A Rudimentary Treatise on Geology: For the Use of Beginners

Joseph Ellison Portlock · 1853 · Historical

An edition of more than 7000 copies having heen sold of this little vohime» I have endeavoured to introduce such improvements into this, the second edition

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Rudimentary Treatise

Oh

Geology:

FOR THE USE OF BEGTNNERSf

By

Lieut.-Colonel Portlock, R.E.,

F.R.S., F.O.S., M.R.I. A., &c.

PmiSIDSRT OF THS OS0L0GICA.L 80CIXTT OW DUBLIN,

Cvtikkian' 80Ciktt Of ^|(C<* \*"»» * * >'

V •»

Third Edition.

Eantran :

Weale.

Architectural Library, 59, High Holborn.

M.Uccc.Liii.

BUGHB8, PmiNTKB, KIIVG*'S RSAB eOXJUr, GOCGR SaTJAKS.

fKEFAUK TO SECOND EDITIUJN

An edition of more than 7000 copies having heen sold of this little vohime» I have endeavoured to introduce such improvements into this, the second edition, as are compatible with its form and object. In doing so, I have availed myself of some valuable suggestions of my friend Mr. Smith, of

I Jordan Hill, regretting at the same time that a limited space

would not allow me to give a perfect analysis of his re-

. searches in Pleistocene and Post -Tertiary Deposits. If the

labours of Travellers and Voyagers produce every year some

^ new additions to our knowledge of the existing creation, can

w

i it be doubted that the Geologist, who is, as it were, a •' traveller in ancient worlds, must equally discover new and ' interesting fects? Geology is indeed a progressive science, which, although it has already produced much fruit, still continues to promise an abundant and never-failing harvest to those who diligently and skilftilly cultivate it, — a truth which has been powerfully illustrated within the last few years, during which it has been shown that the highest type of organic beings, the mammalia, appeared on the earth so early as the Trias, — and still more recently whilst the last

Tl PRKFACE TO THE SECOND EDITION.

sheets of this work were passing through the press, by the fact announced by Sir C. Lyell, that the foot-marks of a fresh-water tortoise had been discovered some years before in the Silurian strata of Canada, and by fresh examples of dicotyledonous plants in the Cretaceous strata, — thus unfolding most remarkable resemblances between the physical conditions of the earth at the most remote epochs and those it now exhibits. What an incentive then is held forth to the labourer in such a field, when to him may be allotted the triumph of penetrating still further into the mysteries of Nature, and discovering new relics of the animals and plants of extinct creations !

J. E. P.

Woolwich, January, 1852.

Contents.

Chapter I.

fe«9TRODUcnoN. — Experience or Practice and Theory mutt be combined for the successful progress of all Science, and for the perfect development of Art p, 1 — 15

CHAPTER II. o}boloot — Its Meaningi Objecti and Utility as a Science . . 15 — 37

Chapter Iii.

fSiOLOGiCAL Formations — ^Their Meaning, Object, and Utility — The Mode of Studying them, and the Physical Phenomena they exhibit — Phenomena of Rocks — Stratification — Flexures and Contortions of Strata — Cleavage (Joint-like and Slaty) — Denudation and Wear— - Faults — Further Effects of formative and destroying Causes as exhibited in modem and ancient Sea Cliffs, Sea Beaches, Glaciers, and Icebergs 38^62

Chapter Iv.

l^lutonic, Metamorphic, and Volcanic Rocks — Condition and Temperature of the Interior of the Earth — Dykes — Elevating Forces — Veins — Metallic Deposits — Economic Value and Uses of the Rocks described

Vlii CONTENTS.

Chapter V.

Fossils — ^Petrifactions — Conditions of Petrified Bodies, and Modes of Petrifaction — Petrifying Substances—- Distributionof Fossils,/i. 101 — 125

Chapter Vi.

General and Practical Remarks on Geological Formations — Cambrian, the earliest known Fossil Deposit — Silurian — Devonian, or Old Red Sandstone — Carboniferous — Permian, including Magnesian Limestone — New Red Sandstone, or Trias — Lias Order — Oolite or Jura Formation — Wealden Formation— Cretaceous — Tertiary Class of Formations — Eocene, Miocene, and Pliocene Formations — Quaternary, Post -Tertiary or Post-Pliocene— Recent — Chemical Deposits — Organic Formations

CHAPTER VII. Theory of Springs 181—190

CHAPTER Vin. Concluding Remarks » • • • . 191 — 196

Rudimentary Geology.

Chapter I.

Introduction. — Experience or Practice and Theory must be combined for the successful progress of all Science, «md for the perfect -development of Art.

As it is hoped that this httle book may be read by many members of that valuable class of persons who are called practical men> it appears desirable to use it as an instrument for dispelling from their minds the prejudice they too often entertain against other men called scientific, and at the same time for supporting their own claim to the high estimation of men of science, which, as their most powerful auxiliaries, they so fully merit. The mutual distrust between scientific and practical men, though decreasing, does still exist, and is to be ascribed, as in most human differences, to the misapprehension or misinterpretation of a term, which i&tm is in this case * Science.' What then does the term Science actually signify ? — simply knowledge : which may be viewed in two different lights, and be understood as implying either

A Knowledge of Facts, the result of observation ; or A Knowledge of Laws, obtained by reasoning on combined facts. If these divisions be kept in view, it will be admitted that every human being must make more or less progress in the first branch of knowledge, as it is impossible to live and not to acquire some experience of facts ; but that few, in comparison,

A

2 Jiudimsnta&Y Geology.

enter upon the second, which requires, in addition to observation, a power and a habit of reflection. And yet, however exalted this exercise of the higher quality of reasoning must intellectually be considered, it cannot dispense with that of observation, as every attempt at mere speculative reasoning has only led to mysticism, and retarded the progress of that real knowledge which proceeds either directly or indirectly from observed facts.

When the comparison of observed facts has led to the discovery of a law or rule according to which those facts are in connection one vdth the other, the mind acquires a power *of extending or developing the law itself beyond the limits of the observed facts; and thus is enabled to advance into new regions of inquiry, and to foretell facts which have yet to be ;l observed. And in like manner, the law or rule which has - been ascertained to connect together one set of facts, may be ; found to agree with or even depend upon a law which connects together another set, the more compound law being thus traced up to the simple ; and laws which from the different nature of the observed facts may have been deemed independent of each other, are brought into connection by being referred to some more simple law of which they are all proved t to be developments. i

Professor Lloyd (' Lectures on the "Wave Theory of Light') 'J has illustrated this subject. " You are aware," he says, " that in one mode of studying that interesting science. Astronomy, the laws of Kepler are assumed as fundamental principles, and from them, when unfolded, all the more obvious appearances of the planetary system are deduced. In Physical Astronomy, on the other hand, the laws of. Kepler J themselves are derived as consequences of a primordial law of ' ' matter and the development of this higher principle has * brought to light a multitude of other laws of the imiverse, which mere observation could have never reached." The name of Kepler suggests how instructive his example ought to be when as a practical man he is observed, submitting his pre- ,:

H^Bes to the test of esperiinent, and, b)' diligently following

^BlE moTementa of the planet Mars, and patiently comparing together its successive places, acquiring e^idenoe that the orbit or curve in which it moved rounfl the sun was not a drcle b-Jt an eUipse, the sun being in one of its fori. This law of elliptic motion, and Kepler's tvro other laws, hiwing been generalized and connected as neceMary consequent with the elementary laws of matter, the range of ohserratioo was expanded over the whole material universe ; and when, from the independent study of the morion of each planetary body, the Astronomer turned to the still more ditfieult investigation of the mutual action of one upon the other, and finally overcame and reduced to order all its difhcidtiee, the Theoretic Astronomer wbs enabled, in the persons of Messrs. Adams and Le Verrier, to advance before tlie observer, and to direct him where to look for a remote and until then undiscovered planet, ' Neptune,' the existence of wbidi they had inferred, by calculation, from its perturbating effects on other planets. To this noble result of patient practical observation, combined with and matured by study and reflection, M. Le Verrier has added another illustration of the aid derived by the practical observer from the labours of the theorist, by determining the dements of Faye's comet within definite limits, and thereby leading to its rediscovery by Professor Challis at Cambridgei on the 2ath of November, 1850. This body, which had been seen before in 1643*^, is, from the passage of its orbit through that of the planet, subject to great perturbation firoTO the planet Jupiter ; and whilst M. Verrier, by calculating the amount of such perturbation, wts enabled to trace the course of the comet through a disturbed orbit, he did not fell to perceive and to point out that the variation of the orbit itself will finally lead to a better appreciation of the disturbing force, or to a more correct determination of the mass of Jupiter : and similar illustrations might be multiplied from

1 this one Science of the aid afforded to each other by the

I Observer and the Theorist,

1

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,i

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Light, for example, is familiar to every one as a fact, however conflicting may be the modes of explaining the laws by which it acts. To our senses, as seen in the flash of a gun, it appears instantaneous, and jet it is progressive. This fact of the progressive movement of light was discovered practically by Roemer, when observing the eclipses of Jupiter's satellites, as he found that the mean time of the emersion of a satellite from the shadow of Jupiter's body was greater or less according as the distance of the earth was greater or less than its mean distance from Jupiter, such difference being due to the different times occupied by light in passing through the respective distances.

By a number of comparisons of the times of the emersions of Jupiter's satellites in the varying positions of the earth, it ^ was ascertained that the reflected Hght occupied about 16' 26" in traversing the earth's orbit, and it may be stated in round numbers that the velocity of light is about equal to 200,000 miles per second, or more precisely 166,072 geographical miles, a velocity almost a million times greater than that of sound. Such a velocity seems beyond human comprehension ; and yet the Astronomer, by pursuing the practical course of observation, has succeeded in measuring distances so vast that they permit the velocity of light to be used as an element in their expression. It is thus that the light of some of the fixed stars, whose distances have been determined, must have taken 3, 9J, and 1 2 years to travel to the earth ; or supposing the whole universe to have been contemporaneously created, 3, 9^, and 12 years must have elapsed before those stars respectively could have been perceived on the earth ; and were they now to be annihilated, the same periods must elapse before they will cease ip be visible. There may indeed be heavenly bodies the light of which has not yet arrived at our terrestrial surface, and others may have been annihilated, although they yet appear to shine upon us ; and we may therefore well say with Humboldt, that •* whilst we penetrate with our large telescopes at once into space and time, and measure the one by the other, we may

nScSre the rays of light which come to us as if th(?y were roicea telling of the past ; and however much we may diminish hoth the supposed distance whence the faint light of file nebulse or the barely diaceniihle glimmer of the remotest cluster of stars reaches us, — and the thousands of years which serve as the measure in time of that distance, — it wilt still remain. I true that, according to the knowledge which we possess of : the velocity of light, it is more than probable that the light of I the most distant cosmical bodies offers us the oldest sensible evidence of the exii^tiT.i^o of matter.'' And !■' tint this a most important testimony for the Geologist ; for i\ hen he too is obliged to speak of vast periods of time, may he not appeal to the Astronomer for proof, that the first act of creative power was exercised at an epoch so remote, that eren the mighty Tclodty of light, and the vast distances of the celestial bodies, are inadequate as meosures to express it ?

The other phenomena of light, as its refraction, its double refraction, and its polarization, — those remarkable effects produced on light in its passage through crystalline bodies and by which their internal constitution may be examined, — might be also adduced as results of a happy union of the practical and theoretical, or, in other words, the observing and reasoning systems. It is indeed by a knowledge first acquired by induction from facts observed, and to the me- ^anicai skill applied in aid of it, that the refracting telescope, and, by a similar knowledge of the laws of reflection of light, the reflecting telescope, have been so perfected as to open to our view an infinity of worlds and to track the very steps of their creation ; whilst the achromatic microscope has been made to reveal to our gaze an infinity of minuteness equally wonderfid, and to teach us the wonderful truth, that some of the solid rocks of our world are but an accumulation of countless myriads of minute organic bodies. Such intellectual triumphs as these demand on our part a tribute of admiration, not merely to the exalted genius which seizes on the laws which connect together great physicfll phenomena, but to the

practical man who, as a patient, careful, and acute o1 diligeutly watches for facts, or subsequently submits the tht established oa them to the test of experiment.

Let us compare the ancient Mariner, cautiously pursu his course along the shore and watching the declining si with (he shtl&l Voyager of the present time, who boldly qi the kud, aiid securely steers over the expanse of ooe the heavens affording him also a guiding light for hia venturous progress ; and how great a difference will app between the mere perception by the one of a regulari^ in movements of the celestial bodies, and that accurate knowlei of the distances and motions of the various hesTenly which has enabled the Astronomer to supply the Sailor with tables and formulae by which he determined celestial observations his exact position and upon ocean as upon land. And on the land itself, where dense forest clothes the surface and forbids the on opernli'ius of tlie Survejor, recourse can be had to celes observations, as was recently done in the determiuatioa e( North-Eastem Americac boundary by the Surveyors, of the Corps of Royal Engineers, who having (irst det the latitudes and knigitades of the ends of a line of 60 deduced the azimuth or bearing of each end from the' oil and then proceeded to cut down the trees according to bearings, beginning simultaneously at each end, and so suing the respective lines through the forest until they nearly met, the two parties emerging not indeed opposite to, but in close proximity to, each other.

Astronomy, therefore, both in its marine and its applications, affords the most powerful proofs of the adi tage of never separating practice from theory; ofconsidei the observer or the practical Astronomer as the fell labourer of the Theorist, and at the same time of acknowledging the benefits derived from the profound gations of the latter. M. Blot has stated his opinion Ljihe only safe method of arriving at knowledge is by it

rudiuentary geology.

tion. " Wlien observations have accumulated, they are compared together, and tlieir errors discovered and eliminated. A correct knowledge is thus acquired of the state of the heavens, as to what is constant and what is variable, irhether it he in a day, in a year, or in some still greater iaterral of time. The task of ohserving, or Practical Astronomy, ceases, and that of Theoretic Astronomy commences. Similar phenomena are compared together, in order to discover the laws by which they are linked together ; and then again the inquiry is extended until the movements of the heavenly bodies have been shown to be in harmony with those mechamcal forces and those laws of attraction which are found to operate upon all material bodies."

Chemistry is replete with illustrations of the principle which these remarks inculcate : it is an experimental science in the highest degree, and at every step of its progress appeals for information to the cmcible and balance. And yet, though b practical science, it is rich in deductions of the highest philoaophical interest which spring from the exercise of powerful reasoning upon carefully observed farts, Thonsands had observed the phenomena of bodies falling to the ground before they suggested to the mind of a pliilosopher the laws of nniveraal gravitation ; and many a patient Chemist had weighed the resulting constituents of his careful analyses, ere the mind of Higgins obtained a glimpse, and that of Balton a dear perception, of the remarkable law of definite proportions, by the discovery of which Chemistry was at once raised to the rank of an exact science. Tliis law has now become so familiar that its beauty and grandeur are leas considered than its convenience ; although it may be doubted whether in the nholc range of science any greater discovery was ever made than that which established the fact, that the combinations of material substances are neither arbitrary in kind nor iiuantity, bnt determined and limited by definite and invariable laws. The atomic theory of Dolton is a philosophic or theoretic expression of this fact ; hut whatever may be the fate of ths

I I

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8 Rudimentary Geology.

theoTj, the fact itself will remain incontrovertible : nor should its importance be lost sight of by the Naturalist, as he may deduce firom the limitation of the powers of combining affinity an analogical reason for beUeving that organic species have been in like manner limited, and not left to the chances of progressive development. The progress made in Chemistry after the establishment of this leading law has been wonderful, and it may be sud that the whole fabric of Organic Chemistry has been built upon it ; whilst by the light it has thrown on the constitution of minerals, and on their variation within certain limits by a substitution of similarly constituted elements, one for the other, it has placed Mineralogy on a sound basis. Nor have the economic lessons of Chemistry been less important : in Agriculture, by showing the true constitution of various plants, they have established the value of inorganic as well as organic man)ires> and proved that the soil ceases to be productive from the exhaustion either of the mineral or the organic elements necessary for the growth of the plant; — they have shown also that the carbon of plants is principally obtained by the direct action of the leaves of the plant on the atmosphere ; — ^they have discovered in vegetables many of the principles which were supposed to belong exclusively to animals^ and pointed out a most singular analogy between the functions of both : " in plants," says Dumas, *' the fruit, or .rather the grain, is rich in fatty matter which is destined to produce heat by its combustion during germination ; in animals the fat is also kept in reserve to be used for combustion in respiration, should the supply of nourishment fall short. There is reason to believe that the fatty matters originate in the leaves, and are thence carried to the embryo to be deposited either around it, or in the seed generally. These fatty matters pass into herbivorous animals, and from them into the camivora, so that the supporter of combustion in the vegetable seed and in herbivorous and carnivorous animals has been elaborated in the green leaves of {dants :" facts which may well excite the admiration of the

Rudimentary Geology.

scientific and command the respect of tlie pmctictil mitn ; and it is by such lessons that the practical man is enabled to understand why he obtains successive crops of some plants from the same ground, as the Botanist finds a plant Tery spot where it has flourished for ages, although his com. crops, by taking away from the ground the neci o^nic elements, quickly render it unfitted for their continued growth. Chemistry goes hand-in-hand with Geology important practical application, and the Farmer is beginning to cast off his ancient prejudice, and to hail, as most nsefnl auiiliftries, sciences which not merely indicate to him the valuable qualities of the various mineral substances which enter into the vegetable structure, but even direct him where they are to be found.

The practical man is however aware that in any occupation of life no theory can supply the place of practical skill ; and the consciousness of the necessity of such skill too often induces him to overlook the fact, that skill was originally set in motion by science, and that what is sometimes called a lost art, ought in reality to he styled a lost science. It is thus that many processes of a very ordinary character, such as those so long adopted in the manufactnre of white lead, a pigment known to the Ancients, involve principles of high scientific interest, which must have been perceived, however obscurely, by their first originators.

The beauty and excellence of church glass during the medtseal ages were probably the consequence of scientific knowledge in some of those early students of Nature, the Monks j and if the art is now reviving, and promises ere long to rival its former condition, the improvement should he ascribed to science applied in aid nf practical skill. Such examples might be multiplied from the processes of bleaching, dyeing, distilling, and of Metallurgy ; and even more strikingly from the RpplicBtion of electric and electro-magnetic science to the gftlvano-plastic processes and to the telegraph ; all tending to demonstrate (hat ivhilst the only sure basis on which any

1

10 Rudimsnta&T Geology.

science can be founded is the observation of facts, or, in other words, practical inquiry, so also the sure basis of every art is science. When, however, an art has been founded on a sound knowledge of principles or laws, practical skill may, by the tact it acquires, greatly improve and advance it, and an art may be even perpetuated in the hands of those who have forgotten, or perhaps have never known the science on which it depends ; and it is thus that, in some refined art which has come down to us from a remote epoch, we may often read a record of scientific labours which have left no other trace behind them. The characteristic of the present age is the continued effort to trace ev^ practical result up to a scientific principle, and to seek in that knowledge of principles a power to modify or extend results. The truly wonderful development of all branches of our manufactures ; the extending application of machinery in aid of human labour of every description ; the state of our communications by sea and land under the impulse of steam power; the application of magnetical and electrical science to so many practical objects ; each, and all of these, testify to this one great axiom, that permanent improvement can be founded on knowledge only. Before the Hght of science secrets disappear or become principles. It is thus that the French Chemists, MM. £belmen and Salvetat, have devoted themselves to an inquiry into the composition of the materials used by the Chinese in the fabrication and decoration of porcelain, and having completed their chemical analysis, have already commenced experiments at Sevres, in order to reproduce in that manufacture the colours of the Chinese artists. But there is perhaps no more striking example of the power of science to dispel mystery than is to be found in the researches of M. Boutigny D'Evreux. That ingenious philosopher has ascertained that the old miracles of the ancient priests of Zoroaster, and the equally wonderful examples of the successful issue of the ordeal by fire in the mediaeval ages, are explicable on sound physical principles, and has tested the accuracy of his reasoning by plunging

RtJDIMENTARy GEOLOGY.

witliotit injury his hand into baths of inolten metals. This remBTkaltle phenomenon he explains hy assuming a ncn force, namely, the repulsive power of caloric at sensible distances acting on liquids in what he calls the spheroidal state; but to the explanation strong objections have been urged, and M. Person considers it unnecessary to seek any new cause, and ascribes the result to the tension of a film of vapour which is suddenly formed between the heating body and the liquid and keeps them separate. If, for example, the hand be either naturally or artificially moist, there will be produced on its approach to the melted metal a film of vapour which will, by its tension, repel the metal from the hand, and for a time preserve it from injury ; or if the hand be dipped into ether, and then iuto boihng water, there will be a coating of vapour of ether formed on the hand, which will repel the boiling water and preserve the hand from scaldiug. In all these cases only part of the protecting fluid is reduced to vapour, and there is between the vapour and the hand a coating of the fluid, which being a bad conductor of heat, further insures safety; the only precaution necessary being that of selecting for the protecting fluid one in which the vaporizing temperature is considerably below that of the melted metal or of the boiling water.

