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+The Project Gutenberg eBook of The Student’s Elements of Geology, by Sir Charles Lyell
+
+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
+www.gutenberg.org. 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.
+
+Title: The Student’s Elements of Geology
+
+Author: Sir Charles Lyell
+
+Release Date: August 29, 2001 [eBook #3772]
+[Most recently updated: February 22, 2021]
+
+Language: English
+
+Character set encoding: UTF-8
+
+Produced by: Sue Asscher
+
+*** START OF THE PROJECT GUTENBERG EBOOK THE STUDENTS’S ELEMENTS OF GEOLOGY ***
+
+
+
+
+The Student’s Elements of Geology
+
+By SIR CHARLES LYELL, BART., F.R.S.
+
+AUTHOR OF
+“THE PRINCIPLES OF GEOLOGY,” “THE ANTIQUITY OF MAN,” ETC.
+
+Thecosmilia annularis
+
+WITH MORE THAN 600 ILLUSTRATIONS ON WOOD.
+
+NEW YORK
+HARPER & BROTHERS, PUBLISHERS
+1878
+
+Tertiary or Cainozoic, Secondary or Mesozoic, Primary or Paleozoic
+
+CONTENTS.
+
+
+
+
+PREFACE
+
+Chapter I—ON THE DIFFERENT CLASSES OF ROCKS.
+Geology defined. — Successive Formation of the Earth’s Crust. —
+Classification of Rocks according to their Origin and Age. — Aqueous
+Rocks. — Their Stratification and imbedded Fossils. — Volcanic Rocks,
+with and without Cones and Craters. — Plutonic Rocks, and their
+Relation to the Volcanic. — Metamorphic Rocks, and their probable
+Origin. — The term Primitive, why erroneously applied to the
+Crystalline Formations. — Leading Division of the Work.
+
+Chapter II—AQUEOUS ROCKS—THEIR COMPOSITION AND FORMS OF STRATIFICATION.
+Mineral Composition of Strata. — Siliceous Rocks. — Argillaceous. —
+Calcareous. — Gypsum. — Forms of Stratification. — Original
+Horizontality. — Thinning out. — Diagonal Arrangement. — Ripple-mark.
+
+Chapter III—ARRANGEMENT OF FOSSILS IN STRATA—FRESH-WATER AND MARINE.
+Successive Deposition indicated by Fossils. — Limestones formed of
+Corals and Shells. — Proofs of gradual Increase of Strata derived from
+Fossils. — Serpula attached to Spatangus. — Wood bored by Teredina. —
+Tripoli formed of Infusoria. — Chalk derived principally from Organic
+Bodies. — Distinction of Fresh-water from Marine Formations. — Genera
+of Fresh-water and Land Shells. — Rules for recognising Marine
+Testacea. — Gyrogonite and Chara. — Fresh-water Fishes. — Alternation
+of Marine and Fresh-water Deposits. — Lym-Fiord.
+
+Chapter IV—CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.
+Chemical and Mechanical Deposits. — Cementing together of Particles. —
+Hardening by Exposure to Air. — Concretionary Nodules. — Consolidating
+Effects of Pressure. — Mineralization of Organic Remains. — Impressions
+and Casts: how formed. — Fossil Wood. — Goppert’s Experiments. —
+Precipitation of Stony Matter most rapid where Putrefaction is going
+on. — Sources of Lime and Silex in Solution.
+
+Chapter V—ELEVATION OF STRATA ABOVE THE SEA.—HORIZONTAL AND INCLINED
+STRATIFICATION.
+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. — Strata of Deep-sea and Shallow-water Origin alternate. — Also
+Marine and Fresh-water Beds and old Land Surfaces. — Vertical,
+inclined, and folded Strata. — Anticlinal and Synclinal Curves. —
+Theories to explain Lateral Movements. — Creeps in Coal-mines. — Dip
+and Strike. — Structure of the Jura. — Various Forms of Outcrop. —
+Synclinal Strata forming Ridges. — Connection of Fracture and Flexure
+of Rocks. — Inverted Strata. — Faults described. — Superficial Signs of
+the same obliterated by Denudation. — Great Faults the Result of
+repeated Movements. — Arrangement and Direction of parallel Folds of
+Strata. — Unconformability. — Overlapping Strata.
+
+Chapter VI—DENUDATION.
+Denudation defined. — Its Amount more than equal to the entire Mass of
+Stratified Deposits in the Earth’s Crust. — subaërial Denudation. —
+Action of the Wind. — Action of Running Water. — Alluvium defined. —
+Different Ages of Alluvium. — Denuding Power of Rivers affected by Rise
+or Fall of Land. — Littoral Denudation. — Inland Sea-Cliffs. —
+Escarpments. — Submarine Denudation. — Dogger-bank. — Newfoundland
+Bank. — Denuding Power of the Ocean during Emergence of Land.
+
+Chapter VII—JOINT ACTION OF DENUDATION, UPHEAVAL, AND SUBSIDENCE IN
+REMODELLING THE EARTH’S CRUST.
+How we obtain an Insight at the Surface, of the Arrangement of Rocks at
+great Depths. — Why the Height of the successive Strata in a given
+Region is so disproportionate to their Thickness. — Computation of the
+average annual Amount of subaërial Denudation. — Antagonism of Volcanic
+Force to the Levelling Power of running Water. — How far the Transfer
+of Sediment from the Land to a neighbouring Sea-bottom may affect
+Subterranean Movements. — Permanence of Continental and Oceanic Areas.
+
+Chapter VIII—CHRONOLOGICAL CLASSIFICATION OF ROCKS.
+Aqueous, Plutonic, volcanic, and metamorphic Rocks considered
+chronologically. — Terms Primary, Secondary, and Tertiary; Palæozoic,
+Mesozoic, and Cainozoic explained. — On the different Ages of the
+aqueous Rocks. — Three principal Tests of relative Age: Superposition,
+Mineral Character, and Fossils. — Change of Mineral Character and
+Fossils in the same continuous Formation. — Proofs that distinct
+Species of Animals and Plants have lived at successive Periods. —
+Distinct Provinces of indigenous Species. — Great Extent of single
+Provinces. — Similar Laws prevailed at successive Geological Periods. —
+Relative Importance of mineral and palæontological Characters. — Test
+of Age by included Fragments. — Frequent Absence of Strata of
+intervening Periods. — Tabular Views of fossiliferous Strata.
+
+Chapter IX—CLASSIFICATION OF TERTIARY FORMATIONS.
+Order of Succession of Sedimentary Formations. — Frequent
+Unconformability of Strata. — Imperfection of the Record. —
+Defectiveness of the Monuments greater in Proportion to their
+Antiquity. — Reasons for studying the newer Groups first. —
+Nomenclature of Formations. — Detached Tertiary Formations scattered
+over Europe. — Value of the Shell-bearing Mollusca in Classification. —
+Classification of Tertiary Strata. — Eocene, Miocene, and Pliocene
+Terms explained.
+
+Chapter X—RECENT AND POST-PLIOCENE PERIODS.
+Recent and Post-pliocene Periods. — Terms defined. — Formations of the
+Recent Period. — Modern littoral Deposits containing Works of Art near
+Naples. — Danish Peat and Shell-mounds. — Swiss Lake-dwellings. —
+Periods of Stone, Bronze, and Iron. — Post-pliocene Formations. —
+Coexistence of Man with extinct Mammalia. — Reindeer Period of South of
+France. — Alluvial Deposits of Paleolithic Age. — Higher and
+Lower-level Valley-gravels. — Loess or Inundation-mud of the Nile,
+Rhine, etc. — Origin of Caverns. — Remains of Man and extinct
+Quadrupeds in Cavern Deposits. — Cave of Kirkdale. — Australian
+Cave-breccias. — Geographical Relationship of the Provinces of living
+Vertebrata and those of extinct Post-pliocene Species. — Extinct
+struthious Birds of New Zealand. — Climate of the Post-pliocene Period.
+— Comparative Longevity of Species in the Mammalia and Testacea. —
+Teeth of Recent and Post-pliocene Mammalia.
+
+Chapter XI—POST-PLIOCENE PERIOD, continued.—GLACIAL CONDITIONS.
+Geographical Distribution, Form, and Characters of Glacial Drift. —
+Fundamental Rocks, polished, grooved, and scratched. — Abrading and
+striating Action of Glaciers. — Moraines, Erratic Blocks, and “Roches
+Moutonnees”. — Alpine Blocks on the Jura. — Continental Ice of
+Greenland. — Ancient Centres of the Dispersion of Erratics. —
+Transportation of Drift by floating Icebergs. — Bed of the Sea furrowed
+and polished by the running aground of floating Ice-islands.
+
+Chapter XII—POST-PLIOCENE PERIOD, continued.—GLACIAL CONDITIONS,
+concluded.
+Glaciation of Scandinavia and Russia. — Glaciation of Scotland. —
+Mammoth in Scotch Till. — Marine Shells in Scotch Glacial Drift. —
+Their Arctic Character. — Rarity of Organic Remains in Glacial
+Deposits. — Contorted Strata in Drift. — Glaciation of Wales, England,
+and Ireland. — Marine Shells of Moel Tryfaen. — Erratics near
+Chichester. — Glacial Formations of North America. — Many Species of
+Testacea and Quadrupeds survived the Glacial Cold. — Connection of the
+Predominance of Lakes with Glacial Action. — Action of Ice in
+preventing the silting up of Lake-basins. — Absence of Lakes in the
+Caucasus. — Equatorial Lakes of Africa.
+
+Chapter XIII—PLIOCENE PERIOD.
+Glacial Formations of Pliocene Age. — Bridlington Beds. — Glacial
+Drifts of Ireland. — Drift of Norfolk Cliffs. — Cromer Forest-bed. —
+Aldeby and Chillesford Beds. — Norwich Crag. — Older Pliocene Strata. —
+Red Crag of Suffolk. — Coprolitic Bed of Red Crag. — White or Coralline
+Crag. — Relative Age, Origin, and Climate of the Crag Deposits. —
+Antwerp Crag. — Newer Pliocene Strata of Sicily. — Newer Pliocene
+Strata of the Upper Val d’Arno. — Older Pliocene of Italy. —
+Subapennine Strata. — Older Pliocene Flora of Italy.
+
+Chapter XIV—MIOCENE PERIOD.—UPPER MIOCENE.
+Upper Miocene Strata of France. — Faluns of Touraine. — Tropical
+Climate implied by Testacea. — Proportion of recent Species of Shells.
+— faluns more ancient than the Suffolk Crag. — Upper Miocene of
+Bordeaux and the South of France. — Upper Miocene of Oeningen, in
+Switzerland. — Plants of the Upper Fresh-water Molasse. — Fossil Fruit
+and Flowers as well as Leaves. — Insects of the Upper Molasse. — Middle
+or Marine Molasse of Switzerland. — Upper Miocene Beds of the
+Bolderberg, in Belgium. — Vienna Basin. — Upper Miocene of Italy and
+Greece. — Upper Miocene of India; Siwalik Hills. — Older Pliocene and
+Miocene of the United States.
+
+Chapter XV—LOWER MIOCENE.
+Lower Miocene Strata of France. — Line between Miocene and Eocene. —
+Lacustrine Strata of Auvergne. — Fossil Mammalia of the Limagne
+d’Auvergne. — Lower Molasse of Switzerland. — Dense Conglomerates and
+Proofs of Subsidence. — Flora of the Lower Molasse. — American
+Character of the Flora. — Theory of a Miocene Atlantis. — Lower Miocene
+of Belgium. — Rupelian Clay of Hermsdorf near Berlin. — Mayence Basin.
+— Lower Miocene of Croatia. — Oligocene Strata of Beyrich. — Lower
+Miocene of Italy. — Lower Miocene of England. — Hempstead Beds. — Bovey
+Tracey Lignites in Devonshire. — Isle of Mull Leaf-Beds. — Arctic
+Miocene Flora. — Disco Island. — Lower Miocene of United States. —
+Fossils of Nebraska.
+
+Chapter XVI—EOCENE FORMATIONS.
+Eocene Areas of North of Europe. — Table of English and French Eocene
+Strata. — Upper Eocene of England. — Bembridge Beds. — Osborne or St.
+Helen’s Beds. — Headon Series. — Fossils of the Barton Sands and Clays.
+— Middle Eocene of England. — Shells, Nummulites, Fish and Reptiles of
+the Bracklesham Beds and Bagshot Sands. — Plants of Alum Bay and
+Bournemouth. — Lower Eocene of England. — London Clay Fossils. —
+Woolwich and Reading Beds formerly called “Plastic Clay”. — Fluviatile
+Beds underlying Deep-sea Strata. — Thanet Sands. — Upper Eocene Strata
+of France. — Gypseous Series of Montmartre and Extinct Quadrupeds. —
+Fossil Footprints in Paris Gypsum. — Imperfection of the Record. —
+Calcaire Silicieux. — Gres de Beauchamp. — Calcaire Grossier. —
+Miliolite Limestone. — Soissonnais Sands. — Lower Eocene of France. —
+Nummulitic Formations of Europe, Africa, and Asia. — Eocene Strata in
+the United States. — Gigantic Cetacean.
+
+Chapter XVII—UPPER CRETACEOUS GROUP.
+Lapse of Time between Cretaceous and Eocene Periods. — Table of
+successive Cretaceous Formations. — Maestricht Beds. — Pisolitic
+Limestone of France. — Chalk of Faxoe. — Geographical Extent and Origin
+of the White Chalk. — Chalky Matter now forming in the Bed of the
+Atlantic. — Marked Difference between the Cretaceous and existing
+Fauna. — Chalk-flints. — Pot-stones of Horstead. — Vitreous Sponges in
+the Chalk. — Isolated Blocks of Foreign Rocks in the White Chalk
+supposed to be ice-borne. — Distinctness of Mineral Character in
+contemporaneous Rocks of the Cretaceous Epoch. — Fossils of the White
+Chalk. — Lower White Chalk without Flints. — Chalk Marl and its
+Fossils. — Chloritic Series or Upper Greensand. — Coprolite Bed near
+Cambridge. — Fossils of the Chloritic Series. — Gault. — Connection
+between Upper and Lower Cretaceous Strata. — Blackdown Beds. — Flora of
+the Upper Cretaceous Period. — Hippurite Limestone. — Cretaceous Rocks
+in the United States.
+
+Chapter XVIII—LOWER CRETACEOUS OR NEOCOMIAN FORMATION.
+Classification of marine and fresh-water Strata. — Upper Neocomian. —
+Folkestone and Hythe Beds. — Atherfield Clay. — Similarity of
+Conditions causing Reappearance of Species after short Intervals. —
+Upper Speeton Clay. — Middle Neocomian. — Tealby Series. — Middle
+Speeton Clay. — Lower Neocomian. — Lower Speeton Clay. — Wealden
+Formation. — Fresh-water Character of the Wealden. — Weald Clay. —
+Hastings Sands. — Punfield Beds of Purbeck, Dorsetshire. — Fossil
+Shells and Fish of the Wealden. — Area of the Wealden. — Flora of the
+Wealden.
+
+Chapter XIX—JURASSIC GROUP.—PURBECK BEDS AND OOLITE.
+The Purbeck Beds a Member of the Jurassic Group. — Subdivisions of that
+Group. — Physical Geography of the Oolite in England and France. —
+Upper Oolite. — Purbeck Beds. — New Genera of fossil Mammalia in the
+Middle Purbeck of Dorsetshire. — Dirt-bed or ancient Soil. — Fossils of
+the Purbeck Beds. — Portland Stone and Fossils. — Kimmeridge Clay. —
+Lithographic Stone of Solenhofen. — Archæopteryx. — Middle Oolite. —
+Coral Rag. — Nerinæa Limestone. — Oxford Clay, Ammonites and
+Belemnites. — Kelloway Rock. — Lower, or Bath, Oolite. — Great Plants
+of the Oolite. — Oolite and Bradford Clay. — Stonesfield Slate. —
+Fossil Mammalia. — Fuller’s Earth. — Inferior Oolite and Fossils. —
+Northamptonshire Slates. — Yorkshire Oolitic Coal-field. — Brora Coal.
+— Palæontological Relations of the several Subdivisions of the Oolitic
+group.
+
+Chapter XX—JURASSIC GROUP, CONTINUED.—LIAS.
+Mineral Character of Lias. — Numerous successive Zones in the Lias,
+marked by distinct Fossils, without Unconformity in the Stratification,
+or Change in the Mineral Character of the Deposits. — Gryphite
+Limestone. — Shells of the Lias. — Fish of the Lias. — Reptiles of the
+Lias. — Ichthyosaur and Plesiosaur. — Marine Reptile of the Galapagos
+Islands. — Sudden Destruction and Burial of Fossil Animals in Lias. —
+Fluvio-marine Beds in Gloucestershire, and Insect Limestone. — Fossil
+Plants. — The origin of the Oolite and Lias, and of alternating
+Calcareous and Argillaceous Formations.
+
+Chapter XXI—TRIAS, OR NEW RED SANDSTONE GROUP.
+Beds of Passage between the Lias and Trias, Rhætic Beds. — Triassic
+Mammifer. — Triple Division of the Trias. — Keuper, or Upper Trias of
+England. — Reptiles of the Upper Trias. — Foot-prints in the Bunter
+formation in England. — Dolomitic Conglomerate of Bristol. — Origin of
+Red Sandstone and Rock-salt. — Precipitation of Salt from inland Lakes
+and Lagoons. — Trias of Germany. — Keuper. — St. Cassian and Hallstadt
+Beds. — Peculiarity of their Fauna. — Muschelkalk and its Fossils. —
+Trias of the United States. — Fossil Foot-prints of Birds and Reptiles
+in the Valley of the Connecticut. — Triassic Mammifer of North
+Carolina. — Triassic Coal-field of Richmond, Virginia. — Low Grade of
+early Mammals favourable to the Theory of Progressive Development.
+
+Chapter XXII—PERMIAN OR MAGNESIAN LIMESTONE GROUP.
+Line of Separation between Mesozoic and Palæozoic Rocks. — Distinctness
+of Triassic and Permian Fossils. — Term Permian. — Thickness of
+calcareous and sedimentary Rocks in North of England. — Upper, Middle,
+and Lower Permian. — Marine Shells and Corals of the English Magnesian
+Limestone. — Reptiles and Fish of Permian Marl-slate. — Foot-prints of
+Reptiles. — Angular Breccias in Lower Permian. — Permian Rocks of the
+Continent. — Zechstein and Rothliegendes of Thuringia. — Permian Flora.
+— Its generic Affinity to the Carboniferous.
+
+Chapter XXIII—THE COAL OR CARBONIFEROUS GROUP.
+Principal Subdivisions of the Carboniferous Group. — Different
+Thickness of the sedimentary and calcareous Members in Scotland and the
+South of England. — Coal-measures. — Terrestrial Nature of the Growth
+of Coal. — Erect fossil Trees. — Uniting of many Coal-seams into one
+thick Bed. — Purity of the Coal explained. — Conversion of Coal into
+Anthracite. — Origin of Clay-ironstone. — Marine and brackish-water
+Strata in Coal. — Fossil Insects. — Batrachian Reptiles. —
+Labyrinthodont Foot-prints in Coal-measures. — Nova Scotia
+Coal-measures with successive Growths of erect fossil Trees. —
+Similarity of American and European Coal. — Air-breathers of the
+American Coal. — Changes of Condition of Land and Sea indicated by the
+Carboniferous Strata of Nova Scotia.
+
+Chapter XXIV—FLORA AND FAUNA OF THE CARBONIFEROUS PERIOD.
+Vegetation of the Coal Period. — Ferns, Lycopodiaceæ, Equisetaceæ,
+Sigillariæ, Stigmariæ, Coniferæ. — Angiosperms. — Climate of the Coal
+Period. — Mountain Limestone. — Marine Fauna of the Carboniferous
+Period. — Corals. — Bryozoa, Crinoidea. — Mollusca. — Great Number of
+fossil Fish. — Foraminifera.
+
+Chapter XXV—DEVONIAN OR OLD RED SANDSTONE GROUP.
+Classification of the Old Red Sandstone in Scotland and in Devonshire.
+— Upper Old Red Sandstone in Scotland, with Fish and Plants. — Middle
+Old Red Sandstone. — Classification of the Ichthyolites of the Old Red,
+and their Relation to Living Types. — Lower Old Red Sandstone, with
+Cephalaspis and Pterygotus. — Marine or Devonian Type of Old Red
+Sandstone. — Table of Devonian Series. — Upper Devonian Rocks and
+Fossils. — Middle. — Lower. — Eifel Limestone of Germany. — Devonian of
+Russia. — Devonian Strata of the United States and Canada. — Devonian
+Plants and Insects of Canada.
+
+Chapter XXVI—SILURIAN GROUP.
+Classification of the Silurian Rocks. — Ludlow Formation and Fossils. —
+Bone-bed of the Upper Ludlow. — Lower Ludlow Shales with Pentamerus. —
+Oldest known Remains of fossil Fish. — Table of the progressive
+Discovery of Vertebrata in older Rocks. — Wenlock Formation, Corals,
+Cystideans and Trilobites. — Llandovery Group or Beds of Passage. —
+Lower Silurian Rocks. — Caradoc and Bala Beds. — Brachiopoda. —
+Trilobites. — Cystideæ. — Graptolites. — Llandeilo Flags. — Arenig or
+Stiper-stones Group. — Foreign Silurian Equivalents in Europe. —
+Silurian Strata of the United States. — Canadian Equivalents. — Amount
+of specific Agreement of Fossils with those of Europe.
+
+Chapter XXVII—CAMBRIAN AND LAURENTIAN GROUPS.
+Classification of the Cambrian Group, and its Equivalent in Bohemia. —
+Upper Cambrian Rocks. — Tremadoc Slates and their Fossils. — Lingula
+Flags. — Lower Cambrian Rocks. — Menevian Beds. — Longmynd Group. —
+Harlech Grits with large Trilobites. — Llanberis Slates. — Cambrian
+Rocks of Bohemia. — Primordial Zone of Barrande. — Metamorphosis of
+Trilobites. — Cambrian Rocks of Sweden and Norway. — Cambrian Rocks of
+the United States and Canada. — Potsdam Sandstone. — Huronian Series. —
+Laurentian Group, upper and lower. — Eozoon Canadense, oldest known
+Fossil. — Fundamental Gneiss of Scotland.
+
+Chapter XXVIII—VOLCANIC ROCKS.
+External Form, Structure, and Origin of Volcanic Mountains. — Cones and
+Craters. — Hypothesis of “Elevation Craters” considered. — Trap Rocks.
+— Name whence derived. — Minerals most abundant in Volcanic Rocks. —
+Table of the Analysis of Minerals in the Volcanic and Hypogene Rocks. —
+Similar Minerals in Meteorites. — Theory of Isomorphism. — Basaltic
+Rocks. — Trachytic Rocks. — Special Forms of Structure. — The columnar
+and globular Forms. — Trap Dikes and Veins. — Alteration of Rocks by
+volcanic Dikes. — Conversion of Chalk into Marble. — Intrusion of Trap
+between Strata. — Relation of trappean Rocks to the Products of active
+Volcanoes.
+
+Chapter XXIX—ON THE AGES OF VOLCANIC ROCKS.
+Tests of relative Age of Volcanic Rocks. — Why ancient and modern Rocks
+cannot be identical. — Tests by Superposition and intrusion. — Test by
+Alteration of Rocks in Contact. — Test by Organic Remains. — Test of
+Age by Mineral Character. — Test by Included Fragments. — Recent and
+Post-pliocene volcanic Rocks. — Vesuvius, Auvergne, Puy de Come, and
+Puy de Pariou. — Newer Pliocene volcanic Rocks. — Cyclopean Isles,
+Etna, Dikes of Palagonia, Madeira. — Older Pliocene volcanic Rocks. —
+Italy. — Pliocene Volcanoes of the Eifel. — Trass.
+
+Chapter XXX—AGE OF VOLCANIC ROCKS—CONTINUED.
+Volcanic Rocks of the Upper Miocene Period. — Madeira. — Grand Canary.
+— Azores. — Lower Miocene Volcanic Rocks. — Isle of Mull. — Staffa and
+Antrim. — The Eifel. — Upper and Lower Miocene Volcanic Rocks of
+Auvergne. — Hill of Gergovia. — Eocene Volcanic Rocks of Monte Bolca. —
+Trap of Cretaceous Period. — Oolitic Period. — Triassic Period. —
+Permian Period. — Carboniferous Period. — Erect Trees buried in
+Volcanic Ash in the Island of Arran. — Old Red Sandstone Period. —
+Silurian Period. — Cambrian Period. — Laurentian Volcanic Rocks.
+
+Chapter XXXI—PLUTONIC ROCKS.
+General Aspect of Plutonic Rocks. — Granite and its Varieties. —
+Decomposing into Spherical Masses. — Rude columnar Structure. — Graphic
+Granite. — Mutual Penetration of Crystals of Quartz and Feldspar. —
+Glass Cavities in Quartz of Granite. — Porphyritic, talcose, and
+syenitic Granite. — Schorlrock and Eurite. — Syenite. — Connection of
+the Granites and Syenites with the Volcanic Rocks. — Analogy in
+Composition of Trachyte and Granite. — Granite Veins in Glen Tilt, Cape
+of Good Hope, and Cornwall. — Metalliferous Veins in Strata near their
+Junction with Granite. — Quartz Veins. — Exposure of Plutonic Rocks at
+the surface due to Denudation.
+
+Chapter XXXII—ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS.
+Difficulty in ascertaining the precise Age of a Plutonic Rock. — Test
+of Age by Relative Position. — Test by Intrusion and Alteration. — Test
+by Mineral Composition. — Test by included Fragments. — Recent and
+Pliocene Plutonic Rocks, why invisible. — Miocene Syenite of the Isle
+of Skye. — Eocene Plutonic Rocks in the Andes. — Granite altering
+Cretaceous Rocks. — Granite altering Lias in the Alps and in Skye. —
+Granite of Dartmoor altering Carboniferous Strata. — Granite of the Old
+Red Sandstone Period. — Syenite altering Silurian Strata in Norway. —
+Blending of the same with Gneiss. — Most ancient Plutonic Rocks. —
+Granite protruded in a solid Form.
+
+Chapter XXXIII—METAMORPHIC ROCKS.
+General Character of Metamorphic Rocks. — Gneiss. — Hornblende-schist.
+— Serpentine. — Mica-schist. — Clay-slate. — Quartzite. —
+Chlorite-schist. — Metamorphic Limestone. — Origin of the metamorphic
+Strata. — Their Stratification. — Fossiliferous Strata near intrusive
+Masses of Granite converted into Rocks identical with different Members
+of the metamorphic Series. — Arguments hence derived as to the Nature
+of Plutonic Action. — Hydrothermal Action, or the Influence of Steam
+and Gases in producing Metamorphism. — Objections to the metamorphic
+Theory considered.
+
+Chapter XXXIV—METAMORPHIC ROCKS—continued.
+Definition of slaty Cleavage and Joints. — Supposed Causes of these
+Structures. — Crystalline Theory of Cleavage. — Mechanical Theory of
+Cleavage. — Condensation and Elongation of slate Rocks by lateral
+Pressure. — Lamination of some volcanic Rocks due to Motion. — Whether
+the Foliation of the crystalline Schists be usually parallel with the
+original Planes of Stratification. — Examples in Norway and Scotland. —
+Causes of Irregularity in the Planes of Foliation.
+
+Chapter XXXV—ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.
+Difficulty of ascertaining the Age of metamorphic Strata. — Metamorphic
+Strata of Eocene date in the Alps of Switzerland and Savoy. — Limestone
+and Shale of Carrara. — Metamorphic Strata of older date than the
+Silurian and Cambrian Rocks. — Order of Succession in metamorphic
+Rocks. — Uniformity of mineral Character. — Supposed Azoic Period. —
+Connection between the Absence of Organic Remains and the Scarcity of
+calcareous Matter in metamorphic Rocks.
+
+Chapter XXXVI—MINERAL VEINS.
+Different Kinds of mineral Veins. — Ordinary metalliferous Veins or
+Lodes. — Their frequent Coincidence with Faults. — Proofs that they
+originated in Fissures in solid Rock. — Veins shifting other Veins. —
+Polishing of their Walls or “Slicken sides”. — Shells and Pebbles in
+Lodes. — Evidence of the successive Enlargement and Reopening of veins.
+— Examples in Cornwall and in Auvergne. — Dimensions of Veins. — Why
+some alternately swell out and contract. — Filling of Lodes by
+Sublimation from below. — Supposed relative Age of the precious Metals.
+— Copper and lead Veins in Ireland older than Cornish Tin. — Lead Vein
+in Lias, Glamorganshire. — Gold in Russia, California, and Australia. —
+Connection of hot Springs and mineral Veins.
+
+INDEX
+
+
+
+PREFACE.
+
+THE LAST or sixth EDITION of my “Elements of Geology” was already out
+of print before the end of 1868, in which year I brought out the tenth
+edition of my “Principles of Geology.”
+
+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 “Elements” 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 “Elements”
+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 “Elements,” that I resolved to give it a
+new title and call it the “Student’s Elements of Geology.”
+
+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 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
+“the cheapest Bible in the largest possible print.”
+
+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.
+
+CHARLES LYELL.
+
+73 HARLEY STREET, LONDON,
+_December_, 1870.
+
+
+
+
+CHAPTER I.
+ON THE DIFFERENT CLASSES OF ROCKS.
+
+
+Geology defined. — Successive Formation of the Earth’s Crust. —
+Classification of Rocks according to their Origin and Age. — Aqueous
+Rocks. — Their Stratification and imbedded Fossils. — Volcanic Rocks,
+with and without Cones and Craters. — Plutonic Rocks, and their
+Relation to the Volcanic. — Metamorphic Rocks, and their probable
+Origin. — The term Primitive, why erroneously applied to the
+Crystalline Formations. — Leading Division of the Work.
+
+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 _ge_, the
+earth, and _logos_, 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’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.
+
+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—that they were created in their present form, and in their
+present position. The geologist soon comes to a different conclusion,
+discovering 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.
+
+By the “earth’s crust,” 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.
+
+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 _rock_
+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 _soils._ 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 _roche_ applied in French, _rocca_ in
+Italian, and _felsart_ 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.
+
+The most natural and convenient mode of classifying the various rocks
+which compose the earth’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.
+
+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.
+
+Aqueous Rocks.—The aqueous rocks, sometimes called the sedimentary, or
+fossiliferous, cover a larger part of the earth’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 _stratified,_ or divided
+into distinct layers, or strata. The term _stratum_ means simply a bed,
+or any thing spread out or _strewed_ 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.
+
+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 _formation_
+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.
+
+The term _formation,_ which I have used in the above explanation,
+expresses in geology any assemblage of rocks which have some character
+in common, whether of origin, 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.
+
+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.
+
+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
+_stratified,_ 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.[1]
+
+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’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.[2]
+
+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 _fossils,_ so abundantly included in the
+earth’s crust. By a _fossil_ 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.[3]
+
+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.
+
+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.
+
+Volcanic Rocks.—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 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 _dikes,_ 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 _volcanic
+tuff,_ 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.
+
+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.
+
+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’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 _tuff_
+in various parts of the British Isles, and forming _dikes,_ 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.
+
+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.
+
+Plutonic Rocks (_Granite,_ etc).—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
+_crystalline schists,_ 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.
+
+As it is admitted that nothing strictly analogous to these crystalline
+productions can now be seen in the progress of formation on the earth’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 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’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.
+
+Metamorphic, or Stratified Crystalline Rocks.—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.
+
+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 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.
+
+In accordance with the hypothesis above alluded to, I proposed in the
+first edition of the Principles of Geology (1833) the term
+“Metamorphic” for the altered strata, a term derived from meta, _
+trans,_ and morphe, _forma._
+
+Hence there are four great classes of rocks considered in reference to
+their origin—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 “primitive,” 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’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 great
+depth, are passing from a solid to a fluid state, and then
+reconsolidating, so as to acquire a new texture.
+
+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 _altered_ rocks), and, on the
+other, must have reference to characters in which those rocks differ,
+both from the volcanic and from the _unaltered_ sedimentary strata. I
+proposed in the Principles of Geology (first edition, vol. iii) the
+term “hypogene” for this purpose, derived from upo, _ under,_ and
+ginomai, _to be,_ or _to be born_; a word implying the theory that
+granite, gneiss, and the other crystalline formations are alike
+_netherformed_ 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 _underlying_ rocks. They never repose on
+the volcanic or trappean formations, nor on strata containing organic
+remains. They are _hypogene,_ as “being under” all the rest.
+
+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’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.
+
+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.
+
+ [1] See Principles of Geology, by the Author, Index, “Nile,” “Rivers,”
+ etc.
+
+ [2] See p. 44, Fig. 7.
+
+ [3] Col. R. J. Strachey found oolitic fossils 18,400 feet high in the
+ Himalaya.
+
+
+
+
+CHAPTER II.
+AQUEOUS ROCKS.—THEIR COMPOSITION AND FORMS OF STRATIFICATION.
+
+
+Mineral Composition of Strata. — Siliceous Rocks. — Argillaceous. —
+Calcareous. — Gypsum. — Forms of Stratification. — Original
+Horizontality. — Thinning out. — Diagonal Arrangement. — Ripple-mark.
+
+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.
+
+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.
+
+Siliceous and Arenaceous Rocks.—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 by a slight quantity of siliceous or
+calcareous matter, or by oxide of iron or clay.
+
+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 _micaceous sandstones_ 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.
+
+When sandstone is coarse-grained, it is usually called _ grit._ If the
+grains are rounded, and large enough to be called pebbles, it becomes a
+_conglomerate_ or _pudding-stone,_ which may consist of pieces of one
+or of many different kinds of rock. A conglomerate, therefore, is
+simply gravel bound together by cement.
+
+Argillaceous Rocks.—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’s lathe, is called a _clay_; 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
+71·15 parts of silex, 15·86 of alumine, 1·92 of lime, and 6·73 of
+water;[1] 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.[2] _ Shale_ 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.
+
+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.[3]
+
+Calcareous Rocks.—This division comprehends those rocks which, like
+chalk, are composed chiefly of lime and carbonic 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
+_compact_ stone, or a stone of which the separate parts are so minute
+as not to be distinguishable from each other by the naked eye.
+
+Many limestones are made up entirely of minute fragments of shells and
+coral, or of calcareous sand cemented together. These last might be
+called “calcareous sandstones;” 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.
+
+The variety of limestone called _oolite_ 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.
+
+Any limestone which is sufficiently hard to take a fine polish is
+called _marble._ 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.
+
+_Siliceous limestone_ is an intimate mixture of carbonate of lime and
+flint, and is harder in proportion as the flinty matter predominates.
+
+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.
+
+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
+_loam._ If there is much calcareous matter in clay it is called _marl_;
+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.
+
+_Marl slate_ 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.
+
+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—magnesian
+limestone or dolomite, and gypsum. _Magnesian limestone_ 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. _Dolomite,_ so common in many parts of
+Germany and France, is also a variety of magnesian limestone, usually
+of a granular texture.
+
+_Gypsum_ 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 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. _
+Gypseous marl_ is a mixture of gypsum and marl. _Alabaster_ 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.
+
+Forms of Stratification.—A series of strata sometimes consists of one
+of the above rocks, sometimes of two or more in alternating beds.
+
+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.
+
+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’s
+surface.[4] 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.
+
+It is not the object of the present work to give a description 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.
+
+Original Horizontality.—It is said generally that the upper and under
+surfaces of strata, or the “planes of stratification,” 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.
+
+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.
+
+
+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 _c, d, e,_ the surface at _e_ 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
+_c_ to _e._ 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 2½ 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.
+
+Fig. 2. Section of strata of sandtone, grit, and congolmerate.
+
+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 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.)
+
+Fig. 3: Section of sand at Sandy Hill, near Biggleswade, Bedfordshire.
+
+Diagonal or Cross Stratification.—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
+“false or cross bedding” 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 _a, b, c_ 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 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.
+
+Fig. 4Fig. 5
+
+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.
+
+Fig. 6: Cliff between Mismer and Dunwich.
+
+Fig. 7: Section from Monte Calvo to the sea by the valley of the
+Magnan, near Nice.
+
+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’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°. 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.
+
+It is well known that the torrents and streams which now 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
+_a_, Fig. 7, or those nearest to Monte Calvo, are older than those
+indicated by _b_, and these again were formed before _c_; 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.
+
+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 _a, b, c, d_ 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.
+
+Fig. 8: Slab of ripple-marked (New Red) sandstone from Cheshire.
+
+Ripple-mark.—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.
+
+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.[5] 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.
+
+ [1] W. Phillips, Mineralogy, p.33.
+
+ [2] Phil. Mag., vol. x, 1837.
+
+ [3] See W. Phillips’s Mineralogy, “Alumine.”
+
+ [4] Consult Index to Principles of Geology, “Stratification,”
+ “Currents,” “Deltas,” “Water,” etc.
+
+ [5] Darwin, Volcanic Islands, p. 134.
+
+
+
+
+CHAPTER III.
+ARRANGEMENT OF FOSSILS IN STRATA.—FRESH-WATER AND MARINE FOSSILS.
+
+
+Successive Deposition indicated by Fossils. — Limestones formed of
+Corals and Shells. — Proofs of gradual Increase of Strata derived from
+Fossils. — Serpula attached to Spatangus. — Wood bored by Teredina. —
+Tripoli formed of Infusoria. — Chalk derived principally from Organic
+Bodies. — Distinction of Fresh-water from Marine Formations. — Genera
+of Fresh-water and Land Shells. — Rules for recognising Marine
+Testacea. — Gyrogonite and Chara. — Fresh-water Fishes. — Alternation
+of Marine and Fresh-water Deposits. — Lym-Fiord.
+
+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.
+
+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.
+
+Rate of Deposition indicated by Fossils.—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 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.
+
+Fossil Gryphæ, covered both on the outside and inside with fossil
+serpulæ.
+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 (_a_) in Fig. 9,
+may often have grown upon an 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 _Gryphæa_ (a kind of oyster) was fixed.
+
+Fig. 10: Serpula attached to a fossil. Fig. 11: Recent Spatangus with
+spines removed from one side.
+Some fossil shells, even if simply attached to the _ outside_ 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 _Echini_, 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 _Spatangus_, 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 _
+Serpula_, therefore, which now adheres externally, could not have begun
+to grow till the _Micraster_ had died, and the spines became detached.
+
+Fig. 12: Ananchytes from the chalk.
+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 (_Ananchytes_) in the chalk (see Fig. 12) which has fixed to
+it the lower valve of a _Crania_, a genus of bivalve mollusca. The
+upper valve (_b_, 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
+lived from youth to age, then died and lost its spines, which were
+carried away. Then the young _Crania_ adhered to the bared shell, grew
+and perished in its turn; after which the upper valve was separated
+from the lower before the _Ananchytes_ became enveloped in chalky mud.
+
+Fig. 13: Fossil wood bored by Teredina.
+
+Fig. 14: Recent wood bored by Teredo.
+
+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, _ e_, a
+representation is given of a piece of recent wood pierced by the
+_Teredo navalis_, or common ship-worm, which destroys wooden piles and
+ships. When the cylindrical tube _d_ has been extracted from the wood,
+the valves are seen at the larger or anterior extremity, as shown at
+_c._ In like manner, a piece of fossil wood (_a_, Fig. 13) has been
+perforated by a kindred but extinct genus, the _Teredina_ of Lamarck.
+The calcareous tube of this mollusk was united and, as it were,
+soldered on to the valves of the shell (_b_), which therefore cannot be
+detached from the tube, like the valves of the recent _Teredo._ 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 _ Teredinæ_ 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.
+
+Strata of Organic Origin.—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’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 _Gaillonella distans_ (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.
+
+Figs 15 and 16: Gaillonella; Fig. 17: Bacillaria parodoxa
+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 _Gaillonella ferruginea_
+(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 “the pan,” and are sometimes of economical value.
+
+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).
+
+“The dust we tread upon was once alive!”—BYRON.
+
+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.
+
+Fresh-water and Marine Fossils.—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 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.
+
+In many parts of France—in Auvergne, for example—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 (_helices_); 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.
+
+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.
+
+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’s system,
+excluding those 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.[1]
+
+Fig. 18: Cyrena obovata. Fig. 19: Cyrena fluminatis.
+
+Fig. 20: Anodonta Cordierii. Fig. 21: Anodonta latimarginata. Fig. 22:
+Unio littoralis.
+
+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 _Cyclas,
+Cyrena, Unio,_ and _Anodonta_ (see Figures); the two first and two last
+of which are so nearly allied as to pass into each other.
+
+Fig. 23: Gryphæa incurva.
+
+Lamarck divided the bivalve mollusca into the Dimyary, or those having
+two large muscular impressions in each valve, as _a b_ in the Cyclas,
+Fig. 18, and Unio, Fig. 22, and the _ Monomyary,_ 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,[2] we may at once presume a deposit
+containing any of them to be marine.
+
+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.
+
+Fig. 35: Neritina globulud. Fig. 36: Nerita granulosa.
+The univalve shells most characteristic of fresh-water deposits are,
+_Planorbis, Limnæa,_ and _Paludina._ (See Figures.) But to these are
+occasionally added _Physa, Succinea, Ancylus, Valvata, Melanopsis,
+Melania, Potamides,_ and _ Neritina_ (see Figures), the four last being
+usually found in estuaries.
+
+Fig. 37: Potamides cinctus.
+
+Some naturalists include _Neritina_ (Fig. 35) and the marine _Nerita_
+(Fig. 36) in the same genus, it being scarcely possible to distinguish
+the two by good generic characters. But, as a general rule, the
+fluviatile species are smaller, smoother, and more globular than the
+marine; and they have never, like the _Neritæ,_ the inner margin of the
+outer lip toothed or crenulated. (See Fig. 36.)
+
+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.
+
+The terrestrial shells are all univalves. The most important genera
+among these, both in a recent and fossil state, are _ Helix_ (Fig. 38),
+_Cyclostoma_ (Fig. 39), _Pupa_ (Fig. 40), _Clausilia_ (Fig. 41),
+_Bulimus_ (Fig. 42), _ Glandina_ and _Achatina._
+
+Fig. 38: Helix Turomensis. Fig. 39: Cyclostoma elegans. Fig. 40: Pupa
+tridens. Fig. 41: Clausilia bidens. Fig. 42: Bulimus lubricus.
+
+_Ampullaria_ (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 _Natica_ and other marine
+genera.
+
+Fig. 43: Ampullaria glauca.
+All univalve shells of land and fresh-water species, with the exception
+of _Melanopsis_ (Fig. 34), and _Achatina,_ 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 _Ampullaria_ and the
+land-shells (Figs 38-42), when its outline is not interrupted by an
+indentation or notch, such as that seen at _b_ in _ Ancillaria_ (Fig.
+45); or is not prolonged into a canal, as that seen at _a_ in
+_Pleurotoma_ (Fig. 44).
+
+Fig. 44: Pleurotoma exorta. Fig. 45: Ancillaria subulata.
+
+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.
+
+There is, however, one genus which affords an occasional exception to
+one of the above rules. The _Potamides_ (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.
+
+Among the fossils very common in fresh-water deposits are the shells of
+_Cypris,_ a minute bivalve crustaceous animal.[3] 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 _Cytherina_ of
+Lamarck, inhabit salt-water; and, although the animal differs slightly,
+the shell is scarcely distinguishable from that of the Cypris.
+
+Fresh-water Fossil Plants.—The seed-vessels and stems of _ Chara,_ 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, _a_.)
+
+The _Charæ_ 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 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 _Charæ,_) 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 _b,_ Fig. 46.)
+
+Fig. 46: Chara medicaginula. Fig. 47: Chara elastica.
+
+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 “Principles of Geology.”
+
+Fresh-water and Marine Fish.—The remains of fish are occasionally
+useful in determining the fresh-water origin of strata. Certain genera,
+such as carp, perch, pike, and loach (_Cyprinus, Perca, Esox,_ and
+_Cobitis_), as also _Lebias,_ being peculiar to fresh-water. Other
+genera contain some fresh-water and some marine species, as _Cottus,
+Mugil,_ and _Anguilla,_ 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; 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.
+
+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.
+
+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.
+
+Lym-Fiord.—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 _Fucus
+vesiculosus,_ together with oysters and other marine mollusca, have
+succeeded the _Cyclas, Lymnæa, Paludina,_ and _Charæ._[4]
+
+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.
+
+ [1] See Woodward’s Manual of Mollusca, 1856.
+
+ [2] 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.
+
+ [3] For figures of fossil species of Purbeck, see Chapter XIX
+
+ [4] See Principles, Index, “Lym-Fiord.”
+
+
+
+
+CHAPTER IV.
+CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.
+
+
+Chemical and Mechanical Deposits. — Cementing together of Particles. —
+Hardening by Exposure to Air. — Concretionary Nodules. — Consolidating
+Effects of Pressure. — Mineralization of Organic Remains. — Impressions
+and Casts: how formed. — Fossil Wood. — Goppert’s Experiments. —
+Precipitation of Stony Matter most rapid where Putrefaction is going
+on. — Sources of Lime and Silex in Solution.
+
+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.
+
+Chemical and Mechanical Deposits.— 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.
+
+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 must be produced
+by vital agency as in the case of coral reefs.
+
+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.
+
+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.
+
+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.
+
+Consolidation of Strata.—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.
+
+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.
+
+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.
+
+In what manner silex and carbonate of lime may become widely diffused
+in small quantities through the waters which permeate the earth’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.
+
+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 “quarry-water,” 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 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.
+
+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.[1]
+
+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.
+
+Fig. 48: Calcareous nodules in Lias.
+Concretionary Structure.—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.
+
+Among the most remarkable examples of concretionary structure are those
+described by Professor Sedgwick as 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 _b_ upward into _a._ In this instance we must suppose the
+deposition of a series of minor layers, first forming the stratum _b,_
+and afterwards the incumbent stratum _a_; 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.
+
+Fig. 49: Spheroidal concretions in magnesian limestone. Fig. 50:
+Section through strata of grit.
+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, _d
+e f,_ forming a portion of the superior stratum, becomes united with B
+into one solid mass of stone. The original line of division, _d e,_
+being thus effaced, the line _d f_ would generally be considered as the
+surface of the bed B, though not strictly a true plane of
+stratification.
+
+Pressure and Heat.—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 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.
+
+Analogous effects of condensation may arise when the solid parts of the
+earth’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 “black lead” 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.
+
+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.
+
+Mineralisation of Organic Remains.—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 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 _a,_ Fig. 51, commonly called a fossil
+screw, would never be suspected by an inexperienced conchologist to be
+the internal shape of the fossil univalve, _ b,_ Fig. 51. Nor should we
+have imagined at first sight that the shell a and the cast _b,_ Fig.
+52, belong to one and the same fossil. The reader will observe, in the
+last-mentioned figure (_b,_ Fig. 52), that an empty space shaded dark,
+which the _ shell itself_ 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 _a,_ 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,
+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.
+
+Fig. 51: Phasianella Heddingtonensis. Fig. 52: Pleurotomaria Anglica.
+
+Fig. 53: Section of a tree from the coal-measures.
+
+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.
+
+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 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.
+
+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 (_Pinus sylvestris_), 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.
+
+The late Dr. Turner observes, that when mineral matter is in a “nascent
+state,” 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.
+
+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.[2] 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.
+
+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.
+
+ [1] Dr. MacCulloch, Syst. of Geol., vol. i, p. 123.
+
+ [2] Piddington, Asiat. Research., vol. xviii, p. 226.
+
+
+
+
+CHAPTER V.
+ELEVATION OF STRATA ABOVE THE SEA.—HORIZONTAL AND INCLINED
+STRATIFICATION.
+
+
+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. — Strata of Deep-sea and Shallow-water Origin alternate. — Also
+Marine and Fresh-water Beds and old Land Surfaces. — Vertical,
+inclined, and folded Strata. — Anticlinal and Synclinal Curves. —
+Theories to explain Lateral Movements. — Creeps in Coal-mines. — Dip
+and Strike. — Structure of the Jura. — Various Forms of Outcrop. —
+Synclinal Strata forming Ridges. — Connection of Fracture and Flexure
+of Rocks. — Inverted Strata. — Faults described. — Superficial Signs of
+the same obliterated by Denudation. — Great Faults the Result of
+repeated Movements. — Arrangement and Direction of parallel Folds of
+Strata. — Unconformability. — Overlapping Strata.
+
+Land has been raised, not the Sea lowered.—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 (p. 29). 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
+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.
+
+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’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.
+
+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.
+
+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 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.
+
+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.[1]
+
+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.
+
+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.
+
+Alternations of Marine and Fresh-water Strata.—It has been shown in the
+third chapter that there is such a differencebetween 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’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.
+
+Vertical, Inclined, and Curved Strata.—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.
+
+Fig. 54: Vertical conglomerate and sandstone.
+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 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’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.
+
+Anticlinal and Synclinal Curves.—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.
+
+Fig. 55: Section of Forfarshire, from N.W. to S.E.
+
+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 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 _dip_, 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 “trough”
+or“basin.” Through the centre of this valley runs an imaginary line A,
+called technically a “synclinal line,” 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 _saddle_, having
+an _anticlinal_ 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, _a_, 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
+_unconformably_ upon strata of the sandstone group, No. 2.
+
+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.[2] It occurs near St. Abb’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.
+
+Folding by Lateral Movement.—An experiment was made by Sir James Hall,
+with a view of illustrating the manner in 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 _denudation_, 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.
+
+Fig. 56: Curved strata of slate near St. Abb’s Head, Berwickshire.
+
+Fig. 57
+
+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.
+
+Fig. 58
+
+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 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’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.
+
+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.
+
+Creeps in Coal-mines.—The “creeps,” as they are called in coal-mines,
+afford an excellent illustration of this fact.—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. “In Yorkshire,” says Mr. Buddle,
+“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.”[3] 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.
+
+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 _a, b,_ 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.
+
+Now it might have been expected that, instead of the floor rising up,
+the ceiling would sink down, and this effect, called a “thrust,” does,
+in fact, take place where the pavement is more solid than the roof. But
+it usually happens, in 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.
+
+Fig. 59: Section of carboniferous strata at Wallsend showing ‘creeps’.
+
+The first symptom of a “creep,” says Mr. Buddle, is a slight curvature
+at the bottom of each gallery, as at _a_, Fig. 59: then the pavement,
+continuing to rise, begins to open with a longitudinal crack, as at
+_b_; then the points of the fractured ridge reach the roof, as at _c_;
+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 _d._ Meanwhile the coal in the props has
+become crushed and cracked by pressure. It is also found that below the
+creeps _a, b, c, d,_ an inferior stratum, called the “metal coal,”
+which is 3 feet thick, has been fractured at the points _e, f, g, h,_
+and has risen, so as to prove that the upward movement, caused by the
+working out of the “main coal,” 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.
+
+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, 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’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.
+
+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.
+
+In like manner, in the interior of the earth, the solid parts of the
+earth’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.
+
+Fig. 60
+Dip and Strike.—In describing the manner in which strata depart from
+their original horizontality, some technical terms, such as “dip” and
+“strike,” “anticlinal” and “synclinal” 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 _dip_; the point of the compass to
+which it is inclined is called the _point of dip_, and the degree of
+deviation from a level or horizontal line is called _ the amount of
+dip_, or _the angle of dip._ 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 degrees. The _strike_, or _line of bearing_, is the
+prolongation or extension of the strata in a direction _at right
+angles_ to the dip; and hence it is sometimes called the _ direction_
+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, _ streichen_ 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.
+
+A stratum which is horizontal, or quite level in all directions, has
+neither dip nor strike.
+
+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.
+
+Fig. 61: Apparent horizontality of inclined strata.
+
+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 would
+be seen by the person on shore to be at an angle of 40°. 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.
+
+Fig. 62: Two hands used to determine the inclination of strata.
+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°, formed by the meeting of the
+hands, so as to give an angle of 45°, 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.
+
+Fig. 63: Section illustrating the structure of the Swiss Jura.
+
+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, of which the nature and dip are
+occasionally displayed in deep transverse gorges, called “cluses,”
+caused by fractures at right angles to the direction of the chain.[4]
+Now let us suppose these ridges and parallel valleys to run north and
+south, we should then say that the _strike_ of the beds is north and
+south, and the _dip_ 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.
+
+Fig. 64: Ground-plan of the denuded ridge C, Fig. 63. Fig. 65:
+Transverse section.
+
+Outcrop of Strata.—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 _a, b, c_
+come out to the day, or, as the miners say, _crop out_, 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 _outcrop_, or _basset._
+
+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—that is,
+turning every way.
+
+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.
+
+Fig. 66: Slope of valley 40°, dip of strata 20°. Fig. 67: Slope of
+valley 20°, dip of strata 50°. Fig. 68: Slope of valley 20°, dip of
+strata 20°, in opposite directions.
+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’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.
+
+Thirdly, if the dip of the beds be steeper than the slope of the
+valley, then the V’s will point downward (see Fig. 67), and those
+formed of the older beds will now appear uppermost, as B appears above
+A.
+
+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°, and crossed by a valley, which declines in an opposite
+direction at 20°.
+
+These rules may often be of great practical utility; for the different
+degrees of dip occurring in the two cases represented in 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.[5]
+
+Section of carboniferous rocks of Lancashire. Section of carboniferous
+rocks of Lancashire. (E. Hull.[6])
+
+Synclinal Strata forming Ridges.—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 _a, b,_
+Fig. 69, while in the intervening valley, _c_, they slope upward,
+forming an arch.
+
+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 _a_,
+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
+p. 62 and in part to the permeation of sea-water while they were yet
+submerged.
+
+Fig. 70: Strata of chert, grit, and marl, near St. Jean de Luz.
+
+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 _a_, 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.
+
+Fig. 71: Bent and undulating gypseous marl.
+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 (_g, g,_ Fig.
+71), while the continuity of the more pliable and ductile marls, _m,
+m,_ has not been interrupted.
+
+Fig. 72: Folded strata.
+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
+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.
+
+Fig. 73
+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.
+
+Fractures of the Strata and Faults.—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.
+
+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
+“slickensides.” 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.
+
+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. “This mode of displacement is called a
+fault, shift, slip, or throw.” “The miner,” says Playfair, describing a
+fault, “is often perplexed, 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 _a, b, c, d_ (Fig. 75), though their
+identity is still to be recognised by their possessing the same
+thickness and the same internal characters.”[7]
+
+Fig. 74: Faults.
+
+Fig. 75: E F, fault or fissure filled with rubbish, on each side of
+which the shifted strata are not parallel.
+
+In Coalbrook Dale, says Mr. Prestwich[8], 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
+_débris_ of the strata. In following the 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.
+
+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.
+
+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.
+
+Fig. 76: Apparent alternations of strata caused by vertical faults.
+
+If, for example, the dark line A H (Fig. 76) represent the surface of a
+country on which the strata _a, b, c_ 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 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—a miner, who has
+not discovered the faults, finding the mass _a_, 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 _b_, and partly on the sandstone _ c_; the same result awaits him
+at the fault F, and on reaching E he is again stopped by a wall
+composed of the rock _d._
+
+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 “ninety-fathom dike,” 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.[9] 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.[10] 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.
+
+Great Faults the Result of Repeated Movements.—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 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.
+
+Fig. 77: Faults and denuded coal-strata, Ashby de la Zouch.
+
+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 _a, b, c, d_ 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 _z z_, is uniformly undulating, without any
+break, and the mass indicated by the dotted outline must have been
+washed away.[11]
+
+The student may refer to Mr. Hull’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—one, for
+example, before, and another after, the Triassic epoch.[12]
+
+The shifting of the beds by faults is often intimately connected with
+those same foldings which constitute the 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.[13] 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.
+
+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 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.
+
+Arrangement and Direction of Parallel Folds of Strata.—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.
+
+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°, 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.
+
+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° 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.
+
+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, 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.[14]
+
+Fig. 78: Unconformable junction of old red sandstone and Silurian
+schist at the Siccar Point, near St. Abb’s Head, Berwickshire.
+
+Unconformability of Strata.— 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, _d, d,_ Fig. 78,
+are also inclined, it is plain that the lower strata _a, a,_ have been
+twice displaced; first, before the deposition of the newer beds, _d,
+d,_ and a second time when these same strata were upraised out of the
+sea, and thrown slightly out of the horizontal position.
+
+Fig. 79: Junction of unconformable strata near Mons, in Belgium.
+
+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 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, _a_, 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 _c_, the work of saxicavous mollusca; and
+many rents, as at _b_, which descend several feet or yards into the
+limestone, have been filled with sand and shells, similar to those in
+the stratum _a._
+
+Overlapping Strata.—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.
+
+ [1] See “Principles of Geology,” 1867, p. 314.
+
+ [2] Edin. Trans., vol. vii, pl. 3.
+
+ [3] Proceedings of Geol. Soc., vol. iii, p. 148.
+
+ [4] Thurmann, “Essai sur les Soulèvemens Jurassiques de Porrentruy,”
+ Paris, 1832.
+
+ [5] 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 _faults._
+
+ [6] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 324, 1868.
+
+ [7] Playfair, Illust. of Hutt. Theory, § 42.
+
+ [8] Geol. Trans., second series. vol. v, p. 452.
+
+ [9] Conybeare and Phillips Outlines, etc., p. 376.
+
+ [10] Phillips, Geology, Lardner’s Cyclop., p. 41.
+
+ [11] See Mammatt’s Geological Facts, etc., p. 90 and plate.
+
+ [12] Hull, Quart. Geol. Journ., vol. xxiv, p. 318, 1868.
+
+ [13] H. D. Rogers, Geol. of Pennsylvania, p. 897.
+
+ [14] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 323.
+
+
+
+
+CHAPTER VI.
+DENUDATION
+
+
+Denudation defined. — Its Amount more than equal to the entire Mass of
+Stratified Deposits in the Earth’s Crust. — Subaërial Denudation. —
+Action of the Wind. — Action of Running Water. — Alluvium defined. —
+Different Ages of Alluvium. — Denuding Power of Rivers affected by Rise
+or Fall of Land. — Littoral Denudation. — Inland Sea-Cliffs. —
+Escarpments. — Submarine Denudation. — Dogger-bank. — Newfoundland
+Bank. — Denuding Power of the Ocean during Emergence of Land.
+
+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’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.
+
+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 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.
+
+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’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.
+
+Subaërial Denudation.—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.
+
+_Action of the Wind._—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.
+
+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°. 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.
+
+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 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.
+
+Fig. 80: Section through several eroded formations.
+
+_Action of Running Water._—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.
+
+In the “Memoirs of the Geological Survey of Great Britain” (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 observations in the same “Survey,” 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’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’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.
+
+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.
+
+Alluvium.—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
+_alluvio_, an inundation, or _alluo_, to wash, because the pebbles and
+sand commonly resemble those of a river’s bed or the mud and gravel
+washed over low lands by a flood.
+
+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 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.
+
+Fig. 81: Lavas of Auvergne resting on alluviums of different ages.
+
+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 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.
+
+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.
+
+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 “glacial.”
+
+Denuding Power of Rivers affected by Rise or Fall of Land.—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.
