UNIVERSITY OF CALIFORNIA. GIFT OF HENRY DOUGLASS BACON. 1877. Accessions No. /$%-& Shelf No, . ., *v V. f VV* v Vv v --v-:-Vv V -Kuwu.. y. - .-::- ,, * *V^W - w ./-',, - n %v . u^ .A-rtsrE D:N y;e D PROFESSOR OF GEOLOGX INT KING'S COLLEGE. LOKDOJT. TTOJ. .2. V o THB UUIVERSITl EDITION. 1852. TKD FOR LOTOWAS-, BROWN, GE.EEN, AND -LOSCtffKS. PAIERSOSIEB. RO^ V.I PREFACE. IN revising this Edition, I have employed, as the basis of classification for successive geological periods, those great natural associations of the forms of life which are expressed by the terms Palaeozoic, Mesozoic, and Cainozoic. In subdivid- ing the great classes of strata which were formed in these successive " life-periods," no material change has been found necessary, except in regard to the Palaeozoic formations. Among these a much improved distribution has been effected, by labours commenced in Britain, in 1831, by Murchison and Sedgwick, and since extended by these and other geologists over great part of the globe. If some of the questions which these researches have raised are as yet only provisionally answered, they are placed in a form which may probably lead to sound and comprehensive solutions. (Vol. I., Palaeozoic Strata.) Among the many objects of geological inquiry which have been successfully prosecuted of late years, the following must be distinguished : The beautiful structure of slate has acquired VOL. i. A IV PREFACE. more accurate expression, as a problem, by some laws of phenomena which my own observations, and those of Mr. Sharpe, have added to the well- known determinations of Sedgwick ; and Mr. Hopkins, ever ready to give a mathematical form to geological truth, has shown how mechanical theory desires to look at this problem. (Vol. II. p. Ill, et seq.) The dispersion of detritus from the mountains of Scandinavia, Britain, and the Alps has undergone critical re-examination, with reference to the change of level of the land, action of great waves of trans- lation, variation of climate, extension of glaciers, and transport of icebergs. The separate labours of Murchison, Hopkins, Agassiz, J. Forbes, Darwin, and others, have thrown on this complicated sub- ject new, varied, and effective illumination. (Vol. II. p. 11, et seq.) I must not be prevented by the share which I have had in the Memoirs of the Geological Survey of Great Britain, from referring to this publication, and the Maps which it illustrates, for some valuable additions which have been made to British and Irish geology. Under the guidance of De la Beche, Mr. Ramsay and my other friends have cleared away from Wales whatever obscurity re- mained, after the strong light thrown on it for so many years by Sedgwick. Professor E. Forbes, now in charge of the Palaeontological department of this Survey, has brought to the philosophical study of its rich collections matured views on the distri- bution of marine life views founded on assiduous dredgings round the British shores, and an ad- mirable survey of the depths of the JEgean. (Vol. I. p. 326 335.) PREFACE. V Of special discoveries, geology and palaeontology are always prolific. Perhaps no more striking warning of the changes which these may yet de- mand in geological hypothesis can be given than MantelTs unexpected Lacertian from the old red sandstone of Scotland. (Vol. L, Palaeozoic Strata.) Since the former publication of these volumes, the favour of sovereigns has been extended to three of the most loved and honoured names in English geology. We have not found it possible to alter, in all our stereotyped pages, their social designations, but this can never be misinterpreted, Geology has but one example each of De la Beche, Lyell, and Murchison. St. Mary's Lodge, York, 1 852. CONTENTS. CHAPTER I. INTRODUCTORY VIEWS. Page Objects of Geological Science - - - 1 Means of Geological Investigation - - - - G Scale of Geological Time - - -8 Series of Stratified Rocks - - - - 9 Lapse of Time inferred from the Nature of the Series of Rocks - 10 Antiquity of the Surface - - -11 Nature of the Scale of Time - - 12 Terms of the Scale of Geological Time - 12 Series of Terms on the Scale of Geological Time - - 14 Interruptions in the Series of Time - - 16 Length of the Scale of Time - - 17 Means of Investigation of Facts - - 18 Means of Interpretation of Phenomena - 20 CHAP. II. GENERAL REASONINGS CONCERNING THE SUBSTANCE OF THE GLOBE. Chemical Data as to the exterior Parts of the Earth - 23 Proportions per cent, of Oxygen in Earths, Minerals, and Rocks - 24 Physical Data as to the interior Constitution of the Earth - - 26 Mass of the Globe, whence derived - - 28 CHAP. III. GENERAL TRUTHS CONCERNING THE STRUCTURE OF THE EXTERNAL PARTS OF THE GLOBE. Structure of the external Parts of the Globe - - 33 Forms of Rock Masses - - 35 Position of Rocks. Declination of Strata - - 36 Local Declinations and unusual Positions of Strata - .39 Faults - . 40 Extent and Frequency of Faults - - 42 Relation of Faults, Mineral Veins, Dikes, &c. to the great Lines of disturbed Rocks - - - - . 44 CONTENTS. Vli Page Structure of the Globe continued. Origin of stratified and unstratified Rocks - - 45 Relative Periods of disturbed Stratification - - - 49 CHAP. IV. SERIES OF STRATIFIED ROCKS. Sections and Maps of Strata - ... 53 Table of British stratified Deposits - - 54 Varieties of Stratification - - - - - 59 Divisional Structures of Rocks - - 62 Geographical Relations of Joints - 65 Cleavage - .... 67 CHAP. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. Fossil Plants - - - - - - 69 Table of their Geological Distribution - - - 73 Fossil Zoophyta - 73 Table of certain Groups - - - - - 76 Fossil Mollusca .... -77 Table of proportionate Number of Species at different Geological Periods - - - 80 Table of proportionate Number of Species in the different Orders or Classes of Mollusca in different Geological Periods - 81 Table of Genera containing many living Species of Gasteropoda - 82 Table of Genera containing many Fossil Species of Conchifera - 83 Table of Genera of Cephalopoda - - 83 Table of Subgenera of Ammonites - - 84 Articulated Animals - - - - - - 84 Table of Crustacea - - - 85 Fossil Fishes - - 86 Agassiz's. Classification of Fishes - - 88 Table "- - - - - - - 90 Fossil Reptiles - - 91 Owen's System of Fossil Saurians - - - - 92 Fossil Birds - - - - - - - 95 Fossil Mammalia - - - - 95 Marsupial of Stonesfield - - - - - 97 Table of Mammalia - ... - 99 General Considerations - - - 100 CHAP. VI. HISTORICAL VIEW OF THE STRATIFIED ROCKS IN THE CRCST OF THE EARTH. Introductory Remarks - - 107 Granitic Basis of the Crust of the Earth - - - -108 Vlll CONTENTS. Page Granite Veins - - - 109 Metamorphism of Rocks - 1 10 HYPOZOIC STRATA. Gneiss and Mica Schist System - - 111 Composition - - - 111 Lamination - - - -114 Stratification - - 115 Succession and Thickness of its Strata - -117 Organic Life - - - - - 118 Extent of Country occupied by - - 119 Physical Geography - -120 Igneous Rocks . - - 121 General Inference concerning - - - 1 22 PALEOZOIC STRATA. Lower Cambrian System of Sedgwick - 124 Composition - - 125 Structure ... - ]26 Cleavage - - 12$ Succession of its Strata - - - - 128 i Organic Remains - - - - - 131 Geographical Extent - - 132 Physical Geography - - 133 Igneous Rocks - - - - - 134 Silurian System of Murchison - - - 136 Composition - - 136 Structure - - 136 Succession and Thickness of its Strata - -133 Table of the Strata - - - 139 Organic Remains - - 140 Tables of ditto - - 141144 Figures of ditto - - - 145 Geographical Extent - - - - - 146 Figure exhibiting ditto - - 147 Physical Geography . ... 148 Igneous Rocks - ... - 148 Mineral Veins - . - 149 Close of the Silurian Period, and ensuing Disturbances of the Crust of the Globe - - -149 Figures exhibiting ditto - - 151.153 Devonian System .... - 154 Composition - - - - - 154 Organic Remains - - 156 Tables exhibiting ditto . - - - 1 57 Figures of ditto - - 158,159 Geographical Extent - - 160 Carboniferous System - - 162 Composition ----,- 162 Structure - - - - . - 160 Figures of ditto .... 164, 165 Succession and Thickness of its Strata - - -166 CONTENTS. ix PALAEOZOIC STRATA Carboniferous System continued. Organic Remains - - - . -170 Figures of ditto - 171,173,175 Physical Geography - _ 175 Geographical Extent - - . - 177 Igneous Rocks - - - - . _ ig4 General View of the Circumstances under which the Carboni- ferous System was deposited - - 186 Extent of British Coal Fields under superior Strata Dis- turbances of the Carboniferous System - -193 Figures illustrating ditto ... 194^ 195 Permian System (Magnesian Limestone Series of England) - 195 Composition - - . ]% Structure of its Deposition - - - 197 Divisional Planes - - - 197 Succession and Thickness of its Strata - . 197 Organic Remains - . . igg Table of ditto - - - .199 Figures of ditto ... . 200 Table of Fauna of - - 201 Geographical Extent - .202 MBSOZOIC STRATA. Triassic System (Part of Saliferotu of former Editions) . 203 Composition - - - 203 Organic Remains ... 205 Geographical Extent - - - - -206 Physical Geography - _ 208 Igneous Rocks - 208 Origin and Aggregation of the Materials of the Triassic and Permian Systems ..... 209 Origin of Rock Salt and Gypsum - - 210 Oolitic System ... - - 214 Composition - 214 Structure - - - . . -217 Divisional Planes - 217 Series of Strata - - - - -218 Table exhibiting ditto - - -219 Figures illustrating ditto - - 220, 221 Organic Remains - - - 222 Tables of ditto .... 222, 224 Figures of ditto - - 224, 225 Geographical Extent - - 226 Figure of ditto ~ - - - - -229 Physical Geography - - i30 Figure illustrating ditto - - 230 General Review of the System - - 231 Cretaceous System ..... 233 Composition ... . 233 Stratification - - - - - - 235 Succession of its Strata ----- 236 X CONTENTS. Page MESOZOIC STRATA Cretaceous System continued. Organic Remains - - 237 Figures of ditto - 238240 Geographical Extent ' - 240 Igneous Rocks - - 243 Close of the Secondary Period, and ensuing Disturbances of the Crust of the Globe - - -244 CAINOZOIC OR TERTIARY STRATA. (Supercretaceous Deposits, #c.) -249 Composition - 250 Structure and Stratification - - 251 Divisional Planes - - 252 Succession and Thickness of its Strata - 252 Freshwater Formations ..... 254 Geographical Extent and Physical Geography - 260 Organic Remains --...- 264 In Marine Deposits - - 272 In "Lacustrine and Lignitic Deposits of known Era - - 273 In Lacustrine Deposits of doubtful Era ... 275 Figures of ditto - - 275 Disturbing Movements during and after the Tertiary Period - 276 POST-TERTIARY AND MODERN STRATA (including Pleistocene and other Deposits') View of the Relation of these to Tertiary Strata - - 278 Classification of - - - 281 Detrital Deposits - -281 Erratic Block Group - - 283 Ossiferous Gravel, Pebbly Clay, Sand, &c. - 298 Ossiferous Caves and Fissures - - - - 303 General Table of Vertebral Remains in Post-Tertiary Accu- mulations - " 304 Description of Caverns - -310 General Considerations on " Diluvial " Phenomena - 316 Zoological and Botanical Character of" Diluvial " Period - 319 Ancient Marine Deposits - - - - 321 Raised Beaches - - - 321 Change of Level of Land adjoining the Baltic - - 324 Marine Deposits in Progress - - 329 Coral Reefs ... 329 Mr. Stutchbury's Views of - - 330 Mr. Darwin, on Coral Islands . . - 333 Shell Beds - - 336 Classes of Shells - - - - -340 Banks of Sand, Clay, Gravel, &c. - - - 341 TREATISE ON GEOLOGY. I CHAPTER I. INTRODUCTORY VIEW OF THE OBJECTS OF GEOLOGICAL SCIENCE, AND THE MEANS FOR INVESTIGATING AND INTERPRETING THE NATURAL HISTOBY OF THE EARTH. 1. OBJECTS OF GEOLOGICAL SCIENCE. THE phenomena of geology are so various and compli- cated, that hardly any class of writers has left them wholly untouched; and the aspect of this science changes according to the peculiar object of different inquirers. Strabo, accustomed to enlarged views of physical geo- graphy, spoke of the existing forms of the surface of a part of Asia Minor, in reference to the ancient revo- lutions of nature which had occasioned them, and thus appeared to include geology among the tributaries to physical geography. Werner, habituated to minute discrimination of minerals and rocks, regarded the science, which sought for philosophical explanations of these differences, as a branch of mineralogy ; while in Button's comprehensive mind geology applied itself to VOL. I. B 2 A TREATISE ON GEOLOGY. all the variable conditions of our planet, in all ascer- tainable or conceivable times, past, present, and to come. Nor is there less diversity of theme among the zeal- ous students of geology. For some regard, as the prin- cipal object of their inquiries, the constitution of rocks and minerals, the chemical effects which are traceable in the earth, and thus merely enlarge the limits of mineralogy ; others turn their whole energy to the de- velopment of the history of fossil plants and animals, and thus constitute the interesting branch of organic geology*; while a third class watches the relation of the phenomena established by geologists to general statical and dynamical truths, and thus strives to found the new and attractive study of physical geology. Nor is there in this apparently imperfect apprehension of the extensive range of geological inquiry much to be reprehended. It is desirable that as many roads as possible should be opened toward the attainment of the varied truths which must be collected, by insulated ob- servers, before it can be practicable for even the most comprehensive intellect to frame a general and con- sistent view of the whole scope of this great branch of the study of nature. The natural sciences are commonly understood to include all inquiries into the history of the inorganic and vital phenomena which take place on and about the surface of the globe, and the relation of these to general terrestrial, and cosmical conditions. The problems thus proposed for discussion are sufficiently ample and di- versified to employ a very large number of observers and reasoners; they are, perhaps, inexhaustible ; yet, were they all resolved, the study of nature would not be ended ; for there would remain the inquiry, whether the present condition of nature is to be taken as a type of all her past and future states, or to be viewed as exhibiting one of many aspects, one of many gra- dations of change a temporary adjustment, not a.con- * for this branch of Geology the term Paleontology is becoming usual. CHAP. 1. OBJECTS OF THE SCIENCE. tinued equilibrium the last known term of a series whose law of variation is to be discovered. Taking up this idea of the aspects of nature, at any particular epoch of the history of the earth (since the present laws of terrestrial and cosmical phenomena were appointed), being the last term of a long series the complex effect of many anterior influences we may proceed to inquire what monuments remain in nature of any previous aspects or conditions, and from these to in- fer the nature and amount of the agencies formerly con- cerned in producing and varying them. Having ascertained the series of past changes, we may venture to speculate on the future revolutions of the face of nature, 'to which the law of variation of the agencies concerned must necessarily lead. Now, these are precisely the problems which it is the province of geology to consider. Gathering, from the labours of mineralogists, botanists, and zoologists, a knowledge of the existing species of inorganic and organic bodies; from geography, the account of the present configuration of the surface of the globe ; from general physical researches, what is known of the con- stitution of the atmosphere, the ocean, and interior of the globe, geology proceeds to inquire further, whether the mechanical, chemical, and vital phenomena, formerly exhibited on the earth, can be traced in their effects, so as to be put in comparison with those daily occurring ; whe- ther the mineral products of earlier eras of the world were identical in kind, and equal in rate of production, with the modern products of this description ; whether the plants and animals of the ancient world were of the same structure as those which now adorn its surface ; and whether the general physical conditions to which all these are correlated have always exerted the same kind and degree of influence as at present. In what- ever way these questions are answered, they inevitably lead to speculation as to future revolutions which may vary the face of the globe ; and thus geology, far from being the limited and narrow subject which B 2 4 A TREATISE ON GEOLOGY. CHAP. I. was illustrated by Werner, after the model of the Saxon mountains, is found to include, perhaps, the largest class of inquiries which has ever been ranked under one head. For, in the attempt which it makes to decipher the history of the past, and to prognosticate the future changes of our planet, it requires the aid of all the gathered knowledge of nature, interpreted by the profoundest researches of abstract science. It is not even enough to know the actual state of the earth, we must further learn the measure of momentary changes in this state ; and thus inquiries of a new order are suggested to naturalists, who are seldom aware, while investigating the problems before them, that these in- clude dynamical as well as statical determinations, and that the former are necessary to the right understanding of the latter. It has been made a reproach to geology, that, in its bold attempts to penetrate the dark veil which time has thrown over the mysteries of ancient nature, it has wandered far from its just mark, beyond the boundary of inductive philosophy and mathematical laws, into the unprofitable regions of cosmogony. Geologists have been equally blamed for stopping short of attainable truth, and declaring, upon inadequate grounds, that the earth shows no trace of a beginning, no prospect of an end. But geology is really distinct from cosmogony. In- quiries into the origin of the planetary bodies belong to one of the highest of human sciences, astronomy. Geology, far from intruding within its precincts, sup- poses the globe to be constituted as a planet moving round the sun ; takes for granted all the laws which this relation implies, and limits itself to the discovery of the strictly terrestrial phenomena which have hap- pened upon this globe under these conditions. On the other hand, it was rash and presumptuous to assert the invariable uniformity of natural causes and effects, through all past time, upon data so insufficient as those known to Dr. Hutton ; and, even if this were esta- blished, it would not be sound logic to infer that the CHAP. I. OBJECTS OP THE SCIENCE. 5 earth showed (( no traces of a beginning no prospect of an end"; because, on that matter, other evidence might have been brought to bear. But yet a candid reasoner need not greatly reprehend either the wandering of geology into cosmogony, or the too forcible acknowledgment of the incompleteness of all human research into the origin of the visible system of nature, which is contained in the much-censured language of Hutton. Neither of these errors is likely to be very injurious in science ; nor can either be justly charged with the slightest tendency to make men forget that all the arrangements of nature are but the ex- pression of the will of the Supreme Creator and Law- giver of the universe. Let us not, therefore, be checked in our inquiries into the history of the globe, by anything but the good rules of philosophising, which are essential to the right use of the intellectual strength which God has conferred upon man, to be exercised on the mighty works of nature ; and least of all let us be deterred from the pursuit of truth, by the vain and impious dread that we may go too far, and penetrate too deeply into those mysteries which, among their other uses, have this one, that they continually excite to ac- tivity the soul of man ; and, the more they are studied, lead to deeper delight and more awful contemplation of their glorious and beneficent Author. Geology, or the natural history of the earth, as a planet revolving in space round a central orb of light and heat, surrounded by an atmosphere, and partially or wholly begirt by water, includes all the phenomena produced on the land, in the sea, and within the mass of the globe, by the operation of those mechanical, chemical, electrical, and vital forces, which are termed natural agencies, from the earliest epoch of which monuments remain, down to the present hour. All variations in the proportions of land and water; all variations of level ; all changes in the combination and distribution of masses or molecules of matter, whether above, upon, qr below the surface ; all changes in the B 3 O A TREATISE ON GEOLOGY. CHAP. I. number, structure, forms, and relations of plants and animals, are to be ascertained as facts, and employed in reasoning, for tracing a general and continuous history of the physical revolutions which the earth has experi- enced since it became a planet. * In this comprehensive definition of the objects of geological science, we include its real and legitimate field of research, without interfering in the least with the independent exercise of collateral sciences. To astronomy belongs the investigation of the history of the globe, as a part of the planetary system, and the results thus reached help to correct and limit geological in- ferences. Chemistry employs itself upon the inquiry into the laws and modes of mutual action among the particles of matter, and gives its results to aid in the general history of terrestrial phenomena. It is the pro- vince of zoology and botany to arrange and interpret the facts connected with life and organisation in plants and animals ; and to these branches of knowledge geology owes immeasurable obligation. Thus the study of the ancient natural history of the earth draws help from every kind of inquiry which man can make into the actual constitution of nature, but robs none of its interest or glory ; on the contrary, by* the novelty of its discovered facts, fresh problems are presented to the cultivators of natural science, and a perpetual excite- ment is kept up, which has proved of infinite service to them all. 2. MEANS OF GEOLOGICAL INVESTIGATION. THUS ample and various are the problems clearly pro- posed in geology : in order to see how far they are de- * " Geology is principally distinguished from Natural History, inasmuch as the latter is limited to the description and classification of the pheno- mena presented by our globe in the three kingdoms of nature, whilst it is tiie business of the former to connect these phenomena with their causes." " It consists in the knowledge of the causes which have acted, and still act, upon this earth, and thus embraces all the knowledge we can gain of nature, by an attentive study of terrestrial phenomena." De Luc, Lettrti Premiere. CHAP. J. MEANS OF INVESTIGATION. 7 terminate, and capable of solution, let us survey the means of investigation placed within our power, from what sources the data are to be collected, and in what manner the methods of interpretation are to be disco- vered. In existing nature, we can examine and collate, for purposes of reasoning, three orders of data ; viz. facts relating to organic beings ; facts relating to inorganic bodies ; facts concerning physical conditions, or modes of dependence of these two classes on each other, on the general laws of matter and motion, and the arrange- ments of the solar system. In this manner, it is seen that the radiation of light and heat from the sun ; the alternation of day and night, caused by the rotation of the earth on its axis ; the variations of seasons, depend- ing on the position of its axis and on its revolution round the centre of the planetary system ; the existence of an ambient atmosphere ; the inequality of elevation of land ; the distribution of land and sea, and other cosmical and terrestrial conditions, have a distinct influence on all the arrangements of organic life, and on some of the phe- nomena of inorganic bodies. Sometimes the law of this dependence is evident ; generally the nature of it is discoverable, always the fact is capable of being satisfactorily ascertained : and thus existing nature is presented to our minds as a system of beautifully adjusted parts, which it is the highest province of the noblest intellect to contemplate in one point of view, and pourtray under the aspect of a general theory. In geology, however, the physical conditions are not known, but are to be inferred, for any particular epoch in the history of the globe, from the facts collected concerning the organic and inorganic bodies which be- longed to that era, and are indicative of the physical influences then operating : and hence arise both the difficulties and the charms of geological reasoning. The difficulties are unavoidably very great ; for, even in the acquisition of the data concerning organic and inorganic bodies, geology is often forced to be satisfied with less A TREATISE ON GEOLOGY. CHAP. I. exactness than is attainable in modern natural history. Certain shells, fishes, &c., are recognised by the geo- logist, but he may not find them of all ages ; cannot know correctly what were the limits of variation, of their magnitude, forms, habits, &c. In some important cases, he can hardly know whether particular mollusca and fishes lived in lakes, rivers, or the sea ; whether certain plants grew on land or in water. Now, as it is only on a correct knowledge of the affinities which the fossil remains of life bear to existing races, that any just inference can be founded concerning the contem- poraneous physical conditions, we see how fertile are the sources of error, and with what justice men of phi- losophic minds have endeavoured to restrain that pro- pensity to speculation which imperceptibly gets possession of the human mind, and has particularly luxuriated among the enthusiastic votaries of geology. There is less difficulty with respect to inorganic bodies, because the laws of their aggregation are such as, in many in- stances, can be tested by experiments which apply with equal exactness to the ancient and modern mineral kingdoms. Scale of Geological Time. It is further to be observed, that the very foundation of all history of geological phenomena is difficult to fix; for if it be embarrassing, even in civil history, to as- certain the relative dates of many most important oc- currences, how careful should we be in marking even the order of succession of geological phenomena of the same kind ; how diffident of our power of determining at all the lines of contemporaneity among occurrences of different nature, which happened in different regions of the globe, and under at least some difference of physical conditions ! The very first inquiry to be an- swered, then, is, what are the limits within which it is possible to determine the relative dates of geological phenomena ? For if no scale of geological time be CHAP. I. MEANS OF INVESTIGATION. 9 known, the problem of the history of the successive conditions of the globe becomes almost desperate. There is, however, at any place considered alone, a scale left us in the crust of the earth, by which to mea- sure exactly the order of antiquity among the terms of the series of organic life, and to compare the relative antiquity of these terms at different and remote places, often with perfect satisfaction, and generally within moderate limits of error. This scale is the series of stratified rocks ; and thus a great difficulty is overcome, and many of the inorganic and organic productions of older nature are capable of being arranged in the order of their successive appearance. We must, therefore, explain the nature of this fundamental scale, and illus- trate its application ; for we are, perhaps, not in a state to define the extent of its applicability. Series of Stratified Rocks. The crust of the earth is, for the most part, stratified that is to say. the most abundant of the materials whereof it is composed, are in the form of widely ex- tended and comparatively thin layers (called strata), laid one upon another, to a great numerical amount ; these strata were, beyond all question, deposited in water, because many of them contain marine or fresh water shells, fishes, corals, and other marine exuviae (and even were this not the case, the fact of the pro- duction of analogous or very similar strata beneath modern waters would justify the inference) ; therefore, the lowest were formed first, the uppermost last. To attempt proof of such a proposition would be to out- rage common sense : he who cannot supply to himself the proof that the lowest layers of sediment produced by the waters of a pond, lake, river, or ocean, were deposited before the upper ones, is incapable of appre- hending any natural truth. Yet, upon this simple and self-evident proposition rests the whole body of geological inferences which include relative time. ]0 A TREATISE ON GEOLOGY. CHAi I. That the lower strata are the oldest, the uppermost the most recent, is a truth independent of all circum- stances but the fact of the rocks being stratified and of aqueous origin : but what is the interval of time ? Whether it was long or short a day or a thousand years how much older one rock is than another if ascertainable at all, cannot be known without adding to the fact of the order of succession a number of other circumstances, characteristic not merely of succes- sion, but of duration. Lapse of Time inferred from the nature of the Series of Rocks. The circumstances \vhich help to define our notions of the time elapsed in the formation of the crust of the globe,, to translate, as it were, the symbolical notation of the geological scale of time into intelligible periods, having relation to the duration of the human race, are various, and all concur in impressing the mind of a candid reasoner with evergrowing convictions of the immense antiquity of the globe ; the many long periods of geological changes which it has experienced before arriving at the state when, in the magnificent language of holy writ, it was said to be expressly re-arranged for the creation of man, and the present system of ter- raqueous conditions. The historic records of man's residence on the earth are, for most parts of the globe, utterly incomplete ; so that, but for the Jewish Scriptures and other documents of eastern nations, we should be in danger of attributing to the human race an origin too recent by thousands of years. Now, as all historic records end, for each country, with the surface, terminate at some point of man's history posterior to the preparation of that tract for his residence, we see how far more ancient than the historic date of the human race is the series of productions which lie below the surface. The limit of least anti- quity of the scale of geological time is in every country CHAP. I. MEANS OF INVESTIGATION*. 1 1 beyond the date of the present surface. The series of strata is so ancient, that even its uppermost and newest term in every country is older than the race of man now existing there ; though we are not entitled to say, without further examination, that it is older than the human species generally, for it is supposable that a former race of men might have existed over an older surface of the same part of the spherical area, under older physical conditions. Antiquity of the Surface. The records and traditions of mankind, which give a few thousand years to the existence of the human species en the globe under its present physical conditions, are in some respects corroborated by geological evidence of the comparatively recent date at which atmospheric agen- cies and drainage waters began to waste the surface of the earth, under the present relations of the level of land and sea. The notices of Herodotus concerning the formation of the alluvial land in Egypt from the inun- dations of the Nile, and similar facts connected with other great rivers, combine with the elaborate argu- ments of De Luc, concerning the formation of deltas in the upper ends of lakes, instances of which abound hi every country, to show that the actual relations of the level of land and sea are, for the most part, not of so ancient a date as to be beyond comparison with the tra- ditionary dates of the antiquity of the human race. Having thus adopted as the limit of least antiquity of the scale of stratified rocks, the traditionary age of the human race, let us turn to consider the nature and meaning of the scale itself, so as to learn its value and range in the interpretation of the phenomena which happened in earlier physical conditions of the globe. 12 A TREATISE ON GEOLOGY. Nature of the Scale of Time. The rocks composing the crust of the globe are for the most part stratified ; but exceptions occur, especi- ally in mountainous countries : the series of strata is commonly definite, or composed of a certain number of simple terms, i. e., layers, each of a particular quality, in every small district ; considered with reference to very large districts, it is found that, by grouping together the layers in natural assemblages, the series of these compound terms is also definite : finally, on comparing the series of even remote tracts, the compound terms themselves combine into groups, which are ranged in the same definite order whenever present together ; for in some countries whole groups are absent, and others interpolated in the series. It is clear, therefore, that amidst all the causes of local diversity in the series of strata, some general influences have prevailed to give a determinate analogy of character to the resulting suc- cession of stratified rocks in all parts of the globe If we can search out the causes of local diversity and general agreement, and thus ascertain the law of the geological scale of time, nothing will remain to be done but the comparison of this law with the analogous oper- ations of modern nature, in order to attain the most precise account of geological time which the human mind can reach. Terms of the Scale of Geological Time. The different strata which are terms of the series cr spaces on the scale of geological time are of various mineral qualities arenaceous, argillaceous, calcareous or composed of mixtures of these in unequal propor- tions. In the substance of many of them, peculiar minerals, as mica, red oxide of iron, silicate of iron, &c., are diffused ; they differ in hardness, granulation, crys- talline structure, and many other circumstances. Every CHAP. I. MEANS OF INVESTIGATION. 13 one of these differences had its cause in some peculiar contemporaneous physical condition ; these strata suc- ceed one another in a settled order over the same area ; were deposited beneath the water on the same part of the bed of the sea ; it is certain, therefore, that in and about ' the same regions of the globe the physical conditions varied thousands of times during the formation of the series of strata. The mere inspection of one stratified rock composed of several analogous beds, gives a strong impression of elapsed time ; but when we see thousands of beds of different qualities, the mind is opened to the further evidence which geologists bring on this import- ant subject.* Many, indeed most, of these strata contain the remains of animals which were living in the water at or before the time of the deposition of the rocks, and several are full of plants which were swept down from the dry land on which they grew into the ancient ocean, and then entombed in the strata at that epoch in progress of formation. By methods of undoubted accuracy, the length of life of some of these buried tre^s is ascertained to have been considerable that they lived a hundred years for instance; the shells entombed often show the growth from young to old during the formation of one or a few thin layers of rock. Thus, in many in- stances, we are forced to suppose the lapse of a period of years during the accumulation of even one thin bed of stone. And even if this conclusion were not circum- stantially exact, if the shells of all ages, living together in the sea, were buried in one bed by one action, or * The entire mass of our continents is composed of strata, similar in this respect to the regular courses of stones in our buildings. A succession of strata indicates a succession of time for their formation ; and the change from one species of stratum to another placed upon it, indicates a change of cause. Thus is the mass of our continents the product of successive operations, during which the producing causes have undergone successive changes. We see, moreover, that many of these strata contain the remains of animals ; and that in some successive strata these organized bodies are of different species. By this we judge that some considerable length of time was necessary for the formation of these strata, both on account of the succession of individuals of the same species of animals in some of thenij and also on account of the change of species in the same.places where the former are buried. De Luc's Letters. 14 A TREATISE ON GEOLOGY. CHAP. I. even brought from small distances to be so buried, yet the inference is little altered by these admissions; for still, between the formation of certain beds, above and below those shells, their lifetime must have passed. Series of Terms on the Scale of Geological Time. But these conclusions become at once strengthened and more definite when we take into consideration the nature of the series of these terms ; each of which in- dicates the lapse of time. For, first, it is found that the terms are recurrent, so that again and again similar or analogous strata are repeated, in different combinations, proving that the physical conditions which governed these depositions of strata were in some respects of periodical occurrence, or rather subject to interruption and fluctuation, so that different combinations prevailed at different periods. If we ask, in modern nature, so uniform in the local results of the same kind, the ex- planation of this, the reply will be immediately found : those periods of*hew combinations among the physical conditions of a given region are far beyond the range of human experience. Moreover, an additional fact of great interest here comes to fortify all our inferences the organic re- mains of plants and animals which abound in the earth are not those of the tribes that now live, but of many wholly extinct, and often quite different, races dif- ferent in form and structure, and, consequently, in function and habits of life, though certainly belonging to a general system of nature founded on analogous principal conditions. Further, it is not sufficient nor correct to say, there is one living and one extinct cre- ation : the plants and animals buried in the earth belong to many distinct and successive creations, which differ among one another no less than they almost all differ from the actual forms of life. These distinct creations of former date are found buried in different parts of the series of strata ; one series of organic forms belongs to CHAP. I. MEANS OP INVESTIGATION*. 15 the lower and older strata, another to those of middle, another to those of later date. The different groups of strata, deposited in successive periods, are thus filled with distinct races of plants and animals, which lived at successive periods, and thus it is proved that in every region the land and the sea were covered and filled at successive times with new creations suited to the new physical conditions of the altered planet. This is not speculation, it is certainty. Each system or group of stratified rocks contains the remains of the plants and animals which existed at or previous to its production in. or near the water in which it was formed : it is the museum of the period, the only repository of the monuments of that age of the world. By collect- ing these, and viewing them in the order of succession in which they occur in nature, we contemplate the forms of life which have successively occupied the globe, and by comparing them, on philosophical grounds, with the creatures that now exist, we can frame conjectures more or less satisfactory as to the state of the atmo- sphere, light, heat, and other circumstances, to which their life was adapted. If we are to reason at all concerning the phenomena of nature, one of two conclusions must be adopted with reference to this subject ; either the physical conditions whereto the existence of those plants and animals was related, changed gradually and equally in obedience to some continuous law the forms of life being varied accordingly or were liable to violent interruptions or revolutions, consequent upon new circumstances, or the accumulated tension of some feeble but continuous disturbing agency. Which of these views is true, will be the subject of inquiry hereafter : for the argument as to the lapse of geological time, it is immaterial which may be preferred ; since in existing nature the rate of such physical changes, supposing them to be con- tinual, is so small, as to have caused almost no changes of organic life in several thousand years ; witness the sculptured monuments of Egyptian grandeur ; and 16 A TREATISE ON GEOLOGY. CHAP. I. violent revolutions, capable of so influencing organic life (if probable at all), require, according to what is known of the earth and planetary system, periods or in- tervals too great for the mind to comprehend. Interruptions of the Series of Time. In certain rocks we find angular fragments, or rolled pebbles, derived by mechanical action from pre-existent and pre-consolidated rocks. The Righi, in Switzerland, is composed of such conglomerate masses ; the red sandstone of Cumberland and Westmorland is full of pieces of the subjacent slaty rocks ; the sands near London are stored with rolled flints from the subjacent chalk. The fragmentary masses, thus imbedded, are often the repositories of organic remains, sometimes of portions of mineral veins, both of anterior date to the rocks now including them. Thus we see proof of the occurrence of different modes of action over the same geographical areas, and our belief in the length of time requisite for all these occurrences becomes immove- able. In general the stratified masses of the earth's crust are placed with their surfaces parallel to each other ; from which we know that during their accumulation no violent disturbance of the external parts of our planet happened in those regions to confuse the regu- larity, and alter the horizontal plane of deposition. But in particular instances this conformity of the strata is departed from, and certain (older) rocks appear in- clined at various, often steep, angles, or standing even vertical, while the more recent deposits lie level or nearly so, upon them. What renders this case of dis- turbed stratification more impressive, with respect to the lapse of time, is the occurrence of positive circum- stantial proof of the intervention of mechanical, che- mical, or vital agencies of considerable duration be- tween the elevation of the older, and the deposition of the newer strata, Thus in diag. No. 1. the inclined MEANS OF INVESTIGATION. 17 beds a of limestone were exposed to watery action, and broken up in part, so that fragments and pebbles of them are found collected into beds among the mass of later level sandy deposits 6 (Mendip Hills): and in . 2. the same inclined limestone beds a are covered by horizontal oolitic strata c; and are worn and polished on the face of junction, and penetrated into holes by boring shells, which lived in the oolitiferous sea, long after the elevation of the older rocks. (1830.) Length of the Scale of Time. The scale of geological time given by the series of stratified rocks is one of unequal parts : for it is almost certain that the deposition of a given thickness of sand- stone, was accomplished in a different time from that consumed in the production of an equal thickness of clay, limestone, coal, &c. Yet as many of the groups of strata contain both, sandy, argillaceous, and calca- reous members, there is less error in estimating the re- VOL. i. c 18 A TREATISE ON GEOLOGY. CHAP. I. lative periods which elapsed in the production of such groups by their proportionate thickness, than in apply- ing the method to the several strata and beds of the groups. In a general sense, then, the total length of the scale of strata is of importance, as an element for direct com- putation of the total time elapsed in the formation of the crust of the globe. This length in some cases amounts to more than ten miles, and is seldom to be estimated at less than five. Means of Investigation of Facts. Having now sufficiently explained the nature and origin of that standard of time to which all geological phenomena are to be referred, it remains to be seen, 1st. What are the means in our power for collecting the facts concerning chemical, mechanical, and vital phenomena, effected in ancient periods, which are to be combined into a history of the physical changes of the globe ? 2d. What are the methods of interpret- ation applicable to these phenomena ? Direct observations of the mineral composition of the globe are the groundwork of geology ; but were our knowledge limited to the depth which is reached by actual penetration of the crust of the globe, by pits, wells, and other excavations, or seen in isolated moun- tain slopes, it would be of little value for the object proposed. The deepest mine in the world (Kitzpuhl in the Tyrol) is only 2?64< feet below the surface, the loftiest summits of the Himalaya only ascend 28.000 feet above it. Yet in consequence of the manner in which the stratified materials are arranged in the crust of the earth, it is possible, by proper combination of direct observations, to know the structure of the globe to the depth of three, five, or ten miles, according to the situation and circumstances of the country. This will be understood by attention to the annexed diagrams where fig. 3 represents a false, and Jig. 4 a true, repre CHAP. MEANS OF INVESTIGATION. sentation of the arrangement of strata, in a part of the crust of the earth. 1! If the globe were conceived to be cut through, the section near the surface would show a number of layers variously inclined to the horizon as in fig. 4., so as +.0 come up to the surface in succession a, 6, c, d t &c. ; not, as in fig. 3., parallel to the horizon, as many per- sons are apt to imagine. The thicknesses of a, b, c, d y &c. separately, may be easily known by pits and wells, or natural sections in ravines or precipices ; their order of succession may be found by the same means, and thus the total thicknesses of all the stratified rocks visible in any one country, may be easily known by direct observation. By a judicious selection of ex- amples, the upper part of the series of strata may be measured in one district, as a, b, c, d, fig. 4*., the middle in another, which contains the lower portions of the former series, as d, e,f, g } in fig. 4. ; and the in- ferior portions in a third, fourth, &c., so as to complete one general table or section of the whole series of strata visible in an island, or continent ; and, finally, on the face of the whole globe. This labour is actually accomplished for many large portions of the globe ; and it is found that the strati- fication of the matter of the earth ceases at some depth which is not the same at different places, three, five, ten, or more miles below which are rocks of different structure, aspect, and origin, and not stratified. Here, then, is the limit of our knowledge, from actual inspection and exact induction of facts concern- c 2 20 A TREATISE ON GEOLOGY. CHAP. I. ing the constitution of the earth : geology, as such, can penetrate no farther than this small fraction of the radius of the earth. But the far-searching power of mathematical science is capable, by correct interpret- ation of astronomical observations, and refined experi- ments on the specific density of the globe, of giving us some further information as to the nature and arrange- ment of even the central masses of our planet. Direct observation of organic remains is the only source of information concerning the ancient orders of living beings, which were in existence at or previous to the deposition of the several strata: no reasoning a priori can be, in this inquiry, of the smallest service ; but may be exceedingly injurious by infusing error and prejudices. It would be a gross error, for instance, to as- sume that the earlier forms of life were less complex in visible structure than those which now exist that the lower orders only of animals and plants had been called into being ; for since the forms of life are most certainly made dependent on physical conditions, unless these latter can be known beforehand, there can be no reasoning on the matter, and there ought to be no spe- culation in inductive geology. Means of Interpretation of Phenomena. Admitting that by direct observation and the aid of higher science, geology has collected the evidence of the nature and arrangement of the mineral masses and organic reliquise, we may proceed to point out the method of interpretation which must be applied to the phenomena, in order to discover the physical conditions which prevailed in the several successive periods of the earth's structure in the situations observed. From the known to the unknown, through some common relations, has ever been the march of philosophical discovery : the skill of the general reasoner consists in the selec- tion and use of these common relations for the deter- mination of the principal conditions or agencies. It is CHAP. I. MEANS OF INVESTIGATION. 21 through the knowledge of the conditions or agencies concerned in the phenomena of existing nature, that we must approach with caution to the solution of the similar problems offered by the phenomena of ancient times : the common relations are found by comparison of the analogous effects ; but if the modern effects are merely known as laws of phenomena, and not reduced, to use Mr. WhewelTs expressive language, to laws of causation, the corresponding phenomena of geology must remain equally unexplained. The intelligent reader will easily see that it is not meant to convey the impression that nothing in older geology can be understood, unless there be known something exactly like it in modern nature ; the laws of causation which regulate the phenomena now oc- curring on the globe, once correctly known, will cer tainlybe recognised in a vast variety of older effects, in which the same agencies however differently com- bined, produced, or predominated so as to charac- terise, the result. Thus the laws of chemical phenomena explain the production of the most ancient minerals, as well as of those daily produced before our eyes the laws of phy- siology apply as well to the fossil flora, and the world of extinct animal life, as to the botanical and zoolo- gical enrichment of the actual land and sea : so also the laws of aggregation of sedimentary substances in water of fused rocks and earthy matters the laws of optical and calorific phenomena these laws of action are limited in their application only by the cir- cumotances of the case or of the experiment, indepen- dent of time, and exempt from change. Geology thus presents itself in an aspect which may surprise those who have not studied the philosophy of the subject. Though it gathers the most striking and beautiful facts, it depends for their interpretation en* tirely upon the progress of collateral science, and puts forth no speculation or hypothesis, except in conformity with the known laws of nature, and as a means of ex- c 3 A TREATISE ON GEOLOGY. CHAP. I citing and directing inquiry. In proportion as the philosophy of chemical, mechanical, and vital phe- nomena advances, so the interpretation of geological phenomena expands ; and if at any time the leaders of geology have substituted conjecture for induction a dogma for a dictum they were then offending not so much geology as chemistry, physiology, and astronomy ; and by these have they been justly condemned. Would that this warning might suffice to keep many hands to the sketch book and hammer, which they know well to use ; and prevent them from attempting, without ade- quate precaution, to hasten the progress of geological theory. CHAP. II. GENERAL REASONINGS CONCERNING THE SUBSTANCE OP THE GLOBE. Chemical Data as to the Exterior Parts of the Earth. WHAT is the nature of the mass of the globe is a question to which chemistry and natural philosophy furnish the only answers which our faculties can com- prehend. The nature of matter, in the abstract sense, it is not given to man to know; but instead of this perhaps useless, and certainly unattainable, knowledge, we are able to discover differences among the sorts of matter when subjected to the same conditions dif- ferences of weight, of hardness, of fusibility, solubi- lity, crystalline arrangement, and many other important circumstances. These properties define the sort of matter to our senses ; and thus it appears that many different compounds of matter exist in the earth. These compounds, resolved into their elements by the processes of chemistry, yield a certain number (fifty-five) of sub- stances which, under the conditions yet applied to them, are found to be incapable of further analysis, and are therefore called simple or elementary substances. They are singularly diversified in weight, mode of existence when separate, and relation to temperature and elec- tricity. In a free state under ordinary pressure and tempera- ture, some (five) exist as gas ; viz., hydrogen, oxygen, chlorine, fluorine, azote. Seven are non-metallic solids and liquids ; viz., sulphur, phosphorus, selenium, iodine, bromine, boron, carbon. The remainder are metallic or metalloid, and, with the c 4 24 A TREATISE ON GEOLOGY. CHAP. II. exception of mercury, which is both liquid and solid within the range of terrestrial temperature at the sur- face, all solid. Thirteen of these are metallic or metalloid bodies, which unite with oxygen to form the earths and alkalies, viz., sodium, potassium, lithium, aluminum, silicium, yttrium, glucinum, donarium, calcium, magnesium, ti- tanium, strontium, barium. Twenty-nine are what are commonly called metals ; viz., manganese, zinc, iron, tin, cadmium, which de- compose water at a red heat ; and arsenic, antimony, copper, molybdenum, uranium, tellurium, chromium, cerium, nickel, vanadium, cobalt, lead, tungstenum, titanium, mercury, columbium, bismuth, osmium, sil- ver, palladium, rhodium, platinum, gold, iridium, which do not decompose water. " With the metallic and non-metallic bodies in the previous lists oxygen enters so generally into combin- ations which yield solid compounds, and in such large proportions, especially with the earthy and alkaline metalloids, that we may venture even to say that one half of the ponderable matter of the globe is composed of oxygen gas. The speculations, to which this conducts as to the concentration from a gaseous condition of the matter of the planetary system, seem to be in agreement with the astronomical views of Herschel and Laplace, but are perhaps beyond the range of geology, which considers not the origin of the globe, but its successive changes of condition." * Table of the Proportions per cent, of Oxygen in certain abundant Earths, Minerals, and Rocks, 100 Silica = 48-4 Silicium -t 51 '6 oxygen. 100 Alumina = 53 '2 Aluminum + 46-8 Oxygen. 100 Magnesia = 61 -4 Magnesium + 38 -6 Oxygen. 100 Lime = 72 Calcium + 28 Oxgen. * Guide to Geology. CHAP. II. THE SUBSTANCE OP THE GLOBE. 25 100 Quartz = 48-4 Metallic base + 51-6 Oxygen. 10O Felspar = 54 Metallic bases + 46 Oxygen. 1GO Mica = 56 Metallic bases + 44 Oxygen. 100 Granite = 52 Metallic bases + 48 Oxygen. 100 Basalt = 57 Metallic bases + 43 Oxygen. 100 Gneiss = 53 Metallic bases + 47 Oxygen. 1 00 Clay Slate = 54? Metallic bases + 46? Oxygen. 100 Sandstone = from 49 to 53 Metallic bases + 47 to 51 Oxygen. 100 Limestone = 52 Metallic base + 48 Oxygen.* In studying the simple and various compound mi- neral masses occasioned by this union of oxygen with the metals and the metallic bases of earths and alkalies, the geologist labours on the same bodies as the mineral- ogist and the chemist, but not for the same end. To take a well known rock, granite, as an example " The geologist considers the circumstances under which this rock occurs in mass or in veins, with a view to determine the agencies which were concerned in its production, the period when it was produced, and other important characters. The composition of the stone is so far a matter of study for him as it helps to clear up these problems. " To the mineralogist granite is an object of study, because it is composed of certain minerals which are characterised by certain constant properties. It is not granite that he studies, but its constituents, quartz, fel- spar, and mica. These minerals are investigated by their qualities of geometrical form, specific gravity, hardness, relation to light, electricity, &c. as separate objects. " Finally, the chemist takes these separate minerals, resolves them into their several ingredients, examines the properties and proportions of these, and investigates the laws of their combination." t * See on the Chemical Constitution of Rocks, De la Heche's Geological Manual, 2d edit. t Guide to Geology, 3d edit. 26 A TREATISE ON GEOLOGY. CHAP. II. Physical Data as to the interior Constitution of the Earth. But these oxygenised substances are only such as are found among the bodies at or near the surface of the earth; and though some of them have been elevated from considerable depths by volcanic action, the in- formation thus acquired may not be at all applicable to the interior parts of our planet. Observation is here entirely at fault,, and we must be content to remain wholly ignorant of the analytical constitution of the interior masses of the globe. We may never know what chemical or optical properties belong to it ; but instead of this kind of knowledge, which, however curious, would be of little value even in theory, we have re- ceived some very important instruction from astronomy and general physics, as to the circumstances under which matter, whatever be its chemical constitution, now exists and was formerly aggregated in the interior parts of our planet. 1. Methods have been devised of measuring the at- tractive force of the whole globe, compared to that of some of its parts, certain mountains, for instance, and thus poising its mass against some known weight ; and these methods, confirmed by astronomical inferences leave no doubt that the density and specific gravity of the globe is above five times as great as that of water at common temperatures and pressures. The average specific gravity of the principal stony masses near the surface of. the earth is about 2^ times that of water ; con- sequently, the interior parts of the earth are occupied by material substances heavier than those near the surface. 2. But it does not follow that they would be heavier if brought to the surface ; for the pressure of the whole mass of the globe toward the centre must necessarily occasion a condensation of the substances, whether solid, liquid, or gaseous, therein occurring. This con- densation due to mere pressure would indeed, upon all CHAP. II. THE SUBSTANCE OF THE GLOBE. 27 mineral compounds known to us, go so far as to aug- ment their density much more than is requisite for the fulfilment of the condition required by the calculation. According to Leslie (as quoted by Mrs. Somerville) water would be as heavy as mercury at 3 62 miles below the surface of the earth, and air as heavy as water at 84 miles. Calculations of this kind, however, involve suppositions as to the continuity of the law of the den- sity of elastic bodies being proportional to the pressure upon them ; they are thus in strictness liable to ob- jection ; but the error which might arise from this cause is quite unimportant for the argument in the text. We must therefore admit that either the interior sub- stances are naturally lighter j that they are of so dif- ferent a nature as to yield but little even to the im- mense pressure upon them ; or that their inherent elas- ticity is aided by some principle of expansion, which balances a part of the pressure to the centre. 3. To aid us in choosing between these cases we may call in the aid of mathematical science and astro- nomical observations, from which it results, 1. That the figure of the earth is an oblate spheroid, such as would be produced by revolution on its axis, provided the constituent matter of the globe were in such a state as to be allowed freely to arrange itself in obedience to the central and tangential forces concerned. 2. It is ascertained as a consequence of the theory of the moon s motions, that the interior parts of the earth are not only more dense than the exterior, but that the inner sur- faces of equal density are symmetrical to the same centre and axis as the external elliptical figure.* From these observations conjoined, there is no doubt that the matter of the globe, having free relative motion, was arranged under the double influence of central and tangential forces: and consequently, that the substances in the interior must be naturally at least as heavy as those near the surface under the same circumstances. Free relative motion to the extent here required, * See Conybeare in Reports of the British Association, voL i. p. 408. 28 A TREATISE ON GEOLOGY. CHAP. II. viz. to the central parts, implies a total incoherence or fluidity of the mass of the globe. Such fluidity appears perfectly intelligible, as the effect of a general and pervading high temperature ; and, perhaps, this is the only supposition which will at all meet the case. But it derives a considerable accession of probability from the fact that the earth is even now hot within ; a point on which all experiments on subterranean tempe- rature, and, perhaps, the grander phenomena of vol- canoes, appear to agree ; and a variety of evidence will be hereafter adduced to show that it was formerly hotter, at small depths below the surface, than it is at present. From all this we obtain, as the most probable solu- tion of the problem of the constitution of the interior parts of the earth, that the substances therein occurring have such analogies to those now seen near the surface, that they would have been subjected to very much greater condensation than they have suffered, the globe would have been denser than it is, were it not for the expansive influence of heat in the interior of the planetary mass. Whether the inner or medial parts of the substance of the globe be fluid or solid, must remain for very refined researches in physical astronomy to decide, if, indeed, evidence can be collected, on points involving the consideration of fixity or motion of the interior masses, sufficiently precise to give authority to the rigorous results of calculations applied for the purpose of testing this great question. Mr. Hopkins concludes, from the phenomena of precession and nutation, that the earth's solid crust cannot be less than one-fourth or one-fifth of its radius. ( Phil. Trans. 1842.) Mass of the Globe whence derived. With this knowledge of the nature of the mass of the globe, the modes of combination of the several ingredients of the mass, and the properties under certain physical conditions of these ingredients ex- isting separately, one of two conclusions must be CHAP. II. THE SUBSTANCE OF THE GLOBE. 29 adopted by the human mind. Either we must believe these combinations to have been original, that is to say, that the ingredients have had no separate exist- ence and properties, till the art of chemistry found the means of disuniting and insulating them ; or view the existing aggregations of matter, as results of com- bination of the separate elements, produced by some change of conditions. If the former view be adopted, there is no room for further discussion ; if the latter, an inexhaustible source of intellectual exertion is opened, and all the mysteries of nature are subjected to the scrutiny of man. There may be persons who view this as a matter of no importance, and would, perhaps, be content to save themselves the trouble of inquiring into the works of creation, by the indolent belief that the world was made as we see it, its complicated phenomena not produced by appropriate laws of causation, but the result of an immediate fiat of Deity. As far as re- gards the reverential thoughts due to the Divine Lawgiver of nature, it may appear, on a first view, un- important whether we admit the creation of the com- plicated phenomena, visible in the structure of the globe, by an immediate act of Almighty Power, or their production from a former state of the same ele- ments by the agency of intermediate laws of causation ; but, on careful examination, it will certainly be found otherwise. If it be true and demonstrated, that in the existing economy of nature all phenomena (whether they ap- pear to our imperfect conceptions simple or complicated) are the result of invariable appointed laws, acting under definite conditions; if it appear that, in our own time, the phenomena of mechanical, chemical, and vital action among the elements and masses of matter are analogous to those of which monuments remain in the crust of the earth ; if the laws which are known to govern and to correspond accurately to the modern effects stand in the same relation to those 30 A TREATISE ON GEOLOGY. CHAP. II. of older date ; who, that looks upon the laws of modern nature, as affording proof of the being and attributes of God, will take a different view of the similar pheno- mena of ancient date, and thus virtually derogate from the respect due to the Lawgiver, by limiting the dura- tion, and questioning the application of the law ? For it cannot be denied, that the appearances in the rocks which compose the crust of the globe, are such as to indicate most clearly that all their ingredients have existed in some other and earlier condition. The pebbles and fragments of stone imbedded in rocks of different nature are such as might be produced by pre- vious mechanical action; crystals such as those imbedded in others are known to be effects of chemical forces; shells, plants, &c. retaining all their delicate external forms, and even their internal structure, can they be supposed to be mere lusus natura, or created to deceive mankind? Which is the more reasonable, to receive as truth the obvious indication of the senses, to acknowledge these effects to have happened through proximate causes, or to attribute to the Divine Wisdom the in- stantaneous creation of effects which, by their very nature and the nature of man, must inevitably mislead right reasoning to a wrong conclusion ? It must, therefore, be allowed that the causes which the effects indicate, when rightly interpreted, are to be admitted as true; if the effects are rightly noted, and correctly interpreted, all the inferences of geology, however re- markable they may be, whatever agencies, conditions, or durations they assign to the composition of the crust of the earth, must be received as natural truths. We may now follow the inquiry into the prior con- ditions of the materials consolidated in the crust of the earth. It is quickly seen that many considerable rocks are composed of parts which were suspended in water, as clays, sands, &c. and deposited from it as sediment; others are such as may be formed from solution in water; others resemble the products of CHAP. II. THE SUBSTANCE OF THE GLOBE. 