In no science has the value of inductive reasoning been more strikingly illustrated than in Geology, which is the more immediate object of this volume ; nor has any more strongly proved the importance of the sound knowledge thus acquired in advancing the practical interests of mankind. Glimps of the fonnative and modifying functions exercised by both fire and water were assuredly obtained by the Ancients it was impossible that thinking men could contemplate the action of rivers and of the sea in wearing, transporting, and deporting the mineral matter of the earth's surface, or that they could watch the glowing flood of melted lava, poured from the volcanic crater, without recognizing the power of those great agencies. To them, however, the labour of eollectmg facts was distasteful, and the passion of specula-

I

tire tlieorizing was so strong, that whilst they played with the dreamy hypotheses of possihilities, by turns advanciDg to or receding from the truth and sometimes even anticipating discovery by conjecture, they never succeeded in establishing a correct theory of the formation of the earth. So long indeed did this spirit of speculation continue to maintain its influence, that the Baconian system of inductive reasoning only slowly made its way in Greology ; and the positive evidence of the senses was rejected in the case of fossil organic bodies, or the remains of ancient and no longer existing animals found imbedded in the stony masses of the earth's strata, and it was attempted to explain their existence by a hypothetic plastic power in Nature which had been exercised in forming so many Itutu naturae. It would be useless to enumerate all the great men who have aided in dispelling the obscurity consequent on mere scholastic discussion by appealing to an observation of facts. In doing so they pursued two leading courses : the one, an examination of the mineral matter of the earth's surface, with a view to determine the actual manner in whidi it had been arranged ; the other, an investigation of the nature and history of those vestiges of animals and vegetables, which, being found in the interior of mineral masses, prove that a portion, at least, of the crust of the globe has been formed subsequently to the existence of organic beings. Lehmann, in 1756, made the first satisfactory step towards a correct knowledge in the mineral inquiry, by his description of the stratified deposits (Flaetzgebirge) of the centre of Germany. Subsequent Geologists pursued the same course of careful • observation, amongst whom may be specially noted the illustrious Saussure; and at the close of the last century, Werner gave new impetus to the science by generalizing the results of his own observations, and arranging them into a system. It was to be expected that the peculiar district or field of inquiry would influence materially the deductions of the first observers ; and that whilst Werner built up an aqueous theory, in which he supposed all mineral

Rvdimentary Geology* 13

matter to be deposited from a solvent fluid. Hall, having derived his knowledge of the action of highlv heated masses from the examination of a totally different country, established an igneous theory; and that modem Geologists, proceeding on the principles so ably set forth by Sir Charles Lyell, who may be considered the founder of our present system of geological reasoning, would hesitate to reject any cause which can be now observed in the operations of Nature, and would carefully combine together in one great system all those forces which, whether aqueous, aerial, or igneous, now act on the earth's surface, and judging from the similarity of effects so palpable in the ancient strata, have also acted at all former periods within the reach of our observation. In the second branch of inquiry the progress was even slower; for though, in 1517> Frascatoro had remarked that all the organic fossils then discovered could uot have been buried at the same epoch, and Stenon, in 1669, had hinted that they might be used to distinguish the relative ages of the masses containing them, the prejudice to be overcome was so strong, that Palaeontology can scarcely be said to have become a recognized branch of geological science until William Smith announced, in 1790, the design of publishing a geological map of Great Britain, which he effected in 1815, and thus promulgated the fact, that £ngland is constituted of strata the superposition of which is constant and never inverted, and that the same fossils being found in all parts of the same bed, it may be characterized by those fossils. The genius of Cuvier shed a new and brilliant light over Palaeontology by establishing the laws of anatomical composition, and building up in conformity with them the remains of the higher animals, so as to exhibit to the Naturalist many remarkable forms which, though they have ceased to exist, are connecting links in the great chain of the animal kingdom. Many are the great men who have continued to work out, with unceasing labour, this great subject ; and it is no small gratification to know that Greenough, Buckland, Sir H. De la Bechc, Lyell,

Sedgewkky Conybeare, Fitton, Phillips, Mnrchison, are still living amongst us, and bj their inquiries and their reasonings, adding new lustre to a science which has, as it were, grown up under their care and guidance. Geology, therefore, is now a true science, being founded on facts and reduced to the dominion of definite laws, and in consequence has become a sure guide to the practical man : the Miner finds in it a torch to guide him, in his subterranean passage, to the stratum where he may expect to find coal or iron, or to the recovery of the mineral vein which he has suddenly lost ; — the Engineer is guided by it in tracing out his roads or canals, as it tells him at once the firmest stratum for supporting the one, and the easiest to cut through for the other, and makes him acquainted vrith the qualities of the materials he should use in his constructions, and the localities where he should seek them; — the Geographer finds his inquiries facilitated by learning from Geology the influence of the mineral masses on the form and magnitude of the mountains and valleys, and on the course of rivers ; — the Agriculturist is taught the influence of the mineral strata on vegetable and animal life, and the Statesman discovers in the eflects of that influence a force which stimulates or retards population ; — the Soldier also may find in Geology a most valuable guide in tracing hiis lines both of attack and defence ; — and it is thus that a science rich in the highest objects of philosophical research is at the same time capable of the widest and most practical application. *

Can it be 'doubted, then, thdt there ought to be an intimate union between practical and theoretic men, — between the observer and the philosopher? — and is it not also evident that the position of the practical man is often most faTourable for the collection of facts whidi he overlooks only because his mind has not been trained to observe ? When the most simple practical man has observed a fact, to that extent, he has acquired knowledge and become scientific ; and though he overlooks many other facts, he has often stored up more knowledge than is supposed by the theorist. To extend his powers of

Rudimsmtart Gs0L06Y. 15

observatioa is the object of this ▼olame» and it is bdievfd that every implied science will acquire additional extaision and stability by availing itself of the qdet labours and sound sense of practical men.

Chapter Ii.

Gkologt — Its Meaning, Object, and Utility as a Science.

Geology, a treatise or discourse on the Earth, is a term which admits of a very wide interpretation, and naturally suggests to the mind inquiries — 1st, into the formation and original condition of the earth; 2ndly, into the successive modifications which it has undergone, and the agencies by which they have been effected ; and 3rdly, into its present condition, and the agencies which are still producing changes in that condition. The first object, then, of the Creologist is to establish, on the principles of inductive reasoning set forth in the introductory chapter, the science as it depends on each of these inquiries, and then to apply it to the practical purposes of life : and it may be premised that a science is practically valuable just in proportion as its facts have been discovered, and its laws established and studied, for so long as we are uncertain whether a known result has proceeded from a definite cause, we are unable to apply the fact or circumstance to the elucidation of other facts or circumstances, and so long as we are unacquainted with the properties of any substance under our examination, we cannot declare with certainty what share it may have had in the phenomena we have observed. This may be illustrated by a reference to gunpowder : its explosive quality is the result of its composition, and we can only depend upon the results when we know that the compound has been accurately formed: to insure, therefore, certainty in the operations depending on it, we must take care that a proper standard of composition has been adhered to. In a similar manner, we can only apply Geology as a practical

science when we hare ascertained and made ourselres familiar with those facts which prore the first principles on which it has been fomided to be correct and stable.

To obtain any idea of the earth*s formation and original condition, we must treat Greology as a branch of the physical sciences. The earth, as one of the planetary bodies revolving round the centre of our solar system, must, like all the other planets, be subject to the great laws by which they are at once retained in their orbits and caused to revolve on their axes; it is only one member of a great whole, and in its density, its volume, and its mass, is in strict relation to all the other bodies of the same system. The first formation, therefore, of the earth, or the manner in which it was probably condensed from nebulous matter, and reduced to the planetary form, may be considered a portion of Astronomical science.

It is thus that Astronomy has assisted in the determination of the form of the earth, and it is now known to be an oblate spheroid, of which the equatorial diameter exceeds the polar by 139,296 feet, or about 23 geographical miles, — a difference equal to more than nine times the ^height of Mont Blanc, or five times the height of the highest point of the Himalaya chain. And in Hke manner, by referring to the laws of matter as exhibited in gravitation and attraction, the Philosopher has been enabled to weigh the earth he had before measured, and has determined its mean density to be about 5|- times that of distilled water : but as the actual mean density of the solid matter of the earth's surface, its rocks and strata, does not exceed 2*9, there must be an increase of density from the surface to the centre of the earth. It is impossible that man should descend so low into the interior of the earth as to discover from within the actual condition and nature of its mineral masses, but he has, at least, obtained from without some clue to it in the falling aerolite, or meteoric stone, — the elementary identity of which with the matter of our earth, — the p|-esence amongst its constituents of the mineral augite, which is an essential ingredient of sab-

17

aqoeous Toknuc pfrodncts, — die ■Mikjuiiu fd coDdhion of its iron, which iiidicatfii Out it hsd sot been exposed to atmospheric agencT, and its h^ lyecifc fTsntr 3*375, that of the iron itself bang 7'71o, — are iOostiatiops of the internal constitotioD of our own pbnet, and of a gcnenl hannoDT in itsminenlmatter and that of the other planetaiT bodies. In other stages of the snbiect theie will be fieqoentlr occasion to refer to gmeral ph jscal laws ; bat if we tnni for the present to the more practical investigation of the past and present state of tL:: earth's surface, ^e shall soon be oonTinced that there is somethii^ more in its rocks and strata than mere masses of stone, or heaps of grarel, sand, and mod, confusedlj thrown together: we shall find, in fact, that these deposits have been the resolt of forces tending, according to the ordinary laws of natore, either to break up and remove, or to deposit and consolidate in new forms the mineral strata, and that Geology is thus connected with the experimental sciences of Meteorology and Chemistry : nor is this all ; for whilst we examine the mud and sands of our own coasts and seas, and find either imbedded in, or resting upon them, the relics of many living species of animals and plants, we cannot overlook the analogy in distribution and arrangement exhibited by the sandstones and days of other epochs, and the wonderful fact that they too are associated with the relics of o^anic beings: we learn indeed the dose connection of (jeology with all the natural sciences, and are taught to view it not merely as an humble investigation of the circumstances of inert matter, but as a lofty exposition of the mysteries of organic creation.

Enough has been said to impress upon the reader the philosophical importance and dignity of Greology ; and it can be easily shown that its practical importance is the result of its philosophical connection with the exact sciences. For example, were all the deposits we meet with, here rock and there sand, gravel, and clay, mere arbitrary heaps which had never been brought under the controlling influences of organic

18

or inorgpnie Ibms, we tkoidd be vnaUe to use the one is an index to the historj of tlK other, and the study of each indhidiial deposit wo«ld cad as it had begun, in itself alone. But if it be proved that certain physical agencies have, according to fixed laws, been in operation from the earliest periods of oor pknef s historj, and that thej hare either cooperated with, or acted npon, orgamc beii^s, ao as to check, modify, or destroy, at s ucccMiie epodis, ammal and Tegetable life, — and if in the atrata diemselves we can find the fossilized rdics of suooessiYe races of organized bdnga, and can make the one a guide to the other, — how difierait is the result, nnoertainty now giving place to certainty, and a knowledge of the strata of one pcMtion of the earth's crost becoming a doe to the investigation of the strata of any other. It is upon this certainty, obtained by the collection and collocation of facts from all parts of the world, that Geology rests its claim on the attention of practical men.

In order to acquire a dear conception of geological phenomena, it is necessary to take a brief review — Ist, of the various elementary substances which enter largely into the composition of the earth's crust, and of the fluids connected with it ; and 2ndly, of the prindpal compounds formed by them.

Including most of the metals, there are more than fifty substances which, having hitherto resisted the efibrts of tbe Chemist, are still considered simple. Of these, sixteen only occur extensively amongst ordinary mineral compounds, vrhether fluid or solid : they are, oxygen^ hydrogen^ aeote or niirogen, carbon, sulphur, chlorine, /luorine, phosphorus, siUehm, aluminium, potassium, sodium, magnesium, calcium, iron, and manganese, which, combined together in various vmys, compose the greater portion of the earth's crust and of its aeas and atmosphere. Some of the other elementary substances, as bromine, iodine, and boring, are highly interesting, and some, as the metals, are most important; and though they do not constitute so large a portion of the whole as to require a

Geology- 19

Specific notice iii this jiart of our subject, the remarkable extension of some of them throughout nature deserves remark, as is especially the case with iodine, ivhich will be therefore included ui the list of Geological elements.

The important offices of some of these substances are gencnlXy known ; as for example, of hjdrogeD and oxygen in water, — of osygen and nitrogen in air, — of carbon as a minute but very essential constituent of air, — of carbon agun as a combustible substance in turf, wood, and coal, — of iron as the most useful of metals -, but in addition to these well-known offices, they have others, which are little less essential aJid narked, to perform in the mineral constitution of the earth's crust, the minerals of which it consists being principally formed hy the combination of some of these elements with the principal metalUc bases ; a fact which will become evident as wo consider them iu order.

Oxygen combines with silicium to form silica, of which it constitutes more than a half; but silica, dther pure, or combined as an acid with metallic bases, has been estimated to form almost one-half of the solid crust of the terrestrial globe ; and hence oxygen, in this one condition, is equivalent to a quarter of the ponderable matter of the earth's surface. Bat oxygen is also combmed with aluminium to form alumina, aa earth which is an essential constituent of certain minerals and rocks, as mica and clay slates, &c., which extend over large tracts of the earth's surface and produce by their decomposition the beds of clay, so general throughout the world,—- the several varieties of clay being essentially silicates of alumiuM proceeding from the decomposition of the felspar and mica of gnmite, gneiss, mica slate, and clay slate, — and when the quantity of mud or clay found in modem alluvium and the beds of clay in more ancient deposits are considered, the importance of alumina is only second to that of silica ; but of this earth, oxygen in weight forms nearly one-half. Again, oxygen forms nearly one-half of carbonate of lime, the basis of limestone, a mineral of which, in many parts of the world.

1

J

mountain masses of many hundreds of feet thickness are cxmstituted. And if we add to these instances its presence in water, which is so abundant in the mineral as well as the vegetable and animal kingdoms, and of which it forms in weight eight-ninths, we may readily believe that of the whole crust of the earth, at least one-half is composed of this remarkable element.

Hydrogeji, as a constituent of water, enters into the composition of many minerals and mineral strata, and forms a part of almost every organic substance.

Azote or nitrogen^ as a constituent of the atmosphere, of most animal and of several vegetable substances, is an important element, although it is scarcely appreciable in the mineral kingdom. Traces of this fundamental element of animal organization are, however, to be observed, in the form of ammonia which is a compound of nitrogen and hydrogen, in strata which contain the fossilized remains of animals, and such traces have been appealed to as a test of the former presence of animals in strata which now exhibit no fosd evidence of their existence ; but however striking this exhibi-* tion of ammonia may be, it is subject to so many sources of uncertainty as to be justly considered insufficient in deciding so obscure and difficult a question. One of its compounds, nitre or saltpetre, nitrate of potash, is well known as a constituent of gunpowder : it is produced naturally and is found efflorescing on old walls. In India it is so abundant as to crystallize on the surface of the soil. The analogous salt, nitrate of soda, occurs in Peru in a bed several feet thick, and extending over a space of more than 40 leagues.

Carbon, the basis of coal, the base of carbonic acid, and the most considerable element of the solid parts of animals and vegetables, is one of the most important substances in nature ; it forms nearly one-eighth part of carbonate of lime, and is therefore an essential constituent of the earth's crust. In its purest form it constitutes the diamond, at once the hardest and st brilliant of gems.

I

Rddimentarv

Sulphur, a coustituent of animal and vegetable substances,

I Is exhaled ia large qutuitities from many volcanoes, eiclier in a

[ pore state or in combination with hydrogen, and has probably

I proceeded from some of the mineral substances with vrhit^h

I they are couiiected or has been sublimed from deeply seated

I beds of sulphur by volcanic heat. It ih also a part of tlie

fclhineral crust of the earth, as it occurs ia the sulphureta of

B metals, and in sulphate of lime or gypsum. As regards

p Bolphurets, its presence is sometimes secondary, being the

alt of the partial decomposition of the sulphuric acid of

bible sulphates in a singular chain of compositious and denpositions

. In beds of shale, iron pyrites (bisulphuret of

fei) is frequently very abundant, and when water gains access

■it, there is a partial decomposition, some of the oxygen of

I water combining with the sulphur to form sulphuric acid,

1 then combines with the iron, also oiydized from the

r, to form sulphate of iron. The soluble sulphate is carried

f by the filtering water, and when it comes in contact with

ir vegetable substances imbedded in the strata, is again

]sed, the oxygen combioiug witb the hydrogen and

a of the organic bodies to form water, carbonic acid, and

vetted hydrogen, and a sulphurct of iron being deposited

r tissues. The results of this process, as exhibited L vegetables and in the organic portions of shells and B sometimes very beautiful, and it may be conjectured i this succession of compositions and decompositions will ■jet be traced up to an earlier commencement ancient geological strata,

M. Ch. Blondeau has recently discovered that sulphuret of arsenic exists, in solution, in all powerful mineral springs or waters, and he ascribes their medicinal effects to its presence. Solphurets of iron and of nnifanese are olso found in thermal

Ckhrine, as a constituent of chloride of sodium (common salt), takes part in the formation of those extensive beds of lock salt which occur in various geological formations. Chlo-

1

rine forms nearly -f^n of chloride of aodimn, and is therefive another example of a gaseous ho^ entering eztenaiTdj into the composition of the earth's crust. United with hydrogen as hydro-chloric add, it is erolyed firom Tcdcanoes.

Fluorine, when combined with oxygen as fluoric add, unites with time to form fluate of lime, or fluor spar, whidi is oftai associated with lead in vein-stones. It is also a omstituent of mica and homhlende, hut it may he considered important rather in a mineralogical than geological sense.

Iodine is well known as a powerful medicinal agent. Conh hined with the hates of potash, soda, and magnesia, it coexists with common salt in sea-water and in marine plants. It has also heen recently proved hy M. Chatin that it exists in fresh-water plants, in the waters of rivers, springs, and wells, and in the Mructure of aquatic animals, so that it is evident that this substance, only discovered in 1811, is widely spread over tl^e surface of the earth, and doubtless forms t part of its internal mass. It has also been found in coal ; and M. Chatin has deduced from the greater or less amount ii the several varieties of coal, Anthradte and Lignite, an argument for ascribing their origin either entirely to cryptogamic aqueous plants, to a combination of aqueous and terrestrisl, or chiefly to terrestrial plants, as the particular case may be. Iodine has been found combined with silver as an iodide of silver in Mexico.

Bromine also occurs in seawater combined with the base of magnesia, and has also been found in salt springs.

Borine combines with oxygen to form boradc acid ; and the salt borax or borate of soda is formed naturally on the soil in Thibet, and is found also at the bottom of certain lakes. Boracic acid occurs in the crater of Volcano, one of the lipari Islands, and is emitted from the earth in combination with hot vapours in Tuscany : it is a constituent of the mineral tourmaline, which contains about 8 per cent, of boracic acid, and the wide distribution of that mineral, estimated by number of localities and not by quantity, combined with the volcanic

RUDIMENTARY GEOLOtjV. 23

of the acid, proves that boring must have formed part r original mass of the earth.

osphoriu. — A constituent of phosphate of lime, which is, latite, rather rare in the mineral kingdom, but is a moat -tant coropouud iu the animal kingdom, being the mineral ra of bone, the strength and stability of which depend it. It is also a constituent of many vegetables, and T from them into the animal structure. Darwin men-two curious secondary productions of phosphate of — one at St. Paul's Islands, where the rocks are coated it, the action of the spray on the dung of sea-fowl g produced jihosphoric acid ; and at Ascension, where utiles of the same mineral have been produced in a similar

■ieiurn or Silicon, the metallic basis of silica. — The rtant position this substance occupies has been shown r ' Oxygen ;' most of the minerals, exclusive of the car- x» and sulphates of lime which form the earth's crust, iring in the form either of silex or of siUcates. The • of springs and wells always contains a Httie soluble

: in mineral waters its quantity is sometimes more conible, aud associated with an alkaline carbonate, it occurs e hot alkaline spring of Reikum, in Iceland, and in the )g jets of the Geyser. These latter modes of occurrence ite the slow but continued destruction of the sihcates of nineral kingdom, and afford a probable explanation of the ition of much of the crystalline quartz in nature: on the ion of many limestones gelatinous silica is found, and its □ce indicates that a similar process was connected with

formation.

umnium, the metallic base of the earth alumina. — Afu- , as one of the principal constituents of clay, and of all ! minerals aud rocks from the decomposition of which it oduced, is, as shown under ' Oxygen," a most important an of tbe earth's crust. It is also well known as one of ^nent parts of alum, a salt extensively used in dyeing.

K

which is a double sulphate of potash and alumina. The sulphate of alumina is fonned naturally by the action of sulphuiic add^ proceeding, as already stated, from the decomposition of iron pyrites, on the beds of clay or of shale in which thst mineral is abundant. The sulphate of alumina being dissolved out, and separated by crystallization from the proto-sulphate of iron formed at the same time, is mixed with sulphate of potash, and the two combine to form the double salt alum. Alum-stone, a natural product of volcanic countries, also yields, by heating, this substance : it is abundant in the ancient crater of Solfatara, near Naples. Though alumina is the principal ingredient of plastic clays, it forms nearly 99 parts out of 1 00 of the beautiful gem sapphire, next to the diamond in hardness.

Potassium, the metallic base of the alkali potash. — Potash is a component of many minerals, especially of felspar (a wdl* known constituent of granite and gneiss), of which, in the condition of a silicate, it forms nearly ^th part. The soil is provided with the potash necessary for the support of varioiis plants from the decomposition of rocks containing felspar; and being again extracted from these plants to be used in the arts, it has obtained the name of vegetable alkali. It is the base of the important mineral compound, nitre or nitrate of potash.

Sodium, the metallic base of soda, an alkali which replaces potash in albite (soda felspar). — Soda has been called the mineral alkali, in contradistinction to potash ; but such distinction is without foundation, as carbonate of soda is obtained from kelp, or the ashes of calcined sea-weeds, and might therefore, as a secondary product, be also called vegetable. Soda is likewise found in all animal fluids, and the base itself is widely diifused in that most valuable salt, the chloride of sodium, or common salt. The importance of sodium as one of the constituents of the mass of the earth will be understood better by estimating the quantity of salt in sea-water than that in beds of rock salt, however extensive. Chloride

25

of sodium forms about the 3T;th part by weight, or about -^th part by bulk, of aea water, and the bulk of the sea being about -j-J-g th of that of the whole earth, the quantity of salt it contains is about ^ ^^g j th part of the whole earth, or about -^th part of the bulk of the actually protruding or dry land. If it be considered probable that the saUne condition of the sGa is only the result of the long-continued action of water upon the solid mass of the earth, there will appear to be good reason for assuiuing with some philosophers that sodium, potassium, and other metallic bases were important original cooatituents of the nucleus of the earth, and that by their sadden combination with chlorine and other gases they produced some at least of the convulsiTe disturbances of its crust. Nitrate of soda abounds in Pern. J Xe^nesium, the metalUc hose of the earth magneua.— I Hbgnesia, as a silicate, is a component of many important |. minerals, especially of pyroxene or augite, of amphibole or ! hornblende, of steatite, and of serpentine. Of hornblende it forms ^th part. It is also remarkable as a constituent of dolomite, or magnesian limestone, a combination of the carbonates of lime and magnesia which is very extensively diffused in nature, and forms occasionally mountain masses. The effect of magnesia on vegetation is well known. As a carbonate, it 1 would in itself perhaps be innocuous, but as it forms on decomposition very soluble salts, it may be carried into the vegetable organism, and thereby prove injurious, Aa an alkaline earth it is dangerous from continuing so long in a caustic state.