+
+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.
+
+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° and 69° N.[1] 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;[2] 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.
+
+Littoral Denudation.—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, 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.
+
+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.
+
+Inland Sea-cliffs.—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.
+
+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 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.
+
+Escarpments.—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 “escarpments,”
+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.
+
+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[3] 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.
+
+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—those, for example, of the greensand and
+chalk—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.
+
+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.
+
+Submarine Denudation.—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.
+
+Dogger-bank.—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 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.[4]
+
+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.
+
+_Newfoundland Bank._—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.
+
+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 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.
+
+ [1] Principles of Geology 7th ed., p. 506; 10th ed., vol. ii, p. 196.
+
+ [2] Second Visit to the United States, vol. i, chap. xxxiv.
+
+ [3] Physical Geography and Geology of Great Britain, p. 78, 1864.
+
+ [4] Principles, 10th ed., vol. i, p. 569.
+
+
+
+
+CHAPTER VII.
+JOINT ACTION OF DENUDATION, UPHEAVAL, AND SUBSIDENCE IN REMODELLING THE
+EARTH’S CRUST.
+
+
+How we obtain an Insight at the Surface, of the Arrangement of Rocks at
+great Depths. — Why the Height of the successive Strata in a given
+Region is so disproportionate to their Thickness. — Computation of the
+average annual Amount of subaërial Denudation. — Antagonism of Volcanic
+Force to the Levelling Power of running Water. — How far the Transfer
+of Sediment from the Land to a neighbouring Sea-bottom may affect
+Subterranean Movements. — Permanence of Continental and Oceanic Areas.
+
+How we obtain an Insight at the Surface, of the Arrangement of Rocks at
+Great Depths.— The reader has been already informed that, in the
+structure of the earth’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’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.
+
+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 the arrangement of rocks composing the earth’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.
+
+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 _lateral compression_ those anticlinal and synclinal
+curves of the beds already described (Fig. 55), which, together with
+denudation, subaërial and submarine, enable us to investigate the
+structure of the earth’s crust many miles below those points which the
+miner can reach. I have already shown in Fig. 56, how, at St. Abb’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,
+Fig. 55.
+
+Why the Height of the Successive Strata in a given Region is so
+Disproportionate to their Thickness.—We cannot too distinctly bear in
+mind how dependent we are on the joint action of the volcanic and
+aqueous forces, the one in
+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?
+
+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 “crop out” 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.
+
+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—namely, more than 4000 feet—as to appear to compensate in
+some measure for the deficiency of contemporaneous sedimentary rock.[1]
+
+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.
+
+The formations 1, 2, 3, the Laurentian, Cambrian, and
+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.
+
+Fig. 82: Unconformable Palæozoic stata, Sutherlandshire (Murchison).
+
+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′,
+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′.
+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 Fig. 563 of _Arenicolites_), hundreds, nay thousands, of which
+I saw as I ascended the mountain.
+
+Fig. 83: Diagrammatic section of the same groups near Queenaig
+(Murchison).
+
+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 limestones, 3_a_, and schists, 3_b_,
+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.
+
+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.
+
+Computation of the Average Annual Amount of Subaërial Denudation.—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 the effects which causes in every
+day action must produce when the multiplying power of time is taken
+into account.
+
+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.[2] 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,[3] 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.
+
+The student, by referring to my “Principles of Geology,”[4] 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.
+
+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 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 _vice versa._[5]
+
+Antagonism of Volcanic Force to the Levelling Power of Running
+Water.—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’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 “Principles of Geology,”[6] that
+running water and volcanic action are two antagonistic forces; the one
+labouring 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.[7]
+
+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.
+
+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 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.
+
+How far the Transfer of Sediment from the Land to a Neighbouring
+Sea-bottom may affect Subterranean Movements.—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.
+
+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’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.
+
+I cannot, at present, discuss this subject, of which I have treated
+more fully elsewhere,[8] 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’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.
+
+Permanence of Continental and Oceanic Areas.—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 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.
+
+I have remarked elsewhere[9] 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.
+
+Suppose, therefore, we had ascertained that the triturating power of
+subaërial denudation might in a given time—in three, or six, or a
+greater number of millions of years—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 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.
+
+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.
+
+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.
+
+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 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.
+
+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.
+
+ [1] Hull, Quart. Geol. Journ., vol. xxiv, p. 322, 1868.
+
+ [2] Tylor, Phil. Mag., 4th series, p. 268, 1850.
+
+ [3] Croll, Phil. Mag., 1868, p. 381.
+
+ [4] Vol. i, p. 442, 1867.
+
+ [5] Trans. Geol. Soc. Glasgow, vol. iii, p. 169.
+
+ [6] 1st ed., chap. x, p. 167, 1830; see also 10th ed., vol. i, chap.
+ xv, p. 327, 1867.
+
+ [7] Principles, vol. ii, p. 237; also 1st ed., p. 447, 1830.
+
+ [8] Principles, vol. ii, p. 229, 1868.
+
+ [9] Principles, vol. i, p. 265, 1867.
+
+
+
+
+CHAPTER VIII.
+CHRONOLOGICAL CLASSIFICATION OF ROCKS.
+
+
+Aqueous, Plutonic, volcanic, and metamorphic Rocks considered
+chronologically. — Terms Primary, Secondary, and Tertiary; Palæozoic,
+Mesozoic, and Cainozoic explained. — On the different Ages of the
+aqueous Rocks. — Three principal Tests of relative Age: Superposition,
+Mineral Character, and Fossils. — Change of Mineral Character and
+Fossils in the same continuous Formation. — Proofs that distinct
+Species of Animals and Plants have lived at successive Periods. —
+Distinct Provinces of indigenous Species. — Great Extent of single
+Provinces. — Similar Laws prevailed at successive Geological Periods. —
+Relative Importance of mineral and palæontological Characters. — Test
+of Age by included Fragments. — Frequent Absence of Strata of
+intervening Periods. — Tabular Views of fossiliferous Strata.
+
+Chronology of Rocks.— 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’s history, and which at
+another.
+
+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.
+
+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’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.
+
+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’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’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’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.
+
+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 “primary,” 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 _palaion,_
+“ancient,” and _zoon,_ “an organic being,” still retaining the terms
+secondary and tertiary; Mr. Phillips, for the sake of uniformity, has
+proposed Mesozoic, for secondary, from _mesos,_ “middle,” etc.; and
+Cainozoic, for tertiary, from _kainos,_ “recent,” etc.; but the terms
+primary, secondary, and tertiary have the claim of priority in their
+favour, and are of corresponding value.
+
+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.
+
+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.
+
+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.
+
+Superposition.—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.
+
+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 p. 73, p. 87.) 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.
+
+Mineral Character.—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 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.
+
+Organic Remains.—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.
+
+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:—
+
+                Natura il fece, e poi ruppe la stampa. ARIOSTO.
+                Nature made him, and then broke the die.
+
+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.
+
+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.
+
+Zoological Provinces.—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 “Principles of Geology,” 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.
+
+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—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—the identification of mineral masses of
+the same age, by means of their included organic contents, would be a
+matter of still greater certainty.
+
+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.
+
+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.
+
+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.
+
+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 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.
+
+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 _terrestrial_ 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 _marine_ organic fossils, be shown to have belonged to
+the same epoch.
+
+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.
+
+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 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.
+
+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.
+
+Test by included Fragments of older Rocks.—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.
+
+Chronological Groups.—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.
+
+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.
+
+Fig. 84: Seven fossiliferous groups.
+
+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.
+
+Section South of Bristol.
+
+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.
+
+By this means the German, French, and English geologists 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.
+
+Abridged General Table of Fossiliferous Strata.
+
+TABULAR VIEW OF THE FOSSILIFEROUS STRATA,
+SHOWING THE ORDER OF SUPERPOSITION OR CHRONOLOGICAL SUCCESSION OF THE
+PRINCIPAL GROUPS DESCRIBED IN THIS WORK.
+
+
+POST-TERTIARY
+EXAMPLES
+
+POST-TERTIARY
+
+EXAMPLES
+
+
+
+POST-
+
+TERTIARY 1.
+
+RECENT
+
+Shells and mammals, all of living species. British
+
+Clyde marine strata, with canoes (p.
+146).
+
+Foreign
+
+Danish kitchen middens (p.
+146).
+
+Lacustrine mud, with remains of Swiss lake-dwellings (p. 148).
+
+Marine strata inclosing Temple of Serapis, at Puzzuoli (p. 146).
+2.
+
+POST-
+
+PLIOCENE.
+
+Shells, recent mammalia in part extinct. British
+
+Loam of Brixham cave, with flint implements and bones of extinct
+and living quadrupeds (p.
+157)
+
+Drift near Salisbury, with bones of mammoth, Spermophilus, and
+stone implements (p. 161).
+
+Glacial drift of Scotland, with marine shells and remains of
+mammoth (p. 176.
+
+Erratics of Pagham and Selsey Bill (p. 182).
+
+Glacial drift of Wales, with marine fossil shells, about 1400
+feet high, on Moel Tryfaen (p.
+181).
+
+Foreign
+
+Dordogne caves of the reindeer period (p. 150).
+
+Older valley-gravels of Amiens, with flint implements and bones
+of extinct mammalia (p.
+152).
+
+Loess of Rhine (p. 154).
+
+Ancient Nile-mud forming river-terraces (p. 154).
+
+Loam and breccia of Liege caverns, with human remains (pp. 156, 157).
+
+Australian cave breccias, with bones of extinct marsupials (p. 158).
+
+Glacial drift of Northern Europe (p.
+166, p. 174).
+
+
+TERTIARY OR CAINOZOIC
+
+PLIOCENE 3.
+NEWER
+PLIOCENE.
+The shells almost all of living species. British
+Bridlington beds, marine Arctic fauna (p. 189).
+Glacial boulder formation of Norfolk cliffs (p. 190).
+Forest-bed of Norfolk cliffs, with bones of _Elephas meridionalis,_
+etc. (p. 191).
+Chillesford and Aldeby beds, with marine shells, chiefly Arctic (p.
+192).
+Norwich crag (p. 193).
+Foreign
+Eastern base of Mount Etna, with marine shells (p. 204).
+Sicilian calcareous and tufaceous strata (p. 205, 206).
+Lacustrine strata of Upper Val d’Arno (p. 207).
+Madeira leaf-bed and land-shells (p. 532). 4.
+OLDER
+PLIOCENE.
+Extinct species of
+shells forming a
+large minority. British
+Red crag of Suffolk, marine shells, some of northern forms (p. 194,
+195).
+White or coralline crag of Suffolk (p. 197).
+Foreign
+Antwerp crag (p. 204).
+Subapennine marls and sands (p. 208).
+
+EXAMPLES
+
+MIOCENE 5.
+UPPER
+MIOCENE.
+Majority of the
+shells extinct. British
+Wanting.
+Foreign
+Faluns of Touraine (p. 211).
+Faluns, proper, of Bordeaux (p. 214).
+Fresh-water strata of Gers (p. 215).
+Swiss Oeningen beds, rich in plants and insects (pp. 215-23).
+Marine Molasse, Switzerland (p. 223).
+Bolderberg beds of Belgium (p. 224).
+Vienna basin (p. 224).
+Beds of the Superga, near Turin (p. 226).
+Deposit at Pikermé, near Athens (p. 226).
+Strata of the Siwâlik hills, India (p. 226).
+Marine strata of the Atlantic border in the United States (p. 227).
+Volcanic tuff and limestone of Madeira, the Canaries, and the Azores
+(). 6.
+LOWER
+MIOCENE.
+Nearly all the
+shells extinct. British
+Hempstead beds, marine and fresh-water strata (p. 244).
+Lignites and clays of Bovey Tracey (p. 245).
+Isle of Mull leaf-bed, volcanic tuff (p. 247).
+Foreign
+Calcaire de la Beauce, etc. (p. 230).
+Grès de Fontainebleau (p. 230).
+Lacustrine strata of the Limagne d’Auvergne, and the Cantal (p. 233).
+Mayence basin (p. 242).
+Radaboj beds of Croatia (p. 242).
+Brown coal of Germany (p. 244).
+Lower Molasse of Switzerland, fresh-water and brackish (p. 235-9).
+Rupelmonde, Kleynspawen, and Tongrian beds of Belgium (p. 241, 242).
+Nebraska beds, United States (p. 248).
+Lower Miocene beds of Italy (p. 244).
+Miocene flora of North Greenland (p. 239). EOCENE 7.
+UPPER
+EOCENE. British
+Bembridge fluvio-marine strata (p. 252).
+Osborne or St. Helen’s series (p. 255).
+Headon series, with marine and fresh-water shells (p. 255).
+Barton sands and clays (p. 258).
+Foreign
+Gypsum of Montmartre, fresh-water with _Palæotherium_ (p. 270).
+Calcaire silicieux, or Travertin inférieur (p. 273),
+Grès de Beauchamp, or Sables moyens (p. 273). 8.
+MIDDLE
+EOCENE. British
+Bracklesham beds and Bagshot sands (p. 259).
+White clays of Alum Bay and Bournemouth (p. 262).
+Foreign
+Calcaire grossier, miliolitic limestone (p. 274).
+Soissonnais sands, or Lits coquilliers, with _Nummulites planulata_ (p.
+275).
+Claiborne beds of the United States, with _Orbitoides_ and _Zeuglodon_
+(p. 279).
+Nummulitic formation of Europe, Asia, etc. (p. 277). 9.
+LOWER
+EOCENE. British
+London clay proper (p. 263).
+Woolwich and Reading series, fluvio-marine (p. 267).
+Thanet sands (p. 269).
+Foreign
+Argile de Londres, near Dunkirk (p. 252).
+Argile plastique (p. 276).
+Sables de Bracheux (p. 276).
+
+SECONDARY OR MESOZOIC.
+
+CRETACEOUS 10.
+UPPER
+CRETACEOUS. British
+Upper white chalk, with flints (p. 290).
+Lower white chalk, without flints (p. 298).
+Chalk marl (p. 298).
+Chloritic series (or Upper Greensand), fire-stone of Surrey (p. 298).
+Gault (p. 300).
+Blackdown beds (p. 301).
+
+EXAMPLES
+
+CRETACEOUS 10.
+UPPER
+CRETACEOUS. Foreign
+Maetricht beds and Faxoe chalk (p. 233).
+Pisolitic limestone of France (p. 285).
+White chalk of France, Sweden, and Russia (p. 286, 287).
+Planer-kalk of Saxony (p. 293).
+Sands and clays of Aix-la-Chapelle (p. 302).
+Hippurite limestone of South of France (p. 305).
+New Jersey, U.S., sands and marls (p. 307). 11.
+LOWER
+CRETACEOUS or
+NEOCOMIAN. British
+Sands of Folkestone, Sandgate, and Hythe (p. 308).
+Atherfield clay, with _Perna mulleti_ (p. 309).
+Punfield marine beds, with _Vicarya lujana_ (p. 318).
+Speeton clay of Flamborough Head and Tealby (p. 311).
+Weald clay of Surrey, Kent, and Sussex, fresh-water, with _Cypris_ (p.
+313-5).
+Hastings sands (p. 316-8).
+Foreign
+Neocomian of Neufchatel, and Hils conglomerate of North Germany (p.
+312).
+Wealden beds of Hanover (p. 319). OOLITE 12.
+UPPER OOLITE. British
+Upper Purbeck beds, fresh-water (p. 323).
+Middle Purbeck, with numerous marsupial quadrupeds, etc. (p. 324).
+Lower Purbeck, fresh-water, with intercalated dirt-bed (p. 330).
+Portland stone and sand. (p. 334).
+Kimmeridge clay (p. 335).
+Foreign
+Marnes à gryphées virgules of Argonne (p. 336).
+Lithographic-stone of Solenhofen, with _Archæopteryx_ (p. 337). 13.
+MIDDLE OOLITE. British
+Coral rag of Berkshire, Wilts, and Yorkshire (p. 339).
+Oxford clay, with belemnites and Ammonite (p. 340).
+Kelloway rock of Wilts and Yorkshire (p. 341).
+Foreign
+Nerinæan limestone of the Jura (p. 339). 14.
+LOWER OOLITE. British
+Cornbrash and forest marble (p. 341).
+Great or Bath oolite of Bradford (p. 342).
+Stonesfield slate, with marsupials and _Araucaria_ (p. 345).
+Fuller’s earth of Bath (p. 348).
+Inferior oolite (p. 349). LIAS 15.
+LIAS. Upper Lias, argillaceous, with _Ammonites striatulus_ (p.
+353).
+Shale and limestone, with _Ammonites bifrons_ (p. 353).
+Middle Lias or Marlstone series, with zones containing characteristic
+Ammonites (p. 353).
+Lower Lias, also with zones characterised by peculiar Ammonites (p.
+356). TRIAS 16.
+UPPER TRIAS. British
+Rhætic, Penarth or _Avicula contorta_ beds (beds of passage) (p. 366).
+Keuper or Upper New Red sandstone, etc. (p. 369).
+Red shales of Cheshire and Lancashire, with rock-salt (p. 371).
+Dolomite conglomerate of Bristol (p. 373).
+Foreign
+Keuper beds of Germany (p. 375).
+St. Cassian or Hallstadt beds, with rich marine fauna (p. 376).
+Coal-field of Richmond, Virginia (p. 382).
+Chatham coal-field, North Carolina (p. 383). 17.
+MIDDLE TRIAS. British
+Wanting.
+Foreign
+Muschelkalk of Germany (p. 378). 18.
+LOWER TRIAS. British
+Bunter or Lower New Red sandstone of Lancashire and Cheshire (p. 372).
+Foreign
+Bunter-sandstein of Germany (p. 380).
+Red sandstone of Connecticut Valley, with footprints of birds and
+reptiles (p. 381).
+
+PRIMARY OR PALÆOZOIC
+EXAMPLES
+
+PERMIAN 19.
+PERMIAN. British
+Upper Permian of St. Bees’ Head, Cumberland (p. 386).
+Middle Permian, magnesian limestone, and marl-slate of Durham and
+Yorkshire, with _Protosaurus_ (p. 387).
+Lower Permian sandstones and breccias of Penrith and Dumfriesshire,
+intercalated (p. 390).
+Foreign
+Dark-coloured shales of Thuringia (p. 392).
+Zechstein or Dolomitic limestone (p. 392).
+Mergel-schiefer or Kupfer-schiefer (p. 392).
+Rothliegendes of Thuringia, with _Psaronius_ (p. 392).
+Magnesian limestones, etc., of Russia (p. 393). CARBONIFEROUS 20.
+UPPER CARBONIFEROUS. British
+Coal-measures of South Wales, with underclays inclosing _Stigmaria_ (p.
+397).
+Coal-measures of north and central England (p. 395).
+Millstone grit (p. 395).
+Yoredale series of Yorkshire (p. 395).
+Coal-field of Kilkenny with _Labyrinthodont_ (p. 407).
+Foreign
+Coal-field of Saarbruck, with _Archegosaurus_ (p. 406).
+Carboniferous strata of South Joggins, Nova Scotia (p. 409).
+Pennsylvania coal-field (p. 403). 21.
+LOWER CARBONIFEROUS. British
+Mountain limestone of Wales and South of England (p. 430).
+Same in Ireland (p. 437437).
+Carboniferous limestone of Scotland alternating with coal-bearing
+sandstones (p. 396).
+Erect trees in volcanic ash in the Island of Arran (p. 546).
+Foreign
+Mountain limestone of Belgium (p. 436). DEVONIAN or
+OLD RED SANDSTONE 22.
+UPPER
+DEVONIAN. British
+Yellow sandstone of Dura Den, with _Holoptychius_, etc. (p. 440); and
+of Ireland with _Anodon Jukesii_ (p. 441).
+Sandstones of Forfarshire and Perthshire, with _Holoptychius_, etc. (p.
+442).
+Pilton group of North Devon (p. 449).
+Petherwyn group of Cornwall, with _Clymenia_ and _Cypridina_ (p. 451).
+Foreign
+Clymenien-kalk and Cypridinen-schiefer of Germany (p. 450) 23.
+MIDDLE
+DEVONIAN. British
+Bituminous schists of Gamrie, Caithness, etc., with numerous fish (p.
+443).
+Ilfracombe beds with peculiar trilobites and corals (p. 450).
+Limestones of Torquay, with broad-winged Spirifers (p. 451).
+Foreign
+Eifel limestone, with underlying schists containing _Calceola_ (p.
+453).
+Devonian strata of Russia (p. 454). 24.
+LOWER
+DEVONIAN. British
+Arbroath paving-stones, with _Cephalaspis_ and _Pterygotus_ (p. 446).
+Lower sandstones of Forfarshire, with _Pterygotus_ (p. 446).
+Sandstones and slates of the Foreland and Linton (p. 454).
+Foreign
+Oriskany sandstone of Western Canada and New York (p. 456).
+Sandstones of Gaspe, with _Cephalaspis_ (p. 455 ).
+
+EXAMPLES
+
+SILURIAN 25.
+UPPER SILURIAN British
+Upper Ludlow formation, Downton sandstone, with bone-bed (p. 459).
+Lower Ludlow formation, with oldest known fish remains (p. 461).
+Wenlock limestone and shale (p. 465).
+Woolhope limestone and grit (p. 467).
+Tarannon shales (p. 468).
+_Beds of passage between Upper and Lower Silurian:_
+Upper Llandovery, or May-hill sandstone, with _Pentamerus oblongus_,
+etc. (p. 468).
+Lower Llandovery slates (p. 469).
+Foreign
+Niagara limestone, with _Calymene, Homalonotus_, etc. (p. 479).
+Clinton group of America, with _Pentamerus oblongus_, etc. (p. 479).
+Silurian strata of Russia, with _Pentamerus_ (p. 477). 26.
+LOWER SILURIAN. British
+Bala and Caradoc beds (p. 470).
+Llandeilo flags (p. 473).
+Arenig or Stiper-stones group (Lower Llandeilo of Murchison) (p. 475).
+Foreign
+Ungulite or Obolus grit of Russia (p. 477).
+Trenton limestone, and other Lower Silurian groups of North America (p.
+479).
+Lower Silurian of Sweden (p. 477). CAMBRIAN 27.
+UPPER CAMBRIAN. British
+Tremadoc slates (p. 483).
+Lingula flags, with _Lingula Davisii_ (p. 484).
+Foreign
+“Primordial” zone of Bohemia in part, with trilobites of the genera
+_Paradoxides_, etc. (p. 487).
+Alum schists of Sweden and Norway (p. 489).
+Potsdam sandstone, with _Dikelocephalus_ and _Obolella_ (p. 489). 28.
+LOWER CAMBRIAN. British
+Menevian beds of Wales, with _Paradoxides Davidis_, etc. (p. 484).
+Longmynd group, comprising the Harlech grits and Llanberis slates (p.
+485).
+Foreign
+Lower portion of Barrande’s “Primordial” zone in Bohemia (p. 486).
+Fucoid sandstones of Sweden (p. 489).
+Huronian series of Canada? (p. 490). LAURENTIAN 29.
+UPPER LAURENTIAN. British
+Fundamental gneiss of the Hebrides? (p. 493).
+Hypersthene rocks of Skye? (p. 491).
+Foreign
+Labradorite series north of the river St. Lawrence in Canada (p. 491).
+Adirondack mountains of New York (p. 491). 30.
+LOWER LAURENTIAN. British
+Wanting?
+Foreign
+Beds of gneiss and quartzite, with interstratified limestones, in one
+of which, 1000 feet thick, occurs a foraminifer, _Eozoon Canadense_,
+the oldest known fossil (p. 491).
+
+
+
+
+CHAPTER IX.
+CLASSIFICATION OF TERTIARY FORMATIONS.
+
+
+Order of Succession of Sedimentary Formations. — Frequent
+Unconformability of Strata. — Imperfection of the Record. —
+Defectiveness of the Monuments greater in Proportion to their
+Antiquity. — Reasons for studying the newer Groups first. —
+Nomenclature of Formations. — Detached Tertiary Formations scattered
+over Europe. — Value of the Shell-bearing Mollusca in Classification. —
+Classification of Tertiary Strata. — Eocene, Miocene, and Pliocene
+Terms explained.
+
+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.
+
+Fig. 86: Order of Superposition of Deposits
+
+Order of Superposition.—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 (p. 107), 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 (p. 94, p. 111), where I pointed out that the discordance
+which implies a considerable lapse of time between two formations in
+juxtaposition is almost invariably accompanied by a great dissimilarity
+in the species of organic remains.
+
+Frequent Unconformability of Strata.—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—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.
+
+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’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.
+
+Imperfection of the Record.—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 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’s history appears as nothing when contrasted with that which
+has been lost.
+
+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.
+
+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 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.
+
+Why newer Groups should be studied first.—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.
+
+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.
+
+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.
+
+Nomenclature.—The origin of the terms Primary and Secondary, and the
+synonymous terms Palaeozoic, and Mesozoic, were explained in Chapter
+VIII, p. 123.
+
+The Tertiary or Cainozoic strata (see p. 123) were so called 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.
+
+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.
+
+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.
+
+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.
+
+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. 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.
+
+Value of Testacean Fossils in Classification.—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 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.
+
+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.
+
+Classification of Tertiary Strata.—Many authors have divided the
+European Tertiary strata into three groups—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.
+
+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
+3½ 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, _dawn_, and cainos, _recent_, 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.
+
+The term Miocene (from meion, _less_, and cainos, _recent_) is intended
+to express a minor proportion of recent species (of testacea), the term
+Pliocene (from pleion, _ more_, and cainos, _recent_) a comparative
+plurality of the same. It may assist the memory of students to remind
+them, that the _Mi_ocene contain a _mi_nor proportion, and _ Pl_iocene
+a comparative _pl_urality of recent species; and that the greater
+number of recent species always implies the more modern origin of the
+strata.
+
+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.
+
+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.
+
+
+
+
+CHAPTER X.
+RECENT AND POST-PLIOCENE PERIODS.
+
+
+Recent and Post-pliocene Periods. — Terms defined. — Formations of the
+Recent Period. — Modern littoral Deposits containing Works of Art near
+Naples. — Danish Peat and Shell-mounds. — Swiss Lake-dwellings. —
+Periods of Stone, Bronze, and Iron. — Post-pliocene Formations. —
+Coexistence of Man with extinct Mammalia. — Reindeer Period of South of
+France. — Alluvial Deposits of Paleolithic Age. — Higher and
+Lower-level Valley-gravels. — Loess or Inundation-mud of the Nile,
+Rhine, etc. — Origin of Caverns. — Remains of Man and extinct
+Quadrupeds in Cavern Deposits. — Cave of Kirkdale. — Australian
+Cave-breccias. — Geographical Relationship of the Provinces of living
+Vertebrata and those of extinct Post-pliocene Species. — Extinct
+struthious Birds of New Zealand. — Climate of the Post-pliocene Period.
+— Comparative Longevity of Species in the Mammalia and Testacea. —
+Teeth of Recent and Post-pliocene Mammalia.
+
+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
+“Recent.”
+
+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.
+
+RECENT PERIOD
+
+It was stated in the sixth chapter, when I treated of denudation, that
+the dry land, or that part of the earth’s surface which is not covered
+by the waters of lakes or seas, is 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.
+
+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.
+
+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’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.
+
+Danish Peat and Shell-mounds or Kitchen-middens.—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
+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, _Pinus sylvestris._ This peat may be referred to that
+part of the stone period for which Sir John Lubbock proposed the name
+of “Neolithic”[1] in contradistinction to a still older era, termed by
+him “Paleolithic,” 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.
+
+On the coasts of the Danish islands in the Baltic, certain mounds,
+called in those countries “Kjökken-mödding,” or “kitchen-middens,”
+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.
+
+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 bronze. It appears that a
+race more advanced in civilisation, armed with weapons of that mixed
+metal, invaded Scandinavia, and ousted the aborigines.
+
+Lacustrine Habitations of Switzerland.—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.[2] 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.
+
+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.
+
+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.
+
+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 also been discovered, so that
+this settlement was evidently not abandoned till that metal had come
+into use.
+
+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.[3] 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.
+
+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.[4] 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.
+
+POST-PLIOCENE PERIOD
+
+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.
+
+Reindeer Period in South of France.—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 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 “reindeer
+period,” 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,
+_Cervus megaceros,_ and of the cave-lion, _Felis spelæa,_ 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.
+
+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.
+
+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.
+
+Alluvial Deposits of the Paleolithic Age.—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. 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.
+
+Fig. 87: Recent and Post-pliocene alluvial deposits.
+
+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′ has in many places been
+deposited by the river during floods which covered nearly the whole
+alluvial plain.
+
+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 (_E. primigenius_) and the Siberian
+rhinoceros (_R. tichorhinus_) are the most common in Europe. No. 3′ 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, 4′. 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.
+
+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—as, for example,
+in those of the Seine and Somme, and of the Thames and Ouse, near
+Bedford—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.
+
+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 “celts.” 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.
+
+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, 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’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 _Elephas primigenius_ and _E.
+antiquus, Rhinoceros tichorhinus, Hippopotamus, Felis spelæa, Hyæna
+spelæa,_ 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.
+
+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.
+
+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.
+
+Inundation-mud of Rivers.—Brick-earth.—Fluviatile Loam, or Loess.—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 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—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.
+
+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.
+
+In some parts of the valley of the Rhine the accumulation of similar
+loam, called in Germany “loess,” 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.
+
+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 _Succinea_, inhabits marshes and wet grassy meadows. The
+_Succinea elongata_ (or _S. oblongata_), Fig. 88, is very
+characteristic both of the loess of the Rhine and of some other
+European river-loams.
+
+Fig. 88: Succinea elongata; Fig. 89: Pupa muscorum (Linn.); Fig. 90:
+Helix hispida (Linn.) (plebia).
+
+Among the land-shells of the Rhenish loess, _Helix hispida_, Fig. 90,
+and _Pupa muscorum_, 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 _Helix nemoralis_, is
+occasionally preserved.
+
+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.
+
+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 the river had thrown down and afterwards removed alluvial matter.
+
+Cavern Deposits containing Human Remains and Bones of Extinct
+Animals.—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.
+
+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.
+
+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.
+
+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 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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+A fine example of a hyæna’s den was afforded by the cave of Kirkdale,
+so well described by the late Dr. Buckland in his _Reliquiæ Diluvianæ._
+In that cave, above twenty-five miles north-north-east of York, the
+remains of about 300 hyænas, belonging to individuals of every age,
+were detected. The species (_Hyæna spelæa_) has been considered by
+palæontologists as extinct; it was larger than the fierce _Hyæna
+crocuta_ 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—an opinion
+quite consistent with the known habits of the living hyæna.
+
+_Australian Cave-breccias._—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.
+
+Fig. 91: Part of a lower jaw of Macropus atlas.
+
+Some of these caves were examined by the late Sir T. Mitchell in the
+Wellington Valley, about 210 miles west of 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.
+
+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 _Phascolomys_, the wombat; _Dasyurus_), the ursine
+opossum; _Phalangista_, the vulpine opossum; and _Hypsiprymnus_, the
+kangaroo-rat.
+
+Fig. 92: Lower jaw of largest living species of kangaroo.
+
+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 (_Macropus atlas_, 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 (_a_, 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.
+
+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 _forms_ dates back to a period
+anterior to the origin of existing _species_; in other words, 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.
+
+Professor Owen, in his excellent “History of British Fossil Mammals,”
+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.
+
+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.
+
+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 (_Apteryx_). 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 _Dinornis_ and _Palapteryx_, 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.
+
+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.
+
+Climate of the Post-pliocene Period.—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 (_Ovibos
+moschatus_), 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 _Cyrena
+fluminalis_, a shell now extinct in Europe but still an inhabitant of
+the Nile and some Asiatic rivers. With it occurs the _Unio littoralis_,
+now living in the Seine and Loire. In the valley of the Somme flint
+tools have been found associated with _Hippopotamus major_ and _Cyrena
+fluminalis_ 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.
+
+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.
+
+In drift at Fisherton, near Salisbury, thirty feet above the river
+Wiley, the Greenland lemming and a new species of the Arctic genus
+_Spermophilus_ 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 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.
+
+Relative Longevity of Species in the Mammalia and Testacea.—I called
+attention in 1830[5] 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, which are among the lowest types of the invertebrata,
+has outlasted that of the mollusca in an equally decided manner.
+
+Teeth of Post-pliocene Mammalia.—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.
+
+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.
+
+Figures 93 through 105 represent the teeth of some of the more common
+species and genera found in alluvial and cavern deposits.
+
+Figs. 95 to 100: Teeth of extinct mammalia.
+
+Figs. 101 to 105: Teeth of extinct mammalia.
+
+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 _E. antiquus_; and most open and fewest in _E.
+meridionalis._ It will be also seen that the enamel in the molar of the
+_Rhinoceros tichorhinus_ (Fig. 97), is much thicker than in that of the
+_Rhinoceros leptorhinus_ (Fig. 96).
+
+ [1] Sir John Lubbock, Pre-historic Times, p. 3, 1865.
+
+ [2] Bulletin de la Sociétié Vaudoise des Sci. Nat., tome vi, Lausanne
+ 1860; and Antiquity of Man, by the author, chap. ii.
+
+ [3] Sir J. Lubbock’s Lecture, Royal Institution, Feb. 27th, 1863.
+
+ [4] Diodorus, v, 21, 22 and Sir H. James Note on Block of Tin dredged
+ up in Falmouth Harbour. Royal Institution of Cornwall, 1863.
+
+ [5] Principles of Geology, 1st ed., vol. iii, p. 140.
+
+
+
+
+CHAPTER XI.
+POST-PLIOCENE PERIOD, continued—GLACIAL CONDITIONS.[1]
+
+
+Geographical Distribution, Form, and Characters of Glacial Drift. —
+Fundamental Rocks, polished, grooved, and scratched. — Abrading and
+striating Action of Glaciers. — Moraines, Erratic Blocks, and “Roches
+Moutonnees.” Alpine Blocks on the Jura. — Continental Ice of Greenland.
+— Ancient Centres of the Dispersion of Erratics. — Transportation of
+Drift by floating Icebergs. — Bed of the Sea furrowed and polished by
+the running aground of floating Ice-islands.
+
+Character and Distribution of Glacial Drift.—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 _till_ 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 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 “erratics,” 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.
+
+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—a fact conspiring with the superficial
+position of the drift to indicate a comparatively modern origin.
+
+The term “diluvium” 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 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.
+
+Fig. 106: Limestone, polished, furrowed, and scratched by the glacier
+of Rosenlau in Switzerland.
+
+Transporting and abrading Power of Glaciers.—I have described elsewhere
+(“Principles” 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, 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 _moraine_, and
+resembling the _till_ before described (p. 166).
+
+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 “roche moutonnee.” 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.
+
+Alpine Blocks on the Jura.—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.
+
+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.
+
+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.
+
+Greenland Continental Ice.—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’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 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—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’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.
+
+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.
+
+Rink mentions that in North Greenland powerful springs of clayey water
+escape in winter from under the ice, where it descends to “the
+outskirts,” and where, as already stated, it is often 2000 feet thick—a
+fact showing how much grinding action is going on upon the surface of
+the subjacent 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° to about 70° 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.
+
+Drift carried by Icebergs.—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° and 70° 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’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.
+
+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 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’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.
+
+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.
+
+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.
+
+ [1] 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, “Vicissitudes of Climate.”
+
+
+
+
+CHAPTER XII.
+POST-PLIOCENE PERIOD, continued.—GLACIAL CONDITIONS, concluded.
+
+
+Glaciation of Scandinavia and Russia. — Glaciation of Scotland. —
+Mammoth in Scotch Till. — Marine Shells in Scotch Glacial Drift. —
+Their Arctic Character. — Rarity of Organic Remains in Glacial
+Deposits. — Contorted Strata in Drift. — Glaciation of Wales, England,
+and Ireland. — Marine Shells of Moel Tryfaen. — Erratics near
+Chichester. — Glacial Formations of North America. — Many Species of
+Testacea and Quadrupeds survived the Glacial Cold. — Connection of the
+Predominance of Lakes with Glacial Action. — Action of Ice in
+preventing the silting up of Lake-basins. — Absence of Lakes in the
+Caucasus. — Equatorial Lakes of Africa.
+
+Glaciation of Scandinavia and Russia.—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 (page 170).
+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.
+
+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, 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.
+
+Glaciation of Scotland.—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. “The glacial
+grooves,” he observed, “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.”
+
+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.[1] 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.
+
+_Mammoth in Scotch Till._—Almost all remains of the terrestrial fauna
+of the Continent which preceded the period of 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’ 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.[2] Still more recent explorations in the
+neighbourhood of Kilmaurs have shown that the fresh-water formation
+contains the seed of the pond-weed _Potamogeton_ 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’ tusks, and detected in these fossils (which
+had been in the Glasgow Museum for half a century) abundance of the
+same seeds.
+
+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.
+
+Figs. 107-112: Northern shells common in the drift of the Clyde, in
+Scotland.
+
+_Marine Shells of Scotch Drift._—The greatest height to which marine
+shells have yet been traced in this boulder 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.
+
+Fig. 113: Leda truncata; Fig. 114: Tellina calcarea, Chem.
+
+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 _Leda truncata,
+Tellina proxima_ (see Figs. 113 and 114), _Pecten Grœnlandicus,
+Crenella lævigata, Crenella nigra,_ and others, some of them first
+brought by Captain Sir E. Parry from the coast of Melville Island,
+latitude 76° 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 from Caithness, and the same number from
+Aberdeenshire and Banff, and in both cases all but six are arctic
+species.
+
+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.
+
+Another curious phenomenon bearing on this subject was styled by the
+late Hugh Miller the “striated pavements” 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.[3]
+
+_Contorted Strata in Drift._—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
+_b_ to _c_, Fig. 115, the horizontal stratification being resumed very
+abruptly at a short distance, as to the right of _f_, _g._ The
+overlying coarse gravel and sand, _ a_, is in some places horizontal,
+in others it exhibits cross bedding, and does not partake of the
+disturbances which the strata _b_, _c_, 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.
+
+Fig. 15: Section of contorted drift overlying till, seen on left bank
+of South Esk, near Cortachie, in 1840.
+
+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’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.
+
+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 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.[4]
+
+Glaciation of Wales and England.—The mountains of North Wales were
+recognised, in 1842, by Dr. Buckland, as having been an independent
+centre of the dispersion of erratics—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.
+
+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—in
+all 57 forms—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—an hypothesis which would require us to ascribe
+to it a high antiquity, since we must allow time, first for its
+sinking, and then for its re-elevation.
+
+The height reached by these fossil shells on Moel Tryfaen is no less
+than 1300 feet—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.
+
+Professor Ramsay[5] 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’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.
+
+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 _Turritella communis,
+Purpura lapillus, Cardium edule,_ and others, among which _Trophon
+clathratum_ (=_Fusus Bamffius_), though still surviving in North
+British seas, indicates a cold climate.
+
+_Erratics near Chichester._—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 promontory called Selsea Bill, in which Mr.
+Godwin-Austen found thirty-eight species of shells, and the number has
+since been raised to seventy.
+
+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, _Lutraria rugosa_ and _ Pecten polymorphous_,
+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.
+
+Glacial Formations of North America.—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 _till_ 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.
+
+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 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.
+
+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 _Mastodon giganteus_ 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.
+
+It would be rash, however, to infer from such data that these
+quadrupeds were mired in _modern_ 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
+_Melania, Lymnea, Planorbis, Velvata, Cyclaz, Unio, Helix,_ 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
+_Mastodon giganteus_ 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.
+
+Connection of the Predominance of Lakes with Glacial Action.—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.
+
+The southern limits of the lake districts of the Northern Hemisphere
+are found at about 40° N. latitude on the American continent, and about
+50° 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 “morainic,” 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.
+
+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
+principal cause of lake-basins, is a question still open to discussion.
+
+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.
+
+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 “Glacial” there have been movements of the earth’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
+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.
+
+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.
+
+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,[6] 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.
+
+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° 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:[7] “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.” 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 “justify the
+assertion that the present glaciers of the Caucasus, like those of the
+Alps, are only the shadows of their former selves.”
+
+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.
+
+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.[8]
+
+On the whole, it appears to me, in accordance with the views of
+Professor Ramsay, M. Mortillet, Mr. Geikie, and others, 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’s crust are gradually brought
+about.
+
+ [1] Jamieson, Quart. Geol. Journ., 1860, vol. xvi, p. 370.
+
+ [2] Bryce, Quart. Geol. Journ., vol. xxi, p. 217, 1865.
+
+ [3] Geikie, Trans. Geol. Soc. Glasgow, vol. i, part ii, p. 68, 1863.
+
+ [4] Milne Home, Trans. Royal Soc. Edinburgh, vol. xxv, 1868-9.
+
+ [5] Quart. Geol. Journ., 1852, vol. viii, p. 372.
+
+ [6] Antiquity of Man, p. 313.
+
+ [7] Travels in Central Caucasus, 1869, p. 452.
+
+ [8] See Principles, vol. i, p. 420, 10th ed., 1867.
+
+
+TERTIARY OR CAINOZOIC PERIOD
+
+
+
+
+CHAPTER XIII.
+PLIOCENE PERIOD
+
+
+Glacial Formations of Pliocene Age. — Bridlington Beds. — Glacial
+Drifts of Ireland. — Drift of Norfolk Cliffs. — Cromer Forest-bed. —
+Aldeby and Chillesford Beds. — Norwich Crag. — Older Pliocene Strata. —
+Red Crag of Suffolk. — Coprolitic Bed of Red Crag. — White or Coralline
+Crag. — Relative Age, Origin, and Climate of the Crag Deposits. —
+Antwerp Crag. — Newer Pliocene Strata of Sicily. — Newer Pliocene
+Strata of the Upper Val d’Arno. — Older Pliocene of Italy. —
+Subapennine Strata. — Older Pliocene Flora of Italy.
+
+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.
+
+Bridlington Drift.—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° 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 _Astarte
+borealis_ (called _A. Withami_); _ A. mutabilis_; the sinistral form of
+_Tritonium carinatum, Cardita analis,_ and _Tellina obliqua,_ Fig. 120,
+p. 194. Mr. Searles Wood also inclines to consider _Nucula Cobboldiæ,_
+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’s Island, which some conchologists regard as
+a variety. _Tellina obliqua_ also approaches very near to a shell now
+living in Japan.
+
+Glacial Drift of Ireland.—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,
+_Conovulus pyramidalis_ and _ Nassa monensis,_ are not known as living;
+while _Turritella incrassata_ and _Cypræa lucida_ 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.[1]
+
+Fig. 116: Tellina balthica
+Drift of Norfolk Cliffs.—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
+of extinct forms, but also abounding in _Tellina balthica_ (_T.
+solidula,_ 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.
+
+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.
+
+Cromer Forest-bed.—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, _E.
+meridionalis,_ Nesti, and _E. antiquus,_ the former found in the Newer
+Pliocene beds of the Val d’Arno, near Florence. In the same bed occur
+_Hippopotamus major, Rhinoceros etruscus,_ both of them also Val d’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 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.
+
+Fig. 117: Natica helicoides
+Chillesford and Aldeby Beds.—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 “Crag,” 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 _Cardium Grœnlandicum, Leda limatula, Tritonium carinatum,_ and
+_Scalaria Grœnlandica._ In the upper part of the laminated clays a
+skeleton of a whale was found associated with casts of the
+characteristic shells, _Nucula Cobboldiæ_ and _Tellina obliqua,_
+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. _ Natica helicoides_ (Fig.
+117) is an example of a species formerly known only as fossil, but
+which has now been found living in our seas.
+
+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 regions. As a rule, the lamellibranchiate
+molluscs have both valves united, and many of them, such as _Mya
+arenaria,_ stand with the siphonal end upward, as when in a living
+state. _Tellina balthica,_ 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.
+
+Fig. 118: <i>Mastodon arvernensis,</i> third milk molar, left side,
+upper jaw: grinding surface. Norwich Crag, Postwick, also found in Red
+Crag, see p. 197.
+
+Norwich or Fluvio-marine Crag.—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 “Crag,” the newest
+member of which has been commonly called the “Norwich Crag.” 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
+“Stone-bed,” composed of unrolled chalk-flints, commonly of large size,
+mingled with the remains of a land fauna comprising _ Mastodon
+arvernensis, Elephas meridionalis,_ 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
+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
+_Pholas crispata,_ 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
+“Fluvio-marine” 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, _Paludina
+lenta,_ has any, and that a very doubtful, claim to be regarded as
+extinct.
+
+Fig. 119: Nucula Cobboldiæ; Fig. 120: Tellina obliqua.
+
+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—such as _Rhynchonella
+psittacea, Scalaria Grœnlandica, Astarte borealis, Panopæa Norvegia,_
+and others—still occur. The _Nucula Cobboldiæ_ and _Tellina obliqua,_
+Figs. 119 and 120, before mentioned, p. 194, are frequent in these
+beds, as are also _Littorina littorea, Cardium edule,_ and _Turritella
+communis,_ of our seas, proving the littoral origin of the beds.
+
+OLDER PLIOCENE STRATA.
+
+Red Crag.—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.
+
+ Fig. 121: Red Crag, London clay and chalk.
+
+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—exclusive of 25 species regarded by Mr. Wood as
+derivative—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.
+
+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, _Nucula Cobboldiæ_, so common
+in the Norwich and certain glacial beds, is found, and _Purpura
+tetragona_ (Fig. 122) is very abundant. On the other hand, at
+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. _Voluta
+Lamberti_ (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.
+
+Fig. 122: Purpura tetragona.
+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.
+
+Fig. 123: Voluta Lamberti; Fig. 124: Voluta Lamberti; Fig. 125: Trophon
+antiquum.
+
+At and near the base of the Red Crag is a loose bed of 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 _Mastodon arvernensis, Rhinoceros Schleiermacheri, Tapirus
+priscus,_ and Hipparion (a quadruped of the horse family), and antlers
+of a stag, _Cervus anoceros._ 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.
+
+White or Coralline Crag.—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—often a mass of comminuted shells, and
+the remains of bryozoa[2] (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.
+
+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.
+
+Fig. 126: Section near Woodbridge, in Suffolk.
+
+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, _b_, had
+suffered denudation, before the newer formation, _a_, 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 _ Pholades_, 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, _Patella_, 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 the palæontologist in deciding which
+species belong severally to each group.
+
+Fig. 127: Fascicularia aurantium, from the inferior or Coralline Crag,
+Suffolk. Fig. 128: Astarte Omalii, species common to Upper and Lower
+Crag.
+
+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 _Astarte_ (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 _Conus, Oliva, Fasciolaria, Crassatella_, and others. The
+absence also of large cowries (_Cyprea_), those found belonging
+exclusively to the section _Trivia_, is remarkable. The large volute,
+called _Voluta Lamberti_ (Fig. 123, p. 196), may seem an exception; but
+it differs in form from the volutes of the torrid zone, and, like the
+living _Voluta Magellanica_, must have been fitted for an
+extra-tropical climate.
+
+Fig. 129: Lingula Dumortieri. Fig. 130: Pyrula reticulata. Fig. 131:
+Temnechinus excavatus.
+
+The occurrence of a species of _Lingula_ at Sutton (see Fig. 129) is
+worthy of remark, as these _Brachiopoda_ seem now confined to more
+equatorial latitudes; and the same may be said still more decidedly of
+a species of _Pyrula_, supposed by Mr. Wood to be identical with _P.
+reticulata_ (Fig. 130), now living in the Indian Ocean. A genus also of
+echinoderms, called by Professor Forbes _Temnechinus_ (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
+“Porcupine.”
+
+Climate of the Crag Deposits.—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.[3] 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, 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.
+
+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.
+
+Relation of the Fauna of the Crag to that of the recent Seas.—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—as, for
+example, _Buccinum Dalei_—while others, rarely met with in a fossil
+state, are now very common, as _Murex erinaceus_ and _Cardium
+echinatum._ 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.
+
+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.
+
+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.
+
+NUMBER OF KNOWN SPECIES OF MARINE TESTACEA IN THE CRAG.
+
+CHILLESFORD AND ALDEBY BEDS Total
+number Not known
+as living Percentage of
+Shells not known
+as living Bivalves   61   4 9·5 Univalves   33   5
+Brachiopods     0   0 NORWICH OR FLUVIO-MARINE CRAG Bivalves  
+61 10 17·5 Univalves   64 12 Brachiopods     1   0
+RED CRAG
+_(Exclusive to many derivative shells)_ Bivalves 128 31 25·0
+Univalves 127 33 Brachiopods     1   1 CORALLINE CRAG
+Bivalves 161 47 31·5 Univalves 184 60 Brachiopods    
+5   3
+
+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 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.
+
+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.
+
+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 _Voluta Lamberti_,
+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, _Trophon antiquum_, so characteristic of the same
+formation, often exhibits. Additional proofs, however, have lately been
+obtained by Mr. Searles Wood that this 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.
+
+Antwerp Crag.—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.
+
+Fig. 132: Murex vaginatus
+
+Newer Pliocene Strata of Sicily.—At several points north of Catania, on
+the eastern sea-coast of Sicily—as at Aci-Castello, for example,
+Trezza, and Nizzeti—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 _Murex vaginatus_, 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.
+
+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 more ancient
+cone, situated 3½ miles to the east of the present one.[4]
+
+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.
+
+There is probably no part of Europe where the Newer Pliocene formations
+enter so largely into the structure of the earth’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.
+
+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, 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.
+
+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 _dikes._
+
+Fig. 133: Pecten jacobæus
+
+No shell is more conspicuous in these Sicilian strata than the great
+scallop, _Pecten jacobæus_ (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 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.
+
+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’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.
+
+Newer Pliocene Strata of the Upper Val D’arno.—When we ascend the Arno
+for about ten miles above Florence, we arrive at a deep narrow valley
+called the Upper Val d’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 “sansino.” Among the imbedded fossil mammalia are _Mastodon
+arvernensis, Elephas meridionalis, Rhinoceros etruscus, Hippopotamus
+major,_ and remains of the genera bear, hyæna, and felis, nearly all of
+which occur in the Cromer forest-bed (see Chap. 13, p. 191).
+
+In the same upper strata are found, according to M. Gaudin, the leaves
+and cones of _Glyptostrobus europæus_, a plant closely allied to _G.
+heterophyllus_, 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).
+
+Older Pliocene of Italy.—Subapennine Strata.—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.
+
+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 _Conus, Cypræa,
+Strombus, Pyrula, Mitra, Fasciolaria, Sigaretus, Delphinula,
+Ancillaria, Oliva, Terebellum, Terebra, Perna, Plicatula,_ and
+_Corbis_, some characteristic of tropical seas, others represented by
+species more numerous or of larger size than those now proper to the
+Mediterranean.
+
+Older Pliocene Flora of Italy.—I have already alluded to the Newer
+Pliocene deposits of the Upper Val d’Arno above Florence, and stated
+that below those sands and conglomerates, containing the remains of the
+_Elephas meridionalis_ 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.
+
+Fig. 134: Creodaphne Heerii. Fig. 135: Liquidambar europæum, var.
+trilobatum Fig. 134: _Creodaphne Heerii_.
+Leaf[5]
+Fig. 135: _Liquidambar europæum_, var. _trilobatum_, A. Br. (sometimes
+four-lobed, and more commonly five-lobed).
+_a._ Leaf. _b._ Part of same. _c._ Fruit. _d._ Seed Œningen.
+
+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 _Oreodaphne Heerii_, Gaud. (see Fig. 134),
+which is probably only a variety of _Oreodaphne foetens_, or the laurel
+called 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[6] (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 _ Liquidambar europæum_, Brong. (see
+Fig. 135), a species nearly allied to _L. styracifluum_, L., which
+flourishes in most places in the Southern States of North America, on
+the borders of the Gulf of Mexico.
+
+ [1] See Antiquity of Man, chap. xiv.
+
+ [2] Ehrenberg proposed in 1831 the term _ Bryozoum_, or “Moss-animal,”
+ for the molluscous or ascidian form of polyp, characterised by having
+ two openings to the digestive sack, as in _Eschara, Flustra,
+ Retepora,_ and other zoophytes popularly included in the corals, but
+ now classed by naturalists as mollusca. The term _Polyzoum,_
+ synonymous with _ Bryozoum,_ was, it seems, proposed in 1830, or the
+ year before, by Mr. J. O. Thompson.
+
+ [3] E. Forbes Mem. Geol. Survey of Gt. Brit., vol. i, p. 386.
+
+ [4] See a Memoir on the Lavas and Mode of Origin of Mount Etna by the
+ Author in Phil. Trans., 1858.
+
+ [5] Feuilles fossiles de la Toscane.
+
+ [6] Contributions à la Flore fossile Italienne. Gaudin and Strozzi.
+ Plate 11, Fig. 3. Gaudin, p. 22.
+
+
+
+
+CHAPTER XIV.
+MIOCENE PERIOD—UPPER MIOCENE.
+
+
+Upper Miocene Strata of France—Faluns of Touraine. — Tropical Climate
+implied by Testacea. — Proportion of recent Species of Shells. — faluns
+more ancient than the Suffolk Crag. — Upper Miocene of Bordeaux and the
+South of France. — Upper Miocene of Œningen, in Switzerland. — Plants
+of the Upper Fresh-water Molasse. — Fossil Fruit and Flowers as well as
+Leaves. — Insects of the Upper Molasse. — Middle or Marine Molasse of
+Switzerland. — Upper Miocene Beds of the Bolderberg, in Belgium. —
+Vienna Basin. — Upper Miocene of Italy and Greece. — Upper Miocene of
+India; Siwalik Hills. — Older Pliocene and Miocene of the United
+States.
+
+Upper Miocene Strata of France—Faluns of Touraine.—The strata which we
+meet with next in the descending order are those called by many
+geologists “Middle Tertiary,” for which in 1833 I proposed the name of
+Miocene, selecting the “faluns” 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.
+
+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’s history. The term “faluns” 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 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 (p. 142), stretches
+continuously from the basin of the Seine to that of the Loire.
+
+Fig. 136: Dinotherium giganteum.
+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, _ Helix turonensis)_
+(Fig. 38) 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.
+
+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 _Oliva, Ancillaria, Mitra, Terebra, Pyrula,
+Fasciolaria,_ and _ Conus._ 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 _Nerita,_ and many others, are also
+represented by individuals 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.
+
+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.
+
+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 _
+Dendrophyllia_, and the bryozoan _Lunulites_, 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.
+
+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.
+
+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.
+
+Fig. 137: Voluta Lamberti.
+Among the conspicuous fossils common to the faluns of the Loire and the
+Suffolk Crag is a variety of the _Voluta Lamberti_, a shell already
+alluded to (Fig. 123). 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.
+
+Upper Miocene of Bordeaux and the South of France.—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.
+
+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 _Dinotherium giganteum_ and _Mastodon
+angustidens_; also 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° 39′ 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
+_Pliopithecus._ Subsequently, in 1856, M. Lartet described another
+species of the same family of long-armed apes (_Hylobates_), 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 _Dryopithecus._ 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.
+
+Upper Miocene Beds of Œningen, in Switzerland.—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 “Flora Tertiaria Helvetiæ.” 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 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’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’s earlier and later works, I may instance the chestnut, elm,
+maple, cinnamon, magnolia, buckbean or Menyanthes, vine, buckthorn
+(_Rhamnus_), _Andromeda_ and _Myrica,_ and among the conifers _Sequoia_
+and _ Taxodium._ 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.
+
+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—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’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 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, _Chamærops_ and _Sabal_, or to the more tropical family of
+the date-palms or _Phœnicites_, 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.
+
+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° N., and in Spitzbergen, latitude 78° 56′, 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 (see p. 240). 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.
+
+The Miocene formations of Switzerland have been called _ Molasse_, a
+term derived from the French _mol_, and applied to a _soft_,
+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.
+
+Upper Fresh-water Molasse.—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 “homo diluvii testis,” a fossil
+afterwards demonstrated by Cuvier to be a reptile, or aquatic
+salamander, of larger dimensions than even its great living
+representative, the salamander of Japan.
+
+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 (_Potamogeton_), together
+with some insects; while in the bed No. 4, below, is a bituminous rock,
+in which the _Mastodon tapiroides_, a characteristic Upper Miocene
+quadruped, has been met with. The 5th bed, two or three inches thick,
+contains fossil fish, e.g., _Leuciscus_ (roach), and the larvæ of
+dragon-flies, with plants such as the elm (_Ulmus_), 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, _Galecynus Œningensis,_ Owen, was
+obtained by Sir R. Murchison. To this succeed other beds with mammalia
+(_Lagomys_), reptiles, (_Emys_), 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.
+
+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
+_Liquidambar, Daphnogene, Podogonium,_ and _ Ulmus_, together with
+tortoises, besides the bones and teeth of a ruminant quadruped, named
+by H. von Meyer _Palæomeryx eminens._ 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 _
+Liquidambar, Daphnogene,_ and _Glyptostrobus_, 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.
+
+Fig. 138: Cinnamomum polymorphum.
+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
+_Cinnamomum polymorphum_ (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 _
+Cinnamomum polymorphum_ (Fig. 138) was in fruit, as well as the
+liquidambar, oak, clematis, 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, _Arundo_, which was very common.
+
+One of the most characteristic shrubs is a papilionaceous and
+leguminous plant of an extinct genus, called by Heer _ Podogonium_, 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.
+
+Fig. 138: Acer trilobatum.
+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 _Podogonium_ 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,
+_Acer trilobatum_, 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 _Acer
+trilobatum_, 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.
+
+Fig. 140: Acer trilobatum.
+
+Among the conspicuous genera which abounded in the Miocene period in
+Europe is the plane-tree, _Platanus,_ the fossil species being
+considered by Heer to come nearer to the American _ P. occidentalis_
+than to _P. orientalis_ 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.
+
+Platanus aceroides.
+The vine of Œningen, _Vitis teutonica_, 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, _S.
+sagittifera_, Fig. 142, _a._
+
+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 _Banksia, Grevillea, Hakea,_ and _Persoonia._ 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
+been found attached to the same stem as the leaf, the proof is
+incomplete.
+
+Fig. 142: Smilax sagittifera.
+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° 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 (see
+Fig. 206). 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 (p. 304) 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.
+
+Fig. 143: Fruit of the fossil and recent species of Hakea, a genus of
+Proteaceæ.
+
+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 Louisiana. Among the Coniferæ of Upper Miocene age is
+found a deciduous cypress nearly allied to the _Taxodium distichum_ of
+North America, and a _Glyptostrobus_ (Fig. 144), very like the Japanese
+_G. heterophyllus,_ now common in our shrubberies.
+
+Fig. 144: Glyptostrobus Europæus.
+Before the appearance of Heer’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.
+
+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.
+
+The patterns and some remains of the colours both of _ Coleoptera_ and
+_Hemiptera_ are preserved at Œningen, as, for example in _Harpactor_
+(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.
+
+Middle or Marine Molasse (Upper Miocene) of Switzerland.—It was before
+stated that the Miocene formation of Switzerland 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.
+
+Fig. 145: Harpactor maculipes.
+
+Fig. 146: Olica Dufresnii.