31 igneous fusion; some appear the result of electrical combinations. All these latter are but forms of che- mical processes among the elements of matter ; and the sedimentary rocks, where their parts are clearly dis- tinguishable, are found to be composed of grains or fragments, originally produced by aqueous, igneous, or electrical combination. Thus all the mineral masses of the earth known to us appear to have existed pre- viously in a different state, when the elements were separated, so as to allow of their combination ac- cording to the forces of affinity, existing in definite proportions among the small portions of all material substance. Take, for example, the very common rock sandstone ; its component grains of quartz, felspar, and mica are, more or less, rolled or fragmented crystals of these substances, derived from rocks like gneiss, mica schist, &c., which are also composed of grains of the same kind, less affected by mechanical processes ; or from granite, porphyry, &c., which are purely crystalline rocks. Such derivative sandstones are formed at this day from such crystallised granite, and other rocks. But the analysis goes further. Quartz is a compound of a metallic basis, silicium, and the air or gas oxygen. Felspar is a compound of silicium, calcium, potassium, &c., each united with its own proportion of oxygen. Mica is a compound of silicium, potassium, magnesium, calcium, &c. similarly combined with oxygen. Under present physical conditions oxygen, being liberated from combination with these bases, would expand into 2000 times the bulk it occupies in the compound, and become a gas : and thus, since oxygen forms half the ponderable mass near the surface, half the crust of the globe, perhaps half its whole mass, would become an expansion or atmosphere round the diminished nucleus. It is evident that the tendency of all this inquiry is to lend some confirmation to the speculations of Herschel and Laplace, as to the con- densation of the planetary masses from gaseous expan- 32 A TREATISE ON GEOLOGY. CHAP. II. sions, like the nebulae and comets ; speculations which, however, can only be changed into probable inferences by the progress of modern astronomy. For the examination of these obscure bodies, most powerful telescopes are required. The observations of Lord Rosse have resolved so many of the nebulae into small stars, that it is doubtful whether any of them can be safely appealed to in illustration of the supposed pro- cess of condensation and arrangement. The progress yet made in chemical philosophy is perhaps not such as to enable us to discover the single condition on which the elements, now so firmly united, could exist separately, in a free gaseous ex- pansion ; yet, since chemical combinations are known to be subject to temperature, liable to be altered and even reversed with a change of this condition, may we not suggest, as the least improbable view, that tht nebulous condition of a planet may be due to intense heat existing among its particles ; that, in fact, a great heat prevents their combination, and maintains them all together in a gaseous state, as it is known to be capable of doing, for most of them singly, and several of them together ? In mixed or combined gases metallic matters are frequently present (as arseniuretted hydrogen), and the atmosphere of our planet is believed by several philosophers to contain so large a proportion of the sub- stances existing in the superficial parts of the globe, as to give origin to the meteoric stones. CHAP. III. GENERAL TRUTHS CONCERNING THE STRUCTURE OP THE EXTERNAL PARTS OF THE GLOBE. FROM these facts and reasonings concerning the nature and constitution of the materials of the globe, derived from chemical and physical science, we may turn to contemplate the general truths obtained by direct pro- cesses of observation and induction, concerning the mode of arrangement of these materials, in that limited por- tion of the earth's mass which it is possible for man to explore by artificial excavations, or to understand by skilful interpretation of the disclosures effected by nature. Beginning at the surface, and passing gradually towards the deeper parts, we shall be able easily to gather clear ideas of this fundamental portion of positive geology, without a right knowledge of which the otherwise pleasing task of following and examining the common reasonings in the science would be use- less, if not presumptuous. STRUCTURE OP THE EXTERNAL PARTS OF THE GLOBE. SOIL, the external investment of the land, though il somewhat veil from geologists the objects of their pecu- liar research, merits attention ; for this thin covering varies in some real relation to the rocks beneath, and appears, in many instances, to be nothing else than the substance of those rocks decomposed by time, and altered by vegetable admixtures. The depth of soil is extremely irregular, some feet thick over certain sandy rocks, a foot thick over clays, only a few incheg VOL. T. D 34f A TREATISE ON GEOLOGY. CHAP. III. thick over chalk. In valleys the soil is accumulated from the waste of the hill sides : the surface of many (especially primary) mountainous regions is devoid of soil. In particular districts the soil is not merely formed by decomposition of the rocks beneath ; it contains sand, pebbles,, &c., brought from a distance, either by actual streams or some extraordinary force of water. Thus, in many instances, a mixture of substances takes place very beneficial to the fertility of the soil. Beneath this thin and irregular layer, in some coun- tries, the solid rock appears ; but in others masses of loose sands, clays, gravel, &c., are found, which lie in hollows, or on the surfaces of the subjacent rocks, 10, 50, 100, or more feet in depth. These have evidently been drifted by water, and deposited from it, but yet they do not properly enter into the structure of the crust of the earth, but must be viewed as superficial and local accumulations, produced under circumstances considerably different from those which determined the formation of rocks. To these accumulations the names of alluvial and diluvial deposits have been applied : it appears desirable at present to use, for them and the soil collectively, the term superficial accumulations. Rocks, and the substances which they enclose, lie beneath the superficial accumulations, and constitute the crust of the earth as known to geologists. The term "rocks" is apt to mislead beginners; for under this title geologists rank clay, sand, coal, and chalk, as well as limestone, granite, slate, and basalt, and other hard and solid masses, to which the use of the term is generally restricted : and they do so because they are all and equally constituent parts of the crust of the earth ; and this crust is generally of a rocky consistence. The embarrassment which may be felt from this un- usual employment of the term will diminish as we proceed, and find ourselves led to adopt various other modes of designating, in detail, the masses which it will yet often be convenient to speak of together under the vague term of Rocks. CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 35 Forms of Rock Masses. On mountain sides, in ravines, and sea cliffs, the rocky masses of the earth are exhibited free from the obscurity of superficial accumulations : the industry of man, in mines, wells, roads, canals, has added to the facilities granted by nature, and from these opportunities the structure of the crust of the earth, the arrangement and relative position of the rocks, are known in the most essential points. The different sorts of rocks are by no means mixed together in confusion, but placed in a regular and ascertained method of occurrence, and often arranged in a certain determinate order of suc- cession. Almost all rocks exhibit to the careful observer some interesting circumstances of interior structure, particular divisions of their substance by joints, cleavage, &c. ; but, neglecting for the present these subjects, we shall fix our attention on the form of the rock masses taken in their totality. A very large proportion of rocks are formed so as to spread over areas of 10, 100, or 1000 square miles, with thicknesses of only as many or fewer feet or even inches: these are said to be stratified (*), or formed like a stratum or layer. Fissures, dividing particular rocks, are sometimes filled up with another sort of rock, which is then said to appear as a dyke (rf) ; various spars, metallic matters filling fissures, or em- bodied in the rocks, are called veins ( v) ; and many rocks, neither stratified nor in the form of dykes or veins, are in this sense amorphous, but are generally ranked with dykes, yeins, &c., as unstratified rocks (M). Dykes and veins form but a small part of the mass of the crust of the globe, which consists principally of D 2 36 A TREATISE ON GEOLOGY. CHAP. III. stratified and unstratified rocks. In the plains, and comparatively low portions of the earth, the rocks are almost universally stratified, the strata being often very thin, even to inches, but sometimes many yards or fathoms in thickness. The superficial area, over which a particular stratified rock expands, is sometimes enormous, chalk, for instance, has a range of many hundred miles in length, by 5, 10, 20, or more in width, in England and France, but sometimes very limited, as the magnesian limestone of the north of England, which ranges from Shields to Nottingham. In more elevated districts, and on the flanks of mountainous regions, the rocks are also seen to be distinctly stratified. By patient attention it will be found that, even in the very midst of chains and groups of mountains, the marks of stratification may often be perceived ; but it almost always happens that the axis of such chains or groups is formed by un- stratified rocks, and these sometimes appear in lower situations. Position of Rocks with respect to the Surface of the Earth. Declination of Strata. Stratified rocks have usually a nearly constant thick- ness, or else vary in this respect by insensible and re- gular gradation ; their surfaces, or the planes of stra- tification, are therefore in general sensibly parallel, and their position may be known with respect to the surface of the earth, by observing the bearing of a level line (or strike) in the plane of stratification, and the an- gular amount of the descending slope (dip) or ascending slope (rise). The result of very numerous trials proves that the strata are over large surfaces often nearly but seldom quite horizontal ; they dip, in fact, below the horizon, pass under the surface, and are covered up by other strata which also mostly clip in the same direction. Thus the surface of the earth in regions where stratified rocks occur is formed partly on their edges ; and a section CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 37 or vertical cut to some depth from the surface would pre- sent on its sides the appearance of the diagram, No. 6. We may say that three fourths of the surface of the dry land of the globe is thus formed on the edges of mode- rately dipping strata : in all large districts the dip is found to be variable in amount and in direction, but, viewed on the great scale, always in harmony with one general law, which may be thus expressed : The strata dip from the chains and groups of mountains under the plains which surround or divide them. Thus, from the group of Cumbrian mountains the stratified rocks dip W. at Whitehaven, N, at Hesket, E. at Shap, S. at Ulverston ; from the chain of the Lammermuirs, they dip N. W. under the great valley of the Forth, and S. E. into Northumberland. The most general dip in England is easterly, the principal mountains being situated on the western border : from Brittany, the Ardennes, and Auvergne, the dips of the strata converge toward the low ground of the Basin of Paris ; from the plains of Languedoc the strata rise to- ward the Pyrenees and the mountains of central France ; the Pyrenees, the Apennines, the Alps, the Car- pathians, the Grampians, are axes from which the stra- tified rocks decline, to pass under the lower ground on each side. Diag. No, 7- It is generally found that the dip of the strata, thus obviously related in direction to the axes and centres of mountain groups, is also related to them in amount, so that the angular value of the dip or the number of feet in one hundred that the strata decline decreases D 3 38 A TREATISE ON GEOLOGY. CHAP. III. continually from the mountains toward the plains, and in the middle of these is sometimes evanescent. Near London, for example, and on the coast of England gene- rally, strata, though not level, dip moderately (1 or 2) toward the east; but on the line to North Wales the dip augments ; on the border of the Principality it measures 5, 10, 15, and in the range of the Berwyn moun- tains, 30 and 40, or still higher angles. The direction of mountain chains, and the position of mountain groups, being extremely diversified, the lines of strike and dip of the strata which depend upon them are also very various. Perhaps in the progress of the science some law of these directions may be established : in the progress of this essay we shall examine one such attempt by a distinguished foreign geologist. At present the most important things taught us by the phenomena of dipping strata are these: 1. The dip is related to the elevation of ground ; and 2. The strata do not descend from one mountain chain below the surface of plain countries more than a very moderate depth (four to five miles) before they begin to rise again toward another axis of elevated ground. The principal mountain chains and groups are thus seen to be the axes of declination of the stratified rocks ; and it was not without reason that De Saussure explored with so much patience the giant elevations of Switzer- land, Dr. Hutton and Werner studied the Scottish and Saxon chains, and Mitchell with a grand gene- ralisation referred to the leading features of physical geography as a basis of laws of geological phenomena. The axes of mountain chains and groups being before shown to be generally occupied by unstratified rocks, we have arrived at the important inference, that the dip, or deviation of stratified rocks from the horizontal posi- tion, depends on the same axes or centres as the exhi- bition of unstratified rocks: the production of the latter is therefore in some way connected with the de- clination of the former. If we suppose the unstratified rocks to have been CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. "9 raised from below, the position of the strata, the re- lations of physical geography, and the relations of the two classes of rocks would be at once explained. In order to see what foundation may exist for such a speculation, let us inquire into further details and other cases of the position of stratified and unstratified rocks. Local Declinations and unusual Positions of Strata, $c. It is not only in mountainous regions that the strata are found dipping at high angles ; the same phenomena are repeated on a smaller scale, and for smaller distances, at many points situated in the midst of the great basins of strata far from the principal axes of declination. The appearances presented at these points of disturbed stratification are extremely various, but they admit of a simple and useful classification. Nothing is more common, in many large districts, than a slight elevation of the plane of stratification along a certain straight line, so that the rocks decline from it on both sides, as a, diag. No. 8. This is called an anticlinal axis, and the elevated ridge a saddle. Its converse (6), the line to which the strata decline, is called a synclinal axis, and the whole depression a trough. It not un frequently happens, on a small scale, as in the Craven district of Yorkshire, in the Abberley hills, Clee hills, the shores of Berwickshire, &c., and still more frequently and remarkably on a great scale, among the Alps (Vale of Chamouni, Lauterbrun, &c.), that the strata near an anticlinal axis, instead of being formed in evenly declining planes, are twisted and contorted in several directions, as if exceeding violence had been re- peatedly exerted in lateral as well as vertical directions (c). In many instances (as on the line of the Penine fault near Crossfell, near Kirby Lonsdale, and near Lancas- ter), the strata are reared on end, so as to be nearly or actually vertical (d) ; in other rarer examples (Malvern hills) they are totally overthrown, or, after having been raised to a vertical position, the upper parts have been D 4 40 A TREATISE ON GEOLOGY. CHAP. III. pushed outwards, so that the strata usually lying upper- most in the group are actually, for a short distance, undermost (i). Faults. Besides these, other forms of disturhed stratification demand attention ; especially those in which the con- tinuity of the strata is broken, and the divided parts placed at different levels. This interruption and dis- location of the strata commonly happens along a plane approaching to the vertical, which is usually marked by a rude and irregular fissure. This fissure, whether empty or in any manner filled (with fragments of the bordering rocks or other substances), is called " a fault," and locally "adyke" "a trouble" "a gall" ' a slip," &c. The most simple and frequent case of faults is re- presented in the annexed vertical section (No. 9.) at the letter a, the strata lying nearly level, the fault vertical, the dislocation moderate in amount, and no particular bending of the rocks near it. In b the fault deviates from the vertical by the angle sc by, and is said to have an underlay ; the strata are considerably depressed, and in such a manner that a perpendicular dropped from b would fall clear of the edges of the depressed beds j not as in c, which represents a rare and exceptional case, so rare, indeed, that a clear example of it with a consider- able depression of beds never occurred to the author, among very numerous instances studied in all classes CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 41 of stratified rocks. In d the strata bend to the fault so as to coincide with its direction. In e the contrary effect is seen, the strata bending so as to meet the fault at right angles, as on the line of the great Tynedale fault, which disturbs the beds 1200 feet. In some instances the fault fissures are open, as f t in others^rull of angular dispersed fragments from the adjoining rocks (#); sometimes a leader of one or more of the softer strata follows up the fissure for a con- siderable distance (A) ; but frequently, as i, the fissure is closed. See the annexed vertical section. 10 The surfaces of the fissure accompanying a fault are often remarkable, and afford good evidence in favour of the dislocation of the masses having been accomplished by great mechanical violence, and perhaps a single con- tinued effort. Let V fig. 1 1 . be any vertical plane crossing /F F' F", the plane of a fault fissure, which is accom- panied by a dislocation of strata through the extent / F" ; a be, being the corresponding beds on the two sides of the fault. The face/ F F' F", one side of the fissure of the fault, is often scored by grooves (g g) parallel to the direction of the dislocation of the strata ; that is to say, deep lines are ploughed on the broken ends of the rocks in the very direction in which they must have been produced, supposing, as the other phe- nomena indicate, the rocks to have slipped along the plane of the fault. A magnificent example of this is A TREATISE ON GEOLOGY. CHAP. III. seen at Cullercoats in the great Tynedale, or 90 fathom dyke,, of the Newcastle Coalfield. Extent and Frequency of Faults. The extent of vertical displacement occasioned by faults varies from a few inches or feet to thousands of feet ; examples of the former are common, of the latter rare. When carefully studied, however, the principal difference between them the extent of the movement, is the only one which appears constant and essential. This is obviously related to the force employed in pro- ducing the fracture. That force may have been different in amount in the two cases contrasted, or different in the duration of its exertion ; for the conformity of the circumstances of fracture seems to forbid a supposition of a different mode of action. Now, as an examination of the smaller and larger faults, when their planes can be clearly seen, appears to show that only one kind ot action has been impressed upon the masses, as they appear to have slided in one direction, have been rubbed CHAP. III. THE EXTERNAL PARTS OP THE GLOBE. 43 on their faces in one direction, and exhibit almost never any signs of repeated action along the same or neigh- bouring planes, we are forced to adopt, as a highly pro- bable view of their origin, one continuous effort of a great force tending to extend, and, consequently in- ducing tension in, and fracture of, the crust of the globe. It appears no more necessary to suppose many interrupted efforts for a great fault like the Tynedale or Craven faults, of a thousand feet or yards, than for the numerous " hitches " in a colliery of one or a dozen feet. It is commonly the case that such faults, when viewed on a horizontal plane, range nearly in straight lines, and for considerable, but very variable, lengths. When many faults occur, each producing only a moderate " throw," " shift," or displacement of the strata, their range is usually of only a few hundred yards, or a few miles, when they fall into and are stopped by some greater faults, or axes of movement. On the contrary, when only a few faults occur in a district, and these have a great effect as to vertical move- ment, their course is usually of very considerable extent, even to many miles (the Tynedale and Craven faults range from 20 to 40 miles); but these also terminate in other faults or great centres or axes of movement. Faults which cross and appear to displace one another laterally, obey the same law of the angles as when their planes are compared to the surfaces of stratification, and the direction of vertical movements. (Fig. 9- &) Faults are the most common of all the forms of dis- turbed stratification : but, except in particular cases, they are the least influential on the physical configur- ation of the country. All the rocks which are disturbed by any fault have experienced on one side the same movement, and to the same extent, excepting only those portions which have been subjected to violent pressure ; and the bottom of the faults has never been reached, except when they terminate in another dislocation. 44 A TREATISE ON GEOLOGY. CHAP. III. Relation of Faults, Mineral Veins, Dykes, fyc., to the great Lines of disturbed Rocks. It is noticed, as a circumstance of common occurrence, that mineral veins are no otherwise different from faults than by reason of the fissures which these have opened in the rocks being filled by sparry and metallic matters. This filling of a fissure constitutes a mineral vein ; a similar fissure filled by basaltic or other rocks would be called a rock dyke; if occupied by clay and soft materials, a clay dyke. The point of importance in each of these cases is the mechanical formation of a fissure of the rocks along the plane of the fault ; and it is to be determined by further inquiry, what was the cause of this particular line being followed by the dis- turbing force, and how the fissure, when made, came to be filled with its sparry, rocky, or soft argillaceous contents. There appears to be some general relation observ- able between the lines of fault and the axes of great subterranean movement : that a " master fault " swallows up the smaller ones, or ramifies into them near the surface, has long been believed by the colliers of Somersetshire (as we learn from Dr. W. Smith). It appears, from our own and other researches, that the fissures accompanying mineral veins in the north of England, in the Penine Chain, and on the side of the Vale of Clwydd, terminate in such master faults ; it also appears, by a careful analysis of phenomena, that mineral veins are so related to axes of disturbed strata, (like the Stiperstones, Greenhow hill, &c.), that they spring out from such, or tend to cross them at right angles, and scarcely appear anywhere abundant except in the vicinity of points or lines of great disruption of the rocks. Faults, dykes, and veins must, therefore, be referred, as to the origin of the fractures, to the same general cause which placed the strata of the moun- tains in their disturbed and inclined positions. CHAP. III. THE EXTEBNAL PABTS OF THE GLOBE. 45 Before adopting, definitively, the conclusion obviously indicated by all the preceding facts, that the stratified rocks in the crust of the earth have been broken up, so that its disrupted masses have been placed in new positions, and that the unstratified rocks have been raised in con- sequence of such disruptions along the axes, and about the centres of mountain chains and groups, it will be proper to inquire further into the nature and origin of these two classes of rocks. Origin of stratified and unstratified Rocks. The great and leading distinction between these rocks, is the form of their whole masses ; but, besides this, we observe, in other respects, very important differences, which facilitate investigations into their origin, differences of internal structure, chemical character, mineral aggregation, and imbedded sub- stances. Stratification is a form of matter seldom produced in perfection among the effects of modern nature, except by the agency of water. The sediment from rivers, the deposits in lakes, the sandy and pebbly accumulations from the sea, all possess the true characters of stratifi- cation, for they tend to be produced in considerable breadths, with comparatively small thicknesses. And as among the ancient rocks we frequently find con- tiguous deposits of different chemical nature, as lime- stone succeeding clay or sandstone, so in these more modern products, similar successions of strata occur : clays and sands, and marly limestones of different colour, consistence, and chemical quality. Many of the ancient sandy strata are laminated parallel to the surface, as are the modern sediments from a river or the tide ; others are irregularly composed of oblique laminae, or ripple- marked on the surface, as are the deposits from agitated rivers and tidal currents. All the comparisons which can be made between ancient strata and analogous products of modern nature, 46 A TREATISE ON GEOLOGY. CHAP. III. appear clearly to evince their common origin, no other essential differences being discoverable between them, except the great thickness and extent of the ancient rocks ; and could we raise for examination the bed of the Atlantic or the Mediterranean, perhaps a part of this discrepancy might vanish ; for Donati's researches on the bed of the Adriatic show the great extent of the modern deposits in that sea. The unstratified rocks tried by the same test, the form of their masses, can in no manner be paralleled to the productions of water. The dykes and veins which belong to the same class as the huge amorphous masses, and are often of the same kind of rock, do resemble in their forms, to a considerable degree, the known pro- ducts of modern volcanoes : particular ancient unstrati- fied rocks, as basalt, exist in forms, and under circum- stances, very similar to analogous rocks, the fruit of volcanic fires. The chemical composition of the two classes of rocks resembles in some points, and differs in others : they are in some points similar, for they contain some identi- cal minerals, and many identical elementary substances ; but numerous minerals are found in the unstratified rocks which are not known among the others. Limestone, sandstone, and clay, which constitute so many of the stratified masses, are forms of mineral aggregations such as never occur among granites, basalts, porphyries, &c., which make up a large portion of the unstratified rocks. But the difference in their mineral aggregation is yet more remarkable. The ingredients of the stratified rocks appear almost always in such a state, as to sug- gest to the observer their aggregation from a state of solution, suspension, or drifting in water : limestone rocks, for instance, appear to have been collected, as smaller quantities are at this day, from the decomposition of water by chemical and vital agencies ; clays were clearly collected from matter finely divided and diffused or suspended in water. Sandstones are as clearly the accu- mulation of grains of quartz, or other minerals worn and CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 47 rounded in water, while conglomerates leave no more doubt of the former action of agitated water, than the pebbles of a river bed, or the sea shore. On the contrary, the unstratified rocks are mostly crystallised ; that is to say, their constituent ingredients are symmetrically arranged and bounded by regular surfaces, meeting at definite angles : they are not such as in general to be separately soluble in water at any temperature ; they never show any marks of arrange- ment such as might arise from suspension or drifting, nor any such proofs of mechanical action, as worn grains of sand, or pebbles of rock. But their compo- sition is in the great mass, and in the nature of the constituent crystals, always analogous, and frequently identical with, the known effects of heat in the furnace of the chemist, or the subterranean laboratory of nature. Finally, these two classes of rocks differ essentially in another most important respect, which, taken in con- junction with the preceding facts, is quite decisive of their difference of origin : the stratified rocks are gene- rally stored with the reliquiae of plants and animals, even to a greater degree than modern marls, clays, and sands deposited from water ; while the unstratified rocks contain none of these things, or if, by chance, a soli- tary shell has been found amongst such rocks, its inclusion is easily explained, just as by some accident volcanic scorise have been found to cover bones in Auvergne. The animal remains found in the stratified rocks are chiefly marine, and nearly all aquatic ; they occur, in many instances, under circumstances of position and relation which prove that they were often quietly buried or drifted by water from small distances, but sometimes worn to pebbles ; just as from the deep and quiet sea we now dredge shells in complete preservation, their spines and ornaments perfect : while nearer the shore, worn shells, and under the cliffs, among the pebbles, rolled and fragmented particles appear. It is, therefore, impossible to doubt that the strati- 48 A TREATISE ON GEOLOGY. CHAP. III. fied rocks, holding remains of aquatic animals or water- drifted portions of land plants, were formed in water : this applies to the far greater number of the strata. But it is equally clear, that those strata which alter- nate with these, and do not yield organic remains, but are of the same general characters, and were, by marks of structure and aggregation, evidently produced in the same way, are also of watery origin. All the really stratified rocks, then, are the product of water ; but the unstratified rocks are generally the fruit of the action of heat. We must, therefore, here divide the subjects for consideration in the structure of the globe according to the aqueous or igneous agency concerned, and shall commence with the history of the deposits from water. The most general view to which we are thus con- ducted, gives to all the stratified rocks an aqueous, and to the unstratified an igneous, origin : the former were deposited from above, in calm or agitated water, along the shores, in the depths of the sea, or in lakes ; the latter were raised from below, by the excitement of internal heat. Subterranean movements affected the stratified rocks, and elevated them from their level position into mountain chains and ranges of hills, and the same influence, or an action consequent upon it, raised the fluid or solid unstratified rocks along the axes, or at the centres, of the elevatory move- ments. Thus, it is a certain and general truth, that in the composition of the crust of the globe, in the ar- rangement of rocks in their present position, in the production of the physical features of our planet, both internal heat and the agency of external water have had their share ; and by studying, carefully, the effects now produced, though apparently on a smaller scale, by the same natural agencies, under varied circumstances, we may hope to arrive at correct general inferences as to the manner in which even the grandest and most sur- prising of the old revolutions of nature were occasioned. CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 49 Relative Periods of disturbed Stratification. One of the most remarkable of all the results yet arrived at, by combining the study of the two classes of rocks just distinguished, is the certainty that the sub- terranean movements of the solid crust of the globe, to which the deranged positions of the strata are owing, were not all of the same date ; but that some mountain ridges, and some lines and points of unstratified rocks, had been uplifted before others, some strata disturbed, before others were formed. The mode by which this has been ascertained is extremely simple. When, as in the section (/$r.l2.), certain old strata (a 6c,&c.) are found displaced from their original nearly level position, and thrown to high angles of elevation, and other more recent strata (hik} are placed level against the slopes, or even covering the ends of the former, it is plain that the dislocation of a b c happened in the interval of geological time which oc- curred between the completion of the newest bed (/) of the dislocated, and the oldest bed (A) of the undisturbed deposits. On different chains of mountains, along different lines of faults, &c., the period when the dis- turbances happened, judged of by this test, is found to be often very different. One of the most singular ex- amples of this dislocation of some strata, in districts where others of more recent deposition remain undis- turbed, was noticed by Dr. William Smith, in 1791 > ** Pucklechurch in Gloucestershire, and in Somersetshire. The coal formation is here found dipping at a high VOL. I. E A TREATISE ON GEOLOGY. CHAP. III. angle below, and covered up by horizontal strata of red marl and lias, thus : Lias. '- 13 Red marl. Coal formation. In Yorkshire and Durham the same thing is observed with respect to the magnesian limestone and the coal, with the addition that the coal strata are broken by faults, which do not affect the limestone above ; thus : The principal difficulty in applying this very simple mode of determination to particular cases, so as to class all faults and other effects of subterranean movements according to the date of their occurrence, consists in ascertaining the indispensable data of what strata are and what are not disturbed along a given line, or at a certain point. When the undisturbed strata lie upon, or abut clearly against, or plainly surround the dis- turbed rocks, the evidence is satisfactory, and easily verified; but, in most cases, this clear testimony is wanting, and it is by considering the relative directions and relative dips of the two sets of strata (the disturbed and undisturbed), that we are to arrive at a deter- mination of the question. The following notices and sketches will illustrate this point. CHAP. III. THE EXTERNAL PARTS OF THE GLOBE. 51 Whenever, in any district, the stratified rocks, in- stead of all lying parallel to one another, suffering the same deviations from horizontality, bending in the same flexures, dropping or rising by the same faults, and regarding in their declinations tne same axis or centre of dips, divide themselves, in these respects, into two or more sets, which differ from one another in all or any of these respects, there is said to be unconformity of the strata. The place of this unconformity is the interval between the tv.-o sets thus disagreeing ; it is said to occur between the oldest of one and the newest of the other set ; it affects the geographical distribution of the strata, as shown on a map, and their relative inclination and exposures, as shown in a section. Thus in the map diagram (^/fy. 15.), 15 the series of strata marked a b c d are parallel in one set, and e fg in another ; but their directions, or strikes, (S, S and s s) on the surface differ, and the lowest of the upper set (e) rests in one place on a, in another on b; in another on c or d. ; the dips, D and d, are in dif- ferent directions. In a section (as fig. 16.), some difference of inclination E 2 52 A TREATISE ON GEOLOGY CHAP. III. commonly occurs. But when the strikes and dips of either the upper or lower set vary, which is a very com - mon case, the same district, as Yorkshire or Derbyshire, may exhibit in the same region both conformity and un- conformity between the same two sets of beds, as in the map diagram (fig. I?-)* where abed are coal strata, with variable dips and strikes, generally unconformed, but on the line W E, for a short distance, conformed to the magnesian strata lying upon them (efg h\ Yet, in this case, the section on the line W E would ex- hibit a want of conformity in the dip (as in fig. 16.), the beds abed being more inclined than e f g h. When the strata are not in contact, or, for any reason the junction cannot be clearly seen, many observations of dip and strike in each set of beds will in general de- termine the existence of unconformity: but it would be folly to rest so important a decision upon testimony less demonstrative than the country will yield ; and, in some cases, sufficient evidence is unattainable by any exertion of industry and skill. 53 CHAP. IV. SERIES OF STRATIFIED BOCKS. BY following the methods previously described (pages 18, 19.) the whole series of strata existing in any country can he known ; by comparing the results thus obtained in different countries, the extent of the strata, and the degree of generality of the causes concerned in pro- ducing them, can also be known. The investigations, in both respects, have now proceeded so far as to fully justify a geologist in asserting, that the principal fea- tures of the stratified rocks in the crust of the globe are very similar over large regions ; the aggregate thick- ness of their mass is everywhere limited to a few miles ; the order of succession among the principal groups is the same, or analogous ; even the minute variations of their composition, aggregation, and struc- ture are observable in remote situations ; their organic contents are reducible to the same schemes of classi- fication, and everywhere indicate several great physical changes on the surface of the globe, since it became the theatre of vegetable and animal life. The foundations of all sound generalisations in geo- logical science are accurate and mutually explanatory sections and maps of the whole series of stratified and igneous rocks existing in each natural geological dis- trict ; a term by which we wish to express a part of the earth's crust, whether large or small, in which the formation of aqueous deposits has followed, amidst many local irregularities, one general law of succession. Such sections and maps express, by one common type or formula, the general result of many separate and local investigations ; the principal local deviations from the general type must be on no account omitted, for these E 3 A TREATISE ON GEOLOGY. CHAP. IV. limited differences are often more important in theory (as well as in practical applications) than all the general resemblances. Assuming that the British islands form such a natural district, we shall be able to present a satisfactory general table or section of the series of strata which here compose the crust of the globe, placed in the order of their succession downwards, from the sur- face of the most recent aqueous deposits. TABLE OP BRITISH DEPOSITS. Superficial Accumulations. Depositions from springs, rivers, glaciers, lakes, the sea, under ordinary circumstances. Depositions from some of these agents under extraordinary circum- stances. STRATIFIED ROCKS. Tertiary or Cainozoic Strata. Names of form- ations. Thick- ness in yards. Subdivisions or groups. Nature of the deposits. r Upper or mammali- Marine and estuary lerous crag. shells, pebbles, bonps, sand, &c. Crag. 16< Middle or red crag. Marine shells, pebbles, bones, sand, &c. Lower or coralline Marine shell> and corals crag. in sand, or coarse lime- stone. Upper freshwater. Vlarly limestone and clays. Freshwater marls. 33 . Estuary beds. Marine or estuary clays, marls, &c. Lower freshwater. Marly limestone and I clays. London clay (upper). Sand and clays. Ulay with septaria, &c. Coloured sands, c:avs. London clay. 200 to j 600 ^ London clay (lower). Plastic clay. Dlay with septaria, &c. Variegated sands, clavs, I lignite, &c. Secondary or Mesozoic Strata. Cretaceous System. Chalk. Green sand. ( Upper chalk. Soft chalk, with flints in layers. 200 < Lower chalk. Harder chalk. ( Chalk marl. Soft argillaceous chalk. r Upper green sand. Gault. Green sands. Blue marl or clay. 160 % fc L . ; Names of Formations. A + 5 * ^ ^ w jg ti S5 c M s , ^ ;* X - J^jT |^J W !U S5 la* Is * * Z ;z 55 ^ ^ * ^' V X * w w w Magnesian limestone 4 1 1 1 1 1 Coal 3 j i 1 ML.stonegrit 13 1 2 41 ' Chert group - Yordale series 17 35 2 1 4 1 fi 8 S| SJ 1 2 1 411 3|2 4 Lower limestone 15 1 4 1 2 1 S 1 1 2 Red sandstone - Whin sill 1 1 i ' 89 1 2 7 7 n 9J ^ i 1 Q 3 2il2!4 7 It appears that some remarkable ^differences of cha- racters belong to the joints and fissures in rocks of different cnemical and mineral quality. In limestone the jom;s are usually rectangled to the planes of strati- fication and frequently open and regular ; in gritstone they are very irregular, but often widely open ; while in argillaceous rocks they are usually much more nume- rous, but far less open, and often oblique to the planes of stratification. In conglomerate rocks there are few regular joints, but the rude fissures are sometimes re- markably large. On considering the occurrence of joints with refer- ence to the age of the rocks, it appears quite certain that it is among the older rocks that joints are most numerous and symmetrical. If we compare in this respect the old argillaceous slate, to the shale of a coal tract, and then with the clays of an oolitic district, or make a similar comparison of the ancient Drpnary * Geology of Yorkshire, vol. ii. i>. ^; . CHAP. IV. DIVISIONAL STRUCTURES. 6? limestone of the highlands, with the calcareous rocks of later production, this dependence of the frequency and regularity of joints, on the age of the rocks, will clearly appear. Cleavage. Among the argillaceous slate rocks, a further pecu- liarity of internal structure takes place, which is deserv- ing of special attention, since it appears to he the case of divisional planes carried to extreme in numher and symmetry. This structure, commonly called cleavage, is really distinct from joints and stratification, and may be, per- haps, understood in its relation to them by the accom- panying sketch. In this drawing, S is a plane of stratification dipping in the direction A ; c c are the edges of planes of cleav- age, which in the plane S continue in lines c' c'. These pianes are continuous, and very numerous in the fine 68 A TREATISE ON GEOLOGY. CHAP. IV. grained beds s, which alternate with the coarse beds g g, but in these latter the laminae of cleavage are often totally absent, j is a joint which varies its angle of dip in the different beds of rock. The line / /, at right angles to the dip of the strata 3 is called the strike of the bed, and is of course level ; and it is frequently observed that the horizontal line, or strike, of the cleavage, coincides with the strike of the strata. The planes of cleavage ge- nerally approach toward the perpendicular, whatever may be the amount of the dip of the strata : their course is almost exactly the same over immense spaces of country (in North Wales, in Cumberland, Charnwood Forest, &c.), and it is to them that the valuable substance called slate is owing. It is quite certain, in some instances, that this beautiful structure of the slate rocks was caused since the strata of these rocks were placed in their disturbed directions, and that it is the fruit of a peculiar degree of crystalline action in the mass ; for in some cases at Aberystwith and elsewhere, the nearly vertical laminae of cleavage cross highly contorted beds of slate dipping in various directions. There are reasons for conjecturing that this cleavage of many of the argillaceous strata is an effect due to the pervading agency of heat; amongst others we may mention the fact that near igneous rocks (as at Coley Hill near Newcastle) something of the same kind is produced in shales of later date ; and that among the Alps of Savoy, the lias clays are so altered near the axis of elevation, as to assume much of the aspect of an old slate country. The relation already pointed out between the strikes of cleavage and axes of elevation, leads to the supposition that pressure may be concerned in the result. Mr. Fox's experiments have given some countenance to the opinion that electrical currents have re-arranged the molecules in slate.* * For suggestions to observers on the subject of cleavage and joints, and a method of calculation to be applied to cases of inclined strata, see Guide to Geology, 3d edition. The Geological Intersector, a small and cheap in- strument, which has been constructed by the author, and engraved by Mr. Lowr}', may be used to represent the phenomena, and save the trouble of calculation. CHAP. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. PERHAPS geology might never have escaped from the domain of empiricism and conjecture but for the innu- merable testimonies of elapsed periods and perished creations, which the stratified rocks of the globe present in the remains of ancient plants and animals. So many important questions concerning their nature, cir- cumstances of existence, and mode of inhumation in the rocks, have been suggested by the examination of these interesting reliquiae, and the natural sciences have in consequence received so powerful an impulse, and been directed with such great success to the solution of problems concerning the past history of the earth, that we scarcely feel disposed to dissent from the opinion of Cuvier, " that without (fossil) zoology,- there was no true geology." The stratified crust of the globe may, without ex- aggeration, be said to be full of these monuments of the vanished forms of life : they are of extremely various kinds ; lie in many different states of preservation ; occur very unequally in rocks of different sorts and ages ; and thus present a large field of contemplation to the philosophic geologist. Fossil Plants. The organic remains both of plants and animals occur abundantly in the earth ; the latter are most numerous. Of fossil plants, many are terrestrial, a few are fluviatile, others are marine. In the present system of nature terrestrial plants are, probably, ten times as numerous as the marine tribes, and it does not appear that the ratio of the fossil tribes is very different. F 3 70 A TREATISE ON GEOLOGY. CHAP. V But the total number, as far as yet known, is wonder- fully disproportionate. For, if we estimate the recent species of plants at only 60,000, and the fossil races, yet clearly distinguished, at 600, numbers which are, per- haps, equally below the truth, the proportion is 100 to 1. To infer, from this fact, that the ancient globe nourished few species of plants compared to the present rich flora of different latitudes, would be unauthorised by the data, though from other phenomena such a conclusion might appear probable. We must recollect that the stratified rocks were formed chiefly on the bed of the sea, and there- fore could not be expected to contain, except rarely, the remains of terrestrial plants ; just as at this day, it is only under particular conditions of the surface drainage that vegetables are carried abundantly to the deep. And, since most of the marine plants are natant or confined to rocky shores, there would be little reason in expecting these to be common among the oceanic sediments. We must further observe, that the cellular substance of the marine tribes of plants might cause many of them to perish under the slow accumulation of the strata : nothing is less common than to find the sub- stance of marine vegetables preserved in the same manner as the ligneous parts of land plants ; and, indeed, among land plants, the experiments of Dr. Lindley show that many of them perish by macera- tion in water, while ferns, cycadeae, and other tribes, resist decomposition for a long time. Hence, it is no wonder that such races of plants are the most frequently met with in a fossil state. The ligneous parts of plants are sometimes (in the blue clays of the oolitic formation especially) converted to jet : sometimes, only the external layers of coniferous wood are so converted, while the internal parts are changed to carbonate of lime. In the latter case, the structure of every cell and vessel is distinctly seen in thin slices. When woody plants lie in limestone rock which contains silica, or in calcareous sandstone (as ii> CH. V. DRGANIC REMAINS OF PLANTS AND ANIMALS. 1 \ the coralline oolite and calcareous grit), they are often silicified : very frequently in clays pyrites aids the beauty, but diminishes the duration of the specimens. In the shales of a coal tract plants of all kinds are converted to coal of different qualities : the same effect happens in the fine grained sandstones of the coal tracts ; but in millstone grit, and other coarse sandstones, the only reliques of the plants are the external impressions of them, and a brown carbonaceous or ochraceous powder. In the upper coal measures of Lancashire, and in the shales of the peculiar oolitic strata of Yorkshire, we have found thin leaves yet retaining their elasticity, and changed to a brown translucent pellicle, in which the impressions of the superficial respiratory pores might be clearly seen. In other cases the nervures and seed vessels of fern leaves are perfectly retained in shale, fine sandstone, and ironstone. The distribution of fossil plants in the earth is remarkable on many accounts. Being for the most part of terrestrial races, it is not surprising that they should be found principally in the sedimentary strata of sandstone and clay, for it is always associated with such sediments that they pass at this day with the Mississippi and other rivers to the ocean. So strict, however, is this connection, that in a series of alternating lime- stones, sandstones, and shales, the two latter may be richly stored with land plants, and the former filled with marine shells ; neither partaking in the treasures of the other. It must be considered much in favour of this view of the dispersion of fossil plants by rivers entering the sea, that the trees are usually in fragments, the branches and leaves scattered, and roots generally wanting altogether. One case, indeed, has been appa- rently established, of the trees being buried in the very spot where they grew, by submergence of the land, " the Dirt Bed " of the Isle of Portland : but this is certainly an exceptional case ; the rule is undoubtedly contrary. Those who expect, consistently with general proba- F 4 72 A TREATISE ON GEOLOGY. CHAP V. bility, that the earliest indications of life on the globe should be of the vegetable kingdom, may be somewhat astonished to learn, that traces of plants are really not known in a distinct form in strata so ancient as those which contain the shells of Brachiopoda in the moun- tains of Wales, and that only fucoids are discovered in the silurian system. What is calculated to add to this feeling of surprise is the circumstance that in the next but one system which lies upon the silurian, two of the formations are the repository of most enormous accumu- lations of fossil plants ; for in these rocks principally lie the coal beds of Europe and America, which are nothing else than a mass of chemically altered vege- tables. How vast must have been the luxuriance of the vegetable world at that era in particular parts, appears from the thickness and continuity of the coal beds ; for it is probable that the most dense forest of tropical America would, if buried under sediments, and subjected to the changes which yield coal, produce but a very thin bed of that substance. Yet, in the coal formation, beds of three, four, six, ten, and more feet are not uncommon, and the different layers yield as much as sixty feet of solid coal. Whatever were the causes which permitted that pro- digious growth and aggregation of trees and other plants during the era of the production of coal, it ap- pears they were never repeated, for the few unimportant deposits of coal in the oolitic system of Sutherland, Yorkshire, Bornholm, and Westphalia, which are chiefly formed of cycadeae and equiseta, hardly deserve men- tion in comparison. The races of plants entombed in the earth at differ- ent periods of its formation, are by no means the same. M. Adolphe Brongniart, to whom we are indebted for almost the first philosophical view of the affinities of Jbssil plants, presents the following comparative table of the extinct and living classes of plants : CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 73 Agamia - - Cryptogamia cellulosa vasculosa Phanerogamia gyranospennia First Period Second Period. Third | Fourth Period. 1 Period. Living. 4 222 16 22 5 8 5 5 18 31 35 3 13 I 6 20 25 100 7000 1500 1700 150 8000 32,000 donia J Indeterminate 264 23 87 166 50,350 540 The first period ends with the carboniferous system ; the second includes the saliferous and magnesian systems; the third comprises trie oolitic and chalk systems ; the fourth is the tertiary period. The numbers of species are now considerably aug- mented since the table was drawn up (1829), hut the proportions are not materially affected. It is still true, that vascular cryptogamia abound in an extraordinary degree among the earlier rocks, where ferns, calamites, and what seem like gigantic lycopodiaceae are very pre- valent ; that in the second and third periods cycadiform and coniferous plants (phanerogamia gymnospermia) be- come remarkable and frequent, though ferns and lycopodiaceae still prevail ; while it is principally in the fourth period that the usual forms of dicotyledonous plants, now so plentiful on the earth, appear at all common. Moreover, on a close examination, it appears that nearly every fossil plant is of an extinct species, and that the several periods distinguished by M. Brong- niart had each its own peculiar vegetable creation, distinct from every other that preceded and succeeded it. Fossil Zoophyta. Zoophyta being in the present system of nature all aquatic, and mostly marine, they may be expected to occur abundantly in the marine strata of the earth. They are, indeed, very plentiful, and it is interesting to observe that all, or nearly all, the species are marine. It 74 A TREATISE ON GEOLOGY. CHAP. V. is further remarkable, that few traces occur of any other zoophytathan such as, like the lithophyta, secreted stony supports; or like spongiadae, had an internal horny or spicular skeleton ; or like echinida, were covered with a crustaceous skin : the soft medusidse, holothuridae, &c., are, perhaps, sometimes recognisable by faint impressions in the rocks, but their substance has wholly vanished. The soft parts of nearly all the zoophyta are absent from the fossil state. The recent zoophyta are either free in the sea, or at- tached for life after a very early period of growth : in- stances of both divisions occur in the earth. The fossil corals do not, perhaps, in general appear in the very place where they grew, but rather seem to have suffered some displacement before being buried in the oceanic sediments. But exceptions occur ; and some of the fossil radiaria which were attached by a pedicle (crinoidea) are found in several places (near Bradford in Wiltshire), yet rooted to the limestone rock. In such cases, how vain is the supposition that the deposition of the substance of the rocks was either rapid, confused, or violent. The limestones of the Devonian and Silurian systems are so very rich in corals as to suggest to good observers the notion that these concretionary and rather irregular rocks were ancient coral reefs. Calcareous matter composes the greater part of the hard parts of zoophyta ; in a few instances besides the family of spongiadae, siliceous spiculse and fibres enter into the skeleton of the animal. In a fossil state corals, echinida, crinoidea, &c., are generally calcareous ; rarely particular tribes of corals (as millepera, syringopora) are converted to siliceous matter: sponges are commonly siliceous, but sometimes calcareous. Occasionally no- thing remains of the original body ; its place in the rock is vacant, and there is left only the external im- pression or mould. These circumstances depend partly on the nature of the rock in which they are imbedded, and partly on the composition and texture of the original body. In limestone rocks the substance of coral is usually CII. V. ORGA>~IC REMAINS OF PLANTS AND ANIMALS. 75 little changed, except by the introduction of calcareous or siliceous matter into the minutest interstices ; but, in the same circumstances, the crusts of echinida and stelle- rida are converted to crystallised calcareous spar. Even in arenaceous and argillaceous strata, and amidst flint nodules where every sponge is silicified, the stems of crinoidea and spines of echinida are thus represented. A curious circumstance was noticed some time ago by the Rev. H. Jelly of Bath, concerning some lamelliferous corals of the oolite : the great mass of the coral was decomposed, and the cavity it once filled was partially occupied by pyramidal crystals of carbonate of lime, in whose transparent substance the radiating plates of the coral were clearly discernible; a fact in harmony with many other phenomena indicative of the power of crystalline attractions to overcome and involve arrange- ments of matter depending on other causes. The laws of the distribution of fossil zoophyta so far agree with what has, been already inferred concerning plants, as to prove that in this class of beings likewise, many distinct systems or assemblages of forms have existed at different ancient periods, which are all now extinct. Yet it is certain that the differences are mostly only such as belong to species, genera, and families, those minor groups of orders and classes which most distinctly reveal differences of physical condition, while agree- ments of a very general kind permit nearly all fossil zocphyta to be ranked as analogous to known living tribes. Even for the crinoidea, the most considerable exception, at least one living type is known. There is, undoubtedly, to be noticed a great difference as to the groups of zoophyta which belong to the different periods of the formation of the stratified crust of the globe ; and a considerable discordance between the forms of the oldest fcssil races, and those now actually existing. Zoophyta were collected by the author (1836) among bivalve shells, in one of the oldest fossiliferous slaty rocks of Britain, on the summit of Snowdon ; they abound to admiration in the bands of Wenlock and 76 A TREATISE ON GEOLOGY. CHAP. V. Aymestry, and in most of the limestones of the Devo- nian and carboniferous rocks. The magnesian lime- stone has a small number j certain oolites are full of them ; the green sand and chalk yield great plenty of sponges ; the calcareous and arenaceous tertiaries of France furnish many beautiful forms, of genera often the same as those now found in the sea. Undoubtedly, as a general rule, zoophyta occur more plentifully in calcareous rocks than in any others ; they are probably more numerous in the older strata ; and there are pro- bably more fossil than recent species, if we exclude from the latter, those whose bodies are unconnected to stony or horny external or internal supports. It was once imagined that the higher orders of zoophyta, those ranked by Lamarck in his group of echinodermata, were absent from the older formations ; and certainly they are, at least, not common among the very oldest fossils. Crinoidea, however, occur in the silurian rocks, and they are more plentiful in the carboniferous lime- stone than in any older or more recent deposits. Echinida and Stellerida first appear in the lower silu- rian rocks (Malvern and Wales), but become far more numerous in the oolitic and chalk systems. Sponges are by far most numerous in the cretaceous rocks. Systems. Spongiae. JLamelliferaj. Crinoidea. Echinida. Stellerida. Tertiary Cretaceous Oolitic Red sandstone Carboniferous Silurian * * * * * * * * * * * * * * * * * * * In the above table, the small stars indicate that some species of the groups of zoophyta whose names occur above are found in the system of strata on the line of which they are situated ; the large stars are placed on the line of that system of strata in which the group of zoophyta is specially numerous. CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 77 Mollusca. Recent mollusca are principally found at mode- rate depths in the sea, and respire the air contained in water; some particular tribes live in fresh water, and either breathe the air in water by branchiae, or come to the surface to respire by lungs ; others live on the land. In a very few cases certain stratified masses appe'ar to have been accumulated either in limited areas of fresh water, or in estuaries so much under the influence of rivers and inundations as to con- tain land and fresh-water shells alone or mixed with the exuviae of marine animals. But these few and excep- tional cases yield, perhaps, altogether in England not one twentieth part of the number of fossil testaceous remains ; on the continent of Europe the proportion is not very different. In the existing economy of nature, however, the land shells are so extremely numerous that, with the fresh-water tribes, they probably constitute one fourth of the total number of known species. We must not, however, conclude, from the comparative rarity of land and fresh-water shells in a fossil state, that the ancient land and fresh waters were but scantily supplied with mollusca; for, in the first place, their remains would seldom be transported to the ocean ; and further, the presumed fresh-water shells are extremely plen- tiful in the coal tracts, weald of Sussex, and fresh water beds of the Isle of Wight. The total number of fossil marine mollusca already collected is about equal to that of the living races : what may be the proportions here- after is difficult to estimate, for it is certain that great additions will be made to both the catalogues. It is not entirely without reason that geologists have been long accustomed to look on the study of fossil shells as more instructive with regard to the physical conditions of the globe in ancient times than most other reliquiae of animal life. They are of all fossils the most numerous, the most generally diffused through rocks of all ages, most perfectly preserved, and of such definable forms as to be easily described, figured, and A TREATISE ON GEOLOGY. CHAP. V. recognised. The state cf perfection in which many delicately ornamented shells occur, is such as to leav^ little doubt of their having been quietly entombed on or near the spots where they lived in the deep sea ; whi'e in other cases the disunion of valves and the fragmen- tary state, even of the most solid shells, recall to our me- mory the agitation of waves over the sands and pebbles of the shore. The hard calcareous coverings of mollusca are per- fectly preserved in a fossil state; the semi-calcareous hinge ligament of bivalves is sometimes observed in cardia, veneridse and unionidae ; very rarely the softer animal tissues. Among recent shells the most contrasted appearances of -structure are those presented by the oyster, which is lamellar, and the venus, which is, apparently, com- pact, and the internal plate of the cuttle, which is of a fibrous nature. All are full of carbonate of lime, as a hardening earth, and all mixed with membranous gela- tine, which, by its different arrangements, determines the above and other interior structures.* It is re- markable that oysters, and shells which like them are composed of distinct broad lamellae of alternating membrane and carbonate of lime, have resisted in almost all rocks, argillaceous, calcareous, arenaceous, the che- mical changes to which veneridse, trigoniae, and others of an apparently compact texture, have completely yielded. While the former retain their lamellae and pearly surfaces, the latter have often been wholly dis- solved in limestone rocks, and their places left vacant : while a cast of the inside of the shell, and an impression of the outside, disclose completely the history of the change. A further process is frequently superadded, by which the cavity is again partially or wholly filled with crystals of carbonate of lime, which has been in- troduced by filtration through the surrounding rock. In other cases siliceous matter, pyrites, and other sub- stances, have passed by a similar process. The common fossil called belemnites, of the same group as the cuttle, * See Mr. Gray on the Structure of Shells in Phil. Trans. CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 79 is a remarkable instance of the force of original struc- ture in controlling the effects of chemical agencies ; fcr in clay, sands, chalk, flint, limestone, pyrites, this sin- gular fossil generally retains its fibrous structure, co- lour, translucency, and chemical properties ; while in the same masses echini are changed to calcareous spar, and sponges to flint, and many shells have totally vanished. The conclusion which so strongly forces itself on the mind of an observer who considers the shelly treasures of the stratified rocks, that each of these was succes- sively the bed of the sea, becomes of undoubted cer- tainty, when the minuter circumstances of the distri- bution of molluscous exuviae are known. In the present seas, some shells, like the oyster, are gregareous, and cover large surfaces, so as to constitute shelly banks in which but a few species live together ; others are dredged promiscuously from a common feeding ground. There are fossil as well as recent beds of oysters, and they are in each case argillaceous beds ; perhaps cardia are more plentiful in old sandy strata, as well as in modern sandy bays ; terebratulse and lingulse are usually associated in nests or families ; and it is certain that much curious information, as to the circumstances of their existence, may be gathered from studying the de- tails of the distribution of fossil mollusca. But on a great scale they present very important truths. From the ancient slates of Snowdon to the most modern deposits in Norfolk and Sicily, the strati- fied rocks abound with shells ; and though it is certain that calcareous rocks, and the strata near to them, con- tain the greatest number, enough are found in the sand- stones and clays to furnish the means of establishing some very important conclusions. The first which arrests our attention is the continual augmentation of the amount of marine life from the primary to the tertiary period. In the following table*, drawn up by the author, the number of species known, and also the pro- portionate number to every 100 feet thickness of strata, were given for the successive systems (in 1836) : * Guide to Geology, 3d. edit. p. 68. 