Calcium, the metalhe base of the earth hme which forms

more than a half of carbonate of lime. — It ia unneceBsary to

dwell on ttic vast importance of the latter mineral, both as an

economical substance and as a constituent of the earth's cnist ;

! but lime \s also found as a component of another valuable

i mineral — sulphate of lime, or gypsum, of which it forms about jth part. Gypsum occurs in extensive beds in more than one geological formation ; in America in the primary or Silurian, in Englaud and Ireland in the secondary, and along the Medi-

!

terraneon id the tertiary strata, divisions which will he hereafter explained. Lime also enters into the composition of a great variety of minerals.

Iron, — The mere name of this metal mnst recall to memoij the multitude of uses to which it is applied, and justify us in regarding it as one of the greatest gifts of creative intelligenoe to man. In addition, however, to its occurrence in a mhienl state in our coal measures, as clay iron-stone and also as spathic iron, hoth of which are carhonates of iron ; in masses and in dissemi|piled nodules as anhydrous and hydrated peroxide of iron, or red and hrown hematite ; in the magnetic oxide and in specular iron, or Elha iron, — minerals whidi are smelted as ores for iron, — ^it is found almost pure in masses of meteoric iron and in a vein traversing mica slate in North America. In combination as an oxide, it is extensively diffused, being found in small quantities in most minerals, and consequently in the soil of the earth's surface. It occurs m many springs, being dissolved as a protoxide by water charged with carbonic acid, and then again deposited as a peroxide either at the bottom of marshes, as bog iron, or on the banks of the springs : and it is deserving of notice that this apparently simple operation is sometimes compound ; the tangled masses of this substance, so frequently found in such situations, proving on examination to be the work of an infusorial animal, — ^the gaillonellaferruginea, — ^which thus interposes and reduces the mineral to an animal substance. This metal is also found in the colouring matter of the blood, of the hair, and of many ■ other tissues, animal and vegetable, and its uses are not there- ;] fore limited to the great works of art, — the machinery of civilized social life, — but may be traced in the many charms which are ^ shed over life itself, \xf the varied colours exhibited, under the ' control of creative power, in the petals of the flower, the e^ and feather of the bird, or the skin of man and other animals.

Manganese enters into the composition of a great number of minerals, though often in a very small quantity, forming, in such cases, their colouring matter. It is also found in the ashes of

i

I

2?

^Ppimts and tlie bones of animals. It is used in the arts, — fof I ( preparing chlorine by the action of its peroxide on hydro-chloric idd, and oxygen hy the action of the same oxide on sulphuric also to deprive glass of its colour by the osydating B of its protoxide, or to colour it purple by itE deutonde. e, then, are the simple elementary substances which ha^e tl combined together in that portion of our globe which, by ing-continued action of meteoric agencies, has been reduced ft'condirion suited for the support of animal and vegetable zatioi) ; and they will next be considered in the mineral Mnnds which form the strata of the earth. These are few raber, for creative power having combined a few elements bA great variety of forms, just as ne observe in the organic i in which many substances, both animal and vegetable, Bsed of the most opposite qualities, — some being alkalis, : ttcids, some poisons, some wholesome food, — have all It compounded of the four simple elements, carbon, oxygen, L, and azote. One point, however, is here deserving Npecial notice, as bearing on the great question of the r condition of our globe; namely, that l^rds of the pon- Ale matter of the earth's crust, taking into consideration , hydrogen, and carbonic acid, have existed, or been d}le of existing, in a gaseous state.

! principal minerals which enter into the composition

ocks, and of stratified beds, are — (juartz, felspar, mica,

B, hornblende, oxydulated iron, carbonate of lime, sulphate

', double carbonate of lime and magnesia or dolomite,

bride of sodium or rock salt, coal, and lignite. Many other

Is occur occasionally in rocks and sedimentary deposits,

I impress upon them a consequent peculiarity, such as

it in mica schist, tourmaline in some varieties of nanite,

1 in chalk and other calcareous formations, iron pyritea

I carbonate of iron in shales, crystallized carbon

md amongst the gravel and other transported or alluvial

S in Borneo and in Brazil ; but these, as well as the vast

1

J

variet y of minerals found in the basaltic and tracbytic lavis of both ancient and modem volcanoes, and those either associated with metallic ores or isolated in mineral Teins, although replete with interest to the Mineralogist, and often of great Talue to the carefully inquiring Greologist, are insignificant as to quantity, when compared with the minerals cited as the princqwl constituents of the earth's crust. The composition of theie minerals may be represented in a tabular form, as in p. 32, and to them, as principal elementary substances, may be added the alkali lithia, its name, derived from the Greek Xt^cor, having been adopted from its first discovery in an earthy mineral* thoQ^ it occurs only in small quantity in rocks. The metallic base lithium was obtained by Davy from the alkali ; its equivalent is very low, 6*44, and its oxide has therefore a high saturating power. The discoverer of the alkali was Arfwedson, in 1818. Rock salt is a compound of sodium 40*5 and chlorine 59*5, or according to the old view, 53*29 of soda and 46*71 of muriatic acid, but it is usually contaminated by a small quantitj of extraneous substances, — the salt of Cheshire containing — Muriate of soda . 98*32 Muriate of magnesia 0*02 Muriate of lime . 0*01 Sulphate of lime . 0*65

Undissolved matter 1*00

Coal and lignite vary considerably in composition. Blind coal, culm, or anthracite, contains for example from 94 to 97 per cent, of carbon mixed only with mineral matter, as bitumen has either not been developed in it, or has been subsequently removed, though traces of vegetables have been discovered even in anthracite; it is therefore a non-flaming coal, and yielding an intense heat, is particularly valuable for the lime-kiln and similar purposes : the coal of Kilkenny in Ireland and the culm of Wales belong to this division. Newcastle coal is a flaimng or bituminous coal, consisting, in the best varieties, of carbon 84*99, hydrogen 3*23, oxygen 1 1*78, bitumen having been developed in its substance by the action of oxygen and hydrogen on a part of its carbon. Lignite still exhibits the structure of wood, and may be considered a fossil charcoal.

nODIHENTAKY GEOLOGY. 29

In studying the minerals which are combined together in the rocky crust of the earth, attention must he paid to certain Tariations in the chemical constitution of a mineral which do not affect its external form- — or, in other words, to the great doctrines of aubstitution by equivalents and of isomorphism. It is thus that substances possessing the same elementary fxiasdtution may replace each other in a mineral, without disturbing its principal or characteristic qualities ; for example, alumina is possessed of the same elementary constitution as peroside of iron, namely, it consists of 2 of base to 3 of oxygen, and can thus replace it ; and magnesiajpossessing a constitution of 1 of base to 1 of oxygen, can replace the protoxide of iron. In green and black augitc this Tariation in the bases is well exemplified : as they contain,

Green augite, — magnesia ll'-I9 + prot.iron 10'02 = 21-51

Black augite,— magnesia 4-99 + prot. iron 1 7'38 = 22-37s the actual composition varying whilst the formula of composition is preserved.

Aa it is difficult to convey fully to the mind of the student, by written description, the physical characters of minerals, he 11 recommended to obtain accurately named specimena, though a few remarks will he given, and may be of use when com- Iwied with the description of rocks.

Quartz is well known as rock-crystal, which is often nlled diamond, as Cornish diamond, Bristol diamond, Quebct diamond, although it has not the slightest relation to that mineral ; and also as common quartz. The prevalent colour is white : when pure if is either transparent or translucent ; when impure it is commonly opaque. Its lustre is vitreous, inclining in some varieties to resinous. The streak is white.

FeUpar. — Prevailing colour white, sometimes grey, and in many granites and syenites flesh red; transparent, translucent, oralmost opaque; lustre, vitreous incliuing to pearly on the faces of cleavage. By observing the tendency to a resinous lustre in quartz, and to a pearly lustre in felspar, these two minerals may generally be distinguished from each other without difficulty,

1

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1

An inspection of the Table will show that under the hetd Felspar is ranged a group of minerals connected together bj general resemblance of composition, but named differently is potash, soda or lime becomes the leading base. Mocto Mineralogists have in this manner subdivided the great group into sections ; and this attention to the chemical vaiiations of the mineral will doubtless be hereafter made an important help in studying the formation of rocks.

Miea. — Prevailing colours, white, grey, yellow, dark brown, or black; transparent and translucent, especially in thin laminae ; lultre, pearly ; flexible and elastic when in lamime^ by which character it is distinguished from chlorite and tsk. This remarkable mineral is at once recognized in granite, gneisfl) and mica slate, by the brilliancy of its plates or kminse.

Talc is distinguished from mica as being flexible but not elastic : in composition it differs from the presence of magneBia. Talc is one of a group of minerals which includes chlorite.

Augite, — Colour varying from green or grey to brown and black 'r generally opaque ; lustre, vitreous inclining to resinous ; brittle. This mineral is very common in volcanic rocks.

Homhlende,'—VTev2Xtxit colour, shades of green, increasing in intensity up to black; generally opaque; lustre, vitreous indian-ing to pearly in light-coloured varieties. Brittle when isolated, but when massive frequently tough, and therefore diffLcoltly frangible. It is an essential ingredient of syenite and greenstone, and often occurs in granite, gneiss, and other mountain rocks.

The two last-named minerals are reducible to the same chemical formula, as they are both bisilicates of lime and magnesia, in which a portion of the acid or silica is sonietimes replaced by alumina, and a portion of the base by protoxide of iron, according to the law already noticed ; they are also an example of dimorphism, the crystalline forms being different The difference of geological position will enable the inquirer to judge in most cases whether he is examining the one or the other ; but as it is sometimes very difficult to determine whether a rock should be classed with greenstone or with basalt, so

B» ' RUDIMBNTARV GEOLOGY. 31 1 also difficult to distinguist between these two minerHla. general the species hornblende contains leas lime than I augite, and ia less fusible ; but as might have been supposed I from the similarity of their elementary constitution, it is possible, by adopting certain conditions of heating ttnd cooling, to change the estemal crystalline form of the one into that of the other ; an experimental fact which has been used in explanation of the difference of their ordinary position.

Ditdlage, or SchiUer Spar.— Colour, dark olive-green, inclining to pinchbeck brown ; lustre, metallic ; part of a group including broiueite and hypersthcne, minerals which eater occasionally into the composition of rocks having the general character of horablcndic rocks.

Oxydnlated Iron or Magnetic Iron, a compound, according to Bentelius, of 2 atoms of peroside and 1 atom of protoxide of iron. — It is highly magnetic, and when massive, more so than tiif other ore of iron. Colour, iron-black; opaque; lustre, metallic. It forms extensive beds in Norway and Sweden Dannemora the beds are excavated to the day, the principal c forming a chasm of 150 il. broad, and 500 ft. deep. The an phona masses of Siberia and the Hartz, which yield the c powerful natural magnets, may be asaocialed with this species.

Carhonate of Lime, and also Douhle Carbonate of Liate and Magnetia, or Dolomite. — The presence of carbonic acid tlwaya be determined by the action of an acid and the i sequent ebullition produced by the escape of the carbonic acid, This is the easiest and most certain method of detecting limestone. Sulphate of Lime is distinguished from carbonate not effervescing with acids ; and from other minerals, whether

rin its fibrous or lamellar state, by its comparative aoflness. Of salt, coal, and lignite, it is unnecessary to say n under this head.

. Such then are the minerals which enter extensively into the

composition of the earth's crust ; and in order to fonn a clear

I idea of its present and past condition it is necessary to inquiro under what combinations they usually occur.

Kddihkntakt Gkologt.

:f:i|:i

I? -is ■.« 1 1" --J J

3s:

D Q e-<Q3:DP O o mPS

Rddiukntary Geology. 33

A survey of any extensive portion of the earth's surface will generally bring before us two distinct forms of mineral compounds ; one, in 'nhich the constituents occur in distinct crystals, which to the eye exhibit no traces of any previous wear, and produce therefore by their combination ^ crystalline rocks ; the other, in tvhich the constituents have nndergone wear, are either mixed together confusedly or separated into distinct beds, and, whether loosely a^regated or cemented together, indicate the action of Tarious meteoric and mechanical agencies and produce rocks of deposition, whether mechanical or chemical. To the first class belong — granites, syenites, greenstones, basalts, gneiss, many varieties of mica slate, granular limestone ; to the second — sandstones, conglomerates, shales, clajs, compact limestones ; and if these forms were always distinctly marked, the divisions would be sufficient and satisfactory : but when the crystalline rocks, formerly called primary, are closely examined, some of them are found to resemble the sedimentary, as for example, mica slate and clay slate, some varieties of which are little more than a highly indurated shale ; and in like manner sedimentaiy rocks in the vicinity of ancient lavas are found to have undergone a change in tiieir characters which assimilates them to the crystalline rocks, whence even the strata are full of organic remains; and on observations of tliis description the metamorphic theory has been established.

If the Geologist, having by a careful scnitiny determined the composition and physical characters of the various rocks he meets with, were to proceed to explain their occurrence on hypothetic assumptions, he would fall into the speculative errors of his predecessors ; but he pursues a different course, and wisely determines to ascertain, by observation, what forces are still in action on the earth's surface, and what effects they produce on its mineral constituents. lie thua studies in lavas issuing from volcanic craters the effect of igneous fusion, and in sand and mud banks, still I, fcnning, the effect of aqueous agency; he discovers in

the dislocating action of the earthquake, in the wearing action of the sea wave, in the accumuhiting Utboura of -pciyipn, as exhibited in coral banks, so many auxiliary or modi^ring forces ; he observes on the sea-shore the exnvin or remains of shell-fish and other animals becoming invested in the deposits of sand or mud f<nrming over them ; and when he turns to the rocky strata of the earth now become dry land, he finds similar evidence of igneous action and of sedimentary deposition, and discovers animal remains imbedded in their substance. The metamorphic theory facilitates the applicatiim of recent analogies in explaining the condition of crystalline rocks which may have proceeded from a species of fluidity, the result of direct igneous action, as in lavas, and probably in some granites and porphyries ; or have been produced by the indirect action of heat on sedimentary deposits, continued for ai long period and combined with pressure, as has been the case in the crystalline schists, and in some other strata in whidi a crystalline or semi-crystalline re-arrangement of the mineral particles has taken place, although the existence of organic bodies still demonstrates their former sedimentary character. By the careful examinati(m of recent and still recurring natural phenomena these truths have been made manifest; and it is by the continuance of such examination that remaining difficulties will be removed. The change produced on mineral beds by contact with highly heated matter has been demonstrated, almost with mathematical precisicm; and though it is very difficult to decide its exact limitation, we can never satisfactorily study the strata of the earth without referring to it. And if the metamorphic theory thus aids us in studying the varying mineral conditions of the earth's crust, the organic remains still visibly imbedded in many of its beds demonstrate that changes equally striking have taken place in the successive organic mhabitants of its surface ; in short, that there have been animal and vegetable as well as mineral epochs. The beautiful combination of facts on which Pa- Iseontology now rests, as one of the most sure bases of geo-

RtJDIlIBNTARY GEOLOGY. 35

logical science, can only be fully appreciated by careful study ; but in this brief memoir it is assumed as a fact, that at various epochs the mineral strata of the surface of our globe were disturbed deeply and widely, shales and slates, sandstones and oon^operates, limestones^ &c., were formed, some in one place, some in another, whilst great modifications took place simultaneously in organic beings ; and if this statement, which is founded^ on facts observed over a large portion of the earth, be correct, the evidence of the epochs of mineral change should harmonize with that of the epochs of organic change, and hence the study of the one may be made to assist that of the other.

This deduction has in a few years elevated Geology to the rank of a science ; and it may be hoped that a more exact study of the operations of the great physical forces which still act and always have acted on the earth's strata, such as magnetism, diamagnetism, electro-magnetism, &c., as well as of the effects of a continued contraction of the earth's nucleus, will render it so practically exact, that not only the probability (under any conditions of strata) of discovering certain useftd products may be stated, but the more abstract and obscure questions of mineral veins and of the distribution of metals be solved on sound principles.

It may then finally be assumed, that as mineral matter is now brought in volcanoes into that state of semi-fluidity which allows of the crystallization of minerals, so at former epochs it experienced a similar fusion, and hence that truly igneous rocks existed at such epochs, and were brought nearer to the surfiice, or even erupted ; — that, in a similar manner, the changes produced by slow igneous action under great pressure, having been observed in strata contiguous to modem and ancient lavas, they may have occurred in strata contiguous to other igneous rocks, and have given rise either to schistose crystalline rocks in all their varieties, or to some simpler modification of the structure of sedimentary deposits ; — and finally, that changes in the combinations of organic beings.

having been proved by extensive observations to have occurred at successive epochs ; when any particular g;roup of animals or plants has been studied in connection with the mineral strata of any one portion of the globe, it becomes a clue to determine their relation with the strata of any other portion in which organic ccMistituents have also been discovered. The certainty thus attained constitutes the value of Geology as a practical science ; and though much caution is yet required to remove mere varieties from the lists of characteristic fossils, and to determine the actual limits of spedes, it must be admitted that the modem applications of the science have been both useful and satisfactory.

A general representation of the combined theories of igneous rocks, metamorphic rocks, and fossiliferous deposits, is given in the ideal diagram, fig. 1, extracted from Cotta. In the diagram, granite is represented as an igneous rock near to the surface, and having its origin at no great depth ; and that this is probably the true state of the case will be subsequentlj shown, the low specific gravity of ordinary granites, which varies from 2*5 to 2*79 whilst that of the lavas of iBtna, Stromboli, and yesttvius> is 2*9, and that of basalt above 3, being a strong argument against their formation at great depths, or under great pressure. The chemical investigation of the composition of rocks as compared to that of their separate mineral constituents, which is now much attended to, is beginning to throw new light on thdr relations to each other. Plutonic rocks are eminently siHcious or quartzose, and volcanic rocks felspathic, and it has been shown that the low specific gravity of the former is closely connected with this excess of silica. It is therefore by no means improbable that granites may have been formed ftom the liquefaction of crystalline stratified rocks, which they so closely resemble in com* position, if not of sedimentary deposits.

Rvdimkntaey Giolooy.

Chapter Iii.

Gkolooical Formations — Their Metning, Object, and Utility — The Mode of Stttdjing them, and the Physical Phenomena they exhibit.

An inquiry into the actual condition of the earth's crust has made known to the Greologist, as stated in the preceding chapter, that the mineral matter of which it consists must, from the great yarietj of its characters, have heen produced under circumstances equally varied. He has thus heen led to trace in variously alternating heds or strata, however indu-rated, a close resemblance to the muds, sands, and gravels now accumulating at the bottom or on the shores of the existing seas and lakes, and to compare the ancient limestones with the calcareous deposits and the coral banks of tropical seas ; he has discovered the affinity between lavas now erupted hy still active volcanoes and the streams poured out either suh-aerally or suh-aqueously by the volcanoes of other times, and has ascertained that crystalline massive rocks, granites, syenites, and porphyries, were brought to the surface at various distinct epochs, and were therefore connected with distinct historic periods of the earth's changes ; and finally, he has ohserved and exemplified the alterations effected in the structure of mere sedimentary deposits hy the combined action of heat and pressure, which have produced that crystalline structure so common in the metamorphic rocks. The knowledge thus acquired and the proofs obtained of a certain sequence and progression in mineral deposits, would not alone have enabled the Geologist to determine that the alternating disturbances and changes they shadowed forth were events antecedent to Man's occupancy of the earth : but he has

Eitdiiibntart Geology. 39

•

found in his researches other evidence, and whilst apparently engaged only in the examination of the mineral structure of the earth> has fallen upon the traces of its former inhabitants, in the many shells and other organic relics imbedded in its strata ; and though yielding to a natural impulse, he first called them by names, such as cockles, &c., which assimilated them to existing shells, — ^just as '' the emigrant to a foreign clime bestows on its fruits and flowers the names familiar to him in his own," — and attributed their anomalous position on land to the Deluge, it was not possible that a careful scrutiny of the drcnmstances under which they occurred could long leave him without a suspicion of their true bearing on geological history. When, for instance, the inquiry was extended from snch fossils as were scattered over the surfiEu;e or were imbedded in loose strata to those which were so intimately mixed up with mineral matter as to form an essential part of vast accumulations of solid rocks, as slates, hmestones, &c., it became eiddent that no single cataclysm or event could account for their existence in such a position. More careful investigation, whilst it explained the changes which had affected their mineral condition, discovered also differences in organic form and structure, until at length the prejudice which still sought to explain such supposed anomalies by the plastic power of Nature was dispelled, and the magnificent truth became apparent and recognized, that Geology teaches the history of past as well as of present creations. This truth, though previously imperfectly developed, was first set before the British student in a dear and distinct form by the late WXiam Smith, who, having with great labour traced out the continuity of many of the British strata and studied the peculiar fossils which each well-marked stratum contained, announced as facts — that

1. The fossils found in any stratum are the relics of animals living at or about the time when that stratum was deposited or formed.

2. The strata not being parts of one confused mass, but following

each other in a distinct progreasiony and the difibrenoes of their mineral character indicating marked difierences in the conditions 'of deposit, it most he assumed that the animal which supplied the organic relics they contain lived at soceessiye, and often widely separated epochs.

3. As the organic differences ohservahle in these relics of animals of other times exceed in amount and kind any probable> nay possihle> yariation of specific characters proceeding from the influence of local circumstances, it must be admitted that at each stage of the earth's history there was a distinct and peculiar assemblage of organic beings which, from causes not clearly known to us in a final sense, became extinct and were replaced by others.

