.
+(see Fig. 542), and this is conspicuous for its large
+<a name="page467"></a>size and flattened form. <i>Sphærexochus mirus</i> (Fig.
+543) is almost a globe when rolled up, the forehead or glabellum of
+this species being extremely inflated. The <i>Homalonotus,</i> a
+form of Trilobite in which the tripartite division of the dorsal
+crust is almost lost (see Fig. 544), is very characteristic of this
+division of the Silurian series.</p>
+
+<img src="images/fig542.jpg" width="108" height="241" alt=
+"Fig. 542: Phacops (Asaphus) caudatus." /><img src=
+"images/fig543.jpg" width="116" height="167" alt=
+"Fig. 543: Sphærexochus mirus." />
+
+<p><i>Wenlock Shale.</i>&mdash;This, observes Sir R. Murchison, is
+infinitely the largest and most persistent member of the Wenlock
+formation, for the limestone often thins out and disappears. The
+shale, like the Lower Ludlow, often contains elliptical concretions
+of impure earthy limestone.</p>
+
+<img src="images/fig544.jpg" width="113" height="255" alt=
+"Fig. 544: Homalonotus delphinocephalus." />
+
+<p>In the Malvern district it is a mass of finely levigated
+argillaceous matter, attaining, according to Professor Phillips, a
+thickness of 640 feet, but it is sometimes more than 1000 feet
+thick in Wales, and is worked for flag-stones and slates. The
+prevailing fossils, besides corals and trilobites, and some
+crinoids, are several small species of <i>Orthis, Cardiola,</i> and
+numerous thin-shelled species of <i>Orthoceratites.</i></p>
+
+<p>About six species of <i>Graptolite,</i> a peculiar group of
+sertularian fossils before alluded to (p. <a href="#page463">
+463</a>) as being confined to Silurian rocks, occur in this shale.
+Of fossils of this genus, which is very characteristic of the Lower
+Silurian, I shall again speak in the sequel (p. <a href=
+"#page474">474</a>).</p>
+
+<img src="images/fig545.jpg" width="204" height="75" alt=
+"Fig. 545: Graptolithus priodon." />
+
+<p><i>b. Woolhope Beds.</i>&mdash;Though not always recognised as a
+separate subdivision of the Wenlock, the Woolhope beds, which
+underlie the Wenlock shale, are of great importance. Usually they
+occur as massive or nodular limestones, underlaid by a fine shale
+or flag-stone; and in other cases, as in the noted Denbighshire
+sandstones, as a coarse grit of very great thickness. This grit
+forms mountain ranges through North and South Wales, and is
+generally marked by the great sterility of the soil where it
+<a name="page468"></a>occurs. It contains the usual Wenlock fossils, but with the
+addition of some common in the uppermost Ludlow rock, such as <i>
+Chonetes lata</i> and <i>Bellerophon trilobatus.</i> The chief
+fossils of the Woolhope limestone are <i>Illænus Barriensis,
+Homalonotus delphinocephalus</i> (Fig. 544), <i>Strophomena
+imbrex,</i> and <i>Rhynchonella Wilsoni</i> (<a href=
+"images/fig531.jpg">Fig. 531</a>). The latter attains in the
+Woolhope beds an unusual size for the species, the specimens being
+sometimes twice as large as those found in the Wenlock
+limestone.</p>
+
+<p>In some places below the Wenlock formation there are shales of a
+pale or purple colour, which near Tarannon attain a thickness of
+about 1000 feet; they can be traced through Radnor and Montgomery
+to North Wales, according to Messrs. Jukes and Aveline. By the
+latter geologist they have been identified with certain shales
+above the May-Hill Sandstone, near Llandovery, but, owing to the
+extreme scarcity of fossils, their exact position remains
+doubtful.</p>
+
+<p><b>3. Llandovery Group&mdash;Beds of Passage.</b>&mdash;We now
+come to beds respecting the classification of which there has been
+much difference of opinion, and which in fact must be considered as
+beds of passage between Upper and Lower Silurian. I formerly
+adopted the plan of those who class them as Middle Silurian, but
+they are scarcely entitled to this distinction, since after about
+1400 Silurian species have been compared the number peculiar to the
+group in question only gives them an importance equal to such minor
+subdivisions as the Ludlow or Bala groups. I therefore prefer to
+regard them as the base of the Upper Silurian, to which group they
+are linked by more than twice as many species as to the Lower
+Silurian. By this arrangement the line of demarkation between the
+two great divisions, though confessedly arbitrary, is less so than
+by any other. They are called Llandovery Rocks, from a town in
+South Wales, in the neighbourhood of which they are well developed,
+and where, especially at a hill called Noeth Grug, in spite of
+several faults, their relations to one another can be clearly
+seen.</p>
+
+<p
+><i>a.&nbsp; Upper Llandovery or May-Hill
+Sandstone.</i>&mdash;The May-Hill group, which has also been named &rdquo;Upper
+Llandovery,&rdquo; by Sir R. Murchison, ranges from the west of the Longmynd to
+Builth, Llandovery, and Llandeilo, and to the sea in Marlow&rsquo;s Bay, where
+it is seen in the cliffs. It consists of brownish and yellow sandstones with
+calcareous nodules, having sometimes a conglomerate at the base derived from
+the waste of the Lower Silurian rocks. These May-Hill beds were formerly
+supposed to be part of the Caradoc formation, but their true position was
+determined by Professor <a name="page469"></a>Sedgwick<a href="#fn-26.4"
+name="fnref-26.4" id="fnref-26.4"><sup>[4]</sup></a> to be at the base of the
+Upper Silurian proper. The more calcareous portions of the rock have been
+called the Pentamerus limestone, because <i>Pentamerus oblongus</i> (Fig. 546)
+is very abundant in them. It is usually accompanied by <i>P. (Stricklandinia)
+lirata</i> (Fig. 547); both forms have a wide geographical range, being also
+met with in the same part of the Silurian series in Russia and the United
+States.
+</p>
+
+<img src="images/fig546.jpg" width="263" height="312" alt=
+"Fig. 546: Pentamerus oblongus." />
+
+<p>About 228 species of fossils are known in the May-Hill division,
+more than half of which are Wenlock species. They consist of
+trilobites of the genera <i>Illænus</i> and <i>Calymene</i>;
+Brachiopods of the genera <i>Orthis, Atrypa, Leptæna,
+Pentamerus, Strophomena,</i> and others; Gasteropods of the genera
+<i>Turbo, Murchisonia</i> (for genus, see <a href=
+"images/fig567.jpg">Fig. 567</a>), and <i>Bellerophon</i>; and
+Pteropods of the genus <i>Conularia.</i> The Brachiopods, of which
+there are 66 species, are almost all Upper Silurian.</p>
+
+<img src="images/fig547.jpg" width="137" height="149" alt=
+"Fig. 547: Stricklandinia (Pentamerus) lirata." /> <img
+src="images/fig548.jpg" width="173" height="164" alt=
+"Fig. 548: Tentaculites annulatus." />
+
+<p>Among the fossils of the May-Hill shelly sandstone at Malvern,
+<i>Tentaculites annulatus</i> (Fig. 548), an annelid, probably
+allied to Serpula, is found.</p>
+
+<p><i>Lower Llandovery Rocks.</i>&mdash;Below the May-Hill Group
+are the Lower Llandovery Rocks, which consist chiefly of hard slaty
+rocks, and beds of conglomerate from 600 to 1000 feet in thickness.
+The fossils, which are somewhat rare in the lower beds, consist of
+128 known species, only eleven of which are peculiar, 83 being
+<a name="page470"></a>common to the May-Hill group above, and 93 common to the rocks
+below. <i>Stricklandinia (Pentamerus) levis,</i> which is common in
+the Lower Llandovery, becomes rare in the Upper, while <i>
+Pentamerus oblongus</i> (Fig. 546), which is the characteristic
+shell of the Upper Llandovery, occurs but seldom in the Lower.
+</p>
+
+<p class="center">
+<small>LOWER SILURIAN ROCKS.</small>
+</p>
+
+<p>The Lower Silurian has been divided into, first, the Bala Group;
+second, the Llandeilo flags; and, third, the Arenig or Lower
+Llandeilo formation.</p>
+
+<p><b>Bala and Caradoc Beds.</b>&mdash;The Caradoc sandstone was
+originally so named by Sir R. I. Murchison from the mountain called
+Caer Caradoc, in Shropshire; it consists of shelly sandstones of
+great thickness, and sometimes containing much calcareous matter.
+The rock is frequently laden with the beautiful trilobite called by
+Murchison <i>Trinucleus Caractaci</i> (see 
+Fig. 553), which ranges from the base to
+the summit of the formation, usually accompanied by <i>Strophomena
+grandis</i> (see Fig. 551), and <i>Orthis vespertilio</i> (Fig.
+550), with many other fossils.</p>
+
+<p><img src="images/fig549.jpg" width="407" height="177" alt=
+"Fig. 549: Orthis tricenaria. Fig. 550: Orthis vespertilio. Fig. 551: Orthis
+(Strophomena) grandis." />
+</p>
+
+<p><i>Brachiopoda.</i>&mdash;Nothing is more remarkable in these
+beds, and in the Silurian strata generally of all countries, than
+the preponderance of brachiopoda over other forms of mollusca.
+Their proportional numbers can by no means be explained by
+supposing them to have inhabited seas of great depth, for the
+contrast between the palæozoic and the present state of
+things has not been essentially altered by the late discoveries
+made in our deep-sea dredgings. We find the living brachiopoda so
+rare as to form about one forty-fourth of the whole bivalve fauna,
+whereas in the Lower Silurian rocks of which we are now about to
+treat, and where the brachiopoda reach their maximum, they are
+represented by more than twice as many species as the
+Lamellibranchiate bivalves.</p>
+
+<p>
+<a name="page471"></a>There may, indeed, be said to be a continued decrease of the
+proportional number of this lower tribe of mollusca as we proceed
+from older to newer rocks. In the British Devonian, for example,
+the Brachiopoda number 99, the Lamellibranchiata 58; while in the
+Carboniferous their proportions are more than reversed, the
+Lamellibranchiata numbering 334 species, and the Brachiopoda only
+157. In the Secondary or Cainozoic formations the preponderance of
+the higher grade of bivalves becomes more and more marked, till in
+the tertiary strata it approaches that observed in the living
+creation.</p>
+
+<p>While on this subject, it may be useful to the student to know
+that a Brachiopod differs from ordinary bivalves, mussels, cockles,
+etc., in being always equal-sided and never quite equi-valved; the
+form of each valve being symmetrical, it may be divided into two
+equal parts by a line drawn from the apex to the centre of the
+margin.</p>
+
+<p><i>Trilobites.</i>&mdash;In the Bala and Caradoc beds the
+trilobites reach their maximum, being represented by 111 species
+referred to 23 genera.</p>
+
+<p>Burmeister, in his work on the organisation of trilobites,
+supposes that they swam at the surface of the water in the open sea
+and near coasts, feeding on smaller marine animals, and to have had
+the power of rolling themselves into a ball as a defence against
+injury. He was also of opinion that they underwent various
+transformations analogous to those of living crustaceans. M.
+Barrande, author of an admirable work on the Silurian rocks of
+Bohemia, confirms the doctrine of their metamorphosis, having
+traced more than twenty species through different stages of growth
+from the young state just after its escape from the egg to the
+adult form. He has followed some of them from a point in which they
+show no eyes, no joints, or body rings, and no distinct tail, up to
+the complete form with the full number of segments. This change is
+brought about before the animal has attained a tenth part of its
+full dimensions, and hence such minute and delicate specimens are
+rarely met with. Some of his figures of the metamorphoses of the
+common <i>Trinucleus</i> are copied in Figs. 552 and 553. It was
+not till 1870 that Mr. Billings was enabled, by means of a specimen
+found in Canada, to prove that the trilobite was provided with
+eight legs.</p>
+
+<p>It has been ascertained that a great thickness of slaty and
+crystalline rocks of South Wales, as well as those of Snowdon and
+Bala, in North Wales, which were first supposed to be of older date
+than the Silurian sandstones and mudstones of
+<a name="page472"></a>Shropshire, are in fact identical in age, and contain the same
+organic remains. At Bala, in Merionethshire, a limestone rich in
+fossils occurs, in which two genera of star-fish, <i>Protaster</i>
+and <i>Palæaster,</i> are found; the fossil specimen of the
+latter (Fig. 554) being almost as uncompressed as if found just
+washed up on the sea-beach. Besides the star-fish there occur
+abundance of those peculiar bodies called <i>Cystideæ.</i>
+They are the <i>Sphæronites</i> of old authors, and were
+considered by Professor E. Forbes as intermediate between the
+crinoids and echinoderms. The <i>Echinosphæronite</i> here
+represented (Fig. 555) is characteristic of the Caradoc beds in
+Wales, and of their equivalents in Sweden and Russia.</p>
+
+<p><img src="images/fig552.jpg" width="402" height="254" alt=
+"Fig. 552: Young individuals of Trinucleus concentricus. Fig. 553: Trinucleus concentricus." />
+</p>
+
+<img src="images/fig554.jpg" width="212" height="168" alt=
+"Fig. 554: Palæaster asperimus." />
+
+<img src="images/fig555.jpg" width="188" height="237" alt=
+"Fig. 555: Echinosphæronites ballicus." />
+
+<p>With it have been found several other genera of the same family,
+such as <i>Sphæronites, Hemicosmites,</i> etc. Among the
+mollusca are Pteropods of the genus <i>Conularia</i> of large size
+(for genus, see <a href="images/fig518.jpg">Fig. 518</a>). About
+eleven species of Graptolite are reckoned as belonging to this
+formation; they are chiefly found in peculiar localities where
+<a name="page473"></a>black mud abounded. The formation, when traced into South Wales
+and Ireland, assumes a greatly altered mineral aspect, but still
+retains its characteristic fossils. The known fauna of the Bala
+group comprises 565 species, 352 of which are peculiar, and 93, as
+before stated, are common to the overlying Llandovery rocks. It is
+worthy of remark that, when it occurs under the form of trappean
+tuff (volcanic ashes of De la Beche), as in the crest of Snowdon,
+the peculiar species which distinguish it from the Llandeilo beds
+are still observable. The formation generally appears to be of
+shallow-water origin, and in that respect is contrasted with the
+group next to be described. Professor Ramsay estimates the
+thickness of the Bala Beds, including the contemporaneous volcanic
+rocks, stratified and unstratified, as being from 10,000 to 12,000
+feet.</p>
+
+<img src="images/fig556.jpg" width="148" height="106" alt=
+"Fig. 556: Didymograpsus (Graptolites) Murchisonii." />
+
+<p><b>Llandeilo Flags.</b>&mdash;The Lower Silurian strata were
+originally divided by Sir R. Murchison into the upper group already
+described, under the name of Caradoc Sandstone, and a lower one,
+called, from a town in Carmarthenshire, the <i>Llandeilo</i> flags.
+The last mentioned strata consist of dark-coloured micaceous flags,
+frequently calcareous, with a great thickness of shales, generally
+black, below them. The same beds are also seen at Builth, in
+Radnorshire, where they are interstratified with volcanic
+matter.</p>
+
+<p>A still lower part of the Llandeilo rocks consists of a black
+carbonaceous slate of great thickness, frequently containing
+sulphate of alumina, and sometimes, as in Dumfriesshire, beds of
+anthracite. It has been conjectured that this carbonaceous matter
+may be due in great measure to large quantities of imbedded animal
+remains, for the number of Graptolites included in these slates was
+certainly very great. In
+<a name="page474"></a>Great Britain eleven genera and about 40 species of Graptolites
+occur in the Llandeilo flags and underlying Arenig beds. The double
+Graptolites, or those with two rows of cells, such as Diplograpsus
+(Fig. 557), are conspicuous.</p>
+
+<p><img src="images/fig557.jpg" width="409" height="191" alt=
+"Fig. 557: Diplograpsus pristis. Fig. 558: Rastrites peregrinus." />
+</p>
+
+<img src="images/fig559.jpg" width="85" height="153" alt=
+"Fig. 559: Diplograpsus folium." />
+
+<p>The brachiopoda of the Llandeilo flags, which number 47 species,
+are in the main the same as those of the Caradoc Sandstone, but the
+other mollusca are in great part of different species.</p>
+
+<p>In Europe generally, as, for example, in Sweden and Russia, no
+shells are so characteristic of this formation as Orthoceratites,
+usually of great size, and with a wide siphuncle placed on one side
+instead of being central (see Fig. 560).</p>
+
+<p><img src="images/fig560.jpg" width="324" height="151" alt=
+"Fig. 560: Orthoceras duplex." /></p>
+
+<p>Among other Cephalopods in the Llandeilo flags is Cyrtoceras; in
+the same beds also are found Bellerophon (see <a href=
+"images/fig488.jpg">Fig. 488</a>) and some Pteropod shells
+(<i>Conularia, Theca,</i> etc.), also in spots where sand abounded,
+lamellibranchiate bivalves of large size. The Crustaceans were
+plentifully represented by the Trilobites, which appear to have
+swarmed in the Silurian seas just as crabs and shrimps do in our
+own; no less than 263 species have been found in the British
+Silurian fauna. The genera <i>Asaphus</i> (Fig. 561), <i>Ogygia</i>
+(Fig. 562),
+<a name="page475"></a>and <i>Trinucleus</i> (<a href="images/fig552.jpg">Figs.
+552</a> and 553) form a marked feature of the rich and varied
+Trilobitic fauna of this age.</p>
+
+<p><img src="images/fig561.jpg" width="317" height="242" alt=
+"Fig. 561: Asaphus tyrannus. Fig. 562: Ogygia Buchii." /></p>
+
+<p>Beneath the black slates above described of the Llandeilo
+formation, Graptolites are still found in great variety and
+abundance, and the characteristic genera of shells and trilobites
+of the Lower Silurian rocks are still traceable downward, in
+Shropshire, Cumberland, and North and South Wales, through a vast
+depth of shaly beds, in some districts interstratified with
+trappean formations of contemporaneous origin; these consist of
+tuffs and lavas, the tuffs being formed of such materials as are
+ejected from craters and deposited immediately on the bed of the
+ocean, or washed into it from the land. According to Professor
+Ramsay, their thickness is about 3300 feet in North Wales,
+including those of the Lower Llandeilo. The lavas are feldspathic,
+and of porphyritic structure, and, according to the same authority,
+of an aggregate thickness of 2500 feet.</p>
+
+<img src="images/fig563.jpg" width="179" height="215" alt=
+"Fig. 563: Arenicolites linearis." />
+
+<p><b>Arenig or Stiper-Stones Group</b> <i>(Lower Llandeilo of
+Murchison).</i>&mdash;Next in the descending order are the shales
+and sandstones in which the quartzose rocks called Stiper-Stones in
+Shropshire occur. Originally these Stiper-Stones were only known as
+arenaceous quartzose strata in which no organic remains were
+conspicuous, except the tubular burrows of annelids (see Fig. 563,
+<i>Arenicolites linearis</i>), which are remarkably common in the
+Lowest Silurian in Shropshire, and in the State of New York, in
+America. They have already been alluded to as occurring by
+thousands in the Silurian strata unconformably overlying the
+Cambrian, in the mountain of Queenaig, in Sutherlandshire (<a href=
+"images/fig82.jpg">Fig. 82</a>). I have seen similar burrows now
+made on the retiring of the tides in the sands of the Bristol
+Channel, near Minehead, by lob-worms which are dug out by fishermen
+and used as bait. When the term Silurian was given by Sir R.
+Murchison, in 1835, to the whole series, he considered the
+Stiper-Stones as the base of the Silurian system, but no fossil
+fauna had then been obtained, such as could alone enable the
+geologist to draw a line between this member of the series and the
+Llandeilo flags above, or a vast thickness of rock below, which was
+seen to form the Longmynd hills, and was called
+&rdquo;unfossiliferous graywacke.&rdquo; Professor Sedgwick had
+described, in
+<a name="page476"></a>1843, strata now ascertained to be of the same age as largely
+developed in the Arenig mountain, in Merionethshire; and the
+Skiddaw slates in the Lake-District of Cumberland, studied by the
+same author, were of corresponding date, though the number of
+fossils was, in both cases, too few for the determination of their
+true chronological relations. The subsequent researches of Messrs.
+Sedgwick and Harkness, in Cumberland, and of Sir R. I. Murchison
+and the Government surveyors in Shropshire, have increased the
+species to more than sixty. These were examined by Mr. Salter, and
+shown in the third edition of &rdquo;Siluria&rdquo; (p. 52, 1859)
+to be quite distinct from the fossils of the overlying Llandeilo
+flags. Among these the <i>Obolella plumbea, Æglina binodosa,
+Ogygia Selwynii,</i> and <i>Didymograpsus geminus</i> (Fig. 564),
+and <i>D. Hirundo,</i> are characteristic.</p>
+
+<img src="images/fig564.jpg" width="230" height="76" alt=
+"Fig. 564: Didymograpsus geminus." />
+
+<p>
+But, although the species are distinct, the genera are the same as those which
+characterise the Silurian rocks above, and none of the characteristic
+primordial or Cambrian forms, presently to be mentioned, are intermixed. The
+same may be said of a set of beds underlying the Arenig rocks at Ramsay Island
+and other places in the neighbourhood of St. David&rsquo;s. These beds, which
+have only lately become known to us through the labours of Dr. Hicks,<a
+href="#fn-26.5" name="fnref-26.5" id="fnref-26.5"><sup>[5]</sup></a> present
+already twenty new species, the greater part of them allied generically to the
+Arenig rocks. This Arenig group may therefore be conveniently regarded as the
+base of the great Silurian system, a system which, by the thickness of its
+strata and the changes in animal life of which it contains the record, is more
+than equal in value to the Devonian, or Carboniferous, or other principal
+divisions, whether of primary or secondary date.
+</p>
+
+<p>It would be unsafe to rely on the mere thickness of the strata,
+considered apart from the great fluctuations in organic life which
+took place between the era of the Llandeilo and that of the Ludlow
+formation, especially as the enormous pile of Silurian rocks
+observed in Great Britain (in Wales more particularly) is derived
+in great part from igneous action, and is not confined to the
+ordinary deposition of sediment from rivers or the waste of
+cliffs.</p>
+
+<p>In volcanic archipelagoes, such as the Canaries, we see the most
+active of all known causes, aqueous and igneous, simultaneously at
+work to produce great results in a
+<a name="page477"></a>comparatively moderate lapse of time. The outpouring of repeated
+streams of lava&mdash;the showering down upon land and sea of volcanic
+ashes&mdash;the sweeping seaward of loose sand and cinders, or of rocks
+ground down to pebbles and sand, by rivers and torrents descending
+steeply inclined channels&mdash;the undermining and eating away of long
+lines of sea-cliff exposed to the swell of a deep and open
+ocean&mdash;these operations combine to produce a considerable volume of
+superimposed matter, without there being time for any extensive
+change of species. Nevertheless, there would seem to be a limit to
+the thickness of stony masses formed even under such favourable
+circumstances, for the analogy of tertiary volcanic regions lends
+no countenance to the notion that sedimentary and igneous rocks
+25,000, much less 45,000 feet thick, like those of Wales, could
+originate while one and the same fauna should continue to people
+the earth. If, then, we allow that about 25,000 feet of matter may
+be ascribed to one system, such as the Silurian, as above
+described, we may be prepared to discover in the next series of
+subjacent rocks a distinct assemblage of species, or even in great
+part of genera, of organic remains. Such appears to be the fact,
+and I shall therefore conclude with the Arenig beds my enumeration
+of the Silurian formations in Great Britain, and proceed to say
+something of their foreign equivalents, before treating of rocks
+older than the Silurian.</p>
+
+<p><b>Silurian Strata of the Continent of Europe.</b>&mdash;When we
+turn to the continent of Europe, we discover the same ancient
+series occupying a wide area, but in no region as yet has it been
+observed to attain great thickness. Thus, in Norway and Sweden, the
+total thickness of strata of Silurian age is considerably less than
+1000 feet, although the representatives both of the Upper and Lower
+Silurian of England are not wanting there. In Russia the Silurian
+strata, so far as they are yet known, seem to be even of smaller
+vertical dimensions than in Scandinavia, and they appear to consist
+chiefly of the Llandovery group, or of a limestone containing <i>
+Pentamerus oblongus,</i> below which are strata with fossils
+corresponding to those of the Llandeilo beds of England. The lowest
+rock with organic remains yet discovered is &rdquo;the Ungulite or
+Obolus grit&rdquo; of St. Petersburg, probably coeval with the
+Llandeilo flags of Wales.</p>
+
+<p>The shales and grits near St. Petersburg, above alluded to,
+contain green grains in their sandy layers, and are in a singularly
+unaltered state, taking into account their high antiquity. The
+prevailing Brachiopods consist of the <i>Obolus</i>
+<a name="page478"></a><i>Shells of the lowest known Fossiliferous Beds in
+Russia.</i></p>
+
+<p><img src="images/fig565.jpg" width="394" height="192" alt=
+"Fig. 565: Siphonotreta unguiculata. Fig. 566: Obolus Apollinis." />
+</p>
+
+<p>or Ungulite of Pander, and a <i>Siphonotreta</i> (Figs. 565,
+566). Notwithstanding the antiquity of this Russian formation, it
+should be stated that both of these genera of brachiopods have been
+also found in the Upper Silurian of England, i.e., in the Wenlock
+limestone.</p>
+
+<p>Among the green grains of the sandy strata above-mentioned,
+Professor Ehrenberg announced in 1854 his discovery of remains of
+foraminifera. These are casts of the cells; and among five or six
+forms three are considered by him as referable to existing genera
+(e.g., <i>Textularia, Rotalia,</i> and <i>Guttulina</i>).</p>
+
+<p><b>Silurian Strata of the United States.</b>&mdash;The Silurian
+formations can be advantageously studied in the States of New York,
+Ohio, and other regions north and south of the great Canadian
+lakes. Here they are often found, as in Russia, nearly in
+horizontal position, and are more rich in well-preserved fossils
+than in almost any spot in Europe. In the State of New York, where
+the succession of the beds and their fossils have been most
+carefully worked out by the Government surveyors, the subdivisions
+given in the first column of the table below have been adopted.</p>
+
+<p class="center">
+<i>Subdivisions of the Silurian Strata of New York.<br/>
+(Strata below the Oriskany sandstone or base of the Devonian.)</i>
+</p>
+
+<table border="1" cellpadding="4" cellspacing="0"
+summary=
+"Left column, New York names; right column, British equivalents.">
+<tr>
+<td align="center">New York Names</td>
+<td align="center">British equivalents</td>
+</tr>
+
+<tr>
+<td >&nbsp;&nbsp; 1. &nbsp;Upper Pentamerus
+Limestone<br/>
+&nbsp;&nbsp; 2. &nbsp;Encrinal Limestone<br/>
+&nbsp;&nbsp; 3. &nbsp;Delthyris Shaly Limestone<br/>
+&nbsp;&nbsp; 4. &nbsp;Pentamerus and Tentaculite Limestones<br/>
+&nbsp;&nbsp; 5. &nbsp;Water Lime Group<br/>
+&nbsp;&nbsp; 6. &nbsp;Onondaga Salt Group<br/>
+&nbsp;&nbsp; 7. &nbsp;Niagara Group</td>
+<td valign="middle">Upper Silurian (or Ludlow<br/>
+and Wenlock formations</td>
+</tr>
+
+<tr>
+<td >&nbsp;&nbsp; 8. &nbsp;Clinton Group<br/>
+&nbsp;&nbsp; 9. &nbsp;Medina Sandstone<br/>
+10. &nbsp;Oneida Conglomerate<br/>
+11. &nbsp;Gray Sandstone</td>
+<td valign="middle">Beds of Passage, Llandovery
+Group.</td>
+</tr>
+
+<tr>
+<td >12. &nbsp;Hudson River Group<br/>
+13. &nbsp;Trenton Limestone<br/>
+14. &nbsp;Black-River Limestone<br/>
+15. &nbsp;Bird&rsquo;s-eye Limestone<br/>
+16. &nbsp;Chazy Limestone<br/>
+17. &nbsp;Calciferous Sandstone</td>
+<td valign="middle">Lower Silurian (or Caradoc and
+Bala,<br/>
+Llandeilo and Arenig Formations).</td>
+</tr>
+</table>
+
+<p>
+<a name="page479"></a>In the second column of the same table I have added the supposed
+British equivalents. All Palæontologists, European and
+American, such as MM. De Verneuil, D. Sharpe, Professor Hall, E.
+Billings, and others, who have entered upon this comparison, admit
+that there is a marked general correspondence in the succession of
+fossil forms, and even species, as we trace the organic remains
+downward from the highest to the lowest beds; but it is impossible
+to parallel each minor subdivision.</p>
+
+<p>That the Niagara Limestone, over which the river of that name is
+precipitated at the great cataract, together with its underlying
+shales, corresponds to the Wenlock limestone and shale of England
+there can be no doubt. Among the species common to this formation
+in America and Europe are <i>Calymene Blumenbachii, Homalonotus
+delphinocephalus</i> (<a href="images/fig544.jpg">Fig. 544</a>),
+with several other trilobites; <i>Rhynchonella Wilsoni,</i> <a
+href="images/fig531.jpg">Fig. 531</a>, and <i>Retzia cuneata;
+Orthis elegantula, Pentamerus galeatus,</i> with many more
+brachiopods; <i>Orthoceras annulatum,</i> among the cephalopodous
+shells; and <i>Favosites gothlandica,</i> with other large
+corals.</p>
+
+<img src="images/fig567.jpg" width="117" height="204" alt=
+"Fig. 567: Murchisonia gracilis." />
+
+<p>The Clinton Group, containing <i>Pentamerus oblongus</i> and <i>
+Stricklandinia,</i> and related more nearly by its fossil species
+with the beds above than with those below, is the equivalent of the
+Llandovery Group or beds of passage.</p>
+
+<p>The Hudson River Group, and the Trenton Limestone, agree
+palæontologically with the Caradoc or Bala group, containing
+in common with them several species of trilobites, such as <i>
+Asaphus (Isotelus) gigas, Trinucleus concentricus</i> (<a href=
+"images/fig552.jpg">Fig. 553</a>); and various shells, such as <i>
+Orthis striatula, Orthis biforata</i> (or <i>O. lynx</i>), <i>O.
+porcata</i> (<i>O. occidentalis</i> of Hall), and <i>Bellerophon
+bilobatus.</i> In the Trenton limestone occurs <i>Murchisonia
+gracilis,</i> Fig. 567, a fossil also common to the Llandeilo beds
+in England.</p>
+
+<p>
+Mr. D. Sharpe, in his report on the mollusca collected by me from these strata
+in North America,<a href="#fn-26.6" name="fnref-26.6"
+id="fnref-26.6"><sup>[6]</sup></a> has concluded that the number of species
+common to the Silurian rocks <a name="page480"></a> on both sides of the
+Atlantic is between 30 and 40 per cent; a result which, although no doubt
+liable to future modification, when a larger comparison shall have been made,
+proves, nevertheless, that many of the species had a wide geographical range.
+It seems that comparatively few of the gasteropods and lamellibranchiate
+bivalves of North America can be identified specifically with European fossils,
+while no less than two-fifths of the brachiopoda, of which my collection
+chiefly consisted, are the same. In explanation of these facts, it is suggested
+that most of the recent brachiopoda (especially the orthidiform ones) are
+inhabitants of deep water, and that they may have had a wider geographical
+range than shells living near shore. The predominance of bivalve mollusca of
+this peculiar class has caused the Silurian period to be sometimes styled
+&rdquo;the age of brachiopods.&rdquo;
+</p>
+
+<p>In Canada, as in the State of New York, the Potsdam Sandstone
+underlies the above-mentioned calcareous rocks, but contains a
+different suite of fossils, as will be hereafter explained. In
+parts of the globe still more remote from Europe the Silurian
+strata have also been recognised, as in South America, Australia,
+and India. In all these regions the facies of the fauna, or the
+types of organic life, enable us to recognise the contemporaneous
+origin of the rocks; but the fossil species are distinct, showing
+that the old notion of a universal diffusion throughout the
+&rdquo;primæval seas&rdquo; of one uniform specific fauna was
+quite unfounded, geographical provinces having evidently existed in
+the oldest as in the most modern times.
+</p>
+
+<p class="footnote">
+<a name="fn-26.1" id="fn-26.1"></a> <a href="#fnref-26.1">[1]</a>
+Murchison&rsquo;s Siluria, p. 140.
+</p>
+
+<p class="footnote">
+<a name="fn-26.2" id="fn-26.2"></a> <a href="#fnref-26.2">[2]</a>
+Murchison&rsquo;s Siluria, chap. vi.
+</p>
+
+<p class="footnote">
+<a name="fn-26.3" id="fn-26.3"></a> <a href="#fnref-26.3">[3]</a>
+E. Forbes, Mem. Geol. Surv., vol. ii, p. 496.
+</p>
+
+<p class="footnote">
+<a name="fn-26.4" id="fn-26.4"></a> <a href="#fnref-26.4">[4]</a>
+Quart. Geol. Journ., vol. iv, p. 215, 1853.
+</p>
+
+<p class="footnote">
+<a name="fn-26.5" id="fn-26.5"></a> <a href="#fnref-26.5">[5]</a>
+Trans. Brit. Assoc., 1866. Proc. Liverpool Geol. Soc., 1869.
+</p>
+
+<p class="footnote">
+<a name="fn-26.6" id="fn-26.6"></a> <a href="#fnref-26.6">[6]</a>
+Quart. Geol. Journ., vol. iv.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap27"></a><a name="page481"></a>CHAPTER XXVII.<br/>
+CAMBRIAN AND LAURENTIAN GROUPS.</h2>
+
+<p class="letter">Classification of the Cambrian Group, and its
+Equivalent in Bohemia. &mdash; Upper Cambrian Rocks. &mdash;
+Tremadoc Slates and their Fossils. &mdash; Lingula Flags. &mdash;
+Lower Cambrian Rocks. &mdash; Menevian Beds. &mdash; Longmynd
+Group. &mdash; Harlech Grits with large Trilobites. &mdash;
+Llanberis Slates. &mdash; Cambrian Rocks of Bohemia. &mdash;
+Primordial Zone of Barrande. &mdash; Metamorphosis of Trilobites.
+&mdash; Cambrian Rocks of Sweden and Norway. &mdash; Cambrian Rocks
+of the United States and Canada. &mdash; Potsdam Sandstone. &mdash;
+Huronian Series. &mdash; Laurentian Group, upper and lower. &mdash;
+Eozoon Canadense, oldest known Fossil. &mdash; Fundamental Gneiss
+of Scotland.</p>
+
+<p class="center">
+<small>CAMBRIAN &nbsp;GROUP.</small>
+</p>
+
+<p>The characters of the Upper and Lower Silurian rocks were
+established so fully, both on stratigraphical and
+palæontological data, by Sir Roderick Murchison after five
+years&rsquo; labour, in 1839, when his &ldquo;Silurian
+System&rdquo; was published, that these formations could from that
+period be recognised and identified in all other parts of Europe
+and in North America, even in countries where most of the fossils
+differed specifically from those of the classical region in
+Britain, where they were first studied.</p>
+
+<p>While Sir R. I. Murchison was exploring in 1833, in Shropshire
+and the borders of Wales, the strata which in 1835 he first called
+Silurian, Professor Sedgwick was surveying the rocks of North
+Wales, which both these geologists considered at that period as of
+older date, and for which in 1836 Sedgwick proposed the name of
+Cambrian. It was afterwards found that a large portion of the slaty
+rocks of North Wales, which had been considered as more ancient
+than the Llandeilo beds and Stiper-Stones before alluded to, were,
+in reality, not inferior in position to those Lower Silurian beds
+of Murchison, but merely extensive undulations of the same, bearing
+fossils identical in species, though these were generally rarer and
+less perfectly preserved, owing to the changes which the rocks had
+undergone from metamorphic action. To such rocks the term
+&ldquo;Cambrian&rdquo; was no longer applicable, although it
+continued to be appropriate to strata inferior to the
+Stiper-Stones, and which were older than those of the Lower
+Silurian group as originally defined. It was not till 1846 that
+fossils were found in Wales in the Lingula
+<a name="page482"></a>flags, the place of which will be seen in the table below. By
+this time Barrande had already published an account of a rich
+collection of fossils which he had discovered in Bohemia, portions
+of which he recognised as of corresponding age with
+Murchison&rsquo;s Upper and Lower Silurian, while others were more
+ancient, to which he gave the name of &ldquo;Primordial,&rdquo; for
+the fossils were sufficiently distinct to entitle the rocks to be
+referred to a new period. They consisted chiefly of trilobites of
+genera distinct from those occurring in the overlying Silurian
+formations. These peculiar genera were afterwards found in rocks
+holding a corresponding position in Wales, and I shall retain for
+them the term Cambrian, as recent discoveries in our own country
+seem to carry the first fauna of Barrande, or his primordial type,
+even into older strata than any which he found to be fossiliferous
+in Bohemia.</p>
+
+<p>The term primordial was intended to express M. Barrande&rsquo;s
+own belief that the fossils of the rocks so-called afforded
+evidence of the first appearance of vital phenomena on this planet,
+and that consequently no fossiliferous strata of older date would
+or could ever be discovered. The acceptance of such a nomenclature
+would seem to imply that we despaired of extending our discoveries
+of new and more ancient fossil groups at some future day when vast
+portions of the globe, hitherto unexplored, should have been
+thoroughly surveyed. Already the discovery of the Laurentian Eozoon
+in Canada, presently to be mentioned, discountenances such
+views.</p>
+
+<p>The following table will show the succession of the strata in
+England and Wales which belong to the Cambrian group or the
+fossiliferous rocks older than the Arenig or Lower Llandeilo
+rocks:</p>
+
+<table border="0" cellspacing="0" cellpadding="4"
+summary=
+"Succession of strata in England and Wales which belong to the Cambrian group.">
+<tr>
+<td align="center" colspan="2">UPPER CAMBRIAN</td>
+</tr>
+
+<tr>
+<td >T<small>REMADOC</small> S<small>LATES</small></td>
+<td><i>(Primordial of Barrande in part)</i></td>
+</tr>
+
+<tr>
+<td >L<small>INGULA</small> F<small>LAGS</small></td>
+<td ><i>(Primordial of Barrande)</i></td>
+</tr>
+
+<tr>
+<td align="center" colspan="2">LOWER CAMBRIAN</td>
+</tr>
+
+<tr>
+<td >M<small>ENEVIAN</small> B<small>EDS</small></td>
+<td ><i>(Primordial of Barrande)</i></td>
+</tr>
+
+<tr>
+<td valign="middle">L<small>ONGMYND</small>
+G<small>ROUP</small></td>
+<td ><i>a.</i> Harlech Grits<br/>
+<i>b.</i> Llanberis Slates</td>
+</tr>
+</table>
+
+<p>
+<b>Tremadoc Slates.</b>&mdash;The Tremadoc slates of Sedgwick are more than
+1000 feet in thickness, and consist of dark earthy slates occurring near the
+little town of Tremadoc, situated on the north side of Cardigan Bay, in
+Carnarvonshire. These <a name="page483"></a>slates were first examined by
+Sedgwick in 1831, and were re-examined by him and described in 1846,<a
+href="#fn-27.1" name="fnref-27.1" id="fnref-27.1"><sup>[1]</sup></a> after some
+fossils had been found in the underlying Lingula flags by Mr. Davis. The
+inferiority in position of these Lingula flags to the Tremadoc beds was at the
+same time established. The overlying Tremadoc beds were traced by their
+pisolitic ore from Tremadoc to Dolgelly. No fossils proper to the Tremadoc
+slates were then observed, but subsequently, thirty-six species of all classes
+have been found in them, thanks to the researches of Messrs. Salter, Homfray,
+and Ash. We have already seen that in the Arenig or Stiper-Stones group, where
+the species are distinct, the genera agree with Silurian types; but in these
+Tremadoc slates, where the species are also peculiar, there is about an equal
+admixture of Silurian types with those which Barrande has termed
+&ldquo;primordial.&rdquo; Here, therefore, it may truly be said that we are
+entering upon a new domain of life in our retrospective survey of the past. The
+trilobites of new species, but of Lower Silurian genera, belong to <i>Ogygia,
+Asaphus,</i> and <i>Cheirurus</i>; whereas those belonging to primordial types,
+or Barrande&rsquo;s first fauna as well as to the Lingula flags of Wales,
+comprise <i>Dikelocephalus, Conocoryphe</i> (for genera see <a
+href="images/fig576.jpg">Fig. 577</a> and 581),<a href="#fn-27.2"
+name="fnref-27.2" id="fnref-27.2"><sup>[2]</sup></a> <i>Olenus,</i> and
+<i>Angelina.</i>
+</p>
+
+<img src="images/fig568.jpg" width="99" height="198" alt=
+"Fig. 568: Theca (Cleidotheca operculata." />
+
+<p>In the Tremadoc slates are found <i>Bellerophon, Orthoceras,</i>
+and <i>Cyrtoceras,</i> all specifically distinct from Lower
+Silurian fossils of the same genera: the Pteropods <i>Theca</i>
+(Fig. 568) and <i>Conularia</i> range throughout these slates;
+there are no Graptolites. The <i>Lingula (Lingulella) Davisii</i>
+ranges from the top to the bottom of the formation, and links it
+with the zone next to be described. The Tremadoc slates are very
+local, and seem to be confined to a small part of North Wales; and
+Professor Ramsay supposes them to lie unconformably on the Lingula
+flags, and that a long interval of time elapsed between these
+formations. Cephalopoda have not yet been found lower than this
+group, but it will be observed that they occur here associated with
+genera of Trilobites considered by Barrande as characteristically
+Primordial, some of which belong to all the divisions of the
+British Cambrian about to be mentioned. This renders the absence of
+cephalopoda of less importance as bearing on the theory of
+development.</p>
+
+<p>
+<a name="page484"></a><b>Lingula Flags.</b>&mdash;Next below the Tremadoc
+slates in North Wales lie micaceous flagstones and slates, in which, in 1846,
+Mr. E. Davis discovered the <i>Lingula (Lingulella),</i> Fig. 570, named after
+him, and from which was derived the name of Lingula flags. These beds, which
+are palæontologically the equivalents of Barrande&rsquo;s primordial zone, are
+represented by more than 5000 feet of strata, and have been studied chiefly in
+the neighbourhood of Dolgelly, Ffestiniog, and Portmadoc in North Wales, and at
+St. David&rsquo;s in South Wales. They have yielded about forty species of
+fossils, of which six only are common to the overlying Tremadoc rocks, but the
+two formations are closely allied by having several characteristic
+&ldquo;primordial&rdquo; genera in common. <i>Dikelocephalus, Olenus</i> (Fig.
+571), and <i>Conocoryphe</i> are prominent forms, as is also <i>Hymenocaris</i>
+(Fig. 569), a genus of phyllopod crustacean entirely confined to the Lingula
+Flags. According to Mr. Belt, who has devoted much attention to these beds,
+there are already palæontological data for subdividing the Lingula Flags into
+three sections.<a href="#fn-27.3" name="fnref-27.3"
+id="fnref-27.3"><sup>[3]</sup></a>
+</p>
+
+<p><img src="images/fig569.jpg" width="387" height="180" alt=
+"“Lingula Flags” of Dolgelly, and Ffestiniog; N. Wales." />
+</p>
+
+<p>In Merionethshire, according to Professor Ramsay, the Lingula
+Flags attain their greatest development; in Carnarvonshire they
+thin out so as to have lost two-thirds of their thickness in eleven
+miles, while in Anglesea and on the Menai Straits both they and the
+Tremadoc beds are entirely absent, and the Lower Silurian rests
+directly on Lower Cambrian strata.</p>
+
+<p class="center">
+<small>LOWER CAMBRIAN.</small>
+</p>
+
+<p>
+<b>Menevian Beds.</b>&mdash;Immediately beneath the Lingula Flags there occurs
+a series of dark grey and black flags and slates alternating at the upper part
+with some beds of sandstone, the whole reaching a thickness of from 500 to 600
+feet. These beds were formerly classed, on purely lithological <a
+name="page485"></a>grounds, as the base of the Lingula Flags, but Messrs. Hicks
+and Salter, to whose exertions we owe almost all our knowledge of the fossils,
+have pointed out<a href="#fn-27.4" name="fnref-27.4"
+id="fnref-27.4"><sup>[4]</sup></a> that the most characteristic genera found in
+them are quite unknown in the Lingula Flags, while they possess many of the
+strictly Lower Cambrian genera, such as <i> Microdiscus</i> and
+<i>Paradoxides.</i> They therefore proposed to place them, and it seems to me
+with good reason, at the top of the Lower Cambrian under the term
+&ldquo;Menevian,&rdquo; Menevia being the classical name of St. David&rsquo;s.
+The beds are well exhibited in the neighbourhood of St. David&rsquo;s in South
+Wales, and near Dolgelly and Maentwrog in North Wales. They are the equivalents
+of the lowest part of Barrande&rsquo;s Primordial Zone (Étage C). More
+than forty species have been found in them, and the group is altogether very
+rich in fossils for so early a period.
+</p>
+
+<img src="images/fig572.jpg" width="138" height="281" alt=
+"Fig. 572: Paradoxides Davidis." />
+
+<p>The trilobites are of large size; <i>Paradoxides Davidis</i>
+(see Fig. 572), the largest trilobite known in England, 22 inches
+or nearly two feet long, is peculiar to the Menevian Beds. By
+referring to the Bohemian trilobite of the same genus (<a href=
+"images/fig576.jpg">Fig. 576</a>), the reader will at once see how
+these fossils (though of such different dimensions) resemble each
+other in Bohemia and Wales, and other closely allied species from
+the two regions might be added, besides some which are common to
+both countries. The Swedish fauna, presently to be mentioned, will
+be found to be still more nearly connected with the Welsh Menevian.
+In all these countries there is an equally marked difference
+between the Cambrian fossils and those of the Upper and Lower
+Silurian rocks. The trilobite with the largest number of rings, <i>
+Erinnys venulosa,</i> occurs here in conjunction with <i>
+Agnostus</i> and <i>Microdiscus,</i> the genera with the smallest
+number. Blind trilobites are also found as well as those which have
+the largest eyes, such as <i>Microdiscus</i> on the one hand, and
+<i>Anoplenus</i> on the other.</p>
+
+<p class="center">
+<small>LONGMYND GROUP.</small>
+</p>
+
+<p>Older than the Menevian Beds are a thick series of olive green,
+purple, red and grey grits and conglomerates found in North and
+South Wales, Shropshire, and parts of Ireland
+<a name="page486"></a>and Scotland. They have been called by Professor Sedgwick the
+Longmynd or Bangor Group, comprising, first, the Harlech and
+Barmouth sandstones; and secondly, the Llanberis slates.</p>
+
+<img src="images/fig573.jpg" width="242" height="225" alt=
+"Fig. 573: Histioderma Hibernica." />
+
+<p><b>Harlech Grits.</b>&mdash;The sandstones of this period attain
+in the Longmynd hills a thickness of no less than 6000 feet without
+any interposition of volcanic matter; in some places in
+Merionethshire they are still thicker. Until recently these rocks
+possessed but a very scanty fauna.</p>
+
+<p>
+With the exception of five species of annelids (see <a href=
+"images/fig460.jpg">Fig. 460</a>) brought to light by Mr. Salter in Shropshire,
+and Dr. Kinahan in Wicklow, and an obscure crustacean form, <i>Palæopyge
+Ramsayi,</i> they were supposed to be barren of organic remains. Now, however,
+through the labours of Mr. Hicks,<a href="#fn-27.5" name="fnref-27.5"
+id="fnref-27.5"><sup>[5]</sup></a> they have yielded at St. David&rsquo;s a
+rich fauna of trilobites, brachiopods, phyllopods, and pteropods, showing,
+together with other fossils, a by no means low state of organisation at this
+early period. Already the fauna amounts to 20 species referred to 17 genera.
+</p>
+
+<p>A new genus of trilobite called <i>Plutonia Sedgwickii,</i> not
+yet figured and described, has been met with in the Harlech grits.
+It is comparable in size to the large <i>Paradoxides Davidis</i>
+before mentioned, has well-developed eyes, and is covered all over
+with tubercles. In the same strata occur other genera of
+trilobites, namely, <i>Conocoryphe, Paradoxides, Microdiscus,</i>
+and the Pteropod <i>Theca</i> (<a href="images/fig568.jpg">Fig.
+568</a>), all represented by species peculiar to the Harlech grits.
+The sands of this formation are often rippled, and were evidently
+left dry at low tides, so that the surface was dried by the sun and
+made to shrink and present sun-cracks. There are also distinct
+impressions of rain-drops on many surfaces, like those in <a href=
+"images/fig444.jpg">Fig. 444</a> and 445.</p>
+
+<p><b>Lanberis Slates.</b>&mdash;The slates of Llanberis and
+Penrhyn in Carnarvonshire, with their associated sandy strata,
+attain a great thickness, sometimes about 3000 feet. They are
+perhaps not more ancient than the Harlech and Barmouth beds last
+mentioned, for they may represent the deposits of fine
+<a name="page487"></a>mud thrown down in the same sea, on the borders of which the
+sands above-mentioned were accumulating. In some of these slaty
+rocks in Ireland, immediately opposite Anglesea and Carnarvon, two
+species of fossils have been found, to which the late Professor E.
+Forbes gave the name of <i>Oldhamia.</i> The nature of these
+organisms is still a matter of discussion among naturalists.</p>
+
+<img src="images/fig574.jpg" width="214" height="159" alt=
+"Fig. 574: Oldhamia radiata." />
+
+<img src="images/fig575.jpg" width="117" height="256" alt=
+"Fig. 575: Oldhamia antiqua." />
+
+<p><b>Cambrian Rocks of Bohemia</b> <i>(Primordial zone of
+Barrande).</i>&mdash;In the year 1846, as before stated, M. Joachim
+Barrande, after ten years&rsquo; exploration of Bohemia, and after
+collecting more than a thousand species of fossils, had ascertained
+the existence in that country of three distinct faunas below the
+Devonian. To his first fauna, which was older than any then known
+in this country, he gave the name of Étage C; his two first
+stages A and B consisting of crystalline and metamorphic rocks and
+unfossiliferous schists. This Étage C or primordial zone
+proved afterwards to be the equivalent of those subdivisions of the
+Cambrian groups which have been above described under the names of
+Menevian and Lingula Flags. The second fauna tallies with
+Murchison&rsquo;s Lower Silurian, as originally defined by him when
+no fossils had been discovered below the Stiper-Stones. The third
+fauna agrees with the Upper Silurian of the same author. Barrande,
+without government assistance, had undertaken single-handed the
+geological survey of Bohemia, the fossils previously obtained from
+that country having scarcely exceeded 20 in number, whereas he had
+already acquired, in 1850, no less than 1100 species, namely, 250
+crustaceans (chiefly Trilobites), 250 Cephalopods, 160 gasteropods
+and pteropods, 130 acephalous mollusks, 210 brachiopods, and 110
+corals and other fossils. These numbers have since been almost
+doubled by subsequent investigations in the same country.</p>
+
+<p>In the primordial zone C, he discovered trilobites of the genera
+<i>Paradoxides, Conocoryphe, Ellipsocephalus, Sao, Arionellus,
+Hydrocephalus,</i> and <i>Agnostus.</i> M. Barrande pointed out
+that these primordial trilobites have a peculiar facies of
+<a name="page488"></a>their own dependent on the multiplication of their thoracic
+segments and the diminution of their caudal shield or pygidium.</p>
+
+<p class="center">
+<i>Fossils of the lowest Fossiliferous Beds in Bohemia,
+or<br/>
+&ldquo;Primordial Zone&rdquo; of Barrande.</i></p>
+
+<p><img src="images/fig576.jpg" width="379" height="400" alt=
+"Fig. 576: Paradoxides Bohemicus. Fig. 577: Conocoryphe striata. Fig. 578:
+Agnostus integer. Fig. 579: Agnostus Rex. Fig. 580: Sao hirsuta in its
+various stages of growth." />
+</p>
+
+<p>One of the &ldquo;primordial&rdquo; or Upper Cambrian Trilobites
+of the genus <i>Sao,</i> a form not found as yet elsewhere in the
+world, afforded M. Barrande a fine illustration of the
+metamorphosis of these creatures, for he traced them through no
+less than twenty stages of their development. A few of these
+changes have been selected for representation in Figure 580, that
+the reader may learn the gradual manner in which different segments
+of the body and the eyes make their appearance.</p>
+
+<p>In Bohemia the primordial fauna of Barrande derived its
+importance exclusively from its numerous and peculiar trilobites.
+Besides these, however, the same ancient schists have yielded two
+genera of brachiopods, <i>Orthis</i> and <i>Orbicula,</i> a
+Pteropod of the genus <i>Theca,</i> and four echinoderms of the
+cystidean family.</p>
+
+<p>
+<a name="page489"></a><b>Cambrian of Sweden and Norway.</b>&mdash;The Cambrian beds of
+Wales are represented in Sweden by strata the fossils of which have
+been described by a most able naturalist, M. Angelin, in his
+&ldquo;Palæontologica Suecica&rdquo; (1852-4). The
+&ldquo;alum-schists,&rdquo; as they are called in Sweden, are
+horizontal argillaceous rocks which underlie conformably certain
+Lower Silurian strata in the mountain called Kinnekulle, south of
+the great Wener Lake in Sweden. These schists contain trilobites
+belonging to the genera <i>Paradoxides, Olenus, Agnostus,</i> and
+others, some of which present rudimentary forms, like the genus
+last mentioned, without eyes, and with the body segments scarcely
+developed, and others, again, have the number of segments
+excessively multiplied, as in <i>Paradoxides.</i> Such
+peculiarities agree with the characters of the crustaceans met with
+in the Cambrian strata of Wales; and Dr. Torell has recently found
+in Sweden the <i>Paradoxides Hicksii,</i> a well-known Lower
+Cambrian fossil.</p>
+
+<p>At the base of the Cambrian strata in Sweden, which in the
+neighbourhood of Lake Wener are perfectly horizontal, lie
+ripple-marked quartzose sandstones with worm-tracks and annelid
+borings, like some of those found in the Harlech grits of the
+Longmynd. Among these are some which have been referred doubtfully
+to plants. These sandstones have been called in Sweden
+&ldquo;fucoid sandstones.&rdquo; The whole thickness of the
+Cambrian rocks of Sweden does not exceed 300 feet from the
+equivalents of the Tremadoc beds to these sandstones, which last
+seem to correspond with the Longmynd, and are regarded by Torell as
+older than any fossiliferous primordial rocks in Bohemia.</p>
+
+<p><b>Cambrian of the United States and Canada</b> <i>(Potsdam
+Sandstone).</i>&mdash;This formation, as we learn from Sir W.
+Logan, is 700 feet thick in Canada; the upper part consists of
+sandstone containing fucoids, and perforated by small vertical
+holes, which are very characteristic of the rock, and appear to
+have been made by annelids <i>(Scolithus linearis).</i> The lower
+portion is a conglomerate with quartz pebbles. I have seen the
+Potsdam sandstone on the banks of the St. Lawrence, and on the
+borders of Lake Champlain, where, as at Keesville, it is a white
+quartzose fine-grained grit, almost passing into quartzite. It is
+divided into horizontal ripple-marked beds, very like those of the
+Lingula Flags of Britain, and replete with a small round-shaped <i>
+Obolella,</i> in such numbers as to divide the rock into parallel
+planes, in the same manner as do the scales of mica in some
+micaceous sandstones. Among the shells of this formation in
+Wisconsin are species of <i>Lingula</i> and <i>Orthis,</i> and
+several trilobites
+<a name="page490"></a>of the primordial genus <i>Dikelocephalus</i> (Fig. 581). On the
+banks of the St. Lawrence, near Beauharnois and elsewhere, many
+fossil footprints have been observed on the surface of the rippled
+layers. They are supposed by Professor Owen to be the trails of
+more than one species of articulate animal, probably allied to the
+King Crab, or <i>Limulus.</i></p>
+
+<img src="images/fig581.jpg" width="156" height="273" alt=
+"Fig. 581: Dikelocephalus Minnesotensis." />
+
+<p>Recent investigations by the naturalists of the Canadian survey
+have rendered it certain that below the level of the Potsdam
+Sandstone there are slates and schists extending from New York to
+Newfoundland, occupied by a series of trilobitic forms similar in
+genera, though not in species, to those found in the European Upper
+Cambrian strata.</p>
+
+<p><b>Huronian Series.</b>&mdash;Next below the Upper Cambrian
+occur strata called the Huronian by Sir W. Logan, which are of vast
+thickness, consisting chiefly of quartzite, with great masses of
+greenish chloritic slate, which sometimes include pebbles of
+crystalline rocks derived from the Laurentian formation, next to be
+described. Limestones are rare in this series, but one band of 300
+feet in thickness has been traced for considerable distances to the
+north of Lake Huron. Beds of greenstone are intercalated
+conformably with the quartzose and argillaceous members of this
+series. No organic remains have yet been found in any of the beds,
+which are about 18,000 feet thick, and rest unconformably on the
+Laurentian rocks.</p>
+
+<p class="center">
+<small>LAURENTIAN GROUP.</small>
+</p>
+
+<p>In the course of the geological survey carried on under the
+direction of Sir W.E. Logan, it has been shown that, northward of
+the river St. Lawrence, there is a vast series of crystalline rocks
+of gneiss, mica-schist, quartzite, and limestone, more than 30,000
+feet in thickness, which have been called Laurentian, and which are
+already known to occupy an area of about 200,000 square miles. They
+are not only more ancient than the fossiliferous Cambrian
+formations above described, but are older than the Huronian last
+mentioned, and had undergone great disturbing movements before the
+Potsdam sandstone and the other &ldquo;primordial&rdquo; or
+Cambrian rocks were formed. The older half of this Laurentian
+series is unconformable to the newer portion of the same.</p>
+
+<p>
+<a name="page491"></a><b>Upper Laurentian or Labrador Series.</b>&mdash;The Upper
+Group, more than 10,000 feet thick, consists of stratified
+crystalline rocks in which no organic remains have yet been found.
+They consist in great part of feldspars, which vary in composition
+from anorthite to andesine, or from those kinds in which there is
+less than one per cent of potash and soda to those in which there
+is more than seven per cent of these alkalies, the soda
+preponderating greatly. These feldsparites sometimes form mountain
+masses almost without any admixture of other minerals; but at other
+times they include augite, which passes into hypersthene. They are
+often granitoid in structure. One of the varieties is the same as
+the apolescent labradorite rock of Labrador. The Adirondack
+Mountains in the State of New York are referred to the same series,
+and it is conjectured that the hypersthene rocks of Skye, which
+resemble this formation in mineral character, may be of the same
+geological age.</p>
+
+<p><b>Lower Laurentian.</b>&mdash;This series, about 20,000 feet in
+thickness, is, as before stated, unconformable to that last
+mentioned; it consists in great part of gneiss of a reddish tint
+with orthoclase feldspar. Beds of nearly pure quartz, from 400 to
+600 feet thick, occur in some places. Hornblendic and micaceous
+schists are often interstratified, and beds of limestone, usually
+crystalline. Beds of plumbago also occur. That this pure carbon may
+have been of organic origin before metamorphism has naturally been
+conjectured.</p>
+
+<p>There are several of these limestones which have been traced to
+great distances, and one of them is from 700 to 1500 feet thick. In
+the most massive of them Sir W. Logan observed, in 1859, what he
+considered to be an organic body much resembling the Silurian
+fossil called <i>Stromatopora rugosa.</i> It had been obtained the
+year before by Mr. J. MacMullen at the Grand Calumet, on the river
+Ottawa. This fossil was examined in 1864 by Dr. Dawson of Montreal,
+who detected in it, by aid of the microscope, the distinct
+structure of a Rhizopod or Foraminifer. Dr. Carpenter and Professor
+T. Rupert Jones have since confirmed this opinion, comparing the
+structure to that of the well-known nummulite. It appears to have
+grown one layer over another, and to have formed reefs of limestone
+as do the living coral-building polyp animals. Parts of the
+original skeleton, consisting of carbonate of lime, are still
+preserved; while certain inter-spaces in the calcareous fossil have
+been filled up with serpentine and white augite. On this oldest of
+known organic remains Dr. Dawson has conferred the name of <i>
+Eozoon</i>
+<a name="page492"></a>
+<i>Canadense</i> (see Figs. 582, 583); its antiquity is such
+that the distance of time which separated it from the Upper
+Cambrian period, or that of the Potsdam sandstone, may, says Sir W.
+Logan, be equal to the time which elapsed between the Potsdam
+sandstone and the nummulitic limestones of the Tertiary period. The
+Laurentian and Huronian rocks united are about 50,000 feet in
+thickness, and the Lower Laurentian was disturbed before the newer
+series was deposited. We may naturally expect the other proofs of
+unconformability will hereafter be detected at more than one point
+in so vast a succession of strata.</p>
+
+<p><img src="images/fig582.jpg" width="340" height="161" alt=
+"Fig. 582 and 583: Eozoon Canadense." /></p>
+
+<p>Fig. 582. <i>a.</i> Chambers of lower tier
+communicating at +, and separated from adjoining chambers at O by
+an intervening septum, traversed by passages. <i>b.</i> Chambers of
+an upper tier. <i>c.</i> Walls of the chambers traversed by fine
+tubules. (These tubules pass with uniform parallelism from the
+inner to the outer surface, opening at regular distances from each
+other.) <i>d.</i> Intermediate skeleton, composed of homogeneous
+shell substance, traversed by <i>f.</i> Stoloniferous passages
+connecting the chambers of the two tiers. <i>e.</i> Canal system in
+intermediate skeleton, showing the arborescent saceodic
+prolongations. (Fig. 583 shows these bodies in a decalcified
+state.) <i>f.</i> Stoloniferous passages.<br/>
+Fig. 583. Decalcified portion of natural rock, showing <i>canal
+system</i> and the several layers; the acuteness of the planes
+prevents more than one or two parallel tiers being observed.</p>
+
+<p>The mineral character of the Upper Laurentian differs, as we
+have seen, from that of the Lower, and the pebbles of gneiss in the
+Huronian conglomerates are thought to prove that the Laurentian
+strata were already in a metamorphic state before they were broken
+up to supply materials for the Huronian. Even if we had not
+discovered the Eozoon, we might fairly have inferred from analogy
+that as the quartzites were once beds of sand, and the gneiss and
+mica-schist derived from shales and argillaceous sandstones, so the
+calcareous masses, from 400 to 1000 feet and more in thickness,
+were originally of organic origin. This is now generally believed
+to have been the case with the Silurian, Devonian, Carboniferous,
+Oolitic, and Cretaceous limestones and those nummulitic rocks of
+tertiary date which bear the closest affinity to the Eozoon reefs
+of the Lower Laurentian. The oldest stratified rock in Scotland is
+that called by Sir R. Murchison
+<a name="page493"></a>&ldquo;the fundamental gneiss,&rdquo; which is found in the
+north-west of Ross-shire, and in Sutherlandshire (see <a href=
+"images/fig82.jpg">Fig. 82</a>), and forms the whole of the
+adjoining island of Lewis, in the Hebrides. It has a strike from
+north-west to south-east, nearly at right angles to the metamorphic
+strata of the Grampians. On this Laurentian gneiss, in parts of the
+western Highlands, the Lower Cambrian and various metamorphic rocks
+rest unconformably. It seems highly probable that this ancient
+gneiss of Scotland may correspond in date with part of the great
+Laurentian group of North America.
+</p>
+
+<p class="footnote">
+<a name="fn-27.1" id="fn-27.1"></a> <a href="#fnref-27.1">[1]</a>
+Quart. Geol. Journ., vol. iii, p. 156.
+</p>
+
+<p class="footnote">
+<a name="fn-27.2" id="fn-27.2"></a> <a href="#fnref-27.2">[2]</a>
+This genus has been substituted for Barrande&rsquo;s <i> Conocephalus,</i> as
+the latter term had been preoccupied by the entomologists.
+</p>
+
+<p class="footnote">
+<a name="fn-27.3" id="fn-27.3"></a> <a href="#fnref-27.3">[3]</a>
+Geol. Mag., vol iv.
+</p>
+
+<p class="footnote">
+<a name="fn-27.4" id="fn-27.4"></a> <a href="#fnref-27.4">[4]</a>
+British Association Report 1865, 1866, 1868 and Quart. Geol. Journ., vols. xxi,
+xxv.
+</p>
+
+<p class="footnote">
+<a name="fn-27.5" id="fn-27.5"></a> <a href="#fnref-27.5">[5]</a>
+Brit. Assoc. Report, 1868.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap28"></a><a name="page494"></a>CHAPTER XXVIII.<br/>
+VOLCANIC ROCKS.</h2>
+
+<p class="letter">External Form, Structure, and Origin of Volcanic
+Mountains. &mdash; Cones and Craters. &mdash; Hypothesis of
+&ldquo;Elevation Craters&rdquo; considered. &mdash; Trap Rocks.
+&mdash; Name whence derived. &mdash; Minerals most abundant in
+Volcanic Rocks. &mdash; Table of the Analysis of Minerals in the
+Volcanic and Hypogene Rocks. &mdash; Similar Minerals in
+Meteorites. &mdash; Theory of Isomorphism. &mdash; Basaltic Rocks.
+&mdash; Trachytic Rocks. &mdash; Special Forms of Structure.
+&mdash; The columnar and globular Forms. &mdash; Trap Dikes and
+Veins. &mdash; Alteration of Rocks by volcanic Dikes. &mdash;
+Conversion of Chalk into Marble. &mdash; Intrusion of Trap between
+Strata. &mdash; Relation of trappean Rocks to the Products of
+active Volcanoes.</p>
+
+<p>The aqueous or fossiliferous rocks having now been described, we
+have next to examine those which may be called volcanic, in the
+most extended sense of that term. In the diagram (Fig. 584) suppose
+<i>a, a</i> to represent the crystalline formations, such as the
+granitic and metamorphic; <i>b, b</i> the fossiliferous strata; and
+<i>c, c</i> the volcanic rocks. These last are sometimes found, as
+was explained in the first chapter, breaking through <i>a</i> and
+<i>b,</i> sometimes overlying both, and occasionally alternating
+with the strata <i>b, b.</i></p>
+
+<p><img src="images/fig584.jpg" width="358" height="105" alt=
+"Fig. 584: a. Hypogene formations, stratified and unstratified. b. Aqueous
+formations. c. Volcanic rocks." />
+</p>
+
+<p><b>External Form, Structure, and Origin of Volcanic
+Mountains.</b>&mdash;The origin of volcanic cones with
+crater-shaped summits has been explained in the &ldquo;Principles
+of Geology&rdquo; (Chapters 23 to 27), where Vesuvius, Etna,
+Santorin, and Barren Island are described. The more ancient
+portions of those mountains or islands, formed long before the
+times of history, exhibit the same external features and internal
+structure which belong to most of the extinct volcanoes of still
+higher antiquity; and these last have evidently been due to a
+complicated series of operations, varied in kind according to
+circumstances; as, for example, whether the accumulation took place
+above or below the level of the sea, whether the lava issued from
+one or several contiguous vents, and, lastly,
+<a name="page495"></a>whether the rocks reduced to fusion in the subterranean regions
+happened to have contained more or less silica, potash, soda, lime,
+iron, and other ingredients. We are best acquainted with the
+effects of eruptions above water, or those called subÆrial or
+supramarine; yet the products even of these are arranged in so many
+ways that their interpretation has given rise to a variety of
+contradictory opinions, some of which will have to be considered in
+this chapter.</p>
+
+<p><img src="images/fig585.jpg" width="321" height="158" alt=
+"Fig. 585: Part of the chain of extinct volcanoes called the Monts Dome, Aurvergne." />
+</p>
+
+<p><i>Cones and Craters.</i>&mdash;In regions where the eruption of
+volcanic matter has taken place in the open air, and where the
+surface has never since been subjected to great aqueous denudation,
+cones and craters constitute the most striking peculiarity of this
+class of formations. Many hundreds of these cones are seen in
+central France, in the ancient provinces of Auvergne, Velay, and
+Vivarais, where they observe, for the most part, a linear
+arrangement, and form chains of hills. Although none of the
+eruptions have happened within the historical era, the streams of
+lava may still be traced distinctly descending from many of the
+craters, and following the lowest levels of the existing valleys.
+The origin of the cone and crater-shaped hill is well understood,
+the growth of many having been watched during volcanic eruptions. A
+chasm or fissure first opens in the earth, from which great volumes
+of steam are evolved. The explosions are so violent as to hurl up
+into the air fragments of broken stone, parts of which are shivered
+into minute atoms. At the same time melted stone or <i>lava</i>
+usually ascends through the chimney or vent by which the gases make
+their escape. Although extremely heavy, this lava is forced up by
+the expansive power of entangled gaseous fluids, chiefly steam or
+aqueous vapour, exactly in the same manner as water is made to boil
+over the edge of a vessel when steam has been generated at the
+bottom by heat. Large quantities of the lava are also shot up into
+the air, where it separates into fragments, and acquires a spongy
+texture by the sudden enlargement
+<a name="page496"></a>of the included gases, and thus forms <i>scoriæ,</i> other
+portions being reduced to an impalpable powder or dust. The
+showering down of the various ejected materials round the orifice
+of eruption gives rise to a conical mound, in which the successive
+envelopes of sand and scoriæ form layers, dipping on all
+sides from a central axis. In the mean time a hollow, called a <i>
+crater,</i> has been kept open in the middle of the mound by the
+continued passage upward of steam and other gaseous fluids. The
+lava sometimes flows over the edge of the crater, and thus thickens
+and strengthens the sides of the cone; but sometimes it breaks down
+the cone on one side (see Fig. 585), and often it flows out from a
+fissure at the base of the hill, or at some distance from its
+base.</p>
+
+<p>Some geologists had erroneously supposed, from observations made
+on recent cones of eruption, that lava which consolidates on steep
+slopes is always of a scoriaceous or vesicular structure, and never
+of that compact texture which we find in those rocks which are
+usually termed &ldquo;trappean.&rdquo; Misled by this theory, they
+have gone so far as to believe that if melted matter has originally
+descended a slope at an angle exceeding four or five degrees, it
+never, on cooling, acquires a stony compact texture. Consequently,
+whenever they found in a volcanic mountain sheets of stony
+materials inclined at angles of from 5&deg; to 20&deg; or even more
+than 30&deg;, they thought themselves warranted in assuming that
+such rocks had been originally horizontal, or very slightly
+inclined, and had acquired their high inclination by subsequent
+upheaval. To such dome-shaped mountains with a cavity in the
+middle, and with the inclined beds having what was called a
+quâquâversal dip or a slope outward on all sides, they
+gave the name of &ldquo;Elevation craters.&rdquo;</p>
+
+<p>
+As the late Leopold Von Buch, the author of this theory, had selected the Isle
+of Palma, one of the Canaries, as a typical illustration of this form of
+volcanic mountain, I visited that island in 1854, in company with my friend Mr.
+Hartung, and I satisfied myself that it owes its origin to a series of
+eruptions of the same nature as those which formed the minor cones, already
+alluded to. In some of the more ancient or Miocene volcanic mountains, such as
+Mont Dor and Cantal in central France, the mode of origin by upheaval as above
+described is attributed to those dome-shaped masses, whether they possess or
+not a great central cavity, as in Palma. Where this cavity is present, it has
+probably been due to one or more great explosions similar to that which
+destroyed a great part of ancient Vesuvius in the time of Pliny. Similar
+paroxysmal catastrophes have caused in historical times <a
+name="page497"></a>the truncation on a grand scale of some large cones in Java
+and elsewhere.<a href="#fn-28.1" name="fnref-28.1"
+id="fnref-28.1"><sup>[1]</sup></a>
+</p>
+
+<p>Among the objections which may be considered as fatal to Von
+Buch&rsquo;s doctrine of upheaval in these cases, I may state that
+a series of volcanic formations extending over an area six or seven
+miles in its shortest diameter, as in Palma, could not be
+accumulated in the form of lavas, tuffs, and volcanic breccias or
+agglomerates without producing a mountain as lofty as that which
+they now constitute. But assuming that they were first horizontal,
+and then lifted up by a force acting most powerfully in the centre
+and tilting the beds on all sides, a central crater having been
+formed by explosion or by a chasm opening in the middle, where the
+continuity of the rocks was interrupted, we should have a right to
+expect that the chief ravines or valleys would open towards the
+central cavity, instead of which the rim of the great crater in
+Palma and other similar ancient volcanoes is entire for more than
+three parts of the whole circumference.</p>
+
+<p>
+If dikes are seen in the precipices surrounding such craters or central
+cavities, they certainly imply rents which were filled up with liquid matter.
+But none of the dislocations producing such rents can have belonged to the
+supposed period of terminal and paroxysmal upheaval, for had a great central
+crater been already formed before they originated, or at the time when they
+took place, the melted matter, instead of filling the narrow vents, would have
+flowed down into the bottom of the cavity, and would have obliterated it to a
+certain extent. Making due allowance for the quantity of matter removed by
+subaërial denudation in volcanic mountains of high antiquity, and for the grand
+explosions which are known to have caused truncation in active volcanoes, there
+is no reason for calling in the violent hypothesis of elevation craters to
+explain the structure of such mountains as Teneriffe, the Grand Canary, Palma,
+or those of central France, Etna, or Vesuvius, all of which I have examined.