80 A TREATISE ON GEOLOGY. CHAP. V. No. of Thickness No. of Species to Species.* of Strata. 100 feet thickness.* Living - 5000 Tertiary - 2728 2000 137 Cretaceous 500 1100 45-5 Oolitic - 771 2500 31 Saliferous and Magnesian Carboniferous 118 - 366 2000 10,000 6 3-6 Silurian, &c. 349 20,000 1-7 The most predominant of the recent forms of mol- lusca are the classes of Conchifera, Gasteropoda, and Cephalopoda ; these are also the most numerous in a fossil state, for of pteropodous mollusca, a few traces only occur in the tertiary strata. If the distinct species of shelly mollusca be supposed to amount to 5000 species, the numbers belonging to each of these great classes may be stated thus, in a recent state : Conch if era Gasteropoda Cephalopoda - 1800 - 3100 100 The same classes, in a fossil state, contain in 5000 : Conchifera - - - 2086 Gasteropoda - - 2230 Cephalopoda - - 684 If we analyse the classes, greater discordances appear. Thus the existing conchifera, ranked in three groups, present the following proportions in 1000 : Conchifera plagimyona (Latreille) - 777 Mesomyona (Latr.) - - 194 Brachiopoda 29 but in a fossil state the proportions are, Conchifera plagimyona - - - 483 Mesomyona - 338 Brachiopoda - - -179 In the same way it appears, that while in existing nature the shelly gasteropoda ranked in two great * The numbers in these columns might now receive considerable aug- mentation ; but the proportions are not materially changed. CH. V. ORGANIC UEMAINS OF PLANTS AND ANIMALS. 81 divisions, according to their principal food, give the following proportions in 1000 : Herbivorous gasteropoda - - - 451 Zoophagous ... 549 these divisions, in the fossil state, yield : Herbivorous gasteropoda - - - 51 1 Zoophagous - - 489 It appears then, that the fossil world of mollusca differs remarkably from the actual creation in the greater proportionate abundance of cephalopoda, herbivorous gasteropoda and brachiopodous and mesomyonous con- chifera. If the whole number of species of shelly mol- lusca of the three classes named, were supposed 1000 in the fossil and recent states, the proportions of the several groups would be nearly as under : Fossil. Conch ifera plagimyona - - 205 mesomyona - - 142 brachiopoda Gasteropoda phj tophaga zoophaga 75 225 215 138 Recent. 280. 70 10 280 34O 20 Cephalopoda These differences, however, are by no means equal in all the several systems of strata: they are least in the newest, and greatest in the older classes of rocks. If the number of shelly mollusca in each of the three great periods be 1000, the proportionate number of the several classes may be seen in the following table, and compared with the recent creation. First or Second or Third or Palaeozic Mesozoic Cainozoic Recent. Period. Period. Period. Conchifera plagimyona 150 228 268 280 mesomyona 102 202 70 70 brachiopoda Gasteropoda phytophaga 320 198 105 127 8 172 10 280 zoophaga Cephalopoda 24 206 19 319 388 94 340 20 VOL. I. A TREATISE ON GEOLOGY. CHAP. V. The analogy of the tertiary to the actual system of organic nature is very apparent in these numerical pro- portions, and the distinctness of both from the older types in the lower strata is one of the most remarkable and important generalisations in geology. Nearly all the fossil mollusca, even in the tertiary system, belong to extinct species, a large proportion to extinct genera, particularly among the cephalopoda, brachiopoda, and mesomyona. The following tables*, will exhibit the numerical pro- portion of species of particular genera in the living and ancient systems of nature, and illustrate other important truths. Table I. GENERA CONTAINING MANY LIVING SPECIES. (GASTEROPODA.) . o a S ft 1 ^ |i t 3 g o "o u 3 3 0) Z2 S" O o K S &H & j" Living species In Cainozoic strata 135 19 181 49 le" 32 45 9 ~75~ 89 ~67 111 220 112 6G 71 15G In Mesozoic strata 2 1 3 I In Palaeozoic strata In this table the strong analogy of the tertiary and living forms of animals, and their distinctness from those of earlier date, are very decided. Taken from the Guide to Geology, 3d edition. CH. V. ORGANIC REMAINS OP PLANTS AND ANIMALS. 83 Table II. GENERA CONTAINING MANY FOSSIL SPECIES. (CONCHIFERA.) * a i 2 | gj 1 4 o 1 1 ^ ; "S o a ^ g i 5. 00 1 E 1 1 I Living snecies In Cainozoic strata 15 18 1 1 1 3 In Mesozoic ... 6 106 33 19 38 20 24 In Palaeozoic strata 64 90 65 10 The unequal periods of existence of different genera are here very apparent. Producta, after abounding in Devonian and carboniferous ages, perishes in the salife- rous period. Spirifera passes through all these periods and ends in the oolitic ; but terebratula occurs through all the strata, and still lives. Table III. GENERA OF CEPHALOPODA. 1 a i 8 I o. "a = ~ s | i 3 S3 1 1 7; F J " E E 3 = ^ PQ Living species ... In Cainozoic strata 2 4 p 3 In Mesozoic ... 83 22 221 30 1 5 In PaUeozoic strata - 24 57 31 53 Most of the fossil cephalopoda belong to extinct genera: of these, bellerophon and orthoceras are abun- dant in the lower and middle palaeozoic strata. Hamites, scaphites (almost peculiar to the cretaceous system, a few only in the oolites), and Belemnites, belong to the mesozoic series, and characterise the oolitic and chalk rocks exclusively. o 2 84 A TREATISE ON GEOLOGY. CHAP. V. Table IV. SUBGENERA OF AMMONITES ACCORDING TO VON BUCK AND MUNSTER. '- ^ 'I 'a .^ . a | ^ ? i 3 I 5 ~ - | ? | H : Si'-i = U T C ^ O ^ i ^ E 3 5 = Living species ... ~ "" In tertiary strata ... In cretaceous system - In oolitic system . In saliferons system In carboniferous system In Devonian strata 11 j!; 3 12 2 22 4 27 1'J >(} 5 11 9 11 14 11 13 4 2 3 5 3 These are all extinct forms, and while the greater number of species and subgenera abound in oolitic, and many in cretaceous rocks, none occur in tertiary rocks ; one group occurs in saliferous, and different types in carboniferous and Devonian strata. Thus general and particular results all agree in de- monstrating that the physical conditions of the ancient ocean must have been very different in some respects from what obtain at present; and that these con- ditions were subject to great variation during the long periods which elapsed in the formation of the crust of the earth. In the course of these changes whole groups of animals perished; others were created, to perish in their turn; and these operations were many times re- peated, not only before the present races of animals were formed, but even before the relative numbers in the leading groups approximated to the proportions which appear in the actual sea. Articulated Animals. The annulose animals form two great series ; those without jointed feet, viz v vermes, annulosa, cirripeda; GH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 85 and those with jointed feet, viz., insecta, myriapoda, arachnida, Crustacea. Many of the vermes being wholly soft, and living as parasites ; many of the true annulosa being also soft, their remains are rarely recognisable in the earth ; while serpula, spirorbis, and other annulosa with tough or shelly tubes, are very numerous. The number of these curious fossils will undoubtedly be much enlarged by careful research in all the arenaceous groups of marine and estuary strata. Already we have them from the very oldest to the most recent of the fossiliferous strata. Cirripeda are not plen- tiful, and only found in the upper secondary and in tertiary deposits. Insects which, though not wholly terrestrial, are not found in the sea, numerous as they are in the air, the soil, and fresh water, are but locally met with in a fossil state. Arachnida and myriapoda, equally unknown in the sea, are as little common as fossil insects ; but Crustacea, mostly a marine race, are not unfrequent in all the series of the strata, though generally unlike existing tribes. The following table of some of the fossil genera of Crustacea may give a correct notion of their distribution in the earth. j 1 i 3 -. 1 3 ! 1 2 I I S 3 Living Cainozoic * * * * * * * Mesozoic * * * Palaeozoic * * * * The whole great family of trilobites, including many other genera besides those named, is confined to the palaeozoic and is especially abundant in the lower palaeozoic strata. 86 A TREATISE ON GEOLOGY. CHAP. V. Fishes. The finny races of the sea and fresh waters amount to many thousand (perhaps 8000 or more) species ; those yet recognised in a fossil state are about 800, or one tenth ; but, since a few years ago the number known was very inconsiderable, and new forms are continually presented to M. Agassiz, the master of this department of fossil zoology, there is reason to suppose that the proportion of recent and fossil numbers will steadily change. One reason of the comparative pau- city of fossil fishes may be their enormous destruction for food ; thus they perish in greater proportion than the other inhabitants of the sea. In the present state of nature, we find very few fishes, or parts of fishes, in the mud of a drained pond, canal, or river ; and it is only in particular parts of the sea that the sounding line brings up from the bottom sharks' teeth, hakes' teeth, &c. It is probable, therefore, that only a small proportion of the number of species of fishes, anciently existing, is now to be obtained from the rocks. It is further to be observed, that the fleshy and liga- mental substance of fishes decomposes more readily than the soft parts of many animals j their bones, teeth, scales, &c., are, for this reason, much scattered in cer- tain rocks, which, like the sandstones of Sussex, and the forest marble of Wilts, appear to have undergone the littoral action of the sea. The circumstances under which the remains of fishes have been imbedded appear to have been various. In the upper part of the silurian system, a thin bed of fragmented fish bones occurs ; a thicker bed of ichthyoid and sauroid bones has been long known in the lias of the Severn cliffs : considerable agi- tation accompanied the deposition of fish teeth in most of the oolites, wealden beds, greensand layers, &c. But in some parts of the old red sandstone, fishes lie in great perfection in Herefordshire and Brecon, as well as at Arbroath in Scotland ; the amblypteri, holop- CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 87 tychi, c. are very perfect in the coal measures of Newhaven, and Burdiehouse near Edinburgh, Bradford, Yorkshire, the Hundriick, c. The marl slates of the magnesian limestone, the slaty lias clays of Lyme Regis, certain clays and limestones of the oolitic system, and the chalk of Lewes, have yielded abundance of beautiful marine and fluviatile fishes in an extraordinary state of perfection. Besides these, the deposits of Monte Bolca and many fresh water strata of later (tertiary) date, are stored with fishes, every part of whose structure remains uninjured. Struck with the contrast offered by these layers of fishes in ancient marine sediments, with the few and scattered fragments which occur in modern deposits, M. Agassiz has conjectured that the rate of deposition of these ancient strata must have been almost inconceivably rapid. An examination of the lamination, frequent changes of composition, alternation of organic remains, and other marks indicating tranquil and slow deposition, which occur in nearly all the localities where the fossil fishes are found in this state of perfection, does not appear to countenance these views : but we must evi- dently ascribe the destruction of whole races of fishes at a certain exact date (as in the copper state of Thuringia) to some remarkable change of physical con- dition in the liquids. The bones of fishes and other vertebrated animals differ from the internal and external shelly appendages of the lower tribes by the admixture of phosphate of lime. The state of conservation of bones differs much, therefore, from that of shells and corals ; their substance, in almost every case, remains ; the peculiar polish of the teeth and scales of many fishes causes their immediate detection ; they are generally heavy, often dark in colour, very compact and brittle ; the cells in bones are often filled with crystallised carbonate of lime, but sometimes remain open. It was therefore possible for naturalists profoundly versed in recent ichthyology, to determine the real analogies between 6 4, 88 A TREATISE ON GEOLOGY. CHAP. V. the ancient and modern finny races of lakes, rivers, and the sea, and many attempts were made to ascertain these analogies. But until modern times, the knowledge of the structure and functions of fishes, their comparative osteology and lepidology (to coin a useful word) was of small value, and it was reserved to Cuvier and Agassiz to introduce precision and certainty where all before had been error and confusion. To the latter of these eminent men M. Cuvier be- queathed his labours ; and M. Agassiz, with a happy boldness, deviated from the ordinary modes of classi- fication, and entered on a totally new contemplation of the subject. The dermal system, as a natural index of important structural and functional differences, has not, in general, been much attended to among vertebrated animals ; though the hair of mammalia, the feathers of birds, the naked or plated skin of reptiles, the scales of fishes, might have allured inquiry into the vari- ations which they undergo, and the uses they might furnish to systematists. M. Agassiz has seized this neglected thread of system, proved the importance of the indications afforded by the nature of the dermal covering, and applied it to the classification of fishes with peculiar success. Instead of the divisions usually adopted from the nature of the skeleton, cartilaginous and osseous he distinguishes four great orders of fishes from the nature of their scales, and finds that with these differ- ences of scales other great and important distinctions harmonize ; but that the possession of a bony or carti- laginous skeleton is a question of comparative unimpor- tance. The abundance and perfection of scales of fishes in a fossil state render this view, valuable as it is in recent zoology, absolutely essential to a study of the fossil kingdom ; for thus a few scales remaining may lead to a knowledge of the species or genera belonging to each epoch ; and as portions of fishes are found in every one system of strata, from the ancient silurian to the most recent of lacustrine deposits, we are presented CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 8.6fc a circle.) To the last two orders with unenamelled scales be- longs by far the greater proportion of existing species * Buckland's Eridgewater Treatise, p. 70. A TREATISE ON GEOLOGY. CHAP. V. of fishes, which, according to Cuvier, exceeded 5000 ; hut are stated by M. Agassiz to amount to 8000. On the contrary, the greater number of fossil fishes belong to the two orders with enamelled scales. In the fol- lowing table the geological distribution of these orders is sketched. Placoid. Ganoid. Ctenoid. Cycloid. Living * * * Tertiary * * * Cretaceous * * * Oolitic * Saliferous * Carboniferous * Silurian * * Among existing fishes it is frequently found that the caudal tail fin divides into two equal branches ; sometimes it is single and rounded, but in the case of some placoid and ganoid fishes (e. g. squalus and lepi- dosteus) the tail fin is double, the dorsal portion being prolonged to a considerable length, and the ven- tral portion much shorter. These three forms are seen in figs. 27, 28, 29-, which represent the trout, the 27 wrasse, and the shark. Now it is a remarkable circurn- CH. V. ORGANIC REMAINS OF PLANTS ANU ANIMALS. 91 stance observed by M. Agassiz, that all, or nearly all, the fossil fishes found in strata in and below the mag- nesian limestone, are heterocercal, or have their tails unequally bilobate, like the shark, sturgeon, lepidosteus, &c. (fig. 29.) j but this form of tail is rarely found in the oolitic and superior systems of strata. What is the general determining cause or function of this remarkable heterocercal structure in fishes is at pre- sent matter of conjecture. In the shark and sturgeon it is accompanied with a remarkable position of the mouth ; but as this is not the case in the recent lepidos- teus, or the fossil palaeoniscus, it is an unsafe basis of reasoning. Perhaps the true solution may be found in the analogy which placoid fishes in general, and certain ganoid fishes, present to the class of reptiles ; an analogy perceived by Linnaeus, and strongly cor- roborated by the recent researches of Agassiz, as to the structure of the teeth, cranial sutures, air-bladder, &c. That the upper lobe of the heterocercal tail may really be viewed as the analogue of the real tail of reptiles, appears from this, that the vertebral column is continued into it. We, therefore, view this remarkable structure as a cha- racter of the organisation of certain ancient geological periods, and refer to the scaly surface of the upper caudal lobe of tetragonolepis, and other oolitic genera, as indications of its gradual change to the truly double or homocercous tail fin (fgs. 27, 28.), which is one of the characteristics of the existing period. All the fishes of the silurian, carboniferous, saliferous, and oolitic systems, and two thirds of those in the cre- taceous system, are stated by Agassiz to belong to ex- tinct genera. Reptiles. Of the existing four orders of reptiles, batrachida, chelonida, ophidia, saurida, the two former are partly aquatic, partly terrestrial ; the two latter principally te- nants of the land. Agreeably to the general rule, the ter- 92 A TREATISE ON GEOLOGY. CHAP. V. restrial families of reptiles, and especially ophidia, are the least common in a fossil state. The greater number of reptiles found in the various formations belong to tribes which now contain many aquatic species. But they were not all destined to live in water. There are fresh water batrachians in the brown coal deposits on the Rhine, and the quarries of Oeningen ; land batra- chians (labyrinthodon) in the new red sandstones, and aquatic batrachians (?) in the old red sandstone of Elgin' (Mantell) ; land tortoises have been traced in the new red sandstone of Scotland, and the oolite of Stonesfield; fresh water turtles in the London clay of Sheppey, the Purbeck beds, Kimmeridge clay, and new red sandstone; marine turtles in the London clay, chalk, greensands, and oolites, perhaps even in the Silurians of Canada ; land lizards in the wealden and oolites ; aquatic lizards, and crocodilians in many tertiary and secondary strata ; and, finally, the bones of flying lizards have been de- tected in the lias, oolite, chalk, and London clay. In his instructive Reports on British Fossil Reptiles*, professor Owen has divided the most numerous group of fossil reptiles the Saurians, into five sub-orders, viz. enaliosauria, or sea lizards ; crocodilia, analogous to gavials, crocodiles, and alligators ; dinosauria, or mon- strous land lizards ; lacertilia, analogous to the smaller lacertae ; and pterosauria, winged lizards. Among enaliosauria, we have sixteen species of ple- siosaurus, ten of ichthyosaurus, and two of pliosaurus, distributed through the lias and oolitic formations, and ceasing in the cretaceous deposits. Crocodilia are re- presented by eight genera, viz. crocodilus, suchosaurus, goniopholis, teleosaurus, steneosaurus, poikilopleuron, streptospondylus, and cetiosaurus, which include four- teen species found in the lias, oolites, wealden and ter- tiary beds. The dinosauria are formed by three generaf, megalo- * Reports of the British Association, 1839, 1841. t Mantell has recently added a new and still mightier genus the Peloro- saurus, from the wealden formation. CH. V. OBGANIC REMAINS OF PLANTS AND ANIMALS. 3 saurus, hylseosaurus, and iguanodon. They occur in the oolitic and wealden deposits. Of the lacertilia we have seven genera, viz. mososaurus, leiodon, raphio- saurus, lacerta; rhynchosaurus, thecodontosaurus, palaeo- saurus, and cladyodon. Of the ten species of these genera, five have been discovered in the new red sand- stone series, one in the oolite, three in the chalk, and one in the crag. Of the pterosauria three species are known in the lias, oolite, and chalk. Finally. Polyptychodon from the lower greensand, and rysosteus from the bone bed of Aust, are not yet referred to their proper sub-order. Among the singularities revealed by these investiga- tions, we may notice in the ichthyosaurus the curious and beautiful combination of the swimming form and retral nostrils of the dolphin ; the teeth of the gavial, or cro- codile ; paddles somewhat like those of the turtle ; vertebrae like those of a fish ; and eyes furnished with sclerotic bones like those of birds and certain lizards. The iguanodon and megalosaurus have the " immania membra " requisite to sustain their vast bulk on land ; but pterodactylus, an almost fabulous creation, unites the wings of a bat with the skeleton of a lizard ; its long neck being formed of only seven vertebrae ; while the snake-like neck of plesiosaurus includes from thirty to forty. In magnitude some of these fossil reptiles surpass the largest crocodiles. The iguanodon not the largest of the wealden saurians may have measured forty or fifty feet in length : the batrachian of the new red must have been something like a toad three or four feet long, and the largest pterodactyl of the chalk may have extended sixteen feet and a half between the tips of the wings. The existing crocodiles offer in the saurian group a particular and distinct type, which seems to unite, in some degree, the characters of the chelonida and true A TREATISE ON GEOLOGY. CHAP. V. lizards : their life is spent, principally, in the waters of rivers which communicate with the sea (Nile, Ganges, Senegal, Mississippi) ; and they sometimes pass from the shore to prey in the salt waters. Three great di- visions of crocodiles correspond to three distinct physical regions : the alligators are wholly American ; the true crocodiles belong entirely to Africa and the West Indian islands; the gavials are found only in India. All the fossil races of crocodiles which occur in the saliferous and oolitic systems are analogous to the long- snouted Indian gavials ; those above the chalk approach the broader beaked Nilotic crocodiles. * The vertebrae of palseosaurus and thecodontosaurus agree with those of ichthyosaurus and common fishes, in being deeply concave at each end a structure evidently adapted for free motion in water. In a fossil crocodile from Sheppey they are concave anteriorly, and convex retrally. The former are really of ichthyoid, as dis- tinguished from the latter, or truly crocodilian type ; and, in a paper read to the Bristol meeting of the British Association, the discoverers of palaeosaurus and thecodontosaurus (Riley and Stutchbury) proposed the speculation that the system of doubly concave vertebrae (fig. 30.) is more ancient than that of the concavo-con- vex (fig. 31.), and that the change from one to the Thecodontosaurus. Crocodile. * Cuvier, Ossemens fossiles. CH. V. OKGANIC REMAINS OF PLANTS AND ANIMALS. 95 other may be found related to geological time. This is so far correct that it is only in and above the chalk, that the recent or true crocodilian type of vertebrae has been recognised. But there is a third and singular modification of fossil saurians ; for in streptospondylus, which occurs in lias, oolite, and wealden, the vertebra? are, contrary to those of crocodile, convex before and concave behind. (Cumer, Ossemens fossiles; Von Meyer, PalcBologica ; Conybeare, De la Beche, Riley, Stutchbury, in Geol. Transactions; Owen, Brit. Assoc. Reports, 1839, 1841.) Birds. The remains of birds are extremely un- common, even among the comparatively recent alluvial lacustrine and cavern deposits, still less frequent among the tertiary strata, and almost unknown among the older strata.* This is one of many instances which agree in proving that the occurrence of the exuviae of land animals and land plants in the stratified rocks, which were formed chiefly in the sea, is the result of causes so local, limited, and rare, as to be, in fact, acci- dental, and therefore no sufficient basis of reasoning as to what was the state of the ancient land at particular geological periods. At the present day we could learn little concerning the vegetables and animals of the land, from the few traces which remain of them in the beds of lakes, rivers, and the sea. Mammalia. The argument just used may be applied with equal justice to the paucity of remains of land mammalia in the marine strata of all ages ; for even in the tertiary rocks such remains are rare. But it is, perhaps, necessary to find other causes for the scarcity of marine mammalia in all except certain of the ter- tiary strata and superficial sediments. The opinion formerly favoured was, that during the whole of the primary and secondary periods, at least, the class of * Birds' bones do, perhaps, occur among the pterodactyls of Stones- field and Sussex, and their foot-prints appear on new red sandstones in New England. 96 A TREATISE ON GEOLOGY. CHAP. V. mammalia had no existence, and only came into being during the tertiary period. But this conclusion, founded upon the mere want of such remains, was easily seen to be insecure, and at length proved to be erroneous by the decision of Cuvier, that certain small jaw bones, with teeth, found in the oolitic system at Stonesfield, near Oxford, belonged to viviparous quad- rupeds, and approximated to the genus DIDELPHYS. Five specimens of these remarkable jaw bones are known, two of which are in the hands of Dr. Buckland, one belongs to Mr. Broderip*, one to Mr. Prevost, and the fifth was selected by the author of this volume from an ancient collection of fossils, the property of the Rev. C. Sykes, of Rooss, in Yorkshire, by whom it was presented to the museum of the Yorkshire Philosophi- cal Society. These specimens are of inestimable value, for were they unknown, the whole of the positive testi- mony that the earth, during the secondary period of geology, nourished land mammalia would vanish, and the course of inferences as to the succession of organic life on the globe be greatly modified. Further research has shown that among the few spe- cimens which Stonesfield has yielded in the course of the last hundred years are two clearly distinct genera, one of them containing two species. The designations under which they have passed are various. Compared in vain to an ichthyoid type by De Blainville, to amphibious mammals by Agassiz, one sec- tion of the fossils was brought back by Valenciennes, under the name of Thylacotherium, to the marsupial division of mammalia, to which the penetrating glance of Cuvier had united it. Professor Owen adopts for them the title of Amphitherium, assigned by De Blain- ville, but associates them with the insectivora. The two species are named after Broderip and Prevost. The lower jaw contained l6 teeth on each side, the * Since transferred to the British Museum. CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 97 five or six posterior true molars are quinquecuspidate ; the anterior false molars are tricuspid and bicuspid, as in the opossums. Of the four remaining teeth, three in front are incisors, the fourth is a canine tooth. (See Buckland's Bridgwater Treatise, pi. 2. B.) Another section, supposed by Owen to be more posi- tively related to marsupialia, is named Phascolotherium. The only species, P. Bucklandi, is represented below (fig. 32.). It has eleven teeth on each side of the lower jaw ; three or four are true quinquecuspid molars, as many tricuspid false molars, three incisors and one canine. Phascolotherium Bucklandi. (From Buckland's Bridgwater Treatise.) Those persons who, confiding in what are somewhat hastily called general views, believe too strictly in the gradual change and sequence of organic life on the globe, and have pictured to themselves the early land and sea as tenanted only by the simpler (and, as they are erro- neously termed, inferior or imperfect) forms of life, while in each succeeding period new, more complicated, and more exalted plants and animals were called into being, till man was at last awakened to the supremacy of creation, will find the fossil quadrupeds of Stonesfield a very puzzling anomaly. On the contrary, the geologist who, in the full spirit of Cuvier, regards the systems of life as definitely related now, and at all past periods, to the contemporaneous physical conditions of the globe, and uses the remains of plants and animals as monu- VOL. I. 98 A TREATISE ON GEOLOGY. CHAP. V. ments and guides to a right knowledge of these con- ditions, draws from this singular and extraordinary dis- covery the confirmation of a hope, that the state of the ancient land may not for ever be wholly concealed from patient inquiry. That these are really the jaws of mammalia, and insectivorous or marsupiferous, we may safely admit, on the competent anatomical authority of Cuvier and Owen, notwithstanding the easy conjecture, that they might belong to Pterodactylus, of which bones but not jaws occur at Stonesfield. When we regard the pointed lobes of the teeth, and consider the position of the incisors, and the shape of the condyles, there appears no reason to doubt that the animal was insectivorous. It is worth remarking that elytra of land beetles (Bu- prestis ?) are found in the same deposit, with terrestrial plants and other indications that the laminated rock, in which the specimens lie, was formed near the sea shore. No other parts of the animal have yet been found than the lower jaw, there is no ascertained or even very probable instance of the occurrence of land or marine mammalia in older rocks than the Stonesfield oolitic beds, none have yet been discovered in any of the superior strata of the oolitic system, it is merely a conjecture that some bones in the marls of the creta- ceous system of New Jersey and Delaware may belong to Balaena. With the exception of Stonesfield, it is only in the tertiary strata and superficial deposits that we can positively admit the occurrence of fossil marine or land mammalia at all. It is chiefly in anthracitic tertiaries, as near Zurich ; in lacustrine sediments, as at Ground and Oeningen ; in gypseous deposits from fresh water, as at Mont- martre ; in shelly marls, as at Market Weigh ton ; in diluvial clay or gravel, as at Harwich, at Lawford, at Hessle ; or in more recent peatbogs, as in Ireland, the Isle of Man, Lancashire ; or in caves and fissures of the rocks, as at Kirkdale, and Gibraltar, that the bones of mammiferous quadrupeds occur. CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 99 Some of these ossiferous deposits are of historical date, the others of greater but various antiquity, so as to permit the construction of the following table of the successive races of mammalia. a i 2 . ruma IL 2 O I 1 o tea 1 1 | p Q> .c fi 3 a u J_ a s 1 3 s o Diluvial - * * * * * * * * p Secondary * Primary The preceding table adds another to the proofs already given of the extreme analogy between the ter- tiary and modern periods of geology. We find in the tertiary formations remains of nearly all the great na- tural orders and groups into which systematists have divided mammalia : in most instances, however, the species, and often the genera, differ ; yet it must be borne in mind that these differences are not greater than now obtain between the animals of the analogous cli- mates of America, Africa, and India. Admitting for the moment, what must hereafter be discussed, the dis- tinctness of the alluvial, diluvial, and tertiary deposits, we may observe that in the diluvial reliquiae of mam- malia, most of the genera, and some of the species, are the same or extremely like to living tribes : while in the modern accumulations it is rare to find an extinct species, though some specimens of the great Elk of Ire- land are probably of this date. But there is one remarkable exception to this analogy of the tertiary and diluvial fauna, with our present races of mammalia ; no remains of Man have yet been found in any of these deposits no trace of his works ; and it is yet entirely doubtful whether the race of man existed at all during what are called the diluvial periods. The same exception almost extends to the order of quadrumana, which, in their animal nature and organisation, most 100 A TREATISE ON GEOLOGY. CHAP. V. nearly resemble ourselves ; for these have rarely been recognised in a fossil state.* Perhaps, however,, we ought not to insist very strongly on either of these negations : for the quadrumana could not be expected to occur often in a fossil state far from the tropical forests which might shelter and feed them ; and man only braves the cold of northern climates by his supe- rior knowledge of nature, and inventions to meet its variations. These arts and that knowledge must be supposed of slow growth ; and we may consistently believe that, though mankind at the diluvial era might not have extended to these far northern lands, where, only, the ossiferous caves and deposits have been ade- quately examined, human remains may yet be discovered in those warmer regions of the globe, which seem more congenial to the easy existence of our race, and have not yet been searched for the bones of our progenitors. The supposed exceptions to this law of the absence of the remains of man from tertiary and diluvial accumula- tions (the bone caves of Bize, near Narbonne, the valley of the Elster, &c.) may be discussed hereafter : suffice it now to say that they are not thought sufficient to establish the affirmative of this important proposition. It appears, therefore, that we must look upon the existence of man and many races of animals which, more strictly than he, are appointed to live under particular physical conditions, as characteristic of the last of several great periods of geological time, each marked by the creation of peculiar races of plants on the land and animals in the sea. From what we now see of the dependence of animal and vegetable life on climate, moisture, soil, and other characters of physical geography, there can be no doubt that to every system of organic life in the successive geological periods belonged certain combinations of physical conditions. These conditions were, indeed, not the cause of those systems of life ; but both are to be looked upon as mutually adjusted phenomena, hap- * Quadrumana have been found by M. Lartet, In the lacustrine deposit ft Sans;m, (Dep, do Gers.), by Capt. Cautley and Dr. Falconer, in the ter- tiary strata of the Sewalik Hills, Hindoostan.and by Mr. Colchester, in the red crag at Kyon in Suffolk. CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 101 pening in a determined order as part of a general plan. Some changes in the constitution of the globe have brought in succession various combinations of the mani- fold influences of those chemical and mechanical agencies which govern inanimate nature ; and such appears to be the law of God's providence, that to these combinations the forms of each newly created system of life should correspond. The several successive systems of organic life which have been discovered in the earth, were, therefore, really successive creations, and must be ex- pected to differ in large and general characters. Thus the species, genera, and families of fossil plants and animals vary from formation to formation, and system to system : yet as the constitution of dif- ferent races, enjoying animal and vegetable life, is un- equally adjusted to external circumstances, it does not follow that the creation of many new should be always accompanied by destruction of all the old forms. On the contrary, the extensive collections of fossils now made in England, prove this to be an erroneous notion : for many fossils, as Terebratulae Astacidae Modiolae Gervillise, generically, and certain species of them individually, existed during the deposition of great ranges of strata, and endured the changes, whatever they were, which brought into existence many new and re- markable forms. It seldom, however, happens that any one species occurs in more than one system of strata ; and thus we may consistently speak of the oolitic fauna and flora, as distinguished from the whole series of plants and animals belonging to the cretaceous or salt- ferous period, satisfied from adequate inquiry that few species are common to any two systems. Though at present geological investigations have not been prosecuted in all accessible parts of the land, so as every where to bring proof of the universality of these laws of successive systems of life, enough is known to assure us that in every country yet examined, the fossils of the tertiary, secondary, and primary strata differ essentially, and by large and general characters. H3 102 A TREATISE ON GEOLOGY. CHAP. V. Everywhere the tertiary fossils are closely analogous to existing types ; but in all countries the fossils of the primary strata appear to belong to a very different series. Wherever the systems of European strata can be paralleled, in North America the Himalaya Aus- tralia so much of analogy is evident in the organic reliquiae, as to prove that the successive changes of phy- sical conditions, and the coincident changes of organic life, were operated over very large parts of the globe ; and nothing, yet known, forbids us to believe that they were universally felt, though in unequal degrees, and under differences of circumstances. Could we suppose produced on the present globe some general change of conditions in the sea, on the land, and in the atmosphere either simultaneously, or by communication from a central area of disturbance the effects upon organic life might be everywhere manifested, though unequally and variously. The ex- tinction of some tribes, the decrease or enlargement of others the creation of new types to fill the void spaces of creation, and be adapted to the new conditions, might seem to us quite in harmony with the designs 01 providence, and fully in accordance with past geologi- cal effects. There would, however, be this difference in the cases: the races of animals and plants of this modern period of the globe are more various in differ- ent countries than the fossils of any one older geological period appear to have been ; there is now more of local diversity in organic life upon the globe, than formerly obtained ; and from this we infer that the physical con- ditions of the globe in former periods were more general more uniform over large areas than at present. This character of uniformity among the organic contents of a system of strata, augments continually from the modern period toward the older, and is greatest among the most ancient strata, whose organic contents, though less numerous, are more similar in all countries yet explored than those of later date. Since it thus appears that general laws of variation CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 103 connect the phenomena of all geological periods, from the most ancient to the most modern epoch, into one grand system of natural revolutions, it follows that we may look upon the present condition of our globe as one term of a magnificent series of appointed changes, to which others may from analogy be expected to follow, according to the same laws. The creation of intelligent man is indeed an event not in the calculation which man can make of the effects of such laws ; nor, indeed, is it given to us creatures of a day exactly to know the laws of variation which bind all the phenomena of nature past, present, and to come into one great system of appointed effects, flowing from a predetermined cause, much less to deduce these effects. Yet let not the search for these laws which comprises the whole of geological theory be censured as a chimerical in- quiry. The augmentation of light that has already been poured on the dark pages of geology encourages per- severance ; the extent of man's power to interpret the phenomena of nature may be vast, compared with his present knowledge ; however small, compared to the amount of things unknown. In searching for general theory we shall at least find limited truth ; and the ex- perience of some thousand years has proved the labour, which seemed vainly tasked in abstract discovery, to be seldom unproductive of practical utility. To understand rightly the daily accumulating stores of organic reliquiae, requires more than a slight know- ledge of existing nature, more even than an acquaintance with animal and vegetable forms. The philosophy of their existence must be considered the variations of their structure, with respiration in air or in water life in fresh or salt water in trees or on the ground carni- vorous or herbivorous food their geographical distribu- tion dependence on climate and atmospheric conditions. Thus viewed, the present system of nature appears, when compared with the older periods, one in which local diversities of condition have gone to extreme where all the peculiarities of climate and surface have H4 304 A TREATISE ON GEOLOGY. CHAP. T. given the fullest effect to the variety of nature, and yielded that astonishing complexity of dependent phe- nomena which incessantly engages the mind of reasoning man in an endless train of inquiry. These local diversi- ties are so great, as to permit us to propose questions con- cerning the degree of resemblance which fossil remains may offer to the recent tribes of different climates and regions of the globe. Where shall we look for the living analogues of the numerous fossil ferns, including arborescent species of great size, the sigillariae, lepidodendra, and gigantic equi- setacese, which fill the coal shales of England, the cycadeae, coniferae of the oolites, and the palms of the tertiary rocks of France ? In what climate grow the modern coral reefs com- parable to the fossil zoophytic rocks ? where live the parallels to thousands of echinida, crinoidea, trilobites, brachiopoda, cephalopoda, sauroid fishes, crocodiles, pa- chydermata, ruminantia, which characterise different geological periods ? It is difficult to answer this inquiry with precision ; for, though upon a comprehensive review, the most pre- valent analogies in modern nature point to a tropical climate ; yet as the species always, and the genera and families frequently, differ, and as, besides, other causes than climate limit the distribution of life, it is not possible to found such a conclusion on individual in- stances. A prevalence of ferns to the extent which we observe among the plants of the coal formation, is only known among the islands and on the shores of warm tro- pical seas ; but if these fossil plants had been much drifted or long immersed before inhumation, such a pre- dominance of ferns, cycadeae, &c., might be expected to happen, whatever was the original proportion ; for Dr. Lindley's experiments on recent plants prove, that long immersion in water would destroy the greater number of plants, but leave the ferns, cycadeae, conifers?, c. comparatively uninjured, as we find them in the earth. Compared as to form, the tree ferns, palms, cyca- CH. V. ORGANIC REMAINS OF PLANTS AND ANIMALS. 1 05 deae, c. indicate growth in a warm climate, as do also the gigantic lycopodiaceae, sigillariae, and calamites ; but this is not the case with coniferae. Zoophyta, hoth spongoid and stony, lead us to the same conclusion ; for the greater part of horny sponges and stony corals belong to the regions within 33 of latitude from the equator (except the S. E. coast of Australia). As far as can be judged by comparing fossil and recent radiaria (echinida, crinoidea, stellerida), the same inference ap- plies. Molluscous remains teach us little in this respect, except the cephalopoda, which, by their size and abun- dance, seem to indicate a warm climate for the cretaceous, oolitic, and older deposits. Enough, perhaps, is not yet known of the relations of fossil and recent fishes, to justify any general conclusion ; but the great families of fossil saurian reptiles prove, by their magnitude, and analogy to crocodiles, iguanas, monitors, the decided influence of a warm climate during the oolitic and cre- taceous periods ; for nothing can be more clear than the dependence of the numerous tribes of living reptiles generally, and the sauroid families in particular, upon a warm climate. More than a thousand species live in the tropical regions of the new and old world ; but only a few dwindled races visit the colder zones of Europe, and mostly enter the earth in winter, a provision where- by the animals which generate little heat in their bodies are preserved during the periods when the sources of external warmth are too feeble to sustain their functions in activity. With regard to the degree of analogy, which the productions of different regions may be found to present with fossil reliquiae, we are not aware that any investigations are on record ; and yet it is impossible to turn to Australia without a suspicion that the anomalous productions of that region have more than the average resemblance to the primeval fauna and flora. For here, and near it, tree ferns, cyca- dese, araucarise, casuarinae, grow upon the land ; corals and sponges abound on the coast even of Van Diemen's Land, while trigonia, cerithium, isocardia, a cardium 106 A TREATISE ON GEOLOGY. CHAP. V. like C. hillanum of the green sand, and quadrupeds of the peculiar marsupial races to which the Stonesfield animal is referred by Cuvier, seem to invite attention to the yet unexplored sea and land of this prolific region, as likely to yield still farther analogies to ancient animals and plants, and, by consequence, to furnish new and important grounds for determining the ancient physical conditions of the globe.* * The view here presorted (in 1836) has been confirmed by further researches, and illustrated by the remarks of professor Owen (Reports of British Association, 1842. p. 74 ). 107 CHAP. VI. HISTORICAL VIEW OF THE STRATIFIED ROCKS IN THE CBUST OF THE EARTH. IN describing the successive phenomena visible in the crust of the earth, we may either begin at the surface, and pass from the operations of to-day, through the monuments of changes performed in historic periods, to those of earlier date ; and thus, proceeding from the known to the unknown, approach by an easy gradation to the remote eras and obscure conditions of our planet, which were once degraded by the misapplied title of " Chaos ;" or take our departure at the most ancient recognisable point of geological time, and trace the events which happened on the globe in the order of their occurrence. The former process offers some advantages to the student who, unaided by or distrustful of the general- isations already arrived at, is desirous of acquiring by his own labours a correct view of the relation of the present to earlier conditions of the globe : for thus, proceeding from diurnal operations to primeval phe- nomena, he is able to classify his observations with reference to causes really acting, to assemble partial truths into laws of phenomena, and by mere comparison of these with the actual condition of nature to arrive at the knowledge he is in quest of. But for the purpose of clearly unfolding the series of geological phenomena whose laws are known, the contrary method is to be preferred. To describe what is known of the structure of the earth in the order of the occurrence of the phenomena to present a series of pictures of its successive conditions to exhibit these 1U8 A TREATISE ON GEOLOGY. CHAP. VI. conditions as influencing others which succeeded them, till the present aspect of nature appears as a con- sequence of all the previous changes, is in fact to write the physical history of our planet upon the same plan as that universally adopted for histories of its human inhabitants. Granitic Basis of the Crust of the Earth. This geological history of the earth must necessarily commence with the earliest (i. e. lowest) stratified form- ations; and the first things to be determined are, the extent to which they can be traced, and the nature of the basis on which they rest. Sufficient information is already gathered on these points to allow of a distinct affirmation, that below all the series of strata existing in any country, masses of crystallised but un stratified rocks exist so as to form a general floor, most irregular in sur- face and of unknown thickness, on which the strata successively rest. These rocks are generally of the nature of granite, that is to say, largely crystallised aggregates of felspar with variable admixtures of mica and quartz or more rarely quartz and hornblende or quartz and hypersthene. Examples of the first kind of granitic basis of the crust of the earth, are almost universal in mountainous regions ; e. g. the Grampians, the Mourne and Wicklow mountains, Cumbria, Corn- wall, Pyrenees, Alps, &c. Sienitic granite (holding horn- blende with or instead of mica) occurs about Strontian and in Ben Cruachan ; and hypersthenic granite shows itself in the Val di Fassa (Alps), gradually changing to common micaceous granite. Seeing then the probably universal extent of the granitic floor beneath the stratified parts of the earth's crust, it becomes of great importance to ascertain if the law which is allowed to hold for all stratified rocks (viz. that the lowest are the oldest), is extensible to the subjacent granite, so that it may be ranked as an older rock than any of the strata which rest upon it. A CH. VI. FORMATION OF THE CRUST OF THE EARTH. 109 Ijfp'l Arraa.1827. striking change has taken place in respect to this matter of late years: formerly, when granite was by many geologists thought to be of aqueous origin, its inferiority of position was held to be sufficient proof of anterior production ; now, when it is known to have been formed by the action of heat, this argument is of no value ; and other circumstances have been observed which leave no doubt that in very many cases the granite has been in a state of fusion since the deposition of several of the older fonnations, so that it has actually been injected into fissures and cracks of these strata, or been raised up in a fluid mass amongst them. (Diagram No. 33.) Granite veins, as these injected portions, once thought so rare, are called, have now been observed in almost every region of old strata ; entering hornblende slates, and primary limestones in Glen Tilt (Blair Athol), and clay slates in Arran, Skiddaw, and Cornwall. Granite which we thus see irrupted through and into the stratified rocks, is, in fact, of no one particular or determinate age, but is the local result and evidence of many independent excitements or periods of critical action among the subterranean agencies of heat. We may, therefore, consistently admit granite, as well as other igneous rocks, to be of any, that is, of all ages ; some of that which is visible in the crust of the globe may have been solidified from fusion before the production 110 A TREATISE ON GEOLOGY. CHAP. VI. of any of the strata ; other granite has been melted or re-melted at various later periods ; granite may yet be forming in the deeper parts of the earth, round the centres of volcanic fires ; but, in general, we must look on this rock as characteristic of particular circumstances accompanying igneous action, not as belonging to par- ticular periods of geological history. These circumstances appear, however, to have oc- curred universally, if not simultaneously ; and the tendency to produce fluid compounds which subse- quently admit of granitic crystallisation, is a cha- racteristic effect of subterranean heat in all past geological periods. It appears, therefore, a probable inference, that the formation of granite was a process which began before the production of any of the strata ; was continued during the accumulation of pri- mary, secondary, and tertiary rocks ; and is yet in action under particular circumstances in the deep parts of the earth. One of the most remarkable speculations of modern geology is that advocated by Mr. Lyell, who, in his " Principles of Geology," defends the somewhat startling speculation, that the granitic floor of the stratified crust of the earth, is nothing else than the fused and re-consolidated materials of older strata than any which are now visible, that at this time granite is forming in the same manner by the fusion of the lower portions of the strata, and that as new stratified rocks, the fruit of water, are slowly deposited above, the older ones which they cover are slowly re-absorbed by the antagonist element of interior heat, and con- verted to crystallised granite. Those who adopt this view must of necessity look on the stratified rocks as an incomplete series of monu- ments of watery action, the earliest being wholly con- sumed by heat. According to them, the history of the globe must unavoidably be imperfect ; it can, as Dr. Button remarked, show no trace of a beginning, no prospect of an end ; the appointed agencies of terrestrial nature are bound in a perpetual circle of compensation, CHAP. VI. HYPOZOIC STRATA. Ill and not united by a continuous chain of effects flowing from some one primal condition toward a determinate and permanent state. It is certain, that the study of igneous rocks alone will never enable us to decide how far this speculation is well founded, since they are not charac- teristic of time, nor capable of giving the least inform- ation as to the organic enrichment and atmospheric investment of the globe,, except by combination with the data afforded by a study of the stratified rocks. To these, therefore, we must immediately apply. HYPOZOIC SYSTEMS OF STRATA. GNEISS AND MICA SCHIST SYSTEM. v\ Composition. It is a general to^th, that to every principal mass of stratified rocks belong some remark- able mineral types of composition. The hypozoic and palaeozoic strata are distinguished by the super-abund- ance of hard siliceous and argillaceous rocks, with crystallised or concretionary limestones ; the secondary rocks have more variety of arenaceous and calcareous members ; in the tertiary strata loose sands, marls, and clays, abound remarkably, while these scarcely occur at all among the older rocks. The same truth is, perhaps, even more clearly per- ceived by comparing the successive systems and form- ations, and deserves more attention than has of late been given to it, since the study of organic remains has opened so many brilliant views of another kind, though equally related to, and characteristic of, geological time. The materials of the rocks which enter into the composition of the gneiss and mica schist systems, are such as to form siliceous, argillaceous, and calcareous ag- gregates, somewhat resembling those of the later systems of rocks ; but they are usually in a very different state of molecular aggregation. The siliceous strata of these ancient rocks (gneiss, mica schist, &c.) consist of the same minerals as those which abound in secondary sand- 112 A TREATISE OJN OTOLOGY. CHAP. VI. stones, viz., quartz, felspar, and mica, principally ; but these minerals, little or not at all worn or decomposed, compose a rock allied to granite. The argillaceous rocks, which often accompany them (clay slate, grau- wacke slate, &c.), have nearly the same chemical com- position as common clays and shales among the secondary rocks ; but the degree of induration and the whole structure of the rocks require the suppo- sition of their having undergone the influence of very different circumstances. In the same way the primary calcareous rocks, though chemically undistinguishable from secondary limestones, are so crystallised in texture as to leave no doubt that modifying agencies of great importance have operated on them since their deposition. If we seek to ascertain the origin of the materials of the oldest or lowest of all the known systems of strata, and take characteristic specimens of gneiss and mica schist for the purpose, we shall be struck with the great resemblance they offer to granite, in the kind, proportionate abundance and admixture, even colour and aspect, of the constituent quartz, felspar, mica, hornblende, &c. So close is the resemblance, that some writers appear disposed to allow for these stratified granitoid rocks, an origin not very distinct from the igneous origin of granite ; but careful attention discloses points of disagreement which are equally important, and tend to a different opinion. Let any one, for example, compare in well characterised granite and gneiss the constituents, felspar and mica: in granite these are always perfectly crystallised within, and have regular external geometrical figure; in gneiss the internal crystallisation remains, but the felspar is granular and disseminated like sand or the parts of broken crystals, and the mica is bent and contorted by irregular pres- sure among the felspar and quartz. Add to these circumstances the lamination of the masses, and we see clearly that the ingredients of gneiss and mica schist re- semble granite, because they have been derived from gra- nitic rocks; but they differ because they were accumulated CHAP. VI. HYPOZOIC STRATA. 113 under the mechanical influence of water, and not aggre- gated by chemical forces from a state of igneous fusion. The divisions of the gneiss and mica schist system are, to a considerable degree, based on the mineralogical differences of the ingredients in the predominant rocks. Gneiss, for instance, is principally composed of the same materials as common granite, viz. quartz, felspar, mica (occasionally hornblende, augite, garnets occur in it) ; mica schist is principally formed of mica and quartz, with garnets, hornblende, &c.) : in both, the ingredients are arranged in laminae ; the mica forming generally con- tinuous sheets in mica schist, but interrupted patches in gneiss. Chlorite schist differs from mica schist by the sub- stitution of chlorite for mica. In hornblende schist the mineral associated with quartz is hornblende or actynolite. In quartz rock, only a little felspar or mica is mixed with the granular quartz, and not generally arranged in layers. In gneiss, mica schist, chlorite schist, and hornblende schist, the magnitude of the grains is indefinite ; and it consequently happens that all of them admit of nu- merous variations, to which it is useless to give names, from largely granular or even conglomerated gneiss (Zetland), to a fine-grained nearly uniform admixture of mica, quartz, and felspar mica and quartz fel- spar and quartz (with or without chlorite, hornblende, &c.) In this state these siliceous rocks become very similar to certain argillaceous slates, which, in fact, in some cases, seem to bear exactly the same relation to gneiss, mica schist, &c., that common clays do to com- mon sandstones : there is every gradation between them ; their origin is undoubtedly similar it may even be called the same ; since one land flood or sea storm will form both stratified sands and laminated clays from the same wasted land or broken cliff, according merely to the difference of circumstances under which the materials are accumulated. Now it is impossible to doubt that clay slates and grauwacke slates have been deposited in water : it is equally certain that the gneiss and other felspathic or quartzose rocks, which are associated with VOL. I. I 114 A TREATISE ON GEOLOGY. CHAP. VI. it, and occasionally with clay slate, are also of aqueous production ; and the composition of gneiss, &c., com- pletes the evidence wanted to prove that the primary strata analogous to sandstones and clays were formed from the waste of granitic rocks. The structure of the rocks which compose the gneiss and mica schist system varies considerably, both in re- lation to lamination and stratification, which depend on the mode of aqueous deposition, and to joints and fissures, which are the result of subsequent agencies. Lamination prevails amongst all the varieties of gneiss, mica schist, chlorite schist, hornblende schist, &c. It is often observable in primary limestone and sometimes in quartz rock. In gneiss, mica schist, and chlorite schist, but especially in the former, the laminae are usually con- torted, sometimes excessively so, indicating a troubled condition of the water from which the ingredients fell, or a source of agitation in the still yielding sediment which seems scarcely ever to have occurred among the secondary and later strata. The only plausible explan- ation of this remarkable cir- 34 cumstance which has occurred to us, is the agitation of the sea, or the soft sediment on its bed by heat ; exactly as in the bottoms S of steam boilers, the calcareous ' sediment is formed in irregular undulating laminae, which ap- pear on a cross section very similar to the flexures in the laminae of gneiss. It will appear hereafter that this spe- culation derives some corroboration from other circum- stances, tending to show what was the condition, as to heat, of the ocean in which the ancient rocks were formed. Dr. M'Culloch informs us (Memoir on Map of Scotland, p. 65.), " wherever there are numerous and conspicuous curvatures the gneiss is granitic ; and it is the same, with little exception, where the position is angular. It is the same also, almost universally, when the beds are in the vicinity of granite. CHAP. VI. HYPOZOIC STRATA. 115 " On the contrary, extensive and prolonged beds are very generally schistose or laminar : the strata, also, are of this character when alternating and continuous with mica slate and quartz rock." Stratification, or bedding, independent of lamination, is less easily traceable in the gneiss and mica schist system than in most other aqueous rocks : yet sometimes in the gneiss of Strontian, the mica schist of the Trosachs, the chloritic schists of Loch Lomond, it is sufficiently plain, to be satisfactory proof of intermitting deposition of the rocks. This intermission of deposit is, perhaps, the true cause of the bedded or stratified structure in all rocks. When different sorts of matter are alternately deposited the bedding is most perfect ; but the reality of aqueous depo- sition is often satisfactorily shown by mere variation of colour in a mass of rocks, otherwise of continuous and uni- form character. Quartz rock (Balachulish) and limestone (Loch Earn, Inverary) associated with gneiss and mica schist, generally show stratification, but less perfectly than among more recent strata. A full examination of primary tracts will, probably in every instance, satisfy a candid inquirer that the gneiss and mica schist rocks are stratified ; but he will certainly notice cases where the bedding of gneiss is lost, the lamination of mica schist unintelligible, and the proofs of aqueous deposition far more obscure than among later rocks. Does this prove a difference of condition in the agencies concerned in accumulating these earliest strata, or can it be ex- plained by considering the original structures of deposi- tion to have undergone partial or entire obliteration through the pervading influence of heat, or local proxi- mity of igneous rocks ? for both these causes are known to have produced important effects in this respect. Superposed Structures. So many circumstances have occurred to change the condition of rocks since their first deposition, that it is probable few or none of them now appear with their original characters of texture, structure, or position. If we represent to ourselves an extended mass of arenaceous, argillaceous, or calcareous sediment, be- 116 A TREATISE ON GEOLOGY. CHAP. VI. coming gradually consolidated under the pressure of water, partially dried by the superposition of other strata, and further subject to the influence of molecular aggregation (aided, perhaps, by subterraneous heat), we shall clearly perceive that the induration of the rock must be accompanied by such a degree of shrinking in a horizontal direction, as well as compression vertically, that numerous fissures and cracks must be formed. According to some peculiar circumstances in the different sorts of rocks, the cracks and fissures assume different appearances in them; there are distinct though not easily defined characters for these divisional planes in arenaceous, argillaceous, and calcareous rocks ; and in each of these the fineness, or coarseness of grain, and the thickness of the beds make important difference. Considering further, that rocks have been, according to difference of age, proximity to the surface of the sea, and other causes, unequally subject to the modifying influences alluded to, we must be prepared to find some characteristic differences of the cracks, joints and fissures, according to the antiquity of the strata. In the rocks of the gneiss and mica schist system, we find these general results perfectly exemplified the coarse grained gneiss and mica schists show very little of either cracks or fissures across the beds ; fine grained examples of these rocks are, however, crossed by many regular divisional planes. The thick beds of crystallised primary limestones (Inverary, Glen Tilt) are less per- fectly and regularly jointed than the thin bedded lime- stones of Loch Earn and the Crinan canal. Argillaceous schists, included among the gneiss or mica schist rocks, are always much more completely or symmetrically fis- sured than any others of the series, apparently because they are of finer grain. It might appear from these observations that divisional planes were, upon the whole, less common in the oldest systems of strata than in those of more recent date j but it would be a more correct in- ference, that the rocks are generally not of a nature to admit these structures. CHAP. VI. HYPOZOTC STRATA. 