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+Project Gutenberg's A Manual of Elementary Geology, by Charles Lyell
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: A Manual of Elementary Geology
+       or, The Ancient Changes of the Earth and its Inhabitants
+       as Illustrated by Geological Monuments
+
+Author: Charles Lyell
+
+Release Date: November 17, 2010 [EBook #34350]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK A MANUAL OF ELEMENTARY GEOLOGY ***
+
+
+
+
+Produced by Julia Miller, Iris Schröder-Gehring and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+(This file was produced from images generously made
+available by The Internet Archive/American Libraries.)
+
+
+
+
+
+
+
+
+
+[Illustration: From a Painting by James Hall, Esq.  Engraved by
+S. Williams.
+
+STRATA OF RED SANDSTONE, SLIGHTLY INCLINED, RESTING ON VERTICAL SCHIST, AT
+THE SICCAR POINT, BERWICKSHIRE.
+
+TO ILLUSTRATE UNCONFORMABLE STRATIFICATION. See page 60.
+
+_"The mind seemed to grow giddy by looking so far into the abyss of time;
+and while we listened with earnestness and admiration to the philosopher
+who was now unfolding to us the order and series of these wonderful events,
+we became sensible how much farther reason may sometimes go than
+imagination can venture to follow."_--PLAYFAIR, Biography of Hutton.]
+
+
+
+
+           A MANUAL OF ELEMENTARY GEOLOGY:
+                        OR,
+  THE ANCIENT CHANGES OF THE EARTH AND ITS INHABITANTS
+
+      AS ILLUSTRATED BY GEOLOGICAL MONUMENTS.
+
+
+         BY SIR CHARLES LYELL, M.A. F.R.S.
+
+AUTHOR OF "PRINCIPLES OF GEOLOGY," "TRAVELS IN NORTH AMERICA," "A SECOND
+VISIT TO THE UNITED STATES," ETC. ETC.
+
+
+
+
+"It is a philosophy which never rests--its law is progress: a point which
+yesterday was invisible is its goal to-day, and will be its starting post
+to-morrow."
+                            EDINBURGH REVIEW, No. 132. p. 83. July, 1837.
+
+
+
+
+  _FOURTH AND ENTIRELY REVISED EDITION._
+  ILLUSTRATED WITH 500 WOODCUTS.
+
+  LONDON:
+  JOHN MURRAY, ALBEMARLE STREET.
+  1852.
+
+
+
+
+  LONDON:
+  SPOTTISWOODES and SHAW,
+  New-street-Square.
+
+
+
+
+PREFACE TO THE FOURTH EDITION.
+
+
+In consequence of the rapid sale of the third edition of the "Manual," of
+which 2000 copies were printed in January last, a new edition has been
+called for in less than a twelvemonth. Even in this short interval some new
+facts of unusual importance in palæontology have come to light, or have
+been verified for the first time. Instead of introducing these new
+discoveries into the body of the work, which would render them inaccessible
+to the purchasers of the former edition, I have given them in a postscript
+to this Preface (printed and sold separately), and have pointed out at the
+same time their bearing on certain questions of the highest theoretical
+interest.[v-A]
+
+As on former occasions, I shall take this opportunity of stating that the
+"Manual" is not an epitome of the "Principles of Geology," nor intended as
+introductory to that work. So much confusion has arisen on this subject,
+that it is desirable to explain fully the different ground occupied by the
+two publications. The first five editions of the "Principles" comprised a
+4th book, in which some account was given of systematic geology, and in
+which the principal rocks composing the earth's crust and their organic
+remains were described. In subsequent editions this book was omitted, it
+having been expanded, in 1838, into a separate treatise called the
+"Elements of Geology," first re-edited in 1842, and again recast and
+enlarged in 1851, and entitled "A Manual of Elementary Geology."
+
+Although the subjects of both treatises relate to geology, as their titles
+imply, their scope is very different; the "Principles" containing a view of
+the _modern_ changes of the earth and its inhabitants, while the "Manual"
+relates to the monuments of _ancient_ changes. In separating the one from
+the other, I have endeavoured to render each complete in itself, and
+independent; but if asked by a student which he should read first, I would
+recommend him to begin with the "Principles," as he may then proceed from
+the known to the unknown, and be provided beforehand with a key for
+interpreting the ancient phenomena, whether of the organic or inorganic
+world, by reference to changes now in progress.
+
+Owing to the former incorporation of the two subjects in one work, and the
+supposed identity of their subject matter, it may be useful to give here a
+brief abstract of the contents of the "Principles," for the sake of
+comparison.
+
+
+_Abstract of the "Principles of Geology," Eighth Edition._
+
+
+BOOK I.
+
+  1. Historical sketch of the early progress of geology, chaps. i. to iv.
+
+  2. Circumstances which combined to make the first cultivators of the
+  science regard the former course of nature as different from the
+  present, and the former changes of the earth's surface as the effects of
+  agents different in kind and degree from those now acting, chap. v.
+
+  3. Whether the former variations in climate established by geology are
+  explicable by reference to existing causes, chaps. vi. to viii.
+
+  4. Theory of the progressive development of organic life in former ages,
+  and the introduction of man into the earth, chap. ix.
+
+  5. Supposed former intensity of aqueous and igneous causes considered,
+  chaps. x. and xi.
+
+  6. How far the older rocks differ in texture from those now
+  forming, chap. xii.
+
+  7. Supposed alternate periods of repose and disorder, chap. xiii.
+
+
+BOOK II.
+
+CHANGES NOW IN PROGRESS IN THE INORGANIC WORLD.
+
+  8. Aqueous causes now in action: Floods--Rivers--Carrying power of
+  ice--Springs and their deposits--Deltas--Waste of cliffs and strata
+  produced by marine currents: chaps. xiv. to xxii.
+
+  9. Permanent effects of igneous causes now in operation: Active volcanos
+  and earthquakes--their effects and causes: chaps. xxiii. to xxxiii.
+
+
+BOOK III.
+
+CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS.
+
+  10. Doctrine of the transmutation of species controverted,
+  chaps. xxxiv. and xxxv.
+
+  11. Whether species have a real existence in nature,
+  chaps. xxxvi. and xxxvii.
+
+  12. Laws which regulate the geographical distribution of species, chaps.
+  xxxviii. to xl.
+
+  13. Creation and extinction of species, chaps. xli. to xliv.
+
+  14. Imbedding of organic bodies, including the remains of man and his
+  works, in strata now forming, chaps. xlv. to l.
+
+  15. Formation of coral reefs, chap. li.
+
+It will be seen on comparing this analysis of the contents of the
+"Principles" with the headings of the chapters of the present work (see p.
+xxiii.), that the two treatises have but little in common; or, to repeat
+what I have said in the Preface to the 8th edition of the "Principles,"
+they have the same kind of connection which Chemistry bears to Natural
+Philosophy, each being subsidiary to the other, and yet admitting of being
+considered as different departments of science.[vi-A]
+                                                             CHARLES LYELL.
+                              _11 Harley Street, London, December 10. 1851._
+
+
+FOOTNOTES:
+
+[v-A] Postscript to 4th edition of the Manual, price 6_d._
+
+[vi-A] As it is impossible to enable the reader to recognize rocks and
+minerals at sight by aid of verbal descriptions or figures, he will do well
+to obtain a well-arranged collection of specimens, such as may be procured
+from Mr. Tennant (149. Strand), teacher of Mineralogy at King's College,
+London.
+
+
+
+
+POSTSCRIPT.
+
+  Tracks of a Lower Silurian reptile in Canada--Chelonian footprints in
+  Old Red Sandstone, Morayshire--Skeleton of a reptile in the same
+  formation in Scotland--Eggs of Batrachians (?) in a lower division of
+  the "Old Red," or Devonian--Footprints of Lower Carboniferous reptiles
+  in the United States--Fossil rain-marks of the Carboniferous period in
+  Nova Scotia--Triassic Mammifer from the Keuper of Stuttgart--Cretaceous
+  Gasteropoda--Dicotyledonous leaves in Lower Cretaceous strata--Bearing
+  of the recent discoveries above-mentioned on the theory of the
+  progressive development of animal life.
+
+
+_Tracks of a Lower Silurian reptile in Canada._--In the year 1847, Mr.
+Robert Abraham announced in the Montreal Gazette, of which he was editor,
+that the track of a freshwater tortoise had been observed on the surface of
+a stratum of sandstone in a quarry opened on the banks of the St. Lawrence
+at Beauharnais in Upper Canada. The inhabitants of the parish being
+perfectly familiar with the track of the amphibious mud-turtles or
+terrapins of their country, assured Mr. Abraham that the fossil impressions
+closely resembled those left by the recent species on sand or mud. Having
+satisfied himself of the truth of their report, he was struck with the
+novelty and geological interest of the phenomenon. Imagining the rock to be
+the lowest member of the old red sandstone, he was aware that no traces had
+as yet been found of a reptile in strata of such high antiquity.
+
+He was soon informed by Mr. Logan, at that time engaged in the geological
+survey of Canada, that the white sandstone above Montreal was really much
+older than the "Old Red," or Devonian. It had in fact been ascertained many
+years before, by the State surveyors of New York (who called it the
+"Potsdam Sandstone"), to lie at the base of the whole Silurian series. As
+such it had been pointed out to me in 1841, in the valley of the Mohawk, by
+Mr. James Hall[vii-A], and its position was correctly described by Mr.
+Emmons, on the borders of Lake Champlain, where I examined it in 1842. It
+has there the character of a shallow-water deposit, ripple-marked
+throughout a considerable thickness, and full of a species of Lingula. The
+flat valves of this shell, of a dark colour, are so numerous, and so
+arranged in horizontal layers, as to play the part of mica, causing the
+rock to divide into laminæ, as in some micaceous sandstones.
+
+When I mentioned this rock in my Travels[vii-B] as occurring between
+Kingston and Montreal, (the same in which the Chelonian foot-prints have
+since been found,) I spoke of it as the lowest member of the Lower Silurian
+series; but no traces of any organic being of a higher grade than the
+Lingula had then been seen in it, and I called attention to the singular
+fact, that the oldest fossil form then known in the world, was a marine
+shell strictly referable to a genus now existing.
+
+Early in the year 1851, Mr. Logan laid before the Geological Society of
+London a slab of this sandstone from Beauharnais, containing no less than
+twenty-eight foot-prints of the fore and hind feet of a quadruped, and six
+casts in plaster of Paris, exhibiting a continuation of the same trail.
+Each cast contained from twenty-six to twenty-eight impressions with a
+median channel equidistant from the two parallel rows of foot-prints, the
+one made by the feet of the right side, the other by those of the left. In
+these specimens a greater number of successive foot-marks belonging to one
+and the same series were displayed than had ever before been observed in
+any rock ancient or modern. Mr. Abraham has inferred that the breadth of
+the quadruped was from five to seven inches. A detailed account of the
+trail was published by Professor Owen, in April 1851, from which the
+following extracts are made.
+
+"The foot-prints are in pairs, and the pairs extend in two parallel series,
+with a channel exactly midway between the right and left series. The pairs
+of the same side succeed each other at intervals, varying from one inch and
+a half to two inches and a half, the common distance being about two
+inches. The interval between the right and left pairs, measured from the
+inner border of the small prints, is three inches and a half, and from the
+outer border of the exterior or large prints, is seven inches. The shallow
+median track is one inch and a quarter in breadth, varying in depth, but
+not in its relative position to the right and left foot prints."
+
+"The inference to be deduced from these characters is, that the impressions
+were made by a quadruped with the hind feet larger and somewhat wider apart
+than the fore feet, with both hind and fore feet either very short, or
+prevented by some other part of the animal's structure from making long
+steps; and with the limbs of the right side wide apart from those of the
+left; consequently, that the quadruped had a broad trunk in proportion to
+its length, supported on limbs either short, or capable only of short
+steps, and with rounded and stumpy feet, not provided with long claws.
+There are faint traces of a fine reticulate pattern of the cuticle of the
+sole at the bottom of some of the foot-prints on one portion of the
+sandstone; and the surface of the sand is generally smoother there than
+where not impressed, which, with the rising of the sand at the border of
+the prints, indicates the weight of the impressing body. The median groove
+may be interpreted as due either to the abdomen or the tail of the animal;
+but as there is no indication of any bending or movement of a tail from
+side to side, it was probably scooped out of the soft sand by a hard
+breast-plate or plastron. If this were so, it may be inferred that
+the species was a freshwater or estuary tortoise rather than
+a land tortoise."[viii-A]
+
+Previously to this discovery, the trias was the oldest stratum in which
+any remains or signs of a Chelonian had been detected. Numerous other
+trails have since been observed (1850-51) in various localities in Canada,
+all in the same very ancient fossiliferous rock; and Mr. Logan, who has
+visited the spots, will shortly publish a description of the phenomena.
+
+_Chelonian foot-prints in Old Red Sandstone, Morayshire._--Captain Lambart
+Brickenden has just communicated to the Geological Society of London a
+drawing and description of a continuous series of no less than thirty-four
+foot-prints of a quadruped observed in the course of last year (1850), on a
+slab of sandstone quarried at Cummingstone, near Elgin, in Morayshire, a
+rock which has always been considered as an upper member of the Devonian or
+"Old Red."[ix-A] A part of the track, the course of which was from A to B,
+is represented in the annexed woodcut, fig. 521. The foot-prints are in
+pairs, forming two parallel rows, which are somewhat less distant from each
+other than those of the Lower Silurian tortoise of Canada above mentioned.
+The stride, on the other hand, is four inches, or twice that of the
+Beauharnais Chelonian. The hind foot is exactly of the same size,
+being one inch in diameter, and larger than the fore foot in the
+proportion of four to three.
+
+[Illustration: Fig. 521. Scale one-sixth the original size.
+
+Part of the trail of a (Chelonian?) quadruped from the Old Red Sandstone of
+Cummingstone, near Elgin, Morayshire.--Captain Brickenden.]
+
+_Skeleton of a reptile, allied to the Batrachians, in the Old Red Sandstone
+of Morayshire._--Mr. Patrick Duff, author of a "Sketch of the Geology of
+Morayshire" (Elgin, 1842), obtained recently (October, 1851), from the rock
+above alluded to, the first example ever seen of the skeleton of a reptile
+in the Old Red Sandstone. He has kindly allowed me to give a figure of this
+fossil, of which Dr. Mantell has drawn up a detailed osteological account
+for publication in the "Journal of the Geological Society of London." The
+bones in this specimen have decomposed, but the natural position of almost
+all of them can be seen, and nearly perfect casts of their form taken from
+the hollow moulds which they have left. The matrix is a fine-grained,
+whitish sandstone, with a cement of carbonate of lime. The skeleton
+exhibits the general characters of the Lacertians, blended with
+peculiarities that are Batrachian. Hence Dr. Mantell infers that this
+reptile was either a freshwater Batrachian, resembling the Triton, or a
+small terrestrial Lizard. Slight indications are visible of very minute
+conical teeth. Captain Brickenden, who is well acquainted with the geology
+of that part of Scotland, informs me that this fossil was found in the Hill
+of Spynie, north of the town of Elgin, in a rock quarried for building, and
+the same in which the Chelonian foot-prints, alluded to in the last page,
+occur. The skeleton is about four and a half inches in length, but part of
+the tail is concealed in the rock. Dr. Mantell has proposed for it the
+generic name of Telerpeton, from +têle+, afar off, and +herpeton+, a
+reptile; while the specific name Elginense commemorates the principal place
+near which it was obtained.
+
+[Illustration: Fig. 522. Natural size. _Telerpeton Elginense._ (Mantell.)
+
+Reptile of Old Red Sandstone, from near Elgin, Morayshire.]
+
+_Eggs of Batrachians (?) in the Old Red Sandstone of Scotland._--At page
+344. of this work I have given two figures (figs. 397 and 398.) of small
+groups of eggs, very common in the shales and sandstones of the "Old Red"
+of Kincardineshire, Forfarshire, and Fife. I threw out as a conjecture,
+that they might belong to gasteropodous mollusca, like those represented in
+fig. 399. p. 345.; but Dr. Mantell, some years ago, showed me a small
+bundle of the dried-up eggs of the common English frog (see fig. 524 _a_.),
+black and carbonaceous, and so identical in appearance with the fossils in
+question, that he suggested the probability of these last being of
+Batrachian origin. The plants by which they are often accompanied (fig.
+398. p. 344.), I formerly supposed to be Fuci, but Mr. Bunbury tells me
+that their grass-like form agrees well with the idea of their being
+freshwater, and of the family Fluviales.
+
+The absence of all shells, so far as our researches have yet gone, in the
+slates and sandstones of Scotland above alluded to, raises a presumption
+against their marine origin, and a still stronger one against the fossil
+eggs being those of Gasteropoda. It is well known that a single female of
+the Batrachian tribe ejects annually an astonishing quantity of spawn. Mr.
+Newport, author of many accurate researches into the metamorphoses of the
+Amphibia, having examined my fossils from Forfarshire, concurs in Dr.
+Mantell's opinion that the clusters of eggs (figs. 397. 398. p. 344.) may
+be those of frogs; while other larger ones, occurring singly or in pairs in
+the same slates, and often attached to a leaf, may be the ova of a gigantic
+Triton or Salamander. (See figs. 523, 524, 525.) I may observe that the
+subdivision of the Old Red Sandstone, in which these plants and ova occur
+(No. 4. of the section, fig. 62. p. 48.), is considerably lower in position
+than the rock in which the Telerpeton of Elgin is imbedded.
+
+[Illustration: Fig. 523. Fossil.--Old Red.
+
+Fig. 523. Slab of Old Red Sandstone, Forfarshire, with eggs of Batrachians.
+
+  _a._ Ova in a carbonized state.
+  _b._ Egg cells; the ova shed.]
+
+[Illustration: Fig. 524. Recent.
+
+Fig. 524. Eggs of the common frog, _Rana temporaria_, in a carbonized
+state, from a dried-up pond in Clapham Common.
+
+  _a._ The ova.
+  _b._ A transverse section of the mass exhibiting the form of the
+       egg-cells.]
+
+[Illustration: Fig. 525. Eggs of Batrachians.--Old Red Sandstone.
+
+Fig. 525. Shale of Old Red Sandstone, or Devonian, Forfarshire, with
+impression of plants and eggs of Batrachians.
+
+  _a._   Two pair of ova resembling those large Salamanders or Tritons
+         on the same leaf.
+  _b b._ Detached ova.
+  _c._   Egg-cells of frogs or _Ranina_.]
+
+_Foot-prints of Lower Carboniferous reptiles in the United States._--I have
+stated, at p. 340., that in 1849, Mr. Isaac Lea observed the foot-marks of
+a large reptile in the lowest beds of the coal formation at Pottsville,
+about seventy miles N.E. of Philadelphia. These researches have since been
+carried farther by Professor H. D. Rogers, in the same region of
+anthracitic coal, lying on the eastern flank of the Alleghany Mountains.
+Beneath the productive coal-measures of that country occurs a dense mass of
+red shales and sandstones, which correspond nearly in position to the
+millstone grit and Mountain Limestone of the south-east of England. In
+these beds foot-prints, referred to three species of quadrupeds, have
+lately been detected, all of them five-toed and in double rows, with an
+opposite symmetry, as if made by right and left feet, while they likewise
+display the alternation of fore foot and hind foot. One species, the
+largest of the three, presents a diameter for each foot-print of about two
+inches, and shows the fore and hind feet to be nearly equal in dimensions.
+It exhibits a length of stride of about nine inches, and a breadth between
+the right and left treads of nearly four inches. The impressions of the
+hind feet are but little in the rear of the fore feet. The animal which
+made them is supposed to have been allied to a Saurian, rather than to a
+Batrachian or Chelonian; but more information is required before so
+difficult a point can be decided. With these foot-marks were seen shrinkage
+cracks, such as are caused by the sun's heat in mud, and rain-spots, with
+the signs of the trickling of water on a wet, sandy beach; all confirming
+the conclusion derived from the foot-prints, that the quadrupeds belonged
+to air-breathers, and not to aquatic races.[xii-A] The Cheirotherian
+foot-prints, figured by me at p. 338., in which the fore and hind feet are
+very unequal in size, betoken a distinct genus, and occur in the midst of
+the productive coal measures, being consequently less ancient.
+
+_On Fossil Rain-marks of the Carboniferous Period in North
+America._--Having alluded to the spots left by rain on the surface of
+carboniferous strata in the Alleghanies, on which quadrupedal foot-prints
+are seen, I may mention that similar rain-prints are conspicuous in the
+coal measures of Cape Breton, in Nova Scotia, in which Mr. Richard Brown
+has described Stigmariæ and erect trunks of trees, and where there are
+proofs, as stated at p. 324., of many fossil forests ranged one above the
+other. In such a region, if anywhere, might we expect to detect evidence of
+the fall of rain on a sea-beach, so repeatedly must the conditions of the
+same area have oscillated between land and sea. The intercalation of
+deposits, containing shells of marine or brackish water, indicate the
+constant proximity of a body of salt water when the clays which supported
+the upright trees were formed. In the course of 1851, Mr. Brown had the
+kindness to send me some greenish slates from Sydney, Cape Breton, on which
+are imprinted very delicate impressions of rain-drops, with several
+worm-tracks (_a_, _b_, fig. 526.), such as usually accompany rain-marks on
+the recent mud of the Bay of Fundy, and other modern beaches.[xii-B]
+
+[Illustration: Fig. 526. Carboniferous rain-prints with worm-tracks (_a_,
+_b_) on green shale, from Cape Breton, Nova Scotia.]
+
+[Illustration: Fig. 527. Casts of rain-prints on a portion of the
+same slab, No. 526. seen on the under side of an incumbent layer
+of arenaceous shale.
+
+The arrow represents the direction of the shower.]
+
+[Illustration: Fig. 528. Casts of carboniferous rain-prints and
+shrinkage-cracks, (_a_) on the under side of a layer of sandstone, Cape
+Breton, Nova Scotia.]
+
+The casts of rain-prints, in figs. 527. and 528., project from the under
+side of two layers, occurring at different levels, the one a sandy shale,
+resting on the green shale (fig. 526.), the other a sandstone presenting a
+similar warty or blistered surface, on which are also observable some small
+ridges as at _a_, which stand out in relief, and afford evidence of cracks
+formed by the shrinkage of subjacent clay, on which rain had fallen. Many
+of the associated sandstones are described by Mr. Brown as ripple-marked.
+
+The great humidity of the climate of the coal period had been previously
+inferred from the nature of its vegetation 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.
+
+_Triassic Mammifer (Microlestes antiquus Plieninger.)_--In the year 1847,
+Professor Plieninger, of Stuttgart, published a description of two fossil
+molar teeth, referred by him to a warm-blooded quadruped[xiii-A], which he
+obtained from a bone-breccia in Würtemberg occurring between the lias and
+the keuper. As the announcement of so novel a fact has never met with the
+attention it deserved, we are indebted to Dr. Jäger, of Stuttgart, for
+having recently reminded us of it in his Memoir on the Fossil Mammalia of
+Würtemberg.[xiii-B]
+
+Fig. 529. represents the tooth first found, taken from the plate published
+in 1847, by Professor Plieninger; and fig. 530. is a drawing of the same
+executed from the original by Mr. Hermann von Meyer, which he has been
+kind enough to send me. Fig. 529. is a second and larger molar, copied from
+Dr. Jäger's plate lxxi., fig. 15.
+
+[Illustration: Fig. 529. _Microlestes antiquus_, Plieninger. Molar tooth
+magnified. Upper Trias, Diegerloch, near Stuttgart, Würtemberg.
+
+  _a._ View of inner side?
+  _b._ same, outer side?
+  _c._ Same in profile.
+  _d._ Crown of same.]
+
+[Illustration: Fig. 530. _Microlestes antiquus_, Plien.
+
+View of same molar as No. 529. From a drawing by Herman von Meyer.
+
+  _a._ View of inner side?
+  _b._ Crown of same.]
+
+[Illustration: Fig. 531. Molar of _Microlestes_? Plien. 4 times as large as
+fig. 529. From the trias of Diegerloch, Stuttgart.]
+
+Professor Plieninger inferred in 1847, from the double fangs of this tooth
+and their unequal size, and from the form and number of the protuberances
+or cusps on the flat crowns, that it was the molar of a Mammifer; and
+considering it as predaceous, probably insectivorous, he called it
+Microlestes, from +mikros+, little, and +lêstês+, a beast of prey. Soon
+afterwards, he found the second tooth also, at the same locality,
+Diegerloch, about two miles to the south-east of Stuttgart. Some of its
+cusps are broken, but there seem to have been six of them originally. From
+its agreement in general characters, it is supposed by Professor Plieninger
+to be referable to the same animal, but as it is four times as big, it may
+perhaps have belonged to another allied species. This molar is attached to
+the matrix consisting of sandstone, whereas the tooth, No. 529., is
+isolated. Several fragments of bone, differing in structure from that of
+the associated saurians and fish, and believed to be mammiferous, were
+imbedded near them in the same rock.
+
+Mr. Waterhouse, of the British Museum, after studying the annexed figs.
+529. 531. and the descriptions of Prof. Plieninger, observes, that not only
+the double roots of the teeth and their crowns presenting several cusps,
+resemble those of Mammalia, but the cingulum also, or ridge surrounding the
+base of that part of the body of the tooth which was exposed or above the
+gum, is a character distinguishing them from fish and reptiles. "The
+arrangement of the six cusps or tubercles in two rows, in fig. 529., with a
+groove or depression between them and the oblong form of the tooth, lead
+him, he says, to regard it as a molar of the lower jaw. Both the teeth
+differ from those of the Stonesfield Mammalia[xiv-A], but do not supply
+sufficient data for determining to what order they belonged. Even in regard
+to the Stonesfield jaws, where we possess so much ampler materials, we
+cannot safely pronounce on the order."
+
+Professor Plieninger has sent me a cast of the smaller tooth, which
+exhibits well the characteristic mammalian test, the double fang; but Mr.
+Owen, to whom I have shown it, is not able to recognize its affinity with
+any mammalian type, recent or extinct, known to him.
+
+It has already been stated that the stratum in which the above-mentioned
+fossils occur is intermediate between the lias and the uppermost member of
+the trias. That it is really triassic may be deduced from the following
+considerations. In Würtemberg there are two "bone-beds," one of great
+extent, and very rich in the remains of fish and reptiles, which intervenes
+between the muschelkalk and keuper, the other, containing the Microlestes,
+less extensive and fossiliferous, which rests on the keuper, or superior
+member of the trias, and is covered by the sandstone of the lias. The
+last-mentioned breccia therefore occupies the same place as the well-known
+English "bone-bed" of Axmouth and Aust-cliff near Bristol, which is
+shown[xv-A] to include characteristic species of muschelkalk fish, of the
+genus Saurichthys, Hybodus, and Gyrolepis. In both the Würtemberg bone-beds
+these three genera are also found, and one of the _species_, Saurichthys
+Mougeotii, is common to both the lower and upper breccias, 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.
+
+Previous to this discovery of Professor Plieninger, the most ancient of
+known fossil Mammalia were those of the Stonesfield slate, a subdivision of
+the Lower Oolite[xv-B] no representative of this class having as yet been
+met with in the Fuller's earth, or inferior Oolite (see Table, p. 258.),
+nor in any member of the lias.
+
+_Thecodont Saurians._--This family of reptiles is common to the Trias and
+Permian groups in Germany, and the geologists employed in the government
+survey of Great Britain have come to the conclusion, that the rock
+containing the two species alluded to at p. 306., and of which the teeth
+are represented in figs. 348, 349., ought rather to be referred to the
+Trias than to the Permian group.
+
+
+CRETACEOUS GASTEROPODA.
+
+In speaking of the chalk of Faxoe in Denmark (p. 210.) or the highest
+member of the Cretaceous series, I have remarked that it is characterized
+by univalve Mollusca, both spiral and patelliform, which are wanting or
+rare in the white chalk of Europe. This last statement requires, I find,
+some modification. It holds true in regard to certain forms, such as Cypræa
+and Oliva, found at Faxoe; but M. A. d'Orbigny enumerates 24 species of
+Gasteropoda from the white chalk (Terrain Sénonien) of France alone. The
+same author describes 134 French species of Gasteropoda from the chloritic
+chalk marl and upper greensand (Turonien), 77 from the gault, and 90 from
+the lower greensand (Neocomien), in all 325 species of Gasteropoda, from
+the cretaceous group below the Maestricht beds. Among these he refers 1 to
+the genus Mitra, 17 to Fusus, 17 to Trochus, 4 to Emarginula, and 36 to
+Cerithium. Notwithstanding, therefore, the peculiarity of the chambered
+univalves of various genera, so abundant in the chalk, the Mollusca of the
+period approximate in character to the tertiary and recent Fauna far more
+than was formerly supposed.
+
+
+DICOTYLEDONOUS LEAVES IN LOWER CRETACEOUS STRATA.
+
+M. Adolphe Brongniart when founding his classification of the fossiliferous
+strata in reference to their imbedded fossil plants, has placed the
+cretaceous group in the same division with the tertiary, that is to say, in
+his "Age of Angiosperms."[xvi-A] This arrangement is based on the fact,
+that the cretaceous plants display a transition character from the
+vegetation of the secondary to that of the tertiary periods. Coniferæ and
+Cycadeæ still flourished as in the preceding oolitic and triassic epochs;
+but with these fossils, some well-marked leaves of dicotyledonous trees
+referred to several species of the genus Credneria, had been found in
+Germany in the Quadersandstein and Pläner-kalk. Still more recently, Dr.
+Debey of Aix-la-Chapelle has met with a great variety of other leaves of
+dicotyledonous plants in the cretaceous flora[xvi-B], of which he
+enumerates no less than 26 species, some of the leaves being from four to
+six inches in length, and in a beautiful state of preservation. In the
+absence of the organs of fructification and of fossil fruits, the number of
+species may be exaggerated; but we may nevertheless affirm, reasoning from
+our present data, that in the lower chalk of Aix-la-Chapelle,
+Dicotyledonous Angiosperms flourished nearly in equal proportions with
+Gymnosperms; a fact of great significance, as some geologists had wished to
+connect the rarity of dicotyledonous trees with a peculiarity in the state
+of the atmosphere in the earlier ages of the planet, imagining that a
+denser air and noxious gases, especially carbonic acid in excess, were
+adverse to the prevalence, not only of the quick-breathing classes of
+animals, (mammalia and birds,) but to a flora like that now existing, while
+it favoured the predominance of reptile life, and a cryptogamic and
+gymnospermous flora. The co-existence, therefore, of dicotyledonous
+angiosperms in abundance with Cycads and Coniferæ, and with a rich
+reptilian fauna comprising the Iguanodon, Ichthyosaurus, Pliosaurus, and
+Pterodactyl, in the lower cretaceous series tends, like the oolitic
+mammalia of Stonesfield and Stuttgart, and the triassic birds of
+Connecticut, to dispel the idea of a meteorological state of things in the
+secondary periods widely distinct from that now prevailing.
+
+_General remarks._--In the preliminary chapters of "The Principles of
+Geology," in the first and subsequent editions, I have considered the
+question, how far the changes of the earth's crust in past times confirm or
+invalidate the popular hypothesis of a gradual improvement in the
+habitable condition of the planet, accompanied by a contemporaneous
+development and progression in organic life. It had long been a favourite
+theory, that in the earlier ages to which we can carry back our geological
+researches, the earth was shaken by more frequent and terrible earthquakes
+than now, and that there was no certainty nor stability in the order of the
+natural world. A few sea-weeds and zoophytes, or plants and animals of the
+simplest organization, were alone capable of existing in a state of things
+so unfixed and unstable. But in proportion as the conditions of existence
+improved, and great convulsions and catastrophes became rarer and more
+partial, flowering plants were added to the cryptogamic class, and by the
+introduction of more and more perfect species, a varied and complex flora
+was at last established. In like manner, in the animal kingdom, the
+zoophyte, the brachiopod, the cephalopod, the fish, the reptile, the bird,
+and the warm-blooded quadruped made their entrance into the earth, one
+after the other, until finally, after the close of the tertiary period,
+came the quadrumanous mammalia, most nearly resembling man in outward form
+and internal structure, and followed soon afterwards, if not accompanied at
+first, by the human race itself.
+
+The objections which, in 1830, I urged against this doctrine[xvii-A], in so
+far as relates to the passage of the earth from a chaotic to a more settled
+condition, have since been embraced by a large and steadily increasing
+school of geologists; and in reference to the animate world, it will be
+seen, on comparing the present state of our knowledge with that which we
+possessed twenty years ago, how fully I was justified in declaring the
+insufficiency of the data on which such bold generalizations, respecting
+progressive development, were based. Speaking of the absence, from the
+tertiary formations, of fossil Quadrumana, I observed, in 1830, that "we
+had no right to expect to have detected any remains of tribes which live in
+trees, until we knew more of those quadrupeds which frequent marshes,
+rivers, and the borders of lakes, such being usually first met with in a
+fossil state."[xvii-B] I also added, "if we are led to infer, from the
+presence of crocodiles and turtles in the London clay, and from the
+cocoa-nuts and spices found in the isle of Sheppey, that at the period when
+our older tertiary strata were formed, the climate was hot enough for the
+Quadrumana, we nevertheless could not hope to discover any of their
+skeletons, until we had made considerable progress in ascertaining what
+were the contemporary Pachydermata; and not one of these has been
+discovered as yet in any strata of this epoch in England."
+
+Nine years afterwards, when these fossil Pachyderms had been found in the
+London clay, and in the sandy strata at its base, the remains of a monkey,
+of the genus Macacus, were detected near Woodbridge, in Suffolk; and other
+Quadrumana had been met with, a short time previously, in different stages
+of the tertiary series, in India, France, and Brazil.
+
+When we consider the small area of the earth's surface hitherto examined
+geologically, and our scanty acquaintance with the fossil Vertebrata, even
+of the environs of great European capitals, it is truly surprising that any
+naturalist should be rash enough to assume that the Lower Eocene deposits
+mark the era of the first creation of Quadrumana. It is, however, still
+more unphilosophical to infer from a single extinct species of this order,
+obtained in a latitude far from the tropics, that the Eocene Quadrumana had
+not attained as high a grade of organization as those of our own times,
+when the naturalist is acquainted with all, or nearly all, the species of
+monkeys, apes and orangs which are contemporary with man.
+
+To return to the year 1830, Mammalia had not then been traced to rocks of
+higher antiquity than the Stonesfield Oolite, whereas we have just seen
+that memorials of this class have at length made their appearance in the
+Trias of Germany. In 1830 birds had been discovered no lower in the series
+than the Paris gypsum, or Middle Eocene. Their bones have now been found
+both in England and the Swiss Alps in the Lower Eocene, and their existence
+has been established by foot-prints in the triassic epoch in North America
+(p. 297.). Reptiles in 1830 had not been detected in rocks older than the
+Magnesian limestone, or Permian formation; whereas the skeletons of four
+species have since been brought to light (see p. 336.) in the
+coal-measures, and one in the Old Red sandstone, of Europe, while the
+footprints of three or four more have been observed in carboniferous rocks
+of North America, not to mention the chelonian trail above described, from
+the most ancient of the fossiliferous rocks of Canada, the "Potsdam
+Sandstone," which lies at the base of the Lower Silurian system.
+(See above, p. vii.)
+
+Lastly, the remains of fish, which in 1830 were scarcely recognized in
+deposits older than the coal, have now been found plentifully in the
+Devonian, and sparingly in the Silurian, strata; though not in any
+formation of such high antiquity as the Chelonian of Montreal.
+
+Previously to the discovery last mentioned, it was by no means uncommon for
+paleontologists to speak with confidence of fish as having been created
+before reptiles. It was deemed reasonable to suppose that the introduction
+of a particular class or order of beings into the planet coincided, in
+date, with the age of the oldest rock to which the remains of that class or
+order happened then to have been traced back. To be consistent with
+themselves, the same naturalists ought now to take for granted that
+reptiles were called into existence before fish. This they will not do,
+because such a conclusion would militate against their favourite hypothesis
+of an ascending scale, according to which Nature "evolved the organic
+world," rendering it more and more perfect in the lapse of ages.
+
+In our efforts to arrive at sound theoretical views on such a question, it
+would seem most natural to turn to the marine invertebrate animals as to a
+class affording the most complete series of monuments that have come down
+to us, and where we can find corresponding terms of comparison, in strata
+of every age. If, in this more complete series of her archives, Nature had
+really exhibited a more simple grade of organization in fossils of the
+remotest antiquity, we might have suspected that there was some foundation
+of facts in the theory of successive development. But what do we find? In
+the Lower Silurian there is a full representation of the Radiata, Mollusca,
+and Articulata proper to the sea. The marine Fauna, indeed, in those three
+classes, is so rich as almost to imply a more perfect development than that
+which now peoples the ocean. Thus, in the great division of the Radiata, we
+find asteroid and helianthoid zoophytes, besides crinoid and cystidean
+echinoderms. In the Mollusca of the same most ancient epoch M. Barrande
+enumerates, in Bohemia alone, the astonishing number of 253 species of
+Cephalopoda. In the Articulata we have the crustaceans, represented by more
+than 200 species of Trilobites, not to mention other genera.
+
+It is only then, in reference to the Vertebrata, that the argument of
+degeneracy in proportion as we trace fossils back to older formations can
+be maintained; and the dogma rests mainly for its support on negative
+evidence, whether deduced from the entire absence of the fossil
+representatives of certain classes in particular rocks, or the low grade of
+the first few species of a class which chance has thrown in our way.
+
+The scarcity of all memorials of birds in strata below the Eocene, has been
+a subject of surprise to some geologists. The bones formerly referred to
+birds in the Wealden and Chalk, are now admitted to have belonged to flying
+reptiles, of various sizes, one of them from the Kentish chalk so large as
+to have measured 16 feet 6 inches from tip to tip of its outstretched
+wings. Whether some elongated bones of the Stonesfield Oolite should be
+referred to birds, which they seem greatly to resemble in microscopic
+structure or to Pterodactyles, is a point now under investigation. If it
+should be proved that no osseous remains of the class Aves have hitherto
+been derived from any secondary or primary formation, we must not too
+hastily conclude that birds were even scarce in these periods. The rarity
+of such fossils in the Eocene marine strata is very striking. In 1846,
+Professor Owen, in his "History of the Fossil Mammalia and Birds of Great
+Britain," was unable to obtain more than four or five fragments of bones
+and skulls of birds from the London Clay, by the aid of which four species
+were recognized. Even so recently, therefore, as 1846, as much was known of
+the Mammalia of the Stonesfield Oolite, as of the ornithic Fauna of our
+English Eocene deposits.
+
+To reason correctly on the value of negative facts in this branch of
+Paleontology, we must first have ascertained how far the relics of birds
+are now becoming preserved in new strata, whether marine, fluviatile, or
+lacustrine. I have explained, in the "Principles of Geology," that the
+imbedding of the bones of living birds in deposits now in progress in
+inland lakes appears to be extremely rare. In the shell-marl of Scotland,
+which is made up bodily of the shells of the genera Limneus, Planorbis,
+Succinea, and Valvata, and in which the skeletons of deer and oxen abound,
+we find no bones of birds. Yet we know that, before the lakes were drained
+which yield this marl used in agriculture, the surface of the water and the
+bordering swamps were covered with wild ducks, herons, and other fowl. They
+left no memorials behind them, because, if they perished on the land, their
+bodies decomposed or became the prey of carnivorous animals; if on the
+water, they were buoyant and floated till they were devoured by predaceous
+fish or birds. The same causes of obliteration have no power to efface the
+foot-prints which the same creatures may leave, under favourable
+circumstances, imprinted on an ancient mud-bank or shore, on which new
+strata may be from time to time thrown down. In the red mud of recent
+origin spread over wide areas by the high tides of the bay of Fundy,
+innumerable foot-tracks of recent birds (Tringa minuta) are preserved in
+successive layers, and hardened by the sun. Yet none of the bones of these
+birds, though diligently searched for, have yet been discovered in digging
+trenches through the red mud. It is true that, in a few spots, the bones of
+birds have been met with plentifully in the older tertiary strata, but
+always in rocks of freshwater origin, such as the Paris gypsum or the
+lacustrine limestone of the Limagne d'Auvergne. In strata of the same
+age, in Belgium and other European countries, or in the United States,
+where no less careful search has been made, few, if any, fossil birds
+have come to light.
+
+We ought, therefore, most clearly to perceive that it is no part of the
+plan of Nature to hand down to after times a complete or systematic record
+of the former history of the animate world. The preservation of the relics,
+even of aquatic tribes of animals, is an exception to the general rule,
+although time may so multiply exceptional cases that they may seem to
+constitute the rule; and may thus impose upon the imagination, leading us
+to infer the non-existence of creatures of which no monuments are extant.
+Hitherto our acquaintance with the birds, and even the Mammalia, of the
+Eocene period has depended, almost everywhere, on single specimens, or on a
+few individuals found in one spot. It has therefore depended on what we
+commonly call chance; and we must not wonder if the casual discovery of a
+tertiary, secondary, or primary rock, rich in fossil impressions of the
+foot-prints of birds or quadrupeds, should modify or suddenly overthrow all
+theories based on negative facts.
+
+The chief reason why we meet more readily with the remains of every class
+in tertiary than in secondary strata, is simply that the older rocks are
+more and more exclusively marine in proportion as we depart farther and
+farther from periods during which the existing continents were built up.
+The secondary and primary formations are, for the most part, marine,--not
+because the ocean was more universal in past times, but because the epochs
+which preceded the Eocene were so distant from our own, that entire
+continents have been since submerged.
+
+I have alluded at p. 299. to Mr. Darwin's account of the South American
+Ostriches, seen on the coast of Buenos Ayres, walking at low water over
+extensive mud-banks, which are then dry, for the sake of feeding on small
+fish. Perhaps no bird of such perfect organization as the eagle or vulture
+may ever accompany these ostriches. Certainly, we cannot expect the condor
+of the Andes to leave its trail on such a shore; and no traveller, after
+searching for footprints along the whole eastern coast of South America,
+would venture to speculate, from the results of such an inquiry, on the
+extent, variety, or development of the feathered Fauna of the interior
+of that continent.
+
+The absence of Cetacea from rocks older than the Eocene has been frequently
+adduced as lending countenance to the theory of the late appearance of the
+highest class of Vertebrata on the earth. That we have hitherto failed to
+detect them in the Oolite or Trias, does not imply, as we have now seen,
+that Mammalia were not then created. Even in the Eocene strata of Europe,
+the discovery of Cetaceans has never kept pace with that of land
+quadrupeds. The only instance cited in Great Britain is a species of
+Monodon, from the London clay, of doubtful authenticity as to its
+geological position. On the other hand, the gigantic Zeuglodon of North
+America (see p. 207.), occurs abundantly in the Middle Eocene strata
+of Georgia and Alabama, from which as yet no bones of land-quadrupeds
+have been obtained.
+
+Professor Sedgwick states in a recent work[xxi-A], that he possesses in the
+Woodwardian Museum, a mass of anchylosed cervical vertebræ of a whale which
+he found near Ely, and which he believes to have been washed out of the
+Kimmeridge clay, a member of the Upper Oolite; but its true geological site
+is not well determined. It differs, says Professor Owen, from any other
+known fossil or recent whale.
+
+In the present imperfect state then of our information, we can scarcely say
+more than that the Cetacea may have been scarce, in the secondary and
+primary periods. It is quite conceivable that when aquatic saurians, some
+of them carnivorous, like the Ichthyosaurus, were swarming in the sea, and
+when there were large herbivorous reptiles, like the Iguanodon, on the
+land, such reptiles may, to a certain extent, have superseded the Cetacea,
+and discharged their functions in the animal economy.
+
+The views which I proposed originally in the Principles of Geology in
+opposition to the theory of progressive development may be thus briefly
+explained. From the earliest period at which plants and animals can be
+proved to have existed, there has been a continual change going on in the
+position of land and sea, accompanied by great fluctuations of climate. To
+these ever-varying geographical and climatal conditions the state of the
+animate world has been unceasingly adapted. No satisfactory proof has yet
+been discovered of the gradual passage of the earth from a chaotic to a
+more habitable state, nor of a law of progressive development governing the
+extinction and renovation of species, and causing the Fauna and Flora to
+pass from an embryonic to a more perfect condition, from a simple to a
+more complex organization.
+
+The principle of adaptation above alluded to, appears to have been
+analogous to that which now peoples the arctic, temperate, and tropical
+regions contemporaneously with distinct assemblages of species and
+genera, or which independently of mere temperature gives rise to a
+predominance of the marsupial tribe of quadrupeds in Australia, and
+of the placental tribe in Asia and Europe, or to a profusion of reptiles
+without mammalia in the Galapagos Archipelago, and of mammalia without
+reptiles in Greenland.[xxii-A]
+
+This theory implies, almost necessarily, a very unequal representation at
+successive periods of the principal classes and orders of plants and
+animals, if not in the whole globe, at least throughout very wide areas.
+Thus, for example, the proportional number of genera, species, and
+individuals in the vertebrate class may differ, in two different and
+distinct epochs, to an extent unparalleled by any two contemporaneous
+Faunas, because in the course of millions of ages, the contrast of climate
+and geographical conditions may exceed the difference now observable in
+polar and equatorial latitudes.
+
+I shall conclude by observing, that if the doctrine of successive
+development had been paleontologically true, as the new discoveries above
+enumerated show that it is not; if the sponge, the cephalopod, the fish,
+the reptile, the bird, and the mammifer had followed each other in regular
+chronological order--the creation of each class being separated from the
+other by vast intervals of time; and if it were admitted that Man was
+created last of all, still we should by no means be able to recognize, in
+his entrance upon the earth, the last term of one and the same series of
+progressive developments. For the superiority of Man, as compared to the
+irrational mammalia, is one of kind, rather than of degree, consisting in a
+rational and moral nature, with an intellect capable of indefinite
+progression, and not in the perfection of his physical organization, or
+those instincts in which he resembles the brutes. He may be considered as a
+link in the same unbroken chain of being, if we regard him simply as a new
+species--a member of the animal kingdom--subject, like other species, to
+certain fixed and invariable laws, and adapted like them to the state of
+the animate and inanimate world prevailing at the time of his creation.
+Physically considered, he may form part of an indefinite series of
+terrestrial changes past, present, and to come; but morally and
+intellectually he may belong to another system of things--of things
+immaterial--a system which is not permitted to interrupt or disturb the
+course of the material world, or the laws which govern its changes.[xxii-B]
+
+
+FOOTNOTES:
+
+[vii-A] Travels in North America by the Author, vol. ii. chap. 22.
+
+[vii-B] Ibid. 1842.
+
+[viii-A] Quart. Journ. Geol. Soc. 1851, vol. vii. p. 250.
+
+[ix-A] The generally received determination of the age of this rock is
+probably correct; but as there are no overlying coal-measures and no
+well-known Devonian fossils in the whitish stone of Elgin, and as I have
+not personally explored the geology of that district, I cannot speak as
+confidently as in regard to the age of the Montreal Chelonian.
+
+[xii-A] H. D. Rogers, Proceedings of Amer. Assoc. of Science, Albany, 1851.
+
+[xii-B] See Memoir by the Author, Quart. Journ. Geol. Soc., vol.
+vii. p. 240.
+
+[xiii-A] Würtembergisch. Naturwissen. Jahreshefte, 3 Jahr. Stuttgart, 1847.
+
+[xiii-B] Nov. Act. Acad. Cæsar. Leopold. Nat. Cur. 1850, p. 902. For
+figures, see ibid. plate xxi. figs. 14, 15, 16, 17.
+
+[xiv-A] See Manual, p. 268.
+
+[xv-A] Manual, p. 289.
+
+[xv-B] Ibid. p. 268.
+
+[xvi-A] For Terminology, see Note, p. 223.
+
+[xvi-B] Quart. Journ. vol. vii. Memoirs, p. 111.
+
+[xvii-A] Principles, 1st ed. chaps. v. and ix.
+
+[xvii-B] Ibid. p. 153.
+
+[xxi-A] Preface to 5th ed. of Studies of University of Cambridge.
+
+[xxii-A] Principles, 4th ed. 1835, vol. i. p. 231, and vol. i. chap. 9.
+subsequent ed.
+
+[xxii-B] In my Anniversary Address, for 1851, to the Geological Society,
+the reader will find a full discussion of the facts and arguments which
+bear on the theory of progressive development.--Quart. Journ. Geol.
+Soc., vol. vii.
+
+
+
+
+  CONTENTS.
+
+
+  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 Page                           1
+
+
+  CHAPTER II.
+
+  AQUEOUS ROCKS--THEIR COMPOSITION AND FORMS OF STRATIFICATION.
+
+  Mineral composition of strata--Arenaceous
+  rocks--Argillaceous--Calcareous--Gypsum--Forms of
+  stratification--Original horizontality--Thinning out--Diagonal
+  arrangement--Ripple mark                                               10
+
+
+  CHAPTER III.
+
+  ARRANGEMENT OF FOSSILS IN STRATA--FRESHWATER 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
+  and semi-opal formed of infusoria--Chalk derived principally from
+  organic bodies--Distinction of freshwater from marine formations--Genera
+  of freshwater and land shells--Rules for recognizing marine
+  testacea--Gyrogonite and chara--Freshwater fishes--Alternation of marine
+  and freshwater deposits--Lym-Fiord                                     21
+
+
+  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--Göppert's
+  experiments--Precipitation of stony matter most rapid where putrefaction
+  is going on--Source of lime in solution--Silex derived from
+  decomposition of felspar--Proofs of the lapidification of some fossils
+  soon after burial, of others when much decayed                         33
+
+
+  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--Upheaval of extensive masses of horizontal strata--Inclined and
+  vertical stratification--Anticlinal and synclinal lines--Bent strata in
+  east of Scotland--Theory of folding by lateral movement--Creeps--Dip and
+  strike--Structure of the Jura--Various forms of outcrop--Rocks broken by
+  flexure--Inverted position of disturbed strata--Unconformable
+  stratification--Hutton and Playfair on the same--Fractures of
+  strata--Polished surfaces--Faults--Appearance of repeated alternations
+  produced by them--Origin of great faults Page                          44
+
+
+  CHAPTER VI.
+
+  DENUDATION.
+
+  Denudation defined--Its amount equal to the entire mass of stratified
+  deposits in the earth's crust--Horizontal sandstone denuded in
+  Ross-shire--Levelled surface of countries in which great faults
+  occur--Coalbrook Dale--Denuding power of the ocean during the emergence
+  of land--Origin of Valleys--Obliteration of sea-cliffs--Inland
+  sea-cliffs and terraces in the Morea and Sicily--Limestone pillars at
+  St. Mihiel, in France--in Canada--in the Bermudas                      66
+
+
+  CHAPTER VII.
+
+  ALLUVIUM.
+
+  Alluvium described--Due to complicated causes--Of various ages, as shown
+  in Auvergne--How distinguished from rocks _in
+  situ_--River-terraces--Parallel roads of Glen Roy--Various theories
+  respecting their origin                                                79
+
+
+  CHAPTER VIII.
+
+  CHRONOLOGICAL CLASSIFICATION OF ROCKS.
+
+  Aqueous, plutonic, volcanic, and metamorphic rocks, considered
+  chronologically--Lehman's division into primitive and
+  secondary--Werner's addition of a transition class--Neptunian
+  theory--Hutton on igneous origin of granite--How the name of primary was
+  still retained for granite--The term "transition," why faulty--The
+  adherence to the old chronological nomenclature retarded the progress of
+  geology--New hypothesis invented to reconcile the igneous origin of
+  granite to the notion of its high antiquity--Explanation of the
+  chronological nomenclature adopted in this work, so far as regards
+  primary, secondary, and tertiary periods                               89
+
+
+  CHAPTER IX.
+
+  ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS.
+
+  On the 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--Principal
+  groups of strata in western Europe                                     96
+
+
+  CHAPTER X.
+
+  CLASSIFICATION OF TERTIARY FORMATIONS.--POST-PLIOCENE GROUP.
+
+  General principles of classification of tertiary strata--Detached
+  formations scattered over Europe--Strata of Paris and London--More
+  modern groups--Peculiar difficulties in determining the chronology of
+  tertiary formations--Increasing proportion of living species of shells
+  in strata of newer origin--Terms Eocene, Miocene, and
+  Pliocene--Post-Pliocene strata--Recent or human period--Older
+  Post-Pliocene formations of Naples, Uddevalla, and Norway--Ancient
+  upraised delta of the Mississippi--Loess of the Rhine Page            104
+
+
+  CHAPTER XI.
+
+  NEWER PLIOCENE PERIOD.--BOULDER FORMATION.
+
+  Drift of Scandinavia, northern Germany, and Russia--Its northern
+  origin--Not all of the same age--Fundamental rocks polished, grooved,
+  and scratched--Action of glaciers and icebergs--Fossil shells of glacial
+  period--Drift of eastern Norfolk--Associated freshwater deposit--Bent
+  and folded strata lying on undisturbed beds--Shells on Moel
+  Tryfane--Ancient glaciers of North Wales--Irish drift                 121
+
+
+  CHAPTER XII.
+
+  BOULDER FORMATION--_continued_.
+
+  Difficulty of interpreting the phenomena of drift before the glacial
+  hypothesis was adopted--Effects of intense cold in augmenting the
+  quantity of alluvium--Analogy of erratics and scored rocks in North
+  America and Europe--Bayfield on shells in drift of Canada--Great
+  subsidence and re-elevation of land from the sea, required to account
+  for glacial appearances--Why organic remains so rare in northern
+  drift--Mastodon giganteus in United States--Many shells and some
+  quadrupeds survived the glacial cold--Alps an independent centre of
+  dispersion of erratics--Alpine blocks on the Jura--Recent transportation
+  of erratics from the Andes to Chiloe--Meteorite in Asiatic drift      131
+
+
+  CHAPTER XIII.
+
+  NEWER PLIOCENE STRATA AND CAVERN DEPOSITS.
+
+  Chronological classification of Pleistocene formations, why
+  difficult--Freshwater deposits in valley of Thames--In Norfolk
+  cliffs--In Patagonia--Comparative longevity of species in the mammalia
+  and testacea--Fluvio-marine crag of Norwich--Newer Pliocene strata of
+  Sicily--Limestone of great thickness and elevation--Alternation of
+  marine and volcanic formations--Proofs of slow accumulation--Great
+  geographical changes in Sicily since the living fauna and flora began to
+  exist--Osseous breccias and cavern deposits--Sicily--Kirkdale--Origin of
+  stalactite--Australian cave-breccias--Geographical relationship of the
+  provinces of living vertebrata and those of the fossil species of the
+  Pliocene periods--Extinct struthious birds of New Zealand--Teeth of
+  fossil quadrupeds                                                     146
+
+
+  CHAPTER XIV.
+
+  OLDER PLIOCENE AND MIOCENE FORMATIONS.
+
+  Strata of Suffolk termed Red and Coralline crag--Fossils, and proportion
+  of recent species--Depth of sea and climate--Reference of Suffolk crag
+  to the older Pliocene period--Migration of many species of shells
+  southwards during the glacial period--Fossil whales--Subapennine
+  beds--Asti, Sienna, Rome--Miocene formations--Faluns of Touraine--Depth
+  of sea and littoral character of fauna--Tropical climate implied by the
+  testacea--Proportion of recent species of shells--Faluns more ancient
+  than the Suffolk crag--Miocene strata of Bordeaux and Piedmont--Molasse
+  of Switzerland--Tertiary strata of Lisbon--Older Pliocene and Miocene
+  formations in the United States--Sewâlik Hills in India               161
+
+
+  CHAPTER XV.
+
+  UPPER EOCENE FORMATIONS.
+
+  Eocene areas in England and France--Tabular view of French Eocene
+  strata--Upper Eocene group of the Paris basin--Same beds in Belgium and
+  at Berlin--Mayence tertiary strata--Freshwater upper Eocene of Central
+  France--Series of geographical changes since the land emerged in
+  Auvergne--Mineral character an uncertain test of age--Marls containing
+  Cypris--Oolite of Eocene period--Indusial limestone and its
+  origin--Fossil mammalia of the upper Eocene strata in
+  Auvergne--Freshwater strata of the Cantal, calcareous and siliceous--Its
+  resemblance to chalk--Proofs of gradual deposition of strata          174
+
+
+  CHAPTER XVI.
+
+  EOCENE FORMATIONS--_continued_.
+
+  Subdivisions of the Eocene group in the Paris basin--Gypseous
+  series--Extinct quadrupeds--Impulse given to geology by Cuvier's
+  osteological discoveries--Shelly sands called sables moyens--Calcaire
+  grossier--Miliolites--Calcaire siliceux--Lower Eocene in France--Lits
+  coquilliers--Sands and plastic clay--English Eocene strata--Freshwater
+  and fluvio-marine beds--Barton beds--Bagshot and Bracklesham
+  division--Large ophidians and saurians--Lower Eocene and London Clay
+  proper--Fossil plants and shells--Strata of Kyson in Suffolk--Fossil
+  monkey and opossum--Mottled clays and sand below London Clay--Nummulitic
+  formation of Alps and Pyrenees--Its wide geographical extent--Eocene
+  strata in the United States--Section at Claiborne, Alabama--Colossal
+  cetacean--Orbitoid limestone--Burr stone                              190
+
+
+  CHAPTER XVII.
+
+  CRETACEOUS GROUP.
+
+  Divisions of the cretaceous series in North-Western Europe--Upper
+  cretaceous strata--Maestricht beds--Chalk of Faxoe--White
+  chalk--Characteristic fossils--Extinct cephalopoda--Sponges and corals
+  of the chalk--Signs of open and deep sea--White area of white chalk--Its
+  origin from corals and shells--Single pebbles in chalk--Siliceous
+  sandstone in Germany contemporaneous with white chalk--Upper greensand
+  and gault--Lower cretaceous strata--Atherfield section, Isle of
+  Wight--Chalk of South of Europe--Hippurite limestone--Cretaceous
+  Flora--Chalk of United States                                         209
+
+
+  CHAPTER XVIII.
+
+  WEALDEN GROUP.
+
+  The Wealden divisible into Weald Clay, Hastings Sand, and Purbeck
+  Beds--Intercalated between two marine formations--Weald clay and
+  Cypris-bearing strata--Iguanodon--Hastings sands--Fossil fish--Strata
+  formed in shallow water--Brackish water-beds--Upper, middle, and lower
+  Purbeck--Alternations of brackish water, freshwater, and land--Dirt-bed,
+  or ancient soil--Distinct species of fossils in each subdivision of the
+  Wealden--Lapse of time implied--Plants and insects of
+  Wealden--Geographical extent of Wealden--Its relation to the cretaceous
+  and oolitic periods--Movements in the earth's crust to which it owed its
+  origin and submergence                                                225
+
+
+  CHAPTER XIX.
+
+  DENUDATION OF THE CHALK AND WEALDEN.
+
+  Physical geography of certain districts composed of Cretaceous and
+  Wealden strata--Lines of inland chalk-cliffs on the Seine in
+  Normandy--Outstanding pillars and needles of chalk--Denudation of the
+  chalk and Wealden in Surrey, Kent, and Sussex--Chalk once continuous
+  from the North to the South Downs--Anticlinal axis and parallel
+  ridges--Longitudinal and transverse valleys--Chalk escarpments--Rise and
+  denudation of the strata gradual--Ridges formed by harder, valleys by
+  softer beds--Why no alluvium, or wreck of the chalk, in the central
+  district of the Weald--At what periods the Weald valley was
+  denuded--Land has most prevailed where denudation has been
+  greatest--Elephant bed, Brighton                                      238
+
+
+  CHAPTER XX.
+
+  OOLITE AND LIAS.
+
+  Subdivisions of the Oolitic or Jurassic group--Physical geography of the
+  Oolite in England and France--Upper Oolite--Portland stone and
+  fossils--Lithographic stone of Solenhofen--Middle Oolite, coral
+  rag--Zoophytes--Nerinæan limestone--Diceras limestone--Oxford clay,
+  Ammonites and Belemnites--Lower Oolite, Crinoideans--Great Oolite and
+  Bradford clay--Stonesfield slate--Fossil mammalia, placental and
+  marsupial--Resemblance to an Australian fauna--Doctrine of progressive
+  development--Collyweston slates--Yorkshire Oolitic coal-field--Brora
+  coal--Inferior Oolite and fossils                                     257
+
+
+  CHAPTER XXI.
+
+  OOLITE AND LIAS--_continued_.
+
+  Mineral character of Lias--Name of Gryphite limestone--Fossil shells and
+  fish--Ichthyodorulites--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--Origin of the Oolite and Lias, and
+  of alternating calcareous and argillaceous formations--Oolitic
+  coal-field of Virginia, in the United States                          273
+
+
+  CHAPTER XXII.
+
+  TRIAS OR NEW RED SANDSTONE GROUP.
+
+  Distinction between New and Old Red Sandstone--Between Upper and Lower
+  New Red--The Trias and its three divisions--Most largely developed in
+  Germany--Keuper and its fossils--Muschelkalk--Fossil plants of
+  Bunter--Triassic group in England--Bone-bed of Axmouth and Aust--Red
+  Sandstone of Warwickshire and Cheshire--Footsteps of _Chirotherium_ in
+  England and Germany--Osteology of the _Labyrinthodon_--Identification of
+  this Batrachian with the Chirotherium--Origin of Red Sandstone and
+  rock-salt--Hypothesis of saline volcanic exhalations--Theory of the
+  precipitation of salt from inland lakes or lagoons--Saltness of the Red
+  Sea--New Red Sandstone in the United States--Fossil footprints of birds
+  and reptiles in the Valley of the Connecticut--Antiquity of the Red
+  Sandstone containing them                                             286
+
+
+  CHAPTER XXIII.
+
+  PERMIAN OR MAGNESIAN LIMESTONE GROUP.
+
+  Fossils of Magnesian Limestone and Lower New Red distinct from the
+  Triassic--Term Permian--English and German equivalents--Marine shells
+  and corals of English Magnesian limestone--Palæoniscus and other fish
+  of the marl slate--Thecodont Saurians of dolomitic conglomerate of
+  Bristol--Zechstein and Rothliegendes of Thuringia--Permian Flora--Its
+  generic affinity to the carboniferous--Psaronites or tree-ferns       301
+
+
+  CHAPTER XXIV.
+
+  THE COAL OR CARBONIFEROUS GROUP.
+
+  Carboniferous strata in the south-west of England--Superposition of
+  Coal-measures to Mountain limestone--Departure from this type in north
+  of England and Scotland--Section in South Wales--Underclays with
+  Stigmaria--Carboniferous Flora--Ferns, Lepidodendra, Calamites,
+  Asterophyllites, Sigillariæ, Stigmariæ,--Coniferæ--Endogens--Absence of
+  Exogens--Coal, how formed--Erect fossil trees--Parkfield Colliery--St.
+  Etienne, Coal-field--Oblique trees or snags--Fossil forests in Nova
+  Scotia--Brackish water and marine strata--Origin of Clay-iron-stone   308
+
+
+  CHAPTER XXV.
+
+  CARBONIFEROUS GROUP--_continued_.
+
+  Coal-fields of the United States--Section of the country between the
+  Atlantic and Mississippi--Position of land in the carboniferous period
+  eastward of the Alleghanies--Mechanically formed rocks thinning out
+  westward, and limestones thickening--Uniting of many coal-seams into one
+  thick one--Horizontal coal at Brownsville, Pennsylvania--Vast extent and
+  continuity of single seams of coal--Ancient river-channel in Forest of
+  Dean coal-field--Absence of earthy matter in coal--Climate of
+  carboniferous period--Insects in coal--Rarity of air-breathing
+  animals--Great number of fossil fish--First discovery of the skeletons
+  of fossil reptiles--Footprints of reptilians--Mountain limestone--Its
+  corals and marine shells                                              326
+
+
+  CHAPTER XXVI.
+
+  OLD RED SANDSTONE, OR DEVONIAN GROUP.
+
+  Old Red Sandstone of Scotland, and borders of Wales--Fossils usually
+  rare--"Old Red" in Forfarshire--Ichthyolites of Caithness--Distinct
+  lithological type of Old Red in Devon and Cornwall--Term
+  "Devonian"--Organic remains of intermediate character between those of
+  the Carboniferous and Silurian systems--Corals and shells--Devonian
+  strata of Westphalia, the Eifel, Russia, and the United States--Coral
+  reef at Falls of the Ohio--Devonian Flora                             342
+
+
+  CHAPTER XXVII.
+
+  SILURIAN GROUP.
+
+  Silurian strata formerly called transition--Term grauwacké--Subdivisions
+  of Upper and Lower Silurian--Ludlow formation and fossils--Wenlock
+  formation, corals and shells--Caradoc and Llandeilo
+  beds--Graptolites--Lingula--Trilobites--Cystideæ--Vast thickness of
+  Silurian strata in North Wales--Unconformability of Caradoc
+  sandstone--Silurian strata of the United States--Amount of specific
+  agreement of fossils with those of Europe--Great number of
+  brachiopods--Deep-sea origin of Silurian strata--Absence of fluviatile
+  formations--Mineral character of the most ancient fossiliferous rocks
+                                                                        350
+
+
+  CHAPTER XXVIII.
+
+  VOLCANIC ROCKS.
+
+  Trap rocks--Name, whence derived--Their igneous origin at first
+  doubted--Their general appearance and character--Volcanic cones and
+  craters, how formed--Mineral composition and texture of volcanic
+  rocks--Varieties of felspar--Hornblende and augite--Isomorphism--Rocks,
+  how to be studied--Basalt, greenstone, trachyte, porphyry, scoria,
+  amygdaloid, lava, tuff--Alphabetical list, and explanation of names and
+  synonyms, of volcanic rocks--Table of the analyses of minerals most
+  abundant in the volcanic and hypogene rocks                           366
+
+
+  CHAPTER XXIX.
+
+  VOLCANIC ROCKS--_continued_.
+
+  Trap dike--sometimes project--sometimes leave fissures vacant by
+  decomposition--Branches and veins of trap--Dikes more crystalline in the
+  centre--Foreign fragments of rock imbedded--Strata altered at or near
+  the contact--Obliteration of organic remains--Conversion of chalk into
+  marble--and of coal into coke--Inequality in the modifying influence of
+  dikes--Trap interposed between strata--Columnar and globular
+  structure--Relation of trappean rocks to the products of active
+  volcanos--Submarine lava and ejected matter correspond generally to
+  ancient trap--Structure and physical features of Palma and some other
+  extinct volcanos                                                      378
+
+
+  CHAPTER XXX.
+
+  ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS.
+
+  Tests of relative age of volcanic rocks--Test by superposition and
+  intrusion--Dike of Quarrington Hill, Durham--Test by alteration of rocks
+  in contact--Test by organic remains--Test of age by mineral
+  character--Test by included fragments--Volcanic rocks of the
+  Post-Pliocene period--Basalt of Bay of Trezza in Sicily--Post-Pliocene
+  volcanic rocks near Naples--Dikes of Somma--Igneous formations of the
+  Newer Pliocene period--Val di Noto in Sicily                          397
+
+
+  CHAPTER XXXI.
+
+  ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS--_continued_.
+
+  Volcanic rocks of the Older Pliocene period--Tuscany--Rome--Volcanic
+  region of Olot in Catalonia--Cones and lava-currents--Ravines and
+  ancient gravel-beds--Jets of air called Bufadors--Age of the Catalonian
+  volcanos--Miocene period--Brown-coal of the Eifel and contemporaneous
+  trachytic breccias--Age of the brown-coal--Peculiar characters of the
+  volcanos of the upper and lower Eifel--Lake craters--Trass--Hungarian
+  volcanos                                                              408
+
+
+  CHAPTER XXXII.
+
+  ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS--_continued_.
+
+  Volcanic rocks of the Pliocene and Miocene periods
+  continued--Auvergne--Mont Dor--Breccias and alluviums of Mont Perrier,
+  with bones of quadrupeds--River dammed up by lava-current--Range of
+  minor cones from Auvergne to the Vivarais--Monts Dome--Puy de Côme--Puy
+  de Pariou--Cones not denuded by general flood--Velay--Bones of
+  quadrupeds buried in scoriæ--Cantal--Eocene volcanic rocks--Tuffs near
+  Clermont--Hill of Gergovia--Trap of Cretaceous period--Oolitic
+  period--New Red Sandstone period--Carboniferous period--Old Red
+  Sandstone period--"Rock and Spindle" near St. Andrews--Silurian
+  period--Cambrian volcanic rocks                                       422
+
+
+  CHAPTER XXXIII.
+
+  PLUTONIC ROCKS--GRANITE.
+
+  General aspect of granite--Decomposing into spherical masses--Rude
+  columnar structure--Analogy and difference of volcanic and plutonic
+  formations--Minerals in granite, and their arrangement--Graphic and
+  porphyritic granite--Mutual penetration of crystals of quartz and
+  felspar--Occasional minerals--Syenite--Syenitic, talcose, and schorly
+  granites--Eurite--Passage of granite into trap--Examples near
+  Christiania and in Aberdeenshire--Analogy in composition of trachyte and
+  granite--Granite veins in Glen Tilt, Cornwall, the Valorsine, and other
+  countries--Different composition of veins from main body of
+  granite--Metalliferous veins in strata near their junction with
+  granite--Apparent isolation of nodules of granite--Quartz veins--Whether
+  plutonic rocks are ever overlying--Their exposure at the surface due
+  to denudation                                                         436
+
+
+  CHAPTER XXXIV.
+
+  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--Tertiary 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--On the
+  probable age of the granites of Arran, in Scotland                    449
+
+
+  CHAPTER XXXV.
+
+  METAMORPHIC ROCKS.
+
+  General character of metamorphic rocks--Gneiss--Hornblende-schist
+  --Mica-schist--Clay-slate--Quartzite--Chlorite-schist--Metamorphic
+  limestone--Alphabetical list and explanation of other rocks of this
+  family--Origin of the metamorphic strata--Their stratification is real
+  and distinct from cleavage--Joints and slaty cleavage--Supposed causes
+  of these structures--how far connected with crystalline action        463
+
+
+  CHAPTER XXXVI.
+
+  METAMORPHIC ROCKS--_continued_.
+
+  Strata near some 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--Time may enable this
+  action to pervade denser masses--From what kinds of sedimentary rock
+  each variety of the metamorphic class may be derived--Certain objections
+  to the metamorphic theory considered--Lamination of trachyte and
+  obsidian due to motion--Whether some kinds of gneiss have become
+  schistose by a similar action                                         473
+
+
+  CHAPTER XXXVII.
+
+  ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.
+
+  Age of each set of metamorphic strata twofold--Test of age by fossils
+  and mineral character not available--Test by superposition
+  ambiguous--Conversion of dense masses of fossiliferous strata into
+  metamorphic rocks--Limestone and shale of Carrara--Metamorphic strata of
+  modern periods in the Alps of Switzerland and Savoy--Why the visible
+  crystalline strata are none of them very modern--Order of succession in
+  metamorphic rocks--Uniformity of mineral character--Why the metamorphic
+  strata are less calcareous than the fossiliferous                     481
+
+
+  CHAPTER XXXVIII.
+
+  MINERAL VEINS.
+
+  Werner's doctrine that mineral veins were fissures filled from
+  above--Veins of segregation--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--Shells and pebbles in lodes--Evidence
+  of the successive enlargement and re-opening of veins--Fournet's
+  observations in Auvergne--Dimensions of veins--Why some alternately
+  swell out and contract--Filling of lodes by sublimation from
+  below--Chemical and electrical action--Relative age of the precious
+  metals--Copper and lead veins in Ireland older than Cornish tin--Lead
+  vein in lias, Glamorganshire--Gold in Russia--Connection of hot springs
+  and mineral veins--Concluding remarks                                 488
+
+       *       *       *       *       *
+
+_Dates of the successive Editions of the "Principles" and "Elements" (or
+Manual) of Geology, by the Author._
+
+
+  Principles, 1st vol. in octavo, published in - - - Jan. 1830.
+
+  ----, 2d vol.  do. - - - - - - - - - - - - - - - - Jan. 1832.
+
+  ----, 1st vol. 2d edition in octavo  - - - - - - -      1832.
+
+  ----, 2d vol. 2d edition  do.  - - - - - - - - - - Jan. 1833.
+
+  ----, 3d vol. 1st edition  do. - - - - - - - - - - May  1833.
+
+  ----, New edition (called the 3d) of the whole work in 4 vols.
+          12mo. - - - - - - - - - - - - - - - - - - - May  1834.
+
+  ----, 4th edition, 4 vols. 12mo. - - - - - - - - - June 1835.
+
+  ----, 5th edition, do. do. - - - - - - - - - - - - Mar. 1837.
+
+  Elements, 1st edition in one vol.  - - - - - - - - July 1838.
+
+  Principles, 6th edition, 3 vols. 12mo. - - - - - - June 1840.
+
+  Elements, 2d edition in 2 vols. 12mo.  - - - - - - July 1841.
+
+  Principles, 7th edition in one vol. 8vo. - - - - - Feb. 1847.
+
+  ----, 8th edition, now published in one vol. 8vo. - May 1850.
+
+  Manual of Elementary Geology (or "Elements," 3d edition), now
+  published in one vol. 8vo.  - - - - - - - - - - - - Jan. 1851.
+
+
+
+
+_Works by Sir Charles Lyell._
+
+
+  I.
+
+  TRAVELS IN NORTH AMERICA,--1841-2. With Geological Observations on the
+  United States, Canada, and Nova Scotia. With large coloured geological
+  Map and Plates. 2 vols. post 8vo. 21_s._
+
+  II.
+
+  A SECOND VISIT TO THE UNITED STATES,--1845-6. _Second Edition._ 2 vols.
+  post 8vo. 18_s._
+
+  III.
+
+  PRINCIPLES OF GEOLOGY; or the Modern Changes of the Earth and its
+  Inhabitants considered, as illustrative of Geology. _Eighth Edition,
+  thoroughly revised._ With Maps, Plates, and Woodcuts. 8vo. 18_s._
+
+  IV.
+
+  A MANUAL OF ELEMENTARY GEOLOGY; or the ANCIENT CHANGES of the Earth and
+  its Inhabitants, as illustrated by Geological Monuments. Fourth Edition.
+  _Thoroughly revised._ With 531 Woodcuts and Plates. 8vo. 12_s._
+
+
+
+
+MANUAL OF ELEMENTARY GEOLOGY.
+
+
+
+
+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 +gê+, _ge_, the
+earth, and +logos+, _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, or 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 older 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.
+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, freshwater 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 colour, and are
+occasionally characterized by containing drift-wood or shells. The shells
+may belong to species peculiar to the river, but are sometimes those of
+marine testacea, washed into the mouth of the estuary during storms.
+
+The annual floods of the Nile in Egypt are well known, and the fertile
+deposits of mud which they leave on the plains. This mud 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.[3-A]
+
+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 different rocks mingled together. They are like the shingle of a
+sea-beach, or pebbles formed in the beds of torrents and rivers, which are
+carried down into the ocean wherever these descend from high grounds
+bordering a coast. There the gravel is spread out by the waves and currents
+over a considerable space; but during seasons of drought the torrents and
+rivers are nearly dry, and have only power to convey fine sand or mud into
+the sea. Hence, alternate layers of gravel and fine sediment accumulate
+under water, and such alternations are found by geologists in the interior
+of every continent.[4-A]
+
+If a stratified arrangement, and the rounded forms 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 8000 feet in the
+Pyrenees, 10,000 in the Alps, 13,000 in the Andes, and above 16,000 feet
+in the Himalayas.[4-B]
+
+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.
+
+When geology was first cultivated, it was a general belief, that these
+marine shells and other fossils were the effects and proofs of the deluge
+of Noah; but all who have carefully investigated the phenomena have long
+rejected this doctrine. A transient flood might be supposed to leave behind
+it, here and there upon the surface, scattered heaps of mud, sand, and
+shingle, with shells confusedly intermixed; but the strata containing
+fossils are not superficial deposits, and do not simply cover the earth,
+but constitute the entire mass of mountains. Nor are the fossils mingled
+without reference to the original habits and natures of the creatures of
+which they are the memorials; those, for example, being found associated
+together which lived in deep or in shallow water, near the shore or far
+from it, in brackish or in salt water.
+
+It has, moreover, been a favourite notion of some modern writers, who were
+aware that fossil bodies could not all be referred to the deluge, that
+they, and the strata in which they are entombed, might have been deposited
+in the bed of the ocean during the period which intervened between the
+creation of man and the deluge. They have imagined that the antediluvian
+bed of the ocean, after having been the receptacle of many stratified
+deposits, became converted, at the time of the flood, into the lands which
+we inhabit, and that the ancient continents were at the same time
+submerged, and became the bed of the present sea. This hypothesis, although
+preferable to the diluvial theory before alluded to, since it admits that
+all fossiliferous strata were successively thrown down from water, is yet
+wholly inadequate to explain the repeated revolutions which the earth has
+undergone, and the signs which the existing continents exhibit, in most
+regions, of having emerged from the ocean at an era far more remote than
+four thousand years from the present time. Ample proofs of these reiterated
+revolutions will be given in the sequel, and it will be seen that many
+distinct sets of sedimentary strata, each several hundreds or thousands of
+feet thick, are piled one upon the other in the earth's crust, each
+containing peculiar fossil animals and plants which are distinguishable
+with few exceptions from species now living. The mass of some of these
+strata consists almost entirely of corals, others are made up of shells,
+others of plants turned into coal, while some are without fossils. In one
+set of strata the species of fossils are marine; in another, lying
+immediately above or below, they as clearly prove that the deposit was
+formed in a brackish estuary or lake. When the student has more fully
+examined into these appearances, he will become convinced that the time
+required for the origin of the rocks composing the actual continents must
+have been far greater than that which is conceded by the theory above
+alluded to; and likewise that no one universal and sudden conversion of sea
+into land will account for geological appearances.
+
+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 characterized 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 Ardèche,
+towards the centre and south of France, in which are several hundred
+conical hills having the forms of modern volcanos, 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 volcanos. 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 volcanos 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
+volcanos, 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
+volcanos. 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 volcanos 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 volcanos. 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 volcanos 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, &c.).--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 by
+which geologists have been led to infer the analogy of the rocks in
+question to others now in progress at the surface. The result, however, may
+be briefly stated. All the various kinds of granite, which constitute the
+plutonic family, are supposed to be of igneous origin, but to have been
+formed under great pressure, at considerable depths in the earth, or
+sometimes, perhaps, under a certain weight of incumbent water. Like the
+lava of volcanos, they have been melted, and have afterwards cooled and
+crystallized, 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.
+
+Although granite has often pierced through other strata, it has rarely, if
+ever, been observed to rest upon them, as if it had overflowed. But as this
+is continually the case with the volcanic rocks, they have been styled,
+from this peculiarity, "overlying" by Dr. MacCulloch; and Mr. Necker has
+proposed the term "underlying" for the granites, to designate the opposite
+mode in which they almost invariably present themselves.
+
+_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 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
+into slates called mica-schist and hornblende-schist, all signs of 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. Whether hot water or
+steam permeating stratified masses, or electricity, or any other causes
+have co-operated to produce the crystalline texture, may be matter of
+speculation, but it is clear that the plutonic influence has sometimes
+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+, meta, _trans_, and +morphê+,
+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. 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, plutonic
+or metamorphic, 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 term
+primary, which was formerly used for the whole, must be abandoned, as it
+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 +hypo+, _under_, and +ginomai+,
+_to be_, or _to be born_; a word implying the theory that granite, gneiss,
+and the other crystalline formations are alike _nether-formed_ rocks, or
+rocks which have not assumed their present form and structure at the
+surface. This occurs in 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.
+
+
+FOOTNOTES:
+
+[3-A] See Principles of Geology, by the Author, Index, "Nile,"
+"Rivers," &c.
+
+[4-A] See p. 18.
+
+[4-B] See Geograph. Journ. vol. iv. p. 64.
+
+
+
+
+CHAPTER II.
+
+AQUEOUS ROCKS--THEIR COMPOSITION AND FORMS OF STRATIFICATION.
+
+   Mineral composition of strata--Arenaceous
+   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 arenaceous, the argillaceous, and the calcareous, which are formed
+respectively of sand, clay, and carbonate of lime. Of these, the
+arenaceous, or sandy masses, are chiefly made up of siliceous 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 consist of carbonic
+acid and lime.
+
+_Arenaceous or siliceous 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 alumine 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 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 a cement.
+
+_Argillaceous rocks._--Clay, strictly speaking, is a mixture of silex or
+flint with a large proportion, usually about one fourth, of alumine, 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 various rocks. The purest
+clay found in nature is porcelain clay, or kaolin, which results from the
+decomposition of a rock composed of felspar and quartz, and it is almost
+always mixed with quartz.[11-A] _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 usually divides into
+irregular laminæ.
+
+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.[11-B]
+
+_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, without vitrifying or melting
+the lime itself. White chalk is often pure carbonate of lime; and this
+rock, although usually in a soft and earthy state, is sometimes
+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 saccharine 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
+acids, 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, 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._--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.[14-A] It is there
+seen that rivers flowing into lakes and seas are charged with sediment,
+varying in quantity, composition, colour, and grain according to the
+seasons; the waters are sometimes flooded and rapid, at other periods low
+and feeble; different tributaries, also, draining peculiar countries and
+soils, and therefore charged with peculiar sediment, are swollen at
+distinct periods. It was also shown that the waves of the sea and
+currents undermine the cliffs during wintry storms, and sweep away
+the materials into the deep, after which a season of tranquillity
+succeeds, when nothing but the finest mud is spread by the movements
+of the ocean over the same submarine area.
+
+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, 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 La
+Roche 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 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 longer suspended, owing to
+its great 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 has generally been said that the upper and
+under surfaces of strata, or the planes of stratification, as they are
+termed, 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. The reason of this
+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 sink, or the water be
+removed 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 downwards,
+and are least in those depressions where the water is deepest.
+
+[Illustration: Fig. 1. Cross section.]
+
+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_. This levelling operation may perhaps be
+rendered more clear to the student by supposing a number of parallel
+trenches to be dug in a plain of moving sand, like the African desert, in
+which case the wind would soon cause all signs of these trenches to
+disappear, and the surface would be as uniform as before. Now, water in
+motion can exert this levelling power on similar materials more easily
+than air, for almost all stones lose in water more than a third of the
+weight which they have in air, the specific gravity of rocks being in
+general as 2-1/2 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.
+
+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.)
+
+[Illustration: Fig. 2. Section of strata of sandstone, grit,
+and conglomerate.]
+
+[Illustration: Fig. 3. Section of sand at Sandy Hill, near Biggleswade,
+Bedfordshire. Height 20 feet. (Greensand formation.)]
+
+_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
+stratification" has been given. Thus in the annexed 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 re-arrangement 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. 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_ (fig. 4.), 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.
+
+[Illustration: Fig. 4. Cross section.]
+
+[Illustration: Fig. 5. Cross section.]
+
+[Illustration: Fig. 6. Cliff between Mismer and Dunwich.]
+
+[Illustration: Fig. 7. Section from Monte Calvo to the sea by the valley of
+Magnan, near Nice.
+
+  A. Dolomite and sandstone. (Greensand formation?)
+  _a_, _b_, _d_. Beds of gravel and sand.
+  _c._ Fine marl and sand of St. Madeleine, with marine shells.]
+
+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
+many 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 annexed 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 9 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 9 miles from the original shore. If subsequently this part of
+the Alps and bed of the sea were raised 700 feet, the coast would acquire
+its present configuration, the delta would emerge, and a deep channel might
+then be cut through it by a river.
+
+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 9 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.
+
+[Illustration: 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
+following is the manner in which I once observed the motion of the air to
+produce this effect on a large extent of level beach, exposed at low tide
+near Calais. Clouds of fine white sand were blown from the neighbouring
+dunes, so as to cover the shore, and whiten a dark level surface of sandy
+mud, and this fresh covering of sand was beautifully rippled. On levelling
+all the small ridges and furrows of this ripple over an area of several
+yards square, I saw them perfectly restored in about ten minutes, the
+general direction of the ridges being always at right angles to that of the
+wind. The restoration began by the appearance here and there of small
+detached heaps of sand, which soon lengthened and joined together, so as to
+form long sinuous ridges with intervening furrows. Each ridge had one side
+slightly inclined, and the other steep; the lee-side being always steep, as
+_b, c,--d, e_; the windward-side a gentle slope, as _a, b,--c, d_, fig. 9.
+When a gust of wind blew with sufficient force to drive along a cloud of
+sand, all the ridges were seen to be in motion at once, each encroaching on
+the furrow before it, and, in the course of a few minutes, filling the
+place which the furrows had occupied. The mode of advance was by the
+continual drifting of grains of sand up the slopes _a b_ and _c d_, many of
+which grains, when they arrived at _b_ and _d_, fell over the scarps _b c_
+and _d e_, and were under shelter from the wind; so that they remained
+stationary, resting, according to their shape and momentum, on different
+parts of the descent, and a few only rolling to the bottom. In this manner
+each ridge was distinctly seen to move slowly on as often as the force of
+the wind augmented. Occasionally part of a ridge, advancing more rapidly
+than the rest, overtook the ridge immediately before it, and became
+confounded with it, thus causing those bifurcations and branches which are
+so common, and two of which are seen in the slab, fig. 8. We may observe
+this configuration in sandstones of all ages, and in them also, as now on
+the sea-coast, we may often detect two systems of ripples interfering with
+each other; one more ancient and half effaced, and a newer one, in which
+the grooves and ridges are more distinct, and in a different direction.
+This crossing of two sets of ripples arises from a change of wind, and the
+new direction in which the waves are thrown on the shore.
+
+[Illustration: Fig. 9. Sketch of ripples.]
+
+The ripple mark is usually an indication of a sea-beach, or of water
+from 6 to 10 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.[21-A]
+
+
+FOOTNOTES:
+
+[11-A] The kaolin of China consists of 71·15 parts of silex, 15·86 of
+alumine, 1·92 of lime, and 6·73 of water (W. Phillips, Mineralogy, p. 33.);
+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. (Phil. Mag. vol. x. 1837.)
+
+[11-B] See W. Phillips's Mineralogy, "Alumine."
+
+[14-A] Consult Index to Principles of Geology, "Stratification,"
+"Currents," "Deltas," "Water," &c.
+
+[21-A] Siau. Edin. New Phil. Journ. vol. xxxi.; and Darwin, Volc.
+Islands, p. 134.
+
+
+
+
+CHAPTER III.
+
+ARRANGEMENT OF FOSSILS IN STRATA--FRESHWATER 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 and semi-opal formed of infusoria--Chalk derived
+   principally from organic bodies--Distinction of freshwater from marine
+   formations--Genera of freshwater and land shells--Rules for
+   recognizing marine testacea--Gyrogonite and chara--Freshwater
+   fishes--Alternation of marine and freshwater 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 filled with 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
+covered immediately by 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.
+
+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 downwards. 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 remained clear and transparent, for
+such corals cannot live in turbid water.
+
+[Illustration: Fig. 10. Fossil _Gryphæa_, covered both on the outside and
+inside with fossil serpulæ.]
+
+In like manner, when we see thousands of full-grown shells dispersed every
+where 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 testacea,
+now adhering to it, grew from an embryo state to full maturity. Attached
+shells which are merely external, like some of the serpulæ (_a_) in the
+annexed figure (fig. 10.), 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. 10., 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.
+
+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
+numerous spines, which serve as organs of motion, and are supported by rows
+of tubercles, which last are only seen after the death of the sea-urchin,
+when the spines have dropped off. In fig. 12. a living species of
+_Spatangus_, common on our coast, is represented with one half of its shell
+stripped of the spines. In fig. 11. a fossil of the same 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 _Spatangus_ had died, and the spines were detached.
+
+[Illustration: Fig. 11. _Serpula_ attached to a fossil _Spatangus_
+from the chalk.]
+
+[Illustration: Fig. 12. Recent _Spatangus_ with the spines removed
+from one side.
+
+  _b._ Spine and tubercles, nat. size.
+  _a._ The same magnified.]
+
+[Illustration: Fig. 13.
+
+  _a._ _Echinus_ from the chalk, with lower valve of the _Crania_ attached.
+  _b._ Upper valve of the _Crania_ detached.]
+
+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 in the
+chalk (see fig. 13.), which has fixed to it the lower valve of a
+_Crania_, a genus of bivalve mollusca. The upper valve (_b_, fig. 13.)
+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 _Echinus_ became
+enveloped in chalky mud.
+
+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 dug out, drilled all over by the holes of these
+borers, the tubes and shells of the mollusk still remaining in the
+cylindrical hollows. In fig. 15. _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, a shell is seen at the larger extremity, composed
+of two pieces, as shown at _c_. In like manner, a piece of fossil wood
+(_a_, fig. 14.) has been perforated by an animal of a kindred but extinct
+genus, called _Teredina_ by 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 it, perforating it
+in all directions. Again, before the infant colony settled upon the drift
+wood, the branch 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.
+
+[2 Illustrations: Fossil and recent wood drilled by perforating Mollusca.
+
+Fig. 14. _a_. Fossil wood from London clay, bored by _Teredina_.
+         _b_. Shell and tube of _Teredina personata_, the right-hand
+              figure the ventral, the left the dorsal view.
+
+Fig. 15. _e_. Recent wood bored by _Teredo_.
+         _d_. Shell and tube of _Teredo navalis_, from the same.
+         _c_. Anterior and posterior view of the valves of same detached
+              from the tube.]
+
+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 stony 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 by the recent
+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 the Prussian naturalist refers to
+microscopic Infusoria, but which most others now believe to be plants.
+They abound in freshwater lakes and ponds in England and other
+countries, and are termed Diatomaceæ by those naturalists who believe in
+their vegetable origin. The substance alluded to has long been well
+known in the arts, being used in the form of powder for polishing stones
+and metals. It has been procured, among other places, from Bilin, in
+Bohemia, where a single stratum, extending over a wide area, is no less
+than 14 feet thick. This stone, when examined with a powerful
+microscope, is found to consist of the siliceous plates or frustules of
+the above-mentioned 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. 17.) 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.
+
+[3 Illustrations: These figures are magnified nearly 300 times, except
+the lower figure of _G. ferruginea_ (fig. 18. _a_), which is magnified
+2000 times.
+
+Fig. 16. _Bacillaria vulgaris?_
+
+Fig. 17. _Gaillonella distans._
+
+Fig. 18. _Gaillonella ferruginea._]
+
+[2 Illustrations: Fragment of semi-opal from the great bed of
+Tripoli, Bilin.
+
+Fig. 19. Natural size.
+
+Fig. 20. The same magnified, showing circular articulations of a species of
+_Gaillonella_, and spiculæ of _Spongilla_.]
+
+The remains of these Diatomaceæ are of pure silex, and their forms are
+various, but very marked and constant in particular genera and species.
+Thus, in the family _Bacillaria_ (see fig. 16.), the fossils preserved in
+tripoli are seen to exhibit the same divisions and transverse lines which
+characterize the living species of kindred form. With these, also, the
+siliceous spiculæ or internal supports of the freshwater sponge, or
+_Spongilla_ of Lamarck, are sometimes intermingled (see the needle-shaped
+bodies in fig. 20.). These flinty cases and spiculæ, although hard, are
+very fragile, breaking like glass, and are therefore admirably adapted,
+when rubbed, for wearing down into a fine powder fit for polishing the
+surface of metals.
+
+Besides the tripoli, formed exclusively of the fossils above described,
+there occurs in the upper part of the great stratum at Bilin another
+heavier and more compact stone, a kind of semi-opal, in which innumerable
+parts of Diatomaceæ and spiculæ of the _Spongilla_ are filled with, and
+cemented together by, siliceous matter. It is supposed that the siliceous
+remains of the most delicate Diatomaceæ have been dissolved by water, and
+have thus given rise to this opal in which the more durable fossils are
+preserved like insects in amber. This opinion is confirmed by the fact that
+the organic bodies decrease in number and sharpness of outline in
+proportion as the opaline cement increases in quantity.
+
+In the Bohemian tripoli above described, as in that of Planitz in Saxony,
+the species of Diatomaceæ (or Infusoria, as termed by Ehrenberg) are
+freshwater; but in other countries, as in the tripoli of the Isle of
+France, they are of marine species, and they all belong to formations of
+the _tertiary_ period, which will be spoken of hereafter.
+
+A well-known substance, called bog-iron ore, often met with in peat-mosses,
+has also been shown by Ehrenberg to consist of innumerable articulated
+threads, of a yellow ochre colour, composed partly of flint and partly of
+oxide of iron. These threads are the cases of a minute microscopic body,
+called _Gaillonella ferruginea_ (fig. 18.).
+
+[4 Illustrations: _Cytheridæ_ and _Foraminifera_ from the chalk.
+
+Fig. 21. _Cythere_, Müll.
+         _Cytherina_, Lam.
+
+Fig. 22. Portion of _Nodosaria_.
+
+Fig. 23. _Cristellaria rotulata._
+
+Fig. 24. _Rosalina._]
+
+It is clear that 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 usually been supposed to be
+inorganic, may in reality have been derived from microscopic organic
+bodies. That this is the case with the white chalk, has often been
+imagined, this rock having been observed to abound in a variety of marine
+fossils, such as shells, echini, corals, sponges, crustacea, and fishes.
+Mr. Lonsdale, on examining, in Oct. 1835, in the museum of the Geological
+Society of London, portions of white chalk from different parts of England,
+found, on carefully pulverizing them in water, that what appear to the eye
+simply as white grains were, in fact, well preserved fossils. He obtained
+above a thousand of these from each pound weight of chalk, some being
+fragments of minute corallines, others entire Foraminifera and Cytheridæ.
+The annexed drawings will give an idea of the beautiful forms of many of
+these bodies. The figures _a_ _a_ represent their natural size, but, minute
+as they seem, the smallest of them, such as _a_, fig. 24., are gigantic in
+comparison with the cases of Diatomaceæ before mentioned. 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. After reflecting on these discoveries, we
+are naturally led on to conjecture that, as the formless cement in the
+semi-opal of Bilin has been derived from the decomposition of animal and
+vegetable remains, so also even those parts of chalk flints in which no
+organic structure can be recognized may nevertheless have constituted a
+part of microscopic animalcules.
+
+  "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.
+
+_Freshwater 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 a formation of marl and limestone, more
+than 50 feet thick, occurs, in which the shells are principally, if not
+all, of extinct species. Yet we recognize their freshwater origin, because
+they are of the same genera as those now abounding in ponds and lakes,
+either in our own country or in warmer latitudes.
+
+In many parts of France, as in Auvergne, for example, strata of
+limestone, marl, and sandstone are found, hundreds of feet thick, which
+contain exclusively freshwater and land shells, together with the
+remains of terrestrial quadrupeds. The number of land shells scattered
+through some of these freshwater 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 strewed over with innumerable dead land shells,
+which have been brought down from 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 freshwater 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.
+
+We may distinguish a freshwater formation, first, by the absence of many
+fossils almost invariably met with in marine strata. For example, there
+are no sea-urchins, no corals, and scarcely any zoophytes; no chambered
+shells, such as the nautilus, nor microscopic Foraminifera. But it is
+chiefly by attending to the forms of the mollusca that we are guided in
+determining the point in question. In a freshwater deposit, the number
+of individual shells is often as great, if not greater, than in a marine
+stratum; but there is a smaller variety of species and genera. This
+might be anticipated from the fact that the genera and species of recent
+freshwater and land shells are few when contrasted with the marine.
+Thus, the genera of true mollusca according to Blainville's system,
+excluding those of extinct species and those without shells, amount to
+about 200 in number, of which the terrestrial and freshwater genera
+scarcely form more than a sixth.[28-A]
+
+[Illustration: Fig. 25. _Cyclas obovata_; fossil. Hants.]
+
+[Illustration: Fig. 26. _Cyrena consobrina_; fossil. Grays, Essex.]
+
+[Illustration: Fig. 27. _Anodonta Cordierii_; fossil. Paris.]
+
+[Illustration: Fig. 28. _Anodonta latimarginatus_; recent. Bahia.]
+
+[Illustration: Fig. 29. _Unio littoralis_; recent. Auvergne.]
+
+Almost all bivalve shells, or those of acephalous mollusca, are marine,
+about ten only out of ninety genera being freshwater. 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.
+
+[Illustration: Fig. 30. _Gryphæa incurva_, Sow. (_G. arcuata_, Lam.) upper
+valve. Lias.]
+
+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.
+25., and the _Monomyary_, such as the oyster and scallop, in which there is
+only one of these impressions, as is seen in fig. 30. Now, as none of these
+last, or the unimuscular bivalves, are freshwater, we may at once presume a
+deposit in which we find any of them to be marine.
+
+[Illustration: Fig. 31. _Planorbis euomphalus_; fossil. Isle of Wight.]
+
+[Illustration: Fig. 32. _Lymnea longiscata_; fossil. Hants.]
+
+[Illustration: Fig. 33. _Paludina lenta_; fossil. Hants.]
+
+The univalve shells most characteristic of freshwater deposits are,
+_Planorbis_, _Lymnea_, and _Paludina_. (See figures.) But to these are
+occasionally added _Physa_, _Succinea_, _Ancylus_, _Valvata_, _Melanopsis_,
+_Melania_, and _Neritina_. (See figures.)
+
+[Illustration: Fig. 34. _Succinea amphibia_; fossil. Loess, Rhine.]
+
+[Illustration: Fig. 35. _Ancylus elegans_; fossil. Hants.]
+
+[Illustration: Fig. 36. _Valvata_; fossil. Grays, Essex.]
+
+[Illustration: Fig. 37. _Physa hypnorum_; recent.]
+
+[Illustration: Fig. 38. _Auricula_; recent. Ava.]
+
+[Illustration: Fig. 39. _Melania inquinata._ Paris Basin.]
+
+[Illustration: Fig. 40. _Physa columnaris._ Paris Basin.]
+
+[Illustration: Fig. 41. _Melanopsis buccinoidea_; recent. Asia.]
+
+In regard to one of these, the _Ancylus_ (fig. 35.), Mr. Gray observes that
+it sometimes differs in no respect from the marine _Siphonaria_, except in
+the animal. The shell, however, of the _Ancylus_ is usually thinner.[29-A]
+
+[Illustration: Fig. 42. _Neritina globulus._ Paris basin.]
+
+[Illustration: Fig. 43. _Nerita granulosa._ Paris basin.]
+
+Some naturalists include _Neritina_ (fig. 42.) and the marine _Nerita_
+(fig. 43.) 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. 43.)
+
+[Illustration: Fig. 44. _Cerithium cinctum._ Paris basin.]
+
+A few genera, among which _Cerithium_ (fig. 44.) is the most abundant, are
+common both to rivers and the sea, having species peculiar to each. Other
+genera, like _Auricula_ (fig. 38.), are amphibious, frequenting marshes,
+especially near the sea.
+
+[Illustration: Fig. 45. _Helix Turonensis._ Faluns, Touraine.]
+
+[Illustration: Fig. 46. _Cyclostoma elegans._ Loess.]
+
+[Illustration: Fig. 47. _Pupa tridens._ Loess.]
+
+[Illustration: Fig. 48. _Clausilia bidens._ Loess.]
+
+[Illustration: Fig. 49. _Bulimus lubricus._ Loess, Rhine.]
+
+The terrestrial shells are all univalves. The most abundant genera among
+these, both in a recent and fossil state, are _Helix_ (fig. 45.),
+_Cyclostoma_ (fig. 46.), _Pupa_ (fig. 47.), _Clausilia_ (fig. 48.),
+_Bulimus_ (fig. 49.), and _Achatina_; which two last are nearly allied and
+pass into each other.
+
+[Illustration: Fig. 50. _Ampullaria glauca_, from the Jumna.]
+
+The _Ampullaria_ (fig. 50.) is another genus of shells, inhabiting
+rivers and ponds in hot countries. Many fossil species have been
+referred to this genus, but they have been found chiefly in marine
+formations, and are suspected by some conchologists to belong to
+_Natica_ and other marine genera.
+
+All univalve shells of land and freshwater species, with the exception of
+_Melanopsis_ (fig. 41.), and _Achatina_, which has a slight indentation,
+have entire mouths; and this circumstance may often serve as a convenient
+rule for distinguishing freshwater 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 _Ampullaria_ and the land shells (figs. 45-49.), when its outline is
+not interrupted by an indentation or notch, such as that seen at _b_ in
+_Ancillaria_ (fig. 52.); or is not prolonged into a canal, as that seen at
+_a_ in _Pleurotoma_ (fig. 51.).
+
+[Illustration: Fig. 51. _Pleurotoma rotata._ Subap. hills, Italy.]
+
+[Illustration: Fig. 52. _Ancillaria subulata._ London clay.]
+
+The mouths of a large proportion of the marine univalves have these notches
+or canals, and almost all such species are carnivorous; whereas nearly all
+testacea having entire mouths, are plant-eaters; whether the species be
+marine, freshwater, or terrestrial.
+
+There is, however, one genus which affords an occasional exception to one
+of the above rules. The _Cerithium_ (fig. 44.), 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 freshwater deposits are the shells of
+_Cypris_, a minute crustaceous animal, having a shell much resembling that
+of the bivalve mollusca.[31-A] Many minute living species of this genus
+swarm in lakes and stagnant pools in Great Britain; but their shells are
+not, if considered separately, conclusive as to the freshwater origin of a
+deposit, because the majority of species in another kindred genus of the
+same order, the _Cytherina_ of Lamarck (see above, fig. 21. p. 26.),
+inhabit salt water; and, although the animal differs slightly, the shell is
+scarcely distinguishable from that of the _Cypris_.
+
+The seed-vessels and stems of _Chara_, a genus of aquatic plants, are very
+frequent in freshwater strata. These seed-vessels were called, before their
+true nature was known, gyrogonites, and were supposed to be foraminiferous
+shells. (See fig. 53. _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. 54.) 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 freshwater formations. They are generally composed of a large tube
+surrounded by smaller tubes; the whole stem being divided at certain
+intervals by transverse partitions or joints. (See _b_, fig. 53.)
+
+[Illustration: Fig. 53. _Chara medicaginula_; fossil. Isle of Wight.
+
+  _a._ Seed-vessel. magnified 20 diameters.
+  _b._ Stem, magnified.]
+
+[Illustration: Fig. 54. _Chara elastica_; recent. Italy.
+
+  _a._ Sessile seed vessel between the division of the leaves of the
+       female plant.
+  _b._ Transverse section of a branch, with five seed-vessels magnified,
+       seen from below upwards.]
+
+It is not uncommon to meet with layers of vegetable matter, impressions of
+leaves, and branches of trees, in strata containing freshwater 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."[32-A]
+
+The remains of fish are occasionally useful in determining the freshwater
+origin of strata. Certain genera, such as carp, perch, pike, and loach
+(_Cyprinus_, _Perca_, _Esox_, and _Cobitis_), as also _Lebias_, being
+peculiar to freshwater. Other genera contain some freshwater 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 freshwater 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 mouths 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.
+
+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 as often formed and removed.
+The last irruption of salt water happened in 1824, when the North Sea
+entered, killing all the freshwater 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_,
+_Lymnea_, _Paludina_, and _Charæ_.[33-A]
+
+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 freshwater strata. When we
+find, as in the south-east of England, a great series of freshwater 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.[33-B]
+
+
+FOOTNOTES:
+
+[28-A] See Synoptic Table in Blainville's Malacologie.
+
+[29-A] Gray, Phil. Trans., 1835, p. 302.
+
+[31-A] For figures of recent species, see below, p. 183., and figs. of
+fossils, see p. 228.
+
+[32-A] See Index of Principles, "Fossilization."
+
+[33-A] See Principles, Index, "Lym-Fiord."
+
+[33-B] See below, Chap. XVIII., on the Wealden.
+
+
+
+
+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--Göppert's
+   experiments--Precipitation of stony matter most rapid where
+   putrefaction is going on--Source of lime in solution--Silex derived
+   from decomposition of felspar--Proofs of the lapidification of some
+   fossils soon after burial, of others when much decayed.
+
+
+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 chemical, and those of a mechanical,
+origin. By the latter name 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
+often precipitated upon the bottom of lakes and seas 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, encrusting shells, fragments of wood and leaves, and
+binding them together.[34-A]
+
+In coral 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 encrusted over
+with a hard coating of limestone.[34-B]
+
+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 encrust 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 veinstones.
+
+_Cementing of particles._--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. The absence of organic remains from
+many aqueous rocks may be thus explained; but we may presume that in many
+of them no fossils were ever imbedded, as there are extensive tracts on the
+bottoms of existing seas even of moderate depth on which no fragment of
+shell, coral, or other living creature can be detected by dredging. On the
+other hand, there are depths where the zero of animal life has been
+approached; as, for example, in the Mediterranean, at the depth of about
+230 fathoms, according to the researches of Prof. E. Forbes. In the Ægean
+Sea a deposit of yellowish mud of a very uniform character, and closely
+resembling chalk, is going on in regions below 230 fathoms, and this
+formation must be wholly devoid of organic remains.[35-A]
+
+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 any sand, pebbles, or fragmentary
+mixture. In some conglomerates, like the pudding-stone of Hertfordshire,
+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 crystallizing, 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 crystallized, 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.[36-A]
+
+The marl recently deposited at the bottom of Lake Superior, in North
+America, is soft, and often filled with freshwater 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 freshwater shells.[36-B]
+
+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 20 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 these cases is brought about by the action of chemical
+affinity on finely comminuted matter previously suspended in water. After
+deposition similar particles seem 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 traced
+in the concretions, remaining parallel to those of the surrounding
+unconsolidated rock. (See fig. 55.) Such nodules of limestone have often a
+shell or other foreign body in the centre.[37-A]
+
+[Illustration: Fig. 55. Calcareous nodules in Lias.]
+
+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 annexed section (fig. 56.) passes from the
+stratum _b_ upwards 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. Crystallization, beginning at the centre, must
+have gone on forming concentric coats, around the original nucleus
+without interfering with the laminated structure of the rock.
+
+[Illustration: Fig. 56. Spheroidal concretions in magnesian limestone.]
+
+When the particles of rocks have been thus re-arranged 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 similar 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 upwards 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.
+
+[Illustration: Fig. 57. Block section.]
+
+_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 afterwards 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, thus compressed, may 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.
+
+_Mineralization 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 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
+fossilization 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. 58., commonly called a fossil screw, would never
+be suspected by an inexperienced conchologist to be the internal shape
+of the fossil univalve, _b_, fig. 58. Nor should we have imagined at
+first sight that the shell _a_ and the cast _b_, fig. 59., were
+different parts of the same fossil. The reader will observe, in the
+last-mentioned figure (_b_, fig. 59.), 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. 59., 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 organization; 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 organization are retained in flint.
+
+[Illustration: Fig. 58. _Phasianella Heddingtonensis_, and cast of the
+same. Coral Rag.]
+
+[Illustration: Fig. 59. _Trochus Anglicus_ and cast. Lias.]
+
+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 pores 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, 72 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 seen in fig. 60. 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 mineralizing matter had penetrated to that portion of the tree.
+
+[Illustration: Fig. 60. Texture of a tree from the coal strata, magnified.
+(Witham.) Transverse section.]
+
+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, which consist chiefly of oxygen,
+hydrogen, 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 and 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 crystallized 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
+Göppert of Breslau attempted recently to imitate the natural process of
+petrifaction. For this purpose he 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 even days, the organic bodies thus immersed
+were mineralized 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.
+
+Another accidental experiment has been recorded by Mr. Pepys in the
+Geological Transactions.[41-A] An earthen pitcher containing several quarts
+of sulphate of iron had remained undisturbed and unnoticed for about a
+twelvemonth in the laboratory. At the end of this time when the liquor was
+examined an oily appearance was observed on the surface, and a yellowish
+powder, which proved to be sulphur, together with a quantity of small
+hairs. At the bottom were discovered the bones of several mice in a
+sediment consisting of small grains of pyrites, others of sulphur, others
+of crystallized green sulphate of iron, and a black muddy oxide of iron. It
+was evident that some mice had accidentally been drowned in the fluid, and
+by the mutual action of the animal matter and the sulphate of iron on each
+other, the metallic sulphate had been deprived of its oxygen; hence the
+pyrites and the other compounds were thrown down. Although the mice were
+not mineralized, or turned into pyrites, the phenomenon shows how mineral
+waters, charged with sulphate of iron, may be deoxydated on coming in
+contact with animal matter undergoing putrefaction, so that atom after atom
+of pyrites may be precipitated, and ready, under favourable circumstances,
+to replace the oxygen, hydrogen, and carbon into which the original body
+would be resolved.
+
+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 gas holding lime in solution.[41-B] 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 Göppert in various
+fluid mixtures.
+
+It is well known that the water of springs, or that which is continually
+percolating the earth's crust, is rarely free from a slight admixture
+either of iron, carbonate of lime, sulphur, silica, potash, or some other
+earthy, alkaline, or metallic ingredient. Hot springs in particular are
+copiously charged with one or more of these elements; and it is only in
+their waters that silex is found in abundance. In certain cases, therefore,
+especially in volcanic regions, we may imagine the flint of silicified wood
+and corals to have been supplied by the waters of thermal springs. In other
+instances, as in tripoli and chalk-flint, it may have been derived in great
+part, if not wholly, from the decomposition of infusoria or diatomaceæ,
+sponges, and other bodies. But even if this be granted, we have still to
+inquire whence a lake or the ocean can be constantly replenished with the
+calcareous and siliceous matter so abundantly withdrawn from it by the
+secretions of these zoophytes.
+
+In regard to carbonate of lime there is no difficulty, because not only are
+calcareous springs very numerous, but even rain-water has the power of
+dissolving a minute portion of the calcareous rocks over which it flows.
+Hence marine corals and mollusca may be provided by rivers with the
+materials of their shells and solid supports. But pure silex, even when
+reduced to the finest powder and boiled, is insoluble in water, except at
+very high temperatures. Nevertheless Dr. Turner has well explained, in an
+essay on the chemistry of geology[42-A], how the decomposition of felspar
+may be a source of silex in solution. He has remarked that the siliceous
+earth, which constitutes more than half the bulk of felspar, is intimately
+combined with alumine, potash, and some other elements. The alkaline matter
+of the felspar has a chemical affinity for water, as also for the carbonic
+acid which is more or less contained in the waters of most springs. The
+water therefore carries away alkaline matter, and leaves behind a clay
+consisting of alumine and silica. But this residue of the decomposed
+mineral, which in its purest state is called porcelain clay, is found to
+contain a part only of the silica which existed in the original felspar.
+The other part, therefore, must have been dissolved and removed; and this
+can be accounted for in two ways; first, because silica when combined with
+an alkali is soluble in water; secondly, because silica in what is
+technically called its nascent state is also soluble in water. Hence an
+endless supply of silica is afforded to rivers and the waters of the sea.
+For the felspathic rocks are universally distributed, constituting, as they
+do, so large a proportion of the volcanic, plutonic, and metamorphic
+formations. Even where they chance to be absent in mass, they rarely fail
+to occur in the superficial gravel or alluvial deposits of the basin of
+every large river.
+
+The disintegration of mica also, another mineral which enters largely
+into the composition of granite and various sandstones, may yield
+silica which may be dissolved in water, for nearly half of this mineral
+consists of silica, combined with alumine, potash, and about a tenth
+part of iron. The oxidation of this iron in the air is the principal
+cause of the waste of mica.
+
+We have still, however, much to learn before the conversion of fossil
+bodies into stone is fully understood. Some phenomena seem to imply that
+the mineralization must proceed with considerable rapidity, for stems of a
+soft and succulent character, and of a most perishable nature, are
+preserved in flint; and there are instances of the complete silicification
+of the young leaves of a palm-tree when just about to shoot forth, and in
+that state which in the West Indies is called the cabbage of the
+palm.[43-A] It may, however, be questioned whether in such cases there may
+not have been some antiseptic quality in the water which retarded
+putrefaction, so that the soft parts of the buried substance may have
+remained for a long time without disintegration, like the flesh of bodies
+imbedded in peat.
+
+Mr. Stokes has pointed out examples of petrifactions in which the more
+perishable, and others where the more durable portions of wood are
+preserved. These variations, he suggests, must doubtless have depended on
+the time when the lapidifying mineral was introduced. Thus, in certain
+silicified stems of palm-trees, the cellular tissue, that most destructible
+part, is in good condition, while all signs of the hard woody fibre have
+disappeared, the spaces once occupied by it being hollow or filled with
+agate. Here, petrifaction must have commenced soon after the wood was
+exposed to the action of moisture, and the supply of mineral matter must
+then have failed, or the water must have become too much diluted before the
+woody fibre decayed. But when this fibre is alone discoverable, we must
+suppose that an interval of time elapsed before the commencement of
+lapidification, during which the cellular tissue was obliterated. When both
+structures, namely, the cellular and the woody fibre, are preserved, the
+process must have commenced at an early period, and continued without
+interruption till it was completed throughout.[43-B]
+
+
+FOOTNOTES:
+
+[34-A] See Principles, Index, "Calcareous Springs," &c.
+
+[34-B] Ibid. "Travertin," "Coral Reefs," &c.
+
+[35-A] Report Brit. Ass. 1843, p. 178.
+
+[36-A] Dr. MacCulloch, Syst. of Geol. vol. i. p. 123.
+
+[36-B] Princ. of Geol., Index, "Superior Lake."
+
+[37-A] De la Beche, Geol. Researches, p. 95., and Geol. Observer
+(1851), p. 686.
+
+[41-A] Vol. i. p. 399. first series.
+
+[41-B] Piddington, Asiat. Research. vol. xviii. p. 226.
+
+[42-A] Jam. Ed. New Phil. Journ. No. 30. p. 246.
+
+[43-A] Stokes, Geol. Trans., vol. v. p. 212. second series.
+
+[43-B] Ibid.
+
+
+
+
+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--Upheaval of extensive masses of horizontal strata--Inclined and
+   vertical stratification--Anticlinal and synclinal lines--Bent strata
+   in east of Scotland--Theory of folding by lateral movement--Creeps--Dip
+   and strike--Structure of the Jura--Various forms of outcrop--Rocks
+   broken by flexure--Inverted position of disturbed strata--Unconformable
+   stratification--Hutton and Playfair on the same--Fractures of
+   strata--Polished surfaces--Faults--Appearance of repeated alternations
+   produced by them--Origin of great faults.
+
+
+_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. 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 upwards 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 other
+alternative, namely, the doctrine that the solid land has been repeatedly
+moved upwards or downwards, 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 lowering of the sea's level in any region, and
+the ocean cannot sink in one place without its level being depressed 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 one of the oldest of the
+fossiliferous deposits, namely that formerly called Transition, and now
+Silurian, 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 about the same age
+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 that
+they were gradually 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. Playfair argued in
+favour of this opinion in 1802; and in 1807, Von Buch, after his travels in
+Scandinavia, announced his conviction that a rising of the land was in
+progress. Celsius and other Swedish writers had, a century before, declared
+their belief that a gradual change had, for ages, been taking place in the
+relative level of land and sea. They attributed the change to a fall of the
+waters both of the ocean and the Baltic. This theory, however, has now been
+refuted by abundant evidence; for the alteration of relative level has
+neither been universal nor every where uniform in quantity, but has
+amounted, in some regions, to several feet in a century, in others to a few
+inches; while in the southernmost part of Sweden, or the province of
+Scania, there has been actually a loss instead of a gain of land, buildings
+having gradually sunk below the level of the sea.[46-A]
+
+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.[46-B] 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, that the original position of strata may, in
+the course of centuries, be modified to any amount.
+
+It has also been shown by Mr. Darwin, 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.
+
+It would require a volume to explain to the reader the various facts which
+establish the reality of these movements of land, whether of elevation or
+depression, whether accompanied by earthquakes or accomplished slowly and
+without local disturbance. Having treated fully of these subjects in the
+Principles of Geology[46-C], I shall assume, in the present work, that such
+changes are part of the actual course of nature; and when admitted, they
+will be found to afford a key to the interpretation of a variety of
+geological appearances, such as the elevation of horizontal, inclined, or
+disturbed marine strata, and the superposition of freshwater to marine
+deposits, afterwards to be described. It will also appear, in the sequel,
+how much light the doctrine of a continued subsidence of land may throw on
+the manner in which a series of strata, formed in shallow water, may have
+accumulated to a great thickness. The excavation of valleys also, and other
+effects of _denudation_, of which I shall presently treat, can alone be
+understood when we duly appreciate the proofs, now on record, of the
+prolonged rising and sinking of land, throughout wide areas.
+
+To conclude this subject, I may remind the reader, that were we to embrace
+the doctrine which ascribes the elevated position of marine formations, and
+the depression of certain freshwater strata, to oscillations in the level
+of the waters instead of the land, we should be compelled to admit that the
+ocean has been sometimes every where much shallower than at present, and at
+others more than three miles deeper.
+
+[Illustration: Fig. 61. Vertical conglomerate and sandstone.]
+
+_Inclined stratification._--The most unequivocal evidence of a change in
+the original position of strata is afforded by their standing up
+perpendicularly on 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. 61.). From this he inferred, that such strata must, at first,
+have been horizontal, each oval pebble having originally 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 we see on a shingle
+beach some oval or flat-sided pebbles resting on their ends or edges; these
+having been forced along the bottom and against each other by a wave or
+current so as to settle in this position.
+
+Vertical strata, when they can be traced continuously upwards or downwards
+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.
+
+The mass of strata here shown may be nearly 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 northerly dip. At Whiteness (see diagram) 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.
+
+[Illustration: Fig. 62. Section of Forfarshire, from N.W. to S.E., from
+foot of the Grampians to the sea at Arbroath (volcanic or trap rocks
+omitted). Length of section twenty miles.]
+
+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.[48-A] 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 upwards.
+
+[Illustration: Fig. 63. Curved strata of slate near St. Abb's Head,
+Berwickshire. (Sir J. Hall.)]
+
+[Illustration: Fig. 64. Block section.]
+
+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 accompanying plan
+(fig. 64.) represent what is actually seen of the strata in part of 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.
+
+[Illustration: Fig. 65. Experimental set-up.]
+
+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 will exactly imitate those of
+the bent strata. (See fig. 65.)
+
+Whether the analogous flexures in stratified rocks have really been due
+to similar sideway movements is a question of considerable difficulty.
+It will appear when the volcanic and granitic rocks are described, that
+some of them have, when melted, been injected forcibly into fissures,
+while others, already in a solid state, have been protruded upwards
+through the incumbent crust of the earth, by which a great displacement
+of flexible strata must have been caused.
+
+But we also know 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 sometimes extending
+over a wide area. The frequent repetition, or continuance throughout long
+periods, of such downward movements seems to imply the formation and
+renewal of cavities at a certain depth below the surface, whether by the
+removal of matter by volcanos and hot springs, or by the contraction of
+argillaceous rocks by heat and pressure, or any other combination of
+circumstances. Whatever conjectures we may indulge respecting the causes,
+it is certain that pliable beds may, in consequence of unequal degrees of
+subsidence, become folded to any amount, and have all the appearance of
+having been compressed suddenly by a lateral thrust.
+
+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."[50-A] The exact amount of
+depression in these cases can only be accurately measured where water
+accumulates on the surface, or a railway traverses a coal-field.
+
+[Illustration: Fig. 66. Section of carboniferous strata, at Wallsend,
+Newcastle, showing "Creeps." (J. Buddle, Esq.) Horizontal length of
+section 174 feet. The upper seam, or main coal, here worked out, was
+630 feet below the surface.]
+
+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. 66., 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.
+
+The first symptom of a "creep," says Mr. Buddle, is a slight curvature
+at the bottom of each gallery, as at _a_, fig. 66.: 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 re-united 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 downwards 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.
+
+Between the layers of shale, accompanying coal, we sometimes see the
+leaves of fossil ferns spread out as regularly as dried plants between
+sheets of paper in the herbarium of a botanist. These fern-leaves, or
+fronds, must have rested horizontally on soft mud, when first deposited.
+If, therefore, they and the layers of shale are now inclined, or
+standing on end, it is obviously the effect of subsequent derangement.
+The proof becomes, if possible, still more striking when these strata,
+including vegetable remains, are curved again and again, and even folded
+into the form of the letter Z, so that the same continuous layer of coal
+is cut through several times in the same perpendicular shaft. Thus, in
+the coal-field near Mons, in Belgium, these zigzag bendings are repeated
+four or five times, in the manner represented in fig. 67., the black
+lines representing seams of coal.[53-A]
+
+[Illustration: Fig. 67. Zigzag flexures of coal near Mons.]
+
+_Dip and Strike._--In the above remarks, several technical terms have been
+used, such as _dip_, the _unconformable position_ of strata, and the
+_anticlinal_ and _synclinal_ lines, which, as well as the _strike_ of the
+beds, I shall now explain. 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. 68.), 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.
+
+[Illustration: Fig. 68. Diagram.]
+
+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.
+
+[Illustration: Fig. 69. Apparent horizontality of inclined strata.]
+
+If the upper surface of a hard stony stratum be uncovered, whether
+artificially in a quarry, or by the 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 their strike, the dip being inwards 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 annexed drawing (fig. 69.), 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.
+
+[Illustration: Fig. 70. Explanatory sketch.]
+
+It is rarely important to determine the angle of inclination with such
+minuteness as to require the aid of the instrument called a clinometer. We
+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. 70. 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. The
+upper dotted line may express a stratum dipping to the north; but should
+the beds dip precisely to the opposite point of the compass as in the
+lower dotted line, it will be seen that the amount of inclination may still
+be measured by the hands with equal facility.
+
+[Illustration: Fig. 71. Section illustrating the structure of
+the Swiss Jura.]
+
+[Illustration: Fig. 72. Ground plan of the denuded ridge, fig. 71.]
+
+[Illustration: Fig. 73. Transverse section.]
+
+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. 71., 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.[55-A] 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. 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. 72.,
+and the cross section of the same by fig. 73. The line D E, fig. 72., 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 qua-quaversal dip--that is, turning each 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.
+
+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 upwards (see fig. 74.), those formed by the newer beds appearing
+in a superior position, and extending highest up the valley, as A
+is seen above B.
+
+[Illustration: Fig. 74. Slope of valley 40°, dip of strata 20°.]
+
+Thirdly, if the dip of the beds be steeper than the slope of the valley,
+then the V's will point downwards (see fig. 75.), and those formed of the
+older beds will now appear uppermost, as B appears above A.
+
+[Illustration: Fig. 75. Slope of valley 20°, dip of strata 50°.]
+
+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. 76.), which exhibits strata rising at an
+angle of 20°, and crossed by a valley, which declines in an opposite
+direction at 20°.[57-A]
+
+[Illustration: Fig. 76. Slope of valley 20°, dip of strata 20°,
+in opposite directions.]
+
+These rules may often be of great practical utility; for the different
+degrees of dip occurring in the two cases represented in figures 74 and 75.
+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. 74.), 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. 75., 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.
+
+In the majority of cases, an anticlinal axis forms a ridge, and a synclinal
+axis a valley, as in A, B, fig. 62. p. 48.; but there are exceptions to
+this rule, the beds sometimes sloping inwards from either side of a
+mountain, as in fig. 77.
+
+[Illustration: Fig. 77. Cross section.]
+
+On following one of the anticlinal ridges of the Jura, before mentioned, A,
+B, C, fig. 71., we often discover longitudinal cracks and sometimes large
+fissures along the line where the flexure was greatest. Some of these, as
+above stated, have been enlarged by denudation into valleys of considerable
+width, as at C, fig. 71., which follow the line of strike, and which we may
+suppose to have been hollowed out at the time when these rocks were still
+beneath the level of the sea, or perhaps at the period of their gradual
+emergence from beneath the waters. The existence of such cracks at the
+point of the sharpest bending of solid strata of limestone is precisely
+what we should have expected; but the occasional want of all similar signs
+of fracture, even where the strain has been greatest, as at _a_, fig. 71.,
+is not always easy to explain. 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. 35.), and in part to the permeation of sea-water while
+they were yet submerged.
+
+[Illustration: Fig. 78. 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. 78., 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 calcedony and quartz.
+
+[Illustration: Fig. 79. Cross section.
+
+  _g._ gypsum.
+  _m._ 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.
+79.), while the continuity of the more pliable and ductile marls, _m m_,
+has not been interrupted.
+
+[Illustration: Fig. 80. Cross section.]
+
+I shall conclude my remarks on bent strata by stating, that, in mountainous
+regions like the Alps, it is often difficult for an experienced geologist
+to determine correctly the relative age of beds by superposition, so often
+have the strata been folded back upon themselves, the upper parts of the
+curve having been removed by denudation. Thus, if we met with the strata
+seen in the section fig. 80., 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. 81., 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. These phenomena are often observable on a magnificent scale in
+certain regions in Switzerland in precipices from 2000 to 3000 feet in
+perpendicular height. In the Iselten Alp, in the valley of the Lutschine,
+between Unterseen and Grindelwald, curves of calcareous shale are seen from
+1000 to 1500 feet in height, in which the beds sometimes plunge down
+vertically for a depth of 1000 feet and more, before they bend round again.
+There are many flexures not inferior in dimensions in the Pyrenees, as
+those near Gavarnie, at the base of Mont Perdu.
+
+[Illustration: Fig. 81. Cross section.]
+
+[Illustration: Fig. 82. Curved strata of the Iselten Alp.]
+
+[Illustration: Fig. 83. Unconformable junction of old red sandstone and
+Silurian schist at the Siccar Point, near St. Abb's Head, Berwickshire. See
+also Frontispiece.]
+
+_Unconformable stratification._--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. 83.). 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, as
+_d_, _d_, fig. 83., 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 thrown out of the horizontal position.
+
+Playfair has remarked[60-A] that this kind of junction which we now call
+unconformable had been described before the time of Hutton, but that he was
+the first geologist who appreciated its importance, as illustrating the
+high antiquity and great revolutions of the globe. He had observed that
+where such contacts occur, the lowest beds of the newer series very
+generally consist of a breccia or conglomerate consisting of angular and
+rounded fragments, derived from the breaking up of the more ancient rocks.
+On one occasion the Scotch geologist took his two distinguished pupils,
+Playfair and Sir James Hall, to the cliffs on the east coast of Scotland,
+near the village of Eyemouth, not far from St. Abb's Head, where the
+schists of the Lammermuir range are undermined and dissected by the sea.
+Here the curved and vertical strata, now known to be of Silurian age, and
+which often exhibit a ripple-marked surface[60-B], are well exposed at the
+headland called the Siccar Point, penetrating with their edges into the
+incumbent beds of slightly inclined sandstone, in which large pieces of the
+schist, some round and others angular, are united by an arenaceous cement.
+"What clearer evidence," exclaims Playfair, "could we have had of the
+different formation of these rocks, and of the long interval which
+separated their formation, had we actually seen them emerging from the
+bosom of the deep? We felt ourselves necessarily carried back to the time
+when the schistus on which we stood was yet at the bottom of the sea, and
+when the sandstone before us was only beginning to be deposited in the
+shape of sand or mud, from the waters of a superincumbent ocean. An epoch
+still more remote presented itself, when even the most ancient of these
+rocks, instead of standing upright in vertical beds, lay in horizontal
+planes at the bottom of the sea, and was not yet disturbed by that
+immeasurable force which has burst asunder the solid pavement of the globe.
+Revolutions still more remote appeared in the distance of this
+extraordinary perspective. The mind seemed to grow giddy by looking so far
+into the abyss of time; and while we listened with earnestness and
+admiration to the philosopher who was now unfolding to us the order and
+series of these wonderful events, we became sensible how much farther
+reason may sometimes go than imagination can venture to follow."[60-C]
+
+In the frontispiece of this volume the reader will see a view of this
+classical spot, reduced from a large picture, faithfully sketched and
+coloured from nature by the youngest son of the late Sir James Hall. It was
+impossible, however, to do justice to the original sketch, in an
+engraving, as the contrast of the red sandstone and the light fawn-coloured
+vertical schists could not be expressed. From the point of view here
+selected, the underlying beds of the perpendicular schist, _a_, are visible
+at _b_ through a small opening in the fractured beds of the covering of red
+sandstone, _d d_, while on the vertical face of the old schist at _a' a"_ a
+conspicuous ripple-mark is displayed.
+
+[Illustration: Fig. 84. 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 (paleozoic) 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_.
+
+_Fractures of the strata and faults._--Numerous rents may often be seen in
+rocks which appear to have been simply broken, the separated parts
+remaining in the same places; 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, and 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 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, which happened about the year 1840, and was described
+to me by an eye-witness, 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 brickdust, evidently produced by trituration.
+
+[Illustration: Fig. 85. Faults. A B perpendicular, C D oblique
+to the horizon.]
+
+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 shift, slip, or
+fault. "The miner," says Playfair, describing a fault, "is often perplexed,
+in his subterraneous 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. 85., 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. 85., so that the strata on each
+side of the 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.
+86.), though their identity is still to be recognized by their possessing
+the same thickness, and the same internal characters."[62-A]
+
+[Illustration: Fig. 86. 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[62-B], 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 separated several yards, but 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, in some cases,
+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 fine 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.
+
+[Illustration: Fig. 87. Apparent alternations of strata caused
+by vertical faults.]
+
+If, for example, the dark line A H (fig. 87.) 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, upon reaching the strata of
+sandstone _c_, or on arriving at the line of fault F he comes partly
+upon the shale _b_, and partly on the sandstone _c_, and on reaching E
+he is again stopped by a wall composed of the rock _d_.
+
+[Illustration: Fig. 88. Cross section.]
+
+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 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.[64-A] The walls of the fissure are scored by grooves, such as would
+have been produced if the broken ends of the rock had been rubbed along the
+plane of the fault.[64-B] In the Tynedale and Craven faults, in the north
+of England, the vertical displacement is still greater, and has extended in
+a horizontal direction for a distance of thirty miles or more. Some
+geologists consider 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. This idea appears to have been
+derived from a notion that the grooved walls have merely been rubbed in one
+direction. But this is so far from being a constant phenomenon in faults,
+that it has often been objected to the received theory respecting those
+polished surfaces called "slickensides" (see above, p. 61.), that the striæ
+are not always parallel, but often curved and irregular. It has, moreover,
+been remarked, that not only the walls of the fissure or fault, but its
+earthy contents, sometimes present the same polished and striated faces.
+Now these facts seem to indicate partial changes in the direction of the
+movement, and some slidings subsequent to the first filling up of the
+fissure. Suppose the mass of rock A, B, C, to overlie an extensive chasm _d
+e_, formed at the depth of several miles, whether by the gradual
+contraction in bulk of a melted mass passing into a solid or crystalline
+state, or the shrinking of argillaceous strata, baked by a moderate heat,
+or by the subtraction of matter by volcanic action, or any other cause.
+Now, if this region be convulsed by earthquakes, the fissures _f g_, and
+others at right angles to them, may sever the mass B from A and from C, so
+that it may move freely, and begin to sink into the chasm. A fracture may
+be conceived so clean and perfect as to allow it to subside at once to the
+bottom of the subterranean cavity; but it is far more probable that the
+sinking will be effected at successive periods during different
+earthquakes, the mass always continuing to slide in the same direction
+along the planes of the fissures _f g_, and the edges of the falling mass
+being continually more broken and triturated at each convulsion. If, as is
+not improbable, the circumstances which have caused the failure of support
+continue in operation, it may happen that when the mass B has filled the
+cavity first formed, its foundations will again give way under it, so that
+it will fall again in the same direction. But, if the direction should
+change, the fact could not be discovered by observing the slickensides,
+because the last scoring would efface the lines of previous friction. In
+the present state of our ignorance of the causes of subsidence, an
+hypothesis which can explain the great amount of displacement in some
+faults, on sound mechanical principles, by 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.
+When some of the ancient marine formations are described in the sequel, it
+will appear that their structure and organic contents point to the
+conclusion, that the floor of the ocean was slowly sinking at the time of
+their origin. The downward movement was very gradual, and in Wales and the
+contiguous parts of England a maximum thickness of 32,000 feet (more than
+six miles) of Carboniferous, Devonian, and Silurian rock was formed, whilst
+the bed of the sea was all the time continuously and tranquilly
+subsiding.[65-A] Whatever may have been the changes which the solid
+foundation underwent, whether accompanied by the melting, consolidation,
+crystallization, or desiccation of subjacent mineral matter, it is clear
+from the fact of the sea having remained shallow all the while that the
+bottom never sank down suddenly to the depth of many hundred feet at once.
+
+It is by assuming such reiterated variations of level, each separately of
+small vertical amount, but multiplied by time till they acquire importance
+in the aggregate, that we are able to explain the phenomena of denudation,
+which will be treated of in the next chapter. By such movements every
+portion of the surface of the land becomes in its turn a line of coast, and
+is exposed to the action of the waves and tides. A country which is
+undergoing such movement is never allowed to settle into a state of
+equilibrium, therefore the force of rivers and torrents to remove or
+excavate soil and rocky masses is sustained in undiminished energy.
+
+
+FOOTNOTES:
+
+[46-A] In the first three editions of my Principles of Geology, I expressed
+many doubts as to the validity of the alleged proofs of a gradual rise of
+land in Sweden; but after visiting that country, in 1834, I retracted these
+objections, and published a detailed statement of the observations which
+led me to alter my opinion in the Phil. Trans. 1835, Part I. See also the
+Principles, 4th and subsequent editions.
+
+[46-B] See his Journal of a Naturalist in Voyage of the Beagle, and his
+work on Coral Reefs.
+
+[46-C] See chapters xxviii. to xxxi. inclusive.
+
+[48-A] Edin. Trans. vol. vii. pl. 3.
+
+[50-A] Proceedings of Geol. Soc. vol. iii. p. 148.
+
+[53-A] See plan by M. Chevalier, Burat's D'Aubuisson, tom. ii. p. 334.
+
+[55-A] See M. Thurmann's work, "Essai sur les Soulèvemens Jurassiques
+du Porrentruy, Paris, 1832," with whom I examined part of these
+mountains in 1835.
+
+[57-A] I am indebted to the kindness of T. Sopwith, Esq., for three
+models which I have copied in the above diagrams; but the beginner may
+find it by no means easy to understand such copies, although, if he were
+to examine and handle the originals, turning them about in different
+ways, he would at once comprehend their meaning as well as the import of
+others far more complicated, which the same engineer has constructed to
+illustrate _faults_.
+
+[60-A] Biographical account of Dr. Hutton.
+
+[60-B] See above, p. 49. and section.
+
+[60-C] Playfair, ibid.; see his Works, Edin. 1822, vol. iv. p. 81.
+
+[62-A] Playfair, Illust. of Hutt. Theory, § 42.
+
+[62-B] Geol. Trans. second series, vol. v. p. 452.
+
+[64-A] Conybeare and Phillips, Outlines, &c. p. 376.
+
+[64-B] Phillips, Geology, Lardner's Cyclop. p. 41.
+
+[65-A] See the results of the "Geological Survey of Great Britain;"
+Memoirs, vols. i. and ii., by Sir H. De la Beche, Mr. A. C. Ramsay,
+and Mr. John Phillips.
+
+
+
+
+CHAPTER VI.
+
+DENUDATION.
+
+   Denudation defined--Its amount equal to the entire mass of stratified
+   deposits in the earth's crust--Horizontal sandstone denuded in
+   Ross-shire--Levelled surface of countries in which great faults
+   occur--Coalbrook Dale--Denuding power of the ocean during the
+   emergence of land--Origin of Valleys--Obliteration of
+   sea-cliffs--Inland sea-cliffs and terraces in the Morea and
+   Sicily--Limestone pillars at St. Mihiel, in France--in Canada--in
+   the Bermudas.