+
+Upper Miocene of the Bolderberg, in Belgium.—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 (p. 204), and contain shells of the
+genera _Oliva, Conus, Ancillaria, Pleurotoma,_ and _ Cancellaria_ in
+abundance. The most common shell is an Olive (Fig. 146), called by Nyst
+_Oliva Dufresnii_; and constituting, as M. Bosquet observes, a smaller
+and shorter variety of the Bordeaux species.
+
+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.
+
+Upper Miocene Beds of the Vienna Basin.—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’s excellent work 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.
+
+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 _Cypræa sanguinolenta,
+Buccinum lyratum,_ and _Oliva flammulata._ In the lowest marine beds of
+the Vienna basin the remains of several mammalia have been found, and
+among them a species of _Dinotherium_, a Mastodon of the _Trilophodon_
+family, a Rhinoceros (allied to _R. megarhinus_, Christol), also an
+animal of the hog tribe, _ Listriodon_, von Meyer, and a carnivorous
+animal of the canine family. The _Helix turonensis_  (Fig. 38), 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
+_Dinotherium giganteum_ (Fig. 136), _Mastodon longirostris, Rhinoceros
+Schleiermacheri, Acerotherium incisivum,_ and _ Hippotherium gracile,_
+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° 50′ N. the bone of a large ape of
+the Gibbon kind, the most northerly example yet discovered of a
+quadrumanous animal.
+
+Fig. 147: Amphistegina Hauerina.
+M. Alcide d’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 _Amphistegina_ (Fig. 147) is very
+characteristic, and is supposed by d’Archiac to take the same place
+among the Rhizopods of the Upper Miocene era which the Nummulites
+occupy in the Eocene period.
+
+The flora of the Vienna basin exhibits some species which have a
+general range through the whole Miocene period, such as _Cinnamomum
+polymorphum_ (Fig. 138), and _C. Scheuchzeri,_ also Planera Richardi,
+Mich., _Liquidambar europæum_ (Fig. 135) _Juglans bilinica, Cassia
+ambigua,_ and _C. lignitum._ Among the plants common to the Upper
+Miocene beds of Œningen, in Switzerland, are _Platanus aceroides_ (Fig.
+141), _Myrica vindobonensis,_ and others.
+
+Upper Miocene Strata of Italy.—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.
+
+Upper Miocene Formations of Greece.—At Pikermé, near Athens, MM. Wagner
+and Roth have described a deposit in which they found the remains of
+the genera _Mastodon, Dinotherium, Hipparion,_ two species of _Giraffe,
+Antelope,_ and others, some living and some extinct. With them were
+also associated fossil bones of the _Semnopithecus,_ 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.
+
+Upper Miocene of India. Siwâlik Hills.—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 _Paludina, Melania, Ampullaria,_ and _Unio,_ all are extinct or
+unknown species with the exception of four, which are still inhabitants
+of Indian rivers. Such 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.
+
+The genera of mammalia point in the same direction. One of them, of the
+genus _Chalicotherium_ (or _Anisodon_ of Lartet), is a pachyderm
+intermediate between the _Rhinoceros_ and _ Anoplothere,_ 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 _Mastodon_, 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 _Stegodon_ of Falconer. With these are
+associated a monkey, allied to the _Semnopithecus entellus_, 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 _Sivatherium,_ like a gigantic four-horned deer. There are
+also new forms of carnivora, both feline and canine, the _Machairodus_
+among the former, also hyænas, and a subursine form called the
+Hyænarctos, and a genus allied to the otter (_Enhydriodon_), of
+formidable size.
+
+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 (_C. Gangeticus_); 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 (_Colossochelys Atlas_), 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.
+
+Numerous fossils of the Siwâlik type have also been found in Perim
+Island, in the Gulf of Cambay, and among these a species of
+_Dinotherium,_ a genus so characteristic of the Upper Miocene period in
+Europe.
+
+Older Pliocene and Miocene Formations in the United States.—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, 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.[1]
+
+Fig. 148: Fulgur canaliculatus. Fig. 149: Fusus quadricostatus.
+
+In the Virginian sands, we find in great abundance a species of Astarte
+(_A. undulata,_ Conrad), which resembles closely, and may possibly be a
+variety of, one of the commonest fossils of the Suffolk Crag (_A.
+Omalii_); the other shells also, of the genera _Natica, Fissurella,
+Artemis, Lucina, Chama, Pectunculus,_ and _Pecten,_ 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 _Fusus quadricostatus,_
+Say (see Fig. 149), and _Venus tridacnoides,_ abundant in these same
+formations, but also some shells which, like _Fulgur carica_ of Say and
+_F. canaliculatus_ (see Fig. 148), _Calyptræa costata, Venus
+mercenaria,_ Lam., _Modiola glandula,_ Totten, and _ Pecten
+magellanicus,_ Lam., are recent species, yet of forms now confined to
+the western side of the Atlantic—a fact implying that some traces of
+the beginning of the present geographical distribution of mollusca date
+back to a period as remote as that of the Miocene strata.
+
+Fig. 150: Astrangia lineata.
+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.
+
+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.
+
+ [1] Proceedings of the Geol. Soc., vol. iv, pt. iii, 1845, p. 547.
+
+
+
+
+CHAPTER XV.
+LOWER MIOCENE (OLIGOCENE OF BEYRICH).
+
+
+Lower Miocene Strata of France. — Line between Miocene and Eocene. —
+Lacustrine Strata of Auvergne. — Fossil mammalia of the Limagne
+d’Auvergne. — Lower Molasse of Switzerland. — Dense Conglomerates and
+Proofs of Subsidence. — Flora of the Lower Molasse. — American
+Character of the Flora. — Theory of a Miocene Atlantis. — Lower Miocene
+of Belgium. — Rupelian Clay of Hermsdorf near Berlin. — Mayence Basin.
+— Lower Miocene of Croatia. — Oligocene Strata of Beyrich. — Lower
+Miocene of Italy. — Lower Miocene of England. — Hempstead Beds. — Bovey
+Tracey Lignites in Devonshire. — Isle of Mull Leaf-Beds. — Arctic
+Miocene Flora. — Disco Island. — Lower Miocene of United States. —
+Fossils of Nebraska.
+
+Line between Miocene and Eocene Formations.—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 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, _Ostrea cyathula,_ 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.[1]
+
+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 _Ostrea cyathula_ 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.
+
+Lower Miocene of Central France.—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.
+
+The study of these regions possesses a peculiar interest very distinct
+in kind from that derivable from the 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—lofty mountains have been formed, by the reiterated
+emission of lava, preceded and followed by showers of sand and
+scoriæ—deep valleys have been subsequently furrowed out through masses
+of lacustrine and volcanic origin—at a still later date, new cones have
+been thrown up in these valleys—new lakes have been formed by the
+damming up of rivers—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
+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.
+
+_Auvergne._—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’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:—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.
+
+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
+called _Cypris_ 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.
+
+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—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.
+
+Lower Miocene Mammalia of the Limagne.—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 _Palæotherium_ 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 _Palæotherium magnum,_ an
+undoubted Upper Eocene fossil, of the Paris gypsum, the other three
+being peculiar.
+
+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 _Microtherium Renggeri_ of the
+Mayence basin. In like manner, the _Amphitragulus elegans_ of Pomel, an
+Auvergne fossil, is identified by Waterhouse with _Dorcatherium nanum_
+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 d’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 (_Didelphis_) 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.
+
+Lower Molasse of Switzerland.—The two upper divisions of the Swiss
+Molasse—the one fresh-water, the other marine—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 _Cerithium margaritaceum,_
+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.
+
+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.
+
+Flora of the Lower Molasse.—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 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—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.
+
+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.
+
+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 (_Ficus populina_), and of a hornbeam (_Carpinus
+grandis_), 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 _Sequoia, Cinnamomum,_ and _Sparganium_ are common. In one
+bed of sandstone the trunk of a large palm-tree was found unaccompanied
+by other fossils, and near Vevay, in the same series of Lower Miocene
+strata, the leaves of a palm of the genus _Sabal_ (Fig. 151), a genus
+now proper to America, were obtained.
+
+Fig. 151: Sabal major
+Among other genera of the same class is a _Flabellaria_ occurring near
+Lausanne, and a magnificent _Phœnicites_ 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.
+
+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, _Pinus abies,_ found scattered over the ground in our
+woods. It is a known fact that 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.
+
+Fig. 152: Fruit of fossil Banksia and leaf of Banksia. Fig. 153:
+Sequoia Langsdorfii.
+
+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’Arno, which I have called Older Pliocene, p.
+208.
+
+Fig. 154: Lastræa stiriaca.
+Among the ferns met with in profusion at Monod is the _ Lastræa
+stiriaca,_ 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.
+
+Among the laurels several species of _Cinnamomum_ are very conspicuous.
+Besides the _C. polymorphum,_ before figured, p. 219, another species
+also ranges from the Lower to the Upper Molasse of Switzerland, and is
+very characteristic of different deposits of Brown Coal in Germany. It
+has been called _Cinnamomum Rossmässleri_ by Heer (see Fig. 155). The
+leaves are easily recognised as having two side veins, which run up
+uninterruptedly to their point.
+
+Fig. 155: Cinnamomum Rossmässleri.
+American Character of the Flora.—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.
+
+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.
+
+Arctic Miocene Flora.—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°), Iceland, Spitzbergen, and
+other parts of the Arctic regions, and has determined that they are of
+Miocene age and indicate a temperate climate.[2] 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.
+
+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 _ Andromeda,_ and two extinct genera, _Daphnogene_ and _
+M’Clintockia,_ with fine leathery leaves, together with hazel,
+blackthorn, holly, logwood, and hawthorn. A species of Zamia
+(_Zamites_) grew in the swamps, with _Potamogeton, Sparganium,_ and
+_Menyanthes,_ 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° 56′, no less than ninety-five species of
+fossil plants have been obtained, including _Taxodium_ 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.
+
+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, 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°), 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’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.
+
+Fig. 156: Leda (Nucula) Deshayesiana. Lower Miocene, Belgium.—The Upper
+Miocene Bolderberg beds, mentioned in p. 224, 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 “London clay,” 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 _Leda_ (or Nucula) _Deshayesiana_ (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
+_Pecten Hœninghausii,_ and a species of _ Cassidaria,_ and several of
+the genus _Pleurotoma._ Not a few of these testacea agree with English
+Eocene species, such as _Actæon simulatus,_ Sowb, _Cancellaria evulsa,_
+Brander, _Corbula pisum_ (Fig. 157), and _Nautilus (Aturia) ziczac._
+They are accompanied by many teeth of sharks, as _Lamna contortidens,_
+Ag., _ Oxyrhinaxiphodon,_ Ag., _Carcharodon angustidens_ (see Fig.
+196), Ag., and other fish, some of them common to the Middle Eocene
+strata.
+
+_Kleyn Spawen beds._—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’Archiac had previously observed that
+these foraminifera characterise his “Lower Tertiary Series,” 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.[3] 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.
+
+Lower Miocene of Germany.—_Rupelian Clay of Hermsdorf, near
+Berlin._—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 _Leda Deshayesiana,_ before mentioned
+(Fig. 156), abounds, together with many species of _ Pleurotoma,
+Voluta,_ etc., a certain proportion of the fossils being identical in
+species with those of Rupelmonde.
+
+_Mayence Basin._—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 _Cassidaria depressa, Tritonium
+argutum,_ Brander (_T. flandricum,_ De Koninck), _ Tornatella simulata,
+Aporrhais Sowbyi, Leda Deshayesiana_ (Fig. 156), _Corbula pisum,_ (Fig.
+158) and others.
+
+Lower Miocene Beds of Croatia.—The Brown Coal of Radaboj, 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,
+Fig. 151, p. 237, and another genus allied to the date-palm _
+Phœnicites spectabilis._ The only abundant plant among the Radaboj
+fossils which is characteristic of the Upper Miocene period is the
+_Populus mutabilis,_ whereas no less than fifty of the Radaboj species
+are common to the more ancient flora of the Lower Molasse of
+Switzerland.
+
+Fig. 157: Vanessa Pluto.
+
+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’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 _V. Hadena_ of India.
+
+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.
+
+Professor Beyrich confines the term “Miocene” to those strata which
+agree in age with the faluns of Touraine, and he has proposed the term
+“Oligocene” for those older formations called Lower Miocene in this
+work.
+
+Lower Miocene of Italy.—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 _Banksia longifolia,_ and _Carpinus
+grandis._ 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 _ Anthracotherium
+magnum_ and _A. minimum,_ besides other mammalia enumerated by
+Gastaldi. In these beds a great number of the Lower Miocene plants of
+Switzerland have been discovered.
+
+Lower Miocene of England—Hempstead Beds.—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, _Palæotherium, Anoplotherium,_ 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:
+
+1. The uppermost or Corbula beds, consisting of marine sands and clays,
+contain _Voluta Rathieri,_ a characteristic Lower Miocene shell;
+_Corbula pisum_ (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.
+
+Fig. 158: Corbula pisum. Fig. 159: Cyrena semistriata. Fig. 160:
+Cerithium plicatum. Fig. 161: Cerithium elegans. Fig. 162: Rissoa
+Chastelii. Fig. 163: Paludina lenta.
+
+2. Next are fresh-water and estuary marls and carbonaceous clays in the
+brackish-water portion of which are found abundantly _ Cerithium
+plicatum,_ Lam. (Fig. 160), _Cerithium elegans_ (Fig. 161), and
+_Cerithium tricinctum_; also _Rissoa Chastelii_ (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
+_Paludina lenta_ (Fig. 163) occurs; a shell identified by some
+conchologists with a species now living, _P. unicolor_; also several
+species of _ Lymneus, Planorbis,_ and _Unio._
+
+3. The next series, or middle fresh-water and estuary marls, are
+distinguished by the presence of _Melania fasciata, Paludina lenta,_
+and clays with _Cypris_; the lowest bed contains _Cyrena semistriata_
+(Fig. 159), mingled with Cerithia and a _panopæa._
+
+4. The lower fresh-water and estuary marls contain _Melania costata,_
+Sowerby, _Melanopsis,_ etc. The bottom bed is carbonaceous, and called
+the “Black band,” in which _ Rissoa Chastelii_ (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, among which is _Hyopotamus bovinus,_ 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, _Sequoia Couttsiæ,_ Heer; _Andromeda reticulata,_ Ettings.;
+_Nelumbium (Nymphœa) doris,_ Heer; and _Carpolithes Websteri,_
+Brong.[4] The seed-vessels of _Chara medicaginula,_ Brong, and _C.
+helicteres_ are characteristic of the Hempstead beds generally.
+
+The _Hyopotamus_ 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.
+
+Lignites and Clays of Bovey Tracey, Devonshire.—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.
+
+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’s opinion that much of the upper portion
+of this old lacustrine formation has been removed by denudation.[5]
+
+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, _Betula nana,_ indicating a
+climate colder than that of Devonshire at the present day.
+
+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 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 (_Buprestis_);
+in a word, no organic remains, except plants, have as yet been found.
+These plants occur in fourteen of the beds—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 _Sequoia Couttsiæ,_
+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 _Sequoia
+Langsdorfii_ (see Fig. 153, p. 238) and _S. Sternbergi,_ the widely
+spread fossil representatives of the two living trees _S. sempervirens_
+and _S. gigantea_ (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 _ Lastræa stiriaca_ (Fig. 154, p. 238), displaying at
+Bovey, as in Switzerland, its fructification.
+
+The croziers of some of the young ferns are very perfect, and were at
+first mistaken by collectors for shells of the genus _ Planorbis._ On
+the whole, the vegetation of Bovey implies the existence of a
+sub-tropical climate in Devonshire, in the Lower Miocene period.
+
+Scotland: Isle of Mull.—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.[6] From his description it
+appears that there are three leaf-beds, varying in thickness from 1½ to
+5½ feet, which are interstratified with volcanic tuff and trap, the
+whole mass being about 130 feet in thickness. A sheet of basalt 40 feet
+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 _Equisetum_
+grew, of which the remains are plentifully imbedded in clay.
+
+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.[7]
+
+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 _Sequoia Langsdorfii_ (Fig. 153, p.
+238), also _Corylus grossedentata,_ 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 _Platanus aceroides_
+(Fig. 141), and a fern which is as yet peculiar to Mull, _Filicites
+hebridica,_ Forbes.
+
+These interesting discoveries in Mull led geologists to suspect that
+the basalt of Antrim, in Ireland, and of the celebrated Giant’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.
+
+Lower Miocene, United states: Nebraska.—In the territory of Nebraska,
+on the Upper Missouri, near the Platte River, lat. 42° N., a tertiary
+formation occurs, consisting of white limestone, marls, and siliceous
+clay, described by Dr. D. Dale Owen,[8] 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 _Titanotherium,_ nearly allied to the _Palæotherium,_ but larger
+than any of the species found in the Paris gypsum. With these are
+several species of the genus _Oreodon,_ Leidy, uniting the characters
+of pachyderms and ruminants also; _Eucrotaphus,_ another new genus of
+the same mixed character; two species of rhinoceros of the sub-genus
+_Acerotherium,_ a Lower Miocene form of Europe before mentioned; two
+species of _Archæotherium,_ a pachyderm allied to _Chæropotamus_ and _
+Hyracotherium_; also _Pæbrotherium,_ an extinct ruminant allied to
+_Dorcatherium,_ Kaup; also _ Agriochoerus,_ of Leidy, a ruminant allied
+to _ Merycopotamus_ of Falconer and Cautley; and, lastly, a large
+carnivorous animal of the genus _Machairodus,_ 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 _Testudo,_ but have some affinity to _Emys._ On
+the whole, the Nebraska formation is probably newer than the Paris
+gypsum, and referable to the Lower Miocene period, as above defined.
+
+ [1] Bulletin, 1856, Journ., vol. xii, p. 768.
+
+ [2] Heer “Miocene baltische Flora” and “Fossil-flora von Alaska” 1869.
+
+ [3] D’Archiac Monogr., pp. 79, 100.
+
+ [4] Pengelly, preface to The Lignite Formation of Bovey Tracey, p.
+ xvii, London, 1863.
+
+ [5] Philos. Trans., 1863. Paper by W. Pengelly, F.R.S., and Dr. Oswald
+ Heer.
+
+ [6] Quart. Geol. Journal, 1851, p. 19.
+
+ [7] Quart. Geol. Journal, 1851, p. 90.
+
+ [8] David Dale Owen, Geol. Survey of Wisconsin, etc., Philad., 1852.
+
+
+
+
+CHAPTER XVI.
+EOCENE FORMATIONS.
+
+
+Eocene Areas of North of Europe. — Table of English and French Eocene
+Strata. — Upper Eocene of England. — Bembridge Beds. — Osborne or St.
+Helen’s Beds. — Headon Series. — Fossils of the Barton Sands and Clays.
+— Middle Eocene of England. — Shells, Nummulites, Fish and Reptiles of
+the Bracklesham Beds and Bagshot Sands. — Plants of Alum Bay and
+Bournemouth. — Lower Eocene of England. — London Clay Fossils. —
+Woolwich and Reading Beds formerly called “Plastic Clay.” Fluviatile
+Beds underlying Deep-sea Strata. — Thanet Sands. — Upper Eocene Strata
+of France. — Gypseous Series of Montmartre and Extinct Quadrupeds. —
+Fossil Footprints in Paris Gypsum. — Imperfection of the Record. —
+Calcaire Silicieux. — Gres de Beauchamp. — Calcaire Grossier. —
+Miliolite Limestone. — Soissonnais Sands. — Lower Eocene of France. —
+Nummulitic Formations of Europe, Africa, and Asia. — Eocene Strata in
+the United States. — Gigantic Cetacean.
+
+Eocene Areas of the North of Europe.—The strata next in order in the
+descending series are those which I term Eocene.
+
+Fig. 164: Map of the principal Eocene areas of North-western Europe.
+
+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 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 p. 244,
+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.
+
+It is in the northern part of the Isle of Wight that we have the
+uppermost beds of the true Eocene best exhibited—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.
+
+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.
+
+TABLE OF ENGLISH AND FRENCH EOCENE STRATA.
+UPPER EOCENE
+
+English subdivisions French equivalents A.1. Bembridge series, Isle
+of Wight, p. 252. A.1. Gypseous series of Montmartre, p. 270. A.2.
+Osborne or St. Helen’s series, Isle of Wight, p. 255. A.2 and 3.
+Calcaire siliceux, or Travertin Inférieur, p. 273. A.3. Headon series,
+Isle of Wight, p. 255. A.4. Barton series. Sands and clays of Barton
+Cliff, Hants, p. 258. A.4. Grès de Beauchamp, or Sables Moyens, p.
+273. MIDDLE EOCENE B.1. Bracklesham series, p. 259. B.1. Calcaire
+Grossier p. 274 B.2. Alum Bay and Bournemouth beds, p. 259. B.2.
+Wanting in France? B.2. Wanting in England? B.2. Soissonnais Sands,
+or Lits Coquilliers, p. 275 LOWER EOCENE C.1. London Clay, p.
+263. C.1. Argile de Londres, Cassel, near Dunkirk. C.2. Woolwich and
+Reading series, p. 267. C.2. Argile plastique and lignite, p. 276
+C.3. Thanet sands, p. 269. C.3. Sables de Bracheux, p. 276
+
+UPPER EOCENE, ENGLAND.
+
+Bembridge Series, A.1.—These beds are about 120 feet thick, and, as
+stated in p. 245, 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 _Cyrena semistriata_ var., and _Paludina lenta,_ Fig. 163,
+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:
+     _a._ Upper marls, distinguished by the abundance of _Melania
+     turritissima,_ Forbes (Fig. 165).
+     _b._ Lower marls, characterised by _Cerithium mutabile, Cyrena
+     pulchra,_ etc., and by the remains of _Trionyx_ (see Fig. 166).
+     _c._ Green marls, often abounding in a peculiar species of oyster,
+     and accompanied by _ Cerithium, Mytilus, Arca, nucula,_ etc.
+     _d._ Bembridge limestones, compact cream-coloured limestones
+     alternating with shales and marls, in all of which land-shells are
+     common, especially at Sconce, near Yarmouth, as described by Mr.
+     F. Edwards. The _Bulimus ellipticus,_ Fig. 167, and _Helix
+     occlusa,_ Fig. 168, are among its best known land-shells.
+     _Paludina orbicularis,_ Fig. 169, is also of frequent occurrence.
+     One of the bands is filled with a little globular _Paludina._
+     Among the fresh-water pulmonifera, _ Lymnea longiscata_ (Fig. 171)
+     and _Planorbis discus_ (Fig. 170) are the most generally
+     distributed: the latter represents or takes the place of the
+     _Planorbis euomphalus_ (see Fig. 175) of the more ancient Headon
+     series. _Chara tuberculata_ (Fig. 172) is the characteristic
+     Bembridge gyrogonite or seed-vessel.
+
+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.
+
+Fig. 173: Lower molar tooth.
+From this formation on the shores of Whitecliff Bay, Dr. Mantell
+obtained a fine specimen of a fan palm, _Flabellaria Lamanonis,_
+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 _
+Palæotherium magnum_ (Fig. 174), _P. medium, P. minus, P. minimum, P.
+curtum, P. crassum_; also _Anoplotherium commune_ (Fig. 173), _A.
+secundarium, Dichobune cervinum,_ and _Chæropotamus Cuvieri._ 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. _Palæotherium magnum_ 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. 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.
+
+Fig. 174: Palæotherium magnum.
+
+Osborne or St. Helen’s Series, A.2.—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 _Paludina,
+Melania,_ and _ Melanopsis,_ as also of _Cypris_ and the seeds of _
+Chara._
+
+Fig. 175: Planorbis euomphalus, Fig. 176: Helix labyrinthica.
+
+Headon Series A.3.—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 _Planorbis
+euomphalus,_ Fig. 175, characterises the fresh-water deposits, just as
+the allied form, P. discus, Fig. 170, does the Bembridge limestone. The
+brackish-water beds contain _Potamomya plana, Cerithium mutabile,_ and
+_Potamides cinctus_ (Fig. 37), and the marine beds _ Venus_ (or
+_Cytherea_) _incrassata,_ 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.
+
+Fig. 177: Neritina concava.
+
+Among the shells which are widely distributed through the Headon series
+are _Neritina concava_ (Fig. 177), _Lymnea caudata_ (Fig. 178), and _
+Cerithium concavum_ (Fig. 179). _Helix labyrinthica,_ 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 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
+_Paludina lenta_ and various species of _Lymnea, Planorbis, Melania,
+Cyclas, Unio, Potamomya, Dreissena,_ etc.
+
+Fig. 178: Lymnea caudata, Fig. 179: Cerithium concavum.
+Among the chelonians we find a species of _Emys,_ and no less than six
+species of _Trionyx_; among the saurians an alligator and a crocodile;
+among the ophidians two species of land-snakes (_Paleryx,_ Owen); and
+among the fish Sir P. Egerton and Mr. Wood have found the jaws, teeth,
+and hard shining scales of the genus _Lepidosteus,_ 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 _Palæotherium (P. minus), Anoplotherium,
+Anthracotherium, Dichodon, Dichobune, Spalacodon,_ and _Hyænodon._ 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.
+
+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 _Cyrena obovata,_ which are common to the
+Bembridge beds, notwithstanding the intervention of the St. Helen’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.
+
+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 _Cancellaria
+muricata,_ Sowerby, _ Fusus labiatus,_ Sowerby, etc. In these beds at
+Brockenhurst, corals, ably described by Dr. Duncan, have recently been
+found in abundance and perfection; see Fig. 180, _Solenastræa
+cellulosa._
+
+Fig. 180: Solenastræa cellulosa.
+
+Baron von Könen[1] 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’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.
+
+Among the fossils found in the Middle Headon are _Cytherea incrassata_
+and _Cerithium plicatum_ (Fig. 160). 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 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.
+
+Fig. 181: Chama squamosa.
+Barton Series (_Sands and Clays_), A.4 Table—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 _ Chama
+squamosa,_ 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.
+
+It was formerly confounded with the London Clay, an older Eocene
+deposit of very similar mineral character, to be mentioned (p. 263),
+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.
+
+SHELLS OF THE BARTON CLAY.
+
+Certain foraminifera called Nummulites begin, when we study the
+Tertiary formations in a descending order, to make their first
+appearance in these beds. A small species called _ Nummulites
+variolaria,_ 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 _Corbula pisum_ (Fig. 158), 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.
+
+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.
+
+MIDDLE EOCENE, ENGLAND.
+
+Bracklesham Beds and Bagshot Sands, B.1, Table—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, and probably of estuarine origin. As some of
+these beds contain _Cardita planicosta_ (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 _Cerithium
+giganteum_ is seen, so conspicuous in the Calcaire Grossier of Paris,
+where it is sometimes two feet in length. The _Nummulites lævigata_
+(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 _N. scabra_ and
+_N. variolaria._ 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.
+
+Fig. 191: Cardita (Venericardia) planicosta, Fig. 192: Nummulites
+(Nummularia) lavigata.
+
+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 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, _Palæophis typhœus_ (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.[2] Among the companions of the sea-snake
+of Bracklesham was an extinct crocodile (_Gavialis Dixoni,_ 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 _ Myliobates_ (see Fig.
+195).
+
+Fig. 193: Palæophis typhoeus, Owen; an Eocene sea-serpent, Fig. 194:
+Defensive spine of Ostracion.
+
+Fig. 195: Dental plates of Myliobates Edwardsi.
+The teeth of sharks also, of the genera _Carcharodon, Otodus, Lamna,
+Galeocerdo,_ and others, are abundant. (See Figs. 196, 197, 198, 199.)
+
+Fig. 196: Carcharodon angustidens, Fig. 197: Otodus obliquus, Fig. 198:
+Lamna elegans, Fig. 199: Galcocerdo latidens.
+
+MARINE SHELLS OF BRACKLESHAM BEDS.
+
+Alum Bay and Bournemouth Beds. (_Lower Bagshot of English Survey_),
+B.2, Table—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.
+
+Fig. 200: Pleurotoma attenuata, Fig. 201: Voluta Selseïensis, Fig. 202:
+Turritella multisulcata, Fig. 203: Lucina serrata, Fig. 204: Conus
+deperditus.
+
+None of the beds are of great horizontal extent, and there is much
+cross-stratification in the sands, and in some places 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.
+
+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
+(_Dryandra,_ 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.[3]
+
+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 _Aralia primigenia_ (of
+which genus a fruit has since been found by Mr. Mitchell at
+Bournemouth), _Daphnogene Veronensis,_ and _ Ficus granadilla,_ 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 (_Sabal_) 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.
+
+LOWER EOCENE FORMATIONS, ENGLAND.
+
+London Clay, C.1, Table—This formation underlies the preceding, and
+sometimes attains a thickness of 500 feet. It consists of tenacious
+brown and bluish-grey clay, 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 “Lits Coquilliers” (p. 275), in which 200
+species are known in France.
+
+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.
+
+Fig. 205: Nipadites ellipticus.
+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 _Nipa,_ 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 _Nipa fruticans_ 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 _Pandanus,_ or
+screw-pine. There are also met with three species of _Anona,_ or
+custard-apple; and cucurbitaceous fruits (of the gourd and melon
+family), and fruits of various species of _Acacia._
+
+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
+_Petrophila_ and _Isopogon._ Of the first there are about fifty, and of
+the second thirty described species now living in Australia.
+
+Ettingshausen remarked in 1851 that five of the fossil species from
+Sheppey, named by Bowerbank[4] 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.
+
+Fig. 206: Eocene Proteaceous Fruit (Petrophiloides Richardsoni.
+
+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
+_Palæophis_ before mentioned (p. 261) has also been described by
+Professor Owen from Sheppey, of a different species from that of
+Bracklesham, and called _P. toliapicus._ A true crocodile, also,
+_Crocodilus toliapicus,_ 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
+_Hyracotherium_ of Owen, of the hog tribe, allied to Chæropotamus,
+another is a _Lophiodon_; a third a pachyderm called _Coryphodon
+eocænus_ 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.
+
+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 _Conus_ and _ Voluta_ occur, a large _Cypræa, C. oviformis,_
+a very large _Rostellaria_ (Fig. 209), a species of _Cancellaria,_ six
+species of _Nautilus_ (Fig. 211), besides other Cephalopoda of extinct
+genera, one of the most remarkable of which is the _ Belosepia_ (Fig.
+212). Among many characteristic bivalve shells are _Leda amygdaloides_
+(Fig. 213) and _Cryptodon angulatum_ (Fig. 214), and among the Radiata
+a star-fish, _Astropecten_ (Fig. 215.)
+
+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.
+
+These fossils are accompanied by a sword-fish (_Tetrapterus priscus,_
+Agassiz), about eight feet long, and a saw-fish (_Pristis bisulcatus,_
+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.
+
+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 _Hyracotherium._ 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.
+
+Woolwich and Reading Series, C.2, Table—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.[5]
+
+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—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 _Ostrea bellovacina,_ so common in France in
+the 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.
+
+Fig. 216: Cyrena cuneiformis, Fig. 217: Melania (Melanatria) inquinata.
+
+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, _ Cyrena
+cuneiformis_ (see Fig. 216) and _Melania inquinata_ (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 _Cyrena tellinella_ 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[6] 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 _Cyrena_ and of a _ Gnathodon,_ 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, but sometimes brackish. At
+Woolwich a body of river-water must have flowed permanently into the
+sea where the _Cyrenæ_ 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 _Unio, Paludina,_ 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.
+
+_Fluviatile Beds underlying Deep-sea Strata._—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.
+
+Thanet Sands, C.3, Table—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 “Thanet
+Sands,” 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, _Pholadomya cuneata,
+Cyprina morrisii, Corbula longirostris, Scalaria Bowerbankii,_ etc. The
+greatest thickness of these beds is 90 feet.
+
+UPPER EOCENE FORMATIONS OF FRANCE.
+
+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.
+
+Gypseous Series of Montmartre, A.1, Table—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.
+
+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 (_Flabellaria_). The remains also of fresh-water fish,
+and of crocodiles and other reptiles, occur in the gypsum. The
+skeletons of 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.
+
+In this formation the relics of about fifty species of quadrupeds,
+including the genera _Palæotherium_ (see Fig. 174), _Anoplotherium_
+(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 _Pachydermata,_ 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 _Hyænodon
+dasyuroides,_ a species of dog, _Canis Parisiensis,_ and a weasel,
+_Cynodon Parisiensis._ Of the _Rodentia_ are found a squirrel; of the
+_Cheiroptera,_ a bat; while the _Marsupalia_ (an order now confined to
+America, Australia, and some contiguous islands) are represented by an
+opossum.
+
+Of birds, about ten species have been ascertained, the skeletons of
+some of which are entire. None of them are referable to existing
+species.[7] 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 _Emys_ and _ Trionyx._
+
+Fig. 218: Xiphodon gracile, or Anoplotherium gracile.
+
+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 _ Palæotherium,_ 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 _Xiphodon._ Their forms were slender and
+elegant, and one, named _Xiphodon gracile_ (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.
+
+_Fossil Footprints._—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.[8] 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 _ Anoplotherium_ with its
+bisulcate hoof, and the trilobed footprints of _Palæotherium,_ 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 (_Emys, Trionyx,_ 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.
+
+_Imperfection of the Record._—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.
+
+Calcaire silicieux, or Travertin inférieur, A.2 and 3, Table—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.
+
+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.
+
+Grès de Beauchamp, or Sables Moyens, A.4, Table—In some parts of the
+Paris basin, sands and marls, called the 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.
+
+MIDDLE EOCENE FORMATIONS OF FRANCE.
+
+Calcaire Grossier, upper and middle, B.1, Table—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 _Cerithium, Cyclostoma,_ and _Corbula_; in others
+_Limnea, Cerithium, Paludina,_ etc. In the latter, the bones of
+reptiles and mammalia, _Palæotherium_ and _ Lophiodon,_ 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 _Cyclostoma_ and _Limnea,_ 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.
+
+Nothing is more striking in this assemblage of fossil testacea than the
+great proportion of species referable to the genus _ Cerithium_ (see p.
+245). 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 _Cerithia_ 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.
+
+In some parts of the calcaire grossier round Paris, certain beds occur
+of a stone used in building, and called by the French geologists
+“Miliolite limestone.” 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 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.
+
+Fig. 219: Calcarina rarispina, Fig. 220: Spirolina stenostoma, Fig.
+221: Triloculina inflata.
+
+Lower Calcaire grossier, or Glauconie grossiere, B.1, Table—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 _N. lævigata, N. scabra,_ and _ N.
+Lamarcki,_ 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.
+
+Fig. 222: Nerita conoidea.
+
+Soissonnais sands, or Lits coquilliers, B.2, Table—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 _Nummulites planulata_ is very abundant, and the most
+characteristic shell is the _Nerita conoidea,_ Lam., a fossil which has
+a very wide geographical range; for, as M. d’Archiac remarks, it
+accompanies the nummulitic formation from Europe to India, having been
+found in Cutch, near the mouths of the Indus, associated with
+_Nummulites scabra._ 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 other localities of the “Sables inférieurs” 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.[9]
+
+LOWER EOCENE FORMATIONS OF FRANCE.
+
+Argile Plastique, C.2, Table—At the base of the tertiary system in
+France are extensive deposits of sands, with occasional beds of clay
+used for pottery, and called “argile plastique.” Fossil oysters
+(_Ostrea bellovacina_) abound in some places, and in others there is a
+mixture of fluviatile shells, such as _Cyrena cuneiformis_ (Fig. 216),
+_ Melania inquinata_ (Fig. 216), 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.
+
+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 _Gastornis Parisiensis_ 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.[10]
+
+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.
+
+Sables de Bracheux, C.3, Table—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 _Arctocyon primævus,_ and supposed by him to be
+related both to the bear and to the Kinkajou (_Cercoleptes_). This
+creature appears to be the oldest known tertiary mammifer.
+
+Nummulitic Formations of Europe, Asia, etc.—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’Archiac, one or two species only are
+found in other tertiary formations whether of older or newer date.
+_Nummulites intermedia,_ 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, _N. variolaria_ in the upper,
+_N. lævigata_ in the middle, and _N. planulata_ 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’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.
+
+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 (Fig. 223) is called by M. d’Archiac
+_Nummulites Puschi._ 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 _Nerita conoidea_ (Fig. 222),
+accompany the nummulites, as in France. The opinion of many observers,
+that the Nummulitic formation belongs partly to the cretaceous era,
+seems chiefly to have arisen from confounding an allied genus,
+Orbitoides, with the true Nummulite.
+
+Fig. 223: Nummulites Puschi.
+
+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.
+
+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
+_flysch_ have actually been converted in the central Alps into
+crystalline rocks, and transformed into marble, quartz-rock,
+micha-schist, and gneiss.[11]
+
+Eocene Strata in the United States.—In North America the Eocene
+formations occupy a large area bordering the 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 _Cardita planicosta,_ before mentioned
+(Fig. 191), 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.[12]
+
+Higher in the series is a remarkable calcareous rock, formerly called
+“the nummulite limestone,” from the great number of discoid bodies
+resembling nummulites which it contains, fossils now referred by A.
+d’Orbigny to the genus _Orbitoides,_ which has been demonstrated by Dr.
+Carpenter to belong to the foraminifera.[13] That naturalist, moreover,
+is of opinion that the Orbitoides alluded to (_O. Mantelli_) is of the
+same species as one found in Cutch, in the Middle Eocene or nummulitic
+formation of India.
+
+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 _N. ziczac_;
+also in its upper bed a gigantic cetacean, called _Zeuglodon_ by
+Owen.[14]
+
+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.
+
+Professor Owen first pointed out that this huge animal was not
+reptilian, since each tooth was furnished with double roots (Fig. 224),
+implanted in corresponding double sockets; and his opinion of the
+cetacean nature of the fossil was afterwards 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.
+
+Fig. 224: Zeuglodon cetoides, Fig 225: Basilosaurus.
+
+ [1] Quart. Geol. Journal, vol. xx, p. 97, 1864.
+
+ [2] Palæont. Soc. Monograph, Rept., pt. ii, p. 61.
+
+ [3] Heer, Climat et Végétation du Pays Tertiaire, p. 172.
+
+ [4] Bowerbank, Fossil Fruits and Seeds of London Clay, Plates ix and
+ x.
+
+ [5] Prestwich, Quart. Geol. Journ., vol. x.
+
+ [6] Second Visit to the United States, vol. ii, p. 104.
+
+ [7] Cuvier, Oss. Foss., tome iii, p. 255.
+
+ [8] Sur des Empreintes de Pas d’Animaux par M. J. Desnoyers. Compte
+ rendu de l’Institut, 1859.
+
+ [9] D’Archiac, Bulletin, tome x; and Prestwich, Quart. Geol. Journ.,
+ 1847, p. 377.
+
+ [10] Quart. Geol. Journ., vol. xii, p. 204, 1856.
+
+ [11] Murchison, Quart. Journ. of Geol. Soc., vol. v, and Lyell, vol.
+ vi, 1850. Anniversary Address.
+
+ [12] 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.
+
+ [13] Quart. Journ. of Geol. Soc., vol. vi, p. 32.
+
+ [14] See Memoir by R. W. Gibbes, Journ. of Acad. Nat. Sci. Philad.,
+ vol. i, 1847.
+
+
+
+
+CHAPTER XVII.
+UPPER CRETACEOUS GROUP.
+
+
+Lapse of Time between Cretaceous and Eocene Periods. — Table of
+successive Cretaceous Formations. — Maestricht Beds. — Pisolitic
+Limestone of France. — Chalk of Faxoe. — Geographical Extent and Origin
+of the White Chalk. — Chalky Matter now forming in the Bed of the
+Atlantic. — Marked Difference between the Cretaceous and existing
+Fauna. — Chalk-flints. — Pot-stones of Horstead. — Vitreous Sponges in
+the Chalk. — Isolated Blocks of Foreign Rocks in the White Chalk
+supposed to be ice-borne. — Distinctness of Mineral Character in
+contemporaneous Rocks of the Cretaceous Epoch. — Fossils of the White
+Chalk. — Lower White Chalk without Flints. — Chalk Marl and its
+Fossils. — Chloritic Series or Upper Greensand. — Coprolite Bed near
+Cambridge. — Fossils of the Chloritic Series. — Gault. — Connection
+between Upper and Lower Cretaceous Strata. — Blackdown Beds. — Flora of
+the Upper Cretaceous Period. — Hippurite Limestone. — Cretaceous Rocks
+in the United States.
+
+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 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.
+
+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.
+
+Classification of the Cretaceous Rocks.—The cretaceous group has
+generally been divided into an Upper and a Lower series, the Upper
+called familiarly _the chalk,_ and the Lower _the greensand_; 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 “Lower Greensand;” 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.
+
+UPPER CRETACEOUS OR CHALK PERIOD.
+
+Maestricht Beds and Faxoe Limestone.
+
+Upper White Chalk, with flints.
+
+Lower White Chalk, without flints.
+
+Chalk Marl.
+
+Chloritic series (or Upper Greensand).
+
+Gault.
+
+LOWER CRETACEOUS OR NEOCOMIAN. Marine Fresh-water
+
+Marine: Upper Neocomian, see p.308
+
+Marine: Middle Neocomian, see p.312
+
+Marine: Lower Neocomian, see p.312
+
+Wealden Beds (upper part).
+
+Belemnitella mucronata. Belemnitella mucronata,
+Maestricht, Faxoe, and White Chalk.
+_a/_ Entire specimen, showing vascular impression on outer surface, and
+characteristic slit. _b._ Section of same, showing place of
+phragmocone.[1]
+
+_Maestricht Beds._—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 _Belemnitella mucronata_ (Fig. 226) and _Pecten
+quadricostatus,_ a shell regarded by many as a mere variety of _P.
+quinquecostatus_ (see Fig. 270). Besides the Belemnite there are other
+_genera,_ such as _Baculites_ and _Hamites,_ never found in strata
+newer than the cretaceous, but frequently met with in these Maestricht
+beds. On the other hand, _Voluta, Fasciolaria,_ and other genera of
+univalve shells, usually met with only in tertiary strata, occur.
+
+The upper part of the rock, about 20 feet thick, as seen in St. Peter’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.
+
+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 the white chalk below. The latter is distinguished by
+regular layers of black flint in nodules, and by several shells, such
+as _Terebratula carnea_ (see Fig. 246), wholly wanting in beds higher
+than the green band. Some of the organic remains, however, for which
+St. Peter’s Mount is celebrated, occur both above and below that
+parting layer, and, among others, the great marine reptile called
+_Mosasaurus_ (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.
+
+Mosasaurus Camperi.
+
+Hemipneustes radiatus.
+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
+_Thecidea papillata_ and _Belemnitella mucronata_ 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 accumulated in a sea
+in which the belemnite and other cretaceous mollusca flourished.
+
+Pisolitic Limestone of France.—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 _Pecten quadricostatus,_ 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’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.
+
+The _Nautilus Danicus,_ Fig. 230, 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.
+
+Chalk of Faxoe.— 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 _Cypræa,_ one of
+_Oliva,_ two of _Mitra,_ four of the genus _Cerithium,_ six of _Fusus,_
+two of _Trochus,_ one of _Patella,_ one of _Emarginula,_ 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
+_Baculites Faujasii_ (Fig. 229), and _Belemnitella mucronata_ (Fig.
+226), shells of the white chalk. The _Nautilus Danicus_ (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, _Brachyurus rugosus_ (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.
+
+Fig. 229: Portion of Baculites Faujasii, Fig. 230: Nautilus Danicus.
+
+Composition, Extent and Origin of the White Chalk.—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 Fig. 231 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.
+
+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 _Inoceramus
+Cuvieri, Belemnitella mucronata,_ and _Ostrea vesicularis_ (Fig. 251).
+
+Diagrammatic section from Hertfordshire, in England, to Sens, in
+France.
+
+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 _Globigerina bulloides_ (see
+Fig. 232.) the organic bodies next in quantity were the siliceous
+shells called _ Polycystineæ,_ and next to them the siliceous skeletons
+of plants called _Diatomaceæ_ (Figs. 233, 234, 235), and occasionally
+some siliceous spiculæ of sponges (Fig. 236) were intermixed. These
+were connected by a mass of living gelatinous matter to which he has
+given the name of _Bathybius,_ and which contains abundance of very
+minute bodies termed Coccoliths and Coccospheres, which have also been
+detected fossil in chalk.
+
+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, R.N., lately brought up from
+the enormous depth of 16,860 feet a white, 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 _ Coccoliths, Discoliths,_ and other minute
+fossils like those of the Chalk classed by Huxley as _Bathybius,_ when
+this term is used in its widest sense. This mud, more than three miles
+deep, was dredged up in latitude 20° 19′ N., longitude 4° 36′ E., or
+about midway between Madeira and the Cape of Good Hope.
+
+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.
+
+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.
+
+Popular Error as to the Geological Continuity of the Cretaceous
+Period.—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: “We are still living in the
+Cretaceous epoch;” 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 (p. 142), 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 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.
+
+When told that the new dredgings prove that “we are still living in the
+Chalk Period,” 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—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—one, and one only,
+_Terebratulina striata,_ is still living, being thought to be identical
+with _Terebratula caput-serpentis._ 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.
+
+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 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.
+
+Chalk-flints.—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 “Bulldog,” already alluded to, it was ascertained that while the
+calcareous _Globigerinæ_ 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 _Diatomaceæ,_
+above mentioned (Figs. 233-235), the solid parts of which are
+siliceous, monopolise the ground at a depth of nearly 400 fathoms, or
+2400 feet.
+
+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.
+
+Pot-stones.—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 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’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.[2]
+
+View of a chalk-pit at Horstead, near Norwich, showing the position of
+the pot-stones.
+
+Vitreous Sponges of the Chalk.—These pear-shaped masses of flint often
+resemble in shape and size the large sponges called Neptune’s Cups
+(_Spongia patera,_ 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.
+
+Fig. 238: Ventriculites radiatus. White chalk.
+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.
+
+Boulders and Groups of Pebbles in Chalk.—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.
+
+Distinctness of Mineral Character in Contemporaneous Rocks of the
+Cretaceous Period.—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 been accumulated contemporaneously even
+in European seas. The siliceous sandstone called “upper quader” by the
+Germans overlies white argillaceous chalk or “pläner-kalk,” 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.
+
+Fig. 239: Ananchytes ovatus. White chalk, upper and lower.
+
+Fossils of the White Chalk.—Among the fossils of the white chalk,
+echinoderms are very numerous; and some of the genera, like
+_Ananchytes_ (see Fig. 239), are exclusively cretaceous. Among the
+Crinoidea, the _Marsupites_ (Fig. 242) is a characteristic genus. Among
+the mollusca, the cephalopoda are represented by Ammonites, Baculites
+(Fig. 229), and Belemnites (Fig. 226). 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.
+
+Among the brachiopoda in the white chalk, the _ Terebratulæ_ are very
+abundant (see Figs. 243-247). With these are associated some forms of
+oyster (see Fig. 251), and other bivalves (Figs. 249, 250).
+
+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.
+
+Among the bivalve mollusca, no form marks the Cretaceous era in Europe,
+America, and India in a more striking manner than the extinct genus
+_Inoceramus_ (_Catillus_ of Lam.; see Fig. 252), the shells of which
+are distinguished by a fibrous texture, and are often met with in
+fragments, having probably been extremely friable.
+
+Of the singular family called _Rudistes_ by Lamarck, hereafter to be
+mentioned as extremely characteristic of the chalk of southern Europe,
+a single representative only (Fig. 253) has been discovered in the
+white chalk of England.
+
+Fig. 251: Ostrea vesicularis. Upper chalk and upper greensand. Fig.
+252: Inoceramus Lamarckii. White chalk.
+
+_Radiolites Mortoni_, Mantell. Houghton, Sussex. White chalk.
+Diameter one-seventh nat. size.
+Fig. 253. Two individuals deprived of their upper valves, adhering
+together.
+Fig. 254. Same seen from above.
+Fig. 255. Transverse section of part of the wall of the shell,
+magnified to show the structure.
+Fig. 256. Vertical section of the same.
+On the side where the shell is thinnest, there is one external furrow
+and corresponding internal ridge, _a_, _b_, figs. 255, 256; but they
+are usually less prominent than in these figures. The upper or
+opercular valve is wanting.
+
+The general absence of univalve mollusca in the white chalk is very
+marked. Of bryozoa there is an abundance, such as _Eschara_ and
+_Escharina_ (Figs. 257, 258). These and other organic bodies,
+especially sponges, such as _Ventriculites_ (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, _a,_ where the hollows in the exterior are caused by the
+branches of a sponge (Fig. 259, _b_), seen on breaking open the flint.
+
+Fig. 257: Eschara disticha. White chalk. Fig. 258: Escharina oceani.
+White chalk. Fig. 259: A branching sponge in a flint, from the white
+chalk.
+
+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 _Ptychodus_ (Fig. 260), which is allied to the living
+Port Jackson shark, _Cestracion Phillippi,_ the anterior teeth of which
+(see Fig. 261, _a_) are sharp and cutting, while the posterior or
+palatal teeth (_b_) are flat (Fig. 260). 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 in leading us to conclude that the white chalk was
+the product of an open sea of considerable depth.
+
+Fig. 260: Palatal tooth of Ptychodus decurrens. Lower white chalk.
+
+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 _ Clathraria Lyellii,_ 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.
+
+Fig. 261: Cestracion Phillipi; recent.
+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.
+
+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 to be the excrement of fish (see
+Fig. 262). They are composed in great part of phosphate of lime.
+
+Fig. 262: Coprolites of fish, from the chalk. Fig. 263: Baculites
+anceps. Lower chalk. Fig. 264: Ammonites Rhotomagensis. Chalk marl.
+
+Lower White Chalk.—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.
+
+Chalk Marl.—The lower chalk without flints passes gradually downward,
+in the south of England, into an argillaceous limestone, “the chalk
+marl,” 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. _ A. Rhotomagensis_ is characteristic of this
+formation. Among the British cephalopods of other genera may be
+mentioned _Scaphites æqualis_ (Fig. 266) and _Turrilites costatus_
+(Fig. 265).
+
+Chloritic Series (or Upper Greensand).—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 (p. 282) 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 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.
+
+Fig. 265: Turrilites costatus. Lower chalk and chalk marl. Fig. 266:
+Scaphites æqualis. Chloritic marl and sand, Dorsetshire.
+_Coprolite Bed._—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.
+
+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.
+
+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.
+
+Fig. 267: Ostrea columba. Chloritic sand. Fig. 268: Ostrea carinata.
+Chalk marl and chloritic sand.
+
+Among the characteristic mollusca of the chloritic sand may be
+mentioned _Terebrirostra lyra_ (Fig. 269), _Plagiostoma Hoperi_ (Fig.
+271), _Pecten quinque-costatus_ (Fig. 270), and _Ostrea columba_ (Fig.
+267).
+
+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.
+
+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.
+
+Gault.—The lowest member of the Upper Cretaceous group, 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 _Hamite_ (Fig. 272),
+and _ Scaphite,_ 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.
+
+Fig. 272: Ancyloceras spinigerum. Near Folkestone.
+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.
+
+Connection between Upper and Lower Cretaceous Strata.—Blackdown
+Beds.—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.
+
+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 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.
+
+Flora of the Upper Cretaceous Period.—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’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.
+
+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 _Pecten quadricostatus,_ and
+several others which are common to the upper and lower part of the
+series, and _ Trigonia limbata,_ D’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
+_Trigonia, Turritella, Pecten,_ etc., established themselves in the
+same area, and plants allied to _Zostera_ and _Fucus_ grew on the
+bottom.
+
+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 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, _Gleichenia,_ 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 _ Asplenium,_ 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.[3]
+
+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—Dryandra, Grevillea, Hakea, Banksia, Persoonia—all now
+belonging to Australia, and Leucospermum, species of which form small
+bushes at the Cape.
+
+  Brongniart. Lindley. Cryptogamic. 1. Cryptogamous amphigens,
+  or cellular cryptogamic. Thallogens. Lichens, sea-weeds,
+  fungi. 2. Cryptogamous acrogens. Acrogens. Mosses,
+  equisetums, ferns, lycopodiums,—Lepidodendra.
+Phænerogamic. 3. Dicotyledonous
+gymnosperms. Gymnogens. Conifers and Cycads. 4. Dicot.
+angiosperms. Exogens. Compositæ, leguminosæ, cruciferæ, healths,
+etc. All native European trees except conifers. 5.
+Monocotyledons. Endogens. Palms, lilies, aloes, rushes, grasses,
+etc.
+
+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.
+
+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.
+
+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.
+
+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.
+
+Hippurite limestone.—_Difference between the Chalk of the North and
+South of Europe._—By the aid of the three tests, 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.
+
+Fig. 273: Map.
+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).
+
+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 _Spatangus,
+Ananchytes, Cidarites, Nucula, Ostrea,_ _Gryphæa (Exogyra), Pecten,
+Plagiostoma (Lima), Trigonia, Catillus (Inoceramus),_ and
+_Terebratula._[4] But Ammonites, as M. d’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 _Hamite,
+Turrilite,_ and _Scaphite,_ and perhaps _Belemnite,_ are entirely
+wanting.
+
+Fig. 274: Radiolites. White chalk of France. Fig. 275: Radiolites
+foliaceus. White chalk of France.
+
+Fig. 276: Hippurites organisans. Upper chalk:—chalk marl of Pyrenees?
+Fig. 276: Hippurites organisans. Upper chalk:—chalk marl of
+Pyrenees?[5]
+
+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 _Hippurites, Sphærulites,_ and other members of that great family
+of mollusca called _Rudistes_ 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 _ Hippurites organisans_ (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, _d,_ 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.
+
+Cretaceous Rocks in the United States.—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.
+
+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—_Ostrea larva, O. vesicularis, Gryphæa costata, Pecten
+quinque-costatus, Belemnitella mucronata._ 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 _Inoceramus_ (see Fig. 252) 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 _Lamna, Galeus,_ and _ Carcharodon_ are common to New Jersey and
+the European cretaceous rocks. So also is the genus _Mosasaurus_ among
+reptiles.
+
+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.
+
+ [1] For particulars of structure see p. 318.
+
+ [2] Geol. Trans., 1st Series, vol. iv, p. 413.
+
+ [3] In this and subsequent remarks on fossil plants I shall often use
+ Dr. Lindley’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.
+
+ [4] D’Archiac, Sur la form. Crétacée du S.-O. de la France Mém. de la
+ Soc. Géol. de France, tome ii.
+
+ [5] D’Orbigny’s Paléontologie français, pl. 533.
+
+
+
+
+CHAPTER XVIII.
+LOWER CRETACEOUS OR NEOCOMIAN FORMATION.
+
+
+Classification of marine and fresh-water Strata. — Upper Neocomian. —
+Folkestone and Hythe Beds. — Atherfield Clay. — Similarity of
+Conditions causing Reappearance of Species after short Intervals. —
+Upper Speeton Clay. — Middle Neocomian. — Tealby Series. — Middle
+Speeton Clay. — Lower Neocomian. — Lower Speeton Clay. — Wealden
+Formation. — Fresh-water Character of the Wealden. — Weald Clay. —
+Hastings Sands. — Punfield Beds of Purbeck, Dorsetshire. — Fossil
+Shells and Fish of the Wealden. — Area of the Wealden. — Flora of the
+Wealden.
+
+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 “Neocomian.”
+
+LOWER CRETACEOUS OR NEOCOMIAN GROUP.
+
+Marine Fresh-water
+
+Upper Neocomian—Greensand of Folkestone, Sandgate, and Hythe,
+Atherfield clay, upper part of Speeton clay.
+
+Middle Neocomian—Punfield Marine bed, Tealby beds, middle part of
+Speeton clay.
+
+Lower Neocomian—Lower part of Speeton clay.
+
+Part of Wealden beds of Kent, Surrey, Sussex, Hants, and Dorset.
+
+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.
+
+UPPER NEOCOMIAN.
+
+Folkstone and Hythe Beds.—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 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 _Nautilus plicatus_ (Fig.
+277), _ Ancyloceras (Scaphites) gigas_ (Fig. 278), which has been aptly
+described as an Ammonite more or less uncoiled; _Trigonia caudata_
+(Fig. 280), _Gervillia anceps_ (Fig. 279), a bivalve genus allied to
+Avicula, and _Terebratula sella_ (Fig. 281). In ferruginous beds of the
+same age in Wiltshire is found a remarkable shell called _Diceras
+Lonsdalii_ (Fig. 282), 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.
+
+Fig. 277: Nautilus licatus. Fig. 278: Ancyloceras gigas. Fig. 279:
+Gervillia anceps. Fig. 280: Trigonia caudata.
+
+Atherfield Clay.—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 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.
+
+Fig. 281: Terebratula sella. Fig. 282: Diceras Lonsdalii. a. The
+bivavle shell, b. Cast of one of the valves enlarged.
+
+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.
+
+Fig. 283: Perna mulleti.
+Among the shells of the Atherfield clay the biggest and most abundant
+shell is the large _Perna Mulleti,_ of which a reduced figure is given
+in Fig. 283.
+
+_Similarity of Conditions causing Reappearance of Species._—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 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.
+
+Fig. 284: Ammonites Deshayesii.
+
+Speeton Clay, Upper Division.—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,[1] 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 _Perna Mulleti_ (Fig. 283) and _Terebratula sella_
+(Fig. 281), and by _ Ammonites Deshayesii_ (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.
+
+MIDDLE NEOCOMIAN.
+
+Tealby Series.—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 _ Pecten cinctus_ (Fig. 285), from 9 to 12
+inches in diameter, _ Ancyloceras Duvallei_ (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 _Ammonites clypeiformis_ and
+_Terebratula hippopus_ characterise the Middle Neocomian of the
+Continent, it is to this stage that the Tealby series containing the
+same fossils may be assigned.[2]
+
+Fig. 285: Pecten cinctus. Fig. 286: Ancyloceras (Crioceras) Duvallei.
+
+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, _Pecten cinctus_ (Fig. 285) and _Ancyloceras
+(Crioceras) Duvallei_ (Fig. 286) occur.
+
+LOWER NEOCOMIAN.
+
+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 _Ammonites Noricus_ (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 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.
+
+Fig. 287: Ammonites Noricus.
+
+WEALDEN FORMATION.
+
+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 “Geology of Sussex,” 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.
+
+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 Fig. 288. 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.
+
+_Weald Clay._—The Upper division, or Weald Clay, is, in great part, of
+fresh-water origin, but in its highest portion 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
+_Iguanodon Mantelli,_ 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.
+
+Fig. 288
+
+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 Figs. 289 _a_ and _b_), 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 of having been chipped off, but never,
+like the fossil teeth of the Iguanodon, have a flat ground surface (see
+Fig. 290, _b_) 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.
+
+Fig. 289 a, b: Tooth of Iguanodon Mantelli. Fig. 290: a. Partially worn
+tooth of young individual of the same; <i>b.</i> Crown of tooth in
+adult worn down.
+
+Fig. 291: Cypris spinigera.