Geology therefore explains to us the history of the organic as well as the mineral changes of the earth, and having esta« blished a connection between the two at various epochs, em« bodies the knowledge thus acquired in a distinct shape, as expressed by the term * Formation,' which impUes ' A Histoiy of the organic and inorganic conditions of the earth's sur&ce at any given epoch,' not limited by time, but by circumstances; so that the term ' Silurian Formation' implies a history of the changes which took place in the earth's surface, of the volcanic eruptions, the various deposits formed by rivers, lakes, and seas, the modifications effected by the action of currents or the beating of the waves of the sea, and of the animals which contemporaneously existed, at an epoch which, though we cannot state its antiquity by years of time, was evidently, by the position of the strata, posterior to some and anterior to other formations.

The practical utility of geological formations when thus established, is this, that having once ascertained that the conditions of the earth were favourable at particular epochs to the production of certain mineral changes and the existence of peculiar organic structures, and that creative power had called into existence the animals and plants which were suited to such conditions, and left them imbued with powers of en-

Ruoiuentary Qeolooy. 41

during only a limited anionnt of change, it becomes practicable to proceed iu an inverse order and to determine the geological age of any straCum from the relics of animals and pkmta it contains ; and even to use the knowledge of the condition of the earth's surface at a particular epoch, which is derired from a study of the organic remains of the strata formed within it, to estimate the probability of finding other substances whether mineral or organic, metals or coal, to the existence of which that condition appears equally favourable.

&#x27; Rocks.

Before proceeding to the study of formations, the relative order of which can be determined by comparing tt^ther the natural history of each, that is, the fossils contained or buried in successive strata, it is desirable to notice those phenomena, or accidents of strata, which have materially aided in first establishing the fact of succession, and must still be consulted in all doubtful cases of position,

Stratification.

Many rocks exhibit a lamellar arrangement throughout their mass, which produces a schistose or slaty structure sometimes related to the greater planes of supposed deposi* tion, sometimes to a plane interaectiog that of deposition, and called the plane of cleavage. In the first case the structure may be the result of original deposition ; in the second, of subsequent or metamorphic modifications. In all cases where rocks are observed to consistof distinct layers, lying one over the other, and each having a considerable extension, they are said to be stradfied. If this stratification had been found every where uniform, it might have been assumed that deposition had gone on regularly and without disturbance ; but stratification is often very irregular, both in the thickness of the beds and in their position and direction, and therefore

Bt be inferred that some interfering cause has disturbed

42

and modified tiieir deporition. Agaio, if to a snccession of beds bariog a considenible mcUnation, called , ' dip,* to the boriion, succeed other beds, perfectly or nearly borizontal, it is reasonably concluded that tbe first beds must have bem tilted-up before the depoiidon of the nndisturfoed homootal beds, and thns an epoch of disturbance or aep&ration is established ; the terms confonnable and unconformable being applied to the strata as they preserre or lose their parallelism.

Thus b is Dnconfbnnable to a, and e is nnconibnnable to i, nhilst the beds of a, h, and e, are conformable within themselves.

As the true position of erery bed or stratum in the system to nhich it belongs most be first determined from the actnsl order of superposition, although fossils may be subsequently nsed to clear up occasional obscurities, the great importance of accurately stud3ring stratification is evident ; and the occasional difficulties which are met with in the investigation may be estimated from the following examples, in which the most ordinaiy cases of doubtfnl superposition arc exhibited. It is very posdble also that the difficulties may be complicated by contortions extending only through the lower portion of amas^ and producing an apparent but not a real nnconfomtalulity.

mVDmXNTART 0X0L06Y.

Fi£f.3.

In fig. 3 the portion x may be found either to overlie or to underlie the stratified beds when sufficiently opened to show the connection.

Fig. 4.

In fig. A, though x overlies the stratified beds, it may be found either conformable or unconformable to them.

Kg. 5.

In fig. 5, X may either underUe or overHe the stratified beds.

44 &#x27;• Budiiieiitart Okoloot.

K hu in thete cssca been raprawnted u itself luutratified; it WMy, howerer, be also stratified, and then the faQowing example will show the possible resulta.

In all of which x is uncoofoniiable to s, excepting in the fourl]), where it is conformable to s, although possibly o( a different mineral character.

It will be obserr^ from these examples how much caution is required in determining the exact conditioas of Btrattficatdon, and m not too hastily deciding that a rock is older or yonoger than another from its apparent position ; and this is shown even more distinctly in

RtlDlMENTABir GEOLOGY. 45

a, though generally lower in natural position, as it is

1 geological age thmi 6, rises up from below it to a

ler level ; aiid again b, though underlaid by a at one

) itself directly on the subjacent rock at another,

night he even, from a mere comparison of levels, sup-underlie

the elevated portion of o.

a are frequently undulating on the large scale, though,

n examined at any one point, they appear to have a uniform

nation.

Kg.fi.

This arrangement may be due either to original deposition on a previously modified surface, or to gentle movements of the underlying mass prior to the consolidation of the overlying strata. The crest or ridge transverse to the highest point of each bend, aa here shown in section, forms the antichiial line nearly in the direction of the strike, and a line running ia a similar direction along the hollow is the aynchnal line.

FLESIiHES AND CONTOBTIONS OF STRATA.

The undulations above noted are simple, but flexures and contortions of strata of the most striking kind are often exhibited on a grand scale, as in fig. 9 : to illustrate them Sir James Hall made the following experiment. Several layers of clay were placed under a weight, and their opposite ends having been pressed by considerable force more closely together, it was found on the removal of the weight that the layers were curved and folded so as to resemble, : ture, the natural strata. Other illustrations have 1 posed, but it may be remarked that in all of them the materials acted upon are supposed to be flexible ; whereas in the crystalline schists, the contorted strata are now so hard

I

&amp;1Iiii1Ibiitabt Gkolooy.

and brittle that titej could not be snppoied cmpable of ai- Bomii^ such formg without being shattered, or at leait extei^ ureljr cracked at the bends. That intemal movements hare

taken place, even in the most indurated strata, may be a^ mitted ; and that one stratum has sometimes been forced ov« another, the surfaces being broken up and formed into a breccia, seems evident from the brecciated structure of some strata; but in many caaes we can scarcely doubt that the now highly indurated and crystalline strata were, at tbe period of flexure, soft and pliable.

In the Carpathian cbun, metamorphic rocks inclnding gneiss, mica schist, talc schist, clay slate, associated with syenite and porphyry, are succeeded by an estensiTe formation of sandstone. Intercalated with this rock, at Tarions phuet, are beds of limestone, which, from their fossils (ammooites, &c.), have been considered either a member of the green-san^ which would place the whole in the cretaceous system, or a connecting link between the oolite and tbe chalk. In rither case tbe formation is comparatively recent, and as it comprisn clays and limestones with the sandstone, is very favourable for studying both tbe mechanical effects of pressure and those

Redimrntab.Y Geology,

BBr metamorphism. For example, some of the schistose clay

^fc^ve become silicioua slafes, with occasional thus of ciDimbar,

"•ihe marls have been concerted iuto jaaperoid rocks, and the

•ittMds tones either into quartz rock or inlo highly quartzose

^?>*it full of pyrites, whilst the mechanical changes during this

^^**etamorpliie action have been as striking as those exhibited

**>■ tlie Alps in similar strata and shown in fig. 9, already

^^^^ferred to. In the tertiary beds of Sicily, where thin beds of

*olid gypsum are interstratified with bent and imdulating

'S^^sous marls, the solid beds have been broken into detached

^*Wgments which still preserve their sharp edges, while the

^ominuity of the more pliable and ductile marls has not beea

■ **lterrupted ; an example equally illnatratiTe,

In endeavouring to explain these phenomi

Objects of scientific research, too great a stress must not ba

T^cl on any one cause of change to the exclusion of othen.

T^here can, for instance, be little doubt that many minfflf

contortions, and some flesures in strata, are the result of

"their original deposition on banks and amidst the eddies <tf

currents ; but we cannot ascribe the flexures in the Alp^

where, as LyeU observes, "curves of calcareous shale

from 1000 to 1500 feet in height (fig. 9), in which the beds

( sometimes plunge down vertically for a depth of 1000 feet

t and more, before they bend round again," to such a caus^

and must consider them striking evidences of disturbance from

internal moTementa ; a subject to which reference will be agara

made.

The preceding observations are sufficient to show the carO'

with which it is necessary to trace the order of superpositiou'

■•f strata, and to guard against the ambiguity produced by

Istions and disturbances of stratification, and sometimes.

by ' Cleavage,' which will be how considered.

In stratification the beds are the result of succeasive i

art "

posits daring a period of time wUch may ha^e wM^gded many exhibitkNis of disturbing forces. It is thus that some stnti may have been broken up, debated, or depressed, prior to the deposition of others, producing one or other of the ciM of stratification described ; but forces which have caused t general corresponding strike in the stratificaticm for hundredi of miles cannot be considered local, — they are general, and fall into the class of great physical forces which afiect tlie earth as a planetary body. As in a future chi^ter thcj will be discussed in respect to deration, it is only here needs-sary to observe that the forces which have produced the more marked ridges of stratified deposits appear to have acted in lines related to the great drdes of the earth. In ended* ▼during to discover the limits of successive beds of sedimentur' deposits, other planes than those of deposition are met with, and it is often difficult to dedde which is the true plane d stratification, and which the plane of deavage. There his been much obscurity on this subject, but accumulated evidence now leads to the conclusion, .that the direction of cleavage is due to the same genend causes which affect stratification, as Mr. Sharpe has specially shown in his examinatioD of the effect produced on the form of fossils. Cleavage planes are often parallel over a large space of country, cuttii^ throiq^ several distinct geological formations, independently of the contortions or undulations which the strata have undeigone^ and of the original bedding, the dip of the strata being to the 8. E., and that of the cleavage perhaps to the n. w., or tnee versd; whilst the strike of both may be nearly the same. Again, the dip of the plane of stratification and that of deavage may both be to the s. e. or n. w., and yet the angles of their dip may be very different. In some cases deavage may assume a fan-like form, the strike still continuing nearly uniform with that of stratification, so that the disturbing forces appear to have acted at successive epochs, nearly in the same direction* In addition, however, to these great disturbing causes, the consideration of matter under heat and pressure would indnce

Iivd1Mentab.Y Geouiqv.

49

ige of a different character, and it is thus that eroaa :, bemg one form of the joint-like cleavage of tuBSfiiTe , haa been probably produced, and frequeotJy also tlw ination or slaty cleavage of slate rocks. The observer L generally be able to clear up this difRculty by discover- |. the plane of deposit of particular fossils, or of beda KSints and pebbles; and if these be wanting, of layers ■^y or of sand, differing in character from the principal studying. In stratified deposits, the direction of ■ planes of strati ticatioii, as they crop out in the cliffs on one )» and slope away on the other, impresses a distinct character e surface of the country ; whereas cleavage, being abrupt X frequently at a high angle, rarely does so, although the J direction of great ridgfs, which is often not quite co- t with the strike of the bedding, is due to the same a that which produced cleavage. On the other hand, Kgreat lines or ridges of strata are often cut through by cross I a passage given to rivers across them ; deep nar- |r dells being the frequent result of cross cleavage, vrhilst wide 1 open valleys are more generally the result of atratificatioQ ■ modified by elevation. The smaller description of cleavage or slaty cleavage -which has been alluded to as probably resnlting from a polarizing action during the consolidation and metamorphism of strata is very remarkable in slates, which are frequently fissile in directions not parallel but transverse to the stratification ; and something similar may be observed in the diagonal lamination of sandstones and of the more recent de-critic (diluvial) deposits, which may be ascribed to a modification in the arrangement of the particles during the process of depontion.

1

I

Wear.

The te.m denudation strictly means the act of laying bare, though geologically it represents the result of tliat operatioi so that a valley is said to be a valley of denudation when it has originated from the removal of a large mass of superjacumbent

strata and the consequent denndation of the nnderlying rock. In reality this is only one form of the general problem of wear, and yet it deserves especial attention, as being peculiarly calcnlated to awaken a lofty conception of the vast effects produced by the most simple natural causes, and to connect together the operations of the present and of the most distant epochs. If it be asked what has been the amount of denudation, the reply should be with Lyell, — that it may be measured by the whole mass of our stratified deposits, as they have all been detached and removed from their primeval positions. If the question be, ''At what time did it commence, and how often has it been repeated?" — that its commencement must at least have been anterior to the deposition of the crystalline schists of the earliest epoch, and that it has been repeated during every successive epoch of the earth's history. Such considerations as these will enable the observer to form a just estimate of the magnitude of the phenomena before him, and will relieve him from that hesitation to admit their possibility which is the consequence of a cramped perception of the forces which produced them. In no other science is this power of philosophic generalization so important as in Geology, as the observer is constantly required to pass from the contemplation of very simple facts to that of great results; though at first he is perhaps disinclined to admit or even unable to comprehend the connection between them.

In studying the denudation or wear of the crystalline schists, a solution is obtained of a difficulty which led into error even Playfair, who, when discussing the probable thickness of tiie known portion of the earth's crust, estimated it from that of successive outcropping strata: For example, in a mica schist^ district an unbroken series of strata may be traced for probably 50 or 60 miles, dipping at an angle of 30° or 35° ; and if it were assumed, with Playfair, that all these beds were originally deposited one upon the other in a horizontal position, and subsequently elevated by a disturbing force, the thickness dedudble from such a consideration would be very caosoAet-

tRODIMENTAHY GEOLOGY. 51

No. 10 represents a section through strata which haw for 30 miles a dip of 30° ; now if this deposit had been once horizontal, and then simply tilted, up, the thickness would be ^^. 30°, or 15 miles, .and the edge of each stratum must

a raified about 12 miles above the horizmtal plane.

With a dip of 4a°, not unusual in the crystalline schists, the thickness nould have been 21 miles, aiid the rise of the Btratom edge 15. Though the inclination of strata has sometimes resulted from original deposition on hanks, it must be ascribed principally, in this description of strata, to subsequent disturbance, as is proved by the frequency of contortions in all districts of gneiss and mica schist. Whoever, indeed, has carefully examined such districts must have noticed the repeated altemationa of certain sets of strata, such as quartz slate, thick beds of quartz with micaceous specks, granitiform gneiss, mica sciiist jiassing into gneiss, mica schist passing into clay slate, layers and beds of granular limestone, &c. ; which, if all considered independent and succcasive beds, vonld imply first an extraordinary amount of variation in the forces acting duriog their production without any great disturbance, and thai the action of some great and controllii^ force, soDieient to modify the whole mass through a thiclAiess of 30 miles, disturbing and elevating it at the same time; vrbereas a lateral pressure, whether produced by the undulating movement of the still hquid nucleus of the earth or by intrusion of liquid igneous matter, explains the phenomenon in a more simple way, by representing these alternations as

foldings of the strata in contortions, mkny of whicli are stiQ visible, wliilst Others have been truncated by denudation, in the manner shown in No. 1 1, the surface having been further modified, by subsequent wear and the removal of the softer strata, so as to form mountain and valley.

n iyi mla

TJnduiating beds were frequently formed during the arboniferous period, and the descending or dipping portions have sometimes been so perfectly truncated by denudation as to exhibit on the surface of the soil a horizontal plane. In the shales of this formation, numerous bribing examples may aba be found of wear, prior to the deposition of the overlying beds, by which the observer is enabled to trace the direction of the current which produced them.

The section by Dr. Lusser, taken in the Alps from 8t Gothard to Asti, on the Zugersee, part of vrhicb is shown in fig. 9, is replete with fine examples of contortions. The strata, although greatly changed by metamorphic action, are not older than the secondary period, as they contain cretaceous fosflls : tbey are, however, in immediate connection with crystalline schists, especially gneiss ; and it seems probable that some partial modification of structure, whether from heat or other cause, must have preceded disturbance, and have rendered them sufficiently tenacious to undergo contoi^ tion, which extends to bends of 2000 feet in extent. The

S3

hollows cut in their sumniits mark also the great deuadatioD which has been effected at points non so elevated.

The contemplation of such tacts prepares an obserrer to espect the vast amount of denudation he will find displayed before him. It has gone on at all periods, and wherever ona formation ts laid bare by tbe removal of the overlying strata, evidences of its previoua wear may he discovered.

Faults.

The preceding phenomena have implied lateral movements and pressure, accompanied or followed by extensive denudation or wear. The present are the result of vertical movements, by which whole masses of dislocated strata have either slid down or been forced up, the same strata appearing thus, as if repeated, at a higher or lower level. In this case, then, the retaining force is lateral, and the moving force either directly vertical, or indirectly so, as tbe result of lateral presaore ; and it is probable, from the frequency of faults in sbjJe districts, that the sliding was similar to that of lii:L'l-slips. In fig. 1 2, the bed a has been first np-thrown alon^ tbe line or fault df to a', and subaeqitently down-thrown along the fault /S to a', the corresponding portion of a being depressed below h.

Fig. 12. ■

Although great and strikjue;, the actual amount of vertical disturbatice, as exhibited in faults, is generally small as com-

I

S4 KUBflf KKTAKT GXOUMY.

puvd with thftt of latenJ as dupkred in con to rti on s. In the Newctstle coal district, the npwud or d ow n w afd movement his ■mounted to nesilj 1000 feet, so that the snrfine must have heen originaDy affsctisd to that extent, portions harmg heen either raised or sank 1000 feet above or heloir the rest. The projections or inequalities prodoced hj sneh movement have been subseqnentlj remored by denudation, and their former existence can only be diaeorered by studyii^ the internal structure of the disturbed strata. In addition to the forces which have tended to derate or depress-the crust oi the earth, and either to disturb and contort the strata by forcing molten mineral matter amongst them, — or, in the case of &ults, first to fracture and then to separate mie portion of them vertically from the other, — another may be traced in the effects of unequal contraction on such varied substances^ as it is highly probable that heat gradually accumulating at oertsin points dried the superincumbent strata of deposition, and caused them suddenly to contract and crack. On every side,, then, and at every level, whetfier we look at the varred surface of our earth as it now exists, and as it is now exposed to the incessant wear of rains, of torrents, of rivers, and of seas, — or seek our information od its condition within the deep re* cesses of the excavated n)ine, — we find the same tale narrated^ of continued disturbance and wear on the one hand^ and of renewed formation on the other.

FURTHER EFFECTS OF FORMATIVE AND DE0TROYING CAUSES AS EXHIBITED IN MODERN AND ANCIENT SEA CLIFFS, SEA BEACHES, GLACIERS, AND ICEBERGS.

So long as the worn materials of the earth's original crust are studied only in deposits which afford no evidence of the existence of air-breathing animals and plants, it is not to be expected that the action of waves on the sea cHfBs, which depends on a partial exposure of their surface above the level of the sea, should be discovered. The vast beds of sandstone and conglomerate which occur at certain geological

Budimentary Oeolooy. Ss

epochs are records both of wear aod deposition, of vrhich the simpleBt analogue will be found in the nccumulatious of sand and gravel which now form submarine banks. The exteut of kuowQ sea banks, such as the banks of Nenfouudland EUid the Bahama bank, is sufficient to support and confirm such an analogy ; and when it is considered that soundings of only moderate depth are obtained on these banks in the inidat of the ocean, they may be fairly considered as analogous to and commensurate with any of the more andent banks which now constitute our beds of conglomerate or of sand-atone. Ancient sandstones and conglomerates were indeed formed by the gradual accurouktion and alternation of sand Utd grave!, just as our modern banks are formed and extended rthe action of marine currents, combined with that of floating 3 and bergs of ice, which have conveyed to and deposited k them the detritus of distant regions. In the hydrographic ions issued by the Admiralty, it is enjoined that the a lead shall be cast at convenient periods, even where f shoal is either known or suspected to exist ; and much lable data will be thus acquired for determining the pro-changes of snch deposits. Every time the lead touches the bottom, a point of comparison is obtained, and a 1 for future investigation secured ; and when a shoal is t discovered, blame should not be imputed to preceding is it is probable that in their time it had not been ■ed within the reach of ordinary soundings. If it were in our power to examine the internal constitutioB of sea banks, the occurrence here and there of the trunk of a id tree, or even of the hard fruits of many plants, would be ascribed to drift ; but if beds of lignite or fossil VDod were discovered, we should infer from them that the bank had either been exposed to the air, and su[ growth of air-breathing plants, or had been formed in some aucieat estuary, adjacent to rivers whose banks had beea. clothed with plants. In a similar manner, though the occur?i i of fragments of anthracite in ancient rocks renders i(

I

probable th«t other parts of the earth at the time of their formation supported a growth of plants, it does not prove that those individual rocks had been clothed with T^ietation; whilst the existence of beds either of lignite or of coal in a formation does prove that its strata had either been covered with plants or were contiguous to other parts of the earth then covered with them. Such is the evidence afforded by the ancient beds of anthracitic and bituminous coal of the carboniferous and other strata, and of the lignites of the stOt more recent tertiaries ; and as the occurrence of deep beds of coal marks the existence of forests of tropical plants prior to their deposition, it is proved that at a very remote geological epoch some portion of the earth's surface had already emerged from beneath the water, — a fact which is supported by the appearance even in the crystalline schists of that descriptkn of wear which is produced by the surges of the ocean, when beating on the shore they either shape out sea diffs, or form gravelly and sandy beaches.

The old red sandstone which underlies the coal strata penetrates into the recesses of the mica schist in districts where the two are in contact, whilst the wear of the crystalline rocks, and the fragments broken from them and found in the old red sandstone conglomerates, show that the former had sometimes attained their crystalline condition prior to the deposition of the latter. The broken and rugged edges of the mica schist correspond to the wear of such a rock ; and the beds of shale of the coal series exhibit wear still more strongly ; for though it is often diiHcult to trace the cliffs, or sea boundaries of these ancient periods, as most of the strata have again been submerged and covered by more recent strata, the presence of large pebbles of mica schist in the conglomerate formed in the ancient bays or recesses of that rock proves that the sea once beat against it, and the deep precipitous banks which are not uncommon in the carboniferous formation may be also ascribed to a similar action. In the case of Lough Erne, in

\Bakd, an ancient sea bottom is observable in the limestone

Diuentaky Geologv. 57

of ita shore, wliicli is covered with projecting corals, i posted by the remove], from denudation, of the shale a just as the sea bottom in warm climates is covered over hjr corallines. Shore wear may be traced at every geological epoch ; hut after the deposition and consolidation of the chalk it becomes more apparent, as the strata subsequently deposited were less extensive and more local. S^r C. Lyell gives several examples of inland chalk chfFs which occur in Normandy, hut none can be more striking than the curved escarpment of chalk which hounds the plain of Dungiven, in Derry, the tertiary clays with their marine shells occurring at its base, and marking in the most striking manner the boundary of a former sea bottom, at levels now raised by elevation 200 feet above the present sea, although the ancient sea cliff wi the present one is, a chalk cliff. As we advance further, new evidences of continued change arc met uith in the occnrrence of more modern sea beaches, which are now far removed from the action of the existing sea ; and in the cave of Uddevalls, in Sweden, this change of level was long since estabhshed by the ciirhipeda found adhering to its walls, and identical with those which now attach themselves to the rocks of the s shore. We are thus, by the combined evidence of mechanical 1 wear and of organic fossils, carried back step by step ti which, though beyond the reach of historic records, can thua be compared with the present ; and when the organic links of identity can no longer be discovered, we can stUl trace in mechanicul effects the working of similar causes up to tho remotest epoch.

