A Treatise on Geology

John Phillips · 1837 · Historical

A Treatise on Geology by John Phillips (1837). Full text and reference in the Mountain Man Mining Library.

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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Contents.

Chapter I.

Iktboductort Tibws.

Page

'Objects of Geological Science . ... . i

Means of Geological Investigation - - . 6

Scale of Geological Hme . . - - - 8

Nature of the Scale ofTInie - - IS

Interruptions in the Series of Time . - 16

Meansof Interpretation of Phenomena - - - 20

Chap. 11.

, Cienbral Ueasoninqs Cokcbkkino Thx Substakcx Of This

i Chemical Data as to tlie exterior Parts of the Earth - . S3

Proportions per cent, of Oxygen in Earths, Minerals, and Rocicc . 24

Physical DaU as to the interior Constitution of the Earth . S6

Mass of the Globe, whence deriTod - - - S8

Chap. Iii.

OENK&AL TRUTHS COKCSRNlKG THE STaUCTDRE OF THE EX- TERKAL PARTS OF THE GLOBE.

structure of the external Parts of the Globe - . SS

Forms or llock Masses - - - - 35

Position of Ilocks.~Decnnatiou of Strato - . . 36

Load Declinations aiul unusual Positions of Strata - - 39

Faulu - - - - - - 40

Extent and Frequency of Faults - - - - 48

Relation of Faults, Mineral Veins, Dikes, &c. to the great Lines of

disturbed Rocks - - - - . 44

Origia of stratified and unstratified Ro(A - - - 45

Relative Periods of disturbed Stratification - - 49

Vi Contents.

Chap. Iv.

8SRISS or STRATIFIED E0CK8.

Page

Sections and Maps of Strata - - - - 53 TobleoTBritish stratified Deposit* - ... 54

Varieties of Stratification . - - 59

Divisional Structure of Rocks . . - 62

Geographical Relations of Joints . . - 65

Cleavage - - - - -67

Chap. V.

Organic Remains Of Plants And Animals.

Fossil Plante - - -69

Table oftbdr Geological Distribution - . - 73

Fossil Zoopbyta . . . . . 73

Table of certain Groups - - - 76

Fossil MoUusca . . - . 77 Table of proportionate Numlier of Species at difflerent Geological

Periods - . . - 80 Table of proportionate Number of Species in the diilbrent Orders

or Classes of Mollusca in different Geological Periods - 81

Table of Genera containing many living Species of Gastenoda - 82

Thble of Genera containing many Fossil jiecies of Conchifera 83

Table of Genera Cephalopoda . - .83

Tbble of Subgenera of Ammonites - - -

Articulated Animals - ' - 84

Table of Crustacea - - - - 85

Fossil Fishes - . - . . - 80

Agassis's Classification of Fishes . - 88

Table . - . .90

FossU Reptiles . . - . . .91

Von Meyer's System of Fossil Saurians .93

Fossil Birds - . . .96

Fossil Mammalia . . . 96

Didelphys of Stonesfield - . . .97

Table of Mammalia - . . . 99

General Considerations . . .100

Chap. Vi.

Historical View Of The Stratipikd Rocks In The Crust

Of The Earth.

Introductory Remarks . -107

Granitic Basis of the Crust of the Earth . . 106

Granite Veins - - - - 109

Metamorphism of Rocks - - - .'110

CONTENTS. Vll

Page Primary Systems of Strata.

GneiM and Mica Schist System - . . Ill

Succession of Strata - - - 117

General Inference concening - 123

Clay-slate and Grauwacke System - 123

Succession of Strata . . -127

Organic Remains of " . 1S8

Figures of ditto - . . - 130

Silurian System - - . 134

Succession of Strata - - . , - 137

Organic Remains of - - 139

Figures of ditto . . 141,142

Close of the Primary Period.— Ensuing Disturbances of the Crust

of the Globe . - - . - 145

Secondary Systems of Strata.

Carboniferous System - - - 151

Particular Structures - - 152

Succession of Strata 154

Organic Remains of - . . 158

Figures of ditto - 159. 161. 163

Duration ofBritish Coal Field . . -170

General View of the Circumstances onder which the Carboni-

- ferous System was deposited - . . 175

Extent of British Coal Fields under superior Strnta.— Disturbs

ances of the Carboniferous System - 181

- Saliferous, or New Red Sandstone System - .184

Succession of Strata - - -187

Organic Remains of . . . 188

Tabular View of ditto - - .189

Figures of ditto - -190

Origin ofRock Salt and Gypsum . .135

Oolitic System - - - 199

Series of Strata - - . . 203

Lines of contemporaneous Deposition - .-205

Organic Remains - ' . - 207

Figures of ditto . -209,210

General Review of - . . - 21G

Cretaceous System . ' - .218

Succession of Strata . . - 2S1

Organic Remains of . ' - - . 222

Figures of ditto . -233—225

Close of the Secondary Period. — Ensuing Disturbances of the

Crust of the Globe - . . . 229

Reflections on the Change of Mineral Deposits - .230

Succession of Organic Life - . 231

Change of Physical Condition . . 232

Tertiary Systems op Strata.

Succession of Deposits in different Basins - 239

Relation oTthese to different existing Seas - 246

Vm OONTENTS.

Organic Remaint - - - - 2t8

Views of Bl Adolphe Brongniart on the Pbutc . . 'i4if

M. Deshayet on the Mollusca - . - 249

Mr. Lyell's Classiflcation - - .251

M. Agassis on the Fishes - - 254

List of Mammalia . - - i256

Figures of FossUs - . -259,260

Disturbances of the Tertiary Strata - %1

FuffT-TBRTIAET AND MODBBH DBPOBITS.

View of the RelatioD of these to Tertiary Strata . 262

ClassifiMtion of - - - . 265

DekritalDeposits . .265

Erratic Block Oroup . .267

Ossiferous OraTel, Pebbly Clay, and band . - S78

Ossiferous Cares, and Fissures . S88 General Table of Vertebral Remains in Post-Tertiary Aoeu.

mulations - - . . iS4

Description of Carems .890

General Considerations on Diluvial " Phenomena - 296 Zoological and Botanical Character of the " Diluvial Period S99

Ancient Marine Deposits . - - SOC

Raited Beaches - - - SOD

Change of Le?d of Land adjoining the Baltic . .304

Marine Deposits in Progress . - .306

Coral Reefs - - - 306

Mr. Stutchbury*8 Views of these - .306

Mr. Darwin on Coral Islands -311

Shell Beds . .313

Banks of Sand, Clay, Gravel, &c. . 315

Ancient Valley Formations . 317

Rock Terraces in Valleys . . .390

Fluviatile Deposits - . . .322

Waste of the Earth's Surface - - .323

EflbctoofRain . - . . 324

Eflfectsof Frost . . .325

Effects of Springs - . .325

Efftcts of Rivers . . .327

Lakes on the Course oi Rivers . . 330

Deep Lakes . . . . 331

Shallow Lakes . . . .333

!

Treatise On Geology.

Chapter I.

INTRODUCTORY VIEW OF TBB OBJECTS OF OBOLOOICAL SCIENCE AND TBB MEANS FOR INVESTIOATINO AND INTEBPRETINO THE NATURAL HI8T0BT OF THE EARTH.

1. Objects of Geolooical Soifjvce.

The phenomena of geology are so various and compli- cated thai hardly any class of writers has left them wholly untouched; and the aspect of this science changes according to the peculiar object of di£ferent 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 whose object it was to propose explanations of these differences, as a branch of mineralogy ; while in Hutton's comprehensive mind geology applied itself to

VOL. I. b

2 A TREATISE ON OEOLOiiY. CHAP. I.

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 object 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 earthy 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 geolc ; 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 ahould be opened toward the attainment of the varied truths which must be collected, by insulated ob- servers, before it shall ])e found possible, for even the most comprehensive intellect, to frame a general and consistent 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 th 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 Palerontology is becoming usual.

Chap. I. Objects Of The Science. 3

tiniial 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 pro- ceed to inquire what monuments remain in nature of any previous aspects or conditions and' from these to infer the nature and amount of the agencies formerly concerned 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. Gatherings from the labours of mineralogists botanists and zoolcsts, 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. Ohap. I.

was illustrated by Werner, after the model of th 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 fhe 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 tile profoundest researches of abstract science. It is not even enough to know the actual state of the earthy 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 bef<re ihem that these in> elude 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 equdly 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 dl the laws which this relation implies, and limits itself to the discovery of the strictly terrestrial phenomena which have hap- pened upon Ibis 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 Of The Science. 5

earth showed " no traces of a beginnings no prospect of an end"; because, on thatmatter 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 m science ; nor can either be justly charged with the slightest tendency to make men Ibrget 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 truths 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 earthy 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, or below the surface ; all changes in the

B 3

b A TREATISE ON GEOLOGY. CHAP. I.

number structure fonns 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-

" Oeolorr 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 i

the business of the former to connect these phenomena with their causes.** I

It cohsists in the knowledge of the causes which hare 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." — Z)e Luc Lettre Premiere.

Ohap. 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 diiflculties 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 Mrith kss

B 4

8 A TBXATI8B ON GEOIiOOT. OHAF. Z.

exactness tban is attainable in modem 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 imp<M-tant cases he can hardly know whether particular moUusca 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 hare 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, becaui 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 modem mineral kingdoms.

Scale of Geologioai 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 dvil 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 rons 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

Ohap. Means Of Inve8Tioation. 9

known, the problem of the history of the saccessive conditions of the gbbe becomes ahnost 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

I the series of organic Ufe, and to compare the relative

w 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 tliis 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 exuvie (and even were this not the case, the fact of the pro- duction of analogous or very similar strata beneath modem waters would justify the inference) ; therefore, the Umest 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 Oeoloot. Chap 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 success sion, but of duration.

Lapse qf Time inferred fr the nature of the Series

of Rocks,

The circunstances which 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 vaiiouH, 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 surfac. 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 tlie 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

f 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 on 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 fomtiation of deltas in the upper ends of lakes, instances of which abound in every country, to show that the historic 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 Geolooy. Chap. I.

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 qpmmonly definite or composed of a certain number of simple terms, u e., layers each of a particular quality in every small district ; copsidered 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 sue- cession of stratified rocks in all parts of the globe If we can search out the causes of local diversity id 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 modem 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 or 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 difiused ; they differ in hardness, granulation, crys- talline structure, and many other circumstances. £very

Guap. 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 th globe the physical conditions varied thousands of times during the formation of the series of strata. The mere inspection of one stratified rock compos 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 ih progress of formation. By methods of undoubt accuracy the length of life of some of these buried trees 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 exacts if the shells of all ages living together in the sea were buried in one bed by one action or

The entire mau 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 fonnation ; 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 organised bodies are of difiteent 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 them, and also on account of the change of species in the same. places where the former are buried. — De Luc's Letten,

'

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 modem nature, so uniform in die local results of the same kind, the ex- planation of this, reply will be immediately found : those periods of new combinations among the physical conditions of a given region are far beyond the range oi 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 sufiicient nor correct to say, there is one having 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 Of Investioation. 1 5

f

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 coUect-

. 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 glohe, and hy 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, lights 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 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

s.

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 masse? 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 confiise 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

r

r

Chap. I.

Uban8 Of Investigation.

beds a of limestone were exposed to watery action, and broken up in party so that fragments and pebbles of

them are found collected into beds among the mass of later level sandy deposhs b (Mendip Ilills): and in

e 1

t

/

fig. 2. the same indined limestone beds a are covered by horkontal oolitic strata c; and are worn and polished on the face of jinctioif, and penetrated into holes by boring shells, Vhich lived in the oolitiferous sea, long after the elevation of the older rocks.

Length of the Scale of Time,

The scale of geological thne given by the series of stratified rocks is one of unequal partia : 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. t.

18 A Treatise Ok Oeoloot. Ohap.

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 bes 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 their 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 die Tyrol) is only 2764 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 fig, 4 a true, repre

Chap. I.

Means Of Investioattok.

W

sentation of the arrangement of strata in a part of the crust of the earth.

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; to come up to the surface in succession a, b, c, d, &c. ; not, as in fi. 3,, parallel to the horizon, as \nany per- sons are apt to imagine. The thicknesses of a, 6, c, d, &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, ft, c, cf, 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 /ace 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-

so A TBEATISB ON OBOLOOY. CHAP. I.

ing the constitution of the earth: geology, as such, can penetrate no farther than this snuiU 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 oiir planet.

Direct observation of organic remains is the onl/ 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 feasoning d priori can be, in this inquiry, of the smallest service ; but tnay be exceedingly injurious by infusing error and prejudices. It would be a groins 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 bCng ; for since the form& of life are most certainly made dependent on physical conditions, unless these latter caii be' known beforehand, there can be no reasoning on the nAtter, and there ought to be no tulatum 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 reliquiae, 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 Invbstigation. 21

throih 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 prohlems offered hy the phenomena of ancient times : the common relations are found hy comparison of the analogous effects ; hut if the modam effects are merely known as laws of phenomena and not reduced, to use Mr. Whewell's expressire language, to laws o£ 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 geolc can he imderstood, unless there he known something exactly like it in modem nature ; the laws of causation which regcdate the phenomena now oc- curring on the glohe, once correcdy known, will cer tainly he 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 ftised rocks and earthy matters — the laws of optical and calorific phenomena — these laws of action are limited in their apptication only by the cir- cumctances 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 ituxe who have not studied the philosophy of the subject : though it gathers the most striking and beautifal facts, it depends for their interpretation 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*

22 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 withoat ade- quate knowledge to aid in the progress of geological theory.

Chap. Ii.

Ckeieral Reasonings Concerning The Substance 01

. The Globe.

Chemical Jbata as to the Exterior Parts of the Earth.

What is the nature of the mass ot 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 die earth. These compounds, resolved into their elements by the processes of chemistry, yield a certain number (fifty-four) 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

24t 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, thorinum 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 yidd solid compounds, and in such large proportions, especially with . ihe 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 peculations, to which this conducts to the coucentration from a gaseous condition of the matter of the planetary system, seem to be in agreement th the tronomical 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 rfthe Proportions per cent, of Oxygen m certain abundant JEartks, Minerals, and Roche

100 Silica 48*4 Silicium 4- 51*6 oxygen. 100 Alumina 53*2 Aluminum + 46*8 Ozygep* 100 Magnesia ss gi liagnesiom + 38*6 Oxygen. 100 lime s 72 Calcium + 28 Oxgen.

Glde to Ecology.

Chap. Ii. The Substance Op The Globe. 25

100 Quartz 48 -4 Metallic base -f 51*6 Oxygen. 100 Felspar 54 Metallic bases + 46 Oxygen. 100 Mica s 56 Metallic bases + 44 Oxygen. 100 Granite 52 Metallic bases + 48 Oxygen. 100 Basalt b 57 Metallic bases + 43 Oxygen.

100 Gneiss 53 Metallic bases + 47 Oxygen.

100 Clay Slate 54 ? Metitllic bases + 46? Oxygen.

100 Sandstone from 49 to 53 Metallic bases + 47 to 51

Oxygen. 100 Limestone a 52 Metallic base + 48 Oxygen.*

In studying the simple and.yuioiu compound mi- neral masses occasioned by this union of oxygen with the metak and the metallie bases of earths and alkalies the geologist labours on the same bodies as the minersl-. 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 diich 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 dear 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 micii ' .These; minerals are investigated by their qualities ff- 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, ei:|anune8 the properties and proportions of them, and investigates the laws of their combioation." t

See on the Chemical Comtttution of Rocks, Dels Becbe*s Geological HaDUBl, Sd edit t Guide to Geology, 3d edit

$6 A Treatise On Geologf. Ohap. 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 these 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 pur 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 nearly 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 times that of water ; cor- 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 coiv- densation due to mere pressure would indeed, upon all

<}aAP. ti, THE SUBSTANCE OF THE QLOBE. 27

mineral compounds known to us go so far as to aug- ment their density much more than is requisite for the folfihnent of the condition required by the calculation. According to Leslie (as quoted by Mrs. Somerville) water would be as heavy as mercury at 36*2 miles below the surface of the earthy and air as heavy as water at 84j 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 ; that they are of so dif- ferent a nature as to yield but little even to the im- mense pressure upon Uiem; 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 esurth is an oblate spheroid, such as would be produced by revolution on its axis, provided the constituent matter of the globewere in such a state as to be allowed freely to arrange itself in obedience to the central and tangential forces concerned. 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 fteports of the British Auodation, toL i. p. 408i

28 A Treatise On Geology. Ohap. Ii*

VIZ. to the central parts implies a total incoherence or fluidity of the mass of the glohe. Such fluidity appears perfectly intelligible as the effect of a general and pervading high temperature ; and perhaps this is the only sujokition which will at all meet the case. But it derives a considerable aceession of probability from the fact that the earth is even now hot within ; a point on wbieh all experiments on subterranean tempe- rature and> pierhaps 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 earthy that the substances therein occurring have sujdii anal$flies to those now seen near the surface that they wottld have been subjected to very much greater condensation than they have suffered — the globe would have been denser thanit is — were it not for the expansive influenoe ef 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 la physioal astronomy to decide if indeed, evidence can be collected, on points involving the consideration of fliiity !or motion of the interior masses, sufficiently pieeisd to give authority to the rigorovs results of caloQaliohs applied for the purpote'-of tMdng this .grelirt; question. Mr. Hopkins k inderstood to haiecbeenenjeed in the great labour 6f' discussing Iii4: phenoBona of pre- cession mil ntRation with this ideiir.

Map/the Glohephnce derived.

With this knoMrkdge of ib nature of the mass of the globe, .the modes of oombination of the several ingredients of the mass, and the properties under certain phyncal. conditions of these ingredients e- isting separately, one of two conclusions must be

Ohap. Ii. The Substance Of The Globe. S9

adopted by tbe 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 farther 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 inquiiing into the works of creation, by dm 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 stracture of the globe, by an immediate act of .Almighty Power, or produced from some former condition in tiie same elements by the agency of intermediate laws of caus- ation ; but, on careful examination, it will certainly be found otherwise.

If it be true and demonstrated, (hat in the existing economy of nature all 'phenomena (whether they ap- pear to ouj iqppiQQt cck|iceptiQ))s simple or complicated) are the result of invariable appointed laws, acting under definite cppditiiona; if it 'appear that, in our own time, th .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 -hich are l:nown to govern and to correspond accurately to the modem effects stand in the same relation to those

30 ▲ Treatise On Oeoloot. -Oeulp. Ii.

of older date ; vfho, that looks upon the laws of modem 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 yirtually 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 lustis naturae, 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, aU 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 he 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

Ohap. 11. The Substance Of The Globe. 31

igrhewjLS fusion ; some appear the result of electrical combinations. All these latter are bat forms of che- mical processes among the elements of matter ; and the sedimentary rocks where their parts are clearly dis tinguishable are fomid to be composed of grains or fragments originally produced by aqueous, igneous, or electrical combination. Thus all die 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, Jess 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 metaUic basis, siUcium, 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 ▲ TREATISE ON GBOLOaY. CHAP. IX.

sions like the nebnls and comets; speculations which appear to be gradually changing into probable inferences by the progress of modem astronomy. For the examination of these obscure bodies with powerful telescopes has shown them to be of extremely various characters, so as to offer many points in illustration of the supposed process of condensation and arrange- ment.

The progress yet made in chemical philosophy is perhaps not sadi 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 tiie least improbable view, tiiat tiie nebulous condition of a phinet may be due to intense heat existing among its particle* ; 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 gaaes metallic matters are frequently present (as arseniuretted hydrogen), and the atmosphere of our planet is beUeved by several philosophers to contain so large a proportion of the sub- stances existing in the superficial parts of tiie globe, as to give origin to the meteoric stones.

S3

Chap. Iii.

GEKEBAIi TJtVTHS OONOBBNINO TBB STRVOTVBB OF THE EXTERNAL PABT8 OP THB OLOBE.

From these facts and reasonings concerning the nature and constitation of the materials of the globe derived from chemical and physical science we may torn 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 disckwures effected by nature.

Beginning at the surface, and passing gradually towards the deeper parts, we shall be able easily to gather dear ideas of this fundamental p<Hrtion of positive geology, without a right knowledge of which the otherwise pleasing task of following and examimng the common reasonings in the sdenoe would be use- less, if not preiamptuous.

Stbuctubb of the external Parts of the

Globe.

Soil, the external investment of the land, though it somewhat veil from geologists the objects of their pecu- liar research, merits attention ; for this thin covering varies in some real relation to die 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 nrregular, — some feet thick over certain sandy rocks, a foot over clays, only a few inches

Vol. I. D

34 A TREATI8S ON OEOIiOOY. CHAP. UI.

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.

Mocks, and the substances which they enclose, lie beneath the superficial accumulations, and constitute the crust of the earth as i known to gedogists. The term rocks*' is apt to mislead beginners; for under this title geologists rank day, sand, coal, and chalk, as well as limestone, granite, date, 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 <;rust 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 Extebnal Pabt8 Of The Globe. 35

Forms of Rock Masses,

On mouutain 8ide8> 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 weUs roads canals has added to the facilities granted by nature and from these opportunities the structure of the crust of the earthy the arrangement and reUtive position of the rocks are knowd in the most essential points. The different sorts of rocks are by no means mixed together in confusion but placed in a rular 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 deavage &c. ; but, neglecting for the present these subjects, we shaU 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, lOQ, 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 (d) ; 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, veins, &c, as unstratified rocks (u).

Dykes and veins form but a small part of the mass of the crust of the globe, which consists principally of

D 2

56 ▲ TBEATIfrE ON GBOLOGT. CHAP. HI,

stratified and unstratified rocks. In the plains, and comparatively low portions of the earthy the rocks are almost universally stratified, — the strata heing often very thin, even to indtes, hut sometimes many yards or fathoms in thickness. The soperficial area, over which a particular stratified rock expands, is sometimes enormous — chalk> for instance, has a range of many hundred miles in length, hy 5, 10, 20, or more in width, in England and France, — hut sometimes very limited, as the magnesian limestone of die north oif 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 he found that, even ii\ the very midst of chains and groups of mountains, the marks of stratification may often he perceived; but it almost always hajns that the axis of such chains or groups is formed by un- stratified rocks, and these sometimes appear in lower situations.

Position of Rocks toith respect to the Surface of the Earth, -— Declination of Strata.

Stratified rocks have usually a nearly constant thidc- ness, or else vary in this respect by insensible and re- gular gradation; their surfaces, or the pkmes 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-K gular amount of the descending slope (dtp) or ascending slope (me). The result of very numerous trials proves that the strata are over large surfiices 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 dip in the same direction. Thus the surface of the earth in regions where stratified nocks occur is formed partly on their edges ; and a section

cAap, iii tue ezteHnal pabts of the globe.

or vertical cut to some depdi from tbe Biir£u would pre- flent on its sides the appeaianoe of die diiram No. 6.

We may say that three fourths of the surface of the dry land of the glohe 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 ehairiB and groups qf mountains under the plains winch Surround or divide them. Thus, from the group of Cumbrian mountains the stratified rocks dip W. at Whitehaven, N, at Hesket, £. at Shap, S. at Ulverston ; from the chain of the Lammermuirs they dip N. W. under the great valley of the Forth, and S. £. into Northumbeiland. The most general dip in England ia easterly, the principal mountains being situated on the western border : from Brittany, the Ardennes, and Auvergne, the dips of the strata converge toward lihe low ground of the Basin of Paris ; from the plains of Languedoc the strata rise to- iirard the Pyrenees and the mountaiuB of central France ; the Pyrenees, the Apennines, the AIps die 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 asLes and centres of mountain groups, ia also related to them in amount, so that the angular value of the dip — or the number of leet iR one hundred that the strata decline— decreases

n 3

38 A Treatise 017 Geology. Gdap. Ui*

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 die 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 shaU 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 9, The strata do not descend from one mountain chain below the surface of plain countries more than a very moderate depth (four to yb miles) before they begin to rise again toward another axis of devated ground.

The principal mountain chains and groi\ps 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 Switier- land. Dr. Hutton and Werner studied the Scottish and Saxon chains, and Mitchell with a grand gene- ralisation referred ta the leading features of physical geography as a basis of laws of geobgical 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. lU. THE EXTERKAL PAHT8 OF THE GLOBE. 39

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 unustial FoHHons of Strata, Sc.

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 decUne from it on both sides as a, diag. No. 8. This is called an anticlinal axis, and ihe 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 unfrequently 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

▲ Tbeati6E On Oeoioot.

Chap. Iii.

pushed oatwards so that the strata usually lying upper, most in the group are actually for a short distance unaermost (e).

FauUi.

Besides these, other forms of disturbed 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 ''a dyke" ''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

y

from the vertiical by the an47 h y, and it said to have an underlay ; the strata are considerably depressed, and in such a manner that a perpendieular dropped from 6 would fall clear of the edges of the depressed beds ; not as in e, which represents a rare and excepttonal 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 inalldassea

CHAP. ill. THE EXTERNAL PARTS OF THE GLOBE.

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, in others full of angular dispersed fragments £rom the adjoining rocks sometimes a leeuier of one or more of the softer strata follows up the fissure for a con- siderable distance (hi) ; but frequently, as i, the fissure is closed. — See the annexed vertical section.

The surfaces of the fissure accompanying a fault are often remarkable, and affinrd 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 Jig. 11 . be any vertical plane crossing /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 £aoe/ F F' ¥"', one side oi fissure of the fault, is often scored by .grooves (gg) parallel to the direction of the disIooati<m ef the strata ; that is to 8ay> deep lines are ploughed on the broken ends of the rocks in the very duection in which they must have been produced, suppoung, as other pher nomena indicate, the rocks to have slipped along the pUoie of the fault A magnificent example of this ia

teen at CullercoaU in the great Tjnedale, dyke, of the Newcaitle Coalfield.

Extent and Frequency qfFauIU.

The extent of Tertical displscement occasioned b; faults Tariei from a few inclieB or ieet to tboniands of feet ; examples of the former are common, of the latter rare. When caiefiill; studied, howerer, the principal dirence between them — the extent of the movement, it the only one which appears constant and essentia]. This is obriously related to the force employed in pro- the fracture. That force may have been difirent. in amount in the two cases contnuted, or different in the duration of its exertion ; for the conformity of the drcumstancea 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 baa been impressed upon the masaes, as they appear to have slided in one direction, have been mbbed

Ohap Iii. The External Parts Of The 6L0Re. 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 adopts 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 efiPorts for a great fault like the Tynedale or Craven faults, of a thousand feet or yards, than for the numerous " hitches " in a coUiery 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 tibe contrary, when only a few faults occur in a district, and these have a great effect as to vertical move- fhent, 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, Faults are the most conmion 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 eittent, 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. Ohap. Iii.

Relation of FauiU, Mineral Veins, Dykes, Sc, to the great Lines of disturbed Rocks,

It is noticed as a circumstance of common occurcence, that mineral veins are no otherwise different faults than by reason of the fissures which these have opened in llie rocks being filled by sparry and metallic matters. This filling of a fissure constitutes a mineral rein ; a similar fissure fiHed by basaltic or other rocks would be called a rock dyke; if occupied by day and soft materials a day 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 folkxnped by the dis- turbing force, and how the fissure when made came to be fiUed with its arry rocky or soft argillaceous contents.

There appears to be some general velatioai 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 ftppears> from our own and other researches, thiU; the fissures accompanying mineral veins in the north of England, in the Penine Chain, and on die 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 rdated to axes of disturbed strata, (like the Stiperatones, Greenhow hill, &c.), that they sjaing out from such, or tend to cross them at right angles, and scarcdy appear anywhere abundant except in the vicinity of points or lines of great disruptioii of the rocks. Faults, dykes, and veins must, therefore, be referred, as to the origin of the fractures, to the same genend cause which placed the strata oi the moun taiis in their disturbed and inclined positions.

CHAP. ni. THB SXTEBNAL PABT8 OF THE GLOBE. 45

Before adopting definitively, the condusion 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 distinctiou 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 sab- stances.

Stratification is a form of matter seldom produced in perfection among the effects of modem 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 tiiese 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, so are the modem sediments from a river or the tide ; others are irregularly composed of oblique lamins, 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 modem nature.

46 A Treatise On Oeolooy. Ghap. Itj.

appear clearly to evince their aqueous origin no other essential differences being discoverable between , except the great thickness and extent of the anjcient rocks ; and could we raise for examination the bed of the Atlantic or the |editerranean perhaps a part of this discrepancy might vanish ; for Donati's researches on the bed of the Adriatic show the great extent of the modem 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 dree, the known pro* ducts of modem 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 igregations such as never occur among granites, basalts, porphyries, &c., ' which make up a large portion of the unstratified rocks.

But the difierence in their mineral aggregation is yet more remarkable. The ingredients of tibe 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 ; days were clearly collected from matter finely divided tod difiused or suspended in water. Sandstones are as clearly the accu- mulation of grains of quartz, or other minerals worn and

Chap. 112. The External Pabts 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 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 ftirnace 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 reliquite of plants and animals even to a greater degree than modem marls days 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 scoriae 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 ' diffs, among the pebbles, are rolled and fragmented particles.

It is, therefore, impossible to doubt that the strati-

48 A TREATISE ON GEOLOGY. CHAP. lit.

fied rocks holding remains of aquatic animak 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 eyidently produced in the same way are also of watery origin. All the really stratified rocks then are the product of watery 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 obe according to the aqueous or igneous agency concerned, and iall commice with the history of the deposits from water.

The most general view to which we are thus con- ducted, gives to aU the stratified rocks an aqueous, and to die unstratified an igneous, origin : the former were deposited from above, in calm or agitated water, aloi 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 die 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 occasional.

Chap* Iii. The External Parts Op The Globe.

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 (fig.12.}, certain old strata (abc,&c,) are found displaced

from their original nearly level position and thrown to high angles of elevation and other more recent strata (h ik) are placed level against the slopes, or even covering the ends of the former, it is plain that the dislocation of a 5 c happenied 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 imdis- 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.

B

A Treatise On Geology.

Chap. Iii.

angle below, and covered up by horizontal strata of red tnarl and lias, thus :

, Lias. Red marl.

"- 13

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 ihis 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 dear 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. IIL THE EXTEBNAt PARTS OF THE OLOBE*

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 respecting in their declinations the 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 lliese respects, there is said to be unconformity of the strata The place of this unconformity is the interval between the two 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 die strata, as shown on a map, and their relative inclination and exposures, as shown in a section. Thus in the map diagram (Jig, 15.),

y

/

the series of strata marked ahcdsre parallel in one set, and efgm another ; but their directions, or strikes, (S, S and a i) on the surface difffer, and the lowest of the upper set (e) rests in one place on a, in another on hf in another on c or d. ; the dips, D and (2, are in dif- ferent directions.

In a section (jafig. 16.), some difference of inclination

B 2

commonly occnra. But when the itnkeu and dipa ol ather the upper or lower let vary, which U a very com man case, the same disDrict, u Yoikihu'e or Deibyshire, may exhibit in the wme region both conformity and un- conformity between the same two sets of beds, as in the

map diagram (j. 17-)i wherea&cdare coal itrau, with variable dips and strikes, generally unconformed, but on the line W E, for a short distance, conformed to the saliferous strata lying upon them (e/g h). Tet, in this case, the section on the line W E would ex- hibit a want of conformity in the dip (as in fig. l€.), the beds abed being more inclined than e / g h. "Whea the strata are not in contact, or, for any reason the junction cannot be clearly sei, many obserratione of dip and strike in each wt ol beds will in general de- termine ihe exietence of UQCtnformity : but it would be folly to rest so important a decision upon tatimong iet demoTittralive than the coimtry will yield ; and, in some cases, snffident evidence is unattainaUe by any exerdon of industry and skiU.

Chap, Iv.

SEBUiS OF STRATIFIED BOOKS*

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 dee 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 strucr 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 die 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 miist be on no account omitted, for these

E 3

54f

A Tbeatisb On Geology.

Chap. Iv.

limited diflferences are often more important in theory (as well as in practical applications) than all the general resemhlanoes. Assuming that the British islands form such a natural district, we shall he ahle to present a satisfactory general tahle or section of the series of strata which here compose the crust of the glohe, placed in the order of their succession downwards, from the sur- face of the most recent aqueous deposits.

Table of British Deposits* Superficial AccumtUations.

Soil Alluvial depositiont.

Diluvial depositions.

From the ordinary action of springs, riTeri,

lakes, the sea. From unusual and violent operations of water ,

Stratifuo Bocks. Tertiary Strata,,

Names of form- ations.

Crag.

Freshwater marls.

London clay.

Thick, ness in yards.

Subdivisions or groups.

Upper or red crag.

Lower or cocalline crag.

Upper freshwater.

Estuary beds.

Lower freshwater.

London clay. Plastic clay.

Nature of the deposits.

Marine shells, pebbles,

sand, Sec Marine shells and corals

in sand, or coarse lime- stone. Marly limestone and

clays. Marine or estuary clays,

marls, &c. Biarly linestone and

clays. Clajr with septaria, ftc. Variegated sands, clays,

lignite, &c.

Chalk.

Oreeu sand.

Soo

Secondary Strata,

Cretaceous System,

Upper chalk.

Lower chalk.

Chalk marl.

Upper green sand.

Oault

Lower green sand.

Soft chalk, with flintiin

layers. Harder chalk. Soft argillaceoiis chalk. Green sands. Blue marl or clay. Ferruginous, brown, or

green sand, with lo.

cal deposits of lime-

stonok

CHAP. IV. SBRIBS OF STRATIFIED ItOCKS.

Oolitic Systenu

Names of form- ations.

Wealden.

Upper oolite.

Middle oolite.

Lower oolite.*

Liaa.

Thick- ness in yards.

S00-(

Iso

850'

Subdivisions or groups.

Weald day. ,

Hastings sands.

Purbeck beds. Portland oolite.

Kimmetidge clay. Upper calcareoub

grit Coralline oolite. Lower calcareous

grit Oxford clay. Rellowayrock.' Combrash. Forest marble.

Great oolite.

Fullers* earth. Inferior oolite.

Sand.

Upper lias shale. Marlstone.

Middle lias shale. Lias IJmestbne.

Lower lias marls.

Nature of the deposits.

Clays and calcareous lay- ers.

Variously coloured sands and clays.

Clays and limestones.

Limestone, often cherty, with sand.

Blue clay, with septaria.

Sandstone (calcareous).

Oolitic limestone. Sandstone (calcareous).

Blue clay, with septaria.

Sandstone (calcareous).

Coarse limestone.

Coarse limestone, sands, and clays.

Limestone, oolitic, com. pact, or sandy.

Limestones, clays, &c.

Limestone, oolitic, fer. ruginous.

Calcareous or ferrugi- nous sand and sand- stone.

Blue laminated clay.

Sandy, calcareous, and irony beds.

Blue laminated clay.

Blue and white com- pact limestones.

Clays of diflferentcolours.

Salerotu or Red Sandstone System*

New red stone.

sand.

Magnesian lim stone (North of England).

100 -(

Variegated clays.

Red and white sand* stone. '

Knottingley lime- stone.

Gtpseous marls.

Magnesian lime- stone.

Marl slate.

Rothetodteliegende.

Red, greenish, &c. clays.

Red and white sandstone and conglomerate.

Grey laminated lime- stone.

Red and white clays, &c.

Yellow, granular, &c., limestone.

Laminated dalcareoua beds.

Red sandstone* and clays.

Aa seen near Bath. In other parts of England it offers important differences, aa will appear hereafter.

B '4

A. Treatise On Qeoloqy,

Phap. Iv.

CarbonyeroiLS System,

Names of form, ations.

Coal.

Carboniferous

llmcfitone (N, of England).

Old red sandstone (Herefordefaire),

Thick- ness in yards.

\m.

to

Subdivisions or groups.

Ludlow rocks.

Wenlock rocks.

Caradoc rocks. Llandeilo rocks.

Plynlymmon

rocics. Bala Limestone.

Snowdon rocks.

The subdivisions are only locally ascer- tained.

Millstone grit

Yoredale rocks.

Scar limestones.

Alternating sand- stones and lime- stones.

Conglomerate group.

Cornstone group.

Tilestone group.

Silurian System,,

Upper Ludlow rock. Aymestrylimestone. Lower Ludlow rock.

Wailock limestone

Wenlock shale.

Limestones and

sandstones. Conglomerates, 8tc.

Nature of the deposits.

Strata of sandstoneale ironstone, with rare deposits of marine or freshwater limestone.

Sandstones, often coarse, grained, or pebbly ; shales, ironstones, tmn limestones.

Limestones, sandstones, shales, coaL

Limestones.

Limestones, sandstones, &c., often red.

Conglomerates and

sandstones. Coloured clays and con-

cretionary limestones. Flagstones and clays.

Laminated sandstone. Subcrystalline limestone Sand shale, with con.

cretionary limestone. Grey and blue subcrys.

talline limestone. Siale and earthy lime.

stone. Laminated limestones

and sandstones. Gritstones, conglomer.

ates, limestones. Dark calcareous flags,

stodstones, &c.

Cambrian or GrauwackS Sh/stem,

s

Q

a

S

Argillaceous indurated rocks, sandy or slaty.

Dark laminated lime- stone and slate.

Fine and coarse-grained slaty rocksl

Skiddaw or Clay Slate System,

Clay slate. Chiastolite slate.

Hornblende slate.

e

o e

Uniform dark slate.

The same, with chiasto- lite.

The same, with horn, blende,

OB A p. IT* SEBISB OF STRATIFIED ROCKS. 57

Mica Schist System,

The subdivisions are only locally ascertained, Chlo- ritic schists lie in the upper parts; quartz rock and primary limestones are interposed among the beds of mica schist.

Gneiss System,

Mica schist alternates with gneiss which is diter- sified by beds of limestone and quartz rocks.

peneath all these systems of stratified rocks the pro* duction of water we find in all places where the base is clearly seen a mass of granite and other unstratified rocks the effect of great and pervading heat. Basalt porphyry and other igneous rocks are frequently found protrudkig through the strata along antidikal axes and penetrating them in dykes along the course of faults and fissures.