+Occasionally bands of limestone, called Sussex Marble, occur in the
+Weald Clay, almost entirely composed of a species of _ Paludina,_
+closely resembling the common _P. vivipara_ of English rivers. Shells
+of the _Cypris,_ a genus of Crustaceans mentioned (p. 57) as abounding
+in lakes and ponds, are also plentifully scattered through the clays of
+the Wealden, sometimes producing, like plates of mica, a thin
+lamination (see Fig. 292).
+
+Fig. 292: Weald clay with Cyprides.
+Hastings Sands.—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:
+
+  Names of Subordinate
+Formations. Mineral Composition
+of the Strata. Thickness
+in feet. Hastings Sand Tunbridge Wells Sand Sandstone and
+loam 150 Wadhurst Clay Blue and brown shale and clay, with
+a little calc-grit 100 Ashdown Sand Hard sand, with some beds of
+calc-grit 160 Ashburnham Beds Mottled white and red clay, with
+some sandstone 330
+
+The picturesque scenery of the “High Rocks” 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 “rock-sand” 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 “sand-rock” 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 _Trionyx_ and _Emys,_ now confined
+to tropical regions.
+
+The fishes of the Wealden are chiefly referable to the Ganoid and
+Placoid orders. Among them the teeth and scales of _ Lepidotus_ are
+most widely diffused (see Fig. 293, next page). These ganoids were
+allied to the _Lepidosteus,_ 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.
+
+Fig. 293: Lepidotus Mantelli, a. Palate and teeth, b. Side view of
+teeth, c. Scale.
+
+Fig. 294: Unio Valdensis. Fig. 295: Under side of slab of sandstone
+about one yard in diameter.
+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).
+
+Near the same place a reddish sandstone occurs in which are innumerable
+traces of a fossil vegetable, apparently _ Sphenopteris,_ 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.[3] 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.
+
+Fig. 296: Sphenopteris gracilis.
+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.
+
+Punfield Beds, Brackish and Marine.—The shells of the Wealden beds
+belong to the genera _Melanopsis, Melania, Paludina, Cyrena, Cyclas,
+Unio_ (see Fig. 294), 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 _Corbula, Mytilus,_ and
+_Ostrea_ occur; and in some places this bed becomes purely marine,
+containing some well-known Neocomian fossils, among which _Ammonites
+Deshayesii_ (Fig. 284) may be mentioned. Others are peculiar as
+British, but very characteristic of the Upper and Middle Neocomian of
+Spain, and among these the _ Vicarya Lujani_ (Fig. 297), a shell allied
+to Nerinea, is conspicuous.
+
+By reference to table (p. 308) it will be seen that the 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
+_Asteracanthus granulosus,_ occurring in the Tilgate beds, is
+characteristic of the lowest beds of the Neocomian of the Jura, and it
+is well known that _Corbula alata,_ common in the Ashburnham beds, is
+found also at the base of the Neocomian of the Continent.
+
+Fig. 297: Vicarya Lujani. Fig. 297: _Vicarya Lujani_, De Verneuil.[4]
+Wealden, Punfield.
+
+_Area of the Wealden._—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.[5] 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 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;[6] and the possibility of such movements and
+their effects must not be lost sight of when we speculate on the origin
+of the Wealden.
+
+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.
+
+_Thickness of the Wealden._—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.
+
+_Wealden Flora._—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.
+
+ [1] Judd, Speeton clay, Quart. Geol. Journ., vol. xxiv, 1868, p. 218.
+
+ [2] Judd, Quart. Geol. Journ., 1867, vol. xxiii, p. 249.
+
+ [3] Mantell, Geol. of S.E. of England, p. 244.
+
+ [4] Foss. de Utrillas.
+
+ [5] Fitton, Geol. of Hastings, p. 58, who cites Lander’s Travels.
+
+ [6] See p. 102 and Second Visit to the United States, vol. ii, chap.
+ xxxiv.
+
+
+
+
+CHAPTER XIX.
+JURASSIC GROUP.—PURBECK BEDS AND OOLITE.
+
+
+The Purbeck Beds a Member of the Jurassic Group. — Subdivisions of that
+Group. — Physical Geography of the Oolite in England and France. —
+Upper Oolite. — Purbeck Beds. — New Genera of fossil Mammalia in the
+Middle Purbeck of Dorsetshire. — Dirt-bed or ancient Soil. — Fossils of
+the Purbeck Beds. — Portland Stone and Fossils. — Kimmeridge Clay. —
+Lithographic Stone of Solenhofen. — Archæopteryx. — Middle Oolite. —
+Coral Rag. — Nerinæa Limestone. — Oxford Clay, Ammonites and
+Belemnites. — Kelloway Rock. — Lower, or Bath, Oolite. — Great Plants
+of the Oolite. — Oolite and Bradford Clay. — Stonesfield Slate. —
+Fossil Mammalia. — Fuller’s Earth. — Inferior Oolite and Fossils. —
+Northamptonshire Slates. — Yorkshire Oolitic Coal-field. — Brora Coal.
+— Palæontological Relations of the several Subdivisions of the Oolitic
+group.
+
+Classification of the Oolite.—Immediately below the Hastings Sands we
+find in Dorsetshire another remarkable fresh-water formation, called
+_the Purbeck,_ 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.
+
+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 “the Oolite and Lias” 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 p. 37). 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.
+
+OOLITE
+
+Upper _a._  Purbeck beds.
+_b._  Portland stone and sand.
+_c._  Kimmeridge clay. Middle _d._  Coral rag.
+_e._  Oxford clay, and Kelloway rock. Lower _f._   Cornbrash and
+Forest marble.
+_g._  Great Oolite and Stonesfield slate.
+_h._  Fuller’s earth.
+_i._   Inferior Oolite.
+
+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.
+
+Physical Geography.—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.
+
+Fig. 298: Configuration of surface.
+
+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. 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.
+
+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 p. 105) 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.
+
+UPPER OOLITE.
+
+Purbeck Beds.—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’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.
+
+_Upper Purbeck._—The highest of the three divisions is purely
+fresh-water, the strata, about fifty feet in thickness, containing
+shells of the genera _Paludina, Physa, Limnæa, Planorbis, Valvata,
+Cyclas,_ and _Unio,_ with _ Cyprides_ and fish. All the species seem
+peculiar, and among these the _Cyprides_ are very abundant and
+characteristic (see Fig. 299, _a, b, c._)
+
+The stone called “Purbeck Marble,” formerly much used in ornamental
+architecture in the old English cathedrals of the southern counties, is
+exclusively procured from this division.
+
+Fig. 299: Cyprides from the Upper Purbecks.
+
+_Middle Purbeck._—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 _Cyrena,_ and traversed by bands abounding in _Corbula_
+and _ Melania._ These are based on a purely marine deposit, with _
+Pecten, Modiola, Avicula,_ and _Thracia._ Below this, again, come
+limestones and shales, partly of brackish and partly of fresh-water
+origin, in which many fish, especially species of _ Lepidotus_ and
+_Microdon radiatus,_ are found, and a crocodilian reptile named
+_Macrorhynchus._ Among the mollusks, a remarkable ribbed _Melania,_ of
+the section _Chilina,_ occurs.
+
+Fig. 300: Ostrea distorta. Fig. 301: Hemicidaris Purbeckensis.
+
+Immediately below is a great and conspicuous stratum, twelve feet
+thick, formed of a vast accumulation of shells of _Ostrea distorta_
+(Fig. 300), long familiar to geologists under the local name of
+“Cinder-bed.” In the uppermost part of this bed Professor Forbes
+discovered the first echinoderm (Fig. 301) as yet known in the Purbeck
+series, a species of _ Hemicidaris,_ 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
+_Perna._ Below the Cinder-bed fresh-water strata are again seen, filled
+in many places with species of _Cypris_ (Fig. 302, _a, b, c_), and with
+_Valvata, Paludina, Planorbis, Limnæa, Physa_ (Fig. 303), and _Cyclas,_
+all different from any occurring higher in the series. It will be seen
+that _Cypris fasciculata_ (Fig. 302, _b_) 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 _Chara_), plants
+never until 1851 discovered in rocks older than the Eocene. About
+twenty feet below the “Cinder-bed” 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 _Zostera,_ forming the base
+of the Middle Purbeck.
+
+Fig. 302: Cyprides from the Middle Purbecks.
+
+Fig. 303: Physa Bristovii
+
+_Fossil Mammalia of the Middle Purbeck._—In 1852,[1] 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, “it was too soon to infer their non-existence on mere negative
+evidence.” Only two years after this remark was in print, Mr. W. R.
+Brodie found in the Middle Purbeck, about twenty feet below the
+“Cinder-bed” 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 _ Amphitherium_ (or _Thylacotherium_) than to any
+existing type.
+
+Four years later (in 1856) the remains of several other species of
+warm-blooded quadrupeds were exhumed by Mr. S. H. Beckles, F.R.S., 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 _Paludina, Planorbis,_ and _Cyclas,_ were found.
+
+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, _Mustela putorius._ 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 _Hypsiprymnus,_
+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.
+
+The largest pre-molar (see Fig. 305) 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—a
+distinction, says Dr. Falconer, which is “trivial, not typical.” 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 _
+Plagiaulax._ The shape and relative size of the incisor, _ a,_ Fig.
+306, exhibit 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.
+
+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.
+
+Fig. 306: Plagiaulax Becklessi. Right ramus of lower jaw.
+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 _Plagiaulax Becklesii_ (Fig. 306) was
+about as big as the English squirrel or the flying phalanger of
+Australia (_Petaurus Australis,_ 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 _ Microlestes_ (Fig. 389), the
+most ancient of known mammalia, of which an account will be given in
+Chapter XXI.
+
+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.
+
+Professor Owen has proposed the name of _Galestes_ for the largest of
+the mammalia discovered in 1858 in Purbeck, equalling the polecat
+(_Mustela putorius_) in size. It is supposed to have been predaceous
+and marsupial.
+
+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; “The corpses,” he said, “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.”
+
+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.
+
+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 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.
+
+_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._
+
+TERTIARY Headon Series and beds between the Paris Gypsum and the
+Grès de Beauchamp 14 10 English
+   4 French Barton Clay and Sables de Beauchamp 0 Bagshot Beds,
+   Calcaire Grossier, and Upper Soissonnais of
+   Cuisse-Lamotte 20 16 French
+   1 English
+   3 U. States[2] London Clay, including the Kyson Sand 7 English
+   Plastic Clay and Lignite 9 7 French
+2 English Sables de Bracheux 1 French Thanet Sands and Lower
+Landenian of Belgium 0
+SECONDARY Maestricht Chalk 0 White Chalk 0 Chalk Marl 0
+Chloritic Series (Upper Greensand) 0 Gault 0 Neocomian (Lower
+Greensand) 0 Wealden 0 Upper Purbeck Oolite 0 Middle Purbeck
+Oolite 14 Swanage Lower Purbeck Oolite 0 Portland Oolite 0
+Kimmeridge Clay 0 Coral Rag 0 Oxford Clay 0 Great
+Oolite 4 Stonesfield Inferior Oolite 0 Lias 0 Upper
+Trias 4 Wurtemberg
+Somersetshire
+N. Carolina Middle Trias 0 Lower Trias 0
+PRIMARY Permian 0 Carboniferous 0 Devonian 0 Silurian 0
+Cambrian 0 Laurentian 0
+
+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 _Arctocyon (Palæocyon) primævus,_ the oldest known tertiary
+mammal.
+
+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.
+
+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
+“dirt-beds,” 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’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!
+
+_Lower Purbeck._—Beneath the thin marine band mentioned at p. 324 as
+the base of the Middle Purbeck, some purely fresh-water marls occur,
+containing species of _Cypris_ (Fig. 307 _a, c_), _Valvata,_ and
+_Limnæa,_ different from those of the Middle Purbeck. This is the
+beginning of the inferior division, which is about 80 feet thick. Below
+the marls are seen, at Meup’s Bay, more than thirty feet of
+brackish-water strata, abounding in a species of _Serpula,_ allied to,
+if not identical with, _Serpula coacervites,_ found in beds of the same
+age in Hanover. There are also shells of the genus _ Rissoa_ (of the
+subgenus _Hydrobia_), and a little _ Cardium_ of the subgenus
+_Protocardium,_ in these marine beds, together with _Cypris._ 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 _Cycadeæ,_ which I shall presently
+describe, underlies these marls, and rests upon the lowest fresh-water
+limestone, a rock about eight feet thick, containing _Cyclas, Valvata,_
+and _Limnæa,_ 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.
+
+Fig. 307: Cyprides from the Lower Purbeck.
+Fig. 308: Mantellia nidiformis.
+_Dirt-bed or ancient Surface-soil._—The most remarkable of all the
+varied succession of beds enumerated in the above list is that called
+by the quarrymen “the dirt,” or “black dirt,” 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 _Cycads_ of the same species, _Mantellia
+nidiformis,_ as those found in the upper bed, but no _Coniferæ._ The
+weight of the incumbent strata squeezing down the compressible dirt-bed
+has caused the _Cycads_ to assume that form which has led the quarrymen
+to call them “petrified birds’ nests,” which suggested to Brongniart
+the specific name of _nidiformis._ 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.
+
+Many silicified trunks of coniferous trees, and the remains of plants
+allied to _Zamia_ and _Cycas,_ 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 _Cycadeæ._
+
+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 3½ 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.
+
+Fig. 309: Section in Isle of Portland, Dorset.
+
+The dirt-bed is by no means confined to the island of Portland, where
+it has been most carefully studied, but is seen 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°, the stumps of the trees are also inclined at the same angle in an
+opposite direction—a beautiful illustration of a change in the position
+of beds originally horizontal (see Fig. 310).
+
+Fig. 310: Section of cliff east of Lulworth Cove.
+
+From the facts above described we may infer, first, that those beds of
+the Upper Oolite, called “the Portland,” 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 _Zamia_ and _Cycas._ 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.
+
+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 _Cycadeæ,_ 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.
+
+_Subdivisions of the Purbeck._—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 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. “The causes which led to a complete change of life
+three times during the deposition of the fresh-water and brackish
+strata must,” says this naturalist, “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.”
+
+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.
+
+The plants of the Purbeck beds, so far as our knowledge extends at
+present, consist chiefly of Ferns, Coniferæ, and Cycadeæ (Fig. 308),
+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.
+
+Portland Oolite and Sand (_b,_ Table p. 321).—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 p.
+331). It supplies the well-known building-stone of which St. Paul’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 called by the
+quarrymen the “Portland screw” (_a,_ Figure 311), is common; the shell
+of the same (_b_) being rarely met with. Also _Trigonia gibbosa_ (Fig.
+313) and _Cardium dissimile_ (Fig. 314). 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).
+
+Fig. 311: Cerithium Portlandicum.
+Fig. 312: Isastræa oblonga. Fig. 313: Trigonia gibbosa.
+
+Kimmeridge Clay.—The _Kimmeridge Clay_ 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 may perhaps be
+of animal origin. Some of the saurians (Pliosaurus) in Dorsetshire are
+among the most gigantic of their kind.
+
+Fig. 314: Cardium dissimile. Fig. 315: Ostrea expansa. Fig. 316:
+Cardium striatulum. Fig. 317: Ostrea deltoidea. Fig. 318: Gryphæa
+(Exogyra) virgula.
+
+Among the fossils, amounting to nearly 100 species, may be mentioned
+_Cardium striatulum_ (Fig. 316) and _Ostrea deltoidea_ (Fig. 317), the
+latter found in the Kimmeridge Clay throughout England and the north of
+France, and also in Scotland, near Brora. The _Gryphæa virgula_ (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 “marnes à gryphées virgules.” 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.
+
+Fig. 319: Trigonellites latus.
+The _Trigonellites latus_ (_Aptychus_ 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.
+
+Solenhofen Stone.—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 _species_ 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.
+
+Fig. 320: Skeleton of Pterodactylus crassirostris.
+
+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 _Archæopteryx macrura._ 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°.
+
+Fig. 321: Tail and feather of Archæopteryx, from Solenhofen, and tail
+of living bird for comparison.
+
+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.
+
+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.
+
+MIDDLE OOLITE.
+
+Coral Rag.—One of the limestones of the Middle Oolite has been called
+the “Coral Rag,” 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
+_Thecosmilia_ (Fig. 322), _Protoseris,_ and _Thamnastræa,_ and
+sometimes form masses of coral fifteen feet thick.
+
+Fig. 322: Thecosmilia annularis. Fig. 323: Thamnastræa.
+
+Fig. 324: Ostrea gregaria. Fig. 325: Nerinæa Goodhallii.
+In Fig. 323 of a _Thamnastræa_ 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 _ Ostrea gregarea_ (Fig. 324) is very characteristic
+of the formation in England and on the Continent.
+
+One of the limestones of the Jura, referred to the age of the English
+Coral Rag, has been called “Nerinæan limestone” (Calcaire à Nérinées)
+by M. Thirria; _Nerinæa_ being an extinct genus of univalve shells
+(Fig. 325) much resembling the _Cerithium_ in external form. The
+section shows the curious and continuous ridges on the columnella and
+whorls.
+
+Oxford Clay.—The coralline limestone, or “Coral Rag,” above described,
+and the accompanying sandy beds, called “calcareous grits,” of the
+Middle Oolite, rest on a thick bed of clay, called the “Oxford Clay,”
+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 (_An. Nat.
+Hist.,_ Nov., 1841).
+
+Fig. 326: Belemnites hastatus. Fig. 327: Ammonites Jason.
+
+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.[3]
+
+Kelloway Rock.—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 23½ per cent, are common to the Oxford clay
+proper. Of the 52 Cephalopoda, 15 (namely 13 species of ammonite, the
+_Ancyloceras Calloviense_ and one Belemnite) are common to the Oxford
+Clay, giving a proportion of nearly 30 per cent.
+
+Fig. 328: Belemnites Puzosianus.
+
+LOWER OOLITE.
+
+Cornbrash and Forest Marble.—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 of echini, and other signs of a neighbouring beach, are
+observed.[4]
+
+Great (or Bath) Oolite.—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 _Eunomia radiata_
+(Fig. 329) is very conspicuous, single individuals forming masses
+several feet in diameter; and having probably required, like the large
+existing brain-coral (_Meandrina_) of the tropics, many centuries
+before their growth was completed.
+
+Fig. 329: Eunomia radiata.
+
+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
+(_c,_ 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 “Great Oolite” 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 _b,_ Fig.
+330, where the darker strata represent the Bradford clay, which is
+however a formation of such local development that in many places it
+cannot easily be separated from the clays of the overlying
+“forest-marble” and underlying “fuller’s earth.” 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
+_serpulæ._ Now these _serpulæ_ 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
+_serpulæ_ were full grown, they had become incrusted over with a
+bryozoan, called _Diastopora diluviana_ (see _b,_ Fig. 331); and many
+generations of these molluscoids had succeeded each other in the pure
+water before they became fossil.
+
+Fig. 330: Apiocrinites rotundus, or Pear Eucrinite.
+
+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.
+
+We may, therefore, perceive distinctly that, as the pines and cycadeous
+plants of the ancient “dirt-bed,” 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.
+
+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 _stations_ 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 _stations,_ 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.
+
+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, “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’
+claws. The shelly strata, also, have occasionally suffered denudation,
+and the removed portions have been replaced by clay.” In such
+shallow-water beds shells of the genera _Patella, Nerita, Rimula,
+Cylindrites_ 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 _Buccinum,
+Pleurotoma, Rostellaria, Murex, Purpuroidea_ (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.
+
+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.
+
+Stonesfield Slate: Mammalia.—The slate of Stonesfield has been shown by
+Mr. Lonsdale to lie at the base of the Great Oolite.[5] It is a
+slightly oolitic shelly limestone, forming large lenticular masses
+imbedded in sand only six feet thick, 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 _Plesiosaur, Crocodile,_ and _ Pterodactyl,_ have been
+discovered in the same limestone.
+
+Fig. 338: Elytron of Buprestis?
+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 _Spalacotherium_ 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 p. 302),
+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.
+
+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 _ Amphitherium,
+Phascolotherium,_ and _Stereognathus_ have been adopted.
+
+Fig. 339: Tupaia Tana. Right ramus of lower jaw.
+
+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 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 (_c,_ Figs. 342 and 343)
+of the lower jaw, as a character of the genus _Didelphys_; 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 _c, d,_ Fig. 342, in the Brazilian
+opossum, whereas in the placental series, as at _c,_ Figs. 340 and 341,
+there is an almost entire absence of such inflection. The _Tupaia Tana_
+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 _Amphitherium._ By clearing
+away the matrix from the specimen of _Amphitherium Prevostii_ here
+represented (Fig. 344), Professor Owen ascertained that the angular
+process (_c_) 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 the _Amphitherium_ might
+not be an insectivorous placental, although it offered some points of
+approximation in its osteology to the marsupials, especially to the
+_Myrmecobius,_ a small insectivorous quadruped of Australia, which has
+nine molars on each side of the lower jaw, besides a canine and three
+incisors.[6] Another species of _Amphitherium_ has been found at
+Stonesfield (Fig. 345), which differs from the former (Fig. 344)
+principally in being larger.
+
+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.
+
+Fig. 344: Amphitherium Prevostii.
+
+Fig. 345: Amphitherium Broderipii. Fig. 346: Phascolotherium
+Bucklandii.
+
+The second mammiferous genus discovered in the same slates was named
+originally by Mr. Broderip _Didelphys Bucklandi_ (see Fig. 346), and
+has since been called _Phascolotherium_ 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.[7]
+
+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 _Stereognathus_ was given to it, and, as is usually the case in
+these old rocks (see p. 328), 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.
+
+Plants of the Oolite.—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 Fig. 348). In the same rock endogens of
+the most perfect structure are met with, as, for example, fruits allied
+to the Pandanus, such as the _Kaidacarpum ooliticum_ of Carruthers in
+the Great Oolite, and the _Podocarya_ of Buckland (see Fig. 347) in the
+Inferior Oolite.
+
+Fuller’s Earth.—Between the Great and Inferior Oolite near Bath, an
+argillaceous deposit, called “the fuller’s earth,” 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.
+
+Fig. 347: Portion of a fossil fruit of Podocarya Bucklandii. Fig. 348:
+Cone of fossil Araucaria sphærocarpa.
+
+Fig. 349: Ostrea acuminata.
+Inferior Oolite.—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 _Aroides Stutterdi,_ 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.
+
+The Inferior Oolite of Yorkshire consists largely of shales and
+sandstones, which assume much the aspect of a true 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 _Equisetum
+Columnare_ (see Fig. 397), which maintains an upright position in
+sandstone strata over a wide area. Shells of _Estheria_ and _Unio,_
+collected by Mr. Bean from these Yorkshire coal-bearing beds, point to
+the estuary or fluviatile origin of the deposit.
+
+Fig. 350: Hemitelites Brownii.
+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.
+
+Fig. 351: Terebratula fimbria. Fig. 352: Rhynchonella spinosa. Fig.
+353: Pholadomya fidicula.
+
+Among the characteristic shells of the Inferior Oolite, I may instance
+_Terebratula fimbria_ (Fig. 351), _Rhynchonella spinosa_ (Fig. 352),
+and _Pholadomya fidicula_ (Fig. 353). The extinct genus _Pleurotomaria_
+is also a form very common in this division as well as in the Oolitic
+system generally. It resembles the _Trochus_ in form, but is marked by
+a deep cleft (_a,_ Figs. 354, 355) on one side of the mouth. The
+_Collyrites (Dysaster) ringens_ (Fig. 356) is an Echinoderm common to
+the Inferior Oolite of England and France, as are the two Ammonites
+(Figs. 357, 358).
+
+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.
+
+Palæontological Relations of the Oolitic Strata.—Observations have
+already been made on the distinctness of the organic remains of the
+Oolitic and Cretaceous strata, and 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.
+
+Fig. 360: Ammonites macrocephalus.
+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, _Rhynchonella obsoleta, Lithodomus
+inclusus, Pholadomya ovalis,_ and _Trigonia costata._
+
+Of all the Jurassic Ammonites of Great Britain, _A. macrocephalus_
+(Fig. 360), which is common to the Great Oolite and Oxford Clay, has
+the widest range.
+
+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.
+
+ [1] Elements of Geology, 4th edition.
+
+ [2] I allude to several Zeuglodons found in Alabama, and referred by
+ some zoologists to three species.
+
+ [3] See Phil. Trans. 1850, p. 363; also Huxley, Memoirs of Geol.
+ Survey, 1864; Phillips, Palæont. Soc.
+
+ [4] P. Scrope, Proc. Geol. Soc., March, 1831.
+
+ [5] Proceedings Geol. Soc., vol. i, p. 414.
+
+ [6] A figure of this recent _Myrmecobius_ will be found in my
+ Principles of Geology, chap. ix.
+
+ [7] Owen’s British Fossil Mammals, p. 62.
+
+
+
+
+CHAPTER XX.
+JURASSIC GROUP—_continued_—LIAS.
+
+
+Mineral Character of Lias. — Numerous successive Zones in the Lias,
+marked by distinct Fossils, without Unconformity in the Stratification,
+or Change in the Mineral Character of the Deposits. — Gryphite
+Limestone. — Shells of the Lias. — Fish of the Lias. — Reptiles of the
+Lias. — Ichthyosaur and Plesiosaur. — Marine Reptile of the Galapagos
+Islands. — Sudden Destruction and Burial of Fossil Animals in Lias. —
+Fluvio-marine Beds in Gloucestershire, and Insect Limestone. — Fossil
+Plants. — The origin of the Oolite and Lias, and of alternating
+Calcareous and Argillaceous Formations.
+
+Lias.—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.
+
+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.
+
+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.
+
+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, 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.
+
+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.
+
+Fig. 361: Plagiostoma (Lima) giganteum. Fig. 362: Gryphæa incurva.
+
+Fossils of the Lias.—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 _ Gryphæa_ (Fig. 362). A large
+heavy shell called _Hippopodium_ (Fig. 365), allied to _Cypricardia,_
+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 _Spirifer_ and _ Leptæna_
+(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 strata older than the Trias; but, so far as we
+yet know, they did not survive the Liassic epoch.
+
+Fig. 363: Avicula inæquivalvis. Fig. 364: Avicula cygnipes. Fig. 365:
+Hippopodium ponderosum. Fig. 366: Spiriferina (Spirifera). Fig. 367:
+Leptæna Moorei.
+
+Fig. 368: Ammonites Bucklandi. Fig. 369: Ammonites planorbis. Fig. 370:
+Nautilus truncatus. Fig. 371: Ammonites bifrons.
+
+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 _Ammonites Bucklandi,_ and
+the lower by _Ammonites planorbis_ (see Figs. 368, 369).[1] Sometimes,
+however, there is a third intermediate zone, that of _Ammonites
+angulatus,_ which is the equivalent of the zone called the infra-lias
+on the Continent, the species of which are for the most part common to
+the superior group marked by _Ammonites Bucklandi._
+
+Fig. 372: Ammonites margaritatus.
+Among the Crinoids or Stone-lilies of the Lias, the Pentacrinites are
+conspicuous. (See Fig. 373.) Of _ Palæocoma (Ophioderma) Egertoni_
+(Fig. 374), referable to the _Ophiuridæ_ of Muller, perfect specimens
+have been met with in the Middle Lias beds of Dorset and Yorkshire.
+
+Fig. 373: Extracrinus (Pentacrinus) Briareus. Fig. 374: Palæocoma
+(Ophioderma) tenuibrachiata.
+
+The _Extracrinus Briareus_ (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 _ Extracrinus_ and several of
+_Pentacrinus_ 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 _Pentacrinus
+caput-medusæ_ 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.
+
+Fig. 375: Scales of Lepidotus gigas. Fig. 376: a. Scales of Æchmodus
+Leachii, b. Æchmodus (restored outline), c. Scales of Dapedius
+monilifer.
+
+Fishes of the Lias.—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 _ Lepidotus_ (_L. gigas,_ Agassiz),
+Fig. 375, which is found in the Lias of England, France, and
+Germany.[2] This genus was before mentioned (p. 316) 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 _Æchmodus_ (Fig. 376), is almost exclusively
+Liassic. The teeth of a species of _ Acrodus,_ also, are very abundant
+in the Lias (Fig. 377).
+
+Fig. 377: Acrodus nobilis. Fig. 378: Hybodus reticulatus, a. Part of
+fin, commonly called Ichthyodorylite, b. Tooth.
+
+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.
+
+Fig. 379: Chimæra monstrosa. Fig. 379: Chimæra monstrosa.[3]
+
+These last appear to have been bony spines which formed the anterior
+part of the dorsal fin, like that of the living genera _ Cestracion_
+and _Chimæra_ (see _a,_ Figure 379). In both of these genera, the
+posterior concave face is armed with small spines, as in that of the
+fossil _Hybodus_ (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. “They serve,” says Dr. Buckland, “as in the
+_Chimæra_ (Fig. 379), to raise and depress the fin, their action
+resembling that of a movable mast, raising and lowering backward the
+sail of a barge.”[4]
+
+Reptiles of the Lias.—It is not, however, the fossil fish which form
+the most striking feature in the organic remains of the Lias; but the
+_Enaliosaurian_ reptiles, which are extraordinary for their number,
+size, and structure. Among the most singular of these are several
+species of _Ichthyosaurus_ and _Plesiosaurus_ (Figs. 380, 381). The
+genus _ Ichthyosaurus,_ 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.
+
+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 _ Plesiosaurus._[5] (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 _
+Ichthyosaurus,_ 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.[6] Some of the reptiles above mentioned were of
+formidable dimensions. One specimen of _ Ichthyosaurus platydon,_ 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
+_Plesiosaurus_ which measure from 18 to 20 feet in length. The form of
+the _ Ichthyosaurus_ 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 _Plesiosaurus,_ at least the long-necked species (Fig. 381),
+was better suited to fish in shallow creeks and bays defended from
+heavy breakers.
+
+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, 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 Pinos (Isle of Pines),
+south of Cuba, and in the open sea round the coast. In 1835 a curious
+lizard (_Amblyrhynchus cristatus_) was discovered by Mr. Darwin in the
+Galapagos Islands.[7] 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.
+
+Fig. 380: Skeleton of Ichthyosaurus communis, restored by Conybeare and
+Cuvier. Fig. 381: Skeleton of Plesiosaurus dolichodeirus, restored by
+Rev. W. D. Conybeare.
+
+The families of Dinosauria, crocodiles, and Pterosauria or winged
+reptiles, are also represented in the Lias.
+
+Sudden Destruction of Saurians.—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.
+
+“Sometimes,” says Dr. Buckland, “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.”[8] 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; “as if,” says Sir H. De la Beche, “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.”[9] 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.
+
+Numerous specimens of the Calamary or pen-and-ink fish, (_Geoteuthis
+bollensis_) 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 sediment; for, if long exposed after death, the membrane
+containing the ink would have decayed.[10]
+
+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 “Principles of
+Geology” 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.
+
+Fig. 382: Wing of a neuropterous insect.
+
+Fresh-water Deposits.—Insect-beds.—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 “insect limestone.” It passes upward, says the Reverend P. B.
+Brodie,[11] into a shale containing _Cypris_ and _ Estheria,_ 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 wood-eating and
+herb-devouring beetles, of the Linnean genera _Elater, Carabus,_ etc.,
+besides grasshoppers (_Gryllus_), and detached wings of dragon-flies
+and may-flies, or insects referable to the Linnean genera _Libellula,
+Ephemera, Hemerobius,_ and _Panorpa,_ 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.
+
+Fossil Plants.—Among the vegetable remains of the Lias, several species
+of _Zamia_ 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 _ Zamites,_ and among the ferns the numerous genera
+with leaves having reticulated veins (as in Fig. 349), are mentioned as
+botanical characteristics of this era.[12] 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 p. 303). 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.
+
+Origin of the Oolite and Lias.—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 p. 353) 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
+Fig. 298).[13] The clay beds, however, as Sir H. de la Beche remarks,
+can be followed over larger areas than the sand or sandstones.[14] 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. 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.
+
+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.
+
+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.
+
+ [1] Quart. Journ., vol. xvi, p. 376.
+
+ [2] Agassiz, Poissons Fossiles, vol. ii, tab. 28, 29.
+
+ [3] Agassiz, Poissons Fossiles, vol. iii, tab. C, Fig. 1.
+
+ [4] Bridgewater Treatise, p. 290.
+
+ [5] Geol. Soc. Transactions, Second Series, vol. i, p. 49.
+
+ [6] Conybeare and De la Beche, Geol. Trans., First Series, vol. v, p.
+ 559; and Buckland, Bridgewater Treatise, p. 203.
+
+ [7] See Darwin, Naturalist’s Voyage, p. 385. Murray.
+
+ [8] Bridgewater Treatise, p. 115.
+
+ [9] Geological Researches, p. 334.
+
+ [10] Buckland, Bridgewater Treatise, p. 307.
+
+ [11] A History of Fossil Insects, etc., 1846. London.
+
+ [12] Tableau des Vég. Foss., 1849, p. 105.
+
+ [13] Conybeare and Philips’s Outlines, etc., p. 166.
+
+ [14] Geological Researches, p. 337.
+
+
+
+
+CHAPTER XXI.
+TRIAS, OR NEW RED SANDSTONE GROUP.
+
+
+Beds of Passage between the Lias and Trias, Rhætic Beds. — Triassic
+Mammifer. — Triple Division of the Trias. — Keuper, or Upper Trias of
+England. — Reptiles of the Upper Trias. — Foot-prints in the Bunter
+formation in England. — Dolomitic Conglomerate of Bristol. — Origin of
+Red Sandstone and Rock-salt. — Precipitation of Salt from inland Lakes
+and Lagoons. — Trias of Germany. — Keuper. — St. Cassian and Hallstadt
+Beds. — Peculiarity of their Fauna. — Muschelkalk and its Fossils. —
+Trias of the United States. — Fossil Foot-prints of Birds and Reptiles
+in the Valley of the Connecticut. — Triassic Mammifer of North
+Carolina. — Triassic Coal-field of Richmond, Virginia. — Low Grade of
+early Mammals favourable to the Theory of Progressive Development.
+
+Beds of Passage between the Lias and Trias—Rhætic Beds.—We have
+mentioned in the last chapter (p. 356) 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 _Ammonites planorbis._ Below this zone, on the
+boundary line between the Lias and the strata of which we are about to
+treat, called “Trias,” 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.
+
+The principal member of this group has been called by Dr. Wright the
+_Avicula contorta_ bed,[1] 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 _ Avicula contorta_ is
+accompanied by _Pecten Valoniensis,_ as in Germany.
+
+The best known member of the group, a thin band or bone-breccia, is
+conspicuous among the black shales in the neighbourhood 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 _Acrodus, Hybodus, Gyrolepis,_
+and _Saurichthys._
+
+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.
+
+Among those common to the English bone-bed and the Muschelkalk of
+Germany are _Hybodus plicatilis_ (Fig. 386), _Saurychthys apicalis_
+(Fig. 387), _Gyrolepis tenuistriatus_ (Fig. 388), and _G. Albertii._
+Remains of saurians, _Plesiosaurus_ among others, have also been found
+in the bone-bed, and plates of an _Encrinus._ It may be questioned
+whether some of those fossils which have the most Triassic character
+may not have been derived from the destruction of older strata, since
+in bone-beds, in general, many of the organic remains are undoubtedly
+derivative.
+
+Fig. 389: Microlestes antiquus, molar tooth.
+_Triassic Mammifer._—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 _ Microlestes antiquus._ 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 _Microlestes_ 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.
+
+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 _Plagiaulax_ (Fig. 306), from the Purbeck
+strata. This would lead us to the conclusion that Microlestes was
+marsupial and plant-eating.
+
+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.
+
+The genera _Saurichthys, Hybodus,_ and _Gyrolepis_ are found in both
+these breccias, and one of the species, _ Saurichthys Mongeoti,_ is
+common to both bone-beds, as is also a remarkable reptile called
+_Nothosaurus mirabilis._ The saurian called _Belodon_ by H. von Meyer,
+of the Thecodont family, is another Triassic form, associated at
+Diegerloch with Microlestes.
+
+TRIAS OF ENGLAND.
+
+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
+“New Red Sandstone formation” was first given, to distinguish it from
+other shales and sandstones called the “Old Red,” often identical in
+mineral character, which lie immediately beneath the coal. The name of
+“Red Marl” has been incorrectly applied to the red clays of this
+formation, as before explained (p. 38), 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.
+
+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 “Keuper,” the “Muschelkalk,” and the
+“Bunter-sandstein.” 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.
+
+Upper Trias or Keuper.—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.
+
+This upper division of the Trias called the Keuper is of great
+thickness in the central counties of England, attaining, according to
+Mr. Hull’s estimate, no less than 3450 feet in Cheshire, and it covers
+a large extent of country between Lancashire and Devonshire.
+
+In Worcestershire and Warwickshire in sandstone belonging to the
+uppermost part of the Keuper the bivalve crustacean _Estheria minuta_
+occurs. The member of the English “New Red” 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 band of sandstone. Ichthyodorulites, or spines of _ Hybodus,_
+teeth of fishes, and footprints of reptiles were observed by the same
+geologists in these strata.
+
+Fig. 390: Estheria minuta.
+Fig. 391: Hyperodapedon Gordoni. Left Plate, Maxillary.
+In the Upper Trias or Keuper the remains of two saurians of the order
+Lacertilia have been found. The one called _ Rhynchosaurus_ occurred at
+Grinsell near Shrewsbury, and is characterised by having a small
+bird-like skull and jaws without teeth. The other _Hyperodapedon_ (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.
+
+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.
+
+Fig. 392: Tooth of Labyrinthodon.
+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 _Mastodonsaurus_ and _Phytosaurus_ by
+Jäger. It appeared that they were of the _Batrachian_ order, and of
+gigantic 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 _Ichthyosaurus._ 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 “Odontography,” 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.
+
+Fig. 393: Transverse section of upper part of tooth of Labyrinthodon
+Jaegeri.
+
+_Rock-salt._—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 “water-stones,” which are
+largely quarried for building. They are often ripple-marked, and are
+impressed with numerous footprints of reptiles.
+
+The basement beds of the Keuper rest with a slight unconformability
+upon an eroded surface of the “Bunter” next to be described.
+
+Fig. 394: Single footstep of Cheirotherium.
+
+Lower Trias or Bunter.—The lower division or English representative of
+the “Bunter” 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.[2] 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 _Cheirotherium_ 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 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.
+
+Fig. 395: Line of footsteps on slab of sandstone.
+
+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
+_Marsupialia_; 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 _Batrachians,_
+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.
+
+Dolomitic Conglomerate of Bristol.—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 (Fig. 85), 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
+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.
+
+Fig. 396: Tooth of Thecodontosaurus.
+Origin of Red Sandstone and Rock-salt.—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.
+
+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.
+
+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.
+
+Major Harris, in his “Highlands of Ethiopia,” describes 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. “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.” “If,” says Mr. Hugh
+Miller, “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.”
+
+The Runn of Cutch, as I have shown elsewhere,[3] 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.
+
+TRIAS OF GERMANY.
+
+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.
+
+NOMENCLATURE OF TRIAS.
+
+German French English Keuper Marnes irisées Saliferous and
+gypseous
+shales and sandstone. Muschelkalk Muschelkalk, on calcaire
+coquillier Wanting in England. Bunter-sandstein Grès
+bigarré Sandtone and quartzose conglomerate.
+
+Keuper.—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.[4] Remains of reptiles called _Nothosaurus_ and
+_Phytosaurus,_ have been found in it with Labyrinthodon; the detached
+teeth, also, of placoid fish and of Rays, and of the genera
+_Saurichthys_ and _Gyrolepis_ (Figs. 387, 388). 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 _Equisetites
+columnaris,_ are common to this group and the oolite.
+
+Fig. 397: Equisetites columnaris.
+_St. Cassian and Hallstadt Beds_ (see Map, Fig. 398).— 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 “St. Cassian beds,” 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. 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.
+
+Fig. 398: Map of Tyrol and Styria showing St. Cassian and Hallstadt
+Beds.
+
+Fig. 399: Scoliotoma. Fig. 400: Koninckia Leonhardi.
+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 _Scoliostoma,_ Fig. 399,
+and _Platystoma,_ Fig. 400, among the Gasteropoda; and _Koninckia,_
+Fig. 401, among the Brachiopoda.
+
+Fig. 401: Koninckia Leonhardi.
+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.
+
+GENERA OF FOSSIL MOLLUSCA IN THE ST. CASSIAN AND HALLSTADT BEDS.
+
+Common to Older Rocks Characteristic Triassic Genera Common to
+Newer Rocks Orthoceras
+Bactrites
+Macrocheilus
+Loxonema
+Holopella
+Murchisonia
+Porcellia
+Athyris
+Retzia
+Cyrtina
+Euomphalus  Ceratites
+Cochloceras
+Choristoceras
+Rhabdoceras
+Aulacoceras
+Scoliostoma [5]
+Naticella
+Platystoma
+Ptychostoma
+Euchrysalis
+Halobia
+Hornesia
+Amphiclina
+Koninckia
+Cassianella [6]
+Myophoria [6]  Ammonites
+Chemnitzia
+Cerithium
+Monodonta
+Opis
+Sphoera
+Cardita
+Myoconcha
+Hinnites
+Monotis
+Plicatula
+Pachyrisma
+Thecidium
+
+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.
+
+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.
+
+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.
+
+Muschelkalk.—The next member of the Trias in Germany, the
+_Muschelkalk,_ which underlies the _Keuper_ 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 the Ammonite,
+called _Ceratites_ by de Haan, in which the descending lobes (Fig. 402)
+terminate in a few small denticulations pointing inward. Among the
+bivalve crustacea, the _Estheria minuta,_ Bronn (see Fig. 390), is
+abundant, ranging through the Keuper, Muschelkalk, and
+Bunter-sandstein; and _Gervillia socialis_ (Fig. 403), having a similar
+range, is found in great numbers in the Muschelkalk of Germany, France,
+and Poland.
+
+Fig. 402: Ceratites nodosus. Fig. 403: Gervillia (Avicula) socialis.
+Fig. 404: Enerinus liliiformis. Fig. 405: Aspidura loricata.
+
+The abundance of the heads and stems of lily encrinites, _ Encrinus
+liliiformis_ (Fig. 404), (or _Encrinites moniliformis_), shows the slow
+manner in which some beds of this limestone have been formed in clear
+sea-water. The star-fish called _Aspidura loricata_ (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 _Placodus_ (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.
+
+Fig. 406: Palatal teeth of Placodus gigas.
+Fig. 407: Voltzia heterophylla.
+Bunter-sandstein.—The _Bunter-sandstein_ 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
+“bunter,” especially conifers of the extinct genus _Voltzia,_ 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 “Grès bigarré,” or Bunter,
+not one is common to the Keuper.
+
+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 of the Trias, the remains of no less than eighty distinct
+species are described and figured.
+
+TRIAS OF THE UNITED STATES.
+
+New Red Sandstone of the Valley of the Connecticut River.—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.
+
+Fig. 408: Foot-prints of a bird, Turner’s Falls, Valley of the
+Connecticut.
+
+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.[7]
+
+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 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’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.
+
+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.
+
+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 _Ischypterus,_ 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.
+
+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.
+
+Coal-field of Richmond, Virginia.—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.
+
+The plants consist chiefly of zamites, calamites, equiseta, and ferns,
+and, upon the whole, are considered by Professor Heer to have the
+nearest affinity to those of the European Keuper.
+
+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.
+
+Fig. 409: Triassic coal-shale, Richmond, Virginia.
+The fossil fish are Ganoids, some of them of the genus _ Catopterus,_
+others belonging to the liassic genus _ Tetragonolepis (Æchmodus),_ see
+Fig. 376. Two species of _ Entomostraca_ called _Estheria_ are in such
+profusion in some shaly beds as to divide them like the plates of mica
+in micaceous shales (see Fig. 409).
+
+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—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.
+
+Triassic Mammifer.—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
+_Dromatherium sylvestre,_ closely allied to _Spalacotherium._ Its
+nearest living analogue, says Professor Owen, “is found in Myrmecobius;
+for each ramus of the lower jaw contained ten small molars in a
+continuous series, one canine, and three conical incisors—the latter
+being divided by short intervals.”
+
+Low Grade of Early Mammals favourable to the Theory of Progressive
+Development.—There is every reason to believe that this fossil
+quadruped is at least as ancient as the Microlestes of the European
+Trias described in p. 368; 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° N., to that of North Carolina, 35°
+N.
+
+If the three localities in Europe where the most ancient mammalia have
+been found—Purbeck, Stonesfield, and Stuttgart—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 “the age of
+reptiles.” 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.
+
+ [1] Dr. Wright, on Lias and Bone Bed, Quart. Geol. Journ., 1860, vol.
+ xvi.
+
+ [2] Buckland, Proc. Geol. Soc., vol. ii, p. 439; and Murchison and
+ Strickland, Geol. Trans., Second Series., vol. v, p. 347.
+
+ [3] Principles of Geology, chap. xxvii.
+
+ [4] Monog. des Bunter-Sandsteins.
+
+ [5] Reaches its maximum in the Trias, but passes down to older rocks.
+
+ [6]
+Reach their maximum in the Trias, but pass up to newer rocks.
+
+ [7] Hitchcock, Mem. of Amer. Acad., New Series, vol. iii, p. 129,
+ 1848.
+
+
+PRIMARY OR PALÆOZOIC SERIES
+
+
+
+
+CHAPTER XXII.
+PERMIAN OR MAGNESIAN LIMESTONE GROUP.
+
+
+Line of Separation between Mesozoic and Palæozoic Rocks. — Distinctness
+of Triassic and Permian Fossils. — Term Permian. — Thickness of
+calcareous and sedimentary Rocks in North of England. — Upper, Middle,
+and Lower Permian. — Marine Shells and Corals of the English Magnesian
+Limestone. — Reptiles and Fish of Permian Marl-slate. — Foot-prints of
+Reptiles. — Angular Breccias in Lower Permian. — Permian Rocks of the
+Continent. — Zechstein and Rothliegendes of Thuringia. — Permian Flora.
+— Its generic Affinity to the Carboniferous.
+
+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.
+
+The term Permian has been proposed for this group by 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[1] 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.
+
+In illustration of this he has given us the following table:
+
+THICKNESS OF PERMIAN STRATA IN NORTH OF ENGLAND.
+
+  N.W. of England N.E. of England Feet Feet Upper Permian
+  (Sedimentary) 600 50–100 Middle Permian
+  (Calcareous) 10–30 600 Lower Permian
+  (Sedimentary) 3000 100–250[2]
+
+Upper Permian.—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’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.
+
+Middle Permian—Magnesian Limestone and Marl-slate.—This formation is
+seen upon the coast of Durham and Yorkshire, between the Wear and the
+Tees. Among its characteristic fossils are _Schizodus Schlotheimi_
+(Fig. 410) and _Mytilus septifer_ (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—for it is
+extremely variable in structure—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.
+
+Fig. 410: Schidozus Schlotheimi, Permian crystalline limestone. Fig.
+411: The hinge of Schizodus truncatus, Permian. Fig. 412: Mytilus
+septifer, Permian crystalline limestone.
+
+The magnesian limestone sometimes becomes very fossiliferous and
+includes in it delicate bryozoa, one of which, _Fenestella retiformis_
+(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.
+
+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 _Lingula Crednerii_
+(Fig. 415) is an example. There are 25 Gasteropods and only one
+cephalopod, _Nautilus Freieslebeni,_ which is also found in the German
+Zechstein.
+
+Fig. 413: Magnesian Limestone. Fig. 413: Magnesian Limestone, Humbleton
+Hill, near Sunderland.[3]
+
+Shells of the genera _Productus_ (Fig. 414) and _ Strophalosia_ (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 _Spirifera_ (Fig.
+416), _Lingula Crednerii_ (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
+_Lingula,_ are specifically the same as fossils of the carboniferous
+rocks. _Avicula, Arca,_ and _Schizodus_ (Fig. 410), and other
+lamellibranchiate bivalves, are abundant, but spiral univalves are very
+rare.
+
+Fig. 414: Productus horridus. Fig. 415: Lingula Crednerii. Fig. 416:
+Spirifera alata.
+
+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 it is thirty feet thick,
+this slate has yielded many fine specimens of fossil fish—of the genera
+_Palæoniscus_ ten species, _Pygopterus_ two species, _Coelacanthus_ two
+species, and _Platysomus_ 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.
+
+Fig. 417: Restored outline of a fish of the genus Palæoniscus. Fig.
+418: Shark, Heterocercal. Fig. 419: Shad. (Clupea. Herring tribe.)
+Homocereal.
+
+The _Palæoniscus_ above mentioned belongs to that division of fishes
+which M. Agassiz has called “Heterocercal,” 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 “Homocercal” 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’s
+history, whereas in the secondary strata, or those newer than the
+Permian, the homocercal tail predominates.
+
+A full description has been given by Sir Philip Egerton of the species
+of fish characteristic of the marl-slate, in Professor King’s monograph
+before referred to, where figures of the 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.
+
+Fig. 420: Palæoniscus comptus. Fig. 421: Palæoniscus elegans. Fig. 422:
+Palæoniscus glaphyrus. Fig. 423: Cœlacanthus granulatus. Fig. 424:
+Pygopterus mandibularis. Fig. 425: Acrolepis Sedgwickii.
+
+We are indebted to Messrs. Hancock and Howse for the discovery in this
+marl-slate at Midderidge, Durham, of two species of _ Protosaurus,_ a
+genus of reptiles, one representative of which, _P. Speneri,_ 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’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.
+
+Lower Permian.—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 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’s table p. 386, 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.
+
+_Angular Breccias in Lower Permian._—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.
+
+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.
+
+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.[4]
+
+Permian Rocks of the Continent.—Germany is the classic ground of the
+Magnesian Limestone now called Permian. 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 _died out_ 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.
+
+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.
+
+Fig. 426: Walchia piniformis.
+
+Permian Flora.—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 _ Alethopteris, Neuropteris,
+Walchia,_ and _Ullmania,_ are common to the two groups. The Permian
+flora on the Continent appears, from the researches of MM. Murchison
+and de Verneuil in Russia, and of MM. Geinitz and von Gutbier in
+Saxony, to be, with a few exceptions, distinct from that of the coal.
+
+Fig. 27: Cardiocarpon Ottonis.
+
+In the Permian rocks of Saxony no less than 60 species of fossil plants
+have been met with. Two or three of these, as _Calamites gigas,
+Sphenopteris erosa,_ and _S. lobata,_ are also met with in the
+government of Perm in Russia. Seven others, and among them _Neuropteris
+Loshii, Pecopteris arborescens,_ and _P. similis,_ and several species
+of _Walchia_ (see Fig. 426), a genus of Conifers, called _Lycopodites_
+by some authors, are said by Geinitz to be common to the coal-measures.
+
+Fig. 428: Noeggerathia cuneifolia. Fig. 428: Noeggerathia cuneifolia.
+Brongniart.[5]
+
+Among the genera also enumerated by Colonel Gutbier are the fruit
+called _Cardiocarpon_ (see Fig. 427), _ Asterophyllites,_ and
+Annularia, so characteristic of the Carboniferous period; also
+_Lepidodendron,_ which is common to the Permian of Saxony, Thuringia,
+and Russia, although not abundant. _Neoggerathia_ (see Fig. 428), the
+leaves of which have parallel veins without a midrib, and to which
+various generic synonyms, such as _Cordaites, Flabellaria,_ and _
+Poacites,_ 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 _Sigillaria_ and _ Stigmaria,_ so marked a feature in
+the Carboniferous period, are as yet wanting in the true Permian.
+
+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 _Psaronius._ 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.
+
+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.
+
+ [1] Trans. Geol. Soc. Lond., Second Series, vol. iii, p. 37.
+
+ [2] Edward Hull, Ternary Classification, Quart. Journ. Science, No.
+ xxiii, 1869.
+
+ [3] King’s Monograph, pl. 2.
+
+ [4] Ramsay, Quart. Geol. Journ., 1855; and Lyell, Principles of
+ Geology, vol. i, p. 223, 10th edit.
+
+ [5] Murchison’s Russia, vol. ii, pl. A, fig. 3.
+
+
+
+
+CHAPTER XXIII.
+THE COAL OR CARBONIFEROUS GROUP.
+
+
+Principal Subdivisions of the Carboniferous Group. — Different
+Thickness of the sedimentary and calcareous Members in Scotland and the
+South of England. — Coal-measures. — Terrestrial Nature of the Growth
+of Coal. — Erect fossil Trees. — Uniting of many Coal-seams into one
+thick Bed. — Purity of the Coal explained. — Conversion of Coal into
+Anthracite. — Origin of Clay-ironstone. — Marine and brackish-water
+Strata in Coal. — Fossil Insects. — Batrachian Reptiles. —
+Labyrinthodont Foot-prints in Coal-measures. — Nova Scotia
+Coal-measures with successive Growths of erect fossil Trees. —
+Similarity of American and European Coal. — Air-breathers of the
+American Coal. — Changes of Condition of Land and Sea indicated by the
+Carboniferous Strata of Nova Scotia.
+
+Principal Subdivisions of the Carboniferous Group.—The next group which
+we meet with in the descending order is the Carboniferous, commonly
+called “The Coal,” 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.
+
+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.
+
+In the south-western part of our island, in Somersetshire and South
+Wales, the three divisions usually spoken of are:
+
+Coal-measures: Strata of shale, sandstone, and grit, from 600 to 12,000
+feet thick, with occasional seams of coal.
+
+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.
+
+Mountain or Carboniferous Limestone: A calcareous rock containing
+marine shells, corals, and encrinites; devoid of coal; thickness
+variable, sometimes more than 1500 feet.
+
+If the reader will refer to the section in Fig. 85, 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).
+
+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
+“Farewell Rock,” 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.
+
+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.
+
+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.
+
+Leicestershire and Warwickshire 2,600 feet North
+Staffordshire 9,000 feet South Lancashire 12,130 feet North
+Lancashire 18,700 feet
+
+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’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.
+
+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.
+
+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 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.[1] 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’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.
+
+COAL-MEASURES.
+
+I shall now treat more particularly of the productive coal-measures,
+and their mode of origin and organic remains.
+
+Coal formed on Land.—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.
+
+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
+_underclay._ 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 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 _floor_ on which the coal rests; and some of them have
+a slight admixture of carbonaceous matter, while others are quite
+blackened by it.
+
+All of them, as Sir William Logan pointed out, are characterised by
+inclosing a peculiar species of fossil vegetable called _ Stigmaria,_
+to the exclusion of other plants. It was also observed that, while in
+the overlying shales, or “roof” of the coal, ferns and trunks of trees
+abound without any _ Stigmariæ,_ 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 _Stigmaria_ 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
+_Sigillaria_ 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.
+
+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 _Sigillariæ, Lepidodendra,_ and _Stigmariæ,_
+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.[2]
+
+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
+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 _Lepidostrobus variabilis_ 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 Fig. 457 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 15½ feet in circumference at the base, 7½ 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.
+
+In a colliery near Newcastle a great number of _ Sigillariæ_ 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.
+
+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 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 _Lepidodendra, Calamites,_ and other trees.
+
+Fig. 429: Ground plan of fossil forest, Parkfield Colliery, near
+Wolverhampton, showing the position of 73 trees in a quarter of an ace.
+Blending of Coal-seams.—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’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 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—a
+theory which the presence of the Stigmaria _in situ_ 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.
+
+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.
+
+Fig. 430: Uniting of distinct coal-seams.
+
+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, _f g,_ 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.
+
+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 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.
+
+Cause of the Purity of Coal.—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 _Sigillariæ_ 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 “Sunk Country,” 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 “cypress swamps” 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
+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 “cypress swamps” a bed of clay is found, with roots of the tall
+cypress (_Taxodium distichum_), just as the under-clays of the coal are
+filled with _Stigmaria._
+
+Conversion of Coal into Anthracite.—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.
+
+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.
+
+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 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.
+
+Clay-ironstone.—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.[3]
+
+Intercalated Marine Beds in Coal.—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 at still more distant points. The
+characteristic fossils are a small bivalve, having the form of a
+_Cyclas_ or _Cyrena,_ also a small entomostracan, _Cythere inflata_
+(Fig. 432), and the microscopic shell of an annelid of an extinct genus
+called _ Microconchus_ (Fig. 431), allied to _Spirorbis._ 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 _ Goniatites Listeri_ (Fig. 433),
+_Orthoceras,_ and _ Aviculopecten papyraceus,_ Goldf. (Fig. 434).
+
+Fig. 431: Microconchus (Spirorbis) carbonarius. Fig. 432: Cythere
+(Leperditia) inflata. Fig. 433: Goniatites Listeri. Fig. 434:
+Aviculopecten papyraceus.
+Insects in European Coal.—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 _Curculionidæ,_ a
+neuropterous insect of the genus _Corydalis,_ and another related to
+the _Phasmidæ,_ have been found.
+
+From the coal of Wetting, in Westphalia, several specimens of the
+cockroach or _Blatta_ family, and the wing of a cricket (_Acridites_)
+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.[4] Among them are several _
+Blattinæ,_ three species of _Neuroptera,_ one beetle of the _Scarabæus_
+family, a grasshopper or locust, _ Gryllacris_ (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.
+
+Fig. 435: Wing of a Grasshopper. Gryllacris lithanthraca.
+
+Fig. 436: Archegosaurus minor. Fossil reptile from the coal-measures,
+Saarbrück.
+Batrachian Reptiles in Coal.—No vertebrated animals more highly
+organised than fish were known in rocks of higher antiquity than the
+Permian until the year 1844, when the _Apateon pedestris,_ 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 _Archegosaurus._ 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, _Archegosaurus Decheni,_ must 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
+_Labyrinthodon_ before mentioned (p. 371), and the remains of the
+extremities leave no doubt they were quadrupeds, “provided,” says Von
+Meyer, “with hands and feet terminating in distinct toes; but these
+limbs were weak, serving only for swimming or creeping.” The same
+anatomist has pointed out certain points of analogy between their bones
+and those of the _Proteus anguinus_; and Professor Owen has observed
+that they make an approach to the _Proteus_ 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).
+
+Fig. 437: Imbricated covering of skin of Archegosaurus medius.
+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.
+
+_Labyrinthodont footprints in coal-measures._—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 (_a, a′_) of various sizes. The origin of such cracks
+in 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 _b,
+c,_ 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.
+
+Fig. 438: Slab of sandstone from the coal-measures of Pennsylvania,
+with foot-prints of air-breathing reptile and casts of cracks.
+
+We may assume that the reptile which left these prints 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.
+
+Nova Scotia Coal-measures.—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 “South
+Joggins,” which I first examined in 1842, and afterwards with Dr.
+Dawson in 1845, have lately been admirably described by the
+last-mentioned geologist[5] 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.
+
+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.
+
+In the section (Fig. 439), which I examined in 1842, the beds from _c_
+to _i_ are seen all dipping the same way, their average inclination
+being at an angle of 24° S.S.W. The vertical height of the cliffs is
+from 150 to 200 feet; and between _d_ and _g_—in which space I observed
+seventeen trees in an upright position, or, to speak more correctly, at
+right angles to the planes of stratification—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 yards from the base of
+the cliff. The thickness of the beds alluded to, between _d_ and _g,_
+is about 2500 feet, the erect trees consisting chiefly of large
+_Sigillariæ,_ 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 _ Calamites,_ on sandstone. The
+erect trees, therefore, appeared in general to have grown on beds of
+vegetable matter. In the underclays _Stigmaria_ abounds.