The enormous wear effected during the last pause of elevatioa • prepares us to estimate that of former epochs ; for example, the wear displayed by the present condition of Portland Island, n cut off from the main land by the removal of an underlying blue clay, and the consequent undermining of its more solid strata. At present, the Chesil Bank, an accumulation of sand and gravel, forms a natural breakwater, and lessens, though it

J, the progress of wear; but should another slight^ c5 J

11

f

:1

elevation bring up the blue claj nearer to the water's edge, til wear will again advance nith rapidity, and tlie island onee q moved, the Chesil Bank itseir will speedily be destroyed. » the sea advance upon the main land. This case is of much pm tical value; the wear of Portland Island is delayed by the dijl the beds, which carriea the subjacent clfl.y to a depth b the action of the moving wbtc, and reduces the wear to thati the more solid rock : the Cbesil Bank has been formed h the Btill projecting portion of solid rock checks the force ofS current, and cause* the deposition of the pebbles moving W it : the pebbles of the bank protect the subjacent clay ta further wear, and thus the general tendency la to pre tottering equilibrium, which the slightest change wilj d In this instance a renewal of elevation woold lead t destruction ; in others, elevation may bring up a solid ^ and thereby retard destruction, and these varying results n have attended elevation at all geological epochs ; and agui elevation stopg for a period extensive wear by bringing np ■ opposing to the efforts of the sea a firmer rock, deprc produces the same effect by removing a soft stratum firom action, as it did at Portland, where the removal of the K clay beyond the action of the waves was probably the res of a depression. In examining any coast, therefore, wiflk view to judge of its probable permanency, the foUowing p ticulars should be especially noticed: 1st, the nature oft shingle or gravel, as showing the direction of prevMlii^ ci rents ; 2ndly, the prevailing and most powerful winds ; 3rd position and character of auy sheltering barrier in respect the prevaJUng winds ; 4thly, position and character of i barrier opposed to the prevailing current.

The ancient or raised beaches of former and not very renM epochs are also examples of the effects of these modllji rauses, and without doubt many such beaches have I swept away ; an alteration of level, by elevation or depressie having favoured the work of denudation. The processes wear on the one hand and deposition on the other can inde

Budihbntary Geology.

59

f rest is an equilibrium when the forces producing them

a state of balance ; and any alteratiou in the one must

a change in the others.

Lfestiges of ancient river as nell as lake wear may also

t discovered; of the former, an example is given in fig. 13

i fig. 14, el the end of the chapter, in which the fanner bed

I' the river Burnthollet, county of Deny, appears to have

I 10 feet higher than its present course, as shown by the

irkable masses of rock still remaining to attest the ancient

a waters : of the latter, the parallel roads of Glenroy,

m aften noted, may be again cited here. These roads are

tent shelves or beaches, formed at the margin of a former

i, and at levels corresponding to its successive depressions.

B highest is 1250 feet above the sea, the nest about 1000,

S the third 50 feet lower. Sir C. Lyell remarks, that "among

a that the parallel roads have really been formed

g the margin of a sheet of water, it may be mentioned, that

a isolated hill rises in the middle of the glen above

H level of any particular shelf, a corresponding shelf is seen

e level, passing round the hiU, as would have hap-

t if it had once formed an island in a lake." The great

« of America exhibit similar lake beaches at various ele-

I above their present surface i the absence of marine

9 concurring with other circumstances to remove sucll

mulationa from the list either of ordinary marine beaches

■iif sea banks.

n addition to gravel deposits of this kind, the researches si« have added others, — the effects of ancient glaciers. I been long known that these vast aecumulations of snow are in motion, proceeding from the liighor valleys of the Alps, where they are formed, to the lower, where they are gradually melted ; the portion cut off or melted at the lower end being replaced by a new mass added at the upper end. As it moves along, the glacier carries with it the fragments of rock which, having fallen from the precipices above, are arranged ^jnm it in lines of deposit, to which the name of

been given. M. Agassis distlDguishes three varieties, — iatenJ, in which the moraine borders the Ytliej of the gkder, festnug either on its surface, or between it and the side of the valley; — ^medial, in which the moraine is formed of a long line of d^iis stretching, like a riband on the surface of the glider, down the course of the valley ; — terminal, in which the moraine is seen at the lower or terminal end of the glacier. These forms of gravel deposit, interesting as regards the history of the glacier itself, become still more so when appHed to the explanation of gravel deposits, now no longer connected with laden.

It will be readily conceived that any considerable variation in the temperature of the air must produce a similar variation in the amount of snow and ice, and an augmentation or a diminution, as the case may be, in the glaciers resulting from them. Within very recent times, the variation has been towards an augmentation of cold, as shown by the inquiries of M . Venetz on the variations of the temperature of the Swiss Alps; but if compared with still more ancient ^>ochs, the evidence is in favour of a rise of temperature. M. Yeaeti estabhshes the first of these positions by historical monuments and documents, which prove that some of the Alpine passes, now scarcely practicable, were then the ordinary lines of communication. In the archives of the Commune de Bagnes, M. Rivaz found the record of a legal process between that commune and the commune of Liddes, relative to the possession of a forest then on the territory of Bagnes, but which has since disappeared and been replaced by a glacier, now entirely cutting off the communication.

Many other examples are cited of the extension of the glaciers within the last 200 years ; but the amount is small when compared with their vast extension, as proved by the existence of ancient moraines, in periods beyond the reach of historical records ; for, as M. Agassiz observes, — " we shall be forced to admit that many moraines, far distant from existing glaciers, must have been formed at the most remote periods, if not anterior to the creation of man." Thc5 careful

exominatioa of those deposits, which he thinks may be elaaaed with moraines, has led him to trace, assisted by other phenomena of glacial action, the former existence of glaciers in countries now far removed, by their comparatively elevated temperature, from the sphere of their production ; and he has thus brought the British Islands within the range of ancient glacial action.

Such inquiries and reasonings lead to the behef that there was a period of intense cold, when ice and snow were spread over a large portion of the northern hemisphere ; and if on the lands of that frozen epoch, the glacier descended, as it now does in Spitzbergen, to the sea, icebergs and floating sheet ice must have been also formed, and the sea covered with them. Glaciers were the carriers on land of those fragments which formed ancient moraines ; — icebergs and floes were the carriers on sea of those vast fragments which now as 'erratics' are dotted here and there along the course of the then marine current, just as the modem floe or iceberg now leaves at the bottom of the ocean, where it grounds and melts, the fragments of rocks it has carried along with it. This period of intense cold is called by Geologists the glacial epoch, and it is very remarkable that no traces of glacial action have as yet heen ' found in the earlier strata.

it is thus that the Geologist, in endeavouring to trace out I sequence of stratified deposits, has been led to discover ; the various changes which the earth's crust ) undergone at successive epochs. He has seen sea and 1 alternately rising and sinking before him ; and standing, it were, unmoved on a rock, has watched and recorded the

9 of each movement as it rose and fell. B refore, in a condition to compare together all the results he I observed, and to frame into one system the mineral and I organic histories of the earth's changes, as recorded ia A of deposition.

I J

Kusihentarv Gsology.

Chapter Iv.

F

^■pici Metunorphic, and VulcBn[c Kocks — Candilion vid Temperature ^* the Interior of the E grth^ I) ykei— Elevating Forces — Veiiu — MetaUic Depoaiti — Eennomic Value and Uses of ibe Rocka deacribed.

N passing from one epoch of deposit to another, rocks hare een ohseTTcd, which, being crystalline and mBssiTe, have eviently niidergoiie igneous fusion, and yet do not resemble Dlcanic rocks; ottiers nhich, though crystalline, sre as regutrly stratified as sandstones and shales ; and others which are sadly recognized as Tolcanic products.

Theee rocks ere the subject of this chapter, as it is ncces- R.ry that the Geological Student should be made more fully ctjtiaintcd with their nature, and with the circumstances conlected with their production.

The rewiarkahle group of Plutonic rocks may be associated LS felspathic with the well-known rock called granite, of which elspar is an essential constituent.

Granite, common. — Febpar, quarts, and mica, disseminated n nearly equal proportions ; the felspar lamellar, and the «sture often granular. Tourmaline and hornblende are frejuently accessory ingredients, and many other minerals occur jcaisionally, either disseminated in the mass or in veins. Colour, which depends materially on the colour of the felspar, is either greyish or reddish.

Granite, jmrphyritie. — Crystals of felspar in a small-grained rrraaite. It is occasionally difficult to separate this rock from some varieties of protogyne.

Granites are divided by joints or planes of cleavage into irregular polyhedral masses. The metals which occur, either

disseminated or in yeins, are principallj tin, uraniTim, gold, silver and its sulphuret, oxjduloos iron, bismuth, &c.

Protogyne, green, — Felspar, grej and red, — talc or chlorite of a deep green : green is the predominant colonr.

Protoggne, red, — Felspar, grey or red, — ^talc and steatite, reddish brown or green, the red prevailing.

Such may be considered the characteristic or peculiar mineral components of protogynes ; but M. Delesse has shown that they generally contain five minerals, — namely, a felspar in which potash abounds, a felspar in which soda prevails, a mica of magnesia and potash base, a variety of talc, quartz.

These rocks are bedded on a grand scale more decided^ than granites, and form the highest peaks oi the Alps.

Syenite, — Felspar, quartz, hornblende ; the felspar lamdlar, and often predominating. This rock has been subdivided into sections, such as granitoid, where mica occurs in small quantity ; porphyritic, where large crystals of felspar are imbedded in a small-grained syenite ; zirconian, hypersthenic, diallagiC) according as one or other of the minerals zircon, hypersthene, diallage, replaces in whole or in part either the hornblende or the quartz. Some of the varieties, particularly the schistoid, connect the granites with the greenstones, and some are so similar to metamorphic rocks as to make it doubtful whether they have a claim to be considered rocks of fusion.

Pegmatite, — Felspar and quartz ; a silvery mica of potassic base is frequently present, as also tourmaline. The quartz is often arranged in broken lines, and produces that variety known as graphic granite, from the resemblance of the quartz lines to Hebrew characters. The felspar combines the two bases, potash and soda, — the former being to the latter in the proportion of 10 to 3 per cent. The quartz sometimes occurs in grains, and passes by the introduction of mica into granit^ or gneiss. Pegmatite is a variety of the granite group^very rich in silica, of which the proportion rises so high as 78 per cent. The finest kaolins, or porcelain clays, are produced by the decomposition of pegmatites.

.Hudimkntary Gkolooy. €$

Second Group

comprises another extensive family of rocks, of which greenstone is a type, the predominant constituent being hornblende.

Hornblende Bock. — Base, hornblende with mica, felspar, garnets, &c. Texture lamellar, and structure sometimes massive, sometimes fissile.

There are many varieties of this rock, such as the granitoid, the serpentine, the micaceous, the schistoid, &c., so named from the peculiar mineral or structure which prevails ; and it is thus that the rock assumes bj turns the true character of a plutonic rock, or those of the metamorphic series.

Greenstone (Diorite, ^c.) — Hornblende and compact felspar, nearly equally disseminated. This rock is also subject to numerous variations, becoming granitoid, schistose, porphyritic, &c. The orbicular granite of Corsica is a greenstone in which spheroidal masses of hornblende and felspar occur in a paste of granular greenstone : a similar rock occurs in America^ in which the spheroids are very small.

In the pyromeride, or orbicular porphyry of Corsica, radiated spheroids occur in a paste of compact felspar and quartz. Such forms are very interesting, as they are examples of concretionary structure, or of a tendency to definite arrangement within a mass.

The eurites, or felspar rocks and felspar porphyries, will be considered with volcanic rocks, though they sometimes approximate closely to the granitic type.

The next class includes the metamorphic rocks, which in many respects approach very closely to the plutonic. They exhibit a schistose and stratified character combined frequently with a highly crystalline structure. For a long time both granites and crystalline schists were considered primary rocks; And after the igneous theory of formation had been admitted )r the massive rocks, it seemed difficult to separate from them

rock composed of felspar, quartz, and mica, and so highly

I

crystalline as gneiss. The altenwttion of gneiss with a slate, graaular limestone, and clay slate under nil the ft of ft definite at ratification, rendered it, however, i adopt some other and distinct theory of their formation, tiiey eren been homogeneous, or all similar lu constitution 9 tither granites or greenstones, thej might have bet?n ascribed to a similar origin, and considered portions of the origind cmst of the earth ; hut no such theory can ar^count for tht altemaUon of layers of limestone with gneiss or mii The same reasoning therefore applies to these as 1 stratified rocks ; aad they must he considered ancient sedimentary deposits, on which some peculiar change has ben effected, which entirely masks their original condition; change, which is signified by the eiEpressiye term i phous or metamorphic, and is, to a certain extent, not p to such rocks, as many sandstones, conglomerates, a Stones have been altered, though not to the same extend Q the loose muddy paste in which they were originally depc The description naturally commences with the rock n character to granite,

Oneiss. — Felspar, mica, and quartz, — the felspar I and the mica abundant, arranged in lines so as to pro lamellar or schistose structure.

There are numerous varieties of this rock, as i a distinct granite in texture, and sometimes merges into next species, mica schist. It is occasionally talcose, appiT mating to protogyne,— sometimes is porphyri " sionally loses its quartz, — whilst in a rare variety graphite in scales replaces the mica; and it may therefore be imagined how difficult it must be to draw a Une of demarcation between some granitic and gneisGOse rocks.

Mica Sc/iUt {Glimmerschiefer of the Germans). — Mia

predominates, and the stnicture is fissile. GHmcts enter u

an accessory constituent into this rock, as well as several othet

minerals. There are many varieties, as it becomes gneissose

I hy the introduction of felspar, granitic by a more irr^piI^J

Rodiusntary Geology. 6?

itroctni'e, porphjritic mith a scaly fracture, or merges into a el&y alAte : it is aometimea talcose.

Clay Slate. — In this rock the diatinction of crystalline elements is lost, but there are frequently accessory crystals of quartz, felspar, &c., by which it may be approximated to mica slate, just as that rock merges into it. It is sometimes so calcareous as to become almost a limestone slate, and the alternation of thin bonds of limestone with the metamorpbic rocks, especially with mica slate, is a remarkable and interesting fact, strongly elucidatory of their origin. Clay slate is ■bo occasionally talcose, or becomes a talc slate.

The porphyritic character, which is common both to the igneous and met&morphic rocka, has been illustrated by the researches of modem Chemists, who have succeeded in retaining stony matter in fusion under such circumstances as should lead to the formation of crystals in the mass, on cooling. Various precious gems have thus been created ic the laboratory ; and to these experimental proofs of the numner in which 'he crystals of porphyries may have been formed, are to be added the researches of Person on alloys, which have shown that metals combined together in due proportions may first consolidate into a definite alloy, on arriving at a common solidifying point of temperature, and yet separate afterwards. The fact that such separation oi^en takes place before consolidation,- — ^thc metals not arriving at a common point of solidification, — had before been noticed ; and both facts, when extended to stony minerals, are highly explanatory of the porphyritic condition of rocks.

Some other leas common rocks, such as serpentine, will be noticed hereafter in reference to their practical value: and the reader should obser\'c generally, that, independent of any theory connected with them, massive and metamorphic rocks q)pear under several distinct forms common to them both ; and as this fact is observable also in volcanic rocks, it is embodied in the accompanying Table, as a ready means to make the observer familiar with such rocks.

jlSSn d

s describing truly volcanic rocks, the connection of tonic and metamorphic rocks with the leading physical tienomena of the universe requires consideration. An hypo-less has been advanced in Aslronomy, that the now solid lanetary bodies were once in a stale of gnaeoiis fusion as ebulous matter, and were gradually condensed into their resent state. The figure of the earth, which is an oblate >faeroid, has been appealed to in support of this theory, as a ijnid body subjected to the conjoint action of gravity and rotatory projecting impulse would assume such a form. lie figure of Jupiter is alsa consistent with the theory, but i*t of Mars appears as yet opposed to it. If, then, the earth Ra passed through a fluid state, the cause of such finidity ppears closely connected with heat, as an examination of ie temperature of the earth's cmst at various depths shows liat the temperature below the cooled surface increases on descending, and that at great depths there is still existing vast reservoir of internal heat. From numerous observations l&de in mines and by Artesian wells in France, England, 'mssia, Rnssia, and elsewhere, Leonhard states that the Btoperature increases by 1° Reaumur, or 2^° Fahrenheit, in 20 feet. M. Reich considers the temperature in the mines f 8a.tony to increase 1° centigrade in 4r84 m. of depth, or f Fahrenheit, in 135 feet. In a boring in the Military Idiool at Paris, the increase was found to be 1° centigrade, or f Fahrenheit, for about 9fi feet. In Mr. Fox's experiments B Cornwall, the increase was found to be about 1° in 47' : in .We of Mr. Oldham, in the copper mines of Knockmahon, WHnty of Waterford, 1° in 82', being a lower rate of increase ibaa that of previous inquirers. It may be therefore assumed u R reasonable approximation, though subject to many van- Uions from the different conducting powers of different strata, that the temperature increases 1" Fahrenheit in fit! feet of J^th ; and if the rate of increase were considered constant, Ihere would, at 60,000 feet, be a temperature of 1000° or that )f low red heat ; but as the temperature will increase with the

•ienrji in in '■"^"■^"■'^■■y raoo* I^mlHRi hrhmi ditf ill I''' vmoffnam -mmd be ictuned ac dboac 33,000 ftct, WngiV liencn miy iuiinie The oiacfat of Cocopcd, tW noil lOMik ^^ abie of ^he P*fnvian vnicmiiei. Dcateadm^ adD loMr, fti temiwncir*. ac a venr modence depth eoDi|MRd with ftl aaasinuie :t '}iis ear^ wnlii be fimd miiilMMid to if(M mineral macre r in a icace ijf 6ssaa ; and it is tkocfoie » I™ nMcaaaxy u oiaix ac a cRac depth the aonree of the hi |>ti which 19 adll pouring oos m w manr pazta of the caitL fk aizmlarirr ot iara, wherever fond, and the doae agnanatMl^ to ccmpoaidon ami phTscal characters a£ the faaaah of anorit epoeha and of that Kill borstmc throw^ and mtersecdug h walls of modem ToLcascea» are farther proofr that aU ni empciotu have a common onsjn, and are due, aa wdlu^ accompanjiss physical phenomena of eafrthqaakcs^ to final ■* actine on the sdii liqaii onion oi the earth.

If then the orieiaal igneoos floiditr of the earth, and ib gradual cooling from the cnist downwards^ be adnutled, itha V b^en demonstrated bv Fourier — |*

1 . That the cooling: of the earth, and the increase of tern- j*^ratnre in proportion to the depth below the surface, his l>«:rj rriuch jrreatcr formerlv than it now is.

2. That more than 30,000 years will be required to lessen, hy onft-half, the present rate of increase of temperature; thit H, U} TcAucj: the increase to \^ in 60 feet.

3* Ttiat the effect of central heat is now scarcely perceptihle on th*^ surface, not raising the thermometer -^°.

4. 'J*liat for nearly 2000 years this effect has not diminished by Jf^'', and that in this, as in all the great phenomena of the iiniverMs a marked character of stability is perceptible.

1*hc density of the earth affords another means of judging of itfi internal condition. It has been stated that the density of tho crust lies between 27 and 2*9; but the density of the whole earth, derived from pendulum experiments, of whidi mon; will be said when treating of eleratory forces, is about •r[f ; no that it ia* evident that the ponderable matter of the

fKmoi of the earth ia very much denser than the matter of he crast, which is quite coDsistent with the previous anppolition of origiiial flntdity ; for though gases mutually permeate ittch other and diffuse themselves, liquids, when they do not :xercise a chemical action on each other, obey the ordinary nws of ^avity, and arrange themselves in the order of their knaity. The density of basalt does not usually exceed 3'I, lo that the difference observ«bIe hy the Geologist in the den- iHiea of rocks is very small. The radius of the earth is W08 miles ; but if we suppose it 4000 miles, and divide it nto 10 equal parts, and then assume that in descending the lensity increases in an arithmetical progression by about 1*5 for each part, the problem will be thus stated: the tverage density in the first annular space of 400 miles will M 2"7 ; in the second 4'2, and so on, — the density of the hat 400 miles being about 16'2; a view of the CBSe which loea not appear inconsistent with facts, as it allows an in- Kease in density of '3 for 100 miles, which is probably more Bkan the thickness of consohdated strata.