In possession of this complete section of all the prin-> dpal masses of stratified rocks in the British isles and guided by a map of the ranges of each of these on the surface* — aware also that within the narrow compass of these islands some of the groups of strata vary extremely (as the lower oolites which are prin- cipally calcareous near Bath but principally arena- ceous near Whitby) and others have only a limited range (as the magnesian limestones) we may proceed to inquire how far the sections of other natural districts agree with that given above.

Throughout the great basins of £urope and parts of Asia and Africa including the countries bordering on the German Ocean the Baltic the Black Sea, and the Mediterranean wiUiin the mountain boundaries of the Ural, Caucasus, Greece,Calabria, the Atlas, Western Spain, Brittany, Cornwall, the west of Ireland, Scotland, and Scandinavia, the same general divisions, viz., primary, secondary, tertiary, and supficial deposits occur, and the

A geological imp of the British Islands haa been oonatnicted by the author of thU treatiae, at a moderate price.

58 A Tbeatise On Geology. Chap It*

general features and succession of these great classes are the same : most of the systems of strata are also to be re- cognised, either in the mountains or the lower ground ; and fresh additions to these analogies are continually added by geological travellers. But when we come to consider the constituent ybrmaion, discordance is ma- nifested of the same kind as that which, as before ob- served, appears between different parts of England with respect to certain oolitic and carboniferous formations.

Among primary strata, for example, the day slate, grauwack and silurian rods, are little known in the Alps; while' mica schist and gneiss are rare in the Harz, Cornwall, and Wales* There is more carbo- niferous limestone in England and Ireland than in all Europe besides. The oolites of Germany and France sometimes perfectly resemble, in composition and succession, that group in England; but on the' Italian side of the Alps, and in Greece, they have different characters. The chalk formation is little seen about or beyond the Alps ; and, in the Carpathians greensand appears in plenty, but little or no chalk. Turning to more distant localities, we find, in North America, primary, secondary, tertiary, and superficial deposits, much aUied to those of Europe, grouped, for the most part, in similar systems ; but the series be- tween the cretaceous and carboniferous rocks is much less developed than in Europe. On the contrary, in the Himalaya mountains, and the basin of the Indus, these formations are greatly developed, and rocks of the lias and oolitic formations are perfectly identified. As a general result, it appears already ascertained that the same great divisions of strata may be applied to nearly aU parts of the globe ; that, even in very distant local- ities, the same systems of strata were produced, though sometimes in isolated patches ; but that the particular formations, though often very extehsively spread, are yet somewhat irregular in their expansion, some extending in one direction, and others in a different one, so as dearly to evince their dependence on local and variable conditions.

CHAP. ir SERIES OF STRATIFIED ROCKS.

S9

Varieties of Stratification.

Stratified rocks are either of equal thickness over a large extent of <ft)untry, or uttenuated to a wedge shape in some one direction or decreasing in thickness every way from a certain point or district, so as to constitute a knticvjktr formation. Strata of one certain kind of rock, which are, in some places, accumulated into a uniform mass, become divided in other districts, and separated into distinct members by the interposition of wedge-shaped deposits. All these circumstances are represented in the annexed diagram (yjr.lS.), where

limestone strata are marked I, slate beds s, gritstone g ; the gritstone and slate being in lenticular or wedge- shaped, and limestone in {Jarallel, beds, divided in one direction, but conjoined in the other.

By observations of this kind in Certain districts (e. g., in the north of England, along the Penine chain, and on the Yorkshire coast), it has been inferred, that the different strata of limestone, shale, and grit, have originated imder different circumstances; the former being an oceanic deposit, but the two latter substances derived from the waste of ancient lands bordering on the sea in which the limestone was formed. This con- clusion is strongly corroborated by the fact, that it is chiefly or wholly in gritstones and shales that land plants occur, while the marine exuvis of shells, corals, &c. abound almost exclusively in the limestones.

The term stratum or layer is of general signification, and independent of the absolute thickness of the mass :

A Treatise On Oboloot.

Ohap, It.

by some writers (Dr. Smith and others) it has been used to express the whole of one mass of layers or beds of the same or nearly the same quality (as the Bath oolite) or one similar series of alterations (as the Weald day). By others (Playfair, &c.) it is applied to the thinner layers of rocks which Smith denominates beds. Neither mode is perhaps inaccurate yet it is conyenient now to settle the nomenclature we must employ in the following descriptions.

Many rocks as limestones are divided by parallel or nearly parallel seams into what are by the quar- rymen called beds or posts,; in some cases these are further divisible into lamina. Moreover it is the custom of geologists to include several rocks which are generally concomitant, and have some common cha- racters of deposition and organic remains, under one title, viz. formation. The subjoined diagram (fy, 19.) will illustrate the use of these terms.

Formation of Bath oolite above.

lias formation.'

Upper lias shales.

Maristone.

Middle lias shales.

Lias limestones.

Lower lias shales.

Formation of red sandstone below.

The shales in this diagram (ace) are from 20 to 300 feet thick, and are composed of lamina parallel to the planes of stratification ; the limestones (b) are thin

CHAP. IV. SERIES OF STRATIFIED BOOKS. 6l

bedded, the beds being separated by thin days: the marlstone series (d) consists of sandstone beds calca- reous beds and ironstone bands, separated by thin clay or shales.

The lias formation is included between the Bath oolite formation above, and the red sandstone formation bdow.

According to this mode of description, the word stra turn need never be used as a special term of definition, but reserved for general reasoning. The word series is found to be extremely serviceable in designating a number of similar or similarly associated rocks: the arbitrary word group is also convenient in geological description.

The lamination of rocks ofiers some interesting facts. Some beds of gritstone (as a) are composed of lamins parallel to thie plane (tf the beds ; such lamination is generally produced by the alternation of mica, whose broad plates cause a partial disunion of the parallel lamins of quartzose grains. Other beds (as 6) are com- posed of oblique or curved laminee, a circumstance gene-

— -- — 2" rally dependent on the irre-

"" gular admixture of pebbles

?", shells, or particles of un-

equal magnitude. The

former may be supposed to

be tranquil, the latter dis*

In shales and other argillaceous rocks, nodules of ironstone or limestone, aggregated round some solid

—

/

bodies (as a leaf or shell), are frequently included, and sometimes these interrupt the lamination of the

62 A Treatisb On Geology. Ohap. Iv.

shade as in fig. 21. Such nodules are frequently traversed by plates of calcareous spar and these receive the name of septaria.

In limestone beds the nodules of chert in chalk the nodules of flint, often appear to have been aggregated round some previously solidified sponge coral, or shelly This process of accretion round a nucleus is beauti- fully exemplified in certain '' oolitic " limestones, so called from their being composed of spherical grains. Each of these consist of several concentric coats col- lected round a previously solidified body as a minute grain of sand, fragment of 'shell, or other centre of at- traction. Radiating fibres frequently cross thespherr ical shells.

Something of this concretionary struc- ture appears in particular unstratified rocks (as pitchstone); but in general all the appearances previously described belong to the stratified formations ex- clusively.

Divisional Structures,

All rocks are traversed by divisional planes of less or greater width and frequency and thus divided into masses of definable shapes and proportions. These joints," as they are often called, present themselves under a great variety of appearances but almost always such as to be intelligible on the supposition of the mass of the rock having been contracted, so as to separate into prismatic and other forms as day, starchy &c. contract and split by drying.

The joints vary in their combination so as to pro- duce masses of different forms in recks of different nature: they also vary in rocks of the same nature which are of different antiquity : their frequency and regularity also depend upon . the mineral aggre- gation of the rock : it is further probable that they are somewhat complicated with additional fissures near axes and centres of. elevation or depression of rocks.

Us. 63

Among tmetraUfied tocIcb the most remarkable and

best known form is that of the divided priama of

basalt, as seen in Staffs and the

Giant's Causeway. This appearance

,1: arises from the intersection of planes

S<. reciangulated to the surface of the

' rock, and meeting one another in

j'i- seTeca! directionB, so as to insulate

polygonal prisnis. These prisms are

divided across, by concavo-convex surfaces, aa fy. ZS.

Much more common in these rocka is the form of an irregular polygonal prism not divided acrosE, aa in the greenstone and pitbBtone of Corygills, Arran. It is interesting to observe, in vertical dykes of these rocks - (as in Cleveland, Yorkshire), the prisms lying hori- zontally, and in other cases curved (aa in Staffa), in . obedience to the general bw of the planes of the prismatic faces being at right angles to the bounding surface of the mase.

Many rocka of igneous origin (as greenstone, clay- Stone, porphyry, sienile,) show this prismatic structure more or leas distinctly, but none so perfectly as baaalt

A prismatic form of the masses is found also among stratified rocks, when these are very thick and of uniform composition, as in the rock-salt mines of Northwich (observed 18S7), in the gypsum quarriea of Montmartre, and in the thick scar limestone of Wharfdale (ob- served 1834).

A great variety of other appearances are presented in the stratified rocka by the various directions and inter- sections of the itifferent aorts of joints.

Under particular circumstances, and especially in the vidnityof faults, andclinal axes, and other forma of dis- placement, the beds of rock are frequently cracked in their substance ; sometimes ihae cracks are filled with sparry subatsnces (carbonate of lime frequently, me. talc matters rarely); sometimes the]| are very minute chinks lined on the aides with dendritical oxide of iron or manganese, in which case they are called dry cracks.

Their direction is very inpilar, and there h do doubt that in many cases they are the effect of mecliaiiical strain or tension in the man of rocks which accom- panied the displacement of the rocks. Near the antj- clinal axes of Ribblesdale, sparry cracks are wonder- fuUy numerooB ; but away from these axes the level beds are little matted by such accidents.

Besides these irregular cracks (c), which ofteo do not pass dirough the whole mass of a bed, are oinf (j) which divide at least one bed, and often sevtral, and which eshitnt some regularity of direction ; these are so situ, ated in the difinent beds, have such diveraity of slopes, irrularity of number, openness, and other characters, and are so abundant in ntnatJona far from Unes and pointa of displacement, as to leave no doubt that they are due to a very genml cause.

Amongst these joints, some more open and extended, than others, passing through a greater number of beds, dividing a whole rock, or even a conmderable portion of a formation, may be distinguished as fissures (/) or mat- ter jointt. The diagram,. 24., is intended to convey a conect notion of &ese several divisional planes.

Viewed on a horiiontal plan, joints frequently end in fissures ; and these latter commonly exhibit a great de- gree of local sywnetry. In the mountain limestone districts of the trf England, the arrangement of the flisnrei bat been aicertained to be correctly repre-

<3Hap. Iv.

Series Of Stratified Rooks.

'sented by the following diagram in which the breadth of shade in any direction corresponds to the number of fissures observed. Thus, in the direction N. N. W. and S. S. E., and E. N. E. and W. S. W., and about these lines, a greater niunber of fissures occur thus producing two principal systems of divisions in the rocks at right angles to eadi other; while in the lines N. E. by N. and N. W. by W., and about these lines few or no fissures have been noticed. Thus there are positive and native axes of frequency and rarity of the fissures situated at right angles to each other respec- tively. The same result of predominance of fissures in N. N. W. directions is found to obtain in Derbyshire (Hopkins), in Cornwall (De la Beche) and in some districts of Ireland (Griffith).

The efiect of these fissures in causing lines of weak- ness of the rocks may be understood from the diagram : the breadth occupied in each radius being proportioned

Tol. X.

A T&Eatise On Geology.

Chap* Iv.

to the number of long joints or fissures, obsenred in that direction.

The following is the table of obsenratioiis referred

General Table of Results for the Seoondabt

Rooks of Yorkshire.

Namei of Fonnationi.

S5

S

z

T

T

z

a:

S

&

?5

5?*

p4

3;

(d

cd

H

Pii

p4 (4 (id

(4

Bfafmetian lioestoue Coal

Millstone grit - Chert group - Yordaie aerie* - Lower limestone Red sandstone Whin siU

?

T

s

It appears that ime remarkable differences of cha- racters belong to the joints and fissures in rocks of different chemical and mineral quality. In limestone the joints 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 rolcks that joints are most numerous and symmetrical. If we compare in this respect the old aigillaceous shite, to the shide of a coal tract, aind then with the clays of an oolitic district, or make a similar comparison of the ancient primary

Geology of Yorkshire, ¥oL ii 97.

luneMone of the highlondB, with Ae calckreona rocks of later production, this dependence of the ftcquency and reg;ularit7 of joints, on the age of the rocks, will dearly

Cleavage.

Among the argillaceous slate rocks, a fiutheT pecu- liarity of internal itmcture takes place, which ig deterv- ii of special attention, mnce it appears to be the cue of diviiional planei carried to extreme in uomber and synunetiy*

Thia atructure, commonly called cleavage, really distinct from joints and stratification, and may be, per. hapi, nndentood in its relation to these by the accom< panying sketch.

In this drawing, S is a plane of stratification dipping in the direction ; c c are the edges of planes of cleav. ige, which in the plane 8 continue in lines <f. These planes are continuous, and very numeroua in the fine

6s X TREATISE ON GEOLOGY. CHAP. IV.

grained beds s, which alternate with the coarse bedcT g g, but in these latter the lamins of cleavage are often totally absent. / is a joint which varies its angle of dip in the different beds of rock. The line / 1, at right angles to the dip of the strata is called the strike of the bed, and is of course level ; and it is frequently observed that the horizontal line, or strikef the cleavage, coincides with the strike of the strataThe planes of cleavage ge- nerally approach toward theierpendicular, 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, Chamwood 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 lamime of cleavage cross highly contorted beds of slate dipping in various directions.

There are good reasons for thinking that this cleav- age of the argillaceous primary 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 days are so altered near the axis of elevation, as to assume much of the aspect of an old slate country.*

For luggestioai to obwrren on the subject of deaTafe and Joints, and a method of calculation to be applied to cases of inclined strata, see Guide to Geology, Sd edition. The Geological Intersector, a small and cheap in. strument, which has been constructed by the author, and engraved by Mr. Lowry, may be used to tepreient 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 hut for the innu- merahle testimonies of elapsed periods and perished creations which the stratified rocks of the glohe 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 tho rocks have heen suggested hy the examination of these interesting reliquiie 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 earthy 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 kinds and ages ; and thus present a large field of contemplation to the philosophic geologist.

FmsU Plants,

The oianic 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 plante 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 Treatisb On Oeoloot. Ohap. T.

But the total number as &r as yet known is wonder- fully disproportionate. For if we estimate the recent species of plants at only 60000, and the fossil races yet clearly distinguished at 600 numbers which are per- haps equally below the truths 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 surfnoe drainage ihat vegetables are carried abundantly to the deep. And, since most of the marine' plants are nataat or confined to rocky shores, there woul4 be little reason in expecting these to be common among the oceanic sediments.

We must fturther 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 sufh- 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, cycadeie and other tribes, resist decomposition for a long time. Hence, it is no , wonder that such races of plants are the moat quently met with in a fossil state.

The ligneous parts of plants are sometimes (in the blue days of the oolitic formation especiaUy) 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 in-

CH. y. ORGANIC REMAINS OF PLANTS AND ANIMALS. 71

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 ihem, and a brown carbonaceous or pchraceous powder. 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 fera 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 ihe 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 usuaUy in fragments the branches and leaves scattered, and roots generally wanting altogether. One case, indeed, has been appa* rendy 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

A Treatise On Oboloqy* <;Hap. T.

bility ttiat the earliest indications of life on the glohe shoved be of the vegetable kingdom may be somewhat astonished to leam that traces of plants are really not known in a distinct form in strata so ancient as those which contain the shells of Snowdon and Tintagel (Snowdonian rocks), and that they are almost unknown even in the silurian system. What is calculated to add to this feeling of surprise is the circumstance that in the next system of strata which lies upon the silu-, rian, two of the formations are the repository of most enormous accumulations of fossil plants ; for in these rocks principally lie the coal beds of Europe and America, which are nothing else than mass of chemi- cally altered vegetables. How vast must have been the luxuriance of the vegetable world at that era in par- ticular 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 imimportant deposits, of coal in the oolitic system of Sutherland, Yorkshire, Bomholm, and Westphalia which are chiefly formed of cycadee 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 fossil plants, presents the following comparative table of the extinct and living classes of plants : —

3H. y. OROANIO REMAINS OF PLANTS AND ANIMALS. 73

CryptogamJA cenulosa ' ' Taiculosa PbanerosaiaiagTniiKMpeniiia

inonocotyle.7

donta J

dicotyledonia

Indeterminate

First Period.

Second Period.

Third Period.

Fourth Period.

a

Is

s

S6

len

Laving.

82,000

50,350

The first period ends with the carhoniferous system ; the second includes the saliferons or new red sandstone system ; the third comprises the oolitic and chalk sys* terns ; the fourth is the tertiary period.

The numbers of species are now considerably aug- mented since the table was drawn up (1829)> but the proportions are not materially affected. It is still truey that yacukr cryptogamia abound in an extraordinary degree among the earlier rocks where ferns, calamites, and what seem like gigantic lycopodiacee 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' lycopodiacee 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 dose 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 firom every other that preceded and succeeded it.

Fwsil 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 0E0L06Y. Chap. V.

is further remarkable that few traces occur of any other zoophyta than such as like the Uthophyta,, secreted stony .supports ; or like spongiadse had an internal homy or spicular skeleton; or like echinida were covered with a crustaceous skin : the soft medusidse holothurids &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 growl : 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 silurian and grauwacke 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 spongiade, siliceous spicule and fibres enter into ihe cdceleton 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 oidy the external im- pression or mould. These circumstances depend pardy on the nature of the rock in which they are imbedded, and partly on the composition and texture of the original body. In Umestone zocks the substance of coral is usually

OH. y. ORGANIC BBKAINS OF PLANTS AND ANIMALS. 7&

little changed except by the introductioii of calcareous or siliceous matter into the minutest interstices ; but in the same drcnmstanoes the crusts of echinida and stelle rida are converted to crystallised calcareous spar. £ven in arenaceous and argillaceous strata and amidst flint nodules where eyery 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 ponfer 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 as8embli;es of forms have existed at different ancient periods which are all now extinct. Yet it is certain that the differences are mossy only such as belong to species genera and families those minor groups of orders and classes which most diinctly reveal difierences of physical condition while agree- ments of a very general kind permit nearly all fossil zoophyta 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 fossil 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 occur in the Bala limestone ; abound to admiration in the calcareous

A Treatise On Geology.

Ghap. V.<

parts of the silurian system and in the limestones of the carhoniferous rocks. The magnesian limestone has a small number ; certain ooUtes are fiill of them ; the green sand amd chalk yield great plenty of sponges ; the isalcareouB and arenaceous terdaries of France ftirnish 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 probably more fossil than reynt species, if we exclude from the latter, those whose bodies are unconnected to stony or homy 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 any of the pri- mary strata. Crinoidea, however, occur in the silurian rocks, and they are more plentiful in the carboniferous Umestone, than in any older or more recent deposits. £chinida first appear in the carboniferous limestone, but become far more numerous in the oolitic and chalk systems. Stellerida are, we believe, unknown below the oolitic system. Sponges are by far most numerous in the cretaceous rocks.-

Syttemi.

LameOiferse.

Crinoidea.

Echinida.

Stellerida.

Tertiary

Cretaceous

♦

Oolitic

3|e

Redianditone

Carboniferous

P

Silurian

Lower systems

?

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 laie 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 ANP ANIMALS. 77

MoUusca.

Recent mollusca are prindpaUy found at mode*- rate depths in the sea and respire the air contained in water; some particular tribes liye in fresh water and either breathe the air in water, by branchiej, or come to the surface to respire by lungs ; others liye on the land. In a very few cases certain stratified masses appear to have been accumulated either in limited areas of fresh water or in estuaries so much under the influence of riyeis and inimdations as to con* tain land and fresh-water shells alone or mixed with the exuyis 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 £urope the proportion is n9t yery different. In the existing economy of nature, howeyer, 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 frresh waters were but scantily suppfied with mollusca; for, in the first place, their remains would seldom be transported to the ocean ; and frirther, 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 difiicult to estimate, for it is certain that great additions will be made to both the catalogues.

It is not entirely without reason that geologists havi been long accustomed to look on the study of fossil sheUs as more instructive with regard to the. physical conditions of the globe in, ancient times than, most other reliquic of animal life. They are of all fossils the most numerous, the most generally diffiised through rocks of aD ages, most perfectly preserved, and of such definable forms as to be easily described, figured, and

78 A TREATISE ON GBOIiOOT. CHAP. V.

recciniaed. The state cf perfection in which many delicately ornamented shells occur is such as to leave little doubt of their having been qiiietly entombed on or near the spots where they lived in the deep sea ; while 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 share.

The hard calcareous coverings of mollusca are per- fectly preserved in a fossil state but it is a rare thing to find a trace of the perishable parts ; even the semi- calcareous hinge lament of bivalves is rarely observed in cardia and venerids.

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 hme 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 lamelle of alternating membrane and carbonate of lime, have resisted in almost all rocks, argil]|iceous, calcareous; arenaceous, the che- mical changes to which venerids, trigonie, and others of an apparently compact texture, have completely yielded. While the former retain their lamelle and pearly surfaces, the latter have often been whoUy 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. troduoed by filtration through the surrounding rock. In other cases siliceous matter, pyrites, and other subu 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 Sheik In PhU. Traoi*

€H. V. Organic Remains Of Plants And Animals. 79

is a remarlcable instance of the force of original struc- tuxe in controlling the effects of chemical agencies; for in clay sands chalky flinty UmeBtone pyrites, this sin- gular fossil generally retains its fibrous structnre, co- lour translucency and chemical properties ; while in the same masses echini are changed to calcareous spar and sponges to flinty and many shells totally vanished.

The conclusion which so strongly forces itself on the mind of an observer who considers the shelly treasures jof the stratified roclcs 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 exuvie are known. In the present seas, some shells, like the oyster, are gregareous, and cover large surfaces, so as tcT 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 modem sandy bays ; terebratuls and Unguis 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 moUusca.

But on a great scale they present very important truths. From the ancient slates of Snowdon to the most modem 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 a{so the proportionate number to every 100 feet thickness of strata, are given for the successive systems : —

' Guide to Geology, 3d edit jx 68.

Bo

Treatise On Geouoqy*

Chap. V.

Living m Tertiary Cretaceous Oolitic Saliferous -

Carboniferous

Silurian and Grauwacke

ThickneM of Strata.

tol 0,000 J 20,000 1 or more J

No. of Species to 100 feet thickness.

3*6

vr

The most predominaiit of the recent fonns of mol- Ittsca are the classes of Conchifera/ Gasteropoda and Cephalopoda ; these are also the most numerous, in a fossil state for of pteropodous molluscaa few traces only occur in the tertiary strata. If the recent species of shelly mollusca be supposed to amount to 5000 species, the numbers belonging to each of these great classes may be stated thus, —

Conchifera - - 1800 Gasteropoda - - 3100 Cephalopoda - 100

As far as yet is knownj, the same dasses, in a fossil state, contain--*

' Conchifera - . 2130

Gasteropoda - 2276 Cephalopoda . 698

If we analyse the classes, greater discordances appear. Thus the existing conchifera ranked in three groups, present the following numbers, —

Conchifera plagimyona (LatreiUe) - 1400

Mesomyona (iig<r.) - 850

' Brachiopoda - 50

but in a fossil state the numbers are about,

#

Conchifera plagimyona - 1030

Brachiopoda - - 380

In the same way it appears, that while in existing

:

CH. v. ORGANIC REMAINS OF PLANTS AND ANIMALS. 81

nature the shelly gasteropoda ranked in two great divisions, according to their principal food, give the following proportions : —

Herbivorous gasteropoda' - 1400

Zoophagous - 1700

these divisions, in the fossil state, yield, —

Herbivorous gasteropoda II60

Zoophagous — — — - 1110

It appears then, that the fossil world of moUusca differs remarkably from the actual creation in the greater proportionate abundance of cephalopoda, herbivorous gas- teropoda and brachiopodouB 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 : —

Concbifera plagiroyona

mesomyona -

brachiopoda

Gasteropoda phytophaga ' zoophaga

Cephalopoda -

Fowil.

Recent.

These differences, however, are by no means equal in all the several systems of strata : tliey are least in the tertiary, and greatest in the older classes of rocks. If the total number of shelly moUusca in any one sys. tern be called 1000, the proportionate number of the several classes may be seen in the following table, and compared with the recent creation.

Conehifera plagimyona brachiopoda

Gasteropoda phytophaga soophaga

Cephalopoda

Pri- mary.

S29

Car-

boni- ferout.

S50

So? 84S

Sali. fer- ons.

OoU- tia

Creta-l ceoui.

S46

Ter- tiary.

Living

30

A Treatise On Geology.

Chap. V.

The analogy of the tertiary to the actual system o£ organic nature is yery 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 moUusca 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. — Geneba containing many Living Species.

(gasteropoda.)

B

a

leurol ma.

Living species

S

&

s

In tertiary strata

Sso

In cretaceous system -

S

In oolitic system

t

In saliferous system

In carboniferous system

In primary strata

In this Uble the strong analogy of the tertiary and living forms of animals, and their distinctness from those of earlier date are very decided,

Taken the Quide to Geology, 9d edition.

Ch. Organic Kemain8 Of Plants And Aniual8. 83

Table II. — Gbneba oontainino hakt Fossil Species.

(Conchifeba.)

s

s

Living species

£

s-

g

s

a N4

In tertiary strata

In cretaceous system -

In oolitic system

4Q

In saliferous system

1?

In carboniferous system

Si

In primary strata

So

The unequal periods of existence of different genera are here very apparent. Producta after existing in primary 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 Uves*

Table III. — Genera of Cephalopoda.

Living spectei

t

h

a

§ S

a

a

t

mm

s s

s

In tertiary strata

?

In cretaceous system

In oolitic system

Im

In saliferous system

In cartxtniferous system

S8

S3

In primary strata

Most of the fossil cephalopoda belong to extinct genera : of these, bellerophon and orthoceras are con- fined to the primary and carboniferous strata: hamites,- scaphites, &c. are almost peculiar to the cretaceous system (a few only in the oolites), Belemnites belong to the oolitic and chalk locks exclusively*

o 2

These are extinct forms, and while tlie greater number of apeeies and subgeneia abound in oolitic, and many in cretaceoua rocks, none occur in tertiary' rocks ; one group occurs in saliferoua, and different types in car- boniferona and primary strata.

TbuB general and particular renilla all agree in de- monstrating that the physical conditions of the ancient ocean nin have been very dififerent in aome respects from what obtain at present ; and that theae con- ditions were subject to great variation during the Img periods which elapsed in the formation of the cniat of the earth. In the course of these changea whole groups of animals perished ; others were created, to perish in their turn ; and these operations were many timei re- peated, not only before the present races of animals were formed, but even before the relative numben in the leading groups approximated to the proportions which appear in the actual sea.

Artinalaied AnimiJ*.

The annulose animals form two great wriei; thOM without jointed feet, viz., vermes, annnloaa, drripeda; and those with jointed feet, viz., inaecta, myriapoda, arachnida, Crustacea. Many of the vermes being wholly

Ch. ▼. Organic Remains Of Plants And Animals. 85

BO% 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 shelly annu- losa are very numerous. Cirripeda are not plentiful and only found in the upper secondary and in tertiary deposits. If we might venture to refer to the articulated animals some portions of the marvellous infusoria whose true structure has lately been developed by Ehrenberg the fossil Tripoli of Bilin and Franzenbad (Bohemia) full of gaillonella navicula and other microscopic animalculay should be mentioned as almost wholly composed of the skeletons of articulated animals with jointed feet. 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 very rarely met with in a fossil state. Arachnida and myriapoda, equally unknown in the sea, aro as little common as fossil insects; but Crustacea, mostly a marine race, are not unfrequent in aU 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.

tacus.

ti

t

living

♦

Tertiary

Cretaceous

♦ ?

Oolitic

Saliferoufl

Carboniferous

Primary

The whole great family of trilobites, including many other genera besides calymene and asaphus, con&ied to the primary and carboniferous strata.

a H

86 A Treatise On Geology. Chai*.

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 ahout 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 speedily change. One reason of the comparative pau- city of fossil fishes may be their enonnous destruction for food ; thus they perish in greater proportion than the other inhabitants of the sea In the presit 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 soimding 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; 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 undeigone 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 difis : considerable agi- tation accompanied the deposition of fish teeth in most of the oolites, wealden beds, greensand layers, &a But in the tilestone of the old red sandstone, fishes lie in great perfection in Herefordshire and Brecon, as well as at Arbroath in Scotland ; the amblypteri, holop-

€H. V. Organic Remains Of Plants And Animals. 8?

tychi, &c. are very perfect in the coal measures of Newhaven and Burdiehouse near Edinburgh, Bradford Yorkshire the Hundrilck &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. Beddes these, tlie 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 fraents which occur in modem 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 h'me. 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 coloiu* 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

o 4

88 A Treatise On Geology. Chap. V.

the ancient and modem finny races of lakes rivers, and the sea and many attempts were made to ascertain these analogies. But until modem times the knowledge of the stmcture and functions of fishes their comparatiTe osteology and lepidology (to coin a useful word) was of small yalue 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 stractural and functional differences has not in general been much attended to among vertebrated animals ; though the hair of mammalia feathers of birds the tuJced or plated skin of reptiles the scales of fishes might have allured inquiry into the vari- ations which they undergo and 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 coverings 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 fishes, 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 ; buthat 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

0H y. OROANIO BEHAIN8 OF PLANTS AND ANIMALS. 89

with a second scale of organisation nearly as complete and as distinctly rdated to time, higher in the ranks of creation and therefore more sensibly dependent on phy steal conditions than the well known and justly vidued series of remains of moUusca.

The orders of fishes according to their scaly cover- ings are four ; riz.

1st. SCALES ENAMELLED.

Placoid fishes whose skin is irregularly covered with large or small plates or points of enamel as the rays and sharks (Etym. a hroad plate) occur recent and numerous in the fossil state heing found in nearly all the systems of strata though the genera are mostly peculiar in each system.

Ganoid fishes are regularly covered with angular thick scales composed internally of bone and exter- nally of enamel generally smooth and bright. (Etym. yavc<;, splendour). Occur recent but more abun- dantly in the fossil kingdom in which fifty extinct genera have beep recognised.*

M. Agassiz appears to have' ascertained that the strata below the cretaceous rocks contain very few if any, other fishes than such as are included in these orders.

2d. SCALES NOT ENAMELLED.

Ctenoid fishes have their scales of a homy or bony substance without enamel ; serrated or pectinated on the free posterior margin (whence their name from %ruf, a comb).

Cycloid fishes have smooth homy or bony imena- melled scales, entire at the posterior margin, with concentric or other lines on the outer surface. (Etym. xvxXo, a circle.)

To the last two orders with unenamelled scales be- longs by far the greater proportion of existing species

Bucklaiid*s Bridgewater Treatise, p. S70.

of fithe*, which, according to Cuvier, exceeded 5000 ; but are sUted b; M. Agamz to inHnint to 8000. On the contniy, (he greter number of fossil fishes bdong to the two orden with enamelled Koles. In the fol- lowing table the geological distribution of these oiden is sketched.

Uilnt

Placold.

Om-M.

CttaM.

CjtWd.

Among existing fishes it is frequently found that the caudal tail fin diTides into two eqiul brandes ; ODietimeB it is single and rounded, but in the case of some placoid and ganoid fishes (e.g. squalus and lepi- doateua) the tail fin is double, the dorsal portion being pi<rionged to a considerable length, and the ven- tral portion much shorter. These three forms are seen in figt. 27, as, 29., which represent the trout, the

and the shark. Xow it is a remarkable drcum-

CH. r, ORGANIC REMAINS OF PLANTS AND ANIMALS. 91

Stance, observed by M. Agassiz that all or nearly all the fossil fishes found in strata in and below* the meg'- nesian limestone are heterocercal or have their tails unequally bilobate> like the sharks sturgeon lepidosteus &c (fig. 29) ; 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 acconipanied with a remarkable position of the mouth ; but as this is not the case in the recent lepidos- teus or the fossil paleoniscus 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 £shes present to the class of reptiles ; an analogy perceived by Linnsus 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 m continued into it. We, therefore, view this remarkable structure as a chcu racter of the organisation qf 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 taU fin (figs. 27 28.), which is one of the characteristics of the existing period.

All the fishes of die 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*

Heptiki.

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 Tbeati8E On Geology. Chap. T.

/estrial families of reptiles and especially ophidia are scarcely known in a fossil state: the fresh water batrachida and chelonida occur only in particular deposits which seem to be whdly or partially of fresh water origin (as the wealden formation, the fresh water formations of the Isle of Wight the brown coal deposits of the Rhine). Marine chelonida aie not unfrequent in the secondary and ter- tiary strata. The saurian order presents us with some singular facts.

The existing orocodiles ofibr in the saurian group a particular and distinct type, whidb seems to unite in some degree, the characters of the chelonida and true 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- "isions 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 sdiferous and oolitic systems are very similar to the long-snouted Indian gavials; those above the chalk approach the broader beaked Nilotic crocodiles.*

There is but little difference of magnitude between the fossil and the living races of crocodiles, for the great gavial of the Ganges measures twenty-five feet long ; and we are not aware that any fossil crocodile has been found of largn dimensions.

Analogous to crocodiles, true lizards, and turtles, occur a great variety of fossil saurians, some of which were terrestrial, and more aquatic ; many of them quite monstrous in dimensions, and extraordinary in organis- ation. The following table is taken from Von Meyer's Palsologica.

Cttvier, Ossemeni Foctiles. The investigation here referred to is ex- tremely important and interetting.

lip! H

-Joi

t

t

E

it

t

i i I".

p

f 'I

if

yi

94 A Treatise On Geology Chap. V

All the saurians of sect A. div. 1. with the ex- ception of mastodonsaurus (which occurs in the sali- ferouB system) belong to the oolitic and lias rocks. In section A. div. Q,, one the protorosaurus or monitor of Thuringia is found in the saliferous the other in the oolitic system.

The saurians of sect. B. are found only in the oolitic system. Those of sect. C. are- chiefly confined to the oolitic rocks ; mososaurus belongs to the chalky phytosaurus to the saliferous rocks. Pterodactylus belongs to the lias and oolites. Thus upon the whole it is in the oolitic period between the eras of the red sandstones and the greensands that the large saurians existed in greatest abundance about the shores in the rivers and on the land in these now cold re- gions of the globe : this was, in Mr. Mantell's lan- guage, the " age of reptiles ; " diough recently two new genera (thecodontosaurus and palseosaurus) have been added to the catalogue from the magnesian limestone of Bristol (by Dr. Riley and Mr. Stutchbury), and one other species is supposed to occur in the limestone asso- ciated with coal at Ardwick near Manchester.

The discoyeries among fossil reptiles of the saurian races by Cuvier, Sommering, St Hilaire, Von Meyer, Conybeare, and the naturalists of Bristol, have equally awakened the attention of zoologists and geologists. Among the singularities reyealed by these investigations, we may notice in the ichthyosaurus, the curious and beautiful combination of the swimming form and retral nostrils of the dolphin ; the teetii of tibe gavial, or cro- codile; paddles somewhat like those of the turtle; vertebrffi like thq of a fish; and eyes furnished with sclerotic bones like those of birds and certain lizards. 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 vertebne, while the snake-like neck of plesiosaurus includes from thirty to forty ! M. St Hilaire, contemplating the many analogies between some crocodilian fossils and the recent gavials, has been led to propose the speculation that the

3H. y, OBOANIO REMAINS OF PLANTS ANP ANIMALS.

recent crocodiles are really the offspring of the older forms ; the differences between them being merely the effect of different physical conditions operating during long geological periods upon one original race.

If instead of this somewhat poetical coicture which cannot be proved we substitute what is really known of the successive stages of reptile organisation from the era of magnesian conglomerates to the present time the results are very remarkable.

The vertebrs of palsosaurus and thecodontosaurus agree with those of ichthyosaurus and common fishes, in being deeply concaye at each end~a structure eyidendy adapted for free motion in water. In plesiosaurus the yertebre are slightly concaye on each face ; but in teleo- saurus, steneosaurus and the recent cr6codiles, they are anteriorly conyex. The former are really of ichthyoid, as distinguished from the latter, or truly crocodilian type ; and, in a paper read to fbe Bristol meeting of the British Association, the discoverers of paleosaurus and thecodontosaurus, proposed the speculation that the system of doubly concave vertebre SO.) is more Ancient than that of tiie concavo-convex {fy, 31.), and

Theoodontosaunii. Crocodile.

that the change from one to the other may be found re* lated to geological time. In the monitor of Thuringia, which, according to this view, should have doubly con- cave vertebre, their front and hind faces are rectangled to the axis,*

Von Meyer, Palsologica, p. £09.

96 A Treatise On Geology. Cbap. V.

Birds.

The remains of biids are extremely micommon even among the dbmparatively recent alluvial laenstrine and cavern deposits still less frequent among the tertiary strata, and almost unknown among the older strata. Tills isone of many instances which agree in proving that the occurrence of the exuviae of land animals and land plants in the stratified rods which were formed chiefly in the sea is the result of causes so local, limited, and rare, as to be, in fact, accidental, and therefore no suf- ficient 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 vege- tables 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 manmialja in the marine strata of all ages ; for even in the tertiary rocks such remains are rare. But it is, perhaps, neces- sary to find other causes for the scarcity of marine mammalia in all except certain of the tertiary strata and superficial sediments. The opinion formerly fa- voured was, that during the whole of the primary and secondary periods, at least, the dass of mammalia had no existence, and only came into being during the ter. tiary period. But this conclusion, founded upon the mere want of such remains, was easily seen to be in- secure, and at length proved to lie 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 quadrupeds, and ap- proximated to the genus Didelphys.

