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PRINCIPLES OF GEOLOGY.
VOLUME THE THIRD.
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GEOLOGY,
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AN ATTEMPT TO EXPLAIN THE FORMER CHANGES OF THE EARTH’S SURFACE,
BY REFERENCE TO CAUSES NOW IN OPERATION.
BY
CHARLES LYELL, Esa., F.R.S.,
FOR, SEC. TO THE GEOL. SOC., PROF. OF GEOL, TO KING'S COLL,, LONDON
IN THREE VOLUMES.
Vou. III.
LONDON: JOHN MURRAY, ALBEMARLE-STREET.
MDCCCXXXIII.
LONDON: PRINTED BY WILLIAM CLOWES, Stamford Street.
TO
RODERICK IMPEY MURCHISON, Esgq., F.R.S., &c. &e. &c.
LATE PRESIDENT OF THE GEOLOGICAL SOCIETY.
My pear Mourcuison,
I nave great pleasure in dedicating this volume to you, as it contains the results of some of our joint labours in the field, in Auvergne, Velay, and Piedmont—results which had not yet been communicated to the public through any other channel.
When we quitted England together for a tour on the con- tinent, in May, 1828, the first sketch only of my < Principles of Geology’ was finished. Since that time you have watched the progress of the work with friendly interest, and, as President of the Geological Society, have twice expressed in your Anni- versary Addresses, your participation in many of my views, which were warmly controverted by others. The eulogy which you have lately pronounced from the chair, on the last part of my work, (whether I attribute your approval to the exercise of an unbiassed judgment or to the partiality of a friend,) could not fail to be most gratifying to my feelings, and I trust that you will long enjoy health and energy to continue to promote with enthusiasm the advancement of your favourite science.
Believe me, my dear Murchison, Yours, &c. &c. Cuaries Lye tt,
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PREFACE.
b)
Tue original MS. of the ‘Principles of Geology was delivered to the publisher at the close of the year 1827, when it was proposed that it should appear in the course of the year followimg, in two volumes octavo. Since that time many causes have concurred to delay the completion of the work, and, in some degree, to modify the original plan. In May, 1828, when the preliminary chapters on the History of Geology, and some others which follow them in the first volume, were nearly finished, I became anxious to visit several parts of the continent, in order to acquire more information concerning the tertiary formations. Accordingly, I set out in May, 1828, in company with Mr. Murchison, on a tour through France and the north of Italy, where we exa- mined together many districts which are particularly mentioned in the body of this work. We visited Auvergne, Velay, Cantal, and the Vivarais, and afterwards the environs of Aix, in Provence, and then passed by the Maritime Alps to Savona, thence - crossing to Piedmont by the Valley of the Bormida. At Turin we found Signor Bonelli engaged in the arrangement of a large collection of tertiary shells
Vill PREFACE.
obtained chiefly from the Italian strata; and as I had already conceived the idea of classing the different tertiary groups, by reference to the proportional number of recent species found fossil in each, I was at pains to learn what number Signor Bonelli had identified with living species, and the degree of precision with which such identifications could be made. With a view of illustrating this point, he showed us suites of shells common to the Sub- apenniné beds and to the Mediterranean, pointing out that in some instances not only the ordinary type of the species, but even the different varieties had their counterparts both in the fossil and recent series. The same naturalist informed us that the fossil shells of the hill of the Superga, at Turin, differed as a group from those of Parma and other localities of the Subapénnine beds of northern Italy; and, on the other hand, that the characteristic shells of the Superga agreed with the species found at Bordeaux and other parts of the South of France.
I was the more struck with this remark, as Mr. Mur- chison and myself had already inferred that the highly- inclined strata of the Valley of the Bormida, which agree with those of the Superga, were older than the more horizontal Subapennine marls, by which the plains of the Tanaro and the Po are skirted.
When we had explored some parts of the Vicentin together, Mr. Murchison re-crossed the Alps, while I directed my course to the south of Italy, first staying
PREFACE. 1x
at Parma, where I studied, in the cabinets of Signor Guidotti, a beautiful collection of Italian tertiary shells, consisting of more than 1000 species, many of which had been identified with living testacea. Signor Guidotti had not examined his fossils with reference to their bearing on geological questions, but computed, on a loose estimate, that there were about 30 per cent. of living species in the Subapennine beds. I then visited Florence, Sienna, and Rome, and the results of my inquiries respecting the ter- tiary strata of those territories will be found partly in the body of the work, and partly in the catalogues given in Appendix II.
On my arrival at Naples I became acquainted with Signor O. G. Costa, who had examined the fossil shells of Otranto and Calabria, and had collected many recent testacea from the seas surrounding the Calabrian coasts. His comparison of the fossil and living species had led him to a very different result in regard to the southern extremity of Italy, from that to which Signors Guidotti and Bonelli had arrived in regard to the north, for he was of opinion that few of the tertiary shells were of extinct species. In con- firmation of this view, he showed me a suite of fossil shells from the territory of Otranto, in which nearly all the species were recent.
In October, 1828, I examined Ischia, and obtained from the strata of that island the fossil shells named
in Appendix IL., p. 57. They were all, with two or
x PREFACE.
three exceptions, recognized by Signor Costa as species now inhabiting the Mediterranean, a circum- stance which greatly astonished me, as I procured some of them at the height of 2000 feet above the level of the sea (Vol. ili. p. 126).
Early in November, 1828, I crossed from Naples to Messina, and immediately afterwards examined Etna, and collected on the flanks of that mountain, near Trezza, the fossil shells alluded to in the third volume (p. 79, and Appendix II., p. 53). The occurrence of shells in this locality was not unknown to the natu- ralists of Catania, but having been recognized by them as recent species, they were supposed to have been carried up from the sea-shore to fertilize the soil, and therefore disregarded. Their position is well known to many of the peasants of the country, by whom the fossils are called ‘roba di diluvio.’
In the course of my tour I had been frequently led to reflect on the precept of Descartes, ‘ that a philo- sopher should once in his life doubt every thing he had been taught;’ but I still retained so much faith in my early geological creed as to feel the most lively surprise, on visiting Sortino, Pentalica, Syracuse, and other parts of the Val di Noto, at beholding a lime- stone of enormous thickness filled with recent shells, or sometimes with the mere casts of shells, resting on marl in which shells of Mediterranean species were imbedded in a high state of preservation. All idea of attaching a high antiquity to a regularly stratified
PREFACE. xi
limestone, in which the casts and impressions of shells alone were discernible, vanished at once from my mind. At the same time, I was struck with the iden- tity of the associated igneous rocks of the Val di Noto with well known varieties of ‘trap’ in Scotland and other parts of Europe, varieties, which I had also seen entering largely into the structure of Etna, | occasionally amused myself with speculating on the different rate of progress which Geology might have made, had it been first cultivated with success at Catania, where the phenomena above alluded to, and the great elevation of the modern tertiary beds in the Val di Noto, and the changes produced in the historical era by the Calabrian earthquakes, would have been familiarly known.
From Cape Passaro I passed on by Spaccaforno and Licata to Girgenti, where I abandoned my design of ex- ploring the western part of Sicily, that I might return again to the Val di Noto and the neighbourhood of Etna, and verify the discoveries which I had made. With this view I travelled by Caltanisetta, Piazza, Caltagirone, Vizzini, Militello, Palagonia, Lago Naftia, and Radusa, to Castrogiovanni, and from thence to Palermo, at which last place I procured the shells named in Appendix II. p. 55. The sections on this new route confirmed me in my first opinions respecting the Val di Noto, as will appear by the 6th, 8th, and 9th chapters of the third Volume.
When I again reached Naples, in January, 1829, I
xil PREFACE.
found that Signor O, G. Costa had examined the ter- tiary fossils which I had sent to him from different parts of Sicily, and declared them to be for the most part of recent species. I then bent my course home- ward, seeing at Genoa, Professor Viviani and Dr. Sasso, the last of whom. put into my hands his memoirs on the strata of Albenga (see vol, iii. p. 166), in which I found, that, according to his list of shells, the tertiary formations at the foot of the maritime Alps contained about 50 per cent. of recent species.
I next re-visited Turin, and communicated to Signor Bonelli the result of my inquiries respecting the ter- tiary beds of the south of Italy, and of Sicily, upon which he kindly offered to review his fossils, some of which had been obtained from those countries, and to compare them with the Subapennine shells of northern Italy. He also promised to draw up imme- diately a list of the shells characteristic of the green- sand of the Superga, and common to that locality and Bordeaux, that I might publish it at the end of my second volume; but the death of this amiable and zealous naturalist soon afterwards deprived me of the benefit of his assistance,
I had now fully decided on attempting to establish four sub-divisions of the great tertiary epoch, the same which are fully illustrated in the present work. I considered the basin of Paris and London to be the type of the first division; the beds of the Superga, of the second; the Subapennine strata of northern Italy,
‘PREFACE. xi
of the third; and Ischia and the Val di Noto, of the fourth. I was also convinced that | had seen proofs, during my tour in Auvergne, Tuscany and Sicily, of volcanic rocks contemporaneous with the sedimentary strata of three of the above periods.
| On my return to Paris, in February, 1829, I com- municated to M. Desnoyers some of the new views to which my examination of Sicily had led me, and my intention to attempt a classification of the different tertiary formations in chronological order, by reference to the comparative proportion of living species of shells found fossil in each. He informed me, that during my tour he had been employed in printing the first part of his memoir, not yet published, ‘on the Tertiary Formations more recent than the Paris basin,’ in which he had insisted on the doctrine ‘of the suc- cession of tertiary formations of different ages.’ At the end of the first part of his memoir, which was published before I left Paris*, he annexed a note on the accordance of many of my views with his own, and my intention of arranging the tertiary formations chronologically, according to the relative number of fossils. in each group, which were identifiable with species now living.
At the same time I learned from M. Desnoyers, that M. Deshayes had, by the mere inspection of the fossil shells in his extensive museum, convinced him- self that the different tertiary formations might be
* Ann, des Sci, Nat., tome xvi. p, 214,
xiv PREFACE.
arranged in a chronological series. I accordingly lost no time in seeing M. Deshayes, who explained to me the data on which he considered that the three ter- tiary periods mentioned in the Tables, Appendix I., might be established. I at once perceived that the fossils obtained by me in my tour would form but an inconsiderable contribution to so great a body of zoological evidence as M. Deshayes had already in his possession. I therefore requested him to examine my shells when they arrived from Italy, and expressed my great desire to obtain his co-operation in my work, in which, as will appear in the sequel, I was fortunate enough to succeed.
The preparation of my first volume had now been suspended for nine months, and was not resumed until my return to London in the beginning of March, 1829. Before the whole was printed another summer arrived, and | again took the field to examine ‘the Crag,’ on the coasts of Essex, Norfolk, and Suffolk. The first volume appeared at length in January, 1830, after which I applied myself to perfect what I had written on ‘the changes in the organic world,’ a subject which merely occupied four or five chapters in my original sketch, but which was now expanded into a small treatise. Before this part was completed another summer overtook me, and I then set out on a geological expedition to the south of France, the Pyrenees, and Catalonia.
On my return to Paris, in September, 1830, I
PREFACE. XV
studied for six weeks in the museum of M. Deshayes, examining his collection of fossil and recent shells, and profiting by his instructions in conchology. As he had not yet published any of the general results deducible from his valuable collection, 1 requested him to furnish me with lists of those species of shells which were common to two or more tertiary periods, as also the names of those known to occur both in some tertiary strata and in a living state. This he engaged to do, and we agreed that the information should be communicated in a tabular form. After several modifications of the plan first proposed for the Tables, we finally agreed upon the manner in which they should be constructed, and the execution was left entirely in the hands of M. Deshayes, in whose name they were to appear in my second volume.
The tables were sent to me in the course of the following spring (1831), and additions and corrections several months later. They contained not only the information which I had expected, but much more, for the names of several hundred species were added, as being common to two or more formations of the same period, whereas it was originally proposed to insert those only which were known to be common to two or more distinet periods. Thus, for example, more than 50 shells are now included in the tables, on the ground that they are common to the tertiary strata both of the London and Paris basins, although they
XVI PREFACE.
only oceur in the Hocene period to which the strata of those basins belong. The names thus added will increase the value of the tables, and give a more com- plete view of the point to which fossil conchology has now reached; at the same time, it must be admitted that tables of shells cannot be perfected on this plan, as the science advances from year to year, without soon outgrowing the space which could reasonably be allotted to fossil conchology in a work on geology, for they would soon embrace the names of the greater number of known shells, nearly all of these being common to different groups of strata of the same period. Some of the catalogues which I have given in Appendix II., of fossil shells from the neighbour- hood of the Red Sea, and from some other localities, may illustrate this remark, as they lead us to antici- pate that, at no distant time, we may find a large pro- portion of all the Recent species in a fossil state.
In treatises on fossil conchology, such as I trust M. Deshayes will soon publish, we cannot have too complete a catalogue of all the species which have been found fossil in every locality, together with their synonyms; but in geological works we can only illus- trate the more important theoretical points by cata- logues of those shells which are either characteristic of particular periods, as being exclusively confined to
them, or which show the connexion of two periods,
. by being common to each, For this purpose we
PREFACE. XViL
must select certain normal groups which do not approximate too closely to each other, and enumerate by name the species common to more than one of these. Thus, for example, we might omit in our tables the Newer Pliocene formations altogether, and enumerate the shells common to the Recent and Older Pliocene beds. |
I have arranged the tertiary formations in four
groups, as I had determined to do before I was acquainted with M. Deshayes; and in his tables he has referred the shells to three periods, according to which he had classed them before he had any commu- nication with me. No confusion, however, will arise . from this want of conformity between the tables and my classification, since I have named two of my periods (the Newer and Older Pliocene) as subdivisions of one of his; and by reference to the Synoptical Table, at p. 61, the reader will see which localities mentioned in M. Deshayes’s Tables belong to the Newer and which to the Older Pliocene period.
In the summer of 1831 I made a yveological excursion to the volcanic district of the Eifel, and on my return I determined to extend my work to three volumés, the second of which appeared in January, 1832. The last volume has been delayed till now by many interruptions, among which I may mention a tour, in the summer of 1832, up the valley of the
Rhine, when I examined the loess (vol. iii. p. 151), .
Vou, III. c
XViil PREFACE.
and a visit, on my way home through Switzerland, to the Valorsine, where I had an opportunity of verify- ing the observations of M. Necker on the granite veins and altered stratified rocks of that district. I may also mention the time occupied in the correction of the second edition of the first and second volumes, and the delivery of a course of Lectures in May and June, 1832, at King’s College, London, on which occasion I had an opportunity of communicating to the scientific world a great part of the views now explained in my last volume.
London, April, 1833.
CONTENTS.
Vou. IIT.
CHAPTER I,
PAGE
Connexion between the subjects treated of in the former parts of this work and those to be discussed in the present volume—Ezroneous assumption of the earlier geologists respecting the discordance of the former and actual causes of change—Opposite system of inquiry adopted in this work—lIllus- trations from the history of the progress of Geology of the respective merits of the two systems—Habit of indulging conjectures respecting irregular and extraordinary agents not yet abandoned—Necessity in the present state of science of prefixing to a work on Geology treatises respecting the changes now in progress in the animate and inanimate world : :
CHAPTER II.
Arxrangement of the materials composing the earth’s crust—The existing continents chiefly composed of subaqueous deposits—Distinction between sedimentary and volcanic rocks—Between primary, secondary, and tertiary— Origin of the primary—tTransition formations—Difference between secondary and tertiary strata—Discovery of tertiary groups of successive periods— Paris basin—London and Hampshire basins—Tertiary strata of Bordeaux, Piedmont, Touraine, &c,—Subapennine beds—English crag—More recent deposits of Sicily, &c. ° ° . . ° .
CHAPTER III.
Different circumstances under which the secondary and tertiary formations may have originated—Secondary series formed when the ocean prevailed: Tertiary during the conversion of sea into land, and the growth of a continent — Origin of interruption in the sequence of formations—The areas where new deposits take place are always varying—-Causes which occasion this transfer- ence of the places of sedimentary deposition—Denudation augments the dis- cordance in age of rocks in contact—Unconformability of overlying forma- tions—In what manner the shifting of the areas of sedimentary deposition may combine with the gradual extinction and introduction of species-to pro- duce a series of deposits having distinct mineral and organic characters c 2
23
XX CONTENTS.
CHAPTER IV.
PAGE
Chronological relations of mineral masses the first object in geological classification —Superposition, proof of more recent origin—Exceptions in re- gard to volcanic rocks—Relative age proved by included fragments of older rocks—Proofs of contemporaneous origin derived from mineral characters— Variations to which these characters are liable—Recurrence of distinct rocks at successive periods—Proofs of contemporaneous origin derived from organic remains— Zoological provinces are of limited extent, yet spread over wider areas than homogeneous mineral deposits—Different modes whereby dis- similar mineral masses and distinct groups of species may be proved to have been contemporaneous ° . . A . ‘
CHAPTER V.
Classification of tertiary formations in chronological order—Comparative value of different classes of organic remains—Fossil remains of testacea the most important—Necessity of accurately determining species—Tables of shells by M. Deshayes—Four subdivisions of the Tertiary epoch—Recent for- mations—Newer Pliocene period—Older Pliocene period—Miocene period -—locene period—The distinct zoological characters of these periods may not imply sudden changes in the animate creation—The recent strata form a common point of departure in distant regions—Numerical proportion of recent species of shells in different tertiary periods—Mammiferous remains of the successive tertiary eras—Synoptical Table of Recent and Tertiary formations . . ° . : ° .
CHAPTER VI.
Newer Pliocene formations—Reasons for considering in the first place the more modern periods—Geological structure of Sicily—Formations of the Val di Noto of newer Pliocene period—Divisible into three groups—Great limestone—Schistose and arenaceous limestone—Blue marl with shells— Strata subjacent to the above—Volcanic rocks of the Val di Noto—Dikes— Tuffs and Peperinos—Volcanic conglomerates—Proofs of long intervals between volcanic eruptions—-Dip and direction of newer Pliocene strata of Sicily ° ° ° : : : . :
CHAPTER VII.
Marine and volcanic formations at the base of Etna—Their connexion with the strata of the Val di Noto—Bay of Trezza—Cyclopian isles—Fossil shells of recent species—Basalt and altered rocks in the Isle of Cyclops—
CONTENTS,
Xx1
PAGE
Submarine lavas of the bay of Trezza not currents from Ktna—IJnternal structure of the cone of Ktna—Val di Calanna—Val del Bove not an ancient crater—Its precipices intersected by countless dikes—Scenery of the Val del Bove—Form, composition, and origin of the dikes—Lavas and breccias intersected by them 2 ‘ ‘ Py .
CHAPTER VIII.
Speculations on the origin of the Val del Bove on Etna—Subsidences— Antiquity of the cone of Etna—Mode of computing the age of voleanos— Their growth analogous to that of exogenous trees—Period required for the production of the lateral cones of Etna—Whether signs of Diluvial Waves are observable on Etna ‘ ° ° ° ° °
CHAPTER IX.
Origin of the newer Pliocene strata of Sicily—Growth of submarine for- mations gradual—Rise of the same above the level of the sea probably caused by subterranean lava—Igneous newer Pliocene rocks formed at great depths, exceed in volume the lavas of Etna—Probable structure of these recent sub- terranean rocks—Changes which they may have superinduced upon strata in contact—Alterations of the surface during and since the emergence of the newer Pliocene strata—Forms of the Sicilian valleys—Sea cliffs—Proofs of successive elevation—Why the valleys in the newer Pliocene districts cor- respond in form to those in regions of higher antiquity—Migrations of animals and plants since the emergence of the newer Pliocene strata—Some species older than the stations they inhabit—Recapitulation :
CHAPTER X,
Tertiary formations of Campania—Comparison of the recorded changes in this region with those commemorated by geological monuments—Differences in the composition of Somma and Vesuvius—Dikes of Somma, their origin —Cause of the parallelism of their opposite sides—Why coarser grained in the centre—Minor cones of the Phlegresan Fields—Age of the voleanic and associated rocks of Campania—Organic remains—External configuration of the country, how produced—No signs of diluvial waves—Marine Newer Pliocene strata visible only in countries of earthquakes—Illustrations from Chili — Peru — Parallel roads of Coquimbo —West-Indian archipelago — Honduras—Hast-Indian archipelago—Red Sea ‘ : °
CHAPTER XI.
Newer Pliocene fresh-water formations—Valley of the Elsa—Travertins of Rome—Osseous breccias—Sicily—Caves near Palermo—Extinct animals
103
118
XX1i CONTENTS.
PAGE
in newer Pliocene breccias— Fossil bones of Marsupial animals in Australian caves—F'ormation of osseous breccias in the Morea—Newer Pliocene allu- viums—Difference between alluviums and regular subaqueous strata—The former of various ages—Marine alluvium—Giooved surface of rocks—Erratic blocks of the Alps—Theory of deluges caused by paroxysmal elevations untenable—How ice may have contributed to transport large blocks from the Alps—Enuropean alluviums chiefly tertiary—Newer Pliocene in Sicily—Léss of the Valley of the Rhine—Its origin—Contains recent shells
CHAPTER XII.