+
+
+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. Geologists have perhaps been seldom in the
+habit of reflecting that 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 inseparable accompaniment 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, 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. The bed of the sea has in one region been raised
+by the accumulation of new matter, in another its depth has been augmented
+by the abstraction of an equal quantity.
+
+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.
+
+If, then, the entire mass of stratified deposits in the earth's crust is at
+once the monument and measure of the denudation which has taken place, on
+how stupendous a scale ought we to find the signs of this removal of
+transported materials in past ages! Accordingly, 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 accompanying diagram (fig. 89.); 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,
+of which a grand exemplification is described by Dr. MacCulloch, on the
+north-western coast of Ross-shire, in Scotland.[67-A] The fundamental rock
+of that country is gneiss, in disturbed strata, on which beds of nearly
+horizontal red sandstone rest unconformably. The latter are often very
+thin, forming mere flags, with their surfaces, distinctly ripple-marked.
+They end abruptly on the declivities of many insulated mountains, which
+rise up at once to the height of about 2000 feet above the gneiss of the
+surrounding plain or table land, and to an average elevation of about 3000
+feet above the sea, which all their summits generally attain. The base of
+gneiss varies in height, so that the lower portions of the sandstone occupy
+different levels, and the thickness of the mass is various, sometimes
+exceeding 3000 feet. It is impossible to compare these scattered and
+detached portions without imagining that the whole country has once been
+covered with a great body of sandstone, and that masses from 1000 to more
+than 3000 feet in thickness have been removed.
+
+[Illustration: Fig. 89. Valleys of denudation. _a._ alluvium.]
+
+[Illustration: Fig. 90. Denudation of red sandstone on north-west coast of
+Ross-shire. (MacCulloch.)]
+
+In the "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 palæozoic strata, not 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 density in another. No doubt the vacant
+space left by the missing rocks, after extensive denudation, is less
+imposing to the imagination than a vast thickness of conglomerate or
+sandstone, or the bodily presence as it were of a mountain-chain, with all
+its inclined and curved strata. But the denuded tracts speak a clear and
+emphatic language to our reason, and, like repeated layers of fossil
+nummulites, corals or shells, or like numerous seams of coal, each based on
+its under clay full of the roots of trees, still remaining in their natural
+position, demand an indefinite lapse of time for their elaboration.
+
+No one will maintain that the fossils entombed in these rocks did not
+belong to many successive generations of plants and animals. In like
+manner, each sedimentary deposit attests a slow and gradual action, and the
+strata not only serve as a measure of the amount of denudation
+simultaneously effected elsewhere, but are also a correct indication of the
+rate at which the denuding operation was carried on.
+
+Perhaps the most convincing evidence of denudation on a magnificent scale
+is derived from the levelled surfaces of districts where large faults
+occur. I have shown, in fig. 87. p. 63., and in fig. 91., how angular and
+protruding masses of rock might naturally have been looked for on the
+surface immediately above great faults, although in fact they rarely exist.
+This phenomenon may be well studied in those districts where coal has been
+extensively worked, for there the former relation of the beds which have
+shifted their position may be determined with great accuracy. Thus in the
+coal field of Ashby de la Zouch, in Leicestershire (see fig. 91.), a fault
+occurs, on one side of which the coal beds _a b c d_ rise 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 uniform and
+unbroken, and the mass indicated by the dotted outline must have been
+washed away.[69-A] There are proofs of this kind in some level countries,
+where dense masses of strata have been cleared away from areas several
+hundred square miles in extent.
+
+[Illustration: Fig. 91. Faults and denuded coal strata, Ashby de
+la Zouch. (Mammat.)]
+
+In the Newcastle coal district it is ascertained that faults occur in
+which the upward or downward movement could not have been less than 140
+fathoms, which, had they affected equally the configuration of the
+surface to that amount, would produce mountains with precipitous
+escarpments nearly 1000 feet high, or chasms of the like depth; yet is
+the actual level of the country absolutely uniform--affording no trace
+whatever of subterranean movements.[69-B]
+
+The ground from which these materials have been removed is usually
+overspread with heaps of sand and gravel, formed out of the ruins of the
+very rocks which have disappeared. Thus, in the districts above referred
+to, they consist of rounded and angular fragments of hard sandstone,
+limestone, and ironstone, with a small quantity of the more destructible
+shale, and even rounded pieces of coal.
+
+Allusion has been already made to the shattered state and discordant
+position of the carboniferous strata in Coalbrook Dale (p. 62.). The
+collier cannot proceed three or four yards without meeting with small
+slips, and from time to time he encounters faults of considerable
+magnitude, which have thrown the rocks up or down several hundred feet. Yet
+the superficial inequalities to which these dislocated masses originally
+gave rise are no longer discernible, and the comparative flatness of the
+existing surface can only be explained, as Mr. Prestwich has observed, by
+supposing the fractured portions to have been removed by water. It is also
+clear that strata of red sandstone, more than 1000 feet thick, which once
+covered the coal, in the same region, have been carried away from large
+areas. That water has, in this case, been the denuding agent, we may infer
+from the fact that the rocks have yielded according to their different
+degrees of hardness; the hard trap of the Wrekin, for example, and other
+hills, having resisted more than the softer shale and sandstone, so as now
+to stand out in bold relief.[70-A]
+
+_Origin of valleys._--Many of the earlier geologists, and Dr. Hutton among
+them, taught that "rivers have in general hollowed out their valleys." This
+is true only of rivulets and torrents which are the feeders of the larger
+streams, and which, descending over rapid slopes, are most subject to
+temporary increase and diminution in the volume of their waters. The
+quantity of mud, sand, and pebbles constituting many a modern delta proves
+indisputably that no small part of the inequalities now existing on the
+earth's surface are due to fluviatile action; but the principal valleys in
+almost every great hydrographical basin in the world, are of a shape and
+magnitude which imply that they have been due to other causes besides the
+mere excavating power of rivers.
+
+Some geologists have imagined that a deluge, or succession of deluges, may
+have been the chief denuding agency, and they have speculated on a series
+of enormous waves raised by the instantaneous upthrow of continents or
+mountain chains out of the sea. But even were we disposed to grant such
+sudden upheavals of the floor of the ocean, and to assume that great waves
+would be the consequence of each convulsion, it is not easy to explain the
+observed phenomena by the aid of so gratuitous an hypothesis.
+
+On the other hand, a machinery of a totally different kind seems capable of
+giving rise to effects of the required magnitude. It has now been
+ascertained that the rising and sinking of extensive portions of the
+earth's crust, whether insensibly or by a repetition of sudden shocks, is
+part of the actual course of nature, and we may easily comprehend how the
+land may have been exposed during these movements to abrasion by the waves
+of the sea. In the same manner as a mountain mass may, in the course of
+ages, be formed by sedimentary deposition, layer after layer, so masses
+equally voluminous may in time waste away by inches; as, for example, if
+beds of incoherent materials are raised slowly in an open sea where a
+strong current prevails. It is well known that some of these oceanic
+currents have a breadth of 200 miles, and that they sometimes run for a
+thousand miles or more in one direction, retaining a considerable velocity
+even at the depth of several hundred feet. Under these circumstances, the
+flowing waters may have power to clear away each stratum of incoherent
+materials as it rises and approaches the surface, where the waves exert the
+greatest force; and in this manner a voluminous deposit may be entirely
+swept away, so that, in the absence of faults, no evidence may remain of
+the denuding operation. It may indeed be affirmed that the signs of waste
+will usually be least obvious where the destruction has been most
+complete; for the annihilation may have proceeded so far, that no ruins are
+left of the dilapidated rocks.
+
+Although denudation has had a levelling influence on some countries of
+shattered and disturbed strata (see fig. 87. p. 63. and fig. 91. p. 69.),
+it has more commonly been the cause of superficial inequalities, especially
+in regions of horizontal stratification. The general outline of these
+regions is that of flat and level platforms, interrupted by valleys often
+of considerable depth, and ramifying in various directions. These hollows
+may once have formed bays and channels between islands, and the steepest
+slope on the sides of each valley may have been a sea-cliff, which was
+undermined for ages, as the land emerged gradually from the deep. We may
+suppose the position and course of each valley to have been originally
+determined by differences in the hardness of the rocks, and by rents and
+joints which usually occur even in horizontal strata. In mountain chains,
+such as the Jura before described (see fig. 71. p. 55.), we perceive at
+once that the principal valleys have not been due to aqueous excavation,
+but to those mechanical movements which have bent the rocks into their
+present form. Yet even in the Jura there are many valleys, such as C (fig.
+71.), which have been hollowed out by water; and it may be stated that in
+every part of the globe the unevenness of the surface of the land has been
+due to the combined influence of subterranean movements and denudation.
+
+I may now recapitulate a few of the conclusions to which we have
+arrived: first, all the mechanical strata have been accumulated
+gradually, and the concomitant denudation has been no less gradual:
+secondly, the dry land consists in great part of strata formed
+originally at the bottom of the sea, and has been made to emerge and
+attain its present height by a force acting from beneath: thirdly, no
+combination of causes has yet been conceived so capable of producing
+extensive and gradual denudation, as the action of the waves and
+currents of the ocean upon land slowly rising out of the deep.
+
+Now, if we adopt these conclusions, we shall naturally be led to look
+everywhere for marks of the former residence of the sea upon the land,
+especially near the coasts from which the last retreat of the waters took
+place, and it will be found that such signs are not wanting.
+
+I shall have occasion to speak of ancient sea-cliffs, now far inland, in
+the south-east of England, when treating in Chapter XIX. of the denudation
+of the chalk in Surrey, Kent, and Sussex. Lines of upraised sea-beaches of
+more modern date are traced, at various levels from 20 to 100 feet and
+upwards above the present sea-level, for great distances on the east and
+west coasts of Scotland, as well as in Devonshire, and other counties in
+England. These ancient beach-lines often form terraces of sand and gravel,
+including littoral shells, some broken, others entire, and corresponding
+with species now living on the adjoining coast. But it would be
+unreasonable to expect to meet everywhere with the signs of ancient shores,
+since no geologist can have failed to observe how soon all recent marks of
+the kind above alluded to are obscured or entirely effaced, wherever, in
+consequence of the altered state of the tides and currents, the sea has
+receded for a few centuries. We see the cliffs crumble down in a few years
+if composed of sand or clay, and soon reduced to a gentle slope. If there
+were shells on the beach they decompose, and their materials are washed
+away, after which the sand and shingle may resemble any other alluviums
+scattered over the interior.
+
+[Illustration: Fig. 92. Section of inland cliff at Abesse, near Dax.
+
+  _a._ Sand of the Landes.
+  _b._ Limestone.
+  _c._ Clay.]
+
+The features of an ancient shore may sometimes be concealed by the
+growth of trees and shrubs, or by a covering of blown sand, a good
+example of which occurs a few miles west from Dax, near Bordeaux, in the
+south of France. About twelve miles inland, a steep bank may be traced
+running in a direction nearly north-east and south-west, or parallel to
+the contiguous coast. This sudden fall of about 50 feet conducts us from
+the higher platform of the Landes to a lower plain which extends to the
+sea. The outline of the ground suggested to me, as it would do to every
+geologist, the opinion that the bank in question was once a sea-cliff,
+when the whole country stood at a lower level. But this is no longer
+matter of conjecture, for, in making excavations in 1830 for the
+foundation of a building at Abesse, a quantity of loose sand, which
+formed the slope _d e_, was removed; and a perpendicular cliff, about 50
+feet in height, which had hitherto been protected from the agency of the
+elements, was exposed. At the bottom appeared the limestone _b_,
+containing tertiary shells and corals, immediately below it the clay
+_c_, and above it the usual tertiary sand _a_, of the department of the
+Landes. At the base of the precipice were seen large partially rounded
+masses of rock, evidently detached from the stratum _b_. The face of the
+limestone was hollowed out and weathered into such forms as are seen in
+the calcareous cliffs of the adjoining coast, especially at Biaritz,
+near Bayonne. It is evident that, when the country was at a somewhat
+lower level, the sea advanced along the surface of the argillaceous
+stratum _c_, which, from its yielding nature, favoured the waste by
+allowing the more solid superincumbent stone _b_ to be readily
+undermined. Afterwards, when the country had been elevated, part of the
+sand, _a_, fell down, or was drifted by the winds, so as to form the
+talus, _d e_, which masked the inland cliff until it was artificially
+laid open to view.
+
+When we are considering the various causes which, in the course of ages,
+may efface the characters of an ancient sea-coast, earthquakes must not be
+forgotten. During violent shocks, steep and overhanging cliffs are often
+thrown down and become a heap of ruins. Sometimes unequal movements of
+upheaval or depression entirely destroy that horizontality of the base-line
+which constitutes the chief peculiarity of an ancient sea-cliff.
+
+It is, however, in countries where hard limestone rocks abound, that inland
+cliffs retain faithfully 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 what were once sea-cliffs are well
+preserved. These have been described, by MM. Boblaye and Virlet, as rising
+one above the other at different distances from the actual shore, the
+summit of the highest and oldest occasionally exceeding 1000 feet in
+elevation. At the base of each there is usually a terrace, which is in some
+places a few yards, in others above 300 yards wide, so that we are
+conducted from the high land of the interior to the sea by a succession of
+great steps. These inland cliffs are most perfect, and most exactly
+resemble those now washed by the waves of the Mediterranean, where they are
+formed of calcareous rock, especially if the rock be a hard crystalline
+marble. The following are the points of correspondence observed between the
+ancient coast lines and the borders of the present sea:--1. A range of
+vertical precipices, with a terrace at their base. 2. A weathered state of
+the surface of the naked rock, such as the spray of the sea produces. 3. A
+line of littoral caverns at the foot of the cliffs. 4. A consolidated beach
+or breccia with occasional marine shells, found at the base of the cliffs,
+or in the caves. 5. Lithodomous perforations.
+
+In regard to the first of these, it would be superfluous to dwell on the
+evidence afforded of the undermining power of waves and currents by
+perpendicular precipices. The littoral caves, also, will be familiar to
+those who have had opportunities of observing the manner in which the waves
+of the sea, when they beat against rocks, have power to scoop out caverns.
+As to the breccia, it is composed of pieces of limestone and rolled
+fragments of thick solid shell, such as _Strombus_ and _Spondylus_, all
+bound together by a crystalline calcareous cement. Similar aggregations are
+now forming on the modern beaches of Greece, and in caverns on the
+sea-side; and they are only distinguishable in character from those of more
+ancient date, by including many pieces of pottery. In regard to the
+_lithodomi_ above alluded to, these bivalve mollusks are well known to have
+the power of excavating holes in the hardest limestones, the size of the
+cavity keeping pace with the growth of the shell. When living they require
+to be always covered by salt water, but similar pear-shaped hollows,
+containing the dead shells of these creatures, are found at different
+heights on the face of the inland cliffs above mentioned. Thus, for
+example, they have been observed near Modon and Navarino on cliffs in the
+interior 125 feet high above the Mediterranean. As to the weathered surface
+of the calcareous rocks, all limestones are known to suffer chemical
+decomposition when moistened by the spray of the salt water, and are
+corroded still more deeply at points lower down where they are just reached
+by the breakers. By this action the stone acquires a wrinkled and furrowed
+outline, and very near the sea it becomes rough and branching, as if
+covered with corals. Such effects are traced not only on the present shore,
+but at the base of the ancient cliffs far in the interior. Lastly, it
+remains only to speak of the terraces, which extend with a gentle slope
+from the base of almost all the inland cliffs, and are for the most part
+narrow where the rock is hard, but sometimes half a mile or more in breadth
+where it is soft. They are the effects of the encroachment of the ancient
+sea upon the shore at those levels at which the land remained for a long
+time stationary. The justness of this view is apparent on examining the
+shape of the modern shore wherever the sea is advancing upon the land, and
+removing annually small portions of undermined rock. By this agency a
+submarine platform is produced on which we may walk for some distance from
+the beach in shallow water, the increase of depth being very gradual, until
+we reach a point where the bottom plunges down suddenly. This platform is
+widened with more or less rapidity according to the hardness of the rocks,
+and when upraised it constitutes an inland terrace.
+
+But the four principal lines of cliff observed in the Morea do not imply,
+as some have imagined, four great eras of sudden upheaval; they simply
+indicate the intermittence of the upheaving force. Had the rise of the land
+been continuous and uninterrupted, there would have been no one prominent
+line of cliff; for every portion of the surface having been, in its turn,
+and for an equal period of time, a sea-shore, would have presented a nearly
+similar aspect. But if pauses occur in the process of upheaval, the waves
+and currents have time to sap, throw down, and clear away considerable
+masses of rock, and to shape out at certain levels lofty ranges of cliffs
+with broad terraces at their base.
+
+There are some levelled spaces, however, both ancient and modern, in the
+Morea, which are not due to denudation, although resembling in outline
+the terraces above described. They may be called Terraces of Deposition,
+since they have resulted from the gain of land upon the sea where rivers
+and torrents have produced deltas. If the sedimentary matter has filled
+up a bay or gulf surrounded by steep mountains, a flat plain is formed
+skirting the inland precipices; and if these deposits are upraised,
+they form a feature in the landscape very similar to the areas of
+denudation before described.
+
+In the island of Sicily I have examined many inland cliffs like those of
+the Morea; as, for example, near Palermo, where a precipice is seen
+consisting of limestone at the base of which are numerous caves. One of
+these called San Ciro, about 2 miles distant from Palermo, is about 20 feet
+high, 10 wide, and 180 above the sea. Within it is found an ancient beach
+(_b_, fig. 93.), formed of pebbles of various rocks, many of which must
+have come from places far remote. Broken pieces of coral and shell,
+especially of oysters and pectens, are seen intermingled with the pebbles.
+Immediately above the level of this beach, _serpulæ_ are still found
+adhering to the face of the rock, and the limestone is perforated by
+_lithodomi_. Within the grotto, also, at the same level, similar
+perforations occur; and so numerous are the holes, that the rock is
+compared by Hoffmann to a target pierced by musket balls. But in order to
+expose to view these marks of boring-shells in the interior of the cave, it
+was necessary first to remove a mass of breccia, which consisted of
+numerous fragments of rock and an immense quantity of bones of the mammoth,
+hippopotamus, and other quadrupeds, imbedded in a dark brown calcareous
+marl. Many of the bones were rolled as if partially subjected to the action
+of the waves. Below this breccia, which is about 20 feet thick, was found a
+bed of sand filled with sea-shells of recent species; and underneath the
+sand, again, is the secondary limestone of Monte Grifone. The state of the
+surface of the limestone in the cave above the level of the marine sand is
+very different from that below it. _Above_, the rock is jagged and uneven,
+as is usual in the roofs and sides of limestone caverns; _below_, the
+surface is smooth and polished, as if by the attrition of the waves.
+
+[Illustration: Fig. 93. Cross section.
+
+  _a._ Monte Grifone.
+  _b._ Cave of San Ciro.[75-A]
+  _c._ Plain of Palermo, in which are Newer Pliocene strata of
+       limestone and sand.
+  _d._ Bay of Palermo.]
+
+The platform indicated at _c_, fig. 93., is formed by a tertiary deposit
+containing marine shells almost all of living species, and it affords an
+illustration of the terrace of deposition, or the last of the two kinds
+before mentioned (p. 74.).
+
+There are also numerous instances in Sicily of terraces of denudation. One
+of these occurs on the east coast to the north of Syracuse, and the same is
+resumed to the south beyond the town of Noto, where it may be traced
+forming a continuous and lofty precipice, _a b_, fig. 94., facing towards
+the sea, and constituting the abrupt termination of a calcareous formation,
+which extends in horizontal strata far inland. This precipice varies in
+height from 500 to 700 feet, and between its base and the sea is an
+inferior platform, _c b_, consisting of similar white limestone. All the
+beds dip towards the sea, but are usually inclined at a very slight angle:
+they are seen to extend uninterruptedly from the base of the escarpment
+into the platform, showing distinctly that the lofty cliff was not produced
+by a fault or vertical shift of the beds, but by the removal of a
+considerable mass of rock. Hence we may conclude that the sea, which is now
+undermining the cliffs of the Sicilian coast, reached at some former
+period the base of the precipice _a b_, at which time the surface of the
+terrace _c b_ must have been covered by the Mediterranean. There was a
+pause, therefore, in the upward movement, when the waves of the sea had
+time to carve out the platform _c b_; but there may have been many other
+stationary periods of minor duration. Suppose, for example, that a series
+of escarpments _e_, _f_, _g_, _h_, once existed, and that the sea, during a
+long interval free from subterranean movements, advances along the line _c
+b_, all preceding cliffs must have been swept away one after the other, and
+reduced to the single precipice _a b_.
+
+[Illustration: Fig. 94. Cross section.]
+
+[Illustration: Fig. 95. Valley called Gozzo degli Martiri, below
+Melilli, Val di Noto.]
+
+That such a series of smaller cliffs, as those represented at _e_, _f_,
+_g_, _h_, fig. 94., did really once exist at intermediate heights in place
+of the single precipice _a b_, is rendered highly probable by the fact,
+that in certain bays and inland valleys opening towards the east coast of
+Sicily, and not far from the section given in fig. 94., the solid limestone
+is shaped out into a great succession of ledges, separated from each other
+by small vertical cliffs. These are sometimes so numerous, one above the
+other, that where there is a bend at the head of a valley, they produce an
+effect singularly resembling the seats of a Roman amphitheatre. A good
+example of this configuration occurs near the town of Melilli, as seen in
+the annexed view (fig. 95.). In the south of the island, near Spaccaforno,
+Scicli, and Modica, precipitous rocks of white limestone, ascending to the
+height of 500 feet, have been carved out into similar forms.
+
+[Illustration: Fig. 96. Cross section.]
+
+This appearance of a range of marble seats circling round the head of a
+valley, or of great flights of steps descending from the top to the bottom,
+on the opposite sides of a gorge, may be accounted for, as already hinted,
+by supposing the sea to have stood successively at many different levels,
+as at _a a_, _b b_, _c c_, in the accompanying fig. 96. But the causes of
+the gradual contraction of the valley from above downwards may still be
+matter of speculation. Such contraction may be due to the greater force
+exerted by the waves when the land at its first emergence was smaller in
+quantity, and more exposed to denudation in an open sea; whereas the wear
+and tear of the rocks might diminish in proportion as this action became
+confined within bays or channels closed in on two or three sides. Or,
+secondly, the separate movements of elevation may have followed each other
+more rapidly as the land continued to rise, so that the times of those
+pauses, during which the greatest denudation was accomplished at certain
+levels, were always growing shorter. It should be remarked, that the cliffs
+and small terraces are rarely found on the opposite sides of the Sicilian
+valleys at heights so precisely answering to each other as those given in
+fig. 96., and this might have been expected, to whichever of the two
+hypotheses above explained we incline; for, according to the direction of
+the prevailing winds and currents, the waves may beat with unequal force on
+different parts of the shore, so that while no impression is made on one
+side of a bay, the sea may encroach so far on the other as to unite several
+smaller cliffs into one.
+
+Before quitting the subject of ancient sea-cliffs, carved out of
+limestone, I shall mention the range of precipitous rocks, composed of a
+white marble of the Oolitic period, which I have seen near the northern
+gate of St. Mihiel in France. They are situated on the right bank of the
+Meuse, at a distance of 200 miles from the nearest sea, and they present
+on the precipice facing the river three or four horizontal grooves, one
+above the other, precisely resembling those which are scooped out by the
+undermining waves. The summits of several of these masses are detached
+from the adjoining hill, in which case the grooves pass all round them,
+facing towards all points of the compass, as if they had once formed
+rocky islets near the shore.[78-A]
+
+Captain Bayfield, in his survey of the Gulf of St. Lawrence, discovered in
+several places, especially in the Mingan islands, a counterpart of the
+inland cliffs of St. Mihiel, and traced a succession of shingle beaches,
+one above the other, which agreed in their level with some of the principal
+grooves scooped out of the limestone pillars. These beaches consisted of
+calcareous shingle, with shells of recent species, the farthest from the
+shore being 60 feet above the level of the highest tides. In addition to
+the drawings of the pillars called the flower-pots, which he has
+published[78-B], I have been favoured with other views of rocks on the same
+coast, drawn by Lieut. A. Bowen, R. N. (See fig. 97.)
+
+[Illustration: Fig. 97. Limestone columns in Niapisca Island, in the Gulf
+of St. Lawrence. Height of the second column on the left, 60 feet.]
+
+In the North-American beaches above mentioned rounded fragments of
+limestone have been found perforated by _lithodomi_; and holes drilled
+by the same mollusks have been detected in the columnar rocks or
+"flower-pots," showing that there has been no great amount of
+atmospheric decomposition on the surface, or the cavities alluded
+to would have disappeared.
+
+[Illustration: Fig. 98. The North Rocks, Bermuda, lying outside the
+great coral reef. A. 16 feet high, and B. 12 feet. _c._ _c._ Hollows
+worn by the sea.]
+
+We have an opportunity of seeing in the Bermuda islands the manner in
+which the waves of the Atlantic have worn, and are now wearing out, deep
+smooth hollows on every side of projecting masses of hard limestone. In the
+annexed drawing, communicated to me by Lieut. Nelson, the excavations _c_,
+_c_, _c_, have been scooped out by the waves in a stone of very modern
+date, which, although extremely hard, is full of recent corals and shells,
+some of which retain their colour.
+
+When the forms of these horizontal grooves, of which the surface is
+sometimes smooth and almost polished, and the roofs of which often overhang
+to the extent of 5 feet or more, have been carefully studied by geologists,
+they will serve to testify the former action of the waves at innumerable
+points far in the interior of the continents. But we must learn to
+distinguish the indentations due to the original action of the sea, and
+those caused by subsequent chemical decomposition of calcareous rocks, to
+which they are liable in the atmosphere.
+
+Notwithstanding the enduring nature of the marks left by littoral action on
+calcareous rocks, we can by no means detect sea-beaches and inland cliffs
+everywhere, even in Sicily and the Morea. 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 calcareous rocks.
+
+
+FOOTNOTES:
+
+[67-A] Western Islands, vol. ii. p. 93. pl. 31. fig. 4.
+
+[69-A] See Mammat's Geological Facts, &c. p. 90. and plate.
+
+[69-B] Conybeare's Report to Brit. Assoc. 1842, p. 381.
+
+[70-A] Prestwich, Geol. Trans. second series, vol. v. pp. 452. 473.
+
+[75-A] Section given by Dr. Christie, Edin. New Phil. Journ. No.
+xxiii., called by mistake the Cave of Mardolce, by the late M. Hoffmann.
+See account by Mr. S. P. Pratt, F. G. S. Proceedings of Geol. Soc.
+No. 32. 1833.
+
+[78-A] I was directed by M. Deshayes to this spot, which I visited
+in June, 1833.
+
+[78-B] See Trans. of Geol. Soc., second series, vol. v. plate v.
+
+
+
+
+CHAPTER VII.
+
+ALLUVIUM.
+
+   Alluvium described--Due to complicated causes--Of various ages, as
+   shown in Auvergne--How distinguished from rocks in
+   situ--River-terraces--Parallel roads of Glen Roy--Various theories
+   respecting their origin.
+
+
+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 the name of alluvium has been 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 spread over low lands by a flood.
+
+A partial covering of such alluvium is found alike in all climates, from
+the equatorial to the polar regions; but in the higher latitudes of Europe
+and North America it assumes a distinct character, being very frequently
+devoid of stratification, and containing huge fragments of rock, some
+angular and others rounded, which have been transported to great distances
+from their parent mountains. When it presents itself in this form, it has
+been called "diluvium," "drift," or the "boulder formation;" and its
+probable connexion with the agency of floating ice and glaciers will be
+treated of more particularly in the eleventh and twelfth chapters.
+
+[Illustration: Fig. 99. Lavas of Auvergne resting on alluviums of
+different ages.]
+
+The student will be prepared, by what I have said in the last chapter on
+denudation, to hear that loose gravel and sand are often met with, not
+only on the low grounds bordering rivers, but also at various points on
+the sides or even summits of mountains. For, 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. 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 complicated. Moreover, 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 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 volcanos 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 bones belonging to distinct groups of land
+animals which flourished in the country in succession.
+
+The annexed drawing 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, but in some cases a
+narrow stripe of solid lava sharing the bottom of the valley with the
+river. In all these accumulations of transported matter of different ages
+the bones of extinct quadrupeds have been found belonging to assemblages of
+land mammalia which flourished in the country in succession, and which vary
+specifically, the one from the other, in a greater or less degree, in
+proportion as the time which separated their entombment has been more or
+less protracted. The streams in the same district are still undermining
+their banks and grinding down into pebbles or sand, columns of basalt and
+fragments of granite and gneiss; but the older alluviums, with the fossil
+remains belonging to them, are prevented from being mingled with the gravel
+of recent date by the cappings of lava before mentioned. But for the
+accidental interference, therefore, of this peculiar cause, all the
+alluviums might have passed so insensibly the one into the other, that
+those formed at the remotest era might have appeared of the same date as
+the newest, and the whole formation might have been regarded by some
+geologists as the result of one sudden and violent catastrophe.
+
+In almost every country, the alluvium consists in its upper part of
+transported materials, but it often passes downwards into a mass of
+broken and angular fragments derived from the subjacent rock. To this
+mass the provincial name of "rubble," or "brash," is given in many
+parts of England. It may be referred to the weathering or disintegration
+of stone on the spot, the effects of air and water, sun and frost,
+and chemical decomposition.
+
+[Illustration: Fig. 100. Cross section.
+
+  _a._ Vegetable soil.
+  _b._ Alluvium.
+  _c._ Mass of same, apparently detached.]
+
+The inferior surface of alluvial deposits is often very irregular,
+conforming to all the inequalities of the fundamental rocks (fig. 100.).
+Occasionally, a small mass, as at _c_, appears detached, and as if included
+in the subjacent formation. Such isolated portions are usually sections of
+winding subterranean hollows filled up with alluvium. They may have been
+the courses of springs or subterranean streamlets, which have flowed
+through and enlarged natural rents; or, when on a small scale and in soft
+strata, they may be spaces which the roots of large trees have once
+occupied, gravel and sand having been introduced after their decay.
+
+[Illustration: Fig. 101. Sand-pipes in the chalk at Eaton, near Norwich.]
+
+But there are other deep hollows of a cylindrical form found in England,
+France, and elsewhere, penetrating the white chalk, and filled with sand
+and gravel, which are not so readily explained. They are sometimes called
+"sand-pipes," or "sand-galls," and "puits naturels," in France. Those
+represented in the annexed cut were observed by me in 1839, laid open in a
+large chalk-pit near Norwich. They were of very symmetrical form, the
+largest more than 12 feet in diameter, and some of them had been traced, by
+boring, to the depth of more than 60 feet. The smaller ones varied from a
+few inches to a foot in diameter, and seldom descended more than 12 feet
+below the surface. Even where three of them occurred, as at _a_, fig. 101.,
+very close together, the parting walls of soft white chalk were not broken
+through. They all taper downwards and end in a point. As a general rule,
+sand and pebbles occupy the central parts of each pipe, while the sides and
+bottom are lined with clay.
+
+Mr. Trimmer, in speaking of appearances of the same kind in the Kentish
+chalk, attributes the origin of such "sand-galls" to the action of the sea
+on a beach or shoal, where the waves, charged with shingle and sand, not
+only wear out longitudinal furrows, such as may be observed on the surface
+of the chalk near Norwich when the incumbent gravel is removed, but also
+drill deep circular hollows by the rotatory motion imparted to sand and
+pebbles. Such furrows, as well as vertical cavities, are now formed, he
+observes, on the coast where the shores are composed of chalk.[82-A]
+
+That the commencement of many of the tubular cavities now under
+consideration has been due to the cause here assigned, I have little doubt.
+But such mechanical action could not have hollowed out the whole of the
+sand-pipes _c_ and _d_, fig. 101., because several large chalk-flints seen
+protruding from the walls of the pipes have not been eroded, while sand and
+gravel have penetrated many feet below them. In other cases, as at _b b_,
+similar unrounded nodules of flint, still preserving their irregular form
+and white coating, are found at various depths in the midst of the loose
+materials filling the pipe. These have evidently been detached from regular
+layers of flints occurring above. It is also to be remarked that the course
+of the same sand-pipe, _b b_, is traceable above the level of the chalk for
+some distance upwards, through the incumbent gravel and sand, by the
+obliteration of all signs of stratification. Occasionally, also, as in the
+pipe _d_, the overlying beds of gravel bend downwards into the mouth of the
+pipe, so as to become in part vertical, as would happen if horizontal
+layers had sunk gradually in consequence of a failure of support. All these
+phenomena may be accounted for by attributing the enlargement and deepening
+of the sand-pipes to the chemical action of water charged with carbonic
+acid, derived from the vegetable soil and the decaying roots of trees. Such
+acid might corrode the chalk, and deepen indefinitely any previously
+existing hollow, but could not dissolve the flints. The water, after it had
+become saturated with carbonate of lime, might freely percolate the
+surrounding porous walls of chalk, and escape through them and from the
+bottom of the tube, so as to carry away in the course of time large masses
+of dissolved calcareous rock[83-A], and leave behind it on the edges of
+each tubular hollow a coating of fine clay, which the white chalk contains.
+
+I have seen tubes precisely similar and from 1 to 5 feet in diameter
+traversing vertically the upper half of the soft calcareous building
+stone, or chalk without flints, constituting St. Peter's Mount,
+Maestricht. These hollows are filled with pebbles and clay, derived from
+overlying beds of gravel, and all terminate downwards like those of
+Norfolk. I was informed that, 6 miles from Maestricht, one of these
+pipes, 2 feet in diameter, was traced downwards to a bed of flattened
+flints, forming an almost continuous layer in the chalk. Here it
+terminated abruptly, but a few small root-like prolongations of it were
+detected immediately below, probably where the dissolving substance had
+penetrated at some points through openings in the siliceous mass.
+
+It is not so easy as may at first appear to draw a clear line of
+distinction between the _fixed_ rocks, or regular strata (rocks _in
+situ_ or _in place_), and _alluvium_. If the bed of a torrent or river
+be dried up, we call the gravel, sand, and mud left in their channels,
+or whatever, during floods, they may have scattered over the
+neighbouring plains, alluvium. The very same materials carried into a
+lake, where they become sorted by water and arranged in more distinct
+layers, especially if they inclose the remains of plants, shells, or
+other fossils, are termed regular strata.
+
+In like manner we may sometimes compare the gravel, sand, and broken
+shells, strewed along the path of a rapid marine current, with a deposit
+formed contemporaneously by the discharge of similar materials, year after
+year, into a deeper and more tranquil part of the sea. In such cases, when
+we detect marine shells or other organic remains entombed in the strata,
+which enable us to determine their age and mode of origin, we regard them
+as part of the regular series of fossiliferous formations, whereas, if
+there are no fossils, we have frequently no power of separating them from
+the general mass of superficial alluvium.
+
+The usual rarity of organic remains in beds of loose gravel and sand is
+partly owing to the rapid and turbid water in which they were formed having
+been in a condition unfavourable to the habitation of aquatic beings, and
+partly to their porous nature, which, by allowing the free percolation of
+rain-water, has promoted the decomposition and removal of organic matter.
+
+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 a rash inference has sometimes been drawn, that rivers in general have
+grown smaller, or become less liable to be flooded than formerly. But such
+phenomena would be a natural result of any considerable oscillations in the
+level of the land experienced since the existing valleys originated.
+
+Suppose 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.[84-A] There might be no encroachment of the sea
+at the river's mouth in consequence of this change of level, but the
+fall of the waters flowing from the interior being lessened, the main
+river and its tributaries would have less power to carry down to its
+delta, and to discharge into the ocean, the sedimentary matter with
+which they are annually loaded. They would all begin to raise their
+channels and alluvial plains by depositing in them the heavier sand and
+pebbles washed down from the upland country, and this operation would
+take place most effectively if the amount of subsidence in the interior
+was unequal, and especially if, on the whole, it exceeded that of the
+region near the sea. If then the same area of land be again upheaved to
+its former height, the fall, and consequently the velocity, of every
+river would begin to augment. Each of them would be less given to
+overflow its alluvial plain; and their power of carrying earthy matter
+seaward, and of scouring out and deepening their channels, would
+continue till, after a lapse of many thousand years, each of them would
+have eroded a new channel or valley through a fluviatile formation of
+modern date. The surface of what was once the river-plain at the period
+of greatest depression, would 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 would 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[85-A]; and the
+freshwater 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.
+
+In many cases, the alluvium in which rivers are now cutting their channels,
+originated when the land first rose out of the sea. If, for example, the
+emergence was caused by a gradual and uniform motion, every bay and
+estuary, or the straits between islands, would dry up slowly, and during
+their conversion into valleys, every part of the upheaved area would in its
+turn be a sea-shore, and might be strewed over with littoral sand and
+pebbles, or each spot might be the point where a delta accumulated during
+the retreat and exclusion of the sea. Materials so accumulated would
+conform to the general slope of a valley from its head to the sea-coast.
+
+_River terraces._--We often observe at a short distance from the present
+bed of a river a steep cliff a few feet or yards high, and on a level with
+the top of it a flat terrace corresponding in appearance to the alluvial
+plain which immediately borders the river. This terrace is again bounded by
+another cliff, above which a second terrace sometimes occurs: and in this
+manner two or three ranges of cliffs and terraces are occasionally seen on
+one or both sides of the stream, the number varying, but those on the
+opposite sides often corresponding in height.
+
+[Illustration: Fig. 102. River Terraces and Parallel Roads.]
+
+These terraces are seldom continuous for great distances, and their
+surface slopes downwards, with an inclination similar to that of the
+river. They are readily explained if we adopt the hypothesis before
+suggested, of a gradual rise of the land; especially if, while rivers
+are shaping out their beds, the upheaving movement be intermittent, so
+that long pauses shall occur, during which the stream will have time to
+encroach upon one of its banks, so as to clear away and flatten a large
+space. This operation being afterwards repeated at lower levels, there
+will be several successive cliffs and terraces.
+
+_Parallel roads._--The parallel shelves, or roads, as they have been
+called, of Lochaber or Glen Roy and other contiguous valleys in Scotland,
+are distinct both in character and origin from the terraces above
+described; for they have no slope towards the sea like the channel of a
+river, nor are they the effect of denudation. Glen Roy is situated in the
+western Highlands, about ten miles north of Fort William, near the western
+end of the great glen of Scotland, or Caledonian Canal, and near the foot
+of the highest of the Grampians, Ben Nevis. Throughout its whole length, a
+distance of more than ten miles, two, and in its lower part three, parallel
+roads or shelves are traced along the steep sides of the mountains, as
+represented in the annexed figure, fig. 102., each maintaining a perfect
+horizontality, and continuing at exactly the same level on the opposite
+sides of the glen. Seen at a distance, they appear like ledges or roads,
+cut artificially out of the sides of the hills; but when we are upon them
+we can scarcely recognize their existence, so uneven is their surface, and
+so covered with boulders. They are from 10 to 60 feet broad, and merely
+differ from the side of the mountain by being somewhat less steep.
+
+On closer inspection, we find that these terraces are stratified in the
+ordinary manner of alluvial or littoral deposits, as may be seen at those
+points where ravines have been excavated by torrents. The parallel shelves,
+therefore, have not been caused by denudation, but by the deposition of
+detritus, precisely similar to that which is dispersed in smaller
+quantities over the declivities of the hills above. These hills consist of
+clay-slate, mica-schist, and granite, which rocks have been worn away and
+laid bare at a few points only, in a line just above the parallel roads.
+The highest of these roads is about 1250 feet above the level of the sea,
+the next about 200 feet lower than the uppermost, and the third still lower
+by about 50 feet. It is only this last, or the lowest of the three, which
+is continued throughout Glen Spean, a large valley with which Glen Roy
+unites. As the shelves are always at the same height above the sea, they
+become continually more elevated above the river in proportion as we
+descend each valley; and they at length terminate very abruptly, without
+any obvious cause, either in the shape of the ground, or any change in the
+composition or hardness of the rocks. I should exceed the limits of this
+work, were I to attempt to give a full description of all the geographical
+circumstances attending these singular terraces, or to discuss the
+ingenious theories which have been severally proposed to account for them
+by Dr. MacCulloch, Sir T. D. Lauder, and Messrs. Darwin, Agassiz, Milne,
+and Chambers. There is one point, however, on which all are agreed, namely,
+that these shelves are ancient beaches, or littoral formations accumulated
+round the edges of one or more sheets of water which once stood at the
+level, first of the highest shelf, and successively at the height of the
+two others. It is well known, that wherever a lake or marine fiord exists
+surrounded by steep mountains subject to disintegration by frost or the
+action of torrents, some loose matter is washed down annually, especially
+during the melting of snow, and a check is given to the descent of this
+detritus at the point where it reaches the waters of the lake. The waves
+then spread out the materials along the shore, and throw some of them upon
+the beach; their dispersing power being aided by the ice, which often
+adheres to pebbles during the winter months, and gives buoyancy to them.
+The annexed diagram illustrates the manner in which Dr. MacCulloch and Mr.
+Darwin suppose "the roads" to constitute mere indentations in a superficial
+alluvial coating which rests upon the hillside, and consists chiefly of
+clay and sharp unrounded stones.
+
+[Illustration: Fig. 103. Cross section.
+
+A B. Supposed original surface of rock.
+
+C D. Roads or shelves in the outer alluvial covering of the hill.]
+
+Among other proofs that the parallel roads have really been formed along
+the margin of a sheet of water, it may be mentioned, that wherever an
+isolated hill rises in the middle of the glen above the level of any
+particular shelf, a corresponding shelf is seen at the same level passing
+round the hill, as would have happened if it had once formed an island in a
+lake or fiord. Another very remarkable peculiarity in these terraces is
+this; each of them comes in some portion of its course to a _col_, or
+passage between the heads of glens, the explanation of which will be
+considered in the sequel.
+
+Those writers who first advocated the doctrine that the roads were the
+ancient beaches of freshwater lakes, were unable to offer any probable
+hypothesis respecting the formation and subsequent removal of barriers of
+sufficient height and solidity to dam up the water. To introduce any
+violent convulsion for their removal was inconsistent with the
+uninterrupted horizontality of the roads, and with the undisturbed aspect
+of those parts of the glens where the shelves come suddenly to an end. Mr.
+Agassiz and Dr. Buckland, desirous, like the defenders of the lake theory,
+to account for the limitation of the shelves to certain glens, and their
+absence in contiguous glens, where the rocks are of the same composition,
+and the slope and inclination of the ground very similar, started the
+conjecture that these valleys were once blocked up by enormous glaciers
+descending from Ben Nevis, giving rise to what are called in Switzerland
+and in the Tyrol, glacier-lakes. After a time the icy barrier was broken
+down, or melted, first, to the level of the second, and afterwards to that
+of the third road or shelf.
+
+In corroboration of this view, they contended that the alluvium of Glen
+Roy, as well as of other parts of Scotland, agrees in character with the
+moraines of glaciers seen in the Alpine valleys of Switzerland. Allusion
+will be made in the eleventh chapter to the former existence of glaciers in
+the Grampians: in the mean time it will readily be conceded that this
+hypothesis is preferable to any previous lacustrine theory, by accounting
+more easily for the temporary existence and entire disappearance of lofty
+transverse barriers, although the height required for the imaginary dams
+of ice may be startling.
+
+Before the idea last alluded to had been entertained, Mr. Darwin examined
+Glen Roy, and came to the opinion that the shelves were formed when the
+glens were still arms of the sea, and, consequently, that there never were
+any barriers. According to him, the land emerged during a slow and uniform
+upward movement, like that now experienced throughout a large part of
+Sweden and Finland; but there were certain pauses in the upheaving process,
+at which times the waters of the sea remained stationary for so many
+centuries as to allow of the accumulation of an extraordinary quantity of
+detrital matter, and the excavation, at points immediately above, of many
+deep notches and bare cliffs in the hard and solid rock.
+
+The phenomena which are most difficult to reconcile with this theory
+are, first, the abrupt cessation of the roads at certain points in the
+different glens; secondly, their unequal number in different valleys
+connecting with each other, there being three, for example, in Glen Roy
+and only one in Glen Spean; thirdly, the precise horizontality of level
+maintained by the same shelf over a space many leagues in length
+requiring us to assume, that during a rise of 1250 feet no one portion
+of the land was raised even a few yards above another; fourthly, the
+coincidence of level already alluded to of each shelf with a _col_, or
+the point forming the head of two glens, from which the rain-waters flow
+in opposite directions. This last-mentioned feature in the physical
+geography of Lochaber seems to have been explained in a satisfactory
+manner by Mr. Darwin. He calls these _cols_ "landstraits," and regards
+them as having been anciently sounds or channels between islands. He
+points out that there is a tendency in such sounds to be silted up, and
+always the more so in proportion to their narrowness. In a chart of the
+Falkland Islands by Capt. Sullivan, R.N., it appears that there are
+several examples there of straits where the soundings diminish regularly
+towards the narrowest part. One is so nearly dry that it can be walked
+over at low water, and another, no longer covered by the sea, is
+supposed to have recently dried up in consequence of a small shift in
+the relative level of sea and land. "Similar straits," observes Mr.
+Chambers, "hovering, in character, between sea and land, and which may
+be called fords, are met with in the Hebrides. Such, for example, is the
+passage dividing the islands of Lewis and Harris, and that between North
+Uist and Benbecula, both of which would undoubtedly appear as _cols_,
+coinciding with a terrace or raised beach, all round the islands, if the
+sea were to subside."[88-A]
+
+The precise horizontality of level maintained by the roads or shelves of
+Lochaber over an area many leagues in length and breadth, is a
+difficulty common in some degree to all the rival hypotheses, whether of
+lakes, or glaciers, or of the simple upheaval of the land above the sea.
+For we cannot suppose the roads to be more ancient than the glacial
+period, or the era of the boulder formation of Scotland, of which I
+shall speak in the eleventh and twelfth chapters. Strata of that era of
+marine origin containing northern shells of existing species have been
+found at various heights in Scotland, some on the east, and others on
+the west coast, from 20 to 400 feet high; and in one region in
+Lanarkshire not less than 524 feet above high-water mark. It seems,
+therefore, in the highest degree improbable that Glen Roy should have
+escaped entirely the upward movement experienced in so many surrounding
+regions,--a movement implied by the position of these marine deposits,
+in which the shells are almost all of known recent species. But if the
+motion has really extended to Glen Roy and the contiguous glens, it must
+have uplifted them bodily, without in the slightest degree affecting
+their horizontality; and this being admitted, the principal objection to
+the theory of marine beaches, founded on the uniformity of upheaval, is
+removed, or is at least common to every theory hitherto proposed.
+
+To assume that the ocean has gone down from the level of the uppermost
+shelf, or 1250 feet, simultaneously all over the globe, while the land
+remained unmoved, is a view which will find favour with very few
+geologists, for the reasons explained in the fifth chapter.
+
+The student will perceive, from the above sketch of the controversy
+respecting the formation of these curious shelves, that this problem, like
+many others in geology, is as yet only solved in part; and that a larger
+number of facts must be collected and reasoned upon before the question
+can be finally settled.
+
+
+FOOTNOTES:
+
+[82-A] Trimmer, Proceedings of Geol. Soc. vol. iv. p. 7. 1842.
+
+[83-A] See Lyell on Sand-pipes, &c., Phil. Mag., third series, vol.
+xv. p. 257., Oct. 1839.
+
+[84-A] Principles of Geology, 7th ed. p. 506., 8th ed. 509.
+
+[85-A] Second Visit to the U. S. vol. ii. chap. 34.
+
+[88-A] "Ancient Sea Margins," p. 114., by R. Chambers.
+
+
+
+
+CHAPTER VIII.
+
+CHRONOLOGICAL CLASSIFICATION OF ROCKS.
+
+   Aqueous, plutonic, volcanic, and metamorphic rocks, considered
+   chronologically--Lehman's division into primitive and
+   secondary--Werner's addition of a transition class--Neptunian
+   theory--Hutton on igneous origin of granite--How the name of primary
+   was still retained for granite--The term "transition," why faulty--The
+   adherence to the old chronological nomenclature retarded the progress
+   of geology--New hypothesis invented to reconcile the igneous origin of
+   granite to the notion of its high antiquity--Explanation of the
+   chronological nomenclature adopted in this work, so far as regards
+   primary, secondary, and tertiary periods.
+
+
+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. The preservation of the
+shelves may have required, says Darwin, the quick growth of green turf
+on a good soil; their abrupt cessation may mark the place where the soil
+was barren, and when a green sward formed slowly. 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 freshwater, 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 fossiliferous strata, and then to endeavour to refer to the same
+divisions, the several groups of plutonic, volcanic, and metamorphic
+rocks. This 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 past changes of
+the inorganic world, and the contemporaneous revolutions of the organic
+creation. For the sedimentary formations of successive periods are most
+readily distinguished by the different species of fossil animals and
+plants which they inclose, and of which one race after another has
+flourished and then disappeared from the earth.
+
+But before entering specially on the subdivisions of the aqueous rocks
+arranged according to the order of time, it will be desirable to say a few
+words on the chronology of rocks in general, although in doing so we shall
+be unavoidably led to allude to some classes of phenomena which the
+beginner must not yet expect fully to comprehend.
+
+It was for many years a received opinion, that the formation of entire
+families of rocks, such as the plutonic and those crystalline schists
+spoken of in the first chapter as metamorphic, began and ended before any
+members of the aqueous and volcanic orders were produced; and although this
+idea has long been modified, and is nearly exploded, it will be necessary
+to give some account of the ancient doctrine, in order that beginners may
+understand whence many prevailing opinions, and some part of the
+nomenclature of geology, still partially in use, was derived.
+
+About the middle of the last century, Lehman, a German miner, proposed to
+divide rocks into three classes, the first and oldest to be called
+primitive, comprising the hypogene, or plutonic and metamorphic rocks; the
+next to be termed secondary, comprehending the aqueous or fossiliferous
+strata; and the remainder, or third class, corresponding to our alluvium,
+ancient and modern, which he referred to "local floods, and the deluge of
+Noah." In the primitive class, he said, such as granite and gneiss, there
+are no organic remains, nor any signs of materials derived from the ruins
+of pre-existing rocks. Their origin, therefore, may have been purely
+chemical, antecedent to the creation of living beings, and probably coeval
+with the birth of the world itself. The secondary formations, on the
+contrary, which often contain sand, pebbles, and organic remains, must have
+been mechanical deposits, produced after the planet had become the
+habitation of animals and plants. This bold generalization, although
+anticipated in some measure by Steno, a century before, in Italy, formed at
+the time an important step in the progress of geology, and sketched out
+correctly some of the leading divisions into which rocks may be separated.
+About half a century later, Werner, so justly celebrated for his improved
+methods of discriminating the mineralogical characters of rocks, attempted
+to improve Lehman's classification, and with this view intercalated a
+class, called by him "the transition formations," between the primitive and
+secondary. Between these last he had discovered, in northern Germany, a
+series of strata, which in their mineral peculiarities were of an
+intermediate character, partaking in some degree of the crystalline nature
+of micaceous schist and clay-slate, and yet exhibiting here and there signs
+of a mechanical origin and organic remains. For this group, therefore,
+forming a passage between Lehman's primitive and secondary rocks, the name
+of _übergang_ or transition was proposed. They consisted principally of
+clay-slate and an argillaceous sandstone, called grauwacke, and partly of
+calcareous beds. It happened in the district which Werner first
+investigated, that both the primitive and transition strata were highly
+inclined, while the beds of the newer fossiliferous rocks, the secondary of
+Lehman, were horizontal. To these latter, therefore, he gave the name
+_flötz_, or "a level floor;" and every deposit more modern than the chalk,
+which was classed as the uppermost of the flötz series, was designated "the
+overflowed land," an expression which may be regarded as equivalent to
+alluvium, although under this appellation were confounded all the strata
+afterwards called tertiary, of which Werner had scarcely any knowledge. As
+the followers of Werner soon discovered that the inclined position of the
+"transition beds," and the horizontality of the flötz, or newer
+fossiliferous strata, were mere local accidents, they soon abandoned the
+term flötz; and the four divisions of the Wernerian school were then named
+primitive, transition, secondary, and alluvial.
+
+As to the trappean rocks, although their igneous origin had been already
+demonstrated by Arduino, Fortis, Faujas, and others, and especially by
+Desmarest, they were all regarded by Werner as aqueous, and as mere
+subordinate members of the secondary series.[91-A]
+
+This theory of Werner's was called the "Neptunian," and for many years
+enjoyed much popularity. It assumed that the globe had been at first
+invested by an universal chaotic ocean, holding the materials of all rocks
+in solution. From the waters of this ocean, granite, gneiss, and other
+crystalline formations, were first precipitated; and afterwards, when the
+waters were purged of these ingredients, and more nearly resembled those of
+our actual seas, the transition strata were deposited. These were of a
+mixed character, not purely chemical, because the waves and currents had
+already begun to wear down solid land, and to give rise to pebbles, sand,
+and mud; nor entirely without fossils, because a few of the first marine
+animals had begun to exist. After this period, the secondary formations
+were accumulated in waters resembling those of the present ocean, except at
+certain intervals, when, from causes wholly unexplained, a partial
+recurrence of the "chaotic fluid" took place, during which various trap
+rocks, some highly crystalline, were formed. This arbitrary hypothesis
+rejected all intervention of igneous agency, volcanos being regarded as
+modern, partial, and superficial accidents, of trifling account among the
+great causes which have modified the external structure of the globe.
+
+Meanwhile Hutton, a contemporary of Werner, began to teach, in Scotland,
+that granite as well as trap was of igneous origin, and had at various
+periods intruded itself in a fluid state into different parts of the
+earth's crust. He recognized and faithfully described many of the
+phenomena of granitic veins, and the alterations produced by them on the
+invaded strata, which will be treated of in the thirty-second chapter.
+He, moreover, advanced the opinion, that the crystalline strata called
+primitive had not been precipitated from a primæval ocean, but were
+sedimentary strata altered by heat. In his writings, therefore, and in
+those of his illustrator, Playfair, we find the germ of that metamorphic
+theory which has been already hinted at in the first chapter, and
+which will be more fully expounded in the thirty-fourth and
+thirty-fifth chapters.
+
+At length, after much controversy, the doctrine of the igneous origin of
+trap and granite made its way into general favour; but although it was, in
+consequence, admitted that both granite and trap had been produced at many
+successive periods, the term primitive or primary still continued to be
+applied to the crystalline formations in general, whether stratified, like
+gneiss, or unstratified, like granite. The pupil was told that granite was
+a primary rock, but that some granites were newer than certain secondary
+formations; and in conformity with the spirit of the ancient language, to
+which the teacher was still determined to adhere, a desire was naturally
+engendered of extenuating the importance of those more modern granites, the
+true dates of which new observations were continually bringing to light.
+
+A no less decided inclination was shown to persist in the use of the
+term "transition," after it had been proved to be almost as faulty in
+its original application as that of flötz. The name of transition, as
+already stated, was first given by Werner, to designate a mineral
+character, intermediate between the highly crystalline or metamorphic
+state and that of an ordinary fossiliferous rock. But the term acquired
+also from the first a chronological import, because it had been
+appropriated to sedimentary formations, which, in the Hartz and other
+parts of Germany, were more ancient than the oldest of the secondary
+series, and were characterized by peculiar fossil zoophytes and shells.
+When, therefore, geologists found in other districts stratified rocks
+occupying the same position, and inclosing similar fossils, they gave to
+them also the name of _transition_, according to rules which will be
+explained in the next chapter; yet, in many cases, such rocks were found
+not to exhibit the same mineral texture which Werner had called
+transition. On the contrary, many of them were not more crystalline than
+different members of the secondary class; while, on the other hand,
+these last were sometimes found to assume a semi-crystalline and almost
+metamorphic aspect, and thus, on lithological grounds, to deserve
+equally the name of transition. So remarkably was this the case in the
+Swiss Alps, that certain rocks, which had for years been regarded by
+some of the most skilful disciples of Werner to be transition, were at
+last acknowledged, when their relative position and fossils were better
+understood, to belong to the newest of the secondary groups; nay, some
+of them have actually been discovered to be members of the lower
+tertiary series! If, under such circumstances, the name of transition
+was retained, it is clear that it ought to have been applied without
+reference to the age of strata, and simply as expressive of a mineral
+peculiarity. The continued appropriation of the term to formations of a
+given date, induced geologists to go on believing that the ancient
+strata so designated bore a less resemblance to the secondary than is
+really the case, and to imagine that these last never pass, as they
+frequently do, into metamorphic rocks.
+
+The poet Waller, when lamenting over the antiquated style of Chaucer,
+complains that--
+
+  We write in sand, our language grows,
+  And, like the tide, our work o'erflows.
+
+But the reverse is true in geology; for here it is our work which
+continually outgrows the language. The tide of observation advances with
+such speed that improvements in theory outrun the changes of nomenclature;
+and the attempt to inculcate new truths by words invented to express a
+different or opposite opinion, tends constantly, by the force of
+association, to perpetuate error; so that dogmas renounced by the reason
+still retain a strong hold upon the imagination.
+
+In order to reconcile the old chronological views with the new doctrine of
+the igneous origin of granite, the following hypothesis was substituted for
+that of the Neptunists. Instead of beginning with an aqueous menstruum or
+chaotic fluid, the materials of the present crust of the earth were
+supposed to have been at first in a state of igneous fusion, until part of
+the heat having been diffused into surrounding space, the surface of the
+fluid consolidated, and formed a crust of granite. This covering of
+crystalline stone, which afterwards grew thicker and thicker as it cooled,
+was so hot, at first, that no water could exist upon it; but as the
+refrigeration proceeded, the aqueous vapour in the atmosphere was
+condensed, and, falling in rain, gave rise to the first _thermal ocean_. So
+high was the temperature of this boiling sea, that no aquatic beings could
+inhabit its waters, and its deposits were not only devoid of fossils, but,
+like those of some hot springs, were highly crystalline. Hence the origin
+of the primary or crystalline strata,--gneiss, mica-schist, and the rest.
+
+Afterwards, when the granitic crust had been partially broken up, land
+and mountains began to rise above the waters, and rains and torrents
+ground down rock, so that sediment was spread over the bottom of the
+seas. Yet the heat still remaining in the solid supporting substances
+was sufficient to increase the chemical action exerted by the water,
+although not so intense as to prevent the introduction and increase of
+some living beings. During this state of things some of the residuary
+mineral ingredients of the primæval ocean were precipitated, and formed
+deposits (the transition strata of Werner), half chemical and half
+mechanical, and containing a few fossils.
+
+By this new theory, which was in part a revival of the doctrine of
+Leibnitz, published in 1680, on the igneous origin of the planet, the old
+ideas respecting the priority of all crystalline rocks to the creation of
+organic beings, were still preserved; and the mistaken notion that all the
+semi-crystalline and partially fossiliferous rocks belonged to one period,
+while all the earthy and uncrystalline formations originated at a
+subsequent epoch, was also perpetuated.
+
+It may or may not be true, as the great Leibnitz imagined, that the whole
+planet was once in a state of liquefaction by heat; but there are certainly
+no geological proofs that the granite which constitutes the foundation of
+so much of the earth's crust was ever at once in a state of universal
+fusion. On the contrary, all our evidence tends to show that the formation
+of granite, like the deposition of the stratified rocks, has been
+successive, and that different portions of granite have been in a melted
+state at distinct and often distant periods. One mass was solid, and had
+been fractured, before another body of granitic matter was injected into
+it, or through it, in the form of veins. Some granites are more ancient
+than any known fossiliferous rocks; others are of secondary; and some, such
+as that of Mont Blanc and part of the central axis of the Alps, of tertiary
+origin. In short, the universal fluidity of the crystalline foundations of
+the earth's crust, can only be understood in the same sense as the
+universality of the ancient ocean. All the land has been under water, but
+not all at one time; so all the subterranean unstratified rocks to which
+man can obtain access have been melted, but not simultaneously.
+
+In the present work 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, p. 68.); 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 counter-balanced 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 stone 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.
+
+After the observations which have now been made, the reader will
+perceive that the term primary must either be entirely renounced, or, if
+retained, must be differently defined, and not made to designate a set
+of crystalline rocks, some of which are already ascertained to be newer
+than all the secondary formations. In this work I shall follow most
+nearly the method proposed by Mr. Boué, who has called all
+_fossiliferous_ rocks older than the secondary by the name of primary.
+To prevent confusion, however, I shall always speak of these, when they
+are of the aqueous class, as the _primary fossiliferous_ formations,
+because the word primary has hitherto been almost inseparably connected
+with the idea of a non-fossiliferous rock.
+
+If we can prove any plutonic, volcanic, or metamorphic rocks to be older
+than the secondary formations, such rocks will also be primary, according
+to this system. Mr. Boué having with great propriety excluded the
+metamorphic rocks, _as a class_, from the primary formations, proposed to
+call them all "crystalline schists."
+
+As there are secondary fossiliferous strata, so we shall find that there
+are plutonic, volcanic, and metamorphic rocks of contemporaneous origin,
+which I shall also term secondary.
+
+In the next chapter it will be shown that the strata above the chalk have
+been called tertiary. If, therefore, we discover any volcanic, plutonic, or
+metamorphic rocks, which have originated since the deposition of the chalk,
+these also will rank as tertiary formations.
+
+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. In the small part of the globe hitherto examined, it
+is hardly to be expected that we should have discovered either the oldest
+or the newest members of each of the four classes of rocks. Thus, if there
+be primary, secondary, and tertiary rocks of the aqueous or fossiliferous
+class, and in like manner primary, secondary, and tertiary hypogene
+formations, we may not be yet acquainted with the most ancient of the
+primary fossiliferous beds, or with the newest of the hypogene.
+
+
+FOOTNOTES:
+
+[91-A] See Principles, vol. i. chap. iv.
+
+
+
+
+CHAPTER IX.
+
+ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS.
+
+   On the 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--Principal groups of strata in western Europe.
+
+
+In the last chapter I spoke generally of the chronological relations of the
+four great classes of rocks, and I shall now treat of the aqueous rocks in
+particular, or of the successive periods at which the different
+fossiliferous formations 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 pp. 58, 59.)
+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, calcareous, argillaceous, and siliceous
+rocks. 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 creation and extinction of
+species 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 relative position.
+
+It was remarked that the same species of organic remains cannot be traced
+horizontally, or in the direction of the planes of stratification 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 a great number of detached
+deposits, in which the mineral nature of the rocks is variable.
+
+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 the 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 they 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.
+Of the bivalve shells, according to Philippi, not more than a fifth are
+common to the Red Sea and the sea around Sicily, while the proportion of
+univalves (or Gasteropoda) is still smaller, not exceeding eighteen in a
+hundred. 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 co-existence 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 south of
+Europe, north of Africa, and north-west of Asia, are different, yet
+their remains are all washed down by rivers flowing from these three
+countries into the Mediterranean.
+
+In some parts of the globe, at the present period, the line of demarcation
+between distinct provinces of animals and plants is not very strongly
+marked, especially where the change is determined by temperature, as 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 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
+independent 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 in one part of a country chalk
+with flints; and, in another, a distinct formation, consisting of
+alternations of clay, sand, and pebbles. If some of these pebbles
+consist of similar flint and fossil shells, sponges, and foraminiferæ,
+of the same species as those in the chalk, we may confidently infer that
+the chalk is 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.
+
+[Illustration: Fig. 104. Block section.]
+
+The thinning out of individual strata was before described (p. 16.). But
+let the annexed diagram 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.
+
+[Illustration: Fig. 105. Section South of Bristol. A. C. Ramsay.
+
+Length of section 4 miles. _a_, _b_. Level of the sea.
+  1. Inferior oolite.
+  2. Lias.
+  3. New red sandstone.
+  4. Magnesian conglomerate.
+  5. Coal measure.
+  6. Carboniferous limestone.
+  7. Old red sandstone.]
+
+In the annexed diagram, fig. 105., 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 and 6. Here at the southern end of the line of section we
+meet with the beds No. 3. (the New Red Sandstone) resting immediately on
+No. 6., while farther north, as at Dundry Hill, we behold six groups
+superimposed one upon the other, comprising all the strata from the
+inferior oolite to the coal and carboniferous limestone. The limited
+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.
+
+In many instances, however, the entire absence of one or more formations of
+intervening periods between two groups, such as 3. and 5. in the same
+section, arises, not from the destruction of what once existed, but because
+no strata of an intermediate age were ever deposited on the inferior rock.
+They were not formed at that place, either because the region was dry land
+during the interval, or because it was part of a sea or lake to which no
+sediment was carried.
+
+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.
+
+_Groups of Fossiliferous Strata observed in Western Europe, arranged in
+what is termed a descending Series, or beginning with the newest._ (_See a
+more detailed Tabular view_, pp. 360. 365.)
+
+  1.  Post-Pliocene, including those of the
+  Recent, or human period.
+
+  2.  Newer Pliocene, or Pleistocene. }
+  3.  Older Pliocene.                 } Tertiary, Supracretaceous[103-A],
+  4.  Miocene.                        } or Cainozoic.[103-B]
+  5.  Eocene.                         }
+
+  6.  Chalk.                          }
+  7.  Greensand.                      }
+  8.  Wealden.                        }
+  9.  Upper Oolite.                   } Secondary, or Mesozoic.[103-B]
+  10.  Middle Oolite.                 }
+  11.  Lower Oolite.                  }
+  12.  Lias.                          }
+  13.  Trias.                         }
+
+  14.  Permian.                                 }
+  15.  Coal.                                    }
+  16.  Old Red sandstone, or Devonian.          } Primary fossiliferous,
+  17.  Upper Silurian.                          }  or paleozoic.[103-B]
+  18.  Lower Silurian.                          }
+  19.  Cambrian and older fossiliferous strata. }
+
+It is not pretended that the three principal sections in the above table,
+called primary, secondary, and tertiary, are of equivalent importance, or
+that the eighteen subordinate groups comprise monuments relating to equal
+portions of past time, or of the earth's history. But we can assert that
+they each relate to successive periods, during which certain animals and
+plants, for the most part peculiar to their respective eras, have
+flourished, and during which different kinds of sediment were deposited in
+the space now occupied by Europe.
+
+If we were disposed, on palæontological grounds[103-C], to divide the
+entire fossiliferous series into a few groups less numerous than those in
+the above table, and more nearly co-ordinate in value than the sections
+called primary, secondary, and tertiary, we might, perhaps, adopt the six
+groups or periods given in the next table (p. 104.).
+
+At the same time, I may observe, that, in the present state of the
+science, when we have not yet compared the evidence derivable from all
+classes of fossils, not even those most generally distributed, such as
+shells, corals, and fish, such generalizations are premature, and can
+only be regarded as conjectural or provisional schemes for the founding
+of large natural groups.
+
+_Fossiliferous Strata of Western Europe divided into Six Groups._
+
+  1. Post Pliocene and       }  from the Post-Pliocene to the
+     Tertiary                }  Eocene inclusive.
+
+  2. Cretaceous              {  from the Maestricht Chalk to the Lower
+                             {  Greensand inclusive.
+
+  3. Oolitic                    from the Wealden to the Lias inclusive.
+
+  4. Triassic                {  including the Keuper, Muschelkalk, and
+                             {  Bunter Sandstein of the Germans.
+
+  5. Permian, Carboniferous, }  including Magnesian Limestone (Zechstein),
+     and Devonian            }  Coal, Mountain Limestone, and
+                             }  Old Red sandstone.
+
+  6. Silurian and Cambrian   }  from the Upper Silurian to the oldest
+                             }  fossiliferous rocks inclusive.
+
+
+FOOTNOTES:
+
+[103-A] For tertiary, Sir H. De la Beche has used the term
+"supracretaceous," a name implying that the strata so called are
+superior in position to the chalk.
+
+[103-B] Professor Phillips has adopted these terms: Cainozoic, from
++kainos+, _cainos_, recent, and +zôon+, _zoon_, animal; Mesozoic,
+from +mesos+, _mesos_, middle, &c.; Paleozoic, from +palaios+,
+_palaios_, ancient, &c.
+
+[103-C] Palæontology is the science which treats of fossil remains, both
+animal and vegetable. Etym. +palaios+, _palaios_, ancient, +onta+, _onta_,
+beings, and +logos+, _logos_, a discourse.
+
+
+
+
+CHAPTER X.
+
+CLASSIFICATION OF TERTIARY FORMATIONS.--POST-PLIOCENE GROUP.
+
+   General principles of classification of tertiary strata--Detached
+   formations scattered over Europe--Strata of Paris and London--More
+   modern groups--Peculiar difficulties in determining the chronology of
+   tertiary formations--Increasing proportion of living species of shells
+   in strata of newer origin--Terms Eocene, Miocene, and
+   Pliocene--Post-Pliocene strata--Recent or human period--Older
+   Post-Pliocene formations of Naples, Uddevalla, and Norway--Ancient
+   upraised delta of the Mississippi--Loess of the Rhine.
+
+
+Before describing the most modern of the sets of strata enumerated in
+the tables given at the end of the last chapter, it will be necessary
+to say something generally of the mode of classifying the formations
+called tertiary.
+
+The name of tertiary has been given to them, because they are all posterior
+in date to the rocks termed "secondary," of which the chalk constitutes the
+newest group. These tertiary strata were at first confounded, as before
+stated, p. 91., 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 recognized. They were observed to occur in patches, some
+of freshwater, 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 freshwater 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 and for the most part not 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.
+
+A variety of deposits were afterwards found in other parts of Europe, all
+reposing immediately on rocks as old or older than the chalk, and which
+exhibited certain general characters of resemblance in their organic
+remains to those previously observed near Paris and London. An attempt was
+therefore made at first to refer the whole to one period; and when at
+length this seemed impracticable, it was contended that as in the Parisian
+series there were many subordinate formations of considerable thickness
+which must have accumulated one after the other, during a great lapse of
+time, so the various patches of tertiary strata scattered over Europe might
+correspond in age, some of them to the older, and others to the newer,
+subdivisions of the Parisian series.
+
+This error, although most unavoidable on the part of those who made the
+first generalizations in this branch of geology, retarded seriously for
+some years the progress of classification. A more scrupulous attention to
+specific distinctions, aided by a careful regard to the relative position
+of the strata containing them, led at length to the conviction that there
+were formations both marine and freshwater of various ages, and all newer
+than the strata of the neighbourhood of Paris and London.
+
+One of the first steps in this chronological reform was made in 1811, by
+an English naturalist, Mr. Parkinson, who pointed out the fact that
+certain shelly strata, provincially termed "Crag" in Suffolk, lay
+decidedly over a deposit which was the continuation of the blue clay of
+London. At the same time he remarked that the fossil testacea in these
+newer beds were distinct from those of the blue clay, and that while
+some of them were of unknown species, others were identical with species
+now inhabiting the British seas.
+
+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 of different ages, all 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.
+
+Without pretending to give a complete sketch of the progress of
+discovery, I may refer to the facts above enumerated, as illustrating
+the course usually pursued by geologists when they attempt to found new
+chronological divisions. The method bears some analogy to that pursued
+by the naturalist in the construction of genera, when he selects a
+typical species, and then classes as congeners all other species of
+animals and plants which agree with this standard within certain limits.
+The genera A. and C. having been founded on these principles, a new
+species is afterwards met with, departing widely both from A. and C.,
+but in many respects of an intermediate character. For this new type it
+becomes necessary to institute the new genus B., in which are included
+all species afterwards brought to light, which agree more nearly with B.
+than with the types of A. or C. In like manner a new formation is met
+with in geology, and the characters of its fossil fauna and flora
+investigated. From that moment it is considered as a record of a certain
+period of the earth's history, and a standard to which other deposits
+may be compared. If any are found containing the same or nearly the same
+organic remains, and occupying the same relative position, they are
+regarded in the light of contemporary annals. All such monuments are
+said to relate to one period, during which certain events occurred, such
+as the formation of particular rocks by aqueous or volcanic agency, or
+the continued existence and fossilization of certain tribes of animals
+and plants. When several of these periods have had their true places
+assigned to them in a chronological series, others are discovered
+which it becomes necessary to intercalate between those first known;
+and the difficulty of assigning clear lines of separation must
+unavoidably increase in proportion as chasms in the past history of
+the globe are filled up.
+
+Every zoologist and botanist is aware that it is a comparatively easy
+task to establish genera in departments which have been enriched with
+only a small number of species, and where there is as yet no tendency in
+one set of characters to pass almost insensibly, by a multitude of
+connecting links, into another. They also know that the difficulty of
+classification augments, and that the artificial nature of their
+divisions becomes more apparent, in proportion to the increased number
+of objects brought to light. But in separating families and genera, they
+have no other alternative than to avail themselves of such breaks as
+still remain, or of every hiatus in the chain of animated beings which
+is not yet filled up. So in geology, we may be eventually compelled to
+resort to sections of time as arbitrary, and as purely conventional, as
+those which divide the history of human events into centuries. But in
+the present state of our knowledge, it is more convenient to use the
+interruptions which still occur in the regular sequence of geological
+monuments, as boundary lines between our principal groups or periods,
+even though the groups thus established are of very unequal value.
+
+The isolated position of distinct tertiary deposits in different parts
+of Europe has been already alluded to. In addition to the difficulty
+presented by this want of continuity when we endeavour to settle the
+chronological relations of these deposits, another arises from the
+frequent dissimilarity in mineral character of strata of contemporaneous
+date, such, for example, as those of London and Paris before mentioned.
+The identity or non-identity of species is also a criterion which often
+fails us. For this we might have been prepared, for we have already
+seen, that the Mediterranean and Red Sea, although within 70 miles of
+each other, on each side of the Isthmus of Suez, have each their
+peculiar fauna; and a marked difference is found in the four groups of
+testacea now living in the Baltic, English Channel, Black Sea, and
+Mediterranean, although all these seas have many species in common. In
+like manner a considerable diversity in the fossils of different
+tertiary formations, which have been thrown down in distinct seas,
+estuaries, bays, and lakes, does not always imply a distinctness in the
+times when they were produced, but may have arisen from climate and
+conditions of physical geography wholly independent of time. On the
+other hand, it is now abundantly clear, as the result of geological
+investigation, that different sets of tertiary strata, immediately
+superimposed upon each other, contain distinct imbedded species of
+fossils, in consequence of fluctuations which have been going on in the
+animate creation, and by which in the course of ages one state of things
+in the organic world has been substituted for another wholly dissimilar.
+It has also been shown that in proportion as the age of a tertiary
+deposit is more modern, so is its fauna more analogous to that now in
+being in the neighbouring seas. It is this law of a nearer agreement of
+the fossil testacea with the species now living, which may often furnish
+us with a clue for the chronological arrangement of scattered deposits,
+where we cannot avail ourselves of any one of the three ordinary
+chronological tests; namely, superposition, mineral character, and the
+specific identity of the fossils.
+
+Thus, for example, on the African border of the Red Sea, at the height
+of 40 feet, and sometimes more, above its level, a white calcareous
+formation has been observed, containing several hundred species of
+shells differing from those found in the clay and volcanic tuff of the
+country round Naples, and of the contiguous island of Ischia. Another
+deposit has been found at Uddevalla, in Sweden, in which the shells do
+not agree with those found near Naples. But although in these three
+cases there may be scarcely a single shell common to the three different
+deposits, we do not hesitate to refer them all to one period (the
+Post-Pliocene), because of the very close agreement of the fossil
+species in every instance with those now living in the contiguous seas.
+
+To take another example, where the fossil fauna recedes a few steps farther
+back from our own times. We may compare, first, the beds of loam and clay
+bordering the Clyde in Scotland (called glacial by some geologists),
+secondly, others of fluvio-marine origin near Norwich, and, lastly, a third
+set often rising to considerable heights in Sicily, and we discover that in
+every case more than three-fourths of the shells agree with species still
+living, while the remainder are extinct. Hence we may conclude that all
+these, greatly diversified as are their organic remains, belong to one and
+the same era, or to a period immediately antecedent to the Post-Pliocene,
+because there has been time in each of the areas alluded to for an equal or
+nearly equal amount of change in the marine testaceous fauna.
+Contemporaneousness of origin is inferred in these cases, in spite of the
+most marked differences of mineral character or organic contents, from a
+similar degree of divergence in the shells from those now living in the
+adjoining seas. The advantage of such a test consists in supplying us with
+a common point of departure in all countries, however remote.
+
+But the farther we recede from the present times, and the smaller the
+relative number of recent as compared with extinct species in the
+tertiary deposits, the less confidence can we place in the exact value
+of such a test, especially when comparing the strata of very distant
+regions; for we cannot presume that the rate of former alterations in
+the animate world, or the continual going out and coming in of species,
+has been every where exactly equal in equal quantities of time. The
+form of the land and sea, and the climate, may have changed more in
+one region than in another; and consequently there may have been a
+more rapid destruction and renovation of species in one part of the
+globe than elsewhere. Considerations of this kind should undoubtedly
+put us on our guard against relying too implicitly on the accuracy of
+this test; yet it can never fail to throw great light on the
+chronological relations of tertiary groups with each other, and with
+the Post-Pliocene period.
+
+We may derive a conviction of this truth not only from a study of
+geological monuments of all ages, but also by reflecting on the tendency
+which prevails in the present state of nature to a uniform rate of
+simultaneous fluctuation in the flora and fauna of the whole globe. The
+grounds of such a doctrine cannot be discussed here, and I have explained
+them at some length in the third Book of the Principles of Geology, where
+the causes of the successive extinction of species are considered. It will
+be there seen that each local change in climate and physical geography is
+attended with the immediate increase of certain species, and the limitation
+of the range of others. A revolution thus effected is rarely, if ever,
+confined to a limited space, or to one geographical province of animals or
+plants, but affects several other surrounding and contiguous provinces. In
+each of these, moreover, analogous alterations of the stations and
+habitations of species are simultaneously in progress, reacting in the
+manner already alluded to on the first province. Hence, long before the
+geography of any particular district can be essentially altered, the flora
+and fauna throughout the world will have been materially modified by
+countless disturbances in the mutual relation of the various members of the
+organic creation to each other. To assume that in one large area inhabited
+exclusively by a single assemblage of species any important revolution in
+physical geography can be brought about, while other areas remain
+stationary in regard to the position of land and sea, the height of
+mountains, and so forth, is a most improbable hypothesis, wholly opposed to
+what we know of the laws now governing the aqueous and igneous causes. On
+the other hand, even were this conceivable, the communication of heat and
+cold between different parts of the atmosphere and ocean is so free and
+rapid, that the temperature of certain zones cannot be materially raised or
+lowered without others being immediately affected; and the elevation or
+diminution in height of an important chain of mountains or the submergence
+of a wide tract of land would modify the climate even of the antipodes.
+
+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, especially in the European tertiary
+formations. 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 freshwater. 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, freshwater, and
+marine species co-existed 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.
+
+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.
+
+When engaged in 1828 in preparing my work on the Principles of Geology, I
+conceived the idea of classing the whole series of tertiary strata in four
+groups, and endeavouring to find characters for each, expressive of their
+different degrees of affinity to the living fauna. With this view, I
+obtained information respecting the specific identity of many tertiary and
+recent shells from several Italian naturalists, and among others from
+Professors Bonelli, Guidotti, and Costa. Having in 1829 become acquainted
+with M. Deshayes, of Paris, already well known by his conchological works,
+I learnt from him that he had arrived, by independent researches, and by
+the study of a large collection of fossil and recent shells, at very
+similar views respecting the arrangement of tertiary formations. At my
+request he drew up, in a tabular form, lists of all the shells known to him
+to occur both in some tertiary formation and in a living state, for the
+express purpose of ascertaining the proportional number of fossil species
+identical with the recent which characterized successive groups; and this
+table, planned by us in common, was published by me in 1833.[110-A] The
+number of tertiary fossil shells examined by M. Deshayes was about 3000;
+and the recent species with which they had been compared about 5000. The
+result then arrived at was, that in the lower tertiary strata, or those of
+London and Paris, there were about 3-1/2 per cent. of species identical
+with recent; in the middle tertiary of the Loire and Gironde about 17 per
+cent.; and in the upper tertiary or Subapennine beds, from 35 to 50 per
+cent. In formations still more modern, some of which I had particularly
+studied in Sicily, where they attain a vast thickness and elevation above
+the sea, the number of species identical with those now living was believed
+to be from 90 to 95 per cent. For the sake of clearness and brevity, I
+proposed to give short technical names to these four groups, or the periods
+to which they respectively belonged. I called the first or oldest of them
+Eocene, the second Miocene, the third Older Pliocene, and the last or
+fourth Newer Pliocene. The first of the above terms, Eocene, is derived
+from +êôs+, eos, _dawn_, and +kainos+, 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+, meion, _less_, and +kainos+, cainos,
+_recent_) is intended to express a minor proportion of recent species (of
+testacea), the term Pliocene (from +pleion+, pleion, _more_, and +kainos+,
+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.
+
+The distribution of the fossil species from which the results before
+mentioned were obtained in 1830 by M. Deshayes was as follows:--
+
+  In the formations of the Pliocene periods, older and newer  777
+  In the Miocene                                             1021
+  In the Eocene                                              1238
+                                                             ----
+                                                             3036
+                                                             ----
+
+Since the year 1830 the progress of conchological science has been most
+rapid, and the number of living species obtained from different parts of
+the globe has been raised from about 5000 to more than 10,000. New
+fossil species have also been added to our collections in great
+abundance; and at the same time a more copious supply of individuals
+both of fossil and recent species, some of which were previously very
+rare, have been procured, affording more ample data for determining the
+specific character. Besides the reforms introduced in consequence of
+these new zoological facilities, other errors of a geological nature
+have been in many instances removed.
+
+
+POST-PLIOCENE FORMATIONS.
+
+I have adopted the term Post-Pliocene for those strata which are sometimes
+called post-tertiary or modern, and which are characterized by having all
+the imbedded fossil shells identical with species now living, whereas even
+the Newer Pliocene, or newest of the tertiary deposits above alluded to,
+contain always some small proportion of shells of extinct species.
+
+These modern formations, thus defined, comprehend not only those strata
+which can be shown to have originated since the earth was inhabited by man,
+but also deposits of far greater extent and thickness, in which no signs of
+man or his works can be detected. In some of these, of a date long anterior
+to the times of history and tradition, the bones of extinct quadrupeds have
+been met with of species which probably never co-existed with the human
+race, as, for example, the mammoth, mastodon, megatherium, and others, and
+yet the shells are the same as those now living.
+
+That portion of the post-pliocene group which belongs to the human epoch,
+and which is sometimes called _Recent_, forms a very unimportant feature in
+the geological structure of the earth's crust. I have shown, however, in
+"The Principles," where the recent changes of the earth illustrative of
+geology are described at length, that the deposits accumulated at the
+bottom of lakes and seas within the last 4000 or 5000 years can neither be
+insignificant in volume or extent. They lie hidden, for the most part, from
+our sight; but we have opportunities of examining them at certain points
+where newly-gained land in the deltas of rivers has been cut through during
+floods, or where coral reefs are growing rapidly, or where the bed of a sea
+or lake has been heaved up by subterranean movements and laid dry. Their
+age may be recognized either by our finding in them the bones of man in a
+fossil state, that is to say, imbedded in them by natural causes, or by
+their containing articles fabricated by the hands of man.
+
+Thus at Puzzuoli, near Naples, marine strata are seen containing
+fragments of sculpture, pottery, and the remains of buildings, together
+with innumerable shells retaining in part their colour, and of the same
+species as those now inhabiting the Bay of Baiæ. The uppermost of these
+beds is about 20 feet above the level of the sea. Their emergence can be
+proved to have taken place since the beginning of the sixteenth
+century.[112-A] Now here, as in almost every instance where any
+alterations of level have been going on in historical periods, it is
+found that rocks containing shells, all, or nearly all, of which still
+inhabit the neighbouring sea, may be traced for some distance into the
+interior, and often to a considerable elevation above the level of the
+sea. Thus, in the country round Naples, the post-pliocene strata,
+consisting of clay and horizontal beds of volcanic tuff, rise at certain
+points to the height of 1500 feet. Although the marine shells are
+exclusively of living species, they are not accompanied like those on
+the coast at Puzzuoli by any traces of man or his works. Had any such
+been discovered, it would have afforded to the antiquary and geologist
+matter of great surprise, since it would have shown that man was an
+inhabitant of that part of the globe, while the materials composing
+the present hills and plains of Campania were still in the progress
+of deposition at the bottom of the sea; whereas we know that for
+nearly 3000 years, or from the times of the earliest Greek colonists,
+no material revolution in the physical geography of that part of
+Italy has occurred.
+
+In Ischia, a small island near Naples, composed in like manner of marine
+and volcanic formations, Dr. Philippi collected in the stratified tuff and
+clay ninety-two species of shells of existing species. In the centre of
+Ischia, the lofty hill called Epomeo, or San Nicola, is composed of
+greenish indurated tuff, of a prodigious thickness, interstratified in some
+parts with marl, and here and there with great beds of solid lava. Visconti
+ascertained by trigonometrical measurement that this mountain was 2605 feet
+above the level of the sea. Not far from its summit, at the height of about
+2000 feet, as also near Moropano, a village only 100 feet lower, on the
+southern declivity of the mountain, I collected, in 1828, many shells of
+species now inhabiting the neighbouring gulf. It is clear, therefore, that
+the great mass of Epomeo was not only raised to its present height, but was
+also _formed_ beneath the waters, within the post-pliocene period.
+
+It is a fact, however, of no small interest, that the fossil shells from
+these modern tuffs of the volcanic region surrounding the Bay of Baiæ,
+although none of them extinct, indicate a slight want of correspondence
+between the ancient fauna and that now inhabiting the Mediterranean.
+Philippi informs us that when he and M. Scacchi had collected ninety-nine
+species of them, he found that only one, _Pecten medius_, now living in the
+Red Sea, was absent from the Mediterranean. Notwithstanding this, he adds,
+"the condition of the sea when the tufaceous beds were deposited must have
+been considerably different from its present state; for _Tellina striata_
+was then common, and is now rare; _Lucina spinosa_ was both more abundant
+and grew to a larger size; _Lucina fragilis_, now rare, and hardly
+measuring 6 lines, then attained the enormous dimensions of 14 lines, and
+was extremely abundant; and _Ostrea lamellosa_, Broc., no longer met with
+near Naples, existed at that time, and attained a size so large that one
+lower valve has been known to measure 5 inches 9 lines in length, 4 inches
+in breadth, 1-1/2 inch in thickness, and weighed 26-1/2 ounces."[113-A]
+
+There are other parts of Europe where no volcanic action manifests itself
+at the surface, as at Naples, whether by the eruption of lava or by
+earthquakes, and yet where the land and bed of the adjoining sea are
+undergoing upheaval. The motion is so gradual as to be insensible to the
+inhabitants, being only ascertainable by careful scientific measurements
+compared after long intervals. Such an upward movement has been proved to
+be in progress in Norway and Sweden throughout an area about 1000 miles N.
+and S., and for an unknown distance E. and W., the amount of elevation
+always increasing as we proceed towards the North Cape, where it may equal
+5 feet in a century. If we could assume that there had been an average rise
+of 2-1/2 feet in each hundred years for the last fifty centuries, this
+would give an elevation of 125 feet in that period. In other words, it
+would follow that the shores, and a considerable area of the former bed of
+the Baltic and North Sea, had been uplifted vertically to that amount, and
+converted into land in the course of the last 5000 years. Accordingly, we
+find near Stockholm, in Sweden, horizontal beds of sand, loam, and marl
+containing the same peculiar assemblage of testacea which now live in the
+brackish waters of the Baltic. Mingled with these, at different depths,
+have been detected various works of art implying a rude state of
+civilization, and some vessels built before the introduction of iron, the
+whole marine formation having been upraised, so that the upper beds are now
+60 feet higher than the surface of the Baltic. In the neighbourhood of
+these recent strata, both to the north-west and south of Stockholm, other
+deposits similar in mineral composition occur, which ascend to greater
+heights, in which precisely the same assemblage of fossil shells is met
+with, but without any intermixture of human bones or fabricated articles.
+
+On the opposite or western coast of Sweden, at Uddevalla, post-pliocene
+strata, containing recent shells, not of that brackish water character
+peculiar to the Baltic, but such as now live in the northern ocean, ascend
+to the height of 200 feet; and beds of clay and sand of the same age attain
+elevations of 300 and even 700 feet in Norway, where they have been usually
+described as "raised beaches." They are, however, thick deposits of
+submarine origin, spreading far and wide, and filling valleys in the
+granite and gneiss, just as the tertiary formations, in different parts of
+Europe, cover or fill depressions in the older rocks.
+
+It is worthy of remark, that although the fossil fauna characterizing these
+upraised sands and clays consists exclusively of existing northern species
+of testacea, yet, according to Lovén (an able living naturalist of Norway),
+the species do not constitute such an assemblage as now inhabits
+corresponding latitudes in the German Ocean. On the contrary, they
+decidedly represent a more arctic fauna.[114-A] In order to find the same
+species flourishing in equal abundance, or in many cases to find them at
+all, we must go northwards to higher latitudes than Uddevalla in Sweden, or
+even nearer the pole than Central Norway.
+
+Judging by the uniformity of climate now prevailing from century to
+century, and the insensible rate of variation in the organic world in our
+own times, we may presume that an extremely lengthened period was required
+even for so slight a modification of the molluscous fauna, as that of which
+the evidence is here brought to light. On the other hand, we have every
+reason for inferring on independent grounds (namely, the rate of upheaval
+of land in modern times) that the antiquity of the deposits in question
+must be very great. For if we assume, as before suggested, that the mean
+rate of continuous vertical elevation has amounted to 2-1/2 feet in a
+century (and this is probably a high average), it would require 27,500
+years for the sea-coast to attain the height of 700 feet, without making
+allowance for any pauses such as are now experienced in a large part of
+Norway, or for any oscillations of level.
+
+In England, buried ships have been found in the ancient and now deserted
+channels of the Rother in Sussex, of the Mersey in Kent, and the Thames
+near London. Canoes and stone hatchets have been dug up, in almost all
+parts of the kingdom, from peat and shell-marl; but there is no evidence,
+as in Sweden, Italy, and many other parts of the world, of the bed of the
+sea, and the adjoining coast, having been uplifted bodily to considerable
+heights within the human period. Recent strata have been traced along the
+coasts of Peru and Chili, inclosing shells in abundance, all agreeing
+specifically with those now swarming in the Pacific. In one bed of this
+kind, in the island of San Lorenzo, near Lima, Mr. Darwin found, at the
+altitude of 85 feet above the sea, pieces of cotton-thread, plaited rush,
+and the head of a stalk of Indian corn, the whole of which had evidently
+been imbedded with the shells. At the same height on the neighbouring
+mainland, he found other signs corroborating the opinion that the ancient
+bed of the sea had there also been uplifted 85 feet, since the region was
+first peopled by the Peruvian race.[115-A] But similar shelly masses are
+also met with at much higher elevations, at innumerable points between the
+Chilian and Peruvian Andes and the sea-coast, in which no human remains
+were ever, or in all probability ever will be, discovered.
+
+In the West Indies, also, in the island of Guadaloupe, a solid limestone
+occurs, at the level of the sea-beach, enveloping human skeletons. The
+stone is extremely hard, and chiefly composed of comminuted shell and
+coral, with here and there some entire corals and shells, of species now
+living in the adjacent ocean. With them are included arrow-heads, fragments
+of pottery, and other articles of human workmanship. A limestone with
+similar contents has been formed, and is still forming, in St. Domingo. But
+there are also more ancient rocks in the West Indian Archipelago, as in
+Cuba, near the Havanna, and in other islands, in which are shells identical
+with those now living in corresponding latitudes; some well-preserved,
+others in the state of casts, all referable to the post-pliocene period.
+
+I have already described in the seventh chapter, p. 84., what would be
+the effects of oscillations and changes of level in any region drained
+by a great river and its tributaries, supposing the area to be first
+depressed several hundred feet, and then re-elevated. I believe that
+such changes in the relative level of land and sea have actually
+occurred in the post-pliocene era in the hydrographical basin of the
+Mississippi and in that of the Rhine. The accumulation of fluviatile
+matter in a delta during a slow subsidence may raise the newly gained
+land superficially at the same rate at which its foundations sink, so
+that these may go down hundreds or thousands of feet perpendicularly,
+and yet the sea bordering the delta may always be excluded, the whole
+deposit continuing to be terrestrial or freshwater in character. This
+appears to have happened in the deltas both of the Po and Ganges, for
+recent artesian borings, penetrating to the depth of 400 feet, have
+there shown that fluviatile strata, with shells of recent species,
+together with ancient surfaces of land supporting turf and forests, are
+depressed hundreds of feet below the sea level.[116-A] Should these
+countries be once more slowly upraised, the rivers would carve out
+valleys through the horizontal and unconsolidated strata as they rose,
+sweeping away the greater portion of them, and leaving mere fragments in
+the shape of terraces skirting newly-formed alluvial plains, as
+monuments of the former levels at which the rivers ran. Of this nature
+are "the bluffs," or river cliffs, now bounding the valley of the
+Mississippi throughout a large portion of its course. Thus let _a b_,
+fig. 106., represent the alluvial plain of the Mississippi, a plain
+which, at the point alluded to, is more than 30 miles broad, and is
+truly a prolongation of the modern delta of that river. It is bounded by
+bluffs, the upper portions of which consist, both on the east and west
+side, of shelly loam, No. 2. rising from 100 to 200 feet above the level
+of the plain, and containing land and freshwater shells of the genera
+_Helix_, _Pupa_, _Succinea_, and _Lymnea_, of the same species as those
+now inhabiting the neighbouring forests and swamps. In the same loam
+also, No. 2., are found the bones of the Mastodon, Elephant, Megalonyx,
+and other extinct quadrupeds.
+
+[Illustration: Fig. 106. Valley of the Mississippi.
+
+  1. Alluvium.
+  2. Loess.
+  3. _f_. Eocene.
+  4. Cretaceous.]
+
+I have endeavoured to show that the deposits forming the delta and alluvial
+plain of the Mississippi consist of sedimentary matter, extending over an
+area of 30,000 square miles, and known in some parts to be several hundred
+feet deep. Although we cannot estimate correctly how many years it may have
+required for the river to bring down from the upper country so large a
+quantity of earthy matter--the data for such a computation being as yet
+incomplete--we may still approximate to a minimum of the time which such an
+operation must have taken, by ascertaining experimentally the annual
+discharge of water by the Mississippi, and the mean annual amount of solid
+matter contained in its waters. The lowest estimate of the time required
+would lead us to assign a high antiquity, amounting to many tens of
+thousands of years to the existing delta, the origin of which is
+nevertheless an event of yesterday when contrasted with those terraces,
+_c_, and _d e_, fig. 106., formed of the loam No. 2. above mentioned. These
+materials of the bluffs _a_ and _d_ were produced, the reader will observe,
+during the first part of that great oscillation of level which depressed to
+a depth of 200 feet a larger area than the modern delta and plain of the
+Mississippi, and then restored the region to its former position.[117-A]
+
+_Loess of the Valley of the Rhine._--A similar succession of geographical
+changes, attended by the production of a fluviatile formation, singularly
+resembling that which bounds the great plain of the Mississippi, seems to
+have occurred in the hydrographical basin of the Rhine, since the time when
+that basin had already acquired its present outline of hill and valley. I
+allude to the deposit provincially termed _loess_ in part of Germany, or
+_lehm_ in Alsace, filled with land and freshwater shells of existing
+species. It is a finely comminuted sand or pulverulent loam of a yellowish
+grey colour, consisting chiefly of argillaceous matter combined with a
+sixth part of carbonate of lime, and a sixth of quartzose and micaceous
+sand. It often contains calcareous sandy concretions or nodules, rarely
+exceeding the size of a man's head. Its entire thickness amounts, in some
+places, to between 200 and 300 feet; yet there are often no signs of
+stratification in the mass, except here and there at the bottom, where
+there is occasionally a slight intermixture of drifted materials derived
+from subjacent rocks. Unsolidified as it is, and of so perishable a nature,
+that every streamlet flowing over it cuts out for itself a deep gully, it
+usually terminates in a vertical cliff, from the surface of which land
+shells are seen here and there to project in relief. In all these features
+it presents a precise counterpart to the loess of the Mississippi. It is so
+homogeneous as generally to exhibit no signs of stratification, owing,
+probably, to its materials having been derived from a common source, and
+having been accumulated by a uniform action. Yet it displays in some few
+places decided marks of successive deposition, where coarser and finer
+materials alternate, especially near the bottom. Calcareous concretions,
+also enclosing land-shells, are sometimes arranged in horizontal layers. It
+is a remarkable deposit, from its position, wide extent, and thickness, its
+homogeneous mineral composition, and freshwater origin. Its distribution
+clearly shows that after the great valley of the Rhine, from Schaffhausen
+to Bonn, had acquired its present form, having its bottom strewed over with
+coarse gravel, a period arrived when it became filled up from side to side
+with fine mud, which was also thrown down in the valleys of the principal
+tributaries of the Rhine.
+
+Thus, for example, it may be traced far into Würtemberg, up the valley of
+the Neckar, and from Frankfort, up the valley of the Main, to above
+Dettelbach. I have also seen it spreading over the country of Mayence,
+Eppelsheim, and Worms, on the left bank of the Rhine, and on the opposite
+side on the table-land above the Bergstrasse, between Wiesloch and
+Bruchsal, where it attains a thickness of 200 feet. Near Strasburg, large
+masses of it appear at the foot of the Vosges on the left bank, and at the
+base of the mountains of the Black Forest on the right bank. The
+Kaiserstuhl, a volcanic mountain which stands in the middle of the plain of
+the Rhine near Freiburg, has been covered almost everywhere with this loam,
+as have the extinct volcanos between Coblentz and Bonn. Near Andernach, in
+the Kirchweg, the loess containing the usual shells alternates with
+volcanic matter; and over the whole are strewed layers of pumice, lapilli,
+and volcanic sand, from 10 to 15 feet thick, very much resembling the
+ejections under which Pompeii lies buried. There is no passage at this
+upper junction from the loess into the pumiceous superstratum; and this
+last follows the slope of the hill, just as it would have done had it
+fallen in showers from the air on a declivity partly formed of loess.
+
+But, in general, the loess overlies all the volcanic products, even those
+between Neuwied and Bonn, which have the most modern aspect; and it has
+filled up in part the crater of the Roderberg, an extinct volcano near
+Bonn. In 1833 a well was sunk at the bottom of this crater, through 70 feet
+of loess, in part of which were the usual calcareous concretions.
+
+The interstratification above alluded to, of loess with layers of pumice
+and volcanic ashes, has led to the opinion that both during and since
+its deposition some of the last volcanic eruptions of the Lower Eifel
+have taken place. Should such a conclusion be adopted, we should be
+called upon to assign a very modern date to these eruptions. This
+curious point, therefore, deserves to be reconsidered; since it may
+possibly have happened that the waters of the Rhine, swollen by the
+melting of snow and ice, and flowing at a great height through a valley
+choked up with loess, may have swept away the loose superficial scoriæ
+and pumice of the Eifel volcanos, and spread them out occasionally over
+the yellow loam. Sometimes, also, the melting of snow on the slope of
+small volcanic cones may have given rise to local floods, capable of
+sweeping down light pumice into the adjacent low grounds.
+
+The first idea which has occurred to most geologists, after examining
+the loess between Mayence and Basle, is to imagine that a great lake
+once extended throughout the valley of the Rhine between those two
+places. Such a lake may have sent off large branches up the course of
+the Main, Neckar, and other tributary valleys, in all of which large
+patches of loess are now seen. The barrier of the lake might be placed
+somewhere in the narrow and picturesque gorge of the Rhine between
+Bingen and Bonn. But this theory fails altogether to explain the
+phenomena; when we discover that that gorge itself has once been filled
+with loess, which must have been tranquilly deposited in it, as also in
+the lateral valley of the Lahn, communicating with the gorge. The loess
+has also overspread the high adjoining platform near the village of
+Plaidt above Andernach. Nay, on proceeding farther down to the north, we
+discover that the hills which skirt the great valley between Bonn and
+Cologne have loess on their flanks, which also covers here and there the
+gravel of the plain as far as Cologne, and the nearest rising grounds.
+
+Besides these objections to the lake theory, the loess is met with near
+Basle, capping hills more than 1200 feet above the sea; so that a barrier
+of land capable of separating the supposed lake from the ocean would
+require to be, at least, as high as the mountains called the Siebengebirge,
+near Bonn, the loftiest summit of which, the Oehlberg, is 1209 feet above
+the Rhine and 1369 feet above the sea. It would be necessary, moreover, to
+place this lofty barrier somewhere below Cologne, or precisely where the
+level of the land is now lowest.
+
+Instead, therefore, of supposing one continuous lake of sufficient extent
+and depth to allow of the simultaneous accumulation of the loess, at
+various heights, throughout the whole area where it now occurs, I formerly
+suggested that, subsequently to the period when the countries now drained
+by the Rhine and its tributaries had nearly acquired their actual form and
+geographical features, they were again depressed gradually by a movement
+like that now in progress on the west coast of Greenland.[119-A] In
+proportion as the whole district was lowered, the general fall of the
+waters between the Alps and the ocean was lessened; and both the main and
+lateral valleys, becoming more subject to river inundations, were partially
+filled up with fluviatile silt, containing land and freshwater shells. When
+a thickness of many hundred feet of loess had been thrown down slowly by
+this operation, the whole region was once more upheaved gradually. During
+this upward movement most of the fine loam would be carried off by the
+denuding power of rains and rivers; and thus the original valleys might
+have been re-excavated, and the country almost restored to its pristine
+state, with the exception of some masses and patches of loess such as still
+remain, and which, by their frequency and remarkable homogeneousness of
+composition and fossils, attest the ancient continuity and common origin of
+the whole. By imagining these oscillations of level, we dispense with the
+necessity of erecting and afterwards removing a mountain barrier
+sufficiently high to exclude the ocean from the valley of the Rhine during
+the period of the accumulation of the loess.
+
+The proportion of land shells of the genera _Helix_, _Pupa_, and _Bulimus_,
+is very large in the loess; but in many places aquatic species of the
+genera _Lymnea_, _Paludina_, and _Planorbis_ are also found. These may have
+been carried away during floods from shallow pools and marshes bordering
+the river; and the great extent of marshy ground caused by the wide
+overflowings of rivers above supposed would favour the multiplication of
+amphibious mollusks, such as the _Succinea_ (fig. 107.), which is almost
+everywhere characteristic of this formation, and is sometimes accompanied,
+as near Bonn, by another species, _S. amphibia_ (fig. 34. p. 29.). Among
+other abundant fossils are _Helix plebeium_ and _Pupa muscorum_. (See
+Figures.) Both the terrestrial and aquatic shells preserved in the loess
+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.
+
+[Illustration: Fig. 107. _Succinea elongata._]
+
+[Illustration: Fig. 108. _Pupa muscorum._]
+
+[Illustration: Fig. 109. _Helix plebeium._]
+
+Bones of vertebrated animals are rare in the loess, but those of the
+mammoth, horse, and some other quadrupeds have been met with. At the
+village of Binningen, and the hills called Bruderholz, near Basle, I found
+the vertebræ of fish, together with the usual shells. These vertebræ,
+according to M. Agassiz, belong decidedly to the Shark family, perhaps to
+the genus _Lamna_. In explanation of their occurrence among land and
+freshwater shells, it may be stated that certain fish of this family ascend
+the Senegal, Amazon, and other great rivers, to the distance of several
+hundred miles from the ocean.[120-A]
+
+At Cannstadt, near Stuttgart, in a valley also belonging to the
+hydrographical basin of the Rhine, I have seen the loess pass downwards
+into beds of calcareous tuff and travertin. Several valleys in northern
+Germany, as that of the Ilm at Weimar, and that of the Tonna, north of
+Gotha, exhibit similar masses of modern limestone filled with recent shells
+of the genera _Planorbis_, _Lymnea_, _Paludina_, &c., from 50 to 80 feet
+thick, with a bed of loess much resembling that of the Rhine, occasionally
+incumbent on them. In these modern limestones used for building, the bones
+of _Elephas primigenius_, _Rhinoceros tichorinus_, _Ursus spelæus_, _Hyæna
+spelæa_, with the horse, ox, deer, and other quadrupeds, occur; and in 1850
+Mr. H. Credner and I obtained in a quarry at Tonna, at the depth of 15
+feet, inclosed in the calcareous rock and surrounded with dicotyledonous
+leaves and petrified leaves, four eggs of a snake of the size of the
+largest European Coluber, which, with three others, had been found lying
+in a series, or string.
+
+They are, I believe, the first reptilian remains which have been met with
+in strata of this age.
+
+The agreement of the shells in these cases with recent European species
+enables us to refer to a very modern period the filling up and
+re-excavation of the valleys; an operation which doubtless consumed
+a long period of time, since which the mammiferous fauna has undergone
+a considerable change.
+
+
+FOOTNOTES:
+
+[110-A] See Princ. of Geol. vol. iii. 1st ed.
+
+[112-A] See Principles, Index, "Serapis."
+
+[113-A] Geol. Quart. Journ. vol. ii. Memoirs, p. 15.
+
+[114-A] Quart. Geol. Journ. 4 Mems. p. 48.
+
+[115-A] Journal, p. 451.
+
+[116-A] See Principles, 8th ed. pp. 260-268.
+
+[117-A] Lyell's Second Visit to the United States, vol. ii. chap. xxxiv.
+
+[119-A] Princ. of Geol. 3d edition, 1834, vol. iii. p. 414.
+
+[120-A] Proceedings Geol. Soc. No. 43. p. 222.
+
+
+
+
+CHAPTER XI.
+
+NEWER PLIOCENE PERIOD.--BOULDER FORMATION.
+
+   Drift of Scandinavia, northern Germany, and Russia--Its northern
+   origin--Not all of the same age--Fundamental rocks polished, grooved,
+   and scratched--Action of glaciers and icebergs--Fossil shells of
+   glacial period--Drift of eastern Norfolk--Associated freshwater
+   deposit--Bent and folded strata lying on undisturbed beds--Shells on
+   Moel Tryfane--Ancient glaciers of North Wales--Irish drift.
+
+
+Among the different kinds of alluvium described in the seventh chapter,
+mention was made of the boulder formation in the north of Europe, the
+peculiar characters of which may now be considered, as it belongs in
+part to the post-pliocene, and partly to the newer pliocene, period. I
+shall first allude briefly to that portion of it which extends from
+Finland and the Scandinavian mountains to the north of Russia, and the
+low countries bordering the Baltic, and which has been traced southwards
+as far as the eastern coast of England. This formation consists of mud,
+sand, and clay, sometimes stratified, but often wholly devoid of
+stratification, for a depth of more than a hundred feet. To this
+unstratified form of the deposit, the name of _till_ has been applied in
+Scotland. It generally contains numerous fragments of rocks, some
+angular and others rounded, which have been derived from formations of
+all ages, both fossiliferous, volcanic, and hypogene, and which have
+often been brought from great distances. Some of the travelled blocks
+are of enormous size, several feet or yards in diameter; their average
+dimensions increasing as we advance northwards. The till is almost
+everywhere devoid of organic remains, unless where these have been
+washed into it from older formations; so that it is chiefly from
+relative position that we must hope to derive a knowledge of its age.
+
+Although a large proportion of the boulder deposit, or "northern drift," as
+it has sometimes been called, is made up of fragments brought from a
+distance, and which have sometimes travelled many hundred miles, the bulk
+of the mass in each locality consists of the ruins of subjacent or
+neighbouring rocks; so that it is red in a region of red sandstone, white
+in a chalk country, and grey or black in a district of coal and coal-shale.
+
+The fundamental rock on which the boulder formation reposes, if it consist
+of granite, gneiss, marble, or other hard stone capable of permanently
+retaining any superficial markings which may have been imprinted upon it,
+is smoothed or polished, and usually exhibits parallel striæ and furrows
+having a determinate direction. This direction, both in Europe and North
+America, is evidently connected with the course taken by the erratic blocks
+in the same district being north or south, or 20 or 30 degrees to the east
+or west of north, according as the large angular and rounded stones have
+travelled. These stones themselves also are often furrowed and scratched
+on more than one side.
+
+[Illustration: Fig. 110. Limestone polished, furrowed, and scratched by the
+glacier of Rosenlaui, in Switzerland. (Agassiz.)
+
+  _a a._ White streaks or scratches, caused by small grains of flint frozen
+         into the ice.
+  _b b._ Furrows.]
+
+In explanation of such phenomena I may refer the student to what was said
+of the action of glaciers and icebergs in the Principles of Geology.[122-A]
+It is ascertained that hard stones, frozen into a moving mass of ice, and
+pushed along under the pressure of that mass, scoop out long rectilinear
+furrows or grooves parallel to each other on the subjacent solid rock. (See
+fig. 110.) Smaller scratches and striæ are made on the polished surface by
+crystals or projecting edges of the hardest minerals, just as a diamond
+cuts glass. The recent polishing and striation of limestone by coast-ice
+carrying boulders even as far south as the coast of Denmark, has been
+observed by Dr. Forchhammer, and helps us to conceive how large icebergs,
+running aground on the bed of the sea, may produce similar furrows on a
+grander scale. An account was given so long ago as the year 1822, by
+Scoresby, of icebergs seen by him drifting along in latitudes 69° and 70°
+N., which rose above the surface from 100 to 200 feet, and measured from a
+few yards to 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.[122-B] 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 northwards, with a large erratic block
+firmly frozen into it. In order to understand in what manner long and
+straight grooves may be cut by such agency, we must remember that these
+floating islands of ice have a singular steadiness of motion, in
+consequence of the larger portion of their bulk being sunk deep under
+water, so that they are not perceptibly moved by the winds and waves even
+in the strongest gales. Many had supposed that the magnitude commonly
+attributed to icebergs by unscientific navigators was exaggerated, but now
+it appears that the popular estimate of their dimensions has rather fallen
+within than beyond the truth. 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 2 to 5 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 the mechanical power they might exert
+when fairly set in motion must be prodigious.[123-A]
+
+Glaciers formed in mountainous regions become laden with mud and stones,
+and if they melt away at their lower extremity before they reach the sea,
+they leave wherever they terminate a confused heap of unstratified rubbish,
+called "a moraine," composed of mud and pieces of all the rocks with which
+they were loaded. We may expect, therefore, to find a formation of the same
+kind, resulting from the liquefaction of icebergs, in tranquil water. But,
+should the action of a current intervene at certain points or at certain
+seasons, then the materials will be sorted as they fall, and arranged in
+layers according to their relative weight and size. Hence there will be
+passages from _till_, as it is called in Scotland, to stratified clay,
+gravel, and sand, and intercalations of one in the other.
+
+I have yet to mention another appearance connected with the boulder
+formation, which has justly attracted much attention in Norway and other
+parts of Europe. Abrupt pinnacles and outstanding ridges of rock are often
+observed to be polished and furrowed on the north, or "strike" side as it
+is called, or on the side facing the region from which the erratics have
+come; while, on the other side, which is usually steeper and often
+perpendicular, called the "lee-side," such superficial markings are
+wanting. There is usually a collection on this lee-side of boulders and
+gravel, or of large angular fragments. In explanation we may suppose that
+the north side was exposed, when still submerged, to the action of
+icebergs, and afterwards, when the land was upheaved, of coast-ice, which
+ran aground upon shoals, or was _packed_ on the beach; so that there would
+be great wear and tear on the seaward slope, while, on the other, gravel
+and boulders might be heaped up in a sheltered position.
+
+_Northern origin of erratics._--That the erratics of northern Europe have
+been carried southward cannot be doubted; those of granite, for example,
+scattered over large districts of Russia and Poland, agree precisely in
+character with rocks of the mountains of Lapland and Finland; while the
+masses of gneiss, syenite, porphyry, and trap, strewed over the low sandy
+countries of Pomerania, Holstein, and Denmark, are identical in mineral
+characters with the mountains of Norway and Sweden.
+
+It is found to be a general rule in Russia, that the smaller blocks are
+carried to greater distances from their point of departure than the larger;
+the distance being sometimes 800 and even 1000 miles from the nearest rocks
+from which they were broken off; the direction having been from N.W. to
+S.E., or from the Scandinavian mountains over the seas and low lands to the
+south-east. That its accumulation throughout this area took place in part
+during the post-pliocene period is proved by its superposition at several
+points to strata containing recent shells. Thus, for example, in European
+Russia, MM. Murchison and De Verneuil found in 1840, that the flat country
+between St. Petersburg and Archangel, for a distance of 600 miles,
+consisted of horizontal strata, full of shells similar to those now
+inhabiting the arctic sea, on which rested the boulder formation,
+containing large erratics.
+
+In Sweden, in the immediate neighbourhood of Upsala, I observed, in 1834, a
+ridge of stratified sand and gravel, in the midst of which is 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, intermixed with some
+of freshwater species. The marine shells are all of dwarfish size, like
+those now inhabiting the brackish waters of the Baltic; and the marl, in
+which myriads 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 9 to
+16 feet in diameter, and which must have been brought into their present
+position since the time when the neighbouring gulf was already
+characterized by its peculiar fauna.[124-A] 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.
+
+It was stated that in Russia the erratics diminished generally in size in
+proportion as they are traced farther from their source. The same
+observation holds true in regard to the average bulk of the Scandinavian
+boulders, when we pursue them southwards, from the south of Norway and
+Sweden through Denmark and Westphalia. This phenomenon is in perfect
+harmony with the theory of ice-islands floating in a sea of variable depth;
+for the heavier erratics require icebergs of a larger size to buoy them up;
+and, even when there are no stones frozen in, more than seven eighths, and
+often nine tenths, of a mass of drift ice is under water. The greater,
+therefore, the volume of the iceberg, the sooner would it impinge on some
+shallower part of the sea; while the smaller and lighter floes, laden with
+finer mud and gravel, may pass freely over the same banks, and be carried
+to much greater distances. In those places, also, where in the course of
+centuries blocks have been carried southwards by coast-ice, having been
+often stranded and again set afloat in the direction of a prevailing
+current, the blocks will be worn and diminish in size the farther they
+travel from their point of departure.
+
+The "northern drift" of the most southern latitudes is usually of the
+highest antiquity. In Scotland it rests immediately on the older rocks,
+and is covered by stratified sand and clay, usually devoid of fossils,
+but in which, at certain points near the east and west coast, as, for
+example, in the estuaries of the Tay and Clyde, marine shells have been
+discovered. The same shells have also been met with in the north, at
+Wick in Caithness, and on the shores of the Moray Frith. The principal
+deposit on the Clyde occurs at the height of about 70 feet, but a few
+shells have been traced in it as high as 554 feet above the sea.
+Although a proportion of between 85 or 90 in 100 of the imbedded shells
+are of recent species, the remainder are unknown; and even many which
+are recent now inhabit more northern seas, where we may, perhaps,
+hereafter find living representatives of some of the unknown fossils.
+The distance to which erratic blocks have been carried southwards in
+Scotland, and the course they have taken, which is often wholly
+independent of the present position of hill and valley, favours the idea
+that ice-rafts rather than glaciers were in general the transporting
+agents. The Grampians in Forfarshire and in Perthshire are from 3000 to
+4000 feet high. To the southward lies the broad and deep valley of
+Strathmore, and to the south of this again rise the Sidlaw Hills[125-A]
+to the height of 1500 feet and upwards. On the highest summits of this
+chain, formed of sandstone and shale, and at various elevations, are
+found huge angular fragments of mica schist, some 3 and others 15 feet
+in diameter, which have been conveyed for a distance of at least 15
+miles from the nearest Grampian rocks from which they could have been
+detached. Others have been left strewed over the bottom of the large
+intervening vale of Strathmore.
+
+Still farther south on the Pentland Hills, at the height of 1100 feet
+above the sea, Mr. Maclaren has observed a fragment of mica-schist
+weighing from 8 to 10 tons, the nearest mountain composed of this
+formation being 50 miles distant.[125-B]
+
+The testaceous fauna of the boulder period, in Scotland, England, and
+Ireland, has been shown by Prof. E. Forbes to contain a much smaller
+number of species than that now belonging to the British seas, and to have
+been also much less rich in species than the Older Pliocene fauna of the
+crag which preceded it. Yet the species are nearly all of them now living
+either in the British or more northern seas, the shells of more arctic
+latitudes being the most abundant and the most wide spread throughout the
+entire area of the drift from north to south.
+
+This extensive range of the fossils can by no means be explained by
+imagining the mollusca of the drift to have been inhabitants of a deep
+sea, where a more uniform temperature prevailed. On the contrary, many
+species were littoral, and others belonged to a shallow sea, not above
+100 feet deep, and very few of them lived, according to Prof. E. Forbes,
+at greater depths than 300 feet.
+
+From what was before stated it will appear that the boulder formation
+displays almost everywhere, in its mineral ingredients, a strange
+heterogeneous mixture of the ruins of adjacent lands, with stones both
+angular and rounded, which have come from points often very remote. Thus we
+find it in our eastern counties, as in Norfolk, Suffolk, Cambridge,
+Huntingdon, Bedford, Hertford, Essex, and Middlesex, containing stones from
+the Silurian and Carboniferous strata, and from the lias, oolite, and
+chalk, all with their peculiar fossils, together with trap, syenite,
+mica-schist, granite, and other crystalline rocks. A fine example of this
+singular mixture extends to the very suburbs of London, being seen on the
+summit of Muswell Hill, Highgate. But south of London the northern drift is
+wanting, as, for example, in the Wealds of Surrey, Kent, and Sussex.
+
+_Norfolk drift._--The drift can nowhere be studied more advantageously in
+England than in the cliffs of the Norfolk coast between Happisburgh and
+Cromer. Vertical sections, having an ordinary height of from 50 to 70 feet,
+are there exposed to view for a distance of about 20 miles. The name of
+diluvium was formerly given to it by those who supposed it to have been
+produced by the violent action of a sudden and transient deluge, but the
+term drift has been substituted by those who reject this hypothesis. Here,
+as elsewhere, it consists for the most part of clay, loam, and sand, in
+part stratified, in part devoid of stratification. Pebbles, together with
+some large boulders of granite, porphyry, greenstone, lias, chalk, and
+other transported rocks, are interspersed, especially through the till.
+That some of the granitic and other fragments came from Scandinavia I have
+no doubt, after having myself traced the course of the continuous stream of
+blocks from Norway and Sweden to Denmark, and across the Elbe, through
+Westphalia, to the borders of Holland. We need not be surprised to find
+them reappear on our eastern coast, between the Tweed and the Thames,
+regions not half so remote from parts of Norway as are many Russian
+erratics from the sources whence they came.
+
+White chalk rubble, unmixed with foreign matter, and even huge fragments
+of solid chalk, also occur in many localities in these Norfolk cliffs.
+No fossils have been detected in this drift, which can positively be
+referred to the era of its accumulation; but at some points it overlies
+a freshwater formation containing recent shells, and at others it is
+blended with the same in such a manner as to force us to conclude that
+both were contemporaneously deposited.
+
+[Illustration: Fig. 111. The shaded portion consists of Freshwater
+beds. Intercalation of freshwater beds and of boulder clay and
+sand at Mundesley.]
+
+This interstratification is expressed in the annexed figure, the dark mass
+indicating the position of the freshwater beds, which contain much
+vegetable matter, and are divided into thin layers. The imbedded shells
+belong to the genera _Planorbis_, _Lymnea_, _Paludina_, _Unio_, _Cyclas_,
+and others, all of British species, except a minute _Paludina_ now
+inhabiting France. (See fig. 112.)
+
+[Illustration: Fig. 112. _Paludina marginata_, Michaud. (_P. minuta_,
+Strickland.) The middle figure is of the natural size.]
+
+The _Cyclas_ (fig. 113.) is merely a remarkable variety of the common
+English species. The scales and teeth of fish of the genera Pike,
+Perch, Roach, and others, accompany these shells; but the species
+are not considered by M. Agassiz to be identical with known British
+or European kinds.
+
+[Illustration: Fig. 113. _Cyclas_ (_Pisidium_) _amnica_, var.? The two
+middle figures are of the natural size.]
+
+The series of formations in the cliffs of eastern Norfolk, now under
+consideration, beginning with the lowest, is as follows:--First, chalk;
+secondly, patches of a marine tertiary formation, called the Norwich
+Crag, hereafter to be described; thirdly, the freshwater beds already
+mentioned; and lastly, the drift. Immediately above the chalk, or crag,
+when that is present, is found here and there a buried forest, or a
+stratum in which the stools and roots of trees stand in their natural
+position, the trunks having been broken short off and imbedded with
+their branches and leaves. It is very remarkable that the strata of the
+overlying boulder formation have often undergone great derangement at
+points where the subjacent forest bed and chalk remain undisturbed.
+There are also cases where the upper portion of the boulder deposit has
+been greatly deranged, while the lower beds of the same have continued
+horizontal. Thus the annexed section (fig. 114.) represents a cliff
+about 50 feet high, at the bottom of which is _till_, or unstratified
+clay, containing boulders, having an even horizontal surface, on which
+repose conformably beds of laminated clay and sand about 5 feet thick,
+which, in their turn, are succeeded by vertical, bent, and contorted
+layers of sand and loam 20 feet thick, the whole being covered by flint
+gravel. Now the curves of the variously coloured beds of loose sand,
+loam, and pebbles are so complicated that not only may we sometimes
+find portions of them which maintain their verticality to a height
+of 10 or 15 feet, but they have also been folded upon themselves in
+such a manner that continuous layers might be thrice pierced in
+one perpendicular boring.
+
+[Illustration: Fig. 114. Cliff 50 feet high between Bacton
+Gap and Mundesley.]
+
+[Illustration: Fig. 115. Folding of the strata between East
+and West Runton.]
+
+[Illustration: Fig. 116. Section of concentric beds west of Cromer.
+
+  1. Blue clay.
+  2. White sand.
+  3. Yellow Sand.
+  4. Striped loam and clay.
+  5. Laminated blue clay.]
+
+At some points there is an apparent folding of the beds round a central
+nucleus, as at _a_, fig. 115., where the strata seem bent round a small
+mass of chalk; or, as in fig. 116., where the blue clay, No. 1., is in the
+centre; and where the other strata, 2, 3, 4, 5, are coiled round it; the
+entire mass being 20 feet in perpendicular height. This appearance of
+concentric arrangement around a nucleus is, nevertheless, delusive, being
+produced by the intersection of beds bent into a convex shape; and that
+which seems the nucleus being, in fact, the innermost bed of the series,
+which has become partially visible by the removal of the protuberant
+portions of the outer layers.
+
+To the north of Cromer are other fine illustrations of contorted drift
+reposing on a floor of chalk horizontally stratified and having a level
+surface. These phenomena, in themselves sufficiently difficult of
+explanation, are rendered still more anomalous by the occasional inclosure
+in the drift of huge fragments of chalk many yards in diameter. One
+striking instance occurs west of Sherringham, where an enormous pinnacle of
+chalk, between 70 and 80 feet in height, is flanked on both sides by
+vertical layers of loam, clay, and gravel. (Fig. 117.)
+
+[Illustration: Fig. 117. Included pinnacle of chalk at Old Hythe point,
+west of Sherringham.
+
+  _d._ Chalk with regular layers of chalk flints.
+  _c._ Layer called "the pan," of loose chalk, flints, and marine shells
+       of recent species, cemented by oxide of iron.]
+
+This chalky fragment is only one of many detached masses which have been
+included in the drift, and forced along with it into their present
+position. The level surface of the chalk _in situ_ (_d_) may be traced for
+miles along the coast, where it has escaped the violent movements to which
+the incumbent drift has been exposed.[129-A]
+
+We are called upon, then, to explain how any force can have been exerted
+against the upper masses, so as to produce movements in which the
+subjacent strata have not participated. It may be answered that, if we
+conceive the _till_ and its boulders to have been drifted to their
+present place by ice, the lateral pressure may have been supplied by the
+stranding of ice-islands. We learn, from the observations of Messrs.
+Dease and Simpson in the polar regions, that such islands, when they run
+aground, push before them large mounds of shingle and sand. It is
+therefore probable that they often cause great alterations in the
+arrangement of pliant and incoherent strata forming the upper part of
+shoals or submerged banks, the inferior portions of the same remaining
+unmoved. Or many of the complicated curvatures of these layers of loose
+sand and gravel may have been due to another cause, the melting on the
+spot of icebergs and coast ice in which successive deposits of pebbles,
+sand, ice, snow, and mud, together with huge masses of rock fallen from
+cliffs, may have become interstratified. Ice-islands so constituted
+often capsize when afloat, and gravel once horizontal may have assumed,
+before the associated ice was melted, an inclined or vertical position.
+The packing of ice forced up on a coast may lead to similar derangement
+in a frozen conglomerate of sand or shingle, and, as Mr. Trimmer has
+suggested[130-A], alternate layers of earthy matter may have sunk
+down slowly during the liquefaction of the intercalated ice, so as
+to assume the most fantastic and anomalous positions, while the
+aqueous strata below, and those afterwards thrown down above, may
+be perfectly horizontal.
+
+A buried forest has been adverted to as underlying the drift on the coast
+of Norfolk. At the time when the trees grew there must have been dry land
+over a large area, which was afterwards submerged, so as to allow a mass of
+stratified and unstratified drift, 200 feet and more in thickness, to be
+superimposed. The undermining of the cliffs by the sea in modern times has
+enabled us to demonstrate, beyond all doubt, the fact of this
+superposition, and that the forest was not formed along the present
+coast-line. Its situation implies a subsidence of several hundred feet
+since the commencement of the drift period, after which there must have
+been an upheaval of the same ground; for the forest bed of Norfolk is now
+again so high as to be exposed to view at many points at low water; and
+this same upward movement may explain why the _till_, which is conceived
+to have been of submarine origin, is now met with far inland, and on
+the summit of hills.
+
+The boulder formation of the west of England, observed in Lancashire,
+Cheshire, Shropshire, Staffordshire, and Worcestershire, contains in some
+places marine shells of recent species, rising to various heights, from 100
+to 350 feet above the sea. The erratics have come partly from the mountains
+of Cumberland, and partly from those of Scotland.
+
+But it is on the mountains of North Wales that the "Northern drift,"
+with its characteristic marine fossils, reaches its greatest altitude.
+On Moel Tryfane, near the Menai Straits, Mr. Trimmer met with shells of
+the species commonly found in the drift at the height of 1392 feet above
+the level of the sea.
+
+It is remarkable that in the same neighbourhood where there is evidence of
+so great a submergence of the land during part of the glacial period, we
+have also the most decisive proofs yet discovered in the British Isles of
+subaerial glaciers. Dr. Buckland published in 1842 his reasons for
+believing that the Snowdonian mountains in Caernarvonshire were formerly
+covered with glaciers, which radiated from the central heights through the
+seven principal valleys of that chain, where striæ and flutings are seen
+on the polished rocks directed towards as many different points of the
+compass. He also described the "moraines" of the ancient glaciers, and the
+rounded "bosses" or small flattened domes of polished rock, such as the
+action of moving glaciers is known to produce in Switzerland, when gravel,
+sand, and boulders, underlying the ice, are forced along over a foundation
+of hard stone. Mr. Darwin, and subsequently Prof. Ramsay, have confirmed
+Dr. Buckland's views in regard to these Welsh glaciers. Nor indeed was it
+to be expected that geologists should discover proofs of icebergs having
+abounded in the area now occupied by the British Isles in the Pleistocene
+period without sometimes meeting with the signs of contemporaneous glaciers
+which covered hills even of moderate elevation between the 50th and 60th
+degrees of latitude.
+
+In Ireland the "drift" exhibits the same general characters and fossil
+remains as in Scotland and England; but in the southern part of that
+island, Prof. E. Forbes and Capt. James found in it some shells which show
+that the glacial sea communicated with one inhabited by a more southern
+fauna. Among other species in the south, they mention at Wexford and
+elsewhere the occurrence of _Nucula Cobboldiæ_ (see fig. 120. p. 149.) and
+_Turritella incrassata_ (a crag fossil); also a southern form of _Fusus_,
+and a _Mitra_ allied to a Spanish species.[131-A]
+
+
+FOOTNOTES:
+
+[122-A] Chap. xvi. and the references there given.
+
+[122-B] Voyage in 1822, p. 233.
+
+[123-A] T. L. Hayes, Boston Journ. Nat. Hist. 1844.
+
+[124-A] See paper by the author, Phil. Trans. 1835, p. 15.
+
+[125-A] See above, section, p. 48.
+
+[125-B] Geol. of Fife, &c. p. 220.
+
+[129-A] For a full account of the drift of East Norfolk, see a paper by the
+author, Phil. Mag. No. 104. May, 1840.
+
+[130-A] Quart. Journ. Geol. Soc. vol. vii. p. 22.
+
+[131-A] Forbes, Memoirs of Geol. Survey of Great Britain, vol. i. p. 377.
+
+
+
+
+CHAPTER XII.
+
+BOULDER FORMATION--_continued_.
+
+   Difficulty of interpreting the phenomena of drift before the glacial
+   hypothesis was adopted--Effects of intense cold in augmenting the
+   quantity of alluvium--Analogy of erratics and scored rocks in North
+   America and Europe--Bayfield on shells in drift of Canada--Great
+   subsidence and re-elevation of land from the sea, required to account
+   for glacial appearances--Why organic remains so rare in northern
+   drift--Mastodon giganteus in United States--Many shells and some
+   quadrupeds survived the glacial cold--Alps an independent centre of
+   dispersion of erratics--Alpine blocks on the Jura--Whether transported
+   by glaciers or floating ice--Recent transportation of erratics from
+   the Andes to Chiloe--Meteorite in Asiatic drift.
+
+
+It will appear from what was said in the last chapter of the marine shells
+characterizing the boulder formation, that nine-tenths or more of them
+belong to species still living. The superficial position of "the drift" is
+in perfect accordance with its imbedded organic remains, leading us to
+refer its origin to a modern period. If, then, we encounter so much
+difficulty in the interpretation of monuments relating to times so near our
+own--if in spite of their recent date they are involved in so much
+obscurity--the student may ask, not without reasonable alarm, how we can
+hope to decipher the records of remote ages.
+
+To remove from the mind as far as possible this natural feeling of
+discouragement, I shall endeavour in this chapter to prove that what seems
+most strikingly anomalous, in the "erratic formation," as some call it, is
+really the result of that glacial action which has already been alluded to.
+If so, it was to be expected that so long as the true origin of so singular
+a deposit remained undiscovered, erroneous theories and terms would be
+invented in the effort to solve the problem. These inventions would
+inevitably retard the reception of more correct views which a wider field
+of observation might afterwards suggest.
+
+The term "diluvium" was for a time the popular name of the boulder
+formation, because it was referred by some geologists to the deluge.
+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 no explanation was offered why such agency should have been
+developed more energetically in modern times than at former periods of
+the earth's history, or why it should be displayed in its fullest
+intensity in northern latitudes; for it is important to insist on the
+fact, that the boulder formation is a _northern_ phenomenon. Even the
+southern extension of the drift, or the large erratics found in the Alps
+and the surrounding lands, especially their occurrence round the highest
+parts of the chain, offers such an exception to the general rule as
+confirms the glacial hypothesis; for it shows that the transportation of
+stony fragments to great distances, and the striation, polishing, and
+grooving of solid floors of rock, are here again intimately connected
+with accumulations of perennial snow and ice.
+
+That there is some intimate connection between a cold or northern climate
+and the various geological appearances now commonly called glacial, cannot
+be doubted by any one who has compared the countries bordering the Baltic
+with those surrounding the Mediterranean. The smoothing and striation of
+rocks, and the erratics, are traced from the sea-shore to the height of
+3000 feet above the level of the Baltic, whereas such phenomena are wholly
+wanting in countries bordering the Mediterranean; and their absence is
+still more marked in the equatorial parts of Asia, Africa, and America; but
+when we cross the southern tropic, and reach Chili and Patagonia, we again
+encounter the boulder formation, between the latitude 41° S. and Cape Horn,
+with precisely the same characters which it assumes in Europe. The evidence
+as to climate derived from the organic remains of the drift is, as we have
+seen, in perfect harmony with the conclusions above alluded to, the former
+habits of the species of mollusca being accurately ascertainable, inasmuch
+as they belong to species still living, and known to have at present a wide
+range in northern seas.
+
+But if we are correct in assuming that the northern hemisphere was
+considerably colder than now during the period under consideration, owing
+probably to the greater area and height of arctic lands, and to the
+quantity of icebergs which such a geographical state of things would
+generate, it may be well to reflect before we proceed farther on the entire
+modification which extreme cold would produce in the operation of those
+causes spoken of in the sixth chapter as most active in the formation of
+alluvium. A large part of the materials derived from the detritus of rocks,
+which in warm climates would go to form deltas, or would be regularly
+stratified by marine currents, would, under arctic influences, assume a
+superficial and alluvial character. Instead of mud being carried farther
+from a coast than sand, and sand farther out than pebbles,--instead of
+dense stratified masses being heaped up in limited areas,--nearly the whole
+materials, whether coarse or fine, would be conveyed by ice to equal
+distances, and huge fragments, which water alone could never move, would be
+borne for hundreds of miles without having their edges worn or fractured;
+and the earthy and stony masses, when melted out of the frozen rafts, would
+be scattered at random over the submarine bottom, whether on mountain tops
+or in low plains, with scarcely any relation to the inequalities of the
+ground, settling on the crests or ridges of hills in tranquil water as
+readily as in valleys and ravines. Occasionally, in those deep and
+uninhabited parts of the ocean, never reached by any but the finest
+sediment in a normal state of things, the bottom would become densely
+overspread by gravel, mud, and boulders.
+
+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 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 half of
+them identical with those already enumerated as belonging to European drift
+10 degrees of latitude farther north. 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. At the southern extremity of its
+course, moreover, it presents an analogy with the drift of the south of
+Ireland, by blending with a more southern fauna, as for example at Brooklyn
+near New York, in lat. 41° N., where, according to MM. Redfield and Desor,
+_Venus mercenaria_ and other southern species of shells begin to occur as
+fossils in the drift.
+
+The extension on the American continent of the range of erratics during the
+Pleistocene 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. Formerly, as now, a more
+extreme climate and a more abundant supply of floating 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 Norway, Sweden, and
+Scotland, as in Canada and the United States, the marine shells are
+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.
+
+[Illustration: Fig. 118. Cross section.
+
+   K.  Mr. Ryland's house.
+  _h_. Clay and sand of higher grounds, with _Saxicava_, &c.
+  _g_. Gravel with boulders.
+  _f_. Mass of _Saxicava rugosa_, 12 feet thick.
+  _e_. Sand and loam with _Mya truncata_, _Scalaria Groenlandica_, &c.
+  _d_. Drift, with boulders of syenite, &c.
+  _c_. Yellow sand.
+  _b_. Laminated clay, 25 feet thick.
+   A.  Horizontal lower Silurian strata.
+   B.  Valley re-excavated.]
+
+I described in 1839 the fossil shells collected by Captain Bayfield from
+strata of drift at Beauport near Quebec, in lat. 47°, and drew from them
+the inference that they indicated a more northern climate, the shells
+agreeing in great part with those of Uddevalla in Sweden.[134-A] The shelly
+beds attain at Beauport and the neighbourhood a height of 200, 300, and
+sometimes 400 feet above the sea, and dispersed through some of them are
+large boulders of granite, which could not have been propelled by a violent
+current, because the accompanying fragile shells are almost all entire.