Five specimens of disse remarkable jaw bones arc

known, two of nblcli ire in the hands of Dr. Buckland, one belongs to Mr. Broderip one to M. PrerMt, and the (fig.S2.) was selected by tbe author of thisVolnme, from aD ancient collection of fotailB, the property of the Rev. C, Sykes, of Rooss, in Yorkshire, by whom it waa preiented to die museum of tbe Yorksh Fbilosophi. cal Society. These apecimeng are of inestiinable value, for were they unknown, tbe whole of the pomdTe teati. monj that the earth, during the aecondMy periods of geology, nonriihed land mammalia, would vaniih, and the CDune of inlerences as to the snccesnm of organic lifb the globe be greatly modified.

nam BueUuid'i Bridgwater TEsHtiiv,

Those peraoQs who, confiding in what ate aomewhat haadly called general views, believe too strictly in the gradual change and sequice of raanic life on the globe, and have pictured to themaelvGa the early land and sea aa tenanted only by the dmpler (and, as are eno- neoualy termed, inferior oi imperfect) forma of life, while in each succeeding period new, more complicated, and more exalted plants and animals were cled into being, till man was at Isat awakened to the supremacy of creation, will find this fosul quadruped of Stoneafield a very punling anomaly. On tbe contrary, the geologist who, in the full spirit of Cuvier, regards the BystWs of Lfe aa definitely related now, and at all past periodsr to the eontempoianeouB physical conditions of the obe, and naea the remains of plants and animbia aa m(niu>

98 ' A Treatise On Cteolooy* ' Chap. Vw

ments and guides to a right knowledge of these oon- ditiom draws from this singular and extraordinary dis. coTory the confirmation of a hope, that the state of the ancient land may not for ever he wholly concealed from patient inquiry.

That these are really the jaws of mammalia — that the genus was at least allied to Didelphis we may safely admit on the competent anatomical authority of Cnvier and Agassiz notwithstanding the easy conjecture that they might dong to Fterodactylus, of which hpnes hut not jaws occur at Stonesfield. When we regard the {Pointed lohes 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 ibe sea shore. No other parts of the animal have yet been found tizan 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 beai discovered in any of the superior strata of the oolitic system, — it is merely a coiecture that some bones in the marls of the creta- ceous system of New Jersey and Delaware may bdong to Bakena. 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 Gmiind and Oeningen ; — in gypseous deposits from fresh water, as at Mont- martre ; — in shelly marls, as at Market Weighton ; — in diluvial day or gravel, as at Harwich, — at Lawford,-* fit Hessle ; — or in more recent peat bogs, ais in Ireland, the Isle of Man, Lancashire ) or in caves and fissures of the rocks, as at Eirkdale, and Gibraltar, that the bones of mammiferous quadrupeds occur.

GH* V. OnOAMIC REMAINS OF PLANTS AND ANIMALS. 99

Some of these ossiferous deposits are of historical date the others of greater bat various antiquity so as to permit the construction of the following table of the successive races of mammalia.

Historical or modeni

a

f

j

?

DiluTial . . -

Tertiary - . -

♦

?

Secondary

?

Primary

The preceding table adds another to the proofs already given of the extreme analogy between the ter- tiary and modem 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 mammaha: 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 reliquis of mam- malia, most of the genera and some of the species are the same or extremely like to living tribes : while in the modem 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 mammaha ; no remains of Man have yet been found inany 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

H 2

100 A Trsati8E On Oeoloot. Ohap.

nearly resemble ourselves ; for these hare rarely been recognised in a fossil state.* Perhaps, howerer, 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 fax from the tropical forests which might shelter and feed thei ; and man only braves the cold of northern dimates by his supe* rior knowledge of nature, and inventions to meet ita variations. These arts and that knowledge must be supposed of slow growth ; and we lay consistently believe that, though mankind at the duvial era might not have extended to these far northern lands, where, only, the ossiferous caves and deposits have been ade- quately examined, human i<emalns may yet be discovered in those warmer regions of the globe, which seem more congenial to the easy existence of our race, and have Vot yet been searched for the bones of our pnnitors.

The supposed exceptions to this law of the absence of the remains of man from tertiary and diluvial accumula- tions (the bone caves Bise, near Narbonne, the valley of the Bister, &c.)may be discussed hereafter: suffice it now to say that they are not thought sufficient to establish the affirmative of important proportion. It appears, therefore, that we must look upon existaioe of man and many races of animals which, more strictly than he, axe 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 comlnnations 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 phencHnena, hap-

Quadrumana hare been found by 11 Lartet, in the lacustrine deposit of Sansan, Dep. de Oers.), and by Capt. Cautley and Dr. Falconer, in unt ttn tiary strata oftli SewaiUc: HiUs, Hindooatan.

CH. y. OBGANIO RBMA1N8 OF PLANTS AKD ANIMALS. 101

pening in a determined order as part of a general plan. Some changes in the constitution of the globe haye brought in succession various combinations of the mani- fold influences of those chemical and mechanical agencies which goyem inanimate nature ; and such appears to be the law of God's providence, that to tliese 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 iJways accompanied by destruction of all the old, forms. On Uie contrary, the extensive collections of fossils now made in England, prove this to be an erroneous notion : for many fossils, as Terebratule — Astacide- Modiolfe — Gervilliee, 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 salv- /erotis 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 dif essentially, and by large and general characters.

H 3

102 A Treatise On Oeoloov. Chap. V.

Everywhere the tertiary fossils are closely analogous to existing types ; hut in all countries the fossils of the primary strata appear to helong to a very different series. Wherever the systems of European strata can he paralleled, — in North America — the Himalaya — Aus-* tralia — so much of analogy is evident in the organic reliquisj 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 glohe ; and nothing, yet known, forhids us to helieve that they were universally felt, though in unequal degrees, and under differences of circumstances.

Could we suppose produced on the present glohe some general change of conditions in the sea, on the land, and in the atmosphere -either simultaneously, or hy communication from a central area of disturhanoe 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 ot 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 modem 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 modem 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 variatioii

Ctt. y. ORGANIC BEHAINS OF PLANTS AND ANIMALS. 1 03

eonbect the phenomena of all geological periods from the most ancient to the most modem epochs into 0710 grand syttem 0/ natural revolutions, it follows that we may look upon the present condition of our glohe as one term of a magnificent series of appointed changes to which others may from anal( he expected to follow, according to the same fiiws. The creation of intelligent man is indeed an event not in the calculation which man can make of the effects of sach laws ; nor indeed, is it given to in creatures of a day exactly to know ihe laws of vazittion which hind all the phenomena of nature past, present, and to come — into one great system of appointed e£fects flowing from a predetermined cause — much less to deduce these eflbcts. Yet let not the search for these laws- — which comprises the whole of geological theory — he censured as a chimerical in- tury. The augmentation of light that has already heen poured on the dark pages of geolc encourages per- severance ; the extent of man's power to interpret the phenomena of nature may he vast, compared with his present knowledge, however small, compared to the amount of things unknown. In seardiing for general theory we shall at least find limited truth ; and the ex perience of some thousand years has proved the lahour, which seemed vainly tasked in ahstract discovery, to he seldom nnproductive of practical utility.

To imdersCand rightly the daily accumulating stores of organic rdiquis, requires more than a slight know- ledge of existingnature, — 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 dimate and atmospheric conditions. Thus viewed, the present system of nature appears, when compared with the older periods, in which local diversities of condition have gone to extreme — where all the peculiarities of climate and surface have

b4

104 ▲ TREATISE ON OEOLOGTi CHAJP.

given the fullest effect to the vaiiety 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 greats as to permit us to propose questions con- cerning the degree of resemblance which fossil remains may offer to the recoit tribes of different climates and rons of the globe*

Where shall we look for the living analogues of the numerous fossil induding arborescent species of great size the sigiUaric lepidodendra and gigantic equi- setaces which M the coal shales of England the cycadee, conifere of the oolites and the palms of the tertiary rocks of France f

In what dimate grow the modem coral reefs com- parable to the fossil zoophytic rocks ? where live the parallels to thousands of ediinida> crinoidea trilohiteSy brachiopoda cephalopoda sauroid fishes crocodiles, pa- chydermata> ruminantiaj which characterise different geological periods ?

It is difficult to answer this inquiry with precision ; for, though upon a comprehensive review the most valent analogies in modem nature point to a tropical" climate; yet as the species always and the genera and families frequently, diffor,, and as, besides, odier causes than climate limit the distribution of life it is not possible to found such a oondusion on individual in- stances. A prevdknce of fems to the extent which we observe among the plants of the coal fcnrmation, is only known among the idands and on the shores of warm tro- pical seas; but if these fossil plants had been much drifted or long immersed bene inhumation, such a pre- dominance of ferns, cyoadeie, &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, cycadee, conifers, &c comparatively uninjured, as we find them in the earthb Compared as to form, the tree ferns, palms cycsa

ea V. ORGANIO REMAINS OF PLANTS AND ANTMALS. ] 05

des &C. indicate growth in a wann cUmate as do also, the gigantic lycopodiacee, sigiUarie and calamites ; bat this is not the case with conifens. Zoophyta, both roongoid and stony> lead us to the same concluon ; for the greater part of homy sponges and stony corals belong to the regions within S3 of latitude om the. equator (except the S. 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 rpect except the cephalopoda which by their size and abun- dance seem to indicate & 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 infiu€;nce 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 reUquis, 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 fems cyca- dee, araucarie, casuarine, grow upon the land ; corals and sponges abound on the coast even of Van Diemen's Land, — while trigonia, cerithium, isocardia, a cardium

1:06 A Tbeatisb On Geology. Chap. T. '

like C. billantiin of the green sand and quadrupeds of the peculiar marsupial races to which the Stonesfield animal is referred hy 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 hy consequence to furnish new and important grounds for determining the ancient physical conditions of the glohe.

Chap. Vi.

HISTORICAL VIEW OF THB BTRATinBD BOOKS IN THE GBU8T OF THB EABTK.

In describing the saccessive phenomena visible in the crust of the earthy 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 acquiriiby 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 reaUy 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 Irhose 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

108 A Treatise Ok Gboloot. Ohap* Yi

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 BaHi of the Crust of the Earth.

This geological history of the earth must necessarily commence with the earliest (i. e. loTest) 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 tiiey 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 unstratified rodu exist so as to form a general floor, most irrular in sur- face and of unknown thidmess, 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 hyperstiiene, Examples of tiie first kind of granitic basis of the crust of the earth, are almost universal in mountainous regions ; e. g. the Grampians, the Moume and Wicklow mountains, Cumbria, Com. 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 tiie anitic 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 tiie subjacent granite, so tiiat it may be ranked as an older rodk than any qf the strata rest ufon A

eS. FORMATIOK OF TBB CBUST OF THB BABTH* 1Q9

Aimitiacr.

striking change lias taken pkoe in leapect to thia matter of late years: fonneriy when granite waa by many geologists thought to he of aqueous origin, itp 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 Uiis argument is of no value; and other circumstances have been observed whi( 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 formations, so that it has actuaUy been ijeteted 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 ; entoing hornblende elates, and primary limestones in Glen Tilt (Blair Athol), and day dates in Arraa, Sldddaw, and Ck). Granite which we tiius see inupted through and into tiie stratified rocks, is, in ict, of no one particular or determinate age, but is the local xeenlt and.evidce of many ind)endent excitements or periods of critical action among the subterranean agendes of heat We may, therefore, consiatently admit gramte, as well as otiier igneous rocks, to be of any, lliat is, of al ages; some of that which is visible in the af the globe may have been solidified from fusion before tiie production

vl 10 A TREATISIL ON GEOLOGY* OHAP. 11.

of any of the strata ; other granite has been melted or re-melted at yarious later periods ; granite may yet be forming in the deeper parts of the earthy round the centres of volcanic fires ; but in general we must look on this rock as characteristic of particular drcnmstanoes 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 compoimds which subse- quently admit of granitic crystallisation, is a cha- racteristic efibct 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 modem 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 earthy is nothing else than the fiised 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. Hutton 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 compensatiQii -

Xihap. Ti. Primary Strata. 1 11

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.

PRIMARY SYSTEMS OF STRATA. Gneiss and Mioa Schist System.

Composition. — It is a general truths that to every principal mass of stratified rocks belong some remark- able mineral types of composition. The primary strata, viewed together, distinguish themselves by the super- dbundance 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 days abound remarkably, while these, scarcely occur at all among the primary 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 <ened so many brilliant views of another kind, though equally related to, and characteristidof, geological time.

The materials of the rocks which enter into the composition of the gneiss and mica schist systems, ase such as to form siliceous, argillaceous, and calcareous ag- grates, somewhat resembling those of the later systems of rocks ; but they are usually in a very difierent state of molecular aggregation. The siliceous strata of these ancient rocks, (gneiss, mica schist, &c.) consist of the 8e minerals, as those wluch abound in secondary sandU

112 A Treatise On Obolooy. 4)Hap. Vi*

ftones, Tiz. quartz felspar and mica principally ; bat they are far more distinct in their characters less worn by watery attrition, and more evidently allied to granite. The argillaceous rocks, which often accompany them, (clay slate, grauwacke slate, &c.) have nearly the same diemical composition as common days and shales among the secondary rocks ; but the degree of induration and the whole structure of the rocks require the supposition of their having undergone the influence of very different circumstances. In the same way the primary calcareous rocks, though chemically undistinguishable from second- ary 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 dose 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 felspar is roimded like sand or small pebbles, or fragmented like a broken crystal, and the mica is bent and contorted by irregular pressure among the felspar and quartz. Add to these cireumstanoes the lamination of the masses, and we see deaily that the ingredients of gneiss and mica sdiist re- semble granite, because they have been derived from gra- nitie odcs; but they di£ because they were accumulated'

CHAP, y I. PRIMARY 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 laminse ; the mica forming generally con- tinuous sheets in mica schist but interrupted patdies 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 caseSj seem to bear exactly the same relation to gneiss mica schist Sec, 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 cliffy according merely to the difference of circimistances under which the materials are accumulated. Now it is impossible to doubt that day 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

Yol. I. I

114 A TREATIBE ONCHOIiOOT. CEAf. VI.

it, and oecuioiiBlIy with da; slate, sre also of aqueous , productioo ; and the comptisition of gneiss, &c., com- pletes the evidence wanted to prove that the primary Btrata analogouB to sandstones and clays were formed from the waste of graniUc rocks.

The structure of the rocks which compose the gneiss and mica schitt system varies considerably, both in re- lation to lunination and stratification, which depend on themodeofaqueousdeposition, and to joints and fissures, which are the result of sabaequent agencies.

LammatioH prevails unongst all the varieties of gneiss, mica schist, thorite scliist, hornblende schist, &c. It is oAen observable in primary limestone and sometimes in quartz rock. In feiss, mica schist, and chlorite schist, but especially in the former, the lamins are usually con- torted, GometimeB excessively so, indicating a troubled condition of the water from which the ingredients fell, or a Bouice of atation in the still yielding sediment which seems scarcely ever to have oecurred among the secondary and later strata. The only plmisible explan- ation of this remarkable cir- cumstance which has occurred , tonSjistheagitationof the sea, jc orthesoftsedimeBtMiitsbedby heat ; exactly as in the bottoms S of steam boilers, the calcareous sediment is formed in irregular undulatirg laminte, which ap- '" pear on a cross section, very similar to the flexures in the Urain of gneiss. Itwillappear hereafter that thisspe- eolation derives some ecnroboration from other ciicum-

Dr.M'Cul]ochinformsUB(Memoiron Map of Scotland, p. 65.), " wherever there are munenms 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 Yidnity of granite.

Chap. Vi. Primary 8Tbuita. 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 chloride schists of Loch Lomond, it is sufficiently plahi to be satisfactory proof of intermittiug deposition of the rocks. This intermission of deposit is, perhaps, the true cause of the bedded 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 difibrenoe of condition in the agencies concerned in accumulating these :earUe8t strata, or can it be ex- plained by considerii theoKiginal structures of deposi. tion to have imdergone 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 Stmctures--SoTaimy circumstances have occurred to change the conditiou 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-

Il6 A TREATISIB 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 eadly 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 rular divisional planes. The thick beds of crystallised primary limestones (Inverary, Glen Tilt) are less per- fectly and regularly jointed dian 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 ; but it would be a more correct in- ference, that the rocks are generally not of a nature to admit diese structures*

Chap. Vi.

PBUfABY 8TBATA.

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.

Mica Schist

In the accompanying diagram the two great formations of which the system consists viz. gneiss and mica schist are placed in dieir 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 (Olen 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 Hoiise or Cairn GU>rum 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 Lodi Earn, Inverary) ; and it seems probable these might be employed to subdirlde the great mass of mica schist, were it likely to be of any use or interest where no organic remains and few minerid 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 chloride, and might, perhaps, deserve

118 A Treatise On Oeolooy. Ghap. 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 few or no traces of organic beings.* To judge from this extraordinary and, perhaps complete deficiency we should say there were ndther plants nor snimals in existence on the globe at the time of the deposition of these rocks. But, before admitting this conclusbn it is necessary to determine whether atiy 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 modem geologists that the peculiar mineral aud structural characters of gneiss and mica schist are not original, but derived from the influ- ence of heat upon common sandstones and idiales — 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 mibstanoe 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 giten 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 suppositioii 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 orthoceratites at Loch Eribol, by M*Cunoch, and of zoopihftic remain*, in clay, state, aMoclated with gneisn in the Riesen gebirge (Von Dechen's Xransl. of de la Beche), require further conaideratioB.

Chap. Vi. Primary Strata. 119

rocks (Snowdon) which are also classed among metSr morphic rocks : and, secondly as we ascend in the series of strata organic remains gradually appear (In the clay slate system) 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 hfe, if it had commenced at all was exhibited at very few points on the surface of the globe. (See Table, p. 80.)

Ea;tent of CountrU'-r-WiiMa 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 i;uust 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 Awe 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 Ben Cruachan, Loch Rannoch, Dalwhinnie, Cairn Gorum, Aberdeen, and Peterhead Mic 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 this 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 ide of Loch Fyne, Colonsay, and greit part of Cantire, appearing likewise in Arranj 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 Schihallipn. From Ben y Gloe to iprae mar, and between the Spey and the Doveran to Cullen, is a mass of quartz rocks, ramified among the gneiss an4

120 A Treatise On Oeology. 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 Bally shannon and stretches inland nearly to border the basaltic platform of Antrim being assodated with granite quartz rock limestone, and old red sandstone. From Donegal Bay to the Bay of Sligo and from this liearly 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 efiect to the bold summits, abrupt precipices, deep glens and lakes, which abound in these tracts. The pointed gneiss rods near Mont Blanc (Aiguilles), — the conical topic of the quartz mountains of Schihallion, — the Paps of Juza,

Chap. Vi. Primary Strata. 11

— 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 drcomstances ; 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 outUne prevents formality ; the immensity of the moun- tains fills while it saddens the mind ; and if the sear- 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 tiie landscape. It is not prettiness nor gentie beauty nor antithetic effect of colour or outhne 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 Bocks. — Granite as was stated before is found almost universally beneath gneiss and mica schist — sometimes touching one (gneiss mostfrequentiy) some- times the other. It generally appears to have been in a state of Vision since the deposition of these superin- cumbent strata force 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 in 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- mdrkable trap dykes run east and west throu£ the mica

12 A Treutise On Oeoikwy. Chap. Yi

scliist and carboniferous limestones of Mayo and SligQ 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 oui 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 pecujUar manner in water, re-aggregated in lamine, 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 Uie emergence of land; but evidence of watery movements, different from the agitation of currents or ihe tide.

To connect all 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 hypotheeie thai the earth at the time of the production of thia earliest system of strata, retained within, and communicated to the surface

Gha. Vi. Pbihabt Strata. 123

a much larger portion of its original heat than is now experienced.

But to this speculatioHy 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 dieir origin £rom granite, but their partial re-conversion to that rock ; that the absence of organic remains in these ancient strata it a fruit of such re-aggregation of the mass of llie 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, but not enough to recrystaUise the fragmentary mica, quartz, and felspar, for these are not re-crystallised. Moreover there are cases where organic remains do occur (Dauphine), amoQg 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 afe intel- ligible and, thus, we appear to be justified in recting the doctrine which denies the power of discovering mo- numents of the commencement of watery action and organic life upon the earth.

124? A Treatise On Gboloqy. Uuap. Ti.

Slate System obClat-slate and Grauwaoke System.

Composition, — The type of this system is upon the whole eminently argillaceous as that of the older systems is arenaceous: but between these two terms the difference is not always very clear. Some proportion of alumina 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 water, might make a good substitute for clay ; if left in a state 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 decomposed 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, hardnessand chemical composition, thatmineralogists have often included it in their arrangements as a peculiar min* eral species. Imbedded in it we sometimes find certain crystallised minerals, as chiastolite or hornblende (in Skiddaw), cubic pyrites (Dunolly, near Oban, Ingleton, in Yorkiire) ; its colour is black (Skiddaw), purple (Snowdon), green (Langdale), yellow (Chamwood Forest), mottled (near Ambleside): some varieties (West- moreland) 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 diffiised amongst and around grains of quartz, fdspar, mica bits

Chap. Vi. Primary Strata. 125

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 may be found in Ben Ledi — the Lammermuir, — the Gavan district,— in Snowdon,— and in the Salopian border of Wales. In colour and hardness the grauwacke rocks vary through as great a range as the day slates.

With these which compose in every country by far the greater portion of the system of argillaceous slaty rocks, are associated limestones of dark colour, concretionary texture and laminated structure (Bala, Coniston), and quartzose grits and conglomerates which may wiUi some inconvenience be called grauwacke (Raymond Hill, Shrewsbury).

The fragmentary character of these coarse grauwacke grits is merely an extreme case of the appearance of these rocks, which universally impress upon the beholder a notion of their derivative origin from the waste of older argillaceous and siliceous rocks.

Structures. — Amongst these rocks the evidence of successive deposition is sometimes most dear and de- ciave, especially amongst the arenaceous and calcareous compounds; in other cases, particularly among the thick masses of uniformly fine grained day slate, very obscure. Yetj 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 comphcation introduced by later agencies.

As a general rule it may be stated that lamination prevails most in the rocks of finest grain ; beds are most distinct and continuous among the coarser grauwackes ; but the lamirus observed in slate rocks are not always,' nor indeed frequently, the effect of intermitting subsidence of the particles from water ; for, in almost all day slates, the predominant lamination and fissility arise from a

change of molecular Btrtingement by inflneucei acting nnce the deposition of the rock. To iUustrate this let the mbjoined dkgramt repreeent portions of da; slate and grsunaeke slate, alike in all respects of stracture, except the nature and direction of the laminatioD, D being in each a plane of Btratifi cation. In grauwacke Blate(Na.37.) the laminee of depoiition show on all the vertical planea, being all paraDel or nearly bo to the plane of stratifica- tion; in clay date laminfe of deposition are not seen.

other laroinc, viz. those of deavie, induced by Bome process since the deposition of the rock, cross the planes of stratification(aeldomBt rightangles),Mithat the stone maybe split by wedges aliDost indefinitdy into thin plates, nearly in a vertical direction. Id some cases, as shown in the lower part of No, 36., the laminte of de- pontion remain in clay slate ; and instances occur in grau- wacke slates where one or more fine grained bands hare the cleavage stmcture, and other coarser bands have noL But the most obvions and constant marks of interrupted deposition from water traceable across cleavage planes are stripes of eohur different from the mass, or thin bands of harder matter, or layers of coarser ingredients. The most perfectly cleavable sUte rock, though it be almost a crystal in respect of its regular structure, shows in the quarry indnhitde marks of stratified deposition ; and whereflne grained and coarse grained slate rocks alternate, a very common circumstance alxiut Snowdon, the &ct is perfectly obvious.

Ckavage must be viewed as a structure imposed on the rock agencies subsequent to its accumulation as

€Hap Vi. Primary Strata. 127

sediment. What was exactly the natare of these is a proMem of some delicacy which may he better discussed hereafter : in the mean time following laws have been established with respect to it. -¥1, it is never so perfectly exhibited as in the ancient argillaceous strata ; is most oonspicnous among lliose of finest grain and most uniform nature; disappeans in very coarse rocks ; ranges in almostxact parallels over many square miles of cotmtry ; preserves these parallels even across contorted stratification (as Plate IV. fig. 17* ' Guide to Geology,* edit. 3.); and mostly coincides in horizontal di- rection 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 HUl, 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 any where known.

Between Skiddaw and Saddleback the base of the clay slate system is found resting on very thin mica schist and 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.

128 A Treatise On Geoloot. Chap. Vi.

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.

E. Uppermost system (Hou-r Great mass of grauwacke (3), above alter- gill, Kentmere), 1000 yards nations (1 and S) of grauwacke and grau- or more. C vacke slate.

D. Slaty limestone(Conl8ton, f Dark argillaceous limestone, with shells and Low Wood), 100 feet. I corals.

' fin the upper part (4) are dark, flaggy, and

I slaty rocks : the middle (2) abounds with

C. Middle slaty group 1 fine green slates ; near the bottom (2) most

(Langdale, Borrowdale),K of the rocks are mottled, amygdaloidal,

1000 yards or more. ] or fragmentary; 1 is a red argillaceous

I mottled rock, which sometimes appears

(. like a ccmglomerate.

rit consists almost wholly of dark, soft, use-

B. Lowest slaty group (Skid- 3 less slate: toward the lower parts chi.

daw) 1000 yards. j astolite abounds in it (S), and near the

C base hornblende. A. Of the gneiss and mica schist system is a mere trace, over granite.

The series in North Wales is considerably sunilar but appears less complete in the lower part. — The fol- lowing is Sedgwick's arrangement.

£. Plynlymmon Rocks, r Grauwacke and grauwacke slate, of giat probably several thousands thickness, with some beds of conglcnne- yards thick. i. rates.

[Dark limestone, associated with slate,

yielding shells and corals. 'Various fine grained purple, blue and green slates, fine and coarse grauwacke and glomerates, often alternating, mostly pos- sessing slaty cleavage. — Organic remains . in particular beds.

Organic Remains.-Tlus is the oldest system of strata in which organic remains are certainly known to occur : they are not found in the lowest group of Skiddaw, but occur to the extent of a dozen species (our own ob- servation) in Snowdon ; and, perhaps, twice that number are found in the limestone of Bala and Coniston, and in the slates of Cornwall, supposed to be of nearly the same antiquity as the rocks of Snowdon. It may surprise the speculators in cosmogony to hear that these, the most ancient forms of Ufe known to us, should be, not plants but animals; not merely zoophyta, but conchifera; not the lowest grades of their respective classes, but perfectly developed lamelliferous zoophyta, and brachiopodous

D. Bala limestone.*

C Snowdon rocks, probably several thousand yardS' thick.

Ghap. Vi* Primary Strata. 129

moUusca. No gasteropods or oephalopods are howdver, as yet mentioned in these rocks in Britain and we do not fed sufficiently acquainted with the geological age of the limestones of the Harz to introduce any of the fossils of that argillaceous range of mountains. Whether at the time of the formation of these ancient rocks in the sea plants were growing on the land (whether indeed there were any neighbouring dry land) we must not even conjecture : that plants might be growing in the sea which nourished the shells and zoophyta of Snowdon is a pro- bable but-not a certain inference ; since sea- weeds do not alone constitute the food of condiifera or zoophyta. We found no satisfactory trace of plants in the fossiliferous rocks of Snowdon nor are they common in Cumberland.

We cannot, from the twenty or thirty species of fossils (yet very imperfectly known) which have been obtained from these ancient rocks, learn the conditions under which they lived : but they are of great value as the oldest monu- ments yet discoveredof the creation of living things. The very rarity of their occurrence and the paucity of species confirm the general views advanced as to the cause of the absence of organic fossils from the still older systems of gneiss and mica schist ; for these few remains, scattered through as many miles of stratified rocks of different nature, appear to indicate that only at a few exceptional points were the conditions established which allowed of organic life being developed. Limestones in later strata full pf fossils, involved very few in these ancient periods.

No clear or general differences of form distinguish the fossils of Cornwall, Snowdon, and Bala, from those of the Silurian system next above : the same predominance of brachiopoda among the shells, the same comparative abundance of zoophyta, and the same rarity of plants appear to show that the circumstances affecting organic life differed only by degrees. We may perhaps consist- ently view the organic beings of the clay slate and Silurian periods, as belonging to one long succession of creative eQergy, the first, if our views as to the origin

Vol. I. K

of the gneiss and mica Bchist be correct, which i

eatablished upon the lobe.

Oeographical Extent. — Tn the British idanda, foitu. nately, tbii valuable Bystem of rocks ia exteusively de- Toped along the flanlie of the great mountain ranges. A narrow band of claj' alate and grauwadce accompanies the eouth-eastem flank of the Grampians, from 8toAe- haven, by Dunkeld, Comrie, Loch Venacher, on Loch Lomond, the lower end of Loch Long, part of Bute, and the north-eastern part of Arran, Detached portions occur in AberdeeuBhiie, at Balachnlish, about Dalmally, &c

The Lunmarmuii' hiUa and the connected ranges from St. Abb's Head to Port Patrick, conaiat principally of these locks : a range oF similar rocks, in the same diiectioD, tends from Donaghadee to Longford ; and, with the nception of the Moume mountains, occupies the ses- ooast to the mouth of the Boyne. Bast of the granite of \Ficldow and Cailow ia a lai tract of aillaceona

CHAP. TI. PiUMART BtRATA* 131

slate and assoeiated quartz rocks from Bray to Water* ford and a much larger tract in the south of Ireland from Dnngaron to Ditigle Bay. Detached masses occur about Dingle and in Tipperary.

The' Isle of Man is principally composed of slaty rocks.

" Nearly the whole of the lake district of Cumberland M'estmoreland and Lancashire is formed of day slate> and grauwacke. Charnwood forest considerable parts of Anglesea An immense crescent stretching from Great Orme's Head by Ruthin, Wdshpool, Rhayader, Llan- dovery, and St. David's Head, belong to this system, as well as a band on the north of Devon, and, with the ex ception of igneous rocks, almost all Cornwall and Deyon, south of a line from Tintagel, by Launceston to Exeter.

On the continent of Europe, Brittany, the Ardennes, the Harz, parts of Norway ; in Africa, the ranges of Adas ; in America, the Alleghanies contain considerable portions of this class of rocks.

Physical Geography, — The slate system, though but a very inferior feature along the Grampian ranges of Scotland, rises to great importance in the south of Ireland, and forms the most elevated points of land in 'England and Wales. Supported by granite, and mixed with igneous masses, the slaty rocks of the English lakes rise to more than 3000 feet in height (Sea fell is 3 160, Skiddaw 3022), and present a variety of out- line, and intricacy of combination, which, in connection with dear lakes and considerable waterfalls, leave to Switzerland Httle superiority, except that beauty and grandeur imparted by. their mighty summits of snow, which is perfectly iaconoeivable to an English tourist, who might shudder by his fireside at the very mention of a wintry view 6f Helvellyn.

Each of the slate formations of Cumbria has its own characters of scenery : broad sweUing forms accompany the Skiddaw rocks ; enormous crags and fearful precis- pices, with broken waterfalls, characterise the middle division, and the upper has, generally, a number of ser*

K 2

)32 'A Treatise On Geology. Chap. Vi.

rated hillB of yery inferior effect in the scenery. The lakes of the Cumbrian ron are often so deep as to pre* elude wholly the notion of their having been eroded by water. The valleys are according to Sedgwick, usually accompanied by great dislocations, radiating from the central elevations of the rocks.

The slaty regions of North Wales are superior in the breadth and grandeur of their effects, though not in picturesque beauty, to the districts of the £nglish lakes. Their effective height is greater, from the entrance of many arms of the sea into the midst of the mountains : there is, besides, something deeper and richer in all the colouring, a greater expanse of surface, largeness of feature, and freedom of outline, which reminds us of the best parts of the Grampians ; while the valleys, sometimes richly wooded and watered (Festiniog, Dol- gelly), and. sometimes dreary and solitary (Uanberis, Beddgelert), furnish, even without their wild lakes and rough cascades, every possible variety of pictorial accon paniment.

If we consider how all these circumstances depend upon the general conditions of a forcible elevation of rocka of different qualities into an atmosphere competent to produce upon them unequal chemical effects, and on their disintegrated particles to nourish correlative vital phenomena, we shaU see how trifling is the enjoyment of beautiful nature which they experience who are satisfied to gaze on effects with the painter, and seek not their appointed causes with the geologist.

Igneous Mocks are associated with the argillaceous slates in every district where they appear in the British islands. Granites touch the slates (called " killas") in Cornwall, in Cumberland, in Cavan and Arran ; serpen- tine occurs at the Lizard, in Cornwall ; porphyry aod greenstone are abundant in the Lammermidr, the Cum- brian mountains, and Snowdonia, both in dykes and partially stratified masses. Mineral veins are found no where so abundantly as in the Lead Hills, and in Cornwall, nor there any where so plentifully as near the

CAP. VI. PRIMARY STllATA. 13

granites or other igneous rocks ; a circumstance which combines with many other facts to demonstrate the dependence of mineral veins on some peculiar agency of sabterranean heat. Quartz, the most frequent matrix or vein stuff of these mineral veins, is very often found ramifying into the fissures and cracks of the slate rocks without any metallic admixtures.

Judging from personal observation, as well, as recorded jAienomena, we should say the effects of locally deve> loped igneous agency are much more frequent among the rocks of the slate system, than in those of earlier date, and that dykes, veins, and interspersed beds of por- phyry and greenstone, are more abundant and varied. The circumstance observed in Cumbria and North Wales of the porphyry beds being subject to the same flexures and inclinations as the slates, leads to the inference that they were effused as lava sometimes is on the bed of the sea, at intervals during the deposition of the slates ;thte dykes of course are of later origin, and the same is gene- rally (we think) true of the mineral and quartz veins, but isome metallic and quartzose masses are probably con- temporaneous with the rocks which enclose them. Cir- cumstances known concerning the arrangement and contents of the veins in slate in the killas" of Cornwall, induce many of the intelligent mining gentlemen and geologists of that interesting county to deny, generally, any distinction of age between the veins and the rocks. We shall probably examine this subject in a future section.

Besides these local effects of subterranean heat the whole structure of the slaty rocks appears to be the result of a general pervading heat, operating on the argillaceous sediments so as to overcome their natural horizontal lamination and induce a new, almost crystaL line, fissility in vertical or highly inclined pines, having one constant direction. We may consistently view this remarkable polarity of the cleavage as a cha- racteristic effect of some very general agency, directing the results of molecular attraction : it is certain that this

184 A TRXATISE ON OBOliOOY. CHAP. V]..

directive energy was never displayed in the same general

way on the argillaceous rocks of later systems and that

even among the rocks of the slate system itself the

lower ones are almost universally cleavable the upper

ones only partially so and that diiefly along the line of

great disruptions of the strata, as 6. g, the Craven

faulty to whose plane of fracture S. £.) the cleavage

planes of the slates are parallel. Indeed we think there

is good reason to adopts provisionally the rule stated by

Sedgwick — that the strikes of cleavage correspond to the

strikes of the strata though their inclination differs in

amount and even in direction; and this leads almost

positively to the inference that the one is dependent on the

other. My own observations have led me formerly to

adopt the opinion that the divisional planes of slate

determined the line of a remarkable elevatio of strata

(Craven fault ); but the parallelism of cleavage planes

across contortions of strata of which striking examples

are given bv Sedgwick, in his Memoir on the Structure

of -Rocks (Geol. Transact,) seems to complicate the

question, t Numerous observations should therefore be

made upon the plan prcosed in the Guide to Geology

3d edition for the procurement of geometrical data on

this curious subject.

Silurian System.

Composition. — The rocks of the Silurian system as it is exhibited in the country investigated by Mr. Murchison (the whole Welcrh border and large tracts in South Wales) may be said to contain types of the usual sedimentary aggrates — argillaceous, arena- ceous calcareous ; nor is there any very clear or exact definition by which they can be discriminated in the

It is curious to observiL along tl>e side of this magnificent fSiult in Oiggleswick Scar (Settle), the mountain limestone crossed by many diyi- ional nlanes, whidi cause it to lit pamUd to the fiiult, with a kind of rude cleavage.

f A trap dyke in the Penrbyn quanrlct loet not affect the slaty detT* .age which it traverses at righ% angles.

Chap. Vi. Pbima&T Strata* 135

eabinet as a mass or individually though in the field they are easily and accurately traceable for limited ranges of country. Compared with the older systems the argillaceous rocks in general less indurated less complicated by divisional planes, and only locally en- dowed with cleavage, retain their original lamination : the arenaceous rocks deviate from the character of grau- wacke, toward ordinary sandstone and conglomerate; the calcareous rocks are not usually so crystalline as in gneiss, nor of so earthy a substance as many of the later secondary limestones, but have a concretionary sub* crystalline texture.

Examined in detail, however, considerable variations appear among the different members of the Silufian system : some of the argillaceous beds are black, others of a liver or grey colour : some arenaceous beds fine-grained, and argillaceous (Ludlow) were aptly Jiaraed by Mr. Murchison mudstone" : others are like common hard gritstone (in the Caradoc) : some appear to be principally composed of volcanic ashes, or the disintegrated particles of trap rocks, and are called 'volcanic sandistones '' (Malvern hills, the Caradoc, &c.). Some of the limestones (Llandeilo) resemble the flaggy beds of the slate system at Coniston and Bala : others {Aymestry, Wenlock) are purer, more concretionary, and more analogous to the calcareous rocks of the carboni- ferous system above.

Structure, — In general the accumulation of these rocks appears to have been regular and tranquil ; the whole series of argillaceous and most of the arenaceous rocks are full of laminc of deposition : beds are very distinct in the sandstones : limestones are also regularly stratified, though nodular and uneven on their surfaces, and sometimes partially lenticular or in- cluded among shales, like other calcareous rocks sup- posed to have originated as coral reefs. According to what we have found to be a general law, that divisional planes abound and are regular in proportion to the re- gularity of the laminee of deposition, the argillaceous beds

K 4

136 A TftEATISB ON GEOLOGY* CHAlP. VI.

of this system are seen to be very exactly divided by joints and fissures some of which seem frequently to coincide with the axis of elevation of the country (in Wales this is frequently N. and others to be rectangulfited thereto. In this respect however variations occur, so that Mr. Murchison has often found two sets of joints, both forming oblique angles with the strike of the strata. In the Wren's Nest at Dudley the long joints in the lime* stofie, observed with care JiUy, 1837 appeared to me to be nearly parallel to the axis of elevation, which is N. and S., or, on the east side of the hill, N. 10° E. The joints in other directions were few and irregular ; and though aracks were not unfrequent in the thinner layers of Baven " (argillo-calcareous and fossihferous), the most general direction of the long joints in this also was N. 10° E. The planes of these joints are not always even nearly rectangled to the stratification — rthey are some- times waving in their outline, and present other circum- stances of interest, particularly striationa and associated strings of calcareous spar. The faults in this hill obey the law of displacement, which is given in the Geology of Yorkshire/ and illustrated p. 40. sup.