Geological monuments of the ofder Pliocene period—Subapennine forma- tions—Opinions of Brocchi—Different groups termed by him Subapennine are not all of the same age—Mineral composition of the Subapennine forma- tions—Marls—Yellow sand and gravel—Subapennine beds how formed— Illustration derived from the Upper Val d’Arno—Organic remains of Sub- apennine hills—Older Pliocene strata at the base of the Maritime Alps— Genoa—Sayvona—Albenga—Nice—Conglomerate of Valley of Magnan—Its origin—Tertiary strata at the eastern extremity of the Pyrenees
CHAPTER XIII.
Crag of Norfolk and Suffolk—Shown by its fossil contents to belong to the older Phoeene period—Heterogeneous in its composition—Superincumbent lacustrine deposits—Relative position of the crag—TForms of stratification —Strata composed of groups of oblique layers—Cause of this arrangement — Dislocations in the crag produced by subterranean movements—Protruded masses of chalk—Passage of marine crag into alluvium—Recent shells in a deposit at Sheppey, Ramsgate, and Brighton . .
@
CHAPTER XIV.
Voleanic rocks of the older Pliocene period—Italy—Volcanic region of Olot in Catalonia—Its extent and geological struacture—Map—Number of econes— Scoria—Lava currents—Ravines in the latter cut by water—Ancient allu- vium underlying lava—Jets of air called ‘ Bufadors’—Age of the Catalonian volcanos uncertain—Harthquake which destroyed Olot in 1421—Sardinian volcanos—District of the Hifel and Lower Rhine—Map—Geological structure of the country—Peculiar characteristics of the Eifel voleanos—Lake craters —Trass—Crater of the Roderberg—Age of the Hifel voleanie rocks uncer- tain—Brown coal formation 5 ‘i
e * e
CHAPTER XV.
Miocene period—Marine formations—Faluns of Touraine—Compatison of the Faluns of the Loire and the English Crag—Basin of the Gironde and
137
155
171
183
CONTENTS. XX1ll
PAGE Landes—Fresh-water limestone of Saucats—Position of the limestone of
Blaye—Eocene strata in the Bordeaux basin—IJnland cliff near Dax—Strata of Piedmont—Superga—Valley of the Bormida—Molasse of Switzerland— Basin of Vienna—Styria—Hungary—Volhynia and Podolia—Montpellier 202
CHAPTER XVI.
Miocene alluviums—Auvergne—Mont Perrier—Extinct quadrupeds — Velay—Orleanais—Alluviums contemporaneous with Faluns of Touraine— Miocene fresh-water formations—Upper Val d’Amo—Extinct mammalia— Coal of Cadibona—Miocene volcanic rocks—Hungary—Transylvania—Styria —Auvergne—Velay : ° ° ° ° ° 217
CHAPTER XVII.
Eocene period—Fresh-water formations —Central France—Map—Limayne d’ Auvergne—Sandstone and conglomerate—Tertiary Red marl and sandstone like the secondary ‘ new red sandstone’—Green and white foliated marls— Indusial limestone—Gypseous marls—General arrangement and origin of the Travertin—Fresh-water formation of the Limagne—Puy en Velay—Analogy of the strata to those of Auverene—Cantal—Resemblance of Aurillac lime- stone and its flints to our upper chalk—Proofs of the gradual deposition of marl-~-Concluding remarks . ‘ ‘ ° ° 225
CHAPTER XVIII.
Marine formations of the Eocene period—Strata of the Paris basin how far analogous to the lacustrine deposits of Central France—Geographical con- nexion of the Limagne d’Auvergne and the Paris basin—Chain of lakes in the Eocene period —Classification of groups in the Paris basin—Observations of M. C, Prevost—Sketch of the different subdivisions of the Paris basin— Contemporaneous marine and fresh-water strata—Abundance of Cerithia in the Caleaire grossier—Upper marine formation indicates a subsidence— Part of the Caleaire prossier destroyed when the upper marine strata origi- nated—All the Parisian groups belong to one great epoch—Microscopic shells—Eones of quadrupeds in gypsum—In what manner entombed—Num- ber of species—All extinct—Strata with and without organic remains alter- nating—Our knowledge of the physical geography, fauna, and flora of the Eocene period considerable—Coneluding remarks ® ‘ » 24)
CHAPTER XIX,
Volcanic rocks of the Eocene period—Auvergne—Jgneous formations associated with lacustrine strata—Hill of Gergovia—Hruptions in Central
XXIV CONTENTS.
PAGE France at successive periods—Mont Dor an extinct voleano—Velay—Plomb
du Cantal—Train of minor volcanos stretching from Auvergne to the Vivarais —Monts Domes—Puy de Come—Puy Rouge—Ravines excavated through lava—Currents of lava at different heights—Subjacent alluviums of distinct ages—The more modern lavas of Central France may belong to the Miocene period—The integrity of the cones not inconsistent with this opinion—No eruptions during the historical era—Division of voleanos into ante-diluvian and post-diluvian inadmissible—Theories respecting the effects of the Flood considered—Hypothesis of a partial flood—Of a universal deluge—Theory of Dr. Buckland as controyerted by Dr. Fleming—Recapitulation 6 op
CHAPTER XX.
Eocene formations, continued—Basin of the Cotentin, or Valognes—Rennes —Basin of Belgium, orthe Netherlands—Aix in Provence—Fossil insects— Tertiary strata of England—Basins of London and Hampshire—Different groups—Plastic clay and sand—London clay—Bagshot sand—Fresh-water strata of the Isle of Wight—Paleotherium and other fossil mammalia of Binstead—English Hocene strata conformable to chalk—Outliers on the elevated parts of the chalk—Inferences drawn from their occurrence—Sketch of a theory of the origin of the English tertiary strata . : 275
CHAPTER XXI.
Denudation of secondary strata during the deposition of the English Eocene formations— Valley of the Weald between the North and South Downs —Map—Secondary rocks of the Weald divisible into five groups—North and South Downs—Section across the valley of the Weald—Anticlinal axis— True scale of heights—Rise and denudation of the strata eradual—Chalk -escarpments once sea-cliffs—Lower terrace of ‘ firestone,’ how caused— Parallel ridges and valleys formed by harder and softer beds—No ruins of the chalk on the central district of the Weald—Explanation of this pheno- menon—Double system of valleys, the longitudinal and the transverse— Transverse how formed—Gorges intersecting the chalk—Lewes Coomb— Transverse valley of the Adur : ° ° - e 285
CHAPTER XXII.
Denudation of the Valley of the Weald, continued—The alternative of the proposition that the chalk of the North and South Downs were once continu- ous, considered—Dr, Buckland on the Valley of Kingsclere—Rise and denudation of secondary rocks gradual—Concomitant deposition of tertiary strata gradual—Composition of the latter such as would result from the wreck of the secondary rocks—Valleys and furrows on the chalk how caused
CONTENTS. XXKV
PAGE —Auvergne, the Paris basin, and south-east of England one region of earth-
quakes during the Hocene period—Why the central parts of the London and Hampshire basins rise nearly as high as the denudation of the Weald— Effects of protruding force counteracted by the levelling operations of water —Thickness of masses removed from the central ridge of the Weald—Great escarpment of the chalk having a direction north-east and south-west— Curved and vertical strata in the Isle of Wight—These were convulsed after the deposition of the fresh-water beds of Headen Hill—Hlevations of land posterior to the crag—Why no Eocene alluviums recognizable— Concluding remarks on the intermittent operations of earthquakes in the south-east of England, and the gradual formation of valleys—Recapitulation : 303
CHAPTER XXIII,
Secondary formations—Brief enumeration of the principal groups—No species common to the secondary and tertiary rocks—Chasm between the Hocene and Maestricht beds—Duration of secondary periods—Former con- tinents placed where it is now sea—Secondary fresh-water deposits why rare —Persistency of mineral composition why apparently greatest in older rocks —Supposed universality of red marl formations—Secondary rocks why more consolidated—Why more fractured and disturbed—Secondary volcanic rocks of many different ages ° : : ° « 324
CHAPTER XXIV.
On the relative antiquity of different mountain-chains—Theory of M. Elie de Beaumont—His opinions controverted—His method of proving that dif- ferent chains were raised at distinct periods—His proof that others were contemporaneous—His reasoning why not conclusive—His doctrine of the parallelism of contemporaneous lines of elevation—Objections—Theory of parallelism at variance with geological phenomena as exhibited in Great Britain—Objections of Mr. Conybeare—How far anticlinal lines formed at the same period are parallel—Difficulties in the way of determining the relative age of mountains : . ° ° ° . 337
CHAPTER XXV.
On the rocks usually termed ‘Primary ’—Their relation to volcanic and sedimentary formations—The ‘ primary’ class divisible into stratified and unstratified—Unstratified rocks called Plutonic—Granite veins—Their vari- ous forms and mineral composition—Proofs of their igneous orizin—Granites of the same character produced at successive eras—Some of these newer than certain fossiliferous strata—Difficulty of determining the age of particular granites—Distinction between the volcanic and the plutonic rocks—Trappean rocks not separable from the voleanic—Passage from trap into granite— Theory of the origin of granite at every period from the earliest to the most recent : : . . . e . ° 302
XXVi : CONTENTS.
PAGE CHAPTER XXVI.
On the stratified rocks usually called ‘primary’—Proofs from the dispo- sition of their strata that they were originally deposited from water—Alter. nation of beds varying in composition and colour—Passage of gneiss into granite—Alteration of sedimentary strata by trappean and granitic dikes— Inference as to the origin of the strata called ¢ primary’—Conversion of argil- laceous into hornblende schist —The term ‘Hypogene’ proposed as a substitute for primary—‘ Metamorphic’ for ‘ stratified primary ’ rocks—No regular order of succession of hypogene formations—Passage from the metamorphic to the sedimentary strata—Cause of the high relative antiquity of the visible hypogene formations—That antiquity consistent with the hypothesis that they have been produced at each successive period in equal quantities—Great volume of hypogene rocks supposed to have been formed since the Eocene period—Concluding remarks ° 5 . . a 365
Table I, Showing the relations of the various classes of rocks, the Alluvial,
the Aqueous, the Voleanic, and the Hypogene, of different periods 386 Table 11. Showing the order of superposition of the principal European
groups of sedimentary strata mentioned in this work 5 . 389 Notes in explanation of the Tables of fossil shells in Appendix I, : 395 Appendix I. Tables of fossil shells by Monsieur G. P. Deshayes 9 Bl Appendix IJ. Lists of fossil Shells chiefly collected by the author in Sicily
and Italy, named by M. Deshayes : — 53 Glossary, containing an explanation of geological and other scientific terms
used in this work é Fa A . AP git Index ° e ° e ° ° 85
LIST OF PLATES AND WOOD-CUTS
IN THE THIRD VOLUME,
PLATES.
‘rontispiece. View of the volcanos around Olot, in Catalonia. See p. 186. This view is taken from a sketch by the author ; an attempt is made to represent by colours the different geo- logical formations of which the country is composed, ‘The blue line of mountains in the distance are the Pyrenees, which are to the north of the spectator, and consist of primary and ancient secondary rocks. In front of these are the secondary for- mations, described in chap. xiv., coloured purplish-grey of different tints, to express different distances. ‘The flank of the hill, in the foreground, called Costa di Pujou, is com- posed partly of secondary rocks, which are seen to the left of a small bridle-road, and partly of volcanic, the red colour expressing lava and scorie.
Several very perfect voleanic cones, chiefly composed of red scoriz, and. having craters on their summits, are seen in the immediate neighbourhood of Olot, coloured red. 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, but which has been in a great measure filled up by lava.
The reader should be informed, that in many impressions of this plate Montsacopa is mis-spelt ‘ Montescopa,’ and Mount Garrinada is mis-spelt ‘ Gradenada.’
Plate I. The shells represented in this plate have been selected by M. Deshayes as characteristic of the Pliocene period of the Tables, Appendix I. The greater part of them are ~ common both to the older and newer Pliocene periods of this work. Eight of ‘the species, Nos. 1, 3, 5, 6, 7, 9, 13, and 14, are now living, but are given as being also found in the Older Pliocene formations. Fusus crispus is not found either recent
XX Vili LIST OF PLATES.
or in the Miocene or Eocene formations, but occurs both in the Newer and Older Pliocene strata. Mitra plicatula has been found only in the older Pliocene deposits. The Turbo rugosus was considered as exclusively Pliocene when selected by M. Deshayes, but M. Boué has since found it in the Miocene strata at Vienna and Morayia (see Tables, Appendix I. p. 26). Buccinum semistriatum is also a Miocene shell, but was in- serted as being peculiarly abundant in the Pliocene strata.
Plate 11. All the shells figured in this plate, except Car- dita Ajar, are very characteristic of the Miocene formations; that is to say, they are found in that period and no other. Cardita Ajar is also very common in the Miocene strata, but is also a Recent species. It has not yet been observed in any Pliocene deposit.
Plate 111. The species of shells figured in this plate are characteristic of the Hocene period, as being exclusively con- fined to deposits of that period, and for the most part abundant in them,
Plate IV. The microscopic shells of the order Cephalo- poda, figured in this plate, are characteristic of the Eocene period, and are distinct from the microscopic shells of the Older Pliocene formations of Italy. The figures are from unpub- lished drawings by M. Deshayes, who has selected some of the most remarkable types of form. The reader will observe, that the minute points, figures 4, 8, 11, 14, and 18, indicate the natural size of the species which are represented. (For obser- vations on these shells see p, 201.)
Plate V. Geological Map of the south-east of England, exhibiting the Denudation of the Weald. This map has been compiled in great part from Mr. Greenough’s Geological Map of England, and Mr. Mantell’s Map of the south-east of England. (Illustrations of Geol. of Sussex, and fossils of Tilgate Forest, 1827.) The eastern extremity of the ‘ denu- dation’ is reduced from Mr. Murchison’s Map of that district. (Geol. 'Trans., 2nd series, vol, ii. parti. plate 14.) The object of this map is fully explained in chapters xxi. and xxii, of this volume.
LIST OF WOOD-CUTS.
No. J, Diagram showing the order of succession of stratified masses ‘ 2, Diagram showing the relative position of the Primary, Secondary, and Tertiary strata . . : ° 3, Diagram showing the relative age of the strata of the Paris basin, and those of the basin of the Loire, in Touraine ° ( 4, Diagram showing the same in the strata of Suffolk and Piedmont 5. Diagram containing sections in the Val di Noto, Sicily 7 , a Horizontal sections of dikes near Palagonia : . 8, Section of horizontal limestone in contact with inclined strata of Tuff in the hill of Novera, near Vizzini z : 3 9. Section of calcareous grit and peperino, east of Palagonia, south side of the pass ; . : c : 10. Section of the same beds on the north side of the pass ‘ . 11. Outline view of the cone of Etna from the summit of the limestone platform of Primosole 2 ° A A 12. Section from Paternd by Lago di Naftid to Palagonia . : 13. Section of beds of clay and sand capped by columnar basalt and con- glomerate at a Motta, near Catania. ° e 14. View of the Isle of Cyclops, in the Bay of Trezza . °
15, Diagram showing the contortions in the newer Pliocene strata of the Isle of Cyclops. : ° . °
16. Horizontal section showing the invasion of the newer Pliocene strata of the Isle of Cyclops by lava . . 7
17, Wood-cut showing the great valley on the east side of Etna A 18. Diagram explanatory of the origin of the Valleys of Calanna and St,
Giacomo, on Hina 4 ° ° . : 19, View of dikes at the base of the Serre del Solfizio, Etna
20. View of tortuous dikes or veins of lava, Punto di Guimento, Etna 21. View of the rocks Finochio, Capra, and Musara, in the Val del Bove 22. View from the summit of Etna into the Val del Bove . 23. View of the Valley called Gozzo degli Martiri, below Melilli
Page 15
20
110
24, Diagram showing the manner of obliteration of successive lines of sea-cliff 11]
25. View of dikes or veins of lava at the Punto del Nasone, on Somma
26. Diagram showing the superposition of alluvium and cave deposits con- taining eatinet quadrupeds to a limestone containing recent shells
27. Diagram showing the position of the Cave of San Ciro, near Palermo 28, Diagram showing the position of Tertiary strata at Genoa .
122
139 141 166
XXX LIST OF WOOD-CUTS.
No,
29. Section from Monte Calvo to the sea by the Valley of Magnan, near Nice . * : A : °
30. Diagram showing the manner in which the Crag may be supposed to rest on the chalk . ; : . -
31. Section of shelly crag near Walton, Suffolk . . .
32, Section at the light-house near Happisborough : “
33. Section of Little Cat Cliff, showing the inclination of the layers of quartzose sand in opposite directions 5 : :
34, Lamination of shelly sand and loam, near the Signal-House, Walton
35. Diagram illustrative of the successive deposition of strata . °
36. Section of ripple marks caused by the wind on loose sand .
37. Bent strata of loam in the cliffs between Cromer and Runton °
38. Folding of the strata between Hast and West Runton :
39. Section in the cliffs east of Sherringham F ‘ °
40. Section east of Sherringham, Norfolk 5 . .
4]. Side view of a promontory of chalk and crag, at Trimmingham, Norfolk
42, Northern protuberance of chalk, Trimmingham . .
43, Map of the volcanic district of Catalonia . : .
44, Section of volcanic sand and ashes in a valley near Olot . .
45. Section above the bridge of Cellent : : :
AG. Section at Castell Follit * : - 3
47, Superposition of rocks in the volcanic district of Catalonia .
48. Map of the voleanic district of the Lower Rhine : .
49. View of the Gemunden Maar . 7 5
50. Section of the same and other contiguous lake-craters . :
51, Section of tertiary strata overlying chalk near Dax . :
52. Section explaining the position of the Hocene strata in the Bordeaux basin
53. Section of Inland cliffnear Dax A : : ‘
54, Position of the Miocene alluviums of Mont Perrier (or Boulade)
55. Section of the fresh-water formation of Cadibona ‘ ‘
56, Map of Auvergne, Cantal, Velay, &e. ‘ i ‘
57. Section of Vertical marls near Clermont . ‘ ‘z
oo, pSuperposition of the formations of the Paris basin : 4
60. Section of the Hill of Gergovia near Clermont a ;
61. Lavas of Auvergne resting on alluviums of different ages . c
62. Map of the principal tertiary basins of the Eocene period :
63, Section from the London to the Hampshire basin across the Valley of the Weald . . 3 : :
64, 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 : “ -
65. View of the chalk escarpment of the South Downs, taken from the Devil’s Dike, looking towards the west and south-west . ;
Page
167
173 174 74
175 175
, 176
176 178 178 178 179 179 180 184 187 188 190 192 194 195 196 207 209 210 217 221 226 231
243
259 267 275
288
288
290
LIST OF WOOD-CUTS. XXX1
No. Page 66. Chalk escarpment as seen from the hill above Steyning, Sussex. The
castle and village of Bramber in the foreground . . 291 67. Section of lower terrace of firestone : : Be 68. Diagram explanatory of anticlinal and synclinal lines . ° 293 69.
70 }Sections illustrating the gradual denudation of the Weald Valley 294, 295
71, Section from the north escarpment of the South Downs to Barcombe 296
72. Section of cliffs west of Sherringham . . . 297 73. View of the transverse valley of the Adur in the South Downs wv 209 74, Supposed section of a transverse valley r . . 300 75, View of Lewes Coomb . ° : : » 301 76. Section of a fault in the cliffhills near Lewes : : 301 77, Hypothetical section to illustrate the question of the denudation of the Weald Valley r : : : » 304 78, Ground plan of the Valley of Kingsclere . ° : 305 79. Section across the Valley of Kingsclere from north to south - 305
80. Section of the Valley of Kinesclere with the heights on a true scale 306 81. Hypothetical section illustrating the denudation of the Weald Valley
and the contemporaneous origin of the Eocene strata : 310 go, } Diagrams illustrative of the relative antiqnity of mountain-chains 340, 341
84, Diagram showing the relative position of the Hypogene sedimentary
and voleanic rocks : : . . 393 85, Granite veins traversing stratified rocks * é . 9304 86. Granite veins traversing gneiss at Cape Wrath in Scotland : 304 87. Granite veins passing through hornblende slate, Carnsilver Cove,
Cornwall. : : : : A 3335) 88. View of the junction of granite and limestone in Glen Tilt ‘c 356 89. Lamination of clay-slate, Montagne de Seguinat, near Gavarnie, in
the Pyrenees 3 . : : . 366 90. Junction of granite with jurassic or oolite strata in the Alps : 3/1 91, Diagram showing the different order of position in the Plutonic and
Sedimentary formations of differentages . ° » 388 92, Diagram to explain the meaning of the term ‘ faul?,’ Glossary . 68
93. Diagram to explain the term ‘ sadient angle,’ Glossary e 79
ERRATA.
Page 89, line 11 from the top, for vivid, read livid.
103, line 10 from the top, for newer, read older.
104, line 9 from the top, for Colosseum, read Coliseum.
110, No. of wood-cut, for No. 22, read No. 23.
11d, Ditto, Sor No. 23, read No. 24.
192, line 10 from the bottom, for with, read without.
193, line 2 from the bottom, for Von Oyenhausen, read Von Oeynhausen. 193, line 3 from the bottom, for M. Néeggerath, read M. Noeggerath. 197, line 19 from the top, for Moseberg, read Mosenberg.
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PRINCIPLES OF GEOLOGY.
CHAPTER I.
Connexion between the subjects treated of in the former parts of this work and those to be discussed in the present volume—Hrroneous assumption of the earlier geologists respecting the discordance of the former and actual causes of change—Opposite system of inquiry adopted in this work—lIIlustrations from the history of the progress of Geology of the respective merits of the two systems—H abit of indulging conjectures respecting irregular and extra- ordinary agents not yet abandoned—Necessity in the present state of science of prefixing to a work on Geology treatises respecting the changes now in progress in the animate and inanimate world.