The increasing density of the earth, from the surface to the lAntre, has an important bearing on the nature of piutonic fOcks. The density of none of the true granites equals that Iff basalt, and it rarely exceeds 2'6, so that it is highly impobable that granite has proceeded from a deep-seated source. Branite does not throw out dykes either cutting through the Bsta or filling up cracks produced by fracture in them ; its fens are principally confined to the metamorpbic rocks, and f does not exhibit lava currents : it may therefore be con- Ndered a tower portion of the immediate crust of the earth ''hich bas been liquefied and forced to the surface at various 'podia, but has not been erupted. The full development ft crystals in these rocks requires stow cooHng but not great

Ere, and there is therefore no reason for supposing that 'ere ever far below the surface, xtendiug the inquiry to the crystalline schists, it will be

natmaUj asked whether any porticm of them may be sidered a part of the crust of the earth as it was at first c domi and consolidated. The alternation of limestone a micaceous beds with the more crystalline schists confinei question within very narrow limits, and if any rocks ▼isible can be supposed not to have passed througl sedimentary stage, they are probably only such rocks a highly inclined and distinctly bedded varieties of prot( which occur in the Alps, — being neither distinctly mi nor distinctly stratified. There is a similar difficulty in ( mining whether the homblendic rocks associated witl crystalline schists are metamorphic or volcanic rocks. ' density being nearly equal to that of basalts, assimilates to erupted rocks ; and modem Geologists have discover strong a resemblance between some of the strata asso( with the crystalline schists and the ashes, lapilli, & volcanoes, as to strengthen the belief that lava cm have been instrumental in the production of some meU phic strata. This portion, therefore, of the Earth's Mi History is a fitting introduction to the next, in which products of volcanic eruptions are recognized by their larity to and even identity with the mineral matter en from volcanoes either now existing or which have ej since the earth's surface assumed its present form, tb now extinct.

The truly volcanic rocks have been divided into three tions, — ^trachy tic, basaltic, and slavic, the last of which an observed amongst volcanic erupted substances whilst dyli basalt penetrate the walls of volcanic cones.

The trachytes are felspathic rocks, consisting of a h crystalline paste of compact felspar, with crystals of a and other minerals disseminated in the mass. Domite, phyritic eurite, pumite, phonolite or clinkstone, belong t division ; and there is a trachytic breccia to the produ of which mechanical action has contributed. Trac occur in countries where volcanoes are still in action as

/

SVDIHeNTAIty GEOLOGY. 73

fts 111 those where they have become estinct, and they nppear to have proceeded from a source immediately below the granitic crust. The chain of the Caucasus, Hungary, Transylvania, Auvei^c, Isles of Greece, Italy, &c., ami the , counties of Antrim and Down in Ireland, are good loeolities. Trachytpj as Andesite, acquires an enormous derclc^ment in South America, in the chain of the Andes of which it forms the summits, the heds being sometimes 14,000 or even 18,001) feet thick, as at Chimborazo and the volcano Guagua-PicLincha, and it is also observed in the volcanic districts of New Zealand. Trachytes are sometimes covered by tertiary strata, but uever by the secondary or older strata, and it has therefore been assumed that the epoch of their first appearance is that of the earlier tertiaries. In Auvergne they often form the boundaries of ancient and partially destroyed volcanic vents ; and it is not improbable that ia like manner the Antrim and Down trachytes are portions of the boundary of some great volcanic vent, which occupied the site of the present Lough Neagh, and through which much of the basalt of the district may have been poured out.

Basaltic rocks, in which augite predominates in quantity over felspar, arc augitic rather than felspathic rocks, and some of the varieties which are highly crystalline like greenstone cut scarcely be distinguished from that rock. Basalt has a considerable density, ranging to 3'3 in the more highly augitic varieties ; it cuts through granite and every succes- Mve rock, carrying with it and enveloping fragments of the rocks broken through. The remarkable lines of this ig^ie-ons matter, which may bo sometimes traced for very long distances, are called dykes, and, when exposed by the decomposition of the softer strata through which they have passed, stand out as walls, from which circumstance they hare derived that name. See fig. l.i, which is the celebrated dyke called Lady O'Cane's Bridge, and fig. 16, which representa another Tiew of it.

Rud1Mkntart Geology. 75

Basalt baring cut through granite, ronst have come from below it and the metamorphic schists, though there is no reason for supposing the depth of its source more than 100 miles. Basalt is rarely fouiKl nenr the summits of volcanoes, but usually at their b&se or surrounding them, and is anterior to the lava currents iriiieh recerfie it : it is very extensively developed in the vicinity of extinct volcanoes, and is justly eonsidered a truly volcanic rock. In many countries, as in Ireland and Scotland, it is spread out in extensive plains or beds, which are divided in section or depth into many successive layers, the structure of which is sometimes globular md sometimes columnar, as at Staffa and the Giant's Causeway, and which alternate with beds of ochre or ferruginous ■coria, as well as with beds which have probably been originally sedimentary, and are therefore metamorphic. Sometimes, as IB the vicinity of JoruUo, in Mexico, the basalt has been puffed up by the elastic gases below into small cones or bosses, which, having been subsequently cracked, emit aqueous and sulphurous vapours. These Hornitos, as they are called, cover in thousands the great plain of Mal- Pais, in which Jorullo rises, so that the surface resembles the hubbies on the top of a boiUng riscons fluid. In 1780 the heat of the hornitos was so great that a cigar couhi be l^hted by plunging it 2 or 3 inches into one of the lateral cracks. By the layers of ochreoua scoria the mass of basalt ia divided into successive flows, some of which either passed over the dried and conaohdat«d oclireous mud, or over the mud stiU under water where it had becu formed by showers of ashes ; and the connection of irregular or orbicularly crystallized basalt with columnar, the former capping the latter, is the result of the more rapid flowing and cooling of the upper portion. A beautiful example of this effect is exhibited at CraignahulHar, in the county of Antrim. 8«e fig. 17, in next page.

■wmmm'd

The slavic division can be studied in the phenomena oi active volcanoes. True lavas have been erupted subseque to the basalts : the kva of extinct Tulcanoes approaches closely to trachytes, being felspathic, whereas that of ej volcanoes, being augitic, is nearer to basalts, flows of lava are frequently separated by beds of ashes, a lapilli, &c., as may be seen in the vicinity of Vesnvius. eruption, supposed to be the first of Vesuvius, which in ti year 79 destroyed the cities of Herculaneum, Pompeii, I Stabise, and caused the death of the elder Pliny, consiatedj| ashes. It is impossible, in this small voluTtie, to describeM the phenomena of volcanoes ; but the great number octo^ recorded is shown by the ibllowiug approximfltive Table f(3 Girardin. And as the number of c.itinct volcanoes has a been very great, the eruptive forces of former and of existing I epochs were eijiial in intensity if estimated by the quantity of I , matter erupted.

aVDIMENTARY GEOLOGY.

n

Portions of the Earth.

On Continent*.

In Islands.

Europe . . . Africa . . . Asia .... America . • . Oceania . . .

4

2

17

86

20

9

29

28

24

11

46

Total. . . .

Peculiarities of some of the igneous rocks, and the effects of ijfmeous, and especially of eruptive rocks, on the eartKs trust; many of these rocks having been important agents in the successive disturbances of the earth's surface.

The wide extension of the granite group over the surface of the g^ohe must he referred to general and not mere local forces ; and the frequent co-existence of granite and metamorphic rocks proves that the causes which produced them were intimately connected together. In the Erzgehirge at Greier the granite has forced itself up, in three blunt hills, through the mica schist, which in its vicinity has been further changed into gneiss ; and in the county of Cavan, in a similar maimer, rounded hills of granite occur amidst an ancient metamorphic schist. In the former case, the granite has evidently been protruded subsequent to the deposition, and even to the partial metamorphism of the schists, though the exact epoch of protrusion is not determinable. In the granite of the valley of the Neckar, near Heidelberg, though the exact age cannot be settled, it is limited upwards, as the new red sandstone, now partially removed by denudation, once covered the granite, and was therefore deposited subsequently to it ; and such examples prove repeated action of elevating forces, by which the surface of the earth was disturbed and igneous rocks protruded at various epochs. — Granite forms either mountain masses, or veins. The veins are of various thicknesses, from a few inches to several feet, and massive granite is frequently penetrated by veins of granite of a different character, so that Leonhard designates the one, which is rendered porphyritic by disseminated felspathic cr^^^t«la^ \fi»vai--

tain granite; and the other, whidi is not porphjridc, yi granite. When granite contains hornblende, it passes ii syenite, and hy the passage of syenite into greenstone a a nection is established between andent and modem erupti rocks. In the Odenwalder, ^enite is trarersed by ma granite Terns, but a yein of the syenite has not as yet be observed in the granite, so that it is assumed that the syen is there older than the granite. Granolite or weisstein, which compact felspar is the principal constituent, has close analogy to trachytes or felspathic layas; it sometin assumes an independent massive form, and its veins travel granite. Veins of granite, granulite, and syenite often conti large fragments of gneiss and other schistose rocks, which the vicinity of the masses from which the veins have proceed are both much contorted and greatly metamorphosed. Meissen and Hohnstein, in Saxony, granite overlies the quad* sandstein, a result, it is supposed, of disturbance : at Chr tiania in Norway, and in the Hartz, it is found between t layers of primary schist and limestone, into which it 1: penetrated by veins, changing the schists into a species homstone; and many such examples might be cited fn similar districts. Greenstone, though it approximates granite by the intervention of syenite, is closely allied basalt, and forms therefore a connecting link between t two groups ; but whilst granite and syenite afford only vc obscure examples of intercalation with or superposition stratified deposits, greenstone is often so closely connect with both the non-fossiliferous crystalline schists and t primary fossiliferous schists, occurring not only in intrud masses and penetrating veins but also in beds alternating wi the regular strata, that Werner classed it with them. Schistc beds penetrated by greenstone are often contorted in a simil manner as by the action of decided igneous rocks ; and wh( the greenstone and schists are disposed in regular and paral strata, a distinct transition from one to the other can f quently be observed, though in some instances, especia where there is a thick bed of limestone, the separation betwe

Rudimentary Geology.

79

the two is very distinctly marked. It is thas that the more decided metamorphic theorists consider greenstone an ultimate result of metamorphism, whilst the eruptive theorists connect it with erupted rocks, and look upon its alternating heds as the products of so many >distinct eruptions. In the neighbourhood of Schwarzenberg the mica schist is penetrated by layers of greenstone more or less parallel to the stratification ; and as fragments of the adjacent rocks have been taken up by the greenstone, it has been suggested that the igneous matter has been forced into fissures corresponding with the natural lines of lamination of the strata. Some of these conformable dykes are more than 30 feet thick. This locality is rich in ores, especially magnetic pyrites, iron pyrites, arsenical pyrites, tin ore, black and brown blende, lead glance, and silver, and in simple minerals, — ^namely, garnets, vesuvian, .:;hlorite, epidote, tourmaline, prase, mica, calcareous and orown spar, and many others, the original composition of the 'o^^k being almost concealed by the ore it contains. Granular ime^tone and dolomite are connected with the greenstone lere as in other localities.

Greenstone is characterized by knoU-lile or conical masses, which are sometimes recognized at a distance as small lump-like excrescences projecting above the stratified deposit, and a columnar structure, though rare, is occasionally observed. The close resemblance between syenite and greenstone makes it desirable to have some rules for distinguishing them : Cotta gives the following —

Syenite.

The dark green hornblende, blended with the yellowish or red Labrador fel- •par and weathering nearly together, both form on the surface an iron-shot crust.

Colour. — Reddish or whitish gp%en.

Occasional Ingredients. — Almost constantly small brown crystals of titanite, and aometimes quartz and mica.

Fissures, lined with epidote.

Forms. — Massive and angular, and stitote mountain masses.

Diorite, Grunstein or Greenstone.

The mostly white albite weathers sooner than the dark green hornblende, so that the crystals of the latter project above the weathered surface.

Green, approaching to black.

Iron pyrites and magnetic pyrites (simple sulphuret of iron).

Also common.

Conical : knolls, masses, small masses, layers, or veins.

Serpentine i» allied to greenstone^ and exhibits cdmikr physical features. Its veins penetrate the crystalline schista, as well as granitic rocks, and it appears to have been protmded amongst the beds of the Jura formation, being abundant in the Alps. The well-known mixture of serpentine ▼eins in marble is a curious example of metamorphic actioDi as it indicates diffusion rather than penetration, the veins having no connection with any great mass. The fissures « and cavities of serpentine are often covered with asbestos. Porphyry Crroup, including felspar porphyry, pitchstone porphyry, and augite porphyry : rocks which all affect a similar physical character, appearing in lump-like masses and in dykes projecting into granite, crystalline schists, and various stratified deposits. They frequently appear as isolated hills amongst other rocks, and have been noticed in all parts of the earth. Felspar porphyry, including homstone and claystone porphyry, forms extensive masses, and also dykes of great length, which frequently contain fragments of the rocks passed through, and are sometimes bounded by a breccia formed by their attrition against them. The pervading form of this group of porphyries is rather angular than round, and as tabular beds and columns are common, there is much analogy in structure to basalts. Metallic veins are rare in the porphyry, though more frequent at its contact with schists. A remarkable examjde of these rocks is seen in the Tharander Walde, where several powerful dykes proceed in tangents rather than in radii, from a roimd knoll more than a mile in diameter. The main mass lies between gneiss and clay slate, and its dykes ramify through both. At the Zeisigsteines it becomes columnar and at the Esberge still more so, the overlying rock being quadersandstein. Between Freiberg and Frauenstein, dykes many miles long cut through gneiss, and are themselves penetrated by metallic veins. Pitchstone porphyry, including pitchstone and pearlstone, is comparatively rare, and is usually connected with other porphyries, which it either penetrates in mass or by dykes : it occurs in Saxony, in Hungary, and ex*

Rudimentary Geology. 81

tensivelj in the island of Arran : it appears also in the felspar porphyry district of Antrim. Melaphyr {augite porphyry, augite rock, ^c.) is sometimes amygdaloidal, and generally forms small knoll-like masses, or irregular dykes which penetrate massive and schistose rocks and effect important changes in the fossiliferous deposits. There are many varieties of this rock, and it hecomes porphyritic from detached crystals of augite, of mica, or of felspar. By its hladder4ike and amygdaloidal structure, and the occasional appearance of columns, it approximates to hasalts, and it has heen rendered remarkable hy being in juxtaposition with masses of magnesian limestone or dolomite, which Von Buch supposed to have been produced by a contemporaneous emanation from the interior of the earth of magnesian vapours and their action on pre-existing Umestone. The Basalt Group brings up the working of ancient igneous forces to the very threshold of the existing epoch. In basaltic countries, isolated conical hills are common, and knob-like masses of all sizes and heights project above the surface of the country, being sometimes connected together in one great mass. Basalt is either spread over other strata, Uke a stream of lava, or alternates with them, having penetrated through both the ancient ig« neous rocks and all the fossiliferous strata up to the post-tertiary, some varieties intersecting others of more ancient date. Where basaltic dykes have crossed other rocks, remarkable chemical and mechanical effects have been produced: granite, gneiss and mica schist have been reddened, and (especially the mica) partially melted ; clay slate burnt and hardened; sandstone reddened, glazed, and reduced to a columnar structure; stone and wood coal, charred; limestone sometimes deprived of its carbonic acid, and frequently reduced from an earthy or compact to a crystalline state; shale changed to jasper ; fragments of imderlying beds raised to a higher level, and the regular strata disturbed and uplifted, though not to the same degree as by granite and porphyry, the chemical exceeding the mechanical effects in this class

d5

of rock. Phonolite (clinkstone and clinkstone porphyry) is not so widely spread as basalt. Passages between clinkstone and trachyte may be traced, and, where this rock occors in masses, the larger generally possess more of the trachytic, and the smaller of the phonolitic character. Ck>lunmar and tabular forms of structure are obsenrable as well as dome-shaped or conical hills. The trachytes which occur in the well-known Siebengebirge, in Hungary, in the South of France, and in the Andes, pass occasionally into phonolite, and on the other hand varieties of phonolite are found associated with basalt. Lava in its basaltic, greenstone -like, trachytic, porpbyritic, leucitic, and slag-Uke yarieties, exhil»ts a dose analogy to other erupted rocks of all epochs.

Volcanoes and Earthquakes, — In order to comprehend the influence of volcanoes, which are the foci of eruption, as a modifying geological force, it is necessary to bear in mind that they are intimately connected with earthquakes, — the earthquake often preceding the volcanic eruption, and both being the result of the movement of matter in the interior of the earth. It is thus that whilst the lava which now flows in streams over the sides of the crater, and the dykes which penetrate its walls, are illustrations of the more ancient igneous products, the movement of the earth's crust, its upheaval or its depression, and the cracks which fissure it under the action of earthquakes, or earth-waves, are equally illustrative of the mechanical effects of former forces of a similar nature.

In the great earthquake of Chili, 19th of November, 1822, the shock was felt along the coast for 240 miles, and by many natural appearances, such as the exposure of beds of shells at times of the tide when they were not before so exposed, it was ascertained that at Valparaiso the uplifting amounted to three, and at Quintero to four feet ; and as the great chain or axis of disturbance along which the volcanoes are arranged is at a considerable distance, it is reasonable to suppose that all the intervening country was similarly raised. There are traces of more ancient shocks which have raised the coast

Htjdimentary Geology. 83

about 50 feet. In the rocks of the coast which are granite and syenite, there are numerous parallel cracks which can he followed landward for 1^ mUe. The effects of this earthquake extended oyer a space of 100,000 square miles. An earthquake shook violently part of Wallachia on the 11th January, 1S38 ; many parallel fissures were formed, and then filled by matter forced upwards. The earthquake which destroyed Lisbon, 1st NoTcmber, 1755, was felt throughout Europe so far as Norway, on the north coast of Africa, in several of the West India Islands, and by many ships at sea. At Lisbon, an adjacent hill was split in two, and the new quay sunk 600 feet below the water. The changes of level of the celebrated Temple of Puzzuoli, near Naples, — the rising and sinking of the land in Scandinavia, — the sudden appearance of islands forced up from below, — are all phenomena which exhibit the still continuing action of elevating forces. JoruUo, in Mexico, is an example of volcanic action combined with extensive elevation, and Skaptaar Jokul, in Iceland, poured out a stream of lava which may vie with many of the ancient basaltic streams — being about 50 miles long, 12 miles wide, and on an average 100 feet thick. The contemplation of such wonderful effects of still acting causes prepares us to estimate forces which acted according to the same laws in former epochs. Whilst, therefore, water has worn down, transported, and re-deposited mineral matter in nearly regular and horizontal order, or, in other words, restored the level of the earth's surface, that level has been disturbed by the action of internal forces, which have elevated some portions of the surface above others. Elevation of the earth's crust is necessarily accompanied by contortions and by cracks var3dng according to peculiar circumstances : where, for example, the elevating force acts on a point or small space, an isolated mass or mountain may be formed with cracks radiating from a centre; or should the superficial pressure be diminished, the crust may be raised like a great bubble, and, finally separating at its apex, form the circular wall of what Yon

Buch calls a crater of eleviLtioii : if it acts on the line of a crack, either one side may be uplifted so as to form a steep precipice orerhanging a plain (an appearance not unusoal in nature), or both sides forming two precipices, with a yallej of elevation between them; and again, if upheaval takes place where one set of cracks crosses others, there will be various modifications of the primary ridges. Such forces, continuing to act at intervals for ages, have produced the great and the cross chains of mountains. Von Buch, pursuing these inquiries, observed that in certain districts the mountain chains, the strike of the strata, and even the great valleys, had certain predominant directions; and £lie de Beaumont, extending Von Buch's researches, foimded upon them, in 1830, his Hieory of Elevadon, according to which aU mountain ehaifu of the same ag% have the same genial direction. His Theory, as now modified, may be thus stated ; that the earth's crust has been elevated into mountains at various periods by forces acting in the direction of great circles of the sphere ; and to determine the relative ages of such upheavals, he assumes that uplifted and highly inclined strata were deposited prior to the upheaval which disturbed them, and that horizontsi strata which overlie the inclined or disturbed must have been deposited subsequently to such upheaval ; and hence that the epoch of elevation may be determined by the relations of successive sedimentary deposits to each other. M. Elie de Beaumont at first distinguished about fifteen systems of elevation, of which the twelve following are the most remarkable.

1. System of Westmoreland and HunsdrUck. — Direction of elevadon, n. e. j- e. and s. w, \ w. No newer strata than the Silurian, and probably a part of Devonian, uplifted. This includes the EiM, the Taunus, the Isle of Man, and South Shetland. 2. System of part of the Vosges, — Direction, b. 15° s., vr. 15° N. Mountain limestone, but not the coal-bearing strata, uplifted. To this belong the hills of Bocage, in Calvados. 3. System of the North of England. — Direction, 8. — N. The coal-bearing strata are the most recent affected

Rudimentary Geology. 85

in this elevation. 4. Systan of the Netherlands and of South Wales. — Direction, n. e. — s. w. The whole of the coal formation affected. 5. System of the Rhine, — Direction, 8. — N. or s. s. w. — N. N. E. Strata to the Zechstein (magnesian limestone) uplifted. The Vosges, Schwarswald. 6. System of Bohemian and Thuringian Forests, — Direction, 8. E. — N. "w. The keuper is the newest formation disturbed. LaVend^, Bretagne. 7. System of the Erzgebirges, — Direction, s. w. — N. E. The oolite or Jura, but not the quadersandsteiu, affected. C6te d*Or, Mount Pilas and the Jura in part. 8. System of Monte Viso, — Direction, n. n. w. — s. s. E. The older but not the newer chalk affected. 9. System of the Pyrenees and Apennines, — Direction, n.w. — s.e. The younger or upper chalk, but 'not the tertiary strata, affected. This system being parallel to No. 6, it is often difficult to separate one from the other. Hartz, Teutoburger Forest, &c. 10. System of Corsica and Sardinia, — Direction, s. — N. The lower tertiaries, but not the upper, affected. The basalt of Hesse. 11. System of the Western Alps. — Direction, n. 26° e. — s. 26° w. The newer tertiaries affected. 12. System of the main chain of the Alps: from Wales to Austria. -^a^ Direction, w. — e. or e. n. e. — w. s. w. A portion of the post-terti%ries affected. Monte Ventoux, Leberon.