11? Succession and Thickness of Strata. In the British islands we have but few opportunities of beholding a complete section of the gneiss and mica schist system ; the Scottish Highlands, in fact, must alone be appealed to and from these, perhaps, the most satisfactory result which can be gathered, is that which is derived from a general view rather than from any one district, like Braemar, Loch Sunart, or Loch Tay. Granite. Gneiss. Mica Schist. In the accompanying diagram the two great formations of which the system consists, viz. gneiss and mica schist, are placed in their order of succession above the granite. The gneiss is generally the lowest, thickest, and most extensive : it includes primary limestone (lona, Assynt) quartz rock (Assynt, Loch Eribol), hornblende schist (Glen Tilt). Estimates of its thickness must be wholly conjectural; but we may believe it to exceed many thou- sand yards. Passing to the south-east from the granite of Strontian King's House, or Cairn Gorum, we traverse the gneiss and reach the mica schist, near the base of which (Schi- hallion, Ben y gloe, Balachulish) quartz rock usually occurs. In different parts of the mica schist, primary limestone occurs in stratified masses, of limited extent and, sometimes, lenticular shape (Balachulish, Killin, Loch Earn, Inverary) ; and it seems probable these might be employed to subdivide the great mass of mica schist, were it likely to be of any use or interest where no organic remains and few mineral variations are to be recorded. The mica schist rocks are some thousand yards in thickness. The upper parts of the mica schist (Loch Earn, Loch Lomond) become chloritic, and might, perhaps, deserve i 3 A TREATISE ON GEOLOGY. CHAP. VI. to be considered as a separate formation of less extent and thickness than the others. Organic Life. In all the enormously thick masses of gneiss and mica schist, and in all the included lime- stones and quartz rocks, we find probably no traces of organic beings.* To judge from this extraordinary, and, perhaps, complete deficiency, we should say there were neither plants nor animals in existence on the globe at the time of the deposition of these rocks. But, before admitting this conclusion, it is necessary to determine whether any thing that is known of the history of these rocks would justify a suspicion that the traces of organic remains were peculiarly liable to be extinguished in them by heat or any other cause. It is a favourite speculation among a certain class of modern geologists, that the peculiar mineral, and structural characters of gneiss and mica schist are not original, but derived from the influ- ence of heat upon common sandstones and shales a greater effect of which heat would convert the gneiss to granite; and they suppose that such transformation of the substance of the rocks was accompanied by a complete extinction of the substance and impressions of the im- bedded organic fossils. Were this speculation of the origin and metamorphism of gneiss true to the extent stated, the supposition de- pending upon it, with regard to the contemporaneous extinction of all traces of organic fossils, would become plausible, perhaps probable ; but if the view which we have given of the origin of gneiss, from disintegrated granite, be correct, there is no need of supposing any considerable change of the texture of the rock by heat, and the supposition concerning organic remains is of no authority. Independent of this circumstance, we know, first, that the forms of plants, crinoidea, and shells, do remain among limestones rendered completely saccharine by heat (Teesdale); among shales indurated to a great degree (Coley Hill Dyke); among coarse and fine slaty * The notices of ortenceratites at Loch Eribol, by M'Culloch, have not been confirmed by later inquiries. CHAP. VI. HYPOZOIC STRATA. 119 rocks (Snowdon, Coniston,) which have undergone me- tamorphosis ; and, secondly, as we ascend in the series of strata, organic remains gradually appear (at first very few), and become continually more and more numerous, as the circumstances of the land and sea more approximated to the present. In the actual state of knowledge the most probable conclusion is, that during the deposition of these most ancient rocks the globe was so circumstanced with regard to heat, or some other agency, that organic life, if it had commenced at all, was exhibited at very few points en the surface of the globe. (See Table, p. 80.) Extent of Country. Within the British islands, it is to the highlands and western isles of Scotland, and to the mountains in the north-west and south-east of Ireland, that we must look for the great masses of gneiss and mica schist. The Hebrides, with Coll and lona, and nearly all the north-western highlands from Suther- land to the Sound of Mull, a length of 120 miles, are composed of gneiss : if lines be drawn from the head of Loch A\ve to Aberdeen, and to the Moray frith, the greater part of the large included area is filled with gneiss resting irregularly on the granites of BenCruachan, Loch Rannoch, Dalwhinnie, Cairn Gorum, Aberdeen, and Peterhead. Mica schist lies along the south-east side of the great valley from Fort Augustus to Lismore, spreading around Ben Nevis ; a much larger space is filled by tliis formation on the south east flank of the gneiss, from Stonehaven by Killicrankie and Dunkeld, to the head of Loch Awe and the mouth of Loch Long ; it fills all Cowal, the north side of Loch Fyne, Colonsay, and great part of Cantire, appearing likewise in Arran, Bute, and the south-western sides of Islay and Jura. Quartz rocks occupy large spaces (north-east and south- west) in Islay, Jura, and Scarba range in a narrow line (north-east and south-west) through Breadalbane by Loch Lyon and Schihallion. From Ben y Gloe to Brae- mar, and between the Spey and the Doveran to Cullen, is a mass of quartz rocks, ramified among the gneiss and i4 120 A TREATISE ON GEOLOGY. CHAP. VI. granite. An interrupted line of quartz rocks borders the western side of the gneiss tract from Loch Eribol to the southern parts of Skye. The primary limestones occupy but little surface. From the Argyleshire highlands the mica schist may be considered as crossing the Channel, south-westward, to Derry and Donegal, where it expands into the large area adjoining the sea, from Lough Foyle to Ballyshannon, and stretches inland nearly to border the basaltic platform of Antrim, being associated with granite, quartz rock, limestone, and old red sandstone. From Donegal Bay to the Bay of Sligo, and from this nearly to the Bay of Gal- way, mica schist with quartz rocks occupies a great part of the mountainous borders of the Atlantic. The Wicklow granites are bordered by narrow belts of gneiss. Except- ing very insignificant traces in Skiddaw, there is hardly any real gneiss or mica schist in England or Wales. To describe the extent of country occupied by gneiss and mica schist on the continent of Europe, would, perhaps, be impracticable, and certainly, in an English treatise, of little use ; the Pyrenees, the Alps, and the great chains of Bohemia and Scandinavia, are full of these rocks, which have much the same characters as in the Grampians and Connemara ; rest in the same way on granite (which enters them in veins); are similarly associated with limestone, quartz rocks, and serpentine; and are equally deficient of organic remains. Most of the great mountain chains of the world contain these rocks, and they may be considered as the most nearly universal strata that we are acquainted with. Physical Geography. Usually exhibited at high angles of inclination along the axes or flanks of great mountain elevations, gneiss and mica schist, with their associated rocks, derive from this circumstance a grandeur of position which gives full effect to the bold summits, abrupt precipices, deep glens and lakes, which abound in these tracts. The pointed gneiss rocks near Mont Blanc (Aiguilles), die conical tops of the quartz mountains of Schihallion, the Paps of Jura, CHAP. VI. HYPOZOiC STRATA. 121 the Sugarloaf in Wicklow, the wildly broken crags of mica schist in the Trosachs, are too familiar to need description ; but, picturesque effects of this high order depend on a combination of circumstances ; the position and hardness of the rocks relative depth of valleys and other causes ; and large tracts of gneiss in Ross and Sutherland, and of mica schist in Argyle, can by no fancy be transformed into the sublime or beautiful. Yet, even in the dreariest wastes around the heads of the highland glens the hills of gneiss, mica schist or quartz rock, contain elements of form and colour which the artist knows how to value. Mo- notonous as they sometimes are, the irregularity of their outline prevents formality ; the immensity of the moun- tains fills while it saddens the mind ; and if the scar- city of wood gives a wildness to the fairest lakes, the partial herbage, lichens and mosses, cover the hills with tints suitable to the other features of the landscape. It is not prettiness nor gentle beauty, nor antithetic effect of co'our or outline, which reward the wanderer among the Grampian Hills ; but a deep feeling of the grand and awful harmonies of nature is sure to steal into his mind, and linger there even after he has climbed the snowy Alps or sunny Pyrenees. Igneous Rock$. Granite, as was stated before, is found almost universally beneath gneiss and mica schist, sometimes touching one (gneiss most frequently), some. times the other. It generally appears to have been in a state of fusion since the deposition of these superin- cumbent strata, since veins of it are injected into their cracks and fissures. (Examples may be seen in Glen Tilt, in Arran, in Skiddaw, in Wicklow, &c.) Porphy- ritic dykes divide mica schist under Ben Cruachan, and gneiss Jn Glen Coe. A mass of porphyry has per- forated the granite and mica schist of Ben Nevis. Greenstone and other trap dykes are frequent (Perth- shire). Serpentine occurs at Portsoy, in lona, Lewis, and Zetland, in Connemara, &c. Very long and re- markable trap dykes run east and west through the mica 122 A TREATISE ON GEOLOGY. CHAP. VI. schist and carboniferous limestones of Mayo and Sligo. Mineral veins are not so abundant in these rocks in Scotland, as in Saxony, Bohemia,, &c. : it is generally near the granitic masses that they occur at all. The lead mine of Strontian is one of the most remarkable ; it may be looked upon as a metalliferous dyke. Neither hot springs nor mineral waters are common in the British tracts of gneiss or mica schist. General Inference. The preceding statements are sufficient to allow of our forming an incomplete notion of the origin and formation of the rocks contained in the gneiss and mica schist system. On a first view of the phenomena, granitic rocks of various composition appear to have been disintegrated, the separated minerals, quartz, felspar, mica, c., agitated in a peculiar manner in water, re-aggregated in laminae, and partially collected into beds. At intervals in this process there was formed in the water a chemical precipitate, limestone, seldom in extended strata, frequently in limited lenticular masses, implying a merely local agency. There is no proof, nor any very high degree of probability, that organic beings had been created no proof of the emergence of land ; but evidence of watery movements, different from the agitation of currents or the tide. To connect ah 1 these circumstances together, the least unreasonable speculation appears to be that the globe had cooled at the surface, so as to allow of the ocean col- lecting itself over the granitic basis of the strata ; that this ocean was warm, agitated by somewhat like ebulli- tion, traversed by certain gases from below, which aided in the general disintegration of the granite and in the partial precipitation of limestone ; and that the general surface of the earth was hotter than the limits of temperature within which organic life has been re- stricted by Providence. The general condition upon which all this explanation might be made to depend is the hypothesis that the earth at the time of the production of this earliest system of strata, retained within, and communicated to the surface, CHAP. VI. HYPOZOIC STRATA. 123 a much larger portion of its original heat than is now experienced. But to this speculation, and indeed to almost all the par- tial inferences which it is intended to embrace, there is the general objection made, that the present mineral aspect of the gneiss and mica schist does not prove their origin from granite, but their partial re-conversion to that rock; that the absence of organic remains in these ancient strata is a fruit of such re-aggregation of the mass of the rocks ; and that thus the whole basis of the reasoning and spe- culation changes, gneiss and mica schist become types of metamorphic rocks, and the monuments of the origin of watery action and organic life on the globe are wholly and irrecoverably lost. It must be confessed, that the doctrine of metamorphism of rocks has well explained the changes near trap dykes, in sandstones, shales, and lime- stones, has fully explained the production of crystallised minerals among sedimentary strata (Teesdale, Plas Newydd) ; but the condition of the grains in mica schist and gneiss is not such, nor is the manner of their ag- gregation such as to justify a belief that these strata have undergone so complete a metamorphosis as Mr. Lyell's doctrine teaches. They are generally indurated ; near granite rocks specially changed : every where they have suffered the influence of pervading heat, always enough to agglutinate, sometimes to recrystallise, the fragmen- tary mica, quartz, and felspar. Moreover there are cases where organic remains do occur (Dauphine'), among strata of analogous composition though different antiquity. The absence of organic remains in these ancient strata is still a fact to be explained otherwise than by the action of heat. The watery origin of these rocks is a truth ; the alterations which they have since undergone are intelligible; and, thus, we appear to be justified in rejecting the doctrine which denies the power of discovering monuments of the commencement of watery action and organic life upon the earth. 124 A TREATISE ON GEOLOGY. CIIAP. VI. PALEOZOIC STRATA. LOWER CAMBRIAN SYSTEM OF SEDGWICK. In several parts of the world the Hypozoic Strata of gneiss and mica schist are succeeded immediately, or almost immediately, by the Silurian strata, as they were defined in 1 836 by sir R. Murchison (Scandinavia, Bohemia, &c.), but in others, (Wales, Cumberland) the Llandeilo rocks, which were assumed as the original base of the Silurians, rest upon a great thickness of arenaceous and argillaceous deposits, among which clay slate is very abundant, and in which organic life is rare. Professor Sedgwick regarded these from 1832 to 1836 as the Cum- brian and lower part of his Cambrian systems ; and it not having then been ascertained that the limestone of Bala, which both he and sir R. Murchison appear to have regarded as far below the Silurian strata, was really the same formation as the limestone of Llandeilo, a partial discordance of nomenclature arose, which is not yet well settled, and which cannot be entirely settled without a full discussion of first principles. Whether we have yet sufficiently investigated all the bearings of the case may be doubted ; but these things at least are clear. If by the term " system " we mean to collect large groups of mineral deposits, with certain general physi- cal relations, and certain general relations to life, then both in Wales and in Cumberland such a system inter- venes between the characteristic Silurians of Murchison and the true hypozoic strata. But if, following views which have lately become prevalent, we fix our atten- tion exclusively on the successive great groups of life, and regard the whole "upper and lower" Silurian series of Murchison as such a group, then certainly there is no other older group known to paleontology, and we may, in the words of an earlier edition of this treatise (1837), " consistently view the organic remains of the clay-slate " and Silurian periods as belonging to one long succes- " sion of creative energy the first, if our views as to '* the origin of the gneiss and mica schist be correct, CHAP. VI. PALEOZOIC STRATA. 125 ** which was established upon the globe." But there is yet another aspect of this question. Sir R. Murchison, when he proposed the Silurian system, was perfectly aware of its divisible character, and did in fact divide it into upper and lower. To each of these divisions belongs a large suite of fossils, and they are so distri- buted that only a small percentage passes from the one to the other. If upon this basis we were to cut the original Silurian series into two systems, the Lower Silu- rians would attach to themselves all the strata above the hypozoic series, and this is really the Cambrian system of Sedgwick. But this will hardly be done without hesitation, and without a more full discussion of evidence from all quarters of the palaeozoic strata, than has yet been attempted. In the Malvern district, though upon the whole the fossils of the upper and lower Silurians are very distinct, limestones which occur in the lower group are full of fossils which are generally viewed as belonging to the upper, but they occur below sand- stones which contain the fossils of the lower series.* Perhaps no conclusion now to be adopted can be entirely satisfactory. As the matter stands at present we prefer to keep the Silurian system within its origi- nal limits, and to treat separately the strata between it and the hypozoic rocks, as a series in which the rarity of life contrasts strongly with the rich variety of organi- zation which fills the true Silurians. It is to professor Sedgwick we are mainly indebted for our knowledge of them. In his nomenclature they are ranked as lower Cambrian. -)- Composition. The type of these rocks is upon the whole eminently argillaceous, as that of the older systems is arenaceous : but between these two terms the differ- ence is not always very clear. Some proportion of alu- mina must, indeed, be present in argillaceous rocks, but it is seldom absent from arenaceous compounds: such a substance as felspar, reduced to fine particles in w r ater, might make a good substitute for clay; if left in a state * Mr-m. of Geol. Survey, vol. ii. pt. i. pp. 7375. t British Palaso/oic Rocks, 1851. 126 A TREATISE ON GEOLOGY. CHAP. VI. of granulation it might constitute an arenaceous rock, and be even called sandstone. The former is, perhaps, almost really true with respect to clay slate ; for this substance is not very distinct, chemically speaking, from decom- posed felspar which has lost or changed the condition of its potash by the operation of water : hence it happens under particular circumstances (which permit the access of alkali and the agency of great heat), that powdered blue slate is actually transformed to white and glassy crystalline grains of felspar. This is one of the results of the yet uncompleted experiments on the effects of long continued heat, instituted by Mr. W. V. Harcourt in Yorkshire. Clay slate, the simplest form of argillaceous fissile rock, is so uniform in its appearance, fineness of grain, colour, hardness and chemical composition, that mine- ralogists have often included it in their arrangements as a peculiar mineral species. Imbedded in it we some- times find certain crystallised minerals, as chiastolite or hornblende (in Skiddaw), cubic pyrites (Dunolly, near Oban, Ingleton, in Yorkshire) ; its colour is black (Skiddaw), purple (Snowdon), green (Langdale), yellow (Charnwood Forest), mottled (near Ambleside) : some varieties (Westmoreland) are translucent at the edges: others (N. Wales) opaque : there are variations of hardness, from the soft perishing slate of Skiddaw to the hard durable rocks of Langdale. If we imagine the substance of clay slate diffused amongst and around grains of quartz, felspar, mica, bits of jasper or other minerals, and the whole indurated considerably, the general title applicable to the whole series of rocks thus composed is Grauwacke, which varies in fineness of grain from what emulates clay slate to a conglomerate with quartz pebbles half an inch in diameter. Examples maybe found in Ben Ledi, the Lammermuir, the Cavan district, at Llanberis.* Structures. Amongst these rocks the evidence of successive deposition is sometimes most clear and de- * The reader will remark that the terms "clay slate," and" grauwaeke," are used to designate rucks, notformalwtis. CHAP. VI. PALEOZOIC STRATA. , 127 cisive, especially amongst the arenaceous and calcareous compounds ; in other cases, particularly among the thick masses of uniformly fine grained clay slate, very obscure. Yet, in no case, have our personal investigations among the slates of Wales or Cumbria been unsuccessful in ve- rifying the statements of Sedgwick, and detecting certain, though not obvious, proofs of consecutive depositions among all the complication introduced by later agencies. As a general rule it may be stated that lamination prevails most in the rocks of finest grain ; bed* are most distinct and continuous among the coarser grauwackes ; but the lamina observed in slate rocks are not always, nor indeed frequently, the effect of intermitting subsidence of the particles from water; for, in almost all clay slates, the predominant lamination and fissility arise from a change of molecular arrangement by influences acting since the deposition of the rock. To illustrate this, let the subjoined diagrams represent portions of clay slate and grauwacke slate, alike in all respects of structure, except the nature and direction of the lamination, D being in each a plane of stratification. In grauwacke slate (No. 37.) the laminae of deposition show on all the vertical planes, being all parallel or nearly so to the plane of stratifica- tion ; in clay slate laminae of deposition are not seen ; 37 other laminae, viz. those of cleavage, induced by some process since the deposition of the rock, cross the planes of stratification (seldom at right angles), so that the stone may be split by wedges almost indefinitely into thin plates, nearly in a vertical direction. In some cases, as shown in the lower part of No. 36., the laminae of de- position remain in clay slate; and instances occur in grau- wacke slates where one or more fine grained bands have 128 A TREATISE ON GEOLOGY. CHAP. VI. the cleavage structure, and other coarser bands have not. But the most obvious and constant marks of interrupted deposition from water traceable across cleavage planes are stripes of colour different from the mass, or thin bands of harder matter, or layers of coarser ingredients. The most perfectly cleavable slate rock, though it be almost a crystal in respect of its regular structure, shows in the quarry indubitable marks of stratified deposition ; arid where fine grained and coarse grained slate rocks alter- nate, a very common circumstance about Snowdon, the fact is perfectly obvious. Cleavage must be viewed as a structure imposed on the rock by agencies subsequent to its accumulation as sediment. What was exactly the nature of these is a problem of some delicacy, which may be better discussed hereafter : in the mean time, the following laws have been established with respect to it. First, it is never so perfectly exhibited as in the ancient argillaceous strata ; is most conspicuous among those of finest grain and most uniform nature ; disappears in very coarse rocks ; ranges in almost exact parallels over many square miles of country ; preserves these parallels even across con- torted stratification (as Plate IV. fig. 17. Guide to Geology," edit. 3.) ; and mostly coincides in horizontal direction with the great axes of elevation and depression of strata in the region observed. Finally, imperfect cleavage structures are produced in argillaceous rocks of later date near trap dykes (Coley Hill, Newcastle), and near great granitic irruptions (Vale of Chamouni). Succession of the Strata. It is only of late years that the real nature of the proof of the stratification of slate rocks has been sufficiently understood, to permit of its application to particular districts for the purpose of con- structing a section of the series of the strata. As yet only two districts in Great Britain can be considered as at all completely investigated, viz. the region of the Cum- brian Lakes, and North Wales ; but they are, perhaps, the very best for the purpose that are anywhere known. Between Skiddaw and Saddleback the base of the clay slate series is found resting on very thin mica schist and CHAP. VI. PALEOZOIC STRATA. 129 gneiss: and declining to the south-east from an axis of elevation which ranges N. E. and S. W. The dip, judged of by appearance on Derwent Water,, in Borrow- dale and Grasmere, appears to be considerable, yet not very steep : probably not exceeding, on an average of many miles, 10. The above diagram represents the whole series of rocks of this system, in their real order of superposition. The following reference will be sufficient to aid the reader's conception. fin the upper part (4) are dark, flaggy, and I slaty rocks ; the middle ('/!) abounds with C. Slaty group of Langdale, | fine green slates; near the bottom (2) most (Borrowdale),10,OOOfeetor-4 of the rocks are mottled, amygdaloidal, more. I or fragmentary : 1 is a red argillaceous I mottled rock, which sometimes appears L lik- a conglomerate. !It consists almost wholly of dark, soft, use- less slate: toward the lower parts chi- astolite abounds in it (2), and near the base hornblende (Graptolites). A. Of the gneiss and mica schist system is a mere trace, over granite. In Wales, also, these very ancient strata may be traced on the west of Snowdonia and between Cader Idris and Moel Siabod. Mr Jukes and Mr. Selwyn have presented a section of the latter district (Geological Proceedings, 1848.). The former is familiar to English geologists, in consequence of the interest inspired by the well known previous researches of Sedgvvick; and as the whole of Wales has at length been coloured on the Ordnance maps by Sir H. De la Beche, Mr. Ramsay, and their friends, and illustrated by measured sections, the data for reasoning are gradually growing complete. The section from Snowdonia westward to the Menai is, on many accounts, one cf the finest in Wales. Com- mencing in Anglesea, we have undulations of micaceous and chloride schists with quartz rocks, apparently the 130 A TREATISE ON GEOLOGY. CHAP VI. lowest (probably hypozoic) strata visible in Wales. Then follow sandstones and conglomerates black shales of Bangor other sandstones and conglomerates interstratified with trappean rocks then the fine pur- ple slates of Llanberis and Nant Francon. In all this vast series no fossils have been discovered. Above are sandstones and slates beneath the trappean group of Snowdon, on the summit of which are the fos- sils of Bala.* These sandstones, however, are much better seen in the section from Cader Idris to Moel Siabod. They are thus described by Sir H. De la Bechet: " A series of sandstones and conglomerates, with some beds of purple and blue slates, and occasionally trap rocks, about 3000 feet thick, constitute the base of that part of Wales. These are known as the * Barmouth and Harlech Sandstones,' and they are brought up by an axis of elevation called by Sedgwick the ' Great Merioneth Anticlinal/ " A trappean group succeeds above, containing con- temporaneous igneous rocks, some felspathic, some hornblendic, with beds of * ash,' probably ejected into the air, and falling in water, arranged like ordinary detritus by tides and currents, about 1 5,000 feet thick. This is formed in two divisions ; the lower, containing blue and gray slates and flagstones, is known as e the Lingula beds,' from the abundance of that shell which, with some others, occurs in them. In the upper divi- sion are many interstratified beds of black slate, often occurring as irregular and lenticular masses, and gra- duating into ' ash.' Lingula and graptolites occur in these beds, though not abundantly." Upon these rests the Bala group. This is in accord- ance with the early general views of Sedgwick. Thus by combining the information which these researches yield we have strata of slate, sandstone, conglomerate, and trappean ash, many thousand yards in thickness, below the lowest band of what was considered, in 1836', * Sedgwick, in Geol. Proceedings. t Address to Geol. Soc. 1849. CHAP. VI. PALAEOZOIC STRATA. 131 the true lower Silurian base. In all this thickness only a few organic remains occur either in Wales or Cum- berland, and all the very lowest beds in Wales appear devoid of them. Perhaps this deficiency of the remains of life is the main character by which this in each di>trici ) Western Districts. Eastern Districts. Total Number <>l Species in each Class. Cardigan. Marloes. Freshwater. Haverfordwcst. Carmarthen. Llamh'ilo. Builth. M D Tortworth. s Woolhopc. Abberley. M;ilvM-n. 4 1 B 2 B 3 5 1 1! 19 2 17 81 1 3 2 2 ~6 7 6 2 a 2 2 1 1 1 24 > 73 1 1 3 24 16 5 2 Zl M 61 2 23 3 9 4 4 B 6 12 72 3 12 in 3 1 13 24 34 2 2G 128 3 5 3 2 6 8 1 1 , 2 3 3 ~7 9 32 19 76 4 I 9 3 1 13 .'1 2 34 143 B 11 6 4 2 4 12 40 22 107 9 17 14 2 2-5 36 9 4 t9S 13 45 28 10 3 44 45 97 15 53 4 187 If, taking the same 353 species, we inquire into their distribution through the strata of the eastern region (in which deposits are most sharply defined and present the greatest variety of mineral composition) we have the following table : , 4 . r: C I 1 II 1 i i I 1 1 | 5" i 1 O M c a T E s. C 1 1 1 j 1 1 PW 1! i Upper Ludlow Avraestry rock 7 n 6 n 4 2 2 16 11 19 1" 20 28 i 5 14 96 78 Lower Ludlow 1 6 :'. 2 4 27 16 68 Wenlock limestone 2 11 7 2 j 4 o 38 ? 40 116 Wenlock shale 3 8 2 1 5 13 32 n 75 Woolhope limestone 2 1 1 20 4 29 ( 2) Caradoc (Upper) - h 4 1 3 10 1 29 2 13 66 Caradoc (lower) . ; r 2 | 2 3 3 _ 12 Black shale 4 4 The maximum, of variety appears in the Wenlock 142 A TREATISE ON GEOLOGY. CHAP, VI. limestones. The series of life appears at first small or null (the lower strata possibly belong to a period older than the true Silurians) ; then swells to a full development in Upper Caradoc ; sinks to a small amount in Wenlock shale ; expands to its fullest extent in Wenlock lime- stone; contracts again; amplifies again to the Upper Ludlow, and dies away in the Downton sandstone, which unites the Silurian rocks to the superjacent old red sandstones. Viewed on a larger scale it appears that only a small portion of the fossils of the Silurian system has been found both in the upper and lower divisions between which undoubtedly, as sir R. Murchison first remarked, a rather strong line is traceable, especially in the eastern regions, where the upper division is calcareo- argillaceous, and the lower one arenaceous. The dif- ference is less obvious in the extreme west, where the limestones nearly vanish. These limestones mark inter- vals of rest, in the generally descending movement to which the bed of the Silurian sea was subject, a move- ment which was continued through later periods, so as to cause the accumulation of many thousands of feet of other sediments brought from other points of the earth's surface by other currents, charged with other forms of marine life. To obtain these 353 species 313 localities were searched diligently. The specimens obtained at almost every locality, even in a limited district, offer something peculiar to and characteristic of place; still greater is the difference between different districts; only 9 ^ G =29 per cent being found in each of the two neighbouring districts of Abberley and Woolhope, which contain the same strata equally exposed. A few species have very wide geographical ranges : such are : Annelida. Cornulites serpularius, Tentaculites annularis, Serpulites longissimus, U. L. Crustacea Dalmannia caudata, Calymene Blumenbachii, Cybele punctata. Cephalopoda. Orthoceras bnllatum, O. ibex, O. annulatum. Heteropoda. Bellerophon trilobatus. Gasteropoda. Euomphalus sculptus, Nerita haliotis, Pleurotoma Lloydii, Turbo Corallii. Lamettibranchiata. Goniophora cymbasformis, Avicula retroflexa. CHAP. VI. PALAEOZOIC SIRATA. 143 Brachiopoda Lingula Lewisii, Orbicula rugata, Atrypa reticularis, Hypothjris Wilsoni, Leptaena depressa, Orthis elegantula, Pentamerns galeatus, Spirifera octoplicata. Echinodermata Actinocrinus moniliformis. Polypiaria. Favosites fibrosa, F. alveolaris, Catenipora escharoides, Petraia bina. Now it is remarkable that many of these are fossils which occur in more than one stratum, often, as the brachiopoda, in several so that they are thus found to be truly characteristic of the Silurian system, or of large thicknesses of it. Other shells are most abundant in particular deposits as Serpulites longissimus in Upper Ludlow, Pentamerus Knightii in Aymestry rock, Graptolithus Ludensis in Lower Ludlow, Cyathophyllum dianthus in Wenlock limestone, Trinucleus Caractaci in Caradoc, Ogygia Buchii in Llandeilo flags. The results obtained by M. Barrande in the small Silurian basin of Bohemia are very similar the same rather strong division of Upper and Lower Silurians being admissible.* In North America we have a numerous list of fossils, derived from a greater number of beds, and the general parallelism of all the deposits from the base of the carboniferous to the top of the hypozoic series, toge- ther with the gradual shading of one group of fossils into another, renders the division into Devonian, Upper Silurian, Lower Silurian, and Cambrian somewhat ob- jectionable. Hall (GeoL of New York) admits what he supposes to be Devonians into the same system as the Upper and Lower Ludlow. This classification may be useful for reference to English geologists. Subdivisions of the Rocks of the Subdivisions of the Silurian and New York System. Old Red System in Great Britain. 1. Chemung group - - -~] c~| -~] c 2. Portage group . - - 1 5 - }> 4 Tu^fy UmSone I I 1(1 ^ Upper and Lower Ludlow Rocks 5. Hamilton group - - -J Q 6. Marcellus shale - 7. Corniferous limestone) .> , c ") 8. Onondaga limestone ' 5 t^ ^ " 9. Schoharie grit- -( 5*55 3 "2 10. Cristagalli grit -) g u *^ 1> Wenlock Rocks. 11. Oriskany sandstone - - -j 12. Upper Pentamerus limestone -| 13. Encrinal limestone -J * From notices by JL Barrande and sir R. I. Murcbiscn. 144 A TREATISE ON GEOLOGY. CHAP. VI. Subdivisions of the Rocks of the Subdivisions of the Silurian and New York System. Old Red System in Great Britain. Wenlock Rocks. - V Caradoc sandstone. 14. Delthyris shaly limestone 15. Pentamerus limestone 16. Waterlime group 17. Onoudaga salt group - 18. Niagara group 19. Clinton group 20. Medina sandstone 21 . Oneida conglomerate - 22. Grey sandstone - 23. Hudson River group 24. Utica slate ----- Llandeilo flags. 25. Trenton limestone -~) 26. Bird's eye and Black River lime- f or ni? t0ne v ----- I These formations are not as fully K8EaK5**: I If [-^d in Great Britain al 29. Potsdam sandstone -J ' The ' lowest of the fossiliferous rocks' the Potsdam sandstone like some of the lower ' Cambrians/ con- tains only or almost only a Lingula. In this rock, how- ever, Mr. Logan reports * traces' of a Chelonian reptile (1851). It requires further study. In the next groups 2, 3. the number increases, but is still small. In the Trenton limestone (4.) organic remains of the Lower Silurian types become plentiful. The distinctness of the organic fossils of the Silurian rocks from those of the carboniferous formation, as far as regards the marine races, is an important truth which has received further and exact confirmation from Mr. Murchison's researches. To what extent the few fossils of the slate system are analogous to the Silurian reliquiae is not accurately known ; but there appears a sufficient resemblance between them to justify a belief that the physical conditions of the ocean were not greatly changed, though evidently rendered more favourable to the development pf a varied system of organic life. Mr. Murchison showed that each of the four formations of the Silurian system contains distinct suites and cha- racteristic species of fossils. The following are among the most common or remarkable : Ogygia Buchii, fig. 1. Pentamerus Knightii. fig. 2. Dal- mannia caudata, fig. 3. Euomphalus rugosus, fig. 4. Lep- tcena depressa, fig. 5. Calymene Blumenbachii, Jig. 6. Or- thoceras pyriforme, fig. 7. Orbicula rugata, fig. 8. Palaeopora interstincta, figs. 10, 10 a magnified. Cateniporalabyiinthica, fig. 11. Cyathophyllum cyathus,^. 12. CHAP. VI. VOL. I. 146 A TREATISE ON GEOLOGY. CHAP. VI. Geographical Extent. Ranging on each side of the Vale of Clwydd, the Silurian system continues by Llangollen, widening southwards to the valley of the Severn, which runs in it from Newton to the plain of Shrewsbury: it borders on the south the coal fields near Shrewsbury, and the Longmont and Stiperstones hills (of older rocks), and enters between these hills and the Clee hills in a long tongue directed N. E. to the Severn at Buildwas. This strike of the Silurian rocks, prolonged in the other direction to the S. W., passes by Knighton and Builth to Llandovery, Llangadock, and Llandeilo : it hence turns in the vale of Towy in a narrow course nearly west to Caermarthen, and with the same range passes Haverfordwest to St. Bride's Bay. From this central line the system expands on the south-east to Ludlow, Aymestry, and Knighton ; and this straight south-eastern border extends parallel to the range from Builth to Llandovery, into a curious narrow tongue or broken anticlinal ridge, which crosses the Wye between Builth and Hay, and ranges towards Trecastle. (From Mr. Murchison's Observations.) About Dudley and Walsall the Ludlow formation is admirably exhibited in singular narrow and short anti- clinal ridges, rising in the midst of the coal formation of South Staffordshire, near the hills of basalt called Rowley Rag. These anticlinal ridges run north and south, in parallel courses (Sedgley, Hurst Hill, the "Wren's Nest, and Dudley Castle Hill make four such ridges, the two latter being extremely clear), and against them all the coal strata rest at considerable angles of inclination. The diagrams fig. 40. and fig. 41. are in- tended to illustrate the curious structure of this region. In Westmoreland and Yorkshire the upper Ludlow formation occurs near Kirkby Lonsdale, yielding fossils, and what I have supposed to represent the Llandeilo rocks in Ribblesdale, a conclusion placed on good evi- dence by a late investigation of Sedgwick (Geo/. Proc. 1852). Ireland contains the Silurian system, especially in CHAP. VI. PALEOZOIC STRATA. 147 a. Sedgley ridge, or anticlinal, containing the Aymestry limestone. 6. Hurst ridge. c. Wren's Nest, Wenlock limestone. d. Dudley Castle ridge, Wenlock limestone. c. The Hayes, upper Ludlow formation. /. Rowley hills of basalt. g. Barrow hill of basalt. h. Coal deposit, resting somewhat unconformedly on the Wenlock formation, and partly resting on, partly passing under, the Rowley basalt which chars it. Tyrone. The Llandeilo limestone forms a line from Broughton by Coniston Waterhead to Hougill fells, and between this and Kirkby Lonsdale are fossiliferous schists. The Lammermuir Hills present on their nor- thern side a considerable exhibition of Silurian strata (Sedgwick, in Brit. Assoc. Rep. for 1850). In Brittany Silurian fossils occur : the limestones of Christiania and Gothland belong to this system. Perhaps the most remarkable and complete series of Silurian deposits on the continent of Europe is that of Bohemia, worked out by M. Barrande, from whose patient hands a valuable memoir is expected. It is said by Mr. Strickland to occur about Smyrna with asaphi. It is found near Oporto with coal (Sharpe). Perhaps it is from these rocks that trilobites are obtained near the Cape of Good Hope, by Sir J . Herschel. In North America the Silurian system is largely developed : its classification contains many more terms than have been found necessary in Europe. The L 2 148 A TREATISE ON GEOLOGY. CHAP, VI. ^ distribution of organic remains in it is in many respects very similar (Hall, Geol. of New York). Physical Geography. Lying on the sloping sides of the slate systems of Wales and Cumberland, the prin- cipal masses of the Silurian rocks show but little boldness of feature, compared to these older rocks : frequently, as in the beautiful neighbourhood of Ludlow and Aymestry, and in the Vale of the Towy, they are richly covered with woods, as ancient, perhaps, as Ca- ractacus. The limestone country about Dudley is pleas- ingly varied. Igneous Rocks. These are abundantly exhibited in irruptive axes and points throughout the Silurian form- ations. Lilleshall Hill, the Wrekin, and other points about it, consist of compact felspar, ranging N. E. and S. W., and they convert sandstones into quartz rock. Caer Caradoc, the Lickey, Helmeath, &c. constitute a similar and parallel group of hills, in which greenstone, actynolitic trap, &c. occur : similar changes happen to the sandstones which touch the trap : the argillaceous rocks are indurated and much altered. The Breiddin group of hills consists of porphyries, compact felspar, greenstone, &c. ; and near these the strata of the Silu- rian system are indurated and fissured. The same range (N. E. to S.W.) is noticed in the trap rocks near Old Radnor, Builth, and Baxter's Bank, near Llandrindod. Hypersthene abounds in traps near Old Radnor, and great changes happen to the Ludlow and Wenlock rocks near them : limestone becomes crystallised ; shale is indurated ; anthracite, copper ore, iron pyrites, and bad serpentine, are generated at the contact. The large trap district of Llandegley, Llandrindod, and Builth, pre- sents a variety of such phenomena, and the mineral springs of Builth, Llandrindod, &c., are supposed to be residual effects of the same igneous agency. In Breck- nockshire and Caermarthenshire, similar phenomena are repeated around several erupted masses of trap. The Malvern hills consist of Silurian rocks resting on a granito-syenitic base, which has been uplifted with CHAP. VI. PALEOZOIC STRATA. 149 them, so that the beds are vertical or even retroverted, and bent in anticlinal and synclinal axes. The Abber- ley Hills, Woolhope Forest and May Hill, are very interesting groups of Silurian strata. Mineral Feins. In the Shelve district of Shrop- shire, and at Nant y Moen, seven miles north of Llan- dovery, the lead mines are so related to the axis of irruption of the igneous rocks, as to leave no doubt of the propriety of classing them as an effect of the same volcanic excitement, not perhaps contemporaneous with the irruption of trap, but certainly and strictly asso- ciated with it, and dependent upon it. Sulphate of barytes, sulphuret of iron and carbonate of lime, ac- company the ores of lead. Close of the Silurian Period. Ensuing Disturbances of the Crust of the Globe. There is almost a total absence of proof, in the mineral composition and organic contents of the Silurian strata, of the contemporaneous existence of dry land : for all the early periods at least, the absence of land plants, and the infrequency of conglomerates, seem to justify a doubt whether the sea of that period was subject, in the regions now dried, to any thing of the nature of violent land flood, or great littoral agitation. Yet it is not only probable but proved by some instances in Wales, that the bed of the Silurian sea had been somewhat disturbed before the completion of the system. For, along considerable lengths of the boundary of the Caradoc sandstone, this littoral rock is found to rest unconformedty on previously disturbed rocks of the Llandeilo and earlier groups, f There is, however, nothing to contradict the assumption that, till the close of the lower palaeozoic period, nearly all the strata of the British Isles and the continent of Europe were covered by the sea in which they were formed : indeed, * Murchison, Proc. of Geol. Soc. 1834. f Ramsay and Aveline, in Geol. Proceedings, 1849. L3 150 A TREATISE ON GEOLOGY. CHAP. VI* it may be doubted, whether any certain proof can be shown that any part of the European region was sub- jected to great displacement during this period. It is true that a survey of the porphyries, green- stones, and other igneous rocks, so strangely interlami- nated among the clay slates and grauwacke slates of Snowdon, and the middle Cumbrian region, from Black Comb to Ulswater, appears to prove that at certain periods during the formation of these rocks, erup- tions of melted rock occurred over a great extent of the oceanic bed ; and such we must suppose were accompa- nied by considerable, if only transient, movements of the solid crust of the globe. Elie de Beaumont has supposed that some of the most considerable displace- ments of primary strata which are observed in Europe, happened before the completion of the newest of those strata ; but it cannot be satisfactorily proved by ex- amples taken from the British Islands. Indeed, every fresh inquiry into the geological dates of particular disturbances of the strata, shows the difficulty of arriving at accurate conclusions on this important subject. The evidence is sometimes insufficient ; in other instances complicated with the effects of convulsions of later date, but similar geographical positions ; and how- ever strange it may appear, it is nevertheless true, that the strongest arguments in favour of the convulsions having occurred within particular limits of geological time, have been based on comprehensive views of a whole physical region, rather than on a minute scrutiny and complete survey of the details of the position of the strata, at the line of junction of the displaced and the undisturbed rocks. After the lapse of most part of the Silurian and before the commencement of the old red period (whatever the interval of time was), great disturbances happened, which uplifted large parts of the bed of the sea, and either raised them above the surface into dry land, or, at least, placed them in such situations that no further deposit of strata was spread upon them at later CHAP. VI. PALEOZOIC STRATA. 151 periods. In many instances the Silurian and old red strata are unconformedly situated with respect to one another, as in the subjoined section (fig. 4-2). and the geological map of the country shows superficial unconformity of direction and dip of strata as in fig. 43. The position of the 43 secondary strata is discordant with re- spect to the primary, both in dip and di- rection ; because these latter were disturbed from their original position by subterra- nean forces, and the bed of the sea upon which the secondary rocks were subsequently spread entirely altered in form. The unconformity, above exemplified, is the geological proof that the older strata had been disturbed previously to the formation of the newer ; and the reason for thinking they had been in many cases actually raised into dry land, is the total absence of any later deposit upon them : the former is a most certain conclusion ; the latter is frequently a highly probable inference. In the British islands we have magnificent examples of these ancient disturbances. The range of the Gram- pian mountains from Aberdeen to Cantire, and indeed most of the Highlands, appear to have been uplifted at this early period, if not to the surface, yet so as to prevent any depositions upon them ; though round the east and west coasts of Scotland, the south border of the Grampians, and in the great valley of the Caledonian canal, the old red sandstone rocks abound. It is sup- L 4 152 A TREATISE ON GEOLOGY. CHAP. VT. posed that about the same period the Lammermuir hills were raised ; and the Cumbrian mountains received one of their great upward movements. It is important to remark in connection with this subject, that along the borders of the Grampian, Lammermuir and Cumbrian ranges, the red conglomerates contain enormous quan- tities of pebbles, which appear to have been gathered by inundations from the surface of the broken rocks of the neighbouring slates, gneiss, &c. : if in addition we remark the fact that, especially in Cumbria, these conglomerates fill valleys at the border of the tract of the slate mountains, we shall see the probability that the slate rocks were raised above the surface to be washed by atmospheric rains, or else so near the surface as to be exposed to the agitation of shallow water. The former is the most probable view. The slate and mica schist tracts of the Isle of Man, Donegal, Galway, Wexford, Wicklow, Cavan, and Down, appear to have been similarly raised ; and the same is supposed to be true for the Snowdon and Berwyn ranges in North Wales, and the Ocrynian chain of Devon and Cornwall.* We must, however, remark on these last-mentioned cases that, on the south-east border of Wales certainly, and in Cornwall probably, there is no observable un- conformity between the old red and the Silurian rocks. Were the displacements thus shown to have happened in the bed of the sea over so large a portion of the British islands, sudden or gradual ? To decide whether violent uplifting, or a gentle intumescence of the rocks, lifted the Grampians or the Cumbrian mountains, would be difficult in the present state of our knowledge ; yet there are considerations which would render it pro- bable that a considerable time elapsed in the process. Amongst others, this appears worthy of notice : the secondary strata, around these and other tracts, dip at high angles from the centre or axis of the older rocks, the most modern rocks occupying the lowest; ranges ; * Sedgwick, in Address and Memoirs to the Geological Society. CHAP. VI. PALAEOZOIC STRATA. 153 and thus appear to teach us that the elevatdry action, whatever might be its first violence, was continually exerted in the same localities, late into the secondary period. 44 The surface of the earth has, however, undergone since so many changes, that it is difficult to say how far this argument can be safely trusted. Another highly interesting problem arises out of the admission that all the displacements of rocks, previously noticed, were nearly contemporaneous : they are found to be all raised on axes nearly parallel to a line from S. W. to N. E. ; and it is required to be determined whether this proximate parallelism of contemporaneous axes of elevation is a general law of the phenomena. M. E. de Beaumont is the geologist who has most strenuously advocated the affirmative of this question ; but it is certain that more rigorous investigations are needed on the subject, before any physical theory, like Mr. Hopkins's ingenious view, can be safely applied to the data. It is extremely diffi- cult to assure ourselves that the elevations above noticed, as on parallel axes, were really contemporaneous, or even very quickly succeeding, because nothing canbemore complete than our ignorance of the duration of past geological periods ; and, in order to render the expla- nation of such parallelism consistent with Mr. Hopkins's demonstrations, the occurrence of parallel elevation must be really synchronous. The elevations on the continent of Europe of or about this ancient period (anterior to the formation of the carboniferous rocks) are located in Brittany, the Harz, the Hundsriick, the Eifel, the Ardennes. Whence came the materials of the great mass of de- posits which rest upon the primary gneiss and mica schist? 154 A TREATISE ON GEOLOGY. CHAP. VI. Probably the true answer to this, though we cannot now give adequate proof of it, is that the disintegration of granitic and other igneous rocks, to which, on what seem good grounds, we have already ascribed the origin of gneiss and mica schist, has been the prolific source of all these sedimentary strata. Analysis of the principal rocks of the slaty systems does certainly not contradict this view ; which neither those who admit with Leibnitz the first solid covering of the globe to have been a mass of rocks cooled from fusion, or, with Lyell, that strata added above, are melted and reabsorbed into granite below, have any reason to deny Moreover, we see daily, on the slopes and at the foot of hills composed of trap rocks, considerable quantities of loosely aggregated sands, which to all appearance, if agitated in water, might be undistinguishable from va- rious secondary or Silurian sandstones. The abundant detritus which surround the basaltic hills of Rowley, the sienites of Mount Sorrel, and the granites of Arran, are in this respect very worthy of attention, and may suggest to those who have the opportunity a train of valuable research, which might elucidate many points now obscure in the history of the disintegrated ma- terials of igneous rocks. DEVONIAN SYSTEM. The composition of this group of strata is formed upon one general model in all the parts of Britain north of the Severn ; but we may distinguish two varieties in this plan. First, the series of the Grampians, Lam- mermuirs, and Cumbrian region, may be thus stated in general terms : Upper part. Conglomerate, full of quartz pebbles, concre- tionary limestone and variegated sandstone. In this group occurs Holoptychius nobilissimus. Middle part. Gray fossil sandstone. Cephalaspis Lyellii is found in this group. Lower part. Red and variegated sandstones ; bituminous schists with dipterus. Coarse sandstone, or sandstone CHAP. VI. PALAEOZOIC STRATA. 155 and clay with calcareous nodules constitute a fish-bed. Thick masses of conglomerate ; the basis red sandstone, the imbedded pebbles of various, often great size, derived from the neighbouring mountains. Pterichthys and Coccosteus are among the characteristic fishes of the lower part of the old red. * On the borders of the English Lake district we have this combination reduced to a small thickness, and deprived of its upper term. The best sections are seen about the foot of Ulswater, in valleys near Kendal, and at Kirkby Lonsdale. At this latter place we have Red and light coloured clays with some concretionary lime- stone Ccornstone) resting on Conglomerate of pebbles derived from the older Silurian strata, which appear higher up on the sides of the valley. A little further to the S. S. E. the old red series is totally deficient (Craven), and nearly so in Flintshire. A second combination of the similar elements appears on the border of Wales, and acquires distinctness in the region south of Shrewsbury. An excellent general section is obtained in the country between Dean Forest and the Silurian Vale of Usk. It may be thus ex- pressed t : Upper part. Conglomerate of quartz pebbles and some other fragments, imbedded in red, purple or greenish sandstone. (Holoptychius occurs here.) Middle part. Thick laminated red sandstones, with thin marls and some cornstones. (Cephalaspis occurs here.) Lower parts. Thick red marls, with greenish bands and blotches, and irregular masses of cornstone. At the base, beds of sandstone gradually passing into or alternating with the top of the upper Ludlow formation. In all the strata enumerated, and in all their locali- ties, the rarity of in vertebral remains and of vegetable fragments is remarkable. Only a small number of bivalves (not brachiopoda, possibly freshwater shells,} has occurred to Mr. Miller in Scotland. Fishes have Miller's Old Red Sandstone. t See Murchison's Silurian System for a full account (the earliest) of the old red in these districts. 156 A TREATISE ON GEOLOGY. CHAP. VI. been found abundantly in many parts of Scotland, and rarely in Herefordshire and Breconshire. We now pass the Severn, and find a great change. North Devon exhibits both the old red series and the true carboniferous series in an aspect much different from their northern types. The series stands thus : Pilton group. A series of sandstones and shales, with sub-cal- careous beds or nodules, very fossiliferous and much ana- logous to the lower carboniferous shale. Below are the more truly Devonian equivalents of old red. Morthoe group. Fine grey, green or purple slaty beds, with sandstones and argillaceous shales. No fossils. Ilfracombe group. Argillaceous slates and limestones, corals, brachiopoda, plants. Martinhoe group. Red, brown, grey and claret coloured grits and slates. No fossils traced. Linton group. This is a thick mass of laminated grey grits and hard shales, partially affected by slaty cleavage. The fossils are not of many species, but are extremely fre- quent, and appear the more strikingly in this protoxidated mass, because the red groups above and below are devoid of organizations. Foreland group. Red and grey grits. We may now proceed to South Devon. The groups here observed are not to be placed in strict mineral or structural affinity with the coeval series in the north. The best section is afforded in Plymouth Sound, but enormous contortions prevail. Red sandstone group. Consists of red sandstone, and schists alternating with grey and purple shales and schists. Poly- piaria, crinoidea, brachiopoda, in the latter. Grey schists and calcareous beds. This is a very large and complicated group with trappean and ashy beds inter- posed irregularly. Polypiaria, crinoidea, brachiopoda. The Plymouth limestone series. A few partings of shale in this otherwise very solid coral rock, for such in a great degree it really is. Purple slaty rocks, still retaining their lamination. No fossils. By tracing these beds farther westward Silurian strata appear beneath them. Organic Remains. By uniting in one summary CHAP. VI. PALEOZOIC STRATA. 157 the fossils of the Devonian and Caledonian types of old red in Britain we have a pretty full catalogue of invertebrata. Polypiaria Crinoidea Lamellibranchiata - Brachiopoda Gasteropoda Cephalopoda - Heteropoda Crustacea - - - 9 No. of Species. 34 16 46 83 36 44 7 Of these, 25 species are also found in the Silurian system; and -51 in the car- boniferous limestone series, 57 occur in the Devonian strata of the Eifel, a kme- stone district wkich corre-! spends with the Plymouth 275 group. * As characteristic Devonian forms we may mention 1. Cystiphyllum damnoniense. a. Lamellae, 2. Strombodes vermicularis. a. Lamellae. 3. Leptaena nodulosa. 4. Calceola sandalina. 5. Palaeopora pyriformis. 6. Strigocephalus Burtini. 7. Cyrtoceras tredecimale. a. Aperture. 8. Clymenia laevigata. a. Aperture. 9. Brontes flabellifer. The fishes of the old red sandstone which have been systematized by Agassiz, and described with much effect by Miller f, are very characteristic of this palseo- zoic period. The classification of Agassiz, presented to the British Association in 1843, includes 63 British species, viz. : Placoid. Ichthyodorulites 6 ; Cestraciontes 1. Ganoid. Lepidoid 33 ; Sauroid 13 ; Coelacanthoid 10. Some of these, as well as a considerable number of the invertebrata, occur also in Russia, the only region which presents something like a fair example of the Phillips in Palaeozoic Fossils of Devon and Cornwall. See also the earlier investigations of Lonsdale (Geol. Trans.), and the later researches of M'Coy (British Palaeozoic Fossils). t The Old Red Sandstone. A TREATISE ON GEOLOGY. CHAP. VI. 2 a. CHAP. VI. PALAEOZOIC STRATA. 6 159 8 a 160 A TREATISE ON GEOLOGY. CHAP. VI. whole fauna of the middle palaeozoic period.* Mantell has recently described a batrachian ? reptile (Telerpeton Elginense) from these strata t, and eggs of the same group are reported from the old red shales of Forfar- shire. Geographical Extent. It is in Scotland that the old red formation is thickest, most varied in composition, and most extensively distributed. It ranges on the N.N.W. coast in interrupted patches from near Cape Wrath to Loch Carron, Skye, and Rum ; on the N. E. it forms a large surface in Caithness, skirts the Dornoch and Moray Friths, passes up the great valley to Meal Favournie, and spreads by Nairn and Elgin to the Vale of the Spey. A large belt of red conglomerates borders the Grampians, from Stonehaven to the islands in the lower part of Loch Lomond, and occupies much of the sea coast to the Frith of Tay. Red sandstones border the northern flanks of the Lammermuir hills, expand in the Vale of Tweed, and margin the slate tracts of Dumfriesshire and Kirkcudbright. Arran, Bute, Can- tire, and the coast about Largs and Ardrossan show the same formation. In England the old red sandstone sometimes appears associated by alternation of beds with the lower part of the mountain limestone series, especially on the eastern border of the Lake district about Penrith. Its conglo- merates appear at the foot of Ulswater, and in valleys about Kendal, Kirkby Lonsdale, and Ulverston. It is enormously developed, and acquires more variety of composition in the counties of Hereford, Monmouth, Brecon, Carmarthen, and Pembroke ; and is slightly exposed in connexion with the limestones of Mendip, Bristol, and Wickwar. The old red changes its character, but occupies a large space, on the southern coast of the Severn, and again in a parallel course along the shore of South Devon. Devonian rocks appear in the Eifel, in the * Murchison's Geology of Russia, t Geol. Proceedings, 1852. CHAP. VI. PALEOZOIC STRATA. l6l Rhine and Moselle, and are largely developed in Russia. ' They pass Livonia by the Lakes of Ilmen and the Waldai hills, and are extended over a vast region to the N. E., where they constitute a large portion of the shores of the White Sea.'* Analogous in mineral aspect to the old red formations of England, they contain, together with the character- istic fishes of Scotland and the brachiopoda of the forma- tions as seen in Devonia, Westphalia, and Belgium ; but they contain, in addition, salt springs and gypsum. A dome-like elevation of Devonian rocks (800 feet) occurs in the centre of European Russia, (Orel, Voro- neje), full of fishes and mollusca imbedded in yellow and white marlstone and limestone, t The changes to which geological classification is rea- sonably liable appear in nothing more conspicuous than in the division of the great carboniferous system, as it was expounded by Conybeare (1829), into two systems, the lower being formed of the old red sandstone, as it appears on the borders of Wales, Cumberland, the Lammermuirs, and Grampians, and in a quite different form in North and South Devon. In the former dis- tricts the old red is still very poor in organic life, except in the class of fishes ; but the Devonian series, poor in fishes, is rich in zoophyta, mollusca, and crus- tacea. As it is mainly by pala?ontological evidence that modern geology is guided, the now prevalent term for these strata is the Devonian system, which is found to be represented extensively in European Russia and North America, and probably in Africa. The fauna of the Devonian beds is certainly distinguishable from that of the rocks above and below : it has enough of an intermediate character to complete the harmony of the palaeozoic groups, and yet enough of distinctiveness to demand an independent place. This place was not assigned till after many examina- tions of the characteristic fossils of South Devon, of which some were first figured by Mr. Sowerby (Min. * Murchison, in Geol. Proceedings, 1841. t Ibid, 1842. VOL. I. M 162 A TREATISE ON GEOLOGY. CHAP. VI. Conchology}. In 1830, when composing the article Geology for the Encyclopaedia Metropolitana, (published 1833,) my attention was caught by the singular fact of the classification of these Devonian rocks among the transition (Silurian) strata, while the fossils then known bore a great analogy to those of the mountain lime- stone ; and I could not avoid expressing a strong doubt that these strata were really of so high antiquity. The doubt was more than confirmed (in 183740) by the united labours of Murchison, Sedgwick, and Lonsdale, the result being the establishment., by Mr. Lonsdale, of an intermediate group of fossils in an intermediate group of strata, the now well-known f Devonian sys- tem' (Geol. Trans., 1837 to 1840). In 1837, Murchison, in his ' Silurian System/ raised, for the first time, the old red to the rank of a system, and in 184-2 completed the evidence on this subject by an examination of Russia. Since that time the Devo- nian system has been generally adopted. Yet still we must not forget that a strong physical relationship binds together the peroxidated old red to the protoxidated blue shales of the mountain limestone ; that in all the districts of Britain they are in parallel deposits ; and that beds of red sandstone enter into the composition of the lower lim&stone series in the north of England. t CARBONIFEROUS SYSTEM. Composition. Six substances are interstratified in this system : arenaceous, argillaceous, and calcareous rocks form the principal masses, and are associated with beds of chert, ironstone, and coal. Some of the arenaceous rocks are conglomerates, as millstone grit, which is partially filled with quartz, felspar, and fragments of shale, the mingled spoils of granitic rocks, quartz veins, and schists; others are freestones of an open grain and equal texture, breaking equally in all directions ; others are compact close grits, called hazle ; or stiil finer grained, called cal- liard ; or laminated with mica, or carbonaceous matter, CHAP. VI. PALAEOZOIC STRATA. l63 as flagstone. In colour these rocks are white, brown, grey, greenish, yellow, or red. There is almost every possible gradation between the sandstones and argilla- ceous deposits ; which latter are frequently much lami- nated, and are then called plate, or bass j less remarkable lamination causes shale ; deficiency of lamination be- longs to some varieties, associated with coal, called clunch, bind, and other local names : most of them are more or less bituminous ; colour blackish, greyish, bluish, yellowish. The limestones are compact or oo- litic, or granularly crystallised ; mostly pure carbonate of lime (except the granular sorts, which usually contain magnesia), white (rarely yellowish), grey, blue, black, red, or mottled. Some beds contain quartz pebbles. Nearly all are of marine origin, but some exceptions occur. Chert nodules and beds, of white, black, yellow, or red colour, lie in the limestone, like lumps and layers of flint in chalk; and require similar suppositions to explain their occurrence. Some considerable beds of chert occur in the north of England (Swaledale), and many sandstones are of a cherty nature (Harrogate). Ironstone (a carbonate of iron) often accompanies the thick dark plates and shales, in rows or layers of nodules (see Diag. No. 21, p. 6l.), aggregated round shells (unio), fern branches, &c. Coal lies always in beds. Its quality varies from nearly pure carbon to a consum- able mixture of carbon, hydrogen, oxygen, and azote ; and it is often mixed with layers of woody fibre, like charcoal, and laminae of earthy matter. Structure. Through out all this mass of varied deposits in the carboniferous system, the most decided proofs of aqueous deposits constantly present themselves. Lamin- ation belongs, but not equally, to every one of the six constituent members ; being often conspicuous in sand- stone's (flagstones), almost always so in argillaceous rocks and coal ; frequent in black limestones, but rare in iron- stone. Real beds occur in all these rocks ; but in the argillaceous plates and shales they are often indiscernible ; M 2 164 A TREATISE ON GEOLOGY. CHAP. VI. in sandstones they are commonly irregular; thick-bedded limestones have nodular or uneven surfaces. The coarse sandstones (as millstone grit) frequently present oblique lamination, which, added to the irregu- larity of the beds, renders it often embarrassing to say what is the true dip of such rocks. (Diag. No. 45.) The divisional structures or cracks, joints, and fis- sures, vary much in relation to the nature of the rock its fineness or coarseness of grain, the thickness or thinness of its beds, and the position of the point with regard to axes of elevation and perhaps other causes. In the accompanying dia- F 46 gram, L may rep resent lime- stone., P plate, G gritstone. The joints in L are gene- rally rectangular to the bed (in thin-bedded limestones iii I/, the joints are more nu- merous). In plate they are often oblique to the bed ; in grit- stone less regularly formed, being mostly cracks : this is especially the case where the beds are thick. The principal fissures F, which some- times go through many beds, are most open and re- gular in the limestone. Coal has sometimes joints of the amse kind, (called CHAP. VI. PALEOZOIC STRATA. 