The planes of the joints and fissures are stated by Mr. Murchison to be nearly rectangled to the planes of the strata.* In the country near Llandovery the lower Silurian rocks are metamorphic slates; the slaty cleavage, induced since their aggregation, predominating over the yet traceable surfaces of deposition. This is sometimes expressed by the convenient though somewhat unlearned

The nodular uneven surface of the limestones of this system is so remarkable, as to. be of great importance in Reasoning on the circumstances concerned in their pro- duction. It is extremely difficult to resist the notion that in many instances the limestone has been collected by molecular attraction from a mingled mass of argil*

See Guide to Geology, Sd edit, for an example of joints reduced by calculation to the plane of stratification, from obserratioos made wita Mr. Murchison on the ridge of Com y Vaen, near Brecon.

Chap. Vu

PRIJIIARY f STRATA.

1S7

laceous and calcareous sediment round corals and other organic marine exuvi©. The. great abundance of corals in these rocks (Aymestry, Dudley, Wenlock, &c.) leads further to the supposition of their being really formed, like a coral reef, in the present seas. If this were correct, the whole of the substance of the rock must be supposed to have been abstracted from sea-water, by that vital action which dissolves the strongest chemical aggregations, and fixes the unwilling elements in new combinations. The perfectly laminated or bedded structure of the rock requires, further, the admission that the materials were arranged in obe(]Uence to the fluctuations of water : this, which implies the removal and partial drifting of the , corals and shells, is strongly confirmed by the worn and rounded forms of some corals (Aymestry), the unattached condition of almost aU (Dudley), the broken and crushed condition of many. If, therefore, we must compare the origin of the Wenlock and Aymestry limestones to that of a modem coral island or group of islands, the Bermuda group, where vital action furnishes the substance, and oceanic currents determine the form and arrangement, ofiTers us the best analogies. The coral islands of thf South Seas are in this respect very dissimilar.

Succession and Thickness of Strata,

The best, or rather the only, complete series yet known of these rocks is that of the Welsh border, of which the above section is a sketch: below is Mr. Murchison's summary.

A Treatise On Oeoloot.

Ohap. Yi.

Qq

Ludlow FonnBtloii* 8000

Thick- nass.

u

as

Wenlock Fonnalion.

Caradoe Formatioiv

Llandello Formation.

Subdiyisionc

1200 "j

Upper Lud. low rock. C

Lrmestry S limestone.

Lower Lud. low rock.

Wenlock limestone.

Wenlock

shale.

Flags.

Lithological Cha. ractets.

Sandstones, grits, and- limestones.

Slitlj micaceous, gray coloured,thin- bedded sandstone.

Subcrvstalline gray or blueargillaceous limestone.

Sandy,liver anddarkl coloured shale and flag, with concre- tions of earthy limestone.

Highly concretion- ary subcrystalline gray and blue lime- stone.

Argillaceous shale, ' Inrer and dark gray coloured, rarely micaceous, with nodules of earthy limestone.

Thin-bedded, im- pure, shelly lime- se, and finely laminated, slightly micaceous, green- ish sandstone.

Thick-bedded, red, purole, green, and white freestones s conglomeritic quartsose gritfx, sandy and gritty limestones.

Dark-coloured flags, mostly calcareous, with some sand- stone and schist

On a careful examination of the vicinity of Ludlow all the upper parts of the Silurian rocks may' he per- fectly traced and clearly discriminated : it is in the vale of the Towey (Dinevawr) that the lower formation is best exhibited. If we were to introduce among these rocks the same principles of classification as those adopted among the secondary strata, perhaps it might appear doubtful how far the Silurian rocks really deserve to be classed as a system in the sense in which this term is now generally employed. The characters of the whole series graduate from one group to another so completely.

Chap. Vi. Primary Strata. 1S9

and there is so great and real an analogy between, the Llandeilo, Caradoc Wenlock and Ludlow fonnations as to permit our viewing them all as one varied series of deposits effected by one general system of medianical, chemical and vital agencies. The succession of the deposits is very simple. The length of geological time which elapsed in their production, if judged of by the merely mineral character of the masses, does not require to be thought greater than that which must be assigned to such a varied formation as the lias ; nor does the in- ference that might be drawn from this comparison fail with respect to the organic remains : for the different mineral groups of the lias formation are quite as well distinguished locally by their different suites of fossils as are the successive formations of the Silurian system.

Organic Remains, — In accordance with the view of the gradual introduction of organic life on the changing globe, which was stated while discussing the history of the date system, we find in these newer rocks a far greater abundance of forms, a far greater predominance of numbers, among the lower orders of animals, but yet few plants. From the Silurian system in England and Wales, theEifd, Norway, the Harz, and N.America, several hundreds of organic fossils have been colleclted, and partially or completely described, by Groldfuess, Miinster, Dalman, Green, Brongniart, Sowerby, Murchison, and others. In 1831 tables were drawn up to the extent of 553 species (Encyc. Metrop.). The following summary of those tables is all that can here be introduced: —

Algae - - 4 Equiestaceae - 2 Filices . -5-{ Lvcopodiacee 2 Asterophyllites 1

.Plants, 14 species, viz. : fThe algc are chiefly from ChristitfniA, the

others mostly from the anthracitic deposits of Baden. It is important to ascertain, exactly true geological place of the latter since the similar culm series of Deron, usually ranked as grauwacke, is thought by Murchison and Sedgwick to belong to the carboniferous system.

Should' this suggestion prove correct, a considerable anomaly will be removed from Geology, for all the genera found on the Rhine occur more plentifully in the car*, boniferous system, and are not. known elsewhere in th

A TREATISE ON GEOIiOOY.

CHAP. Vt.

Silurian rocks. Several oi the species are also identical (Sphoenopteris dissecta Pecopteris aspera) with plants of the carboniferous deposit of St. George ChateUaison and Montrelais. The plants found in the culm series of Devon appear identical with those of the ordinary coal measures.

Polyparia, 87 species, yt. Corticifera . S Cellulifera - 44 LamelUfera - S4.

Crinoidea, 34 species, which are mostly distinct from those of later date

These are all, or nearly all, distinct from the corals of the carboniferous system.

Conchifera, 206 species, viz. " Flagimyona - 55 Mesomyona - Brachiopoda - 128

Gasteropoda, 64 species, viz. Holostomata - 58 Solenostomata 6

Ceialopoda, 79 species, viz. Monothalamia II Polythalamia - 68

Mostly (or all?) distinct from the shells of the carboniferous rocks. ThePlvmouth and South Devon shells, supposeU to be identical with species of mountain lime- stone, are in general,excepting, perhaps, some from Newton Bushel, quite distinct, as I learn from a sight. of Mr.Hennah's and other specimens.

Annulosa, 4.

Crustacea, 65, mostly distinct from those of the carboniferous system even

genericidly. Fishes. A bed of fragments of fish-bones and teeth occurs in the Ludlow

formation.

The distinctness of the organic fossik 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 qf the slate system are analogous to the Silurian reliquiffi 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 dianged though evidently rendered more favourable to the development of a varied systen of organic life. Mr. Murchison believes that each of the four formations of the Silurian system contains distinct suites and charac- teristic species of fossils. The following are among the most common or remarkable : —

Homonolotus Rnightii, jfS. . 1. Leptensk lata. Pentamerut Knighit fig, 2. Terebratula Wilsoni. Terebratula nsca. Jig- 9. ABaphus caudatus) fig* Euomphalus rugosus € 6\acon,

Ohap. Vi. Pblhrv Stbata. 141

j%f. 4, Producta depresa*, 5. Calymeoe Blamenbachii, . G. Orthocenu BDnulatum. Orthu callactii. LinguU Lewi- tii. Urbicula rugsU, 9. 8. Fhngmoceiu. CordioEa. Aupbus Buclui,j!(i. T- Acdnocriiiiu moDUiformis. CjftlhomDus ni- goeuL BbodocrinuB verug. Catamopua polTmorphi. Fam- atea gotbUndica. Catenipora labyrinoiica, fy. 1 1 . Retepora. BeliopoTB porosa, fig. 1 0. Cyathophyllum cyatlius, fig, 1 2. FucoideB leira.

GeographKol Extent. — Ranging on each ade of the Vale of Clwydd, the Silurian Byilem continues b; Llatllen, widening southwards to the valley of the Seven), 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, £. to the Severn atBuildwas. This strike of the Silurian roclis, 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 natrow course nearly west to Caermarthen, and with 'the same range passes Haverfordwest to St. Bride's Bay. From this ceDtral 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 Built and Hay, and ranges towards Trccastle. (From Mr. Murcfaison'a Observations.)

In Devon and part of Cornwall the Silurian system is with difficulty separable from the grauwackc and culmi' ferous rocks of Plymouth and Barnstaple, &c. About Dudley and Walsall the Ludlow formation is admiratdy

Chap. Vi. Primary Strata. 14

exhibited in singular narrow and short anticlinal ridges rising in the midst of the coal formation of South Staf- fordshire 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/. 4fO, and fig. 41. are intended to illustrate the curious structure of this region.

!

h

#

Cs

a. Sedgley ridge, or anticlinal, containing the Aymefltry limestone.

b. Hurst ridge.

c. Wren's Nest, Wenlock limestone.

4. Dudl Castle ridge, Wenlock limestone. e. The Hayes, um>er Ludlow formation. jr. Rowley hills of basalt.

f. Barrow hill of basalt . Coal deposit, resting somewhat unconformedly on the Wenlock formation, and partly resting on, partly passing under, the Rowley basalt which chars it.

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 ; but from a recent examination of the Ludlow rocks, in company with Mr. Lewis of Aymestry, whose judgment in die matter is very im- portant, I think it not improbable they are the equivalent of the lower Ludlow rocks.

In the south of Ireland the Silurian system occurs;

144 A Treatise On Geology. Chap. Vi.

but we cannot particularise the formations : in M. de Bonnard's description of the Harz limestones we seem to behold the Silurian rocks : the Eifel limestone is ex- actly equivalent to the Wenlock formation : in Brittany Silurian fossils occur: the Christianian limestones certainly belong to this system. It is said by Mr. Strickland to occur about Smyrna with asaphi. Perhaps it is from these rocks that trilobites are obtained near the Cape of Good Hope, by Sir J. Herschel. In North America the borders of the great lakes (Huron, Su- perior &c.) show limestones of the Silurian system.

Physical Geography, — Lying on the sloping sides of the slate systems of Wales the principal masses of the Silurian rocks show but little boldness of feature, com- pared 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 Caractacus. The Devonian portions of the Silurians do not, we beUeve, offer any very re- markable characters of scenery: the limestones about Torquay and Plymouth are romantically broken ; the limestone country about Dudley is pleasingly 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. £. 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 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 Silurian 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

Chap. Vi. Primary Strata. 145

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 Llandley, Llandrindod, and Builth, present 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 Brecknockshire and Oaermarthenshire, similar phenomena are repeated aroimd several erupted masses of trap.

The Malvern and Abberley Hills consist chiefly of sienitic rocks, which have burst up among the Silurian strata, and partially thrown them into retroverted posi- tions. The grauwacke rocks are much altered (so as to assume the aspect of chloritic and micaceous schists) by the trap which is protruded among them.

Mineral Veins, — In the Shelve district of Shropshire, and at Nanty Moen, seven miles north of Llandovery, 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 ir- ruption of trap, but certainly and strictly associated with it, and dependent upon it. Sulphate of barytes, sulphurer of iron and carbonate of Hme, accompany the ores of lead.*

Close of the Primary 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 primary strata, of the contemporaneous existence of dry land: for all the early periods at least, the absence of land plants, and the non-occurrence of conglomerates, seem to jus- tify a doubt whether the sea of that period was subject, in the regions now dried, to any thing of the nature of land flood, or littoral agitation. In the slate and Silu* rian systems the marks of agitation in the sea become

Murchlsnn. Proc. of Geo! Sioc. 1834. VOL. I. L

I4t) A TBBATISIS ON OEOIiOOlT. CHAP. VX

more distinct ; and from the land plants referred by Brongniart to the grauwacke rocks of the Rhine> with those which really belong to them in North Devon the proof of upraised land is condusiye though we know not where it was situated.

There is no sufficient evidence to be gathered on the question J whether such uprising might be sudden or gra- dual; the general conformity of the whole series of rocks of the Cambrian and Silurian systems would not justify an inference that no violent elevation of land had happened elsewhere ; especially as some unconformity is supposed to have been observed by Mr. Murchison between the Flynlymmon and Silurian rocks south of Shrewsbury. There is however nothing to contradict the assumption that till the close of the primary 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 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 the primary period.

It is true that a survey of the porphyries greenstones and other igneous rocks so strangely interlaminated among the clay slates and grauwacke slates of Snow don 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 ftt accurate conclusions on this important subject.

The evidence is sometimes insufficient; in other

Chap. Yi.

Primary Strata*

instances complicated with the effects of convulsions of Uter date, but sunilar 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 primary and before the commencement of the secondary 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 periods. In many instances the primary and secondary strata are unconformedly situated with respect to one another, as in the subjoined section {fig. 42).

and the geological map of the country shows superficial unconformity of direction and dip of strata as in. 43.

The position of the 43

secondary strata is discordant tvith 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 bod of the sea upon which the secondary rocks were subsequently spread,

148 A Tbbatisb On Oeoloot. Chap. Ti.

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* plan 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- posed that about the same period the Lammermuir hills were raised ; and Ihe 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, giieiss, &c. : if in addition we remark the fact that, especially in Cumbria, these conglomerates fill vaOeys at the border of the tract of the slate mountains, we shall see the probability that the slate rocks were raised above the siufSaoe 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 mostrobable view* The skte and mica schist tracts of the Isle of Man, Donegal, Galway, Cork, 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 ComwalL* We

Sedgwick, in Address and Memoirs to the Qeologieal Society.

CHAP. n. PRtMART STRATA* 149

must, however remark on these last-mentioned cases- that, on the south-east border of Wales certainly, and in Devonshire probably, there is no observable uncon. formity between the old red and the Silurian rocks, and hardly any between these and the Plynlymmon series.

Were ihe displacements thus shown to have happened in the bed of tike 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 proba- ble 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 modem rocks occupying the lowest ranges and thus appear to teach us that the elevatory action, whatever might be its first violence, was continually exerted in the same localities, late into the secondary period.

The sur&ce of the earth has, however, undergone mnce 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 aU 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. £. ; and it is required to be determined whether this proximate parallelism of contemporaneous axes of elevation is a general law of . the phenomena. M. £. de Beaumont is the geologist who has most strenuously advocated the affirmative of this question ; but it is certain that more

350 A Treatise On Oeologt. Chap, Vi.

rigorous investigations are needed on the subject before any physical theory like Mr. Hopkins's ingenious yiew 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 can be more 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 devations on the continent of Europe of or about this andent period (anterior to the formation of the carboniferous rocks) are located in Brittany the, Harz, the Hundsriick, the £ifel, the Ardennes.

Whence came the materials of the great mass of de posits which rest upon the primary gneiss and mica schist?

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 ihe 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 fbe sienites of Mount Sorrel, and the granites of Arran are in this respect very worthy of attention, and may suggest to those who have lihe opportunity a train of

Cbap. Vi. Bec0Ndar7 Strata. 151

valuable research, which might elucidate many points now obscure in the history of the dintegrated ma- terials of igneous rocks*

SECONDARY SYSTEMS OF STRATA. Cabbonifebous 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. Sor;>e of the arenaceous rocks are conglomerates, as millstone grit, which is par- tially filled with quartz, felspar, and fragments of shale, and old red conglomerate, which is iiU of rock fragments ; others are freestones of an open grain and equal texture, breaking equally in aU directions ; others are compact dose grits, called hazle; or still finer grained, called calliard ; or laminated with mica, or carbonaceous matter, 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 ; less remarkable lamination causes shale; deficiency of lamination be- longs to some varieties, associated with coal, called dunch, 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, Hke lumps and layers of flint in chalk; and require similar suppositions to explain their occurrence. Some considerable beds of

A Treatise Ok Oeolooy.

Chap. Vi.

chert occur in the north of England (Swaledale) and many sandstones are of a cherty nature (Harrowgate).

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 oxyn and azote ; and it is often mixed with layers of woody fibre, like charcoal and lamins of earthy matter.

Structure, — Throughout 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 con- stituent members ; being often conspicuous in sandstones (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 andshales they are often indiscernible ; 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, aind 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 accompanjing dia- gram, L may represent Lme- Btone, P pUte, G gritatone. The joints in L are gene- rally recUngukr to the bed (in thin-bedded " L', the joints an

In plate they are often oblique to the bed ; in grit- -z Btone less regularly formed, ' being mostly craclig: this is especially the case where the beds are thick. The principal fissures F, which some- times go throih many beds, are most open and rular in the limestone.

Co&l has sometimes joints of the same kind, (called ' ends ' or 'backs,') and, in addition, a minute flssility, generally in one certain di- rection across the bed, which ' does not occur in the shales above or bdow. It is a sort of crystallisation. Ironstone sometimes shows con- centric iaminse, and often sparry divunmiE, when it be- comes a septahum.

A very singular structure is freqnendy noticed in the n ores of a coal district, without however

being peculiar to them, which is represented . 49. The substance of the Iron ore is formeil into conical (heaths, involving one another, and marked byconcentiic

154 A Treatise On Geology. Chap. Vi.

undulations and radiating stris. Large spheroidal masses of iron ore weighing at least a ton are thus founds in connection witii the coal, at Ingleton, in Yorkdiire ; and in the coal fields of Staffordshire and South Wales, it is a well known form of aggregation. This structure also occurs in many otiier formations, as in the slate of Skiddaw, the lias, oolites, &c., tiiough with considerahle variations. It is usually called cone in cone,' cone coralloid/ conical limestone, conical ironstone, &c. A different hut yet closely allied phenomenon, noticed by Mr. DiUwyn 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 fig, 48. Such a of coal, however solid, is found to separate not along a plane, parallel to the bed, but with deep hollows, and acute sinuous ridges, situated on their dopes, and undulated on tiieir edges. The striations on the slopes are very similar to tiiose on tiie conical ironstone ; and though tiie differences are in other respects great, tiiey 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 tiie circumstances which determine this pecuUar structure 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 tiie soutii of England), the carboni- ferous system consists of tiiree formations : viz. —

Coal formation. — A mass, 1000 yards or more in thickness, consisting of indefinite alternations of shales and sand- stones of different kinds, with about 50 feet of coal in many beds, some ironstone layers, and (very rarely) thin layers of limestone.

Mouiitain 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.

Chap. Vi. 6Ec0Ndabt 8Trata 155

Old red sandstone.— A mass of arenaceous and argillaceous rocks, — the former containing conglomerates of ex- treme or moderate coarseness, and sandstones of many kinds : among the argillaceous beds are concretionary limestones, irregularly developed. Colour mostly red, or grey liable to become red. Ttuckness variable, from 100 to 10,000 feet

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.

Millstone grit group. — A series of very pebbly quartzose and felspaothic 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. 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 norths viz* in the north-western parts of Yorkshire the series is still more complicated and varied : as under : —

1. Coal formation.

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 ; iron-stones ; 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

6. 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-

156 A TBBATISB ON OBOCiOa?. CHAP. VI.

positions of grits, shale, and abundance of coal ; one of the grits being pebbly. Thus the whole method of variation of the systein of carboniferous strata becomes known and appears nearly as in the diagram (fig, 18. 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 careM examination we should be disposed to ex- press it, where only small and diminished members of the mountain limestone formation (in one place yielding coal) appear buried in masses of red conglomerate, sand- stone and shale, of very geat thickness, there being no certain criterion for deciding that any of this series belongs to the new red sandstone. This section is, however, much in accordance with the views of Hoff- man, who, in north-western Germany, finds the car- boniferous 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 existing in the Englisli and Scottish coal fields, is generally about 50 or 6O feet: this is, in most districts, divided into SO or more beds, of a thickness from 6 feet to a few inches, alternating 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 deptnding 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 : —

Ohap. Vi. Sbgondaby Strata. ;]57

W

la

Yds.

Ft

In.

/

Brown post, or grindstone sill

/

Coal -

Rock measures

Coal . .

Rock measures -

Coal

.Rock measures

/f.

Coal - - -

f

Rock measures

Coal - - - .

1 '

Rock measures

to

S

Coal

Rock measures -

Coal

m

Rock measures

m

Coal

Rock measures

Coal (High Main)

ift

Rock measures

Coal (Metal Coal)

Rock measures

Coal (Stone Coal)

w

%

Rock measures

m

Coal (Yard Coal)

m

Rock measures

m

Coal

m

Rock measures

m

Coal (Bensham)

m

Rock measures

m

Coal

Rock measures

Coal

Rock measures

Coal

Rock measures

Coal (Low Main)

Rock measures

Coal

Rock measures

Coal

to

Rock measures

Coal

Rock measures

Coal

to

Rock measures

to

Coal

to

158 A Tbeatise On 6E0L06T. Chap. Vi.

Yds. Ft In. Yds. Ft. In.

Rock measures - - 12

(Whickbam St.) - 2

Rock measures - - 10 O

Coal (Brock well) - - 10 9

Various rock measures 50 2 Millstone grit

380 6 15 2 3

In Mr. Buddie's excelleiit 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 very little ironstone in the coal tracts of theTyne and Wear. In Yorkshire, the total thickness of the coal formation is from 1000 to 1500 yards. In Lancashire perhaps a greater thickness must be ascribed to it. In South Staffordshire (Dudley), it does not exceed 1000 feet. The most variable partSj in all coal tracts, are the sandstones and shales ; itie most regular parts are the coal beds and ironstones.

Organic Remains. — The' forms of life buried in the carboniferous system of strata are exceedingly numerous and varied, and, being generally in an excellent state of preservation, allow of a most strict comparison with exist* in types. They consist of very many races of plants, abundance of zoophyta, multitudes of moUusca, 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 terrestrial growtii : aU the zoophyta, and nearly all the mollusca, Crustacea, and shes, are marine. The excepted mollusca occur among the remains of plants swept down from the land : the excepted Crustacea are those referred to by Dr, Hibbert, in his account of the fiurdiehouse lime- stones, with which also a few fishes are found, which, by (Ms 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 altogetiier unlike them, as the large.furrowed stems of

Chap, vi, secondaut strata. 159

BigiUaria, the qoincuncially orDamented stigmariB, &c On making the most close comparison which the spb- ject admits, we find that among the foBdl fems are arboTescent species, to which we can only find paiaQelB iu warm or else Australian regions ; that the same analogy to the productions of a warm climate ia suggested by fossil equiaeta, and confirmed by the lepidodendra, which seem rdated to existing lycopodiacec in structure, though enormously surpassing them in dimenuons. Even the sigiilariE, when caiefiilly studied, though they be not cacti nor euphorbiie, nor arborescent fems, are so much like those singular plants of hot climates, as to add conderably to the accumulating evidence in this directioD.

The following is a brief summary of the plants ; — Crypttaniia niculosa — EquUetaceM (bout SO ipecies, niioea mboTG 100

lijcopodiaecB about 60 PbsiKrogamia monocotf-

Conifers . . . 10

CsclesceM ... 50

l60 ▲ TBBATISB ON GEOLOGY. CHAP. VI.

Of the accumulated remains of these plants coal seams are really composed and one cause of the differ- ences amongst them is the different structural composu tion of the original plants. How far the ahove fossil flora is to be taken 9s 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 tbe waters.

As a general rule it may be said that the plants are confined to arenaceous and argillaceous deposits : they Abound in the upper parts of the carboniferous system, where cpal 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, and are rare in the old red sandstone. It appears the most probable view that the plants forming coal were, with tbe arenaceous and argillaceous substances, swept into the sea by inundations from the land, and subsided into strata on the bed of the sea : forests or peat mosses submerged might be com-* pressed into coal, and covered by inundated sediments ; but this notion of De Luc requires in a coal district 50 or more elevations and subsidences of the same tract of land, a phenomenon too remarkable not to have left evidence of an independent character.

The plants appear, however, not to have been carried far into the deep sea, but rather (at least in the upper or true coal formation) to have been lodged in estuaries where shells of fluviatile genera might exist. Nothing offers a more striking similitude in modem nature to the processes whereby, as we suppose, an old coal form- ation was produced, than the accumulations of timber, and various sediments, at the mouth of the Mississippi. See (Lyell*s Principles of Geology.)

The zoophyta of the carboniferous system are almost

LTA. I6l

(perbapa wholly) abfient from the coal fonnation: ihej are almost confined to the monniain hmmtane fonnation and to its calcareous portions, thua offering tu most clear proof of the marine origin of that rock. When to this, we add .the absence of land reliquige from these limestones, it is evident that the materials of which these rocks are formed were not Swept from the land like the sahatance of the arenaceous rocks, but elabo~ rated from the salts of lime diffiised in sea water. The zoophyta are partly of families almost extinct, as cii- noidea; and partly of tribes yet abundant in the lea, U lunelliferous corals : the genera of corals often bt not always (e. g. astrsa, Uthodendron) diSer from diose now living. The following summary is extracted from the " Geology of YMkshire," vol. ii. p, 24fl. : —

Zocb — Polypsria - - 41

Crinuidea . . - 40 Echinida . - 3

1. STnngDnn™ nmiiliiH. OoliffUl,

S. CmUioplisUuni (or UltacDtroUaii) bmltifOnac. FkiOlpi.

The molluscons reliquia are numerous ; 326 species being described in the " Geology of Yorkshire," without

l62 A TREATISE ON OBOLOOT. CHAP. YT*-

noticing about a dozen t)ther8 from the coal formation, which are included in the following general summary :—

Mollusca — G>nchifera plagimyona - 40

mesomyona - 28

brachiopoda - 100

Gasteropoda -92

Cephalopoda monothalamia - 10

polytbalamia - 69

S39

Of these, only about 10 can by any means be consi- dered 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 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

Explanation Of Figures, 163L

1. Producta icabriculuf. Sovierhy. It occurs in mountain Umettone ge-

nerally, and in ooai strata at Coalbrook Dale

2. Froducta punctata. Sowerdy. Common in Uiecaiteniferous limestone.

3. Terebratula pleurodon. FhiUipt. Common in tbe carboniferous lime-

stone.

4. Spiriferacuspidata. Sowerbff. Not rare in the carboniferous limestone.

5. Pleurorhyncnus minax. PhUUpt, From the caiboniferous limestone of

Ireland, Yorkshire, I>erbyshire. & Inoceramus vetustus. Sowerby. From the limestones and shales of tbe north of Enaland, the north of Ireland, kc

7. Ooniatites spnericus. Sawerbu. A common shell in the limestone.

8. Bellerophon tangentialis. FkUiipt. From the limestone of Ireland,

Yorkshire, ftc

9. Orthoceras cinctcm. Sowerby* From tbe limestone of Irdand, north

of England.

10. MeUnia constricta. Sowerby. From the limestone of Derbyshire,

Yorkshire, ftc.

11. Pleurotomaria flammigera. Philip. From the limestone of Bolland.

12. Natica plicistria. PUUipt, From BoUand in Yorkshire, Ireland, &c.

13. Euomphalus pentagmialis. Sowerbu, Common in the limestone of Ireland, nortn of £2ngland, &c. Its internal cavity Is divided into chambers by imperforate septa, u was first noticed by Mr. W. Gilbert- son of Preston.

I. YI. WKOHpABY STIUTA.

l64 A TREATISE ON GSOIiOOT. CRAP. YSt

beautiM and characteristic features of this fonnation 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, how- ever, less numerous and varied than in the older Silu- rian rocks where they are remarkably numerous.

The fishes of the carboniferous system (Caithness Biirdiehouse Leeds Bnulford Manchester) are mostly of the ganoid division of Agassiz: some of them are comparable to lepidosteus ; and according to this able writer the larger sorts (megalichthys holoptychus) had so much of a real analogy to reptiles (in the bones of the head and character of coverings) as to justify the application to them of the title Sauroid Fishes." From this general review the reader will infer that most of the forms of plants and animals of the carboniferous system are very distinct from existing types but yet comparable with them and intelligible by them ; but that genera are mixed with them iirhich cannot be or at least have not been at all discriminated from recent; 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-deft valleys and rock-breasted hills of the mountain limestone which in Cheddar diffs on the banks of the Wye in Derbyshire the Yorkshire dales and parts of Cumberland Westmoreland Lancashire Flintshire and Glamorganshire offers most attractive features to the artist. In Ireland this rock is the source of very fine effects about Sligo and £nniskiUen. The Mouse flows from Namur to Huy through a succession of predpioes of limestone comparable to those of the Vye. There is not Ihe same praise to be bestowed on the scenery of the old red sandstone, which, however, on the border of the Grampians, makes some interesdjig rock scenes (Braclyn Bridge), and in Breconshire and

CHAP. VI. fiBOONDABT STRATA. l65

Cannartlienshire rises into the Beacons and Vans. The coal formation is generally found in countries deficient of heauty of form and luxuriance of vegetation; yet the undulations of tlie large coal tracts of Yorkshire and Soudi Wales, wi1& the nohle oak woods which fill some of thevaUeys, are worthy of notice.

The millstone grit and Yoredale rocks form in the north of Enand a peculiar order of scenery; for resting in detached masses upon broad, bare surfaces of scar limestone, their bold craggy tops and edges, and abrupt precipices, produce often a grand, though sometimes a formal effect, and their combinations are frequently fine. To this country belong also many beau- tiful waterfalls, originating in the decay of soft shales, and grits below ledges of limestone, over which the stream flings itself, in a free and lofty leap< into a dark jmd precipitous glen. (Hardrow force, in Wensley Dale; AshgiU force, in Aldstone Moor.)

Anotaer thing worthy of notice in the scenery of the limestone districts in the north of England, especially Derbyshke, is the diflrence of herbage in the millstone grit, limestone shale, and limestone. On the latter (/), a fine green turf — on the shale (s), bluish een sedgy pastures — on the grit rocks (m), brown or purple heath, enable a gedost to mark out the leading features of dis- tricts with great facility, suggest to the botanist many interesting inquiries, and demonstrate to the agriculturist the dependence of the quality of on the rocks which they cover.

Geographical EatenU

The surface of country occupied by the rocks of the carboniferous system is proportionably much larger in the British islands than in oth parts of the globe. In

M S

l66 A TREATISE ON OEOLOOY. CHAP. Vi;

Ireland, the greatest part of the plains and broadl undulated interior consists of the mountain limestone in places covered by coal measures, and in other parts supported by the old red sandstone. In fact, ex- cluding the parts previously described as gneiss, mica schist, day 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, nearly all the rest of Ireland belongs to the carboniferous system. But the quantity of coal yielded by the coal fields about Lough £am 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. The old red sandstone appears in Tyrone; about Omagh ; near £n- niskillen; on the south side of Donegal Bay; about Boyle and Longford : large tracts of the same appear N. W. of Lough Derg; about Killaloe andRoscrea; south of Tipperary ; south of Clonmel; about Waterford and Thomas Town. But the greater part of the spaoe between the primary tracts of Cork, Galway, Mayo, Donegal, Down, Cavan, Wicklow, Carlow, 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 old red sandstone ranges on the north-west coast of Scotland, in interrupted patches from near Cape Wrath to Loch Carron, Skye, and Rum : on the north- east side, it forms a large surface in Caithness, skirts the Dornoch and Moray Friths, passes up the great valley to ealefavoumie, and spreads by Nairn and Elgin to the vale of the Spey. A lai belt of red conglomerates borders the Grampians, from Stonehaven

CHAP. VI. SEOONDABY STRATA. l67

to the islands in the lower part of Loch Lomond, and occupies much of the seaF-coast to the Frith of Tay. Red sandstones border the northern flanks of the Lam- mermuir Hills expand in the vale of the Tweedy and margin the slate tracts of Dumfries-shire and Kirkcud- bright. Arran Bute Cantire and the coast about Largs and Ardrossan show the same formation.

In England the carboniferous system of rocks is widely expanded. Old red sandstone appears in the parts adjacent to the Tweedy often associated with the lower beds of limestone into a transition group : it is seen along the line of the Penine chain about Duf ton ; and appears in the lake district at the base of Ulswater, in the valley of the Lune and other parts. It is deve- loped enormously in the counties of Hereford Monmouth, Brecon Carmarthen and Pembroke; but is slightly exposed in connection with the limestone of Mendip Bristol and Wickwar.

The mountain limestone formation occupies an im- . mense tract in Northumberland Durham and Yorkshire, from which country it runs out in a curve, to encircle 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 Angesea ; shows slightly round the Clee hills in Shropshire; and presents 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 prolonged on the south side by Bridgend, Swansea, and Tenby, to Mil- ford Haven. Detached masses of limestone appear about Bristol and in the Mendip Hills, and, according to Messrs. Murchison's and Sedgwick's recent researches, the limestones of Barnstaple may. be of the same age.

*The carboniferous limestone is supposed to occur in a narrow band below the coal formation of the Clee hills, and this is probably the correct explanation of the phenomena viuble under Eoiowle hill, at Orelton, &c :

M 4

but we muEt chU attention to the fact that die white (aometimes intemitllyblae) oetMclimeMone there oeoir- ring is associated not only with dark shalea (eluDch), and lit marly beds, altogether of a conuderable thickncM, at least 100 feet, but is also orerlaid by an important deposit of Ted, whitish, and greenish argillaceoua etrata, altogether of the eame nature as the "old red formation" of the Ticinity. The whok aenea of the south Clee hills may be thu exprened in general terms ;—

n EnBi, nme of Uwm iTOQ-edtcil iDd

CIcveoui laren, undT or ,.

Bluk cLunch rbnlllfcraiu. (CrinoldBa, , lenbntuU,] Umcttoneliiio1idlwdi,HieHlTTDotitkc,m[Kh dlsturtKd In the iLni Arabon, u Ell the ikeicn {Ctenicanthutud other foeuti.)

Admitting the limestone and shale beds (b, e, d, to be the equiTalcmt of the \omet acar hmestone (Derby- shire limeaume) of the north of Ensnd, the quartzose conglomerate (j) may be ranked as milbtone grit ; and the red and white eUys (/) most be considered as a recurring hed of Ihc <Jd red mari, intttpolat among the carbonifmous roat, joat as the red grits and claya of Orton and RaTenttone dale have been described as marking one form of a transitiMi between the lAA red sandatoue and the carboDiferona fbrmaiion, on the bonier of the primary ditnct of WcatmoreU&d.

Chap. Yi. Sxoondart Strata.

The millstone grit is an important deposit in th 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 Ribble. 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 coal 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 Derl)yshiie; 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 moimtains about Enniskillen.

7he coal formation of Northumberland and Durham extends from the Coquet across the Tyne Derwent, and Weax, to Cockfield where it suddenly breaks off, and ends against the valley of the Tees; and no more appears between the magneaian 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 Whiter haven : a small field of coal lies at the foot of Ingle- borough (corresponding to one at Hartley Bum, on the South Tyne). The coal dMsits of Lancashire form a considerable breadth, ranging east and west, from Man* cheater by Prescot and Wigan to near Liverpool, and ap- pear to be connected underground with the coal tract of FUntshirej and, perhaps of Shrewsbury. The detached

170 A Trbati8B On Oeolooy* Chap. Vi.

coal fields of Ashby de la Zouch Coventry Dudley and Colebrook Daleare very valuable: some smaller fields are known south of Sbrewsbury, in the Clee HiUs and at Newent. The Forest of Deui is a rich though small tracts and the disonited patches of coal in Kingswood, and south of the Bath Avon are valuable. Almost the largest coal field in Great Britain is the great oval don* gated tract of South Wales from Pontypool to St. Bride's Bay which furnishes fuel to the great ir6n works of Merthyr Tredegar Neath, &c. It is thought by some geologists that the culm of Devonshire (Bideford &c.) lies 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) exists 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 ve hundred years, and during that period meet the hourly enlaing 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 coal 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- wise than with praise of the working of the collieries

Ohap. Vi. Secomdaby Strata'. .171

in which much judgment and humanity are often to he noticed hut in the irregular and accidental manner (depending on distribution of property private in- terests, &c.) in wiiich the sites of collieries are chosen, and their field of work defined. Many portions of country are thus left full of unattainahle coal ; others untouched from dread of the water in long-ahandoned works : heds of coal, of inferior quality or thickness, are abandoned till the fUture scarcity of fuel shall render it profitable to work them, imder 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 lslative 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 maniactures; 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 imattainable 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,

172 A TREATISE ON GEOLOGY. CHAP. VIr

near Boulogne and passing under the chalk and green sandy continues in an easterly direction by Valenciennes, MonSy Charleroiy and Namur, to Liege and Eschweiler near Aix-huChapelle. 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 WestphaUa 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 esia, 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 moimtain 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 ooal fields.

Chap. Vi* Seoondabt Strata. 173

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 fekpathic, 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 Tau- tallan and the Bass are the extremities of a lai body of trap in Haddingtonshire : these rocks abound between Linlithgow and Bothwell ; and a great variety of igneous masses occur about Kinghorn the Lomond hiUs 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 daystone homstone trachytic porphyry clay porphyry basalt and greenstone appear in many dikes taid form interposed

17 A Treatise On Qeoloot. Chap. Ti.

beds of great interest in the theory of the formaticm of sQch rocks. (Jameson M'CuIloch Sec)

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, eoal 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 Nortbumber. land and Durham, but totally imknown in those of Yorkshire, Derbyshire, Nottinghamshire, and Lanca- shire. In Derbyshire, the limestones are separated by an irregular mass of interposed amygdaloidal trap, called toadstone;" (by some, more than one such bed is supposed to exist).