+They seem, therefore, said Captain Bayfield, writing in 1838, to have been
+dropped down from melting ice, like similar stones which are now annually
+deposited in the St. Lawrence.[134-B] I visited this locality in 1842, and
+made the annexed section, fig. 118., which will give an idea of the general
+position of the drift in Canada and the United States. I imagine that the
+whole of the valley B was once filled up with the beds _b_, _c_, _d_, _e_,
+_f_, which were deposited during a period of subsidence, and that
+subsequently the higher country (_h_) was submerged and overspread with
+drift. The partial re-excavation of B took place when this region was again
+uplifted above the sea to its present height. Among the twenty-three
+species of fossil shells collected by me from these beds at Beauport, all
+were of recent northern species, except one, which is unknown as living,
+and may be extinct (see fig. 119.). I also examined the same formation
+farther up the valley of the St. Lawrence, in the suburbs of Montreal,
+where some of the beds of loam are filled with great numbers of the
+_Mytilus edulis_, or our common European mussel, retaining both its valves
+and purple colour. This shelly deposit, containing _Saxicava rugosa_ and
+other characteristic marine shells, also occurs at an elevated point on
+the mountain of Montreal, 450 feet above the level of the sea.[135-A]
+
+[Illustration: Fig. 119. _Astarte Laurentiana._
+
+  _a._ Outside.
+  _b._ Inside of right valve.
+  _c._ Inside of left valve.]
+
+In my account of Canada and the United States, published in 1845, I
+announced the conclusion to which I had then arrived, that to explain
+the position of the erratics and the polished surfaces of rocks, and
+their striæ and flutings, we must assume first a gradual submergence of
+the land in North America, after it had acquired its present outline of
+hill and valley, cliff and ravine, and then its re-emergence from the
+ocean. When the land was slowly sinking, the sea which bordered it was
+covered with islands of floating ice coming from the north, which, as
+they grounded on the coast and on shoals, pushed along such loose
+materials of sand and pebbles as lay strewed over the bottom. By this
+force all angular and projecting points were broken off, and fragments
+of hard stone, frozen into the lower surface of the ice, had power to
+scoop out grooves in the subjacent solid rock. The sloping beach, as
+well as the floor of the ocean, might be polished and scored by this
+machinery; but no flood of water, however violent, or however great the
+quantity of detritus or size of the rocky fragments swept along by it,
+could produce such long, perfectly straight and parallel furrows, as are
+everywhere visible in the Niagara district, and generally in the region
+north of the 40th parallel of latitude.[135-B]
+
+By the hypothesis of such a slow and gradual subsidence of the land we may
+account for the fact that almost everywhere in N. America and Northern
+Europe the boulder formation rests on a polished and furrowed surface of
+rock,--a fact by no means obliging us to imagine, as some think, that the
+polishing and grooving action was, as a whole, anterior in date to the
+transportation of the erratics. During the successive depression of high
+land, varying originally in height from 1000 to 3000 feet above the
+sea-level, every portion of the surface would be brought down by turns to
+the level of the ocean, so as to be converted first into a coast-line, and
+then into a shoal; and at length, after being well scored by the stranding
+upon it of thousands of icebergs, might be sunk to a depth of several
+hundred fathoms. By the constant depression of land, the coast would recede
+farther and farther from the successively formed zones of polished and
+striated rock, each outer zone becoming in its turn so deep under water as
+to be no longer grated upon by the heaviest icebergs. Such sunken areas
+would then simply serve as receptacles of mud, sand, and boulders dropped
+from melting ice, perhaps to a depth scarcely, if at all, inhabited by
+testacea and zoophytes. Meanwhile, during the formation of the unstratified
+and unfossiliferous mass in deeper water, the smoothing and furrowing of
+shoals and beaches is still going on elsewhere upon and near the coast in
+full activity. If at length the subsidence should cease, and the direction
+of the movement of the earth's crust be reversed, the sunken area covered
+with drift would be slowly reconverted into land. The boulder deposit,
+before emerging, would then for a time be brought within the action of the
+waves, tides, and currents, so that its upper portion, being partially
+disturbed, would have its materials re-arranged and stratified. Streams
+also flowing from the land would in some places throw down layers of
+sediment upon the _till_. In that case, the order of superposition will be,
+first and uppermost, sand, loam, and gravel occasionally fossiliferous;
+secondly, an unstratified and unfossiliferous mass, for the most part of
+much older date than the preceding, with angular erratics, or with boulders
+interspersed; and, thirdly, beneath the whole, a surface of polished and
+furrowed rock. Such a succession of events seems to have prevailed very
+widely on both sides of the Atlantic, the travelled blocks having been
+carried in general from the North Pole southwards, but mountain chains
+having in some cases served as independent centres of dispersion, of which
+the Alps present the most conspicuous example.
+
+It is by no means rare to meet with boulders imbedded in drift which are
+worn flat on one or more of their sides, the surface being at the same time
+polished, furrowed, and striated. They may have been so shaped in a glacier
+before they reached the sea, or when they were fixed in the bottom of an
+iceberg as it ran aground. We learn from Mr. Charles Martins that the
+glaciers of Spitzbergen project from the coast into a sea between 100 and
+400 feet deep; and that numbers of striated pebbles or blocks are there
+seen to disengage themselves from the overhanging masses of ice as they
+melt, so as to fall at once into deep water.[136-A]
+
+That they should retain such markings when again upraised above the sea
+ought not to surprise us, when we remember that rippled sands, and the
+cracks in clay dried between high and low water, and the foot-tracks of
+animals and rain-drops impressed on mud, and other superficial markings,
+are all found fossil in rocks of various ages.
+
+On the other hand, it is not difficult to account for the absence in many
+districts of striated and scored pebbles and boulders in glacial deposits,
+for they may have been exposed to the action of the waves on a coast while
+it was sinking beneath or rising above the sea. No shingle on an ordinary
+sea-beach exhibits such striæ, and at a very short distance from the
+termination of a glacier every stone in the bed of the torrent which gushes
+out from the melting ice is found to have lost its glacial markings by
+being rolled for a distance even of a few hundred yards.
+
+The usual dearth of fossil shells in glacial clays well fitted to preserve
+organic remains may, perhaps, be owing, as already hinted, to the absence
+of testacea in the deep sea, where the undisturbed accumulation of boulders
+melted out of very large bergs may take place. In the Ægean and other parts
+of the Mediterranean, the zero of animal life, according to Prof. E.
+Forbes, is approached at a depth of about 300 fathoms. In tropical seas it
+would descend farther down, just as vegetation ascends higher on the
+mountains of hot countries. Near the pole, on the other hand, the same zero
+would be reached much sooner both on the hills and in the sea. If the ocean
+was filled with floating bergs, and a low temperature prevailed in the
+northern hemisphere during the glacial period, even the shallow part of the
+sea might have been uninhabitable, or very thinly peopled with living
+beings. It may also be remarked that the melting of ice in some fiords in
+Norway freshens the water so as to destroy marine life, and famines have
+been caused in Iceland by the stranding of icebergs drifted from the
+Greenland coast, which have required several years to melt, and have not
+only injured the hay harvest by cooling the atmosphere, but have driven
+away the fish from the shore by chilling and freshening the sea.
+
+If the cold of the glacial epoch came on slowly, if it was long before it
+reached its greatest intensity, and again if it abated gradually, we may
+expect to find the earliest and latest formed drift less barren of organic
+remains than that deposited during the coldest period. We may also expect
+that along the southern limits of the drift during the whole glacial epoch,
+there would be an intimate association of transported matter of northern
+origin with fossil-bearing sediment, whether marine or freshwater,
+belonging to more southern seas, rivers, and continents.
+
+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 drift. They sometimes occur in the bottom even of small ponds recently
+drained by the agriculturist for the sake of the shell marl. I examined one
+of these spots at Geneseo in the state of New York, from which the bones,
+skull, and tusk of a Mastodon had been procured in the marl below a layer
+of black peaty earth, and ascertained that all the associated freshwater
+and land shells were of a species now common in the same district. They
+consisted of several species of _Lymnea_, of _Planorbis bicarinatus_,
+_Physa heterostropha_, &c.
+
+In 1845 no less than six skeletons of the same species of Mastodon were
+found in Warren County, New Jersey, 6 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. But nearly the
+whole of the other skeleton, which lay about 10 feet apart from the rest,
+was preserved entire, and proved the correctness of Cuvier's conjecture
+respecting this extinct animal, namely, that it had twenty ribs like the
+living elephant. From the clay in the interior within the ribs, just where
+the contents of the stomach might naturally have been looked for, seven
+bushels of vegetable matter were extracted. I submitted some of this matter
+to Mr. A. Henfrey of London for microscopic examination, and he informs me
+that it consists of pieces of small twigs of a coniferous tree of the
+Cypress family, probably the young shoots of the white cedar, _Thuja
+occidentalis_, still a native of North America, on which therefore we may
+conclude that this extinct Mastodon once fed.
+
+Another specimen of the same quadruped, the most complete and probably the
+largest ever found, was exhumed in 1845 in the town of Newburg, New York,
+the length of the skeleton being 25 feet, and its height 12 feet. The
+anchylosing of the last two ribs on the right side afforded Dr. John C.
+Warren a true gauge for the space occupied by the intervertebrate
+substance, so as to enable him to form a correct estimate of the entire
+length. The tusks when discovered were 10 feet long, but a part only could
+be preserved. The large proportion of animal matter in the tusk, teeth, and
+bones of some of these fossil mammalia is truly astonishing. It amounts in
+some cases, as Dr. C. T. Jackson has ascertained by analysis, to 27 per
+cent., so that when all the earthy ingredients are removed by acids, the
+form of the bone remains as perfect, and the mass of animal matter is
+almost as firm, as in a recent bone subjected to similar treatment.
+
+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_, _Valvata_, _Cyclas_, _Unio_, and _Helix_, &c.,
+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.
+
+Whether or not, in assigning a period of more than 30,000 years for the
+recession of the Falls from Queenstown to their present site, I have over
+or under estimated the time required for that operation, no one can doubt
+that a vast number of centuries must have elapsed before so great a series
+of geographical changes were brought about as have occurred since the
+entombment of this elephantine quadruped. The freshwater gravel which
+incloses it is decidedly of much more modern origin than the drift or
+boulder clay of the same region.[138-A]
+
+Other extinct animals accompany the _Mastodon giganteus_ in the
+post-glacial deposits of the United States, among which the _Castoroides
+ohioensis_, Foster and Wyman, a huge rodent allied to the beaver, and
+the _Capybara_ may be mentioned. But whether the "loess," and other
+freshwater and marine strata of the Southern States, in which skeletons
+of the same Mastodon are mingled with the bones of the Megatherium,
+Mylodon, and Megalonyx, were contemporaneous with the drift, or were of
+subsequent date, is a chronological question still open to discussion.
+It appears clear, however, from what we know of the tertiary fossils of
+Europe--and I believe the same will hold true in North America--that
+many species of testacea and some mammalia, which existed prior to the
+glacial epoch, survived that era. As European examples among the
+warm-blooded quadrupeds, the _Elephas primigenius_ and _Rhinoceros
+tichorinus_ may be mentioned. As to the shells, whether fresh water,
+terrestrial, or marine, they need not be enumerated here, as allusion
+will be made to them in the sequel, when the pliocene tertiary fossils
+of Suffolk are described. The fact is important, as refuting the
+hypothesis that the cold of the glacial period was so intense and
+universal as to annihilate all living creatures throughout the globe.
+
+That the cold was greater for a time than it is now in certain parts of
+Siberia, Europe, and North America, will not be disputed; but, before we
+can infer the universality of a colder climate, we must ascertain what was
+the condition of other parts of the northern, and of the whole southern,
+hemisphere at the time when the Scandinavian, British, and Alpine erratics
+were transported into their present position. It must not be forgotten that
+a great deposit of drift and erratic blocks is now in full progress of
+formation in the southern hemisphere, in a zone corresponding in latitude
+to the Baltic, and to Northern Italy, Switzerland, France, and England.
+Should the uneven bed of the southern ocean be hereafter converted by
+upheaval into land, the hills and valleys will be strewed over with
+transported fragments, some derived from the antarctic continent, others
+from islands covered with glaciers, like South Georgia, which must now be
+centres of the dispersion of drift, although situated in a latitude,
+agreeing with that of the Cumberland mountains in England.
+
+Not only are these operations going on between the 45th and 60th parallels
+of latitude south of the line, while the corresponding zone of Europe is
+free from ice; but, what is still more worthy of remark, we find in the
+southern hemisphere itself, only 900 miles distant from South Georgia,
+where the perpetual snow reaches to the sea-beach, lands covered with
+forests, as in Terra del Fuego. There is here no difference of latitude to
+account for the luxuriance of vegetation in one spot, and the absolute want
+of it in the other; but among other refrigerating causes in South Georgia
+may be enumerated the countless icebergs which float from the antarctic
+zone, and which chill, as they melt, the waters of the ocean, and the
+surrounding air, which they fill with dense fogs.
+
+I have endeavoured in the "Principles of Geology," chapters 7. and 8., to
+point out the intimate connexion of climate and the physical geography of
+the globe, and the dependence of the mean annual temperature, not only on
+the height of the dry land, but on its distribution in high or low
+latitudes at particular epochs. If, for example, at certain periods of the
+past, the antarctic land was less elevated and less extensive than now,
+while that at the north pole was higher and more continuous, the conditions
+of the northern and southern hemispheres might have been the reverse of
+what we now witness in regard to climate, although the mountains of
+Scandinavia, Scotland, and Switzerland, may have been less elevated than at
+present. But if in both of the polar regions a considerable area of
+elevated dry land existed, such a concurrence of refrigerating conditions
+in both hemispheres might have created for a time an intensity of cold
+never experienced since; and such probably was the state of things during
+that period of submergence to which I have alluded in this chapter.
+
+_Alpine erratics._--Although the arctic regions constitute the great centre
+from which erratics have travelled southwards in all directions in Europe
+and North America, yet there are some mountains, as I have already stated,
+like those of North Wales and the Alps, which have served as separate and
+independent centres for the dispersion of blocks. In illustration of this
+fact, the Alps deserve particular attention, not only from their magnitude,
+but because they lie beyond the ordinary limits of the "northern drift" of
+Europe, being situated between the 44th and 47th degrees of north latitude.
+On the flanks of these mountains, and on the Subalpine ranges of hills or
+plains adjoining them, those appearances which have been so often alluded
+to, as distinguishing or accompanying the drift, between the 50th and 70th
+parallels of north latitude, suddenly reappear, to assume in a more
+southern country their most exaggerated form. Where the Alps are highest,
+the largest erratic blocks have been sent forth, as, for example, from the
+regions of Mont Blanc and Monte Rosa, into the adjoining parts of France,
+Switzerland, Austria, and Italy, while in districts where the great chain
+sinks in altitude, as in Carinthia, Carniola, and elsewhere, no such rocky
+fragments, or a few only and of smaller bulk, have been detached and
+transported to a distance.
+
+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
+afterwards acknowledged by M. Charpentier, who strengthened them by new
+observations and arguments, and declared, in 1836, his conviction that the
+glaciers of the Alps must once have reached as far as the Jura, and have
+carried thither their moraines across the great valley of Switzerland. M.
+Agassiz, after several excursions in the Alps with M. Charpentier, and
+after devoting himself some years to the study of glaciers, published, in
+1840, an admirable description of them, and of the marks which attest the
+former action of great masses of ice over the entire surface of the Alps
+and the surrounding country.[140-A] He pointed out that the surface of
+every large glacier is strewed over with gravel and stones detached from
+the surrounding precipices by frost, rain, lightning, or avalanches. And he
+described more carefully than preceding writers the long lines of these
+stones, which settle on the sides of the glacier, and are called the
+lateral moraines; those found at the lower end of the ice being called
+terminal moraines. Such heaps of earth and boulders every glacier pushes
+before it when advancing, and leaves behind it when retreating. When the
+Alpine glacier reaches a lower and warmer situation, about 3000 or 4000
+feet above the sea, it melts so rapidly that, in spite of the downward
+movement of the mass, it can advance no farther. Its precise limits are
+variable from year to year, and still more so from century to century; one
+example being on record of a recession of half a mile in a single year. We
+also learn from M. Venetz, that whereas, between the eleventh and fifteenth
+centuries, all the Alpine glaciers were less advanced than now, they began
+in the seventeenth and eighteenth centuries to push forward so as to cover
+roads formerly open, and to overwhelm forests of ancient growth.
+
+These oscillations enable the geologist to note the marks which they leave
+behind them as they retrograde, and among these the most prominent, as
+before stated, are the terminal moraines, or mounds of unstratified earth
+and stones, often divided by subsequent floods into hillocks, which cross
+the valley like ancient earth-works, or embankments made to dam up the
+river. Some of these transverse barriers were formerly pointed out by
+Saussure below the glacier of the Rhone, as proving how far it had once
+transgressed its present boundaries. On these moraines we see many large
+angular fragments, which, having been carried along on the surface of the
+ice, have not had their edges worn off by friction; but the greater number
+of the boulders, even those of large size, have been well rounded, not by
+the power of water, but by the mechanical force of the ice, which has
+pushed them against each other, or against the rocks flanking the valley.
+Others have fallen down the numerous fissures which intersect the glacier,
+where, being subject to the pressure of the whole mass of ice, they have
+been forced along, and either well rounded or ground down into sand, or
+even the finest mud, of which the moraine is largely constituted.
+
+As the terminal moraines are the most prominent of all the monuments left
+by a receding glacier, so are they the most liable to obliteration; for
+violent floods or debacles are often occasioned in the Alps by the sudden
+bursting of what are called glacier-lakes. These temporary sheets of water
+are caused by the damming up of a river by a glacier which has increased
+during a succession of cold seasons, and, descending from a tributary into
+the main valley, has crossed it from side to side. On the failure of this
+icy barrier, the accumulated waters are let loose, which sweep away and
+level all transverse mounds of gravel and loose boulder below, and spread
+their materials in confused and irregular beds over the river-plain.
+
+Another mark of the former action of glaciers, in situations where they
+exist no longer, is the polished, striated, and grooved surfaces of rocks
+already alluded to. Stones which lie underneath the glacier and are pushed
+along by it, sometimes adhere to the ice, and as the mass glides slowly
+along at the rate of a few inches, or at the utmost two or three feet, per
+day, abrade, groove, and polish the rock, and the larger blocks are
+reciprocally grooved and polished by the rock on their lower sides. As the
+forces both of pressure and propulsion are enormous, the sand, acting like
+emery, polishes the surface; the pebbles, like coarse gravers, scratch and
+furrow it; and the large stones scoop out grooves in it. Another effect
+also of this action, not yet adverted to, is called "roches moutonnées."
+Projecting eminences of rock are smoothed and worn into the shape of
+flattened domes, where the glaciers have passed over them.
+
+Although the surface of almost every kind of rock, when exposed in the open
+air, wastes away by decomposition, yet some retain for ages their polished
+and furrowed exterior; and, if they are well protected by a covering of
+clay or turf, these marks of abrasion seem capable of enduring for ever.
+They have been traced in the Alps to great heights above the present
+glaciers, and to great horizontal distances beyond them.
+
+There are also found, on the sides of the Swiss valleys, round and deep
+holes, with polished sides, such holes as waterfalls make in the solid
+rock, but in places remote from running waters, and where the form of the
+surface will not permit us to suppose that any cascade could ever have
+existed. Similar cavities are common in hard rocks, such as gneiss, in
+Sweden, where they are called _giant caldrons_, and are sometimes 10 feet
+and more in depth; but in the Alps and Jura they often pass into
+spoon-shaped excavations and prolonged gutters. We learn from M. Agassiz
+that hollows of this form are now cut out by streams of water, which flow
+along the surface of glaciers, and then fall into fissures which are open
+to the bottom. Here, forming a cascade, the stream cuts a round cavity in
+the rock with the gravel and sand, which it either finds there or carries
+down with it, and causes to rotate; and, as it usually happens that the
+glacier is advancing, a locomotive cascade is produced, which converts the
+first circular hole into a deep groove.
+
+Another effect of a glacier is to lodge a ring of stones round the summit
+of a conical peak which may happen to project through the ice. If the
+glacier is lowered greatly by melting, these circles of large angular
+fragments, which are called "perched blocks," are left in a singular
+situation near the top of a steep hill or pinnacle, the lower parts of
+which may be destitute of boulders.
+
+_Alpine blocks on the Jura._--Now some or all the marks above
+enumerated,--the moraines, erratics, polished surfaces, domes, striæ,
+caldrons, and perched rocks, are observed in the Alps at great heights
+above the present glaciers, and far below their actual extremities; also
+in the great valley of Switzerland, 50 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
+is now entirely destitute of glaciers, yet it presents almost everywhere
+similar moraines, and the same polished and grooved surfaces, and
+water-worn cavities. 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 incontestible 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 50 miles and upwards across one of the widest and deepest
+valleys of the world, so that they are now lodged on the hills and
+valleys of 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, celebrated under the name of Pierre à Bot, rests on the side
+of a hill about 900 feet above the lake of Neufchatel, and is no less
+than 40 feet in diameter.
+
+It will be remarked that these blocks on the Jura offer an exception to the
+rule before laid down, as applicable in general to erratics, since they
+have gone from south to north. Some of the largest masses of granite and
+gneiss have been found to contain 50,000 and 60,000 cubic feet of stone,
+and one limestone block near Devens, which has travelled 30 miles, contains
+161,000 cubic feet, its angles being sharp and unworn.[143-A]
+
+Von Buch, Escher, and Studer have shown, from an examination of the
+mineral composition of the boulders, that those on the western Jura,
+near Neufchatel, have come from the region of Mont Blanc and the Valais;
+those on the middle parts of the Jura from the Bernese Oberland; and
+those on the eastern Jura from the Alps of the small cantons, Glaris,
+Schwytz, Uri, and Zug. The blocks, therefore, of these three great
+districts have been derived from parts of the Alps nearest to the
+localities in the Jura where we now find them, as if they had crossed
+the great valley in a direction at right angles to its length: the most
+western stream having followed the course of the Rhone; the central,
+that of the Aar; and the eastern, that of the two great rivers, Reuss
+and Limmat. The non-intermixture of these groups of travelled fragments,
+except near their confines, was always regarded as most enigmatical by
+those who adopted the opinion of Saussure, that they were all whirled
+along by a rapid current of muddy water rushing from the Alps.
+
+M. Charpentier first suggested, as before mentioned, that the Swiss
+glaciers once reached continuously to the Jura, and conveyed to them
+these erratics; but at the same time he conceived that the Alps were
+formerly higher than now. M. Agassiz, on the other hand, instead of
+introducing distinct and separate glaciers, imagines that the whole
+valley of Switzerland was filled with ice, and that one great sheet of
+it extended from the Alps to the Jura, when the two chains were of the
+same height as now relatively to each other. Such an hypothesis labours
+under this difficulty, that the difference of altitude, when distributed
+over a space of 50 miles, gives an inclination of no more than two
+degrees, or far less than that of any known glaciers. It has, however,
+since received the able support of Professor James Forbes, in his
+excellent work on the Alps, published in 1843.
+
+In the theory which I formerly advanced, jointly with Mr. Darwin[143-B],
+it was suggested that the erratics may have been transferred by floating
+ice to the Jura, at the time when the greater part of that chain, and the
+whole of the Swiss valley to the south, was under the sea. At that period
+the Alps may have attained only half their present altitude, and may yet
+have constituted a chain as lofty as the Chilian Andes, which, in a
+latitude corresponding to Switzerland, now send down glaciers to the head
+of every sound, from which icebergs, covered with blocks of granite, are
+floated seaward.[144-A] Opposite that part of Chili where the glaciers
+abound is situated the island of Chiloe, 100 miles in length, with a
+breadth of 30 miles, running parallel to the continent. The channel which
+separates it from the main land is of considerable depth, and 25 miles
+broad. Parts of its surface, like the adjacent coast of Chili, are
+overspread with recent marine shells, showing an upheaval of the land
+during a very modern period; and beneath these shells is a boulder deposit,
+in which Mr. Darwin found large travelled blocks. One group of fragments
+were of granite, which had evidently come from the Andes, while in another
+place angular blocks of syenite were met with. Their arrangement may have
+been due to successive crops of icebergs issuing from different sounds, to
+the heads of which glaciers descend from the Andes. These icebergs, taking
+their departure year after year from distinct points, may have been
+stranded repeatedly, in equally distinct groups, in bays or creeks of
+Chiloe, and on islets off the coast, so as afterwards to appear, some on
+hills and others in valleys, when that country and the bed of the adjacent
+sea had been upheaved. A continuance in future of the elevatory movement,
+in the region of the Andes and of Chiloe, might cause the former chain to
+rival the Alps in altitude, and give to Chiloe a height equal to that of
+the Jura. The same rise might dry up the channel between Chiloe and the
+main land, so that it would then represent the great valley of Switzerland.
+In the course of these changes, all parts of Chiloe and the intervening
+strait, having in their turn been a sea-shore, may have been polished and
+scratched by coast-ice, and by innumerable icebergs running aground and
+grating on the bottom.
+
+If we apply this hypothesis to Switzerland and the Jura, we are by no means
+precluded from the supposition that, in proportion as the land acquired
+additional height, and the bed of the sea emerged, the Jura itself may have
+had its glaciers; and those existing in the Alps, which had at first
+extended to the sea, may, during some part of the period of upheaval, have
+been prolonged much farther into the valleys than now. At a later period,
+when the climate grew milder, these glaciers may have entirely disappeared
+from the Jura, and may have receded in the Alps to their present limits,
+leaving behind them in both districts those moraines which now attest the
+former extension of the ice.[144-B]
+
+_Meteorites in drift._--Before concluding my remarks on the northern drift
+of the Old World, I shall refer to a fact recently announced, the discovery
+of a meteoric stone at a great depth in the alluvium of Northern Asia.
+
+Erman, in his Archives of Russia for 1841 (p. 314.), cites a very
+circumstantial account drawn up by a Russian miner of the finding of a mass
+of meteoric iron in the auriferous alluvium of the Altai. Some small
+fragments of native iron were first met with in the gold-washings of
+Petropawlowsker in the Mrassker Circle; but though they attracted
+attention, it was supposed that they must have been broken off from the
+tools of the workmen. At length, at the depth of 31 feet 5 inches from the
+surface, they dug out a piece of iron weighing 17-1/2 pounds, of a
+steel-grey colour, somewhat harder than ordinary iron, and, on analysing
+it, found it to consist of native iron, with a small proportion of nickel,
+as usual in meteoric stones. It was buried in the bottom of the deposit
+where the gravel rested on a flaggy limestone. Much brown iron ore, as well
+as gold, occurs in the same gravel, which appears to be part of that
+extensive auriferous formation in which the bones of the mammoth, the
+_Rhinoceros tichorhinus_, and other extinct quadrupeds abound. No
+sufficient data are supplied to enable us to determine whether it be of
+Post-Pliocene or Newer Pliocene date.
+
+We ought not, I think, to feel surprise that we have not hitherto succeeded
+in detecting the signs of such aërolites in older rocks, for, besides their
+rarity in our own days, those which fell into the sea (and it is with
+marine strata that geologists have usually to deal), being chiefly composed
+of native iron, would rapidly enter into new chemical combinations, the
+water and mud being charged with chloride of sodium and other salts. We
+find that anchors, cannon, and other cast-iron implements which have been
+buried for a few hundred years off our English coast have decomposed in
+part or entirely, turning the sand and gravel which enclosed them into a
+conglomerate, cemented together by oxide of iron. In like manner meteoric
+iron, although its rusting would be somewhat checked by the alloy of
+nickel, could scarcely ever fail to decompose in the course of thousands of
+years, becoming oxide, sulphuret or carbonate of iron, and its origin being
+then no longer distinguishable. The greater the antiquity of rocks,--the
+oftener they have been heated and cooled, permeated by gases or by the
+waters of the sea, the atmosphere or mineral springs,--the smaller must be
+the chance of meeting with a mass of native iron unaltered; but the
+preservation of the ancient meteorite of the Altai, and the presence of
+nickel in these curious bodies, renders the recognition of them in deposits
+of remote periods less hopeless than we might have anticipated.
+
+
+FOOTNOTES:
+
+[134-A] Geol. Trans. 2d series, vol. vi. p. 135. Mr. Smith of Jordanhill
+had arrived at similar conclusions as to climate from the shells of the
+Scotch Pleistocene deposits.
+
+[134-B] Proceedings of Geol. Soc. No. 63. p. 119.
+
+[135-A] Travels in N. America, vol. ii. p. 141.
+
+[135-B] Ibid. p. 99. chap. xix.
+
+[136-A] Bulletin Soc. Géol. de France, tom. iv. 2de sér. p. 1121.
+
+[138-A] See Travels in N. America, vol. i. chap. ii.
+
+[140-A] Agassiz, Etudes sur les Glaciers.
+
+[143-A] Archiac, Hist. des Progrès, &c. vol. ii. p. 249.
+
+[143-B] See Elements of Geology, 2d ed. 1841.
+
+[144-A] Darwin's Journal, p. 283.
+
+[144-B] More recently Sir R. Murchison, having revisited the Alps, has
+declared his opinion that "the great granitic blocks of Mont Blanc were
+translated to the Jura when the intermediate country was under
+water."--Paper read to Geol. Soc. London, May 30, 1849.
+
+
+
+
+CHAPTER XIII.
+
+NEWER PLIOCENE STRATA AND CAVERN DEPOSITS.
+
+   Chronological classification of Pleistocene formations, why
+   difficult--Freshwater deposits in valley of Thames--In Norfolk
+   cliffs--In Patagonia--Comparative longevity of species in the mammalia
+   and testacea--Fluvio-marine crag of Norwich--Newer Pliocene strata of
+   Sicily--Limestone of great thickness and elevation--Alternation of
+   marine and volcanic formations--Proofs of slow accumulation--Great
+   geographical changes in Sicily since the living fauna and flora began
+   to exist--Osseous breccias and cavern deposits--Sicily--Kirkdale--Origin
+   of stalactite--Australian cave-breccias--Geographical relationship of
+   the provinces of living vertebrata and those of the fossil species of
+   the Pliocene periods--Extinct struthious birds of New Zealand--Teeth
+   of fossil quadrupeds.
+
+
+Having in the last chapter treated of the boulder formation and its
+associated freshwater and marine strata as belonging chiefly to the close
+of the Newer Pliocene period, we may now proceed to other deposits of the
+same or nearly the same age. It should, however, be stated that it is
+difficult to draw the line of separation between these modern formations,
+especially when we are called upon to compare deposits of marine and
+freshwater origin, or these again with the ossiferous contents of caverns.
+
+If as often as the carcasses of quadrupeds were buried in alluvium during
+floods, or mired in swamps, or imbedded in lacustrine strata, a stream of
+lava had descended and preserved the alluvial or freshwater deposits, as
+frequently happened in Auvergne (see above, p. 80,), keeping them free from
+intermixture with strata subsequently formed, then indeed the task of
+arranging chronologically the whole series of mammaliferous formations
+might have been easy, even though many species were common to several
+successive groups. But when there have been oscillations in the levels of
+the land, accompanied by the widening and deepening of valleys at more than
+one period,--when the same surface has sometimes been submerged beneath the
+sea, after supporting forests and land quadrupeds, and then raised again,
+and subject during each change of level to sedimentary deposition and
+partial denudation,--and when the drifting of ice by marine currents or by
+rivers, during an epoch of intense cold, has for a season interfered with
+the ordinary mode of transport, or with the geographical range of species,
+we cannot hope speedily to extricate ourselves from the confusion in which
+the classification of these Pleistocene formations is involved.
+
+At several points in the valley of the Thames, remnants of ancient
+fluviatile deposits occur, which may differ considerably in age,
+although the imbedded land and freshwater shells in each are of recent
+species. At Brentford, for example, the bones of the Siberian Mammoth,
+or _Elephas primigenius_, and the _Rhinoceros tichorhinus_, both of
+them quadrupeds of which the flesh and hair have been found preserved in
+the frozen soil of Siberia, occur abundantly, with the bones of an
+hippopotamus, aurochs, short-horned ox, red deer, rein-deer, and great
+cave-tiger or lion.[147-A] A similar group has been found fossil at
+Maidstone, in Kent, and other places, agreeing in general specifically
+with the fossil bones detected in the caverns of England. When we see
+the existing rein-deer and an extinct hippopotamus in the same
+fluviatile loam, we are tempted to indulge our imaginations in
+speculating on the climatal conditions which could have enabled these
+genera to co-exist in the same region. Wherever there is a continuity of
+land from polar to temperate and equatorial regions, there will always
+be points where the southern limit of an arctic species meets the
+northern range of a southern species; and if one or both have migratory
+habits, like the Bengal tiger, the American bison, the musk ox, and
+others, they may each penetrate mutually far into the respective
+provinces of the other. There may also have been several oscillations of
+temperature during the periods which immediately preceded and followed
+the more intense cold of the glacial epoch.
+
+The strata bordering the left bank of the Thames at Grays Thurrock, in
+Essex, are probably of older date than those of Brentford, although the
+associated land and freshwater shells are nearly all, if not all,
+identical with species now living. Three of the shells, however, are no
+longer inhabitants of Great Britain; namely, _Paludina marginata_ (fig.
+112. p. 127.), now living in France; _Unio littoralis_ (fig. 29. p.
+28.), now inhabiting the Loire; and _Cyrena consobrina_ (fig. 26. p.
+28.). The last-mentioned fossil (a recent Egyptian shell of the Nile) is
+very abundant at Grays, and deserves notice, because the genus _Cyrena_
+is now no longer European.
+
+The rhinoceros occurring in the same beds (_R. leptorhinus_, see fig. 131.
+p. 160.) is of a different species from that of Brentford above mentioned,
+and the accompanying elephant belongs to the variety called _Elephas
+meridionalis_, which, according to MM. Owen and H. von Meyer, two high
+authorities, is the same species as the Siberian mammoth, although some
+naturalists regard it as distinct. With the above mammalia is also found
+the _Hippopotamus major_, and what is most remarkable in so modern and
+northern a deposit, a monkey, called by Owen, _Macacus pliocenus_.
+
+The submerged forest already alluded to (p. 130.) as underlying the drift
+at the base of the cliffs of Norfolk is associated with a bed of lignite
+and loam, in which a great number of fossil bones occur, apparently of the
+same group as that of Grays, just mentioned. It has sometimes been called
+"the Elephant bed." One portion of it, which stretches out under the sea at
+Happisburgh, was overgrown in 1820 by a bank of recent oysters, and there
+the fishermen dredged up, according to Woodward, in the course of thirteen
+years, together with the oysters, above 2000 mammoths' grinders.[147-B]
+Another portion of the same continuous stratum has yielded at Bacton,
+Cromer, and other places on the coast, the bones of a gigantic beaver
+(_Trogontherium Cuvierii_, Fischer), as well as the ox, horse, and deer,
+and both species of rhinoceros, _R. tichorhinus_ and _R. leptorhinus_.
+
+In studying these and various other similar assemblages of fossils, we have
+a good exemplification of the more rapid rate at which the mammiferous
+fauna, as compared to the testaceous, diverges when traced backwards in
+time from the recent type. I have before hinted, that the longevity of
+species in the class of warm-blooded quadrupeds is less great than in that
+of the mollusca, the latter having probably more capacity for enduring
+those changes of climate and other external circumstances which take place
+in the course of ages on the earth's surface. This phenomenon is by no
+means confined to Europe, for Mr. Darwin found at Bahia Blanca, in South
+America, lat. 39° S., near the northern confines of Patagonia, fossil
+remains of the extinct mammiferous genera Megatherium, Megalonyx, Toxodon,
+and others, associated with shells, almost all of species already
+ascertained to be still living in the contiguous sea[148-A]; the marine
+mollusca, as well as those of rivers, lakes, or the land, having died out
+more slowly than the terrestrial mammalia.
+
+I alluded before (p. 125.) to certain marine strata overlying till near
+Glasgow, and at other points on the Clyde, in which the shells are for the
+most part British, with an intermixture of some arctic species; while
+others, about a tenth of the whole, are supposed to be extinct. This
+formation may also be called Newer Pliocene.
+
+_Fluvio-marine crag of Norwich._--At several places within five miles of
+Norwich, on both banks of the Yare, beds of sand, loam, and gravel,
+provincially termed "crag," occur, in which there is a mixture of marine,
+land, and freshwater shells, with ichthyolites and bones of mammalia. It is
+clear that these beds have been accumulated at the bottom of the sea near
+the mouth of a river. They form patches of variable thickness, resting on
+white chalk, and are covered by a dense mass of stratified flint gravel.
+The surface of the chalk is often perforated to the depth of several inches
+by the _Pholas crispata_, each fossil shell still remaining at the bottom
+of its cylindrical cavity, now filled up with loose sand which has fallen
+from the incumbent crag. This species of Pholas still exists and drills the
+rocks between high and low water on the British coast. The most common
+shells of these strata, such as _Fusus striatus_, _Turritella terebra_,
+_Cardium edule_, and _Cyprina islandica_, are now abundant in the British
+seas; but with them are some extinct species, such as _Nucula Cobboldiæ_
+(fig. 120.) and _Tellina obliqua_ (fig. 121.). _Natica helicoides_ (fig.
+122.) is an example of a species formerly known only as fossil, but which
+has now been found living in our seas.
+
+Among the accompanying bones of mammalia is the _Mastodon_
+_angustidens_[149-A] (see fig. 130.), a portion of the upper jawbone with a
+tooth having been found by Mr. Wigham at Postwick, near Norwich. As this
+species has also been found in the Red Crag, both at Sutton and at
+Felixstow, and had hitherto been regarded as characteristic of formations
+older than the Pleistocene, it may possibly have been washed out of the Red
+into the Norwich Crag.
+
+[Illustration: Fig. 120. _Nucula Cobboldiæ._]
+
+[Illustration: Fig. 121. _Tellina obliqua._]
+
+[Illustration: Fig. 122. _Natica helicoides_, Johnston.]
+
+Among the bones, however, respecting the authenticity of which there
+seems no doubt, may be mentioned those of the elephant, horse, pig,
+deer, and the jaws and teeth of field mice (fig. 141.). I have seen the
+tusk of an elephant from Bramerton near Norwich, to which, many serpulæ
+were attached, showing that it had lain for some time at the bottom of
+the sea of the Norwich Crag.
+
+At Thorpe, near Aldborough, and at Southwold, in Suffolk, this
+fluvio-marine formation is well exposed in the sea-cliffs, consisting of
+sand, shingle, loam, and laminated clay. Some of the strata there bear
+the marks of tranquil deposition, and in one section a thickness of 40
+feet is sometimes exposed to view. Some of the lamellibranchiate shells
+have both valves united, although mixed with land and freshwater
+testacea, and with the bones and teeth of elephant, rhinoceros, horse,
+and deer. Captain Alexander, with whom I examined these strata in 1835,
+showed me a bed rich in marine shells, in which he had found a large
+specimen of the _Fusus striatus_, filled with sand, and in the interior
+of which was the tooth of a horse.
+
+Among the freshwater shells I obtained the _Cyrena consobrina_ (fig. 26.
+p. 28.), before mentioned, supposed to agree with a species now
+living in the Nile.
+
+I formerly classed the Norwich Crag as older Pliocene, conceiving that more
+than a third of the fossil testacea were extinct; but there now seems good
+reason for believing that several of the rarer shells obtained from these
+strata do not really belong to a contemporary fauna, but have been washed
+out of the older beds of the "Red Crag;" while other species, once supposed
+to have died out, have lately been met with living in the British seas.
+According to Mr. Searles Wood, the total number of marine species does not
+exceed seventy-six, of which one tenth only are extinct. Of the fourteen
+associated freshwater shells, all the species appear to be living. Strata
+containing the same shells as those near Norwich have been found by Mr.
+Bean, at Bridlington, in Yorkshire.
+
+_Newer Pliocene strata of Sicily._--In no part of Europe are the Newer
+Pliocene formations seen to enter so largely into the structure of the
+earth's crust, or to rise to such heights above the level of the sea, as in
+Sicily. They cover nearly half the island, and near its centre, at
+Castrogiovanni, they reach an elevation of 3000 feet. They consist
+principally of two divisions, the upper calcareous, 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. Of the
+remainder, which still live, five species are no longer inhabitants of the
+Mediterranean. When I visited Sicily in 1828 I estimated the proportion of
+living species as somewhat greater, partly because I confounded with the
+tertiary formation of central Sicily the strata at the base of Etna, and
+some other localities, where the fossils are now proved to agree entirely
+with the present Mediterranean fauna.
+
+Philippi came to the conclusion, that in Sicily there is a gradual
+passage from beds containing 70 per cent. of recent shells, to those in
+which the whole of the fossils are identical with recent species; but
+his tables appear scarcely to bear out so important a generalization,
+several of the places cited by him in confirmation having as yet
+furnished no more than twenty or thirty species of testacea. The
+Sicilian beds in question probably belong to about the same period as
+the Norwich Crag, although a geologist, accustomed to see nearly all the
+Pleistocene 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 downwards into a sandstone and conglomerate, below
+which is clay and blue marl, like that of the Subapennine hills, 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, volcanos 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_.
+
+In part of the region above alluded to, as, for example, near Lentini, a
+conglomerate occurs in which I observed many pebbles of volcanic rocks
+covered by full grown _serpulæ_. We may explain the origin of these by
+supposing that there were some small volcanic islands which may have been
+destroyed from time to time by the waves, as Graham Island has been swept
+away since 1831. The rounded blocks and pebbles of solid volcanic matter,
+after being rolled for a time on the beach of such temporary islands, were
+carried at length into some tranquil part of the sea, where they lay for
+years, while the marine _serpulæ_ adhered to them, their shells growing and
+covering their surface, as they are seen adhering to the shell figured in
+p. 22. Finally, the bed of pebbles was itself covered with strata of shelly
+limestone. At Vizzini, a town not many miles distant to the S.W., I
+remarked another striking proof of the gradual manner in which these modern
+rocks were formed, and the long intervals of time which elapsed between the
+pouring out of distinct sheets of lava. A bed of oysters no less than 20
+feet in thickness rests upon a current of basaltic lava. The oysters are
+perfectly identifiable with our common eatable species. Upon the oyster
+bed, again, is superimposed a second mass of lava, together with tuff or
+peperino. In the midst of the same alternating igneous and aqueous
+formations is seen near Galieri, not far from Vizzini, a horizontal bed,
+about a foot and a half in thickness, composed entirely of a common
+Mediterranean coral (_Caryophyllia cæspitosa_, Lam.). These corals stand
+erect as they grew; and, after being traced for hundreds of yards, are
+again found at a corresponding height on the opposite side of the valley.
+
+[Illustration: Fig. 123. _Caryophyllia cæspitosa_, Lam.
+(_Cladocora cæspitosa_, Ehr.)
+
+  _a._  Stem with young stem growing from its side.
+  _a*._ Young stem of same twice magnified.
+  _b._  Portion of branch, twice magnified, with the base of a lateral
+        branch; the exterior ridges of the main branch appearing through
+        the lamellæ of the lateral one.
+  _c._  Transverse section of same, proving, by the integrity of the main
+        branch, that the lateral one did not originate in a subdivision
+        of the animal.
+  _d._  A branch, having at its base another laterally united to it, and
+        two young corals at its upper part.
+  _e._  A main branch, with a full grown lateral one.
+  _f._  A perfect terminal star.]
+
+The corals are usually branched, but not by the division of the animals as
+some have supposed, but by the attachment of young individuals to the sides
+of the older ones; and we must understand this mode of increase, in order
+to appreciate the time which was required for the building up of the whole
+bed of coral during the growth of many successive generations.[152-A]
+
+Among the other fossil shells met with in these Sicilian strata, which
+still continue to abound in the Mediterranean, no shell is more
+conspicuous, from its size and frequent occurrence, than the great
+scallop, _Pecten jacobæus_ (see fig. 124.), now so common in the
+neighbouring seas. We see this shell in the calcareous beds at Palermo
+in great numbers, in the limestone at Girgenti, and in that which
+alternates with volcanic rocks in the country between Syracuse and
+Vizzini, often at great heights above the sea.
+
+[Illustration: Fig. 124. _Pecten jacobæus_; half natural size.]
+
+The more we reflect on the preponderating number of these 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 appearance unaltered
+since the Greeks first colonised the island.
+
+The modern geological date of the rocks in this region leads to another
+singular and unexpected conclusion, namely, that the fauna and flora of a
+large part of Sicily are of higher antiquity than the country itself,
+having not only flourished before the lands were raised from the deep, but
+even before their materials were brought together beneath the waters. The
+chain of reasoning which conducts us to this opinion may be stated in a few
+words. The larger part of the island has been converted from sea into land
+since the Mediterranean was peopled with nearly all the living species of
+testacea and zoophytes. We may therefore presume that, before this region
+emerged, the same land and river shells, and almost all the same animals
+and plants, were in existence which now people Sicily; for the terrestrial
+fauna and flora of this island are precisely the same as that of other
+lands surrounding the Mediterranean. There appear to be no peculiar or
+indigenous species, and those which are now established there must be
+supposed to have migrated from pre-existing lands, just as the plants and
+animals of the Neapolitan territory have colonised Monte Nuovo, since that
+volcanic cone was thrown up in the sixteenth century.
+
+Such conclusions throw a new light on the adaptation of the attributes
+and migratory habits of animals and plants to the changes which are
+unceasingly in progress in the physical geography of the globe. It is
+clear that the duration of species is so great, that they are destined
+to outlive many important revolutions in the configuration of the
+earth's surface; and hence those innumerable contrivances for enabling
+the subjects of the animal and vegetable creation to extend their range;
+the inhabitants of the land being often carried across the ocean, and
+the aquatic tribes over great continental spaces. It is obviously
+expedient that the terrestrial and fluviatile species should not only be
+fitted for the rivers, valleys, plains, and mountains which exist at the
+era of their creation, but for others that are destined to be formed
+before the species shall become extinct; and, in like manner, the marine
+species are not only made for the deep and shallow regions of the ocean
+existing at the time when they are called into being, but for tracts
+that may be submerged or variously altered in depth during the time that
+is allotted for their continuance on the globe.
+
+
+OSSEOUS BRECCIAS AND DEPOSITS IN CAVES OF THE PLIOCENE PERIOD.
+
+_Sicily._--Caverns filled with marine breccias, at the base of ancient
+sea-cliffs, have been already mentioned in the sixth chapter; and it was
+noticed, respecting the cave of San Ciro, near Palermo (p. 75.), that upon
+a bed of sand filled with sea-shells, almost all of recent species, rests
+a breccia (_b_, fig. 93.), composed of fragments of calcareous rock, and
+the bones of animals. In the sand at the bottom of that cave, Dr. Philippi
+found about forty-five marine shells, all clearly identical with recent
+species, except two or three. The bones in the incumbent breccia are
+chiefly those of the mammoth (_E. primigenius_), with some belonging to an
+hippopotamus, distinct from the recent species, and smaller than that
+usually found fossil. (See fig. 132.) Several species of deer also, and,
+according to some accounts, the remains of a bear, were discovered. These
+mammalia are probably referable to the Post-Pliocene period.
+
+The Newer Pliocene tertiary limestone of the south of Sicily, already
+described, is sometimes full of caverns; and the student will at once
+perceive that all the quadrupeds of which the remains are found in the
+stalactite of these caverns, being of later origin than the rocks, must be
+referable to the close of the tertiary epoch, if not of still later date.
+The situation of one of these caves, in the valley of Sortino, is
+represented in the annexed section.
+
+[Illustration: Fig. 125. Cross section.
+
+  _a_. Alluvium,                 } containing the remains of quadrupeds
+  _b_, _b_. Deposits in caves,   } for the most part extinct.
+
+  C. Limestone, containing the remains of shells, of which between 70 and
+                80 per cent. are recent.]
+
+_England._--In a cave at Kirkdale, about twenty-five miles N.N.E. of York,
+the remains of about 300 hyænas, belonging to individuals of every age,
+have been detected. The species (_Hyæna spelæa_) is extinct, and was larger
+than the fierce _Hyæna crocuta_ of South Africa, which it most resembled.
+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.
+
+No less than thirty-seven species of mammalia are enumerated by Professor
+Owen as having been discovered in the caves of the British islands, of
+which eighteen appear to be extinct, while the others still survive in
+Europe. They were not washed to the spots where the fossils now occur by a
+great flood; but lived and died, one generation after another, in the
+places where they lie buried. Among other arguments in favour of this
+conclusion may be mentioned the great numbers of the shed antlers of deer
+discovered in caves and in freshwater strata throughout England.[155-A]
+
+Examples also occur of fissures into which animals have fallen from time to
+time, or have been washed in from above, together with alluvial matter and
+fragments of rock detached by frost, forming a mass which may be united
+into a bony breccia by stalagmitic infiltrations. Frequently we discover a
+long suite of caverns connected by narrow and irregular galleries, which
+hold a tortuous course through the interior of mountains, and seem to have
+served as the subterranean channels of springs and engulphed rivers. Many
+streams in the Morea are now carrying bones, pebbles, and mud into
+underground passages of this kind.[155-B] If, at some future period, the
+form of that country should be wholly altered by subterranean movements and
+new valleys shaped out by denudation, many portions of the former channels
+of these engulphed streams may communicate with the surface, and become the
+dens of wild beasts, or the recesses to which quadrupeds retreat to die.
+Certain caves of France, Germany, and Belgium, may have passed successively
+through these different conditions, and in their last state may have
+remained open to the day for several tertiary periods. It is nevertheless
+remarkable, that on the continent of Europe, as in England, the fossil
+remains of mammalia belong almost exclusively to those of the Newer
+Pliocene and Post-Pliocene periods, and not to the Miocene or Eocene
+epochs, and when they are accompanied by land or river shells, these agree
+in great part, or entirely, with recent species.
+
+As the preservation of the fossil bones is due to a slow and constant
+supply of stalactite, brought into the caverns by water dropping from the
+roof, the source and origin of this deposit has been a subject of curious
+inquiry. The following explanation of the phenomenon has been recently
+suggested by the eminent chemist Liebig. On the surface of Franconia, where
+the limestone abounds in caverns, is a fertile soil, in which vegetable
+matter is continually decaying. This 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.
+
+_Australian cave-breccias._--Ossiferous breccias are not confined to
+Europe, but occur in all parts of the globe; and those lately 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.
+
+Some of these caves have been examined by 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 found most abundantly are those of the kangaroo, of which there
+are four species, besides which the genera _Hypsiprymnus_, _Phalangista_,
+_Phascolomys_, and _Dasyurus_, occur. There are also bones, formerly
+conjectured by some osteologists to belong to the hippopotamus, and by
+others to the dugong, but which are now referred by Mr. Owen to a marsupial
+genus, allied to the _Wombat_.
+
+[Illustration: Fig. 126. _Macropus atlas_, Owen.
+
+_a._ permanent false molar, in the alveolus.]
+
+[Illustration: Fig. 127. Lowest jaw of largest living species of kangaroo.
+(_Macropus major._)]
+
+In the fossils above enumerated, several species are larger than the
+largest living ones of the same genera now known in Australia. The annexed
+figure 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. 127. 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. 126.) 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. In fig. 128. a
+front tooth of the same species of kangaroo is represented.
+
+[Illustration: Fig. 128. Incisor of _Macropus_.]
+
+Whether the breccias, above alluded to, of the Wellington Valley, appertain
+strictly to the Pliocene period cannot be affirmed with certainty, until we
+are more thoroughly acquainted with the recent quadrupeds of the same
+district, and until we learn what species of fossil land shells, if any,
+are buried in the deposits of the same caves.
+
+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 organization 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 the eras immediately antecedent to the human,
+namely, that the present geographical distribution of organic _forms_ dates
+back to a period anterior to the creation of existing _species_; in other
+words, the limitation of particular genera or families of quadrupeds,
+mollusca, &c., to certain existing provinces of land and sea, began before
+the species now contemporary with man had been introduced into the earth.
+
+Mr. 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 characterize 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; and when in
+Georgia in 1845, I ascertained that the Megatherium, Mylodon, _Harlanus
+americanus_ (Owen), _Equus curvidens_, and other quadrupeds allied to the
+Pampean type were posterior in date to beds containing marine shells
+belonging to forty-five recent species of the neighbouring sea.
+
+There are indeed some cosmopolite genera, such as the Mastodon (a genus of
+the elephant family), and the horse, which were simultaneously represented
+by different fossil species in Europe, North America, and South America;
+but these few exceptions can by no means invalidate the rule which has been
+thus expressed by Professor Owen, "that in the highest organized class of
+animals the same forms were restricted to the same great provinces at the
+Pliocene periods as they are at the present day."
+
+However modern, in a geological point of view, we may consider the
+Pleistocene epoch, it is evident that causes more general and powerful
+than the intervention of man have occasioned the disappearance of the
+ancient fauna from so many extensive regions. Not a few of the species
+had a wide range; the same Megatherium, for instance, extended from
+Patagonia and the river Plata in South America, between latitudes 31°
+and 39° south, to corresponding latitudes in North America, the same
+animal being also an inhabitant of the intermediate country of Brazil,
+where its fossil remains have been met with in caves. The extinct
+elephant, likewise, of Georgia (_Elephas primigenius_) has been traced
+in a fossil state northward from the river Alatamaha, in lat. 33° 50' N.
+to the polar regions, and then again in the eastern hemisphere from
+Siberia to the south of Europe. If it be objected that, notwithstanding
+the adaptation of such quadrupeds to a variety of climates and
+geographical conditions, their great size exposed them to extermination
+by the first hunter tribes, we may observe that the investigations of
+Lund and Clausen in the ossiferous limestone caves of Brazil have
+demonstrated that these large mammalia were associated with a great many
+smaller quadrupeds, some of them as diminutive as field mice, which have
+all died out together, while the land shells formerly their
+contemporaries still continue to exist in the same countries. As we may
+feel assured that these minute quadrupeds could never have been
+extirpated by man, so we may conclude that all the species, small and
+great, have been annihilated one after the other, in the course of
+indefinite ages, by those changes of circumstances in the organic and
+inorganic world which are always in progress, and are capable in the
+course of time of greatly modifying the physical geography, climate, and
+all other conditions on which the continuance upon the earth of any
+living being must depend.[158-A]
+
+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 Xivi, by the natives (_Apteryx_). In the fossils of
+the Post-Pliocene and Pleistocene 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 4, some 7, others 9, and others 11 feet
+in height! It seems doubtful whether any contemporary mammalia shared
+the land with this population of gigantic feathered bipeds.
+
+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 quadruped 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. The
+annexed figures, all taken from original specimens, may be useful in
+assisting the student to recognize the teeth of many genera most frequently
+found fossil in Europe:--
+
+[Illustration: Fig. 129. _Elephas primigenius_ (or Mammoth); molar of upper
+jaw, right side; one third of nat. size.
+
+  _a._ grinding surface.
+  _b._ side view.]
+
+[Illustration: Fig. 130. _Mastodon angustidens_ (Norwich Crag, Postwick,
+also found in Red Crag, see p. 149.); second true molar, left side, upper
+jaw; grinding surface, nat. size. (See p. 149.)]
+
+[Illustration: Fig. 131. Rhinoceros.
+
+_Rhinoceros leptorhinus_; fossil from freshwater beds of Grays, Essex
+(see p. 147.); penultimate molar, lower jaw, left side; two-thirds
+of nat. size.]
+
+[Illustration: Fig. 132. Hippopotamus.
+
+Hippopotamus; from cave near Palermo (see p. 154.); molar tooth; two-thirds
+of nat. size.]
+
+[Illustration: Fig. 133. Pig.
+
+_Sus scrofa_, Lin. (common pig); from shell-marl, Forfarshire; posterior
+molar, lower jaw, nat. size.]
+
+[Illustration: Fig. 134. Horse.
+
+_Equus caballus_, Lin. (common horse); from the shell marl, Forfarshire;
+second molar, lower jaw.
+
+  _a._ grinding surface, two-thirds nat. size.
+  _b._ side view of same, half nat. size.]
+
+[Illustration: Fig. 135. Tapir.
+
+_Tapirus Americanus_; recent; third molar, upper jaw; nat. size.]
+
+[Illustration: Fig. 136. _a._ _b._ Deer.
+
+Elk (_Cervus alces_, Lin.); recent; molar of upper jaw.
+
+  _a._ grinding surface.
+  _b._ side view; two-thirds of nat. size.]
+
+[Illustration: Fig. 137. _c._ _d._ Ox.
+
+Ox, common, from shell marl, Forfarshire; true molar upper jaw;
+two-thirds nat. size.
+
+  _c._ grinding surface.
+  _d._ side view.]
+
+[Illustration: Fig. 138. Bear.
+
+  _a._ canine tooth or tusk of bear (_Ursus spelæus_); from cave
+       near Liege.
+  _b._ molar of left side, upper jaw; one third of nat. size.]
+
+[Illustration: Fig. 139. Tiger.
+
+  _c._ canine tooth of tiger (_Felis tigris_); recent.
+  _d._ outside view of posterior molar, lower jaw; one-third of nat. size.]
+
+[Illustration: Fig. 140. _Hyæna spelæa_; second molar, left side, lower
+jaw; nat. size. Cave of Kirkdale. (See p. 154.)]
+
+[Illustration: Fig. 141. Teeth of a new species of _Arvicola_
+(field-mouse); from the Norwich Crag. (See p. 149.)
+
+  _a._ grinding surface.
+  _b._ side view of same.
+  _c._ nat. size of a and b.]
+
+
+FOOTNOTES:
+
+[147-A] Morris, Geol. Soc. Proceed., 1849.
+
+[147-B] Woodward's Geology of Norfolk.
+
+[148-A] Zool. of Beagle, part 1. pp. 9. 111.
+
+[149-A] Owen, Brit. Foss. Mamm. 271. _Mastodon longirostris_,
+Kaup, see _ibid._
+
+[152-A] I am indebted to Mr. Lonsdale for the details above given
+respecting the structure of this coral.
+
+[155-A] Owen, Brit. Foss. Mam. xxvi., and Buckland, Rel. Dil. 19. 24.
+
+[155-B] See Principles of Geology.
+
+[158-A] See Principles of Geology, chaps. xli. to xliv.
+
+
+
+
+CHAPTER XIV.
+
+OLDER PLIOCENE AND MIOCENE FORMATIONS.
+
+   Strata of Suffolk termed Red and Coralline crag--Fossils, and
+   proportion of recent species--Depth of sea and climate--Reference of
+   Suffolk crag to the older Pliocene period--Migration of many species
+   of shells southwards during the glacial period--Fossil whales--Sub-
+   apennine beds--Asti, Sienna, Rome--Miocene formations--Faluns of
+   Touraine--Depth of sea and littoral character of fauna--Tropical
+   climate implied by the testacea--Proportion of recent species of
+   shells--Faluns more ancient than the Suffolk crag--Miocene strata of
+   Bordeaux and Piedmont--Molasse of Switzerland--Tertiary strata of
+   Lisbon--Older Pliocene and Miocene formations in the United
+   States--Sewâlik Hills in India.
+
+
+The older Pliocene strata, which next claim our attention, are chiefly
+confined, in Great Britain, to the eastern part of the county of Suffolk,
+where, like the Norwich beds already described, they are called "Crag," a
+provincial name given particularly to those masses of shelly sand which
+have been used from very ancient times in agriculture, to fertilize soils
+deficient in calcareous matter. The relative position of the "red crag" in
+Essex to the London clay, may be understood by reference to the
+accompanying diagram (fig. 142.).
+
+[Illustration: Fig. 142. Cross section.]
+
+These deposits, judging by the shells which they contain, appear, according
+to Professor Edward Forbes, to have been formed in a sea of moderate depth,
+generally from 15 to 25 fathoms deep, although in some few spots perhaps
+deeper. But they may, nevertheless, have been accumulated at the distance
+of 40 or 50 miles from land.
+
+The Suffolk crag is divisible into two masses, the upper of which has been
+termed the Red, and the lower the Coralline Crag.[162-A] The upper deposit
+consists chiefly of quartzose sand, with an occasional intermixture of
+shells, for the most part rolled, and sometimes comminuted. The lower or
+Coralline crag is of very limited extent, ranging over an area about 20
+miles in length, and 3 or 4 in breadth, between the rivers Alde and Stour.
+It is generally calcareous and marly--a mass of shells and small corals,
+passing occasionally into a soft building stone. At Sudbourn, near Orford,
+where it assumes this character, are large quarries, in which the bottom of
+it has not been reached at the depth of 50 feet. At some places in the
+neighbourhood, the softer mass is divided by thin flags of hard limestone,
+and corals placed in the upright position in which they grew.
+
+The Red crag is distinguished by the deep ferruginous or ochreous colour of
+its sands and fossils, the Coralline by its white colour. Both formations
+are of moderate thickness; the red crag rarely exceeding 40, and the
+coralline seldom amounting to 20, feet. But their importance is not to be
+estimated by the density of the mass of strata or its geographical extent,
+but by the extraordinary richness of its organic remains, belonging to a
+very peculiar type, which seems to characterize the state of the living
+creation in the north of Europe during the older Pliocene era.
+
+For a large collection of the fish, echinoderms, shells, and corals of the
+deposits in Suffolk, we are indebted to the labours of Mr. Searles Wood. Of
+testacea alone he has obtained from 230 species from the Red, and 345 from
+the Coralline crag, about 150 being common to each. The proportion of
+recent species in the new group is considered by Mr. Wood to be about
+70[162-B] per cent., and that in the older or coralline about 60. When I
+examined these shells of Suffolk in 1835, with the assistance of Dr. Beck,
+Mr. George Sowerby, Mr. Searles Wood, and other eminent conchologists, I
+came to the opinion that the extinct species predominated very decidedly in
+number over the living. Recent investigations, however, have thrown much
+new light on the conchology of the Arctic, Scandinavian, British, and
+Mediterranean Seas. Many of the species formerly known only as fossils of
+the Crag, and supposed to have died out, have been dredged up in a living
+state from depths not previously explored. Other recent species, before
+regarded as distinct from the nearest allied Crag fossils, have been
+observed, when numerous individuals were procured, to be liable to much
+greater variation, both in size and form, than had been suspected, and thus
+have been identified. Consequently, the Crag fauna has been found to
+approach much more nearly to the recent fauna of the Northern, British, and
+Mediterranean Seas than had been imagined. The analogy of the whole group
+of testacea to the European type is very marked, whether we refer to the
+large development of certain genera in number of species or to their size,
+or to the suppression or feeble representation of others. The indication
+also afforded by the entire fauna of a climate not much warmer than that
+now prevailing in corresponding latitudes, prepares us to believe that they
+are not of higher antiquity than the Older Pliocene era.[163-A]
+
+[Illustration: Fig. 143. Section near Ipswich, in Suffolk.
+
+  _a._ Red crag.
+  _b._ Coralline crag.
+  _c._ London clay.]
+
+The position of the red crag in Essex to the subjacent London clay and
+chalk has been already pointed out (fig. 142.). Whenever the two
+divisions are met with in the same district, the red crag lies
+uppermost; and, in some cases, as in the section represented in fig.
+143., it is observed that the older or coralline mass _b_ had suffered
+denudation before the newer formation _a_ was thrown down upon it. At D
+there is not only a distinct cliff, 8 or 10 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. As the older
+formation is shown by its fossils to have accumulated in a deeper sea
+(15, and sometimes 25, fathoms deep or more), there must no doubt have
+been an upheaval of the sea-bottom before the cliff here alluded to was
+shaped out. We may also conclude that so great an amount of denudation
+could scarcely take place, in such incoherent materials, without many 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. The red crag being formed in a shallower sea, often resembles in
+structure a shifting sand bank, its layers being inclined diagonally,
+and the planes of stratification being sometimes directed in the same
+quarry to the four cardinal points of the compass, as at Butley. That
+in this and many other localities, such a structure is not deceptive or
+due to any subsequent concretionary re-arrangement of particles, or to
+mere lines of colour, is proved by each bed being made up of flat pieces
+of shell which lie parallel to the planes of the smaller strata.
+
+Some fossils, which are very abundant in the red crag, have never been
+found in the white or coralline division; as, for example, the _Fusus
+contrarius_ (fig. 144.), and several species of _Buccinum_ (or _Nassa_)
+and _Murex_ (see figs. 145, 146.), which two genera seem wanting in
+the lower crag.
+
+[4 Illustrations: Fossils characteristic of the Red Crag.
+
+Fig. 144. _Fusus contrarius._
+
+Fig. 145. _Murex alveolatus._
+
+Fig. 146. _Nassa granulata._
+
+Fig. 147. _Cypræa coccinelloides._
+
+Fig. 144. half nat. size; the others nat. size.]
+
+Among the bones and teeth of fishes are those of large sharks
+(_Carcharias_), and a gigantic skate of the extinct genus _Myliobates_, and
+many other forms, some common to our seas, and many foreign to them.
+
+The distinctness of the fossils of the coralline crag arises in part from
+higher antiquity, and, in some degree, from a difference in the
+geographical conditions of the submarine bottom. The prolific growth of
+corals, echini, and a prodigious variety of testacea, implies a region of
+deeper and more tranquil water; whereas, the red crag may have formed
+afterwards on the same spot, when the water was shallower. In the mean time
+the climate may have become somewhat cooler, and some of the zoophytes
+which flourished in the first period may have disappeared, so that the
+fauna of the red crag acquired a character somewhat more nearly resembling
+that of our northern seas, as is implied by the large development of
+certain sections of the genera _Fusus_, _Buccinum_, _Purpura_, and
+_Trochus_, proper to higher latitudes, and which are wanting or feebly
+represented in the inferior crag.
+
+Some of the corals of the lower crag of Suffolk belong to genera unknown in
+the living creation, and of a very peculiar structure; as, for example,
+that represented in the annexed fig. (148.), which is one of several
+species having a globular form. The great number and variety of these
+zoophytes probably indicate an equable climate, free from intense cold in
+winter. On the other hand, that the heat was never excessive is confirmed
+by the prevalence of northern forms among the testacea, such as the
+_Glycimeris_, _Cyprina_, and _Astarte_. Of the genus last mentioned (see
+fig. 149.) there are about fourteen species, many of them being rich in
+individuals; and there is an absence of genera peculiar to hot climates,
+such as _Conus_, _Oliva_, _Mitra_, _Fasciolaria_, _Crassatella_, and
+others. The cowries (_Cypræa_, fig. 147.), also, are small, and belong to a
+section (_Trivia_) now inhabiting the colder regions. A large volute,
+called _Voluta Lamberti_ (fig. 150.), may seem an exception; but it differs
+in form from the volutes of the torrid zone, and may, like the living
+_Voluta Magellanica_, have been fitted for an extra-tropical climate.
+
+[Illustration: Fig. 148. _Fascicularia aurantium_, Milne Edwards. Family,
+_Tubuliporidæ_, of same author.
+
+Coral of extinct genus, from the inferior or coralline crag, Suffolk.
+
+  _a._ exterior.
+  _b._ vertical section of interior.
+  _c._ portion of exterior magnified.
+  _d._ portion of interior magnified, showing that it is made up of long,
+       thin, straight tubes, united in conical bundles.]
+
+[Illustration: Fig. 149. _Astarte_ (_Crassina_, Lam.); species common to
+upper and lower crag.
+
+_Astarte Omalii_, Lajonkaire; Syn. _A. bipartita_, Sow. Min. Con. T.
+521. f. 3.; a very variable species most characteristic of the
+coralline crag, Suffolk.]
+
+[Illustration: Fig. 150. _Voluta Lamberti_, young individ.]
+
+The occurrence of a species of _Lingula_ at Sutton 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_,
+allied to _P. reticulata_. Whether, therefore, we may incline to the
+belief that the mean annual temperature was higher or lower than now,
+we may at least infer that the climate and geographical conditions were
+by no means the same at the period of the Suffolk crag as those now
+prevailing in the same region.
+
+Of the echinoderms of the coralline crag about eleven species are known,
+but some of these are in too fragmentary a condition to admit of exact
+comparison. Of six which are the most perfect, Prof. E. Forbes has been
+able to identify three with recent species: one of which, of the genus
+_Echinus_, is British; a second, _Echinocyamus_, British and Mediterranean;
+and a third, _Echinus monilis_, a Mediterranean species, also found fossil
+in the faluns of Touraine.
+
+One of the most interesting conclusions deduced from a careful comparison
+of the shells of these British Older Pliocene strata and those now
+inhabiting our seas, has been pointed out by Prof. E. Forbes. It appears
+that, during the glacial period, a period intermediate, as we have seen,
+between that of the crag and our own times, many shells, previously
+established in the temperate zone, retreated southwards to avoid an
+uncongenial climate. The Professor has given a list of fifty shells which
+inhabited the British seas while the coralline and red crag were forming,
+and which are wanting in the Pleistocene or glacial deposits. They must,
+therefore, after their migration to the south, have made their way
+northwards again. In corroboration of these views, it is stated that all
+these fifty species occur 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.[166-A]
+
+In the red crag at Felixstow, in Suffolk, Professor Henslow has found the
+ear-bones of no less than four species of cetacea, which, according to Mr.
+Owen, are the remains of true whales of the family _Balænidæ_. Mr. Wood is
+of opinion that these cetacea may be of the age of the red crag, or if not
+that they may be derived from the destruction of beds of coralline crag. I
+agree with him that the supposition of their having been washed out of the
+London clay, in which no _Balænidæ_ have yet been met with, is improbable.
+
+Strata containing fossil shells, like those of the Suffolk crag, above
+described, have been found at Antwerp, and on the banks of the Scheldt
+below that city. In 1840 I observed a small patch of them near Valognes, in
+Normandy; and there is also a deposit containing similar fossils at St.
+George Bohon, and several places a few leagues to the S. of Carentan, in
+Normandy; but they have never been traced farther southwards.
+
+_Subapennine strata._--The Apennines, it is well known, are composed
+chiefly of secondary 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, as we have seen (p. 105.), was the first Italian
+geologist who described this newer group in detail, giving it the name of
+the Subapennines; and he classed all the tertiary strata of Italy, from
+Piedmont to Calabria, as parts of the same system. Certain mineral
+characters, he observed, were common to the whole; for the strata consist
+generally of light brown or blue marl, covered by yellow calcareous sand
+and gravel. There are also, he added, some species of fossil shells which
+are found in these deposits throughout the whole of Italy.
+
+We have now, however, satisfactory evidence that the Subapennine beds of
+Brocchi belong, at least, to three periods. To the Miocene we can refer a
+portion of the strata of Piedmont, those of the hill of the Superga, for
+example; to the Older Pliocene, part of the strata of northern Italy, of
+Tuscany, and of Rome; while the tufaceous formations of Naples, of Ischia,
+and the calcareous strata of Otranto, are referable to the Newer Pliocene,
+and in great part to the Post-Pliocene period.
+
+That there is a considerable correspondence in the mineral composition of
+these different Italian groups is undeniable; but not that exact
+resemblance which should lead us to assume a precise identity of age,
+unless the fossil remains agreed very closely. It is now indispensable that
+a new scrutiny should be made in each particular district, of the fossils
+derived from the upper and lower beds--especially such localities as Asti
+and Parma, where the formation attains a great thickness; and at Sienna,
+where the shells of the incumbent yellow sand are generally believed to
+approach much more nearly, as a whole, to the recent fauna of the
+Mediterranean than those in the subjacent blue marl.
+
+The greyish brown or blue marl of the Subapennine formation is very
+aluminous, and usually contains much calcareous matter and scales of mica.
+Near Parma it attains a thickness of 2000 feet, and is charged throughout
+with marine shells, some of which lived in deep, others in shallow water,
+while a few belong to freshwater genera, and must have been washed in by
+rivers. Among these last I have seen the common _Limnea palustris_ in the
+blue marl, filled with small marine shells. The wood and leaves, which
+occasionally form beds of lignite in the same deposit, may have been
+carried into the sea by similar causes. The shells, in general, are soft
+when first taken from the marl, but they become hard when dried. The
+superficial enamel is often well preserved, and many shells retain their
+pearly lustre, part of their external colour, and even the ligament which
+unites the valves. No shells are more usually perfect than the microscopic
+foraminifera, which abound near Sienna, where more than a thousand
+full-grown individuals may be sometimes poured out of the interior of a
+single univalve of moderate dimensions.
+
+The other member of the Subapennine group, the yellow sand and
+conglomerate, constitutes, in most places, a border formation near the
+junction of the tertiary and secondary rocks. In some cases, as near the
+town of Sienna, we see sand and calcareous gravel resting immediately on
+the Apennine limestone, without the intervention of any blue marl.
+Alternations are there seen of beds containing fluviatile shells, with
+others filled exclusively with marine species; and I observed oysters
+attached to many limestone pebbles. This appears to have been a point
+where a river, flowing from the Apennines, entered the sea when the
+tertiary strata were formed.
+
+The sand passes in some districts into a calcareous sandstone, as at San
+Vignone. Its general superposition to the marl, even in parts of Italy and
+Sicily where the date of its origin is very distinct, may be explained if
+we consider that it may represent the deltas of rivers and torrents, which
+gained upon the bed of the sea where blue marl had previously been
+deposited. The latter, being composed of the finer and more transportable
+mud, would be conveyed to a distance, and first occupy the bottom, over
+which sand and pebbles would afterwards be spread, in proportion as rivers
+pushed their deltas farther outwards. In some large tracts of yellow sand
+it is impossible to detect a single fossil, while in other places they
+occur in profusion. Occasionally the shells are silicified, as at San
+Vitale, near Parma, from whence I saw two individuals of recent species,
+one freshwater and the other marine (_Limnea palustris_, and _Cytherea
+concentrica_, Lam.), both perfectly converted into flint.
+
+_Rome._--The seven hills of Rome are composed partly of marine tertiary
+strata, those of Monte Mario, for example, of the Older Pliocene period,
+and partly of superimposed volcanic tuff, on the top of which are usually
+cappings of a fluviatile and lacustrine deposit. Thus, on Mount Aventine,
+the Vatican, and the Capitol, we find beds of calcareous tufa with
+incrusted reeds, and recent terrestrial shells, at the height of about 200
+feet above the alluvial plain of the Tiber. The tusk of the mammoth has
+been procured from this formation, but the shells appear to be all of
+living species, and must have been embedded when the summit of the Capitol
+was a marsh, and constituted one of the lowest hollows of the country as it
+then existed. It is not without interest that we thus discover the
+extremely recent date of a geological event which preceded an historical
+era so remote as the building of Rome.
+
+
+MIOCENE FORMATIONS.
+
+_Faluns of Touraine._--The Miocene strata, corresponding with those named
+by many geologists "Middle Tertiary," will next claim our attention. Near
+the towns of Dinan and Rennes, in Brittany, and again in the provinces
+bordering the Loire, a tertiary formation, containing another assemblage of
+fossils, is met with, to which the name of _Faluns_ has been long given by
+the French agriculturists, who spread the shelly sand and marl over the
+land, in the same manner as the crag was formerly much used in Suffolk.
+Isolated masses of these faluns occur from near the mouth of the Loire,
+near Nantes, as far as a district south of Tours. They are also found at
+Pontlevoy, on the Cher, about 70 miles above the junction of that river
+with the Loire, and 30 miles S.E. of Tours. I have visited all the
+localities above mentioned, and found the beds 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, 10 miles S.W. of Saumur, they form a soft
+building-stone, chiefly composed of an aggregate of broken shells, 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 50
+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, and various secondary formations, including the chalk; and,
+lastly, upon the upper freshwater limestone of the Parisian tertiary
+series, which, as before mentioned (p. 106.), stretches continuously from
+the basin of the Seine to that of the Loire.
+
+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. 45. p. 30.)
+is the most abundant. Remains of terrestrial quadrupeds are here and there
+intermixed, belonging to the genera Deinotherium, Mastodon, Rhinoceros,
+Hippopotamus, Chæropotamus, Dichobune, Deer, and others, and these are
+accompanied by cetacea, such as the Lamantine, Morse, Sea-calf, and
+Dolphin, all of extinct species.
+
+Professor E. Forbes, after studying the fossil testacea which I obtained
+from these beds; informs me that he has no doubt they were formed partly on
+the shore itself at the level of low water, and partly at very moderate
+depths, not exceeding 10 fathoms below that level. The molluscous fauna of
+the "faluns" is on the whole much more littoral than that of the 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 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 20 miles south of Tours;
+and at Savigné, about 15 miles north-west of that place; 72 only could
+be identified with recent species, which is in the proportion of 25 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 mollusca from the faluns, in my possession, is 302,
+of which 45 only were found by Mr. Wood to be common to the Suffolk
+crag. The number of corals obtained by me at Doué, and other localities
+before adverted to, amounts to 43, as determined by Mr. Lonsdale, of
+which 7 agree specifically with those of the Suffolk crag. Only one has,
+as yet, been identified with a living species. But it is difficult, if
+not impossible, to institute at present a satisfactory comparison
+between fossil and recent _Polyparia_, from the deficiency of our
+knowledge of the living species. Some of the genera occurring fossil in
+Touraine, as the _Astrea_, _Lunulites_, and _Dendrophyllia_, have not
+been found in European seas north of the Mediterranean; nevertheless the
+_Polyparia_ 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, 45 only were found to be common to
+both, which is in the proportion of only 15 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, 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
+southwards in Normandy to within 70 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.
+
+On a comparison of 280 Mediterranean shells with 600 British species, made
+for me by an experienced conchologist in 1841, 160 were found to be common
+to both collections, which is in the proportion of 57 per cent., a fourfold
+greater specific resemblance than between the seas of the crag and the
+faluns, notwithstanding the greater geographical distance between England
+and the Mediterranean than between Suffolk and the Loire. The principal
+grounds, however, for referring the English crag to the older Pliocene and
+the French faluns to the 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 characterize Europe. In
+the faluns, on the contrary, the recent species are in a decided minority,
+and many of them, like the associated extinct testacea, are much less
+European in character, and point to the prevalence of a warmer climate,--in
+other words, to a state of things receding farther from the present
+condition of Europe, geographically and climatologically, and doubtless,
+therefore, receding farther in time.
+
+_Bordeaux._--A great extent of country between the Pyrenees and the Gironde
+is overspread by tertiary deposits, which have been more particularly
+studied in the environs of Bordeaux and Dax, from whence about 700 species
+of shells have been obtained. A large proportion of these shells belong to
+the same zoological type as those of Touraine; but many are peculiar, and
+the whole may possibly constitute a somewhat older division of the Miocene
+period than the faluns of the Loire. We must wait, however, for farther
+investigations, in order to decide this question with accuracy.
+
+_Piedmont._--Many of the shells peculiar to the hill of the Superga, near
+Turin, agree with those found at Bordeaux and Dax; but the proportion of
+recent species is much less. The strata of the Superga consist of a bright
+green sand and marl, and a conglomerate with pebbles, chiefly of green
+serpentine, and are inclined at an angle of more than 70°. This formation,
+which attains a great thickness in the valley of the Bormida, is probably
+one of the oldest Miocene groups hitherto discovered.
+
+_Molasse of Switzerland._--If we cross the Alps, and pass from Piedmont
+to Savoy, we find there, at the northern base of the great chain, and
+throughout the lower country of Switzerland, a soft green sandstone much
+resembling some of the beds of the basin of the Bormida, above
+described, and associated in a similar manner with marls and
+conglomerate. This formation is called in Switzerland "molasse," said to
+be derived from "mol," "_soft_" because the stone is easily cut in the
+quarry. It is of vast thickness, and probably divisible into several
+formations. How large a portion of these belong to the Miocene period
+cannot yet be determined, as fossil shells are often entirely wanting.
+In some places a decided agreement of the fossil fishes of the molasse
+and faluns has been observed. Among those common to both, M. Agassiz
+pointed out to me _Lamna contortidens_, _Myliobates Studeri_, _Spherodus
+cinctus_, _Notidanus primigenius_, and others.
+
+_Lisbon._--Marine tertiary strata near Lisbon contain shells which agree
+very closely with those of Bordeaux, and are therefore referred to the
+Miocene era. Thus, out of 112 species collected by Mr. Smith of Jordanhill,
+between 60 and 70 were found to be common to the strata of Bordeaux and
+Dax, the recent species being in the proportion of 21 per cent.
+
+_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, and Delaware, more
+modern strata predominate, which I have assimilated in age to the English
+crag and Faluns of Touraine.[172-A] If, chronologically speaking, they can
+be truly said to be the representatives of these two European formations,
+they may range in age from the Older Pliocene to the Miocene epoch,
+according to the classification of European strata adopted in this chapter.
+
+The proportion of fossil shells agreeing with recent, out of 147 species
+collected by me, amounted to about 17 per cent., or one-sixth of the
+whole; but as the fossils so assimilated were almost always the same as
+species now living in the neighbouring Atlantic, the number may
+hereafter be augmented, when the recent fauna of that ocean is better
+known. In different localities, also, the proportion of recent
+species varied considerably.
+
+[Illustration: Fig. 151. _Fulgur canaliculatus._ Maryland.]
+
+[Illustration: Fig. 152. _Fusus quadricostatus_, Say. Maryland.]
+
+On the banks of the James River, in Virginia, about 20 miles below
+Richmond, in a cliff about 30 feet high, I observed yellow and white sands
+overlying an Eocene marl, just as the yellow sands of the crag lie on the
+blue London clay in Suffolk and Essex in England. In the Virginian sands,
+we find a profusion of an Astarte (_A. undulata_, Conrad), which resembles
+closely, and may possibly be a variety of, one of the commonest fossils of
+the Suffolk crag (_A. bipartita_); the other shells also, of the genera
+_Natica_, _Fissurella_, _Artemis_, _Lucina_, _Chama_, _Pectunculus_, and
+_Pecten_, are analogous 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 13 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. 152.), and _Venus tridacnoides_, abundant in these same
+formations, but also some shells which, like _Fulgur carica_ of Say, and
+_F. canaliculatus_ (see fig. 151.), _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 the beginning of the present
+geographical distribution of mollusca dates back to a period as remote as
+that of the Miocene strata.
+
+Of ten species of zoophytes which I procured on the banks of the James
+River, two were identical with species of the Faluns of Touraine. With
+respect to climate, Mr. Lonsdale regards 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, and the
+Maltese tertiaries.
+
+_India._--The freshwater deposits of the Sub-Himalayan or Sewâlik Hills,
+described by Dr. Falconer and Captain Cautley, may perhaps be regarded as
+Miocene. Like the faluns of Touraine, they contain the Deinotherium and
+Mastodon. Whether any of the associated freshwater and land shells are of
+recent species is not yet determined. The occurrence in them of a fossil
+giraffe and hippopotamus, genera now only living in Africa, as well as of a
+camel, implies a geographical state of things very different from that now
+established in the same parts of India. The huge Sivatherium of the same
+era appears to have been a ruminating quadruped bigger than the rhinoceros,
+and provided with a large upper lip, or probably a short proboscis, and
+having two pair of horns, resembling those of antelopes. Several species of
+monkey belonged to the same fauna; and among the reptiles, several
+crocodiles, larger than any now living, and an enormous tortoise, _Testudo
+Atlas_, the curved shell of which measured 20 feet across.
+
+
+FOOTNOTES:
+
+[162-A] See paper by E. Charlesworth, Esq.; London and Ed. Phil. Mag. No.
+xxxviii. p. 81., Aug. 1835.
+
+[162-B] See Monograph on the Crag Mollusca. Searles Wood, Paleont.
+Soc. 1848.
+
+[163-A] In regarding the Suffolk crag, both red and coralline, as
+older Pliocene instead of Miocene, I am only returning to the
+classification adopted by me in the Principles and Elements of
+Geology up to the year 1838.
+
+[166-A] E. Forbes, Mem. Geol. Survey, Gt. Brit., vol. i. 386.
+
+[172-A] Proceedings of the Geol. Soc. vol. iv. part 3. 1845, p. 547.
+
+
+
+
+CHAPTER XV.
+
+UPPER EOCENE FORMATIONS.
+
+   Eocene areas in England and France--Tabular view of French Eocene
+   strata--Upper Eocene group of the Paris basin--Same beds in Belgium
+   and at Berlin--Mayence tertiary strata--Freshwater upper Eocene of
+   Central France--Series of geographical changes since the land emerged
+   in Auvergne--Mineral character an uncertain test of age--Marls
+   containing Cypris--Oolite of Eocene period--Indusial limestone and its
+   origin--Fossil mammalia of the upper Eocene strata in
+   Auvergne--Freshwater strata of the Cantal, calcareous and
+   siliceous--Its resemblance to chalk--Proofs of gradual deposition
+   of strata.
+
+
+[Illustration: Fig. 153. Map of the principal tertiary basins of
+the Eocene period.
+
+N. B. The space left blank is occupied by secondary formations from the
+Devonian or old red sandstone to the chalk inclusive.]
+
+The tertiary strata described in the preceding chapters are all of them
+characterized by fossil shells, of which a considerable proportion are
+specifically identical with the living mollusca; and the greater the
+number, the more nearly does the entire fauna approach in species and
+genera to that now inhabiting the adjoining seas. But in the Eocene
+formations next to be considered, the proportion of recent species is very
+small, and sometimes scarcely appreciable, and those agreeing with the
+fossil testacea often belong to remote parts of the globe, and to various
+zoological provinces. This difference in conchological character implies a
+considerable interval of time between the Eocene and Miocene periods,
+during which the whole fauna and flora underwent other changes as great,
+and often greater, than those exhibited by the mollusca. In the
+accompanying map, the position of several Eocene areas is pointed out, such
+as the basin of the Thames, part of Hampshire, part of the Netherlands,
+and the country round Paris. The deposits, however, occupying these spaces
+comprise a great succession of marine and freshwater formations, which,
+although they may all be termed Eocene, as being newer than the chalk, and
+older than the faluns, are nevertheless divisible into separate groups, of
+high geological importance.
+
+The newest of these, like the Faluns of the Loire, have no true
+representatives, or exact chronological equivalents, in the British Isles.
+Their place in the series will best be understood by referring to the order
+of superposition of the successive deposits found in the neighbourhood of
+Paris. The area which has been called the Paris basin is about 180 miles in
+its greatest length from north-east to south-west, and about 90 miles from
+east to west. This space may be described as a depression in the chalk,
+which has been filled up by alternating groups of marine and freshwater
+strata. MM. Cuvier and Brongniart attempted, in 1810, to distinguish five
+different formations, comprising three freshwater and two marine, which
+alternated with each other. It was imagined that the waters of the ocean
+had been by turns admitted and excluded from the same region; but the
+subsequent investigations of several geologists, especially of M. Constant
+Prevost,[175-A] have led to great modifications in these theoretical views;
+and now that the true order of succession is better understood, it appears
+that several of the deposits, which were supposed to have originated one
+after the other, were, in fact, in progress at the same time by the joint
+action of the sea and rivers.
+
+The whole series of strata may be divided into three groups, as expressed
+in the following table:--
+
+                   { _a._ Upper freshwater limestone, marls, and siliceous
+  1. Upper Eocene  {      millstone.
+                   { _b._ Upper marine sands, or Fontainebleau sandstone
+                   {      and sand.
+
+                   { _a._ Lower freshwater limestone and marl, or
+                   {      gypseous series.
+                   { _b._ Sandstone and sands with marine shells (_Sables_
+  2. Middle Eocene {      _moyens_, or _grès de Beauchamp_).
+                   { _c._ Calcaire grossier, limestone with marine shells.
+                   { _d._ Calcaire siliceux, hard siliceous freshwater
+                   {      limestone, for the most part contemporaneous
+                   {      with _c_.
+
+                   { _a._ Lower sands with marine shelly beds (_Sables_
+  3. Lower Eocene  {      _inférieurs et lits coquilliers_).
+                   { _b._ Lower sands, with lignite and plastic clay
+                   {      (_Sables inférieurs et argiles plastiques_).
+
+Postponing to the next chapter the consideration of the Middle and Lower
+Eocene groups, I shall now speak of the Upper Eocene of Paris, and
+its foreign equivalents.
+
+The upper freshwater marls and limestone (1. _a_) seem to have been formed
+in a great number of marshes and shallow lakes, such as frequently
+overspread the newest parts of great deltas. It appears that many layers of
+marl, tufaceous limestone, and travertin, with beds of flint, continuous
+or in nodules, accumulated in these lakes. _Charæ_, aquatic plants, already
+alluded to (see p. 32.) left their stems and seed-vessels imbedded both in
+the marl and flint, together with freshwater and land shells. Some of the
+siliceous rocks of this formation are used extensively for millstones. The
+flat summits or platforms of the hills round Paris, large areas in the
+forest of Fontainebleau, and the Plateau de la Beauce, between the Seine
+and the Loire, are chiefly composed of these upper freshwater strata.
+
+The upper marine sands (1. _b_), consist chiefly of micaceous and quartzose
+sands, 80 feet thick. As they succeed throughout an extensive area deposit
+of a purely freshwater origin (2 _a_.), they appear to mark a subsidence of
+the subjacent soil, whether it had formed the bottom of an estuary or a
+lake. The sea, which afterwards took possession of the same space, was
+inhabited by testacea, almost all of them differing from those found in the
+lower formations (2. _b_ and 2. _c_) and equally or still more distinct
+from the Miocene Faluns of subsequent date. One of these upper Eocene
+strata in the neighbourhood of Paris has been called the oyster bed,
+"couche à _Ostrea cyathula_, Lamk.," which is spread over a remarkably wide
+area. From the manner in which the oysters lie, it is inferred that they
+did not grow on the spot, but that some current swept them away from a bed
+of oysters formed in some other part of the bay. The strata of sand which
+immediately repose on the oyster-bed are quite destitute of organic
+remains; and nothing is more common in the Paris basin, and in other
+formations, than alternations of shelly beds with others entirely devoid of
+them. The temporary extinction and renewal of animal life at successive
+periods have been rashly inferred from such phenomena, which may
+nevertheless be explained, as M. Prevost justly remarks, without appealing
+to any such extraordinary revolutions in the state of the animate creation.
+A current one day scoops out a channel in a bed of shelly sand and mud, and
+the next day, by a slight alteration of its course, ceases to prey upon the
+same bank. It may then become charged with sand unmixed with shells,
+derived from some dune, or brought down by a river. In the course of ages
+an indefinite number of transitions from shelly strata to those without
+shells may thus be caused.
+
+Besides these oysters, M. Deshayes has described 29 species of shells,
+in his work (Coquilles fossiles de Paris), as belonging to this
+formation, all save one regarded by him as differing from fossils of the
+calcaire grossier. Since that time the railway cuttings near Etampes
+have enabled M. Hébert to raise the number to 90. I have myself
+collected fossils in that district, where the shells are very entire,
+and detachable from the yellow sandy matrix. M. Hébert first pointed out
+that most of them agree specifically with those of Kleyn Spauwen, Boom,
+and other localities of Limburg in Flanders, where they have been
+studied by MM. Nyst and De Koninck.[176-A]
+
+The position in Belgium of this formation above the older Eocene group is
+well seen in the small hill of Pellenberg, rising abruptly from the great
+plain, half a mile south-east of the city of Louvain, where I examined it
+in company with M. Nyst in 1850. At the top of the hill, a thin bed of dark
+greyish green tile-clay is seen 1-1/2 foot thick, with casts of _Nucula
+Deshaysiana_. This clay rests on 12 feet of yellow sand, separated, by a
+band of flint and quartz pebbles, from a mass of subjacent white sand 15
+feet thick, in which casts of the Kleyn Spauwen fossils have been met with.
+Under this is a bed of yellow sand 12 feet thick, and, at a lower level,
+the railway cuttings have passed through calcareous sands like those of
+Brussels, in which the _Nautilus Burtini_, and various shells common to the
+older Eocene strata of the neighbourhood of London, have been obtained.
+Every new fact which throws light on the true paleontological relations of
+the strata now under consideration, (the Upper Marine or Fontainebleau beds
+of the Paris basin, 1. _b_, p. 175.), deserves more particular attention,
+because geologists of high authority differ in opinion as to whether they
+should be classed as Eocene or Miocene.
+
+Professor Beyrich has lately described a formation of the same age,
+occurring within 7 miles of the gates of Berlin, near the village of
+Hermsdorf, where, in the midst of the sands of which that country
+chiefly consists, a mass of tile-clay, more than 40 feet thick, and of a
+dark blueish grey colour, is found, full of shells, among which the
+genera _Fusus_ and _Pleurotoma_ predominate, and among the bivalves,
+_Nucula Deshaysiana_, Nyst, an extremely common shell in the Belgian
+beds above-mentioned. M. Beyrich has identified eighteen out of
+forty-five species of the Hermsdorf fossils with the Belgian species;
+and I believe that a much larger proportion agree with the Upper Eocene
+of Belgium, France, and the Rhine. On the other hand, eight of the
+forty-five species are supposed by him to agree with English Eocene
+shells. Messrs. Morris, Edwards, and S. Wood have compared a small
+collection, which I obtained of these Berlin shells, with the Eocene
+fossils of their museums, and confirmed the result of M. Beyrich, the
+species common to the English fossils belonging not simply to the
+uppermost of our marine beds, or those of Barton, but some of them to
+lower parts of the series, such as Bracklesham and Highgate. On the
+other hand, while these testacea, like those of Kleyn Spauwen and
+Etampes, present many analogies to the Middle and Lower Eocene group,
+they differ widely from the Falun shells,--a fact the more important in
+reference to Etampes, as that locality approaches within 70 miles of
+Pontlevoy, near Blois, and within 100 miles of Savigné, near Tours,
+where Falun shells are found. It is evident that the discordance of
+species cannot be attributed to distance or geographical causes, but
+must be referred to time, or the different epoch at which the upper
+marine beds of the Paris basin and the Faluns of the Loire originated.
+
+_Mayence._--The true chronological relation of many tertiary strata on
+the banks of the Rhine has always presented a problem of considerable
+difficulty. They occupy a tract from 5 to 12 miles in breadth, extending
+along the left bank of the Rhine from Mayence to the neighbourhood of
+Manheim, and are again found to the east, north, and south-west of
+Frankfort. In some places they have the appearance of a freshwater
+formation; but in others, as at Alzey, the shells are for the most part
+marine. _Cerithia_ are in great profusion, which indicates that the sea
+where the deposit was formed was fed by rivers; and the great quantity
+of fossil land shells, chiefly of the genus _Helix_, confirm the same
+opinion. The variety in the species of shells is small, while the
+individuals are exceedingly numerous; a fact which accords perfectly
+with the idea that the formation may have originated in a gulf or sea
+which, like the Baltic, was brackish in some parts, and almost fresh in
+others. A species of _Paludina_ (fig. 154.), very nearly resembling the
+recent _Littorina ulva_, is found throughout this basin. These shells
+are like grains of rice in size, and are often in such quantity as to
+form entire beds of marl and limestone. They are as thick as grains of
+sand, in stratified masses from 15 to 30 feet in thickness.
+
+[Illustration: Fig. 154. _Paludina._ Mayence.]
+
+That these Rhenish tertiary formations agree more nearly with the Upper
+Eocene deposits above enumerated, than with any others, I have no doubt,
+since I had the advantage of comparing (August, 1850), with the
+assistance of M. De Koninck of Liége, the fossils from Kleyn Spauwen,
+Boom, and other Limburg localities, with those from Mayence, Alzey,
+Weinheim, and other Rhenish strata. Among the common Belgian and Rhenish
+shells which are identical, I may mention _Cassidaria depressa_,
+_Tritonium flandricum_ De Koninck, _Cerithium tricinctum_ Nyst,
+_Tornatella simulata_, _Rostellaria Sowerbyi_, _Nucula Deshaysiana_,
+_Corbula pisum_, and _Pectunculus terebratularis_.
+
+From these Upper Eocene deposits of the Rhine M. H. von Meyer has
+obtained a great number of characteristic fossil mammalia, such as
+_Palæomæryx medius_, _Hyotherium Meissneri_, _Tapirus Helveticus_,
+_Anthracotherium Alsaticum_, and others. The three first of these are
+species common to some of the lignite, or brown coal beds in
+Switzerland, commonly classed with the molasse, but of which the true
+age has not yet been distinctly made out.
+
+The fossils of the sandy beds of Eppelsheim, comprising bones of the
+Deinotherium, Mastodon, and other quadrupeds, are regarded by H. von Meyer
+as belonging to a mammiferous fauna quite distinct from that of the Mayence
+basin, and they are probably referable to the Miocene period.
+
+The upper freshwater strata (1. _a_, p. 175.), of the neighbourhood of
+Paris, stretch southwards from the valley of the Seine to that of the
+Loire, and in the last-mentioned region are seen to be older than the
+marine faluns, so that the perforating shells of the Miocene sea have
+sometimes bored the hard compact freshwater limestones; and fragments of
+the Upper Eocene rocks are found at Pontlevoy and elsewhere, which have
+been rolled in the bed of the Miocene sea.
+
+[Illustration: Fig. 155. Simplified geological map south of Paris.]
+
+_Central France._--Lacustrine strata belonging, for the most part, to
+the same Upper Eocene series, are again met with in Auvergne, Cantal,
+and Velay, the sites of which may be seen in the annexed map. 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
+probably suffered great denudation. There are also some vast piles
+of volcanic matter (see the map), the greater part of which is newer
+than the freshwater 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 another
+part of this work.
+
+Before entering upon any details, I may observe, that 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
+strata. 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 creation 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, some of them belonging to the same genera as those
+entombed in the Eocene gypsum of Paris. 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 after the disappearance of the Eocene fauna, and in the Miocene
+epoch, the mastodon, rhinoceros, elephant, tapir, hippopotamus, together
+with the ox, various kinds of deer, the bear, hyæna, and many beasts of
+prey, 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 to Pliocene mammalia, and these, in their turn, to 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, 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 freshwater 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. It is inclosed by two parallel mountain ranges,--that of the
+Forèz, which divides the waters of the Loire and Allier, on the east; and
+that of the Monts Domes, which separates the Allier from the Sioule, on the
+west.[181-A] The average breadth of this tract is about 20 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 freshwater 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 and granitic
+beds is rarely seen, as a small valley usually intervenes between them. The
+freshwater 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:--1st,
+Sandstone, grit, and conglomerate, including red marl and red sandstone.
+2dly, Green and white foliated marls. 3dly, Limestone or travertin, often
+oolitic. 4thly, Gypseous marls.
+
+1. _a_. _Sandstone and conglomerate._--Strata of sand and gravel, sometimes
+bound together into a solid rock, are found in great abundance around the
+confines of the lacustrine basin, containing, in different places, pebbles
+of all the ancient rocks of the adjoining elevated country; namely,
+granite, gneiss, mica-schist, clay-slate, porphyry, and others. But these
+strata do not form one continuous band around the margin of the basin,
+being rather disposed like the independent deltas which grow at the mouths
+of torrents along the borders of existing lakes.
+
+At Chamalieres, near Clermont, we have an example of one of these deltas,
+or littoral deposits, of local extent, where the pebbly beds slope away
+from the granite, as if they had formed a talus beneath the waters of the
+lake near the steep shore. A section of about 50 feet in vertical height
+has been laid open by a torrent, and the pebbles are seen to consist
+throughout of rounded and angular fragments of granite, quartz, primary
+slate, and red sandstone; but without any intermixture of those volcanic
+rocks which now abound in the neighbourhood, and which could not have been
+there when the conglomerate was formed. Partial layers of lignite and
+pieces of wood are found in these beds.
+
+At some localities on the margin of the basin quartzose grits are found;
+and, where these rest on granite, they are sometimes formed of separate
+crystals of quartz, mica, and felspar, derived from the disintegrated
+granite, the crystals having been subsequently bound together by a
+siliceous cement. In these cases the granite seems regenerated in a new and
+more solid form; and so gradual a passage takes place between the rock of
+crystalline and that of mechanical origin, that we can scarcely distinguish
+where one ends and the other begins.
+
+In the hills called the Puy de Jussat and La Roche, we have the advantage
+of seeing a section continuously exposed for about 700 feet in thickness.
+At the bottom are foliated marls, white and green, about 400 feet thick;
+and above, resting on the marls, are the quartzose grits, cemented by
+calcareous matter, which is sometimes so abundant as to form imbedded
+nodules. These sometimes constitute spheroidal concretions 6 feet in
+diameter, and pass into beds of solid limestone, resembling the Italian
+travertins, or the deposits of mineral springs. This section is close to
+the confines of the basin; so that the lake must here have been filled up
+near the shore with fine mud, before the coarse superincumbent sand was
+introduced. There are other cases where sand is seen below the marl.
+
+1. _b._ _Red marl and sandstone_.--But the most remarkable of the
+arenaceous groups is one of red sandstone and red marl, which are identical
+in all their mineral characters with the secondary _New Red sandstone_ and
+marl of England. In these secondary rocks the red ground is sometimes
+variegated with light greenish spots, and the same may be seen in the
+tertiary formation of freshwater origin at Coudes, on the Allier. The marls
+are sometimes of a purplish-red colour, as at Champheix, and are
+accompanied by a reddish limestone, like the well-known "cornstone," which
+is associated with the Old Red sandstone of English geologists. The red
+sandstone and marl of Auvergne have evidently been derived from the
+degradation of gneiss and mica-schist, which are seen _in situ_ on the
+adjoining hills, decomposing into a soil very similar to the tertiary red
+sand and marl. We also find pebbles of gneiss, mica-schist, and quartz in
+the coarser sandstones of this group, clearly pointing to the parent rocks
+from which the sand and marl are derived. The red beds, although destitute
+themselves of organic remains, pass upwards into strata containing Eocene
+fossils, and are certainly an integral part of the lacustrine formation.
+From this example the student will learn how small is the value of mineral
+character alone, as a test of the relative age of rocks.
+
+2. _Green and white foliated marls._--The same primary rocks of Auvergne,
+which, by the partial degradation of their harder parts, gave rise to the
+quartzose grits and conglomerates before mentioned, would, by the reduction
+of the same materials into powder, and by the decomposition of their
+felspar, mica, and hornblende, produce aluminous clay, and, if a sufficient
+quantity of carbonate of lime was present, calcareous marl. This fine
+sediment would naturally be carried out to a greater distance from the
+shore, as are the various finer marls now deposited in Lake Superior. And,
+as in the American lake, shingle and sand are annually amassed near the
+northern shores, so in Auvergne the grits and conglomerates before
+mentioned were evidently formed near the borders.
+
+[Illustration: Fig. 156. _Cypris unifasciata_, a living species,
+greatly magnified.
+
+  _a._ Upper part.
+  _b._ Side view of the same.]
+
+[Illustration: Fig. 157. _Cypris vidua_, a living species,
+greatly magnified.[183-A]]
+
+The entire thickness of these marls is unknown; but it certainly exceeds,
+in some places, 700 feet. They are, for the most part, either light-green
+or white, and usually calcareous. They are thinly foliated,--a character
+which frequently arises from the innumerable thin shells, or
+carapace-valves, of that small animal called _Cypris_; a genus which
+comprises several species, of which some are recent, and may be seen
+swimming swiftly through the waters of our stagnant pools and ditches. The
+antennæ, at the end of which are fine pencils of hair, are the principal
+organs of motion, and are seen to vibrate with great rapidity. This animal
+resides within two small valves, not unlike those of a bivalve shell, and
+moults its integuments periodically, which the conchiferous mollusks do
+not. This circumstance may partly explain the countless myriads of the
+shells of _Cypris_ which were shed in the ancient lakes of Auvergne, so as
+to give rise to divisions in the marl as thin as paper, and that, too, in
+stratified masses several hundred feet thick. A more convincing proof of
+the tranquillity and clearness of the waters, and of the slow and gradual
+process by which the lake was filled up with fine mud, cannot be desired.
+But we may easily suppose that, while this fine sediment was thrown down in
+the deep and central parts of the basin, gravel, sand, and rocky fragments
+were hurried into the lake, and deposited near the shore, forming the group
+described in the preceding section.
+
+Not far from Clermont, the green marls, containing the _Cypris_ in
+abundance, approach to within a few yards of the granite which forms the
+borders of the basin. The occurrence of these marls so near the ancient
+margin may be explained by considering that, at the bottom of the
+ancient lake, no coarse ingredients were deposited in spaces
+intermediate between the points where rivers and torrents entered, but
+finer mud only was drifted there by currents. The _verticality_ of some
+of the beds in the above section bears testimony to considerable local
+disturbance subsequent to the deposition of the marls; but such inclined
+and vertical strata are very rare.
+
+[Illustration: Fig. 158. Vertical strata of marl, at Champradelle,
+near Clermont.
+
+  A. Granite.
+  B. Space of 60 feet, in which no section is seen.
+  C. Green marl, vertical and inclined.
+  D. White marl.]
+
+3. _Limestone, travertin, oolite._--Both the preceding members of the
+lacustrine deposit, the marls and grits, pass occasionally into
+limestone. Sometimes only concretionary nodules abound in them; but
+these, where there is an increase in the quantity of calcareous matter,
+unite into regular beds.
+
+On each side of the basin of the Limagne, both on the west at Gannat, and
+on the east at Vichy, a white oolitic limestone is quarried. At Vichy, the
+oolite resembles our Bath stone in appearance and beauty; and, like it, is
+soft when first taken from the quarry, but soon hardens on exposure to the
+air. At Gannat, the stone contains land-shells and bones of quadrupeds,
+resembling those of the Paris gypsum. At Chadrat, in the hill of La Serre,
+the limestone is pisolitic, the small spheroids combining both the radiated
+and concentric structure.
+
+_Indusial limestone._--There is another remarkable form of freshwater
+limestone in Auvergne, called "indusial," from the cases, or _indusiæ_,
+of caddis-worms (the larvæ of _Phryganea_); great heaps of which have
+been incrusted, as they lay, by carbonate of lime, and formed into a
+hard travertin. The rock is sometimes purely calcareous, but there is
+occasionally an intermixture of siliceous matter. Several beds of it are
+frequently seen, either in continuous masses, or in concretionary
+nodules, one upon another, with layers of marl interposed. The annexed
+drawing (fig. 159.) will show the manner in which one of these indusial
+beds (_a_) is laid open at the surface, between the marls (_b b_), near
+the base of the hill of Gergovia; and affords, at the same time, an
+example of the extent to which the lacustrine strata, which must once
+have filled a hollow, have been denuded, and shaped out into hills and
+valleys, on the site of the ancient lakes.
+
+[Illustration: Fig. 159. Bed of indusial limestone, interstratified with
+freshwater marl, near Clermont (Kleinschrod.)]
+
+[Illustration: Fig. 160. Larva of recent Phryganea.[185-A]]
+
+[Illustration: Fig. 161.
+
+  _a_. Indusial limestone of Auvergne.
+  _b_. Fossil _Paludina_ magnified.]
+
+We may often observe in our ponds the _Phryganea_ (or Caddis-fly), in its
+caterpillar state, covered with small freshwater shells, which they have
+the power of fixing to the outside of their tubular cases, in order,
+probably, to give them weight and strength. The individual figured in the
+annexed cut, which belongs to a species very abundant in England, has
+covered its case with shells of a small _Planorbis_. In the same manner a
+large species of caddis-worm, which swarmed in the Eocene lakes of
+Auvergne, was accustomed to attach to its dwelling the shells of a small
+spiral univalve of the genus _Paludina_. A hundred of these minute shells
+are sometimes seen arranged around one tube, part of the central cavity of
+which is often empty, the rest being filled up with thin concentric layers
+of travertin. The cases have been thrown together confusedly, and often
+lie, as in fig. 161., at right angles one to the other. When we consider
+that ten or twelve tubes are packed within the compass of a cubic inch, and
+that some single strata of this limestone are 6 feet thick, and may be
+traced over a considerable area, we may form some idea of the countless
+number of insects and mollusca which contributed their integuments and
+shells to compose this singularly constructed rock. It is unnecessary to
+suppose that the _Phryganeæ_ lived on the spots where their cases are now
+found; they may have multiplied in the shallows near the margin of the
+lake, or in the streams by which it was fed, and their cases may have been
+drifted by a current far into the deep water.
+
+In the summer of 1837, when examining, in company with Dr. Beck, a small
+lake near Copenhagen, I had an opportunity of witnessing a beautiful
+exemplification of the manner in which the tubular cases of Auvergne were
+probably accumulated. This lake, called the Fuure-Soe, occurring in the
+interior of Seeland, is about twenty English miles in circumference, and in
+some parts 200 feet in depth. Round the shallow borders an abundant crop of
+reeds and rushes may be observed, covered with the indusiæ of the
+_Phryganea grandis_ and other species, to which shells are attached. The
+plants which support them are the bullrush, _Scirpus lacustris_, and common
+reed, _Arundo phragmitis_, but chiefly the former. In summer, especially in
+the month of June, a violent gust of wind sometimes causes a current by
+which these plants are torn up by the roots, washed away, and floated off
+in long bands, more than a mile in length, into deep water. The _Cypris_
+swarms in the same lake; and calcareous springs alone are wanting to form
+extensive beds of indusial limestone, like those of Auvergne.
+
+4. _Gypseous marls._--More than 50 feet of thinly laminated gypseous marls,
+exactly resembling those in the hill of Montmartre, at Paris, are worked
+for gypsum at St. Romain, on the right bank of the Allier. They rest on a
+series of green cypriferous marls which alternate with grit, the united
+thickness of this inferior group being seen, in a vertical section on the
+banks of the river, to exceed 250 feet.
+
+_General arrangement, origin, and age of the freshwater formations of
+Auvergne._--The relations of the different groups above described 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 marls, a contemporaneous central deposit; and the limestone is
+for the most part subordinate to the newer portions of both. The uppermost
+marls and sands are more calcareous than the lower; and we never meet with
+calcareous rocks covered by a considerable thickness of quartzose sand or
+green marl. From the resemblance of the limestones to the Italian
+travertins, we may conclude that they were derived from the waters of
+mineral springs,--such springs as even now exist in Auvergne, and which may
+be seen rising up through the granite, and precipitating travertin. They
+are sometimes thermal, but this character is by no means constant.
+
+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
+embedded 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 farther accumulation of
+regular freshwater strata to cease.
+
+We may easily conceive a similar series of events to give rise to
+analogous results in any modern basin, such as that of Lake Superior,
+for example, where numerous rivers and torrents are carrying down the
+detritus of a chain of mountains into the lake. The transported
+materials must be arranged according to their size and weight, the
+coarser near the shore, the finer at a greater distance from land; but
+in the gravelly and sandy beds of Lake Superior no pebbles of modern
+volcanic rocks can be included, since there are none of these at present
+in the district. If igneous action should break out in that country, and
+produce lava, scoriæ, and thermal springs, the deposition of gravel,
+sand, and marl might still continue as before; but, in addition, there
+would then be an intermixture of volcanic gravel and tuff, and of rocks
+precipitated from the waters of mineral springs.
+
+Although the freshwater strata of the Limagne approach generally to a
+horizontal position, the proofs of local disturbance are sufficiently
+numerous and violent to allow us to suppose great changes of level since
+the lacustrine period. We are unable to assign a northern barrier to the
+ancient lake, although we can still trace its limits to the east, west,
+and south, where they were formed of bold granite eminences. Nor need we
+be surprised at our inability to restore entirely the physical geography
+of the country after so great a series of volcanic eruptions; for it is
+by no means improbable that one part of it, the southern, for example,
+may have been moved upwards bodily, while others remained at rest, or
+even suffered a movement of depression.
+
+Whether all the freshwater formations of the Limagne d'Auvergne belong to
+one period, I cannot pretend to decide, as large masses both of the
+arenaceous and marly groups are often devoid of fossils. Much light has
+been thrown on the mammiferous fauna by the labours of MM. Bravard and
+Croizet, and by those of M. Pomel. The last-mentioned naturalist has
+pointed out the specific distinction of all, or nearly all, the species of
+mammalia, from those of the gypseous series near Paris. Nevertheless, many
+of the forms are analogous to those of Eocene quadrupeds. The
+_Cainotherium_, for example, is not far removed from the _Anoplotherium_,
+and is, according to Waterhouse, the same as the genus _Microtherium_ of
+the Germans. There are two species of marsupial animals allied to
+_Didelphys_, a genus also found in the Paris gypsum. The _Amphitragulus
+elegans_ of Pomel, has been identified with a Rhenish species from
+Weissenau near Mayence, called by Kaup _Dorcatherium nanum_; and other
+Auvergne fossils, e.g., _Microtherium Reuggeri_, and a small rodent,
+_Titanomys_, are specifically the same with mammalia of the Mayence basin.
+
+_Cantal._--A freshwater formation, very analogous to that of Auvergne,
+is situated in the department of Haute Loire, near the town of Le Puy,
+in Velay, and another occurs near Aurillac, in Cantal. The leading
+feature of the formation last mentioned, as distinguished from those of
+Auvergne and Velay, is the immense abundance of silex associated with
+calcareous marls and limestone.
+
+The whole series may be separated into two divisions; the lower, composed
+of gravel, sand, and clay, such as might have been derived from the wearing
+down and decomposition of the granitic schists of the surrounding country;
+the upper system, consisting of siliceous and calcareous marls, contains
+subordinately gypsum, silex, and limestone.
+
+The resemblance of the freshwater limestone of the Cantal, and its
+accompanying flint, to the upper chalk of England, is very instructive, and
+well calculated to put the student upon his guard against relying too
+implicitly on mineral character alone as a safe criterion of relative age.
+
+When we approach Aurillac from the west, we pass over great heathy plains,
+where the sterile mica-schist is barely covered with vegetation. Near
+Ytrac, and between La Capelle and Viscamp, the surface is strewed over with
+loose broken flints, some of them black in the interior, but with a white
+external coating; others stained with tints of yellow and red, and in
+appearance precisely like the flint gravel of our chalk districts. When
+heaps of this gravel have thus announced our approach to a new formation,
+we arrive at length at the escarpment of the lacustrine beds. At the bottom
+of the hill which rises before us, we see strata of clay and sand, resting
+on mica-schist; and above, in the quarries of Belbet, Leybros, and Bruel, a
+white limestone, in horizontal strata, the surface of which has been
+hollowed out into irregular furrows, since filled up with broken flint,
+marl, and dark vegetable mound. In these cavities we recognize an exact
+counterpart to those which are so numerous on the furrowed surface of our
+own white chalk. Advancing from these quarries along a road made of the
+white limestone, which reflects as glaring a light in the sun, as do our
+roads composed of chalk, we reach, at length, in the neighbourhood of
+Aurillac, hills of limestone and calcareous marl, in horizontal strata,
+separated in some places by regular layers of flint in nodules, the coating
+of each nodule being of an opaque white colour, like the exterior of the
+flinty nodules of our chalk.
+
+It will be remembered that the siliceous stone of Bilin, called _tripoli_,
+is a freshwater deposit, and has been shown, by Ehrenberg, to be of
+infusorial origin (see p. 24.). What is true of the Bohemian flint and
+opal, where the beds attain a thickness of 14 feet, may also, perhaps, be
+found to hold good respecting the silex of Aurillac, which may also have
+been immediately derived from the minute cases of microscopic animalcules.
+But even if this conclusion be established, the abundant supply both of
+siliceous, calcareous, and gypseous matter, which the ancient lakes of
+France received, may have been connected with the subterranean volcanic
+agency of which those regions were so long the theatre, and which may have
+impregnated the springs with mineral matter, even before the great outbreak
+of lava. It is well known that the hot springs of Iceland, and many other
+countries, contain silex in solution; and it has been lately affirmed, that
+steam at a high temperature is capable of dissolving quartzose rocks
+without the aid of any alkaline or other flux.[189-A]
+
+Travellers not unfrequently mention, in their accounts of India, Australia,
+and other distant lands, that they have seen chalk with flints, which they
+have assumed to be of the same age as the Cretaceous system of Europe. A
+hasty observation of the white limestone and flint of Aurillac might convey
+the same idea; but when we turn from the mineral aspect and composition to
+the organic remains, we find in the flints of the Cantal the seed-vessels
+of the freshwater _Chara_, instead of the marine zoophytes so abundantly
+imbedded in chalk flints; and in the limestone we meet with shells of
+_Limnea_, _Planorbis_, and other lacustrine genera, instead of the oyster,
+terebratula, and echinus of the Cretaceous period.
+
+_Proofs of gradual deposition_.--Some sections of the foliated marls in the
+valley of the Cer, near Aurillac, attest, in the most unequivocal manner,
+the extreme slowness with which the materials of the lacustrine series were
+amassed. In the hill of Barrat, for example, we find an assemblage of
+calcareous and siliceous marls; in which, for a depth of at least 60 feet,
+the layers are so thin, that thirty are sometimes contained in the
+thickness of an inch; and when they are separated, we see preserved in
+every one of them the flattened stems of _Charæ_, or other plants, or
+sometimes myriads of small _Paludinæ_ and other freshwater shells. These
+minute foliations of the marl resemble precisely some of the recent
+laminated beds of the Scotch marl lakes, and may be compared to the pages
+of a book, each containing a history of a certain period of the past. The
+different layers may be grouped together in beds from a foot to a foot and
+a half in thickness, which are distinguished by differences of composition
+and colour, the tints being white, green, and brown. Occasionally there is
+a parting layer of pure flint, or of black carbonaceous vegetable matter,
+about an inch thick, or of white pulverulent marl. We find several hills in
+the neighbourhood of Aurillac composed of such materials, for the height of
+more than 200 feet from their base, the whole sometimes covered by rocky
+currents of trachytic or basaltic lava.[190-A]
+
+Thus wonderfully minute are the separate parts of which some of the most
+massive geological monuments are made up! When we desire to classify, it
+is necessary to contemplate entire groups of strata in the aggregate;
+but if we wish to understand the mode of their formation, and to explain
+their origin, we must think only of the minute subdivisions of which
+each mass is composed. We must bear in mind how many thin leaf-like
+seams of matter, each containing the remains of myriads of testacea and
+plants, frequently enter into the composition of a single stratum, and
+how vast a succession of these strata unite to form a single group! We
+must remember, also, that piles of volcanic matter, like the Plomb du
+Cantal, which rises in the immediate neighbourhood of Aurillac, are
+themselves equally the result of successive accumulation, consisting of
+reiterated sheets of lava, showers of scoriæ, and ejected fragments of
+rock.--Lastly, we must not forget that continents and mountain-chains,
+colossal as are their dimensions, are nothing more than an assemblage of
+many such igneous and aqueous groups, formed in succession during an
+indefinite lapse of ages, and superimposed upon each other.
+
+
+FOOTNOTES:
+
+[175-A] Bulletin des Sci. de la Soc. Philom., May, 1825, p. 74.
+
+[176-A] Hébert. Bulletin. 1849, vol. vi. 2d series, p. 459.
+
+[181-A] Scrope, Geology of Central France, p. 15.
+
+[183-A] See Desmarest's Crustacea, plate 55.
+
+[185-A] I believe that the British specimen here figured is
+P. _rhombica_, Linn.
+
+[189-A] See Proceedings of Roy. Soc., No. 44. p. 233.
+
+[190-A] Lyell and Murchison, sur les Dépôts Lacust. Tertiaries du Cantal,
+&c. Ann. des Sci. Nat. Oct. 1829.
+
+
+
+
+CHAPTER XVI.
+
+EOCENE FORMATIONS--_continued_.
+
+   Subdivisions of the Eocene group in the Paris basin--Gypseous
+   series--Extinct quadrupeds--Impulse given to geology by Cuvier's
+   osteological discoveries--Shelly sands called sables moyens--Calcaire
+   grossier--Miliolites--Calcaire siliceux--Lower Eocene in France--Lits
+   coquilliers--Sands and plastic clay--English Eocene strata--Freshwater
+   and fluvio-marine beds--Barton beds--Bagshot and Bracklesham
+   division--Large ophidians and saurians--Lower Eocene and London Clay
+   proper--Fossil plants and shells--Strata of Kyson in Suffolk--Fossil
+   monkey and opossum--Mottled clays and sands below London
+   Clay--Nummulitic formation of Alps and Pyrenees--Its wide geographical
+   extent--Eocene strata in the United States--Section at Claiborne,
+   Alabama--Colossal cetacean--Orbitoid limestone--Burr stone.
+
+
+From what was said in the two preceding chapters, it has already
+appeared that we have in England no true chronological representative of
+the Miocene faluns of the Loire, and none of the Upper Eocene group
+described in the last chapter. But, when we descend to the middle and
+inferior divisions of the Eocene system of France, we find that they
+have their equivalents in Great Britain.
+
+
+MIDDLE EOCENE.--FRANCE.
+
+_Gypseous series_ (2. _a_, Table, p. 175.).--Next below the upper marine
+sands of the neighbourhood of Paris, we find 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 M. 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 freshwater 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 swoln 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.
+
+M. Prevost has therefore suggested that a river may have swept away the
+bodies of animals, and the plants which lived on its borders, or in the
+lakes which it traversed, and may have carried them down into the centre
+of the gulf into which flowed the waters impregnated with sulphate of
+lime. We know that the Fiume Salso in Sicily enters the sea so charged
+with various salts that the thirsty cattle refuse to drink of it. A
+stream of sulphureous water, as white as milk, descends into the sea
+from the volcanic mountain of Idienne on the east of Java; and a great
+body of hot water, charged with sulphuric acid, rushed down from the
+same volcano on one occasion, and inundated a large tract of country,
+destroying, by its noxious properties, all the vegetation.[191-A] In
+like manner the Pusanibio, or "Vinegar River," of Colombia, which rises
+at the foot of Puracé, an extinct volcano, 7,500 feet above the level of
+the sea, is strongly impregnated with sulphuric and muriatic acids and
+with oxide of iron. We may easily suppose the waters of such streams to
+have properties noxious to marine animals, and in this manner the entire
+absence of marine remains in the ossiferous gypsum may be
+explained.[191-B] There are no pebbles or coarse sand in the gypsum; a
+circumstance which agrees well with the hypothesis that these beds were
+precipitated from water holding sulphate of lime in solution, and
+floating the remains of different animals.
+
+In this formation the relics of about fifty species of quadrupeds,
+including the genera _Paleotherium_, _Anoplotherium_, and others, have been
+found, all extinct, and nearly four-fifths of them belonging to a division
+of the order _Pachydermata_, which is now represented by only four living
+species; namely three tapirs and the daman of the Cape. With them a few
+carnivorous animals are associated, among which are a species of fox and
+gennet. Of the _Rodentia_, a dormouse and a squirrel; of the _Insectivora_,
+a bat; and of the _Marsupialia_ (an order now confined to America,
+Australia, and some contiguous islands), an opossum, have been discovered.
+
+Of birds, about ten species have been ascertained, the skeletons of some of
+which are entire. None of them are referable to existing species.[192-A]
+The same remark applies to the fish, according to MM. Cuvier, and Agassiz,
+as also to the reptiles. Among the last are crocodiles and tortoises of the
+genera _Emys_ and _Trionyx_.
+
+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. Whether the
+disproportion of carnivorous animals can be ascribed to this cause, or
+whether they were comparatively small in number and dimensions, as in
+the indigenous fauna of Australia, when first known to Europeans, is a
+point on which it would be rash, perhaps, to offer an opinion in the
+present state of our knowledge.
+
+[Illustration: Fig. 162. _Paleotherium magnum._]
+
+The Paleothere, 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 (see fig. 163.). _Paleotherium magnum_ was of
+the size of a horse, 3 or 4 feet high. The annexed woodcut, fig. 162., is
+one of the restorations which Cuvier attempted of the outline of the living
+animal, derived from the study of the entire skeleton. When the French
+osteologist declared in the early part of the present century, that all the
+fossil quadrupeds of the gypsum of Paris were extinct, the announcement of
+so startling a fact, on such high authority, created a powerful sensation,
+and from that time a new impulse was given throughout Europe to the
+progress of geological investigation. Eminent naturalists, it is true, had
+long before maintained that the shells and zoophytes, met with in many
+ancient European rocks, had ceased to be inhabitants of the earth, but the
+majority even of the educated classes continued to believe that the species
+of animals and plants now contemporary with man, were the same as those
+which had been called into being when the planet itself was created. It was
+easy to throw discredit upon the new doctrine by asking whether corals,
+shells, and other creatures previously unknown, were not annually
+discovered? and whether living forms corresponding with the fossils might
+not yet be dredged up from seas hitherto unexamined? But from the era of
+the publication of Cuvier's Ossements Fossiles, and still more his popular
+Treatise called "A Theory of the Earth," sounder views began to prevail. It
+was clearly demonstrated that most of the mammalia found in the gypsum of
+Montmartre differed even generically from any now existing, and the extreme
+improbability that any of them, especially the larger ones, would ever be
+found surviving in continents yet unexplored, was made manifest. Moreover,
+the non-admixture of a single living species in the midst of so rich a
+fossil fauna was a striking proof that there had existed a state of the
+earth's surface zoologically unconnected with the present order of things.
+
+[Illustration: Fig. 163. Upper molar tooth of _Paleotherium magnum_ from
+Isle of Wight. (Owen's Brit. Foss. p. 317.)
+
+Reduced one-third.]
+
+_Grès de Beauchamp_ (2. _b_, Table, p. 175.).--In some parts of the Paris
+basin, sands and marls, called the Grès de Beauchamp, or Sables Moyens,
+divide the gypseous beds from the underlying Calcaire grossier. These sands
+contain more than 300 species of marine shells, many of them peculiar, but
+others common to the underlying marine deposit (No. 2. _c_.).
+
+_Calcaire grossier_ (2. _c_, Table, p. 175.).--The formation called
+Calcaire grossier consists of a coarse limestone, often passing into sand.
+It contains the greater number of the fossil shells which characterize the
+Paris basin. No less than 400 distinct species have been procured from a
+single spot near Grignon, where they are embedded in a calcareous sand,
+chiefly formed of comminuted shells, in which, nevertheless, individuals in
+a perfect state of preservation, both of marine, terrestrial, and
+freshwater species, are mingled together. Some of the marine shells may
+have lived on the spot; but the _Cyclostoma_ and _Limnea_ 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 fig.
+164.). There occur no less than 137 species of this genus in the Paris
+basin, and almost all of them in the calcaire grossier. Now 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, the sediment of some of
+which gave rise to the beds of clay and lignite before mentioned; while
+a distinct freshwater limestone, called calcaire siliceux, which will
+presently be described, was precipitated from the waters of others
+situated farther to the south.
+
+[Illustration: Fig. 164. Cerithium cinctum.[194-A]]
+
+[4 Illustrations: EOCENE FORAMINIFERA.
+
+Fig. 165. _Calcarina rarispina_, Desh.
+         _b_. natural size.
+         _a_, _c_. same magnified.
+
+Fig. 166. _Spirolina stenostoma_, Desh.
+         B. natural size.
+         A, C, D. same magnified.
+
+Fig. 167. _Triloculina inflata_, Desh.
+         _b_. natural size.
+         _a_, _c_, _d_, same magnified.
+
+Fig. 168. _Clavulina corrugata_, Desh.
+          _a_. natural size.
+          _b_, _c_. same magnified.]
+
+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. Figures of some of these are given in the annexed woodcut. As
+this miliolitic stone never occurs in the Faluns, or Miocene strata of
+Brittany and Touraine, it often furnishes the geologist with a useful
+criterion for distinguishing the detached Eocene and Miocene formations,
+scattered over those and other adjoining provinces. The discovery of the
+remains of Paleotherium 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.
+
+_Calcaire siliceux_.--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 freshwater and land species, and never any marine
+fossils. The siliceous limestone and the calcaire grossier occupy
+distinct parts of the Paris basin, the one attaining its fullest
+development in those places where the other is of slight thickness.
+They also alternate with each other towards the centre of the basin,
+as at Sergy and Osny; and there are even points where the two rocks are
+so blended together that portions of each may be seen in hand specimens.
+Thus, in the same bed, at Triel, we have the compact freshwater
+limestone, characterized by its _Limneæ_, mingled with the coarse marine
+limestone, with its small multilocular shells, or "miliolites,"
+dispersed through it in countless numbers. These microscopic testacea
+are also accompanied by _Cerithia_ and other shells of the calcaire
+grossier. It is very extraordinary that in this instance both kinds of
+sediment must have been thrown down together on the same spot, yet each
+retains its own peculiar organic remains.
+
+From these facts we may conclude, that while to the north, where the bay
+was probably open to the sea, a marine limestone was formed, another
+deposit of freshwater origin was introduced to the southward, or at the
+head of the bay; for it appears that during the Eocene period, as now, the
+ocean was to the north, and the continent, where the great lakes existed,
+to the south. From that southern region we may suppose a body of fresh
+water to have descended, charged with carbonate of lime and silica, the
+water being perhaps in sufficient volume to freshen the upper end of the
+bay. The gypseous series (2. _a_, Table, p. 175.), before described, was
+once supposed to be entirely subsequent in origin to the two groups, called
+calcaire grossier and calcaire siliceux. But M. Prevost has pointed out
+that in some localities they alternate repeatedly with both.
+
+The gypsum, with its associated marl and limestone, is in greatest force
+towards the centre of the basin, where the calcaire grossier and calcaire
+siliceux are less fully developed. Hence M. Prevost infers, that while
+those two principal deposits were gradually in progress, the one towards
+the north, and the other towards the south, a river descending from the
+east may have brought down the gypseous and marly sediment.
+
+It must be admitted, as highly probable, that a bay or narrow sea, 180
+miles in length, would receive, at more points than one, the waters of the
+adjoining continent. At the same time, we must be prepared to find that
+the simultaneous deposition of two or more sets of strata in one basin,
+some freshwater and others marine, must have produced very complex results.
+But, in proportion as it is more difficult in these cases to discover any
+fixed order of superposition in the associated mineral masses, so also is
+it more easy to explain the manner of their origin, and to reconcile their
+relations to the agency of known causes. Instead of the successive
+irruptions and retreats of the sea, and changes in the chemical nature of
+the fluid, and other speculations of the earlier geologists, we are now
+simply called upon to imagine a gulf, into one extremity of which the sea
+entered, and at the other a large river, while other streams may have
+flowed in at different points, whereby an indefinite number of alternations
+of marine and freshwater beds would be occasioned.
+
+
+LOWER EOCENE, FRANCE.
+
+_Lits coquilliers_ (3. _a_, Table, p. 175.).--Below the calcaire grossier
+are extensive deposits of sand, in the upper parts of which some marine
+beds, called "lits coquilliers," occur, in which M. d'Archiac has
+discovered 200 species of shells. Many of these are peculiar, but the
+larger portion appear to agree with species of the calcaire grossier, so
+that the line of demarcation usually adopted between the French Lower and
+Middle Eocene formations, seems not to be very strongly drawn. _Sands and
+plastic clay_ (3. _b_, Table, p. 175.)--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. 187. p. 204.),
+_Melania inquinata_ (fig. 188.), and others, frequently met with in beds
+occupying the same position in the valley of the Thames. Layers of lignite
+also accompany the inferior clays and sands.
+
+Immediately upon the chalk at the bottom of all the tertiary strata
+there is often 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 some portions of the chalk,
+and its waste by denudation.
+
+[Illustration: Fig. 169. _Cardium porulosum_. Paris and London basins.]
+
+The lower sandy beds of the Paris basin are often called the sands of the
+Soissonais, from a district so named 50 miles N.E. of Paris. One of the
+shells of the formation is adduced by M. Deshayes as an example of the
+changes which certain species underwent in the successive stages of their
+existence. It seems that different varieties of the _Cardium porulosum_ are
+characteristic of different formations. In the Lower Eocene of the
+Soissonais this shell acquires but a small volume, and has many
+peculiarities, which disappear in the lowest beds of the calcaire grossier.
+In these the shell attains its full size, and many distinctive characters,
+which are again modified in the uppermost beds of the calcaire grossier;
+and these last modifications of form are preserved throughout the whole of
+the "upper marine" (or Upper Eocene) series.[197-A]
+
+
+ENGLISH EOCENE FORMATIONS.
+
+The Eocene areas of Hampshire and London are delineated in the map
+(fig. 153. p. 174.).
+
+The following table will show the succession of the principal deposits
+found in our island. The true place of the Bagshot sands, in this
+series, was never accurately ascertained till Mr. Prestwich published,
+in 1847, his classification of the English Eocene strata, dividing them
+into three principal formations, in which the Bagshot sands occupied
+the central place.[197-B]
+
+                                                     Localities.
+  1. Upper Eocene.    Wanting in Great Britain.
+
+                    { _a._ Freshwater and            Headon Hill, Isle of
+                    {      fluvio-marine beds.       Wight; and Hordwell
+                    {                                Cliff, Hants.
+  2. Middle Eocene  { _b._ Barton beds.              Barton Cliff, Hants.
+                    { _c._ Bagshot and Bracklesham   Bagshot Heath, Surrey;
+                    {      sands and clays.          Bracklesham Bay,
+                    {                                Sussex.
+
+                    { _a._ London Clay Proper,       Highgate Hill,
+                    {      and Bognor beds.          Middlesex; I. of
+                    {                                Sheppey; Bognor,
+  3. Lower Eocene   {                                Sussex.
+                    { _b._ Mottled and Plastic       Newhaven, Sussex;
+                    {      clays and sands.          Reading, Berks;
+                    {                                Woolwich, Kent.
+
+[Illustration: Fig. 170. _Lymnea longiscata._
+
+Freshwater Eocene strata, Isle of Wight.]
+
+_Freshwater beds_ (2. _a_, Table, p. 175.).--In the northern part of the
+Isle of Wight, beds of marl, clay, and sand, and a friable limestone,
+containing freshwater shells, are seen, containing shells of the genera
+_Lymnea_ (see fig. 170.), _Planorbis_, _Melanopsis_, _Cyrena_, &c., several
+of them of the same species as those occurring in the Eocene beds of the
+Paris basin. Gyrogonites, also, or seed-vessels of _Chara_, exhibiting a
+similar specific identity, occur. At Headon Hill, on the western side of
+the island, where these beds are seen in the sea-cliffs, some of the strata
+contain a few marine and estuary shells, such as _Cytheræa_, _Corbula_,
+&c., showing a temporary occupation of the area by brackish or salt water,
+after which the river or a lake seems again to have prevailed. A species
+of fan-palm, _Flabellaria Lamanonis_, Brong., like one which characterizes
+the Parisian Eocene beds, has been recently detected by Dr. Mantell in this
+formation, in Whitecliff Bay, at the eastern end of the island.
+
+Several of the species of extinct quadrupeds already alluded to as
+characterizing the gypsum of Montmartre have been discovered by Messrs.
+Pratt and Fox, in the Isle of Wight, chiefly at Binstead, near Ryde, as
+_Palæotherium magnum_, _P. medium_, _P. minus_, _P. minimum_, _P. curtum_,
+_P. crassum_, also _Anoplotherium commune_, _A. secundarium_, _Dichobune
+cervinum_, and _Chæropotamus Cuvieri_. In Hordwell cliff, also on the
+Hampshire coast, several of these species, with other quadrupeds of new
+genera, such as _Paloplotherium_, Owen, have been met with; and remains of
+a remarkable carnivorous genus, _Hyænodon_. These fossils are accompanied
+by the bones of _Trionyx_, and other tortoises, and by two land snakes of
+the genus _Paleryx_, Owen, from 3 to 4 feet long, also a species of
+crocodile, and an alligator. Among other fossils collected by Lady
+Hastings, Sir Philip Egerton has recognized the well-known gar or bony pike
+of the American rivers, a ganoid fish of the genus _Lepidotus_, with its
+hard shining scales. The shells of Hordwell are similar to those of the
+freshwater beds of the Isle of Wight, and among them are a few specifically
+undistinguishable from recent testacea, as _Paludina lenta_ and _Helix
+labyrinthica_, the latter discovered by Mr. S. Wood, and identified with an
+existing N. American helix.