165 ' ends' or ' backs/) and, in addition, a minute fissility, generally in one certain di- rection across the bed, which does not occur in the shales above or below. It is a sort of crystallisation. Ironstone sometimes shows con- centric laminae, and often sparry divisions, when it be- comes a septarium. A very singular structure is frequently noticed in the argillaceous iron ores of a coal district, without however being peculiar to them, which is represented in fig. 4p. The substance of the iron ore is formed into conical sheaths, involving one another, and marked by concen- tric undulations and radiating striae. Large spheroidal masses of iron ore, weighing at least a ton, are thus found, in connexion with the coal, at Ingleton, in Yorkshire ; and in the coal fields of Staffordshire and South Wales it is a well known form of aggregation. This structure also occurs in many other formations, as in the slate of Skiddaw, the lias, oolites, &c., though with considerable variations. It is usually called * cone in cone,' * cone coralloid,' conical limestone, conical iron- stone, &c. A different but yet closely allied phenomenon, noticed by Mr. Dillwyn in the substance of the coal of Swan- sea and other parts of South Wales, which we have also seen at Ingleton, is represented in^. 48. Such a mass of coal, however solid, is found to separate not along a plane, parallel to the bed, but with deep hollows, and acute sinuous ridges, sulcated on their slopes, and undu- M 3 166 A TREATISE ON GEOLOGY. CHAP. VI. fated on their edges. The striations on the slopes are very similar to those on the conical ironstone ; and though the differences are in other respects great, they both probably depend on some general law of concre- tionary action, modified in operation by the nature of the substances acted on: but we are quite ignorant of the circumstances which determine this peculiar struc- ture in coal. Succession and Thickness of Strata. Considered in its greatest generality, and with refer- ence to countries where the masses appear in the greatest simplicity (as in the south of England), the carboni- ferous system consists of three formations: viz. Coal formation. A mass, 1000 yards or more in thick- ness, consisting of indefinite alternations of shales and sandstones of different kinds, with about 50 feet of coal in many beds, some ironstone layers, and (very rarely) thin layers of limestone. Millstone grit. A variable mass of cherty rock, or hard gritstone, with some shales, incompletely distinguished from the coal series above and the limestone series below. Mountain limestone. A mass of calcareous rocks, with very few partings of argillaceous matter, almost no grits, no coal, some chert nodules, and occa- sionally layers of red oxide of iron 500 to 1500 feet in thickness. This triple system becomes modified in the north of England, so as to constitute, in Derbyshire, a quadruple system, without any red sandstone, thus : Coal formation, 2000 feet. Millstone grit group. A series of very pebbly quartzose and felspathic gritstones, with other sandstones and shales, and some thin bad coal, several hundred feet. Limestone shale. A nearly uniform series of laminated shales or plates, mostly bituminous, with some iron- stone and thin black limestones, but no coal 1000 feet or more. CHAP. VI. PALEOZOIC STRATA. l67 Mountain limestone formation. (Old red sandstone almost wholly absent.) Slight representatives of millstone grit and limestone shale may be seen at the gorge of the Avon, at Bristol, round the South Wales coal field, base of the Clee hills, &c. Further north, viz. in the north-western parts of Yorkshire, the series is still more complicated and varied : as under : 1. Coal formation, 3000 or 4000 feet 2. Millstone grit. A series of three mostly pebbly grit- stones, separated by shales and several other flaggy, calliard and freestone grits ; cherts ; thin limestones ; ironstones ; and several coal seams. 1000 feet. 3. Yoredale rocks (equivalent of the lower part of lime- stone shale), a series of five or more limestones, with many freestones, flagstones, abundance of plates, some ironstone, chert, and several coal seams. 1000 feet. 4. Scar limestone, divided by partitions of grits and shales, and even some beds of coal. 800 feet. 5. Alternations of red sandstone, red clays, and limestone. 800 feet. (Red sandstone and conglomerate, very limited in their range ; thickness variable. 100 feet and upwards.) Pursuing the system to Northumberland, we find the scar limestone broken up into very many parts by inter- positions of grits, shale, and abundance of coal ; one of the grits being pebbly. Thus the whole method of va- riation of the system of carboniferous strata becomes known and appears nearly as in the diagram (fig. 1 8. p. 59-). We may here notice the remarkable section presented in the Island of Arran, where, according to Murchison and Sedgwick, the new and old .red formations are merely separated by a thin zone of limestone and coal, or, as from a careful examination we should be dis- posed to express it, where only small and diminished members of the mountain limestone formation (in one place yielding coal) appear buried in masses of red con- glomerate, sandstone and shale, of very great thickness, there being no certain criterion for deciding that any of this series belongs to the new red sandstone. This M 4 168 A TREATISE ON GEOLOGY. CHAP. VI. section is, however, much in accordance with the views of Hoffman, who, in north-western Germany, finds the carboniferous limestone and coal buried in a great body of red sandstones ; the lower ones being attributed to old red, the upper ones to new red. The total thickness of coal workable in the English and Scottish coal fields, is generally about 50 or 60 feet : this is, in most districts, divided into 20 or more beds, of a thickness from 6 feet to a few inches, alternat- ing with from 20 to 50 or 100 times as great a quantity of sandstones and shales. But in some districts (Cum- nock in Ayrshire, Dudley and Bilston in Staffordshire) many beds of coal, deposited one upon another with but little intervening earthy matter, constitute one mass 30 or 40 feet in thickness, in which the different beds are easily traced, and possess different qualities, probably depending on the original differences of the component vegetables, and the manner of their accumulation. In the Newcastle coal district, the coal beds are arranged in the following order by Mr. Westgarth Forster : Yds. Ft. In. Yds. Ft. In. Brown post, or grindstone sill - 24 Coal - 006 Rock measures - 10 Coal - 008 Rock measures - - 22 Coal - 006 Rock measures - - 15 2 6 Coal - _ 010 Rock measures - - 1 1 1 Coal - - . 006 Rock measures - - 7 1 Coal - 008 Rock measures - - 6 1 Coal - _ 008 Rock measures - - 19 1 Coal - 010 Rock measures - - 16 Coal (High Main) - 2 O Rock measures - - 11 Coal CMetal Coal) - 017 CHAP. VI. PALAEOZOIC STRATA. l Yds. Ft. In. Yds. Ft. In. Rock measures - 10 1 2 Coal (Stone Coal) . 1 9 Rock measures - 19 7 Coal (Yard Coal) - 1 Rock measures 7 1 3 Coal - - - _ 6 Rock measures - 18 11 Coal (Bensham) - 1 g Rock measures - 25 6 Coal - _ 1 6 Rock measures - 9 1 10 Coal - _ 1 2 Rock measures - 1 1 Coal - _ 9 Rock measures - 9 2 9 Coal (Low Main) - 2 6 Rock measures - 27 Coal - _ 1 G Rock measures - 15 Coal - . 6 Rock measures - 6 Coal - . 2 Rock measures - 10 Coal - _ 6 Rock measures 4 Coal - . 6' Rock measures - 12 Coal (Wbickham St.)- . 2 Rock measures - 10 Coal (Brockwell) - 1 2 Various rock measures - 50 2 Millstone grit 360 06 15 2 3 In Mr. Buddie's excellent sections, published in the ' Transactions of the Natural History Society of New- castle,' the extent of the several alternations of coal, sandstone, shale, &c., in the upper parts of this series are clearly shown. There is not much ironstone in the coal tracts of the Tyne and Wear. In Yorkshire, the total thickness of the coal formation is from 1000 to 1500 yards. In Lancashire arid Wales greater thickness must be ascribed to it. In South Stafford- 170 A TREATISE ON GEOLOGY. CHAP. VI. shire (Dudley), it does not exceed 1000 feet. The most variable parts, in all coal tracts, are the sandstones and shales ; the most regular parts are the coal beds and ironstones. Organic Remains. The forms of life buried in the carboniferous system of strata are exceedingly nume- rous and varied, and, being generally in an excellent state of preservation, allow of a most strict comparison with existing types. They consist of very many races of plants, abundance of zoophyta, multitudes of mollusca, some Crustacea, many fishes, but, as far as we yet know, neither reptiles, birds, nor mammalia. Many of the plants, indeed by far the greater number, are of terres- trial growth : all the zoophyta, and nearly all the mol- lusca, Crustacea, and fishes, are marine. The excepted mollusca occur among the remains of plants swept down from the land : the excepted Crustacea are those re- ferred to by Dr. Hibbert, in his account of the Burdie- house limestones, with which also a few fishes are found, which, by this author, are referred to a freshwater origin. The plants are partly very similar to existing races, as the large group of ferns generally, and partly appear altogether unlike them, as the large-furrowed stems of sigillaria, the quincuncially ornamented stigrnaria, &c. On making the most close comparison which the subject admits, we find that among the fossil ferns are arbores- cent species, to which we can only find parallels in warm or else Australian regions ; that the same analogy to the productions of a warm climate is suggested by fossil equiseta, and confirmed by the lepidodendra, which seem related to existing lycopodiaceae in structure, though enormously surpassing them in dimensions. Even the sigillarise, when carefully studied, though they be not cacti, nor euphorbias, nor arborescent ferns, are so much like those singular plants of hot climates, as to add considerably to the accumulating evidence in this direction. The following is a brief summary of the plants : CHAP. VI. PALEOZOIC STRATA. 171 Cryptogamia vasculosa Equisetacea? - about 9O species. Filices - above 100 Lycopodiaceae about 60 Phanerogamia monocoty- ledoneae Coniferae Cacteaceae Indeterminate 10 10 50 50 300 species Fig. 1. Stem of a sigillaria always denuded of leaves. 2. Stem of a large catamites. 3. Stem and leaves of asterophyllites. 4. Branch and leaves of lepidodendron. Of the accumulated remains of these plants coal seams are really composed, and one cause of the differences amongst them is the different structural composition of the original plants. How far the above fossil flora is to be taken as exhibiting the true proportions of the tribes of plants living on the globe, at the time of the production of the rocks of the carboniferous system, is uncertain : since, when plants are swept down from the land into the sea, it depends on many unknown condi- tions what sorts of them shall escape the floods, or perish by maceration in the waters. As a general rule, it may be said that the plants are confined to arenaceous and argillaceous deposits : they ] 72 A TREATISE O.V GEOLOGY. CHAP. VI. abound in the upper parts of the carboniferous system, where coal abounds ; they also occur in the midst of the millstone grits, and in sandstones and shales among limestones, especially where coal beds also are found ; but they are almost unknown in the midst of the undi- vided limestone, where, however, a few algae occur. In the true coal formation they are often accompanied by estuary, if not fresh water, shells, (unionidse) ; but in Coalbrook Dale marine shells (such as lie in the mountain limestone) take their place. The large trees are sometimes found upright above the coal, while below it spread what seem to be their roots. Much of the substance of coal contains the structure of coniferous trees. The suppositions which best connect the whole of the phenomena are, that the plants grew in and around swampy tracts by estuaries ; that the land was sink- ing continually or by intermission ; that thus the vege- table matter was gradually accumulated at and near the place of growth, and gradually or by intermission covered by marine estuary or river sediments. The zoophyta of the carboniferous system are almost (perhaps wholly) absent from the coal formation : they are almost confined to the mountain limestone formation and to its calcareous portions, thus offering us most clear proof of the marine origin of that rock. When to this we add the absence of land reliquiae from these lime- stones, it is evident that the materials of which these rocks are formed were not swept from the land like the substance of the arenaceous rocks, but elaborated from the salts of lime diffused in sea water. The zoophyta are partly of families almost extirrct, as crinoidea ; and partly of tribes yet abundant in the sea, as lamelliferous corals : the genera of corals often but not always (e. g. astraea, lithodendron) differ from those now living. The following summary is extracted from the ' Geology of Yorkshire,' vol. ii. p. 241. : CHAP. VI. PALAEOZOIC STRATA. 173 Zoopbyta Polyparia Crinoidea Echinida 41 40 Fig. 1- Syringopora ramulosa. Goldfust. 2. Cyathophyllum (or Lithostrotion) basaltiforme. Phillips. 3. Actinocrinus triaconta dactylus. Miller. 4. Platycrinus laevis. ? Miller. The molluscous reliquiae are numerous ; 326 species being described in the * Geology of Yorkshire, ' without noticing about a dozen others from the coal formation, which are included in the following general summary : Mollusca Conchifera plagimyona mesomyona brachiopoda Gasteropoda Cephalopoda monothalamia - polythalamia 40 28 100 92 10 69 339 Of these, only about 10 can by any means be con- sidered as of freshwater, or even estuary, origin : and these all belong to the coal formation (unio, anodon, &c.). Many of the genera are the same as those now 174 A TREATISE ON GEOLOGY. CHAP. VJ. existing (e. g. nucula, lingula, isocardia) ; but others are quite different, (as pleurorhynchus, producta, euom- phalus, goniatites, &c.), and seem to belong to another order of creation. About 60 per cent, of the species belong to extinct genera ; and it is very remarkable, that brachiopodous bivalves, which, in existing nature, are perhaps to other shells as 10 in 1000, were in these ancient periods as 10 in 34. The goniatites are most beautiful and characteristic features of this system, being found in none of the more recent strata. Crustacea existed during the accumulation of these rocks, but bore little resemblance to the present forms of the class : the trilobites of these rocks are, however, less numerous and varied than in the older Silurian rocks, where they are remarkably plentiful. Annelida have left many as yet undescribed remains on the surfaces of the flagstones in the millstone grit and limestone series. Some are enough like Nereis to be referred to the wandering setigerous tribes. The fishes of the carboniferous system (Burdiehouse, Leeds, Bradford, Manchester, Bristol, Wales, EXPLANATION OF FIGURES, p. 175. 1. Producta scabriculus. Sowerby. It occurs in mountain limestone ge- nerally, and in coal strata at Coalbrook Dale. 2. Producta punctata. Sowerby. Common in the carboniferous lime- stone. 3. Terebratula pleurodon. Phillips. Common in the carboniferous limestone. 4. Spirifera cuspidata. Sowerby. Not rare in the carboniferous lime- stone. 5. Pleurorhynchus minax. Phillips. From the carboniferous limestone of Ireland, Yorkshire, Derbyshire. 6. Posiclonia vetusta. Sowerby. From the limestones and shales of the north of England, the north of Ireland, &c. 7. Goniatites sphericus. Sou-erby. A common shell in the limestone. 8. Bellerophon tangentialis. Phillips. From the limestone of Ireland, Yorkshire, &c. 9. Orthoceras cinctum. Sowerby. From the limestone of Ireland, north of England. 10. Melania constricta. Sowerby. From the limestone of Derbyshire, Yorkshire, &c. 11. Pleurotomariaflammigera. Phillips. From the limestone of Bolland. 12. Natica plicistria. Phillips. From Bo:land in Yorkshire, Ireland, &c. 13. Euomphalus pentagonalis. Sotrerby. Common in the limestone of Ireland, north of England, &c. Its internal cavi'y is divided into chambers by imperforate septa, as was first noticed by Mr. W. Gilbertson of Preston. CHAP. VI. PALEOZOIC STRATA. 175 176 A TREATISE ON GEOLOGY. CHAP. VI. are numerous. Agassiz (1843) enumerates Placoid. Ichthyodorulites 43, Cestraciontes 56, Hybodon- tes 10, Squalides 1. Ganoid. Lepidoid 14, Sauroid 11, Coilacanthoid 13. Of reptiles we may quote Archigosaurus Decheni from Saarbruck. From this general review, the reader will infer that most of the forms of plants and animals of the carbon- iferous system are very distinct from existing types, but yet comparable with them and intelligible by them ; but that genera are mixed with them, which cannot be, or at least have not been, at all discriminated from re- cent ; and among plants in particular, some fossil forms (ferns) have a resemblance to recent species which is quite surprising. Physical Geography. Much of the most picturesque contracted scenery of England is situated among the deep-cleft valleys and rock-breasted hills of the moun- tain limestone, which, in Cheddar cliffs, on the banks of the Wye, in Derbyshire, the Yorkshire dales, and parts of Cumberland, Westmoreland, Lancashire, Flint- shire, and Glamorganshire, offers most attractive fea- tures to the artist. In Ireland, this rock is the source of very fine effects, about Sligo and Enniskillen. The Meuse flows from Namur to Huy through a succession of precipices of limestone comparable to those of the Wye, Coal deposits are generally found in countries deficient of beauty of form and luxuriance of vegetation ; yet the undulations of the large coal tracts of Yorkshire and South Wales, with the noble oak woods which fill some of the valleys, are worthy of notice. The millstone grit and Yoredale rocks form in the north of England a peculiar order of scenery ; for rest- ing in detached masses upon broad, bare surfaces of scar limestone, their bold craggy tops and edges, and abrupt precipices, produce often a grand, though some- times a formal effect, and their combinations are fre- quently fine. To this country belong also many beau- tiful waterfalls, originating in the decay of soft shales CHAP. VI. PALAEOZOIC STRATA. 177 and grits below ledges of limestone, over which the stream flings itself, in a free and lofty leap, into a dark and precipitous glen. (Hardrow force, in Wensley Dale; Ashgill force, in Aldstone Moor.) Another thing worthy of notice in the scenery of the limestone districts in the north of England, especially Derbyshire, is the difference of herbage on the millstone grit, limestone shale, and limestone. On the latter (/)", a fine green turf on the shale (*), bluish green sedgy pastures on the grit rocks (w), brown or purple heath, enable a geologist to mark out the leading fea- tures of districts with great facility, suggest to the botanist many interesting inquiries, and demonstrate to the agriculturist the dependence of the quality of soils on the rocks which they cover. Geographical Extent. The surface of country occupied by the rocks of the carboniferous system is proportionably much larger in the British islands than in other parts of the globe. In Ireland the greater part of the plains and broadly un- dulated interior consists of the mountain limestone, in places covered by coal measures, and in other parts supported by the old red sandstone. In fact, excluding the parts previously described as gneiss, mica schisf, clay slate, and grauwacke slate, and a large tract of later strata (red sandstone, green sand, chalk, &c., capped by basalt) extending from Lough Neagh to Lough Foyle, and to the sea-coast of Antrim, much of the rest of Ireland belongs to the carboniferous system. But the quantity of coal yielded by the coal fields about VOL. i. N 178 A TREATISE ON GEOLOUY. CHAP. VI. Lough Earn and Lough Allen, Monaghan, Dungannon, Newcastle, the counties of Clare, Kerry, and Limerick, about Cashel and Kilkenny, is not very considerable, nor is the coal of good quality. The Kilkenny coal is nearly pure carbon. A great part of the space in the interior of Ireland within its mountain border, Kerry, Mayo, Galway, Donegal, Down, Cavan, Wicklow, Car- low, Wexford, is filled by mountain limestone. (Mr. Griffith's map.) In Scotland the mountain limestone is, on the con- trary, very slightly developed, in connection with the large coal field which stretches from St. Andrews to Ardrossan, and from Haddington to Ayr, filling large spaces in the valleys of the Forth, Clyde, Ayr, Irvine, &c. (M'Culloch's map.) The mountain limestone formation occupies an im- mense tract in Northumberland, Durham and York- shire, from which country it runs out in a curve, to en- circle on the north, and partially on the south, the group of Cumbrian slate mountains. It also appears in great force in Derbyshire; ranges through Flint and Denbigh, to St. Orme's Head and Anglesea ; shows slightly round the Clee Hills in Shropshire ; and pre- sents picturesque cliffs on the Wye, near Monmouth. There is a long belt of mountain limestone on the north and east sides of the coal fields of South Wales, from Narberth by Abergavenny to Caerphilly ; and it is pro- longed on the south side by Bridgend, Swansea, and Tenby, to Milford Haven. Detached masses of lime- stone appear about Bristol, and in the Mendip Hills, and, according to Messrs. Murchison's and Sedgwick's recent researches, the limestones of Barnstaple are classed in the same series. The carboniferous limestone is supposed to occur in a narrow band below the coal formation of the Clee Hills, arid this is probably the correct explanation of the phenomena visible under Knowle Hill, at Orelton, &c. : but we must call attention to the fact that the white CHAP. VI. PALEOZOIC STRATA. 1 79 (sometimes internally blue) oolitic limestone there occur- ring is associated not only with dark shales (chinch), and light marly beds., altogether of a considerable thickness, at least 100 feet, but is also overlaid by an important deposit of red, whitish, and greenish argillaceous strata, altogether of the same nature as the " old red formation" of the vicinity. The whole series of the south Clee hills may be thus expressed in general terms: ,31 Jewstone basalt. Coal formation Two, three, or more beds of coal, some of it coked, some of it cannel coal ; under it occur g Conglomerates and other gritsones, some of them iron-specked and heavy. (Galena occurs in some beds.) f Red and coloured clays. e Bluish clunch beds. f Light yellow, marly and argillaceous beds. Calcareous layers, sandy or marly. c Black clunch fossiliferous. (Crinoidea, spirifera, terebratula.) b Limestone in solid beds, generally oolitic, much disturbed in the strati- fication, as in the sketch below (Ctenacanthus and other fossils.) It is worked for marble at Orelton. a Thick red clays and sandstones. Admitting the limestone and shale beds (b, c, d, e) to be the equivalent of the lower scar limestone (Derby- shire limestone) of the north of England, the quartzose conglomerate (#) may be ranked as millstone grit; and the red and white clays (/) must be considered as a recurring bed of the old red marl, interpolated among the carboniferous rocks, just as the red grits and clays of Orton and Ravenstone dale have been described as marking one form of a transition between the old red sandstone and the carboniferous formation, on the border of the primary districts of Westmoreland. N 2 180 A TREATISE ON GEOLOGY. CHAP. VI. The millstone grit is an important deposit in the north of England, from the Coquet to the Tyne, and on the hills between the dales of Durham and Yorkshire, from the Tyne to the Aire and the Kibble. A large mass of these rocks occupies the higher parts of Bolland; and a far larger tract extends from the Yore at East Witton, nearly S. W. to Ormskirk in Lancashire, and spreads from this line to the east, under the magne- sian limestone of Yorkshire, from Masham to Aberford, and under the ccal of Yorkshire, by Leeds and Bradford, to Penistone. Near this place it divides into two branches, one of which separates the limestone of Derbyshire from the coal of Yorkshire, Nottinghamshire, and Derbyshire; the other in like manner divides that limestone from the coal of Manchester and Congleton. In the south of England the millstone grit is feebly represented by the " Farewell rock " of the Forest of Dean, South Wales, and Somersetshire; but in Ireland it appears in great force on Kulkeagh, Belmore, and other mountains about Enniskillen. The coal formation of Northumberland and Durham extends from the Coquet across the Tyne, Derwent, and Wear, to Cockfield, where it suddenly breaks off, and ends against the valley of the Tees; and no more appears between the magnesian limestone and the mill- stone grit till the south side of Wharfdale. Here from Aberford to Bradford it runs out, in a counterpart of the Durham recession, and then returns by Halifax and Huddersfield to Sheffield, Dronfield, Chesterfield, Al- freton and Belper, and ends near Nottingham. On the western side of the Cumbrian mountains is a narrow belt of coal formation, about Workington and White- haven : a small field of coal lies at the foot of Ingle- borough (corresponding to one at Hartley Burn, on the South Tyne). The coal deposits of Lancashire form a considerable breadth, ranging east and west, from Man- chester by Prescot and Wigan to near Liverpool, and ap- pear to be connected underground with the coal tract of Flintshire, and, perhaps, of Shrewsbury. The detachec 7 CHAP. VI. PALEOZOIC STRATA. 181 coal fields of Ashby de la Zouch, Coventry, Dudley, and Colebrook Dale, are very valuable : some smaller fields are known south of Shrewsbury, in the Glee Hills, and at Newent. The Forest of Dean is a rich though small tract, and the disunited patches of coal in Kings- wood, and south of the Bath Avon, are valuable. Al- most the largest coal field in Great Britain is the great oval elongated tract of South Wales, from Pontypool to St. Bride's Bay, which furnishes fuel to the great iron works of Merthyr, Tredegar, Neath, &c. Murchison and Sedgwick show the culm of Devonshire (Bideford, &c.) to be in a deposit of the same Age as the culm of Swansea and other parts of South Wales, which is known to belong to the true coal formation. When we recollect, that, in addition to this large expansion of rich coal tracts, in most of which 50 feet of coal (in many beds) exist, the millstone grit and mountain limestone tracts, north of Derbyshire, also yield some coal, it is easy to see that the popular opinion of the extraordinary abundance of coal in Great Britain is perfectly well founded. But does it follow that the supply of British coal is inexhaustible ? will it last for one thousand or five hundred years, and during that period meet the hourly enlarging con- sumption at home, and the augmenting demands from abroad ? This question has often been replied to, never answered. Nor have the replies been often dictated by a comprehensive view of the subject. If indeed the- only data required were the superficial area of a coat tract, and the sum of the thickness of the several coal beds, nothing could be more easy than to convert this into a term of years, by assuming some fixed or regularly varying rate of annual consumption. But to this it must be objected, that all the coal in a given district cannot be worked, in consequence of natural impedi- ments (thinness, bad quality, disturbed position, &c.), and of the wasteful and unscientific method of establish- ing coal works. It is not here meant to speak other- : se than with praise of the working of the collieries, K 3 182 A TREATISE ON GEOLOGY. CHAP. VI. in which much judgment and humanity are often to be noticed, but in the irregular and accidental manner (depending on distribution of property, private in- terests, &c.) in which the sites of collieries are chosen, and their field of work defined. Many portions of country are thus left full of unattainable coal ; others untouched from dread of the water in long-abandoned works : beds of coal, of inferior quality or thickness, are abandoned till the future scarcity of fuel shall render it profitable to work them, under great disadvantages. Finally, as the thickness of the entire coal series often exceeds 1000 yards, and it is only in the Newcastle and Durham tract that pits descend even to 500, and then brave great dangers and difficulties, it is clear that, however long the coal of Great Britain may last, its price must gradually rise, because the cost of its production, relative to that of other articles of con- sumption, is necessarily on the increase. It is thus that coal will become scarce ; and if the country be not yet sufficiently enlightened in this matter to prepare the way for some act of legislative wisdom, the time of trial may not be far remote. It is a striking fact that no known coal district in the British islands (excepting, perhaps, a small part of Ayrshire) is unwrought: most of them are covered by manufactures; and ere long the geologist will be called upon to decide as to the propriety of sinking for coal in situations where it does not appear on the sur. face, yet is really spread beneath our feet in areas, perhaps, not less extensive than some of our largest coal fields. It may exist, for instance, beneath the plains of Cheshire, but who will have the boldness to penetrate the red sandstone, in search of that which may be placed by nature at an unattainable depth ? On the continent of Europe the carboniferous system is variously and locally developed in France, Belgium, Westphalia, Saxony, Bohemia, on the north of the Carpathians, &c. One of the most important deposits of coal and mountain limestone begins at Hardingen, CHAP. VI. PALAEOZOIC STRATA. 183 near Boulogne, and, passing under the chalk and green sand, continues in an easterly direction by Valenciennes, Mons, Charleroi, and Namur, to Liege and Eschweiler, near Aix-la-Chapelle. On the right bank of the Rhine, the coal tract near Elberfeld may be viewed as a pro- longation of this great Belgian deposit. Some traces of millstone grit, and more of aluminous shales, divide the coal from the limestone, in the valley of the Meuse, and also in Westphalia, at Lintdorf, and between Werden and Velbert. These representatives of the millstone grit group (flotzleerer) sandstein ac- quire, farther east, a great development about Arnsberg, Meschede, and Warstein. No old red sandstone is known in Westphalia, but red conglomerates represent it on the Meuse. The Saarbruck coal field contains thick red sand- stones in its upper part, resembling the South Lancashire section. The same, on a greater scale, appears in Lower Silesia, and there, as in Lancashire, the true hunter sand- stein covers unconformedly the coal. In Upper Silesia the coal without either limestone or old red sandstone rests on grauwacke. (Von Dechen.) The coal of Saxony, about Zwickau and Dresden, rests on igneous rocks. At Litry near Bayeux, and between Angers and Nantes, coal occurs under relations to the older rocks, which appear like those of the Devonshire culm. " In the centre and south of France are some limited coal deposits, lying in the valleys of the Loire, the Allier, the Creuse, and the Dordogne, the Aveyron, and the Ardeche, between ridges proceeding from the primary central group connected with the Cevennes." (These coal fields are devoid of mountain limestone.) Coal is mentioned as occurring in eight places in Catalonia, in three in Aragon, and one in New Castile. (Mr. Conybeare, in " Geology of England and Wales.") In Russia (provinces of Tula and Kalouga), in Syria, in the basin of the Indus, at Batavia, and in China, in Van Diemen's Land and New South Wales, in Virginia, and at several points west of the Alleghany Mountains, are extensive coal fields. v 4 184 A TREATISE ON GEOLOGY. CHAP VI. Igneous Rocks. A very considerable proportion of the trap rocks for which Scotland has long been cele- brated is found amongst the strata of the carboniferous system. About Stonehaven, Bervie, Montrose, Arbroath, the Sidlay hills, south of Dunkeld, at Perth, KinnouL, and Moncrieff, felspathic, basaltic, and amygdaloidal rocks (at Kinnoul yielding various agates) appear among the old red sandstones. The Ochill ranges from the mouth of the Frith of Tay to Stirling, continued in the Campsie hills to Dumbarton, and thence expanding to Greenock and Ardrossan, divide the red sandstone from the coal formation of the Forth and Clyde. From Greenock to Kilmarnock and the Haughshaw hills is a prodigious mass of trap : detached portions occur in Ayrshire; a long range extends from Tinto by the Pentlands to Edinburgh. North Berwick Law, Tan- tallan, and the Bass, are the extremities of a large body of trap in Haddingtonshire : these rocks abound between Linlithgow and Bothwell ; and a great variety of igneous masses occur about Kinghorn, the Lomond hills, and between Cupar and Largo. A considerable proportion of all these extended igneous rocks is connected with the coal formation. The variety of composition among these rocks is so great, as to defy description in any moderate compass. These rocks, felspathic (porphyry, claystone, clinkstone, &c.), felspatho-pyroxenic (greenstone, basalt, wacke), produce at many points remarkable changes on the ad- jacent sandstones and shales ; hardening both to an ex- traordinary degree, so as to resemble jasper of different colours. (Salisbury Craig, Stirling Castle, hill of Kinnoul, &c.) At Cumnock, coal is converted to an- thracite and plumbago. (See Boue, p. 122. et seq.) Perhaps the most remarkable variety of igneous rocks yet known in a small compass appears in the island of Arran, generally associated with the red sandstones, and conglomerates. Pitchstone, claystone, hornstone, trachytic porphyry, clay porphyry, basalt, and greenstone, appear in many dikes, and form interposed CHAP. VI. PALEOZOIC STRATA. 185 beds of great interest in the theory of the formation of such rocks. (Jameson, M'Culloch, c.) In the north of England, the porphyritic masses of the Cheviot hills, the range of greenstone and basalt in Northumberland from Belford, by Alnwick, Rothbury, Whelpington, and the Roman Wall to the South Tyne, and thence along the west front of the Penine chain, to Hilton, near Appleby, and down the Tees to Middleton, with dykes passing through the mountain limestone, coal and newer strata, are the principal masses of trap rock associated with the carboniferous system. Dykes of basalt are common in the coal fields of Northumber- land and Durham, but totally unknown in those of Yorkshire, Derbyshire, Nottinghamshire, and Lanca- shire. In Derbyshire, the limestones are separated by an irregular mass of interposed amygdaloidal trap, called " loadstone ; " (indeed, more than one such bed can be proved to occur in certain districts.) Mr. Murchison has described the trap rocks which penetrate the coal measures of the Titterstone and Clee hills, and cut and injure the coal : at Kinlet, Arley, and Shatterford the coal based on old red is divided by eruptive masses and dykes of trap. The trap rocks which rise in bosses within the coal fields of Colebrook Dale do not appear to have charred the coal: they never appear as dykes, or enter into the fissures of the rocks. (Mr. Prestwich.) Basaltic hills adjoin coal and limestone at Rowley, near Dudley, and at Griffe, in the Warwickshire coal field : a dyke of basalt appears in Birchhill colliery, Walsall. It is impossible in many cases to refer the igneous rocks, associated with the carboniferous system, to their true geological date. The bedded rocks of Northum- berland, Teesdale, and Derbyshire, are certainly of the same age as the mountain limestone; but the dykes of Northumberland, Durham, and Walsall, and the other basaltic excrescences and ridges, are not easily determinable in age. This difficulty belongs to almost 186 A TREATISE OX GEOLOOY. CHAP. VI. all cases of dykes, except when, as in the Quarrington dyke, in Durham, the igneous rock cutting through one formation (coal) is overlaid by another (magnesian limestone), which it does not divide. Even here the conclusion of the anteriority of the dyke to the over- lying rock is somewhat insecure ; because the extent of the dykes in the coal formation itself is very irregular and accidental. Trap rocks are associated with the Irish mountain limestone between Limerick and Tipperary. General View of the Circumstances under which the Carboniferous System was deposited. If in the early part of the formation of the primary strata the ancient ocean was in a peculiar state, both as to temperature and extent, never since experienced, the effect of partial eruptions of igneous rocks, and per- haps of great displacements of the crust of the globe, was to vary the depths and localise the currents of the original ocean. But the effects of this change, apparent among the sedimentary deposits of the upper " transition" strata, were augmented to a vast degree, after the com- pletion of the whole primary period, and the decided movements to which large parts of the globe were then subjected. The Northern Ocean, at the commence- ment of the carboniferous era, was certainly divided into basins, varied by islands, bounded by shores, sup- plied by inundations from extended land. The agitation on its shores is proved by conglomerates ; the amount of inundations from the land is demonstrated by abundance of argillaceous and arenaceous sediments, plants, and beds of coal ; while in the more tranquil laboratory of the deeper water limestone rocks were generated in great abundance. The carboniferous and Devonian formations are, as compared with the older primary rocks, very limited in area, broken into many detached parts, and charac- terised by local conditions. Hence the red conglo- CHAP. VI. PALEOZOIC STRATA. 187 merates of the Grampians, the Lammermuirs, and the Cumbrian valleys, hold fragments of the neighbouring and but lately uplifted rocks ; hence the absence of old red sandstone in Derbyshire, its great predominance and complication on the south-east border of Wales ; hence the unmingled oceanic character of the limestone of Derbyshire and Ingleborough, contrasted with the divided, sandy, shaly, carbonaceous littoral group of Northumberland. The small extent of coal in many countries is merely a fact indicative of the previous revolutions which affected the primary strata there; while the abundance of coal in Great Britain confirms to us the conclusion drawn from other considerations, that in this region of the globe, soon after the formation of primary strata, much land had been raised above the sea. But there is yet to be explained the excessive abun- dance of the vegetation of that early land, which should be capable, whether overwhelmed in situ or drifted to sea, of collecting into so enormous a mass of coal. On this point, if we turn our eyes on existing nature, nothing appears so likely to aid our conception as the damp forests on the Oronoko, Maranon, or Mississippi, from whose mere waste the mighty rivers roll every year to the Atlantic an immeasurable mass of trees and herbs, with soil, sand, and clay, which are in process of time arranged on the bed of the ocean, as we rind the coal and its accompanying sands and clays to be. The analogy is strengthened by the general con- sent of botanists, in regarding the plants of which coal was formed to be decidedly analogous (though differing much) to tropical vegetation, and especially to the vegetation of a tropical region contiguous to the sea, where palm s, cacteacese, and lycopodiaceae might abound, and yet varied with mauntain slopes on which tree ferns and pines might flourish. If further we suppose, with M. Brongniart, that the atmosphere of that early time might be loaded with an extra proportion of carbonic acid, against which no law of nature militates, (for 188 A TREATISE ON GEOLOGY. CHAP. VI. we know not if the proportion of carbonic acid be now constant in the air, and must admit that a reconversion of all the coal to carbonic acid gas would give a very large addition of this gas to the atmosphere,) we shall understand how the vegetation of the carboniferous period might be even more abundant than that now seen between the tropics, and at the same time comprehend the possibility of few land animals existing on the globe. Within what limits of proportion of carbonic acid in the air plants and animals can live, we do not know ; but in this respect they are reciprocally circumstanced, plants require most, animals require least. De Luc, Brongniart, and other writers, prefer to ex- plain the origin of coal from somewhat like peat-bogs, or from the decay or overwhelming of forests in situ : if we admit further so much of waterdrift as the case requires, we have a general explanation. In most coal districts are from 20 to 60 seams of coal, alternating with sandy and argillaceous strata ; each of these coal seams is composed of many parallel layers of different quality and structure, often separated by scattered patches and fragments of woody fibre. A bed or seam of coal is, in fact, an aggregate of many successive deposits of vege- table matter. Under almost every bed of coal, as Mr. Logan in particular has shown in South Wales, is a peculiar fire-clay, or a fine-grained sandstone (ganister in Yorkshire) traversed by the rootlets of a plant (stig- maria) : over some beds of coal stand erect the stems of sigillaria and lepidodendron ; and finally, at Dixonfold, near Manchester, and in other places, lepidodendra and sigillariae rise erect out of a bed of coal, the former being connected below with roots which are stigmaria. In such cases, we seem to behold a nearly level swamp, often many miles in breadth, and of great longitudinal extent, covered with a peculiar deposit from water (the under clay), on which grew lepidodendra and other trees of the period. Spreading their symmetrical roots and root- lets through this mud, and rising to a considerable height above, a peaty accumulation happened around them, CHAP. VI. PALEOZOIC STRATA. 189 partly by the growth of cryptogaraia, and the accumula- tions of leaves, branches, and fruits, the decay of local ve- getation, partly by water-floated additions from not far distant surfaces. The land on which this accumulation was proceeding is then seen to subside in level, so as to be covered by river, estuary, or sea deposits, on which a new series of growths and water drifts accumulate a new bed of coal. In some cases the accumulation may be wholly from plants in situ, in other cases, all the raass may have been water-drifted ; often these causes have concurred or alternated. What is here sketched as the most probable general theory, is quite in harmony with the facts observable in connexion with the often buried forests of late Cainozoic and even historical age. Chat Moss, Waghen Fen, Thorn Moor, the Holderness lakes and river channels, yield plenty of cases so analo- gous that we cannot doubt of their illustrating the principles on which a large part of the ancient coal was accumulated. Inundations from the upraised land, littoral action of the sea, chemical decomposition of the oceanic waters, eruptive action of subterranean heat, vital action on the land and in the water, these are the causes to which the formation of the whole carbon- iferous system is clearly traceable ; and by comparing the effects of all these causes in that ancient period with what happen at this day, we shall find modern effects precisely comparable in kind, but altogether in- ferior in magnitude. Where then was situated that ancient land, from which, according to our view, were swept the materials of the 1000 yards of sandstones and shales which inclose the coal deposits in most parts of England, and the continent of Europe ? And recollecting that in the series of millstone grit and carboniferous limestone in the north of England occur other beds of coal, and several hundred yards in thickness of other sandstones and shales, again we ask from what land were the plants and earthy sediments drifted in such abundance over this limited area ? In the discussion of this im 190 A TREATISE ON GEOLOGY. CHAP. VI. portant question, which appears in my e Illustrations of the Geology of Yorkshire/ I have found it necessary to analyse the phenomena, so as to be able to inquire separately into the local origin of the three substances of principal importance limestone, sandstone, shale : the former is of oceanic origin, for it contains only marine exuviae, and when in greatest thickness and purity, was evidently deposited by water in a state of great tranquillity, or slow decomposition. In the same south-eastern direction that the limestone grows thicker from a certain point in the district, the sand- stone and shales grows thinner : in the opposite direction they thicken, but not equally ; the sandstones thicken toward the north, the shales toward the west, and in this direction certain limestones and sandstones totally vanish. With these sandstones the coal beds also vanish ; where the sandstones thicken and grow nume- rous toward the north, the coal beds also augment in number and thickness; and the limestones change gradually from an undivided mass to many distinct members, separated by sandstones, shales, coal, and ironstone. Thus to any point A, in diagram No. 52., where a se- ries of limestone, sandstone, shales, coal, ironstone, occurs, the limestone may be supposed to have been brought by CHAP. VI. PALEOZOIC STRATA. 191 diffusion in the ocean from an area situated to the south-east ; the shale transported from the west, ami the sandstone, plants, &c., drifted from the north. We may imagine two rivers, one flowing from the west, and bringing across the regions where now are Ireland, Lancashire, Derbyshire, and South Yorkshire, a vast body of argillaceous sediments, slightly charged with sand, and but little varied by floating trees and plants ; the other rushing from the north, loaded with sandy matter, and bearing abundance of trees of differ- ent kinds, but not many ferns or delicate herbaceous plants. Alternately or contemporaneously, these rivers might fill the sea with deposits, such as we behold and in the manner that we see them, united with the proper calcareous deposit of the ocean. This explanation of different sediments coming to the same part of the sea from various quarters, may probably be applied to every system of stratified rocks, containing, as constituent members, limestone, sand- stone, and clay ; but it is necessary previously to inves- tigate the directions in which the agencies concerned in producing each sort of sediment were most powerful; i. e. the points or lines of their greatest intensity. In some cases it appears highly probable that one such irregular fiuviatile action, modifying the continuous depositions from the sea, would sufficiently explain the phenomena of the association of sandstone, shale, and limestone ; because, by such action, the shores would be margined by a sandy deposit, beyond which clay would predominate in the sediments, and at a greater distance calcareous matter would be nearly unmixed with the effects of littoral agitation. In the diagram No. 53. S represents the sandy accu- mulation near the shore, passing by gradation to the 53 192 A TREATISE ON GEOLOGY. CHAP. VI. deposit of clay, c, which extends further, and is finally replaced by nearly pure carbonate of lime, b, which grows thicker farther from shore. Still the question recurs, where was the land from which the materials were drifted ? The slaty mountains of Cumberland, the Isle of Man, Cavan, &c.,were perhaps above the water ; but could they alone yield the mate- rials for the argillaceous sediments, 1000 feet thick, of Enniskillen, Derbyshire, and Craven, even if we suppose them to have been much diminished by the operation ? The Lammermuir mountains, to the north, seem not to be of such composition as would yield the coarse quartzose sandstones j we must therefore appeal to the Grampians or Scandinavian ranges, or finally close all further discussion, by admitting that tracts of land which supplied part of the sediments, mixed with the limestones of the carboniferous period, have disappeared from the Northern and Western Oceans. The coal formation, lying above these limestones, appears in many cases (Yorkshire, Lancashire, &c.) to have been accumulated, or according to the other hypo- thesis, submerged, in estuaries or lakes : if so, the local origin of the materials must be sought around those lakes, and in one or more directions from those estuaries. If, as seems probable, the coal fields of Yorkshire and Lancashire were once united, as those of Durham and Newcastle still are, the margins of the estuary in which they were formed are lost, except toward the mountains of Lancashire and Westmoreland. In like manner, no margin can be fixed for the estuary of the coal fields of Durham and Newcastle, except the Lam- mermuir range; and thus we are again conducted to the conclusion, that, unless those mountains be thought to have yielded all the sediments, great displacements of the crust of the globe have confused the ancient boundaries of the carboniferous sea, and reduced to mere conjecture the extent of the bordering land, and the circumstances of its drainage. This important, CHAP. VI. PALEOZOIC STRATA. 1$3 though dark inquiry, will, however, again arrest our attention. Extent of British Coal Fields under superior Strata. Disturbances of the Carboniferous System. To what extent the relative level of land and sea was disturbed during the period which elapsed in the pro- duction of the carboniferous rocks cannot be known : to judge from the universal conformity of all the strata which compose it, and the rarity of coarse conglomerates (except at the base of the system), it might appear that no considerable displacement of the crust of the globe happened any where near the British Islands, during the whole carboniferous period. Yet the occurrence of a marine conchiferous bed among the estuary or freshwater strata of the Yorkshire coal field, seems ab- solutely to require the admission of considerable dis- turbing movements at a distance. After, however, the deposition of this whole system, and before, at least, any considerable part of the next (magnesian system) was laid upon it, the scene was totally changed, and the carboniferous rocks of the British islands broken and contorted by subterranean movements of an extensive and complicated description. Every coal field in these islands is remarkably dislocated by faults, often traversed by rock dykes, sometimes ridged or furrowed by anticlinal or synclinal dips, which cause great trouble and expense to the coalworker, and call forth all the resources of his art. Into the history of these disturbances we shall only enter, so far as to present a fair basis of comparison with physical theories. One of the most remarkable great faults or dislocations yet known in the world belongs to this period ; viz. that great and continuous fracture of the earth's crust from Cullercoats, near Newcastle, westward along the valley of the South Tyne to Brampton ; thence south- ward to Brough, Kirkby-Stephen, Dent, and Kirkby- Lonsdale ; arid afterwards eastward to near Grassing- VOL. i. o A TREATISE ON GEOLOGY. CHAP. VI. ton, in Wharfdale, a distance of 110 miles.* whole of the somewhat ^ rectangular tract of ^ fc ^X included The country Tymedale ELEVATED 54 be- tween the northern (Tynedale), southern (Craven), and middle (Penine) portions of this fault, is elevated above the correspond- ing strata in the de- pressed surrounding re- gions, not less than from 1200 to 4000 feet ; in consequence of which silurian rocks show themselves along the Penine and Craven portions, while small coal fields appear on the parts at h and i thrown down 2000 feet below the summits of millstone grit ! On the south side of the Craven branch of this great fault are found many anticlinal ridges, severally rang- ing north-east and south-west, or nearly, and throwing the whole Craven country into a series of parallel un- dulations. Through Derbyshire runs an axis, from which the rocks dip eastward and westward ; and this ridge, continued northwards towards Colne, effects a complete disunion of the great coal field on the east (Yorkshire, Derbyshire, Nottinghamshire), from that on the west (Lancashire, Cheshire) which it appears most probable were once united on the bed of the sea. It is only by considering the effects of subterranean move- ments, that we can at all account for the disjointed and fragmentary condition of the central coal fields of Eng- land. Their disunion is sometimes real, but very fre- quently only apparent, since they often dip towards each other, as c c, and would perhaps be seen to unite * See separate Memoirs by Sedgwick and Phillips in Geological Trans- actions ; also Geology of Yorkshire, vol. ii., and Geol. Proceedings, Dec. 1851. CHAP. VI. PALAEOZOIC STRATA, 55 195 but for the covering of red sandstone, which conceals the coal along the middle of the basin. The great South Wales coal field is a vast double trough, having an included anticlinal axis, ranging east and west ; as diag. 56. 56 In the Barnstaple and Bideford beds belonging to this system, the principal dislocations range also east and west : this is, perhaps, the most general line of move- ment in the Somersetshire tracts, where dislocations are numerous and remarkable : it is renewed in the north of France and Belgium (at Mons and Namur), and about Elberfeld. Without now stopping to discuss the bear- ing of these results on M. de Beaumont's views, we shall observe, that a careful study of the phenomena in the north of England has left but slight doubt on our mind that the application of Mr. Hopkins's mechanical theory (see Cambridge Transactions) to the dislocations of the carboniferous system, will be successful. Mineral veins commonly range a little N. of E. and a little W. of N. in the carboniferous system of the north of England. PERMIAN SYSTEM. Magnesian Limestone Series of England. We now enter upon the last great member of the palaeozoic series of strata the magnesian limestone long ranked as a part of the new red or saliferous system. In the Encyclopaedia Metropolitana (article Geology, 1830, et seq.) I stated, as the result of a general examination of the fossil conchifera of the saliferous o 2 196 A TREATISE ON GEOLOG1 CHAP. VI. system, that in the upper strata a general analogy to the oolitic sera can be recognised by the trigonise, plagiosto- mata, ostreae, &c. ; and by their products and spiriferae the lower strata as distinctly claim affinity with the car- boniferous limestone. While composing my work on the Palaeozoic Fossils of Devon and Cornwall (published 1841) the lower group came necessarily under review, and I concluded that in respect of organic life its affinity was really with the carboniferous limestone, though its mineral association was with the new red. This view is now generally adopted*; and Murchison, De Ver- neuil and Keyserling, by a large examination in Russia of strata which are the equivalents there of the magne- sian limestone of England and Germany, have founded on these strata the Permian system.f Composition. After examining the carboniferous rocks, the red sandstones and the associated strata pre- sent themselves with an air of novelty and freshness, not less striking to the geologist than a new country to the traveller. Instead of the black, blue, or grey limestone, full of crineidal columns, productse, &c., we have now yellow, sandy, or granular rocks, with few organic re- mains : the dark shales of the coal series are exchanged for red, green, and blue marls, and the micaceous yellow, ochraceous or brown grits, for red or white sandstones. On a general view the contrast is sharp and defined, even where the strata of the two groups are parallel, but close examination points out several instances (Man- chester and Salop) of transition coal deposits, in which red grits and clays inclose coal, with shales and lime- stones of a peculiar aspect. The limestones of this system vary much. They are often loaded with magnesia, and in general called "mag- nesian limestone;" but there are many beds in which little or no foreign admixture deteriorates the carbonate of lime. The colours are white, grey, smoky, but more frequently yellow; and in some districts reddened, or * Scdgwick, Pritisb Paleozoic Rocks (1851). t Memoir in Geol. Proceedings, 1842, 1843, &c. CHAP. VI. PALAEOZOIC STRATA. 197 even very red. In texture, a few limestones are com- pact, some oolitic, many cellular, the cells lined with crystallised carbonate of lime, a large proportion of a fine sandy grain, some quite powdery, with crystallised balls included ; and in Nottinghamshire, considerable tracts yield granular crystallised limestones. Near Sunderland laminated rocks are really of sparry texture. Strings and plates of spar are very common, and render build- ings of the magnesian limestone very irregular in their decay, from the unequal perishing of the stone between the ribs of spar. Structures of Deposition. Stratification is distinct in all these rocks ; but in all of them some peculiarities appear in this respect. The fine-grained upper limestones of Knottingley are thin-bedded : the granular rocks of Nottinghamshire are either thick-bedded or flag-like ; it is sometimes difficult to trace the beds at all in the powdery magnesian rocks ; and in certain sparry rocks near Sunderland, the bedded structure is almost overlooked in admiration of the coral- loidal forms of the concretionary masses, which some- times are enveloped in soft yellow powder (Building Hill). Divisional Planes. The fine-grained limestones of Knottingley are traversed by vertical divisions from top to bottom, which in some places are open to a foot in width, or filled with clay and rolled pebbles ; in other cases they are merely thin cuts in the rock ; always their regularity, parallelism, and polarity (if we may so term their direction to N. or N. N. W., and its rect- angle E. or E. N. E.), are remarkable. In other thick- bedded limestones, the joints are less symmetrical, though always numerous : most of the rocks are tra- versed by small secret cracks, which, on being exposed by fracture, are found covered by dendritical markings of a dark colour. The joints are often coated by carbo- nate of lime, sometimes by carbonate of copper, or sul- phuret of lead. Succession and Thickness of Strata. The most, or o 3 3 98 A TREATISE ON GEOLOGY. CHAP. VI. rather the only, complete series of the Permian system in the British islands, is that of the north of England, where alone certain lower members are clearly exhibited. The following synopsis is founded on the views of Pro- fessor Sedgwick. (' On Magnesian Limestone/ Geolo- gical Transactions.) e. Laminated limestones of Knottingley, Doncaster, &c., with layers of coloured marls, 30 or 40 feet. d. Gypseous red, bluish, &c., marls, 50 feet. c. Magnesian limestone, yellow, white; of various texture and structure; some parts full of fragmentary masses, 100 feet. 6. Marl slates ; laminated, impure, calcareous rocks, of a soft argillaceous or sandy nature, 20 feet. a. Lower red sandstone, with red and purple marls and mica- ceous beds ; sometimes the grits are white or yellow ; and pebbly, or loose sand. Occasionally passes into coal mea- sures, on which it rests, 50 feet. Magnesian conglomerates border the Staffordshire and Salopian coal fields, and have a lower red sandstone be- neath them. At Manchester, the magnesian limestone is somewhat better defined ; at Kirkby Stephen, it is re- presented by a brecciated limestone rock ; and at St. Bee's Head is a complicated formation of considerable thickness, in which the calcareous part is an important feature. Germany. England. France. Lower Bunter. Stinkstein, rauchwacke, Upper limestone. &c. Gypseous marls. Zech stein. _ Kupfer schiefer. Gypseous marls. Magnesian limestone. Marl slate. Gres de Vosges. Kothetodteliegende. Lower red sandstone. Gres rouge. The Organic Remains of this system, though not nu- merous, are exceedingly interesting to the naturalist and geologist, from the strong testimony they offer of the successive changes of the living creation, according to the new circumstances of the land and sea. The fossil CHAP. VI. PALEOZOIC STRATA. 199 plants, shells, fishes, and reptiles of this system appear to partake more of the character of those in the older carboniferous, than newer oolitic deposits. The few plants which occur in the rotheliegende are of the car- boniferous, and especially Lepidendroid type. Products, so common in mountain limestone, occur in the zechstein with terebratulae, and spirifera abundantly. Fishes of the genus palaeoniscus here occur for the last time, in ascending the series of strata ; above come in Labyrin- thodon Thecodontosaurus, &c. These interesting rela- tions appear in the following table, which also contains the names of some fossils, which are found in only one of the three systems : Belemnitfj. Ammonites. H OOLITIC FORMATION. *2 3 8 Zowiia. c c "i Keuper. " *! Ceratites. 60 J? Muschelkalk. c- s * * * Foftaa. H Red sandstone. ** er - Pk *! Zechstein. n S fc. eg 3 """ O *- 2 3 o Marl slate. o I a Rotheliegende. o d a. * Ortkoceras. Goniatites. >. PUU COAL FORMATION. J Sigillaria. According to the organic remains, the lower half of these rocks must be ranked with the carboniferous, the upper with the oolitic rocks : but, by its own mineral characters, it is one great series of deposits which hap- o 4 200 A TREATISE ON GEOLOGY. CHAP. VI. pened at the period when a decided change was taking place in the conditions which determine the forms of life upon the globe. 1. Retepora flustracea. Phillips. 2. Mytilus acuminatus. Sowerby. 3. Avicula gryphaeoides. Sedgwick. 4. Axinus ohscurus. Sowerby. 5. Producta horrida. Sowerby. All these are from the magnesian limestone of Durham and 'Yorkshire. The fauna of the magnesian limestone in England has been fully treated by King*, who presents in a synoptic table the following summary of British and foreign species. (See table at top of next page.) In regard to the Reptilia we should prefer to omit the British fossils (Thecodontosaurus and Palaeosaurus) as really belonging to a triassic conglomerate. The plants of the Permian system have been exa- mined by Morris and others. They are in a consider- able degree marine ; but a certain number of ferns, lopidodendra, and calamites, are identical with, or else very nearly allied to, known carboniferous species. The table which follows was drawn up as the result of the labours of Murchison, Dr. Verneuil and Keyser- ling, in 1844. (Geol. Proceedings.) * Trans, of Palaeontol. Soc. 1850. CHAP. VI. PALEOZOIC STRATA. 201 FAUNA OF THE MAGNESIAN LIMESTONE. 2 .| 0* i t |1 II 1 f 11 is 1| II g 5 Sa j5n s" C. S(S I 1 If *l I Plants - 17 60 7 ?6 27 26 Spongiae . 4 5 5 5 Foraminifera 3 6 6 6 ^ . Polyparia 14 18 11 4 5 2 Echinodermata 2 2 2 _ __ Annelida - 4 5 5 4 mm ^_ Crustacea 3 13 12 12 1 ^ Palliobranchiata 14 37 23 9 14 Lamellibranchiata 19 47 30 16 16 ? 1 Gasteropoda - ? 10 26 21 ? 18 3 2 Cephalopoda - 3 4 2 1 1 1 Pisces - ? 14 ?45 16 ? 16 C 2( ?) ? 27 i more. Reptilia ... 7 9 3 3 4 2 114 277 143 100 73 61 FAUNA OF THE PERMIAN SYSTEM IN EUROPE. j i Species found in Russia. 8, s S 3 * i. O II s A Previously found elsewhere. E? cL| V e , 00 - 9 "is fe * . r If 1 2 || H > ' t 3 ll 00 t" 1 II 1! CO a 3 Polyparia ... Echinodermata 7 15 2 13 1 2 3 i ? 2 Conchil'era Brachiopoda 7 30 20 10 8 3 4 5 Dimyaria - Monomyaria Mollusca Gasteropoda - Cephalopoda - Annelida 10 5 11 1 1 26 16 22 3 2 26 15 19 3 2 1 3 8 4 3 3 3 Crustacea ... 2 2 2 Pisces .... 16 43 42 1 2 Reptilia ... 4 5 5 Total . - 66 166 148 18 32 3or4 12 5 202 A TREATISE ON GEOLOGY. CHAP. VI. Geographical Extent. England, Germany, and Russia are the three main centres of these latest palaeo- zoic strata, and the limestones are the most characteristic parts. The range of magnesian limestone is very limited in England. Commencing at Cullercoats, north of Tynemouth, the lower limestone (zechstein) ranges through a part of Northumberland and across Durham to Coniscliffe on the Tees, being in this course pene- trated by many coal pits. Below it is the fish-bed or marl slate, and a coarse yellow pebbly sand (rotheliegende). In the North of Yorkshire the magnesian limestone is poorly developed in patches at Catterick, Crakenhall, &c., but grows prominent near Masham, and then continues uninterruptedly by Knaresborough, Wetherby, Ferry- bridge, Doncaster, Tickhill, Barlborough, and Bolsover to Nottingham. Through the whole of this range it is the lower lime- stone which prevails and makes the general feature, a low regular continuous terrace ; but it is only in the middle part between the river Wharfe and the vicinity of Tickhill that the whole series is visible. As already observed, a few detached parts of magnesian conglome- rate (probably coeval with zechstein) occur under the Penine chain near Brough and Ingleton, and along the border of the Salopian coal field, while a more developed section appears in St. Bee's Head, and a mass of the oldest red conglomerate of Malvern may be referred to this period. The magnesian conglomerate of South Wales rests unconformedly upon the coal. Zechstein is exhibited along the Thuringerwald, in Hesse Cassel, on the southern and eastern sides of the Harz, between the Elster and the Saale, and about Wai- deck. In Russia coeval rocks are spread out in the west of the Ural so as to occupy the whole of the ancient kingdom of Perm (whence the name). They consist of limestones, marls, masses of gypsum, rock salt, and repeated alternations of cupriferous strata, and contain a fauna and flora of characters intermediate between CHAP. VI. MESOZOIC STRATA. 