+
+Fig. 439: Section of the cliffs of the South Joggins, near Minudie,
+Nova Scotia.
+
+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.
+
+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 _e_ to _f_ 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.
+
+Fig. 440: Erect fossil trees, Coal-measures, Nova Scotia.
+In the sandstone which filled their interiors, I frequently observed
+fern-leaves, and sometimes fragments of _Stigmaria,_ 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, _a,_ Fig. 440, represented in the bed _e_ 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 (_b,_ Fig. 440) one foot
+thick. On this coal again stood two large trees (_c_ and _d_), while at
+a greater height the trees _f_ and _g_ rest upon a thin seam of coal
+(_e_), and above them is an underclay, supporting the four-foot coal.
+
+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—the cast of the
+interior of a tree—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 _Calamites_; the _Calamites_ having
+begun to grow after the older _Sigillariæ_ had been partially buried.
+
+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 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
+(_Betula papyracea_) 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 _Coniferæ_ of the Coal period grew in the same
+swamps as _Sigillariæ,_ just as now the deciduous Cypress (_Taxodium
+distichum_) abounds in the marshes of Louisiana even to the edge of the
+sea.
+
+When the carboniferous forests sank below high-water mark, a species of
+_Spirorbis_ or _Serpula_ (Fig. 431), attached itself to the outside of
+the stumps and stems of the erect trees, adhering occasionally even to
+the interior of the bark—another proof that the process of envelopment
+was very gradual. These hollow upright trees, covered with innumerable
+marine annelids, reminded me of a “cane-brake,” as it is commonly
+called, consisting of tall reeds, _Arundinaria macrosperma,_ 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 _ Sigillariæ,_ hollow as
+they were but supported by strong roots, may have resisted an incursion
+of the sea.
+
+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.
+
+_Structure of Coal._—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 _ Cordaites_ (_Noeggerathia,_ etc., for
+genus, see Fig. 428), 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 _Asterophyllites_ (see Fig. 461), 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.
+
+Air-breathers of the Coal.—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 2½ feet in
+length (_Dendrerpeton Acadianum,_ Owen), were scattered through this
+stony matrix. The shell, also, of a _ Pupa_ (see Fig. 442), the first
+land-shell ever met with in the coal or in beds older than the
+tertiary, was observed in the same stony mass. Dr. Wyman of Boston
+pronounced the reptile to be allied in structure to _Menobranchus_ and
+_Menopoma,_ 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 _Archegosaurus_ and _Labyrinthodon._[6] 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.
+
+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, Fig. 447), 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, _D. Oweni,_ 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, _Hylonomus Lyelli,_ 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.[7]
+
+Fig. 441: Xylobius Sigillariæ. Coal, Nova Scotia.
+
+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 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.
+
+Fig. 442: Pupa vetusta.
+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.
+
+Fig. 443: Zonites (Conulus) priseus.
+
+The surface striæ of _Pupa vetusta,_ when magnified 50 diameters,
+present exactly the same appearance as a portion corresponding in size
+of the common English _Pupa juniperi,_ and the internal hexagonal
+cells, magnified 500 diameters, show the internal structure of the
+fossil and recent Pupa to be identical. In 1866[8] 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.
+
+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.
+
+Except some obscure traces of an insect found by Dr. 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—larger than any known living
+insect of the Neuropterous family.
+
+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—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.
+
+Carboniferous Rain-prints.—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 (_a, b,_ Fig. 444), such as
+are often seen between high and low water mark on the recent mud of the
+Bay of Fundy.
+
+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
+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.
+
+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.
+
+Folding and Denudation of the Beds indicated by the Nova Scotia
+Coal-strata.—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 p. 407).
+
+Fig. 446: Cone and branch of Lepidodendron corrugatum.
+Though no regular seams of coal were formed, the characteristic
+imbedded coal-plants are of the genera _Cyclopteris_ and _
+Alethopteris,_ agreeing with species occurring at much higher levels,
+and distinct from those of the antecedent Devonian group. The
+_Lepidodendron corrugatum_ (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 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.
+
+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.
+
+Fig. 447: Diagram showing the curvature and supposed denudation of the
+Carboniferous strata in Nova Scotia.
+
+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 (_h_ and _i,_
+Fig. 439) are found fresh-water bivalves or mussels allied to Anodon,
+though not identical with that or any living genus, and called
+_Naiadites carbonarius_ 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.
+
+In order to interpret the great coast section exposed to view on the
+shores of the Bay of Fundy, the student must, 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.
+
+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° 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° to one of more than
+40°, 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.
+
+ [1] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 327.
+
+ [2] Quart. Geol. Journ., vol. v, Mem., p. 17.
+
+ [3] Memoirs of the Geol. Survey, pp. 51, 255, etc.
+
+ [4] Dunker and V. Meyer, Palæont., vol. iv, p. 17.
+
+ [5] Acadian Geology, 2nd edit., 1868.
+
+ [6] Quart. Geol. Journ., vol. ix, p. 58.
+
+ [7] Dawson, Air-Breathers of the Coal in Nova Scotia, Montreal, 1863.
+
+ [8] Dawson, Acadian Geology, 1868, p. 385.
+
+
+
+
+CHAPTER XXIV.
+FLORA AND FAUNA OF THE CARBONIFEROUS PERIOD.
+
+
+Vegetation of the Coal Period. — Ferns, Lycopodiaceæ, Equisetaceæ,
+Sigillariæ, Stigmariæ, Coniferæ. — Angiosperms. — Climate of the Coal
+Period. — Mountain Limestone. — Marine Fauna of the Carboniferous
+Period. — Corals. — Bryozoa, Crinoidea. — Mollusca. — Great Number of
+fossil Fish. — Foraminifera.
+
+Vegetation of the Coal Period.—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—a fact which adds greatly to the geological interest of this
+flora.
+
+The coal-period was called by Adolphe Brongniart the age of
+Acrogens,[1] 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’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.
+
+Ferns.—We are struck at the first glance with the similarity of the
+ferns to those now living. In the fossil genus _Pecopteris,_ 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.
+
+Fig. 448: Pecopteris elliptica. Fig. 449: Caulopteris primæva. Fig.
+448: _Pecopteris elliptica_, Bunbury.[2] Frostburg.
+Fig. 449: _Caulopteris primæva_, Lindley.
+
+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 _Caulopteris_
+(see Fig. 449) by Lindley, and the _Psaronius_ of the upper or newest
+coal-measures, before alluded to (p. 393). All the recent tree-ferns
+belong to one tribe (_Polypodiaceæ_), and to a small number only of
+genera in that tribe, in which the surface of the trunk is marked with
+scars, or cicatrices, left after the fall of the fronds. These scars
+resemble those of _Caulopteris._
+
+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.
+
+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.
+
+Lycopodiaceæ—_Lepidodendron._—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 Fig. 454). They belong to the
+_Lycopodiaceæ,_ bearing sporangia and spores similar to those of the
+living representatives of this family (Fig. 457); 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 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.
+
+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.
+
+Fig. 456: a. Lycopodium densum. Living species, New Zealand; b. Branch;
+c. Part of same, magnified.
+The Figs. 453–455 represent a fossil _Lepidodendron,_ 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.
+
+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 _Lycopodium densum_ from New Zealand (see Fig.
+456), which attains a height of three feet.
+
+In the Carboniferous strata of Coalbrook Dale, and in many other
+coal-fields, elongated cylindrical bodies, called fossil cones, named
+_Lepidostrobus_ 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 _ Lepidostrobus_ is the fruit of _Lepidodendron_
+has been confirmed, for these _strobili_ or fruits have been found
+terminating the tip of a branch of a well-characterised _
+Lepidodendron_ in Coalbrook Dale and elsewhere.
+
+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.
+
+Fig. 458: Calamites Sucowii, common throughout Europe. Fig. 459: Stem
+of Fig. 458, as retored by Dr. Dawson.
+
+Equisetaceæ.—To this family belong two fossil genera of the coal,
+_Equisetites_ and _Calamites._ 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 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).
+
+Fig. 460: Radical termination of a Calamite. Fig. 461: Asterophyllites
+foliosus, Coal-measures, Newcastle.
+
+Botanists are not yet agreed whether the _Asterophyllites,_ 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.
+
+Fig. 462: Annularia sphenophylloides.Fig. 463: Sphenophyllum erosum.
+Figs. 462 and 463 represent leaves of _Annularia_ and _ Sphenophyllum,_
+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.
+
+Sigillaria.—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 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.
+
+Fig. 464: Sigillaria lævigata.
+Dr. Hooker inclined to the belief that the _ Sigillariæ_ 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.
+
+_Stigmaria._—This fossil, the importance of which has already been
+pointed out in p. 398, was originally conjectured to be an aquatic
+plant. It is now ascertained to be the root of _Sigillaria._ 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 _Stigmariæ_ 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.
+
+Fig. 465: Stigmaria attached to a trunk of Sigillaria.
+
+In the sea-cliffs of the South Joggins in Nova Scotia, I examined
+several erect _Sigillariæ,_ in company with Dr. Dawson, and we found
+that from the lower extremities of the trunk they sent out _Stigmariæ_
+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.
+
+Fig. 466: Stigmaria ficoides. Fig. 467: Surface of another individual
+of same species, showing form of tubercles.
+
+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 _Sigillaria,_ the structure of the
+vessels being, like it, scalariform.
+
+Coniferæ.—The coniferous trees of this period are referred to five
+genera; 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
+_Coniferæ_ in having large piths; for Professor Williamson has
+demonstrated the fossil of the coal-measures called _Sternbergia_ 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 _Sternbergia_ (_d, d,_ Fig.
+468) was given. In the above specimen the structure of the wood (_b,_
+Figs. 468 and 469) is coniferous, and the fossil is referable to
+Endlicher’s fossil genus _ Dadoxylon._
+
+Fig. 468: Fragment of coniferous wood. Fig. 468: Fragment of coniferous
+wood, _Dadoxylon_, of Endlicher, fractured longitudinally; from
+Coalbrook Dale.
+W.C. Williamson[3]
+
+Fig. 469: Magnified portion of Fig. 468; transverse section.
+
+The fossil named _Trigonocarpon_ (Figs. 470 and 471), formerly supposed
+to be the fruit of a palm, may now, according to Dr. Hooker, be
+referred, like the _Sternbergia,_ to the _ Coniferæ._ Its geological
+importance is great, for so abundant is it in the coal-measures, that
+in certain localities the fruit of 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 _
+Trigonocarpon_ 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 _ Salisburia,_ one of the
+Yew tribe, or Taxoid conifers.
+
+Fig. 470: Trigonocarpum ovatum.Fig. 471: Trigonocarpum olivæforme.
+Fig. 472: Antholithes.
+Angiosperms.—The curious fossils called _ Antholithes_ 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
+_Bromeliaceæ,_ 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 _
+Orobanche_ (broom-rape), which grew, not on the soil, but parasitically
+on the trees of the coal forests.
+
+In the coal-measures of Granton, near Edinburgh, a remarkable fossil
+(Fig. 473) was found and described in 1840,[4] by Dr. Robert Paterson.
+It was compressed between layers of bituminous shale, and consists of a
+stem bearing a cylindrical spike, _a,_ 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 _b,_ 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 _ Aroidiæ,_ and 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.
+
+Fig. 473: Pothocites Grantonii.
+Climate of the Coal Period.—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.
+
+MARINE FAUNA OF THE CARBONIFEROUS PERIOD.
+
+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 with marine
+remains—the greater part, indeed, of the rock being made up bodily of
+crinoids, corals, and bryozoa with interspersed mollusca.
+
+Corals.—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 _Palæozoic,_
+and a modern or _Neozoic_ 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.
+
+Fig. 474: Palæozoic type of lamelliferous cup-shaped Coral.
+
+Vertical section of _Campophyllum flexuosum,_ (_Cyathophyllum,_
+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 _ tubulæ,_ divide the interior into chambers.
+
+Arrangement of the _lamellæ_ in _Polycoelia profunda,_ 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.
+
+_Stauria astræiformis,_ 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.
+
+Fig. 475: Neozoic type of lamelliferous cup-shaped Coral.
+_Parasmilia centralis,_ 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, _ a._
+
+_Cyathina Bowerbankii,_ 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 _pali._
+
+_Fungia patellaris,_ 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.
+
+It will be seen that the more ancient corals have what is called a
+quadripartite arrangement of the chief plates or _ lamellæ_—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, _
+a,_ and 475, _a,_ or aggregate clusters of corallites, as in 474, _c._
+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 _ Holocystis elegans_ (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.
+
+Fig. 476: Lithostrotion basaltiforme. Fig. 477: Lonsdaleia floriformis.
+
+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 _Zaphrentis, Amplexus,
+Cyathophyllum, Clisiophyllum, Syringopora,_ and _Michelinia,_[5] form a
+group of rugose corals widely different from any that followed them.
+
+Bryozoa and Crinoidea.—Of the _Bryozoa,_ the prevailing forms are
+_Fenestella, Hemitrypa,_ and _ Polypora,_ and these often form
+considerable beds. Their net-like fronds are easily recognised.
+_Crinoidea_ are also numerous in the Mountain Limestone (see Figs. 478,
+479), two genera, _Pentremites_ and _Codonaster,_ being peculiar to
+this formation in Europe and North America.
+
+Fig. 478: Cyathocrinus planus. Fig. 479: Cyathocrinus caryocrinoides.
+
+Fig. 480: Palæchinus gigas.
+In the greater part of them, the cup or pelvis, Figure 479, _ b,_ is
+greatly developed in size in proportion to the arms, although this is
+not the case in Fig. 478. The genera _ Poteriocrinus, Cyathocrinus,
+Pentremites, Actinocrinus,_ and _ Platycrinus,_ 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 _Palæchinus_ (Fig. 480), is the analogue of
+the modern _Echinus,_ but has four, five, or six rows of plates in the
+interambulacral region or area, whereas the modern genera have only
+two. The other, _Archæocidaris,_ represents, in like manner, the
+_Cidaris_ of the present seas.
+
+Mollusca.—The British Carboniferous mollusca enumerated by Mr.
+Etheridge[6] comprise 653 species referable to 86 genera, occurring
+chiefly in the Mountain Limestone. Of 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 _
+Productus,_ such as _P. giganteus, p. hemisphericus, P.
+semireticulatus_ (Fig. 481), and _P. scabriculus._ Large plaited
+spirifers, as _Spirifera striata, S. rotundata,_ and _S. trigonalis_
+(Fig. 482), also abound; and smooth species, such as _Spirifera glabra_
+(Fig. 483), with its numerous varieties.
+
+Fig. 481: Productus semireticulatus. Fig. 482: Spirifera trigonalis.
+
+Fig. 483: Spirifera glabra.
+Fig. 484: Terebratula hastata. Fig. 485: Aviculopecten sublobatus. Fig.
+486: Pleurotomaria carinata.
+
+Among the brachiopoda, _Terebratula hastata_ (Fig. 484) deserves
+mention, not only for its wide range, but because it often retains the
+pattern of the original coloured stripes which ornamented the living
+shell. These coloured bands are also preserved in several
+lamellibranchiate bivalves, as in _ Aviculopecten_ (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 _ Pleurotomaria_ (Fig. 486), which displays wavy blotches,
+resembling the colouring in many recent trochidæ.
+
+Fig. 487: Euomphalus pentagulatus.
+
+Some few of the carboniferous mollusca, such as Avicula, _ Nucula_
+(sub-genus _Ctenodonta_), _Solemya,_ and _ Lithodomus,_ belong no doubt
+to existing genera; but the majority, though often referred to as
+living types, such as _ Isocardia, Turritella,_ and _Buccinum,_ belong
+really to forms which appear to have become extinct at the close of the
+Palæozoic epoch. _Euomphalus_ is a characteristic univalve shell of
+this period. In the interior it is divided into chambers (Fig. 487,
+_d_), 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
+_Turritella communis_ partitions off in like manner as it advances in
+age a part of its spire, forming a shelly septum.
+
+More than twenty species of the genus _Bellerophon_ (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,
+_Carinaria_; but by some few it is thought to be a simple form of
+Cephalopod.
+
+Fig. 488: Bellerophon costatus.
+Fig. 489: Portion of Orthoxeras laterale. Fig. 490: Goniatites
+crenistra.
+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
+_Orthoceras,_ a siphuncled and chambered shell, like a Nautilus
+uncoiled and straightened (Fig. 489). Some species of this genus are
+several feet long. The _Goniatite_ is another genus, nearly allied to
+the _Ammonite,_ 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.
+
+Fossil Fish.—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 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
+“bone-bed,” 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 _Cladodus_ afford an
+illustration; but the majority, as in _Psammodus_ and _ Cochliodus,_
+are, like the teeth of the Cestracion of Port Jackson (see Fig. 261),
+massive palatal teeth fitted for grinding. (See Figs. 491, 492.)
+
+Fig. 491: Psammodus porosus.
+Fig. 492: Cochliodus controtus.
+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 _Oracanthus, Ctenocanthus,_ and _ Onchus_ are often of a very large
+size. Ganoid fish, such as _ Holoptychius,_ also occur; but these are
+far less numerous. The great _Megalichthys Hibberti_ appears to range
+from the Upper Coal-measures to the lowest Carboniferous strata.
+
+Foraminifera.—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 _Textularia, Nodosaria,
+Endothyra,_ and _Fusulina_ (Fig. 493), have been 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.
+
+Fig. 493: Fusulina cylindrica.
+
+ [1] For botanical nomenclature see p. 304.
+
+ [2] Sir C. Bunbury, Quart. Geol. Journ., vol. ii, 1845.
+
+ [3] Manchester Phil. Mem., vol. ix, 1851.
+
+ [4] Trans. of Bot. Soc. of Edinburgh, vol. i, 1844.
+
+ [5] For figures of these corals, see Palæontographical Society’s
+ Monographs, 1852.
+
+ [6] Quart. Geol. Journ., vol. xxiii, p. 674, 1867.
+
+
+
+
+CHAPTER XXV.
+DEVONIAN OR OLD RED SANDSTONE GROUP.
+
+
+Classification of the Old Red Sandstone in Scotland and in Devonshire.
+— Upper Old Red Sandstone in Scotland, with Fish and Plants. — Middle
+Old Red Sandstone. — Classification of the Ichthyolites of the Old Red,
+and their Relation to Living Types. — Lower Old Red Sandstone, with
+Cephalaspis and Pterygotus. — Marine or Devonian Type of Old Red
+Sandstone. — Table of Devonian Series. — Upper Devonian Rocks and
+Fossils. — Middle. — Lower. — Eifel Limestone of Germany. — Devonian of
+Russia. — Devonian Strata of the United States and Canada. — Devonian
+Plants and Insects of Canada.
+
+Classification of the two Types of Old Red Sandstone.—We have seen that
+the Carboniferous strata are surmounted by the Permian and Trias, both
+originally included in England under the name “New Red Sandstone,” from
+the prevailing red colour of the strata. Under the coal came other red
+sandstones and shales which were distinguished by the title of “Old Red
+Sandstone.” Afterwards the name of “Devonian” 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.
+
+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 _ Anodonta,_ 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 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.
+
+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.
+
+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.
+
+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.
+
+Upper Old Red Sandstone.—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 _ Holoptychius, Pamphractus,
+Glyptopomus,_ 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 Old Red Sandstone
+and by one only in the Carboniferous group), and _Glytolepis_ and
+_Asterolepis,_ both exclusively confined to the “Old Red.” In the same
+Irish sandstone at Kiltorkan has been found an _Anodonta_ or
+fresh-water mussel, the only shell hitherto discovered in the Old Red
+Sandstone of the British Isles (see Fig. 494).
+
+Fig. 494: Anodonta Jukesii.
+Fig. 495: Bifurcating branch of Lepidendron Griffithsii.
+Fig. 496: Palæopteris Hibernia.
+In the same formation are found the fern (Fig. 496) and the _
+Lepidodendron_ (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
+“Carboniferous slate,” 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.
+
+It is a remarkable result of the recent examination of the fossil flora
+of Bear Island, latitude 74° 30′ 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 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.
+
+Fig. 497: Scale of Holoptychius nobilissimus.
+
+Outliers of the Upper “Old Red” occur unconformably on older members of
+the group, and the formation represented at Whiteness, near Arbroath,
+_a,_ Fig. 55, 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
+_Holoptychius nobilissimus_ have been found scattered through these
+beds, No. 2, in Strathmore. Another nearly allied _Holoptychius_ 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.[1] The number of fish obtained from the
+British Upper Old Red Sandstone amounts to fifteen species referred to
+eleven genera.
+
+Fig. 498: Holoptychius, as restored by Professor Huxley.
+
+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. They contain Calamites and other plants
+which agree generically with Carboniferous forms.
+
+Middle Old Red Sandstone.—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
+_Pteraspis_ 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’s previous suspicion that the
+rocks in which it occurs belong to the Lower “Old Red,” or agree in age
+with the Arbroath paving-stone.[2]
+
+_Fossil Fish of the Middle Old Red Sandstone._—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 _ Onchus, Odontacanthus,_ and _Ctenodus,_ a
+supposed cestraciont, and some others, have been established.
+
+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 _ Crossopterygidæ_,[3] 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 _a,_ 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 _ Osteolepis_ (Fig. 500), one of the
+common fishes of the Old Red Sandstone, many points of analogy with
+_Polypterus._ 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
+_Osteolepis,_ 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.
+
+Fig. 499: Polypterus. Living in the Nile and other rivers.
+
+Fig. 500: Restoration of Osteolepis.
+
+Among the “fringe-finned” Ganoids we find some with rhomboidal scales,
+such as _Osteolepis,_ Fig. 500; others with cycloidal scales, as
+_Holoptychius,_ before mentioned (see Fig. 498). In the genera
+_Dipterus_ and _Diplopterus,_ as Hugh Miller pointed out, and in
+several other of the fringe-finned genera, as in _Gyroptychius_ and
+_Glyptolepis,_ the two dorsals are placed far backward, or directly
+over the ventral and anal fins. The _Asterolepis_ was a ganoid fish of
+gigantic dimensions. _A. Asmusii,_ 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 _Asterolepis_ occurs also in the Devonian
+rocks of North America.
+
+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, _Lepidosteus,_ or the
+_Amia,_ genera now found in North American rivers, and one of them,
+_Lepidosteus,_ extending as far south as Guatemala, the Crossopterygii,
+or fringe-finned Ichthyolites, of the Old Red are closely related to
+the African _Polypterus,_ 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 _Polypterus_ 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.
+
+Fig. 501: Pterichthys. Upper side, showing mouth.
+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.
+
+Among the anomalous forms of Old Red fishes not referable to Huxley’s
+Crossopterygii is the _Pterichthys,_ 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.
+
+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 _Osteolepis_ and _ Pterichthys,_ already
+mentioned, are _Glyptolepis, Diplacanthus, Dendrodus, Coccosteus,
+Cheirancanthus,_ and _ Acanthoides._
+
+Fig. 502: Cephalapsis Lyellii.
+
+Lower Old Red Sandstone.—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 _ Cephalaspis,_ or
+“buckler-headed,” from the extraordinary shield which covers the head
+(see Fig. 502), and which has often been mistaken for that of a
+trilobite, such as _ Asaphus._ A species of _Pteraspis,_ 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.[4]
+
+Fig. 503: Pteygotus anglicus.
+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
+“Seraphim,” from the 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 “Poissons Fossiles du Vieux Grès Rouge.”
+
+Fig. 504: Pterygotus anglicus. Ventral aspect.
+Carapace, showing the large sessile eyes at the anterior angles.
+
+The _metastoma_ or post-oral plate (serving the office of a lower lip).
+
+Chelate appendages (antennules).
+
+First pair of simple palpi (antennæ).
+
+Second pair of simple palpi (mandibles).
+
+Third pair of simple palpi (first maxillæ).
+
+Pair of swimming feet with their broad basal joints, whose serrated
+edges serve the office of maxillæ.
+
+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.)
+
+A restoration in correct proportion to the size of the fragments of _P.
+anglicus_ (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.
+
+The largest crustaceans living at the present day are the _ Inachus
+Kaempferi,_ 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
+_Limulus Moluccanus,_ the great King Crab of China and the Eastern
+seas, which, when adult, measures 1½ foot across its carapace, and is
+three feet in length.
+
+Besides some species of _Pterygotus,_ several of the allied genus
+_Eurypterus_ 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 plants may be of the family _Fluviales,_ and of
+fresh-water genera. They are accompanied by fossils, called “berries”
+by the quarrymen, which they compared to a compressed blackberry (see
+Figs. 505, 506), and which were called “Parka” 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 _Pterygotus
+anglicus_ in Forfarshire and Perthshire, but also in the Upper Silurian
+strata of England, in which species of the same genus, Pterygotus,
+occur.
+
+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.
+
+Fig. 507: Shale of Old Red Sandstone. Forfarshire. With impression of
+plants and eggs of Crustaceans.
+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 “corn-stones,” which may be described as mottled red and green
+earthy limestones. The fishes of this lowest English Old Red are
+_Cephalaspis_ and _Pteraspis,_ specifically different from species of
+the same genera which occur in the uppermost Ludlow or Silurian
+tilestones. Crustaceans also of the genus _Eurypterus_ are met with.
+
+Marine or Devonian Type.—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 “graywacke,” 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.
+
+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.
+
+DEVONIAN SERIES IN NORTH DEVON.
+
+UPPER DEVONIAN OR PILTON GROUP (a) 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
+(b) Yellow, brown, and red sandstone, with land plants (_Cyclopteris,_
+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.) MIDDLE DEVONIAN OR ILFRACOMBE GROUP. (a) Green
+glossy slates of considerable thickness, no fossils yet recorded from
+these beds (Mortenoe, Lee Bay, etc.).
+(b) Slates and schists, with several irregular courses of limestone
+containing shells and corals like those of the Plymouth Limestone
+(Combe Martin, Ilfracombe, etc.). LOWER DEVONIAN OR LYNTON
+GROUP. (a) Hard, greenish, red, and purple sandstone—no fossils yet
+found (Hangman Hill, etc.).
+(b) Soft slates with subordinate sandstones—fossils numerous at various
+horizons—Orthis, Corals, Encrinites, etc. (Valley of Rocks, Lynmouth,
+etc.).
+
+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 in all main points it agrees with the
+table drawn up in 1864 for the sixth edition of my “Elements.” Mr.
+Etheridge[5] 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’s memoir as our guide.
+
+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.
+
+Fig. 508: Spirifera disjuncta. Fig. 509: Phacops latifrons.
+Upper Devonian Rocks.—The slates and sandstones of Barnstaple (_a_ and
+_b_ of the preceding section) contain the shell _Spirifera disjuncta,_
+Sowerby (S. Verneuilii, Murch.), (see Fig. 508), which has a very wide
+range in Europe, Asia Minor, and even China; also _Strophalosia
+caperata,_ together with the large trilobite _Phacops latifrons,_
+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 _ Clymenia_ (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 _ Cypridina serrato-striata_ (Fig. 511), which
+is found in these beds, in the Rhenish provinces, the Harz, Saxony, and
+Silesia, as well as in Cornwall and Belgium.
+
+Middle Devonian Rocks.—We come next to the most typical portion of the
+Devonian system, including the great limestones of Plymouth and Torbay,
+replete with 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 _Favosites,
+Heliolites,_ and _Cyathophyllum._ 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, _Favosites
+cervicornis_ (Fig. 513), one of the commonest of all the Devonshire
+fossils. The _Cyathophyllum cæspitosum_ (Fig. 514) and _Heliolites
+pyriformis_ (Fig. 512) are species peculiar to this formation.
+
+Fig. 510: Clymenia linearis. Fig. 511: Cypridina serrato-striata.
+
+Fig. 512: Heliolites porosa.
+Fig. 513: Favosites cervicornis. Fig. 514: Cyathophyllum cæspitosum.
+
+Fig. 515: Stringocephalus Burtini. Fig. 516: Uncites Gryphus.
+
+With the above are found no less than eleven genera of stone-lilies or
+crinoids, some of them, such as _ Cupressocrinites,_ 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 _Stringocephalus Burtini_ (Fig. 515) and _Uncites
+Gryphus_ (Fig. 516) may be mentioned as exclusively Middle Devonian
+genera, and extremely characteristic of the same division in Belgium.
+The _Stringocephalus_ is also so abundant in the Middle Devonian of the
+banks of the Rhine as to have suggested the name of Stringocephalus
+Limestone.
+
+Fig. 517: Megalodon cucullatus.
+The only two species of Brachiopoda common to the Silurian and Devonian
+formations are _Atrypa reticularis_ (Fig. 532), which seems to have
+been a cosmopolite species, and _Strophomena rhomboidalis._
+
+Among the peculiar lamellibranchiate bivalves common to the Plymouth
+limestone of Devonshire and the Continent, we find the _ Megalodon_
+(Fig. 517). There are also twelve genera of Gasteropods which have
+yielded 36 species, four of which pass to the Carboniferous group,
+namely _Macrocheilus,_ _Acroculia, Euomphalus,_ and _Murchisonia._
+Pteropods occur, such as _Conularia_ (Fig. 518), and Cephalopods, such
+as _Cyrtoceras, Gyroceras, Orthoceras,_ 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 _Bronteus flabellifer_
+(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.
+
+Fig. 518: Conularia ornata.Fig. 519: Bronteus flabellifer.
+Fig. 520: Calceola sandalina.
+Beneath the Eifel Limestone (the great central and typical member of
+“the Devonian” on the Continent) lie certain schists called by German
+writers “Calceola-schiefer,” because they contain in abundance a fossil
+body of very curious structure, _Calceola sandalina_ (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 _Zoantharia rugosa_ (see Fig. 474), 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.
+
+Lower Devonian Rocks.—A great series of sandstones and glossy slates,
+with Crinoids, Brachiopods, and some corals, occurring on the coast at
+Lynmouth and the neighbourhood, and called the Lynton Group (see Table
+p. 449, 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 _
+Atrypa reticularis,_ can with certainty be identified with Silurian
+species. Among the characteristic forms are _Alveolites
+suborbicularis,_ also common to this formation in the Rhine, and
+_Orthis arcuata,_ 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.
+
+Fig. 521: Spirifora mucronata.
+Fig. 522: Homalonotus armatus.
+Among the Trilobites of this era several large species of _
+Homalonotus_ (Fig. 522) are conspicuous. The genus is still better
+known as a Silurian form, but the spinose species appear to belong
+exclusively to the “Lower Devonian,” and are found in Britain, Europe,
+and the Cape of Good Hope.
+
+Devonian of Russia.—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
+“Old Red” 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.[6] 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.
+
+Fig. 523: Psilophyton princeps.
+Devonian Strata in the United States and Canada.—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 _Cephalaspis,_ 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 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.
+
+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,[7]
+comprising _Coniferæ, Sigillariæ, Calamites, Asterophyllites,
+Lepidodendra,_ and ferns of the genera _Cyclopteris, Neuropteris,
+Sphenopteris,_ and others, together with fruits, such as _Cardiocarpum_
+and _Trigonocarpum,_ 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.
+
+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 _P. princeps,_
+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, _a,_ supposed to belong to the same plant,
+are described by Dawson as having inclosed the fructification. The
+remains of _Psilophyton princeps_ have been traced through 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.
+
+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.
+
+Devonian Insects of Canada.—The earliest known insects were brought to
+light in 1865 in the Devonian strata of St. John’s, New Brunswick, and
+are referred by Mr. Scudder to four species of _Neuroptera._ One of
+them is a gigantic Ephemera, and measured five inches in expanse of
+wing.
+
+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 “synthetic types.” Of this kind is a
+stridulating or musical apparatus like that of the cricket in an insect
+otherwise allied to the _ Neuroptera._ 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.
+
+ [1] Siluria, 4th ed., p. 265.
+
+ [2] Siluria, 4th ed., p. 258.
+
+ [3] Abridged from _crossotos,_ a fringe, and _ pteryx,_ a fin.
+
+ [4] Powrie, Geol. Quart. Journ., vol. xx, p. 417.
+
+ [5] Quart. Geol. Journ., vol. xxiii., 1867.
+
+ [6] Murchison’s Siluria, p. 329.
+
+ [7] Quart. Geol. Journ., vol. xv, p. 477, 1859; also vol. xviii, p.
+ 296, 1862.
+
+
+
+
+CHAPTER XXVI.
+SILURIAN GROUP.
+
+
+Classification of the Silurian Rocks. — Ludlow Formation and Fossils. —
+Bone-bed of the Upper Ludlow. — Lower Ludlow Shales with Pentamerus. —
+Oldest known Remains of fossil Fish. — Table of the progressive
+Discovery of Vertebrata in older Rocks. — Wenlock Formation, Corals,
+Cystideans and Trilobites. — Llandovery Group or Beds of Passage. —
+Lower Silurian Rocks. — Caradoc and Bala Beds. — Brachiopoda. —
+Trilobites. — Cystideæ. — Graptolites. — Llandeilo Flags. — Arenig or
+Stiper-stones Group. — Foreign Silurian Equivalents in Europe. —
+Silurian Strata of the United States. — Canadian Equivalents. — Amount
+of specific Agreement of Fossils with those of Europe.
+
+Classification of the Silurian Rocks.—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 _Silures,_ 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 “Primordial” or Cambrian group
+is described.
+
+UPPER SILURIAN ROCKS. Thickness
+in feet 1. LUDLOW FORMATION:
+     _a._  Upper Ludlow beds 780 _b._ Lower Ludlow beds: 1,050 2.
+     WENLOCK FORMATION:
+     _a._  Wenlock limestone and shale above 4,000 _b._ Woolhope
+     limestone and shale, and Denbighshire grits: 3. LLANDOVERY
+     FORMATION
+     (Beds of passage between Upper and Lower Silurian):
+     _a._  Upper Llandovery (May-Hill beds): 800 _b._ Lower
+     Llandovery: 600–1,000 LOWER SILURIAN ROCKS. 1. BALA AND CARADOC
+     BEDS, including volcanic rocks: 12,000 2. LLANDEILO FLAGS,
+     including volcanic rocks: 4,500 3. ARENIG OR STIPER-STONES
+     GROUP, including volcanic rocks: above 10,000
+
+UPPER SILURIAN ROCKS.
+
+1. Ludlow Formation.—This member of the Upper Silurian group, as will
+be seen by above table, is of great thickness, and subdivided into two
+parts—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’s Siluria for a list of the organic
+remains of all classes distributed through the different subdivisions
+of the Upper and Lower Silurian.
+
+_a._ Upper Ludlow: _Downton Sandstone._—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 “Tilestones.” 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 _Orthoceras bullatum, Platyschisma helicites, Bellerophon
+trilobatus, Chonetes lata,_ etc., with numerous defenses of fishes.
+
+These beds, therefore, now generally called the “Downton Sandstone,”
+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
+Fig. 504) and Eurypterus are met with.
+
+_Bone-bed of the Upper Ludlow._—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 intervening strata full of Upper Ludlow fossils.[1] 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.
+
+Fig. 524: Onchus tenuistriatus. Fig. 525: Shagreen-scales of a placoid
+fish, Thelodus parvidens.
+
+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.
+
+Fig. 526: Plectrodus mirabilis.
+The jaw and teeth of another predaceous genus (Fig. 526) have also been
+detected, together with some specimens of _Pteraspis Ludensis._ As
+usual in bone-beds, the teeth and bones are, for the most part,
+fragmentary and rolled.
+
+Fig. 527: Orthis elegantula.Fig. 528: Rhynchonella navicula.
+_Grey Sandstone and Mudstone, etc._—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, _Lingula cornea, Orthis orbicularis,_ a
+round variety of _O. elegantula, Modiolopsis platyphylla, Grammysia
+cingulata,_ all characteristic of the Upper Ludlow. The lowest or
+mud-stone beds contain _Rhynchonella navicula_ (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 p. 470); but the latter are by no means
+unrepresented. Among other genera, for example, we observe _Avicula_
+and _Pterinea, Cardiola, Ctenodonta_ (sub-genus of _ Nucula_),
+_Orthonota, Modiolopsis,_ and _ Palæarca._
+
+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 “mud-stones.” 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.
+
+Fig. 529: Pentamerus Knightii.
+
+_b._ Lower Ludlow Beds.—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 _Pentamerus Knightii,_ 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 _pente,_ five, and _meros,_ a
+part, because both valves are divided by a central septum, making four
+chambers, and in one valve 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 _
+Spirifera, Terebratula,_ 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.
+
+Fig. 530: Lingula Lewisii.
+Three other abundant shells in the Aymestry limestone are, first,
+_Lingula Lewisii_ (Fig. 530); second, _Rhynchonella Wilsoni,_ Sowerby
+(Fig. 531), which is also common to the Lower Ludlow and Wenlock
+limestone; third, _Atrypa reticularis,_ 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.
+
+Fig. 531: Rhynchonella (Terebratula) Wilsoni.
+
+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.
+
+Fig. 532: Atrypa reticularis. The Lower Ludlow Shale contains, among
+other fossils, many large cephalopoda not known in newer rocks, as the
+_Phragmoceras_ of Broderip, and the _Lituites_ of Breynius (see Figs.
+533, 534). The latter is partly straight and partly convoluted in a
+very flat spire. The _Orthoceras Ludense_ (Fig. 535), as well as the
+cephalopod last mentioned, occurs in this member of the species.
+
+Fig. 533: Phragmoceras ventricosum.
+
+A species of Graptolite, _G. priodon,_ Bronn (Fig. 545), 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.
+
+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 _Asteriadæ_ and _ Ophiuridæ._
+
+Fig. 534: Lituites (Trochoceras) giganteus. Fig. 535: Fragment of
+Orthoceras Ludense.
+
+Oldest known Fossil Fish.—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, F.G.S., in shale below the
+Aymestry limestone, associated with fossil shells of the Lower Ludlow
+formation—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.
+
+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.
+
+When we reflect on the hundreds of Mollusks, Echinoderms, 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.
+
+_Dates of the Discovery of different Classes of Fossil Vertebrata;
+showing the gradual progress made in tracing them to rocks of higher
+antiquity._
+
+  Year Formations Geographical localities
+  Mammalia 1798 Upper Eocene Paris (Gypsum of Montmartre).1
+  1818 Lower Oolite Stonesfield.2 1847 Upper
+  Trias Stuttgart.3 Aves 1782 Upper Eocene Paris (Gypsum
+  of Montmartre).4 1839 Lower Eocene Isle of Sheppey (London
+  Clay).5 1854 Lower Eocene Woolwich Beds.6 1855 Lower
+  Eocene Mendon (Plastic Clay).7 1858 Chloritic Series, or
+  Upper Greensand Cambridge.8 1863 Upper
+  Oolite Solenhofen.9 Reptilia 1710 Permian (or
+  Zechstein) Thuringia.10 1844 Carboniferous Saarbrück,
+  near Trèves.11 Pisces 1709 Permian (or
+  Kupferschiefer) Thuringia.12 1793 Carboniferous (Mountain
+  Limestone) Glasgow.13 1828 Devonian Caithness.14
+  1840 Upper Ludlow Ludlow.15 1859 Lower
+  Ludlow Leintwardine.16
+
+1. George Cuvier, Bulletin Soc. Philom. xx.
+2. In 1818, Cuvier, visiting the Museum of Oxford, decided on the
+mammalian character of a jaw from Stonesfield. See also p. 347.
+3. Prof. Plieninger. See p. 368.
+4. Cuvier, Ossemens Foss. Art. “Oiseaux.”
+5. Prof. Owen, Geol. Trans., 2nd series, vol. vi, p. 203, 1839.
+6. Upper part of the Woolwich beds. Prestwich, Quart. Geol. Journ.,
+vol. x, p. 157.
+7. _Gastornis Parisiensis._ Owen, Quart. Geol. Journ., vol. xii, p.
+204, 1856.
+8. Coprolitic bed, in the Upper Greensand. See p. 299.
+9. The _Archæopteryx macrura,_ Owen. See p. 338.
+10. The fossil monitor of Thuringia (_Protosaurus Speneri,_ V. Meyer)
+was figured by Spener of Berlin in 1810. (Miscel. Berlin.)
+11. See p. 406.
+12. Memorabilia Saxoniæ Subterr., Leipsic, 1709.
+13. History of Rutherglen by Rev. David Ure, 1793.
+14. Sedgwick and Murchison, Geol. Trans., 2nd series, vol. ii, p. 141,
+1828.
+15. Sir R. Murchison. See p. 459.
+16. See p. 461.
+
+Obs.—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.
+
+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 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.
+
+2. Wenlock Formation.—We next come to the Wenlock formation, which has
+been divided (see Table, p. 458) into Wenlock limestone, Wenlock shale,
+and Woolhope limestone and Denbighshire grits.
+
+Fig. 536: Halysites catenularius.
+
+_a. Wenlock Limestone._—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 “ball-stones” 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[2] Sometimes in the Malvern Hills this limestone,
+according to Professor Phillips, is oolitic.
+
+Fig. 537: Favosites Gothlandica.
+Among the corals, in which this formation is so rich, 53 species being
+known, the “chain-coral,” _Halysites catenularius_ (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
+_Favosites Gothlandica_ (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, _b_). Another common form
+in the Wenlock limestone is the _Omphyma turbinatum_ (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
+(p. 432), exhibiting the quadripartite arrangement of the septalamellæ
+within the cup.
+
+Fig. 538: Omphyma turbinatum.Fig. 539: Pseudocrinites bifasciatus.
+
+Among the numerous Crinoids, several peculiar species of _
+Cyathocrinus_ (for genus see Figs. 478, 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 _
+Pseudocrinites,_ which was furnished with pinnated fixed arms,[3] as
+represented in Fig. 539.
+
+Fig. 540: Strophomena (Leptæna) depressa.
+The Brachiopoda are, many of them, of the same species as those of the
+Aymestry limestone; as, for example, _Atrypa reticularis_ (Fig. 532),
+and _Strophomena depressa_ (Fig. 540); but the latter species ranges
+also from the Ludlow rocks, through the Wenlock shale, to the Caradoc
+Sandstone.
+
+Fig. 541: Calymene Blumenbachii.
+The crustaceans are represented almost exclusively by Trilobites, which
+are very conspicuous, 22 being peculiar. The _ Calymene Blumenbachii_
+(Fig. 541), called the ”Dudley Trilobite,” was known to collectors long
+before its true place in the animal kingdom was ascertained. It is
+often found coiled up like the common _Oniscus_ 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 _Phacops caudatus (Asaphus caudatus),_ Brong. (see Fig. 542), and
+this is conspicuous for its large size and flattened form.
+_Sphærexochus mirus_ (Fig. 543) is almost a globe when rolled up, the
+forehead or glabellum of this species being extremely inflated. The
+_Homalonotus,_ 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.
+
+Fig. 542: Phacops (Asaphus) caudatus.Fig. 543: Sphærexochus mirus.
+_Wenlock Shale._—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.
+
+Fig. 544: Homalonotus delphinocephalus.
+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
+_Orthis, Cardiola,_ and numerous thin-shelled species of
+_Orthoceratites._
+
+About six species of _Graptolite,_ a peculiar group of sertularian
+fossils before alluded to (p. 463) 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. 474).
+
+Fig. 545: Graptolithus priodon.
+_b. Woolhope Beds._—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 occurs. It contains the usual Wenlock fossils, but with
+the addition of some common in the uppermost Ludlow rock, such as _
+Chonetes lata_ and _Bellerophon trilobatus._ The chief fossils of the
+Woolhope limestone are _Illænus Barriensis, Homalonotus
+delphinocephalus_ (Fig. 544), _Strophomena imbrex,_ and _Rhynchonella
+Wilsoni_ (Fig. 531). 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.
+
+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.
+
+3. Llandovery Group—Beds of Passage.—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.
+
+_a.  Upper Llandovery or May-Hill Sandstone._—The May-Hill group, which
+has also been named ”Upper Llandovery,” by Sir R. Murchison, ranges
+from the west of the Longmynd to Builth, Llandovery, and Llandeilo, and
+to the sea in Marlow’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 Sedgwick[4] to be at the base of the Upper Silurian
+proper. The more calcareous portions of the rock have been called the
+Pentamerus limestone, because _Pentamerus oblongus_ (Fig. 546) is very
+abundant in them. It is usually accompanied by _P. (Stricklandinia)
+lirata_ (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.
+
+Fig. 546: Pentamerus oblongus.
+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 _Illænus_ and _Calymene_; Brachiopods of the genera _Orthis,
+Atrypa, Leptæna, Pentamerus, Strophomena,_ and others; Gasteropods of
+the genera _Turbo, Murchisonia_ (for genus, see Fig. 567), and
+_Bellerophon_; and Pteropods of the genus _Conularia._ The Brachiopods,
+of which there are 66 species, are almost all Upper Silurian.
+
+Fig. 547: Stricklandinia (Pentamerus) lirata. Fig. 548: Tentaculites
+annulatus.
+Among the fossils of the May-Hill shelly sandstone at Malvern,
+_Tentaculites annulatus_ (Fig. 548), an annelid, probably allied to
+Serpula, is found.
+
+_Lower Llandovery Rocks._—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 common to the May-Hill group
+above, and 93 common to the rocks below. _Stricklandinia (Pentamerus)
+levis,_ which is common in the Lower Llandovery, becomes rare in the
+Upper, while _ Pentamerus oblongus_ (Fig. 546), which is the
+characteristic shell of the Upper Llandovery, occurs but seldom in the
+Lower.
+
+LOWER SILURIAN ROCKS.
+
+The Lower Silurian has been divided into, first, the Bala Group;
+second, the Llandeilo flags; and, third, the Arenig or Lower Llandeilo
+formation.
+
+Bala and Caradoc Beds.—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 _Trinucleus
+Caractaci_ (see Fig. 553), which ranges from the base to the summit of
+the formation, usually accompanied by _Strophomena grandis_ (see Fig.
+551), and _Orthis vespertilio_ (Fig. 550), with many other fossils.
+
+Fig. 549: Orthis tricenaria. Fig. 550: Orthis vespertilio. Fig. 551:
+Orthis (Strophomena) grandis.
+
+_Brachiopoda._—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.
+
+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.
+
+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.
+
+_Trilobites._—In the Bala and Caradoc beds the trilobites reach their
+maximum, being represented by 111 species referred to 23 genera.
+
+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
+_Trinucleus_ 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.
+
+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 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,
+_Protaster_ and _Palæaster,_ 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 _Cystideæ._ They are the _Sphæronites_ of
+old authors, and were considered by Professor E. Forbes as intermediate
+between the crinoids and echinoderms. The _Echinosphæronite_ here
+represented (Fig. 555) is characteristic of the Caradoc beds in Wales,
+and of their equivalents in Sweden and Russia.
+
+Fig. 552: Young individuals of Trinucleus concentricus. Fig. 553:
+Trinucleus concentricus.
+
+Fig. 554: Palæaster asperimus.
+Fig. 555: Echinosphæronites ballicus.
+With it have been found several other genera of the same family, such
+as _Sphæronites, Hemicosmites,_ etc. Among the mollusca are Pteropods
+of the genus _Conularia_ of large size (for genus, see Fig. 518). About
+eleven species of Graptolite are reckoned as belonging to this
+formation; they are chiefly found in peculiar localities where 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.
+
+Fig. 556: Didymograpsus (Graptolites) Murchisonii.
+Llandeilo Flags.—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 _Llandeilo_ 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.
+
+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
+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.
+
+Fig. 557: Diplograpsus pristis. Fig. 558: Rastrites peregrinus.
+
+Fig. 559: Diplograpsus folium.
+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.
+
+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).
+
+Fig. 560: Orthoceras duplex.
+
+Among other Cephalopods in the Llandeilo flags is Cyrtoceras; in the
+same beds also are found Bellerophon (see Fig. 488) and some Pteropod
+shells (_Conularia, Theca,_ 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 _Asaphus_ (Fig. 561), _Ogygia_ (Fig. 562), and _Trinucleus_
+(Figs. 552 and 553) form a marked feature of the rich and varied
+Trilobitic fauna of this age.
+
+Fig. 561: Asaphus tyrannus. Fig. 562: Ogygia Buchii.
+
+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.
+
+Fig. 563: Arenicolites linearis.
+Arenig or Stiper-Stones Group _(Lower Llandeilo of Murchison)._—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, _Arenicolites linearis_), 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 (Fig.
+82). 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 ”unfossiliferous graywacke.”
+Professor Sedgwick had described, in 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 ”Siluria” (p. 52, 1859) to be
+quite distinct from the fossils of the overlying Llandeilo flags. Among
+these the _Obolella plumbea, Æglina binodosa, Ogygia Selwynii,_ and
+_Didymograpsus geminus_ (Fig. 564), and _D. Hirundo,_ are
+characteristic.
+
+Fig. 564: Didymograpsus geminus.
+
+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’s. These beds, which have only lately become known to us
+through the labours of Dr. Hicks,[5] 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.
+
+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.
+
+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 comparatively moderate lapse of time. The
+outpouring of repeated streams of lava—the showering down upon land and
+sea of volcanic ashes—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—the undermining and eating away of
+long lines of sea-cliff exposed to the swell of a deep and open
+ocean—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.
+
+Silurian Strata of the Continent of Europe.—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 _ Pentamerus oblongus,_ below which
+are strata with fossils corresponding to those of the Llandeilo beds of
+England. The lowest rock with organic remains yet discovered is ”the
+Ungulite or Obolus grit” of St. Petersburg, probably coeval with the
+Llandeilo flags of Wales.
+
+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 _Obolus_ _Shells of the lowest known
+Fossiliferous Beds in Russia._
+
+Fig. 565: Siphonotreta unguiculata. Fig. 566: Obolus Apollinis.
+
+or Ungulite of Pander, and a _Siphonotreta_ (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.
+
+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., _Textularia,
+Rotalia,_ and _Guttulina_).
+
+Silurian Strata of the United States.—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.
+
+_Subdivisions of the Silurian Strata of New York.
+(Strata below the Oriskany sandstone or base of the Devonian.)_
+
+New York Names British equivalents 1.  Upper Pentamerus Limestone
+   2.  Encrinal Limestone
+   3.  Delthyris Shaly Limestone
+   4.  Pentamerus and Tentaculite Limestones
+   5.  Water Lime Group
+   6.  Onondaga Salt Group
+   7.  Niagara Group Upper Silurian (or Ludlow
+and Wenlock formations 8.  Clinton Group
+   9.  Medina Sandstone
+10.  Oneida Conglomerate
+11.  Gray Sandstone Beds of Passage, Llandovery Group. 12.  Hudson
+River Group
+13.  Trenton Limestone
+14.  Black-River Limestone
+15.  Bird’s-eye Limestone
+16.  Chazy Limestone
+17.  Calciferous Sandstone Lower Silurian (or Caradoc and Bala,
+Llandeilo and Arenig Formations).
+
+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.
+
+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 _Calymene Blumenbachii, Homalonotus delphinocephalus_
+(Fig. 544), with several other trilobites; _Rhynchonella Wilsoni,_ Fig.
+531, and _Retzia cuneata; Orthis elegantula, Pentamerus galeatus,_ with
+many more brachiopods; _Orthoceras annulatum,_ among the cephalopodous
+shells; and _Favosites gothlandica,_ with other large corals.
+
+Fig. 567: Murchisonia gracilis.
+The Clinton Group, containing _Pentamerus oblongus_ and _
+Stricklandinia,_ 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.
+
+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 _ Asaphus (Isotelus)
+gigas, Trinucleus concentricus_ (Fig. 553); and various shells, such as
+_ Orthis striatula, Orthis biforata_ (or _O. lynx_), _O. porcata_ (_O.
+occidentalis_ of Hall), and _Bellerophon bilobatus._ In the Trenton
+limestone occurs _Murchisonia gracilis,_ Fig. 567, a fossil also common
+to the Llandeilo beds in England.
+
+Mr. D. Sharpe, in his report on the mollusca collected by me from these
+strata in North America,[6] has concluded that the number of species
+common to the Silurian rocks 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
+”the age of brachiopods.”
+
+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 ”primæval seas” of one uniform specific fauna
+was quite unfounded, geographical provinces having evidently existed in
+the oldest as in the most modern times.
+
+ [1] Murchison’s Siluria, p. 140.
+
+ [2] Murchison’s Siluria, chap. vi.
+
+ [3] E. Forbes, Mem. Geol. Surv., vol. ii, p. 496.
+
+ [4] Quart. Geol. Journ., vol. iv, p. 215, 1853.
+
+ [5] Trans. Brit. Assoc., 1866. Proc. Liverpool Geol. Soc., 1869.
+
+ [6] Quart. Geol. Journ., vol. iv.
+
+
+
+
+CHAPTER XXVII.
+CAMBRIAN AND LAURENTIAN GROUPS.
+
+
+Classification of the Cambrian Group, and its Equivalent in Bohemia. —
+Upper Cambrian Rocks. — Tremadoc Slates and their Fossils. — Lingula
+Flags. — Lower Cambrian Rocks. — Menevian Beds. — Longmynd Group. —
+Harlech Grits with large Trilobites. — Llanberis Slates. — Cambrian
+Rocks of Bohemia. — Primordial Zone of Barrande. — Metamorphosis of
+Trilobites. — Cambrian Rocks of Sweden and Norway. — Cambrian Rocks of
+the United States and Canada. — Potsdam Sandstone. — Huronian Series. —
+Laurentian Group, upper and lower. — Eozoon Canadense, oldest known
+Fossil. — Fundamental Gneiss of Scotland.
+
+CAMBRIAN  GROUP.
+
+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’ labour, in 1839, when his
+“Silurian System” 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.
+
+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 “Cambrian” 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 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’s Upper and Lower Silurian, while others were more ancient,
+to which he gave the name of “Primordial,” 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.
+
+The term primordial was intended to express M. Barrande’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.
+
+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:
+
+UPPER CAMBRIAN TREMADOC SLATES _(Primordial of Barrande in part)_
+LINGULA FLAGS _(Primordial of Barrande)_ LOWER CAMBRIAN MENEVIAN
+BEDS _(Primordial of Barrande)_ LONGMYND GROUP _a._ Harlech Grits
+_b._ Llanberis Slates
+
+Tremadoc Slates.—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 slates were first examined by Sedgwick in 1831,
+and were re-examined by him and described in 1846,[1] 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
+“primordial.” 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 _Ogygia, Asaphus,_ and _Cheirurus_; whereas those belonging
+to primordial types, or Barrande’s first fauna as well as to the
+Lingula flags of Wales, comprise _Dikelocephalus, Conocoryphe_ (for
+genera see Fig. 577 and 581),[2] _Olenus,_ and _Angelina._
+
+Fig. 568: Theca (Cleidotheca operculata.
+In the Tremadoc slates are found _Bellerophon, Orthoceras,_ and
+_Cyrtoceras,_ all specifically distinct from Lower Silurian fossils of
+the same genera: the Pteropods _Theca_ (Fig. 568) and _Conularia_ range
+throughout these slates; there are no Graptolites. The _Lingula
+(Lingulella) Davisii_ 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.
+
+Lingula Flags.—Next below the Tremadoc slates in North Wales lie
+micaceous flagstones and slates, in which, in 1846, Mr. E. Davis
+discovered the _Lingula (Lingulella),_ Fig. 570, named after him, and
+from which was derived the name of Lingula flags. These beds, which are
+palæontologically the equivalents of Barrande’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’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 “primordial” genera in common. _Dikelocephalus,
+Olenus_ (Fig. 571), and _Conocoryphe_ are prominent forms, as is also
+_Hymenocaris_ (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.[3]
+
+“Lingula Flags” of Dolgelly, and Ffestiniog; N. Wales.
+
+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.
+
+LOWER CAMBRIAN.
+
+Menevian Beds.—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 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[4] 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 _
+Microdiscus_ and _Paradoxides._ They therefore proposed to place them,
+and it seems to me with good reason, at the top of the Lower Cambrian
+under the term “Menevian,” Menevia being the classical name of St.
+David’s. The beds are well exhibited in the neighbourhood of St.
+David’s in South Wales, and near Dolgelly and Maentwrog in North Wales.
+They are the equivalents of the lowest part of Barrande’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.
+
+Fig. 572: Paradoxides Davidis.
+The trilobites are of large size; _Paradoxides Davidis_ (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 (Fig. 576), 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, _ Erinnys venulosa,_ occurs here in
+conjunction with _ Agnostus_ and _Microdiscus,_ the genera with the
+smallest number. Blind trilobites are also found as well as those which
+have the largest eyes, such as _Microdiscus_ on the one hand, and
+_Anoplenus_ on the other.
+
+LONGMYND GROUP.
+
+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 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.
+
+Fig. 573: Histioderma Hibernica.
+Harlech Grits.—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.
+
+With the exception of five species of annelids (see Fig. 460) brought
+to light by Mr. Salter in Shropshire, and Dr. Kinahan in Wicklow, and
+an obscure crustacean form, _Palæopyge Ramsayi,_ they were supposed to
+be barren of organic remains. Now, however, through the labours of Mr.
+Hicks,[5] they have yielded at St. David’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.
+
+A new genus of trilobite called _Plutonia Sedgwickii,_ not yet figured
+and described, has been met with in the Harlech grits. It is comparable
+in size to the large _Paradoxides Davidis_ before mentioned, has
+well-developed eyes, and is covered all over with tubercles. In the
+same strata occur other genera of trilobites, namely, _Conocoryphe,
+Paradoxides, Microdiscus,_ and the Pteropod _Theca_ (Fig. 568), 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 Fig. 444 and 445.
+
+Lanberis Slates.—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 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 _Oldhamia._ The nature of these organisms is still a matter of
+discussion among naturalists.
+
+Fig. 574: Oldhamia radiata.
+Fig. 575: Oldhamia antiqua.
+Cambrian Rocks of Bohemia _(Primordial zone of Barrande)._—In the year
+1846, as before stated, M. Joachim Barrande, after ten years’
+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’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.
+
+In the primordial zone C, he discovered trilobites of the genera
+_Paradoxides, Conocoryphe, Ellipsocephalus, Sao, Arionellus,
+Hydrocephalus,_ and _Agnostus._ M. Barrande pointed out that these
+primordial trilobites have a peculiar facies of their own dependent on
+the multiplication of their thoracic segments and the diminution of
+their caudal shield or pygidium.
+
+_Fossils of the lowest Fossiliferous Beds in Bohemia, or
+“Primordial Zone” of Barrande._
+
+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.
+
+One of the “primordial” or Upper Cambrian Trilobites of the genus
+_Sao,_ 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.
+
+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, _Orthis_ and _Orbicula,_ a Pteropod of the genus _Theca,_
+and four echinoderms of the cystidean family.
+
+Cambrian of Sweden and Norway.—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 “Palæontologica
+Suecica” (1852-4). The “alum-schists,” 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 _Paradoxides, Olenus, Agnostus,_ 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
+_Paradoxides._ 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 _Paradoxides Hicksii,_ a well-known
+Lower Cambrian fossil.