Mr. Murchison has described the trap rocks which penetrate the coal measures of the Titterstone and Glee 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 hiUs 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 ahnost

CHAP. VI SEGO.niARY STRATA. 175

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 formations are extensive, but, 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-

176 A TREATISE ON OE0L0o¥. CBAF.

merates of the Grampians the Lammennuirs, and the Comhrian valleys hold fragments of the neighbouring and hut lately uplifted rocks ; hence the ahsence 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, even when swept down into estuaries and the 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 find 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 palms, cacteaces, and lycopodiacese 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 add, against which no law of nature militates, (for

Ohap. Vi. 8E0Ondaby Strata. 177

we know not if this 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 there being no land animal on the globe, Wiitiin 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 reqidre most animals require least.

De Luc, Brongniart, and other writers, prefer to explain the origin of coal from somewhat like peat-bogs, or from the decay or overwhelming of forests in situ : and this may possibly be found true of particular cases ; but it is not to be admitted as a general explanation. In most coal districts are from 20 to 60 seams of coal, alternating with sandy and argillaceous strata, for each series of which (coal, sandstone, shale) the land must have been raised, decomposed to soil, covered by forests or peat, and then again submerged to receive sediments from the land or littoral agitation ; and these nume- rous risings and fallings of the bed of the sea have left no independent proof of their occurrence. Un- doubtedly there is a plausible argument furnished to De Luc's hypothesis, by the stems of sigillaria, sup- posed to be in attitude and place of growth ; but until lepidodendra and coniferous trees, of which coal at least in part consists, shall have been similarly found, and in equal abundance, and until the reality of these stems being rooted shall be proved, we must not yield the general arguments to this exceptional and imper- fectly ascertained phenomenon.* Inundations from the upraised land, littoral action of the sea, chemical decomposition of the oceanic waters, eruptive action

What have been called the roots of those erect trees are no? always really parts of the same kind of plant. "We do not yet know uthat the roots of sigillaria.

Vol. I. N

78 A Treatise On Geology. Ch.. Vi.

of sobterranean heat vital action on the land and in the water — these are the causes to which the formation of the whole carboniferous 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 modem effects precisely comparable in kind, but altogether inferior in magnitude.

Where then was sitnated 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 important question which appears in my 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 exuviie and xwhen 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- stones and shales grow 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 norths the coal beds also augment in number and thickness; and the limestones change gradu- ally from an undivided mass to many distinct members separated by sandstones shales coal and ironstone.

Ohap. Ti,

Seoondart Strata.

Thus to any point in diagram No. 5S.where a ae- ries of limestone sandstone shales coal ironstone occiin

Is

k

the limestone may be supposed to have been brought by division in the ocean om an area situated to the south-east ; the shale transported from the west and the sandstone plants &c drifted from the north. We may imagine two riv.ers, 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 norths loaded with sandy ipatter and bearing abundance of trees of difier- ent kinds hut not many ferns or delicate herbaceous plants. Alternately or contemporaneously these rivers might fill the sea with deposits such as we behold and in die 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 day ; but it is necessary previously to inves- tigate the directions in which the agencies concerned in producing each sort of sediment were most powerfiil; I. e. the points or lines of their greatest intensity.

N 2

180 A Xbeatue On Oboiagt. Ohaf. Ti.

In 8ome cases it appears highly prohable that one ifttch irrulax flayiatile action modifying the continuou depositions from the sea would sufficiently explain the phenomena of the association of sandstone shale and limestone; hecause hy such action the shores would he margined hy a sandy deposit heyond which day would predominate in the sediments and at a greater distance calcareous matter would he nearly unmixed with the effects of littoral agitation*

In the diagram No. 53. S represents the sandy accu- mulation near the shore passing hy gradation to the

I iiiiDlltTT

deposit of clay c, which extends further and is finally replaced hy nearly pure carhonate 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, Caran, &c., were perhaps ahove 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 ; 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 disap- peared 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.

Chap. Ti. Second Abt Strata. 181

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 maiin 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 lose 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 though dark inquiry, will, however again arrest our attention.

Extent of British Cwd FieMs 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 cimnot be kUown : 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 obe 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 disturb- ing mJyemru at . distance.

After, however, the deposition of this whole system and before, at least, any considerable part of the next (red sandstone 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.

N 3

A Tbeatudb On 6E0L0Ot.

Chap. Ti.

Every coal field in these islands is remarkably dislocated by faults, often traversed by rock dykes, sometimes ridged or furrowed by anticlinal or syndinal 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, Bent, and Kirkby- Lonsdale; and afterwards eastward to near Grassing- ton, in Wharfdale, a distance of 110 miles.* The whole of the somewhat rectangular tract of country, included be- tween the northern (Tynedale), southern (Crayen), and middle (Penine) portions of this faidt, 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 grauwacke rocks show themselves along the Penine and Craven portions, while small coalfields appear on the parts at h and t, 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

See separate Memoirs bjr Sedgwick andlhiUin in Geoloeical Ttani.

ikuit

Chap. Vi.

8Ec0Ndabt Strata*

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 disimion 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 but for the covering of red sandstone, which conceals the coal along the middle of the basin.

The great South Wales coalfield is a vast double trough, having an included anticlinal axis, ranging east and west ; as Diag. 56*.

and if the Barnstaple and Bideford beds belong to. this system, their principal dislocatipus range also east and west : this is, perhaps, the most general line of move-> ment in the Somerset&liire tracts, where dislocations are numerous and remarkable : it is renewed in the north of Prance and Belghim (at Mons and Namur), and about Elberfdd. Without now stopping to discuss the bear- ing of these results on M. de Beaimaont'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

N 4

184 A Treatise On Geology. Chap*

(See Cambridge Transactions) to the dislocations of th6 carboniferous system will be successful. Mineral veins commonly range a little N. of £. and a little W. of N. on the carboniferous system of the north of £ngland.

Sauferous System.

New Red Sandstone System of Authors; Poidlitic System. (jConyheare.)

Composition, — After examining the carboniferous rocks the red sandstones and the associated strata pre* sent diemselves with an air of novelty and freshness, not less striking to the geologist than a new country to the traveller. Instead of the blacky blue or grey limestone full of crinoidal columns, products, &c., we have now yellow, sandy, or granular rocks, with few organic re* niains : 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. One feature, indeed, the systems have in common ; viz. red conglomerates at or near the bottom ; and close ex* amination points out several instances (Manchester and Salop) of transition coal deposits, in which red grits and clays inclose coal, with shales and Umestones of a pe- culiar aspect.

The arenaceous deposits are a considerable part of the red sandstone system ; they are generally red, and not micaceous. Some of them are coarse brecciated rocks (Kirkby-Stephen), containing limestone fragments; others conglomerates full of various pebbles (Notting- ham castle) ; others holding a few pebbles (Runcorn). Many are coarse red grits (Penrith Beacon) ; or finer buil(ting stone (Meriden Hill, near Coventry), often white or greenish (Warwickshire). It is worthy of notice, that the grains of red sandstones near Manchester were found by Dr. Dalton to be internally a clear quartz the red oxide of iron being merely an external coating.. In Germany Tu% grits (keuper), somewhat resembling certain of the coal measure sandstones.

;09AP Yh SECONDARY STJEtATA. ' 185

The argillaceous members are usually called marl," though they contain little calcareous matter : they are often laminated ; their cobur is usually very red ; but in the reddest cUfis occur distinct bands and spots of a iiluiah greenish or white colour; and in particular jMtrts of these variegated marls lie nodules and irregular .beds and yertical plates of gypsum very strangely rami- fied or completely insulated in the mass of argiUaceous -matter.

The limestones of this systn vary much. They are often loaded with magnesia, and in general called mag- nedao limestone ;" but there are many beds in whi little or no foreign admixture deteritnrates the carbonate of lime. The colo|p:8 are white, grey smoky, but more frequently yellow; and in some distaicts reddened, or even very red. In texture a few limestones are compact, 'fiome oolitic maay cellular, the cells lined with crystal- sed carbonate of Ume a large proportion of a fine sandy grain, some quite powdery, with crystallised bdk incbbdeiH ; and in Nottinghamdire, c(isiderable tracts yield granular crystaUised limestones. Near Sunderland laminated rocks are really of sparry textmre. Strings md plates of spar are very common, and render build- ings of the magnesian limestone very irregular in their idecay, from the unequal perishing of the stone between the ribs of spar.

The muschelkalk of Gennany, not yet admitted as an English rock (the upper part of the magnesian lime- stoie of the north of England is somewhat similar in min- eral properties, but is apparently lower in the series), is usually a compact, hard limestone, of a grey or smoky tint; sometimes (Courcelles) it deviates to a whitish soft stone, more analogous to the magnesian type.

Rock salt occurs in the state of clear, white cubic- ally crystallised masses, or reddened by the argillaceous sediment among which it occurs ; sometimes in Cheshire the red salt is fibrous. Brine springs, which issue frcHU rock salt," contain combinations of iodine and bro- mine though in the rock itself that substance can hardly

186 A Treatise On Geology. Chap. Vx.

1)6 detected ; a drcumstance depending on the extreme solubility of the iodic and bromic salts.

Gypsum a very general product of the red argillaceous members of this system and very commonly found in the Tidnity of rock salt, is largely foliated (selenite) at Fairbnm, near Ferrybridge, granular at Chelweston, near Derby but generally fibrous as at Pocklington Nottingham Aust Passage, &c.

Structures of Deposition. — Stratification is distinct in all these rocks ; but in all of them some peculiarities appear in this respect. Among the argillaceous beds lamination prevails; but the gypseous interpolatiouB produce great anomalies and suggest what is probably true that this mineral is often 'a fregation of later date. The sandstones are laminated or bedded and the pebbly varieties commonly present most decided proofs of the agitation under which they were collected in the abundance of oblique lamination false bedding " of authors), as in Nottingham Castle HilL

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).

IHfjisionaJ 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 day and roUed pebbles ; in other cases they are merely thin cuts in the rock ; always their regularity, paralldism, and polarity (if we may so term their direction to N. or N. N. W., and it rectangle £. or £. N. £.), are remarkable. In other thick-bedded limestones, the joints are less symmetrical, though always numerous: most of the rocks are traversed by small secret cracks which, on being exposed by frac-

Chap. Vi.

Secondary Strata*

Red MDdstone formation, in places sunk into 600 It

ture are found covered by dendritical markings of a dark colour. The joints are often coated by carbonate of lime, sometimes by carbonate of copper, or sulphuret of lead.

Succession and Thickness of Strata, — The most, or rather the only, complete series of the new red system in the British islands, is that of the north of England, where alone certain lower members are clearly exhibited. In Warwickshire, principally lie the grits (white, grey, and greenish), which are supposed to correspond to the keuper of Germany. The following synopsis is founded on the views of Professor Sedgwick. On Magnesian Limestone/' Geological Transactions,)

'k. Variegated marls. Red, with bluish, greenish, and whitish laminated days or marls, holding gypsum generally, and rock salt partially (as in Cheshire); in- cluded in these marls are certain white and grey sandstones, supposed to represent the keuper grits of Germany.

/. Variegated sandstones. Red sandstones, with some white and mottled portions ; the lower parts in some districts (Notting- hamshire) pebbly.

e. Laminated limestones of Knottingky, Doncaster, &c., with layevs of coloured marls, SO or 40 ft.

d. Gypseous red, bluish, fte.. marls.

c. Magnesian limestone, yellow, white of various texture and structure j some parts All! of fragmentary masses.

b. Marl slates ; laminated, impure, cal- careous rocks, of a soft argillaceous or sandy nature

a. Lower red sandstone, with red and purine marls and micaceous beds ; some- times the grits are white or yeOow ; and pebbly, or loose sand. Occasionally passes into coal measures, on which it rests.

In Somersetshire, and other parts of the south of England, the section consists almost wholly of gypseous red and variously coloured marls, with a few beds of red sandstone, having near the bottom a pebbly or brec. ciated rock called millstone, or magnesian conglomerate. The fragments imbedded are usually calcareous ; but near older gritstone rocks conglomerates of the' red marl are foimd to contain gritstone pebbles ; magnesian con- glomerates border the Staffordshire and Salopian coal fields, and have a lower red sandstone beneath them. At Manchester, the magnesian limestone is somewhat

Magnesian limestone form- ation, 200 or SOOft. thick.

A Treatise On Geology.

Chap. Vi.

better defined; at Kirkby-Stephen, it is represented by a brecdated limestone rock ; and at St. Bee's Hea4 is a complicated formation of considerable thickness, in which the calcareous part is an important feature.

The principal difference between the complete Ger- man series and the English, lies in the addition to the former of the limestone called muschelkalk, above the variegated sandstones; the greater variety of substances corresponding to the variegated marls, and the far greater mass of thelowor red sandstone. In the following table the complete French series is induded : —

Gennany.

Keuper xomxU and grits.

Muaohelkalk. Bunter sandBtem. Stinkstein, rauchwacke,

&c. 6]rpeoiu aarla. Zechstein. Kupfer schieFer.

Rothetodtefiende.

England.

C Variegated mariSyand ") white and grayS- C griU. J

Variegated sandstonei . U{4ier limestone.

Gypseous marls. Magnesian limestone. Marl slate.

Lower red sandstone.

France.

Mames Irise

Muschelkalk. Gres bigarre.

Gres de Vosges. I Gres rouge.

It is evident that the limestones are the least ex- tensive members of the series. Rock salt, which, in England, is found only in the variegated marls, lies in them bodi in France and Germany, but is even more common in the muschelkalk.

The Organic Remains of this system, though few in number, 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 plants, shells, fishes, and reptiles of this system appear to partake both of the character of those in the older carboniferous, and the newer oolitic, deposits. Calamites, like those of the coal formation, are mingled with cyca- dese, resembling dosely those of the oolites. Productie, so common in mountain limestone, occur in the zechstein

Ohap. Vi.

Sboondary Strata.

with teebratalse like those of the lias and oolites. Fishes of the genus palsoniscus here occur for the last time in ascending the series of strata ; and here per- haps for the first time, we have remains of oviparous quackupeds — the protorosaurus phytosaurus. These interesting relations appear in the following tahle which also contains the names of some fossils which are found' in only one of the three systems :—

SeUmmtet. AmmomUM,

as

.saJS

'Oolitic Formation.

Ceratite$.

Orthoceras, Gontatites.

g

H09

a

tt C

Keuper.

— a

Muicfaelkalk.

Red sandscone.

ZechateiD'

Mrl slate.

Rotheliegenda

a

o u

o 6

o

o o s

u

Zanua.

VoUvta.

Piiu' Coal Formation.

O as

Stgaiarta.

According to the organic remains the lower half of this system might he 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- pened at the period when a decided change was taking place in the conditions which determine the forms of life upon the globe.

The following summary of the organic remains of the red sandstone and magnesian formations of England, includes some species in the possession of the author, which have not yet been figured : —

Pbnto -

Zoophjta — poljpuia. ITiree ipecie

On

Traces in the limestone, DurbaTn. Volltis in the limestone, Durham.

Dictjophyllum, Ac, &c., in Che.

shire, Worcestershire, &c. llree (pedes beloDgiog to retepora.

CnchiJen — plsgimyoiiL Ten or more ipecie*.

meioinyOTU. ThreeormareBpedes.

brschiopodii. Ten or more spedes. Molluua — guteropodo. Four or more tpedo.

cephalopoda. (Nautilus.)

Crustacea. ?

Fiilies — About 10 ipedes, chiefly of the genus pi

in liroealone, Durham ; in undstone, Tyroiw. Reptiles — (thecodoDlosauniB — palMouunu) in limestone.

pbytoBurus? b sandstone Warwick.

Thiu, aboat 50 specieB of fosaili occiu in these locka in England, while SOO have been noticed in Griiian; and France. Everj where, however, the red undEtont ppeu to have been accumulated under circumstancea un&votintble to the occurrence of vegetable and animal

OHAP. yz. SECONDARY 8ZBATA. 1 91

Geographical Extent — Slight traces of new red sand- stone occur on the western coasts and Islands of Scot- land : some considerahle area is occupied by it in the country between Coleraine and Dungannon about Bel- fast and on the coast of Antrim ; but it is in England that the system takes its great development. The Solway Firth is in red marls and sandstones and all the rivers which enter it from the Scottish frontier flow through the same (Dumfries, Lochmaben, Long- town) ; the plain of Carlisle, with nearly the whole course of the £den, is on these strata, which also appear on the western coasts, from Whitehaven to Fumess, and exist under the peat mosses of South Lancashire. The Vale of Clwydd is formed in the red formation. The river Tees, in Yorkshire and Durham, enters the sea in gypseous red. marls and sandstones; so does the river £xe in Devonshire : and between these two points is an almost imintemipted line of the same strata, ranging by Stockton, Northallerton, Boroughbridge, York, Snaith, Doncaster, Retford, Nottingham, Leicester, Warwick, "Worcester, Tewkesbury, Newnham, Aust Passage, Wells, Taunton, and Honiton. From Hartlepool it is bounded on the west by magnesian limestone at Pierse Bridge, Catterjck Brieve, Ripon, Knaresborough, Ferrybridge, TickhiU, Mansfield, to Nottingham : but from this point to Worcester, as a base Une, it expands westwards across ' the whole island from Nottingham to Derby, Ashboum, Newcastle-under-Line, Macclesfield, Stockport, Man. diester, Newton, Liverpool; from Worcester to Kid- derminster, Bricenorth, Newport, Shrewsbury, EUes- mere, Wrexham, Runcorn, Liverpool — thus occupying an enormous area in the centre of England, partially broken by the upheaved coal measures of Leicestershire, Warwickshire, and Sta£Pordshire Small detached por- tions 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

192 ▲ TRBATIgE OK GEOLOGY. CBAP. Vl.

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 Widich and Vlanden, southward to Thionville, Pont- a>Chaussy Chateau Salins and Vic (where rock salt occurs), Mirecour, Jussy, and Villersexel ; eastward to Treves, Wadem, Kaiserslautern, Neustadt, Weisspen- bourg Weshofien, 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, and 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 enormous areas, oh a line from Waldshut

Chap. Vi. 6Ec0Ndaby Strata. 19

to the Thuringerwald and all around the Harz. Salt occurs in*the keuper and muschelkalk especially. Con- siderable tracts o£ new red sandstone adjoin theRiesenge- birge ; and Hne of these rocks occasionally saliferous borders the priniary ranges of the Alps from the vale of the Danube by Rottenmann Radstadt, to near Inns- pruck* On the south side of the AIps 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 scdiferous 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 subterraneaif 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 south of England constitutes a fine natural ter- race of 100 to 500 or 600 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.

VOL. I. o

194 A TilEATISE ON GEOLOGY. OHAP. VI.

Origin and Aggregation of the Materials of the Saliferous

System.

Peculiar in their mineral composition, rocky Btructure 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 freeij 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 yeUow 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 offier 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 ?

In the same manner the limestones offer curious topics of remark. Where they degenerate to a sandy state (near Nottingham) they assume a decided red tint; or is this tinge any where entirely absent from large

<3Bap. Vi. Secondary Strata. 19

tracts of magnesian limestone. It is complicated with pul-ple (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, dif- ferent modes of aggregation : for the shelly rocks of Hawthomdean and Humbleton (Durham), we may, with some confidence, claim a corallaginous 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 Ume and magnesia, which were after. warcfs 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 weU 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 Gffpmnu

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 rooks, 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 solution of the problem of the formation of rock sdt.

This general investigation would here be out of place;

19' A TREATISE Oli OEOLOGY. CBAp. YM*

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 yaluable 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 aU 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 Ameiican 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 actiop 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 remfu-kable and frequent in the new red sandstone system. This may, therefore without impropriety, be palled the saliferous system.

Hence we may securely infer that although salt was more or less diffused through all the mane 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

Gsp. Vi. 8E00Ndart 8Tbata. 197

Europe, more frequent in a particular period of the earth*s lamellar incrustation.

It is yery 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 heal heat, or some other cause at great depths, or else to evaporation from a limited area filled at intervals by the sea.

In order to diecover the nature of these local pecu iiaritiee, we must compare the different salt deposits with reference to their Htuation, accompanying minerals, and other leading circumstances.

So littie relation appears between the actaal form of the ocean and tiie boundaries of the ancient seas in which the strata were formed that it will probably be of littie 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 : tiiose of Wieliczlca lie at the foot of the Carpathian momitains on the north, and those of Cardona beneatii the Pyrenees on tiie soutii: many mines in Wurtemburg and central Germany axe in. tiie 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 otiiers far distant.

It does not seem possible to extract from sudh 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 tiie Cheshire salt district, tiie local circumstances are such as to have given occasion for Dr. Holland's hypothesis, that the salt tiiere was de- rived from the neighbouring sea, it will be worth while to discuss the formation of tiiat salt basin separately.

The Cheshire deposits of salt lie along the line of the valley of the river Weaver, in small patches, about

o S

198 A Treatise On Qeqlooy. Chap. ?&

Northwicb. 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- irrularly oval area, in length one mile and a half, in breadth about 1300 yards, ranging from N. £. to S. W. Gypsum, so abundant in many other salt minesy and ge- nerally plentiful in the tracts of red marl, is found in most of the days 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 DeUrmere forest, and the Feckforton hills, and from the course of the Mersey by an extension of the elevated ridge, called Alderley Edge. Below Northwidi these bordering hills come very dose together, and naturally suggest the idea that in ancient times there might at this place have been acddental bars formed, whidi while they lasted, would exdude 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 fresfa-water streams finm 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

CHAP, SEOONDA.RY STBAtA. 199

t /

alt would naturally be occasioned upon any renewed blocking up of the entrance. '

The entire absence of marine exuvis 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 eyident that this hypothesis is wdl 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 dat it employs data Jawn from the present relations of land and se to elucidate the phenomena of a period long gone by and when, from unquestionable evidence it is pertain that their relations were generally yery different. It is tiowever, not impossible that the district in question may have been imdisturbed by any subsequent con-* - yulsion, and only altered in its physical features by tiie general elevation which our island appears to have un- dergone, by tile rapid transition of diluvial currents, and the erosive action of rains and rivers. This is perfectly aupposable, and may be true ; for, as far as yet known, the circumstances of tiie case do not appear to contradict it ; but before adopting thisexplanation, wemust examine other salt deposits, and see whether a similar mode of origin can be reasonably ascribed to tiiem.

Oolitic System.

Composition, — The change of deposits from the saliferous to tiie oplitic 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 rocjts. Nothing can b? a clearer trutii tiian tiiat this great difference of chemical and mechanical depo sits requires the supposition of some great physical Involution in the relations of land and sea. If we suppose

200 A Theatisu On 6E0L0Qy. Chap. Vi.

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 £ngland, 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 test 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

Chap. Vi. Secondary Strata. 201

Stones occur with ironstone beds and diffused oxide 0/ 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 days 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 lamime 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, vellow, 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 sheUs, corals, grains of sand, &c., which served as the points

803 ▲ TAEAT18E ON GBOLOOlT. CHAP. VI.

of attraction for the calcareous matter while it, was in a soft condition.

Structure, — In the whole series not a mass occurs which can he viewed otherwise than as an original dosition 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 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 lamins parallel to the stratification, being nothing less than choically altered coniferous wood. -

Thin limestones associated with thick days, as the lias limestones, are usually laminated or thinly vedded, 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 day often occur between the beds. Oblique lamination bdongs to many of the coarse sheUy oolites: spongoid bodies enveloped in silice- ous matter, lie in the oolitic rocks of Portland and Oxford, but not sa regularly as flints do in chalk : there is very little pyrites, and, except in the lower Bath oolite, UttLe oxide or carbonate of iron in the calcareous rocks, above the lias.

DiviHonal planes.— AVL these rocks are traversed by divisional planes, but very unequally, for the massive days show few of them; in the calcareous rocks they are both numerous and regular; in the coarse and iriegular bedded grits of Yorkshire and Su83

Chap. Vi. Secondary Stbata. 203

the joints are ako 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 certain Unes to produce the phe* nomenon of sliding ground ; this is especially the case in the Hambleton hills Yorkshire firom 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 masseii 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,y and parallel to the immense natural escarpment of the Hambleton hills.

Series of Strata. — On the continent of Europe the t>oHtic 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 proo& 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 aU 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 die 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 formaf

S04

A TBEAtlSE ON 6E0L0OY.

cuAP* vr;

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, hut 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

Inferior oolite and sand.

Upper lias shale. Marlstbne bcdit. Middle lias shale. Lias lirae8toiie. Lower lias shale.

If, comparing Britain with Europe, Yifi view the oolitic system in gross, we shall find as the most general result, three considerable groups of rocks, viz. : — Upper group, coilsisting 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

Chap. Vi. Secondary Strata. S05

followed by calcareous accmnulations 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 manyaltemationsof oceanicrest and littoral moyement 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 thirds 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 rjr,r, — T, 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'\

S06

A Tbeati8E On Qeojjoqy.

CBAP. Til

and h, If, b*', 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 would completely coalesce towards A— and the lines r and 2, and 3, and 4 and 5 toward B The sandstones would yanisfa indefinitely towards and the limestones towards B : a certain portion of sand would be diffused through the calcareous bed toward and some portion of calcareous matter through the sand towards B : the lines of contemporaneity would intersect obliquely the surface of the bedsas in the Diag.(No. 58.)

If the rate of deposition were uniform from each pointy there would be only one calcareous and one arenaceous mass (fig, 59*) ; but if from either of these points the

depositions were subject to periodical changes of intenmty 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 dP beds of different nature proves either cessations or varying intensities of deposition in one of the de- posits ; that consequently, such a system as the oolites must have taken a long time for its accumulation and could not possibly have been generated with that rapidly

CHAP. VI. SECOKDAnT STRATA. 20?

which has been ascribed to the deposition of fonnations from considerations founded merely on the state of con- servation of organic remains.

Organic Remains,-— -Tike numerous remains of plants, zoophyta, moUusca articulosa and vertebral animals, belonging to the oolitic system, have long been celebrated and represented in many works of merit in £ngland 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,)

PlanU — marine - - - 4 — In limestone chiefly.

terrestrial cryptogamous S9 "l

monocotyledonous - 33 (in sandstones and shales

gymnospermous 7 a C chiefly.

uncertain S ' J

Polyparia fibrous - 75 )

oortidferous and ceUu- 7 44 f Cbieflv in limestones, but liferous J f rardy in the lias.

lamelUferous . - 59 3

Raduuna — crinoidea - - . 31

stellerida - . .17

echinida -' - - 47 C Chiefly in limestone, rarely

C. inliast Conchifen-plagimyona .189

metomyona - - 134

brachiopoda . 61

MoUusca — gasteropoda . . 114

cephalopoda - . . S73

annulosa . .55

Crustacea . S8 — Chiefly astacidse.

insects . SO Solenhofen and Stonesfleld.

fishes . . . 40

reptiles - .40

mammalia - . S or 3 ( Only in the lower oolit*

(, formation at Stonesfield.

In the wealden formation, are no zoophyta, no cephalopoda — various land plants — some fre- water bivalves and univalves — a few estuary shells — cyprides, lepidotus, and other fishes — iguanodon, hyleosaurus plesiosaurus, &c., with various chelonida, both of iteah and salt water.

The most characteristic of the plants are the group of cycadee, 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 Goo4 Hope and in India and Austraha. Compared with

08 A Treatise On Oeolooy. Chap. Vi.

existing races, the polyparia present some general re- semblance, with constant and obvious lesser difFerencest. 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 echinlda, 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 buprestids of Stones6eld were not the only beetles that fed its pte- rodactyle and didelphides : 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 t6 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.

TL SBCOIIDAIIS SntATA.

UpjKi Oolite FsnutliiD.

Middle OallteFomution.

Older SysTBUs of Strata,

muktDDfl bodi In tiK ttu

A Trbatisb

L Flan the KeUonT tbA nd , Fall, Frmii Uw Imei ooUW RmuUon,

eBAI. VI. SECONDARY STRATA. 211

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 to 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 ftom a survey of all those monuments of earUer 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 AVestem Islands), Ireland (about Bally castle), and in Wales ( Aberthaw, Glamorganshire). Th&lias form- ation has its western edge continuous, or nearly so, on the surface from the sea-coast near Redcar in Yorkshire to the rival cHffs of Lyme Regis in Dorsetshire. In this long bourse 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 by Bel voir, Leicester, Lutterworth, and Southam to Evesham. From Pershore a long projection of lias 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'

p 2

312 ▲ Taeatise On Oeolooy. Cuaf* Vi.

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 out Bath oolitic form- ation is equally continuous except where un conform- ably covered by the chalk between the Yorkshire Dpr- went and the Humber 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, near Bri and passes by Sleaford, Peterborough and Bedford, to <ttmoor 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 IL. minster, where it is covered by the Dorsetshire chalky but reappears on the soutli 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 Humber 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 day passes byShotoverCumuer Hurst, FaringdoUj

Cbap. Vi. 8Ec0Ndaby Strata, 213

and Swindon to Wotton Basset ; turns south to Seend and Westbury ; appears about Wincaunton and Sturmin- 8ter, 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, can only be understood by consulting a good geological map ; but the preceding no- tices will suffice to show how remarkable is the ejBTect, in the geolc of England, of their parallel courses from sea to sea— from Yorkshire to Dorsetshire. In this respect their ranges are of great importance, o£fering to the inquiring mind a proof of the long succession of quiet processes by which the bed of the sea was gradually filled with aregular series of varyihgdeposits — alternations of chemical and mechanical products — and afterwards, it is almost certain, gradually Ufted so as to changt with a certain regularity the ancient boundary of the sea. The Wealden formation, in this, as in aU else, contrasts very strongly with the truly marine deponts. 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 Hytheand Ashford, the whole breadth pf 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 fuUy 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,

p 3

A TBEATISB ON OBOLOCnr.

Chap.

Narbonne*

Mexiirei.

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 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 difierent age. The limestone, north of die Caiipathians 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, andLajTbach, 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 EngUsh 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

Chap. Vt. 8B00Ndaby Stbata. 215

with which the arglLaceouff rocks in the south slope of the Himalaya represent the English lias, — an agreement which perhaps hy further researches may be found not less complete than that presented by the lias of Wurtemburg and Franconia which can hardly be aaid even to differ from the argillaceous rocks of the Yorkshire coast (See Geol. Proceedings for Mr. fur- chison's notices of the Banz Series and Voltz on Be- lemnites for proof of the identity of the Wurtemburg and Whitby lias.)

Spain the Balearic Islands and the Apennines con- tain the ooUtic 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- bility of the rocks; for in some parts of the Swiss Jura the h arder 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 clays ; as Bredon Hill, which stands up in the vale of Gloucester to attest the powerful 'effects of ancient water.

Upper oolite. Middle oolite. Lower ooUle.

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.

p 4

2l6 A. TaEATI8J9 OK SSeLOOT. CHAP. TI

£ach oolitic rock forms an escarpment over the sulgacent days, so that several longitudinal hollows and ridges undidate the area occupied bj the oolitic system.

Igneow Rodct. — 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 fractiml 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* denbly both by induration and debitumenisatiop*

GamnAii Rbyiew. — OoUHe System.

Ferhapsnothingmore clearly demonstrates the Sequent dependence of geological phenomena upon causes acting at a distance than tibe total dissimilitude of the rocks 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 interpdationof 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 the oolitiferous sea. If, as appears pro. baUe from the thickening of the interpolations towards the north, we suppose that the same land yielded the saadp* stones, shales, and vegetable basis of coal in the carbonifier> ous and oolitic periods, the change of the land plants in the interval from lepidodendra to cycadites is very re markaUe, espedally when we take into account the ex* oeptional case stated by Dr. 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 Dauphin.

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

€Uap. Vi. Eeoonbart Stbata. 17

great river flowed into the estaary, through forests of large endogenous plants, tenanted by (he iguanodon, hy- lieosaurus, and other large land reptiles. The linuted range of the Wealden deposits, their quick termination toward the north-west and south-west and their expan. sions though feeble to Beauvais and Bouloge 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 tliat the primary tracts of the Scandinavian peninsula and Scotland with other land now sunk beneath the German Ooean has beoi the source of most of the arenaceous and a];illaceou8 depo. sits of the carboniferous oolitic and Wealden fonxuu tions of England ? In this point of view, the local strata of Brora the thick coal series of Bomholm the oolitic coal tracts of Yorkshire and Westphalia, the Wealden oi 3oulogne, Beauvais Sussex, Dorset, Wilts, are all par tial and local deposits due to a similar suooession of causes, and arising from the same or neighbouring phy- sical regions, as the materials of some of the older coal strata. In Bomholm, cgal occurs with marine beds of all geological ages from the transition era to the creta- ceous group; and die dependence of its dqionts on the waste of the Scandinavian mountains is decided. The dependence of the other deposits on tUSe 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 uniti, the whole of the phenomena are intelli* gible as varied deposits on the shores of one limited sea. The distinction of quantity between the fiew oolitic and wealden plants, and the vast heaps of vegetable re. llquie preserved in the older coal strata, is important and might be explained as an effiset 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 (Buddand's Bridg-

.218 A Treatise On Oeoloot. Chjlp. Yu

water Treatise) that the dirt bed in the island of Port- land contains the remains of trees which really grew on theyery spot and were, by a general and quiet subsidence overspread by oceanic sediments : the character of the cycadioidee 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 dear 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 smaUness, feebleness summer life, and winter sleep, of the very few speeies 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 molluscs or Crustacea for such a purpose ; and, with rard 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 day appears to join itself with the golt. These transitions are merely examples of the general harmony which con- faects together the whole system of stratified deposits into tue varied and locally disturbed series of phenomena.

Cretaceous System

CompoHtiim. — As in all the older great assemblages of strata calcareous, argillaceous, and arenaceous rocks

Ohap. Vi. 8Eg0Ndaby Strata. 19

combine to form the Cretaceous System ; but all of these iiave peculiarities by which they may upon a great 8eale, be distinguished from diie aqueous products of other periods. The arenaceous rocks are often found in the state of unindurJEited or eyen loose sand the clays are generally soft and marly the limestones soft and earthy. Peculiar- colours also belong to these difierent members of the group: the sands are often green sometimes very ochraoeous the days 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- bum 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 day and in the superincumbent dialk. Nor is its diffusion confined .to Europe : it, is so abundant in the cretaceous rocks of the New Worlds as to be used for manure in New Jersey. FuUer's earth and good ochre lie in the lowest arenaceous sands (Wobum, Nutfield Shotover). Layers of chert nodules occur in the sand and sometimes beds of chert. Ii) Kent beds of whitish limestone of considerable tiiick-i* Jiess, interlaminate the lower green sands; harder limcr stone lies in tiiem in Lincolnshire. The day is usually of a marly or e?en 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.

8t0 A noUTISE ON OSOLOOT* OHAP. Yh

But the most peculiar cliaracten bekmg to the caicib. nous rocks, which are of all the limestones known (excepting some in the tertiary depodts) the soffcest imd most eartJiy. Not that the whole mass is correctly described by the term chalky as technically applied by geologists ; but yet a large proportion of the rock would be 80 termed even by ordinary obseryers from the whiteness and comparative softness of it In the lower parts green grains are common ; at the base in Idncolnshire and Yorkshire, a red band of from 6 to 12 feet in thickness is traced. Throughout the lower and indeed the greatest part of tiie chalk in Yorkshire, flint nodules occur in layers ; but in the south of England they are nearly confined to iJie upper chalk," in wludi they form layers 4 to 6 feet apart. At Sudbury, flint la. mine occur in the planes of stratification, as at Meudon near Paris.

;S!fra<$foa<lofk— Tbedearestpoadbleeridenceof regular deposition from water is found in all the rocks of this system, but in few instances are either beds or lamins Iraoeable so clearly or for such distances as among the older formations* In tiie 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, Hyihe, and in Lincolnshire, bedded limestones necessarily introduce this structure among tiie sands. In other cases the layers of chert nodules, or tiiin chert beds, mark the successiTe stages of deposi- tion : where none of these causes exist, oblique Ismina tion, and concretionary geodes and oilier arrangements of oxide of iron, render it almost vain to look for stra* tification.

The golt days axe sometimes laminated (Speeton Folkstone), and often, by the courses of small nodules, or by interposed beds of sand, show proofis of succes- Hre deposition.

The chalk is only partially bedded, and not at all laminated : its slow, and quiet, and intermitting accu-

Ghap. Vi.

Second Art Strata*

mulation however perfectly proved by the regnlar arrangement of the flint nodules which are so common in its upp part. No layers sand (or clay ?) occor in any part of its thickness. Joints are not, in ge neral, either numerous or regular 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 : —

t Upper chalk, usually a soft white calcare. ous mass, with chert nodules at regular intervals : the upper part in the Isle of 'Wight is of a marly nature.

t Middle chalk, not very deadydeflnable; of intermediate character as well as place be* tween the upper and lower chalk.

e liower chalk, harder and less white than the

Chalk fonnation,600 ft. thick.