+
+The white and green marls of this freshwater series in Hampshire, and some
+of the accompanying limestones, often resemble those 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.
+
+_Barton beds._--Both in the cliffs of Headon Hill and Hordwell, already
+mentioned, the freshwater series rests on a mass of pure white sand without
+fossils, and this is seen in Barton Cliff to overlie a marine deposit, in
+which 209 species of testacea have been found. More than half of these are
+peculiar; and, according to Mr. Prestwich, only 11 of them common to the
+London Clay proper, being in the proportion of only 5 per cent. On the
+other hand, 70 of them agree with the _calcaire grossier_ shells. As this
+is the newest purely marine bed of the Eocene series known in England, we
+might have expected that some of its peculiar fossils would be found to
+agree with the upper Eocene strata described in the last chapter, and
+accordingly some identifications have been cited with testacea, both of the
+Berlin and Belgian strata. It is nearly a century since Brander published,
+in 1766, an account of the organic remains collected from these cliffs, and
+his excellent figures of the shells then deposited in the British Museum
+are justly admired by conchologists for their accuracy.
+
+_Bagshot Sands_ (2. _c_, Table, p. 197.).--These beds, consisting
+chiefly of siliceous sand, occupy extensive tracts round Bagshot, in
+Surrey, and in the New Forest, Hampshire. They succeed next in
+chronological order, and may be separated into three divisions, the
+upper and lower consisting of light yellow sands, and the central of
+dark green sands and brown clays, the whole reposing on the London clay
+proper.[199-A] Although the Bagshot beds are usually devoid of fossils,
+they contain marine shells in some places, among which _Venericardia
+planicosta_ (see fig. 171.) is abundant, with _Turritella sulcifera_ and
+_Nummulites lævigatus_. (See fig. 174. p. 200.)
+
+[Illustration: Fig. 171. _Venericardia planicosta_, Lamck.
+
+_Cardita planicosta_, Deshayes.]
+
+At Bracklesham Bay, near Chichester, in Sussex, the characteristic shells
+of this member of the Eocene series are best seen; among others, the huge
+_Cerithium giganteum_, so conspicuous in the calcaire grossier of Paris,
+where it is sometimes 2 feet in length. The volutes and cowries of this
+formation, as well as the lunulites and other corals, seem to favour the
+idea of a warm climate having prevailed, which is borne out by the
+discovery of a serpent _Palæophis typhæus_, exceeding, according to Mr.
+Owen, 20 feet in length, and allied 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 the Hunterian professor
+to pronounce the extinct ophidian to have been marine.[199-B] He had
+previously combated with so much success the evidence advanced, to prove
+the existence in the Northern Ocean of sea-serpents in our own times, that
+he will not be suspected of any undue bias in contending for their former
+existence in the British Eocene seas. The climate, however, of the Middle
+Eocene period was evidently far more genial; and amongst the companions of
+the sea-serpent of Bracklesham was an extinct Gavial (_Gavialis Dixoni_,
+Owen), and numerous fish, such as now frequent the seas of warm latitudes,
+as the sword-fish (see fig. 172. p. 200.) and gigantic rays of the genus
+Miliobates. (See fig. 173.)
+
+Out of 193 species of testacea procured from the Bagshot and Bracklesham
+beds in England, 126 occur in the French calcaire grossier. It was
+clearly, therefore, coeval with that part of the Parisian series more
+nearly than with any other. The _Nummulites lævigatus_ (see fig. 174.),
+a fossil characteristic of the lower beds of the calcaire grossier,
+is abundant at Bracklesham.
+
+[Illustration: Fig. 172. Prolonged premaxillary bone or "sword" of
+a fossil sword-fish (_Cælorhynchus_). Bracklesham. Dixon's Fossils
+of Sussex, pl. 8.]
+
+[Illustration: Fig. 173. Dental plates of _Myliobates Edwardsi_.
+Bracklesham Bay. Ibid. pl. 8.]
+
+[Illustration: Fig. 174. _Nummulites_ (_Nummularia_) _lævigatus._
+Bracklesham. Ibid. pl. 8.
+
+  _a._ section of the nummulite.
+  _b._ group, with an individual showing the exterior of the shell.]
+
+_London clay proper_ (3. _a_, Table, p. 197.).--This formation underlies
+the preceding, and consists of tenacious brown and blueish grey clay, with
+layers of concretions called septaria, which abound chiefly in the brown
+clay, and are obtained in sufficient numbers from the cliffs near Harwich,
+and from shoals of the Essex coast, to be used for making Roman cement. The
+principal localities of fossils in the London clay are Highgate Hill, near
+London, the island of Sheppey, and Bognor in Hampshire. 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. 196.), in which only 200 species are known in France.
+We may presume, therefore, that the London clay proper is older than the
+calcaire grossier. This may perhaps remove a difficulty which M. Adolphe
+Brongniart has experienced when comparing the Eocene Flora of the
+neighbourhoods of London and Paris. The fossil species of the island of
+Sheppey, he observes, indicate a much more tropical climate than the Eocene
+Flora of France, which has been derived principally from the "gypseous
+series." The latter resembles the vegetation of the borders of the
+Mediterranean rather than that of an equatorial region.
+
+Mr. Bowerbank, in a valuable publication on the fossil fruits and seeds of
+the island of Sheppey, near London, has described no less than thirteen
+fruits of palms of the recent type _Nipa_, now only found in the Molucca
+and Philippine islands. (See fig. 175.) These plants are allied to the
+cocoa-nut tribe on the one side, and on the other to the _Pandanus_, or
+screw-pine. Species of cocoa-nuts are also met with, and other kinds of
+palms; also three species of _Anona_, or custard-apple; cucurbitaceous
+fruits, also (the gourd and melon family), are in considerable abundance.
+Fruits of various species of _Acacia_ are in profusion; and, although less
+decidedly tropical, imply a warm climate.
+
+[Illustration: Fig. 175. _Nipadites ellipticus._ Bow. Fossil
+palm of Sheppey.]
+
+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 Mr. Conybeare has remarked, must have resorted to
+some shore to lay their eggs. Of turtles there were numerous species
+referred to extinct genera, and, for the most part, not equal in size to
+the largest living tropical turtles. A snake, which must have been 13 feet
+long, of the genus _Palæophis_ before mentioned, has also been described by
+Mr. Owen from Sheppey, of a different species from that of Bracklesham. A
+true crocodile, also, _Crocodilus toliapicus_, and another Saurian more
+nearly allied to the gravial, accompany the above fossils. A bird allied to
+the vultures, and a quadruped of the new genus _Hyracotherium_, allied to
+the Hyrax, Hog, and Chæropotamus, are also among the additions made of late
+years to the palæontology of this division.
+
+[3 Illustrations: FOSSIL SHELLS OF THE LONDON CLAY.
+
+Fig. 176. _Mitra scabra_.
+
+Fig. 177. _Rostellaria macroptera_, Sow. One-third of nat. size.
+
+Fig. 178. _Crassatella sulcata._]
+
+The marine shells of the London clay confirm the inference derivable from
+the plants and reptiles of a high temperature. Thus, many species of
+_Conus_, _Mitra_, and _Voluta_ occur, a large _Cypræa_, a very large
+_Rostellaria_, and shells of the genera _Terebellum_, _Cancellaria_,
+_Crassatella_, and others, with four or more species of _Nautilus_ (see
+fig. 182.) and other cephalopoda of extinct genera, one of the most
+remarkable of which is the _Belosepia_.[202-A] (See fig. 183.)
+
+[Illustration: Fig. 179. _Nautilus centralis._]
+
+[Illustration: Fig. 180. _Voluta athleta._]
+
+[Illustration: Fig. 181. _Terebellum fusiforme._]
+
+[Illustration: Fig. 182. _Aturia zigzag._ Bronn. Syn. _Nautilus zigzag._
+Sow. London clay. Sheppey.]
+
+[Illustration: Fig. 183. _Belosepia sepiodea_, De Blainv.
+London clay. Sheppey.]
+
+The above shells are accompanied by a sword-fish (_Tetrapterus priscus_,
+Agassiz), about 8 feet long, and a saw-fish (_Pristis bisulcatus_, Ag.),
+about 10 feet in length; genera now foreign to the British seas. On the
+whole, no less than 50 species of fish have been described by
+M. Agassiz from these beds in Sheppey, and they indicate, in his
+opinion, a warm climate.
+
+[Illustration: Fig. 184. Molar of monkey (_Macacus_).]
+
+_Strata of Kyson in Suffolk._--At Kyson, a few miles east of Woodbridge, a
+bed of Eocene clay, 12 feet thick, underlies the red crag. Beneath it is a
+deposit of yellow and white sand, of considerable interest, in consequence
+of many peculiar fossils contained in it. Its geological position is
+probably the lowest part of the London clay proper. In this sand has been
+found the first example of a fossil quadrumanous animal discovered in Great
+Britain, namely, the teeth and part of a jaw, shown by Mr. Owen to belong
+to a monkey of the genus _Macacus_ (see fig. 184.). The mammiferous
+fossils, first met with in the same bed, were those of an opossum
+(_Didelphys_) (see fig. 185.), and an insectivorous bat (fig. 186.),
+together with many teeth of fishes of the shark family. Mr. Colchester in
+1840 obtained other mammalian relics from Kyson, among which Mr. Owen has
+recognized several teeth of the genus _Hyracotherium_, and the vertebræ of
+a large serpent, probably a _Palæophis_. As the remains both of the
+_Hyracotherium_ and _Palæophis_ were afterwards met with in the London
+clay, as before remarked, these fossils confirmed the opinion previously
+entertained, that the Kyson sand belongs to the Eocene period. The
+_Macacus_, therefore, constitutes the first example of any quadrumanous
+animal found in strata as old as the Eocene, or so far from the equator as
+lat. 52° N. It was not until after the year 1836 that the existence of any
+fossil quadrumana was brought to light. Since that period they have been
+found in France, India, and Brazil.
+
+[Illustration: Fig. 185. Molar tooth and part of jaw of opossum.
+From Kyson.[203-A]]
+
+[Illustration: Fig. 186. Molars of insectivorous bats, twice nat. size.
+From Kyson, Suffolk.]
+
+_Mottled or Plastic Clays_, _&c._ (3. _b_, Table, p. 197.).--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 a coarse white limestone, and compact
+siliceous limestone with beds of crystalline gypsum and siliceous
+sandstone, and sometimes pure flint used for millstones. Hence it is by
+no means an easy task to institute an exact comparison between the
+various members of the English and French series, and to settle their
+respective ages. It is clear that a continual change was going on in the
+fauna and flora by the coming in of new species and the dying out of
+others; and contemporaneous changes of geographical conditions were also
+in progress in consequence of the rising and sinking of the land and
+bottom of the sea. A particular subdivision, therefore, of time was
+occasionally represented in one area by land, in another by an estuary,
+in a third by the sea, and even where the conditions were in both
+areas of a marine character, there was often shallow water in one,
+and deep sea in another, producing a want of agreement in the state
+of animal life.
+
+At the commencement, however, of the Eocene formations in France and
+England, we find an exception to this rule, for a marked similarity of
+mineral character reigns in the lowest division, whether in the basins
+of Paris, Hampshire, or London. This uniformity of aspect must be seen
+in order to be fully appreciated, since the beds consist simply of sand,
+mottled clays, and well-rolled flint pebbles, derived from the chalk,
+and varying in size from that of a pea to an egg. These strata may be
+seen at Reading, at Blackheath, near London, and at Woolwich. In some
+of the lowest of them, banks of oysters are observed, consisting of
+_Ostrea bellovicina_, so common in France in the same relative position,
+and _Ostrea edulina_, scarcely distinguishable from the living eatable
+species. In this formation at Bromley, Dr. Buckland found one 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.
+
+In several places, as at Woolwich on the Thames, at Newhaven in Sussex, and
+elsewhere, a mixture of marine and freshwater testacea distinguishes this
+member of the series. Among the latter, _Melania inquinata_ (see fig. 188.)
+and _Cyrena cuneiformis_ are very common. They probably indicate points
+where rivers entered the Eocene sea.
+
+[Illustration: Fig. 187. _Cyrena cuneiformis_, Min. Con. Natural size.]
+
+[Illustration: Fig. 188. _Melania inquinata_, Des. Nat. size.
+
+Syn. _Cerithium melanoides_, Min. Con.]
+
+With us as in France, clay of this formation is used in some places, as
+near Poole in Dorsetshire, for pottery; and hence the name of plastic clay
+was adopted for the group by Mr. T. Webster. Lignite also is associated
+with it in some spots, as in the Paris basin.
+
+Before the minds of geologists had become familiar with the theory of the
+gradual sinking of the land, and its conversion into sea at different
+periods, and the consequent change from shallow to deep water, the
+freshwater and littoral character of this inferior group appeared strange
+and anomalous. After passing through many hundred feet of London clay,
+proved by its fossils to have been deposited in salt water of considerable
+depth, we arrive at beds of fluviatile origin. Thick masses, also, of
+shingle indicate the proximity of land, where the flints of the chalk were
+rolled into sand and pebbles, and spread continuously over wide spaces, as
+in the Isle of Wight, in the south of Hampshire, and near London, always
+appearing at the bottom of the Eocene series. It may be asked why they did
+not constitute simply a narrow littoral zone, such as we might look for in
+strata formed at a moderate distance from the shore. In answer to this
+inquiry, the student must be reminded, that wherever a gently-sloping land
+is gradually sinking and becoming submerged, shingle may be heaped up
+successively over a wide area, although marine currents have no power of
+dispersing it simultaneously over a large space. In such cases it is not
+the shingle which recedes from the coast, but the coast which recedes from
+the shingle, which is formed one mass after another as often as successive
+portions of the land are converted into sea and others into a sea beach.
+
+The London area appears to have been upraised before that of Hampshire, so
+that it never became the receptacle of the Barton clays, nor of the
+overlying fluvio-marine and freshwater beds of Hordwell and the north part
+of the Isle of Wight. On the other hand, the Hampshire Eocene area seems to
+have emerged before that of Paris, so that no marine beds of the Upper
+Eocene era were ever thrown down in Hampshire.
+
+_Nummulitic formation of the Alps and Pyrenees._--It has long been
+matter of controversy, whether the nummulitic rocks of the Alps and
+Pyrenees should be regarded as Eocene or Cretaceous; but the number of
+geologists of high authority who regard this important group as
+belonging to the lowest tertiary system of Europe has for many years
+been steadily increasing. The late M. Alex. Brongniart first declared
+the specific identity of many of the shells of this formation with those
+of the marine strata near Paris, although he obtained them from the
+summit of the Diablerets, one of the loftiest of the Swiss Alps, which
+rises more than 10,000 feet above the level of the sea.
+
+Deposits of the same age, found on the flanks of the Pyrenees, contain also
+a great number of shells common to the Paris and London areas, and three or
+four species only which are common to the cretaceous formation.
+
+The calcareous division consists often of a compact crystalline marble,
+full of nummulites (see fig. 189.), shells of the class _Foraminifera_.
+
+[Illustration: Fig. 189. _Nummulites_. Peyrehorade, Pyrenees.
+
+  _a._ external surface of one of the nummulites, of which longitudinal
+       sections are seen in the limestone.
+  _b._ transverse section of same.]
+
+The nummulitic limestone of the Alps is often of great thickness, and is
+immediately covered by another series of strata of dark-coloured slates,
+marls, and fucoidal sandstones, to the whole of which the provincial name
+of "flysch" has been given in parts of Switzerland. The researches of Sir
+Roderick Murchison in the Alps in 1847 enable us to refer the whole of
+these beds to the Eocene period, and it seems probable that they most
+nearly coincide in age with the Lower Eocene. They enter into the disturbed
+and loftiest portions of the Alpine chain, to the elevation of which they
+enable us therefore to assign a comparatively modern date.
+
+The nummulitic formation, with its characteristic fossils, plays 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 often attains a
+thickness of many thousand feet, and extends from the Alps to the
+Apennines. It is found in the Carpathians, and in full force in the north
+of Africa, as, for example, in Algeria and Morocco. It has also been traced
+from Egypt into Asia Minor, and across Persia by Bagdad to the mouths of
+the Indus. It occurs 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.
+
+Some members of this lower tertiary formation in the central Alps,
+including even the superior strata called _flysch_, have been converted
+into crystalline rocks, and changed into saccharoid marble, quartz,
+rock, and mica-schist.[206-A]
+
+
+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
+southwards 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 four hundred species of
+marine shells, with many echinoderms and teeth of fish, characterize one
+member of this system. Among the shells the _Cardita planicosta_, before
+mentioned (fig. 171. p. 199.), 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 the calcaire grossier of Paris.[206-B]
+
+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.[206-C] The following section will enable the reader to
+understand the position of the three subdivisions of the series, Nos. 1,
+2, and 3., the relations of which I ascertained in Clarke County, between
+the rivers Alabama and Tombeckbee.
+
+[Illustration: Fig. 190. Cross section.
+
+  1. Sand, marl, &c., with numerous fossils.              }
+  2. White or rotten limestone, with _Zeuglodon_.         } Eocene.
+  3. Orbitoidal, or so called nummulitic limestone.       }
+  4. Overlying formation of sand and clay without fossils. Age unknown.]
+
+The lowest set of strata, No. 1., having a thickness of more than 100
+feet, comprise marly beds, in which the _Ostrea sellæformis_ occurs, a
+shell ranging from Alabama to Virginia, and being a representative form
+of the _Ostrea flabellula_ of the Eocene group of Europe. In others beds
+of No. 1., two European shells, _Cardita planicosta_, before mentioned,
+and _Solarium canaliculatum_ are found, with a great many other species
+peculiar to America. Numerous corals, also, and the remains of placoid
+fish and of rays occur, and the "swords," as they are called, of sword
+fishes, all bearing a great generic likeness to those of the Eocene
+strata of England and France.
+
+No. 2. (fig. 190.) 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. zigzag_, also in its upper bed a
+gigantic cetacean, called _Zeuglodon_ by Owen.[207-A]
+
+[2 Illustrations: _Zeuglodon cetoides_, Owen. _Basilosaurus_, Harlan.]
+
+Fig. 191. Molar tooth, natural size.]
+
+Fig. 192. Vertebra, reduced.]
+
+The colossal bones of this cetacean are so plentiful in the interior of
+Clarke County 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 70 feet, and not far off part of another
+backbone nearly 50 feet long was dug up. I obtained evidence, during a
+short excursion, of so many localities of this fossil animal within a
+distance of 10 miles, as to lead me to conclude that they must have
+belonged to at least forty distinct individuals.
+
+Mr. Owen first pointed out that the huge animal was not reptilian, since
+each tooth was furnished with double roots (see fig. 191.), implanted in
+corresponding double sockets; and his opinion of the cetacean nature of
+the fossil was afterwards confirmed by Dr. Wyman and Professor R. W.
+Gibbes. That it was an extinct species of the whale tribe has since been
+placed beyond all doubt by the discovery of the entire skull of another
+fossil of the same family, found to have the double occipital condyles
+only met with in mammals, and the convoluted tympanic bones which are
+characteristic of cetaceans.
+
+Near the junction of No. 2. and the incumbent limestone, No. 3., next to be
+mentioned, are strata characterized by the following shells: Spondylus
+dumosus (_Plagiostoma dumosum_, Morton), _Pecten Poulsoni_, _Pecten
+perplanus_, and _Ostrea cretacea_.
+
+No. 3. (fig. 190.) is a white limestone, for the most part made up of the
+_Orbitoides_ of d'Orbigny before mentioned (p. 206.), formerly supposed to
+be a nummulite, and called _N. Mantelli_, mixed with a few lunulites and
+small corals and shells.[208-A] The origin of this cream-coloured soft
+stone, like that of our white chalk, which it much resembles, is, I
+believe, due to the decomposition of the orbitoides. The surface of the
+country where it prevails is sometimes marked by the absence of wood, like
+our chalk downs, or is covered exclusively by the _Juniperus Virginiana_,
+as certain chalk districts in England by yew trees and juniper.
+
+Some of the shells of this limestone are common to the Claiborne beds, but
+many of them are peculiar.
+
+It will be seen in the section (fig. 190. p. 155.) that the strata, Nos. 1,
+2, 3., are, for the most part, overlaid by a dense formation of sand or
+clay without fossils. In some points of the bluff or cliff of the Alabama
+river, at Claiborne, the beds Nos. 1, 2., are exposed nearly from top to
+bottom, whereas at other points the newer formation, No. 4., occupies the
+face of nearly the whole cliff. The age of this overlying mass has not yet
+been determined, as it has hitherto proved destitute of organic remains.
+
+The burr-stone strata of the Southern States contain so many fossils
+agreeing with those of Claiborne, that it doubtless belongs to the same
+part of the Eocene group, though I was not fortunate enough to see the
+relations of the two deposits in a continuous section. Mr. Tuomey considers
+it as the lower portion of the series. It may, perhaps, be a form of the
+Claiborne beds in places where lime was wanting, and where silex, derived
+from the decomposition of felspar, predominated. It consists chiefly of
+slaty clays, quartzose sands, and loam, of a brick red colour, with layers
+of chert or burr-stone, used in some places for millstones.
+
+
+FOOTNOTES:
+
+[191-A] Leyde Magaz. voor Wetensch Konst en Lett., partie v. cahier i. p.
+71. Cited by Rozet, Journ. de Géologie, tom. i. p. 43.
+
+[191-B] M. C. Prevost, Submersions Itératives, &c. Note 23.
+
+[192-A] Cuvier, Oss. Foss., tom. iii. p. 255.
+
+[194-A] This species is found both in the Paris and London basins.
+
+[197-A] Coquilles caractérist. des Terrains, 1831.
+
+[197-B] Quarterly Geol. Journal, vol. iii. p. 353.
+
+[199-A] Prestwich, Quart. Geol. Journ. vol. iii. p. 386.
+
+[199-B] Palæont. Soc. Monograph. Rept. pt. ii. p. 61.
+
+[202-A] For description of Eocene Cephalopoda, see Monograph by F. E.
+Edwards, Palæontograph. Soc. 1849.
+
+[203-A] Annals of Nat. Hist. vol. iv. No. 23. Nov. 1839.
+
+[206-A] Murchison, Quart. Journ. of Geol. Soc. vol. v., and Lyell, vol. vi.
+1850. Anniversary Address.
+
+[206-B] See paper by the author, Quart. Journ. Geol. Soc. vol. iv, p. 12.;
+and Second Visit to the U. S. vol. ii. p. 59.
+
+[206-C] Quart. Journ. Geol Soc. vol. vi. p. 32.
+
+[207-A] See Memoir by R. W. Gibbes, Journ. of Acad. Nat. Sci. Philad.
+vol. i. 1847.
+
+[208-A] Lyell, Quart. Journ. Geol. Soc. 1847, vol. iv. p. 15.
+
+
+
+
+CHAPTER XVII.
+
+CRETACEOUS GROUP.
+
+   Divisions of the cretaceous series in North-Western Europe--Upper
+   cretaceous strata--Maestricht beds--Chalk of Faxoe--White
+   chalk--Characteristic fossils--Extinct cephalopoda--Sponges and corals
+   of the chalk--Signs of open and deep sea--Wide area of white
+   chalk--Its origin from corals and shells--Single pebbles in
+   chalk--Siliceous sandstone in Germany contemporaneous with white
+   chalk--Upper greensand and gault--Lower cretaceous strata--Atherfield
+   section, Isle of Wight--Chalk of South of Europe--Hippurite
+   limestone--Cretaceous Flora--Chalk of United States.
+
+
+Having treated in the preceding chapters of the tertiary strata, we have
+next to speak of the uppermost of the secondary groups, called the Chalk
+or Cretaceous (No. 6. Table, p. 103.), because in those parts of Europe
+where it was first studied its upper members are formed of that
+remarkable white earthy limestone, termed chalk (_creta_). The inferior
+division consists, for the most part, of clays and sands, called
+Greensand, because some of the sands derive a bright green colour from
+intermixed grains of chloritic matter. The cretaceous strata in the
+north-west of Europe may be thus divided[209-A]:
+
+                       _Upper Cretaceous._
+
+  1. Maestricht beds and Faxoe limestone.
+  2. Upper white chalk, with flints.
+  3. Lower white chalk, without flints, passing downwards into chalk marl,
+     which is slightly argillaceous.
+  4. Upper greensand.
+  5. Gault.
+
+                       _Lower Cretaceous._
+
+  6. Lower greensand--Ironsand, clay, and occasional beds of limestone
+    (Kentish rag).
+
+_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
+_Belemnites mucronatus_ (see fig. 197.) and _Pecten quadricostatus_.
+Besides the Belemnite there are other _genera_, such as Ammonite, Baculite,
+and Hamite, never found in strata newer than the cretaceous, but frequently
+met with in these Maestricht beds. On the other hand, Volutes 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, 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 lately examined this formation (August, 1850),
+pointed out to me a layer of chalk from 2 to 4 inches thick, containing
+green earth and numerous encrinital stems, which forms the line of
+demarcation 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. 201.), 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_, 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.
+
+_Chalk of Faxoe._--In the island of Seeland, in Denmark, the newest member
+of the chalk series, seen in the sea-cliffs at Stevens Klint 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, as they strictly belong to the Cretaceous era, are worthy
+of notice, since such forms, whether spiral or patelliform, are wanting in
+the white chalk of Europe generally. 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 _Patella_, one _Emarginula_, &c., on
+the whole, more than thirty univalves, spiral or patelliform, not one of
+which is common to the white chalk. At the same time, a large proportion of
+the accompanying bivalve shells, echinoderms, and zoophytes, are
+specifically identical with fossils of older parts of the Cretaceous
+series. Among the cephalopoda of Faxoe, may be mentioned _Baculites
+Faujasii_ and _Belemnites mucronatus_, shells of the white chalk.
+
+The claws and entire shell of a small crab, _Brachyurus rugosus_
+(Schlotheim), are scattered through the Faxoe stone, reminding us of
+similar crustaceans enclosed in the rocks of many modern coral
+reefs.[211-A] Some small portions of this coralline formation consist of
+white earthy chalk; it is, therefore, clear that this substance must
+have been produced simultaneously, a fact of some importance, as bearing
+on the theory of the origin of white chalk; for the decomposition of
+such corals as we see at Faxoe is capable, we know, of forming white
+mud, undistinguishable from chalk, and which we may suppose to have
+been dispersed far and wide through the ocean, in which such reefs as
+that of Faxoe grew.
+
+[Illustration: Fig. 193. Section from Hertfordshire, in England, to
+Sena, in France.]
+
+_White Chalk_ (2. and 3. Tab. p. 209.).--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 from
+2 to 4 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.[211-B]
+
+The annexed section, fig. 193., 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.
+
+Among the conspicuous forms of mollusca wholly foreign to the tertiary and
+recent periods, and which we meet with in the white chalk, are the
+Belemnite, Ammonite, Baculite, and Turrilite, all genera of _Cephalopoda_,
+a family to which the living cuttle-fish and nautilus belong.
+
+[Illustration: Fig. 194. Portion of _Baculites Faujasii_. Maestricht and
+Faxoe beds and white chalk.]
+
+[Illustration: Fig. 195. Portion of _Baculites anceps_. Maestricht and
+Faxoe beds and white chalk.]
+
+[Illustration: Fig. 196. Turrilites.
+
+  _a._ _Turrilites costatus._ Chalk marl.
+  _b._ Same, showing the indented border of the partition of the chambers.]
+
+[Illustration: Fig. 197. Belemnites.
+
+  _a._ _Belemnites mucronatus._
+  _b._ Same, showing internal structure.
+
+Maestricht, Faxoe, and white chalk.]
+
+Among the brachiopoda in the white chalk, the _Terebratulæ_ are very
+abundant. These shells are known to live at the bottom of the sea, where
+the water is tranquil and of some depth (see figs. 198, 199, 200, 201.).
+With these are associated some forms of oyster (see figs. 202. and 204.),
+and other bivalves (figs. 203, 205, 206, 207, 208.).
+
+[Illustration: Fig. 198. _Terebratula plicatilis_, dorsal view.
+Upper white chalk.]
+
+[Illustration: Fig. 199. _Terebratula plicatilis_, side view.]
+
+[Illustration: Fig. 200. _Terebratula pumilus._ (_Magas pumilus_, Sow.)
+Upper white chalk.]
+
+[Illustration: Fig. 201. _Terebratula carnea._ Upper white chalk.]
+
+[Illustration: Fig. 202. _Ostrea vesicularis._ _Gryphæa globosa_, Min. Con.
+Upper chalk and upper greensand.]
+
+[Illustration: Fig. 203. _Pecten 5-costatus._ White chalk, upper
+and lower greensands.]
+
+[Illustration: Fig. 204. _Ostrea carinata._ Chalk marl, upper
+and lower greensands.]
+
+[Illustration: Fig. 205. _Crania Parisiensis_, inferior or attached valve.
+Upper white chalk.]
+
+[Illustration: Fig. 206. _Plagiostoma Hoperi_, Sow. Syn. _Lima Hoperi_.
+White chalk and upper greensand.]
+
+[Illustration: Fig. 207. _Plagiostoma spinosum_, Sow. Syn. _Spondylus
+spinosus_. Upper white chalk.]
+
+Among the rest, no form marks the cretaceous era in Europe, America, and
+India, in a more striking manner than the extinct genus _Inoceramus_
+(_Catillus_ of Lamk.), the shells of which are distinguished by a
+fibrous texture, and are often met with in fragments, having, probably,
+been extremely friable.
+
+[Illustration: Fig. 208. _Inoceramus Lamarckii._
+
+Syn. _Catillus Lamarckii_.
+
+White Chalk (Dixon's Geol. Sussex, Tab. 28. fig. 29.)]
+
+[Illustration: Fig. 209. _Eschara disticha._
+
+_a._ Natural size.
+_b._ Portion magnified.
+
+White chalk.]
+
+[2 Illustrations: Fig. 210. Fig. 211. A branching sponge in a flint, from
+the white chalk. From the collection of Mr. Bowerbank.]
+
+With these mollusca are many corals (figs. 209, 210, 211.) and sea urchins
+(fig. 212.), which are alike marine, and, for the most part, indicative of
+a deep sea. They are dispersed indifferently through the soft chalk, and
+hard flint, and some of the flinty nodules owe their irregular forms to
+inclosed zoophytes, as in the specimen represented in fig. 211., where the
+hollows in the exterior are caused by the branches of a sponge seen on
+breaking open the flint, fig. 210.
+
+[Illustration: Fig. 212. _Ananchytes ovata_. White chalk, upper and lower.
+
+  _a_. Side view.
+  _b_. Bottom of the shell on which both the oral and anal apertures are
+       placed; the anal being more round, and at the smaller end.]
+
+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. 213.) has been discovered in the
+white chalk of England.
+
+[4 Illustrations: _Hippurites Mortoni_, Mantell. Houghton, Sussex. White
+chalk. Diameter one seventh of nat. size.
+
+Fig. 213. Two individuals deprived of their opercula, adhering together.
+
+Fig. 214. Same seen from above.
+
+Fig. 215. Transverse section of part of the wall of the shell, magnified
+          to show the structure.
+
+Fig. 216. 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. 213, 214.; but they are usually
+less prominent than in these figures. This species has been referred to
+_Hippurites_, but does not, I believe, fully agree in character with that
+genus. I have never seen the opercular piece, or _valve_, as it is called
+by those conchologists who regard the _Rudistes_ as bivalve mollusca. The
+specimen above figured was discovered by the late Mr. Dixon.]
+
+The remains of fishes of the Upper Cretaceous formations consist chiefly
+of teeth of the shark family of genera, in part common to the tertiary,
+and partly distinct. 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.
+
+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, so much frequented by migratory droves of turtles, might perhaps
+have afforded the required retreat where these creatures might lay 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 cycadeous plants; for a fragment of one of these
+was found by Capt. 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.
+
+_Geographical extent and origin of the While Chalk._--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_, _Belemnites mucronatus_, and _Ostrea vesicularis_.
+
+But it would be an error to imagine, that the chalk was ever spread out
+continuously over the whole of the space comprised within these limits,
+although it prevailed in greater or less thickness over large portions of
+that area. On turning to those regions of the Pacific where coral reefs
+abound, we find some archipelagoes of lagoon islands, such as that of the
+Dangerous Archipelago, for instance, and that of Radack, with several
+adjoining groups, which are from 1100 to 1200 miles in length, and 300 or
+400 miles broad; and the space to which Flinders proposed to give the name
+of the Corralline Sea is still larger; for it is bounded on the east by the
+Australian barrier--all formed of coral rock,--on the west by New
+Caledonia, and on the north by the reefs of Louisiade. Although the islands
+in these areas may be thinly sown, the mud of the decomposing zoophytes may
+be scattered far and wide by oceanic currents. That this mud would resemble
+chalk I have already hinted when speaking of the Faxoe limestone, p. 211.;
+and it was also remarked in an early part of this volume, that some even of
+that chalk which appears to an ordinary observer quite destitute of organic
+remains, is nevertheless, when seen under the microscope, full of fragments
+of corals and sponges; together with the valves of entomostraca, the shells
+of foraminifera, and still more minute infusoria.[215-A] (See p. 26.)
+
+Now it had been often suspected, before these discoveries, that white
+chalk might be of animal origin, even where every trace of organic
+structure has vanished. This bold idea was partly founded on the fact,
+that the chalk consisted of pure carbonate of lime, such as would result
+from the decomposition of testacea, echini, and corals; and partly on
+the passage observable between these fossils when half decomposed and
+chalk. But this conjecture seemed to many naturalists quite vague and
+visionary, until its probability was strengthened by new evidence
+brought to light by modern geologists.
+
+We learn from Lieutenant Nelson, that, in the Bermuda Islands, there are
+several basins or lagoons almost surrounded and enclosed by reefs of
+coral. At the bottom of these lagoons a soft white calcareous mud is
+formed by the decomposition of _Eschara_, _Flustra_, _Cellepora_, and
+other corallines. This mud, when dried, is undistinguishable from common
+white earthy chalk; and some portions of it, presented to the Museum of
+the Geological Society of London, might, after full examination, be
+mistaken for ancient chalk, but for the labels attached to them. About
+the same time Mr. C. Darwin observed similar facts in the coral islands
+of the Pacific; and came also to the opinion, that much of the soft
+white mud found at the bottom of the sea near coral reefs has passed
+through the bodies of worms, by which the stony masses of coral are
+everywhere bored; and other portions through the intestines of fishes;
+for certain gregarious fishes of the genus _Sparus_ are visible through
+the clear water, browsing quietly, in great numbers, on living corals,
+like grazing herds of graminivorous quadrupeds. On opening their bodies,
+Mr. Darwin found their intestines filled with impure chalk. This
+circumstance is the more in point, when we recollect how the fossilist
+was formerly puzzled by meeting, in chalk, with certain bodies, called
+cones of the larch, which were afterwards recognized by Dr. Buckland to
+be the excrement of fish.[216-A] These spiral coprolites (see figures),
+like the scales and bones of fossil fish in the chalk, are composed
+chiefly of phosphate of lime.
+
+[2 Illustrations: Fig. 217. Fig. 218. Coprolites of fish called
+_Iulo-eido-copri_, from the chalk.]
+
+Mr. Dana, when describing the elevated coral reef of Oahu, in the Sandwich
+Islands, says, that some varieties of the rock consist of aggregated
+shells, imbedded in a compact calcareous base as firm in texture as any
+secondary limestone; while others are like chalk, having its colour, its
+earthy fracture, its soft homogeneous texture, and being an equally good
+writing material. The same author describes, in many growing coral reefs, a
+similar formation of modern chalk, undistinguishable from the
+ancient.[216-B] The extension over a wide submarine area of the calcareous
+matrix of the chalk, as well as of the imbedded fossils, would take place
+the more readily, in consequence of the low specific gravity of the shells
+of mollusca and zoophytes, when compared with ordinary sand and mineral
+matter. The mud also derived from their decomposition would be much lighter
+than argillaceous and other inorganic mud, and very easily transported by
+currents, especially in salt water.
+
+_Single pebbles in chalk._--The general absence of sand and pebbles in
+the white chalk has been already mentioned; but the occurrence here and
+there, in the south-east of England, of a few isolated pebbles of quartz
+and green schist, some of them 2 or 3 inches in diameter, has justly
+excited much wonder. If these had been carried to the spots where we now
+find them by waves or currents from the lands once bordering the
+cretaceous sea, how happened it that no sand or mud were transported
+thither at the same time? We cannot conceive such rounded stones to have
+been drifted like erratic blocks by ice[217-A], for that would imply a
+cold climate in the Cretaceous period; a supposition inconsistent with
+the luxuriant growth of large chambered univalves, numerous corals, and
+many fish, and other fossils of tropical forms.
+
+Now in Keeling Island, one of those detached masses of coral which rise up
+in the wide Pacific, Captain Ross found a single fragment of greenstone,
+where every other particle of matter was calcareous; and Mr. Darwin
+concludes that it must have come there entangled in the roots of a large
+tree. He reminds us that Chamisso, the distinguished naturalist who
+accompanied Kotzebue, affirms, that the inhabitants of the Radack
+archipelago, a group of lagoon islands, in the midst of the Pacific,
+obtained stones for sharpening their instruments by searching the roots of
+trees which are cast up on the beach.[217-B]
+
+It may perhaps be objected, that a similar mode of transport cannot have
+happened in the cretaceous sea, because fossil wood is very rare in the
+chalk. Nevertheless wood is sometimes met with, and in the same parts of
+the chalk where the pebbles are found, both in soft stone and in a
+silicified state in flints. In these cases it has often every appearance of
+having been floated from a distance, being usually perforated by
+boring-shells, such as the _Teredo_ and _Fistulana_.[217-C]
+
+The only other mode of transport which suggests itself is sea-weed. Dr.
+Beck informs me, that in the Lym-Fiord, in Jutland, the _Fucus
+vesiculosus_, often called kelp, sometimes grows to the height of 10
+feet, and the branches rising from a single root form a cluster several
+feet in diameter. When the bladders are distended, the plant becomes so
+buoyant as to float up loose stones several inches in diameter, and
+these are often thrown by the waves high up on the beach. The _Fucus
+giganteus_ of Solander, so common in Terra del Fuego, is said by Captain
+Cook to attain the length of 360 feet, although the stem is not much
+thicker than a man's thumb. It is often met with floating at sea, with
+shells attached, several hundred miles from the spots where it grew.
+Some of these plants, says Mr. Darwin, were found adhering to large
+loose stones in the inland channels of Terra del Fuego, during the
+voyage of the Beagle in 1834; and that so firmly, that the stones were
+drawn up from the bottom into the boat, although so heavy that they
+could scarcely be lifted in by one person. Some fossil sea-weeds have
+been found in the Cretaceous formation, but none, as yet, of large size.
+
+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 the 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.
+
+_Upper greensand_ (4. Tab. p. 209.).--The lower chalk without flints passes
+gradually downwards, in the south of England, into an argillaceous
+limestone, "the chalk marl," already alluded to, in which ammonites and
+other cephalopoda, so rare in the higher parts of the series, appear. This
+marly deposit passes in its turn into beds containing green particles of a
+chloritic mineral, called the upper greensand. In parts of Surrey
+calcareous matter is largely intermixed, forming a stone called
+_firestone_. In the cliffs of the southern coast of the Isle of Wight, this
+upper greensand is 100 feet thick, and contains bands of siliceous
+limestone and calcareous sandstone with nodules of chert.
+
+[2 Illustrations: Fossils of the Upper Greensand.
+
+Fig. 219.
+
+  _a._ _Terebratula lyra._       } Upper greensand.
+  _b._ Same, seen in profile.    } France.
+
+Fig. 220. _Ammonites Rhotomagensis._ Upper greensand.]
+
+[Illustration: Fig. 221. _Hamites spiniger_ (Fitton);
+near Folkstone. Gault.]
+
+_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 greensand. Many
+peculiar forms of cephalopoda, such as the _Hamite_ (fig. 221.) and
+_Scaphite_, with other fossils, characterize 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.
+
+The phosphate of lime, found lately near Farnham, in Surrey, in such
+abundance as to be used largely by the agriculturist for fertilizing soils,
+occurs exclusively, according to Mr. R. A. C. Austen, in the upper
+greensand and gault. It is doubtless of animal origin, and partly
+coprolitic, probably derived from the excrement of fish.
+
+
+LOWER CRETACEOUS DIVISION. (No. 6. Tab. p. 209.)
+
+That part of the Cretaceous series which is older than the Gault has been
+commonly called the Lower Greensand. The greater number of its fossils are
+specifically distinct from those of the upper cretaceous system. Dr.
+Fitton, to whom we are indebted for an excellent monograph on this
+formation as developed in England, gives the following as the succession of
+rocks seen in parts of Kent.
+
+  No. 1. Sand, white, yellowish, or ferruginous, with
+         concretions of limestone and chert                70 feet.
+      2. Sand with green matter                            70 to 100 feet.
+      3. Calcareous stone, called Kentish rag              60 to 80 feet.
+
+In his detailed description of the fine section displayed at Atherfield,
+in the south of the Isle of Wight, we find the limestone wholly wanting;
+in fact, the variations in the mineral composition of this group, even
+in contiguous districts, is very great; and on comparing the Atherfield
+beds with corresponding strata at Hythe in Kent, distant 95 miles,
+the whole series has lost half its thickness, and presents a very
+dissimilar aspect.[219-A]
+
+On the other hand, Professor E. Forbes has shown that when the sixty-three
+strata at Atherfield are severally examined, the total thickness of which
+he gives as 843 feet, there are some fossils which range through the whole
+series, others which are peculiar to particular divisions. As a proof that
+all belong chronologically to one system, he states that whenever similar
+conditions are repeated in overlying strata the same species reappear.
+Changes of depth, or of the mineral nature of the 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 nothing to do with
+the extinction, throughout a large area, of certain animals or plants. The
+rule laid down by this eminent naturalist for enabling us to test the
+arrival of a new state of things in the animate world, is the
+representation by new and different species of corresponding genera of
+mollusca or other beings. When the forms proper to loose sand or soft clay,
+or a stony or calcareous bottom, or a moderate or a great depth of water,
+recur with all the same species, 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. On passing from the lower greensand to the gault, we suddenly
+reach one of these new epochs, scarcely any of the fossil species being
+common to the lower and upper cretaceous systems, a break in the chain
+implying no doubt many missing links in the series of geological monuments
+which we may some day be able to supply.
+
+One of the largest and most abundant shells in the lowest strata of the
+lower greensand, as displayed in the Atherfield section, is the large
+_Perna mulleti_ of which a reduced figure is here given (fig. 222.).
+
+[Illustration: Fig. 222. _Perna mulleti._ Desh. in Leym.
+
+  _a._ Exterior.
+  _b._ Hinge of upper valve.]
+
+In the south of England, during the accumulation of the lower greensand
+above described, the bed of the sea appears to have been continually
+sinking, from the commencement of the period, when the freshwater
+Wealden beds were submerged, to the deposition of those strata on which
+the gault immediately reposes.
+
+Pebbles of quartzose sandstone, jasper, and flinty slate, together with
+grains of chlorite and mica, speak plainly of the nature of the
+pre-existing rocks, from the wearing down of which the greensand beds
+were derived. The land, consisting of such rocks, was doubtless
+submerged before the origin of the white chalk, as corals can only
+multiply in the clear waters of the sea in spaces to which no mud or
+sand are conveyed by currents.
+
+
+HIPPURITE LIMESTONE.
+
+_Difference between the chalk of the north and south of Europe._--By the
+aid of the three tests of relative age, namely, 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.
+
+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 the chalk and Greensand in the neighbourhood of London and Paris 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 the annexed map, fig. 223., in which the
+shaded part represents chalk).
+
+[Illustration: Fig. 223. Map of south-western France.]
+
+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 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 a formation which we at once recognize by its
+mineral character to be chalk, although there are some places where the
+rock becomes oolitic. The fossils are, upon the whole, very similar;
+especially certain species of the genera _Spatangus_, _Ananchytes_,
+_Cidarites_, _Nucula_, _Ostrea_, _Gryphæa_ (_Exogyra_), _Pecten_,
+_Plagiostoma_ (_Lima_), _Trigonia_, _Catillus_, (_Inoceramus_), and
+_Terebratula_.[221-A] 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.
+
+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.
+
+[Illustration: Fig. 224.
+
+  _a._ _Radiolites radiosus_, D'Orb. (_Hippurites_, Lamk.)
+  _b._ Opercular valve of same.
+
+White chalk of France.]
+
+[Illustration: Fig. 225. _Radiolites foliaceus_, D'Orb. Syn. _Sphærulites
+agariciformis_, Blainv. White chalk of France.]
+
+[Illustration: Fig. 226. _Hippurites organisans_, Desmoulins. Upper
+chalk:--chalk marl of Pyrenees?[222-A]
+
+  _a._ Young individual; when full grown they occur in groups adhering
+       laterally to each other.
+  _b._ Upper side of the opercular valve, showing a reticulated structure
+       in those parts, _b_, where the external coating is worn off.
+  _c._ Upper side of the lower and cylindrical valve.
+  _d._ Cast of the interior of the lower conical valve.]
+
+The species called _Hippurites organisans_ (fig. 226.) is more abundant
+than any other in the south of Europe; and the geologist should make
+himself well acquainted with the cast _d_, which is far more common in many
+compact marbles of the upper cretaceous period than the shell itself, which
+has often wholly disappeared. The flutings, or smooth, rounded,
+longitudinal ribs, representing the form of the interior, are wholly
+unlike the hippurite itself, and in some individuals, which attain a great
+size and length, are very conspicuous.
+
+Between the region of chalk last mentioned in which Perigueux is situated,
+and the Pyrenees, the space B intervenes. (See Map, p. 221.) Here the
+tertiary strata cover, and for the most part conceal, the cretaceous rocks,
+except in some spots where they have been laid open by the denudation of
+newer formations. In these places they are seen still preserving the form
+of a white chalky rock, which is charged in part with grains of green sand.
+Even as far south as Tercis, on the Adour, near Dax, where I examined them
+in 1828, the cretaceous rocks retain this character. In that region M.
+Grateloup has found in them _Ananchytes ovata_ (fig. 212.), and other
+fossils of the English chalk, together with _Hippurites_.
+
+
+FLORA OF THE CRETACEOUS PERIOD.
+
+Although the fossil plants of the Cretaceous era at present known are
+few in number, the rocks being principally marine, they suffice,
+according to M. Ad. Brongniart, to show a transition character between
+the vegetation of the secondary and that of the tertiary formations. The
+tertiary strata, when compared to the older rocks, are marked by the
+predominance of _Exogens_, which now constitute three-fourths of the
+living plants of the globe.[223-A]
+
+These exogens are wanting in the secondary strata generally, but in the
+Cretaceous period they equal in number the _Gymnogens_ (_Coniferæ_ and
+_Cycadeæ_) which abounded so much in the preceding Oolitic period, and
+disappeared before the Eocene rocks were formed.[223-B] The discovery of a
+tree-fern in the ferruginous sands of the Lower Cretaceous group of the
+department of Ardennes in France is one of many signs of the contrast of
+the flora, and doubtless of the climate, of this era with that of the
+Pliocene and Modern periods.
+
+
+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 our Upper Cretaceous
+system; which we can, nevertheless, recognize as referable,
+paleontologically, to the same division.
+
+That they were about the same age generally as the European chalk and
+greensand, was the conclusion to which Dr. Morton and Mr. Conrad came after
+their investigation of the fossils in 1834. The strata consist chiefly of
+greensand 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_, _Belemnites
+mucronatus_. 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 are different, the generic forms, such as
+the Baculite and certain sections of Ammonites, as also the Inoceramus (see
+above, fig. 208.) 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.[224-A]
+
+Fish of the genera _Lamna_, _Galeus_, and _Carcharias_ are common to New
+Jersey and the European cretaceous rocks. So also is the genus _Mosasaurus_
+among reptiles, and _Pliosaurus_ (Owen), another saurian likewise obtained
+from the English chalk. From New Jersey the cretaceous formation extends
+southwards to North Carolina, Georgia, and Alabama, cropping out at
+intervals from beneath the tertiary strata, between the Appalachian
+Mountains and the Atlantic. They then sweep round the southern extremity of
+that chain, and stretch northwards again to Tennessee and Kentucky. They
+have also been traced far up the valley of the Missouri 275 English miles
+above its mouth, to the neighbourhood of Fort Leavenworth; and southwards
+to Texas, according to the observations of Ferdinand Römer; so that already
+the area which they are ascertained to occupy in North America may perhaps
+equal their extent in Europe. So little do they resemble mineralogically
+the European white chalk, that limestone in North America is, upon the
+whole, an exception to the rule; and, even in Alabama, where I saw a
+calcareous member of this group, the marlstones are much more like the
+English and French Lias than any other secondary deposit of the Old World.
+
+At the base of the system in Alabama I found dense masses of shingle,
+perfectly loose and unconsolidated, derived from the waste of paleozoic
+(or carboniferous) rocks, a mass in no way distinguishable, except
+by its position, from ordinary alluvium, but covered with marls
+abounding in Inocerami.
+
+In Texas, according to F. Römer, the chalk assumes a new lithological type,
+a large portion of it consisting of hard siliceous limestone, but the
+organic remains leaving no doubt in regard to its age.
+
+In South America the cretaceous strata have been discovered in Columbia, as
+at Bogota and elsewhere, containing Ammonites, Hamites, Inocerami, and
+other characteristic shells.[225-A]
+
+In the South of India, also, at Pondicherry, Verdachellum, and
+Trinconopoly, Messrs. Kaye and Egerton have collected fossils belonging to
+the cretaceous system. Taken in connection with those from the United
+States they prove, says Prof. E. Forbes, that those powerful causes which
+stamped a peculiar character on the forms of marine animal life at this
+period, exerted their full intensity through the Indian, European, and
+American seas.[225-B] Here, as in North and South America, the cretaceous
+character can be recognized even where there is no specific identity in the
+fossils; and the same may be said of the organic type of those rocks in
+Europe and India which succeed next in the ascending and descending order,
+the Eocene and the Oolitic.
+
+
+FOOTNOTES:
+
+[209-A] M. Alcide d'Orbigny, in his valuable work entitled Paléontologie
+Française, has adopted new terms for the French subdivisions of the
+Cretaceous Series, which, so far as they can be made to tally with English
+equivalents, seem explicable thus:
+
+  Danien.      Maestricht beds.
+  Senonien.    Upper and lower white chalk, and chalk marl.
+  Turonien.    Part of the chalk marl and the upper greensand, the latter
+               being in his last work (Cours Elémentaire) termed
+               Cénomanien.
+  Albien.      Gault.
+  Aptien.      Upper part of lower greensand.
+  Neocomien.   Lower part of same.
+
+[211-A] See paper by the author, Trans. of Geol. Soc., vol. v.
+p. 246., 1840.
+
+[211-B] Fitton, Geol. Trans., 2d series, vol. iv. p. 319.
+
+[215-A] Proceedings of Geol. Soc., vol. iii. pp. 7, 8., 1842.
+
+[216-A] Geol. Trans. Second Series, vol. iii. p. 232. plate 31.
+figs. 3. and 11.
+
+[216-B] Geol. of U. S. Exploring Exped. p. 252. 1849.
+
+[217-A] See Chapters X. and XI.
+
+[217-B] Darwin, p. 549. Kotzebue's First Voyage, vol. iii. p. 155.
+
+[217-C] Mantell, Geol. of S. E. of England, p. 96.
+
+[219-A] Dr. Fitton, Quart. Geol. Journ., vol. i. p. 179., ii. p. 55.,
+and iii. p. 289., where comparative sections and a valuable table
+showing the vertical range of the various fossils of the lower greensand
+at Atherfield is given.
+
+[221-A] Archiac, sur la Form. Crétacée du S. O. de la France, Mém. de la
+Soc. Géol. de France, tom. ii.
+
+[222-A] D'Orbigny's Paléontologie Française, pl. 533.
+
+[223-A] 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.
+
+       |         Brongniart.
+       |             |        |Lindley.
+       |             |        |           Examples.
+  Cryptogamic.
+       |             |1. Cryptogamous amphigens, or cellular cryptogamic.
+       |             |        |Thallogens.
+       |             |        |           |Lichens, sea-weeds, fungi.
+       |             |2. Cryptogamous acrogens.
+       |             |        |Acrogens.
+       |             |        |           |Mosses, equisetums, ferns,
+       |             |        |           |lycopodiums--Lepidodendron.
+       |             |        |           |
+  Phanerogamic.
+       |             |3. Dicotyledonous gymnosperms.
+       |             |        |Gymnogens.
+       |             |        |           |Conifers and Cycads.
+       |             |4. Dicot. Angiosperms.
+       |             |        |Exogens.
+       |             |        |           |Compositæ, leguminosæ, umbelliferæ,
+       |             |        |           |cruciferæ, heaths, &c. All native
+       |             |        |           |European trees except conifers.
+       |             |5. Monocotyledons.
+       |             |        |Endogens.
+       |             |        |           |Palms, lilies, aloes, rushes,
+       |             |        |           |grasses, &c.
+
+[223-B] A. Brongniart, Veget. Foss. Dict. Univ., p. 111., 1849.
+
+[224-A] See a paper by the author, Quart. Journ. Geol. Soc., vol. i. p. 55.
+
+[225-A] Proceed. Geol. Soc. iv. p. 391.
+
+[225-B] See Forbes, Quart. Geol. Journ. vol. i. p. 79.
+
+
+
+
+CHAPTER XVIII.
+
+WEALDEN GROUP.
+
+   The Wealden divisible into Weald Clay, Hastings Sand, and Purbeck
+   Beds--Intercalated between two marine formations--Weald clay and
+   Cypris-bearing strata--Iguanodon--Hastings sands--Fossil fish--Strata
+   formed in shallow water--Brackish water-beds--Upper, middle, and lower
+   Purbeck--Alternations of brackish water, freshwater, and
+   land--Dirt-bed, or ancient soil--Distinct species of fossils in each
+   subdivision of the Wealden--Lapse of time implied--Plants and insects
+   of Wealden--Geographical extent of Wealden--Its relation to the
+   cretaceous and oolitic periods--Movements in the earth's crust to
+   which it owed its origin and submergence.
+
+
+Beneath the cretaceous rocks in the S.E. of England, a freshwater formation
+is found, called the Wealden (see Nos. 5. and 6. Map, p. 242.), which,
+although it occupies a small horizontal area in Europe, as compared to the
+chalk, is nevertheless of great geological interest, not only from its
+position, as being interpolated between two great marine formations (Nos.
+7. and 9. Table, p. 103.), but also because the imbedded fossils indicate a
+grand succession of changes in organic life, effected during its
+accumulation. It is composed of three minor divisions, the Weald Clay, the
+Hastings, and the Purbeck Beds, of which the aggregate thickness in some
+districts may be 700 or 800 feet; but which would be much more considerable
+(perhaps 2000 feet), were we to add together the extreme thickness acquired
+by each of them in their fullest development.
+
+The common name of Wealden was given to the whole, because it was first
+studied in parts of Kent, Surrey, and Sussex, called the Weald, (see Map,
+p. 242.), 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, Terebratulæ, Echinites, Corals, and other marine fossils, so
+characteristic of the cretaceous rocks above, and of the Oolitic strata
+below, and to the presence of Paludinæ, Melaniæ, and various fluviatile
+shells, as well as the bones of terrestrial reptiles and the trunks and
+leaves of land plants.
+
+[Illustration: Fig. 227. Position of the Wealden between two
+marine formations.]
+
+The evidence of so unexpected a fact as the infra-position of a dense mass
+of purely freshwater origin to a deep-sea deposit (a phenomenon with which
+we have since become familiar, in other chapters of the earth's
+autobiography), 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 Greensand in various
+parts of Surrey, Kent, and Sussex; and if we proceed from Sussex westward
+to the Vale of Wardour, we there again observe the same formation, or, at
+least, the lower division of it, the Purbeck, occupying the same relative
+position, and resting on the Oolite (see fig. 228.). Or if we pass from the
+base of the South Downs in Sussex, and cross to the Isle of Wight, we there
+again meet with the Wealden series reappearing beneath the Greensand, and
+cannot doubt that the beds are prolonged subterraneously, as indicated by
+the dotted lines in fig. 229.
+
+[Illustration: Fig. 228. Cross section.
+
+  O, Oolite.
+  G S, Greensand, or Lower Cretaceous.]
+
+[Illustration: Fig. 229. Cross section.]
+
+The minor groups into which the Wealden has been commonly divided in
+England are, as before stated, three, and they succeed each other in the
+following descending order[227-A]:--
+
+                                                            Thickness.
+  1st. Weald Clay, sometimes including thin beds of
+       sand and shelly limestone                            140 to 280 ft.
+  2d.  Hastings Sand, in which occur some clays and
+       calcareous grits                                     400 to 500 ft.
+  3d.  Purbeck Beds, consisting of various kinds of
+       limestones and marls                                 150 to 200 ft.
+
+
+_Weald Clay._
+
+The first division, or Weald Clay, is of purely freshwater origin. The
+uppermost beds are not only conformable, as Dr. Fitton observes, to the
+inferior strata of the Lower Greensand, 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 freshwater, 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 Lower Greensand. Hence we may infer that some of the
+saurians which inhabited the country of the great river continued to live
+when part of the country 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 freshwater 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 freshwater
+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 freshwater strata.
+
+The Iguanodon, first discovered by Dr. Mantell, has left more of its
+remains in the Wealden strata of the south-eastern counties, and Isle of
+Wight, than any other genus of associated saurians. It was an
+herbivorous reptile, and regarded by Cuvier as more extraordinary than
+any with which he was acquainted; for the teeth, though bearing a great
+analogy to the modern Iguanas which now frequent the tropical woods of
+America and the West Indies, exhibit many striking and important
+differences (see fig. 230.). It appears that they have been worn by
+mastication; whereas the existing herbivorous reptiles clip and gnaw off
+the vegetable productions on which they feed, but do not chew them.
+Their teeth, when worn, present an appearance of having been chipped
+off, and never, like the fossil teeth of the Iguanodon, have a flat
+ground surface (see fig. 231.), resembling the grinders of herbivorous
+mammalia. Dr. Mantell computes that the teeth and bones of this animal
+which have passed under his examination during the last 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 24 inches in circumference. Yet
+notwithstanding that the teeth were more numerous than any other bones,
+it is remarkable that it was not till the relics of all these
+individuals had been found, that a solitary example of part of a
+jaw-bone was obtained. More recently remains both of the upper and lower
+jaw have been met with in the Hastings Beds in Tilgate Forest. Their
+size was somewhat greater than had been anticipated, and even allowing
+that the tail was short, which Professor Owen infers from the short
+bodies of the caudal vertebræ, Dr. Mantell estimates the probable length
+of some of these saurians at between 30 and 40 feet. The largest femur
+yet found measures 4 feet 8 inches in length, the circumference of the
+shaft being 25 inches, and round the condyles 42 inches.
+
+[2 Illustrations: Teeth of Iguanodon.
+
+Fig. 230. Partially worn tooth of a young animal. (Mantell.)
+
+Fig. 231. Crown of tooth in adult, worn down. (Mantell.)]
+
+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.
+
+[Illustration: Fig. 232. _Cypris spinigera_, Fitton.]
+
+[Illustration: Fig. 233. _Cypris Valdensis_, Fitton. (_C. faba_,
+Min. Con. 485.)]
+
+[Illustration: Fig. 234. _Cypris tuberculata_, Fitton.]
+
+[Illustration: Fig. 235. Sample with lamination.]
+
+Shells of the _Cypris_, an animal belonging to the Crustacea, and before
+mentioned (p. 31.) as abounding in lakes and ponds, are also plentifully
+scattered through the clays of the Wealden, sometimes producing, like
+the plates of mica, a thin lamination (see fig. 235.). Similar
+cypriferous marls are found in the lacustrine tertiary beds of
+Auvergne (see above, p. 183.).
+
+
+_Hastings Sands._
+
+This middle division of the Wealden consists of sand, calciferous grit,
+clay, and shale; the argillaceous strata, notwithstanding the name,
+being nearly in the same proportion as the arenaceous. The calcareous
+sandstone and grit of Tilgate Forest, near Cuckfield, in which the
+remains of the Iguanodon and Hyleosaurus were first found, constitute an
+upper member of this formation. The white "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 it, consist partly of saurians,
+already 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 Testudinata of the genera _Trionyx_ and
+_Emys_, now confined to tropical regions.
+
+[Illustration: Fig. 236. _Lepidotus Mantelli_, Agass. Wealden.
+
+  _a._ palate and teeth.
+  _b._ side view of teeth.
+  _c._ scale.]
+
+The fishes of the Wealden belong partly to the genera _Pycnodus_ and
+_Hybodus_ (see figure of genus in Chap. XXI.), forms common to the Wealden
+and Oolite; but the teeth and scales of a species of _Lepidotus_ are most
+widely diffused (see fig. 236.). The general form of these fish was that of
+the carp tribe, although perfectly distinct in anatomical character, and
+more allied to the pike. The whole body was covered with large rhomboidal
+scales, very thick, and having the exposed part covered with enamel. Most
+of the species of this genus are supposed to have been either river fish,
+or inhabitants of the coasts, having not sufficient powers of swimming to
+advance into the deep sea.
+
+[Illustration: Fig. 237. _Corbula alata_, Fitton. Magnified.]
+
+The shells of the Hastings beds belong to the genera _Melanopsis_,
+_Melania_, _Paludina_, _Cyrena_, _Cyclas_, _Unio_, and others, which
+inhabit rivers or lakes; but one band has been found in Dorsetshire
+indicating a brackish state of the water, and, in some places, even a
+saltness, like that of the sea, where the genera _Corbula_ (see fig. 237.),
+_Mytilus_, and _Ostrea_ occur. At different heights in the Hastings Sand,
+in the middle of the Wealden, 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, near Horsham, 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. 238.).
+
+[Illustration: Fig. 238. Underside of slab of sandstone about one yard in
+diameter. Stammerham, Sussex.]
+
+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.[230-A] In the same division also of the Wealden, at
+Cuckfield, is a bed of gravel or conglomerate, consisting of water-worn
+pebbles of quartz and jasper, with rolled bones of reptiles. These must
+have been drifted by a current, probably in water of no great depth.
+
+[Illustration: Fig. 239. _Sphenopteris gracilis_ (Fitton), from
+near Tunbridge Wells.
+
+_a._ portion of the same magnified.]
+
+From such facts we may infer that, notwithstanding the great thickness of
+this division of the Wealden (and the same observation applies to the Weald
+Clay and Purbeck Beds), 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, such as the Portland Oolite, 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.
+
+
+_Purbeck Beds._
+
+Immediately below the Hastings Sands we find a series of calcareous
+slates, marls, and limestones, called the Purbeck Beds, because well
+exposed to view in the sea-cliffs of the Peninsula of Purbeck,
+especially in Durlestone Bay, near Swanage. They may also be
+advantageously studied at Lulworth Cove and the neighbouring bays
+between Weymouth and Dorchester. At Meup's Bay in particular, Prof. E.
+Forbes has recently examined minutely the organic remains of the three
+members of the Purbeck group, displayed there in a vertical section 155
+feet thick. To the information previously supplied in the works of
+Messrs. Webster, Fitton, De la Beche, Buckland, and Mantell, he has made
+most ample and important additions, so that it will be desirable to give
+them at some length, it appearing 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. This
+result cannot fail to excite much wonder, and it leads us to suspect
+that the Wealden period, which many geologists have scarcely deigned
+to notice in their classification, may comprehend the history of a
+lapse of time as great as that of the Oolitic or Cretaceous
+eras respectively.[231-A]
+
+_Upper Purbeck._--The highest of the three divisions is purely freshwater,
+the strata, about 50 feet in thickness, containing shells of the genera
+_Paludina_, _Physa_, _Lymnea_, _Planorbis_, _Valvata_, _Cyclas_, and
+_Unio_, with cyprides, and fish.
+
+_Middle Purbeck._--To these succeed the Middle Purbeck, about 30 feet
+thick, the uppermost part of which consists of freshwater 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 _Corvulæ_ and _Melaniæ_.
+These are based on a purely marine deposit, with _Pecten_, _Modiola_,
+_Avicula_, and _Thracia_, all undescribed shells. Below this, again, come
+limestones and shales, partly of brackish and partly of freshwater origin,
+in which many fish, especially species of _Lepidotus_ and _Microdon
+radiatus_, are found, and a reptile named _Macrorhyncus_. Among the
+mollusks, a remarkable ribbed _Melania_, of the section _Chilira_, occurs.
+
+Immediately below is the great and conspicuous stratum, 12 feet thick, long
+familiar to geologists under the local name of "Cinder-bed," formed of a
+vast accumulation of shells of _Ostrea distorta_ (fig. 240.). In the
+uppermost part of this bed Mr. Forbes discovered the first echinoderm as
+yet known in the Purbeck series, a species of _Hemicidaris_, a genus
+characteristic of the Oolitic period. It was accompanied by a species of
+_Perna_. Below the Cinder-bed freshwater strata are again seen, filled in
+many places with species of _Cypris_, _Valvata_, _Paludina_, _Planorbis_,
+_Lymnea_, _Physa_, and _Cyclas_, all different from any we had previously
+seen above. Thick siliceous beds of chert, filled with these fossils, occur
+in a beautiful state of preservation, often converted into chalcedony.
+Among these Mr. Forbes met with gyrogonites (the spore vesicles of
+_Charæ_), plants never before discovered in rocks older than the Eocene.
+Again, beneath these freshwater strata, a very thin band of greenish
+shales, with marine shells and impressions of leaves, like those of a large
+_Zostera_, succeeds, forming the base of the Middle Purbeck.
+
+[Illustration: Fig. 240. Ostrea distorta. Cinder-bed.]
+
+_Lower Purbeck._--Beneath the thin marine band last mentioned, purely
+freshwater marls occur, containing species of _Cypris_, _Valvata_, and
+_Lymnea_, 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 more than 30 feet of brackish-water beds, at Meup's Bay, abounding in
+a species of _Serpula_, allied to, if not identical with, _Serpula
+coacervites_, found in the Wealden of Hanover. There are also shells of the
+genus _Rissoa_ (of the subgenus _Hydrobia_), and a little _Cardium_ of the
+subgenus _Protocardium_, in the same 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, resting upon the lowest freshwater
+limestone, a rock about 8 feet thick, containing _Cyclades_, _Valvata_, and
+_Lymnea_, of the same species as those of the uppermost part of the Lower
+Purbeck. This rock rests upon the top beds of the Portland stone, which is
+purely marine, and between which and the Purbecks there is no passage.
+
+The most remarkable of all the varied successions 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 fragments of stone,
+from 3 to 9 inches in diameter, in such numbers that it almost deserves the
+name of gravel. Many silicified trunks of coniferous trees, and the remains
+of plants allied to _Zamia_ and _Cycas_, are buried in this dirt-bed (see
+figure of living _Zamia_, fig. 241.).
+
+These plants must have become fossil on the spots where they grew. The
+stumps of the trees stand erect for a height of from 1 to 3 feet, and even
+in one instance to 6 feet, with their roots attached to the soil at about
+the same distances from one another as the trees in a modern
+forest.[233-A] The carbonaceous matter is most abundant immediately around
+the stumps, and round the remains of fossil _Cycadeæ_.[233-B]
+
+[Illustration: Fig. 241. Zamia spiralis; Southern Australia.[233-C]]
+
+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 3 or 4
+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 roots is about 1 foot.[233-D] Root-shaped
+cavities were observed by Professor Henslow to descend from the bottom of
+the dirt-bed into the subjacent freshwater stone, which, though now solid,
+must have been in a soft and penetrable state when the trees grew.[233-E]
+
+[Illustration: Fig. 242. Section in Isle of Portland, Dorset.
+(Buckland and De la Beche.)]
+
+The thin layers of calcareous slate (fig. 242.) 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.
+
+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. 243.). Traces of the dirt-bed have also been observed
+by Dr. Buckland, about two miles north of Thame, in Oxfordshire; and by Dr.
+Fitton, in the cliffs of the Boulonnois, on the French coast; but, as might
+be expected, this freshwater deposit is of limited extent when compared to
+most marine formations.
+
+[Illustration: Fig. 243. Section in cliff east of Lulworth Cove.
+(Buckland and De la Beche.)]
+
+From the facts above described, we may infer, first, that the superior
+beds of the 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 admit the growth of
+the _Zamia_ and _Cycas_. 2dly. 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. 3dly. 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
+freshwater 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 then taken place.
+
+The dirt-bed has been described above in its most simple form, but in some
+sections the appearances are more complicated. The forest of the dirt-bed
+was not everywhere the first vegetation which grew in this region. Two
+other beds of carbonaceous clay, one of them containing _Cycadeæ_, in an
+upright position, have been found below it, and one above it[234-A], which
+implies other oscillations in the level of the same ground, and its
+alternate occupation by land and water more than once.
+
+_Table showing the changes of medium in which the strata were formed,
+from the Lower Greensand to the Portland Stone inclusive, in the
+south-east of England._
+
+  1. Marine              Lower greensand.
+
+  2. Freshwater          Weald clay.
+
+  3. Freshwater       }
+     Brackish         }  Hastings sand.
+     Freshwater       }
+
+  4. Freshwater          Upper Purbeck.
+
+  5. Freshwater       }
+     Brackish         }
+     Marine           }
+     Brackish         }  Middle Purbeck.
+     Marine           }
+     Freshwater       }
+     Marine           }
+
+  6. Freshwater       }
+     Brackish         }
+     Land             }
+     Freshwater       }
+     Land (dirt-bed)  }  Lower Purbeck.
+     Freshwater       }
+     Land             }
+     Freshwater       }
+     Land             }
+     Freshwater       }
+
+  7. Marine              Portland stone.
+
+The annexed tabular view will enable the reader to take in at a glance the
+successive changes from sea to river, and from river to sea, or from these
+again to a state of land, which have occurred in this part of England
+between the Cretaceous and Oolitic periods. That there have been at least
+four changes in the species of testacea during the deposition of the
+Wealden, seems to follow from the observations recently made by Professor
+E. Forbes, so that, should we hereafter find the signs of many more
+alternate occupations of the same area by different elements, it is no more
+than we might expect. Even during a small part of a zoological period, not
+sufficient to allow time for many species to die out, we find that the same
+area has been laid dry, and then submerged, and then again laid dry, as in
+the deltas of the Po and Ganges, the history of which has been brought to
+light by Artesian borings.[235-A] We also know that similar revolutions
+have occurred within the present century (1819) in the delta of the Indus
+in Cutch[235-B], where land has been laid permanently under the waters both
+of the river and sea, without its soil or shrubs having been swept away.
+Even, independently of any vertical movements of the ground, we see in the
+principal deltas, such as that of the Mississippi, that the sea extends its
+salt waters annually for many months over considerable spaces, which, at
+other seasons, are occupied by the river during its inundations.
+
+It will be observed that the division of the Purbecks into upper, middle,
+and lower, has been made by Professor E. Forbes, strictly on the principle
+of the entire distinctness of the species of organic remains which they
+include. The lines of demarcation 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 organized beings. "The causes which led to a
+complete change of life three times during the deposition of the freshwater
+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 2 or 3 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 imagined the fossil soils of the Lower Purbeck to represent as
+many ages, we need not expect on that account to find them constituting the
+lines of separation between successive strata characterized 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 dirt-beds were probably formed in succession, and annihilated in
+the Wealden, besides those few which now remain.
+
+[Illustration: Fig. 244. Cone from the Isle of Purbeck, resembling the
+_Dammara_ of the Moluccas. (Fitton.)]
+
+The plants of the Wealden, so far as our knowledge extends at present,
+consist chiefly of Ferns, Coniferæ (see fig. 244.), and Cycadeæ, without
+any exogens; the whole more allied to the Oolitic than to the Cretaceous
+vegetation, although some of the species seem to be common to the chalk.
+But the vertebrate and invertebrate animals indicate, in like manner, a
+relationship to both these periods, though a nearer affinity to the
+Oolitic. Mr. Brodie has found the remains of beetles and several insects of
+the homopterous and trichopterous orders, some of which now live on plants,
+like those of the Wealden, while others hover over the surface of our
+present rivers. But no bones of mammalia have been met with among those of
+land-reptiles. Yet, as the reader will learn, in Chapter XX., that the
+relics of marsupial quadrupeds have been detected in still older beds, and,
+as it was so long before a single portion of the jaw of an iguanodon was
+met with in the Tilgate quarries (see p. 228.), we need by no means despair
+of discovering hereafter some evidence of the existence of warm-blooded
+quadrupeds at this era. It is, at least, too soon to infer, on mere
+negative evidence, that the mammalia were foreign to this fauna.
+
+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 200 English miles from west to
+east, from Lulworth Cove to near Boulogne, in France; and about 220 miles
+from north-west to south-east, from Whitchurch, in Buckinghamshire, to
+Beauvais, 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 change 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.[237-A] Besides, we know not, in such cases, how far the fluviatile
+sediment and organic remains of the river and the land may be carried out
+from the coast, and spread over the bed of the sea. I have 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[237-B]; and
+the possibility of such movements, and their effects, must not be lost
+sight of when we speculate on the origin of the Wealden.
+
+If it 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, we are half tempted to speculate on the former existence
+of the Atlantis of Plato. The story of the submergence of an ancient
+continent, however fabulous in history, must have been true again and
+again as a geological event.
+
+The real difficulty consists in the persistence of a large hydrographical
+basin, from whence a great body of fresh water was poured into the sea,
+precisely at a period when the neighbouring area of the Wealden was
+gradually going downwards 1000 feet or more perpendicularly. If the
+adjoining land participated in the movement, how could it escape being
+submerged, or how could it retain its size and altitude so as to continue
+to be the source of such an inexhaustible supply of fresh water and
+sediment? In answer to this question, we are fairly entitled to suggest
+that the neighbouring land may have been stationary, or may even have
+undergone a contemporaneous slow upheaval. There may have been an ascending
+movement in one region, and a descending one in a contiguous parallel zone
+of country; just as the northern part of Scandinavia is now rising, while
+the middle portion (that south of Stockholm) is unmoved, and the southern
+extremity in Scania is sinking, or at least has sunk within the historical
+period.[237-C] We must, nevertheless, conclude, if we adopt the above
+hypothesis, that the depression of the land became general throughout a
+large part of Europe at the close of the Wealden period, a subsidence which
+brought in the cretaceous ocean.
+
+
+FOOTNOTES:
+
+[227-A] Dr. Fitton, Geol. Trans. vol. iv. p. 320. Second Series.
+
+[230-A] Mantell, Geol. of S. E. of England, p. 244.
+
+[231-A] "On the Dorsetshire Purbecks," by Prof. E. Forbes, Edinb. Brit.
+Assoc., Aug. 1850.
+
+[233-A] Mr. Webster first noticed the erect position of the trees and
+described the Dirt-bed.
+
+[233-B] Fitton, Geol. Trans., Second Series, vol. iv. pp. 220, 221.
+
+[233-C] See Flinders' Voyage.
+
+[233-D] Fitton, ibid.
+
+[233-E] Buckland and De la Beche, Geol. Trans., Second Series, vol. iv.
+p. 16. Mr. Forbes has ascertained that the subjacent rock is a
+freshwater limestone, and not a portion of the Portland oolite, as
+was previously imagined.
+
+[234-A] E. Forbes, ibid.
+
+[235-A] See Principles of Geol., 8th ed. pp. 260-268.
+
+[235-B] Ibid. p. 443.
+
+[237-A] Fitton, Geol. of Hastings, p. 58.; who cites Lander's Travels.
+
+[237-B] See above, p. 85.; and Second Visit to the U. S. vol. ii.
+chap. xxxiv.
+
+[237-C] See the Author's Anniv. Address, Geol. Soc. 1850, Quart. Geol.
+Journ. vol. vi. p. 52.
+
+
+
+
+CHAPTER XIX.
+
+DENUDATION OF THE CHALK AND WEALDEN.
+
+   Physical geography of certain districts composed of Cretaceous and
+   Wealden strata--Lines of inland chalk-cliffs on the Seine in
+   Normandy--Outstanding pillars and needles of chalk--Denudation of the
+   chalk and Wealden in Surrey, Kent, and Sussex--Chalk once continuous
+   from the North to the South Downs--Anticlinal axis and parallel
+   ridges--Longitudinal and transverse valleys--Chalk escarpments--Rise
+   and denudation of the strata gradual--Ridges formed by harder, valleys
+   by softer beds--Why no alluvium, or wreck of the chalk, in the central
+   district of the Weald--At what periods the Weald valley was
+   denuded--Land has most prevailed where denudation has been
+   greatest--Elephant bed, Brighton.
+
+
+All the fossiliferous formations may be studied by the geologist in two
+distinct points of view: first, in reference to their position in the
+series, their mineral character and fossils; and, secondly, in regard to
+their physical geography, or the manner in which they now enter, as mineral
+masses, into the external structure of the earth; forming the bed of lakes
+and seas, or the surface and foundation of hills and valleys, plains and
+table-lands. Some account has already been given on the first head of the
+Tertiary, the Cretaceous, and Wealden strata; and we may now proceed to
+consider certain features in the physical geography of these groups as they
+occur in parts of England and France.
+
+The hills composed of white chalk in the S.E. of England have a smooth
+rounded outline, and being usually in the state of sheep pastures, are free
+from trees or hedgerows; so that we have an opportunity of observing how
+the valleys by which they are drained ramify in all directions, and become
+wider and deeper as they descend. Although these valleys are now for the
+most part dry, except during heavy rains and the melting of snow, they may
+have been due to aqueous denudation, as explained in the sixth chapter;
+having been excavated when the chalk emerged gradually from the sea. This
+opinion is confirmed by the occasional occurrence of long lines of inland
+cliffs, in which the strata are cut off abruptly in steep and often
+vertical precipices. The true nature of such escarpments is nowhere more
+obvious than in parts of Normandy, where the river Seine and its
+tributaries flow through deep winding valleys, hollowed out of chalk
+horizontally stratified. Thus, for example, if we follow the Seine for a
+distance of about 30 miles from Andelys to Elboeuf, we find the valley
+flanked on both sides by a deep slope of chalk, with numerous beds of
+flint, the formation being laid open for a thickness of about 250 and 300
+feet. Above the chalk is an overlying mass of sand, gravel, and clay, from
+30 to 100 feet thick. The two opposite slopes of the hills _a_ and _b_,
+where the chalk appears at the surface, are from 2 to 4 miles apart, and
+they are often perfectly smooth and even, like the steepest of our downs in
+England; but at many points they are broken by one, two, or more ranges of
+vertical and even overhanging cliffs of bare white chalk with flints. At
+some points detached needles and pinnacles stand in the line of the cliffs,
+or in front of them, as at _c_, fig. 245. On the right bank of the Seine,
+at Andelys, one range, about 2 miles long, is seen varying from 50 to 100
+feet in perpendicular height, and having its continuity broken by a number
+of dry valleys or coombs, in one of which occurs a detached rock or needle,
+called the Tête d'Homme (see figs. 246, 247.). The top of this rock
+presents a precipitous face towards every point of the compass; its
+vertical height being more than 20 feet on the side of the downs, and 40
+towards the Seine, the average diameter of the pillar being 36 feet. Its
+composition is the same as that of the larger cliffs in its neighbourhood,
+namely, white chalk, having occasionally a crystalline texture like marble,
+with layers of flint in nodules and tabular masses. The flinty beds often
+project in relief 4 or 5 feet beyond the white chalk, which is generally in
+a state of slow decomposition, either exfoliating or being covered with
+white powder, like the chalk cliffs on the English coast; and, as in them,
+this superficial powder contains in some places common salt.
+
+[Illustration: Fig. 245. Section across Valley of Seine.]
+
+[Illustration: Fig. 246. View of the Tête d'Homme, Andelys,
+seen from above.]
+
+Other cliffs are situated on the right bank of the Seine, opposite
+Tournedos, between Andelys and Pont de l'Arche, where the precipices are
+from 50 to 80 feet high: several of their summits terminate in pinnacles;
+and one of them, in particular, is so completely detached as to present a
+perpendicular face 50 feet high towards the sloping down. On these cliffs
+several ledges are seen, which mark so many levels at which the waves of
+the sea may be supposed to have encroached for a long period. At a still
+greater height, immediately above the top of this range, are three much
+smaller cliffs, each about 4 feet high, with as many intervening terraces,
+which are continued so as to sweep in a semicircular form round an
+adjoining coomb, like those in Sicily before described (p. 76.).
+
+[Illustration: Fig. 247. Side view of the Tête d'Homme.
+White chalk with flints.]
+
+[Illustration: Fig. 248. Chalk pinnacle at Senneville.]
+
+[Illustration: Fig. 249. Roches d'Orival, Elboeuf.]
+
+If we then descend the river from Vatteville to a place called Senneville,
+we meet with a singular needle about 50 feet high, perfectly isolated on
+the escarpment of chalk on the right bank of the Seine (see fig. 248.).
+Another conspicuous range of inland cliffs is situated about 12 miles below
+on the left bank of the Seine, beginning at Elboeuf, and comprehending the
+Roches d'Orival (see fig. 249.). Like those before described, it has an
+irregular surface, often overhanging, and with beds of flint projecting
+several feet. Like them, also, it exhibits a white powdery surface, and
+consists entirely of horizontal chalk with flints. It is 40 miles inland,
+its height, in some parts, exceeding 200 feet, and its base only a few feet
+above the level of the Seine. It is broken, in one place, by a pyramidal
+mass or needle, 200 feet high, called the Roche de Pignon, which stands out
+about 25 feet in front of the upper portion of the main cliffs, with which
+it is united by a narrow ridge about 40 feet lower than its summit (see
+fig. 250.). Like the detached rocks before mentioned at Senneville,
+Vatteville, and Andelys, it may be compared to those needles of chalk which
+occur on the coast of Normandy, as well as in the Isle of Wight and in
+Purbeck[241-A] (see fig. 251.).
+
+[Illustration: Fig. 250. View of the Roche de Pignon, seen from the south.]
+
+[Illustration: Fig. 251. Needle and Arch of Etretat, in the chalk cliffs of
+Normandy. Height of Arch 100 feet. (Passy.)[241-B]]
+
+The foregoing description and drawings will show, that the evidence of
+certain escarpments of the chalk having been originally sea-cliffs, is far
+more full and satisfactory in France than in England. If it be asked why,
+in the interior of our own country, we meet with no ranges of precipices
+equally vertical and overhanging, and no isolated pillars or needles, we
+may reply that the greater hardness of the chalk in Normandy may, no doubt,
+be the chief cause of this difference. But the frequent absence of all
+signs of littoral denudation in the valley of the Seine itself is a
+negative fact of a far more striking and perplexing character. The cliffs,
+after being almost continuous for miles, are then wholly wanting for much
+greater distances, being replaced by a green sloping down, although the
+beds remain of the same composition, and are equally horizontal; and
+although we may feel assured that the manner of the upheaval of the land,
+whether intermittent or not, must have been the same at those intermediate
+points where no cliffs exist, as at others where they are so fully
+developed. But, in order to explain such apparent anomalies, the reader
+must refer again to the theory of denudation, as expounded in the 6th
+chapter; where it was shown, first, that the undermining force of the waves
+and marine currents varies greatly at different parts of every coast;
+secondly, that precipitous rocks have often decomposed and crumbled down;
+and thirdly, that many terraces and small cliffs may now lie concealed
+beneath a talus of detrital matter.
+
+_Denudation of the Weald Valley._--No district is better fitted to
+illustrate the manner in which a great series of strata may have been
+upheaved and gradually denuded than the country intervening between the
+North and South Downs. This region, of which a ground plan is given in the
+accompanying map (fig. 252.), comprises within it the whole of Sussex, and
+parts of the counties of Kent, Surrey, and Hampshire. The space in which
+the formations older than the White Chalk, or those from the Gault to the
+Hastings sand inclusive, crop out, is bounded everywhere by a great
+escarpment of chalk, which is continued on the opposite side of the channel
+in the Bas Boulonnais in France, where it forms the semicircular boundary
+of a tract in which older strata also appear at the surface. The whole of
+this district may therefore be considered geologically as one and the same.
+
+[Illustration: Fig. 252. Geological Map of the south-east of England and
+part of France, exhibiting the denudation of the Weald.
+
+ 1. Tertiary.
+ 2. Chalk and upper greensand.
+ 3. Gault.
+ 4. Lower Greensand.
+ 5. Weald clay.
+ 6. Hastings sand.
+ 7. Purbeck beds.
+ 8. Oolite.]
+
+[Illustration: Fig. 253. Section from the London to the Hampshire basin
+across the valley of the Weald.
+
+  1. Tertiary strata.
+  2. Chalk and firestone.
+  3. Gault.
+  4. Lower greensand.
+  5. Weald clay.
+  6. Hastings sands.]
+
+[Illustration: Fig. 254. Highest point of South Downs, 858 feet.
+
+Anticlinal axis of the Weald. Crowborough Hill, 804 feet.
+
+Highest point of North Downs, 880 feet.[243-A]
+
+Section of the country from the confines of the basin of London to
+that of Hants, with the principal heights above the level of the sea
+on a true scale.[243-B]]
+
+The space here inclosed within the escarpment of the chalk affords an
+example of what has been sometimes called a "valley of elevation" (more
+properly "of denudation"); where the strata, partially removed by
+aqueous excavation, dip away on all sides from a central axis. Thus, it
+is supposed that the area now occupied by the Hastings sand (No. 6.) was
+once covered by the Weald clay (No. 5.), and this again by the Greensand
+(No. 4.), and this by the Gault (No. 3.); and, lastly, that the Chalk
+(No. 2.) extended originally over the whole space between the North and
+the South Downs. This theory will be better understood by consulting the
+annexed diagram (fig. 253.), where the dark lines represent what now
+remains, and the fainter ones those portions of rock which are believed
+to have been carried away.
+
+At each end of the diagram the tertiary strata (No. 1.) are exhibited
+reposing on the chalk. In the middle are seen the Hastings sands (No. 6.)
+forming an anticlinal axis, on each side of which the other formations are
+arranged with an opposite dip. It has been necessary, however, in order to
+give a clear view of the different formations, to exaggerate the
+proportional height of each in comparison to its horizontal extent; and a
+true scale is therefore subjoined in another diagram (fig. 254.), in order
+to correct the erroneous impression which might otherwise be made on the
+reader's mind. In this section the distance between the North and South
+Downs is represented to exceed forty miles; for the Valley of the Weald is
+here intersected in its longest diameter, in the direction of a line
+between Lewes and Maidstone.
+
+Through the central portion, then, of the district supposed to be denuded
+runs a great anticlinal line, having a direction nearly east and west, on
+both sides of which the beds 5, 4, 3, and 2, crop out in succession. But,
+although, for the sake of rendering the physical structure of this region
+more intelligible, the central line of elevation has alone been introduced,
+as in the diagrams of Smith, Mantell, Conybeare, and others, geologists
+have always been well aware that numerous minor lines of dislocation and
+flexure run parallel to the great central axis.
+
+In the central area of the Hastings sand the strata have undergone the
+greatest displacement; one fault being known, where the vertical shift
+of a bed of calcareous grit is no less than 60 fathoms.[244-A] Much of
+the picturesque scenery of this district arises from the depth of the
+narrow valleys and ridges to which the sharp bends and fractures of
+the strata have given rise; but it is also in part to be attributed
+to the excavating power exerted by water, especially on the
+interstratified argillaceous beds.
+
+Besides the series of longitudinal valleys and ridges in the Weald, there
+are valleys which run in a transverse direction, passing through the chalk
+to the basin of the Thames on the one side, and to the English Channel on
+the other. In this manner the chain of the North Downs is broken by the
+rivers Wey, Mole, Darent, Medway, and Stour; the South Downs by the Arun,
+Adur, Ouse, and Cuckmere.[244-B] If these transverse hollows could be
+filled up, all the rivers, observes Mr. Conybeare, would be forced to take
+an easterly course, and to empty themselves into the sea by Romney Marsh
+and Pevensey Levels.[245-A]
+
+Mr. Martin has suggested that the great cross fractures of the chalk, which
+have become river channels, have a remarkable correspondence on each side
+of the valley of the Weald; in several instances the gorges in the North
+and South Downs appearing to be directly opposed to each other. Thus, for
+example, the defiles of the Wey in the North Downs, and of the Arun in the
+South, seemed to coincide in direction; and, in like manner, the Ouse
+corresponds to the Darent, and the Cuckmere to the Medway.[245-B]
+
+[Illustration: Fig. 255. View of the chalk escarpment of the South Downs.
+Taken from the Devil's Dike, looking towards the west and south-west.
+
+  _a._ The town of Steyning is hidden by this point.
+  _b._ Edburton church.
+  _c._ Road.
+  _d._ River Adur.]
+
+Although these coincidences may, perhaps, be accidental, it is by no means
+improbable, as hinted by the author above mentioned, that great amount of
+elevation towards the centre of the Weald district gave rise to transverse
+fissures. And as the longitudinal valleys were connected with that linear
+movement which caused the anticlinal lines running east and west, so the
+cross fissures might have been occasioned by the intensity of the upheaving
+force towards the centre of the line.
+
+But before treating of the manner in which the upheaving movement may
+have acted, I shall endeavour to make the reader more intimately
+acquainted with the leading geographical features of the district, so
+far as they are of geological interest.
+
+In whatever direction we travel from the tertiary strata of the basins of
+London and Hampshire towards the valley of the Weald, we first ascend a
+slope of white chalk, with flints, and then find ourselves on the summit of
+a declivity consisting, for the most part, of different members of the
+chalk formation; below which the upper greensand, and sometimes, also, the
+gault, crop out. This steep declivity is the great escarpment of the chalk
+before mentioned, which overhangs a valley excavated chiefly out of the
+argillaceous or marly bed, termed Gault (No. 3.). The escarpment is
+continuous along the southern termination of the North Downs, and may be
+traced from the sea, at Folkestone, westward to Guildford and the
+neighbourhood of Petersfield, and from thence to the termination of the
+South Downs at Beachy Head. In this precipice or steep slope the strata are
+cut off abruptly, and it is evident that they must originally have extended
+farther. In the woodcut (fig. 255. p. 245.), part of the escarpment of the
+South Downs is faithfully represented, where the denudation at the base of
+the declivity has been somewhat more extensive than usual, in consequence
+of the upper and lower greensand being formed of very incoherent materials,
+the upper, indeed, being extremely thin and almost wanting.
+
+[Illustration: Fig. 256. Chalk escarpment, as seen from the hill above
+Steyning, Sussex. The castle and village of Bramber in the foreground.]
+
+The geologist cannot fail to recognize in this view the exact likeness of a
+sea cliff; and if he turns and looks in an opposite direction, or eastward,
+towards Beachy Head (see fig. 256.), he will see the same line of heights
+prolonged. Even those who are not accustomed to speculate on the former
+changes which the surface has undergone may fancy the broad and level plain
+to resemble the flat sands which were laid dry by the receding tide, and
+the different projecting masses of chalk to be the headlands of a coast
+which separated the different bays from each other.
+
+In regard to the transverse valleys before mentioned, as intersecting the
+chalk hills, some idea of them may be derived from the subjoined sketch
+(fig. 257.), of the gorge of the river Adur, taken from the summit of the
+chalk downs, at a point in the bridle-way leading from the towns of Bramber
+and Steyning to Shoreham. If the reader will refer again to the view given
+in a former woodcut (fig. 255. p. 245.), he will there see the exact point
+where the gorge of which I am now speaking interrupts the chalk escarpment.
+A projecting hill, at the point _a_, hides the town of Steyning, near which
+the valley commences where the Adur passes directly to the sea at Old
+Shoreham. The river flows through a nearly level plain, as do most of the
+others which intersect the hills of Surrey, Kent, and Sussex; and it is
+evident that these openings, so far at least as they are due to aqueous
+erosion, have not been produced by the rivers, many of which, like the Ouse
+near Lewes, have filled up arms of the sea, instead of deepening the
+hollows which they traverse.
+
+[Illustration: Fig. 257. Transverse Valley of the Adur in the South Downs.
+
+  _a._ Town of Steyning.
+  _b._ River Adur.
+  _c._ Old Shoreham.]
+
+Now, in order to account for the manner in which the five groups of
+strata, 2, 3, 4, 5, 6, represented in the map, fig. 252. and in the
+section fig. 253., may have been brought into their present position,
+the following hypothesis has been very generally adopted:--Suppose the
+five formations to lie in horizontal stratification at the bottom of the
+sea; then let a movement from below press them upwards into the form of
+a flattened dome, and let the crown of this dome be afterwards cut off,
+so that the incision should penetrate to the lowest of the five groups.
+The different beds would then be exposed on the surface, in the manner
+exhibited in the map, fig. 252.[247-A]
+
+The quantity of denudation or removal by water of stratified masses assumed
+to have once reached continuously from the North to the South Downs is so
+enormous, that the reader may at first be startled by the boldness of the
+hypothesis. But the difficulty vanishes when once sufficient time is
+allowed for the gradual and successive rise of the strata, during which the
+waves and currents of the ocean might slowly accomplish an operation, which
+no sudden diluvial rush of waters could possibly have effected.
+
+Among other proofs of the action of water, it may be stated that the great
+longitudinal valleys follow the outcrop of the softer and more incoherent
+beds, while ridges or lines of cliff usually occur at those points where
+the strata are composed of harder stone. Thus, for example, the chalk with
+flints, together with the subjacent upper greensand, which is often used
+for building, under the provincial name of "firestone," has been cut into a
+steep cliff on that side on which the sea encroached. This escarpment
+bounds a deep valley, excavated chiefly out of the soft argillaceous or
+marly bed, termed gault (No. 3.). In some places the upper greensand is in
+a loose and incoherent state, and there it has been as much denuded as the
+gault; as, for example, near Beachy Head; but farther to the westward it is
+of great thickness, and contains hard beds of blue chert and calcareous
+sandstone or firestone. Here, accordingly, we find that it produces a
+corresponding influence on the scenery of the country; for it runs out like
+a step beyond the foot of the chalk-hills, and constitutes a lower terrace,
+varying in breadth from a quarter of a mile to three miles, and following
+the sinuosities of the chalk escarpment.[248-A]
+
+[Illustration: Fig. 258. Cross section.
+
+  _a._ Chalk with flints.
+  _b._ Chalk without flints.
+  _c._ Upper greensand, or firestone.
+  _d._ Gault.]
+
+It is impossible to desire a more satisfactory proof that the escarpment
+is due to the excavating power of water during the rise of the strata;
+for I have shown, in my account of the coast of Sicily, in what manner
+the encroachments of the sea tend to efface that succession of terraces
+which must otherwise result from the intermittent upheaval of a coast
+preyed upon by the waves.[248-B] During the interval between two
+elevatory movements, the lower terrace will usually be destroyed,
+wherever it is composed of incoherent materials; whereas the sea will
+not have time entirely to sweep away another part of the same terrace,
+or lower platform, which happens to be composed of rocks of a harder
+texture, and capable of offering a firmer resistance to the erosive
+action of water. As the yielding clay termed gault would be readily
+washed away, we find its outcrop marked everywhere by a valley which
+skirts the base of the chalk hills, and which is usually bounded on the
+opposite side by the lower greensand; but as the upper beds of this last
+formation are most commonly loose and incoherent, they also have usually
+disappeared and increased the breadth of the valley. But in those
+districts where chert, limestone, and other solid materials enter
+largely into the composition of this formation (No. 4.), they give rise
+to a range of hills parallel to the chalk, which sometimes rival the
+escarpment of the chalk itself in height, or even surpass it, as in
+Leith Hill, near Dorking. This ridge often presents a steep escarpment
+towards the soft argillaceous deposit called the Weald clay (No. 5.;
+see the strong lines in fig. 253. p. 243.), which usually forms a broad
+valley, separating the lower greensand from the Hastings sands or Forest
+ridge; but where subordinate beds of sandstone of a firmer texture
+occur, the uniformity of the plain of No. 5. is broken by waving
+irregularities and hillocks.
+
+It will be easy to show how closely the superficial inequalities agree with
+those which we might naturally expect to originate during the gradual rise
+of the Wealden district. Suppose the line of the most energetic movement to
+have coincided with what is now the central ridge of the Weald valley; in
+that case the first land which emerged must have been situated where the
+Forest ridge is now placed. Here many shoals and reefs may first have
+existed, and islands of chalk devoured in the course of ages by the ocean
+(see fig. 253.); so that the top of the shattered dome which first appeared
+above water may have been utterly destroyed, and the masses represented by
+the fainter lines (fig. 253.) removed.
+
+[2 Illustrations: Fig. 259., Fig. 260.
+
+The dotted lines represent the sea-level.]
+
+The upper greensand is represented (fig. 259.) as forming on the left
+hand a single precipice with the chalk; while on the right there are two
+cliffs, with an intervening terrace, as before described in fig. 258.
+Two strips of land would then remain on each side of a channel,
+presenting ranges of white cliffs facing each other. A powerful current
+might then scoop out a channel in the gault (No. 2.). This softer bed
+would yield with ease in proportion as parts of it were brought up from
+time to time and exposed to the fury of the waves, so that large spaces
+occupied by the harder formation or greensand (No. 3.) would be laid
+bare. This last rock, opposing a more effectual resistance, would next
+emerge; while the chalk cliffs, at the base of which the gault is
+rapidly undermined, would recede farther from each other, after which
+four parallel strips of land, or rows of islands, would be caused, which
+are represented by the masses which in fig. 260. rise above the dotted
+line indicating the sea-level. In this diagram, however, the inclination
+of the upper surface of the formations (Nos. 1. and 3.), is exaggerated.
+Originally this surface must have been level, like the submarine
+terraces produced by denudation, and described before (p. 74. and 77.);
+but they were afterwards more and more tilted by that general movement
+to which the region of the Weald owes its structure. At length, by the
+farther elevation of the dome-shaped mass, the clay (No. 4.) would be
+brought within reach of the waves, which would probably gain the more
+easy access to the subjacent deposit by the rents which would be caused
+in No. 3., and in the central part of the ridge where the uplifting
+force had been exerted with the greatest energy. The opposite cliffs, in
+which the greensand (No. 3.) terminates, would now begin to recede from
+each other, having at their base a yielding stratum of clay (No. 4.).
+Lastly, the sea would penetrate to the sand (No. 5.), and then the
+state of things indicated in the dark lines of the upper section
+(fig. 253.), would be consummated.
+
+[Illustration: Fig. 261. The Coomb, near Lewes.]
+
+It was stated that there are many lines of flexure and dislocation, running
+east and west, or parallel to the central axis of the Wealden. They are
+numerous in the district of the Hastings sand, and sometimes occur in the
+chalk itself. One of the latter kind has given rise to the ravine called
+the Coomb, near Lewes, and was first traced out by Dr. Mantell, in whose
+company I examined it. This coomb is seen on the eastern side of the valley
+of the Ouse, in the suburbs of the town of Lewes. The steep declivities on
+each side are covered with green turf, as is the bottom, which is perfectly
+dry. No outward signs of disturbance are visible; and the connection of the
+hollow with subterranean movements would not have been suspected by the
+geologist, had not the evidence of great convulsions been clearly exposed
+in the escarpment of the valley of the Ouse, and the numerous chalk pits
+worked at the termination of the Coomb. By the aid of these we discover
+that the ravine coincides precisely with a line of fault, on one side of
+which the chalk with flints (_a_, fig. 262.), appears at the summit of the
+hill, while it is thrown down to the bottom on the other.
+
+Mr. Martin, in his work on the geology of Western Sussex, published in
+1828, threw much light on the structure of the Wealden by tracing out
+continuously for miles the direction of many anticlinal lines and cross
+fractures; and the same course of investigation has since been followed
+out in greater detail by Mr. Hopkins. The mathematician last-mentioned
+has shown that the observed direction of the lines of flexure and
+dislocation in the Weald district coincide with those which might have
+been anticipated theoretically on mechanical principles, if we assume
+certain simple conditions under which the strata were lifted up by an
+expansive subterranean force. He finds by calculation that if this force
+was applied so as to act uniformly upwards within an elliptic area, the
+longitudinal fissures thereby produced would nearly coincide with the
+outlines of the ellipse, forming cracks, which are portions of smaller
+concentric ellipses, parallel to the margin of the larger one. These
+longitudinal fissures would also be intercepted by others running at
+right angles to them, and both lines of fracture may have been produced
+at the same time.[251-A] In this illustration it is supposed that the
+expansive force acted simultaneously and with equal intensity at every
+point within the upheaved area, and not with greater energy along the
+central axis or region of principal elevation.
+
+[Illustration: Fig. 262. Fault in the cliff hills near Lewes. Mantell.
+
+  _a._ Chalk with flints.
+  _b._ Lower chalk.[251-B]]
+
+The geologist cannot fail to derive great advantage in his speculations
+from the mathematical investigation of a problem of this kind, where
+results free from all uncertainty are obtained on the assumption of certain
+simple conditions. Such results, when once ascertained by mathematical
+methods, may serve as standard cases, to which others occurring in nature
+of a more complicated kind may be referred. In order that a uniform force
+should cause the strata to attain in the centre of the ellipse a height so
+far exceeding that which they have reached round the margin, it is
+necessary to assume that the mass of upheaved strata offered originally a
+very unequal degree of resistance to the subterranean force. This may have
+happened either from their being more fractured in one place than in
+another, or from being pressed down by a less weight of incumbent strata;
+as if we suppose, what is far from improbable, that great denudation had
+taken place in the middle of the Wealden before the final and principal
+upheaval occurred. It is suggested that the beds may have been acted upon
+somewhat in the manner of a carpet spread out loosely on a floor, and
+nailed down round the edges, which would swell into the shape of a dome if
+pressed up equally at every point by air admitted from beneath. But when we
+are reasoning on the particular phenomena of the Weald, we have no
+geological data for determining whether it be more probable that originally
+the resistance to be overcome was so extremely unequal in different
+places, or whether the subterranean force, instead of being everywhere
+uniform, was not applied with very different degrees of intensity beneath
+distinct portions of the upraised area.
+
+The opinion that both the longitudinal and transverse lines of fracture
+may have been produced simultaneously, accords well with that expressed
+by M. Thurmann, in his work on the anticlinal ridges and valleys of
+elevation of the Bernese Jura.[252-A] For the accuracy of his map and
+sections I can vouch, from personal examination, in 1835, of part of the
+region surveyed by him. Among other results, at which this author
+arrived, it appears that the breadth of all the numerous anticlinal
+ridges and dome-shaped masses in the Jura is invariably great in
+proportion to the number of the formations exposed to view; or, in other
+words, to the depth to which the superimposed groups of secondary strata
+have been laid open. (See fig. 71. p. 55. for structure of Jura.) He
+also remarks, that the anticlinal lines are occasionally oblique and
+cross each other, in which case the greatest dislocation of the beds
+takes place. Some of the cross fractures are imagined by him to have
+been contemporaneous, others subsequent to the longitudinal ones.
+
+I have assumed, in the former part of this chapter, that the rise of the
+Weald was gradual, whereas many geologists have attributed its elevation to
+a single effort of subterranean violence. There appears to them such a
+unity of effect in this and other lines of deranged strata in the
+south-east of England, such as that of the Isle of Wight, as is
+inconsistent with the supposition of a great number of separate movements
+recurring after long intervals of time. But we know that earthquakes are
+repeated throughout a long series of ages in the same spots, like volcanic
+eruptions. The oldest lavas of Etna were poured out many thousands, perhaps
+myriads of years before the newest, and yet they, and the movements
+accompanying their emission, have produced a symmetrical mountain; and if
+rivers of melted matter thus continue to flow in the same direction, and
+towards the same point, for an indefinite lapse of ages, what difficulty is
+there in conceiving that the subterranean volcanic force, occasioning the
+rise or fall of certain parts of the earth's crust, may, by reiterated
+movements, produce the most perfect unity of result?
+
+_Alluvium of the Weald._--Our next inquiry may be directed to the alluvium
+strewed over the surface of the supposed area of denudation. Has any wreck
+been left behind of the strata removed? To this we may answer, that the
+chalk downs even on their summits are covered every where with gravel
+composed of unrounded and partially rounded chalk flints, such as might
+remain after masses of white chalk had been softened and removed by water.
+This superficial accumulation of the hard or siliceous materials of the
+disintegrated strata may be due in some degree to pluvial action; for
+during extraordinary rains a rush of water charged with calcareous matter,
+of a milk-white colour, may be seen to descend even gently sloping hills of
+chalk. If a layer no thicker than the tenth of an inch be removed once in a
+century, a considerable mass may in the course of indefinite ages melt
+away, leaving nothing save a layer of flinty nodules to attest its former
+existence. These unrolled flints may remain mixed with others more or less
+rounded, which the waves left originally on the surface of the chalk, when
+it first emerged from the sea. A stratum of fine clay sometimes covers the
+surface of slight depressions and the bottom of valleys in the white chalk,
+which may represent the aluminous residue of the rock, after the pure
+carbonate of lime has been dissolved by rain water, charged with excess of
+carbonic acid derived from decayed vegetable matter.[253-A]
+
+Although flint gravel is so abundant on the chalk itself, it is usually
+wanting in the deep longitudinal valleys at the foot of the chalk
+escarpment, although, in some few instances, the detritus of the chalk has
+been traced in patches over the gault, and even the lower greensand, for a
+distance of several miles from the escarpment of the North and South Downs.
+But no vestige of the chalk and its flints has been seen on the central
+ridge of the Weald or the Hastings sands, but merely gravel derived from
+the rocks immediately subjacent. This distribution of alluvium, and
+especially the absence of chalk detritus in the central district, agrees
+well with the theory of denudation before set forth; for to return to fig.
+259., if the chalk (No. 1.) were once continuous and covered every where
+with flint gravel, this superficial covering would be the first to be
+carried away from the highest part of the dome long before any of the gault
+(No. 2.) was laid bare. Now if some ruins of the chalk remain at first on
+the gault, these would be, in a great degree, cleared away before any part
+of the lower greensand (No. 3.) is denuded. Thus in proportion to the
+number and thickness of the groups removed in succession, is the
+probability lessened of our finding any remnants of the highest group
+strewed over the bared surface of the lowest.
+
+As an exception to the general rule of the small distance to which any
+wreck of the chalk can be traced from the escarpments of the North and
+South Downs, I may mention a thick bed of chalk flints which occurs near
+Barcombe, about three miles to the north of Lewes (see fig. 263.), a place
+which I visited with Dr. Mantell, to whom I am indebted for the
+accompanying section. Even here it will be seen that the gravel reaches no
+farther than the Weald Clay. The same section shows one of the minor east
+and west anticlinal lines before alluded to (p. 244.).
+
+[Illustration: Fig. 263. Section from the north escarpment of the South
+Downs to Barcombe.
+
+  1. Gravel composed of partially rounded chalk flints.
+  2. Chalk with and without flints.
+  3. Lowest chalk or chalk marl (upper greensand wanting).
+  4. Gault.
+  5. Lower greensand.
+  6. Weald clay.]
+
+_At what period the Weald Valley was denuded._--If we inquire at what
+geological period the denudation of the Weald was effected, we shall
+immediately perceive that the question is limited to this point, whether it
+took place during or subsequent to the deposition of the Eocene strata of
+the south of England. For in the basins of London and Hampshire the Eocene
+strata are conformable to the chalk, being horizontal where the beds of
+chalk are horizontal, and vertical where they are vertical, so that both
+series of rocks appear to have participated in nearly the same movements.
+At the eastern extremity of the Isle of Wight, some beds even of the
+freshwater series have been thrown on their edges, like those of the London
+clay. Nevertheless we can by no means infer that all the tertiary deposits
+of the London and Hampshire basins once extended like the chalk over the
+entire valley of the Weald, because the denudation of the chalk and
+greensand may have been going on in the centre of that area, while
+contiguous parts of the sea were sufficiently deep to receive and retain
+the matter derived from that waste. Thus while the waves and currents were
+excavating the longitudinal valleys D and C (fig. 264.), the deposits _a_
+may have been thrown down to the bottom of the contiguous deep water E, the
+sediment being drifted through transverse fissures, as before explained. In
+this case, the rise of the formations Nos. 1, 2, 3, 4, 5, may have been
+going on contemporaneously with the excavation of the valleys C and D, and
+with the accumulation of the tertiary strata _a_.
+
+[Illustration: Fig. 264. Cross section.]
+
+This idea receives some countenance from the fact of the tertiary strata,
+near their junction with the chalk of the London and Hampshire basins,
+often consisting of dense beds of sand and shingle, as at Blackheath and in
+the Addington Hills near Croydon. They also contain occasionally freshwater
+shells and the remains of land animals and plants, which indicate the
+former presence of land at no great distance, some part of which may have
+occupied the centre of the Weald.
+
+Such masses of well-rolled pebbles occurring in the lowest Eocene
+strata, or those called "the plastic clay and sands" before described
+(No. 3. _b_, Tab. p. 197.), imply the neighbourhood of an ancient shore.
+They also indicate the destruction of pre-existing chalk with flints. At
+the same time fossil shells of the genera _Melania_, _Cyclas_, and
+_Unio_, appearing here and there in beds of the same age, together with
+plants and the bones of land animals, bear testimony to contiguous land,
+which probably constituted islands scattered over the space now occupied
+by the tertiary basins of the Seine and Thames. The stage of denudation
+represented in fig. 259., p. 249., may explain the state of things
+prevailing at points where such islands existed. By the alternate rising
+and sinking of the white chalk and older beds, a large area may have
+become overspread with gravelly sandy, and clayey beds of fluvio-marine
+and shallow-water origin, before any of the London clay proper (or
+Calcaire grossier in France) were superimposed. This may account for the
+fact that patches of "plastic clay and sand" (No. 3. _b_, Tab. p. 197.),
+are scattered over the surface of the chalk, reaching in some places to
+great heights, and approaching even the edges of the escarpments. We
+must suppose that subsequently a gradual subsidence took place in
+certain areas, which allowed the London clay proper to accumulate over
+the Lower Eocene sands and clays, in a deep sea. During this sinking
+down (the vertical amount of which equalled 800, and in parts of the
+Isle of Wight, according to Mr. Prestwich, 1800 feet), the work of
+denudation would be unceasing, being always however confined to those
+areas where land or islands existed. At length, when the Bagshot sand
+had been in its turn thrown down on the London clay, the space covered
+by these two formations was again upraised from the sea to about the
+height which it has since retained. During this upheaval, the waves
+would again exert their power, not only on the white chalk and lower
+cretaceous and Wealden strata, but also on the Eocene formations of
+the London basin, excavating valleys and undermining cliffs as the
+strata emerged from the deep.
+
+There are grounds, as before stated (p. 205.), for presuming that the
+tertiary area of London was converted into land before that of
+Hampshire, and for this reason it contains no marine Eocene deposits so
+modern as those of Barton Cliff, or the still newer freshwater and
+fluvio-marine beds of Hordwell and the Isle of Wight. These last seem
+unequivocally to demonstrate the local inequality of the upheaving and
+depressing movements of the period alluded to; for we find, in spite of
+the evidence afforded in Alum and White Cliff Bays, of continued
+depression to the extent of 1800 or 2000 feet, that at the close of the
+Eocene period a dense formation of freshwater strata was produced. The
+fossils of these strata bear testimony to rivers draining adjacent
+lands, and the existence of numerous quadrupeds on those lands.
+Instead of such phenomena, the signs of an open sea might naturally
+have been expected as the consequence of so much subsidence, had
+not the depression been accompanied or followed by upheaval in a
+region immediately adjoining.
+
+When we attempt to speculate on the geographical changes which took place
+in the earlier part of the Eocene epoch, and to restore in imagination the
+former state of the physical geography of the south-east of England, we
+shall do well to bear in mind that wherever there are proofs of great
+denudation, there also the greatest area of land has probably existed. In
+the same space, moreover, the oscillations of level, and the alternate
+submergence and emergence of coasts, may be presumed to have been most
+frequent; for these fluctuations facilitate the wasting and removing power
+of waves, currents, and rivers.
+
+We should also remember that there is always a tendency in the last
+denuding operations, to efface all signs of preceding denudation, or at
+least all those marks of waste from which alone a geologist can ascertain
+the date of the removal of the missing strata within the denuded area. It
+may often be difficult to settle the chronology even of the last of a
+series of such acts of removal, but it must be, in the nature of things,
+almost always impossible to assign a date to each of the antecedent
+denudations. If we wish to determine the times of the destruction of rocks,
+we must look any where rather than to the spaces once occupied by the
+missing rocks. We must inquire to what regions the ruins of the white
+chalk, greensand, Wealden, and other strata which have disappeared were
+transported. We are then led at once to the examination of all the deposits
+newer than the chalk, and first to the oldest of these, the Lower Eocene,
+and its sand, shingle, and clay. In them, so largely developed in the
+immediate neighbourhood of the denuded area, we discover the wreck we are
+in search of, regularly stratified, and inclosing, in some of its layers,
+organic remains of a littoral, and sometimes fluviatile character. What
+more can we desire? The shores must have consisted of chalk, greensand, and
+Wealden, since these were the only superficial rocks in the south-east of
+England, at the commencement of the Eocene epoch. The waves of the sea,
+therefore, and the rivers were grinding down chalk-flints and chert from
+the greensand into shingle and sand, or were washing away calcareous and
+argillaceous matter from the cretaceous and Wealden beds, during the whole
+of the Eocene period. Thus we obtain the date of a great part at least of
+that enormous amount of denudation of which we have such striking monuments
+in the space intervening between the North and South Downs.
+
+[Illustration: Fig. 265. Cross section.
+
+   A.  Chalk with layers of flint dipping slightly to the south.
+  _b._ Ancient beach, consisting of fine sand, from one to four feet thick,
+       covered by shingle from five to eight feet thick of pebbles of
+       chalk-flint, granite, and other rocks, with broken shells of recent
+       marine species, and bones of cetacea.
+  _c._ Elephant bed, about fifty feet thick, consisting of layers of white
+       chalk rubble, with broken chalk-flints, in which deposit are found
+       bones of ox, deer, horse, and mammoth.
+  _d._ Sand and shingle of modern beach.]
+
+There have been some movements of land on a smaller scale since the Eocene
+period in the south-east of England. One of the latest of these happened in
+the Pleistocene, or even perhaps as late as the Post-Pliocene period. The
+formation called by Dr. Mantell the Elephant Bed, at the foot of the chalk
+cliffs at Brighton, is not merely a talus of calcareous rubble collected at
+the base of an inland cliff, but exhibits every appearance of having been
+spread out in successive horizontal layers by water in motion.
+
+The deposit alluded to skirts the shores between Brighton and Rottingdean,
+and another mass apparently of the same age occurs at Dover. The phenomena
+appear to me to suggest the following conclusions:--First, the
+south-eastern part of England had acquired its actual configuration when
+the ancient chalk cliff A _a_ was formed, the beach of sand and shingle _b_
+having then been thrown up at the base of the cliff. Afterwards the whole
+coast, or at least that part of it where the elephant bed now extends,
+subsided to the depth of 50 or 60 feet; and during the period of
+submergence successive layers of white calcareous rubble _c_ were
+accumulated, so as to cover the ancient beach _b_. Subsequently, the coast
+was again raised, so that the ancient shore was elevated to a level
+somewhat higher than its original position.[257-A]
+
+
+FOOTNOTES:
+
+[241-A] An account of these cliffs was read by the author to the British
+Assoc. at Glasgow, Sept. 1840.
+
+[241-B] Seine-Inferieure, p. 142. and pl. 6. fig. 1.
+
+[243-A] Botley Hill, near Godstone, in Surrey, was found by
+trigonometrical measurement to be 880 feet above the level of the sea;
+and Wrotham Hill, near Maidstone, which appears to be next in height of
+the North Downs, 795 feet.
+
+[243-B] My friend Dr. Mantell has kindly drawn up this scale at my request.
+
+[244-A] Fitton, Geol. of Hastings, p. 55.
+
+[244-B] Conybeare, Outlines of Geol., p. 81.
+
+[245-A] Ibid., p. 145.
+
+[245-B] Geol. of Western Sussex, p. 61.
+
+[247-A] See illustrations of this theory by Dr. Fitton, Geol.
+Sketch of Hastings.
+
+[248-A] Sir E. Murchison, Geol. Sketch of Sussex, &c., Geol. Trans., Second
+Series, vol. ii. p. 98.
+
+[248-B] See fig. 94. p. 76.
+
+[251-A] Geol. Soc. Proceed. No. 74. p. 363. 1841, and G. S. Trans.
+2 Ser. v. 7.
+
+[251-B] For farther information, see Mantell's Geol. of S. E.
+of England, p. 352.
+
+[252-A] Soulèvemens Jurassiques. Paris, 1832.
+
+[253-A] See above, p. 82.
+
+[257-A] See Mantell's Geol. of S. E. of England, p. 32. After
+re-examining the elephant bed in 1834, I was no longer in doubt of its
+having been a regular subaqueous deposit. In 1828, Dr. Mantell
+discovered in the shingle below the chalk-rubble the jawbone of a whale
+12 feet long, which must have belonged to an individual from 60 to 70
+feet in length, Medals of Creation, p. 825.
+
+
+
+
+CHAPTER XX.
+
+OOLITE AND LIAS.
+
+   Subdivisions of the Oolitic or Jurassic group--Physical geography of
+   the Oolite in England and France--Upper Oolite--Portland stone and
+   fossils--Lithographic stone of Solenhofen--Middle Oolite, coral
+   rag--Zoophytes--Nerinæan limestone--Diceras limestone--Oxford clay,
+   Ammonites and Belemnites--Lower Oolite, Crinoideans--Great Oolite and
+   Bradford clay--Stonesfield slate--Fossil mammalia, placental and
+   marsupial--Resemblance to an Australian fauna--Doctrine of progressive
+   development--Collyweston slates--Yorkshire Oolitic coal-field--Brora
+   coal--Inferior Oolite and fossils.
+
+
+_OOLITIC OR JURASSIC GROUP._--Below the freshwater group called the
+Wealden, or, where this is wanting, immediately beneath the Cretaceous
+formation, a great series of marine strata, commonly called "the Oolite,"
+occurs in England and many other parts of Europe. This group has been so
+named, because, in the countries where it was first examined, the
+limestones belonging to it had an oolitic structure (see p. 12.). These
+rocks occupy in England a zone which is nearly 30 miles in average breadth,
+and 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._ Portland stone and sand.
+         { _b._ Kimmeridge clay.
+
+  Middle { _c._ Coral rag.
+         { _d._ Oxford clay.
+
+  Lower  { _e._ Cornbrash and Forest marble.
+         { _f._ Great Oolite and Stonesfield slate.
+         { _g._ Fuller's earth.
+         { _h._ Inferior Oolite.
+
+     The Lias then succeeds to the 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 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
+bounds of country where the argillaceous strata crop out; and between these
+valleys the limestones are observed, composing 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.
+
+[Illustration: Fig. 266. Cross section.]
+
+The annexed diagram 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 cliff, 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.
+
+The Chalk crops out from beneath the tertiary sands and clays of the Paris
+basin, near Epernay, and the Gault from beneath the Chalk and Upper
+Greensand at Clermont-en-Argonne; and passing from this place by Verdun and
+Etain to Metz, we find two limestone ranges, with intervening vales of
+clay, precisely resembling those of southern and central England, until we
+reach the great plain of Lias at the base of the Inferior Oolite at Metz.
+
+It is evident, therefore, that the denuding causes have acted similarly
+over an area several hundred miles in diameter, sweeping away the softer
+clays more extensively than the limestones, and undermining these last so
+as to cause them to form steep cliffs wherever the harder calcareous rock
+was based upon a more yielding and destructible clay. This denudation
+probably occurred while the land was slowly rising out of the sea.[259-A]
+
+
+_Upper Oolite._
+
+The Portland stone has already been mentioned as forming in Dorsetshire
+the foundation on which the freshwater limestone of the Lower Purbeck
+reposes (see p. 232.). It supplies the well-known building stone of
+which St. Paul's and so many of the principal edifices of London are
+constructed. This upper member, characterized by peculiar marine
+fossils, rests on a dense bed of sand, called the Portland sand, below
+which is the Kimmeridge clay. In England these Upper Oolite formations
+are almost wholly confined to the southern counties. Corals are rare in
+them, although one species is found plentifully at Tisbury, in
+Wiltshire, in the Portland sand converted into flint and chert, the
+original calcareous matter being replaced by silex (fig. 267.).
+
+[Illustration: Fig. 267. _Columnaria oblonga_, Blainv.
+
+As seen on a polished slab of chert from the sand of the
+Upper Oolite, Tisbury.]
+
+Among the characteristic fossils of the Upper Oolite, may be mentioned
+the _Ostrea deltoidea_ (fig. 269.), found in the Kimmeridge clay
+throughout England and the north of France, and also in Scotland, near
+Brora. The _Gryphæa virgula_ (fig. 268.), also met with in the same 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.
+
+[2 Illustrations: Upper Oolite: Kimmeridge clay. 1/4 nat. size.
+
+Fig. 268. _Gryphæa virgula._
+
+Fig. 269. _Ostrea deltoidea._]
+
+[Illustration: Fig. 270. _Trigonia gibbosa._ 1/2 nat. size. _a._ the hinge.
+
+Portland Oolite, Tisbury.]
+
+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, the bitumen
+may perhaps be of animal origin.
+
+The celebrated lithographic stone of Solenhofen, in Bavaria, belongs to one
+of the upper divisions of the oolite, and 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 lizards, or pterodactyls, 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 flying lizards, and other contemporaneous reptiles, resorted.
+
+
+_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, for the most part retaining the position in which they
+grew at the bottom of the sea. They belong chiefly to the genera
+_Caryophyllia_ (fig. 271.), _Agaricia_, and _Astrea_, and sometimes form
+masses of coral 15 feet thick. In the annexed figure of an _Astrea_, 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, till those
+on the left side are nearly filled up. The last-named stars are supposed to
+be Polyparia of advanced age. These coralline strata extend through the
+calcareous hills of the N.W. of Berkshire, and north of Wilts, and again
+recur in Yorkshire, near Scarborough.
+
+[Illustration: Fig. 271. _Caryophyllia annularis_, Parkin. Coral
+rag, Steeple Ashton.]
+
+[Illustration: Fig 272. _Astrea._ Coral rag.]
+
+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, much
+resembling the _Cerithium_ in external form. The annexed section (fig.
+273.) shows the curious form of the hollow part of each whorl, and also
+the perforation which passes up the middle of the columella. _N.
+Goodhallii_ (fig. 274.) is another English species of the same genus,
+from a formation which seems to form a passage from the Kimmeridge clay
+to the coral rag.[261-A]
+
+[Illustration: Fig. 273. _Nerinæa hieroglyphica._ Coral rag.]
+
+[Illustration: Fig. 274. _Nerinæa Goodhallii_, Fitton. Coral rag,
+Weymouth. 1/4 nat. size.]
+
+A division of the oolite in the Alps, regarded by most geologists as coeval
+with the English coral rag, has been often named "Calcaire à Dicerates," or
+"Diceras limestone," from its containing abundantly a bivalve shell (see
+fig. 275.) of a genus allied to the _Chama_.
+
+[Illustration: Fig. 275. Cast of _Diceras arietina_. Coral rag, France.]
+
+[Illustration: Fig. 276. _Cidaris coronata._ Coral rag.]
+
+_Oxford Clay._--The coralline limestone, or "coral rag," above described,
+and the accompanying sandy beds, called "calcareous grits" of the Middle
+Oolite, rests on a thick bed of clay, called the Oxford clay, sometimes not
+less than 500 feet thick. In this there are no corals, but great abundance
+of cephalopoda of the genera Ammonite and Belemnite. (See fig. 277.) In
+some of the clay of very fine texture ammonites are very perfect, although
+somewhat compressed, and are seen to be furnished on each side of the
+aperture with a single horn-like projection (see fig. 278.). These were
+discovered in the cuttings of the Great Western Railway, near Chippenham,
+in 1841, and have been described by Mr. Pratt.[262-A]
+
+[Illustration: Fig. 277. _Belemnites hastatus._ Oxford Clay.]
+
+[Illustration: Fig. 278. _Ammonites Jason_, Reinecke. Syn. _A. Elizabethæ_,
+Pratt. Oxford clay, Christian Malford, Wiltshire.]
+
+[Illustration: Fig. 279. _Belemnites Puzosianus_, D'Orb. Oxford
+Clay, Christian Malford.
+
+  _a, a._ projecting processes of the shell or phragmocone.
+  _b, c._ broken exterior of a conical shell called the phragmocone, which
+          is chambered within, or composed of a series of shallow concave
+          cells pierced by a siphuncle.
+  _c, d._ The guard or osselet, which is commonly called the belemnite.]
+
+Similar elongated processes have been also observed to extend from the
+shells of some belemnites discovered by Dr. Mantell in the same clay
+(see fig. 279.), who, by the aid of this and other specimens, has been
+able to throw much light on the structure of this singular extinct
+form of cuttle-fish.[263-A]
+
+
+_Lower Oolite._
+
+The upper division of this series, which is more extensive than the
+preceding or Middle Oolite, is called in England the Cornbrash. It
+consists of clays and calcareous sandstones, which pass downwards 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 crabs, 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.[263-B]
+
+_Great Oolite._--Although the name of coral-rag has been appropriated,
+as we have seen, to a member of the Upper Oolite before described,
+some portions of the Lower Oolite are equally intitled in many places
+to be called coralline limestones. Thus the Great Oolite near Bath
+contains various corals, among which the _Eunomia radiata_ (fig. 280.)
+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.
+
+[Illustration: Fig. 280. _Eunomia radiata_, Lamouroux.
+
+  _a._ section transverse to the tubes.
+  _b._ vertical section, showing the radiation of the tubes.
+  _c._ portion of interior of tubes magnified, showing striated surface.]
+
+[Illustration: Fig. 281. _Apiocrinites rotundus_, or Pear Encrinite;
+Miller. Fossil at Bradford, Wilts.
+
+  _a._ Stem of _Apiocrinites_, and one of the articulations, natural size.
+  _b._ Section at Bradford of great oolite and overlying clay, containing
+       the fossil encrinites. See text.
+  _c._ Three perfect individuals of Apiocrinites, represented as they grew
+       on the surface of the Great Oolite.
+  _d._ Body of the _Apiocrinites rotundus_.]
+
+Different species of _Crinoideans_, or stone-lilies, are also common in the
+same rocks with corals; and, like them, must have enjoyed a firm bottom,
+where their root, or base of attachment, remained undisturbed for years
+(_c_, fig. 281.). Such fossils, therefore, are almost confined to the
+limestones; but an exception occurs at Bradford, near Bath, where they are
+enveloped in clay. 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 zoophyte, were
+scattered at random through the argillaceous deposit in which some now lie
+prostrate. These appearances are represented in the section _b_, fig. 281.,
+where the darker strata represent the Bradford clay, which some geologists
+class with the Forest marble, others with the Great Oolite. 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 coral, called _Berenicea diluviana_; and many
+generations of these polyps had succeeded each other in the pure water
+before they became fossil.
+
+[Illustration: Fig. 282.
+
+  _a._ Single plate or articulation of an Encrinite overgrown with
+       _serpulæ_ and corals. Natural size Bradford clay.
+  _b._ Portion of the same magnified, showing the coral _Berenicea_
+       _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.[265-A]
+
+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 creative and destroying law above
+alluded to. But we recognize 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 there
+is scarcely any lithological resemblance; and 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.
+
+[Illustration: Fig. 283. _Terebratula digona._ Bradford clay. Nat. size.]
+
+The Bradford clay above alluded to is sometimes 60 feet thick, but, in many
+places, it is wanting; and, in others, where there are no limestones, it
+cannot easily be separated from the clays of the overlying "forest marble"
+and underlying "fuller's earth."
+
+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."[266-A] In such
+shallow-water beds cephalopoda are rare, and, instead of ammonites and
+belemnites, numerous genera of carnivorous trachelipods appear. Out of
+one hundred and forty-two species of univalves obtained from the
+Minchinhampton beds, Mr. Lycett found no less than forty-one to be
+carnivorous. They belong principally to the genera _Buccinum_,
+_Pleurotoma_, _Rostellaria_, _Murex_, and _Fusus_, and exhibit a
+proportion of zoophagous species not very different from that which
+obtains in warm seas of the recent period. These conchological 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, had become extinct.
+
+_Stonesfield slate._--The slate of Stonesfield has been shown by Mr.
+Lonsdale to lie at the base of the Great Oolite.[266-B] It is a slightly
+oolitic shelly limestone, forming large spheroidal masses imbedded in
+sand, only 6 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 wing-covers
+of beetles, are perfectly preserved (see fig. 284.), some of them
+approaching nearly to the genus _Buprestis_.[267-A] The remains, also, of
+many genera of reptiles, such as _Plesiosaur_, _Crocodile_, and
+_Pterodactyl_, have been discovered in the same limestone.
+
+[Illustration: Fig. 284. Elytron of _Buprestis_? Stonesfield.]
+
+[Illustration: Fig. 285. Bone of a reptile, formerly supposed to be the
+ulna of a Cetacean; from the Great Oolite of Enstone, near Woodstock.]
+
+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,
+have been discovered. Yet we have seen that terrestrial plants were not
+rare in the lower cretaceous formation, and that in the Wealden there was
+evidence of freshwater sediment on a large scale, containing various
+plants, and even ancient vegetable soils with the roots and erect stumps of
+trees. We had also in the same Wealden many land-reptiles and
+winged-insects, which renders 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. Formerly, indeed, a bone from
+the great oolite of Enstone, near Woodstock, in Oxfordshire, was cited, on
+the authority of Cuvier, as referable to this class. Dr. Buckland, who
+stated this in his Bridgewater Treatise[267-B], had the kindness to send me
+the supposed ulna of a whale, that Mr. Owen might examine into its claims
+to be considered as cetaceous. It is the opinion of that eminent
+comparative anatomist that it cannot have belonged to the cetacea, because
+the fore-arm in these marine mammalia is invariably much flatter, and
+devoid of all muscular depressions and ridges, one of which is so prominent
+in the middle of this bone, represented in the above cut (fig. 285.). In
+saurians, on the contrary, such ridges exist for the attachment of muscles;
+and to some animal of that class the bone is probably referable.
+
+[Illustration: Fig. 286. _Amphitherium Prevostii_. Stonesfield
+Slate. Natural size.
+
+  _a_. coronoid process.
+  _b_. condyle.
+  _c_. angle of jaw.
+  _d_. double-fanged molars.]
+
+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 seven specimens of lower jaws of mammiferous
+quadrupeds, belonging to three different species and to two distinct
+genera, for which the names of _Amphitherium_ and _Phascolotherium_ have
+been adopted. When Cuvier was first shown one of these fossils in 1818, he
+pronounced it to belong to a small ferine mammal, with a jaw much
+resembling that of an opossum, but differing from all known ferine genera,
+in the great number of the molar teeth, of which it had at least ten in a
+row. Since that period, a much more perfect specimen of the same fossil,
+obtained by Dr. Buckland (see fig. 286.), has been examined by Mr. Owen,
+who finds that the jaw contained on the whole twelve molar teeth, with the
+socket of a small canine, and three small incisors, which are _in situ_,
+altogether amounting to sixteen teeth on each side of the lower jaw.
+
+[Illustration: Fig. 287. _Amphitherium Broderipii_. Natural size.
+Stonesfield Slate.]
+
+The only question which could be raised respecting the nature of these
+fossils was, whether they belonged to a mammifer, a reptile, or a fish. Now
+on this head the osteologist observes that each of the seven half jaws is
+composed of but one single piece, and not of two or more separate bones, as
+in fishes and most reptiles, or of two bones, united by a suture, as in
+some few species belonging to those classes. The condyle, moreover (_b_,
+fig. 286.), or articular surface, by which the lower jaw unites with the
+upper, is convex in the Stonesfield specimens, and not concave as in fishes
+and reptiles. The coronoid process (_a_, fig. 286.) is well developed,
+whereas it is wanting or very small, in the inferior classes of vertebrata.
+Lastly, the molar teeth in the _Amphitherium_ and _Phascolotherium_ have
+complicated crowns, and two roots (see _d_, fig. 286.), instead of being
+simple and with single fangs.[269-A]
+
+[Illustration: Fig. 288. _Tupaia Tana._ Right ramus of lower jaw, natural
+size. A recent insectivorous mammal from Sumatra.]
+
+[2 Illustrations: Part of lower jaw of _Tupaia Tana_; twice natural size.
+
+Fig. 289. End view seen from behind, showing the very slight inflection of
+the angle at _c_.
+
+Fig. 290. Side view of same.]
+
+[2 Illustrations: Part of lower jaw of _Didelphis Azaræ_; recent,
+Brazil. Natural size.
+
+Fig. 291. End view seen from behind, showing the inflection of the angle of
+the jaw, _c. d._
+
+Fig. 292. Side view of same.]
+
+The only question, therefore, which could fairly admit of controversy
+was 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.
+291. and 292.) of the lower jaw, as a character of the genus
+_Didelphys_; and Mr. Owen has since established its generality in the
+entire marsupial series. In all these pouched quadrupeds, this process
+is turned inwards, as at _c d_, fig. 291. in the Brazilian opossum,
+whereas in the placental series, as at _c_, figs. 290. and 289. there is
+an almost entire absence of such inflection. The _Tupaia Tana_ of
+Sumatra has been selected by my friend Mr. Waterhouse, for this
+illustration, because that small insectivorous quadruped bears a great
+resemblance to those of the Stonesfield _Amphitherium_. By clearing away
+the matrix from the specimen of _Amphitherium Prevostii_ above
+represented (fig. 286.), Mr. Owen ascertained that the angular process
+(_c_) bent inwards 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 turns the scale in favour of its affinities to
+the placental insectivora. Nevertheless, the _Amphitherium_ offers 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.[269-B]
+
+Another species of _Amphitherium_ has been found at Stonesfield (fig.
+287. p. 268.), which differs from the former (fig. 286.) principally
+in being larger.
+
+[Illustration: Fig. 293. _Phascolotherium Bucklandi_, Owen.
+
+  _a._ natural size.
+  _b._ molar of same magnified.]
+
+The second mammiferous genus discovered in the same slates was named
+originally by Mr. Broderip _Didelphys Bucklandi_ (see fig. 293.), 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 premolar and
+molar teeth, is complete.[270-A]
+
+On reviewing, therefore, the whole of the osteological evidence, it will be
+seen that we have every reason to presume that the _Amphitherium_ and
+_Phascolotherium_ of Stonesfield represent both the placental and marsupial
+classes of mammalia; and if so, they warn us in a most emphatic manner, not
+to found rash generalizations respecting the non-existence of certain
+classes of animals at particular periods of the past, on mere negative
+evidence. The singular accident of our having as yet found nothing but the
+lower jaws of seven individuals, and no other bones of their skeletons, is
+alone sufficient to demonstrate the fragmentary manner in which the
+memorials of an ancient terrestrial fauna are handed down to us. We can
+scarcely avoid suspecting that the two genera above described, may have
+borne a like insignificant proportion to the entire assemblage of
+warm-blooded quadrupeds which flourished in the islands of the oolitic sea.