203 those of the carboniferous and triassic periods.* The cupreous element is attributed to springs flowing from the Ural in the ancient zechstein period : to similar causes we may probably ascribe the copper in the Kup- ferschiefef of Maarfeld, and in the limestone at a few localities in Yorkshire : the fishes extended in a perfect form on this shale may have been the victims of such infusions. In Thuringia and Hesse Cassel the zechstein is sur- mounted by red and spotted sandstones (Lower Bunter) with calamites arenarius, a coal measure plant ; these sandstones are referred to the Permian series, which thus becomes triple, viz. : Lower Bunter. Zechstein. Rotheliegende.f MESOZOIC STRATA. TRIASSIC SYSTEM. (Part of Saliferous System in the former editions.) Judging by mineral associations and great struc- tural analogies, Mr. Conybeare united this group of variable strata with the subjacent magnesian limestone ; nor is it without a species of divulsion that they can be separated. Yet their organic history is different, and it is by their palaeontological relations that the strata are now most successfully gathered into large associations, which can be recognised over distant regions. The red marls and sandstones which compose the trias in Germany form three main groups, viz. : Keuper. A series of sandstones and variegated marls, red, grey, greenish, or white, with plants, shells, fishes, and reptiles. Muscbelkalk. A grey limestone, also fossiliferous. Bunter. A series of variegated sandstones, red, grey, or white, rarely fossiliferous. Murchison's Address to Geol. Soc., 1842. See also Geology of Russia, f Murchison and De Verneuil in Geol. Proc., 1844, p. 329. 204 A TREATISE ON GEOLOGY. CHAP. VI. In France and England the muschelkalk is absent. Rock salt and brine springs occur in England and France only in the Keuper series : in Germany both in this and in the muschelkalk. Gypsum usually ac- companies the marls which yield salt, but is also of more extensive occurrence. In England the most complete section is probably that furnished by the beautiful and fertile vale of Severn, where every bed between the lias and the Palaeozoic rocks of the Malvern and Abberley hills is easily traceable, in a thickness of 400 to 500 yards. The lowest of these beds, trappoid conglomerate, is probably of Palaeozoic age, a representation of some part of the Permian system. The series in general terms stands thus, Upper red marls ; 200 to 250 feet. Enclosing a thin layer of light-coloured sandstone, and many bands of white and greenish marl, with strings and masses of gypsum. The uppermost part of the group is white, or greenish. (No fossils.) Keuper grits and shales ; 20 ft. Sandstone and thin shales, with false bedding littoral characters. ( A few plants, shells, and fish remains.) Lower red marls ; 400 to 500 feet. Enclosing sand- stone near the base, and laminated sandstone near the top. (Calamites?) Red sandstone and conglomerate ; 200 to 400 feet. False bedding and other marls of cements and water conglomerates; irregularly mixed with sandstones, and thin marls, mostly red. (No fossils.) Farther south, the lower sandstones nearly vanish (in Somersetshire), but the marls receive a peculiar (local) calcareous conglomerate (millstone), to which pro- bably the reptiles of Durdham Down may be referred. Farther north, the series is continued and very widely expanded the marly upper portions admitting rock salt in Worcestershire and Cheshire * : the sandy * Mr. Ormerod estimates the gypseous and saliferons marls of Cheshire at 700 feet, the waterstone beds below 400 feet, and the subjacent Bunter 600 Geol. Proc., 1848. CHAP. VI. MESOZOIC STRATA. 205 lower part more distinctly splits into sandstone (above) and conglomerate (below) as we approach Nottingham- shire,, Derbyshire, and Yorkshire. Here the series be- comes triple. Great red marl series, with interstratified thin sandstones (" waterstone") bands of white and greenish colour; masses and layers of gypsum, (no fossils), a few sand- stone bands near the base. Red and white sandstones the latter irregularly super- posed or inclosed. (No fossils.) Red and white conglomerate, of great but variable thick- ness, growing less conspicuous toward the north. (No fossils ) The abundance of red oxide of iron in almost every part of this and the older Permian system deserves the more attention from the fact, that it is in general an investing substance a sort of varnish covering the white clear rounded grains of quartz which compose the main part of the sandstones of these systems. Rock salt occurs in the state of clear white cubically crystallized masses, or reddened by the argillaceous sediments among which it occurs : sometimes in Che- shire the red salt is fibrous. Brine springs, which issue from rock salt, contain combinations of iodine and bromine, though in the rock itself those substances can hardly be detected : a circumstance depending on the extreme solubility of the iodic and bromic salts. * Gypsum, a very frequent product of the red argilla- ceous members of this system, and very commonly found in the vicinity of rock salt, is granular at Chel- werton near Derby, but generally fibrous, as at Tees Mouth, Pocklington, Nottingham, Aust Passage. Sul- phate of strontian forms nodules in these marls in Somersetshire. Organic Remains. In England we have scarcely an example of the true flora and fauna of this system ; for the ramified leaves (Dictyophyllum) of the sandstone near Liverpool, and the almost traceless calamites in marl Daubeny on Mineral Springs, British Association Reports. 206 A TREATISE ON GEOLOGY. CHAP. VI. near Malvern, are poor representatives of the voltziae, calamites, and ferns of the German trias : nor could we, from the little bivalve which occurs in the Keuper of Salop (Posidonomya minuta), conjecture the variety of testacea which is yielded hy the coeval strata of Sulz les Bains. Our fish and reptile remains are more nume- rous. The latter in particular (Labyrinthodon), known by footprints in Cheshire and Dumfriesshire, and by bones and teeth from Warwickshire, are ex- tremely interesting. The German trias yields a sufficiently large series to remove all doubt as to the truly mesozoic character of the deposits. Geographical Extent. Slight traces of new red sandstone occur on the western coasts and islands of Scotland : some considerable area is occupied by it in the country between Coleraine and Dungannon, about Belfast, and on the coast of Antrim. The Solway Firth is in red marls and sandstones, and all the rivers which enter it from the Scottish frontier flow through the same ; the plain of Carlisle ; the western coasts, from Whitehaven to Furness ; the peat mosses of South Lancashire, and the Vale of Clwydd are in the red formation. The river Tees enters the sea in gyp- seous red marls and sandstones ; so does the river Exe in Devonshire ; and between these two points is an almost uninterrupted line of the same strata, ranging by York, Nottingham, Warwick, Worcester, Aust Passage, Taunton, and Honiton. It expands westward from Nottingham to Derby, Manchester, Liverpool, and Shrewsbury, thus occupying an enormous area in the centre of England, partially broken by the up- heaved coal measures of Leicestershire, Warwickshire, and Staffordshire. Small detached portions appear in Monmouthshire, Glamorganshire, and Devonshire. On the continent of Europe, still larger spaces are covered by the saliferous system than in England. A small continuation of the Devonshire red rocks appears CHAP. VI. MESOZOIC STRATA. 20? in Normandy, about St. Lo : a much larger area lies between the Ardennes and the Vosges, running west- ward from Luxemburg to Florenville, northward to Witlich and Vlanden, southward to Thionville, Pont- a-Chaussy, Chateau Salins, and Vic (where rock salt occurs), Mirecour, Jussy, and Villersexel ; eastward to Treves, Wadern, Kaiserslautern, Neustadt, Weisspen- bourg, Weshoffen, St. Diey, &c. In this large and intricate tract, the hunter sandstein, muschelkalk, and keuper, are fully developed : there are some mag- nesian bands in the keuper, but no zechstein below the red sandstone. The Vosges are almost wholly sur- rounded by these rocks. In like manner the Black Forest is principally sur- rounded by saliferous deposits, continuously so on the eastern side, from which spreads to the north and east an enormous area of the red rocks, which represent the bed of a sea ramifying in several directions, among islands and promontories of older, and slopes of newer, rocks. The principal part of the mass lies to the east of a long line drawn nearly north from Waldshut on the Rhine, to Minden on the Weser, including the Oden- wald, Spessart, and Habichtwald. Portions run out east- ward towards Osnaburgh. From Waldshut, by Stutgard, to Dietfurt, nearly parallel to the Danube, is the south- eastern boundary : it thence turns northwards to the Maine, and returns to the Danube at Ratisbon, and fills the narrow space between the Franconian oolites and the primary igneous rocks of the Bohemian border and Thuringerwald. Round the end of these latter moun- tains it bends to the east, fills all the space between the Harz and the grauwacke border of the Erzgebirge, arid passes the end of the Harz in a long tongue between Magdeburg and Brunswick. (In this enormous area, the zechstein, or magnesian limestone, is exhibited along the Thuringerwald, in Hesse Cassel, on the southern and eastern sides of the Harz, between the Elster and the Saale, and about Waldeck.) The muschel- kalk occupies extensive areas, on a line from Waldshut 208 A TREATISE ON GEOLOGY. CHAP VI. to the Thuringerwald, and all around the Harz. Salt occurs in the keuper and muschelkalk especially. Con- siderable tracts of new red sandstone adjoin theRiesenge- birge ; and a line of these rocks, occasionally saliferous, borders the primary ranges of the Alps, from the vale of the Danube, by Rottenmann, Radstadt, to near Inns- pruck. On the south side of the Alps, the range is equally extensive, from Cilli, near the Save, by Villach to St. Lorenzen on the Eisach. Physical Geography. Spread over so immense a space in England, the triassic system offers the remarkable fact of never rising to elevations much above 800 feet (Barr Beacon, in Staffordshire, is a gravel hill on a base of red rocks) ; a circumstance probably not explicable by the mere wasting of these soft rocks by floods of water, but due to some law of physical geology yet un- explained. We only can conjecture that it is connected with the repose of subterranean forces, which prevailed after the violent commotions of the coal strata, over nearly all Europe till the tertiary epoch. The red sandstone system, folding its level surfaces round the broken coal strata, seems to be like the large uplifted bed of a shallow sea, full of rocky islands, and bounded by bold promontories. (The magnesian limestone range in the north of England constitutes a fine natural ter- race of 100 to 500 or 6'00 feet in height above the sea; its escarpment being always to the west.) Igneous Rocks. Almost the only cases known in England, are dykes of greenstone. One of these, the great Cockfield dyke, extends from Middleton, in Tees- dale, to near Robin Hood's Bay, and passes through mountain limestone, coal, magnesian limestone, red sandstone, red marl, the lias, and oolites. Another passes from the Breiddin hills across the plain of Shrewsbury, and dislocates and alters red sandstone at Acton Reynolds. In the Isle of Arran, dykes of pitch- stone, claystone, trap porphyry, &c., divide red and white sandstones, supposed to be of this era. CHAP. VI. MESOZOIC STRATA. 209 Origin and Aggregation of the Materials of the Triassic and Permian Systems. Peculiar in their mineral composition, rocky structure, and the nature and distribution of their imbedded organic remains, the constituent members of the red sandstone and magnesian limestone sometimes offer many points of inquiry to the inductive geologist, and much that seizes on the imagination of those who venture freely into the unsafe regions of speculation. What has caused in the sandstones, clays, and marls of these formations, such various tints of the oxides of iron ? If the greenish and bluish tints of the clays and gritstones be due to pro- toxide of iron, what have been the circumstances which determined in these small portions that particular state, while all around, above, and below them, the masses are tinged, and the particles enveloped by the peroxide ? In particular cases blue centres to yellow rocks occur (oolite, calcareous sandstones), and may be thought to be the residuary primary tint, the outward parts having been decolorised. But this does not apply to the red marls and sandstones, among which (except at the wea- thered surfaces and in the soil), yellow tints are rare ; the prevalent tint of red appears rather to be the original, and the rarer and detached tints of white, green, and blue, to be the decolorised portions of the mass. We may imagine chemical processes of change from protoxide to peroxide, but it is very difficult to find data for apply- ing them to the cases before us. The general extension of these tints appears to imply a very general cause. This can hardly be understood as a mere process of common oxidation ; for this gives greater variety of tints, and cannot be supposed so uni- form or extensive in its action. May we venture to offer as a question deserving attention, the possibility of explain- ing the red colour of these rocks by a general influence of volcanic eruptions on the sediments of the ocean ? The Permian limestones offer other curious topics of remark. Where they degenerate to a sandy state (near Nottingham), they assume a decided red tint ; nor is this tinge any where entirely absent from large VOL. I. p 210 A TREATISE ON GEOLOGY. CHAP. VI. tracts of magnesian limestone. It is complicated with purple (Doncaster), yellow (Sunderland), or is totally replaced by a pure or creamy whiteness. The various modes and degrees of consolidation already noticed among these limestones imply, of course, different modes of aggregation : for the shelly rocks of Hawthorndean and Humbleton (Durham), we may, with some confidence, claim a coralligenous origin : the globular concretions of Sunderland remind us of the pisolite of Carlsbad, and, according to an unpublished suggestion of Dr. Forchhammer, may be really due to ancient submarine springs of great force, yielding min- gled carbonates of lime and magnesia, which were after- wards consolidated together, or separately deposited. The dusty portions of rock seem to be really decom- posed ; and it is worthy of remark, that the tufaceous deposits from these rocks, as well as the crystallised spars in geodes, consist of carbonate of lime. There appears no reason whatever to apply to these magnesian rocks either the speculation of Von Buch concerning Alpine dolomites, that they are common limestones impregnated with carbonate of magnesia by heat, or the notion of their mechanical origin from disin- tegrated magnesian beds of the carboniferous limestone. Origin of Rock Salt and Gypsum. In the present state of nature salt (chloride of sodium) appears in solution at the surface, under the following circumstances : 1. In the sea, every where, but in variable quantities. 2. In springs arising from salt rocks, known or pre- sumed to exist. 3. In springs arising in volcanic regions. 4. In small quantity in all springs whatever. It is only by considering these existing sources of salt in combination with the phenomena accompanying an- cient salt deposits, that we can expect to gain light toward the solution of the problem of the formation of rock salt. This general investigation would here be out of place CHAP. VI. MESOZOIC STRATA. 2 1 1 but we shall present a short view of some of the principal conditions ascertained to accompany these deposits. First, as to the Rocks which inclose Salt. The great abundance of this valuable substance in the red sand- stone and red marl of England, as well as in the contemporaneous rocks of Germany, naturally produced a general impression that salt was peculiarly the pro- duct of that geological era; and it was sometimes assumed without evidence that all the well-known salt works of Switzerland, Poland, Spain, &c., drew their supplies from the new red sandstone formation. The inference was extended not only to the salt lakes and springs of European, but also of Asiatic, Russia, to the sands of Persia and salt-houses of Ormuz, and the saltworks of India, between the Indus and the Chellum. Even the American salt deposits were thought to be- long to the red sandstone formation of Europe. The progress of information has corrected this over- extension of a well-grounded inference: salt springs rise in Durham and Northumberland, and Leicester- shire, from the coal system ; some of the saltworks of the Alps are supplied from the oolitic system : the famous mines of Cardona and Wieliczka have been re- ferred, the former to green sand, the latter to tertiary rocks; and, to complete the series, salt springs abound in the volcanic regions of Sicily and Auvergne. It appears then that salt is derived by the action of water from almost every stratum, formerly left by the sea, and from many volcanic and other products, and that large beds of salt occur at several stages of the series of marine formations, but that in Europe they are remarkable and frequent in the new red sandstone system. This may still, and without impropriety, be called the saliferous system. Hence we may securely infer that although salt was more or less diffused through all the marine deposits, the enormous accumulation of this substance in certain places can only have happened in consequence of local peculiarities several times recurring, but at least, in p 2 212 A TREATISE ON GEOLOGY. CHAP. VI, Europe^ more frequent in a particular period of the earth's lamellar incrustation. It is very important to remark that the salt lies always in small narrow patches ; therefore, most evi- dently it was not produced by a general extrication from the marine water, and most probably is to be referred to local heat, or some other cause at great depths, or else to evaporation from a limited area, rilled at intervals by the sea. In order to discover the nature of these local pecu- liarities, we must compare the different salt deposits, with reference to their situation, accompanying minerals, and other leading circumstances. So little relation appears between the actual form of the ocean and the boundaries of the ancient seas in which the strata were formed, that it will probably be of little use to notice the geographical situation of the beds of rocksalt as compared to the present distribution of land and water. The salt mines of England are in very low ground : those of Wieliczka lie at the foot of the Carpathian mountains on the north, and those of Cardona beneath the Pyrenees on the south: many mines in Wurtemburg and central Germany are in the midst of rather elevated plains; and at Bex salt lies in an ancient valley, some distance above the Lake of Geneva, itself 1000 feet above the sea. With respect to the present ocean, the mines of England and Cardona are near to it, but the others far distant. It does not seem possible to extract from such a discordant assemblage of facts any general character of situation depending on the present distribution of land and water, nor perhaps has it ever been attempted ; but because in the instance of the Cheshire salt district, the local circumstances are such as to have given occasion for Dr. Holland's hypothesis, that the salt there was de- rived from the neighbouring sea, it will be worth while to discuss the formation of that salt basin separately. The Cheshire deposits of salt lie along the line of the valley of the river Weaver, in small patches, about CHAP. VI." MESOZOIC STRATA. 213 Northwich. There are two beds of rock salt, lying beneath 40 yards of coloured marls, in which no traces of animal or vegetable fossils occur. The upper bed of salt is 25 yards thick : it is separated from the lower one by 10 yards of coloured marls, similar to the general cover ; and the lower bed of salt is above 35 yards thick, but has nowhere been perforated. Whether any other beds lie below these two is at present unknown. They lie horizontal, or nearly so, and both beds of salt are below the level of the sea. They extend into an irregularly oval area, in length one mile and a half, in breadth about 1 300 yards, ranging from N. E. to S. W. Gypsum, so abundant in many other salt mines, and ge- nerally plentiful in the tracts of red marl, is found in most of the clays associated with the Cheshire salt. The physical features of the country about Northwich are not very peculiar, yet sufficiently favourable to Dr. Holland's hypothesis. The valley of the Weaver is se- parated from that of the Dee by the sandstone ranges of Delamere forest, and the Peckforton hills, and from the course of the Mersey by an extension of the elevated ridge, called Alderley Edge. Below Northwich these bordering hills come very close together, and naturally sjggest the idea, that in ancient times there might at this place have been accidental bars formed, which while they lasted, would exclude the inroads of the sea. If by such an event the sea lake flowing up the valley of the Weaver was converted into an inland sea, and if the supply of fresh-water streams from the neighbouring country was very scanty, the natural progress of eva- poration would certainly tend to dissipate the water, to concentrate the solution of salt, and finally to cause in it a partial precipitation. At first, gypsum or any other of the less soluble salts would be formed, and perhaps mixed with the earthy sediments mechanically deposited in the lake, and afterwards the salt be accumulated in the deepest parts of the water, in quantity proportioned to the evaporation of the liquid. If, at a subsequent time, the sea should again burst the barrier and inundate the valley, a new deposit of gypseous marls, and a bed of p 3 214 A TREATISE ON GEOLOGY. CHAP. VI. salt would naturally be occasioned, upon any renewed blocking up of the entrance. The entire absence of marine exuvise from these strata is no objection to the hypothesis ; because this is the case with almost the whole extent of the red sandstone form- ation in England. Upon the whole, it seems evident that this hypothesis is well adapted to the circumstances of the case for which it was framed, and is in itself very simple and plausible, but is liable to the serious objection that it employs data drawn from the present relations of land and sea to elucidate the phenomena of a period long gone by, and when, from unquestionable evidence, it is certain that their relations were generally very different. It is, however, not impossible that the district in question may have been undisturbed by any subsequent con- vulsion, and only altered in its physical features by the general elevation which our island appears to have un- dergone, by the rapid transition of diluvial currents, and the erosive action of rains and rivers. This is perfectly supposable, and may be true ; for, as far as yet known, the circumstances of the case do not appear to contradict it ; but before adopting this explanation, we must examine other salt deposits, and see whether a similar mode of origin can be reasonably ascribed to them. OOLITIC SYSTEM. Composition. The change of deposits from the saliferous to the oolitic system is in all respects great, and, from the contrast of colours in the rocks generally, very obvious. Instead of red, green, or white marls, we have blue clays : the red and white sandstones are ex- changed for calcareous grits, tinted yellow, or ochraceous, by iron in a different state of oxidation: instead of powdery magnesian limestones, we have compact or oolitic rocks. Nothing can be a clearer truth than that this great difference of chemical and mechanical depo- sits requires the supposition of some great physical revolution in the relations of land and sea. If we suppose CHAP. VI. MESOZOIC STRATA. 215 that, in consequence of a subterranean movement some- where, the oceanic basins were filled by sediments from other lands, or other lines of wasting coasts, the change from coloured sandstones to oolitic deposits in the same basin would be intelligible, though we might never know the local position of such tracts of land or lines of coast- Most frequently, the arenaceous deposits associated with the oolitic system are easily and obviously distin- guishable from those of earlier date : they are not micaceous, and seldom felspathic, as many of the carbo- niferous grits are ; they are never of the same red, and seldom so white as those of the saliferous period. A yellow tint prevails among them, which sometimes deepens into ferruginous stains ; the grain is generally fine ; quartz pebbles seldom occur ; their substance is mixed with carbonate of lime. But from this descrip- tion, which applies to the south of England, great variations occur in particular districts, as in York- shire, Sutherland, and Westphalia, in the wealden districts of Kent and Sussex. The first three tracts may be sufficiently illustrated by the Yorkshire type, which is eminently distinguished from the rest of England, by having, in the lower parts of the group, enormous masses of sandstone and shale, greatly ana- logous to the sedimentary rocks of the carboniferous system, interpolated among the reduced and deteriorated strata of oolitic limestone. What renders the resem- blance of these to the older grits and shales the more striking, is the circumstance that thin beds of coal, with fossil plants, occur among them, and that some beds of ironstone, and abundance of diffused oxide of iron, augment the analogy. There can be no doubt that these great and numerous points of similitude between the oolitic and carboniferous systems, in the north of England, point to a similarity of causes, extensively acting in the earlier, but reduced to limited effects in the later periods. In the wealden tracts of Sussex and Kent, an almost similar series of sandstones (quartzose, coarse or fine- grained) and clays, with impure, but not oolitic lime* 216' A TREATISE ON GEOLOGY. CHAP. VI. stones, occur, with ironstone beds and diffused oxide of iron, traces of coal and fossil plants. Were the beds of this local deposit placed by the side of others of the old carboniferous era, it would be difficult to distinguish them by any mineral characters capable of being ex- pressed in language ; we may therefore admit for this district, and some small tracts related to it, a renewal for a short period of the actions by which the carboniferous rocks were formed ; and this is easily intelligible upon the principle of changes in the direction and depositions of oceanic currents, occasioned by subterranean movements. The clays of the oolitic system are mostly of a decided blue colour (near the surface changing to yellow), often laminated, especially in the lias formation, but more frequently appearing like a nearly uniform mass of argillaceous sediment obscurely divided by a few laminae of shelly limestone, or lines of septaria: pyrites and jet lie in many of them. The gradation from these clays to the limestones and sandstones is usually very gentle. The limestones of this system are various: those associated with a great abundance of blue clays (as the lias limestones) are mostly of a compact texture, and of white, yellow, grey, blue, or blackish colour. Frequently, nodular masses collected by molecular attraction round organic bodies constitute the whole mass of the lias limestones. Those which appear in considerable thick- ness, as the Bath oolite, Portland oolite, Oxford oolite, are generally of the oolitic texture in the middle, though below and above this may be exchanged for compact or shelly beds. Thin detached limestones, like the forest marble, are sometimes very coarsely oolitic : cal- careous layers in sand are usually charged with siliceous matter and often cleaveable to slate or flags (Stonesfield). The grains of oolite vary much in size ; the smallest are perfectly spherical, the largest irregular ; they generally cohere; the interstices are sometimes filled by calcareous spar: the centres of the large grains of oolite are com- monly occupied by small shells or portions of shells, corals, grains of sand, &c., which served as the points CHAP. VI. MESOZOIC STRATA. 217 of attraction for the calcareous matter, while it was in a soft condition. Structure. In the whole series, not a mass occurs which can be viewed otherwise than as an original deposition, or a subsequent concretion of aqueous se- diment. The sandstones are always stratified : sometimes the coarse-grained sorts (Whitby, Tilgate forest) ex- hibit oblique laminations, the finer sorts often split into flags or slate : shells and plates of oxide or carbonate of iron appear as the result of molecular arrangement round particular masses, as centres of attraction. The clays, as above stated, are either laminated, or appear as vast uniform masses of sediment ; bedded they can hardly ever be said to be, unless where interposed between beds of sandstone, or limestone. The ironstones, septaria, and fc cone-in- cone" masses occur in the clays, in surfaces always parallel to the planes of stratification, and thus appear to mark periodical changes in the nature of the sediments ; but this accumulation is generally the result of molecular attraction round organic bodies. Jet, another frequent substance in the clays, (especially in lias,) lies in laminae parallel to the stratification, being nothing less than chemically altered coniferous wood. Thin limestones associated with thick clays, as the lias limestones, are usually laminated or thinly bedded, and interstratified with the clays : thicker rocks, as the Bath oolite, are formed in regular beds of two to four feet in thickness ; thin layers of clay often occur between the beds. Oblique lamination belongs to many of the coarse shelly oolites: spongoid bodies, enveloped in silice- ous matter, lie in the oolitic rocks of Portland and Oxford, but not so regularly as flints do in chalk : there is very little pyrites, and, except in the lower Bath oolite, little oxide or carbonate of iron in the calcareous rocks, above the lias. Divisional planes. All these rocks are traversed by divisional planes, but very unequally, for the massive clays show few of them; in the calcareous rocks they are both numerous and regular ; in the coarse and irregular bedded grits of Yorkshire and Sussex, 218 A TREATISE ON GEOLOGY. CHAP. VI. the joints are also irregular ; but in the slaty beds of Collyweston, Stonesfield, &c., the contrary is true. The joints are most open in the thick oolites, where they 'are frequently lined by stalagmitic incrustations, and filled with clay from above, and sometimes terminate in caverns, which, in Yorkshire and Franconia, contain bones of quadrupeds introduced at much later dates. In certain districts these joints contribute, by weak- ening the rocks in definite lines, to produce the phe- nomenon of sliding ground ; this is especially the case in the Hambleton hills, Yorkshire, from which, at different historical times, even as late as 1790, great landslips have occurred by the sliding of the clays below the calcareous grit, and the separation of m assess of that grit and the superincumbent oolite along the planes of great vertical joints. The main line of these joints is about N. by W., and parallel to the immense natural escarpment of the Hambleton hills. Series of Strata. On the continent of Europe, the oolitic system, as characteristically exhibited in the Jura mountains, shows less distinctly than in England the minor groups, which furnished to Dr. William Smith the first proofs that England was regularly divided into strata, following one another for great distances on the surface, and sinking in the same direction beneath it. The divisions of the oolitic system, re- cognised by that distinguished observer, near Bath, are found however to apply with sufficient general accu- racy to all European countries; and, there is reason to think, the European type will be found applicable even to the flanks of the Himalaya. Of the five formations which compose the oolitic system in England, the upper or wealden formation is the most local the lower or lias formation the most extensive : the three intermediate or properly oolitic formations are easily distinguishable in the south of England and the north of France; but in the south of France, and generally in the Jura mountains, from Geneva to Bayreuth, this discrimination is a work of difficulty. Even in England, the three oolitic forma. CHAP. VI. MESOZOIC STRATA. 219 tions are not coextensive, at least their calcareous por- tions : the upper or Portland limestone is the most limited and interrupted ; the lower or Bath rocks are the most extensive and connected, but at the same time, perhaps, the most variable. These and other results will appear in the following comparative table, suited to the north and south of England. Peculiar to the North. Common to both. Peculiar to the South. Wealden clay. Hastings sand. Purbeck beds. Kimmeridge clay. Portland oolite. Sands. Upper calcareous grit Coralline oolite. Lower calcareous grit Oxford clay. Kelloways rock. Carbonaceous gritstones and shales. Cornbrash and clays. Hinton sandstones and sands. Forest marble and clay. Fullers' earth rocks. Carbonaceous gritstone, shale, and coal. Great oolite. Inferior oolite and sand. Upper lias shale. Marlstone beds. Middle lias shale. Lias limestone. [Lower lias shale. If, comparing Britain with Europe, we view the oolitic system in gross, we shall find as the most general result, three considerable groups of rocks, viz. : Upper group, consisting of arenaceous (wealden) formation ; Middle group, consisting of the calcareous (oolitic) formations ; Lower group, consisting of the argillaceous (lias) formation ; and may consequently view the whole as a succession of argillaceous sediments widely disseminated in the sea, 220 A TREATISE ON GEOLOGY. CHAP. VI. followed by calcareous accumulations from the oceanic waters, and closed by a local rush from some parts of the land. But analysis of these groups shows the effects of many alternations of oceanicrest and littoral movement, prevailing in the same parts of the sea, and producing at one time limestone with quietly imbedded shells and attached corals ; at another, sandstones; at a third, clays. If we admit what is perhaps impossible to be denied that the production of each sort of rock spread from some centre, and that these centres were not coincident for different rocks, it becomes a very curious problem to determine what are the lines of contemporaneity in the oolitic system. For let A be a point from whence a deposition of carbonate of lime spreads slowly through the ocean, but not reaching to B, a point from which depositions of sand happen, not reaching to A the general basis r,r,r, being red marl and sandstone. The surfaces of strati- fication r,r,r, 1, 1, 1, 2, 2, 2, &c., are usually spoken of in geological works as marking distinct periods in the deposition of the beds, and the matter at any point on one of the three surfaces is usually supposed to have been contemporaneously deposited. In the diagram re- ferred to, five lines of contemporaneity thus appear to be designated, but this inference is by no means perfectly correct. If the calcareous and arenaceous deposits were supposed to happen in alternate periods, those parts of the former which were furthest from A, on the planes 1, 1, 1, 3, 3, 3, and 5, 5, 5, would be of somewhat later date than the others, though exactly similar in substance, organic contents, &c.; and the like reasoning with refer- ence to the point B, applies to the arenaceous deposits on the planes 2, 2, 2, and 4, 4, 4. Yet the beds a, a', a" t CHAP. VI. MESOZOIC STRATA. 221 and b, V, V, would be correctly described as the deposits of a certain period. But if the deposits from A and B were continuously and contemporaneously spreading, the lines 1 and 2, 3 and 4, would completely coalesce towards A, and the lines r and 1, 2, and 3, and 4 and 5 toward B The sandstones would vanish indefinitely towards A, and the limestones towards B : a certain portion of sand would be diffused through the calcareous bed toward A, and some portion of calcareous matter through the sand towards B : the lines of contemporaneity would intersect obliquely the surface of the beds, as in the Diag.(No. 58.) If the rate of deposition were uniform from each point, there would be only one calcareous and one arenaceous S J (fig* 59.) ', but if from either of these points the depositions were subject to periodical changes of intensity, this would occasion alternations of calcareous and aren- aceous beds more or less distinct, according to the va- riations of intensity. From this it may be concluded that the alternations of beds of different nature, proves either cessations or varying intensities of deposition, in one of the de- posits ; that, consequently, sucU a system as the oolites must have taken a long time for its accumulation and could not possibly have been generated with that rapidity 222 A TREATISE ON GEOLOGY. CHAP. VI. which has been ascribed to the deposition of formations, from considerations founded merely on the state of con- servation of organic remains. Organic Remains. The numerous remains of plants, zoophyta, mollusca, articulosa, and vertebral animals, belonging to the oolitic system, have long been celebrated and represented in many works of merit in England and Germany. Some general considerations arise from a contemplation of them, which deserve attention. The following estimate of the numbers of specific forms in the whole system (exclusive of the wealden formations), drawn up by the author, is at this time undoubtedly below the truth. (Encycl. Metrop. p. 653.) Plants marine - 4 In limestone chiefly. terrestrial cryptogamous 39 ) monocotyledonous - 33 f In sandstones and shales gymnospermous 7 4 f chiefly. uncertain 3 J Polyparia fibrous - - 75 } corticiferous and cellu- 7 44 (Chiefly in limestones, but liferous 3 f rarely in the lias. lamelliferous - 59 } Kadiaria crinoidea 31 stellerida - - 17 echinida - - 47 C Chiefly in limestone, rarely I in lias. Conchifera plagimyona - - 189 mesomyona - - 134 brachiopoda - - 61 Mollusca gasteropoda . - 114 cephalopoda - - 273 annulosa . .55 Crustacea - 22 Chiefly astacida?. insects - - - 20 Solenhofen and Stonesfield. fishes .... 40 reptiles - - - 40 mammalia - - 2 or 3 t Only in the lower oolite (. formation at Stonesfield. In the wealden formation, are no zoophyta, no cephalopoda various land plants some fresh- water bivalves and univalves a few estuary shells cy prides, lepidotus, and other fishes iguanodon, hylseosaurus plesiosaurus, &c., with various chelonida, both of fresh and salt water. The most characteristic of the plants are the group of cycadeae, of which stems in the isle of Portland, and leaves and fruits in Yorkshire, show considerable analogy to the existing forms of the tribe, at the Cape of Good Hope, and in India and Australia. Compared with CHAP. VI. MESOZOIC STRATA. 223 existing races, the polyparia present some general re- semblance, with constant and obvious lesser differences. The sponges are seldom so large as those of the South Seas, and appear most to resemble those of New Holland. It would be difficult to doubt that the radiaria of this system are altogether more like the existing pen- tacrinus, stellerida, and echinida, than are those of earlier date. The beautiful genus cidaris, in particular, exhibits in many ways a decided analogy to recent tropical species. The mesomyona and brachiopoda, taken to- gether, still predominate over the plagimyona ; and ce- phalopoda are more numerous than any other group of mollusca ; thus offering a broad distinction between the system of oolitic and modern life in the sea. The fishes belong mostly to the ganoid division of Agassiz, and are remarkable for the beauty of their preservation in the lias of Dorsetshire, Leicestershire, and Yorkshire. Among the saurians, those which frequented the water predominate in number, but the largest forms were ter- restrial (iguanodon, megalosaurus). The natural order of turtles was exceedingly developed in this period. Hugi has found in the Jura formation, about Soleure alone, more than twenty species of emys (fresh water). We are not to imagine the few mammalia, insects, and plants, yet published from these formations, a fair specimen of these races, as they existed on the land during the oolitic period. Doubtless we may believe that the buprestidae of Stonesfield were not the only beetles that fed its pte- rodactyls and marsupials : of these latter the few jaws yet found convey only partial information ; but it is in- teresting to know that the earliest mammalia, of which we have yet any trace, were of the marsupial division, now almost characteristic of Australia, the country where yet remain the trigonia, cerithium, isocardia, zamia, tree fern, and other forms of life so analogous to those of the oolitic periods. The following table will show somewhat of the dis- tribution of remarkable families and genera in the oolitic system, which appears cut off from the cretaceous rocks above by a more decided line than the older formations. 224 A TREATISE ON GEOLOGY. CHAP. VI. Hamites Turrtiites. .' ' CRETACEOUS SYSTEM. Clypeus. Apiocrinus. Megalosaurus. ';* 3 3 ~**.- >*"" oS oa ,.. * E -<> "*< o 9 43 - ^*- fc HwT Wealden Formation. jSpirifera. Upper Oolite Formation. Middle OoliteFormation. Lower Oolite Formation. Lias Formation. 1. Gryphaa dilatata. Sowerby. From the Kelloway rock and Oxford 2 * Gry il > as aEa hlCUrVa- Sowerb y- ( G - arcuata, Schlotheim.) From the 3. Glyphia rostrata. Phillips. From the lias, lower oolite, and middle oolite formations. 4. Nucleolites clunicularis. Llwyd. From the lower and middle oolite formations. 5. Cardium truncation. Sowerby. From the marlstone beds in the lias formation. CHAP. VI. MESOZOIC STRATA. 225 6. Tngoma costata. Sowerby. From the lower and middle oolite form- ations. 7. Mya V.scripta. Sowerby. From the lias, lower and middle oolite formations. 8. Pterophyllum comptum. Phillips. From the carboniferous shales of the lower oolite series near Scarborough. 9. Cicians intermedia. Fleming. From the middle oolite formation. 10 Gervillia acuta. Sowerby. From the lower oolite formation. (Gold. tuss thinks it a different species.) 11. Vertebra of plesiosaurus. From the lias. 12. Ammonites calloviensis. Sowerby. From the Kelloway rock and Ox ford clay. 13. Terebratula acuta. Sowerby. From the marlstone beds in the lias, &c. 14. Kerinea cingenda. Volt%. From the lower oolite formation. VOL. I. Q 226 A TREATISE ON GEOLOGY. CHAP. VI, During the oolitic period the arctic land was covered by plants like those of hot regions, whose vegetable ruins have locally generated coal beds adorned by coleop- terous, neuropterous, and other insects among which the flying lizard (pterodactylus) spread his filmy wings. The rivers and shores were watched by saurians more or less amphibious (megalosaurus, iguanodon), or tenanted by reptiles, which by imaginative men have been thought 10 be the originals of our gavials and crocodiles ; while the sea was full of forms of zoophyta, mollusca, articulosa, and fishes. Undoubtedly, the general impression, gathered from a survey of all those monuments of earlier creations, is that they lived in a warm climate ; and we might wonder that the result of all inquiry has shown no trace of manor his works, did we not clearly perceive the oolitic fossils to be all very distinct from existing types, and combined in such, different proportions,, as to prove that circumstances then prevailed on the globe, materially different from what we now see, and probably incom- patible with the existence of those plants and animals, which belong to the creation whereof man is the ap- pointed head. Geographical Extent. The oolitic system occupies a considerable surface in England, but is very slightly re- presented in Scotland (at Brora in Sutherland, in Skye, and other Western Islands), Ireland (about Ballycastle), andin Wales ( Aberthaw, Glamorganshire). Thelias form- ation has its western edge continuous, or nearly so, on the surface from the sea-coast near Redcar in Yorkshire to the rival cliffs of Lyme Regis in Dorsetshire. In this long course it passes by Northallerton, Easingwold, and Market Weighton to the confluence of the Trent and Humber ; thence due south to Newark ; afterwards in a generally south-west course byBelvoir, Leicester, Lutterworth, and Southam to Evesham. From Pershore a long projection of Has runs out northward to Hanbury, but the principal range returns by Tewkesbury, Gloucester, Berkeley, and Sodbury to the Avon at Keynsham. From the Avon to CHAP. VI. MESOZOIC STRATA. 227 the Mendip Hills the distribution of the lias is intricate ; south of that chain of limestone, the lias runs out west- ward between the rivers, and even extends beyond Wat- chet ; from Langport and near Taunton it turns south and (resting on red marl) it passes under the over-ex- tended strata of green sand and chalk. An extraordinary patch of lias occurs in the red marl between Whitchurch and Wem. Within this long range the lower or Bath oolitic form- ation is equally continuous, except where unconform- ably covered by the chalk between the Yorkshire Der- went and the H umber, and in Dorsetshire; and its course may be described as parallel to, and lying on, the eastern side of the lias. Guisborough, Coxwold, Whitwell, South Cave, Lincoln, Grantham, Uppingham, North- ampton, Banbury, Stow, Cheltenham, Stroud, Marshfleld, Frome, Yeovil, Ilchester, and Bridport, are situated near its western boundary. Parallel to this, and more to the east, is the less continuous range of the coralline oolites, which passes from Scarborough due west to Hambleton, then turns south-east to Malton, beyond which it is con- cealed beneath the chalk. The argillaceous part of this group (Oxford clay) reappears in Lincolnshire, nearBrigg, and passes by Sleaford, Peterborough and Bedford, to Ottmoor near Oxford, From this point the oolitic rocks are added to the series, and the formation fills the vale of Isis to Cricklade, turns south to Chippenham, Calne, and Melksham, and, with some interruption in the oolites, continues by Wincaunton and Sturminster toward II- minster, where it is covered by the Dorsetshire chalk, but reappears on the south side of it about Weymouth. The Portland oolite formation, represented only by the Kimmeridge clay, fills the vale of Pickering in Yorkshire, borders the chalk and lower green sand of Lincolnshire, from the Hum her at Ferraby to Spilsby ; underlays a large part of the Fens, and with the Portland oolite fills a considerable breadth in the vale of Aylesbury. Irregu- larly capped by the same oolite, and sands, the Kimme- ridge clay passes byShotover,Cumner Hurst, Faringdon, Q 2 228 A TREATISE ON GEOLOGY. CHAP. VI. and Swindon, to Wotton Basset ; turns south to Seend and Westbury ; appears about Wincaunton and Sturmin- ster, passes under the Dorsetshire chalk, and reappears near Weymouth and in the isle of Portland. The minute flexures, irregularities, and breaks in the ranges of these formations, ca,n only be understood by consul-ting a good geological map ; but the preceding no tices will suffice to show how remarkable is the effect, in the geology of England, of their parallel courses from sea to sea from Yorkshire to Dorsetshire. In this respect their ranges are of great importance, offering to the inquiring mind a proof of the long succession of qui-et processes by which the bed of the sea was gradually filled with a regular series of vary ing deposits alternations of chemical and mechanical products and afterwards, it is almost certain, gradually lifted so as to changt with a certain regularity the ancient boundary of the sea. The Wealden formation, in this, as in all else, contrasts very strongly with the truly marine deposits. It makes no part of this parallel series, but lies principally in Kent and Sussex, occupying all the drainage of the Medway above Yalding, the upper branches of the Mole, Wey, Arun, and Adur, and the Ouse. From near Beachy Head to near HytheandAshford, the whole breadth of the Weald of Kent and Sussex is formed on these rocks, which are therefore happily named. Detached portions occur in the isle of Purbeck and in the vale of Wardour in Wiltshire, and analogous accumulations near Boulogne and Beauvais. On the continent of Europe the oolitic rocks appear connected by direction in Normandy with those of England, and the series there is extremely similar and not less fully developed. The figure of the geographical area occupied by these rocks in France and Germany is so singularly ramified as almost to defy description. One portion surrounds the basin of Paris in a course from Caen by Mortagne near Angers, Saumur, Poitiers, Chatelherault, Bourges, Auxerre, Bar le Due, Mezieres, spreading to Luxemburg, Metz, Nancy, and Dijon, CHAP. VI. MESOZOIC STRATA. 229 Caen, Xarbonne. Metises. and running south to near Lyons. From near Poi- tiers branches pass off westward to La Rochelle, and south-eastward to theCevennes. The north flank of the Pyrenees has a belt of oolitic rocks. Another range passes from near Narbonne due N. E. to Savoy, where it bifurcates ; one branch forming the French and Swiss Jura, which, crossing the Rhine above Basle, continues north of the Danube to Ratisbon, and thence turns north to the Mayne at Banz. The other branch keeps the south side of the Rhone, to the Vallais, and thence forward to Vienna forms part of the great chain of the Alps, but is so altered in aspect from ordi- nary " Jura kalk " as to have been for a long time con- sidered as quite of a different age. The limestone, north of the Carpathians about Krakow, may be looked upon as of the same age. The south side of the Alps is in like manner bordered by a similar range of the Jura kalk, from the Lago Mag- giore, by Lago di Guarda, Belluno, and Lay bach, where it expands greatly, and sends off ridges through Illyria, Dalmatia, Albania, and Greece. Throughout the greater part of this range, except in France, the minute distinctions of the English formations vanish. In the Swiss and German Jura, and the Alpine borders, the oolitic rocks, though connected with the strata of Normandy, vary greatly from that type, so that in some districts hardly any member but the lias can be perfectly discriminated from the general oolitic mass. This renders very singular the perfect exactness 230 A TREATISE ON GEOLOGY. CHAP. VI. with which the argillaceous rocks in the south slope of the Himalaya represent the English lias, an agreement which, perhaps, by further researches, may be found not less complete than that presented by the lias of Wurtemburg and Franconia, which can hardly be said even to differ from the argillaceous rocks of the Yorkshire coast. (See Geol. Proceedings, for Murchison's notices of the Banz Series, and Voltz on Belemnites, for proof of the identity of the Wurtemburg and Whitby Spain, the Balearic Islands, and the Apennines, con- tain the oolitic system, which also appears in the range of the Atlas. Physical Geography. The oolitic tracts of England present a broad band of dry limestone surface, rising westward to elevations of 800 and 1100 feet (in York- shire 1485 feet), with escarpments commanding very extensive prospects over the undulating plains of lias and red marl. Even where the valleys are abrupt, as about Stroud and Bath, the scenery, though pleasing, ap- pears tame to one acquainted with the older strata. This arises from the comparative softness and easy destructi- lility of the rocks; for in some parts of the Swiss Jura the harder limestones appear in mighty precipices. The faci- lity of waste has permitted, on the western border of the districts in England, the production of frequent outlines of the limestones on the c'ays ; as Bredon Hill, which stands up in the vale of Gloucester to attest the powerful effects of ancient water. Upper oolite. Middle oolite. Lower oolite. 61 The whole tortuous line of oolitic .escarpment from the Humber to the Avon may be regarded as the wasting effect of .water on the subjacent red marls and lias clays ; but what that water, when and how applied, is a problem of general geology, on which we may enlarge hereafter. CHAP. VI. MESOZOIC STRATA. 2.31 Each oolitic rock forms an escarpment over the subjacent clays, so that several longitudinal hollows and ridges undulate the area occupied by the oolitic system. Igneous Rocks. In Scotland, the Ord of Caithness offers a case of granitic rocks uplifted in a solid form among the oolitic strata, which are in consequence much fractured and displaced. In Yorkshire, the great Whin- dyke of Cockfield fell crosses the lias and lower oolites, and affects the argillaceous and arenaceous beds consi- derably, both by induration and debitumenisation. GENERAL REVIEW. Oolitic System. Perhaps nothing more clearly demonstrates the frequent dependence of geological phenomena upon causes acting at a distance, than the total dissimilitude of the rocks of the oolitic and saliferous periods; for not the slightest unconformity of dip or direction appears at their line of junction, to mark any local disturbance. The repetition of clay sandstone and oolitic limestone observed at least four times in this system, shows the persistence of the new conditions impressed upon the land and sea, while the very local interpolation of grits, shales, and coal, like those of older periods, may be viewed as the result of a tempo- rary restoration of communication from some particular tracts of land to die oolitiferous sea. If, as appears pro. bable from the thickening of the interpolations towards the north, we suppose that the same land yielded the sand- stones, shales, and vegetable basis of coal in the carbonifer- ous and oolitic periods, the change of the land plants in the interval from lepidodendra to cycadites is very re- markable, especially* when we take into account the ex- ceptional case stated by l>e Beaumont, of plants of the true carboniferous era occurring above and below beds containing fossils of the true lias at the Col du Chardonet in Dauphine. The Wealden formation suggests inquiries of the same order as to the situation and character of the ancient land, from which it has been assumed that a a 4 232 A TREATISE ON GEOLOGY. CHAP. VI. great river flowed into the estuary, through forests of large endogenous plants, tenanted by the iguanodon, hy- Iseosaurus, and other large land reptiles. The limited range of the Wealden deposits, their quick termination toward the north-west and south-west, and their expan- sions, though feeble, to Beauvais and Boulogne, seem to render the supposition of a single river flowing from the west less probable than the concurrence of partial streams from the south and east, with a great current from the north. May we venture to suppose that the primary tracts of the Scandinavian peninsula and Scotland, with other land now sunk beneath the German Ocean, has been the source of most of the arenaceous and argillaceous depo- sits of the carboniferous, oolitic, and Wealden forma- tions of England ? In this point of view, the local strata of Brora, the thick coal series of Bornholm, the oolitic coal tracts of Yorkshire and Westphalia, the Wealden of Boulogne, Beauvais, Sussex, Dorset, Wilts, are all par- tial and local deposits due to a similar succession of causes, and arising from the same or neighbouring phy- sical regions, as the materials of some of the older coal strata. In Bornholm, coal occurs with marine beds of all geological ages from the transition era to the creta- ceous group; and the dependence of its deposits on the waste of the Scandinavian mountains is decided. The dependence of the other deposits on the waste of land in the north is a probable inference ; and if we imagine, what is probably true, that the Scottish and Scandinavian coasts were once united, the whole of the phenomena are intelli- gible as varied deposits on the shores of one limited sea. The distinction of quantity between the few oolitic and wealden plants, and the vast heaps of vegetable re- liquiae preserved in the older coal strata, is important, and might be explained as an effect of the diminution of the quantity of carbonic acid gas in the atmosphere, did not the uncertainty of our knowledge of the position of the ancient land, and the too local occurrence of the phe- nomenon, prohibit the application of such general views. It is supposed to be certainly proved (Buckland's Bridg- CHAP. VI. MESOZOIC STRATA. 233 water Treatise), that the dirt bed in the island of Port- land contains the remains of trees which really grew on the very spot, and were, by a general and quiet subsidence, overspread by oceanic sediments : the character of the cycadioideae here buried demands our belief that the cli- mate of the northern lands was then warm. It would be altogether unreasonable to doubt that the same explan- ation is required by the numerous and varied forms of reptile life, which, with the oolitic era, sprung into such wondrous magnitude : nothing can be more clear than the dependence of the geographical distribution of reptiles upon the feeble power of generating heat in their own bodies, in consequence of the nature of their respiration ; for this renders their existence impossible without a certain amount of heat communicated from without. Hence the magnitude,, and variety, and activity of reptile life under the tropics ; hence the smallness, feebleness, summer life, and winter sleep, of the very few species which occur in the northern regions. Perhaps we may properly appeal to the fossil corals of the oolitic rocks in support of this conclusion ; but it would be ridiculous to quote mollusca or Crustacea for such a purpose ; and, with regard to fishes, we must wait for the deliberate decision of M. Agassiz. It is remarkable that something like a gradation of deposits connects the red marls and lias marls of England ; sandstones which might be referred either to keuper or to lias occur in Luxemburg and on the Rhine ; while in the Alps of Savoy we see the oolites intercalated with green sands, and in Yorkshire and at Havre the Kimmeridge clay appears to join itself with the golt. These transitions are merely examples of the general harmony which con- nects together the whole system of stratified deposits into Vie varied and locally disturbed series of phenomena. CRETACEOUS SYSTEM Composition. As in all the older great assemblages of strata, calcareous, argillaceous, and arenaceous rocks 234 A TREATISE ON GEOLOGY. CHAP. VI. combine to form the Cretaceous System ; but all of these have peculiarities by which they may, upon a great scale, be distinguished from the aqueous products of other periods. The arenaceous rocks are often found in the state of unindurated or even loose sand, the clays are generally soft and marly, the limestones soft and earthy. Peculiar colours also belong to these different members of the group : the sands are often green, sometimes very ochraceous, the clays of a pale greenish blue, the limestones white or red. Variations, however, occur in particular districts. The sands and limestones are usually rather coarsely grained, composed of clear worn quartz grains and pebbles, mixed with some calcareous matter, and coloured by disseminated ochraceous oxide of iron to yellow or brown tints (Wo- burn, Ryegate), or rendered green by interspersed large or small grains of a peculiar mineral (silicate of iron). This granular mineral is, indeed, eminently charac- teristic of the lower portions of the cretaceous system, being found commonly in two great groups of " green sands," in an intermediate clay, and in the superincumbent chalk. Nor is its diffusion confined to Europe : it is so abundant in the cretaceous rocks of the New World, as to be used for manure in New Jersey. Fuller's earth and good ochre lie in the lowest arenaceous sands (Woburn, Nutfield, Shotover). Layers of chert nodules occur in the sand, and sometimes beds of chert. In Kent, beds of whitish limestone, of considerable thick- ness, interlaminate the lower green sands; harder lime- stone lies in them in Lincolnshire. The clay is usually of a marly or even chalky type, and of a light blue tint (golt of Cambridge), but also of a full blue colour (Folkstone) and somewhat laminar texture ; generally it holds small balls and irregular masses of clay indur- ated by oxide of iron, or crusted over by pyrites. In the Wealden district are some red layers. Green grains are commonly found in it : analysis generally shows it to contain much calcareous matter. Phosphatic grains and nodules cling to the Lower chalk, green sand and golt (BAP. VI. MESOZOIC STRATA. 235 But the most peculiar characters belong to the calca- reous rocks, which are, of all the limestones known (excepting some in the tertiary deposits), the softest and most earthy. Not that the whole mass is correctly described by the term chalk, as technically applied by geologists ; but yet a large proportion of the rock would be so termed even by ordinary observers, from the whiteness and comparative softness of it. In the lower parts, green grains are common ; at the base in Lincolnshire and Yorkshire, a red band of from 6 to 12 feet in thickness is traced. Throughout the lower and indeed the greatest part of the chalk in Yorkshire, flint nodules occur in layers ; but in the south of England they are nearly confined to the " uppei chalk," in which they form layers 4 to 6 feet apart. At Sudbury, flint la- minae occur in the planes of stratification, as at Meudon near Paris. Stratification. The clearest possible evidence of regular deposition from water is found in all the rocks of this system, but in few instances are either beds or laminae traceable so clearly or for such distances as among the older formations. In the green sands, beds are seldom clearly traceable, except where, as in the Isle of Wight and at Folkstone, argillaceous beds occur below and above, and are interpolated among the sands, or where, as at Maidstone, Hythe, and in Lincolnshire, bedded limestones necessarily introduce this structure among the sands. In other cases the layers of chert nodules, or thin chert beds, mark the successive stages of deposi- tion : where none of these causes exist, oblique lamina- tion, and concretionary geodes and other arrangements of oxide of iron, render it almost vain to look for stra- tification. The golt clays are sometimes laminated (Speeton, Folkstone), and often, by the courses of small nodules, or by interposed beds of sand, show proofs of succes- sive deposition. The chalk is only partially bedded, and not at all laminated : its slow, and quiet, and intermitting accu- 236 A TREATISE ON GEOLOGY. CHAP. VI. mulation is, however, perfectly proved by the regular arrangement of the flint nodules, which are so common in its upper part. No layers of sand (or clay ?) occur in any part of its thickr:ess. Joints are not, in ge- neral, either numerous or regujar in these formations, nor, excepting geodes and shells of oxides of iron, and the nodules of flint and chert, are concretionary struc- tures common among them Succession of Strata. The basin of Europe offers generally the same succession of cretaceous deposits, as in the British islands; but there are local variations of importance. Two formations constitute this system in England and Ireland, which may be thus analysed and described : (g Upper chalk, usually a soft white calcare- ous mass, with flint nodules at regular intervals : the unper part in the Isle of Wight is of a marly nature. f Middle chalk, not very clearly definable; of intermediate character as well as place be- thick. 1 tween the upper and lower chalk. e Lower chalk, harder and less white than the Upper, sometimes varied by green grains, generally with fewer flints (red in the North of England). d Chalk marl ; a soft argillaceous form of chalk, "c Upper green sand (firestone, malm rock, &c.); a mass of sands, occasionally indurated to chalky or cherty sandstone, of green, gray, or white colour ; with nodules or laminae of chert. Green sand formation, J b Golt (Tetsworth clay, Folk-tone clay, &c.) ; 600ft. j soft bluish marly clay, with green grains. a Lower green sand (iron sand, Shanklin sand) ; ja. considerable mass of green, or ferruginous "sands, with layers of chert, local beds of golt, rocks of chalky or cherty limestone, and deposits of ochre and fullers' earth. In the north of England the upper green sand is totally deficient ; nor is it so distinct from the chalk formation in Kent and Sussex as in Berkshire and Wilt- shire. In Yorkshire there is BO lower green sand, but in Lincolnshire it is greatly developed, and contains useful calcareous beds. In the north of Ireland the series of cretaceous rocks corresponds nearly to the Englis type, the green sand being called mulatto, but the chalk is generally harder. Round the basin of Paris the series CHAP. VI. MESOZOIC STRATA. 