+With regard to Etna, I have shown, from observations made by me in 1857, that
+modern lavas, several of them of known date, have formed continuous beds of
+compact stone even on slopes of 15, 36, and 38 degrees, and, in the case of the
+lava of 1852, more than 40 degrees. The thickness of these tabular layers
+varies from 1&frac12; foot to 26 feet. And their planes of stratification are
+parallel to those of the overlying and underlying scoriæ which form part of the
+same currents.<a href="#fn-28.2" name="fnref-28.2"
+id="fnref-28.2"><sup>[2]</sup></a>
+</p>
+
+<p><b>Nomenclature of Trappean Rocks.</b>&mdash;When geologists
+first began to examine attentively the structure of the
+northern
+<a name="page498"></a>and western parts of Europe, they were almost entirely ignorant
+of the phenomena of existing volcanoes. They found certain rocks,
+for the most part without stratification, and of a peculiar mineral
+composition, to which they gave different names, such as basalt,
+greenstone, porphyry, trap tuff, and amygdaloid. All these, which
+were recognised as belonging to one family, were called
+&ldquo;trap&rdquo; by Bergmann, from <i>trappa,</i> Swedish for a
+flight of steps&mdash;a name since adopted very generally into the
+nomenclature of the science; for it was observed that many rocks of
+this class occurred in great tabular masses of unequal extent, so
+as to form a succession of terraces or steps. It was also felt that
+some general term was indispensable, because these rocks, although
+very diversified in form and composition, evidently belonged to one
+group, distinguishable from the Plutonic as well as from the
+non-volcanic fossiliferous rocks.</p>
+
+<p>By degrees familiarity with the products of active volcanoes
+convinced geologists more and more that they were identical with
+the trappean rocks. In every stream of modern lava there is some
+variation in character and composition, and even where no important
+difference can be recognised in the proportions of silica, alumina,
+lime, potash, iron, and other elementary materials, the resulting
+materials are often not the same, for reasons which we are as yet
+unable to explain. The difference also of the lavas poured out from
+the same mountain at two distinct periods, especially in the
+quantity of silica which they contain, is often so great as to give
+rise to rocks which are regarded as forming distinct families,
+although there may be every intermediate gradation between the two
+extremes, and although some rocks, forming a transition from the
+one class to the other, may often be so abundant as to demand
+special names. These species might be multiplied indefinitely, and
+I can only afford space to name a few of the principal ones, about
+the composition and aspect of which there is the least discordance
+of opinion.</p>
+
+<p><b>Minerals most abundant in Volcanic Rocks.</b>&mdash;The
+minerals which form the chief constituents of these igneous rocks
+are few in number. Next to quartz, which is nearly pure silica or
+silicic acid, the most important are those silicates commonly
+classed under the several heads of feldspar, mica, hornblende or
+augite, and olivine. In Table 28.1, in drawing up which I have
+received the able assistance of Mr. David Forbes, the chemical
+analysis of these minerals and their varieties is shown, and he has
+added the specific gravity of the different mineral species, the
+geological application of which in determining the rocks formed by
+these minerals will be explained in the sequel (p.504).</p>
+
+<p class="center">
+<a name="page499"></a><i>Analysis of Minerals most abundant in the Volcanic and
+Hypogene Rocks.</i></p>
+
+<table border="1" cellspacing="0" cellpadding="6" summary=
+"Mineral Groups and Analysis.">
+<tr>
+<td align="center" colspan="5">THE QUARTZ GROUP</td>
+</tr>
+
+<tr>
+<td valign="middle">QUARTZ</td>
+<td >100&middot;0<br/>
+2&middot;6</td>
+<td >Silica<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td >TRIDYMITE</td>
+<td >100&middot;0<br/>
+2&middot;3</td>
+<td >Silica<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td align="center" colspan="5">THE FELDSPAR GROUP</td>
+</tr>
+
+<tr>
+<td valign="middle">ORTHOCLASE.<br/>
+&mdash;&mdash; Carisbad, in granite (bulk)</td>
+<td valign="top">65&middot;23<br/>
+16&middot;26<br/>
+0&middot;27<br/>
+nil<br/>
+trace<br/>
+nil<br/>
+14&middot;66<br/>
+1&middot;45<br/>
+nil<br/>
+2&middot;55</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Sanadine,
+Drachenfels in trachyte (Rammelsberg)</td>
+<td valign="top">65&middot;87<br/>
+18&middot;53<br/>
+nil<br/>
+nil<br/>
+0&middot;95<br/>
+0&middot;30<br/>
+10&middot;32<br/>
+3&middot;49<br/>
+W.&nbsp;0&middot;44<br/>
+2&middot;55</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">ALBITE.<br/>
+&mdash;&mdash; Arendal, in granite (G. Rose)</td>
+<td valign="top">68&middot;46<br/>
+19&middot;30<br/>
+nil<br/>
+0&middot;28<br/>
+0&middot;68<br/>
+nil<br/>
+nil<br/>
+11&middot;27<br/>
+nil<br/>
+2&middot;61</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">OLIGOCLASE.<br/>
+&mdash;&mdash; Ytterby, in granite (Berzelius)</td>
+<td valign="top">61&middot;55<br/>
+23&middot;80<br/>
+nil<br/>
+nil<br/>
+3&middot;18<br/>
+0&middot;80<br/>
+0&middot;38<br/>
+9&middot;67<br/>
+nil<br/>
+2&middot;65</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Teneriffe, in
+trachyte (Deville)</td>
+<td valign="top">61&middot;55<br/>
+22&middot;03<br/>
+nil<br/>
+nil<br/>
+2&middot;81<br/>
+0&middot;47<br/>
+3&middot;44<br/>
+7&middot;74<br/>
+nil<br/>
+2&middot;59</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">LABRADORITE.<br/>
+&mdash;&mdash; Hitteroe, in Labrador-rock (Waage)</td>
+<td valign="top">51&middot;39<br/>
+29&middot;42<br/>
+2&middot;90<br/>
+nil<br/>
+9&middot;44<br/>
+0&middot;37<br/>
+1&middot;10<br/>
+5&middot;03<br/>
+W.&nbsp;0&middot;71<br/>
+2&middot;72</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Iceland, in
+volcanic (Damour)</td>
+<td valign="top">52&middot;17<br/>
+29&middot;22<br/>
+1&middot;90<br/>
+nil<br/>
+13&middot;11<br/>
+nil<br/>
+nil<br/>
+3&middot;40<br/>
+nil<br/>
+2&middot;71</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">ANORTHITE.<br/>
+&mdash;&mdash; Harzburg, in diorite (Streng)</td>
+<td valign="top">45&middot;37<br/>
+34&middot;81<br/>
+0&middot;59<br/>
+nil<br/>
+16&middot;52<br/>
+0&middot;83<br/>
+0&middot;40<br/>
+1&middot;45<br/>
+W.&nbsp;0&middot;87<br/>
+2&middot;74</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Hecla, in volcanic
+(Waltershausen)</td>
+<td valign="top">45&middot;14<br/>
+32&middot;10<br/>
+2&middot;03<br/>
+0&middot;78<br/>
+18&middot;32<br/>
+nil<br/>
+0&middot;22<br/>
+1&middot;06<br/>
+nil<br/>
+2&middot;74</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">LEUCITE.<br/>
+&mdash;&mdash; Vesuvius, 1811, in lava (Rammelsberg)</td>
+<td valign="top">56&middot;10<br/>
+23&middot;22<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+20&middot;59<br/>
+0&middot;57<br/>
+nil<br/>
+2&middot;48</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">NEPHELINE.<br/>
+&mdash;&mdash; Miask, in Miascite (Scheerer)</td>
+<td valign="top">44&middot;30<br/>
+33&middot;25<br/>
+0&middot;82<br/>
+nil<br/>
+0&middot;32<br/>
+0&middot;07<br/>
+5&middot;82<br/>
+16&middot;02<br/>
+nil<br/>
+2&middot;59</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Vesuvius, in
+volcanic (Arfvedson)</td>
+<td valign="top">44&middot;11<br/>
+33&middot;73<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+20&middot;46<br/>
+W.&nbsp;0&middot;62<br/>
+2&middot;60</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td align="center" colspan="5">THE MICA GROUP</td>
+</tr>
+
+<tr>
+<td valign="middle">MUSCOVITE.<br/>
+&mdash;&mdash; Finland, in grante (Rose)</td>
+<td valign="top">46&middot;36<br/>
+36&middot;80<br/>
+4&middot;53<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+9&middot;22<br/>
+nil<br/>
+F.&nbsp;0&middot;67<br/>
+W.&nbsp;1&middot;84<br/>
+2&middot;90</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+&nbsp;<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">LEPIDOLITE.<br/>
+&mdash;&mdash; Cornwall, in granite (Regnault)</td>
+<td valign="top">52&middot;40<br/>
+26&middot;80<br/>
+nil<br/>
+1&middot;50<br/>
+nil<br/>
+nil<br/>
+9&middot;14<br/>
+nil<br/>
+F.&nbsp;4&middot;18<br/>
+Li.&nbsp;4&middot;85<br/>
+2&middot;90</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+&nbsp;<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">BIOTITE.<br/>
+&mdash;&mdash; Bodennais (V. Kobel&gt;</td>
+<td valign="top">40&middot;86<br/>
+15&middot;13<br/>
+13&middot;00<br/>
+nil<br/>
+nil<br/>
+22&middot;00<br/>
+8&middot;83<br/>
+nil<br/>
+W.&nbsp;0&middot;44<br/>
+2&middot;70</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Vesuvius, in
+volcanic (Chodnef)</td>
+<td valign="top">40&middot;91<br/>
+17&middot;71<br/>
+11&middot;02<br/>
+nil<br/>
+0&middot;30<br/>
+19&middot;04<br/>
+9&middot;96<br/>
+nil<br/>
+nil<br/>
+2&middot;75</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">PHLOGOPITE.<br/>
+&mdash;&mdash; New York, in metamorphic limestone
+(Rammelsberg)</td>
+<td valign="top">41&middot;96<br/>
+13&middot;47<br/>
+nil<br/>
+2&middot;67<br/>
+0&middot;34<br/>
+27&middot;12<br/>
+9&middot;37<br/>
+nil<br/>
+F.&nbsp;2&middot;93<br/>
+W.&nbsp;0&middot;60<br/>
+2&middot;81</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+&nbsp;<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">MARGARITE.<br/>
+&mdash;&mdash; Nexos (Smith)</td>
+<td valign="top">30&middot;02<br/>
+49&middot;52<br/>
+1&middot;65<br/>
+nil<br/>
+10&middot;82<br/>
+0&middot;48<br/>
+1&middot;25<br/>
+&nbsp;<br/>
+W.&nbsp;5&middot;55<br/>
+2&middot;99</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+=Potash<br/>
+=Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">RAPIDOLITE.<br/>
+&mdash;&mdash; Pyrenees (Delesse)</td>
+<td valign="top">32&middot;10<br/>
+18&middot;50<br/>
+nil<br/>
+0&middot;06<br/>
+nil<br/>
+36&middot;70<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;12&middot;10<br/>
+2&middot;61</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">TALC.<br/>
+&mdash;&mdash; Zillerthal (Delesse)</td>
+<td valign="top">63&middot;00<br/>
+nil<br/>
+nil<br/>
+trace<br/>
+nil<br/>
+33&middot;60<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;3&middot;10<br/>
+2&middot;78</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td align="center" colspan="5">THE AMPHIBOLE AND PYROXENE
+GROUP</td>
+</tr>
+
+<tr>
+<td valign="middle">TREMOLITE.<br/>
+&mdash;&mdash; St. Gothard (Rammelsbeg)</td>
+<td valign="top">58&middot;55<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+13&middot;90<br/>
+26&middot;63<br/>
+nil<br/>
+nil<br/>
+F.W.&nbsp;0&middot;34<br/>
+2&middot;93</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">ACTINOLITE.<br/>
+&mdash;&mdash; Arendal, in granite (Rammelsberg)</td>
+<td valign="top">56&middot;77<br/>
+0&middot;97<br/>
+nil<br/>
+5&middot;88<br/>
+13&middot;56<br/>
+21&middot;48<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;2&middot;20<br/>
+3&middot;02</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">HORNBLENDE.<br/>
+&mdash;&mdash; Faymont, in diorite (Deville)</td>
+<td valign="top">41&middot;99<br/>
+11&middot;66<br/>
+nil<br/>
+22&middot;22<br/>
+9&middot;55<br/>
+12&middot;59<br/>
+nil<br/>
+1&middot;02<br/>
+W.&nbsp;1&middot;47<br/>
+3&middot;20</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Etna, in volcanic
+(Waltershausen)</td>
+<td valign="top">40&middot;91<br/>
+13&middot;68<br/>
+nil<br/>
+17&middot;49<br/>
+13&middot;44<br/>
+13&middot;19<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;0&middot;85<br/>
+3&middot;01</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">URALITE.<br/>
+&mdash;&mdash; Ural, (Rammelsberg)</td>
+<td valign="top">50&middot;75<br/>
+5&middot;65<br/>
+nil<br/>
+17&middot;27<br/>
+11&middot;59<br/>
+12&middot;28<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;1&middot;80<br/>
+3&middot;14</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">AUGITE.<br/>
+&mdash;&mdash; Bohemia, in dolerite (Rammelsberg)</td>
+<td valign="top">51&middot;12<br/>
+3&middot;38<br/>
+0&middot;95<br/>
+8&middot;08<br/>
+23&middot;54<br/>
+12&middot;82<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;35</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Vesuvius, in lava
+of 1858 (Rammelsberg)</td>
+<td valign="top">49&middot;61<br/>
+4&middot;42<br/>
+nil<br/>
+9&middot;08<br/>
+22&middot;83<br/>
+14&middot;22<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;25</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">DIALLAGE.<br/>
+&mdash;&mdash; Harz, in Gabbro (Rammelsberg)</td>
+<td valign="top">52&middot;00<br/>
+3&middot;10<br/>
+nil<br/>
+9&middot;36<br/>
+16&middot;29<br/>
+18&middot;51<br/>
+nil<br/>
+nil<br/>
+W.&nbsp;1&middot;10<br/>
+3&middot;23</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">HYPERSTHENE.<br/>
+&mdash;&mdash; Labrador, in Labrador-Rock (Damour)</td>
+<td valign="top">51&middot;36<br/>
+0&middot;37<br/>
+nil<br/>
+22&middot;59<br/>
+3&middot;09<br/>
+21&middot;31<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;39</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td align="center" colspan="5">THE OLIVINE GROUP</td>
+</tr>
+
+<tr>
+<td valign="middle">BRONZITE.<br/>
+&mdash;&mdash; Greenland (V. Kobell)</td>
+<td valign="top">58&middot;00<br/>
+1&middot;33<br/>
+11&middot;14<br/>
+nil<br/>
+nil<br/>
+29&middot;66<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;20</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">OLIVINE.<br/>
+&mdash;&mdash; Carlsbad, in basalt (Rammelsberg)</td>
+<td valign="top">39&middot;34<br/>
+nil<br/>
+nil<br/>
+14&middot;85<br/>
+nil<br/>
+45&middot;81<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;40</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+
+<tr>
+<td valign="middle">&mdash;&mdash; Mount Somma, in
+volcanic (Walmstedt)</td>
+<td valign="top">10&middot;08<br/>
+0&middot;18<br/>
+nil<br/>
+15&middot;74<br/>
+nil<br/>
+44&middot;22<br/>
+nil<br/>
+nil<br/>
+nil<br/>
+3&middot;33</td>
+<td valign="top">Silica<br/>
+Alumina<br/>
+Sesquioxide of Iron<br/>
+Protoxides of Iron and Manganese<br/>
+Lime<br/>
+Magnesia<br/>
+Potash<br/>
+Soda<br/>
+Other constituents<br/>
+Specific gravity</td>
+</tr>
+</table>
+
+<p class="footnote">In the &ldquo;Other constituents&rdquo; the
+following signs are used: F=Fluorine, Li=Lithia, W=Loss on igniting
+the mineral, in most instances only Water.</p>
+
+<p>
+<a name="page500"></a>From the table above it will be observed that many
+minerals are omitted which, even if they are of common occurrence, are more to
+be regarded as accessory than as essential components of the rocks in which
+they are found.<a href="#fn-28.3" name="fnref-28.3"
+id="fnref-28.3"><sup>[3]</sup></a> Such are, for example, Garnet, Epidote,
+Tourmaline, Idocrase, Andalusite, Scapolite, the various Zeolites, and several
+other silicates of somewhat rarer occurrence. Magnetite, Titanoferrite, and
+Iron-pyrites also occur as normal constituents of various igneous rocks,
+although in very small amount, as also Apatite, or phosphate of lime. The other
+salts of lime, including its carbonate or calcite, although often met with, are
+invariably products of secondary chemical action.
+</p>
+
+<p>The Zeolites, above mentioned, so named from the manner in which
+they froth up under the blow-pipe and melt into a glass, differ in
+their chemical composition from all the other mineral constituents
+of volcanic rocks, since they are hydrated silicates containing
+from 10 to 25 per cent of water. They abound in some trappean rocks
+and ancient lavas, where they fill up vesicular cavities and
+interstices in the substance of the rocks, but are rarely found in
+any quantity in recent lavas; in most cases they are to be regarded
+as secondary products formed by the action of water on the other
+constituents of the rocks. Among them the species Analcime,
+Stilbite, Natrolite, and Chabazite may be mentioned as of most
+common occurrence.</p>
+
+<p><b>Quartz Group.</b>&mdash;The microscope has shown that pure
+quartz is oftener present in lavas than was formerly supposed. It
+had been argued that the quartz in granite having a specific
+gravity of 2&middot;6, was not of purely igneous origin, because
+the silica resulting from fusion in the laboratory has only a
+specific gravity of 2&middot;3. But Mr. David Forbes has
+ascertained that the free quartz in trachytes, which are known to
+have flowed as lava, has the same specific gravity as the ordinary
+quartz of granite; and the recent researches of Von Rath and others
+prove that the mineral Tridymite, which is crystallised silica of
+specific gravity 2&middot;3 (see Table, p. 499), is of common
+occurrence in the volcanic rocks of Mexico, Auvergne, the Rhine,
+and elsewhere, although hitherto entirely overlooked.</p>
+
+<p><b>Feldspar Group.</b>&mdash;In the Feldspar group (Table, p.
+499) the five mineral species most commonly met with as rock
+constituents are: 1. Orthoclase, often called common or
+potash-feldspar. 2. Albite, or soda-feldspar, a mineral which plays
+a more subordinate part than was formerly supposed, this name
+having been given to much which has since been proved to be
+Oligoclase. 3. Oligoclase, or soda-lime feldspar,
+<a name="page501"></a>in which soda is present in much larger proportion than lime,
+and of which mineral andesite are andesine, is considered to be a
+variety. 4. Labradorite, or lime-soda-feldspar, in which the
+proportions of lime and soda are the reverse to what they are in
+Oligoclase. 5. Anorthite or lime-feldspar. The two latter feldspars
+are rarely if ever found to enter into the composition of rocks
+containing quartz.</p>
+
+<p>In employing such terms as potash-feldspar, etc., it must,
+however, always be borne in mind that it is only intended to direct
+attention to the predominant alkali or alkaline earth in the
+mineral, not to assert the absence of the others, which in most
+cases will be found to be present in minor quantity. Thus
+potash-feldspar (orthoclase) almost always contains a little soda,
+and often traces of lime or magnesia; and in like manner with the
+others. The terms &ldquo;glassy&rdquo; and &ldquo;compact&rdquo;
+feldspars only refer to structure, and not to species or
+composition; the student should be prepared to meet with any of the
+above feldspars in either of these conditions: the glassy state
+being apparently due to quick cooling, and the compact to
+conditions unfavourable to crystallisation; the so-called
+&ldquo;compact feldspar&rdquo; is also very commonly found to be an
+admixture of more than one feldspar species, and frequently also
+contains quartz and other extraneous mineral matter only to be
+detected by the microscope.</p>
+
+<p>Feldspars when arranged according to their system of
+crystallisation are <i>monoclinic,</i> having one axis obliquely
+inclined; or <i>triclinic,</i> having the three axes all obliquely
+inclined to each other. If arranged with reference to their
+cleavage they are <i>orthoclastic,</i> the fracture taking place
+always at a right angle; or <i>plagioclastic,</i> in which the
+cleavages are oblique to one another. Orthoclase is orthoclastic
+and monoclinic; all the other feldspars are plagioclastic and
+triclinic.</p>
+
+<p><i>Minerals in Meteorites.</i>&mdash;That variety of the
+Feldspar Group which is called Anorthite has been shown by
+Rammelsberg to occur in a meteoric stone, and his analysis proves
+it to be almost identical in its chemical proportions to the same
+mineral in the lavas of modern volcanoes. So also Bronzite
+(Enstatite) and Olivine have been met with in meteorites shown by
+analysis to come remarkably near to these minerals in ordinary
+rocks.</p>
+
+<p><b>Mica Group.</b>&mdash;With regard to the micas, the four
+principal species (Table, p. 499) all contain potash in nearly the
+same proportion, but differ greatly in the proportion and nature of
+their other ingredients. Muscovite is often called common or potash
+mica; Lepidolite is characterised by containing lithia in addition;
+Biotite contains a large amount of
+<a name="page502"></a>magnesia and oxide of iron; whilst Phlogopite contains still
+more of the former substance. In rocks containing quartz, muscovite
+or lepidolite are most common. The mica in recent volcanic rocks,
+gabbros, and diorites is usually Biotite, while that so common in
+metamorphic limestones is usually, if not always, Phlogopite.</p>
+
+<p><b>Amphibole and Pyroxene Group.</b>&mdash;The minerals included
+in the table under the Amphibole and Pyroxene Group differ somewhat
+in their crystallisation form, though they all belong to the
+monoclinic system. Amphibole is a general name for all the
+different varieties of Hornblende, Actinolite, Tremolite, etc.,
+while Pyroxene includes Augite, Diallage, Malacolite, Sahlite, etc.
+The two divisions are so much allied in chemical composition and
+crystallographic characters, and blend so completely one into the
+other in Uralite (see <a href="#page499">page 499</a>), that it is
+perhaps best to unite them in one group.</p>
+
+<p><b>Theory of Isomorphism.</b>&mdash;The history of the changes
+of opinion on this point is curious and instructive. Werner first
+distinguished augite from hornblende; and his proposal to separate
+them obtained afterwards the sanction of Haüy, Mohs, and other
+celebrated mineralogists. It was agreed that the form of the
+crystals of the two species was different, and also their
+structure, as shown by <i>cleavage</i>&mdash;that is to say, by breaking
+or cleaving the mineral with a chisel, or a blow of the hammer, in
+the direction in which it yields most readily. It was also found by
+analysis that augite usually contained more lime, less alumina, and
+no fluoric acid; which last, though not always found in hornblende,
+often enters into its composition in minute quantity. In addition
+to these characters, it was remarked as a geological fact, that
+augite and hornblende are very rarely associated together in the
+same rock. It was also remarked that in the crystalline slags of
+furnaces augitic forms were frequent, the hornblendic entirely
+absent; hence it was conjectured that hornblende might be the
+result of slow, and augite of rapid cooling. This view was
+confirmed by the fact that Mitscherlich and Berthier were able to
+make augite artificially, but could never succeed in forming
+hornblende. Lastly, Gustavus Rose fused a mass of hornblende in a
+porcelain furnace, and found that it did not, on cooling, assume
+its previous shape, but invariably took that of augite. The same
+mineralogist observed certain crystals called Uralite (see Table,
+<a href="#page499">p. 499</a>) in rocks from Siberia, which
+possessed the cleavage and chemical composition of hornblende,
+while they had the external form of augite.</p>
+
+<p>If, from these data, it is inferred that the same substance
+<a name="page503"></a>may assume the crystalline forms of hornblende or augite
+indifferently, according to the more or less rapid cooling of the
+melted mass, it is nevertheless certain that the variety commonly
+called augite, and recognised by a peculiar crystalline form, has
+usually more lime in it, and less alumina, than that called
+hornblende, although the quantities of these elements do not seem
+to be always the same. Unquestionably the facts and experiments
+above mentioned show the very near affinity of hornblende and
+augite; but even the convertibility of one into the other, by
+melting and recrystallising, does not perhaps demonstrate their
+absolute identity. For there is often some portion of the materials
+in a crystal which are not in perfect chemical combination with the
+rest. Carbonate of lime, for example, sometimes carries with it a
+considerable quantity of silex into its own form of crystal, the
+silex being mechanically mixed as sand, and yet not preventing the
+carbonate of lime from assuming the form proper to it. This is an
+extreme case, but in many others some one or more of the
+ingredients in a crystal may be excluded from perfect chemical
+union; and after fusion, when the mass recrystallises, the same
+elements may combine perfectly or in new proportions, and thus a
+new mineral may be produced. Or some one of the gaseous elements of
+the atmosphere, the oxygen for example, may, when the melted matter
+reconsolidates, combine with some one of the component
+elements.</p>
+
+<p>The different quantity of the impurities or the refuse above
+alluded to, which may occur in all but the most transparent and
+perfect crystals, may partly explain the discordant results at
+which experienced chemists have arrived in their analysis of the
+same mineral. For the reader will often find that crystals of a
+mineral determined to be the same by physical characters,
+crystalline form, and optical properties, have been declared by
+skilful analysers to be composed of distinct elements. This
+disagreement seemed at first subversive of the atomic theory, or
+the doctrine that there is a fixed and constant relation between
+the crystalline form and structure of a mineral and its chemical
+composition. The apparent anomaly, however, which threatened to
+throw the whole science of mineralogy into confusion, was
+reconciled to fixed principles by the discoveries of Professor
+Mitscherlich at Berlin, who ascertained that the composition of the
+minerals which had appeared so variable was governed by a general
+law, to which he gave the name of <i>isomorphism</i> (from <i>
+isos,</i> equal, and <i>morphe,</i> form). According to this law,
+the ingredients of a given species of mineral are not
+<a name="page504"></a>absolutely fixed as to their kind and quality; but one
+ingredient may be replaced by an equivalent portion of some
+analogous ingredient. Thus, in augite, the lime may be in part
+replaced by portions of protoxide of iron, or of manganese, while
+the form of the crystal, and the angle of its cleavage planes,
+remain the same. These vicarious substitutions, however, of
+particular elements cannot exceed certain defined limits.</p>
+
+<p>
+<b>Basaltic Rocks.</b>&mdash;The two principal families of trappean or volcanic
+rocks are the basalts and the trachytes, which differ chiefly from each other
+in the quantity of silica which they contain. The basaltic rocks are
+comparatively poor in silica, containing less than 50 per cent of that mineral,
+and none in a pure state or as free quartz, apart from the rest of the matrix.
+They contain a larger proportion of lime and magnesia than the trachytes, so
+that they are heavier, independently of the frequent presence of the oxides of
+iron which in some cases forms more than a fourth part of the whole mass. Abich
+has, therefore, proposed that we should weigh these rocks, in order to
+appreciate their composition in cases where it is impossible to separate their
+component minerals. Thus, basalt from Staffa, containing 47&middot;80 per cent
+of silica, has a specific gravity of 2&middot;95; whereas trachyte, which has
+66 per cent of silica, has a specific gravity of only 2&middot;68; trachytic
+porphyry, containing 69 per cent of silica, a specific gravity of only
+2&middot;58. If we then take a rock of intermediate composition, such as that
+prevailing in the Peak of Teneriffe, which Abich calls Trachyte-dolerite, its
+proportion of silica being intermediate, or 58 per cent, it weighs 2&middot;78,
+or more than trachyte, and less than basalt.<a href="#fn-28.4"
+name="fnref-28.4" id="fnref-28.4"><sup>[4]</sup></a>
+</p>
+
+<p><i>Basalt.</i>&mdash;The different varieties of this rock are
+distinguished by the names of basalts, anamezites, and dolerites,
+names which, however, only denote differences in texture without
+implying any difference in mineral or chemical composition: the
+term <i>Basalt</i> being used only when the rock is compact,
+amorphous, and often semi-vitreous in texture, and when it breaks
+with a perfect conchoidal fracture; when, however, it is uniformly
+crystalline in appearance, yet very close-grained, the name <i>
+Anamesite</i> (from <i>anamesos,</i> intermediate) is employed, but
+if the rock be so coarsely crystallised that its different mineral
+constituents can be easily recognised by the eye, it is called <i>
+Dolerite</i> (from <i>doleros,</i> deceitful), in allusion to the
+difficulty of distinguishing it from some of the rocks known as
+Plutonic.</p>
+
+<p><i>Melaphyre</i> is often quite undistinguishable in
+external
+<a name="page505"></a>appearance from basalt, for although rarely so heavy,
+dark-coloured, or compact, it may present at times all these
+varieties of texture. Both these rocks are composed of triclinic
+feldspar and augite with more or less olivine, magnetic or
+titaniferous oxide of iron, and usually a little nepheline,
+leucite, and apatite; basalt usually contains considerably more
+olivine than melaphyre, but chemically they are closely allied,
+although the melaphyres usually contain more silica and alumina,
+with less oxides of iron, lime, and magnesia, than the basalts. The
+Rowley Hills in Staffordshire, commonly known as Rowley Ragstone,
+are melaphyre.</p>
+
+<p><i>Greenstone.</i>&mdash;This name has usually been extended to
+all granular mixtures, whether of hornblende and feldspar, or of
+augite and feldspar. The term <i>diorite</i> has been applied
+exclusively to compounds of hornblende and triclinic feldspar. <i>
+Labrador-rock</i> is a term used for a compound of labradorite or
+labrador-feldspar and hypersthene; when the hypersthene
+predominates it is sometimes known under the name of <i>
+Hypersthene-rock.</i> <i>Gabbro</i> and <i>Diabase</i> are rocks
+mainly composed of triclinic feldspars and diallage. All these
+rocks become sometimes very crystalline, and help to connect the
+volcanic with the Plutonic formations, which will be treated of in
+Chapter XXXI.</p>
+
+<p><b>Trachytic Rocks.</b>&mdash;The name trachyte (from [**Greek]<i>
+trachus,</i> rough) was originally given to a coarse granular
+feldspathic rock which was rough and gritty to the touch. The term
+was subsequently made to include other rocks, such as clinkstone
+and obsidian, which have the same mineral composition, but to
+which, owing to their different texture, the word in its original
+meaning would not apply. The feldspars which occur in Trachytic
+rocks are invariably those which contain the largest proportion of
+silica, or from 60 to 70 per cent of that mineral. Through the base
+are usually disseminated crystals of glassy feldspar, mica, and
+sometimes hornblende. Although quartz is not a necessary ingredient
+in the composition of this rock, it is very frequently present, and
+the quartz trachytes are very largely developed in many volcanic
+districts. In this respect the trachytes differ entirely from the
+members of the Basaltic family, and are more nearly allied to the
+granites.</p>
+
+<p><i>Obsidian.</i>&mdash;Obsidian, Pitchstone, and Pearlstone are
+only different forms of a volcanic glass produced by the fusion of
+trachytic rocks. The distinction between them is caused by
+different rates of cooling from the melted state, as has been
+proved by experiment. Obsidian is of a black or ash-grey colour,
+and though opaque in mass is transparent in thin edges.</p>
+
+<p>
+<a name="page506"></a><i>Clinkstone or Phonolite.</i>&mdash;Among the rocks of the
+trachytic family, or those in which the feldspars are rich in
+silica, that termed Clinkstone or Phonolite is conspicuous by its
+fissile structure, and its tendency to lamination, which is such as
+sometimes to render it useful as roofing-slate. It rings when
+struck with the hammer, whence its name; is compact, and usually of
+a greyish blue or brownish colour; is variable in composition, but
+almost entirely composed of feldspar. When it contains disseminated
+crystals of feldspar, it is called <i>Clinkstone porphyry.</i></p>
+
+<p><b>Volcanic Rocks distinguished by special Forms of
+Structure.</b>&mdash;Many volcanic rocks are commonly spoken of
+under names denoting structure alone, which must not be taken to
+imply that they are distinct rocks, i.e., that they differ from one
+another either in mineral or chemical composition. Thus the terms
+Trachytic porphyry, Trachytic tuff, etc., merely refer to the same
+rock under different conditions of mechanical aggregation or
+crystalline development which would be more correctly expressed by
+the use of the adjective, as porphyritic trachyte, etc., but as
+these terms are so commonly employed it is considered advisable to
+direct the student&rsquo;s attention to them.</p>
+
+<img src="images/fig586.jpg" width="179" height="232" alt=
+"Fig. 586: Porphyry. White crystals of feldspar in a dark base of hornblende
+and feldspar." />
+
+<p><i>Porphyry</i> is one of this class, and very characteristic of
+the volcanic formations. When distinct crystals of one or more
+minerals are scattered through an earthy or compact base, the rock
+is termed a porphyry (see Fig. 586). Thus trachyte is usually
+porphyritic; for in it, as in many modern lavas, there are crystals
+of feldspar; but in some porphyries the crystals are of augite,
+olivine, or other minerals. If the base be greenstone, basalt, or
+pitchstone, the rock may be denominated greenstone-porphyry,
+pitchstone-porphyry, and so forth. The old classical type of this
+form of rock is the red porphyry of Egypt, or the well-known
+&ldquo;Rosso antico.&rdquo; It consists, according to Delesse, of a
+red feldspathic base in which are disseminated rose-coloured
+crystals of the feldspar called oligoclase, with some plates of
+blackish hornblende and grains of oxide of iron (iron-glance). <i>
+Red quartziferous porphyry</i> is a much more siliceous rock,
+containing about 70 or 80 per cent of silex, while that of Egypt
+has only 62 per cent.</p>
+
+<p>
+<a name="page507"></a><i>Amygdaloid.</i>&mdash;This is also another form of igneous
+rock, admitting of every variety of composition. It comprehends any
+rock in which round or almond-shaped nodules of some mineral, such
+as agate, chalcedony, calcareous spar, or zeolite, are scattered
+through a base of wacke, basalt, greenstone, or other kind of trap.
+It derives its name from the Greek word <i>amygdalon,</i> an
+almond. The origin of this structure cannot be doubted, for we may
+trace the process of its formation in modern lavas. Small pores or
+cells are caused by bubbles of steam and gas confined in the melted
+matter. After or during consolidation, these empty spaces are
+gradually filled up by matter separating from the mass, or
+infiltered by water permeating the rock. As these bubbles have been
+sometimes lengthened by the flow of the lava before it finally
+cooled, the contents of such cavities have the form of almonds. In
+some of the amygdaloidal traps of Scotland, where the nodules have
+decomposed, the empty cells are seen to have a glazed or vitreous
+coating, and in this respect exactly resemble scoriaceous lavas, or
+the slags of furnaces.</p>
+
+<img src="images/fig587.jpg" width="206" height="259" alt=
+"Fig. 587: Scoriaceous lava in part converted into an amygdaloid." />
+
+<p>Fig. 587 represents a fragment of stone taken from the upper
+part of a sheet of basaltic lava in Auvergne. One-half is
+scoriaceous, the pores being perfectly empty; the other part is
+amygdaloidal, the pores or cells being mostly filled up with
+carbonate of lime, forming white kernels.</p>
+
+<p><i>Lava.</i>&mdash;This term has a somewhat vague signification,
+having been applied to all melted matter observed to flow in
+streams from volcanic vents. When this matter consolidates in the
+open air, the upper part is usually scoriaceous, and the mass
+becomes more and more stony as we descend, or in proportion as it
+has consolidated more slowly and under greater pressure. At the
+bottom, however, of a stream of lava, a small portion of
+scoriaceous rock very frequently occurs, formed by the first thin
+sheet of liquid matter, which often precedes the main current, and
+solidifies under slight pressure.</p>
+
+<p>
+The more compact lavas are often porphyritic, but even the scoriaceous part
+sometimes contains imperfect crystals, which have been derived from some older
+rocks, in which <a name="page508"></a>the crystals pre-existed, but were not
+melted, as being more infusible in their nature. Although melted matter rising
+in a crater, and even that which enters a rent on the side of a crater, is
+called lava, yet this term belongs more properly to that which has flowed
+either in the open air or on the bed of a lake or sea. If the same fluid has
+not reached the surface, but has been merely injected into fissures below
+ground, it is called trap. There is every variety of composition in lavas; some
+are trachytic, as in the Peak of Teneriffe; a great number are basaltic, as in
+Vesuvius and Auvergne; others are andesitic, as those of Chili; some of the
+most modern in Vesuvius consist of green augite, and many of those of Etna of
+augite and labrador-feldspar.<a href="#fn-28.5" name="fnref-28.5"
+id="fnref-28.5"><sup>[5]</sup></a>
+</p>
+
+<p><i>Scoriæ</i> and <i>Pumice</i> may next be mentioned, as
+porous rocks produced by the action of gases on materials melted by
+volcanic heat. <i>Scoriæ</i> are usually of a reddish-brown
+and black colour, and are the cinders and slags of basaltic or
+augitic lavas. <i>Pumice</i> is a light, spongy, fibrous substance,
+produced by the action of gases on trachytic and other lavas; the
+relation, however, of its origin to the composition of lava is not
+yet well understood. Von Buch says that it never occurs where only
+labrador-feldspar is present.</p>
+
+<p><i>Volcanic Ash or Tuff, Trap Tuff.</i>&mdash;Small angular
+fragments of the scoriæ and pumice, above-mentioned, and the
+dust of the same, produced by volcanic explosions, form the tuffs
+which abound in all regions of active volcanoes, where showers of
+these materials, together with small pieces of other rocks ejected
+from the crater, and more or less burnt, fall down upon the land or
+into the sea. Here they often become mingled with shells, and are
+stratified. Such tuffs are sometimes bound together by a calcareous
+cement, and form a stone susceptible of a beautiful polish. But
+even when little or no lime is present, there is a great tendency
+in the materials of ordinary tuffs to cohere together. The term <i>
+volcanic ash</i> has been much used for rocks of all ages supposed
+to have been derived from matter ejected in a melted state from
+volcanic orifices. We meet occasionally with extremely compact beds
+of volcanic materials, interstratified with fossiliferous rocks.
+These may sometimes be tuffs, although their density or compactness
+is such as the cause them to resemble many of those kinds of trap
+which are found in ordinary dikes.</p>
+
+<p><i>Wacke</i> is a name given to a decomposed state of various
+trap rocks of the basaltic family, or those which are poor in
+silica. It resembles clay of a yellowish or brown colour, and
+<a name="page509"></a>passes gradually from the soft state to the hard dolerite,
+greenstone, or other trap rock from which it has been derived.</p>
+
+<p><i>Agglomerate.</i>&mdash;In the neighbourhood of volcanic
+vents, we frequently observe accumulations of angular fragments of
+rocks formed during eruptions by the explosive action of steam,
+which shatters the subjacent stony formations, and hurls them up
+into the air. They then fall in showers around the cone or crater,
+or may be spread for some distance over the surrounding country.
+The fragments consist usually of different varieties of scoriaceous
+and compact lavas; but other kinds of rock, such as granite or even
+fossiliferous limestones, may be intermixed; in short, any
+substance through which the expansive gases have forced their way.
+The dispersion of such materials may be aided by the wind, as it
+varies in direction or intensity, and by the slope of the cone down
+which they roll, or by floods of rain, which often accompany
+eruptions. But if the power of running water, or of the waves and
+currents of the sea, be sufficient to carry the fragments to a
+distance, it can scarcely fail to wear off their angles, and the
+formation then becomes a <i>conglomerate.</i> If occasionally
+globular pieces of scoriæ abound in an agglomerate, they may
+not owe their round form to attrition. When all the angular
+fragments are of volcanic rocks the mass is usually termed a
+volcanic breccia.</p>
+
+<p><i>Laterite</i> is a red or brick-like rock composed of silicate
+of alumina and oxide of iron. The red layers called &ldquo;ochre
+beds,&rdquo; dividing the lavas of the Giant&rsquo;s Causeway, are
+laterites. These were found by Delesse to be trap impregnated with
+the red oxide of iron, and in part reduced to kaolin. When still
+more decomposed, they were found to be clay coloured by red ochre.
+As two of the lavas of the Giant&rsquo;s Causeway are parted by a
+bed of lignite, it is not improbable that the layers of laterite
+seen in the Antrim cliffs resulted from atmospheric decomposition.
+In Madeira and the Canary Islands streams of lava of subaërial
+origin are often divided by red bands of laterite, probably ancient
+soils formed by the decomposition of the surfaces of lava-currents,
+many of these soils having been coloured red in the atmosphere by
+oxide of iron, others burnt into a red brick by the overflowing of
+heated lavas. These red bands are sometimes prismatic, the small
+prisms being at right angles to the sheets of lava. Red clay or red
+marl, formed as above stated by the disintegration of lava,
+scoriæ, or tuff, has often accumulated to a great thickness
+in the valleys of Madeira, being washed into them by alluvial
+action; and some of the thick beds of
+<a name="page510"></a>laterite in India may have had a similar origin. In India,
+however, especially in the Deccan, the term &ldquo;laterite&rdquo;
+seems to have been used too vaguely to answer the above definition.
+The vegetable soil in the gardens of the suburbs of Catania which
+was overflowed by the lava of 1669 was turned or burnt into a layer
+of red brick-coloured stone, or in other words, into laterite,
+which may now be seen supporting the old lava-current.</p>
+
+<p>
+<b>Columnar and Globular Structure.</b>&mdash;One of the characteristic forms
+of volcanic rocks, especially of basalt, is the columnar, where large masses
+are divided into regular prisms, sometimes easily separable, but in other cases
+adhering firmly together. The columns vary, in the number of angles, from three
+to twelve; but they have most commonly from five to seven sides. They are often
+divided transversely, at nearly equal distances, like the joints in a vertebral
+column, as in the Giant&rsquo;s Causeway, in Ireland. They vary exceedingly in
+respect to length and diameter. Dr. MacCulloch mentions some in Skye which are
+about 400 feet long; others, in Morven, not exceeding an inch. In regard to
+diameter, those of Ailsa measure nine feet, and those of Morven an inch or
+less.<a href="#fn-28.6" name="fnref-28.6" id="fnref-28.6"><sup>[6]</sup></a>
+They are usually straight, but sometimes curved; and examples of both these
+occur in the island of Staffa. In a horizontal bed or sheet of trap the columns
+are vertical; in a vertical dike they are horizontal.
+</p>
+
+<p><img src="images/fig588.jpg" width="332" height="181" alt=
+"Fig. 588: Lava of La Coupe d’Ayzac, near Antraigue, in the Department of Ardêche." />
+</p>
+
+<p>It being assumed that columnar trap has consolidated from a
+fluid state, the prisms are said to be always at right angles to
+the <i>cooling surfaces.</i> If these surfaces, therefore, instead
+of being either perpendicular or horizontal, are curved, the
+columns ought to be inclined at every angle to the horizon; and
+there is a beautiful exemplification of this phenomenon in one of
+the valleys of the Vivarais, a mountainous
+<a name="page511"></a>district in the South of France, where, in the midst of a region
+of gneiss, a geologist encounters unexpectedly several volcanic
+cones of loose sand and scoriæ. From the crater of one of
+these cones, called La Coupe d&rsquo;Ayzac, a stream of lava has
+descended and occupied the bottom of a narrow valley, except at
+those points where the river Volant, or the torrents which join it,
+have cut away portions of the solid lava. Fig. 588 represents the
+remnant of the lava at one of these points. It is clear that the
+lava once filled the whole valley up to the dotted line <i>d a</i>;
+but the river has gradually swept away all below that line, while
+the tributary torrent has laid open a transverse section; by which
+we perceive, in the first place, that the lava is composed, as
+usual in this country, of three parts: the uppermost, at <i>a,</i>
+being scoriaceous, the second <i>b,</i> presenting irregular
+prisms; and the third, <i>c,</i> with regular columns, which are
+vertical on the banks of the Volant, where they rest on a
+horizontal base of gneiss, but which are inclined at an angle of
+45&deg;, at <i>g,</i> and are nearly horizontal at <i>f,</i> their
+position having been everywhere determined, according to the law
+before mentioned, by the form of the original valley.</p>
+
+<img src="images/fig589.jpg" width="172" height="251" alt=
+"Fig. 589: Columnar basalt in the Vicentin." />
+
+<p>
+In Fig. 589, a view is given of some of the inclined and curved columns which
+present themselves on the sides of the valleys in the hilly region north of
+Vicenza, in Italy, and at the foot of the higher Alps.<a href="#fn-28.7"
+name="fnref-28.7" id="fnref-28.7"><sup>[7]</sup></a> Unlike those of the
+Vivarais, last mentioned, the basalt of this country was evidently submarine,
+and the present valleys have since been hollowed out by denudation.
+</p>
+
+<p>The columnar structure is by no means peculiar to the trap rocks
+in which augite abounds; it is also observed in trachyte, and other
+feldspathic rocks of the igneous class, although in these it is
+rarely exhibited in such regular polygonal forms. It has been
+already stated that basaltic columns are often divided by
+cross-joints. Sometimes each segment, instead of an angular,
+assumes a spheroidal form, so that a pillar is made up of a pile of
+balls, usually flattened, as in the Cheese-grotto at
+Bertrich-Baden, in the Eifel, near the Moselle (Fig. 590). The
+basalt there is part of a small
+<a name="page512"></a>stream of lava, from 30 to 40 feet thick, which has proceeded
+from one of several volcanic craters, still extant, on the
+neighbouring heights.</p>
+
+<img src="images/fig590.jpg" width="281" height="269" alt=
+"Fig. 590: Basaltic pillars of Käsegrotte, Bertrich-Baden, half-way between
+Trèves and Coblenz." />
+
+<p>
+In some masses of decomposing greenstone, basalt, and other trap rocks, the
+globular structure is so conspicuous that the rock has the appearance of a heap
+of large cannon balls. According to M. Delesse, the centre of each spheroid has
+been a centre of crystallisation, around which the different minerals of the
+rock arranged themselves symmetrically during the process of cooling. But it
+was also, he says, a centre of contraction, produced by the same cooling, the
+globular form, therefore, of such spheroids being the combined result of
+crystallisation and contraction.<a href="#fn-28.8" name="fnref-28.8"
+id="fnref-28.8"><sup>[8]</sup></a>
+</p>
+
+<img src="images/fig591.jpg" width="172" height="337" alt=
+"Fig. 591: Globiform pitchstone. Chiaja di Luna, Isle of Ponza." />
+
+<p>
+Mr. Scrope gives as an illustration of this structure a resinous trachyte or
+pitchstone-porphyry in one of the Ponza islands, which rise from the
+Mediterranean, off the coast of Terracina and Gaeta. The globes vary from a few
+inches to three feet in diameter, and are of an ellipsoidal form (see Fig.
+591). The whole rock is in a state of decomposition, &ldquo;and when the
+balls,&rdquo; says Mr. Scrope, &ldquo;have been exposed a short time to the
+weather, they scale off at a touch into numerous concentric coats, like those
+of a bulbous root, inclosing a compact nucleus. The laminæ <a
+name="page513"></a>of this nucleus have not been so much loosened by
+decomposition; but the application of a ruder blow will produce a still further
+exfoliation.&rdquo;<a href="#fn-28.9" name="fnref-28.9"
+id="fnref-28.9"><sup>[9]</sup></a>
+</p>
+
+<img src="images/fig592.jpg" width="243" height="226" alt=
+"Fig. 592: Dike in valley, near Brazen Head, Madeira. (From a drawing of
+Captain Basil Hall, R.N.)" />
+
+<p><b>Volcanic or Trap Dikes.</b>&mdash;The leading varieties of
+the trappean rocks&mdash;basalt, greenstone, trachyte, and the rest&mdash;are
+found sometimes in dikes penetrating stratified and unstratified
+formations, sometimes in shapeless masses protruding through or
+overlying them, or in horizontal sheets intercalated between
+strata. Fissures have already been spoken of as occurring in all
+kinds of rocks, some a few feet, others many yards in width, and
+often filled up with earth or angular pieces of stone, or with sand
+and pebbles. Instead of such materials, suppose a quantity of
+melted stone to be driven or injected into an open rent, and there
+consolidated, we have then a tabular mass resembling a wall, and
+called a trap dike. It is not uncommon to find such dikes passing
+through strata of soft materials, such as tuff, scoriæ, or
+shale, which, being more perishable than the trap, are often washed
+away by the sea, rivers, or rain, in which case the dike stands
+prominently out in the face of precipices, or on the level surface
+of a country (see Fig. 592).</p>
+
+<p>In the islands of Arran and Skye, and in other parts of
+Scotland, where sandstone, conglomerate, and other hard rocks are
+traversed by dikes of trap, the converse of the above phenomenon is
+seen. The dike, having decomposed more rapidly than the containing
+rock, has once more left open the original fissure, often for a
+distance of many yards inland from the sea-coast. There is yet
+another case, by no means uncommon in Arran and other parts of
+Scotland, where the strata in contact with the dike, and for a
+certain distance from it, have been hardened, so as to resist the
+action of the weather more than the dike itself, or the surrounding
+rocks. When this happens, two parallel walls of indurated strata
+are seen protruding above the general level of the country and
+following the course of the dike. In Fig. 593, a ground plan is
+given of a ramifying dike of greenstone,
+<a name="page514"></a>which I observed cutting through sandstone on the beach near
+Kildonan Castle, in Arran. The larger branch varies from five to
+seven feet in width, which will afford a scale of measurement for
+the whole.</p>
+
+<p><img src="images/fig593.jpg" width="303" height="148" alt=
+"Fig. 593: Ground-plan of greenstone dikes traversing sandstone." />
+</p>
+
+<p>In the Hebrides and other countries, the same masses of trap
+which occupy the surface of the country far and wide, concealing
+the subjacent stratified rocks, are seen also in the sea-cliffs,
+prolonged downward in veins or dikes, which probably unite with
+other masses of igneous rock at a greater depth. The largest of the
+dikes represented in Fig. 594, and which are seen in part of the
+coast of Skye, is no less than 100 feet in width.</p>
+
+<p><img src="images/fig594.jpg" width="329" height="101" alt=
+"Fig. 594: Trap dividing and covering sandstone near Suishnish, in Skye." />
+</p>
+
+<p>Every variety of trap-rock is sometimes found in dikes, as
+basalt, greenstone, feldspar-porphyry, and trachyte. The
+amygdaloidal traps also occur, though more rarely, and even tuff
+and breccia, for the materials of these last may be washed down
+into open fissures at the bottom of the sea, or during eruption on
+the land may be showered into them from the air. Some dikes of trap
+may be followed for leagues uninterruptedly in nearly a straight
+direction, as in the north of England, showing that the fissures
+which they fill must have been of extraordinary length.</p>
+
+<p><b>Rocks altered by Volcanic Dikes.</b>&mdash;After these
+remarks on the form and composition of dikes themselves, I shall
+describe the alterations which they sometimes produce in the rocks
+in contact with them. The changes are usually such as the heat of
+melted matter and of the entangled steam and gases might be
+expected to cause.</p>
+
+<p>
+<i>Plas-Newydd: Dike cutting through Shale.</i>&mdash;A striking example, <a
+name="page515"></a>near Plas-Newydd, in Anglesea, has been described by
+Professor Henslow.<a href="#fn-28.10" name="fnref-28.10"
+id="fnref-28.10"><sup>[10]</sup></a> The dike is 134 feet wide, and consists of
+a rock which is a compound of feldspar and augite (dolerite of some authors).
+Strata of shale and argillaceous limestone, through which it cuts
+perpendicularly, are altered to a distance of 30, or even, in some places, of
+35 feet from the edge of the dike. The shale, as it approaches the trap,
+becomes gradually more compact, and is most indurated where nearest the
+junction. Here it loses part of its schistose structure, but the separation
+into parallel layers is still discernible. In several places the shale is
+converted into hard porcelanous jasper. In the most hardened part of the mass
+the fossil shells, principally <i>Producti,</i> are nearly obliterated; yet
+even here their impressions may frequently be traced. The argillaceous
+limestone undergoes analogous mutations, losing its earthy texture as it
+approaches the dike, and becoming granular and crystalline. But the most
+extraordinary phenomenon is the appearance in the shale of numerous crystals of
+analcime and garnet, which are distinctly confined to those portions of the
+rock affected by the dike.<a href="#fn-28.11" name="fnref-28.11"
+id="fnref-28.11"><sup>[11]</sup></a> Some garnets contain as much as 20 per
+cent of lime, which they may have derived from the decomposition of the fossil
+shells or <i>Producti.</i> The same mineral has been observed, under very
+analogous circumstances, in High Teesdale, by Professor Sedgwick, where it also
+occurs in shale and limestone, altered by basalt.<a href="#fn-28.12"
+name="fnref-28.12" id="fnref-28.12"><sup>[12]</sup></a>
+</p>
+
+<p>
+<i>Antrim: Dike cutting through Chalk.</i>&mdash;In several parts of the county
+of Antrim, in the north of Ireland, chalk with flints is traversed by basaltic
+dikes. The chalk is there converted into granular marble near the basalt, the
+change sometimes extending eight or ten feet from the wall of the dike, being
+greatest near the point of contact, and thence gradually decreasing till it
+becomes evanescent. &ldquo;The extreme effect,&rdquo; says Dr. Berger,
+&ldquo;presents a dark brown crystalline limestone, the crystals running in
+flakes as large as those of coarse primitive (<i>metamorphic</i>) limestone;
+the next state is saccharine, then fine grained and arenaceous; a compact
+variety, having a porcelanous aspect and a bluish-grey colour, succeeds: this,
+towards the outer edge, becomes yellowish-white, and insensibly graduates into
+the unaltered chalk. The flints in the altered chalk usually assume a grey
+yellowish colour.&rdquo;<a href="#fn-28.13" name="fnref-28.13"
+id="fnref-28.13"><sup>[13]</sup></a> All traces of organic remains are effaced
+in that part of the limestone which is most crystalline. <a name="page516"></a>
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig595.jpg" width="337" height="147" alt="Fig. 595: Basaltic
+dikes in chalk in Island of Rathlin, Antrim. Ground-plan as seen on the beach." />
+<p class="caption">Fig. 595: Basaltic dikes in chalk in Island of Rathlin,
+Antrim. Ground-plan as seen on the beach. (Conybeare and
+Buckland<a href="#fn-28.14" name="fnref-28.14" id="fnref-28.14"><sup>[14]</sup></a>)<br/></p>
+</div>
+
+<p>
+Fig. 595 represents three basaltic dikes traversing the chalk, all within the
+distance of 90 feet. The chalk contiguous to the two outer dikes is converted
+into a finely granular marble, <i>m, m,</i> as are the whole of the masses
+between the outer dikes and the central one. The entire contrast in the
+composition and colour of the intrusive and invaded rocks, in these cases,
+renders the phenomena peculiarly clear and interesting. Another of the dikes of
+the north-east of Ireland has converted a mass of red sandstone into hornstone.
+By another, the shale of the coal-measures has been indurated, assuming the
+character of flinty slate; and in another place the slate-clay of the lias has
+been changed into flinty slate, which still retains numerous impressions of
+ammonites.<a href="#fn-28.15" name="fnref-28.15"
+id="fnref-28.15"><sup>[15]</sup></a>
+</p>
+
+<p>
+It might have been anticipated that beds of coal would, from their combustible
+nature, be affected in an extraordinary degree by the contact of melted rock.
+Accordingly, one of the greenstone dikes of Antrim, on passing through a bed of
+coal, reduces it to a cinder for the space of nine feet on each side. At
+Cockfield Fell, in the north of England, a similar change is observed.
+Specimens taken at the distance of about thirty yards from the trap are not
+distinguishable from ordinary pit-coal; those nearer the dike are like cinders,
+and have all the character of coke; while those close to it are converted into
+a substance resembling soot.<a href="#fn-28.16" name="fnref-28.16"
+id="fnref-28.16"><sup>[16]</sup></a>
+</p>
+
+<p>It is by no means uncommon to meet with the same rocks, even in
+the same districts, absolutely unchanged in the proximity of
+volcanic dikes. This great inequality in the effects of the igneous
+rocks may often arise from an original difference in their
+temperature, and in that of the entangled gases, such as is
+ascertained to prevail in different lavas, or in the same lava near
+its source and at a distance from it. The power also of the invaded
+rocks to conduct heat may vary,
+<a name="page517"></a>according to their composition, structure, and the fractures
+which they may have experienced, and perhaps, also, according to
+the quantity of water (so capable of being heated) which they
+contain. It must happen in some cases that the component materials
+are mixed in such proportions as to prepare them readily to enter
+into chemical union, and form new minerals; while in other cases
+the mass may be more homogeneous, or the proportions less adapted
+for such union.</p>
+
+<p>We must also take into consideration, that one fissure may be
+simply filled with lava, which may begin to cool from the first;
+whereas in other cases the fissure may give passage to a current of
+melted matter, which may ascend for days or months, feeding streams
+which are overflowing the country above, or being ejected in the
+shape of scoriæ from some crater. If the walls of a rent,
+moreover, are heated by hot vapour before the lava rises, as we
+know may happen on the flanks of a volcano, the additional heat
+supplied by the dike and its gases will act more powerfully.</p>
+
+<p><b>Intrusion of Trap between Strata.</b>&mdash;Masses of trap
+are not unfrequently met with intercalated between strata, and
+maintaining their parallelism to the planes of stratification
+throughout large areas. They must in some places have forced their
+way laterally between the divisions of the strata, a direction in
+which there would be the least resistance to an advancing fluid, if
+no vertical rents communicated with the surface, and a powerful
+hydrostatic pressure were caused by gases propelling the lava
+upward.</p>
+
+<p><b>Relation of Trappean Rocks to the Products of active
+Volcanoes.</b>&mdash;When we reflect on the changes above described
+in the strata near their contact with trap dikes, and consider how
+complete is the analogy or often identity in composition and
+structure of the rocks called trappean and the lavas of active
+volcanoes, it seems difficult at first to understand how so much
+doubt could have prevailed for half a century as to whether trap
+was of igneous or aqueous origin. To a certain extent, however,
+there was a real distinction between the trappean formations and
+those to which the term volcanic was almost exclusively confined. A
+large portion of the trappean rocks first studied in the north of
+Germany, and in Norway, France, Scotland, and other countries, were
+such as had been formed entirely under water, or had been injected
+into fissures and intruded between strata, and which had never
+flowed out in the air, or over the bottom of a shallow sea. When
+these products, therefore, of submarine or subterranean igneous
+action were contrasted with loose cones of scoriæ, tuff, and
+lava, or with narrow streams of lava in
+<a name="page518"></a>great part scoriaceous and porous, such as were observed to have
+proceeded from Vesuvius and Etna, the resemblance seemed remote and
+equivocal. It was, in truth, like comparing the roots of a tree
+with its leaves and branches, which, although the belong to the
+same plant, differ in form, texture, colour, mode of growth, and
+position. The external cone, with its loose ashes and porous lava,
+may be likened to the light foliage and branches, and the rocks
+concealed far below, to the roots. But it is not enough to say of
+the volcano,</p>
+
+<p class="poem">
+                  &ldquo;Quantum vertice in auras<br/>
+     Ætherias, tantum radice in Tartara tendit,&rdquo;
+</p>
+
+<p class="noindent">
+for its roots do literally reach downward to Tartarus, or to the regions of
+subterranean fire; and what is concealed far below is probably always more
+important in volume and extent than what is visible above ground.
+</p>
+
+<img src="images/fig596.jpg" width="171" height="164" alt=
+"Fig. 596: Strata intercepted by a trap dike, and covered with alluvium." />
+
+<p>
+We have already stated how frequently dense masses of strata have been removed
+by denudation from wide areas (see Chapter VI); and this fact prepares us to
+expect a similar destruction of whatever may once have formed the uppermost
+part of ancient submarine or subaërial volcanoes, more especially as those
+superficial parts are always of the lightest and most perishable materials. The
+abrupt manner in which dikes of trap usually terminate at the surface (see Fig.
+596), and the water-worn pebbles of trap in the alluvium which covers the dike,
+prove incontestably that whatever was uppermost in these formations has been
+swept away. It is easy, therefore, to conceive that what is gone in regions of
+trap may have corresponded to what is now visible in active volcanoes.
+</p>
+
+<p>
+As to the absence of porosity in the trappean formations, the appearances are
+in a great degree deceptive, for all amygdaloids are, as already explained,
+porous rocks, into the cells of which mineral matter such as silex, carbonate
+of lime, and other ingredients, have been subsequently introduced (see <a href=
+"#page507">p. 507</a>); sometimes, perhaps, by secretion during the cooling and
+consolidation of lavas. In the Little Cumbray, one of the Western Islands, near
+Arran, the amygdaloid sometimes contains elongated cavities filled with brown
+spar; and when the nodules have been washed out, the <a
+name="page519"></a>interior of the cavities is glazed with the vitreous varnish
+so characteristic of the pores of slaggy lavas. Even in some parts of this rock
+which are excluded from air and water, the cells are empty, and seem to have
+always remained in this state, and are therefore undistinguishable from some
+modern lavas.<a href="#fn-28.17" name="fnref-28.17"
+id="fnref-28.17"><sup>[17]</sup></a>
+</p>
+
+<p>
+Dr. MacCulloch, after examining with great attention these and the other
+igneous rocks of Scotland, observes, &ldquo;that it is a mere dispute about
+terms, to refuse to the ancient eruptions of trap the name of submarine
+volcanoes; for they are such in every essential point, although they no longer
+eject fire and smoke.&rdquo; The same author also considers it not improbable
+that some of the volcanic rocks of the same country may have been poured out in
+the open air.<a href="#fn-28.18" name="fnref-28.18"
+id="fnref-28.18"><sup>[18]</sup></a>
+</p>
+
+<p>It will be seen in the following chapters that in the
+earth&rsquo;s crust there are volcanic tuffs of all ages,
+containing marine shells, which bear witness to eruptions at many
+successive geological periods. These tuffs, and the associated
+trappean rocks, must not be compared to lava and scoriæ which
+had cooled in the open air. Their counterparts must be sought in
+the products of modern submarine volcanic eruptions. If it be
+objected that we have no opportunity of studying these last, it may
+be answered, that subterranean movements have caused, almost
+everywhere in regions of active volcanoes, great changes in the
+relative level of land and sea, in times comparatively modern, so
+as to expose to view the effects of volcanic operations at the
+bottom of the sea.</p>
+
+<p class="footnote">
+<a name="fn-28.1" id="fn-28.1"></a> <a href="#fnref-28.1">[1]</a>
+Principles, vol. ii, pp. 56 and 145.
+</p>
+
+<p class="footnote">
+<a name="fn-28.2" id="fn-28.2"></a> <a href="#fnref-28.2">[2]</a>
+Memoir on Mount Etna, Phil. Trans., 1858.
+</p>
+
+<p class="footnote">
+<a name="fn-28.3" id="fn-28.3"></a> <a href="#fnref-28.3">[3]</a>
+For analyses of these minerals see the Mineralogies of Dana and Bristow.
+</p>
+
+<p class="footnote">
+<a name="fn-28.4" id="fn-28.4"></a> <a href="#fnref-28.4">[4]</a>
+Dr. Daubeny on Volcanoes, 2nd ed., pp. 14, 15.
+</p>
+
+<p class="footnote">
+<a name="fn-28.5" id="fn-28.5"></a> <a href="#fnref-28.5">[5]</a>
+G. Hose, Ann. des Mines, tome viii, p. 32.
+</p>
+
+<p class="footnote">
+<a name="fn-28.6" id="fn-28.6"></a> <a href="#fnref-28.6">[6]</a>
+MacCulloch Sys. of Geol., vol. ii, p. 137.
+</p>
+
+<p class="footnote">
+<a name="fn-28.7" id="fn-28.7"></a> <a href="#fnref-28.7">[7]</a>
+Fortis, Mém. sur l&rsquo;Hist. Nat. de l&rsquo;Italie, tome 1., p. 233, plate
+7.
+</p>
+
+<p class="footnote">
+<a name="fn-28.8" id="fn-28.8"></a> <a href="#fnref-28.8">[8]</a>
+Delesse, sur les Roches Globuleuses, Mém. de la Soc. Géol. de France, 2 sér.,
+tome iv.
+</p>
+
+<p class="footnote">
+<a name="fn-28.9" id="fn-28.9"></a> <a href="#fnref-28.9">[9]</a>
+Scrope, Geol. Trans., 2nd series, vol. ii, p. 205.
+</p>
+
+<p class="footnote">
+<a name="fn-28.10" id="fn-28.10"></a> <a href="#fnref-28.10">[10]</a>
+Cambridge Transactions, vol. i, p. 402.
+</p>
+
+<p class="footnote">
+<a name="fn-28.11" id="fn-28.11"></a> <a href="#fnref-28.11">[11]</a>
+Ibid., vol. i, p. 410.
+</p>
+
+<p class="footnote">
+<a name="fn-28.12" id="fn-28.12"></a> <a href="#fnref-28.12">[12]</a>
+Ibid., vol. ii, p. 175.
+</p>
+
+<p class="footnote">
+<a name="fn-28.13" id="fn-28.13"></a> <a href="#fnref-28.13">[13]</a>
+Dr. Berger, Geol. Trans., 1st series, vol. iii, p. 172.
+</p>
+
+<p class="footnote">
+<a name="fn-28.14" id="fn-28.14"></a> <a href="#fnref-28.14">[14]</a>
+Geol. Trans., 1st series, vol. iii, p. 210 and plate 10.
+</p>
+
+<p class="footnote">
+<a name="fn-28.15" id="fn-28.15"></a> <a href="#fnref-28.15">[15]</a>
+Ibid., vol. iii, p. 213; and Playfair, Illus. of Hutt. Theory, s. 253.
+</p>
+
+<p class="footnote">
+<a name="fn-28.16" id="fn-28.16"></a> <a href="#fnref-28.16">[16]</a>
+Sedgwick, Camb. Trans., vol. ii, p. 37.)
+</p>
+
+<p class="footnote">
+<a name="fn-28.17" id="fn-28.17"></a> <a href="#fnref-28.17">[17]</a>
+MacCulloch, West. Islands, vol. ii, p. 487.
+</p>
+
+<p class="footnote">
+<a name="fn-28.18" id="fn-28.18"></a> <a href="#fnref-28.18">[18]</a>
+Syst. of Geol., vol. ii, p. 114.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap29"></a><a name="page520"></a>CHAPTER XXIX.<br/>
+ON THE AGES OF VOLCANIC ROCKS.</h2>
+
+<p class="letter">Tests of relative Age of Volcanic Rocks. &mdash;
+Why ancient and modern Rocks cannot be identical. &mdash; Tests by
+Superposition and intrusion. &mdash; Test by Alteration of Rocks in
+Contact. &mdash; Test by Organic Remains. &mdash; Test of Age by
+Mineral Character. &mdash; Test by Included Fragments. &mdash;
+Recent and Post-pliocene volcanic Rocks. &mdash; Vesuvius,
+Auvergne, Puy de Côme, and Puy de Pariou. &mdash; Newer
+Pliocene volcanic Rocks. &mdash; Cyclopean Isles, Etna, Dikes of
+Palagonia, Madeira. &mdash; Older Pliocene volcanic Rocks. &mdash;
+Italy. &mdash; Pliocene Volcanoes of the Eifel. &mdash; Trass.</p>
+
+<p>Having in the former part of this work referred the sedimentary
+strata to a long succession of geological periods, we have now to
+consider how far the volcanic formations can be classed in a
+similar chronological order. The tests of relative age in this
+class of rocks are four: first, superposition and intrusion, with
+or without alteration of the rocks in contact; second, organic
+remains; third, mineral characters; fourth, included fragments of
+older rocks.</p>
+
+<p>Besides these four tests it may be said, in a general way, that
+volcanic rocks of Primary or Palæozoic antiquity differ from
+those of the Secondary or Mesozoic age, and these again from the
+Tertiary and Recent. Not, perhaps, that they differed originally in
+a greater degree than the modern volcanic rocks of one region, such
+as that of the Andes, differ from those of another, such as
+Iceland, but because all rocks permeated by water, especially if
+its temperature be high, are liable to undergo a slow
+transmutation, even when they do not assume a new crystalline form
+like that of the hypogene rocks.</p>
+
+<p>Although subaërial and submarine denudation, as before
+stated, remove, in the course of ages, large portions of the upper
+or more superficial products of volcanoes, yet these are sometimes
+preserved by subsidence, becoming covered by the sea or by
+superimposed marine deposits. In this way they may be protected for
+ages from the waves of the sea, or the destroying action of rivers,
+while, at the same time, they may not sink so deep as to be exposed
+to that Plutonic action (to be spoken of in Chapter XXXI) which
+would convert them into crystalline rocks. But even in this case
+they will not remain unaltered, because they will be percolated by
+water often of high temperature, and charged with
+<a name="page521"></a>carbonate of lime, silex, iron, and other mineral ingredients,
+whereby gradual changes in the constitution of the rocks may be
+superinduced. Every geologist is aware how often silicified trees
+occur in volcanic tuffs, the perfect preservation of their internal
+structure showing that they have not decayed before the petrifying
+material was supplied.</p>
+
+<p>The porous and vesicular nature of a large part, both of the
+basaltic and trachytic lavas, affords cavities in which silex and
+carbonate of lime are readily deposited. Minerals of the zeolite
+family, the composition of which has already been alluded to, <a
+href="#page500">p. 500</a>, occur in amygdaloids and
+other trap-rocks in great abundance, and Daubrée&rsquo;s
+observations have proved that they are not always simple deposits
+of substances held in solution by the percolating waters, being
+occasionally products of the chemical action of that water on the
+rock through which they are filtered, and portions of which are
+decomposed. From these considerations it follows that the perfect
+identity of very ancient and very modern volcanic formations is
+scarcely possible.</p>
+
+<p><img src="images/fig597.jpg" width="337" height="83" alt=
+"Fig. 597: Showing melted matter forced between two strata." />
+</p>
+
+<p><b>Tests by Superposition.</b>&mdash;If a volcanic rock rest
+upon an aqueous deposit, the volcanic must be the newest of the
+two; but the like rule does not hold good where the aqueous
+formation rests upon the volcanic, for melted matter, rising from
+below, may penetrate a sedimentary mass without reaching the
+surface, or may be forced in conformably between two strata, as <i>
+b</i> below D in Fig. 597, after which it may cool down and
+consolidate. Superposition, therefore, is not of the same value as
+a test of age in the unstratified volcanic rocks as in
+fossiliferous formations. We can only rely implicitly on this test
+where the volcanic rocks are contemporaneous, not where they are
+intrusive. Now, they are said to be contemporaneous if produced by
+volcanic action which was going on simultaneously with the
+deposition of the strata with which they are associated. Thus in
+the section at D (Fig. 597), we may perhaps ascertain that the trap
+<i>b</i> flowed over the fossiliferous bed <i>c,</i> and that,
+after its consolidation, <i>a</i> was deposited upon it, <i>a</i>
+and <i>c</i> both belonging to the same geological period. But, on
+the other hand, we must conclude the trap to be intrusive, if the
+stratum <i>a</i> be altered by <i>b</i> at the point of
+contact,
+<a name="page522"></a>or if, in pursuing <i>b</i> for some distance, we find at length
+that it cuts through the stratum <i>a,</i> and then overlies it as
+at E.</p>
+
+<img src="images/fig598.jpg" width="168" height="106" alt=
+"Fig. 598: Section through sedimentary mass with melted matter." />
+
+<p>We may, however, be easily deceived in supposing the volcanic
+rock to be intrusive, when in reality it is contemporaneous; for a
+sheet of lava, as it spreads over the bottom of the sea, cannot
+rest everywhere upon the same stratum, either because these have
+been denuded, or because, if newly thrown down, they thin out in
+certain places, thus allowing the lava to cross their edges.
+Besides, the heavy igneous fluid will often, as it moves along, cut
+a channel into beds of soft mud and sand. Suppose the submarine
+lava F (Fig. 598) to have come in contact in this manner with the
+strata <i>a, b, c,</i> and that after its consolidation the strata
+<i>d, e</i> are thrown down in a nearly horizontal position, yet so
+as to lie unconformably to F, the appearance of subsequent
+intrusion will here be complete, although the trap is in fact
+contemporaneous. We must not, therefore, hastily infer that the
+rock F is intrusive, unless we find the overlying strata, <i>d,
+e,</i> to have been altered at their junction, as if by heat.</p>
+
+<p>The test of age by superposition is strictly applicable to all
+stratified volcanic tuffs, according to the rules already explained
+in the case of sedimentary deposits (see <a href=
+"#page124">p. 124</a>).</p>
+
+<p><b>Test of Age by Organic Remains.</b>&mdash;We have seen how,
+in the vicinity of active volcanoes, scoriæ, pumice, fine
+sand, and fragments of rock are thrown up into the air, and then
+showered down upon the land, or into neighbouring lakes or seas. In
+the tuffs so formed shells, corals, or any other durable organic
+bodies which may happen to be strewed over the bottom of a lake or
+sea will be imbedded, and thus continue as permanent memorials of
+the geological period when the volcanic eruption occurred.
+Tufaceous strata thus formed in the neighbourhood of Vesuvius,
+Etna, Stromboli, and other volcanoes now in islands or near the
+sea, may give information of the relative age of these tuffs at
+some remote future period when the fires of these mountains are
+extinguished. By evidence of this kind we can establish a
+coincidence in age between volcanic rocks and the different
+primary, secondary, and tertiary fossiliferous strata.</p>
+
+<p>
+The tuffs alluded to may not always be marine, but may include, in some places,
+fresh-water shells; in others, the bones of terrestrial quadrupeds. The
+diversity of organic remains in formations of this nature is perfectly
+intelligible, <a name="page523"></a>if we reflect on the wide dispersion of
+ejected matter during late eruptions, such as that of the volcano of Coseguina,
+in the province of Nicaragua, January 19, 1835. Hot cinders and fine scoriæ
+were then cast up to a vast height, and covered the ground as they fell to the
+depth of more than ten feet, for a distance of eight leagues from the crater,
+in a southerly direction. Birds, cattle, and wild animals were scorched to
+death in great numbers, and buried in ashes. Some volcanic dust fell at Chiapa,
+upward of 1200 miles, not to leeward of the volcano, as might have been
+anticipated, but to windward, a striking proof of a counter-current in the
+upper region of the atmosphere; and some on Jamaica, about 700 miles distant to
+the north-east. In the sea, also, at the distance of 1100 miles from the point
+of eruption, Captain Eden of the &ldquo;Conway&rdquo; sailed 40 miles through
+floating pumice, among which were some pieces of considerable size.<a
+href="#fn-29.1" name="fnref-29.1" id="fnref-29.1"><sup>[1]</sup></a>
+</p>
+
+<p>
+<b>Test of Age by Mineral Composition.</b>&mdash;As sediment of homogeneous
+composition, when discharged from the mouth of a large river, is often
+deposited simultaneously over a wide space, so a particular kind of lava
+flowing from a crater during one eruption may spread over an extensive area;
+thus in Iceland, in 1783, the melted matter, pouring from Skaptar Jokul, flowed
+in streams in opposite directions, and caused a continuous mass the extreme
+points of which were 90 miles distant from each other. This enormous current of
+lava varied in thickness from 100 feet to 600 feet, and in breadth from that of
+a narrow river gorge to 15 miles.<a href="#fn-29.2" name="fnref-29.2"
+id="fnref-29.2"><sup>[2]</sup></a> Now, if such a mass should afterwards be
+divided into separate fragments by denudation, we might still, perhaps,
+identify the detached portions by their similarity in mineral composition.
+Nevertheless, this test will not always avail the geologist; for, although
+there is usually a prevailing character in lava emitted during the same
+eruption, and even in the successive currents flowing from the same volcano,
+still, in many cases, the different parts even of one lava-stream, or, as
+before stated, of one continuous mass of trap, vary much in mineral composition
+and texture.
+</p>
+
+<p>In Auvergne, the Eifel, and other countries where trachyte and
+basalt are both present, the trachytic rocks are for the most part
+older than the basaltic. These rocks do, indeed, sometimes
+alternate partially, as in the volcano of Mont Dor, in Auvergne;
+and in Madeira trachytic rocks overlie an older basaltic series;
+but the trachyte occupies more generally an inferior position, and
+is cut through and overflowed by
+<a name="page524"></a>basalt. It can by no means be inferred that trachyte
+predominated at one period of the earth&rsquo;s history and basalt
+at another, for we know that trachytic lavas have been formed at
+many successive periods, and are still emitted from many active
+craters; but it seems that in each region, where a long series of
+eruptions have occurred, the lavas containing feldspar more rich in
+silica have been first emitted, and the escape of the more augitic
+kinds has followed. The hypothesis suggested by Mr. Scrope may,
+perhaps, afford a solution of this problem. The minerals, he
+observes, which abound in basalt are of greater specific gravity
+than those composing the feldspathic lavas; thus, for example,
+hornblende, augite, and olivine are each more than three times the
+weight of water; whereas common feldspar and albite have each
+scarcely more than 2&frac12; times the specific gravity of water;
+and the difference is increased in consequence of there being much
+more iron in a metallic state in basalt and greenstone than in
+trachyte and other allied feldspathic lavas. If, therefore, a large
+quantity of rock be melted up in the bowels of the earth by
+volcanic heat, the denser ingredients of the boiling fluid may sink
+to the bottom, and the lighter remaining above would in that case
+be first propelled upward to the surface by the expansive power of
+gases. Those materials, therefore, which occupy the lowest place in
+the subterranean reservoir will always be emitted last, and take
+the uppermost place on the exterior of the earth&rsquo;s crust.</p>
+
+<p><b>Test by Included Fragments.</b>&mdash;We may sometimes
+discover the relative age of two trap-rocks, or of an aqueous
+deposit and the trap on which it rests, by finding fragments of one
+included in the other in cases such as those before alluded to,
+where the evidence of superposition alone would be insufficient. It
+is also not uncommon to find a conglomerate almost exclusively
+composed of rolled pebbles of trap, associated with some
+fossiliferous stratified formation in the neighbourhood of massive
+trap. If the pebbles agree generally in mineral character with the
+latter, we are then enabled to determine its relative age by
+knowing that of the fossiliferous strata associated with the
+conglomerate. The origin of such conglomerates is explained by
+observing the shingle beaches composed of trap-pebbles in modern
+volcanoes, as at the base of Etna.</p>
+
+<p><b>Recent and Post-pliocene Volcanic Rocks.</b>&mdash;I shall
+now select examples of contemporaneous volcanic rocks of successive
+geological periods, to show that igneous causes have been in
+activity in all past ages of the world. They have been perpetually
+shifting the places where they have broken out
+<a name="page525"></a>at the earth&rsquo;s surface, and we can sometimes prove that
+those areas which are now the great theatres of volcanic action
+were in a state of perfect tranquillity at remote geological
+epochs, and that, on the other hand, in places where at former
+periods the most violent eruptions took place at the surface and
+continued for a great length of time, there has been an entire
+suspension of igneous action in historical times, and even, as in
+the British Isles, throughout a large part of the antecedent
+Tertiary Period.</p>
+
+<p>In the absence of British examples of volcanic rocks newer than
+the Upper Miocene, I may state that in other parts of the world,
+especially in those where volcanic eruptions are now taking place
+from time to time, there are tuffs and lavas belonging to that part
+of the Tertiary era the antiquity of which is proved by the
+presence of the bones of extinct quadrupeds which co-existed with
+terrestrial, fresh-water, and marine mollusca of species still
+living. One portion of the lavas, tuffs, and trap-dikes of Etna,
+Vesuvius, and the island of Ischia has been produced within the
+historical era; another and a far more considerable part originated
+at times immediately antecedent, when the waters of the
+Mediterranean were already inhabited by the existing testacea, but
+when certain species of elephant, rhinoceros, and other quadrupeds
+now extinct, inhabited Europe.</p>
+
+<p><i>Vesuvius.</i>&mdash;I have traced in the &ldquo;Principles of
+Geology&rdquo; the history of the changes which the volcanic region
+of Campania is known to have undergone during the last 2000 years.