+
+Mr. Owen has remarked that as the marsupial genera, to which the
+_Phascolotherium_ is most nearly allied, are now confined to New South
+Wales and Van Diemen's Land, so also is it in the Australian seas, that we
+find the _Cestracion_, a cartilaginous fish which has a bony palate, allied
+to those called _Acrodus_ and _Psammodus_ (see figs. 307, 308. p. 275.), so
+common in the oolite and lias. In the same Australian seas, also, near the
+shore, we find the living _Trigonia_, a genus of mollusca so frequently met
+with in the Stonesfield slate. So, also, the Araucarian pines are now
+abundant, together with ferns, in Australia and its islands, as they were
+in Europe in the oolitic period. Many botanists incline to the opinion,
+that the _Thuja_, _Pine_, _Cycas_, _Zamia_, in short, all the gymnogens,
+belong to a less highly developed type of flowering plants than do the
+exogens; but even if this be admitted, no naturalist can ascribe a low
+standard of organization to the oolitic flora, since we meet with endogens
+of the most perfect structure in oolitic rocks, both above and below the
+Stonesfield slate, as, for example, the _Podocarya_ of Buckland, a fruit
+allied to the _Pandanus_, found in the Inferior Oolite (see fig. 294.), and
+the _Carpolithes conica_ of the Coral rag. The doctrine, therefore, of a
+regular series of progressive development at successive eras in the animal
+and vegetable kingdoms, from beings of a more simple to those of a more
+complex organization, receives a check, if not a refutation, from the facts
+revealed to us by the study of the Lower Oolites.
+
+[Illustration: Fig. 294. Portion of a fossil fruit of _Podocarya_
+magnified. (Buckland's Bridgew. Treat. Pl. 63.) Inferior Oolite,
+Charmouth, Dorset.]
+
+The Stonesfield slate, in its range from Oxfordshire to the north-east,
+is represented by flaggy and fissile sandstones, as at Collyweston in
+Northamptonshire, where, according to the researches of Messrs. Ibbetson
+and Morris, it contains many shells, such as _Trigonia angulata_, also
+found at Stonesfield. But the Northamptonshire strata of this age assume
+a more marine character, or appear at least to have been formed farther
+from land. They inclose, however, some fossil ferns, such as _Pecopteris
+polypodioides_, of species common to the oolites of the Yorkshire
+coast[271-A], where rocks of this age put on all the aspect of a true
+coal-field; thin seams of coal having actually been worked in them
+for more than a century.
+
+[Illustration: Fig. 295. _Pterophyllum comptum._ (Syn. _Cycadites
+comptus_.) Upper sandstone and shale, Gristhorpe, near Scarborough.]
+
+In the north-west of Yorkshire, the formation alluded to consists of an
+upper and a lower carbonaceous shale, abounding in impressions of
+plants, divided by a limestone considered by many geologists as the
+representative of the Great Oolite; but the scarcity of marine fossils
+makes all comparisons with the subdivisions adopted in the south
+extremely difficult. A rich harvest of fossil ferns has been obtained
+from the upper carbonaceous shales and sandstones at Gristhorpe, near
+Scarborough (see figs. 295, 296.). The lower shales are well exposed in
+the sea-cliffs at Whitby, and are chiefly characterized by ferns and
+cycadeæ. They contain, also, a species of calamite, and a fossil called
+_Equisetum columnare_, which maintains an upright position in sandstone
+strata over a wide area. Shells of the genus _Cypris_ and _Unio_,
+collected by Mr. Bean from these Yorkshire coal-bearing beds, point to
+the estuary or fluviatile origin of the deposit.
+
+[Illustration: Fig. 296. _Hemitelites Brownii_, Goepp. Syn.
+_Phlebopteris contigua_, Lind. & Hutt. Upper carbonaceous strata, Lower
+Oolite, Gristhorpe, Yorkshire.]
+
+At Brora, in Sutherlandshire, a coal formation, probably coeval with the
+above, or 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 3-1/2 feet thick,
+and there are several feet more of pyritous coal resting upon it.
+
+_Inferior Oolite._--Between the Great and Inferior Oolite, near Bath, an
+argillaceous deposit called "the fuller's earth," occurs, but is wanting in
+the north of England. The Inferior Oolite is a calcareous freestone,
+usually of small thickness, which sometimes rests upon, or is replaced by,
+yellow sands, called the sands of the Inferior Oolite. These last, in their
+turn, repose upon the lias in the south and west of England.
+
+Among the characteristic shells of the Inferior Oolite, I may instance
+_Terebratula spinosa_ (fig. 297.), and _Pholadomya fidicula_ (fig. 298.).
+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 singular cleft (_a_, fig. 299.) on
+the right side of the mouth.
+
+[Illustration: Fig. 297. _Terebratula spinosa._ Inferior Oolite.]
+
+[Illustration: Fig. 298.
+
+  _a._ _Pholadomya fidicula_, 1/3 nat. size. Inf. Ool.
+  _b._ Heart-shaped anterior termination of the same.]
+
+[Illustration: Fig. 299. _Pleurotomaria ornata._ Ferruginous Oolite,
+Normandy. Inferior Oolite, England.]
+
+As illustrations of shells having a great vertical range, I may allude to
+_Trigonia clavellata_, found in the Upper and Inferior Oolite, and _T.
+costata_, common to the Upper, Middle, and Lower Oolite; also _Ostrea
+Marshii_ (fig. 300.), common to the Cornbrash of Wilts and the Inferior
+Oolite of Yorkshire; and _Ammonites striatulus_ (fig. 301.) common to the
+Inferior Oolite and Lias.
+
+[Illustration: Fig. 300. _Ostrea Marshii._ 1/2 nat. size. Middle
+and Lower Oolite.]
+
+[Illustration: Fig. 301. _Ammonites striatulus_, Sow. 1/3 nat. size.
+Inferior Oolite and Lias.]
+
+Such facts by no means invalidate the general rule, that certain fossils
+are good chronological tests of geological periods; but they serve to
+caution us against attaching too much importance to single species, some
+of which may have a wider, others a more confined vertical range. We
+have before seen that, in the successive tertiary formations, there are
+species common to older and newer groups, yet these groups are
+distinguishable from one another by a comparison of the whole assemblage
+of fossil shells proper to each.
+
+
+FOOTNOTES:
+
+[259-A] See Chapters VI. and XIX.
+
+[261-A] Fitton, Geol. Trans., Second Series, vol. iv. pl. 23. fig. 12.
+
+[262-A] S. P. Pratt, Annals of Nat. Hist., November, 1841.
+
+[263-A] See Phil. Trans. 1850, p. 393.
+
+[263-B] P. Scrope, Geol. Proceed., March, 1831.
+
+[265-A] For a fuller account of these Encrinites, see Buckland's
+Bridgewater Treatise, vol. i. p. 429.
+
+[266-A] Lycett, Quart. Geol. Journ. vol. iv. p. 183.
+
+[266-B] Proceedings Geol. Soc. vol. i. p. 414.
+
+[267-A] See Buckland's Bridgewater Treatise; and Brodie's Fossil Insects,
+where it is suggested that these elytra may belong to _Priomus_.
+
+[267-B] Vol. i. p. 115.
+
+[269-A] I have given a figure in the Principles of Geology, chap. ix., of
+another Stonesfield specimen of _Amphitherium Prevostii_, in which the
+sockets and roots of the teeth are finely exposed.
+
+[269-B] A figure of this recent _Myrmecobius_ will be found in the
+Principles, chap. ix.
+
+[270-A] Owen's British Fossil Mammals, p. 62.
+
+[271-A] Ibbetson and Morris, Report of Brit. Ass., 1847, p. 131.
+
+
+
+
+CHAPTER XXI.
+
+OOLITE AND LIAS--_continued_.
+
+   Mineral character of Lias--Name of Gryphite limestone--Fossil shells
+   and fish--Ichthyodorulites--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--Origin of the Oolite and
+   Lias, and of alternating calcareous and argillaceous
+   formations--Oolitic coal-field of Virginia, in the United States.
+
+
+_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. They pass, indeed, into each other in some places, as near
+Bath, a sandy marl called the marlstone of the Lias being interposed, and
+partaking of the mineral characters of the upper lias and inferior oolite.
+These last-mentioned divisions have also some fossils in common, such as
+the _Avicula inæquivalvis_ (fig. 302.). Nevertheless the Lias may be traced
+throughout a great part of Europe as a separate and independent group, of
+considerable thickness, varying from 500 to 1000 feet, containing many
+peculiar fossils, and having a very uniform lithological aspect. Although
+usually conformable to the oolite, it is sometimes, as in the Jura,
+unconformable. In the environs of Lons-le-Saulnier, for instance, in the
+department of Jura, the strata of lias are inclined at an angle of about
+45°, while the incumbent oolitic marls are horizontal.
+
+[Illustration: Fig. 302. _Avicula inæquivalvis_, Sow.]
+
+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 with a surface becoming 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
+riband-like appearance.[274-A]
+
+Although the prevailing colour of the limestone of this formation is blue,
+yet some beds of the lower lias are of a yellowish white colour, and have
+been called white lias. In some parts of France, near the Vosges mountains,
+and in Luxembourg, M. E. de Beaumont has shown that the lias containing
+_Gryphæa arcuata_, _Plagiostoma giganteum_ (see fig. 303.), and other
+characteristic fossils, becomes arenaceous; and around the Hartz, in
+Westphalia and Bavaria, the inferior parts of the lias are sandy, and
+sometimes afford a building stone.
+
+[Illustration: Fig. 303. _Plagiostoma giganteum._ Lias.]
+
+[Illustration: Fig. 304. _Gryphæa incurva_, Sow. (_G. arcuata_, Lam.)]
+
+[Illustration: Fig. 305. _Nautilus truncatus._ 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. 304., see also fig. 30. p. 29.). Many
+cephalopoda, also, such as _Ammonite_, _Belemnite_, and _Nautilus_ (fig.
+305.), prove the marine origin of the formation.
+
+[Illustration: Fig. 306. Scales of _Lepidotus gigas_, Agas.
+
+_a._ two of the scales detached.]
+
+The fossil fish resemble generically those of the oolite, belonging all,
+according to M. Agassiz, to extinct genera, and differing remarkably from
+the ichthyolites of the Cretaceous period. Among them is a species of
+_Lepidotus_ (_L. gigas_, Agas.) (fig. 306.), which is found in the lias of
+England, France, and Germany.[275-A] This genus was before mentioned (p.
+229.) as occurring in the Wealden, and is supposed to have frequented both
+rivers and coasts. The teeth of a species of _Acrodus_, also, are very
+abundant in the lias (fig. 307.).
+
+[Illustration: Fig. 307. _Acrodus nobilis_, Agas. (tooth); commonly called
+fossil leach. Lias, Lyme Regis, and Germany.]
+
+[Illustration: Fig. 308. _Hybodus reticulatus_, Agas. Lias, Lyme Regis.
+
+  _a._ Part of fin, commonly called Ichthyodorulite.
+  _b._ Tooth.]
+
+But the remains of fish which have excited more attention than any others,
+are those large bony spines called _ichthyodorulites_ (_a_, fig. 308.),
+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. 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_, fig. 309.). In both of these genera, the posterior concave face is
+armed with small spines like that of the fossil _Hybodus_ (fig. 308.), one
+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. 309.), to raise and depress the
+fin, their action resembling that of a moveable mast, raising and lowering
+backwards the sail of a barge."[276-A]
+
+[Illustration: Fig. 309. _Chimæra monstrosa._[276-B]
+
+_a._ Spine forming anterior part of the dorsal fin.]
+
+_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 reptiles,
+which are extraordinary for their number, size, and structure. Among the
+most singular of these are several species of _Ichthyosaurus_ and
+_Plesiosaurus_. The genus _Ichthyosaurus_, or fish-lizard, is not confined
+to this formation, but has been found in strata as high as the chalk-marl
+and gault of England, and as low as the muschelkalk of Germany, a formation
+which immediately succeeds the lias in the descending order.[276-C] 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 habits of 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.[276-D]
+
+A specimen of the hinder fin or paddle of _Ichthyosaurus communis_ was
+discovered in 1840 at Barrow-on-Soar, by Sir P. Egerton, which
+distinctly exhibits on its posterior margin the remains of cartilaginous
+rays that bifurcate as they approach the edge, like those in the fin of
+a fish (see _a_, fig. 312.). It had previously been supposed, says Mr.
+Owen, that the locomotive organs of the Ichthyosaurus were enveloped,
+while living, in a smooth integument, like that of the turtle and
+porpoise, which has no other support than is afforded by the bones and
+ligaments within; but it now appears that the fin was much larger,
+expanding far beyond its osseous framework, and deviating widely in its
+fish-like rays from the ordinary reptilian type. In fig. 312. the
+posterior bones, or digital ossicles of the paddle, are seen near _b_;
+and beyond these is the dark carbonized integument of the terminal half
+of the fin, the outline of which is beautifully defined.[277-A] Mr. Owen
+believes that, besides the fore-paddles, these short-and stiff-necked
+saurians were furnished with a tail-fin without bones and purely
+tegumentary, expanding in a vertical direction; an organ of motion which
+enabled them to turn their heads rapidly.[277-B]
+
+[Illustration: Fig. 310. _Ichthyosaurus communis_, restored by
+Conybeare and Cuvier.
+
+_a._ costal vertebræ.]
+
+[Illustration: Fig. 311. _Plesiosaurus dolichodeirus_, restored by
+Rev. W. D. Conybeare.
+
+_a._ cervical vertebra.]
+
+[Illustration: Fig. 312. Posterior part of hind fin or paddle of
+_Ichthyosaurus communis_.]
+
+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_.[278-A] (See figs. 310, 311.) 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.[278-B] Some
+of the reptiles above mentioned were of formidable dimensions. One specimen
+of _Ichthyosaurus platyodon_, from the lias at Lyme, now in the British
+Museum, must have belonged to an animal more than 24 feet in length; and
+another of the _Plesiosaurus_, in the same collection, is 11 feet long. The
+form of the _Ichthyosaurus_ may have fitted it to cut through the waves
+like the porpoise; but it is supposed that the _Plesiosaurus_, at least the
+long-necked species (fig. 311.), was better suited to fish in shallow
+creeks and bays defended from heavy breakers.
+
+In many specimens both of Ichthyosaur and Plesiosaur the bones of the head,
+neck, and tail, are in their natural position, while those of the rest of
+the skeleton are detached and in confusion. Mr. Stutchburg has suggested
+that their bodies after death became inflated with gases, and, while the
+abdominal viscera were decomposing, the bones, though disunited, were
+retained within the tough dermal covering as in a bag, until the whole,
+becoming water-logged, sank to the bottom.[278-C] As they belonged to
+individuals of all ages they are supposed, by Dr. Buckland, to have
+experienced a violent death; and the same conclusion might also be drawn
+from their having escaped the attacks of their own predaceous race, or of
+fishes, found fossil in the same beds.
+
+[Illustration: Fig 313. _Amblyrhynchus cristatus_, Bell. Length varying
+from 3 to 4 feet. The only existing marine lizard now known.
+
+_a._ Tooth, natural size and magnified.]
+
+For the last twenty years, anatomists have agreed that these extinct
+saurians must have inhabited the sea; and it was argued 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 (or
+Isle of Pines), south of Cuba, and in the open sea round the coast. More
+recently a saurian has been discovered of aquatic habits and exclusively
+marine. This creature was found in the Galapagos Islands, during the
+visit of H. M. S. Beagle to that archipelago, in 1835, and its habits
+were then observed by Mr. Darwin. The islands alluded to are situated
+under the equator, nearly 600 miles to the westward of the coast of
+South America. They are volcanic, some of them being 3000 or 4000 feet
+high; and one of them, Albemarle Island, 75 miles long. The climate is
+mild; very little rain falls; and, in the whole archipelago, there is
+only one rill of fresh water that reaches the coast. The soil is for the
+most part dry and harsh, and the vegetation scanty. The birds, reptiles,
+plants, and insects are, with very few exceptions, of species found no
+where else in the world, although all partake, in their general form, of
+a South American type. Of the mammalia, says Mr. Darwin, one species
+alone appears to be indigenous, namely, a large and peculiar kind of
+mouse; but the number of lizards, tortoises, and snakes is so great,
+that it may be called a land of reptiles. The variety, indeed, of
+species is small; but the individuals of each are in wonderful
+abundance. There is a turtle, a large tortoise (_Testudo Indicus_), four
+lizards, and about the same number of snakes, but no frogs or toads. Two
+of the lizards belong to the family _Iguanidæ_ of Bell, and to a
+peculiar genus (_Amblyrhynchus_) established by that naturalist, and so
+named from their obtusely truncated head and short snout.[279-A] Of
+these lizards one is terrestrial in its habits, and burrows in the
+ground, swarming everywhere on the land, having a round tail, and a
+mouth somewhat resembling in form that of the tortoise. The other is
+aquatic, and has its tail flattened laterally for swimming (see fig.
+313.). "This marine saurian," says Mr. Darwin, "is extremely common on
+all the islands throughout the archipelago. It lives exclusively on the
+rocky sea-beaches, and I never saw one even ten yards inshore. The usual
+length is about a yard, but there are some even 4 feet long. It is of a
+dirty black colour, sluggish in its movements on the land; but, when in
+the water, it swims with perfect ease and quickness by a serpentine
+movement of its body and flattened tail, the legs during this time being
+motionless, and closely collapsed on its sides. Their limbs and strong
+claws are admirably adapted for crawling over the rugged and fissured
+masses of lava which everywhere form the coast. In such situations, a
+group of six or seven of these hideous reptiles may oftentimes be seen
+on the black rocks, a few feet above the surf, basking in the sun with
+outstretched legs. Their stomachs, on being opened, were found to be
+largely distended with minced sea-weed, of a kind which grows at the
+bottom of the sea at some little distance from the coast. To obtain
+this, the lizards go out to sea in shoals. One of these animals was sunk
+in salt water, from the ship, with a heavy weight attached to it, and
+on being drawn up again after an hour it was quite active and unharmed.
+It is not yet known by the inhabitants where this animal lays its eggs;
+a singular fact, considering its abundance, and that the natives are
+well acquainted with the eggs of the terrestrial _Amblyrhynchus_,
+which is also herbivorous."[280-A]
+
+In those deposits now forming by the sediment washed away from the
+wasting shores of the Galapagos Islands the remains of saurians, both of
+the land and sea, as well as of chelonians and fish, may be mingled with
+marine shells, without any bones of land quadrupeds or batrachian
+reptiles; yet even here we should expect the remains of marine mammalia
+to be imbedded in the new strata, for there are seals, besides several
+kinds of cetacea, on the Galapagian shores; and, in this respect, the
+parallel between the modern fauna, above described, and the ancient one
+of the lias, would not hold good.
+
+_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."[280-B] 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."[281-A] It is
+farther 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.[281-B]
+
+Numerous specimens of the pen-and-ink fish (_Sepia loligo_, Lin.; _Loligo
+vulgaris_, Lam.) 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.[281-C]
+
+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 into 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
+undescribable multitudes of dead fishes have been seen floating on the sea
+after a discharge of noxious vapours during similar convulsions.[281-D]
+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.
+
+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, especially in
+the lowest part of it, have an estuary character, and must have been formed
+within the influence of rivers. In Gloucestershire, where there is a good
+type of the lias of the West of England, it may be divided into an upper
+mass of shale with a base of marlstone, and a lower series of shales with
+underlying limestones and shales. We learn from the researches of the Rev.
+P. B. Brodie[281-E], that in the superior of these two divisions numerous
+remains of insects and plants have been detected in several places, mingled
+with marine shells; but in the inferior division similar fossils are still
+more plentiful. One band, rarely exceeding a foot in thickness, has been
+named the "insect limestone." It passes upwards into a shale containing
+_Cypris_ and _Estheria_, and is charged with the wing-cases of several
+genera of coleoptera, and with some nearly entire beetles, of which the
+eyes are preserved. The nervures of the wings of neuropterous insects
+(fig. 314.) are beautifully perfect in this bed. Ferns, with leaves of
+monocotyledonous plants, and freshwater shells, such as _Cyclas_ and
+_Unio_, accompany the insects in some 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. There are two, or even three, bands of "insect limestone" in
+several sections, and they have been ascertained by Mr. Brodie to retain
+the same lithological and zoological characters when traced from the centre
+of Warwickshire to the borders of the southern part of Wales. 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_, &c., 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.
+
+[Illustration: Fig. 314. Wing of a neuropterous insect, from the Lower
+Lias, Gloucestershire. (Rev. B. Brodie.)]
+
+_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. Fragments of wood are common, and often converted into
+limestone. That some of this wood, though now petrified, was soft when it
+first lay at the bottom of the sea, is shown by a specimen now in the
+museum of the Geological Society (see fig. 315.), which has the form of an
+_ammonite_ indented on its surface.
+
+[Illustration: Fig. 315. Petrified wood.]
+
+M. Ad. Brongniart enumerates forty-seven liassic acrogens, most of them
+ferns; and fifty gymnogens, of which thirty-nine are cycads, and eleven
+conifers. Among the cycads the predominance of _Zamites_ and _Nilsonia_,
+and among the ferns the numerous genera with leaves having reticulated
+veins (as in fig. 296. p. 272.), are mentioned as botanical
+characteristics of this era.[282-A]
+
+_Origin of the Oolite and Lias._--If we now endeavour to restore, in
+imagination, the ancient condition of the European area at the period of
+the Oolite and Lias, we must conceive a sea in which the growth of coral
+reefs and shelly limestones, after proceeding without interruption for
+ages, was liable to be stopped suddenly by the deposition of clayey
+sediment. Then, again, the argillaceous matter, devoid of corals, was
+deposited for ages, and attained a thickness of hundreds of feet, until
+another period arrived when the same space was again occupied by
+calcareous sand, or solid rocks of shell and coral, to be again succeeded
+by the recurrence of another period of argillaceous deposition. Mr.
+Conybeare has remarked of the entire group of Oolite and Lias, that it
+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 of the inferior oolite, and these again by shelly and
+coralline limestone (Bath oolite, &c.); 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.[283-A] The clay beds, however, as Sir H. De la Beche remarks,
+can be followed over larger areas than the sands or sandstones.[283-B] It
+should also be remembered that while the oolitic 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, in reality, retain a pretty uniform character, for distances
+of from 400 to 600 miles from east to west and north to south.
+
+According to M. Thirria, the entire oolitic group in the department of the
+Haute-Saône, in France, may be equal in thickness to that of England; but
+the importance of the argillaceous divisions is in the inverse ratio to
+that which they exhibit in England, where they are about equal to twice the
+thickness of the limestones, whereas, in the part of France alluded to,
+they reach only about a third of that thickness.[283-C] In the Jura the
+clays are still thinner; and in the Alps they thin out and almost vanish.
+
+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.
+
+In order to account for another great formation, like the Oxford clay,
+again covering one of coral limestone, we must suppose a sinking down
+like that which is now taking place in some existing regions of coral
+between Australia and South America. The occurrence of subsidences, on
+so vast a scale, may have caused the bed of the ocean and the adjoining
+land, throughout great parts of the European area, to assume a shape
+favourable to the deposition of another set of clayey strata; and this
+change may have been succeeded by a series of events analogous to that
+already explained, and these again by a third series in similar order.
+Both the ascending and descending movements may have been extremely
+slow, like those now going on in the Pacific; and the growth of every
+stratum of coral, a few feet of thickness, may have required centuries
+for its completion, during which certain species of organic beings
+disappeared from the earth, and others were introduced in their place;
+so that, in each set of strata, from the Upper Oolite to the Lias, some
+peculiar and characteristic fossils were embedded.
+
+
+_Oolite and Lias of the United States._
+
+[Illustration: Fig. 316. Section showing the geological position of the
+James River, or East Virginian Coal-field.
+
+  A. Granite, gneiss, &c.
+  B. Coal-measures.
+  C. Tertiary strata.
+  D. Drift or _ancient alluvium_.]
+
+There are large tracts on the globe, as in Russia and the United States,
+where all the members of the oolitic series are unrepresented. In the state
+of Virginia, however, at the distance of about 13 miles eastward of
+Richmond, the capital of that State, there is a regular coal-field
+occurring in a depression of the granite rocks (see section, fig. 316.),
+which Professor W. B. Rogers first correctly referred to the age of the
+lower part of the Jurassic group. This opinion I was enabled to confirm
+after collecting a large number of fossil plants, fish, and shells, and
+examining the coal-field throughout its whole area. It extends 26 miles
+from north to south, and from 4 to 12, from east to west. The plants
+consist chiefly of zamites, calamites, and equisetums, and these last 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 now
+lie buried in strata of hardened sand and mud. I found them maintaining
+their erect attitude, at points many miles distant from others, 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.
+
+It is worthy of remark that the _Equisetum columnare_ of these Virginian
+rocks appears to be undistinguishable from the species found in the
+oolitic sandstones near Whitby in Yorkshire, where it also is met with
+in an upright position. One of the American ferns, _Pecopteris
+Whitbyensis_, is also a species common to the Yorkshire oolites.[285-A]
+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 seams. One of these, the main seam, is in some places
+from 30 to 40 feet thick, composed of pure bituminous coal. On
+descending a shaft 800 feet deep, in the Blackheath mines in
+Chesterfield county, I found myself in a chamber more than 40 feet high,
+caused by the removal of this coal. Timber props of great strength
+supported the roof, but they were seen to bend under the incumbent
+weight. 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 paleozoic coal.
+
+The fossil fish of these Richmond strata belong to the liassic genus
+_Tetragonolepis_, and to a new genus which I have called _Dictyopyge_.
+Shells are very rare, as usually in all coal-bearing deposits, but a
+species of _Posidonomya_ is in such profusion in some shaley beds as to
+divide them like the plates of mica in micaceous shales (see fig. 317.).
+
+[Illustration: Fig. 317. Oolitic coal-shale, Richmond, Virginia.
+
+  _a._ _Posidonomya._
+  _b._ young of same.]
+
+In India, especially in Cutch, a formation occurs clearly referable to the
+oolitic and liassic type, as shown by the shells, corals, and plants; and
+there also coal has been procured from one member of the group.
+
+
+FOOTNOTES:
+
+[274-A] Conyb. and Phil. p. 261.
+
+[275-A] Agassiz, Pois. Fos. vol. ii. tab. 28, 29.
+
+[276-A] Bridgewater Treatise, p. 290.
+
+[276-B] Agassiz, Poissons Fossiles, vol. iii. tab. C. fig. 1.
+
+[276-C] Ibid. p. 168.
+
+[276-D] Ibid. p. 187.
+
+[277-A] Geol. Soc. Proceedings, vol. iii. p. 157. 1839.
+
+[277-B] Geol. Trans. Second Series, vol. v. p. 511.
+
+[278-A] Geol. Trans., Second Series, vol. i. pl. 49.
+
+[278-B] Conybeare and De la Beche. Geol. Trans.; and Buckland,
+Bridgew. Treat., p. 203.
+
+[278-C] Quart. Geol. Journ. vol. ii. p. 411.
+
+[279-A] +Amblys+, _amblys_, blunt; and +rhygchos+, _rhynchus_, snout.
+
+[280-A] Darwin's Journal, chap. xix.
+
+[280-B] Bridgew. Treat., p. 125.
+
+[281-A] Geological Researches, p. 334.
+
+[281-B] Buckland, Bridgew. Treat., p. 307.
+
+[281-C] Ibid.
+
+[281-D] See Principles, _Index_, Lancerote, Graham Island, Calabria.
+
+[281-E] A History of Fossil Insects, &c. 1845. London.
+
+[282-A] Tableau des Veg. Fos. 1849, p. 105.
+
+[283-A] Con. and Phil., p. 166.
+
+[283-B] Geol. Researches, p. 337.
+
+[283-C] Burat's D'Aubuisson, tom. ii. p. 456.
+
+[285-A] See description of the coal-field by the author, and the plants by
+C. J. F. Bunbury, Esq., Quart. Geol. Journ., vol. iii. p. 281.
+
+
+
+
+CHAPTER XXII.
+
+TRIAS OR NEW RED SANDSTONE GROUP.
+
+   Distinction between New and Old Red Sandstone--Between Upper and Lower
+   New Red--The Trias and its three divisions--Most largely developed in
+   Germany--Keuper and its fossils--Muschelkalk--Fossil plants of
+   Bunter--Triassic group in England--Bone-bed of Axmouth and Aust--Red
+   Sandstone of Warwickshire and Cheshire--Footsteps of _Chirotherium_ in
+   England and Germany--Osteology of the _Labyrinthodon_--Identification
+   of this Batrachian with the Chirotherium--Origin of Red Sandstone and
+   Rock-salt--Hypothesis of saline volcanic exhalations--Theory of the
+   precipitation of salt from inland lakes or lagoons--Saltness of the
+   Red Sea--New Red Sandstone in the United States--Fossil footprints of
+   birds and reptiles in the Valley of the Connecticut--Antiquity of the
+   Red Sandstone containing them.
+
+
+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" (_c_, fig. 318.), often identical in
+mineral character, which lie immediately beneath the coal (_b_).
+
+[Illustration: Fig. 318. Cross section.
+
+  _a._ New red sandstone.
+  _b._ Coal.
+  _c._ Old red.]
+
+The name of "Red Marl" has been incorrectly applied to the red clays of
+this formation, as before explained (p. 13.), 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.
+
+Before the distinctness of the fossil remains characterizing the upper and
+lower part of the English New Red had been clearly recognized, it was found
+convenient to have a common name for all the strata intermediate in
+position between the Lias and Coal; and the term "Poikilitic" was proposed
+by Messrs. Conybeare and Buckland[286-A], from +poikilos+, poikilos,
+_variegated_, some of the most characteristic strata of this group having
+been called _variegated_ by Werner, from their exhibiting spots and streaks
+of light-blue, green, and buff colour, in a red base.
+
+A single term, thus comprehending both Upper and Lower New Red, or the
+Triassic and Permian groups of modern classifications, may still be useful
+in describing districts where we have to speak of masses of red sandstone
+and shale, referable, in part, to both these eras, but which, in the
+absence of fossils, it is impossible to divide.
+
+
+_Trias or Upper New Red Sandstone Group._
+
+The accompanying table will explain the subdivisions generally adopted for
+the uppermost of the two systems above alluded to, and the names given to
+them in England and on the Continent.
+
+                                                       Synonyms.
+                                                  German.       French.
+
+                 { _a._ Saliferous and          }             }
+                 {      gypseous shales and     } Keuper      } Marnes irisées.
+  Trias or Upper {      sandstone               }             }
+    New Red      {
+    Sandstone    { _b._ (wanting in England)    } Muschelkalk { Muschelkalk, ou
+                 {                                            { calcaire
+                 {                                            { coquillier.
+                 {
+                 { _c._ Sandstone and           } Bunter-     } Grès bigarré.
+                 {      quartzose conglomerate  } sandstein   }
+
+I shall first describe this group as it occurs in South Western and North
+Western Germany, for it is far more fully developed there 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."
+
+[Illustration: Fig. 319. _Equisetites columnaris._ (Syn. _Equisetum
+columnare_.) Fragment of stem, and small portion of same
+magnified. Keuper.]
+
+_The Keuper_, the first or newest of these, is 1000 feet thick in
+Würtemberg, and is divided by Alberti into sandstone, gypsum, and
+carbonaceous slate-clay.[287-A] 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. 325, 326, p. 289.). The plants of the Keuper are
+generically very analogous to those of the lias and oolite, 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.
+
+_The Muschelkalk_ consists chiefly of a compact, greyish limestone, but
+includes beds of dolomite in many places, together with gypsum and
+rock-salt. This limestone, a rock 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 incumbent
+lias and oolite, but a genus allied to the Ammonite, called _Ceratite_ by
+De Haan, in which the descending lobes (see _a_, _b_, _c_, fig. 320.)
+terminate in a few small denticulations pointing inwards. Among the
+bivalve shells, the _Posidonia minuta_, Goldf. (_Posidonomya minuta_,
+Bronn) (see fig. 321.), is abundant, ranging through the Keuper,
+Muschelkalk, and Bunter-sandstein; and _Avicula socialis_, fig. 322.,
+having a similar range, is very characteristic of the Muschelkalk in
+Germany, France, and Poland.
+
+[Illustration: Fig. 320. _Ceratites nodosus._ Muschelkalk.
+
+  _a._ Side view.
+  _b._ Front view.
+  _c._ Partially denticulated outline of the septa dividing the chambers.]
+
+[Illustration: Fig. 321. _Posidonia minuta_, Goldf. (_Posidonomya
+minuta_, Bronn.)]
+
+[Illustration: Fig. 322. Avicula. Characteristic of the Muschelkalk.
+
+  _a._ _Avicula socialis._
+  _b._ Side view of same.]
+
+The abundance of the heads and stems of lily encrinites, _Encrinus
+liliiformis_ (or _Encrinites moniliformis_), show the slow manner in which
+some beds of this limestone have been formed in clear sea-water.
+
+[Illustration: Fig. 323. Voltzia. Bunter-sandstein.
+
+  _a._ _Voltzia heterophylla._ (Syn. _Voltzia brevifolia_.)
+  _b._  portion of same magnified to show fructification. Sulzbad.]
+
+_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, according
+to Von Meyer, is proved, by the presence of _Labyrinthodon_, 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_, peculiar to this period, in which even the
+fructification has been preserved. (See fig. 323.)
+
+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.[288-A]
+
+The footprints of a reptile (_Labyrinthodon_) have been observed on the
+clays of this member of the Trias, near Hildburghausen, in Saxony,
+impressed on the upper surface of the beds, and standing out as casts in
+relief from the under sides of incumbent slabs of sandstone. To these I
+shall again allude in the sequel; they attest, as well as the accompanying
+ripple-marks, and the cracks which traverse the clays, the gradual
+formation in shallow water, and sometimes between high and low water, of
+the beds of this formation.
+
+
+_Triassic group in England._
+
+In England the Lias is succeeded by conformable strata of red and green
+marl, or clay. There intervenes, however, both in the neighbourhood of
+Axmouth, in Devonshire, and in the cliffs of Westbury and Aust, in
+Gloucestershire, on the banks of the Severn, a dark-coloured stratum, well
+known by the name of the "bone-bed." It abounds in the remains of saurians
+and fish, and was formerly classed as the lowest bed of the Lias; but Sir
+P. Egerton has shown that it should be referred to the Upper New Red
+Sandstone, for it contains 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_.
+
+Among those common to the English bone-bed and the Muschelkalk of Germany
+are _Hybodus plicatilis_ (fig. 324.), _Saurichthys apicalis_ (fig. 325.),
+_Gyrolepis tenuistriatus_ (fig. 326.), and _G. Albertii_. Remains of
+saurians have also been found in the bone-bed, and plates of an _Encrinus_.
+
+[Illustration: Fig. 324. _Hybodus plicatilis._ Teeth. Bone-bed,
+Aust and Axmouth.]
+
+[Illustration: Fig. 325. _Saurichthys apicalis._ Tooth; nat. size,
+and magnified. Axmouth.]
+
+[Illustration: Fig. 326. _Gyrolepis tenuistriatus._ Scale; nat. size,
+and magnified. Axmouth.]
+
+The strata of red and green marl, which follow the bone-bed in the
+descending order at Axmouth and Aust, are destitute of organic remains;
+as is the case, for the most part, in the corresponding beds in almost
+every part of England. But fossils have lately been found at a few
+localities in sandstones of this formation, in Worcestershire and
+Warwickshire, and among them the bivalve shell called _Posidonia
+minuta_, Goldf., before mentioned (fig. 321. p. 288.).
+
+The upper member of the English "New Red" containing this shell, in
+those parts of England, is, according to Messrs. Murchison and
+Strickland, 600 feet thick, and consists chiefly of red marl or
+slate, with a band of sandstone. Spines of _Hybodus_, called
+_ichthyodorulites_, teeth of fishes, and footprints of reptiles, with
+remains of a saurian called _Rhyncosaurus_, were observed by the same
+geologists in these strata.[290-A]
+
+In Cheshire and Lancashire the gypseous and saliferous red shales and loams
+of the Trias are between 1000 and 1500 feet thick. In some places
+lenticular masses of rock-salt are interpolated between the argillaceous
+beds, the origin of which will be spoken of in the sequel.
+
+[Illustration: Fig. 327. Single footstep of _Chirotherium_. Bunter
+Sandstein, Saxony; one eighth of nat. size.]
+
+[Illustration: Fig. 328. Line of footsteps on slab of sandstone.
+Hildburghausen, in Saxony.]
+
+The lower division or English representative of the "Bunter" attains a
+thickness of 600 feet in the counties last mentioned. 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.[290-B] 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 a member
+of the Upper New Red Sandstone, at the village of Hesseberg, near
+Hildburghausen, in Saxony, to which I have already alluded. For many years
+these footprints have been referred to a large unknown quadruped,
+provisionally named _Chirotherium_ by Professor Kaup, because the marks
+both of the fore and hind feet resembled impressions made by a human hand.
+(See fig. 327.) The footmarks 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 8 inches in length, and 5 in width, and one was 12 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, 4 inches long and
+3 inches wide, occurs. The footsteps follow each other in pairs, each pair
+in the same line, at intervals of 14 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 inwards like a thumb. Though the fore and hind foot differ so
+much in size, they are nearly similar in form.
+
+The similar footmarks afterwards observed in a rock of corresponding age at
+Storton Hill, were imprinted on five thin beds of clay, superimposed one
+upon the other in the same quarry, and separated by beds of sandstone. On
+the lower surface of the sandstone strata, the solid casts of each
+impression are salient, in high relief, and afford models of the feet,
+toes, and claws of the animals which trod on the clay.
+
+As neither in Germany nor in England any bones or teeth had 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 Dr. Buckland designated some of
+the footsteps as those of a small web-footed animal, probably crocodilean.
+
+In the course of these discussions several naturalists of Liverpool, in
+their report on the Storton quarries, declared their opinion that each of
+the thin seams of clay in which the sandstone casts were moulded had formed
+successively a surface above water, over which the _Chirotherium_ and other
+animals walked, leaving impressions of their footsteps, and that each layer
+had been afterwards submerged by a sinking down of the surface, so that a
+new beach was formed at low water above the former, on which other tracks
+were then made. The repeated occurrence of ripple-marks at various heights
+and depths in the red sandstone of Cheshire had been explained in the same
+manner. It was also remarked that impressions of such depth and clearness
+could only have been made by animals walking on the land, as their weight
+would have been insufficient to make them sink so deeply in yielding clay
+under water. They must therefore have been air-breathers.
+
+When the inquiry had been brought to this point, the reptilian remains
+discovered in the Trias, both of Germany and England, were carefully
+examined by Mr. Owen. He found, after a microscopic investigation of the
+teeth from the German sandstone called Keuper, and from the sandstone of
+Warwick and Leamington, that neither of them could be referred to true
+saurians, although they had been named _Mastodonsaurus_ and _Phytosaurus_
+by Jäger (fig. 329.). It appeared that they were of the _Batrachian_ order,
+and attested the former existence of frogs of gigantic dimensions in
+comparison with any 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 Mr. Owen has proposed the
+name _Labyrinthodon_ for the new genus. By his permission, the annexed
+representation (fig. 330.) 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.
+
+[Illustration: Fig. 329. Tooth of _Labyrinthodon_; nat. size.
+Warwick sandstone.]
+
+[Illustration: Fig. 330. Transverse section of tooth of _Labyrinthodon
+Jaegeri_, Owen (_Mastodonsaurus Jaegeri_, Meyer); nat. size, and
+a segment magnified.
+
+_a._ Pulp cavity, from which the processes of pulp and dentine radiate.]
+
+When Mr. Owen had satisfied himself, from an inspection of the cranium,
+jaws, and teeth, that a gigantic _Batrachian_ had existed at the period of
+the Trias or Upper New Red Sandstone, he soon found, from the examination
+of various bones derived from the same formation, that he could define
+three species of _Labyrinthodon_, and that in this genus the hind
+extremities were much larger than the anterior ones. This circumstance,
+coupled with the fact of the _Labyrinthodon_ having existed at the period
+when the _Chirotherian_ footsteps were made, was the first step towards the
+identification of those tracks with the newly discovered _Batrachian_. It
+was at the same time observed that the footmarks of _Chirotherium_ were
+more like those of toads than of any other living animal; and, lastly,
+that the size of the three species of _Labyrinthodon_ corresponded with the
+size of three different kinds of footprints which had already been supposed
+to belong to three distinct _Chirotheria_. It was moreover inferred, with
+confidence, that the _Labyrinthodon_ was an _air-breathing_ reptile from
+the structure of the nasal cavity, in which the posterior outlets were at
+the back part of the mouth, instead of being directly under the anterior or
+external nostrils. It must have respired air after the manner of saurians,
+and may therefore have imprinted on the shore those footsteps, which, as we
+have seen, could not have originated from an animal walking under water.
+
+It is true that the structure of the foot is still wanting, and that a
+more connected and complete skeleton is required for demonstration; but
+the circumstantial evidence above stated is strong enough to produce
+the conviction that the _Chirotherium_ and _Labyrinthodon_ are one
+and the same.
+
+In order to show the manner in which one of these formidable _Batrachians_
+may have impressed the mark of its feet upon the shore, Mr. Owen has
+attempted a restoration, of which a reduced copy is annexed.
+
+[Illustration: Fig. 331. _Labyrinthodon pachygnathus_, Owen.]
+
+The only bones of this species at present known are those of the head, the
+pelvis, and part of the scapula, which are shown by stronger lines in the
+above figure. There is reason for believing that the head was not smooth
+externally, but protected by bony scutella.
+
+
+_Origin of Red Sandstone and Rock Salt._
+
+We have seen that, in various parts of the world, red and mottled clays,
+and sandstones, of several distinct geological epochs, are found associated
+with salt, gypsum, 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 muriate of soda,
+as in the blue clay formation of Sicily, without any accompanying red
+sandstone or red clay.
+
+To account for deposits of red mud and red sand, we have simply to suppose
+the disintegration of ordinary crystalline or metamorphic schists. Thus, in
+the eastern Grampians of Scotland, as, for example, in the north of
+Forfarshire, the mountains of gneiss, mica-schist, and clay-slate, are
+overspread with alluvium, derived from the disintegration of those rocks;
+and the mass of detritus is stained by oxide of iron, of precisely the same
+colour as the Old Red Sandstone of the adjoining Lowlands. Now this
+alluvium merely requires to be swept down to the sea, or into a lake, to
+form strata of red sandstone and red marl, precisely like the mass of the
+"Old Red" or New Red systems of England, or those tertiary deposits of
+Auvergne (see p. 182.), before described, which are in lithological
+characters quite undistinguishable. The pebbles of gneiss in the Eocene red
+sandstone of Auvergne point clearly to the rocks from which it has been
+derived. The red colouring matter may, as in the Grampians, have been
+furnished by the decomposition of hornblende, or mica, which contain oxide
+of iron in large quantity.
+
+It is a general fact, and one not yet accounted for, that scarcely any
+fossil remains are 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 gypsum and saline matter, occasionally interstratified with such red
+clays and sandstones of various ages, primary, secondary, and tertiary,
+have been thought by some geologists to be of volcanic origin. Submarine
+and subaerial exhalations often occur in regions of earthquakes and
+volcanos far from points of actual eruption, and charged with sulphur,
+sulphuric salts, and with common salt or muriate of soda. In a word, they
+are vents by which all the products which issue in a state of sublimation
+from the craters of active volcanos, obtain a passage from the interior of
+the earth to the surface. That such gaseous emanations and mineral springs,
+impregnated with the ingredients before enumerated, and often intensely
+heated, continue to flow out unaltered in composition and temperature for
+ages, is well known. But before we can decide on their real instrumentality
+in producing in the course of ages beds of gypsum, salt, and dolomite, we
+require to know what are the chemical changes actually in progress in seas
+where this volcanic agency is at work.
+
+Yet the origin of rock-salt is a problem of so much interest in
+theoretical geology as to demand a full discussion of another hypothesis
+advanced on the subject; namely, that which attributes the precipitation
+of the salt to evaporation, whether of inland lakes or of lagoons
+communicating with the ocean.
+
+At Northwich, in Cheshire, two beds of salt, in great part unmixed with
+earthy matter, attain the extraordinary thickness of 90 and even 100 feet.
+The upper surface of the highest bed is very uneven, forming cones and
+irregular figures. Between the two masses there intervenes a bed of
+indurated clay, traversed with veins of salt. The highest bed thins off
+towards the south-west, losing 15 feet in thickness in the course of a
+mile.[295-A] The horizontal extent of these particular masses in Cheshire
+and Lancashire is not exactly known; but the area, containing saliferous
+clays and sandstones, is supposed to exceed 150 miles in diameter, while
+the total thickness of the trias in the same region is estimated by Mr.
+Ormerod at more than 1700 feet. Ripple-marked sandstones, and the
+footprints of animals, before described, are observed at so many levels
+that we may safely assume the whole area to have undergone a slow and
+gradual depression during the formation of the Red Sandstone. The evidence
+of such a movement, wholly independent of the presence of salt itself, is
+very important in reference to the theory under consideration.
+
+In the "Principles of Geology" (chap. 28.), I published a map, furnished to
+me by the late Sir Alexander Burnes, of that singular flat region called
+the Runn of Cutch, near the delta of the Indus, which is 7000 square miles
+in area, or equal in extent to about one-fourth of Ireland. It is neither
+land nor sea, but is dry during a part of every year, and again covered by
+salt water during the monsoons. Some parts of it are liable, after long
+intervals, to be overflowed by river-water. Its surface supports no grass,
+but is encrusted over, here and there, by a layer of salt, about an inch in
+depth, caused by the evaporation of sea-water. Certain tracts have been
+converted into dry land by upheaval during earthquakes since the
+commencement of the present century, and, in other directions, the
+boundaries of the Runn have been enlarged by subsidence. That successive
+layers of salt might be thrown down, one upon the other, over thousands of
+square miles, in such a region, is undeniable. The supply of brine from the
+ocean would be as inexhaustible as the supply of heat from the sun to cause
+evaporation. The only assumption required to enable us to explain a great
+thickness of salt in such as area is, the continuance, for an indefinite
+period, of a subsiding movement, the country preserving all the time a
+general approach to horizontality. Pure salt could only be formed in the
+central parts of basins, where no sand could be drifted by the wind, or
+sediment be brought by currents. Should the sinking of the ground be
+accelerated, so as to let in the sea freely, and deepen the water, a
+temporary suspension of the precipitation of salt would be the only result.
+On the other hand, if the area should dry up, ripple-marked sands and the
+footprints of animals might be formed, where salt had previously
+accumulated. According to this view the thickness of the salt, as well as
+of the accompanying beds of mud and sand, becomes a mere question of time,
+or requires simply a repetition of similar operations.
+
+Mr. Hugh Miller, in an able discussion of this question, refers to Dr.
+Frederick Parrot's account, in his journey to Ararat (1836), of the salt
+lakes of Asia. In several of these lakes west of the river Manech, "the
+water, during the hottest season of the year, is covered on its surface
+with a crust of salt nearly an inch thick, which is collected with shovels
+into boats. The crystallization of the salt is effected by rapid
+evaporation from the sun's heat and the supersaturation of the water with
+muriate of soda; the lake being so shallow that the little boats trail on
+the bottom and leave a furrow behind them, so that the lake must be
+regarded as a wide pan of enormous superficial extent, in which the brine
+can easily reach the degree of concentration required."
+
+Another traveller, 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
+cærulian 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.[296-A]
+
+We may add that the permanent impregnation of the waters of a large shallow
+basin with salt, beyond the proportion which is usual in the ocean, would
+cause it to be uninhabitable by mollusca or fish, as is the case in the
+Dead Sea, and the muriate of soda might remain in excess, even though it
+were occasionally replenished by irruptions of the sea. Should the saline
+deposit be eventually submerged, it might, as we have seen from the example
+of the Runn of Cutch, be covered by a freshwater formation containing
+fluviatile organic remains; and in this way the apparent anomaly of beds of
+sea-salt and clays devoid of marine fossils, alternating with others of
+freshwater origin, may be explained.
+
+Dr. G. Buist, in a recent communication to the Bombay Geographical Society
+(vol. ix.), has asked how it happens that the Red Sea should not exceed the
+open ocean in saltness, by more than 1/10th per cent. The Red Sea receives
+no supply of water from any quarter save through the Straits of
+Babelmandeb; and there is not a single river or rivulet flowing into it
+from a circuit of 4000 miles of shore. The countries around are all
+excessively sterile and arid, and composed, for the most part, of burning
+deserts. From the ascertained evaporation in the sea itself, Dr. Buist
+computes that nearly 8 feet of pure water must be carried off from the
+whole of its surface annually, this being probably equivalent to 1/100th
+part of its whole volume. The Red Sea, therefore, ought to have 1 per cent.
+added annually to its saline contents; and as these constitute 4 per cent.
+by weight, or 2-1/2 per cent. in volume of its entire mass, it ought,
+assuming the average depth to be 800 feet, which is supposed to be far
+beyond the truth, to have been converted into one solid salt formation in
+less than 3000 years.[297-A] Does the Red Sea receive a supply of water
+from the ocean, through the narrow Straits of Babelmandeb, sufficient to
+balance the loss by evaporation? And is there an undercurrent of heavier
+saline water annually flowing outwards? If not, in what manner is the
+excess of salt disposed of? An investigation of this subject by our
+nautical surveyors may perhaps aid the geologist in framing a true theory
+of the origin of rock-salt.
+
+
+_On the New Red Sandstone of the valley of the Connecticut River
+in the United States._
+
+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 5 to 10 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. The red flags of thin-bedded sandstone are often
+ripple-marked, and exhibit on their under sides casts of cracks formed in
+the underlying red and green shales. These last must have shrunk by drying
+before the sand was spread over them. On some shales of the finest texture
+impressions of rain drops may be seen, and casts of them in the incumbent
+argillaceous sandstones. Having observed similar markings produced by
+showers, of which the precise date was known, on the recent red mud of the
+Bay of Fundy, and casts in relief of the same, on layers of dried mud
+thrown down by subsequent tides, I feel no doubt in regard to the origin of
+some of the ancient Connecticut impressions. I have also seen on the
+mud-flats of the Bay of Fundy the footmarks of birds (_Tringa minuta_),
+which daily run along the borders of that estuary at low water, and which I
+have described in my Travels.[297-B] Similar layers of red mud, now
+hardened and compressed into shale, are laid open on the banks of the
+Connecticut, and retain faithfully the impressions and casts of the feet of
+numerous birds and reptiles which walked over them at the time when they
+were deposited, probably in the Triassic Period.
+
+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, which may
+have been thousands of years in forming.[298-A]
+
+[Illustration: Fig. 332. Footprints of a bird. Turner's Falls, Valley of
+the Connecticut. (See Dr. Deane, Mem. of Amer. Acad. vol. iv. 1849.)]
+
+As considerable scepticism is naturally entertained in regard to the nature
+of the evidence derived from footprints, it may be well to enumerate some
+facts respecting them on which the faith of the geologist may rest. When I
+visited the United States in 1842, more than 2000 impressions had been
+observed by Professor Hitchcock, in the district alluded to, and all of
+them were indented on the upper surface of the layers, while the
+corresponding casts, standing out in relief, were always on the lower
+surfaces or planes of the strata. If we follow a single line of marks we
+find them uniform in size, and nearly uniform in distance from each other,
+the toes of two successive footprints, turning alternately right and left
+(see fig. 332.). Such single lines indicate a biped; and there is generally
+such a deviation from a straight line, in any three successive prints, as
+we remark in the tracks left by birds. There is also a striking relation
+between the distance separating two footprints in one series and the size
+of the impressions; in other words, an obvious proportion between the
+length of the stride and the dimension of the creature which walked over
+the mud. If the marks are small, they may be half an inch asunder; if
+gigantic, as, for example, where the toes are 20 inches long, they are
+occasionally 4 feet and a half apart. 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.
+332.); 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 outwards, first on the one side
+and then on the other. 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 recognized by Mr. Owen as
+resembling the skin of the ostrich, and not that of reptiles.[298-B] Much
+care is required to ascertain the precise layer of a laminated rock on
+which an animal has walked, because the impression usually extends
+downwards through several laminæ; and if the upper layer originally trodden
+upon is wanting, one or more joints, or even in some cases an entire toe,
+which sank less deep into the soft ground, may disappear, and yet the
+remainder of the footprint be well defined.
+
+The size of several of the fossil impressions of the Connecticut red
+sandstone so far exceeds that of any living ostrich, that naturalists at
+first were extremely adverse to the opinion of their having been made by
+birds, until the bones and almost entire skeleton of the _Dinornis_ and of
+other feathered giants of New Zealand were discovered. Their dimensions
+have at least destroyed the force of this particular objection. The
+magnitude of the impressions of the feet of a heavy animal, which has
+walked on soft mud, increases for some distance below the surface
+originally trodden upon. In order, therefore, to guard against
+exaggeration, the casts rather than the mould are relied on. These casts
+show that some of the fossil birds had feet four times as large as the
+ostrich, but not perhaps larger than the _Dinornis_.
+
+Some of the quadrupedal footprints which accompany those of birds are
+analogous to European _Chirotheria_, and with a similar disproportion
+between the hind and fore feet. Others resemble that remarkable reptile,
+the _Rhyncosaurus_ of the English Trias, a creature having some relation
+in its osteology both to chelonians and birds. Other imprints, again,
+are like those of turtles.
+
+Among the supposed bipedal tracks, a single distinct example only has been
+observed of feet in which there are four toes directed forwards. In this
+case a series of four footprints is seen, each 22 inches long and 12 wide,
+with joints much resembling those in the toes of birds. Professor Agassiz
+has suggested that it might have belonged to a gigantic bipedal batrachian;
+but the evidence on this subject is too defective to warrant such a bold
+conjecture, and if we were to give the reins to our imagination, we might
+as well conceive a bird having four toes projecting forwards as a huge
+two-legged frog. Nor should we forget that some quadrupeds place the hind
+foot so precisely on the spot just quitted by the fore foot, as to produce
+a single line of imprints like a biped.
+
+No bones have as yet been met with, whether of reptiles or birds, in the
+rocks of the Connecticut, but there are numerous coprolites; and an
+ingenious argument has been derived by Mr. Dana, from the analysis of these
+bodies, and the proportion they contain of uric acid, phosphate of lime,
+carbonate of lime, and organic matter, to show that, like guano, they are
+the droppings of birds, rather than of reptiles.[299-A]
+
+Mr. Darwin, in his "Journal of a Voyage in the Beagle," informs us that the
+"South American ostriches, although they live on vegetable matter, such as
+roots and grass, are repeatedly seen at Bahia Blanca (lat. 39° S.), on the
+coast of Buenos Ayres, coming down at low water to the extensive mud-banks
+which are then dry, for the sake, as the Gauchos say, of feeding on small
+fish." They readily take to the water, and have been seen at the bay of San
+Blas, and at Port Valdez, in Patagonia, swimming from island to
+island.[300-A] It is therefore evident, that in our times a South American
+mud-bank might be trodden simultaneously by ostriches, alligators,
+tortoises, and frogs; and the impressions left, in the nineteenth century,
+by the feet of these various tribes of animals, would not differ from each
+other more entirely than do those attributed to birds, saurians,
+chelonians, and batrachians, in the rocks of the Connecticut.
+
+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, which was originally referred to the genus
+_Palæoniscus_, but has since, with propriety, been ascribed, by Sir Philip
+Egerton, to a new genus. To this he has given the name of _Ischypterus_,
+from the great size and strength of the fulcral rays of the dorsal fin
+(from +ischys+; strength, and +pteron+, a fin). They differ from
+_Palæoniscus_, as Mr. Redfield first pointed out, by having the vertebral
+column prolonged to a more limited extent into the upper lobe of the tail,
+or, in the language of M. Agassiz, they are less heterocercal. The teeth
+also, according to Sir P. Egerton, who, in 1844, examined for me a fine
+series of specimens which I procured at Durham, Connecticut, differ from
+those of _Palæoniscus_ in being strong and conical.
+
+That the sandstones containing these fish are of older date than the
+strata containing coal, before described (p. 284.) as occurring near
+Richmond in Virginia, is highly probable. These were shown to be as old
+at least as the oolite and lias. The higher antiquity 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 Alleghany chain
+owes its flexures, and this chain includes the ancient coal formation
+among its contorted rocks. The unconformable position of this _New Red_
+with ornithichnites on the edges of the inclined primary or paleozoic
+rocks of the Appalachians is seen at 4. of the section, fig. 379. p.
+327. The absence of fish with decidedly heterocercal tails may afford an
+argument against the Permian age of the formation; and the opinion that
+the red sandstone is triassic, seems, on the whole, the best that we can
+embrace in the present state of our knowledge.
+
+
+FOOTNOTES:
+
+[286-A] Buckland, Bridgew. Treat., vol. ii. p. 38.
+
+[287-A] Monog. des Bunten Sandsteins.
+
+[288-A] Tableau des Genres de Veg. Fos., Dict. Univ. 1849.
+
+[290-A] Geol. Trans., Second Series, vol. v.
+
+[290-B] Buckland, Proc. Geol. Soc. vol. ii. p. 439.; and Murchison and
+Strickland Geol. Trans., Second Ser., vol. v. p. 347.
+
+[295-A] Ormerod, Quart. Geol. Journ. 1848, vol. iv. p. 277.
+
+[296-A] Hugh Miller, First Impressions of England, 1847, pp. 183. 214.
+
+[297-A] Buist, Trans. of Bombay Geograph. Soc. 1850, vol. ix. p. 38.
+
+[297-B] Travels in North America, vol. ii. p. 168.
+
+[298-A] Hitchcock, Mem. of Amer. Acad. New Ser., vol. iii. p. 129.
+
+[298-B] This specimen is now in Dr. Mantell's museum.
+
+[299-A] Amer. Journ. of Sci. vol. xlviii. p. 46.
+
+[300-A] Journal of Voyage of Beagle, &c. 2d edition, p. 89. 1845.
+
+
+
+
+CHAPTER XXIII.
+
+PERMIAN OR MAGNESIAN LIMESTONE GROUP.
+
+   Fossils of Magnesian Limestone and Lower New Red distinct from the
+   Triassic--Term Permian--English and German equivalents--Marine shells
+   and corals of English Magnesian limestone--Palæoniscus and other fish
+   of the marl slate--Thecodont Saurians of dolomitic conglomerate of
+   Bristol--Zechstein and Rothliegendes of Thuringia--Permian Flora--Its
+   generic affinity to the carboniferous--Psaronites or tree-ferns.
+
+
+When the use of the term "Poikilitic" was explained in the last chapter, I
+stated, that in some parts of England it is scarcely possible to separate
+the red marls and sandstones so called (originally named "the New Red"),
+into two distinct geological systems. Nevertheless, the progress of
+investigation, and a careful comparison of English rocks between the lias
+and the coal with those occupying a similar geological position in Germany
+and Russia, has enabled geologists to divide the Poikilitic formation; and
+has even shown that the lowermost of the two divisions is more closely
+connected, by its fossil remains, with the carboniferous group than with
+the trias. If, therefore, we are to draw a line between the secondary and
+primary fossiliferous strata, as between the tertiary and secondary, it
+must run through the middle of what was once called the "New Red," or
+Poikilitic group. The inferior half of this group will rank as Primary or
+Paleozoic, while its upper member will form the base of the Secondary
+series. For the lower, or Magnesian Limestone division of English
+geologists, Sir R. Murchison has proposed the name of Permian, from Perm, a
+Russian government where these strata are more extensively developed than
+elsewhere, occupying an area twice the size of France, and containing an
+abundant and varied suite of fossils.
+
+Mr. King, in his valuable monograph, recently published, of the Permian
+fossils of England, has given a table of the following six members of the
+Permian system of the north of England, with what he conceives to be the
+corresponding formations in Thuringia.[301-A]
+
+          North of England.                      Thuringia.
+
+  1. Crystalline or concretionary,     |1. Stinkstein.
+     and non-crystalline limestone.    |
+  2. Brecciated and pseudo-brecciated  |2. Rauchwacke.
+     limestone.                        |
+  3. Fossiliferous limestone.          |3. Dolomit, or Upper Zechstein.
+  4. Compact limestone.                |4. Zechstein, or Lower Zechstein.
+  5. Marl-slate.                       |5. Mergel-schiefer, or Kupferschiefer.
+  6. Inferior sandstones of various    |6. Rothliegendes.
+     colours.                          |
+
+I shall proceed, therefore, to treat briefly of these subdivisions,
+beginning with the highest, and referring the reader, for a fuller
+description of the lithological character of the whole group, as it occurs
+in the north of England, to a valuable memoir by Professor Sedgwick,
+published in 1835.[302-A]
+
+_Crystalline or concretionary limestone_ (No. 1.).--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. 333.)
+and _Mytilus septifer_ (fig. 335.).
+
+[Illustration: Fig. 333. _Schizodus Schlotheimi_, Geinitz. Syn. _Axinus
+obscurus_, Sow. Crystalline limestone, Permian.]
+
+[Illustration: Fig. 334. _Schizodus truncatus_, King; to show
+hinge. Permian.]
+
+[Illustration: Fig. 335. _Mytilus septifer_, King. Syn. _Modiola
+acuminata_, James Sow. Permian crystalline limestone.]
+
+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; and Mr. King imagines that the absence of corals and the
+character of the shells indicate shallow water. In some parts of the coast
+of Durham, where the rock is not crystalline, it contains as much as
+forty-four 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. The
+stratification is very irregular, in some places well-defined, in others
+obliterated by the concretionary action which has re-arranged the materials
+of the rocks subsequently to their original deposition. Examples of this
+are seen at Pontefract and Ripon in Yorkshire.
+
+_The brecciated limestone_ (No. 2.) contains no fragments of foreign
+rocks, but seems 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 2 feet in diameter. This breccia is considered by
+Professor Sedgwick as one of the forms of the preceding limestone, No.
+1., rather than as regularly underlying it. The fragments are angular
+and never water-worn, and appear to have been re-cemented on the spot
+where they were formed. It is, therefore, suggested that they may have
+been due to those internal movements of the mass which produced the
+concretionary structure; but the subject is very obscure, and after
+studying the phenomenon in the Marston Rocks, on the coast of Durham, I
+found it impossible to form any positive opinion on the subject. The
+well-known brecciated limestones of the Pyrenees appeared to me to
+present the nearest analogy, but on a much smaller scale.
+
+_The fossiliferous limestone_ (No. 3.) is regarded by Mr. King as a
+deep-water formation, from the numerous delicate corals which it includes.
+One of these, _Fenestella retiformis_ (fig. 336.), is a very variable
+species, and has received many different names. It sometimes attains a
+large size, measuring 8 inches in width. The same zoophyte is also found
+abundantly in the Permian of Germany.
+
+[Illustration: Fig. 336. Fenestella.
+
+  _a._ _Fenestella retiformis_, Schlot.
+       Syn. _Gorgonia infundibuliformis_, Goldf.; _Retepora flustracea_,
+       Phillips.
+  _b._ Part of the same highly magnified.
+
+Magnesian limestone, Humbleton Hill, near Sunderland.[303-A]]
+
+Shells of the genera _Spirifer_ and _Productus_, which do not occur in
+strata newer than the Permian, are abundant in this division of the series
+in the ordinary yellow magnesian limestone. (See figs. 337, 338.)
+
+[Illustration: Fig. 337. _Productus calvus_, Sow. Min. Con. Syn. _Productus
+horridus_, Bronn's Index, &c., King's Monogr., &c.; _Leptæna_, Dalman.
+
+Magnesian Limestone.]
+
+[Illustration: Fig. 338. _Spirifer undulatus_, Sow. Min. Con. Syn.
+_Triogonotreta undulata_, King's Monogr.
+
+Magnesian Limestone.]
+
+_The compact limestone_ (No. 4.) also contains organic remains,
+especially corallines, and is intimately connected with the preceding.
+Beneath it lies the _marl-slate_ (No. 5.), 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_,
+_Pygopterus_, _Coelacanthus_, and _Platysomus_, genera which are all
+found in the coal-measures of the carboniferous epoch, and which
+therefore, says Mr. King, probably lived at no great distance from
+the shore. But the Permian species are peculiar, and, for the
+most part, identical with those found in the marl-slate or
+copper-slate of Thuringia.
+
+[Illustration: Fig. 339. Restored outline of a fish of the genus
+_Palæoniscus_, Agass. _Palæothrissum_, Blainville.]
+
+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. 340.)
+The "Homocercal" fish, which comprise almost all the 8000 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. 341.)
+
+[Illustration: Fig. 340. Shark.
+
+_Heterocercal._]
+
+[Illustration: Fig. 341. Shad. (_Clupea_, Herring tribe.)
+
+_Homocercal._]
+
+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 characterizes the earlier periods of the
+earth's history, when the organization of fishes made a greater approach to
+that of saurian reptiles than at later epochs. In all the strata above the
+Magnesian limestone 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 Mr. 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
+maybe useful to a geologist in determining the age of the rock.
+
+[Illustration: Fig. 342. _Palæoniscus comtus_, Agassiz. Scale
+magnified. Marl-slate.]
+
+[Illustration: Fig. 343. _Palæoniscus elegans_, Sedg. Under surface of
+scale magnified. Marl-slate.]
+
+[Illustration: Fig. 344. _Palæoniscus glaphyrus_, Ag. Under surface of
+scale magnified. Marl-slate.]
+
+[Illustration: Fig. 345. _Coelacanthus caudalis_, Egerton. Scale showing
+granulated surface magnified. Marl-slate.]
+
+[2 Illustrations: Scales of fish. Magnesian limestone.
+
+Fig. 346. _Pygopterus mandibularis_, Ag. Marl-slate.
+    _a._ Outside of scale magnified.
+    _b._ Under surface of same.
+
+Fig. 347. _Acrolepis Sedgwickii_, Ag. Marl-slate.]
+
+The _inferior sandstones_ (No. 6. Tab. p. 301.), 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. In some regions we find it stated that the imbedded plants are all
+specifically identical with those of the carboniferous series; and, if so,
+they probably belong to that epoch; for the true Permian flora appears,
+from the researches of MM. Murchison and de Verneuil in Russia, and of
+Colonel von Gutbier in Saxony, to be, with few exceptions, distinct from
+that of the coal (see p. 307.).
+
+_Dolomitic conglomerate of Bristol._--Near Bristol, in Somersetshire,
+and in other counties bordering the Severn, the unconformable beds of
+the Lower New Red, resting immediately upon the Coal, consist of a
+conglomerate called "dolomitic," because the pebbles of older rocks are
+cemented together by a red or yellow base of dolomite or magnesian
+limestone. This conglomerate or breccia, for the imbedded fragments are
+sometimes angular, occurs in patches over the whole of the downs near
+Bristol, filling up the hollows and irregularities in the mountain
+limestone, and being principally composed at every spot of the debris of
+those rocks on which it immediately rests. At one point we find pieces
+of coal shale, in another of mountain limestone, recognizable by its
+peculiar shells and zoophytes. Fractured bones, also, and teeth of
+saurians, are dispersed through some parts of the breccia.
+
+These saurians (which until the discovery of the _Archegosaurus_ in the
+coal were the most ancient examples of fossil reptiles) are all
+distinguished by having the teeth implanted deeply in the jaw-bone, and
+in distinct sockets, instead of being soldered, as in frogs, to a simple
+alveolar parapet. In the dolomitic conglomerate near Bristol the remains
+of species of two distinct genera have been found, called
+_Thecodontosaurus_ and _Palæosaurus_ by Dr. Riley and Mr.
+Stutchbury[306-A]; the teeth of which are conical, compressed, and with
+finely serrated edges (figs. 348 and 349.).
+
+[Illustration: Fig. 348. Tooth of _Palæosaurus_ platyodon, nat. size.]
+
+[Illustration: Fig. 349. Tooth of _Thecodontosaurus_, 3 times magnified.]
+
+In Russia, also, Thecodont saurians occur, in beds of the Permian age, of
+several genera, while others named _Protorosaurus_ are met with in the
+Zechstein of Thuringia. This family of reptiles is allied to the living
+monitor, and its appearance in a primary or paleozoic formation, observes
+Mr. Owen, is opposed to the doctrine of the progressive development of
+reptiles from fish, or from simpler to more complex forms; for, if they
+existed at the present day, these monitors would take rank at the head of
+the Lacertian order.[306-B]
+
+In Russia the Permian rocks are composed of white limestone, with gypsum
+and white salt; and of red and green grits, with occasionally copper ore;
+also magnesian limestones, marlstones, and conglomerates.
+
+The country of Mansfeld, in Thuringia, may be called the classic ground of
+the Lower New Red, or Magnesian Limestone, or Permian formation, on the
+Continent. It consists there principally of, first, the Zechstein,
+corresponding to the upper portion of our English series; and, secondly,
+the marl-slate, with fish of species identical with those of the bed so
+called in Durham. This slaty marlstone is richly impregnated with copper
+pyrites, for which it is extensively worked. Magnesian limestone, gypsum,
+and rock-salt, occur among the superior strata of this group. At its base
+lies the Rothliegendes, supposed to correspond with the Inferior or Lower
+New Red Sandstone above mentioned, which occupies a similar place in
+England between the marl-slate and coal. Its local name of Rothliegendes,
+_red-lyer_, or "Roth-todt-liegendes," _red-dead-lyer_, was given by the
+workmen in the German mines from its red colour, and because the copper has
+_died out_ when they reach this rock, which is not metalliferous. It is, in
+fact, a great deposit of red sandstone and conglomerate, with associated
+porphyry, basaltic trap, and amygdaloid.
+
+_Permian Flora._--We learn from the recent investigation of Colonel von
+Gutbier, that in the Permian rocks of Saxony no less than sixty species of
+fossil plants have been met with, forty of which have not yet been found
+elsewhere. 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_, with several species of _Walchia_
+(Lycopodites), are common to the coal-measures.
+
+Among the genera also enumerated by Colonel Gutbier are _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. _Noeggerathia_ (see fig. 350.), supposed by
+A. Brongniart to be allied to _Cycas_, 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.
+
+[Illustration: Fig. 350. _Noeggerathia cuneifolia._ Ad. Brongniart.[307-A]]
+
+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.
+
+Psaronites are also found in the uppermost coal of Autun in France, and in
+the upper coal-measures of the State of Ohio in the United States, but
+specifically different from those of the rothliegendes. They serve to
+connect the Permian flora with the more modern portion of the preceding or
+carboniferous group. Upon the whole, it is evident that the Permian plants
+approach nearer to the carboniferous ones than to the triassic; and the
+same may be said of the Permian fauna.
+
+
+FOOTNOTES:
+
+[301-A] Palæontographical Society, 1848, London.
+
+[302-A] Trans. Geol. Soc. Lond., Second Series, vol. iii. p. 37.
+
+[303-A] King's Monograph, pl. 2.
+
+[306-A] See paper by Messrs. Riley and Stutchbury, Geol. Trans., Second
+Series, vol. v. p. 349., plate 29., figures 2. and 5.
+
+[306-B] Owen, Report on Reptiles, British Assoc., Eleventh Meeting,
+1841, p. 197.
+
+[307-A] Murchison's Russia, vol. ii. pl. A. fig. 3.
+
+
+
+
+CHAPTER XXIV.
+
+THE COAL, OR CARBONIFEROUS GROUP.
+
+   Carboniferous strata in the south-west of England--Superposition of
+   Coal-measures to Mountain limestone--Departure from this type in North
+   of England and Scotland--Section in South Wales--Underclays with
+   Stigmaria--Carboniferous Flora--Ferns, Lepidodendra, Calamites,
+   Asterophyllites, Sigillariæ, Stigmariæ--Coniferæ--Endogens--Absence of
+   Exogens--Coal, how formed--Erect fossil trees--Parkfield Colliery--St.
+   Etienne, Coal-field--Oblique trees or snags--Fossil forests in Nova
+   Scotia--Brackish water and marine strata--Origin of Clay-iron-stone.
+
+
+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 the north of England, for
+example, the thickness of the coal-bearing strata has been estimated at
+3000 feet, while the various coal-seams, 20 or 30 in number, do not in
+the aggregate exceed 60 feet.[308-A]
+
+The carboniferous formation comprises two very distinct members: 1st, that
+usually called the Coal-measures, of mixed freshwater, terrestrial, and
+marine origin, often including seams of coal; 2dly, that named in England
+the Mountain or Carboniferous limestone, of purely marine origin, and
+containing corals, shells, and encrinites.
+
+In the south-western part of our island, in Somersetshire and South Wales,
+the three divisions usually spoken of by English geologists are:
+
+  1. Coal-measures   { Strata of shale, sandstone, and grit, with
+                     {   occasional seams of coal, from 600 to 12,000
+                     {   feet thick.
+
+  2. 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.
+
+  3. Mountain or     } A calcareous rock containing marine shells and
+     Carboniferous   }   corals; devoid of coal; thickness variable,
+     limestone       }   sometimes 900 feet.
+
+The millstone grit may be considered as one of the coal sandstones of
+coarser texture than usual, with some accompanying shales, in which coal
+plants are occasionally found. In the north of England some bands of
+limestone, with pectens, oysters, and other marine shells, occur in this
+grit, just as in the regular coal-measures, and even a few seams of coal. I
+shall treat, therefore, of the whole group, as consisting of two divisions
+only, the Coal-measures and Mountain Limestone. The latter is found in the
+southern British coal-fields, at the base of the system, or immediately in
+contact with the subjacent Old Red Sandstone; but as we proceed northwards
+to Yorkshire and Northumberland it begins to alternate with true
+coal-measures, the two deposits forming together a series of strata about
+1000 feet in thickness. To this mixed formation succeeds the great mass of
+genuine mountain limestone.[309-A] Farther north, in the Fifeshire
+coal-field in Scotland, we observe a still wider departure from the type of
+the south of England, or a more complete intercalation of dense masses of
+marine limestones with sandstones, and shales containing coal.
+
+
+COAL-MEASURES.
+
+In South Wales the coal-measures have been ascertained by actual
+measurement to attain the extraordinary thickness of 12,000 feet, the beds
+throughout, with the exception of the coal itself, appearing 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 1 to 5 feet thick, one of
+them, which has two or three layers of clay interposed, attaining 9
+feet.[309-B] At other points in the same coal-field the shales predominate
+over the sandstones. The horizontal extent of some seams of coal is much
+greater than that of others, but 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 firestone, because it can be made into bricks which
+stand the fire of a furnace. They vary in thickness from 6 inches to more
+than 10 feet; and Mr. 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 one hundred 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 Mr. Logan pointed out, are characterized 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 in the
+underclays always retain their natural forms, branching freely, and sending
+out their slender leaves, as they were formerly styled, 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. It was conjectured that they might be aquatic,
+perhaps floating plants, which sometimes extended their branches and leaves
+freely in fluid mud, and which were finally enveloped in the same mud.
+
+
+CARBONIFEROUS FLORA.
+
+These statements will suffice to convince the reader that we cannot arrive
+at a satisfactory theory of the origin of coal till we understand the true
+nature of _Stigmaria_; and in order to explain what is now known of this
+plant, and of others which have contributed by their decay to produce coal,
+it will be necessary to offer a brief preliminary sketch of the whole
+carboniferous flora, an assemblage of fossil plants, with which we are
+better acquainted than with any other which flourished antecedently to the
+tertiary epoch. It should also be remarked that Göppert has ascertained
+that the remains of every family of plants scattered through the
+coal-measures are sometimes met with in the pure coal itself, a fact which
+adds greatly to the geological interest attached to this flora.
+
+_Ferns._--The number of species of carboniferous plants hitherto
+described amounts, according to M. Ad. Brongniart, to about 500. These
+may perhaps be a fragment only of the entire flora, but they are enough
+to show that the state of the vegetable world was then extremely
+different from that now established. We are struck at the first glance
+with the similarity of many of the ferns to those now living, and the
+dissimilarity of almost all the other fossils except the coniferæ. Among
+the ferns, as in the case of _Pecopteris_ for example (fig. 351.), it is
+not always easy to decide whether they should be referred to different
+genera from those established for the classification of living species;
+whereas, in regard to most of the other contemporary tribes, with the
+exception of the coniferæ, it is often difficult to guess the family,
+or even the class, to which they belong. The ferns of the carboniferous
+period are generally without organs of fructification, but in some
+specimens these are well preserved. 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_, by Lindley,
+and the _Psaronius_ of the upper or newest coal-measures, before
+alluded to (p. 307.).
+
+[Illustration: Fig. 351. _Pecopteris lonchitica._ (Foss. Flo. 153.)]
+
+[Illustration: Fig. 352. Sphenopteris. (Foss. Flo. 101.)
+
+  _a._ _Sphenopteris crenata._
+  _b._ The same, magnified.]
+
+[Illustration: Fig. 353. _Caulopteris primæva_, Lindley.]
+
+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_ (see fig. 353.). No
+less than 250 ferns have already been obtained from the coal strata; and
+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 50 indigenous species.
+
+[3 Illustrations: Living tree-ferns of different genera. (Ad. Brong.)
+
+Fig. 354. Tree-fern from Isle of Bourbon.
+
+Fig. 355. _Cyathea glauca_, Mauritius.
+
+Fig. 356. Tree fern from Brazil.]
+
+[3 Illustrations: _Lepidodendron Sternbergii._ Coal-measures,
+near Newcastle.
+
+Fig. 357. Branching trunk, 49 feet long, supposed to have belonged to _L.
+Sternbergii_. (Foss. Flo. 203.)
+
+Fig. 358. Branching stem with bark and leaves of _L. Sternbergii_.
+(Foss. Flo. 4.)
+
+Fig. 359. Portion of same nearer the root; natural size. (Ibid.)]
+
+_Lepidodendra._--These fossils belong to the family of _Lycopodiums_, yet
+most of them grew to the size of large trees. The annexed figures represent
+a large 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 abundant in tropical
+climates, where one species is sometimes met with attaining a height of 3
+feet. They usually creep on the ground, but some stand erect, as the _L.
+densum_, from New Zealand (fig. 360.).
+
+[Illustration: Fig. 360. Lycopodium.
+
+  _a._ _Lycopodium densum_; banks of R. Thames, New Zealand.
+  _b._ branch, natural size.
+  _c._ part of same, magnified.]
+
+In the carboniferous strata of Coalbrook Dale, and in many other
+coal-fields, elongated cylindrical bodies, called fossil cones, named by
+M. Adolphe Brongniart _Lepidostrobus_, are met with. (See fig. 361.)
+They often form the nucleus of concretionary balls of clay-iron-stone,
+and are well preserved, exhibiting a conical axis, around which a great
+quantity of scales were compactly imbricated. The opinion of M.
+Brongniart is now generally adopted, that the _Lepidostrobus_ is
+the fruit of _Lepidodendron_.
+
+[Illustration: Fig. 361. _Lepidostrobus ornatus_, Brong.; half
+nat. size. Shropshire.]
+
+[Illustration: Fig. 362. _Calamites cannæformis_, Schlot. (Foss. Flo. 79.)
+Lower end with rootlets.]
+
+[Illustration: Fig. 363. _Calamites Suckowii_, Brong.; natural size. Common
+in coal throughout Europe.]
+
+_Equisetaceæ._--To this family belong two species of the genus
+_Equisetites_, allied to the living "horse-tail" which now grows in marshy
+grounds. Other species, which have jointed stems, depart more widely from
+_Equisetum_, but are yet of analogous organization. They differed from it
+principally in being furnished with a thin bark, which is represented in
+the stem of _C. Suckowii_ (fig. 363.), in which it will be seen that the
+striped external pattern does not agree with that left on the stone where
+the bark is stripped off; so that if the two impressions were seen
+separately, they might be mistaken for two distinct species.
+
+The tallest living "horse-tails" are only 2 or 3 feet high in Europe, and
+even in tropical climates only attain, as in the case of _Equisetum
+giganteum_, discovered by Humboldt and Bonpland, in South America, a height
+of about 5 feet, the stem being an inch in diameter. Several of the
+Calamites of the coal acquired the height and dimensions of small trees.
+
+[Illustration: Fig. 364. _Asterophyllites foliosa._ (Foss. Flo. 25.)
+Coal-measures, Newcastle.]
+
+_Asterophyllites._--In this family, M. Brongniart includes several genera,
+and among them _Calamodendron_, _Asterophyllites_, and _Annularia_. The
+graceful plant, represented in the annexed figure, is supposed to be the
+branch of a shrub called _Calamodendron_, a new genus, divided off by
+Brongniart from the _Calamites_ of former authors. Its pith and medullary
+rays seem to show that it was dicotyledonous, and it appears to have been
+allied, by the nature of its tissue, to the gymnogens, or, still more, to
+the _Sigillaria_, which will next be mentioned.
+
+_Sigillaria._--A large portion of the trees of the carboniferous period
+belonged to this genus, of which about thirty-five species are known. 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 leafstalks which have fallen off (see
+fig. 365.). But with these points of analogy to cryptogamia, they combine
+an internal organization much resembling that of cycads, and 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 1 to 5 feet in
+diameter, appear to have decayed rapidly in the interior, so as to become
+hollow, when standing; when, therefore, they were thrown prostrate on the
+mud, they were squeezed down and flattened. Hence, we find the bark of the
+two opposite sides (now converted into bright shining coal) to constitute
+two horizontal layers, one upon the other, half an inch, or an inch, in
+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.
+
+[Illustration: Fig. 365. _Sigillaria lævigata_, Brong.]
+
+_Stigmaria._--This fossil, the importance of which has already been pointed
+out, was formerly 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 underclays of the
+coal-seams of the Island of Cape Breton, in Nova Scotia.
+
+[Illustration: Fig. 366. Stigmaria attached to a trunk of
+_Sigillaria_.[315-A]]
+
+In a specimen of one of these, represented in the annexed figure (fig.
+366.), the spread of the roots was 16 feet, and some of them sent out
+rootlets, in all directions, into the surrounding clay.
+
+The manner of attachment of the fibres to the stem resembles that of a ball
+and socket joint, the base of each rootlet being concave, and fitting on to
+a tubercle (see figs. 367 and 368.). Rows of these tubercles are arranged
+spirally round each root, which have always a medullary cavity and woody
+texture, much resembling that of _Sigillaria_, the structure of the
+vessels being, like it, scalariform.
+
+[Illustration: Fig. 367. Surface of another individual of same species,
+showing form of tubercles. (Foss. Flo. 34.)]
+
+[Illustration: Fig. 368. _Stigmaria ficoides_, Brong. One fourth of
+nat. size. (Foss. Flo. 32.)]
+
+_Conifers._--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 44 feet in height.
+
+_Endogens._--Hitherto but few monocotyledonous plants have been
+discovered in the coal-strata. Most of these consist of fruits referred
+by some botanists to palms. The three-sided nuts, called
+_Trigonocarpum_, seven species of which are known, appear to have the
+best claim to rank as palms, although M. Ad. Brongniart entertains some
+doubt even as to their being monocotyledons.
+
+
+_Exogens._
+
+The entire absence, so far as our paleontological investigations have
+hitherto gone, of ordinary dicotyledons or exogens in the coal measures, is
+most remarkable. Hence, M. Adolphe Brongniart has called this period the
+age of acrogens, in consequence of the vast preponderance of ferns and
+_Lepidodendra_.[316-A] Nevertheless, a forest of the period, now under
+consideration, may have borne a considerable resemblance to those woody
+regions of New Zealand, in which ferns, arborescent and herbaceous, and
+lycopodiums, with many coniferæ, abound.
+
+The comparative proportion of living ferns and _Araucariæ_, in Norfolk
+Island, to all the other plants, appears to be very similar to that
+formerly borne by these tribes respectively in a forest of the coal-period.
+
+I have already stated that Professor Göppert, 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 coal. Many seams, he remarks, are rich in _Sigillaria_,
+_Lepidodendron_, and _Stigmaria_, the latter in such abundance, as to
+appear to form the bulk of the coal. In some places, almost all the plants
+are calamites, in others ferns.[316-B]
+
+_Coal, how formed--Erect trees._--I shall now consider the manner in
+which the above-mentioned plants are imbedded in the strata, and how
+they may have contributed to produce coal. "Some of the plants of our
+coal," says Dr. Buckland, "grew on the identical banks of sand, silt,
+and mud, which, being now indurated to stone and shale, form the strata
+that accompany the coal; whilst other portions of these plants have been
+drifted to various distances from the swamps, savannahs, and forests
+that gave them birth, particularly those that are dispersed through the
+sandstones, or mixed with fishes in the shale beds." "At Balgray, three
+miles north of Glasgow," says the same author, "I saw in the year 1824,
+as there still may be seen, an unequivocal example of the stumps of
+several stems of large trees, standing close together in their native
+place, in a quarry of sandstone of the coal formation."[317-A]
+
+Between the years 1837 and 1840, six fossil trees were discovered in the
+coal-field of Lancashire, where it is intersected by the Bolton railway.
+They were all in a vertical position, with respect to the plane of the
+bed, which dips about 15° 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 ascertained 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 the trees (see figure of this genus,
+p. 313.). The exterior trunk of each was marked by a coating of friable
+coal, varying from one quarter to three quarters of an inch in
+thickness; but it crumbled away on removing the matrix. The dimensions
+of one of the trees is 15-1/2 feet in circumference at the base, 7-1/2
+feet at the top, its height being 11 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. Mr.
+Hawkshaw, who has described these fossils, thinks that, although they
+were hollow when submerged, they may have consisted originally of hard
+wood throughout; for solid dicotyledonous trees, when prostrated in
+tropical forests, as in Venezuela, on the shore of the Caribbean Sea,
+were observed by him to be destroyed in the interior, so that little
+more is left than an outer shell, consisting chiefly of the bark. This
+decay, he says, goes on most rapidly in low and flat tracks, in which
+there is a deep rich soil and excessive moisture, supporting tall
+forest-trees and large palms, below which bamboos, canes, and minor
+palms flourish luxuriantly. Such tracts, from their lowness, would be
+most easily submerged, and their dense vegetation might then give rise
+to a seam of coal.[317-B]
+
+In a deep valley near Capel-Coelbren, branching from the higher part of the
+Swansea valley, four stems of upright _Sigillariæ_ were seen, in 1838,
+piercing through the coal-measures of S. Wales; one of them was 2 feet in
+diameter, and one 13 feet and a half high, and they were all found to
+terminate downwards in a bed of coal. "They appear," says Sir H. De la
+Beche, "to have constituted a portion of a subterranean forest at the epoch
+when the lower carboniferous strata were formed.[318-A]
+
+In a colliery near Newcastle, say the authors of the Fossil Flora, a great
+number of _Sigillariæ_ were placed in the rock as if they had retained the
+position in which they grew. Not less than thirty, some of them 4 or 5 feet
+in diameter, were visible within an area of 50 yards square, the interior
+being sandstone, and the bark having been converted into coal. The roots of
+one individual were found imbedded in shale; and the trunk, after
+maintaining a perpendicular course and circular form for the height of
+about 10 feet, was then bent over so as to become horizontal. Here it was
+distended laterally, and flattened so as to be only one inch thick, the
+flutings being comparatively distinct.[318-B] Such vertical stems are
+familiar to our miners, under the name of coal-pipes. One of them, 72 feet
+in length, was discovered, in 1829, near Gosforth, about five miles from
+Newcastle, in coal-grit, the strata of which it penetrated. The exterior of
+the trunk was marked at intervals with knots, indicating the points at
+which branches had shot off. The wood of the interior had been converted
+into carbonate of lime; and its structure was beautifully shown by cutting
+transverse slices, so thin as to be transparent. (See p. 40.)
+
+These "coal-pipes" are much dreaded by our miners, 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 downwards, 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 the annexed plan (fig.
+369.), some of them more than 8 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 10 inches thick, which rested on a layer of clay 2 inches thick,
+below which was a second forest, resting on a 2-foot seam of coal. Five
+feet below this again was a third forest with large stumps of
+_Lepidodendra_, _Calamites_, and other trees.
+
+[Illustration: Fig. 369. Ground-plan of a fossil forest, Parkfield
+Colliery, near Wolverhampton, showing the position of 73 trees in a
+quarter of an acre.[319-A]]
+
+In the account given, in 1821, by M. Alex. Brongniart of the coal-mine
+of Treuil, at St. Etienne, near Lyons, he states, that distinct
+horizontal strata of micaceous sandstone are traversed by vertical
+trunks of monocotyledonous vegetables, resembling bamboos or large
+_Equiseta_.[319-B] Since the consolidation of the stone, there has been
+here and there a sliding movement, which has broken the continuity of
+the stems, throwing the upper parts of them on one side, so that they
+are often not continuous with the lower.
+
+From these appearances it was inferred that we have here the monuments
+of a submerged forest. I formerly objected to this conclusion,
+suggesting that, in that case, all the roots ought to have been found at
+one and the same level, and not scattered irregularly through the mass.
+I also imagined that the soil to which the roots were attached should
+have been different from the sandstone in which the trunks are enclosed.
+Having, however, seen calamites near Pictou, in Nova Scotia, buried at
+various heights in sandstone and in similar erect attitudes, I have now
+little doubt that M. Brongniart's view was correct. These plants seem
+to have grown on a sandy soil, liable to be flooded from time to time,
+and raised by new accessions of sediment, as may happen in swamps near
+the banks of a large river in its delta. Trees which delight in marshy
+grounds are not injured by being buried several feet deep at their base;
+and other trees are continually rising up from new soils, several feet
+above the level of the original foundation of the morass. In the banks
+of the Mississippi, when the water has fallen, I have seen sections of a
+similar deposit in which portions of the stumps of trees with their
+roots _in situ_ appeared at many different heights.[320-A]
+
+[Illustration: Fig. 370. Section showing the erect position of fossil trees
+in coal sandstone at St. Etienne. (Alex. Brongniart.)]
+
+When I visited, in 1843, the quarries of Treuil above-mentioned, the fossil
+trees seen in fig. 370. were removed, but I obtained proofs of other
+forests of erect trees in the same coal-field.
+
+[Illustration: Fig. 371. Inclined position of a fossil tree, cutting
+through horizontal beds of sandstone, Craigleith quarry, Edinburgh. Angle
+of inclination from _a_ to _b_ 27°.]
+
+_Snags._--In 1830, a slanting trunk was exposed in Craigleith quarry,
+near Edinburgh, the total length of which exceeded 60 feet. Its diameter
+at the top was about 7 inches, and near the base it measured 5 feet in
+its greater, and 2 feet in its lesser width. The bark was converted into
+a thin coating of the purest and finest coal, forming a striking
+contrast in colour with the white quartzose sandstone in which it lay.
+The annexed figure represents a portion of this tree, about 15 feet
+long, which I saw exposed in 1830, when all the strata had been removed
+from one side. The beds which remained were so unaltered and undisturbed
+at the point of junction, as clearly to show that they had been
+tranquilly deposited round the tree, and that the tree had not
+subsequently pierced through them, while they were yet in a soft state.
+They were composed chiefly of siliceous sandstone, for the most part
+white; and divided into laminæ so thin, that from six to fourteen of
+them might be reckoned in the thickness of an inch. Some of these thin
+layers were dark, and contained coaly matter; but the lowest of the
+intersected beds were calcareous. The tree could not have been hollow
+when imbedded, for the interior still preserved the woody texture in a
+perfect state, the petrifying matter being, for the most part,
+calcareous.[321-A] It is also clear, that the lapidifying matter was not
+introduced laterally from the strata through which the fossil passes, as
+most of these were not calcareous. It is well known that, in the
+Mississippi and other great American rivers, where thousands of trees
+float annually down the stream, some sink with their roots downwards,
+and become fixed in the mud. Thus placed, they have been compared to a
+lance in rest; and so often do they pierce through the bows of vessels
+which run against them, that they render the navigation extremely
+dangerous. Mr. Hugh Miller mentions four other huge trunks exposed in
+quarries near Edinburgh, which lay diagonally across the strata at an
+angle of about 30°, with their lower or heavier portions downwards, the
+roots of all, save one, rubbed off by attrition. One of these was 60 and
+another 70 feet in length, and from 4 to 6 feet in diameter.
+
+[Illustration: Fig. 372. Section of the cliffs of the South Joggins,
+near Minudie, Nova Scotia.]
+
+The number of years for which the trunks of trees, when constantly
+submerged, can resist decomposition, is very great; as we might suppose
+from the durability of wood, in artificial piles, permanently covered by
+water. Hence these fossil snags may not imply a rapid accumulation of beds
+of sand, although the channel of a river or part of a lagoon is often
+filled up in a very few years.
+
+_Nova Scotia._--One of the finest examples in the world of a succession of
+fossil forests of the carboniferous period, laid open to view in a natural
+section, is that seen in the lofty cliffs bordering the Chignecto Channel,
+a branch of the Bay of Fundy, in Nova Scotia.[321-B]
+
+In the annexed section (fig. 372.), which I examined in July, 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 2 inches to 4 feet. At
+low tide a fine horizontal section of the same beds is exposed to view on
+the beach. The thickness of the beds alluded to, between _d_ and _g_, is
+about 2,500 feet, the erect trees consisting chiefly of large _Sigillariæ_,
+occurring at ten distinct levels, one above the other; but Mr. Logan, who
+afterwards made a more detailed survey of the same line of cliffs, found
+erect trees at seventeen levels, extending through a vertical thickness of
+4,515 feet of strata; and he estimated the total thickness of the
+carboniferous formation, with and without coal, at no less than 14,570
+feet, every where devoid of marine organic remains.[322-A] The usual height
+of the buried trees seen by me was from 6 to 8 feet; but one trunk was
+about 25 feet high and 4 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 downwards in seams of coal.
+Some few only were based in clay and shale, none of them in sandstone. The
+erect trees, therefore, appeared in general to have grown on beds of coal.
+In some of the underclays I observed _Stigmaria_.
+
+[Illustration: Fig. 373. Fossil tree at right angles to planes of
+stratification. Coal measures, Nova Scotia.]
+
+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. 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 b_, fig. 373., the same which is represented at _a_, fig. 374., or in
+the bed _e_ in the larger section, fig. 372., is a hollow trunk 5 feet 8
+inches in length, traversing various strata, and cut off at the top by a
+layer of clay 2 feet thick on which rests a seam of coal (_b_, fig. 374.)
+1 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 4-foot coal.
+
+[Illustration: Fig. 374. Erect fossil trees. Coal-measures, Nova Scotia.]
+
+If we now return to the tree first mentioned (fig. 373.), we find the
+diameter (_a b_) 14 inches at the top and 16 inches at the bottom, the
+length of the trunk 5 feet 8 inches. The strata in the interior
+consisted of a series entirely different from those on the outside. The
+lowest of the three outer beds which it traversed consisted of purplish
+and blue shale (_c_, fig. 373.), 2 feet thick, above which was sandstone
+(_d_) 1 foot thick, and, above this, clay (_e_) 2 feet 8 inches. But, in
+the interior, were nine distinct layers of different composition: at the
+bottom, first, shale 4 inches, then sandstone 1 foot, then shale 4
+inches, then sandstone 4 inches, then shale 11 inches, then clay (_f_)
+with nodules of ironstone 2 inches, then pure clay 2 feet, then
+sandstone 3 inches, and, lastly, clay 4 inches. Owing to the outward
+slope of the face of the cliff, the section (fig. 373.) was not exactly
+perpendicular to the axis of the tree; and hence, probably, the apparent
+sudden termination at the base without a stump and roots.
+
+In this example 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.
+
+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 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.
+
+In Cape Breton, Mr. Richard Brown has observed in the Sydney coal-field a
+total thickness of coal-measures, without including the underlying
+millstone grit, of 1843 feet, dipping at an angle of 8°. He has published
+minute details of the whole series, showing at how many different levels
+erect trees occur, consisting of _Sigillaria_, _Lepidodendron_, _Calamite_,
+and other genera. In one place eight erect trunks, with roots and rootlets
+attached to them, were seen at the same level, within a horizontal space 80
+feet in length. Beds of coal of various thickness are interstratified. Some
+of the associated strata are ripple-marked, with impressions of rain-drops.
+Taking into account forty-one clays filled with roots of _Stigmaria_ in
+their natural position, and eighteen layers of upright trees at other
+levels, there is, on the whole, clear evidence of at least fifty-nine
+fossil forests, ranged one above the other, in this coal-field, in the
+above-mentioned thickness of strata.[324-A]
+
+The fossil shells in Cape Breton and in the Nova Scotia section (fig.
+372.), consisting of _Cypris_, _Unio_ (?), _Modiola_, _Microconchus
+carbonarius_ (see fig. 375.), and _Spirorbis_, seem to indicate brackish
+water; but we ought never to be surprised if, in pursuing the same stratum,
+we come to a fresh or purely marine deposit; for this will depend upon our
+taking a direction higher up or lower down the ancient river or delta
+deposit. When the Purbeck beds of the Wealden were described in Chap.
+XVIII., I endeavoured to explain the intimate connection of strata formed
+at a river's mouth, or in the tranquil lagoons of the delta, or in the sea,
+after a slight submergence of the land, with its dirt-beds.
+
+In the English coal-fields the same association of fresh, or rather
+brackish water with marine strata, in close connection with beds of coal of
+terrestrial origin, has been frequently recognized. 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 carboniferous
+series of that district, at the point where the coal-measures are in
+contact with the Permian or "Lower New Red." It consists of shales and
+sandstones about 150 feet thick, with coal and traces of plants; including
+a bed of limestone, varying from 2 to 9 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 recognized
+at still more distant points. The characteristic fossils are a small
+bivalve, having the form of a _Cyclas_, a small _Cypris_ (fig. 376.), and
+the microscopic shell of an annelid of an extinct genus called
+_Microconchus_ (fig. 375.), allied to _Serpula_ or _Spirorbis_.
+
+In the lower coal-measures of Coalbrook Dale, the strata, according to Mr.
+Prestwich, often change completely within very short distances, beds of
+sandstone passing horizontally into clay, and clay into sandstone. The
+coal-seams often wedge out or disappear; and sections, at places nearly
+contiguous, present marked lithological distinctions. In this single field,
+in which the strata are from 700 to 800 feet thick, between forty and
+fifty species of terrestrial plants have been discovered, besides several
+fishes and trilobites of forms distinct from those occurring in the
+Silurian strata. Also upwards of forty species of mollusca, among which are
+two or three referred to the freshwater genus _Unio_, and others of marine
+forms, such as _Nautilus_, _Orthoceras_, _Spirifer_, and _Productus_. Mr.
+Prestwich suggests that the intermixture of beds containing freshwater
+shells with others full of marine remains, and the alternation of coarse
+sandstone and conglomerate with beds of fine clay or shale containing the
+remains of plants, may be explained by supposing the deposit of Coalbrook
+Dale to have originated in a bay of the sea or estuary into which flowed a
+considerable river subject to occasional freshes.[325-A]
+
+[2 Illustrations: Freshwater Fossils--Coal.
+
+Fig. 375.
+
+  _a._ _Microconchus carbonarius_.
+  _b._ var. of same; nat. size, and magnified.
+
+Fig. 376. _Cypris inflata_, natural size, and magnified. Murchison.[325-B]]
+
+In the Edinburgh coal-field, at Burdiehouse, fossil fishes, mollusca,
+and cypris, very similar to those in Shropshire and Staffordshire, have
+been found by Dr. Hibbert.[325-C] In the coal-field also of Yorkshire
+there are freshwater strata, some of which contain shells referred to
+the genus _Unio_; but in the midst of the series there is one thin but
+very widely spread stratum, abounding in fishes and marine shells, such
+as _Ammonites Listeri_ (fig. 377.), _Orthoceras_, and _Avicula
+papyracea_, Goldf. (fig. 378.)[325-D]
+
+[Illustration: Fig. 377. _Ammonites Listeri_, Sow.]
+
+[Illustration: Fig. 378. _Avicula papyracea_, Goldf. (_Pecten
+papyraceus_, Sow.)]
+
+No similarly intercalated layer of marine shells has been noticed in the
+neighbouring coal-field of Newcastle, where, as in South Wales and
+Somersetshire, the marine deposits are entirely below those containing
+terrestrial and freshwater remains.[326-A]
+
+_Clay-iron-stone._--Bands and nodules of clay-iron-stone 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 farther 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 iron-stone.[326-B]
+
+
+FOOTNOTES:
+
+[308-A] Phillips; art. "Geology," Encyc. Britan.
+
+[309-A] Sedgwick, Geol. Trans., Second Series, vol. iv.; and Phillips,
+Geol. of Yorksh. part 2.
+
+[309-B] Memoirs of Geol. Survey, vol. i. p. 195.
+
+[315-A] The trunk in this case is referred by Mr. Brown to _Lepidodendron_,
+but his illustrations seem to show the usual markings assumed by
+_Sigillaria_ near its base.
+
+[316-A] For terminology of classification of plants, see above,
+note, p. 223.
+
+[316-B] Quart. Geol. Journ., vol. v., Mem., p. 17.
+
+[317-A] Anniv. Address to Geol. Soc., 1840.
+
+[317-B] Hawkshaw, Geol. Soc. Proceedings, Nos. 64. and 69.
+
+[318-A] Geol. Report on Cornwall, &c. p. 143.
+
+[318-B] Lindley and Hutton, Foss. Flo. part 6. p. 150.
+
+[319-A] See papers by Messrs. Beckett and Ick. Proceed. in Geol. Soc.,
+vol. iv. p. 287.
+
+[319-B] Annales des Mines, 1821.
+
+[320-A] Principles of Geol., 8th ed., p. 215.
+
+[321-A] See figures of texture, Witham, Foss. Veget., pl. 3.
+
+[321-B] See Lyell's Travels in N. America, vol. ii. p. 179.
+
+[322-A] Quart. Geol. Journ., vol. ii. p. 177.
+
+[324-A] Geol. Quart. Journ., vol. ii. p. 393.; and vol. vi. p. 115.
+
+[325-A] Prestwich, Geol. Trans., 2d Series, vol. v. p. 440. Murchison,
+Silurian System, p. 105.
+
+[325-B] Silurian System, p. 84.
+
+[325-C] Trans. Roy. Soc. Edin. vol. xiii. Horner, Edin. New Phil.
+Journ., April, 1836.
+
+[325-D] Phillips; art. "Geology," Encyc. Metrop., p. 590.
+
+[326-A] Phillips; art. "Geology," Encyc. Metrop., p. 592.
+
+[326-B] Memoirs of Geol. Survey, pp. 51. 255, &c.
+
+
+
+
+CHAPTER XXV.
+
+CARBONIFEROUS GROUP--_continued_.
+
+   Coal-fields of the United States--Section of the country between the
+   Atlantic and Mississippi--Position of land in the carboniferous period
+   eastward of the Alleghanies--Mechanically formed rocks thinning out
+   westward, and limestones thickening--Uniting of many coal-seams into
+   one thick one--Horizontal coal at Brownsville, Pennsylvania--Vast
+   extent and continuity of single seams of coal--Ancient river-channel
+   in Forest of Dean coal-field--Absence of earthy matter in
+   coal--Climate of carboniferous period--Insects in coal--Rarity of
+   air-breathing animals--Great number of fossil fish--First discovery of
+   the skeletons of fossil reptiles--Footprints of reptilians--Mountain
+   limestone--Its corals and marine shells.
+
+
+It was stated in the last chapter that a great uniformity prevails in the
+fossil plants of the coal-measures of Europe and North America; and I may
+add that four-fifths of those collected in Nova Scotia have been identified
+with European species. Hence the former existence at the remote period
+under consideration (the carboniferous) of a continent or chain of islands
+where the Atlantic now rolls its waves seems a fair inference. Nor are
+there wanting other and independent proofs of such an ancient land situated
+to the eastward of the present Atlantic coast of North America; for the
+geologist deduces the same conclusion from the mineral composition of the
+carboniferous and some older groups of rocks as they are developed on the
+eastern flanks of the Alleghanies, contrasted with their character in the
+low country to the westward of those mountains.
+
+The annexed diagram (fig. 379.) will assist the reader in understanding
+the phenomena now alluded to, although I must guard him against
+supposing that it is a true section. A great number of details have of
+necessity been omitted, and the scale of heights and horizontal
+distances are unavoidably falsified.
+
+[Illustration: Fig. 379. Diagram explanatory of the geological structure of
+a part of the United States between the Atlantic and the Mississippi.
+
+Length from E. to W. 850 miles.
+
+  Appalachian Coal Field.  Alleghanies, or Appalachians.
+
+Same section--_continued_.
+
+  Mississippi.  Illinois Coal Field.  Cincinnati.  Appalachian Coal Field.
+
+  A B. Atlantic plain.
+  B C. Atlantic slope.
+  C D. Alleghanies or Appalachian chain.
+  D E. Appalachian coal-field west of the mountains.
+  E F. Dome-shaped outcrop of strata on the Ohio, older than the coal.
+  F G. Illinois coal-field.
+  _h._ Falls and rapids of the rivers at the junction of the hypogene and
+       newer formations.
+  _i_, _k_, _l_, _m_. Parallel folds of Appalachians becoming successively
+                      more open, and flatter in going from E. to W.
+
+_References to the different Formations._
+
+  1. Miocene tertiary.
+  2. Eocene tertiary.
+  3. Cretaceous strata.
+  4. Red sandstone with ornithichnites (new red or trias?) usually much
+     invaded by trap.
+  5. Coal-measures (bituminous coal).
+  5' Anthracitic coal-measures.
+  5'' Carboniferous limestone of the Illinois coal-field, wanting in the
+     Appalachian.
+  6. Old red or Devonian, Olive slate, &c.
+  7. Primary fossiliferous or Silurian strata.
+  8. Hypogene strata, or gneiss, mica schist, &c., with granite veins.
+
+_Note._ The dotted lines at _i_ and _k_ express portions of rock removed
+by denudation, the amount of which may be estimated by supposing similar
+lines prolonged from other points where different strata end abruptly
+at the surface.
+
+_N.B._ The lower section at ** joins on to the upper one at *.]
+
+Starting from the shores of the Atlantic, on the eastern side of the
+Continent, we first come to a low region (A B), which was called the
+alluvial plain by the first geographers. It is occupied by tertiary and
+cretaceous strata, before described (pp. 171. 206. and 224.), which are
+nearly horizontal. The next belt, from B to C, consists of granitic rocks
+(hypogene), chiefly gneiss and mica-schist, covered occasionally with
+unconformable red sandstone, No. 4. (New Red or Trias?), remarkable for its
+ornithichnites (see p. 327.). Sometimes, also, this sandstone rests on the
+edges of the disturbed paleozoic rocks (as seen in the section). The region
+(B C), sometimes called the "Atlantic Slope," corresponds nearly in average
+width with the low and flat plain (A, B), and is characterized by hills of
+moderate height, contrasting strongly, in their rounded shape and altitude,
+with the long, steep, and lofty parallel ridges of the Alleghany mountains.
+The outcrop of the strata in these ridges, like the two belts of hypogene
+and newer rocks (A B, and B C), above alluded to, when laid down on a
+geological map, exhibit long stripes of different colours, running in a
+N.E. and S.W. direction, in the same way as the lias, chalk, and other
+secondary formations in the middle and eastern half of England.
+
+The narrow and parallel zones of the Appalachians here mentioned, consist
+of strata, folded into a succession of convex and concave flexures,
+subsequently laid open by denudation. The component rocks are of great
+thickness, all referable to the Silurian, Devonian, and Carboniferous
+formations. There is no principal or central axis, as in the Pyrenees and
+many other chains--no nucleus to which all the minor ridges conform; but
+the chain consists of many nearly equal and parallel foldings, having what
+is termed an anticlinal and synclinal arrangement (see above, p. 48.). This
+system of hills extends, geologically considered, from Vermont to Alabama,
+being more than 1000 miles long, from 50 to 150 miles broad, and varying in
+height from 2000 to 6000 feet. Sometimes the whole assemblage of ridges
+runs perfectly straight for a distance of more than 50 miles, after which
+all of them wheel round together, and take a new direction, at an angle of
+20 or 30 degrees to the first.
+
+We are indebted to the state surveyors of Virginia and Pennsylvania, Prof.
+W. B. Rogers and his brother Prof. H. D. Rogers, for the important
+discovery of a clue to the general law of structure prevailing throughout
+this range of mountains, which, however simple it may appear when once made
+out and clearly explained, might long have been overlooked; amidst so great
+a mass of complicated details. It appears that the bending and fracture of
+the beds is greatest on the south-eastern or Atlantic side of the chain,
+and the strata become less and less disturbed as we go westward, until at
+length they regain their original or horizontal position. By reference to
+the section (fig. 379.), it will be seen that on the eastern side, or in
+the ridges and troughs nearest the Atlantic, south-eastern dips
+predominate, in consequence of the beds having been folded back upon
+themselves, as in _i_, those on the north-western side of each arch having
+been inverted. The next set of arches (such as _k_) are more open, each
+having its western side steepest; the next (_l_) opens out still more
+widely, the next (_m_) still more, and this continues until we arrive at
+the low and level part of the Appalachian coal-field (D E).
+
+In nature or in a true section, the number of bendings or parallel folds is
+so much greater that they could not be expressed in a diagram without
+confusion. It is also clear that large quantities of rock have been removed
+by aqueous action or denudation, as will appear if we attempt to complete
+all the curves in the manner indicated by the dotted lines at _i_ and _k_.
+
+The movements which imparted so uniform an order of arrangement to this
+vast system of rocks must have been, if not contemporaneous, at least
+parts of one and the same series, depending on some common cause. Their
+geological date is well defined, at least within certain limits, for
+they must have taken place after the deposition of the carboniferous
+strata (No. 5.), and before the formation of the red sandstone (No. 4.).
+The greatest disturbing and denuding forces have evidently been exerted
+on the south-eastern side of the chain; and it is here that igneous or
+plutonic rocks are observed to have invaded the strata, forming dykes,
+some of which run for miles in lines parallel to the main direction of
+the Appalachians, or N.N.E. and S.S.W.
+
+The thickness of the carboniferous rocks in the region C is very great, and
+diminishes rapidly as we proceed to the westward. The surveys of
+Pennsylvania and Virginia show that the south-east was the quarter whence
+the coarser materials of these strata were derived, so that the ancient
+land lay in that direction. The conglomerate which forms the general base
+of the coal-measures is 1500 feet thick in the Sharp Mountain, where I saw
+it (at C) near Pottsville; whereas it has only a thickness of 500 feet,
+about thirty miles to the north-west, and dwindles gradually away when
+followed still farther in the same direction, till its thickness is reduced
+to 30 feet.[329-A] The limestones, on the other hand, of the coal-measures,
+augment as we trace them westward. Similar observations have been made in
+regard to the Silurian and Devonian formations in New York; the sandstones
+and all the mechanically-formed rocks thinning out as they go westward, and
+the limestones thickening, as it were, at their expense. It is, therefore,
+clear that the ancient land was to the east, where the Atlantic now is; the
+deep sea, with its banks of coral and shells to the west, or where the
+hydrographical basin of the Mississippi is now situated.
+
+In that region, near Pottsville, where the thickness of the coal-measures
+is greatest, there are thirteen seams of anthracitic coal, several of them
+more than 2 yards thick. Some of the lowest of these alternate with beds of
+white grit and conglomerate of coarser grain than I ever saw elsewhere,
+associated with pure coal. The pebbles of quartz are often of the size of a
+hen's egg. On following these pudding-stones and grits for several miles
+from Pottsville, by Tamaqua, to the Lehigh Summit Mine, in company with Mr.
+H. D. Rogers, in 1841, he pointed out to me that the coarse-grained strata
+and their accompanying shales gradually thin out, until seven seams of
+coal, at first widely separated, are brought nearer and nearer together,
+until they successively unite; so that at last they form one mass, between
+40 and 50 feet thick. I saw this enormous bed of anthracitic coal quarried
+in the open air at Mauch Chunk (or the Bear Mountain), the overlying
+sandstone, 40 feet thick, having been removed bodily from the top of the
+hill, which, to use the miner's expression, had been "scalped." The
+accumulation of vegetable matter now constituting this vast bed of
+anthracite, may perhaps, before it was condensed by pressure and the
+discharge of its hydrogen, oxygen, and other volatile ingredients, have
+been between 200 and 300 feet thick. The origin of such a vast thickness of
+vegetable remains, so unmixed with earthy ingredients, can, I think, 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 absence of sediment, or, in this
+case, of sand and pebbles, wholly unexplained.
+
+[Illustration: Fig. 380. Cross section.]
+
+[Illustration: Fig. 381. Cross section.]
+
+But the student will naturally ask, what can have caused so many seams of
+coal, after they had been persistent for miles, to come together and blend
+into one single seam, and that one equal in the aggregate to the thickness
+of the several separate seams? Often had the same question been put by
+English miners before a satisfactory answer was given to it by the late Mr.
+Bowman. The following is his solution of the problem. Let _a a'_, fig.
+380., be a mass of vegetable matter, capable, when condensed, of forming a
+3-foot seam of coal. It rests on the underclay _b b'_, filled with roots of
+trees _in situ_, and it supports a growing forest (C D). Suppose that part
+of the same forest D E had become submerged by the ground sinking down 25
+feet, so that the trees have been partly thrown down and partly remain
+erect in water, slowly decaying, their stumps and the lower parts of their
+trunks being enveloped in layers of sand and mud, which are gradually
+filling up the lake D F. When this lake or lagoon has at length been
+entirely silted up and converted into land, say, in the course of a
+century, the forest C D will extend once more continuously over the whole
+area C F, as in fig. 381., and another mass of vegetable matter (_g g'_),
+forming 3 feet more of coal, may accumulate from C to F. We then find in
+the region F, two seams of coal (_a'_ and _g'_) each 3 feet thick, and
+separated by 25 feet of sandstone and shale, with erect trees based upon
+the lower coal, while, between D and C, we find these two seams united into
+a 2-yard coal. It may be objected that the uninterrupted growth of plants
+during the interval of a century will have caused the vegetable matter in
+the region C D to be thicker than the two distinct seams _a'_ and _g'_ at
+F; and no doubt there would actually be a slight excess representing one
+generation of trees with the remains of other plants, forming half an inch
+or an inch of coal; but this would not prevent the miner from affirming
+that the seam _a g_, throughout the area C D, was equal to the two seams
+_a'_ and _g'_ at F.
+
+The reader has seen, by reference to the section (fig. 379. p. 327.), that
+the strata of the Appalachian coal-field assume an horizontal position west
+of the mountains. In that less elevated country, the coal-measures are
+intersected by three great navigable rivers, and are capable of supplying
+for ages, to the inhabitants of a densely peopled region, an inexhaustible
+supply of fuel. These rivers are the Monongahela, the Alleghany, and the
+Ohio, all of which lay open on their banks the level seams of coal. Looking
+down the first of these at Brownsville, we have a fine view of the main
+seam of bituminous coal 10 feet thick, commonly called the Pittsburg seam,
+breaking out in the steep cliff at the water's edge; and I made the
+accompanying sketch of its appearance from the bridge over the river (see
+fig. 382.). Here the coal, 10 feet thick, is covered by carbonaceous shale
+(_b_), and this again by micaceous sandstone (_c_). Horizontal galleries
+may be driven everywhere at very slight expense, and so worked as to drain
+themselves, while the cars, laden with coal and attached to each other,
+glide down on a railway, so as to deliver their burden into barges moored
+to the river's bank. The same seam is seen at a distance, on the right bank
+(at _a_), and may be followed the whole way to Pittsburg, fifty miles
+distant. As it is nearly horizontal, while the river descends it crops out
+at a continually increasing, but never at an inconvenient, height above the
+Monongahela. Below the great bed of coal at Brownsville is a fire-clay 18
+inches thick, and below this, several beds of limestone, below which again
+are other coal seams. I have also shown in my sketch another layer of
+workable coal (at _d d_), which breaks out on the slope of the hills at a
+greater height. Here almost every proprietor can open a coal-pit on his own
+land, and the stratification being very regular, he may calculate with
+precision the depth at which coal may be won.
+
+The Appalachian coal-field, of which these strata form a part (from C
+to E, section, fig. 379., p. 327.), is remarkable for its vast area;
+for, according to Professor H. D. Rogers, it stretches continuously from
+N.E. to S.W., for a distance of 720 miles, its greatest width being
+about 180 miles. On a moderate estimate, its superficial area amounts to
+63,000 square miles.
+
+[Illustration: Fig. 382. View of the great Coal Seam on the Monongahela at
+Brownsville, Pennsylvania, U. S.
+
+  _a._ Ten-foot seam of coal.
+  _b._ Black bituminous or carbonaceous shale, 10 feet thick.
+  _c._ Micaceous sandstone.
+  _d d._ Upper seam of coal, 6 feet thick.]
+
+This coal formation, before its original limits were reduced by
+denudation, must have measured 900 miles in length, and in some places more
+than 200 miles in breadth. By again referring to the section (fig. 379., p.
+327.), it will be seen that the strata of coal are horizontal to the
+westward of the mountains in the region D E, and become more and more
+inclined and folded as we proceed eastward. Now it is invariably found, as
+Professor H. D. Rogers has shown by chemical analysis, that the coal is
+most bituminous towards its western limit, where it remains level and
+unbroken, and that it becomes progressively debituminized as we travel
+south-eastward towards the more bent and distorted rocks. Thus, on the
+Ohio, 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 (5', fig. 379.) 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
+to twelve per cent. of bitumen, thus becoming a genuine anthracite.[333-A]
+
+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 carburetted 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, carburetted hydrogen, nitrogen, and olefiant gas.
+The disengagement of all these gradually transforms ordinary or bituminous
+coal into anthracite, to which the various names of splint coal, glance
+coal, culm, and many others, have been given.
+
+We have seen that, in the Appalachian coal-field, there is an intimate
+connection between the extent to which the coal has 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,
+where the fracturing of the rocks had produced an infinite number of
+cracks and crevices, and also to the heat of the gases and water
+penetrating these cracks, when the great movements took place, which
+have rent and folded the Appalachian strata. 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.
+
+_Continuity of seams of coal._--As single seams of coal are continuous over
+very wide areas, it has been asked, how forests could have prevailed
+uninterruptedly over such wide spaces, without being oftener flooded by
+turbid rivers, or, when submerged, denuded by marine currents. It appears,
+from the description of the Cape Breton coal-field, by Mr. Richard Brown,
+that false stratification is common in the beds of sand, and some partial
+denudation of these, at least, must often have taken place during the
+accumulation of the carboniferous series.
+
+In the Forest of Dean, ancient river-channels are found, which pass through
+beds of coal, and in which rounded pebbles of coal occur. They are of older
+date than the overlying and undisturbed coal-measures. The late Mr. Buddle,
+who described them to me, told me he had seen similar phenomena in the
+Newcastle coal-field. Nevertheless, instances of these channels are much
+more rare than we might have anticipated, especially when we remember how
+often the roots of trees (_Stigmariæ_) have been torn up, and drifted in
+broken fragments into the grits and sandstones. The prevalence of a
+downward movement is, no doubt, the principal cause which has saved so many
+extensive seams of coal from destruction by fluviatile action.
+
+The purity of the coal, or its non-intermixture with earthy matter,
+presents another theoretical difficulty to many geologists, who are
+inclined to believe that the trees and smaller plants of the
+carboniferous period grew in extensive swamps, rather than on land not
+liable to be inundated. It appears, however, that in the alluvial plain
+and delta of the Mississippi, extensive "cypress swamps," as they are
+called, densely covered with various trees, occur, into which no matter
+held in mechanical suspension is ever introduced during the greatest
+inundations, inasmuch as they are all surrounded by a dense marginal
+belt of reeds, canes, and brushwood. Through this thick barrier the
+river-water must pass, so that it is invariably well filtered before it
+can reach the interior of the forest-covered area, within which,
+vegetable matter is continually accumulating from the decay of trees and
+semi-aquatic plants. In proof of this, I may observe, that whenever any
+part of a swamp 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.[334-A]
+At the bottom of these "cypress swamps" of the Mississippi, a bed of
+clay is found, with roots of the tall cypress (_Taxodium distichum_),
+just as the underclays of the coal are filled with _Stigmaria_.
+
+_Climate of Coal Period._--So long as the botanist taught that a tropical
+climate was implied by the carboniferous flora, geologists might well be at
+a loss to reconcile the preservation of so much vegetable matter with a
+high temperature; for heat hastens the decomposition of fallen leaves and
+trunks of trees, whether in the atmosphere or in water.[335-A] It is well
+known that peat, so abundant in the bogs of high latitudes, ceases to grow
+in the swamps of warmer regions. It seems, however, to have become a more
+and more received opinion, that the coal-plants do not, on the whole,
+indicate a climate resembling that now enjoyed in the equatorial zone.
+Tree-ferns range as far south as the southern part of New Zealand, and
+Araucarian pines occur in Norfolk Island. A great predominance of ferns and
+lycopodiums indicates warmth, moisture, equability of temperature, and
+freedom from frost, rather than intense heat; and we know too little of the
+sigillariæ, calamites, asterophyllites, and other peculiar forms of the
+carboniferous period, to be able to speculate with confidence on the kind
+of climate they may have required.
+
+No doubt, we are entitled to presume, from the corals and cephalopoda of
+the mountain limestone, that a warm temperature characterized the northern
+seas in the carboniferous era; but the absence of cold may have given rise
+(as at present in the seas of the Bermudas, under the influence of the gulf
+stream) to a very wide geographical range of stone-building corals and
+shell-bearing cuttle-fish, without its being necessary to call in the aid
+of tropical heat.[335-B]
+
+
+CARBONIFEROUS REPTILES.
+
+Where we have evidence in a single coal-field, as in that of Nova Scotia,
+or South Wales, of fifty or even a hundred ancient forests buried one above
+the other, with the roots of trees still in their original position, and
+with some of the trunks still remaining erect, we are apt to wonder that
+until the year 1844 no remains of contemporaneous air-breathing creatures,
+except a few insects, had been discovered. No vertebrated animals more
+highly organized than fish, no mammalia or birds, no saurians, frogs,
+tortoises, or snakes, were yet known in rocks of such high antiquity. In
+the coal-field of Coalbrook Dale mention had been made of two species of
+beetles of the family _Curculionidæ_, and of a neuropterous insect
+resembling the genus _Corydalis_, with another related to the
+_Phasmidæ_.[335-C] In other coal-measures in Europe we find notice of a
+scorpion and of a moth allied to _Tinea_, also of one air-breathing
+crustacean, or land-crab. Yet Agassiz had already described in his great
+work on fossil fishes more than one hundred and fifty species of
+ichthyolites from the coal strata, ninety-four belonging to the families of
+shark and ray, and fifty-eight to the class of ganoids. Some of these fish
+are very remote in their organization from any now living, especially
+those of the family called _Sauroid_ by Agassiz; as _Megalichthys_,
+_Holoptychius_, and others, which are often of great size, and all
+predaceous. Their osteology, says M. Agassiz, reminds us in many respects
+of the skeletons of saurian reptiles, both by the close sutures of the
+bones of the skull, their large conical teeth striated longitudinally (see
+fig. 383.), the articulations of the spinous processes with the vertebræ,
+and other characters. Yet they do not form a family intermediate between
+fish and reptiles, but are true _fish_, though doubtless more highly
+organized than any living fish.[336-A]
+
+[Illustration: Fig. 383. _Holoptychius Hibberti_, Ag. Fifeshire
+coal-field; natural size.]
+
+The annexed figure represents a large tooth of the _Megalichthys_,
+found by Mr. Horner in the Cannel coal of Fifeshire. It probably
+inhabited an estuary, like many of its contemporaries, and frequented
+both rivers and the sea.
+
+[Illustration: Fig. 384. _Archegosaurus minor_, Goldfuss. Fossil reptile
+from the coal-measures, Saarbrück.]
+
+At length, in 1844, the first skeleton of a true reptile was announced from
+the coal of Münster-Appel in Rhenish Bavaria, by H. von Meyer, under the
+name of _Apateon pedestris_, the animal being supposed to be nearly related
+to the salamanders. Three years later, in 1847, Prof. von Dechen found in
+the coal-field of Saarbrück, at the village of Lebach, between Strasburg
+and Treves, the skeletons of no less than three distinct species of
+air-breathing reptiles, which were described by the late Prof. Goldfuss
+under the generic name of _Archegosaurus_. The ichthyolites and plants
+found in the same strata, left no doubt that these remains belonged to the
+true coal period. 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-iron-stone. The largest of these lizards, _Archegosaurus Decheni_,
+must have been 3 feet 6 inches long. The annexed drawing represents 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_, and therefore connected with the batrachians, as well as
+the lizards. The remains of the extremities leave no doubt that 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 Mr. Owen has
+observed to me that they make an approach to the _Proteus_ in the shortness
+of their ribs. Two 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. 385.).
+
+[Illustration: Fig. 385. Imbricated covering of skin of _Archegosaurus
+medius_, Goldf.; magnified.[337-A]]
+
+_Cheirotherian footprints in coal measures, United States._--In 1844,
+the very year when the Apateon or Salamander 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 in 1846. I was at once convinced of their genuineness, and declared
+my conviction on that point, on which doubts had been entertained both
+in Europe and the United States. 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 the accompanying drawing (fig.
+386.). 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.
+
+No less than twenty-three footsteps were observed by Dr. King in the
+same quarry before it was abandoned, the greater part of them so
+arranged (see fig. 387.) on the surface of one stratum as to imply that
+they were made successively by the same animal. Everywhere there was a
+double row of tracks, and in each row they occur in pairs, each pair
+consisting of a hind and fore foot, and each being at nearly equal
+distances from the next pair. In each parallel row the toes turn the one
+set to the right, the other to the left. In the European
+_Cheirotherium_, before mentioned (p. 290.), both the hind and fore feet
+have each five toes, and the size of the hind foot is about five times
+as large as the fore foot. In the American fossil the posterior
+footprint is not even twice as large as the anterior, and the number of
+toes is unequal, being five in the hinder and four in the anterior foot.
+In this, as in the European _Cheirotherium_, one toe stands out like a
+thumb, and these thumb-like toes turn the one set to the right, and the
+other to the left. The American _Cheirotherium_ was evidently a broader
+animal, and belonged to a distinct genus from that of the triassic
+age in Europe.[338-A]
+
+[Illustration: Fig. 386. _Scale one-sixth the original._ Slab of sandstone
+from the coal-measures of Pennsylvania, with footprints 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.
+
+[Illustration: Fig. 387. Series of reptilian footprints in the coal-strata
+of Westmoreland County, Pennsylvania.
+
+_a._ Mark of nail?]
+
+The geological position of the sandstone of Greensburg is perfectly clear,
+being situated in the midst of the Appalachian coal-field, having the main
+bed of coal, called the Pittsburg seam, above mentioned (p. 331.), 3 yards
+thick, 100 feet above it, and worked in the neighbourhood, with several
+other seams of coal at lower levels. The impressions of _Lepidodendron_,
+_Sigillaria_, _Stigmaria_, and other characteristic carboniferous plants,
+are found both above and below the level of the reptilian footsteps.
+
+Analogous footprints of a large reptile of still older date have since
+been found (1849), by Mr. Isaac Lea, in the lowest beds of the coal
+formation at Pottsville, near Philadelphia, so that we may now be said
+to have the footmarks of two reptilians of the coal period, and the
+skeletons of four.[340-A]
+
+
+CARBONIFEROUS OR MOUNTAIN LIMESTONE.
+
+We have already seen that this rock lies sometimes entirely beneath the
+coal-measures, while, in other districts, it alternates with the shales and
+sandstone of the coal. In both cases it is destitute of land plants, and
+usually charged with corals, which are often of large size; and several
+species belong to the lamelliferous class of Lamarck, which enter largely
+into the structure of coral reefs now growing. There are also a great
+number of _Crinoidea_ (see fig. 388.), and a few _Echinoderms_, associated
+with the zoophytes above mentioned. The _Brachiopoda_ constitute a large
+proportion of the Mollusca, many species being referable to two extinct
+genera, _Spirifer_ (or _Spirifera_) (fig. 389.), and _Productus_
+(_Leptæna_) (fig. 390.).
+
+[Illustration: Fig. 388. _Cyathocrinites planus_, Miller.
+Mountain limestone.]
+
+[Illustration: Fig. 389. _Spirifer glaber_, Sow. Mountain limestone.]
+
+[Illustration: Fig. 390. _Productus Martini_, Sow. (_P. semireticulatus_,
+Flem.) Mountain limestone.]
+
+Among the spiral univalve shells the extinct genus _Euomphalus_ (see fig.
+391.) is one of the commonest fossils of the Mountain limestone. In the
+interior it is often divided into chambers (see fig. 391. _d_); the septa
+or partitions not being perforated, as in foraminiferous shells, or in
+those having siphuncles, like the Nautilus. The animal appears, like the
+recent _Bulimus decollatus_, 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.
+
+[Illustration: Fig. 391. _Euomphalus pentagulatus_, Min. Con.
+Mountain limestone.
+
+_a._ Upper side; _b._ lower, or umbilical side; _c._ view showing mouth
+which is less pentagonal in older individuals; _d._ view of polished
+section, showing internal chambers.]
+
+[Illustration: Fig. 392. Portion of _Orthoceras laterale_,
+Phillips. Mountain limestone.]
+
+There are also many univalve and bivalve shells of existing genera in the
+Mountain limestone, such as _Turritella_, _Buccinum_, _Patella_,
+_Isocardia_, _Nucula_, and _Pecten_.[341-A] But the _Cephalopoda_ depart,
+in general, more widely from living forms, some being generically distinct
+from all those found in strata newer than the coal. In this number may be
+mentioned _Orthoceras_, a siphuncled and chambered shell, like a _Nautilus_
+uncoiled and straightened. Some species of this genus are several feet long
+(fig. 392.). 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
+continuous and uninterrupted (see _a_, fig. 393.). Their siphon is small,
+and in the form of the striæ of growth they resemble _Nautili_. Another
+extinct generic form of Cephalopod, abounding in the Mountain limestone,
+and not found in strata of later date, is the _Bellerophon_ (fig. 394.), of
+which the shell, like the living Argonaut, was without chambers.
+
+[Illustration: Fig. 393. _Goniatites evolutus_, Phillips.[342-A]
+Mountain limestone.]
+
+[Illustration: Fig. 394. _Bellerophon costatus_, Sow.[342-B]
+Mountain limestone.]
+
+
+FOOTNOTES:
+
+[329-A] H. D. Rogers, Trans. Assoc. Amer. Geol., 1840-42, p. 440.
+
+[333-A] Trans. of Ass. of Amer. Geol., p. 470.
+
+[334-A] Lyell's Second Visit to the U. S., vol. ii. p. 245. American
+Journ. of Sci., 2d series, vol. v. p. 17.
+
+[335-A] Principles of Geol., p. 696.
+
+[335-B] For changes in climate, see Principles of Geol., chaps.
+vii. and viii.
+
+[335-C] Geol. Trans., 2d series, vol. vi. p. 330.
+
+[336-A] Agassiz, Poiss. Foss., lib. 4. p. 62. and liv. 5. p. 88.
+
+[337-A] Goldfuss, Neue Jenaische Lit. Zeit., 1848; and Von Meyer, Quart.
+Geol. Journ., vol. iv. p. 51., memoirs.
+
+[338-A] See Lyell's Second Visit, &c., vol. ii. p. 305.
+
+[340-A] These impressions, found by Mr. Lea, were imagined to be in a rock
+as ancient as the old red sandstone; but, according to Mr. H. D. Rogers,
+they are in the lowest part of the coal formation.
+
+[341-A] Phillips, Geol. of Yorksh., vol. ii. p. 208.
+
+[342-A] Phillips, Geol. of Yorksh., pl. 20. fig. 65.
+
+[342-B] Ibid., pl. 17. fig. 15.
+
+
+
+
+CHAPTER XXVI.
+
+OLD RED SANDSTONE, OR DEVONIAN GROUP.
+
+   Old Red Sandstone of Scotland, and borders of Wales--Fossils usually
+   rare--"Old Red" in Forfarshire--Ichthyolites of Caithness--Distinct
+   lithological type of Old Red in Devon and Cornwall--Term
+   "Devonian"--Organic remains of intermediate character between those of
+   the Carboniferous and Silurian systems--Corals and shells--Devonian
+   strata of Westphalia, the Eifel, Russia, and the United States--Coral
+   reef at Falls of the Ohio--Devonian flora.
+
+
+It was stated in Chap. XXII. that the Carboniferous formation is
+surmounted by one called the "New Red," and underlaid by another called
+the "Old Red Sandstone."[342-C] The British strata of the last mentioned
+series were first recognized in Herefordshire and Scotland as of great
+thickness, and immediately subjacent to the coal; but they were in
+general so barren of organic remains, that it was difficult to find
+paleontological characters of sufficient importance to distinguish them
+as an independent group. In Scotland, and on the borders of Wales, the
+"Old Red" consists chiefly of red sandstone, conglomerate, and shale,
+with few fossils; but limestones of the same age, peculiarly rich in
+organic remains, were at length found in Devonshire.
+
+I shall first advert to the characters of the group as developed in
+Herefordshire, Worcestershire, Shropshire, and South Wales. Its thickness
+has been estimated at 8000 feet, and it has been subdivided into--
+
+  1st. A quartzose conglomerate passing downwards into chocolate-red and
+  green sandstone and marl.
+
+  2d. Cornstone and marl--red and green argillaceous spotted marls, with
+  irregular courses of impure concretionary limestone, provincially
+  called Cornstone.
+
+Here, as usual, fossils are extremely rare in the clays and sandstones in
+which the red oxide of iron prevails; but remains of fishes of the genera
+_Cephalaspis_ and _Onchus_ have been discovered in the Cornstone.
+
+The whole of the northern part of Scotland, from Cape Wrath to the
+southern flank of the Grampians, has been well described by Mr. Miller
+as consisting of a nucleus of granite, gneiss, and other hypogene rocks,
+which seem as if set in a sandstone frame.[343-A] The beds of the Old
+Red Sandstone constituting this frame, may once perhaps have extended
+continuously over the entire Grampians before the upheaval of that
+mountain range; for one band of the sandstone follows the course of the
+Moray Frith far into the interior of the great Caledonian valley; and
+detached hills and island-like patches occur in several parts of the
+interior, capping some of the higher summits in Sutherlandshire, and
+appearing in Morayshire like oases among the granite rocks of
+Strathspey. On the western coast of Ross-shire, the Old Red forms those
+three immense insulated hills before described (p. 67.), where beds of
+horizontal sandstone, 3000 feet high, rest unconformably on a base of
+gneiss, attesting the vast denudation which has taken place.
+
+But in order to observe the uppermost part of the Old Red, we must travel
+south of the Grampians, and examine its junction with the bottom of the
+Carboniferous series in Fifeshire. This upper member may be seen in Dura
+Den, south of Cupar, to consist of a belt of yellow sandstone, in which Dr.
+Fleming first discovered scales of _Holoptychius_, and in which species of
+fish of the genera _Pterichthys_, _Pamphractus_, and others, have been met
+with. (For genus _Pterichthys_, see fig. 400. p. 345.)