M. Elie de Beaumont has since extended his determination to at least twenty-one systems of mountains, the relative ages of which have been determined with more or less precision, — namely, the systems of La Vend($e, of Finist^re, of Longmynd, of Morbihan, of Hundsriick, of the Ballons, of Forez, of the North of England, of the Low Countries, of the Rhine, of Thuringerwald, of the C6te d'Or, of Monte Viso, of the Pyrenees, of Tatra, of Sancerrois, of the Western Alps, of the main chain of the Alps, of Tenare and of Vercors ; and M. Durocher has pointed out several other systems in Scandinavia. The difficulty in determining the actual connection of a chain of mountains with some definite system is sometimes great, as disturbances and eleva.tions frequently occur in the same district

and nearly in the same direction. This periodic recurrence of pulsations, as it were, of the earth's crust in particular districts, rather than indefinitely over the whole surfiue, has ted M. de Beaumont to inquire whether the various systems of mountains resulting from the action of some central force, and therefore necessarily exhibited in great circles on the surfiuie, may not he reduced to some geometric law ; and the result of his investigation is, that the phenomena may be best exhibited by dividing the surface of the sphere or earth into tw^ regular spherical pentagons produced by the intersections of fifteen great circles. The various systems of mountains may then be arranged around the angles of the pentagons, and be considered as produced by disturbances acting in auxiliaiy great circles passing through the angles of the pentagon and forming so many bulging or even geometric projections (like tibe boss of a shield) of which the angles of the primary pentagmis are the apices.

Whatever opinion may be formed of the details of M. Brongniart's theories, in their groundwork they are correct, and they have had and will have a most powerful effect on the progress of geological science.

The fact has thus been established, that at successive epochs the earth's crust has been broken up and elevated, whilst various igneous rocks, the most superficial of which was probably granite, were lifted up and forced into the cracks of the disturbed crust ; but the mode in which the great elevating force has been developed has yet to be investigated, and here indeed is a difficulty, as direct observation can only extend to a mere film of that earth the surface of which it has affected in so striking a manner. The facts, however, of disturbance are palpable, and the nature even of the forces producing them can be inferred, though not demonstrated by observation. Electricity may be fairly classed with these forces, if only as a secondary cause ; and it may be affirmed on sufficient reasons that heat was a primary one. In 1837 Gustav Bischoff assumed a fluid condition of the central portions of the earth

from heat, and from physical considerations deduced that hot springs, the production of massive rocks from the cooling of the fluid mineral matter, Tolcanic eruptions and earthquakes consequent on the expansive force of steam produced by contact of water with the still heated and fluid internal mass, were the results of such a condition.

Sir H. Davy proposed a chemical theory of earthquakes, founded on the properties of the newly discovered bases of the alkalis and earths. These bodies, when brought in contact with air and water, are oxydated with great rapidity, producing an intense ignition : he therefore considered it probable that potassium, sodium|», calcium, &c. exist in great quantity in the interior of the earth, and coming into contact with water which had penetrated by cracks or filtration, is suddenly ignited and oxydated, giving rise to volcanic fires and to the formation of various stony compounds, which, as lavas, are then erupted. The great quantity of sodium in combination with chlorine, iodine, and bromine in sea water and in salt deposits indicates that this cause must not be entirely rejected in accounting for local phenomena, though it is insuflicient to accoimt for the more general phenomena of disturbance.

The theory of Cordier is purely thermometrical, and is very generally adopted by Greologists : it may be expressed under the following heads :

1. The earth has an internal temperature, which is independent of the solar heat, and increases rapidly with the depth.

2. The rate of augmentation is different at different places ; in one country it may be double that of another, and the difference is not in a constant ratio with either latitude or longitude.

3. As the total mass of the earth is about 10,000 times greater than that of the waters connected with it, it is more probable that the original fluidity of the earth was due to heat than to aqueous solution. The heat was very great, as the present temperature at the centre of the earth, supposing a

regular progression in the increase downwards, exceeds 3500 of Wedgewood's pyrometer = 450,000^ Fahrenheit.

4. A temperature of upwards of 12»000^ Fahrenheit^ which is sufficient to melt most of the known rocks, would exist at depths below the surface varying from 80 to 160 miles, supposing the increase to he regularly progressiye ; hut it is highly probable that the dense fluid portions of the earth are much better conductors of heat than the crust, and therefore that this high melting temperature is acquired, and that the actual fluid portion commences at a still less depth.

5. As the crust of the earth, leaving out of consideration sedimentary deposits, has been consolidate^ by cooling, its formation must have taken place from without inwards, so that the more superficial crystalline rocks are the most ancient; and this accords well with the small density of granite which appears to have been uplifted under so small a comparative pressure as not to have been actually erupted. The thickness of the crust will continue to increase until the cooling has attained its final limits.

6. There is no reason for believing that the solid crust can be more than from 60 to 100 miles thick, and it is probably much less : that it is very unequal, is shown by the variation of iutemal temperature, which cannot be explained by different conductibility alone. It possesses some degree of flexibility, and the phenomena of earthquakes are due to the expansive force and consequent pressure which the fluid nucleus within exercises upon it.

7. The solid crust continues to contract as its temperature diminishes in a greater ratio than the central mass ; and as the velocity of rotation must increase as the diameter of the planet diminishes, there will be a tendency to diverge further firom ' the spherical form, and hence the fluid matter within will press against the contracting crust, and produce volcanic eruptions. M. Cordier has calculated that a contraction of

^ a ^ g ^^ of an inch in the mean radius of the earth would be sufficient to force out the matter of a volcanic eruption.

I

Rudihentaby Geologv. 89

In this hypothesis, the zones of least tliickness of the earth must te the sites of volcanoes. Professor Kogers, of Philadelphia, has traced the progress of three great earthquakes in the United States, the synchronous lines of which, or lines Blong which the shock was felt at the sanie moment, extended 31)0 miles in a direction from n. e. to s.w,, the progressive motion being to the eastward, at the rale of 30 railea a minute. It is highly probable that electric forces called into action by change of temperature have aided in the production of these effects, and that partial differences in the conductibility of different strata have increased or diminished the intensity of earthquake shocks or waves, and by producing local cracks have been one of the causes of the various subterranean noises which accompany these great and fearful phenomena.

It may be added that M. Rozet, by comparing a series ot' pendulum experiments with the geodetic measurements in France and with barometric observations, has proved that lofty mountain chains are not the only evidences of the disturbance of the crust, but on the contrary, that the apparently level surface of the earth conceals many undulations which, by their effects on the pendulum, have evidently been pro- . dnced by the swelling up of denser matter within them. M. Rozet has further established the fact that the ocean has not, as BO many English Geologists imagine, an invariable level, but participates in the movements, and conforms itself to the I Tarying level of the solid crust. " We find," he says, " that the true level of the ocean is below the mean elliptic level in 1 the Polar Sea, on the coasts of Spitzbergen and Greenland, as dso on the coasts of Great Britain, at the Equator, and in the Southern Ocean, and that it is above that level on the coasts of Norway and ot the Cape of Good Hope." This inequality of absolute level ia the ocean, consequent on the protuberances and hollows of the crust of the earth, must have varied with, Uid been in proportion to, every great disturbance, or to the ■mount of matter protruded above the mean elliptical level of the liquid nucleus. Ey the caluuktions of M. Rozet, the mass

of the Alps, if entirely composed of basalt, should deflect the plumb-line only 13'''5, whereas on the eastern flank of these mountains the deflection amounts to 28'', and on Mount Cenis itself to 8"*5 ; whence it is concluded that this great deflection is due not merely fjo the mountain itself, but to the denser matter proceeding from the interior of the earth, which had been forced into the protuberance, on the summit of which the mountain chain rests. It is not therefore the sedimentary deposits alone which have acquired an irregularity of sur&ce; the general form of the earth has been altered from its origiiial condition, not by one but by many successive eommotioD8» and as the thickness of the solidified crust has continued to increase, the most recent chains of mountains are necessuilj the most elevated.

The violent intrusion of igneous matter either into cracks of the crystalline portion of the earth's crust or amongst the more purely sedimentary strata must tend to crush, consolidate, and contort the strata, and, wherever the crust has been rent asunder, to produce a jar or vibration of the solid matter, which jar is transmitted like the vibrations of sound through the solid crust, and constitutes an earth-quake or wave. TliiB theory of Young and Gay Lussac has been lately most admirably worked out by Mr. Mallett in his Reports to the British Association. It is highly probable that in some ctses the igneous matter injected from below and the wave of the solid matter has only affected the lower strata, which haTe been contorted, whilst the beds above them have remained apparently unaffected by the disturbance. In such cases then would be an apparent but not a real want of conformabilitf. In other cases igneous matter may be forced to the sur&oe, u in volcanoes, and comparatively little jar or earthquake produced. In the theory of Cordier, the central nucleus of the earth is considered a liquid of ignition, but it has been mged that the great pressure would retain it in a solid state: i( however, such be the case, wherever the pressure was relieved the matter would become locally liquid, and thus agree with

Rudimentary Geology. 91

the opinion of Mr. Hopkins, that there is not a universal central sea of molten mineral matter, but local lakes from which volcanic cents are supplied. These two theories are therefore reducible to one. To the probable influence of electricity should also be added that of magnetism, as the beautiful discoveries of Mr. Faraday have made it easy to connect it with great physical phenomena. All bodies are either paramagnetic or diamagnetic, that is, they are either in a state of magnetic attraction or of repulsion : if, therefore, a change in these conditions be brought about by any agency, whether it be heat or electricity, the cohesion of matter will suddenly cease in one place and at another be called into action, giving rise to violent disturbances even in the solid matter of the earth.

Practical Applications. — The practical importance of metamorphic, plutonic, and volcanic rocks requires a brief notice. The metamorphic includes those varieties of clay slate which are used as roofing slates ; and the physical condition of the strata is therefore a guide in searching for slates, as their peculiarities and value are due to metamorphic action. The lesser cleavage of the slate is usually transverse to the dip of the beds ^ and the probable value of the slaty beds may be estimated by the presence or absence of this character, as the planes of separation by cleavage are more regular, and possess a more even surface than those of stratification. For flagging, many crystalline schists are excellent, as the surface of stratification is sufficiently even in the gneisose varieties of mica flate and in gneiss ; and they also often furnish good rough

^ building stones, affording a flat bedding and a very durable composition. In these three varieties of metamorphic schists

. the important physical character of specific gravity is nearly uniform, as it ranges in each from about 2*6 to 3*1, which is the specific gravity of the more dense or indurated varieties which are frequently homblendic or greenstone schists. As road stones, the latter only should be used, as other varieties ipeedily break up and are reduced to mud. Roofing slates

ought to split thin and even, hnt should neither deare into fragments nor hreak off in scales ; they should not absorb much T?ater, as it induces the growth of moss, which speedilj disfigures them and produces damp. Though the dark grej Tarieties are most approved, the silver grey are usually the most durable. Some varieties of mica slate afford good roofii^ slates, which, however, are seldom so thin and even as the less crystalline schists. Wales is the most important locality of the United Kingdom, but there are very good slates in the South-west and in the South of Ireland, as at Killaloe on the Shannon, and in the island of Valentia, and some from the mica slate of the North of Ireland though they are inferior to the true slates. Of foreign localities, that of Lehesten in the Thuringian Forest may be mentioned.

When mica slate and gneiss are used as building stones, gneiss, or highly gneisose varieties of mica slate, should be selected for situations exposed to much wet, as the &ier grained, or more slaty varieties, rapidly disintegrate; but where the building or any of its parts are likely to be exposed to much heat, as in the sides of chinmeys and fireplaces, the true mica schists, or the fine-grained varieties, are preferable. The city of Freiberg is built of gneiss, and its streets paved with the same material.

The most important of the plutonic and volcanic rocks are, granite, syenite, porphyry, greenstone, basalt. Many varieties of granite are excellent as building stones, though expensive in working to definite forms. Some of the most important public works of Great Britain and Ireland, France, and Russia (Petersburg), are of this material. In selecting gra^ nite, those varieties in which the constituent minerals are very small and the scales of mica superabundant should be avoided; and as a practical test it is wise to notice the country imme* diately around the quarry, as the sandy varieties rapidly dis' integrate, and form accumulations of micaceous sand. The Hayter or Dartmoor granite, the Aberdeen granite, the Kingston (Dublin) granite, some beds of the Moume or county of

Kodiuentary Geoldgv. 93

n

u)ite, and the Guernsey or Channel Islaud granite, Iknown for their excellence. In some of the quarries mg of the grEinite is more defined thtui in others ; rever this is the ease, or where marked cleavages or Bvail, the working is much facilitated. Many old 1 works and statues were formed of granite, and it is 1 for colossal works, as it takes a fine polish ; for i, the great fountain shell or vase before the Museum Berlin, and the pedestal of the statue of Peter the Great St. Petersburg, are of Northern granite, being sculptured 31 erratic blocks. The splendid Scotch granite columns in Tcstibule of the Fitiwilliam Museum at Cambridge are .ntifbl examples of a modern application of this rock to the 1. Millstones are occasionally manufactured of granite. a road stone, those rarieties which have at once a fine-ined and a close firm texture should be preferred, as the ■e crystals of coarser granite are liable to cleave into frag-its. The specific gravity of this important stone varies n 2'5 tfl 2-6, vihich is very analogous to that of the metarphic Bchiats, — a circumstance which gives weight to Keil- 's (pinion that in many cases it is a metamorphic and not :niptive rock. Syenite is even a firmer stone than granite, its specific gravity, which ranges from 2'5 so high as 3'0, roximates it to greenstone. Many beautiful varieties of rock arc found in Ireland. In Dresden, syenite is hewn regular parellelopiped blocks for paving, a purpose for ;h its dnrabUity and firmness peculiarly fit it ; and as a L stone generally it is excellent. Many ancient Eastern CB were formed of it, and from its tenacity large objects ! been fashioned out of single blocks. 'OTphyry. — This term baa an extensive application, as it be used in reference to any rock in which isolated crystals, illy of felspar, are imbedded in a distinct paste. As a iing stone, all those varieties having a soft argillaceous ) must be rejected ; but there are many which afi^ord ^h building stones, and also good road stones, easily

U.

breaking into proper forms and sicesy binding well, keejang dry, and being tolerably free from dust, — a consideration too little attended to in the selection of road stones. From the beauty of its colours, some varieties of this rock have been largely used for columns, monuments, and vases. The red, brown, black, and green antique porphyries are well known to the student of ancient art. The red porphyry of the ancientB is composed of a felspathic paste of a violet-red or wine-red colour having small crystals of black hornblende and grains of specular iron disseminated through the mass, and isolated crystals of a rose-red felspar. The paste contains 62 per cent of silica, the isolated crystals 59. The crystals contain nearly 8 per cent, of soda and potash, of which only -}- is potash; the paste 6 per cent., of which ^ is potash. The paste is very rich in magnesia, the proportion being so high as 5 per cent. ; in the crystals it is less than 2 per cent. This porphyry is distill-: guished from that of Elfdal by a lesser proportion of silica and a greater specific gravity, the quantities being thus : Red po^ phyry, silica 64; specific gravity 2*763: Elfdal porphyry, silica 78 ; specific gravity 2*623. It is to this excess of silica that the superior hardness of the Elfdal porphyry may be ascribed; and, as M. Delesse observes, the density of the po^ phyry may be considered an index of the quantity of its silica and consequently of its hardness. In modem times, the meet remarkable porphyry works are at Elfdal, in Sweden, and Kol3rvan, in Siberia. The Elfdal works have been established about sixty years ; they are in the province of Dalame, amidst wooded mountains, and in a wild country. The blocks are worked into form and polished by well-adjusted machinery;. I and most beautiful works of art as columns, vases, chimney ornaments, and tables, are produced, rivalling the rosso-antico» or ancient red porphyry. A magnificent vase of this porphyryi at the country palace of Johannsthal, is 10 feet high, and at its summit 1 6 feet in diameter : it rests on a base of granite. The principal d^p6t of this manufacture is Stockholm. In the workshops of Kolvvan, in Siberia, equally beautiful sped-

RUDIMENTAttV GEOLOGY. 95

R of art are maaiifactared, aud forwarded in large quan-ft

to St. Petersburg. The blocks are sometimes of great

a being employed to draw a single block. Some

i porphyries of Hungary resemble tbe grey porphyry,

diglioue of Romaa artists. The specific gravity of

s from 2'4 to 2'8, aud it may be observed that

intiful polish it takes is a principal cause of its extreme

ility; many works formed of it remaining uuinjured for

moiigst the ruins surrounding them.

lutene. — The specific gravity of this rock ranges from

■'3'0, and though its e:(treme hardness, and the difficulty

g it without sphnters, render it less fitted for regular

t may he used with advantage as a rough building

i, and for a road stone is excellent. The porfido verde-

r green porphyry of the ancients, noticed under por-

i a greenstone porphyry, the base being greenstone,

kirhite and green isolated crystals of felspar. TheCorsican

^»ck is a compact greeustaae with globular concretions.

—This rock, so remarkable for the columnar struc-

D beautifully exhibited by many of its beds, as at Staffn

e gravity, varying from 2'8 to 3'1. In the more dense

s its very great hardness makes it difficult of use for

i work ; but for rough building, and especially for sea

B exposed to much wear, it is excellent. For paving

i it would also be admirable, were it not that the sur-cs

polished and shppery j but as a road stone it

jxcelled, making at once a firm, durable, and dry

Though not common, some of the sphynxes and hons

p Egyptians were formed of basalt. Trachyte and the

r felspathic lavas, and the various other products of

t and modem volcanoes, naturally come into this sec-

■ In the county of Antrim largely, and in the county of

E in small quantity, trachytic porphyry has been found,

n Antrim a columnar structure. It appears also to

Pjiroduct of the volcanic districts of New Zealand, It

forms a hBndsonie and durable building stone. Uva products, such na tuCi, the Romnns used thi tHvely, as is observed in tbe ruins of Pumjicii : wlu they Bse very light, and may therefore be often ap advantage where that quality, combined with strci^ importance : their absorbent quality renders walls fi them very dry.

Ophiolite or Serpentinf. — The mineral ' serpen which name a massive and coniparatively impure vt designated, la a bisilii^te of magnesia, and has I known from the earliest times. In all parts of tt some of its larietiea have been used in the fonv images for idol worship, and iu the manufacture \ columns, pipes, &e. The rich green and bronze ti finer varieties, and the high poUsh of which they ceptible, render it highly ornamental and valuabk Saxony it is still extensively worked. When veining ( of lime, it becomes the ophicalce of Brongniart, of » green marble of Galway js an esnmple ; when porjj is his ophite.

Limestone. — It is associated with other metumorpl in a manner which deserves especial attention. It stratified with mica schist, in layers varying in thick a mere film to beds several feet thick, and exhit^ metamorphic change by a highly crystalline structarbl the crystals are not too large, it becomes a graoul and when veined, as in the county of Galway, serpentine, forms a verde-antico. Such marble i including the finest statuary marble, which were ,| called primitive limestones, are of various ages; here noticed, ond that of Donegal, belonging to mela tocks of a remote epoch, whereas that of Carrara it lively recent. In metamorphic districts, such t schist country of Derry, Donegal, Scotland, &c., this S becomes a resource for lime, but it is impossible to n mode of distribution and the narrow scale of its devefi

Jlogy. 97

led with the inountaiii limestone of the cwbomleroin dulk of the cretaceous systems, without perceiriiig Saceous or muddy deposits there predominated. te Depontg. — la Europe the plutonic and metainor-

■ Bie the great d^6ta of metallic ores ; and in South idough gneiss is less productive and the ores con- i the overlying strata, it is highly probable that the K also been subject to metamorphic action, and that reins have been connected in them, as in the crystal- tSj with electric phenomena.

-English iron is obt^ed from an ore not connected wnorphic strata, which will be noticed in its proper at the celebrated Swedish iron is procured from mag- I ore connected with rocks of this class, and forming iDiBsses in Taberg, in Smoland. This ore occurs in pb sometimes altemate with the metamoiphic strata mora, and various other places in Sweden, Norway, fee., and it has also been found associated vrith plu- l Talcanic rocks. The fer ohgiste, specular or Elba BOmetimes replaces mica in mica schist, and is ussohh adularia at St. Gothard. The peroxide of iron UU and beds in these rocks, though it is also found,

■ the other ores of iron, in other deposits. Manga- B peroxide has been found in metamorphic rocks, but B more especially to sedimentary deposits.

k — Copper pyrites, or bisulphuret of copper and iron, L important of copper ores, occurs principally on the It in gneiss and mica schist; in Cornwall, and in the

Ireland, in varieties of clay slate ; in the Hartz in nrata (or the old grauwacke) ; and in Tuscany at pott of serpentine trapp (gabbro) with the tertiary hrhis mineral occurs also in the bituminous or copper npferachiefer), a portion of the zechstein, magnesian i, or Permian formation. In the Oural mountains,

, the double sulphuret of iron and copper is rare, placed by the simple sulphuret of copper, the strm

being probably sedimentary : this ore occurs also in the porphyritic district of Tyrone. The other ores of copper do not here require a practical notice.

Lead. — Galena, or bisulphuret of lead, occurs in plutonic, metamorphic, and fossiliferous sedimentary deposits.

Silver. — Bisulphuret of silver, the most important of its ores, has been found in gneiss and mica schist and in their associated limestone, in greenstone slate, clay slate, syenite, and porphyritic greenstone. It extends up to the zechstein; but it should be here observed, that in some of these cases, as in Mexico and Peru, the veins run from the metamorphic to the ordinary sedimentary deposits, and have therefore been manifestly connected with the cause of metamorphic action.

Tin. — Binoxide (deutoxide) is the most important ore. In Cornwall, the great source of British tin and the most important one in the world, the ore occurs in granite, and also in killas, a partially metamorphic schist ; and in other parts of the world, in granite, in metamorphic schists, or in porphyry, or porphyritic schists of the secondary class. Like gold, it is also worked as stream tin in sands proceeding from the disintegration of the tin-bearing rocks. Zinc. — Bisulphuret, usually associated with bisulphuret of lead. The carbonate belongs to various mineral deposits, extending even to the tertiary.

Mercury especially belongs to primary and secondary fossiliferous strata, though it is foimd occasionally in mica schist or crystalline metamorphic rocks, and in Haute -Vienne dispersed in globules in granite. The rich ore of mercury, cinnabar, of Almaden in Spain, is procured from grauwacke (primary) strata, and has been worked for ages.

Antimony. — Bisulphuret of antimony is rare, and found in veins traversing granite, gneiss, and mica schist. Molyhdena, — The bisulphuret is found generally, in small masses, in granite and mica schist, and occasionally associated, though sparingly, with ores of tin, as in Cornwall, &c., and still more rarely with copper pyrites, as in Norway.