+The aggregate effect of igneous operations during that period is
+far from insignificant, comprising as it does the formation of the
+modern cone of Vesuvius since the year 79, and the production of
+several minor cones in Ischia, together with that of Monte Nuovo in
+the year 1538. Lava-currents have also flowed upon the land and
+along the bottom of the sea&mdash;volcanic sand, pumice, and
+scoriæ have been showered down so abundantly that whole
+cities were buried&mdash;tracts of the sea have been filled up or
+converted into shoals&mdash;and tufaceous sediment has been
+transported by rivers and land-floods to the sea. There are also
+proofs, during the same recent period, of a permanent alteration of
+the relative levels of the land and sea in several places, and of
+the same tract having, near Puzzuoli, been alternately upheaved and
+depressed to the amount of more than twenty feet. In connection
+with these convulsions, there are found, on the shores of the Bay
+of Baiæ, recent tufaceous strata, filled with articles
+fabricated by the hands of man, and mingled with marine shells.</p>
+
+<p><a name="page526"></a>It has also been stated (<a href="#page206">p.
+206</a>), that when we examine this same region, it is found to
+consist largely of tufaceous strata, of a date anterior to human
+history or tradition, which are of such thickness as to constitute
+hills from 500 to more than 2000 feet in height. Some of these
+strata contain marine shells which are exclusively of living
+species, others contain a slight mixture, one or two per cent of
+species not known as living.</p>
+
+<p>The ancient part of Vesuvius is called Somma, and consists of
+the remains of an older cone which appears to have been partly
+destroyed by explosion. In the great escarpment which this remnant
+of the ancient mountain presents towards the modern cone of
+Vesuvius, there are many dikes which are for the most part
+vertical, and traverse the inclined beds of lava and scoriæ
+which were successively superimposed during those eruptions by
+which the old cone was formed. They project in relief several
+inches, or sometimes feet, from the face of the cliff, being
+extremely compact, and less destructible than the intersected tuffs
+and porous lavas. In vertical extent they vary from a few yards to
+500 feet, and in breadth from one to twelve feet. Many of them cut
+all the inclined beds in the escarpment of Somma from top to
+bottom, others stop short before they ascend above halfway. In
+mineral composition they scarcely differ from the lavas of Somma,
+the rock consisting of a base of leucite and augite, through which
+large crystals of augite and some of leucite are scattered.</p>
+
+<p>Nothing is more remarkable than the usual parallelism of the
+opposite sides of the dikes, which correspond almost as regularly
+as the two opposite faces of a wall of masonry. This character
+appears at first the more inexplicable, when we consider how jagged
+and uneven are the rents caused by earthquakes in masses of
+heterogeneous composition, like those composing the cone of Somma.
+In explanation of this phenomenon, M. Necker refers us to Sir W.
+Hamilton&rsquo;s account of an eruption of Vesuvius in the year
+1779, who records the following fact: &ldquo;The lavas, when they
+either boiled over the crater, or broke out from the conical parts
+of the volcano, constantly formed channels as regular as if they
+had been cut by art down the steep part of the mountain; and whilst
+in a state of perfect fusion, continued their course in those
+channels, which were sometimes full to the brim, and at other times
+more or less so, according to the quantity of matter in motion.</p>
+
+<p>
+&rdquo;These channels (says the same observer), I have found, upon examination
+after an eruption, to be in general from <a name="page527"></a>two to five or
+six feet wide, and seven or eight feet deep. They were often hid from the sight
+by a quantity of scoriæ that had formed a crust over them; and the lava, having
+been conveyed in a covered way for some yards, came out fresh again into an
+open channel. After an eruption, I have walked in some of those subterraneous
+or covered galleries, which were exceedingly curious, the sides, top, and
+bottom <i>being worn perfectly smooth and even</i> in most parts by the
+violence of the currents of the red-hot lavas which they had conveyed for many
+weeks successively.&rdquo; I was able to verify this phenomenon in 1858, when a
+stream of lava issued from a lateral cone.<a href="#fn-29.3" name="fnref-29.3"
+id="fnref-29.3"><sup>[3]</sup></a> Now, the walls of a vertical fissure,
+through which lava has ascended in its way to a volcanic vent, must have been
+exposed to the same erosion as the sides of the channels before adverted to.
+The prolonged and uniform friction of the heavy fluid, as it is forced and made
+to flow upward, cannot fail to wear and smooth down the surfaces on which it
+rubs, and the intense heat must melt all such masses as project and obstruct
+the passage of the incandescent fluid.
+</p>
+
+<p>
+The rock composing the dikes both in the modern and ancient part of Vesuvius is
+far more compact than that of ordinary lava, for the pressure of a column of
+melted matter in a fissure greatly exceeds that in an ordinary stream of lava;
+and pressure checks the expansion of those gases which give rise to vesicles in
+lava. There is a tendency in almost all the Vesuvian dikes to divide into
+horizontal prisms, a phenomenon in accordance with the formation of vertical
+columns in horizontal beds of lava; for in both cases the divisions which give
+rise to the prismatic structure are at right angles to the cooling surfaces.
+(See <a href="#page510"> p. 510</a>.)
+</p>
+
+<p><i>Auvergne.</i>&mdash;Although the latest eruptions in central
+France seem to have long preceded the historical era, they are so
+modern as to have a very intimate connection with the present
+superficial outline of the country and with the existing valleys
+and river-courses. Among a great number of cones with perfect
+craters, one called the Puy de Tartaret sent forth a lava-current
+which can be traced up to its crater, and which flowed for a
+distance of thirteen miles along the bottom of the present valley
+to the village of Nechers, covering the alluvium of the old valley
+in which were preserved the bones of an extinct species of horse,
+and of a lagomys and other quadrupeds all closely allied to recent
+animals, while the associated land-shells were of species now
+living, such as <i>Cyclostoma elegans, Helix hortensis, H.
+nemoralis,</i>
+<a name="page528"></a>
+<i>H. lapicida,</i> and <i>Clausilia rugosa.</i> That the
+current which has issued from the Puy de Tartaret may,
+nevertheless, be very ancient in reference to the events of human
+history, we may conclude, not only from the divergence of the
+mammiferous fauna from that of our day, but from the fact that a
+Roman bridge of such form and construction as continued in use only
+down to the fifth century, but which may be older, is now seen at a
+place about a mile and a half from St. Nectaire. This ancient
+bridge spans the river Couze with two arches, each about fourteen
+feet wide. These arches spring from the lava of Tartaret, on both
+banks, showing that a ravine precisely like that now existing had
+already been excavated by the river through that lava thirteen or
+fourteen centuries ago.</p>
+
+<p>While the river Couze has in most cases, as at the site of this
+ancient bridge, been simply able to cut a deep channel through the
+lava, the lower portion of which is shown to be columnar, the same
+torrent has in other places, where the valley was contracted to a
+narrow gorge, had power to remove the entire mass of basaltic rock,
+causing for a short space a complete breach of continuity in the
+volcanic current. The work of erosion has been very slow, as the
+basalt is tough and hard, and one column after another must have
+been undermined and reduced to pebbles, and then to sand. During
+the time required for this operation, the perishable cone of
+Tartaret, occupying the lowest part of the great valley descending
+from Mont Dor (see <a href="#page542">p. 542</a>), and
+damming up the river so as to cause the Lake of Chambon, has stood
+uninjured, proving that no great flood or deluge can have passed
+over this region in the interval between the eruption of Tartaret
+and our own times.</p>
+
+<p>
+<i>Puy de Côme.</i>&mdash;The Puy de Côme and its lava-current, near Clermont,
+may be mentioned as another minor volcano of about the same age. This conical
+hill rises from the granitic platform, at an angle of between 30&deg; and
+40&deg;, to the height of more than 900 feet. Its summit presents two distinct
+craters, one of them with a vertical depth of 250 feet. A stream of lava takes
+its rise at the western base of the hill instead of issuing from either crater,
+and descends the granitic slope towards the present site of the town of Pont
+Gibaud. Thence it pours in a broad sheet down a steep declivity into the valley
+of the Sioule, filling the ancient river-channel for the distance of more than
+a mile. The Sioule, thus dispossessed of its bed, has worked out a fresh one
+between the lava and the granite of its western bank; and the excavation <a
+name="page529"></a>has disclosed, in one spot, a wall of columnar basalt about
+fifty feet high.<a href="#fn-29.4" name="fnref-29.4"
+id="fnref-29.4"><sup>[4]</sup></a>
+</p>
+
+<p>The excavation of the ravine is still in progress, every winter
+some columns of basalt being undermined and carried down the
+channel of the river, and in the course of a few miles rolled to
+sand and pebbles. Meanwhile the cone of Côme remains
+unimpaired, its loose materials being protected by a dense
+vegetation, and the hill standing on a ridge not commanded by any
+higher ground, so that no floods of rain-water can descend upon it.
+There is no end to the waste which the hard basalt may undergo in
+future, if the physical geography of the country continue
+unchanged&mdash;no limit to the number of years during which the
+heap of incoherent and transportable materials called the Puy de
+Côme may remain in an almost stationary condition.</p>
+
+<p><i>Puy de Pariou.</i>&mdash;The brim of the crater of the Puy de
+Pariou, near Clermont, is so sharp, and has been so little blunted
+by time, that it scarcely affords room to stand upon. This and
+other cones in an equally remarkable state of integrity have stood,
+I conceive, uninjured, not <i>in spite</i> of their loose porous
+nature, as might at first be naturally supposed, but in consequence
+of it. No rills can collect where all the rain is instantly
+absorbed by the sand and scoriæ, as is remarkably the case on
+Etna; and nothing but a water-spout breaking directly upon the Puy
+de Pariou could carry away a portion of the hill, so long as it is
+not rent or ingulfed by earthquakes.</p>
+
+<p><b>Newer Pliocene Volcanic Rocks.</b>&mdash;The more ancient
+portion of Vesuvius and Etna originated at the close of the Newer
+Pliocene period, when less than ten, sometimes only one, in a
+hundred of the shells differed from those now living. In the case
+of Etna, it was before stated (<a href="#page205">p.
+205</a>) that Post-pliocene formations occur in the neighbourhood
+of Catania, while the oldest lavas of the great volcano are
+Pliocene. These last are seen associated with sedimentary deposits
+at Trezza and other places on the southern and eastern flanks of
+the great cone (see <a href="#page205">p. 205</a>).</p>
+
+<p><i>Cyclopean Islands.</i>&mdash;The Cyclopean Islands, called by
+the Sicilians Dei Faraglioni, in the sea-cliffs of which these beds
+of clay, tuff, and associated lava are laid open to view, are
+situated in the Bay of Trezza, and may be regarded as the extremity
+of a promontory severed from the main land. Here numerous proofs
+are seen of submarine eruptions, by which the argillaceous and
+sandy strata were invaded and cut through, and tufaceous breccias
+formed. Inclosed in
+<a name="page530"></a>these breccias are many angular and hardened fragments of
+laminated clay in different states of alteration by heat, and
+intermixed with volcanic sands.</p>
+
+<p><img src="images/fig599.jpg" width="350" height="255" alt=
+"Fig. 599: View of the Isle of Cyclops, in the Bay of Trezza." />
+</p>
+
+<p>The loftiest of the Cyclopean islets, or rather rocks, is about
+200 feet in height, the summit being formed of a mass of stratified
+clay, the laminæ of which are occasionally subdivided by thin
+arenaceous layers. These strata dip to the N.W., and rest on a mass
+of columnar lava (see Fig. 599) in which the tops of the pillars
+are weathered, and so rounded as to be often hemispherical.</p>
+
+<img src="images/fig600.jpg" width="172" height="294" alt=
+"Fig. 600: Contortions of strata in the largest of the Cyclopean Islands." />
+
+<p>In some places in the adjoining and largest islet of the group,
+which lies to the north-eastward of that represented in Figure
+599), the overlying clay has been greatly altered and hardened by
+the igneous rock, and occasionally contorted in the most
+extraordinary manner; yet the lamination has not been obliterated,
+but, on the contrary, rendered much more conspicuous, by the
+indurating process.</p>
+
+<p>In Fig. 600 I have represented a portion of the altered rock, a
+few feet square, where the alternating thin laminæ of sand
+and clay are contorted in a manner often observed in ancient
+metamorphic schists. A great fissure, running
+<a name="page531"></a>from east to west, nearly divides this larger island into two
+parts, and lays open its internal structure. In the section thus
+exhibited, a dike of lava is seen, first cutting through an older
+mass of lava, and then penetrating the superincumbent tertiary
+strata. In one place the lava ramifies and terminates in thin
+veins, from a few feet to a few inches in thickness (see Fig. 601).
+The arenaceous laminæ are much hardened at the point of
+contact, and the clays are converted into siliceous schist. In this
+island the altered rocks assume a honey-comb structure on their
+weathered surface, singularly contrasted with the smooth and even
+outline which the same beds present in their usual soft and
+yielding state. The pores of the lava are sometimes coated, or
+entirely filled with carbonate of lime, and with a zeolite
+resembling analcime, which has been called cyclopite. The latter
+mineral has also been found in small fissures traversing the
+altered marl, showing that the same cause which introduced the
+minerals into the cavities of the lava, whether we suppose
+sublimation or aqueous infiltration, conveyed it also into the open
+rents of the contiguous sedimentary strata.</p>
+
+<img src="images/fig601.jpg" width="184" height="248" alt=
+"Fig. 601: Newer pliocene strata invaded by lava. Isle of Cyclops (horizontal section)." />
+
+<p><i>Dikes of Palagonia.</i>&mdash;Dikes of vesicular and
+amygdaloidal lava are also seen traversing marine tuff or peperino,
+west of Palagonia, some of the pores of the lava being empty, while
+others are filled with carbonate of lime. In such cases we may
+suppose the tuff to have resulted from showers of volcanic sand and
+scoriæ, together with fragments of limestone, thrown out by a
+submarine explosion, similar to that which gave rise to Graham
+Island in 1831. When the mass was, to a certain degree,
+consolidated, it may have been rent open, so that the lava ascended
+through fissures, the walls of which were perfectly even and
+parallel. In one case, after the melted matter that filled the rent
+(Fig. 602) had cooled down, it must have been fractured and shifted
+horizontally by a lateral movement.</p>
+
+<p>In Fig. 603, the lava has more the appearance of a vein, which
+forced its way through the peperino. It is highly probable that
+similar appearances would be seen, if we could examine the floor of
+the sea in that part
+<a name="page532"></a>of the Mediterranean where the waves have recently washed away
+the new volcanic island; for when a superincumbent mass of ejected
+fragments has been removed by denudation, we may expect to see
+sections of dikes traversing tuff, or, in other words, sections of
+the channels of communication by which the subterranean lavas
+reached the surface.</p>
+
+<img src="images/fig602.jpg" width="237" height="201" alt=
+"Figs. 602 and 603: Ground-plan of dikes near Palagonia." />
+
+<p>
+<i>Madeira.</i>&mdash;Although the more ancient portion of the volcanic
+eruptions by which the island of Madeira and the neighbouring one of Porto
+Santo were built up occurred, as we shall presently see, in the Upper Miocene
+Period, a still larger part of the island is of Pliocene date. That the latest
+outbreaks belonged to the Newer Pliocene Period, I infer from the close
+affinity to the present flora of Madeira of the fossil plants preserved in a
+leaf-bed in the north-eastern part of the island. These fossils, associated
+with some lignite in the ravine of the river San Jorge, can none of them be
+proved to be of extinct species, but their antiquity may be inferred from the
+following considerations: Firstly&mdash;The leaf-bed, discovered by Mr. Hartung
+and myself in 1853, at the height of 1000 feet above the level of the sea,
+crops out at the base of a cliff formed by the erosion of a gorge cut through
+alternating layers of basalt and scoriæ, the product of a vast succession of
+eruptions of unknown date, piled up to a thickness of 1000 feet, and which were
+all poured out after the plants, of which about twenty species have been
+recognised, flourished in Madeira. These lavas are inclined at an angle of
+about 15&deg; to the north, and came down from the great central region of
+eruption. Their accumulation implies a long period of intermittent volcanic
+action, subsequently to which the ravine of San Jorge was hollowed out.
+Secondly&mdash;Some few of the plants, though perhaps all of living species,
+are supposed to be of genera not now existing in the island. They have been
+described by Sir Charles Bunbury and Professor Heer, and the former first
+pointed out that many of the leaves are of the laurel type, and analogous to
+those now flourishing in the modern forests of Madeira. He also recognised
+among them the leaves of <i>Woodwardia radicans</i>, <a
+name="page533"></a><i>and Davallia Canariensis,</i> ferns now abundant in
+Madeira. Thirdly&mdash;the great age of this leaf-bed of San Jorge, which was
+perhaps originally formed in the crater of some ancient volcanic cone
+afterwards buried under lava, is proved by its belonging to a part of the
+eastern extremity of Madeira, which, after the close of the igneous eruptions,
+became covered in the adjoining district of Caniçal with blown sand in which a
+vast number of land-shells were buried. These fossil shells belonged to no less
+than 36 species, among which are many now extremely rare in the island, and
+others, about five per cent, extinct or unknown in any part of the world.
+Several of these of the genus <i>Helix</i> are conspicuous from the peculiarity
+of their forms, others from their large dimensions. The geographical
+configuration of the country shows that this shell-bed is considerably more
+modern than the leaf-bed; it must therefore be referred to the Newer Pliocene,
+according to the definition of this period given in a former chapter (<a
+href="#page143">p. 143</a>).
+</p>
+
+<p>
+<b>Older Pliocene Period.</b>&mdash;<i>Italy.</i>&mdash;In Tuscany, as at
+Radicofani, Viterbo, and Aquapendente, and in the Campagna di Roma, submarine
+volcanic tuffs are interstratified with the Older Pliocene strata of the
+Sub-apennine hills in such a manner as to leave no doubt that they were the
+products of eruptions which occurred when the shelly marls and sands of the
+Sub-appenine hills were in the course of deposition. This opinion I expressed<a
+href="#fn-29.5" name="fnref-29.5" id="fnref-29.5"><sup>[5]</sup></a> after my
+visit to Italy in 1828 and it has recently (1850) been confirmed by the
+argument adduced by Sir R. Murchison in favour of the submarine origin of the
+tertiary volcanic rocks of Italy.<a href="#fn-29.6" name="fnref-29.6"
+id="fnref-29.6"><sup>[6]</sup></a> These rocks are well-known to rest
+conformably on the Sub-apennine marls, even as far south as Monte Mario, in the
+suburbs of Rome. On the exact age of the deposits of Monte Mario new light has
+recently been thrown by a careful study of their marine fossil shells,
+undertaken by MM. Rayneval, Van den Hecke, and Ponzi. They have compared no
+less than 160 species with the shells of the Coralline Crag of Suffolk, so well
+described by Mr. Searles Wood; and the specific agreement between the British
+and Italian fossils is so great, if we make due allowance for geographical
+distance and the difference of latitude, that we can have little hesitation in
+referring both to the same period, or to the Older Pliocene of this work. It is
+highly probable that, between the oldest trachytes of Tuscany and the newest
+rocks in the neighbourhood of Naples, a <a name="page534"></a>series of
+volcanic products might be detected of every age from the Older Pliocene to the
+historical epoch.
+</p>
+
+<p><i>Pliocene Volcanoes of the Eifel.</i>&mdash;Some of the most
+perfect cones and craters in Europe, not even excepting those of
+the district round Vesuvius, may be seen on the left or west bank
+of the Rhine, near Bonn and Andernach. They exhibit characters
+distinct from any which I have observed elsewhere, owing to the
+large part which the escape of aqueous vapour has played in the
+eruptions and the small quantities of lava emitted. The fundamental
+rocks of the district are grey and red sandstones and shales, with
+some associated limestones, replete with fossils of the Devonian or
+Old Red Sandstone group. The volcanoes broke out in the midst of
+these inclined strata, and when the present systems of hills and
+valleys had already been formed. The eruptions occurred sometimes
+at the bottom of deep valleys, sometimes on the summit of hills,
+and frequently on intervening platforms. In travelling through this
+district we often come upon them most unexpectedly, and may find
+ourselves on the very edge of a crater before we had been led to
+suspect that we were approaching the site of any igneous outburst.
+Thus, for example, on arriving at the village of Gemund,
+immediately south of Daun, we leave the stream, which flows at the
+bottom of a deep valley in which strata of sandstone and shale crop
+out. We then climb a steep hill, on the surface of which we see the
+edges of the same strata dipping inward towards the mountain. When
+we have ascended to a considerable height, we see fragments of
+scoriæ sparingly scattered over the surface; until at length,
+on reaching the summit, we find ourselves suddenly on the edge of a
+<i>tarn,</i> or deep circular lake-basin called the Gemunder Maar.
+In it we recognise the ordinary form of a crater, for which we have
+been prepared by the occurrence of scoriæ scattered over the
+surface of the soil. But on examining the walls of the crater we
+find precipices of sandstone and shale which exhibit no signs of
+the action of heat; and we look in vain for those beds of lava and
+scoriæ, dipping outward on every side, which we have been
+accustomed to consider as characteristic of volcanic vents. As we
+proceed, however, to the opposite side of the lake, we find a
+considerable quantity of scoriæ and some lava, and see the
+whole surface of the soil sparkling with volcanic sand, and strewed
+with ejected fragments of half-fused shale, which preserves its
+laminated texture in the interior, while it has a vitrified or
+scoriform coating.</p>
+
+<p>Other crater lakes of circular or oval form, and hollowed out of
+similar ancient strata, occur in the Upper Eifel, where
+<a name="page535"></a>copious aëriform discharges have taken place, throwing out
+vast heaps of pulverized shale into the air. I know of no other
+extinct volcanoes where gaseous explosions of such magnitude have
+been attended by the emission of so small a quantity of lava. Yet I
+looked in vain in the Eifel for any appearances which could lend
+support to the hypothesis that the sudden rushing out of such
+enormous volumes of gas had ever lifted up the stratified rocks
+immediately around the vent so as to form conical masses, having
+their strata dipping outward on all sides from a central axis, as
+is assumed in the theory of elevation craters, alluded to in the
+last chapter.</p>
+
+<p>I have already given (<a href="images/fig590.jpg">Fig. 590</a>)
+an example in the Eifel of a small stream of lava which issued from
+one of the craters of that district at Bertrich-Baden. It shows
+that when some of these volcanoes were in action the valleys had
+already been eroded to their present depth.</p>
+
+<p><i>Trass.</i>&mdash;The tufaceous alluvium called <i>trass,</i>
+which has covered large areas in the Eifel, and choked up some
+valleys now partially re-excavated, is unstratified. Its base
+consists almost entirely of pumice, in which are included fragments
+of basalt and other lavas, pieces of burnt shale, slate, and
+sandstone, and numerous trunks and branches of trees. If, as is
+probable, this trass was formed during the period of volcanic
+eruptions, it may have originated in the manner of the moya of the
+Andes.</p>
+
+<p>We may easily conceive that a similar mass might now be
+produced, if a copious evolution of gases should occur in one of
+the lake-basins. If a breach should be made in the side of the
+cone, the flood would sweep away great heaps of ejected fragments
+of shale and sandstone, which would be borne down into the
+adjoining valleys. Forests might be torn up by such a flood, and
+thus the occurrence of the numerous trunks of trees dispersed
+irregularly through the trass can be explained. The manner in which
+this trass conforms to the shape of the present valleys implies its
+comparatively modern origin, probably not dating farther back than
+the Pliocene Period.
+</p>
+
+<p class="footnote">
+<a name="fn-29.1" id="fn-29.1"></a> <a href="#fnref-29.1">[1]</a>
+Caldcleugh, Phil. Trans., 1836, p. 27.
+</p>
+
+<p class="footnote">
+<a name="fn-29.2" id="fn-29.2"></a> <a href="#fnref-29.2">[2]</a>
+See Principles, <i>Index,</i> &ldquo;Skaptar Jokul.&rdquo;
+</p>
+
+<p class="footnote">
+<a name="fn-29.3" id="fn-29.3"></a> <a href="#fnref-29.3">[3]</a>
+Principles of Geology, vol. i, p. 626.
+</p>
+
+<p class="footnote">
+<a name="fn-29.4" id="fn-29.4"></a> <a href="#fnref-29.4">[4]</a>
+Scrope&rsquo;s Central France, p. 60, and plate.
+</p>
+
+<p class="footnote">
+<a name="fn-29.5" id="fn-29.5"></a> <a href="#fnref-29.5">[5]</a>
+See 1st edit. of Principles of Geology, vol. iii, chaps. xiii and xiv, 1833;
+and former editions of this work, chap. xxxi.
+</p>
+
+<p class="footnote">
+<a name="fn-29.6" id="fn-29.6"></a> <a href="#fnref-29.6">[6]</a>
+Quart. Geol. Journ., vol. vi, p. 281.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap30"></a><a name="page536"></a>CHAPTER XXX.<br/>
+AGE OF VOLCANIC ROCKS&mdash;<i>continued.</i></h2>
+
+<p class="letter">Volcanic Rocks of the Upper Miocene Period.
+&mdash; Madeira. &mdash; Grand Canary. &mdash; Azores. &mdash;
+Lower Miocene Volcanic Rocks. &mdash; Isle of Mull. &mdash; Staffa
+and Antrim. &mdash; The Eifel. &mdash; Upper and Lower Miocene
+Volcanic Rocks of Auvergne. &mdash; Hill of Gergovia. &mdash;
+Eocene Volcanic Rocks of Monte Bolca. &mdash; Trap of Cretaceous
+Period. &mdash; Oolitic Period. &mdash; Triassic Period. &mdash;
+Permian Period. &mdash; Carboniferous Period. &mdash; Erect Trees
+buried in Volcanic Ash in the Island of Arran. &mdash; Old Red
+Sandstone Period. &mdash; Silurian Period. &mdash; Cambrian Period.
+&mdash; Laurentian Volcanic Rocks.</p>
+
+<p><b>Volcanic Rocks of the Upper Miocene
+Period.</b>&mdash;<i>Madeira.</i>&mdash;The greater part of the
+volcanic eruptions of Madeira, as we have already seen (<a href=
+"#page532">p. 532</a>), belong to the Pliocene Period,
+but the most ancient of them are of Upper Miocene date, as shown by
+the fossil shells included in the marine tuffs which have been
+upraised at San Vicente, in the northern part of the island, to the
+height of 1300 feet above the level of the sea. A similar marine
+and volcanic formation constitutes the fundamental portion of the
+neighbouring island of Porto Santo, forty miles distant from
+Madeira, and is there elevated to an equal height, and covered, as
+in Madeira, with lavas of supra-marine origin.</p>
+
+<p>The largest number of fossils have been collected from the tuffs
+and conglomerates and some beds of limestone in the island of
+Baixo, off the southern extremity of Porto Santo. They amount in
+this single locality to more than sixty in number, of which about
+fifty are mollusca, but many of these are only casts. Some of the
+shells probably lived on the spot during the intervals between
+eruptions, and some may have been cast up into the water or air
+together with muddy ejections, and, falling down again, have been
+deposited on the bottom of the sea. The hollows in some of the
+fragments of vesicular lava of which the breccias and conglomerates
+are composed are partially filled with calc-sinter, being thus half
+converted into amygdaloids. Among the fossil shells common to
+Madeira and Porto Santo, large cones, strombs, and cowries are
+conspicuous among the univalves, and <i>Cardium, Spondylus,</i> and
+<i>Lithodomus</i> among the lamellibranchiate bivalves, and among
+the <i>Echinoderms</i> the large Clypeaster called <i>C. altus,</i>
+an extinct European Miocene fossil.</p>
+
+<p>
+<a name="page537"></a>The largest list of fossils has been published by Mr. Karl
+Meyer, in Hartung&rsquo;s &ldquo;Madeira;&rdquo; but in the
+collection made by myself, and in a still larger one formed by Mr.
+J. Yate Johnson, several remarkable forms not in Meyer&rsquo;s list
+occur, as, for example, <i>Pholadomya,</i> and a large <i>
+Terebra.</i> Mr. Johnson also found a fine specimen of <i>Nautilus
+(Atruria) ziczac</i> (<a href="images/fig207.jpg">Fig. 211</a>), a
+well-known Falunian fossil of Europe; and in the same volcanic tuff
+of Baixo, the Echinoderm <i>Brissus Scillæ,</i> a living
+Mediterranean species, found fossil in the Miocene strata of Malta.
+Mr. Meyer identifies one-third of the Madeira shells with known
+European Miocene (or Falunian) forms. The huge Strombus of San
+Vicente and Porto Santo, <i>S. Italicus,</i> is an extinct shell of
+the Sub-apennine or Older Pliocene formations. The mollusca already
+obtained from various localities of Madeira and Porto Santo are not
+less than one hundred in number, and, according to the late Dr. S.
+P. Woodward, rather more than a third are of species still living,
+but many of these are not now inhabitants of the neighbouring
+sea.</p>
+
+<p>
+It has been remarked (<a href="#page212">p. 212</a>), that in the Older
+Pliocene and Upper Miocene deposits of Europe many forms occur of a more
+southern aspect than those now inhabiting the nearest sea. In like manner the
+fossil corals, or Zoantharia, six in number, which I obtained from Madeira, of
+the genera <i>Astræa, Sarcinula, Hydnophora,</i> were pronounced by Mr.
+Lonsdale to be forms foreign to the adjacent coasts, and agreeing with the
+fauna of a sea warmer than that now separating Madeira from the nearest part of
+the African coast. We learn, indeed, from the observations made in 1859, by the
+Reverend R. T. Lowe, that more than one-half, or fifty-three in ninety, of the
+marine mollusks collected by him from the sandy beach of Mogador are common
+British species, although Mogador is 18&frac12; degrees south of the nearest
+shores of England. The living shells of Madeira and Porto Santo are in like
+manner those of a temperate climate, although in great part differing
+specifically from those of Mogador.<a href="#fn-30.1" name="fnref-30.1"
+id="fnref-30.1"><sup>[1]</sup></a>
+</p>
+
+<p><i>Grand Canary.</i>&mdash;In the Canaries, especially in the
+Grand Canary, the same marine Upper Miocene formation is found.
+Stratified tuffs, with intercalated conglomerates and lavas, are
+there seen in nearly horizontal layers in sea-cliffs about 300 feet
+high, near Las Palmas. Mr. Hartung and I were unable to find marine
+shells in these tuffs at a greater elevation than 400 feet above
+the sea; but as the deposit to which they belong reaches to the
+height of 1100 feet or more in the interior, we conceive that an
+upheaval of at least that amount has
+<a name="page538"></a>taken place. The <i>Clypeaster altus, Spondylus gæderopus,
+Pectunculus pilosus, Cardita calyculata,</i> and several other
+shells, serve to identify this formation with that of the Madeiras,
+and <i>Ancillaria glandiformis,</i> which is not rare, and some
+other fossils, remind us of the faluns of Touraine.</p>
+
+<p>The sixty-two Miocene species which I collected in the Grand
+Canary were referred by the late Dr. S. P. Woodward to forty-seven
+genera, ten of which are no longer represented in the neighbouring
+sea, namely <i>Corbis,</i> an African form, Hinnites, now living in
+Oregon, <i>Thecidium</i> (<i>T. Mediterranean,</i> identical with
+the Miocene fossil of St. Juvat, in Brittany), <i>Calyptræa,
+Hipponyx, Nerita, Erato, Oliva, Ancillaria,</i> and <i>
+Fasciolaria.</i></p>
+
+<p>These tuffs of the southern shores of the Grand Canary,
+containing the Upper Miocene shells, appear to be about the same
+age as the most ancient volcanic rocks of the island, composed of
+slaty diabase, phonolite, and trachyte. Over the marine lavas and
+tuffs trachytic and basaltic products of subaërial volcanic
+origin, between 4000 and 5000 feet in thickness, have been piled,
+the central parts of the Grand Canary reaching the height of about
+6000 feet above the level of the sea. A large portion of this mass
+is of Pliocene date, and some of the latest lavas have been poured
+out since the time when the valleys were already excavated to
+within a few feet of their present depth.</p>
+
+<p>On the whole, the rocks of the Grand Canary, an island of a
+nearly circular shape, and 6&frac12; geographical miles diameter,
+exhibit proofs of a long series of eruptions beginning like those
+of Madeira, Porto Santo, and the Azores, in the Upper Miocene
+period, and continued to the Post-Pliocene. The building up of the
+Grand Canary by subaërial eruptions, several thousand feet
+thick, went on simultaneously with the gradual upheaval of the
+earliest products of submarine eruptions, in the same manner as the
+Pliocene marine strata of the oldest parts of Vesuvius and Etna
+have been upraised during eruptions of Post-tertiary date.</p>
+
+<p>In proof that movements of elevation have actually continued
+down to Post-tertiary times, I may remark that I found raised
+beaches containing shells of the Recent Period in the Grand Canary,
+Teneriffe, and Porto Santo. The most remarkable raised beach which
+I observed in the Grand Canary, in the study of which I was
+assisted by Don Pedro Maffiotte, is situated in the north-eastern
+part of the island at San Catalina, about a quarter of a mile north
+of Las Palmas. It intervenes between the base of the high cliff
+formed of the tuffs with Miocene shells and the sea-shore. From
+<a name="page539"></a>this beach, at an elevation of twenty-five feet above high-water
+mark, and at a distance of about 150 feet from the present shore, I
+obtained more than fifty species of living marine shells. Many of
+them, according to Dr. S. P. Woodward, are no longer inhabitants of
+the contiguous sea, as, for example, <i>Strombus bubonius,</i>
+which is still living on the West Coast of Africa, and <i>Cerithium
+procerum,</i> found at Mozambique; others are Mediterranean
+species, as <i>Pecten Jacobæus</i> and <i>P. polymorphus.</i>
+Some of these testacea, such as <i>Cardita squamosa,</i> are
+inhabitants of deep water, and the deposit on the whole seems to
+indicate a depth of water exceeding a hundred feet.</p>
+
+<p><i>Azores.</i>&mdash;In the island of St. Mary&rsquo;s, one of
+the Azores, marine fossil shells have long been known. They are
+found on the north-east coast on a small projecting promontory
+called Ponta do Papagaio (or Point-Parrot), chiefly in a limestone
+about twenty feet thick, which rests upon, and is again covered by,
+basaltic lavas, scoriæ, and conglomerates. The pebbles in the
+conglomerate are cemented together with carbonate of lime.</p>
+
+<p>
+Mr. Hartung, in his account of the Azores, published in 1860, describes
+twenty-three shells from St. Mary&rsquo;s,<a href="#fn-30.2" name="fnref-30.2"
+id="fnref-30.2"><sup>[2]</sup></a> of which eight perhaps are identical with
+living species, and twelve are with more or less certainty referred to European
+Tertiary forms, chiefly Upper Miocene. One of the most characteristic and
+abundant of the new species, <i>Cardium Hartungi,</i> not known as fossil in
+Europe, is very common in Porto Santo and Baixo, and serves to connect the
+Miocene fauna of the Azores and the Madeiras. In some of the Azores, as well as
+in the Canary islands, the volcanic fires are not yet extinct, as the recorded
+eruptions of Lanzerote, Teneriffe, Palma, St. Michael&rsquo;s, and others,
+attest.
+</p>
+
+<p><b>Lower Miocene Volcanic Rocks.</b>&mdash;<i>Isle of Mull and
+Antrim.</i>&mdash;I may refer the reader to the account already
+given (<a href="#page247">p. 247</a>) of leaf-beds at
+Ardtun, in the Isle of Mull in the Hebrides, which bear a relation
+to the associated volcanic rocks of Lower Miocene date analogous to
+that which the Madeira leaf-bed, above described (<a href=
+"#page532">p. 532</a>), bears to the Pliocene lavas of
+that island. Mr. Geikie has shown that the volcanic rocks in Mull
+are above 3000 feet in thickness. There seems little doubt that the
+well-known columnar basalt of Staffa, as well as that of Antrim in
+Ireland, are of the same age, and not of higher antiquity, as once
+suspected.</p>
+
+<p><i>The Eifel.</i>&mdash;A large portion of the volcanic rocks of
+the
+<a name="page540"></a>Lower Rhine and the Eifel are coeval with the Lower Miocene
+deposits to which most of the &ldquo;Brown-Coal&rdquo; of Germany
+belongs. The Tertiary strata of that age are seen on both sides of
+the Rhine, in the neighbourhood of Bonn, resting unconformably on
+highly inclined and vertical strata of Silurian and Devonian rocks.
+The Brown-Coal formation of that region consists of beds of loose
+sand, sandstone, and conglomerate, clay with nodules of
+clay-iron-stone, and occasionally silex. Layers of light brown and
+sometimes black lignite are interstratified with the clays and
+sands, and often irregularly diffused through them. They contain
+numerous impressions of leaves and stems of trees, and are
+extensively worked for fuel, whence the name of the formation. In
+several places layers of trachytic tuff are interstratified, and in
+these tuffs are leaves of plants identical with those found in the
+brown-coal, showing that, during the period of the accumulation of
+the latter, some volcanic products were ejected. The igneous rocks
+of the Westerwald, and of the mountains called the Siebengebirge,
+consist partly of basaltic and partly of trachytic lavas, the
+latter being in general the more ancient of the two. There are many
+varieties of trachyte, some of which are highly crystalline,
+resembling a coarse-grained granite, with large separate crystals
+of feldspar. Trachytic tuff is also very abundant.</p>
+
+<p>
+M. Von Dechen, in his work on the Siebengebirge,<a href="#fn-30.3"
+name="fnref-30.3" id="fnref-30.3"><sup>[3]</sup></a> has given a copious list
+of the animal and vegetable remains of the fresh-water strata associated with
+the brown-coal of that part of Germany. Plants of the genera <i>Flabellaria,
+Ceanothus,</i> and <i> Daphnogene,</i> including <i>D. cinnamomifolia</i> (<a
+href= "images/fig155.jpg">Fig. 155</a>), occur in these beds, with nearly 150
+other plants. The fishes of the brown-coal near Bonn are found in a bituminous
+shale, called paper-coal, from being divisible into extremely thin leaves. The
+individuals are very numerous; but they appear to belong to a small number of
+species, some of which were referred by Agassiz to the genera <i>Leuciscus,
+Aspius,</i> and <i>Perca.</i> The remains of frogs also, of extinct species,
+have been discovered in the paper-coal; and a complete series may be seen in
+the museum at Bonn, from the most imperfect state of the tadpole to that of the
+full-grown animal. With these a salamander, scarcely distinguishable from the
+recent species, has been found, and the remains of many insects.
+</p>
+
+<p><b>Upper and Lower Miocene Volcanic Rocks of
+Auvergne.</b>&mdash;The extinct volcanoes of Auvergne and Cantal,
+in central France, seem to have commenced their eruptions in the
+Lower
+<a name="page541"></a>Miocene period, but to have been most active during the Upper
+Miocene and Pliocene eras. I have already alluded to the grand
+succession of events of which there is evidence in Auvergne since
+the last retreat of the sea (see <a href="#page527">p.
+527</a>).</p>
+
+<p>The earliest monuments of the Tertiary Period in that region are
+lacustrine deposits of great thickness, in the lowest conglomerates
+of which are rounded pebbles of quartz, mica-schist, granite, and
+other non-volcanic rocks, without the slightest intermixture of
+igneous products. To these conglomerates succeed argillaceous and
+calcareous marls and limestones, containing Lower Miocene shells
+and bones of mammalia, the higher beds of which sometimes alternate
+with volcanic tuff of contemporaneous origin. After the filling up
+or drainage of the ancient lakes, huge piles of trachytic and
+basaltic rocks, with volcanic breccias, accumulated to a thickness
+of several thousand feet, and were superimposed upon granite, or
+the contiguous lacustrine strata. The greater portion of these
+igneous rocks appear to have originated during the Upper Miocene
+and Pliocene periods; and extinct quadrupeds of those eras,
+belonging to the genera Mastodon, Rhinoceros, and others, were
+buried in ashes and beds of alluvial sand and gravel, which owe
+their preservation to overspreading sheets of lava.</p>
+
+<p>
+In Auvergne, the most ancient and conspicuous of the volcanic masses is Mont
+Dor, which rests immediately on the granitic rocks standing apart from the
+fresh-water strata. This great mountain rises suddenly to the height of several
+thousand feet above the surrounding platform, and retains the shape of a
+flattened and somewhat irregular cone, the slope of which is gradually lost in
+the high plain around. This cone is composed of layers of scoriæ,
+pumice-stones, and their fine detritus, with interposed beds of trachyte and
+basalt, which descend often in uninterrupted sheets until they reach and spread
+themselves round the base of the mountain.<a href="#fn-30.4" name="fnref-30.4"
+id="fnref-30.4"><sup>[4]</sup></a> Conglomerates, also, composed of angular and
+rounded fragments of igneous rocks, are observed to alternate with the above;
+and the various masses are seen to dip off from the central axis, and to lie
+parallel to the sloping flanks of the mountain. The summit of Mont Dor
+terminates in seven or eight rocky peaks, where no regular crater can now be
+traced, but where we may easily imagine one to have existed, which may have
+been shattered by earthquakes, and have suffered degradation by aqueous agents.
+Originally, perhaps, like the highest crater of Etna, it may have formed <a
+name="page542"></a>an insignificant feature in the great pile, and, like it,
+may frequently have been destroyed and renovated.
+</p>
+
+<p>Respecting the age of the great mass of Mont Dor, we cannot
+come at present to any positive decision, because no organic
+remains have yet been found in the tuffs, except impressions of the
+leaves of trees of species not yet determined. It has already been
+stated (<a href="#page234">p. 234</a>) that the earliest
+eruptions must have been posterior in origin to those grits and
+conglomerates of the fresh-water formation of the Limagne which
+contain no pebbles of volcanic rocks. But there is evidence at a
+few points, as in the hill of Gergovia, presently to be mentioned,
+that some eruptions took place before the great lakes were drained,
+while others occurred after the desiccation of those lakes, and
+when deep valleys had already been excavated through fresh-water
+strata.</p>
+
+<p>The valley in which the cone of Tartaret, above-mentioned (<a
+href="#page527">p. 527</a>), is situated affords an
+impressive monument of the very different dates at which the
+igneous eruptions of Auvergne have happened; for while the cone
+itself is of Post-Pliocene date, the valley is bounded by lofty
+precipices composed of sheets of ancient columnar trachyte and
+basalt, which once flowed from the summit of Mont Dor in some part
+of the Miocene period. These Miocene lavas had accumulated to a
+thickness of nearly 1000 feet before the ravine was cut down to the
+level of the river Couze, a river which was at length dammed up by
+the modern cone and the upper part of its course transformed into a
+lake.</p>
+
+<p><i>Gergovia.</i>&mdash;It has been supposed by some observers
+that there is an alternation of a contemporaneous sheet of lava
+with fresh-water strata in the hill of Gergovia, near Clermont.
+<a name="page543"></a>But this idea has arisen from the intrusion of the dike
+represented in Fig. 604, which has altered the green and white
+marls both above and below. Nevertheless, there is a real
+alternation of volcanic tuff with strata containing Lower Miocene
+fresh-water shells, among others a Melania allied to <i>M.
+inquinata</i> (<a href="images/fig216.jpg">Fig. 217</a>), with a
+Melanopsis and a Unio; there can, therefore, be no doubt that in
+Auvergne some volcanic explosions took place before the drainage of
+the lakes, and at a time when the Lower Miocene species of animals
+and plants still flourished.</p>
+
+<p><img src="images/fig604.jpg" width="406" height="237" alt=
+"Fig. 604: Hill of Gergovia." /></p>
+
+<p>
+<b>Eocene Volcanic Rocks.</b>&mdash;<i>Monte Bolca.</i>&mdash;The fissile
+limestone of Monte Bolca, near Verona, has for many centuries been celebrated
+in Italy for the number of perfect Ichthyolites which it contains. Agassiz has
+described no less than 133 species of fossil fish from this single deposit, and
+the multitude of individuals by which many of the species are represented is
+attested by the variety of specimens treasured up in the principal museums of
+Europe. They have been all obtained from quarries worked exclusively by lovers
+of natural history, for the sake of the fossils. Had the lithographic stone of
+Solenhofen, now regarded as so rich in fossils, been in like manner quarried
+solely for scientific objects, it would have remained almost a sealed book to
+palæontologists, so sparsely are the organic remains scattered through it. When
+I visited Monte Bolca, in company with Sir Roderick Murchison, in 1828, we
+ascertained that the fish-bearing beds were of Eocene date, containing
+well-known species of Nummulites, and that a long series of submarine volcanic
+eruptions, evidently contemporaneous, had produced beds of tuff, which are cut
+through by dikes of basalt. There is evidence here of a long series of
+submarine volcanic eruptions of Eocene date, and during some of them, as Sir R.
+Murchison has suggested, shoals of fish were probably destroyed by the
+evolution of heat, noxious gases, and tufaceous mud, just as happened when
+Graham&rsquo;s Island was thrown up between Sicily and Africa in 1831, at which
+time the waters of the Mediterranean were seen to be charged with red mud, and
+covered with dead fish over a wide area.<a href="#fn-30.5" name="fnref-30.5"
+id="fnref-30.5"><sup>[5]</sup></a>
+</p>
+
+<p>Associated with the marls and limestones of Monte Bolca are beds
+containing lignite and shale with numerous plants, which have been
+described by Unger and Massalongo, and referred by them to the
+Eocene period. I have already cited (<a href=
+"#page263">p. 263</a>) Professor Heer&rsquo;s remark,
+that several of the species are common to Monte Bolca and the white
+clay of Alum Bay, a Middle Eocene deposit; and the same botanist
+dwells on
+<a name="page544"></a>the tropical character of the flora of Monte Bolca and its
+distinctness from the sub-tropical flora of the Lower Miocene of
+Switzerland and Italy, in which last there is a far more
+considerable mixture of forms of a temperate climate, such as the
+willow, poplar, birch, elm, and others. That scarcely any one of
+the Monte Bolca fish should have been found in any other locality
+in Europe, is a striking illustration of the extreme imperfection
+of the palæontological record. We are in the habit of
+imagining that our insight into the geology of the Eocene period is
+more than usually perfect, and we are certainly acquainted with an
+almost unbroken succession of assemblages of shells passing one
+into the other from the era of the Thanet sands to that of the
+Bembridge beds or Paris gypsum. The general dearth, therefore, of
+fish in the different members of the Eocene series, Upper, Middle,
+and Lower, might induce a hasty reasoner to conclude that there was
+a poverty of ichthyic forms during this period; but when a local
+accident, like the volcanic eruptions of Monte Bolca, occurs,
+proofs are suddenly revealed to us of the richness and variety of
+this great class of vertebrata in the Eocene sea. The number of
+genera of Monte Bolca fish is, according to Agassiz, no less than
+seventy-five, twenty of them peculiar to that locality, and only
+eight common to the antecedent Cretaceous period. No less than
+forty-seven out of the seventy-five genera make their appearance
+for the first time in the Monte Bolca rocks, none of them having
+been met with as yet in the antecedent formations. They form a
+great contrast to the fish of the secondary strata, as, with the
+exception of the Placoids, they are all Teleosteans, only one
+genus, <i>Pycnodus,</i> belonging to the order of Ganoids, which
+form, as before stated, the vast majority of the ichthyolites
+entombed in the secondary are Mesozoic rocks.</p>
+
+<p><b>Cretaceous Period.</b>&mdash;M. Virlet, in his account of the
+geology of the Morea, p. 205, has clearly shown that certain traps
+in Greece are of Cretaceous date; as those, for example, which
+alternate conformably with cretaceous limestone and greensand
+between Kastri and Damala, in the Morea. They consist in great part
+of diallage rocks and serpentine, and of an amygdaloid with
+calcareous kernels, and a base of serpentine. In certain parts of
+the Morea, the age of these volcanic rocks is established by the
+following proofs: first, the lithographic limestones of the
+Cretaceous era are cut through by trap, and then a conglomerate
+occurs, at Nauplia and other places, containing in its calcareous
+cement many well-known fossils of the chalk and greensand, together
+with pebbles
+<a name="page545"></a>formed of rolled pieces of the same serpentinous trap, which
+appear in the dikes above alluded to.</p>
+
+<p>
+<b>Period of Oolite and Lias.</b>&mdash;Although the green and serpentinous
+trap-rocks of the Morea belong chiefly to the Cretaceous era, as before
+mentioned, yet it seems that some eruptions of similar rocks began during the
+Oolitic period;<a href="#fn-30.6" name="fnref-30.6"
+id="fnref-30.6"><sup>[6]</sup></a> and it is probable that a large part of the
+trappean masses, called ophiolites in the Apennines, and associated with the
+limestone of that chain, are of corresponding age.
+</p>
+
+<p>
+<b>Trap of the New Red Sandstone Period.</b>&mdash;In the southern part of
+Devonshire, trappean rocks are associated with New Red Sandstone, and,
+according to Sir H. De la Beche, have not been intruded subsequently into the
+sandstone, but were produced by contemporaneous volcanic action. Some beds of
+grit, mingled with ordinary red marl, resemble sands ejected from a crater; and
+in the stratified conglomerates occurring near Tiverton are many angular
+fragments of trap porphyry, some of them one or two tons in weight,
+intermingled with pebbles of other rocks. These angular fragments were probably
+thrown out from volcanic vents, and fell upon sedimentary matter then in the
+course of deposition.<a href="#fn-30.7" name="fnref-30.7"
+id="fnref-30.7"><sup>[7]</sup></a>
+</p>
+
+<p><b>Trap of the Permian Period.</b>&mdash;The recent
+investigations of Mr. Archibald Geikie in Ayrshire have shown that
+some of the volcanic rocks in that county are of Permian age, and
+it appears highly probable that the uppermost portion of
+Arthur&rsquo;s Seat in the suburbs of Edinburgh marks the site of
+an eruption of the same era.</p>
+
+<p><b>Trap of the Carboniferous Period.</b>&mdash;Two classes of
+contemporaneous trap-rocks occur in the coal-field of the Forth, in
+Scotland. The newest of these, connected with the higher series of
+coal-measures, is well exhibited along the shores of the Forth, in
+Fifeshire, where they consist of basalt with olivine, amygdaloid,
+greenstone, wacke, and tuff. They appear to have been erupted while
+the sedimentary strata were in a horizontal position, and to have
+suffered the same dislocations which those strata have subsequently
+undergone. In the volcanic tuffs of this age are found not only
+fragments of limestone, shale, flinty slate, and sandstone, but
+also pieces of coal. The other or older class of carboniferous
+traps are traced along the south margin of Stratheden, and
+constitute a ridge parallel with the Ochils, and extending from
+Stirling to near St. Andrews. They consist almost exclusively of
+greenstone, becoming, in a few instances, earthy and amygdaloidal.
+They are regularly interstratified with the
+<a name="page546"></a>sandstone, shale, and iron-stone of the lower coal-measures,
+and, on the East Lomond, with Mountain Limestone. I examined these
+trap-rocks in 1838, in the cliffs south of St. Andrews, where they
+consist in great part of stratified tuffs, which are curved,
+vertical, and contorted, like the associated coal-measures. In the
+tuff I found fragments of carboniferous shale and limestone, and
+intersecting veins of greenstone.</p>
+
+<p><i>Fife&mdash;Flisk Dike.</i>&mdash;A trap dike was pointed out
+to me by Dr. Fleming, in the parish of Flisk, in the northern part
+of the county of Fife, which cuts through the grey sandstone and
+shale, forming the lowest part of the Old Red Sandstone, but which
+may probably be of carboniferous date. It may be traced for many
+miles, passing through the amygdaloidal and other traps of the hill
+called Norman&rsquo;s Law in that parish. In its course it affords
+a good exemplification of the passage from the trappean into the
+Plutonic, or highly crystalline texture. Professor Gustavus Rose,
+to whom I submitted specimens of this dike, found it to be
+dolerite, and composed of greenish black augite and Labrador
+feldspar, the latter being the most abundant ingredient. A small
+quantity of magnetic iron, perhaps titaniferous, is also present.
+The result of this analysis is interesting, because both the
+ancient and modern lavas of Etna consist in like manner of augite,
+Labradorite, and titaniferous iron.</p>
+
+<p><i>Erect Trees buried in Volcanic Ash at Arran.</i>&mdash;An
+interesting discovery was made in 1867 by Mr. E. A. Wünsch in
+the carboniferous strata of the north-eastern part of the island of
+Arran. In the sea-cliff about five miles north of Corrie, near the
+village of Laggan, strata of volcanic ash occur, forming a solid
+rock cemented by carbonate of lime and enveloping trunks of trees,
+determined by Mr. Binney to belong to the genera Sigillaria and
+Lepidodendron. Some of these trees are at right angles to the
+planes of stratification, while others are prostrate and
+accompanied by leaves and fruits of the same genera. I visited the
+spot in company with Mr. Wünsch in 1870, and saw that the
+trees with their roots, of which about fourteen had been observed,
+occur at two distinct levels in volcanic tuffs parallel to each
+other, and inclined at an angle of about 40&deg;, having between
+them beds of shale and coaly matter seven feet thick. It is evident
+that the trees were overwhelmed by a shower of ashes from some
+neighbouring volcanic vent, as Pompeii was buried by matter ejected
+from Vesuvius. The trunks, several of them from three to five feet
+in circumference, remained with their Stigmarian roots spreading
+through the stratum below, which had served as a soil. The trees
+must have continued for
+<a name="page547"></a>years in an upright position after they were killed by the
+shower of burning ashes, giving time for a partial decay of the
+interior, so as to afford hollow cylinders into which the spores of
+plants were wafted. These spores germinated and grew, until finally
+their stems were petrified by carbonate of lime like some of the
+remaining portions of the wood of the containing Sigillaria. Mr.
+Carruthers has discovered that sometimes the plants which had thus
+grown and become fossil in the inside of a single trunk belonged to
+several distinct genera. The fact that the tree-bearing deposits
+now dip at an angle of 40&deg; is the more striking, as they must
+clearly have remained horizontal and undisturbed during a long
+period of intermittent and contemporaneous volcanic action.</p>
+
+<p>In some of the associated carboniferous shales, ferns and
+calamites occur, and all the phenomena of the successive buried
+forests remind us of the sections in <a href="#page410">
+pp. 410 and 411</a> of the Nova Scotia coal-measures, with this
+difference only, that in the case of the South Joggins the
+fossilisation of the trees was effected without the eruption of
+volcanic matter.</p>
+
+<p><b>Trap of the Old Red Sandstone Period.</b>&mdash;By referring
+to the section explanatory of the structure of Forfarshire, already
+given (<a href="#page74">p. 74</a>), the reader will
+perceive that beds of conglomerate, No. 3, occur in the middle of
+the Old Red Sandstone system, 1, 2, 3, 4. The pebbles in these
+conglomerates are sometimes composed of granitic and quartzose
+rocks, sometimes exclusively of different varieties of trap, which
+last, although purposely omitted in the section referred to, is
+often found either intruding itself in amorphous masses and dikes
+into the old fossiliferous tilestones, No. 4, or alternating with
+them in conformable beds. All the different divisions of the red
+sandstone, 1, 2, 3, 4, are occasionally intersected by dikes, but
+they are very rare in Nos. 1 and 2, the upper members of the group
+consisting of red shale and red sandstone. These phenomena, which
+occur at the foot of the Grampians, are repeated in the Sidlaw
+Hills; and it appears that in this part of Scotland volcanic
+eruptions were most frequent in the earlier part of the Old Red
+Sandstone period. The trap-rocks alluded to consist chiefly of
+feldspathic porphyry and amygdaloid, the kernels of the latter
+being sometimes calcareous, often chalcedonic, and forming
+beautiful agates. We meet also with claystone, greenstone, compact
+feldspar, and tuff. Some of these rocks look as if they had flowed
+as lavas over the bottom of the sea, and enveloped quartz pebbles
+which were lying there, so as to form conglomerates with a base of
+greenstone, as is seen in Lumley Den, in the Sidlaw Hills. On
+either side of the axis of this chain of hills
+<a name="page548"></a>(see <a href="images/fig55.jpg">Fig. 55</a>), the beds of
+massive trap, and the tuffs composed of volcanic sand and ashes,
+dip regularly to the south-east or north-west, conformably with the
+shales and sandstones.</p>
+
+<p>
+But the geological structure of the Pentland Hills, near Edinburgh, shows that
+igneous rocks were there formed during the newer part of the Devonian or
+&ldquo;Old Red&rdquo; period. These hills are 1900 feet high above the sea, and
+consist of conglomerates and sandstones of Upper Devonian age, resting on the
+inclined edges of grits and slates of Lower Devonian and Upper Silurian date.
+The contemporaneous volcanic rocks intercalated in this Upper Old Red consist
+of feldspathic lavas, or feldstones, with associated tuffs or ashy beds. The
+lavas were some of them originally compact, others vesicular, and these last
+have been converted into amygdaloids. They consist chiefly of feldstone or
+compact feldspar. The Pentland Hills, say Messrs. Maclaren and Geikie, afford
+evidence that at the time of the Upper Old Red Sandstone, the district to the
+south-west of Edinburgh was for a long while the seat of a powerful volcano,
+which sent out massive streams of lava and showers of ash, and continued active
+until well-nigh the dawn of the Carboniferous period.<a href="#fn-30.8"
+name="fnref-30.8" id="fnref-30.8"><sup>[8]</sup></a>
+</p>
+
+<p>
+<b>Silurian Volcanic Rocks.</b>&mdash;It appears from the investigations of Sir
+R. Murchison in Shropshire, that when the Lower Silurian strata of that country
+were accumulating, there were frequent volcanic eruptions beneath the sea; and
+the ashes and scoriæ then ejected gave rise to a peculiar kind of tufaceous
+sandstone or grit, dissimilar to the other rocks of the Silurian series, and
+only observable in places where syenitic and other trap-rocks protrude. These
+tuffs occur on the flanks of the Wrekin and Caer Caradoc, and contain Silurian
+fossils, such as casts of encrinites, trilobites, and mollusca. Although
+fossiliferous, the stone resembles a sandy claystone of the trap family.<a
+href="#fn-30.9" name="fnref-30.9" id="fnref-30.9"><sup>[9]</sup></a>
+</p>
+
+<p>
+Thin layers of trap, only a few inches thick, alternate in some parts of
+Shropshire and Montgomeryshire with sedimentary strata of the Lower Silurian
+system. This trap consists of slaty porphyry and granular feldspar rock, the
+beds being traversed by joints like those in the associated sandstone,
+limestone, and shale, and having the same strike and dip.<a href="#fn-30.10"
+name="fnref-30.10" id="fnref-30.10"><sup>[10]</sup></a>
+</p>
+
+<p>
+In Radnorshire there is an example of twelve bands of stratified trap,
+alternating with Silurian schists and flagstones, <a name="page549"></a>in a
+thickness of 350 feet. The bedded traps consist of feldspar porphyry, and other
+varieties; and the interposed Llandeilo flags are of sandstone and shale, with
+trilobites and graptolites.<a href="#fn-30.11" name="fnref-30.11"
+id="fnref-30.11"><sup>[11]</sup></a>
+</p>
+
+<p>The Snowdonian hills in Carnarvonshire consist in great part of
+volcanic tuffs, the oldest of which are interstratified with the
+Bala and Llandeilo beds. There are some contemporaneous feldspathic
+lavas of this era, which, says Professor Ramsay, alter the slates
+on which they repose, having doubtless been poured out over them,
+in a melted state, whereas the slates which overlie them having
+been subsequently deposited after the lava had cooled and
+consolidated, have entirely escaped alteration. But there are
+greenstones associated with the same formation, which, although
+they are often conformable to the slates, are in reality intrusive
+rocks. They alter the stratified deposits both above and below
+them, and when traced to great distances are sometimes seen to cut
+through the slates, and to send off branches. Nevertheless, these
+greenstones appear to belong, like the lavas, to the Lower Silurian
+period.</p>
+
+<p>
+<b>Cambrian Volcanic Rocks.</b>&mdash;The Lingula beds in North Wales have been
+described as 5000 feet in thickness. In the upper portion of these deposits
+volcanic tuffs or ashy materials are interstratified with ordinary muddy
+sediment, and here and there associated with thick beds of feldspathic lava.
+These rocks form the mountains called the Arans and the Arenigs; numerous
+greenstones are associated with them, which are intrusive, although they often
+run in the lines of bedding for a space. &ldquo;Much of the ash,&rdquo; says
+Professor Ramsay, &ldquo;seems to have been subaërial. Islands, like
+Graham&rsquo;s Island, may have sometimes raised their craters for various
+periods above the water, and by the waste of such islands some of the ashy
+matter became waterworn, whence the ashy conglomerate. Viscous matter seems
+also to have been shot into the air as volcanic bombs, which fell among the
+dust and broken crystals (that often form the ashes) before perfect cooling and
+consolidation had taken place.&rdquo;<a href="#fn-30.12" name="fnref-30.12"
+id="fnref-30.12"><sup>[12]</sup></a>
+</p>
+
+<p>
+<b>Laurentian Volcanic Rocks.</b>&mdash;The Laurentian rocks in Canada,
+especially in Ottawa and Argenteuil, are the oldest intrusive masses yet known.
+They form a set of dikes of a fine-grained dark greenstone or dolerite,
+composed of feldspar and pyroxene, with occasional scales of mica and grains of
+pyrites. Their width varies from a few feet to a hundred yards, and they have a
+columnar structure, the columns <a name="page550"></a>being truly at right
+angles to the plane of the dike. Some of the dikes send off branches. These
+dolerites are cut through by intrusive syenite, and this syenite, in its turn,
+is again cut and penetrated by feldspar porphyry, the base of which consists of
+petrosilex, or a mixture of orthoclase and quartz. All these trap-rocks appear
+to be of Laurentian date, as the Cambrian and Huronian rocks rest unconformably
+upon them.<a href="#fn-30.13" name="fnref-30.13"
+id="fnref-30.13"><sup>[13]</sup></a> Whether some of the various conformable
+crystalline rocks of the Laurentian series, such as the coarse-grained
+granitoid and porphyritic varieties of gneiss, exhibiting scarcely any signs of
+stratification, and some of the serpentines, may not also be of volcanic
+origin, is a point very difficult to determine in a region which has undergone
+so much metamorphic action.
+</p>
+
+<p class="footnote">
+<a name="fn-30.1" id="fn-30.1"></a> <a href="#fnref-30.1">[1]</a>
+Linnean Proceedings; Zoology, 1860.
+</p>
+
+<p class="footnote">
+<a name="fn-30.2" id="fn-30.2"></a> <a href="#fnref-30.2">[2]</a>
+Hartung, Die Azoren, 1860; also Insel Gran Canaria, Madeira und Porto Santo,
+1864, Leipsig.
+</p>
+
+<p class="footnote">
+<a name="fn-30.3" id="fn-30.3"></a> <a href="#fnref-30.3">[3]</a>
+Geognost. Beschreib. des Siebengebirges am Rhein. Bonn, 1852.
+</p>
+
+<p class="footnote">
+<a name="fn-30.4" id="fn-30.4"></a> <a href="#fnref-30.4">[4]</a>
+Scrope&rsquo;s Central France, p. 98.
+</p>
+
+<p class="footnote">
+<a name="fn-30.5" id="fn-30.5"></a> <a href="#fnref-30.5">[5]</a>
+Principles of Geology, chap. xxvi, 9th ed., p. 432.
+</p>
+
+<p class="footnote">
+<a name="fn-30.6" id="fn-30.6"></a> <a href="#fnref-30.6">[6]</a>
+Boblaye and Virlet, Morea, p. 23.
+</p>
+
+<p class="footnote">
+<a name="fn-30.7" id="fn-30.7"></a> <a href="#fnref-30.7">[7]</a>
+De la Beche, Geol. Proceedings, vol. ii, p. 198.
+</p>
+
+<p class="footnote">
+<a name="fn-30.8" id="fn-30.8"></a> <a href="#fnref-30.8">[8]</a>
+Maclaren, Geology of Fife and Lothians. Geikie, Trans. Royal Soc. Edinburgh,
+1860-1861.
+</p>
+
+<p class="footnote">
+<a name="fn-30.9" id="fn-30.9"></a> <a href="#fnref-30.9">[9]</a>
+Murchison, Silurian System, etc., p. 230.
+</p>
+
+<p class="footnote">
+<a name="fn-30.10" id="fn-30.10"></a> <a href="#fnref-30.10">[10]</a>
+Ibid., p. 212.
+</p>
+
+<p class="footnote">
+<a name="fn-30.11" id="fn-30.11"></a> <a href="#fnref-30.11">[11]</a>
+Murchison, Silurian System, etc., p. 325.
+</p>
+
+<p class="footnote">
+<a name="fn-30.12" id="fn-30.12"></a> <a href="#fnref-30.12">[12]</a>
+Quart. Geol. Journ., vol. ix, p. 170, 1852.
+</p>
+
+<p class="footnote">
+<a name="fn-30.13" id="fn-30.13"></a> <a href="#fnref-30.13">[13]</a>
+Logan, Geology of Canada, 1863.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap31"></a><a name="page551"></a>CHAPTER XXXI.<br/>
+PLUTONIC ROCKS.</h2>
+
+<p class="letter">
+General Aspect of Plutonic Rocks. &mdash; Granite and its Varieties. &mdash;
+Decomposing into Spherical Masses. &mdash; Rude columnar Structure. &mdash;
+Graphic Granite. &mdash; Mutual Penetration of Crystals of Quartz and Feldspar.
+&mdash; Glass Cavities in Quartz of Granite. &mdash; Porphyritic, talcose, and
+syenitic Granite. &mdash; Schorlrock and Eurite. &mdash; Syenite. &mdash;
+Connection of the Granites and Syenites with the Volcanic Rocks. &mdash;
+Analogy in Composition of Trachyte and Granite. &mdash; Granite Veins in Glen
+Tilt, Cape of Good Hope, and Cornwall. &mdash; Metalliferous Veins in Strata
+near their Junction with Granite. &mdash; Quartz Veins. &mdash; Exposure of
+Plutonic Rocks at the surface due to Denudation.
+</p>
+
+<p>
+The Plutonic rocks may be treated of next in order, as they are most nearly
+allied to the volcanic class already considered. I have described, in the first
+chapter, these Plutonic rocks as the unstratified division of the crystalline
+or hypogene formations, and have stated that they differ from the volcanic
+rocks, not only by their more crystalline texture, but also by the absence of
+tuffs and breccias, which are the products of eruptions at the earth&rsquo;s
+surface, whether thrown up into the air or the sea. They differ also by the
+absence of pores or cellular cavities, to which the expansion of the entangled
+gases gives rise in ordinary lava, never being scoriaceous or amygdaloidal, and
+never forming a porphyry with an uncrystalline base, nor alternating with
+tuffs.
+</p>
+
+<p>
+From these and other peculiarities it has been inferred that the granites have
+been formed at considerable depths in the earth, and have cooled and
+crystallised slowly under great pressure, where the contained gases could not
+expand. The volcanic rocks, on the contrary, although they also have risen up
+from below, have cooled from a melted state more rapidly upon or near the
+surface. From this hypothesis of the great depth at which the granites
+originated, has been derived the name of &ldquo;Plutonic rocks.&rdquo; The
+beginner will easily conceive that the influence of subterranean heat may
+extend downward from the crater of every active volcano to a great depth below,
+perhaps several miles or leagues, and the effects which are produced deep in
+the bowels of the earth may, or rather must, be distinct; so that volcanic and
+Plutonic rocks, each different in texture, and sometimes even in composition,
+may originate simultaneously, the one at the <a name="page552"></a>surface, the
+other far beneath it. The Plutonic formations also agree with the volcanic in
+having veins or ramifications proceeding from central masses into the adjoining
+rocks, and causing alterations in these last, which will be presently
+described. They also resemble trap in containing no organic remains; but they
+differ in being more uniform in texture, whole mountain masses of indefinite
+extent appearing to have originated under conditions precisely similar.
+</p>
+
+<p>
+The two principal members of the Plutonic family of rocks are Granite and
+Syenite, each of which, with their varieties, bear very much the same relation
+to each other as the trachytes bear to the basalts. Granite is a compound of
+feldspar, quartz, and mica, the feldspars being rich in silica, which forms
+from 60 to 70 per cent of the whole aggregate. In Syenite quartz is rare or
+wanting, hornblende taking the place of mica, and the proportion of silica not
+exceeding 50 to 60 per cent.
+</p>
+
+<p>
+<img src="images/fig605.jpg" width="338" height="152" alt="Fig. 605: Mass of
+granite near the Sharp Tor, Cornwall." />
+</p>
+
+<p>
+<b>Granite and its Varieties.</b>&mdash;Granite often preserves a very uniform
+character throughout a wide range of territory, forming hills of a peculiar
+rounded form, usually clad with a scanty vegetation. The surface of the rock is
+for the most part in a crumbling state, and the hills are often surmounted by
+piles of stones like the remains of a stratified mass, as in Figure 605, and
+sometimes like heaps of boulders, for which they have been mistaken. The
+exterior of these stones, originally quadrangular, acquires a rounded form by
+the action of air and water, for the edges and angles waste away more rapidly
+than the sides. A similar spherical structure has already been described as
+characteristic of basalt and other volcanic formations, and it must be referred
+to analogous causes, as yet but imperfectly understood. Although it is the
+general peculiarity of granite to assume no definite shapes, it is nevertheless
+occasionally subdivided by fissures, so as to assume a cuboidal, and even a
+columnar, structure. Examples of these appearances may be seen near the
+Land&rsquo;s End, in Cornwall. (See Fig. 606.)
+</p>
+
+<p>
+<a name="page553"></a>Feldspar, quartz, and mica are usually considered as the
+minerals essential to granite, the feldspar being most abundant in quantity,
+and the proportion of quartz exceeding that of mica. These minerals are united
+in what is termed a confused crystallisation; that is to say, there is no
+regular arrangement of the crystals in granite, as in gneiss (see <a
+href="images/fig622.jpg">Fig. 622</a>), except in the variety termed graphic
+granite, which occurs mostly in granitic veins. This variety is a compound of
+feldspar and quartz, so arranged as to produce an imperfect laminar structure.
+The crystals of feldspar appear to have been first formed, leaving between them
+the space now occupied by the darker-coloured quartz. This mineral, when a
+section is made at right angles to the alternate plates of feldspar and quartz,
+presents broken lines, which have been compared to Hebrew characters. (See Fig.
+608.) The variety of granite called by the French <i>Pegmatite,</i> which is a
+mixture of quartz and common feldspar, usually with some small admixture of
+white silvery mica, often passes into graphic granite.
+</p>
+
+<p>
+<img src="images/fig606.jpg" width="369" height="351" alt="Fig. 606: Granite
+having a cuboidal and rude columnar structure, Land’s End, Cornwall." />
+</p>
+
+<p>
+Ordinary granite, as well as syenite and eurite, usually contains two kinds of
+feldspar: First, the common, or orthoclase, in which potash is the prevailing
+alkali, and this <a name="page554"></a>generally occurs in large crystals of a
+white or flesh colour; and secondly, feldspar in smaller crystals, in which
+soda predominates, usually of a dead white or spotted, and striated like
+albite, but not the same in composition.<a href="#fn-31.1" name="fnref-31.1"
+id="fnref-31.1"><sup>[1]</sup></a>
+</p>
+
+<p>
+<img src="images/fig607.jpg" width="327" height="177" alt="Graphic granite.
+Fig. 607: Section parallel to the laminæ. Fig. 608: Section transverse to the laminæ." />
+</p>
+
+<p>
+As a general rule, quartz, in a compact or amorphous state, forms a vitreous
+mass, serving as the base in which feldspar and mica have crystallised; for
+although these minerals are much more fusible than silex, they have often
+imprinted their shapes upon the quartz. This fact, apparently so paradoxical,
+has given rise to much ingenious speculation. We should naturally have
+anticipated that, during the cooling of the mass, the flinty portion would be
+the first to consolidate; and that the different varieties of feldspar, as well
+as garnets and tourmalines, being more easily liquefied by heat, would be the
+last. Precisely the reverse has taken place in the passage of most granite
+aggregates from a fluid to a solid state, crystals of the more fusible minerals
+being found enveloped in hard, transparent, glassy quartz, which has often
+taken very faithful casts of each, so as to preserve even the microscopically
+minute striations on the surface of prisms of tourmaline. Various explanations
+of this phenomenon have been proposed by MM. de Beaumont, Fournet, and
+Durocher. They refer to M. Gaudin&rsquo;s experiments on the fusion of quartz,
+which show that silex, as it cools, has the property of remaining in a viscous
+state, whereas alumina never does. This &ldquo;gelatinous flint&rdquo; is
+supposed to retain a considerable degree of plasticity long after the granitic
+mixture has acquired a low temperature. Occasionally we find the quartz and
+feldspar mutually imprinting their forms on each other, affording evidence of
+the simultaneous crystallisation of both.<a href="#fn-31.2" name="fnref-31.2"
+id="fnref-31.2"><sup>[2]</sup></a>
+</p>
+
+<p>
+<a name="page555"></a>According to the experiments and observations of Gustavus
+Rose, the quartz of granite has the specific gravity of 2·6, which
+characterises silica when it is precipitated from a liquid solvent, and not
+that inferior density, namely, 2·3, which belongs to it when it cools in the
+laboratory from a state of fusion in what is called the dry way. By some it had
+been rashly inferred that the manner in which the consolidation of granite
+takes place is exceedingly different from the cooling of lavas, and that the
+intense heat supposed to be necessary for the production of mountain masses of
+Plutonic rocks might be dispensed with. But Mr. David Forbes informs me that
+silica can crystallise in the dry way, and he has found in quartz forming a
+constituent part of some trachytes, both from Guadeloupe and Iceland, glass
+cavities quite similar to those met with in genuine volcanic minerals.