+
+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 “fucoid sandstones.” 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.
+
+Cambrian of the United States and Canada _(Potsdam Sandstone)._—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 _(Scolithus linearis)._ 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 _ Obolella,_ 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 _Lingula_ and _Orthis,_ and
+several trilobites of the primordial genus _Dikelocephalus_ (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 _Limulus._
+
+Fig. 581: Dikelocephalus Minnesotensis.
+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.
+
+Huronian Series.—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.
+
+LAURENTIAN GROUP.
+
+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 “primordial” or Cambrian rocks were formed. The older half of
+this Laurentian series is unconformable to the newer portion of the
+same.
+
+Upper Laurentian or Labrador Series.—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.
+
+Lower Laurentian.—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.
+
+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
+_Stromatopora rugosa._ 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 _ Eozoon_
+_Canadense_ (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.
+
+Fig. 582 and 583: Eozoon Canadense.
+
+Fig. 582. _a._ Chambers of lower tier communicating at +, and separated
+from adjoining chambers at O by an intervening septum, traversed by
+passages. _b._ Chambers of an upper tier. _c._ 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.) _d._ Intermediate skeleton, composed of homogeneous shell
+substance, traversed by _f._ Stoloniferous passages connecting the
+chambers of the two tiers. _e._ Canal system in intermediate skeleton,
+showing the arborescent saceodic prolongations. (Fig. 583 shows these
+bodies in a decalcified state.) _f._ Stoloniferous passages.
+Fig. 583. Decalcified portion of natural rock, showing _canal system_
+and the several layers; the acuteness of the planes prevents more than
+one or two parallel tiers being observed.
+
+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 “the fundamental gneiss,”
+which is found in the north-west of Ross-shire, and in Sutherlandshire
+(see Fig. 82), 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.
+
+ [1] Quart. Geol. Journ., vol. iii, p. 156.
+
+ [2] This genus has been substituted for Barrande’s _ Conocephalus,_ as
+ the latter term had been preoccupied by the entomologists.
+
+ [3] Geol. Mag., vol iv.
+
+ [4] British Association Report 1865, 1866, 1868 and Quart. Geol.
+ Journ., vols. xxi, xxv.
+
+ [5] Brit. Assoc. Report, 1868.
+
+
+
+
+CHAPTER XXVIII.
+VOLCANIC ROCKS.
+
+
+External Form, Structure, and Origin of Volcanic Mountains. — Cones and
+Craters. — Hypothesis of “Elevation Craters” considered. — Trap Rocks.
+— Name whence derived. — Minerals most abundant in Volcanic Rocks. —
+Table of the Analysis of Minerals in the Volcanic and Hypogene Rocks. —
+Similar Minerals in Meteorites. — Theory of Isomorphism. — Basaltic
+Rocks. — Trachytic Rocks. — Special Forms of Structure. — The columnar
+and globular Forms. — Trap Dikes and Veins. — Alteration of Rocks by
+volcanic Dikes. — Conversion of Chalk into Marble. — Intrusion of Trap
+between Strata. — Relation of trappean Rocks to the Products of active
+Volcanoes.
+
+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 _a, a_
+to represent the crystalline formations, such as the granitic and
+metamorphic; _b, b_ the fossiliferous strata; and _c, c_ the volcanic
+rocks. These last are sometimes found, as was explained in the first
+chapter, breaking through _a_ and _b,_ sometimes overlying both, and
+occasionally alternating with the strata _b, b._
+
+Fig. 584: a. Hypogene formations, stratified and unstratified. b.
+Aqueous formations. c. Volcanic rocks.
+
+External Form, Structure, and Origin of Volcanic Mountains.—The origin
+of volcanic cones with crater-shaped summits has been explained in the
+“Principles of Geology” (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,
+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.
+
+Fig. 585: Part of the chain of extinct volcanoes called the Monts Dome,
+Aurvergne.
+
+_Cones and Craters._—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 _lava_ 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 of the included
+gases, and thus forms _scoriæ,_ 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 _ crater,_ 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.
+
+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
+“trappean.” 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° to 20°
+or even more than 30°, 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 “Elevation
+craters.”
+
+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 the
+truncation on a grand scale of some large cones in Java and
+elsewhere.[1]
+
+Among the objections which may be considered as fatal to Von Buch’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.
+
+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 1½ 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.[2]
+
+Nomenclature of Trappean Rocks.—When geologists first began to examine
+attentively the structure of the northern 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 “trap” by Bergmann, from _trappa,_ Swedish for a
+flight of steps—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.
+
+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.
+
+Minerals most abundant in Volcanic Rocks.—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).
+
+_Analysis of Minerals most abundant in the Volcanic and Hypogene
+Rocks._
+
+THE QUARTZ GROUP QUARTZ 100·0
+2·6 Silica
+Specific gravity TRIDYMITE 100·0
+2·3 Silica
+Specific gravity THE FELDSPAR GROUP ORTHOCLASE.
+—— Carisbad, in granite (bulk) 65·23
+16·26
+0·27
+nil
+trace
+nil
+14·66
+1·45
+nil
+2·55 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Sanadine, Drachenfels in trachyte
+(Rammelsberg) 65·87
+18·53
+nil
+nil
+0·95
+0·30
+10·32
+3·49
+W. 0·44
+2·55 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity ALBITE.
+—— Arendal, in granite (G. Rose) 68·46
+19·30
+nil
+0·28
+0·68
+nil
+nil
+11·27
+nil
+2·61 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity OLIGOCLASE.
+—— Ytterby, in granite (Berzelius) 61·55
+23·80
+nil
+nil
+3·18
+0·80
+0·38
+9·67
+nil
+2·65 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Teneriffe, in trachyte (Deville) 61·55
+22·03
+nil
+nil
+2·81
+0·47
+3·44
+7·74
+nil
+2·59 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity LABRADORITE.
+—— Hitteroe, in Labrador-rock (Waage) 51·39
+29·42
+2·90
+nil
+9·44
+0·37
+1·10
+5·03
+W. 0·71
+2·72 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Iceland, in volcanic (Damour) 52·17
+29·22
+1·90
+nil
+13·11
+nil
+nil
+3·40
+nil
+2·71 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity ANORTHITE.
+—— Harzburg, in diorite (Streng) 45·37
+34·81
+0·59
+nil
+16·52
+0·83
+0·40
+1·45
+W. 0·87
+2·74 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Hecla, in volcanic (Waltershausen) 45·14
+32·10
+2·03
+0·78
+18·32
+nil
+0·22
+1·06
+nil
+2·74 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity LEUCITE.
+—— Vesuvius, 1811, in lava (Rammelsberg) 56·10
+23·22
+nil
+nil
+nil
+nil
+20·59
+0·57
+nil
+2·48 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity NEPHELINE.
+—— Miask, in Miascite (Scheerer) 44·30
+33·25
+0·82
+nil
+0·32
+0·07
+5·82
+16·02
+nil
+2·59 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Vesuvius, in volcanic (Arfvedson) 44·11
+33·73
+nil
+nil
+nil
+nil
+nil
+20·46
+W. 0·62
+2·60 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity THE MICA GROUP MUSCOVITE.
+—— Finland, in grante (Rose) 46·36
+36·80
+4·53
+nil
+nil
+nil
+9·22
+nil
+F. 0·67
+W. 1·84
+2·90 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+
+Specific gravity LEPIDOLITE.
+—— Cornwall, in granite (Regnault) 52·40
+26·80
+nil
+1·50
+nil
+nil
+9·14
+nil
+F. 4·18
+Li. 4·85
+2·90 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+
+Specific gravity BIOTITE.
+—— Bodennais (V. Kobel> 40·86
+15·13
+13·00
+nil
+nil
+22·00
+8·83
+nil
+W. 0·44
+2·70 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Vesuvius, in volcanic (Chodnef) 40·91
+17·71
+11·02
+nil
+0·30
+19·04
+9·96
+nil
+nil
+2·75 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity PHLOGOPITE.
+—— New York, in metamorphic limestone (Rammelsberg) 41·96
+13·47
+nil
+2·67
+0·34
+27·12
+9·37
+nil
+F. 2·93
+W. 0·60
+2·81 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+
+Specific gravity MARGARITE.
+—— Nexos (Smith) 30·02
+49·52
+1·65
+nil
+10·82
+0·48
+1·25
+
+W. 5·55
+2·99 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+=Potash
+=Soda
+Other constituents
+Specific gravity RAPIDOLITE.
+—— Pyrenees (Delesse) 32·10
+18·50
+nil
+0·06
+nil
+36·70
+nil
+nil
+W. 12·10
+2·61 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity TALC.
+—— Zillerthal (Delesse) 63·00
+nil
+nil
+trace
+nil
+33·60
+nil
+nil
+W. 3·10
+2·78 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity THE AMPHIBOLE AND PYROXENE GROUP TREMOLITE.
+—— St. Gothard (Rammelsbeg) 58·55
+nil
+nil
+nil
+13·90
+26·63
+nil
+nil
+F.W. 0·34
+2·93 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity ACTINOLITE.
+—— Arendal, in granite (Rammelsberg) 56·77
+0·97
+nil
+5·88
+13·56
+21·48
+nil
+nil
+W. 2·20
+3·02 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity HORNBLENDE.
+—— Faymont, in diorite (Deville) 41·99
+11·66
+nil
+22·22
+9·55
+12·59
+nil
+1·02
+W. 1·47
+3·20 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Etna, in volcanic (Waltershausen) 40·91
+13·68
+nil
+17·49
+13·44
+13·19
+nil
+nil
+W. 0·85
+3·01 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity URALITE.
+—— Ural, (Rammelsberg) 50·75
+5·65
+nil
+17·27
+11·59
+12·28
+nil
+nil
+W. 1·80
+3·14 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity AUGITE.
+—— Bohemia, in dolerite (Rammelsberg) 51·12
+3·38
+0·95
+8·08
+23·54
+12·82
+nil
+nil
+nil
+3·35 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Vesuvius, in lava of 1858 (Rammelsberg) 49·61
+4·42
+nil
+9·08
+22·83
+14·22
+nil
+nil
+nil
+3·25 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity DIALLAGE.
+—— Harz, in Gabbro (Rammelsberg) 52·00
+3·10
+nil
+9·36
+16·29
+18·51
+nil
+nil
+W. 1·10
+3·23 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity HYPERSTHENE.
+—— Labrador, in Labrador-Rock (Damour) 51·36
+0·37
+nil
+22·59
+3·09
+21·31
+nil
+nil
+nil
+3·39 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity THE OLIVINE GROUP BRONZITE.
+—— Greenland (V. Kobell) 58·00
+1·33
+11·14
+nil
+nil
+29·66
+nil
+nil
+nil
+3·20 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity OLIVINE.
+—— Carlsbad, in basalt (Rammelsberg) 39·34
+nil
+nil
+14·85
+nil
+45·81
+nil
+nil
+nil
+3·40 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity —— Mount Somma, in volcanic (Walmstedt) 10·08
+0·18
+nil
+15·74
+nil
+44·22
+nil
+nil
+nil
+3·33 Silica
+Alumina
+Sesquioxide of Iron
+Protoxides of Iron and Manganese
+Lime
+Magnesia
+Potash
+Soda
+Other constituents
+Specific gravity
+
+In the “Other constituents” the following signs are used: F=Fluorine,
+Li=Lithia, W=Loss on igniting the mineral, in most instances only
+Water.
+
+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.[3] 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.
+
+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.
+
+Quartz Group.—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 2·6, was not of
+purely igneous origin, because the silica resulting from fusion in the
+laboratory has only a specific gravity of 2·3. 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
+2·3 (see Table, p. 499), is of common occurrence in the volcanic rocks
+of Mexico, Auvergne, the Rhine, and elsewhere, although hitherto
+entirely overlooked.
+
+Feldspar Group.—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, 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.
+
+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 “glassy” and “compact”
+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 “compact feldspar” 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.
+
+Feldspars when arranged according to their system of crystallisation
+are _monoclinic,_ having one axis obliquely inclined; or _triclinic,_
+having the three axes all obliquely inclined to each other. If arranged
+with reference to their cleavage they are _orthoclastic,_ the fracture
+taking place always at a right angle; or _plagioclastic,_ in which the
+cleavages are oblique to one another. Orthoclase is orthoclastic and
+monoclinic; all the other feldspars are plagioclastic and triclinic.
+
+_Minerals in Meteorites._—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.
+
+Mica Group.—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 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.
+
+Amphibole and Pyroxene Group.—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 page 499),
+that it is perhaps best to unite them in one group.
+
+Theory of Isomorphism.—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 _cleavage_—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, p. 499) in rocks from Siberia, which possessed the cleavage
+and chemical composition of hornblende, while they had the external
+form of augite.
+
+If, from these data, it is inferred that the same substance 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.
+
+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 _isomorphism_ (from _ isos,_
+equal, and _morphe,_ form). According to this law, the ingredients of a
+given species of mineral are not 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.
+
+Basaltic Rocks.—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 47·80 per cent of
+silica, has a specific gravity of 2·95; whereas trachyte, which has 66
+per cent of silica, has a specific gravity of only 2·68; trachytic
+porphyry, containing 69 per cent of silica, a specific gravity of only
+2·58. 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 2·78, or more than trachyte, and less than
+basalt.[4]
+
+_Basalt._—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 _Basalt_ 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 _
+Anamesite_ (from _anamesos,_ 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 _ Dolerite_ (from
+_doleros,_ deceitful), in allusion to the difficulty of distinguishing
+it from some of the rocks known as Plutonic.
+
+_Melaphyre_ is often quite undistinguishable in external 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.
+
+_Greenstone._—This name has usually been extended to all granular
+mixtures, whether of hornblende and feldspar, or of augite and
+feldspar. The term _diorite_ has been applied exclusively to compounds
+of hornblende and triclinic feldspar. _ Labrador-rock_ 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 _ Hypersthene-rock._ _Gabbro_ and _Diabase_ 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.
+
+Trachytic Rocks.—The name trachyte (from [**Greek]_ trachus,_ 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.
+
+_Obsidian._—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.
+
+_Clinkstone or Phonolite._—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 _Clinkstone
+porphyry._
+
+Volcanic Rocks distinguished by special Forms of Structure.—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’s attention to them.
+
+Fig. 586: Porphyry. White crystals of feldspar in a dark base of
+hornblende and feldspar.
+_Porphyry_ 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 “Rosso antico.” 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). _ Red
+quartziferous porphyry_ is a much more siliceous rock, containing about
+70 or 80 per cent of silex, while that of Egypt has only 62 per cent.
+
+_Amygdaloid._—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 _amygdalon,_ 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.
+
+Fig. 587: Scoriaceous lava in part converted into an amygdaloid.
+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.
+
+_Lava._—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.
+
+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 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.[5]
+
+_Scoriæ_ and _Pumice_ may next be mentioned, as porous rocks produced
+by the action of gases on materials melted by volcanic heat. _Scoriæ_
+are usually of a reddish-brown and black colour, and are the cinders
+and slags of basaltic or augitic lavas. _Pumice_ 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.
+
+_Volcanic Ash or Tuff, Trap Tuff._—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 _ volcanic ash_ 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.
+
+_Wacke_ 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 passes gradually from the soft
+state to the hard dolerite, greenstone, or other trap rock from which
+it has been derived.
+
+_Agglomerate._—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 _conglomerate._ 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.
+
+_Laterite_ is a red or brick-like rock composed of silicate of alumina
+and oxide of iron. The red layers called “ochre beds,” dividing the
+lavas of the Giant’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’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 laterite in India may have had a similar origin.
+In India, however, especially in the Deccan, the term “laterite” 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.
+
+Columnar and Globular Structure.—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’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.[6] 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.
+
+Fig. 588: Lava of La Coupe d’Ayzac, near Antraigue, in the Department
+of Ardêche.
+
+It being assumed that columnar trap has consolidated from a fluid
+state, the prisms are said to be always at right angles to the _cooling
+surfaces._ 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 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’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 _d a_; 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 _a,_ being scoriaceous, the second _b,_ presenting
+irregular prisms; and the third, _c,_ 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°, at _g,_ and
+are nearly horizontal at _f,_ their position having been everywhere
+determined, according to the law before mentioned, by the form of the
+original valley.
+
+Fig. 589: Columnar basalt in the Vicentin.
+
+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.[7] 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.
+
+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 stream of lava, from 30 to 40
+feet thick, which has proceeded from one of several volcanic craters,
+still extant, on the neighbouring heights.
+
+Fig. 590: Basaltic pillars of Käsegrotte, Bertrich-Baden, half-way
+between Trèves and Coblenz.
+
+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.[8]
+
+Fig. 591: Globiform pitchstone. Chiaja di Luna, Isle of Ponza.
+
+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, “and when the balls,” says Mr. Scrope, “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 of this nucleus have not been so much
+loosened by decomposition; but the application of a ruder blow will
+produce a still further exfoliation.”[9]
+
+Fig. 592: Dike in valley, near Brazen Head, Madeira. (From a drawing of
+Captain Basil Hall, R.N.)
+Volcanic or Trap Dikes.—The leading varieties of the trappean
+rocks—basalt, greenstone, trachyte, and the rest—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).
+
+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, 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.
+
+Fig. 593: Ground-plan of greenstone dikes traversing sandstone.
+
+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.
+
+Fig. 594: Trap dividing and covering sandstone near Suishnish, in Skye.
+
+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.
+
+Rocks altered by Volcanic Dikes.—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.
+
+_Plas-Newydd: Dike cutting through Shale._—A striking example, near
+Plas-Newydd, in Anglesea, has been described by Professor Henslow.[10]
+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 _Producti,_
+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.[11] Some garnets contain as much as 20 per cent of lime,
+which they may have derived from the decomposition of the fossil shells
+or _Producti._ 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.[12]
+
+_Antrim: Dike cutting through Chalk._—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. “The extreme effect,”
+says Dr. Berger, “presents a dark brown crystalline limestone, the
+crystals running in flakes as large as those of coarse primitive
+(_metamorphic_) 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.”[13] All traces of organic remains are effaced in that part of
+the limestone which is most crystalline.
+
+Fig. 595: Basaltic dikes in chalk in Island of Rathlin, Antrim.
+Ground-plan as seen on the beach. Fig. 595: Basaltic dikes in chalk in
+Island of Rathlin, Antrim. Ground-plan as seen on the beach. (Conybeare
+and Buckland[14])
+
+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, _m, m,_ 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.[15]
+
+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.[16]
+
+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,
+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.
+
+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.
+
+Intrusion of Trap between Strata.—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.
+
+Relation of Trappean Rocks to the Products of active Volcanoes.—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 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,
+
+                  “Quantum vertice in auras
+     Ætherias, tantum radice in Tartara tendit,”
+
+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.
+
+Fig. 596: Strata intercepted by a trap dike, and covered with alluvium.
+
+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.
+
+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 p. 507); 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 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.[17]
+
+Dr. MacCulloch, after examining with great attention these and the
+other igneous rocks of Scotland, observes, “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.” 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.[18]
+
+It will be seen in the following chapters that in the earth’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.
+
+ [1] Principles, vol. ii, pp. 56 and 145.
+
+ [2] Memoir on Mount Etna, Phil. Trans., 1858.
+
+ [3] For analyses of these minerals see the Mineralogies of Dana and
+ Bristow.
+
+ [4] Dr. Daubeny on Volcanoes, 2nd ed., pp. 14, 15.
+
+ [5] G. Hose, Ann. des Mines, tome viii, p. 32.
+
+ [6] MacCulloch Sys. of Geol., vol. ii, p. 137.
+
+ [7] Fortis, Mém. sur l’Hist. Nat. de l’Italie, tome 1., p. 233, plate
+ 7.
+
+ [8] Delesse, sur les Roches Globuleuses, Mém. de la Soc. Géol. de
+ France, 2 sér., tome iv.
+
+ [9] Scrope, Geol. Trans., 2nd series, vol. ii, p. 205.
+
+ [10] Cambridge Transactions, vol. i, p. 402.
+
+ [11] Ibid., vol. i, p. 410.
+
+ [12] Ibid., vol. ii, p. 175.
+
+ [13] Dr. Berger, Geol. Trans., 1st series, vol. iii, p. 172.
+
+ [14] Geol. Trans., 1st series, vol. iii, p. 210 and plate 10.
+
+ [15] Ibid., vol. iii, p. 213; and Playfair, Illus. of Hutt. Theory, s.
+ 253.
+
+ [16] Sedgwick, Camb. Trans., vol. ii, p. 37.)
+
+ [17] MacCulloch, West. Islands, vol. ii, p. 487.
+
+ [18] Syst. of Geol., vol. ii, p. 114.
+
+
+
+
+CHAPTER XXIX.
+ON THE AGES OF VOLCANIC ROCKS.
+
+
+Tests of relative Age of Volcanic Rocks. — Why ancient and modern Rocks
+cannot be identical. — Tests by Superposition and intrusion. — Test by
+Alteration of Rocks in Contact. — Test by Organic Remains. — Test of
+Age by Mineral Character. — Test by Included Fragments. — Recent and
+Post-pliocene volcanic Rocks. — Vesuvius, Auvergne, Puy de Côme, and
+Puy de Pariou. — Newer Pliocene volcanic Rocks. — Cyclopean Isles,
+Etna, Dikes of Palagonia, Madeira. — Older Pliocene volcanic Rocks. —
+Italy. — Pliocene Volcanoes of the Eifel. — Trass.
+
+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.
+
+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.
+
+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
+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.
+
+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, p. 500, occur in
+amygdaloids and other trap-rocks in great abundance, and Daubrée’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.
+
+Fig. 597: Showing melted matter forced between two strata.
+
+Tests by Superposition.—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 _ b_ 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 _b_ flowed over the fossiliferous bed
+_c,_ and that, after its consolidation, _a_ was deposited upon it, _a_
+and _c_ both belonging to the same geological period. But, on the other
+hand, we must conclude the trap to be intrusive, if the stratum _a_ be
+altered by _b_ at the point of contact, or if, in pursuing _b_ for some
+distance, we find at length that it cuts through the stratum _a,_ and
+then overlies it as at E.
+
+Fig. 598: Section through sedimentary mass with melted matter.
+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 _a, b, c,_ and that after its
+consolidation the strata _d, e_ 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, _d, e,_ to
+have been altered at their junction, as if by heat.
+
+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 p. 124).
+
+Test of Age by Organic Remains.—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.
+
+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, 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 “Conway” sailed 40 miles
+through floating pumice, among which were some pieces of considerable
+size.[1]
+
+Test of Age by Mineral Composition.—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.[2] 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.
+
+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
+basalt. It can by no means be inferred that trachyte predominated at
+one period of the earth’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 2½ 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’s crust.
+
+Test by Included Fragments.—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.
+
+Recent and Post-pliocene Volcanic Rocks.—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 at the earth’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.
+
+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.
+
+_Vesuvius._—I have traced in the “Principles of Geology” 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—volcanic sand, pumice, and
+scoriæ have been showered down so abundantly that whole cities were
+buried—tracts of the sea have been filled up or converted into
+shoals—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.
+
+It has also been stated (p. 206), 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.
+
+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.
+
+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’s account of an
+eruption of Vesuvius in the year 1779, who records the following fact:
+“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.
+
+”These channels (says the same observer), I have found, upon
+examination after an eruption, to be in general from 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 _being worn perfectly
+smooth and even_ in most parts by the violence of the currents of the
+red-hot lavas which they had conveyed for many weeks successively.” I
+was able to verify this phenomenon in 1858, when a stream of lava
+issued from a lateral cone.[3] 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.
+
+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  p. 510.)
+
+_Auvergne._—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 _Cyclostoma elegans, Helix hortensis, H. nemoralis,_
+_H. lapicida,_ and _Clausilia rugosa._ 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.
+
+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 p. 542), 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.
+
+_Puy de Côme._—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° and 40°, 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 has
+disclosed, in one spot, a wall of columnar basalt about fifty feet
+high.[4]
+
+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—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.
+
+_Puy de Pariou._—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
+_in spite_ 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.
+
+Newer Pliocene Volcanic Rocks.—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 (p. 205)
+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 p.
+205).
+
+_Cyclopean Islands._—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 these breccias
+are many angular and hardened fragments of laminated clay in different
+states of alteration by heat, and intermixed with volcanic sands.
+
+Fig. 599: View of the Isle of Cyclops, in the Bay of Trezza.
+
+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.
+
+Fig. 600: Contortions of strata in the largest of the Cyclopean
+Islands.
+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.
+
+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 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.
+
+Fig. 601: Newer pliocene strata invaded by lava. Isle of Cyclops
+(horizontal section).
+_Dikes of Palagonia._—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.
+
+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 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.
+
+Figs. 602 and 603: Ground-plan of dikes near Palagonia.
+_Madeira._—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—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° 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—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 _Woodwardia radicans_, _and Davallia Canariensis,_
+ferns now abundant in Madeira. Thirdly—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 _Helix_ 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 (p. 143).
+
+Older Pliocene Period.—_Italy._—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[5] 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.[6] 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 series of volcanic products might be detected of every age
+from the Older Pliocene to the historical epoch.
+
+_Pliocene Volcanoes of the Eifel._—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 _tarn,_ 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.
+
+Other crater lakes of circular or oval form, and hollowed out of
+similar ancient strata, occur in the Upper Eifel, where 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.
+
+I have already given (Fig. 590) 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.
+
+_Trass._—The tufaceous alluvium called _trass,_ 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.
+
+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.
+
+ [1] Caldcleugh, Phil. Trans., 1836, p. 27.
+
+ [2] See Principles, _Index,_ “Skaptar Jokul.”
+
+ [3] Principles of Geology, vol. i, p. 626.
+
+ [4] Scrope’s Central France, p. 60, and plate.
+
+ [5] See 1st edit. of Principles of Geology, vol. iii, chaps. xiii and
+ xiv, 1833; and former editions of this work, chap. xxxi.
+
+ [6] Quart. Geol. Journ., vol. vi, p. 281.
+
+
+
+
+CHAPTER XXX.
+AGE OF VOLCANIC ROCKS—_continued._
+
+
+Volcanic Rocks of the Upper Miocene Period. — Madeira. — Grand Canary.
+— Azores. — Lower Miocene Volcanic Rocks. — Isle of Mull. — Staffa and
+Antrim. — The Eifel. — Upper and Lower Miocene Volcanic Rocks of
+Auvergne. — Hill of Gergovia. — Eocene Volcanic Rocks of Monte Bolca. —
+Trap of Cretaceous Period. — Oolitic Period. — Triassic Period. —
+Permian Period. — Carboniferous Period. — Erect Trees buried in
+Volcanic Ash in the Island of Arran. — Old Red Sandstone Period. —
+Silurian Period. — Cambrian Period. — Laurentian Volcanic Rocks.
+
+Volcanic Rocks of the Upper Miocene Period.—_Madeira._—The greater part
+of the volcanic eruptions of Madeira, as we have already seen (p. 532),
+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.
+
+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 _Cardium,
+Spondylus,_ and _Lithodomus_ among the lamellibranchiate bivalves, and
+among the _Echinoderms_ the large Clypeaster called _C. altus,_ an
+extinct European Miocene fossil.
+
+The largest list of fossils has been published by Mr. Karl Meyer, in
+Hartung’s “Madeira;” 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’s list occur, as, for example, _Pholadomya,_ and a
+large _ Terebra._ Mr. Johnson also found a fine specimen of _Nautilus
+(Atruria) ziczac_ (Fig. 211), a well-known Falunian fossil of Europe;
+and in the same volcanic tuff of Baixo, the Echinoderm _Brissus
+Scillæ,_ 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, _S. Italicus,_ 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.
+
+It has been remarked (p. 212), 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 _Astræa, Sarcinula, Hydnophora,_ 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 18½ 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.[1]
+
+_Grand Canary._—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
+taken place. The _Clypeaster altus, Spondylus gæderopus, Pectunculus
+pilosus, Cardita calyculata,_ and several other shells, serve to
+identify this formation with that of the Madeiras, and _Ancillaria
+glandiformis,_ which is not rare, and some other fossils, remind us of
+the faluns of Touraine.
+
+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
+_Corbis,_ an African form, Hinnites, now living in Oregon, _Thecidium_
+(_T. Mediterranean,_ identical with the Miocene fossil of St. Juvat, in
+Brittany), _Calyptræa, Hipponyx, Nerita, Erato, Oliva, Ancillaria,_ and
+_ Fasciolaria._
+
+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.
+
+On the whole, the rocks of the Grand Canary, an island of a nearly
+circular shape, and 6½ 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.
+
+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 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,
+_Strombus bubonius,_ which is still living on the West Coast of Africa,
+and _Cerithium procerum,_ found at Mozambique; others are Mediterranean
+species, as _Pecten Jacobæus_ and _P. polymorphus._ Some of these
+testacea, such as _Cardita squamosa,_ are inhabitants of deep water,
+and the deposit on the whole seems to indicate a depth of water
+exceeding a hundred feet.
+
+_Azores._—In the island of St. Mary’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.
+
+Mr. Hartung, in his account of the Azores, published in 1860, describes
+twenty-three shells from St. Mary’s,[2] 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,
+_Cardium Hartungi,_ 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’s, and others,
+attest.
+
+Lower Miocene Volcanic Rocks.—_Isle of Mull and Antrim._—I may refer
+the reader to the account already given (p. 247) 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 (p. 532), 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.
+
+_The Eifel._—A large portion of the volcanic rocks of the Lower Rhine
+and the Eifel are coeval with the Lower Miocene deposits to which most
+of the “Brown-Coal” 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.
+
+M. Von Dechen, in his work on the Siebengebirge,[3] 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 _Flabellaria, Ceanothus,_ and _ Daphnogene,_ including _D.
+cinnamomifolia_ (Fig. 155), 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 _Leuciscus, Aspius,_ and _Perca._ 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.
+
+Upper and Lower Miocene Volcanic Rocks of Auvergne.—The extinct
+volcanoes of Auvergne and Cantal, in central France, seem to have
+commenced their eruptions in the Lower 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 p. 527).
+
+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.
+
+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.[4] 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 an insignificant feature in
+the great pile, and, like it, may frequently have been destroyed and
+renovated.
+
+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 (p. 234) 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.
+
+The valley in which the cone of Tartaret, above-mentioned (p. 527), 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.
+
+_Gergovia._—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. 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 _M.
+inquinata_ (Fig. 217), 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.
+
+Fig. 604: Hill of Gergovia.
+
+Eocene Volcanic Rocks.—_Monte Bolca._—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’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.[5]
+
+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 (p. 263) Professor Heer’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 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, _Pycnodus,_ belonging to the order of
+Ganoids, which form, as before stated, the vast majority of the
+ichthyolites entombed in the secondary are Mesozoic rocks.
+
+Cretaceous Period.—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 formed of rolled pieces of the same serpentinous trap,
+which appear in the dikes above alluded to.
+
+Period of Oolite and Lias.—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;[6] 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.
+
+Trap of the New Red Sandstone Period.—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.[7]
+
+Trap of the Permian Period.—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’s Seat in the suburbs of Edinburgh marks
+the site of an eruption of the same era.
+
+Trap of the Carboniferous Period.—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 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.
+
+_Fife—Flisk Dike._—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’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.
+
+_Erect Trees buried in Volcanic Ash at Arran._—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°, 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 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° is the more striking,
+as they must clearly have remained horizontal and undisturbed during a
+long period of intermittent and contemporaneous volcanic action.
+
+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 pp. 410 and 411 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.
+
+Trap of the Old Red Sandstone Period.—By referring to the section
+explanatory of the structure of Forfarshire, already given (p. 74), 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 (see Fig. 55), 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.
+
+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 “Old Red” 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.[8]
+
+Silurian Volcanic Rocks.—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.[9]
+
+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.[10]
+
+In Radnorshire there is an example of twelve bands of stratified trap,
+alternating with Silurian schists and flagstones, 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.[11]
+
+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.
+
+Cambrian Volcanic Rocks.—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. “Much of the ash,” says Professor Ramsay, “seems to have been
+subaërial. Islands, like Graham’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.”[12]
+
+Laurentian Volcanic Rocks.—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 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.[13] 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.
+
+ [1] Linnean Proceedings; Zoology, 1860.
+
+ [2] Hartung, Die Azoren, 1860; also Insel Gran Canaria, Madeira und
+ Porto Santo, 1864, Leipsig.
+
+ [3] Geognost. Beschreib. des Siebengebirges am Rhein. Bonn, 1852.
+
+ [4] Scrope’s Central France, p. 98.
+
+ [5] Principles of Geology, chap. xxvi, 9th ed., p. 432.
+
+ [6] Boblaye and Virlet, Morea, p. 23.
+
+ [7] De la Beche, Geol. Proceedings, vol. ii, p. 198.
+
+ [8] Maclaren, Geology of Fife and Lothians. Geikie, Trans. Royal Soc.
+ Edinburgh, 1860-1861.
+
+ [9] Murchison, Silurian System, etc., p. 230.
+
+ [10] Ibid., p. 212.
+
+ [11] Murchison, Silurian System, etc., p. 325.
+
+ [12] Quart. Geol. Journ., vol. ix, p. 170, 1852.
+
+ [13] Logan, Geology of Canada, 1863.
+
+
+
+
+CHAPTER XXXI.
+PLUTONIC ROCKS.
+
+
+General Aspect of Plutonic Rocks. — Granite and its Varieties. —
+Decomposing into Spherical Masses. — Rude columnar Structure. — Graphic
+Granite. — Mutual Penetration of Crystals of Quartz and Feldspar. —
+Glass Cavities in Quartz of Granite. — Porphyritic, talcose, and
+syenitic Granite. — Schorlrock and Eurite. — Syenite. — Connection of
+the Granites and Syenites with the Volcanic Rocks. — Analogy in
+Composition of Trachyte and Granite. — Granite Veins in Glen Tilt, Cape
+of Good Hope, and Cornwall. — Metalliferous Veins in Strata near their
+Junction with Granite. — Quartz Veins. — Exposure of Plutonic Rocks at
+the surface due to Denudation.
+
+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’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.
+
+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 “Plutonic rocks.” 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 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.
+
+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.
+
+Fig. 605: Mass of granite near the Sharp Tor, Cornwall.
+
+Granite and its Varieties.—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’s End, in Cornwall. (See Fig.
+606.)
+
+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 Fig. 622), 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 _Pegmatite,_ which is a mixture of quartz
+and common feldspar, usually with some small admixture of white silvery
+mica, often passes into graphic granite.
+
+Fig. 606: Granite having a cuboidal and rude columnar structure, Land’s
+End, Cornwall.
+
+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 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.[1]
+
+Graphic granite. Fig. 607: Section parallel to the laminæ. Fig. 608:
+Section transverse to the laminæ.
+
+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’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 “gelatinous flint” 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.[2]
+
+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.
+
+These “glass cavities,” 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’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—the proof, he says, of the operation
+of water in the formation of granite being quite as strong as of that
+of heat.[3]
+
+When rocks are melted at great depths water must be present, for two
+reasons—First, because rainwater and seawater 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.
+
+Fig. 609: Porphyritic granite. Land’s End, Cornwall.
+
+_Porphyritic Granite._—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’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.
+
+The uniform mineral character of large masses of granite seems to
+indicate that large quantities of the component elements were
+thoroughly mixed up together, and then crystallised under precisely
+similar conditions. There are, however, many accidental, or
+“occasional,” 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.
+
+_Talcose Granite,_ 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.
+
+_Schorl-rock, and Schorly Granite._—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.
+
+_Eurite, Feldstone._—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 _Feldstone,_ and when the
+crystals of feldspar are conspicuous it becomes _Feldspar porphyry._
+All these and other varieties of granite pass into certain kinds of
+trap—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.
+
+_Syenitic Granite._—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.
+
+Syenite.—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 compound of feldspar and hornblende, and regarded quartz as
+merely one of its occasional minerals.
+
+_Miascite._—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. _Zircon-syenite_ is another variety closely allied to
+Miascite, but containing crystals of Zircon.
+
+Connection of the Granites and Syenites with the Volcanic Rocks.—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 p. 449); 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.
+
+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.
+
+“The ordinary granite of Aberdeenshire,” says Dr. MacCulloch, “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.”
+The same author mentions, that in Shetland a granite composed of
+hornblende, mica, feldspar, and quartz graduates in an equally perfect
+manner into basalt.[4] 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 to conceive how such volcanic masses may, at a
+certain depth from the surface, pass downward into granite.
+
+Granitic Veins.—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.
+
+Fig. 610 and Fig. 611: Junction of granite and arbillaceous schist in
+Glen Tilt. (MacCulloch.) Fig. 610 and Fig. 611: Junction of granite and
+arbillaceous schist in Glen Tilt. (MacCulloch.)[5]
+
+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.
+
+In the Plutonic, as in the volcanic rocks, there is every gradation
+from a tortuous vein to the most regular form of 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.
+
+Fig. 612: Granite veins traversing clay slate, Table Mountain, Cape of
+Good Hope. Fig. 612: Granite veins traversing clay slate, Table
+Mountain, Cape of Good Hope.[6]
+
+Fig. 613: Granite veins traversing gneiss, Cape Wrath. Fig. 613:
+Granite veins traversing gneiss, Cape Wrath.[7]
+
+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.[8]
+
+Fig. 614 is a sketch of a group of granite veins in Cornwall, given by
+Messrs. Von Oeynhausen and Von Dechen.[9] 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.
+
+Fig. 614: Granite veins passing through hornblende slate, Carnsilver
+Cove, Cornwall.
+
+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.[10]
+
+Fig. 615: a, b. Quartz vein passing through gneiss and greenstone.
+Tronstad Strand, near Christiania.
+
+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 first cut by a greenstone dike, about 2½
+feet wide; then the crack _a, b,_ 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.
+
+Fig. 616: Euritic porphyry alternating with primary fossiliferous
+strata, near Christiania.
+
+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 (_a, c,_ Fig. 616) which divide the bituminous shales
+and argillaceous limestones, _f, f._ But some of these same porphyries
+are partially unconformable, as _b,_ 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 “overlying” can in this instance be applied to
+a Plutonic rock, it is only in proportion as that rock begins to
+acquire a trappean aspect.
+
+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’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.
+
+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.
+
+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’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.
+
+ [1] Delesse, Ann. des Mines, 1852, tome iii, p. 409, and 1848, tome
+ xiii, p. 675.
+
+ [2] Bulletin, 2e série, iv, 1304; and D’Archiac, Hist. des Progrès de
+ la Géol., i, 38.
+
+ [3] See Quart. Geol. Journ., vol. xiv, pp. 465, 488.
+
+ [4] Syst. of Geol., vol. i, pp. 157 and 158.
+
+ [5] Geol. Trans., First Series, vol. iii, pl. 21.
+
+ [6] Captain B. Hall, Trans. Roy. Soc. Edinburgh, vol. vii.
+
+ [7] Western Islands, pl. 31.
+
+ [8] MacCulloch, Syst. of Geol., vol. ii, p. 58.
+
+ [9] Phil. Mag. and Annals, No. 27, New Series, March, 1829.
+
+ [10] Necker, Proceedings of the Geol. Soc., No. 26, p. 392.
+
+
+
+
+CHAPTER XXXII.
+ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS.
+
+
+Difficulty in ascertaining the precise Age of a Plutonic Rock. — Test
+of Age by Relative Position. — Test by Intrusion and Alteration. — Test
+by Mineral Composition. — Test by included Fragments. — Recent and
+Pliocene Plutonic Rocks, why invisible. — Miocene Syenite of the Isle
+of Skye. — Eocene Plutonic Rocks in the Andes. — Granite altering
+Cretaceous Rocks. — Granite altering Lias in the Alps and in Skye. —
+Granite of Dartmoor altering Carboniferous Strata. — Granite of the Old
+Red Sandstone Period. — Syenite altering Silurian Strata in Norway. —
+Blending of the same with Gneiss. — Most ancient Plutonic Rocks. —
+Granite protruded in a solid Form.
+
+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.
+
+Test of Age by Relative Position.—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.
+
+Test by Intrusion and Alteration.—But when Plutonic rocks send veins
+into strata, and alter them near the point of contact, in the manner
+before described (p. 559), 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.
+
+Test by Mineral Composition.—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.
+
+Test by Included Fragments.—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,[1] and thus the granite is shown to be newer than those slaty
+and trappean formations from which the fragments were derived.
+
+Recent and Pliocene Plutonic Rocks, why invisible.—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
+
+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.[2] 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,[3] it will follow that the quantity of Plutonic rock
+generated or in progress during the Recent epoch must already have been
+considerable.
+
+But as the Plutonic rocks originate at some depth in the earth’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—subterposition in the Plutonic, like
+superposition in the sedimentary rocks, being usually characteristic of
+a newer origin.
+
+Fig. 617: Diagram showing the relative position which the Plutonic and
+sedimentary formations of different ages may occupy.
+
+In Fig. 617 an attempt is made to show the inverted order in which
+sedimentary and Plutonic formations may occur in the earth’s crust. The
+oldest Plutonic rock, No. I, has been upheaved at successive periods
+until it has become exposed to view in 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 _strata_ No. 4 and the Recent _ granite_ 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 _recent_ strata No. 4 might be
+covered by a great many newer sedimentary formations.
+
+Miocene Plutonic Rocks.—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.[4] 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.
+
+Eocene Plutonic Rocks.—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 _flysch,_ 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 _flysch_ 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.
+
+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’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.
+
+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.
+
+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’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.
+
+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,[5] 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’s crust, within
+the same period, an amount of subterranean change corresponding to this
+vast alteration of level affecting a whole continent.
+
+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 _tertiary_ and _ recent_ 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.
+
+Fig. 618: Section through three layers (b, c, d) of the Cretaceous
+series over granite (A).
+Plutonic Rocks of Cretaceous Period.—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 _b, c, d,_ Fig. 618, to be three
+members of the Cretaceous series, the lowest of which, _b,_ has been
+altered by the granite A, the modifying influence not having extended
+so far as _c,_ or having but slightly affected its lowest beds. Now it
+can rarely be possible for the geologist to decide whether the beds _d_
+existed at the time of the intrusion of A, and alteration of _ b_ and
+_c,_ or whether they were subsequently thrown down upon _c._ 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 exposed by denudation, at the height of 2000 or 3000 feet on the
+flanks of that chain.
+
+Fig. 619: Junction of granite with Jurassic or Oolite strata in the
+Alps, near Champoleon.
+
+Plutonic Rocks of the Oolite and Lias.—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.[6] 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.
+
+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 is changed into granular
+marble, with a band of serpentine at the junction.[7]
+
+Plutonic Rocks of Carboniferous Period.—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 “elvans.”[8] The granite of Cornwall is probably
+of the same date, and, therefore, as modern as the Carboniferous
+strata, if not newer.
+
+Fig. 620: Section through Silurian strata and Granite.
+
+Plutonic Rocks of Silurian Period.—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 p. 562)
+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 _a,_ Fig. 620, and then again on the opposite
+side of the same mountain, as at _b,_ dip away from the same granite.
+When the junctions, however, are carefully examined, it is found that
+the Plutonic rock intrudes itself in veins, and nowhere covers the
+fossiliferous strata in large overlying masses, as is so commonly the
+case with trappean formations.[9]
+
+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.
+
+Fig. 621: Granite sending veins into Silurian strata and gneiss.
+Christiania, Norway.
+
+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 p. 584). 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, 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.
+
+Oldest Granites.—It is not half a century since the doctrine was very
+general that all granitic rocks were _ primitive,_ that is to say, that
+they originated before the deposition of the first sedimentary strata,
+and before the creation of organic beings (see p. 34). 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 (p. 464), 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 _known_ fossiliferous
+formations.
+
+Protrusion of Solid Granite.—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.[10]
+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.
+
+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.
+
+ [1] Silliman’s Journ., No. 69, p. 123.
+
+ [2] See “Principles,” _Index,_ “Jorullo.”
+
+ [3] Ibid., “Volcanic Eruptions.”
+
+ [4] “Western Islands,” vol. i, p. 330.
+
+ [5] See map of Europe, and explanation, in Principles, book i.
+
+ [6] Élie de Beaumont sur les Montagnes de l’Oisans, etc. Mém. de la
+ Soc. d’Hist. Nat. de Paris, tome v.
+
+ [7] Von Buch, Annales de Chimie, etc.
+
+ [8] Proceed. Geol. Soc., vol. ii, p. 562; and Trans., 2nd series, vol.
+ v, p. 686.
+
+ [9] See the Gæa Norvegica and other works of Keilhau, with whom I
+ examined this country.
+
+ [10] Murchison, Geol. Trans., 2nd series, vol. ii, p. 307.
+
+
+
+
+CHAPTER XXXIII.
+METAMORPHIC ROCKS.
+
+
+General Character of Metamorphic Rocks. — Gneiss. — Hornblende-schist.
+— Serpentine. — Mica-schist. — Clay-slate. — Quartzite. —
+Chlorite-schist. — Metamorphic Limestone. — Origin of the metamorphic
+Strata. — Their Stratification. — Fossiliferous Strata near intrusive
+Masses of Granite converted into Rocks identical with different Members
+of the metamorphic Series. — Arguments hence derived as to the Nature
+of Plutonic Action. — Hydrothermal Action, or the Influence of Steam
+and Gases in producing Metamorphism. — Objections to the metamorphic
+Theory considered.
+
+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 _ metamorphic_ 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.
+
+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.
+
+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 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.
+
+Principal Metamorphic Rocks.—The following may be enumerated as the
+principal members of the metamorphic class:—gneiss, mica-schist,
+hornblende-schist, clay-slate, chlorite-schist, hypogene or metamorphic
+limestone, and certain kinds of quartz-rock or quartzite.
+
+Fig. 622: Fragment of gneiss; section made at right angles to the
+planes of foliation.
+
+_Gneiss._—The first of these, gneiss, may be called stratified—or by
+those who object to that term, foliated—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.
+
+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 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.
+
+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.
+
+_Eurite,_ which has already been mentioned as a Plutonic rock, occurs
+also with precisely the same composition in beds subordinate to gneiss
+or mica-slate.
+
+_Hornblende-schist_ 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 “primitive
+greenstone.” 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.
+
+_Serpentine_ 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.
+
+_Actinolite Schist_ is a slaty foliated rock, composed chiefly of
+actinolite, an emerald-green mineral, allied to hornblende, with some
+admixture of garnet, mica, and quartz.
+
+_Mica-schist_ or _Micaceous Schist_ 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 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.
+
+_Clay-slate—Argillaceous Schist—Argillite._—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.
+
+_Chlorite Schist_ 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.
+
+_Quartzite,_ or _Quartz Rock,_ 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.
+
+_Crystalline,_ or _Metamorphic Limestone._—This hypogene rock, called
+by the earlier geologists _primary limestone,_ 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.
+
+Origin of the Metamorphic Strata.—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 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.
+
+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.
+
+Fossiliferous Strata rendered metamorphic by intrusive Masses of
+Granite.—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.
+
+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.
+
+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 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.[1]
+
+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’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 “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.”[2]
+
+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, “couzeranite.”
+
+“Hornblende-schist,” says Dr. MacCulloch, “may at first have been mere
+clay; for clay or shale is found altered by trap into Lydian stone, a
+substance differing from hornblende-schist almost solely in compactness
+and uniformity of texture.”[3] “In Shetland,” remarks the same author,
+“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.” 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.
+
+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 _Pecopteris, Neuropteris, Calamites,_ 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.[4]
+
+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 constituting the component materials
+common to both classes of rocks. These elements, which are enumerated
+in the table at p. 499, 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.
+
+Hydrothermal Action, or the Influence of Steam and Gases in producing
+Metamorphism.—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.[5] 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.
+
+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.
+
+The changes which Daubrée has shown to have been produced by the
+alkaline waters of Plombières in the Vosges, are more especially
+instructive.[6] These waters have a heat of 160° F., or an excess of
+109° above the average temperature of ordinary springs in that
+district. They were 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—apophyllite and
+chabazite among others; also to calcareous spar, arragonite, and fluor
+spar, together with siliceous minerals, such as opal—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.
+
+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.
+
+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.[7]
+
+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 “stufas,”
+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.
+
+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 (p. 558), 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° to 167° 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. 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.
+
+Objections to the Metamorphic Theory considered.—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.
+
+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.
+
+ [1] Keilhau, Gæa Norvegica, pp. 61-63.
+
+ [2] Geol. Manual, p. 479.
+
+ [3] Syst. of Geol., vol. i, pp. 210, 211.
+
+ [4] See Lyell, Quart. Geol. Journ., vol. i, p. 199.
+
+ [5] Phil. Trans., 1804.
+
+ [6] Daubrée, Sur le Métamorphisme. Paris, 1860.
+
+ [7] See Principles, _Index,_ “Carbonated Springs,” etc.
+
+
+
+
+CHAPTER XXXIV.
+METAMORPHIC ROCKS—_continued._
+
+
+Definition of slaty Cleavage and Joints. — Supposed Causes of these
+Structures. — Crystalline Theory of Cleavage. — Mechanical Theory of
+Cleavage. — Condensation and Elongation of slate Rocks by lateral
+Pressure. — Lamination of some volcanic Rocks due to Motion. — Whether
+the Foliation of the crystalline Schists be usually parallel with the
+original Planes of Stratification. — Examples in Norway and Scotland. —
+Causes of Irregularity in the Planes of Foliation.
+
+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.
+
+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.
+
+Slaty Cleavage.—Professor Sedgwick, whose essay “On the Structure of
+large Mineral Masses” 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 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° to 40°. Sometimes the cleavage
+planes dip towards the same point of the compass as those of
+stratification, but often to opposite points.[1] 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.
+
+Fig. 624: Parallel planes of cleavage intersecting curved strata.
+
+Fig. 625: Section in Lower Silurian slates of Cardiganshire, showing
+the cleavage planes bent along the junction of the beds.
+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° 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.
+
+Jointed Structure.—In regard to joints, they are natural 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.[2]
+
+Fig. 626: Stratification, joints, and cleavage.
+
+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.
+
+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.[3]
+
+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 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’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.
+
+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.
+
+Crystalline Theory of Cleavage.—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.
+
+Sir John Herschel, in allusion to slaty cleavage, has suggested that
+“if rocks have been so heated as to allow a commencement of
+crystallisation—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[4] exist,
+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.”[5]
+
+Mechanical Theory of Cleavage.—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 “creeping movement” 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.[6] 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.[7]
+
+Subsequently (1853) Mr. Sorby demonstrated the great extent to which
+this mechanical theory is applicable to the slate rocks of North Wales
+and Devonshire,[8] 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 _d
+f,_ which has offered greater resistance, has been sharply contorted,
+while the fine-grained strata, _a, b, c,_ have remained comparatively
+unbent. The points _d_ and _f_ in the stratum _d f_ 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 _d f_ is now about four times greater in those parts lying in
+the main direction of the flexures than in a plane 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.
+
+Fig. 627: Vertical section of slate rock in the cliffs near Ilfracombe,
+North Devon.
+Above the sandy bed _d f,_ the stratum _c_ is somewhat disturbed, while
+the next bed, _b,_ is much less so, and a not at all; yet all these
+beds, _c, b,_ and _a,_ must have undergone an equal amount of pressure
+with _d,_ the points a and g having approximated as much towards each
+other as have _ d_ and _f._ The same phenomena are also repeated in the
+beds below _d,_ 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. “These
+and numerous other cases in North Devon are analogous,” says Mr. Sorby,
+“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.”
+
+By microscopic examination of minute crystals, and by 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.[9]
+
+Dr. Tyndall, when commenting in 1856 on Mr. Sorby’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 “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.”[10] 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 “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.”
+
+Mr. Darwin attributes the lamination and fissile structure 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.[11]
+
+Foliation of Crystalline Schists.—After studying, in 1835, the
+crystalline rocks of South America, Mr. Darwin proposed the term
+_foliation_ 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.
+
+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.[12] 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’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° N.E.[13] 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.
+
+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 p. 63). Hence we must expect to be frequently baffled
+when we attempt to decide 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—diagonal lamination (p.
+42)—ripple-marked, unconformable stratification,—the fantastic folds
+produced by lateral pressure—faults of various width—intrusive dikes of
+trap—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.[14]
+
+Fig. 628: Lamination of clay-stone. Montagne de Seguinat, near
+Gavarnie, in the Pyrenees.
+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.
+
+ [1] Geol. Trans., 2nd series, vol. iii, p. 461.
+
+ [2] Silurian System, p. 246.
+
+ [3] Introduction to Geology, chap. iv.
+
+ [4] 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.
+
+ [5] Letter to the author, dated Cape of Good Hope, Feb. 20, 1836.
+
+ [6] Report, Brit. Assoc., Cork, 1843, Sect. p. 60.
+
+ [7] Quart. Geol. Journ., vol. iii, p. 87, 1847.
+
+ [8] On the Origin of Slaty Cleavage, by H. C. Sorby, Edin. New Phil.
+ Journ., 1853, vol. lv, p. 137.
+
+ [9] Sorby, as cited above, p. 741, note.
+
+ [10] Tyndall, View of the Cleavage of Crystals and Slate rocks.
+
+ [11] Darwin, Volcanic Islands, pp. 69, 70.
+
+ [12] Norske Mag. Naturvidsk., vol. i, p. 71.
+
+ [13] Memoir read before the Geol. Soc. London, Jan. 31, 1855.
+
+ [14] H. C. Sorby, Quart. Geol. Journ., vol. xix., p. 401.
+
+
+
+
+CHAPTER XXXV.
+ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.
+
+
+Difficulty of ascertaining the Age of metamorphic Strata. — Metamorphic
+Strata of Eocene date in the Alps of Switzerland and Savoy. — Limestone
+and Shale of Carrara. — Metamorphic Strata of older date than the
+Silurian and Cambrian Rocks. — Order of Succession in metamorphic
+Rocks. — Uniformity of mineral Character. — Supposed Azoic Period. —
+Connection between the Absence of Organic Remains and the Scarcity of
+calcareous Matter in metamorphic Rocks.
+
+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.
+
+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 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.
+
+Eocene Strata rendered metamorphic in the Alps.—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.
+
+As an illustration of the partial conversion into gneiss of portions of
+a highly inclined set of beds, I may cite Sir R. Murchison’s memoir on
+the structure of the Alps. Slates provincially termed “flysch” (see p.
+278), 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 the Valorsine,
+near Mont Blanc, granite and granitic veins are observable, piercing
+through talcose gneiss, which passes insensibly upward into secondary
+strata.
+
+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.
+
+Northern Apennines.—Carrara.—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 “Apuan Alps,” 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 invaded by certain trappean and Plutonic rocks,
+such as diorite, serpentine, and granite, occurring in the same
+country.
+
+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.[1] 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.
+
+Metamorphic Strata of older date than the Silurian and Cambrian
+Rocks.—It was remarked (Fig. 617) 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.
+
+In Canada, as we have seen (p. 491), the Lower Laurentian gneiss,
+quartzite, and limestone may be regarded as metamorphic, because, among
+other reasons, organic remains (_Eozoon Canadense_) have been detected
+in a part of one of the calcareous masses. The Upper Laurentian or
+Labrador 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 (p. 490).
+
+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 Fig. 82. It is the same
+as that intersected by numerous granite veins which forms the cliffs of
+Cape Wrath, in Sutherlandshire (see Fig. 613), and is conjectured to be
+of Laurentian age. Above it, as shown in the section (Fig. 82), 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 (p. 112), and limestone in which Mr.
+Charles Peach was the first to find, in 1854, three or four species of
+_Orthoceras,_ also the genera _Cyrtoceras_ and _ Lituites,_ two species
+of _Murchisonia,_ a _ Pleurotomaria,_ a species of _Maclurea,_ one of _
+Euomphalus,_ and an _Orthis._ Several of the species are believed by
+Mr. Salter to be identical with Lower Silurian fossils of Canada and
+the United States.
+
+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.
+
+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 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 _Cephalaspis Lyelli,
+Pterygotus Anglicus,_ and _Parka decipiens,_ rests unconformably.
+
+Order of Succession in Metamorphic Rocks.—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.
+
+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.
+
+_Uniformity of Mineral Character in Hypogene Rocks._—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—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 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 p. 503 and table, p. 499).
+
+Supposed Azoic Period.—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.
+
+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 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.
+
+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’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.
+
+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 _Eozoon Canadense_ 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.
+
+ [1] 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.
+
+
+
+
+CHAPTER XXXVI.
+MINERAL VEINS.
+
+
+Different Kinds of mineral Veins. — Ordinary metalliferous Veins or
+Lodes. — Their frequent Coincidence with Faults. — Proofs that they
+originated in Fissures in solid Rock. — Veins shifting other Veins. —
+Polishing of their Walls or “Slicken sides.” Shells and Pebbles in
+Lodes. — Evidence of the successive Enlargement and Reopening of veins.
+— Examples in Cornwall and in Auvergne. — Dimensions of Veins. — Why
+some alternately swell out and contract. — Filling of Lodes by
+Sublimation from below. — Supposed relative Age of the precious Metals.
+— Copper and lead Veins in Ireland older than Cornish Tin. — Lead Vein
+in Lias, Glamorganshire. — Gold in Russia, California, and Australia. —
+Connection of hot Springs and mineral Veins.
+
+The manner in which metallic substances are distributed through the
+earth’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.
+
+On different Kinds of Mineral Veins.—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 “stockwerk,” in allusion to the different
+floors on which the mining operations are in such cases carried on.
+
+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 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.
+
+That Metalliferous Veins were Fissures.—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
+_faults,_ or those dislocations of rocks which are indisputably due to
+mechanical force, as above explained (p. 87). 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 _a a,_ Fig. 629,
+to be a tin lode in Cornwall, the term _lode_ being applied to veins
+containing metallic ores. This lode, running east and west, is a yard
+wide, and is shifted by a copper lode (_b b_) of similar width. The
+first fissure (_a a_) 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.
+
+It is clear that, after the gradual introduction of the tin and other
+substances, the second rent (_b b_) was produced by another fracture
+accompanied by a displacement of the rocks along the plane of _b b._
+This new opening was then filled with minerals, some of them resembling
+those in _a a,_ 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 _c c,_ 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 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 (_b b_), 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.
+
+Vertical sections of the mine at Huel Peever, Redruth, Cornwall. Fig.
+629: Tin; Fig. 630: Copper; Fig. 631: Clay.
+
+Again, in Fig. 631 we see evidence of a fourth fissure (_d d_), also
+filled with clay, which has cut through the tin vein (_a a_), 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.[1] The principal movement here referred to, or that of _c c,_
+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, _d, c, b, a,_ etc., or the geographical 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 p. 93.) 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.
+
+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 Fig. 106). They are common even in
+cases where there has been no shift, and occur equally in
+non-metalliferous fissures. They are called by miners “slicken-sides,”
+from the German _schlichten,_ to plane, and _seite,_ side. It is
+supposed that the lines of the striæ indicate the direction in which
+the rocks were moved.
+
+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.[2]
+
+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.[3] In Bohemia, similar pebbles
+have been met with at the depth of 180 fathoms; and in Cornwall, Mr.