+
+The beds next below the yellow sandstone are well seen in the large zone of
+Old Red which skirts the southern flank of the Grampians from Stonehaven to
+the Frith of Clyde. It there forms, together with trap, the Sidlaw Hills
+and the strata of the valley of Strathmore. A section of this region has
+been already given (p. 48.), extending from the foot of the Grampians in
+Forfarshire to the sea at Arbroath, a distance of about 20 miles, where the
+entire series of strata is several thousand feet thick, and may be divided
+into three principal masses: 1st, and uppermost, red and mottled marls,
+cornstone, and sandstone (Nos. 1. and 2. of the section); 2d, Conglomerate,
+often of vast thickness (No. 3. ibid.); 3d, Roofing and paving stone,
+highly micaceous, and containing a slight admixture of carbonate of lime
+(No. 4. ibid.). In the first of these divisions, which may be considered as
+succeeding the yellow sandstone of Fifeshire before mentioned, a gigantic
+species of fish of the genus _Holoptychius_ has been found at Clashbinnie
+near Perth. Some scales (see fig. 395.) have been seen which measured 3
+inches in length by 2-1/2 in breadth.
+
+At the top of the next division, or immediately under the conglomerate
+(No. 3. p. 48.), there have been found in Forfarshire some remarkable
+crustaceans, with several fish of the genus named by Agassiz _Cephalaspis_,
+or "buckler-headed," from the extraordinary shield which covers the head
+(see fig. 396.), and which has often been mistaken for that of a trilobite,
+of the division _Asaphus_.
+
+[Illustration: Fig. 395. Scale of _Holoptychius nobilissimus_, Agas.
+Clashbinnie. Nat. size.]
+
+Species of the same genus are considered in England as characteristic of
+the second or Cornstone division (p. 343.).
+
+[Illustration: Fig. 396. _Cephalaspis Lyellii_, Agass. Length 6-3/4 inches.
+From a specimen in my collection found at Glammiss, in Forfarshire. See
+other figures, Agassiz, vol. ii. tab. 1. _a_. and 1. _b_.
+
+  _a._ One of the peculiar scales with which the head is covered when
+       perfect. These scales are generally removed, as in the specimen
+       above figured.
+  _b, c._ Scales from different parts of the body and tail.]
+
+[Illustration: Fig. 397. _Eggs of gasteropodous mollusk?_ Lower beds of
+Old Red, Ley's Mill, Forfarshire.]
+
+[Illustration: Fig. 398. _Fucoids and eggs of gasteropodous mollusk?_
+Lower Old Red, Fife.]
+
+In the same grey paving-stones and coarse roofing-slates, in which the
+_Cephalaspis_ occurs, in Forfarshire and Kincardineshire, the remains of
+marine plants or fucoids abound. They are frequently accompanied by groups
+of hexagonal, or nearly hexagonal markings, which consist of small
+flattened carbonaceous bodies, placed in a slight depression of the
+sandstone or shale. (See figs. 397 and 398.) They much resemble in form the
+spawn of the recent Natica (see fig. 399.), in which the eggs are arranged
+in a thin layer of sand, and seem to have acquired a polygonal form by
+pressing against each other. The substance of the egg, if fossilized, might
+give rise to small pellicles of carbonaceous matter.
+
+[Illustration: Fig. 399. Fragment of spawn of British species of _Natica_.]
+
+These fossils I have met with, both to the north of Strathmore, in the
+vertical shale beneath the conglomerate, and in the same beds in the Sidlaw
+hills, at all the points where fig. 4. is introduced in the section, p. 48.
+
+[Illustration: Fig. 400. _Pterichthys_, Agassiz; upper side, showing mouth;
+as restored by H. Miller.[345-A]]
+
+Beds of red shale and red sandstone, sometimes associated with
+pudding-stone (older than No. 3., fig. 62. p. 48.), and destitute of
+organic remains, separate, in the region of Strathmore, the above-described
+fossiliferous strata from the older crystalline rocks of the Grampians.
+But, in the north of Scotland, we find, at the base of the Old Red, other
+grey slaty sandstones, in the counties of Banff, Nairn, Moray, Cromarty,
+Caithness, and in Orkney, rich in ichthyolites of peculiar forms, belonging
+to the genera _Pterichthys_ (fig. 400.), _Coccosteus_, _Diplopterus_,
+_Dipterus_, _Cheiracanthus_, and others of Agassiz.
+
+Five species of _Pterichthys_ have been found in this lowest division of
+the Old Red. The wing-like appendages, whence the genus is named, were
+first supposed by Mr. Miller to be paddles, like those of the turtle;
+but Agassiz regards them as weapons of defence, like the occipital
+spines of the River Bull-head (_Cottus gobio_, Linn.); and considers the
+tail to have been the only organ of motion. The genera _Dipterus_ and
+_Diplopterus_ are so named, because their two dorsal fins are so placed
+as to front the anal and ventral fins, so as to appear like two pairs of
+wings. They have bony enamelled scales.
+
+_South Devon and Cornwall._--A great step was made in the classification of
+the slaty and calciferous strata of South Devon and Cornwall in 1837, when
+a large portion of the beds, previously referred to the "transition" or
+most ancient fossiliferous series, were found to belong in reality to the
+period of the Old Red Sandstone. For this reform we are indebted to the
+labours of Professor Sedgwick and Sir R. Murchison, assisted by a
+suggestion of Mr. Lonsdale, who, in 1837, after examining the South
+Devonshire fossils, perceived that some of them agreed with those of the
+Carboniferous group, others with those of the Silurian, while many could
+not be assigned to either system, the whole taken together exhibiting a
+peculiar and intermediate character. But these paleontological observations
+alone would not have enabled us to assign, with accuracy, the true place in
+the geological series of these slate-rocks and limestones of South Devon,
+had not Messrs. Sedgwick and Murchison, in 1836 and 1837, discovered that
+the culmiferous or anthracitic shales of North Devon belonged to the Coal,
+and not, as preceding observers had imagined, to the transition period.
+
+As the strata of South Devon here alluded to are far richer in organic
+remains than the red sandstones of contemporaneous date in Herefordshire
+and Scotland, the new name of the "Devonian system" was proposed as a
+substitute for that of Old Red Sandstone.
+
+The rocks of this group in South Devon consist, in great part, of green
+chloritic slates, alternating with hard quartzose slates and sandstones.
+Here and there calcareous slates are interstratified with blue crystalline
+limestone, and in some divisions conglomerates, passing into red sandstone.
+
+The link supplied by the whole assemblage of imbedded fossils, connecting
+as it does the paleontology of the Silurian and Carboniferous groups, is
+one of the highest interest, and equally striking, whether we regard the
+_genera_ of corals or of shells. The _species_ are almost all distinct.
+
+Among the more abundant corals, we find the genera _Favosites_ and
+_Cyathophyllum_, common on the one hand to the Mountain limestone, and on
+the other to the Silurian system. Some few even of the _species_ are common
+to the Devonian and Silurian groups, as, for example, _Favosites
+polymorpha_ (fig. 401.), very abundant in South Devon.
+
+[Illustration: Fig. 401. _Favosites polymorpha_, Goldf., S. Devon.
+From a polished specimen.
+
+_a._ portion of the same, magnified to show the pores.]
+
+The _Cyathophyllum cæspitosum_ (fig. 402.) and _Porites pyriformis_ (fig.
+424. p. 356.) are more peculiarly characteristic of the Devonian rocks.
+
+In regard to the shells, all the brachiopodous genera, such as
+_Terebratula_, _Orthis_, _Spirifer_, _Atrypa_, and _Productus_, which are
+found in the Mountain limestone, occur, together with those of the Silurian
+system, except the _Pentamerus_. Some forms, however, seem exclusively
+Devonian, as for example, _Calceola sandalina_ (fig. 403.) and
+_Strygocephalus Burtini_ (fig. 404.), which have been met with both in the
+Eifel, in Germany, and in Devonshire, in the very lowest Devonian beds.
+
+[Illustration: Fig. 402. Cyathophyllum.
+
+  _a._ _Cyathophyllum cæspitosum_, Goldf., Plymouth.
+  _b._ a terminal star.
+  _c._ vertical section exhibiting transverse plates, and part of
+       another branch.]
+
+Among the peculiar lamellibranchiate bivalves, also common to Devonshire
+and the Eifel, we find _Megalodon cucullatus_ (fig. 405.). Several spiral
+univalves are abundant, among which are many species of _Pleurotomaria_ and
+_Euomphalus_. Among the Cephalopoda we find _Bellerophon_ and _Orthoceras_,
+as in the Silurian and Carboniferous groups, and _Goniatite_ and
+_Cyrtoceras_, as in the Carboniferous. In some of the upper Devonian beds,
+a shell, resembling a flattened _Goniatite_, occurs, called _Clymenia_, by
+Munster (_Endosiphonites_, Ansted.[347-A]).
+
+[Illustration: Fig. 403. _Calceola sandalina_, Lam. Eifel; also South
+Devon.
+
+  _a._ both valves united.
+  _b._ inner side of opercular valve.]
+
+[Illustration: Fig. 404. _Strygocephalus Burtini_. (_Terebratula porrecta_,
+Sow.) Eifel; also South Devon.
+
+  _a._ valves united.
+  _b_. side view of same.
+  _c._ interior of larger valve, showing thick partition, and thinner one
+       continued from it.]
+
+[Illustration: Fig. 405. _Megalodon cucullatus_, Sow. Eifel; also
+Bradley, S. Devon.
+
+  _a._ the valves united.
+  _b._ interior of valve, showing the large cardinal tooth.]
+
+[Illustration: Fig. 406. _Clymenia linearis_, Munster. (_Endosiphonites
+carinatus_, Ansted.) Cornwall.]
+
+A peculiar species of trilobite, called _Brontes flabellifer_ (fig. 407.),
+is found in the Devonian strata of the Eifel and in South Devon. It should
+be observed, however, that the head in the specimen here figured by
+Goldfuss, the most perfect which could be obtained, is incomplete, and a
+restoration has been attempted by Mr. Salter in fig. 408., from data
+supplied by other species of the same genus occurring in older rocks.
+
+[Illustration: Fig. 407. _Brontes flabellifer_, Goldf. Eifel;
+also S. Devon.]
+
+[Illustration: Fig. 408. Restored outline of head of
+_Brontes flabellifer_.]
+
+For determining the true equivalents of the Devonian group in the Rhenish
+provinces and adjacent parts of Germany, we are indebted to the labours of
+Messrs. Sedgwick and Murchison, in 1839, from which it appears that rocks
+of that age emerge from beneath the coal-field of Westphalia, and are also
+found in troughs among the Silurian rocks in Nassau. Many of the
+limestones, particularly those on the river Lahn, are identical, both in
+structure and in coralline remains, with the beautiful marbles of
+Babbacombe, Torquay, and Plymouth.
+
+The limestones of the Eifel, long ago celebrated for their fossils, and
+which lie in a basin supported by Silurian rocks, are found to be referable
+to the lower part of the Devonian system.
+
+In Russia, also, Messrs. Murchison and De Verneuil have shown (1840) that
+the "Old Red" group occupies a wide area south from St. Petersburg. It was
+formerly supposed to be the New Red Sandstone, on account of its saliferous
+and gypseous beds; but it is now proved to be the Old Red by containing
+ichthyolites of genera which characterize this group in the British Isles,
+as, for example, _Holoptychius_, _Coccosteus_, _Diplopterus_, &c.[349-A],
+associated with mollusca found in the Devonian of Western Europe. Among the
+fish are also many species of sharks of the Cestraciont division, a fact
+worthy of notice, because the squaloid fishes of the present day offer the
+highest organization of the brain and of the generative organs, and make,
+in these respects, the nearest approach to the higher vertebrate classes.
+
+
+_Devonian Strata in the United States._
+
+The position of this formation between the carboniferous rocks of
+Pennsylvania and Ohio, is pointed out in the section, fig. 379. p. 327.,
+and it is a remark of M. de Verneuil that in no European country is
+there so complete and uninterrupted a development of the Devonian system
+as in North America. At the falls of the Ohio, at Louisville, in
+Kentucky, there is a grand display of one of the limestones of this
+period, resembling a modern coral reef. A wide extent of surface is
+exposed in a series of horizontal ledges, at all seasons, when the water
+is not high; and the softer parts of the stone having decomposed and
+wasted away, the harder calcareous corals stand out in relief, and many
+of them send out branches from their erect stems precisely as if they
+were living. Among other species I observed large masses, not less than
+5 feet in diameter, of _Favosites gothlandica_, with its beautiful
+honeycomb structure well displayed, and, by the side of it, the
+_Favistella_, combining a similar honeycombed form with the star of the
+_Astrea_. There was also the cup-shaped _Cyathophyllum_, and the
+delicate network of the _Fenestella_, and that elegant and well-known
+European species of fossil, called "the chain coral," _Catenipora
+escharoides_, with a profusion of others (see fig. 423. p. 355.). These
+coralline forms were mingled with the joints, stems, and occasionally
+the heads, of lily encrinites. Although hundreds of fine specimens have
+been detached from these rocks, to enrich the museums of Europe and
+America, another crop is constantly working its way out, under the
+action of the stream, and of the sun and rain, in the warm season when
+the channel is laid dry. The waters of the Ohio, when I visited the
+spot in April, 1846, were more than 40 feet below their highest level,
+and 20 feet above their lowest, so that large spaces of bare rock were
+exposed to view.[349-B]
+
+
+_Devonian Flora._
+
+With the exception of the fucoids above mentioned (p. 344.), but little
+is known with certainty of the plants of the Devonian group. Those found
+in the department of La Sarthe in France, and in various parts of
+Brittany, formerly referred to the Devonian era, have been shown (in
+1850), by M. de Verneuil, to belong to the carboniferous series. The
+same may be said of the species of _Lepidodendron_, _Knorria_,
+_Calamite_, _Sagenaria_, and other genera recently figured (1850), by
+Mr. F. A. Römer, from the formation called "Greywacké à Posodonomyes" in
+the Hartz.[350-A] They are accompanied by _Goniatites reticulatus_
+Phillips, _G. intercostatus_ Phil., and other mountain limestone
+species, and had been previously assigned to the oldest part of the
+carboniferous series by Messrs. Murchison and Sedgwick.
+
+If hereafter we should become well acquainted with the land plants of the
+Devonian era, we may confidently expect that nearly all of them will agree
+generically with those of the carboniferous period, but the species will be
+as different as are the Devonian vertebrate and invertebrate animals from
+the fossil species of the Coal.
+
+
+FOOTNOTES:
+
+[342-C] See section, fig. 318. p. 287.
+
+[343-A] The Old Red Sandstone, by Hugh Miller, 1841.
+
+[345-A] Old Red Sandstone. Plate 1. fig. 1. Mr. M.'s description of the
+fish is most graphic and correct.
+
+[347-A] Camb. Phil. Trans., vol. vi. pl. 8. fig. 2.
+
+[349-A] See Proceedings of Geol. Soc., and the anniversary speech of
+Dr. Buckland, P. G. S., for 1841.
+
+[349-B] Lyell's Second Visit to the United States, vol. ii. p. 277.
+
+[350-A] Memoir on the Hartz, Palæontographica of Dunker and Von Meyer,
+part iii.
+
+
+
+
+CHAPTER XXVII.
+
+SILURIAN GROUP.
+
+   Silurian strata formerly called transition--Term
+   grauwacké--Subdivisions of Upper and Lower Silurian--Ludlow formation
+   and fossils--Wenlock formation, corals and shells--Caradoc and
+   Llandeilo beds--Graptolites--Lingula--Trilobites--Cystideæ--Vast
+   thickness of Silurian strata in North Wales--Unconformability of
+   Caradoc sandstone--Silurian strata of the United States--Amount of
+   specific agreement of fossils with those of Europe--Great number of
+   brachiopods--Deep-sea origin of Silurian strata--Absence of fluviatile
+   formations--Mineral character of the most ancient fossiliferous rocks.
+
+
+We come next in the descending order to the most ancient of the primary
+fossiliferous rocks, that series which comprises the greater part of the
+strata formerly called "transition" by Werner, for reasons explained in
+Chap. VIII., pp. 91 and 92. Geologists have also applied to these older
+strata the general name of "grauwacké," by which the German miners
+designate a particular variety of sandstone, usually an aggregate of small
+fragments of quartz, flinty slate (or Lydian stone), and clay-slate
+cemented together by argillaceous matter. Far too much importance has been
+attached to this kind of rock, as if it belonged to a certain epoch in the
+earth's history, whereas a similar sandstone or grit is found sometimes in
+the Old Red, and in the Millstone Grit of the Coal, and sometimes in
+certain Cretaceous and even Eocene formations in the Alps.
+
+The name of _Silurian_ was first proposed by Sir Roderick Murchison, for a
+series of fossiliferous strata lying below the Old Red Sandstone, and
+occupying that part of Wales and some contiguous counties of England, which
+once constituted the kingdom of the _Silures_, a tribe of ancient Britons.
+The strata have been divided into Upper and Lower Silurian, and these
+again in the region alluded to admit of several well-marked subdivisions,
+all of them explained in the following table.
+
+                         UPPER SILURIAN ROCKS.
+
+                               Prevailing         Thickness   Organic
+                               Lithological       in Feet.    Remains.
+                               characters.
+
+             {                {Finely laminated   }      }
+             {Tilestones.     { reddish and       }800?  }
+             {                { green sandstones  }      }
+             {                { and shales.       }      }
+  1. Ludlow  {                                           }Marine mollusca of
+  formation  {Upper           {Micaceous grey     }      } almost every order,
+             {Ludlow.         { sandstone.        }      } the Brachiopoda most
+             {                                    }      } abundant. Serpula,
+             {Aymestry        {Argillaceous       }      } Corals, Sauroid fish,
+             {limestone.      { limestone.        }2000  } Fuci.
+             {                                    }      }
+             {Lower           {Shale, with        }      }
+             {Ludlow.         { concretions of    }      }
+             {                { limestone.        }      }
+
+             {Wenlock         }Concretionary      }      {Marine mollusca of
+             {limestone.      } limestone.        }      { various orders as
+  2. Wenlock {                }                   }1800  { before, Crustaceans
+  formation. {                }                   }      { of the Trilobite
+             {                }                   }      { family.
+             {Wenlock         }Argillaceous       }      {Oldest bones of
+             {shale.          } shale.            }      { fish yet known.
+
+
+                         LOWER SILURIAN ROCKS.
+
+                              {Flags of shelly    }     {
+                              { limestone and     }     {Crinoidea, Corals,
+  3. Caradoc {Caradoc         { sandstone, thick  }2500 { Mollusca, chiefly
+  formation. {sandstones.     { bedded white      }     { Brachiopoda,
+                              { freestone.        }     { Trilobites.
+
+  4. Llandeilo {Llandeilo     }Dark coloured      }1200 {Mollusca,
+  formation.   {flags.        } calcareous flags. }     { Trilobites.
+
+
+UPPER SILURIAN ROCKS.
+
+_Ludlow formation._--This member of the Upper Silurian group, as will
+be seen by the above table, is of great thickness, and subdivided into
+four parts,--the Tilestone, the Upper and Lower Ludlow, and the
+intervening Aymestry limestone. Each of these may be distinguished near
+the town of Ludlow, and at other places in Shropshire and Herefordshire,
+by peculiar organic remains.
+
+1. _Tilestones._--This uppermost division was originally classed by
+Sir R. Murchison with the Old Red Sandstone, because they decompose
+into a red soil throughout the Silurian region. At the same time he
+regarded the tilestones as a transition group forming a passage from
+Silurian to Old Red. It is now ascertained that the fossils agree in
+great part specifically, and in general character entirely, with those
+of the succeeding formation.
+
+2. _Upper Ludlow._--The next division, called the Upper Ludlow, consists of
+grey calcareous sandstone, decomposing into soft mud, and contains, among
+other shells, the _Lingula cornea_, which is common to it and the lowest,
+or tilestone beds of the Old Red. But the _Orthis orbicularis_ is peculiar
+to the Upper Ludlow, and very common; and the lowest or mudstone beds, are
+loaded for a thickness of 30 feet with _Terebratula navicula_ (fig. 410.),
+in vast numbers. Among the cephalopodous mollusca occur the genera
+_Bellerophon_ and _Orthoceras_, and among the crustacea the _Homalonotus_
+(fig. 418. p. 354.). A coral called _Favosites polymorpha_, Goldf. (fig.
+401. p. 346.) is found both in this subdivision and in the Devonian system.
+
+[Illustration: Fig. 409. _Orthis orbicularis_, J. Sow. Delbury.
+Upper Ludlow.]
+
+[Illustration: Fig. 410. _Terebratula navicula_, J. Sow. Aymestry
+limestone; also in Upper and Lower Ludlow.]
+
+Among the fossil shells are species of _Leptæna_, _Orthis_, _Terebratula_,
+_Avicula_, _Trochus_, _Orthoceras_, _Bellerophon_, and others.[352-A]
+
+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 "mudstones." In these shales many zoophytes
+are found enveloped 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.
+
+The scales, spines (_ichthyodorulites_), jaws, and teeth of fish of the
+genera _Onchus_, _Plectrodus_, and others of the same family, have been met
+with in the Upper Ludlow rocks.
+
+[Illustration: Fig. 411. _Pentamerus Knightii_, Sow. Aymestry.
+
+  _a._ view of both valves united.
+  _b._ longitudinal section through both valves, showing the central plate
+       or septum; half nat. size.]
+
+3. _Aymestry limestone._--The next group is a subcrystalline and
+argillaceous limestone, which is in some places 50 feet thick, and
+distinguished around Aymestry by the abundance of _Pentamerus Knightii_,
+Sow. (fig. 411.), also found in the Lower Ludlow. This genus of
+brachiopoda has only been found in the Silurian strata. The name was
+derived from +pente+, _pente_, five, and +meros+, _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; but
+neither the structure of this shell, nor the connection of the animal with
+its several parts, are as yet understood. 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.
+
+[Illustration: Fig. 412. _Lingula Lewisii_, J. Sow. Abberley Hills.]
+
+Three other abundant shells in the Aymestry limestone are, 1st, _Lingula
+Lewisii_ (fig. 412.); 2d, _Terebratula Wilsoni_, Sow. (fig. 413.), which is
+also common to the Lower Ludlow and Wenlock limestone; 3d, _Atrypa
+reticularis_, Lin. (fig. 414.), which has a very wide range, being found in
+every part of the Silurian system, except the Llandeilo flags.
+
+[Illustration: Fig. 413. _Terebratula Wilsoni_, Sow. Aymestry.]
+
+[Illustration: Fig. 414. _Atrypa reticularis._ Linn. Syn. _Terebratula
+affinis_, Min. Con. Aymestry.
+
+  _a._ upper valve.
+  _b._ lower.
+  _c._ anterior margin of the valves.]
+
+4. _Lower Ludlow shale._--A dark grey argillaceous deposit, containing,
+among other fossils, the new genera of chambered shells, the _Phragmoceras_
+of Broderip, and the _Lituites_ of Breyn (see figs. 415, 416.). The latter
+is partly straight and partly convoluted, nearly as in _Spirula_.
+
+[Illustration: Fig. 415. _Phragmoceras ventricosum_, J. Sow. (_Orthoceras
+ventricosum_, Stein.) Aymestry; 1/4 nat. size.]
+
+[Illustration: Fig. 416. _Lituites giganteus_, J. Sow. Near Ludlow; also in
+the Aymestry and Wenlock limestones; 1/4 nat. size.]
+
+[Illustration: Fig. 417. Fragments of Orthoceras.
+
+  _a._ Fragment of _Orthoceras Ludense_, J. Sow.
+  _b._ Polished section, showing siphuncle. Ludlow.]
+
+The _Orthoceras Ludense_ (fig. 417.), as well as the shell last mentioned,
+is peculiar to this member of the series. The _Homalonotus
+delphinocephalus_ (fig. 418.) is common to this division and to the Wenlock
+limestone. This crustacean belongs to a group of trilobites which has been
+met with in the Silurian rocks only, and in which the tripartite character
+of the dorsal crust is almost lost.
+
+[Illustration: Fig. 418. _Homalonotus delphinocephalus_, König.[354-A]
+Dudley Castle; 1/2 nat. size.]
+
+A species of Graptolite, _G. Ludensis_, Murch. (fig. 419.), a form of
+zoophyte which has not yet been met with in strata newer than the Silurian,
+occurs in the Lower Ludlow.
+
+_Wenlock formation._--We next come to the Wenlock formation, which has been
+divided (see Table, p. 351.) into
+
+1. Wenlock limestone, formerly well known to collectors by the name of the
+Dudley limestone, which forms a continuous ridge, ranging for about 20
+miles from S.W. to N.E., about a mile distant from the nearly parallel
+escarpment of the Aymestry limestone. The prominence of this rock in
+Shropshire, like that of Aymestry, is due to its solidity, and to the
+softness of the shales above and below. It is divided into large
+concretional masses of pure limestone, and abounds in trilobites, among
+which the prevailing species are _Phacops caudatus_ (fig. 422.) and
+_Calymene Blumenbachii_, commonly called the Dudley trilobite. The latter
+is often found coiled up like a wood-louse (see fig. 420.).
+
+[Illustration: Fig. 419. _Graptolithus Ludensis_, Murchison. Lower Ludlow.]
+
+[Illustration: Fig. 420. _Calymene Blumenbachii_, Brong. Wenlock, L.
+Ludlow, and Aym. limest.]
+
+[Illustration: Fig. 421. _Leptæna depressa._ Wenlock.]
+
+[Illustration: Fig. 422. _Phacops caudatus_, Brong. Wenlock, Aym.
+limest., and L. Ludlow.]
+
+_Leptæna depressa_, Sow., is common in this rock, but also ranges through
+the Lower Ludlow, Wenlock shale, and Caradoc Sandstone.
+
+[Illustration: Fig. 423. _Catenipora escharoides._]
+
+Among the corals in which this formation is very rich, the _Catenipora
+escharoides_, Lam. (fig. 423.), or chain coral, may be pointed out as
+one very easily recognized, and widely spread in Europe, ranging
+through all parts of the Silurian group, from the Aymestry limestone
+to the bottom of the series.
+
+Another coral, the _Porites pyriformis_, is also met with in profusion; a
+species common to the Devonian rocks.
+
+_Cystiphyllum Siluriense_ (fig. 425.) is a species peculiar to the Wenlock
+limestone. This new genus, the name of which is derived from +kystis+, a
+_bladder_, and +phyllon+, a _leaf_, was instituted by Mr. Lonsdale for
+corals of the Silurian and Devonian groups. It is composed of small
+bladder-like cells (see fig. 425. _b._).
+
+2. The Wenlock Shale, which exceeds 700 feet in thickness, contains
+many species of brachiopoda, such as a small variety of the _Lingula
+Lewisii_ (fig. 412.), and the _Atrypa reticularis_ (fig. 414.) before
+mentioned, and it will be seen that several other fossils before
+enumerated range into this shale.
+
+[Illustration: Fig. 424. _Porites pyriformis_, Ehren. Wenlock limest. and
+shale. Also in Aymestry limestone, and L. Ludlow.
+
+_a._ Vertical section, showing transverse lamellæ.]
+
+[Illustration: Fig. 425. Cystiphyllum.
+
+  _a._ _Cystiphyllum Siluriense_, Lonsd. Wenlock.
+  _b._ Section of portion, showing cells.]
+
+
+LOWER SILURIAN ROCKS.
+
+The Lower Silurian rocks have been subdivided into two portions.
+
+1. The Caradoc sandstone, which abuts against the trappean chain called the
+Caradoc Hills, in Shropshire. Its thickness is estimated at 2500 feet, and
+the larger proportion of its fossils are specifically distinct from those
+of the Upper Silurian rocks. Among them we find many trilobites and shells
+of the genera _Orthoceras_, _Nautilus_, and _Bellerophon_; and among the
+Brachiopoda the _Pentamerus oblongus_ and _P. lævis_ (fig. 426.), which are
+very abundant and peculiar to this bed; also _Orthis grandis_ (fig. 427.),
+and a fossil of well-defined form, _Tentaculites annulatus_, Schlot. (fig.
+428.), which Mr. Salter has shown to be referable to the Annelids and to
+the same tribe as _Serpula_.
+
+[Illustration: Fig. 426. _Pentamerus lævis_, Sow. Caradoc Sandstone.
+Perhaps the young of _Pentamerus oblongus_.
+
+  _a, b._ Views of the shell itself, from figures in Murchison's Sil. Syst.
+   _c._   Cast with portion of shell remaining, and with the hollow of the
+          central septum filled with spar.
+   _d._   Internal cast of a valve, the space once occupied by the septum
+          being represented by a hollow in which is seen a cast of the
+          chamber within the septum.]
+
+[Illustration: Fig. 427. Cast of _Orthis grandis_, J. Sow. Horderley;
+two-thirds of nat. size.]
+
+[Illustration: Fig. 428. _Tentaculites scalaris_, Schlot. Eastnor Park;
+nat. size, and magnified.]
+
+The most ancient bony remains of fish yet discovered in Great Britain are
+those obtained from the Wenlock limestones; but coprolites referred to fish
+occur still lower in the Silurian series in Wales.
+
+[Illustration: Fig. 429. _Ogygia Buchii_, Burmeister. Syn. _Asaphus
+Buchii_, Brong. 1/4 nat. size. Radnorshire.]
+
+2. The _Llandeilo flags_, so named from a town in Caermarthenshire, form
+the base of the Silurian system, consisting of dark-coloured micaceous
+grit, frequently calcareous, and distinguished by containing the large
+trilobites _Asaphus Buchii_ and _A. tyrannus_, Murch., both of which are
+peculiar to these rocks. Several species of Graptolites (fig. 430.)
+occur in these beds.
+
+[Illustration: Fig. 430. _a_, _b_. _Graptolithus Murchisonii_,
+Beck. Llandeilo flags.]
+
+[Illustration: Fig. 431. _G. foliaceus_, _Murchison_. Llandeilo flags.]
+
+In the fine shales of this formation Graptolites are very abundant. I
+collected these same bodies in great numbers in Sweden and Norway in
+1835-6, both in the higher and lower shales of the Silurian system; and
+was informed by Dr. Beck of Copenhagen, that they were fossil zoophytes
+related to the genera _Pennatula_ and _Virgularia_, of which the living
+species now inhabit mud and slimy sediment. The most eminent naturalists
+still hold to this opinion.
+
+A species of _Lingula_ is met with in the lowest part of the Llandeilo
+beds; and it is remarkable that this brachiopod is among the earliest, if
+not the most ancient animal form detected in the lowest Silurian of North
+America. These inhabitants of the seas, of so remote an epoch, belonged so
+strictly to the living genus _Lingula_, as to demonstrate, like the
+pteriform ferns of the coal, through what incalculable periods of time the
+same plan and type of organization has sometimes prevailed.
+
+Among the forms of trilobite extremely characteristic of the Lower Silurian
+throughout Europe and North America, the _Trinucleus_ may be mentioned.
+This family of crustaceans appears to have swarmed in the Silurian seas,
+just as crabs, shrimps, and other genera of crustaceans abound in our own.
+Burmeister, in his work on the organization of trilobites, supposes them to
+have swum 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. They underwent various
+transformations analogous to those of living crustaceans. M. Barrande,
+author of a work on the Silurian rocks of Bohemia, has traced the same
+species from the young state just after its escape from the egg to the
+adult form, through various metamorphoses, each having the appearance of a
+distinct species. Yet, notwithstanding the numerous species of preceding
+naturalists which he has thus succeeded in uniting into one, he announces a
+forthcoming work in which descriptions and figures of 250 species of
+Trilobite will be given.
+
+[Illustration: Fig. 432. _Trinucleus ornatus_, Burm.]
+
+_Cystideæ._--Among the additions which recent research has made to the
+paleontology of the oldest Silurian rocks, none are more remarkable than
+the radiated animals called _Cystideæ_. Their structure and relations were
+first elucidated in an essay published by Von Buch at Berlin in 1845. They
+are usually met with as spheroidal bodies covered with polygonal plates,
+with a mouth on the upper side, and a point of attachment for a stem _b_
+(which is almost always broken off) on the lower. (See fig. 433.) They are
+considered by Professor E. Forbes as intermediate between the crinoids and
+echinoderms. The _Sphæronites_ here represented (fig. 433.) occurs in the
+Llandeilo beds in Wales.[358-A]
+
+[Illustration: Fig. 433. _Sphæronites balticus_, Eichwald. (Of the
+family _Cystideæ_.)
+
+  _a._ mouth.
+  _b._ point of attachment of stem.
+
+Lower Silurian, Shole's Hook and Bala.]
+
+_Thickness and unconformability of Silurian strata._--According to the
+observation of our government surveyors in North Wales, the Lower Silurian
+strata of that region attain, in conjunction with the contemporaneous
+volcanic rocks, the extraordinary thickness of 27,000 feet. One of the
+groups, called the trappean, consisting of slates and associated volcanic
+ash and greenstone, is 15,000 feet thick. Another series, called the Bala
+group, composed of slates and grits with an impure limestone rich in
+organic remains, is 9,000 feet thick.[359-A]
+
+Throughout North Wales the Wenlock shales rest unconformably upon the
+Caradoc sandstones; and the Caradoc is in its turn unconformable to the
+Llandeilo beds, showing a considerable interval of time between the
+deposition of this group and that of the formations next above and below
+it. The Caradoc sandstone in the neighbourhood of the Longmynd Hills in
+Shropshire, appears to Professor E. Forbes to have been a deep-sea deposit
+formed around the margin of high and steep land. That land consisted partly
+of upraised Llandeilo flags and partly of rocks of still older date.[359-B]
+
+Such evidence of the successive disturbance of strata during the Silurian
+period in Great Britain is what we might look for when we have discovered
+the signs of so grand a series of volcanic eruptions as the contemporaneous
+greenstones and tuffs of the Welsh mountains afford.
+
+
+_Silurian Strata of the United States._
+
+The position of some of these strata, where they are bent and highly
+inclined in the Appalachian chain, or where they are nearly horizontal
+to the west of that chain, is shown in the section, fig. 379. p. 327.
+But these formations can be studied still more advantageously north of
+the same line of section, in the states of New York, Ohio, and other
+regions north and south of the great Canadian lakes. Here they are
+found, as in Russia, in horizontal position, and are more rich in
+well-preserved fossils than in almost any spot in Europe. The American
+strata may readily be divided into Upper and Lower Silurian,
+corresponding in age and fossils to the European divisions bearing the
+same names. The subordinate members of the New York series, founded on
+lithological and geographical considerations, are most useful in the
+United States, but even there are only of local importance. Some few of
+them, however, tally very exactly with English divisions, as for example
+the limestone, over which the Niagara is precipitated at the great
+cataract, which, with its underlying shales, agrees paleontologically
+with the Wenlock limestone and shale of Siluria. There is also a marked
+general correspondence in the succession of fossil forms, and even
+species, as we trace the organic remains downwards from the highest
+to the lowest beds.
+
+Mr. D. Sharpe, in his report on the mollusca collected by me from these
+strata in North America[359-C], 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 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 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.
+
+_Whether the Silurian rocks are of deep-water origin._--The grounds relied
+upon by Professor E. Forbes, for inferring that the larger part of the
+Silurian Fauna is indicative of a sea more than 70 fathoms deep, are the
+following: first, the small size of the greater number of conchifera;
+secondly, the paucity of pectinibranchiata (or spiral univalves); thirdly,
+the great number of floaters, such as _Bellerophon_, _Orthoceras_, &c.;
+fourthly, the abundance of orthidiform brachiopoda; fifthly, the absence or
+great rarity of fossil fish.
+
+It is doubtless true that some living _Terebratulæ_, on the coast of
+Australia, inhabit shallow water; but all the known species, allied in
+form to the extinct _Orthis_, inhabit the depths of the sea. It should
+also be remarked that Mr. Forbes, in advocating these views, was well
+aware of the existence of shores, bounding the Silurian sea in
+Shropshire, and of the occurrence of littoral species of this early date
+in the northern hemisphere. Such facts are not inconsistent with his
+theory; for he has shown, in another work, how, on the coast of Lycia,
+deep-sea strata are at present forming in the Mediterranean, in the
+vicinity of high and steep land.
+
+Had we discovered the ancient delta of some large Silurian river, we should
+doubtless have known more of the shallow, and brackish water, and
+fluviatile animals, and of the terrestrial flora of the period under
+consideration. To assume that there were no such deltas in the Silurian
+world, would be almost as gratuitous an hypothesis, as for the inhabitants
+of the coral islands of the Pacific to indulge in a similar generalization
+respecting the actual condition of the globe.[360-A]
+
+
+_Mineral Character of Silurian Strata._
+
+In lithological character, the Silurian strata vary greatly when we
+trace them through Europe and North America. The shales called
+mudstones are as little altered from some deposits, found in recent
+submarine banks, as are those of many tertiary formations. We meet
+with red sandstone and red marl, with gypsum and salt, of Upper
+Silurian date, in the Niagara district, which might be mistaken for
+trias. The whitish granular sandstone at the base of the Silurian series
+in Sweden resembles the tertiary siliceous grit of Fontainebleau. The
+Calcareous Grit, oolite, and pisolite of Upper Silurian age in
+Gothland, are described by Sir R. Murchison as singularly like rocks
+of the oolitic period near Cheltenham; and, not to cite more examples,
+the Wenlock or Dudley limestone often resembles a modern coral-reef. If,
+therefore, uniformity of aspect has been thought characteristic of rocks
+of this age, the idea must have arisen from the similarity of feature
+acquired by strata subject to metamorphic action. This influence, seeing
+that the causes of change are always shifting the theatre of their
+principal development, must be multiplied throughout a wider
+geographical area by time, and become more general in any given system
+of rocks in proportion to their antiquity. We are now acquainted with
+dense groups of Eocene slates in the Alps, which were once mistaken by
+experienced geologists for Transition or Silurian formations. The error
+arose from attaching too great importance to mineral character as a
+test of age, for the tertiary slates in question having acquired that
+crystalline texture which is in reality most prevalent in the most
+ancient sedimentary formations.
+
+
+CAMBRIAN GROUP.
+
+Below the Silurian strata in North Wales, and in the region of the
+Cumberland lakes, there are some slaty rocks, devoid of organic remains, or
+in which a few obscure traces only of fossils have been detected (for which
+the names of Cambrian and Cumbrian have been proposed). Whether these will
+ever be entitled by the specific distinctness of their fossils to rank as
+independent groups, we have not yet sufficient data to determine.
+
+       *       *       *       *       *
+
+TABULAR VIEW OF FOSSILIFEROUS STRATA,
+
+_Showing the Order of Superposition or Chronological Succession of the
+principal European Groups_.
+
+
+                         I. POST-TERTIARY.
+
+                         A. POST-PLIOCENE.
+
+  Periods and Groups.       Examples.                      Observations.
+
+  1. Recent.         { Peat mosses and shell-marl,    } All the imbedded shells,
+                     {   with bones of land animals,  }   freshwater and marine,
+                     {   human remains, and works     }   of living species,
+                     {   of art.                      }   with occasional
+                     {                                }   human remains and
+                     { Newer parts of modern deltas   }   works of art.
+                     {   and coral reefs.             }
+
+  2. Post-Pliocene.  { Clay, marl, and volcanic tuff  } All the shells of living
+                     {   of Ischia, p. 113.           }   species. No human
+                     {                                }   remains or works
+                     { Loess of the Rhine, p. 117.    }   of art. Bones of
+                     {                                }   quadrupeds, partly
+                     { Newer part of boulder          }   of extinct species.
+                     {   formation, with erratics,    }
+                     {   p. 124.                      }
+
+                         II. TERTIARY.
+
+                         B. PLIOCENE.
+
+  3. Newer Pliocene  { Boulder formation or drift of  { Three-fourths of the
+     or Pleistocene. {   northern Europe and North    {   fossil shells of
+                     {   America, chaps. 11. & 12.    {   existing species.
+                     {                                {
+                     { Cavern deposits and osseous    { A majority of the
+                     {   breccias, p. 153.            {   mammalia extinct;
+                     {                                {   but the genera
+                     { Fluvio-marine crag of Norwich, {   corresponding with
+                     {   p. 148.                      {   those now surviving in
+                     {                                {   the same great
+                     { Limestone of Girgenti,         {   geographical and
+                     {   in Sicily, p. 152.           {   zoological province,
+                                                      {   p. 157.
+                                                      {
+                                                      { During part of this
+                                                      {   period icebergs
+                                                      {   frequent in the seas
+                                                      {   of the northern
+                                                      {   hemisphere, and
+                                                      {   glaciers on hills
+                                                      {   of moderate height.
+
+  4. Older Pliocene. { Red and Coralline crag of      { A third or more of the
+                     {   Suffolk, p. 162.             {   species of mollusca
+                     {                                {   extinct.
+                     { Subapennine beds, p. 166.      {
+                                                      { Nearly, if not all, the
+                                                      {   mammalia extinct.
+
+                         C. MIOCENE.
+
+  5. Miocene.        { Faluns of Touraine, p. 168.    { About two-thirds of the
+                     {                                {   species of shells
+                     { Part of Bordeaux beds, p. 171. {   extinct.
+                     {                                {
+                     { Part of Molasse of             { The recent species of
+                     {   Switzerland, p. 171.         {   shells often not
+                                                      {   found in the
+                                                      {   adjoining seas, but
+                                                      {   in warmer latitudes.
+                                                      {
+                                                      { All the mammalia
+                                                      {   extinct.
+
+                         D. EOCENE.
+
+  6. Upper Eocene.   { Upper marine of Paris basin,   } Fossil shells of the
+                     {   Fontainebleau sandstone,     }   Eocene period, with
+                     {   p. 175.                      }   very few exceptions,
+                     {                                }   extinct. Those which
+                     { Upper freshwater and millstone }   are identified with
+                     {   of same.                     }   living species rarely
+                     { Kleyn Spauwen beds, p. 176.    }   belong to neighbouring
+                     {                                }   regions.
+                     { Hermsdorf tile-clay, near      }
+                     {   Berlin.                      } All the mammalia of
+                     {                                }   extinct species, and
+                     { Mayence tertiary strata,       }   the greater part of
+                     {   p. 177.                      }   them of extinct
+                     {                                }   genera.
+                     { Freshwater beds of Limagne     }
+                     {   d'Auvergne, p. 181.          } Plants of Upper Eocene,
+                                                      }   indicating a south
+  7. Middle Eocene.  { Paris gypsum with              }   European or
+                     {   Paleotherium, &c., p. 191.   }   Mediterranean climate;
+                     {                                }   those of Lower Eocene,
+                     { Freshwater and fluvio-marine   }   a tropical climate.
+                     {   beds of Headon Hill, Isle    }
+                     {   of Wight, p. 197.            }
+                     {                                }
+                     { Barton beds, Hants, p. 198.    }
+                     {                                }
+                     { Calcaire Grossier, Paris,      }
+                     {   p. 193.                      }
+                     {                                }
+                     { Bagshot and Bracklesham beds,  }
+                     {   Surrey and Sussex, p. 198.   }
+                                                      }
+  8. Lower Eocene.   { London clay proper of Highgate }
+                     {   Hill and Sheppey,--Bognor    }
+                     {   beds, Sussex, p. 200.        }
+                     {                                }
+                     { Sables inférieurs, and lits    }
+                     {   coquilliers of Paris basin,  }
+                     {   p. 196.                      }
+                     {                                }
+                     { Mottled and plastic clays and  }
+                     {   sands of the Hampshire and   }
+                     {   London basins, p. 203.       }
+                     {                                }
+                     { Sables inférieurs and argiles  }
+                     {   plastiques of Paris basin,   }
+                     {   p. 196.                      }
+                     {                                }
+                     { Nummulitic formation of the    }
+                     {   Alps, p. 205.                }
+
+                         III. SECONDARY.
+
+                         E. CRETACEOUS.
+
+                         § UPPER CRETACEOUS.
+
+  9. Maestricht      { Yellowish white limestone of   { Ammonite, Baculite, and
+     beds.           {   Maestricht, p. 209.          {   Belemnite, associated
+                     {                                {   with Cypræa, Oliva,
+                     { Coralline limestone of Faxoe,  {   Mitra, Trochus, &c.
+                     {   Denmark, p. 210.             {   Large marine saurians.
+
+  10. Upper White    { White chalk with flints of     } Marine limestone
+      Chalk.         {   North and South              }   formed in part of
+                     {   Downs,--Surrey and Sussex,   }   decomposed corals.
+                     {   p. 211.                      }
+
+  11. Lower White    { Chalk without flints, and      }
+      Chalk.         {   chalk marl, ibid.            }
+
+  12. Upper          { Loose sand, with bright green  }
+      Greensand.     {   particles, ibid.             }
+                     {                                }
+                     { Firestone of Merstham, Kent,   }
+                     {   p. 218.                      }
+                     {                                }
+                     { Marly stone, with layers of    }
+                     {   chert, south of Isle of      }
+                     {   Wight.                       }
+
+  13. Gault.         { Dark blue marl at base of      { Numerous extinct genera
+                     {   chalk escarpment,--Kent      {   of conchiferous
+                     {   and Sussex, p. 218.          {   cephalopoda, Hamite,
+                                                      { Scaphite, Ammonite, &c.
+
+                         §§ LOWER CRETACEOUS.
+
+  14. Lower          { Sand with green matter,--Weald } Species of shells, &c.,
+      Greensand.     {   of Kent and Sussex,          }   nearly all distinct
+                     {   p. 219.                      }   from those of Upper
+                     {                                }   Cretaceous; most of
+                     { White, yellowish, and          }   the genera the same.
+                     {   ferruginous sand, with       }
+                     {   concretions of limestone and }
+                     {   chert,--Atherfield, Isle     }
+                     {   of Wight.                    }
+                     {                                }
+                     { Limestone called Kentish Rag   }
+
+                         F. WEALDEN.
+
+  15. Weald Clay.    { Clay with occasional bands of  { Of freshwater origin.
+                     {   limestone,--Weald of Kent,   {   Shells of
+                     {   Surrey, and Sussex, p. 227.  {   pulmoniferous
+                                                      {   mollusca, and of
+                                                      {   Cypris. Land reptiles.
+
+  16. Hastings Sand. { Sand with calciferous grit and { Freshwater with
+                     {   clay,--Hastings, Sussex,     {   intercalated bed of
+                     {   Cuckfield, Kent, p. 229.     {   brackish and salt
+                                                      {   water origin. Shells
+                                                      {   of fluviatile and
+                                                      {   lacustrine genera.
+                                                      {   Reptiles of the genera
+                                                      {   Pterodactyle,
+                                                      {   Iguanodon,
+                                                      {   Megalosaurus,
+                                                      {   Plesiosaurus, Trionyx,
+                                                      {   and Emys.
+
+  17. Purbeck Beds.  Limestones, calcareous slates    { Chiefly freshwater, and
+                       and marls, p. 231.             {   divisible into three
+                                                      {   groups, each
+                                                      {   containing distinct
+                                                      {   species of freshwater
+                                                      {   mollusca and of
+                                                      {   entomostraca.
+                                                      {   Alternations of
+                                                      {   deposits formed in
+                                                      {   fresh, brackish, and
+                                                      {   marine water, and of
+                                                      {   ancient soils formed
+                                                      {   on land and retaining
+                                                      {   roots of trees.
+                                                      {   Plants chiefly cycads
+                                                      {   and conifers, p. 231.
+
+                         G. OOLITE.
+
+  18. Upper Oolite.  { _a._ Portland  building stone, } Ammonites and Belemnites
+                     {    p. 259.                     }   numerous.
+                     {                                }
+                     { _b._ Portland sand.            } Large saurians, as
+                     {                                }   Pterodactyles,
+                     { _c._ Kimmeridge clay,          }   Plesiosaurs,
+                     {     Dorsetshire, p. 260.       }   Ichthyosaurs.
+                                                      }
+  19. Middle Oolite. { _a._ Coral Rag, p. 260.        } No cetaceans yet known,
+                     {    Calcareous freestones,      }   but three species of
+                     {    oolitic, often full of      }   terrestrial mammalia,
+                     {    corals. Oxfordshire.        }   p. 267, 268.
+                     {                                }   Preponderance of
+                     { _b._ Oxford clay--Dark blue    }   ganoid fish. The
+                     {    clay,--Oxfordshire and      }   plants chiefly cycads,
+                     {    midland counties, p. 262.   }   conifers, and ferns,
+                                                      }   with a few palms.
+  20. Lower Oolite.  { _a._ Cornbrash and forest      }
+                     {    marble, Wiltshire, p. 263.  }
+                     {                                }
+                     { _b._ Great oolite and          }
+                     {    Stonesfield slate,--Bath,   }
+                     {    Bradford, Stonesfield near  }
+                     {    Woodstock, Oxfordshire,     }
+                     {    p. 266.                     }
+                     {                                }
+                     { _c._ Fuller's earth,--Clay     }
+                     {    containing fuller's earth   }
+                     {    near Bath, p. 272.          }
+                     {                                }
+                     { _d._ Inferior oolite,          }
+                     {    calcareous freestone, and   }
+                     {    yellow sands,--Cotteswold   }
+                     {    Hills, Dundry Hill, near    }
+                     {    Bristol, p. 272.            }
+
+                         H. LIAS.
+
+  21. Lias.          { Argillaceous limestone, marl   { Mollusca, reptiles,
+                     {   and clay,--Lyme Regis,       {   and fish of genera
+                     {   Dorsetshire, p. 273.         {   analogous to the
+                                                      {   oolitic.
+
+                         I. TRIAS.
+
+  22. Upper Trias.   { Keuper of Germany, or          } Batrachian reptiles,
+                     {   variegated marls--Red, grey, }   _e.g._ Labyrinthodon,
+                     {   green, blue, and white marls }   Rhyncosaurus, &c.
+                     {   and sandstones with          }   Cephalopoda:
+                     {   gypsum--Würtemberg, bone-bed }   Ceratites. No
+                     {   of Axmouth, Dorset, p. 289.  }   Belemnites. Plants:
+                                                      }   Ferns, Cycads,
+                                                      }   Conifers.
+
+  23. Middle Trias   { Compact greyish limestone      } With Equisetites
+      or             {   with beds of dolomite and    }   and Calamite.
+      Muschelkalk.   {   gypsum,--North of Germany,   }
+                     {   p. 287. Wanting in           }
+                     {   England.                     }
+
+  24. Lower Trias.   { Variegated or Bunter sandstone } Plants different for
+                     {   of Germans--Red and white    }   the most part from
+                     {   spotted sandstone with       }   those of the Upper
+                     {   gypsum and rock-salt, P. 288 }   Trias.
+                     {                                }
+                     { Part of New Red sandstone of   }
+                     {   of Cheshire with rock-salt,  }
+                     {   p. 294.                      }
+
+                         IV. PRIMARY.
+
+                         K. PERMIAN.
+
+  25. Upper Permian. { Yellow magnesian limestone,    } Organic remains, both
+                     {   Yorkshire and Durham,        }   animal and vegetable,
+                     {   P. 301.                      }   more allied to primary
+                     {                                }   than to secondary
+                     { Zechstein of Thuringia, Upper  }   periods.
+                     {   part of Permian beds,        }
+                     {   Russia.                      }
+
+  26. Lower Permian. { _a._ Marl slate of Durham and  } Thecodont saurians.
+                     {    Thuringia.                  }   Heterocercal fish of
+                     {                                }   genus Palæoniscus, &c.
+                     { _b._ Lower New Red sandstone   }
+                     {    of north of England and     }
+                     {    Rothliegendes of Germany.   }
+                     {                                }
+                     { _a._ and _b._ Lower part of    }
+                     {    Permian beds, Russia,       }
+                     {    p. 301.                     }
+
+                         L. CARBONIFEROUS.
+
+  27. Coal measures. { _a._ Strata of sandstone and   } Great thickness of
+                     {    shale, with beds of         }   strata of
+                     {    coal,--S. Wales and         }   fluvio-marine origin,
+                     {    Northumberland, p. 309.     }   with beds of coal of
+                     {                                }   vegetable origin,
+                     { _b._ Millstone grit,--S.       }   based on soils
+                     {    Wales, Bristol coal-field,  }   retaining the roots
+                     {    Yorkshire, p. 308.          }   of trees.
+                                                      }
+                                                      } Oldest of known reptiles
+                                                      }   or  Archegosaurus.
+                                                      }   Sauroid fish.
+
+  28. Mountain       { Carboniferous or mountain      { Brachiopoda of genus
+      limestone.     {   limestone, with marine       {   Productus.
+                     {   shells and corals.           {
+                     {                                { Cephalopoda of genera
+                     { Mendip Hills, and many parts   {   Cyrtoceras, Goniatite,
+                     {   of Ireland, p. 340.          {   Orthoceras.
+                                                      {
+                                                      { Crustaceans of the
+                                                      {   genus Phillipsia.
+                                                      {
+                                                      { Crinoideans abundant.
+
+                         M. DEVONIAN.
+
+  29. Upper          { _a._ Yellow sandstone of Dura  } Tribe of fish with hard
+      Devonian.      {    Den, Fife.                  }   coverings like
+                     {                                }   chelonians,
+                     { _b._ Red sandstone and marl    }   Pterichthys,
+                     {    with cornstone of           }   Pamphractus, &c.;
+                     {    Herefordshire and           }   also of genera
+                     {    Forfarshire.                }   Cephalaspis,
+                     {                                }   Holoptichius, &c.
+                     { Paving and roofing-stone,      }
+                     {   Forfarshire.                 } No reptiles yet known.
+                     {                                }
+                     { Upper part of Devonian beds    }
+                     {    of South Devon.             }
+
+  30. Lower          { Grey sandstone with            } Fish, partly of same
+      Devonian.      {   Ichthyolites,--Caithness,    }   genera, but of
+                     {   Cromarty, and Orkney, Lower  }   distinct species from
+                     {   part of Devonian beds of     }   those in Upper
+                     {   South Devon, and green       }   Devonian; also
+                     {   chloritic slates of          }   Osteolepis,
+                     {   Cornwall, limestone of       }   Coccosteus,
+                     {   Gerolstein, Eifel.           }   Glyptolepis,
+                                                      }   Dipterus, &c.
+
+                         N. SILURIAN.
+
+  31. Upper          { _a._ Tilestone of Brecon and   { Oldest of fossil fish
+      Silurian.      {    Caermarthen.                {   yet discovered.
+                     {                                {
+                     { _b._ Limestone and shale,      { Trilobites and
+                     {    Ludlow, Shropshire.         {   Graptolites abundant.
+                     {                                {
+                     { _c._ Wenlock or Dudley         { Brachiopoda very
+                     {    limestone.                  {   numerous.
+                                                      {
+                                                      { Cephalopoda:
+                                                      {   Bellerophon,
+                                                      {   Orthoceras.
+
+                                                      { Same genera of
+  32. Lower          { _a._ Caradoc sandstone, Caer   {   invertebrate animals
+      Silurian.      {    Caradoc, Shropshire.        {   as in Upper Silurian,
+                     {                                {   but species chiefly
+                     { _b._ Llandeilo flags,          {   distinct. Trinucleus
+                     {    calcareous flags and        {   caractaci, Cystideæ,
+                     {    schists,--Builth,           {   p. 358.
+                     {    Radnorshire, Llandeilo,     {
+                     {    Caermarthenshire.           { No land plants yet
+                                                      {   known.
+                                                      {
+                                                      { Footprints of tortoise,
+                                                      {   see note, p. 360.
+
+
+FOOTNOTES:
+
+[352-A] Murchison, Silurian System, p. 198, 199.
+
+[354-A] Silurian System, pl. 7. bis. fig. 1. b.
+
+[358-A] Quart. Geol. Journ., vol. ii. p. 11.; and Memoirs of Geol. Survey,
+vol. ii. p. 518.
+
+[359-A] Quart. Geol. Journ., vol. iv. p. 300.
+
+[359-B] Ibid., 299.
+
+[359-C] Ibid., 145.
+
+[360-A] Since this was written, Mr. Logan has discovered chelonian
+footprints in the lowest fossiliferous beds of the Silurian series, near
+Montreal, in Canada. Professor Owen inclines to refer them to the genus
+_Emys_.--_Quart. Journ. G. S._, vol. vii. p. lxxvi.
+
+
+
+
+CHAPTER XXVIII.
+
+VOLCANIC ROCKS.
+
+   Trap rocks--Name, whence derived--Their igneous origin at first
+   doubted--Their general appearance and character--Volcanic cones and
+   craters, how formed--Mineral composition and texture of volcanic
+   rocks--Varieties of felspar--Hornblende and augite--Isomorphism--Rocks,
+   how to be studied--Basalt, greenstone, trachyte, porphyry, scoria,
+   amygdaloid, lava, tuff--Alphabetical list, and explanation of names
+   and synonyms, of volcanic rocks--Table of the analyses of minerals
+   most abundant in the volcanic and hypogene rocks.
+
+
+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. Suppose _a a_ in the annexed diagram, 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_. They also are seen, in some instances, to pass insensibly
+into the unstratified division of _a_, or the Plutonic rocks.
+
+[Illustration: Fig. 434. Cross section.
+
+  _a._ Hypogene formations, stratified and unstratified.
+  _b._ Aqueous formations.
+  _c._ Volcanic 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 volcanos. They also 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, and
+amygdaloid. All these, which were recognized 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 on the sides of hills. This configuration appears to be
+derived from two causes. First, the abrupt original terminations of sheets
+of melted matter, which have spread, whether on the land or bottom of the
+sea, over a level surface. For we know, in the case of lava flowing from a
+volcano, that a stream, when it has ceased to flow, and grown solid, very
+commonly ends in a steep slope, as at _a_, fig. 435. But, secondly, the
+step-like appearance arises more frequently from the mode in which
+horizontal masses of igneous rock, such as _b c_, intercalated between
+aqueous strata, have, subsequently to their origin, been exposed, at
+different heights, by denudation. Such an outline, it is true, is not
+peculiar to trap rocks; great beds of limestone, and other hard kinds of
+stone, often presenting similar terraces and precipices: but these are
+usually on a smaller scale, or less numerous, than the volcanic _steps_, or
+form less decided features in the landscape, as being less distinct in
+structure and composition from the associated rocks.
+
+[Illustration: Fig. 435. Step-like appearance of trap.]
+
+Although the characters of trap rocks are greatly diversified, the
+beginner will easily learn to distinguish them as a class from the
+aqueous formations. Sometimes they present themselves, as already
+stated, in tabular masses, which are not divided into strata: sometimes
+in shapeless lumps and irregular cones, forming chains of small hills.
+Often they are seen in dikes and wall-like masses, intersecting
+fossiliferous beds. The rock is occasionally found divided into columns,
+often decomposing into balls of various sizes, from a few inches to
+several feet in diameter. The decomposing surface very commonly assumes
+a coating of a rusty iron colour, from the oxidation of ferruginous
+matter, so abundant in the traps in which augite or hornblende occur;
+or, in the felspathic varieties of trap, it acquires a white opaque
+coating, from the bleaching of the mineral called felspar. On examining
+any of these volcanic rocks, where they have not suffered
+disintegration, we rarely fail to detect a crystalline arrangement in
+one or more of the component minerals. Sometimes the texture of the mass
+is cellular or porous, or we perceive that it has once been full of
+pores and cells, which have afterwards become filled with carbonate of
+lime, or other infiltrated mineral.
+
+Most of the volcanic rocks produce a fertile soil by their disintegration.
+It seems that their component ingredients, silica, alumina, lime, potash,
+iron, and the rest, are in proportions well fitted for vegetation. As they
+do not effervesce with acids, a deficiency of calcareous matter might at
+first be suspected; but although _the carbonate_ of lime is rare, except in
+the nodules of amygdaloids, yet it will be seen that lime sometimes enters
+largely into the composition of augite and hornblende. (See Table, p. 377.)
+
+_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 and other gases
+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 upwards 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 it down on
+one side, and often it flows out from a fissure at the base of the
+hill (see fig. 436.).[368-A]
+
+[Illustration: Fig. 436. Part of the chain of extinct volcanos called the
+Monts Dome, Auvergne. (Scrope.)]
+
+_Composition and nomenclature._--Before speaking of the connection between
+the products of modern volcanos and the rocks usually styled trappean, and
+before describing the external forms of both, and the manner and position
+in which they occur in the earth's crust, it will be desirable to treat of
+their mineral composition and names. The varieties most frequently spoken
+of are basalt, greenstone, syenitic greenstone, clinkstone, claystone, and
+trachyte; while those founded chiefly on peculiarities of texture, are
+porphyry, amygdaloid, lava, tuff, scoriæ, and pumice. It may be stated
+generally, that all these are mainly composed of two minerals, or families
+of simple minerals, _felspar_ and _hornblende_; some almost entirely of
+hornblende, others of felspar.
+
+These two minerals may be regarded as two groups, rather than species.
+Felspar, for example, may be, first, common felspar, that is to say,
+potash-felspar, in which the alkali is potash (see table, p. 377.); or,
+secondly, albite, that is to say, soda-felspar, where the alkali is soda
+instead of potash; or, thirdly, Labrador-felspar (Labradorite), which
+differs not only in its iridescent hues, but also in its angle of
+fracture or cleavage, and its composition. We also read much of two
+other kinds, called glassy felspar and compact felspar, which, however,
+cannot rank as varieties of equal importance, for both the albitic and
+common felspar appear sometimes in transparent or _glassy_ crystals; and
+as to compact felspar, it is a compound of a less definite nature,
+sometimes containing both soda and potash; and which might be called a
+felspathic paste, being the residuary matter after portions of the
+original matrix have crystallized.
+
+The other group, or _hornblende_, consists principally of two varieties;
+first, hornblende, and, secondly, augite, which were once regarded as very
+distinct, although now some eminent mineralogists are in doubt whether they
+are not one and the same mineral, differing only as one crystalline form of
+native sulphur differs from another.
+
+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 were different, and 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; and that when this happened, as in some lavas
+of modern date, the hornblende occurs in the mass of the rock, where
+crystallization may have taken place more slowly, while the augite
+merely lines cavities where the crystals may have been produced rapidly.
+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 in rocks from
+Siberia which presented a hornblende _cleavage_, 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
+recognized 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 recrystallizing, 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 recrystallizes, 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 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 find that a
+mineral determined to be the same by its physical characters, crystalline
+form, and optical properties, has often been declared by skilful analyzers
+to be composed of distinct elements. (See the table at p. 377.) 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 in a great degree 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+, _isos_, equal, and +morphê+, _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.
+
+Having been led into this digression on the recent progress of mineralogy,
+I may here observe that the geological student must endeavour as soon as
+possible to familiarize himself with the characters of five at least of
+the most abundant simple minerals of which rocks are composed. These are,
+felspar, quartz, mica, hornblende, and carbonate of lime. This knowledge
+cannot be acquired from books, but requires personal inspection, and the
+aid of a teacher. It is well to accustom the eye to know the appearance of
+rocks under the lens. To learn to distinguish felspar from quartz is the
+most important step to be first aimed at. In general we may know the
+felspar because it can be scratched with the point of a knife, whereas the
+quartz, from its extreme hardness, receives no impression. But when these
+two minerals occur in a granular and uncrystallized state, the young
+geologist must not be discouraged if, after considerable practice, he often
+fails to distinguish them by the eye alone. If the felspar is in crystals,
+it is easily recognized by its cleavage: but when in grains the blow-pipe
+must be used, for the edges of the grains can be rounded in the flame,
+whereas those of _quartz_ are infusible. If the geologist is desirous of
+distinguishing the three varieties of felspar above enumerated, or
+hornblende from augite, it will often be necessary to use the reflecting
+goniometer as a test of the angle of cleavage, and shape of the crystal.
+The use of this instrument will not be found difficult.
+
+The external characters and composition of the felspars are extremely
+different from those of augite or hornblende; so that the volcanic rocks in
+which either of these minerals decidedly predominates, are easily
+recognized. But there are mixtures of the two elements in every possible
+proportion, the mass being sometimes exclusively composed of felspar, at
+other times solely of augite, or, again, of both in equal quantities.
+Occasionally, the two extremes, and all the intermediate gradations, may be
+detected in one continuous mass. Nevertheless there are certain varieties
+or compounds which prevail so largely in nature, and preserve so much
+uniformity of aspect and composition, that it is useful in geology to
+regard them as distinct rocks, and to assign names to them, such as basalt,
+greenstone, trachyte, and others, already mentioned.
+
+_Basalt._--As an example of rocks in which augite greatly prevails, basalt
+may first be mentioned. Although we are more familiar with this term than
+with that of any other kind of trap, it is difficult to define it, the name
+having been used so vaguely. It has been very generally applied to any trap
+rock of a black, bluish, or leaden-grey colour, having a uniform and
+compact texture. Most strictly, it consists of an intimate mixture of
+augite, felspar, and iron, to which a mineral of an olive green colour,
+called olivine, is often superadded, in distinct grains or nodular masses.
+The iron is usually magnetic, and is often accompanied by another metal,
+titanium. Augite is the predominant mineral, the felspar being in much
+smaller proportions. There is no doubt that many of the fine-grained and
+dark-coloured trap rocks, called basalt, contained hornblende in the place
+of augite; but this will be deemed of small importance after the remarks
+above made. Other minerals are occasionally found in basalt; and this rock
+may pass insensibly into almost every variety of trap, especially into
+greenstone, clinkstone, and wacké, which will be presently described.
+
+_Greenstone_, or _Dolerite_, is usually defined as a granular rock, the
+constituent parts of which are hornblende and imperfectly crystallized
+felspar; the felspar being more abundant than in basalt; and the grains or
+crystals of the two minerals more distinct from each other. This name may
+also be extended to those rocks in which augite is substituted for
+hornblende (the dolorite of some authors), or to those in which albite
+replaces common felspar, forming the rock sometimes called Andesite.
+
+_Syenitic greenstone._--The highly crystalline compounds of the same two
+minerals, felspar and hornblende, having a granitiform texture, and
+with occasionally some quartz accompanying, may be called Syenitic
+greenstone, a rock which frequently passes into ordinary trap, and
+as frequently into granite.
+
+_Trachyte._--A porphyritic rock of a whitish or greyish colour, composed
+principally of glassy felspar, with crystals of the same, generally with
+some hornblende and some titaniferous iron. In composition it is extremely
+different from basalt, this being a felspathic, as the other is an augitic,
+rock. It has a peculiar rough feel, whence the name +trachys+, _trachus_,
+rough. Some varieties of trachyte contain crystals of quartz.
+
+[Illustration: Fig. 437. Porphyry.
+
+White crystals of felspar in a dark base of hornblende and felspar.]
+
+_Porphyry_ is merely a certain form of rock, 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. 437.). Thus trachyte is porphyritic; for in it, as in many modern
+lavas, there are crystals of felspar; 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.
+
+_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, calcedony, calcareous
+spar, or zeolite, are scattered through a base of wacké, basalt,
+greenstone, or other kind of trap. It derives its name from the Greek word
+_amygdala_, 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.
+
+[Illustration: Fig. 438. Scoriaceous lava in part converted into
+an amygdaloid.
+
+Montagne de la Veille, Department of Puy de Dome, France.]
+
+The annexed figure 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.
+
+_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-felspar is present.
+
+_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, or in consequence of the
+contact with water in or upon the damp soil.
+
+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 rents
+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-felspar.[374-A]
+
+_Trap tuff, volcanic 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
+volcanos, where showers of these materials, together with small pieces
+of other rocks ejected from the crater, 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.
+
+Besides the peculiarity of their composition, some tuffs, or _volcanic
+grits_, as they have been termed, differ from ordinary sandstones by
+the angularity of their grains. When the fragments are coarse, the
+rock is styled a volcanic _breccia_. _Tufaceous conglomerates_ result
+from the intermixture of rolled fragments or pebbles of volcanic and
+other rocks with tuff.
+
+According to Mr. Scrope, the Italian geologists confine the term
+_tuff_, or tufa, to felspathose mixtures, and those composed
+principally of pumice, using the term _peperino_ for the basaltic
+tuffs.[374-B] The peperinos thus distinguished are usually brown,
+and the tuffs grey or white.
+
+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 to cause them to resemble
+many of those kinds of trap which are found in ordinary dikes. The
+chocolate-coloured mud, which was poured for weeks out of the crater of
+Graham's Island, in the Mediterranean, in 1831, must, when unmixed with
+other materials, have constituted a stone heavier than granite. Each cubic
+inch of the impalpable powder which has fallen for days through the
+atmosphere, during some modern eruptions, has been found to weigh, without
+being compressed, as much as ordinary trap rocks, and to be often identical
+with these in mineral composition.
+
+The fusibility of the igneous rocks generally exceeds that of other rocks,
+for there is much alkaline matter and lime in their composition, which
+serves as a flux to the large quantity of silica, which would be otherwise
+so refractory an ingredient.
+
+It is remarkable that, notwithstanding the abundance of this silica,
+quartz, that is, crystalline silica, is usually wanting in the volcanic
+rocks, or is present only as an occasional mineral, like mica. The elements
+of mica, as of quartz, occur in lava and trap; but the circumstances under
+which these rocks are formed are evidently unfavourable to the development
+of mica and quartz, minerals so characteristic of the hypogene formations.
+
+It would be tedious to enumerate all the varieties of trap and lava which
+have been regarded by different observers as sufficiently abundant to
+deserve distinct names, especially as each investigator is too apt to
+exaggerate the importance of local varieties which happen to prevail in
+districts best known to him. It will be useful, however, to subjoin here,
+in the form of a glossary, an alphabetical list of the names and synonyms
+most commonly in use, with brief explanations, to which I have added a
+table of the analysis of the simple minerals most abundant in the volcanic
+and hypogene rocks.
+
+
+_Explanation of the names, synonyms, and mineral composition of the more
+abundant volcanic rocks._
+
+AMPHIBOLITE. _See_ Hornblende rock, amphibole being Haüy's name
+for hornblende.
+
+AMYGDALOID. A particular form of volcanic rock; _see_ p. 372.
+
+AUGITE ROCK. A kind of basalt or greenstone, composed wholly or principally
+of granular augite. (_Leonhard's Mineralreich_, 2d edition, p. 85.)
+
+AUGITIC-PORPHYRY. Crystals of Labrador-felspar and of augite, in a green or
+dark grey base. (_Rose_, _Ann. des Mines_, tom. 8. p. 22. 1835.)
+
+BASALT. Chiefly augite--an intimate mixture of augite and felspar with
+magnetic iron, olivine, &c. _See_ p. 371. The yellowish green mineral
+called olivine, can easily be distinguished from yellowish felspar by
+its infusibility, and having no cleavage. The edges turn brown in the
+flame of the blow-pipe.
+
+BASANITE. Name given by Alex. Brongniart to a rock, having a base of
+basalt, with more or less distinct crystals of augite disseminated
+through it.
+
+CLAYSTONE and CLAYSTONE-PORPHYRY. An earthy and compact stone, usually of a
+purplish colour, like an indurated clay; passes into hornstone; generally
+contains scattered crystals of felspar and sometimes of quartz.
+
+CLINKSTONE. _Syn._ Phonolite, fissile Petrosilex; a greenish or greyish
+rock, having a tendency to divide into slabs and columns; hard, with clean
+fracture, ringing under the hammer; principally composed of compact
+felspar, and, according to Gmelin, of felspar and mesotype. (_Leonhard_,
+_Mineralreich_, p. 102.) A rock much resembling clinkstone, and called by
+some Petrosilex, contains a considerable percentage of quartz and felspar.
+As both trachyte and basalt pass into clinkstone, the rock so called must
+be very various in composition.
+
+COMPACT FELSPAR, which has also been called Petrosilex; the rock so called
+includes the hornstone of some mineralogists, is allied to clinkstone, but
+is harder, more compact, and translucent. It is a varying rock, of which
+the chemical composition is not well defined, and is perhaps the same as
+that of clay. (_MacCulloch's Classification of Rocks_, p. 481.) Dr.
+MacCulloch says, that it contains both potash and soda.
+
+CORNEAN. A variety of claystone allied to hornstone. A fine homogeneous
+paste, supposed to consist of an aggregate of felspar, quartz, and
+hornblende, with occasionally epidote, and perhaps chlorite; it passes into
+compact felspar and hornstone. (_De la Beche_, _Geol. Trans._ second
+series, vol. 2. p. 3.)
+
+DIALLAGE ROCK. _Syn_. Euphotide, Gabbro, and some Ophiolites. Compounded of
+felspar and diallage, sometimes with the addition of serpentine, or mica,
+or quartz. (_MacCulloch. ibid_. p. 648.)
+
+DIORITE. A kind of greenstone, which see. Components, felspar and
+hornblende in grains. According to _Rose_, _Ann. des Mines_, tom. 8. p. 4.,
+_diorite_ consists of albite and hornblende.
+
+DIORITIC-PORPHYRY. A porphyritic greenstone, composed of crystals of albite
+and hornblende, in a greenish or blackish base. (_Rose_, _ibid._ p. 10.)
+
+DOLERITE. Formerly defined as a synonym of greenstone, which see. But,
+according to Rose (_ibid._ p. 32.), its composition is black augite and
+Labrador-felspar; according to Leonhard (_Mineralreich_, &c. p. 77.),
+augite, Labrador-felspar, and magnetic iron.
+
+DOMITE. An earthy _trachyte_, found in the Puy de Dome, in Auvergne.
+
+EUPHOTIDE. A mixture of grains of Labrador-felspar and diallage. (_Rose_,
+_ibid._ p. 19.) According to some, this rock is defined to be a mixture of
+augite or hornblende, and saussurite, a mineral allied to jade. (_Allan's
+Mineralogy_, p. 158.) _See_ Diallage rock.
+
+FELSPAR-PORPHYRY. _Syn._ Hornstone-porphyry; a base of felspar,
+with crystals of felspar, and crystals and grains of quartz. _See_
+also Hornstone.
+
+GABBRO, _see_ Diallage rock.
+
+GREENSTONE. _Syn._ Dolerite and diorite; components, hornblende and
+felspar, or augite and felspar in grains. See above, p. 372.
+
+GREYSTONE. (Graustein of Werner.) Lead grey and greenish rock, composed of
+felspar and augite, the felspar being more than seventy-five per cent.
+(_Scrope_, _Journ. of Sci._ No. 42. p. 221.) Greystone lavas are
+intermediate in composition between basaltic and trachytic lavas.
+
+HORNBLENDE ROCK. A greenstone, composed principally of granular hornblende,
+or augite. (_Leonhard_, _Mineralreich_, &c., p. 85.)
+
+HORNSTONE, HORNSTONE-PORPHYRY. A kind of felspar porphyry (_Leonhard_,
+_ibid._), with a base of hornstone, a mineral approaching near to flint,
+differing from compact felspar in being infusible.
+
+HYPERSTHENE ROCK, a mixture of grains of Labrador-felspar and hypersthene
+(_Rose_, _Ann. des Mines_, tom. 8. p. 13.), having the structure of syenite
+or granite; abundant among the traps of Skye. Some geologists consider it a
+greenstone, in which hypersthene replaces hornblende.
+
+LATERITE. A red jaspery rock, composed of silicate of alumina and oxide of
+iron. Abundant in the Deccan, in India; and referred to the trap formation;
+from Later, a brick or tile.
+
+MELAPHYRE. A variety of black porphyry, the base being black augite with
+crystals of felspar; from +melas+, _melas_, black.
+
+OBSIDIAN. Vitreous lava like melted glass, nearly allied to pitchstone.
+
+OPHIOLITE, sometimes same as Diallage rocks (_Leonhard_, p. 77.); sometimes
+a kind of serpentine.
+
+OPHITE. A green porphyritic rock composed chiefly of hornblende, with
+crystals of that mineral in a base of the same, mixed with some felspar.
+It passes into serpentine by a mixture of talc. (_Burat's d'Aubuisson_,
+tom. ii. p. 63.)
+
+PEARLSTONE. A volcanic rock, having the lustre of mother of pearl;
+usually having a nodular structure; intimately related to obsidian,
+but less glassy.
+
+PEPERINO. A form of volcanic tuff, composed of basaltic scoriæ.
+_See_ p. 374.
+
+PETROSILEX. _See_ Clinkstone and Compact Felspar.
+
+PHONOLITE. _Syn._ of Clinkstone, which see.
+
+PITCHSTONE. Vitreous lava, less glassy than obsidian; a blackish green rock
+resembling glass, having a resinous lustre and appearance of pitch;
+composition various, usually felspar and augite; passes into basalt; occurs
+in veins, and in Arran forms a dike thirty feet wide, cutting through
+sandstone; forms the outer walls of some basaltic dikes.
+
+PORPHYRY. Any rock in which detached crystals of felspar, or of one or more
+minerals, are diffused through a base. _See_ p. 372.
+
+POZZOLANA. A kind of tuff. _See_ p. 36.
+
+PUMICE. A light, spongy, fibrous form of trachyte. _See_ p. 373.
+
+PYROXENIC-PORPHYRY, same as augitic-porphyry, pyroxene being Haüy's
+name for augite.
+
+SCORIÆ. _Syn._ volcanic cinders; reddish brown or black porous form of
+lava. _See_ p. 373.
+
+SERPENTINE. A greenish rock, in which there is much magnesia; usually
+contains diallage, which is nearly allied to the simple mineral called
+serpentine. Occurs sometimes, though rarely, in dikes, altering the
+contiguous strata; is indifferently a member of the trappean or
+hypogene series.
+
+SYENITIC-GREENSTONE; composition, crystals or grains of felspar and
+hornblende. _See_ p. 372.
+
+TEPHRINE, synonymous with lava. Name proposed by Alex. Brongniart.
+
+TOADSTONE. A local name in Derbyshire for a kind of wacké, which see.
+
+TRACHYTE. Chiefly composed of glassy felspar, with crystals of glassy
+felspar. _See_ p. 372.
+
+TRAP TUFF. _See_ p. 374.
+
+TRASS. A kind of tuff or mud poured out by lake craters during eruptions;
+common in the Eifel, in Germany.
+
+TUFACEOUS CONGLOMERATE. _See_ p. 374.
+
+TUFF. _Syn._ Trap-tuff, volcanic tuff. _See_ p. 374.
+
+VITREOUS LAVA. _See_ Pitchstone and Obsidian.
+
+VOLCANIC TUFF. _See_ p. 374.
+
+WACKÉ. A soft and earthy variety of trap, having an argillaceous aspect. It
+resembles indurated clay, and when scratched exhibits a shining streak.
+
+WHINSTONE. A Scotch provincial term for greenstone and other hard
+trap rocks.
+
+
+ANALYSIS OF MINERALS MOST ABUNDANT IN THE VOLCANIC AND HYPOGENE ROCKS.
+
+               Silica.  Alu-   Mag-    Lime.  Pot-  Soda.  Iron.  Manga- Remain-
+                        mina.  nesia.         ash.         Oxide. nese.  der.
+
+  Actinolite     64·      --     22·     --    --     --     3·    a   43·05 C.
+    (Bergman)                                                    trace
+
+  Albite (Rose) 68·84   20·53     --   a trace --    9·12    --    --     --
+  --(mean of 4  69·45   19·44    0·13   0·22   --    9·95    a     --     --
+    analyses)                                              trace
+
+  Augite (Rose) 53·36     --     4·99  22·19   --     --   17·38  0·09    --
+  --(mean of 4  53·57     1·    11·26   20·9   --     --   10·75  0·67    --
+    analyses)
+
+  Carbonate of    --      --      --   56·33   --     --     --    --     --
+    Lime (Biot)
+
+  Chiastolite   68·49   30·17    4·12    --    --     --    2·7    --   0·27 W.
+    (Landgrabe)
+
+  Chlorite       26·     18·5     8·     --    --     2·    43·    --     --
+    (Vauquelin)
+  --(mean of 3  27·43    17·9   14·56   0·50  1·56    --   30·63   --   6·92 W.
+    analyses)
+
+  Diallage       60·      --     27·5    --    --     --    10·5   --     --
+    (Klaproth)
+  --(mean of 3  43·33    2·2    26·41   5·58   --     --   11·53   --   8·54 W.
+    analyses)
+
+  Epidote        37·     21·      --    15·    --     --    24·   1·5     --
+    (Vauquelin)
+
+  Felspar,      62·83   17·02     --    3· -  13·     --     1·    --     --
+    common (Vauq.)
+  --(Rose)      66·75    17·5     --    1·25  12·     --    0·75   --     --
+  --(mean of 7  64·04   18·94     --    0·76 13·66    --    0·74   --     --
+  analyses)
+
+  Garnet        35·75   27·25     --     --    --     --    36·   0·25    --
+    (Klaproth)
+  --(Phillips)   43·     16·      --    20·    --     --    16·    --     --
+
+  Hornblende     42·     12·     2·25   11·    a      --    30·   0·25    --
+    (Klap.)                                  trace
+  --(Bonsdorff.) 45·69   12·18   18·79  13·85  --     --   7·32   0·22  1·5 F.
+
+  Hypersthene   54·25    2·25    14·    1·5    --     --    24·5   a     1· W.
+    (Klaproth)                                                   trace
+
+  Labrador-     55·75    26·5     --    11·    --     4·    1·25   --   0·5 W.
+    felspar (Klap.)
+
+  Leucite       53·75   24·62     --     --  21·35    --     --    --     --
+    (Klap.)
+
+  Mesotype      54·64   19·70     --    1·61   --   15·09    --    --   9·83 W.
+    (Gehlen)
+
+  Mica           42·5    11·5     9·     --   10·     --    22·    2·     --
+    (Klaproth)
+  --(Vauquelin)  50·     35·      --    1·33   --     --     7·    --     --
+  --(mean of 3  45·83   22·58     --     --  11·08    --    14·   1·45    --
+    analyses)
+
+  Olivine        50·      --     38·5    --    --     --    12·    --     --
+    (Klaproth)
+
+  Schorl or     35·48   34·75    4·68    --   0·48   1·75  17·44  1·89  4·02 B.
+    Tourmaline (Gmelin)
+  --(mean of 6  36·03   35·82    4·44   0·28  0·71   1·96  13·71  1·62    --
+    analyses)
+
+  Serpentine    43·07    0·25   40·37   0·5    --     --    1·17   --  12·45 W.
+    (Hisinger)
+  --(mean of 5  37·29    4·97    36·8   2·89   --     --    3·14   --  12·77 W.
+    analyses)
+
+  Steatite       64·      --     22·     --    --     --     3·    --    5· W.
+    (Vauquelin)
+  --(mean of 3   48·3    6·18   26·65    --    --     --     2·    --   9·5 W.
+    anal. by Klap.)
+
+  Talc.         61·75     --     30·5    --   2·75    --    2·5    --     --
+  (Klaproth)
+
+In the last column of the above Table, the letters B. C. F. W. represent
+Boracic acid, Carbonic acid, Fluoric acid, and Water.
+
+
+FOOTNOTES:
+
+[368-A] For a description and theory of active volcanos, see Principles of
+Geology, chaps. xxiv. to xxvii.
+
+[374-A] G. Rose, Ann. des Mines, tom. viii. p. 32.
+
+[374-B] Geol. Trans. vol. ii. p. 211. 2d series.
+
+
+
+
+CHAPTER XXIX.
+
+VOLCANIC ROCKS--_continued_.
+
+   Trap dikes--sometimes project--sometimes leave fissures vacant by
+   decomposition--Branches and veins of trap--Dikes more crystalline in
+   the centre--Foreign fragments of rock imbedded--Strata altered at or
+   near the contact--Obliteration of organic remains--Conversion of chalk
+   into marble--and of coal into coke--Inequality in the modifying
+   influence of dikes--Trap interposed between strata--Columnar and
+   globular structure--Relation of trappean rocks to the products of
+   active volcanos--Submarine lava and ejected matter corresponds
+   generally to ancient trap--Structure and physical features of Palma
+   and some other extinct volcanos.
+
+
+Having in the last chapter spoken of the composition and mineral characters
+of volcanic rocks, I shall next describe the manner and position in which
+they occur in the earth's crust, and their external forms. Now the leading
+varieties, such as basalt, greenstone, trachyte, porphyry, 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.
+
+_Volcanic dikes._--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 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 the annexed figure.[378-A])
+
+[Illustration: Fig. 439. Dike in inland valley, near the Brazen
+Head, Madeira.]
+
+In the islands of Arran, Skye, and 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, as represented in the annexed view (fig. 440.). In these
+instances, the greenstone of the dike is usually more tough and hard than
+the sandstone; but chemical action, and chiefly the oxidation of the iron,
+has given rise to the more rapid decay.
+
+[Illustration: Fig. 440. Fissures left vacant by decomposed trap.
+Strathaird, Skye. (MacCulloch.)]
+
+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.
+
+[Illustration: Fig. 441. Trap veins in Airdnamurchan.]
+
+As fissures sometimes send off branches, or divide into two or more
+fissures of equal size, so also we find trap dikes bifurcating and
+ramifying, and sometimes they are so tortuous as to be called veins, though
+this is more common in granite than in trap. The accompanying sketch (fig.
+441.) by Dr. MacCulloch represents part of a sea-cliff in Argyleshire,
+where an overlying mass of trap, _b_, sends out some veins which terminate
+downwards. Another trap vein, _a a_, cuts through both the limestone, _c_,
+and the trap, _b_.
+
+In fig. 442., 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 5 to 7 feet in width, which
+will afford a scale of measurement for the whole.
+
+[Illustration: Fig. 442. Ground plan of greenstone dike traversing
+sandstone. Arran.]
+
+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 downwards
+in veins or dikes, which probably unite with other masses of igneous
+rock at a greater depth. The largest of the dikes represented in the
+annexed diagram, and which are seen in part of the coast of Skye, is no
+less than 100 feet in width.
+
+[Illustration: Fig. 443. Trap dividing and covering sandstone near
+Suishnish in Skye. (MacCulloch.)]
+
+Every variety of trap-rock is sometimes found in these dikes, as basalt,
+greenstone, felspar-porphyry, and more rarely trachyte. The amygdaloidal
+traps also occur, 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 eruptions 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.
+
+_Dikes more crystalline in the centre._--In many cases trap at the edges or
+sides of a dike is less crystalline or more earthy than in the centre, in
+consequence of the melted matter having cooled more rapidly by coming in
+contact with the cold sides of the fissure; whereas, in the centre, the
+matter of the dike being kept long in a fluid or soft state, the crystals
+are slowly formed. In the ancient part of Vesuvius, called Somma, a thin
+band of half-vitreous lava is found at the edge of some dikes. At the
+junction of greenstone dikes with limestone, a _sahlband_, or selvage, of
+serpentine is occasionally observed.
+
+[Illustration: Fig. 444. Syenitic greenstone dike of Næsodden, Christiania.
+
+_b._ imbedded fragment of crystalline schist surrounded by a band
+of greenstone.]
+
+On the left shore of the fiord of Christiania, in Norway, I examined, in
+company with Professor Keilhau, a remarkable dike of syenitic greenstone,
+which is traced through Silurian strata, until at length, in the promontory
+of Næsodden, it enters mica-schist. Fig. 444. represents a ground plan,
+where the dike appears 8 paces in width. In the middle it is highly
+crystalline and granitiform, of a purplish colour, and containing a few
+crystals of mica, and strongly contrasted with the whitish mica-schist,
+between which and the syenitic rock there is usually on each side a
+distinct black band, 18 inches wide, of dark greenstone. When first seen,
+these bands have the appearance of two accompanying dikes; yet they are, in
+fact, only the different form which the syenitic materials have assumed
+where near to or in contact with the mica-schist. At one point, _a_, one
+of the sahlbands terminates for a space; but near this there is a large
+detached block, _b_, having a gneiss-like structure, consisting of
+hornblende and felspar, which is included in the midst of the dike. Round
+this a smaller encircling zone is seen, of dark basalt, or fine-grained
+greenstone, nearly corresponding to the larger ones which border the dike,
+but only 1 inch wide.
+
+It seems, therefore, evident that the fragment, _b_, has acted on the
+matter of the dike, probably by causing it to cool more rapidly, in the
+same manner as the walls of the fissure have acted on a larger scale. The
+facts, also, illustrate the facility with which a granitiform syenite may
+pass into ordinary rocks of the volcanic family.
+
+[Illustration: Fig. 445. Greenstone dike, with fragments of gneiss.
+Sorgenfri, Christiania.]
+
+The fact above alluded to, of a foreign fragment, such as _b_, fig.
+444., included in the midst of the trap, as if torn off from some
+subjacent rock or the walls of a fissure, is by no means uncommon. A
+fine example is seen in another dike of greenstone, 10 feet wide, in the
+northern suburbs of Christiania, in Norway, of which the annexed figure
+is a ground plan. The dike passes through shale, known by its fossils to
+belong to the Silurian series. In the black base of greenstone are
+angular and roundish pieces of gneiss, some white, others of a light
+flesh-colour, some without lamination, like granite, others with laminæ,
+which, by their various and often opposite directions, show that they
+have been scattered at random through the matrix. These imbedded pieces
+of gneiss measure from 1 to about 8 inches in diameter.
+
+_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 intense heat of melted matter and the entangled gases
+might be expected to cause.
+
+_Plas-Newydd._--A striking example, near Plas-Newydd, in Anglesea, has
+been described by Professor Henslow.[381-A] The dike is 134 feet wide,
+and consists of a rock which is a compound of felspar 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, to 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
+porcellanous 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.[382-A] Some garnets contain
+as much as 20 per cent. of lime, which they may have derived from the
+decomposition of the fossil shells or 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.[382-B]
+
+_Antrim._--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 8 or 10 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 porcellanous
+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."[382-C] All traces of organic remains are effaced in that part of
+the limestone which is most crystalline.
+
+[Illustration: Fig. 446. Basaltic dikes in chalk in island of
+Rathlin, Antrim. Ground plan, as seen on the beach. (Conybeare
+and Buckland.[382-D])]
+
+The annexed drawing (fig. 446.) 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.[382-E] By another, the slate clay of
+the coal measures has been indurated, and has assumed the character of
+flinty slate[383-A]; and in another place the slate clay of the lias
+has been changed into flinty slate, which still retains numerous
+impressions of ammonites.[383-B]
+
+It might have been anticipated that beds of coal would, from their
+combustible nature, be effected 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 9 feet on each side.[383-C]
+
+At Cockfield Fell, in the north of England, a similar change is observed.
+Specimens taken at the distance of about 30 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.[383-D]
+
+As examples might be multiplied without end, I shall merely select one
+or two others, and then conclude. The rock of Stirling Castle is a
+calcareous sandstone, fractured and forcibly displaced by a mass of
+greenstone which has evidently invaded the strata in a melted state. The
+sandstone has been indurated, and has assumed a texture approaching to
+hornstone near the junction. In Arthur's Seat and Salisbury Craig, near
+Edinburgh, a sandstone which comes in contact with greenstone is
+converted into a jaspideous rock.[383-E]
+
+The secondary sandstones in Skye are converted into solid quartz in
+several places, where they come in contact with veins or masses of trap;
+and a bed of quartz, says Dr. MacCulloch, found near a mass of trap,
+among the coal strata of Fife, was in all probability a stratum of
+ordinary sandstone, having been subsequently indurated and turned into
+quartzite by the action of heat.[383-F]
+
+But although strata in the neighbourhood of dikes are thus altered in a
+variety of cases, shale being turned into flinty slate or jasper, limestone
+into crystalline marble, sandstone into quartz, coal into coke, and the
+fossil remains of all such strata wholly and in part obliterated, 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 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 are 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
+caloric supplied by the dike and its gases will act more powerfully.
+
+[Illustration: Fig. 447. Trap interposed between displaced beds
+of limestone and shale, at White Force, High Teesdale, Durham.
+(Sedgwick.[384-A])]
+
+_Intrusion of trap between strata._--In proof of the mechanical force
+which the fluid trap has sometimes exerted on the rocks into which it
+has intruded itself, I may refer to the Whin-Sill, where a mass of
+basalt, from 60 to 80 feet in height, represented by _a_, fig. 447., is
+in part wedged in between the rocks of limestone, _b_, and shale, _c_,
+which have been separated from the great mass of limestone and shale,
+_d_, with which they were united.
+
+The shale in this place is indurated; and the limestone, which at a
+distance from the trap is blue, and contains fossil corals, is here
+converted into granular marble without fossils.
+
+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 was
+caused by gases propelling the lava upwards.
+
+_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 9 feet,
+and those of Morven an inch or less.[385-A] They are usually straight, but
+sometimes curved; and examples of both these occur in the island of Staffa.
+In a horizontal bed or sheet of trap the columns are vertical; in a
+vertical dike they are horizontal. Among other examples of the
+last-mentioned phenomenon is the mass of basalt, called the Chimney, in St.
+Helena (see fig. 448.), a pile of hexagonal prisms, 64 feet high, evidently
+the remainder of a narrow dike, the walls of rock which the dike originally
+traversed having been removed down to the level of the sea. In fig. 449. a
+small portion of this dike is represented on a less reduced scale.[385-B]
+
+[Illustration: Fig. 448. Volcanic dike composed of horizontal prisms.
+St. Helena.]
+
+[Illustration: Fig. 449. Small portion of the dyke in Fig. 448.]
+
+[Illustration: Fig. 450. Lava of La Coupe d'Ayzac, near Antraigue, in the
+province of Ardèche.]
+
+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
+descends and occupies 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. The accompanying sketch (fig. 450.) represents
+the remnant of the lava at one of the points where a lateral torrent joins
+the main valley of the Volant. 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 then horizontal at _f_, their
+position having been every where determined, according to the law before
+mentioned, by the concave form of the original valley.
+
+[Illustration: Fig 451. Columnar basalt in the Vicentin. (Fortis.)]
+
+In the annexed figure (451.) 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.[386-A] Unlike those of the Vivarais, last mentioned, the basalt of
+this country was evidently submarine, and the present valleys have since
+been hollowed out by denudation.
+
+The columnar structure is by no means peculiar to the trap rocks in which
+hornblende or augite predominate; it is also observed in clinkstone,
+trachyte, and other felspathic rocks of the igneous class, although in
+these it is rarely exhibited in such regular polygonal forms.
+
+[Illustration: Fig. 452. Basaltic pillars of the Käsegrotte,
+Bertrich-Baden, half way between Treves and Coblentz. Height of
+grotto, from 7 to 8 feet.]
+
+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. 452.). 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. The position
+of the lava bordering the river in this valley might be represented by a
+section like that already given at fig. 450. p. 385., if we merely supposed
+inclined strata of slate and the argillaceous sandstone called greywacké to
+be substituted for gneiss.
+
+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.
+
+[Illustration: Fig. 453. Globiform pitchstone. Chiaja di Luna, Isle
+of Ponza. (Scrope.)]
+
+A striking example of this structure occurs in 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. 453.). 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."[387-A]
+
+A fissile texture is occasionally assumed by clinkstone and other trap
+rocks, so that they have been used for roofing houses. Sometimes the
+prismatic and slaty structure is found in the same mass. The causes which
+give rise to such arrangements are very obscure, but are supposed to be
+connected with changes of temperature during the cooling of the mass, as
+will be pointed out in the sequel. (See Chaps. XXXV. and XXXVI.)
+
+
+_Relation of Trappean Rocks to the products of active Volcanos._
+
+When we reflect on the changes above described in the strata near their
+contact with trap dikes, and consider how great is the analogy in
+composition and structure of the rocks called trappean and the lavas of
+active volcanos, 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. The trappean rocks first studied
+in the north of Germany, and in Norway, France, Scotland, and other
+countries, were either such as had been formed entirely under deep 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 they 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 downwards 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.
+
+[Illustration: Fig. 454. Strata intersected 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 Chap. VI.); and this fact
+prepares us to expect a similar destruction of whatever may once have
+formed the uppermost part of ancient submarine or subaerial volcanos, 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. 454.), 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 volcanos.
+
+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
+volcanos, 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.
+
+Thus, for example, the recent examination of the igneous rocks of Sicily,
+especially those of the Val di Noto, has proved that all the more ordinary
+varieties of European trap have been there produced under the waters of the
+sea, at a modern period; that is to say, since the Mediterranean has been
+inhabited by a great proportion of the existing species of testacea.
+
+These igneous rocks of the Val di Noto, and the more ancient trappean rocks
+of Scotland and other countries, differ from subaerial volcanic formations
+in being more compact and heavy, and in forming sometimes extensive sheets
+of matter intercalated between marine strata, and sometimes stratified
+conglomerates, of which the rounded pebbles are all trap. They differ also
+in the absence of regular cones and craters, and in the want of conformity
+of the lava to the lowest levels of existing valleys.
+
+It is highly probable, however, that insular cones did exist in some
+parts of the Val di Noto: and that they were removed by the waves, in
+the same manner as the cone of Graham island, in the Mediterranean, was
+swept away in 1831, and that of Nyöe, off Iceland, in 1783.[389-A] All
+that would remain in such cases, after the bed of the sea has been
+upheaved and laid dry, would be dikes and shapeless masses of igneous
+rock, cutting through sheets of lava which may have spread over the
+level bottom of the sea, and strata of tuff, formed of materials first
+scattered far and wide by the winds and waves, and then deposited. Trap
+conglomerates also, to which the action of the waves must give rise
+during the denudation of such volcanic islands, will emerge from the
+deep whenever the bottom of the sea becomes land.
+
+The proportion of volcanic matter which is originally submarine must
+always be very great, as those volcanic vents which are not entirely
+beneath the sea, are almost all of them in islands, or, if on
+continents, near the shore. This may explain why extended sheets of trap
+so often occur, instead of narrow threads, like lava streams. For, a
+multitude of causes tend, near the land, to reduce the bottom of the sea
+to a nearly uniform level,--the sediment of rivers,--materials
+transported by the waves and currents of the sea from wasting
+cliffs,--showers of sand and scoriæ ejected by volcanos, and scattered
+by the wind and waves. When, therefore, lava is poured out on such a
+surface, it will spread far and wide in every direction in a liquid
+sheet, which may afterwards, when raised up, form the tabular capping
+of the land.
+
+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. 373.); 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.[390-A]
+
+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
+volcanos; for they are such in every essential point, although they no
+longer eject fire and smoke."[390-B] 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.[390-C]
+
+Although the principal component minerals of subaerial lavas are the same
+as those of intrusive trap, and both the columnar and globular structure
+are common to both, there are, nevertheless, some volcanic rocks which
+never occur as lava, such as greenstone, clinkstone, the more crystalline
+porphyries, and those traps in which quartz and mica appear as constituent
+parts. In short, the intrusive trap rocks, forming the intermediate step
+between lava and the plutonic rocks, depart in their characters from lava
+in proportion as they approximate to granite.
+
+These views respecting the relations of the volcanic and trap rocks will be
+better understood when the reader has studied, in the 33d chapter, what is
+said of the plutonic formations.
+
+
+FORM, STRUCTURE, AND ORIGIN OF VOLCANIC MOUNTAINS.
+
+The origin of volcanic cones with crater-shaped summits has been alluded to
+in the last chapter (p. 368.), and more fully explained in the "Principles
+of Geology" (chaps. xxiv. to xxvii.), where Vesuvius, Etna, Santorin, and
+Barren Island were 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 volcanos of still higher antiquity.
+
+The island of Palma, for example, one of the Canaries, offers an excellent
+illustration of what, in common with many others, I regard as the ruins of
+a large dome-shaped mass formed by a series of eruptions proceeding from a
+crater at the summit, this crater having been since replaced by a larger
+cavity, the origin of which has afforded geologists an ample field for
+discussion and speculation.
+
+[Illustration: Fig. 455. View of the Isle of Palma, and of the entrance
+into the central cavity or Caldera. From Von Buch's "Canary Islands."]
+
+[Illustration: Fig. 456. Map of the Caldera of Palma and the great
+ravine, called "Barranco de las Angustias." From Survey of Capt.
+Vidal, R.N., 1837.]
+
+Von Buch, in his excellent account of the Canaries, has given us a
+graphic picture of this island, which consists chiefly of a single
+mountain (fig. 455.). This mountain has the general form of a great
+truncated cone, with a huge and deep cavity in the middle, about six
+miles in diameter, called by the inhabitants "the Caldera," or cauldron.
+The range of precipices surrounding the Caldera are no less than 4000
+feet in their average height; at one point, where they are highest, they
+are 7730 feet above the level of the sea. The external flanks of the
+cone incline gently in every direction towards the base of the island,
+and are in part cultivated; but the walls and bottom of the Caldera
+present on all sides rugged and uncultivated rocks, almost completely
+devoid of vegetation. So steep are these walls, that there is no part by
+which they can be descended, and the only entrance is by a great ravine,
+or Barranco, as it is called (see _b b'_, map, fig. 456.), which extends
+from the sea to the interior of the great cavity, and by its jagged,
+broken, and precipitous sides, exhibits to the geologist a transverse
+section of the rocks of which the whole mountain is composed. By this
+means, we learn that the cone is made up of a great number of sloping
+beds, which dip outwards in every direction from the centre of the void
+space, or from the hollow axis of the cone. The beds consist chiefly of
+sheets of basalt, alternating with conglomerates; the materials of the
+latter being in part rounded, as if rolled by water in motion. The
+inclination of all the beds corresponds to that of the external slope of
+the island, being greatest towards the Caldera, and least steep when
+they are nearest the sea. There are a great number of tortuous veins,
+and many dikes of lava or trap, chiefly basaltic, and most of them
+vertical, which cut through the sloping beds laid open to view in the
+great gorge or Barranco. These dikes and veins are more and more
+abundant as we approach the Caldera, being therefore most numerous where
+the slope of the beds is greatest.
+
+Assuming the cone to be a pile of volcanic materials ejected by a long
+succession of eruptions (a point on which all geologists are agreed), we
+have to account for the Caldera and the great Barranco. I conceive that the
+cone itself may be explained, in accordance with what we know of the
+ordinary growth of volcanos[392-A], by supposing most of the eruptions to
+have taken place from one or more central vents, at or near the summit of
+the cone, before it was truncated. From this culminating point, sheets of
+lava flowed down one after the other, and showers of ashes or ejected
+stones. The volcano may, in the earlier stages of its growth, have been in
+great part submerged, like Stromboli, in the sea; and, therefore, some of
+the fragments of rock cast out of its crater may not only have been rolled
+by torrents sweeping down the mountain's side, but have also been rounded
+by the waves of the sea, as we see happen on the beach near Catania, on
+which the modern lavas of Etna are broken up. The increased number of
+dykes, as we approach the axis of the cone, agrees well with the hypothesis
+of the eruptions having been most frequent towards the centre.
+
+There are three known causes or modes of operation, which may have
+conduced towards the vast size of the Caldera. First, the summit of a
+conical mountain may have fallen in, as happened in the case of
+Capacurcu, one of the Andes, according to tradition, in the year 1462,
+and of many other volcanic mountains.[393-A] Sections seem wanting, to
+supply us with all the data required for judging fairly of the
+tenability of this hypothesis. It appears, however, from Captain Vidal's
+survey (see fig. 456.), that a hill of considerable height rises up from
+the bottom of the Caldera, the structure of which, if it be any where
+laid open, might doubtless throw much light on this subject. Secondly,
+an original crater may have been enlarged by a vast gaseous explosion,
+never followed by any subsequent eruption. A serious objection to this
+theory arises from our not finding that the exterior of the cone
+supports a mass of ruins, such as ought to cover it, had so enormous a
+volume of matter, partly made up of the solid contents of the dikes,
+been blown out into the air. In that case, an extensive bed of angular
+fragments of stone, and of fine dust, might be looked for, enveloping
+the entire exterior of the mountain up to the very rim of the Caldera,
+and ought nowhere to be intersected by a dike. The absence of such a
+formation has induced Von Buch to suppose that the missing portion
+of the cone was engulphed. It should, however, be remembered, that
+in existing volcanos, large craters, two or three miles in diameter,
+are sometimes formed by explosions, or by the discharge of great
+volumes of steam.
+
+There is yet another cause to which the extraordinary dimensions of the
+Caldera may, in part at least, be owing; namely, aqueous denudation. Von
+Buch has observed, that the existence of a single deep ravine, like the
+Great Barranco, is a phenomenon common to many extinct volcanos, as well as
+to some active ones. Now, it will be seen by Captain Vidal's map (fig. 456.
+p. 391.), that the sea-cliff at Point Juan Graje, 780 feet high, now
+constituting the coast at the entrance of the great ravine, is continuous
+with an inland cliff which bounds the same ravine on its north-western
+side. No one will dispute that the precipice, at the base of which the
+waves are now beating, owes its origin to the undermining power of the sea.
+It is natural, therefore, to attribute the extension of the same cliff to
+the former action of the waves, exerted at a time when the relative level
+of the island and the ocean were different from what they are now. But if
+the waves and tides had power to remove the rocks once filling a great
+gorge which is 7 miles long, and, in its upper part, 2000 feet deep, can we
+doubt that the same power may have cleared out much of the solid mass now
+missing in the Great Caldera?
+
+The theory advanced to account for the configuration of Palma, commonly
+called the "elevation crater theory," is this. All the alternating masses
+of basalt and conglomerate, intersected in the Barranco, or abruptly cut
+off in the escarpment or walls of the Caldera, were at first disposed in
+horizontal masses on the level floor of the ocean, and traversed, when in
+that position, by all the basaltic dikes which now cut through them. At
+length they were suddenly uplifted by the explosive force of elastic
+vapours, which raised the mass bodily, so as to tilt the beds on all sides
+away from the centre of elevation, causing at the same time an opening at
+the culminating point. Besides many other objections which may be urged
+against this hypothesis, it leaves unexplained the unbroken continuity of
+the rim of the Caldera, which is uninterrupted in all places save
+one[394-A], namely, that where the great gorge or Barranco occurs.
+
+As a more natural way of explaining the phenomenon, the following series of
+events may be imagined. The principal vent, from which a large part of the
+materials of the cone were poured or thrown out, was left empty after the
+last escape of vapour, when the volcano became extinct. We learn from Mr.
+Dana's valuable work on the geology of the United States' Exploring
+Expedition, published in 1849, that two of the principal volcanos of the
+Sandwich Islands, Mounts Loa and Kea in Owyhee, are huge flattened volcanic
+cones, 15,000 feet high (see fig. 457.), each equalling two and a half
+Etnas in their dimensions.
+
+[Illustration: Fig. 457. Mount Loa, in the Sandwich Islands. (Dana)
+
+  _a._ Crater at the summit.
+  _b._ The lateral crater of Kilauea.
+
+The dotted lines indicate a supposed column of solid rock caused by the
+lava consolidating after eruptions.]
+
+From the summits of these lofty though featureless hills, and from vents
+not far below their summits, successive streams of lava, often 2 miles or
+more in width, and sometimes 26 miles long, have flowed. They have been
+poured out one after the other, some of them in recent times, in every
+direction from the apex of the cone, down slopes varying on an average from
+4 degrees to 8 degrees; but at some places considerably steeper.[394-B]
+Sometimes deep rents open on the sides of these cones, which are filled by
+streams of lava passing over them, the liquid matter in such cases probably
+uniting in the fissure with other lava melted in subterranean reservoirs
+below, and thus explaining the origin of one great class of lateral dikes,
+on Etna, Palma, and other cones.
+
+If the flattened domes, such as those here alluded to in the Sandwich
+Islands, instead of being inland, and above water, were situated in
+mid-ocean, like the Island of St. Paul, and for the most part submerged
+(see figs. 458, 459, 460.), and if a gradual upheaval of such a dome should
+then take place, the denuding power of the sea could scarcely fail to play
+an important part in modifying the form of the volcanic mountain as it
+rose. The crater will almost invariably have one side much lower than all
+the others, namely, that side towards which the prevailing winds never
+blow, and to which, therefore, showers of dust and scoriæ are rarely
+carried during eruptions. There will also be one point on this windward or
+lowest side more depressed than all the rest, by which the sea may enter as
+often as the tide rises, or as often as the wind blows from that quarter.
+For the same reason that the sea continues to keep open a single entrance
+into the lagoon of an atoll or annular coral reef, it will not allow this
+passage into the crater to be stopped up, but scour it out, at low tide, or
+as often as the wind changes. The channel, therefore, will always be
+deepened in proportion as the island rises above the level of the sea, at
+the rate perhaps of a few feet or yards in a century.
+
+[Illustration: Fig. 458. Map of the Island of St. Paul, in the Indian
+Ocean, lat. 38° 44´ S., long. 77° 37´ E., surveyed by Capt. Blackwood,
+R.N., 1842.]
+
+[Illustration: Fig. 459. View of the Crater of the Island of St. Paul.]
+
+The island of St. Paul may perhaps be motionless; but if, like many
+other parts of the earth's crust, it should begin to undergo a gradual
+upheaval, or if, as has happened to the shores of the Bay of Baiæ, its
+level should oscillate, with a tendency upon the whole to increased
+elevation, the same power which has cut away part of the cone, and
+caused the cliffs now seen on the north-east side of the island, would
+have power to undermine the walls of the crater, and enlarge its
+diameter, keeping open the channel, by which it enters into it. This
+ravine might be excavated to the depth of 180 feet (the present depth of
+the crater), and its length might be extended to many miles according to
+the size of the submerged part of the cone. The crater is only a mile in
+diameter, and the surrounding cliffs, where loftiest, only 800 feet
+high, so that the size of this cone and crater is insignificant when
+compared to those in the Sandwich Islands, and I have merely selected
+it because it affords an example of a class of insular volcanos, into
+the craters of which the sea now enters by a single passage. The crater
+of Vesuvius in 1822 was 2000 feet deep; and if it were a half submerged
+cone, like St. Paul, the excavating power of the ocean might in
+conjunction with gaseous explosions and co-operating with a gradual
+upheaving force, give rise to a caldera on as grand a scale as
+that exhibited by Palma.
+
+[Illustration: Fig. 460. Side view of the Island of St. Paul (N.E. side).
+Nine-pin rocks two miles distant. (Captain Blackwood.)]
+
+If, after the geographical changes above supposed, the volcanic fires
+long dormant should recover their energy, they might, as in the case of
+Teneriffe, Vesuvius, Santorin, and Barren Island, discharge from the old
+central vent, long sealed up at the bottom of the caldera, new floods of
+lava and clouds of elastic vapours. Should this happen, a new cone will
+be built up in the middle of the cavity or circular bay, formed, partly
+by explosion, partly perhaps by engulphment, and partly by aqueous
+denudation. In the island of Palma this last phase of volcanic activity
+has never occurred; but the subterranean heat is still in full operation
+beneath the Canary Islands, so that we know not what future changes it
+may be destined to undergo.
+
+
+FOOTNOTES:
+
+[378-A] I have been favoured with this drawing by Captain B. Hall.
+
+[381-A] Cambridge Transactions, vol. i. p. 402.
+
+[382-A] Cambridge Trans., vol. i. p. 410.
+
+[382-B] Ibid. vol. ii. p. 175.
+
+[382-C] Dr. Berger, Geol. Trans., 1st series, vol. iii. p. 172.
+
+[382-D] Geol. Trans., 1st series, vol. iii. p. 210. and plate 10.
+
+[382-E] Ibid. p. 201.
+
+[383-A] Geol. Trans., 1st series, vol. iii. p. 205.
+
+[383-B] Ibid. p. 213.; and Playfair, Illust. of Hutt. Theory, p. 253.
+
+[383-C] Geol. Trans., 1st series, vol. iii. p. 206.
+
+[383-D] Sedgwick, Camb. Trans. vol. ii. p. 37.
+
+[383-E] Illust. of Hutt. Theory, § 253. and 261. Dr. MacCulloch, Geol.
+Trans., 1st series, vol. ii. p. 305.
+
+[383-F] Syst. of Geol. vol. i. p. 206.
+
+[384-A] Camb. Trans. vol. ii. p. 180.
+
+[385-A] MacCul. Syst. of Geol. vol. ii. p. 137.
+
+[385-B] Seale's Geognosy of St. Helena, plate 9.
+
+[386-A] Fortis. Mém. sur l'Hist. Nat. de l'Italie, tom. i. p. 233. plate 7.
+
+[387-A] Scrope, Geol. Trans. vol. ii. p. 205. 2d series.
+
+[389-A] See Princ. of Geol., _Index_, "Graham Island," "Nyöe,"
+"Conglomerates, volcanic," &c.
+
+[390-A] MacCulloch, West. Isl., vol. ii. p. 487.
+
+[390-B] Syst. of Geol., vol. ii. p. 114.
+
+[390-C] Ibid.
+
+[392-A] See Principles, chaps. xxiv-xxvii.
+
+[393-A] See Principles, chaps. xxvi. and xxx.; 8th ed. p. 397-475.
+
+[394-A] See Principles of Geol. ch. xxiv. (8th ed. p. 355.).
+
+[394-B] See Lyell on Craters of Denudation, Quart. Geol. Journ.
+vol. vi. p. 232.
+
+
+
+
+CHAPTER XXX.
+
+ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS.
+
+   Tests of relative age of volcanic rocks--Test by superposition and
+   intrusion--Dike of Quarrington Hill, Durham--Test by alteration of
+   rocks in contact--Test by organic remains--Test of age by mineral
+   character--Test by included fragments--Volcanic rocks of the
+   Post-Pliocene period--Basalt of Bay of Trezza in Sicily--Post-Pliocene
+   volcanic rocks near Naples--Dikes of Somma--Igneous formations of the
+   Newer Pliocene period--Val di Noto in Sicily.
+
+
+Having referred the sedimentary strata to a long succession of geological
+periods, we have next 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:--1st, superposition and intrusion, with or without
+alteration of the rocks in contact; 2d, organic remains; 3d, mineral
+character; 4th, included fragments of older rocks.
+
+[Illustration: Fig. 461. Cross section.]
+
+_Tests by superposition, &c._--If a volcanic rock rests upon an aqueous
+deposit, the former 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_ at D in the annexed figure (fig. 461.), 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. 461.), 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 if the stratum _a_ be altered by _b_ at the
+point of contact, we must then conclude the trap to have been intrusive, 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.
+
+We may, however, be easily deceived in supposing a 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 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 strata _d_ or _e_ to have been
+altered at their junction, as if by heat.
+
+[Illustration: Fig. 462. Cross section.]
+
+When trap dikes were described in the preceding chapter, they were shown to
+be more modern than all the strata which they traverse. A basaltic dike at
+Quarrington Hill, near Durham, passes through coal-measures, the strata of
+which are inclined, and shifted so that those on the north side of the dike
+are 24 feet above the level of the corresponding beds on the south side
+(see section, fig. 463.). But the horizontal beds of overlying Red
+Sandstone and Magnesian Limestone are not cut through by the dike. Now here
+the coal-measures were not only deposited, but had subsequently been
+disturbed, fissured, and shifted, before the fluid trap now forming the
+dike was introduced into a rent. It is also clear that some of the upper
+edges of the coal strata, together with the upper part of the dike, had
+been subsequently removed by denudation before the lower New Red Sandstone
+and Magnesian Limestone were superimposed. Even in this case, however,
+although the date of the volcanic eruption is brought within narrow limits,
+it cannot be defined with precision; it may have happened either at the
+close of the Carboniferous period, or early in that of the Lower New Red
+Sandstone, or between these two periods, when the state of the animate
+creation and the physical geography of Europe were gradually changing from
+the type of the Carboniferous era to that of the Permian.
+
+[Illustration: Fig. 463. Section at Quarrington Hill, east of
+Durham. (Sedgwick.)
+
+  _a._ Magnesian Limestone (Permian).
+  _b._ Lower New Red Sandstone.
+  _c._ Coal strata.]
+
+The test of age by superposition is strictly applicable to all stratified
+volcanic tuffs, according to the rules already explained in the case of
+other sedimentary deposits. (See p. 96.)
+
+_Test of age by organic remains._--We have seen how, in the vicinity of
+active volcanos, 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 volcanos now active 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
+such evidence we can distinctly establish the coincidence in age of
+volcanic rocks, and the different primary, secondary, and tertiary
+fossiliferous strata already considered.
+
+The tuffs now alluded to are not exclusively marine, but include, in some
+places, freshwater 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 10 feet, and for a distance of 8 leagues from the crater in a
+southerly direction. Birds, cattle, and wild animals were scorched to death
+in great numbers, and buried in these ashes. Some volcanic dust fell at
+Chiapa, upwards of 1200 miles to windward of the volcano, 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.[399-A]
+
+_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; as in Iceland in 1783, when 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.[399-B]
+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 so much in mineral composition and texture as to render these
+characters of minor importance when compared to their value in the
+chronology of the fossiliferous rocks.
+
+It will, however, be seen in the description which follows, of the European
+trap rocks of different ages, that they had often a peculiar lithological
+character, resembling the differences before remarked as existing between
+the modern lavas of Vesuvius, Etna, and Chili. (See p. 378.)
+
+It has been remarked that 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; but the great mass
+of trachyte occupies in general an inferior position, and is cut through
+and overflowed by basalt. It can by no means be inferred that trachyte
+predominated greatly 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 more felspathic lavas 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 felspathic lavas; thus, for example, hornblende, augite, and olivine
+are each more than three times the weight of water; whereas common felspar,
+albite, and Labrador felspar, have each scarcely more than 2-1/2 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 felspathic lavas and traps. 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
+upwards to the surface by the expansive power of gases. Those materials,
+therefore, which occupied 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 conglomerates almost
+exclusively composed of rolled pebbles of trap, associated with stratified
+rocks in the neighbourhood of masses of intrusive trap. If the pebbles
+agree generally in mineral character with the latter, we are then enabled
+to determine the age of the intrusive rock 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 volcanic islands, or at the base of Etna.
+
+_Post-Pliocene Period (including the Recent)._--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,
+and that they have been ever shifting the places where they have broken out
+at the earth's surface.
+
+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 species of testacea. The southern and
+eastern flanks of Etna are skirted by a fringe of alternating
+sedimentary and volcanic deposits, of submarine origin, as at Adernò,
+Trezza, and other places. Of sixty-five species of fossil shells which I
+procured in 1828 from this formation, near Trezza, it was impossible to
+distinguish any from species now living in the neighbouring sea.
+
+[Illustration: Fig. 464. View of the Isle of Cyclops in the Bay
+of Trezza.[401-A]]
+
+The Cyclopian 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.
+
+The loftiest of the Cyclopian 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. 464.) in
+which the tops of the pillars are weathered, and so rounded as to be often
+hemispherical. In some places in the adjoining and largest islet of the
+group, which lies to the north-eastward of that represented in the drawing
+(fig. 464.), 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.
+
+[Illustration: Fig. 465. Contortions of strata in the largest of
+the Cyclopian Islands.]
+
+In the annexed woodcut (fig. 465.) I have represented a portion of the
+altered rock, a few feet square, where the alternating thin laminæ of sand
+and clay have put on the appearance which we often observe in some of the
+most contorted of the 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. 466.)
+
+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 honeycombed 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.
+
+[Illustration: Fig. 466. Post-Pliocene strata invaded by lava, Isle of
+Cyclops (horizontal section).
+
+  _a._ Lava.
+  _b._ Laminated clay and sand.
+  _c._ The same altered.]
+
+_Post-Pliocene formations near Naples._--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 20 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 was also stated in this work (p. 113.), 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. These
+post-pliocene strata, containing recent marine shells, alternate with
+distinct currents and sheets of lava which were of contemporaneous origin;
+and we find that in Vesuvius itself, the ancient cone called Somma is of
+far greater volume than the modern cone, and is intersected by a far
+greater number of dikes. In contrasting this ancient part of the mountain
+with that of modern date, one principal point of difference is observed;
+namely, the greater frequency in the older cone of fragments of altered
+sedimentary rocks ejected during eruptions. We may easily conceive that the
+first explosions would act with the greatest violence, rending and
+shattering whatever solid masses obstructed the escape of lava and the
+accompanying gases, so that great heaps of ejected pieces of rock would
+naturally occur in the tufaceous breccias formed by the earliest eruptions.
+But when a passage had once been opened, and an habitual vent established,
+the materials thrown out would consist of liquid lava, which would take the
+form of sand and scoriæ, or of angular fragments of such solid lavas as may
+have choked up the vent.
+
+Among the fragments which abound in the tufaceous breccias of Somma, none
+are more common than a saccharoid dolomite, supposed to have been derived
+from an ordinary limestone altered by heat and volcanic vapours.
+
+Carbonate of lime enters into the composition of so many of the simple
+minerals found in Somma, that M. Mitscherlich, with much probability,
+ascribes their great variety to the action of the volcanic heat on
+subjacent masses of limestone.
+
+_Dikes of Somma._--The dikes seen in the great escarpment which Somma
+presents towards the modern cone of Vesuvius are very numerous. They are
+for the most part vertical, and traverse at right angles the beds of
+lava, scoriæ, volcanic breccia, and sand, of which the ancient cone is
+composed. 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 1 to 12 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 half way, and
+a few terminate at both ends, either in a point or abruptly. 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.[404-A] Examples are not
+rare of one dike cutting through another, and in one instance a shift or
+fault is seen at the point of intersection.
+
+In some cases, however, the rents seem to have been filled laterally, when
+the walls of the crater had been broken by star-shaped cracks, as seen in
+the accompanying woodcut (fig. 467.). But the shape of these rents is an
+exception to the general rule; for 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 facts:--"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.
+
+[Illustration: Fig. 467. Dikes or veins at the Punta del Nasone on
+Somma. (Necker.[405-A])]
+
+"These channels, upon examination after an eruption, I have found 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."[405-B]
+
+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 upwards,
+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 texture of the Vesuvian dikes is different at the edges and in the
+middle. Towards the centre, observes M. Necker, the rock is larger
+grained, the component elements being in a far more crystalline state;
+while at the edge the lava is sometimes vitreous, and always finer
+grained. A thin parting band, approaching in its character to
+pitchstone, occasionally intervenes, on the contact of the vertical dike
+and intersected beds. M. Necker mentions one of these at the place
+called Primo Monte, in the Atrio del Cavallo; and when on Somma, in
+1828, I saw three or four others in different parts of the great
+escarpment. These phenomena are in perfect harmony with the results of
+the experiments of Sir James Hall and Mr. Gregory Watt, which have shown
+that a glassy texture is the effect of sudden cooling, and that, on the
+contrary, a crystalline grain is produced where fused minerals are
+allowed to consolidate slowly and tranquilly under high pressure.
+
+It is evident that the central portion of the lava in a fissure would,
+during consolidation, part with its heat more slowly than the sides,
+although the contrast of circumstances would not be so great as when we
+compare the lava at the bottom and at the surface of a current flowing in
+the open air. In this case the uppermost part, where it has been in contact
+with the atmosphere, and where refrigeration has been most rapid, is always
+found to consist of scoriform, vitreous, and porous lava; while at a
+greater depth the mass assumes a more lithoidal structure, and then becomes
+more and more stony as we descend, until at length we are able to recognize
+with a magnifying glass the simple minerals of which the rock is composed.
+On penetrating still deeper, we can detect the constituent parts by the
+naked eye, and in the Vesuvian currents distinct crystals of augite and
+leucite become apparent.
+
+The same phenomenon, observes M. Necker, may readily be exhibited on a
+smaller scale, if we detach a piece of liquid lava from a moving current.
+The fragment cools instantly, and we find the surface covered with a
+vitreous coat; while the interior, although extremely fine-grained, has a
+more stony appearance.
+
+It must, however, be observed, that although the lateral portions of the
+dikes are finer grained than the central, yet the vitreous parting layer
+before alluded to is rare in Vesuvius. This may, perhaps, be accounted for,
+as the above-mentioned author suggests, by the great heat which the walls
+of a fissure may acquire before the fluid mass begins to consolidate, in
+which case the lava, even at the sides, would cool very slowly. Some
+fissures, also, may be filled from above, as frequently happens in the
+volcanos of the Sandwich Islands, according to the observations of Mr.
+Dana; and in this case the refrigeration at the sides would be more rapid
+than when the melted matter flowed upwards from the volcanic foci, in an
+intensely heated state. Mr. Darwin informs me that in St. Helena almost
+every dike has a vitreous selvage.
+
+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.
+
+_Newer Pliocene Period--Val di Noto._--I have already alluded (see p. 150.)
+to the igneous rocks which are associated with a great marine formation of
+limestone, sand, and marl, in the southern part of Sicily, as at Vizzini
+and other places. In this formation, which was shown to belong to the Newer
+Pliocene period, large beds of oysters and corals repose upon lava, and are
+unaltered at the point of contact. In other places we find dikes of igneous
+rock intersecting the fossiliferous beds, and converting the clays into
+siliceous schist, the laminæ being contorted and shivered into innumerable
+fragments at the junction, as near the town of Vizzini.
+
+The volcanic formations of the Val di Noto usually consist of the most
+ordinary variety of basalt, with or without olivine. The rock is sometimes
+compact, often very vesicular. The vesicles are occasionally empty, both in
+dikes and currents, and are in some localities filled with calcareous spar,
+arragonite, and zeolites. The structure is, in some places, spheroidal; in
+others, though rarely, columnar. I found dikes of amygdaloid, wacké, and
+prismatic basalt, intersecting the limestone at the bottom of the hollow
+called Gozzo degli Martiri, below Melilli.
+
+[2 Illustrations: Fig. 468. Fig. 469. Ground-plan of dikes near Palagonia.
+
+  _a._ Lava.
+  _b._ Peperino, consisting of volcanic sand, mixed with fragments of lava
+       and limestone.]
+
+_Dikes._--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 peperino 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. After the melted matter that filled the rent
+in fig. 468. had cooled down, it must have been fractured and shifted
+horizontally by a lateral movement.
+
+In the second figure (fig. 469.), 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.
+
+
+FOOTNOTES:
+
+[399-A] Caldcleugh, Phil. Trans. 1836. p. 27., and Official Documents
+of Nicaragua.
+
+[399-B] See Principles, _Index_, "Skaptar Jokul."
+
+[401-A] This view of the Isle of Cyclops is from an original drawing by my
+friend the late Captain Basil Hall, R. N.
+
+[404-A] Consult the valuable memoir of M. L. A. Necker, Mém. de la Soc. de
+Phys. et d'Hist. Nat. de Génève, tom. ii. part i. Nov. 1822.
+
+[405-A] From a drawing of M. Necker, in Mém. above cited.
+
+[405-B] Phil. Trans., vol. lxx., 1780.
+
+
+
+
+CHAPTER XXXI.
+
+ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS--_continued_.
+
+   Volcanic rocks of the Older Pliocene period--Tuscany--Rome--Volcanic
+   region of Olot in Catalonia--Cones and lava-currents--Ravines and
+   ancient gravel-beds--Jets of air called Bufadors--Age of the
+   Catalonian volcanos--Miocene period--Brown-coal of the Eifel and
+   contemporaneous trachytic breccias--Age of the brown-coal--Peculiar
+   characters of the volcanos of the upper and lower Eifel--Lake
+   craters--Trass--Hungarian volcanos.
+
+
+_Older Pliocene period--Tuscany._--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 Subapennine 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 Subapennine hills
+were in the course of deposition.
+
+_Catalonia._--Geologists are far from being able, as yet, to assign to
+each of the volcanic groups scattered over Europe a precise
+chronological place in the tertiary series; but I shall describe here,
+as probably referable to some part of the Pliocene period, a district of
+extinct volcanos near Olot, in the north of Spain, which is little
+known, and which I visited in the summer of 1830.
+
+The whole extent of country occupied by volcanic products in Catalonia is
+not more than fifteen geographical miles from north to south, and about six
+from east to west. The vents of eruption range entirely within a narrow
+band running north and south; and the branches, which are represented as
+extending eastward in the map, are formed simply of two lava-streams--those
+of Castell Follit and Cellent.
+
+[Illustration: Fig. 470. Volcanic district of Catalonia.]
+
+Dr. Maclure, the American geologist, was the first who made known the
+existence of these volcanos[409-A]; and, according to his description, the
+volcanic region extended over twenty square leagues, from Amer to Massanet.
+I searched in vain in the environs of Massanet, in the Pyrenees, for traces
+of a lava-current; and I can say, with confidence, that the adjoining map
+gives a correct view of the true area of the volcanic action.
+
+_Geological structure of the district._--The eruptions have burst entirely
+through fossiliferous rocks, composed in great part of grey and greenish
+sandstone and conglomerate, with some thick beds of nummulitic limestone.
+The conglomerate contains pebbles of quartz, limestone, and Lydian stone.
+This system of rocks is very extensively spread throughout Catalonia; one
+of its members being a red sandstone, to which the celebrated salt-rock of
+Cardona, usually considered as of the cretaceous era, is subordinate.
+
+Near Amer, in the Valley of the Ter, on the southern borders of the region
+delineated in the map, primary rocks are seen, consisting of gneiss,
+mica-schist, and clay-slate. They run in a line nearly parallel to the
+Pyrenees, and throw off the fossiliferous strata from their flanks, causing
+them to dip to the north and north-west. This dip, which is towards the
+Pyrenees, is connected with a distinct axis of elevation, and prevails
+through the whole area described in the map, the inclination of the beds
+being sometimes at an angle of between 40 and 50 degrees.
+
+It is evident that the physical geography of the country has undergone
+no material change since the commencement of the era of the volcanic
+eruptions, except such as has resulted from the introduction of new
+hills of scoriæ, and currents of lava upon the surface. If the lavas
+could be remelted and poured out again from their respective craters,
+they would descend the same valleys in which they are now seen, and
+re-occupy the spaces which they at present fill. The only difference in
+the external configuration of the fresh lavas would consist in this,
+that they would nowhere be intersected by ravines, or exhibit marks of
+erosion by running water.
+
+_Volcanic cones and lavas._--There are about fourteen distinct cones with
+craters in this part of Spain, besides several points whence lavas may have
+issued; all of them arranged along a narrow line running north and south,
+as will be seen in the map. The greatest number of perfect cones are in the
+immediate neighbourhood of Olot, some of which (Nos. 2, 3. and 5.) are
+represented in the annexed woodcut; and the level plain on which that town
+stands has clearly been produced by the flowing down of many lava-streams
+from those hills into the bottom of a valley, probably once of considerable
+depth, like those of the surrounding country.
+
+[Illustration: Fig. 471. View of the Volcanos around Olot in Catalonia.]
+
+In this drawing an attempt is made to represent, by the shading of the
+landscape, the different geological formations of which the country is
+composed.[410-A] The white line of mountains (No. 1.) in the distance is
+the Pyrenees, which are to the north of the spectator, and consist of
+hypogene and ancient fossiliferous rocks. In front of these are the
+fossiliferous formations (No. 4.) which are in shade. The hills 2, 3. 5.
+are volcanic cones, and the rest of the ground on which the sunshine falls
+is strewed over with volcanic ashes and lava.
+
+The Fluvia, which flows near the town of Olot, has cut to the depth of only
+40 feet through the lavas of the plain before mentioned. The bed of the
+river is hard basalt; and at the bridge of Santa Madalena are seen two
+distinct lava-currents, one above the other, separated by a horizontal bed
+of scoriæ 8 feet thick.
+
+In one place, to the south of Olot, the even surface of the plain is
+broken by a mound of lava, called the "Bosque de Tosca," the upper part
+of which is scoriaceous, and covered with enormous heaps of fragments of
+basalt, more or less porous. Between the numerous hummocks thus formed
+are deep cavities, having the appearance of small craters. The whole
+precisely resembles some of the modern currents of Etna, or that of
+Côme, near Clermont; the last of which, like the Bosque de Tosca,
+supports only a scanty vegetation.
+
+Most of the Catalonian volcanos are as entire as those in the neighbourhood
+of Naples, or on the flanks of Etna. One of these, called Montsacopa (No.
+3. fig. 471.), is of a very regular form, and has a circular depression or
+crater at the summit. It is chiefly made up of red scoriæ,
+undistinguishable from that of the minor cones of Etna. The neighbouring
+hills of Olivet (No. 2.) and Garrinada (No. 5.) are of similar composition
+and shape. The largest crater of the whole district occurs farther to the
+east of Olot, and is called Santa Margarita. It is 455 feet deep, and about
+a mile in circumference. Like Astroni, near Naples, it is richly covered
+with wood, wherein game of various kinds abounds.
+
+[Illustration: Fig. 472. Cross section.
+
+  _a._ Secondary conglomerate.
+  _b._ Thin seams of volcanic sand and scoriæ.]
+
+Although the volcanos of Catalonia have broken out through sandstone,
+shale, and limestone, as have those of the Eifel, in Germany, to be
+described in the sequel, there is a remarkable difference in the nature of
+the ejections composing the cones in these two regions. In the Eifel, the
+quantity of pieces of sandstone and shale thrown out from the vents is
+often so immense as far to exceed in volume the scoriæ, pumice, and lava;
+but I sought in vain in the cones near Olot for a single fragment of any
+extraneous rock; and Don Francisco Bolos, an eminent botanist of Olot,
+informed me that he had never been able to detect any. Volcanic sand and
+ashes are not confined to the cones, but have been sometimes scattered by
+the wind over the country, and drifted into narrow valleys, as is seen
+between Olot and Cellent, where the annexed section (fig. 472.) is exposed.
+The light cindery volcanic matter rests in thin regular layers, just as it
+alighted on the slope formed by the solid conglomerate. No flood could have
+passed through the valley since the scoriæ fell, or these would have been
+for the most part removed.
+
+[Illustration: Fig. 473. Section above the bridge of Cellent.
+
+  _a._ Scoriaceous lava.
+  _b._ Schistose basalt.
+  _c._ Columnar basalt.
+  _d._ Scoria, vegetable soil, and alluvium.
+  _e._ Nummulitic limestone.
+  _.f_ Micaceous grey sandstone.]
+
+The currents of lava in Catalonia, like those of Auvergne, the Vivarais,
+Iceland, and all mountainous countries, are of considerable depth in narrow
+defiles, but spread out into comparatively thin sheets in places where the
+valleys widen. If a river has flowed on nearly level ground, as in the
+great plain near Olot, the water has only excavated a channel of slight
+depth; but where the declivity is great, the stream has cut a deep section,
+sometimes by penetrating directly through the central part of a
+lava-current, but more frequently by passing between the lava and the
+secondary rock which bounds the valley. Thus, in the accompanying section,
+at the bridge of Cellent, six miles east of Olot, we see the lava on one
+side of the small stream; while the inclined stratified rocks constitute
+the channel and opposite bank. The upper part of the lava at that place, as
+is usual in the currents of Etna and Vesuvius, is scoriaceous; farther down
+it becomes less porous, and assumes a spheroidal structure; still lower it
+divides in horizontal plates, each about 2 inches in thickness, and is more
+compact. Lastly, at the bottom is a mass of prismatic basalt about 5 feet
+thick. The vertical columns often rest immediately on the subjacent
+secondary rocks; but there is sometimes an intervention of such sand and
+scoriæ as cover the country during volcanic eruptions, and which when
+unprotected, as here, by superincumbent lava, is washed away from the
+surface of the land. Sometimes, the bed _d_ contains a few pebbles and
+angular fragments of rock; in other places fine earth, which may have
+constituted an ancient vegetable soil.
+
+In several localities, beds of sand and ashes are interposed between the
+lava and subjacent stratified rock, as may be seen if we follow the course
+of the lava-current which descends from Las Planas towards Amer, and stops
+two miles short of that town. The river there has often cut through the
+lava, and through 18 feet of underlying limestone. Occasionally an
+alluvium, several feet thick, is interspersed between the igneous and
+marine formation; and it is interesting to remark that in this, as in other
+beds of pebbles occupying a similar position, there are no rounded
+fragments of lava; whereas in the most modern gravel-beds of rivers of this
+country, volcanic pebbles are abundant.
+
+The deepest excavation made by a river through lava, which I observed in
+this part of Spain, is that seen in the bottom of a valley near San Feliu
+de Palleróls, opposite the Castell de Stolles. The lava there has filled up
+the bottom of a valley, and a narrow ravine has been cut through it to the
+depth of 100 feet. In the lower part the lava has a columnar structure. A
+great number of ages were probably required for the erosion of so deep a
+ravine; but we have no reason to infer that this current is of higher
+antiquity than those of the plain near Olot. The fall of the ground, and
+consequent velocity of the stream, being in this case greater, a more
+considerable volume of rock may have been removed in the same time.