+</p>
+
+<p>
+These &ldquo;glass cavities,&rdquo; which with many other kindred phenomena
+have been carefully studied by Mr. Sorby, are those in which a liquid, on
+cooling, has become first viscous and then solid without crystallising or
+undergoing a definite change in its physical structure. Other cavities which,
+like those just mentioned, are frequently discernible under the microscope in
+the minerals composing granitic rocks, are filled, some of them with gas or
+vapour, others with liquid, and by the movements of the bubbles thus included
+the distinctness of such cavities from those filled with a glassy substance can
+be tested. Mr. Sorby admits that the frequent occurrence of fluid cavities in
+the quartz of granite implies that water was almost always present in the
+formation of this rock; but the same may be said of almost all lavas, and it is
+now more than forty years since Mr. Scrope insisted on the important part which
+water plays in volcanic eruptions, being so intimately mixed up with the
+materials of the lava that he supposed it to aid in giving mobility to the
+fluid mass. It is well known that steam escapes for months, sometimes for
+years, from the cavities of lava when it is cooling and consolidating. As to
+the result of Mr. Sorby&rsquo;s experiments and speculations on this difficult
+subject, they may be stated in a few words. He concludes that the physical
+conditions under which the volcanic and granitic rocks originate are so far
+similar that in both cases they combine igneous fusion, aqueous solution, and
+gaseous sublimation&mdash;the proof, he says, of the operation of water in the
+formation of granite being quite as strong as of that of
+heat.<a href="#fn-31.3" name="fnref-31.3" id="fnref-31.3"><sup>[3]</sup></a>
+</p>
+
+<p>
+When rocks are melted at great depths water must be present, for two
+reasons&mdash;First, because rainwater and seawater
+<a name="page556"></a>are always descending through fissured and porous rocks, and must at length
+find their way into the regions of subterranean heat; and secondly, because in
+a state of combination water enters largely into the composition of some of the
+most common minerals, especially those of the aluminous class. But the
+existence of water under great pressure affords no argument against our
+attributing an excessively high temperature to the mass with which it is mixed
+up. Bunsen, indeed, imagines that in Iceland water attains a white heat at a
+very moderate depth. To what extent some of the metamorphic rocks containing
+the same minerals as the granites may have been formed by hydrothermal action
+without the intervention of intense heat comparable to that brought into play
+in a volcanic eruption, will be considered when we treat of the metamorphic
+rocks in the thirty-third chapter.
+</p>
+
+<p>
+<img src="images/fig609.jpg" width="326" height="184" alt="Fig. 609:
+Porphyritic granite. Land’s End, Cornwall." />
+</p>
+
+<p>
+<i>Porphyritic Granite.</i>&mdash;This name has been sometimes given to that
+variety in which large crystals of common feldspar, sometimes more than three
+inches in length, are scattered through an ordinary base of granite. An example
+of this texture may be seen in the granite of the Land&rsquo;s End, in Cornwall
+(Fig. 609). The two larger prismatic crystals in this drawing represent
+feldspar, smaller crystals of which are also seen, similar in form, scattered
+through the base. In this base also appear black specks of mica, the crystals
+of which have a more or less perfect hexagonal outline. The remainder of the
+mass is quartz, the translucency of which is strongly contrasted to the
+opaqueness of the white feldspar and black mica. But neither the transparency
+of the quartz nor the silvery lustre of the mica can be expressed in the
+engraving.
+</p>
+
+<p>
+The uniform mineral character of large masses of granite seems to indicate that
+large quantities of the component <a name="page557"></a>elements were
+thoroughly mixed up together, and then crystallised under precisely similar
+conditions. There are, however, many accidental, or &ldquo;occasional,&rdquo;
+minerals, as they are termed, which belong to granite. Among these black schorl
+or tourmaline, actinolite, zircon, garnet, and fluor spar are not uncommon; but
+they are too sparingly dispersed to modify the general aspect of the rock. They
+show, nevertheless, that the ingredients were not everywhere exactly the same;
+and a still greater difference may be traced in the ever-varying proportions of
+the feldspar, quartz, and mica.
+</p>
+
+<p>
+<i>Talcose Granite,</i> or Protogine of the French, is a mixture of feldspar,
+quartz, and talc. It abounds in the Alps, and in some parts of Cornwall,
+producing by its decomposition the kaolin or china clay, more than 12,000 tons
+of which are annually exported from that country for the potteries.
+</p>
+
+<p>
+<i>Schorl-rock, and Schorly Granite.</i>&mdash;The former of these is an
+aggregate of schorl, or tourmaline, and quartz. When feldspar and mica are also
+present, it may be called schorly granite. This kind of granite is
+comparatively rare.
+</p>
+
+<p>
+<i>Eurite, Feldstone.</i>&mdash;Eurite is a rock in which the ingredients of
+granite are blended into a finely granular mass, mica being usually absent,
+and, when present, in such minute flakes as to be invisible to the naked eye.
+It is sometimes called <i>Feldstone,</i> and when the crystals of feldspar are
+conspicuous it becomes <i>Feldspar porphyry.</i> All these and other varieties
+of granite pass into certain kinds of trap&mdash;a circumstance which affords
+one of many arguments in favour of what is now the prevailing opinion, that the
+granites are also of igneous origin. The contrast of the most crystalline form
+of granite to that of the most common and earthy trap is undoubtedly great; but
+each member of the volcanic class is capable of becoming porphyritic, and the
+base of the porphyry may be more and more crystalline, until the mass passes to
+the kind of granite most nearly allied in mineral composition.
+</p>
+
+<p>
+<i>Syenitic Granite.</i>&mdash;The quadruple compound of quartz, feldspar,
+mica, and hornblende, may be termed Syenitic Granite, and forms a passage
+between the granites and the syenites. This rock occurs in Scotland and in
+Guernsey.
+</p>
+
+<p>
+<b>Syenite.</b>&mdash;We now come to the second division of the Plutonic rocks,
+or those having less than 60 per cent of silica, and which, as before stated
+(p. 552), are usually called syenitic. Syenite originally received its name
+from the celebrated ancient quarries of Syene, in Egypt. It differs from
+granite in having hornblende as a substitute for mica, and being without
+quartz. Werner at least considered syenite as a binary
+<a name="page558"></a>compound of feldspar and hornblende, and regarded quartz
+as merely one of its occasional minerals.
+</p>
+
+<p>
+<i>Miascite.</i>&mdash;Miascite is one of the varieties of syenite most
+frequently spoken of; it is composed chiefly of orthoclase and nepheline, with
+hornblende and quartz as occasional accessory minerals. It derives its name
+from Miask, in the Ural Mountains, where it was first discovered by Gustavus
+Rose. <i>Zircon-syenite</i> is another variety closely allied to Miascite, but
+containing crystals of Zircon.
+</p>
+
+<p>
+<b>Connection of the Granites and Syenites with the Volcanic
+Rocks.</b>&mdash;The minerals which constitute alike the Plutonic and volcanic
+rocks consist, almost exclusively, of seven elements, namely, silica, alumina,
+magnesia, lime, soda, potash, and iron (see Table <a href="#page449">p.
+449</a>); and these may sometimes exist in about the same proportions in a
+porous lava, a compact trap, and a crystalline granite. The same lava, for
+example, may be glassy, or scoriaceous, or stony, or porphyritic, according to
+the more or less rapid rate at which it cools.
+</p>
+
+<p>
+It would be easy to multiply examples and authorities to prove the gradation of
+the Plutonic into the trap rocks. On the western side of the Fiord of
+Christiania, in Norway, there is a large district of trap, chiefly
+greenstone-porphyry and syenitic-greenstone, resting on fossiliferous strata.
+To this, on its southern limit, succeeds a region equally extensive of syenite,
+the passage from the trappean to the crystalline Plutonic rock being so gradual
+that it is impossible to draw a line of demarkation between them.
+</p>
+
+<p>
+&ldquo;The ordinary granite of Aberdeenshire,&rdquo; says Dr. MacCulloch,
+&ldquo;is the usual ternary compound of quartz, feldspar, and mica; though
+sometimes hornblende is substituted for the mica. But in many places a variety
+occurs which is composed simply of feldspar and hornblende; and in examining
+more minutely this duplicate compound, it is observed in some places to assume
+a fine grain, and at length to become undistinguishable from the greenstones of
+the trap family. It also passes in the same uninterrupted manner into a basalt,
+and at length into a soft claystone, with a schistose tendency on exposure, in
+no respect differing from those of the trap islands of the western
+coast.&rdquo; The same author mentions, that in Shetland a granite composed of
+hornblende, mica, feldspar, and quartz graduates in an equally perfect manner
+into basalt.<a href="#fn-31.4" name="fnref-31.4"
+id="fnref-31.4"><sup>[4]</sup></a> In Hungary there are varieties of trachyte,
+which, geologically speaking, are of modern origin, in which crystals, not only
+of mica, but of quartz, are common, together with feldspar and hornblende. It
+is easy <a name="page559"></a>to conceive how such volcanic masses may, at a
+certain depth from the surface, pass downward into granite.
+</p>
+
+<p>
+<b>Granitic Veins.</b>&mdash;I have already hinted at the close analogy in the
+forms of certain granitic and trappean veins; and it will be found that strata
+penetrated by Plutonic rocks have suffered changes very similar to those
+exhibited near the contact of volcanic dikes. Thus, in Glen Tilt, in Scotland,
+alternating strata of limestone and argillaceous schist come in contact with a
+mass of granite. The contact does not take place as might have been looked for
+if the granite had been formed there before the strata were deposited, in which
+case the section would have appeared as in Fig. 610; but the union is as
+represented in Fig. 611, the undulating outline of the granite intersecting
+different strata, and occasionally intruding itself in torturous veins into the
+beds of clay-slate and limestone, from which it differs so remarkably in
+composition. The limestone is sometimes changed in character by the proximity
+of the granitic mass or its veins, and acquires a more compact texture, like
+that of hornstone or chert, with a splintery fracture, and effervescing freely
+with acids.
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig610.jpg" width="366" height="191" alt="Fig. 610 and Fig.
+611: Junction of granite and arbillaceous schist in Glen Tilt. (MacCulloch.)" />
+<p class="caption">Fig. 610 and Fig. 611: Junction of granite and arbillaceous
+schist in Glen Tilt. (MacCulloch.)<a href="#fn-31.5" name="fnref-31.5" id="fnref-31.5"><sup>[5]</sup></a><br/></p>
+</div>
+
+<p>
+The conversion of the limestone and these and many other instances into a
+siliceous rock, effervescing slowly with acids, would be difficult of
+explanation, were it not ascertained that such limestones are always impure,
+containing grains of quartz, mica, or feldspar disseminated through them. The
+elements of these minerals, when the rock has been subjected to great heat, may
+have been fused, and so spread more uniformly through the whole mass.
+</p>
+
+<p>
+In the Plutonic, as in the volcanic rocks, there is every gradation from a
+tortuous vein to the most regular form of <a name="page560"></a>a dike, such as
+intersect the tuffs and lavas of Vesuvius and Etna. Dikes of granite may be
+seen, among other places, on the southern flank of Mount Battock, one of the
+Grampians, the opposite walls sometimes preserving an exact parallelism for a
+considerable distance. As a general rule, however, granite veins in all
+quarters of the globe are more sinuous in their course than those of trap. They
+present similar shapes at the most northern point of Scotland, and the
+southernmost extremity of Africa, as Figs. 612 and 613 will show.
+</p>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig612.jpg" width="162" height="253" alt="Fig. 612: Granite
+veins traversing clay slate, Table Mountain, Cape of Good Hope." />
+<p class="caption">Fig. 612: Granite veins traversing clay slate, Table
+Mountain, Cape of Good Hope.<a href="#fn-31.6" name="fnref-31.6" id="fnref-31.6"><sup>[6]</sup></a><br/></p>
+</div>
+
+<div class="fig" style="width:100%;">
+<img src="images/fig613.jpg" width="218" height="205" alt="Fig. 613: Granite
+veins traversing gneiss, Cape Wrath." />
+<p class="caption">Fig. 613: Granite veins traversing gneiss, Cape
+Wrath.<a href="#fn-31.7" name="fnref-31.7" id="fnref-31.7"><sup>[7]</sup></a><br/></p>
+</div>
+
+<p>
+It is not uncommon for one set of granite veins to intersect another; and
+sometimes there are three sets, as in the environs of Heidelberg, where the
+granite on the banks of the river Necker is seen to consist of three varieties,
+differing in colour, grain, and various peculiarities of mineral composition.
+One of these, which is evidently the second in age, is seen to cut through an
+older granite; and another, still newer, traverses both the second and the
+first. In Shetland there are two kinds of granite. One of them, composed of
+hornblende, mica, feldspar, and quartz, is of a dark colour, and is seen
+underlying gneiss. The other is a red granite, which penetrates the dark
+variety everywhere in veins.<a href="#fn-31.8" name="fnref-31.8"
+id="fnref-31.8"><sup>[8]</sup></a>
+</p>
+
+<p>
+Fig. 614 is a sketch of a group of granite veins in Cornwall, given by Messrs.
+Von Oeynhausen and Von Dechen.<a href="#fn-31.9" name="fnref-31.9"
+id="fnref-31.9"><sup>[9]</sup></a> The main body of the granite here is of a
+porphyritic appearance, with large crystals of feldspar; but in the veins it is
+fine-grained, and without these large crystals. The general height of the veins
+is from 16 to 20 feet, but some are much higher. <a name="page561"></a>
+</p>
+
+<p>
+<img src="images/fig614.jpg" width="381" height="227" alt="Fig. 614: Granite
+veins passing through hornblende slate, Carnsilver Cove, Cornwall." />
+</p>
+
+<p>
+Granite, syenite, and those porphyries which have a granitiform structure, in
+short all Plutonic rocks, are frequently observed to contain metals, at or near
+their junction with stratified formations. On the other hand, the veins which
+traverse stratified rocks are, as a general law, more metalliferous near such
+junctions than in other positions. Hence it has been inferred that these metals
+may have been spread in a gaseous form through the fused mass, and that the
+contact of another rock, in a different state of temperature, or sometimes the
+existence of rents in other rocks in the vicinity, may have caused the
+sublimation of the metals.<a href="#fn-31.10" name="fnref-31.10"
+id="fnref-31.10"><sup>[10]</sup></a>
+</p>
+
+<img src="images/fig615.jpg" width="243" height="190" alt="Fig. 615: a, b.
+Quartz vein passing through gneiss and greenstone. Tronstad Strand, near
+Christiania." />
+
+<p>
+Veins of pure quartz are often found in granite as in many stratified rocks,
+but they are not traceable, like veins of granite or trap, to large bodies of
+rock of similar composition. They appear to have been cracks, into which
+siliceous matter was infiltered. Such segregation, as it is called, can
+sometimes clearly be shown to have taken place long subsequently to the
+original consolidation of the containing rock. Thus, for example, I observed in
+the gneiss of Tronstad Strand, near Drammen, in Norway, the section on the
+beach shown in Figure 615. It appears that the alternating strata of whitish
+granitiform gneiss and black hornblende-schist were <a name="page562"></a>first
+cut by a greenstone dike, about 2&frac12; feet wide; then the crack <i>a,
+b,</i> passed through all these rocks, and was filled up with quartz. The
+opposite walls of the vein are in some parts incrusted with transparent
+crystals of quartz, the middle of the vein being filled up with common opaque
+white quartz.
+</p>
+
+<img src="images/fig616.jpg" width="284" height="136" alt="Fig. 616: Euritic
+porphyry alternating with primary fossiliferous strata, near Christiania." />
+
+<p>
+We have seen that the volcanic formations have been called overlying, because
+they not only penetrate others but spread over them. M. Necker has proposed to
+call the granites the underlying igneous rocks, and the distinction here
+indicated is highly characteristic. It was, indeed, supposed by some of the
+earlier observers that the granite of Christiania, in Norway, was intercalated
+in mountain masses between the primary or palæozoic strata of that country, so
+as to overlie fossiliferous shale and limestone. But although the granite sends
+veins into these fossiliferous rocks, and is decidedly posterior in origin, its
+actual superposition in mass has been disproved by Professor Keilhau, whose
+observations on this controverted point I had opportunities, in 1837, of
+verifying. There are, however, on a smaller scale, certain beds of euritic
+porphyry, some a few feet, others many yards in thickness, which pass into
+granite, and deserve, perhaps, to be classed as Plutonic rather than trappean
+rocks, which may truly be described as interposed conformably between
+fossiliferous strata, as the porphyries (<i>a, c,</i> Fig. 616) which divide
+the bituminous shales and argillaceous limestones, <i>f, f.</i> But some of
+these same porphyries are partially unconformable, as <i>b,</i> and may lead us
+to suspect that the others also, notwithstanding their appearance of
+interstratification, have been forcibly injected. Some of the porphyritic rocks
+above mentioned are highly quartzose, others very feldspathic. In proportion as
+the masses are more voluminous, they become more granitic in their texture,
+less conformable, and even begin to send forth veins into contiguous strata. In
+a word, we have here a beautiful illustration of the intermediate gradations
+between volcanic and Plutonic rocks, not only in their mineralogical
+composition and structure, but also in their relations of position to
+associated formations. If the term &ldquo;overlying&rdquo; can in this instance
+be applied to a <a name="page563"></a>Plutonic rock, it is only in proportion
+as that rock begins to acquire a trappean aspect.
+</p>
+
+<p>
+It has been already hinted that the heat which in every active volcano extends
+downward to indefinite depths must produce simultaneously very different
+effects near the surface and far below it; and we cannot suppose that rocks
+resulting from the crystallising of fused matter under a pressure of several
+thousand feet, much less several miles, of the earth&rsquo;s crust can exactly
+resemble those formed at or near the surface. Hence the production at great
+depths of a class of rocks analogous to the volcanic, and yet differing in many
+particulars, might have been predicted, even had we no Plutonic formations to
+account for. How well these agree, both in their positive and negative
+characters, with the theory of their deep subterranean origin, the student will
+be able to judge by considering the descriptions already given.
+</p>
+
+<p>
+It has, however, been objected, that if the granitic and volcanic rocks were
+simply different parts of one great series, we ought to find in mountain chains
+volcanic dikes passing upward into lava and downward into granite. But we may
+answer that our vertical sections are usually of small extent; and if we find
+in certain places a transition from trap to porous lava, and in others a
+passage from granite to trap, it is as much as could be expected of this
+evidence.
+</p>
+
+<p>
+The prodigious extent of denudation which has been already demonstrated to have
+occurred at former periods, will reconcile the student to the belief that
+crystalline rocks of high antiquity, although deep in the earth&rsquo;s crust
+when originally formed, may have become uncovered and exposed at the surface.
+Their actual elevation above the sea may be referred to the same causes to
+which we have attributed the upheaval of marine strata, even to the summits of
+some mountain chains.
+</p>
+
+<p class="footnote">
+<a name="fn-31.1" id="fn-31.1"></a> <a href="#fnref-31.1">[1]</a>
+Delesse, Ann. des Mines, 1852, tome iii, p. 409, and 1848, tome xiii, p. 675.
+</p>
+
+<p class="footnote">
+<a name="fn-31.2" id="fn-31.2"></a> <a href="#fnref-31.2">[2]</a>
+Bulletin, 2e série, iv, 1304; and D&rsquo;Archiac, Hist. des Progrès de la
+Géol., i, 38.
+</p>
+
+<p class="footnote">
+<a name="fn-31.3" id="fn-31.3"></a> <a href="#fnref-31.3">[3]</a>
+See Quart. Geol. Journ., vol. xiv, pp. 465, 488.
+</p>
+
+<p class="footnote">
+<a name="fn-31.4" id="fn-31.4"></a> <a href="#fnref-31.4">[4]</a>
+Syst. of Geol., vol. i, pp. 157 and 158.
+</p>
+
+<p class="footnote">
+<a name="fn-31.5" id="fn-31.5"></a> <a href="#fnref-31.5">[5]</a>
+Geol. Trans., First Series, vol. iii, pl. 21.
+</p>
+
+<p class="footnote">
+<a name="fn-31.6" id="fn-31.6"></a> <a href="#fnref-31.6">[6]</a>
+Captain B. Hall, Trans. Roy. Soc. Edinburgh, vol. vii.
+</p>
+
+<p class="footnote">
+<a name="fn-31.7" id="fn-31.7"></a> <a href="#fnref-31.7">[7]</a>
+Western Islands, pl. 31.
+</p>
+
+<p class="footnote">
+<a name="fn-31.8" id="fn-31.8"></a> <a href="#fnref-31.8">[8]</a>
+MacCulloch, Syst. of Geol., vol. ii, p. 58.
+</p>
+
+<p class="footnote">
+<a name="fn-31.9" id="fn-31.9"></a> <a href="#fnref-31.9">[9]</a>
+Phil. Mag. and Annals, No. 27, New Series, March, 1829.
+</p>
+
+<p class="footnote">
+<a name="fn-31.10" id="fn-31.10"></a> <a href="#fnref-31.10">[10]</a>
+Necker, Proceedings of the Geol. Soc., No. 26, p. 392.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap32"></a><a name="page564"></a>CHAPTER XXXII.<br/>
+ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS.</h2>
+
+<p class="letter">Difficulty in ascertaining the precise Age of a
+Plutonic Rock. &mdash; Test of Age by Relative Position. &mdash;
+Test by Intrusion and Alteration. &mdash; Test by Mineral
+Composition. &mdash; Test by included Fragments. &mdash; Recent and
+Pliocene Plutonic Rocks, why invisible. &mdash; Miocene Syenite of
+the Isle of Skye. &mdash; Eocene Plutonic Rocks in the Andes.
+&mdash; Granite altering Cretaceous Rocks. &mdash; Granite altering
+Lias in the Alps and in Skye. &mdash; Granite of Dartmoor altering
+Carboniferous Strata. &mdash; Granite of the Old Red Sandstone
+Period. &mdash; Syenite altering Silurian Strata in Norway. &mdash;
+Blending of the same with Gneiss. &mdash; Most ancient Plutonic
+Rocks. &mdash; Granite protruded in a solid Form.</p>
+
+<p>When we adopt the igneous theory of granite, as explained in the
+last chapter, and believe that different Plutonic rocks have
+originated at successive periods beneath the surface of the planet,
+we must be prepared to encounter greater difficulty in ascertaining
+the precise age of such rocks than in the case of volcanic and
+fossiliferous formations. We must bear in mind that the evidence of
+the age of each contemporaneous volcanic rock was derived either
+from lavas poured out upon the ancient surface, whether in the sea
+or in the atmosphere, or from tuffs and conglomerates, also
+deposited at the surface, and either containing organic remains
+themselves or intercalated between strata containing fossils. But
+the same tests entirely fail, or are only applicable in a modified
+degree, when we endeavour to fix the chronology of a rock which has
+crystallised from a state of fusion in the bowels of the earth. In
+that case we are reduced to the tests of relative position,
+intrusion, alteration of the rocks in contact, included fragments,
+and mineral character; but all these may yield at best a somewhat
+ambiguous result.</p>
+
+<p><b>Test of Age by Relative Position.</b>&mdash;Unaltered
+fossiliferous strata of every age are met with reposing immediately
+on Plutonic rocks; as at Christiania, in Norway, where the
+Post-pliocene deposits rest on granite; in Auvergne, where the
+fresh-water Miocene strata, and at Heidelberg, on the Rhine, where
+the New Red sandstone occupy a similar place. In all these, and
+similar instances, inferiority in position is connected with the
+superior antiquity of granite. The crystalline rock was solid
+before the sedimentary beds were superimposed, and the latter
+usually contain in them rounded pebbles of the subjacent
+granite.</p>
+
+<p>
+<a name="page565"></a><b>Test by Intrusion and Alteration.</b>&mdash;But when Plutonic
+rocks send veins into strata, and alter them near the point of
+contact, in the manner before described (<a href=
+"#page559">p. 559</a>), it is clear that, like intrusive
+traps, they are newer than the strata which they invade and alter.
+Examples of the application of this test will be given in the
+sequel.</p>
+
+<p><b>Test by Mineral Composition.</b>&mdash;Notwithstanding a
+general uniformity in the aspect of Plutonic rocks, we have seen in
+the last chapter that there are many varieties, such as syenite,
+talcose granite, and others. One of these varieties is sometimes
+found exclusively prevailing throughout an extensive region, where
+it preserves a homogeneous character; so that, having ascertained
+its relative age in one place, we can recognise its identity in
+others, and thus determine from a single section the chronological
+relations of large mountain masses. Having observed, for example,
+that the syenitic granite of Norway, in which the mineral called
+zircon abounds, has altered the Silurian strata wherever it is in
+contact, we do not hesitate to refer other masses of the same
+zircon-syenite in the south of Norway to a post-Silurian date. Some
+have imagined that the age of different granites might, to a great
+extent, be determined by their mineral characters alone; syenite,
+for instance, or granite with hornblende, being more modern than
+common or micaceous granite. But modern investigations have proved
+these generalisations to have been premature.</p>
+
+<p>
+<b>Test by Included Fragments.</b>&mdash;This criterion can rarely be of much
+importance, because the fragments involved in granite are usually so much
+altered that they cannot be referred with certainty to the rocks whence they
+were derived. In the White Mountains, in North America, according to Professor
+Hubbard, a granite vein, traversing granite, contains fragments of slate and
+trap which must have fallen into the fissure when the fused materials of the
+vein were injected from below,<a href="#fn-32.1" name="fnref-32.1"
+id="fnref-32.1"><sup>[1]</sup></a> and thus the granite is shown to be newer
+than those slaty and trappean formations from which the fragments were derived.
+</p>
+
+<p><b>Recent and Pliocene Plutonic Rocks, why
+invisible.</b>&mdash;The explanations already given in the 28th and
+in the last chapter of the probable relation of the Plutonic to the
+volcanic formations, will naturally lead the reader to infer that
+rocks of the one class can never be produced at or near the surface
+without some members of the other being formed below. It is not
+uncommon for lava-streams to require more than ten years to cool in
+the open air; and where they are of great</p>
+
+<p>
+<a name="page566"></a>depth, a much longer period. The melted matter poured
+from Jorullo, in Mexico, in the year 1759, which accumulated in some places to
+the height of 550 feet, was found to retain a high temperature half a century
+after the eruption.<a href="#fn-32.2" name="fnref-32.2"
+id="fnref-32.2"><sup>[2]</sup></a> We may conceive, therefore, that great
+masses of subterranean lava may remain in a red-hot or incandescent state in
+the volcanic foci for immense periods, and the process of refrigeration may be
+extremely gradual. Sometimes, indeed, this process may be retarded for an
+indefinite period by the accession of fresh supplies of heat; for we find that
+the lava in the crater of Stromboli, one of the Lipari Islands, has been in a
+state of constant ebullition for the last two thousand years; and we may
+suppose this fluid mass to communicate with some caldron or reservoir of fused
+matter below. In the Isle of Bourbon, also, where there has been an emission of
+lava once in every two years for a long period, the lava below can scarcely
+fail to have been permanently in a state of liquefaction. If then it be a
+reasonable conjecture, that about 2000 volcanic eruptions occur in the course
+of every century, either above the waters of the sea or beneath them,<a
+href="#fn-32.3" name="fnref-32.3" id="fnref-32.3"><sup>[3]</sup></a> it will
+follow that the quantity of Plutonic rock generated or in progress during the
+Recent epoch must already have been considerable.
+</p>
+
+<p>But as the Plutonic rocks originate at some depth in the
+earth&rsquo;s crust, they can only be rendered accessible to human
+observation by subsequent upheaval and denudation. Between the
+period when a Plutonic rock crystallises in the subterranean
+regions and the era of its protrusion at any single point of the
+surface, one or two geological periods must usually intervene.
+Hence, we must not expect to find the Recent or even the Pliocene
+granites laid open to view, unless we are prepared to assume that
+sufficient time has elapsed since the commencement of the Pliocene
+period for great upheaval and denudation. A Plutonic rock,
+therefore, must, in general, be of considerable antiquity
+relatively to the fossiliferous and volcanic formations, before it
+becomes extensively visible. As we know that the upheaval of land
+has been sometimes accompanied in South America by volcanic
+eruptions and the emission of lava, we may conceive the more
+ancient Plutonic rocks to be forced upward to the surface by the
+newer rocks of the same class formed successively
+below&mdash;subterposition in the Plutonic, like superposition in the
+sedimentary rocks, being usually characteristic of a newer
+origin.
+<a name="page567"></a></p>
+
+<p><img src="images/fig617.jpg" width="611" height="317" alt=
+"Fig. 617: Diagram showing the relative position which the Plutonic and
+sedimentary formations of different ages may occupy." />
+</p>
+
+<p>
+In Fig. 617 an attempt is made to show the inverted order in
+which sedimentary and Plutonic formations may occur in the
+earth&rsquo;s crust. The oldest Plutonic rock, No. I, has been
+upheaved at successive periods until it has become exposed to view in a
+<a name="page568"></a>mountain-chain. This protrusion of No. I has been caused
+by the igneous agency which produced the newer Plutonic rocks Nos. II, III and
+IV. Part of the primary fossiliferous strata, No. I, have also been raised to
+the surface by the same gradual process. It will be observed that the Recent
+<i>strata</i> No. 4 and the Recent <i> granite</i> or Plutonic rock No. IV are
+the most remote from each other in position, although of contemporaneous date.
+According to this hypothesis, the convulsions of many periods will be required
+before Recent or Post-tertiary granite will be upraised so as to form the
+highest ridges and central axes of mountain-chains. During that time the
+<i>recent</i> strata No. 4 might be covered by a great many newer sedimentary
+formations.
+</p>
+
+<p>
+<b>Miocene Plutonic Rocks.</b>&mdash;A considerable mass of syenite, in the
+Isle of Skye, is described by Dr. MacCulloch as intersecting limestone and
+shale, which are of the age of the lias. The limestone, which at a greater
+distance from the granite contains shells, exhibits no traces of them near its
+junction, where it has been converted into a pure crystalline marble.<a
+href="#fn-32.4" name="fnref-32.4" id="fnref-32.4"><sup>[4]</sup></a> MacCulloch
+pointed out that the syenite here, as in Raasay, was newer than the secondary
+rocks, and Mr. Geikie has since shown that there is a strong probability that
+this Plutonic rock may be of Miocene age, because a similar Syenite having a
+true granitic character in its crystallisation has modified the Tertiary
+volcanic rocks of Ben More, in Mull, some of which have undergone considerable
+metamorphism.
+</p>
+
+<p><b>Eocene Plutonic Rocks.</b>&mdash;In a former part of this
+volume (Chapter 16), the great nummulitic formation of the Alps and
+Pyrenees was referred to the Eocene period, and it follows that
+vast movements which have raised those fossiliferous rocks from the
+level of the sea to the height of more than 10,000 feet above its
+level have taken place since the commencement of the Tertiary
+epoch. Here, therefore, if anywhere, we might expect to find
+hypogene formations of Eocene date breaking out in the central axis
+or most disturbed region of the loftiest chain in Europe.
+Accordingly, in the Swiss Alps, even the <i>flysch,</i> or upper
+portion of the nummulitic series, has been occasionally invaded by
+Plutonic rocks, and converted into crystalline schists of the
+hypogene class. There can be little doubt that even the talcose
+granite or gneiss of Mont Blanc itself has been in a fused or pasty
+state since the <i>flysch</i> was deposited at the bottom of the
+sea; and the question as to its age is not so much whether it be a
+secondary or tertiary granite or gneiss, as whether it should be
+assigned to the Eocene or Miocene epoch.</p>
+
+<p>
+<a name="page569"></a>Great upheaving movements have been experienced in the region of
+the Andes, during the Post-tertiary period. In some part,
+therefore, of this chain, we may expect to discover tertiary
+Plutonic rocks laid open to view; and Mr. Darwin&rsquo;s account of
+the Chilian Andes, to which the reader may refer, fully realises
+this expectation: for he shows that we have strong ground to
+presume that Plutonic rocks there exposed on a large scale are of
+later date than certain Secondary and Tertiary formations.</p>
+
+<p>But the theory adopted in this work of the subterranean origin
+of the hypogene formations would be untenable, if the supposed fact
+here alluded to, of the appearance of tertiary granite at the
+surface, was not a rare exception to the general rule. A
+considerable lapse of time must intervene between the formation of
+Plutonic and metamorphic rocks in the nether regions and their
+emergence at the surface. For a long series of subterranean
+movements must occur before such rocks can be uplifted into the
+atmosphere or the ocean; and, before they can be rendered visible
+to man, some strata which previously covered them must have been
+stripped off by denudation.</p>
+
+<p>We know that in the Bay of Baiæ in 1538, in Cutch in 1819,
+and on several occasions in Peru and Chili, since the commencement
+of the present century, the permanent upheaval or subsidence of
+land has been accompanied by the simultaneous emission of lava at
+one or more points in the same volcanic region. From these and
+other examples it may be inferred that the rising or sinking of the
+earth&rsquo;s crust, operations by which sea is converted into
+land, and land into sea, are a part only of the consequences of
+subterranean igneous action. It can scarcely be doubted that this
+action consists, in a great degree, of the baking, and occasionally
+the liquefaction, of rocks, causing them to assume, in some cases a
+larger, in others a smaller volume than before the application of
+heat. It consists also in the generation of gases, and their
+expansion by heat, and the injection of liquid matter into rents
+formed in superincumbent rocks. The prodigious scale on which these
+subterranean causes have operated in Sicily since the deposition of
+the Newer Pliocene strata will be appreciated when we remember that
+throughout half the surface of that island such strata are met
+with, raised to the height of from 50 to that of 2000 and even 3000
+feet above the level of the sea. In the same island also the older
+rocks which are contiguous to these marine tertiary strata must
+have undergone, within the same period, a similar amount of
+upheaval.</p>
+
+<p>
+<a name="page570"></a>The like observations may be extended to nearly the whole
+of Europe, for, since the commencement of the Eocene Period, the entire
+European area, including some of the central and very lofty portions of the
+Alps themselves, as I have elsewhere shown,<a href="#fn-32.5" name="fnref-32.5"
+id="fnref-32.5"><sup>[5]</sup></a> has, with the exception of a few districts,
+emerged from the deep to its present altitude. There must, therefore, have been
+at great depths in the earth&rsquo;s crust, within the same period, an amount
+of subterranean change corresponding to this vast alteration of level affecting
+a whole continent.
+</p>
+
+<p>The principal effect of subterranean movements during the
+Tertiary Period seems to have consisted in the upheaval of hypogene
+formations of an age anterior to the Carboniferous. The repetition
+of another series of movements, of equal violence, might upraise
+the Plutonic and metamorphic rocks of many secondary periods; and,
+if the same force should still continue to act, the next
+convulsions might bring up to the day the <i>tertiary</i> and <i>
+recent</i> hypogene rocks. In the course of such changes many of
+the existing sedimentary strata would suffer greatly by denudation,
+others might assume a metamorphic structure, or become melted down
+into Plutonic and volcanic rocks. Meanwhile the deposition of a
+great thickness of new strata would not fail to take place during
+the upheaval and partial destruction of the older rocks. But I must
+refer the reader to the last chapter but one of this volume for a
+fuller explanation of these views.</p>
+
+<img src="images/fig618.jpg" width="175" height="107" alt=
+"Fig. 618: Section through three layers (b, c, d) of the Cretaceous series over
+granite (A)." />
+
+<p><b>Plutonic Rocks of Cretaceous Period.</b>&mdash;It will be
+shown in the next chapter that chalk, as well as lias, has been
+altered by granite in the eastern Pyrenees. Whether such granite be
+cretaceous or tertiary, cannot easily be decided. Suppose <i>b, c,
+d,</i> Fig. 618, to be three members of the Cretaceous series, the
+lowest of which, <i>b,</i> has been altered by the granite A, the
+modifying influence not having extended so far as <i>c,</i> or
+having but slightly affected its lowest beds. Now it can rarely be
+possible for the geologist to decide whether the beds <i>d</i>
+existed at the time of the intrusion of A, and alteration of <i>
+b</i> and <i>c,</i> or whether they were subsequently thrown down
+upon <i>c.</i> But as some Cretaceous and even Tertiary rocks have
+been raised to the height of more than 9000 feet in the Pyrenees,
+we must not assume that plutonic formations of the same periods may
+not have been brought up and
+<a name="page571"></a>exposed by denudation, at the height of 2000 or 3000 feet on the
+flanks of that chain.</p>
+
+<img src="images/fig619.jpg" width="237" height="281" alt=
+"Fig. 619: Junction of granite with Jurassic or Oolite strata in the Alps,
+near Champoleon." />
+
+<p>
+<b>Plutonic Rocks of the Oolite and Lias.</b>&mdash;In the Department of the
+Hautes Alpes, in France, M. Élie de Beaumont traced a black argillaceous
+limestone, charged with belemnites, to within a few yards of a mass of granite.
+Here the limestone begins to put on a granular texture, but is extremely
+fine-grained. When nearer the junction it becomes grey, and has a saccharoid
+structure. In another locality, near Champoleon, a granite composed of quartz,
+black mica, and rose-coloured feldspar is observed partly to overlie the
+secondary rocks, producing an alteration which extends for about 30 feet
+downward, diminishing in the beds which lie farthest from the granite. (See
+Fig. 619.) In the altered mass the argillaceous beds are hardened, the
+limestone is saccharoid, the grits quartzose, and in the midst of them is a
+thin layer of an imperfect granite. It is also an important circumstance that
+near the point of contact, both the granite and the secondary rocks become
+metalliferous, and contain nests and small veins of blende, galena, iron, and
+copper pyrites. The stratified rocks become harder and more crystalline, but
+the granite, on the contrary, softer and less perfectly crystallised near the
+junction.<a href="#fn-32.6" name="fnref-32.6"
+id="fnref-32.6"><sup>[6]</sup></a> Although the granite is incumbent in the
+section (Fig. 619), we cannot assume that it overflowed the strata, for the
+disturbances of the rocks are so great in this part of the Alps that their
+original position is often inverted.
+</p>
+
+<p>
+At Predazzo, in the Tyrol, secondary strata, some of which are limestones of
+the Oolitic period, have been traversed and altered by Plutonic rocks, one
+portion of which is an augitic porphyry, which passes insensibly into granite.
+The limestone <a name="page572"></a>is changed into granular marble, with a
+band of serpentine at the junction.<a href="#fn-32.7" name="fnref-32.7"
+id="fnref-32.7"><sup>[7]</sup></a>
+</p>
+
+<p>
+<b>Plutonic Rocks of Carboniferous Period.</b>&mdash;The granite of Dartmoor,
+in Devonshire, was formerly supposed to be one of the most ancient of the
+Plutonic rocks, but is now ascertained to be posterior in date to the
+culm-measures of that county, which from their position, and, as containing
+true coal-plants, are now known to be members of the true Carboniferous series.
+This granite, like the syenitic granite of Christiania, has broken through the
+stratified formations, on the north-west side of Dartmoor, the successive
+members of the culm-measures abutting against the granite, and becoming
+metamorphic as they approach. These strata are also penetrated by granite
+veins, and Plutonic dikes, called &ldquo;elvans.&rdquo;<a href="#fn-32.8"
+name="fnref-32.8" id="fnref-32.8"><sup>[8]</sup></a> The granite of Cornwall is
+probably of the same date, and, therefore, as modern as the Carboniferous
+strata, if not newer.
+</p>
+
+<p><img src="images/fig620.jpg" width="338" height="94" alt=
+"Fig. 620: Section through Silurian strata and Granite." /></p>
+
+<p>
+<b>Plutonic Rocks of Silurian Period.</b>&mdash;It has long been known that a
+very ancient granite near Christiania, in Norway, is posterior in date to the
+Lower Silurian strata of that region, although its exact position in the
+Palæozoic series cannot be defined. Von Buch first announced, in 1813, that it
+was of newer origin than certain limestones containing orthocerata and
+trilobites. The proofs consist in the penetration of granite veins into the
+shale and limestone, and the alteration of the strata, for a considerable
+distance from the point of contact, both of these veins and the central mass
+from which they emanate. (See <a href= "#page562">p. 562</a>) Von Buch supposed
+that the Plutonic rock alternated with the fossiliferous strata, and that large
+masses of granite were sometimes incumbent upon the strata; but this idea was
+erroneous, and arose from the fact that the beds of shale and limestone often
+dip towards the granite up to the point of contact, appearing as if they would
+pass under it in mass, as at <i>a,</i> Fig. 620, and then again on the opposite
+side of the same mountain, as at <i>b,</i> dip away from the same granite. When
+the junctions, however, are carefully examined, it is found that the Plutonic
+rock <a name="page573"></a>intrudes itself in veins, and nowhere covers the
+fossiliferous strata in large overlying masses, as is so commonly the case with
+trappean formations.<a href="#fn-32.9" name="fnref-32.9"
+id="fnref-32.9"><sup>[9]</sup></a>
+</p>
+
+<p>Now this granite, which is more modern than the Silurian strata
+of Norway, also sends veins in the same country into an ancient
+formation of gneiss; and the relations of the Plutonic rock and the
+gneiss, at their junction, are full of interest when we duly
+consider the wide difference of epoch which must have separated
+their origin.</p>
+
+<p><img src="images/fig621.jpg" width="334" height="146" alt=
+"Fig. 621: Granite sending veins into Silurian strata and gneiss. Christiania, Norway." />
+</p>
+
+<p>The length of this interval of time is attested by the following
+facts: The fossiliferous, or Silurian, beds rest unconformably upon
+the truncated edges of the gneiss, the inclined strata of which had
+been denuded before the sedimentary beds were superimposed (see
+Figure 621). The signs of denudation are twofold; first, the
+surface of the gneiss is seen occasionally, on the removal of the
+newer beds containing organic remains, to be worn and smoothed;
+secondly, pebbles of gneiss have been found in some of these
+Silurian strata. Between the origin, therefore, of the gneiss and
+the granite there intervened, first, the period when the strata of
+gneiss were denuded; secondly, the period of the deposition of the
+Silurian deposits upon the denuded and inclined gneiss, a. Yet the
+granite produced after this long interval is often so intimately
+blended with the ancient gneiss, at the point of junction, that it
+is impossible to draw any other than an arbitrary line of
+separation between them; and where this is not the case, tortuous
+veins of granite pass freely through gneiss, ending sometimes in
+threads, as if the older rock had offered no resistance to their
+passage. These appearances may probably be due to hydrothermal
+action (see <a href="#page584">p. 584</a>). I shall
+merely observe in this place that had such junctions alone been
+visible, and had we not learnt, from other sections, how long a
+period elapsed between the consolidation of the gneiss and the
+injection of this granite, we might have suspected that the gneiss
+was scarcely solidified,
+<a name="page574"></a>or had not yet assumed its complete metamorphic character when
+invaded by the Plutonic rock. From this example we may learn how
+impossible it is to conjecture whether certain granites in
+Scotland, and other countries, which send veins into gneiss and
+other metamorphic rocks, are primary, or whether they may not
+belong to some secondary or tertiary period.</p>
+
+<p><b>Oldest Granites.</b>&mdash;It is not half a century since the
+doctrine was very general that all granitic rocks were <i>
+primitive,</i> that is to say, that they originated before the
+deposition of the first sedimentary strata, and before the creation
+of organic beings (see <a href="#page34">p. 34</a>). But
+so greatly are our views now changed, that we find it no easy task
+to point out a single mass of granite demonstrably more ancient
+than known fossiliferous deposits. Could we discover some
+Laurentian strata resting immediately on granite, there being no
+alterations at the point of contact, nor any intersecting granitic
+veins, we might then affirm the Plutonic rock to have originated
+before the oldest known fossiliferous strata. Still it would be
+presumptuous, as we have already pointed out (<a href=
+"#page464">p. 464</a>), to suppose that when a small part
+only of the globe has been investigated, we are acquainted with the
+oldest fossiliferous strata in the crust of our planet. Even when
+these are found, we cannot assume that there never were any
+antecedent strata containing organic remains, which may have become
+metamorphic. If we find pebbles of granite in a conglomerate of the
+Lower Laurentian system, we may then feel assured that the parent
+granite was formed before the Laurentian formation. But if the
+incumbent strata be merely Cambrian or Silurian, the fundamental
+granite, although of high antiquity, may be posterior in date to
+<i>known</i> fossiliferous formations.</p>
+
+<p>
+<b>Protrusion of Solid Granite.</b>&mdash;In part of Sutherlandshire, near
+Brora, common granite, composed of feldspar, quartz, and mica is in immediate
+contact with Oolitic strata, and has clearly been elevated to the surface at a
+period subsequent to the deposition of those strata.<a href="#fn-32.10"
+name="fnref-32.10" id="fnref-32.10"><sup>[10]</sup></a> Professor Sedgwick and
+Sir R. Murchison conceive that this granite has been upheaved in a solid form;
+and that in breaking through the submarine deposits, with which it was not
+perhaps originally in contact, it has fractured them so as to form a breccia
+along the line of junction. This breccia consists of fragments of shale,
+sandstone, and limestone, with fossils of the oolite, all united together by a
+calcareous cement. The secondary strata at some distance from the granite are
+but slightly disturbed, but in proportion to their proximity the amount of
+dislocation becomes greater.
+</p>
+
+<p>
+<a name="page575"></a>Mr. T. McKenney Hughes has suggested to me in explanation of
+these phenomena that they may be the effect of the association of
+more pliant strata with hard unyielding rocks, the whole of which
+were subjected simultaneously to great movements, whether of
+elevation or subsidence, and of lateral pressure, during which the
+more solid granite, being incapable of compression, was forced
+through the softer beds of shale, sandstone, and limestone. He
+remarks that similar breccias with slickensides are observed on a
+minor scale where rocks of different composition and rigidity are
+contorted together. Such protrusion may have been brought about by
+degrees by innumerable shocks of earthquakes repeated after long
+intervals of time along the same tract of country. The opening of
+new fissures in the hardest rocks is a frequent accompaniment of
+such convulsions, and during the consequent vibrations, breccias
+must often be caused. But these catastrophes, as we well know, do
+not imply that the land or sea of the disturbed region are rendered
+uninhabitable by living beings, and by no means indicate a state of
+things different from that witnessed in the ordinary course of
+nature.
+</p>
+
+<p class="footnote">
+<a name="fn-32.1" id="fn-32.1"></a> <a href="#fnref-32.1">[1]</a>
+Silliman&rsquo;s Journ., No. 69, p. 123.
+</p>
+
+<p class="footnote">
+<a name="fn-32.2" id="fn-32.2"></a> <a href="#fnref-32.2">[2]</a>
+See &ldquo;Principles,&rdquo; <i>Index,</i> &ldquo;Jorullo.&rdquo;
+</p>
+
+<p class="footnote">
+<a name="fn-32.3" id="fn-32.3"></a> <a href="#fnref-32.3">[3]</a>
+Ibid., &ldquo;Volcanic Eruptions.&rdquo;
+</p>
+
+<p class="footnote">
+<a name="fn-32.4" id="fn-32.4"></a> <a href="#fnref-32.4">[4]</a>
+&ldquo;Western Islands,&rdquo; vol. i, p. 330.
+</p>
+
+<p class="footnote">
+<a name="fn-32.5" id="fn-32.5"></a> <a href="#fnref-32.5">[5]</a>
+See map of Europe, and explanation, in Principles, book i.
+</p>
+
+<p class="footnote">
+<a name="fn-32.6" id="fn-32.6"></a> <a href="#fnref-32.6">[6]</a>
+Élie de Beaumont sur les Montagnes de l&rsquo;Oisans, etc. Mém. de la Soc.
+d&rsquo;Hist. Nat. de Paris, tome v.
+</p>
+
+<p class="footnote">
+<a name="fn-32.7" id="fn-32.7"></a> <a href="#fnref-32.7">[7]</a>
+Von Buch, Annales de Chimie, etc.
+</p>
+
+<p class="footnote">
+<a name="fn-32.8" id="fn-32.8"></a> <a href="#fnref-32.8">[8]</a>
+Proceed. Geol. Soc., vol. ii, p. 562; and Trans., 2nd series, vol. v, p. 686.
+</p>
+
+<p class="footnote">
+<a name="fn-32.9" id="fn-32.9"></a> <a href="#fnref-32.9">[9]</a>
+See the Gæa Norvegica and other works of Keilhau, with whom I examined this
+country.
+</p>
+
+<p class="footnote">
+<a name="fn-32.10" id="fn-32.10"></a> <a href="#fnref-32.10">[10]</a>
+Murchison, Geol. Trans., 2nd series, vol. ii, p. 307.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap33"></a><a name="page576"></a>CHAPTER XXXIII.<br/>
+METAMORPHIC ROCKS.</h2>
+
+<p class="letter">General Character of Metamorphic Rocks. &mdash;
+Gneiss. &mdash; Hornblende-schist. &mdash; Serpentine. &mdash;
+Mica-schist. &mdash; Clay-slate. &mdash; Quartzite. &mdash;
+Chlorite-schist. &mdash; Metamorphic Limestone. &mdash; Origin of
+the metamorphic Strata. &mdash; Their Stratification. &mdash;
+Fossiliferous Strata near intrusive Masses of Granite converted
+into Rocks identical with different Members of the metamorphic
+Series. &mdash; Arguments hence derived as to the Nature of
+Plutonic Action. &mdash; Hydrothermal Action, or the Influence of
+Steam and Gases in producing Metamorphism. &mdash; Objections to
+the metamorphic Theory considered.</p>
+
+<p>We have now considered three distinct classes of rocks: first,
+the aqueous, or fossiliferous; secondly, the volcanic; and,
+thirdly, the Plutonic; and it remains for us to examine those
+crystalline (or hypogene) strata to which the name of <i>
+metamorphic</i> has been assigned. The last-mentioned term
+expresses, as before explained, a theoretical opinion that such
+strata, after having been deposited from water, acquired, by the
+influence of heat and other causes, a highly crystalline texture.
+They who still question this opinion may call the rocks under
+consideration the stratified hypogene formations or crystalline
+schists.</p>
+
+<p>These rocks, when in their characteristic or normal state, are
+wholly devoid of organic remains, and contain no distinct fragments
+of other rocks, whether rounded or angular. They sometimes break
+out in the central parts of mountain chains, but in other cases
+extend over areas of vast dimensions, occupying, for example,
+nearly the whole of Norway and Sweden, where, as in Brazil, they
+appear alike in the lower and higher grounds. However crystalline
+these rocks may become in certain regions, they never, like granite
+or trap, send veins into contiguous formations. In Great Britain,
+those members of the series which approach most nearly to granite
+in their composition, as gneiss, mica-schist, and
+hornblende-schist, are confined to the country north of the rivers
+Forth and Clyde.</p>
+
+<p>Many attempts have been made to trace a general order of
+succession or superposition in the members of this family;
+clay-slate, for example, having been often supposed to hold
+invariably a higher geological position than mica-schist, and
+<a name="page577"></a>mica-schist to overlie gneiss. But although such an order may
+prevail throughout limited districts, it is by no means universal.
+To this subject, however, I shall again revert, in Chapter XXXV,
+where the chronological relations of the metamorphic rocks are
+pointed out.</p>
+
+<p><b>Principal Metamorphic Rocks.</b>&mdash;The following may be
+enumerated as the principal members of the metamorphic
+class:&mdash;gneiss, mica-schist, hornblende-schist, clay-slate,
+chlorite-schist, hypogene or metamorphic limestone, and certain
+kinds of quartz-rock or quartzite.</p>
+
+<p><img src="images/fig622.jpg" width="302" height="176" alt=
+"Fig. 622: Fragment of gneiss; section made at right angles to the planes of
+foliation." />
+</p>
+
+<p><i>Gneiss.</i>&mdash;The first of these, gneiss, may be called
+stratified&mdash;or by those who object to that term, foliated&mdash;granite,
+being formed of the same materials as granite, namely, feldspar,
+quartz, and mica. In the specimen in Fig. 622, the white layers
+consist almost exclusively of granular feldspar, with here and
+there a speck of mica and grain of quartz. The dark layers are
+composed of grey quartz and black mica, with occasionally a grain
+of feldspar intermixed. The rock splits most easily in the plane of
+these darker layers, and the surface thus exposed is almost
+entirely covered with shining spangles of mica. The accompanying
+quartz, however, greatly predominates in quantity, but the most
+ready cleavage is determined by the abundance of mica in certain
+parts of the dark layer. Instead of consisting of these thin
+laminæ, gneiss is sometimes simply divided into thick beds,
+in which the mica has only a slight degree of parallelism to the
+planes of stratification.</p>
+
+<p>Hand specimens may often be obtained from such gneiss which are
+undistinguishable from granite, affording an argument to which we
+shall allude in the concluding part of this chapter, in favour of
+those who regard all granite and syenite not as igneous rocks, but
+as aqueous formations so altered as to have lost all signs of their
+original stratified arrangement. Gneiss in geology is commonly used
+to designate not merely
+<a name="page578"></a>stratified and foliated rocks having the same component
+materials as granite or syenite, but also in a wider sense to
+embrace the formation with which other members of the metamorphic
+series, such as hornblende-schist, may alternate, and which are
+then considered subordinate to the true gneiss.</p>
+
+<p>The different varieties of rock allied to gneiss, into which
+feldspar enters as an essential ingredient, will be understood by
+referring to what was said of granite. Thus, for example,
+hornblende may be superadded to mica, quartz, and feldspar, forming
+a hornblendic or syenitic gneiss; or talc may be substituted for
+mica, constituting talcose gneiss (called stratified protogine by
+the French), a rock composed of feldspar, quartz, and talc, in
+distinct crystals or grains.</p>
+
+<p><i>Eurite,</i> which has already been mentioned as a Plutonic
+rock, occurs also with precisely the same composition in beds
+subordinate to gneiss or mica-slate.</p>
+
+<p><i>Hornblende-schist</i> is usually black, and composed
+principally of hornblende, with a variable quantity of feldspar,
+and sometimes grains of quartz. When the hornblende and feldspar
+are in nearly equal quantities, and the rock is not slaty, it
+corresponds in character with the greenstones of the trap family,
+and has been called &ldquo;primitive greenstone.&rdquo; It may be
+termed hornblende rock, or amphibolite. Some of these hornblendic
+masses may really have been volcanic rocks, which have since
+assumed a more crystalline or metamorphic texture.</p>
+
+<p><i>Serpentine</i> is a greenish rock, a silicate of magnesia, in
+which there is sometimes from 30 to 40 per cent of magnesia. It
+enters largely into the composition of a trap dike cutting through
+Old Red Sandstone in Forfarshire, and in that case is probably an
+altered basaltic dike which had contained much olivine. The theory
+of its having been originally a volcanic product subsequently
+altered by metamorphism may at first sight seem inconsistent with
+its occurrence in large and regularly stratified masses in the
+metamorphic series in Scotland, as in Aberdeenshire. But it has
+been suggested in explanation that such serpentine may have been
+originally regularly-bedded trap tuff, and volcanic breccia, with
+much olivine, which would still retain a stratified appearance
+after their conversion into a metamorphic rock.</p>
+
+<p><i>Actinolite Schist</i> is a slaty foliated rock, composed
+chiefly of actinolite, an emerald-green mineral, allied to
+hornblende, with some admixture of garnet, mica, and quartz.</p>
+
+<p><i>Mica-schist</i> or <i>Micaceous Schist</i> is, next to
+gneiss, one of the most abundant rocks of the metamorphic series.
+It is slaty, essentially composed of mica and quartz, the mica
+<a name="page579"></a>sometimes appearing to constitute the whole mass. Beds of pure
+quartz also occur in this formation. In some districts, garnets in
+regular twelve-sided crystals form an integrant part of
+mica-schist. This rock passes by insensible gradations into
+clay-slate.</p>
+
+<p><i>Clay-slate&mdash;Argillaceous
+Schist&mdash;Argillite.</i>&mdash;This rock sometimes resembles an
+indurated clay or shale. It is for the most part extremely fissile,
+often affording good roofing-slate. Occasionally it derives a
+shining and silky lustre from the minute particles of mica or talc
+which it contains. It varies from greenish or bluish-grey to a lead
+colour; and it may be said of this, more than of any other schist,
+that it is common to the metamorphic and fossiliferous series, for
+some clay-slates taken from each division would not be
+distinguishable by mineral characters alone. It is not uncommon to
+meet with an argillaceous rock having the same composition, without
+the slaty cleavage, which may be called argillite.</p>
+
+<p><i>Chlorite Schist</i> is a green slaty rock, in which chlorite
+is abundant in foliated plates, usually blended with minute grains
+of quartz, or sometimes with feldspar or mica; often associated
+with, and graduating into, gneiss and clay-slate.</p>
+
+<p><i>Quartzite,</i> or <i>Quartz Rock,</i> is an aggregate of
+grains of quartz which are either in minute crystals, or in many
+cases slightly rounded, occurring in regular strata, associated
+with gneiss or other metamorphic rocks. Compact quartz, like that
+so frequently found in veins, is also found together with granular
+quartzite. Both of these alternate with gneiss or mica-schist, or
+pass into those rocks by the addition of mica, or of feldspar and
+mica.</p>
+
+<p><i>Crystalline,</i> or <i>Metamorphic Limestone.</i>&mdash;This
+hypogene rock, called by the earlier geologists <i>primary
+limestone,</i> is sometimes a white crystalline granular marble,
+which when in thick beds can be used in sculpture; but more
+frequently it occurs in thin beds, forming a foliated schist much
+resembling in colour and arrangement certain varieties of gneiss
+and mica-schist. When it alternates with these rocks, it often
+contains some crystals of mica, and occasionally quartz, feldspar,
+hornblende, talc, chlorite, garnet, and other minerals. It enters
+sparingly into the structure of the hypogene districts of Norway,
+Sweden, and Scotland, but is largely developed in the Alps.</p>
+
+<p><b>Origin of the Metamorphic Strata.</b>&mdash;Having said thus
+much of the mineral composition of the metamorphic rocks, I may
+combine what remains to be said of their structure and history with
+an account of the opinions entertained of their probable origin. At
+the same time, it may be well to
+<a name="page580"></a>forewarn the reader that we are here entering upon ground of
+controversy, and soon reach the limits where positive induction
+ends, and beyond which we can only indulge in speculations. It was
+once a favourite doctrine, and is still maintained by many, that
+these rocks owe their crystalline texture, their want of all signs
+of a mechanical origin, or of fossil contents, to a peculiar and
+nascent condition of the planet at the period of their formation.
+The arguments in refutation of this hypothesis will be more fully
+considered when I show, in Chapter XXXV, to how many different ages
+the metamorphic formations are referable, and how gneiss,
+mica-schist, clay-slate, and hypogene limestone (that of Carrara,
+for example) have been formed, not only since the first
+introduction of organic beings into this planet, but even long
+after many distinct races of plants and animals had flourished and
+passed away in succession.</p>
+
+<p>The doctrine respecting the crystalline strata implied in the
+name metamorphic may properly be treated of in this place; and we
+must first inquire whether these rocks are really entitled to be
+called stratified in the strict sense of having been originally
+deposited as sediment from water. The general adoption by
+geologists of the term stratified, as applied to these rocks,
+sufficiently attests their division into beds very analogous, at
+least in form, to ordinary fossiliferous strata. This resemblance
+is by no means confined to the existence in both occasionally of a
+laminated structure, but extends to every kind of arrangement which
+is compatible with the absence of fossils, and of sand, pebbles,
+ripple-mark, and other characters which the metamorphic theory
+supposes to have been obliterated by Plutonic action. Thus, for
+example, we behold alike in the crystalline and fossiliferous
+formations an alternation of beds varying greatly in composition,
+colour, and thickness. We observe, for instance, gneiss alternating
+with layers of black hornblende-schist or of green chlorite-schist,
+or with granular quartz or limestone; and the interchange of these
+different strata may be repeated for an indefinite number of times.
+In the like manner, mica-schist alternates with chlorite-schist,
+and with beds of pure quartz or of granular limestone. We have
+already seen that, near the immediate contact of granitic veins and
+volcanic dikes, very extraordinary alterations in rocks have taken
+place, more especially in the neighbourhood of granite. It will be
+useful here to add other illustrations, showing that a texture
+undistinguishable from that which characterises the more
+crystalline metamorphic formations has actually been superinduced
+in strata once fossiliferous.</p>
+
+<p>
+<a name="page581"></a><b>Fossiliferous Strata rendered metamorphic by intrusive Masses
+of Granite.</b>&mdash;In the southern extremity of Norway there is
+a large district, on the west side of the fiord of Christiania,
+which I visited in 1837 with the late Professor Keilhau, in which
+syenitic granite protrudes in mountain masses through fossiliferous
+strata, and usually sends veins into them at the point of contact.
+The stratified rocks, replete with shells and zoophytes, consist
+chiefly of shale, limestone, and some sandstone, and all these are
+invariably altered near the granite for a distance of from 50 to
+400 yards. The aluminous shales are hardened, and have become
+flinty. Sometimes they resemble jasper. Ribboned jasper is produced
+by the hardening of alternate layers of green and
+chocolate-coloured schist, each stripe faithfully representing the
+original lines of stratification. Nearer the granite the schist
+often contains crystals of hornblende, which are even met with in
+some places for a distance of several hundred yards from the
+junction; and this black hornblende is so abundant that eminent
+geologists, when passing through the country, have confounded it
+with the ancient hornblende-schist, subordinate to the great gneiss
+formation of Norway. Frequently, between the granite and the
+hornblende-slate above-mentioned, grains of mica and crystalline
+feldspar appear in the schist, so that rocks resembling gneiss and
+mica-schist are produced. Fossils can rarely be detected in these
+schists, and they are more completely effaced in proportion to the
+more crystalline texture of the beds, and their vicinity to the
+granite.</p>
+
+<p><img src="images/fig623.jpg" width="341" height="219" alt=
+"Fig. 623: Ground-plan of altered slate and limestone near granite.
+Christiania. The arrows indicate the dip, and the oblique lines the strike of
+the beds." />
+</p>
+
+<p>
+In some places the siliceous matter of the schist becomes a granular quartz;
+and when hornblende and mica are added, the altered rock loses its
+stratification, and passes into a kind of granite. The limestone, which at
+points remote <a name="page582"></a>from the granite is of an earthy texture
+and blue colour, and often abounds in corals, becomes a white granular marble
+near the granite, sometimes siliceous, the granular structure extending
+occasionally upward of 400 yards from the junction; the corals being for the
+most part obliterated, though sometimes preserved, even in the white marble.
+Both the altered limestone and hardened slate contain garnets in many places,
+also ores of iron, lead, and copper, with some silver. These alterations occur
+equally whether the granite invades the strata in a line parallel to the
+general strike of the fossiliferous beds, or in a line at right angles to their
+strike, both of which modes of junction will be seen by the ground-plan in Fig.
+623.<a href="#fn-33.1" name="fnref-33.1" id="fnref-33.1"><sup>[1]</sup></a>
+</p>
+
+<p>
+The granite of Cornwall sends forth veins into a coarse argillaceous-schist,
+provincially termed killas. This killas is converted into hornblende-schist
+near the contact with the veins. These appearances are well seen at the
+junction of the granite and killas, in St. Michael&rsquo;s Mount, a small
+island nearly 300 feet high, situated in the bay, at a distance of about three
+miles from Penzance. The granite of Dartmoor, in Devonshire, says Sir H. De la
+Beche, has intruded itself into the Carboniferous slate and slaty sandstone,
+twisting and contorting the strata, and sending veins into them. Hence some of
+the slate rocks have become &ldquo;micaceous; others more indurated, and with
+the characters of mica-slate and gneiss; while others again appear converted
+into a hard zoned rock strongly impregnated with feldspar.&rdquo;<a
+href="#fn-33.2" name="fnref-33.2" id="fnref-33.2"><sup>[2]</sup></a>
+</p>
+
+<p>We learn from the investigation of M. Dufrenoy that in the
+eastern Pyrenees there are mountain masses of granite posterior in
+date to the formations called lias and chalk of that district, and
+that these fossiliferous rocks are greatly altered in texture, and
+often charged with iron-ore, in the neighbourhood of the granite.
+Thus in the environs of St. Martin, near St. Paul de Fenouillet,
+the chalky limestone becomes more crystalline and saccharoid as it
+approaches the granite, and loses all trace of the fossils which it
+previously contained in abundance. At some points, also, it becomes
+dolomitic, and filled with small veins of carbonate of iron, and
+spots of red iron-ore. At Rancie the lias nearest the granite is
+not only filled with iron-ore, but charged with pyrites, tremolite,
+garnet, and a new mineral somewhat allied to feldspar, called, from
+the place in the Pyrenees where it occurs,
+&ldquo;couzeranite.&rdquo;</p>
+
+<p>
+&ldquo;Hornblende-schist,&rdquo; says Dr. MacCulloch, &ldquo;may at first have
+been mere clay; for clay or shale is found altered by <a
+name="page583"></a>trap into Lydian stone, a substance differing from
+hornblende-schist almost solely in compactness and uniformity of
+texture.&rdquo;<a href="#fn-33.3" name="fnref-33.3"
+id="fnref-33.3"><sup>[3]</sup></a> &ldquo;In Shetland,&rdquo; remarks the same
+author, &ldquo;argillaceous-schist (or clay-slate), when in contact with
+granite, is sometimes converted into hornblende-schist, the schist becoming
+first siliceous, and ultimately, at the contact, hornblende-schist.&rdquo; In
+like manner gneiss and mica-schist may be nothing more than altered micaceous
+and argillaceous sandstones, granular quartz may have been derived from
+siliceous sandstone, and compact quartz from the same materials. Clay-slate may
+be altered shale, and granular marble may have originated in the form of
+ordinary limestone, replete with shells and corals, which have since been
+obliterated; and, lastly, calcareous sands and marls may have been changed into
+impure crystalline limestones.
+</p>
+
+<p>
+The anthracite and plumbago associated with hypogene rocks may have been coal;
+for not only is coal converted into anthracite in the vicinity of some trap
+dikes, but we have seen that a like change has taken place generally even far
+from the contact of igneous rocks, in the disturbed region of the Appalachians.
+At Worcester, in the State of Massachusetts, 45 miles due west of Boston, a bed
+of plumbago and impure anthracite occurs, interstratified with mica-schist. It
+is about two feet in thickness, and has been made use of both as fuel, and in
+the manufacture of lead pencils. At the distance of 30 miles from the plumbago,
+there occurs, on the borders of Rhode Island, an impure anthracite in slates
+containing impressions of coal-plants of the genera <i>Pecopteris, Neuropteris,
+Calamites,</i> etc. This anthracite is intermediate in character between that
+of Pennsylvania and the plumbago of Worcester, in which last the gaseous or
+volatile matter (hydrogen, oxygen, and nitrogen) is to the carbon only in the
+proportion of three per cent. After traversing the country in various
+directions, I came to the conclusion that the carboniferous shales or slates
+with anthracite and plants, which in Rhode Island often pass into mica-schists,
+have at Worcester assumed a perfectly crystalline and metamorphic texture; the
+anthracite having been nearly transmuted into that state of pure carbon which
+is called plumbago or graphite.<a href="#fn-33.4" name="fnref-33.4"
+id="fnref-33.4"><sup>[4]</sup></a>
+</p>
+
+<p>Now the alterations above described as superinduced in rocks by
+volcanic dikes and granite veins prove incontestably that powers
+exist in nature capable of transforming fossiliferous into
+crystalline strata, a very few simple elements
+<a name="page584"></a>constituting the component materials common to both classes of
+rocks. These elements, which are enumerated in the table at <a
+href="#page499">p. 499</a>, may be made to form new
+combinations by what has been termed Plutonic action, or those
+chemical changes which are no doubt connected with the passage of
+heat, unusually heated steam and waters, through the strata.</p>
+
+<p>
+<b>Hydrothermal Action, or the Influence of Steam and Gases in producing
+Metamorphism.</b>&mdash;The experiments of Gregory Watt, in fusing rocks in the
+laboratory, and allowing them to consolidate by slow cooling, prove distinctly
+that a rock need not be perfectly melted in order that a re-arrangement of its
+component particles should take place, and a partial crystallisation ensue.<a
+href="#fn-33.5" name="fnref-33.5" id="fnref-33.5"><sup>[5]</sup></a> We may
+easily suppose, therefore, that all traces of shells and other organic remains
+may be destroyed, and that new chemical combinations may arise, without the
+mass being so fused as that the lines of stratification should be wholly
+obliterated. We must not, however, imagine that heat alone, such as may be
+applied to a stone in the open air, can constitute all that is comprised in
+Plutonic action. We know that volcanoes in eruption not only emit fluid lava,
+but give off steam and other heated gases, which rush out in enormous volume,
+for days, weeks, or years continuously, and are even disengaged from lava
+during its consolidation.
+</p>
+
+<p>We also know that long after volcanoes have spent their force,
+hot springs continue for ages to flow out at various points in the
+same area. In regions, also, subject to violent earthquakes such
+springs are frequently observed issuing from rents, usually along
+lines of fault or displacement of the rocks. These thermal waters
+are most commonly charged with a variety of mineral ingredients,
+and they retain a remarkable uniformity of temperature from century
+to century. A like uniformity is also persistent in the nature of
+the earthy, metallic, and gaseous substances with which they are
+impregnated. It is well ascertained that springs, whether hot or
+cold, charged with carbonic acid, especially with hydrofluoric
+acid, which is often present in small quantities, are powerful
+causes of decomposition and chemical reaction in rocks through
+which they percolate.</p>
+
+<p>
+The changes which Daubrée has shown to have been produced by the alkaline
+waters of Plombières in the Vosges, are more especially instructive.<a
+href="#fn-33.6" name="fnref-33.6" id="fnref-33.6"><sup>[6]</sup></a> These
+waters have a heat of 160&deg; F., or an excess of 109&deg; above the average
+temperature of ordinary springs in that district. They were <a
+name="page585"></a>conveyed by the Romans to baths through long conduits or
+aqueducts. The foundations of some of their works consisted of a bed of
+concrete made of lime, fragments of brick, and sandstone. Through this and
+other masonry the hot waters have been percolating for centuries, and have
+given rise to various zeolites&mdash;apophyllite and chabazite among others;
+also to calcareous spar, arragonite, and fluor spar, together with siliceous
+minerals, such as opal&mdash;all found in the inter-spaces of the bricks and
+mortar, or constituting part of their re-arranged materials. The quantity of
+heat brought into action in this instance in the course of 2000 years has, no
+doubt, been enormous, but the intensity of it developed at any one moment has
+been always inconsiderable.
+</p>
+
+<p>From these facts and from the experiments and observations of
+Sénarmont, Daubrée, Delesse, Scheerer, Sorby, Sterry
+Hunt, and others, we are led to infer that when in the bowels of
+the earth there are large volumes of matter containing water and
+various acids intensely heated under enormous pressure, these
+subterranean fluid masses will gradually part with their heat by
+the escape of steam and various gases through fissures, producing
+hot springs; or by the passage of the same through the pores of the
+overlying and injected rocks. Even the most compact rocks may be
+regarded, before they have been exposed to the air and dried, in
+the light of sponges filled with water. According to the
+experiments of Henry, water, under a hydrostatic pressure of 96
+feet, will absorb three times as much carbonic acid gas as it can
+under the ordinary pressure of the atmosphere. There are other
+gases, as well as the carbonic acid, which water absorbs, and more
+rapidly in proportion to the amount of pressure. Although the
+gaseous matter first absorbed would soon be condensed, and part
+with its heat, yet the continual arrival of fresh supplies from
+below might, in the course of ages, cause the temperature of the
+water, and with it that of the containing rock, to be materially
+raised; the water acts not only as a vehicle of heat, but also by
+its affinity for various silicates, which, when some of the
+materials of the invaded rocks are decomposed, form quartz,
+feldspar, mica, and other minerals. As for quartz, it can be
+produced under the influence of heat by water holding alkaline
+silicates in solution, as in the case of the Plombières
+springs. The quantity of water required, according to
+Daubrée, to produce great transformations in the mineral
+structure of rocks, is very small. As to the heat required,
+silicates may be produced in the moist way at about incipient red
+heat, whereas to form the same in the dry way would require a much
+higher temperature.</p>
+
+<p>
+<a name="page586"></a>M. Fournet, in his description of the metalliferous
+gneiss near Clermont, in Auvergne, states that all the minute fissures of the
+rock are quite saturated with free carbonic acid gas; which gas rises
+plentifully from the soil there and in many parts of the surrounding country.
+The various elements of the gneiss, with the exception of the quartz, are all
+softened; and new combinations of the acid with lime, iron, and manganese are
+continually in progress.<a href="#fn-33.7" name="fnref-33.7"
+id="fnref-33.7"><sup>[7]</sup></a>
+</p>
+
+<p>The power of subterranean gases is well illustrated by the
+stufas of St. Calogero in the Lipari Islands, where the horizontal
+strata of tuffs, forming cliffs 200 feet high, have been
+discoloured in places by the jets of steam often above the boiling
+point, called &ldquo;stufas,&rdquo; issuing from the fissures; and
+similar instances are recorded by M. Virlet of corrosion of rocks
+near Corinth, and by Dr. Daubeny of decomposition of trachytic
+rocks by sulphureted hydrogen and muriatic acid gases in the
+Solfatara, near Naples. In all these instances it is clear that the
+gaseous fluids must have made their way through vast thicknesses of
+porous or fissured rocks, and their modifying influence may spread
+through the crust for thousands of yards in thickness.</p>
+
+<p>It has been urged as an argument against the metamorphic theory,
+that rocks have a small power of conducting heat, and it is true
+that when dry, and in the air, they differ remarkably from metals
+in this respect. The syenite of Norway, as we have seen (<a href=
+"#page558">p. 558</a>), has sometimes altered
+fossiliferous strata both in the direction of their dip and strike
+for a distance of a quarter of a mile, but the theory of gneiss and
+mica-schist above proposed requires us to imagine that the same
+influence has extended through strata miles in thickness. Professor
+Bischof has shown what changes may be superinduced, on black marble
+and other rocks, by the steam of a hot spring having a temperature
+of no more than 133&deg; to 167&deg; Fahrenheit, and we are
+becoming more and more acquainted with the prominent part which
+water is playing in distributing the heat of the interior through
+mountain masses of incumbent strata, and of introducing into them
+various mineral elements in a fluid or gaseous state. Such facts
+may induce us to consider whether many granites and other rocks of
+that class may not sometimes represent merely the extreme of a
+similar slow metamorphism. But, on the other hand, the heat of lava
+in a volcanic crater when it is white and glowing like the sun must
+convince us that the temperature of a column of such a fluid at the
+depth of many miles exceeds any heat which can ever be witnessed at
+the surface.
+<a name="page587"></a>That large portions of the Plutonic rocks had been formed under
+the influence of such intense heat is in perfect accordance with
+their great volume, uniform composition, and absence of
+stratification. The forcing also of veins into contiguous
+stratified or schistose rocks is a natural consequence of the
+hydrostatic pressure to which columns of molten matter many miles
+in height must give rise.</p>
+
+<p><b>Objections to the Metamorphic Theory considered.</b>&mdash;It
+has been objected to the metamorphic theory that the crystalline
+schists contain a considerable proportion of potash and soda,
+whilst the sedimentary strata out of which they are supposed to
+have been formed are usually wanting in alkaline matter. But this
+reasoning proceeds on mistaken data, for clay, marl, shale, and
+slate often contain a considerable proportion of alkali, so much so
+as to make them frequently unfit to be burnt into bricks or
+pottery, and the Old Red Sandstone in Forfarshire and other parts
+of Scotland, derived from disintegration of granite, contains much
+triturated feldspar rich in potash. In the common salt by which
+strata are often largely impregnated, as in Patagonia, much soda is
+present, and potash enters largely into the composition of fossil
+sea-weeds, and recent analysis has also shown that the
+carboniferous strata in England, the Upper and Lower Silurian in
+East Canada, and the oldest clay-slates in Norway, all contain as
+much alkali as is generally present in metamorphic rocks.</p>
+
+<p>Another objection has been derived from the alternation of
+highly crystalline strata with others less crystalline. The heat,
+it is said, in its ascent from below, must have traversed the less
+altered schists before it reached a higher and more crystalline
+bed. In answer to this, it may be observed, that if a number of
+strata differing greatly in composition from each other be
+subjected to equal quantities of heat, or hydrothermal action,
+there is every probability that some will be much more fusible or
+soluble than others. Some, for example, will contain soda, potash,
+lime, or some other ingredient capable of acting as a flux or
+solvent; while others may be destitute of the same elements, and so
+refractory as to be very slightly affected by the same causes. Nor
+should it be forgotten that, as a general rule, the less
+crystalline rocks do really occur in the upper, and the more
+crystalline in the lower part of each metamorphic series.
+</p>
+
+<p class="footnote">
+<a name="fn-33.1" id="fn-33.1"></a> <a href="#fnref-33.1">[1]</a>
+Keilhau, Gæa Norvegica, pp. 61-63.
+</p>
+
+<p class="footnote">
+<a name="fn-33.2" id="fn-33.2"></a> <a href="#fnref-33.2">[2]</a>
+Geol. Manual, p. 479.
+</p>
+
+<p class="footnote">
+<a name="fn-33.3" id="fn-33.3"></a> <a href="#fnref-33.3">[3]</a>
+Syst. of Geol., vol. i, pp. 210, 211.