237 is also similar, as may be seen by consulting the classifi- cation of Cuvier and Brongniart. About Aix-la-Cha- pelle, the same formations and groups appear ; and the general features, at least, are retained through Westpha- lia (Essen, Paderborn) and along the plains of northern Germany. On the Elbe, about Dresden and Pirna, the lower green sand is called quadersandstein, the represen- tative of the chalk planerkalk. In the Carpathians is no chalk, the green sand being greatly developed. In the Alps is no chalk, and beds of green sand are intercalated among the upper Jurassic oolites (Saleve). But the most remarkable case is the addition of another limestone rock, above the upper chalk, very coarse and sandy in texture, but containing layers of flints, in St. Peter's Mountain, near Maestricht. This rock seems, by its composition and organic contents, to offer an imperfect transition from chalk to the calcaire grossier, one of the next incumbent tertiary strata (Fitton). Murchison and Sedgwick sup- pose the shelly marls of Gosau to present a somewhat dif- ferent case of transition from the cretaceous system of the Styrian Alps to the tertiary rocks. The whole creta- ceous sjstem of America may be taken together into two great masses, a chalky, or at least calcareous, mass above, and a green sand mass below. Thus very general analogies appear at very distant points, and the most constant of the formations is the sedimentary or green sand group. (Rogers, in Rep. to Brit. Assoc.) Organic Remains. The fossils of the cretaceous system are eminently marine : nearly all the plants which it contains (they are few) are of marine types; and the sponges, stellerida, mollusca, Crustacea, fishes, and reptiles, all appear to have been inhabitants of the ocean. Mammalia are not known in the cretaceous rocks. It appears that (excluding the Maestricht and Gosau beds) nearly the same large proportion of extinct genera, and the same differences of proportionate deve- lopment of molluscous groups, is traced in the cre- taceous as in the oolitic system ; so that both the oolitic and cretaceous fossils are reliques of a condition of land 238 A TREATISE ON GEOLOGY. CHAP. VI. and sea very different from what we now witness. The fossils of the two systems are, however, very materially different, even in the same natural groups, as sponges, crinoidea, stellerida, echinida, cephalopoda, Crustacea, fishes, and reptiles, in most of which groups the chalk and green sands contain genera never found in any rocks more ancient or more modern ; while oolitic and tertiary genera are not found in the cretaceous rocks. There appears no sufficient evidence in the fossils of this system to justify any positive inference as to the character of the climate then prevailing in the northern zones ; but we may be sure that the sea was very little disturbed by inundations from the land, otherwise ferns and other land plants, and not fuci, would have been found in the sandy strata. The condition in which the zoophyta especially are preserved in the chalk and green sands deserves notice. Sponges are silicified in both deposits possibly from some peculiar affinity which those organic bodies, even in a recent state, appear to possess for silica ; but in the same flint nodules which envelope silicified sponges, the crusts of echinodermata and stellerida are found converted to crystallised carbonate of lime, and lamellar shells of the genus gryphaea, and radiated sheaths of belemnites, are not at all changed in texture, and very slightly altered in chemical composition. It is a very common fact that iron pyrites collects around sponges and other organic bodies in the chalk, and, when decomposed, leaves an ochraceous oxide of iron. 1. Ammonites varians. Sowerby. From the lower chalk, chiefly. 2. Pecten quinquecostatus. Suwerby. From the upper green sand chiefly. CHAP. VI. MESOZOIC STRATA. 239 3. Spongia plana. Phillips, from the chalk. 4. Plagiostoma spinosum. Sowerby. From the chalk. 5. Hamites intermedius. Phillips. From the Gault. (It belongs to the new genus Crioceratites.) 6. Spatangus hemisphsricus. Phillips. From the chalk. 7. Apiocrinus ellipticus. Milter, from Oie chalk. & Belemnites mucronatus. Brongniart. Trom the upper chalk. Se- veral other species occur in the, English and European chalk. 240 A TREATISE ON GEOLOGY. CHAP. VI. 9. Marsupites ornatus. Mnier. From the chalk. 10. Scaphites equalis. Sowerby. From the chalk. Geographical Extent. In a general sense, the cre- taceous system ranges parallel to the oolitic formations from Yorkshire to Dorsetshire, and sends branches from the plains of Hampshire which border on the north and the south the Wealden formation of Kent and Sussex. The green sand formation is, in all parts of England, so closely connected with the chalk (except in Yorkshire, where it is almost deficient, and in Blackdown, Devon), that it appears unnecessary to notice more than the characteristic range of the chalk. This distinguishing feature of English geology overlooks the German Ocean at Flamborough Head, and sweeps in a large curve inland by Birdsall and Pocklington to the H umber, at Hessle ; thence it pursues a south-eastward course to Candlesby in Lincolnshire ; and, after the interruption of the " Wash," reappears in the cliffs at Hunstanton. Hence to StokeFerryits course is south; but it turns S.W., parallel to the oolities, by Cambridge, Baldock, Wendover, Wallingford, to above Wantage and Devizes. Hence it returns east to the sources of theKennet, and gives origin to a great ridge (the North Downs) dipping north, and passing by Kingsclere, Guildfcrd, Reigate, Wrotham, and Maidstone to Dover ; which corresponds to another great ridge (the South Downs) dipping south, and passing from Beachy Head by Lewes, Steyning, Peters- field, and Alton, to join the North Downs at Farnham. From the sources of the Rennet to Salisbury, and from Farnham to Bishop Waltham, the chalk expands over a vast space in Hampshire ; but its proper outcrop is the western boundary of Salisbury Plain, by Lavington, CHAP. VI. MESOZOIC STRATA. 241 Westbury, and Maiden Bradley. The Vale of Wardour is another deep indentation reaching almost to Wilton, from which the chalk returns to Shaftesbury, and then sweeps in a concave arch by Cerne Abbas to Beamin- ster, and suddenly retires in a narrow eastward course by Abbotsbury and Upway to Corfe Castle. This remark- able ridge of chalk (nearly vertical), reappears in the Isle of Wight at the Needles, and ends at the Culver Cliffs. Detached portions of chalk lie on the green sands of Blackdown ; Portsdown and Thanet are detached In Ireland, a large detached tract of chalk lies under the basalt of Antrim. About Ballycastle, Glenarm Bay, and Larne, and at Belfast, the superposition of the basalt on the chalk is very plainly seen. There is no chalk in Scotland or Wales. On the continent of Europe, the cretaceous rocks are no where more perfectly developed than in France, where a complete series of the chalk and green sand for- mations encircles with a broad ring the tertiary basin of Paris; filling large tracts in Artois, Picardy, Noi- mandy, Touraine, and Champagne; bordering the Channel from Boulogne to the mouth of the Seine, and resting every where on an oolitic basis, except on the Belgian frontier about Avesnes and Mons. Here it touches the slaty rocks of the Ardennes, and covers their parallel bands of coal and limestone. It continues north of the Meuse to Maestricht and Aix-la-Chapelle, and reap- pears beyond the Rhine in a narrow range and argilla- ceous condition, north of the Westphalian continuation of the Ardennes from Essen to beyond Paderborn. De- tached portions occur about Hanover and Brunswick* ; and from the appearance of it at Grodno, Prentzlow, Luneburg, the isle of Rugen,and many parts in Jutland, Zealand, and Scania, there can be little doubt that chalk * The upper part, or slaty, marly limestone, rather than chalk, is called planerkalk ; the lower or sandy rock is called quadersandstein : distinc- tions still clearer in the large area within the Bohemian mountains, where on the course of the Elbe the rocks of this system are widely spread. VOL. J. R 242 A TREATISE ON GEOLOGY. CHAP. VI. lies very extensively under the plains of northern Germany. (Heiligoland is formed of wasting green sand.) The green sand formation is more extensively spread than the chalk, for it is chiefly in this form that we recognise the cretaceous system about Dresden, in the Alps, in the Carpathians, and even the Pyrenees. On the Italian side of the Alps, the chalk is supposed to be represented by the scaglia of Genoa and Lombardy. In North America, according to Dr. Morton and Professor Rogers, the cretaceous system is largely deve- loped on the Atlantic coast in New Jersey, whence it may be traced locally through Delaware, Mary- land, Virginia, North and South Carolina, Georgia Florida, Alabama, Mississippi, Tenessee, Louisiana, Ar- kansas, and Missouri. In the northern parts of this extensive range, yellow ferruginous and green sands, and some argillaceous beds, constitute the greater part of the system, as in the Carpathians, and are excessively rich in the green silicate of iron ; they are covered by friable limestones and calcareous sandstones. Such green sands occur more rarely in the south-western tracts, and are there associated with, and finally superseded by, very thick cretaceous and compact shelly limestones, ap- parently superior in position, which rise into bold hills. It is curious that, for a great part of this range, the green sands are separated from the primary strata more inland by a narrow belt of tertiary and alluvial deposits. " By specimens brought from time to time from the interior of the continent, it would appear to occur abundantly on the Missouri, far across towards the Rocky Mountains/'* Physical Geography. In England, the range of the chalk is one of the most conspicuous features of the eastern and southern counties, in which it forms a noble chain of hills, still partially left (as, perhaps, they all should have been) open for sheep -pasture. These * Rogers, in Report to Brit. Association. CHAP. VI. MESOZOIC STRATA. 243 cc wolds" or " downs" are covered with a sweet short herbage, generally bare of trees, and singularly dry, even in the valleys, which for miles wind and receive com- plicated branches, all descending in a regular slope, yet are frequently entirely dry, and, what is most singular, contain no channel, and but little other circumstantial proof of the action of water, by which certainly they were excavated. Both the dry valleys and the bare hills have characteristically smooth and flowing outlines (represented with excellent taste by Fielding), very different from the tabular hills of oolite, and the rugged chains of older rocks. The same characters accompany the chalk in France, The green sand ranges are less characteristic, though in Leith Hill and Hazlemere Forest they rise to nearly 1000 feet in height, and thus rival the chalk, which generally swells to 800 feet, but no where, except at I nkpen Beacon, equals 1011. Copious springs flow from the chalk, over the subjacent golt; or issue on the dip side at low levels : wells sunk in the chalk to some hundred feet yield water, at different levels according to the impediments in the subterranean currents. Where tertiary clays cover the chalk, as in the basin of London, the boring rod no sooner pierces them than strong streams arise, with a temperature much superior to that of the surface, over which they some- times flow in a constant stream. Igneous Rocks. In no part of England is there the smallest trace of igneous rocks associated with the chalk. In Ireland, a very large tract of basaltic rocks occupies the greater part of the drainage of Lough Neagh, and the river which issues from it to Coleraine. If a line be drawn from the mouth of Lough Foyle to Lurgan on Lough Neagh, nearly all the country to the east of it is trap, here and there in the interior, and generally on the coast, exposing chalk, and more locally mulatto, lias, new red sandstone or coal measures. The thickness is in places (Knockhead) supposed to be little short of 1000 feet, and the superficial area 800 miles ! What a B 2 244" A TREATISE ON GEOLOGY. CHAP. VI. magnificent volcanic eruption is here pictured in its sub- marine lava currents ! For it undoubtedly was a mass or series of expansions of liquid lava poured on the bed of the sea after the deposition of the chalk. It is a series of basaltic and ochraceous beds, some of the former being eminently columnar. Near the Giant's Causeway, the following succession is given by Dr. Richardson : 1. Basalt rudely columnar 2. Red ochre or bole - . 3. Basalt rudely prismatic 4. Basalt columnar 5. Intermediate between bole and basalt 6. Basalt coarsely columnar 7. Basalt columnar ; the upper range of pillars atBengore Head 8. Basalt irregularly prismatic; inclosing the wacke and wood coal of Port Noffer - , 9. Basalt columnar forming the Causeway . 10. Bole or red ochre 11, 12, 13. Basalt, tabular, divided by the layers of bole 14, 15, 1& Basalt, tabular, with zeolite 60ft. 9 The stratified rocks on which the basaltic masses rest, are variously altered by the effect of their former heat. Lias is changed, at Portrush, into a hard rock like flinty slate : by the side of basaltic dykes at Fair- head, the coal shales are similarly hardened : red sand- stone is indurated at the foot of Lurgethan ; and in RatKlin, at Glenarm, &c. the chalk is changed by dykes into a largely crystalline marble. The quadersandstein (?) of Weinbohla (on the Da- nube) is overlaid by a syenitic v rock. In the Pyrenees, cretaceous strata are in contact with granitic and serpentinous rocks, and mineral veins are in consequence introduced among them. (M. Du- frenoy.) Close of the Secondary Period. Ensuing Disturbances of the Crust of the Globe. With the cretaceous system ends the long series of deposits which are, by general consent, ranked as strata of the secondary periods of geology. In reviewing the successive secondary formations, from the red sandstones CHAP. VI. MESOZOIC STRATA. 24.5 to the green sand, and from the mountain limestone to the chaik, it is impossible not to recognise, on a great scale, the gradual change of the physical conditions of the globe which took place during this period. Miner- alogically, the rocks successively deposited deviate more and more from the types of the primary strata ; consi- dered as to their zoological and botanical relations, it is evident that the circumstances influencing organic life were undergoing gradual but great changes; and a careful study of the geographical areas over which the secondary strata spread, demonstrates that an equal amount of variation occurred in the relations of land and sea. It may, indeed, be objected, that these con- clusions, however true, are almost limited to Europe, North America, and India, since elsewhere the second- ary rocks are but imperfectly known ; but if the data for reasoning are satisfactory, the geographical area of their application, is ample. Several distinct mineral types appear predominant in the secondary rocks of Europe^ constituting various groups of strata, which may not always be found to combine into exactly the five systems adopted in these pages. The really oceanic types of- limestone mountain uraqsion>v ^Mfl^^ ** To each of these belong similiar corretetionary masse? of flint or chert, often aggregated "H "*-mtr rnrrfee r and sometimes extended into thin interrupted layers. The really littoral types of sandstone are various : Green or ferruginous sands. Pale coloured calcareous grits. Red and white sandstone. Red conglomerates. Felspathic sandstones. Quartzose grits. B S 246 A TREATISE ON GEOLOGY. CHAP. VI. Of argillaceous beds are three principal types : Blue clays, often inclosing nodules and beds of compact limestone. Red, white, and blue clays, with gypsum. Blue or black shales. Not one of all these rocks can be considered as uni- versally coextensive with the secondary series : but it appears from examination, that, in most districts, the conditions under which these various deposits happened, were contemporaneous, or at least succeeded one another in the same order. A very general view of the mineral relations of the rocks would allow us to consider the whole secondary series in two parts, the lower one characterised by red sandstones and red clays, the upper by blue clays and light coloured sandstones ; while in each of these divisions occur carboniferous deposits breaking the uniformity of the series. This arrange- ment is seen below : Cretaceous group. \ Including the coal deposits of the Weal- Oolitic group. J den, Yorkshire, and Bornholm. New red sandstone group. "1 Including the principal coal de- Old red sandstone group. J posits of Europe. Nor would such a classification be inapplicable to the calcareous portions of the series, though, as might be expected, these admit of other combinations. When- ever the causes of these successive mineral characters in the secondary rocks shall be known, a great advance will have been made toward a general theory of the stratified crust of the globe. Turning to the organic remains of the several second- ary systems, it is apparent that, within the period of time which elapsed between the deposition of the pri- mary and tertiary strata, two very distinct assemblages of terrestrial plants had flourished and become extinct. The ancient and abundant flora of the carboniferous era, with its lepidodendra, sigillariae, and calamites, had CHAP. VI. MESOZOIC STRATA. 247 been replaced by new races of zamiae and cycadese, which, in their turn, vanished from the northern zones of the globe before the completion of the cretaceous system. The marine zoophyta were changed, though not to the same extent, both as regards the polyparia and crinoidea. One total change had come over the Crustacea, not a single trilobite being known in the strata more recent than coal : the brachiopodous con- chifera, the gasteropodous and cephalopodous mollusca, were equally altered. Two large assemblages of fishes had vanished before the deposition of the chalk ; and both on the land and in the sea, gigantic reptile forms had come into being reproduced themselves to a mar- vellous extent and then all perished with the close of the secondary period. How, then, can they, by whom the magnificent truths of elapsed time and successive creations have been put in clear and strong evidence, how can they be expected to yield to false notions of philosophy, and narrow views of religion, the secure conviction that, in the formation of the crust of the earth, Almighty wisdom was glorified, the permitted laws of nature were in beneficent operation, and thousands of beautiful and active things enjoyed their appointed life, long before man was formed of the dust of the ancient earth, and endowed with a divine power of comprehending the wonders of its construction ? It is something worse than philosophical prejudice, to close the eyes of reason on the evidence which the earth offers to the eyes of sense ; it is a dangerous theological error to put in unequal conflict a few ill-understood words of the Pen- tateuch, and the thousands of facts which the finger of God has plainly written in the book of Nature ; folly, past all excuse, to suppose that the moral evidence of an eternity of the future shall be weakened by admitting the physical evidence for an immensity of the past. Since the close of the secondary period, the earth's surface has been greatly altered and the boundaries of 24-8 A TREATISE ON GEOLOGY. CHAP. VI. the ocean entirely changed in the northern zones, on the Mediterranean shores, and on the coasts of India and America. It is difficult to collect very certain evidence of the occurrence of general subterranean move- ments immediately after the completion of the chalk, though the great extent of sands, and pebbles, and lignitic beds which cover it, and the deep wasting on its sur- face, as seen beneath those sands and pebbles, leaves no doubt that what had been deep sea was converted to shallow water, and subject to inundations from the land. In many cases, these pebbles appear to be nothing else than broken and rolled flints, derived from the chalk itself ; some of the white sands which form part of the tertiary series, when magnified, appear to be frag- mentary particles of flint, very slightly worn by attri- tion ; but, upon the whole, the great mass of tertiary deposits in every country can only be understood as derived from the older strata, and, in some cases, trans- ported from considerable distances. Clear proof of local disturbance of the chalk and older strata, before the production of any tertiary strata, can no where be given in England or Ire- land, unless the pebble beds of the former country, and the basaltic eruption of the latter, be admitted in evidence. In the south-east of France De Beaumont ascribes to a late epoch in the cretaceous period the system of dislocations ranging from N. N. W. to S. S. E., which traverses Mont Viso, the French Alps, and the south-west extremity of the Jura. After the cretaceous period occurred the great disruptions of the Pyrenees and Apennines ; but there is yet too little known of the geology of the Ghauts and the Allegha- nies, to allow us to determine whether these ranges, w.hich are rudely parallel to the same great circle as the Pyrenees and the Apennines, were (as De Beaumont sup- poses, and his speculation on the relation of age and direction among mountain chains requires) uplifted at the same geological epoch. CHAP. VI. CALXOZOIC STRATA. 24Q To determine exactly the geological date of a disrup- tion of the crust of the globe is "not easy, even when the case is so simple as that of a common " fault;" when it is to apply to a whole chain" of mountains no more difficult problem can be proposed to geological observers. In the present case it is rendered still more perplexing by the change of mineral and organic characters which, on the flanks of the Pyrenees, almost destroys the distinc- tion of secondary and tertiary deposits, and leaves little relation between the Apennine limestone and the chalk of Northern Europe, except what the scaglia of Lom- bardy has afforded. As far as regards the British islands, a gradual or interrupted rising of the whole bed of the sea* would much better suit the phenomena than one mighty con- vulsion ; and Mr. LyelTs views of the gradual rising of the Weald *, though, perhaps, not entirely satisfactory in that particular instance, contain an important illus- tration of the consequences of such an hypothesis. CAINOZOIC OR TERTIARY STRATA. Supracretaceous Deposits. Terrain Tertiare. Ter- tidrgebilde. Offering a most decided contrast with the secondary and older strata in most of their essential characters, the tertiary strata form a division of the series which may be considered as of more elevated rank than the term " system," in our mode of using it (which is now become common) denotes. But, on the other hand, so many analogies appear among these strata of all ages, that, though with great propriety distinguishable into " formations," they must, for the present at least, be ranked in one general system. Principles of Geology, voL iii. 1st edit. 250 A TREATISE ON GEOLOGY. CHAP. VI. Composition. Arenaceous deposits predominate in most parts of the tertiary system; argillaceous types, however, abound in particular districts ; calcareous rocks, marine or of freshwater origin, pure, sandy, shelly, or siliceous, lie in many basins ; marls and gyp- sum are locally accumulated. Marine, freshwater, and terrestrial exuviae occur in strata of all these descrip- tions ; and so much information is now accumulated concerning them, and so many comparisons have been made between tertiary and modern products, that it is probable the origin of no part of the series of strata is so well understood. The sea, sudden land floods, river currents, lakes, springs, have all contributed to the accu- mulation of the supracretaceous strata, and left charac- teristic marks of their action. But confining our views, at this time, to the composition of the masses, those dis- tinctions of the origin of the deposits vanish, for it is not directly by the mineral nature of the strata that their freshwater or marine origin could be known. The arenaceous rocks are either in the form of con- glomerates, holding fragments, pebbles, and enor- mous boulders of the neighbouring mountains, as the molasse of the northern slope of the Alps; or appear as sand (rarely indurated to sandstone), tinted of many varying hues, as at Alum Bay, in the Isle of Wight, where the effect of the many colours imparted by oxide of iron is of a magical description ; left white and co- lourless, as in the Dorsetshire heaths and forests, and at Fontainbleau ; or dyed of a general green, as near Paris, at Reading, Sudbury, &c., by silicate of iron. Beds of rolled pebbles (flints from the chalk) and layers of lignite appear not unfrequently among them, and are generally accompanied by sulphuret of iron and clay (Isle of Wight). Mica occurs, but is not plentiful, in these tertiary sands, which convey the impression of much and long abrasion in water, and various exposure to oxygenating processes. The argillaceous sediments of the tertiary system CHAP. VI. CAINOZOIC STRATA. 251 offer also a considerable variety. The principal mass in the vicinity of London is of a dull bluish or brownish tint, not unlike a clay of the oolitic era. The suba- pennine "marls" are more sandy. Light greenish and bluish marls accompany the limestones of Headon Hill in the Isle of Wight, and occur, with prismatised beds of gypsum, at Montmartre. But the most singular clays are those which accompany the coloured sands of Alum Bay and the neighbourhood of Paris ; for these are almost black, or brown, or mottled in the richest manner with red or white, or almost entirely red, so that the same causes of diversity of colour appear to have affected nearly all the deposits of that particular tertiary period. The tertiary limestones might, perhaps, generally be discriminated from all those of older date by their very inferior degree of induration, though to this certain fresh- water limestones (as near Weimar) offer exceptions. The marine calcaire grossier of Paris is a coarse sandy or chalky limestone ; the leithakalk of Austria is a co- ralline rock, somewhat like the English crag ; the fresh- water limestones of Headon Hill are soft, marly, and full of shells ; that of Oeningen marly and laminated ; near Weimar are very hard and compact beds, which inclose nodules of flint, like some in Cantal, described by Mr. Lyell ; a peculiar siliceous limestone occurs in the basin of Paris. From all these variations of composition, it is evident that the accumulation of tertiary strata is the fruit of a great diversity of causes, or else a great amount of local influences has modified the effects of the general agen- cies. It is not merely that some are of marine, and others of fluviatile, or of lacustrine origin : these are, in- deed, the leading considerations to guide our inquiries, but local peculiarities of physical geography are also clearly indicated as important conditions in determining the nature of tertiary strata. Structure. Stratification. The whole of the ter- 252 A TREATISE ON GEOLOftY. CHAP. VI. tiary accumulations are plainly stratiform deposits ; and they exhibit the different kinds of lamination and bed- dipg which have been so often noticed before, while speaking of older rocks. The molasse of Switzerland, sandstone of Fontainbleau, and sands of the Isle of Wight, are stratified ; sometimes, also, parted by oblique or parallel laminae : the London clay and Headon marls are partially, the Montmartre marl perfectly, laminated : the marine calcaire grossier, and most of the freshwater limestones, are regularly bedded, and the latter very fre- quently laminated : gypsum occurs at Montmartre, and elsewhere in France, in a bedded mass. Divisional Planes. Agreeably to a very general law, which connects the divisional structures with the age of the rocks, and expresses their relative abundance and regularity in terms of their antiquity, we find them less remarkable in the tertiary sands, clays, and marly or chalky limestones, than in any of the older rocks. Joints do certainly exist in them, and especially in the lamellated limestones; and it is probable, from general considerations of the agency of heat in developing these structures, that, near large masses of igneous rocks, as in the Alps, they may be found more numerous. Nor does it appear that many cases of re-arrangement among the particles occur : some oolitic beds occur in the leithakalk; menilite is con- centrated in certain marl beds near Paris ; flint is col- lected in nodules in some fresh water limestones; sulphuret of iron gathers round and in the substance of lignite. Succession and Thickness of the Strata. Diffi- culties unfelt with regard to the older systems em. barrass the history, or rather the classification, of the tertiary strata. The lower boundary of this system is in general very clearly marked by the peculiar mineral character and remarkable organic remains of the cre- taceous rocks ; but the upper boundary, the line of dis- tinction between the " tertiary" deposits and those which we may agree to call " modern," is not at all clear. This difficulty arises in various ways : the mineral cha- CHAP. VI. CAINOZOIC STRATA. 253 racter and circumstances of aggregation of the tertiary rocks are extremely various according to locality ; and in this respect so closely resemble formations now in progress, that were the bed of the Adriatic raised to our view, it would, according to the observations of Donati, most closely resemble the subapennine tertiaries; the German Ocean would disclose shelly sand-banks, com- parable, perhaps, to the Norfolk crag; and the coral reefs of Bermudas may be thought to resemble the lei- thakalk of Transylvania. The analogy of tertiary and modern shells and vertebral reliquiae is also very great, so great, indeed, that nothing but very refined know- ledge can establish differences between them. When, in addition to these facts, we are further em- barrassed by the intermixture of lacustrine, estuary, and marine deposits, which belong naturally to as many dis- tinct series of operations, and certain organic exuviae which may have unequal degrees of relation to existing types, what wonder if it be sometimes impossible to dis tinguish tertiary from modern accumulations? The progress of research has, indeed, shown us the necessity of separating from the tertiary class a considerable quan- tity and variety of superficial accumulations, more or less evidently related in their position to the present features of physical geography; but it has also placed the distinction on its true ground, viz. the difference of organic life in the modern and tertiary periods. This difference, however, is probably of a positive character only in the classes of vertebra ted animals, which are chiefly met with in lacustrine sediments ; and is with difficulty applied to, marine races, which constitute by far the largest portion of tertiary fossils, and are the principal means of linking the history of supracretaceous deposits to those of the older periods, which contain almost no traces of mammalia or birds, and only a very limited number of fluviatile reptilia or lacustrine fishes. It is hardly to be doubted, that hereafter the mode of studying supracretaceous deposits will be so far changed, 254 A TREATISE ON GEOLOGY, CHAP. VI. that the whole series of marine accumulations of every age, from the cretaceous period to the present day, will be grouped together, but distinguished from another equally extended series of lacustrine and fluviatile sedi- ments ; the principle of investigation in each case being founded on a rigorous study of the characters of mine- ral structure, and the organic exuviae, which are charac- teristic of the sea, the streams, and the land. At present, however, not to deviate too far from the method now familiar to geologists, we shall assume that, in spite of the difficulties above noticed, the tertiary strata and modern deposits can be distinguished in par- ticular cases, though not in conformity with any gene- ral definition. If the account of the modern deposits be in like manner arranged with reference to the same really influential conditions, their marine or fresh- water origin, no confusion will, under any circum- stances, be caused. The English series of marine tertiaries is principally exhibited in the basin of Hampshire and the Isle of Wight, in the basin of London, and on the eastern coast, from the mouth of the Thames to that of the Yare ; and each of these districts exhibits peculiarities of the component terms. The section of the Isle of Wight, at Alum Bay, one of the most remarkable known in the world, exhibits a great and varied mass of sands and clays, whose planes of stratification, origin- ally horizontal, are now vertical. The whole may be considered as one formation; for, in the lower part, which is principally sandy, argillaceous beds occur, with fossils the same or very similar to those in the upper part. The following is a synopsis of these vertical beds: Freshwater Formations above. Upper group, or Barton clay. Yellow and white sands. Dark clay, with green earth and septaria, rich in fossil shells. 250 feet thick. CHAP. VI. CAINOZOIC STRATA. 255 Bracklesham sands. Layers of black flint pebbles, in yellow sand. Pipeclays and sands of many colours, enclosing several beds of lignite. 543 feet. Bognor beds. Coloured sands of many tints. 321 feet. Dark blue clay, with green earth and shelly nodules. 200 feet Plastic clay and sands. Clay, red, &c., between layers of yellow sand. 100 feet. In the basin of London, the series is less complete. Mr. Prestwich has determined the place of the London clay in the series to be below the Bagshot sand, and on the parallel of the Bognor beds. (GeoL Proc. 184-7.) Hence the following general section : Bagshot sands. London clay, of a dull grey, or blue, or brown, sometimes red ; often full of green grains. Septaria abound in certain parts : the rocks of Bognor and Selsea are supposed to belong to the lower part of it. 350 feet. Sand of various colours, with occasional beds of lignite or plants. Sand, and layers of clay, with or without shells. Sand, green and ferruginous, accompanied by flint pebbles, oyster shells, &c. In Essex, Suffolk, and Norfolk, the plastic clay group is chiefly represented by the lower green sandy portions, which appear seldom deficient (being found in the Isle of Wight, at Reading, Woolwich, Sudbury, &c). The London clay is seen at Harwich ; and a superior marine deposit, the " Crag," unknown elsewhere in England, appears at Ramsholt, Orford, &c. in two divisions, while a third is added above in the vicinity of Norwich. Thus we have : Upper, or mammaliferous crag ; rich in remains of pachy- dermata, &c., and containing littoral shells. Middle, or red crag; resembles a raised sea-beach, being composed of layers of sand and pebbles, mixed with marine shells and polypifers, worn fish teeth and bones, cetacean bones, &c., the whole generally ochraceous. Lower or coralline crag, less ochraceous, almost without pebbles; containing abundance of shells not at all 256 A TREATISE ON GEOLOGY. CHAP. VL worn, at Ramsholt, and abundance of corals not of European forms at Orford, where it is used as a lime- stone.* Below the Crag deposits of Essex and Suffolk the London clay is seen very extensively in the cliffs, and along the eastern valleys. It is singularly poor in organic remains; now and then a chelonian skeleton appears in the nodules of impure carbonate of lime which yield the ' Roman Cement.' These are now scarce on the shore and in the cliffs, and are obtained by dredging at small distances from the land. In the cliffs at Felixston, faults appear in this clay. A deposit of tertiary shells in green and irony sands, and in blue clay, occurs at Bridlington in Yorkshire ; it probably is of the age of the mammaliferous crag, and is covered by northern drift. The most general view of the English marine tertiaries shows sands to be more extensively diffused than clays ; the latter are almost limited to the southern basins ; the former are no where wholly deficient, and their lower green por- tions very characteristic. The calcareous crag is merely a local product. Turning now to the district where first the genius of Cuvier awakened the philosophical study of the tertiary strata, the basin of Paris, we obtain highly interest- ing results for comparison with the English series and those of the south of France, Italy, and the Danube. The Parisian series is quintuple, but only two of the terms are marine ; two are decidedly of freshwater origin as to the materials (one certainly even lacustrine); the fifth (and lowest) is rather to be viewed as a trou- bled estuary or river deposit, and may be united with the lower marine formation. The whole stands in general terms according to the example on p. 257. ; -but we must observe that the several groups are partially mingled with one another by intercalation : there are, in fact, many marine and many freshwater strata, The crag has been investigated with great success by Charlesworth, Wood, Lyeil, Henslow, and Colchester. At the base of the red crag lie the valuable bands of phosphatic nodules. CHAP. VI. CAIXOZOTC STRATA. 257 Lower term. < fEpilimnic or upper freshwater formation the uppermost of all the stratified depo- sits near Paris; consisting chiefly of siliceous limestone, or burrstone, marl, and marly Upper term. -^ sands. Upper marine formation consisting of sand- stone, generally white, or partially reddened or ochraceous, and but slightly aggregated, L except at Fontainbleau. f~ Palaeotherian freshwater formation charac- terised near Paris by its ossiferous gypsum and marls, siliceous limestones, &c. Lower marine formation consisting princi- pally of limestone (calcaire grossier) of various degrees of coarseness, with lamin- ated flint, marls both calcareous and argillaceous, green sands. Plastic clay group an irregular mass of de- posits varying with locality, in places yield- ing plastic elay and sands ; in other situ- (_ ations, lignites or pebble beds. There is no trace in the basin of Paris of the shelly and gravelly deposits (falun coquillier) of Touraine, which M. J. Desnoyers compares to the English crag, and considers to be more recent than the epilimnic group of the Parisian basin. It is obvious that the agreement between the Parisian and English tertiaries is merely in the great features of succession : the lower marine formation in England is principally clay in France, limestone: gypsum abounds in the palaeotherian freshwater beds of France, but not in England. Yet the basin of the Seine, and that of Hampshire, were connected with the same sea, and sub- ject to very similar successions of marine and fluviatile agencies. The difference of deposits is due to the dif- ferent materials transported in the currents of the sea. In the south of France the tertiary deposits of the large basin of the Garonne, contain shells like those of Touraine ; the beds of Narboime and Montpellier more resemble the Parisian series. In M. Dufrenoy's recent memoir, he arranges the tertiaries of the south of France VOL. I. S 258 A TREATISE ON GEOLOGY. CHAP. VI. in a series of three terms, the upper one of which does not exist at all in the basin of Paris ; while, on the other hand, the lower one, well developed near Paris, is only locally seen in the south. Upper term Middle term Lower term (Composed principally of beds of pebbles, sands, and coarse sandy clays, which appear all to be eminently detrital formations, so that | Elie de Beaumont formerly called them Terrain de transport ancien.' Perpignan L offers the best type of these beds. f Comprising a great variety of deposits, partly freshwater and partly marine ; freshwater deposits of limestone on hills (Agenois, Provence) ; sands and pebbles (faluns) on the plains (Landes); sands and marls (molasse) in low hills in Languedoc ; conglomerates at Pau; gypsum and lig- nites at Aix, and in Provence ; concretionary limestones (calcaire moellon) at Mont- pellier. It contains locally sulphur, and generally iron ore. These variations are the result of local circumstances influencing the borders of an oceanic basin. " Chiefly consists of calcaire grossier, and this is almost confined to the ' Landes' between the A dour and Garonne. The beds of limestone alternate with marls and clays, and rest on the cretaceous rocks. They are full of miliolites. The middle term of this series corresponds to the upper term of Paris : it expands greatly in Spain and Switzerland. In Spain abundance of freshwater deposits occur ; in Switzerland the sandy and conglomerate beds (molasse) expand into a vast thickness, include beds of limestone and layers of lignite yielding bones, and extend along the north front of the oolites of the Alps towards Vienna. Here in the basin of Lower Styria, Murchison and Sedg- wick give us the following general section of the ter- tiary series. CHAP. VI. Upper group. Middle group. Lower group. CAINOZOIC STRATA. 25.9 "Calcareous sands and pebble beds, calcareous grits and oolitic limestone in the low ground of Hungary full of shells, as in the highest beds of the basin of Vienna. White and blue marl, calcareous grit, white marlstone, and concretionary white lime- stone: shelly. Coralline limestone and marl, of a yellowish white colour, very thick and shelly (Leitha- kalkof Vienna.) Conglomerate, with micaceo-calcareous sand and millstone conglomerate : thick. Blue marly shale, sand, &c., full of shells com- pared to those of London clay and calcaire grossier. Shale and sandstone, with coal or lignite, containing bones of anthracotheria, gyro- gonites, &c. Micaceous sandstones, grits, and conglo- merates, made up of the detritus of the primary slaty rocks, on which they rest at high angles of inclination. The authors consider the lower group to correspond with the calcaire grossier and Palseotherian deposits ; the middle to the English crag, and middle subapen- nines. According to M. Dufrenoy, the former would rather appear to belong to the middle tertiary period. In his latest memoir on the Alps and Carpathians, Sir R. Murchison expresses the conviction that the flanks of the Alps exhibit a true transition from the younger secondary into the older tertiary strata, and that the older supracretaceous rocks occur abundantly, and well characterized, in the South of Europe, extending thence eastward into Asia. The cretaceous beds, containing inoceramus and ananchytes, are conformed in position to the overlying tertiary rocks characterized by nummu- lites, and in this latter series we still find gryphcea vesicularis.* The sections of Transylvania, Hungary, and Moravia * Proceedings of Geol. Soc. 1849. S 2 260 A TREATISE ON GEOLOGY. CHAP. VI. may be reduced to the above general type ; the lower beds being more argillaceous. The Italian tertiaries constitute a triple series, but the lower and upper terms appear only at particular points. Sicilian, or upper tertiaries, best seen in the Val di Noto (and Calabria), consist of thick limestone (700 or 800 feet), rising in the hill of Castrogiovanni to 3000 feet elevation ; shells nearly all of existing species ; white calcareous sand, sandy limestone, and conglo- merates. Subapennine, or middle tertiaries, of very great thickness, consisting of innumerable laminae of marls, calcareous and argillaceous, blue or brownish, like the mud now gathered on the bed of the Adriatic ; some sandstones, limestones, and gypsum are locally traceable : 40 per cent, of the shells belong to existing species. Superga, or lower tertiaries, consisting of fine green sand and marl, resting on conglomerate, full of boulders of primary rocks; unconformed beneath the subapen- nine marls, and containing only a small proportion of recent shells. The relation of these tertiary to the subjacent creta- ceous groups has again been the subject of an elaborate investigation by Murchison. Taking the limestone of La Spezia and Carrara (of Lower Jurassic age) to be the oldest of the Italian secondaries,, we have above the ammonitico rosso and the cretaceous series, this latter being well exhibited on the flanks of the Venetian Alps and about Nice. In these localities they are covered conformably by tertiary accumulations, characterized by nummulites, and devoid of types of secondary fossils. In such sections it is only by the sequence and combi- nations of the forms of life that the separation of tertiary and secondary strata can be safely attempted, nor can a hard line be drawn where nature has employed the softening pencil.* Geographical Extent, and Physical Geography. * Geol. Proc., 1849. See also the addresses of De la Beche, 1849, and Lyell, 1850, on this subject. CHAP. VI. CAINOZOIC STRATA. 26l The tertiary system of strata is the most recent of all the regular marine series of deposits : its relation to the existing oceans is therefore a highly interesting subject of inquiry ; the more so, as, from the phenomena of alternating marine and freshwater deposits, conclusions have long since been presented by distinguished writers that particular tracts were alternately raised above and sunk below the sea. Cuvier and Brongniart proposed this hypothesis to explain the freshwater interpolations among the marine strata of Paris ; and the notion has gradually become a popular part of geological specula- tion. The solution of an old geological problem re- quires far more caution than the explanation of a modern geographical phenomenon. For in regard to the older events we are seldom aware of all the essential facts, from which not only the nature of the physical agency is to be ascertained, but the measure of its force, the local centre of its effect, and the sudden or gradual, the continuous or interrupted mode of its application. The geographical relations of tertiary strata must be understood before venturing to adopt or to reject the hypothesis of partial elevation and subsidence. Before the deposition of the tertiary system, Europe had acquired many of its marking features: the Pyrenees, Brittany, parts of Wales and Scotland, Scandinavia, the Carpathians, Apennines, the mountains of Bohemia, the Vosges, Auvergne, and other tracts, were uplifted above the sea. But these appear to have stood up like uncon- nected islands, round which the ocean currents passed variously into wide basins like those of the Danube, Paris, &c. ; or poured into insulated bays, like what may be termed the Gulf of Bohemia. The direction, force, and materials mixed with these currents, would be materially influenced by the submarine slopes from these insulated ridges, and by other undulations in the bed of the sea ; the nature and abundance of the ter- tiary sediments, and the organic forms which are buried in them, would be greatly dependent on the force and origin of the currents : and thus we see a reason why 8 3 262 A TREATISE ON GEOLOGY. CHAP. VI. tertiary strata should be so distinctly related to the present configuration of the surface of the earth, and so various both as to mineral character and organic contents,, though the basins, as we terra them, in which they now appear, were parts of one general ocean. In a few instances, however, the tertiary deposits were almost totally formed in vast lakes or inland seas, as in the valley of the Rhine, from Basle to Bingen. The relation of tertiary deposits to existing seas will appear from the following classification of the Eu- ropean deposits : 1. Connected by gradual inclinations with the North Sea. The basin of London, Norfolk, Yorkshire. The north-east of France, Belgium, Westphalia, Hoi- stein, Jutland. 2. Between the Baltic and the Black Sea. The extensive sandy deposits of Prussia, Poland, Vol- hynia, Wallachia. 3. Dependent on the English Channel. The basin of Hampshire. The basin of Paris. 4. Bordering the Atlantic. The basin of the Garonne. 5. Bordering the Mediterranean. Tertiaries of Catalonia. of the south coast of France, and the valley of the Rhone. of the northern sub-apennine regions and Sicily. of the northern parts of Africa. Besides these are the following secluded tracts ; The valley of the Rhine from Basle to Bingen. The interior basin of Bohemia. The great hollow of the northern Swiss lakes, and the vale of the Danube, with the Moravian, Hungarian, and Transylvanian strata. CHAP. VI. CAIKOZOIC STRATA. 2()3 These latter may be viewed as seas wholly drained ; the former as merely the raised margins and bays of the actual seas. But this view is imperfect : since the date or during the progress of the tertiary deposits, the partial as well as general uprising of the bed of the sea has materially changed their geographical relations, by sepa- rating parts once united, and giving to the detached parts a delusive character of basin-shaped insulated accumulation, which further researches will not justify. For instance, the uprising of the chalk and Wealden tracts between London and Portsmouth has divided the basins of the Solent and the Thames ; on a far grander scale, the Alps, raised, at least in part, since all the ter- tiaries were formed, have given a more complete geo- graphical opposition than originally existed between the tertiaries of the Danube and the Po. It may indeed be supposed, in conformity with Mr. Ly ell's views, that the insulation thus attributed to the subsequent rising of mountains, may have been begun by their contem- poraneous rising, a mode of explanation well suited to the case of the difference in the Hampshire and Lon- don basins. Before the production of the earliest tertiaries, inun- dations from several uplifted ranges of country (as the Pyrenees, Brittany, Auvergne, the Ardennes, and parts of the Jura, sent detritus into the sea of Paris : the London tertiaries are supposed by Mr. Lyell to have been derived from the waste of the previously raised or then rising Weald: oceanic currents would plough the sloping parts of the submarine land; and thus we have a clear ex- planation of the mixture of marine and fluviatile sedi- ments, as well as the local diversity of their nature, which so remarkably characterises the tertiary strata. The purely lacustrine deposits, with their embedded mammalia, tell a different history. The tertiary land was raised where they occur at the time of the existence of these mam- malia ; and thus it is often possible to prove that con- siderable movements of the bed of the sea occurred during the tertiary period. With regard to the age of s 3 26* A TREATISE ON GEOLOGY. CHAP. VI. lacustrine and fluviatile deposits, it is to be observed, that when a series of such beds lies inclosed in marine sediments, as the gypsum of Montmartre, the lignites of the Isle of Wight, Zurich, and Styria, they must of course be ranked according to the marine strata with which they are associated; but when, as at Headen Hill in the Isle of Wight, on most of the plateaux round Paris, at (Eningin, at Georges Gmiind, the freshwater deposits are uncovered by any but superficial accumulations, how can their true geological age, on the scale of marine formations, be known ? No method but one is likely to be at all satisfactory, the study of their embedded organic exuviae; which therefore is the method now generally adopted. Mr. Conrad and Pro- fessor Rogers have thus classed the tertiaries of North America. How far this mode can be safely trusted will be considered in the next section. Organic Remains. In general, no contrast can be greater than that offered by comparison of the tertiary with secondary and primary plants, shells, and vertebral reliquiae no analogy more striking than between the tertiary and living forms of life. Plants, shells,, insects, and even quadrupeds, of the same genera, sometimes even of the same species (as far as naturalists can decide so nice a point), often so similar as to be only distinguishable by minute cir- cumstances, render it doubtful to the inexperienced, whether they are not rather looking upon the buried remains of the present creation, than upon the work of one of those systems which passed away before the birth of man. The number of the species of tertiary fossils is very great, as compared with that of even the rich and well-explored oolites; among them are far more fresh water tribes, and far more terrestrial forms, than among all the older strata taken together ; a conclusion which har-< monises perfectly with the leading fact of the history of their formation, viz. that before the period of their formation, the great sea of Europe was broken into CHAP. VI. CAINOZOIC STRATA. 265 basins between ranges of mountains and masses of land, which in various ways influenced the deposits and supplied some of their organic contents. Yet, upon the whole, the number of terrestrial and freshwater remains is small compared to the marine ; a circumstance which. as far as relates to the products of fresh water, is analogous to the present condition of nature. With re- gard to plants on the land, it has been already shown, (page 70.) that, however numerous these might be, only a few of them would reach the sea, except under particular circumstances of physical geography. The number of land animals already found in tertiary lacustrine, fluvia- tile, and marine deposits, ought perhaps to strike us by its magnitude, rather than by its inferiority to the catalogue of the living quadrupeds. Referred to the groups of the basin of Paris, M. Adolphe Brongniart presented, in 1829> the following synopsis of the tertiary plants: In the group of plastic clay and lignites Marine plants, none Land and freshwater plants, chiefly coniferae, ~\ palms, and amentaceas - - J In calcaire grossier and Monte Bolca beds Marine plants - - 16 Land and freshwater plants - - 16 In the palaeotherian and epilimnic freshwater beds Marine plants, none Land and freshwater plants - - 21 , From the laborious and successful researches of M. Deshayes concerning tertiary mollusca (see L yell's Geology, vol. iii. first edition), we shall extract some of the leading results. The recent species examined by this eminent concho- "| 478O legist amounted to J ' The fossil species of the tertiary system alone - 3036 Together - - 7816 266 A TKEATISE ON GEOLOGY. CHAP. VI. Of which were found both recent and fossil 426, leaving"! for the total number of species examined J The ratio of the species which are both recent \?.~ t and fossil, to the whole number is - J The 4780 living species consisted of - univalves 36161 f 75'6 bivalves 1164 j r per cent. | 24 . 4 The 3036 tertiary species" univalves 20981 1 60'1 bivalves 938 J ~ ~ J 80 '9 Among the shells examined were included 1465 recent, and 259 fossil. Shells of the land and freshwater, viz. Freshwater species, living bivalves 1 1 8 univalves 151 Land species, living univalves 1 1 96 fossil 30 fossil 151 fossil 78 As before observed, the ratio of-, the number of species, both re- j cent and fossil,to the total num- > 426 to 7390, or, 5.7 to 100 ber of recent and fossil ob- served, is The ratio of the same to the number of recent"! species, 4780, is - J And to the number of fossil species, 3036, is - 14-0 But this last general average of the number of ter- tiary species now living, is composed of many very different ratios, by the study of which M. Deshayes has been led to class the tertiary formations upon a new principle. He assumes, as a general truth, that those tertiary deposits which contain the greatest proportion of existing species are of the most recent date ; and on the contrary, that those in which the ratio of existing species is smallest are the oldest. Applying this prin- ciple to the most important localities of tertiary strata, and grouping together those which have the greatest agreements in ratio of living species, he arrives at the following series of three terms for the whole mass of tertiary strata. Localities. Upper or most J Sic /}y ; . the lPe beds; the crag. /T> " an( l the Morea agree in their C Sicily ; the I (Perpignan (_ fossils with recent group. \" v*e>\""' , '" .*" i j Y r (_ fossils with the subapennine beds. ) CHAP. VI. CAIXOZOIC STRATA. So? Bordeaux; Dax ; Touraine , Turin; Baden; Vienna ; Angers ; Ronca. The Viennese Middle group. -( and Baden fossils are a general type for Moravia, Hungary, Cracovia, Volhynia, Podolia, and Transylvania. ( Paris, London, Hants, Valognes, Belgium. (The fossils of Castel, Gomberto and Pau- Lower group. ^ li&c ^ ^ ^ mQ near]y &s ^^ of ^ \^ basin of Paris. From each of these localities, the ratio of the species now living has been determined by M. Deshayes as under : Upper group. General proportion of living species. 49 per cent. (Allowance being made for occurrence at more than one locality. ) Sicily has yielded 226 species, of which 216, or 95-0 per cent, are living. Subapennine - 569 - - 238-41-8 Crag . Ill* - 45-40-1 Middle group. General proportion of living species, 18 per cent Vienna has yielded 134 species, of which 35, or 28'2 per cent, are living. Baden 99 - 26 . 26'2 Bordeaux and Dax 594 - 136-22-9 Touraine - 298 - 68 - 227 Turin 97 17 - 17'5 Angers 166 - 25 - 15t) Lower group. General proportion of living species, 3j per cent Roncaf has yielded 40 species, of which 3, or, 7'5 per cent are living. London 239 - 12-5-0 Paris 1122 - 38 - 3'4 Mr. Lyell, by independent researches, was induced to class the Sicilian deposits as a separate formation from the rest of the upper group of Deshayes ; but in other respects his scheme of nomenclature subjoined is per- fectly in accordance with Deshayes' results. Newer pleiocene of Lyell Sicilian deposits, with 95 per cent recent species. Elder pleiocene - Italian and crag deposits, with 41. Meiocene Vienna, Bordeaux, Turin, &c, 18. Eocene - Paris, London, Belgium, 3$. The terms are derived from the Greek Kaivog, recent, combined with fag, the dawn, p.uwv } less, and TrXawv, more. * There are above 450 species of fossils in the crag, and on the relation of its shells to recent types. Dr. Beck of Copenhagen holds a different opinion from M. Deshayes. See also Mr. Charlesworth on the crag form- ation, in PhiL Mag. and Annals, 1836. t Placed by Deshayes in the middle group, but with hesitation. 2f)8 A TREATISE ON GEOLOGY. CHAP. VI. I have elsewhere tested the results of M. Deshayes' researches in a peculiar manner, and shown that, tried by the relations existing among one another, the classi- fication which he has proposed is well founded : there may be doubts as to the exact discrimination of the spe- cies, and the precise proportions of recent forms included among the fossils ; but as the whole have been examined by an eminent naturalist, it is probable that, even if the species supposed to be identical were not so, the conclusion of the order of antiquity of the several de- posits would be correct. The only thing remaining to be examined, before adopting these conclusions, is, the general principle upon which they all depend, (p. 266.) This principle is not collected, as an inference, from many observations on the order of tertiary strata, and determinations of the proportion of living species in each, according to its known position in the series ; nor is it to be considered in the same light as a mathematical principle, assumed as the basis of certain deductions, which, being compared with phenomena, may serve to test the truth of the assumption ; but, in the absence of proof, it is to be admitted or denied upon the follow- ing statement of the reasons. In all the series of stra- tified rocks, the systems of organic nature are found to be different, according to the period : these differences are sometimes gradually, and sometimes abruptly, pro- duced between system and system : in any one clearly defined system, the strata differ as to their organic con- tents, according to their order of superposition, and the nature of the rock; and, upon the great scale, are charac- teristic both of geological period and local conditions. Below the tertiary system are no recent species : at the base of that system the lower strata, determined to be such by observation of their position, undoubtedly con- tain only a very small proportion of recent forms (basin of Paris) : in the middle of that system, determined as before, the strata contain about 20 per cent, of recent forms (Bordeaux): in the highest of the system (in CHAP. VI. . CAINOZOIC STRATA. 2^9 only one locality, Sicily), the strata contain 95 per cent, of existing forms. Supposing these statements (which might be fortified by other equally important but more refined results) are thought sufficient to establish the principle, that the affinity of fossils to recent forms, commencing with the geological date of the chalk, has gone on increasing gra- dually to the close of the tertiary period, and that, there- fore, the relative age of tertiary strata is to be judged of by the proportion of recent forms in them, let us inquire what difficulties lie in the way of the practical appli- cation of the doctrine. There is a real difficulty in determining upon what basis to make the required comparison between fossil and recent forms : whether the fossils of a particular re- gion, as, for example, the subapeimine countries, should be compared with the whole series of known testacea, or with the shells of the adjoining Mediterranean, to whose products they are extremely similar, and from whose waters they may be thought to have been raised. In certain cases it appears probable that the strict- ness of the rule must be relaxed to avoid important errors. For example, the long basin of the Danube, the valley of the Rhine, the basin of Paris, contain a great variety of organic forms, which must have been peculiar to those arms and gulfs of the sea, as we find at this day peculiar shells in almost every partially insulated bay of the sea. But these tertiary tracte having been wholly raised to dry land, all their peculiar shells have perished ; and the analogy of the fossil to recent types appears less than would be the case with strata like the subapennine beds, which are yet margined by the sea, out of which they were uplifted. Peculiar shells live in the German Ocean and English Channel: the crag formation is supposed to contain many now living in these waters; but,had the whole of these seas been obliterated by the rising of their bed, the extensive shelly sand thus brought to the surface would have pre- sented but slight analogies with the general catalogue of 270 A TREATISE ON GEOLOGY. CHAP. VI. recent shells from which the peculiar forms were ex- cluded. These remarks are by no means brought forward to discredit the highly important results of M. Deshayes and Mr. Lyell, but to draw attention to the basis on which they rest, and to induce geologists to follow steadily a plan of observation, which may place the principle assumed on such a foundation as to authorise its being used as the origin of deductions, which may have undoubted influence both in theoretical and posi- tive geology. Professor Rogers, in his Report on the Tertiary and Secondary Rocks of North America, has adopted the nomenclature of Mr. Lyell, and ranked the deposits on the eastern coast chiefly according to their proportionate numbers of recent forms, as eocene, meiocene, and pleiocene. Both the recent and fossil species of America are, however, almost wholly different from those of Europe: of 210 ' eocene' species in America, only 6 belong to Europe; of 195 meiocene and pleiocene shells, only 6 belong to Europe ; not more than 32 recent testacea and shelly annulosa are stated by Mr. Conrad to be common to the two sides of the Atlantic. The number of species of other invertebral animals buried in tertiary sediments, is very much too small to justify any general inferences ; but we may attend to what M. Agassiz has stated concerning the subject of his successful studies. f< The fishes of the tertiary strata are so nearly related to existing forms, that it is often difficult, considering the enormous number (above 8000) of living species, and the imperfect state of preservation of the fossils, to determine exactly their specific relations. In general, I may say that I have not yet found a single species which was perfectly identical with any marine existing fish, except the little species which is found in nodules of clay, of unknown geological age, in Greenland. The species of the Norfolk crag, of the upper subapennine formation, and of the molasse, are mostly referable to CHAP. VI. CAINOZOIC STRATA. 271 genera common in tropical regions ; such as platax, cartharias, myliobates, &c. In the lower tertiaries of London, the basin of Paris, and Monte Bolca, at least a third of the species belong to genera which are now extinct." In the chalk, two thirds of the species belong to extinct genera ; and in the oolitic system, not a single species can be referred to a living genus ! The same conclusion as to the great general analogy and real specific differences between the fossils of the tertiary series and living races comes with equal force from a consideration of the families of reptiles. Among chelonida, occur freshwater trionyces and emydes, as well as marine cheloniae and terrestrial testudines : among saurians we have no more the geosaurus, mas- todonsaurus, streptospondylus, megalosaurus, ichthyo- saurus, plesiosaurus, nor iguanodon ; but instead of these extraordinary creatures of the oolitic and saliferous epochs, genuine crocodiles, very nearly agreeing with existing types, appear for the first time, and in consider- able variety : decided batrachia show themselves in the freshwater beds of CEningen and the brown coal of the Rhine, and in this latter deposit are accompanied by snakes. Without stopping to notice the few remains of birds, which are rare even in tertiary formations, we shall pass to consider the very interesting question of the relation of the quadrupeds of the tertiary periods to the present free and domesticated tribes. In general it is to be remarked, that, concerning the date of some of the fossil animals, especially when they occur in lacustrine deposits not interstratified with marine formations, there is danger of confounding ter- tiary with diluvial species ; but this difficulty applies only to some particular cases, and will be better dis- cussed when we come to speak of the diluvial deposits, to which we shall defer the reasonings we have to offer on fossil mammalia in general. 272 A TREATISE ON GEOLOGY. CHAP. VI. In the following catalogue of remains of mammalia in tertiary strata, chiefly taken from Meyer's Palseologi- ca, extinct genera are marked by an asterisk. SECTION A. In Marine Deposits. Gulo antediluvianus Canis Felis aphanistes ogygia prisca Phoca Carnivora. fin sand. Eppelsheim on the I Rhine. - In Volhynia, with marine shells. - Eppelsheim. - Eppelsheim. - Eppelsheim. Hungary. Rodentia. Castor - Crag of Essex. Palaeomys castoroides - Eppelsheim. Hare - Faluns of Touraine. Aulacodon (chelodus) typhus Eppelsheim. Chalicomys Jageri - Eppelsheim. Myoxus primigenius - Eppelsheim. Spermophilus superciliosus - Eppelsheim. Cricetus vulgaris Chloromys - - Eppelsheim. f Volhynia. ( Also in freshwater (_ deposits.) Maotodon angustidens arvernensis Hippopotamus major minutus Pachydermata. f In subapennine formation. - < In the faluns of Touraine. {_ Eppelsheim. - Eppelsheim. - In faluns of Touraine. - In faluns of Touraine. undetermined [ J^molasse, Galicia, and Switzer^ Rhinoceros Schleiermacheri - In sand. Eppelsheim. incisivus - Eppelsheim. leptodon - Wiesbaden. fin sandstone, 456 ft. Warsaw. Elephas primigenius - J f n sa dstone a ' Wieliczka. In molasse, near .Lstavayer, Switzerland. CHAP. VI. CAINOZOIC STRATA. * Diehobune * Dinotherium Bavaricum giganteum Equus caballus primigenius mulus primigenius asinus primigenius Sus antiquus palaeochaerus * Palaotherium * Lophiodon Tapirus priscus Cen*us anocerus brachycerus trigonocerus dicranocerus curtocerus Deer Antelope Moschus antiquus Manatus fossilis Balsena fossilis - France, Bavaria, Eppelsheim. - Eppelsheim. fin the faluns of Touraine. \ In sand. Eppelsheim. - Eppelsheim. - Eppelsheim. - Eppelsheim. - Eppelsheim. - In molasse. Estavayer. Under calcaire grossier in the department of Gironde ; at Provins ; in Touraine ; at Zurich. Under calcaire grossier at Pro- vins. Eppelsheim. - Eppelsheim. Ruminantia. - Eppelsheim. - Eppelsheim. - Eppelsheim. - Eppelsheim. - Eppelsheim. - In the faluns of Touraine. - In molasse. Estavayer. - Eppelsheim. Cetacea. f Calcaire grossier. East coast of 1 Maryland. J Virginia, Wurtemburg, Dau- \ phine, Berne, Montpellier. SECT. B. In Lacustrine and Lignitic Deposits of known Geological Era. Vespertilic Parisiensis murinus fossilis Nasua Viverra Parisiensis Hyaena Parisiensis, Clift Vulpes vulgaris, ManttU VOL. I. - Gypsum of Montmartre. - (Eningen. - Gypsum of Montmartre. - Gypsum of Montmartre. - Styrian brown coal. - (Eningen (Murchison). 