Green sand formation, 600 ft.

upper, sometimes varied by green grains, generally with fewer flintrCred in the North of England), d Chalk marl ; a soft arglllaceotts fiirm of ehalk.

c Upper green sand (flrestone, malm roi&, Ac); a mass of sands, occasionally indurated to dialky or eherty sandstone, of green, gray, or white colour} with nodules or lamina of chert

b CMt (Tefcsworth clav, Folk-ttone clay, &e.) ; soft bluish marly clay, with green grains.

ft Lower green sand (iron sand, ShankHn sand) ;

a considerable mass of green, or ferruginous

"nds, layers of chert, local beds of

golt, rocks of chalky or eherty limesfoneb

and deposits of ochre and ftiUers* 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 no 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 English type the green sand being called mulatto, but the series is generally harder. Round the basin of Paris the dudk

822 A Tbbatisb On Oeoloot. Chap. Ti.

is also similar as may be seen by consulting th classifi- cation of Cuvier and Brongniart. — Aboat Aix-la-Cha- pelle the same fonnations and groups appear ; and the general features at leasts are retained through Westpha- lia (Essen Paderbom) and along the plains of nortiiem Germany. On the Elbe about Dresden and Pima the lower green sand is called quadersandstein the represen- tative of the chalk planerkalk. In the Carpathians is no chalky the green sand being greatly developed. In the Alps is no chalky and beds of green sand are intercalated among the upper Jurassic oolites (Saleve). But the most remarkable case is the addition of another limestone rocky above the nipper chalky very coarse and sandy in texturey but containing layers of flints in St. Peter's MountaiUy near Maestricht. This rock seems by its composition and organic contentSy 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 ous system of America may be taken together into two great masses, — a chalky or at least calcareous mass abovcy and a green sand mass below. These very general anflJogles appeu* 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 eroinentiy marine: nearly all the plants which it contains (they are few) are of marine types ; and the spongesy stelleriday moUuscay Crustacea' fiesy 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 tiie same large proportion of extinct geneniy and die same differences of proportionate deve- lopment of molluscous groupsy is traced in the cre- taceous as in the oolitic system ; so that both the oolitic and cretaceous fossils are reliques of a condition oi land

ATA.. SiS

and sea very dideient froin what we now witness. The fasBils of the two systems are, howeFer, Tery materially diStrent, even in the same natural groups, aa spoieg, crinoidea, stellerida, echinida, cephalopoda, Crustacea, fishes, and reptiles, in moat of which groups the chalk and green sanda 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 fossUs of this system to justify any positive inference as to the character of the climate then prevailing in the northern zones ; but we may he sure that the sea was very little disturbed by inundations from the land, otherwise fems 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 wlicified in both deposits — possiUy from some pecidiar affinity which those organic bodies, even in a recent state, appear to possess for sihca ; but in the same flint nodules which envelope ailicified sponges, the crusts of echinodermata and stellerida are found converted to crystallised carbonate of lime, and lamellar shells of the genus gryphea, and radiated sheatha of belnnnites, are not at all changed in texture, and very slightly altered in chemical composition. It is a very common fact that iron pyrites coUecCa around sponges aod . , other organic bodies in the chalk, and, when decomposed, leaves an ochraceous oxide of iron.

- From Iha low eh

t. HiglcaKmia iiiiMaum. Sww%. Ftm tlM chalk.

S. HunitH IntcnsHlliu. PUIi. Fna Uw Siult. (11 Msaga to tl

nn (UHu Criocxnlitei.) 6- SpiMhui iKiniinbATieui. i*Affitej. Fnn (be dulk. 7. XpiDCiTniii clllpiktu. Vi/In-TniiB chalk. BclcBOIIci iBucniaitui. AviuatePt Fran th> ntiptr didk. a

mal iNha (eta omir is Hie aiflUli vtt, EuniipHB clulk.

SECOND Any STRATA.

to. Hapti&nt

Geographical Eaitent. — In a general tenae, the ere- taceouB system ranges parallel to the oolitic formations from Yorkshire to Donetshiie, and sends branches from the plains of Hampshire nhidi border on the north and the south tbe Wealden formation of Kent and Bnvex. The green sand formation is, in all parts of England, w closely connected with the chalk (except in YorkihiK, where it is almost defiuent, and in Blackdown, DerOn), that it appears unnecessuj to notice more dian tbc characteristic range of the chalk. This distinguishing feature of English geolt overlooks the Gennan Ocean at Plamborough Head, and sweeps in a large corre inland by Biidsall pnd Pocklington to the Humber, at Hessle ; thence it pursues a south-eastward conrse to Candlesby in Lincolnshire ; and, after the intemiptioD of the " Wash," reappears in the cli at Hunstanton, Hence to StokeFerry its course issonth.'butittunwS.W., parallel to thewilities, by Camlwidge, Baldock,WendoTer, Wallingford, to above Wantage and Devizes. Hence it returns east to the Eources of the Kennet, and gives origin to B great lidge (the North Downs) dipping north, and passing by Kingsclere, Guildford, Reigate, Wrotham, and Maidstone to Dover; which C(Teeponds to another great ridge (the South Downs) dipping south, and paving from Beachy Head by Lewes, Steyning, Pelers- iield, and Alton, to join the North Downs at Famham. From the sources of the Kennet to Balisbury, and ironi Famham to Bishop Waltham, the dialk expands 0vr a vast space in Hampshire ; but Its proper outcrop is the western boundary of Salisbnry Plain, by Lavington,

226 A Treatise On Oeolooy.' Chap. Yu

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 Ceme 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 ridges.

In Ireland, a large detached tract of chalk lies under the basalt of Antrim. About Ballycastle, Glenarm Bay, and Lame, 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, Nor- 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 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 Paderbom. 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 lUtty, marly limectone, rather than chalk, is called planerkalk ; the lower or sandy rock Is called quadersandstein : distino tions still clearer in the large area within the Bohemian mountains, whwe on the ooune of the EXb the rocks of this system are widely spread.

Chap. Vi. 8B00Ndary Strata. £27

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 ehalk for it is chiefly in this form that we recognise the cretaceous system ahout Dresden in the Alps in the Carpathians and even the Pyrenees. On the Italian side of the Alps the chalk is supposed to he 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 nd green sands, and some argillaceous beds, constitute the greater part of the system, aa in the Carpathians, and are excessively rich in the green sUicate of iron ; they are covered by liable 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 Uie prim)Gury strata more inland by & narrow belt of tertiary and alluvial deposits. By.spedmena brought from tune to time from the interior of the continent, it would appear to occur abundantly on the Missouri far across towards the Rocky Mountains."*

PhyHcat 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 sheepasture. These

Risers, in Report to Brit. AModation. Q 2

S28 ▲ TREATISR ON GfiOLOGT. OHAP. YI,

" wolda" or downs'* are covered with a sweet short herhage 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 diflbrent from the tabular hills of oolite, and the rugged chains of older rocks. The sanie 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 nkpeh Beacon, equals 1011. Copious springs flow &om 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 kt)eU according to the impedirhente in the euhterraneau currents. . Where tertiary clays cover Ae chalk, as in the basin- of London, thfe boring rod Uo 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 Keagh, 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 ! Whit a

Chap. Vu S£Oonoaiiy Strata. 29

magnificent volcanic eruption is here pictured in its sub- marine lava currents ! For it undoubtedly was a mass or series of expansions of liqmd lava poured on the bed of th 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 Uie following succession is given by Dr. Richiurdson : —

1. rudely (Kduinny - -60 ft.

£. Red ochre or bole - - - -9

S. Basalt rudely prUmatio - - fH}

4. Basalt columnar - . - .7

5. Intermediate between bole and basalt - - .8 & Basalt coaniely colunuiar 10

7. Basalt columnar ; tbe upper range of pillars atBengore Head 54

8. Basidt irregularly priamatic; incloauig the wacte and wood

coal of Noifer - - - 54

9. Basalt columnar forming the Causeway . - 44 10. Bole or red ochrp - - .

Basalt, tabular, divided by the layers of bole - 80

Basalt, tabular, with zeoUte - . . 80

11. 12, 13. 14, 15, la.

The stratified rocks on the basaltic masses rest are variously altered by the efiect of their former heat. Liaa la duuiged at Portrush into a hard rock like flinty slate : hy the side of basaltic dykes at Fair- head the co shales are similarly hardened : red sind- stone is indurated the foot of Lurgethan ; and in Rathlin at Glenarm, &c. the chalk is changed by dykes into a largely crystalline marble.

The quadersandstein (?) of Weinbohla (on the Ba- nube) is overlaid by a syemtic jock.

In the Pyrenees cretaceous strata are in contact with granitic and serpentinous rocks and miiieral veins are in oonseuence introduced among thm. Q\. Qu- frenoy.)

Close lla Seeondary Period. — Jnsuiug JHirbanoes of the Crust of the Globe.

With the cretaceous system ends thci 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 th red sandstones

Q 3

StSO A TREATISE OX GEOLOa?. CHAF. YU

to the green fiand and from the mountain limestone to the dialk, it is impossiUe 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 applicatiouv 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 pf* limestone are three, vii.—

Chalk. Oolite. Mountain limestone.

To eadi of these belong, similiar concretionary masses of flint or chert, often aggregated round organic bodies, and sometimes extended into thin interrupted layers. The really littoral types of sandstone are various : —

Green or femiginoufl aands. Pale coloured calcareous grita. Red and white sandstone. Red conglomerates. Felspathic sandstones. Quartsose grits.

CHAP. YI. SECONDARY STRATA. 2Sl

Of aigillaceouB beds are three principal types :—

Blue claysy often indoAing nodules and beds of compact

limestone. Red, white, and blue days, 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 imder which these various deposits happened, were contemporaneous, or at least succeeded one another in the same order. A very general view of the mineral rdations 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. 1 Including the coal deposits of the Weal- Oolitic group. J den, Yorkshire, and Bombolm.

New red sandstone group, "l Including the prindpal coal de- Old red sandstone group. J posits of Europe.

Nor would such a dassification 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 dapsed between the deposition of the pri- mary and tertiary strata, two very distinct assemblages of terrestrial plants had flourished and become extinct. The andent and abundant flora of the carboniferous ex% with its lepidodendra, sigillarie, and calamites, had

Q 4

23 A TREATISE ON OEOLOeY. OtfAP. Tl.

ben replaced by - new races of zami and cyeadete which in their turn, vanished from the northern zones of the globe before the completion of the cretaceoas system. The marine zoophyte weie chiged, 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 akd. 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 tiiey, 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 cqnvictiop that, in the formation of the crust of the eaxth. Almighty wisdont was glorified, the permitted laws of nature were in beneficent operation,, and thousands of beautiful and active things enjoyed their appointed Ufe, long before man was formed of the dust of the ancient oarth, and endowed with a divine powev of comprdiending the wonder of its construction ? It is. something worse than phikiaophieal prejudioe, to dose the eyes of reason on the evidence which the earth offers to the eyens of sense ; it is a dangerous theolccal 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, piist aU excuse, to suppose that the moral evidence of an etmity of the future shall be weakened by admitting the physical evidence for an immoiaity of tibe past.

Since the dose of the secondary period, the eartha surface teen greatly altered and the boundamt of

qHAF.. S£CONDABir STftATA. 233

tl pean entirely changed in the northern zones on t)ie Mediterranean shores and on the coasts of India and America. It is difficult to collect very certain evidence of the occuirence of general subterranean move* mente immediately after the completion of the chalk, though the great extent of sands and pebbles and lignitic beds which covr it, and the deep wasting on its sur- face, a$ seen beneath those sanda 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 ; \mt, 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 give in £]igl$nd or Ire- land, unless the pebble beds of the former country, and the basaltic eruption of the latter, 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. 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 6haut9 and the Allegha- nies, to allow us to determine whether these ritnges, ich are rudely parallel to the same great circle m the Pyrenees and the Apennines were (as De Beaumont sup- poses, and his speculation on the relation of .4g and direction among mountain chains requires) uplifted at the same geological epoch..

234 ▲ Treatise On Geology. Chap. Vi.

To detei . ine exactly the geological date of a dismp- tion of the oust of the glohe 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 chuige 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 IKorthem Europe, except what the scaglia of Lom- hardy 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- vuLuon ; and Mr. Lyell's 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.

Tertiary System Op Strata.

SupracretaeeauB Deponts. — Terrain Tertiaire, — Ter

txdrgdnlde.

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 gencaral system.

Plrlnciiilcsor QwAagj, vol. iil. lH edit.

Chap. Vi. Tertiary Strata. 235

Compotion.-t— Arenaceous deposits predominate in most parts of the tertiary system; argillaceous types however abound in particular districts; calcareous rocks marine or of fbwater origin pure sandy shelly or siliceous lie ih many basins ; marls and gyp- sum are locally accumulated. Marine, freshwater, and terrestrial exuyise occur in strata of all these descrip- tions; and so much information is now accumulated concerning diem, and so many comparisons have been made between tertiary and modem 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 arenaceouss rocks are either in the fom 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 die Isle of 'Wight> where the efiect of the many colomrs iqiparted by oxide of iron is of a magical description ; left white aod co- lourless, as in the Dorsetshire heaths and forests, and at Fontainbleau ; or dyed of a general green; as near Paris, at Beading, 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 day (Isle of Wight). Mica occurs, but is not plentiful in these tertiary sands, which convey the impresaon of much and long abrasion in water, and various exposoie to oxygenating processes.

The argillaceous sediments of the tertiary system

%S6 A TREATlflE ON OEOLOOT. CHAP. VI.

fier 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 occur with prismatised beds of gypsum at Montmartre and accompany the limestones of Headon Hill in the Isle of Wight. But the most singular clays are those which accompany the coloured sands of Alum Bay and the neighbourhood of Paris ; for these are almost blacky 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 ajSected nearly all the deposits of that particular tertiary period*

The tertiary limestones mighty perhaps gene]:ally 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 tbe basin of Paris.

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 lias modified the effects of the gena*al agen- cies. It is not merely that some are of marine, and others of fluviatile, or of lacustrine origin : these are, in- deed, the leadig considerations to guide our inquiries, but h<xU peeuliaritie9 of physical geography are ako dearly indicated as important conditions in determining the nature of tertiary strata.

iSVfiiSciUtoii.— The whole of the ter-

Chap. Vi. Teiitiabt Strata. 23?

tiary accumulations are plainly stratifonn deposits; and they exhibit the different kinds of lamination and bed- ding 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 lamins : the London clay and Headon marls are partially, the Montmartre marl perfectly, laminated : the marine calcaire grossier, and most of tJie 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 freshwater 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 modem," is not at all clear. This difficulty arises in various ways : the mineral cha-

233 A TREATISfi ON OEOLOGY. CHAP. VI.

ractor and circamstances of aggregation of the tertiary rocks are extremely various according to locality; and in this respect so closely resemble formations now in press that were the bed of the Adriatic raised to our view it would according to the observations of Donati, most closely resemble the subapehnine tertiaries; the German Ocean would disclose shelly sand-banks, com. parable perhaps, to the Norfolk crag; and the coral reefs of Bermudas may thought'to resemble the lei. thakalk of Transylvania. The analogy of tertiary and modern shells and vertebral reliquie 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, ich belong naturally to as many dis- tinct series of operations, and certain organic exuvis which may have unequal degrees of relation to existing types, what wonder if it be sometimes impossible to dis tinguish tertiary from modern accumulafions ? 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 modem and tertiary periods. This difference, however, is probably of a positive character only in the classes of vertebrated 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 reptUia or lacustrine fishes.

It is hardly to be doubted, that hereafter the mode of studying supracretaceous deposits will be so far changed.

Chap. Vi. Tertiary Strata. Ss9

that the whole series of marine accumulations of every age from the cretaceous period to the present day wiU he grouped together hut distinguished from another equally extended series of lacustrine and fluviatile sedi- ments ; the principle of investigation in each case heii founded on a rigorous study of the characters of mine- ral structure, and the organic exuvie which are charac- teristic of the sea the streams and 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 ahove noticed the tertiary strata and modem deposits can be distinguished in par- ticular cases though not in conformity with any gene- ral definition. If the account of the modem 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 die Isle of Wight in the basin of London and on the eastern coasts 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 worlds exhibits a great and varied mass of sands and days, 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 ahove.

(Yellow and white sands. Dark clay with green earth and sep- tana, rich in fossil shells. 250i feet thick.

A Tbeatise On Geology.

Chap. Vi.

Lower or plas- tic clay group

Layers of black flint pebbles in yellow sand Upper Pipeclays and sands of many part colours, enclosing several

beds of lignite Coloured sands of many tints Middle f Dark blue clay, with green part earth and shelly nodules

j- Green, red, and yellow sand

S21

In the basin of London, the series is very similar ; but the London clay is of double or triple the thickness, and the plastic clays and sands are much thinner. The situation of the Bagshot sand at Hampstead and Bag- shot Heath appears to be above the London clay, from which it may perhaps be proper to distinguigh it as a superior group.

Upper group or London clay

Ix>wer group of astic clay and.

Bagshot sands.

London clay of a dull gray, or blue, or brown, sometimes red ; often full of green grains. Septaria abound in certain parts : the rocks of Bcnor and Selsea are sup* posed to belong to the lower part of it. 700 feet.

" Sand of various co ours, 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 gi-een 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.

Crag formation.

CHAP. 71. TE&TIARY STRATA. 24fl

'Upper 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, quadrupeds' bones, &c., the whole generally ochraceous.

Lower or coralline crag, less ochraceous, almost without pebbles; containing abundance of shells not at all worn, at Ramsholt, and abundance of corals not of European forms at Orford where it is used as a limestone. ( Mr. Charles worth. )

London clay of Harwich, &c.

Green sands ovei the chalk at Sudbury.

A deposit of tertiary shells in green and irony sands, and in blue clay occurs at Bridlington in Yorkshire ; it is perhaps of the age of the crag but certainly contains only a few species known to occur in. that formation. 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 Bouthem basins ; the former are no where wholly deficient and their lower green portions 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 Faris — 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 widi the lower marine formation. The whole stands thus in general terms ; but we must observe that the several groups are partially mingled with one another by inter- calation : there are, in fact, many marine and many freshwater strata.

Yol. B

Jk TREATISE ON GEOLOGY.

CHAP. tl.

Upper term.

"Epilimnic or upper freskieater formation—' the uppermost of all the stratified depo- sits near Paris ; consisting chiefly o£ siliceous limestone, or burrstone, mar], and marly sands. Upper marine formation — oonnsting of sand- stone, generally white, or partially reddened or ochraceous, and but slightly aggregated except at Fontainbleau.

" Paheotherian freshwater formation — charac- terised near Paris by its ossiferous gypsum and marls, siliceous limestones, &c. Lower marine formation — consisting princi- pally of limestone (calcaire grassier) of various degrees of coarseness, with lamin- ated flint, marls both calcareous and argillaceous, green sands. Plastic dag group — an irregular mass of de- posits varying with locality, in places yield- ing plastic dag and sands ; in other situ-

ations, lignites or pebble beds.

There is no trace in the basin of Paris of the shelly and graveUy deposits (falun coquiUier) of Touraine which M. J. Desnoyers compares to the Bnglish 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 tertiries is merely in the great features of succession : the lower marine formation in England is principally clay — in France limestone: gypsum abounds in the paleotherian 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 Jertiary deposits of the large basin of the Garonne contain shells like those of Touraine ; the beds of Narbonne and Montpellier more resemble the Parisian series. In M. Dufrenoy's recent memoir, he arranges the tertiaries of the south of France

Chap. Vi.

TEBTIABr STRATA.

in a series of three tenns 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

' Composed principally of beds of pebbles, sands and coarse sandy clays, which appear all to be eminently detritiQ formations, so that £lie de Beamnont formerly caUed them Terrtdn de transport ancien.* Ferpignan offers the best type of these beds.

Comprising a great variety of deposits, partly freshwater and partly marine; freiwater deposits of limestone on hills (Agenois, Provence); sands and pebbles (&]uns) on the plains (Landes); ds and marls (molasse) in low hiUs in Languedoc ; conglomerates at Pau; gypsmn and lig- nites at Aix, and in Provence ; concretionary limestones (calcaire moeUon) at Mont- pellier. It contains locally sulphur, and generally iron ore. These variations are Uie result of local circumstances influencing the borders of an oceanic basin.

Chiefly consists of calcaire grosser, and this is almost confined to the Landes' between the Adour and Garonne. The beds of limestone alternate with marls and days, and rest on the cretaceous rocks. They are fiill 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.

A Treatise On Geolooy

OH A P. Vf.

'Calcareous sands and pebble beds, calcareous grits and oolitic limestone — in the lovr ground of Hungary fuU of shells, as In tbe Upper group. highest beds of the basin of Vienna.

I White and blue marl, calcareous grit, white I marlstone, and concretionary white lime- stone: shelly.

r Coralline limestone and marl, of a yellowisli Middle group, i white colour, very thick and shMIy (Leitha- kalk of 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 anthraootheria, gyro- gonites, &c.

Micaceous sandstones, grits, and conglo- merates, made up of th 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 Falsotherian deposits ; the middle to the £ng1ish crag and middle subapen- nines. According to M. Dufrenoy the former would rather appear to belong to the middle tertiary period.

The sections of Transylvania, Hungary, and Mo- ravia 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 ele- vation; shells nearly all of existing species; white calcareous sand, sandy limestone, and conglomerates.

Subapennine or middle tertiaries, of very great thickness, con- sisting of innumerable laminae of marls, calcareous and argillaceous, blue or brownish, like the mud now gathered on the bed of the Adriatic : some sandstones,

Ohap. Vi. Tbrtiaby Strata. 245

limestooes, 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 Gv>ntamiiig Qnly a small proportion of feesnX ells.

Geographical Eatent, ' and Physical Geography, — 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, fropi the phenomena of al ternating marine and freshwater deposits conclusions have long since been presented hy distinguished writers that particular tracts were alternately raised above and sunk below the sea. Cuvier and Brongniart pro- posed this hypothesis to explain the freshwater in- terpolatipn among the marine strata of Paris; and the notion has gradually become a popular part of geological speculation. The geographical relations of tertiary strata. must be understood before venturing to adopt or to reject the hypqtbesis.

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 ajid other tracts, were uplifted ahove 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 ilopes from these insulated ridges, and by other undulations in the bed of the sea ; the iature and abundance of the ter- tiary sediments, and the organic forms which are_ buried in diem, would be greatly dependent on the force and origin of the currents ; and thus we see a jason why

B 3

246 ▲ Treatise On Oeolooy. Chap. Vx

tertiary strata should be so distinctly related to the present configuration of the surface of the earthy and so yarious both as to mineral character and organic contents though the basins as we term 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 Bisle to Bingen.

The relation of tertiary deposits to existing seas will appear froto 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, Hol- stein, Jutland.

S. Between the Baltic and the Black Sea.

The extensive sandy deposits of Prussia, Poland, Vol- bynia, 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. yi TERTIARY STRATA. i247

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 durii 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 aU 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. Lyell's views, that the insulation thus attributed to the subsequent rising of mountains, may have been begun by their contents poraneous rising, — a mode of explanation well suited to the case of the di£Perence 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 £rom 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 n$iture, which so remarkably characterises the tertiary strata. The purely lacustrine deposits, with their embedded mammalia, teD. 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

R 4

s-

24*8 A Treatise On Geology. Chap. Vt,

lacustrine and fluviatile deposits it is to be observed, that when a series of soch 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 HiJl in the Isle of Wight on most of the plateaux round Paris at CEningin, at Georges Gmund, the freshwater deposits are uncovered by any but superficial accumulation? how can their true geological lige on the scale of marine formations be known P No method but one is likely to be at all satisfactory, — the study of ,their embedded organic exuvie; 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 csm 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 reliquise — no analcy 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 greats as compared with that of even the rich and weIl-<expIored oolites; among them are far more freshwater 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

Ohap. Yi. Tertiabt Strata.

basins between ranges of mountains and masses of land) which in various ways influenced the deposits and supplied soipe of their organic contents. Yet, upon the whole,' the niunber 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, radier 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

Liand and freshwater plants,' chiefly coniferae, on n 4o palms, and amentaceae . . J

in calcaire grossier and Monte Bolca beds—-

Marine plants - - - 16

Iand and freshwater pJants - - 16

In the palseotherian and epilimnic freshwater beds —

Marine plants, none

Jjand and freshwater plants - 21

From the laborious and successful researches of M. Deshayes concerning tertiary mollusca (see Lyell's Geology, vol. iii. first edition), we shall extract some of the leading results.

The recent species examined by this eminent concho* T

logist amounted to - . J

The fossil species of the tertiary system alone - 3036

Together .- . - 7816

426 to 7390, or, 5.7 to 100

250 A TREATISE ON OEOTiOOY. OQAP. VI.

Of wliich 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 "I5.7 tQ looo

and fossil, to the whole number is - J

The 4780 living species consisted

of - univalves 36161 f 75*6

The 3036 tertiary species

univalves 20981 60*1

bivalves 938 J J 80-9

Among the shells examined were included 1465 recent, and

259 fossil. Shells of the hood and freshwater, viz.

Freshwater species, living bivalves 1 1 8 fossil 30

univalves 151 fossil 151 Land species, living univalves 1 1 96 fossil 78

As before observed, the ratio of- the number of species, both re- cent and fossal,to the total num- ber of recent and fossil ob- served, is The ratio of the same to the number of recent"! -v..

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 truths 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.

UDoeror most f subapennine beds; the crag.

int erouD I (Prpignan and the Morea agree in their

I, fossils with the subapennine beds.)

Chap. Vi. Tertxab7 Strata 251

(Bordeaux ; Dax ; Touraine ; Turin ; Baden ; Vienna ; Angers ; Ronca. Tlie Viennese 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- liac are the same nearly as those of the basin of Paris.

From each of these localities the ratip 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 9S6 species, of which S16, or 95*0- per cent, are living. Subapennine .569 - 238. '41 -8

Crag - 111* - - 45-40-1

Middle group — General proportion of living species, 18 per cent

Vienna has yielded 1S4 species, of which 35, or S8'2 per cent, are living.

Baden .99 . S6 . S6*2

Bordeaux and Dax 594 - 136 . £8*9

Touraine . S98 - 68 . i237

Turin - 97 - 17 - 17-5

Angei - 166 - 25 - 15-0

Lower group. — General proportion of living species, per cent

Roncaf has yielded 40 species, of which 3, or, 7*5 per cent are living. London - 239 - 12 - . St)

Paris . 1128 . 38 - 34

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, wilh 41.

Meiocene - - — Vienna, Bordeaux, Turin, &c. 18. Eocene — Paris, London, Belgium, 3|.

The terms are derived from the Greek Kaivog, recent, combined with rjf**Q, the dawn, ficiwv, less, and TrX3v, more.

There arfe 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 o)>inion from M. De*hayeg. See also Mr. Cbarlesworth on the crag f(urm ation, in PhiL Mag. and Annals, 183&

t Placed by Deshayes in the middle group, but with hesitation*

S52 A Trkatise 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 ynay 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. 250.)

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 i>f 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 difierent, according to the period : these difierences 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 Uature 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, imdoubtedly 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

f

OHAP. VI. TfiBTIARY STRATA. 25

only one locality, Sicily), the strata contain 95 per cent* of existing forms.

Supposing these statements (which might he fortified by other equally important but more refined results) are diought sufficient to establish th6 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 subapennine countries, should be compared with the lohole 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 tracts having been wholly raised to dry land, all their peculiar shells have perished ; and tiie 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

S54 A TREATISE ON GEOLOGY. CHAP. Vf.

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 foUow steadily a plan of observation which may place the principle assumed on such a foimdation as to authorise its being used as the origin of deductions which may have undoubted influence both in theoretical and pod- tive geology.

Professor Rogers in his Report on the Tertiary and Secondary Rocks of North America has adopted the nomenclature of Mr. Lyelland raYiked 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 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.

" 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 fosdls, to determine exactly their specific relations. In genera], I may say that I have not yet found a single species which was perfecdy identical with any marine existing fish, except the little species which is found in nodules of day, 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

Ohap. Yi. Tebtiabt Stb Ata. 255

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 chalky 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 tertiary series and lying races comes with equal force from a consideration of the families of reptiles. Among chelonida occur freshwater trionyces and emydes as well as marine chelonis 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 (Eningen 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 lie (exclusively ?) in tertiary formations we slall 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

2o6 A TREATISE ON OEOLOOY. CHAP. VI

In the following catalogue of remains of mammalia in tertiary strata chiefly taken from Meyer's Paleologi- ca, extinct genera are marii:ed hy an asterisk.

Section A. — In Marine Deposits,

Camivora,

Gulo antedauvianus - Eppelsheim on the

Canis - - - In Volhynia, with marine shells.

Fells aphanistes - - Eppelsheim.

prisca - - Eppelsheim.

Phoca - Hungary.

RoderUia,

Castor . . Crag of Essex.

Pakeomys castoroides - Eppelsheim.

Hare ... Faluns of Touraine.

Aulacodon (chelodus) typhus Eppelsheim.

Chalicomys Jageri - Eppelsheim.

Myoxus primigenius - Eppelsheim.

Spermophilussuperciliosus - Eppelsheino.

Cricetus vulgaris - - Eppelsheim.

Chloromys . f Vomy ( Also in freshwater

Pachydermatiu

r In subapennine formation. ]Vf aotodon angustidens - -j In the &luns of Touraine. t

Eppelsheim. arvemensis - Eppelsheim.

Hippopotamus major In faluns of Touraine.

minutus - In faluns of Touraine.

land.

Rhinoceros Schleiermacheri - In sand. EppeLsheim.

incisivus - Eppelsheim,

leptodon - Wiesbaden.

" In sandstone, 456 ft. Warsaw.

Elephas primigenius -

In sandstone at Wieliezka. In molasse, near Estavayer* Switzerland.

CHAP. Vf.

Dichobune

Tertiary Strata. 257

calcaire grossier near Naii-

rin

teire.

Dinotherium Bavaricum - France Bavaria, Eppelsheim.

giganteum - Eppelsheixn.

1. 11 ... r In the faluns of Tourauie*

1 r e j„ sand. Eppelsheim.

mulus primigenitis - Eppelsheim.

asinus primigenius - Eppelsheim

Sus antiquus

Falasotherium

Lophiodon Tapinis prisons

Cervus anocerus

brachyeenis trigonocerus dicranocerus curtocerus

Deer

Antelope

Mosohus antiquus

Manatus fossilis Balttna fiassilis

- Eppelsheim.

- Eppelsheim.

- In molasse. Estavayer.

r Under calcaire grossier in the J department of Gironde; at Provins; in Touraine; at Zurich. Under calcaire grossier at Fro>. ▼ins. Eppelsheim.

Eppelsheim.

Ruminantici,

Eppelsheim.

- Eppelsheim.

- Eppelsheim.

- Eppelsheim.

- Eppelsheim.

- In the faluns of Touraine.

- In molasse. Estavayer.

- Eppelsheim.

Cetaeecu

f Calcaire grossier. East coast of Maryland. Virginia, Wurtemburg, Dau- phind, Berne, Montpellier.

Sect. B. — In Lacustrine and Lignitic Deposits qf . known Geological Era.

Vespertilic Parisiensis

murinus fosalis Nasua

Viverra Parisiensis Hyna Parisiensis, Oifi Vulpes vulgaris, ManteU VOL. I.

Gypsum of Montmartre.

(Eningen.

Gypsum of Montmartre.

Gypsum of Montmartre.

Styrian brown coal.

CEningen (Murchison).

S

A Treatise On Geology,

OHAP. Vl

Canis

Didelphis Cuvierii

Castor

Ancema CEningensU Mus musculus Myozus

Sciurus Lagomys

Mastodon tapiroides

turicense Adapis Parisiensis Chceropotamus Meisneri

Anthraootherium magnum

minus minimum Alsaticum Velaunum 1 and 2

undetermined

- Gypsum of Montmartre.

- Gypsum of Montmartre.

- Brown coal near Zurichr

- CEningen.

- CEningen.

CEningen ; Montmartre. Montmartre.

- CEningen.

- Montabusard near Orleans.

- In brown ooal near Zurich.

- Gypsum of Montmartre.

- Brown coal near Zurich.

f Brown coal of Cadibona ; marl of Limagne.

- Cadibona.

- Lot et Garonne.

- Lobsan.

- Puy en Velay.

f Brown coal of Scheineck in Styria.

Montmartre ; Isle of Wight.

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Anoplotherium commune

secundarium

Xiphodon gracile

Dichobune leporina

murina obliqua

Palieotherium magnum

medium crassum latum curtuxn

minus

minimum - Aurelianense Isselanum - Velaunum - Lophiodon tapirotherium - occitanicum Isselense mediiun minimum tapiroides buxoyillanum - giganteum

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Montmartre.

Orleans; Argenton.

Issel.

Puy en Velay.

Issel.

Issel.

Issel ; Argenton ; Soissons.

Argenton.

Argenton.

Buchsweiler.

Buchsweiler.

Montabusard.

)n Monspasulii uberimLnx

fin limestone. Gaveinmcm of 1 Orenburg.

iLfBonnois; Anrenton : Paris:

Cervui cspreolua Aurelisnensis Monubusanl

Sect. C.—In Lacuilrine Depotili <if Doubtful Era.

Urnu apdKiu - - Georges GmiiDd.

Vulpes - - Georges Gmiind.

Hfsiu, HiU - - Gjpsiun of Unterturkheim.

Miutela - - Georges Gmiind.

QueropoUmiu SoenuiKriDgii George* Gmiind.

PBlBotherium AucelisDCDM Geoes Gmiind

ADoplatheriuin commune ? - Georgei Gmiind Mastodad niinutum Georges Gmtind Bhinoceros pygmiEui - Geoea Gmiind

iuL Samcrbt. FiDm atf of Suflolk.

iatum- Sowirdy. f ChtvUjibimdiiithiLaDdaiiclij,

lo England, two lines of subterranean movement have long been known, b; which ihe tertiary and Be. condaiy strata Lave been raised into anticlinal ridgea and iunk into synclinal holIowB. They both range east and west, or nearly so ; one line, viz. from the Vale of Pevsey by Kingsclere, Famham, Goildford, and thnnih the Weald of Sussex lo Boul<e, is somewhat parallel to the vale of the Thames ; the other, from Weymouth b; ihe isle of Purbeck through the Isle of

Chap. Vi. Tertiary Strata. 26 1

'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 continuous ( they are not), the northern one would nearly coincide with the sou side of the South Wales coal and the southern one pass across the southern part of Devonshire. Each of these two lines of didocation 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:'—

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

s 3

62 A TBEATISB ON GEOLOGY. CHAP. Vl,

an easy gradation to the phenomena which mark the former violence of the now silent fires of Auyergne the 'Euganean Hills and Hungary. The relation of these to the basaltic streams of Ireland and Scotland is cleiar 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 bum 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-TEBTIABY AND MoDEBN DEPOSITS.

{Syn, DUumunif* and Alluvium.** — " Superficial

Deposits,**)

Since the tertiiqry formations were completed in most parts of Europe and America the energies of nature have gone on to accumulate over them 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 gravely 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 coUected 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. 26$

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 palseotheria in the formations of Paris the same physical regions have been tenanted by wholly difierent 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 aUuvial 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 dkcriminate between the Sicilian ter- 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, &Qd to be classed in the . modem epoch, why are the Sidhan 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 e£ of elevation of mountain ranges, may we not expect somewhere to find

8

264 A Treatise On 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 Weighton in York- shire, the Val d'Arno CEningen, 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 lacustrixie deposits have happened on the land in various parts of, at least, the northern zones the globe; and though impartial researches have led us to doubt the practicability and advantage of this broad distinction, we shaU now endeavour to deve lope the history of the post-tertiary" or diluvial, allu vial, and modem 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 modem nature by causes which are known. The posttertiary accumula- tions consist of detrital deposits, reminding us 6f 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 othei hand, almost every thing that we see among these deposits is clearly intelligible 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. 265

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. Detritaldepodts. J Cteiferous gravel, pebbly clay, sand,

c. Ossiferous caves and breccia.

a. Raised from the sea, or,.

b. Yet in progress. *a. Terraces on the valley side.

b. Deposits in the valley.

c. Deposits at the mouth of the river.

a. Completed in former times.

b. Yet in progress.

2. Marine deposits.

3. Fluviatile deposits.

4. Laeusfarine deposits. '

DetrUal Depotiur — Drifts — DUuvium:* —

Boulder Formation**

Since the date of the ' reliquie diluvians' and osse- mens fossiles,' many geologists have been accustomed 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 epochs over large tracts of the globe>

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 hy water moving in dif- ferent directions, and with various degrees of force : the remains of elephants mastodons &c. werefound though rarely in redly tertiary strata hoth marine and fresh- water ; it was Airther observed that the diluvial masses were totally ahsent 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 modem 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 modem 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 " di- luvial catastrophe" with the Scriptural deluge, may learn from this example the danger of confounding the really independent bases of religious and natural truth ; the former resting on moral evidence and the nature of man, the latter on physical facts and the sure laws o£ nature. Both are tme and cannot disagree, but we

CHAP. TI. POST-TERTIABY STRATA. 2t)7

must knoY them both well before we attempt the serious task of determining the manner of their union.

a. — Erratic Block Group

In the British islands very considerable tracts of country have been traversed since the land had its pre- sent general aspect of hill and dale and was inhabited by large quadrupeds by currents of water due to some un- known cause which transported rock masses with so great a degree of force to points so elevated in such directions and at such distances that we cannot avoid feeling ex- treme astonishment and look around in disappointment on the physical processes now at work on the earthy for any thing similar. But it is only in particular tracts that the magnitude of the transported rocks is such as to deserve the title of erratic blocks; and among several examples we know of none which more strikingly ex- emplify the phenomena as the dispersion of granite slate, pdrphyry, &c. from the vicinity of the £hglish lakes because 'the nature of the rocks and the limited extent of that region render the observations and infer- ences more precise than when reference is made to the Grampians Lammermuirs, or mountains of Wales.

Many, perhaps most, of the Cumbrian mountains have yielded detritus to the diluvial currents (a term we here employ for its convenience, without wishing to convey any hypothetical notion beyond that of the force of their movement); but certain of them contain rocks so remarkable, that wherever fragments of these are seen in the gravelly deposits of the neighbouring regions, an experienced eye may at once refer the pebbles to their parent site. Such are the granites of Ravenglass and Devock lake: in a still higher degree the porphy- ritic granite of Shap fell, the sienitic and hypersthenic rocks of Carrock fell, e- amygdaloidal slaty rocks of Borrowdale, some kinds of slaty rocks full of frag- ments about Grasmere, certain felspathic rocks at the base of Helvellyn. It appears to be certain that, in the dispersion of boulders of these rocks, the present

268 A Treatise On Geology. Chap. Vi.

physical configuration of the neighbouring re|;ions had great influence: .they are found to descend from the Cumbrian mountains northward in the Vale of Eden to Carlisle, eastward to the foot of the Penine chain, south, ward by the Lune and the Kent to the narrow tract between BoUand Forest and the bay of Morecambe ; and from the vicinity of Lancaster they are traced at in* tervals through the comparatively low country of Pres. ton and Manchester, lying between the sea and the Yorkshire and Derbyiire hills, to the valley of the Trent, the plains of Cheshire and Staffordshire and the vale of the Severn, where they occur of great magni- tude. It thus appears, that the Penine chain, ranging north and south, acted as a great natural dam limiting the eastward distributi<ui of the blocks ; but at Stain- moor, directly east of Shap fells, a comparatively low part of the chain (1400 feet above the sea), granite from Shap fell, which is about 1500 feet, as well as sienitic rocks from Carrock fell, which is 2200 feet and red conglomeritic masses from Kirby Stephen, only 500 feet above the sea, have been drifted over the ridge.