+</p>
+
+<p class="footnote">
+<a name="fn-33.4" id="fn-33.4"></a> <a href="#fnref-33.4">[4]</a>
+See Lyell, Quart. Geol. Journ., vol. i, p. 199.
+</p>
+
+<p class="footnote">
+<a name="fn-33.5" id="fn-33.5"></a> <a href="#fnref-33.5">[5]</a>
+Phil. Trans., 1804.
+</p>
+
+<p class="footnote">
+<a name="fn-33.6" id="fn-33.6"></a> <a href="#fnref-33.6">[6]</a>
+Daubrée, Sur le Métamorphisme. Paris, 1860.
+</p>
+
+<p class="footnote">
+<a name="fn-33.7" id="fn-33.7"></a> <a href="#fnref-33.7">[7]</a>
+See Principles, <i>Index,</i> &ldquo;Carbonated Springs,&rdquo; etc.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap34"></a><a name="page588"></a>CHAPTER XXXIV.<br/>
+METAMORPHIC ROCKS&mdash;<i>continued.</i></h2>
+
+<p class="letter">Definition of slaty Cleavage and Joints. &mdash;
+Supposed Causes of these Structures. &mdash; Crystalline Theory of
+Cleavage. &mdash; Mechanical Theory of Cleavage. &mdash;
+Condensation and Elongation of slate Rocks by lateral Pressure.
+&mdash; Lamination of some volcanic Rocks due to Motion. &mdash;
+Whether the Foliation of the crystalline Schists be usually
+parallel with the original Planes of Stratification. &mdash;
+Examples in Norway and Scotland. &mdash; Causes of Irregularity in
+the Planes of Foliation.</p>
+
+<p>We have already seen that chemical forces of great intensity
+have frequently acted upon sedimentary and fossiliferous strata
+long subsequently to their consolidation, and we may next inquire
+whether the component minerals of the altered rocks usually arrange
+themselves in planes parallel to the original planes of
+stratification, or whether, after crystallisation, they more
+commonly take up a different position.</p>
+
+<p>In order to estimate fairly the merits of this question, we must
+first define what is meant by the terms cleavage and foliation.
+There are four distinct forms of structure exhibited in rocks,
+namely, stratification, joints, slaty cleavage, and foliation; and
+all these must have different names, even though there be cases
+where it is impossible, after carefully studying the appearances,
+to decide upon the class to which they belong.</p>
+
+<p>
+<b>Slaty Cleavage.</b>&mdash;Professor Sedgwick, whose essay &ldquo;On the
+Structure of large Mineral Masses&rdquo; first cleared the way towards a better
+understanding of this difficult subject, observes, that joints are
+distinguishable from lines of slaty cleavage in this, that the rock intervening
+between two joints has no tendency to cleave in a direction parallel to the
+planes of the joints, whereas a rock is capable of indefinite subdivision in
+the direction of its slaty cleavage. In cases where the strata are curved, the
+planes of cleavage are still perfectly parallel. This has been observed in the
+slate rocks of part of Wales (see Fig. 624), which consists of a hard greenish
+slate. The true bedding is there indicated by a number of parallel stripes,
+some of a lighter and some of a darker colour than the general mass. Such
+stripes are found to be parallel to the true planes of stratification, wherever
+these are manifested by ripple-mark or by beds <a name="page589"></a>containing
+peculiar organic remains. Some of the contorted strata are of a coarse
+mechanical structure, alternating with fine-grained crystalline chloritic
+slates, in which case the same slaty cleavage extends through the coarser and
+finer beds, though it is brought out in greater perfection in proportion as the
+materials of the rock are fine and homogeneous. It is only when these are very
+coarse that the cleavage planes entirely vanish. In the Welsh hills these
+planes are usually inclined at a very considerable angle to the planes of the
+strata, the average angle being as much as from 30&deg; to 40&deg;. Sometimes
+the cleavage planes dip towards the same point of the compass as those of
+stratification, but often to opposite points.<a href="#fn-34.1"
+name="fnref-34.1" id="fnref-34.1"><sup>[1]</sup></a> The cleavage, as
+represented in Fig. 624, is generally constant over the whole of any area
+affected by one great set of disturbances, as if the same lateral pressure
+which caused the crumpling up of the rock along parallel, anticlinal, and
+synclinal axes caused also the cleavage.
+</p>
+
+<p><img src="images/fig624.jpg" width="331" height="102" alt=
+"Fig. 624: Parallel planes of cleavage intersecting curved strata." />
+</p>
+
+<img src="images/fig625.jpg" width="282" height="186" alt=
+"Fig. 625: Section in Lower Silurian slates of Cardiganshire, showing the
+cleavage planes bent along the junction of the beds." />
+
+<p>Mr. T. McK. Hughes remarks, that where a rough cleavage cuts
+flag-stones at a considerable angle to the planes of
+stratification, the rock often splits into large slabs, across
+which the lines of bedding are frequently seen, but when the
+cleavage planes approach within about 15&deg; of stratification,
+the rock is apt to split along the lines of bedding. He has also
+called my attention to the fact that subsequent movements in a
+cleaved rock sometimes drag and bend the cleavage planes along the
+junction of the beds in the manner indicated in Fig. 625.</p>
+
+<p>
+<b>Jointed Structure.</b>&mdash;In regard to joints, they are natural <a
+name="page590"></a>fissures which often traverse rocks in straight and
+well-determined lines. They afford to the quarryman, as Sir R. Murchison
+observes, when speaking of the phenomenon, as exhibited in Shropshire and the
+neighbouring counties, the greatest aid in the extraction of blocks of stone;
+and, if a sufficient number cross each other, the whole mass of rock is split
+into symmetrical blocks. The faces of the joints are for the most part smoother
+and more regular than the surfaces of true strata. The joints are straight-cut
+chinks, sometimes slightly open, and often passing, not only through layers of
+successive deposition, but also through balls of limestone or other matter
+which have been formed by concretionary action since the original accumulation
+of the strata. Such joints, therefore, must often have resulted from one of the
+last changes superinduced upon sedimentary deposits.<a href="#fn-34.2"
+name="fnref-34.2" id="fnref-34.2"><sup>[2]</sup></a>
+</p>
+
+<p><img src="images/fig626.jpg" width="344" height="194" alt=
+"Fig. 626: Stratification, joints, and cleavage." /></p>
+
+<p>In Fig. 626 the flat-surfaces of rock, A, B, C, represent
+exposed faces of joints, to which the walls of other joints, J J,
+are parallel. S S are the lines of stratification; D D are lines of
+slaty cleavage, which intersect the rock at a considerable angle to
+the planes of stratification.</p>
+
+<p>
+In the Swiss and Savoy Alps, as Mr. Bakewell has remarked, enormous masses of
+limestone are cut through so regularly by nearly vertical partings, and these
+joints are often so much more conspicuous than the seams of stratification,
+that an inexperienced observer will almost inevitably confound them, and
+suppose the strata to be perpendicular in places where in fact they are almost
+horizontal.<a href="#fn-34.3" name="fnref-34.3"
+id="fnref-34.3"><sup>[3]</sup></a>
+</p>
+
+<p>Now such joints are supposed to be analogous to the partings
+which separate volcanic and Plutonic rocks into cuboidal and
+prismatic masses. On a small scale we see clay and starch when dry
+split into similar shapes; this is often caused by simple
+contraction, whether the shrinking be due
+<a name="page591"></a>to the evaporation of water, or to a change of temperature. It
+is well known that many sandstones and other rocks expand by the
+application of moderate degrees of heat, and then contract again on
+cooling; and there can be no doubt that large portions of the
+earth&rsquo;s crust have, in the course of past ages, been
+subjected again and again to very different degrees of heat and
+cold. These alternations of temperature have probably contributed
+largely to the production of joints in rocks.</p>
+
+<p>In many countries where masses of basalt rest on sandstone, the
+aqueous rock has, for the distance of several feet from the point
+of junction, assumed a columnar structure similar to that of the
+trap. In like manner some hearth-stones, after exposure to the heat
+of a furnace without being melted, have become prismatic. Certain
+crystals also acquire by the application of heat a new internal
+arrangement, so as to break in a new direction, their external form
+remaining unaltered.</p>
+
+<p><b>Crystalline Theory of Cleavage.</b>&mdash;Professor Sedgwick,
+speaking of the planes of slaty cleavage, where they are decidedly
+distinct from those of sedimentary deposition, declared, in the
+essay before alluded to, his opinion that no retreat of parts, no
+contraction in the dimensions of rocks in passing to a solid state,
+can account for the phenomenon. He accordingly referred it to
+crystalline or polar forces acting simultaneously, and somewhat
+uniformly, in given directions, on large masses having a
+homogeneous composition.</p>
+
+<p>
+Sir John Herschel, in allusion to slaty cleavage, has suggested that &ldquo;if
+rocks have been so heated as to allow a commencement of
+crystallisation&mdash;that is to say, if they have been heated to a point at
+which the particles can begin to move among themselves, or at least on their
+own axes, some general law must then determine the position in which these
+particles will rest on cooling. Probably, that position will have some relation
+to the direction in which the heat escapes. Now, when all, or a majority of
+particles of the same nature have a general tendency to one position, that must
+of course determine a cleavage-plane. Thus we see the infinitesimal crystals of
+fresh-precipitated sulphate of barytes, and some other such bodies, arrange
+themselves alike in the fluid in which they float; so as, when stirred, all to
+glance with one light, and give the appearance of silky filaments. Some sorts
+of soap, in which insoluble margarates<a href="#fn-34.4" name="fnref-34.4"
+id="fnref-34.4"><sup>[4]</sup></a> exist, <a name="page592"></a>exhibit the
+same phenomenon when mixed with water; and what occurs in our experiments on a
+minute scale may occur in nature on a great one.&rdquo;<a href="#fn-34.5"
+name="fnref-34.5" id="fnref-34.5"><sup>[5]</sup></a>
+</p>
+
+<p>
+<b>Mechanical Theory of Cleavage.</b>&mdash;Professor Phillips has remarked
+that in some slaty rocks the form of the outline of fossil shells and
+trilobites has been much changed by distortion, which has taken place in a
+longitudinal, transverse, or oblique direction. This change, he adds, seems to
+be the result of a &ldquo;creeping movement&rdquo; of the particles of the rock
+along the planes of cleavage, its direction being always uniform over the same
+tract of country, and its amount in space being sometimes measurable, and being
+as much as a quarter or even half an inch. The hard shells are not affected,
+but only those which are thin.<a href="#fn-34.6" name="fnref-34.6"
+id="fnref-34.6"><sup>[6]</sup></a> Mr. D. Sharpe, following up the same line of
+inquiry, came to the conclusion that the present distorted forms of the shells
+in certain British slate rocks may be accounted for by supposing that the rocks
+in which they are imbedded have undergone compression in a direction
+perpendicular to the planes of cleavage, and a corresponding expansion in the
+direction of the dip of the cleavage.<a href="#fn-34.7" name="fnref-34.7"
+id="fnref-34.7"><sup>[7]</sup></a>
+</p>
+
+<p>
+Subsequently (1853) Mr. Sorby demonstrated the great extent to which this
+mechanical theory is applicable to the slate rocks of North Wales and
+Devonshire,<a href="#fn-34.8" name="fnref-34.8"
+id="fnref-34.8"><sup>[8]</sup></a> districts where the amount of change in
+dimensions can be tested and measured by comparing the different effects
+exerted by lateral pressure on alternating beds of finer and coarser materials.
+Thus, for example, in Fig. 627 it will be seen that the sandy bed <i>d f,</i>
+which has offered greater resistance, has been sharply contorted, while the
+fine-grained strata, <i>a, b, c,</i> have remained comparatively unbent. The
+points <i>d</i> and <i>f</i> in the stratum <i>d f</i> must have been
+originally four times as far apart as they are now. They have been forced so
+much nearer to each other, partly by bending, and partly by becoming elongated
+in the direction of what may be called the longer axes of their contortions,
+and lastly, to a certain small amount, by condensation. The chief result has
+obviously been due to the bending; but, in proof of elongation, it will be
+observed that the thickness of the bed <i>d f</i> is now about four times
+greater in those parts lying in the main direction of the flexures than in a
+plane <a name="page593"></a>perpendicular to them; and the same bed exhibits
+cleavage planes in the direction of the greatest movement, although they are
+much fewer than in the slaty strata above and below.
+</p>
+
+<img src="images/fig627.jpg" width="216" height="537" alt=
+"Fig. 627: Vertical section of slate rock in the cliffs near Ilfracombe, North
+Devon." />
+
+<p>Above the sandy bed <i>d f,</i> the stratum <i>c</i> is somewhat
+disturbed, while the next bed, <i>b,</i> is much less so, and a not
+at all; yet all these beds, <i>c, b,</i> and <i>a,</i> must have
+undergone an equal amount of pressure with <i>d,</i> the points a
+and g having approximated as much towards each other as have <i>
+d</i> and <i>f.</i> The same phenomena are also repeated in the
+beds below <i>d,</i> and might have been shown, had the section
+been extended downward. Hence it appears that the finer beds have
+been squeezed into a fourth of the space they previously occupied,
+partly by condensation, or the closer packing of their ultimate
+particles (which has given rise to the great specific gravity of
+such slates), and partly by elongation in the line of the dip of
+the cleavage, of which the general direction is perpendicular to
+that of the pressure. &ldquo;These and numerous other cases in
+North Devon are analogous,&rdquo; says Mr. Sorby, &ldquo;to what
+would occur if a strip of paper were included in a mass of some
+soft plastic material which would readily change its dimensions. If
+the whole were then compressed in the direction of the length of
+the strip of paper, it would be bent and puckered up into
+contortions, while the plastic material would readily change its
+dimensions without undergoing such contortions; and the difference
+in distance of the ends of the paper, as measured in a direct line
+or along it, would indicate the change in the dimensions of the
+plastic material.&rdquo;</p>
+
+<p>
+By microscopic examination of minute crystals, and by <a
+name="page594"></a>other observations, Mr. Sorby has come to the conclusion
+that the absolute condensation of the slate rocks amounts upon an average to
+about one half their original volume. Most of the scales of mica occurring in
+certain slates examined by Mr. Sorby lie in the plane of cleavage; whereas in a
+similar rock not exhibiting cleavage they lie with their longer axes in all
+directions. May not their position in the slates have been determined by the
+movement of elongation before alluded to? To illustrate this theory some scales
+of oxide of iron were mixed with soft pipe-clay in such a manner that they
+inclined in all directions. The dimensions of the mass were then changed
+artificially to a similar extent to what has occurred in slate rocks, and the
+pipe-clay was then dried and baked. When it was afterwards rubbed to a flat
+surface perpendicular to the pressure and in the line of elongation, or in a
+plane corresponding to that of the dip of cleavage, the particles were found to
+have become arranged in the same manner as in natural slates, and the mass
+admitted of easy fracture into thin flat pieces in the plane alluded to,
+whereas it would not yield in that perpendicular to the cleavage.<a
+href="#fn-34.9" name="fnref-34.9" id="fnref-34.9"><sup>[9]</sup></a>
+</p>
+
+<p>
+Dr. Tyndall, when commenting in 1856 on Mr. Sorby&rsquo;s experiments, observed
+that pressure alone is sufficient to produce cleavage, and that the
+intervention of plates of mica or scales of oxide of iron, or any other
+substances having flat surfaces, is quite unnecessary. In proof of this he
+showed experimentally that a mass of &ldquo;pure white wax, after having been
+submitted to great pressure, exhibited a cleavage more clean than that of any
+slate-rock, splitting into laminæ of surpassing tenuity.&rdquo;<a
+href="#fn-34.10" name="fnref-34.10" id="fnref-34.10"><sup>[10]</sup></a> He
+remarks that every mass of clay or mud is divided and subdivided by surfaces
+among which the cohesion is comparatively small. On being subjected to
+pressure, such masses yield and spread out in the direction of least
+resistance, small nodules become converted into laminæ separated from each
+other by surfaces of weak cohesion, and the result is that the mass cleaves at
+right angles to the line in which the pressure is exerted. In further
+illustration of this, Mr. Hughes remarks that &ldquo;concretions which in the
+undisturbed beds have their longer axes parallel to the bedding are, where the
+rock is much cleaved, frequently found flattened laterally, so as to have their
+longer axes parallel to the cleavage planes, and at a considerable angle, even
+right angles, to their former position.&rdquo;
+</p>
+
+<p>
+Mr. Darwin attributes the lamination and fissile structure <a
+name="page595"></a>of volcanic rocks of the trachytic series, including some
+obsidians in Ascension, Mexico, and elsewhere, to their having moved when
+liquid in the direction of the laminæ. The zones consist sometimes of layers of
+air-cells drawn out and lengthened in the supposed direction of the moving
+mass.<a href="#fn-34.11" name="fnref-34.11"
+id="fnref-34.11"><sup>[11]</sup></a>
+</p>
+
+<p><b>Foliation of Crystalline Schists.</b>&mdash;After studying,
+in 1835, the crystalline rocks of South America, Mr. Darwin
+proposed the term <i>foliation</i> for the laminæ or plates
+into which gneiss, mica-schist, and other crystalline rocks are
+divided. Cleavage, he observes, may be applied to those divisional
+planes which render a rock fissile, although it may appear to the
+eye quite or nearly homogeneous. Foliation may be used for those
+alternating layers or plates of different mineralogical nature of
+which gneiss and other metamorphic schists are composed.</p>
+
+<p>
+That the planes of foliation of the crystalline schists in Norway accord very
+generally with those of original stratification is a conclusion long since
+espoused by Keilhau.<a href="#fn-34.12" name="fnref-34.12"
+id="fnref-34.12"><sup>[12]</sup></a> Numerous observations made by Mr. David
+Forbes in the same country (the best probably in Europe for studying such
+phenomena on a grand scale) confirm Keilhau&rsquo;s opinion. In Scotland, also,
+Mr. D. Forbes has pointed out a striking case where the foliation is identical
+with the lines of stratification in rocks well seen near Crianlorich on the
+road to Tyndrum, about eight miles from Inverarnon, in Perthshire. There is in
+that locality a blue limestone foliated by the intercalation of small plates of
+white mica, so that the rock is often scarcely distinguishable in aspect from
+gneiss or mica-schist. The stratification is shown by the large beds and
+coloured bands of limestone all dipping, like the folia, at an angle of 32&deg;
+N.E.<a href="#fn-34.13" name="fnref-34.13" id="fnref-34.13"><sup>[13]</sup></a>
+In stratified formations of every age we see layers of siliceous sand with or
+without mica, alternating with clay, with fragments of shells or corals, or
+with seams of vegetable matter, and we should expect the mutual attraction of
+like particles to favour the crystallisation of the quartz, or mica, or
+feldspar, or carbonate of lime, along the planes of original deposition, rather
+than in planes placed at angles of 20 or 40 degrees to those of stratification.
+</p>
+
+<p>
+We have seen how much the original planes of stratification may be interfered
+with or even obliterated by concretionary action in deposits still retaining
+their fossils, as in the case of the magnesian limestone (see <a
+href="#page63">p. 63</a>). Hence we must expect to be frequently baffled when
+we attempt to decide <a name="page596"></a>whether the foliation does or does
+not accord with that arrangement which gravitation, combined with
+current-action, imparted to a deposit from water. Moreover, when we look for
+stratification in crystalline rocks, we must be on our guard not to expect too
+much regularity. The occurrence of wedge-shaped masses, such as belong to
+coarse sand and pebbles&mdash;diagonal lamination (p. 42)&mdash;ripple-marked,
+unconformable stratification,&mdash;the fantastic folds produced by lateral
+pressure&mdash;faults of various width&mdash;intrusive dikes of
+trap&mdash;organic bodies of diversified shapes, and other causes of unevenness
+in the planes of deposition, both on the small and on the large scale, will
+interfere with parallelism. If complex and enigmatical appearances did not
+present themselves, it would be a serious objection to the metamorphic theory.
+Mr. Sorby has shown that the peculiar structure belonging to ripple-marked
+sands, or that which is generated when ripples are formed during the deposition
+of the materials, is distinctly recognisable in many varieties of mica-schists
+in Scotland.<a href="#fn-34.14" name="fnref-34.14"
+id="fnref-34.14"><sup>[14]</sup></a>
+</p>
+
+<img src="images/fig628.jpg" width="205" height="169" alt=
+"Fig. 628: Lamination of clay-stone. Montagne de Seguinat, near Gavarnie, in
+the Pyrenees." />
+
+<p>In Fig. 628 I have represented carefully the lamination of a
+coarse argillaceous schist which I examined in 1830 in the
+Pyrenees. In part it approaches in character to a green and blue
+roofing-slate, while part is extremely quartzose, the whole mass
+passing downward into micaceous schist. The vertical section here
+exhibited is about three feet in height, and the layers are
+sometimes so thin that fifty may be counted in the thickness of an
+inch. Some of them consist of pure quartz. There is a resemblance
+in such cases to the diagonal lamination which we see in
+sedimentary rocks, even though the layers of quartz and of mica, or
+of feldspar and other minerals, may be more distinct in alternating
+folia than they were originally.</p>
+
+<p class="footnote">
+<a name="fn-34.1" id="fn-34.1"></a> <a href="#fnref-34.1">[1]</a>
+Geol. Trans., 2nd series, vol. iii, p. 461.
+</p>
+
+<p class="footnote">
+<a name="fn-34.2" id="fn-34.2"></a> <a href="#fnref-34.2">[2]</a>
+Silurian System, p. 246.
+</p>
+
+<p class="footnote">
+<a name="fn-34.3" id="fn-34.3"></a> <a href="#fnref-34.3">[3]</a>
+Introduction to Geology, chap. iv.
+</p>
+
+<p class="footnote">
+<a name="fn-34.4" id="fn-34.4"></a> <a href="#fnref-34.4">[4]</a>
+Margaric acid is an oleaginous acid, formed from different animal and vegetable
+fatty substances. A margarate is a compound of this acid with soda, potash, or
+some other base, and is so named from its pearly lustre.
+</p>
+
+<p class="footnote">
+<a name="fn-34.5" id="fn-34.5"></a> <a href="#fnref-34.5">[5]</a>
+Letter to the author, dated Cape of Good Hope, Feb. 20, 1836.
+</p>
+
+<p class="footnote">
+<a name="fn-34.6" id="fn-34.6"></a> <a href="#fnref-34.6">[6]</a>
+Report, Brit. Assoc., Cork, 1843, Sect. p. 60.
+</p>
+
+<p class="footnote">
+<a name="fn-34.7" id="fn-34.7"></a> <a href="#fnref-34.7">[7]</a>
+Quart. Geol. Journ., vol. iii, p. 87, 1847.
+</p>
+
+<p class="footnote">
+<a name="fn-34.8" id="fn-34.8"></a> <a href="#fnref-34.8">[8]</a>
+On the Origin of Slaty Cleavage, by H. C. Sorby, Edin. New Phil. Journ., 1853,
+vol. lv, p. 137.
+</p>
+
+<p class="footnote">
+<a name="fn-34.9" id="fn-34.9"></a> <a href="#fnref-34.9">[9]</a>
+Sorby, as cited above, p. 741, note.
+</p>
+
+<p class="footnote">
+<a name="fn-34.10" id="fn-34.10"></a> <a href="#fnref-34.10">[10]</a>
+Tyndall, View of the Cleavage of Crystals and Slate rocks.
+</p>
+
+<p class="footnote">
+<a name="fn-34.11" id="fn-34.11"></a> <a href="#fnref-34.11">[11]</a>
+Darwin, Volcanic Islands, pp. 69, 70.
+</p>
+
+<p class="footnote">
+<a name="fn-34.12" id="fn-34.12"></a> <a href="#fnref-34.12">[12]</a>
+Norske Mag. Naturvidsk., vol. i, p. 71.
+</p>
+
+<p class="footnote">
+<a name="fn-34.13" id="fn-34.13"></a> <a href="#fnref-34.13">[13]</a>
+Memoir read before the Geol. Soc. London, Jan. 31, 1855.
+</p>
+
+<p class="footnote">
+<a name="fn-34.14" id="fn-34.14"></a> <a href="#fnref-34.14">[14]</a>
+H. C. Sorby, Quart. Geol. Journ., vol. xix., p. 401.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap35"></a><a name="page597"></a>CHAPTER XXXV.<br/>
+ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.</h2>
+
+<p class="letter">Difficulty of ascertaining the Age of metamorphic
+Strata. &mdash; Metamorphic Strata of Eocene date in the Alps of
+Switzerland and Savoy. &mdash; Limestone and Shale of Carrara.
+&mdash; Metamorphic Strata of older date than the Silurian and
+Cambrian Rocks. &mdash; Order of Succession in metamorphic Rocks.
+&mdash; Uniformity of mineral Character. &mdash; Supposed Azoic
+Period. &mdash; Connection between the Absence of Organic Remains
+and the Scarcity of calcareous Matter in metamorphic Rocks.
+</p>
+
+<p>
+According to the theory adopted in the last chapter, the
+metamorphic strata have been deposited at one period, and have
+become crystalline at another. We can rarely hope to define with
+exactness the date of both these periods, the fossils having been
+destroyed by Plutonic action, and the mineral characters being the
+same, whatever the age. Superposition itself is an ambiguous test,
+especially when we desire to determine the period of
+crystallisation. Suppose, for example, we are convinced that
+certain metamorphic strata in the Alps, which are covered by
+cretaceous beds, are altered lias; this lias may have assumed its
+crystalline texture in the cretaceous or in some tertiary period,
+the Eocene for example.
+</p>
+
+<p>When discussing the ages of the Plutonic rocks, we have seen
+that examples occur of various primary, secondary, and tertiary
+deposits converted into metamorphic strata near their contact with
+granite. There can be no doubt in these cases that strata once
+composed of mud, sand, and gravel, or of clay, marl, and shelly
+limestone, have for the distance of several yards, and in some
+instances several hundred feet, been turned into gneiss,
+mica-schist, hornblende-schist, chlorite-schist, quartz rock,
+statuary marble, and the rest. (See the two preceding chapters.) It
+may be easy to prove the identity of two different parts of the
+same stratum; one, where the rock has been in contact with a
+volcanic or Plutonic mass, and has been changed into marble or
+hornblende-schist, and another not far distant, where the same bed
+remains unaltered and fossiliferous; but when hydrothermal action,
+as described in Chapter XXXIII, has operated gradually on a more
+extensive scale, it may have finally destroyed
+<a name="page598"></a>all monuments of the date of its development throughout a whole
+mountain chain, and all the labour and skill of the most practised
+observers are required, and may sometimes be at fault. I shall
+mention one or two examples of alteration on a grand scale, in
+order to explain to the student the kind of reasoning by which we
+are led to infer that dense masses of fossiliferous strata have
+been converted into crystalline rocks.</p>
+
+<p><b>Eocene Strata rendered metamorphic in the Alps.</b>&mdash;In
+the eastern part of the Alps, some of the Palæozoic strata,
+as well as the older Mesozoic formations, including the oolitic and
+cretaceous rocks, are distinctly recognisable. Tertiary deposits
+also appear in a less elevated position on the flanks of the
+Eastern Alps; but in the Central or Swiss Alps, the Palæozoic
+and older Mesozoic formations disappear, and the Cretaceous,
+Oolitic, Liassic, and at some points even the Eocene strata,
+graduate insensibly into metamorphic rocks, consisting of granular
+limestone, talc-schist, talcose-gneiss, micaceous schist, and other
+varieties.</p>
+
+<p>As an illustration of the partial conversion into gneiss of
+portions of a highly inclined set of beds, I may cite Sir R.
+Murchison&rsquo;s memoir on the structure of the Alps. Slates
+provincially termed &ldquo;flysch&rdquo; (see <a href=
+"#page278">p. 278</a>), overlying the nummulite limestone
+of Eocene date, and comprising some arenaceous and some calcareous
+layers, are seen to alternate several times with bands of granitoid
+rock, answering in character to gneiss. In this case heat, vapour,
+or water at a high temperature may have traversed the more
+permeable beds, and altered them so far as to admit of an internal
+movement and re-arrangement of the molecules, while the adjoining
+strata did not give passage to the same heated gases or water, or,
+if so, remained unchanged because they were composed of less
+fusible or decomposable materials. Whatever hypothesis we adopt,
+the phenomena establish beyond a doubt the possibility of the
+development of the metamorphic structure in a tertiary deposit in
+planes parallel to those of stratification. The strata appear
+clearly to have been affected, though in a less intense degree, by
+that same Plutonic action which has entirely altered and rendered
+metamorphic so many of the subjacent formations; for in the Alps
+this action has by no means been confined to the immediate vicinity
+of granite. Granite, indeed, and other Plutonic rocks, rarely make
+their appearance at the surface, notwithstanding the deep ravines
+which lay open to view the internal structure of these mountains.
+That they exist below at no great depth we cannot doubt, for at
+some points, as in
+<a name="page599"></a>the Valorsine, near Mont Blanc, granite and granitic veins are
+observable, piercing through talcose gneiss, which passes
+insensibly upward into secondary strata.</p>
+
+<p>It is certainly in the Alps of Switzerland and Savoy, more than
+in any other district in Europe, that the geologist is prepared to
+meet with the signs of an intense development of Plutonic action;
+for here strata thousands of feet thick have been bent, folded, and
+overturned, and marine secondary formations of a comparatively
+modern date, such as the Oolitic and Cretaceous, have been upheaved
+to the height of 12,000, and some Eocene strata to elevations of
+10,000 feet above the level of the sea; and even deposits of the
+Miocene era have been raised 4000 or 5000 feet, so as to rival in
+height the loftiest mountains in Great Britain. In one of the
+sections described by M. Studer in the highest of the Bernese Alps,
+namely in the Roththal, a valley bordering the line of perpetual
+snow on the northern side of the Jungfrau, there occurs a mass of
+gneiss 1000 feet thick, and 15,000 feet long, which I examined, not
+only resting upon, but also again covered by strata containing
+oolitic fossils. These anomalous appearances may partly be
+explained by supposing great solid wedges of intrusive gneiss to
+have been forced in laterally between strata to which I found them
+to be in many sections unconformable. The superposition, also, of
+the gneiss to the oolite may, in some cases, be due to a reversal
+of the original position of the beds in a region where the
+convulsions have been on so stupendous a scale.</p>
+
+<p><b>Northern Apennines.&mdash;Carrara.</b>&mdash;The celebrated
+marble of Carrara, used in sculpture, was once regarded as a type
+of primitive limestone. It abounds in the mountains of Massa
+Carrara, or the &ldquo;Apuan Alps,&rdquo; as they have been called,
+the highest peaks of which are nearly 6000 feet high. Its great
+antiquity was inferred from its mineral texture, from the absence
+of fossils, and its passage downward into talc-schist and
+garnetiferous mica-schist; these rocks again graduating downward
+into gneiss, which is penetrated, at Forno, by granite veins. But
+the researches of MM. Savi, Boué, Pareto, Guidoni, De la
+Beche, Hoffman, and Pilla demonstrated that this marble, once
+supposed to be formed before the existence of organic beings, is,
+in fact, an altered limestone of the Oolitic period, and the
+underlying crystalline schists are secondary sandstones and shales,
+modified by Plutonic action. In order to establish these
+conclusions it was first pointed out that the calcareous rocks
+bordering the Gulf of Spezia, and abounding in Oolitic fossils,
+assume a texture like that of Carrara marble, in proportion as they
+are more and more
+<a name="page600"></a>invaded by certain trappean and Plutonic rocks, such as diorite,
+serpentine, and granite, occurring in the same country.</p>
+
+<p>
+It was then observed that, in places where the secondary formations are
+unaltered, the uppermost consist of common Apennine limestone with nodules of
+flint, below which are shales, and at the base of all, argillaceous and
+siliceous sandstones. In the limestone fossils are frequent, but very rare in
+the underlying shale and sandstone. Then a gradation was traced laterally from
+these rocks into another and corresponding series, which is completely
+metamorphic; for at the top of this we find a white granular marble, wholly
+devoid of fossils, and almost without stratification, in which there are no
+nodules of flint, but in its place siliceous matter disseminated through the
+mass in the form of prisms of quartz. Below this, and in place of the shales,
+are talc-schists, jasper, and hornstone; and at the bottom, instead of the
+siliceous and argillaceous sandstones, are quartzite and gneiss.<a
+href="#fn-35.1" name="fnref-35.1" id="fnref-35.1"><sup>[1]</sup></a> Had these
+secondary strata of the Apennines undergone universally as great an amount of
+transmutation, it would have been impossible to form a conjecture respecting
+their true age; and then, according to the method of classification adopted by
+the earlier geologists, they would have ranked as primary rocks. In that case
+the date of their origin would have been thrown back to an era antecedent to
+the deposition of the Lower Silurian or Cambrian strata, although in reality
+they were formed in the Oolitic period, and altered at some subsequent and
+perhaps much later epoch.
+</p>
+
+<p><b>Metamorphic Strata of older date than the Silurian and
+Cambrian Rocks.</b>&mdash;It was remarked (<a href=
+"images/fig617.jpg">Fig. 617</a>) that as the hypogene rocks, both
+stratified and unstratified, crystallise originally at a certain
+depth beneath the surface, they must always, before they are
+upraised and exposed at the surface, be of considerable antiquity,
+relatively to a large portion of the fossiliferous and volcanic
+rocks. They may be forming at all periods; but before any of them
+can become visible, they must be raised above the level of the sea,
+and some of the rocks which previously concealed them must have
+been removed by denudation.</p>
+
+<p>In Canada, as we have seen (<a href="#page491">p.
+491</a>), the Lower Laurentian gneiss, quartzite, and limestone may
+be regarded as metamorphic, because, among other reasons, organic
+remains (<i>Eozoon Canadense</i>) have been detected in a part of
+one of the calcareous masses. The Upper Laurentian or Labrador
+<a name="page601"></a>series lies unconformably upon the Lower, and differs from it
+chiefly in having as yet yielded no fossils. It consists of gneiss
+with Labrador-feldspar and feldstones, in all 10,000 feet thick,
+and both its composition and structure lead us to suppose that,
+like the Lower Laurentian, it was originally of sedimentary origin
+and owes its crystalline condition to metamorphic action. The
+remote date of the period when some of these old Laurentian strata
+of Canada were converted into gneiss may be inferred from the fact
+that pebbles of that rock are found in the overlying Huronian
+formation, which is probably of Cambrian age (<a href=
+"#page490">p. 490</a>).</p>
+
+<p>The oldest stratified rock of Scotland is the hornblendic gneiss
+of Lewis, in the Hebrides, and that of the north-west coast of
+Ross-shire, represented at the base of the section given at <a
+href="images/fig82.jpg">Fig. 82</a>. It is the same as that
+intersected by numerous granite veins which forms the cliffs of
+Cape Wrath, in Sutherlandshire (see <a href="images/fig613.jpg">
+Fig. 613</a>), and is conjectured to be of Laurentian age. Above
+it, as shown in the section (<a href="images/fig82.jpg">Fig.
+82</a>), lie unconformable beds of a reddish or purple sandstone
+and conglomerate, nearly horizontal, and between 3000 and 4000 feet
+thick. In these ancient grits no fossils have been found, but they
+are supposed to be of Cambrian date, for Sir R. Murchison found
+Lower Silurian strata resting unconformably upon them. These strata
+consist of quartzite with annelid burrows already alluded to (<a
+href="#page112">p. 112</a>), and limestone in which Mr.
+Charles Peach was the first to find, in 1854, three or four species
+of <i>Orthoceras,</i> also the genera <i>Cyrtoceras</i> and <i>
+Lituites,</i> two species of <i>Murchisonia,</i> a <i>
+Pleurotomaria,</i> a species of <i>Maclurea,</i> one of <i>
+Euomphalus,</i> and an <i>Orthis.</i> Several of the species are
+believed by Mr. Salter to be identical with Lower Silurian fossils
+of Canada and the United States.</p>
+
+<p>The discovery of the true age of these fossiliferous rocks was
+one of the most important steps made of late years in the progress
+of British Geology, for it led to the unexpected conclusion that
+all the Scotch crystalline strata to the eastward, once called
+primitive, which overlie the limestone and quartzite in question,
+are referable to some part of the Silurian series.</p>
+
+<p>These Scotch metamorphic strata are of gneiss, mica-schist, and
+clay-slate of vast thickness, and having a strike from north-east
+to south-west almost at right angles to that of the older
+Laurentian gneiss before mentioned. The newer crystalline series,
+comprising the crystalline rocks of Aberdeenshire, Perthshire, and
+Forfarshire, were inferred by Sir R. Murchison to be altered
+Silurian strata; and his opinion
+<a name="page602"></a>has been since confirmed by the observations of three able
+geologists, Messrs. Ramsay, Harkness, and Geikie. The newest of the
+series is a clay-slate, on which, along the southern borders of the
+Grampians, the Lower Old Red, containing <i>Cephalaspis Lyelli,
+Pterygotus Anglicus,</i> and <i>Parka decipiens,</i> rests
+unconformably.</p>
+
+<p><b>Order of Succession in Metamorphic Rocks.</b>&mdash;There is
+no universal and invariable order of superposition in metamorphic
+rocks, although a particular arrangement may prevail throughout
+countries of great extent, for the same reason that it is traceable
+in those sedimentary formations from which crystalline strata are
+derived. Thus, for example, we have seen that in the Apennines,
+near Carrara, the descending series, where it is metamorphic,
+consists of, first, saccharine marble; second, talcose-schist; and
+third, of quartz-rock and gneiss: where unaltered, of, first,
+fossiliferous limestone; second, shale; and third, sandstone.</p>
+
+<p>But if we investigate different mountain chains, we find gneiss,
+mica-schist, hornblende-schist, chlorite-schist, hypogene
+limestone, and other rocks, succeeding each other, and alternating
+with each other in every possible order. It is, indeed, more common
+to meet with some variety of clay-slate forming the uppermost
+member of a metamorphic series than any other rock; but this fact
+by no means implies, as some have imagined, that all clay-slates
+were formed at the close of an imaginary period when the deposition
+of the crystalline strata gave way to that of ordinary sedimentary
+deposits. Such clay-slates, in fact, are variable in composition,
+and sometimes alternate with fossiliferous strata, so that they may
+be said to belong almost equally to the sedimentary and metamorphic
+order of rocks. It is probable that, had they been subjected to
+more intense Plutonic action, they would have been transformed into
+hornblende-schist, foliated chlorite-schist, scaly talcose-schist,
+mica-schist, or other more perfectly crystalline rocks, such as are
+usually associated with gneiss.</p>
+
+<p><i>Uniformity of Mineral Character in Hypogene
+Rocks.</i>&mdash;It is true, as Humboldt has happily remarked, that
+when we pass to another hemisphere, we see new forms of animals and
+plants, and even new constellations in the heavens; but in the
+rocks we still recognise our old acquaintances&mdash;the same granite,
+the same gneiss, the same micaceous schist, quartz-rock, and the
+rest. There is certainly a great and striking general resemblance
+in the principal kinds of hypogene rocks in all countries, however
+different their ages; but each of them, as we have seen, must be
+regarded as geological
+<a name="page603"></a>families of rocks, and not as definite mineral compounds. They
+are more uniform in aspect than sedimentary strata, because these
+last are often composed of fragments varying greatly in form, size,
+and colour, and contain fossils of different shapes and mineral
+composition, and acquire a variety of tints from the mixture of
+various kinds of sediment. The materials of such strata, if they
+underwent metamorphism, would be subject to chemical laws, simple
+and uniform in their action, the same in every climate, and wholly
+undisturbed by mechanical and organic causes. It would, however, be
+a great error to assume, as some have done, that the hypogene
+rocks, considered as aggregates of simple minerals, are really more
+homogeneous in their composition than the several members of the
+sedimentary series. Not only do the proportional quantities of
+feldspar, quartz, mica, hornblende, and other minerals, vary in
+hypogene rocks bearing the same name; but what is still more
+important, the ingredients, as we have seen, of the same simple
+mineral are not always constant (see <a href="#page503">
+p. 503</a> and table, <a href="#page499">p. 499</a>).</p>
+
+<p><b>Supposed Azoic Period.</b>&mdash;The total absence of any
+trace of fossils has inclined many geologists to attribute the
+origin of the most ancient strata to an azoic period, or one
+antecedent to the existence of organic beings. Admitting, they say,
+the obliteration, in some cases, of fossils by Plutonic action, we
+might still expect that traces of them would oftener be found in
+certain ancient systems of slate which can scarcely be said to have
+assumed a crystalline structure. But in urging this argument it
+seems to have been forgotten that there are stratified formations
+of enormous thickness, and of various ages, some of them even of
+Tertiary date, and which we know were formed after the earth had
+become the abode of living creatures, which are, nevertheless, in
+some districts, entirely destitute of all vestiges of organic
+bodies. In some, the traces of fossils may have been effaced by
+water and acids, at many successive periods; indeed the removal of
+the calcareous matter of fossil shells is proved by the fact of
+such organic remains being often replaced by silex or other
+minerals, and sometimes by the space once occupied by the fossil
+being left empty, or only marked by a faint impression.</p>
+
+<p>Those who believed the hypogene rocks to have originated
+antecedently to the creation of organic beings, imputed the absence
+of lime, so remarkable in metamorphic strata, to the non-existence
+of those mollusca and zoophytes by which shells and corals are
+secreted; but when we ascribe the crystalline formations to
+Plutonic action, it is natural to inquire whether this action
+itself may not tend to expel carbonic
+<a name="page604"></a>acid and lime from the materials which it reduces to fusion or
+semi-fusion. Not only carbonate of lime, but also free carbonic
+acid gas, is given off plentifully from the soil and crevices of
+rocks in regions of active and spent volcanoes, as near Naples and
+in Auvergne. By this process, fossil shells or corals may often
+lose their carbonic acid, and the residual lime may enter into the
+composition of augite, hornblende, garnet, and other hypogene
+minerals. Although we cannot descend into the subterranean regions
+where volcanic heat is developed, we can observe in regions of
+extinct volcanoes, such as Auvergne and Tuscany, hundreds of
+springs, both cold and thermal, flowing out from granite and other
+rocks, and having their waters plentifully charged with carbonate
+of lime.</p>
+
+<p>If all the calcareous matter transferred in the course of ages
+by these and thousands of other springs from the lower part of the
+earth&rsquo;s crust to the atmosphere could be presented to us in a
+solid form, we should find that its volume was comparable to that
+of many a chain of hills. Calcareous matter is poured into lakes
+and the ocean by a thousand springs and rivers; so that part of
+almost every new calcareous rock chemically precipitated, and of
+many reefs of shelly and coralline stone, must be derived from
+mineral matter subtracted by Plutonic agency, and driven up by gas
+and steam from fused and heated rocks in the bowels of the
+earth.</p>
+
+<p>The scarcity of limestone in many extensive regions of
+metamorphic rocks, as in the Eastern and Southern Grampians of
+Scotland, may have been the result of some action of this kind; and
+if the limestones of the Lower Laurentian in Canada afford a
+remarkable exception to the general rule, we must not forget that
+it is precisely in this most ancient formation that the <i>Eozoon
+Canadense</i> has been found. The fact that some distinct bands of
+limestone from 700 to 1500 feet thick occur here, may be connected
+with the escape from destruction of some few traces of organic
+life, even in a rock in which metamorphic action has gone so far as
+to produce serpentine, augite, and other minerals found largely
+intermixed with the carbonate of lime.
+</p>
+
+<p class="footnote">
+<a name="fn-35.1" id="fn-35.1"></a> <a href="#fnref-35.1">[1]</a>
+See notices of Savi, Hoffman, and others, referred to by Boué, Bull. de la Soc.
+Géol. de France, tome v, p. 317 and tome iii, p. 44; also Pilla, cited by
+Murchison, Quart. Geol. Journ., vol. v, p. 266.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap36"></a><a name="page605"></a>CHAPTER XXXVI.<br/>
+MINERAL VEINS.</h2>
+
+<p class="letter">
+Different Kinds of mineral Veins. &mdash; Ordinary metalliferous Veins or
+Lodes. &mdash; Their frequent Coincidence with Faults. &mdash; Proofs that they
+originated in Fissures in solid Rock. &mdash; Veins shifting other Veins.
+&mdash; Polishing of their Walls or &ldquo;Slicken sides.&rdquo; Shells and
+Pebbles in Lodes. &mdash; Evidence of the successive Enlargement and Reopening
+of veins. &mdash; Examples in Cornwall and in Auvergne. &mdash; Dimensions of
+Veins. &mdash; Why some alternately swell out and contract. &mdash; Filling of
+Lodes by Sublimation from below. &mdash; Supposed relative Age of the precious
+Metals. &mdash; Copper and lead Veins in Ireland older than Cornish Tin.
+&mdash; Lead Vein in Lias, Glamorganshire. &mdash; Gold in Russia, California,
+and Australia. &mdash; Connection of hot Springs and mineral Veins.
+</p>
+
+<p>
+The manner in which metallic substances are distributed through the
+earth&rsquo;s crust, and more especially the phenomena of those more or less
+connected masses of ore called mineral veins, from which the larger part of the
+precious metals used by man are obtained, are subjects of the highest practical
+importance to the miner, and of no less theoretical interest to the geologist.
+</p>
+
+<p>
+<b>On different Kinds of Mineral Veins.</b>&mdash;The mineral veins with which
+we are most familiarly acquainted are those of quartz and carbonate of lime,
+which are often observed to form lenticular masses of limited extent traversing
+both hypogene strata and fossiliferous rocks. Such veins appear to have once
+been chinks or small cavities, caused, like cracks in clay, by the shrinking of
+the mass, during desiccation, or in passing from a higher to a lower
+temperature. Siliceous, calcareous, and occasionally metallic matters have
+sometimes found their way simultaneously into such empty spaces, by
+infiltration from the surrounding rocks. Mixed with hot water and steam,
+metallic ores may have permeated the mass until they reached those receptacles
+formed by shrinkage, and thus gave rise to that irregular assemblage of veins,
+called by the Germans a &ldquo;stockwerk,&rdquo; in allusion to the different
+floors on which the mining operations are in such cases carried on.
+</p>
+
+<p>
+The more ordinary or regular veins are usually worked in vertical shafts, and
+have evidently been fissures produced by mechanical violence. They traverse all
+kinds of rocks, both <a name="page606"></a>hypogene and fossiliferous, and
+extend downward to indefinite or unknown depths. We may assume that they
+correspond with such rents as we see caused from time to time by the shock of
+an earthquake. Metalliferous veins referable to such agency are occasionally a
+few inches wide, but more commonly three or four feet. They hold their course
+continuously in a certain prevailing direction for miles or leagues, passing
+through rocks varying in mineral composition.
+</p>
+
+<p>
+<b>That Metalliferous Veins were Fissures.</b>&mdash;As some intelligent
+miners, after an attentive study of metalliferous veins, have been unable to
+reconcile many of their characteristics with the hypothesis of fissures, I
+shall begin by stating the evidence in its favour. The most striking fact,
+perhaps, which can be adduced in its support is, the coincidence of a
+considerable proportion of mineral veins with <i>faults,</i> or those
+dislocations of rocks which are indisputably due to mechanical force, as above
+explained (<a href="#page87">p. 87</a>). There are even proofs in almost every
+mining district of a succession of faults, by which the opposite walls of
+rents, now the receptacles of metallic substances, have suffered displacement.
+Thus, for example, suppose <i>a a,</i> Fig. 629, to be a tin lode in Cornwall,
+the term <i>lode</i> being applied to veins containing metallic ores. This
+lode, running east and west, is a yard wide, and is shifted by a copper lode
+(<i>b b</i>) of similar width. The first fissure (<i>a a</i>) has been filled
+with various materials, partly of chemical origin, such as quartz, fluor-spar,
+peroxide of tin, sulphuret of copper, arsenical pyrites, bismuth, and sulphuret
+of nickel, and partly of mechanical origin, comprising clay and angular
+fragments or detritus of the intersected rocks. The plates of quartz and the
+ores are, in some places, parallel to the vertical sides or walls of the vein,
+being divided from each other by alternating layers of clay or other earthy
+matter. Occasionally the metallic ores are disseminated in detached masses
+among the vein-stones.
+</p>
+
+<p>
+It is clear that, after the gradual introduction of the tin and other
+substances, the second rent (<i>b b</i>) was produced by another fracture
+accompanied by a displacement of the rocks along the plane of <i>b b.</i> This
+new opening was then filled with minerals, some of them resembling those in
+<i>a a,</i> as fluor-spar (or fluate of lime) and quartz; others different, the
+copper being plentiful and the tin wanting or very scarce. We must next suppose
+a third movement to occur, breaking asunder all the rocks along the line <i>c
+c,</i> Fig. 630; the fissure, in this instance, being only six inches wide, and
+simply filled with clay, derived, probably, from the friction of the walls <a
+name="page607"></a>of the rent, or partly, perhaps, washed in from above. This
+new movement has displaced the rock in such a manner as to interrupt the
+continuity of the copper vein (<i>b b</i>), and, at the same time, to shift or
+heave laterally in the same direction a portion of the tin vein which had not
+previously been broken.
+</p>
+
+<img src="images/fig629.jpg" width="281" height="581" alt="Vertical sections of
+the mine at Huel Peever, Redruth, Cornwall. Fig. 629: Tin; Fig. 630: Copper;
+Fig. 631: Clay." />
+
+<p>
+Again, in Fig. 631 we see evidence of a fourth fissure (<i>d d</i>), also
+filled with clay, which has cut through the tin vein (<i>a a</i>), and has
+lifted it slightly upward towards the south. The various changes here
+represented are not ideal, but are exhibited in a section obtained in working
+an old Cornish mine, long since abandoned, in the parish of Redruth, called
+Huel Peever, and described both by Mr. Williams and Mr. Carne.<a
+href="#fn-36.1" name="fnref-36.1" id="fnref-36.1"><sup>[1]</sup></a> The
+principal movement here referred to, or that of <i>c c,</i> Fig. 631, extends
+through a space of no less than 84 feet; but in this, as in the case of the
+other three, it will be seen that the outline of the country above, <i>d, c, b,
+a,</i> etc., or the geographical <a name="page608"></a>features of Cornwall,
+are not affected by any of the dislocations, a powerful denuding force having
+clearly been exerted subsequently to all the faults. (See <a href="#page93">p.
+93</a>.) It is commonly said in Cornwall, that there are eight distinct systems
+of veins, which can in like manner be referred to as many successive movements
+or fractures; and the German miners of the Hartz Mountains speak also of eight
+systems of veins, referable to as many periods.
+</p>
+
+<p>
+Besides the proofs of mechanical action already explained, the opposite walls
+of veins are often beautifully polished, as if glazed, and are not unfrequently
+striated or scored with parallel furrows and ridges, such as would be produced
+by the continued rubbing together of surfaces of unequal hardness. These
+smoothed surfaces resemble the rocky floor over which a glacier has passed (see
+<a href="images/fig106.jpg">Fig. 106</a>). They are common even in cases where
+there has been no shift, and occur equally in non-metalliferous fissures. They
+are called by miners &ldquo;slicken-sides,&rdquo; from the German
+<i>schlichten,</i> to plane, and <i>seite,</i> side. It is supposed that the
+lines of the striæ indicate the direction in which the rocks were moved.
+</p>
+
+<p>
+In some of the veins in the mountain limestone of Derbyshire, containing lead,
+the vein-stuff, which is nearly compact, is occasionally traversed by what may
+be called a vertical crack passing down the middle of the vein. The two faces
+in contact are slicken-sides, well polished and fluted, and sometimes covered
+by a thin coating of lead-ore. When one side of the vein-stuff is removed, the
+other side cracks, especially if small holes be made in it, and fragments fly
+off with loud explosions, and continue to do so for some days. The miner,
+availing himself of this circumstance, makes with his pick small holes about
+six inches apart, and four inches deep, and on his return in a few hours finds
+every part ready broken to his hand.<a href="#fn-36.2" name="fnref-36.2"
+id="fnref-36.2"><sup>[2]</sup></a>
+</p>
+
+<p>
+That a great many veins communicated originally with the surface of the country
+above, or with the bed of the sea, is proved by the occurrence in them of
+well-rounded pebbles, agreeing with those in superficial alluviums, as in
+Auvergne and Saxony. Marine fossil shells, also, have been found at great
+depths, having probably been ingulfed during submarine earthquakes. Thus, a
+gryphæa is stated by M. Virlet to have been met with in a lead-mine near Semur,
+in France, and a madrepore in a compact vein of cinnabar in Hungary.<a
+href="#fn-36.3" name="fnref-36.3" id="fnref-36.3"><sup>[3]</sup></a> In
+Bohemia, similar pebbles have been met with at the depth of 180 fathoms; and in
+Cornwall, Mr. Carne mentions <a name="page609"></a>true pebbles of quartz and
+slate in a tin lode of the Relistran Mine, at the depth of 600 feet below the
+surface. They were cemented by oxide of tin and bisulphuret of copper, and were
+traced over a space more than twelve feet long and as many wide.<a
+href="#fn-36.4" name="fnref-36.4" id="fnref-36.4"><sup>[4]</sup></a> When
+different sets or systems of veins occur in the same country, those which are
+supposed to be of contemporaneous origin, and which are filled with the same
+kind of metals, often maintain a general parallelism of direction. Thus, for
+example, both the tin and copper veins in Cornwall run nearly east and west,
+while the lead veins run north and south; but there is no general law of
+direction common to different mining districts. The parallelism of the veins is
+another reason for regarding them as ordinary fissures, for we observe that
+faults and trap dikes, admitted by all to be masses of melted matter which have
+filled rents, are often parallel.
+</p>
+
+<p>
+<i>Fracture, Re-opening and Successive Formation of Veins.</i>&mdash;Assuming,
+then, that veins are simply fissures in which chemical and mechanical deposits
+have accumulated, we may next consider the proofs of their having been filled
+gradually and often during successive enlargements.
+</p>
+
+<p>
+Werner observed, in a vein near Gersdorff, in Saxony, no less than thirteen
+beds of different minerals, arranged with the utmost regularity on each side of
+the central layer. This layer was formed of two plates of calcareous spar,
+which had evidently lined the opposite walls of a vertical cavity. The thirteen
+beds followed each other in corresponding order, consisting of fluor-spar,
+heavy spar, galena, etc. In these cases the central mass has been last formed,
+and the two plates which coat the walls of the rent on each side are the oldest
+of all. If they consist of crystalline precipitates, they may be explained by
+supposing the fissure to have remained unaltered in its dimensions, while a
+series of changes occurred in the nature of the solutions which rose up from
+below: but such a mode of deposition, in the case of many successive and
+parallel layers, appears to be exceptional.
+</p>
+
+<p>
+If a vein-stone consist of crystalline matter, the points of the crystals are
+always turned inward, or towards the centre of the vein; in other words, they
+point in the direction where there was space for the development of the
+crystals. Thus each new layer receives the impression of the crystals of the
+preceding layer, and imprints its crystals on the one which follows, until at
+length the whole of the vein is filled: the two layers which meet dovetail the
+points of their crystals the one into the other. But in Cornwall, some lodes <a
+name="page610"></a>occur where the vertical plates, or <i>combs,</i> as they
+are there called, exhibit crystals so dovetailed as to prove that the same
+fissure has been often enlarged. Sir H. De la Beche gives the following curious
+and instructive example (Fig. 632), from a copper-mine in granite, near
+Redruth.<a href="#fn-36.5" name="fnref-36.5" id="fnref-36.5"><sup>[5]</sup></a>
+Each of the plates or combs (<i>a, b, c, d, e, f</i>) is double, having the
+points of their crystals turned inward along the axis of the comb. The sides or
+walls (2, 3, 4, 5 and 6) are parted by a thin covering of ochreous clay, so
+that each comb is readily separable from another by a moderate blow of the
+hammer. The breadth of each represents the whole width of the fissure at six
+successive periods, and the outer walls of the vein, where the first narrow
+rent was formed, consisted of the granitic surfaces 1 and 7.
+</p>
+
+<img src="images/fig632.jpg" width="206" height="175" alt="Fig. 632: Copper
+lode, near Redruth, enlarged at six successive periods." />
+
+<p>
+A somewhat analogous interpretation is applicable to many other cases, where
+clay, sand, or angular detritus, alternate with ores and vein-stones. Thus, we
+may imagine the sides of a fissure to be incrusted with siliceous matter, as
+Von Buch observed, in Lancerote, the walls of a volcanic crater formed in 1731
+to be traversed by an open rent in which hot vapours had deposited hydrate of
+silica, the incrustation nearly extending to the middle.<a href="#fn-36.6"
+name="fnref-36.6" id="fnref-36.6"><sup>[6]</sup></a> Such a vein may then be
+filled with clay or sand, and afterwards re-opened, the new rent dividing the
+argillaceous deposit, and allowing a quantity of rubbish to fall down. Various
+metals and spars may then be precipitated from aqueous solutions among the
+interstices of this heterogeneous mass.
+</p>
+
+<p>
+That such changes have repeatedly occurred, is demonstrated by occasional
+cross-veins, implying the oblique fracture of previously formed chemical and
+mechanical deposits. Thus, for example, M. Fournet, in his description of some
+mines in Auvergne worked under his superintendence, observes that the granite
+of that country was first penetrated by veins of granite, and then dislocated,
+so that open rents crossed both the granite and the granitic veins. Into such
+openings, quartz, accompanied by sulphurets of iron and arsenical pyrites, was
+introduced. Another convulsion then burst open the rocks along the old line of
+fracture, and the <a name="page611"></a>first set of deposits were cracked and
+often shattered, so that the new rent was filled, not only with angular
+fragments of the adjoining rocks, but with pieces of the older vein-stones.
+Polished and striated surfaces on the sides or in the contents of the vein also
+attest the reality of these movements. A new period of repose then ensued,
+during which various sulphurets were introduced, together with hornstone
+quartz, by which angular fragments of the older quartz before mentioned were
+cemented into a breccia. This period was followed by other dilatations of the
+same veins, and the introduction of other sets of mineral deposits, as well as
+of pebbles of the basaltic lavas of Auvergne, derived from superficial
+alluviums, probably of Miocene or even Older Pliocene date. Such repeated
+enlargement and re-opening of veins might have been anticipated, if we adopt
+the theory of fissures, and reflect how few of them have ever been sealed up
+entirely, and that a country with fissures only partially filled must naturally
+offer much feebler resistance along the old lines of fracture than anywhere
+else.
+</p>
+
+<p>
+<b>Cause of alternate Contraction and Swelling of Veins.</b>&mdash;A large
+proportion of metalliferous veins have their opposite walls nearly parallel,
+and sometimes over a wide extent of country. There is a fine example of this in
+the celebrated vein of Andreasburg in the Hartz, which has been worked for a
+depth of 500 yards perpendicularly, and 200 horizontally, retaining almost
+everywhere a width of three feet. But many lodes in Cornwall and elsewhere are
+extremely variable in size, being one or two inches in one part, and then eight
+or ten feet in another, at the distance of a few fathoms, and then again
+narrowing as before. Such alternate swelling and contraction is so often
+characteristic as to require explanation. The walls of fissures in general,
+observes Sir H. De la Beche, are rarely perfect planes throughout their entire
+course, nor could we well expect them to be so, since they commonly pass
+through rocks of unequal hardness and different mineral composition. If,
+therefore, the opposite sides of such irregular fissures slide upon each other,
+that is to say, if there be a fault, as in the case of so many mineral veins,
+the parallelism of the opposite walls is at once entirely destroyed, as will be
+readily seen by studying Figs. 633 to 635.
+</p>
+
+<p>
+Let <i>a b,</i> Fig. 633, be a line of fracture traversing a rock, and let <i>a
+b,</i> Fig. 634, represent the same line. Now, if we cut in two a piece of
+paper representing this line, and then move the lower portion of this cut paper
+sideways from <i>a</i> to <i>a&#x2032;</i>, taking care that the two pieces of
+paper still touch each other at <a name="page612"></a>the points 1, 2, 3, 4, 5,
+we obtain an irregular aperture at <i>c,</i> and isolated cavities at <i>d, d,
+d,</i> and when we compare such figures with nature we find that, with certain
+modifications, they represent the interior of faults and mineral veins. If,
+instead of sliding the cut paper to the right hand, we move the lower part
+towards the left, about the same distance that it was previously slid to the
+right, we obtain considerable variation in the cavities so produced, two long
+irregular open spaces, <i>f, f,</i> Fig. 635, being then formed. This will
+serve to show to what slight circumstances considerable variations in the
+character of the openings between unevenly fractured surfaces may be due, such
+surfaces being moved upon each other, so as to have numerous points of contact.
+</p>
+
+<p>
+<img src="images/fig633.jpg" width="368" height="138" alt="Figs. 633, 634, 635:
+Lines of fracture traversing a rock." />
+</p>
+
+<img src="images/fig636.jpg" width="78" height="158" alt="Fig. 636: Nipped ores
+where the course of a vein departs from verticality." />
+
+<p>
+Most lodes are perpendicular to the horizon, or nearly so; but some of them
+have a considerable inclination or &ldquo;hade,&rdquo; as it is termed, the
+angles of dip being very various. The course of a vein is frequently very
+straight; but if tortuous, it is found to be choked up with clay, stones, and
+pebbles, at points where it departs most widely from verticality. Hence at
+places, such as <i>a,</i> Fig. 636, the miner complains that the ores are
+&ldquo;nipped,&rdquo; or greatly reduced in quantity, the space for their free
+deposition having been interfered with in consequence of the pre-occupancy of
+the lode by earthy materials. When lodes are many fathoms wide, they are
+usually filled for the most part with earthy matter, and fragments of rock,
+through which the ores are disseminated. The metallic substances frequently
+coat or encircle detached pieces of rock, which our miners call
+&ldquo;horses&rdquo; or &ldquo;riders.&rdquo; That we should find some mineral
+veins which split into branches is also natural, for we observe the same in
+regard to open fissures.
+</p>
+
+<p>
+<b>Chemical Deposits in Veins.</b>&mdash;If we now turn from the mechanical to
+the chemical agencies which have been instrumental in the production of mineral
+veins, it may be remarked that those parts of fissures which were choked up <a
+name="page613"></a>with the ruins of fractured rocks must always have been
+filled with water; and almost every vein has probably been the channel by which
+hot springs, so common in countries of volcanoes and earthquakes, have made
+their way to the surface. For we know that the rents in which ores abound
+extend downward to vast depths, where the temperature of the interior of the
+earth is more elevated. We also know that mineral veins are most metalliferous
+near the contact of Plutonic and stratified formations, especially where the
+former send veins into the latter, a circumstance which indicates an original
+proximity of veins at their inferior extremity to igneous and heated rocks. It
+is moreover acknowledged that even those mineral and thermal springs which, in
+the present state of the globe, are far from volcanoes, are nevertheless
+observed to burst out along great lines of upheaval and dislocation of rocks.<a
+href="#fn-36.7" name="fnref-36.7" id="fnref-36.7"><sup>[7]</sup></a> It is also
+ascertained that all the substances with which hot springs are impregnated
+agree with those discharged in a gaseous form from volcanoes. Many of these
+bodies occur as vein-stones; such as silex, carbonate of lime, sulphur,
+fluor-spar, sulphate of barytes, magnesia, oxide of iron, and others. I may add
+that, if veins have been filled with gaseous emanations from masses of melted
+matter, slowly cooling in the subterranean regions, the contraction of such
+masses as they pass from a plastic to a solid state would, according to the
+experiments of Deville on granite (a rock which may be taken as a standard),
+produce a reduction in volume amounting to 10 per cent. The slow
+crystallisation, therefore, of such Plutonic rocks supplies us with a force not
+only capable of rending open the incumbent rocks by causing a failure of
+support, but also of giving rise to faults whenever one portion of the
+earth&rsquo;s crust subsides slowly while another contiguous to it happens to
+rest on a different foundation, so as to remain unmoved.
+</p>
+
+<p>
+Although we are led to infer, from the foregoing reasoning, that there has
+often been an intimate connection between metalliferous veins and hot springs
+holding mineral matter in solution, yet we must not on that account expect that
+the contents of hot springs and mineral veins would be identical. On the
+contrary, M. E. de Beaumont has judiciously observed that we ought to find in
+veins those substances which, being least soluble, are not discharged by hot
+springs&mdash;or that class of simple and compound bodies which the thermal
+waters ascending from below would first precipitate on the walls of a fissure,
+as soon as their temperature began slightly to diminish. The higher they mount
+towards the surface, <a name="page614"></a>the more will they cool, till they
+acquire the average temperature of springs, being in that case chiefly charged
+with the most soluble substances, such as the alkalies, soda and potash. These
+are not met with in veins, although they enter so largely into the composition
+of granitic rocks.<a href="#fn-36.8" name="fnref-36.8"
+id="fnref-36.8"><sup>[8]</sup></a>
+</p>
+
+<p>
+To a certain extent, therefore, the arrangement and distribution of metallic
+matter in veins may be referred to ordinary chemical action, or to those
+variations in temperature which waters holding the ores in solution must
+undergo, as they rise upward from great depths in the earth. But there are
+other phenomena which do not admit of the same simple explanation. Thus, for
+example, in Derbyshire, veins containing ores of lead, zinc, and copper, but
+chiefly lead, traverse alternate beds of limestone and greenstone. The ore is
+plentiful where the walls of the rent consist of limestone, but is reduced to a
+mere string when they are formed of greenstone, or &ldquo;toad-stone,&rdquo; as
+it is called provincially. Not that the original fissure is narrower where the
+greenstone occurs, but because more of the space is there filled with
+vein-stones, and the waters at such points have not parted so freely with their
+metallic contents.
+</p>
+
+<p>
+&ldquo;Lodes in Cornwall,&rdquo; says Mr. Robert W. Fox, &ldquo;are very much
+influenced in their metallic riches by the nature of the rock which they
+traverse, and they often change in this respect very suddenly, in passing from
+one rock to another. Thus many lodes which yield abundance of ore in granite,
+are unproductive in clay-slate, or killas and <i>vice versa.</i>
+</p>
+
+<p>
+<b>Supposed relative Age of the different Metals.</b>&mdash;After duly
+reflecting on the facts above described, we cannot doubt that mineral veins,
+like eruptions of granite or trap, are referable to many distinct periods of
+the earth&rsquo;s history, although it may be more difficult to determine the
+precise age of veins; because they have often remained open for ages, and
+because, as we have seen, the same fissure, after having been once filled, has
+frequently been re-opened or enlarged. But besides this diversity of age, it
+has been supposed by some geologists that certain metals have been produced
+exclusively in earlier, others in more modern times; that tin, for example, is
+of higher antiquity than copper, copper than lead or silver, and all of them
+more ancient than gold. I shall first point out that the facts once relied upon
+in support of some of these views are contradicted by later experience, and
+then consider how far any chronological order of arrangement can be recognised
+in the position of the precious and other metals in the earth&rsquo;s crust.
+</p>
+
+<p>
+<a name="page615"></a>In the first place, it is not true that veins in which
+tin abounds are the oldest lodes worked in Great Britain. The government survey
+of Ireland has demonstrated that in Wexford veins of copper and lead (the
+latter as usual being argentiferous) are much older than the tin of Cornwall.
+In each of the two countries a very similar series of geological changes has
+occurred at two distinct epochs&mdash;in Wexford, before the Devonian strata
+were deposited; in Cornwall, after the Carboniferous epoch. To begin with the
+Irish mining district: We have granite in Wexford traversed by granite veins,
+which veins also intrude themselves into the Silurian strata, the same Silurian
+rocks as well as the veins having been denuded before the Devonian beds were
+superimposed. Next we find, in the same county, that elvans, or straight dikes
+of porphyritic granite, have cut through the granite and the veins before
+mentioned, but have not penetrated the Devonian rocks. Subsequently to these
+elvans, veins of copper and lead were produced, being of a date certainly
+posterior to the Silurian, and anterior to the Devonian; for they do not enter
+the latter, and, what is still more decisive, streaks or layers of derivative
+copper have been found near Wexford in the Devonian, not far from points where
+mines of copper are worked in the Silurian strata.
+</p>
+
+<p>
+Although the precise age of such copper lodes cannot be defined, we may safely
+affirm that they were either filled at the close of the Silurian or
+commencement of the Devonian period. Besides copper, lead, and silver, there is
+some gold in these ancient or primary metalliferous veins. A few fragments also
+of tin found in Wicklow in the drift are supposed to have been derived from
+veins of the same age.<a href="#fn-36.9" name="fnref-36.9" id="fnref-36.9"><sup>[9]</sup></a>
+</p>
+
+<p>
+Next, if we turn to Cornwall, we find there also the monuments of a very
+analogous sequence of events. First, the granite was formed; then, about the
+same period, veins of fine-grained granite, often tortuous (see <a
+href="images/fig614.jpg">Fig. 614</a>), penetrating both the outer crust of
+granite and the adjoining fossiliferous or primary rocks, including the
+coal-measures; thirdly, elvans, holding their course straight through granite,
+granitic veins, and fossiliferous slates; fourthly, veins of tin also
+containing copper, the first of those eight systems of fissures of different
+ages already alluded to, p. 607. Here, then, the tin lodes are newer than the
+elvans. It has, indeed, been stated by some Cornish miners that the elvans are
+in some instances posterior to the oldest tin-bearing lodes, but the
+observations of Sir H. de la Beche during the survey led him to an opposite
+conclusion, and he has shown how the <a name="page616"></a>cases referred to in
+corroboration can be otherwise interpreted.<a href="#fn-36.10"
+name="fnref-36.10" id="fnref-36.10"><sup>[10]</sup></a> We may, therefore,
+assert that the most ancient Cornish lodes are younger than the coal-measures
+of that part of England, and it follows that they are of a much later date than
+the Irish copper and lead of Wexford and some adjoining counties. How much
+later, it is not so easy to declare, although probably they are not newer than
+the beginning of the Permian period, as no tin lodes have been discovered in
+any red sandstone which overlies the coal in the south-west of England.
+</p>
+
+<p>
+There are lead veins in Glamorganshire which enter the lias, and others near
+Frome, in Somersetshire, which have been traced into the Inferior Oolite. In
+Bohemia, the rich veins of silver of Joachimsthal cut through basalt containing
+olivine, which overlies tertiary lignite, in which are leaves of dicotyledonous
+trees. This silver, therefore, is decidedly a tertiary formation. In regard to
+the age of the gold of the Ural mountains, in Russia, which, like that of
+California, is obtained chiefly from auriferous alluvium, it occurs in veins of
+quartz in the schistose and granitic rocks of that chain, and is supposed by
+Sir R. Murchison, MM. Deverneuil and Keyserling to be newer than the syenitic
+granite of the Ural&mdash;perhaps of tertiary date. They observe that no gold
+has yet been found in the Permian conglomerates which lie at the base of the
+Ural Mountains, although large quantities of iron and copper detritus are mixed
+with the pebbles of those Permian strata. Hence it seems that the Uralian
+quartz veins, containing gold and platinum, were not formed, or certainly not
+exposed to aqueous denudation, during the Permian era.
+</p>
+
+<p>
+In the auriferous alluvium of Russia, California, and Australia, the bones of
+extinct land-quadrupeds have been met with, those of the mammoth being common
+in the gravel at the foot of the Ural Mountains, while in Australia they
+consist of huge marsupials, some of them of the size of the rhinoceros and
+allied to the living wombat. They belong to the genera Diprotodon and
+Nototherium of Professor Owen. The gold of Northern Chili is associated in the
+mines of Los Hornos with copper pyrites, in veins traversing the
+cretaceo-oolitic formations, so-called because its fossils have the character
+partly of the cretaceous and partly of the oolitic fauna of Europe.<a
+href="#fn-36.11" name="fnref-36.11" id="fnref-36.11"><sup>[11]</sup></a> The
+gold found in the United States, in the mountainous parts of Virginia, North
+and South Carolina, and Georgia, occurs in metamorphic Silurian strata, as well
+as in auriferous gravel derived from the same.
+</p>
+
+<p>
+<a name="page617"></a>Gold has now been detected in almost every kind of rock,
+in slate, quartzite, sandstone, limestone, granite, and serpentine, both in
+veins and in the rocks themselves at short distances from the veins. In
+Australia it has been worked successfully not only in alluvium, but in
+vein-stones in the native rock, generally consisting of Silurian shales and
+slates. It has been traced on that continent over more than nine degrees of
+latitude (between the parallels of 30° and 39° S.), and over twelve of
+longitude, and yielded in 1853 an annual supply equal, if not superior, to that
+of California; nor is there any apparent prospect of this supply diminishing,
+still less of the exhaustion of the gold-fields.
+</p>
+
+<p>
+<i>Origin of Gold in California.</i>&mdash;Mr. J. Arthur Phillips,<a
+href="#fn-36.12" name="fnref-36.12" id="fnref-36.12"><sup>[12]</sup></a> in his
+treatise &ldquo;On the Gold Fields of California,&rdquo; has shown that the ore
+in the gold workings is derived from drifts, or gravel clay, and sand, of two
+distinct geological ages, both comparatively modern, but belonging to different
+river-systems, the older of which is so ancient as to be capped by a thick
+sheet of lava divided by basaltic columns. The auriferous quartz of these
+drifts is derived from veins apparently due to hydrothermal agency, proceeding
+from granite and penetrating strata supposed to be of Jurassic and Triassic
+date. The fossil wood of the drift is sometimes beautifully silicified, and
+occasionally the trunks of trees are replaced by iron pyrites, but gold seems
+not to have been found as in the pyrites of similarly petrified trees in the
+drift of Australia.
+</p>
+
+<p>
+The formation of recent metalliferous veins is now going on, according to Mr.
+Phillips, in various parts of the Pacific coast. Thus, for example, there are
+fissures at the foot of the eastern declivity of the Sierra Nevada in the state
+of that name, from which boiling water and steam escape, forming siliceous
+incrustations on the sides of the fissures. In one case, where the fissure is
+partially filled up with silica inclosing iron and copper pyrites, gold has
+also been found in the vein-stone.
+</p>
+
+<p>
+It has been remarked by M. de Beaumont, that lead and some other metals are
+found in dikes of basalt and greenstone, as well as in mineral veins connected
+with trap-rock, whereas tin is met with in granite and in veins associated with
+the Plutonic series. If this rule hold true generally, the geological position
+of tin accessible to the miner will belong, for the most part, to rocks older
+than those bearing lead. The tin veins will be of higher relative antiquity for
+the same reason that the &ldquo;underlying&rdquo; igneous formations or <a
+name="page618"></a>granites which are visible to man are older, on the whole,
+than the overlying or trappean formations.
+</p>
+
+<p>
+If different sets of fissures, originating simultaneously at different levels
+in the earth&rsquo;s crust, and communicating, some of them with volcanic,
+others with heated Plutonic masses, be filled with different metals, it will
+follow that those formed farthest from the surface will usually require the
+longest time before they can be exposed superficially. In order to bring them
+into view, or within reach of the miner, a greater amount of upheaval and
+denudation must take place in proportion as they have lain deeper when first
+formed and filled. A considerable series of geological revolutions must
+intervene before any part of the fissure which has been for ages in the
+proximity of the Plutonic rock, so as to receive the gases discharged from it
+when it was cooling, can emerge into the atmosphere. But I need not enlarge on
+this subject, as the reader will remember what was said in the 30th, 32nd, and
+35th chapters on the chronology of the volcanic and hypogene formations.
+</p>
+
+<p class="footnote">
+<a name="fn-36.1" id="fn-36.1"></a> <a href="#fnref-36.1">[1]</a>
+Geol. Trans., vol. iv, p. 139; Trans. Royal Geol. Society, Cornwall, vol. ii,
+p. 90
+</p>
+
+<p class="footnote">
+<a name="fn-36.2" id="fn-36.2"></a> <a href="#fnref-36.2">[2]</a>
+Conybeare and Phil. Geol., p. 401, and Farey&rsquo;s Derbyshire, p. 243.
+</p>
+
+<p class="footnote">
+<a name="fn-36.3" id="fn-36.3"></a> <a href="#fnref-36.3">[3]</a>
+Fournet, Études sur les Dépôts Métallifères.