Havine considered, in the preceding volumes, the actual opera- tion of the causes of change which affect the earth’s surface and its inhabitants, we are now about to enter upon a new division of our inquiry, and shall therefore offer a few preliminary observations, to fix in the reader’s mind the connexion between two distinct parts of our work, and to explain in what manner the plan pursued by us differs from that more usually followed by preceding writers on Geology.
All naturalists, who have carefully examined the arrange- ment of the mineral masses composing the earth’s crust, and who have studied their internal structure and fossil contents, have recognized therein the signs of a great succession of former changes; and the causes of these changes have been the object of anxious inquiry. As the first theorists possessed but a scanty acquaintance with the present economy of the animate and inanimate world, and the vicissitudes to which these are sub- ject, we find them in the situation of novices, who attempt to read a history written in a foreign language, doubting about
the meaning of the most ordinary terms; disputing, for Von, III. B
2 METHODS OF THEORIZING IN GEOLOGY. [Ch, I,
example, whether a shell was really a shell,—whether sand and pebbles were the result of aqueous trituration,—whether stra- tification was the effect of successive deposition from water; and a thousand other elementary questions which now appear to us so easy and simple, that we can hardly conceive them to have once afforded matter for warm and tedious controversy.
In the first volume we enumerated many prepossessions which biassed the minds of the earlier inquirers, and checked an impartial desire of arriving at truth. But of all the causes to which we alluded, no one contributed so powerfully to give rise to a false method of philosophizing as the entire uncon- sciousness of the first geologists of the extent of their own ignorance respecting the operations of the existing agents of change,
They imagined themselves sufficiently acquainted with the mutations now in progress in the animate and inanimate world, to entitle them at once to affirm, whether the solution of certain problems in geology could ever be derived from the observa- tion of the actual economy of nature, and having decided that they could not, they felt themselves at liberty to indulge their imaginations, in guessing at what might be, rather than in in- quiring what is; in other words, they employed themselves in conjecturing what might have been the course of nature at a remote period, rather than in the investigation of what was the course of nature in their own times,
It appeared to them more philosophical to speculate on the possibilities of the past, than patiently to explore the realities of the present, and having invented theories under the influence of such maxims, they were consistently unwilling to test their validity by the criterion of their accordance with the ordinary operations of nature. On the contrary, the claims of each new hypothesis to credibility appeared enhanced by the great con- trast of the causes or forces introduced to those now developed in our terrestrial system during a period, as it has been termed, of repose.
Never was there a dogma more calculated to foster indolence,
Ch. 1] METHODS OF THEORIZING IN GEOLOGY. 3
and to blunt the keen edge of curiosity, than this assumption of the discordance between the former and the existing causes of change. It produced a state of mind unfavourable in the highest conceivable degree to the candid reception of the evi- dence of those minute, but incessant mutations, which every part of the earth’s surface is undergoing, and by which the condition of its living inhabitants is continually made to vary. The student, instead of being encouraged with the hope of interpreting the enigmas presented to him in the earth’s struc- ture,—instead of being prompted to undertake laborious inquiries into the natural history of the organic world, and the complicated effects of the igneous and aqueous causes now in operation, was taught to despond from the first. Geology, it was affirmed, could never rise to the rank of an exact science,— the greater number of phenomena must for ever remain inex- plicable, or only be partially elucidated by ingenious conjec- tures. Even the mystery which invested the subject was said to constitute one of its principal charms, affording, as it did, full scope to the fancy to indulge in a boundless field of speculation.
‘The course directly opposed to these theoretical views con- sists In an earnest and patient endeavour to reconcile the former indications of change with the evidence of gradual mutations now in progress ; restricting us, in the first instance, to known causes, and then speculating on those which may be in activity in regions inaccessible to us. It seeks an interpretation of geological monuments by comparing the changes of which they give evidence with the vicissitudes now in progress, or which may be in progress.
We shall give a few examples in illustration of the practical results already derived from the two distinct methods of theo- rizing, for we have now the advantage of being enabled to judge by experience of their respective merits, and by the rela- tive value of the fruits which they have produced.
In our historical sketch of the progress of geology, the reader has seen that a controversy was maintained for more than a
century, respecting the origin of fossil shells and bones—were B2
4 METHODS OF THEORIZING IN GEOLOGY. [Ch. I.
they organic or inorganic substances? That the latter opinion should for a long time have prevailed, and that these bodies should have been supposed to be fashioned into their present form by a plastic virtue, or some other mysterious agency, may appear absurd; but it was, perhaps, as reasonable a conjec- ture as could be expected from those who did not appeal, in the first instance, to the analogy of the living creation, as affording the only source of authentic information. It was only by an accurate examination of living testacea, and by a comparison of the osteology of the existing vertebrated animals with the remains found entombed in ancient strata, that this favourite dogma was exploded, and all were, at leneth, per- suaded that these substances were exclusively of organic origin.
In like manner, when a discussion had arisen as to the nature of basalt and other mineral masses, evidently constituting a par- ticular class of rocks, the popular opinion inclined to a belief that they were of aqueous, not of igneous origin. These rocks, it was said, might have been precipitated from an aqueous solu- tion, from a chaotic fluid, or an ocean which rose over the con- tinents, charged with the requisite mineral ingredients, All are now agreed that it would have been impossible for human ingenuity to invent a theory more distant from the truth; yet we must cease to wonder, on that account, that it gained so many proselytes, when we remember that its claims to proba- bility arose partly from its confirming the assumed want of all analogy between geological causes and those now in action.
By what train of investigation were all theorists brought round at length to an opposite opinion, and induced to assent to the igneous origin of these formations? By an examination of the structure of active volcanos, the mineral composition of their lavas and ejections, and by comparing the undoubted pro- ducts of fire with the ancient rocks in question.
We shall conclude with one more example. When the organic origin of fossil shells had been conceded, their occur- rence in strata forming some of the loftiest mountains in the world, was admitted as a proof of a great alteration of the
Ch, T.] METHODS OF THEORIZING IN GEOLOGY. 5
relative level of sea and land, and doubts were then entertained whether this change might be accounted for by the partial drying up of the ocean, or by the elevation of the solid land. The former hypothesis, although afterwards abandoned by general consent, was at first embraced by a vast majority. A multitude of ingenious speculations were hazarded to show how the level of the ocean might have been depressed, and when these theories had all failed, the inquiry, as to what vicissitudes of this nature might now be taking place, was, as usual, resorted to in the last instance. The question was agi- tated, whether any changes in the level of sea and land had occurred during the historical period, and, by patient research, it was soon discovered that considerable tracts of land had been permanently elevated and depressed, while the level of the ocean remained unaltered. It was therefore necessary to reverse the doctrine which had acquired so much popularity, and the unexpected solution of a problem at first regarded as so enigmatical, gave perhaps the strongest stimulus ever yet afforded to investigate the ordinary operations of nature. For it must have appeared almost as improbable to the earlier geolo- gists, that the laws of earthquakes should one day throw light on the origin of mountains, as it must to the first astronomers, that the fall of an apple should assist in explaining the motions of the moon.
Of late years the points of discussion in geology have been transferred to new questions, and those, for the most part, of a higher and more general nature; but, notwithstanding the repeated warnings of experience, the ancient method of philo- sophising has not been materially modified.
We are now, for the most part, agreed as to what rocks are of igneous, and what of aqueous origin,—in what manner fossil shells, whether of the sea or of lakes, have been imbedded in strata,—how sand may have been converted into sandstone,— and are unanimous as to other propositions which are not of a complicated nature; but when we ascend to those of a higher order, we find as little disposition, as formerly, tomake a strenu- ous effort, in the first instance, to search out an explanation in
6 METHODS OF THEORIZING IN GEOLOGY, [Ch. I.
the ordinary economy of Nature. If, for example, we seek for the causes why mineral masses are associated together in certain groups; why they are arranged ina certain order which is never inverted; why there are many breaks in the continuity of the series; why different organic remains are found in distinct sets of strata; why there is often an abrupt passage from an assem- blage of species contained in one formation to that in another immediately superimposed,—when these and other topics of an equally extensive kind are discussed, we find the habit of indulging conjectures, respecting irregular and extraordinary causes, to be still in full force.
We hear of sudden and violent revolutions of the globe, of the instantaneous elevation of mountain chains, of paroxysms of voleanic energy, declining according to some, and according to others increasing in violence, from the earliest to the latest ages. Weare also told of general catastrophes and a succes- sion of deluges, of the alternation of periods of repose and disorder, of the refrigeration of the globe, of the sudden anni- hilation of whole races of animals and plants, and other hypo- theses, in which we see the ancient spirit of speculation revived, and a desire manifested to cut, rather than patiently to untie, the Gordian knot.
- Tn our attempt to unravel these difficult questions, we shall adopt a different course, restricting ourselves to the known or possible operations of existing causes; feeling assured that we have not yet exhausted the resources which the study of the present course of nature may provide, and therefore that we are not authorized, in the infancy of our science, to recur to extra- ordinary agents. We shall adhere to this plan, not only on the grounds explained in the first volume, but because, as we have above stated, history informs us that this method has always put geologists on the road that leads to truth, —suggest- ing views which, although imperfect at first, have been found capable of improvement, until at last adopted by universal consent. On the other hand, the opposite method, that of speculating on a former distinct state of things, has led inva- riably to a multitude of contradictory systems, which have been
Ch. I,J METHODS OF THEORIZING IN GEOLOGY. 7
overthrown one after the other,—which have been found quite incapable of modification,—and which are often required to be precisely reversed.
In regard to the subjects treated of in our first two volumes, if systematic treatises had been written on these topics, we should willingly have entered at once upon the description of geological monuments properly so called, referring to other authors for the elucidation of elementary and collateral ques- tions, just as we shall appeal to the best authorities in conchology and comparative anatomy, in proof of mary posi- tions which, but for the labours of naturalists devoted to these departments, would have demanded long digressions. When we find it asserted, for example, that the bones of a fossil animal at QCiningen were those of man, and the fact adduced asa proof of the deluge, we are now able at once to dismiss the argument as nugatory, and to affirm the skeleton to be that of a reptile, on the authority of an able anatomist ; and when we find among ancient writers the opinion of the gigan- tie stature of the human race in times of old, grounded on the magnitude of certain fossil teeth and bones, we are able to affirm these remains to belong to the elephant and rhinoceros, on the same authority.
But since in our attempt to solve geological problems, we shall be called upon to refer to the operation of aqueous and igneous causes, the geographical distribution of animals and plants, the real existence of species, their successive extinction, and so forth, we were under the necessity of collecting together a variety of facts, and of entering into long trains of reasoning, which could only be accomplished in preliminary treatises.
These topics we regard as constituting the alphabet and grammar of geology ; not that we expect from such studies to obtain a key to the interpretation of all geological phenomena, ‘but because they form the groundwork from which we must rise to the contemplation of more general questions relating to the complicated results to which, in an indefinite lapse of ages, the existing causes of change may give rise.
( 8~)
CHAPTER II.
Arrangement of the materials composing the earth’s crust—The existing con- tinents chiefly composed of subaqueous deposits—Distinction between sedi- mentary and voleanic rocks—Between primary, secondary, and tertiary— Origin of the primary—Transition formations—Difference between secondary and tertiary strata—Discovery of tertiary groups of successive periods—Paris basin—London and Hampshire basins—Tertiary strata of Bordeaux, Pied- mont, Touraine, &c,—Subapennine beds—English crag—More recent deposits of Sicily, &c.
GENERAL ARRANGEMENT OF THE MATERIALS COMPOSING THE EARTH’S CRUST.
WHEN we examine into the structure of the earth’s crust (by which we mean the small portion of the exterior of our planet accessible to human observation),whether we pursue our investi- gations by aid of mining operations, or by observing the sections laid open in the sea cliffs, or in the deep ravines of mountainous countries, we discover everywhere a series of mineral masses, which are not thrown together in a confused heap, but arranged with considerable order; and even where their original position has undergone great subsequent disturbance, there still remain proofs of the order that once reigned.
We have already observed, that if we drain a lake, we fre- quently find at the bottom a series of recent deposits disposed with considerable regularity one above the other; the upper- most, perhaps, may be a stratum of peat, next below a more compact variety of the same, still lower a bed of laminated shell marl, alternating with peat, and then other beds of marl, divided by layers of clay. Now if a second pit be sunk through the same continuous lacustrine deposit, at some distance from the first, we often meet with nearly the same series of beds, yet with slight variations; some, for example, of the layers of sand, clay, or marl may be wanting, one or more of
Ch. IL.] SUBAQUEOUS DEPOSITS. 9
them having thinned out and given place to others, or some- times one of the masses, first examined, is observed to increase m. thickness to the exclusion of other beds. Besides this limited continuity of particular strata, it is obvious that the whole assemblage must terminate somewhere ; as, for example, where they reach the boundary of the original lake-basin, and where they will come in contact with the rocks which form the boundary of, and, at the same time, pass under all the recent accumulations:
In almost every estuary we may see, at low water, analogous phenomena where the current has cut away part of some newly- formed bank, consisting of a series of horizontal strata of peat, sand, clay, and, sometimes, interposed beds of shells. Each of these may often be traced over a considerable area, some ex- tending farther than others, but all of necessity confined within the basin of the estuary. Similar remarks are applicable, on a much more extended scale, to the recent delta of a great river, like the Ganges, after the periodical inundations have subsided, and when sections are exposed of the river-banks and the cliffs of numerous islands, in which horizontal beds of clay and sand may be traced over an area many hundred miles in length, and more than a hundred in breadth.
Subaqueous deposits. ‘The greater part of our continents are evidently composed of subaqueous deposits; and in the manner of their arrangement we discover many characters precisely simi- Jar to those above described ; but the different groups of strata are, for the most part, on a greater scale, both in regard to depth and area, than any observable in the new formations of lakes, deltas, or estuaries. We find, for example, beds of limestone several hundred feet in thickness, containing imbedded corils and shells, stretching from one country to another, yet always giving place, at length, to a distinct set of strata, which either rise up from under it like the rocks before alluded to as forming the borders of a lake, or cover and conceal it. In other places, we find beds of pebbles, and sand, or of clay of great thick- ness, ‘The different formations composed of these materials
-
10 VOLCANIC AND PRIMARY ROCKS. [Ch. I.
usually contain some peculiar organic remains; as, for example, certain species of shells and corals, or certain plants.
Volcanic rocks. Besides these strata of aqueous origin, we find other rocks which are immediately recognized to be the products of fire, from their exact resemblance to those which have been produced in modern times by volcanos, and thus we immediately establish two distinct orders of mineral masses composing the crust of the globe—the sedimentary and the volcanic,
Primary rocks. But if we investigate a large portion of a continent which contains within it a lofty mountain range, we rarely fail to discover another class, very distinct from either of those above alluded to, and which we can neither assimilate to depositssuch as are nowaccumulated in lakes or seas, nor to those generated by ordinary volcanic action. The class alluded to, consists of granite, granitic schist, roofing slate, and many other rocks, of a much more compact and crystalline texture than the sedimentary and volcanic divisions before mentioned. In the unstratified portion of these crystalline rocks, as in the granite for example, no organic fossil remains have ever been discovered, and only afew faint traces of them im some of the stratified masses of the same class; for we should state, that a consider- able portion of these rocks are divided, not only into strata, but into laminze, so closely imitating the internal arrangement of well-known aqueous deposits, as to leave scarcely any rea- sonable doubt that they owe this part of their texture to similar causes.
These remarkable formations have been called primitive, from being supposed to constitute the most ancient mineral productions known to us, and from a notion that they origi- nated before the earth was inhabited by living beings, and while yet the planet was in a nascent state. ‘Their high relative antiquity is indisputable ; for in the oldest sedimentary strata, containing organic remains, we often meet with rounded pebbles of the older erystalline rocks, which must therefore lave been consolidated before the derivative strata were formed out of
Ch, IL] ORIGIN OF THE PRIMARY ROCKS. ‘aI
their ruins, They rise up from beneath the rocks of mechanical origin, entering into the structure of lofty mountains, so as to constitute, at the same time, the lowest and the most elevated portions of the crust of the globe.
Origin of primary rocks. Nothing strictly analogous to these ancient formations ean now be seen in the progress of formation on the habitable surface of the earth, nothing, at least, within the range of human observation. ‘The first speculators, however, in Geology, found no difficulty in ex- plaining their origin, by supposing a former condition of the planet perfectly distinct from the present, when certain chemi- eal processes were developed on a great scale, and whereby crystalline precipitates were formed, some more suddenly, in huge amorphous masses, such as granite; others by successive deposition and with a foliated and stratified structure, as in the rocks termed gneiss and mica-schist. A great part of these views have since been entirely abandoned, more especially with regard to the origin of granite, but it is interesting to trace the train of reasoning by which they were suggested. First, the stratified primitive rocks exhibited, as we before mentioned, well-defined marks of successive accumulation, analogous to those so common in ordinary subaqueous deposits. As the latter formations were found divisible into natural groups, characterized by certain peculiarities of mineral com- position, so also were the primitive. In the next place, there were discovered, in many districts, certain members of the so-called primitive series, either alternating with, or passing by intermediate gradations into rocks of a decidedly mechani- eal origin, containing traces of organic remains, From such gradual passage the aqueous origin of the stratified crystalline rocks was fairly inferred ; and as we find in the different strata of subaqueous origin every gradation between a mechanical and a purely crystalline texture; between sand, for example, and saccharoid gypsum, the latter having, probably, been pre- cipitated originally in a erystalline form, from water containing sulphate of lime in solution, so it was imagined that, in a
12 STRATIFIED PRIMARY ROCKS. [Ch, II.
former condition of the planet, the different degrees of crys- tallization in the older rocks might have been dependent on the varying state of the menstruum from which they were precipitated. ;
The presence of certain crystalline ingredients in the com- position of many of the primary rocks, rendered it necessary to resort to many arbitrary hypotheses, in order to explain their precipitation from aqueous solution, and for this reason a difference in the condition of the planet, and of the pristine energy of chemical causes, was assumed. A train of specula- tion originally suggested by the observed effects of aqueous agents, was thus pushed beyond the limits of analogy, and it was not until a different and almost opposite course of induc- tion was pursued, beginning with an examination of volcanic products, that more sound theoretical views were established.
Granite of igneous origin. As we are merely desirous, in this chapter, of fixing in the reader’s mind the leading divisions of the rocks composing the earth’s crust, we cannot enter, at present, into a detailed account of these researches, but shall only observe, that a passage was first traced from lava into other more crystalline igneous rocks, and from these again to granite, which last was found to send forth dikes and veins into the con- tiguous strata in a manner strictly analogous to that observed in volcanic rocks, and producing at the point of contact such changes as might be expected to result from the influence of a heated mass cooling down slowly under great pressure from a state of fusion. ‘The want of stratification in granite supplied another point of analogy in confirmation of its igneous origin ; and as some masses were found to send out veins through others, it was evident that there were granites of different ages, and that instead of forming in all cases the oldest part of the earth’s crust, as had at first been supposed, the granites were often of comparatively recent origin, sometimes newer than the stratified rocks which covered them.
Stratified primary rocks. 'The theory of the origin of the other crystalline rocks was soon modified by these new views
Ch. IL] TRANSITION FORMATIONS, 13
respecting the nature of granite. First it was shown, by nume- — rous examples, that ordinary voleanic dikes might produce great alterations in the sedimentary strata which they traversed, caus- ing them to assume a more crystalline texture, and obliterating all traces of organic remains, without, at the same time, destroy- ing either the lines of stratification, or even those which mark the division into lamin. It was also found, that granite dikes and veins produced analogous, though somewhat different changes ; and hence it was suggested as highly probable, that the effects to which small veins gave rise, to the distance of a few yards, might be superinduced on a much grander scale where immense masses of fused rock, intensely heated for ages, came in contact at great depths from the surface with sedimentary formations. The slow action of heat in such cases,it was thought, might occasion a state of semi-fusion, so that, on the cooling down of the masses, the different materials might be re-arranged in new forms, according to their chemical affinities, and all traces of organic remains might disappear, while the stratiform and lamellar texture remained.
May be of different ages. According to these views, the primary strata may have assumed their crystalline structure at as Inany successive periods as there have been distinct eras of the formation of granite, and their difference of mineral com- position may be attributed, not to an original difference of the conditions under which they were deposited at the surface, but to subsequent modifications superinduced by heat at great depths below the surface.
The strict propriety of the term primitive, as applied to gra- nite and to the granitiform and associated rocks, thus became questionable, and the term primary was very generally eub- stituted, as simply expressing the fact, that the crystalline rocks, as a mass, were older than the secondary, or those which are unequivocally of a mechanical origin and contain organic remains, '
Transition formations. ‘The reader may readily conceive, even from the hasty sketch which we have thus given of the supposed origin of the stratified primary rocks, that they may
14 SUCCESSION OF STRATIFIED MASSES, [Ch, 11.
occasionally graduate into the secondary ; accordingly, an at- tempt was made, when the classification of rocks was chiefly derived from mineral structure, to institute an order called transition, the characters of which were intermediate between those of the primary and secondary formations. Some of the shales, for example, associated with these strata, often passed insensibly into clay slates, undistinguishable from those of the granitic series; and it was often difficult to determine whether some of the compound rocks of this transition series, called greywacke, were of mechanical or chemical origin. The imbedded organic remains were rare, and sometimes nearly obliterated ; but by their aid the groups first called transition were at length identified with rocks, in other countries, which had undergone much less alteration, and wherein shells and zoophytes were abundant,
The term transition, however, was still retained, although no longer applicable in its original signification. It was now made to depend on the identity of certain species of organized fossils; yet reliance on mineral peculiarities was not fairly abandoned, as constituting part of the characters of the group. This circumstance became a fertile source of ambiguity and confusion; for although the species of the transition strata denoted a certain epoch, the intermediate state of mineral character gave no such indications, and ought never to have been made the basis of a chronological division of rocks.