1. "Shap fellt whence the granite blocks have been drifted to

2. Orton Scar, a range of umestone hills, and firom these have passed

3. The Vale of Eden, in new red sandstone.

4. Stainmoor Forest, across which, in the lowest part of the range of the

Penine chain of hills, the boulders hae gone to

5. The Vale of York, Ac f). The Oolitic moorlands.

This great barrier passed, the blocks are scattered from Stainmoor, as from a new centre to Darlington, Redcar, Stokesley, Osmotheriy, Thirsk, and the whole front of the Hambleton hills ; they have gone down the whole length of the vale of York and by the base of the chalk wolds to the Humber. But die barrier of oolite and chalk has been in places surmounted, and the

Chap. Vi. P08T-Tbbtiart Strata. 269

Shap fell granite lies on the moors near Lastingham, and near Scarborough and on die wolds near Flam- borough Middleton, &c.

The Penine chain ends abruptly on the north against Brampton, Hartley Bum, Hexham, &c.; and a great depression is formed on the line of the 90 fathom dyke and the vale of the Tyne. Along this depression, and far down to the mouth of the Tyne, the Cumbrian detritus is found, though no streams now flowing there have any connection with the mountains from which the materials came.

The larg quantity of detritus from the Cumbrian mountains, which has been drifted to the south, on the western side of the high mountain border of Yorkshire and Derbyshire, has gone across the drainage of the Lune (Lancaster), Wyre, (Garstang), Kibble (Preston), Mersey (Manchester), Weaver (Northwich), into and beyond the drainage of the Trent, the Dee, and the Severn (Bridgnorth). Not in any instance have they overstepped to the east the mountain barrier previously noticed; but they lie up against it in enormous quantity, and in the most inextricable confusion, not to be ex- plained by any thing like the action of the sea on its coasts, even during the most violent storms.

In and under Barr Beacon, is a mighy mass of drifted quartz gravel, and sand, with fragments of limestone, trap, and coal sandstone rocks from Dudley, Rowley, &c. ; but I found no distinct proofs of Cum- brian rocks, — not a bit of granite, and no bones. This seems to be analogous to the great drifted mass of gravel, coal, and sand at Durham, which has followed the drainage of the Wear.

The distributionof pebbles of quartz rock from Broms. grove Lickey to the north and east, even to the valley of the Thames, and along the hills which border it, is well known from Dr. Buckland's description, and cer- tainly it is one of the most striking examples of the efiect of ancient currents; but it appears totally inde. pendent of the drift " from Cumberland.

270 A TREATISE ON OEOIiOGY. IHAP. YI.

Let us then return to the Cumhrian jnountains and mark the nature of the forces indicated by the superficial area and the geographical features of the region covered by the erratic detritus. It is remarkable in the first place that the detritus in question has been transported chiefly to the south and east, slightly to the norths and hardly at all to the West. The same thing is true for the greater part of the diluvial accumulations in Eng- land. In the southward direction, the moving forces were sufilcient to iX)nquer such obstacles as the bay of Morecambe, and all the undulated and hilly region between the mountain border of Yorkshire* and Derby- shire, and the Irish Sea, but hot to pass that mountain boundary ; and of such continuity, as to be recognised as far at least as Bridgnorth, 130 miles and more from their origin. In an eastward direction, the boulders have crossed the bold limestone ridges of Orton and the deep and broad vale of the £den ; from this they have been raised over the Penine chain of mountainous land, but only at one and that the easiest pass, which, however, is 900 feet above the £den. Could we ven- ture to assume, in this case, that one long slope of surface formerly continued from Shap fells, and Carrock fell, to Stainmoor, the arrival of the blocks on the latter point might be explained : but the hypothesis is wholly gratuitous ; for the rocks of the Penine chain, of which Staimnoor is a part, must, have been elevated above the strata of what is now the vale of Eden, even at so an. cient a period as the deposition of the new red sandstone; since the Penine fault, to which that elevation is due, was anterior to all, or nearly all, the red sandstone form- ation; and there is no proof, nor reason to imagine, that any strata were superimposed on that red sand- stone, so as to fill up in any degree the ancient vale of the Eden.

m

Whatever hypothesis be proposed for the transit of the blocks from Shap to Stainmoor, must indude the consideration of this original diflerence of level on the line of the movement. Once on the summit of the pass

OHAP. Vr. P06T-TEBTIARY STRATA; 271

of Stainmoor the natural course of the vales of Tees and Greta may account for the directions at first taken by the boulders to Darhngton ; and the plains of Cleve- land and the vales of Mowbray and York easily con- duct us to the Humber. But still the same kind of difficulty as that presented by Stainmoor meets us at the foot of the Hambleton hills and the wolds of York- shire over which high and continuous ranges the boul- ders have been lifted from the vale of York, which spreads wide and far several hundred feet below and drifted onward till they reach the sea 1 00 and more miles from their parent rocks.

Oh the line of these hills there is no great dislocation of strata: their elevation was probably effected by a general upward movement of the whole area of the eastern side of England affecting equally the chalk wolds oolitic hills a*d red sandstone vale. As therefore, it by no means follows in this case that such distinctions of level were aboriginal (as in the instance of Stainmoor and the vale of Eden), it may be iknagined, that from the Penine ridge to \he German Ocean, one long slope permitted descending streams to transport the detritus; and that to the same or subsequent watery force we must ascribe the production of the inequalitiea which render the transport of the boulders, in the' directions they once took, impossible now, without extraordinary dynamical means.

But, granting this, we shall still advance but little in the explanation of the phenomena* For if it be ad- mitted that currents flowing from the Penine ridge toward the east could remove all the mass of materials, thus imagined to rest on the carboniferous rocks, why have they left on the summits of the hills, and on the lower ground of this very region, plenty of the blocks of granite, which, by the hypothesis, should have been swept away over the unwasted surface ? Dismissing, then, for the present, the notion that drainage waters, under any possible condition of levels of the dry land, could disperse these erratic boulders, let us inquire

272 A Treatise On 6E0L00T. Chap. Vi,

under what circumstances they might be moved by the waters of the ocean.

Either we may suppose the waters to be thrown in a body over the land so as to conquer by their violence and volume certain inequalities of the surface, and to cause particular local currents depending on the resist- ance offered by the physical configuration of different districts; or we may imagine alterations in the relative level of land and water, in the whole region where die detritus is spread, of sufficient amount to permit the transfer of heavy bodies by oceanic currents over .sur. faces which subsequently (at once or in succession) be- came dry land. This latter supposition admits of many gentle or many violent upward movements of the land round a vertical axis; and in this instance ihe axis may be imagined to pass parallel to the extreme points whereto the detritus has reachlNl, viz. Bridgnorth and the mouth of the Humber, or north-east and south- west ; and the movement to be upwards in all the ron between this and the Cumbrian mountains. The con- sequence might be, dispersion of gravel, &c. from the primary mountains, in various directions within the semicircle from N.£. to S.W. ; and it is entirely within this range that aU the Cumbrian detritus is really located. To determine whether the upward movements assumed were gentle or violent, we must look to the deposits of boulders and gravel which have resulted ; and as the leading facts which they exhibit are un- doubtedly the heterogeneous admixture of substances of different magnitude and density, the absence of parallel and continuous stratification, and the frequency of con- torted and inexplicably jumbled masses, we cannot hesitate to pronounce in favour of sudden and violent movements of incomparably greater energy than those by which most of the old conglomerate rocks were formed.

Geologists to whom this reasoning is not satisfactory may take as a basis of deduction the other speculation, that the ocean has been violently thrown over the land.

Obap. Vi. P08T-Tebtl4Bt 8T1U.Ta. S?

This is impossible as an ordinary occurrence. No ordi- nary combination of circumstances could much augment the fluctuations of the ocean beyond their present amoimt : if the equatorial course of the tide were £ree, and the impulses of the sun and moon eould be supposed to conspire in augmenting the rise sucoessively, as iso- chronous appticadons of small forces will enlarge the vi- brations of a suspended bar, this would not correspond either in magnitude or violence to the phenomena which require explanation. It is impossible, therefore, to assign a physical cause for such a mighty overflow of the ocean, except we suppose the earth*s flgure to be changed; its axis displaced, and thus the sea moved in mass, or its crust broken, and thus new basins opened to the waters. The displacement of the earth's axis cannot be assumed, on satisfactory grounds, as a thing within the range of probability; for the earth is a flgure of equilibrium, and therefore its aaU U Jiaed, as far as any oifdinary tendencies in the mass itself are concerned ; and neither comets nor planetary attractions are thought to be influential for such an object We are, therefore, reduced to the supposition of violent disruption of the crust of the earth, if we wish to explain dQuvial phe- nomena by one or many transient overflows of the sea. Whether, therefore, we suppose the dry land to have been covered by boulders through an inroad of the ele- vated sea, or the unequal bed of the sea to have been raised, in either case it is necessary to admit violent fracture of the earth's crust, and on either view we may venture to generalise the phenomena connected with the dispersion of boulders from the Grampians Scandi- navian ranges, Cumbrian rocks, and primary strata of the north of Ireland, in one point of view. For the same speculation of a rise of land parallelr to an east- ward or north-eastward line, if it will account for the phenomena in the north of England, will also explain those of the other localities, if the axis be taken far enough south, and the area moved be supposed to ex-

. Vol. I. T

274 A Treatise On Geology. Chap. Vi.

tend at least as far as the Irish Scotch and Scandi- nayian coasts; and a great oceanic current from the north or north-west, if possible and applicable in the case of Shap and Stainmoor must be supposed to have left traces of its power on other mountain ranges. It is unnecessary to extend these reflections arising from the phenomena of the dispersion of Cumbrian rocks farther than to observe, that the line followed by the blocks southward from Shap through Lancashire and northward to Carlisle, is in a great depression parallel to the fault of the Penine chain; and that the depression on Stalnmoor, and that farther north near Brampton, by which similar blocks have gone eastward, are occa- sioned by cross faidts which break the continuity of that same chain. These circumstances are obviously important.

The most prevalent direction in which the blocks have been transported in the British isles, is from north to south ; but, in general, the natural configuration of the ground appears to have had considerable influence in determining many minor currents. The. same con- clusion, of the influence exercised by the local configur- ation of land, results from the laborious examination of the phenomena of the dispersed blocks of the rocks of the Alps. The existing valleys are the lines by which the fragments of the mountains have been drifted away to the lower grounds of France, the Pays de Vaud, Switzerland, the great vale of the Danube, and the plains of Lombardy. Not that the rock masses are carried along the course of the actual stream, or even confined to the course of the valley; for mountains lying in the main directum of the valley, through 3000 or 4000 feet high, are as thickly, and even, in the case of the Saleve and Mont Sion near Geneva, more thickly, covered than the hollow of the Arve, or the banks or bed of the Rhine and Leman Lake. It appears, there- fore, that some great violence of water acting along the line, but not limited to the level, of the present drain- age, has brought the blocks from the western Alps, by

Ojsap. Vi. Post-Tertiary Strata. 275

the valleys of the Isere and the Durance to the plains of the Rhone : thus have the rocks wasted from around Mont Blanc and the Col di Balme been strewn over the valley and along the hilly borders of the Rhone even to the height of s6me thousand feet on the Jura ; near Soleure the same range of mountains bears the spoils of the Bernese Oberland, swept down by the valley of the Aar the Glaris boulders have gone to Zurich and those of the Grisons have descended the valley of the Rhine. But after thus falling to the great Swiss tertiary basins of Geneva and the valley of the Aar the blocks have crossed those hollows and been driven up the opposite slopes of the Jura to a level 2000 feet higher. De Luc (Mm. de la Soc. d'Hist. Nat. de Geneve) notices the origin of other rocks be- sides the granites dispersed in the basin of Geneva and they support the same conclusion of the decided influ- ence exercised by the present configuration of the country in modifying the direction of diluvial currents. This influence is however in other cases less sensi- ble. For example, the zircon sienites, porphyries, and transition limestones of Sweden and Norway, have been transported southwards over the country of Scania and across the Baltic, and scattered over the sandy plains of Westphalia, Hanover, Holstein, Zealand, Mecklenburg, Brandenburg, Pomerania, Prussia, and part of Poland be- tween Warsaw and Grodno. Thus, om the £ms and theWeser to the Niemen and theDwina (and even to the Neva), the country is covered with ruins of the Scandi- navian rocks brought across the sea, and carried toward the Carpathians/ and the Bohemian and Westphalian mountains, contrary to the natural currents of drainage. De Luc and Brongniart have given many details con- cerning these remarkable boulders, which appear not equally spread over the large tracts of country men- tioned, but assembled in groups in particular situations. These groups are often elliptical in form; the major axis of the figure pointing north and south, or toward the Baltic Sea, across which they have been transported.

276' A TREATI8B ON GBOIiOG7. OHAP. VI.

firuckner mentions a trainSe of blocks north of Meck- lenburg Strelitz which runs from N.N.W. to S.S.E. They are said to be In general more abundant on the elevations than in lower ground, the largest masses being nearest the summits as if the lighter gravel and sand had been removed from them.

De Luc observed in Lower Saxony, circular ridges of hills with a single outlet firom these natural amphi- theatres ; and on the inner faces of the hills abundance of granite, porphyry &c. There can be no doubt that the great masses of granite, porphyry, transition lime- stone, &c. scattered over the north of Germany, have been derived from the Scandinavian mountains, because the limestones contain organic fossils peculiar to the transition rocks of Sweden ; the porphyries and granites are equally identified by their mineral characters ; and the distribution of the groups of blocks on the south of the Baltic, as well as the traces of their passage across Scania, completely agree with this conclusion. The era when these Mocks were drifted across the Baltic, though modem when compared even with tertiary strata, is yet tery remote, for they lie under the ancient peat mosses of East Friesland; and there appears reason to think that more than one such migra- tion of erratic blocks has accompanied the Upward move- ments of the Scandinavian primary regions. " Almost the whole surface of North America, as far as examined, may be said to be covered with an investment of earth, pebbles, and boulders, obviously of diluvial origin. The thickness of this deposit varies, though its average depth may be said to be from ten to twenty feet AH lliat low and level tract described as the Atlantic plain, and also the lower sections of the great valley of the Missia* sippi, appear to be the districts where it eonceals the underlying strata to the greatest depth." — The boulders may ahnost invariably be traced to formations which lie at some miles' distance to the north-west and ' north. This distribution of the diluvimn from the north and north-west is not confined to the rivers whose

Chap. Vi. P08Ttbbtiabt Strata. 77

valleys nm in these directions, bat belongs, it is believed, to at least all the middle and northern latitudes of the eminent. It is seen west of the AUeghanies, through-> out the regions of the Ohio and Mississippi, as well as extensively over the Atlantic slope and the tertiary Atlantic plain. Bigsby, and the travellers to the north, have already shown it to prevail in the latitudes north of the United States/'

These and many other cases demonstrate—*

1. That the course of the blocks from their original site has been influenced by the present configuration of the country ; because they are accumulated in greatest abundance in the lower regions of the earth, and have often gone by the line (though not limited to the level) of the great drainage hoUows of the surface.

2. The mechanical forces which transported these boulders must have operated under totally different conditions from those which determine the course of the actual streams ; because the boulders have crossed great vales and seas, and ascended ridges, quite contrary to the course of existing drainage.

3. It is impossible to comprehend the phenomenon as one capable of being produced by the watery agencies now at work in nature, except under different dynami- cal conditions ; such as a disturbance of the oce(inic level to an enormous degree, hardly conceivable except as the result of a general change of the figure of the globe, produced by a displacement of its axis of movement ; an incredible and irregular alteration of dimensions ; or a series of elevatory and depressing movements operating in certain directions. Ignorant as we are of the extent and character of diluvial phenomena in all the southern zones of the world, it is desirable to avoid a decision on the much controverted origin of the erratic blocks, espe- cially as some of the proposed solutions are mechanicsdly absurd. One of the most ingenious, and perhaps least hypothetical, of the modern notions on the subject, is,

Rogers, in Reportf of Brit. Assoc, vol. liL Dr. Bigsby's Observaaons on the travelled Boulders about Lake Huron and Lake Erie (GeoLlYanai ▼oL vL pt 2.).

T 3

278 A Treatise On Oeolooy. Chap. Ti

that the great hlocks of the Alps and Scandinavia were floated away on icehergs and so dropped on the sea bed or on the temporarily submerged land. That Ice- bergs are detached from the land with stones on their surface is known to northern navigators ; it is a pheno- menon well understood in the Gulf of Bothnia ; and to an imaginative mind the mer de glace, with its border of moraine, might seem a natural component of such a glacier current as that to which the Saleve, the Jura and the borders of the Lake of Greneva are supposed in this hypothesis to owe their accumulated blocks! It is thought to be a plausible argument in favour of this speculation, that ihe blocks of granite, porphyry, lime stone, &c. are grouped together in distinct patches oe- cording to their hcai origin, both in the vicinity of the Alps and on the plains of northern Germany.*

Ossiferous Gravel, Pebbly Clay Sand bto.

While a few 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 interest from the discussions of De Luc and the splendid researches of Cuvier into the bones of quadrupeds which lie abundantly in these deposits. Large portions of £ng land, Wales, Scotland, and Ireland are covered by \r- regular 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 diey 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

See Mr. LyeUI Geology , Brongnlart, Tableau det Temdni ; De Letten,ftc

Chap. Yi. P08T-Tebtiabt Strata. 279

in some cases very positively as to the direction in which they have heen drifted. Generally in all the north of £ngland the diluvial gravel has heen transported hy the same routes or the same points of origin as the boulders ; but there is some variety in this respect worthy of notice. On the eastern side of the island from the Tyne to the Humber the gravelly deposits appear partly of local and partly of distant origin. On the Yorkshire coast local gravely derived from the chalk wolds or oolitic moors lies in very irregular beds distinct altogetiier from the days full of pebbles brought from tiie Cumbrian and Penine mountains ; at Bridlington local chalk and flint gravel lies over tiie other diluvium and at Hessle on the Humber similar local gravel Hes under it.

It might be proper in tiiese cases to confine the term diluvium to that portion of the gravelly masses which by tiie abundance of the fragments from very distant parts requires tiie supposition of extraordinary circum- stances for its accumulation. It is not solely, nor, per- haps, even principally, in this proper diluvium, tiiat the bones of elephants, hippopotami, horses, deer, &c. occur ; they seem, on the contrary, to be rather more plentiful ill the local gravel deposits. Cases, however, occur, as at Brandsburton, and at Middleton on the Wolds, near Beverley, of elephantine and other remains in the midst of erratic gravel derived from great distances.

The most singular circumstance attending tiie accu- mulation of the proper diluvium is tiie extreme con- fusion, 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 regions, lie mixed indiscriminately in clay many yards in tiiick- ness ; 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 specific gravity, but were heaped confusedly together by a force of ex- traordinary intensity and short duration.

T 4

t80

A TRBATI8B ON GEOLOaT.

QBAP. Yim

Similar. ezplanatioDs seem applicable to the pebbly clays of Lincolnshire Huntingdonshire, and Northampton- shire, &c. ; and to the whole track of the diluvium from the lake moimtains 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 districts contain abundance of local gravel deposits, which sometimes appear to be quite as ancient as diluvium, and may justly be styled '' Ancient Alluvium ;" for their aggregation seems not, in general, to require the sup. position of watery agencies flowing in, other than the directions of actual streams and inundations. Much of 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 coimtry, has been drifted from greater distances, and appears due to more general agency.

Mr. Murchiflon's examination of the Welsh border appears to show that the gravelly deposits formed from

Chap. Vi. Post-Tbbtiaby Strata. 281

the waste of those districts and forced down to the great hoUow uniting the vales of the Dee and the Severn were transported according to the descent of the coun try, previdus 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 oflr to the reasoning geologist. Gravel is not neces- sarily of diluvial origin ; does not necessarily imply the action of violent iorcba, 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 Dauphine by the Isre and the Durance, have one local origin ; almost every valley of the Alps and the Grampians has served for 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 efibcts in all cases to have been produced by the same agencies. Before any particular masses of sand, gravely 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 surf)lce with ordinary measures of local watery forces, the accumu-

282 A TREATISE ON OEOtOGY. CHAP. VI.

lation of such masses is imposdble. This can be shoiim, if the component pebbles of the presumed diluvium can be referred precisdy 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 ihe 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 miEusses, so as to deter- mine the direction really followed by llie 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 casea 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 lights masses indiscri- minately mixed ? Are the fragments angular greatly rounded, or. flatly elliptical ? Are bones of quadrupeds or shells of moUusca found in the mass, or lying in marly beds above, below, or inclosid ? The problems thus suggested are of great importanee toward a correct view of the origin of the diluvial accumulations and the contemporaneous races of organic being*

Ossiferous Caves, and Fissures in the Rooks.

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

Chap. Ti. Post-Tertiary Strata. 283

buried in the gravel ; for their bones are also found in caves and fissures of the rocks under circumstances generally indicative and often demonstratiye 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 recognisaUe, and capable of being rigor- ously compared widi 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 fiJl 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 <]hfierences, when difierent districts, as Franconia and Yorkshire, or Narbonne, are compared. These local difiPerences are unportant 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 rppears improbable that the remains of ihe human aace found in the caves of Bize, Belgium, &c. are really of the same date as the elephantine exuvie in northern climates. (See Desnoyers' Report to the Geol. Society of France.)

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Chap. Vi.

Post-Tertiary Strata.

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£9 A TREATISF ON GEOLOGY. CBAP. Yl*

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 io 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 pecuUar 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 5 but it is certain that, in two districts of tbe 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 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 stalagnutic

Chap. Vi. P0St-Tebtxar7 Strata. 29 1

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. l<et us admit, then, as sufficiently proved, the existence of open caves and fissures in limestone rocks, at the time when elephants, tigers, hysnas, rhinoceroses, &c. lived in £urope ; and inquire Airther 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 (JReliq. JDiluv,). 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 mitture 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 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

u 2

292 A Treatise On Geolooy. Chap V

the shore and subsequently the whole coast raise<L (Pratt and Christie, in Geol. Proceedings.)

2. Into other caves it may be thought other tribes of animals, especially predacious raes, 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 RosenmuUer 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, Zalmloch, Rewig, Rabenstein, Schneiderloch, Kuhloch) ; on the south-western border of the Thurin-'' gerwald (Gluchsbrunn, 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 spelsus, U. arctoideus) ; two thirds of the remain- der to extinct hysenas ; a few to a large felis, a glutton, wolf, fox, and polecat.

In all the caverns, M. RosenmuUer found the bones disposed nearly after the same manner; sometimes scattered separately, sometimes accumulated in beds and ]ieaps 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.

Jp0St*Tsrtiary Strata.

brown argillaceous or marly earth in which a consider- |bie 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 9,0 or 30 feet thick full of bones, and over the whole one layer of slagmite which has been formed by the droppings from the roof and tricklings from the sides. {Reliq, Diluv,)

KIHKDikLB CATB.

A. Hud 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, {tartly inclosing bones.

D. Stalagmitic boss on the crust, derived from dropping water. £i Stalactites hanging from the roof.

294! A Treatise On Geology. Ohap Vi.

3, It is sufficiently ascertained that some particular caverns rich in hones as Kirkdale Cave in Yorkshire Kent's Hole at Torquay, &c., have nqt 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 die 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 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 Hodgle 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 j in other parts, its height is augmented by open fissures, which communicate through the roof, and allow a tnan to stand erect. The breadth varies from four or five feet to a mere passage ; at th 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 rQof 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 bken 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. Fost.Tebtiart Strata. $95

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 crusty 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 : — -

Camivora, Hyaena, felis, bear, wolf, fox, weasel. Pachydermata, £lephant, rhinoceros, hippopotamus, horse. Jtuminantiiu Ox, three species of cerrus (not the Irish elk). RodenHa, Hare, rabbit, water-rat, mouse.

Sirdi. Raven, pigeon, lark, duck, snipe.

The hyenas' bones and teeth were very numeroua ; probably 00 or 800 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 wateT'tate 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 hyena ; — they were distributed as in a 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 grecum) of hyenas was not rare — the teeth of hyenas were found in the jaws of every age, from the milk tooth of the yoimg 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 hyenas acquires much force by com- paring the fragmentary state of the bones of oxen, hares, &€,, in it, with the far more complete condition of the same ftnima in other caves, which, like Banwell, con- tained few or no relics of hyena, and with the pro- ductionBDf Kent's Hole, whidi are similar in all resjiects

296* A Treatise On Geology. Chap. Ti.

to those of Kirkdale/ and among which hyenas' hones and teeth abound. We may therefore admits 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 conjee- tares, 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, accori 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 days, bone caves, and fissures, as phenomena related to a certain geological period, and a particular set of dynamical agencies. Such effects are not, at this day, in progress ; nor, in general, can we conceive the possibility of their being produced by the operation of existing agencies ' operating with their present intensities, or in their pre- sent directions. 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; and it seems not at all improper to class under

Ohap. Vi. Post-Tebtiary Strata. ' 297

the same point of view the pebbly deposits of an earlier stage in the history of the tertiary strata, viz. the plastic clays and sands of London and Paris. So strong is this analogy that Dr. Forchhammer has adopted the view of the boulder formation " of Denmark being one very long series of detrital deposits including the whole ter- tiary series and extending 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 distribu- tion 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 these 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.

The principal difficulties of the question relating to the agencies concerned in the dispersion of diluvial detritus would be not removed, nor, perhaps, even diminished, but rendered at least more definite, and therefore more within the scope of geological and phy- sical research, could we be quite sure of the fact whether this mass of heterogeneous materials was deposited by great inundations upon the land, or thrown into the sea. We know that the violence of the watery movement was great, and the accumulation of the matenals rapid, since, in some considerable deposits of diluvium, there is no sorting of the materials into portions according to their weight or magnitude ; but the finest clay has larg bouldered rocks scattered through its whole thickness in the utmost confusion.

Further, it appears from some examples (Holdemess, vale of York), ihat gravelly and detrital beds, intimately associated with ordinary diluvium, and full of blocks and boulders brought from great distances, contain marine shells. If we should consider these to be, like the Lancashire and Cheshire examples, raised parts of the littoral bed of the sea, the diluvial deposits resting

298 A Treatise On Oeol06Y. Chap. Vi.

upon them may plausibly be viewed as accumulations in the same water, depending on convulsive movements of the areas from which the materials were drifted.

On the other hand it seems clear from the occurrence of the bones of land mammalia among some of the diluvial gravel and clays that the track of the watery currents was in places at leasts over the solid land ; though it seems not necessary to imagine that the ossi- ferous accumulations in question (Brandsburton gravel hills, Overton near York, Wilford in Essex, Harwich, Brentford, &c.) were heaped upon the land. They might be finally aggregated in die sea ; and thus the seemingly contradictory evidence of marine shells and quadrupedal bones, in the same set of deposits, be re- conciled.

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, 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.

CHAP. VI. POST-TBBTIABV STUAf A. fHQQ

Zoological auj> 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 £p- peisheira, on the Rhine, in which occur a vast number of species very nearly approaching to existing races ; secondly, among the animals of the dUuvial 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 founds 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* 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 diluvial deposits. It is confirmed by the gradual change in the proportion of existing among extinct species of tertiary sheUs ; so that the most recent groups of tertiary strata contain 40 to 90 per cent of living forms while among dozen or twenty shells in the gravel of Holdemess, one extinct species is met with.

On the other hand, it must be remembered, that no paleotheria, 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 Gmund, lophiodontes oxen, hippopotami, &c. occur together.

Again, certain animals which lived in the dUuviil

$00 A Treatise On Geology. Ohap. Vi.

period as ervus 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, iJiat no one has yet succeeded in showing a real and certain distinction between the common red deer and the common ox of Europe, and the analogous bones of Kirkdale and other caverns.

Upon the whole, it seems probable that the paleothe- 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 modem species (stag, ox) were co-existent with the elephant and hippopotamus in northern zones ; others (elephas primigenius, rhinoberos 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, Among living tribes, the diagnosis of species is far from dear, what errors may not be incurred by pronouncing a, verdict on the imperfect evidence of a few fragmented or detached fossil bones ?

Ancient Mabine Deposits.

liaised Beaches, — Perhaps nothing more fully illus- trates the rate and progress of geological research, than the attention given of late years to the phenomena, first brought prominently forward by M. Biongniart, which demonstrate, that within a comparatively modern period, certainly since the actual seas were filled with .their existing mollusca, the beds of these seas have been suliject to elevation and depression, so that, in par- ticular places, large qutities of shells attached to their :parent rocks or mixed with the pebbles and sand of

Cbap. Vi. Post-Tebtiary Strata. Soi

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 of 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 dass of facts noticed above ; which appeared to M. Brongniart of so general a character as to justify a supposition that the ocean waters had every where 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 leveis at which the raised beaches ap\ar above the sea, are extremely varied, even on points of the coast of die 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 (fiffnUsement de ki croiite du globe dans un point), should have left accord- ant 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 (Gilbertson) ; 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 upUfting of the shores of the Moray Frith has taken place subsequent to its having assumed its present online, is considered by Mr. Prestwich as proved by the existence, in several places, of raised beach. In Banffshire, this beach varies from six to twelve feet

302 A TREATISE ON GEOLOGY. CHAP, ru

above the present high water lerel ; and contains shells now inhabiting the neighbouring sea as patelia vulgata patella leevis trochus zlzlphinus littorina littorea turbo retusus. At Gamrie, oeleln'ated for its ichthyolites Mr. Prestwich founds in light coloured sands associated with rolled gravel and dark clay beds, the following recent shells : — Astarte Scotica tellina tenuis hue- cinum undatum, natica glaucina fusus turricola, den- talium deiitalis See. They were extremely friable, but perfect. The deposit attains, in some places, a thick- ness of 250 feet, and rises to an 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 rocks below the bed of shells worn and scratched by the drift- ing of the pebbly masses, t

In Cheshire, the shelly gravel and sands, containing turritella terebra, murex erinaceus, and cardium edule, are covered by the ordinary sandy diluvium of Cheshire, in which are many erratic blocks from the North of Eng- land, as well as pebbles from the Welsh border.

In and near the valley of the Itibble, for some miles inland, from its mouth, near Blackpool, by Preston to the base of Longridge fell, and on Whittle hills, from the level of the sea to 300 feet above it, occur beds of marl, sand, and gravel, unde' the ordinary diluvium with erratic blocks, locally full of sheUs of moUusca now living on the neighbouring coast — such as turritella terebra, cardium edule, tellina solidula, &c. The lamination of thede shelly beds is irregular, resembling a modem beach accumulated under the influence of strong currents.

Somewhat different appearances are seen in the op- posite parts of Yorkshire, especially in the district of Holderness, where sandy and gravelly beds, full of pebbles and fragments of Cumbrian rocks, contain, at

Geological Proceedings. 18S7 i Geological Proccedingc.

Chap. Vi Post-Tertiart Stbata. 505

particular spots (Brandsburton, Faul Ridgmont), layers of shells all marine and aU except one now living in the neighbouring seas. Besides the strong shells of turbo littoreus purpura lapillus and buccinum undatum we have mya arenaria, tellina solidula, t. tenuis mac- tra subtruncata cardium edule &c. ; and it is cer- tainly very strange to discover these and other tender shells in a good state of conservation among the twisted and confused lamins of so coarse and irregular a deposit as that in the vicinity of Ridgmont

On the same coasts at Speeton, is a much more re. gular sandy deposit full of cardium edule amphidesma Listeria tellina solidula Sic, on the top of the cliff.

From the Wexford coast of Ireland Mr. Griffith pro- duced at the D,ublin meeting of the British Association shells of existing and also of extinct species, from what seemed a raised beach. A similar deposit, on a very extensive scale, occurs on the coast of Devon. — (Murchison and Sedgwick.)

From these short notices, the reader may be assured, that, even on the British coasts, the phenomenon of raised beaches is one of the most general yet known : that the deposits called by this name were accumulated under considerably different circumstances, is certain ; their high antiquity is proved by the superposition (in general) of the erratic boulders; and th& general analogies they offer to the Sicilian and other tertiary deposits are obvious and important. A philosophical study of these till lately neglected phenomena will certainly re* ward investigation, and probably strengthen in a high degree the basis of geological induction.

Turning to other countries, we find abundance of analogous facts. As on the south coast of England, so on the north coast of France, on the hills of St. Michel, form., ations of the nature above described occur, and have been described by M. Fleuriau de Bellevue and M. Brongniart, under the name of '' gravier coquillier." The shells of St.Michel consist of many species, univalves and bivalves; the two pieces of the latter often remaining in their proper position; the whole retaining both their natural

804 A Treatise On Geology. Chap Vi."

colour and texture and lying as similar shells are asso- ciated at this day on the neighbouring coast. Ostrea edulis, anomia ephippium pecten sanguineus modiola barbata mureii imbricatus buccinum reticulatum are mentioned as the principal species. They are placed nearly fifty feet above the sea. At Nice similar banks occur at nearly the same elevation ; the coasts of Sicily, Greece, and Asia Minor give similar evidence.

Both on the Baltic and the Atlantic coasts of the Scan- dinavian peninsula, phenomena of the same nature have been long known and rendered famous by the relation they bear to the hypothesis of the gradual subsidence of the level of the Baltic. Von Buch, Brongnit, Strom, Lyell,and Forchhammer have investigated the facts with attention and success. On the western coast of Sweden, at Uddevalla in the province of Gotheburg, in a little bay of gneiss rocks, occurs so vast a quantity of shells, 70 metres (76 yards) above the sea, that they have from time immemorial been collected for use on footpaths. In hollows of the gneiss rocks, M. Brong- niart found balani yet adhering, and detached fragments to prove the interesting fact.

In a recent visit to Sweden, Mr. Lyellhas confirmed and extended these observations, and connected the re- sults with the general question of subterranean move- ments and the local speculation of the lowering of the Baltic, — an expression which may very properly be trans- formed into a rising of the horders of that sea. Near Stockholm, remarkable ridges of sand and gravel called sand oasar (asar), 50 to 100 feet high, range north and fiouth, and yield good rOad materials. Under one of these ridges in the same sand and gravel, 30 feet above the Baltic, are found shells in abundance, such as now live in the Baltic, viz. cardium edule, tellina Baltica, mytilus edulis, littorina crassior, 1. littorea, &c. At other spots, 70, 90, 100 feet above the sea, shells in general simUar to the above (with neritina fiu- yiatilis and bulimus lubricus, a land shell) were found abundantly, about Stockholm, Upsala, and Gefle ; and Bometimea covered by erratic blocks (Upsala). It was

Chap. Vi. Post-Tertiary Strata. 305

noticed at Uddevalla that several species of fusus occur there though none are now found in the Baltic. From the whole investigation it appears certain, that both on the Atlantic and the Baltic shore, the land has in some ancient periods risen considerably (200 feet at least), so that Lake Wener on the west, and Lake Maeler on the east, were formerly parts of the ocean: it also appears probable, that a part of the Scandinavian peninsula is, at this day, gradually rising higher above the sea, but this rise does hot affect the south of Scania ; the rate of rise is supposed to be three feet in a century at Lofgrundet, north of Upsula.

In connection with this subject, we may mention the extended deposits of sea shells (though their identity with existing species may be doubtful) on the plains round the Caspian ; the sheUy sands at the Cape of .Good Hope; the elevated terraces of shells on the coast of Valparaiso, and on the plains of Patagonia; the coral masses in the interior of Antigua ; the shelly beds of Barbuda ; the Keys or sand islands on the coast of Florida ; and the sandy portion of the Atlantic plain which borders the United States (Rogers, in Brit. Assoc. Sfeports) ; for it seems difficult not to recognise, in these and many other examples, proof of the very great extent to which the level of land and sea has been and still is locally variable.

But in order to guide generalisations on these striking

phenomena, it is desirable to establish the experiments

suggested by Mr. Whewell at the Bristol meeting of

the British Association, and, by means of two hues at

right angles to one another, to ascertain perfectly whe-

ther at this time, in England for example, the presumed

'- movements of the land take place ; whether there be an

i axis of movement, such that on one side of it the land

rises, but on tlie other sinks ; what is the direction of

such axis, and the rate of the movement.

./

Vol. I.

306 A Treatise On Geology. Cuav. Vi.

Mabine Deposits in Progress.

The elevated portions of the borders of the modem oceans which have been noticed are so fraught with in- structive analogies to the processes of nature in more ancient times that we cannot help feeling regret at the limited means which man possesses of penetrating the great deep, and watching the phenomena which happen on its quiet bed. There we should behold, it is pro. bable, a number of circumstances connected with the life of marine mollusca, radiaria Crustacea, fishes, which would throw quite a new light on many of the problems of old geology ; inform us of the probable depths, distance from the shore, and river mouths, and other conditions most important for us to know in con- structing trustworthy inferences regarding the formation of the fossiliferous rocks.

Coral Reefs. — That the very deep parts of the sea (nine miles is a probable estimate for the Atlantic depths) are as devoid of life as the centre of an African desert of moving sand, is extremely probable, from the known fact of the dependence of organic life on air and light ; the former must be greatly modified, the latter extinguished, in passing through such a mass of absorb- ent fluid. The voyagers of modem date (captain Beechey, MM. Quoy and Gaimard, Freycinet, Stutch- bury, Darwin) concur in removing one error of import- ance on this subject; they have rendered it highly probable that the coral reefs and coral islands which abound so much in the Pacific Ocean, do not rise from even the depth of many hundred yards, but commence on the summit of some volcanic elevations, or other submarine ridges and rocks, not far below the surface of the sea.