+</p>
+
+<p class="footnote">
+<a name="fn-36.4" id="fn-36.4"></a> <a href="#fnref-36.4">[4]</a>
+Carne, Trans. Geol. Soc., Cornwall, vol. iii, p. 238.
+</p>
+
+<p class="footnote">
+<a name="fn-36.5" id="fn-36.5"></a> <a href="#fnref-36.5">[5]</a>
+Geol. Rep. on Cornwall, p. 340.
+</p>
+
+<p class="footnote">
+<a name="fn-36.6" id="fn-36.6"></a> <a href="#fnref-36.6">[6]</a>
+Principles, chap. xxvii, 8th edit., p. 422.
+</p>
+
+<p class="footnote">
+<a name="fn-36.7" id="fn-36.7"></a> <a href="#fnref-36.7">[7]</a>
+See Dr. Daubeny&rsquo;s Volcanoes.
+</p>
+
+<p class="footnote">
+<a name="fn-36.8" id="fn-36.8"></a> <a href="#fnref-36.8">[8]</a>
+Bulletin, iv, p. 1278.
+</p>
+
+<p class="footnote">
+<a name="fn-36.9" id="fn-36.9"></a> <a href="#fnref-36.9">[9]</a>
+Sir H. De la Beche, MS. Notes on Irish Survey.
+</p>
+
+<p class="footnote">
+<a name="fn-36.10" id="fn-36.10"></a> <a href="#fnref-36.10">[10]</a>
+Report on Geology of Cornwall, p. 310.
+</p>
+
+<p class="footnote">
+<a name="fn-36.11" id="fn-36.11"></a> <a href="#fnref-36.11">[11]</a>
+Darwin&rsquo;s South America, p. 209, etc.
+</p>
+
+<p class="footnote">
+<a name="fn-36.12" id="fn-36.12"></a> <a href="#fnref-36.12">[12]</a>
+Proc. Royal Soc., 1868, p. 294.
+</p>
+
+</div><!--end chapter-->
+
+<div class="chapter">
+
+<h2><a name="chap37"></a>INDEX.</h2>
+
+<p class="center">
+&mdash;&mdash;::&mdash;&mdash;<br/>
+<br/>
+<br/>
+<i>The Fossils, the names of which appear in Italics, are figured in the
+Text.</i>
+</p>
+
+<p class="noindent">
+A<small>BBEVILLE</small>, flint tools of, <a href="#page152">152</a><br/>
+Aberdeenshire, granite of, <a href="#page558">558</a><br/>
+Abich, M., on trachytic rocks, <a href="#page504">504</a><br/>
+<i>Acer trilobatum,</i> Miocene, <a href="#page220">220</a>, <a href="#page221">221</a><br/>
+<i>Acrodus nobilis,</i> Lias, <a href="#page359">359</a><br/>
+Acrogens, term explained, <a href="#page303">303</a><br/>
+<i>Acrolepis Sedgwickii,</i> Permian, <a href="#page390">390</a><br/>
+<i>Actæon acutus,</i> Great Oolite, <a href="#page345">345</a><br/>
+<i>Actinocyclas,</i> in Atlantic mud, <a href="#page288">288</a><br/>
+Actinolite, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+&mdash;&mdash; schist, <a href="#page578">578</a><br/>
+<i>Æchmodus Leachii,</i> Lias, <a href="#page358">358</a><br/>
+<i>Adiantites Hibernica,</i> Old Red, <a href="#page441">441</a><br/>
+Agassiz on fish of Sheppey, <a href="#page267">267</a><br/>
+&mdash;&mdash; on fish of the Brown-Coal, <a href="#page540">540</a><br/>
+&mdash;&mdash; on fish of Monte Bolca, <a href="#page544">544</a><br/>
+&mdash;&mdash; on Old Red fossil fish, <a href="#page443">443</a>, <a href="#page447">447</a><br/>
+&mdash;&mdash; on Silurian fish, <a href="#page460">460</a><br/>
+Age of metamorphic rocks, <a href="#page597">597</a><br/>
+&mdash;&mdash; of Plutonic rocks, <a href="#page564">564</a><br/>
+&mdash;&mdash; of strata, tests of, <a href="#page123">123</a><br/>
+&mdash;&mdash; of volcanic rocks, <a href="#page520">520</a><br/>
+Agglomerate described, <a href="#page509">509</a><br/>
+<i>Agnostus integer. A. Rex</i>, <a href="#page488">488</a><br/>
+Air-breathers of the Coal, <a href="#page413">413</a><br/>
+Aix-la-Chapelle, Cretaceous flora of, <a href="#page302">302</a><br/>
+Alabaster defined, <a href="#page39">39</a><br/>
+Alberti on Keuper, <a href="#page376">376</a><br/>
+Albite, <a href="#page499">499</a>, <a href="#page500">500</a><br/>
+Aldeby and Chillesford beds, <a href="#page192">192</a><br/>
+Alkali, present in the Palæozoic strata, <a href="#page587">587</a><br/>
+Alpine blocks on the Jura, <a href="#page169">169</a><br/>
+Alps, age of metamorphic rocks in, <a href="#page599">599</a><br/>
+&mdash;&mdash;, nummulitic limestone and flysch of, <a href="#page77">77</a><br/>
+Alum schists of Norway and Sweden, <a href="#page489">489</a><br/>
+Alluvial deposits, Recent and Post-pliocene, <a href="#page151">151</a><br/>
+Alluvium, term explained, <a href="#page99">99</a><br/>
+&mdash;&mdash; in Auvergne, <a href="#page100">100</a><br/>
+Alternations of marine and fresh-water strata, <a href="#page72">72</a><br/>
+Alum Bay beds, plants of the, <a href="#page262">262</a><br/>
+Amblyrhynchus cristatus, a living marine saurian, <a href="#page362">362</a><br/>
+America. <i>See</i> United States, Canada, Nova Scotia.<br/>
+&mdash;&mdash;, North, Glacial formations of, <a href="#page182">182</a><br/>
+&mdash;&mdash;, South, gradual rise of land in, <a href="#page72">72</a><br/>
+&mdash;&mdash;, Silurian strata of, <a href="#page478">478</a><br/>
+American character of Lower Miocene flora, <a href="#page238">238</a><br/>
+&mdash;&mdash; forms in Swiss Miocene flora, <a href="#page223">223</a><br/>
+Amiens, flint tools of, <a href="#page152">152</a><br/>
+<i>Ammonites bifrons,</i> Lias, <a href="#page356">356</a><br/>
+&mdash;&mdash; <i>Braikenridgii,</i> Oolite, <a href="#page351">351</a><br/>
+&mdash;&mdash; <i>Bucklandi,</i> Lias, <a href="#page356">356</a><br/>
+&mdash;&mdash; <i>Deshayesii,</i> Neocomian, <a href="#page311">311</a><br/>
+&mdash;&mdash; <i>Humphresianus,</i> Inferior Oolite, <a href="#page351">351</a><br/>
+&mdash;&mdash; <i>Jason,</i> Oxford Clay, <a href="#page340">340</a><br/>
+&mdash;&mdash; <i>Noricus,</i> Speeton, <a href="#page312">312</a><br/>
+&mdash;&mdash; <i>macrocephalus,</i> Oolite, <a href="#page352">352</a><br/>
+&mdash;&mdash; <i>margaritatus,</i> Lias, <a href="#page357">357</a><br/>
+&mdash;&mdash; <i>planorbis,</i> Lias, <a href="#page356">356</a><br/>
+&mdash;&mdash; <i>rhotomagensis,</i> Chalk marl, <a href="#page298">298</a><br/>
+Amphibole group of minerals, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+<i>Amphistegina Hauerina,</i> Vienna basin, <a href="#page225">225</a><br/>
+<i>Amphitherium Broderipii,</i> in Stonesfield, <a href="#page348">348</a><br/>
+&mdash;&mdash; <i>Prevostii,</i> Stonesfield slate, <a href="#page347">347</a><br/>
+<i>Ampullaria glauca</i>, <a href="#page56">56</a><br/>
+<i>Amygdaloid</i>, <a href="#page507">507</a><br/>
+Analcime, <a href="#page500">500</a><br/>
+Anamesite, a variety of basalt, <a href="#page504">504</a><br/>
+<i>Ananchytes ovatus,</i> White chalk, <a href="#page293">293</a><br/>
+&mdash;&mdash;, with crania attached, <a href="#page49">49</a><br/>
+<i>Ancillaria subulata,</i> Eocene, <a href="#page57">57</a><br/>
+<i>Ancyloceras gigas</i>, <a href="#page309">309</a><br/>
+&mdash;&mdash; <i>spinigerum,</i> Gault, <a href="#page301">301</a><br/>
+&mdash;&mdash; <i>Duvallei,</i> Neocomian, <a href="#page312">312</a><br/>
+<i>Ancylus velletia (A. elegans)</i>, <a href="#page55">55</a><br/>
+Andalusite, <a href="#page500">500</a><br/>
+Andes, Plutonic rocks of the, <a href="#page569">569</a><br/>
+Andreasburg, metalliferous vein of, <a href="#page611">611</a><br/>
+Angelin, on Cambrian of Sweden, <a href="#page489">489</a><br/>
+Angiosperms, <a href="#page303">303</a><br/>
+&mdash;&mdash; of the Coal, <a href="#page429">429</a><br/>
+Anglesea, dike cutting through shale in, <a href="#page514">514</a><br/>
+<i>Anodonta Cordierii</i>, <a href="#page54">54</a><br/>
+&mdash;&mdash; <i>Jukesii,</i> Upper Old Red, <a href="#page441">441</a><br/>
+&mdash;&mdash; <i>latimarginata</i>, <a href="#page54">54</a><br/>
+<i>Anoplotherium commune,</i> Binstead, <a href="#page254">254</a><br/>
+&mdash;&mdash; <i>gracile,</i> Paris basin, <a href="#page271">271</a><br/>
+Anorthite, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+<i>Annularia sphenophylloides,</i> Coal, <a href="#page425">425</a><br/>
+<i>Antholithes,</i> coal-measures, <a href="#page429">429</a><br/>
+Anthracite, conversion of coal into, <a href="#page408">408</a><br/>
+Anticlinal and synclinal curves, <a href="#page74">74</a>, <a href="#page85">85</a><br/>
+Antrim, Chalk altered by a dike in, <a href="#page516">516</a><br/>
+&mdash;&mdash;, Lower Miocene, volcanic rocks of, <a href="#page539">539</a><br/>
+Antwerp Crag, <a href="#page204">204</a><br/>
+Apateon pedestris, a carboniferous reptile, <a href="#page406">406</a><br/>
+Apatite, <a href="#page500">500</a><br/>
+Apennines, Northern, metamorphic rocks of, <a href="#page599">599</a><br/>
+Apes, fossil of the Upper Miocene, <a href="#page215">215</a><br/>
+<i>Apiocrinites rotundus,</i> Bradford, <a href="#page343">343</a><br/>
+Appalachians, long lines of flexures in, <a href="#page92">92</a>, <a href="#page93">93</a><br/>
+&mdash;&mdash;, vast thickness of successive strata in, <a href="#page110">110</a><br/>
+<i>Aptychus,</i> part of ammonite, <a href="#page336">336</a><br/>
+Aqueous rocks defined, <a href="#page27">27</a>, <a href="#page35">35</a><br/>
+<i>Araucaria sphærocarpa,</i> Inferior Oolite, <a href="#page348">348</a><br/>
+Arbroath, section of Old Red at, <a href="#page74">74</a><br/>
+<i>Archæopteryx macrura,</i> Solenhofen, <a href="#page338">338</a><br/>
+<i>Archegosaurus minor and A. medius,</i> coal measures, <a href="#page406">406</a>, <a href="#page407">407</a><br/>
+Archiac, M. de, on nummulites, <a href="#page277">277</a><br/>
+&mdash;&mdash;, on chalk of France, <a href="#page306">306</a><br/>
+Arctic Miocene Flora, <a href="#page239">239</a><br/>
+Area of the Wealden, <a href="#page319">319</a><br/>
+Areas, permanence of continental, <a href="#page117">117</a><br/>
+Arenaceous rocks described, <a href="#page35">35</a><br/>
+<i>Arenicolites linearis,</i> Arenig beds, <a href="#page475">475</a><br/>
+Arenig or Stiper-Stones group, <a href="#page474">474</a><br/>
+&mdash;&mdash;, volcanic formations of, <a href="#page549">549</a><br/>
+Argile plastique, <a href="#page276">276</a><br/>
+Argillaceous rocks described, <a href="#page36">36</a><br/>
+Argillite, Argillaceous schist, <a href="#page579">579</a><br/>
+Argyll, Duke of, on Isle of Mull leaf-beds, <a href="#page247">247</a><br/>
+Armagh, bone-beds in Mountain Limestone at, <a href="#page437">437</a><br/>
+Arran, amygdaloid filled with spar near, <a href="#page518">518</a><br/>
+&mdash;&mdash;, erect trees in volcanic ash of, <a href="#page546">546</a><br/>
+&mdash;&mdash;, Greenstone dike in, <a href="#page514">514</a><br/>
+Arthur&rsquo;s seat, trap rocks of, <a href="#page545">545</a><br/>
+<i>Arvicola,</i> tooth of, <a href="#page165">165</a><br/>
+<i>Asaphus caudatus,</i> Silurian, <a href="#page467">467</a><br/>
+&mdash;&mdash; <i>tyrannus, A. Buchii</i>, <a href="#page474">474</a><br/>
+Ascension, lamination of volcanic rocks in, <a href="#page595">595</a><br/>
+Ash, Mr., on fossils of Tremadoc beds, <a href="#page483">483</a><br/>
+Ashby-de-la-Zouch, fault in coal field of, <a href="#page91">91</a><br/>
+<i>Aspidura loricata,</i> Muschelkalk, <a href="#page379">379</a><br/>
+<i>Astarte borealis</i> (=<i>A. arctica=A. compressa</i>), <a href="#page176">176</a><br/>
+&mdash;&mdash; <i>Omalii,</i> Crag, <a href="#page199">199</a><br/>
+<i>Asterophyllites foliosus,</i> Coal, <a href="#page425">425</a><br/>
+<i>Astrangia lineata (Anthophyllum lineatum)</i>, <a href="#page229">229</a><br/>
+<i>Astræa basaltiforme,</i> Carboniferous, <a href="#page432">432</a><br/>
+<i>Astropecten crispatus,</i> London clay, <a href="#page266">266</a><br/>
+Atherfield clay, <a href="#page309">309</a><br/>
+Atlantic mud, composition of, <a href="#page287">287</a><br/>
+<i>Atrypa reticularis,</i> Aymestry, <a href="#page462">462</a><br/>
+<i>Aturia ziczac (Nautilus ziczac)</i>, <a href="#page266">266</a><br/>
+Augite, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+<i>Auricula,</i> recent, <a href="#page55">55</a><br/>
+Austen, Mr. Godwin, on marine deposit of Selsea Bill, <a href="#page182">182</a><br/>
+&mdash;&mdash;, on boulders in chalk, <a href="#page292">292</a><br/>
+Australian cave breccias, <a href="#page158">158</a><br/>
+Australia, auriferous gravel of, <a href="#page617">617</a><br/>
+Auvergne, alluvium in, <a href="#page100">100</a><br/>
+&mdash;&mdash;, chain of extinct volcanoes in, <a href="#page495">495</a><br/>
+&mdash;&mdash;, granite veins in, <a href="#page610">610</a><br/>
+&mdash;&mdash;, Lower Miocene of, <a href="#page233">233</a><br/>
+&mdash;&mdash;, Miocene volcanic rocks of, <a href="#page540">540</a><br/>
+&mdash;&mdash;, Post-pliocene volcanic eruptions in, <a href="#page527">527</a><br/>
+&mdash;&mdash;, springs from spent volcanoes in, <a href="#page604">604</a><br/>
+Aveline Mr., on Tarannon shales, <a href="#page468">468</a><br/>
+<i>Avicula contorta,</i> Rhætic beds, <a href="#page366">366</a><br/>
+&mdash;&mdash; <i>cygnipes,</i> Lias, <a href="#page355">355</a><br/>
+&mdash;&mdash; <i>inæquivalvis,</i> Lias, <a href="#page355">355</a><br/>
+&mdash;&mdash; <i>socialis,</i> Muschelkalk, <a href="#page379">379</a><br/>
+<i>Aviculopecten papyraceus,</i> coal measures, <a href="#page405">405</a><br/>
+&mdash;&mdash; <i>sublobatus,</i> mountain limestone, <a href="#page434">434</a><br/>
+Aymestry Limestone, <a href="#page461">461</a><br/>
+Azoic period, supposed, <a href="#page603">603</a><br/>
+Azores, Miocene lavas with shells, <a href="#page539">539</a><br/><br/>
+</p>
+
+<p class="noindent">
+<i>B<small>ACILLARIA</small> paradoxa</i>, <a href="#page51">51</a><br/>
+<i>Baculites anceps,</i> Lower Chalk, <a href="#page298">298</a><br/>
+&mdash;&mdash; <i>Fauiasii,</i> chalk, <a href="#page286">286</a><br/>
+Baffin&rsquo;s Bay, formation of drift in, <a href="#page171">171</a>, <a href="#page173">173</a><br/>
+Bagshot sands, <a href="#page258">258</a>, <a href="#page259">259</a>, <a href="#page262">262</a><br/>
+Baiæ, Bay of, subterranean igneous action in, <a href="#page569">569</a><br/>
+Bakewell, Mr., on cleavage in Swiss Alps, <a href="#page590">590</a><br/>
+Bala and Caradoc beds, <a href="#page470">470</a><br/>
+<i>Balistidæ,</i> defensive spine of, <a href="#page261">261</a><br/>
+Bangor, or Longmynd group, <a href="#page485">485</a><br/>
+<i>Banksia,</i> seed and fruit of, Lower Miocene, <a href="#page238">238</a><br/>
+Barmouth sandstones, <a href="#page486">486</a><br/>
+Barnes, Mr. J., on insects in American coal, <a href="#page416">416</a><br/>
+Barnstaple, Upper Devonian of, <a href="#page450">450</a><br/>
+Barrande, M. Joachim, his &ldquo;Primordial Zone,&rdquo; <a href="#page471">471</a>, <a href="#page482">482</a>, <a href="#page487">487</a><br/>
+&mdash;&mdash;, on metamorphosis of trilobites, <a href="#page471">471</a><br/>
+Barrett, Mr., on bird in Blackdown beds, <a href="#page299">299</a><br/>
+Barton series sands and clays, <a href="#page258">258</a><br/>
+&mdash;&mdash; shells, percentage of, common to London clay, <a href="#page258">258</a><br/>
+Basalt, columnar, <a href="#page511">511</a><br/>
+&mdash;&mdash;, composition of, <a href="#page504">504</a><br/>
+Basaltic rocks, poor in silica, <a href="#page504">504</a><br/>
+&mdash;&mdash;, specific gravity of minerals in, <a href="#page504">504</a><br/>
+<i>Basilosaurus,</i> Eocene, United States, <a href="#page280">280</a><br/>
+Basset, term explained, <a href="#page83">83</a><br/>
+Basterot, M. de, on Bordeaux tertiary strata, <a href="#page141">141</a><br/>
+Bath Oolite, <a href="#page342">342</a><br/>
+Batrachian reptiles in coal, <a href="#page406">406</a><br/>
+Bay of Fundy, denudation in coalfield in, <a href="#page418">418</a><br/>
+Bean, Mr., on Yorkshire Oolite, <a href="#page350">350</a><br/>
+Bear Island carboniferous flora, <a href="#page441">441</a><br/>
+Beaumont, M. E. de, on island in Cretaceous sea, <a href="#page305">305</a><br/>
+&mdash;&mdash;, on mineral veins, <a href="#page613">613</a><br/>
+&mdash;&mdash;, on Jurassic plutonic rocks, <a href="#page571">571</a><br/>
+&mdash;&mdash;, on formation of granite, <a href="#page553">553</a><br/>
+Beckles, Mr. S. H., on footprints in Hastings sands, <a href="#page315">315</a>, <a href="#page330">330</a><br/>
+&mdash;&mdash; on Mammalia of Purbeck, <a href="#page326">326</a><br/>
+<i>Belemnitella mucronata,</i> Chalk, <a href="#page283">283</a><br/>
+<i>Belemnites hastatus,</i> Oxford clay, <a href="#page340">340</a><br/>
+&mdash;&mdash; <i>Puzosianus,</i> Oxford clay, <a href="#page341">341</a><br/>
+Belgium, Lower Miocene of, <a href="#page241">241</a><br/>
+<i>Bellerophon costatus,</i> Mountain Limestone, <a href="#page436">436</a><br/>
+<i>Belosepia sepioidea,</i> Sheppey, <a href="#page266">266</a><br/>
+Belt, Mr., on subdivision of Lingula Flags, <a href="#page484">484</a><br/>
+Bembridge beds, Yarmouth, <a href="#page252">252</a><br/>
+Berger, Dr., on rocks altered by dikes, <a href="#page515">515</a><br/>
+Berlin, Miocene strata near, <a href="#page242">242</a><br/>
+Bernese Alps, gneiss in the, <a href="#page599">599</a><br/>
+Berthier on isomorphism, <a href="#page502">502</a><br/>
+Bertrich-Baden, columnar basalt of, <a href="#page512">512</a><br/>
+Beyrich on term Oligocene for Lower Miocene, <a href="#page244">244</a><br/>
+Billings, Mr., on trilobites, <a href="#page471">471</a><br/>
+Binney, Mr., on Sigillariæ in volcanic ash, <a href="#page546">546</a><br/>
+&mdash;&mdash;, on Stigmaria, the root of Sigillaria, <a href="#page426">426</a><br/>
+Biotite, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+Bird in argile plastique, <a href="#page276">276</a><br/>
+Bischoff, Professor, on Nile and Rhine mud, <a href="#page154">154</a><br/>
+&mdash;&mdash;, on conversion of coal into anthracite, <a href="#page403">403</a><br/>
+&mdash;&mdash;, on hydrothermal action, <a href="#page586">586</a><br/>
+Blackdown beds, <a href="#page301">301</a><br/>
+Blacklead of Borrowdale, <a href="#page65">65</a><br/>
+Bog-iron-ore, <a href="#page52">52</a><br/>
+Bohemia, Cambrian rocks of, <a href="#page487">487</a><br/>
+&mdash;&mdash;, silver veins in, <a href="#page616">616</a><br/>
+Bolderberg, in Belgium, Upper Miocene of, <a href="#page224">224</a><br/>
+Bone-bed of fish remains, Armagh, <a href="#page437">437</a><br/>
+&mdash;&mdash; of Upper Ludlow, <a href="#page450">450</a><br/>
+&mdash;&mdash; of the Trias, <a href="#page367">367</a><br/>
+Boom, Lower Miocene of, <a href="#page241">241</a><br/>
+Bordeaux, Upper Miocene of, <a href="#page214">214</a><br/>
+Borrowdale, blacklead of, <a href="#page65">65</a><br/>
+Bosquet, M. on chalk fossils, <a href="#page283">283</a><br/>
+&mdash;&mdash;, on Maestricht beds, <a href="#page283">283</a><br/>
+Botanical nomenclature, <a href="#page303">303</a><br/>
+Boucher de Perthes on Abbeville alluvium, <a href="#page152">152</a><br/>
+Boulder-clay, whether formed by icebergs or land-ice, <a href="#page166">166-73</a>, <a href="#page178">178</a><br/>
+Boulder-clay of Canada, <a href="#page182">182</a><br/>
+&mdash;&mdash; fauna of, <a href="#page176">176</a>, <a href="#page189">189</a><br/>
+Boulders and pebbles in chalk, <a href="#page292">292</a><br/>
+Bournemouth beds (Lower Bagshot), <a href="#page262">262</a><br/>
+Bovey Tracey, lignites and clays of, <a href="#page246">246</a><br/>
+Bowerbank, Mr., on fossil fruits of London Clay, <a href="#page265">265</a><br/>
+&mdash;&mdash;, on fossil fruits of Sheppey, <a href="#page265">265</a><br/>
+Bowman, Mr., on uniting of distinct coal-seams, <a href="#page401">401</a><br/>
+Brachiopoda, preponderance of, in older rocks, <a href="#page470">470</a><br/>
+&mdash;&mdash;, mode of recognising shells of, <a href="#page471">471</a><br/>
+Bracklesham beds and Bagshot Sands, <a href="#page259">259</a><br/>
+Bradford encrinites, <a href="#page342">342</a><br/>
+Breccias of Lower Permian, <a href="#page391">391</a><br/>
+Brick-earth or fluviatile loam, <a href="#page153">153</a><br/>
+Bridlington drift, <a href="#page189">189</a><br/>
+Bristol, dolomitic conglomerate of, <a href="#page373">373</a><br/>
+Bristow, Mr., on volcanic minerals, <a href="#page500">500</a><br/>
+Brixham cave near Torquay, <a href="#page158">158</a><br/>
+Brocchi on Italian tertiary strata, <a href="#page141">141</a><br/>
+&mdash;&mdash; on subapennine strata, <a href="#page208">208</a><br/>
+Brockenhurst, corals and shells of, <a href="#page257">257</a><br/>
+Brodie, Rev. P. B., on Lias insects, <a href="#page363">363</a><br/>
+Brodie, Mr. W. R., on Purbeck mammalia, <a href="#page326">326</a><br/>
+Brongniart, M. Adolphe, on botanical nomenclature, <a href="#page303">303</a><br/>
+&mdash;&mdash;, on Lias plants, <a href="#page364">364</a><br/>
+&mdash;&mdash;, on flora of the Bunter, <a href="#page380">380</a><br/>
+&mdash;&mdash;, on flora of the coal, <a href="#page420">420</a><br/>
+&mdash;&mdash;, on fruit of Lepidodendron, <a href="#page424">424</a><br/>
+&mdash;&mdash;, M. Alex., on Tertiary series, <a href="#page141">141</a><br/>
+<i>Bronteus flabellifer</i>, Devonian, <a href="#page453">453</a><br/>
+Brora, oolitic coal formation of, <a href="#page350">350</a><br/>
+Brown, Mr. Richard, on Stigmaria, <a href="#page426">426</a><br/>
+&mdash;&mdash;, on carboniferous rain-prints, <a href="#page416">416</a><br/>
+Brown, Robert, on Eocene protaceous fruit, <a href="#page264">264</a><br/>
+Brown, Reverend T., on marine shells in Scotch drift, <a href="#page177">177</a><br/>
+Brown-coal of Germany, <a href="#page540">540</a><br/>
+Bryce, Mr., on Scotch till, <a href="#page176">176</a><br/>
+Bryozoa of Mountain Limestone, <a href="#page433">433</a><br/>
+&mdash;&mdash; and polyzoa, terms explained, <a href="#page197">197</a><br/>
+Buch, von. <i>See</i> Von Buch.<br/>
+Buckland, Dr., on Kirkdale cave, <a href="#page158">158</a><br/>
+&mdash;&mdash;, on violent death of saurians, <a href="#page362">362</a><br/>
+&mdash;&mdash;, on spines of fish, <a href="#page359">359</a><br/>
+&mdash;&mdash;, on Eocene oysters, <a href="#page268">268</a><br/>
+&mdash;&mdash;, on pot-stones in chalk, <a href="#page291">291</a><br/>
+Buddle, Mr., on creeps in coal-mines, <a href="#page78">78</a><br/>
+<i>Bulimus ellipticus</i>, Bembridge, <a href="#page253">253</a><br/>
+&mdash;&mdash; <i>lubricus</i>, Loess, <a href="#page56">56</a><br/>
+Bullock, Capt., <small>R.N.</small>, on Atlantic mud, <a href="#page287">287</a><br/>
+Bunbury, Sir C., on leaf-bed of Madeira, <a href="#page532">532</a><br/>
+&mdash;&mdash;, on ferns of the Maryland coal, <a href="#page421">421</a><br/>
+Bunter of Germany, <a href="#page380">380</a><br/>
+&mdash;&mdash; or Lower Trias of England, <a href="#page372">372</a><br/>
+<i>Buprestis? Elytron of</i>, Stonesfield, <a href="#page346">346</a><br/>
+Burmeister on trilobites, <a href="#page471">471</a><br/><br/>
+</p>
+
+<p class="noindent">
+C<small>AINOZOIC</small>, term defined, <a href="#page123">123</a><br/>
+Caithness, fish beds of, <a href="#page443">443</a><br/>
+<i>Calamite</i>, root of, <a href="#page425">425</a><br/>
+<i>Calamites Sucowii</i>, coal, and restored stem, <a href="#page424">424</a><br/>
+<i>Calamophyllia radiata</i>, Bath Oolite, <a href="#page342">342</a><br/>
+Calcaire de la Beauce, age of the, <a href="#page230">230</a><br/>
+&mdash;&mdash; grossier, fossils of the, <a href="#page274">274</a><br/>
+&mdash;&mdash; siliceux of France, <a href="#page273">273</a><br/>
+Calcareous matter poured out by springs, <a href="#page604">604</a><br/>
+&mdash;&mdash; rocks described, <a href="#page36">36</a><br/>
+&mdash;&mdash; nodules in Lias, <a href="#page63">63</a><br/>
+<i>Calcarina rarispina</i>, Eocene, <a href="#page275">275</a><br/>
+<i>Calceola sandalina</i>, Devonian, <a href="#page453">453</a><br/>
+&mdash;&mdash;, schiefer of Germany, <a href="#page453">453</a><br/>
+California, aurifrous gravel of, <a href="#page617">617</a><br/>
+&mdash;&mdash;, gold in petrified wood of age of alluvium, <a href="#page601">601</a><br/>
+<i>Calymene Blumenbachii</i>, Silurian, <a href="#page466">466</a><br/>
+Cambrian Group, classification of the, <a href="#page481">481</a><br/>
+Cambrian, Upper, <a href="#page482">482</a><br/>
+&mdash;&mdash;, Lower, <a href="#page484">484</a><br/>
+&mdash;&mdash;, of Sweden and Norway, <a href="#page489">489</a><br/>
+&mdash;&mdash;, strata of Bohemia, <a href="#page487">487</a><br/>
+&mdash;&mdash;, of North America, <a href="#page489">489</a><br/>
+&mdash;&mdash;, volcanic rocks, <a href="#page549">549</a><br/>
+<i>Campophyllum flexuosum</i>, <a href="#page431">431</a><br/>
+Canada, Cambrian of, <a href="#page489">489</a><br/>
+&mdash;&mdash;, Devonian of, <a href="#page455">455</a><br/>
+&mdash;&mdash;, trap-rocks of, <a href="#page549">549</a><br/>
+Canadian drift, <a href="#page182">182</a><br/>
+Canary, Grand, shelly tuffs of, <a href="#page538">538</a><br/>
+Cantal, Lower Miocene of the, <a href="#page231">231</a><br/>
+Cape Breton, rain-prints in coal-measures of, <a href="#page416">416</a><br/>
+Cape Wrath, granite veins in gneiss at, <a href="#page560">560</a><br/>
+Caradoc and Bala beds, <a href="#page470">470</a><br/>
+Carbonate of lime in rocks, how tested, <a href="#page37">37</a><br/>
+Carboniferous Group, subdivisions of the, <a href="#page394">394</a><br/>
+&mdash;&mdash; flora, <a href="#page420">420-30</a><br/>
+&mdash;&mdash; limestone, thickness of, <a href="#page396">396</a><br/>
+&mdash;&mdash;, marine fauna of the, <a href="#page432">432</a><br/>
+&mdash;&mdash; Period, trap-rocks of, <a href="#page545">545</a><br/>
+&mdash;&mdash; plutonic rocks, <a href="#page572">572</a><br/>
+&mdash;&mdash; reptiles, <a href="#page406">406</a><br/>
+&mdash;&mdash; insects, <a href="#page405">405</a><br/>
+<i>Carcharodon angustidens</i>, Bracklesham, <a href="#page262">262</a><br/>
+Cardiganshire, section of slaty cleavage in, <a href="#page589">589</a><br/>
+<i>Cardiocarpon Ottonis</i>, Permian, <a href="#page393">393</a><br/>
+<i>Cardita (Venericardia) planicosta</i>, <a href="#page260">260</a><br/>
+&mdash;&mdash; <i>sulcata</i>, Barton, <a href="#page259">259</a><br/>
+<i>Cardium dissimile</i>, Portland Stone, <a href="#page336">336</a><br/>
+&mdash;&mdash; <i>rhæticum</i>, Rhætic Beds, <a href="#page366">366</a><br/>
+&mdash;&mdash; <i>striatulum</i>, Kimmeridge clay, <a href="#page336">336</a><br/>
+Carne, Mr. N., on Cornish lodes, <a href="#page607">607</a><br/>
+Carpenter, Dr., on Atlantic mud, <a href="#page288">288</a><br/>
+&mdash;&mdash;, on Eozoon Canadense, <a href="#page491">491</a><br/>
+Carrara, marble of, <a href="#page599">599</a><br/>
+Carruthers, Mr., on Eocene proteaceous fruit, <a href="#page265">265</a><br/>
+&mdash;&mdash;, on cycads of the Purbeck, <a href="#page332">332</a><br/>
+&mdash;&mdash;, on leaves of calamite, <a href="#page425">425</a><br/>
+&mdash;&mdash;, on spores of carboniferous Lycopodiaceæ, <a href="#page422">422</a><br/>
+&mdash;&mdash;, on structure of sigillaria, <a href="#page426">426</a><br/>
+&mdash;&mdash;, on trees in volcanic ash, <a href="#page547">547</a><br/>
+Cashmere, recent formations in, <a href="#page146">146</a><br/>
+Cassian, St., Triassic strata of, <a href="#page376">376</a><br/>
+Castrogiovanni, curved strata near, <a href="#page86">86</a><br/>
+Catania, laterite formed in, <a href="#page510">510</a><br/>
+&mdash;&mdash;, Tertiary beds in, <a href="#page206">206</a><br/>
+<i>Catillus Lamarckii</i>, White Chalk, <a href="#page295">295</a><br/>
+Caucasus, absence of lakes in the, <a href="#page187">187</a><br/>
+<i>Caulopteris primæva</i>, Coal, <a href="#page421">421</a><br/>
+Cave-breccias of Australia, <a href="#page158">158</a><br/>
+Cavern deposits with human and animal remains, <a href="#page156">156</a><br/>
+Caves of Kirkdale and Brixham, <a href="#page157">157</a><br/>
+Celts described, <a href="#page152">152</a><br/>
+Cementing of strata, <a href="#page61">61</a><br/>
+<i>Cephalaspis Lyelli</i>, Old Red, <a href="#page446">446</a><br/>
+<i>Ceratites nodosus</i>, Muschelkalk, <a href="#page379">379</a><br/>
+<i>Cerithium concavum</i>, Headon, <a href="#page256">256</a><br/>
+&mdash;&mdash; <i>elegans</i>, Hempstead beds, <a href="#page245">245</a><br/>
+&mdash;&mdash; (<i>Terebra</i>) Portlandicum, <a href="#page335">335</a><br/>
+&mdash;&mdash; <i>plicatum</i>, Hempstead beds, <a href="#page245">245</a><br/>
+&mdash;&mdash; <i>melanoides</i>, <a href="#page268">268</a><br/>
+<i>Cervus alces</i>, tooth of, <a href="#page164">164</a><br/>
+<i>Cestracion Phillippi</i>, Recent, <a href="#page297">297</a><br/>
+Chabasite, <a href="#page500">500</a><br/>
+Chalk, composition, extent, and origin of, <a href="#page286">286</a><br/>
+&mdash;&mdash; of Faxoe, <a href="#page286">286</a><br/>
+&mdash;&mdash; flints, origin of, <a href="#page290">290</a><br/>
+&mdash;&mdash; fossils of the White, <a href="#page293">293-6</a><br/>
+&mdash;&mdash;, iceborne boulders in the, <a href="#page292">292</a><br/>
+&mdash;&mdash; of North and South Europe, <a href="#page305">305</a><br/>
+&mdash;&mdash;, Lower White, without flints, <a href="#page298">298</a><br/>
+&mdash;&mdash; marl, fossils of the, <a href="#page298">298</a><br/>
+&mdash;&mdash; Period, popular error concerning, <a href="#page288">288</a><br/>
+Chalk-pit with pot-stones, view of, <a href="#page291">291</a><br/>
+<i>Chama squamosa</i>, Barton, <a href="#page258">258</a><br/>
+Champoleon, junction of granite with Jurassic strata near, <a href="#page571">571</a><br/>
+<i>Chara elastica, C. medicaginula</i>, <a href="#page58">58</a><br/>
+&mdash;&mdash; <i>tuberculata</i>, Bembridge, <a href="#page253">253</a><br/>
+Charpentier, M., on Alpine glaciers, <a href="#page170">170</a><br/>
+&mdash;&mdash;, on depression of Alps in Glacial Period, <a href="#page185">185</a><br/>
+Chatham coal-field, <a href="#page383">383</a><br/>
+<i>Cheirotherium</i>, footprints of, <a href="#page372">372</a><br/>
+Chemical deposits in veins, <a href="#page612">612</a><br/>
+&mdash;&mdash; and mechanical deposits, <a href="#page60">60</a><br/>
+Chiapa, fall of volcanic dust at, <a href="#page523">523</a><br/>
+Chichester, erratics near, <a href="#page181">181</a><br/>
+Chili, copper pyrites with gold in, <a href="#page616">616</a><br/>
+&mdash;&mdash;, walls cracked by earthquake in, <a href="#page87">87</a><br/>
+Chillesford and Aldeby beds, <a href="#page192">192</a><br/>
+<i>Chimæra monstrosa</i>, Lias, <a href="#page359">359</a><br/>
+Chlorite-schist, <a href="#page579">579</a><br/>
+Chloritic series, or Upper Greensand, <a href="#page298">298</a><br/>
+Christiania, Euritic porphyry at, <a href="#page562">562</a><br/>
+&mdash;&mdash;, granite veins in Silurian strata of, <a href="#page572">572</a><br/>
+&mdash;&mdash;, quartz vein in gneiss at, <a href="#page561">561</a><br/>
+Chronological groups of formations, <a href="#page129">129</a><br/>
+Chronology, test of, in rocks, <a href="#page121">121</a><br/>
+Cinder-bed of the Purbeck, <a href="#page325">325</a><br/>
+<i>Cinnamomum polymorphum</i>, Miocene, <a href="#page219">219</a><br/>
+&mdash;&mdash; <i>Rossmässleri</i>, Miocene, <a href="#page239">239</a><br/>
+Claiborne beds, Eocene fossils of, <a href="#page279">279</a><br/>
+Clarke County, United States, Zeuglodon of, <a href="#page279">279</a><br/>
+Classification of Tertiary formations, <a href="#page137">137</a>, <a href="#page143">143</a><br/>
+&mdash;&mdash;, value of shells in, <a href="#page142">142</a><br/>
+<i>Clausilia bidens</i>, Loess, <a href="#page56">56</a><br/>
+Clay defined, <a href="#page36">36</a><br/>
+&mdash;&mdash; iron-stone defined, <a href="#page404">404</a><br/>
+&mdash;&mdash;, plastic, <a href="#page267">267</a><br/>
+&mdash;&mdash; slate, <a href="#page579">579</a><br/>
+&mdash;&mdash;, Weald, <a href="#page313">313</a><br/>
+Cleavage explained, <a href="#page502">502</a><br/>
+&mdash;&mdash;, crystalline theory of, <a href="#page591">591</a><br/>
+&mdash;&mdash;, mechanical theory of, <a href="#page592">592</a><br/>
+&mdash;&mdash; of metamorphic rocks, <a href="#page588">588</a><br/>
+<i>Cleidotheca operculata</i>, <a href="#page483">483</a><br/>
+Clermont, metalliferous gneiss near, <a href="#page586">586</a><br/>
+Climate of the Crags, <a href="#page200">200</a><br/>
+&mdash;&mdash; of the Coal, <a href="#page430">430</a><br/>
+&mdash;&mdash; of the Miocene in the Arctic regions, <a href="#page240">240</a><br/>
+&mdash;&mdash; of the Post-pliocene period, <a href="#page161">161</a><br/>
+Clinkstone, <a href="#page506">506</a><br/>
+Clinton group, fossils of the, <a href="#page479">479</a><br/>
+Clyde, buried canoes in estuary of, <a href="#page146">146</a><br/>
+&mdash;&mdash;, arctic marine shells in drifts of, <a href="#page176">176</a><br/>
+<i>Clymenia linearis</i>, Devonian, <a href="#page451">451</a><br/>
+Clymenien-Kalk of Germany, <a href="#page450">450</a><br/>
+Coal, conversion into anthracite of, <a href="#page403">403</a><br/>
+&mdash;&mdash; a land and swamp formation, <a href="#page397">397</a><br/>
+&mdash;&mdash;, cause of the purity of, <a href="#page402">402</a><br/>
+&mdash;&mdash;, conversion of lignite into, <a href="#page403">403</a><br/>
+&mdash;&mdash;, erect trees in, <a href="#page411">411</a><br/>
+&mdash;&mdash;, structure of the, <a href="#page412">412</a><br/>
+&mdash;&mdash;, vegetation of the, <a href="#page420">420</a><br/>
+&mdash;&mdash;, air-breathers in the, <a href="#page405">405</a>, <a href="#page413">413</a><br/>
+Coal Period, climate of the, <a href="#page430">430</a><br/>
+&mdash;&mdash; field of Virginia, <a href="#page382">382</a><br/>
+&mdash;&mdash; measures of Nova Scotia, <a href="#page408">408</a><br/>
+&mdash;&mdash; measures, thickness of, in Wales, <a href="#page397">397</a><br/>
+&mdash;&mdash; pipes, danger of, <a href="#page390">390</a><br/>
+&mdash;&mdash;, rainprints in, <a href="#page416">416</a><br/>
+&mdash;&mdash; seams, uniting of, <a href="#page400">400</a><br/>
+Coalbrook-Dale, faults in, <a href="#page88">88</a><br/>
+<i>Cochliodus contortus</i>, <a href="#page437">437</a><br/>
+Cockfield Fell rocks, altered by dikes, <a href="#page516">516</a><br/>
+<i>Coelacanthus granulatus,</i> Permian, <a href="#page390">390</a><br/>
+Coleoptera of Œningen beds, <a href="#page223">223</a><br/>
+<i>Collyrites ringens,</i> Inferior Oolite, <a href="#page351">351</a><br/>
+Columnar structure of volcanic rocks, <a href="#page510">510</a><br/>
+&mdash;&mdash; basalt in the Vicentin, <a href="#page511">511</a><br/>
+Compact feldspar, <a href="#page501">501</a><br/>
+Concretionary structure, <a href="#page63">63</a><br/>
+Cone of Tartaret, <a href="#page527">527</a>, <a href="#page542">542</a><br/>
+&mdash;&mdash; of Côme, <a href="#page28">28</a><br/>
+Cones and craters described, <a href="#page495">495</a><br/>
+&mdash;&mdash;, absence of, in England, <a href="#page30">30</a><br/>
+Conformable stratification, <a href="#page39">39</a><br/>
+Conglomerate or pudding-stone, <a href="#page36">36</a><br/>
+&mdash;&mdash;, Dolomitic, of Bristol, <a href="#page373">373</a><br/>
+Coniferæ of the coal-measures, <a href="#page427">427</a><br/>
+Connecticut Valley, New Red Sandstone of, <a href="#page381">381</a><br/>
+<i>Conocephalus striatus</i>, <a href="#page488">488</a><br/>
+<i>Conocoryphe striata</i>, <a href="#page488">488</a><br/>
+Conrad, Mr., on age of American cretaceous rocks, <a href="#page307">307</a><br/>
+Consolidation of strata, <a href="#page61">61</a><br/>
+Continents and oceans, permanence of, <a href="#page117">117</a><br/>
+Contorted strata, in drift, <a href="#page178">178</a><br/>
+<i>Conularia ornata,</i> Devonian, <a href="#page453">453</a><br/>
+<i>Conulus priscus,</i> Coal, <a href="#page415">415</a><br/>
+<i>Conus deperditus,</i> Bracklesham, <a href="#page262">262</a><br/>
+Conybeare and Phillips on ninety-fathom dike, <a href="#page90">90</a><br/>
+Conybeare, Mr., on reptiles of the Lias, <a href="#page360">360</a><br/>
+Copper lode near Redruth, <a href="#page607">607</a><br/>
+Coprolite bed of Chloritic Series, <a href="#page299">299</a><br/>
+&mdash;&mdash; beds of Red and Coralline crags, <a href="#page197">197</a>, <a href="#page198">198</a><br/>
+<i>Coprolites of fish from the chalk</i>, <a href="#page298">298</a><br/>
+Coral Rag, fossils of the, <a href="#page339">339</a><br/>
+Coralline of White Crag, <a href="#page197">197</a><br/>
+Corals of the Devonian, <a href="#page451">451</a><br/>
+&mdash;&mdash; of the Mountain Limestone, <a href="#page433">433</a><br/>
+&mdash;&mdash;, <i>Neozoic type of</i>, <a href="#page431">431</a><br/>
+&mdash;&mdash;, <i>Palæozoic type of</i>, <a href="#page431">431</a><br/>
+<i>Corbicella (Cyrena) fluminalis</i>, <a href="#page54">54</a><br/>
+<i>Corbula pisum,</i> Hempstead beds, <a href="#page245">245</a><br/>
+Corinth, corrosion of rocks by gases near, <a href="#page586">586</a><br/>
+Cornbrash or Forest Marble, <a href="#page341">341</a><br/>
+Cornwall, granite veins in, <a href="#page561">561</a>, <a href="#page582">582</a><br/>
+&mdash;&mdash;, lodes in, <a href="#page615">615</a><br/>
+&mdash;&mdash;, mass of granite in, <a href="#page552">552</a><br/>
+&mdash;&mdash;, vertical sections of veins in mine, <a href="#page607">607</a><br/>
+Cosequina volcano, burying of organic remains by, <a href="#page523">523</a><br/>
+Crag, term defined, <a href="#page192">192</a><br/>
+&mdash;&mdash; of Antwerp, <a href="#page204">204</a><br/>
+&mdash;&mdash;, fauna of, its relation to that of present seas, <a href="#page201">201</a><br/>
+&mdash;&mdash;, Norwich, <a href="#page193">193</a><br/>
+&mdash;&mdash;, Coralline or White, <a href="#page197">197</a><br/>
+&mdash;&mdash;, Red, <a href="#page194">194</a><br/>
+&mdash;&mdash;, tables of marine testacea in, <a href="#page202">202</a><br/>
+&mdash;&mdash; deposits, climate of, <a href="#page200">200</a><br/>
+<i>Crania</i> attached to a sea-urchin, <a href="#page49">49</a><br/>
+&mdash;&mdash; <i>Parisiensis,</i> White Chalk, <a href="#page294">294</a><br/>
+<i>Crassatella sulcata,</i> Barton, <a href="#page259">259</a><br/>
+Craters and cones described, <a href="#page495">495</a><br/>
+&mdash;&mdash;, Theory of Elevation, <a href="#page496">496</a><br/>
+Craven fault, <a href="#page90">90</a><br/>
+Creeps in coal-mines, <a href="#page78">78</a><br/>
+Cretaceous rocks of United States, <a href="#page307">307</a><br/>
+&mdash;&mdash; Period, error as to continuity of, <a href="#page288">288</a><br/>
+&mdash;&mdash;, flora of the Upper, <a href="#page302">302</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page544">544</a><br/>
+&mdash;&mdash; plutonic rocks, <a href="#page570">570</a><br/>
+&mdash;&mdash; Period, distinct mineral character of rocks in, <a href="#page292">292</a><br/>
+&mdash;&mdash; rocks, classification of, <a href="#page282">282</a><br/>
+&mdash;&mdash; strata, connection between Upper and Lower, <a href="#page301">301</a><br/>
+Crinoidea of Mountain Limestone, <a href="#page433">433</a><br/>
+Croatia, Lower Miocene beds of, <a href="#page242">242</a><br/>
+Croll, Mr., on amount of subaërial denudation, <a href="#page114">114</a><br/>
+Cromer forest-bed, <a href="#page191">191</a><br/>
+Crop out, term explained, <a href="#page83">83</a><br/>
+Crossopterygidæ, or fringe-finned fish, <a href="#page443">443</a><br/>
+Crowfoot, Mr., on shells of Aldeby beds, <a href="#page192">192</a><br/>
+Crust of the earth defined, <a href="#page26">26</a><br/>
+Crustaceans of Old Red Sandstone, <a href="#page446">446</a><br/>
+<i>Cryptodon angulatum,</i> London Clay, <a href="#page266">266</a><br/>
+Crystalline Limestone, <a href="#page579">579</a><br/>
+&mdash;&mdash; rocks defined, <a href="#page32">32</a><br/>
+&mdash;&mdash; schists, much alkali in the, <a href="#page587">587</a><br/>
+&mdash;&mdash; theory of cleavage, <a href="#page591">591</a><br/>
+Cup and Star corals, <a href="#page431">431</a><br/>
+Curved strata, <a href="#page73">73-76</a><br/>
+Cutch, salt-layers in the Runn of, <a href="#page375">375</a><br/>
+Cuvier, M., on fauna of the Paris basin, <a href="#page271">271</a><br/>
+&mdash;&mdash;, on Mammalia of Paris gypsum, <a href="#page231">231</a><br/>
+&mdash;&mdash;, on Tertiary series, <a href="#page141">141</a><br/>
+<i>Cyathocrinus caryocrinoides</i>, <a href="#page433">433</a><br/>
+&mdash;&mdash; <i>planus</i>, <a href="#page433">433</a><br/>
+<i>Cyathophyllum cæspitosum</i>, <a href="#page451">451</a><br/>
+Cyclopean isles, beds of tuff and clay in, <a href="#page529">529</a><br/>
+&mdash;&mdash;, contorted strata in, <a href="#page530">530</a><br/>
+<i>Cyclopteris Hibernica,</i> Old Red, <a href="#page441">441</a><br/>
+<i>Cyclostigma (Lepidodendron),</i> Old Red, <a href="#page441">441</a><br/>
+<i>Cyclostoma elegans,</i> Loess, <a href="#page56">56</a><br/>
+<i>Cylindrites acutus,</i> Great Oolite, <a href="#page345">345</a><br/>
+Cypress swamps of the Mississippi, <a href="#page402">402</a><br/>
+Cyprides in the Weald Clay, <a href="#page315">315</a><br/>
+<i>Cypridina serrato-striata</i>, <a href="#page451">451</a><br/>
+Cypris in fresh-water deposits, <a href="#page57">57</a><br/>
+&mdash;&mdash; <i>gibbosa, C. tuberculata, C. leguminella</i>, <a href="#page324">324</a><br/>
+&mdash;&mdash; <i>striato-punctata, C. fasciculata, C. granulata</i>, <a href="#page325">325</a><br/>
+&mdash;&mdash; <i>Purbeckensis, Cypris punctata</i>, <a href="#page331">331</a><br/>
+&mdash;&mdash; <i>spinigera,</i> Weald Clay, <a href="#page315">315</a><br/>
+<i>Cyrena (Corbicella) fluminalis</i>, <a href="#page54">54</a><br/>
+&mdash;&mdash; <i>cuneiformis,</i> Woolwich Clays, <a href="#page268">268</a><br/>
+&mdash;&mdash; <i>obovata</i>, <a href="#page54">54</a><br/>
+&mdash;&mdash; <i>semistriata,</i> Hempstead beds, <a href="#page245">245</a><br/>
+Cystideæ of Silurian rocks, <a href="#page466">466</a><br/>
+<i>Cythere inflata,</i> coal-measures, <a href="#page405">405</a><br/><br/>
+</p>
+
+<p class="noindent">
+D<small>ADOXYLON</small>, fragment of coniferous wood, <a href="#page428">428</a><br/>
+Dana, on volcanic minerals, <a href="#page500">500</a><br/>
+Danish kitchen-middens, <a href="#page146">146</a><br/>
+<i>Dapedius monilifer</i>, Lias, <a href="#page358">358</a><br/>
+Darbishire on shells of Moel Tryfaen, <a href="#page180">180</a><br/>
+Dartmoor, post-carboniferous granite of, <a href="#page572">572</a><br/>
+&mdash;&mdash; intrusive granite at, <a href="#page572">572</a><br/>
+Darwin, Mr., on foliation and lamination, <a href="#page595">595</a><br/>
+&mdash;&mdash;, on mammalia of South America, <a href="#page160">160</a><br/>
+&mdash;&mdash;, on marine saurian, <a href="#page362">362</a><br/>
+&mdash;&mdash;, on rise of part of South America, <a href="#page72">72</a><br/>
+&mdash;&mdash;, on sinking of coral reefs, <a href="#page72">72</a><br/>
+&mdash;&mdash;, on plutonic rocks of the Andes, <a href="#page569">569</a><br/>
+&mdash;&mdash;, on relationship of extinct to living types, <a href="#page160">160</a><br/>
+Dates of discovery of fossil vertebrata, <a href="#page464">464</a><br/>
+Daubeny, Dr., on decomposition of trachytic rocks, <a href="#page586">586</a><br/>
+Daubrée, on formation of zeolites, <a href="#page521">521</a><br/>
+&mdash;&mdash;, on alkaline waters of Plombières, <a href="#page584">584</a><br/>
+Davidson, Mr., on Spiriferina, <a href="#page355">355</a><br/>
+Davis, Mr. E., on fossils of Lingula Flags, <a href="#page484">484</a><br/>
+Dawkins, Mr. Boyd, on Hyæna spelæa, <a href="#page158">158</a><br/>
+&mdash;&mdash;, on mammalia of Cromer Forest-bed, <a href="#page191">191</a><br/>
+&mdash;&mdash;, on Triassic mammifer, <a href="#page369">369</a><br/>
+Dawson, Dr., on Devonian flora and insects, <a href="#page456">456</a>, <a href="#page457">457</a><br/>
+&mdash;&mdash;, on Eozoon Canadense, <a href="#page491">491</a><br/>
+&mdash;&mdash;, on Nova Scotia coal-measures, <a href="#page409">409</a><br/>
+&mdash;&mdash;, on Nova Scotia coal-plants, <a href="#page410">410</a>, <a href="#page412">412</a><br/>
+&mdash;&mdash;, on Pupa vetusta, <a href="#page415">415</a><br/>
+&mdash;&mdash;, on reptiles and shells in Nova Scotia coal, <a href="#page413">413</a><br/>
+&mdash;&mdash;, on structure of calamite, <a href="#page425">425</a><br/>
+&mdash;&mdash;, on structure of sigillaria, <a href="#page426">426</a><br/>
+Deane, Dr., on footprints in Trias, <a href="#page382">382</a><br/>
+Debey, Dr., on flora and fauna of Aix, <a href="#page302">302-04</a><br/>
+Dechen, M. von, on organic remains of the brown coal, <a href="#page540">540</a><br/>
+&mdash;&mdash;, on Cornish granite veins, <a href="#page560">560</a><br/>
+De la Beche, Sir H., on granite of Dartmoor, <a href="#page582">582</a><br/>
+&mdash;&mdash;, on Carrara marble, <a href="#page599">599</a><br/>
+&mdash;&mdash;, on mineral veins, <a href="#page616">616</a><br/>
+&mdash;&mdash;, on Redruth copper-mine, <a href="#page610">610</a><br/>
+&mdash;&mdash;, on saurians of the Lias, <a href="#page362">362</a><br/>
+&mdash;&mdash;, on trap-rocks of New Red, <a href="#page545">545</a><br/>
+&mdash;&mdash;, on Welsh coal-measures, <a href="#page397">397</a><br/>
+Delesse, on action of water in metamorphism, <a href="#page585">585</a><br/>
+Deltas, strata accumulated in, <a href="#page28">28</a><br/>
+Dendrerpeton in Coal, <a href="#page413">413</a><br/>
+Denudation defined, <a href="#page96">96</a><br/>
+&mdash;&mdash;, subaërial, <a href="#page97">97</a><br/>
+&mdash;&mdash;, littoral, <a href="#page102">102</a><br/>
+&mdash;&mdash;, submarine, <a href="#page105">105</a><br/>
+&mdash;&mdash;, average annual amount of subaërial, <a href="#page113">113</a><br/>
+&mdash;&mdash; of carboniferous strata, <a href="#page396">396</a><br/>
+&mdash;&mdash; counteracting upheaval, <a href="#page106">106-15</a>, <a href="#page108">108-15</a><br/>
+&mdash;&mdash; a means of exposing crystalline rocks, <a href="#page563">563</a><br/>
+&mdash;&mdash;, trap-dikes cut off by, <a href="#page518">518</a><br/>
+&mdash;&mdash; and volcanic force antagonistic powers, <a href="#page115">115</a><br/>
+Deposition, rate of, shown by fossils, <a href="#page47">47</a><br/>
+Derbyshire, veins in Mountain Limestone, <a href="#page608">608</a><br/>
+Derivative shells of the Red Crag, <a href="#page195">195-203</a><br/>
+Desnoyers, M., on age of Faluns, <a href="#page142">142</a><br/>
+&mdash;&mdash;, on Eocene fossil footprints, <a href="#page272">272</a><br/>
+Desor, M., on Celtic coins in lake-dwellings, <a href="#page149">149</a><br/>
+Devonian Period, Upper, <a href="#page450">450</a><br/>
+Middle, <a href="#page450">450</a><br/>
+Lower, <a href="#page453">453</a><br/>
+&mdash;&mdash; fossils of the Eifel, <a href="#page534">534</a><br/>
+&mdash;&mdash; of Russia, <a href="#page454">454</a><br/>
+&mdash;&mdash; of United States and Canada, <a href="#page455">455</a><br/>
+&mdash;&mdash; insects of Canada, <a href="#page457">457</a><br/>
+&mdash;&mdash; strata, classification of, <a href="#page439">439-50</a><br/>
+Devonshire, cleavage of slate rocks in, <a href="#page593">593</a><br/>
+Diabase, <a href="#page505">505</a><br/>
+Diagonal, or cross-stratification, <a href="#page42">42</a><br/>
+Diagram of fossiliferous rocks, <a href="#page137">137</a><br/>
+&mdash;&mdash; of plutonic and sedimentary formations, <a href="#page567">567</a><br/>
+Diallage, <a href="#page500">500</a>, <a href="#page502">502</a><br/>
+<i>Diastopora diluviana</i>, Bath Oolite, <a href="#page343">343</a><br/>
+Diatomaceæ forming tripoli, <a href="#page51">51</a><br/>
+<i>Diceras Lonsdalii</i>, Neocomian, <a href="#page310">310</a><br/>
+<i>Didelphys Azaræ</i>, Recent, <a href="#page347">347</a><br/>
+<i>Didymograpsus geminus</i>, <a href="#page476">476</a><br/>
+&mdash;&mdash; <i>Murchisonii</i>, <a href="#page473">473</a><br/>
+Dike cutting through shale, Anglesea, <a href="#page515">515</a><br/>
+&mdash;&mdash; cutting through chalk, Antrim, <a href="#page515">515</a>, <a href="#page516">516</a><br/>
+<i>Dikelocephalus Minnesotensis</i>, <a href="#page490">490</a><br/>
+Dikes defined, <a href="#page30">30</a><br/>
+&mdash;&mdash; of Monte Somma, <a href="#page526">526</a><br/>
+&mdash;&mdash; in Palagonia, ground-plan of, <a href="#page532">532</a><br/>
+&mdash;&mdash;, volcanic or trap, <a href="#page513">513-7</a><br/>
+Diluvium, origin of term, <a href="#page167">167</a><br/>
+Dinornis Palapteryx, of New Zealand, <a href="#page160">160</a><br/>
+<i>Dinotherium giganteum</i>, <a href="#page212">212</a><br/>
+Diorite, <a href="#page505">505</a><br/>
+Dip and strike, terms explained, <a href="#page80">80</a><br/>
+<i>Diplograpsus folium</i>, Llandeilo Flags, <a href="#page474">474</a><br/>
+&mdash;&mdash; <i>pristis</i>, Llandeilo beds, <a href="#page473">473</a><br/>
+Dirt-bed of the Purbeck, <a href="#page331">331</a><br/>
+Dogger-bank described, <a href="#page105">105</a><br/>
+Dolerite, a variety of basalt, <a href="#page504">504</a><br/>
+Dolomite defined, <a href="#page38">38</a><br/>
+Dolomitic conglomerate of Bristol, <a href="#page373">373</a><br/>
+Downs, escarpments of North and South, <a href="#page104">104</a><br/>
+Downton Sandstone, <a href="#page459">459</a><br/>
+Dowson, Mr., on shells of Aldeby beds, <a href="#page192">192</a><br/>
+Drew, Mr., on Hastings Sands, <a href="#page316">316</a><br/>
+Drift of Ireland, <a href="#page190">190</a><br/>
+&mdash;&mdash; of Norfolk cliffs, <a href="#page190">190</a><br/>
+&mdash;&mdash; of Scandinavia, <a href="#page174">174</a><br/>
+&mdash;&mdash; of Bridlington, <a href="#page189">189</a><br/>
+&mdash;&mdash; carried by icebergs, <a href="#page172">172</a><br/>
+&mdash;&mdash; shells in Canada, <a href="#page183">183</a><br/>
+&mdash;&mdash;, contorted strata in, <a href="#page178">178</a><br/>
+&mdash;&mdash;, marine shells in Scotch, <a href="#page175">175</a><br/>
+Dudley Limestone, <a href="#page465">465</a><br/>
+Dufrenoy, M., on granite of Pyrenees, <a href="#page582">582</a><br/>
+Dumont, Professor, on Belgian Lower Eocene, <a href="#page282">282</a><br/>
+Duncan, Dr., on Neozoic corals passing down to Devonian, <a href="#page432">432</a><br/>
+Dundry Hill, near Bristol, section of, <a href="#page130">130</a><br/>
+Dunker, Dr., on wealden of Germany, <a href="#page319">319</a><br/>
+Dura Den, yellow sandstone of, <a href="#page440">440</a><br/><br/>
+</p>
+
+<p class="noindent">
+E<small>ARTH&rsquo;S</small> crust defined, <a href="#page26">26</a><br/>
+Echinoderms of Suffolk Crag, <a href="#page200">200</a><br/>
+<i>Echinosphæronites balticus</i>, <a href="#page472">472</a><br/>
+Egerton, Sir P., on fish of Headon series, <a href="#page256">256</a><br/>
+&mdash;&mdash;, on fish of the Permian, <a href="#page389">389</a><br/>
+&mdash;&mdash;, on fish of Penarth beds, <a href="#page366">366</a><br/>
+Ehrenberg, Professor, on term Bryozoum, <a href="#page197">197</a><br/>
+&mdash;&mdash;, on Silurian foraminifera, <a href="#page478">478</a><br/>
+&mdash;&mdash;, on infusoria, <a href="#page51">51</a><br/>
+Eifel Limestone, <a href="#page453">453</a><br/>
+&mdash;&mdash;, Lake-craters of, <a href="#page534">534</a><br/>
+&mdash;&mdash; Miocene, volcanic rocks of, <a href="#page539">539</a><br/>
+&mdash;&mdash; Pliocene, volcanoes of the, <a href="#page534">534</a><br/>
+&mdash;&mdash;, trass of the, <a href="#page535">535</a><br/>
+<i>Elephas antiquus</i>, molar of, <a href="#page163">163</a><br/>
+&mdash;&mdash; <i>meridionalis</i>, molar of, <a href="#page163">163</a><br/>
+&mdash;&mdash; <i>primigenius</i>, molar of, <a href="#page162">162</a><br/>
+Elevation craters, theory of, <a href="#page496">496</a><br/>
+Elvans, term explained, <a href="#page572">572</a><br/>
+&mdash;&mdash; of Ireland and Cornwall, <a href="#page615">615</a><br/>
+<i>Elytron of Buprestis?</i> Stonesfield, <a href="#page346">346</a><br/>
+Emmons, Professor, on jaws of Triassic quadruped, <a href="#page383">383</a><br/>
+&mdash;&mdash;, on Dromatherium, <a href="#page383">383</a><br/>
+Encrinites of Bradford, <a href="#page342">342</a><br/>
+<i>Encrinus liliiformis</i>, Muschelkalk, <a href="#page379">379</a><br/>
+Endogens, term explained, <a href="#page303">303</a><br/>
+Engihoul cave, human and animal remains in, <a href="#page157">157</a><br/>
+England and Wales, glaciation of, <a href="#page180">180</a><br/>
+Enstatite, <a href="#page501">501</a><br/>
+Eocene areas of Europe, map of, <a href="#page250">250</a><br/>
+&mdash;&mdash; foraminifera, <a href="#page274">274</a><br/>
+&mdash;&mdash; formations of France, <a href="#page270">270-6</a><br/>
+&mdash;&mdash; of England, <a href="#page252">252</a><br/>
+&mdash;&mdash; period, volcanic rocks of, <a href="#page543">543</a><br/>
+&mdash;&mdash;, plutonic rocks of the, <a href="#page568">568</a><br/>
+&mdash;&mdash;, metamorphic rocks of the, <a href="#page598">598</a><br/>
+&mdash;&mdash; of France, footprints in, <a href="#page272">272</a><br/>
+&mdash;&mdash; and Miocene, line between the, <a href="#page230">230</a>, <a href="#page250">250</a><br/>
+&mdash;&mdash;, term defined, <a href="#page143">143</a><br/>
+&mdash;&mdash; of the United States, <a href="#page278">278</a><br/>
+<i>Eozoon Canadense</i>, oldest known fossil, <a href="#page492">492</a><br/>
+Epidote, <a href="#page500">500</a><br/>
+Eppelsheim, Dinotherium of, <a href="#page225">225</a><br/>
+Equisetaceæ of the Coal, <a href="#page424">424</a><br/>
+<i>Equisetites columnaris</i>, Keuper, <a href="#page376">376</a><br/>
+<i>Equus caballus</i>, tooth of, <a href="#page164">164</a><br/>
+Erratic blocks, nature of, <a href="#page167">167</a><br/>
+&mdash;&mdash; of Greenland, <a href="#page171">171</a><br/>
+&mdash;&mdash; near Chichester, <a href="#page181">181</a><br/>
+&mdash;&mdash; in the Red Crag, <a href="#page201">201</a><br/>
+Erratics, Alpine, <a href="#page169">169</a><br/>
+Escarpments explained, <a href="#page104">104</a><br/>
+<i>Eschara disticha</i>, White Chalk, <a href="#page296">296</a><br/>
+<i>Escharina oceani</i>, White Chalk, <a href="#page296">296</a><br/>
+<i>Estheria minuta</i>, Trias, <a href="#page370">370</a><br/>
+&mdash;&mdash; <i>ovata</i>, Richmond, Virginia, <a href="#page383">383</a><br/>
+Ethridge, Mr., on Atlantic mud, <a href="#page288">288</a><br/>
+&mdash;&mdash;, on Devonian series, in Devon, <a href="#page450">450</a><br/>
+&mdash;&mdash;, on Devonian fauna, <a href="#page451">451</a>, <a href="#page454">454</a><br/>
+&mdash;&mdash;, on mollusca of Bracklesham, <a href="#page260">260</a><br/>
+&mdash;&mdash;, on St. Cassian fossils, <a href="#page377">377</a><br/>
+Etna, built up since Newer Pliocene, <a href="#page204">204</a><br/>
+&mdash;&mdash;, Pliocene lavas of, <a href="#page529">529</a><br/>
+Ettingshausen on Sheppey Eocene fruit, <a href="#page265">265</a><br/>
+<i>Eunomia radiata</i>, Bath Oolite, <a href="#page342">342</a><br/>
+<i>Eunotia bidens</i>, Atlantic mud, <a href="#page288">288</a><br/>
+<i>Euomphalus pentangulatus</i>, <a href="#page435">435</a><br/>
+Eurite, <a href="#page557">557</a>, <a href="#page578">578</a><br/>
+Euritic porphyry of Norway, <a href="#page562">562</a><br/>
+Evans, Mr., on Archæopteryx, <a href="#page337">337</a><br/>
+Exogens, <a href="#page297">297</a><br/>
+<i>Exogyra virgula</i>, Kimmeridge Clay, <a href="#page336">336</a><br/>
+<i>Extracrinus (Pentacrinus) Briareus</i>, Lias, <a href="#page357">357</a><br/><br/>
+</p>
+
+<p class="noindent">
+F<small>ALCONER</small>, Dr., on Miocene fauna of Siwalik Hills, <a href="#page226">226</a><br/>
+&mdash;&mdash;, on Brixham Cave flint knives, <a href="#page157">157</a><br/>
+&mdash;&mdash;, on Purbeck mammalia, <a href="#page326">326</a><br/>
+Faluns of Loire, recent shells in, <a href="#page214">214</a><br/>
+&mdash;&mdash; of Touraine, <a href="#page211">211</a><br/>
+Farnham, phosphate of lime near, <a href="#page299">299</a><br/>
+<i>Fascicularia aurantium</i>, Coralline crag, <a href="#page199">199</a><br/>
+Faults in coal-measures of Coalbrook Dale, <a href="#page88">88</a><br/>
+&mdash;&mdash; described, <a href="#page87">87-92</a><br/>
+&mdash;&mdash; often the result of repeated movements, <a href="#page90">90</a><br/>
+Fauna of the crag, its relation to that of our present seas, <a href="#page201">201</a><br/>
+&mdash;&mdash; of the Mountain Limestone, <a href="#page430">430</a><br/>
+&mdash;&mdash; of the Paris basin, <a href="#page271">271</a><br/>
+<i>Favosites cervicornis</i>, Devonian, <a href="#page451">451</a><br/>
+&mdash;&mdash; <i>Gothlandica</i>, Silurian, <a href="#page465">465</a><br/>
+Favre, M. E., on glaciers and moraines of the Caucasus, <a href="#page187">187</a><br/>
+Faxoe, chalk of, <a href="#page285">285</a><br/>
+Feldspar-porphyry, <a href="#page557">557</a><br/>
+Feldspar, varieties of, <a href="#page499">499</a>, <a href="#page500">500</a><br/>
+Feldstone, <a href="#page557">557</a><br/>
+<i>Felis tigris</i>, tooth of, <a href="#page166">166</a><br/>
+<i>Fenestella retiformis</i>, Magnesian Limestone, <a href="#page388">388</a><br/>
+Ferns of the coal, <a href="#page421">421</a><br/>
+Fife, trap-dike in, <a href="#page543">543</a><br/>
+Fish, fossil of the Carboniferous, <a href="#page436">436</a><br/>
+&mdash;&mdash;, Eocene of Monte Bolca, <a href="#page544">544</a><br/>
+&mdash;&mdash;, oldest known fossil, <a href="#page463">463</a><br/>
+&mdash;&mdash;, number of living, <a href="#page445">445</a><br/>
+&mdash;&mdash;, fresh-water and marine, <a href="#page58">58</a><br/>
+&mdash;&mdash; of the Upper Ludlow, <a href="#page459">459</a><br/>
+&mdash;&mdash; of the Old Red Sandstone, <a href="#page443">443-5</a><br/>
+&mdash;&mdash; of the Permian marl slate, <a href="#page389">389</a><br/>
+&mdash;&mdash; of the brown coal, <a href="#page540">540</a><br/>
+&mdash;&mdash; of the Lias, <a href="#page358">358</a><br/>
+Fisherton, Greenland lemming in drift of, <a href="#page161">161</a><br/>
+Fissures, filled with metallic matter, <a href="#page606">606</a><br/>
+Fitton, Dr., on the Neocomian strata, <a href="#page314">314</a><br/>
+Fleming, Dr., on Parka decipiens, <a href="#page448">448</a><br/>
+&mdash;&mdash;, on trap-dike in Fife, <a href="#page546">546</a><br/>
+Flints in the Chalk, <a href="#page290">290</a><br/>
+Flisk dike of Fife, <a href="#page546">546</a><br/>
+Flora of the Carboniferous, <a href="#page420">420</a><br/>
+&mdash;&mdash;, Devonian, compared to Carboniferous, <a href="#page457">457</a><br/>
+&mdash;&mdash; of the Subapennines, <a href="#page208">208</a><br/>
+&mdash;&mdash;, Lower Miocene of Switzerland, <a href="#page235">235</a><br/>
+&mdash;&mdash;, Miocene of the Arctic Regions, <a href="#page239">239</a><br/>
+&mdash;&mdash;, Older Pliocene of Italy, <a href="#page208">208</a><br/>
+&mdash;&mdash; of the Permian, <a href="#page392">392</a><br/>
+&mdash;&mdash; of the Upper Cretaceous, <a href="#page302">302</a><br/>
+&mdash;&mdash;, Upper Miocene of Switzerland, <a href="#page215">215-22</a><br/>
+&mdash;&mdash; of the Wealden, <a href="#page320">320</a><br/>
+Fluvio-marine or Norwich Crag, <a href="#page193">193</a><br/>
+Flysch of the Alps, <a href="#page278">278</a><br/>
+&mdash;&mdash;, plutonic rocks invading, <a href="#page568">568</a><br/>
+Folding and denudation of Nova Scotia Carboniferous rocks, <a href="#page417">417</a><br/>
+Folds of parallel strata, arrangement and direction of, <a href="#page93">93</a><br/>
+Foliation of crystalline rocks, <a href="#page595">595</a><br/>
+&mdash;&mdash;, irregularities in, <a href="#page596">596</a><br/>
+Folkestone and Hythe beds, <a href="#page308">308</a><br/>
+Fontainebleau, Gres de, <a href="#page230">230</a><br/>
+Footprints in Potsdam sandstone, <a href="#page490">490</a><br/>
+&mdash;&mdash; <i>of reptiles in Coal-measures</i>, <a href="#page408">408</a><br/>
+&mdash;&mdash;, <i>fossil in New red</i>, <a href="#page381">381</a><br/>
+&mdash;&mdash; in Paris gypsum, <a href="#page272">272</a><br/>
+Foraminifera, Eocene, <a href="#page275">275</a><br/>
+&mdash;&mdash; of Mountain Limestone, <a href="#page437">437</a><br/>
+&mdash;&mdash; of the Chalk, <a href="#page287">287</a><br/>
+Forbes, Mr. David, on glass cavities in quartz, <a href="#page555">555</a><br/>
+&mdash;&mdash;, on planes of foliation, <a href="#page595">595</a><br/>
+&mdash;&mdash;, on specific gravity of quartz, <a href="#page500">500</a><br/>
+&mdash;&mdash;, on volcanic minerals, <a href="#page498">498</a><br/>
+Forbes, Professor E., on fossils of Bembridge beds, <a href="#page252">252</a><br/>
+&mdash;&mdash;, on Hempstead beds, <a href="#page244">244</a><br/>
+&mdash;&mdash;, on shells of the crag, <a href="#page200">200</a><br/>
+&mdash;&mdash;, on sphæronites, <a href="#page472">472</a><br/>
+&mdash;&mdash;, on subdivisions of the Purbeck, <a href="#page333">333</a><br/>
+&mdash;&mdash;, on testacea of the Faluns, <a href="#page212">212</a><br/>
+&mdash;&mdash;, on thickness of Upper Neocomian, <a href="#page309">309</a><br/>
+Forest-bed at Cromer, <a href="#page191">191</a><br/>
+&mdash;&mdash; marble or cornbrash, <a href="#page341">341</a><br/>
+&mdash;&mdash;, submerged, <a href="#page103">103</a>, <a href="#page104">104</a><br/>
+&mdash;&mdash;, fossil in Coal, <a href="#page400">400</a><br/>
+&mdash;&mdash;, fossil of Isle of Portland, <a href="#page332">332</a><br/>
+Forfarshire, Cephalaspis beds of, <a href="#page446">446</a><br/>
+&mdash;&mdash;, contorted strata in, <a href="#page178">178</a><br/>
+Formation, term defined, <a href="#page27">27</a><br/>
+Fossil, term defined, <a href="#page29">29</a><br/>
+&mdash;&mdash; trees erect in coal, <a href="#page410">410</a><br/>
+&mdash;&mdash; Fish of Old Red Sandstone, <a href="#page442">442</a><br/>
+Fossiliferous groups, table of succession of, <a href="#page131">131</a><br/>
+Fossils, arrangement of, in strata, <a href="#page47">47</a><br/>
+&mdash;&mdash;, destruction of, in older formations, <a href="#page139">139</a><br/>