Order of succession of stratified masses. All the subaqueous strata which we before alluded to as overlying the primary, were at first called secondary ; and when they had been found divisible into different groups, characterised by certain organic remains and mineral peculiarities, the relative position of these groups became a matter of high interest. It was soon found that the order of succession was never inverted, although the different formations were not coextensively distributed; so that, if there be four different formations, as a, 6, c, d, in the annexed diagram (No. 1), which, in certain localities, may be seen in vertical superposition, the uppermost or newest of them,
Ch. II.] CHARACTER OF THE TERTIARY STRATA, 15
a, will in other places be in contact with ce, or with the lowest
No. 1.
of the whole series, d, all the intermediate formations being absent.
Tertiary formations. After some progress had been made in classifying the secondary rocks, and in assigning to each its relative place in a chronological series, another division ot sedimentary formations was established, called tertiary, as being of newer origin than the secondary. 'The fossil contents of the deposits belonging to this newly-instituted order are, upon the whole, very dissimilar from those of the secondary rocks, not only all the species, but many of the most remarkable animal and vegetable forms, being distinct. The tertiary for- mations were also found to consist very generally of detached and isolated masses, surrounded on all sides by primary and secondary rocks, and occupying a position, in reference to the latter, very like that of the waters of lakes, inland seas, and gulfs, in relation to a continent, and, like such waters, being often of great depth, though of limited area. The imbedded organic remains were chiefly those of marine animals, but with frequent intermixtures of terrestrial and freshwater species so rarely found among the secondary fossils. Frequently there was evidence of the deposits having been purely lacustrine, a circumstance which has never yet been clearly ascertained in regard to any secondary group.
We shall consider more particularly, in the next chapter, how far this distinction of rocks into secondary and tertiary is founded in nature, and in what relation these two orders of mineral masses may be supposed to stand to each other. But before we offer any general views of this kind, it may be useful to present the reader with a succinct sketch of the principal
16 TERTIARY STRATA OF THE PARIS BASIN, [Ch. II.
points in the history of the discovery and classification of the tertiary strata.
Paris Basin. The first series of deposits belonging to this class, of which the characters were accurately determined, were those which occur in the neighbourhood of Paris, first described. by MM. Cuvier and Brongniart*. They were ascertained to fill a depression in the chalk (as the beds d, in diagram No. 2,
rest upon ¢), and to be composed of different materials, some- No. 2.
a, Primary rocks. 6, Older secondary formations, c, Chalk, d, Tertiary formation.
times including the remains of marine animals, and sometimes of freshwater. By the aid of these fossils, several distinct alter- nations of marine and freshwater formations were clearly shown to lie superimposed upon each other, and various speculations were hazarded respecting the manner in which the sea had successively abandoned and regained possession of tracts which had been occupied in the intervals by the waters of rivers or lakes. In one of the subordinate members of this Parisian series, a great number of scattered bones and skeletons of land animals were found entombed, the species being perfectly dis- similar from any known to exist, as indeed were those of almost all the animals and plants of which any portions were discovered in the associated deposits.
We shall defer, to another part of this work, a more detailed account of this interesting formation, and shall merely observe in this place, that the investigation of the fossil contents of these beds forms an era in the progress of the science. The
* Environs de Paris, 1811.
Ch. II.] TERTIARY STRATA OF SUCCESSIVE PERIODS. 17 French naturalists brought to bear upon their geological re- searches so much skill and proficiency in comparative anatomy and conchology, as to place in a strong light the importance of the study of organic remains, and the comparatively subordinate interest attached to the mere investigation of the structure and mineral ingredients of rocks.
A variety of tertiary formations were soon afterwards found in other parts of Europe, as in the south-east of England, in Italy, Austria, and different parts of France, especially in the basins of the Loire and Gironde, all strongly contrasted to the secondary rocks. As in the latter class many different divisions had been observed to preserve the same mineral cha- racters and organic remains over wide areas, it was natural that an attempt should first be made to trace the different subdivi- sions of the Parisian tertiary strata throughout Europe, for some of these were not inferior in thickness to several of the secondary formations that had a wide range.
But in this case the analogy, however probable, was not found to hold good, and the error, though almost unavoidable, retarded seriously the progress of geology. For as often as a new tertiary group was discovered, as that of Italy, for exam- ple, an attempt was invariably made, in the first instance, to discover in what characters it agreed with some one or more subordinate members of the Parisian type. Every fancied point of correspondence was magnified into undue importance, and such trifling circumstances, as the colour of a bed of sand or clay, were dwelt upon as proofs of identification, while the difference in the mineral character and organic contents of the group from the whole Parisian series was slurred over and thrown into the shade.
By the influence of this illusion, the succession and chrono- logical relations of different tertiary groups were kept out of sight. ‘The difficulty of clearly discerning these, arose from the frequent isolation of the position of the tertiary forma- tions before described, since, a proportion as the areas occupied
by them are limited, it is rare to discover a place where one Vor. IIT. Cc
18 ORIGIN Of THE EUROPEAN TERTIARY [Ch 11,
set of strata overlap another, in such a manner that the geologist might be enabled to determine the difference of age by direct superposition.
ORIGIN OF THE EUROPEAN TERTIARY STRATA AT SUCCHSSIVE PERIODS.
We shall now very briefly enumerate some of the principal steps which eventually led to a conviction of the necessity of referring the European tertiary formations to distinct periods, and the leading data by which such a chronological series may be established.
London and Hampshire Basins.—Very soon after the inves- tigation, before alluded to, of the Parisian strata, those of Hampshire and of the basin of the Thames were examined in our own country. Mr. Webster found these English tertiary deposits to repose, like those in France, upon the chalk or newest rock of the secondary series. He identified a great variety of the shells occurring in the British and Parisian strata, and ascertained that, in the Isle of Wight, an alter- nation of marine and freshwater beds occurred, very analogous to that observed in the basin of the Seine*. But no two sets of strata could well be more dissimilar in mineral composition, and they were only recognized to belong to the same era, by aid of the specific identity of their organic remains. ‘The dis- cordance, in other respects, was as complete as could well be imagined, for the principal marine formation in the one country - consisted of blue clay, in the other of white limestone, and a variety of curious rocks in the neighbourhood of Paris, had no representatives whatever in the south of England.
Subapennine Beds.—'The next important discovery of ter~ tiary strata was in Italy, where Brocchi traced them along the flanks of the Apennines, from one extremity of the peninsula to the other, usually forming a lower range of hills, called by him the Subapennines+. ‘These formations, it is true, had
* ‘Webster in Englefield’s Isle of Wight and Geol. Trans,, vol. ii, p. 161, + Conch. Foss. Subap., 1814,
Ch. I1.] STRATA AT SUCCESSIVE PERIODS. 19
been pointed out by the older Italian writers, and some correct ideas, as we have seen, had been entertained respecting their recent origin, as compared to the inclined secondary rocks on which they rested*. But accurate data were now for the first time collected, for instituting a comparison between them and other members of the great Huropean series of tertiary for- mations.
Brocchi came to the conclusion that nearly one-half of several hundred species of fossil shells procured by him from these Subapennine beds were identical with those now living in existing seas, an observation which did not hold true in respect to the organic remains of the Paris basin. It might have been supposed that this important point of discrepancy would at once have engendered great doubt as to the identity, in age, of any part of the Subapennine beds to any one mem- ber of the Parisian series ; but, for reasons above alluded to, this objection was not thought of much weight, and it was supposed that a group of strata, called ‘the upper marine for- mation,’ in the basin of the Seine, might be represented by all the Subapennine clays and yellow sand.
English Crag.—Several years before, an English naturalist, Mr. Parkinson, had observed, that certain shelly strata, in Suffolk, which overlaid the blue clay of London, contained distinct fossil species of testacea, and that a considerable por- tion of these might be identified with species now inhabiting the neighbouring sea‘+. These overlying beds, which were provincially termed ‘ Crag,’ were of small thickness, and were not regarded as of much geological importance. But when duly considered, they presented a fact worthy of great atten- tion, viz., the superposition of a tertiary group, inclosing, like the Subapennine beds, a great intermixture of recent species of shells, upon beds wherein a very few remains of recent or living species were entombed.
Mr. Conybeare, in his excellent classification of the English
* See vel. i. p. 51, for opinions of Odoardi, in 1761,
+ Geol. Trans., vol, i. p. 324, 1811, C2
20 ORIGIN OF THE EUROPEAN TERTIARY [Ch. I.
strata*, placed the crag as the uppermost of the British series, and several geologists began soon to entertain an opinion that this newest of our tertiary formations might correspond in age to the Italian strata described by Brocchi.
Tertiary Strata of Touraine.—The next step towards esta- blishing a succession of tertiary periods was the evidence adduced to prove that certain formations, more recent than the uppermost members of the Parisian series, were also older than the Subapennine beds, so that they constituted deposits of an age intermediate between the two types above alluded to. M. Desnoyers, for example, ascertained that a group of marine strata in ‘Touraine, in the basin of the Loire (e, dia- gram No, 3), rest upon the uppermost subdivision of the
No. 3.
Paris
Touraineg
C, Chalk and other secondary formations. d, Tertiary formation of Paris basin. e, Superimposed marine tertiary beds of the Loire.
Parisian group d, which consists of a lacustrine formation, ex- tending continuously throughout a platform which intervenes between the basin of the Seine and that of the Loire. These overlying marine strata, M. Desnoyers assimilated to the En- glish crag, to which they bear some analogy, although their -or- ganic remains differ considerably, as will be afterwards shown.
A large tertiary deposit had already been observed in the south-west of France, around Bordeaux and Dax, and a de- scription of its fossils had been published by M. de Basterot}. Many of the species were peculiar, and differed from those of the strata now called Subapennine; yet these same peculiar and characteristic fossils reappeared in Piedmont, in a series of
* Outlines of the Geology of England and Wales, 1822. + Mem, de la Soc, d’ Hist, Nat, de Paris, tome ii., 1825,
Ch. 11] STRATA AT SUCCESSIVE PERIODS. 21
strata inferior in position to the Subapennines (as e underlies /, diagram No. 4).
/
Suffo lk
©, Chalk and older formations.
d, London clay (older tertiary).
e, Tertiary strata of same age as beds of the Loire. J, Crag and Subapennine tertiary deposits,
This inferior group, e, composed principally of green sand, occurs in the hills of Mont Ferrat, and beds of the same age are seen in the valley of the Bormida. They also form the hill of the Superga, near Turin, where M. Bonelli formed a large col- lection of their fossils, and identified them with those discovered near Bordeaux and in the basin of the Gironde.
But we are indebted to M. Deshayes for having proved, by a careful comparison of the entire assemblage of shells found in the above-mentioned localities, in Touraine, in the south-east of France, and in Piedmont, that the whole of these three groups possess the same zoological characters, and belong to the same epoch, as also do the shells described by M. Constant Prevost, as occurring in the basin of Vienna*.
Now the reader will perceive, by reference to the observa- tions above made, and to the accompanying diagrams, that one of the formations of this intervening period, e, has been found superimposed upon the highest member of the Parisian series, d; while another of the same set has been observed to under- lie the Subapennine beds, f. ‘Thus the chronological series, d, e, f, is made out, in which the deposits, originally called tertiary, those of the Paris and London basins, for example, occupy the lowest position, and the beds called ‘ the Crag,’ and ‘ the Subapennines,’ the highest.
Tertiary Strata newer than the Subapennine.—The fossil
* Sur la Constitution, &¢. du bassin de Vienne, Journ. de Phys., Nov, 1820.
2a NEWEST TERTIARY STRATA. (Ch. 11,
remains which characterize each of the three successive periods above alluded to, approximate more nearly to the assemblage of species now existing, in proportion as their origin is less remote from our own era, or, in other words, the recent species are always more numerous, and the extinct more rare, in proportion to the low antiquity of the formation. But the discordance between the -state of the organic world indi- cated by the fossils of the Subapennine beds and the actual state of things is still considerable, and we naturally ask, are there no monuments of an intervening period ?—no evidences of a gradual passage from one condition of the animate creation to that which now prevails, and which differs so widely ?
It will appear in the sequel, that such monuments are not wanting, and that there are marine strata entering into the composition of extensive districts, and of hills of no trifling height, which contain the exuviee of testacea and zoophytes, hardly distinguishable, as a group, from those now peopling the neighbouring seas. ‘Thus the line of demarcation between the actual period and that immediately antecedent, is quite evanescent, and the newest members of the tertiary series will be often found to blend with the formations of the historical era.
In Europe, these modern strata have been found in the dis- trict around Naples, in the territory of Otranto and Calabria, and more particularly in the island of Sicily; and the bare enumeration of these localities cannot fail to remind the reader, that they belong to regions where the volcano and the earth- quake are now active, and where we might have anticipated the discovery of emphatic proofs, that the conversion of sea into land had been of frequent occurrence at very modern periods,
Hie aes
CHAPTER III.
Different circumstances under which the secondary and tertiary formations may have originated—Secondary series formed when ihe ocean prevailed; Tertiary
during the conversion of sea into land, and the growth of a continent—Ongin of interruption in the sequence of formations—The areas where new deposits take place are always varying—Causes which occasion this transference of the places of sedimentary deposition—Denndation augments the discordance in age of rocks in contact—Unconformability of overlying formations—In what manner the shifting of the areas of sedimentary deposition may combine with the gradual extinction and introduction of species to produce a series of deposits having distinct mineral and organic characters.
DIFFERENT CIRCUMSTANCES UNDER WHICH THE SECONDARY AND TERTIARY FORMATIONS MAY HAVE ORIGINATED.
We have already glanced at the origin of some of the prin- cipal points of difference in the characters of the primary and secondary rocks, and may now briefly consider the relation in which the secondary stand to the tertiary, and the causes of that succession of tertiary formations described in the last chapter.
It is evident that large parts of Europe were simultaneously submerged beneath the sea when different portions of the secon- dary series were formed, because we find homogeneous mineral masses, including the remains of marine animals, referrible to the secondary period, extending over great areas; whereas the detached and isolated position of tertiary groups, in basin or depressions bounded by secondary and primary rocks, favours the hypothesis of a sea interrupted by extensive tracts of dry land.
State of the Surface when the Secondary Strata were formed.
Let us consider the changes that must be expected to accom- pany the gradual conversion of part of the bed of an ocean into a continent, and the different characters that might be imparted
a DIFFERENT ORIGIN OF SECONDARY [Ch. III.
to subaqueous deposits formed during the period when the sea prevailed, as contrasted with those that might belong to the subsequent epoch when the land should predominate. First, we may suppose a vast submarine region, such as the bed of the western Atlantic, to receive for ages the turbid waters of several great rivers, like the Amazon, Orinoco, or Mississippi, each draining a considerable continent. The sediment thus introduced might be characterized by a peculiar colour and composition, and the same homogeneous mixture might be spread out over an immense area by the action of a powerful current, like the Gulf-stream. First one submarine basin, and then another, might be filled, or rendered shallow, by the influx of transported matter, the same species of animals and plants still continuing to inhabit the sea, so that the organic, as well as the mineral characters, might be constant throughout the whole series of deposits.
In another part of the same ocean, let us suppose masses of coralline and shelly limestone to grow, like those of the Pacific, simultaneously over a space several thousand miles in length, and thirty or forty degrees of latitude in breadth, while vol- canic eruptions give rise, at different intervals, to igneous rocks, haying a common subaqueous character in different parts of the vast area.
It is evident that, during such a state of a certain quarter of the globe, beds of limestone and other rocks might be formed, and retain a common character over spaces equal to a large portion of Europe.
State of the Surface when the Tertiary Groups were formed.
But when the area under consideration began to be con- verted into land, a very different condition of things would succeed. A series of subterranean movements might first give rise to small rocks and isles, and then, by subsequent eleva- tions, to larger islands, by the junction of the former. ‘These lands would consist partly of the mineral masses before de- scribed, whether coralline, sedimentary, or volcanic, and partly
Ch. III] AND TERTIARY STRATA. 20 of the subjacent rocks, whatever they may have been, which constituted the original bed of the ocean. Now the degrada- tion of these lands would commence immediately upon their emergence, the waves of the sea undermining the cliffs, and torrents flowing from the surface, so that new strata would begin to form in different places; and in proportion as the lands increased, these deposits would augment.
At length by the continued rising and sinking of different parts of the bed of the ocean, a number of distinct basins would be formed, wherein different kinds of sediment, each distinguished by some local character, might accumulate. Some of the groups of isles that had first risen would, in the course of ages, become the central mountain ranges of con- tinents, and different lofty chains might thus be characterized by similar rocks of contemporaneous origin, the component strata having originated under analogous circumstances in the ocean before described.
Finally, when large tracts of land existed, there would be a variety of disconnected gulfs, inland seas, and lakes, each re- ceiving the drainage of distinct hydrographical basins, and becoming the receptacles of strata distinguished by marked peculiarities of mineral composition. The organic remains would also be more varied, for in one locality freshwater species would be imbedded, as in deposits now forming in the lakes of Switzerland and the north of Italy; in another, marine species, as in the Aral and Caspian; in a third region, eulfs of brackish water would be converted into land, like these of Bothnia and Finland in the Baltic; in a fourth, there might be great fluvi- atile and marine formations along the borders of a chain of inland seas, like the deltas now growing at the mouths of the Don, Danube, Nile, Po, and Rhone, along the shores of the Azof, Euxine, and Mediterranean. These deposits would each partake more or less of the peculiar mineral character of adjoining lands, the degradation of which would supply sedi- ment to the different rivers.
Now if such be, in a great measure, the distinction between
26 CAUSES OF THE SUPERPOSITION [Ch, 111,
the circumstances under which the secondary and tertiary series originated, it is quite natural that particular tertiary groups should oceupy areas of comparatively small extent,— that they should frequently- consist of littoral and lacustrine deposits, and that they should often contain those admixtures of terrestrial, freshwater, and marine remains, which are so rare in secondary rocks. It might also be expected, that the tertiary volcanic formations should be much less exclusively submarine, and this we accordingly find to be the case.
CAUSES OF THE SUPERPOSITION OF SUCCESSIVE FORMATIONS HAVING DISTINCT MINERAL AND ORGANIC CHARACTERS.
But we have still to account for those remarkable breaks in the series of superimposed formations, which are common both to the secondary and tertiary rocks, but are more particularly frequent in the latter.
The elucidation of this curious point is the more important, because geologists of a certain school appeal to phenomena of this kind in support of their doctrine of great catastrophes, out of the ordinary course of nature, and sudden reyolutions of the globe. :
It is only by carefully considering the combined action of all the causes of change now in operation, whether in the animate or inanimate world, that we can hope to explain such compli- cated appearances as are exhibited in the general arrangement of mineral masses. In attempting, therefore, to trace the origin of these violations of continuity, we must re-consider many of the topics treated of in our two former volumes, such as the effects of the various agents of decay and reproduction, the imbedding of organic remains, and the extinction of species.
Shifting of the Areas of Sedimentary Deposition.—By re- verting to our survey of the destroying and renovating agents, it will be seen that the surface of the terraqueous globe may be divided into two parts, one of which is undergoing repair, while the other, constituting, at any one period, by far the
Ch, 11] OF SUCCESSIVE FORMATIONS. 27 largest portion of the whole, is either suffering degradation, or remaining stationary without loss or increment. ‘The reader will assent at once to this proposition, when he reflects that the dry land is, for the most part, wasting by the action of rain, rivers, and torrents, while the effects of vegetation have, as we have shown, only a conservative tendency, being very rarely instrumental in adding new masses of mineral matter to the surface of emerged lands; and when he also reflects that part of the bed of the sea is exposed to the excavating action of currents, while the greater part, remote from continents and islands, probably receives no new deposits whatever, being covered for ages with the clear blue waters uncharged with sediment. Here the relics of organic beings, lying in the ooze of the deep, may decompose like the leaves of the forest in autumn, and leave no wreck behind, but merely stipply nourishment, by their decomposition, to succeeding races of marine animals and plants,
The other part of the terraqueous surface is the receptacle of new deposits, and in this portion alone, as we pointed out in the last volume, the remains of animals and plants become fossilized. Now the position of this area, where new forma- tions are in progress, and where alone any memorials of the state of organic life are preserved, is always varying, and must for ever continue to vary ; and, for the same reason, that por- tion of the terraqueous globe which is undergoing waste, also shifts its position, and these fluctuations depend partly on the action of aqueous, and partly of igneous causes.