274 A TREATISE ON GEOLOGY. Can is Didelphis Cuvierii Castor * Anoema CEningensis Mus musculus Myoxus Sciurus Lagomys * Mastodon tapiroides turicense * Adapis Parisiensis Chceropotamus Meisneri * Anthracotherium magnum minus minimum Alsaticum Velaunum 1 and 2 undetermined - Gypsum of Montmartre. - Gypsum of Montmartre. - Brown coal near Zurich. - CEningen. - CEningen. - CEningen ; Montmartre. - Montmartre. - CEningen. - Montabusard, near Orleans. - In brown coal near Zurich. - Gypsum of Montmartre. - Brown coal near Zurich. J* Brown coal of Cadibona ; marl [_ of Limagne. - Cadibona. - Lot et Garonne. - Lobsan. - Puy en Velay. Brown coal of Scheineck in * Anoplotherium commune . Montmartre ; Isle of Wight. secundarium Montmartre. * Xiphodon gracile - Montmartre. * Dichobune leporina - Montmartre. murina - Montmartre. obliqua - Montmartre. * Cainotherium 2 species BTQ \ Puy de Dome. vard J * Palaeotherium magnum - Montmartre. medium - Montmartre. crassum - Montmartre. latum - Montmartre. curtum - Montmartre. minus - Montmartre. minimum - Montmartre. Aurelianense Orleans; Argenton. Isselanum - Issel. Velaunum - Puv en Velay. * Lophiodon tapirotherium - Issel. occitanicum - Issel. Isselense - Issel ; Argenton ; Soissons. medium - Argenton. minimum - Argenton. tapiroides - Buchsweiler. buxovillanum - Buchsweiler. giganteum - Montabusard. CHAP. VI. CAlNOZOfC STRATA. * Lophiodon Monspessulanum Montpellier. 275 Siberia - o ther species, Cervus capreolus Aurelianensis Montabusard. * Pa ; SECT. C. In Lacustrine Ursus spelseus Vulpes Hyana, Hehl Mustela Choeropotamus Soemmeringii * Palarotherium Aurelianense * Anoplotherium commune ? - * Mastodon minutum Rhinoceros pygmaeus Hippopotamus, "1 ~.^ Bos, J Deposits of Doubtful Era. Georges Gmiind. Georges Gmiind. Gypsum of Unterturkheim. Georges Gmiind. Georges Gmiind. Georges Gmund. Georges Gmiind. Georges Gmiind. Georges GmiinA Georges Gmiind. 1. Crassatella aulcata. Sowerby. 1. Venericardia planicosUta. Sowerby. ( 3* Conus scabriculus. Sowerby. i 4. V'oluta dubia. Brander Chiefly found in the London day. T 2 276 A TREATISE ON GEOLOGY. 6 CHAP, VI. 5. Fusus contrarius. Sowerby. 6. Fusus bulbiformis. Sowerby. 7. Dentalium striatum. Sowerby. 8. Paludina lenta. Sowerby. From the crag of Suffolk. Chiefly found in the London clay. Disturbing Movements during and after the Tertiary Period. In England, two lines of subterranean movement have long been known, by which the tertiary and se- condary strata have been raised into anticlinal ridges and sunk into synclinal hollows. They both range east and west, or nearly so ; one line, viz. from the Vale of Pewsey by Kingsclere, Farnbam, Guildford, and through the Weald of Sussex to Boulogne, is somewhat parallel to the vale of the Thames; the other, from Weymouth by the isle of Purbeck through the Isle of CHAP. VI. CAINOZOIC STRATA. 277 Wight, is nearly parallel to the south coast of England. Thus the lines would converge toward the east some- where ahout Boulogne ; and diverge westwards, so that, if continuous (which they are not), the northern one would nearly coincide with the south side of the South Wales coal field, and the southern one pass across the southern part of Devonshire. Each of these two lines of dislocation has caused the strata to dip with great steep- ness to the north (in the Isle of Wight, the beds on this dip are vertical), but the southward dip is in each case moderate. A cross section gives the following appearance : Isle of Wight V" Basin of Hogsback. To disturbances during the tertiary periods, M. de Beaumont ascribes the elevation on a north and south line of the ridges of high land in Corsica and Sardinia : the Western Alps (from the Mediterranean to Mont Blanc) are considered to have been raised after the de- position of the Swiss molasse, in a direction N.N.E. and S.S.W. ; and the principal chain of the Alps, from the Valais into Austria, E. \ N.E., to be of so recent a date as to have succeeded all the true tertiary deposits, and to have coincided with the dispersion of the great blocks and masses of diluvium on both slopes of the Alps. Igneous rocks are no where in England associated with the tertiary strata ; but in many parts of Europe, as in Central France, the north and south of Italy, Sicily, on the Rhine and in Hungary, volcanic pheno- mena are even specially abundant among lacustrine ter- tiaries. From the activity of Etna and Vesuvius, we pass by T 3 278 A TREATISE ON GEOLOGY CHAP. VI, an easy gradation to the phenomena which mark the former violence of the now silent fires of Auvergne, the Euganean Hills, and Hungary. The relation of these to the basaltic streams of Ireland and Scotland is clear enough as far as relates to the general agency ; but the determination of the period when these igneous rocks were formed is difficult. Etna may have begun to burn as soon or even sooner than the now decaying lavas were poured from the craters of Auvergne, the Eifel, and Hungary ; and the mere fact of igneous rocks being associated with particular strata, is no criterion of their antiquity. We must therefore endeavour to combine the history of the tertiary volcanic products with those of later and earlier date, in a general discussion of the effects of subterra- nean heat, which we propose to place after the descrip- tion of the superficial aqueous deposits, which are in- timately related to the tertiary products. POST-TERTIARY AND MODERN DEPOSITS. (Including " Pleistocene," " Diluvium," and "Allu- vium. " " Superficial Deposits.") Since the tertiary formations were completed in most parts of Europe and America, the energies of nature have gone on to accumulate over these and earlier de- posits a great quantity of additional matter, under many varied circumstances. It is often extremely difficult to say, whether certain aggregations of sand, gravel, and shells, are of tertiary date, or the productions of later times : enormous heaps of pebbles and bones lie in particular situations, and are evidently of great antiquity; but whether of the tertiary era or not, requires much care in determining. Certain lacustrine deposits, full of shells, marls, peat, and bones of stags, cannot, by a hasty glance, be known from tertiary strata collected from ancient lakes. But, upon farther and closer scru- tiny, geologists have generally agreed to think that a whole series of deposits, partly marine, partly terrestrial. CHAP. VI. POST-TERTIARY STRATA. 27.9 lacustrine, and fluviatile, has been formed since the date of the truly tertiary strata. The evidence for this opinion is absolutely conclusive, as to the great body of tertiary strata : it is past a doubt, that, since the age of the palaeotheria in the formations of Paris, the same physical regions have been tenanted by wholly different races of animals. The same conclusion is equally and easily proved for the basins of London and Hampshire, and for many other tracts in Europe ; and, if we did not inquire very scrupulously, these partial truths might be thought to justify a general inference that the tertiary strata could always be clearly separated from the overlying diluvial and alluvial sediments. But we must not disguise the real difficulty which occurs to the candid inquirer, who wishes to find out laws of phenomena as a basis for theory, rather than to rest satisfied with a conventional system. By what rule of practice, or deduction from theory, does the geologist discriminate between the Sicilian ter- tiaries, with 95 per cent, of existing species of shells, and the conchiferous gravels and sands of Holderness and Lancashire, in which, among twenty species of shells now living in the German Ocean, one occurs which is not yet known ? If the Lancashire shells are, like those of Speeton, Uddevalla, and the coasts of Devon and Calvados, raised beaches,, and to be classed in the modern epoch, why are the Sicilian deposits ranked as tertiary ? At what place in the scale of percentage of species is the line of division to be drawn, and how is this division to be justified ? The gravel which is spread over great surfaces in England, is called diluvial, and supposed to be the pro- duct of great but transient disturbances in the level of land and sea: for another example, the dispersion of blocks and gravel from the High Alps might be quoted as an effect of this kind, according to the view of M. Elie de Beaumont; but, if such be the effect of elevation of mountain ranges, may we not expect somewhere to find T 4 280 A TREATISE OK GEOLOGY. CHAP. VI. traces of a " diluvium" of tertiary, secondary, or even primary date ? Lacustrine deposits formed in and since the tertiary era, are not so clearly distinct even by position, as to allow us, in all cases, to be well satisfied about their date ; witness the ossiferous beds of Weigh ton in York- shire, the Val d'Arno, (Eningen, Gmiind, and many other localities. Yet, notwithstanding these objections, geologists have for a long time recognised the classifications which are based on the principle that, since the tertiary era, ma- rine, fluviatile, and lacustrine deposits have happened on the land in various parts of, at least, the northern zones of the globe ; and though impartial researches have led us to doubt the practicability and advantage of this broad distinction, we shall now endeavour to deve- lope the history of the ' ' post- tertiary," or diluvial, allu- vial, and modern aqueous deposits ; reserving for the section on organic remains what general reasoning we are disposed to advance. In one point of view, these deposits of post-tertiary periods are of the highest possible importance : they form the connecting links between the great phenomena of long past time, whose causes we are to seek, and the less obvious effects occasioned in modern nature by causes which are known. The post-tertiary accumula- tions consist of detrital deposits, reminding us of ancient conglomerates, lignitic beds like ancient coal strata, calcareous, arenaceous, and argillaceous layers, which are specially comparable with tertiary, and through them with secondary strata. On the other hand, almost every thing that we see among these deposits is clearly intelligib-e by study of analogous diurnal operations in nature ; and thus it is desirable to include in one sec- tion the consideration of post- tertiary and modern aqueous products, and to reason on the agencies con- cerned, as if the whole were one connected series of events still in continuation. To preserve clear ideas on the subject of these super- CHAP. VI. POST-TERTIARY STRATA. 281 ficial deposits, it is requisite to classify them, not ac- cording to a scale of time, which is seldom applicable, but in relation to the predominant agency concerned in their production. Thus we shall have the several prin- cipal groups further subdivided as under : a. Erratic block group. 1. Detrital deposits. 3. Fluviatile deposits. 4. Lacustrine deposits. b. Ossiferous gravel, pebbly clay, sand, &c. c. Ossiferous caves and breccia. a. Raised from the sea, or, b. Yet in progress. a. Terraces on the valley side. a. Raised from the sea, or, 2. Marine deposits. Yet ^ progress> b. Deposits in the valley. c. Deposits at the mouth of the river. a. Completed in former times. 6. let in progress. " Detrital Deposits." " Drift." Diluvium." " Boulder Formation." Since the date of the ' Reliquiae Diluvianae' and ' Ossemens Fossiles/ many geologists have been accus- tomed to refer to a particular era and a violent agency the destruction of many land animals which lived with elephants and mastodons on the surface of Europe : the era was supposed to be the termination of a long post- tertiary period in which these animals lived; the agency something of the nature of a cataclysm, and very ex- tensive, if not universal. Their opinions were founded principally on the superficiality of situation, confused aggregation, and similarity of organic contents, in the gravel, sands, and clays which constituted the deposits, and in many instances appeared to have been moved enormous distances across valleys and seas or over ele- vated ranges of ground. These deposits were supposed to have happened on the dried and elevated land, be- cause of the occasional abundance of bones of land animals in them ; yet they appeared to be due to the action of large bodies of water: and the notion com- monly entertained was, that the sea had been, by some violence of nature, thrown over the land, so as to destroy, at one definite epoch, over large tracts of the globe, 282 A TREATISE ON GEOLOGY. CHAP. VI. whole races of the -'existing mammalia, and greatly modify the physical aspect of our planet. Fresh discoveries showed, that the diluvial accumu- lations contained a great variety of deposits accumulated under different circumstances, by water moving in dif- ferent directions and with various degrees of force : the remainsof elephants, mastodons, &c., were found, though rarely, in really tertiary strata, both marine and fresh- water ; it was further observed, that the diluvial masses were totally absent from some districts, and in others appeared to have gone in various directions from a par- ticular group or range of mountains. Influenced by these considerations and the growing importance of the study of modern causes in action, some of the most eminent geologists of England dissented totally from the views of Dr. Buckland, and declared, from the chair of the Geological Society, their conviction that the diluvial deposits did not belong to the effects of one general flood, and were not really distinguishable in origin, on the one hand, from the tertiary ; and, on the other, from the modern effects of the sea, the rivers, and the land. Perhaps we may be allowed to regret both that the " diluvial" theory, as it was termed, was at first so confidently embraced, and extended to so many pheno- mena, and that afterwards it was formally abandoned, without that full and patient discussion of the reasons which should ever precede the rejection as well as the adoption of generalisations in science. In one point of view, the sudden rise and decline in popularity of this doctrine may be very advantageous to geology, since many persons who were so inconsiderate as to attach much importance to the seeming conformity of the melted, overthrown, or stranded, they yield up the stony masses, which glaciers had brought down, or shore ice had raised up, and thus encumber the sea bed with the spoils of distant lands. When the antarctic expedition had reached 78 south latitude, the vessels were stopped by a barrier of ice, from 100 to 180 feet in height, and 300 miles in extent from east to west ; beyond these cliffs of ice, a range of lofty mountains was visible about 60 miles distant, the westernmost of which appeared to be 12,000 feet high. From the face of these ice-cliffs masses were constantly breaking off, and floating north- ward, bearing with them fragments of rock, probably derived from the mountains from which the glaciers ap- peared to descend. In the lat. of 66 and 67, at a distance of 700 miles from the glacier, the ice formed a floating barrier, through which the ships could with * See Lyell's Geology, Brongniart, Tableau des Terrains ; De Luc's Letters, &c. CHAP. VI. POST-TERTIARY STRATA. 295 difficulty force their way. Over the intermediate area the ice-bergs would be constantly strewing masses of rock and detritus, particularly at their northern limit, where they would probably form mounds resembling terminal glacial moraines ! * As the stranding of ice- bergs would happen on sandbanks and shoals, we might expect accumulations from this cause to be more preva- lent on hill tops, and along the sides of broad vales, than in the depths of valleys ; and such is well known to be the fact in many examples of erratic blocks. Thus, in describing the vast extent of detrital de- posits on the broad surface of European Russia, in fact, from the German Ocean on the west to the White Sea on the east, Murchison expressly marks the discon- tinuity of the erratic masses, and their greater fre- quency on plateaux, and especially on the southern sides of these plateaux. f Accumulations of like nature form hills (escars in Ireland, osars in Scandinavia, barfs in England), in which often some peculiar dis- arrangements may be remarked in the accumulated de- tritus, not unlike that in true ' moraine. 'J A difficulty which occurs in receiving glaciers on land and icebergs at sea as a full explanation of the phenomenon of transported blocks is this : Two cases have been pointed out by the author of this treatise, where, beyond all doubt, portions of remarkable rocks have been lifted by the transporting force to much higher levels on neighbouring hills, and under conditions which leave no room for supposition that the difference of land has been occasioned by unequal movement of ground since the dispersion of the blocks. In one case (Craven) large masses of lower palaeozoic slaty rocks are lifted up in great numbers on to the limestone which lies level on this very slate. In another (Stainmoor), a red conglomerate, of very peculiar character and local Sabine, in British Association Reports, 1843. t See Geology of Russia, p. 547, for an excellent illustration of the Author's meaning. J Mr. Trimmer refers some singular phenomena in the Cromer cliffs to melting of buried ice (Geol. Proceedings). U 4 296 A TREATISE ON GEOLOGY. CHAP. VI. origin, has been raised over the narrow pass in the hills above, from a height of 500 to one exceeding 1,400 feet. For these and many other cases mentioned by other authors, Mr. Darwin offers the ingenious explana- tion afforded by shore-ice, formed during a general and continual subsidence of the land over large areas. By this combination, the boulders on the shore might be frozen and refrozen at levels necessarily higher and higher, as compared with the land, drifted and redrifted in floating ice, and subject to more or less of rolling and attrition, till in small numbers, in limited tracts, and under peculiar geographical conditions, they might as- sume the paradoxical situations for which mere sea- currents cannot account.* The supposition that erratic blocks have been trans- ported by floating ice, leads to an admission that much of the surface of the northern circumpolar regions, which is now dry land, was under a sea periodically chilled by abundance of ice, if not placed permanently on lower isothermal bands than at present. It is an equally clear inference that the lands from which the ice-rafts started for example, the Scandinavian and British Highlands were extensively overspread by gla- ciers. But they were, by the hypothesis, at a lower level ; and it becomes necessary to assign a reason for their greater cold under a condition which in the given ex- amples is actually favourable to augmented temperature. As things are, if our British mountains were lowered a few hundred feet, their summits would grow warmer, and there would be even less chance than at present for the production of glaciers on them. By the same de- pression the Scandinavian glaciers would be contracted, 'The cause is probably given correctly by Mr. Hopkins, j and is simply the displacement of the northward current of warmed water (' gulf stream'), which, bathing the shores of Britain and Norway, exalts their temperature at present about 15 above that of the corresponding latitude on the east coast of North America. This gulf * Proc. of Geol. Soc., 1848. f Ibid., 1852. CHAP. VI. POST-TERTIARY STRATA. 2$7 stream, or rather the general flow of warmed water to the north, is variable by slight causes in the present system of nature, and may be admitted to be displace- able by a great disturbance of the sea-bed. Such dis- turbance must have happened. But further, the north- ward warm flow of the sea is balanced by a return cold current. It is conceivable that this return of cold water may have passed through the area where erratic blocks occur in Europe, and thus we should have abundantly the elements of cold required for glaciers on the land which stood above the waves in Britain and Scandi- navia, It is no small confirmation of this view that we find in the gravel and clay, associated with erratic blocks, and clearly forming the sea-bed of their era, shells which, upon the whole, indicate an arctic character of the marine fauna of the period.* It is further im- portant that we find in the valleys of Scandinavia, and the Irish Cumbrian and Grampian Highlands, marks of radiating glaciers, rocks worn and striated for hun- dreds of feet below the summits ; in fact, almost or quite down to the actual sea level, and much below the probable level of the ancient sea which floated the ice- bergs. Spitzbergen, according to Dr. Martins, gives us at present examples of glaciers which pass to some distance from land, and to some depth below the sea. Striation and broader grooving of hard rocks on the line of glacier movement are found extensively round the Scandinavian mountains. But it occurs also in low ground in Russia, as on Lake Onega, where the con- figuration of land to the north forbids the belief that glaciers could be formed. From these and other in- stances, we must admit with Murchison, that ice dragged on the stony bed of the sea might become a powerful agent. for scratching the rocks, the stones which covered them being also scratched, a circumstance which has caught the attention of Mr. Miller, f in his examination of the boulder clay. It does not occur on sea beaches, * Forbes in jVIm. of Geol. Survey, vol. i. t Reports of British Association lor 1850. 298 A TREATISE ON GEOLOGY. CHAP. VI. in the channels of rough streams, or in ordinary gravel beds. The former boundaries of the glacial sea may be in some degree conjectured by the distribution of the northern drift, for it must have extended beyond the area of that drift. The depth to which the mountain regions from which the most abundant erratics have been distributed were sunk, may be in some degree conjectured; the Grampian, Cumbrian, and Cambrian Highlands, may, perhaps, have been 1500 feet, and the Alps, perhaps, 3000 feet lower. Under these condi- tions all the lower grounds of northern Europe would be submerged ; the masses of mountainous land would appear above the waves, covered with snow, and sur- rounded by icy floods. In this broad ocean, cold sea currents flowed most abundantly, though not exclusively, from the north and north-west*, and drifted the rocks of Finland and Scandinavia to the plains of Russia and North Germany; the syenites of CrifFell to the slopes of Skiddaw, the granites of Shap and Ravenglass to Yorkshire and Staffordshire. Agitations of water, anterior to and co- incident with the elevation of the land toward its pre- sent height, have disturbed and modified the materials left by the ice-rafts, and mixed them with materials derived from wasting coasts, river floods, and the wear- ing of the sea-bed. These we shall now consider. OSSIFEROUS GRAVEL, PEBBLY CLAY, SAND, ETC. While some remarkable cases of dispersed boulders have engaged the attention of geologists following in the track of Saussure and De Luc, thousands of examples offered themselves of accumulations similarly at variance with the existing agencies of water ; but they were never accurately studied till they acquired a new in- terest from the discussions of De Luc, and the splendid researches of Cuvier into the bones of quadrupeds which * Buckland, Reliquiae Diluvianae ; Murchison, Geol. of Russia; Rogers, to Proc. of American Naturalists. CHAP. VI. POST-TERTIARY STRATA. 299 lie abundantly in these deposits. Large portions of England, Wales, Scotland, and Ireland, are covered by irregular aggregations of gravelly sands and pebbly clays, locally stored with the bones of various land quadrupeds, which appear to have lived not far from the spots where they now occur buried. The parts where they occur were therefore dry land, or, at least, not far removed from the native haunts of the animals. The pebbles constitute the essential and characteristic part of these deposits, and enable the geologist to decide, in some cases very positively, as to the direction in which they have been drifted. Generally, in all the north of England, the diluvial gravel has been trans- ported by the same routes or the same points of origin as the boulders ; but there is some variety in this re- spect worthy of notice. On the eastern side of the island, from the Tyne to the Humber, the gravelly de- posits appear partly of local and partly of distant origin. On the Yorkshire coast, local gravel, derived from the chalk wolds or oolitic moors, lies in very irregular beds, distinct altogether from the clays full of pebbles brought from the Cumbrian and Penine mountains ; at Brid- lington, local chalk and flint gravel lies over the other diluvium, and at Hessle, on the Humber, similar local gravel lies under it. It might be proper, in these cases, to confine the term diluvium to that portion of the gravelly masses which, by the abundance of the fragments from very distant parts, requires the supposition of extraordinary circumstances for its accumulation. It is not solely, nor, perhaps, even principally, in this proper diluvium, that the bones of elephants, hippopotami, horses, deer, &c. occur ; they seem, on the contrary, to be rather more plentiful in the local gravel deposits. Cases, how- ever, occur, as at Brandsburton, and at Middleton on the Wolds, near Beverley, of elephantine and other re- mains in the midst of erratic gravel derived from great distances. The most singular circumstance attending the accu- mulation of the proper diluvium is the extreme confu- 300 A TREATISE ON GEOLOGY. CHAP. VI. sion, and almost total want of laminar or stratified structure, in its mass : pebbles, and fragments of rock, of all sizes, of different nature, and from different re- gions, lie mixed indiscriminately in clay many yards in thickness ; which seems clearly to prove that the whole was rapidly accumulated, and that the particles had not time to be arranged according to magnitude or spe- cific gravity, but were heaped confusedly together by a force of extraordinary intensity and short duration. 64 ,:> &v ^ "?- '' Jf * ~ Similar explanations seem applicable to the pebbly clays of Lincolnshire, Huntingdonshire, and Northampton- shire, &c. ; and to the whole track of the diluvium from the lake mountains through Lancashire. Cheshire, Staf- fordshire, &c. Many parts of England are almost totally free from the accumulation of proper diluvium, as the York- shire coal-field, the Wealden denudation, large tracts in North Wales, the vicinity of Bath, &c. But these dis- tricts contain abundance of local gravel deposits, which sometimes appear to be quite as ancient as the diluvium, and may justly be styled "ancient alluvium;" for their aggregation seems not, in general, to require the supposition of watery agencies flowing in other than the directions of actual streams and inundations. Much of CHAP. VI. POST-TERTIARY STRATA. 301 the gravel which is collected below the openings of the valleys which descend from the Grampians is of this local character ; but that which abounds in the central plains of Ireland, constituting the 'escars' of that country, has been drifted from greater distances, and appears due to more general agency. Mr. Murchison's examination of the Welsh border appears to show that the gravelly deposits formed from the waste of those districts, and forced down to the great hollow uniting the vales of the Dee and the Severn, were transported, according to the descent of the coun- try, previous to the dispersion of the erratic blocks from Cumberland ; and he supposes that, between the moun- tains of Wales and the oolitic ranges, the vale of the Severn was submerged, and constituted part of a long strait uniting the Irish and Bristol Channels, since the northern zones were inhabited by quadrupeds. The abundance of shelly deposits mixed with and lying under the detrital accumulation of Cheshire, Worcestershire, &c. appears to justify this view. It is, therefore, by no means a simple problem which the superficial gravel deposits of even a limited district offer to the reasoning geologist. Gravel is not neces- sarily of diluvial origin ; does not necessarily imply the action of violent forces, or currents moving in directions which could only be rendered possible by a great change of the relative level of land and water. We must, in all cases, distinguish between the local and general agencies which, separately or in combination, effected the transfer of the gravel. The pebbles on the plain of Crau at the mouth of the Rhone, and those vast heaps brought from the Alps of Dauphin e by the I sere and the Durance, have one local origin ; almost every valley of the Alps and the Grampians has served for the passage of a pe- culiar suite of broken rocks ; only at one point of the Penine chain of England have the Cumbrian rocks been drifted to the drainage of the Humber. Geographical circumstances appear to have been more important in determining the distribution of gravel, than of erratic blocks, even though we assume the effects in all cases to 302 A TREATISE ON GEOLOGY. CHAP. VI. have been produced by the same agencies. Before any particular masses of sand, gravel, or pebbly clays can be pronounced to be of diluvial origin, and adduced in evidence on the question as to the origin and operation of violent waters, it is indispensably necessary to show that, under the present configuration of the surface, with ordinary measures of local watery forces, the accumu- lation of such masses is impossible. This can be shown, if the component pebbles of the presumed diluvium can be referred precisely to the situations whence they were dislodged, and these situations are separated by natural obstacles from any part of the drainage hollows con. nected with the locality where the gravel is found. Some gravel is, or may be, of local origin, the effect of existing streams, or of waters which may be conceived to have formerly flowed according to the present slopes and physical features of the country ; and descriptions of gravel deposits are almost useless, in which the question of local or distant origin of the masses is not examined. Supposing this point settled, and the deposits to pos- sess the characters of diluvial accumulation, the next thing is to determine how far similar deposits are trace- able in the neighbouring districts, and toward the pre- sumed origin of the fragmentary masses, so as to deter- mine the direction really followed by the currents which transported them. The circumstances of the accumu- lation should be carefully studied. If accompanied by local gravel, does this lie upon, or below, the diluvial masses ? for both these cases occur. Is the mass in any respect stratified ? Does its composition suddenly vary ? Is there oblique lamination of any of its (sandy) parts ? Are large and small, heavy and light, masses indiscri- minately mixed ? Are the fragments angular, greatly rounded, or flatly elliptical ? Are bones of quadrupeds or shells of mollusca found in the mass, or lying in marly beds above, below, or inclosed ? The problems thus suggested are of great importance toward a correct view of the origin of the diluvial accumulations, and the contemporaneous races of organic beings. CHAP. VI. POST-TERTIARY STRATA. 303 OSSIFEROUS CAVES, AND FISSURES IN THE ROCKS. The land animals mentioned in the last section ap- pear to have been, for a considerable geological period, inhabitants of the countries where their remains are buried in the gravel ; for their bones are also found in caves, and fissures of the rocks, under circumstances generally indicative, and often demonstrative, of their habitual existence in the cave, or the vicinity of it. Here, buried in mud, or covered by calcareous deposits, inclosed and perfectly preserved, lie the separated bones of many kinds of extinct quadrupeds, young and old, entire, broken as by falling into a pit, worn by currents of water, or gnawed by ravenous beasts ; but often perfectly recognisable, and capable of being rigor- ously compared with living races of mammalia. The result is extremely remarkable : instead of a large proportion of the existing species of animals, which, during the early periods of history, if not in later times, might have been expected to fall into fissures, retire into caves, or be dragged by wolves to their dens ; we find the greater number of bones to belong to elephants, large feline animals, the rhinoceros, hippopotamus, elk, hyaena, indiscriminately entombed with oxen, deer, and many smaller animals. The contents of the caves have a considerable general analogy in a given country, as Eng- land ; but they exhibit some characteristic differences, when different districts, as Franconia and Yorkshire, or Narbonne, are compared. These local differences are important additions to the evidence afforded by the state of inhumation and conservation of the bones, in favour of the conclusion that the animals found in the caves were really the inhabitants of the neighbourhood. The following general list of the species of mammalia found in alluvial and diluvial deposits may be useful for reference. Man is included in the catalogue, though it appears improbable that the remains of the human race found in the caves of Bize, Belgium, &c. are really of the same date as the elephantine exuviae in northern climates. (See Desnoyers' Report to the Geol. Society of France.) 304 A TREATISE ON GEOLOGY. CHAP. VI. ll 1 ll I >Q Caverns ofall Periods. Bize,Sommieres, Itancogne, Us- NI sg-s s-fll iH a l^|33 louvent, &c. g|| byshire,Preston Pondrcs ? Chookier. 1 rt I i i 'p M J i H ll I i i ri j s 1 ,4. O J5 C52 '5 So T a 01 ? g'c'-o . <3 "' H - | 5 i Q f| || S o g'S'l ^H = a aS a - * = S -CB > g-lg-f m^2S^> , pB I* fliall W Q^;^ ill" |.j iii III 1 | 3 5 e. g < 11 ic III 1 6* 1 1 1 1 III 1 , % | 1 5 '! 1 1 fcT 3 1 s 3 i u 1 8 Ji -dd 5 nn and huma .? I ! priscus, G 3 "3 r.~ 1 -s'i >3 1 111 1 ! S w K tf CHAP. VI. POST-TERTIARY STRATA. 305 3 < 3 4 9 < . ...Jl 1 1 -r* < & I 3 1 Is'cs 1 Li | ' g s ^ 1 I J I ' t 11 1 ' 306 A TBEAT1SE ON GEOLOGY. CHAP. VI. O M '5 ns of al riods. | H 3 JiaiSi ' if II 1 Sg^w-og '~->-l>- g.t: s 'cl ' o 5 ! l .1 I I ' ' ' 't3 ' CHAP. VI. POST-TERTIARY STRATA. SO? Jj ||| O OOtS K > 3 I ^ rs c -3 = ~ v> *^ "] O * [ II ||-|2 S ^ ^ 1 ^"sll: 5 W""'K <>- oo? "g 1 ill i!. Ill i s .....I ^ 3 ' . ilium ? i I 1UH S 3 ' it! K & ll? x 2 308 A TREATISE ON GEOLOGY. CHAP. VI Volcanic Detritus. ll &H a .g Is" . .== . i* if -1 -3 -3 3 '-si* 5 I 1 g* M y^S o 5 5w^^ 5 .2 52 2 > s uC < {H 1 , 1 ffi ^ * - ' 1 Porcupine Osteopora platycephalus. Megatherium australe, O Megalonix boreale, Okes Manis gigantea, Cuv. Dasyurus . . Hypsiprymnus Phascolomys Halmaturus Gryphus antiquitatii Motacilla, Lin. Corvus Alauda Phasianus gallus ? Gallinacea Columba Anas (sponsor ?) 4 undetermined specief 7 species Ardea . gig" x 3 310 A TREATISP ON GEOLOGY. CHAP. VI. The origin of the caves and fissures is obscure, yet the following facts seem to favour the opinion that they owe their formation partly to disturbing movements, and partly to the solvent power of water. It is a remarkable and general fact, that the ossiferous caves and fissures are situated almost exclusively in limestone, not only in England, but in France, Belgium, Westphalia, Franconia, Wurtemburg, along the Medi- terranean coasts, in North America, in Australia. This is, however, not at all peculiar to ossiferous caves, for it is a rare thing to meet with considerable cavities under- ground in any other rock than limestone. It does not appear that these cavities are specially abundant in districts where subterranean movements have been most powerful or numerous ; hardly one cave in the North of England can thus be accounted for; but it is certain that, in two districts of the same cal- careous formation, caves may abound in the thick and massive rocks, but be unknown in those where thinner layers are associated with sandstones and shales. This is remarkably the case with the carboniferous limestone of Yorkshire and Derbyshire: where several hundred feet of 4f Scar " limestone exist in one thick mass, caves abound, as at Matlock, Castleton, Buxton, Yorda's Cave, Wethercote Cave near Ingleton, Gowden Pot Hole in Nidderdale, Dunald Mill Hole near Lancaster, &c. but not a single cave is known among the thinner and more varied " Yoredale Rocks." Kirkdale Cave is in a very thick part of the coralline oolite, and calcareous grit ; the Franconian and other German caves are also in thick rocks of limestone. It appears remarkable, that so large a proportion of the known caves are situated near, and open on the sides of, existing valleys, though often much above their actual level ; along some vast bodies of water are now running, and daily enlarging the passage (Peak Cavern, great cavern in Nidderdale); and from the mud mixed with the bonesineven the driest repositories, from the decomposition and wearing of the surface of the bones, the stalagmitic CHAP. VI. POST-TERTIARY STRATA. 311 floors, stalactitical canopies, and other signs, there is no room to doubt that in all the ossiferous and common caves the solvent and mechanical powers of water have been exerted in modifying the size and form of the cavities. Inspection of the sea coast demonstrates how, at this day, the wasting and undermining agency of water forms caves very similar, in general character, to those containing fossil bones. In some cases (Kirkdale, Rabenstein in Franconia), it appears probable that the existing valley has been deepened since the time when the cave was tenanted by wild animals, because the mouth of the cave opens on a steep breast of rock several yards above the bed of the valley. Let us admit, then, as sufficiently proved, the existence of open caves and fissures in limestone rocks, at the time when elephants, tigers, hyaenas, rhinoceroses, &c. lived in Europe ; and inquire further how it happened that their bones came to be entombed in the dark chambers of the rocks. 1. Into open fissures they might fall alive, or be drifted by inundations when dead. It seems difficult to account otherwise for the nearly entire skeleton of a rhinoceros found enveloped in mud and pebbles in the Dream Cavern, near Wirksworth, described by Dr. Buckland (Reliq. Diluv.). Some such mode of ex- planation must be resorted to for explanation of the accumulation of bones in Banwell Cave, Hutton Hole, and other singular fissures in the Mendip hills. The osseous breccia, as it is called (a mixture of red loam, pieces of stone, and bones), which fills fissures of the calcareous rocks on the Mediterranean coast of Aragon, France (Antibes), Italy (Nice, Pisa), Corsica, Sardinia, &c., appears to have been introduced by currents of water ; and from the occurrence of land shells and marine shells and zoophyta in some of these repositories (Ville- franche), it is clear that both freshwater inundations, and overflowings of the sea, have influenced the results. The probability seems to be, that the land has there ex- perienced changes of level: in some cases (Palermo) the bones are thought to have been deposited in the sea near 312 A TREATISE ON GEOLOGY. CHAP VI. the shore, and subsequently the whole coast raised. (Pratt and Christie,, in Geol. Proceedings.) 2. Into other caves it may be thought other tribes of animals, especially predacious races, might retire to die in quiet. This is the supposition of De Luc, Cuvier, and Buckland, with respect to certain German caves filled to admiration by an enormous mass of bones and decom- posed animal matter of extinct species of bears; and the habits of that tribe of quadrupeds, and the circumstances of the caverns, seem to justify this hypothesis, which is also adopted by Blumenbach. In particular, it appears that Rosenmuller has found " bones of a bear so small that it must have died immediately after its birth, and other bones of individuals that must have died in early life." Caves thus characterised are situated in the tran- sition limestone of the Harz and Baiiman's Hohle ; in magnesian limestone near the Harz (Scharzfeld) ; in the Carpathians ; abundantly in the Jurakalk of Fran- conia, near the sources of the Mayne (Gailenreuth, Mockas, Zahnloch, Rewig, Rabenstein, Schneiderloch, Kuhloch) ; on the south-western border of the Thurin- gerwald (Gliichsbrunn, Leibenstein) ; Westphalia ( Klu- terhohle, Sundwick). M. Cuvier states, that the bones in these caverns belong to the same species of animals, over an extent of 200 leagues : that three fourths of the whole belong to two species of bear, both extinct (ursus spelaeus, U. arctoideus) ; two thirds of the remain- der to extinct hyaenas ; a few to a large felis, a glutton, wolf, fox, and polecat. In all the caverns, M. Rosenmuller found the bones disposed nearly after the same manner ; sometimes scattered separately, sometimes accumulated in beds and heaps of many feet in thickness ; they occur from the entrance to the deepest recesses ; never in entire skele- tons, but single bones mixed confusedly from all parts of the animals, and animals of all ages. The crania are generally in the lowest parts of the ossiferous mass, the longer and lighter bones above, the lower jaws always detached from the skull. They are often buried in a CHAP. VI. POST-TERTIARY STRATA, 313 brown argillaceous or marly earth in which a consider- able proportion of animal earth has been detected. No teeth marks are mentioned on the bones, which appear to have been somehow agitated together by the water which introduced the argillaceous loam. This loam sometimes contains pebbles. The general fact is, that on the solid and sometimes worn and polished rock lies a quantity of sand or loam, sometimes 20 or 30 feet thick, full of bones, and over the whole one layer of stalagmite, which has been formed by the droppings from the roof and tricklings from the sides. (Reliq. Diluv.) KIRKDALE CAVE. A. Mud on the floor of the cave, one foot thick, including bones. B. The cavern, usually less than four feet high. C. Stalagmitic crust over the mud, partly inclosing bones. D. Stalagmitic boss on the crust, derived from dropping water. . Stalactites hanging from the roof. 314 A TREATISE ON GEOLOGY. CHAP VI. 3. It is sufficiently ascertained, that some particular caverns, rich in bones, as Kirkdale Cave in Yorkshire, Kent's Hole at Torquay, &c., have not been filled by inrushing of water, nor by the voluntary retirement of wild animals for shelter or for quiet death, but heaped with bones by ravenous beasts, who used the cavern as a den, and dragged into it the carcases of other more peaceful quadrupeds then living in the vicinity. This inference is so important -for the right understanding of the ancient condition of the country, both as to level, climate, and productions, that it appears proper to ex- plain clearly the evidence on which Dr. Buckland founded his opinions. Kirkdale Cave, accidentally discovered by workmen employed on the road, is about twenty-five miles N.N..E. of York, above the northern edge of the broad vale of Pickering, on the east side of the Hodge Beck, and thirty feet above its waters. (This is from our own measure- ment.) Its floor is upon the great scale, level for the whole length yet explored, 250 feet, and nearly con- formable to the plane of stratification of the coralline oolite in which it is situated. In some parts, the cave is three or four feet high, and roofed, as well as floored, by the level beds of this rock ; in other parts, its height is augmented by open fissures, which communicate through the roof, and allow a man to stand erect. The breadth varies from four or five feet to a mere passage ; at the outlet, or mouth, against the valley, was a wide expansion, or antechamber, in which a large proportion of the greater bones, ox, rhinoceros, &c. were found. This mouth was, it is believed, choked with stones, bones, and earth, so that the cave was found by opening upon its side in a stone quarry. On entering the cave, the roof and sides were found incrusted with stalactites ; and a general sheet of stalagmite, rising irregularly into bosses and ridges, lay beneath the feet. This being broken through, yellowish mud was found about a foot in thickness, fine and loamy toward the opening, coarser and more sandy in the interior. In this loam chiefly, CHAP. VI. POST-TERTIARY STRATA. 315 at all depths, from the surface down to the rock (said to have been partially covered by a thin layer of sta- lagmite under the mud), in the midst of the stalagmitic upper crust, and, as Dr. Buckland expresses it, sticking through it like the legs of pigeons through a pie crust, lay multitudes of bones, of the following animals : Carnivora. Hyaena, felis, bear, wolf, fox, weasel. Pachydermata. Elephant, rhinoceros, hippopotamus, horse. Ruminantia. Ox, three species of cervus (not the Irish elk). Rodentia. Hare, rabbit, water-rat, mouse. Birds. Raven, pigeon, lark, duck, snipe. The hyaenas' bones and teeth were very numerous ; probably 200 or 300 individuals had left their bodies in this cave : remains of the ox were very abundant : the elephants' teeth were mostly of very young animals: teeth of hippopotamus and rhinoceros were scarce ; those of water-rats very abundant. The bones were almost all broken by simple fracture, but in such a manner as to indicate the action of hyaenas' teeth, and to resemble the appearance of recent bones broken and gnawed by the living Cape hyaena ; they were distributed " as in a dog-kennel," having clearly been much disturbed, so that elephants, oxen, deer, water-rats, &c., were indiscriminately mixed ; and large bones were found in the narrowest parts of the cavern. The peculiar excrement (album graecum) of hyaenas was not rare the teeth of hyaenas were found in the jaws of every age, from the milk tooth of the young animal to the old grinders worn to the stump : some of the bones are polished in a peculiar manner, as if by the trampling of animals. This evidence of the former occupation of Kirkdale Cave as a den of hysenas acquires much force by com- paring the fragmentary state of the bones of oxen, hares, &c., in it, with the far more complete condition of the same animals in other caves, which, like Banwell, con- tained few or no relics of hyaena, and with the pro- ductions of Kent's Hole, which are similar in all respects 316 A TREATISE ON GEOLOGY. CHAP. VI. to those of Kirkdale, and among which hyaenas' bones and teeth abound. We may therefore admit, as a thing sufficiently proved on the evidence of caves and ossi- ferous gravel beds, that Kirkdale, and some parts of the neighbouring country, were dry land in the " elephantine period " of the northern zones of the world. But was the whole of this part of Yorkshire dry land ? or was the vale of Pickering a lake, as Dr. Buckland conjec- tures, on whose margins lived elephants, hippopotami, &c.? an arm of the sea, as the occurrence of a raised shelly beach at Speeton may perhaps lead some to sup- pose ? or a strait connecting the German Ocean with the water which may be imagined to have flowed down the vale of York from the Tees to the Humber, according to the views of some authors on the distribution of diluvium ? Whatever may have been the condition of these com- paratively low lands, there can be no doubt that, above the level of Kirkdale Cave (itself only 200 feet above the level of the sea), the land in the N. E. of Yorkshire was wholly dry at the period of the existence of ele- phants; and this is a point of great importance among the many partial truths which must be established before we can look for a general theory of diluvial deposits. General Considerations on Diluvial Phenomena. It will appear from what has been said, that we look upon the erratic blocks, ossiferous gravel and clays, bone caves, and fissures, as phenomena related to a certain geological period, and a particular set of dynamical agencies. Taken as a whole, such a combination of effects is not, at this day, in progress ; nor, in general, can we conceive the possibility of their being combined by the concurrence of existing agencies operating with their present intensities, or in their present directions. But considered analytically, there is, perhaps, no single phenomenon of the "northern drift" and the associated gravelly and ossiferous deposits which does not meet a CHAP. VI. POST-TERTIARY STRATA. 317 sufficient explanation in the known daily operation of physical laws, aided by displacements of the relative level of land and sea, such as geology has established. Compared with tertiary phenomena, we must allow that the pebbly conglomerates on the flanks of the Alps are really detrital deposits of an earlier era. Dr. Forch- hammer has adopted the view of the ' boulder forma- tion' of Denmark being one very long series of detrital deposits, including the whole tertiary series, and extend- ing from the plastic clay group beyond the ordinary diluvial epoch. Whether this be correct or not, it is certain that we must apply, for solutions of the problem of the distri- bution of the diluvial blocks, to the same agencies which have been invoked to explain the accumulation of the tertiary molasse of Switzerland, and the conglomerates of the red sandstones of England. All their causes we do not know ; but the predominant one is known to be great change of the level of land and sea, and the con- sequent origin of new and powerful oceanic currents. It is certain that during the * diluvial' period a large portion of the northern zone, which is now dry land, was under the sea. Murchison has shown that this was not the case in Siberia*, which, like other then dry lands, may be regarded as the ' feeding ground' of the mammalia, whose remains characterize some of the deposits we are now considering. Those ancient sea beds, now dried, show, besides sands and gravels, the effect of strong and variable currents, great masses of fine clay, strangely enclosing far tra- velled rock masses of various magnitude, much, little, or not at all worn, and occasionally marine shells, in which, upon the whole, an arctic character is recog- nised.t However this may be, it appears absolutely certain that none but oceanic currents are adequate to explain the extensive ravages of the solid land which produced, * Geol. of Russia, p. 494. t Forbes, Mem. of Geol. Surrey, vol. i. 318 A TREATISE ON GEOLOGY. CHAP. VI. and the violent currents which distributed, the diluvium. Nor would the ordinary currents of the sea be adequate to the effect. It is requisite further to conceive that the sea was most violently disturbed, either over the points whence the detritus was brought (which supposes those points also to have been under the waves), or at some other situation. In the latter case, we may, perhaps, imagine so great a violence of water to be generated, as to permit the waves to be thrown to some height over the land ; and it seems not impossible hereafter, when the geographical relations of the diluvium are well un- derstood, to offer some reasonable explanation of the whole matter, on the principle now known to be true, of great and sudden changes of relative level of land and sea, which, though limited in the area of the masses moved, might have very extended effects through the agency of water. Floating glaciers may also be called to aid the speculation ; but they would be useless for any other purpose than to explain particular cases of erratic blocks, and small tracts of peculiarly associated gravel masses. The best general view of these phenomena recognises in the greater portion of the materials of these deposits the spoils of neighbouring or not far distant land, de- rived from the sudden ruin of sea cliffs and the gradual waste occasioned by atmospheric action and river erosion. These materials are sorted into gravel beds, sand beds, and broad masses of clay. In addition, we have consi- derable quantities of far travelled rock masses, often quite unworn, which are so mixed with the fine clay as to indicate the probability that they were not drifted with it by excessive violence of water, but thrown into it, and inextricably mixed with it by a distant operation, the melting or overturning of stone-covered icebergs. Similar stones, but worn and rounded, occur in the gravels, and no doubt have often been washed out of their original sites in the boulder clay.* Perhaps it * Trimmer in Geol. Proceedings, 1851. CHAP. VI. POST-TERTIARY STRATA. 31Q was in the latest period of the ice rafts that the large erratic blocks were scattered in greatest ahundance. None of these phenomena appear to require more violent watery movements than such as the sinking and rising of the land must have occasioned, even if it were accomplished by many small gradations. In particular cases, to which the agency of icebergs is inapplicable, excessive local violence of water has been appealed to. For explanation of the bands of angular chalk flints parallel to the axis of the Wealden, Murchison requires the violent concussion of limited tracts, from which he supposes these flint bands to have been mainly derived.* There is no antecedent improbability in a postulate of this kind ; its necessity must be judged of as a special problem on appropriate evidence. ZOOLOGICAL AND BOTANICAL CHARACTER OF THE DILUVIAL PERIOD. The diluvial deposits appear, in general, characterised by the presence of a great number of land animals, and some sorts of trees, which are much more similar to existing forms of life than are the tertiary quadrupeds and plants. But this general or average result requires to be limited by several considerations : first, there are deposits reputed tertiary, as the sandy deposits of Ep- pelsheim, on the Rhine, in which occur a vast number of species very nearly approaching to existing races ; secondly, among the animals of the diluvial period are species, and even genera, as totally distinct from the actual creation as any of the tertiary groups ; thirdly, in deposits of undoubtedly tertiary date, as the sub- apennines of Italy, the sands and marls of the Danube, and flanks of the Carpathians, the crag of Norfolk, bones and teeth of elephant, rhinoceros, mastodon, and other genera of the diluvial period, have been found, though not frequently. It appears, therefore, certain, on this evidence, that the transition from the tertiary to later periods was not accompanied by a sudden de- * Geol. Proc., 1852. 320 A TREATISE ON GEOLOGY. CHAP. VI. struction of old or a general creation of new quadru- pedal forms of life. The same appears to be true with reference to the buried forests so often associated with diluvial deposits. It is confirmed by the gradual change in the proportion of existing among extinct species of tertiary shells; so that the most recent groups of tertiary strata contain 40 to 90 per cent, of living forms, while among a dozen or twenty shells in the gravel of Holder- ness one extinct species is met with. On the other hand, it must be remembered, that no pala?otheria, lophiodontes, or other genera, chiefly be- longing to the older tertiary genera, are mentioned as occurring among the diluvial accumulations, though in certain freshwater deposits, as at Grniind, lophiodontes, oxen, hippopotami, &c. occur together. Again, certain animals which lived in the diluvial period, as cervus megaceros, appear, by various evidence, not to have been extinct till later times; though we should not venture to adopt Dr. Hibbert's opinion, that they have really lived within the historic ages of Europe. However, it deserves remark, in connection with this subject, that no one has yet succeeded in showing a real and certain distinction between the common red deer and domestic ox of Europe, and the analogous bones of Kirkdale and other caverns. Upon the whole it seems probable that the palseothe- rian and other tertiary races of quadrupeds died and became extinct gradually, but not by any one law of uniform progression ; that the elephant, and his accom- panying tribes, began to exist during tertiary eras, rose to predominance before the close of the diluvial period, and, for the most part, perished in that period, or soon after. Some modern species (stag, ox) were co-existent with the elephant and hippopotamus in northern zones; others (elephas primigenius, rhinoceros tichorhinus), which abounded in diluvial, were also living in tertiary periods ; and, perhaps, a few (as the horse) may have been in existence during all these periods. This is a point, however, extremely hard to determine ; since, if, CHAP. VI. POST-TERTIARY STRATA. 321 among living tribes, the diagnosis of species is far from clear, what errors may not be incurred by pronouncing a verdict on the imperfect evidence of a few fragments of detached fossil bones ? ANCIENT MARINE DEPOSITS. Raised Beaches. These curious phenomena, first brought prominently forward by M. Brongniart, are a part of the great system of "Pleistocene" deposits, which includes the erratics and drifts. They demonstrate, that within a comparatively modern period, certainly since the actual seas were rilled with yet existing mol- lusca, the beds of these seas have been subject to eleva- tion and depression, so that, in particular places, large quantities of shells attached to their parent rocks, or mixed with the pebbles and sand of their native beaches, have been raised 10, 20, 100, or several hundred feet above high water mark. Within the reach of history, slight displacements of the relative level cf land and sea have taken place, as the temple of Serapis near Puzzuoli, Lisbon, Port Royal, are supposed to prove. But these phenomena, connected with local earthquakes and volcanic eruption, are small and limited in comparison with the class of facts noticed above ; which appeared to M. Brongniart of so general a character as to justify a supposition that the ocean waters had everywhere suffered a depression of level, even since the creation of existing races of mollusca, and the establishment of the main features of physical geography, though anterior to historic times. To this view of M. Brongniart it is, apparently, a fatal objec- tion, that the levels at which the raised beaches appear, above the sea are extremely varied, even on points of the coast of the same country, and much more when we compare distant coasts; whereas, upon his view of a general lowering of the surface of the sea by one de- pression of the crust of the globe (affaissement de la VOL. I. Y 322 A TREATISE ON GEOLOGY. CHAP. VI. croute du globe dans un point), we should see accordant indications of the former height of the water. The following examples are selected to illustrate the nature of these deposits : On the coasts of Great Britain, phenomena of this kind have been observed in the valleys of the Forth (Boue, Maclaren) and the Clyde (Laskey), chiefly in the form of low terraces considerably above the actual flow of the tide ; on the coast of Lancashire, about Preston (Gilberston); at the base of the Forest Hills, and other places in Cheshire (sir P. Egerton); near Shrewsbury ; on the Mersey at Runcorn ; and on Moel Tryvaen, near Caernarvon (Trimmer). That an uplifting of the shores of the Moray Frith has taken place subsequent to its having assumed its present outline, is considered by Mr. Prestwich as proved, by the existence, in several places, of a raised beach. In BanfFshire, this beach varies from six to twelve feet above the present high water level ; and contains shells now inhabiting the neighbouring sea, as patelia vulgata, patelia laevis, trochus ziziphinus, littorina littorea, turbo retusus. At Gamrie, celebrated for its ichthyolites, Mr. Prestwich found, in light- coloured sands, associated with rolled gravel and dark clay beds, the following recent shells : Astarte Scotica, tellina tenuis, buc- cinum undatum, natica glaucina, fusus turricola, den- talium dentalis, &c. They were extremely friable, but perfect. The deposit attains, in some places, a thick- ness of 250 feet, and rises to a height of 350 feet. * On Moel Tryvaen (1450 feet above the sea), the shells (buccinum, natica, turbo, Venus) were in fragments, adhering to the tongue, very much as in some tertiary deposits : they lie in sands and gravel, with granite boulders, 1000 feet above the sea, the country between them and the Menai being greatly broken, the rocl g I S rt o It Regions of Depth. > 3 - 1 J3 s H Holosto o j: II Brachio mellibr; tit f 73 K hi I. 3 11 4 50 40 1 38 147 II. 2 3 4 40 27 53 1*9 III. 2 2 40 30 52 124 IV. 2 3 2 44 41 2 68 142 V. 2 5 1 35 36 4 58 141 VI. 6 1 28 30 5 48 119 VII. I 6 2 17 16 3 7 34 85 VIII. 1 2 15 5 It 3 28 66 Total species Total occurrences 7 11 20 37 6 18 115 269 104 225 12 16 8 21 135 379 in depth. Ratio of number 1-6 1-8 3-0 2-3 2-1 1-1 2-6 2-8 of occurrences to number of spe- cies. To all the eight regions only two species of mollusca are common, viz. area lactsea, cerithium lima. Nine are found in six regions, seventeen in five regions. The observed distribution of other species which occur in more than one region agrees with a general inference that the extent of range of a species in depth is propor- tioned to the extent of its geographical distribution. CHAP. VI. POST-TERTIARY STRATA. 341 Supposing, what is believed to be true, that the shelly inhabitants of the sea, like the zoophytic tribes, exist in abundance only to a small depth (say 1000 feet), it must follow, that during the formation of the stratified crust of the earth, very general and long continued depression occurred in the ancient bed of the sea : for as the series of strata, full, at least partially, of organic remains, which lived on or near the spots they now occupy, exceeds in almost all countries many thousands of feet in thickness, the successively deposited surfaces of strata must have successively sunk lower and lower, till the whole depressing force being exhausted, a con- trary action raised them again. To this highly im- portant subject we shall recur in another part of this treatise. It is further deserving of remark, that if, at this day, contemporaneous deposits of pebbles, sand, clay, and calcareous matter happen even in the same oceanic bed, as the bottom of the German Ocean, each strewed with different groups of shells, the distribution of organic fossils in the different primary and later strata, if at all governed by the same laws as those now traceable in nature, though affected by some general characteristics of period, must also exhibit specific relations to the nature of the rocks. We have already shown this to be the fact ; and it serves to strengthen our confidence in the reasoning employed, when we find the results of the same causes harmonise in the most ancient as well as the most modern instances. Banks of Sand, Clay, Gravel, c. A very slight observation of the action of the marine currents on our shores is enough to determine many circumstances re- garding such accumulations. The first remarkable act is the sorting of the mingled materials brought down to the sea by inundations from steep land, like the ma- ritime Alps, or gathered from the falling cliffs by the action of the waves. According to specific gravity and magnitude, the masses are separated, transported, de- posited pebbly deposits -lie under the gravelly cliffs 342 A TREATISE ON GEOLOGY. CHAP. VI. the sands are swept to a greater distance the fine clay carried far in the waters. Of all these circumstances the English coasts offer abundant examples especially Teesmouth, the Bristol Channel, and the Bay of More- cambe, which, on their wide sands, present a wonderful variety of appearances, proper to furnish the specula- tive geologist with more accurate and applicable data than are commonly relied on. Among others, the as- pect of the surface of the sand its ripple marks, vary- ing in an exact proportion to the depth of water and the direction of the wind the numerous little valleys and rills which modify the slopes the countless prints and seeming prints of the feet of birds the trails of mollusca and annulosa, may suggest to the reasoning geologist proofs of the important truth, that all our la- minated sandstones and flagstones were littoral deposits, a point of departure for accurate inferences concern- ing the rising and falling of the level of the land, as compared with that of the sea. It is hardly necessary to observe, that the nature of these deposits varies with that of the supply ; near peb- bly cliffs, the shore is a shingly beach ; low sandy cliffs, or a rough river, cause expanded breadths of sands sloping gently to the sea ; on an argillaceous coast, the bay may be full of sand, drifted by littoral currents, which very much modify all the ordinary results, and are the principal agents in first wasting the high ground, then filling up the low parts of the shore, and thus de- positing new land, which subsists either by a natural defence of blown sand, gathered pebbles, or the pru- dent skill of the engineer, till some unheard-of storm returns to reclaim again the gradual gift of generous nature, or the bold theft of craving man. The distance to which currents can transport solid matter in the ocean may be well illustrated by the ac- tion of the gulf stream which sweeps from the Guinea coast by the Gulf of Mexico, and then traverses so great a portion of the North Atlantic ; for it carries timber and tropical fruits within the influence of the CHAP. VI. POST-TERTIARY STRATA. 343 littoral indraughts of Iceland, Norway, and Ireland; and Col. Sabine's observations on the sea current of the Maranon show, that, at a distance of 300 miles from its mouth, the fresh water of that mighty river floats on the heavier water of the sea, and retains its earthy discoloration. END OF VOLUME L LONDON: SPOTTISWOODES and SHAW, New-street-Square. BEEKELEY THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW Books not returned on time are subject to a fine of 50c per volume after the third day overdue, increasing to $1.00 per volume after the sixth day. 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