+Carne mentions 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.[4] 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.
+
+_Fracture, Re-opening and Successive Formation of Veins._—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.
+
+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.
+
+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 occur
+where the vertical plates, or _combs,_ 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.[5] Each of the plates or combs (_a, b, c, d, e, f_) 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.
+
+Fig. 632: Copper lode, near Redruth, enlarged at six successive
+periods.
+
+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.[6] 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.
+
+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 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.
+
+Cause of alternate Contraction and Swelling of Veins.—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.
+
+Let _a b,_ Fig. 633, be a line of fracture traversing a rock, and let
+_a b,_ 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 _a_ to _a′_, taking care that the two
+pieces of paper still touch each other at the points 1, 2, 3, 4, 5, we
+obtain an irregular aperture at _c,_ and isolated cavities at _d, d,
+d,_ 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, _f, f,_
+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.
+
+Figs. 633, 634, 635: Lines of fracture traversing a rock.
+
+Fig. 636: Nipped ores where the course of a vein departs from
+verticality.
+
+Most lodes are perpendicular to the horizon, or nearly so; but some of
+them have a considerable inclination or “hade,” 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 _a,_ Fig. 636, the miner
+complains that the ores are “nipped,” 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 “horses” or “riders.”
+That we should find some mineral veins which split into branches is
+also natural, for we observe the same in regard to open fissures.
+
+Chemical Deposits in Veins.—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 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.[7] 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’s crust subsides slowly while another
+contiguous to it happens to rest on a different foundation, so as to
+remain unmoved.
+
+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—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, 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.[8]
+
+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 “toad-stone,” 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.
+
+“Lodes in Cornwall,” says Mr. Robert W. Fox, “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 _vice versa._
+
+Supposed relative Age of the different Metals.—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’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’s crust.
+
+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—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.
+
+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.[9]
+
+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 Fig. 614), 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
+cases referred to in corroboration can be otherwise interpreted.[10] 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.
+
+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—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.
+
+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.[11] 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.
+
+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.
+
+_Origin of Gold in California._—Mr. J. Arthur Phillips,[12] in his
+treatise “On the Gold Fields of California,” 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.
+
+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.
+
+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 “underlying” igneous formations or granites which are visible to
+man are older, on the whole, than the overlying or trappean formations.
+
+If different sets of fissures, originating simultaneously at different
+levels in the earth’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.
+
+ [1] Geol. Trans., vol. iv, p. 139; Trans. Royal Geol. Society,
+ Cornwall, vol. ii, p. 90
+
+ [2] Conybeare and Phil. Geol., p. 401, and Farey’s Derbyshire, p. 243.
+
+ [3] Fournet, Études sur les Dépôts Métallifères.
+
+ [4] Carne, Trans. Geol. Soc., Cornwall, vol. iii, p. 238.
+
+ [5] Geol. Rep. on Cornwall, p. 340.
+
+ [6] Principles, chap. xxvii, 8th edit., p. 422.
+
+ [7] See Dr. Daubeny’s Volcanoes.
+
+ [8] Bulletin, iv, p. 1278.
+
+ [9] Sir H. De la Beche, MS. Notes on Irish Survey.
+
+ [10] Report on Geology of Cornwall, p. 310.
+
+ [11] Darwin’s South America, p. 209, etc.
+
+ [12] Proc. Royal Soc., 1868, p. 294.
+
+
+INDEX.
+
+——::——
+
+_The Fossils, the names of which appear in Italics, are figured in the
+Text._
+
+ABBEVILLE, flint tools of, 152
+Aberdeenshire, granite of, 558
+Abich, M., on trachytic rocks, 504
+_Acer trilobatum,_ Miocene, 220, 221
+_Acrodus nobilis,_ Lias, 359
+Acrogens, term explained, 303
+_Acrolepis Sedgwickii,_ Permian, 390
+_Actæon acutus,_ Great Oolite, 345
+_Actinocyclas,_ in Atlantic mud, 288
+Actinolite, 499, 502
+—— schist, 578
+_Æchmodus Leachii,_ Lias, 358
+_Adiantites Hibernica,_ Old Red, 441
+Agassiz on fish of Sheppey, 267
+—— on fish of the Brown-Coal, 540
+—— on fish of Monte Bolca, 544
+—— on Old Red fossil fish, 443, 447
+—— on Silurian fish, 460
+Age of metamorphic rocks, 597
+—— of Plutonic rocks, 564
+—— of strata, tests of, 123
+—— of volcanic rocks, 520
+Agglomerate described, 509
+_Agnostus integer. A. Rex_, 488
+Air-breathers of the Coal, 413
+Aix-la-Chapelle, Cretaceous flora of, 302
+Alabaster defined, 39
+Alberti on Keuper, 376
+Albite, 499, 500
+Aldeby and Chillesford beds, 192
+Alkali, present in the Palæozoic strata, 587
+Alpine blocks on the Jura, 169
+Alps, age of metamorphic rocks in, 599
+——, nummulitic limestone and flysch of, 77
+Alum schists of Norway and Sweden, 489
+Alluvial deposits, Recent and Post-pliocene, 151
+Alluvium, term explained, 99
+—— in Auvergne, 100
+Alternations of marine and fresh-water strata, 72
+Alum Bay beds, plants of the, 262
+Amblyrhynchus cristatus, a living marine saurian, 362
+America. _See_ United States, Canada, Nova Scotia.
+——, North, Glacial formations of, 182
+——, South, gradual rise of land in, 72
+——, Silurian strata of, 478
+American character of Lower Miocene flora, 238
+—— forms in Swiss Miocene flora, 223
+Amiens, flint tools of, 152
+_Ammonites bifrons,_ Lias, 356
+—— _Braikenridgii,_ Oolite, 351
+—— _Bucklandi,_ Lias, 356
+—— _Deshayesii,_ Neocomian, 311
+—— _Humphresianus,_ Inferior Oolite, 351
+—— _Jason,_ Oxford Clay, 340
+—— _Noricus,_ Speeton, 312
+—— _macrocephalus,_ Oolite, 352
+—— _margaritatus,_ Lias, 357
+—— _planorbis,_ Lias, 356
+—— _rhotomagensis,_ Chalk marl, 298
+Amphibole group of minerals, 499, 502
+_Amphistegina Hauerina,_ Vienna basin, 225
+_Amphitherium Broderipii,_ in Stonesfield, 348
+—— _Prevostii,_ Stonesfield slate, 347
+_Ampullaria glauca_, 56
+_Amygdaloid_, 507
+Analcime, 500
+Anamesite, a variety of basalt, 504
+_Ananchytes ovatus,_ White chalk, 293
+——, with crania attached, 49
+_Ancillaria subulata,_ Eocene, 57
+_Ancyloceras gigas_, 309
+—— _spinigerum,_ Gault, 301
+—— _Duvallei,_ Neocomian, 312
+_Ancylus velletia (A. elegans)_, 55
+Andalusite, 500
+Andes, Plutonic rocks of the, 569
+Andreasburg, metalliferous vein of, 611
+Angelin, on Cambrian of Sweden, 489
+Angiosperms, 303
+—— of the Coal, 429
+Anglesea, dike cutting through shale in, 514
+_Anodonta Cordierii_, 54
+—— _Jukesii,_ Upper Old Red, 441
+—— _latimarginata_, 54
+_Anoplotherium commune,_ Binstead, 254
+—— _gracile,_ Paris basin, 271
+Anorthite, 499, 501
+_Annularia sphenophylloides,_ Coal, 425
+_Antholithes,_ coal-measures, 429
+Anthracite, conversion of coal into, 408
+Anticlinal and synclinal curves, 74, 85
+Antrim, Chalk altered by a dike in, 516
+——, Lower Miocene, volcanic rocks of, 539
+Antwerp Crag, 204
+Apateon pedestris, a carboniferous reptile, 406
+Apatite, 500
+Apennines, Northern, metamorphic rocks of, 599
+Apes, fossil of the Upper Miocene, 215
+_Apiocrinites rotundus,_ Bradford, 343
+Appalachians, long lines of flexures in, 92, 93
+——, vast thickness of successive strata in, 110
+_Aptychus,_ part of ammonite, 336
+Aqueous rocks defined, 27, 35
+_Araucaria sphærocarpa,_ Inferior Oolite, 348
+Arbroath, section of Old Red at, 74
+_Archæopteryx macrura,_ Solenhofen, 338
+_Archegosaurus minor and A. medius,_ coal measures, 406, 407
+Archiac, M. de, on nummulites, 277
+——, on chalk of France, 306
+Arctic Miocene Flora, 239
+Area of the Wealden, 319
+Areas, permanence of continental, 117
+Arenaceous rocks described, 35
+_Arenicolites linearis,_ Arenig beds, 475
+Arenig or Stiper-Stones group, 474
+——, volcanic formations of, 549
+Argile plastique, 276
+Argillaceous rocks described, 36
+Argillite, Argillaceous schist, 579
+Argyll, Duke of, on Isle of Mull leaf-beds, 247
+Armagh, bone-beds in Mountain Limestone at, 437
+Arran, amygdaloid filled with spar near, 518
+——, erect trees in volcanic ash of, 546
+——, Greenstone dike in, 514
+Arthur’s seat, trap rocks of, 545
+_Arvicola,_ tooth of, 165
+_Asaphus caudatus,_ Silurian, 467
+—— _tyrannus, A. Buchii_, 474
+Ascension, lamination of volcanic rocks in, 595
+Ash, Mr., on fossils of Tremadoc beds, 483
+Ashby-de-la-Zouch, fault in coal field of, 91
+_Aspidura loricata,_ Muschelkalk, 379
+_Astarte borealis_ (=_A. arctica=A. compressa_), 176
+—— _Omalii,_ Crag, 199
+_Asterophyllites foliosus,_ Coal, 425
+_Astrangia lineata (Anthophyllum lineatum)_, 229
+_Astræa basaltiforme,_ Carboniferous, 432
+_Astropecten crispatus,_ London clay, 266
+Atherfield clay, 309
+Atlantic mud, composition of, 287
+_Atrypa reticularis,_ Aymestry, 462
+_Aturia ziczac (Nautilus ziczac)_, 266
+Augite, 499, 502
+_Auricula,_ recent, 55
+Austen, Mr. Godwin, on marine deposit of Selsea Bill, 182
+——, on boulders in chalk, 292
+Australian cave breccias, 158
+Australia, auriferous gravel of, 617
+Auvergne, alluvium in, 100
+——, chain of extinct volcanoes in, 495
+——, granite veins in, 610
+——, Lower Miocene of, 233
+——, Miocene volcanic rocks of, 540
+——, Post-pliocene volcanic eruptions in, 527
+——, springs from spent volcanoes in, 604
+Aveline Mr., on Tarannon shales, 468
+_Avicula contorta,_ Rhætic beds, 366
+—— _cygnipes,_ Lias, 355
+—— _inæquivalvis,_ Lias, 355
+—— _socialis,_ Muschelkalk, 379
+_Aviculopecten papyraceus,_ coal measures, 405
+—— _sublobatus,_ mountain limestone, 434
+Aymestry Limestone, 461
+Azoic period, supposed, 603
+Azores, Miocene lavas with shells, 539
+
+_BACILLARIA paradoxa_, 51
+_Baculites anceps,_ Lower Chalk, 298
+—— _Fauiasii,_ chalk, 286
+Baffin’s Bay, formation of drift in, 171, 173
+Bagshot sands, 258, 259, 262
+Baiæ, Bay of, subterranean igneous action in, 569
+Bakewell, Mr., on cleavage in Swiss Alps, 590
+Bala and Caradoc beds, 470
+_Balistidæ,_ defensive spine of, 261
+Bangor, or Longmynd group, 485
+_Banksia,_ seed and fruit of, Lower Miocene, 238
+Barmouth sandstones, 486
+Barnes, Mr. J., on insects in American coal, 416
+Barnstaple, Upper Devonian of, 450
+Barrande, M. Joachim, his “Primordial Zone,” 471, 482, 487
+——, on metamorphosis of trilobites, 471
+Barrett, Mr., on bird in Blackdown beds, 299
+Barton series sands and clays, 258
+—— shells, percentage of, common to London clay, 258
+Basalt, columnar, 511
+——, composition of, 504
+Basaltic rocks, poor in silica, 504
+——, specific gravity of minerals in, 504
+_Basilosaurus,_ Eocene, United States, 280
+Basset, term explained, 83
+Basterot, M. de, on Bordeaux tertiary strata, 141
+Bath Oolite, 342
+Batrachian reptiles in coal, 406
+Bay of Fundy, denudation in coalfield in, 418
+Bean, Mr., on Yorkshire Oolite, 350
+Bear Island carboniferous flora, 441
+Beaumont, M. E. de, on island in Cretaceous sea, 305
+——, on mineral veins, 613
+——, on Jurassic plutonic rocks, 571
+——, on formation of granite, 553
+Beckles, Mr. S. H., on footprints in Hastings sands, 315, 330
+—— on Mammalia of Purbeck, 326
+_Belemnitella mucronata,_ Chalk, 283
+_Belemnites hastatus,_ Oxford clay, 340
+—— _Puzosianus,_ Oxford clay, 341
+Belgium, Lower Miocene of, 241
+_Bellerophon costatus,_ Mountain Limestone, 436
+_Belosepia sepioidea,_ Sheppey, 266
+Belt, Mr., on subdivision of Lingula Flags, 484
+Bembridge beds, Yarmouth, 252
+Berger, Dr., on rocks altered by dikes, 515
+Berlin, Miocene strata near, 242
+Bernese Alps, gneiss in the, 599
+Berthier on isomorphism, 502
+Bertrich-Baden, columnar basalt of, 512
+Beyrich on term Oligocene for Lower Miocene, 244
+Billings, Mr., on trilobites, 471
+Binney, Mr., on Sigillariæ in volcanic ash, 546
+——, on Stigmaria, the root of Sigillaria, 426
+Biotite, 499, 501
+Bird in argile plastique, 276
+Bischoff, Professor, on Nile and Rhine mud, 154
+——, on conversion of coal into anthracite, 403
+——, on hydrothermal action, 586
+Blackdown beds, 301
+Blacklead of Borrowdale, 65
+Bog-iron-ore, 52
+Bohemia, Cambrian rocks of, 487
+——, silver veins in, 616
+Bolderberg, in Belgium, Upper Miocene of, 224
+Bone-bed of fish remains, Armagh, 437
+—— of Upper Ludlow, 450
+—— of the Trias, 367
+Boom, Lower Miocene of, 241
+Bordeaux, Upper Miocene of, 214
+Borrowdale, blacklead of, 65
+Bosquet, M. on chalk fossils, 283
+——, on Maestricht beds, 283
+Botanical nomenclature, 303
+Boucher de Perthes on Abbeville alluvium, 152
+Boulder-clay, whether formed by icebergs or land-ice, 166-73, 178
+Boulder-clay of Canada, 182
+—— fauna of, 176, 189
+Boulders and pebbles in chalk, 292
+Bournemouth beds (Lower Bagshot), 262
+Bovey Tracey, lignites and clays of, 246
+Bowerbank, Mr., on fossil fruits of London Clay, 265
+——, on fossil fruits of Sheppey, 265
+Bowman, Mr., on uniting of distinct coal-seams, 401
+Brachiopoda, preponderance of, in older rocks, 470
+——, mode of recognising shells of, 471
+Bracklesham beds and Bagshot Sands, 259
+Bradford encrinites, 342
+Breccias of Lower Permian, 391
+Brick-earth or fluviatile loam, 153
+Bridlington drift, 189
+Bristol, dolomitic conglomerate of, 373
+Bristow, Mr., on volcanic minerals, 500
+Brixham cave near Torquay, 158
+Brocchi on Italian tertiary strata, 141
+—— on subapennine strata, 208
+Brockenhurst, corals and shells of, 257
+Brodie, Rev. P. B., on Lias insects, 363
+Brodie, Mr. W. R., on Purbeck mammalia, 326
+Brongniart, M. Adolphe, on botanical nomenclature, 303
+——, on Lias plants, 364
+——, on flora of the Bunter, 380
+——, on flora of the coal, 420
+——, on fruit of Lepidodendron, 424
+——, M. Alex., on Tertiary series, 141
+_Bronteus flabellifer_, Devonian, 453
+Brora, oolitic coal formation of, 350
+Brown, Mr. Richard, on Stigmaria, 426
+——, on carboniferous rain-prints, 416
+Brown, Robert, on Eocene protaceous fruit, 264
+Brown, Reverend T., on marine shells in Scotch drift, 177
+Brown-coal of Germany, 540
+Bryce, Mr., on Scotch till, 176
+Bryozoa of Mountain Limestone, 433
+—— and polyzoa, terms explained, 197
+Buch, von. _See_ Von Buch.
+Buckland, Dr., on Kirkdale cave, 158
+——, on violent death of saurians, 362
+——, on spines of fish, 359
+——, on Eocene oysters, 268
+——, on pot-stones in chalk, 291
+Buddle, Mr., on creeps in coal-mines, 78
+_Bulimus ellipticus_, Bembridge, 253
+—— _lubricus_, Loess, 56
+Bullock, Capt., R.N., on Atlantic mud, 287
+Bunbury, Sir C., on leaf-bed of Madeira, 532
+——, on ferns of the Maryland coal, 421
+Bunter of Germany, 380
+—— or Lower Trias of England, 372
+_Buprestis? Elytron of_, Stonesfield, 346
+Burmeister on trilobites, 471
+
+CAINOZOIC, term defined, 123
+Caithness, fish beds of, 443
+_Calamite_, root of, 425
+_Calamites Sucowii_, coal, and restored stem, 424
+_Calamophyllia radiata_, Bath Oolite, 342
+Calcaire de la Beauce, age of the, 230
+—— grossier, fossils of the, 274
+—— siliceux of France, 273
+Calcareous matter poured out by springs, 604
+—— rocks described, 36
+—— nodules in Lias, 63
+_Calcarina rarispina_, Eocene, 275
+_Calceola sandalina_, Devonian, 453
+——, schiefer of Germany, 453
+California, aurifrous gravel of, 617
+——, gold in petrified wood of age of alluvium, 601
+_Calymene Blumenbachii_, Silurian, 466
+Cambrian Group, classification of the, 481
+Cambrian, Upper, 482
+——, Lower, 484
+——, of Sweden and Norway, 489
+——, strata of Bohemia, 487
+——, of North America, 489
+——, volcanic rocks, 549
+_Campophyllum flexuosum_, 431
+Canada, Cambrian of, 489
+——, Devonian of, 455
+——, trap-rocks of, 549
+Canadian drift, 182
+Canary, Grand, shelly tuffs of, 538
+Cantal, Lower Miocene of the, 231
+Cape Breton, rain-prints in coal-measures of, 416
+Cape Wrath, granite veins in gneiss at, 560
+Caradoc and Bala beds, 470
+Carbonate of lime in rocks, how tested, 37
+Carboniferous Group, subdivisions of the, 394
+—— flora, 420-30
+—— limestone, thickness of, 396
+——, marine fauna of the, 432
+—— Period, trap-rocks of, 545
+—— plutonic rocks, 572
+—— reptiles, 406
+—— insects, 405
+_Carcharodon angustidens_, Bracklesham, 262
+Cardiganshire, section of slaty cleavage in, 589
+_Cardiocarpon Ottonis_, Permian, 393
+_Cardita (Venericardia) planicosta_, 260
+—— _sulcata_, Barton, 259
+_Cardium dissimile_, Portland Stone, 336
+—— _rhæticum_, Rhætic Beds, 366
+—— _striatulum_, Kimmeridge clay, 336
+Carne, Mr. N., on Cornish lodes, 607
+Carpenter, Dr., on Atlantic mud, 288
+——, on Eozoon Canadense, 491
+Carrara, marble of, 599
+Carruthers, Mr., on Eocene proteaceous fruit, 265
+——, on cycads of the Purbeck, 332
+——, on leaves of calamite, 425
+——, on spores of carboniferous Lycopodiaceæ, 422
+——, on structure of sigillaria, 426
+——, on trees in volcanic ash, 547
+Cashmere, recent formations in, 146
+Cassian, St., Triassic strata of, 376
+Castrogiovanni, curved strata near, 86
+Catania, laterite formed in, 510
+——, Tertiary beds in, 206
+_Catillus Lamarckii_, White Chalk, 295
+Caucasus, absence of lakes in the, 187
+_Caulopteris primæva_, Coal, 421
+Cave-breccias of Australia, 158
+Cavern deposits with human and animal remains, 156
+Caves of Kirkdale and Brixham, 157
+Celts described, 152
+Cementing of strata, 61
+_Cephalaspis Lyelli_, Old Red, 446
+_Ceratites nodosus_, Muschelkalk, 379
+_Cerithium concavum_, Headon, 256
+—— _elegans_, Hempstead beds, 245
+—— (_Terebra_) Portlandicum, 335
+—— _plicatum_, Hempstead beds, 245
+—— _melanoides_, 268
+_Cervus alces_, tooth of, 164
+_Cestracion Phillippi_, Recent, 297
+Chabasite, 500
+Chalk, composition, extent, and origin of, 286
+—— of Faxoe, 286
+—— flints, origin of, 290
+—— fossils of the White, 293-6
+——, iceborne boulders in the, 292
+—— of North and South Europe, 305
+——, Lower White, without flints, 298
+—— marl, fossils of the, 298
+—— Period, popular error concerning, 288
+Chalk-pit with pot-stones, view of, 291
+_Chama squamosa_, Barton, 258
+Champoleon, junction of granite with Jurassic strata near, 571
+_Chara elastica, C. medicaginula_, 58
+—— _tuberculata_, Bembridge, 253
+Charpentier, M., on Alpine glaciers, 170
+——, on depression of Alps in Glacial Period, 185
+Chatham coal-field, 383
+_Cheirotherium_, footprints of, 372
+Chemical deposits in veins, 612
+—— and mechanical deposits, 60
+Chiapa, fall of volcanic dust at, 523
+Chichester, erratics near, 181
+Chili, copper pyrites with gold in, 616
+——, walls cracked by earthquake in, 87
+Chillesford and Aldeby beds, 192
+_Chimæra monstrosa_, Lias, 359
+Chlorite-schist, 579
+Chloritic series, or Upper Greensand, 298
+Christiania, Euritic porphyry at, 562
+——, granite veins in Silurian strata of, 572
+——, quartz vein in gneiss at, 561
+Chronological groups of formations, 129
+Chronology, test of, in rocks, 121
+Cinder-bed of the Purbeck, 325
+_Cinnamomum polymorphum_, Miocene, 219
+—— _Rossmässleri_, Miocene, 239
+Claiborne beds, Eocene fossils of, 279
+Clarke County, United States, Zeuglodon of, 279
+Classification of Tertiary formations, 137, 143
+——, value of shells in, 142
+_Clausilia bidens_, Loess, 56
+Clay defined, 36
+—— iron-stone defined, 404
+——, plastic, 267
+—— slate, 579
+——, Weald, 313
+Cleavage explained, 502
+——, crystalline theory of, 591
+——, mechanical theory of, 592
+—— of metamorphic rocks, 588
+_Cleidotheca operculata_, 483
+Clermont, metalliferous gneiss near, 586
+Climate of the Crags, 200
+—— of the Coal, 430
+—— of the Miocene in the Arctic regions, 240
+—— of the Post-pliocene period, 161
+Clinkstone, 506
+Clinton group, fossils of the, 479
+Clyde, buried canoes in estuary of, 146
+——, arctic marine shells in drifts of, 176
+_Clymenia linearis_, Devonian, 451
+Clymenien-Kalk of Germany, 450
+Coal, conversion into anthracite of, 403
+—— a land and swamp formation, 397
+——, cause of the purity of, 402
+——, conversion of lignite into, 403
+——, erect trees in, 411
+——, structure of the, 412
+——, vegetation of the, 420
+——, air-breathers in the, 405, 413
+Coal Period, climate of the, 430
+—— field of Virginia, 382
+—— measures of Nova Scotia, 408
+—— measures, thickness of, in Wales, 397
+—— pipes, danger of, 390
+——, rainprints in, 416
+—— seams, uniting of, 400
+Coalbrook-Dale, faults in, 88
+_Cochliodus contortus_, 437
+Cockfield Fell rocks, altered by dikes, 516
+_Coelacanthus granulatus,_ Permian, 390
+Coleoptera of Œningen beds, 223
+_Collyrites ringens,_ Inferior Oolite, 351
+Columnar structure of volcanic rocks, 510
+—— basalt in the Vicentin, 511
+Compact feldspar, 501
+Concretionary structure, 63
+Cone of Tartaret, 527, 542
+—— of Côme, 28
+Cones and craters described, 495
+——, absence of, in England, 30
+Conformable stratification, 39
+Conglomerate or pudding-stone, 36
+——, Dolomitic, of Bristol, 373
+Coniferæ of the coal-measures, 427
+Connecticut Valley, New Red Sandstone of, 381
+_Conocephalus striatus_, 488
+_Conocoryphe striata_, 488
+Conrad, Mr., on age of American cretaceous rocks, 307
+Consolidation of strata, 61
+Continents and oceans, permanence of, 117
+Contorted strata, in drift, 178
+_Conularia ornata,_ Devonian, 453
+_Conulus priscus,_ Coal, 415
+_Conus deperditus,_ Bracklesham, 262
+Conybeare and Phillips on ninety-fathom dike, 90
+Conybeare, Mr., on reptiles of the Lias, 360
+Copper lode near Redruth, 607
+Coprolite bed of Chloritic Series, 299
+—— beds of Red and Coralline crags, 197, 198
+_Coprolites of fish from the chalk_, 298
+Coral Rag, fossils of the, 339
+Coralline of White Crag, 197
+Corals of the Devonian, 451
+—— of the Mountain Limestone, 433
+——, _Neozoic type of_, 431
+——, _Palæozoic type of_, 431
+_Corbicella (Cyrena) fluminalis_, 54
+_Corbula pisum,_ Hempstead beds, 245
+Corinth, corrosion of rocks by gases near, 586
+Cornbrash or Forest Marble, 341
+Cornwall, granite veins in, 561, 582
+——, lodes in, 615
+——, mass of granite in, 552
+——, vertical sections of veins in mine, 607
+Cosequina volcano, burying of organic remains by, 523
+Crag, term defined, 192
+—— of Antwerp, 204
+——, fauna of, its relation to that of present seas, 201
+——, Norwich, 193
+——, Coralline or White, 197
+——, Red, 194
+——, tables of marine testacea in, 202
+—— deposits, climate of, 200
+_Crania_ attached to a sea-urchin, 49
+—— _Parisiensis,_ White Chalk, 294
+_Crassatella sulcata,_ Barton, 259
+Craters and cones described, 495
+——, Theory of Elevation, 496
+Craven fault, 90
+Creeps in coal-mines, 78
+Cretaceous rocks of United States, 307
+—— Period, error as to continuity of, 288
+——, flora of the Upper, 302
+—— volcanic rocks, 544
+—— plutonic rocks, 570
+—— Period, distinct mineral character of rocks in, 292
+—— rocks, classification of, 282
+—— strata, connection between Upper and Lower, 301
+Crinoidea of Mountain Limestone, 433
+Croatia, Lower Miocene beds of, 242
+Croll, Mr., on amount of subaërial denudation, 114
+Cromer forest-bed, 191
+Crop out, term explained, 83
+Crossopterygidæ, or fringe-finned fish, 443
+Crowfoot, Mr., on shells of Aldeby beds, 192
+Crust of the earth defined, 26
+Crustaceans of Old Red Sandstone, 446
+_Cryptodon angulatum,_ London Clay, 266
+Crystalline Limestone, 579
+—— rocks defined, 32
+—— schists, much alkali in the, 587
+—— theory of cleavage, 591
+Cup and Star corals, 431
+Curved strata, 73-76
+Cutch, salt-layers in the Runn of, 375
+Cuvier, M., on fauna of the Paris basin, 271
+——, on Mammalia of Paris gypsum, 231
+——, on Tertiary series, 141
+_Cyathocrinus caryocrinoides_, 433
+—— _planus_, 433
+_Cyathophyllum cæspitosum_, 451
+Cyclopean isles, beds of tuff and clay in, 529
+——, contorted strata in, 530
+_Cyclopteris Hibernica,_ Old Red, 441
+_Cyclostigma (Lepidodendron),_ Old Red, 441
+_Cyclostoma elegans,_ Loess, 56
+_Cylindrites acutus,_ Great Oolite, 345
+Cypress swamps of the Mississippi, 402
+Cyprides in the Weald Clay, 315
+_Cypridina serrato-striata_, 451
+Cypris in fresh-water deposits, 57
+—— _gibbosa, C. tuberculata, C. leguminella_, 324
+—— _striato-punctata, C. fasciculata, C. granulata_, 325
+—— _Purbeckensis, Cypris punctata_, 331
+—— _spinigera,_ Weald Clay, 315
+_Cyrena (Corbicella) fluminalis_, 54
+—— _cuneiformis,_ Woolwich Clays, 268
+—— _obovata_, 54
+—— _semistriata,_ Hempstead beds, 245
+Cystideæ of Silurian rocks, 466
+_Cythere inflata,_ coal-measures, 405
+
+DADOXYLON, fragment of coniferous wood, 428
+Dana, on volcanic minerals, 500
+Danish kitchen-middens, 146
+_Dapedius monilifer_, Lias, 358
+Darbishire on shells of Moel Tryfaen, 180
+Dartmoor, post-carboniferous granite of, 572
+—— intrusive granite at, 572
+Darwin, Mr., on foliation and lamination, 595
+——, on mammalia of South America, 160
+——, on marine saurian, 362
+——, on rise of part of South America, 72
+——, on sinking of coral reefs, 72
+——, on plutonic rocks of the Andes, 569
+——, on relationship of extinct to living types, 160
+Dates of discovery of fossil vertebrata, 464
+Daubeny, Dr., on decomposition of trachytic rocks, 586
+Daubrée, on formation of zeolites, 521
+——, on alkaline waters of Plombières, 584
+Davidson, Mr., on Spiriferina, 355
+Davis, Mr. E., on fossils of Lingula Flags, 484
+Dawkins, Mr. Boyd, on Hyæna spelæa, 158
+——, on mammalia of Cromer Forest-bed, 191
+——, on Triassic mammifer, 369
+Dawson, Dr., on Devonian flora and insects, 456, 457
+——, on Eozoon Canadense, 491
+——, on Nova Scotia coal-measures, 409
+——, on Nova Scotia coal-plants, 410, 412
+——, on Pupa vetusta, 415
+——, on reptiles and shells in Nova Scotia coal, 413
+——, on structure of calamite, 425
+——, on structure of sigillaria, 426
+Deane, Dr., on footprints in Trias, 382
+Debey, Dr., on flora and fauna of Aix, 302-04
+Dechen, M. von, on organic remains of the brown coal, 540
+——, on Cornish granite veins, 560
+De la Beche, Sir H., on granite of Dartmoor, 582
+——, on Carrara marble, 599
+——, on mineral veins, 616
+——, on Redruth copper-mine, 610
+——, on saurians of the Lias, 362
+——, on trap-rocks of New Red, 545
+——, on Welsh coal-measures, 397
+Delesse, on action of water in metamorphism, 585
+Deltas, strata accumulated in, 28
+Dendrerpeton in Coal, 413
+Denudation defined, 96
+——, subaërial, 97
+——, littoral, 102
+——, submarine, 105
+——, average annual amount of subaërial, 113
+—— of carboniferous strata, 396
+—— counteracting upheaval, 106-15, 108-15
+—— a means of exposing crystalline rocks, 563
+——, trap-dikes cut off by, 518
+—— and volcanic force antagonistic powers, 115
+Deposition, rate of, shown by fossils, 47
+Derbyshire, veins in Mountain Limestone, 608
+Derivative shells of the Red Crag, 195-203
+Desnoyers, M., on age of Faluns, 142
+——, on Eocene fossil footprints, 272
+Desor, M., on Celtic coins in lake-dwellings, 149
+Devonian Period, Upper, 450
+Middle, 450
+Lower, 453
+—— fossils of the Eifel, 534
+—— of Russia, 454
+—— of United States and Canada, 455
+—— insects of Canada, 457
+—— strata, classification of, 439-50
+Devonshire, cleavage of slate rocks in, 593
+Diabase, 505
+Diagonal, or cross-stratification, 42
+Diagram of fossiliferous rocks, 137
+—— of plutonic and sedimentary formations, 567
+Diallage, 500, 502
+_Diastopora diluviana_, Bath Oolite, 343
+Diatomaceæ forming tripoli, 51
+_Diceras Lonsdalii_, Neocomian, 310
+_Didelphys Azaræ_, Recent, 347
+_Didymograpsus geminus_, 476
+—— _Murchisonii_, 473
+Dike cutting through shale, Anglesea, 515
+—— cutting through chalk, Antrim, 515, 516
+_Dikelocephalus Minnesotensis_, 490
+Dikes defined, 30
+—— of Monte Somma, 526
+—— in Palagonia, ground-plan of, 532
+——, volcanic or trap, 513-7
+Diluvium, origin of term, 167
+Dinornis Palapteryx, of New Zealand, 160
+_Dinotherium giganteum_, 212
+Diorite, 505
+Dip and strike, terms explained, 80
+_Diplograpsus folium_, Llandeilo Flags, 474
+—— _pristis_, Llandeilo beds, 473
+Dirt-bed of the Purbeck, 331
+Dogger-bank described, 105
+Dolerite, a variety of basalt, 504
+Dolomite defined, 38
+Dolomitic conglomerate of Bristol, 373
+Downs, escarpments of North and South, 104
+Downton Sandstone, 459
+Dowson, Mr., on shells of Aldeby beds, 192
+Drew, Mr., on Hastings Sands, 316
+Drift of Ireland, 190
+—— of Norfolk cliffs, 190
+—— of Scandinavia, 174
+—— of Bridlington, 189
+—— carried by icebergs, 172
+—— shells in Canada, 183
+——, contorted strata in, 178
+——, marine shells in Scotch, 175
+Dudley Limestone, 465
+Dufrenoy, M., on granite of Pyrenees, 582
+Dumont, Professor, on Belgian Lower Eocene, 282
+Duncan, Dr., on Neozoic corals passing down to Devonian, 432
+Dundry Hill, near Bristol, section of, 130
+Dunker, Dr., on wealden of Germany, 319
+Dura Den, yellow sandstone of, 440
+
+EARTH’S crust defined, 26
+Echinoderms of Suffolk Crag, 200
+_Echinosphæronites balticus_, 472
+Egerton, Sir P., on fish of Headon series, 256
+——, on fish of the Permian, 389
+——, on fish of Penarth beds, 366
+Ehrenberg, Professor, on term Bryozoum, 197
+——, on Silurian foraminifera, 478
+——, on infusoria, 51
+Eifel Limestone, 453
+——, Lake-craters of, 534
+—— Miocene, volcanic rocks of, 539
+—— Pliocene, volcanoes of the, 534
+——, trass of the, 535
+_Elephas antiquus_, molar of, 163
+—— _meridionalis_, molar of, 163
+—— _primigenius_, molar of, 162
+Elevation craters, theory of, 496
+Elvans, term explained, 572
+—— of Ireland and Cornwall, 615
+_Elytron of Buprestis?_ Stonesfield, 346
+Emmons, Professor, on jaws of Triassic quadruped, 383
+——, on Dromatherium, 383
+Encrinites of Bradford, 342
+_Encrinus liliiformis_, Muschelkalk, 379
+Endogens, term explained, 303
+Engihoul cave, human and animal remains in, 157
+England and Wales, glaciation of, 180
+Enstatite, 501
+Eocene areas of Europe, map of, 250
+—— foraminifera, 274
+—— formations of France, 270-6
+—— of England, 252
+—— period, volcanic rocks of, 543
+——, plutonic rocks of the, 568
+——, metamorphic rocks of the, 598
+—— of France, footprints in, 272
+—— and Miocene, line between the, 230, 250
+——, term defined, 143
+—— of the United States, 278
+_Eozoon Canadense_, oldest known fossil, 492
+Epidote, 500
+Eppelsheim, Dinotherium of, 225
+Equisetaceæ of the Coal, 424
+_Equisetites columnaris_, Keuper, 376
+_Equus caballus_, tooth of, 164
+Erratic blocks, nature of, 167
+—— of Greenland, 171
+—— near Chichester, 181
+—— in the Red Crag, 201
+Erratics, Alpine, 169
+Escarpments explained, 104
+_Eschara disticha_, White Chalk, 296
+_Escharina oceani_, White Chalk, 296
+_Estheria minuta_, Trias, 370
+—— _ovata_, Richmond, Virginia, 383
+Ethridge, Mr., on Atlantic mud, 288
+——, on Devonian series, in Devon, 450
+——, on Devonian fauna, 451, 454
+——, on mollusca of Bracklesham, 260
+——, on St. Cassian fossils, 377
+Etna, built up since Newer Pliocene, 204
+——, Pliocene lavas of, 529
+Ettingshausen on Sheppey Eocene fruit, 265
+_Eunomia radiata_, Bath Oolite, 342
+_Eunotia bidens_, Atlantic mud, 288
+_Euomphalus pentangulatus_, 435
+Eurite, 557, 578
+Euritic porphyry of Norway, 562
+Evans, Mr., on Archæopteryx, 337
+Exogens, 297
+_Exogyra virgula_, Kimmeridge Clay, 336
+_Extracrinus (Pentacrinus) Briareus_, Lias, 357
+
+FALCONER, Dr., on Miocene fauna of Siwalik Hills, 226
+——, on Brixham Cave flint knives, 157
+——, on Purbeck mammalia, 326
+Faluns of Loire, recent shells in, 214
+—— of Touraine, 211
+Farnham, phosphate of lime near, 299
+_Fascicularia aurantium_, Coralline crag, 199
+Faults in coal-measures of Coalbrook Dale, 88
+—— described, 87-92
+—— often the result of repeated movements, 90
+Fauna of the crag, its relation to that of our present seas, 201
+—— of the Mountain Limestone, 430
+—— of the Paris basin, 271
+_Favosites cervicornis_, Devonian, 451
+—— _Gothlandica_, Silurian, 465
+Favre, M. E., on glaciers and moraines of the Caucasus, 187
+Faxoe, chalk of, 285
+Feldspar-porphyry, 557
+Feldspar, varieties of, 499, 500
+Feldstone, 557
+_Felis tigris_, tooth of, 166
+_Fenestella retiformis_, Magnesian Limestone, 388
+Ferns of the coal, 421
+Fife, trap-dike in, 543
+Fish, fossil of the Carboniferous, 436
+——, Eocene of Monte Bolca, 544
+——, oldest known fossil, 463
+——, number of living, 445
+——, fresh-water and marine, 58
+—— of the Upper Ludlow, 459
+—— of the Old Red Sandstone, 443-5
+—— of the Permian marl slate, 389
+—— of the brown coal, 540
+—— of the Lias, 358
+Fisherton, Greenland lemming in drift of, 161
+Fissures, filled with metallic matter, 606
+Fitton, Dr., on the Neocomian strata, 314
+Fleming, Dr., on Parka decipiens, 448
+——, on trap-dike in Fife, 546
+Flints in the Chalk, 290
+Flisk dike of Fife, 546
+Flora of the Carboniferous, 420
+——, Devonian, compared to Carboniferous, 457
+—— of the Subapennines, 208
+——, Lower Miocene of Switzerland, 235
+——, Miocene of the Arctic Regions, 239
+——, Older Pliocene of Italy, 208
+—— of the Permian, 392
+—— of the Upper Cretaceous, 302
+——, Upper Miocene of Switzerland, 215-22
+—— of the Wealden, 320
+Fluvio-marine or Norwich Crag, 193
+Flysch of the Alps, 278
+——, plutonic rocks invading, 568
+Folding and denudation of Nova Scotia Carboniferous rocks, 417
+Folds of parallel strata, arrangement and direction of, 93
+Foliation of crystalline rocks, 595
+——, irregularities in, 596
+Folkestone and Hythe beds, 308
+Fontainebleau, Gres de, 230
+Footprints in Potsdam sandstone, 490
+—— _of reptiles in Coal-measures_, 408
+——, _fossil in New red_, 381
+—— in Paris gypsum, 272
+Foraminifera, Eocene, 275
+—— of Mountain Limestone, 437
+—— of the Chalk, 287
+Forbes, Mr. David, on glass cavities in quartz, 555
+——, on planes of foliation, 595
+——, on specific gravity of quartz, 500
+——, on volcanic minerals, 498
+Forbes, Professor E., on fossils of Bembridge beds, 252
+——, on Hempstead beds, 244
+——, on shells of the crag, 200
+——, on sphæronites, 472
+——, on subdivisions of the Purbeck, 333
+——, on testacea of the Faluns, 212
+——, on thickness of Upper Neocomian, 309
+Forest-bed at Cromer, 191
+—— marble or cornbrash, 341
+——, submerged, 103, 104
+——, fossil in Coal, 400
+——, fossil of Isle of Portland, 332
+Forfarshire, Cephalaspis beds of, 446
+——, contorted strata in, 178
+Formation, term defined, 27
+Fossil, term defined, 29
+—— trees erect in coal, 410
+—— Fish of Old Red Sandstone, 442
+Fossiliferous groups, table of succession of, 131
+Fossils, arrangement of, in strata, 47
+——, destruction of, in older formations, 139
+——, fresh-water and marine, 52
+—— obliterated by metamorphic action, 603
+——, recent, and Post-pliocene, 154-65
+—— of the drift, 176, 180, 192
+—— of the Crags, 193-203
+——, Upper Miocene, 214-29
+——, Lower Miocene of Switzerland, 236
+—— of the Hempstead Beds, 244
+——, Eocene, 253
+—— of the Barton Clay, 259
+—— of the White Chalk, 293
+—— of the Neocomian, 309
+—— of the Oolite, 324
+—— of the Stonesfield Slate, 347
+—— of the Lias, 354
+—— of the Trias, 370
+—— of the Magnesian Limestone, 387
+—— of the Coal, 405
+—— plants of the Coal, 421
+—— of the Mountain Limestone, 430
+——, Devonian, 449
+——, Silurian, 460
+——, Cambrian, 484
+—— Laurentian, 492
+Fournet, M. on metalliferous gneiss, 586
+——, on veins in granite, 610
+Fox, Rev. D., on Isle of Wight Eocene fossils, 254
+Fox, Mr. R., on lodes in Cornwall, 614
+Fractures of strata, and faults, 87
+Fragments, included, a test of age of plutonic rocks, 565
+——, included, a test of age of strata, 129
+—— a test of age in volcanic rocks, 524
+France, Eocene formations of, 270-6
+——, Lower Miocene of, 231
+——, Upper Miocene of, 211
+Freshfield, Mr., on absence of lakes in the Caucasus, 187
+Fresh-water strata, how distinguished from marine, 53-9
+—— formation of Auvergne, 233
+Fucoid sandstones of Sweden, 489
+_Fulgur canaliculatus_, Maryland, 228
+Fuller’s earth, fossils of the, 348
+Fundy, Bay of, fossil trees exposed in cliffs at, 412
+_Fusilina cylindrica_, 438
+Fusion of quartz, 500
+_Fusus contrarius (Trophon antiquum)_, 196
+—— _quadricostatus_, Maryland, 228
+
+GABBRO, 505
+_Gaillonella ferruginea_, and _G. distans,_ 52
+Galapagos Islands, living marine saurian in, 362
+_Galeocerdo latidens_, Bracklesham, 262
+_Galerites albogalerus_, White Chalk, 294
+Galestes in Middle Purbeck, 328
+Ganoids, the type of Old Red Sandstone fish, 443
+—— of the Wealden, 316
+—— of the Trias, 383
+Gaps in the sequence of fossil remains, 138
+Garnet, 500
+Gases, corrosion of rocks by, 586
+Gaudin on Lower Miocene of Switzerland, 236
+—— on Pliocene flora of Italy, 209
+—— on Proteaceæ in Bournemouth Eocene, 263
+Gault, thickness and fossils of, 300
+Geikie, Mr. A., on Ayrshire Permian trap-rocks, 545
+——, on subaërial denudation, 115
+——, on ice erosion of lake-basins, 187
+——, on Isle of Mull volcanic rocks, 539
+——, on Pentland Old Red volcanic rocks, 548
+——, on Silurian metamorphic rocks, 602
+——, on syenite of Skye, 568
+Geinitz, M., on Permian flora, 393
+Gemunder Maar, volcanic rocks of, 534
+Geneva, Lower Miocene of, 236
+Geology defined, 25
+Gergovia, tuffs and associated lacustrine strata of, 542
+Germany, Lower Miocene of, 242
+——, Triassic fauna of, 375
+Gers, Upper Miocene of, 215
+_Gervillia anceps_, Neocomian, 310
+—— _socialis_, Muschelkalk, 379
+Giant’s Causeway basalt, age of, 248
+——, laterite of the, 509
+——, columnar basalt of, 510
+Girgenti, Newer Pliocene of, 207
+Glacial drift, distribution and nature of, 166
+—— epoch in the Post-pliocene, 166
+—— formations of Pliocene age, 189-92
+Glaciation of Russia and Scandinavia, 174
+—— of Scotland, 175
+—— of Wales and England, 180
+—— of North America, 182
+Glaciers, transporting and abrading power of, 168
+Glasgow, marine strata near, 146
+Glauconie grossiere, 275
+Glen Tilt, junction of granite and schist at, 559
+Globiform pitchstone, 512
+_Globigerina bulloides_, 288
+Globular structure of volcanic rocks, 510
+_Glyptostrobus, Europæus,_ Œningen, 223
+Gneiss, granite veins traversing, 560
+—— defined and figured, 577
+——, fundamental, of Scotland, 493
+Gold mines of Australia and Chili, 616
+—— veins of Russia, 616
+—— of California, of age of alluvium, 617
+Goldenberg, Professor, on Saarbrück coal insects, 406
+Goldfuss, Professor, on reptiles in coal, 406
+_Goniatites crenistria_, 436
+—— _Listeri,_ coal-measures, 405
+Göppert, on American forms in Swiss Miocene flora, 223
+—— on petrification, 68
+—— on plants of coal-measures, 398
+_Gorgonia infundibuliformis,_ Permian, 388
+Graham’s Island, forming ashy conglomerate, 549
+Grampians, Old Red conglomerates of, 73
+——, trap-rocks of the, 547
+——, former glaciers in the, 175
+Grand Canary, Upper Miocene, shelly tuffs of, 558
+Granite, composition of, 552
+——, graphic and columnar, 553, 554
+——, how far connected with trap-rocks, 558
+——, hydrothermal action in formation of, 555
+—— metamorphosing fossiliferous strata, 581
+——, porphyritic, 556
+——, oldest, 574
+——, protrusion of solid, 574
+——, passage of, into trap, 558
+——, schorly, 557
+—— veins, 559
+—— veins in talcose gneiss, 560
+Granton, angiosperm found in coal at, 429
+Graptolites of Llandeilo flags, 474
+_Graptolites Murchisonii._ Llandeilo flags, 473
+_Graptolithus priodon,_ Silurian, 467
+Gray’s, Essex, pachyderms found at, 161
+Great (or Bath) Oolite, 342
+Greece, Upper Miocene formations of, 226
+Greenland, continental ice of, 170
+——, gradual sinking of, 72
+Greenstone, 505
+Gres de Beauchamp, Paris basin, 273
+Gres de Fontainebleau, age of the, 230
+Griffiths, Sir R., on yellow sandstone of Ireland, 441
+Grit defined, 36
+Groups, older, rise highest above the sea, 139
+—— why the newest to be studied first, 140
+_Gryllacris lithanthraca,_ coal, 405
+_Gryphæa_ coated with _serpulæ_, 48
+—— _columba,_ Chloritic Sand, 300
+—— _convexa,_ Chalk, 295
+—— _incurva (G. arcuata)_, 54, 354
+—— _virgula,_ Kimmeridge clay, 336
+Gryphite Limestone, 354
+Guadaloupe, glass cavities in quartz of, 555
+Gulf-Stream, probable abrading power of, 105
+Gümbel, M., on Rhætic beds, 366
+Gunn, Mrs., on pot-stones in the chalk, 291
+Gutbier, Colonel, on Permian flora, 393
+Gymnogens, term explained, 303
+Gypseous marls of Auvergne, 233
+Gypsum and gypseous marl defined, 38, 39
+_Gyrolepis tenuistriatus,_ Rhætic beds, 367
+
+HAIME, Mr., on palæozoic corals, 431
+_Hakea silicina_ and _Hakea saligna,_ Œningen, 222
+Hall, Captain Basil, on Cyclopean Isles, 530
+Hall, Sir James, on curved strata, 75
+Hall, Mr. J., on Appalachian palæozoic rocks, 110
+Hallstadt and St. Cassian beds, 376
+_Halysites catenularis,_ Silurian, 465
+Hamilton, Sir W., on eruption of Vesuvius, 1779, 526
+_Hamites spiniger,_ Gault, 301
+Hancock, Mr., on Protosaurus in Permian, 390
+Harkness, Professor, on Silurian metamorphic rocks, 602
+Harlech grits, fossils of the, 486
+Harris, Major, on the Salt Lakes, 374
+_Harpactor maculipes,_ Œningen, 224
+Harpe, M. de la, on Bournemouth Eocene flora, 263
+Hartung, Mr., cited, 496
+Hartz mountains, mineral veins of, 608
+——, Bunter Sandstein of, 380
+Hastings Sands, subdivisions of the, 316
+Hautes Alpes, granite of the, 571
+Hauy on isomorphism, 502
+Headon series, fossils of the, 255
+Heat, powerful in consolidating rocks, 65
+——, rocks upraised and folded by, 92
+Hébert, M., on age of Sables de Bracheux, 330
+——, comparison of Sables Moyens and Barton shells, 258
+——, on pisolitic limestone, 285
+Hebrides, dikes in the, 514
+Heer, Professor, on American genera in Swiss Miocene, 239
+——, on age of Madeira leaf-bed, 532
+——, on Arctic Miocene flora, 239
+——, on Bear Island flora, 441
+——, on Bovey Tracey Miocene flora, 247
+——, on fossil plants of Switzerland, 215, 219, 221, 224, 236
+——, on Lower Miocene plants of Mull, 248
+——, on Monte Bolca Eocene plants, 263, 543
+——, on Proteas of Lower Miocene, 237
+——, on plants of Hempstead beds, 246
+——, on plants of coal-field, Virginia, 383
+——, on Swiss Miocene insects, 223
+——, on supposed Proteaceæ of Œningen beds, 221
+——, on Superga fossil plants, 244
+Heidelberg, varieties of granite near, 560
+_Heliolites porosa_, Devonian, 451
+_Helix hispida (plebeia)_, 155
+—— _labyrinthica,_ Headon, 255
+—— _occlusa,_ Bembridge, 253
+—— _Turonensis,_ faluns, 56
+_Hemicidaris Purbeckensis,_ Purbeck, 324
+_Hemipneustes radiatus,_ Chalk, 284
+_Hemitelites Brownii,_ Inferior Oolite, 350
+Hempstead beds, subdivisions of the, 244
+Henry, on absorption of carbonic acid gas in water, 585
+Henslow, Professor, on dike in Anglesea, 515
+——, on Red Crag coprolite bed, 197
+Herschel, Sir J., on slaty cleavage, 590
+Hertfordshire pudding-stone, 62
+_Heterocercal tail of fish_, 389
+Hicks, Dr., on fossils of Arenig beds, 476
+——, on fossils of Harlech grits, 486
+——, on Menevian beds, 485
+Himalaya, shells 18,000 feet high in, 29
+——, Upper Miocene of, 226
+_Hippopodium ponderosum,_ Lias, 355
+_Hippopotamus, tooth of_, 164
+Hippurite Limestone, 304
+_Hippurites organisans,_ Chalk, 306
+_Histioderma hibernica_, 486
+Hitchcock, Professor, on Trias footprints, 381
+_Holoptychius nobilissimus,_ scale of, and restoration, 442
+_Homalonotus Delphinocephalus_, 467
+—— _armatus,_ Devonian, 454
+Homfray, Mr., on fossils of Tremadoc beds, 483
+_Homocercal tail of fish_, 389
+Hooghly River, analysis of water, 69
+Hooker, Dr., on coniferæ, 429, 430
+——, on structure of sigillaria, 426
+——, on sporangia of Silurian plant, 460
+Horizontality of strata, 40
+Horizontal strata, upheaval of, 71
+Hornblende, 499, 502
+Hornblende-schist, 578
+Hörnes, Dr., on fossil mollusca of Vienna basin, 225
+Horstead, pot-stones at, 291
+Hour-glass illustrating the destruction and renovation of land, 119
+Howse, Mr., on Protosaurus in Permian, 390
+Hubbard, Professor, on granite of White Mountains, 565
+Hudson River Group, fossils of the, 479
+Hughes, Mr. T. McKenny, cited, 450
+——, on slaty cleavage, 589
+——, on protrusion of solid granite, 575
+Hull, Mr. E., on breccias in Permian, 391
+——, on carboniferous of Lancashire, 395
+——, on carboniferous rocks of north of England, 111
+——, on faults in Lancashire coal-field, 91
+——, on anticlinals and synclinals, Lancashire, 85
+——, on thickness of the Upper Trias, 369
+——, on thickness of Permian, 386
+——, on three lines of flexure since the coal in Lancashire, 94
+Human remains of Recent Period, 157
+—— in cavern deposits, 156
+Humboldt, on mineral character of rocks, 602
+Humphrey and Abbot on Mississippi denudation, 114
+Hungary, trachyte of, 558
+Hunt, Sterry, on action of water in metamorphism, 585
+Huronian series, thickness of the, 490
+Huxley, Professor, on Atlantic chalk-mud, 287
+——, on affinity between reptiles and birds, 338
+——, on batrachians of the coal, 407
+——, on fish of Old Red Sandstone, 443-5
+——, on Pteraspis, 463
+Hyæna den of Kirkdale cave, 157
+_Hyæna spelæa,_ tooth of, 165
+_Hybodus plicatilis,_ Rhætic beds, 367
+—— _reticulatus,_ Lias, 359
+Hydrothermal action producing metamorphism, 584
+—— in formation of granite, 555
+—— forming granite veins, 573
+_Hymenocaris vermicauda_, 484
+_Hyperodapedon Gordoni,_ Trias, 370
+Hypersthene, 499, 502
+—— rock, 505
+—— rocks of Skye, 491
+Hypogene rocks, uniformity of mineral character in, 602
+—— rocks, term defined, 26
+_Hypsiprymnus Gaimardi,_ molar of recent, 327
+Hythe, Neocomian beds of, 308
+
+ICE, erosion of lake-basins considered, 184, 188
+——, abrading power of, 168
+——, continental, of Greenland, 170
+Icebergs, drift carried by, 172
+—— stranded in Baffin’s Bay, 173
+Ice-borne erratics at Chichester, 181
+Iceland, glass cavities in quartz of, 555
+——, flow of lava in, 523
+_Ichthyosaurus communis,_ Lias, 361
+Idocrase, 500
+Ichthyodorulite of the Lias, 359
+_Iguanodon Mantelli,_ Weald Clay, 315
+Ilfracombe Group of Devon, 449
+Inclined strata, 73
+India, Miocene formations of, 226
+India, Upper Miocene of, 226
+Inferior Oolite, thickness and fossils of, 349
+Infusoria in tripoli, 51
+Inland sea-cliffs, 103
+_Inoceramus Lamarckii,_ White Chalk, 295
+Insect in American coal, 416
+—— beds of the Lias, 363
+_Insect wing of neuropterous_, 363
+Insects, Devonian, of Canada, 457
+—— in European coal, 405
+——, Miocene, of Croatia, 243
+——, Upper Miocene, at Œningen, 223
+Intrusion, a test of age of Plutonic rocks, 565
+——, a test of age of volcanic rocks, 521
+Inundation mud of rivers, 153
+Ireland, glacial drift of, 190
+——, yellow sandstone of, 441
+Iron pyrites, 500
+—— weapons of Swiss lake-dwellings, 148
+_Isastræa oblonga,_ Portland Sand, 335
+Isle of Bourbon, lava current of the, 566
+—— Wight, Hempstead beds, 244
+—— Wight, Eocene beds, 255
+—— Mull, Miocene leaf-bed of, 247
+—— Mull, volcanic rocks, 248
+Isomorphism, theory of, 502
+Italy, Lower Miocene of, 244
+——, Older Pliocene volcanoes of, 523
+——, Pliocene of, 207
+——, Older Pliocene flora of, 208
+——, Upper Miocene strata of, 226
+
+JAMIESON, Mr. T. F., on Scotch glacial drift, 175
+Jaws of mammalia in Purbeck, 327
+Jeffreys, Mr. Gwyn, on Atlantic mud, 288
+Jointed structure of metamorphic rocks, 589
+Jones, Dr. Rupert, on Eozoon Canadense, 491
+Jorullo, lava stream of, 566
+Judd, Mr., on Speeton clay, 311
+Jukes, Mr., on Tarannon shales, 468
+Jura, erratic blocks on the, 169
+——, structure of the, 82
+
+KANGAROO, jaws of, 159
+Käsegrotte, Bertrich Baden, Basaltic pillars of, 512
+Kaup, Professor, on footprints of the Trias, 373
+Keilhau, Professor, on granite veins, 562
+——, on planes of foliation, 595
+——, on Silurian granite of Norway, 573
+——, on protrusion of granite, 581
+Keller, Dr. F., on lake-dwellings, 148
+Kelloway Rock, percentage of Oxford clay fossils in, 341
+Kentish Rag, 308
+Keuper, of Germany, 375
+—— or Upper Trias of England, 369
+Kilkenny, fossil plants of, 441
+Killas, altered by granite in Cornwall, 582
+Kiltorkan, yellow sandstone of, with Anodonta, 441
+Kimmeridge Clay, 335
+King, Dr., on reptile footprints in coal, 407
+King, Mr., on Permian fossils, 388
+Kirkdale cave, hyæna’s den of, 157
+Kitchen-middens of Denmark, 146
+Kleyn Spawen beds, 242
+Könen, Baron von, on Brockenhurst shells, 257
+Koninck, M. de, on Mountain Limestone fish, 436
+——, on shells of Mayence basin, 242
+_Koninckia Leonhardi,_ Hallstadt, 377
+
+LABRADOR rock, 505
+—— series, 490
+Labradorite, 499, 501
+_Labyrinthodon Jægeri, section of tooth_, 371
+——, _tooth of_, 370
+Labyrinthodonts of Coal, 407
+Lake-craters of the Eifel, 534
+Lake districts, southern limits of the, 184
+Lake-dwellings, scarcity of human remains in, 149
+—— of Switzerland, 148
+Lakes, deposits in, 27
+——, connection of, with glacial action, 184-8
+Lamarck on bivalve mollusca, 54
+Lamination of clay slate, 594
+_Lamna elegans,_ Bracklesham, 262
+Lancashire, vast thickness of rocks without corresponding altitude in,
+111
+Land, balance of dry, how preserved, 116, 118
+—— has been raised, not the sea lowered, 70
+——, mean height of, above the sea, 115
+——, rise of, in Sweden, 72
+——, rise and fall of, affecting denudation, 101
+Land-ice, action of, in Greenland, 171
+Land’s End, columnar granite at, 553
+——, porphyritic granite at, 556
+La Roche, recent deposits in estuary of, 40
+Lartet, M., on mammalia of Faluns, 214
+——, on Gastornis Parisiensis, 276
+——, on reindeer period, 150
+_Lastræa stiriaca,_ Monod, 239
+Lateral compression causing curved strata, 75
+Laterite of Giant’s Causeway, 509
+Laurentian gneiss of Scotland, 493
+—— Group, Upper and Lower, 491
+—— metamorphic rocks, 601
+—— volcanic rocks, 549
+Lava, 507
+—— consolidating on slopes, 496
+—— currents of Auvergne, 541
+—— streams, effect of, 30
+—— of La Coupe d’Ayzac, 511
+—— of Jorullo, 566
+Lead veins, age of, 616
+Leaf-bed of Madeira in basalt and scoriæ, 532
+——, Isle of Mull Miocene, 248
+_Leda amygdaloides,_ London Clay, 266
+—— _Deshayesiana (Nucula Deshayesiana)_, 241
+—— _lanceolata (L. oblonga),_ Scotch drift, 176
+—— _truncata,_ Scotch drift, 177
+Lee, Mr. J.E., on Pteraspis of Lower Ludlow, 463
+Leidy, Dr., on fossil quadrupeds of Nebraska, 249
+_Leperditia inflata,_ coal-measures, 405
+_Lepidodendron,_ Griffithsii, 441
+—— _corrugatum,_ carboniferous., 417
+—— _Sternbergii,_ coal-measures, 423
+Lepidolite, 499, 501
+_Lepidostrobus ornatus,_ Coal, 424
+_Lepidotus gigas,_ Lias, 358
+—— _Mantelli,_ Wealden, 317
+_Leptæna depressa,_ Wenlock, 466
+—— _Moorei,_ Lias, 355
+Level of surface altered by change of subterranean heat, 119
+Lewis, hornblendic gneiss of, 601
+Lias, fishes of the, 358
+——, fossils of the, 354
+—— and Oolite, origin of the, 364
+——, reptiles of the, 360
+——, insects of the, 363
+——, plants of the, 364
+——, plutonic rocks of the, 571
+——, subdivisions of the, 353
+——, volcanic rocks of the, 544
+Liebig, on conversion of coal into anthracite, 403
+——, on origin of stalactite, 156
+Liége, limestone caverns at, 156
+Lightbody, Mr., on Lower Ludlow shales, 461
+Lignite, conversion of into coal, 403
+_Lima giganteum_, 354
+—— _Hoperi,_ Chalk, 300
+—— _spinosa,_ White Chalk, 294
+Limagne d’Auvergne, Lower Miocene mammalia of the, 234
+Limburg beds, 242
+Lime, scarcity of, in metamorphic rocks, 604
+—— in solution, source of, 69
+Limestone, block of striated, 168
+——, brecciated, 387
+—— of chemical and organic origin, 61
+——, compact, 501
+——, Hippurite, 304
+——, magnesian, 387
+——, metamorphic or crystalline, 579
+——, Mountain, and its fossils, 430-8
+——, striated, 168
+_Limnæa longiscata_, 55
+Lingula beds, volcanic tuffs of the, 549
+_Lingula Credneri_, Permian, 388
+Lingula Flags, fossils of the, 484
+_Lingula Dumortieri,_ Crag, 200
+—— _Lewisii,_ Ludlow, 462
+_Lingulella Davisii_, 484
+Lipari Isles, tufas in, 586
+_Liquidambar europæum_, 209
+_Lithrostrotion basaltiforme,_ Carboniferous, 432
+Lits coquilliers, 275
+Littoral denudation defined, 102
+_Lituites giganteus,_ Ludlow, 463
+Llanberis slates, 486
+Llandeilo Flags, fossils of the, 473-5
+Llandeilo formation, thickness of the, 475
+——, Lower, 475
+Llandovery Group, classification of the, 468
+—— Rocks, thickness of the Lower, 469
+Loam defined, 38, 153
+Lodes, shells and pebbles in, 608
+—— _See_ Mineral Veins.