+&mdash;&mdash;, fresh-water and marine, <a href="#page52">52</a><br/>
+&mdash;&mdash; obliterated by metamorphic action, <a href="#page603">603</a><br/>
+&mdash;&mdash;, recent, and Post-pliocene, <a href="#page154">154-65</a><br/>
+&mdash;&mdash; of the drift, <a href="#page176">176</a>, <a href="#page180">180</a>, <a href="#page192">192</a><br/>
+&mdash;&mdash; of the Crags, <a href="#page193">193-203</a><br/>
+&mdash;&mdash;, Upper Miocene, <a href="#page214">214-29</a><br/>
+&mdash;&mdash;, Lower Miocene of Switzerland, <a href="#page236">236</a><br/>
+&mdash;&mdash; of the Hempstead Beds, <a href="#page244">244</a><br/>
+&mdash;&mdash;, Eocene, <a href="#page253">253</a><br/>
+&mdash;&mdash; of the Barton Clay, <a href="#page259">259</a><br/>
+&mdash;&mdash; of the White Chalk, <a href="#page293">293</a><br/>
+&mdash;&mdash; of the Neocomian, <a href="#page309">309</a><br/>
+&mdash;&mdash; of the Oolite, <a href="#page324">324</a><br/>
+&mdash;&mdash; of the Stonesfield Slate, <a href="#page347">347</a><br/>
+&mdash;&mdash; of the Lias, <a href="#page354">354</a><br/>
+&mdash;&mdash; of the Trias, <a href="#page370">370</a><br/>
+&mdash;&mdash; of the Magnesian Limestone, <a href="#page387">387</a><br/>
+&mdash;&mdash; of the Coal, <a href="#page405">405</a><br/>
+&mdash;&mdash; plants of the Coal, <a href="#page421">421</a><br/>
+&mdash;&mdash; of the Mountain Limestone, <a href="#page430">430</a><br/>
+&mdash;&mdash;, Devonian, <a href="#page449">449</a><br/>
+&mdash;&mdash;, Silurian, <a href="#page460">460</a><br/>
+&mdash;&mdash;, Cambrian, <a href="#page484">484</a><br/>
+&mdash;&mdash; Laurentian, <a href="#page492">492</a><br/>
+Fournet, M. on metalliferous gneiss, <a href="#page586">586</a><br/>
+&mdash;&mdash;, on veins in granite, <a href="#page610">610</a><br/>
+Fox, Rev. D., on Isle of Wight Eocene fossils, <a href="#page254">254</a><br/>
+Fox, Mr. R., on lodes in Cornwall, <a href="#page614">614</a><br/>
+Fractures of strata, and faults, <a href="#page87">87</a><br/>
+Fragments, included, a test of age of plutonic rocks, <a href="#page565">565</a><br/>
+&mdash;&mdash;, included, a test of age of strata, <a href="#page129">129</a><br/>
+&mdash;&mdash; a test of age in volcanic rocks, <a href="#page524">524</a><br/>
+France, Eocene formations of, <a href="#page270">270-6</a><br/>
+&mdash;&mdash;, Lower Miocene of, <a href="#page231">231</a><br/>
+&mdash;&mdash;, Upper Miocene of, <a href="#page211">211</a><br/>
+Freshfield, Mr., on absence of lakes in the Caucasus, <a href="#page187">187</a><br/>
+Fresh-water strata, how distinguished from marine, <a href="#page53">53-9</a><br/>
+&mdash;&mdash; formation of Auvergne, <a href="#page233">233</a><br/>
+Fucoid sandstones of Sweden, <a href="#page489">489</a><br/>
+<i>Fulgur canaliculatus</i>, Maryland, <a href="#page228">228</a><br/>
+Fuller&rsquo;s earth, fossils of the, <a href="#page348">348</a><br/>
+Fundy, Bay of, fossil trees exposed in cliffs at, <a href="#page412">412</a><br/>
+<i>Fusilina cylindrica</i>, <a href="#page438">438</a><br/>
+Fusion of quartz, <a href="#page500">500</a><br/>
+<i>Fusus contrarius (Trophon antiquum)</i>, <a href="#page196">196</a><br/>
+&mdash;&mdash; <i>quadricostatus</i>, Maryland, <a href="#page228">228</a><br/><br/>
+</p>
+
+<p class="noindent">
+G<small>ABBRO</small>, <a href="#page505">505</a><br/>
+<i>Gaillonella ferruginea</i>, and <i>G. distans,</i> <a href="#page52">52</a><br/>
+Galapagos Islands, living marine saurian in, <a href="#page362">362</a><br/>
+<i>Galeocerdo latidens</i>, Bracklesham, <a href="#page262">262</a><br/>
+<i>Galerites albogalerus</i>, White Chalk, <a href="#page294">294</a><br/>
+Galestes in Middle Purbeck, <a href="#page328">328</a><br/>
+Ganoids, the type of Old Red Sandstone fish, <a href="#page443">443</a><br/>
+&mdash;&mdash; of the Wealden, <a href="#page316">316</a><br/>
+&mdash;&mdash; of the Trias, <a href="#page383">383</a><br/>
+Gaps in the sequence of fossil remains, <a href="#page138">138</a><br/>
+Garnet, <a href="#page500">500</a><br/>
+Gases, corrosion of rocks by, <a href="#page586">586</a><br/>
+Gaudin on Lower Miocene of Switzerland, <a href="#page236">236</a><br/>
+&mdash;&mdash; on Pliocene flora of Italy, <a href="#page209">209</a><br/>
+&mdash;&mdash; on Proteaceæ in Bournemouth Eocene, <a href="#page263">263</a><br/>
+Gault, thickness and fossils of, <a href="#page300">300</a><br/>
+Geikie, Mr. A., on Ayrshire Permian trap-rocks, <a href="#page545">545</a><br/>
+&mdash;&mdash;, on subaërial denudation, <a href="#page115">115</a><br/>
+&mdash;&mdash;, on ice erosion of lake-basins, <a href="#page187">187</a><br/>
+&mdash;&mdash;, on Isle of Mull volcanic rocks, <a href="#page539">539</a><br/>
+&mdash;&mdash;, on Pentland Old Red volcanic rocks, <a href="#page548">548</a><br/>
+&mdash;&mdash;, on Silurian metamorphic rocks, <a href="#page602">602</a><br/>
+&mdash;&mdash;, on syenite of Skye, <a href="#page568">568</a><br/>
+Geinitz, M., on Permian flora, <a href="#page393">393</a><br/>
+Gemunder Maar, volcanic rocks of, <a href="#page534">534</a><br/>
+Geneva, Lower Miocene of, <a href="#page236">236</a><br/>
+Geology defined, <a href="#page25">25</a><br/>
+Gergovia, tuffs and associated lacustrine strata of, <a href="#page542">542</a><br/>
+Germany, Lower Miocene of, <a href="#page242">242</a><br/>
+&mdash;&mdash;, Triassic fauna of, <a href="#page375">375</a><br/>
+Gers, Upper Miocene of, <a href="#page215">215</a><br/>
+<i>Gervillia anceps</i>, Neocomian, <a href="#page310">310</a><br/>
+&mdash;&mdash; <i>socialis</i>, Muschelkalk, <a href="#page379">379</a><br/>
+Giant&rsquo;s Causeway basalt, age of, <a href="#page248">248</a><br/>
+&mdash;&mdash;, laterite of the, <a href="#page509">509</a><br/>
+&mdash;&mdash;, columnar basalt of, <a href="#page510">510</a><br/>
+Girgenti, Newer Pliocene of, <a href="#page207">207</a><br/>
+Glacial drift, distribution and nature of, <a href="#page166">166</a><br/>
+&mdash;&mdash; epoch in the Post-pliocene, <a href="#page166">166</a><br/>
+&mdash;&mdash; formations of Pliocene age, <a href="#page189">189-92</a><br/>
+Glaciation of Russia and Scandinavia, <a href="#page174">174</a><br/>
+&mdash;&mdash; of Scotland, <a href="#page175">175</a><br/>
+&mdash;&mdash; of Wales and England, <a href="#page180">180</a><br/>
+&mdash;&mdash; of North America, <a href="#page182">182</a><br/>
+Glaciers, transporting and abrading power of, <a href="#page168">168</a><br/>
+Glasgow, marine strata near, <a href="#page146">146</a><br/>
+Glauconie grossiere, <a href="#page275">275</a><br/>
+Glen Tilt, junction of granite and schist at, <a href="#page559">559</a><br/>
+Globiform pitchstone, <a href="#page512">512</a><br/>
+<i>Globigerina bulloides</i>, <a href="#page288">288</a><br/>
+Globular structure of volcanic rocks, <a href="#page510">510</a><br/>
+<i>Glyptostrobus, Europæus,</i> Œningen, <a href="#page223">223</a><br/>
+Gneiss, granite veins traversing, <a href="#page560">560</a><br/>
+&mdash;&mdash; defined and figured, <a href="#page577">577</a><br/>
+&mdash;&mdash;, fundamental, of Scotland, <a href="#page493">493</a><br/>
+Gold mines of Australia and Chili, <a href="#page616">616</a><br/>
+&mdash;&mdash; veins of Russia, <a href="#page616">616</a><br/>
+&mdash;&mdash; of California, of age of alluvium, <a href="#page617">617</a><br/>
+Goldenberg, Professor, on Saarbrück coal insects, <a href="#page406">406</a><br/>
+Goldfuss, Professor, on reptiles in coal, <a href="#page406">406</a><br/>
+<i>Goniatites crenistria</i>, <a href="#page436">436</a><br/>
+&mdash;&mdash; <i>Listeri,</i> coal-measures, <a href="#page405">405</a><br/>
+Göppert, on American forms in Swiss Miocene flora, <a href="#page223">223</a><br/>
+&mdash;&mdash; on petrification, <a href="#page68">68</a><br/>
+&mdash;&mdash; on plants of coal-measures, <a href="#page398">398</a><br/>
+<i>Gorgonia infundibuliformis,</i> Permian, <a href="#page388">388</a><br/>
+Graham&rsquo;s Island, forming ashy conglomerate, <a href="#page549">549</a><br/>
+Grampians, Old Red conglomerates of, <a href="#page73">73</a><br/>
+&mdash;&mdash;, trap-rocks of the, <a href="#page547">547</a><br/>
+&mdash;&mdash;, former glaciers in the, <a href="#page175">175</a><br/>
+Grand Canary, Upper Miocene, shelly tuffs of, <a href="#page558">558</a><br/>
+Granite, composition of, <a href="#page552">552</a><br/>
+&mdash;&mdash;, graphic and columnar, <a href="#page553">553</a>, <a href="#page554">554</a><br/>
+&mdash;&mdash;, how far connected with trap-rocks, <a href="#page558">558</a><br/>
+&mdash;&mdash;, hydrothermal action in formation of, <a href="#page555">555</a><br/>
+&mdash;&mdash; metamorphosing fossiliferous strata, <a href="#page581">581</a><br/>
+&mdash;&mdash;, porphyritic, <a href="#page556">556</a><br/>
+&mdash;&mdash;, oldest, <a href="#page574">574</a><br/>
+&mdash;&mdash;, protrusion of solid, <a href="#page574">574</a><br/>
+&mdash;&mdash;, passage of, into trap, <a href="#page558">558</a><br/>
+&mdash;&mdash;, schorly, <a href="#page557">557</a><br/>
+&mdash;&mdash; veins, <a href="#page559">559</a><br/>
+&mdash;&mdash; veins in talcose gneiss, <a href="#page560">560</a><br/>
+Granton, angiosperm found in coal at, <a href="#page429">429</a><br/>
+Graptolites of Llandeilo flags, <a href="#page474">474</a><br/>
+<i>Graptolites Murchisonii.</i> Llandeilo flags, <a href="#page473">473</a><br/>
+<i>Graptolithus priodon,</i> Silurian, <a href="#page467">467</a><br/>
+Gray&rsquo;s, Essex, pachyderms found at, <a href="#page161">161</a><br/>
+Great (or Bath) Oolite, <a href="#page342">342</a><br/>
+Greece, Upper Miocene formations of, <a href="#page226">226</a><br/>
+Greenland, continental ice of, <a href="#page170">170</a><br/>
+&mdash;&mdash;, gradual sinking of, <a href="#page72">72</a><br/>
+Greenstone, <a href="#page505">505</a><br/>
+Gres de Beauchamp, Paris basin, <a href="#page273">273</a><br/>
+Gres de Fontainebleau, age of the, <a href="#page230">230</a><br/>
+Griffiths, Sir R., on yellow sandstone of Ireland, <a href="#page441">441</a><br/>
+Grit defined, <a href="#page36">36</a><br/>
+Groups, older, rise highest above the sea, <a href="#page139">139</a><br/>
+&mdash;&mdash; why the newest to be studied first, <a href="#page140">140</a><br/>
+<i>Gryllacris lithanthraca,</i> coal, <a href="#page405">405</a><br/>
+<i>Gryphæa</i> coated with <i>serpulæ</i>, <a href="#page48">48</a><br/>
+&mdash;&mdash; <i>columba,</i> Chloritic Sand, <a href="#page300">300</a><br/>
+&mdash;&mdash; <i>convexa,</i> Chalk, <a href="#page295">295</a><br/>
+&mdash;&mdash; <i>incurva (G. arcuata)</i>, <a href="#page54">54</a>, <a href="#page354">354</a><br/>
+&mdash;&mdash; <i>virgula,</i> Kimmeridge clay, <a href="#page336">336</a><br/>
+Gryphite Limestone, <a href="#page354">354</a><br/>
+Guadaloupe, glass cavities in quartz of, <a href="#page555">555</a><br/>
+Gulf-Stream, probable abrading power of, <a href="#page105">105</a><br/>
+Gümbel, M., on Rhætic beds, <a href="#page366">366</a><br/>
+Gunn, Mrs., on pot-stones in the chalk, <a href="#page291">291</a><br/>
+Gutbier, Colonel, on Permian flora, <a href="#page393">393</a><br/>
+Gymnogens, term explained, <a href="#page303">303</a><br/>
+Gypseous marls of Auvergne, <a href="#page233">233</a><br/>
+Gypsum and gypseous marl defined, <a href="#page38">38</a>, <a href="#page39">39</a><br/>
+<i>Gyrolepis tenuistriatus,</i> Rhætic beds, <a href="#page367">367</a><br/><br/>
+</p>
+
+<p class="noindent">
+H<small>AIME</small>, Mr., on palæozoic corals, <a href="#page431">431</a><br/>
+<i>Hakea silicina</i> and <i>Hakea saligna,</i> Œningen, <a href="#page222">222</a><br/>
+Hall, Captain Basil, on Cyclopean Isles, <a href="#page530">530</a><br/>
+Hall, Sir James, on curved strata, <a href="#page75">75</a><br/>
+Hall, Mr. J., on Appalachian palæozoic rocks, <a href="#page110">110</a><br/>
+Hallstadt and St. Cassian beds, <a href="#page376">376</a><br/>
+<i>Halysites catenularis,</i> Silurian, <a href="#page465">465</a><br/>
+Hamilton, Sir W., on eruption of Vesuvius, 1779, <a href="#page526">526</a><br/>
+<i>Hamites spiniger,</i> Gault, <a href="#page301">301</a><br/>
+Hancock, Mr., on Protosaurus in Permian, <a href="#page390">390</a><br/>
+Harkness, Professor, on Silurian metamorphic rocks, <a href="#page602">602</a><br/>
+Harlech grits, fossils of the, <a href="#page486">486</a><br/>
+Harris, Major, on the Salt Lakes, <a href="#page374">374</a><br/>
+<i>Harpactor maculipes,</i> Œningen, <a href="#page224">224</a><br/>
+Harpe, M. de la, on Bournemouth Eocene flora, <a href="#page263">263</a><br/>
+Hartung, Mr., cited, <a href="#page496">496</a><br/>
+Hartz mountains, mineral veins of, <a href="#page608">608</a><br/>
+&mdash;&mdash;, Bunter Sandstein of, <a href="#page380">380</a><br/>
+Hastings Sands, subdivisions of the, <a href="#page316">316</a><br/>
+Hautes Alpes, granite of the, <a href="#page571">571</a><br/>
+Hauy on isomorphism, <a href="#page502">502</a><br/>
+Headon series, fossils of the, <a href="#page255">255</a><br/>
+Heat, powerful in consolidating rocks, <a href="#page65">65</a><br/>
+&mdash;&mdash;, rocks upraised and folded by, <a href="#page92">92</a><br/>
+Hébert, M., on age of Sables de Bracheux, <a href="#page330">330</a><br/>
+&mdash;&mdash;, comparison of Sables Moyens and Barton shells, <a href="#page258">258</a><br/>
+&mdash;&mdash;, on pisolitic limestone, <a href="#page285">285</a><br/>
+Hebrides, dikes in the, <a href="#page514">514</a><br/>
+Heer, Professor, on American genera in Swiss Miocene, <a href="#page239">239</a><br/>
+&mdash;&mdash;, on age of Madeira leaf-bed, <a href="#page532">532</a><br/>
+&mdash;&mdash;, on Arctic Miocene flora, <a href="#page239">239</a><br/>
+&mdash;&mdash;, on Bear Island flora, <a href="#page441">441</a><br/>
+&mdash;&mdash;, on Bovey Tracey Miocene flora, <a href="#page247">247</a><br/>
+&mdash;&mdash;, on fossil plants of Switzerland, <a href="#page215">215</a>, <a href="#page219">219</a>, <a href="#page221">221</a>, <a href="#page224">224</a>, <a href="#page236">236</a><br/>
+&mdash;&mdash;, on Lower Miocene plants of Mull, <a href="#page248">248</a><br/>
+&mdash;&mdash;, on Monte Bolca Eocene plants, <a href="#page263">263</a>, <a href="#page543">543</a><br/>
+&mdash;&mdash;, on Proteas of Lower Miocene, <a href="#page237">237</a><br/>
+&mdash;&mdash;, on plants of Hempstead beds, <a href="#page246">246</a><br/>
+&mdash;&mdash;, on plants of coal-field, Virginia, <a href="#page383">383</a><br/>
+&mdash;&mdash;, on Swiss Miocene insects, <a href="#page223">223</a><br/>
+&mdash;&mdash;, on supposed Proteaceæ of Œningen beds, <a href="#page221">221</a><br/>
+&mdash;&mdash;, on Superga fossil plants, <a href="#page244">244</a><br/>
+Heidelberg, varieties of granite near, <a href="#page560">560</a><br/>
+<i>Heliolites porosa</i>, Devonian, <a href="#page451">451</a><br/>
+<i>Helix hispida (plebeia)</i>, <a href="#page155">155</a><br/>
+&mdash;&mdash; <i>labyrinthica,</i> Headon, <a href="#page255">255</a><br/>
+&mdash;&mdash; <i>occlusa,</i> Bembridge, <a href="#page253">253</a><br/>
+&mdash;&mdash; <i>Turonensis,</i> faluns, <a href="#page56">56</a><br/>
+<i>Hemicidaris Purbeckensis,</i> Purbeck, <a href="#page324">324</a><br/>
+<i>Hemipneustes radiatus,</i> Chalk, <a href="#page284">284</a><br/>
+<i>Hemitelites Brownii,</i> Inferior Oolite, <a href="#page350">350</a><br/>
+Hempstead beds, subdivisions of the, <a href="#page244">244</a><br/>
+Henry, on absorption of carbonic acid gas in water, <a href="#page585">585</a><br/>
+Henslow, Professor, on dike in Anglesea, <a href="#page515">515</a><br/>
+&mdash;&mdash;, on Red Crag coprolite bed, <a href="#page197">197</a><br/>
+Herschel, Sir J., on slaty cleavage, <a href="#page590">590</a><br/>
+Hertfordshire pudding-stone, <a href="#page62">62</a><br/>
+<i>Heterocercal tail of fish</i>, <a href="#page389">389</a><br/>
+Hicks, Dr., on fossils of Arenig beds, <a href="#page476">476</a><br/>
+&mdash;&mdash;, on fossils of Harlech grits, <a href="#page486">486</a><br/>
+&mdash;&mdash;, on Menevian beds, <a href="#page485">485</a><br/>
+Himalaya, shells 18,000 feet high in, <a href="#page29">29</a><br/>
+&mdash;&mdash;, Upper Miocene of, <a href="#page226">226</a><br/>
+<i>Hippopodium ponderosum,</i> Lias, <a href="#page355">355</a><br/>
+<i>Hippopotamus, tooth of</i>, <a href="#page164">164</a><br/>
+Hippurite Limestone, <a href="#page304">304</a><br/>
+<i>Hippurites organisans,</i> Chalk, <a href="#page306">306</a><br/>
+<i>Histioderma hibernica</i>, <a href="#page486">486</a><br/>
+Hitchcock, Professor, on Trias footprints, <a href="#page381">381</a><br/>
+<i>Holoptychius nobilissimus,</i> scale of, and restoration, <a href="#page442">442</a><br/>
+<i>Homalonotus Delphinocephalus</i>, <a href="#page467">467</a><br/>
+&mdash;&mdash; <i>armatus,</i> Devonian, <a href="#page454">454</a><br/>
+Homfray, Mr., on fossils of Tremadoc beds, <a href="#page483">483</a><br/>
+<i>Homocercal tail of fish</i>, <a href="#page389">389</a><br/>
+Hooghly River, analysis of water, <a href="#page69">69</a><br/>
+Hooker, Dr., on coniferæ, <a href="#page429">429</a>, <a href="#page430">430</a><br/>
+&mdash;&mdash;, on structure of sigillaria, <a href="#page426">426</a><br/>
+&mdash;&mdash;, on sporangia of Silurian plant, <a href="#page460">460</a><br/>
+Horizontality of strata, <a href="#page40">40</a><br/>
+Horizontal strata, upheaval of, <a href="#page71">71</a><br/>
+Hornblende, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+Hornblende-schist, <a href="#page578">578</a><br/>
+Hörnes, Dr., on fossil mollusca of Vienna basin, <a href="#page225">225</a><br/>
+Horstead, pot-stones at, <a href="#page291">291</a><br/>
+Hour-glass illustrating the destruction and renovation of land, <a href="#page119">119</a><br/>
+Howse, Mr., on Protosaurus in Permian, <a href="#page390">390</a><br/>
+Hubbard, Professor, on granite of White Mountains, <a href="#page565">565</a><br/>
+Hudson River Group, fossils of the, <a href="#page479">479</a><br/>
+Hughes, Mr. T. McKenny, cited, <a href="#page450">450</a><br/>
+&mdash;&mdash;, on slaty cleavage, <a href="#page589">589</a><br/>
+&mdash;&mdash;, on protrusion of solid granite, <a href="#page575">575</a><br/>
+Hull, Mr. E., on breccias in Permian, <a href="#page391">391</a><br/>
+&mdash;&mdash;, on carboniferous of Lancashire, <a href="#page395">395</a><br/>
+&mdash;&mdash;, on carboniferous rocks of north of England, <a href="#page111">111</a><br/>
+&mdash;&mdash;, on faults in Lancashire coal-field, <a href="#page91">91</a><br/>
+&mdash;&mdash;, on anticlinals and synclinals, Lancashire, <a href="#page85">85</a><br/>
+&mdash;&mdash;, on thickness of the Upper Trias, <a href="#page369">369</a><br/>
+&mdash;&mdash;, on thickness of Permian, <a href="#page386">386</a><br/>
+&mdash;&mdash;, on three lines of flexure since the coal in Lancashire, <a href="#page94">94</a><br/>
+Human remains of Recent Period, <a href="#page157">157</a><br/>
+&mdash;&mdash; in cavern deposits, <a href="#page156">156</a><br/>
+Humboldt, on mineral character of rocks, <a href="#page602">602</a><br/>
+Humphrey and Abbot on Mississippi denudation, <a href="#page114">114</a><br/>
+Hungary, trachyte of, <a href="#page558">558</a><br/>
+Hunt, Sterry, on action of water in metamorphism, <a href="#page585">585</a><br/>
+Huronian series, thickness of the, <a href="#page490">490</a><br/>
+Huxley, Professor, on Atlantic chalk-mud, <a href="#page287">287</a><br/>
+&mdash;&mdash;, on affinity between reptiles and birds, <a href="#page338">338</a><br/>
+&mdash;&mdash;, on batrachians of the coal, <a href="#page407">407</a><br/>
+&mdash;&mdash;, on fish of Old Red Sandstone, <a href="#page443">443-5</a><br/>
+&mdash;&mdash;, on Pteraspis, <a href="#page463">463</a><br/>
+Hyæna den of Kirkdale cave, <a href="#page157">157</a><br/>
+<i>Hyæna spelæa,</i> tooth of, <a href="#page165">165</a><br/>
+<i>Hybodus plicatilis,</i> Rhætic beds, <a href="#page367">367</a><br/>
+&mdash;&mdash; <i>reticulatus,</i> Lias, <a href="#page359">359</a><br/>
+Hydrothermal action producing metamorphism, <a href="#page584">584</a><br/>
+&mdash;&mdash; in formation of granite, <a href="#page555">555</a><br/>
+&mdash;&mdash; forming granite veins, <a href="#page573">573</a><br/>
+<i>Hymenocaris vermicauda</i>, <a href="#page484">484</a><br/>
+<i>Hyperodapedon Gordoni,</i> Trias, <a href="#page370">370</a><br/>
+Hypersthene, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+&mdash;&mdash; rock, <a href="#page505">505</a><br/>
+&mdash;&mdash; rocks of Skye, <a href="#page491">491</a><br/>
+Hypogene rocks, uniformity of mineral character in, <a href="#page602">602</a><br/>
+&mdash;&mdash; rocks, term defined, <a href="#page26">26</a><br/>
+<i>Hypsiprymnus Gaimardi,</i> molar of recent, <a href="#page327">327</a><br/>
+Hythe, Neocomian beds of, <a href="#page308">308</a><br/><br/>
+</p>
+
+<p class="noindent">
+I<small>CE</small>, erosion of lake-basins considered, <a href="#page184">184</a>, <a href="#page188">188</a><br/>
+&mdash;&mdash;, abrading power of, <a href="#page168">168</a><br/>
+&mdash;&mdash;, continental, of Greenland, <a href="#page170">170</a><br/>
+Icebergs, drift carried by, <a href="#page172">172</a><br/>
+&mdash;&mdash; stranded in Baffin&rsquo;s Bay, <a href="#page173">173</a><br/>
+Ice-borne erratics at Chichester, <a href="#page181">181</a><br/>
+Iceland, glass cavities in quartz of, <a href="#page555">555</a><br/>
+&mdash;&mdash;, flow of lava in, <a href="#page523">523</a><br/>
+<i>Ichthyosaurus communis,</i> Lias, <a href="#page361">361</a><br/>
+Idocrase, <a href="#page500">500</a><br/>
+Ichthyodorulite of the Lias, <a href="#page359">359</a><br/>
+<i>Iguanodon Mantelli,</i> Weald Clay, <a href="#page315">315</a><br/>
+Ilfracombe Group of Devon, <a href="#page449">449</a><br/>
+Inclined strata, <a href="#page73">73</a><br/>
+India, Miocene formations of, <a href="#page226">226</a><br/>
+India, Upper Miocene of, <a href="#page226">226</a><br/>
+Inferior Oolite, thickness and fossils of, <a href="#page349">349</a><br/>
+Infusoria in tripoli, <a href="#page51">51</a><br/>
+Inland sea-cliffs, <a href="#page103">103</a><br/>
+<i>Inoceramus Lamarckii,</i> White Chalk, <a href="#page295">295</a><br/>
+Insect in American coal, <a href="#page416">416</a><br/>
+&mdash;&mdash; beds of the Lias, <a href="#page363">363</a><br/>
+<i>Insect wing of neuropterous</i>, <a href="#page363">363</a><br/>
+Insects, Devonian, of Canada, <a href="#page457">457</a><br/>
+&mdash;&mdash; in European coal, <a href="#page405">405</a><br/>
+&mdash;&mdash;, Miocene, of Croatia, <a href="#page243">243</a><br/>
+&mdash;&mdash;, Upper Miocene, at Œningen, <a href="#page223">223</a><br/>
+Intrusion, a test of age of Plutonic rocks, <a href="#page565">565</a><br/>
+&mdash;&mdash;, a test of age of volcanic rocks, <a href="#page521">521</a><br/>
+Inundation mud of rivers, <a href="#page153">153</a><br/>
+Ireland, glacial drift of, <a href="#page190">190</a><br/>
+&mdash;&mdash;, yellow sandstone of, <a href="#page441">441</a><br/>
+Iron pyrites, <a href="#page500">500</a><br/>
+&mdash;&mdash; weapons of Swiss lake-dwellings, <a href="#page148">148</a><br/>
+<i>Isastræa oblonga,</i> Portland Sand, <a href="#page335">335</a><br/>
+Isle of Bourbon, lava current of the, <a href="#page566">566</a><br/>
+&mdash;&mdash; Wight, Hempstead beds, <a href="#page244">244</a><br/>
+&mdash;&mdash; Wight, Eocene beds, <a href="#page255">255</a><br/>
+&mdash;&mdash; Mull, Miocene leaf-bed of, <a href="#page247">247</a><br/>
+&mdash;&mdash; Mull, volcanic rocks, <a href="#page248">248</a><br/>
+Isomorphism, theory of, <a href="#page502">502</a><br/>
+Italy, Lower Miocene of, <a href="#page244">244</a><br/>
+&mdash;&mdash;, Older Pliocene volcanoes of, <a href="#page523">523</a><br/>
+&mdash;&mdash;, Pliocene of, <a href="#page207">207</a><br/>
+&mdash;&mdash;, Older Pliocene flora of, <a href="#page208">208</a><br/>
+&mdash;&mdash;, Upper Miocene strata of, <a href="#page226">226</a><br/><br/>
+</p>
+
+<p class="noindent">
+J<small>AMIESON</small>, Mr. T. F., on Scotch glacial drift, <a href="#page175">175</a><br/>
+Jaws of mammalia in Purbeck, <a href="#page327">327</a><br/>
+Jeffreys, Mr. Gwyn, on Atlantic mud, <a href="#page288">288</a><br/>
+Jointed structure of metamorphic rocks, <a href="#page589">589</a><br/>
+Jones, Dr. Rupert, on Eozoon Canadense, <a href="#page491">491</a><br/>
+Jorullo, lava stream of, <a href="#page566">566</a><br/>
+Judd, Mr., on Speeton clay, <a href="#page311">311</a><br/>
+Jukes, Mr., on Tarannon shales, <a href="#page468">468</a><br/>
+Jura, erratic blocks on the, <a href="#page169">169</a><br/>
+&mdash;&mdash;, structure of the, <a href="#page82">82</a><br/><br/>
+</p>
+
+<p class="noindent">
+K<small>ANGAROO</small>, jaws of, <a href="#page159">159</a><br/>
+Käsegrotte, Bertrich Baden, Basaltic pillars of, <a href="#page512">512</a><br/>
+Kaup, Professor, on footprints of the Trias, <a href="#page373">373</a><br/>
+Keilhau, Professor, on granite veins, <a href="#page562">562</a><br/>
+&mdash;&mdash;, on planes of foliation, <a href="#page595">595</a><br/>
+&mdash;&mdash;, on Silurian granite of Norway, <a href="#page573">573</a><br/>
+&mdash;&mdash;, on protrusion of granite, <a href="#page581">581</a><br/>
+Keller, Dr. F., on lake-dwellings, <a href="#page148">148</a><br/>
+Kelloway Rock, percentage of Oxford clay fossils in, <a href="#page341">341</a><br/>
+Kentish Rag, <a href="#page308">308</a><br/>
+Keuper, of Germany, <a href="#page375">375</a><br/>
+&mdash;&mdash; or Upper Trias of England, <a href="#page369">369</a><br/>
+Kilkenny, fossil plants of, <a href="#page441">441</a><br/>
+Killas, altered by granite in Cornwall, <a href="#page582">582</a><br/>
+Kiltorkan, yellow sandstone of, with Anodonta, <a href="#page441">441</a><br/>
+Kimmeridge Clay, <a href="#page335">335</a><br/>
+King, Dr., on reptile footprints in coal, <a href="#page407">407</a><br/>
+King, Mr., on Permian fossils, <a href="#page388">388</a><br/>
+Kirkdale cave, hyæna&rsquo;s den of, <a href="#page157">157</a><br/>
+Kitchen-middens of Denmark, <a href="#page146">146</a><br/>
+Kleyn Spawen beds, <a href="#page242">242</a><br/>
+Könen, Baron von, on Brockenhurst shells, <a href="#page257">257</a><br/>
+Koninck, M. de, on Mountain Limestone fish, <a href="#page436">436</a><br/>
+&mdash;&mdash;, on shells of Mayence basin, <a href="#page242">242</a><br/>
+<i>Koninckia Leonhardi,</i> Hallstadt, <a href="#page377">377</a><br/><br/>
+</p>
+
+<p class="noindent">
+L<small>ABRADOR</small> rock, <a href="#page505">505</a><br/>
+&mdash;&mdash; series, <a href="#page490">490</a><br/>
+Labradorite, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+<i>Labyrinthodon Jægeri, section of tooth</i>, <a href="#page371">371</a><br/>
+&mdash;&mdash;, <i>tooth of</i>, <a href="#page370">370</a><br/>
+Labyrinthodonts of Coal, <a href="#page407">407</a><br/>
+Lake-craters of the Eifel, <a href="#page534">534</a><br/>
+Lake districts, southern limits of the, <a href="#page184">184</a><br/>
+Lake-dwellings, scarcity of human remains in, <a href="#page149">149</a><br/>
+&mdash;&mdash; of Switzerland, <a href="#page148">148</a><br/>
+Lakes, deposits in, <a href="#page27">27</a><br/>
+&mdash;&mdash;, connection of, with glacial action, <a href="#page184">184-8</a><br/>
+Lamarck on bivalve mollusca, <a href="#page54">54</a><br/>
+Lamination of clay slate, <a href="#page594">594</a><br/>
+<i>Lamna elegans,</i> Bracklesham, <a href="#page262">262</a><br/>
+Lancashire, vast thickness of rocks without corresponding altitude in, <a href="#page111">111</a><br/>
+Land, balance of dry, how preserved, <a href="#page116">116</a>, <a href="#page118">118</a><br/>
+&mdash;&mdash; has been raised, not the sea lowered, <a href="#page70">70</a><br/>
+&mdash;&mdash;, mean height of, above the sea, <a href="#page115">115</a><br/>
+&mdash;&mdash;, rise of, in Sweden, <a href="#page72">72</a><br/>
+&mdash;&mdash;, rise and fall of, affecting denudation, <a href="#page101">101</a><br/>
+Land-ice, action of, in Greenland, <a href="#page171">171</a><br/>
+Land&rsquo;s End, columnar granite at, <a href="#page553">553</a><br/>
+&mdash;&mdash;, porphyritic granite at, <a href="#page556">556</a><br/>
+La Roche, recent deposits in estuary of, <a href="#page40">40</a><br/>
+Lartet, M., on mammalia of Faluns, <a href="#page214">214</a><br/>
+&mdash;&mdash;, on Gastornis Parisiensis, <a href="#page276">276</a><br/>
+&mdash;&mdash;, on reindeer period, <a href="#page150">150</a><br/>
+<i>Lastræa stiriaca,</i> Monod, <a href="#page239">239</a><br/>
+Lateral compression causing curved strata, <a href="#page75">75</a><br/>
+Laterite of Giant&rsquo;s Causeway, <a href="#page509">509</a><br/>
+Laurentian gneiss of Scotland, <a href="#page493">493</a><br/>
+&mdash;&mdash; Group, Upper and Lower, <a href="#page491">491</a><br/>
+&mdash;&mdash; metamorphic rocks, <a href="#page601">601</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page549">549</a><br/>
+Lava, <a href="#page507">507</a><br/>
+&mdash;&mdash; consolidating on slopes, <a href="#page496">496</a><br/>
+&mdash;&mdash; currents of Auvergne, <a href="#page541">541</a><br/>
+&mdash;&mdash; streams, effect of, <a href="#page30">30</a><br/>
+&mdash;&mdash; of La Coupe d&rsquo;Ayzac, <a href="#page511">511</a><br/>
+&mdash;&mdash; of Jorullo, <a href="#page566">566</a><br/>
+Lead veins, age of, <a href="#page616">616</a><br/>
+Leaf-bed of Madeira in basalt and scoriæ, <a href="#page532">532</a><br/>
+&mdash;&mdash;, Isle of Mull Miocene, <a href="#page248">248</a><br/>
+<i>Leda amygdaloides,</i> London Clay, <a href="#page266">266</a><br/>
+&mdash;&mdash; <i>Deshayesiana (Nucula Deshayesiana)</i>, <a href="#page241">241</a><br/>
+&mdash;&mdash; <i>lanceolata (L. oblonga),</i> Scotch drift, <a href="#page176">176</a><br/>
+&mdash;&mdash; <i>truncata,</i> Scotch drift, <a href="#page177">177</a><br/>
+Lee, Mr. J.E., on Pteraspis of Lower Ludlow, <a href="#page463">463</a><br/>
+Leidy, Dr., on fossil quadrupeds of Nebraska, <a href="#page249">249</a><br/>
+<i>Leperditia inflata,</i> coal-measures, <a href="#page405">405</a><br/>
+<i>Lepidodendron,</i> Griffithsii, <a href="#page441">441</a><br/>
+&mdash;&mdash; <i>corrugatum,</i> carboniferous., <a href="#page417">417</a><br/>
+&mdash;&mdash; <i>Sternbergii,</i> coal-measures, <a href="#page423">423</a><br/>
+Lepidolite, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+<i>Lepidostrobus ornatus,</i> Coal, <a href="#page424">424</a><br/>
+<i>Lepidotus gigas,</i> Lias, <a href="#page358">358</a><br/>
+&mdash;&mdash; <i>Mantelli,</i> Wealden, <a href="#page317">317</a><br/>
+<i>Leptæna depressa,</i> Wenlock, <a href="#page466">466</a><br/>
+&mdash;&mdash; <i>Moorei,</i> Lias, <a href="#page355">355</a><br/>
+Level of surface altered by change of subterranean heat, <a href="#page119">119</a><br/>
+Lewis, hornblendic gneiss of, <a href="#page601">601</a><br/>
+Lias, fishes of the, <a href="#page358">358</a><br/>
+&mdash;&mdash;, fossils of the, <a href="#page354">354</a><br/>
+&mdash;&mdash; and Oolite, origin of the, <a href="#page364">364</a><br/>
+&mdash;&mdash;, reptiles of the, <a href="#page360">360</a><br/>
+&mdash;&mdash;, insects of the, <a href="#page363">363</a><br/>
+&mdash;&mdash;, plants of the, <a href="#page364">364</a><br/>
+&mdash;&mdash;, plutonic rocks of the, <a href="#page571">571</a><br/>
+&mdash;&mdash;, subdivisions of the, <a href="#page353">353</a><br/>
+&mdash;&mdash;, volcanic rocks of the, <a href="#page544">544</a><br/>
+Liebig, on conversion of coal into anthracite, <a href="#page403">403</a><br/>
+&mdash;&mdash;, on origin of stalactite, <a href="#page156">156</a><br/>
+Liége, limestone caverns at, <a href="#page156">156</a><br/>
+Lightbody, Mr., on Lower Ludlow shales, <a href="#page461">461</a><br/>
+Lignite, conversion of into coal, <a href="#page403">403</a><br/>
+<i>Lima giganteum</i>, <a href="#page354">354</a><br/>
+&mdash;&mdash; <i>Hoperi,</i> Chalk, <a href="#page300">300</a><br/>
+&mdash;&mdash; <i>spinosa,</i> White Chalk, <a href="#page294">294</a><br/>
+Limagne d&rsquo;Auvergne, Lower Miocene mammalia of the, <a href="#page234">234</a><br/>
+Limburg beds, <a href="#page242">242</a><br/>
+Lime, scarcity of, in metamorphic rocks, <a href="#page604">604</a><br/>
+&mdash;&mdash; in solution, source of, <a href="#page69">69</a><br/>
+Limestone, block of striated, <a href="#page168">168</a><br/>
+&mdash;&mdash;, brecciated, <a href="#page387">387</a><br/>
+&mdash;&mdash; of chemical and organic origin, <a href="#page61">61</a><br/>
+&mdash;&mdash;, compact, <a href="#page501">501</a><br/>
+&mdash;&mdash;, Hippurite, <a href="#page304">304</a><br/>
+&mdash;&mdash;, magnesian, <a href="#page387">387</a><br/>
+&mdash;&mdash;, metamorphic or crystalline, <a href="#page579">579</a><br/>
+&mdash;&mdash;, Mountain, and its fossils, <a href="#page430">430-8</a><br/>
+&mdash;&mdash;, striated, <a href="#page168">168</a><br/>
+<i>Limnæa longiscata</i>, <a href="#page55">55</a><br/>
+Lingula beds, volcanic tuffs of the, <a href="#page549">549</a><br/>
+<i>Lingula Credneri</i>, Permian, <a href="#page388">388</a><br/>
+Lingula Flags, fossils of the, <a href="#page484">484</a><br/>
+<i>Lingula Dumortieri,</i> Crag, <a href="#page200">200</a><br/>
+&mdash;&mdash; <i>Lewisii,</i> Ludlow, <a href="#page462">462</a><br/>
+<i>Lingulella Davisii</i>, <a href="#page484">484</a><br/>
+Lipari Isles, tufas in, <a href="#page586">586</a><br/>
+<i>Liquidambar europæum</i>, <a href="#page209">209</a><br/>
+<i>Lithrostrotion basaltiforme,</i> Carboniferous, <a href="#page432">432</a><br/>
+Lits coquilliers, <a href="#page275">275</a><br/>
+Littoral denudation defined, <a href="#page102">102</a><br/>
+<i>Lituites giganteus,</i> Ludlow, <a href="#page463">463</a><br/>
+Llanberis slates, <a href="#page486">486</a><br/>
+Llandeilo Flags, fossils of the, <a href="#page473">473-5</a><br/>
+Llandeilo formation, thickness of the, <a href="#page475">475</a><br/>
+&mdash;&mdash;, Lower, <a href="#page475">475</a><br/>
+Llandovery Group, classification of the, <a href="#page468">468</a><br/>
+&mdash;&mdash; Rocks, thickness of the Lower, <a href="#page469">469</a><br/>
+Loam defined, <a href="#page38">38</a>, <a href="#page153">153</a><br/>
+Lodes, shells and pebbles in, <a href="#page608">608</a><br/>
+&mdash;&mdash; <i>See</i> Mineral Veins.<br/>
+Loess of fluviatile loam described, <a href="#page153">153</a><br/>
+&mdash;&mdash;, fossil shells of the, <a href="#page154">154</a><br/>
+Logan, Sir W., on Eozoon Canadense, <a href="#page490">490</a><br/>
+&mdash;&mdash;, on Gaspe sandstones, <a href="#page455">455</a><br/>
+&mdash;&mdash;, on Huronian and Laurentian, <a href="#page490">490</a><br/>
+&mdash;&mdash;, on stigmaria in under-clays, <a href="#page398">398</a><br/>
+&mdash;&mdash;, on thickness of Nova Scotia coal, <a href="#page409">409</a><br/>
+&mdash;&mdash;, on thickness of Laurentian in Canada, <a href="#page113">113</a><br/>
+Loire, faluns of the, <a href="#page211">211</a><br/>
+London Clay, fossils of the, <a href="#page264">264</a>, <a href="#page266">266</a><br/>
+Longevity, relative, of mammalia and testacea, <a href="#page162">162</a><br/>
+Longmynd Group, fauna of the, <a href="#page486">486</a><br/>
+Lonsdale, Mr., on corals of America, <a href="#page229">229</a><br/>
+&mdash;&mdash;, on Devonian fossils, <a href="#page449">449</a><br/>
+&mdash;&mdash;, on Stonesfield slate, <a href="#page345">345</a><br/>
+&mdash;&mdash;, on United States Miocene corals, <a href="#page229">229</a><br/>
+<i>Lonsdaleia floriformis,</i> Carboniferous, <a href="#page432">432</a><br/>
+Lowe, Reverend R. T., on Mogador shells, <a href="#page537">537</a><br/>
+Lubbock, Sir J., on the two stone-periods, <a href="#page147">147</a><br/>
+<i>Lucina serrata,</i> Bracklesham, <a href="#page262">262</a><br/>
+Ludlow formation, Upper, <a href="#page459">459</a>; Lower, <a href="#page461">461</a><br/>
+&mdash;&mdash;, bone-bed of the Upper, <a href="#page459">459</a><br/>
+Lulworth Cove, dirt-bed of, <a href="#page333">333</a><br/>
+Lycett, Mr., on fossils of the Great Oolite, <a href="#page344">344</a><br/>
+Lycopodiaceæ of Coal, <a href="#page422">422</a><br/>
+<i>Lycopodium densum,</i> living species, <a href="#page423">423</a><br/>
+Lym-fiord, mingled fresh-water and marine strata of, <a href="#page59">59</a><br/>
+<i>Lymnea caudata,</i> Headon, <a href="#page256">256</a><br/>
+&mdash;&mdash; <i>longiscata,</i> Bembridge, <a href="#page253">253</a><br/>
+Lynton Group of Devon, <a href="#page454">454</a><br/><br/>
+</p>
+
+<p class="noindent">
+M<small>ACLAREN</small>, Mr., on Pentland Hills, volcanic rocks, <a href="#page548">548</a><br/>
+Macclesfield, marine shells 1,200 feet high at, <a href="#page181">181</a><br/>
+MacClintock, Sir L., on Atlantic mud, <a href="#page287">287</a><br/>
+MacCulloch, Dr., on Aberdeenshire granite, <a href="#page558">558</a><br/>
+&mdash;&mdash;, on basaltic columns in Skye, <a href="#page510">510</a><br/>
+&mdash;&mdash;, on formation of hornblende-schist, <a href="#page582">582</a><br/>
+&mdash;&mdash;, on trap, <a href="#page519">519</a><br/>
+MacMullen, Mr. J., on Eozoon Canadense, <a href="#page491">491</a><br/>
+<i>Macropus atlas,</i> lower jaw of, <a href="#page158">158</a><br/>
+&mdash;&mdash; <i>major</i> (living), lower jaw of, <a href="#page159">159</a><br/>
+Madeira, beds of laterite in, <a href="#page509">509</a><br/>
+&mdash;&mdash;, dike in valley in, <a href="#page513">513</a><br/>
+&mdash;&mdash;, Pliocene leaf-bed and shells in lavas of, <a href="#page532">532</a><br/>
+&mdash;&mdash;, Miocene volcanic rocks of, <a href="#page536">536</a><br/>
+&mdash;&mdash;, wind, removing scoriæ in, <a href="#page97">97</a><br/>
+Maestricht beds and their fossils, <a href="#page283">283</a><br/>
+Maffiotte, Don Pedro, cited, <a href="#page538">538</a><br/>
+<i>Magas pumila,</i> White Chalk, <a href="#page294">294</a><br/>
+Magnesian Limestone defined, <a href="#page38">38</a><br/>
+&mdash;&mdash; and marl-slate, <a href="#page387">387</a><br/>
+Magnetite, <a href="#page500">500</a><br/>
+Maidstone, Upper Cretaceous fossils of, <a href="#page297">297</a><br/>
+Malacolite, <a href="#page502">502</a><br/>
+Malaise, Professor, on Engihoul cave, <a href="#page157">157</a><br/>
+Mammalia, anterior to Paris gypsum, table of, <a href="#page329">329</a><br/>
+&mdash;&mdash;, extinct, coeval with man, <a href="#page152">152</a>, <a href="#page157">157</a><br/>
+&mdash;&mdash;, fossil, of Middle Purbeck, <a href="#page325">325</a><br/>
+&mdash;&mdash;, fossil, in Pliocene in Val d&rsquo;Arno, <a href="#page208">208</a><br/>
+&mdash;&mdash;, fossil, in the Crag, <a href="#page193">193</a>, <a href="#page197">197</a><br/>
+&mdash;&mdash;, fossil, of Vienna basin, <a href="#page225">225</a><br/>
+&mdash;&mdash; of the Limagne d&rsquo;Auvergne, <a href="#page234">234</a><br/>
+&mdash;&mdash; of Siwalik Hills, <a href="#page227">227</a><br/>
+&mdash;&mdash; of the Stonesfield slate, <a href="#page345">345</a><br/>
+&mdash;&mdash;, <i>teeth of Post-pliocene</i>, <a href="#page165">165</a><br/>
+Mammalia and testacea, comparative longevity of, <a href="#page162">162</a><br/>
+Mammoth, rude carving of in Perigord cave, <a href="#page150">150</a><br/>
+&mdash;&mdash; in Scotch till, <a href="#page175">175</a><br/>
+&mdash;&mdash; <i>See</i> Elephas primigenius.<br/>
+Man, antiquity of, <a href="#page152">152</a><br/>
+Manfredi on amount of subaërial denudation, <a href="#page114">114</a><br/>
+Mantell, Dr., on iguanodon of Wealden, <a href="#page313">313</a><br/>
+&mdash;&mdash;, on Oxford Clay belemnites, <a href="#page340">340</a><br/>
+&mdash;&mdash;, on Wealden fossils, <a href="#page316">316</a><br/>
+<i>Mantellia nidiformis,</i> Purbeck, <a href="#page331">331</a><br/>
+Map of Chalk formation in France, <a href="#page305">305</a><br/>
+&mdash;&mdash; of Eocene tertiary basins, <a href="#page250">250</a><br/>
+&mdash;&mdash; of Hallstadt and St. Cassian beds, <a href="#page376">376</a><br/>
+Marble defined, <a href="#page37">37</a><br/>
+&mdash;&mdash; of Carrara, metamorphic, <a href="#page599">599</a><br/>
+Marcou, M., on age of Wealden beds, <a href="#page319">319</a><br/>
+Margaric acid, <a href="#page591">591</a><br/>
+Marine fauna of the Carboniferous, <a href="#page432">432</a><br/>
+&mdash;&mdash; beds underlying the London Clay, <a href="#page269">269</a><br/>
+&mdash;&mdash; and brackish-water strata in coal, <a href="#page404">404</a><br/>
+&mdash;&mdash; strata, how distinguished from fresh-water, <a href="#page53">53-59</a><br/>
+Marl from Lake Superior, <a href="#page63">63</a><br/>
+&mdash;&mdash; and marl-slate defined, <a href="#page38">38</a><br/>
+&mdash;&mdash;, red, green, and white, of Auvergne, <a href="#page233">233</a><br/>
+&mdash;&mdash; slate of Middle Permian, <a href="#page387">387</a><br/>
+Marsupials, extinct, of Australia, <a href="#page159">159</a><br/>
+<i>Marsupites Milleri,</i> White Chalk, <a href="#page294">294</a><br/>
+Massachusetts, plumbago of, <a href="#page583">583</a><br/>
+<i>Mastodon arvernensis,</i> molar of, Norwich crag, <a href="#page193">193</a><br/>
+&mdash;&mdash; <i>giganteus,</i> in United States after the drift, <a href="#page183">183</a><br/>
+Mayence basin tertiaries, <a href="#page242">242</a><br/>
+May-Hill Sandstone, <a href="#page468">468</a><br/>
+Mechanical and chemical deposits, <a href="#page60">60</a><br/>
+&mdash;&mdash; theory of cleavage, <a href="#page592">592</a><br/>
+Mediterranean, one zoological province, <a href="#page127">127</a><br/>
+<i>Megalodon cucullatus,</i> Devonian, <a href="#page452">452</a><br/>
+<i>Melania inquinata (Cerithium melanoides)</i>, <a href="#page55">55</a>, <a href="#page268">268</a><br/>
+<i>Melania turritissima,</i> Bembridge, <a href="#page253">253</a><br/>
+<i>Melanopsis buccinoidea</i>, <a href="#page55">55</a><br/>
+Melaphyre, a variety of basalt, <a href="#page504">504</a><br/>
+Menevian beds and their fossils, <a href="#page484">484</a><br/>
+Mesozoic, term explained, <a href="#page123">123</a><br/>
+&mdash;&mdash; and Cainozoic periods, gap between the, <a href="#page282">282</a><br/>
+&mdash;&mdash; and Palæozoic rocks, limits of the, <a href="#page385">385</a><br/>
+Metals, relative age of different, <a href="#page614">614</a><br/>
+Metamorphic limestone, <a href="#page579">579</a><br/>
+&mdash;&mdash; strata, origin of, <a href="#page579">579</a><br/>
+&mdash;&mdash; theory, objections to, considered, <a href="#page587">587</a><br/>
+&mdash;&mdash; rocks defined, <a href="#page32">32</a><br/>
+Metamorphic rocks, <a href="#page576">576</a><br/>
+&mdash;&mdash;, cleavage of, <a href="#page588">588</a><br/>
+&mdash;&mdash;, scarcity of lime in, <a href="#page604">604</a><br/>
+&mdash;&mdash;, ages of, <a href="#page597">597</a><br/>
+&mdash;&mdash;, order of succession of, <a href="#page602">602</a><br/>
+&mdash;&mdash;, uniformity of mineral character in, <a href="#page602">602</a><br/>
+Metamorphism, hydrothermal action producing, <a href="#page584">584</a><br/>
+Metamorphosis of trilobites, <a href="#page471">471</a>, <a href="#page487">487</a><br/>
+Meteorites, minerals in, <a href="#page501">501</a><br/>
+Mexico, Gulf of, terrestrial remains washed into, <a href="#page128">128</a><br/>
+Meyer, Mr. Karl, on fossil shells of Madeira, <a href="#page537">537</a><br/>
+&mdash;&mdash;, M. H. von, on reptiles in coal, <a href="#page407">407</a><br/>
+&mdash;&mdash;, on Wealden of Germany, <a href="#page319">319</a><br/>
+Miascite, <a href="#page558">558</a><br/>
+Mica and its varieties, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+&mdash;&mdash;, how deposited, <a href="#page40">40</a><br/>
+&mdash;&mdash; schist or micaceous schist, <a href="#page578">578</a><br/>
+Micaceous sandstone, origin of, <a href="#page36">36</a><br/>
+<i>Micraster cor-anguinum</i>, <a href="#page294">294</a><br/>
+<i>Microconchus carbonarius,</i> coal-measures, <a href="#page405">405</a><br/>
+<i>Microlestes antiquus,</i> Upper Trias, <a href="#page368">368</a><br/>
+Migrations of quadrupeds, <a href="#page161">161</a><br/>
+Miliolite limestone, <a href="#page274">274</a><br/>
+Miller, Hugh, on Old Red Sandstone fish, <a href="#page443">443</a><br/>
+&mdash;&mdash;, on salt lakes, <a href="#page375">375</a><br/>
+Milne Edwards, Mr., on Palæozoic corals, <a href="#page432">432</a><br/>
+Minchinhampton, Great Oolite of, <a href="#page344">344</a><br/>
+Mineral composition a test of age of volcanic rocks, <a href="#page523">523</a><br/>
+&mdash;&mdash; a test of age of plutonic rocks, <a href="#page565">565</a><br/>
+&mdash;&mdash; a test of age of strata, <a href="#page124">124</a><br/>
+&mdash;&mdash; character of hypogene rocks, <a href="#page602">602</a><br/>
+&mdash;&mdash; springs of Auvergne, <a href="#page604">604</a><br/>
+Mineral veins, <a href="#page605">605</a><br/>
+&mdash;&mdash; formed in fissures, <a href="#page606">606</a><br/>
+&mdash;&mdash;, successive formation of, <a href="#page609">609</a><br/>
+&mdash;&mdash;, swelling and contraction of, <a href="#page611">611</a><br/>
+&mdash;&mdash;, relative age of, <a href="#page614">614</a><br/>
+&mdash;&mdash;, pebbles in, <a href="#page608">608</a><br/>
+Mineralisation of organic remains, <a href="#page65">65</a><br/>
+Minerals in meteorites, <a href="#page501">501</a><br/>
+&mdash;&mdash;, table of the most abundant in hypogene rocks, <a href="#page499">499</a><br/>
+Miocene of Bordeaux and south of France, <a href="#page214">214</a><br/>
+&mdash;&mdash; and Eocene, line between the, <a href="#page230">230</a>, <a href="#page251">251</a><br/>
+&mdash;&mdash;, Lower, of England, <a href="#page244">244</a><br/>
+&mdash;&mdash;, Lower, of Germany and Croatia, <a href="#page242">242</a><br/>
+&mdash;&mdash;, Lower, of Central France, <a href="#page231">231</a><br/>
+&mdash;&mdash;, Lower, of Italy, <a href="#page244">244</a><br/>
+&mdash;&mdash;, Lower, of Nebraska, United States, <a href="#page248">248</a><br/>
+&mdash;&mdash;, term defined, <a href="#page143">143</a><br/>
+&mdash;&mdash;, Upper, of the Bolderberg, <a href="#page224">224</a><br/>
+&mdash;&mdash;, Upper, of France, <a href="#page211">211</a><br/>
+&mdash;&mdash;, Upper, of Italy, <a href="#page226">226</a><br/>
+&mdash;&mdash;, Upper, of Greece, <a href="#page226">226</a><br/>
+&mdash;&mdash;, Upper, of India, <a href="#page226">226</a><br/>
+&mdash;&mdash;, Upper, of Vienna basin, <a href="#page224">224</a><br/>
+Mississippi, sediment of, used as a test of denudation by rivers, <a href="#page114">114</a><br/>
+&mdash;&mdash; valley, deposition and denudation in the, <a href="#page102">102</a><br/>
+Mitchell, Mr., on Aralia fruit in Alum Bay, Eocene, <a href="#page263">263</a><br/>
+Mitchell, Sir T., on Wellington caves, <a href="#page158">158</a><br/>
+Mitchell, Rev. Hugh, on Pteraspis, <a href="#page446">446</a><br/>
+<i>Mitra Scabra,</i> Barton clay, <a href="#page259">259</a><br/>
+Mitscherlich, on Isomorphism, <a href="#page502">502</a><br/>
+<i>Modiola acuminata,</i> Permian, <a href="#page387">387</a><br/>
+Moel Tryfaen, shells found at, <a href="#page181">181</a><br/>
+Mohs on isomorphism, <a href="#page502">502</a><br/>
+Molasse, Lower, of Switzerland, <a href="#page235">235</a><br/>
+&mdash;&mdash;, Middle, or Marine, of Switzerland, <a href="#page223">223</a><br/>
+&mdash;&mdash;, Upper, fresh-water, of Switzerland, <a href="#page217">217</a><br/>
+&mdash;&mdash;, term explained, <a href="#page217">217</a><br/>
+Mollusca. <i>See</i> Shells.<br/>
+&mdash;&mdash;, longevity of species of, <a href="#page162">162</a><br/>
+&mdash;&mdash; of Hallstadt beds, <a href="#page377">377</a><br/>
+&mdash;&mdash;, value of, in classification, <a href="#page142">142</a><br/>
+&mdash;&mdash; of the Carboniferous, <a href="#page435">435</a><br/>
+Monitor of Thuringia, <a href="#page463">463</a><br/>
+Monoclinic feldspars, <a href="#page501">501</a><br/>
+Monod, flora of the Lower Molasse at, <a href="#page236">236</a><br/>
+Mons, unconformable strata near, <a href="#page95">95</a><br/>
+Montblanc, talcose granite of, <a href="#page568">568</a><br/>
+&mdash;&mdash; Dor, Auvergne, extinct volcanoes of, <a href="#page232">232</a><br/>
+&mdash;&mdash;, age of volcano of, <a href="#page541">541</a><br/>
+Monte Bolca, fossil fish of, <a href="#page543">543</a><br/>
+&mdash;&mdash; Calvo, section of cross stratification, <a href="#page44">44</a><br/>
+&mdash;&mdash; Mario, age of volcanic deposits of, <a href="#page533">533</a><br/>
+&mdash;&mdash; Nuovo, formed 1538, <a href="#page525">525</a><br/>
+Montmartre, gypseous series of, <a href="#page270">270</a><br/>
+Monts Dome, Auvergne, extinct volcanoes, <a href="#page495">495</a><br/>
+Moore, Mr. C., on Rhætic beds, <a href="#page366">366</a><br/>
+&mdash;&mdash;, on Upper Trias quadrupeds, <a href="#page369">369</a><br/>
+Moraines described, <a href="#page169">169</a><br/>
+Morea, cretaceous volcanic rocks of, <a href="#page544">544</a><br/>
+Mortillet, M. de, on ice-erosion of lake-basins, <a href="#page184">184</a><br/>
+Morton, Dr., on age of American cretaceous rocks, <a href="#page307">307</a><br/>
+<i>Mosasaurus Camperi,</i> Chalk, <a href="#page284">284</a><br/>
+Mountain Limestone, fossils of the, <a href="#page433">433-8</a><br/>
+Mull, Isle of, leaf-bed, <a href="#page247">247</a><br/>
+Münster, Count, on fossils of Solenhofen, <a href="#page337">337</a><br/>
+Murchison, Sir R., on brackish-water strata in coal, <a href="#page404">404</a><br/>
+&mdash;&mdash;, on Devonian series, <a href="#page439">439</a>, <a href="#page449">449</a>, <a href="#page454">454</a><br/>
+&mdash;&mdash;, on Devonian ichthyolites, <a href="#page453">453</a><br/>
+&mdash;&mdash;, on Eocene igneous rocks, <a href="#page278">278</a><br/>
+&mdash;&mdash;, on Llandovery beds, <a href="#page468">468</a><br/>
+&mdash;&mdash;, on Laurentian gneiss of Scotland, <a href="#page492">492</a><br/>
+&mdash;&mdash;, on metamorphic rocks of North Highlands, <a href="#page601">601</a><br/>
+&mdash;&mdash;, on Monte Bolca fish-beds, <a href="#page543">543</a><br/>
+&mdash;&mdash;, on name Permian, <a href="#page385">385</a><br/>
+&mdash;&mdash;, on Old Red Sandstone, <a href="#page449">449</a><br/>
+&mdash;&mdash;, on Palæozoic strata, Queenaig, <a href="#page112">112</a>, <a href="#page113">113</a><br/>
+&mdash;&mdash;, on protrusion of solid granite, <a href="#page574">574</a><br/>
+&mdash;&mdash;, on Silurian, <a href="#page458">458</a>, <a href="#page459">459</a>, <a href="#page461">461</a>, <a href="#page467">467</a>, <a href="#page470">470</a>, <a href="#page473">473</a>, <a href="#page475">475</a><br/>
+&mdash;&mdash;, on Tertiary volcanic rocks of Italy, <a href="#page533">533</a><br/>
+&mdash;&mdash;, on thickness of chalk in Russia, <a href="#page287">287</a><br/>
+&mdash;&mdash;, on thickness of the Trias, <a href="#page369">369</a><br/>
+&mdash;&mdash;, on the Upper &ldquo;Old Red&rdquo;, <a href="#page468">468</a><br/>
+<i>Murchisonia gracilis</i>, <a href="#page479">479</a><br/>
+<i>Murex vaginatus</i>, <a href="#page204">204</a><br/>
+Muschelkalk, fossils of the, <a href="#page378">378</a><br/>
+Muscovite, or common mica, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+Musk-ox, fossil, in Thames valley, <a href="#page161">161</a><br/>
+<i>Myliobates Edwardsi,</i> Bracklesham, <a href="#page261">261</a><br/>
+<i>Mytilus septifer,</i> Permian, <a href="#page387">387</a><br/><br/>
+</p>
+
+<p class="noindent">
+N<small>APLES</small>, Post-pliocene volcanic rocks of, <a href="#page525">525</a><br/>
+&mdash;&mdash;, escape of carbonic acid near, <a href="#page604">604</a><br/>
+<i>Natica clausa,</i> Scotch drift, <a href="#page176">176</a><br/>
+&mdash;&mdash; <i>helicoides,</i> Chillesford beds, <a href="#page192">192</a><br/>
+Natrolite, <a href="#page500">500</a><br/>
+<i>Nautilus centralis,</i> London Clay, <a href="#page266">266</a><br/>
+&mdash;&mdash; <i>Danicus,</i> Faxoe Chalk, <a href="#page286">286</a><br/>
+&mdash;&mdash; <i>plicatus,</i> Hythe beds, <a href="#page309">309</a><br/>
+&mdash;&mdash; <i>truncatus,</i> Lias, <a href="#page356">356</a><br/>
+&mdash;&mdash; <i>ziczac (Aturia ziczac)</i>, <a href="#page266">266</a><br/>
+Nebraska, Miocene strata of, <a href="#page248">248</a><br/>
+Necker, M., on &ldquo;underlying&rdquo; igneous rocks, <a href="#page562">562</a><br/>
+&mdash;&mdash;, on dikes in Vesuvius, <a href="#page526">526</a><br/>
+Neocomian, Upper, <a href="#page308">308</a><br/>
+&mdash;&mdash;, Middle, <a href="#page312">312</a><br/>
+&mdash;&mdash;, Lower, <a href="#page312">312</a><br/>
+&mdash;&mdash;, use of the term, <a href="#page282">282</a><br/>
+Neolithic era, <a href="#page147">147</a><br/>
+Neozoic type of corals, <a href="#page431">431</a><br/>
+<i>Nerinæa Goodhallii,</i> Coral Rag, <a href="#page339">339</a><br/>
+Nerinæan limestone, <a href="#page340">340</a><br/>
+<i>Nerita conoidea (N. Schmidelliana)</i>, <a href="#page275">275</a><br/>
+&mdash;&mdash; <i>costulata,</i> Great Oolite, <a href="#page345">345</a><br/>
+&mdash;&mdash; <i>granulosa</i>, <a href="#page55">55</a><br/>
+<i>Neritina concava,</i> Headon, <a href="#page255">255</a><br/>
+&mdash;&mdash; <i>globulus</i>, <a href="#page55">55</a><br/>
+Neufchâtel, coins and iron tools in lake of, <a href="#page149">149</a><br/>
+Newberry, Dr., on flora of American cretaceous rocks, <a href="#page307">307</a><br/>
+Newcastle coal-field, faults in, <a href="#page90">90</a><br/>
+Newfoundland bank described, <a href="#page106">106</a><br/>
+New Jersey, mastodon in, <a href="#page183">183</a><br/>
+New Madrid, &ldquo;Sunk Country&rdquo; in, <a href="#page402">402</a><br/>
+New Red sandstone of Connecticut Valley, <a href="#page381">381</a><br/>
+&mdash;&mdash;, trappean rocks of the, <a href="#page545">545</a><br/>
+New York, Devonian strata of, <a href="#page456">456</a><br/>
+&mdash;&mdash;, Cambrian strata of, <a href="#page490">490</a><br/>
+&mdash;&mdash;, Silurian strata of, <a href="#page478">478</a><br/>
+&mdash;&mdash;, Laurentian strata of, <a href="#page491">491</a><br/>
+Niagara Limestone, fossils of the, <a href="#page479">479</a><br/>
+Nidau, iron tools in lake of, <a href="#page148">148</a><br/>
+Nile, homogeneous mud of the, <a href="#page154">154</a><br/>
+Ninety-fathom dike in coal, <a href="#page90">90</a><br/>
+<i>Nipadites ellipticus,</i> Sheppey, <a href="#page264">264</a><br/>
+Nodules in strata, how formed, <a href="#page63">63</a><br/>
+<i>Noeggerathia cuneifolia,</i> Permian, <a href="#page393">393</a><br/>
+Nomenclature of rocks, <a href="#page140">140</a><br/>
+&mdash;&mdash; of volcanic minerals, <a href="#page499">499</a><br/>
+Norfolk cliffs, drift of, <a href="#page190">190</a><br/>
+North America. <i>See</i> America.<br/>
+Norway, Cambrian of, <a href="#page489">489</a><br/>
+&mdash;&mdash;, foliation of crystalline schists in, <a href="#page595">595</a><br/>
+&mdash;&mdash;, granite veins in gneiss of, <a href="#page573">573</a><br/>
+&mdash;&mdash;, granite altering fossiliferous strata in, <a href="#page581">581</a><br/>
+Norwich, or Fluvio-marine crag, <a href="#page193">193</a><br/>
+Nova Scotia coal-measures, <a href="#page409">409</a><br/>
+&mdash;&mdash; coal, reptiles and shells in, <a href="#page414">414</a><br/>
+&mdash;&mdash;, folding and denudation of beds in, <a href="#page417">417</a><br/>
+<i>Nucula Cobboldiæ,</i> Crag, <a href="#page194">194</a><br/>
+<i>Nummulites lævigata,</i> Bracklesham, <a href="#page260">260</a><br/>
+&mdash;&mdash; <i>Puschi,</i> Pyrenees, <a href="#page278">278</a><br/>
+&mdash;&mdash; <i>variolaria,</i> Bracklesham, <a href="#page259">259</a><br/>
+Nummulitic formations, <a href="#page277">277</a><br/><br/>
+</p>
+
+<p class="noindent">
+<i>O<small>BOLUS</small> A<small>POLLINIS</small>,</i> in Russian grit, <a href="#page478">478</a><br/>
+Obsidian, <a href="#page505">505</a><br/>
+Oceanic areas, permanence of, <a href="#page117">117</a><br/>
+Œningen, Upper Miocene beds of, <a href="#page215">215</a><br/>
+Oeynhausen, M. von, on Cornish granite veins, <a href="#page560">560</a><br/>
+<i>Ogygia Buchii</i>, <a href="#page474">474</a><br/>
+<i>Oldhamia radiata: O. antiqua</i>, <a href="#page487">487</a><br/>
+Old Red Sandstone, Upper, <a href="#page440">440</a><br/>
+&mdash;&mdash;, Middle, with fish, <a href="#page443">443</a><br/>
+&mdash;&mdash;, Lower, <a href="#page446">446</a><br/>
+&mdash;&mdash;, trap of the, <a href="#page547">547</a><br/>
+&mdash;&mdash;, classification of, <a href="#page439">439</a><br/>
+<i>Olenus micrurus</i>, <a href="#page484">484</a><br/>
+Oligocene, term for Lower Miocene, <a href="#page230">230</a>, <a href="#page244">244</a><br/>
+Oligoclase, <a href="#page499">499</a>, <a href="#page500">500</a><br/>
+<i>Oliva Dufresnii,</i> Bolderberg, Belgium, <a href="#page224">224</a><br/>
+Olivine, <a href="#page499">499</a><br/>
+<i>Omphyma turbinatum,</i> Silurian, <a href="#page466">466</a><br/>
+<i>Onchus tenuistriatus,</i> Silurian, <a href="#page460">460</a><br/>
+Oolite, classification and physical geography of the, <a href="#page321">321</a><br/>
+&mdash;&mdash;, defined, <a href="#page37">37</a><br/>
+&mdash;&mdash;, Inferior, fossils of the, <a href="#page349">349</a>, <a href="#page350">350</a><br/>
+&mdash;&mdash; and Lias, origin of the, <a href="#page364">364</a><br/>
+&mdash;&mdash; and Chalk, Palæontological break between, <a href="#page338">338</a><br/>
+Oolitic strata, palæontological relations of, <a href="#page351">351</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page545">545</a><br/>
+<i>Ophioderma tenuibrachiata,</i> Lias, <a href="#page357">357</a><br/>
+Oppel on zones of Lias, <a href="#page353">353</a><br/>
+Orbigny, Alcide de, on foraminifera of Vienna basin, <a href="#page225">225</a><br/>
+&mdash;&mdash;, on orbitoidal limestone, <a href="#page279">279</a><br/>
+&mdash;&mdash;, on Pisolitic limestone, <a href="#page285">285</a><br/>
+&mdash;&mdash;, on Sénonian, <a href="#page302">302</a><br/>
+<i>Oreodaphne Heerii,</i> Italian Pliocene, <a href="#page209">209</a><br/>
+Organic remains, mineralisation of, <a href="#page65">65</a><br/>
+&mdash;&mdash;, tests of age of strata, <a href="#page125">125</a><br/>
+&mdash;&mdash;, tests of age of volcanic rocks, <a href="#page522">522</a><br/>
+&mdash;&mdash;, geological provinces of, <a href="#page127">127</a><br/>
+Oriskany Sandstone, <a href="#page478">478</a><br/>
+<i>Orthis elegantula,</i> Ludlow, <a href="#page46">46</a><br/>
+&mdash;&mdash; <i>grandis,</i> Caradoc beds, <a href="#page470">470</a><br/>
+&mdash;&mdash; <i>tricenaria,</i> Bala beds, <a href="#page470">470</a><br/>
+&mdash;&mdash; <i>vespertilio,</i> Bala beds, <a href="#page470">470</a><br/>
+<i>Orthoceras duplex,</i> <a href="#page474">474</a><br/>
+&mdash;&mdash; <i>Ludense,</i> Silurian, <a href="#page463">463</a><br/>
+&mdash;&mdash; <i>laterale</i>, <a href="#page436">436</a><br/>
+&mdash;&mdash; <i>ventricosum,</i> Silurian, <a href="#page462">462</a><br/>
+Orthoclase, <a href="#page499">499</a>, <a href="#page500">500</a><br/>
+Orthoclastic feldspars, <a href="#page501">501</a><br/>
+Osborne or St. Helen&rsquo;s series, Eocene, <a href="#page255">255</a><br/>
+<i>Osteolepis,</i> Old Red Sandstone, <a href="#page444">444</a><br/>
+<i>Ostraceon,</i> spine of, Bracklesham, <a href="#page261">261</a><br/>
+<i>Ostrea acuminata,</i> Fuller&rsquo;s earth, <a href="#page349">349</a><br/>
+&mdash;&mdash; <i>carinata,</i> Chalk marl, <a href="#page300">300</a><br/>
+&mdash;&mdash; <i>columba,</i> Chloritic sand, <a href="#page300">300</a><br/>
+&mdash;&mdash; <i>gregarea,</i> Coral Rag, <a href="#page339">339</a><br/>
+&mdash;&mdash; <i>deltoidea,</i> Kimmeridge clay, <a href="#page336">336</a><br/>
+&mdash;&mdash; <i>distorta,</i> Middle Purbeck, <a href="#page324">324</a><br/>
+&mdash;&mdash; <i>expansa,</i> Portland sand, <a href="#page336">336</a><br/>
+&mdash;&mdash; <i>Marshii,</i> Oolite, <a href="#page351">351</a><br/>
+&mdash;&mdash; <i>vesicularis,</i> Chalk, <a href="#page295">295</a><br/>
+<i>Otodus obliquus,</i> Bracklesham, <a href="#page262">262</a><br/>
+Outcrop of strata, <a href="#page83">83</a><br/>
+Overlapping strata, <a href="#page95">95</a><br/>
+Owen, Professor on Archæopteryx, <a href="#page337">337</a><br/>
+&mdash;&mdash;, on Eocene Zeuglodon, <a href="#page279">279</a><br/>
+&mdash;&mdash;, on footprints in Trias, <a href="#page382">382</a><br/>
+&mdash;&mdash;, on fauna of Sheppey, <a href="#page265">265</a>, <a href="#page267">267</a><br/>
+&mdash;&mdash;, on Gastornis Parisiensis, <a href="#page276">276</a><br/>
+&mdash;&mdash;, on Labyrinthodon, <a href="#page370">370</a><br/>
+&mdash;&mdash;, on mammalia of Stonesfield, <a href="#page347">347</a><br/>
+&mdash;&mdash;, on Purbeck mammalia, <a href="#page326">326</a>, <a href="#page328">328</a><br/>
+&mdash;&mdash;, on reptiles of coal, <a href="#page407">407</a>, <a href="#page414">414</a><br/>
+&mdash;&mdash;, on zoological provinces of extinct animals, <a href="#page160">160</a><br/>
+<i>Ox, tooth of</i> (recent), <a href="#page165">165</a><br/>
+Oxford Clay, thickness and fossils of, <a href="#page340">340</a><br/><br/>
+</p>
+
+<p class="noindent">
+P<small>AGHAM</small>, erratic block at, <a href="#page182">182</a><br/>