In illustration of these positions we may observe, that the sediment of the Rhone, which is thrown into the lake of Ge- neva, is now conveyed to a spot a mile and a half distant from that where it accumulated in the tenth century, and six miles from the point where the delta began originally to form. We may lock forward to the period when the lake will be filled up, and then a sudden change will take place in the distribution of the transported matter; for the mud and sand brought down from the Alps will thenceforth, instead of being deposited
28 SHIFTING OF THE AREAS [Ch. III.
near Geneva, be carried nearly two hundred miles southwards, where the Rhone enters the Mediterranean,
The additional matter thus borne down to the lower delta of the Rhone would not only accelerate its increase, but might affect the mineral character of the strata there deposited, and thus give rise to an upper group, or subdivision of beds, having a distinct character. But the filling up of a lake, and the consequent transfer of the sediment to a new place, may some- times give rise to a more abrupt transition from one group to another; as, for example, in a gulf like that of the St. Law- rence, where no deposits are now accumulated, the river being purged of all its impurities in its previous course through the Canadian lakes, Should the lowermost of these lakes be at any time filled up with sediment, or laid dry by earthquakes, the waters of the river would thenceforth become turbid, and strata would begin to be deposited in the gulf, where a new formation would immediately overlie the ancient rocks now constituting the bottom. In this case there would be an abrupt passage from the inferior and more ancient, to the newer superimposed formation.
The same sudden coming on of new sedimentary deposits, or the suspension of those which were in progress, must fre- quently occur in different submarine basins where there are currents which are always lable, in the course of ages, to change their direction. Suppose, for instance, a sea to be filling up in the same manner as the Adriatic, by the influx of the Po, Adige, and other rivers. ‘The deltas, after advancing and converging, may at last come within the action of a transverse current, which may arrest the further deposition of matter, and sweep it away to a distant point. Such a current now appears to prey upon the delta of the Nile, and to carry eastward the annual accessions of sediment that once added rapidly to the plains of Egypt.
On the other hand, if a current charged with sediment vary its course, a circumstance which, as we have shown, must hap- pen to all of them in the lapse of ages, the accumulation of
Ch, II.] OF SEDIMENTARY DEPOSITION. 29
transported matter will at once cease in one region, and com- mence in another.
Although the causes which occasion the transference of the places of sedimentary deposition are continually in action in every region, yet they are most frequent where subterranean movements alter, from time to time, the levels of land, and they must be immense during the successive elevations and depressions which must be supposed to accompany the rise of a great continent from the deep. A trifling change of level may sometimes throw a current into a new direction, or alter the course of a considerable river. Some tracts will be alter- nately submerged and laid dry by subterranean movements ; in one place a shoal will be formed, whereby the waters will drift matter over spaces where they once threw down their burden, and new cavities will elsewhere be produced, both marine and lacustrine, which will intercept the waters bearing sediment, and thereby stop the supply once carried to some distant basin.
We have before stated, that a few earthquakes of moderate power might cause a subsidence which would connect the sea of Azof with a large part of Asia now below the level of the ocean. ‘This vast depression, recently shown by Humboldt to extend over an area of eighteen thousand square leagues, sur- rounds Lake Aral and the Caspian, on the shores of which seas it sinks in some parts to the depth of three hundred feet below the level of the ocean. ‘The whole area might thus sud- denly become the receptacle of new beds of sand and shells, probably differing in mineral character from the masses pre- viously existing in that country, for an exact correspondence could only arise from a precise identity in the whole combina- tion of circumstances which should give rise to formations produced at different periods m the same place.
Without entering into more detailed explanations, the reader will perceive that, according to the laws now governing the aqueous and igneous causes, distinct deposits must, at different periods, be thrown down on yarious parts of the earth’s surface,
30 CAUSES OF DIFFERENCE [Ch. IZ.
and that, in the course of ages the same area may become, again and again, the receptacle of such dissimilar sets of strata, During intervening periods, the space may either remain un- altered, or suffer what is termed denudation, in which case a superior set of strata are removed by the power of running water, and subjacent beds are laid bare, as happens wherever a sea encroaches upon a line of coast. By such means, it is ob- vious that the discordance in age of rocks in contact must often be greatly increased.
The frequent unconformability in the stratification of the inferior and overlying formation is another phenomenon in their arrangement, which may be considered as a natural con- sequence of those movements that accompany the gradual con- version of part of an ocean into land; for by such convulsions the older set of strata may become rent, shattered, inclined, and contorted to any amount. If the movement entirely cease before a new deposit is formed in the same tract, the superior strata may repose horizontally upon the dislocated series. But even if the subterranean convulsions continue with increasing violence, the more recent formations must remain comparatively undisturbed, because they cannot share in the immense de- rangement previously produced in the older beds, while the latter, on the contrary, cannot fail to participate in all the movements subsequently communicated to the newer.
Change of Species everywhere in progress.—If, then, it be conceded, that the combined action of the volcanic and the - aqueous forces would give rise to a succession of distinct for- mations, and that these would be sometimes unconformable, let us next inquire in what manner these groups might become characterized by different assemblages of fossil remains.
We endeavoured to show, in the last volume, that the hypo- thesis of the gradual extinction of certain animals and plants, and the successive introduction of new species, was quite con- sistent with all that is known of the existing economy of the animate world ; and if it be found the only hypothesis which is reconcilable with geological phenomena, we shall have
Ch, I11.] OF ORGANIC REMAINS, 31
strong grounds for coticeiving that such is the order of na- ture. |
Fossilization of Plants and Animals partial—We have seen that the causes which limit the duration of species are not confined, at any one time, to a particular part of the globe; and, for the same reason, if we suppose that their place is supplied, from time to time, by new species; we may sup- pose their introduction to be no less generally in progress. Hence, from all the foregoing premises, it would follow, that the change of species would be in simultaneous operation every- where throughout the habitable surface of sea and land ; whereas the fossilization of plants and animals must always be confined to those areas where new strata are produced. These areas, as we have proved, are always shifting their position, so that the fossilizing process, whereby the commemoration of the particular state of the organic world, at any given time, is effected, may be said to move about, visiting and revisiting different tracts in succession.
In order more distinctly to elucidate our idea of the working of this machinery, let us compare it to a somewhat analogous case that might easily be imagined to occur in the history of human affairs. Let the mortality of the population of a large country represent the successive extinction of species, and the births of new individuals the introduction of new species. While these fluctuations are gradually taking place everywhere, suppose commissioners to be appointed to visit each province of the country in succession, taking an exact account of the number, names, and individual peculiarities of all the inhabitants, and leaving in each district a register con- taining a record of this information. If, after the completion of one census, another is immediately made after the same plan, and then another, there will, at last, be a series of statistical documents in each province. When these are arranged in chronological order, the contents of those which stand next to each other will differ according to the length of the intervals of time between the taking of each census.
32 EFFECTS OF DENUDATION. [Ch. III.
If, for example, all the registers are made in a single year, the proportion of deaths and births will be so small during the interval between the compiling of two consecutive docu- ments, that the individuals described in each will be nearly identical ; whereas, if there are sixty provinces, and the survey of each requires a year, there will be an almost entire discord- ance between the persons enumerated in two consecutive regis- ters.
There are undoubtedly some other cavises besides the mere quantity of time which may augment or diminish the amount of discrepancy. ‘Uhus, for example, at some periods a pesti- lential disease may lessen the average duration of human life, or a variety of circumstances may cause the births to be unusually numerous, and the population to multiply ; or,a pro- vince may be suddenly colonized by persons migrating from surrounding districts.
We must also remind the reader, that we do not propose the above case as an exact parallel to those geological phenomena which we desire to illustrate ; for the commissioners are sup- posed to visit the different provinces in rotation, whereas the commemorating processes by which organic remains become fossihzed, although they are always shifting from one area to another, are yet very irregular in their movements. ‘They may abandon and revisit many spaces again and again, before they once approach another district ; and besides this source of uregularity, it may often happen, that while the depositing process is suspended, denudation may take place, which may be compared to the occasional destruction of some of the statistical documents before mentioned. It is evident, that where such accidents occur, the want of continuity in the series may be- come indefinitely great, and that the monuments which follow next in succession will by no means be equidistant from each other in point of time.
If this train of reasoning be admitted, the frequent distinct- ness of the fossil remains, in formations immediately in contact, would be a necessary consequence of the existing laws of
Ch. IIL] CAUSE OF VIOLATIONS OF CONTINUITY. 33
sedimentary deposition, accompanied by the gradual birth and death of species.
We have already stated, that we should naturally look for a change in the mineral character in strata thrown down at distant intervals in the same place; and, in like manner, we must also expect, for the reason last set forth, to meet occasion- ally with sudden transitions from one set of organic remains to another. But the causes which have given rise to such differ- ences in mineral characters, have no necessary connexion with those which have produced a change in the species of imbedded plants and animals. :
When the lowest of two sets of strata are much dis- located over a wide area, the upper being undisturbed, there is usually a considerable discordance in the organic re- mains of the two groups; but this coincidence must not be ascribed to the agency of the disturbing forces, as if they had exterminated the living inhabitants of the surface. ‘The im- mense lapse of time required for the development of so great a series of subterranean movements, has in these cases allowed the species also throughout the globe to vary, and hence the two phenomena are usually concomitant.
Although these inferences appear to us very obvious, we are aware that they are directly opposed to many popular theories respecting catastrophes; we shall, therefore, endeavour to place our views in a still clearer light before the reader. Suppose we had discovered two buried cities at the foot of Vesuvius, immediately superimposed upon each other, with a great mass of tuff and lava intervening, just as Portici and Resina, if now covered with ashes, would overlie Herculaneum. An antiquary might possibly be entitled to infer, from the in- scriptions on public edifices, that the inhabitants of the inferior and older town were Greeks, and those of the modern, Italians. But he would reason very hastily, if he also concluded from these data, that there had been a sudden change from the Greek to the Italian language in Campania. Suppose he afterwards found three buried cities, one above the other, the intermediate
Vor. IIT, D
a4. CAUSE OF VIOLATIONS OF CONTINUITY. [Ch. 111.
one being Roman, while, as in the former example, the lowest was Greek, and the uppermost Italian, he would then perceive the fallacy of his former opinion, and would begin to suspect that the catastrophes, whereby the cities were inhumed, might have no relation whatever to the fluctuations in the language of the inhabitants ; and that, as the Roman tongue had evidently intervened between the Greek and Italian, so many other dialects may have been spoken in succession, and the passage from the Greek to the Italian may have been very gradual, some terms growing obsolete, while others were introduced from time to time.
If this antiquary could have shown that the volcanic pa- roxysms of Vesuvius were so governed as that cities should be buried one above the other, just as often as any variation occurred in the language of the inhabitants, then, indeed, the abrupt passage from a Greek to a Roman, and from a Roman to an Italian city, would afford proof of fluctuations no less sudden in the language of the people.
So in Geology, if we could assume that it is part of the plan of nature to preserve, in every region of the globe, an unbroken series of monuments to commemorate the vicissitudes of the organic creation, we might infer the sudden extirpation: of Species, and the simultaneous introduction of others, as often as two formations in contact include dissimilar organic fossils. But we must shut our eyes to the whole economy of the existing causes, aqueous, igneous, and organic, if we fail to perceive that such is not the plan of Nature.
( 85)
CHAPTER IV.
Chronological relations of mineral masses the first object in geological classifica- tion—Snperposition, proof of more recent origin—Exceptions in regard to voleanic rocks—Relative age proved by included fragments of older rocks— Proofs of contemporaneous origin derived from mineral characters—Variations to which these characters are liable—Recurrence of distinct rocks at successive periods—Proofs of contemporaneous origin derived from organic remains— Zoological provinces are of limited extent, yet spread over wider areas than homogeneous mineral deposits—Different modes whereby dissimilar mineral masses and distinct groups of species may be proved to have been contempo-
Yaneous,
DETERMINATION OF THE RELATIVE AGES OF ROCKS,
In attempting to classify the mineral masses which compose the crust of the earth, the principal object which the geologist must keep in view, is to determine with accuracy their chrono- logical relations, for it is abundantly clear, that different rocks have been formed in succession; and in order thoroughly to comprehend the manner in which they enter into the structure of our continents, we should study them with reference to the time and mode of their formation.
We shall now, therefore, consider by what characters the relative ages of different rocks may be established, whereby we may be supplied at once with sound information of the greatest practical utility, and which may throw, at the same time, the fullest light on the ancient history of the globe,
Proofs of relative age by superposition.
It is evident that where we find a series of horizontal strata, of sedimentary origin, the uppermost bed must be older than those which it overlies, and that when we observe one distinct set of strata reposing upon another, the inferior is the older
of the two. In countries where the original position of mineral D 2
36 DETERMINATION OF THE [Ch. IV.
masses has been disturbed, at different periods, by convulsions of extraordinary violence, as in the Alps and other mountain- ous districts, there are instances where the original position of strata has been reversed; but such exceptions are rare, and are usually on a small scale, and an experienced observer can generally ascertain the true relations of the rocks in question, by examining some adjoining districts where the derangement has been less extensive.
In regard to volcanic formations, if we find a stratum of tuff or ejected matter, or a stream of lava covering sedimentary strata, we may infer, with confidence, that the igneous rock is the more recent; but, on the other hand, the superposition of aqueous deposits to a volcanic mass does not always prove the former to be of newer origin. If, indeed, we discover strata of tuff with imbedded shells, or, as in the Vicentine and other places, rolled blocks of Java with adhering shells and corals, we may then be sure that these masses of volcanic origin covered the bottom of the sea, before the superincumbent strata were thrown down. But as lava rises from below, and does not always reach the surface, it may sometimes penetrate a certain number of strata, and then cool down, so as to constitute a solid mass of newer origin, although inferior in position. It is, for the most part, by the passage of veins proceeding from such igneous rocks through contiguous sedimentary strata, or by such hardening and other alteration of the overlying bed, as might be expected to result from contact with a heated mass, that we are enabled to decide whether the volcanic matter was previously consolidated, or subsequently introduced.
Proofs by included fragments of older rocks.
A. geologist is sometimes at a loss, after investigating a dis- trict composed of two distinct formations, to determine the relative ages of each, from want of sections exhibiting their superposition. In such cases, another kind of evidence, of a character no less conclusive, can sometimes be obtained. One group of strata has frequently been derived from the degrada-
Ch. IV.] RELATIVE AGES OF ROCKS. 37
tion of another in the immediate neighbourhood, and may be observed to include within it fragments of such older rocks. Thus, for example, we may find chalk with flints, and in another part of the same country, a distinct series, consisting of alternations of clay, sand, and pebbles. If some of these peb- bles consist of flints, with silicified fossil shells of the same species as those in the chalk, we may confidently infer, that the chalk is the oldest of the two formations.
We remarked in the second chapter, that some granite must have existed before the most ancient of our secondary rocks, because some of the latter contain rounded pebbles of granite. But for the existence of such evidence, we might not have felt assured that all the granite which we see had not been pro- truded from below in a state of fusion, subsequently to the origin of the secondary strata.
Proofs of contemporaneous origin derwed from mineral characters.
When we have established the relative age of two forma- tions in a given place, by direct superposition, or by other evidence, a far more difficult task remains, to trace the conti- nuity of the same formation, or, in other cases, to find means of referring detached groups of rocks to a contemporaneous origin. Such identifications in age are chiefly derivable from two sources—mineral character and organic contents; but the utmost skill and caution are required in the application of such tests, for scarcely any general rules can be laid down re- specting either, that do not admit of important exceptions.
If, at certain periods of the past, rocks of peculiar mineral composition had been precipitated simultaneously upon the floor of an < universal ocean,’ so as to invest the whole earth in a succession of concentric coats, the determination of relative dates in geology might have been a matter of the greatest sim- plicity. ‘To explain, indeed, the phenomenon would have been difficult, or rather impossible, as such appearances would have implied a former state of the globe, without any analogy
38 DETERMINATION OF THE [Ch IV,
to that now prevailing. Suppose, for example, there were three masses extending over every continent,—the upper of chalk and chloritic sand; the next below, of blue argillaceous lime- stone; and the third and lowest, of red marl and sandstone ; we must imagine that all the rivers and currents of the world had been charged, at the first period; with red mud and sand ; at the second, with blue calcareo-argillaceous mud ; and at a subsequent epoch, with chalky sediment and chloritic sand,
But if the ocean were universal, there could have been no land to waste away by the action of the sea and rivers, and, therefore, no known source whence the homogeneous sedimen- tary matter could have been derived. Few, perhaps, of the earlier geologists went so far as to believe implicitly in such universality of formations, but they inclined to an opinion, that they were continuous over areas almost indefinite; and since such a disposition of mineral masses would, if true, have been the least complex and most convenient for the purposes of clas- sification, it is probable that a belief in its reality was often promoted by the hope that it. might prove true. As to the objection, that such an arrangement of mineral masses could never result from any combination of causes now in action, it never weighed with the earlier cultivators of the science, since they indulged no expectation of being ever able to account for geological phenomena by reference to the known economy of nature. On the contrary, they set out, as we haye already seen, with the assumption that the past and present conditions of the planet were too dissimilar to admit of exact comparison,
But if we inquire into the true composition of any stratum, or set of strata, and endeavour to pursue these continuously through a country, we often find that the character of the mass changes gradually, and becomes at length so different, that we should never have suspected its identity, if we had net been enabled to trace its passage from one form to another,
We soon discover that rocks dissimilar in mineral compo- sition have originated simultaneously; we find, moreover, evidence in certain districts, of the recurrence of rocks of pre-
ChIVJ RELATIVE AGES OF ROCKS. 39
cisely the same mineral character at very different periods; as, for example, two formations of red sandstone, with a great series of other strata intervening between them. Such repeti~ tions might have been anticipated, since these red sandstones are produced by the decomposition of granite, gneiss, and mica- schist ; and districts composed exclusively of these, must again and again be exposed to decomposition, and to the erosive action of running water.
But notwithstanding the variations before alluded to in the composition of one continuous set of strata, many rocks retain the same homogeneous structure and composition, throughout considerable areas, and frequently, after a change of mineral-character, preserve their new peculiarities throughout another tract of great extent. ‘Thus, for example, we may trace a limestone for a hundred miles, and then observe that it becomes more arenaceous, until it finally passes into sand or sandstone. .We may then follow the last-mentioned formation throughout another district. as extensive as that occupied by the limestone first examined,
Proofs of contemporaneous origin derived from organic remains.
We devoted several chapters, in the last yolume, to show 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, and we endea- voured to point out the origin of these separate divisions It was shown that climate is only one of many causes on which they depend, and that difference of longitude, as well as lati- tude, is generally accompanied by a dissimilarity of indigenous species of organic beings.
As different seas, therefore, and lakes are mhepoed at the same period, by different species of aquatic animals and plants, and as the lands adjoining these may be peopled by distinct terrestrial species, it follows that distinct organic remains are imbedded in contemporaneous deposits, If it were otherwise
40 CONTEMPORANEOUS ORIGIN OF ROCKS [Ch. IV,
—if the same species abounded in every climate, or even in every part of the globe where a corresponding temperature, and other conditions favourable to their existence were found, the identification of mineral masses of the same age, by means of their included organic contents, would be a matter of much greater facility.
But, fortunately, the extent of the same zoological provinces; especially those of marine animals, is very great, so that we are entitled to expect, from analogy, that the identity of fossil species, throughout large areas, will often enable us to connect together a great variety of detached and dissimilar formations.
Thus, for example, it will be seen, by reference to our first volume, that deposits now forming in different parts of the Mediterranean, as in the deltas of the Rhone and the Nile, are distinct in mineral composition ; for calcareous rocks are precipitated from the waters of the former river, while pebbles are carried into its delta, and there cemented, by carbonate of lime, into a conglomerate; whereas strata of soft mud and fine sand, are formed exclusively in the Nilotic delta. The Po, again, carries down fine sand and mud into the Adriatic; but since this sediment is derived from the degradation of a differ- ent assemblage of mountains from those drained by the Rhone or the Nile, we may safely assume that there will never be an exact identity in their respective deposits.
If we pass to another quarter of the Mediterranean, as, for example, to the sea on the coast of Campania, or near the base of Etna in Sicily, or to the Grecian archipelago, we find in all these localities that distinct combinations of rocks are in pro- gress. Occasional showers of volcanic ashes are falling into the sea, and streams of laya are flowing along its bottom; and 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, while shells and corals accumulate m yarious localities, Yet the entire Mediterranean, where the
Ch. IV.] PROVED BY ORGANIC REMAINS. 41
above-mentioned formations are simultaneously in progress, may be considered as one zoological province ; for, although certain species of testacea and zoophytes may be very local, and each region may probably have some species peculiar to it, still a considerable number are common to the whole sea. 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 throughout a space equal in area to a great portion of Europe. The Black Sea, moreover, is inhabited by so many identical species, that the delta of the Danube and the Don might, by the same evidence, be shown to have originated simultaneously.
Such identity of fossils, we may remark, not only enables us to refer to the same era, distinct rocks widely separated from each other in the horizontal plane, but also others which may be considerably distant in the vertical series. ‘Thus, for ex- ample, we may find alternating beds of clay, sand, and lava, two thousand feet in thickness, the whole of which may be proved to belong to the same epoch, by the specific identity of the fossil shells dispersed throughout the whole series. It may be objected, that different species would, during the same zoological period, inhabit the sea at different depths, and that the case above supposed could never occur; but, for reasons explained in the last volume*, we believe that rivers and tidal currents often act upon the banks of littoral shells, so that a sea of great depth may be filled with strata, containing throughout a considerable number of the same fossils.
The reader, however, will perceive, by referring to what we have said of zoological provinces, that they are sometimes sepa- rated from each other by very narrow barriers, and for this reason contiguous rocks may be formed at the same time, dif- fering widely both in mineral contents and organic remains. Thus, for example, the testacea, zoophytes, and fish of the Red Sea, may be considered, as a group, to be very distinct from
* Chap. xvii. p. 280.