+Loess of fluviatile loam described, 153
+——, fossil shells of the, 154
+Logan, Sir W., on Eozoon Canadense, 490
+——, on Gaspe sandstones, 455
+——, on Huronian and Laurentian, 490
+——, on stigmaria in under-clays, 398
+——, on thickness of Nova Scotia coal, 409
+——, on thickness of Laurentian in Canada, 113
+Loire, faluns of the, 211
+London Clay, fossils of the, 264, 266
+Longevity, relative, of mammalia and testacea, 162
+Longmynd Group, fauna of the, 486
+Lonsdale, Mr., on corals of America, 229
+——, on Devonian fossils, 449
+——, on Stonesfield slate, 345
+——, on United States Miocene corals, 229
+_Lonsdaleia floriformis,_ Carboniferous, 432
+Lowe, Reverend R. T., on Mogador shells, 537
+Lubbock, Sir J., on the two stone-periods, 147
+_Lucina serrata,_ Bracklesham, 262
+Ludlow formation, Upper, 459; Lower, 461
+——, bone-bed of the Upper, 459
+Lulworth Cove, dirt-bed of, 333
+Lycett, Mr., on fossils of the Great Oolite, 344
+Lycopodiaceæ of Coal, 422
+_Lycopodium densum,_ living species, 423
+Lym-fiord, mingled fresh-water and marine strata of, 59
+_Lymnea caudata,_ Headon, 256
+—— _longiscata,_ Bembridge, 253
+Lynton Group of Devon, 454
+
+MACLAREN, Mr., on Pentland Hills, volcanic rocks, 548
+Macclesfield, marine shells 1,200 feet high at, 181
+MacClintock, Sir L., on Atlantic mud, 287
+MacCulloch, Dr., on Aberdeenshire granite, 558
+——, on basaltic columns in Skye, 510
+——, on formation of hornblende-schist, 582
+——, on trap, 519
+MacMullen, Mr. J., on Eozoon Canadense, 491
+_Macropus atlas,_ lower jaw of, 158
+—— _major_ (living), lower jaw of, 159
+Madeira, beds of laterite in, 509
+——, dike in valley in, 513
+——, Pliocene leaf-bed and shells in lavas of, 532
+——, Miocene volcanic rocks of, 536
+——, wind, removing scoriæ in, 97
+Maestricht beds and their fossils, 283
+Maffiotte, Don Pedro, cited, 538
+_Magas pumila,_ White Chalk, 294
+Magnesian Limestone defined, 38
+—— and marl-slate, 387
+Magnetite, 500
+Maidstone, Upper Cretaceous fossils of, 297
+Malacolite, 502
+Malaise, Professor, on Engihoul cave, 157
+Mammalia, anterior to Paris gypsum, table of, 329
+——, extinct, coeval with man, 152, 157
+——, fossil, of Middle Purbeck, 325
+——, fossil, in Pliocene in Val d’Arno, 208
+——, fossil, in the Crag, 193, 197
+——, fossil, of Vienna basin, 225
+—— of the Limagne d’Auvergne, 234
+—— of Siwalik Hills, 227
+—— of the Stonesfield slate, 345
+——, _teeth of Post-pliocene_, 165
+Mammalia and testacea, comparative longevity of, 162
+Mammoth, rude carving of in Perigord cave, 150
+—— in Scotch till, 175
+—— _See_ Elephas primigenius.
+Man, antiquity of, 152
+Manfredi on amount of subaërial denudation, 114
+Mantell, Dr., on iguanodon of Wealden, 313
+——, on Oxford Clay belemnites, 340
+——, on Wealden fossils, 316
+_Mantellia nidiformis,_ Purbeck, 331
+Map of Chalk formation in France, 305
+—— of Eocene tertiary basins, 250
+—— of Hallstadt and St. Cassian beds, 376
+Marble defined, 37
+—— of Carrara, metamorphic, 599
+Marcou, M., on age of Wealden beds, 319
+Margaric acid, 591
+Marine fauna of the Carboniferous, 432
+—— beds underlying the London Clay, 269
+—— and brackish-water strata in coal, 404
+—— strata, how distinguished from fresh-water, 53-59
+Marl from Lake Superior, 63
+—— and marl-slate defined, 38
+——, red, green, and white, of Auvergne, 233
+—— slate of Middle Permian, 387
+Marsupials, extinct, of Australia, 159
+_Marsupites Milleri,_ White Chalk, 294
+Massachusetts, plumbago of, 583
+_Mastodon arvernensis,_ molar of, Norwich crag, 193
+—— _giganteus,_ in United States after the drift, 183
+Mayence basin tertiaries, 242
+May-Hill Sandstone, 468
+Mechanical and chemical deposits, 60
+—— theory of cleavage, 592
+Mediterranean, one zoological province, 127
+_Megalodon cucullatus,_ Devonian, 452
+_Melania inquinata (Cerithium melanoides)_, 55, 268
+_Melania turritissima,_ Bembridge, 253
+_Melanopsis buccinoidea_, 55
+Melaphyre, a variety of basalt, 504
+Menevian beds and their fossils, 484
+Mesozoic, term explained, 123
+—— and Cainozoic periods, gap between the, 282
+—— and Palæozoic rocks, limits of the, 385
+Metals, relative age of different, 614
+Metamorphic limestone, 579
+—— strata, origin of, 579
+—— theory, objections to, considered, 587
+—— rocks defined, 32
+Metamorphic rocks, 576
+——, cleavage of, 588
+——, scarcity of lime in, 604
+——, ages of, 597
+——, order of succession of, 602
+——, uniformity of mineral character in, 602
+Metamorphism, hydrothermal action producing, 584
+Metamorphosis of trilobites, 471, 487
+Meteorites, minerals in, 501
+Mexico, Gulf of, terrestrial remains washed into, 128
+Meyer, Mr. Karl, on fossil shells of Madeira, 537
+——, M. H. von, on reptiles in coal, 407
+——, on Wealden of Germany, 319
+Miascite, 558
+Mica and its varieties, 499, 501
+——, how deposited, 40
+—— schist or micaceous schist, 578
+Micaceous sandstone, origin of, 36
+_Micraster cor-anguinum_, 294
+_Microconchus carbonarius,_ coal-measures, 405
+_Microlestes antiquus,_ Upper Trias, 368
+Migrations of quadrupeds, 161
+Miliolite limestone, 274
+Miller, Hugh, on Old Red Sandstone fish, 443
+——, on salt lakes, 375
+Milne Edwards, Mr., on Palæozoic corals, 432
+Minchinhampton, Great Oolite of, 344
+Mineral composition a test of age of volcanic rocks, 523
+—— a test of age of plutonic rocks, 565
+—— a test of age of strata, 124
+—— character of hypogene rocks, 602
+—— springs of Auvergne, 604
+Mineral veins, 605
+—— formed in fissures, 606
+——, successive formation of, 609
+——, swelling and contraction of, 611
+——, relative age of, 614
+——, pebbles in, 608
+Mineralisation of organic remains, 65
+Minerals in meteorites, 501
+——, table of the most abundant in hypogene rocks, 499
+Miocene of Bordeaux and south of France, 214
+—— and Eocene, line between the, 230, 251
+——, Lower, of England, 244
+——, Lower, of Germany and Croatia, 242
+——, Lower, of Central France, 231
+——, Lower, of Italy, 244
+——, Lower, of Nebraska, United States, 248
+——, term defined, 143
+——, Upper, of the Bolderberg, 224
+——, Upper, of France, 211
+——, Upper, of Italy, 226
+——, Upper, of Greece, 226
+——, Upper, of India, 226
+——, Upper, of Vienna basin, 224
+Mississippi, sediment of, used as a test of denudation by rivers, 114
+—— valley, deposition and denudation in the, 102
+Mitchell, Mr., on Aralia fruit in Alum Bay, Eocene, 263
+Mitchell, Sir T., on Wellington caves, 158
+Mitchell, Rev. Hugh, on Pteraspis, 446
+_Mitra Scabra,_ Barton clay, 259
+Mitscherlich, on Isomorphism, 502
+_Modiola acuminata,_ Permian, 387
+Moel Tryfaen, shells found at, 181
+Mohs on isomorphism, 502
+Molasse, Lower, of Switzerland, 235
+——, Middle, or Marine, of Switzerland, 223
+——, Upper, fresh-water, of Switzerland, 217
+——, term explained, 217
+Mollusca. _See_ Shells.
+——, longevity of species of, 162
+—— of Hallstadt beds, 377
+——, value of, in classification, 142
+—— of the Carboniferous, 435
+Monitor of Thuringia, 463
+Monoclinic feldspars, 501
+Monod, flora of the Lower Molasse at, 236
+Mons, unconformable strata near, 95
+Montblanc, talcose granite of, 568
+—— Dor, Auvergne, extinct volcanoes of, 232
+——, age of volcano of, 541
+Monte Bolca, fossil fish of, 543
+—— Calvo, section of cross stratification, 44
+—— Mario, age of volcanic deposits of, 533
+—— Nuovo, formed 1538, 525
+Montmartre, gypseous series of, 270
+Monts Dome, Auvergne, extinct volcanoes, 495
+Moore, Mr. C., on Rhætic beds, 366
+——, on Upper Trias quadrupeds, 369
+Moraines described, 169
+Morea, cretaceous volcanic rocks of, 544
+Mortillet, M. de, on ice-erosion of lake-basins, 184
+Morton, Dr., on age of American cretaceous rocks, 307
+_Mosasaurus Camperi,_ Chalk, 284
+Mountain Limestone, fossils of the, 433-8
+Mull, Isle of, leaf-bed, 247
+Münster, Count, on fossils of Solenhofen, 337
+Murchison, Sir R., on brackish-water strata in coal, 404
+——, on Devonian series, 439, 449, 454
+——, on Devonian ichthyolites, 453
+——, on Eocene igneous rocks, 278
+——, on Llandovery beds, 468
+——, on Laurentian gneiss of Scotland, 492
+——, on metamorphic rocks of North Highlands, 601
+——, on Monte Bolca fish-beds, 543
+——, on name Permian, 385
+——, on Old Red Sandstone, 449
+——, on Palæozoic strata, Queenaig, 112, 113
+——, on protrusion of solid granite, 574
+——, on Silurian, 458, 459, 461, 467, 470, 473, 475
+——, on Tertiary volcanic rocks of Italy, 533
+——, on thickness of chalk in Russia, 287
+——, on thickness of the Trias, 369
+——, on the Upper “Old Red”, 468
+_Murchisonia gracilis_, 479
+_Murex vaginatus_, 204
+Muschelkalk, fossils of the, 378
+Muscovite, or common mica, 499, 501
+Musk-ox, fossil, in Thames valley, 161
+_Myliobates Edwardsi,_ Bracklesham, 261
+_Mytilus septifer,_ Permian, 387
+
+NAPLES, Post-pliocene volcanic rocks of, 525
+——, escape of carbonic acid near, 604
+_Natica clausa,_ Scotch drift, 176
+—— _helicoides,_ Chillesford beds, 192
+Natrolite, 500
+_Nautilus centralis,_ London Clay, 266
+—— _Danicus,_ Faxoe Chalk, 286
+—— _plicatus,_ Hythe beds, 309
+—— _truncatus,_ Lias, 356
+—— _ziczac (Aturia ziczac)_, 266
+Nebraska, Miocene strata of, 248
+Necker, M., on “underlying” igneous rocks, 562
+——, on dikes in Vesuvius, 526
+Neocomian, Upper, 308
+——, Middle, 312
+——, Lower, 312
+——, use of the term, 282
+Neolithic era, 147
+Neozoic type of corals, 431
+_Nerinæa Goodhallii,_ Coral Rag, 339
+Nerinæan limestone, 340
+_Nerita conoidea (N. Schmidelliana)_, 275
+—— _costulata,_ Great Oolite, 345
+—— _granulosa_, 55
+_Neritina concava,_ Headon, 255
+—— _globulus_, 55
+Neufchâtel, coins and iron tools in lake of, 149
+Newberry, Dr., on flora of American cretaceous rocks, 307
+Newcastle coal-field, faults in, 90
+Newfoundland bank described, 106
+New Jersey, mastodon in, 183
+New Madrid, “Sunk Country” in, 402
+New Red sandstone of Connecticut Valley, 381
+——, trappean rocks of the, 545
+New York, Devonian strata of, 456
+——, Cambrian strata of, 490
+——, Silurian strata of, 478
+——, Laurentian strata of, 491
+Niagara Limestone, fossils of the, 479
+Nidau, iron tools in lake of, 148
+Nile, homogeneous mud of the, 154
+Ninety-fathom dike in coal, 90
+_Nipadites ellipticus,_ Sheppey, 264
+Nodules in strata, how formed, 63
+_Noeggerathia cuneifolia,_ Permian, 393
+Nomenclature of rocks, 140
+—— of volcanic minerals, 499
+Norfolk cliffs, drift of, 190
+North America. _See_ America.
+Norway, Cambrian of, 489
+——, foliation of crystalline schists in, 595
+——, granite veins in gneiss of, 573
+——, granite altering fossiliferous strata in, 581
+Norwich, or Fluvio-marine crag, 193
+Nova Scotia coal-measures, 409
+—— coal, reptiles and shells in, 414
+——, folding and denudation of beds in, 417
+_Nucula Cobboldiæ,_ Crag, 194
+_Nummulites lævigata,_ Bracklesham, 260
+—— _Puschi,_ Pyrenees, 278
+—— _variolaria,_ Bracklesham, 259
+Nummulitic formations, 277
+
+_OBOLUS APOLLINIS,_ in Russian grit, 478
+Obsidian, 505
+Oceanic areas, permanence of, 117
+Œningen, Upper Miocene beds of, 215
+Oeynhausen, M. von, on Cornish granite veins, 560
+_Ogygia Buchii_, 474
+_Oldhamia radiata: O. antiqua_, 487
+Old Red Sandstone, Upper, 440
+——, Middle, with fish, 443
+——, Lower, 446
+——, trap of the, 547
+——, classification of, 439
+_Olenus micrurus_, 484
+Oligocene, term for Lower Miocene, 230, 244
+Oligoclase, 499, 500
+_Oliva Dufresnii,_ Bolderberg, Belgium, 224
+Olivine, 499
+_Omphyma turbinatum,_ Silurian, 466
+_Onchus tenuistriatus,_ Silurian, 460
+Oolite, classification and physical geography of the, 321
+——, defined, 37
+——, Inferior, fossils of the, 349, 350
+—— and Lias, origin of the, 364
+—— and Chalk, Palæontological break between, 338
+Oolitic strata, palæontological relations of, 351
+—— volcanic rocks, 545
+_Ophioderma tenuibrachiata,_ Lias, 357
+Oppel on zones of Lias, 353
+Orbigny, Alcide de, on foraminifera of Vienna basin, 225
+——, on orbitoidal limestone, 279
+——, on Pisolitic limestone, 285
+——, on Sénonian, 302
+_Oreodaphne Heerii,_ Italian Pliocene, 209
+Organic remains, mineralisation of, 65
+——, tests of age of strata, 125
+——, tests of age of volcanic rocks, 522
+——, geological provinces of, 127
+Oriskany Sandstone, 478
+_Orthis elegantula,_ Ludlow, 46
+—— _grandis,_ Caradoc beds, 470
+—— _tricenaria,_ Bala beds, 470
+—— _vespertilio,_ Bala beds, 470
+_Orthoceras duplex,_ 474
+—— _Ludense,_ Silurian, 463
+—— _laterale_, 436
+—— _ventricosum,_ Silurian, 462
+Orthoclase, 499, 500
+Orthoclastic feldspars, 501
+Osborne or St. Helen’s series, Eocene, 255
+_Osteolepis,_ Old Red Sandstone, 444
+_Ostraceon,_ spine of, Bracklesham, 261
+_Ostrea acuminata,_ Fuller’s earth, 349
+—— _carinata,_ Chalk marl, 300
+—— _columba,_ Chloritic sand, 300
+—— _gregarea,_ Coral Rag, 339
+—— _deltoidea,_ Kimmeridge clay, 336
+—— _distorta,_ Middle Purbeck, 324
+—— _expansa,_ Portland sand, 336
+—— _Marshii,_ Oolite, 351
+—— _vesicularis,_ Chalk, 295
+_Otodus obliquus,_ Bracklesham, 262
+Outcrop of strata, 83
+Overlapping strata, 95
+Owen, Professor on Archæopteryx, 337
+——, on Eocene Zeuglodon, 279
+——, on footprints in Trias, 382
+——, on fauna of Sheppey, 265, 267
+——, on Gastornis Parisiensis, 276
+——, on Labyrinthodon, 370
+——, on mammalia of Stonesfield, 347
+——, on Purbeck mammalia, 326, 328
+——, on reptiles of coal, 407, 414
+——, on zoological provinces of extinct animals, 160
+_Ox, tooth of_ (recent), 165
+Oxford Clay, thickness and fossils of, 340
+
+PAGHAM, erratic block at, 182
+_Palæaster asperimus,_ 472
+_Palæchinus gigas,_ Mountain Limestone, 43
+_Palæocoma tenuibrachiata,_ Lias, 357
+_Palæoniscus,_ Permian fish, 389
+—— _comptus, P. elegans, P. glaphyrus_, 390
+_Palæotherium magnum_, 254
+_Palæophis typhoeus,_ Bracklesham, 261
+Palæozoic or Paleozoic, term defined, 123
+—— Plutonic rocks, 572
+—— rocks, 458
+—— type of corals, 431
+Palagonia, dikes of lava in, 531
+Paleolithic era, 147, 149
+——, alluvial deposits of, 150
+Palm in Swiss Miocene, 237
+Palma, volcanic crater of, 497
+_Paludina lenta,_ Hempstead beds, 55
+—— _orbicularis,_ Bembridge, 253
+_Paradoxides Bohemicus_, 488
+—— _Davidis,_ Lower Cambrian, 485
+Parallelism of folded strata for long distances, 93
+Paris basin, Tertiary group first studied in, 141
+——, Tertiaries of the, 270
+_Parka decipiens,_ “Old Red,” 448
+Parkfield Colliery, ground-plan of, 400
+Patagonia, strata of, rich in soda, 587
+_Patella rugosa,_ Great Oolite, 345
+Paterson, Dr., on angiosperm of the Coal, 429
+Peach, Mr. C, cited, 601
+——, Pteraspis, found by, 443
+Pearlstone, 505
+Pebbles in mineral veins, 608
+—— in chalk, 292
+_Pecopteris elliptica,_ Coal, 421
+_Pecten Beaveri,_ White Chalk, 294
+—— _cinctus,_ Neocomian, 312
+—— _islandicus,_ Scotch Drift, 176
+—— _jacobæus,_ in tertiary of Sicily, 206
+—— _quinque-costatus_, 300
+—— _Valoniensis,_ Rhætic beds, 366
+Pegmatite, 553
+Penarth beds, 366
+Pengelly, Mr., on Bovey Tracey lignite, 246
+——, on flint-knives of Brixham Cave, 157
+_Pentacrinus Briareus,_ Lias, 357
+_Pentamerus Knightii,_ Aymestry, 461
+—— _oblongus,_ and _P. lirata_, 469
+Pentland Hills, volcanic rocks of the, 548
+Perigord cave, carving of mammoth in, 150
+Permanence of continents and oceans, 117
+Permian Flora, 392
+—— of Germany, 393
+—— strata, thickness of, in north of England, 386
+——, Upper and Middle, 386, 387
+——, Lower, 390
+_Perna Mulleti,_ Neocomian, 310
+Petherwyn, Devonian fossils of, 450
+Petrifaction, process of, 67
+_Petrophiloides Richardsoni,_ Sheppey, 25
+_Pahcops caudatus,_ Silurian, 467
+—— _latifrons,_ Devonian, 450
+_Phascolotherium Bucklandi_, 348
+_Phasianella Heddingtonensis,_ and cast, 66
+Phillippi, on tertiary shells of Sicily, 205
+Phillips, Professor, on fossils distorted by cleavage, 592
+——, on ninety fathom dike, 90
+——, on Wenlock limestone and shale, 465, 467
+——, on Yoredale series, 395
+Phillips, Mr. J. Arthur, on origin of gold of California, 617
+_Phlebopteris contigua,_ Inferior Oolite, 350
+Phlogopite, 499, 501
+_Pholadomya fidicula,_ Inferior Oolite, 350
+Phonolite, 506
+_Phorus extensus,_ London Clay, 266
+_Phragmoceras ventricosum,_ Silurian, 463
+_Physa Bristovii,_ Middle Purbeck, 325
+—— _columnaris_, 55
+—— _hypnorum_, 55
+Piedmont, absence of lakes in, 186
+Pile dwellings of Switzerland, 148
+Pilton, group of, Devon, 449
+_Pinnularia in Atlantic mud_, 288
+Pinus sylvestris in peat, 147
+Pisolitic limestone of France, 285
+Pitchstone, 505
+_Placodus gigas,_ Muschelkalk, 380
+Placoids, rare in Old Red Sandstone, 443
+_Plagiaulax Becklesii, jaw and molar of_, 327
+Plagioclastic feldspars, 501
+_Plagiostoma giganteum,_ Lias, 354
+—— _Hoperi,_ Chalk, 300
+_Planorbis discus,_ Bembridge, 253
+—— _euomphalus_, 55, 255
+Plants of Bovey Tracey, Miocene, 247
+——, fossil fresh-water, 57
+—— of the Coal, 420
+—— of the Lias, 364
+—— of the Swiss Upper Miocene, 219
+Plas Newydd, rock altered by dike near, 515
+Plastic Clay, Eocene, 267
+_Platanus aceroides,_ Miocene, 221
+_Platystoma Suessii,_ Hallstadt, 377
+Playfair, on amount of subaërial denudation, 114
+—— on faults, 87
+_Plectrodus mirabilis,_ Ludlow, 460
+_Plesiosaurus dolichodeirus,_ Lias, 361
+_Pleurotoma attenuata,_ Bracklesham, 262
+—— _exorta,_ Eocene, 57
+_Pleurotomaria anglica,_ and cast, 66
+—— _carinata (flammigera)_, 434
+—— _granulata,_ Inferior Oolite, 351
+—— _ornata,_ Inferior Oolite, 351
+Plieninger, Professor, on Triassic mammifer, 368
+Pliocene glacial formations, 189-92
+—— Period, 189
+—— plutonic rocks, 565
+—— strata of Sicily, 204
+——, term defined, 143
+—— volcanic rocks, 529
+Plombières, alkaline waters of, 585
+Plumbago of Massachusetts, 583
+Plutonic and sedimentary formations, diagram of, 567
+——, origin of the term, 551
+—— rocks, Mesozoic, 570
+——, Recent and Pliocene, 565
+——, Miocene and Eocene, 568
+——, uncertain tests of age of, 564
+—— defined, 31
+_Podocarya Bucklandi,_ Oolite, 348
+_Polypterus_ of the Nile, 444
+Polyzoa and Bryozoa, terms explained, 197
+Pomel, M., on fossil mammalia of the Limagne, 235
+Ponza Islands, globiform pitchstone of, 512
+_Porites pyriformis,_ Devonian, 451
+Porphyritic granite, 556
+Porphyry, 506
+Portland, Cycads in dirt-bed of, 331
+—— oolite and sand, 334
+“_Portland screw,_” a cast of a shell, 335
+Porto Santo, marine shells in volcanic tuff of, 536
+Post-pliocene period, climate of the, 161
+—— mammalia, teeth of, 163
+——, term defined, 145
+—— lakes of Switzerland, 185
+—— volcanic rocks, 524
+_Potamides cinctus_, 56
+_Pothocites Grantonii,_ coal-measures, 429
+Potsdam Sandstone, 480, 489
+Pot-stones in the Chalk, 290
+Pottsville, coal seams of, 400
+Powrie, Mr., on Cephalaspis beds, 446
+——, on Parka decipiens, 448
+Pratt, Mr., on Eocene Isle of Wight mammalia, 254
+Predazzo, altered rocks at, 571
+Pressure, solidifying rocks, 65
+Prestwich, Mr., on age of Sables inferieurs, 276
+——, on Chillesford beds, 192
+——, on Coalbrook Dale insects, 405
+——, on Eocene strata, 267, 269
+——, on faults in coal-measure of Coalbrook Dale, 88
+——, on shells of London clay, 264
+——, on thickness of Coralline Crag, 198
+Prévost, M. Constant, on Paris basin, 270
+Primary Limestone, 579
+—— rocks, 458
+——, term defined, 123
+“Primordial Zone” of Bohemia, 481, 482
+_Productus horridus,_ Permian, 388
+—— _semireticulatus (antiquatus)_, 434
+Progressive development indicated by low grade of early mammals, 384
+Proteaceæ of Aix-la-Chapelle flora, 304
+—— of Lower Molasse, Switzerland, 237
+—— of Œningen beds, 221
+Protogine, 578
+Protosaurus of Thuringia, 390, 464
+Protrusion of solid granite, 574
+Provinces of animals and plants, 126
+_Psammodus porosus_, 437
+_Pseudocrinites bifasciatus,_ Silurian, 466
+_Psilophyton princeps,_ Devonian, 455
+Pteraspis in Lower Ludlow shale, 463
+_Pterichthys,_ Old Red Sandstone, 445
+Pterodactyl of Kentish chalk, 297
+_Pterodactylus anglicus,_ Old Red, 447
+—— _crassirostris,_ Solenhofen, 337
+_Ptychodus decurrens,_ White Chalk, 297
+Pudding-stone or conglomerate, 36
+——, formation of, 62
+Pumice, 508
+Punfield beds, brackish and marine, 318
+_Pupa muscorum_, 155
+—— _tridens,_ Loess, 56
+—— _vetusta,_ Coal, 415
+Purbeck beds, Upper, Middle, and Lower, 323, 324, 336
+——, fossil mammalia of the Middle, 325
+—— marble, 324
+——, subdivisions of the, 333
+Purity of coal, cause of, 402
+_Purpura tetragona,_ Red Crag, 196
+_Purpuroidea nodulata,_ Great Oolite, 345
+Puy de Côme, cone and lava-current of, 528
+—— de Tartaret, lava-current and cone of, 527, 542
+—— de Pariou, crater of the, 529
+Puzzuoli, elevation of land at, 525
+_Pygopterus mandibularis,_ Permian, 390
+Pyrenees, chalk altered by granite in the, 570
+——, curved strata in, 86
+——, lamination of clay-slate in, 596
+Pyroxene group of minerals, 499, 502
+_Pyrula reticulata,_ Crag, 200
+
+QUADER-SANDSTEIN, Cretaceous age of the, 293
+Quadrumana of Gers, 215
+Quadrupeds, extinct, in Paleolithic gravels, 152
+Quartz, specific gravity of, 499, 500, 555
+Quartzite or Quartz Rock, 579
+Queenaig, unconformable Palæozoic strata at, 112
+Quenstedt on zones of Lias, 353
+
+RADABOJ Miocene, brown coal of, 242
+_Radiolites foliaceus,_ White Chalk, 306
+—— _Mortoni,_ White Chalk, 295
+—— _radiosa,_ White Chalk, 306
+Radnorshire, stratified trap in, 549
+Rain-prints with worm tracks in Coal, 416
+——, carboniferous, 416
+Ramsay, Professor, on break between Upper and Lower Cretaceous, 301
+——, on breccias in Permian, 391
+——, on escarpments, 104
+——, on denudation, 98
+——, on ice-erosion of lake-basins, 184
+——, on Lingula Flags, 484
+——, on position of Tremadoc beds, 483
+——, on Silurian metamorphic rocks, 602
+——, on submergence in glacial period, 181
+——, on thickness of the Lower Trias, 372
+——, on thickness of Llandeilo beds, 475
+——, on thickness of the Bala beds, 473
+——, on volcanic tuffs of Snowdon, 549
+——, on zones of the Lias, 353
+_Rastrites peregrinus,_ Llandeilo Flags, 473
+Rath, Von, on Tridymite, 500
+Recent Period defined, 145
+—— volcanic rocks, 524
+Record, imperfection of, in the earth’s crust, 138
+Red Crag, older Pliocene, 194
+—— Sandstone, Origin of, 374
+—— Sea and Mediterranean, distinct species in, 127
+Redruth, Cornwall, section of veins in mine, 607
+Reindeer Period in South of France, 149
+Relistran mine, pebbles in tin of, 609
+Reptiles of the Coal, 406, 413
+Reptiles of the Lias, 360
+_Retepora flustracea,_ Permian, 388
+Rhætic beds between Lias and Trias, 366
+Rhine, fresh-water strata of the, 53
+——, loess of the, 154
+Rhinoceros in drift of Abbeville, 153
+—— _leptorhinus (megarhinus),_ molar of, 164
+—— _tichorhinus,_ molar of, 164
+Rhode Island, metamorphic rocks of, 583
+_Rhynchonella navicula,_ Ludlow, 460
+—— _octoplicata,_ White Chalk, 294
+—— _spinosa,_ Inferior Oolite, 350
+—— _Wilsoni,_ Aymestry, 462
+Richmond, Virginia, Triassic coal-field of, 382
+Rigi and Speer, Lower Miocene of the, 235
+_Rimula clathrata,_ Great Oolite, 345
+Rink, Mr., on Greenland land-ice, 171
+Ripple-marked sandstone, how formed, 46
+Rise and fall of land, 146
+_Rissoa Chastelii,_ Hempstead beds, 245
+Rivers, denuding powers of, 101, 114
+Roches moutonnees described, 169
+Rock, term defined, 26
+Rocks altered by volcanic dikes, 514
+—— altered by subterranean gases, 586
+——, analysis of minerals in, 499
+——, aqueous or stratified, 27
+——, classification of, 121
+——, great thickness of palæozoic, 110
+——, glacial scorings on, 169
+——, metamorphic, age of, 597
+——, plutonic age of, 564
+——, volcanic, age of, 520
+——, trappean, 497
+——, metamorphic, defined, 32
+——, four classes of contemporaneous, 33
+——, plutonic, defined, 31
+——, tests of age of, 123, 125, 520, 564, 597
+——, four contemporaneous classes of, 122
+——, underlying, not always the oldest, 122
+——, volcanic, defined, 29
+Rock-salt of Trias, 371
+——, origin of, 374
+Rogers, Mr. H. D., on blending of coal-seams, 400
+——, on Virginian fault, 92
+Rose, Gustavus, on isomorphism, 502
+——, on Fifeshire dike, 546
+——, on quartz in granite, 555
+Rosso antico, red porphyry of Egypt, 506
+_Rostellaria (Hippocrenes) ampla,_ London Clay, 266
+Roth, M., on Miocene of Greece, 226
+Runn of Cutch, salt of, 375
+Rupelian beds of Dumont, 241, 242
+Russia, glaciation of, 174
+——, Devonian of, 454
+——, Silurian strata of, 478
+
+SAARBRUCK, reptiles in coal-field of, 406
+_Sabal major,_ Lower Miocene, 237
+Sables de Bracheux, 276
+—— moyens, Paris basin, 273
+Sahlite, 502
+St. Abb’s Head, curved strata of, 76
+——, unconformable stratification at, 94
+St. Andrews, carboniferous trap-rocks of, 545
+St. Cassian, fossil mollusca of, 377
+—— and Hallstadt beds, 376
+St. David’s, Menevian beds of, 485
+St. Mary’s, shells of, 539
+Salt, rock, origin of, 372
+Salter, Mr., on fossils of Arenig group, 476
+——, on Menevian beds, 485
+——, on Tremadoc fossils, 483
+Sandberger, Dr. F., on Mayence basin, 242
+Sandstone, New Red, 369
+——, Old Red, 439
+—— slab with cracks, 317
+——, slab of ripple-marked, 45
+—— slab with footprints, 408
+_Sao hirsuta_, 488
+Saurians of the Lias, 361
+——, sudden destruction of, 362
+_Saurichthys apicalis,_ Rhætic Beds, 367
+Saussure, on vertical conglomerates, 73
+_Saxicava rugosa,_ Scotch drift, 176
+Saxony, beds of minerals in, 609
+Scandinavia, glaciation of, 174
+_Scaphites æqualis,_ Chloritic marl, 299
+Scapolite, 506
+Scheerer on action of water in metamorphism, 585
+Schist, mica, 578
+——, argillaceous, 579
+——, hornblende, 578
+_Schizodus Schlotheimi,_ Permian, 387
+—— _truncatus,_ Permian, 387
+Schmerling, Dr., on Liége caverns, 157
+Schorl-rock, and schorly granite, 557
+Schwab, M., on Celtic coins in lake-dwellings, 149
+_Scoliostoma,_ St. Cassian, 377
+Scoresby, on Arctic icebergs, 172
+Scoriaceous lava, 507
+Scoriæ, 508
+Scotland, “Fundamental gneiss” of, 493
+——, Old Red Sandstone of, 440
+——, glaciation of, 175
+Screws, fossil, internal casts of shells, 66
+Scrope, Mr., on Isle of Ponza, globiform pitchstone, 512
+——, on minerals in lava, 524
+——, on water in lava, 555
+Scudder, Mr., on Devonian insects of Canada, 457
+Sea, apparent fall of, caused by rise of land, 70
+——, denuding power of the, 105
+——, deep soundings in, 287
+——, mean depth of the, 118
+—— cliffs, inland, 103
+Secondary and Tertiary, gap between the, 281
+——, term defined, 123
+Section of Auvergne alluvium, 100
+—— of carboniferous rocks, Lancashire, 85
+—— of chalk and greensand, 287
+—— of crags near Woodbridge, Suffolk, 198
+—— of cross-stratification, 42-44
+—— of curved strata of the Jura, 82
+—— of dirt-bed in Isle of Portland, 332
+—— of Forfarshire, showing curved strata, 74
+—— of fossil tree, showing texture, 67
+—— of folded and denuded carboniferous beds, Nova Scotia, 418
+—— of the Oolitic strata, 322
+—— of Recent and Post-pliocene alluvial deposits, 151
+—— showing creeps in coal-mines, 79
+—— of slaty cleavage, 589
+—— showing valleys of denudation, 98
+—— showing the Weald formation, 313
+—— of strata thinning out, 41
+—— of superimposed groups at Dundry Hill, 130
+—— of unconformable strata near Mons, 95
+Sections illustrating faults, 88, 90, 91
+Sedgwick, Professor, on the Cambrian Group, 481, 482, 486
+——, on classification of Arenig group, 476
+——, on Devonian series, 439, 449
+——, on position of the May-Hill beds, 568
+——, on protrusion of solid granite, 574
+——, on slaty cleavage, 588, 591
+——, on garnet in altered rock, 515
+——, on concretionary structure, 63
+Sediment, accumulation of, causing a shifting of the subterranean, 117
+isothermals. Sedimentary beds of the Carboniferous, 396
+Selsea Bill, erratics at, 182
+Senarmont on action of water in metamorphism, 585
+_Sequoia Langsdorfii_, 238
+_“Seraphim,” head of Pterygotus anglicus_, 446
+Serapis, marine littoral deposits of, 146
+Serpentine, 578
+_Serpulæ_ attached to _Gryphæa_, 48
+—— attached to _Spatangus_, 49
+—— attached to _Apiocrinus_, 343
+Shale defined, 36
+—— of the Lower Ludlow, 461
+Sharpe, Mr. D., on American Silurian fossils, 479
+——, on fossils distorted by cleavage, 592
+Shell-mounds of Denmark, 146
+Shells, Arctic, in Scotch drift, 177
+——, derivative, in the Crag, 195-203
+——, marine, found at great heights above the sea, 29
+——, proportion of living, in the Crags, 194, 195, 199
+——, value of, in classification, 142
+——, fossil, of Virginia, 228
+—— of the London clay, 266
+—— of the mountain limestone, 433
+—— of the Barton clay, 258
+—— of the Oolite, 335, 345, 350
+——, marine, of Moel Tryfaen, 180
+Sheppey, fauna and flora of, 264
+——, Eocene fish of, 267
+Sherringham, erratic block at, 191
+Shetland, granite of, 558
+——, hornblende-schist of, 583
+Sicily, fauna and flora of, older than the country itself, 207
+——, newer Pliocene strata of, 204
+——, subterranean igneous action in, 569
+——, undulating gypseous marls of, 86
+——, volcanic dikes of, 531
+Sidlaw Hills, trap of, 548
+Sigillaria in coal-measures, 380, 411, 425
+_Sigillaria lævigata,_ coal-measures, 426
+Siliceous limestone defined, 37
+Silurian, derivation of the name, 458
+——, granite of Norway, 573
+——, metamorphic, of North Highlands, 601
+—— rocks, classification of, 458
+—— strata of the continent of Europe, 477
+—— strata of United States, 478
+—— volcanic rocks, 548
+_Siphonotreta unguiculata,_ obolus grits, 478
+Siwâlik Hills, fresh-water deposits of, 226
+Skaptar Jokul, flow of lava from, 523
+Skye, hypersthene rocks of, 491
+——, Isle of, Miocene syenite of the, 568
+——, trap dike in, 514
+Slaty cleavage, 588
+Slicken-sides, in opposite walls of veins, 608
+——, term defined, 87
+_Smilax sagittifera,_ Œningen, 222
+Smith, Mr. W., on White Lias bed, 366
+Snowdon, volcanic tuffs of, 549
+Soissonnais sands, 275
+_Solenastræa cellulosa,_ Brockenhurst, 257
+Solenhofen stone, fossils in the, 337
+Solfatara, decomposition of rocks in the, 586
+Somma, cone and dikes of, 526
+Sopwith, Mr. T., models of outcrop of strata, 85
+Sorby, Mr., on action of water in metamorphism, 585
+——, on glass cavities in quartz, 555
+——, on mechanical theory of cleavage, 592
+——, on ripple-marks in mica schist, 596
+South Joggins, section of cliffs at, 410
+Spalacotherium, Purbeck, 346
+_Spatangus radiatus,_ Chalk, 284
+—— with serpula attached, 49
+Species, gradual change of, 139
+—— older than the land they inhabit, 207
+——, similarity of conditions causing reappearance of, 311
+Specific gravity of basalt and trachyte, 504
+Speer and Rigi, Lower Miocene of the, 235
+Speeton Clay, 311
+_Sphærexochus mirus,_ Silurian, 467
+_Sphærulites agariciformis,_ White Chalk, 306
+—— of volcanic minerals, 499
+_Sphenophyllum erosum,_ Coal, 425
+_Sphenopteris gracilis,_ Hastings sands, 318
+Spheroidal concretions in limestone, 64
+_Spicula of sponge,_ Atlantic mud, 288
+_Spirifera disjuncta,_ Devonian, 450
+—— _alata,_ Permian, 388
+—— _mucronata_, 454
+—— _trigonalis,_ and _S. glabra_, 434
+_Spiriferina Walcotti,_ Lias, 355
+_Spirolina stenostoma,_ Eocene, 275
+_Spirorbis carbonarius,_ coal-measures, 405
+_Spondylus spinosus,_ White Chalk, 294
+_Sponge in flint from White Chalk_, 296
+Sponges, vitreous, in the chalk, 291
+Springs, mineral of Auvergne, 604
+Staffa, age of columnar basalt of, 539
+Stalactite, origin of, explained, 156
+_Starfish_ in Silurian strata, 472
+Stations of species affecting distribution of fossils, 354
+_Stauria astræiformis_, 431
+Stereognathus of Stonesfield, 348
+Sternberg, Count, on insects in coal, 495
+_Stigmaria attached to trunk of Sigillaria_, 427
+—— in coal-measures, 398, 411, 426
+—— _ficoides_ and surface showing tubercles, Coal, 427
+Stilbite, 500
+Stiper-Stones or Arenig Group, 475
+Stockwerk, assemblage of veins, 605
+Stonesfield slate, mammalia of the, 345
+Strata, term defined, alternations of fresh-water, and shallow and
+deep, 27
+sea. ——, alternations of marine and fresh-water, 108
+——, curved, inclined, and vertical, 73
+——, apparent horizontality of inclined, 81
+——, contorted in drift, 178
+——, contortion of, in Cyclopean Isles, 530
+——, general table of fossiliferous, 131
+——, horizontality of, 40
+——, origin of metamorphic, 83
+——, overlapping, 95
+—— repeated by being doubled back, 87
+——, slow growth of, attested by fossils, 47-50
+—— of organic origin, 51
+——, tests of age of, 123
+——, unconformability of, 94, 138
+——, vast thickness of, not forming high mountains, 109-13
+Stratification, diagonal or cross, 42, 44
+——, different forms described, 39
+—— of metamorphic rocks considered, 580
+Stratified rocks, composition of, 35
+Striæ, production of, 168
+Strickland, Mr., on thickness of the Trias, 369
+_Stricklandinia lirata_, 469
+Strike, term explained, 80
+_Stringocephalus Burtini_, 452
+Stromboli, lava of, 566
+_Strophomena depressa,_ Wenlock, 466
+—— _grandis_, 471
+Studer, Mr., on gneiss of the Jungfrau, 599
+subaërial denudation, average annual amount of, 113
+Subapennine beds, proportion of recent species in, 143
+—— strata, older Pliocene, 208
+Submarine denudation, 105
+Subsidence of land must preponderate over upheaval, 116
+_Succinea amphibia_, 55
+—— _elongata_, 155
+Suess, M., on fossils of St. Cassian beds, 376, 377
+——, on Vienna basin, 225
+Suffolk, Crag of, 195
+“Sunk country,” New Madrid, 402
+Superga, Lower Miocene of the, 244
+Superior, Lake, marl in, 63
+Superposition of deposits, a test of age, 124
+—— a test of age of volcanic rocks, 521
+Sutherlandshire, unconformable Palæozoic strata in, 112
+Swanage, fossil mammalia found at, 326
+Sweden, Cambrian of, 489
+——, slow rise of land in, 72
+——, small thickness of Silurian strata in, 477
+Switzerland, lake-dwellings of, 148
+——, Lower Molasse of, 235
+——, Middle or Marine Molasse of, 223
+——, Upper Miocene of, at Œningen, 215
+Sydney coal-field, rain-prints in, 416
+Syenite, composition of, 552, 557
+——, how far connected with trap-rocks, 558
+Syenitic granite, 557
+Symonds, Rev. W. S., on Moel Tryfaen shells, 180
+Synclinal and anticlinal curves, 74, 85
+
+TABLE of Botanical Nomenclature, 303
+—— of St. Cassian fossil mollusca, 377
+—— of Cretaceous formations, 283
+—— of Devonian series in Devon, 449
+—— of divisions of Hastings Sand, 316
+—— of English and French Eocene strata, 252
+—— of ages of fossil vertebrata, 464
+—— of Neocomian strata, 308
+—— of mammalia older than Paris gypsum, 329
+—— of marine testacea in the Crag, 202
+—— of Oolitic strata, 321
+—— of volcanic minerals, 499
+—— of Silurian strata of United States, 478
+—— of Silurian rocks, 458
+—— of Triassic strata, 375
+—— of Cambrian strata, 482
+—— of Permian of north of England, 386
+—— of Welsh coal-measures, 394
+—— of thicknesses of Carboniferous limestone, 395
+——, general, of fossiliferous strata, 131
+Table Mountain, granite veins in clay-slate of, 560
+Tails of homocercal and heterocercal fish, 389
+Talcose granite, 557
+—— gneiss, 578
+Tarannon shales, 468
+Tartaret cone, and lava of, 527, 542
+Tate, Mr., on St Cassian fossils, 377
+Tealby series, Middle Neocomian, 312
+Teeth of extinct mammalia, 163, 164
+_Tellina balthica (T. solidula)_, 190
+—— _calcarea (T. proxima)_, 177
+—— _obliqua,_ Crag, 194
+_Temnechinus excavatus_, 200
+_Temnopleurus excavatus_, 200
+_Tentaculites annulatus,_ Silurian, 489
+_Terebellum fusiforme,_ Barton, 259
+—— _sopita,_ Barton, 259
+_Terebratula affinis,_ Aymestry, 462
+—— _biplicata,_ White Chalk, 294
+—— _carnea,_ White Chalk, 294
+—— _digona,_ Bradford clay, 345
+—— _fimbria,_ Inferior Oolite, 350
+—— _hastata,_ Mountain Limestone, 434
+—— _sella,_ Neocomian, 310
+—— _Wilsoni,_ Aymestry, 462
+_Terebratulina striata,_ White Chalk, 294
+_Terebrirostra lyra,_ Chloritic Sand, 300
+_Teredo navalis,_ boring wood, 50
+Tertiary formations, classification of, 137, 143
+—— strata, subdivisions of, 143
+——, term defined, 123
+Testacea. _See_ Shells.
+Thallogens, 303
+_Thamnastræa,_ Coral Rag, 339
+Thanet sands, 269
+_Theca operculata,_ Tremadoc beds, 483
+_Thecodontosaurus, tooth of,_ 374
+_Thecodus parvidens,_ Ludlow, 460
+_Thecosmilia annularis,_ Coral Rag, 339
+Thirria, M., on Nerinæan limestone, 340
+Thompson, Dr., on Nummulites of Thibet, 277
+Thomson, Wyville, on Atlantic mud, 288
+——, on sponges in chalk mud, 292
+Thuringia, monitor of, 390, 463
+Thurmann, M., on Bernese Jura Oolite, 344
+——, on structure of the Jura, 83
+_Thylacotherium Prevostii,_ Stonesfield, 347
+Tile-stones of the Upper Ludlow, 459
+Tilgate forest, fossil Iguanodon in, 315
+Till described, 166
+——, mammoth in Scotch, 175
+—— of North America, 182
+Tin veins, age of, in Cornwall, 615
+Titanoferrite, 500
+Torell, Dr., on ice-action in Greenland, 172
+——, on Swedish Cambrian fossils, 489
+Touraine, faluns of, 211
+Tourmaline, 500
+Trachytic rocks, 505
+—— tuff, 506
+—— porphyry, 506
+—— lava, age of, 523
+Trap, term defined, 498
+—— dike, intercepting strata, 518
+—— dikes, 513-17
+——, intrusion of, between strata, 517
+—— rocks, ages of, 524-50
+—— rocks passing into granite, 559
+—— tuff described, 508
+Trappean rocks, nomenclature of, 497
+—— rocks, their relation to active volcanoes, 517
+Trass of Lower Eifel, 535
+Travertin, how deposited, 60
+——, inférieur of Paris basin, 273
+_Tree ferns, living_, 422
+Trees erect in coal, Nova Scotia, 411
+Tremadoc slates and their fossils, 482
+Tremolite, 499, 502
+Trenton limestone, fossils of the, 479
+Trezza, volcanic rocks of, 529
+Trias, beds of passage between Lias and, 366
+—— of England, 369-74
+—— of Germany, 375
+——, Saurians of the, 370
+—— of the United States, 381
+Triassic mammifer, North Carolina, 383
+Triclinic feldspars, 501
+Tridymite, crystallised silica, 500
+_Trigonellites latus,_ Kimmeridge clay, 336
+_Trigonia caudata,_ Neocomian, 310
+—— gibbosa, Portland stone, 335
+_Trigonocarpum ovatum,_ and _T. olivæforme,_ Coal, 429
+_Trigonotreta undulata,_ Permian, 388
+Trilobites of Bala and Caradoc beds, 471
+——, metamorphosis of, 471, 488
+—— of primordial zone, 487
+_Triloculina inflata,_ Eocene, 275
+Trimmer, Mr., on contorted strata, 179
+——, on shells of Moel Tryfaen, 186
+_Trinucleus concentricus, T. Caractaci_, 472
+_Trionyx, carapace of,_ Bembridge, 253
+Tripoli composed of diatomaceæ, 51
+_Trochoceras giganteus,_ Ludlow, 463
+_Trophon antiquum (Fusus contrarius)_, 196
+—— _clathratum,_ Scotch drift, 176
+Tuff defined, 30
+——, shelly, of the Grand Canary, 538
+——, trappean, of Llandeilo rocks, 473
+——, shelly, of Gergovia, 542
+_Tupaia Tana,_ recent, 347
+Turner, Dr., on chemical decomposition, 68
+_Turrilites costatus,_ Chalk, 299
+_Turritella multisulcata,_ Bracklesham, 262
+Tuscany, mineral springs of, 604
+Tylor, Mr., on amount of subaërial denudation, 114
+Tyndall, Dr., on slaty cleavage, 594
+Tynedale fault, 90
+Tynemouth cliff, brecciated limestone of, 387
+_Typhis pungens,_ Barton clay, 259
+
+_UNCITES Gryphus,_ Devonian, 452
+Unconformability of strata, 94, 138
+Underlying, term applied to plutonic rocks, 34
+Unger on American forms in Swiss Miocene flora, 223, 239
+—— on Miocene plants of Croatia, 243
+Ungulite, or Obolus grit of Russia, 477
+_Unio littoralis_, 54
+—— _Valdensis,_ Hastings Sands, 317
+United States, Cambrian of the, 489
+——, Cretaceous rocks of, 307
+——, Devonian of, 455
+——, Eocene strata in the, 278
+——, footprints in Carboniferous of, 407
+——, Lower Miocene of, 248
+——, older Pliocene and Miocene formations of, 227
+——, Silurian strata of, 478
+——, Trias of the, 381
+Upheaval of land more than counteracted by subsidence, 116
+——, power of denudation to counteract, 105, 115
+Upper Greensand, or Chloritic series, 298
+Upsala, erratics on modern marine drift near, 174
+Ural Mountains, auriferous alluvium of, 616
+Uralite, 499
+_Ursus spelæus, tooth of_, 165
+Urville, Captain de, on size of icebergs, 172
+
+VAL D&RSQUO;ARNO, Newer Pliocene of, 207
+Valleys, origin of, 102
+Valorsine, granite veins in talcose gneiss in, 599
+_Valvata piscinalis_, 55
+_Vanessa Pluto,_ Lower Miocene, Croatia, 243
+Vegetation of the Coal, 420
+—— of the Devonian of America, 455
+——. _See_ Plants.
+Veins, chemical deposits in, 612
+——, granite rocks altered by, 559
+——, different kinds of minerals, 605
+——. _See_ Mineral veins.
+Vein-stones, 610
+_Venericardia planicosta_, 260
+Venetz, M., on Alpine glaciers, 170
+_Ventriculites radiatus,_ Chalk, 292
+Verneuil, M. de, on Russian Silurian, 462
+——, on Permian flora, 392
+Vertebrata, progress of discovery of fossil, 464
+Vertical strata, 73
+Vesuvius, Recent and Post-pliocene volcanic rocks of, 525
+——, basaltic lavas of, 508
+——, tufaceous strata of, 522
+——, dikes of, 527
+_Vicarya Lujani,_ Punfield, 319
+Vicentin, columnar basalt of the, 511
+Vienna Basin, Upper Miocene beds of, 224
+Vine in Upper Miocene beds at Œningen, 221
+Virginia, eighty miles of fault in, 92
+——, coal-field of, 382
+Virlet, M, on corrosion of rocks near Corinth, 586
+——, on Cretaceous traps of Greece, 544
+——, on fossils in veins, 608
+——, on volcanic rocks of the Morea, 544
+Volcanic ash or tuff, 508
+—— breccia, 509
+—— dikes, 513-16
+—— force and denudation opposing powers, 117
+—— mountains, structure and origin of, 494
+Volcanic rocks defined, 29
+——, mineral composition of, 498
+——, Recent and Post-pliocene, 524
+——, Pliocene, 529
+——, Miocene, 536-43
+——, Eocene, 543
+——, Cretaceous and Liassic, 544, 545
+——, New Red, Permian and Carboniferous, 545
+——, Old Red Sandstone, 547
+——, Silurian, Cambrian and Laurentian, 548, 549
+—— of Auvergne, 540
+——, columnar and globular, structure of, 510
+—— of Grand Canary, 528
+—— of Silurian age, 477
+——, special forms of structure of, 506
+——, tests of age of, 520-4
+Volcanoes, extinct, 30
+—— of Auvergne, 495
+_Voltzia heterophylla,_ Bunter, 380
+_Voluta ambigua,_ Barton clay, 259
+—— _athleta,_ Barton, 259
+—— _Lamberti,_ coralline and Red Crag, 196
+—— _Lamberti,_ faluns, 214
+—— _nodosa,_ London clay, 266
+—— _Selseïensis,_ Bracklesham, 262
+Von Buch, Leopold, on “elevation craters,” 496
+——, on Silurian plutonic rocks, 572
+
+WACKE described, 508
+Wagner, M., on Miocene of Greece, 226
+_Walchia piniformis,_ Permian, 392
+Wales and England, glaciation of, 180
+Wallich, Dr., on Atlantic mud, 287
+Water, denuding power of running, 98, 115
+——, action of, in metamorphism, 584
+Watt, Gregory, on fusion of rock, 584
+Weald clay and its fossils, 317
+Wealden area, thickness of the, 319
+—— formation, 313
+—— flora, 320
+Webster, Mr. T., on Tertiary strata, 141
+Wellington Valley caves, 158
+Wenlock formation, fossils of the, 465-8
+—— limestone, 465
+—— shale, 467
+Werner on mineral veins in Saxony, 609
+—— on isomorphism, 502
+Westwood, Mr., on Lias beetles, 363
+Wexford, veins of copper at, 615
+Whitaker, Mr., on subaërial origin of escarpments, 104
+White or coralline crag, 197
+—— sand of Alum Bay, 38
+Whymper, Mr., on Arctic Miocene plants, 240
+Williams, Mr., on Cornish lodes, 607
+Williamson, Professor, on Conifers of the Coal, 428
+——, on structure of calamite, 425
+Wind, denuding action of the, 97
+Wood, Mr. Searles, on Bridlington shells, 190
+——, on Chillesford and Aldeby beds, 192
+——, on shells of the Crags, 194, 195, 199
+——, on shells of Crag and faluns compared, 213
+——, on fish of Headon series, 255
+——, table of marine testacea of the Crag, 202
+——, on thickness of coralline crag, 198
+Woodward, Dr., on St. Cassian fossils, 377
+Woodward, Mr. H., on Pterygotus, 447
+Woolhope beds, 467
+Woolwich and Reading series, 267
+Wright, Dr., on Barton shells, 258
+——, on zones of the Lias, 353
+Wunsch, Mr. E. A., on trees in volcanic ash, 546
+Wyville Thomson. _See_ Thomson.
+
+_XIPHODON gracile,_ Paris basin, 271
+_Xylobius Sigillariæ,_ Nova Scotia coal, 415
+
+YOREDALE beds, thickness of the, 395
+Yorkshire, Oolite of, 349
+Young, Mr., on seeds washed out of mammoth tusks, 176
+
+ZECHSTEIN of Germany, 392
+Zeolites, secondary volcanic minerals, 500
+_Zeuglodon cetoides,_ Eocene, United States, 280
+Zircon-syenite, 558
+_Zoantharia rugosa_ and _Z. aporosa_, 431
+Zones of the Lias, 353
+_Zonites priscus,_ Coal, 415
+Zoological provinces, great extent of, 127
+Zoophytes, fossil, 48
+——. _See_ Corals, Bryozoa, etc.
+Zurich, lake-dwellings in Lake of, 148
+
+
+
+
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