+
+[Illustration: Fig. 474. Section at Castell Follit.
+
+  A. Church and town of Castell Follit, overlooking precipices of basalt.
+  B. Small island, on each side of which branches of the river Teronel flow
+     to meet the Fluvia.
+  _c._ Precipice of basaltic lava, chiefly columnar, about 130 feet
+     in height.
+  _d._ Ancient alluvium, underlying the lava-current.
+  _e._ Inclined strata of secondary sandstone.]
+
+I shall describe one more section to elucidate the phenomena of this
+district. A lava-stream, flowing from a ridge of hills on the east of
+Olot, descends a considerable slope, until it reaches the valley of the
+river Fluvia. Here, for the first time, it comes in contact with running
+water, which has removed a portion, and laid open its internal structure
+in a precipice about 130 feet in height, at the edge of which stands the
+town of Castell Follit.
+
+By the junction of the rivers Fluvia and Teronel, the mass of lava has been
+cut away on two sides; and the insular rock B (fig. 474.) has been left,
+which was probably never so high as the cliff A, as it may have constituted
+the lower part of the sloping side of the original current.
+
+From an examination of the vertical cliffs, it appears that the upper part
+of the lava on which the town is built is scoriaceous, passing downwards
+into a spheroidal basalt; some of the huge spheroids being no less than 6
+feet in diameter. Below this is a more compact basalt, with crystals of
+olivine. There are in all five distinct ranges of basalt, the uppermost
+spheroidal, and the rest prismatic, separated by thinner beds not columnar,
+and some of which are schistose. These were probably formed by successive
+flows of lava, whether during the same eruption or at different periods.
+The whole mass rests on alluvium, ten or twelve feet in thickness, composed
+of pebbles of limestone and quartz, but without any intermixture of igneous
+rocks; in which circumstance alone it appears to differ from the modern
+gravel of the Fluvia.
+
+_Bufadors._--The volcanic rocks near Olot have often a cavernous structure,
+like some of the lavas of Etna; and in many parts of the hill of Batet, in
+the environs of the town, the sound returned by the earth, when struck, is
+like that of an archway. At the base of the same hill are the mouths of
+several subterranean caverns, about twelve in number, which are called in
+the country "bufadors," from which a current of cold air issues during
+summer, but which in winter is said to be scarcely perceptible. I visited
+one of these bufadors in the beginning of August, 1830, when the heat of
+the season was unusually intense, and found a cold wind blowing from it,
+which may easily be explained; for as the external air, when rarefied by
+heat, ascends, the pressure of the colder and heavier air of the caverns in
+the interior of the mountain causes it to rush out to supply its place.
+
+In regard to the age of these Spanish volcanos, attempts have been made
+to prove, that in this country, as well as in Auvergne and the Eifel,
+the earliest inhabitants were eye-witnesses to the volcanic action. In
+the year 1421, it is said, when Olot was destroyed by an earthquake, an
+eruption broke out near Amer, and consumed the town. The researches of
+Don Francisco Bolos have, I think, shown, in the most satisfactory
+manner, that there is no good historical foundation for the latter part
+of this story; and any geologist who has visited Amer must be convinced
+that there never was any eruption on that spot. It is true that, in the
+year above mentioned, the whole of Olot, with the exception of a single
+house, was cast down by an earthquake; one of those shocks which, at
+distant intervals during the last five centuries, have shaken the
+Pyrenees, and particularly the country between Perpignan and Olot, where
+the movements, at the period alluded to, were most violent.
+
+The annihilation of the town may, perhaps, have been due to the cavernous
+nature of the subjacent rocks; for Catalonia is beyond the line of those
+European earthquakes which have, within the period of history, destroyed
+towns throughout extensive areas.
+
+As we have no historical records, then, to guide us in regard to the
+extinct volcanos, we must appeal to geological monuments. The annexed
+diagram will present to the reader, in a synoptical form, the results
+obtained from numerous sections.
+
+The more modern alluvium (_d_) is partial, and has been formed by the
+action of rivers and floods upon the lava; whereas the older gravel (_b_)
+was strewed over the country before the volcanic eruptions. In neither have
+any organic remains been discovered; so that we can merely affirm, as yet,
+that the volcanos broke out after the elevation of some of the newest rocks
+of the nummulitic (Eocene?) series of Catalonia, and before the formation
+of an alluvium (_d_) of unknown date. The integrity of the cones merely
+shows that the country has not been agitated by violent earthquakes, or
+subjected to the action of any great transient flood since their origin.
+
+[Illustration: Fig. 475. Superposition of rocks in the volcanic
+district of Catalonia.
+
+  _a._ Sandstone and nummulitic limestone.
+  _b._ Older alluvium without volcanic pebbles.
+  _c._ Cones of scoriæ and lava.
+  _d._ Newer alluvium.]
+
+East of Olot, on the Catalonian coast, marine tertiary strata occur, which,
+near Barcelona, attain the height of about 500 feet. From the shells which
+I collected, these strata appear to correspond in age with the Subapennine
+beds; and it is not improbable that their upheaval from beneath the sea
+took place during the period of volcanic eruption round Olot. In that case
+these eruptions may have occurred at the close of the Older Pliocene era,
+but perhaps subsequently, for their age is at present quite uncertain.
+
+_Miocene period--Volcanic rocks of the Eifel._--The chronological relations
+of the volcanic rocks of the Lower Rhine and the Eifel are also involved in
+a considerable degree of ambiguity; but we know that some portion of them
+were coeval with the deposition of a tertiary formation, called
+"Brown-Coal" by the Germans, which probably belongs to the Miocene, if not
+referable to the Upper Eocene, epoch.
+
+This Brown-Coal is 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. Its position, and the space occupied by the
+volcanic rocks, both of the Westerwald and Eifel, will be seen by
+referring to the map in the next page (fig. 476.), for which I am
+indebted to Mr. Horner, whose residence in the country has enabled him
+to verify the maps of MM. Noeggerath and Von Oeynhausen, from which that
+now given has been principally compiled.
+
+The Brown-Coal formation consists of beds of loose sand, sandstone, and
+conglomerate, clay with nodules of clay-ironstone, 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.
+
+[Illustration: Fig. 476. Map of the volcanic region of the Upper
+and Lower Eifel.
+
+  ____1____2____3____4____5 English Miles.
+
+  Volcanic District {A. of the Upper Eifel.
+                    {B. of the Lower Eifel.
+  Trachyte.
+  Points of eruption, with craters and scoriæ.
+  Basalt.
+  Brown-coal.
+
+_N.B._ The country in that part of the map which is left blank is composed
+of inclined Silurian and Devonian rocks.]
+
+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 varieties of wood in the lignite are said to belong entirely to
+dicotyledonous trees; but among the impressions of leaves, collected by Mr.
+Horner, some were referred by Mr. Lindley to a palm, perhaps of the genus
+_Chamærops_, and others resembled the _Cinnamomum dulce_, and _Podocarpus
+macrophylla_, which would also indicate a warm climate.[416-A]
+
+The other organic remains of the brown-coal are principally fishes; they
+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 about five species, which M. Agassiz informs me are all
+extinct, and hitherto peculiar to this brown-coal. They belong to the
+freshwater genera _Leuciscus_, _Aspius_, and _Perca_. The remains of frogs
+also, of an 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 several remains of insects.
+
+The brown-coal was evidently a freshwater formation; but fossil shells have
+been scarcely ever found in it; although near Marienforst, in the vicinity
+of Bonn, large blocks have been met with of a white opaque chert,
+containing numerous casts of freshwater shells, which appear to belong to
+_Planorbis rotundatus_ and _Limnea longiscata_, two species common both to
+the Middle and Upper Eocene periods. It is very probable that the
+brown-coal may be connected in age with those fluvio-marine formations
+which are found in higher parts of the valley of the Rhine, as at Mayence
+before mentioned (p. 177.).
+
+A vast deposit of gravel, chiefly composed of pebbles of white quartz, but
+containing also a few fragments of other rocks, lies over the brown-coal
+formation, forming sometimes only a thin covering, at others attaining a
+thickness of more than 100 feet. This gravel is very distinct in character
+from that now forming the bed of the Rhine. It is called "Kiesel gerolle"
+by the Germans, often reaches great elevations, and is covered in several
+places with volcanic ejections. It is evident that the country has
+undergone great changes in its physical geography since this gravel was
+formed; for its position has scarcely any relation to the existing drainage
+of the country, and all the more modern volcanic rocks of the same region
+are posterior to it in date.
+
+Some of the newest beds of volcanic sand, pumice, and scoriæ are
+interstratified near Andernach and elsewhere with the loam called loess,
+which was before described as being full of land and freshwater shells of
+recent species, and referable to the Post-Pliocene period. I have before
+hinted (see p. 118.) that this intercalation of volcanic matter between
+beds of loess may possibly be explained without supposing the last
+eruptions of the Lower Eifel to have taken place so recently as the era of
+the deposition of the loess; but farther researches should be directed to
+the investigation of this curious point.
+
+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 felspar. Trachytic
+tuff is also very abundant. These formations, some of which were certainly
+contemporaneous with the origin of the brown-coal, were the first of a long
+series of eruptions, the more recent of which happened when the country
+had acquired nearly all its present geographical features.
+
+_Newer volcanos of the Eifel.--Lake-craters._--As I recognized in the
+more modern volcanos of the Eifel characters distinct from any
+previously observed by me in those of France, Italy, or Spain, I shall
+briefly describe them. 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 volcanos
+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 fall 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 inwards towards the mountain. When we have ascended to a
+considerable height, we see fragments of scoriæ sparingly scattered over
+the surface; till, at length, on reaching the summit, we find ourselves
+suddenly on the edge of a _tarn_, or deep circular lake-basin.
+
+[Illustration: Fig. 477. The Gemunder Maar.]
+
+[Illustration: Fig. 478. Cross section.
+
+  _a._ Village of Gemund.
+  _b._ Gemunder Maar.
+  _c._ Weinfelder Maar.
+  _d._ Schalkenmehren Maar.]
+
+This, which is called the Gemunder Maar, is the first of three lakes which
+are in immediate contact, the same ridge forming the barrier of two
+neighbouring cavities (see fig. 477.). On viewing the first of these, we
+recognize 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 in opposite directions on every side,
+which we have been accustomed to consider as characteristic of volcanic
+craters. As we proceed, however, to the opposite side of the lake, and
+afterwards visit the craters _c_ and _d_ (fig. 478.), 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.
+
+A few miles to the south of the lakes above mentioned occurs the Pulvermaar
+of Gillenfeld, an oval lake of very regular form, and surrounded by an
+unbroken ridge of fragmentary materials, consisting of ejected shale and
+sandstone, and preserving a uniform height of about 150 feet above the
+water. The side slope in the interior is at an angle of about 45 degrees;
+on the exterior, of 35 degrees. Volcanic substances are intermixed very
+sparingly with the ejections, which in this place entirely conceal from
+view the stratified rocks of the country.[419-A]
+
+[Illustration: Fig. 479. Outline of Mosenberg, Upper Eifel.]
+
+The Meerfelder Maar is a cavity of far greater size and depth, hollowed
+out of similar strata; the sides presenting some abrupt sections of
+inclined secondary rocks, which in other places are buried under vast
+heaps of pulverized shale. I could discover no scoriæ amongst the
+ejected materials, but balls of olivine and other volcanic substances
+are mentioned as having been found.[419-B] This cavity, which we must
+suppose to have discharged an immense volume of gas, is nearly a mile in
+diameter, and is said to be more than one hundred fathoms deep. In the
+neighbourhood is a mountain called the Mosenberg, which consists of red
+sandstone and shale in its lower parts, but supports on its summit a
+triple volcanic cone, while a distinct current of lava is seen
+descending the flanks of the mountain. The edge of the crater of the
+largest cone reminded me much of the form and characters of that of
+Vesuvius; but I was much struck with the precipitous and almost
+overhanging wall or parapet which the scoriæ presented towards the
+exterior, as at _a b_ (fig. 479.); which I can only explain by supposing
+that fragments of red-hot lava, as they fell round the vent, were
+cemented together into one compact mass, in consequence of continuing to
+be in a half-melted state.
+
+If we pass from the Upper to the Lower Eifel, from A to B (see map, p.
+416.), we find the celebrated lake-crater of Laach, which has a greater
+resemblance than any of those before mentioned to the Lago di Bolsena, and
+others in Italy--being surrounded by a ridge of gently sloping hills,
+composed of loose tuffs, scoriæ, and blocks of a variety of lavas.
+
+One of the most interesting volcanos on the left bank of the Rhine is
+called the Roderberg. It forms a circular crater nearly a quarter of a mile
+in diameter, and 100 feet deep, now covered with fields of corn. The highly
+inclined strata of ancient sandstone and shale rise even to the rim of one
+side of the crater; but they are overspread by quartzose gravel, and this
+again is covered by volcanic scoriæ and tufaceous sand. The opposite wall
+of the crater is composed of cinders and scorified rock, like that at the
+summit of Vesuvius. It is quite evident that the eruption in this case
+burst through the sandstone and alluvium which immediately overlies it; and
+I observed some of the quartz pebbles mixed with scoriæ on the flanks of
+the mountain, as if they had been cast up into the air, and had fallen
+again with the volcanic ashes. I have already observed, that a large part
+of this crater has been filled up with loess (p. 118.).
+
+The most striking peculiarity of a great many of the craters above
+described, is the absence of any signs of alteration or torrefaction in
+their walls, when these are composed of regular strata of ancient sandstone
+and shale. It is evident that the summits of hills formed of the
+above-mentioned stratified rocks have, in some cases, been carried away by
+gaseous explosions, while at the same time no lava, and often a very small
+quantity only of scoriæ, has escaped from the newly formed cavity. There
+is, indeed, no feature in the Eifel volcanos more worthy of note, than the
+proofs they afford of very copious aëriform discharges, unaccompanied by
+the pouring out of melted matter, except, here and there, in very
+insignificant volume. I know of no other extinct volcanos 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 outwards on all sides from a central axis, as is assumed in
+the theory of elevation craters, alluded to at the end of Chap. XXIX.
+
+_Trass._--In the Lower Eifel, eruptions of trachytic lava preceded the
+emission of currents of basalt, and immense quantities of pumice were
+thrown out wherever trachyte issued. The tufaceous alluvium called
+_trass_, which has covered large areas in this region 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 this trass was formed during the period
+of volcanic eruptions it may perhaps 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. The
+water might remain for weeks in a state of violent ebullition, until it
+became of the consistency of mud, just as the sea continued to be charged
+with red mud round Graham's Island, in the Mediterranean, in the year 1831.
+If a breach should then 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.
+
+_Hungary._--M. Beudant, in his elaborate work on Hungary, describes five
+distinct groups of volcanic rocks, which although nowhere of great
+extent, form striking features in the physical geography of that
+country, rising as they do abruptly from extensive plains composed of
+tertiary strata. They may have constituted islands in the ancient sea,
+as Santorin and Milo now do in the Grecian Archipelago; and M. Beudant
+has remarked that the mineral products of the last-mentioned islands
+resemble remarkably those of the Hungarian extinct volcanos, where many
+of the same minerals as opal, calcedony, resinous silex (_silex
+resinite_), pearlite, obsidian, and pitchstone abound.
+
+The Hungarian lavas are chiefly felspathic, consisting of different
+varieties of trachyte; many are cellular, and used as millstones; some so
+porous and even scoriform as to resemble those which have issued in the
+open air. Pumice occurs in great quantity; and there are conglomerates, or
+rather breccias, wherein fragments of trachyte are bound together by
+pumiceous tuff, or sometimes by silex.
+
+It is probable that these rocks were permeated by the waters of hot
+springs, impregnated, like the Geysers, with silica; or in some instances,
+perhaps, by aqueous vapours, which, like those of Lancerote, may have
+precipitated hydrate of silica.
+
+By the influence of such springs or vapours the trunks and branches of
+trees washed down during floods, and buried in tuffs on the flanks of the
+mountains, are supposed to have become silicified. It is scarcely possible,
+says M. Beudant, to dig into any of the pumiceous deposits of these
+mountains without meeting with opalized wood, and sometimes entire
+silicified trunks of trees of great size and weight.
+
+It appears from the species of shells collected principally by M. Boué,
+and examined by M. Deshayes, that the fossil remains imbedded in the
+volcanic tuffs, and in strata alternating with them in Hungary, are of
+the Miocene type, and not identical, as was formerly supposed, with the
+fossils of the Paris basin.
+
+
+FOOTNOTES:
+
+[409-A] Maclure, Journ. de Phys., vol. lxvi. p. 219., 1808; cited by
+Daubeny, Description of Volcanos, p. 24.
+
+[410-A] This view is taken from a sketch which I made on the spot in 1830.
+
+[416-A] Trans. of Geol. Soc., 2d series, vol. v.
+
+[419-A] Scrope, Edin. Journ. of Sci., June, 1826, p. 145.
+
+[419-B] Hibbert, Extinct Volcanos of the Rhine, p. 24.
+
+
+
+
+CHAPTER XXXII.
+
+ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS--_continued_.
+
+   Volcanic rocks of the Pliocene and Miocene periods
+   continued--Auvergne--Mont Dor--Breccias and alluviums of Mont Perrier,
+   with bones of quadrupeds--River dammed up by lava-current--Range of
+   minor cones from Auvergne to the Vivarais--Monts Dome--Puy de
+   Côme--Puy de Pariou--Cones not denuded by general flood--Velay--Bones
+   of quadrupeds buried in scoriæ--Cantal--Eocene volcanic rocks--Tuffs
+   near Clermont--Hill of Gergovia--Trap of Cretaceous period--Oolitic
+   period--New Red Sandstone period--Carboniferous period--Old Red
+   Sandstone period--"Rock and Spindle" near St. Andrews--Silurian
+   period--Cambrian volcanic rocks.
+
+
+_Tertiary Volcanic Rocks.--Auvergne._--The extinct volcanos of Auvergne
+and Cantal in Central France seem to have commenced their eruptions in
+the Upper Eocene period, but to have been most active during the 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. 178.).
+
+The earliest monuments of the tertiary period in that region are
+lacustrine deposits of great thickness (2. fig. 480. p. 424.), 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 (3. fig. 480.)
+containing Upper Eocene 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 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 freshwater strata.[422-A] 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, all the
+sides sloping more or less rapidly, until their inclination 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, till
+they reach and spread themselves round the base of the mountain.[423-A]
+Conglomerates, also, composed of angular and rounded fragments of
+igneous rocks, are observed to alternate with the above; and the various
+masses are seen to dip off from the central axis, and to lie parallel to
+the sloping flanks of the mountain.
+
+The summit of Mont Dor terminates in seven or eight rocky peaks, where no
+regular crater can now be traced, but where we may easily imagine one to
+have existed, which may have been shattered by earthquakes, and have
+suffered degradation by aqueous agents. Originally, perhaps, like the
+highest crater of Etna, it may have formed an insignificant feature in the
+great pile, and may frequently have been destroyed and renovated.
+
+According to some geologists, this mountain, as well as Vesuvius, Etna, and
+all large volcanos, has derived its dome-like form not from the
+preponderance of eruptions from one or more central points, but from the
+upheaval of horizontal beds of lava and scoriæ. I have explained my reasons
+for objecting to this view at the close of Chap. XXIX., when speaking of
+Palma, and in the Principles of Geology.[423-B] The average inclination of
+the dome-shaped mass of Mont Dor is 8° 6', whereas in Mounts Loa and Kea,
+before mentioned, in the Sandwich Islands (see fig. 457. p. 394.), the
+flanks of which have been raised by recent lavas, we find from Mr. Dana's
+description that the one has a slope of 6° 30', the other of 7° 46'. We
+may, therefore, reasonably question whether there is any absolute necessity
+for supposing that the basaltic currents of the ancient French volcano were
+at first more horizontal than they are now. Nevertheless it is highly
+probable that during the long series of eruptions required to give rise to
+so vast a pile of volcanic matter, which is thickest at the summit or
+centre of the dome, some dislocation and upheaval took place; and during
+the distension of the mass, beds of lava and scoriæ may, in some places,
+have acquired a greater, in others a less inclination, than that which at
+first belonged to them.
+
+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. We may certainly conclude, that the earliest eruptions were
+posterior in origin to those grits, and conglomerates of the freshwater
+formation of the Limagne, which contain no pebbles of volcanic rocks;
+while, on the other hand, some eruptions took place before the great lakes
+were drained; and others occurred after the desiccation of those lakes, and
+when deep valleys had already been excavated through freshwater strata.
+
+In the annexed section, I have endeavoured to explain the geological
+structure of a portion of Auvergne, which I re-examined in 1843.[423-C] It
+may convey some idea to the reader of the long and complicated series of
+events, which have occurred in that country, since the first lacustrine
+strata (No. 2.) were deposited on the granite (No. 1.). The changes of
+which we have evidence are the more striking, because they imply great
+denudation, without there being any proofs of the intervention of the sea
+during the whole period. It will be seen that the upper freshwater beds
+(No. 3.), once formed in a lake, must have suffered great destruction
+before the excavation of the valleys of the Couze and Allier had begun. In
+these freshwater beds, Upper Eocene fossils, as described in Chap. XV.,
+have been found. The basaltic dike 4' is one of many examples of the
+intrusion of volcanic matter through the Eocene freshwater beds, and may
+have been of Upper Eocene or Miocene date, giving rise, when it reached the
+surface and overflowed, to such platforms of basalt, as often cap the
+tertiary hills in Auvergne, and one of which (4) is seen on Mont Perrier.
+
+[Illustration: Fig. 480. Section from the valley of the Couze at Nechers,
+through Mont Perrier and Issoire to the Valley of the Allier, and the Tour
+de Boulade, Auvergne.
+
+  10. Lava-current of Tartaret near its termination at Nechers.
+   9. Bone-bed, red sandy clay under the lava of Tartaret.
+   8. Bone-bed of the Tour de Boulade.
+   7. Alluvium newer than No. 6.
+   6. Alluvium with bones of hippopotamus.
+   5 _c._ Trachytic breccia resembling 5 _a._
+   5 _b._ Upper bone-bed of Perrier, gravel, &c.
+   5 _a._ Pumiceous breccia and conglomerate, angular masses of trachyte,
+          quartz, pebbles, &c.
+   5. Lower bone-bed of Perrier, ochreous sand and gravel.
+   4 _a._ Basaltic dyke.
+   4. Basaltic platform.
+   3. Upper freshwater beds, limestone, marl, gypsum, &c.
+   2. Lower freshwater formation, red clay, green sand, &c.
+   1. Granite.]
+
+It not unfrequently happens that beds of gravel containing bones of extinct
+mammalia are detected under these very ancient sheets of basalt, as between
+No. 4. and the freshwater strata, No. 3., at A, from which it is clear that
+the surface of 3 formed at that period the lowest level at which the waters
+then draining the country flowed. Next in age to this basaltic platform
+comes a patch of ochreous sand and gravel (No. 5.), containing many bones
+of quadrupeds. Upon this rests a pumiceous breccia and conglomerate, with
+angular masses of trachyte, and some quartz pebbles. This deposit is
+followed by 5 _b_, which is similar to 5, and 5 _c_ similar to the
+trachytic breccia 5 _a_. These two breccias are supposed, from their
+similarity to others found on Mount Dor, to have descended from the flanks
+of that mountain during eruptions; and the interstratified alluvial
+deposits contain the remains of mastodon, rhinoceros, tapir, deer, beaver,
+and quadrupeds of other genera referable to about forty species, all of
+which are extinct. I formerly supposed them to belong to the same era as
+the Miocene faluns of Touraine; but, whether they may not rather be
+ascribed to the older Pliocene epoch is a question which farther inquiries
+and comparisons must determine.
+
+Whatever be their date in the tertiary series, they are quadrupeds which
+inhabited the country when the formations 5 and 5 _c_ originated.
+Probably they were drowned during floods, such as rush down the flanks
+of volcanos during eruptions, when great bodies of steam are emitted
+from the crater, or when, as we have seen, both on Etna and in Iceland
+in modern times, large masses of snow are suddenly melted by lava,
+causing a deluge of water to bear down fragments of igneous rocks mixed
+with mud, to the valleys and plains below.
+
+It will be seen that the valley of the Issoire, down which these ancient
+inundations swept, was first excavated at the expense of the formations
+2, 3, and 4, and then filled up by the masses 5 and 5 _c_, after which
+it was re-excavated before the more modern alluviums (Nos. 6. and 7.)
+were formed. In these again other fossil mammalia of distinct species
+have been detected by M. Bravard, the bones of an hippopotamus having
+been found among the rest.
+
+At length, when the valley of the Allier was eroded at Issoire down to its
+lowest level, a talus of angular fragments of basalt and freshwater
+limestone (No. 8.) was formed, called the bone-bed of the Tour de Boulade,
+from which a great many other mammalia have been collected by MM. Bravard
+and Pomel. In this assemblage the _Elephas primigenius_, _Rhinoceros
+tichorinus_, _Deer_ (including rein-deer), _Equus_, _Bos_, _Antelope_,
+_Felis_, and _Canis_, were included. Even this deposit seems hardly to be
+the newest in the neighbourhood, for if we cross from the town of Issoire
+(see fig. 480.) over Mont Perrier to the adjoining valley of the Couze, we
+find another bone-bed (No. 9.), overlaid by a current of lava (No. 10.).
+
+The history of this lava-current, which terminates a few hundred yards
+below the point No. 10., in the suburbs of the village of Nechers, is
+interesting. It forms a long narrow stripe more than 13 miles in length, at
+the bottom of the valley of the Couze, which flows out of a lake at the
+foot of Mont Dor. This lake is caused by a barrier thrown across the
+ancient channel of the Couze, consisting partly of the volcanic cone called
+the Puy de Tartaret, formed of loose scoriæ, from the base of which has
+issued the lava-current before mentioned. The materials of the dam which
+blocked up the river, and caused the Lac de Chambon, are also, in part,
+derived from a land-slip which may have happened at the time of the great
+eruption which formed the cone.
+
+This cone of Tartaret affords an impressive monument of the very different
+dates at which the igneous eruptions of Auvergne have happened; for it was
+evidently thrown up at the bottom of the existing valley, which is bounded
+by lofty precipices composed of sheets of ancient columnar trachyte and
+basalt, which once flowed at very high levels from Mont Dor.[425-A]
+
+When we follow the course of the river Couze, from its source in the
+lake of Chambon, to the termination of the lava-current at Nechers, a
+distance of thirteen miles, we find that the torrent has in most places
+cut a deep channel through the lava, the lower portion of which is
+columnar. In some narrow gorges it has even had power to remove the
+entire mass of basaltic rock, though the work of erosion must have 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, composed of sand and ashes, 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.
+
+If we now return to the section (fig. 480.), I may observe that the
+lava-current of Tartaret, which has diminished greatly in height and
+volume near its termination, presents here a steep and perpendicular
+face 25 feet in height towards the river. Beneath it is the alluvium No.
+9., consisting of a red sandy clay, which must have covered the bottom
+of the valley when the current of melted rock flowed down. The bones
+found in this alluvium, which I obtained myself, consisted of a species
+of field-mouse, _Arvicola_, and the molar tooth of an extinct horse,
+_Equus fossilis_. The other species, obtained from the same bed, are
+referable to the genera _Sus_, _Bos_, _Cervus_, _Felis_, _Canis_,
+_Martes_, _Talpa_, _Sorex_, _Lepus_, _Sciurus_, _Mus_, and _Lagomys_, in
+all no less than forty-three species, all closely allied to recent
+animals, yet nearly all of them, according to M. Bravard, showing some
+points of difference, like those which Mr. Owen discovered in the case
+of the horse above alluded to. The bones, also, of a frog, snake, and
+lizard, and of several birds, were associated with the fossils before
+enumerated, and several recent land shells, such as _Cyclostoma
+elegans_, _Helix hortensis_, _H. nemoralis_, _H. lapicida_, and
+_Clausilia rugosa_. If the animals were drowned by floods, which
+accompanied the eruptions of the Puy de Tartaret, they would give an
+exceedingly modern geological date to that event, which must, in that
+case, have belonged to the Newer-Pliocene, or, perhaps, the
+Post-Pliocene period. 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 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 14 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.
+
+In Central France there are several hundred minor cones, like that of
+Tartaret, a great number of which, like Monte Nuovo, near Naples, may have
+been principally due to a single eruption. Most of these cones range in a
+linear direction from Auvergne to the Vivarais, and they were faithfully
+described so early as the year 1802, by M. de Montlosier. They have given
+rise chiefly to currents of basaltic lava. Those of Auvergne called the
+Monts Dome, placed on a granitic platform, form an irregular ridge (see
+fig. 436.), about 18 miles in length, and 2 in breadth. They are usually
+truncated at the summit, where the crater is often preserved entire, the
+lava having issued from the base of the hill. But frequently the crater is
+broken down on one side, where the lava has flowed out. The hills are
+composed of loose scoriæ, blocks of lava, lapilli, and pozzuolana, with
+fragments of trachyte and granite.
+
+_Puy de Côme._--The Puy de Côme and its lava-current, near Clermont, may
+be mentioned as one of these minor volcanos. This conical hill rises
+from the granitic platform, at an angle of about 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 50 feet high.[427-A]
+
+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 stationary, its loose materials being
+protected by a dense vegetation, and the hill standing on a ridge not
+commanded by any higher ground whence floods of rain-water may descend.
+
+_Puy Rouge._--At another point, farther down the course of the Sioule,
+we find a second illustration of the same phenomenon in the Puy Rouge, a
+conical hill to the north of the village of Pranal. The cone is composed
+entirely of red and black scoriæ, tuff, and volcanic bombs. On its
+western side there is a worn-down crater, whence a powerful stream of
+lava has issued, and flowed into the valley of the Sioule. The river has
+since excavated a ravine through the lava and subjacent gneiss, to the
+depth of 400 feet.
+
+On the upper part of the precipice forming the left side of this ravine,
+we see a great mass of black and red scoriaceous lava; below this a thin
+bed of gravel, evidently an ancient river-bed, now at an elevation of 50
+feet above the channel of the Sioule. The gravel again rests upon
+gneiss, which has been eroded to the depth of 50 feet. It is quite
+evident in this case, that, while the basalt was gradually undermined
+and carried away by the force of running water, the cone whence the lava
+issued escaped destruction, because it stood upon a platform of gneiss
+several hundred feet above the level of the valley in which the force of
+running water was exerted.
+
+_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 waterspout breaking directly upon the Puy de Pariou
+could carry away a portion of the hill, so long as it is not rent or
+engulphed by earthquakes.
+
+Hence it is conceivable that even those cones which have the freshest
+aspect, and most perfect shape, may lay claim to very high antiquity. Dr.
+Daubeny has justly observed, that had any of these volcanos been in a state
+of activity in the age of Julius Cæsar, that general, who encamped upon the
+plains of Auvergne, and laid siege to its principal city (Gergovia, near
+Clermont), could hardly have failed to notice them. Had there been any
+record of their eruptions in the time of Pliny or Sidonius Apollinaris, the
+one would scarcely have omitted to make mention of it in his Natural
+History, nor the other to introduce some allusion to it among the
+descriptions of this his native province. This poet's residence was on the
+borders of the Lake Aidat, which owed its very existence to the damming up
+of a river by one of the most modern lava-currents.[428-A]
+
+_Velay._--The observations of M. Bertrand de Doue have not yet established
+that any of the most ancient volcanos of Velay were in action during the
+Eocene period. There are beds of gravel in Velay, as in Auvergne, covered
+by lava at different heights above the channels of the existing rivers. In
+the highest and most ancient of these alluviums the pebbles are exclusively
+of granitic rocks; but in the newer, which are found at lower levels, and
+which originated when the valleys had been cut to a greater depth, an
+intermixture of volcanic rocks has been observed.
+
+At St. Privat d'Allier a bed of volcanic scoriæ and tuff was discovered
+by Dr. Hibbert, inclosed between two sheets of basaltic lava; and in
+this tuff were found the bones of several quadrupeds, some of them
+adhering to masses of slaggy lava. Among other animals were _Rhinoceros
+leptorhinus_, _Hyæna spelæa_, and a species allied to the spotted hyæna
+of the Cape, together with four undetermined species of deer.[428-B] The
+manner of the occurrence of these bones reminds us of the published
+accounts of an eruption of Coseguina, 1835, in Central America (see p.
+399.), during which hot cinders and scoriæ fell and scorched to death
+great numbers of wild and domestic animals and birds.
+
+_Plomb du Cantal._--In regard to the age of the igneous rocks of the
+Cantal, we can at present merely affirm, that they overlie the Eocene
+lacustrine strata of that country (see Map, p. 179.). They form a great
+dome-shaped mass, having an average slope of only 4°, which has evidently
+been accumulated, like the cone of Etna, during a long series of eruptions.
+It is composed of trachytic, phonolitic, and basaltic lavas, tuffs, and
+conglomerates, or breccias, forming a mountain several thousand feet in
+height. Dikes also of phonolite, trachyte, and basalt are numerous,
+especially in the neighbourhood of the large cavity, probably once a
+crater, around which the loftiest summits of the Cantal are ranged
+circularly, few of them, except the Plomb du Cantal, rising far above the
+border or ridge of this supposed crater. A pyramidal hill, called the Puy
+Griou, occupies the middle of the cavity.[429-A] It is clear that the
+volcano of the Cantal broke out precisely on the site of the lacustrine
+deposit before described (p. 188.), which had accumulated in a depression
+of a tract composed of micaceous schist. In the breccias, even to the very
+summit of the mountain, we find ejected masses of the freshwater beds, and
+sometimes fragments of flint, containing Eocene shells. Valleys radiate in
+all directions from the central heights of the mountain, increasing in size
+as they recede from those heights. Those of the Cer and Jourdanne, which
+are more than 20 miles in length, are of great depth, and lay open the
+geological structure of the mountain. No alternation of lavas with
+undisturbed Eocene strata has been observed, nor any tuffs containing
+freshwater shells, although some of these tuffs include fossil remains of
+terrestrial plants, said to imply several distinct restorations of the
+vegetation of the mountain in the intervals between great eruptions. On the
+northern side of the Plomb du Cantal, at La Vissiere, near Murat, is a
+spot, pointed out on the Map (p. 179.), where freshwater limestone and marl
+are seen covered by a thickness of about 800 feet of volcanic rock. Shifts
+are here seen in the strata of limestone and marl.[429-B]
+
+_Eocene period._--In treating of the lacustrine deposits of Central
+France, in the fifteenth chapter, it was stated that, in the arenaceous
+and pebbly group of the lacustrine basins of Auvergne, Cantal, and
+Velay, no volcanic pebbles had ever been detected, although massive
+piles of igneous rocks are now found in the immediate vicinity. As this
+observation has been confirmed by minute research, we are warranted in
+inferring that the volcanic eruptions had not commenced when the older
+subdivisions of the freshwater groups originated.
+
+In Cantal and Velay no decisive proofs have yet been brought to light that
+any of the igneous outbursts happened during the deposition of the
+freshwater strata; but there can be no doubt that in Auvergne some volcanic
+explosions took place before the drainage of the lakes, and at a time when
+the Upper Eocene species of animals and plants still flourished. Thus, for
+example, at Pont du Chateau, near Clermont, a section is seen in a
+precipice on the right bank of the river Allier, in which beds of volcanic
+tuff alternate with a freshwater limestone, which is in some places pure,
+but in others spotted with fragments of volcanic matter, as if it were
+deposited while showers of sand and scoriæ were projected from a
+neighbouring vent.[430-A]
+
+Another example occurs in the Puy de Marmont, near Veyres, where a
+freshwater marl alternates with volcanic tuff containing Eocene shells. The
+tuff or breccia in this locality is precisely such as is known to result
+from volcanic ashes falling into water, and subsiding together with ejected
+fragments of marl and other stratified rocks. These tuffs and marls are
+highly inclined, and traversed by a thick vein of basalt, which, as it
+rises in the hill, divides into two branches.
+
+_Gergovia._--The hill of Gergovia, near Clermont, affords a third example.
+I agree with MM. Dufrénoy and Jobert that there is no alternation here of a
+contemporaneous sheet of lava with freshwater strata, in the manner
+supposed by some other observers[430-B]; but the position and contents of
+some of the associated tuffs, prove them to have been derived from volcanic
+eruptions which occurred during the deposition of the lacustrine strata.
+
+[Illustration: Fig. 481. Hill of Gergovia.]
+
+The bottom of the hill consists of slightly inclined beds of white and
+greenish marls, more than 300 feet in thickness, intersected by a dike of
+basalt, which may be studied in the ravine above the village of Merdogne.
+The dike here cuts through the marly strata at a considerable angle,
+producing, in general, great alteration and confusion in them for some
+distance from the point of contact. Above the white and green marls, a
+series of beds of limestone and marl, containing freshwater shells, are
+seen to alternate with volcanic tuff. In the lowest part of this division,
+beds of pure marl alternate with compact fissile tuff, resembling some of
+the subaqueous tuffs of Italy and Sicily called _peperinos_. Occasionally
+fragments of scoriæ are visible in this rock. Still higher is seen another
+group of some thickness, consisting exclusively of tuff, upon which lie
+other marly strata intermixed with volcanic matter. Among the species of
+fossil shells which I found in these strata were _Melania inquinata_, a
+_Unio_, and a _Melanopsis_, but they were not sufficient to enable me to
+determine with precision the age of the formation.
+
+There are many points in Auvergne where igneous rocks have been forced by
+subsequent injection through clays and marly limestones, in such a manner
+that the whole has become blended in one confused and brecciated mass,
+between which and the basalt there is sometimes no very distinct line of
+demarcation. In the cavities of such mixed rocks we often find calcedony,
+and crystals of mesotype, stilbite, and arragonite. To formations of this
+class may belong some of the breccias immediately adjoining the dike in the
+hill of Gergovia; but it cannot be contended that the volcanic sand and
+scoriæ interstratified with the marls and limestones in the upper part of
+that hill were introduced, like the dike, subsequently, by intrusion from
+below. They must have been thrown down like sediment from water, and can
+only have resulted from igneous action, which was going on
+contemporaneously with the deposition of the lacustrine strata.
+
+The reader will bear in mind that this conclusion agrees well with the
+proofs, adverted to in the fifteenth chapter, of the abundance of silex,
+travertin, and gypsum precipitated when the upper lacustrine strata were
+formed; for these rocks are such as the waters of mineral and thermal
+springs might generate.
+
+_Cretaceous period._--Although we have no proof of volcanic rocks
+erupted in England during the deposition of the chalk and greensand, it
+would be an error to suppose that no theatres of igneous action existed
+in the cretaceous period. M. Virlet, in his account of the geology of
+the Morea, p. 205., has clearly shown that certain traps in Greece,
+called by him ophiolites, are of this 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 ophiolite, 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[431-A]; and it is probable, that a large part of the
+trappean masses, called ophiolites in the Apennines, and associated with
+the limestone of that chain, are of corresponding age.
+
+That part of the volcanic rocks of the Hebrides, in our own country,
+originated contemporaneously with the Oolite which they traverse and
+overlie, has been ascertained by Prof. E. Forbes, in 1850.
+
+_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.[432-A]
+
+_Carboniferous period._--Two classes of contemporaneous trap rocks have
+been ascertained by Dr. Fleming to 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, wacké, 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 ironstone 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. At one spot, about two miles from St. Andrews, the
+encroachment of the sea on the cliffs has isolated several masses of trap,
+one of which (fig. 482.) is aptly called the "rock and spindle,"[432-B] for
+it consists of a pinnacle of tuff, which may be compared to a distaff, and
+near the base is a mass of columnar greenstone, in which the pillars
+radiate from a centre, and appear at a distance like the spokes of a wheel.
+The largest diameter of this wheel is about twelve feet, and the polygonal
+terminations of the columns are seen round the circumference (or tire, as
+it were, of the wheel), as in the accompanying figure. I conceive this mass
+to be the extremity of a string or vein of greenstone, which penetrated the
+tuff. The prisms point in every direction, because they were surrounded on
+all sides by cooling surfaces, to which they always, arrange themselves at
+right angles, as before explained (p. 385.).
+
+[Illustration: Fig. 482. Rock and Spindle, St. Andrews.
+
+  _a._ Unstratified tuff.
+  _b._ Columnar greenstone.
+  _c._ Stratified tuff.]
+
+[Illustration: Fig. 483. Columns of Greenstone, seen endwise.]
+
+A trap dike was pointed out to me by Dr. Fleming, in the parish of Flisk,
+in the northern part of Fifeshire, which cuts through the grey sandstone
+and shale, forming the lowest part of the Old Red Sandstone. It may be
+traced for many miles, passing through the amygdaloidal and other traps of
+the hill called Normans Law. 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, finds the rock, which he calls dolerite, to consist
+of greenish black augite and Labrador felspar, 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.
+
+_Trap of the Old Red sandstone period._--By referring to the section
+explanatory of the structure of Forfarshire, already given (p. 48.), 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 quartz rocks,
+sometimes exclusively of different varieties of trap, which, although
+purposely omitted in the above section, are often found either intruding
+themselves 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 felspathic porphyry and
+amygdaloid, the kernels of the latter being sometimes calcareous, often
+calcedonic, and forming beautiful agates. We meet also with claystone,
+clinkstone, greenstone, compact felspar, and tuff. Some of these rocks
+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 section, p. 48.), 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.
+
+_Silurian period._--It appears from the investigations of Sir R.
+Murchison in Shropshire, that when the lower Silurian strata of that
+county 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.[435-A]
+
+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 felspar
+rock, the beds being traversed by joints like those in the associated
+sandstone, limestone, and shale, and having the same strike and dip.[435-B]
+
+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 felspar-porphyry, clinkstone, and other
+varieties; and the interposed Llandeilo flags are of sandstone and shale,
+with trilobites and graptolites.[435-C]
+
+The vast thickness of contemporaneous trappean rocks of lower Silurian
+date in North Wales, explored by our government surveyors, has been
+already alluded to.[435-D]
+
+_Cambrian volcanic rocks._--Professor Sedgwick, in his account of the
+geology of Cumberland, has described various trap rocks which accompany the
+green slates of the Cambrian system, beneath all the rocks containing
+organic remains. Different felspathic and porphyritic rocks and greenstones
+occur, not only in dikes, but in conformable beds; and there is
+occasionally a passage from these igneous rocks to some of the green
+quartzose slates. Professor Sedgwick supposes these porphyries to have
+originated contemporaneously with the stratified chloritic slates, the
+materials of the slates having been supplied, in part at least, by
+submarine eruptions oftentimes repeated.[435-E]
+
+
+FOOTNOTES:
+
+[422-A] See the map, p. 179.
+
+[423-A] Scrope's Central France, p. 98.
+
+[423-B] See chaps. xxiv., xxv., and xxvi., 7th and 8th editions.
+
+[423-C] See Quarterly Geol. Journ., vol. ii. p. 77.
+
+[425-A] For a view of Puy de Tartaret and Mont Dor, see Scrope's Volcanos
+of Central France.
+
+[427-A] Scrope's Central France, p. 60., and plate.
+
+[428-A] Daubeny on Volcanos, p. 14.
+
+[428-B] Edin. Journ. of Sci., No. iv. N. S. p. 276. Figures of some
+of these remains are given by M. Bertrand de Doue, Ann. De la Soc.
+d'Agricult. de Puy, 1828.
+
+[429-A] Mém. de la Soc. Géol. de France, tom. i. p. 175.
+
+[429-B] See Lyell and Murchison, Ann. de Sci. Nat., Oct. 1829.
+
+[430-A] See Scrope's Central France, p. 21.
+
+[430-B] Ibid, p. 7.
+
+[431-A] Boblaye and Virlet, Morea, p. 23.
+
+[432-A] De la Beche, Geol. Proceedings, No. 41. p. 196.
+
+[432-B] "The rock," as English readers of Burn's poems may remember, is a
+Scotch term for distaff.
+
+[435-A] Murchison, Silurian System, &c. p. 230.
+
+[435-B] Ibid., p. 272.
+
+[435-C] Ibid., p. 325.
+
+[435-D] Chap. XXVII. p. 356.
+
+[435-E] Geol. Trans., 2d series, vol. iv. p. 55.
+
+
+
+
+CHAPTER XXXIII.
+
+PLUTONIC ROCKS--GRANITE.
+
+   General aspect of granite--Decomposing into spherical masses--Rude
+   columnar structure--Analogy and difference of volcanic and plutonic
+   formations--Minerals in granite, and their arrangement--Graphic and
+   porphyritic granite--Mutual penetration of crystals of quartz and
+   felspar--Occasional minerals--Syenite--Syenitic, talcose, and schorly
+   granites--Eurite--Passage of granite into trap--Examples near
+   Christiania and in Aberdeenshire--Analogy in composition of trachyte
+   and granite--Granite veins in Glen Tilt, Cornwall, the Valorsine, and
+   other countries--Different composition of veins from main body of
+   granite--Metalliferous veins in strata near their junction with
+   granite--Apparent isolation of nodules of granite--Quartz
+   veins--Whether plutonic rocks are ever overlying--Their exposure 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, 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. 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 crystallized 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
+downwards 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.
+
+By some writers, all the rocks now under consideration have been
+comprehended under the name of granite, which is, then, understood to
+embrace a large family of crystalline and compound rocks, usually found
+underlying all other formations; whereas we have seen that trap very
+commonly overlies strata of different ages. 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 the annexed figure, 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.
+
+[Illustration: Fig. 484. Mass of granite near the Sharp Tor, Cornwall.]
+
+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 figure.)
+
+[Illustration: Fig. 485. Granite having a cuboidal and rude columnar
+structure, Land's End, Cornwall.]
+
+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. They also
+differ in never being scoriaceous or amygdaloidal, and never forming a
+porphyry with an uncrystalline base, or alternating with tuffs. Nor do they
+form conglomerates, although there is sometimes an insensible passage from
+a fine to a coarse-grained granite, and occasionally patches of a fine
+texture are imbedded in a coarser variety.
+
+[Illustration: Fig. 486. Gneiss. (See description, p. 464.)]
+
+Felspar, quartz, and mica are usually considered as the minerals essential
+to granite, the felspar being most abundant in quantity, and the proportion
+of quartz exceeding that of mica. These minerals are united in what is
+termed a confused crystallization; that is to say, there is no regular
+arrangement of the crystals in granite, as in gneiss (see fig. 486.),
+except in the variety termed graphic granite, which occurs mostly in
+granitic veins. This variety is a compound of felspar and quartz, so
+arranged as to produce an imperfect laminar structure. The crystals of
+felspar 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 felspar and quartz,
+presents broken lines, which have been compared to Hebrew characters.
+
+[2 Illustrations: Graphic granite.
+
+Fig. 487. Section parallel to the laminæ.
+
+Fig. 488. 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 felspar and mica have
+crystallized; 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 felspar, 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 granitic 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; and M. E. de Beaumont suggests, that electric action may
+prolong the duration of the viscosity of silex. Occasionally, however, we
+find the quartz and felspar mutually imprinting their forms on each other,
+affording evidence of the simultaneous crystallization of both.[439-A]
+
+[Illustration: Fig. 489. Porphyritic granite. Land's End, Cornwall.]
+
+_Porphyritic granite._--This name has been sometimes given to that variety
+in which large crystals of felspar, sometimes more than 3 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.
+489.). The two larger prismatic crystals in this drawing represent felspar,
+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 felspar 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 crystallized 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 variation may be traced in the ever-varying
+proportions of the felspar, quartz, and mica.
+
+_Syenite._--When hornblende is the substitute for mica, which is very
+commonly the case, the rock becomes Syenite: so called from the celebrated
+ancient quarries of Syene in Egypt. It has all the appearance of ordinary
+granite, except when mineralogically examined in hand specimens, and is
+fully entitled to rank as a geological member of the same plutonic family
+as granite. Syenite, however, after maintaining the granitic character
+throughout extensive regions, is not uncommonly found to lose its quartz,
+and to pass insensibly into syenitic greenstone, a rock of the trap family.
+Werner considered syenite as a binary compound of felspar and hornblende,
+and regarded quartz as merely one of its occasional minerals.
+
+_Syenitic-granite._--The quadruple compound of quartz, felspar, mica, and
+hornblende, may be so termed. This rock occurs in Scotland and in Guernsey.
+
+_Talcose granite_, or Protogine of the French, is a mixture of felspar,
+quartz, and talc. It abounds in the Alps, and in some parts of Cornwall,
+producing by its decomposition the china clay, more than 12,000 tons of
+which are annually exported from that country for the potteries.[440-A]
+
+_Schorl rock, and schorly granite._--The former of these is an aggregate
+of schorl, or tourmaline, and quartz. When felspar and mica are also
+present, it may be called schorly granite. This kind of granite is
+comparatively rare.
+
+_Eurite._--A rock in which all the ingredients of granite are blended into
+a finely granular mass. Crystals of quartz and mica are sometimes scattered
+through the base of Eurite.
+
+_Pegmatite._--A name given by French writers to a variety of granite; a
+granular mixture of quartz and felspar; frequent in granite veins; passes
+into graphic granite.
+
+All these granites 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.
+
+The minerals which constitute alike the granitic and volcanic rocks
+consist, almost exclusively, of seven elements, namely, silica, alumina,
+magnesia, lime, soda, potash, and iron; and these may sometimes exist in
+about the same proportions in a porous lava, a compact trap, or a
+crystalline granite. It may perhaps be found, on farther examination--for
+on this subject we have yet much to learn--that the presence of these
+elements in certain proportions is more favourable than in others to their
+assuming a crystalline or true granitic structure; but it is also
+ascertained by experiment, that the same materials may, under different
+circumstances, form very different rocks. 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; and some trachytes and
+syenitic-greenstones may doubtless form granite and syenite, if the
+crystallization take place slowly.
+
+It has also been suggested that the peculiar nature and structure of
+granite may be due to its retaining in it that water which is seen to
+escape from lavas when they cool slowly, and consolidate in the atmosphere.
+Boutigny's experiments have shown that melted matter, at a white heat,
+requires to have its temperature lowered before it can vapourize water; and
+such discoveries, if they fail to explain the manner in which granites have
+been formed, serve at least to remind us of the entire distinctness of the
+conditions under which plutonic and volcanic rocks must be produced.[441-A]
+
+It would be easy to multiply examples and authorities to prove the
+gradation of the granitic 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 volcanic to the plutonic rock being so
+gradual that it is impossible to draw a line of demarcation between them.
+
+"The ordinary granite of Aberdeenshire," says Dr. MacCulloch, "is the usual
+ternary compound of quartz, felspar, and mica; but sometimes hornblende is
+substituted for the mica. But in many places a variety occurs which is
+composed simply of felspar 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."[441-B] The same author mentions, that in Shetland, a
+granite composed of hornblende, mica, felspar, and quartz, graduates in an
+equally perfect manner into basalt.[441-C]
+
+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 felspar and hornblende. It is easy to conceive
+how such volcanic masses may, at a certain depth from the surface, pass
+downwards into granite.
+
+[2 Illustrations: Fig. 490. Fig. 491.
+
+Junction of granite and argillaceous schist in Glen Tilt.
+(MacCulloch.)[442-A]]
+
+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. 490.; but the union
+is as represented in fig. 491., the undulating outline of the granite
+intersecting different strata, and occasionally intruding itself in
+tortuous 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, effervescing feebly with acids.
+
+The annexed diagram (fig. 492.) represents another junction, in the same
+district, where the granite sends forth so many veins as to reticulate the
+limestone and schist, the veins diminishing towards their termination to
+the thickness of a leaf of paper or a thread. In some places fragments of
+granite appear entangled, as it were, in the limestone, and are not visibly
+connected with any larger mass; while sometimes, on the other hand, a lump
+of the limestone is found in the midst of the granite. The ordinary colour
+of the limestone of Glen Tilt is lead blue, and its texture large-grained
+and highly crystalline; but where it approximates to the granite,
+particularly where it is penetrated by the smaller veins, the crystalline
+texture disappears, and it assumes an appearance exactly resembling that of
+hornstone. The associated argillaceous schist often passes into hornblende
+slate, where it approaches very near to the granite.[442-B]
+
+[Illustration: Fig. 492. Junction of granite and limestone in Glen
+Tilt. (MacCulloch.)
+
+  _a._ Granite. _b._ Limestone.
+  _c._ Blue argillaceous schist.]
+
+The conversion of the limestone in 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 felspar 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.
+
+[Illustration: Fig. 493. Granite veins traversing clay slate. Table
+Mountain, Cape of Good Hope.[443-A]]
+
+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 the annexed drawings will show.
+
+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, felspar, 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.[444-A]
+
+[Illustration: Fig. 494. Granite veins traversing gneiss, Cape Wrath.
+(MacCulloch.)[444-B]]
+
+[Illustration: Fig. 495. Granite veins traversing gneiss at Cape Wrath, in
+Scotland. (MacCulloch.)]
+
+The accompanying sketches will explain the manner in which granite veins
+often ramify and cut each other (figs. 494. and 495.). They represent
+the manner in which the gneiss at Cape Wrath, in Sutherlandshire, is
+intersected by veins. Their light colour, strongly contrasted with that
+of the hornblende-schist, here associated with the gneiss, renders them
+very conspicuous.
+
+Granite very generally assumes a finer grain, and undergoes a change in
+mineral composition, in the veins which it sends into contiguous rocks.
+Thus, according to Professor Sedgwick, the main body of the Cornish granite
+is an aggregate of mica, quartz, and felspar; but the veins are sometimes
+without mica, being a granular aggregate of quartz and felspar. In other
+varieties quartz prevails to the almost entire exclusion both of felspar
+and mica; in others, the mica and quartz both disappear, and the vein is
+simply composed of white granular felspar.[444-C]
+
+Fig. 496. is a sketch of a group of granite veins in Cornwall, given by
+Messrs. Von Oeynhausen and Von Dechen.[445-A] The main body of the granite
+here is of a porphyritic appearance, with large crystals of felspar; 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.
+
+[Illustration: Fig. 496. Granite veins passing through hornblende slate,
+Carnsilver Cove, Cornwall.]
+
+In the Valorsine, a valley not far from Mont Blanc in Switzerland, an
+ordinary granite, consisting of felspar, quartz, and mica, sends forth
+veins into a talcose gneiss (or stratified protogine), and in some places
+lateral ramifications are thrown off from the principal veins at right
+angles (see fig. 497.), the veins, especially the minute ones, being finer
+grained than the granite in mass.
+
+[Illustration: Fig. 497. Veins of granite in talcose gneiss.
+(L. A. Necker.)]
+
+It is here remarked, that the schist and granite, as they approach, seem to
+exercise a reciprocal influence on each other, for both undergo a
+modification of mineral character. The granite, still remaining
+unstratified, becomes charged with green particles; and the talcose gneiss
+assumes a granitiform structure without losing its stratification.[445-B]
+
+Professor Keilhau drew my attention to several localities in the country
+near Christiania, where the mineral character of gneiss appears to have
+been affected by a granite of much newer origin, for some distance from the
+point of contact. The gneiss, without losing its laminated structure, seems
+to have become charged with a larger quantity of felspar, and that of a
+redder colour, than the felspar usually belonging to the gneiss of Norway.
+
+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.[446-A]
+
+There are many instances, as at Markerud, near Christiania, in Norway,
+where the strike of the beds has not been deranged throughout a large area
+by the intrusion of granite, both in large masses and in veins. This fact
+is considered by some geologists to militate against the theory of the
+forcible injection of granite in a fluid state. But it may be stated in
+reply, that ramifying dikes of trap, which almost all now admit to have
+been once fluid, pass through the same fossiliferous strata, near
+Christiania, without deranging their strike or dip.[446-B]
+
+[Illustration: Fig. 498. General view of junction of granite and schist of
+the Valorsine. (L. A. Necker.)]
+
+The real or apparent isolation of large or small masses of granite detached
+from the main body, as at _a b_, fig. 498., and above, fig. 492., and _a_,
+fig. 497., has been thought by some writers to be irreconcilable with the
+doctrine usually taught respecting veins; but many of them may, in fact, be
+sections of root-shaped prolongations of granite; while, in other cases,
+they may in reality be detached portions of rock having the plutonic
+structure. For there may have been spots in the midst of the invaded
+strata, in which there was an assemblage of materials more fusible than the
+rest, or more fitted to combine readily into some form of granite.
+
+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 be shown to have clearly taken place long
+subsequently to the original consolidation of the containing rock. Thus,
+for example, in the gneiss of Tronstad Strand, near Drammen, in Norway,
+the annexed section is seen on the beach. It appears that the
+alternating strata of whitish granitiform gneiss, and black
+hornblende-schist, were first cut through by a greenstone dike, about
+2-1/2 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.
+
+[Illustration: Fig. 499. _a, b._ Quartz vein passing through gneiss and
+greenstone, Tronstad Strand, near Christiania.]
+
+[Illustration: Fig. 500. 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. Mr. 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 paleozoic 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. 500.), 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 felspathic. 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 downwards 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 crystallizing of fused matter under a
+pressure of several thousand feet, much less miles, of the earth's crust
+can 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 almost 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 upwards into lava, and downwards
+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. But to these and other topics, I shall
+revert when speaking, in the next chapter, of the relative ages of
+different masses of granite.
+
+
+FOOTNOTES:
+
+[439-A] Bulletin, 2d sèrie, iv. 1304.; and Archiac, Hist. des Progrès
+de Geol., i. 38.
+
+[440-A] Boase on Primary Geology, p. 16.
+
+[441-A] Bulletin, vol. iv., 2d ser., pp. 1318. and 1320.
+
+[441-B] Syst. of Geol., vol. i. p. 157.
+
+[441-C] Ibid., p. 158.
+
+[442-A] Geol. Trans., 1st series, vol. iii. pl. 21.
+
+[442-B] MacCulloch, Geol. Trans., vol. iii. p. 259.
+
+[443-A] Capt. B. Hall, Trans. Roy. Soc. Edin., vol. vii.
+
+[444-A] MacCulloch, Syst. of Geol., vol. i. p. 58.
+
+[444-B] Western Islands, pl. 31.
+
+[444-C] On Geol. of Cornwall, Camb. Trans. vol. i. p. 124.
+
+[445-A] Phil. Mag. and Annals, No. 27. new series, March, 1829.
+
+[445-B] Necker, sur la Val. de Valorsine, Mém. de la Soc. de Phys. de
+Génève, 1828. I visited, in 1832, the spot referred to in fig. 497.
+
+[446-A] Necker, Proceedings of Geol. Soc., No. 26. p. 392.
+
+[446-B] See Keilhau's Gæa Norvegica; Christiania, 1838.
+
+
+
+
+CHAPTER XXXIV.
+
+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--Tertiary 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--On the
+   probable age of the granites of Arran, in Scotland.
+
+
+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 all
+these tests fail when we endeavour to fix the chronology of a rock which
+has crystallized from a state of fusion in the bowels of the earth. In that
+case, we are reduced to the following tests; 1st, relative position; 2dly,
+intrusion, and alteration of the rocks in contact; 3dly, mineral
+characters; 4thly, included fragments.
+
+_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 Newer Pliocene deposits rest on granite;
+in Auvergne, where the freshwater Eocene 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. 442.), 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 easily recognize 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 the same era.
+
+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
+generalizations to have been premature. The syenitic granite of Norway
+already alluded to may be of the same age as the Silurian strata, which it
+traverses and alters, or may belong to the Old Red sandstone period;
+whereas the granite of Dartmoor, although consisting of mica, quartz, and
+felspar, is newer than the coal. (See p. 456.)
+
+_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[450-A], and thus the granite is shown to be newer than certain
+superficial slaty and trappean formations.
+
+_Recent and Pliocene plutonic rocks, why invisible._--The explanation
+already given in the 29th 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
+simultaneously, or soon afterwards. 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.[450-B] 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[451-A], 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
+crystallizes 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 Newer Pliocene
+granites laid open to view, unless we are prepared to assume that
+sufficient time has elapsed since the commencement of the Newer 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 upwards 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.
+
+In the accompanying diagram (fig. 501.), 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. 1., 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_ 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.
+
+[Illustration: Fig. 501. Diagram showing the relative position which the
+plutonic and sedimentary formations of different ages may occupy.
+
+  I. Primary plutonic.        4. Recent strata.
+  II. Secondary plutonic.     3. Tertiary strata.
+  III. Tertiary plutonic.     2. Secondary strata.
+  IV. Recent plutonic.        1. Primary fossiliferous strata.
+
+The metamorphic rocks are not indicated in this diagram; but the student
+will infer, from what has been said in Chap. XXXII., that some portions
+of the stratified formations Nos. 1. and 2. invaded by granite will
+have become metamorphic.]
+
+_Eocene granite and plutonic rocks._--In a former part of this volume (p.
+205.), the great nummulitic formation of the Alps and Pyrenees was
+referred to the Eocene period, and it follows that those vast movements
+which have raised 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 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, 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-Pliocene period. In some part, therefore, of this
+chain, we may expect to discover tertiary plutonic rocks laid open to
+view. What we already know of the structure of the Chilian Andes seems
+to realize this expectation. In a transverse section, examined by Mr.
+Darwin, between Valparaiso and Mendoza, the Cordillera was found to
+consist of two separate and parallel chains, formed of sedimentary rocks
+of different ages, the strata in both resting on plutonic rocks, by
+which they have been altered. In the western or oldest range, called the
+Peuquenes, are black calcareous clay-slates, rising to the height of
+nearly 14,000 feet above the sea, in which are shells of the genera
+_Gryphæa_, _Turritella_, _Terebratula_, and _Ammonite_. These rocks are
+supposed to be of the age of the central parts of the secondary series
+of Europe. They are penetrated and altered by dikes and mountain masses
+of a plutonic rock, which has the texture of ordinary granite, but
+rarely contains quartz, being a compound of albite and hornblende.
+
+The second or eastern chain consists chiefly of sandstones and
+conglomerates, of vast thickness, the materials of which are derived
+from the ruins of the western chain. The pebbles of the conglomerates
+are, for the most part, rounded fragments of the fossiliferous slates
+before mentioned. The resemblance of the whole series to certain
+tertiary deposits on the shores of the Pacific, not only in mineral
+character, but in the imbedded lignite and silicified woods, leads to
+the conjecture that they also are tertiary. Yet these strata are not
+only associated with trap rocks and volcanic tuffs, but are also altered
+by a granite consisting of quartz, felspar, and talc. They are
+traversed, moreover, by dikes of the same granite, and by numerous veins
+of iron, copper, arsenic, silver, and gold; all of which can be traced
+to the underlying granite.[453-A] We have, therefore, strong ground to
+presume that the plutonic rock, here exposed on a large scale in the
+Chilian Andes, is of later date than certain 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 in the nether regions of plutonic and metamorphic
+rocks, 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 usually 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[454-A], has, with the exception of a
+few districts, emerged from the deep to its present altitude; and even
+those tracts, which were already dry land before the Eocene era, have
+almost everywhere acquired additional height. A large amount of subsidence
+has also occurred during the same period, so that the extent of the
+subterranean spaces which have either become the receptacles of sunken
+fragments of the earth's crust, or have been rendered capable of supporting
+other fragments at a much greater height than before, must be so great that
+they probably equal, if not exceed in volume, the entire continent of
+Europe. We are entitled, therefore, to ask what amount of change of
+equivalent importance can be proved to have occurred in the earth's crust
+within an equal quantity of time anterior to the Eocene epoch. They who
+contend for the more intense energy of subterranean causes in the remoter
+eras of the earth's history, may find it more difficult to give an answer
+to this question than they anticipated.
+
+The principal effect of volcanic action in the nether regions, during
+the tertiary period, seems to have consisted in the upheaval to the
+surface 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 vast 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.
+
+[Illustration: Fig. 502. Block section.]
+
+_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_, 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_.
+
+As some Cretaceous rocks, however, have been raised to the height of more
+than 9000 feet in the Pyrenees, we must not assume that plutonic formations
+of the same age may not have been brought up and exposed by denudation, at
+the height of 2000 or 3000 feet on the flanks of that chain.
+
+_Period of Oolite and Lias._--In the department of the Hautes Alpes, in
+France, near Vizille, M. Elie 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 felspar, is
+observed partly to overlie the secondary rocks, producing an alteration
+which extends for about 30 feet downwards, diminishing in the beds which
+lie farthest from the granite. (See fig. 503.) 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 crystallized
+near the junction.[456-A]
+
+[Illustration: Fig. 503. Junction of granite with Jurassic or Oolite strata
+in the Alps, near Champoleon.]
+
+Although the granite is incumbent in the above section (fig. 503.), we
+cannot assume that it overflowed the strata, for the disturbances of the
+rocks are so great in this part of the Alps that they seldom retain the
+position which they must originally have occupied.
+
+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.[456-B] 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.[456-C]
+
+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.[456-D]
+
+_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
+regarded by Professor Sedgwick and Sir R. Murchison as members of the true
+carboniferous series. This granite, like the syenitic granite of
+Christiania, has broken through the stratified formations without much
+changing their strike. Hence, on the north-west side of Dartmoor, the
+successive members of the culm-measures abut against the granite, and
+become metamorphic as they approach. These strata are also penetrated by
+granite veins, and plutonic dikes, called "elvans."[457-A] The granite of
+Cornwall is probably of the same date, and, therefore, as modern as the
+Carboniferous strata, if not much newer.
+
+_Silurian period._--It has long been known that the granite near
+Christiania, in Norway, is of newer origin than the Silurian strata
+of that region. Von Buch first announced, in 1813, the discovery
+of its posteriority in date to 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. 447.)
+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. 504., 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.[457-B]
+
+[Illustration: Fig. 504. Cross section.]
+
+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.
+
+[Illustration: Fig. 505. 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
+disturbed and denuded before the sedimentary beds were superimposed (see
+fig. 505.). 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 the transition strata. Between the origin, therefore,
+of the gneiss and the granite there intervened, first, the period when the
+strata of gneiss were inclined; secondly, the period when they were
+denuded; thirdly, the period of the deposition of the transition deposits.
+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. It seems necessary, therefore, to
+conceive that the gneiss was softened and more or less melted when
+penetrated by the granite. But 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 above, p. 9.). 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 all the known
+fossiliferous deposits. Could we discover some Lower Cambrian 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 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 Cambrian system, we may then feel
+assured that the parent granite was formed before the Lower Cambrian
+formation. But if the incumbent strata be merely Silurian or Upper
+Cambrian, 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 felspar, 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.[459-A] Professor
+Sedgwick and Sir R. Murchison conceive that this granite has been upheaved
+in a solid form; and that in breaking through the submarine deposits, with
+which it was not perhaps originally in contact, it has fractured them so as
+to form a breccia along the line of junction. This breccia consists of
+fragments of shale, sandstone, and limestone, with fossils of the oolite,
+all united together by a calcareous cement. The secondary strata, at some
+distance from the granite, are but slightly disturbed, but in proportion to
+their proximity the amount of dislocation becomes greater.
+
+If we admit that solid hypogene rocks, whether stratified or
+unstratified, have in such cases been driven upwards so as to pierce
+through yielding sedimentary deposits, we shall be enabled to account
+for many geological appearances otherwise inexplicable. Thus, for
+example, at Weinböhla and Hohnstein, near Meissen, in Saxony, a mass of
+granite has been observed covering strata of the Cretaceous and Oolitic
+periods for the space of between 300 and 400 yards square. It appears
+clearly from a recent Memoir of Dr. B. Cotta on this subject[459-B],
+that the granite was thrust into its actual position when solid. There
+are no intersecting veins at the junction--no alteration as if by heat,
+but evident signs of rubbing, and a breccia in some places, in which
+pieces of granite are mingled with broken fragments of the secondary
+rocks. As the granite overhangs both the lias and chalk, so the lias is
+in some places bent over strata of the cretaceous era.
+
+_Relative age of the granites of Arran._--In this island, the largest in
+the Firth of Clyde, being twenty miles in length from north to south, the
+four great classes of rocks, the fossiliferous, volcanic, plutonic, and
+metamorphic, are all conspicuously displayed within a very small area, and
+with their peculiar characters strongly contrasted. In the north of the
+island the granite rises to the height of nearly 3000 feet above the sea,
+terminating in mountainous peaks. (See section, fig. 506.) On the flanks of
+the same mountains are chloritic-schists, blue roofing-slate, and other
+rocks of the metamorphic order (No. 1.), into which the granite (No. 2.)
+sends veins. This granite, therefore, is newer than the hypogene schists
+(No. 1.), which it penetrates.
+
+These schists are highly inclined. Upon them rest beds of conglomerate
+and sandstone (No. 3.), which are referable to the Old Red formation, to
+which succeed various shales and limestones (No. 4.) containing the
+fossils of the Carboniferous period, upon which are other strata of
+sandstone and conglomerate (upper part of No. 4.), in which no fossils
+have been met with, which it is conjectured may belong to the New Red
+sandstone period. All the preceding formations are cut through by the
+volcanic rocks (No. 5.), which consist of greenstone, basalt,
+pitchstone, claystone-porphyry, and other varieties. These appear either
+in the form of dikes, or in dense masses from 50 to 700 feet in
+thickness, overlying the strata (No. 4.). They sometimes pass into
+syenite of so crystalline a form, that it may rank as a plutonic
+formation; and in one region, at Ploverfield, in Glen Cloy, a
+fine-grained granite (6. _a_) is seen associated with the trap
+formation, and sending veins into the sandstone or into the upper strata
+of No. 4. This interesting discovery of granite in the southern region
+of Arran, at a point where it is separated from the northern mass of
+granite by a great thickness of secondary strata and overlying trap, was
+made by Mr. L. A. Necker of Geneva, during his survey of Arran in 1839.
+We also learn from the recent investigations of Prof. A. C. Ramsay, that
+a similar fine-grained granite (No. 6. _b_) appears in the interior of
+the northern granitic district, forming the nucleus of it, and sending
+veins into the older coarse-grained granite (No. 2.). The trap dikes
+which penetrate the older granite are cut off, according to Mr. Ramsay,
+at the junction of the fine grained.
+
+It is not improbable that the granite (No. 6. _b_) may be of the same age
+as that of Ploverfield (No. 6. _a_), and this again may belong to the same
+geological epoch as the trap formations (No. 5.). If there be any
+difference of date, it would seem that the fine-grained granite must be
+newer than the trappean rocks. But, on the other hand, the coarser granite
+(No. 2.) may be the oldest rock in Arran, with the exception of the
+hypogene slates (No. 1.), into which it sends veins.
+
+[Illustration: Fig. 506. General Section of Arran from north to south.
+
+  1. Metamorphic or Hypogene schists, the oldest formations in Arran.
+  2. Coarse-grained granite sending veins into the schists, No. 1.
+  3. Old Red Sandstone and Conglomerate containing pebbles exclusively
+     derived from the rocks, No 1., without any intermixture of granitic
+     fragments.
+  4. Carboniferous strata and red sandstone (New Red?).
+  5. Trap, overlying and in dikes, passing occasionally into Syenites of
+     the Plutonic class.
+  6. _a._ Fine-grained granite, associated with the overlying trap, No. 5.
+  6. _b._ Similar fine-grained granite, sending veins into the older
+     granite, No. 2., and cutting off the trappean dikes, _c_, _d_.[461-A]]
+
+An objection may perhaps at first be started to this conclusion, derived
+from the curious and striking fact, the importance of which was first
+emphatically pointed out by Dr. MacCulloch, that no pebbles of granite
+occur in the conglomerates of the red sandstone in Arran, although these
+conglomerates are several hundred feet in thickness, and lie at the foot of
+lofty granite mountains, which tower above them. As a general rule, all
+such aggregates of pebbles and sand are mainly composed of the wreck of
+pre-existing rocks occurring in the immediate vicinity. The total absence
+therefore of granitic pebbles has justly been a theme of wonder to those
+geologists who have successively visited Arran, and they have carefully
+searched there, as I have done myself, to find an exception, but in vain.
+The rounded masses consist exclusively of quartz, chlorite-schist, and
+other members of the metamorphic series; nor in the newer conglomerates of
+No. 4. have any granitic fragments been discovered. Are we then entitled to
+affirm that the coarse-grained granite (No. 2.), like the fine-grained
+variety (No. 6. _a_), is more modern than all the other rocks of the
+island? This we cannot assume at present, but we may confidently infer that
+when the various beds of sandstone and conglomerate were formed, no granite
+had reached the surface, or had been exposed to denudation in Arran. It is
+clear that the crystalline schists were ground into sand and shingle when
+the strata No. 3. were deposited, and at that time the waves had never
+acted upon the granite, which now sends its veins into the schist. May we
+then conclude, that the schists suffered denudation before they were
+invaded by granite? This opinion, although not inadmissible, is by no
+means fully borne out by the evidence. For at the time when the Old Red
+sandstone originated, the metamorphic strata may have formed islands in the
+sea, as in fig. 507., over which the breakers rolled, or from which
+torrents and rivers descended, carrying down gravel and sand. The plutonic
+rock or granite (B) may even then have been previously injected at a
+certain depth below, and yet may never have been exposed to denudation.
+
+[Illustration: Fig. 507. Cross section.]
+
+As to the time and manner of the subsequent protrusion of the
+coarse-grained granite (No. 2.), this rock may have been thrust up
+bodily, in a solid form, during that long series of igneous operations
+which produced the trappean and plutonic formations (Nos. 5., 6.
+_a_, and 6. _b_).
+
+We have shown that these eruptions, whatever their date, were posterior to
+the deposition of all the fossiliferous strata of Arran. We can also prove
+that subsequently both the granitic and trappean rocks underwent great
+aqueous denudation, which they probably suffered during their emergence
+from the sea. The fact is demonstrated by the abrupt truncation of numerous
+dikes, such as those at _c_, _d_, _e_, which are cut off on the surface of
+the granite and trap. The overlying trap also ceases very abruptly on
+approaching the boundary of the great hypogene region, and terminates in a
+steep escarpment facing towards it as at _f_, fig. 506. When in its
+original fluid state it could not have come thus suddenly to an end, but
+must have filled up the hollow now separating it from the hypogene rocks,
+had such a hollow then existed. This necessity of supposing that both the
+trap and the conglomerate once extended farther, and that veins such as
+_c_, _d_, fig. 506., were once prolonged farther upwards, prepares us to
+believe that the whole of the northern granite may at one time have been
+covered by newer formations, under the pressure of which, before its
+protrusion, it assumed its highly crystalline texture.
+
+The theory of the protrusion in a solid form of the northern nucleus of
+granite is confirmed by the manner in which the hypogene slates (No. 1.)
+and the beds of conglomerate (No. 3.) dip away from it on all sides. In
+some places indeed the slates are inclined towards the granite, but this
+exception might have been looked for, because these hypogene strata have
+undergone disturbances at more than one geological epoch, and may at some
+points, perhaps, have their original order of position inverted. The high
+inclination, therefore, and the quâquâversal dip of the beds around the
+borders of the granitic boss, and the comparative horizontality of the
+fossiliferous strata in the southern part of the island, are facts which
+all accord with the hypothesis of a great amount of movement at that point
+where the granite is supposed to have been thrust up bodily, and where we
+may conceive it to have been distended laterally by the repeated injection
+of fresh supplies of melted materials.[463-A]
+
+
+FOOTNOTES:
+
+[450-A] Silliman's Journ., No. 69. p. 123.
+
+[450-B] See "Principles," _Index_, "Jorullo."
+
+[451-A] "Principles," _Index_, "Volcanic Eruptions."
+
+[453-A] Darwin, pp. 390. 406.; second edition, p. 319.
+
+[454-A] See map of Europe and explanation, in Principles, book i.
+
+[456-A] Elie de Beaumont, sur les Montagnes de l'Oisans, &c. Mém. de la
+Soc. d'Hist. Nat. de Paris, tom. v.
+
+[456-B] See Murchison, Geol. Trans., 2d series, vol. ii. part ii.
+pp. 311-321.
+
+[456-C] Western Islands, vol. i. p. 330. plate 18., figs. 3, 4.
+
+[456-D] Von Buch, Annales de Chimie, &c.
+
+[457-A] Proceedings of Geol. Soc., vol. ii. p. 562.
+
+[457-B] See the Gæa Norvegica and other works of Keilhau, with whom I
+examined this country.
+
+[459-A] Murchison, Geol. Trans., 2d series, vol. ii. p. 307.
+
+[459-B] Geognostische Wanderungen, Leipzig, 1838.
+
+[461-A] In the above section I have attempted to represent the new
+discoveries made since 1839, by Mr. Necker and Mr. A. C. Ramsay, in regard
+to the plutonic formations, 6. _a_, and 6. _b_.
+
+[463-A] For the geology of Arran consult the works of Drs. Hutton and
+MacCulloch, the Memoirs of Messrs. Von Dechen and Oeynhausen, that of
+Professor Sedgwick and Sir R. Murchison (Geol. Trans. 2d series), Mr. L.
+A. Necker's Memoir, read to the Royal Soc. of Edin. 20th April, 1840,
+and Mr. Ramsay's Geol. of Arran, 1841. I examined myself a large part
+of Arran in 1836.
+
+
+
+
+CHAPTER XXXV.
+
+METAMORPHIC ROCKS.
+
+   General character of metamorphic rocks--Gneiss--Hornblende-schist--
+   Mica-schist--Clay-slate--Quartzite--Chlorite-schist--Metamorphic
+   limestone--Alphabetical list and explanation of other rocks of this
+   family--Origin of the metamorphic strata--Their stratification is real
+   and distinct from cleavage--Joints and slaty cleavage--Supposed causes
+   of these structures--How far connected with crystalline action.
+
+
+We have now considered three distinct classes of rocks: first, the aqueous,
+or fossiliferous; secondly, the volcanic; and, thirdly, the plutonic, or
+granitic; and we have now, lastly, 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, or schistose hypogene formations.
+
+These rocks, when in their most 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 narrow 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. 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; gneiss, for example, having
+been often supposed to hold invariably a lower geological position than
+mica-schist. But although such an order may prevail throughout limited
+districts, it is by no means universal, nor even general, throughout the
+globe. To this subject, however, I shall again revert, in the last
+chapter of this volume, when the chronological relations of the
+metamorphic rocks are pointed out.
+
+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.
+
+[Illustration: Fig. 508. Fragment of gneiss, natural size; section at right
+angles to planes of stratification.]
+
+_Gneiss._--The first of these, gneiss, may be called stratified granite,
+being formed of the same materials as granite, namely, felspar, quartz,
+and mica. In the specimen here figured, the white layers consist almost
+exclusively of granular felspar, 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 felspar 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 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.
+
+The term "gneiss," however, in geology is commonly used in a wider sense,
+to designate a formation in which the above-mentioned rock prevails, but
+with which any one of the other metamorphic rocks, and more especially
+hornblende-schist, may alternate. These other members of the metamorphic
+series are, in this case, considered as subordinate to the true gneiss.
+
+The different varieties of rock allied to gneiss, into which felspar
+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 felspar, forming a syenitic gneiss; or
+talc may be substituted for mica, constituting talcose gneiss, a rock
+composed of felspar, quartz, and talc, in distinct crystals or grains
+(stratified protogine of the French).
+
+_Hornblende-schist_ is usually black, and composed principally of
+hornblende, with a variable quantity of felspar, and sometimes grains of
+quartz. When the hornblende and felspar are nearly in 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. Some of these hornblendic
+masses may really have been volcanic rocks, which have since assumed a
+more crystalline or metamorphic texture.
+
+_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_, or _Argillaceous schist_.--This rock resembles an
+indurated clay or shale, is for the most part extremely fissile, often
+affording good roofing slate. It may consist of the ingredients of
+gneiss, or of an extremely fine mixture of mica and quartz, or talc and
+quartz. 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. 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 mineralogical characters.
+
+_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 felspar and mica.
+
+_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 felspar or mica. Often associated with, and graduating
+into, gneiss and clay-slate.
+
+_Hypogene_, or _Metamorphic limestone_.--This rock, commonly called
+_primary limestone_, is sometimes a thick bedded white crystalline
+granular marble used in sculpture; but more frequently it occurs in thin
+beds, forming a foliated schist much resembling in colour and appearance
+certain varieties of gneiss and mica-schist. It alternates with both
+these rocks, and in like manner with argillaceous schist. It then
+usually contains some crystals of mica, and occasionally quartz,
+felspar, hornblende, and talc. This member of the metamorphic series
+enters sparingly into the structure of the hypogene districts of Norway,
+Sweden, and Scotland, but is largely developed in the Alps.
+
+
+Before offering any farther observations on the probable origin of the
+metamorphic rocks, I subjoin, in the form of a glossary, a brief
+explanation of some of the principal varieties and their synonymies.
+
+ACTINOLITE-SCHIST. A slaty foliated rock, composed chiefly of actinolite,
+(an emerald-green mineral, allied to hornblende,) with some admixture of
+felspar, or quartz, or mica.
+
+AMPELITE. Aluminous slate (Brongniart); occurs both in the metamorphic
+and fossiliferous series.
+
+AMPHIBOLITE. Hornblende rock, which see.
+
+ARGILLACEOUS-SCHIST, or CLAY-SLATE. _See_ p. 465.
+
+ARKOSE. Term used by Brongniart for granular Quartzite, which see.
+
+CHIASTOLITE-SLATE scarcely differs from clay-slate, but includes numerous
+crystals of Chiastolite; in considerable thickness in Cumberland.
+Chiastolite occurs in long slender rhomboidal crystals. For composition,
+see Table, p. 377.
+
+CHLORITE-SCHIST. A green slaty rock, in which chlorite, a green scaly
+mineral, is abundant. _See_ p. 465.
+
+CLAY-SLATE, or ARGILLACEOUS-SCHIST. _See_ p. 465.
+
+EURITE and EURITIC PORPHYRY. A base of compact felspar, with grains of
+laminar felspar, and often mica and other minerals disseminated
+(Brongniart). M. D'Aubuisson regards eurite as an extremely fine-grained
+granite, in which felspar predominates, the whole forming an apparently
+homogeneous rock. Eurite has been already mentioned as a plutonic rock, but
+occurs also in beds subordinate to gneiss or mica-slate.
+
+GNEISS. A stratified or laminated rock, same composition as granite.
+_See_ p. 464.
+
+HORNBLENDE ROCK, or AMPHIBOLITE. Composed of hornblende and felspar.
+The same composition as hornblende-schist, stratified, but not fissile.
+_See_ p. 376.
+
+HORNBLENDE-SCHIST, or SLATE. Composed chiefly of hornblende, with
+occasionally some felspar. _See_ p. 464.
+
+HORNBLENDIC or SYENITIC-GNEISS. Composed of felspar, quartz,
+and hornblende.
+
+HYPOGENE LIMESTONE. _See_ p. 465.
+
+MARBLE. _See_ p. 465.
+
+MICA-SCHIST, or MICACEOUS-SCHIST. A slaty rock, composed of mica and quartz
+in variable proportions. _See_ p. 465.
+
+MICA-SLATE. _See_ MICA-SCHIST, p. 465.
+
+PHYLLADE. D'Aubuisson's term for clay-slate, from +phullas+,
+a heap of leaves.
+
+PRIMARY LIMESTONE. _See_ HYPOGENE LIMESTONE, p. 465.
+
+PROTOGINE. _See_ TALCOSE-GNEISS, p. 464.; when unstratified
+it is Talcose-granite.
+
+QUARTZ ROCK, or QUARTZITE. A stratified rock; an aggregate of grains of
+quartz. _See_ p. 465.
+
+SERPENTINE occurs in both divisions of the hypogene series, as a stratified
+or unstratified rock; contains much magnesia; is chiefly composed of the
+mineral called serpentine, mixed with diallage, talc, and steatite. The
+pure varieties of this rock, called noble serpentine, consist of a hydrated
+silicate of magnesia, generally of a greenish colour: this base is commonly
+mixed with oxide of iron.
+
+TALCOSE-GNEISS. Same composition as talcose-granite or protogine, but
+either stratified or laminated. _See_ p. 464.
+
+TALCOSE-SCHIST consists chiefly of talc, or of talc and quartz, or of talc
+and felspar, and has a texture something like that of clay-slate.
+
+WHITESTONE. Same as Eurite.
+
+
+_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 the last chapter of this volume, 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 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 of an
+occasional slaty 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 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 granular limestone in thin layers.
+
+As in fossiliferous formations strata of pure siliceous sand alternate with
+micaceous sand and with layers of clay, so in the crystalline or
+metamorphic rocks we have beds of pure quartzite alternating with
+mica-schist and clay-slate. As in the secondary and tertiary series we meet
+with limestone alternating again and again with micaceous or argillaceous
+sand, so we find in the hypogene, gneiss and mica-schist alternating with
+pure and impure granular limestones.
+
+It has also been shown that the ripple-mark is very commonly repeated
+throughout a considerable thickness of fossiliferous strata; so in
+mica-schist and gneiss, there is sometimes an undulation of the laminæ on a
+minute scale, which may, perhaps, be a modification of similar inequalities
+in the original deposit.
+
+In the crystalline formations also, as in many of the sedimentary before
+described, single strata are sometimes made up of laminæ placed diagonally,
+such laminæ not being regularly parallel to the planes of cleavage.
+
+[Illustration: Fig. 509. Lamination of clay-slate, Montagne de Seguinat,
+near Gavarnie, in the Pyrenees.]
+
+This disposition of the layers is illustrated in the accompanying diagram,
+in which I have represented carefully the stratification of a coarse
+argillaceous schist, which I examined in the Pyrenees, part of which
+approaches in character to a green and blue roofing slate, while part is
+extremely quartzose, the whole mass passing downwards into micaceous
+schist. The vertical section here exhibited is about 3 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.
+
+The inference drawn from the phenomena above described in favour of the
+aqueous origin of clay-slate and other crystalline strata, is greatly
+strengthened by the fact that many of these metamorphic rocks occasionally
+alternate with, and sometimes pass by intermediate gradations into, rocks
+of a decidedly mechanical origin, and exhibiting traces of organic remains.
+The fossiliferous formations, moreover, into which this passage is
+effected, are by no means invariably of the same age nor of the highest
+antiquity, as will be afterwards explained.
+
+_Stratification of the metamorphic rocks distinct from cleavage._--The beds
+into which gneiss, mica-schist, and hypogene limestone divide, exhibit most
+commonly, like ordinary strata, a want of perfect geometrical parallelism.
+For this reason, therefore, in addition to the alternate recurrence of
+layers of distinct materials, the stratified arrangement of the crystalline
+rocks cannot be explained away by supposing it to be simply a divisional
+structure like that to which we owe some of the slates used for writing and
+roofing. _Slaty cleavage_, as it has been called, has in many cases been
+produced by the regular deposition of thin plates of fine sediment one upon
+another; but there are many instances where it is decidedly unconnected
+with such a mode of origin, and where it is not even confined to the
+aqueous formations. Some kinds of trap, for example, as clinkstone, split
+into laminæ, and are used for roofing.
+
+There are, says Professor Sedgwick, three distinct forms of structure
+exhibited in certain rocks throughout large districts: viz.--First,
+stratification; secondly, joints; and thirdly, slaty cleavage; the two
+last having no connection with true bedding, and having been superinduced
+by causes absolutely independent of gravitation. All these different
+structures must have different names, even though there be some cases where
+it is impossible, after carefully studying the appearances, to decide upon
+the class to which they belong.[469-A]
+
+_Joints._--Now, in regard to the second of these forms of structure or
+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 phenomena, 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.[469-B] 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, often
+slightly open, 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.[469-C]
+
+In the annexed diagram 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.
+
+[Illustration: Fig. 510. Stratification, joints, and cleavage.]
+
+Joints, according to Professor Sedgwick, 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 some 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. 511.), which consist 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.
+These planes are usually inclined at a very considerable angle to the
+planes of the strata. In the Welsh chains, for example, the average angle
+is as much as from 30° to 40°. Sometimes the cleavage planes dip towards
+the same point of the compass as those of stratification, but more
+frequently to opposite points. It may be stated as a general rule, that
+when beds of coarser materials alternate with those composed of finer
+particles, the slaty cleavage is either entirely confined to the
+fine-grained rock, or is very imperfectly exhibited in that of coarser
+texture. This rule holds, whether the cleavage is parallel to the planes of
+stratification or not.
+
+[Illustration: Fig. 511. Parallel planes of cleavage intersecting
+curved strata. (Sedgwick.)]
+
+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 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.[470-A]
+
+Now these joints are supposed to be analogous to those partings which have
+been already observed to 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, which 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 some countries, as in Saxony, 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 hearthstones, 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.
+
+Sir R. Murchison observes, that in referring both joints and slaty cleavage
+to crystalline action, we are borne out by a well-known analogy in which
+crystallization has in like manner given rise to two distinct kinds of
+structure in the same body. Thus, for example, in a six-sided prism of
+quartz, the planes of cleavage are distinct from those of the prism. It is
+impossible to cleave the crystals parallel to the plane of the prism, just
+as slaty rocks cannot be cleaved parallel to the joints; but the quartz
+crystal, like the older schists, may be cleaved _ad infinitum_ in the
+direction of the cleavage planes.[471-A]
+
+It seems, therefore, that the fissures called joints may have been the
+result of different causes, as of some modification of crystalline action,
+or simple contraction during consolidation, or during a change of
+temperature. And there are cases where joints may have been due to
+mechanical violence, and the strain exerted on strata during their
+upheaval, or when they have sunk down below their former level. Professor
+Phillips has suggested that the previous existence of divisional planes may
+often have determined, and must greatly have modified, the lines and points
+of fracture caused in rocks by those forces to which they owe their
+elevation or dislocations. These lines and points being those of least
+resistance, cannot fail to have influenced the direction in which the solid
+mass would give way on the application of external force.
+
+Professor Phillips has also 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.[471-B] 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.[471-C]
+
+Mr. Darwin infers from his observations, that in South America the
+strike of the cleavage planes is very uniform over wide regions, and
+that it corresponds with the strike of the planes of foliation in the
+gneiss and mica-schists of the same parts of Chili, Tierra del Fuego,
+&c. The explanation which he suggests, is based upon a combination of
+mechanical and crystalline forces. The planes, he says, of cleavage, and
+even the foliation of mica-schist and gneiss, may be intimately
+connected with the planes of different tension to which the area was
+long subjected, _after_ the main fissures or axis of upheavement had
+been formed, but _before_ the final consolidation of the mass and the
+total cessation of all molecular movement.[472-A]
+
+I have already stated that some extremely fine slates are perfectly
+parallel to the planes of stratification, as those of the Niesen, for
+example, near the Lake of Thun, in Switzerland, which contain fucoids, and
+are no doubt due to successive aqueous deposition. Even where the slates
+are oblique to the general planes of the strata, it by no means follows as
+a matter of course that they have been caused by crystalline action, for
+they may be the result of that diagonal lamination which I have before
+described (p. 17.). In this case, however, there is usually much
+irregularity, whereas cleavage planes oblique to the true stratification,
+which are referred to a crystalline action, are often perfectly
+symmetrical, and observe a strict geometrical parallelism, even when the
+strata are contorted, as already described (p. 470.).
+
+Professor Sedgwick, speaking of the planes of slaty cleavage, where they
+are decidedly distinct from those of sedimentary deposition, declares
+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. It
+must be referred 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
+crystallization; that is to say, if they have been heated to a point
+at which the particles can begin to move amongst 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[472-B]
+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."[472-C]
+
+
+FOOTNOTES:
+
+[469-A] Geol. Trans., 2d series, vol. iii. p. 480.
+
+[469-B] The Silurian System of Rocks, as developed in Salop, Hereford,
+&c., p. 245.
+
+[469-C] Ibid., p. 246.
+
+[470-A] Introduction to Geology, chap. iv.
+
+[471-A] Silurian System of Rocks, &c., p. 246.
+
+[471-B] Report, Brit. Ass., Cork, 1843, p. 60.
+
+[471-C] Quart. Geol. Journ., vol. iii. p. 87. 1847.
+
+[472-A] Geol. Obs. on S. America, 1846, p. 168.
+
+[472-B] 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.
+
+[472-C] Letter to the author, dated Cape of Good Hope, Feb. 20. 1836.
+
+
+
+
+CHAPTER XXXVI.
+
+METAMORPHIC ROCKS--_continued_.
+
+   Strata near some 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--Time may enable
+   this action to pervade denser masses--From what kinds of sedimentary
+   rock each variety of the metamorphic class may be derived--Certain
+   objections to the metamorphic theory considered--Lamination of
+   trachyte and obsidian due to motion--Whether some kinds of gneiss have
+   become schistose by a similar action.
+
+
+It has been seen that geologists have been very generally led to infer,
+from the phenomena of joints and slaty cleavage, that mountain masses, of
+which the sedimentary origin is unquestionable, have been acted upon
+simultaneously by vast crystalline forces. That the structure of
+fossiliferous strata has often been modified by some general cause since
+their original deposition, and even subsequently to their consolidation and
+dislocation, is undeniable. These facts prepare us to believe that still
+greater changes may have been worked out by a greater intensity, or more
+prolonged development of the same agency, combined, perhaps, with other
+causes. Now we have 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 characterizes the more crystalline metamorphic formations,
+has actually been superinduced in strata once fossiliferous.
+
+In the southern extremity of Norway there is a large district, on the west
+side of the fiord of Christiania, in which granite or syenite 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 felspar 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. 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, blue colour, and often abounds in corals, becomes a white granular
+marble near the granite, sometimes siliceous, the granular structure
+extending occasionally upwards of 400 yards from the junction; and 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, as will be seen by the
+accompanying ground plan.[474-A]
+
+[Illustration: Fig. 512. Altered zone of fossiliferous slate and limestone
+near granite. Christiania.
+
+_The arrows indicate the dip, and the straight lines the strike,
+of the beds._]
+
+The indurated and ribboned schists above mentioned bear a strong
+resemblance to certain shales of the coal found at Russell's Hall, near
+Dudley, where coal-mines have been on fire for ages. Beds of shale of
+considerable thickness, lying over the burning coal, have been baked and
+hardened so as to acquire a flinty fracture, the layers being alternately
+green and brick-coloured.
+
+The granite of Cornwall, in like manner, 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 slate and slaty sandstone called greywacké,
+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 felspar."[475-A]
+
+We learn from the investigations of M. Dufrénoy, 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 Fénouillet, 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 Rancié 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 felspar, called,
+from the place in the Pyrenees where it occurs, "couzeranite."
+
+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--powers
+capable of generating in them a new mineral character, similar, nay, often
+absolutely identical, with that of gneiss, mica-schist, and other
+stratified members of the hypogene series. The precise nature of these
+altering causes, which may provisionally be termed plutonic, is in a great
+degree obscure and doubtful; but their reality is no less clear, and we
+must suppose the influence of heat to be in some way connected with the
+transmutation, if, for reasons before explained, we concede the igneous
+origin of granite.
+
+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 crystallization
+ensue.[475-B] 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 volcanos 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. When the materials of
+granite, therefore, came in contact with the fossiliferous stratum in
+the bowels of the earth under great pressure, the contained gases might
+be unable to escape; yet when brought into contact with rocks, might
+pass through their pores with greater facility than water is known to do
+(p. 35.). These aëriform fluids, such as sulphuretted hydrogen, muriatic
+acid, and carbonic acid, issue in many places from rents in rocks, which
+they have discoloured and corroded, softening some and hardening others.
+If the rocks are charged with water, they would pass through more
+readily; for, according to the experiments of Henry, water, under an
+hydrostatic pressure of 96 feet, will absorb three times as much
+carbonic acid gas as it can under the ordinary pressure of the
+atmosphere. Although this increased power of absorption would be
+diminished, in consequence of the higher temperature found to exist as
+we descend in the earth, yet Professor Bischoff has shown that the heat
+by no means augments in such a proportion as to counteract the effect of
+augmented pressure.[476-A] There are other gases, as well as the
+carbonic acid, which water absorbs, and more rapidly in proportion to
+the amount of pressure. Now 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; and it is conceivable that heated gases
+brought into contact with them, at great depths, may be absorbed
+readily, and transfused through their pores. Although the gaseous matter
+first observed 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.
+
+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 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.[476-B]
+
+Another illustration of the power of subterranean gases is afforded by the
+stufas of St. Calogero, situated in the largest of the Lipari Islands.
+Here, according to the description published by Hoffmann, horizontal strata
+of tuff, extending for 4 miles along the coast, and forming cliffs more
+than 200 feet high, have been discoloured in various places, and strangely
+altered by the "all-penetrating vapours." Dark clays have become yellow, or
+often snow-white; or have assumed a chequered or brecciated appearance,
+being crossed with ferruginous red stripes. In some places the fumaroles
+have been found by analysis to consist partly of sublimations of oxide of
+iron; but it also appears that veins of chalcedony and opal, and others of
+fibrous gypsum, have resulted from these volcanic exhalations.[476-C]
+
+The reader may also refer to M. Virlet's account of the corrosion of hard,
+flinty, and jaspideous rocks near Corinth, by the prolonged agency of
+subterranean gases[477-A]; and to Dr. Daubeny's description of the
+decomposition of trachytic rocks in the Solfatara, near Naples, by
+sulphuretted hydrogen and muriatic acid gases.[477-B]
+
+Although in all these instances we can only study the phenomena as
+exhibited at the surface, it is clear that the gaseous fluids must have
+made their way through the whole thickness of porous or fissured rocks,
+which intervene between the subterranean reservoirs of gas and the external
+air. The extent, therefore, of the earth's crust, which the vapours have
+permeated and are now permeating, may be thousands of fathoms in thickness,
+and their heating and modifying influence may be spread throughout the
+whole of this solid mass.
+
+We learn from Professor Bischoff that the steam of a hot spring at
+Aix-la-Chapelle, although its temperature is only from 133° to 167° F., has
+converted the surface of some blocks of black marble into a doughy mass. He
+conceives, therefore, that steam in the bowels of the earth having a
+temperature equal or even greater than the melting point of lava, and
+having an elasticity of which even Papin's digester can give but a faint
+idea, may convert rocks into liquid matter.[477-C]
+
+The above observations are calculated to meet some of the objections which
+have been urged against the metamorphic theory on the ground of the small
+power of rocks to conduct heat; for it is well known that rocks, when dry
+and in the air, differ remarkably from metals in this respect. It has been
+asked how the changes which extend merely for a few feet from the contact
+of a dike could have penetrated through mountain masses of crystalline
+strata several miles in thickness. Now it has been stated that the plutonic
+influence of the syenite of Norway has sometimes altered fossiliferous
+strata for a distance of a quarter of a mile, both in the direction of
+their dip and of their strike. (See fig. 512. p. 474.) This is undoubtedly
+an extreme case; but is it not far more philosophical to suppose that this
+influence may, under favourable circumstances, affect denser masses, than
+to invent an entirely new cause to account for effects merely differing in
+quantity, and not in kind? The metamorphic theory does not require us to
+affirm that some contiguous mass of granite has been the altering power;
+but merely that an action, existing in the interior of the earth at an
+unknown depth, whether thermal, electrical, or other, analogous to that
+exerted near intruding masses of granite, has, in the course of vast and
+indefinite periods, and when rising perhaps from a large heated surface,
+reduced strata thousands of yards thick to a state of semi-fusion, so that
+on cooling they have become crystalline, like gneiss. Granite may have been
+another result of the same action in a higher state of intensity, by which
+a thorough fusion has been produced; and in this manner the passage from
+granite into gneiss may be explained.
+
+Some geologists are of opinion, that the alternate layers of mica and
+quartz, or mica and felspar, or lime and felspar, are so much more
+distinct, in certain metamorphic rocks, than the ingredients composing
+alternate layers in many sedimentary deposits, that the similar particles
+must be supposed to have exerted a molecular attraction for each other, and
+to have thus congregated together in layers more distinct in mineral
+composition than before they were crystallized.
+
+In considering, then, the various data already enumerated, the forms of
+stratification in metamorphic rocks, their passage on the one hand into the
+fossiliferous, and on the other into the plutonic formations, and the
+conversions which can be ascertained to have occurred in the vicinity of
+granite, we may conclude that gneiss and mica-schist may be nothing more
+than altered micaceous and argillaceous sandstones that 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.
+
+"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."[478-A] "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."[478-B]
+
+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.[478-C] 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 2 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_, &c. 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 3 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-schist, 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.[479-A]
+
+The total absence of any trace of fossils has inclined many geologists to
+attribute the origin of crystalline strata to a period 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 occur in certain ancient systems of slate, in which, as
+in Cumberland, some conglomerates occur. But in urging this argument, it
+seems to have been forgotten that there are stratified formations of
+enormous thickness, and of various ages, and some of them very modern, all
+formed after the earth had become the abode of living creatures, which are,
+nevertheless, in certain 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; and it is clear, that, the
+older the stratum, the greater is the chance of its being
+non-fossiliferous, even if it has escaped all metamorphic action.
+
+It has been also objected to the metamorphic theory, that the chemical
+composition of the secondary strata differs essentially from that of the
+crystalline schists, into which they are supposed to be convertible.[479-B]
+The "primary" schists, it is said, usually contain a considerable
+proportion of potash or of soda, which the secondary clays, shales, and
+slates do not, these last being the result of the decomposition of
+felspathic rocks, from which the alkaline matter has been abstracted during
+the process of decomposition. But this reasoning proceeds on insufficient
+and apparently mistaken data; for a large portion of what is usually called
+clay, marl, shale, and slate does actually contain a certain, and often a
+considerable, proportion of alkali; so that it is difficult, in many
+countries, to obtain clay or shale sufficiently free from alkaline
+ingredients to allow of their being burnt into bricks or used for pottery.
+
+Thus the argillaceous shales and slates of the Old Red sandstone, in
+Forfarshire and other parts of Scotland, are so much charged with
+alkali, derived from triturated felspar, that, instead of hardening when
+exposed to fire, they sometimes melt into a glass. They contain no lime,
+but appear to consist of extremely minute grains of the various
+ingredients of granite, which are distinctly visible in the
+coarser-grained varieties, and in almost all the interposed sandstones.
+These laminated clays and shales might certainly, if crystallized,
+resemble in composition many of the primary strata.
+
+There is also potash in fossil vegetable remains, and soda in the salts by
+which strata are sometimes so largely impregnated, as in Patagonia.
+
+Another objection has been derived from the alternation of highly
+crystalline strata with others having a less crystalline texture. 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, there
+is every probability that some will be more fusible than others. Some, for
+example, will contain soda, potash, lime, or some other ingredient capable
+of acting as a flux; while others may be destitute of the same elements,
+and so refractory as to be very slightly affected by a degree of heat
+capable of reducing others to semi-fusion. 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.
+
+There are geologists, however, of high authority, who admit the
+metamorphic origin of gneiss and mica-schist even on a grand scale in
+some mountain-chains, and who nevertheless believe that gneiss has in
+some instances been an eruptive rock, deriving its lamination from
+motion when in a fluid or viscous state. Mr. Scrope, in his description
+of the Ponza Islands, ascribes "the zoned structure of the Hungarian
+perlite (a semi-vitreous trachyte) to its having subsided, in obedience
+to the impulse of its own gravity, down a slightly inclined plane, while
+possessed of an imperfect fluidity. In the islands of Ponza and
+Palmarola, the direction of the zones is more frequently vertical than
+horizontal, because the mass was impelled from below upwards."[480-A] In
+like manner, 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. He compares this division into parallel zones, thus caused
+by the stretching of a pasty mass as it flowed slowly onwards, to the
+zoned or ribboned structure of ice, which Professor James Forbes has
+so ably explained, showing that it is due to the fissuring of a
+viscous body in motion.[480-B] Mr. Darwin also imagines the lamination
+or _foliation_, as he terms it, of gneiss and mica-schist in South
+America to be the extreme result of that process of which cleavage
+is the first effect.[480-C]
+
+M. Elie de Beaumont, while he regards the greater part of the gneiss and
+mica-schist of the Alps as sedimentary strata altered by plutonic action,
+still conceives that some of the Alpine gneiss may have been erupted, or,
+in other words, may be granite drawn out into parallel laminæ in the manner
+of trachyte as above alluded to.[480-D]
+
+Opinions such as these, and others which might be cited, prove the
+difficulty of arriving at clear theoretical views on this subject. I may
+also add another difficulty. In many extensive regions experienced
+geologists have been at a loss to decide which of two sets of divisional
+planes were referable to cleavage and which to stratification; and that,
+too, where the rocks are of undisputed aqueous origin. After much doubt,
+they have sometimes discovered that they had at first mistaken the lines of
+cleavage for those of deposition, because the former were by far the most
+marked of the two. Now if such slaty masses should become highly
+crystalline, and be converted into gneiss, hornblende-schist, or any other
+member of the hypogene class, the cleavage planes would be more likely to
+remain visible than those of stratification.
+
+But although the cause last-mentioned may, in some instances, be a "vera
+causa," as applied to gneiss and mica-schist, I believe it to be an
+exception to the general rule. Nor would it, I conceive, produce that kind
+of irregular parallelism in the laminæ which belongs to so many of the
+hypogene rocks of the Grampians, Pyrenees, and the White mountains of North
+America, where I have chiefly studied them.
+
+But it will be impossible for the reader duly to appreciate the propriety
+of the term metamorphic, as applied to the strata formerly called
+primitive, until I have shown, in the next chapter, at how many distinct
+periods these crystalline strata have been formed.
+
+
+FOOTNOTES:
+
+[474-A] Keilhau, Gæa Norvegica, pp. 61-63.
+
+[475-A] Geol. Manual, p. 479.
+
+[475-B] Phil. Trans., 1804.
+
+[476-A] Poggendorf's Annalen, No. xvi., 2d series, vol. iii.
+
+[476-B] See Principles, _Index_, "Carbonated Springs," &c.
+
+[476-C] Hoffmann's Liparischen Inseln, p. 38. Leipzig, 1832.
+
+[477-A] See Princ. of Geol.; and Bulletin de la Soc. Géol. de France,
+tom. ii. p. 230.
+
+[477-B] See Princ. of Geol.; and Daubeny's Volcanos, p. 167.
+
+[477-C] Jam. Ed. New Phil. Journ., No. 51. p. 43.
+
+[478-A] Syst. of Geol., vol. i. p. 210.
+
+[478-B] Ibid., p. 211.
+
+[478-C] See above, pp. 327, 333.
+
+[479-A] See Lyell, Quart. Geol. Journ., vol. i. p. 199.
+
+[479-B] Dr. Boase, Primary Geology, p. 319.
+
+[480-A] Geol. Trans., 2d series, vol. ii. p. 227.
+
+[480-B] Darwin, Volcanic Islands, pp. 69, 70.
+
+[480-C] Geol. Obs. in S. America, p. 167. See also above, p. 471.
+
+[480-D] Bulletin, vol. iv. p. 1301.
+
+
+
+
+CHAPTER XXXVII.
+
+ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.
+
+   Age of each set of metamorphic strata twofold--Test of age by fossils
+   and mineral character not available--Test by superposition
+   ambiguous--Conversion of dense masses of fossiliferous strata into
+   metamorphic rocks--Limestone and shale of Carrara--Metamorphic strata
+   of modern periods in the Alps of Switzerland and Savoy--Why the
+   visible crystalline strata are none of them very modern--Order of
+   succession in metamorphic rocks--Uniformity of mineral character--Why
+   the metamorphic strata are less calcareous than the fossiliferous.
+
+
+According to the theory adopted in the last chapter, the age of each set of
+metamorphic strata is twofold--they have been deposited at one period, they
+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 crystallization. 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. If in the latter, it should be called Eocene when
+regarded as a metamorphic rock, although it be liassic when considered in
+reference to the era of its deposition. According to this view, the
+superposition of chalk does not prevent the subjacent _metamorphic_ rock
+from being Eocene. If, however, in the progress of science, we should
+succeed in ascertaining the twofold chronological relations of the
+metamorphic formations, it might be useful to adopt a twofold terminology.
+We might call the strata above alluded to Liassic-Eocene, or
+Liassic-Cretaceous strata of the Hypogene class; the first term referring
+to the era of deposition, the second to that of crystallization.
+
+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.)
+
+But when the metamorphic action has operated on a grander scale, it tends
+entirely to destroy all monuments of the date of its development. 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
+we have to compare two portions of a mountain chain--the one metamorphic,
+and the other unaltered--all the labour and skill of the most practised
+observers are required. 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.
+
+_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 downwards into talc-schist and garnetiferous
+mica-schist; these rocks again graduating downwards into gneiss, which is
+penetrated, at Forno, by granite veins. Now the researches of MM. Savi,
+Boué, Pareto, Guidoni, De la Beche, Hoffmann, and Pilla, have 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, euphotide, 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.[483-A]
+Had these secondary strata of the Apennines undergone universally as
+great an amount of transmutation, it would have been impossible to form
+a conjecture respecting their true age; and then, according to the
+common method of geological classification, 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.
+
+_Alps of Switzerland._--In the Alps, analogous conclusions have been drawn
+respecting the alteration of strata on a still more extended scale. In the
+eastern part of that chain, some of the primary fossiliferous strata, as
+well as the older secondary formations, together with the oolitic and
+cretaceous rocks, are distinctly recognizable. Tertiary deposits also
+appear in a less elevated position on the flanks of the Eastern Alps; but
+in the Central or Swiss Alps, the primary fossiliferous and older secondary
+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. In regard to the age of this vast assemblage
+of crystalline strata, we can merely affirm that some of the upper portions
+are altered newer secondary, and some of them even Eocene deposits; but we
+cannot avoid suspecting that the disappearance both of the older secondary
+and primary fossiliferous rocks may be owing to their having been all
+converted in this region into crystalline schist.
+
+It is difficult to convey to those who have never visited the Alps a just
+idea of the various proofs which concur to produce this conviction. In the
+first place, there are certain regions where Oolitic, Cretaceous, and
+Eocene strata have been turned into granular marble, gneiss, and other
+metamorphic schists, near their contact with granite. This fact shows
+undeniably that plutonic causes continued to be in operation in the Alps
+down to a late period, even after the deposition of some of the nummulitic
+or older Eocene formations. Having established this point, we are the more
+willing to believe that many inferior fossiliferous rocks, probably exposed
+for longer periods to a similar action, may have become metamorphic to a
+still greater extent.
+
+We also discover in parts of the Swiss Alps dense masses of secondary
+and even tertiary strata, which have assumed that semi-crystalline
+texture which Werner called transition, and which naturally led his
+followers, who attached great importance to mineral characters taken
+alone, to class them as transition formations, or as groups older than
+the lowest secondary rocks. (See p. 92.) Now, it is probable that these
+strata have been affected, although 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, and we have already seen (p. 445.) that at some
+points, as in the Valorsine, near Mont Blanc, granite and granitic veins
+are observable, piercing through talcose gneiss, which passes insensibly
+upwards 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 we find the
+most stupendous monuments of mechanical violence, by which strata thousands
+of feet thick have been bent, folded, and overturned. (See p. 58.) It is
+here that 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.
+
+If the reader will consult the works of many eminent geologists who have
+explored the Alps, especially those of MM. De Beaumont, Studer, Necker,
+Boué, and Murchison, he will learn that they all share, more or less fully,
+in the opinions above expressed. It has, indeed, been stated by MM. Studer
+and Hugi, that there are complete alternations on a large scale of
+secondary strata, containing fossils, with gneiss and other rocks, of a
+perfectly metamorphic structure. I have visited some of the most remarkable
+localities referred to by these authors; but although agreeing with them
+that there are passages from the fossiliferous to the metamorphic series
+far from the contact of granite or other plutonic rocks, I was unable to
+convince myself that the distinct alternations of highly crystalline, with
+unaltered strata above alluded to, might not admit of a different
+explanation. 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.
+
+On the Sattel also, at the base of the Gestellihorn, above Enzen, in the
+valley of Urbach, near Meyringen, some of the intercalations of gneiss
+between fossiliferous strata may, I conceive, be ascribed to mechanical
+derangement. Almost any hypothesis of repeated changes of position may be
+resorted to in a region of such extraordinary confusion. The secondary
+strata may first have been vertical, and then certain portions may have
+become metamorphic (the plutonic influence ascending from below), while
+intervening strata remained unchanged. The whole series of beds may then
+again have been thrown into a nearly horizontal position, giving rise to
+the superposition of crystalline upon fossiliferous formations.
+
+It was remarked, in Chap. XXXIV., that as the hypogene rocks, both
+stratified and unstratified, crystallize 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.
+
+_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, 1st, saccharine marble; 2dly, talcose-schist; and
+3dly, of quartz-rock and gneiss; where unaltered, of, 1st, fossiliferous
+limestone; 2dly, shale; and 3dly, 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._--Humboldt has
+emphatically 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 recognize our old acquaintances,--the
+same granite, the same gneiss, the same micaceous schist, quartz-rock,
+and the rest. It is certainly true that there is a great and striking
+general resemblance in the principal kinds of hypogene rocks, although
+of very different ages and countries; but it has been shown that each of
+these are, in fact, geological families of rocks, and not definite
+mineral compounds. They are much 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
+melted and made to crystallize, 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.
+
+Nevertheless, it would be a great error to assume 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. In
+the first place, different assemblages of hypogene rocks occur in different
+countries; and, secondly, in any one district, the rocks which pass under
+the same name are often extremely variable in their component ingredients,
+or at least in the proportions in which each of these are present. Thus,
+for example, gneiss and mica-schist, so abundant in the Grampians, are
+wanting in Cumberland, Wales, and Cornwall; in parts of the Swiss and
+Italian Alps, the gneiss and granite are talcose, and not micaceous, as in
+Scotland; hornblende prevails in the granite of Scotland--schorl in that of
+Cornwall--albite in the plutonic rocks of the Andes--common felspar in
+those of Europe. In one part of Scotland, the mica-schist is full of
+garnets; in another it is wholly devoid of them: while in South America,
+according to Mr. Darwin, it is the gneiss, and not the mica-schist, which
+is most commonly garnetiferous. And not only do the proportional quantities
+of felspar, 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 (p. 369., and table, p. 377.).
+
+_The Metamorphic strata, why less calcareous than the fossiliferous._--It
+has been remarked, that the quantity of calcareous matter in metamorphic
+strata, or, indeed, in the hypogene formations generally, is far less than
+in fossiliferous deposits. Thus the crystalline schists of the Grampians in
+Scotland, consisting of gneiss, mica-schist, hornblende-schist, and other
+rocks, many thousands of yards in thickness, contain an exceedingly small
+proportion of interstratified calcareous beds, although these have been the
+objects of careful search for economical purposes. Yet limestone is not
+wanting in the Grampians, and it is associated sometimes with gneiss,
+sometimes with mica-schist, and in other places with other members of the
+metamorphic series. But where limestone occurs abundantly, as at Carrara,
+and in parts of the Alps, in connection with hypogene rocks, it usually
+forms one of the superior members of the crystalline group.
+
+The scarcity, then, of carbonate of lime in the plutonic and metamorphic
+rocks generally, seems to be the result of some general cause. So long as
+the hypogene rocks were believed to have originated antecedently to the
+creation of organic beings, it was easy to impute the absence of lime 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. Although we cannot descend into the
+subterranean regions where volcanic heat is developed, we can observe in
+regions of spent volcanos, 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. The
+quantity of calcareous matter which these springs transfer, in the course
+of ages, from the lower parts of the earth's crust to the superior or newly
+formed parts of the same, must be considerable.[487-A]
+
+If the quantity of siliceous and aluminous ingredients brought up by
+such springs were great, instead of being utterly insignificant, it
+might be contended that the mineral matter thus expelled implies simply
+the decomposition of ordinary subterranean rocks; but the prodigious
+excess of carbonate of lime over every other element must, in the course
+of time, cause the crust of the earth below to be almost entirely
+deprived of its calcareous constituents, while we know that the same
+action imparts to newer deposits, ever forming in seas and lakes, an
+excess of carbonate of lime. Calcareous matter is poured into these
+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.
+
+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 volcanos, 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. That the removal of the calcareous matter of fossil
+shells is of frequent occurrence, 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. We ought not indeed to marvel at the general absence of
+organic remains from the crystalline strata, when we bear in mind how often
+fossils are obliterated, wholly or in part, even in tertiary
+formations--how often vast masses of sandstone and shale, of different
+ages, and thousands of feet thick, are devoid of fossils--how certain
+strata may first have been deprived of a portion of their fossils when they
+became semi-crystalline, or assumed the _transition_ state of Werner--and
+how the remaining organic remains have been effaced when they were rendered
+metamorphic. Some rocks of the last-mentioned class, moreover, must have
+been exposed again and again to renewed plutonic action.
+
+
+FOOTNOTES:
+
+[483-A] See notices of Savi, Hoffmann, and others, referred to by Boué,
+Bull. de la Soc. Géol. de France, tom. v. p. 317.; and tom. iii. p. xliv.;
+also Pilla, cited by Murchison, Quart. Geol. Journ., vol. v. p. 266.
+
+[487-A] See Principles, _Index_, "Calcareous Springs."
+
+
+
+
+CHAPTER XXXVIII.
+
+MINERAL VEINS.
+
+   Werner's doctrine that mineral veins were fissures filled from
+   above--Veins of segregation--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--Shells and pebbles in lodes--Evidence
+   of the successive enlargement and re-opening of veins--Fournet's
+   observations in Auvergne--Dimensions of veins--Why some alternately
+   swell out and contract--Filling of lodes by sublimation from
+   below--Chemical and electrical action--Relative age of the precious
+   metals--Copper and lead veins in Ireland older than Cornish tin--Lead
+   vein in lias, Glamorganshire--Gold in Russia--Connection of hot
+   springs and mineral veins--Concluding remarks.
+
+
+The manner in which metallic substances are distributed through the earth's
+crust, and more especially the phenomena of those nearly vertical and
+tabular masses of ore called mineral veins, from which the larger part of
+the precious metals used by man are obtained,--these are subjects of the
+highest practical importance to the miner, and of no less theoretical
+interest to the geologist.
+
+The views entertained respecting metalliferous veins have been modified,
+or, rather, have undergone an almost complete revolution, since the middle
+of the last century, when Werner, as director of the School of Mines, at
+Freiberg in Saxony, first attempted to generalize the facts then known. He
+taught that mineral veins had originally been open fissures which were
+gradually filled up with crystalline and metallic matter, and that many of
+them, after being once filled, had been again enlarged or re-opened. He
+also pointed out that veins thus formed are not all referable to one era,
+but are of various geological dates.
+
+Such opinions, although slightly hinted at by earlier writers, had never
+before been generally received, and their announcement by one of high
+authority and great experience constituted an era in the science.
+Nevertheless, I have shown, when tracing, in another work, the history and
+progress of geology, that Werner was far behind some of his predecessors in
+his theory of the volcanic rocks, and less enlightened than his
+contemporary, Dr. Hutton, in his speculations as to the origin of
+granite.[489-A] According to him, the plutonic formations, as well as the
+crystalline schists, were substances precipitated from a chaotic fluid in
+some primeval or nascent condition of the planet; and the metals,
+therefore, being closely connected with them, had partaken, according to
+him, of a like mysterious origin. He also held that the trap rocks were
+aqueous deposits, and that dikes of porphyry, greenstone, and basalt, were
+fissures filled with their several contents from above. Hence he naturally
+inferred that mineral veins had derived their component materials from an
+incumbent ocean, rather than from a subterranean source; that these
+materials had been first dissolved in the waters above, instead of having
+risen up by sublimation from lakes and seas of igneous matter below.
+
+In proportion as the hypothesis of a primeval fluid, or "chaotic
+menstruum," was abandoned, in reference to the plutonic formations, and
+when all geologists had come to be of one mind as to the true relation of
+the volcanic and trappean rocks, reasonable hopes began to be entertained
+that the phenomena of mineral veins might be explained by known causes, or
+by chemical, thermal, and electrical agency still at work in the interior
+of the earth. The grounds of this conclusion will be better understood when
+the geological facts brought to light by mining operations have been
+described and explained.
+
+_On different kinds of mineral veins._--Every geologist is familiarly
+acquainted with those veins of quartz which abound in hypogene strata,
+forming lenticular masses of limited extent. They are sometimes observed,
+also, in sandstones and shales. Veins of carbonate of lime are equally
+common in fossiliferous rocks, especially in limestones. Such veins appear
+to have once been chinks or small cavities, caused, like cracks in clay, by
+the shrinking of the mass, which has consolidated from a fluid state, or
+has simply contracted its dimensions 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, or by segregation, as it is often
+termed. Mixed with hot water and steam, metallic ores may have permeated a
+pasty matrix 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
+downwards 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 3 or 4 feet. They hold
+their course continuously in a certain prevailing direction for miles or
+leagues, passing through rocks varying in mineral composition.
+
+[3 Illustrations: Fig. 513. Fig. 514. Fig. 515. Vertical sections of the
+mine of Huel Peever, Redruth, Cornwall.]
+
+_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. 62.). 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. 513., 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 veinstones.
+
+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 the shock of a third earthquake to occur, breaking
+asunder all the rocks along the line c _c_, fig. 514.; the fissure in this
+instance, being only 6 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 heaved 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.
+
+Again, in fig. 515. 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 upwards 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.[491-A] The principal movement here referred to, or that of _c c_,
+fig. 515., 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, 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 above, p. 69.) 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 frequently polished and striated, as if they had
+undergone great friction, and this even in cases where there has been no
+shift. We may attribute such rubbing to a vibratory motion known to
+accompany earthquakes, and to produce trituration on the opposite walls of
+rents. Similar movements have sometimes occurred in mineral veins which
+had been wholly or partially filled up; for included pieces of rock,
+detached from the sides, are found to be rounded, polished, and striated.
+
+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. In Bohemia, such pebbles have been
+met with at the depth of 180 fathoms. 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 12
+feet long and as many wide.[492-A] Marine fossil shells, also, have been
+found at great depths, having probably been engulphed during submarine
+earthquakes. Thus, a gryphæa is stated by M. Virlet to have been met
+with in a lead-mine near Sémur, in France, and a madrepore in a compact
+vein of cinnabar in Hungary.[492-B]
+
+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 contemporaneous trap dikes, admitted by all
+to be masses of melted matter which have filled rents, are often parallel.
+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. I have already spoken of parallel layers of clay, quartz, and
+ore. Werner himself 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
+beds 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, &c. In these cases,
+the central mass has been last formed, and the two plates which coat the
+outer 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 veinstone consist of crystalline matter, the points of the crystals
+are always turned inwards, or towards the centre of the vein; in other
+words, they point in that direction where there was most 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. 516.) from a
+copper-mine in granite, near Redruth.[493-A] Each of the plates or combs
+(_a_, _b_, _c_, _d_, _e_, _f_) are double, having the points of their
+crystals turned inwards 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.
+
+[Illustration: Fig. 516. Copper lode, near Redruth, enlarged at
+six successive periods.]
+
+A somewhat analogous interpretation is applicable to numbers of other
+cases, where clay, sand, or angular detritus, alternate with ores and
+veinstones. Thus, we may imagine the sides of a fissure to be encrusted
+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.[493-B] 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
+veinstones. 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 other
+sets of mineral deposits, until, at last, pebbles of the basaltic lavas
+of Auvergne, derived from superficial alluviums, probably of Miocene or
+older Pliocene date, were swept into the veins. I have not space to
+enumerate all the changes minutely detailed by M. Fournet, but they are
+valuable, both to the miner and geologist, as showing how the supposed
+signs of violent catastrophes may be the monuments, not of one
+paroxysmal shock, but of reiterated movements.
+
+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 any where else. It is quite otherwise in the
+case of dikes, where each opening has been the receptacle of one continuous
+and homogeneous mass of melted matter, the consolidation of which has taken
+place under considerable pressure. Trappean dikes can rarely fail to
+strengthen the rocks at the points where before they were weakest; and if
+the upheaving force is again exerted in the same direction, the crust of
+the earth will give way anywhere rather than at the precise points where
+the first rents were produced.
+
+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 Andreasberg in the Hartz, which
+has been worked for a depth of 500 yards perpendicularly, and 200
+horizontally, retaining almost every where a width of 3 feet. But many
+lodes in Cornwall and elsewhere are extremely variable in size, being 1 or
+2 inches in one part, and then 8 or 10 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 the annexed diagrams.
+
+[Illustration: Fig. 517. Schematic sketch.]
+
+[Illustration: Fig. 518. Schematic sketch.]
+
+[Illustration: Fig. 519. Schematic sketch.]
+
+Let _a b_, fig. 517., be a line of fracture traversing a rock, and let _a
+b_, fig. 518., represent the same line. Now, if we cut 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. 519., 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.
+
+[Illustration: Fig. 520. Schematic sketch.]
+
+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 varying from 15° to 45°. 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. 520., 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
+much 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 not
+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 volcanos and earthquakes, have made
+their way to the surface. For we know that the rents in which ores abound
+extend downwards 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 volcanos, are nevertheless observed to burst out along great lines
+of upheaval and dislocation of rocks.[496-A] It is also ascertained that
+all the substances with which hot springs are impregnated agree with those
+discharged in a gaseous form from volcanos. Many of these bodies occur as
+veinstones; 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
+crystallization, 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 alkalis,
+soda and potash. These are not met with in veins, although they enter so
+largely into the composition of granitic rocks.[496-B]
+
+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 upwards 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 "toadstone," 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 veinstones, 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 versâ_.
+The same observation applies to killas and the granitic porphyry called
+elvan. Sometimes, in the same continuous vein, the granite will contain
+copper, and the killas tin, or _vice versâ_."[497-A] Mr. Fox, after
+ascertaining the existence at present of electric currents in some of
+the metalliferous veins in Cornwall, has speculated on the probability
+of the same cause having acted originally on the sulphurets and muriates
+of copper, tin, iron, and zinc, dissolved in the hot water of fissures,
+so as to determine the peculiar mode of their distribution. After
+instituting experiments on this subject, he even endeavoured to account
+for the prevalence of an east and west direction in the principal
+Cornish lodes by their position at right angles to the earth's
+magnetism; but Mr. Henwood and other experienced miners have pointed out
+objections to the theory; and it must be owned that the direction of
+veins in different mining districts varies so entirely that it seems to
+depend on lines of fracture, rather than on the laws of voltaic
+electricity. Nevertheless, as different kinds of rock would be often in
+different electrical conditions, we may readily believe that electricity
+must often govern the arrangement of metallic precipitates in a rent.
+
+"I have observed," says Mr. R. Fox, "that when the chloride of tin in
+solution is placed in the voltaic circuit, part of the tin is deposited in
+a metallic state at the negative pole, and part at the positive one, in the
+state of a peroxide, such as it occurs in our Cornish mines. This
+experiment may serve to explain why tin is found contiguous to, and
+intermixed with, copper ore, and likewise separated from it, in other parts
+of the same lode."[497-B]
+
+_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 recognized 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.[498-A]
+
+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.[498-B]
+
+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.
+496., p. 445.), 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. 491. 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 few 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.[499-A] We may, therefore,
+assert that the most ancient Cornish lodes are younger than the
+coal-measures of that part of England, and it follows that they are of a
+much later date than the Irish copper and lead of Wexford and some
+adjoining counties. How much later it is not so easy to declare,
+although probably they are not newer than the beginning of the Permian
+period, as no tin lodes have been discovered in any red sandstone of the
+Poikilitic group, which overlies the coal in the south-west of England.
+
+There are lead veins in the Mendip hills which extend through the mountain
+limestone into the Permian or Dolomitic conglomerate, and others in
+Glamorganshire which enter the lias. Those worked near Frome, in
+Somersetshire, 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, we can merely
+affirm that it occurs in veins of quartz in the schistose and granitic
+rocks of that chain. Sir R. Murchison observes, 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 rolled pebbles of these same Permian strata. Hence it seems that
+the Uralian quartz veins, containing gold and platinum, were not exposed to
+aqueous denudation during the Permian era. But we cannot feel sure, from
+any data yet before us, that such auriferous veins of quartz may not be as
+old as the tin lodes of Cornwall, in which, as well as the more ancient
+copper lodes of Ireland, some gold has been detected. We are also unable at
+present to assign to the gold veins of Brazil, Peru, or California, their
+respective geological dates. But, although enough is known to show that
+Ovid's line about the "Age of Gold," "Aurea prima sata est ætas," would, by
+no means, be an apt motto for a treatise on mining, it would be equally
+rash in the present state of our inquiries to affirm, as some have done,
+that gold was the last-formed of metals.
+
+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 rocks, whereas tin is met with in granite and in veins
+associated with the granitic series. If this rule hold true generally, the
+geological position of tin in localities accessible to the miners 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. 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 rocks, 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, 34th, and 37th chapters, on the chronology of the
+volcanic and hypogene formations.
+
+       *       *       *       *       *
+
+_Concluding Remarks._--The theory of the origin of the hypogene rocks, at a
+variety of successive periods, as expounded in two of the chapters just
+cited, and still more the doctrine that such rocks may be now in the daily
+course of formation, has made and still makes its way, but slowly, into
+favour. The disinclination to embrace it has arisen partly from an inherent
+obscurity in the very nature of the evidence of plutonic action when
+developed on a great scale, at particular periods. It has also sprung, in
+some degree, from extrinsic considerations; many geologists having been
+unwilling to believe the doctrine of the transmutation of fossiliferous
+into crystalline rocks, because they were desirous of finding proofs of a
+beginning, and of tracing back the history of our terraqueous system to
+times anterior to the creation of organic beings. But if these expectations
+have been disappointed, if we have found it impossible to assign a limit to
+that time throughout which it has pleased an Omnipotent and Eternal Being
+to manifest his creative power, we have at least succeeded beyond all hope
+in carrying back our researches to times antecedent to the existence of
+man. We can prove that man had a beginning, and that, all the species now
+contemporary with man, and many others which preceded, had also a
+beginning, and that, consequently, the present state of the organic world
+has not gone on from all eternity, as some philosophers have maintained.
+
+It can be shown that the earth's surface has been remodelled again and
+again; mountain chains have been raised or sunk; valleys formed, filled
+up, and then re-excavated; sea and land have changed places; yet
+throughout all these revolutions, and the consequent alterations of
+local and general climate, animal and vegetable life has been sustained.
+This has been accomplished without violation of the laws now governing
+the organic creation, by which limits are assigned to the variability of
+species. The succession of living beings appears to have been continued
+not by the transmutation of species, but by the introduction into the
+earth from time to time of new plants and animals, and each assemblage
+of new species must have been admirably fitted for the new states of the
+globe as they arose, or they would not have increased and multiplied and
+endured for indefinite periods.[501-A]
+
+Astronomy had been unable to establish the plurality of habitable worlds
+throughout space, however favourite a subject of conjecture and
+speculation; but geology, although it cannot prove that other planets
+are peopled with appropriate races of living beings, has demonstrated
+the truth of conclusions scarcely less wonderful,--the existence on our
+own planet of so many habitable surfaces, or worlds as they have been
+called, each distinct in time, and peopled with its peculiar races of
+aquatic and terrestrial beings.
+
+The proofs now accumulated of the close analogy between extinct and recent
+species are such as to leave no doubt on the mind that the same harmony of
+parts and beauty of contrivance which we admire in the living creation, has
+equally characterized the organic world at remote periods. Thus as we
+increase our knowledge of the inexhaustible variety displayed in living
+nature, and admire the infinite wisdom and power which it displays, our
+admiration is multiplied by the reflection, that it is only the last of a
+great series of pre-existing creations, of which we cannot estimate the
+number or limit in times past.[501-B]
+
+
+FOOTNOTES:
+
+[489-A] Principles, &c. chap. iv. 8th ed. p. 49.
+
+[491-A] Geol. Trans. vol. iv. p. 139.; Trans. Roy. Geol. Society
+Cornwall, vol. ii. p. 90.
+
+[492-A] Carne, Trans. of Geol. Soc. Cornwall, vol. iii. p. 238.
+
+[492-B] Fournet, Etudes sur les Dépots Metalliferes.
+
+[493-A] Geol. Rep. on Cornwall, p. 340.
+
+[493-B] Principles, ch. xxvii. 8th ed. p. 422.
+
+[496-A] See Dr. Daubeny's Volcanos.
+
+[496-B] Bulletin, iv. p. 1278.
+
+[497-A] R. W. Fox on Mineral Veins, p. 10.
+
+[497-B] Ibid. p. 38.
+
+[498-A] I am indebted to Sir H. De la Beche for this information. See also
+maps and sections of Irish Survey.
+
+[498-B] Sir H. De la Beche, MS. notes on Irish Survey.
+
+[499-A] Report on Geology of Cornwall, p. 310.
+
+[501-A] See Principles of Geol., Book 3.
+
+[501-B] See the author's Anniv. Address to the Geol. Soc. 1837. Proceedings
+of G. S. No. 49. p. 520.
+
+
+
+
+INDEX.
+
+
+  A.
+
+  Ægean Sea, mud of, 35.
+    animal life in depths of, 137.
+
+  Agassiz, M., cited, 192. 276. 300. 335. 344. 345.
+    on parallel roads, 87.
+    on fossil fishes of molasse and faluns, 171.
+    on fossil fish of Lias, 275.
+    on fossil fish in Permian marl-slate, 304.
+    on fish from Sheppey, 202.
+    on foot-prints, 299.
+    on fishes of brown coal, 417.
+    on glaciers, 140. 143.
+
+  Age of formation determined by fragments of older rock, 101.
+    of metamorphic rocks, 482.
+    test of, in plutonic rocks by relative position, 449.
+    of Spanish volcanos, 414.
+    of volcanic rocks, how tested, 397-400.
+
+  Aix-la-Chapelle, hot spring at, 477.
+
+  Alabaster defined, 13.
+
+  Alabama, cretaceous shingle of, 225.
+
+  Alberti on the Keuper, 287.
+
+  Alexander, Capt., marine shells in crag, found by, 149.
+
+  Alluvium, term explained, 79.
+    in Auvergne, 80.
+    of the Wealden, 252.
+
+  Alps, nummulitic formation of, 205.
+    curved strata of, 58.
+    Swiss and Savoy, cleavage of, 470.
+    of Switzerland, 483.
+
+  Alpine blocks on the Jura, 142.
+    erratics, 140.
+
+  Altered rocks, 381. 456.
+    by subterranean gases, 476.
+
+  Alternations of rocks, 14.
+    of marine and freshwater formations, 32.
+
+  Alumine in rocks, 11.
+
+  _Amblyrhynchus cristatus_, 279.
+
+  America, North, lithodomi in beaches of, 78.
+    South, cretaceous strata, 225.
+    South, gradual rise of parts of, 46.
+    South, fossils of, 157.
+
+  Amygdaloid, 372.
+
+  Amphitherium, 268.
+
+  Andelys, chalk cliffs at, 239.
+
+  Andernach, strata near, 417.
+
+  Andes, plutonic rocks of, 453.
+    rocks drifted from to Chiloe, 144.
+
+  Anthracite in Rhode Island, 478.
+
+  Anticlinal line, 48. 57.
+
+  Antrim, rocks altered by dikes in, 382.
+
+  Antwerp, strata like Suffolk crag near, 166.
+
+  _Apateon pedestris_, a carboniferous reptile, 336.
+
+  Apennines, limestone in, 482.
+
+  Appalachian coal-field, 329.
+
+  Appalachians, altered rocks in, 478.
+
+  _Apteryx_ in New Zealand, 158.
+
+  Aqueous rocks defined, 2.
+    rocks, mineral character of, 97.
+    deposits, superposition of, 96.
+
+  Arbroath, section from, to the Grampians, 48.
+
+  Archegosaurus, figure of, 337.
+
+  Archiac, M., cited, 143.
+    on fossils in chalk, 221.
+    on shells in French Lower Eocene, 196.