42 CONTEMPORANEOUS ORIGIN OF ROCKS (Ch. IV,
those inhabiting the adjoining parts of the Mediterranean, | although the two seas are only separated by the narrow isthmus of Suez. We shall show, in a subsequent chapter, that calea- reous formations have accumulated, on a great scale, in the Red Sea, in modern times, and that fossil shells of existing species are well preserved therein; while we know that, at the mouth of the Nile, large deposits of mud are amassed, including the remains of Mediterranean species. Hence it follows that if, at some future period, the bed of the Red Sea should be laid dry, the geologist might experience great difficulties in en- deavouring to ascertain the relative age of these formations, which, although dissimilar both in organic and mineral charac- ters, were of synchronous origin.
There might, perhaps, be no means of clearing up the ob- scurity of such a question, yet 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 ferres- trial 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, 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.
In like manner, the rivers which descend into the Caribbean Sea and Gulf of Mexico on one side, and into the Pacific on the other, carry down the same fluviatile and terrestrial spoils into seas which are inhabited by different groups of marine species.
But it will much more frequently happen, that the coexist- ence of terrestrial species, of distinct zoological and botanical provinces, will be proved by the specific identity of the marine organic remains which inhabited the intervening space. Thus, for example, the distinct terrestrial species of the south of Europe, north of Africa, and north-west of Asia, might all be
Ch. 1V,] PROVED BY ORGANIC REMAINS, Ad
shown to have been contemporaneous, if we suppose the rivers flowing from those three countries to carry the remains of different species of the animal and vegetable kingdoms into the Mediterranean,
In like manner, the sea intervening between the northern shores of Australia and the islands of the Indian ocean, con- tains a great proportion of the same species of corallines and testacea, yet the land animals and plants of the two regions are very dissimilar, even the islands nearest to Australia, as Java, New Guinea, and others, being inhabited by a distinct assem- blage of terrestrial species. It is well known that there are calcareous rocks, volcanic tuff, and other strata in progress, in different parts of these intermediate seas, wherein marine organic remains might be preserved and associated with the terrestrial fossils above alluded to.
As it frequently happens that the barriers between differ- ent proyinces of animals and plants are not very strongly marked, especially where they are determined by differences of temperature, there will usually be a passage from one set of species to another, as in a sea extending from the temperate to the tropical zone. In such cases, we may be enabled to prove, by the fossils of intermediate deposits, the connexion between the distinct provinces, since these intervening spaces will be inhabited by many species, common both to the temperate and equatorial seas.
On the other hand, we may be sometimes able, by aid of a peculiar homogeneous deposit, to prove the former coexistence of distinct animals and plants in distant regions. Suppose, for example, that in the course of ages the sediment of a river, like that of the Red River in Louisiana, is dispersed over an area several hundred leagues in length, so as to pass from the tropies into the temperate zone, the fossil remains imbedded in red mud might indicate the different forms which inhabited, at the same period, those remote regions of the earth.
It appears, then, that mineral and organic characters, although often inconstant, may, nevertheless, enable us to establish the
44 WIDE RANGE OF MARINE TESTACEA. [Ch. IV.
contemporaneous origin of formations in distant countries. As the same species of organic beings usually extend over wider areas than deposits of a homogeneous composition, they are more valuable in geological classification than mineral peculia- rities; but it fortunately happens, that where the one criterion fails, we can often avail ourselves of the other. Thus, for example, sedimentary strata are as likely to preserve the same colour and composition in a part of the ocean reaching from the borders of the tropics to the temperate zone, as in any other quarter of the globe; but in such spaces the variation of species is always most considerable.
In regard to the habitations of species, the marine tribes are of more importance than the terrestrial, not only because they are liable to be fossilized in subaqueous deposits in the great- est abundance, but because they have, for the most part, a wider geographical range. Sometimes, however, it may hap- pen, as we have shown, that the remains of species of some one province of terrestrial plants and animals may be carried down into two seas inhabited by distinct marine species; and here again we have an illustration of the principle, that when one means of identification fails, another is often at hand to assist us. ,
In conclusion, we may observe, that in endeavouring to prove the contemporaneous origin of strata in remote countries by organic remains, we must form our conclusions from a great number of species, since a single species may be enabled to survive vicissitudes in the earth’s surface, whereby thousands of others are exterminated. When a change of climate takes place, some may migrate and become denizens of other latitudes, and so abound there, as to characterize strata of a subsequent era. In the last volume we have stated our reasons for in- ferring that such migrations are never sufficiently general to interfere seriously with geological conclusions, provided we do not found our theories on the occurrence of a small number of fossil species.
( 45 )
CHAPTER V.
Classification of tertiary formations in chronological order—Comparative value of different classes of organic remains—Fossil remains of testacea the most im- portant—Necessity of accurately determining species—Tables of shells by M. Deshayes—Four subdivisions of the Tertiary epoch—Recent formations— _ Newer Pliocene period—Older Pliocene period—Miocene period—Hocene period —The distinct zoological characters of these periods may not imply sudden changes in the animate creation—The recent strata form a common point of departure in distant regions—Numerical proportion of recent species of shells in different tertiary periods—Mammiferous remains of the successive tertiary eras—Synoptical Table of Recent and Tertiary formations.
CLASSIFICATION OF TERTIARY FORMATIONS IN CHRONOLOGICAL ORDER.
WE explained in the last chapter the principles on which the relative ages of different formations may be ascertained, and we found the character to be chiefly derivable from superposition, mineral structure, and organic remains. It is by combining the evidence deducible from all these sources, that we deter- mine the chronological succession of distinct formations, and this principle is well illustrated by the investigation of those European tertiary strata to the discovery of which we have already alluded. 7 |
It will be seen, that in proportion as we have extended our inquiries over a larger area, it has become necessary to interca- late new groups of an age intermediate between those first exa- mined, and we have every reason to expect that, as the science advances, new links in the chain will be supplied, and that the passage from one period to another will become less abrupt. We may even hope, without travelling to distant regions,— without even transgressing the limits of western Europe, to render the series far more complete. The fossil shells, for example, of many of the Subalpine formations, on the northern limits of the plain of the Po, have not yet been carefully col-
46 CLASSIFICATION OF TERTIARY FORMATIONS [Ch. Vv.
lected and compared with those of other countries, and we are almost entirely ignorant of many deposits known to exist in Spain and Portugal.
The theoretical views developed in the last chapter, respect- ing breaks in the sequence of geological monuments, will ex- plain our reasons for anticipating the discovery of intermediate gradations as often as new regions of great extent are explored.
Comparative value of different classes of organic remains.
In the mean time, we must endeavour to make the most syste- matic arrangement in our power of those formations which are already known, and in attempting to classify these in chrono- logical order, we have already stated that we must chiefly depend on the evidence afforded by their fossil organic con- tents. In the execution of this task, we have first to consider what class of remains are most useful, for although every kind of fossil animal and plant is interesting, and cannot fail ‘to throw light on the former history of the globe at a certain period, yet those classes of remains which are of rare and casual occurrence, are absolutely of no use for the purposes of general classification. If we have nothing but plants in one assemblage of strata, and the bones’of mammalia in another, we can ob- viously draw no conclusion respecting: the number of species of organic beings common to two epochs; or if we have a great variety, both of vertebrated animals and plants, in one series, and only shells in another, we can form no opinion respecting the remoteness or proximity of the two eras. We might, per- haps, draw some conclusions as to relative antiquity, if we could compare each of these monuments toa third ; as, for example, if the species of shells should be almost all identical with those now living, while the plants and vertebrated animals were all ex tinct; for we might then infer that the shelly deposit was the most recent of the two. But in this case it will be seen that the information flows from a direct comparison of the species of corresponding orders of the animal and vegetable kinedoms,— of plants with plants, and shells with shells; the only mode of
Ch. Vi] IN CHRONOLOGICAL ORDER. AT
making a systematic arrangement by reference to organic remains.
Although the bones of mammalia in the tertiary strata, and those of reptiles in the secondary, afford us instruction of the most interesting kind, yet the species are too few, and confined to too small a number of localities, to be of great importance in characterizing the minor subdivisions of geological formations, Skeleton of fish are by no means frequent in a good state of preservation, and the science of ichthyology must be farther advanced, before we can hope to determine their specific cha- racter with sufficient precision. The same may be said of fossil botany, notwithstanding the great progress that has recently been made in that department ; and even-in regard to zoophytes, which are so much more abundant in a fossil state than any of the classes above enumerated, we are still greatly impeded in our endeavour to classify strata by their aid, in consequence of the smallness of the number of recent species which have been examined in those tropical seas where they occur in the greatest profusion.
Fossil remains of testacea of chief importance. The testacea are by far the most important of all classes of organic beings which have left their spoils in the subaqueous deposits; they are the medals which nature has chiefly selected to record the history of the former changes of the globe. There is scarcely any great series of strata that does not contain some marine of freshwater shells, and these fossils are often found so entire, especially in the tertiary formations, that when disengaged from the matrix, they have all the appearance of having been just procured from the sea, Their colour, indeed, is usually want- ing, but the parts whereon specific characters are founded remain unimpaired; and although the animals themselves are gone, yet their form and habits can generally be inferred from the shell which covered them.
The utility of the testacea, in geological classification, is greatly enhanced by the circumstance, that some forms are proper to the sea, others to the land, and others to freshwater.
48 CLASSIFICATION OF TERTIARY FORMATIONS [Ch. V.
Rivers scarcely ever fail to carry down into their deltas some land shells, together with species which are at once fluviatile and lacustrine. The Rhone, for example, receives annually, from the Durance, many shells which are drifted down in an entire state from the higher Alps of Dauphiny, and these species, such as Bulimus montanus, are carried down into the delta of the Rhone to a climate far different from that of their native habitation. ‘The young hermit crabs may often be seen on the shores of the Mediterranean, near the mouth of the Rhone, inhabiting these univalves, brought down to them from so great a distance*. At the same time that some freshwater and land species are carried into the sea, other individuals of the same become fossil in inland lakes, and by this means we learn what species of freshwater and marine testacea coexisted at particular eras; and from this again we areable to make out the connexion between various plants and mammifers imbedded in those lacustrine deposits, and the testacea which lived in the ocean at the same time.
There are two other characters of the molluscous animals which render them extremely valuable in settling chronological questions in Geology. ‘The first of these is a wide geographical range, and the second (probably a consequence of the former), is the superior duration of species in this class. It is evident that if the habitation of a species be very local, it cannot aid us greatly in establishing the contemporaneous origin of distant groups of strata, in the manner pointed out in the last chapter ; and if a wide geographical range be useful in connecting for- mations far separated in space, the longevity of species is no less serviceable in establishing the relations of strata consider- ably distant from each other in point of time.
We shall revert in the sequel to the curious fact, that in tracing back these series of tertiary deposits, many of the exist- ing species of testacea accompany us after the disappearance of all the recent mammalia, as well as the fossil remains of living
* M. Marcel de Serres pointed out this fact to me when I visited Montpellier, July, 1828.
Ch. V.] IN CHRONOLOGICAL ORDER. AG
species of several other classes. We even find the skeletons of extinct quadrupeds in deposits wherein all the land and fresh- water shells are of recent species*.
Necessity of accurately determining species.—The reader will already perceive that the systematic arrangement of strata, so far as it rests on organic remains, must depend essentially on the accurate determination of species, and the geologist must therefore have recourse to the ablest naturalists, who have devoted their lives to the study of certain departments of organic nature. It is scarcely possible that they who are con- tinually employed in laborious investigations in the field, and in ascertaining the relative position and characters of mineral masses, should have leisure to acquire a profound knowledge of fossil osteology, conchology, and other branches; but it is desirable that, in the latter science at least, they should become acquainted with the principles on which the specific characters are determined, and on which the habits of species are inferred
from their peculiar forms. When the specimens are in an im- _ perfect state of preservation, or the shells happen to belong to genera in which it is difficult to decide on the species, ex- cept when the inhabitant itself is present, or when any other grounds of ambiguity arise, we must reject, or lay small stress upon, the evidence, lest we vitiate our general results by false identifications and analogies. We cannot do better than consider the steps by which the science of botanical geography has reached its present stage of advancement, and endeavour to ‘introduce the same severe comparison of the specific characters, in drawing all our geological inferences.
Tables of shells by M. Deshayes.—In the Appendix the reader will find a tabular view of the results obtained by the compa- rison of more than three thousand tertiary shells, with nearly five thousand living species, all of which, with few exceptions, are contained in the rich collection of M. Deshayes. Having enjoyed an opportunity of examining, again and again, the specimens
oD? on which this eminent conchologist has founded his identifica-
* See yol. i. chap. vi. Vor. III. E
50 M. DESHAYES’ TABLES OF SHELLS. [Ch. V.
tions, and having been witness to the great time and labour devoted by him to this arduous work, I feel confidence in the results, so far as the data given in his list will carry us. It was necessary to compare nearly forty thousand specimens, in order to construct these tables, since not only the varieties of every species required examination, but the different individuals, also, belonging to each which had been found fossil in various loca- lities. 'The correctness of the localities themselves was ascer- tained with scrupulous exactness, together with the relative position of the strata; and if any doubts existed on these ques- tions, the specimens were discarded as of no geological value. A large proportion of the shells were procured, by M. Deshayes himself, from the Paris basin, many were contributed by dif- ferent French geologists, and some were collected by myself from different parts of Europe.
It would haye been impossible to give lists of more than three thousand fossil shells in a work not devoted exclusively to conchology ; but we were desirous of presenting the reader with a catalogue of those fossils which M. Deshayes has been able to identify with living species, as also of those which are common to two distinct tertiary eras, By this means a com- parison may be made of the testacea of each geological epoch, with the actual state of the organic creation, and, at the same time, the relations of different tertiary deposits to each other exhibited. The number of shells mentioned by name in the tables, in order to convey this information, is seven hundred and eighty-two, of which four hundred and twenty-six have. been found both living and fossil, and three hundred and fifty- six fossil only, but in the deposits of more than one era. An exception, however, to the strictness of this rule, has been made in regard to the fossil shells common to the London and Paris basins, fifty-one of which have been enumerated by name, though these formations do not belong to different eras.
It has been more usual for geologists to give tables of cha- racteristic shells; that is to say, of those found in the strata of one period and not common to any other. These typical species are certainly of the first importance, and some of them
Ch, V.] DETERMINATION OF SPECIES, 51
will be seen figured in the plates, illustrative of the different tertiary eras; but we were more anxious, in this work, to place in aclear light, a point of the greatest theoretical interest, which has been often overlooked or controverted, viz., the identity of many living and fossil species, as also the connexion of the zoological remains of deposits formed at successive periods.
The value of such extensive comparisons, as those of which the annexed tables of M. Deshayes give the results, depends greatly on the circumstance, that all the identifications have been made by the same naturalist. The amount of variation which ought to determine a species is, in cases where they ap- proach near to each other, a question of the nicest discrimina- tion, and requires a degree of judgment and tact that can hardly be possessed by different zoologists in exactly the same degree. The standard, therefore, by which differences are to be mea- sured, can scarcely ever be perfectly invariable, and one great object to be sought for is, that, at least, it should be uniform. If the distinctions are all made by the same naturalist, and his knowledge and skill be considerable, the results may be relied on with sufficient confidence, as far as regards our geological conclusions,
If one conchologist should inform us that out of 1122 species of fossil testacea, discovered in the Paris basin, he has only been enabled to identify thirty-eight with recent species, while another should declare, that out of two hundred and twenty-six Sicilian fossil shells, no less than two hundred and sixteen be- longed to living species, we might suspect that one of these observers allowed a greater degree of latitude to the variability of the specific character than the other; but when, in both in- stances, the conclusions are drawn by the same eminent con- chologist, we are immediately satisfied that the relations of these two groups, to the existing state of the animate creation, are as distinct as are indicated by the numerical results.
_ It is not pretended that the tables, to which we refer, com-
prise all the known tertiary shells, In the museums of Italy
there are magnificent collections, to which M. Deshayes had no ‘K2
oe SUBDIVISIONS OF [Ch. V.
access, and the additions to the recent species in the cabinets | of conchologists in London, have been so great of late years, that in many extensive genera the number of species has been more than doubled. But as the greater part of these newly- discovered shells have been brought from the Pacific and other distant seas, it is probable that: these accessions would not ma- terially alter the results given in the tables, and it must, at all events, be remembered, that the only effect of such additional information would be, to increase the number of identifications of recent with fossil species, while the proportional number of analogues in the different periods might probably remain nearly the same,
SUBDIVISIONS OF THE TERTIARY EPOCH.
Recent formations.—We shall now proceed to consider the subdivisions of tertiary strata which may be founded on the results of a comparison of their respective fossils, and to give names to the periods to which they each belong. The tertiary epoch has been divided into three periods in the tables; we shall, however, endeavour to establish four, all distinct from the actual period, or that which has elapsed since the earth has been tenanted by man. ‘To the events of this latter era, which we shall term the recent, we have exclusively confined ourselves in the two preceding volumes. All sedimentary deposits, all vol- canic recks, in a word, every geological monument, whether belonging to the animate or inanimate world, which appertains to this epoch, may be termed recent. Some recent species, there- fore, are found fossil in various tertiary periods, and, on the other hand, others, like the Dodo, may be extinct, for it is suf- ficient that they should once have coexisted with man, to make them referrible to this era.
Some authors apply the term contemporaneous to all the formations which have originated during the human epoch; but as the word is so frequently in use to express the synchro- nous origin of distinct formations, it would be a source of great inconvenience and ambiguity, if we were to attach to it a tech- nical sense.
Ch, V.] THE TERTIARY EPOCH. “5d
We may sometimes prove, that certain strata belong to the recent period by aid of historical evidence, as parts of the delta of the Po, Rhone, and Nile, for example; at other times, by discovering imbedded remains of man or his works ; but when we have no evidence of this kind, and we hesitate whether to ascribe a particular deposit to the recent era, or that immedi- ately preceding, we must generally incline to refer it to the latter, for it will appear in the sequel, that the changes of the historical era are quite insignificant when contrasted with those even of the newest tertiary period.
Newer Pliocene period.cThis most modern of the four subdivisions of the whole tertiary epoch, we propose to call the Newer Pliocene, which, together with the Older Pliocene, con- stitute one group in the annexed tables of M. Deshayes.
We derive the term Pliocene from wdeiwy, major, and xatvos, recens, as the major part of the fossil testacea of this epoch are referrible to recent species*. Whether in all cases there may hereafter prove to be an absolute preponderance of recent species, in every group of strata assigned to this period in the tables, is very doubtful; but the proportion of living species, where least considerable, usually approaches to one-half of the total number, and appears always to exceed a third; and as our acquaintance with the testacea of the Mediterranean, and some’ other seas, increases, it is probable that a greater proportion
will be identified.
* In the terms Pliocene, Miocene, and Eocene, the Greek diphthongs e: and ai are changed into the vowels 7 and e, in conformity with the idiom of our lan- guage. ‘Thus we have Encenia, an inaugural ceremony, derived from ¢y and xaos, recens; and as examples of the conversion of ei into 7, we have icosahedron.
I have been much indebted to my friend, the Rev. W. Whewell, for assisting me in inventing and anglicizing these terms,and I sincerely wish that the numer- ous foreign diphthongs, barbarous termiuations, and Latin plurals, which have been so plentifully introduced of late years into our scientific language, had been avoided as successfully as they are by French Naturalists, and asthey were by the earlier English writers, when our language was more flexible than itis now. But while I commend the French for accommodating foreign terms to the structure of their own language, I must confess that no naturalists have been more unscholar- like in their mode of fabricating Greek derivatives and compounds, many of the latter being a bastard offspring of Greek and Latin.
5A SUBDIVISIONS OF [Ch. V.
The newer Pliocene formations, before alluded to, pass in- sensibly into those of the Recent epoch, and contain an immense preponderance of recent species. It will be seen that of two hundred and twenty-six species, found in the Sicilian beds, only ten are of extinct or unknown species, although the anti- quity of these tertiary deposits, as contrasted with our most remote historical eras, is immensely great. In the voleanie and sedimentary strata of the district round Naples, the pro- portion appears to be even still smaller.
Older Pliocene period.—These formations, therefore, and others wherein the plurality of living species is so very decided, we shall term the Newer Pliocene, while those of the tertiary period immediately preceding may be called the Older Pliocene. To the latter belong the formations of Tuscany, and of the Sub- apennine hills in the north of Italy, as also the English Crag.
It appears that in the period last mentioned, the proportion of recent species varies from upwards of a third to somewhat more than half of the entire number; but it must be recol- lected, that this relation to the recent epoch is only one of its zoological characters, and that certain peculiar species of tes- tacea also distinguish its deposits from all other strata. ‘The relative position of the beds referrible to this era has been ex- plamed in diagrams Nos. 3 and 4, letter f, chapter II.
Miocene period.-—The next antecedent tertiary epoch we shall name Miocene, from uewy, minor, and xevos, recens, a minority only of fossil shells imbedded in the formations of this period, being of recent species. The total number of Miocene shells, referred to in the annexed tables, amounts to 1021, of which one hundred and seventy-six only are recent, being in the proportion of rather less than eighteen in one hundred. Of species common to this period, and to the two divisions of the Pliocene epoch before alluded to, there are one hundred and ninety-six, whereof one hundred and fourteen are living, and the remaining eighty-two extinct, or only known as fossil.