These coral islands and reefs, which may be viewed as lines of islands, are certainly remarkable for their extent and mass of matter, even as compared with the ancient calcareous rocks, which derive much of their

Chap. Vi. Post-Tertiary Strata. So?

substance from zoophytic exuviae. They form the basis of or surround the shores of most of the islands in the warm parts of the Pacific and stretch for a thousand miles parsdlel to the north -east coast of Australia in a narrow reef of several hundred miles' length. In like manner about the Indian and West Indian islands in the Red Sea Persian Gulf and Mediterranean coral abounds so as to constitute a considerable portion of the products of the sea.

It has long been the custom to compare the rapid and abundant growth of coral islands with the limited breadths of marine limestone which lie amidst the sedi- mentary sandstones and shales of the stratified rocks ; and on the comparison conjectures have been founded that the stony crag of Orford, the coral rag of Wilts, the transition limestone of the Eifel and Rymouth, were, in efiect, ancient coral r&efs. It appears, on a first glance, a fatal objection to this view, that these an- dent rocks are regularly stratified ; the corals in them occupying particular (often thin) beds, not lying con- fusedly through the mass, nor growing one to another, so as to resemble in structure what is popularly imder- stood by a coral reef. But this notion of a coral reef, exact enough in many instances, is incorrect when applied to the Bermudas, which grow up a mingled mass of coral, shells, comminuted calcareous substances, and sands drifted by the current of the gulf stream. Parts of this calcareous mass, raised above the sea in' hills, are drifted by the wind and dispersed into beds.* In such accumulations, not far from land, under the in- fiuence of sea currents, we ought to find very different results from those which take place in the broad calm waters of the wider ocean.

In Mr. Stutchbury's excellent dissertation on the form- ation and growth of coral reefs and islands (West of England Journal), the construction of the. principad part of the coral mass is ascribed to the genera caryophiUia, . meandrina, astraa, porites, and msdrepora; while the

Neilflon, Geol. Soc lroceedingi.

308 A TtlBATISE ON GEOLOGY. OUAP. VI

ornamental parts are made up by a difiusion of the other forms of Linnaean madrepores viz. fungia pavonia agaricia monticularia, echinophora podllopora seriate- pora and oeulina together with gorgonia isis corall lium melitea corallina spongia, alcyonium actinia &c. independent of the locomotive asteris echini, testacea.

The coral islands are classed by Mr. Stutchbury as circular flat long narrow, and encircling high land.

The coral islands of the Dangerous Archipelago (lat. S. 12° to 27°, long. W. 130° to 155°) are all of the first kind and consist of strips or belts of coral of an annulate or circular form from 400 or 500 yards to one mile across the ring which always incloses a la- goon ; seldom raised above the water more than from 4 or 5 feet; abrupt towards the ocean which rapidly deepens to more than 120 fathoms. The islands vary from 2 or 3 to 1 50 miles round ; the ring being often divided across by a fissure admits vessels to enter the lagoon. The depth at which the coralligenous zoo. phyta commence their labours is said not to exceed 15 or 20 fathoms (Quoy and Gaimard say 20 or 30 feet Mr. Darwin has recently given the same estimate as Mr. Stutchbury). The bottom of the lagoons is seen in calm weather at a depth of 1 00 feet or more strewed over with dead shells and broken fragments of coral, rarely showing any living specimen hehw sixteen or seven- teen fathoms ; at which depths smaller reefs rise within the lagoon ; and beyond which depth, broken masses of rock may be seen without any living portion attached.

It would appear that, during the formation of a reef, portions of it become compact, and as dense as any limestone rock ; a circumstance indicative of the partial dissolution and re-precipitation of the coral masses, and apparently analogous to the process whereby coral shells, &c. have been imbedded in the compact limestone of ancient stratified rocks. Extensive beds of particular shells appear among the islands.

Islands often occur of a flat or tabular form, generally

Cuaf. Vi. Post-Tertiary Strata. 309

oval or irregularly rounded at their circumference : of this form are the group called by Cook the Friendly Isles, consisting of numerous islands the majority of which are tabular.

There are also many crescent-shaped reefs, with the most convex portion of their arc the highest, often de- noting themselves to the mariner only by the breaking of the waves, and here and there a rock above the level of the ocean, while the horns of {he crescent are de- pressed, and gradually lost in the greater depth : in a few instances, as at Gambler's Island, they are suffi- ciently raised to have become verdant and inhabited.

Of those which form long narrow strips of land, Mr. Stutchbury refers to Tehuro, a few leagues from Tahiti, and the great reef which takes the course of the north-eastern shore of New Holland, which Captain Flinders describes as being more than 1000 miles in lenth : in the course of which there is a continued por- tion exceeding 350 miles with scarcely a break or passage through it.

Of the last group of coral islands, or rather reefs, encircling elevated land, the Society Islands, including Tahiti, offer striking examples; being often surrounded by coral reefs, generally situated 400 or 500 yards off shore, with a deep channel between, having numerous openings, through which ships can enter and lie at anchor in perfect safety. These breaks in the coral barrier are, in most instances opposite the mouths of freshwater rivulets.

The islands Raiatea and Tahaa (Ulietea and Otaha of Cook) are divided by a strait, by which ships can enter at the windward side of the islands, and get to sea again through the leeward channels. These two islands are entirely surrounded by one coral reef, extending throughout the circumference of both ; the openings through the reefs are, in most cases, denoted by the points being rather higher and more verdant, having trees, principally cocoa nut trees, planted by the natives f upon them. The passage is seldom more than 100

The form of the coral islands must very maCerialljr depend upon tlutt of the base on which the; happen to be built ; hence theii circular, lunulate, oval, or irregular forma give information as to the shape and even nature of the subjacent rocks. In most cases, the base of the small islands appears to be a volcanic crater, entire or broken ; islands of volcanic rock, as Tahiti, are surrounded by rings of coral. The elevation of the coral islands is not owing to the mere accumuladon bj the rough action of the sea, but to a gradual rising of the low islands, and a violent subterranean movement of the lofty ones, like Tahiti, v)hich heart on the apes of one of the highest mouniaina a dittinct and regular ttra- tian of lemi'fogBil coral, and near it, but on a tower level, a volcanic crater with two lateral gorges.

In this case, had the upward movement been gradual, why should not the coral growths have covered the edges of the crater, or rested on other points ?

Mr. Darwin has recently been conducted, by a con- sideration of the structure of coral islands, annular and linear, whether immediately Investing, or at a dia-

tance guarding, insulated pointa or long coaals of land, to a remarkable geneial speculation; viz. that in the Southern Ocean the distribution of the coral raaasea on a great scale, and their peculiar forma in detail, ore ex- plicable on the supposition of certain lines, or rather, long narrow spaces of ocean, in which the land has undergone and is still suffering gradual depressions, and alternating with these other long spaces in which the land " is rising. Whete depression has taken place, coral ia supposed to have grown on the submeed points ; and, as the depression proceeded, to have con- tinued to grow and keep the surface as high as ihe sea. A depressed mountain chain might tbua be the origin of a long line of coral islands, or of a continuous reef, as on the east coast of New Holland; a single island of rock, at first sMrted by a fringing growth of coral, would, npon Airther depression, assume the appearance of a central rock, and a circular ring of coral; and, finally, the rock would vanish, and nothing but an annular coral reef appear, indoeiog a lagoon, which might sub- sequently be filled up. The principle of this explanation may be understood by reference to the figures annexed, where a', a', a, a', ate snccesrive levels of water, sur- rounding and finally covering the insulated rock r, upon which, at c, coral began to grow where the depth was small enough. On a further subsidence, more coral, e, was added upon, but not uHfAin, the reef e; and, fiiudly, e being raised to the surface of the sea, while T luid sunk below it, and fragments of the coral broken

; B lagoon. The island and reef would thus present a plan the following features eucGessively.

If, instead of a sinking, we next imagine a gradual rising or a stationary situation of some island, on which a circle of coral waa fixed, the additional growth of this substance would be always on the outside, and the land would never be separated from a uiide/y eaniTclmg reef by a channel of deep water.

In Mr. Darwin's Tiews, tlie presence of a ligoon coral island is an evidence of depreaion of the solid . land there ; and, on the contrary, matgiiial coral reefs often supply evidence of riting, in addition to that fur- nished by shelly beaches at high levels. Thtu tnty

Chap. Vi. Post-Tertiary Strata. 313

yre comprehend, in the former case, the formation of a long bank of coral, by the successive submersion of a line of mountain summits ; and the filling of a sea with many small annular reefs, by the sinking of island rocks : in som cases, the circular form of lagoon islands may, however, be as well understood by supposing them to have grown on a submarine volcanic crater. A decisive proof of the truth of Mr. Darwin's views, in the particular instance, would be the discovery of solid coral rock at a much greater depth than that which is stated to limit the existence of the lamelliferous polypi.

The general results of and views arising from Mr. Darwin's investigations include the following very im. portant points : —

1. That Hnear spaces of great extent in the equatorial regions are undergoing movements of an astonishing uniformity, and that the bands of elevation and subsi- dence alternate.

2. From an extended examination, the points of volcanic eruption all fall on the areas of elevation. The importance of this law is evident, as affording some means of speculating, wherever volcanic rocks occur, on the changes of level even during ancient geological periods.

3. Certain coral formations acting as monuments over subsided land, the geographical distribution of or- ganic beings is elucidated by the discovery of former centres, whence the germs could be disseminated.

4. Some degree of light might thus be thrown on the question, whether certain groups of living beings pecu- liar to small spots are the remnants of a former large population, or a new one springing into existence. (From Geol. Proceedings, 1837 ; and notes taken dur- ing the reading of Mr. Darwin's paper to the Geol. Society.)

Shell Beds. — What the circumstances are, which

favour in a special degree the accumulation of shells

on the bed of the sea, may be patMtly conjectured ; but

314 A TREATISE ON GEOLOGY. CHAP. Vi.

the subject deserves to be considered as one of the most important problems which geology looks to the naturalist to resolve. Very different oonditions are knoim to govern the aggregation of the different tribes : they choose different soils — so to speak — love different depths bear unequally the influence of currents fresh water, climate. Oysters, for example by their stationary habits and mutual attachment exclude nearly all other concbi fera from those patches of the sea where they thrive. So, among the fossil ostrese we find whole beds of vast ex tent; in the Kimmeridge clay (O. deltoidea) and in the lias (gryphea incurva). Near the muddy mouths of tide rivers, uniones anodontes &c. abound, and are little mixed with other genera ; and their ancient prototypes in the estuary deposits of the coal tracts and Wealden form- ation are similarly circumstanced. Donati found the Adriatic covered with shells and sediments almost iden- tical with the subapennine deposits ; the German Ocean yields sands and shells like those of the raised beach at Speeton ; the Bay of Morecambe, upraised, would re- semble the deposits at Preston ; the Baltic bed, with its living shells, is like the undulated gravel heaps and buried testacea of Sweden ; and there can be no doubt that a careful scrutiny of the borders and bed of the existing sea would show many conchiferous formations in progress extremely like those of ancient date. It ap- pears a very general fact, that the existence of living marine testacea is limited to a small dispth from the surface. In Mr. Broderip's table (De la Beche's Theo- retical Researches), the greatest depth mentioned (for terebratula) is 90 fathoms. It is much to be wished that this interesting subject should attract the attention of the scientific officers of the British navy. ,

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)j it must follow, that during the formation of the strati- fied crust of the earth, very general and long continued depression occurred in the ancient bed of the sea : for

Chap. Vi. Post-Tertiary Strata. 315

as the series of strata foll at least partially of organic remains which lited 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 heing exhausted, a contrary action raised them again. To this highly important 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 German Ocean, each strewed with difier- ent groups of sheUs, the distribution of organic fossils in the different primary and later strata, if at all governed hy the same laws as those now traceahle in nature, though affected by some general characteristics of pe- riod, must also exhibit specific relations to the nature of the rocks. We lave 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, 8c, — 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 maritime Alps, or gathered from the falling cliff by the action of the waves. According to specific gravity and magnitude, the masses are separated, trans- ported, deposited — pebbly deposits lie under the gravelly cliffs — the sands are swept to a greater distance — the fine clay carried far in the waters. Of all these circumstances the English coasts ofiisr abundant ex* amples — especially Teesmouth, the Bristol Channel, and the Bay of Morecambe, which, on their wide sands, present a wonderful variety of appearances, proper to

31 6 A Treatise On Geology. Chap. Vi.

furnish the speculative geologist with more accurate and applicahle data than are commonly relied on. Among others, the aspect of the surface of the sand — its ripple marks, varying in an exact proportion to the depth of water and the direction of the wind — the numerous little valleys and ri]Is which modify the slopes — the count- less prints and seeming prints of the feet of birds the trails of mollusca and annulosa, may suggest to the rea- soning geologist proofs of the important truth, that all our laminated sandstones and flagstones were littoral de- posits,— a point of departure for accurate inferences con- cerning 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 cliflfs, 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 depositing new land, which subsists either by a natural defence of blown sand, gathered pebbles, or the prudent skill of the engineer, till some unheard-of storm returns to re- claim 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 action 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 littoral in- draughts of Iceland, Norway, and Ireland. Captain Sabine's observations on the sea current of the Maranon show, that, at a distance of 800 miles from its mouth, the fresh water of that mighty river floats on the heavier water of the sea, and retains its earthy discoloration.

chap. vx. post-tebtiaby strata. 317

Ancient Valley Formations.

I have some time ago proposed this term for the purpose of combining in one point of view a great number of remarkable ancient phenomena attesting the former action of water in existing vaUeys, but flowing at higher levels than the actual stream, unless the land has been raised and sunk. Deposits of gravel at the mouth of a valley, in the form of terraces, abound in most mountain countries (e, g. foot of Glen Roy), on the sides of a valley (as in Tjmedale, above Newcastle), at the head of a valley (as at the head of several Cum- berland glens).

In Glen Roy, at a very high level, are two parallel lines, or terraces, which run round the mountain sides, and communicate with other drainage streams. The deposit called Loss, on the Rhine, appears of the same nature, so far, at least, as to indicate the deposition of sediments in water flowing at a level many hundred feet above the present River Rhine, and extending beyond what is now its proper valley on the north side of the range of the Ardennes.

In some of these cases,.there is sufficient proof that the water was not marine, land shells being not unfrequently found in the deposits, especially the finer sorts of sedi- ments. The level character of the terraces, which is the most usual form of these accumulations, seems to indicate the existence of ancient lakes at a high level in the valleys where they occur.

Fluviatile Depotiis.

U]>ptrTemM

Bl of the Valley

This, however, is less certain tlian may be commonly imagined ; for streams like the rough Arve scatter the detritus lurougac down from the glaciers over a surface

Ljell, in Geol. Proc.

318 A Treatise On Geology. Chap. Vi*

gendy dedining, as the stream rons but nearly level in. the transverse section. If by any change of the physical conditions the stream should cut its way to a greater depth, the banks would have that terrace form which belongs to the Lune, the Ouse the Tees, the Tyne and many rivers of the North of England. It not un- commonly happens, that two such terraces, at (tifferent levels, can be traced for some distance on the sides of a valley, as on the Lune ; — occasionally, in the midst of a valley, rises a low hiU of gravel corresponding to the lateral terraces. In most valleys, the materials of the ter- races are such as the rocks on the sides of the mountains yield ; but this is not the case on the Lune about Kirkby Lonsdale, or the Tyne above Newcastle, in both of which situations, boulders and gravel from the Cumbrian mountains constitute a considerable part of the deposit. For this reason, they would probably be called diluvial deposits by some writers, and described as raised breaches by others. The confused aggregation of the pebbles sand, &c. is such as to imply sudden and violent in- undations, which delivered a vast body of detritus in a short time, and perhaps followed the line of the valley, but deposited the coarse earthy matters near the sides when the velocity was lessened, as powerful streams are always found to do.

H. W. High water mark.

1. Surface of chalk excavated by water ih some ancient period.

a. Surface of ancient tertiary sands, or alluvial sediment left in the chalk

valley. S. Surface of detrital (diluvial) deposit extended over hill and valley. Surface of comparatively modern alluvial deposit in the valley of the

diluvium, consisting ofchalk and flint gravel.

Existing valleys have, then, in many cases, been tra- versed by floods of water which have left evidence of their voltune, force, and direction. Did they excavate the

Chap. Vi. Post-Tertiary Strata.. 319

valleys ? or merely follow the traces left by earlier watery violence ? Perhaps we must not yet ventm'e to propose a general answer to such questions there exists how- ever, cases which bear very decided evidence with refer- ence to them. At a little vaUey in the chalk of Yorkshire (represented in the diagram, p. 31 8.), which opens to the sea near Bridlington, we behold, as in the above sketch, the solid, laminated, chalk, gently declining to the south, excavated in a broad undulation across the lamins ; over nearly the whole breadth of the hollow thus occasioned, rests an irregular sandy deposit very much of tertiary aspect ; above tis, a thick mass of diluvial clay with bouldered stones in great confusion ; the whole sur- mounted, in places, by a widely laminated deposit, of chalk and flint gravel. Finally, the channel of the ex- i£ting little rill is cut, certainly by that rill, in places through the whole series of deposits, into the solid chalk beneath. What does this teach us? First, the ex- cavation of the chalk by an agent which wholly swept away the spoils; secondly, a less turbulent agency in- troducing sand and gravel, so as partially to fill up the hollow, but not to cover the parts of the chalk beyond ; thirdly, a violent impulse of mud and stones brought from a distance over this valley, and the surfaces for miles on each side of it ; fourthly, variable but exten- sive deposits of local gravel ; fifthly, the work of the- actual stream, which gathered in the ancient hollow.

As we know the chalk to have been raised from the sea, this upward movement may suggest to us the excavation of the rock by oceanic currents, and the partial deposition of sand ; the general accumulation of boulders and clay demands a general disturbance affecting other, and even remote, districts ; while the mass of chalk, flint, gravel, seems the natursd efiect of a more local and less violent convulsion. In some instances, local gravel of this de- scription lies both above and below the proper diluvium.

The interval of time here supposed to occur between the original excavation of a hollow or valley in the rocks, and the accumulation in it of the spoils of a

320 A Treatise On 6E0L0&7. Chap. Vi.

violent commotion of water is indeterminate. So in- deed, is that between the cessation of the diluvial floods (whatever they were) and the commencement of the actual stream. For if the great hollow was both ex- cavated and afterwards filled before the chalk rose com- pletely out of the sea water we have no easy means of knowing when the whole became dry land, and ad- mitted the descent of fresh water. If, however, the bones of quadrupeds which occur in the diluvium be thought sufficient to prove these accumulations to have happened on dry land, the actual stream may be looked upon as a feeble but immediate successor of the de- vastating floods.

Rock Terraces in Valleys. -rhere is a peculiar class of terraces in valleys, which indicate in the same manner the successive lowering of the level of descend- ing water (or the successive rising of the land) ; these terraces are formed by solid rock, with little or no trace of gravel, or other detritus. Such cases are fre- quent in the mining dales of the North of £ngland, which cut deep into the " Yoredale Rocks," or upper mountain limestone series.

In this varied series of limestone, sandstone, and shale, almost every limestone which overlies shale projects into a terrace ; and this sometimes happens to strong sand- stones similarly circumstanced. It is easy to see that, as this occurs in many of the branching lesser dales, as well as in the principal valley, it may plausibly be argued that the whole efiect is due to atmospheric action. It is probable, however, that this is not a sufficient cause ; since additional debris might thus be expected to be falling every day, or, at least, more of this accumulation should remain than we see. We must further observe, that the presumed levels of the water are only clebrly marked by continuous terraces when the strata dip nearly in the plane of the valley. It appears, that just as, at this day, a mountain stream crossing the Yoredale Rocks

Geo], of Yorkshire, vol

Chap, Ti.

Post-Tertiart Strata.

Ssi

fomiB waterfalls and clifis at every ledge of limestone, of the wearing away of the subjacent shales — so the great currents which anciently flowed in the valley (whatever they were) excavated the softer strata and left the hard prominent in terrace clifis as in diag.

No. 72.

fN. Millstone grit fummit retting on shatee and grits to /, which ii lime, tone, and project* orers, the euttjacent argillaceous beds. The same occurs with each lower ledge of limestone /, which, with the gritstone jf, usuaUy found beneath, forms a terrace cm the hillsides, above a slope of shale.

A different caae occurs in valleys which cross and enter deeply into thick masses of red sandstone, such as occurs at Nottingham, Kidderminster, Bridgnorth, &c. At Bridgnorth, for example, occurs a remarkable triple row of terraces on the east bank of the Severn, which appear decisive as to the successive operations by which changes of relative level of the land and the water which excavated the valley were brought about.

All the terraces represented in the diagram No. 73.

Vfper Terrace,

BfidtUe Ter*aee.

Lower Terrace.

Severn*

are formed on the face of the thick and easily excavated red sandstone ; but it is only on the left (east) bank of the Severn that they are conspicuous, because this is the VOL. I. ' r

$22 ,il. TREATISE ON GEOLOGY. CHAP. VI

salient angle, — for it is always observed among tlie common daily effects of inundations that such terrace- like levels are only marked on the projecting land, while the re-entering angle is excavated to vertical or steep faces*

Fluviatilb Deposits.

To discuss fully the origin and history of valleys is an object reserved for a later section ; we may now pro- ceed to consider the effects produced in valleys already formed, and partially filled with old detritus by the water running therein. This is a large subject ; for besides the mechanical and chemical actions of the rivers and brooks which vary according to the hardness and nature of the rocks there is to be examined the influence of atmospheric vicissitudes, heat and cold, moisture, dryness, frost, &c. ; and all the complicated effects thus occasioned are, in relation to the valleys, further modified by the form and slope of the surface, the occurrence of lakes, and other circumstances.. Streams flowing along a valley under the various con- ditions which we observe, are to be considered both as eroding and transporting agents ; and it is not only con- ceivable from the admitted instability of the level of land and sea, but perfectly demonstrated by observation, that these seemingly opposite effects have been exhibited at different times by the same river, at the same points of a valley. Moreover, in the course of the changes of level of land and sea, some rivers appear to have quitted their ancient valleys entirely, and to have taken up new courses corresponding to the new conditions ; and this, not merely in marshy countries where a river's course is almost accidental, but in hilly and rocky districts like the vicinity of Ludlow or the borders of Teesdale. It will, therefore, be proper to present as full an account of the phenomena relating to the actual configuration of valleys under different circumstances, as a due regard to reasonable limits will allow. The first thing to be con-

CHAP. VI. ' POST-TEBTIART elTftATA& 32 B

sidered is the degree in which the earth*s surface is wasted hy atmospheric changes and aqueous agency.

Waste of the Earth's Surface,

If we consider that the aggregation of rocks and minerals, whether we regard it as a fruit <of chemical or mechanical actions is no otherwise fixed or stable than as the forces which tend to keep them imited are su- perior to those which from all sides strive to separate them, we shall he prepared to comprehend how the vari- ations of these constringent and divellent forces accord- ing to heat moisture new elementary combinations &c. bring a silent hut sure and often rapid decay on all the structures of man, and on aU the mightier monuments of nature which are exposed to the ever-changing atmo- sphere. It is painful to mark the injuries ej9ect&d by a few centuries on the richly sculptured arches of the Normans the graceful mouldings of the early English architects, and the rich foliage of the decorated and later Gothic styles. The changing temperature end moisture of the air communicated to the slowly con- ducting stone especially on the western and southeni fronts of buildings, bursts the pai:|;s near the surface into powder, or, by introducing a new arrangement of the particles, separates the external from the internal parts, and causes the exfoliation or desquamation, as Maccul- loch calls it, of whole sheets of stone parallel to the ornamental work of the mason. From these attacks, no shelter can wholly protect; the parts of a building which are below a ledge, often decay the first; oiling and painting will only retard the destruction; and stones which resist all watery agency, and refuse to burst with changes of temperature, are secretly eaten away by the chemical forces of carbonic acid and other mospheric influences. What is thought to be moi durable than granite ? Yet this rock is rapidly con- sumed by the decomposition of its felspar, effected by tarbonic acid gas,— a process which is sometimes con-

Y 2

324s A. TREATI8B ON GEOLOGY. CHAP, TI.

Spicuous eyen in Britain (Arran Muncaster Fell, Cum- berland), but is rapidly performed in Auveie, where carbonic acid gas issues plentifully from the volcanic regions.

Effects of Rain.

Mere rain is a powerful agent of disintegration ; and its frequent attacks leave at lengthy in sandstones and limestones, otherwise very durable, channels of consider- able dimensions, which have sometimes been ascribed to other causes. The Devil's Arrows at Boroughbridge, in Yorkshire, are fluted from this cause from top to bottom (except on the underhanging sides, where they cease not far below the summit)--the work of two or three thousand years: and when we turn from these monuments of man to the native crags whence they were cut, Brinham rocks/' and regard the awful waste and ruin there, well marked by the pinnacles and rocking stones which remain in picturesque desola- tion, it is difficult to avoid indulging a long train of reflection on the processes of decay and renovation which thus seem to visit even the inanimate kingdoms of nature, subjecting all its material elements to continually renewed combinations.

On the broad limestone floors which support the noble mountains of Ingleborough Penyghent, and Wharnside, the rain channels are bo abundant as to have attracted the attention of artists and tour- ists; and on Hutton roof crags, as well as among the limestones of the Alps, they change their direction with the slope of the ground, collect into larger furrows like valleys on a broad surface, and terminate in the large deep fissures, as small valleys often end in a great hollow of drainage. Another remarkable phenomenon of the moorland districts of the North of England, which are formed on the Yoredale series of mountain limestone may perhaps admit of the same explanation. These are the Swallow " holes, as they are termed which

Chap. Vi. Post-Tertiary Strata. 325

range above the outcrop edge of the limestone beds and act as drainage channels from the surface to the jointed jcalcareous rocks below. These round or irregular pits and holes are smoothed on the faces and joints of stone as if by the action of acidulated water the origin of which from the air or the neighbouring vegetable substances, is not hypotheticaL

Effects of Frost

In no form is the moisture of the atmosphere in- efficient in accelerating the disintegration of rocks. Col- lected in the joints and cavities of mountains it loosens every thing by its expansion and relaxation ; heaped into enormous glaciers on the summits and down the valleys of the Alps it melts at its lower edges and on the lower surfaces, and thus is ever in motion down- wards; augmented from above and diminished from below, its moving masses plough up the solid earth, and, by a wonderful and momentarily insensible energy, pile up, on each side of the icy vaUey, vast quantities of blocks of stone and heaps of earth, which' slowly ad- vance into the lower ground ; and these sometimes bear trees and admit cultivation ; tUl, in the course of changes which these rude climates experience, the whole is transported away by the river which flows beneath, and space is left for new augmentations from above. Per. haps no circumstances are so favourable to the collection of materials for rivers to sweep away, as the glacier crown and icy valleys of the Alps, accompanied by the thundering avalanche and frequent landslips, like those of the Rossberg and the Righi. What further happens to these materials, belongs to the history of the river.

Effects of Springs.

Collected in the atmosphere, the rain is filtered through the sandy rocks, passes rapidly by the joints of the calcareous strata, and is stopped by the clays, and

Y 3

S2Q TRKATISIB ON QEOOY. CHAP. Vl

by dykes and faults ; it then issuing in springs. Bat it is no longer the same water : rain water is indeed, far from being in a state of purity ; it contains, always car* bonic acid, frequently some muriatic acid or chloride of sodium, besides other irrular admixtures. In passing through the rocks it absorbs lime, oxide of iron, &c and on issuing in the form of springs, loses its excess of, carbonic acid, and again deposits carbonate of lime, carbonate of iron, &c. From some springs the quantity of carbonate of lime deposited is enormous ; with the water of others, sand, gravel, fossil shells, and zoophy- tic fragments issue. Thus the first operation of water' in and upon the earth is the same, viz. to consume away the solid substance of the rocks, and either de- posit it in new situations not far from the source, or deliver it to flowing streams to be carried further away. Springs which have an impeded issue to the surface, are the most general cause of landslips : we may con- sider the great fall of the Roasberg as a case of dus kind, the water entering and moistening a particular layer of strata, aU inclined very highly, so as easily to acquire a descending force, if the cohesion of the parts were weakened by interposed moisture.

Eossberg.

G i.'dau.

Tlie spring, or rather river (Arve), which issues from the foot of the mer de glace, near Mont Blanc, brings a vast quantity of detritus, which the grinding motion of the glacier on its rocky bed had broken and rolled to pebbles.

Cuap. Vi. . Post- Tertiary Strata S27

Effects of Rivers,

A river thus fed by springs of water not pure, par- tially filled with earthy matter, flowing with various velocities through soil and among rocks of unequal re- sisting power, and formed of particles of different mag. nitude and specific gravity, must exhibit in its long course a great diversity of appearances. Some rocks and soils it may corrode chemically, others it may grind away by its own force and the aid of the sand and par- ticles which go with it: from steep slopes it must, in general, transport away all the loose materials; but when its course relents, these must drop and augment the land. The finest particles are first taken up and last laid down, the larger masses make the shortest transit.

Rivers, on whose course no lake interposes its trAuquillising waters, may be considered as constantly gathering, incessantly transporting, and continually de- positing earthy materials. It is, of course, princi- pally in times of flood, that they both gather the most materials, and transport them farthest; yet even in the driest season, the feeblest river does act on its bed, wears by little and little even the hardest stones, iand works its channel deeper or wider. This it does partly by the help of some chemical power, from car- bonic acid, and other admixtures, but principally by the grinding agency of the sand, pebbles, &c. which it moves along. In times of flood, these act with violence like so many hammers on the rocks, ploughing long channels on their surface, or whirling round and round in deep pits, especially beneath a fall, or where the current breaks into eddies over an uneven floor of stone. This is admirably seen at Stenkrith Bridge in West- moreland, under the waterfalls about Blair Athol, and in North Wales, and, indeed, very commonly. Not un- Irequently, on mountain sides or tops, far from any stream or channel, phenomena somewhat similar oc- cur, sometimes the efl*ect of rain, sometimes, we may

Y 4

328 A Treati8B On Ob0L0O7. Ouap. Yi.

suppoeey the remaining eyidence of the fonner passi of running water, when the levels of the country were differently adjusted.

As the slopes are greatest in the upper parts of valleys (generidly) and gradually flatten towards the 8ea> it is commonly observed that from all the upper parts of these valleys rivers abstract large quantities of the finer matter and in times of inundation not a little of the coarser fragments of rocks ; much of this is deposited in the lower ground where the current is more tranquil and generally (unless the river be very deep) slower. We must indeed suppose that every where some wearing effect on its bed and sides is produced by every river even to its mouth ; but this effect grows almost insensi- ble far from the high ground which gives birth to the streams ; and long ere we approach the estuary the wide flat meadows which fill the whole breadth of the valley for miles in lengthy show what a mass of materials has been drifted away from the higher ground. Finally where the tides and freshes meet, the sediment of boUi is disposed to drop ; and some rivers may be viewed as sending little or no sediment to the sea.

Thus the whole effect of drainage including all the preliminary influences of the atmosphere rain springs &c. is to waste the high ground, and to raise the low; to smooth the original ruggedness of the valley in which it flows, by removing prominences and filling up hollows ; and notwithstanding the length of years that rivers have flowed, they have, in general, not yet completed this work : they still continue to add materials to the lower ground, and, in a few instances, to carry out sediment into the sea.

The whole surface of the earth, then is changing its level, by the mere precipitations of the atmosphere and their subsequent effects ; the high land sinks and the low land rises ; but what is the rate of this pro gress, we have no complete means of knowing. Few ancient measures of the height of the land which has Leen wasted or the area of that which has been accuma-

tfHAP. VI. POST-TBRTIABT STRATA. 329

lated are worthy of notice; we are however sure from various causes, that many vaJleys have not been altogether worked out by the rivers now running in them; and some natural chronometers have been pointed out hy De Luc and others, which rudely limit the length of time during which rivers have flowed, and might be more useftilly employed to determine the rate and amount of fluviatile action.

Rivers certainly did not excavate the whole valley in which they flow, for they have not even removed the diluvial detritus brought into them from other drain- ages, and heaped on the previously excavated rocks.

Rivers have certainly not excavated more than an inconsiderable part of their valleys, for otherwise the Lakes of Geneva and Constance would have been long since filled by the sediments of the Rhone and the Rhine, which issue fr(n these lakes of at lovely hue and transparency which marks their total freedom from all tinge of earthy impurity. When, indeed, we look at the small but growing deltas of the heads of the English lakes, as Derwentwater, Windermere, or Ulswater, and consider the Derwent or the Rothay in its time of furious flood, we shall be disposed to set a high value on De Luc's opinion, sanctioned by Cuvier, Sedgwick, and others, that these deltas prove the com- paratively recent date of the present disposition of drainage on the surface of the earth. Rivers flow in certain channels, because these were previously formed by eonvidsions, and violent movements of water; they have exerted all their force in merely smoothing and filling the inequalities of their valleys, and this partial labour they have not accomplished. Will any one, after this, require to be told that rivers did not make their own valleys ; and only yield to this truth when, on the chalk and limestone hills, hundreds of valleys are shown him, down which water never runs, and which, indeed, ha;Ve no trace of a channel?

The upfiUings of a valley by the operations of a river ever tend to be formed in horizontal lamine;

3S0 4 Tkeati8B On Geology. Chap. Vi.

or at least their surface is generally level in the direc- tion across the valley, whatever undulations exist be- neath, and however rapid may be the longitudinal de- clivity of the valley. This is well seen in many valleys of the Swiss Jura, the Cotswold Hills, &c.

A. Irregular surface which is the original basis of the valley, b. The sedi. ment left in it, with a plane surface as if deposited in a lake. c. The surface of the vailey, uniformly declining among h, the bordering moun. tains.

When the materials are gravel and coarse sand, de- posited by an impetuous stream, the general surface may be level, and yet the laminae beneath are frequently much inclined, with slopes in various directions, as Mr. Lyell has noticed with regard to the detritus left by the stormy waters of the Arve. The same thing occurs in many of the stratified rocks which appear to have been accumulated under violent agitation near the sea-shore. (See Piag. No. 20. p. 6l.)

LaJces on the Course of Rivers,

Plane surfaces existing along the course of valleys, are commonly, without further question, supposed to be indicative of the site of ancient lakes, which have been slowly but completely filled : the supposition is often cdrrect, but it is sometimes erroneous. Rapid rivers, which, in times of inundation, drift coarse ma- terials down their rough beds, and deposit them in the expansions of their valleys, are thus partly choked in their courses, and turned, into new channels. Thus they wander irregularly over a large area, every where

CfiAP. VI. POST-TERTIARY STRATA. SSI

filling it to about the same height with a mass of partial deposits related to the successive positions of the chamiel which when unconfined by man seeks always the lowest passage. On a cross section of such a valley these many distinct streams bf gravel and sands appear nearly as in the annexed diagram.

But such a distribution of materials appears not to occur in lakes ; whether they receive sediments from gentle streams rapid rivers or sudden inundations. The reason of this is the great lateral difiusion of motion in water. Where any great depth of quiet water is interposed on the path of a river/ the lacus- trine sediments assume various modes of arrangement depending on their own fineness, and the velocity of the water by which they are hurried along.

Deep Lakes on the Course of a River. — On en- tering a deep lake the mingled sediment of a river is subjected to a new influence, -— the descending force of gravity, in addition to the direct horizontal force imparted by the current, and the lateral move- ments which it occasions. Each particle, in conse- quence, tends to faU from the surface of the water, as it moves forward, or to the right and left of the point of entry of the river, and with an accelerated velocity in the lower part. The path of each particle will be more or less influenced by the direct, lateral, or vertical forces, according to its magnitude and weight. Thus, in the diagram No. which is to ipepresent a vertical section along the path of the river as it enters the lake at the point o, P p p, particles of unequal liiagni-

S32

A Treatise On Oeolooy.

Chap. Ti.

tude entering together describe curves of unequal cur. vature (they are all related to the same vertical axis, G); the smallest particles being transported furthest, because they have, proportionally, the largest surface, and therefore subside most slowly in the water.

On the horizontal plan (No. 78.) the courses of such deposits are shown to be concentrical, or nearly so, to the point of influx of the river. By such deposits, the Delta of the Rhone in the Lake of Geneva as well as that of the Derwent in the Lake of Keswick has been formed; and, in fact, in every lake a similar explaoatioii

is found applicable. Returning to the vertical section (No. 77O9 ™y remark, that the parabolic lines there given, if considered as representing successive deposi- tions, require to be modified above and below : above, by the shifting of (0) the point of influx forward ; be- low, by the circumstance, that the curve ceases at a cer-

Ohap. Vt. Post-Tertiaby Stbata, Ss$

tain depth (n), when it coincides with the line n /, drawn to represent the greatest slope on which the par. ticles will rest. This slope varies somewhat in particles of different size and form. Generally speakings the struc- ture of these deltas corresponds to the subjoined diagram ; where the surface o' is level ; the lines a n, a! n' are curved, and lie in surfaces of contemporaneous depo-

sitions ; and the lines nhy nV are straight lines corre- sponding to the angle of rest in deep water.

We may further ohserve that the unequal dispersion of the sediments in water causes another modification of the lamination of such delta. Fine clay is spread far in the water and settles at length in a general thin deposit over the curved and sloping faces anhy and on the hed of the lake hh'*, after the agitation of the water produced by the inundation has ceased and the coarser sediment has settled to its place.

If further we imagine the waters of such a lake to be calcareous, and liable to slow decomposition, so that layers of carbonate of lime (or shelly marls) are formed, these will be still di£ferently arranged. If the cal- careous matter be generally cUfiused the layers will not radiate from or collect round a pointy but be very ge- nerally spread over the bed of the lake; and even when the calcareous substance enters in solution with a particular stream (as often happens), it mixes with the water of the lake so extensively as to yield wider and more regular deposits than those produced by merely mechanical agency.

Shallow lakes, subject to fluctuation, produce on the deposits of coarse gravel and sand, which are brought into them bv rivers, an effect intermediate between tat of deep water and mere fluviatile currents. The

334 A Treatise On Geology. Cuap. Vi.

Conoidal lamination due to the former is compli- cated with variation of the point of influx arising from the latter ; and thus the upper ends of such lakes become irregular in outline and are filled by insulated sub- aqueous banks.

End Of The First Volume.

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