+
+  Ardèche, lava in, 385.
+
+  Arenaceous rocks described, 11.
+
+  Argillaceous rocks, 11.
+    schist, 465.
+
+  Argile plastique, or Lower Eocene, 196.
+
+  Argyleshire, trap-vein in cliff, 379.
+
+  Arran, age of granite in, 459.
+    section of, 461.
+    dike of greenstone in, 379.
+
+  Arthur's Seat, altered strata of, 383.
+
+  Ashby-de-la-Zouch, fault in coal-field of, 69.
+
+  Ascension, lamination of volcanic rocks in, 480.
+
+  Asterophyllites, 314.
+
+  Asti, formations at, 167.
+
+  Atherfield, cretaceous strata of, 219.
+
+  Augite, 369.
+
+  Aurillac, freshwater strata of, 188.
+
+  Austen, Mr., R. A. C., on phosphate of lime, 219.
+
+  Australian cave-breccias, 155.
+
+  Auvergne freshwater formations, 186.
+    succession of changes in, 180.
+    lacustrine strata, 181.
+    mineral veins of, 493.
+    indusial limestone, 184.
+    extinct volcanos of, 422.
+    alluvium in, 80.
+
+  Aymestry limestone, 352.
+
+
+  B.
+
+  Bagshot sands, 199.
+
+  Bacillaria, fossil in tripoli, 25.
+
+  Baiæ, Bay of, strata in, 403.
+
+  Bakewell, Mr., on cleavages of Alps, 470.
+
+  Balgray, near Glasgow, stumps of trees in coal, 317.
+
+  Bahia Blanca, fossil remains at, 148.
+
+  Baltic, brackish water strata on coast of, 114.
+
+  Barcombe, chalk flints near, 253.
+
+  Barton Cliff, 198.
+
+  Barrande, M., on trilobites, 358.
+
+  Basterot, M. de, on tertiaries of south of France, 105.
+
+  Basalt, 371.
+    columnar in the Eifel, 387.
+    columnar, near Vicenza, 386.
+    columnar, structure of, 384.
+
+  Basset, term explained, 56.
+
+  Batrachian, eggs of, in Old Red, Scotland, Postscript, x.
+
+  Bayfield, Capt., on fossil shells in Canada, 134.
+    on inland cliffs in Gulf of St. Lawrence, 78.
+
+  Bean, Mr., shells similar to those in Norwich crag found in Yorkshire
+    by, 149.
+
+  Bean, Mr., on fossil shells from oolite, 272.
+
+  Beachy Head, chalk cliffs near, 246.
+
+  Beaumont, M. E. de, on rocks of Hautes Alpes, 455.
+    on lamination of volcanic rocks, 480.
+
+  Beaumont, M. E. de, on Swiss Alps, 484.
+    on quartz, 439.
+    on oolite formation in France, 221.
+
+  Beck, Dr., on kelp, 217.
+    on graptolites, 357.
+    cited, 162. 186.
+
+  Belemnite in Oxford clay, 262.
+
+  Berger, Dr., on rocks altered by dikes, 382.
+
+  Bergmann on trap, 366.
+
+  Berlin, tertiary strata near, 177.
+
+  Bermuda Islands, lagoons in, 216.
+    rocks of, 78.
+
+  Bernese Alps, gneiss in, 484.
+
+  Berthier, on augite and hornblende, 369.
+
+  Beudant, M., on Hungary, 421.
+
+  Beyrich, Prof., on tertiary strata near Berlin, 177.
+
+  Biaritz, calcareous cliffs of, 72.
+
+  Bilin, tripoli, composed of infusoria, 25.
+
+  Binney, Mr., on stigmaria and sigillaria, 315.
+
+  Birds, footprints of, 298.
+     fossil, scarcity of, Postscript, xix.
+
+  Bischoff, Prof., experiments on heat, 476.
+    on steam at a high temperature, 477.
+
+  Blainville, on number of genera of mollusca, 28.
+
+  Boase, Dr., cited, 479.
+
+  Boblaye, M., on inland cliffs, 73.
+    cited, 431.
+
+  Bog-iron ore, 26.
+
+  Borrowdale, black-lead of, 38.
+
+  Bordeaux, tertiary deposits of, 171.
+
+  Bosquet, M., on Maestricht beds, 210.
+
+  Bothnia, Gulf of, land upheaved, 45.
+
+  Boué, M., on arrangement of rocks, 95.
+    on fossil shells in Hungary, 421.
+    on Carrara marble, 482.
+    on Swiss Alps, 484.
+
+  Bonelli, on strata in Italy, 106.
+
+  Boulder formation in Canada, 133.
+    period, fauna of, 126.
+    formation, mineral ingredients of, 126.
+    formation in England, 130.
+
+  Boulders, 123.
+    striated, 136.
+
+  Boutigny, M., cited, 441.
+
+  Bowen, Lieut. A., R.N., drawings of rocks in Gulf of St. Lawrence, 78.
+
+  Bowerbank, Mr., on fossil flora of Sheppey, 200.
+
+  Bowman, Mr., on coal-seams, 330.
+
+  Bracklesham Bay, characteristic shells of, 199.
+
+  Brash, term, explained, 81.
+
+  Bravard, M., on Auvergne mammalia, 188. 425.
+
+  Breccia on ancient coast lines, 73.
+
+  Brickenden, Captain, on Elgin fossils, Postscript, ix.
+
+  Brighton, elephant bed of, 256.
+
+  Bristol, dolomitic conglomerate near, 305.
+    section of strata near, 102.
+
+  Brocchi, on Subapennines, 105. 167.
+
+  Brockedon, Mr., on black-lead, 38.
+
+  Broderip, Mr., cited, 270.
+
+  Brodie, Rev. P.B., on fossil insects, 281.
+    cited, 207.
+
+  Bromley, oyster-bed near, 204.
+
+  Brongniart, M. Adolphe, on Eocene flora, 200.
+    on flora of cretaceous period, 223.
+    on fossil plants in lias, 282.
+    on plants of Bunter sandstein, 288.
+    on fossil fir-cones, 313.
+    on Permian flora, 307.
+    on sigillaria, 314.
+    on asterophyllites, 314.
+    on stigmaria, 315.
+    age of acrogens, 316.
+    on endogens, 316.
+
+  Brongniart, M. Alex., on Paris tertiaries, 104.
+    on Eocene formation, 175.
+    on shells of nummulitic formation, 205.
+    on coal mine near Lyons, 319.
+
+  Brora, coal formation, 272.
+
+  Brora, granite near, 458.
+
+  Brown, Mr. Richard, on stigmariæ, 315.
+    on coal formation, 415.
+    on Cape Breton coal-field, 324. 334.
+    on carboniferous rain-prints, Postscript, xii.
+
+  Buckland, Dr., on cave at Kirkdale, 154.
+    on coal plants, 317.
+    on coprolites in chalk, 216.
+    on fish of Lias, 276.
+    on footprints, 291.
+    on mountains of Caernarvonshire, 130.
+    on oyster bed near Bromley, 204.
+    on parallel roads, 87.
+    on term Poikilitic, 286.
+    on saurians of Lias, 278.
+    on sudden destruction of saurians, 280.
+    cited, 155. 231. 233. 267. 268.
+
+  Buddle, Mr., on creeps in coal mines, 50.
+    on ancient river-channels of coal period, 334.
+
+  Buist, Dr. G., on saltness of Red Sea, 296.
+
+  Bunbury, Mr. C. J. F., on plants of coal-field, 285.
+
+  Bunter sandstein, 288.
+
+  Burmeister on trilobites, 358.
+
+  Burnes, Sir A., cited, 295.
+
+
+  C.
+
+  Caernarvonshire, ancient glaciers of, 130.
+
+  Calamites, figures of, 313.
+    near Pictou, 319.
+
+  Calcaire grossier, 193.
+    siliceux, 195.
+
+  Calcareous rocks, 12.
+    rocks of Gulf of Spezia, 482.
+    cliffs of Biaritz, 72.
+
+  Caldcleugh, Mr., cited, 399.
+
+  Caldera of Palma, 392.
+
+  Cambrian group, 361.
+    volcanic rocks, 435.
+
+  Campagna di Roma, tuffs of, 408.
+
+  Canada, shells in drift of, 134.
+
+  Cantal, freshwater formation of, 188.
+    igneous rocks of, 429.
+    freshwater beds of, 429.
+
+  Cape Breton, coal measures of, 324.
+    Wrath, granite veins in, 444.
+
+  Caradoc sandstone, 356.
+
+  Carbonaceous shale, 271.
+
+  Carbonate of lime scarce in metamorphic rocks, 487.
+
+  Carbonate of lime in rocks, how tested, 12.
+
+  Carboniferous group, 308.
+    flora, 310.
+    period, plutonic rocks of, 456.
+    period, volcanic rocks of, 432.
+    reptiles, 335.
+
+  Carne, Mr., on Cornish lodes, 491. 492.
+
+  Carrara marble, 482.
+
+  _Caryophyllia cæspitosa_, bed of, in Sicily, 151.
+
+  Castrogiovanni, bent strata near, 58.
+
+  Catalonia, volcanic region of, 408.
+
+  Cautley, Captain, on Sewâlik hills, 173.
+
+  Caves in Europe, 155.
+    at Kirkdale, 154.
+    in Sicily, 153.
+    in Australia, 156.
+
+  Central France, Upper Eocene of, 178.
+
+  Cetacea, fossil, rarity of, Postscript, xxi.
+
+  Chalk, pinnacle of, near Sherringham, 129.
+    of Faxoe, 210. and Postscript, xv.
+    white, fossils of, 26.
+    white, section of, 211.
+    white, extent and origin of, 215.
+    white, animal origin of, 216.
+    pebbles in, 217.
+    difference of, in north and south of Europe, 221.
+
+  Chalk cliffs, inland, on Seine, 238.
+    needles of, in Normandy, 241.
+    flints, bed of, near Barcombe, 253.
+
+  Chambers, Mr., cited, 88.
+
+  Chamisso, cited, 217.
+
+  Chara, in freshwater strata, 31.
+    in flints of Cantal, 189.
+    in Eocene strata of France, 176.
+    in Purbeck beds, 232.
+
+  Charlesworth, Mr. E., cited, on Crag, 162.
+
+  Charpentier, M., on Alpine glaciers, 140.
+    on Swiss glaciers, 143.
+
+  Cheirotherium, footprints of, 290. 337.
+
+  Chemical and mechanical deposits, 33.
+
+  Chili, earthquake in, 61.
+    gold mines in, 472.
+
+  Chiloe, rocks drifted from Andes to, 144.
+
+  Chlorite schist, 465.
+
+  Christiania, dike near, 380.
+    trap rocks, passage of granite into, at, 441.
+    granite near, 457.
+    gneiss near, 446.
+    intrusion of granite into beds near, 446.
+
+  Chronological groups, 101.
+
+  Cinder-bed, Purbeck, 231.
+
+  Claiborne, marine shells of, 206.
+
+  Clausen, Mr., cited, 158.
+
+  Clay, defined, 11.
+
+  Clay-slate, 465. 468.
+
+  Clay-ironstone, 326.
+
+  Clays, plastic, 203.
+
+  Cleavage of rocks, 468.
+
+  Climate of drift period, 139.
+    of coal period, 335.
+
+  Coal, zigzag flexures of, near Mons
+    group, 308.
+    measures, 308. 309.
+    how formed, 317.
+    pipes, danger of, 318.
+    mine, near Lyons, 319.
+    seam at Brownsville, Pennsylvania, view of, 332.
+    conversion of into lignite, 333.
+    formation at Brora, 272.
+    seams, continuity of, 334.
+    period, climate of, 335.
+    strata, footprints of reptiles in, 337.
+
+  Coal-field at Burdiehouse, 325.
+    of Ashby-de-la-Zouch, 69.
+    United States, diagram of, 327.
+    of Yorkshire, fossils of, 325.
+
+  Coalbrook Dale, beetles in coal of, 335.
+    fossil cones in, 313.
+    coal measures of, 324.
+    faults in, 62.
+
+  Cockfield Fell, rocks altered by dikes, 383.
+
+  Columbia, vinegar river of, 191.
+
+  Colchester, Mr., on mammalian remains at Kyson, 203.
+
+  Côme, ravine in lava of, 427.
+
+  Cones in Val di Noto, 389.
+    and craters, absence of, in England, 6.
+    and craters, 367.
+
+  Conifers, fossil trees, 316.
+
+  Concretionary structure, 37.
+
+  Conglomerate, or pudding-stone, 11.
+    dolomitic, 305.
+    vertical in Scotland, &c., 47.
+
+  Connecticut, valley of the, 297.
+    beds, antiquity of, 300.
+
+  Conrad, Mr., on cretaceous rocks, 224.
+
+  Conybeare, Mr., cited, 64. 69. 244. 274.
+    on Plesiosaurus, 278.
+    on oolite and lias, 283.
+    on term Poikilitic, 286.
+    on crocodiles, 201.
+
+  Cook, Capt., on _Fucus giganteus_, 217.
+
+  Coprolites in chalk, 216.
+
+  Coralline crag, fossils in, 164.
+
+  Coral islands and reefs, 34. 46.
+    rag of Oolite, 260.
+
+  Corals, figures of, in crag, 165.
+    of Devonian system, 346.
+    of Devonian strata in United States, 349.
+    in Wenlock formation, 355.
+
+  Corinth, corrosion of rocks by gases near, 477.
+
+  Cornbrash, 263.
+
+  Cornwall, granite veins in, 445. 474.
+    mineral veins in, 490. 494.
+    tin of, newer than Irish copper, 499.
+
+  Cotta, Dr. B., on granite in Saxony, 459.
+
+  Crag coralline, fossils in, 164.
+    comparison of faluns and, 170.
+    of Suffolk, red and coralline, 105. 162.
+    fluvio-marine, Norwich, 148.
+
+  Craigleith fossil trees, 40.
+    quarry, slanting tree in, 320.
+
+  Crater of Island of St. Paul, 395.
+
+  Craven fault, 64.
+
+  Creeps in coal-mines described, 52.
+
+  Credneria in Quadersandstein, Postscript, xvi.
+
+  Cretaceous rocks of Pyrenees, 455.
+    group, 209. 219. and Postscript, xvi.
+    strata in South America and India, 225.
+    period, plutonic rocks of, 455.
+    volcanic rocks, 431.
+    rocks in United States, 224.
+
+  Crocodiles near Cuba, 279.
+
+  Croizet, M., on Auvergne fossil mammalia, 188.
+
+  Cromer, contorted drift near, 129.
+
+  "Crop out," term explained, 55.
+
+  Crust of earth defined, 2.
+
+  Crystalline limestone, 302.
+    rocks, erroneously termed primitive, 9.
+    schists defined, 7.
+
+  Curved strata, 47.
+    strata, experiments to illustrate, 49.
+
+  Cutch, Runn of, 295.
+
+  Cuvier, M., on Eocene formation, 175.
+    on Amphitherium, 268.
+    cited, 192.
+    on tertiary strata near Paris, 104.
+    on fossils of Montmartre, 191.
+
+  Cyclopian Islands, 401.
+
+  Cypris in Lias, 281.
+    in Wealden, 228.
+    in marl of Auvergne, 183.
+
+  Cystideæ in Silurian rocks, 358.
+
+
+  D.
+
+  Dana, Mr., on coprolites of birds, 299.
+    on coral reef in Sandwich Islands, 216.
+    on volcanos of Sandwich Islands, 394. 406. 423.
+
+  Dartmoor, granite of, 456.
+
+  Darwin, Mr., cited, 217.
+    on boulders and glaciers in South America, 144.
+    on cleavage in South America, 471.
+    on coral islands of Pacific, 216.
+    on dike in St. Helena, 406.
+    on habits of ostrich, 299. and Postscript, xx.
+    on fossils in South America, 148.
+    on _Fucus giganteus_, 217.
+    on gradual rise of part of S. America, 46.
+    on lamination of volcanic rocks, 480.
+    on parallel roads, 87.
+    on plutonic rocks of Andes, 453.
+    on recent strata near Lima, 115.
+    on saurians in Galapagos Islands, 279.
+    on sinking of coral reefs, 46.
+    on Welsh glaciers, 131.
+
+  Daubeny, Dr., on the Solfatara, 477.
+
+  Daubeny, Dr., on volcanos in Auvergne, 428.
+
+  Dax, inland cliff at, 72.
+
+  Deane, Dr., on footprints, 298.
+
+  Dean, forest of, coal in, 334.
+
+  Dechen, Prof. von, on reptiles in Saarbrück coal-field, 336.
+
+  De Koninck, cited, 176. 178.
+
+  De la Beche, Sir H., cited, 231. 233. 281.
+    on Carrara marble, 482.
+    on clay beds, 283.
+    on clay-ironstone, 326.
+    on coal-measures near Swansea, 309.
+    on fossil trees, S. Wales, 318.
+    on granite of Dartmoor, 474.
+    on mineral veins, 493. 495. 498.
+    on term supracretaceous, 103.
+    on trap of New Red Sandstone period, 432.
+
+  Deluge, 4.
+
+  Denudation explained, 66.
+    of the Weald Valley, 242.
+    terraces of, in Sicily, 75.
+
+  Derbyshire, lead veins of, 497.
+
+  Deshayes, M., identification of shells, 176.
+    on fossil shells in Hungary, 421.
+    on Lower Eocene shells, 196.
+    on tertiary classification, 110.
+
+  Desmarest, cited, 183.
+    on trappean rocks, 91.
+
+  Desnoyers, M., on Faluns of Touraine, 106.
+
+  Desor, M., on glacial fauna in N. America, 133.
+
+  Devonian flora, 349.
+    strata in United States, 349.
+    system, term explained, 346.
+
+  Diagonal, or cross stratification, 16.
+
+  Dicotyledonous leaves in chalk, Postscript, xvi.
+
+  Dike in St. Helena, 406.
+
+  Dikes at Palagonia in Sicily, 407.
+    trappean, crystalline in centre, 380.
+    defined, 6.
+    in Scotland, 378.
+    of Somma, 404.
+
+  Diluvium, popular explanation of term, 132.
+
+  Dip, term explained, 53.
+
+  Dolerite, or greenstone, 372.
+
+  Dolomite defined, 13.
+
+  Dolomitic conglomerate, 305.
+
+  Doue, M. B. de, on volcanos of Velay, 428.
+
+  Drift contorted, near Cromer, 129.
+    in Ireland, 131.
+    in Norfolk, 126.
+    meteorites in, 145.
+    northern, in Scotland, 125.
+    northern, in North Wales, 130.
+    of Scandinavia, North Germany, and Russia, 121.
+    period, climate of, 139.
+    period, subsidence in, 135.
+    shells in Canada, 134.
+
+  Dudley limestone, 354.
+    shales of coal near, 474.
+
+  Dufrénoy, M., on granite of Pyrenees, 475.
+
+  Duff, Mr. P., on reptile of Old Red, Postscript, ix.
+    on hill of Gergovia, 430.
+
+  Dunker, Dr., on Wealden of Hanover, 237.
+
+
+  E.
+
+  Echinoderms of coralline crag, 166.
+
+  Echinus, figure of, 23.
+
+  Egerton, Mr., on fossils of Southern India, 225.
+
+  Egerton, Sir P., on fish of marl slate, 304.
+    on fossil fish of Connecticut beds, 300.
+    on fossils of Isle of Wight, 198.
+    on saurians and fish in New Red Sandstone, 289.
+    on Ichthyosaurus, 276.
+
+  Eggs, fossil, of snake, 120.
+
+  Ehrenberg, Prof., on bog-iron ore, 26.
+    on infusoria, 24.
+
+  Elephant bed, Brighton, 256.
+
+  _Elephas primigenius_, jaw figured, 159.
+
+  Elvans of Ireland and Cornwall, 498.
+    term explained, 457.
+
+  Encrinites, figure of, 264.
+
+  Endogens, 316.
+
+  Eocene, foraminifera, 194.
+    formations, 174.
+    formations in England, 197.
+    granite, 451.
+    lower, in France, 176-191.
+    middle, in France, 191.
+    strata, in United States, 206.
+    upper, near Louvain, 177.
+    term defined, 111.
+    upper, of Central France, 178.
+    volcanic rocks, 429.
+
+  Equisetaceæ, 313.
+
+  Equisetum of Virginian oolite, 284.
+
+  _Equisetum_ giganteum, 314.
+
+  Erman on meteoric iron in Russia, 145.
+
+  Erratics, Alpine, 140.
+    northern origin of, 123.
+
+  Escher, M., on boulders of Jura, 143.
+
+  Etna, deposits of, 401.
+
+  Eurite, 440.
+
+  Euritic porphyry described, 447.
+
+  Exogens, 316.
+
+
+  F.
+
+  Faluns of Touraine, 106. 168.
+
+  Faluns, comparison of, and crag, 170.
+
+  Falconer, Dr., on Sewâlik Hills, 173.
+
+  Falkland Islands, 88.
+
+  Farnham, phosphate of lime near, 219.
+
+  Fault, term explained, 62.
+
+  Faults, origin of, 64.
+
+  Faxoe, chalk of, 210. and Postscript, xv.
+
+  Felixstow, remains of cetacea found near, 166.
+
+  Felspar, 369.
+
+  Ferns in coal-measures, 310.
+
+  Fife, altered rock in, 383.
+
+  Fifeshire, trap dike in, 434.
+    Megalichthys found in Cannel coal in, 336.
+
+  Fishes, fossil, of Upper Cretaceous, 214.
+    of Old Red Sandstone, 343.
+    of Wealden, 229.
+    fossil, of brown coal, 416.
+
+  Fissures filled with metallic matter, 490.
+    _See_ mineral veins.
+
+  Fitton, Dr., on division of lower cretaceous formation, 219.
+    cited, 227. 231. 233. 237. 244. 247.
+
+  Fleming, Dr., on scales of fish in Old Red, 343.
+    on trap-rocks in coal-field of Forth, 432.
+    on trap dike in Fifeshire, 434.
+
+  Flora, carboniferous, 310.
+    cretaceous, 223.
+    Devonian, 349.
+    of London Clay, 200.
+    permian, 305. 307.
+
+  Flötz, term explained, 91.
+
+  Flysch, explanation of term, 206.
+
+  Footprints of birds, 297. and Postscript, xx.
+    of reptilians, 337.
+    fossil, 289. 290. 291. 297.
+
+  Foraminifera in chalk, 26.
+    Eocene, 194.
+
+  Forbes, Prof. E., on Caradoc sandstone, 359.
+    on Cystideæ, 358.
+    on shells in crag deposits, 162.
+    on cretaceous fossil shells, 224.
+    on fossils of the faluns, 169.
+    on fossils in drift in South Ireland, 131.
+    on deep-sea origin of Silurian strata, 360.
+    on echinoderms of coralline crag, 166.
+    on fauna of boulder period, 125.
+    on migrations of mollusca in glacial period, 166.
+    on fossils of Purbeck group, 231. 233.
+    on strata at Atherfield, 219.
+    on changes of Wealden testacea, 235.
+    on volcanic rocks of Oolite period, 432.
+    on depth of animal life in Ægean, 35. 137.
+    cited, 225.
+
+  Forbes, Prof. James, on zones in volcanic rocks, 480.
+    on the Alps, 143.
+
+  Forchhammer, on scratched limestone, 122.
+
+  Forest, fossil, in Norfolk, 127. 130.
+
+  Forfarshire, Old Red Sandstone in, 479.
+
+  Formation, term defined, 3.
+
+  Fossil, term defined, 4.
+
+  Fossils of chalk and greensand, figures of, 212.
+    in chalk at Faxoe, 210.
+    of coralline crag, 164.
+    of Devonian system, 346. and Postscript, x. xi.
+    of Eocene strata in United States, 207.
+    in faluns of Touraine, 169.
+    freshwater and marine, 27.
+    of Isle of Wight, 198.
+    of Lias, 274.
+    of Ludlow formation, 352.
+    of mountain limestone, 340.
+    of London Clay, 200.
+    of Maestricht beds, 209.
+    of Lower Greensand, 220.
+    of New Red Sandstone, 287. and Postscript, xiii.
+    of Oolite, 259. 266.
+    of Red Crag, 164.
+    of Silurian rocks, 353. and Postscript, vii.
+    of Solenhofen, 260.
+    of Upper Greensand, 218.
+    of Wealden, 236.
+    test of the age of formations, 98.
+
+  Fossil fish of Permian limestone, 303.
+    of Connecticut beds, 300.
+    of Richmond, U. S., strata, 285.
+    of Old Red Sandstone, 343.
+    scales of Permian, figured, 305.
+    footsteps, 289. 290. 291.
+    ferns in carbonaceous shale, 271.
+    forest in Nova Scotia, 321.
+    forest near Wolverhampton, 319.
+    forest in Isle of Portland, 233.
+    plants in Wealden, 230.
+    plants of Lias, 282.
+    plants of Bunter sandstein, 288.
+    trees erect, 317.
+    wood, petrifaction of, 39.
+    wood perforated by Teredina, 24.
+    remains in caves, 154.
+    shells from Etna, 401.
+    shells near Grignon, 193.
+    shells of Mayence strata, 178.
+    shells in Virginia, 172.
+
+  Fossiliferous strata, tabular view of, 361.
+
+  Fournet, M., on mineral veins of Auvergne, 493.
+    on disintegration of rocks, 476.
+    on quartz, 439.
+
+  Fox, Mr. R. W., 472.
+    on Cornish lodes, 497.
+
+  Fox, Rev. Mr., on extinct quadrupeds of Isle of Wight, 198.
+
+  Freshwater beds of Isle of Wight, 197.
+    deposits in valley of Thames, 146.
+    land shells numerous in, 27.
+
+  Freshwater formations of Auvergne, 186.
+
+  Freshwater formation, how distinguished from marine, 27. 28. 30.
+    remains of fish in, 32.
+    associated with Norfolk drift, 127.
+    Chara in, 31.
+    Cypris in, 31.
+
+  Freshwater shells in brown coal near Bonn, 417.
+
+  _Fucus giganteus_, 217.
+    _vesiculosus_, growth of, in Jutland, 217.
+    _vesiculosus_ in Lym-Fiord, 33.
+
+  Fundy, Bay of, impressions in red mud of, 297.
+
+
+  G.
+
+  Gaillonella fossil in Tripoli, 25.
+    ferruginea in bog-iron ore, 26.
+
+  Galapagos Islands, animals of, 279.
+
+  Garnets in altered rock, 382.
+
+  Gases, subterranean rocks altered by, 476.
+
+  Gault, 218.
+
+  Gavarnie, flexures of strata, 59.
+
+  Geology defined, 1.
+
+  Gergovia, hill of, 430.
+
+  Giant's Causeway, columns at, 384.
+
+  Gibbes, R. W., cited, 207.
+
+  Glacial phenomena, northern, origin of, 132.
+
+  Glaciers, Alpine, 140.
+
+  Glaciers on Caernarvonshire mountains, 130.
+
+  Glasgow, marine strata near, 148.
+
+  Glen Roy, parallel roads of, 86.
+
+  Glen Tilt, granite of, 442.
+
+  Gneiss, altered by granite, 445.
+    in Bernese Alps, 484.
+    at Cape Wrath, 444.
+    near Christiania, 446.
+    described, 464.
+
+  Gold, age of, in Ireland, 498.
+    age of, in Ural Mountains, 499.
+
+  Goldfuss, Prof., on reptiles in coal-field, 336.
+
+  Göppert, Prof., on beds of coal, 316.
+    on petrifaction, 40.
+
+  Graham's Island, 389. 407.
+
+  Grampians, old red conglomerates in, 47.
+
+  Granite described, 7. 436. 438. 444.
+    passage of into trap, 441.
+    porphyritic, 439.
+    and limestone, junction of in Glen Tilt, 442.
+    syenitic, 440.
+    talcose, 440.
+    schorly, 440.
+    of Cornwall and Dartmoor, 474.
+    of Swiss Alps, 484.
+    rocks in connection with mineral veins, 500.
+    of Saxony, 459.
+
+  Granites, oldest, 458.
+    varieties of, 444.
+    veins in Cornwall, 445.
+    veins in Cape Wrath, 444.
+    veins in Table Mountain, 443.
+    vein in White Mountains, 450.
+    of Arran, age of, 459.
+    near Christiania, 457.
+    dikes in Mount Battock, 443.
+
+  Graphite, powder of, consolidated by pressure, 38.
+
+  Graptolites, 357.
+
+  Grateloup, M., on fossils in chalk, 223.
+
+  Grauwacke, term explained, 350.
+
+  Greenland, sinking of coast, 46.
+
+  Greensand, upper, 218.
+    fossils of, 212.
+
+  Greensburg, Pennsylvania, footprints of reptile in coal strata at, 337.
+
+  Greenstone or Dolerite, 372.
+    dike of, in Arran, 379.
+
+  Grès de Beauchamp, Paris Basin, 193.
+
+  Grignon, fossil shells near, 193.
+
+  Grit defined, 11.
+
+  Guadaloupe, human skeleton of, 115.
+
+  Guidoni on Carrara marble, 482.
+
+  Gutbier, Col. von, on Permian flora, 305. 307.
+
+  Gryphæa, fossil figure of, 22.
+
+  Gypseous marls, 186.
+    series, 191.
+
+  Gypsum defined, 13.
+
+
+  H.
+
+  Hall, Sir Jas., experiments on fused minerals, 406.
+    on curved strata, 48.
+    Capt. B., cited, 378. 401. 443.
+
+  Hamilton, Sir W., on eruption of Vesuvius, 405.
+
+  Harris, Major, on salt lake in Ethiopia, 296.
+
+  Hartz, Bunter sandstein of, 288.
+
+  Hastings, Lady, fossils collected by, 198.
+
+  Hastings sand, 229.
+    bed, shells of, 229.
+
+  Hautes Alpes, rocks of, 455.
+
+  Haüy cited, 369.
+
+  Hawkshaw, Mr., on fossil trees in coal, 317.
+
+  Hayes, T. L., on icebergs, 123.
+
+  Hébert, M., cited on Upper Eocene beds, 176.
+
+  Hebrides, dikes of trap in, 379.
+
+  Heidelberg, varieties of granite near, 444.
+
+  Henfrey, Mr. A., on food of Mastodon, 138.
+
+  Henslow, Prof., on fossil cetacea in Suffolk, 166.
+    on fossil forests, 233.
+    on dike and altered rock near Plas Newydd, 381.
+
+  Henry, Mr., cited, 476.
+
+  Herschel, Sir J., on slaty cleavage, 472.
+
+  Hertfordshire pudding-stone, 35.
+
+  Hibbert, Dr., on volcanic rocks, 428.
+    on coal field at Burdiehouse, 325.
+    cited, 419.
+
+  High Teesdale, garnets in altered rock at, 382.
+
+  Hildburghausen, footprints of reptile at, 289. 290.
+
+  Hippurite limestone, 221.
+
+  Hitchcock, Prof., on footprints, 297.
+
+  Hoffmann, Mr., on Lipari Islands, cited, 476.
+    on cave near Palermo, 74.
+    on Carrara marble, 482.
+
+  Hooghly river, analysis of water, 41.
+
+  Hopkins, Mr., on fractures in Weald, 251.
+
+  Horizontality of strata, 15.
+    of roads of Lochaber, 88.
+
+  Hornblende, 369.
+    schist, 464. 478.
+
+  Horner, Mr., on geology of Eifel, 415.
+    on Megalichthys, 336.
+
+  Hubbard, Prof., on granite vein in White Mountains, 450.
+
+  Hugi, M., on Swiss Alps, 484.
+
+  Humboldt, cited, 314.
+    on uniform character of rocks, 486.
+
+  Hungary, trachyte of, 442.
+    volcanic rocks of, 421.
+
+  Hunt, Mr., experiments on clay-ironstone, 326.
+
+  Hutton, opinions of, 60.
+
+  Huttonian theory, 92.
+
+  Hypogene, term defined, 9.
+    rocks, mineral character of, 485.
+    or metamorphic limestone, 465.
+
+
+  I.
+
+  Ibbetson, Capt., on chalk Isle of Wight, 215.
+
+  Ice, rocks drifted by, 122.
+
+  Icebergs, stranding of, 129. 137.
+
+  Iceland, icebergs drifted to, 137.
+
+  Ichthyolites of Old Red Sandstone, 349.
+
+  _Ichthyosaurus communis_, figure of, 277.
+
+  Igneous rocks, 6.
+    of Siebengebirge and Westerwald, 417.
+    rocks of Val di Noto, 389.
+
+  _Iguanodon Mantelli_, 227. 229.
+
+  India, cretaceous system in, 225.
+    freshwater deposits of, 173.
+    oolitic formation in, 285.
+
+  Indusial limestone, Auvergne, 184.
+
+  Infusoria in tripoli, 24.
+
+  Inland sea-cliffs in South of England, 71.
+
+  Insects in Lias, 281.
+
+  Ireland, drift in, 131.
+
+  Ischia, volcanic cones in, 403.
+    Post-Pliocene strata of, 113.
+
+  Isle of Wight, freshwater beds of, 197.
+
+  Isomorphism, theory of, 370.
+
+
+  J.
+
+  Jackson, Dr. C. T., analysis of fossil bones, 138.
+
+  James, Capt., on fossils in drift South Ireland, 131.
+
+  Java, stream of sulphureous water, 191.
+
+  Jobert, M., on hill of Gergovia, 430.
+
+  Joints, 469.
+
+  Jorullo, lava stream of, 450.
+
+  Jura, alpine blocks on, 142.
+    limestone, 261.
+    structure of, 55.
+
+
+  K.
+
+  Kangaroo, fossil and recent, jaws figured, 156.
+
+  Kaup, Prof., on footprints of Cheirotherium, 290.
+
+  Kaye, Mr., on fossils of Southern India, 225.
+
+  Keeling Island, fragment of greenstone in, 217.
+
+  Keilhau, Prof., cited, 457. 474.
+    on dike of greenstone, 380.
+    on gneiss near Christiania, 446.
+    on granite, 447.
+
+  Kelloway rock, 34.
+
+  Kentish chalk, sand-galls in, 82.
+
+  Keuper, the, 287.
+
+  Killas in granite of Cornwall, 474.
+
+  Kimmeridge clay, 260. and Postscript, xxi.
+
+  King, Dr., on footprints of reptile, 337.
+
+  King, Mr., on Permian group and fossils, 301. 302.
+
+  Kirkdale, cave at, 154.
+
+  Kotzebue cited, 217.
+
+  Kyson, in Suffolk, strata of, 202.
+
+
+  L.
+
+  Labyrinthodon, 292. 288. 289.
+
+  Lacustrine strata of Auvergne, 181.
+
+  Lagoons at mouth of rivers, 33.
+    of Bermuda Islands, 216.
+
+  Lake craters of Eifel, 419.
+    crater of Laach, 420.
+
+  Lamarck on bivalve mollusca, 29.
+
+  Land, rising and sinking, 45.
+
+  Laterite, 376.
+
+  Lava, 373.
+    current, Auvergne, 425.
+    relation to trap, 387.
+    stream of Jorullo, 450.
+    of Stromboli, 450.
+
+  Lea, Mr., footprints of reptile discovered by, 340.
+
+  Lead, veins of, in Permian rocks, 499.
+
+  Lehman on classification of rocks, 90.
+
+  Leibnitz, theory of, 94.
+
+  Lepidodendra, 312.
+
+  Lewes, coomb near, 250.
+
+  Lias, 273.
+    period, Volcanic rocks, 431.
+    at Lyme Regis, 281.
+    plutonic rocks of, 455.
+    and oolite, origin of, 282.
+    fossil plants of, 282.
+
+  Liebig, Prof., on conversion of coal into lignite, 333.
+    on preservation of fossil bones in caverns, 155.
+
+  Lima, recent strata of, 115.
+
+  Limagne d'Auvergne, freshwater formations of, 187.
+
+  Lime, scarcity of, in metamorphic rocks, 487.
+
+  Limestone, brecciated, 302.
+    crystalline, 302.
+    compact, 303.
+    fossiliferous, 303.
+    hippurite, 221.
+    indusial, Auvergne, 184.
+    of Jura, 261.
+    magnesian, 301.
+    mountain fossils of, 340.
+    primary or metamorphic, 465.
+    in Germany, of Devonian system, 348.
+
+  Lindley, Dr., cited, 223.
+    on leaves in lignite, 416.
+
+  Link, M., on footprints, 291.
+
+  Lipari Islands, rocks altered by gases in, 476.
+
+  Lisbon, marine tertiary strata near, 171.
+
+  Lithodomi in beaches of N. America, 78.
+    in inland cliffs, 73.
+
+  Llandeilo flags, 357.
+
+  Loam defined, 13.
+
+  Lochaber, parallel roads of, 86.
+
+  Lodes. _See_ Mineral Veins, 490.
+
+  Loess of valley of Rhine, 117.
+    fossil land shells of, figured, 120.
+
+  Logan, Mr., on coal measures of South Wales, 310.
+    on fossil forest in Nova Scotia, 322.
+    on reptilian foot-prints in lowest Silurian in
+  Canada, Postscript, viii.
+
+  London clay, 200.
+
+  Lonsdale, Mr., cited, 152.; on corals, 173.
+    on corals of Normandy, 170.
+    on corals in Wenlock formation, 355.
+    on fossils in white chalk, 26.
+    on old red sandstone of S. Devon, 345.
+    on Stonesfield slate, 266.
+
+  Louvain, Eocene strata near, 177.
+
+  Lovén on shells of Norway, 114.
+
+  Ludlow formation, 351.
+
+  Lund, cited, 158.
+
+  Lycett, Mr., on shells of oolite, 266.
+
+  Lyme Regis, lias at, 281.
+
+  Lym-Fiord invaded by the sea, 33.
+    kelp in, 217.
+
+  Lyons, coal mine near, 319.
+
+
+  M.
+
+  Macacus, in Eocene formation, 203.
+
+  Maclaren, Mr., on erratic blocks in Pentlands, 125.
+
+  Maclure, Dr., on volcanos in Catalonia, 409.
+
+  MacCulloch, Dr., cited, 442.
+    on altered rock in Fife, 383.
+    on basaltic columns in Skye, 385.
+    on denudation, 67.
+    on granite of Aberdeenshire, 441.
+    on igneous rocks of Scotland, 390.
+    on Isle of Skye, 36. 456.
+    on hornblende schist, 478.
+    on overlying rocks, 8.
+    on parallel roads, 87.
+    on pebbles of granite, 460.
+    on trap vein in Argyleshire, 379.
+
+  Madeira, view of dike in inland valley in, 378.
+
+  Maestricht beds, 209.
+
+  Magnesian limestone, concretionary structure of, 37.
+    defined, 13.
+    groups, 301.
+
+  Maidstone, fossils in white chalk of, 214.
+
+  Mammalia, extinct, above drift in United States, 138.
+    extinct, of basin of Mississippi, 116.
+    fossil teeth of, figured, 160.
+
+  Mammat's "Geological Facts" cited, 69.
+
+  Mammifer in trias near Stuttgart, Postscript, xiii.
+
+  Mansfield in Thuringia, Permian formation at, 306.
+
+  Mantell, Dr., cited, 217. 229. 231. 251.
+    on belemnite, 263.
+    on chalk flints, 253.
+    on Brighton elephant bed, 257.
+    on freshwater beds of Isle of Wight, 198.
+    on iguanodon, 227.
+    on Wealden group, 226.
+    on reptile in Old Red, Postscript, x.
+
+  Marble defined, 12.
+
+  Marl defined, 13.
+    in Lake Superior, 36.
+    red and green in England, 289.
+
+  Marl-slate defined, 13.
+
+  Martin, Mr., cited, 250.
+    on cross fractures in chalk, 245.
+
+  Martins, Mr. C., on glaciers of Spitzbergen, 136.
+
+  Map to illustrate denudation of Weald, 242.
+
+  Map of Eocene beds of central France, 179.
+
+  Massachusetts, plumbago in, 478.
+
+  _Mastodon angustidens_, jaw, figure of, 159.
+
+  _Mastodon giganteus_, in United States, 137.
+
+  Mayence tertiary strata, 177.
+
+  Mediterranean and Red Sea, distinct species in, 100.
+    deposits forming in, 99.
+
+  Megalichthys in Cannel coal of Fifeshire, 336.
+
+  Megatherium in South America, 158.
+
+  Menai Straits, marine shells in drift, 130.
+
+  Mendips, denudation in, 68.
+
+  Metalliferous veins. _See_ Mineral Veins.
+
+  Metals, supposed relative ages of, 497.
+
+  Metamorphic rocks, 463.
+    defined, 8.
+    why less calcareous than fossiliferous, 487.
+    order of succession, 485.
+    glossary of, 466.
+
+  Metamorphic strata, origin of, 467.
+
+  Metamorphic structure, origin of, 477.
+
+  Meteorites in drift, 145.
+
+  Mexico, lamination of volcanic rocks in, 480.
+
+  Meyer, M. H. von, cited, 147.
+    on fossil mammalia of Rhine, 178.
+    on reptile in coal, 336. 337.
+    on sandstone of Vosges, 288.
+    on Wealden of Hanover and Westphalia, 237.
+
+  Mica schist, 465.
+
+  Micaceous sandstone, origin of, 14.
+
+  Microlestes antiquus, triassic mammifer, Postscr., xiv.
+
+  Miller, Mr. H., on origin of rock salt, 295.
+    on old red sandstone, 343.
+    on fossil trees of coal near Edinburgh, 321.
+
+  Minchinhampton, fossil shells at, 266.
+
+  Mineral character of aqueous rocks, 97.
+    composition, test of age of volcanic rocks, 399.
+    springs, connected with mineral veins, 496.
+    veins and faults, 488. 490.
+    of different ages, 490. 498. 499.
+    veins, pebbles in, 492.
+    subsequently enlarged and re-opened, 492.
+    veins, various forms of, 489.
+    veins near granite, 496.
+
+  Mineralization of organic remains, 38.
+
+  Miocene formations, 168.
+    in United States, 171.
+    period, volcanic rocks of, 415.
+    term defined, 111.
+
+  Mississippi, fluviatile strata and delta of, 115. 116.
+
+  Mitchell, Sir T., on Australian caves, 156.
+
+  Mitscherlich, Prof., on augite and hornblende, 369.
+    on isomorphism, 370.
+    on mineral composition of Somma, 404.
+
+  Modon, lithodomi in cliff at, 73.
+
+  Molasse of Switzerland, 171.
+
+  Mons, flexures of coal at, 53.
+
+  Mont Blanc, granite of, 453.
+
+  Mont Dor, Auvergne, 422.
+
+  Monte Calvo, section of, 18.
+
+  Montlosier, M., on Auvergne volcanos, 427.
+
+  Moraine, term explained, 123.
+
+  Moraines of glaciers, 141.
+
+  Morea, inland sea-cliffs of, 73.
+    trap of, 431.
+
+  Morris, Mr., cited, 177.
+    on fossils at Brentford, 147.
+
+  Morton, Dr., on cretaceous rocks, 224.
+
+  Morven, basaltic columns in, 385.
+
+  Mosasaurus in St. Peter's Mount, 210.
+
+  Mountain limestone, fossils of, 340.
+
+  Munster, Count, on fossils of Solenhofen, 260.
+
+  Murchison, Sir R., cited, 248. 324.
+    on new red sandstone, 290.
+    on age of Alps, 206.
+    on age of gold in Russia, 499.
+    on erratic blocks of Alps, 144.
+    on granite, 456. 459.
+    on primary strata in Russia, 124.
+    on joints and cleavage, 469. 471.
+    on old red sandstone of S. Devon, 345. 348.
+    on pentamerus, 353.
+    on Permian flora, 305.
+    on Silurian strata of Shropshire, 434.
+    on Swiss Alps, 484.
+    on term Permian, 301.
+    on term Silurian, 350.
+    on tilestones, 351.
+
+  Muschelkalk, 287.
+
+
+  N.
+
+  Naples, post-pliocene formations near, 403.
+    recent strata near, 112.
+
+  Navarino, lithodomi found in cliff at, 73.
+
+  Necker, M. L. A., cited, 445.
+    on composition of cone of Somma, 404.
+    on granite in Arran, 460.
+    on granitic rocks, 447.
+    on Swiss Alps, 484.
+    terms granite underlying, 8.
+
+  Nelson, Lieut., drawing of Bermuda, 79.
+    on Bermuda Island, 216.
+
+  Neptunian theory, 91.
+
+  Newcastle coal field, great faults in, 64.
+
+  Newcastle, fossil tree near, 312. 318.
+
+  New Jersey, _Mastodon giganteus_ in, 137.
+
+  New red sandstone, distinction from old, 286.
+    its subdivisions, 287.
+    of United States, 297.
+    trap of, 432.
+
+  New Zealand, absence of quadrupeds, 158.
+
+  Niagara, recent shells in valley of, 138.
+
+  Noeggerath, M., cited, 415.
+
+  Nomenclature, changes of, 93.
+
+  Norfolk, buried forest, 127. 130. 147.
+    drift, 126.
+
+  Normandy chalk, cliffs, and needles, 241.
+
+  Northwich, beds of salt at, 294.
+
+  Norwich crag, fluvio-marine, 148.
+    sand-pipes near, 82.
+
+  Nova Scotia, coal seams of Cape Breton, 315.
+    fossil forest of coal in, 321.
+
+  Nummulites, figures of, 200. 205.
+
+  Nummulitic formation, 205.
+
+  Nyst, M., cited, 176.
+
+
+  O.
+
+  Oeynhausen, M. von, on Cornish granite veins, 445.
+
+  Olot, extinct volcanos near, 408.
+
+  Old red sandstone, 342.
+    in Forfarshire, 478.
+    trap of, 434.
+
+  Oolite, 257.
+    and lias, origin of, 282.
+    inferior, fossils of, 272.
+    in France, 259.
+    plutonic rocks of, 455.
+    term defined, 12.
+    volcanic rocks of, 431.
+
+  Oolitic group in France, 283.
+
+  Orbigny, M. d', cited, 222.
+    on fossils of nummulitic limestone, 206.
+    on subdivisions of cretaceous series, 209.
+
+  Organic remains, criterion of age of formation, 98.
+    test of age of volcanic rocks, 399.
+
+  Ormerod, Mr., on trias of Cheshire, 295.
+
+  Overlying, term applied to volcanic rocks, 8.
+
+  Owen, Prof., cited, 155. 166. 229. 267. 268. 270. 291.
+    on amphitherium, 269.
+    on birds in New Zealand, 158.
+    on caves in England, 154.
+    on footprints, 298.
+    on fossils in Australia, 156.
+    on fossil monkey, 202.
+    on fossil quadrupeds, 157.
+    on ichthyosaurus, 276.
+    on reptile in coal, 337.
+    on serpent of Bracklesham, 199.
+    on snake at Sheppey, 201.
+    on thecodont saurians, 306.
+    on zeuglodon, 207. 208.
+    on reptile in Silurian rocks, Postscript, viii.
+
+  Oxford clay, 262.
+
+  Oyster beds, 204.
+
+
+  P.
+
+  Pacific, coral reefs of, 215.
+
+  Palæontology, term explained, 103.
+
+  Palagonia, dikes at, 407.
+
+  _Paleotherium magnum_, figure of, 192.
+    tooth of, 193.
+
+  Palermo, caves near, 74.
+
+  Palma, Isle of, map and view of, 391.
+
+  Parallel roads, 86.
+
+  Pareto, M., on Carrara marble, 482.
+
+  Paris basin, 93.
+
+  Parkinson, Mr., on crag, 105.
+
+  Parrot, Dr. F., on salt lakes of Asia, 295.
+
+  Pebbles in chalk, 217.
+
+  Pegmatite, 440.
+
+  _Pentamerus Knightii_, 352.
+
+  Pentland hills, Mr. Maclaren on, 125.
+
+  Pepys, Mr., cited, 41.
+
+  Permian flora, distinct from coal, 305.
+    formation in Thuringia, 306.
+    group, term explained, 301.
+
+  Petrifaction of fossil wood, 39.
+
+  Petrifaction, process of, 43.
+
+  Philippi, Dr., on fossil shells near Naples, 113.
+    on marine shells in caves of Sicily, 154.
+    on tertiary shells of Sicily, 150.
+
+  Phillips, Prof., cited, 274. 309.
+    on cleavage, 471.
+    on terminology, 103.
+
+  Phillips, Mr. W., on kaolin of China, 11.
+
+  Phosphate of lime, 219.
+
+  Phryganea, figure of, 185.
+    indusiæ of, 186.
+
+  Pictou, Nova Scotia, calamites near, 319.
+
+  Pilla, M., on age of Carrara marble, 482.
+
+  Planitz, tripoli of, 26.
+
+  Plas Newydd, rock altered by dike near, 381.
+
+  Plastic clays, 203.
+
+  Playfair, cited, 45. 92. 383.
+    on faults, 62.
+    on Huttonian theory of stratification, 60.
+
+  Plesiosaurus, figure of, 277.
+
+  Plieninger, Professor, on triassic mammifer, Postscript, xiii.
+
+  Pliocene, newer period, 121.
+    newer, strata, 146.
+    strata in Sicily, 150.
+    older, in United States, 171.
+    strata, 161.
+    period, volcanic rocks of, 407. 408.
+    term defined, 111.
+
+  Plomb du Cantal, described, 429.
+
+  Plumbago in Massachusetts, 478.
+
+  Plutonic rocks, 7. 446.
+    age of, 439.
+    of carboniferous period, 456.
+    of oolite and lias, 455.
+    recent and pliocene, 450.
+    of Silurian period, 457.
+    age, how tested, 449.
+
+  Plutonic and sedimentary rocks, diagram of, 452.
+
+  Poggendorf, cited, 476.
+
+  Poikilitic formation, 301.
+    term explained, 286.
+
+  Pomel, M., on mammalia of Auvergne, 188. 425.
+
+  Ponza Islands, structure of, 387. 480.
+
+  Porphyritic granite, 439.
+
+  Porphyry, 372.
+
+  Portland, Isle of, fossil forest in, 233.
+
+  Portland stone, 259.
+
+  Post-pliocene formations, 111.
+    period, volcanic rocks, 401.
+
+  Potsdam sandstone, reptilian, Postscript, vii. xviii.
+
+  Pottsville, coal seams near, 329.
+    footprints of reptile near, 340.
+
+  Pozzolana, 36.
+
+  Pratt, Mr., on ammonites, 262.
+    on extinct quadrupeds of Isle of Wight, 198.
+
+  Predazzo, altered rocks at, 456.
+
+  Prestwich, Mr., cited, 69.
+    on English Eocene strata, 197. 198. 200.
+    on coal measures of Coalbrook Dale, 62. 324.
+
+  Prevost, M. C., on Paris basin, 175. 176. 195.
+
+  Progressive development, theory of, Postscript, xvi.
+
+  Psaronites in Germany and France, 307.
+
+  Pumice, 373.
+
+  Purbeck beds, 231.
+
+  Puy de Tartaret, 425.
+
+  Puy de Pariou, 428.
+
+  Puzzuoli, elevation and depression of land at, 403.
+
+  Pyrenees, cretaceous rocks of, 455.
+    curvatures of strata, 58.
+    granite of, 475.
+    nummulitic formation of, 205.
+
+
+  Q.
+
+  Quadrumana fossil, Postscript, xvii.
+
+  Quarrington Hill, basaltic dike near, 398.
+
+  Quartz, 438.
+
+  Quartzite, or quartz rock, 465.
+
+
+  R.
+
+  Radnorshire, stratified trap of, 425.
+
+  Rain-prints, fossil in coal shale, Postscript, xii.
+
+  Ramsay, Prof. A. C., on denudation, 68.
+    on granite in Arran, 460.
+    on section near Bristol, 102.
+    on Welsh glaciers, 131.
+
+  Recent strata defined, 112.
+    near Naples, 112.
+
+  Redfield, Mr., on glacial fauna in America, 133.
+    on fossil fish, 300.
+
+  Red sandstone, origin of, 293.
+
+  Red Sea and Mediterranean, distinct species in, 100.
+
+  Red Sea, saltness of, 296.
+
+  Reptiles, carboniferous, 335. 336.
+    of lias, 276.
+    fossil eggs of, 120.
+
+  Reptile, in Lower Silurian, Postscript, vii.
+    in Old Red Sandstone of Morayshire, Postscript, ix.
+
+  Rhine, valley, loess of, 117.
+
+  Ripple-mark, formation of, 19.
+
+  River channels, ancient, 334.
+
+  River, excavation through lava by, 413.
+    terraces, 85.
+
+  Rock, term defined, 2.
+
+  Rocks, four classes of, contemporaneous, 9.
+    classification of, 90.
+    composed of fossil zoophytes and shells, 24.
+    trappean, 91.
+
+  Roderberg, extinct volcano of, 420.
+
+  Rogers, Prof. H. D., on coal field, United States, 328.
+    cited, 340.
+    on reptilian footprints in coal, Postscript, xi.
+
+  Rogers, Prof. W. B., on oolitic coal field, United States, 284. 328.
+
+  Rome, formations at, 168.
+
+  Römer, F., on chalk in Texas, 225.
+    M. F. A., on flora of Hartz, 350.
+
+  Rose, Prof. G., cited, 374. 434.
+    on hornblende, 369.
+
+  Rosenlaui, limestone scratched by glacier of, 122.
+
+  Ross, Captain, on greenstone in Keeling Island, 217.
+
+  Ross-shire, denudation in, 67.
+
+  Rothliegendes, lower, or Permian, 306.
+
+  Rozet, M., cited, 191.
+
+  Rubble, term explained, 81.
+
+  Russia, erratic blocks in, 124.
+    fossil meteoric iron in, 145.
+    Permian rocks in, 306.
+
+
+  S.
+
+  Saarbrück coal field, reptile found in, 336.
+
+  St. Abb's Head, curved strata near, 49.
+
+  St. Andrews, trap rocks in cliffs near, 432. 433.
+
+  St. Helena, basalt in, 385. 406.
+
+  St. Lawrence, gulf of, inland beaches and cliffs, 78.
+
+  St. Mihiel, inland cliffs near, 77.
+
+  St. Paul, island of, 394.
+
+  St. Peter's Mount, Maestricht, fossils in, 210.
+    sand-pipes in, 83.
+
+  Salisbury Crag, altered strata of, 383.
+
+  Salt rock, origin of, 294.
+    precipitation of, 294.
+    at Northwich, 294.
+    lakes of Asia, 296.
+
+  Salter, Mr., on fossil of Caradoc sandstone, 356.
+
+  Sand-pipes near Maestricht, 83.
+    or sand-galls, term explained, 82.
+    near Norwich, 82.
+
+  Sandstone, siliceous, 218.
+    with cracks in Wealden, 230.
+
+  Sandwich Islands, coral reef in, 216.
+    volcanos of, 394. 406. 423.
+
+  Saurians of lias, 278.
+    thecodont, 306.
+
+  Saussure, M., on moraines, 141.
+    on vertical conglomerates, 47.
+
+  Savi, M., on Carrara marble, 482.
+
+  Saxony, granite in, 459.
+
+  Schist, hornblende, and mica, 464. 465.
+    argillaceous, 465.
+    chlorite, 465.
+
+  Schorl rock and schorly granite, 440.
+
+  Scoresby on icebergs, 122.
+
+  Scoriæ, 373.
+
+  Scotland, carboniferous traps of, 432.
+    northern drift in, 125.
+    old red sandstone of, 343.
+
+  Scrope, Mr., cited, 181. 263. 419. 423. 425. 427. 430.
+    on globular structure of traps, 387.
+    on Ponza Islands, 480.
+    on trachyte, basalt, and tuff, 374. 400.
+
+  Sea cliffs, inland, 71.
+
+  Section of Wealden, 243.
+
+  Section of white chalk from England to France, 211.
+
+  Section of volcanic rocks, Auvergne, 424.
+
+  Sedgwick, Prof., cited, 309. 383.
+    on brecciated limestone, 302.
+    on concretionary magnesian limestone, 37.
+    on Devonian group, 348.
+    on garnets in altered rock, 382.
+    on granite, 456. 459.
+    on Permian sandstones, 305.
+    on joints and cleavage, 469. 471.
+    on mineral composition of granite, 444.
+    on old red of Devon and Cornwall, 345.
+    on structure of rocks, 468.
+    on trap rocks of Cumberland, 435.
+
+  Segregation in mineral veins, 489.
+
+  Semi-opal, infusoria in, 26.
+
+  Serpulæ, on volcanic rocks, in Sicily, 151.
+
+  Sewâlik Hills, freshwater deposits, 173.
+
+  Shale, carbonaceous, 271.
+    defined, 11.
+
+  Shales of coal near Dudley, 474.
+
+  Sharpe, Mr. D., on mollusca in Silurian strata, 359.
+    on slaty cleavage, 471.
+
+  Shells, fossil, in Purbeck, 231.
+    fossil, useful in classification, 109.
+    in Canada drift, 134.
+    recent, in valley of Niagara, 138.
+    species of, near Lisbon, 171.
+
+  Sheppey, Isle of, fossil flora of, 200.
+
+  Sherringham, mass of chalk in drift, 129.
+
+  Shetland, granite of, 441. 444.
+    hornblende schist of, 478.
+
+  Shrewsbury, coal deposit near, 324.
+
+  Sicily, Fiume Salso in, 191.
+    inland cliffs in, 74.
+    newer pliocene strata of, 150.
+    terraces of denudation in, 75.
+
+  Sidlaw Hills, trap of old red sandstone, 434.
+
+  Siebengebirge, igneous rocks of, 417.
+
+  Sienna, formations at, 167.
+
+  Sigillaria, 314. 318.
+
+  Siliceous limestone defined, 12.
+    rocks defined, 11.
+
+  Silliman, Prof., cited, 450.
+
+  Silurian, name explained, 350.
+    period, plutonic rocks of, 457.
+    rocks, table of, 351.
+    strata, mineral character of, 360.
+    strata of United States, 359.
+    strata, thickness of, 358.
+    strata, reptile in, Postscript, vii.
+    volcanic rocks, 434.
+
+  Simpson, Mr., on ice islands, 129.
+
+  Sivatherium described, 173.
+
+  Skaptar Jokul, eruption of, 399.
+
+  Skye, rocks of, 383. 456.
+    basaltic columns in, 385.
+    dikes in Isle of, 380.
+    sandstone in, 36.
+
+  Slaty cleavage, 468.
+
+  Slickensides, term defined, 61.
+
+  Smith, Mr., of Jordan Hill, on Pleistocene, 134.
+    on shells near Lisbon, 171.
+
+  Snags, fossil, 320.
+
+  Snakes' eggs, fossil at Tonna near Gotha, 120.
+
+  Solenhofen, lithographic stone of, 260.
+
+  Solfatara, decomposition of rocks in the, 477.
+
+  Somma, 404.
+    lava at, 380.
+
+  Sopwith, Mr. T., models by, 57.
+
+  Sortino, cave in valley of, 154.
+
+  South Devon and Cornwall, old red of, 315.
+
+  South Downs, view of, 245.
+
+  Sowerby, Mr. G., cited, 162.
+
+  Spatangus, figure of, 23.
+
+  Spezia, gulf of, calcareous rocks in, 482.
+
+  Spitzbergen, glaciers of, 136.
+
+  Sponges, figures of, in chalk, 213.
+
+  Spongilla of Lamarck, in tripoli, 25.
+
+  Springs, mineral. See Mineral Springs, 490.
+
+  Staffa, basaltic columns in, 385.
+
+  Steno on classification of rocks, 90.
+
+  Stigmaria, 310. 315.
+    in fossil forest, Nova Scotia, 322.
+
+  Stirling Castle, rock of, altered by dike, 383.
+
+  Stokes, Mr., on petrifaction, 43.
+
+  Stonesfield slate, 266.
+
+  Stonesfield, fossil mammalia, 268. and Postscript, xviii.
+
+  Storton Hill, footprints at, 291.
+
+  Strata, term defined, 2.
+    arrangement of, determined by fossils, 21. 22.
+    consolidation of, 34.
+    curved and vertical, 47. 58.
+    elevation of, above the sea, 44.
+    fossiliferous, tabular view of, 361.
+    horizontality of, 15. 45.
+    metamorphic origin of, 467.
+    mineral composition of, 10.
+    outcrop of, 56.
+    tertiary classification of, 134.
+
+  Stratification, forms of, 13. 16. 47.
+    unconformable, 59.
+
+  Strickland, Mr., on new red sandstone, 290.
+
+  Strike, term explained, 53.
+
+  Stromboli, lava of, 450.
+
+  Studer, M., on Swiss Alps, 484.
+    on boulders of Jura, 143.
+
+  Stutchbury, Mr., cited, 306.
+
+  Subapennine strata, 105. 166.
+
+  Subsidence in drift period, 135.
+
+  Suffolk crag, 162.
+
+  Sullivan, Capt., chart of Falkland Islands, 88.
+
+  Superior, Lake, marl in, 36.
+
+  Superposition of aqueous deposits, 96.
+    of volcanic rocks, test of age, 327.
+
+  Supracretaceous, term explained, 103.
+
+  Sussex marble, 228.
+
+  Swansea, coal measures near, 309.
+    valley stems of _Sigillaria_, 317.
+
+  Sydney coal field, Cape Breton, 324.
+
+  Syenite, 440.
+
+  Syenitic granite, 440.
+    greenstone, 372.
+
+  Synclinal line, term defined, 48.
+
+
+  T.
+
+  Table Mountain, strata horizontal, 45.
+    Mountain, granite veins in, 443.
+
+  Talcose granite, 440.
+
+  Tartaret, Puy de, cone of, 425.
+
+  Teeth of fossil mammalia, figures of, 160.
+
+  Teredina, fossil wood bored by, 24.
+
+  Teredo navalis boring wood, 23.
+
+  Terra del Fuego, 139.
+    _Fucus giganteus_ in, 217.
+
+  Tertiary, term explained, 104.
+    strata, tabular view of, 362.
+
+  Touraine, faluns of, 168.
+
+  Trachyte, 372.
+    of Hungary, 442.
+
+  Trachytic rocks, older than basalt, 400.
+
+  Transition, term explained, 92.
+
+  Trap, term explained, 366.
+    dike in Fifeshire, 434.
+    globular structure of, 387.
+    intrusion of, between strata, 384.
+    various ages of, 432. 434.
+    passage of granite into, 441.
+    in Radnorshire, 435.
+    rocks, relation to lava, 387.
+    rocks, lithological character of, 400.
+    in Lower Eifel, 420.
+
+  Trappean rocks, 91.
+
+  Trap-tuff, 374.
+
+  Tertiary deposits, 171. 177. 178.
+
+  Texas, chalk in, 225.
+
+  Thames valley, freshwater deposits in, 146.
+
+  Thecodont Saurians, 306.
+    Saurians, age of, Postscript, xv.
+
+  Thirria, M., on oolitic group in France, 283.
+
+  Thurmann, M., cited, 55. 252. 266.
+
+  _Thuja occidentalis_ in stomach of mastodon, 138.
+
+  Till, term explained, 121.
+    origin of, 123.
+
+  Tilestone, 351.
+
+  Tilgate Forest, remains in, 229.
+
+  Tin, veins of, in Cornwall, 490. 498.
+
+  Tiverton trap, porphyry near, 432.
+
+  Travertin, how deposited, 34.
+
+  Tree ferns in Permian formation, 307.
+
+  Trias, or new red sandstone, 286. 289. and Postsc., xiii.
+    in Cheshire and Lancashire, 290. 295.
+
+  Trilobite in Devonian strata, 348.
+
+  Trilobites of Lower Silurian, 357.
+
+  Trimmer, Mr., on sand-galls, 82.
+    on shells in drift near Menai Straits, 130.
+
+  Tripoli composed of infusoria, 24.
+
+  Tuff, volcanic, and trap, 6. 374.
+
+  Tuffs on Wrekin and Caer Caradoc, 434.
+
+  Tuomey, Mr., cited, 208.
+
+  Turner, Dr., cited, 41. 42.
+
+  Tuscany, volcanic rocks of, 408.
+
+  Tynedale fault, 64.
+
+  Tynemouth Cliff, limestone at, 302.
+
+
+  U.
+
+  Uddevalla, shells of, compared with those near Naples, 108.
+
+  Underlying, term applied to granite, 8.
+
+  United States, coal field of, 326.
+    cretaceous formation in, 224.
+    Devonian strata in, 349.
+    Eocene strata in, 206.
+    older Pliocene and Miocene formations in, 171.
+    oolite and lias of, 284.
+    Silurian strata of, 359.
+
+  Upsala, strata containing Baltic shells near, 124.
+
+
+  V.
+
+  Val di Noto, composition of, 407.
+    igneous rocks of, 389.
+    inland cliffs in, 76.
+
+  Valleys, origin of, 70.
+    transverse of Weald, 244.
+
+  Valorsine granite, 445.
+
+  Veins, mineral. See Mineral Veins, 488.
+
+  Veinstones in parallel layers, 493.
+
+  Velay, volcanos of, 428.
+
+  Venetz, M., on Alpine glaciers, 140.
+
+  Verneuil, M. de, on Devonian Flora, 350.
+    on horizontal strata in Russia, 124.
+    on the old red sandstone in Russia, 348.
+    on _Pentamerus Knightii_, 353.
+    on Permian flora, 305.
+
+  Vesuvius, eruption of, 405.
+
+  Vicenza, basaltic columns near, 386.
+
+  Vidal, Capt., survey by, 393.
+
+  Virginia, U. S., fossil shells in, 172.
+
+  Virlet, M., on corrosion of rocks by gases, 477.
+    on geology of Morea, 431.
+    on inland cliffs, 73.
+
+  Volcanic mountains, form of, 5. 390.
+    dikes, 378.
+
+  Volcanic rocks, age of, 397.
+    described, 5. 385.
+    analysis of minerals in, 377.
+    Cambrian, 435.
+    composition and nomenclature, 368.
+    of Hungary, 421.
+    post-pliocene period, 401.
+    test of age of, 400.
+    Silurian, 434.
+
+  Volcanic tuff, 374.
+
+  Volcanos of Auvergne, 422.
+    extinct, 408. 420. 422.
+    newer, of Eifel, 418.
+    in Spain, age of, 414.
+    round Olot in Catalonia, 410.
+
+  Von Buch, Baron, cited, 373. 456. 457.
+    on boulders of Jura, 143.
+    on Canary Islands, 392.
+    on Cystideæ, 358.
+    on land rising, 45.
+
+  Von Dechen, M., on granite veins in Cornwall, 445.
+    Oeynhausen, M., cited, 415.
+
+
+  W.
+
+  Waller quoted, 93.
+
+  Warren, Dr. J. C., on skeleton of _Mastodon giganteus_, 138.
+
+  Waterhouse, Mr., cited, 188. 269.
+    on triassic mammifer, Postscript, xiv.
+
+  Watt, Mr. G., experiments on fused rocks, 406. 475.
+
+  Weald clay, 227.
+
+  Weald valley, denuded at what period, 254.
+
+  Wealden, term explained, 225. 226.
+    the fracture and upheaval of, 251.
+    extent of formation, 236.
+    period, changes during, 235.
+
+  Wealden, plants and animals of, 229. 236.
+
+  Webster, Mr. T., cited, 105. 231. 233.
+
+  Wellington Valley, caves in, 156.
+
+  Wener Lake, horizontal Silurian strata of, 45.
+
+  Wenlock formation, 354.
+
+  Werner on classification of rocks, 90.
+    on mineral veins, 488.
+    on volcanic rocks, 369.
+
+  Westerwald, igneous rocks of, 417.
+
+  Westwood, Mr., on beetles in lias, 282.
+
+  Whin-Sill, intrusion of trap between strata, 384.
+
+  White chalk, 211.
+
+  White mountains, granite vein in, 450.
+
+  Wigham, Mr., on fossils near Norwich, 149.
+
+  Wolverhampton, fossil forest near, 319.
+
+  Wood, Mr. Searles, on fossils of crag, 162.
+    on fossils of Isle of Wight, 198.
+    on number of shells in crag, 149.
+    on cetacea of crag, 166.
+    cited, 170. 177.
+
+  Woodward, Mr., on mammoth bones, Norfolk, 147.
+
+  Wrekin, trap of, 70.
+
+  Wyman, Dr., cited, 208.
+
+
+  Z.
+
+  _Zamia_, at Lyme Regis, 282.
+
+  _Zamia spiralis_, figure of, 233.
+
+  Zechstein, 306.
+
+  _Zeuglodon cetoides_, 207. and Postscript, xxi.
+
+
+  LONDON:
+  SPOTTISWOODES and SHAW,
+  New-street-Square.
+
+
+
+  ALBEMARLE STREET,
+  _July 5, 1851_.
+
+
+
+
+                          MR. MURRAY'S
+
+                     =List of Recent Works=
+
+       *       *       *       *       *
+
+
+                 HISTORY OF THE ROMAN STATE;
+
+            FROM 1815-1850. BY LUGIA CARLO FARINI.
+
+                TRANSLATED FROM THE ITALIAN
+           BY THE RIGHT HON. W. E. GLADSTONE, M.P.
+
+                    2 Vols. 8vo. 24_s._
+
+       *       *       *       *       *
+
+
+                   THE EXPOSITION OF 1851;
+
+OR, VIEWS OF THE INDUSTRY, THE SCIENCE, AND THE GOVERNMENT OF ENGLAND.
+
+                  BY CHARLES BABBAGE, ESQ.,
+     Author of the "Economy of Manufactures and Machinery."
+
+      _Second Edition_, with an Appendix. 8vo. 6_s._ 6_d._
+
+       *       *       *       *       *
+
+
+                THE DOVECOTE AND THE AVIARY;
+
+OR, THE NATURAL HISTORY OF PIGEONS AND OTHER DOMESTIC BIRDS, WITH HINTS
+                   FOR THEIR MANAGEMENT.
+
+            BY THE REV. EDMUND SAUL DIXON, M.A.,
+         Author of "Ornamental and Domestic Poultry."
+
+       With Numerous Woodcuts. Fcap. 8vo. 7_s_. 6_d_.
+
+       *       *       *       *       *
+
+
+      MEMOIR OF THE LIFE OF THE LATE BISHOP STANLEY.
+
+ PREFIXED TO A SELECTION FROM HIS ADDRESSES AND CHARGES.
+
+       BY THE REV. ARTHUR PENRHYN STANLEY, M.A.
+
+                 8vo. 10_s._ 6_d._
+
+"The memoir is executed with feeling, and, as might be expected from the
+biographer of Dr. Arnold, with great skill. Mr. Stanley brings out into
+strong relief the more attractive parts of his father's character, and
+suggests the best defence--namely, the consistent uprightness and perfect
+sincerity of his motives--for the more questionable policy, on some
+memorable occasions, of the bishop."
+
+                                             _Morning Chronicle._
+
+       *       *       *       *       *
+
+
+       A PASTORAL LETTER ON THE STATE OF THE CHURCH,
+
+            BY HENRY LORD BISHOP OF EXETER.
+
+             _Eighth Edition._ 8vo. 4_s._
+
+       *       *       *       *       *
+
+
+             THE ACTS OF THE SYNOD OF EXETER.
+
+  HOLDEN IN THE CHAPTER HOUSE OF THE CATHEDRAL CHURCH OF EXETER.
+
+             ON JUNE 25, 26, and 27, 1851.
+
+                         8vo.
+    :: _The Sermon may be had separately, price 1s._
+
+       *       *       *       *       *
+
+
+       THE EVANGELICAL AND TRACTARIAN MOVEMENTS.
+
+             BY ARCHDEACON WILBERFORCE.
+
+(A Charge delivered to and published by Request of the Clergy.)
+                      8vo. 1_s._
+
+       *       *       *       *       *
+
+
+              A HISTORY OF ERASTIANISM.
+
+             BY ARCHDEACON WILBERFORCE.
+
+                     16mo. 3_s._
+
+       *       *       *       *       *
+
+
+                    CATHOLIC SAFEGUARDS
+
+ AGAINST THE ERRORS, CORRUPTIONS, AND NOVELTIES OF THE CHURCH OF ROME.
+
+ BEING DISCOURSES AND TRACTS SELECTED FROM THE WORKS OF EMINENT DIVINES OF
+   THE CHURCH OF ENGLAND WHO LIVED DURING THE 17TH CENTURY; WITH PREFACE,
+              RECORDS, AND A CAREFULLY COMPILED INDEX.
+
+                 BY REV. JAMES BROGDEN, M.A.
+
+                     3 Vols. 8vo. 36_s._
+
+       *       *       *       *       *
+
+
+            RECORDS OF THE SUPREMACY OF THE CROWN,
+
+ AND THE CIVIL AND RELIGIOUS LIBERTIES OF THE PEOPLE OF ENGLAND.
+
+                   BY REV. JAMES BROGDEN.
+
+                       8vo. 4_s._
+
+       *       *       *       *       *
+
+
+                       HORÆ ÆGYPTIACÆ;
+
+            OR, THE CHRONOLOGY OF ANCIENT EGYPT.
+
+   DISCOVERED FROM ASTRONOMICAL AND HIEROGLYPHIC RECORDS UPON
+ ITS MONUMENTS INCLUDING MANY DATES FOUND IN COEVAL INSCRIPTIONS.
+
+               BY REGINALD STUART POOLE, ESQ.
+
+               With Plates. 8vo. 10_s._ 6_d._
+
+"The substance of Mr. Poole's valuable work appeared originally in a
+series of papers in this journal. Since their publication the author has
+devoted further time and attention to the subject; and it may safely be
+asserted that in their present amended and enlarged form, they are among
+the most important contributions that have yet been made to the study of
+Egyptian Chronology and history. We are indebted for the publication of
+the present valuable work to the liberality of the Duke of
+Northumberland, whose warm and generous support of literature and art
+deserves our grateful acknowledgments."
+
+                                                     _Literary Gazette._
+
+       *       *       *       *       *
+
+
+                        LAVENGRO;
+           THE SCHOLAR--THE GIPSY--AND THE PRIEST.
+
+                  BY GEORGE BORROW, ESQ.
+
+  Author of "The Bible in Spain," "The Gipsies of Spain," &c. &c.
+           With a Portrait. 3 Vols. Post 8vo. 30_s._
+
+"We trust our extracts have exhibited enough of one at least of the many
+aspects of 'Lavengro' to convince the reader that neither is it a work to
+be read cursorily, nor to be handled easily, by any of the silver-fork
+school of critics. These volumes are indeed replete with life, with earnest
+sympathy for all genuine workers, with profound insight into the wants and
+wishes of the poor and uneducated, and a lofty disdain of the conventional
+'shams' and pretensions which fetter the spirits or impede the energies of
+mankind. Nor is a feeling for the beautiful less conspicuous in its pages.
+A quiet market-town, environed by green meadows or bosomed in tufted trees;
+an old mercantile and ecclesiastical city, with a history stretching from
+the times of the Cæsars to the times of George III.; the treeless plain,
+the broad river, the holt, the dingle, the blacksmith's forge, are all in
+their turn sketched freely and vividly by Mr. Borrow's pencil. In his
+portraitures of ruder life he is unsurpassed; a dog-fight, a prize-fight,
+an ale-house kitchen, Greenwich Fair, a savage group of wandering tinkers,
+are delineated in words as Wilkie or Hogarth might have depicted them in
+colours. We are embarrassed by the riches spread before us.
+
+"We have not touched upon the gipsy scenes in 'Lavengro' because in any
+work of Mr. Borrow's these will naturally be the first to draw the reader's
+attention. Neither have we aimed at abridging or forestalling any portions
+of a book which has a panoramic unity of its own, and of which scarcely a
+page is without its proper interest. If we have succeeded in persuading our
+readers to regard Mr. Borrow as partly an historian and partly as a poet,
+as well as to look for more in his volumes than mere excitement or
+amusement, our purpose is attained, and we may securely commend him to the
+goodly company he will find therein. 'Lavengro,' however, is not concluded;
+a fourth volume will explain and gather up much of what is now somewhat
+obscure and fragmentary, and impart a more definite character to the
+philological and physiological hints comprised in those now before us.
+Enough, indeed, and more than enough, is written to prove that the author
+possesses, in no ordinary measure, 'the vision and the faculty divine' for
+discerning and discriminating what is noble in man and what is beautiful in
+nature. We trust Mr. Borrow will speedily bring forth the remaining acts of
+his 'dream of adventure,' and with good heart and hope pursue his way
+rejoicing, regardless of the misconceptions or misrepresentations of
+critics who judge through a mist of conventionalities, and who themselves,
+whether travelled or untravelled, have not, like Lavengro, grappled with
+the deeper thoughts and veracities of human life."--_Tait's Magazine._
+
+       *       *       *       *       *
+
+
+              ENGLAND IN THE NINETEENTH CENTURY:
+
+              POLITICAL, SOCIAL, AND INDUSTRIAL.
+
+                  BY WILLIAM JOHNSTON, ESQ.
+
+                  2 Vols. Post 8vo. 18_s._
+
+"This book is a somewhat undigested mass of valuable matter, interspersed
+occasionally with reflections of much interest and observations of
+considerable originality. The author is unquestionably a man of talent; he
+writes with vigour and smartness; he has taken pains in the collection of
+most of his materials; and his statistics are arranged with great care and
+managed with unusual skill. In this point he is much superior to his
+prototype and apparent master, Mr. Alison."
+
+"Mr. Johnston's work is readable and well-written, abounding with
+information of many kinds."--_Edinburgh Review._
+
+       *       *       *       *       *
+
+
+                     THE SAXON IN IRELAND:
+
+  BEING NOTES OF THE RAMBLES OF AN ENGLISHMAN IN THE WEST OF IRELAND
+                   IN SEARCH OF A SETTLEMENT.
+
+                 With Map. Post 8vo. 9_s._ 6_d._
+
+"A valuable testimony to the capabilities of Ireland."--_Observer._
+
+"Let the intending emigrant devote a few hours to the perusal of this
+volume. The work possesses deeper interest than even could be claimed for
+it from its fascinating descriptions."--_Illustrated News._
+
+       *       *       *       *       *
+
+
+                      SLEEP AND DREAMS:
+
+  TWO LECTURES DELIVERED AT THE BRISTOL LITERARY AND PHILOSOPHICAL
+                         INSTITUTION.
+
+               BY JOHN ADDINGTON SYMONDS, M.D.,
+
+      Consulting Physician to the Bristol General Hospital.
+
+                      8vo. 2_s._ 6_d._
+
+       *       *       *       *       *
+
+
+                       THE PALACES OF
+              NINEVEH AND PERSEPOLIS RESTORED.
+
+    AN ESSAY ON ANCIENT ASSYRIAN AND PERSIAN ARCHITECTURE.
+
+                  BY JAMES FERGUSSON ESQ.,
+
+                 With Woodcuts. 8vo. 16_s._
+
+"This book contains many things of general interest relating to one of the
+most wonderful discoveries that has occurred in the history of the world.
+Mr. Fergusson writes very dispassionately. What he has said deserves
+serious consideration."--_Gentleman's Magazine._
+
+       *       *       *       *       *
+
+
+             SHALL WE KEEP THE CRYSTAL PALACE
+
+  AND HAVE RIDING AND WALKING IN ALL WEATHERS, AMONG FLOWERS,
+                SCULPTURE, AND FOUNTAINS?
+
+                      BY DENARIUS.
+
+                       8vo. 6_d._
+
+       *       *       *       *       *
+
+
+             MEMOIRS OF ROBERT PLUMER WARD.
+
+  WITH HIS CORRESPONDENCE, DIARIES, AND LITERARY REMAINS.
+
+              BY THE HON. EDMUND PHIPPS.
+
+           With Portrait. 2 Vols. 8vo. 28_s._
+
+"The most valuable portions of Mr. Ward's diary are its illustrations of
+the character of the Duke of Wellington. The great soldier, then in the
+flush of his military triumph, was also in the prime of his power and
+activity; and Mr. Ward gives us an insight into his business habits, his
+method of arguing public questions, his ready resource and never-tiring
+energy, which possesses occasionally a striking interest."--_Examiner._
+
+       *       *       *       *       *
+
+
+         THE MILITARY EVENTS IN ITALY, 1848-9.
+
+              TRANSLATED FROM THE GERMAN.
+        BY THE RIGHT HON. THE EARL OF ELLESMERE.
+
+             With a Map. Post 8vo. 9_s._
+
+"Military history is, as the Earl of Ellesmere declares, a rare article in
+English literature; and, therefore, he thought that the most authentic
+extant narrative of the operations implied in the title page of the present
+book, written by an impartial Swiss, would not be an unwelcome addition to
+the British library. His lordship has judged rightly; the work of which he
+has presented a version is a worthy labour, and the events to which it
+relates are of the last importance. It is written with judgment, and has
+been translated with care."--_Morning Chronicle._
+
+       *       *       *       *       *
+
+
+          A TRANSPORT VOYAGE TO THE MAURITIUS,
+
+     BY WAY OF THE CAPE OF GOOD HOPE AND ST. HELENA.
+
+              BY THE AUTHOR OF "PADDIANA."
+
+                Post 8vo. 9_s._ 6_d._
+
+"This book reminds us of one of those pleasant fellows, whom one sometimes
+meets with in company, who has an anecdote or a story ready à propos of
+everything, whose fund of amusing tales is inexhaustible, and who rattling
+on from one thing to another, will keep a whole table in a roar, or a whole
+drawing-room in high glee. Even such is our author. He gossips on and on,
+telling now of one adventure, and then of another; his volume is a perfect
+chaos of racy reminiscences graphically told."--_John Bull._
+
+       *       *       *       *       *
+
+
+           ADMIRALTY MANUAL OF SCIENTIFIC ENQUIRY
+
+      FOR THE USE OF OFFICERS AND TRAVELLERS IN GENERAL.
+
+  BY PROFESSORS WHEWELL, AIRY, OWEN, SIR W. HOOKER, CAPT. BEECHEY,
+        J. R. HAMILTON, ESQ., SIR JOHN HERSCHEL, &c.
+
+           EDITED BY SIR JOHN F. HERSCHEL, BART.
+           Second Edition. Post 8vo. 10_s._ 6_d._
+
+:: _Published by Authority of the Lords Commissioners of the Admiralty._
+
+       *       *       *       *       *
+
+
+         LIVES OF THE CHIEF JUSTICES OF ENGLAND.
+
+  FROM THE NORMAN CONQUEST TO THE DEATH OF LORD MANSFIELD.
+
+           BY LORD CHIEF JUSTICE CAMPBELL.
+
+                2 Vols. 8vo. 30_s._
+
+"There is, indeed, in Lord Campbell's works much instruction; his subjects
+have been so happily selected, that it was scarcely possible that there
+should not be. An eminent lawyer and statesman could not write the lives of
+great statesmen and lawyers without interweaving curious information, and
+suggesting valuable principles of judgment and useful practical maxims: but
+it is not for these that his works will be read. Their principal merit is
+their easy animated flow of interesting narrative. No one possesses better
+than Lord Campbell the art of telling a story: of passing over what is
+commonplace; of merely suggesting what may be inferred; of explaining what
+is obscure; and of placing in strong light the details of what is
+interesting."--_Edinburgh Review._
+
+       *       *       *       *       *
+
+
+                    THE FORTY-FIVE.
+
+  BEING A NARRATIVE OF THE REBELLION IN SCOTLAND OF 1745;
+
+                    BY LORD MAHON.
+
+                   Post 8vo. 3_s._
+
+"This is a very comprehensive and lively sketch of the famous 'Rebellion'
+so vividly remembered, even after the lapse of a century, by the people of
+Scotland. The incidents of that unfortunate invasion from first to last,
+from the landing of Charles (July 25th) in Borrodale, with the 'seven men
+of Moidart,' to the fatal battle of Culloden (16th April, 1746), are
+minutely and faithfully recorded; but we have no doubt the reader will be
+most and mainly interested in the personal history and adventures of the
+Pretender himself. The character of the Prince is admirably drawn, and
+generously vindicated from the calumnies heaped upon him by his adversaries
+after his fall. It will perhaps surprise some to learn, that he was so
+illiterate as scarcely to be master of the most common elements of
+education. 'His letters,' says Lord Mahon, 'which I have seen among the
+Stuart papers, are written in a large, rude, rambling hand, like a
+schoolboy's. In spelling they are still more deficient.' We recommend Lord
+Mahon's narrative as a very agreeable sketch of a stirring and eventful
+period."--_Edinburgh Advertiser._
+
+       *       *       *       *       *
+
+
+                    A HISTORY OF GREECE.
+
+  FROM THE EARLIEST PERIOD TO THE END OF THE PELOPONNESIAN WAR.
+
+                    BY GEORGE GROTE, ESQ.
+
+        Vols. I.-VIII. With Maps. 8vo. 16_s._ each.
+  _The Work may be obtained in Portions, as it was published_:--
+
+                       VOLS. I.-II.
+
+  LEGENDARY GREECE.
+  GRECIAN HISTORY TO THE REIGN OF PEISISTRATUS AT ATHENS.
+
+                      VOLS. III.-IV.
+
+  HISTORY OF EARLY ATHENS, AND THE LEGISLATION OF SOLON.
+  GRECIAN COLONIES.
+  VIEW OF THE CONTEMPORARY NATIONS SURROUNDING GREECE.
+  GRECIAN HISTORY DOWN TO THE FIRST PERSIAN INVASION, AND THE BATTLE OF
+    MARATHON.
+
+                       VOLS. V.-VI.
+
+  PERSIAN WAR AND INVASION OF GREECE BY XERXES.
+  PERIOD BETWEEN THE PERSIAN AND THE PELOPONNESIAN WARS.
+  PELOPONNESIAN WAR DOWN TO THE EXPEDITION OF THE ATHENIANS AGAINST
+    SYRACUSE.
+
+                      VOLS. VII.-VIII.
+
+  THE PEACE OF NIKIAS DOWN TO THE BATTLE OF KNIDUS [B.C. 421 TO 394.]
+  SOCRATES AND THE SOPHISTS.
+
+       *       *       *       *       *
+
+
+                KUGLER'S HANDBOOK ILLUSTRATED.
+
+              THE SCHOOLS OF PAINTING IN ITALY.
+                 FROM THE EARLIEST TIMES.
+
+   TRANSLATED FROM THE GERMAN BY A LADY, AND EDITED WITH NOTES
+
+               BY SIR CHARLES LOCK EASTLAKE,
+              President of the Royal Academy.
+
+         _A New Edition._ 2 Vols. Post 8vo. 24_s._
+
+"We cannot leave this subject (_Christian Art, its present state and its
+prospects_), without reverting to Sir C. Eastlake's edition of Kugler's
+Handbook of Painting, not for the sake of reviewing it,--for it is a work
+now of established reputation,--but for the purpose of recommending it as
+being upon the whole by far the best manual we are acquainted with, for
+every one who, without the opportunity of foreign and particularly Italian
+travel, desires to make a real study of art. Its method, its chronological
+arrangement, and its generally judicious criticism, make it most
+instructive to a learner. We may add that the present edition is enlarged
+just where the former one needed enlargement, and the Handbook is now far
+more satisfactory as to the early religious schools than it was before. The
+edition is beautifully got up, and so profusely and judiciously illustrated
+by one hundred woodcuts drawn by Scharf, that it would be next to
+impossible to speak too highly in its praise, even were its matter less
+valuable and important than it is."--_The Ecclesiastic._
+
+       *       *       *       *       *
+
+
+                CHRISTIANITY IN CEYLON:
+
+  ITS INTRODUCTION AND PROGRESS UNDER THE PORTUGUESE, DUTCH,
+            BRITISH, AND AMERICAN MISSIONS.
+
+      BY SIR JAMES EMERSON TENNENT, K.C.S., LL.D.
+
+             With Illustrations. 8vo. 14_s._
+
+"To those who take either a religious or a philosophical interest in the
+subject, Sir Emerson Tennent's volume may be safely recommended, as a
+clear, succinct, sensible, and flowing account. The work also possesses a
+living animation arising from the author's knowledge of the country and the
+people."--_Spectator._
+
+       *       *       *       *       *
+
+
+                     THE LEXINGTON PAPERS.
+
+              THE COURTS OF LONDON AND VIENNA
+                     IN THE 17TH CENTURY.
+
+   EXTRACTED FROM THE PRIVATE AND OFFICIAL CORRESPONDENCE OF
+   LORD LEXINGTON, WHILE BRITISH MINISTER AT VIENNA, 1694-98.
+
+           EDITED BY THE HON. H. MANNERS SUTTON.
+
+                          8vo. 14_s._
+
+       *       *       *       *       *
+
+
+        THE LAW AND PRACTICE OF NAVAL COURTS-MARTIAL.
+
+                 BY WILLIAM HICKMAN, R.N.,
+    Late Secretary to Commodore Sir Charles Hotham, K.C.B.
+
+                   8vo. 10_s._ 6_d._
+
+       *       *       *       *       *
+
+
+                A MANUAL OF ELEMENTARY GEOLOGY;
+
+   OR, THE ANCIENT CHANGES OF THE EARTH AND ITS INHABITANTS,
+         AS ILLUSTRATED BY ITS GEOLOGICAL MONUMENTS.
+
+              BY SIR CHARLES LYELL, F.R.S., P.G.S.
+
+               Third Edition, thoroughly revised,
+               and illustrated with 520 Woodcuts.
+                           8vo. 12_s._
+
+"The production of one of our most eminent geologists in an age of many.
+Though styled a 'third edition,' it is in reality a new book. This could
+not be otherwise if the task were well done; for the science of which Sir
+Charles Lyell treats is assuming new aspects every year. It is continually
+advancing and ever growing. As it advances, its steps become firmer and
+surer; as it grows, its framework becomes more compact, and its
+organization more perfect. They who take up the hammer to follow it must
+toil with unflagging tread to keep pace with its onward progress. If they
+lag behind, they can scarcely hope to overtake. None among its votaries has
+marked each movement more minutely, or weighed its value and purpose more
+judiciously, than the distinguished author of this Manual. He has indeed
+done his task well, and both the beginner and the experienced investigator
+will find his book an invaluable guide and companion."--_Literary Gazette._
+
+       *       *       *       *       *
+
+
+                       COMMENTARIES ON
+           THE WAR IN RUSSIA AND GERMANY OF 1813-14.
+
+              BY COLONEL THE HON. GEORGE CATHCART,
+            Deputy-Lieutenant of the Tower of London.
+
+                   With Plans. 8vo. 14_s._
+
+"As a Treatise on the Science of War, these Commentaries ought to find
+their way into the hands of every soldier. In them is to be found an
+accurate record of events of which no military man should be
+ignorant."--_Morning Chronicle._
+
+       *       *       *       *       *
+
+
+                  MODERN DOMESTIC COOKERY.
+
+  FOUNDED UPON PRINCIPLES OF ECONOMY AND PRACTICAL KNOWLEDGE.
+        AND ADAPTED FOR THE USE OF PRIVATE FAMILIES.
+
+             With 100 Woodcuts. Post 8vo. 6_s._
+
+"The advanced state of cookery having rendered Mrs. Rundell's work
+obsolete, the publisher has caused it to be remodelled and improved to
+such an extent as to give it a claim to the title of an original
+production. The receipts of the late Miss Emma Roberts have been revised
+and added to the work; and it has had the advantage of being subjected
+besides to the careful inspection of a 'professional gentleman'--Economy
+combined with excellence--is the aim, end, and object which it cannot be
+doubted will be obtained if its prescriptions are attended to. It is
+fuller than the former _Domestic Cookery_, of which it is an improved
+and amended edition--it is more simple and comprehensible in its
+language; it contains several diagrams not to be found in its
+predecessor; and it possesses various minor qualities, which increase
+its value in a tenfold degree, and make it, to say the least, equal to
+any other book of the kind in the English language."--_Observer._
+
+
+
+
+  ALBEMARLE STREET,
+  _July 5, 1851_.
+
+
+
+
+                          MR. MURRAY'S
+
+                  =List of Works in the Press.=
+
+       *       *       *       *       *
+
+
+          Selections from the Despatches of the Duke of
+                          Wellington.
+
+           BY THE LATE COL. GURWOOD, C.B., K.C.T.S.
+
+                A New Edition. One Volume. 8vo.
+
+       *       *       *       *       *
+
+
+           History of England, from the Peace of Utrecht.
+
+    VOLS. 5 & 6--THE FIRST YEARS OF THE AMERICAN WAR: 1763--1780.
+
+                       BY LORD MAHON, M.P.
+
+                         2 Vols. 8vo.
+
+       *       *       *       *       *
+
+
+         Lives of the Friends and Contemporaries of Lord
+                      Chancellor Clarendon.
+
+  ILLUSTRATIVE OF PORTRAITS IN HIS GALLERY; WITH AN ACCOUNT OF THE
+      ORIGIN OF THE COLLECTION; AND A DESCRIPTIVE CATALOGUE
+                       OF THE PICTURES.
+
+                    BY LADY THERESA LEWIS.
+
+                With Portraits. 2 Vols. 8vo.
+
+       *       *       *       *       *
+
+
+            The Treasures of Art in Great Britain.
+
+  BEING AN ACCOUNT OF THE CHIEF COLLECTIONS OF PAINTINGS, SCULPTURE,
+                  MSS. MINIATURES, &c., &c.,
+
+  OBTAINED FROM PERSONAL INSPECTION DURING VISITS IN 1836 AND 1850.
+
+       (BEING A REVISED AND GREATLY ENLARGED VERSION OF
+                "ART AND ARTISTS IN ENGLAND.")
+
+                     BY DR. WAAGEN,
+   Director of the Royal Gallery of Pictures at Berlin.
+
+                     2 Vols. 8vo.
+
+       *       *       *       *       *
+
+
+                     The Grenville Papers;
+
+                            BEING
+  THE PRIVATE CORRESPONDENCE OF RICHARD GRENVILLE, EARL TEMPLE, K.G.,
+        AND HIS BROTHER, THE RIGHT HONOURABLE GEORGE GRENVILLE,
+                 THEIR FRIENDS AND CONTEMPORARIES,
+
+  FORMERLY PRESERVED AT STOWE--NOW FOR THE FIRST TIME MADE PUBLIC.
+
+_Among the contents of this highly important accession to the History
+of Great Britain in the middle of the Eighteenth Century, will be
+found Letters from_
+
+  H. M. KING GEORGE THE THIRD.
+
+  H. R. H. WILLIAM DUKE OF CUMBERLAND.
+
+  DUKES OF:--
+    NEWCASTLE.
+    DEVONSHIRE.
+    GRAFTON.
+    BEDFORD.
+
+  MARQUESS:--
+    GRANBY.
+
+  EARLS:--
+    BUTE.
+    TEMPLE.
+    SANDWICH.
+    EGREMONT.
+    HALIFAX.
+    HARDWICKE.
+    CHATHAM.
+    MANSFIELD.
+    NORTHINGTON.
+    SUFFOLK.
+    HILLSBOROUGH.
+    HERTFORD.
+
+  LORDS:--
+    LYTTLETON.
+    CAMDEN.
+    HOLLAND.
+    CLIVE.
+    GEORGE SACKVILLE.
+          ----
+    MARSHAL CONWAY.
+    HORACE WALPOLE (EARL OF ORFORD).
+    EDMUND BURKE.
+    GEORGE GRENVILLE.
+    JOHN WILKES.
+    WILLIAM GERARD HAMILTON.
+    AUGUSTUS HERVEY.
+    MR. JENKINSON (first EARL OF LIVERPOOL).
+    MR. WHATELY.
+    MR. WEDDERBURN (EARL OF ROSLYN).
+    MR. CHARLES YORKE.
+    MR. HANS STANLEY.
+    MR. CHARLES TOWNSEND.
+    MR. CALCRAFT.
+    MR. RIGBY.
+    MR. KNOX.
+    MR. CHARLES LLOYD.
+
+
+                                AND THE
+
+                   _AUTHOR OF THE LETTERS OF JUNIUS_.
+
+                            INCLUDING ALSO,
+
+                Mr. Grenville's Diary of Political Events;
+
+   PARTICULARLY DURING THE PERIOD OF HIS ADMINISTRATION AS FIRST LORD
+                   OF THE TREASURY, FROM 1763 TO 1765.
+
+                  EDITED BY WILLIAM JAMES SMITH, ESQ.
+
+                                 8vo.
+
+       *       *       *       *       *
+
+
+           Personal Narrative of an Englishman Domesticated
+                            in Abyssinia.
+
+                       BY MANSFIELD PARKYNS, ESQ.
+
+                       With Illustrations. 8vo.
+
+       *       *       *       *       *
+
+
+             Lives of the Three Devereux, Earls of Essex,
+
+                        FROM 1540 TO 1646.
+
+  1. THE EARL MARSHALL OF IRELAND.--2. THE FAVOURITE.--3. THE GENERAL OF
+                        THE PARLIAMENT.
+
+        FOUNDED UPON LETTERS AND DOCUMENTS CHIEFLY UNPUBLISHED.
+
+                 BY THE HON. CAPTAIN DEVEREUX, R.N.
+
+                         2 Vols. 8vo.
+
+       *       *       *       *       *
+
+
+         The Present State of the Republic of the Rio de la
+                      Plata (Buenos Ayres).
+
+  ITS GEOGRAPHY, RESOURCES, STATISTICS, COMMERCE, DEBT, ETC., DESCRIBED.
+
+    WITH THE HISTORY OF THE CONQUEST OF THE COUNTRY BY THE SPANIARDS.
+
+            BY SIR WOODBINE PARISH, F.R.S., K.C.H, F.G.S.,
+       Formerly Her Majesty's Consul General and Chargé d' Affaires
+                      at Buenos Ayres.
+
+              With New Map and Illustrations. 8vo.
+
+       *       *       *       *       *
+
+
+            Contrasts of Foreign and English Society;
+
+   OR, RECORDS AND RECOLLECTIONS OF A RESIDENCE IN VARIOUS PARTS
+                OF THE CONTINENT AND ENGLAND.
+
+                      BY MRS. AUSTIN.
+
+                     2 Vols. Post 8vo.
+
+       *       *       *       *       *
+
+
+                           The Hand;
+
+        ITS MECHANISM AND ENDOWMENTS, AS EVINCING DESIGN.
+
+                  BY THE LATE SIR CHARLES BELL.
+
+               _A New Edition._ Woodcuts. Post 8vo.
+
+       *       *       *       *       *
+
+
+         Naval and Military Technological Dictionary.
+
+          ENGLISH AND FRENCH.--FRENCH AND ENGLISH.
+
+       FOR THE USE OF SOLDIERS, SAILORS, AND ENGINEERS.
+
+      BY COLONEL BURN, Assistant Inspector of Artillery.
+
+                          Small 8vo.
+
+       *       *       *       *       *
+
+
+       The Life and Reminiscences of Thomas Stothard, R.A.
+
+                        BY MRS. BRAY.
+
+  With numerous Illustrations from his Chief Works, drawn on Wood by
+    G. SCHARF, Jun., and printed in a novel and beautiful style.
+
+                 With a Portrait. Small 4to.
+
+       *       *       *       *       *
+
+
+              Life and Works of Alexander Pope.
+
+                     EDITED WITH NOTES.
+
+            BY THE RIGHT HON. JOHN WILSON CROKER.
+
+                  Portraits. 4 vols. 8vo.
+
+       *       *       *       *       *
+
+
+          Dictionary of Greek and Roman Geography.
+
+                 BY WILLIAM SMITH, LL.D.
+
+              With an Historical Atlas. 8vo.
+
+       *       *       *       *       *
+
+
+                 A Church Dictionary.
+
+      BY WALTER FARQUHAR HOOK, D.D., Vicar of Leeds.
+
+  _Sixth Edition_, revised and enlarged. One Volume. 8vo.
+
+"In this edition, besides the addition of many new articles, all those
+relating to important Doctrinal and Liturgical Subjects have been enlarged.
+The authorities on which statements have been made, are given, with copious
+extracts from the works of our Standard Divines. Special reference has been
+made to the Romish Controversy. Attention has also been paid to the
+subjects of Ecclesiastical and Civil Law, and to the Statute Law of England
+in Church Matters."--_Extract from the Preface._
+
+       *       *       *       *       *
+
+
+               History of Ancient Pottery;
+
+   EGYPTIAN, ASIATIC, GREEK, ROMAN, ETRUSCAN, AND CELTIC.
+
+                BY SAMUEL BIRCH, F.S.A.
+  Assistant Keeper of the Antiquities in the British Museum.
+
+                With Illustrations. 8vo.
+
+    UNIFORM WITH "MARRYAT'S MODERN POTTERY AND PORCELAIN."
+
+       *       *       *       *       *
+
+
+                 A Sketch of Madeira in 1850.
+
+                   BY EDWARD VERNON HARCOURT.
+
+  A HANDBOOK FOR THE USE OF TRAVELLERS OR INVALIDS VISITING THE ISLAND.
+
+              With a Map and Woodcuts. Post 8vo.
+
+       *       *       *       *       *
+
+
+                     The History of Herodotus.
+
+  A NEW ENGLISH VERSION. TRANSLATED FROM THE TEXT OF GAISFORD, AND EDITED
+
+         BY REV. GEORGE RAWLINSON, M.A., Exeter College, Oxford.
+                             ASSISTED BY
+       COLONEL RAWLINSON, C.B., AND SIR J. G. WILKINSON, F.R.S.,
+
+    WITH COPIOUS NOTES AND APPENDICES, ILLUSTRATING THE HISTORY AND
+          GEOGRAPHY OF HERODOTUS, FROM THE MOST RECENT SOURCES
+                          OF INFORMATION,
+
+  EMBODYING THE CHIEF RESULTS, HISTORICAL AND ETHNOGRAPHICAL, WHICH HAVE
+            BEEN ARRIVED AT IN THE PROGRESS OF CUNEIFORM AND
+                       HIEROGLYPHICAL DISCOVERY.
+
+                           4 Vols. 8vo.
+
+The translation itself has been undertaken from a conviction of the
+entire inadequacy of any existing version to the wants of the time. The
+gross unfaithfulness of Beloe, and the extreme unpleasantness of his
+style, render his translation completely insufficient in an age which
+dislikes affectation and requires accuracy; while the only other
+complete English versions which exist are at once too close to the
+original to be perused with any pleasure by the general reader, and also
+defective in respect of scholarship.
+
+       *       *       *       *       *
+
+
+                     A Treatise on Naval Gunnery,
+
+    FOR THE USE OF OFFICERS AND FOR THE TRAINING OF SEAMEN GUNNERS.
+
+     WITH DESCRIPTIONS OF THE GUNS INTRODUCED SINCE THE LATE WAR.
+
+            BY LIEUT.-GEN. SIR HOWARD DOUGLAS, BART., G.C.B.
+
+               _Third Edition_, revised. Plates. 8vo.
+
+       *       *       *       *       *
+
+
+      Considerations on Steam Warfare and Naval Shell-Firing;
+
+             BY LIEUT.-GEN. SIR HOWARD DOUGLAS, BART.
+
+                               8vo.
+
+       *       *       *       *       *
+
+
+         Letters and Journals of General Sir Hudson Lowe,
+
+      REVEALING THE TRUE HISTORY OF NAPOLEON AT ST. HELENA.
+
+                  PARTLY COMPILED AND ARRANGED
+
+             BY THE LATE SIR NICHOLAS HARRIS NICOLAS.
+
+                  With Portrait. 3 Vols. 8vo.
+
+"From these papers the world will at last learn, as it ought long ago to
+have learnt, the _truth_, and the _whole truth_, respecting the captivity
+of Napoleon."--_Quarterly Review._
+
+       *       *       *       *       *
+
+
+                          Home Sermons;
+
+         OR, SERMONS WRITTEN FOR SUNDAY READING IN FAMILIES.
+
+                  BY REV. JOHN PENROSE, M.A.,
+
+                             8vo.
+
+       *       *       *       *       *
+
+
+                   History of Greece for Schools.
+
+             ON THE PLAN OF "MRS. MARKHAM'S HISTORIES."
+
+                       With Woodcuts. Post 8vo.
+
+       *       *       *       *       *
+
+
+            State Papers of Henry the Eighth's Reign,
+
+        COMPRISING THE CORRESPONDENCE BETWEEN THE ENGLISH
+             GOVERNMENT AND THE CONTINENTAL POWERS,
+
+       FROM THE PERIOD OF THE ELECTION OF CHARLES V. TO
+                   THE DEATH OF HENRY VIII.
+
+                With Indexes. Vols. VI-XI. 4to.
+
+       *       *       *       *       *
+
+
+                       The Official Handbook.
+
+  BEING A MANUAL OF HISTORICAL AND POLITICAL REFERENCE FOR ALL CLASSES.
+
+                      One Volume. Fcap. 8vo.
+
+The design of this Work is to show concisely the machinery by which the
+GOVERNMENT of the country is carried on, giving such a succinct account of
+the duties, emoluments, and authorities of the various PUBLIC DEPARTMENTS,
+with their political relations, as will, it is hoped, render the volume a
+useful manual of reference to all strangers and Foreigners desirous to make
+themselves acquainted with British Institutions.
+
+       *       *       *       *       *
+
+
+                        The British Museum;
+
+           HANDBOOK TO THE ANTIQUITIES AND SCULPTURE THERE.
+
+                   BY W. S. W. VAUX, M.A., F.S.A.,
+  Assistant in the Department of Antiquities in the British Museum.
+
+                    With Woodcuts. Post 8vo.
+
+       *       *       *       *       *
+
+
+                     Handbook of Chronology.
+
+          ALPHABETICALLY ARRANGED TO FACILITATE REFERENCE.
+
+                       One Volume, 8vo.
+
+This work will enable the student or general reader, or man of the world,
+to put his finger at once upon the date of any particular event by means of
+a careful _alphabetical_ classified arrangement of the various elaborate
+chronologies which have been given to the world. It has been prepared with
+such care as will render it--it is hoped--a trustworthy book of reference.
+
+It contains the dates of the events which mark the rise, progress, decline,
+and fall of states; and the changes in the fortunes of nations. Alliances,
+wars, battles, sieges, and treaties of peace; geographical discoveries, the
+settlement of colonies, and their subsequent story;--with all occurrences
+of general historic interest--are recorded in it. It further includes the
+years of the leading incidents in the lives of men eminent for worth,
+knowledge, rank, or fame; and of the writings, &c., &c., by which they are
+chiefly known; discoveries in every department of science; and inventions
+and improvements, mechanical, social, domestic, and economical.
+
+       *       *       *       *       *
+
+
+            Handbook for Syria and the Holy Land.
+
+                  With Maps. Post 8vo.
+
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+
+              Handbook for England and Wales;
+
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+
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+
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+           CAMBRIDGE, AND LINCOLN. (_Nearly Ready._)
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+            BUCKS, NOTTINGHAMSHIRE.
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+            CUMBERLAND, THE LAKES.
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+
+                         ALSO,
+
+           A CONDENSED HANDBOOK OF ALL ENGLAND
+
+                    IN ONE VOLUME.
+
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+
+                  Handbook of Architecture.
+
+   BEING A CONCISE AND POPULAR ACCOUNT OF THE DIFFERENT STYLES
+       PREVAILING IN ALL AGES AND COUNTRIES OF THE WORLD.
+
+      WITH A DESCRIPTION OF THE MOST REMARKABLE BUILDINGS.
+
+                 BY JAMES FERGUSSON, ESQ.,
+  Author of "Indian Architecture," "Palaces of Nineveh and
+                  Persepolis Restored."
+
+     With very numerous Illustrations on Wood. 8vo.
+
+     Uniform with "KUGLER'S HANDBOOK OF PAINTING."
+
+       *       *       *       *       *
+
+
+            Handbook to the Cathedrals of England.
+
+           CONTAINING A SHORT DESCRIPTION OF EACH.
+
+      BY THE REV. G. A. POOLE, M.A., Vicar of Welford.
+
+           With Illustrative Woodcuts. Small 8vo.
+
+       *       *       *       *       *
+
+
+            Handbook for the Environs of London;
+
+     WITH HINTS FOR EXCURSIONS BY RAIL--RIVER--AND ROAD.
+
+              BY PETER CUNNINGHAM, F.S.A.
+
+                      Post 8vo.
+
+       *       *       *       *       *
+
+
+                  Handbook of Modern London;
+                     OR, LONDON AS IT IS.
+
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+              IN THE METROPOLIS AND ITS VICINITY.
+
+          With a Clue-Map of London, Plans, &c. 18mo.
+
+       *       *       *       *       *
+
+
+       A Popular Account of Nineveh and its Remains.
+
+              BY AUSTEN H. LAYARD, D.C.L.
+
+      ABRIDGED AND CONDENSED FROM HIS LARGER WORK.
+
+           With Numerous Woodcuts. Post 8vo.
+
+       *       *       *       *       *
+
+
+          BRADBURY AND EVANS, PRINTERS, WHITEFRIARS.
+
+
+
+
+Transcriber's Notes:
+
+Passages in italics are indicated by _underscore_.
+Passages in fracture style are indicated by =fracture=.
+All Greek has been transliterated and placed between +Greek+.
+
+Illustrations have been moved from the middle of a paragraph to the
+closest paragraph break.
+
+In the footnote 336-A (page 336) lib. or liv. might be printed wrong.
+
+On page 185 a footnote anchor was added to fig. 160 185-A.
+
+On page 215 an potential anchor for footnote 215-A was guessed and
+added.
+
+On page 245 an anchor for footnote 245-A was added.
+
+On page 280 a footnote anchor 280-B was added.
+
+Other than the corrections listed below, printer's inconsistencies in
+spelling, punctuation, hyphenation, and ligature usage have been retained.
+
+The use of capital letters in names, scientific classifications, locations,
+and time periods/eras is not consistent in this book, they have been kept
+as printed and only changed when an obvious error occurred.
+
+The system of abbreviations and punctuation in citations and figure
+captions can vary, the text has been kept as printed and only changed when
+an obvious error occurred.
+
+The punctuation in the index was inconsistent, all commas in listings for
+page numbers have been changed into full stops, they are not specially
+mentioned/marked in the list of changes. The alphabetic order in the index
+is sometimes inconsistent but has been kept as printed.
+
+Palæomæryx (page 178) is known in the literature by Paleomeryx
+(http://www.paleodatabase.org) as well as Palaeomeryx.
+
+Palæoniscus is known in the literature as Palaeoniscus.
+
+Inoceramus Cuvieri is today known as Inoceramus cuvieri (ref: Cretaceous
+Fossils of North America).
+
+Different spelling of Ashby de la Zouch (text) and Ashby-de-la-Zouch
+(index) was retained.
+
+Older or unusual forms of spelling of some German and French towns and
+locations have been retained (e.g. Bertrich-Baden--Bad Bertrich,
+Roderberg--Rodderberg, Gemunder Maar--Gemünder Maar, Boulade--Boulaide,
+Pont Gibaud--Pontgibaud, Saarbrück--Saarbrücken).
+
+The following words have been retained in both versions:
+
+  Agas. and Agass.
+  brachiopod, brachiopods and brachiopoda (as well as with capital
+    letters or lower case)
+  Bunter Sandstein and Bunter-Sandstein (as well as various combinations
+    with Bunter, bunter, sandstein, Sandstein)
+  Cheirotherium and Chirotherium as cheirotherian and chirotherian
+  Didelphis and Didelphys
+  dike/s and dyke/s
+  foot-print/s and footprint/s
+  foot-marks and footmarks
+  gault and Gault
+  G/grauwacke and G/grauwacké and their English translations (greywacke)
+  greensand and Greensand as well as their variations
+  Holoptichius (e.g. Lyell) and Holoptychius (general usage)
+  Ichthyolites and Icthyolites
+  iron-stones and ironstones
+  jaw-bone and jawbone
+  Keuper and keuper
+  Lias and lias
+  Liége and Liege
+  Muschelkalk and muschelkalk
+  non-fossiliferous and nonfossiliferous
+  Old Red Sandstone and old red sandstone with all variations
+  P/palæo** and P/paleo** with all variations from paleontological to
+    paleozoic
+  Pozzolana and Pozzuolana (recent form)
+  primæval and primeval
+  quâquâversal and qua-quaversal
+  Rhinoceros tichorhinus and Rhinoceros tichorinus
+  scoria and scoriæ
+  Sénonien and Senonien
+  tilestone/s and T/tile-stone/s
+
+The following misprints have been corrected:
+
+  changed "to recognise rocks" into "to recognize rocks" page vi
+  changed "a fresh-water or" into "a freshwater or" page viii
+  changed "belong to gasterodous" into "belong to gasteropodous" page x
+  changed "Ova in a carbonised state." into "Ova in a carbonized state."
+          page xi (fig. 523a)
+  changed "Würtembergisch. Naturwissen Jahreshefte" into "Würtembergisch.
+          Naturwissen. Jahreshefte" footnote xiii-A
+  changed "by Herman von Meyer" into "by Herman von Meyer." page xiv
+          (fig. 530)
+  changed "near Stuttgart, Wurtemberg." into "near Stuttgart,
+          Würtemberg." page xiv
+  changed "is characterised by" into "is characterized by" page xvi
+  changed "genus Sauricthys, Hybodus," into "genus Saurichthys, Hybodus,"
+          page xv
+  changed "Sauricthys Mougeotii, is" into "Saurichthys Mougeotii, is"
+          page xv
+  changed "in the Quader Sand-stein and" into "in the Quadersandstein
+          and" page xvi
+  changed "of organisation in fossils" into "of organization in fossils"
+          page xix
+  changed "or to Plerodactyles" into "or to Pterodactyles" page xix
+  changed "class Aves have hither to" into "class Aves have hitherto"
+          page xix
+  changed "bored by teredina" into "bored by Teredina" page xxiii
+  changed "near St. Andrew's" into "near St. Andrews" page xxix
+  changed "Sub-marine lava" and into "Submarine lava and" page xxix
+  changed "Granite of Dartmore altering" into "Granite of Dartmoor
+          altering" page xxx
+  changed "Concluding remarks 489" into "Concluding remarks 488" page xxxi
+  changed "occasionally characterised" by into "occasionally
+          characterized" by page 3
+  changed "are all characterised" into "are all characterized" page 5
+  changed "Loire, and Ardêche," into "Loire, and Ardèche," page 5
+  changed "Giants' Causeway, called" into "Giant's Causeway, called" page 6
+  changed "cooled and crystallised," into "cooled and crystallized," page 7
+  changed "by Dr. Mac Culloch" into "by Dr. MacCulloch" page 8
+  changed "afterwards super-imposed, and" into "afterwards superimposed,
+          and" page 9
+  changed "causes, while super-imposed" into "causes, while superimposed"
+          page 9
+  changed "(Green-sand formation.)" into "(Greensand formation.)" page 16
+  changed "annexed fig. (7.)," into "annexed fig. 7.," page 18
+  changed "(Green-sand formation?)" into "(Greensand formation?)" page 18
+  changed "bored by teredina" into "bored by Teredina" page 21
+  changed "great bed of tripoli, Bilin." into "great bed of Tripoli,
+          Bilin." page 25 (figs. 19/20)
+  changed figure number figure "34" into figure "33" page 29
+  changed "information from icthyolites" into "information from
+          ichthyolites" page 32
+  changed "confined to vein-stones." into "confined to veinstones." page 34
+  changed "the drying and skrinking" into "the drying and shrinking"
+          page 63
+  changed "conglomerate, N. 2. clay," into" conglomerate, No. 2. clay,"
+          page 67
+  changed "described by Dr. Macculloch," into "described by Dr.
+          MacCulloch," page 67
+  changed "of Ross-shire. (Macculloch.)" into "of Ross-shire.
+          (MacCulloch.)" page 67 (fig. 90)
+  changed "Dax, near Bourdeaux" into "Dax, near Bordeaux" page 72
+  changed "indicate the intermittance" into "indicate the intermittence"
+          page 74
+  changed figure number "96" to figure "93" page 75
+  changed "Modica, precipitious" into "Modica, precipitous" page 77
+  changed "them by Dr. Macculloch," into "them by Dr. MacCulloch," page 86
+  changed "Dr. Macculloch and" into "Dr. MacCulloch and" page 87
+  changed "have ever re-appeared" into "have ever reappeared" page 98
+  changed "fossilisation of certain" into "fossilization of certain"
+          page 106
+  changed "hills called Bruder Holz" into "hills called Bruderholz"
+          page 120
+  changed "near Stuttgardt, in" into "near Stuttgart, in" page 120
+  changed "stones have travelled" into "stones have travelled." page 121
+  changed "already characterised by" into "already characterized by"
+          page 124
+  changed "neighbourhood of Upsal," into "neighbourhood of Upsala,"
+          page 124
+  changed "Isles of sub-aerial glaciers." into "Isles of subaerial
+          glaciers." page 130
+  added "BOULDER FORMATION--continued." to chapter heading page 131
+  changed "its materials rearranged" into "its materials re-arranged"
+          page 136
+  changed "chapters 7 and 8.," into "chapters 7. and 8.," page 139
+  changed "to coexist in" into "to co-exist in" page 147
+  changed "class of warm-blodded" into "class of warm-blooded" page 148
+  changed "speces of deer" into "species of deer" page 154
+  changed "skeletons of Magatherium," into "skeletons of Megatherium,"
+          page 157
+  changed "student to recognise the" into "student to recognize the"
+          page 159
+  changed "b. nat. size of a and b." into "c. nat. size of a and b."
+          page 161 (fig. 141)
+  changed "overan are a" into "over an area" page 162
+  changed "concretionary rearrangement of" into "concretionary
+          re-arrangement of" page 164
+  changed "Faseicularia aurantium" into "Fascicularia aurantium" page 165
+          (fig. 148)
+  changed "v. exterior." into "a. exterior." page 165 (fig. 148.)
+  changed "climates, such a" into "climates, such as" page 165
+  changed "clayslate, and various" into "clay-slate, and various" page 169
+  changed "from the Appenines" into "from the Apennines" page 168
+  changed "17 per cent," into "17 per cent.," page 172
+  changed "beds (Sables inferieurs" into "beds (Sables inférieurs" page 175
+  changed "inferieurs et argiles" into "inférieurs et argiles" page 175
+  changed "Upper Marine or Fontainbleau" into "Upper Marine or
+          Fontainebleau" page 177
+  changed "M. de Koninck of Liége" into "M. De Koninck of Liége" page 178
+  changed "or Caddice-fly" into "or Caddis-fly" page 185
+  changed "lake of the Lemagne" into "lake of the Limagne" page 187
+  changed "Bagshot and Brocklesham division" into "Bagshot and
+          Bracklesham division" page 190
+  changed "Nome of them" into "None of them" page 192
+  changed "genera Emys and Trionix." into "genera Emys and Trionyx."
+          page 192
+  changed "Sables Moyens. divide" into "Sables Moyens, divide" page 193
+  changed "of the English Eocenestrata," into "of the English Eocene
+          strata," page 197
+  changed "Headen Hill, on" into "Headon Hill, on" page 197
+  changed "Egerton has recognised" into "Egerton has recognized" page 198
+  changed "brown and blueish gray" into "brown and blueish grey" page 200
+  changed "beds Nos. 1, 2. are" into "beds Nos. 1, 2., are" page 208
+  changed "places for mill-stones." into "places for millstones." page 208
+  changed "of D'Orbigny before" into "of d'Orbigny before" page 208
+  changed "sea-cliffs at Stevensklint" into "sea-cliffs at Stevens Klint"
+          page 210
+  changed "and Ostrea, vesicularis." into "and Ostrea vesicularis."
+          page 215
+  changed "bivalves (figs. 203. 205," into "bivalves (figs. 203, 205,"
+          page 216
+  changed "the Dammura of" into "the Dammara of" page 216
+  changed "afterwards recognised by" into "afterwards recognized by"
+          page 216
+  changed "of the Radack achipelago," into "of the Radack archipelago,"
+          page 217
+  changed "observations of Ferdinand Roemer;" into "observations of
+          Ferdinand Römer;" page 224
+  changed "the marl-stones are" into "the marlstones are" page 224
+  changed "Wealden (see Nos. 5" into "Wealden (see Nos. 5." page 225
+  changed "purely fresh-water origin." into "purely freshwater origin."
+          page 227
+  changed "Auvergne (see above, p. 183.)" into "Auvergne (see above, p.
+          183.)." page 228
+  changed "genera Trioynx and Emys," into "genera Trionyx and Emys,"
+          page 229
+  changed "See Flinder's Voyage." into "See Flinders' Voyage."
+          footnote 233-A
+  changed "Author's Annivers. Address," into "Author's Anniv. Address,"
+          footnote 237-C
+  changed "those from the Gualt" into "those from the Gault" page 242
+  changed "eological Map of" into "Geological Map of" page 242 (fig. 252)
+  changed "(fig. 254.), where" into "(fig. 253.), where" page 244
+  changed "in the north" into "in the North" page 245
+  changed "In the wood-cut" into "In the woodcut" page 246
+  changed "South Downs at Beachy head." into "South Downs at Beachy Head."
+          page 246
+  changed "fail to recognise in" into "fail to recognize in" page 246
+  changed "voll. ii. p. 98." into "vol. ii. p. 98." footnote 248-A
+  changed "of clay aud limestone," into "of clay and limestone," page 258
+  changed "Coral rag," into "Coral rag." page 261 (fig. 273)
+  changed "in their orginal" into "in their original" page 264
+  changed "says Mr Lycett," into "says Mr. Lycett," page 266
+  changed "such as Pleiosaur," into "such as Plesiosaur," page 267
+  changed "obtained by Dr Buckland" into "obtained by Dr. Buckland"
+          page 268
+  changed "that the Thuia," into "that the Thuja," page 270
+  changed "Buckland's Bridgw. Treat." into "Buckland's Bridgew. Treat."
+          page 271 (fig. 294)
+  changed "lower shales are wel" into "lower shales are well" page 271
+  changed "the Oolitic system generally" into "the Oolitic system
+          generally." page 272
+  changed "1/3 nat size." into "1/3 nat. size." page 273 (fig. 301)
+  changed "(G. arcuata, Lam)" into "(G. arcuata, Lam.)" page 274 (fig. 304)
+  changed "their own predacious race" into "their own predaceous race"
+          page 278
+  changed "both of Icthyosaur and Plesiosaur" into "both of Ichthyosaur
+          and Plesiosaur" page 278
+  changed "for swimming (see fig. 313.)" into "for swimming (see fig.
+          313.)." page 279
+  changed "Sir H. de la Beche," into "Sir H. De la Beche," page 281
+  changed "of the Haute Saône," into "of the Haute-Saône," page 283
+  changed "in Germany-Keupar" into "in Germany-Keuper" page 286
+  changed "Buckland, Bridg. Treat.," into "Buckland, Bridgew. Treat.,"
+          footnote 286-A
+  changed calcaire coquillier into "calcaire coquillier." page 287
+  changed "Württemberg, and is" into "Würtemberg, and is" page 287
+  changed "genera Sauricthys and Gyrolepis" into "genera Saurichthys and
+          Gyrolepis" page 287
+  changed "near Strazburg, on" into "near Strasburg, on" page 288
+  changed "the "gres bigarré," or" into "the "grès bigarré," or" page 288
+  changed "vol. v. p. 347" into "vol. v. p. 347." footnote 290-B
+  changed "in the gray, and" into "in the grey, and" page 294
+  changed "with ornithicnites on" into "with ornithichnites on" page 300
+  changed "and botroidal character." into "and botryoidal character."
+          page 302
+  changed "the icthyolites which" into "the ichthyolites which" page 304
+  changed "Pygopteris mandibularis" into "Pygopterus mandibularis" page 305
+          (fig. 346)
+  changed "Gutbier are Asterophillites" into "Gutbier are Asterophyllites"
+          page 307
+  changed "Lepidodendra, Calamites, Asterophillites," into "Lepidodendra,
+          Calamites, Asterophyllites," page 308
+  changed "same bands of" into "some bands of" page 309
+  changed "sometimes called fire-stone," into "sometimes called firestone,"
+          page 309
+  changed "Geol. Soc Proceedings," into "Geol. Soc. Proceedings,"
+          footnote 317-B
+  changed "f. 4. feet oal" into "f. 4. feet coal." page 321 (fig. 372)
+  changed "at an angle of 8°," into "at an angle of 8°." page 324
+  changed "genus called Michroconchus" into "genus called Microconchus"
+          page 324
+  changed "of Sigillaria, Lepidodrendon," into "of Sigillaria,
+          Lepidodendron," page 324
+  changed "frequently recognised. Thus," into "frequently recognized.
+          Thus," page 324
+  changed "be recognised at still" into "be recognized at still" page 324
+  changed "Clay iron-stone.--Bands and nodules of clay iron-stone" into
+          "Clay-iron-stone.--Bands and nodules of clay-iron-stone"
+          page 326
+  changed Dome-shaped out-crop of into Dome-shaped outcrop of page 327
+  changed "ornithichnites (see p. 297.)." into "ornithichnites (see p.
+          327.)." page 328
+  changed "The out-crop of" into "The outcrop of" page 328
+  changed "olifiant gas. The" into "olefiant gas. The" page 333
+  changed "American Journ. of Sci," into "American Journ. of Sci.,"
+          footnote 334-A
+  changed "a neucleus of granite," into "a nucleus of granite," page 343
+  changed "Scale of Holoptychus nobilissimus," into "Scale of
+          Holoptychius nobilissimus," page 344 (fig. 395)
+  changed "peculiar lamelli-branchiate" into "peculiar lamellibranchiate"
+          page 347
+  changed "south from St. Petersburgh." into "south from St. Petersburg."
+          page 348
+  changed "of the Astræa." into "of the Astrea." page 349
+  changed "lowest or mud-stone beds," into "lowest or mudstone beds,"
+          page 352
+  changed "showing siphuncle. Ludlow" into "showing siphuncle. Ludlow."
+          page 354 (fig. 417)
+  changed "the Welch mountains afford." into "the Welsh mountains afford."
+          page 359
+  changed "Kleyn Spawen beds," into "Kleyn Spauwen beds," page 362
+  changed "belong to neighboring" into "belong to neighbouring" page 362
+  changed "with gypsum--Wirtemberg," into "with gypsum--Würtemberg,"
+          page 364
+  changed "Crinoidians abundant" into "Crinoideans abundant" page 365
+  changed "like chelonians, Ptericthys," into "like chelonians,
+          Pterichthys," page 365
+  changed "were recognised as" into "were recognized as" page 366
+  changed "Their igneons origin" into "Their igneous origin" page 366
+  changed "recognised by a peculiar" into "recognized by a peculiar"
+          page 370
+  changed "One half I scoriaceous," into "One half is scoriaceous,"
+          page 373
+  changed "others are Andesitic," into "others are andesitic," page 373
+  changed "tom. 8. p. 22. 1835." into "tom. 8. p. 22. 1835.)" page 375
+  changed "A green porphyritic rocks" into "A green porphyritic rock"
+          page 376
+  changed "Saussurite, a mineral" into "saussurite, a mineral" page 376
+  changed "oxyde of iron." into "oxide of iron." page 376
+  changed "of talc. Burat's" into "of talc. (Burat's" page 376
+  changed "Sub-marine lava and" into "Submarine lava and" page 378
+  changes "much as 20 per cent of" into "much as 20 per cent. of" page 382
+  changed "of Hutt. Theory, s. 253." into "of Hutt. Theory, p. 253."
+          footnote 383-B
+  changed "Giants' Causeway, in Ireland." into "Giant's Causeway, in
+          Ireland." page 384
+  changed "bottom of a shallow sea" into "bottom of a shallow sea."
+          page 388
+  changed "to larva and" into "to lava and" page 388
+  changed "PORM, STRUCTURE, AND" into "FORM, STRUCTURE, AND" page 390
+  changed "Baranco de las Angustias." into "Barranco de las Angustias."
+          page 391
+  changed "lie uncomformably to" into "lie unconformably to" page 398
+  changed "trap-dikes of Etna," into "trap dikes of Etna," page 401
+  changed "the accompanying wood-cut" into "the accompanying woodcut"
+          page 404
+  changed "in once instance" into "in one instance" page 404
+  changed "Punto del Nasone on Somma" into "Punta del Nasone on Somma"
+          page 405 (fig. 467)
+  changed "we recognise the ordinary" into "we recognize the ordinary"
+          page 418
+  changed "near St. Andrew's" into "near St. Andrews" page 422
+  changed "crystals of mesotyge" into "crystals of mesotype" page 431
+  changed "H. de la Beche during" into "H. De la Beche during" page 432
+  changed "Geol. Trans, 2d" into "Geol. Trans., 2d" footnote 435-E
+  changed "silex, thay have" into "silex, they have" page 439
+  changed "except when mineralogicaly" into "except when mineralogically"
+          page 440
+  changed "Bontigny's experiments have" into "Boutigny's experiments have"
+          page 441
+  changed "mineral camposition-Test" into "mineral composition-Test"
+          page 449
+  changed "Granite of Dartmore altering" into "Granite of Dartmoor
+          altering" page 449
+  changed "are many vareties" into "are many varieties" page 450
+  changed "the gritz quartzose" into "the grits quartzose" page 456
+  changed "ay at smome" into "may at some" page 462
+  changed "and their synonymes." into "and their synonymies." page 465
+  changed "These aeriform fluids," into "These aëriform fluids," page 476
+  changed "fumeroles have been" into "fumaroles have been" page 476
+  changed "its being nonfossiliferous," into "its being non-fossiliferous,"
+          page 479
+  changed "have become matamorphic" into "have become metamorphic" page 484
+  changed "MM. Studer, and Hugi," into "MM. Studer and Hugi," page 484
+  changed "hornblende-schist, chlorine-schist," into "hornblende-schist,
+          chlorite-schist," page 485
+  changed "enlarged or reopened." into "enlarged or re-opened." page 488
+  changed "vein of Andreasburg" into "vein of Andreasberg" page 494
+  changed "greenstone, or "toad-stone,"" into "greenstone, or "toadstone,""
+          page 497
+  changed "can be recognised in" into "can be recognized in" page 498
+  changed "H. de la Beche during" into "H. De la Beche during" page 499
+  changed "Lithodomi in beaches" into "lithodomi in beaches," page 502
+  changed "Barrarde, M., on trilobites, 358." into "Barrande, M., on
+          trilobites, 358." page 502
+  changed "Argile plastiqne, or" into "Argile plastique, or" page 502
+  changed "or inland" into "on inland" page 502
+  changed "on cornish lodes," into "on Cornish lodes," page 503
+  changed "on Sewalik hills," into "on Sewâlik hills," page 503
+  changed "Caryophillia cespitosa, bed" into "Caryophyllia cæspitosa,
+          bed" page 503
+  changed "Cystidiæ in Silurian rocks, 358." into "Cystideæ in Silurian
+          rocks, 358." page 504
+  changed "Decken, Prof. von, on reptiles in Saarbrück coalfield, 336."
+          into "Dechen, Prof. von, on reptiles in Saarbrück coal-field,
+          336." page 505
+  changed "France, 176-196." into "France, 176-191." page 505
+  changed "Doué, M. B. de, on" into "Doue, M. B. de, on" page 505
+  changed "Desroyers, M., on" into "Desnoyers, M., on" page 505
+  changed "on Icthyosaurus, 276." into "on Ichthyosaurus, 276." page 505
+  changed "hill of Gergovla," into "hill of Gergovia," page 505
+  changed "on Cystidiæ, 358." into "on Cystideæ, 358." page 505
+  changed "Glenroy, parallel" into "Glen Roy, parallel" page 506
+  changed "sienitic, 440." into "syenitic, 440." page 506
+  changed "vesiculosus in Lym-fiord, 33." into "vesiculosus in Lym-Fiord,
+          33." page 506
+  changed "Hamilton. Sir W.," into "Hamilton, Sir W.," page 507
+  changed "Hooghley river, analysis" into "Hooghly river, analysis"
+          page 507
+  changed "Icthyolites of Old" into "Ichthyolites of Old" page 507
+  changed "Icthyosaurus communis, figure" into "Ichthyosaurus communis,
+          figure" page 507
+  changed "period, Volcanic rocks," into "period. Volcanic rocks," page 507
+  changed "Kentish chalk, sandgalls" into "Kentish chalk, sand-galls"
+          page 507
+  changed "Limestone, fosslliferous," into "Limestone, fossiliferous,"
+          page 508
+  changed "Lochabar, parallel roads" into "Lochaber, parallel roads"
+          page 508
+  changed "in cannel coal" into "in Cannel coal" page 508
+  changed "enlarged and reopened, 492." into "enlarged and re-opened,
+          492." page 508
+  changed "teeth of. figured," into "teeth of, figured," page 508
+  changed "Mammifer in trlas" into "Mammifer in trias" page 508
+  changed "on Stonefield slate, 266." into "on Stonesfield slate, 266."
+          page 508
+  changed "Mososaurus in St. Peter's" into "Mosasaurus in St. Peter's"
+          page 509
+  changed "Oeynhansen, M. von, on" into "Oeynhausen, M. von, on" page 509
+  changed "Saarbruck coal field," into "Saarbrück coal field," page 510
+  changed "sandpipes near," into "sand-pipes near," page 509
+  changed "St. Andrew's, trap" into "St. Andrews, trap" page 510
+  changed "Plutonic rocks, 7-446." into "Plutonic rocks, 7. 446." page 510
+  changed "Rose, Frof. G.," into "Rose, Prof. G.," page 510
+  changed "of Colebrook Dale," into "of Coalbrook Dale," page 510
+  changed "sandpipes in, 83." into "sand-pipes in, 83." page 510
+  changed "Sandpipes near Maestricht" into "Sand-pipes near Maestricht"
+          page 510
+  changed "or sandgalls, term" into "or sand-galls, term" page 510
+  changed "Seacliffs, inland, 71." into "Sea cliffs, inland, 71." page 510
+  changed "Sedgewick, Prof., cited," into "Sedgwick, Prof., cited,"
+          page 510
+  changed "Sedgewick, Prof., on" into "Sedgwick, Prof., on" page 511
+  changed "Sewalik Hills, freshwater" into "Sewâlik Hills, freshwater"
+          page 511
+  changed "Skapter Jokul, eruption" into "Skaptar Jokul, eruption" page 511
+  changed "Sub-Apennine strata, 105. 166." into "Subapennine strata, 105,
+          166." page 511
+  changed "on sand galls, 82." into "on sand-galls, 82." page 512
+  added Header "W." in index page 512
+  changed "Wenlok formation, 354." into "Wenlock formation, 354." page 512
+  changed "Whin-Sil, intrusion of" into "Whin-Sill, intrusion of" page 512
+  changed "on Cystidæ, 358." into "on Cystideæ, 358." page 512
+  changed "in 'Lavengro.' because" into "in 'Lavengro' because"
+          Advertisements
+  changed "Vols. I-VIII. With" into "Vols. I.-VIII. With" Advertiesements
+  changed "early religous schools" into "early religious schools"
+          Advertisements
+  changed "its organisation more" into "its organization more"
+          Advertisements
+  changed "with unfagging tread" into "with unflagging tread"
+          Advertisements
+  changed "of time and money" into "of time and money." Advertisements
+  changed "A CONDENSED HAND-BOOK OF ALL ENGLAND" into "A CONDENSED
+          HANDBOOK OF ALL ENGLAND" Advertisements
+  changed "Leicester, Bucks Nottinghamshire." into "Leicester, Bucks,
+          Nottinghamshire." Advertisements
+  changed "Warwick, Glocester, Worcester," into "Warwick, Gloucester,
+          Worcester," Advertisements
+
+
+
+
+
+
+End of Project Gutenberg's A Manual of Elementary Geology, by Charles Lyell
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