As there are a certain number of fossil species which are characteristic of the Pliocene strata before described, so also
Ch. V.] THE TERTIARY EPOCH. 55
there are many shells exclusively confined to the Miocene period. We have already stated, that in Touraine and in the South of France near Bordeaux, in Piedmont, in the basin of Vienna, and other localities, these Miocene formations are largely developed, and their relative position has been shown in diagrams Nos. 3 and 4, letter e, chapter II.
Eocene period.—The period next antecedent we shall call Eocene, from *ws, aurora, and xaivos, recens, because the ex- tremely small proportion of living species contained in these strata, indicates what may be considered the first commence- ment, or dawn, of the existing state of the animate creation. To this era the formations first called tertiary, of the Paris and London basins, are referrible. Their position is shown in the diagrams Nos, 3 and 4, letter d, in the second chapter.
The total number of fossil shells of this period already known, is one thousand two hundred and thirty-eight, of which num- ber forty-two only are living species, being nearly in the pro- portion of three and a half in one hundred. Of fossil species, not known as recent, forty-two are common to the Eocene and Miocene epochs. In the Paris basin alone, 1122 species have been found fossil, of which thirty-eight only are still living.
The geographical distribution of those recent species which are found fossil in formations of such high antiquity as those of the Paris and London basins, is a subject of the highest interest, .
It will be seen by reference to the tables, that in the more modern formations, where so large a proportion of the fossil shells belong to species still living, they also belong, for the most part, to species now inhabiting the seas immediately ad- joining the countries where they occur fossil; whereas the recent species, found in the older tertiary strata, are frequently inhabitants of distant latitudes, and usually of warmer climates. Of the forty-two Eocene species, which oceur fossil in England, France, and Beleium, and which are still living, about half now inhabit within, or near the tropics, and almost all the rest are denizens of the more southern parts of Europe. If some
56 SUBDIVISIONS OF [Ch. V.
Eocene species still flourish in the same latitudes where they are found fossil, they are species which, like Lucina divaricata, are now found in many seas, even those of different quarters of the globe, and this wide geographical range indicates a capacity of enduring a variety of external circumstances, which may enable a species to survive considerable changes of climate and other re- volutions of the earth’s surface. One fluviatile species (Melania inquinata), fossil in the Paris basin, is now only known in the Philippe islands, and during the lowering of the temperature of the earth’s surface, may perhaps have escaped destruction by transportation to the south. We have pointed out in the second volume (chap. vil.), how rapidly the eggs of freshwater species might, by the instrumentality of water-fowl, be transported from one region to another. Other Eocene species, which still survive and range from the temperate zone to the equator, may formerly have extended from the pole to the temperate zone, and what was once the southern limit of their range may now be the most northern.
Even if we had not established several remarkable facts in attestation of the longevity of certain tertiary species, we might still have anticipated that the duration of the living species of aquatic and terrestrial testacea would be very unequal. For it is clear that those which now inhabit many different regions and climates, may survive the influence of destroying causes, which might extirpate the greater part of the species now living. We might expect, therefore, some species to survive several successive states of the organic world, just as Nestor was said to have outlived three generations of men.
The distinctness of periods may indicate our imperfect infor- mation.—In regard to distinct zoological periods, the reader will understand, from our observations in the third chapter, that we consider the wide lines of demarcation that sometimes separate different tertiary epochs, as quite unconnected with extraordmary revolutions of the surface of the globe, and as arising, partly, like chasms in the history of nations, out of the present imperfect state of our information, and partly from
Ch, V.] THE TERTIARY EPOCH. 57
the irregular manner in which geological memorials are pre- served, as already explained. We have little doubt that it will be necessary hereafter to intercalate other periods, and that many of the deposits, now referred to a single era, will be found to have been formed at very distinct periods of time, so that, notwithstanding our separation of tertiary strata into four groups, we shall continue to use the term contemporaneous with a great deal of latitude.
We throw out these hints, because we are apprehensive lest zoological periods in Geology, like artificial divisions in other branches of Natural History, should acquire too much impor- tance, from being supposed to be founded on some great inter- ruptions in the regular series of events in the organic world, whereas, like the genera and orders in zoology and botany, we ought to regard them as invented for the convenience of systematic arrangement, always expecting to discover interme- diate gradations between the boundary lines that we have first drawn. |
In Natural History we select a certain species as a generic type, and then arrange all its congeners in a series, according to the degrees of their deviation from that type, or accord- ing as they approach to the characters of the genus which pre- cedes or follows. In like manner, we may select certain Geo- logical formations as typical of particular epochs ; and having accomplished this step, we may then arrange the groups referred to the same period in chronological order, according as they deviate in their organic contents from the normal groups, or according as they approximate to the type of an antecedent or subsequent epoch.
If intermediate formations shall hereafter be found between the Eocene and Miocene, and between those of the last period and the Pliocene, we may still find an appropriate place for all, by forming subdivisions on the same principle as that which has determined us to separate the lower from the upper Plio- cene groups. ‘Thus, for example, we might have three divisions of the Eocene epoch,—the older, middle, and newer; and
58 NUMERICAL PROPORTION OF RECENT SHELLS [Ch, V.
three similar subdivisions, both of the Miocene and Pliocene epochs. In that case, the formations of the middle period must be considered as the types from which the assemblage of organic remains in the groups immediately antecedent or sub- sequent. will diverge.
The Recent strata form a common point of departure in all countries.— We derive one great advantage from beginning our classification of formations by a comparison of the fossils of the more recent strata with the species now living, namely, the ac- quisition of a common point of departure in every region of the globe. Thus, for example, if strata should be discovered in India or South America, containing the same small proportion of recent shells as are found in the Paris basin, they also might be termed Eocene, and, on analogous data, an approximation might be made to the relative dates of strata placed in the arctic and tropical regions, or the comparative age ascertained of European deposits, and those which are trodden by our anti- podes.
There might be no species common to the two groups; yet we might infer their synchronous origin from the common relation which they bear to the existing state of the animate creation. We may afterwards avail ourselves of the dates thus established, as eras to which the monuments of preceding periods may be referred.
Numerical proportion of recent shells in the different Ter- diary periods.—'There are seventeen species of shells discovered, which are common to all the tertiary periods, thirteen of which are still living, while four are extinct, or only known as fossil *. These seventeen species show a connexion between all these geological epochs, whilst we have seen that a much greater number are common to the Eocene and Miocene periods, and a still greater to the Miocene and Pliocene.
We have already stated, that in the older tertiary formations, we find a very small proportion of fossil species identical with
* See the Tables of M. Deshayes in Appendix I,
Ch. V.] IN DIFFERENT TERTIARY PERIODS. 59
those now living, and that, as we approach the superior and newer sets of strata, we find the remains of existing animals and plants in greater abundance. It is almost as difficult to find an unknown species in some of the newer Pliocene de- posits, although very ancient and elevated at great heights above the level of the sea, as to meet with recent species in the Hocene strata.
This increase of existing species, and gradual disappearance of the extinct, as we trace the series of formations from the older to the newer, is strictly analogous, as we before observed, to the fluctuations of a population such as might be recorded at successive periods, from the time when the oldest of the individuals now living was born to the present moment. The disappearance of persons who never were contemporaries of the greater part of the present generation, would be seen to have kept pace with the birth of those who now rank amongst the oldest men living, just as the Eocene and Miocene species are observed to have given place to those Pliocene testacea which are now contemporary with man.
In reference to the organic remains of the different groups which we have named, we may say that about a thirtieth part of the Eocene shells are of recent species, about one-fifth of the Miocene, more than a third, and often more than half, of the older Pliocene, and nine-tenths of the newer Pliocene.
Mammiferous remains of the successive tertiary eras.—But although a thirtieth part of the Eocene testacéa have been identified with species now living, none of the associated mam- miferous remains belong to species which now exist, either in Europe or elsewhere. Some of these equalled the horse, and others the rhinoceros, in size, and they could not possibly have escaped observation, had they survived down to our time. More than forty of these Eocene mammifers are referrible to a division of the order Pachydermata, which has now only four
-living representatives on the globe. Of these, not only the
species but the genera are distinct from any of those which have been established for the classification of living animals.
60 TERTIARY MAMMIFEROUS REMAINS. [Ch. V.
In the Miocene mammalia we find a few of the generic forms most frequent in the Eocene strata associated with some of those now existing, and in the Pliocene we find an intermixture of extinct and recent species of quadrupeds. ‘There is, there~ fore, a considerable degree of accordance between the results deducible from an examination of the fossil testacea, and those derived from the mammiferous fossils. But although the latter are more important in respect to the unequivocal evidence afforded by them of the extinction of species, yet, for reasons before explained, they are of comparatively small value in the general classification of strata in Geology.
It will appear evident, from what we have said in the last volume respecting the fossilization of terrestrial species, that the imbedding of their remains depends on rare casualties, and that they are, for the most part, preserved in detached allu- vions covering the emerged land, or in osseous breccias and stalagmites formed in caverns and fissures, or in isolated lacus- trine formations. ‘These fissures and caves may sometimes remain open during successive geological periods, and the allu- vions, spread over the surface, may be disturbed, again and again, until the mammalia of successive epochs are mingled and confounded together. Hence we must be careful, when we endeavour to refer the remains of mammalia to certain ter- tiary periods, that we ascertain, not only their association with testacea of which the date is known, but, also, that the remains were intermixed in such a manner as to leave no doubt of the former coexistence of the species.
In the next page will be found a Synoptical Table of the Recent and Tertiary formations alluded to in this chapter.
N.B. By aid of this table, the reader will be able to refer almost all the localities of the Pliocene formations enumerated in the Tables of M. Deshayes (Appendix I.) to the newer or older division of the Pliocene period established in the fore- going chapter.
( 61 ) { | Synoptical Table of Recent and Tertiary Formations. ' Character PERIODS. of | Localities of the different Formations. \ Formations. Marine. { Coral formations of Pacific. Delta of Po, Ganges, &c, ; Modern deposits in Lake Superior— Breshwaten. alee? Geneva—Marl lakes of I. Recenr. Scotland—Italian travertin, &c. : . Jorullo — Monte Nuovo — Modern Volcanic. ae of Iceland, Etna, Vesuvius, : Strata of the Val di Noto in Sicily, Mane: { Ischia, Morea? Uddevalla. Tan Newer Freshwater, ety of the Elsa around Colle in } Pliocene, Tuscany. | Older parts of Vesuvius, Etna, and | Volcanic, Ischia—Voleanie rocks of the | Val di Noto in Sicily. ! =. Northern Subapennine formations, as Marine. at Parma, Asti, Sienna, Perpig- : nan, Nice—English Crag. j | 2, _ Older Alternating with marine beds near | Pliocene. Hest ater! { the en of Sienna. Wallessaro. | Molegnos of Muscany and Campagna pls. Teerrary. ; Strata of Touraine, Bordeaux, Valley Marine, of the Bormida, and the Superga near Turin—Basin of Vienna. Freshwater, Alternating with marine at Saucats 3. Miocene. { twelve miles south of Bordeaux. ’ etigaeg and Transylvanian vol- i canic rocks. . Voleanic. Part of the volcanos of Auvergne, Cantal, and Velay ? Marine. Paris and London Basins. Alternating with marine in Paris ba- 4, Eocene. Freshwater. sin—Isle of Wight—purely la- custrine in Auvergne, Cantal, and Velay. Voleanic. | Oldest part of voleanic rocks of Au- vergne.
( 62 )
CHAPTER VI.
Newer Pliocene formations—-Reasons for considering in the first place the more modern periods—Geological structure of Sicily—Formations of the Val di Noto of newer Pliocene period—Divisible into three groups—Great limestone— Schistose and arenaceous limestone—Blue marl with shells—Strata subjacent to the above—Volcanic rocks of the Val di Noto—Dikes—Tufis and Peperinos —Volcanic conglomerates—Proofs of long intervals between volcanic eruptions —Dip and direction of newer Pliocene strata of Sicily.
NEWER PLIOCENE FORMATIONS.
Havine endeavoured, in the last chapter, to explain the prin- ciples on which the different tertiary formations may be ar- ranged in chronological order, we shall now proceed to consider the newest division of formations, or that which we have named the newer Pliocene.
It may appear to some of our readers, that we reverse the natural order of historical research by thus describing, in the first place, the monuments of a period which immediately pre- ceded our own era, and passing afterwards to the events of antecedent ages. But, in the present state of our science, this retrospective order of inquiry is the only one which can con- duct us gradually from the known to the unknown, from the simple to the more complex phenomena. We have already explained our reasons for beginning this work with an exami- nation, in the first two volumes, of the events of the recent epoch, from which the greater number of rules of interpretation in geology may be derived. ‘The formations of the newer Pliocene period will be considered next in order, because these have undergone the least degree of alteration, both in position and internal structure, subsequently to their origin. ‘They are monuments of which the characters are more easily deciphered than those belonging to more remote periods, for they have been less mutilated by the hand of time, ‘The organic remains, more
Ch, VL.J GEOLOGICAL STRUCTURE OF SICILY, 63
especially of this era, are most important, not only as being in a more perfect state of preservation, but also as being chiefly referrible to species now living ; so that their habits are known to us by direct comparison, and not merely by inference from analogy, as in the case of extinct species.
Geological structure of Sicily—We shall first describe an extensive district in Sicily, where the newer Pliocene strata are largely developed, and where they are raised to considerable heights above the level of the sea. After presenting the reader with a view of these formations, we shall endeavour to explain the manner in which they originated, and speculate on the subterranean changes of which their present position affords evidence,
The island of Sicily consists partly of primary and secondary rocks, which occupy, perhaps, about two-thirds of its super- ficial area*, and the remaining part is covered by tertiary formations, which are of great extent in the southern and cen- tral parts of the island, while portions are found bordering nearly the whole of the coasts.
Formations of the Val di Noto.—If we first turn our atten- tion to the Val di Noto, a district which intervenes between Etna and the southern promontory of Sicily, we find a con- siderable tract, containing within it hills which are from one to two thousand feet in height, entirely composed of limestone, marl, sandstone, and associated volcanic rocks, which belong to the newer Pliocene era. ‘The recent shells of the Mediterra- nean abound throughout the sedimentary strata, and there are abundant proofs that the igneous rocks were the produce of successive submarine eruptions, repeated at intervals during the time when the subaqueous formations were in progress.
These rising grounds of the Val di Noto are separated from the cone of Etna, and the mafine strata whereon it rests, by the low level plain of Catania, just elevated above the level of the sea, and watered by the Simeto, The traveller who passes
* We may shortly expect a full account of the Geology of this island from Professor Hoffmann, who has devoted more than a year to its examination,
64 NEWER PLIOCENE PERIOD, [Ch, VI.
from Catania to Syracuse, has an opportunity of observing, on the sides of the valley, many deep sections of the modern formations above described, especially if he makes a. slight detour by Sortino and the Valley of Pentalica,
The whole series of strata, in the Val di Noto, is divisible into three principal groups, exclusive of the associated volcanic rocks. ‘The uppermost mass consists of limestone, which some- times acquires the enormous thickness of seven or eight hun dred feet, below which is a series much inferior in thickness, consisting of a calcareous sandstone, conglomerate and schistose limestone, and beneath this again, blue marl. The whole of the above groups contain shells and zoophytes, nearly all of which are referrible to species now inhabiting the contiguous sea.
Castrogiovanni. No. 5,
Syracuse, Gir genti.
a, Great limestone of Val di Noto.
6, Schistose and arenaceous limestone of Floridia, &c. ce, Blue marl with shells.
d, White Jaminated marl.
e, Blue clay and gypsum, &c. without shells.
Great limestone formation (a, diagram No. 5).—In mineral character this rock often corresponds to the yellowish white building-stone of Paris, well known by the name of Calcaire grossier, but it often passes into a much more compact stone. In the deep ravine-like valleys of Sortino and Pentalica, it is seen in nearly horizontal strata, as solid and as regularly bedded as the greater part of our ancient secondary formations. It abounds in natural caverns, which, in many places, as in the valley of Pentalica, have been enlarged and TALS ea by ar- tificial excayations.
————
Ch. VI.] SICILY—VAL DI NOTO, 65
The shells in the limestone are often very indistinct, somé- times nothing but casts remaining, but in many localities, especially where there is a slight intermixture of volcanic sand, they are more entire, and, as we have already stated, can almost all be identified with recent Mediterranean testacea. Several species of the genus Pecten, are exceedingly numerous, par- ticularly the large scallop (P. Jacobeus), now so common on the coasts of Sicily. ‘The shells which I collected from this limestone at Syracuse, Villasmonde, Militello (V. di Noto), and Girgenti, have been examined by M. Deshayes, and found to be all referrible to species now living, with three or four exceptions™.
The mineral characters of this great calcareous formation vary considerably in different parts of the island. In the south, near the town of Noto, the rock puts on the compactness, together with the spheroidal concretionary structure of some of the Italian travertins. At the same place, also, it contains the leaves of plants and reeds, as if a stream of freshwater, charged with carbonate of lime and terrestrial vegetable remains, had entered the sea in the neighbourhood. At Spaccaforno, and other places in the south of Sicily, a similar compact variety of the limestone occurs, where it is for the most part pure white, often very thick bedded, and occasionally without any lines of stratification, This hard white rock is often four or five hun- dred feet in thickness, and appears to contain no fossil shells. It has much the appearance of having been precipitated from the waters of mineral springs, such as frequently rise up at the bottom of the sea in the volcanic regions of the Mediterranean. As these springs give out an equal quantity of mineral matter
-at all seasons, they are much more likely to give rise to unstra-
tified masses, than a river which is swoln and charged with
* For lists of these see Appendix II. I procured at Villasmonde, seven species ; at Militello, ten; in the limestone of Girgenti, of which the ancient temples are built, ten species; from the limestone and subjacent clay at Syracuse, twenty-six species; in the limestone and clay near Palermo, also belonging to the newer Pli- ocene formation, one hundred shells,
Vou. III, EF
66 NEWER PLIOCENE PERIOD. [Ch, VI.
sedimentary matter of different kinds, and in unequal quan- tities, at particular seasons of the year.
The great limestone, above mentioned, prevails not only in the Val di Noto, but reappears in the centre of the island, capping the hill of Castrogiovanni, at the height of three thou- sand feet above the level of the sea. It is cavernous there, as at Sortino and Syracuse, and contains fossil shells and casts of shells of the same species*,
Schistose and arenaceous limestone, §c. (b, diagram No. 5).— The limestone above-mentioned passes downwards into a white calcareous sand, which has sometimes a tendency to an oolitic and pisolitic structure, analogous to that which we have described when speaking of the travertin of Tivoli}. At Floridia, near Syracuse, it contains a sufficient number of small calcareous pebbles to constitute a conglomerate, where also beds of sandy limestone are associated, replete with numerous fragments of shells, and much resembling, in structure, the English corn- brash. A diagonal lamination is often observable in the cal- careous sandy beds analogous to that represented in the first volume (chap. xiv. diagram No. 6), and to that exhibited in many sections of the English crag, to which we shall after- wards allude.
In some parts of the island this sandy caleareous division, b, seems to be represented by yellow sand, exactly resembling that so frequently superimposed on the blue shelly marl of the Subapennines in the Italian peninsula. Thus, near Gram- michele, on the road to Caltagirone, beds of incoherent yellow sand, several hundred feet in thickness, with occasional layers of shells, repose upon the blue shelly marl of Caltagirone.
When we consider the arenaceous character of this forma- tion, the disposition of the lamings, and the broken shells some- times imbedded in it, it is difficult not to suspect that it was
* Dr. Daubeny correctly identified the Val di Noto limestone of Syracuse with that of the summit of Castrogiovanni—Jameson, Ed, Phil. Journ., No. xxv. p. 107, July, 1825.
+ Vol. i, chap. xii,
Ch. VIL] SICGILY—VAL DI NOTO, 67
formed in shallower water, and nearer the action of superficial currents, than the superincumbent limestone, which was evi- dently accumulated in a sea of considerable depth. If we adopt this view, we must suppose a considerable subsidence of the bed of the sea, subsequent to the deposition of the arena~ ceous beds in the Val di Noto.
Blue marl with shells (c, diagram No. 5).—Under the sandy beds, last mentioned, is found an argillaceous deposit of variable thickness, called Creta in Sicily. It resembles the blue marl of the Subapennine hills, and, like it, encloses fossil shells and corals in a beautiful state of preservation. Of these I collected a great abundance from the clay, on the south side of the harbour of Syracuse, and twenty species in the environs of Caltanisetta, all of which, with three exceptions, M. Deshayes was able to identify with recent species*. From similar blue marl, alternating with yellow sand, at Caltagirone, at an eleva- tion of about five hundred feet above the level of the sea, I obtained forty species of shells, of which all but six were recog- nized as identical with recent species}. The position of this argillaceous formation is well seen at Castrogiovanni and Gir- genti, as represented in the sections, diagram No. 5. In both of these localities, the limestone of the Val di Noto re-appears, passing downwards into a caleareous sandstone, below which is a shelly blue clay.
Strata beneath the blue marl.—The dee rests, in both loca- lities, on an older series of white and blue marls, probably belonging to the tertiary period, but of which I was unable to. determine the age, having procured from it no organic remains save the skeletons of fish which I found in the white thinly-
laminated marls{.