+<i>Palæaster asperimus,</i> <a href="#page472">472</a><br/>
+<i>Palæchinus gigas,</i> Mountain Limestone, <a href="#page43">43</a><br/>
+<i>Palæocoma tenuibrachiata,</i> Lias, <a href="#page357">357</a><br/>
+<i>Palæoniscus,</i> Permian fish, <a href="#page389">389</a><br/>
+&mdash;&mdash; <i>comptus, P. elegans, P. glaphyrus</i>, <a href="#page390">390</a><br/>
+<i>Palæotherium magnum</i>, <a href="#page254">254</a><br/>
+<i>Palæophis typhoeus,</i> Bracklesham, <a href="#page261">261</a><br/>
+Palæozoic or Paleozoic, term defined, <a href="#page123">123</a><br/>
+&mdash;&mdash; Plutonic rocks, <a href="#page572">572</a><br/>
+&mdash;&mdash; rocks, <a href="#page458">458</a><br/>
+&mdash;&mdash; type of corals, <a href="#page431">431</a><br/>
+Palagonia, dikes of lava in, <a href="#page531">531</a><br/>
+Paleolithic era, <a href="#page147">147</a>, <a href="#page149">149</a><br/>
+&mdash;&mdash;, alluvial deposits of, <a href="#page150">150</a><br/>
+Palm in Swiss Miocene, <a href="#page237">237</a><br/>
+Palma, volcanic crater of, <a href="#page497">497</a><br/>
+<i>Paludina lenta,</i> Hempstead beds, <a href="#page55">55</a><br/>
+&mdash;&mdash; <i>orbicularis,</i> Bembridge, <a href="#page253">253</a><br/>
+<i>Paradoxides Bohemicus</i>, <a href="#page488">488</a><br/>
+&mdash;&mdash; <i>Davidis,</i> Lower Cambrian, <a href="#page485">485</a><br/>
+Parallelism of folded strata for long distances, <a href="#page93">93</a><br/>
+Paris basin, Tertiary group first studied in, <a href="#page141">141</a><br/>
+&mdash;&mdash;, Tertiaries of the, <a href="#page270">270</a><br/>
+<i>Parka decipiens,</i> &ldquo;Old Red,&rdquo; <a href="#page448">448</a><br/>
+Parkfield Colliery, ground-plan of, <a href="#page400">400</a><br/>
+Patagonia, strata of, rich in soda, <a href="#page587">587</a><br/>
+<i>Patella rugosa,</i> Great Oolite, <a href="#page345">345</a><br/>
+Paterson, Dr., on angiosperm of the Coal, <a href="#page429">429</a><br/>
+Peach, Mr. C, cited, <a href="#page601">601</a><br/>
+&mdash;&mdash;, Pteraspis, found by, <a href="#page443">443</a><br/>
+Pearlstone, <a href="#page505">505</a><br/>
+Pebbles in mineral veins, <a href="#page608">608</a><br/>
+&mdash;&mdash; in chalk, <a href="#page292">292</a><br/>
+<i>Pecopteris elliptica,</i> Coal, <a href="#page421">421</a><br/>
+<i>Pecten Beaveri,</i> White Chalk, <a href="#page294">294</a><br/>
+&mdash;&mdash; <i>cinctus,</i> Neocomian, <a href="#page312">312</a><br/>
+&mdash;&mdash; <i>islandicus,</i> Scotch Drift, <a href="#page176">176</a><br/>
+&mdash;&mdash; <i>jacobæus,</i> in tertiary of Sicily, <a href="#page206">206</a><br/>
+&mdash;&mdash; <i>quinque-costatus</i>, <a href="#page300">300</a><br/>
+&mdash;&mdash; <i>Valoniensis,</i> Rhætic beds, <a href="#page366">366</a><br/>
+Pegmatite, <a href="#page553">553</a><br/>
+Penarth beds, <a href="#page366">366</a><br/>
+Pengelly, Mr., on Bovey Tracey lignite, <a href="#page246">246</a><br/>
+&mdash;&mdash;, on flint-knives of Brixham Cave, <a href="#page157">157</a><br/>
+<i>Pentacrinus Briareus,</i> Lias, <a href="#page357">357</a><br/>
+<i>Pentamerus Knightii,</i> Aymestry, <a href="#page461">461</a><br/>
+&mdash;&mdash; <i>oblongus,</i> and <i>P. lirata</i>, <a href="#page469">469</a><br/>
+Pentland Hills, volcanic rocks of the, <a href="#page548">548</a><br/>
+Perigord cave, carving of mammoth in, <a href="#page150">150</a><br/>
+Permanence of continents and oceans, <a href="#page117">117</a><br/>
+Permian Flora, <a href="#page392">392</a><br/>
+&mdash;&mdash; of Germany, <a href="#page393">393</a><br/>
+&mdash;&mdash; strata, thickness of, in north of England, <a href="#page386">386</a><br/>
+&mdash;&mdash;, Upper and Middle, <a href="#page386">386</a>, <a href="#page387">387</a><br/>
+&mdash;&mdash;, Lower, <a href="#page390">390</a><br/>
+<i>Perna Mulleti,</i> Neocomian, <a href="#page310">310</a><br/>
+Petherwyn, Devonian fossils of, <a href="#page450">450</a><br/>
+Petrifaction, process of, <a href="#page67">67</a><br/>
+<i>Petrophiloides Richardsoni,</i> Sheppey, <a href="#page265">25</a><br/>
+<i>Pahcops caudatus,</i> Silurian, <a href="#page467">467</a><br/>
+&mdash;&mdash; <i>latifrons,</i> Devonian, <a href="#page450">450</a><br/>
+<i>Phascolotherium Bucklandi</i>, <a href="#page348">348</a><br/>
+<i>Phasianella Heddingtonensis,</i> and cast, <a href="#page66">66</a><br/>
+Phillippi, on tertiary shells of Sicily, <a href="#page205">205</a><br/>
+Phillips, Professor, on fossils distorted by cleavage, <a href="#page592">592</a><br/>
+&mdash;&mdash;, on ninety fathom dike, <a href="#page90">90</a><br/>
+&mdash;&mdash;, on Wenlock limestone and shale, <a href="#page465">465</a>, <a href="#page467">467</a><br/>
+&mdash;&mdash;, on Yoredale series, <a href="#page395">395</a><br/>
+Phillips, Mr. J. Arthur, on origin of gold of California, <a href="#page617">617</a><br/>
+<i>Phlebopteris contigua,</i> Inferior Oolite, <a href="#page350">350</a><br/>
+Phlogopite, <a href="#page499">499</a>, <a href="#page501">501</a><br/>
+<i>Pholadomya fidicula,</i> Inferior Oolite, <a href="#page350">350</a><br/>
+Phonolite, <a href="#page506">506</a><br/>
+<i>Phorus extensus,</i> London Clay, <a href="#page266">266</a><br/>
+<i>Phragmoceras ventricosum,</i> Silurian, <a href="#page463">463</a><br/>
+<i>Physa Bristovii,</i> Middle Purbeck, <a href="#page325">325</a><br/>
+&mdash;&mdash; <i>columnaris</i>, <a href="#page55">55</a><br/>
+&mdash;&mdash; <i>hypnorum</i>, <a href="#page55">55</a><br/>
+Piedmont, absence of lakes in, <a href="#page186">186</a><br/>
+Pile dwellings of Switzerland, <a href="#page148">148</a><br/>
+Pilton, group of, Devon, <a href="#page449">449</a><br/>
+<i>Pinnularia in Atlantic mud</i>, <a href="#page288">288</a><br/>
+Pinus sylvestris in peat, <a href="#page147">147</a><br/>
+Pisolitic limestone of France, <a href="#page285">285</a><br/>
+Pitchstone, <a href="#page505">505</a><br/>
+<i>Placodus gigas,</i> Muschelkalk, <a href="#page380">380</a><br/>
+Placoids, rare in Old Red Sandstone, <a href="#page443">443</a><br/>
+<i>Plagiaulax Becklesii, jaw and molar of</i>, <a href="#page327">327</a><br/>
+Plagioclastic feldspars, <a href="#page501">501</a><br/>
+<i>Plagiostoma giganteum,</i> Lias, <a href="#page354">354</a><br/>
+&mdash;&mdash; <i>Hoperi,</i> Chalk, <a href="#page300">300</a><br/>
+<i>Planorbis discus,</i> Bembridge, <a href="#page253">253</a><br/>
+&mdash;&mdash; <i>euomphalus</i>, <a href="#page55">55</a>, <a href="#page255">255</a><br/>
+Plants of Bovey Tracey, Miocene, <a href="#page247">247</a><br/>
+&mdash;&mdash;, fossil fresh-water, <a href="#page57">57</a><br/>
+&mdash;&mdash; of the Coal, <a href="#page420">420</a><br/>
+&mdash;&mdash; of the Lias, <a href="#page364">364</a><br/>
+&mdash;&mdash; of the Swiss Upper Miocene, <a href="#page219">219</a><br/>
+Plas Newydd, rock altered by dike near, <a href="#page515">515</a><br/>
+Plastic Clay, Eocene, <a href="#page267">267</a><br/>
+<i>Platanus aceroides,</i> Miocene, <a href="#page221">221</a><br/>
+<i>Platystoma Suessii,</i> Hallstadt, <a href="#page377">377</a><br/>
+Playfair, on amount of subaërial denudation, <a href="#page114">114</a><br/>
+&mdash;&mdash; on faults, <a href="#page87">87</a><br/>
+<i>Plectrodus mirabilis,</i> Ludlow, <a href="#page460">460</a><br/>
+<i>Plesiosaurus dolichodeirus,</i> Lias, <a href="#page361">361</a><br/>
+<i>Pleurotoma attenuata,</i> Bracklesham, <a href="#page262">262</a><br/>
+&mdash;&mdash; <i>exorta,</i> Eocene, <a href="#page57">57</a><br/>
+<i>Pleurotomaria anglica,</i> and cast, <a href="#page66">66</a><br/>
+&mdash;&mdash; <i>carinata (flammigera)</i>, <a href="#page434">434</a><br/>
+&mdash;&mdash; <i>granulata,</i> Inferior Oolite, <a href="#page351">351</a><br/>
+&mdash;&mdash; <i>ornata,</i> Inferior Oolite, <a href="#page351">351</a><br/>
+Plieninger, Professor, on Triassic mammifer, <a href="#page368">368</a><br/>
+Pliocene glacial formations, <a href="#page189">189-92</a><br/>
+&mdash;&mdash; Period, <a href="#page189">189</a><br/>
+&mdash;&mdash; plutonic rocks, <a href="#page565">565</a><br/>
+&mdash;&mdash; strata of Sicily, <a href="#page204">204</a><br/>
+&mdash;&mdash;, term defined, <a href="#page143">143</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page529">529</a><br/>
+Plombières, alkaline waters of, <a href="#page585">585</a><br/>
+Plumbago of Massachusetts, <a href="#page583">583</a><br/>
+Plutonic and sedimentary formations, diagram of, <a href="#page567">567</a><br/>
+&mdash;&mdash;, origin of the term, <a href="#page551">551</a><br/>
+&mdash;&mdash; rocks, Mesozoic, <a href="#page570">570</a><br/>
+&mdash;&mdash;, Recent and Pliocene, <a href="#page565">565</a><br/>
+&mdash;&mdash;, Miocene and Eocene, <a href="#page568">568</a><br/>
+&mdash;&mdash;, uncertain tests of age of, <a href="#page564">564</a><br/>
+&mdash;&mdash; defined, <a href="#page31">31</a><br/>
+<i>Podocarya Bucklandi,</i> Oolite, <a href="#page348">348</a><br/>
+<i>Polypterus</i> of the Nile, <a href="#page444">444</a><br/>
+Polyzoa and Bryozoa, terms explained, <a href="#page197">197</a><br/>
+Pomel, M., on fossil mammalia of the Limagne, <a href="#page235">235</a><br/>
+Ponza Islands, globiform pitchstone of, <a href="#page512">512</a><br/>
+<i>Porites pyriformis,</i> Devonian, <a href="#page451">451</a><br/>
+Porphyritic granite, <a href="#page556">556</a><br/>
+Porphyry, <a href="#page506">506</a><br/>
+Portland, Cycads in dirt-bed of, <a href="#page331">331</a><br/>
+&mdash;&mdash; oolite and sand, <a href="#page334">334</a><br/>
+&ldquo;<i>Portland screw,</i>&rdquo; a cast of a shell, <a href="#page335">335</a><br/>
+Porto Santo, marine shells in volcanic tuff of, <a href="#page536">536</a><br/>
+Post-pliocene period, climate of the, <a href="#page161">161</a><br/>
+&mdash;&mdash; mammalia, teeth of, <a href="#page163">163</a><br/>
+&mdash;&mdash;, term defined, <a href="#page145">145</a><br/>
+&mdash;&mdash; lakes of Switzerland, <a href="#page185">185</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page524">524</a><br/>
+<i>Potamides cinctus</i>, <a href="#page56">56</a><br/>
+<i>Pothocites Grantonii,</i> coal-measures, <a href="#page429">429</a><br/>
+Potsdam Sandstone, <a href="#page480">480</a>, <a href="#page489">489</a><br/>
+Pot-stones in the Chalk, <a href="#page290">290</a><br/>
+Pottsville, coal seams of, <a href="#page400">400</a><br/>
+Powrie, Mr., on Cephalaspis beds, <a href="#page446">446</a><br/>
+&mdash;&mdash;, on Parka decipiens, <a href="#page448">448</a><br/>
+Pratt, Mr., on Eocene Isle of Wight mammalia, <a href="#page254">254</a><br/>
+Predazzo, altered rocks at, <a href="#page571">571</a><br/>
+Pressure, solidifying rocks, <a href="#page65">65</a><br/>
+Prestwich, Mr., on age of Sables inferieurs, <a href="#page276">276</a><br/>
+&mdash;&mdash;, on Chillesford beds, <a href="#page192">192</a><br/>
+&mdash;&mdash;, on Coalbrook Dale insects, <a href="#page405">405</a><br/>
+&mdash;&mdash;, on Eocene strata, <a href="#page267">267</a>, <a href="#page269">269</a><br/>
+&mdash;&mdash;, on faults in coal-measure of Coalbrook Dale, <a href="#page88">88</a><br/>
+&mdash;&mdash;, on shells of London clay, <a href="#page264">264</a><br/>
+&mdash;&mdash;, on thickness of Coralline Crag, <a href="#page198">198</a><br/>
+Prévost, M. Constant, on Paris basin, <a href="#page270">270</a><br/>
+Primary Limestone, <a href="#page579">579</a><br/>
+&mdash;&mdash; rocks, <a href="#page458">458</a><br/>
+&mdash;&mdash;, term defined, <a href="#page123">123</a><br/>
+&ldquo;Primordial Zone&rdquo; of Bohemia, <a href="#page481">481</a>, <a href="#page482">482</a><br/>
+<i>Productus horridus,</i> Permian, <a href="#page388">388</a><br/>
+&mdash;&mdash; <i>semireticulatus (antiquatus)</i>, <a href="#page434">434</a><br/>
+Progressive development indicated by low grade of early mammals, <a href="#page384">384</a><br/>
+Proteaceæ of Aix-la-Chapelle flora, <a href="#page304">304</a><br/>
+&mdash;&mdash; of Lower Molasse, Switzerland, <a href="#page237">237</a><br/>
+&mdash;&mdash; of Œningen beds, <a href="#page221">221</a><br/>
+Protogine, <a href="#page578">578</a><br/>
+Protosaurus of Thuringia, <a href="#page390">390</a>, <a href="#page464">464</a><br/>
+Protrusion of solid granite, <a href="#page574">574</a><br/>
+Provinces of animals and plants, <a href="#page126">126</a><br/>
+<i>Psammodus porosus</i>, <a href="#page437">437</a><br/>
+<i>Pseudocrinites bifasciatus,</i> Silurian, <a href="#page466">466</a><br/>
+<i>Psilophyton princeps,</i> Devonian, <a href="#page455">455</a><br/>
+Pteraspis in Lower Ludlow shale, <a href="#page463">463</a><br/>
+<i>Pterichthys,</i> Old Red Sandstone, <a href="#page445">445</a><br/>
+Pterodactyl of Kentish chalk, <a href="#page297">297</a><br/>
+<i>Pterodactylus anglicus,</i> Old Red, <a href="#page447">447</a><br/>
+&mdash;&mdash; <i>crassirostris,</i> Solenhofen, <a href="#page337">337</a><br/>
+<i>Ptychodus decurrens,</i> White Chalk, <a href="#page297">297</a><br/>
+Pudding-stone or conglomerate, <a href="#page36">36</a><br/>
+&mdash;&mdash;, formation of, <a href="#page62">62</a><br/>
+Pumice, <a href="#page508">508</a><br/>
+Punfield beds, brackish and marine, <a href="#page318">318</a><br/>
+<i>Pupa muscorum</i>, <a href="#page155">155</a><br/>
+&mdash;&mdash; <i>tridens,</i> Loess, <a href="#page56">56</a><br/>
+&mdash;&mdash; <i>vetusta,</i> Coal, <a href="#page415">415</a><br/>
+Purbeck beds, Upper, Middle, and Lower, <a href="#page323">323</a>, <a href="#page324">324</a>, <a href="#page336">336</a><br/>
+&mdash;&mdash;, fossil mammalia of the Middle, <a href="#page325">325</a><br/>
+&mdash;&mdash; marble, <a href="#page324">324</a><br/>
+&mdash;&mdash;, subdivisions of the, <a href="#page333">333</a><br/>
+Purity of coal, cause of, <a href="#page402">402</a><br/>
+<i>Purpura tetragona,</i> Red Crag, <a href="#page196">196</a><br/>
+<i>Purpuroidea nodulata,</i> Great Oolite, <a href="#page345">345</a><br/>
+Puy de Côme, cone and lava-current of, <a href="#page528">528</a><br/>
+&mdash;&mdash; de Tartaret, lava-current and cone of, <a href="#page527">527</a>, <a href="#page542">542</a><br/>
+&mdash;&mdash; de Pariou, crater of the, <a href="#page529">529</a><br/>
+Puzzuoli, elevation of land at, <a href="#page525">525</a><br/>
+<i>Pygopterus mandibularis,</i> Permian, <a href="#page390">390</a><br/>
+Pyrenees, chalk altered by granite in the, <a href="#page570">570</a><br/>
+&mdash;&mdash;, curved strata in, <a href="#page86">86</a><br/>
+&mdash;&mdash;, lamination of clay-slate in, <a href="#page596">596</a><br/>
+Pyroxene group of minerals, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+<i>Pyrula reticulata,</i> Crag, <a href="#page200">200</a><br/><br/>
+</p>
+
+<p class="noindent">
+Q<small>UADER</small>-S<small>ANDSTEIN</small>, Cretaceous age of the, <a href="#page293">293</a><br/>
+Quadrumana of Gers, <a href="#page215">215</a><br/>
+Quadrupeds, extinct, in Paleolithic gravels, <a href="#page152">152</a><br/>
+Quartz, specific gravity of, <a href="#page499">499</a>, <a href="#page500">500</a>, <a href="#page555">555</a><br/>
+Quartzite or Quartz Rock, <a href="#page579">579</a><br/>
+Queenaig, unconformable Palæozoic strata at, <a href="#page112">112</a><br/>
+Quenstedt on zones of Lias, <a href="#page353">353</a><br/><br/>
+</p>
+
+<p class="noindent">
+R<small>ADABOJ</small> Miocene, brown coal of, <a href="#page242">242</a><br/>
+<i>Radiolites foliaceus,</i> White Chalk, <a href="#page306">306</a><br/>
+&mdash;&mdash; <i>Mortoni,</i> White Chalk, <a href="#page295">295</a><br/>
+&mdash;&mdash; <i>radiosa,</i> White Chalk, <a href="#page306">306</a><br/>
+Radnorshire, stratified trap in, <a href="#page549">549</a><br/>
+Rain-prints with worm tracks in Coal, <a href="#page416">416</a><br/>
+&mdash;&mdash;, carboniferous, <a href="#page416">416</a><br/>
+Ramsay, Professor, on break between Upper and Lower Cretaceous, <a href="#page301">301</a><br/>
+&mdash;&mdash;, on breccias in Permian, <a href="#page391">391</a><br/>
+&mdash;&mdash;, on escarpments, <a href="#page104">104</a><br/>
+&mdash;&mdash;, on denudation, <a href="#page98">98</a><br/>
+&mdash;&mdash;, on ice-erosion of lake-basins, <a href="#page184">184</a><br/>
+&mdash;&mdash;, on Lingula Flags, <a href="#page484">484</a><br/>
+&mdash;&mdash;, on position of Tremadoc beds, <a href="#page483">483</a><br/>
+&mdash;&mdash;, on Silurian metamorphic rocks, <a href="#page602">602</a><br/>
+&mdash;&mdash;, on submergence in glacial period, <a href="#page181">181</a><br/>
+&mdash;&mdash;, on thickness of the Lower Trias, <a href="#page372">372</a><br/>
+&mdash;&mdash;, on thickness of Llandeilo beds, <a href="#page475">475</a><br/>
+&mdash;&mdash;, on thickness of the Bala beds, <a href="#page473">473</a><br/>
+&mdash;&mdash;, on volcanic tuffs of Snowdon, <a href="#page549">549</a><br/>
+&mdash;&mdash;, on zones of the Lias, <a href="#page353">353</a><br/>
+<i>Rastrites peregrinus,</i> Llandeilo Flags, <a href="#page473">473</a><br/>
+Rath, Von, on Tridymite, <a href="#page500">500</a><br/>
+Recent Period defined, <a href="#page145">145</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page524">524</a><br/>
+Record, imperfection of, in the earth&rsquo;s crust, <a href="#page138">138</a><br/>
+Red Crag, older Pliocene, <a href="#page194">194</a><br/>
+&mdash;&mdash; Sandstone, Origin of, <a href="#page374">374</a><br/>
+&mdash;&mdash; Sea and Mediterranean, distinct species in, <a href="#page127">127</a><br/>
+Redruth, Cornwall, section of veins in mine, <a href="#page607">607</a><br/>
+Reindeer Period in South of France, <a href="#page149">149</a><br/>
+Relistran mine, pebbles in tin of, <a href="#page609">609</a><br/>
+Reptiles of the Coal, <a href="#page406">406</a>, <a href="#page413">413</a><br/>
+Reptiles of the Lias, <a href="#page360">360</a><br/>
+<i>Retepora flustracea,</i> Permian, <a href="#page388">388</a><br/>
+Rhætic beds between Lias and Trias, <a href="#page366">366</a><br/>
+Rhine, fresh-water strata of the, <a href="#page53">53</a><br/>
+&mdash;&mdash;, loess of the, <a href="#page154">154</a><br/>
+Rhinoceros in drift of Abbeville, <a href="#page153">153</a><br/>
+&mdash;&mdash; <i>leptorhinus (megarhinus),</i> molar of, <a href="#page164">164</a><br/>
+&mdash;&mdash; <i>tichorhinus,</i> molar of, <a href="#page164">164</a><br/>
+Rhode Island, metamorphic rocks of, <a href="#page583">583</a><br/>
+<i>Rhynchonella navicula,</i> Ludlow, <a href="#page460">460</a><br/>
+&mdash;&mdash; <i>octoplicata,</i> White Chalk, <a href="#page294">294</a><br/>
+&mdash;&mdash; <i>spinosa,</i> Inferior Oolite, <a href="#page350">350</a><br/>
+&mdash;&mdash; <i>Wilsoni,</i> Aymestry, <a href="#page462">462</a><br/>
+Richmond, Virginia, Triassic coal-field of, <a href="#page382">382</a><br/>
+Rigi and Speer, Lower Miocene of the, <a href="#page235">235</a><br/>
+<i>Rimula clathrata,</i> Great Oolite, <a href="#page345">345</a><br/>
+Rink, Mr., on Greenland land-ice, <a href="#page171">171</a><br/>
+Ripple-marked sandstone, how formed, <a href="#page46">46</a><br/>
+Rise and fall of land, <a href="#page146">146</a><br/>
+<i>Rissoa Chastelii,</i> Hempstead beds, <a href="#page245">245</a><br/>
+Rivers, denuding powers of, <a href="#page101">101</a>, <a href="#page114">114</a><br/>
+Roches moutonnees described, <a href="#page169">169</a><br/>
+Rock, term defined, <a href="#page26">26</a><br/>
+Rocks altered by volcanic dikes, <a href="#page514">514</a><br/>
+&mdash;&mdash; altered by subterranean gases, <a href="#page586">586</a><br/>
+&mdash;&mdash;, analysis of minerals in, <a href="#page499">499</a><br/>
+&mdash;&mdash;, aqueous or stratified, <a href="#page27">27</a><br/>
+&mdash;&mdash;, classification of, <a href="#page121">121</a><br/>
+&mdash;&mdash;, great thickness of palæozoic, <a href="#page110">110</a><br/>
+&mdash;&mdash;, glacial scorings on, <a href="#page169">169</a><br/>
+&mdash;&mdash;, metamorphic, age of, <a href="#page597">597</a><br/>
+&mdash;&mdash;, plutonic age of, <a href="#page564">564</a><br/>
+&mdash;&mdash;, volcanic, age of, <a href="#page520">520</a><br/>
+&mdash;&mdash;, trappean, <a href="#page497">497</a><br/>
+&mdash;&mdash;, metamorphic, defined, <a href="#page32">32</a><br/>
+&mdash;&mdash;, four classes of contemporaneous, <a href="#page33">33</a><br/>
+&mdash;&mdash;, plutonic, defined, <a href="#page31">31</a><br/>
+&mdash;&mdash;, tests of age of, <a href="#page123">123</a>, <a href="#page125">125</a>, <a href="#page520">520</a>, <a href="#page564">564</a>, <a href="#page597">597</a><br/>
+&mdash;&mdash;, four contemporaneous classes of, <a href="#page122">122</a><br/>
+&mdash;&mdash;, underlying, not always the oldest, <a href="#page122">122</a><br/>
+&mdash;&mdash;, volcanic, defined, <a href="#page29">29</a><br/>
+Rock-salt of Trias, <a href="#page371">371</a><br/>
+&mdash;&mdash;, origin of, <a href="#page374">374</a><br/>
+Rogers, Mr. H. D., on blending of coal-seams, <a href="#page400">400</a><br/>
+&mdash;&mdash;, on Virginian fault, <a href="#page92">92</a><br/>
+Rose, Gustavus, on isomorphism, <a href="#page502">502</a><br/>
+&mdash;&mdash;, on Fifeshire dike, <a href="#page546">546</a><br/>
+&mdash;&mdash;, on quartz in granite, <a href="#page555">555</a><br/>
+Rosso antico, red porphyry of Egypt, <a href="#page506">506</a><br/>
+<i>Rostellaria (Hippocrenes) ampla,</i> London Clay, <a href="#page266">266</a><br/>
+Roth, M., on Miocene of Greece, <a href="#page226">226</a><br/>
+Runn of Cutch, salt of, <a href="#page375">375</a><br/>
+Rupelian beds of Dumont, <a href="#page241">241</a>, <a href="#page242">242</a><br/>
+Russia, glaciation of, <a href="#page174">174</a><br/>
+&mdash;&mdash;, Devonian of, <a href="#page454">454</a><br/>
+&mdash;&mdash;, Silurian strata of, <a href="#page478">478</a><br/><br/>
+</p>
+
+<p class="noindent">
+S<small>AARBRUCK</small>, reptiles in coal-field of, <a href="#page406">406</a><br/>
+<i>Sabal major,</i> Lower Miocene, <a href="#page237">237</a><br/>
+Sables de Bracheux, <a href="#page276">276</a><br/>
+&mdash;&mdash; moyens, Paris basin, <a href="#page273">273</a><br/>
+Sahlite, <a href="#page502">502</a><br/>
+St. Abb&rsquo;s Head, curved strata of, <a href="#page76">76</a><br/>
+&mdash;&mdash;, unconformable stratification at, <a href="#page94">94</a><br/>
+St. Andrews, carboniferous trap-rocks of, <a href="#page545">545</a><br/>
+St. Cassian, fossil mollusca of, <a href="#page377">377</a><br/>
+&mdash;&mdash; and Hallstadt beds, <a href="#page376">376</a><br/>
+St. David&rsquo;s, Menevian beds of, <a href="#page485">485</a><br/>
+St. Mary&rsquo;s, shells of, <a href="#page539">539</a><br/>
+Salt, rock, origin of, <a href="#page372">372</a><br/>
+Salter, Mr., on fossils of Arenig group, <a href="#page476">476</a><br/>
+&mdash;&mdash;, on Menevian beds, <a href="#page485">485</a><br/>
+&mdash;&mdash;, on Tremadoc fossils, <a href="#page483">483</a><br/>
+Sandberger, Dr. F., on Mayence basin, <a href="#page242">242</a><br/>
+Sandstone, New Red, <a href="#page369">369</a><br/>
+&mdash;&mdash;, Old Red, <a href="#page439">439</a><br/>
+&mdash;&mdash; slab with cracks, <a href="#page317">317</a><br/>
+&mdash;&mdash;, slab of ripple-marked, <a href="#page45">45</a><br/>
+&mdash;&mdash; slab with footprints, <a href="#page408">408</a><br/>
+<i>Sao hirsuta</i>, <a href="#page488">488</a><br/>
+Saurians of the Lias, <a href="#page361">361</a><br/>
+&mdash;&mdash;, sudden destruction of, <a href="#page362">362</a><br/>
+<i>Saurichthys apicalis,</i> Rhætic Beds, <a href="#page367">367</a><br/>
+Saussure, on vertical conglomerates, <a href="#page73">73</a><br/>
+<i>Saxicava rugosa,</i> Scotch drift, <a href="#page176">176</a><br/>
+Saxony, beds of minerals in, <a href="#page609">609</a><br/>
+Scandinavia, glaciation of, <a href="#page174">174</a><br/>
+<i>Scaphites æqualis,</i> Chloritic marl, <a href="#page299">299</a><br/>
+Scapolite, <a href="#page506">506</a><br/>
+Scheerer on action of water in metamorphism, <a href="#page585">585</a><br/>
+Schist, mica, <a href="#page578">578</a><br/>
+&mdash;&mdash;, argillaceous, <a href="#page579">579</a><br/>
+&mdash;&mdash;, hornblende, <a href="#page578">578</a><br/>
+<i>Schizodus Schlotheimi,</i> Permian, <a href="#page387">387</a><br/>
+&mdash;&mdash; <i>truncatus,</i> Permian, <a href="#page387">387</a><br/>
+Schmerling, Dr., on Liége caverns, <a href="#page157">157</a><br/>
+Schorl-rock, and schorly granite, <a href="#page557">557</a><br/>
+Schwab, M., on Celtic coins in lake-dwellings, <a href="#page149">149</a><br/>
+<i>Scoliostoma,</i> St. Cassian, <a href="#page377">377</a><br/>
+Scoresby, on Arctic icebergs, <a href="#page172">172</a><br/>
+Scoriaceous lava, <a href="#page507">507</a><br/>
+Scoriæ, <a href="#page508">508</a><br/>
+Scotland, &ldquo;Fundamental gneiss&rdquo; of, <a href="#page493">493</a><br/>
+&mdash;&mdash;, Old Red Sandstone of, <a href="#page440">440</a><br/>
+&mdash;&mdash;, glaciation of, <a href="#page175">175</a><br/>
+Screws, fossil, internal casts of shells, <a href="#page66">66</a><br/>
+Scrope, Mr., on Isle of Ponza, globiform pitchstone, <a href="#page512">512</a><br/>
+&mdash;&mdash;, on minerals in lava, <a href="#page524">524</a><br/>
+&mdash;&mdash;, on water in lava, <a href="#page555">555</a><br/>
+Scudder, Mr., on Devonian insects of Canada, <a href="#page457">457</a><br/>
+Sea, apparent fall of, caused by rise of land, <a href="#page70">70</a><br/>
+&mdash;&mdash;, denuding power of the, <a href="#page105">105</a><br/>
+&mdash;&mdash;, deep soundings in, <a href="#page287">287</a><br/>
+&mdash;&mdash;, mean depth of the, <a href="#page118">118</a><br/>
+&mdash;&mdash; cliffs, inland, <a href="#page103">103</a><br/>
+Secondary and Tertiary, gap between the, <a href="#page281">281</a><br/>
+&mdash;&mdash;, term defined, <a href="#page123">123</a><br/>
+Section of Auvergne alluvium, <a href="#page100">100</a><br/>
+&mdash;&mdash; of carboniferous rocks, Lancashire, <a href="#page85">85</a><br/>
+&mdash;&mdash; of chalk and greensand, <a href="#page287">287</a><br/>
+&mdash;&mdash; of crags near Woodbridge, Suffolk, <a href="#page198">198</a><br/>
+&mdash;&mdash; of cross-stratification, <a href="#page42">42-44</a><br/>
+&mdash;&mdash; of curved strata of the Jura, <a href="#page82">82</a><br/>
+&mdash;&mdash; of dirt-bed in Isle of Portland, <a href="#page332">332</a><br/>
+&mdash;&mdash; of Forfarshire, showing curved strata, <a href="#page74">74</a><br/>
+&mdash;&mdash; of fossil tree, showing texture, <a href="#page67">67</a><br/>
+&mdash;&mdash; of folded and denuded carboniferous beds, Nova Scotia, <a href="#page418">418</a><br/>
+&mdash;&mdash; of the Oolitic strata, <a href="#page322">322</a><br/>
+&mdash;&mdash; of Recent and Post-pliocene alluvial deposits, <a href="#page151">151</a><br/>
+&mdash;&mdash; showing creeps in coal-mines, <a href="#page79">79</a><br/>
+&mdash;&mdash; of slaty cleavage, <a href="#page589">589</a><br/>
+&mdash;&mdash; showing valleys of denudation, <a href="#page98">98</a><br/>
+&mdash;&mdash; showing the Weald formation, <a href="#page313">313</a><br/>
+&mdash;&mdash; of strata thinning out, <a href="#page41">41</a><br/>
+&mdash;&mdash; of superimposed groups at Dundry Hill, <a href="#page130">130</a><br/>
+&mdash;&mdash; of unconformable strata near Mons, <a href="#page95">95</a><br/>
+Sections illustrating faults, <a href="#page88">88</a>, <a href="#page90">90</a>, <a href="#page91">91</a><br/>
+Sedgwick, Professor, on the Cambrian Group, <a href="#page481">481</a>, <a href="#page482">482</a>, <a href="#page486">486</a><br/>
+&mdash;&mdash;, on classification of Arenig group, <a href="#page476">476</a><br/>
+&mdash;&mdash;, on Devonian series, <a href="#page439">439</a>, <a href="#page449">449</a><br/>
+&mdash;&mdash;, on position of the May-Hill beds, <a href="#page568">568</a><br/>
+&mdash;&mdash;, on protrusion of solid granite, <a href="#page574">574</a><br/>
+&mdash;&mdash;, on slaty cleavage, <a href="#page588">588</a>, <a href="#page591">591</a><br/>
+&mdash;&mdash;, on garnet in altered rock, <a href="#page515">515</a><br/>
+&mdash;&mdash;, on concretionary structure, <a href="#page63">63</a><br/>
+Sediment, accumulation of, causing a shifting of the subterranean, <a href="#page117">117</a><br/>
+isothermals. Sedimentary beds of the Carboniferous, <a href="#page396">396</a><br/>
+Selsea Bill, erratics at, <a href="#page182">182</a><br/>
+Senarmont on action of water in metamorphism, <a href="#page585">585</a><br/>
+<i>Sequoia Langsdorfii</i>, <a href="#page238">238</a><br/>
+<i>&ldquo;Seraphim,&rdquo; head of Pterygotus anglicus</i>, <a href="#page446">446</a><br/>
+Serapis, marine littoral deposits of, <a href="#page146">146</a><br/>
+Serpentine, <a href="#page578">578</a><br/>
+<i>Serpulæ</i> attached to <i>Gryphæa</i>, <a href="#page48">48</a><br/>
+&mdash;&mdash; attached to <i>Spatangus</i>, <a href="#page49">49</a><br/>
+&mdash;&mdash; attached to <i>Apiocrinus</i>, <a href="#page343">343</a><br/>
+Shale defined, <a href="#page36">36</a><br/>
+&mdash;&mdash; of the Lower Ludlow, <a href="#page461">461</a><br/>
+Sharpe, Mr. D., on American Silurian fossils, <a href="#page479">479</a><br/>
+&mdash;&mdash;, on fossils distorted by cleavage, <a href="#page592">592</a><br/>
+Shell-mounds of Denmark, <a href="#page146">146</a><br/>
+Shells, Arctic, in Scotch drift, <a href="#page177">177</a><br/>
+&mdash;&mdash;, derivative, in the Crag, <a href="#page195">195-203</a><br/>
+&mdash;&mdash;, marine, found at great heights above the sea, <a href="#page29">29</a><br/>
+&mdash;&mdash;, proportion of living, in the Crags, <a href="#page194">194</a>, <a href="#page195">195</a>, <a href="#page199">199</a><br/>
+&mdash;&mdash;, value of, in classification, <a href="#page142">142</a><br/>
+&mdash;&mdash;, fossil, of Virginia, <a href="#page228">228</a><br/>
+&mdash;&mdash; of the London clay, <a href="#page266">266</a><br/>
+&mdash;&mdash; of the mountain limestone, <a href="#page433">433</a><br/>
+&mdash;&mdash; of the Barton clay, <a href="#page258">258</a><br/>
+&mdash;&mdash; of the Oolite, <a href="#page335">335</a>, <a href="#page345">345</a>, <a href="#page350">350</a><br/>
+&mdash;&mdash;, marine, of Moel Tryfaen, <a href="#page180">180</a><br/>
+Sheppey, fauna and flora of, <a href="#page264">264</a><br/>
+&mdash;&mdash;, Eocene fish of, <a href="#page267">267</a><br/>
+Sherringham, erratic block at, <a href="#page191">191</a><br/>
+Shetland, granite of, <a href="#page558">558</a><br/>
+&mdash;&mdash;, hornblende-schist of, <a href="#page583">583</a><br/>
+Sicily, fauna and flora of, older than the country itself, <a href="#page207">207</a><br/>
+&mdash;&mdash;, newer Pliocene strata of, <a href="#page204">204</a><br/>
+&mdash;&mdash;, subterranean igneous action in, <a href="#page569">569</a><br/>
+&mdash;&mdash;, undulating gypseous marls of, <a href="#page86">86</a><br/>
+&mdash;&mdash;, volcanic dikes of, <a href="#page531">531</a><br/>
+Sidlaw Hills, trap of, <a href="#page548">548</a><br/>
+Sigillaria in coal-measures, <a href="#page380">380</a>, <a href="#page411">411</a>, <a href="#page425">425</a><br/>
+<i>Sigillaria lævigata,</i> coal-measures, <a href="#page426">426</a><br/>
+Siliceous limestone defined, <a href="#page37">37</a><br/>
+Silurian, derivation of the name, <a href="#page458">458</a><br/>
+&mdash;&mdash;, granite of Norway, <a href="#page573">573</a><br/>
+&mdash;&mdash;, metamorphic, of North Highlands, <a href="#page601">601</a><br/>
+&mdash;&mdash; rocks, classification of, <a href="#page458">458</a><br/>
+&mdash;&mdash; strata of the continent of Europe, <a href="#page477">477</a><br/>
+&mdash;&mdash; strata of United States, <a href="#page478">478</a><br/>
+&mdash;&mdash; volcanic rocks, <a href="#page548">548</a><br/>
+<i>Siphonotreta unguiculata,</i> obolus grits, <a href="#page478">478</a><br/>
+Siwâlik Hills, fresh-water deposits of, <a href="#page226">226</a><br/>
+Skaptar Jokul, flow of lava from, <a href="#page523">523</a><br/>
+Skye, hypersthene rocks of, <a href="#page491">491</a><br/>
+&mdash;&mdash;, Isle of, Miocene syenite of the, <a href="#page568">568</a><br/>
+&mdash;&mdash;, trap dike in, <a href="#page514">514</a><br/>
+Slaty cleavage, <a href="#page588">588</a><br/>
+Slicken-sides, in opposite walls of veins, <a href="#page608">608</a><br/>
+&mdash;&mdash;, term defined, <a href="#page87">87</a><br/>
+<i>Smilax sagittifera,</i> Œningen, <a href="#page222">222</a><br/>
+Smith, Mr. W., on White Lias bed, <a href="#page366">366</a><br/>
+Snowdon, volcanic tuffs of, <a href="#page549">549</a><br/>
+Soissonnais sands, <a href="#page275">275</a><br/>
+<i>Solenastræa cellulosa,</i> Brockenhurst, <a href="#page257">257</a><br/>
+Solenhofen stone, fossils in the, <a href="#page337">337</a><br/>
+Solfatara, decomposition of rocks in the, <a href="#page586">586</a><br/>
+Somma, cone and dikes of, <a href="#page526">526</a><br/>
+Sopwith, Mr. T., models of outcrop of strata, <a href="#page85">85</a><br/>
+Sorby, Mr., on action of water in metamorphism, <a href="#page585">585</a><br/>
+&mdash;&mdash;, on glass cavities in quartz, <a href="#page555">555</a><br/>
+&mdash;&mdash;, on mechanical theory of cleavage, <a href="#page592">592</a><br/>
+&mdash;&mdash;, on ripple-marks in mica schist, <a href="#page596">596</a><br/>
+South Joggins, section of cliffs at, <a href="#page410">410</a><br/>
+Spalacotherium, Purbeck, <a href="#page346">346</a><br/>
+<i>Spatangus radiatus,</i> Chalk, <a href="#page284">284</a><br/>
+&mdash;&mdash; with serpula attached, <a href="#page49">49</a><br/>
+Species, gradual change of, <a href="#page139">139</a><br/>
+&mdash;&mdash; older than the land they inhabit, <a href="#page207">207</a><br/>
+&mdash;&mdash;, similarity of conditions causing reappearance of, <a href="#page311">311</a><br/>
+Specific gravity of basalt and trachyte, <a href="#page504">504</a><br/>
+Speer and Rigi, Lower Miocene of the, <a href="#page235">235</a><br/>
+Speeton Clay, <a href="#page311">311</a><br/>
+<i>Sphærexochus mirus,</i> Silurian, <a href="#page467">467</a><br/>
+<i>Sphærulites agariciformis,</i> White Chalk, <a href="#page306">306</a><br/>
+&mdash;&mdash; of volcanic minerals, <a href="#page499">499</a><br/>
+<i>Sphenophyllum erosum,</i> Coal, <a href="#page425">425</a><br/>
+<i>Sphenopteris gracilis,</i> Hastings sands, <a href="#page318">318</a><br/>
+Spheroidal concretions in limestone, <a href="#page64">64</a><br/>
+<i>Spicula of sponge,</i> Atlantic mud, <a href="#page288">288</a><br/>
+<i>Spirifera disjuncta,</i> Devonian, <a href="#page450">450</a><br/>
+&mdash;&mdash; <i>alata,</i> Permian, <a href="#page388">388</a><br/>
+&mdash;&mdash; <i>mucronata</i>, <a href="#page454">454</a><br/>
+&mdash;&mdash; <i>trigonalis,</i> and <i>S. glabra</i>, <a href="#page434">434</a><br/>
+<i>Spiriferina Walcotti,</i> Lias, <a href="#page355">355</a><br/>
+<i>Spirolina stenostoma,</i> Eocene, <a href="#page275">275</a><br/>
+<i>Spirorbis carbonarius,</i> coal-measures, <a href="#page405">405</a><br/>
+<i>Spondylus spinosus,</i> White Chalk, <a href="#page294">294</a><br/>
+<i>Sponge in flint from White Chalk</i>, <a href="#page296">296</a><br/>
+Sponges, vitreous, in the chalk, <a href="#page291">291</a><br/>
+Springs, mineral of Auvergne, <a href="#page604">604</a><br/>
+Staffa, age of columnar basalt of, <a href="#page539">539</a><br/>
+Stalactite, origin of, explained, <a href="#page156">156</a><br/>
+<i>Starfish</i> in Silurian strata, <a href="#page472">472</a><br/>
+Stations of species affecting distribution of fossils, <a href="#page354">354</a><br/>
+<i>Stauria astræiformis</i>, <a href="#page431">431</a><br/>
+Stereognathus of Stonesfield, <a href="#page348">348</a><br/>
+Sternberg, Count, on insects in coal, <a href="#page495">495</a><br/>
+<i>Stigmaria attached to trunk of Sigillaria</i>, <a href="#page427">427</a><br/>
+&mdash;&mdash; in coal-measures, <a href="#page398">398</a>, <a href="#page411">411</a>, <a href="#page426">426</a><br/>
+&mdash;&mdash; <i>ficoides</i> and surface showing tubercles, Coal, <a href="#page427">427</a><br/>
+Stilbite, <a href="#page500">500</a><br/>
+Stiper-Stones or Arenig Group, <a href="#page475">475</a><br/>
+Stockwerk, assemblage of veins, <a href="#page605">605</a><br/>
+Stonesfield slate, mammalia of the, <a href="#page345">345</a><br/>
+Strata, term defined, alternations of fresh-water, and shallow and deep, <a href="#page27">27</a><br/>
+sea. &mdash;&mdash;, alternations of marine and fresh-water, <a href="#page108">108</a><br/>
+&mdash;&mdash;, curved, inclined, and vertical, <a href="#page73">73</a><br/>
+&mdash;&mdash;, apparent horizontality of inclined, <a href="#page81">81</a><br/>
+&mdash;&mdash;, contorted in drift, <a href="#page178">178</a><br/>
+&mdash;&mdash;, contortion of, in Cyclopean Isles, <a href="#page530">530</a><br/>
+&mdash;&mdash;, general table of fossiliferous, <a href="#page131">131</a><br/>
+&mdash;&mdash;, horizontality of, <a href="#page40">40</a><br/>
+&mdash;&mdash;, origin of metamorphic, <a href="#page83">83</a><br/>
+&mdash;&mdash;, overlapping, <a href="#page95">95</a><br/>
+&mdash;&mdash; repeated by being doubled back, <a href="#page87">87</a><br/>
+&mdash;&mdash;, slow growth of, attested by fossils, <a href="#page47">47-50</a><br/>
+&mdash;&mdash; of organic origin, <a href="#page51">51</a><br/>
+&mdash;&mdash;, tests of age of, <a href="#page123">123</a><br/>
+&mdash;&mdash;, unconformability of, <a href="#page94">94</a>, <a href="#page138">138</a><br/>
+&mdash;&mdash;, vast thickness of, not forming high mountains, <a href="#page109">109-13</a><br/>
+Stratification, diagonal or cross, <a href="#page42">42</a>, <a href="#page44">44</a><br/>
+&mdash;&mdash;, different forms described, <a href="#page39">39</a><br/>
+&mdash;&mdash; of metamorphic rocks considered, <a href="#page580">580</a><br/>
+Stratified rocks, composition of, <a href="#page35">35</a><br/>
+Striæ, production of, <a href="#page168">168</a><br/>
+Strickland, Mr., on thickness of the Trias, <a href="#page369">369</a><br/>
+<i>Stricklandinia lirata</i>, <a href="#page469">469</a><br/>
+Strike, term explained, <a href="#page80">80</a><br/>
+<i>Stringocephalus Burtini</i>, <a href="#page452">452</a><br/>
+Stromboli, lava of, <a href="#page566">566</a><br/>
+<i>Strophomena depressa,</i> Wenlock, <a href="#page466">466</a><br/>
+&mdash;&mdash; <i>grandis</i>, <a href="#page471">471</a><br/>
+Studer, Mr., on gneiss of the Jungfrau, <a href="#page599">599</a><br/>
+subaërial denudation, average annual amount of, <a href="#page113">113</a><br/>
+Subapennine beds, proportion of recent species in, <a href="#page143">143</a><br/>
+&mdash;&mdash; strata, older Pliocene, <a href="#page208">208</a><br/>
+Submarine denudation, <a href="#page105">105</a><br/>
+Subsidence of land must preponderate over upheaval, <a href="#page116">116</a><br/>
+<i>Succinea amphibia</i>, <a href="#page55">55</a><br/>
+&mdash;&mdash; <i>elongata</i>, <a href="#page155">155</a><br/>
+Suess, M., on fossils of St. Cassian beds, <a href="#page376">376</a>, <a href="#page377">377</a><br/>
+&mdash;&mdash;, on Vienna basin, <a href="#page225">225</a><br/>
+Suffolk, Crag of, <a href="#page195">195</a><br/>
+&ldquo;Sunk country,&rdquo; New Madrid, <a href="#page402">402</a><br/>
+Superga, Lower Miocene of the, <a href="#page244">244</a><br/>
+Superior, Lake, marl in, <a href="#page63">63</a><br/>
+Superposition of deposits, a test of age, <a href="#page124">124</a><br/>
+&mdash;&mdash; a test of age of volcanic rocks, <a href="#page521">521</a><br/>
+Sutherlandshire, unconformable Palæozoic strata in, <a href="#page112">112</a><br/>
+Swanage, fossil mammalia found at, <a href="#page326">326</a><br/>
+Sweden, Cambrian of, <a href="#page489">489</a><br/>
+&mdash;&mdash;, slow rise of land in, <a href="#page72">72</a><br/>
+&mdash;&mdash;, small thickness of Silurian strata in, <a href="#page477">477</a><br/>
+Switzerland, lake-dwellings of, <a href="#page148">148</a><br/>
+&mdash;&mdash;, Lower Molasse of, <a href="#page235">235</a><br/>
+&mdash;&mdash;, Middle or Marine Molasse of, <a href="#page223">223</a><br/>
+&mdash;&mdash;, Upper Miocene of, at Œningen, <a href="#page215">215</a><br/>
+Sydney coal-field, rain-prints in, <a href="#page416">416</a><br/>
+Syenite, composition of, <a href="#page552">552</a>, <a href="#page557">557</a><br/>
+&mdash;&mdash;, how far connected with trap-rocks, <a href="#page558">558</a><br/>
+Syenitic granite, <a href="#page557">557</a><br/>
+Symonds, Rev. W. S., on Moel Tryfaen shells, <a href="#page180">180</a><br/>
+Synclinal and anticlinal curves, <a href="#page74">74</a>, <a href="#page85">85</a><br/><br/>
+</p>
+
+<p class="noindent">
+T<small>ABLE</small> of Botanical Nomenclature, <a href="#page303">303</a><br/>
+&mdash;&mdash; of St. Cassian fossil mollusca, <a href="#page377">377</a><br/>
+&mdash;&mdash; of Cretaceous formations, <a href="#page283">283</a><br/>
+&mdash;&mdash; of Devonian series in Devon, <a href="#page449">449</a><br/>
+&mdash;&mdash; of divisions of Hastings Sand, <a href="#page316">316</a><br/>
+&mdash;&mdash; of English and French Eocene strata, <a href="#page252">252</a><br/>
+&mdash;&mdash; of ages of fossil vertebrata, <a href="#page464">464</a><br/>
+&mdash;&mdash; of Neocomian strata, <a href="#page308">308</a><br/>
+&mdash;&mdash; of mammalia older than Paris gypsum, <a href="#page329">329</a><br/>
+&mdash;&mdash; of marine testacea in the Crag, <a href="#page202">202</a><br/>
+&mdash;&mdash; of Oolitic strata, <a href="#page321">321</a><br/>
+&mdash;&mdash; of volcanic minerals, <a href="#page499">499</a><br/>
+&mdash;&mdash; of Silurian strata of United States, <a href="#page478">478</a><br/>
+&mdash;&mdash; of Silurian rocks, <a href="#page458">458</a><br/>
+&mdash;&mdash; of Triassic strata, <a href="#page375">375</a><br/>
+&mdash;&mdash; of Cambrian strata, <a href="#page482">482</a><br/>
+&mdash;&mdash; of Permian of north of England, <a href="#page386">386</a><br/>
+&mdash;&mdash; of Welsh coal-measures, <a href="#page394">394</a><br/>
+&mdash;&mdash; of thicknesses of Carboniferous limestone, <a href="#page395">395</a><br/>
+&mdash;&mdash;, general, of fossiliferous strata, <a href="#page131">131</a><br/>
+Table Mountain, granite veins in clay-slate of, <a href="#page560">560</a><br/>
+Tails of homocercal and heterocercal fish, <a href="#page389">389</a><br/>
+Talcose granite, <a href="#page557">557</a><br/>
+&mdash;&mdash; gneiss, <a href="#page578">578</a><br/>
+Tarannon shales, <a href="#page468">468</a><br/>
+Tartaret cone, and lava of, <a href="#page527">527</a>, <a href="#page542">542</a><br/>
+Tate, Mr., on St Cassian fossils, <a href="#page377">377</a><br/>
+Tealby series, Middle Neocomian, <a href="#page312">312</a><br/>
+Teeth of extinct mammalia, <a href="#page163">163</a>, <a href="#page164">164</a><br/>
+<i>Tellina balthica (T. solidula)</i>, <a href="#page190">190</a><br/>
+&mdash;&mdash; <i>calcarea (T. proxima)</i>, <a href="#page177">177</a><br/>
+&mdash;&mdash; <i>obliqua,</i> Crag, <a href="#page194">194</a><br/>
+<i>Temnechinus excavatus</i>, <a href="#page200">200</a><br/>
+<i>Temnopleurus excavatus</i>, <a href="#page200">200</a><br/>
+<i>Tentaculites annulatus,</i> Silurian, <a href="#page489">489</a><br/>
+<i>Terebellum fusiforme,</i> Barton, <a href="#page259">259</a><br/>
+&mdash;&mdash; <i>sopita,</i> Barton, <a href="#page259">259</a><br/>
+<i>Terebratula affinis,</i> Aymestry, <a href="#page462">462</a><br/>
+&mdash;&mdash; <i>biplicata,</i> White Chalk, <a href="#page294">294</a><br/>
+&mdash;&mdash; <i>carnea,</i> White Chalk, <a href="#page294">294</a><br/>
+&mdash;&mdash; <i>digona,</i> Bradford clay, <a href="#page345">345</a><br/>
+&mdash;&mdash; <i>fimbria,</i> Inferior Oolite, <a href="#page350">350</a><br/>
+&mdash;&mdash; <i>hastata,</i> Mountain Limestone, <a href="#page434">434</a><br/>
+&mdash;&mdash; <i>sella,</i> Neocomian, <a href="#page310">310</a><br/>
+&mdash;&mdash; <i>Wilsoni,</i> Aymestry, <a href="#page462">462</a><br/>
+<i>Terebratulina striata,</i> White Chalk, <a href="#page294">294</a><br/>
+<i>Terebrirostra lyra,</i> Chloritic Sand, <a href="#page300">300</a><br/>
+<i>Teredo navalis,</i> boring wood, <a href="#page50">50</a><br/>
+Tertiary formations, classification of, <a href="#page137">137</a>, <a href="#page143">143</a><br/>
+&mdash;&mdash; strata, subdivisions of, <a href="#page143">143</a><br/>
+&mdash;&mdash;, term defined, <a href="#page123">123</a><br/>
+Testacea. <i>See</i> Shells.<br/>
+Thallogens, <a href="#page303">303</a><br/>
+<i>Thamnastræa,</i> Coral Rag, <a href="#page339">339</a><br/>
+Thanet sands, <a href="#page269">269</a><br/>
+<i>Theca operculata,</i> Tremadoc beds, <a href="#page483">483</a><br/>
+<i>Thecodontosaurus, tooth of,</i> <a href="#page374">374</a><br/>
+<i>Thecodus parvidens,</i> Ludlow, <a href="#page460">460</a><br/>
+<i>Thecosmilia annularis,</i> Coral Rag, <a href="#page339">339</a><br/>
+Thirria, M., on Nerinæan limestone, <a href="#page340">340</a><br/>
+Thompson, Dr., on Nummulites of Thibet, <a href="#page277">277</a><br/>
+Thomson, Wyville, on Atlantic mud, <a href="#page288">288</a><br/>
+&mdash;&mdash;, on sponges in chalk mud, <a href="#page292">292</a><br/>
+Thuringia, monitor of, <a href="#page390">390</a>, <a href="#page463">463</a><br/>
+Thurmann, M., on Bernese Jura Oolite, <a href="#page344">344</a><br/>
+&mdash;&mdash;, on structure of the Jura, <a href="#page83">83</a><br/>
+<i>Thylacotherium Prevostii,</i> Stonesfield, <a href="#page347">347</a><br/>
+Tile-stones of the Upper Ludlow, <a href="#page459">459</a><br/>
+Tilgate forest, fossil Iguanodon in, <a href="#page315">315</a><br/>
+Till described, <a href="#page166">166</a><br/>
+&mdash;&mdash;, mammoth in Scotch, <a href="#page175">175</a><br/>
+&mdash;&mdash; of North America, <a href="#page182">182</a><br/>
+Tin veins, age of, in Cornwall, <a href="#page615">615</a><br/>
+Titanoferrite, <a href="#page500">500</a><br/>
+Torell, Dr., on ice-action in Greenland, <a href="#page172">172</a><br/>
+&mdash;&mdash;, on Swedish Cambrian fossils, <a href="#page489">489</a><br/>
+Touraine, faluns of, <a href="#page211">211</a><br/>
+Tourmaline, <a href="#page500">500</a><br/>
+Trachytic rocks, <a href="#page505">505</a><br/>
+&mdash;&mdash; tuff, <a href="#page506">506</a><br/>
+&mdash;&mdash; porphyry, <a href="#page506">506</a><br/>
+&mdash;&mdash; lava, age of, <a href="#page523">523</a><br/>
+Trap, term defined, <a href="#page498">498</a><br/>
+&mdash;&mdash; dike, intercepting strata, <a href="#page518">518</a><br/>
+&mdash;&mdash; dikes, <a href="#page513">513-17</a><br/>
+&mdash;&mdash;, intrusion of, between strata, <a href="#page517">517</a><br/>
+&mdash;&mdash; rocks, ages of, <a href="#page524">524-50</a><br/>
+&mdash;&mdash; rocks passing into granite, <a href="#page559">559</a><br/>
+&mdash;&mdash; tuff described, <a href="#page508">508</a><br/>
+Trappean rocks, nomenclature of, <a href="#page497">497</a><br/>
+&mdash;&mdash; rocks, their relation to active volcanoes, <a href="#page517">517</a><br/>
+Trass of Lower Eifel, <a href="#page535">535</a><br/>
+Travertin, how deposited, <a href="#page60">60</a><br/>
+&mdash;&mdash;, inférieur of Paris basin, <a href="#page273">273</a><br/>
+<i>Tree ferns, living</i>, <a href="#page422">422</a><br/>
+Trees erect in coal, Nova Scotia, <a href="#page411">411</a><br/>
+Tremadoc slates and their fossils, <a href="#page482">482</a><br/>
+Tremolite, <a href="#page499">499</a>, <a href="#page502">502</a><br/>
+Trenton limestone, fossils of the, <a href="#page479">479</a><br/>
+Trezza, volcanic rocks of, <a href="#page529">529</a><br/>
+Trias, beds of passage between Lias and, <a href="#page366">366</a><br/>
+&mdash;&mdash; of England, <a href="#page369">369-74</a><br/>
+&mdash;&mdash; of Germany, <a href="#page375">375</a><br/>
+&mdash;&mdash;, Saurians of the, <a href="#page370">370</a><br/>
+&mdash;&mdash; of the United States, <a href="#page381">381</a><br/>
+Triassic mammifer, North Carolina, <a href="#page383">383</a><br/>
+Triclinic feldspars, <a href="#page501">501</a><br/>
+Tridymite, crystallised silica, <a href="#page500">500</a><br/>
+<i>Trigonellites latus,</i> Kimmeridge clay, <a href="#page336">336</a><br/>
+<i>Trigonia caudata,</i> Neocomian, <a href="#page310">310</a><br/>
+&mdash;&mdash; gibbosa, Portland stone, <a href="#page335">335</a><br/>
+<i>Trigonocarpum ovatum,</i> and <i>T. olivæforme,</i> Coal, <a href="#page429">429</a><br/>
+<i>Trigonotreta undulata,</i> Permian, <a href="#page388">388</a><br/>
+Trilobites of Bala and Caradoc beds, <a href="#page471">471</a><br/>
+&mdash;&mdash;, metamorphosis of, <a href="#page471">471</a>, <a href="#page488">488</a><br/>
+&mdash;&mdash; of primordial zone, <a href="#page487">487</a><br/>
+<i>Triloculina inflata,</i> Eocene, <a href="#page275">275</a><br/>
+Trimmer, Mr., on contorted strata, <a href="#page179">179</a><br/>
+&mdash;&mdash;, on shells of Moel Tryfaen, <a href="#page186">186</a><br/>
+<i>Trinucleus concentricus, T. Caractaci</i>, <a href="#page472">472</a><br/>
+<i>Trionyx, carapace of,</i> Bembridge, <a href="#page253">253</a><br/>
+Tripoli composed of diatomaceæ, <a href="#page51">51</a><br/>
+<i>Trochoceras giganteus,</i> Ludlow, <a href="#page463">463</a><br/>
+<i>Trophon antiquum (Fusus contrarius)</i>, <a href="#page196">196</a><br/>
+&mdash;&mdash; <i>clathratum,</i> Scotch drift, <a href="#page176">176</a><br/>
+Tuff defined, <a href="#page30">30</a><br/>
+&mdash;&mdash;, shelly, of the Grand Canary, <a href="#page538">538</a><br/>
+&mdash;&mdash;, trappean, of Llandeilo rocks, <a href="#page473">473</a><br/>
+&mdash;&mdash;, shelly, of Gergovia, <a href="#page542">542</a><br/>
+<i>Tupaia Tana,</i> recent, <a href="#page347">347</a><br/>
+Turner, Dr., on chemical decomposition, <a href="#page68">68</a><br/>
+<i>Turrilites costatus,</i> Chalk, <a href="#page299">299</a><br/>
+<i>Turritella multisulcata,</i> Bracklesham, <a href="#page262">262</a><br/>
+Tuscany, mineral springs of, <a href="#page604">604</a><br/>
+Tylor, Mr., on amount of subaërial denudation, <a href="#page114">114</a><br/>
+Tyndall, Dr., on slaty cleavage, <a href="#page594">594</a><br/>
+Tynedale fault, <a href="#page90">90</a><br/>
+Tynemouth cliff, brecciated limestone of, <a href="#page387">387</a><br/>
+<i>Typhis pungens,</i> Barton clay, <a href="#page259">259</a><br/><br/>
+</p>
+
+<p class="noindent">
+<i>U<small>NCITES</small> Gryphus,</i> Devonian, <a href="#page452">452</a><br/>
+Unconformability of strata, <a href="#page94">94</a>, <a href="#page138">138</a><br/>
+Underlying, term applied to plutonic rocks, <a href="#page34">34</a><br/>
+Unger on American forms in Swiss Miocene flora, <a href="#page223">223</a>, <a href="#page239">239</a><br/>
+&mdash;&mdash; on Miocene plants of Croatia, <a href="#page243">243</a><br/>
+Ungulite, or Obolus grit of Russia, <a href="#page477">477</a><br/>
+<i>Unio littoralis</i>, <a href="#page54">54</a><br/>
+&mdash;&mdash; <i>Valdensis,</i> Hastings Sands, <a href="#page317">317</a><br/>
+United States, Cambrian of the, <a href="#page489">489</a><br/>
+&mdash;&mdash;, Cretaceous rocks of, <a href="#page307">307</a><br/>
+&mdash;&mdash;, Devonian of, <a href="#page455">455</a><br/>
+&mdash;&mdash;, Eocene strata in the, <a href="#page278">278</a><br/>
+&mdash;&mdash;, footprints in Carboniferous of, <a href="#page407">407</a><br/>
+&mdash;&mdash;, Lower Miocene of, <a href="#page248">248</a><br/>
+&mdash;&mdash;, older Pliocene and Miocene formations of, <a href="#page227">227</a><br/>
+&mdash;&mdash;, Silurian strata of, <a href="#page478">478</a><br/>
+&mdash;&mdash;, Trias of the, <a href="#page381">381</a><br/>
+Upheaval of land more than counteracted by subsidence, <a href="#page116">116</a><br/>
+&mdash;&mdash;, power of denudation to counteract, <a href="#page105">105</a>, <a href="#page115">115</a><br/>
+Upper Greensand, or Chloritic series, <a href="#page298">298</a><br/>
+Upsala, erratics on modern marine drift near, <a href="#page174">174</a><br/>
+Ural Mountains, auriferous alluvium of, <a href="#page616">616</a><br/>
+Uralite, <a href="#page499">499</a><br/>
+<i>Ursus spelæus, tooth of</i>, <a href="#page165">165</a><br/>
+Urville, Captain de, on size of icebergs, <a href="#page172">172</a><br/><br/>
+</p>
+
+<p class="noindent">
+V<small>AL D&amp;RSQUO;ARNO</small>, Newer Pliocene of, <a href="#page207">207</a><br/>
+Valleys, origin of, <a href="#page102">102</a><br/>
+Valorsine, granite veins in talcose gneiss in, <a href="#page599">599</a><br/>
+<i>Valvata piscinalis</i>, <a href="#page55">55</a><br/>
+<i>Vanessa Pluto,</i> Lower Miocene, Croatia, <a href="#page243">243</a><br/>
+Vegetation of the Coal, <a href="#page420">420</a><br/>
+&mdash;&mdash; of the Devonian of America, <a href="#page455">455</a><br/>
+&mdash;&mdash;. <i>See</i> Plants.<br/>
+Veins, chemical deposits in, <a href="#page612">612</a><br/>
+&mdash;&mdash;, granite rocks altered by, <a href="#page559">559</a><br/>
+&mdash;&mdash;, different kinds of minerals, <a href="#page605">605</a><br/>
+&mdash;&mdash;. <i>See</i> Mineral veins.<br/>
+Vein-stones, <a href="#page610">610</a><br/>
+<i>Venericardia planicosta</i>, <a href="#page260">260</a><br/>
+Venetz, M., on Alpine glaciers, <a href="#page170">170</a><br/>
+<i>Ventriculites radiatus,</i> Chalk, <a href="#page292">292</a><br/>
+Verneuil, M. de, on Russian Silurian, <a href="#page462">462</a><br/>
+&mdash;&mdash;, on Permian flora, <a href="#page392">392</a><br/>
+Vertebrata, progress of discovery of fossil, <a href="#page464">464</a><br/>
+Vertical strata, <a href="#page73">73</a><br/>
+Vesuvius, Recent and Post-pliocene volcanic rocks of, <a href="#page525">525</a><br/>
+&mdash;&mdash;, basaltic lavas of, <a href="#page508">508</a><br/>
+&mdash;&mdash;, tufaceous strata of, <a href="#page522">522</a><br/>
+&mdash;&mdash;, dikes of, <a href="#page527">527</a><br/>
+<i>Vicarya Lujani,</i> Punfield, <a href="#page319">319</a><br/>
+Vicentin, columnar basalt of the, <a href="#page511">511</a><br/>
+Vienna Basin, Upper Miocene beds of, <a href="#page224">224</a><br/>
+Vine in Upper Miocene beds at Œningen, <a href="#page221">221</a><br/>
+Virginia, eighty miles of fault in, <a href="#page92">92</a><br/>
+&mdash;&mdash;, coal-field of, <a href="#page382">382</a><br/>
+Virlet, M, on corrosion of rocks near Corinth, <a href="#page586">586</a><br/>
+&mdash;&mdash;, on Cretaceous traps of Greece, <a href="#page544">544</a><br/>
+&mdash;&mdash;, on fossils in veins, <a href="#page608">608</a><br/>
+&mdash;&mdash;, on volcanic rocks of the Morea, <a href="#page544">544</a><br/>
+Volcanic ash or tuff, <a href="#page508">508</a><br/>
+&mdash;&mdash; breccia, <a href="#page509">509</a><br/>
+&mdash;&mdash; dikes, <a href="#page513">513-16</a><br/>
+&mdash;&mdash; force and denudation opposing powers, <a href="#page117">117</a><br/>
+&mdash;&mdash; mountains, structure and origin of, <a href="#page494">494</a><br/>
+Volcanic rocks defined, <a href="#page29">29</a><br/>
+&mdash;&mdash;, mineral composition of, <a href="#page498">498</a><br/>
+&mdash;&mdash;, Recent and Post-pliocene, <a href="#page524">524</a><br/>
+&mdash;&mdash;, Pliocene, <a href="#page529">529</a><br/>
+&mdash;&mdash;, Miocene, <a href="#page536">536-43</a><br/>
+&mdash;&mdash;, Eocene, <a href="#page543">543</a><br/>
+&mdash;&mdash;, Cretaceous and Liassic, <a href="#page544">544</a>, <a href="#page545">545</a><br/>
+&mdash;&mdash;, New Red, Permian and Carboniferous, <a href="#page545">545</a><br/>
+&mdash;&mdash;, Old Red Sandstone, <a href="#page547">547</a><br/>
+&mdash;&mdash;, Silurian, Cambrian and Laurentian, <a href="#page548">548</a>, <a href="#page549">549</a><br/>
+&mdash;&mdash; of Auvergne, <a href="#page540">540</a><br/>
+&mdash;&mdash;, columnar and globular, structure of, <a href="#page510">510</a><br/>
+&mdash;&mdash; of Grand Canary, <a href="#page528">528</a><br/>
+&mdash;&mdash; of Silurian age, <a href="#page477">477</a><br/>
+&mdash;&mdash;, special forms of structure of, <a href="#page506">506</a><br/>
+&mdash;&mdash;, tests of age of, <a href="#page520">520-4</a><br/>
+Volcanoes, extinct, <a href="#page30">30</a><br/>
+&mdash;&mdash; of Auvergne, <a href="#page495">495</a><br/>
+<i>Voltzia heterophylla,</i> Bunter, <a href="#page380">380</a><br/>
+<i>Voluta ambigua,</i> Barton clay, <a href="#page259">259</a><br/>
+&mdash;&mdash; <i>athleta,</i> Barton, <a href="#page259">259</a><br/>
+&mdash;&mdash; <i>Lamberti,</i> coralline and Red Crag, <a href="#page196">196</a><br/>
+&mdash;&mdash; <i>Lamberti,</i> faluns, <a href="#page214">214</a><br/>
+&mdash;&mdash; <i>nodosa,</i> London clay, <a href="#page266">266</a><br/>
+&mdash;&mdash; <i>Selseïensis,</i> Bracklesham, <a href="#page262">262</a><br/>
+Von Buch, Leopold, on &ldquo;elevation craters,&rdquo; <a href="#page496">496</a><br/>
+&mdash;&mdash;, on Silurian plutonic rocks, <a href="#page572">572</a><br/><br/>
+</p>
+
+<p class="noindent">
+W<small>ACKE</small> described, <a href="#page508">508</a><br/>
+Wagner, M., on Miocene of Greece, <a href="#page226">226</a><br/>
+<i>Walchia piniformis,</i> Permian, <a href="#page392">392</a><br/>
+Wales and England, glaciation of, <a href="#page180">180</a><br/>
+Wallich, Dr., on Atlantic mud, <a href="#page287">287</a><br/>
+Water, denuding power of running, <a href="#page98">98</a>, <a href="#page115">115</a><br/>
+&mdash;&mdash;, action of, in metamorphism, <a href="#page584">584</a><br/>
+Watt, Gregory, on fusion of rock, <a href="#page584">584</a><br/>
+Weald clay and its fossils, <a href="#page317">317</a><br/>
+Wealden area, thickness of the, <a href="#page319">319</a><br/>
+&mdash;&mdash; formation, <a href="#page313">313</a><br/>
+&mdash;&mdash; flora, <a href="#page320">320</a><br/>
+Webster, Mr. T., on Tertiary strata, <a href="#page141">141</a><br/>
+Wellington Valley caves, <a href="#page158">158</a><br/>
+Wenlock formation, fossils of the, <a href="#page465">465-8</a><br/>
+&mdash;&mdash; limestone, <a href="#page465">465</a><br/>
+&mdash;&mdash; shale, <a href="#page467">467</a><br/>
+Werner on mineral veins in Saxony, <a href="#page609">609</a><br/>
+&mdash;&mdash; on isomorphism, <a href="#page502">502</a><br/>
+Westwood, Mr., on Lias beetles, <a href="#page363">363</a><br/>
+Wexford, veins of copper at, <a href="#page615">615</a><br/>
+Whitaker, Mr., on subaërial origin of escarpments, <a href="#page104">104</a><br/>
+White or coralline crag, <a href="#page197">197</a><br/>
+&mdash;&mdash; sand of Alum Bay, <a href="#page38">38</a><br/>
+Whymper, Mr., on Arctic Miocene plants, <a href="#page240">240</a><br/>
+Williams, Mr., on Cornish lodes, <a href="#page607">607</a><br/>
+Williamson, Professor, on Conifers of the Coal, <a href="#page428">428</a><br/>
+&mdash;&mdash;, on structure of calamite, <a href="#page425">425</a><br/>
+Wind, denuding action of the, <a href="#page97">97</a><br/>
+Wood, Mr. Searles, on Bridlington shells, <a href="#page190">190</a><br/>
+&mdash;&mdash;, on Chillesford and Aldeby beds, <a href="#page192">192</a><br/>
+&mdash;&mdash;, on shells of the Crags, <a href="#page194">194</a>, <a href="#page195">195</a>, <a href="#page199">199</a><br/>
+&mdash;&mdash;, on shells of Crag and faluns compared, <a href="#page213">213</a><br/>
+&mdash;&mdash;, on fish of Headon series, <a href="#page255">255</a><br/>
+&mdash;&mdash;, table of marine testacea of the Crag, <a href="#page202">202</a><br/>
+&mdash;&mdash;, on thickness of coralline crag, <a href="#page198">198</a><br/>
+Woodward, Dr., on St. Cassian fossils, <a href="#page377">377</a><br/>
+Woodward, Mr. H., on Pterygotus, <a href="#page447">447</a><br/>
+Woolhope beds, <a href="#page467">467</a><br/>
+Woolwich and Reading series, <a href="#page267">267</a><br/>
+Wright, Dr., on Barton shells, <a href="#page258">258</a><br/>
+&mdash;&mdash;, on zones of the Lias, <a href="#page353">353</a><br/>
+Wunsch, Mr. E. A., on trees in volcanic ash, <a href="#page546">546</a><br/>
+Wyville Thomson. <i>See</i> Thomson.<br/><br/>
+</p>
+
+<p class="noindent">
+<i>X<small>IPHODON</small> gracile,</i> Paris basin, <a href="#page271">271</a><br/>
+<i>Xylobius Sigillariæ,</i> Nova Scotia coal, <a href="#page415">415</a><br/><br/>
+</p>
+
+<p class="noindent">
+Y<small>OREDALE</small> beds, thickness of the, <a href="#page395">395</a><br/>
+Yorkshire, Oolite of, <a href="#page349">349</a><br/>
+Young, Mr., on seeds washed out of mammoth tusks, <a href="#page176">176</a><br/><br/>
+</p>
+
+<p class="noindent">
+Z<small>ECHSTEIN</small> of Germany, <a href="#page392">392</a><br/>
+Zeolites, secondary volcanic minerals, <a href="#page500">500</a><br/>
+<i>Zeuglodon cetoides,</i> Eocene, United States, <a href="#page280">280</a><br/>
+Zircon-syenite, <a href="#page558">558</a><br/>
+<i>Zoantharia rugosa</i> and <i>Z. aporosa</i>, <a href="#page431">431</a><br/>
+Zones of the Lias, <a href="#page353">353</a><br/>
+<i>Zonites priscus,</i> Coal, <a href="#page415">415</a><br/>
+Zoological provinces, great extent of, <a href="#page127">127</a><br/>
+Zoophytes, fossil, <a href="#page48">48</a><br/>
+&mdash;&mdash;. <i>See</i> Corals, Bryozoa, etc.<br/>
+Zurich, lake-dwellings in Lake of, <a href="#page148">148</a>
+</p>
+
+</div><!--end chapter-->
+
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