* See list of these shells, Appendix II. + See Appendix II.
t 1 found these fossil fish in great abundance on the road, half a mile north- west of Radusa, on the road to Castrogiovanni, where the marls are fetid, and near Castrogiovanni in gypseous marls, at the mile-stone No. 88, and between that and No. 89, Lord Northampton has since presented to the Geological Society
EF 2
68 NEWER PLIOCENE PERIOD. [Ch. VI.
These marls are sometimes gypseous, and belong to a great argillaceous formation which stretches over a considerable part of Sicily, and contains sulphur and salt in great abundance. The strata of this group have been in some places contorted in the most extraordinary manner, their convolutions often resem- bling those seen in the most disturbed districts of primary clay slate.
But we wish, at present, to direct the reader’s exclusive at- tention to strata decidedly referrible to the newer Pliocene era, and we have yet to mention the igneous rocks associated with the sedimentary formations already alluded to.
Volcanic Rocks of the Val di Noto.—The voleanic rocks occasionally associated with the limestones, sands, and marls already described, constitute a very prominent feature through- out the Val di Noto. Great confusion might have been ex- pected to prevail, where lava and ejected sand and scorize are intermixed with the marine strata, and, accordingly, we find it often impossible to recognize the exact part of the series to which the beds thus interfered with belong.
Sometimes there are proofs of the posterior origin of the lava, and sometimes of the newer date of the stratified rock, for we find dikes of lava intersecting both the marl and limestone, while, in other places, calcareous beds repose upon lava, and are unaltered at the point of contact. Thus the shelly lime- stone of Capo Santa Croce rests in horizontal strata upon amass of lava, which had evidently been long exposed to the action of the waves, so that the surface has been worn perfectly smooth. ‘The limestone is unchanged at its junction with the igneous rock, and incloses within it pebbles of the lava*.
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
some which he obtained from the same localities, but I have met with no zoolo- gists who could name the species.
* This locality is described by Professor Hoffmann, Archiv fir Mineralogie, &c. Berlin, 1831,
—— |
Ch, VI] VOLCANIC ROCKS—VAL DI NOTO. 69
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 amygda- loid, wacke, and prismatic basalt, intersecting the limestone at the bottom of the hollow, called Gozzo degli Martiri, below Melilli.
Dikes,x—Dikes of vesicular and amygdaloidal lava are also seen traversing peperino, west of Palagonia, near a mill by the road side.
Horizontal section of Dikes near Palagonia.
a, Lava, b, Peperino, consisting of volcanic sand, mixed with fragments of lava and : of limestone.
In this case we may suppose the peperino to have resulted from showers of volcanic sand and scorie, together with frag- ments of limestone thrown out by a submarine explosion, similar to that which lately gave rise to the volcanic island off Sciacca. When the mass was, to a certain degree, consoli- dated, it may have been rent open, so that the lava ascended through fissures, the walls of which were perfectly even and pa- rallel. After the melted matter that filled the rent had cooled down, it must have been fractured and shifted horizontally by a lateral movement.
In the second figure, No.7, the lava has more the appear- ance ofa vein which forced its way through the peperino, avail- ing itself, perhaps, of a slight passage opened by rents caused by earthquakes. Some of the pores of the lava, in these dikes, are empty, while others are filled with carbonate of lime.
70 NEWER PLIOCENE PERIOD, [Ch VI.
The annexed diagrams (Nos. 6 and 7) represent a ground plan of the rocks as they are exposed to view on a horizontal surface. We think it highly probable that similar appear- ances 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 superincum- bent mass of ejected fragments has been removed by denuda- tion, 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,
On the summit of the limestone platform of the Val di Noto, I more than once saw analogous dikes, not only of lava but of volcanic tuff, rising vertically through the horizontal strata, and having no connexion with any igneous masses now appa- rent on the surface. In regard to the dikes of tuff or peperino, we may suppose them to have been open fissures at the bottom of the sea, into which volcanic sand and scoriz were drifted by a current.
Tuffs and Peperinos.—In the hill of Novera, between Viz- zini and Militelli, a mass of limestone, horizontally stratified, comes in contact with inclined strata of tuff (see diagram No.8),
A, Limestone. aa, Calcareous breccia with fragments of lava, b, Black tuff, ce, Tuff.
while a mixed calcareous and volcanic breccia, a a, supports the inclined layers of tuff, c. The vertical fissure, b b, is filled with volcanic sand of a different colour. An inspection of this section will convince the reader that the limestone must have been greatly dislocated during the time that the submarine eruptions were taking place.
At the town of Vizzini, a dike of lava intersects the argilla- ceous strata, and converts them into siliceous schist, which has
Ch. VI.J VOLCANIC TUFFS AND PEPERINOS, 71
been contorted and shivered into an immense number of frag- ments,
We have stated that the beds of limestone, clay, and sand, in the Val di Noto, are often partially intermixed with volcanic ejections, such as may have been showered down into the sea during eruptions, or may have been swept by rivers from the land. When the volcanic matter predominates, these com- pound rocks constitute the peperinos of the Italian minera- logists, some of which are highly calcareous, full of shells, and extremely hard, being capable of a high polish like marble. In some parts of the Val di Noto they are variously mottled with spots of red and yellow, and contain small angular frag- ments, similar to the lapilli thrown from volcanos.
It is recorded that, during the late eruption off the southern coast of Sicily, opposite Sciacca, the sea was in a state of violent ebullition, and filled, for several weeks continuously, with red or chocolate-coloured mud, consisting of finely-comminuted scoriz. During this period, it is clear that the waves and cur- rents that have since had power to sweep away the island, and disperse its materials far and wide oyer the bed of the sea, must with still greater ease have carried to vast distances the fine red mud, which was seen boiling up from the bottom, so that it may have entered largely into the composition of modern peperinos.
Professor Hoffmann relates that, during the eruption (June, 1831), the surface of the sea was strewed over, at the distance of thirty miles from the new volcano, with so dense a covering of scoriz, that the fishermen were obliged to part it with their oars, in order to propel their boats through the water. It is, therefore, quite consistent with analogy, that we should find the ancient tuffs and peperinos so much more generally dis- tributed than the submarine lavas.
In the road which leads from Palagonia to Lago Naftia, and at the distance of about a mile and a half from the former place, there is a small pass where the hills, on both sides, consist
of a calcareous grit, intermixed with some grains of volcanic sand,
72 NEWER PLIOCENE PERIOD. [Ch. VI.
No. 9.
Section of calcareous grit and peperino, east of Palagonia. South side of pass. Fertical height about thirly feet.
No, 10.
Section of the sume beds on the north side of the pass.
The disposition of the strata, on both sides of the pass, is most singular, and remarkably well exposed, as the harder layers have resisted the weathering of the atmosphere and project in relief. ‘The sections exhibited on both sides of the pass are nearly vertical, and do not exactly correspond, as will be seen in the annexed diagrams (Nos. 9 and 10). It is somewhat difficult to conceive in what manner this arrangement of the layers was occasioned, but we may, perhaps, suppose it to have arisen from the throwing down of calcareous sand and volcanic matter, upon steep slanting banks at the bottom of the sea, in which case they might have accumulated at various angles of between thirty and fifty degrees, as may be frequently seen in the sections of voleanic cones in Ischia and elsewhere. 'The denuding power of the waves may, then, have cut off the upper
Ch. VI] SICILY—VAL DI NOTO. 73
portion of these banks, so that nearly horizontal layers may have been superimposed unconformably, after which another bank may have been formed in a similar manner to the first.
Volcanic conglomerates.—In the Val di Noto we sometimes meet with conglomerates entirely composed of volcanic pebbles. They usually occur in the neighbourhood of masses of lava, and may, perhaps, have been the shingle produced by the wasting cliffs of small islands in a volcanic archipelago. ‘The formation of similar beds of volcanic pebbles may now be seen in progress on the beach north of Catania, where the waves are undermining one of the modern lavas of Etna; and the same may also be seen on the shores of Ischia.
Proofs of gradual accwmulation.—In one part of the great limestone formation near Lentini, I found some imbedded vol- canic pebbles, covered with full-grown serpule, supplying a beautiful proof of a considerable interval of time having elapsed between the rounding of these pebbles and their inclosure in a solid stratum. I also observed, not far from Vizzini, a very striking illustration of the length of the intervals which occa- sionally separated the flows of distinct lava-currents. A bed of oysters, perfectly identifiable with our common eatable species, no less than twenty feet in thickness, is there seen resting upon a current of basaltic lava; upon the oyster-bed again is super- imposed a second mass of lava, together with tuff or peperino. Near Galieri, not far from the same locality, a horizontal bed, about a foot and a half in thickness, composed entirely of a common Mediterranean coral (Caryophyllia cespitosa, Lam.), is also seen in the midst of the same series of alternating igneous and aqueous formations. 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.
Dip and direction.— The disturbance which the newer Pliocene strata haye undergone in Sicily, subsequent to their deposition, differs greatly in different places; in general, however, the beds are nearly horizontal, and are not often
74 NEWER PLIOCENE PERIOD. [Ch. VI.
highly inclined. The calcareous schists, on which part of the town of Lentini is built, are much fractured, and dip at an angle of twenty-five degrees to the north-west. In some of the valleys in the neighbourhood an anticlinal dip is seen, the beds on one side being inclined to the north-west, and on the other to the south-east.
Throughout a considerable part of Sicily which I examined, the dips of the tertiary strata were north-east and south-west ; as, for example, in the district included between Terranuova, Girgenti, Caltanisetta, and Piazza, where there are several parallel lines, or ridges of elevation, which run north-west and south-east.
—~ =} Cr
CHAPTER VII.
Marine and volcanic formations at the base of Htna—Their connexion with the strata of the Val di Noto—Bay of Trezza—Cyclopian isles—Fossil shells of recent species—Basalt and altered rocks in the Isle of Cyclops—Submarine lavas of the Bay of Trezza not currents from Etna—Internal structure of the cone of Etna—Val di Calanna—Val del Bove not an ancient crater—lIts preci- pices intersected by countless dikes—Scenery of the Val del Bove—Form, composition, and origin of the dikes—Lavas and breccias intersected by them.
MARINE AND VOLCANIC FORMATIONS AT THE BASE OF ETNA,
Tur phenomena considered in the last chapter suggest many theoretical views of the highest interest in Geology; but before we enter upon these topics we are desirous of describing some formations in Valdemone, which are analogous to those of the Val di Noto, and to point out the relation of such rocks to the modern lavas of Etna.
If the traveller passes along the table-land, formed by the great limestone of the Val di Noto, until it terminates suddenly near Primosole, he there sees the plain of Catania at his feet,
No. 11.
Ve, ae ; Se TE Miinardo SS ie Sy ee Licadiag yr
View of Etna from the summit of the limestone platform of Primosole.
a, Highest cone. 6, Montagnuola, ec, Monte Minardo, with smaller lateral cones above. d, Town of Licodiadei Monaci. e, Marine formation called creta, argillaceous and sandy beds with a few shells, and associated volcanic rocks, J; Escarpment of stratified subaqueous volcanic tuff, &c., north-west of Catania. g, Town of Catania. h, i, Dotted line expressing the highest boundary along which the marine strata are occasionally seen, &, Plain of Catania. 7, Lime- stone platform of Primosole of the newer Pliocene. m, La Motta di Catania,
"6 NEWER PLIOCENE PERIOD. [Ch. VII.
and before him, to the north, the cone of Etna (see diagram No. 11). At the base of the cone he beholds a low line of hills e, e (No. 11), formed of clays and marls, associated with yellowish sand, similar to the formation provincially termed ‘Creta,’ in various parts of Sicily.
This marine formation, which is composed partly of volcanic and partly of sedimentary rocks, is seen to underlie the modern lavas of Etna. ‘To what extent it forms the base of the moun- tain cannot be observed, for want of sections of the lower part of the cone, but the marine sub-Etnean beds are not observed to rise to a greater elevation than eight hundred, or, at the utmost, one thousand feet above the level of the sea. We should remind the reader, that the annexed drawing is not a section, but an outline view of Etna, as seen from Primosole, so that the proportional height of the voleanic cone, which is, in reality, ten times greater than that of the hills of « Creta,’ at its base, is not represented, the summit of the cone being ten or twelve miles more distant from ‘the plain of Catania, than Licodia.
Connexion of the sub-Etnean strata with those of the Val di Noto.—T hese marine strata are found both on the southern and eastern foot of Kitna, and it is impossible not to infer that they belong to the inferior argillaceous series of the Val di Noto, which they resemble both in mineral and organic characters. In one locality they appear on the opposite sides of the Valley of the Simeto, covered on the north by the lavas of Etna, and on the south by the Val di Noto limestone.
Val di Noto. No, 12, Kina,
a a Section from Paternd by Lago di Naftia to Palagonia.
a, Plain of theSimeto. 6, Base of the cone of Etna, composed of modern lavas. c, Limestone of the Val di Noto. d, Clay, sand, and associated submarine vol- canic rocks.
If in the country adjacent to the Lago di Naftia, through
Ch. VIL] SUB-ETNEAN FORMATIONS. 77 which the annexed section is drawn, and in several other dis- tricts where the < creta’ prevails, together with associated sub- g, a vol- cano should now burst forth, and give rise to a great cone, the
marine lavas, and where there is no limestone cappin
position of such a cone would exactly correspond to that of the modern Etna, with relation to the rocks on which it rests.
Southern base of Etna.—The marine strata of clay and sand already alluded to, alternate in thin layers at the southern base of Etna, sometimes attaining a thickness of three hundred feet, or more, without any intermixture of volcanic matter. Crystals of selenite are dispersed through the clay, accompanied by a few shells, almost entirely of recent Mediterranean species. This formation of blue marl and yellow sand greatly resembles in character that of the Italian Subapennine beds, and, like them, often presents a surface denuded of vegetation, in con- sequence of the action of the rains on soft incoherent materials.
In travelling by Paternd, Misterbianco, and La Motta, we pass through deep narrow valleys excavated through these beds, which are sometimes capped, as at La Motta, by columnar basalt, accompanied by strata of tuff and volcanic conglome- rate. (Diagram No. 13.)
No, 13.
La Motta near Catania,
The latter rock is composed of rolled masses of basalt, which may either have originated when first the lava was produced in a voleanic archipelago, or subsequently when the whole coun- try was rising from beneath the level of the sea. Its occur- rence in this situation is striking, as not a single pebble can be
Wie} NEWER PLIOCENE PERIOD. [ Ch. VII.
observed in the entire thickness of subjacent beds of sand and clay.
The dip of the marine strata, at the base of Etna, is by no means uniform ; on the eastern side, for example, they are some- times inclined towards the sea, and at others towards the moun- tain. Near the aqueduct at Aderno, on the southern side, I observed two sections, in quarries not far distant from each other, where beds of clay and yellow sand dipped, in one locality, at an angle of forty-five degrees to the east-south-east, and in the other at a much higher inclination in the opposite direction. These facts would be of small interest, if an attempt had not been made to represent these mixed marine and volcanic de- posits which encircle part of the base of Etna, as the outer margin of a so-called ‘ elevation crater*.’
Near Catania the marine formation, consisting chiefly of volcanic tuff thinly laminated, terminates in a steep inland cliff, or escarpment, which is from six hundred to eight hundred feet in height. A low flat, composed of recent lava and volcanic sand, intervenes between the sea and the base of this escarp- ment, which may be well seen at Fasano. (/, diagram No.11.)
Eastern side of Eina—Bay of Trezza.—Proceeding north- wards from Catania, we have opportunities of examining the same sub-Etnean formations laid open more distinctly in the modern sea cliffs, especially in the Bay of Trezza and in the Cyclopian islands (Dei Faraglioni), which may be regarded as the extremity of a promontory severed from the main Jand. Numerous are the proofs of submarine eruptions of high an- tiquity in this spot, where the argillaceous and sandy beds have been invaded and intersected by lava, and where those peculiar tufaceous breccias eccur which result from ejections of fragmen- tary matter, projected from a volcanic vent. I observed many angular and hardened fragments of laminated clay (creta), in different states of alteration, between La Trezza and Nizzitta, and in the hills above Aci Castello, a town on the main land contiguous to the Cyclopian isles, which could not be mistaken
* See vol, i. chap, xxii,
Ch, VIL] SICILY—CYCLOPIAN ISLES. 79
by one familiar with Somma and the minor cones of Ischia, for anything but masses thrown out by voleanicexplosions. From the tuffs and marls of this district I collected a great variety of marine shells*, almost all of which have been identified with species now inhabiting the Mediteranean, and, for the most part, now frequent on the coast immediately adjacent. Some few of these fossil shells retain part of their colour, which is the same as in their living analogues.
The largest of the Cyclopian islets, or rather rocks, is distant two hundred yards from the land, and is only three hundred yards in circumference, and about two hundred feet in height. The summit and northern sides are formed of a mass of strati- fied marl (creta), the laminze of which are occasionally subdi- vided by thin arenaceous layers. These strata rest on a mass of columnar lava (see wood-cut, No. 14)+, which appears to have forced itself into, and to have heaved up the stratified mass,
No, 14.
oll es ag S| cmt
View of the Isle of Cyclops in the Bay of Trezza.
* See, in Appendix Wo. I1,, a list, by M. Deshayes, of sixty-five species, which I procured from the hills called Monte Cavalaccio, Rocca di Ferro, and Rocca di Bempolere (or Borgia). f This cut is from an original drawing by my friend Capt. W. H. Smyth, R,N,
SO NEWER PLIOCENE PERIOD. [Ch. VII,
This theory of the intrusion of the basalt is confirmed by the fact, that in some places the clay has been greatly altered, and hardened by the action of heat, and occasionally contorted in the most extraordinary manner, the lamination not having been obliterated, but, on the contrary, rendered much more con- spicuous by the indurating process.
The annexed wood-cut (No. 15) is a careful representation of a portion of the altered rock, a few feet square, where the alternate thin laminze of sand and clay have put on the appear- ance which we often observe in some of the most contorted of the primary schists. |
No. 15,
Contortions in the newer Pliocene strata, Isle of Cyclops.
A great fissure, running from east to west, nearly divides the island into two parts, and lays open its internal structure. In the section thus exhibited, a dike of lava is seen, first cut- ting through an older mass of lava, and then penetrating the superincumbent tertiary strata. In one locality, the lava rami- fies and terminates in thin veins, from a few feet to a few inches in thickness (see diagram No. 16).
Ch. VIL] CYCLOPIAN ISLES, 81
No. 16.
Newer Pliocene strata invaded by lava, Isle of Cyclops (horizontal section).
a, Lava. 6, laminated clay and sand. cc, the same altered.
The arenaceous laminze are much hardened at the point of con- tact, 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, show- ing 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 con- tiguous sedimentary strata.
Lavas af the Cyclopian Isles not currents from Etna.—The phenomena of the Bay of Trezza are very important, for it is evident that the submarine lavas were produced by eruptions on the spot, an inference which follows not only from the pre- sence of dikes and veins, but from those tuffs above Castello @’Aci, which contain angular fragments of hardened marl, evi-
dently thrown up, together with the sand and scorize, by volcanic Vor, IIT, G
82 NEWER PLIOCENE PERIOD. [Ch, VII.
explosions. We may, therefore, suppose this volcanic action to have been as independent of the modern vents of Etna, as that which gave rise to the analogous formations in the Val di Noto. It is quite evident that the lavas of the Cyclopian isles are not the lower extremities of currents which flowed down from the highest crater of Etna, or from the region where lateral eruptions are now frequent,—lavas which, after entering the sea, were afterwards upraised into their present position. It is more probable that the basalts of the Bay of Trezza, and those along the southern foot of Etna, at La Motta, Aderno, Paternd, Licodia, and other places, originated in the same sea in which the eruptions of the Val di Noto took place.
There are, however, as we have observed, no sections to prove that the central and oldest parts of Etna repose on similar submarine formations. The modern lavas of the volcano are continually extending their area, and covering, from time to time, a larger portion of the marine strata; but we know not where this operation commenced, so that we cannot demonstrate the posteriority of the whole cone to these newer Pliocene Strata.
We might imagine that when the volcanos of the Val di Noto were in activity, and when the eruptions of the Bay of Trezza were taking place, Etna already existed as a volcano, the upper part only of the cone projecting above the level of the waters, as in the case of Stromboli at present. By such an hypothesis, we might refer the origin of the older part of Etna to the same period as that of the sedimentary strata and vol- canic rocks of the Val di Noto.
But, for our own part, we see no grounds for inclining to such a theory, since we must admit that a sufficient series of ages has elapsed since the limestone of the Val di Noto was de- posited, to allow the same to be elevated to the height of from two thousand to three thousand feet, in which case there may also have been sufficient time for the growth of a volcanic pile like Etna, since the newer Pliocene strata now seen at the base of the volcano originated,
Ch, VII.] ETNA, 83
INTERNAL STRUCTURE OF THE CONE OF ETNA,
In our first volume we merely described that part of Etna which has been formed during the historical era; an insigni- ficant portion of the whole mass. Nearly all the remainder may be referred to the tertiary period immediately antecedent to the recent epoch. We before stated, that the great cone is,
in general, of a very symmetrical form, but is broken, on its eastern side, by a deep valley, called the Val del Bove*, which, No. 17.
Great valley on the east side of Etna.
a, highest cone. 6, Montagnuola. c, Head of Val del Bove. d, d, Serre del Solfizio. e, Zaffarana. jf, One of the lateral cones. g, Monti Rossi. commencing near the summit of the mountain, descends into the woody region, and is then continued, on one side, by a second and narrower valley, called the Val’di Galanna. Below the latter another, named the Val di St. Giacomo, begins,—a long