Gold has been found in Brazil disseminated in considerable

Rudimentary Geology. 99

quantity in quartzose and cbloritic rocks, which belong to the metamorphic system; and auriferous sands, which contain also platinum and diamonds, are the result of the decomposition of such rocks. Gold has in other places heen found in veins traversing metamorphic rocks, from which the Wicklow gold sands have proceeded ; and indeed the greater proportion of gold is obtained by washing from auriferous sands. Gold is very widely difPused in Nature, though usually in small quantities. In Bussia the value of gold obtained from the Oural mountains amounts annually to about three millions sterling ; but that procured from the New World exceeds greatly even this large return. Independently of the old mines of South America and those of the southern portion of the United States, California furnished to the Philadelphia Mint in 1850 six and a half millions sterUng of gold, — a quantity which probably exceeds that furnished by the rest of the world. An announcement has also been made in the public journals of the recent discovery of valuable gold mines in Australia. Platinum is associated with gold in the auriferous sands of Brazil, of Russia, and of Wicklow in Ireland ; it has also been discovered in France.

This general occurrence of metallic ores in rocks which have undergone a metamorphic change, though at very various epochs, their occurrence in veins, and the facts observed by Mr. Fox of the conduction of electricity by mineral veins, and the development of metals and minerals near the contact of highly metamorphic strata, stated by Keilhau, are strong reasons for ascribing their jpresence under such circumstances to an electric cause.

FeiTis, — As the term vein occurs frequently in this section, it is desirable to explain it. The idea which the word conveys is distinguished from that of dykes, as it implies a waving rather than a rectilineal course ; but this distinction is not always preserved, as many veins, and particularly metallic lodes, are rectihnear. Veins may, however, be placed in two sections ; namely^ those which^ unconnected with any great

extraneous mass of matter, originate in and are confined to the rock in which they occur, and those which spring from and are connected with some great extraneous mass. The first may he found in all rocks, are often so fine as to be quite capillary, and frequently intersect each other, forming a complete net-work: they are considered veins of segregation, having heen probably cracks into which the crystalline matter now filling them has been gradually removed from the surrounding mass. They consist sometimes of quartz, and sometimes of carbonate of lime. The others are often connected with large masses of external rock, the matter of which is identical with that of the veins ; and it has therefore been very generally assumed that such veins are veins of intrusion, though by Keilhau they are considered an advanced product of metamorphic action. Where metalHc veins pass through various strata, the sedimentary included, they have most probably originated in cracks consequent on disturbing movements from below, and have been filled partly by segregation, modified as to its results by electric currents, partly by sublimation, partly by the decomposition of volatile per-chlorides, fluorides, and borides which have permeated the earth's crust through such channels, and partly by infiltration. Some of these veins are of great magnitude, an example of which may be cited in the great ironstone vein of the red mountain near Schwarzenberg, which is between 40 and 50 feet thick, and stretching along the boundary between the granite and gneiss (partly in the gneiss itself) has been traced for about four miles. f

Chapter V.

Fossils — Petrifactions — Conditions of Petrified Bodies, and Modes of Petrifaction — ^Petrilfying Substances — Distribution of Fossils.

The term fossil, in its original and natural sense, might be applied^ as it formerly was, to any body dug out of the earth^

Rudimentary Geology. 101

and would then comprise minerals, metals, and all other substances thus obtained. Amongst such fossils there were occasionally found mineral bodies which exhibited so strong a resemblance in their external forms to known organic structures, that it was impossible not to ask — are these bodies merely the production of some fanciful operation of Nature's powers, or are they really relies of organized beings? The pn^ress of discovery soon led to the rejection of the first of these theories, and for a time geologists, deceived by a general resemblance and overlooking the specific distinction between fossil and existing organisms, explained the occurrence of organic fossils within the solid matter of the earth by the operation of the great Deluge, which they supposed to have tpm up the crust of the earth and spread its comminuted fragments over the surface mixed up with shells and other organic bodies which were living at the time of the great catastrophe. The labours of modem philosophers have dispelled this second error, and established a new science, l^alseohtology (doctrine of ancient or extinct animals), by discovering that fossil organic bodies are specifically and often generically distinct from any now living, and are therefore, as relics of extinct animals, the records of successive phenomena which involve the appearance and disappearance of organic bodies, under forms and combinations suited to the varying conditions of the earth's surface.

The weight of this evidence in favour of the existence of assemblages of animals and plants, which at successive epochs of the earth's history have been swept away, may be estimated from the fact that probably nearly 30,000 species of fossil animals and plants have been discovered and described; a number which is very great, for though more than 170,000 existing animals and plants are known to Naturalists, it must be remembered that very many of them belong to classes representatives of which, either from the nature of their habitation or from the soft and perishable character of their bodies, cannot be expected to be found

in a fossil state. Of the number of plants which have thus liTed at ancient epochs and passed away, some idea may be formed from the rich collection of Goeppert, author of 'Les Genres des Plantes Fossiles/ &c., which contains more than 3000 specimens of vegetable petrifactions ; namely, 236 from Cambrian and Silurian strata, 1548 from the carboniferous, 95 from the trias or new red sandstone, 61 from the lias and oolite, 242 from the green-sand, chalk, and gypsum, 742 froni lignites, 259 of unknown localities, and 50 of recent forms, which occur in three conditions.

1 . Stems, leaves, flowers, fruits, interposed between layers of stony or earthy matter, and either slightly browned, or in various states (up to the most perfect) of carbonization.

2. Impressions of the bark of plants, the interior of whidi is either empty or filled with stony matter.

3. Complete petrifactions, in which the whole of the interior mass, as the several organs, cells, and vessels of the plant, are filled with stony matter, and not, as is commonly said, changed into stone.

M. Goeppert illustrates the first by experimental imitations of the distribution of fossil plants in shales and grits. Living • plants, particularly ferns, were placed between layers of soft clay, which were then dried in the shade, and afterwards exposed to heat varying in intensity up to a red heat. According to the degree of heat, the plants were found either shghtly browned or perfectly carbonized; and when either powdered coal or asphalte had been mixed with the clay, they exhibited a shining black tint, and adhered to the layer of clay. When the heat had been pushed to redness, and the plants were entirely consumed, impressions of both faces were found, just as in the grits of Sflesia. tn the second experiment, the plants were placed between layers of clay, and were left immersed six feet deep in a ditch for a whole year, when they were more or less browned (as plants are when naturally immersed in the mire at the bottom of ponds), and might have been mistaken for the impressions of fossil plants.

In the second condition^ which has not heen faHj illustrated by experiment, the bark of the plants sometimes remains and resembles coal, whilst all its external peculiarities are impressed on the surrounding matrix, and the markings of the internal surface are exhibited on the stony cast formed within it ; so that in such cases the cast and the mould have frequently been taken for different bodies. Sometimes the bark is reduced to a film of coaly powder between the impression of the mould and the cast ; and as the decomposition of the thin bark of such plants preceded the formation of the cast, the impression of the mould corresponds at once to the original external surface of the plant, and to that of the cast. When decomposition and petrifaction have taken place under pressure, the stems are more or less flattened ; and in some calamites the opposite surfaces have been pressed close together, the whole internal substance having been removed before the consolidation of the surrounding mass had secured it from the effect of pressure.

In the third condition, mineral matter has been infiltrated into and has soUdified within the interstices of the cells and vessels, the walls of which have been more or less preserved. In vegetable fossils the ordinary petrifying substances are silica, carbonate and sulphate of Ume which are soluble in water, peroxide of iron, smooth clay, or a mixture of several of these ingredients ; and M. Goeppert proves that the process is still going forward, by specimens of oak received from M. Cotta and from M. Laspe, which were taken from a brook, and having been fossilized by carbonate of lime are hard enough to take a fine poHsh, the vessels and cells, excepting some of the medullary rays, being entirely filled with carbonate of Ume. In a specimen of wood from a Koman aqueduct, petrifaction is confined to cyUndrical spaces traversing the ligneous structure longitudinally, which were probably vacant spaces produced by decomposition and filled up by stony matter. The wood surrounding the petrified portions is perfectly sound; and imder the

microscope the exact identity of stnieture of the woody and stony portions can be clearly traced. On applying an add the earthy matter is removed, uid sa the ligneous portion still contains tannin, perfect decomposition had not preceded petrifaction. The stave of a cask which had probably been immersed in the well of the castle of Gotha for one hundred and fifty years, was in part, especially at the junction of the hoops, petrified by peroxide of iron, and was so hard as to take a polish by friction. Where the iron has been removed by muriatic acid, the wood continues in a solid and coherent state. In calcified specimens of the fossil woods of the ancient world, from various localities and of different ages, including that from Craigleith, in Scotland, the same results are observable, the woody fibre remaining after the removal of the earthy matter by very dilute hydrochloric acid; and from some specimens, a bituminous oil, emitting a mixed odour of creosote and petroleum, may be obtained, which is an additional proof of the formation of bitumen under aqueous pressure. M. Goeppert has not discovered any recent siiicxoas petrifaction.

Though wood fossilized by gypsum is very rare, there is a specimen from Silesia, weighing 4 quintals, in the museum of the University of Breslau, of which the Ugneous fibre is only in part fossilized, the rest being flexible. In many siHcious vegetable fossils, M. Goeppert, after removing the siHca by hydrofluoric acid, found the woody fibre so well preserved that it might be used in determining the genus of the plant. When in fossil woods treated with hydrofluoric acid no organic matter can be discovered, it has been doubtless removed after fossilization, either by long aqueous action, or by heat. When slices of the petrified coniferse of Silesia which stiD retain a portion of ligneous fibre are exposed to the action of a furnace, the fibre is destroyed, and the specimens, before variously coloured, become uniformly white and opaque, the characteristic structure of the coniferse being very distinct. It is, however, remarkable that the ligneous fibre has been

Rudimentary Geology. 105

preserved in some fossil woods found in ligneous rocks, as

porphyry^ basaltic tufa, and even basalt, wbicb must have

been subjected to heat, and it appears therefore certain that

water is a principal agent in the removal of organic matter,

as M. Goeppert has proved by specimens of fossil wood from

Glatz, which had been rolled about in a brook running from

the mountain and contained less organic matter in proportion

as they were more rounded, or had been more subjected to •

the action of air and water, the diminution taking place from 1

the centre outwards. As in this instance the disorganization

was effected in a very short time, is it not surprising that any

traces of organic matter should be found in specimens which

have been exposed to the air for more than 1000 years ? The

agatized woods of Hungary, which occur in the horizontal

beds of a conglomerate of pumice which forms the basis of

a trachytic group, are externally beautifully transparent, from

the absence of organic matter, and from the presence of water

in the outer portion. Exposed to the flame of the blow-pipe,

they lose their transparency, become white and opaque, and,

from the dilatation of the water, split along the direction of the

Ugneous fibre, so that it is possible to separate the ligneous

cells from each other. In the Tokay fossil wood, the colour, as

well as the organic matter, is still preserved; and in the

Antigua agatized palms, the deUcate spiral vessels can still

be recognized. In general, when much organic matter is left,

the specimen is more highly coloured ; but at times the tint

is derived from the mineral matter. The organic fibre of

fossil plants which remains upon the removal of the stony

matter by an acid when subjected to great heat, is burnt

away, and leaves, as in recent plants, a silicious skeleton ; and

when we reflect on all these curious facts, we learn with

admiration that not merely the forms of bodies, but the

organic matter itself of ancient creations has been preserved

for our contemplation and study.

The various circumstances and conditions of fossil vegetables at all epochs have led M. Goeppert to conclude that the forces

E 5

which are now in action were sufficient to produce the effects observed^ and that the water of the ancient world did not possess a higher solvent power than that of the present. Water dissolves about ^ ^^ ^ th part of silica, and the ease ^th which it entered, as a fossilizing agent, into the v^table structure is proved by the concretions on the bamboo, called tabasheer, and the large quantity of silica deposited in the tissues of some other living vegetables.

Coal and lignite are vegetable fossils, and M. Wiegmann has made experiments in the moist way to illustrate the formation both of turf and of lignite; and examples might be cited of corresponding changes taking place in a natural way, as in fragments of ancient carpentry changed into lignite from the mines of Charlottenbrunn, and in specimens of woodwork sent to M. Goeppert from the iron mines of Zurrach in Stiria, which, in the space of less than sixty years, had been changed into resinous lignite ; and in others from the sepulchres of the aborigines of Bohemia. According to M. Liebig, hydrogen escapes in disintegration; whilst in putrefaction, oxygen is disengaged: when, therefore, the latter change takes place under a high pressure, and at an elevated temperature, considerable quantities of carbonic acid will be disengaged, and at the same time much carbon be deposited in combination vidth a part of the hydrogen of the organic substance, and it is probable that coal and some lignites have been the result of such operations. M. Link has endeavoured to show, by comparative microscopic observations, that turf and coal are analogous in structure, and may have been produced the one from the other ; and stems of trees which occur in coal are very analogous to those which are frequently found in successive layers in the deep turf of Ireland. The formation of coal by immersion in water, under pressure, was suggested long since by Dr. M^Culloch. Messrs. Mareel de Serres and L. Figuier have illustrated the general principles of petrifaction, by the petrifaction of shells in the Mediterranean. They suppose, however, that the waters of the ancient ocean did possess a higher solvent power than they do at present;

Rudimentary Gsologt. 107

but in reality this difference is apparent rather than real, as the presence of so much alkaline matter since deposited in combination with silicic and other acids must have rendered the water a more powerful solvent than it now is. The action of every natural force tends to a resulting equilibrium, and if that has now been attained, the same processes will continue without producing any difference in the great aggregate of the animal, vegetable, and mineral kingdoms ; but if not, such a difference must, however gradually, be produced. The long existence of the present assemblage of created beings, and the effective condition of the atmosphere, which remains unaltered by vital agencies, are strong reasons for believing that an equilibrium has been attained ; and as a further proof, it should be stated that the world has only lost, during 6000 years, about twelve vertebrate animals, and that principally from the action of man, although the distribution of animals has been materially modified by the local extinction of some, and the lateral extension of other species.

Fossils and Petrifactions, — From the preceding pages the student must have alre^y learnt that the terms ' Fossil' and * Petrifaction' cannot be used indiscriminately or considered synonymous. The word fossil, as understood by Geologists, means indeed the remains of some organic body found in a position and under circumstances which prove that it never could have been a member of the existing system of living organisms; but it is not necessary that every fossil should have become a petrifaction — that is to say, have been changed into stone — as is proved by the condition of coal, and still more by that of lignite, which retains, though manifestly an organic fossil, the ligneous structure and fibre. Coal has indeed undergone a chemical change by the partial re-adjustment of its elementary constituents, and the consequent development within its substance of bitumen, but it has made no approach to the state of petrifaction. In like manner, the examples cited have shown that many organic bodies, in all respects identical with those now hving, may have become petrified

during the coarse of the still passing sTstem of creation, and have therefore no claim to he called fossil. In either case the mere condition of the hody is not sufficient to determine whether it is er is not a fossil ; and much caution, therefore, is required in using these terms. The passage of an organic hody from the ordinary to a petrified state, which is often improperly called fossilization, is influenced hy many circumstance, of which the chemical constitution is one and will he first noted, — though it is necessary to premise with Messrs. Serres and Figuier, that in order to induce the petri-faction of organic bodies, in which process the animal matter is replaced by mineral substances, they must be plunged either in a considerable quantity of water which contains in solution a sufficient proportion of silicious, calcareous, or other salts, or in semi-liquid muds or other deposits which permit a free access of such saHne solutions : a condition which was fulfilled in the ancient world when the waters spread over large spaces now occupied by land which, both from its mineral and organic characteristics, must have been deposited under water, and when they were rich in dissolvedjsalts, as is manifest from the extensive deposits of carbonate of lime, of gypsum, and of rock salt.

The bones and teeth of MammaU are closely connected with the mineral kingdom in their natural condition ; — bones containing 55 j- parts in a hundred of phosphate of lime with a little phosphate of magnesia and fluoride of calcium, 1 2\ parts of carbonate of lime with a small quantity of soda and chloride of sodium, or nearly 68 parts of mineral matter combined with about 32 parts of organic matter ; and teeth contnlj^ , sometimes from 64 to 66 per cent, of phosphate of liiJMl^'.Iiir * cartilages the gelatine increases to so large a propoaHl dM ■ there are only 1 or 2 per cent, of mineral matter, and tflfXit therefore, be easily understood how rapidly they ii!||ki|lNA^ and pass away, and how little they could be expected tOjflMM. their form and admit of a petrifying change. The twM^ animals and the horm of deer are very analogous to te€th ax^

4

Rudimentary Geology. 109

es. The composition of birds' bones is nearly the same as : of quadrupeds, but as they are porous, their density is ;h less, and the quantity of earthy matter is therefore less the same hulk. The bones oi fishes contain much less hy matter, and on that account are rarely found in a fossil 3. The horns of ruminants, as oxen, sheep, &c., the scales 3ptiles, and tortoise-shell, are very analogous, being modifi- )ns of the skin, and are poor in mineral matter. Scales of is, on the contrary, contain from 42 to 46 per cent, of $phate of lime, and hence are frequently found fossil, whilst e of reptiles are comparatively rare. M. D'Orbigny obes, that whilst the fossil scales of reptiles are either petri-by silica or carbonate of lime, those of fishes retain a iderable quantity of phosphate of lime, as proved by the yses of M. Huyard; and hence suggests chemical examinaas a test when there remains a doubt to which class the ;s should be referred. Claws, spines, bristles, hairs, and lers, are merely appendages to the skin, and, containing little mineral matter, putrefy and decompose so easily as ly, if ever, to be found, fossil. The shells or crusts of that ion of the Annelides called Crustacea, of which lobsters and s are familiar types, contain from 50 to more than 60 per . of mineral salts united with various organic substances, were, therefore, sufficiently stable to be preserved in a fossil

ut, vnthout dwelling on other organic bodies which have I rarely, and then from accidental circumstances only, dis-red in a fossil state, let us pass to those which, from their position alone, might be classed with minerals, — namely, shells of Mollusca, Of all animals, they have left the test variety and number of fossil relics, — a fact which their aical composition would of itself explain, even were it not Ift a result of the peculiar conditions and circumstances |jr which they lived. The shells of Mollusca consist of it 96 per cent, of carbonate of lime, 1^ of phosphate of , \\ of water, and of animal matter only 1 per cent. ; or

in some shells, sach as those of oysters, scarcely an appreciable quantity, which accounts for the great masses of oyster-shells (including the allied genera exogyra and gryphsea) which are found in so many formations. The stony cases of Polyps, or corals, are in like manner mineral bodies, as they contain from 97 to 98 per cent, of carhonate of lime, hesides small quantities of magnesia, alumina, iron, and sihca, combined with phosphoric and fluoric acids ; and such a composition explains the formation of those extensive heds at many geological epodis which are almost entirely made up of corals, and are so analogous to the coral reefs and islands of our present tropical seas.

Fossil shells, like fossil plants, occur under various forms: in some the interior has heen filled, after the death and decay of the animals which inhabited them, with foreign mineral matter either analogous to that of the shells or at times not so, and a cast has been thus formed in which may be frequently observed in relief the muscular impressions which the animal had made on the internal surface of its shell : in others, a mould has been formed round the shell, and in this manner the peculiar markings, as ribs, furrows, &c. of the external surface were preserved, even though the shell itself had been removed ; and a cast being subsequently formed by the infiltration of sedimentary or dissolved matter into the hollow space, the external form of the shell was reproduced, though frequently in a substance totally different from the original carbonate of lime ; and again it often happens, that thou^ the shell appears the same in form and substance as it originally was, the structure is physically quite different ; and this leads us briefly to notice the processes of petrifaction, or those processes by which an organic body loses more or less of its primitive nature, and is converted into a new substance, thoag^ still preserving the organic form.

Petrifaction by abstraction of matter, — This is the case with most comparatively recent fossils, as the bones of caverns, &c., in which the change is almost Umited to the removal of organic matter. It might be supposed that this limit would

RUDIMENTARY GEOLOGY. Ill

be always observed in fossils of contemporaneous origin with the shells and other organic bodies still existing, but in the Mediterranean examples have been discovered of much higher changes, whilst it has been ascertained that the change is not perfect even in many older fossils. Thus Messrs. Serres and Figuier observe, — Istly, that shells are found in the Mediterranean in all stages of the petrifying process, from simple discoloration to the complete transformation into crystalline carbonate of Hme; 2ndly, that the molecular structure of recently petrified shells is very often different from that of ancient fossil shells, the first being usually crystalline, the others usually compact; though in many ancient fossil shells a crystalline structure is very perceptible, distinguishing them at a glance from the surrounding compact limestone; and thus affording another confirmatory argument in favour of the identity of the process at all ages of the world. By a comparative analysis of the substance of living, of recently petrified, and of fossil shells, genera common to the three epochs of comparison being selected, the effects of petrifaction were tested ; and it was ascertained that a portion of animal matter was still existing in shells of the pliocene formation.

The officers of the French Engineers submitted to Messrs. Serres and Figuier specimens from the neighbourhood of Algiers, of masses of shells transformed into a crystalline white Hmestone of a peculiar lustre, hke that of alabaster. In these shelly masses, small rolled pebbles are observed in-crusted by a stalagmitic glaze, which appears to be similar to the cementing substance which binds the pebbles together. The shells are all of recent species of the genera pectunculus and cardium, with a few univalves, and the rock itself is considered by the officers of Engineers to be decidedly of recent origin; and another interesting fact may be cited in the remarkable conglomerate now forming on the shore of Santa Maura, and at other localities, and which in its cohesion is fully equal to many ancient rocks of the same description ; there being a continued tendency to such aggregations, even

from other than calcareous agencies, as is seen b an btenstiii gnecimen, also from Santa Maura, presented to the mitliOT d till* volume by Mr. Cottam, in which several pebVks hut been agglutinated finely together by the decomposition m'l noil, to nliich ihcy still strongly adhere ; and in a simil* instance at one of the batteries of Portamouth, niitn' i. iw glomerate has been formed round the iron shoes of the piln Messrs. Serres and Figuier state also, on the authority of i that the cardium edule, in a petrified state, forms com beds at the mouth of the Somme, and that at Coneale the of oysters have been petrified in the same manner as i Mediterranean.

Petrifaction by incruetalion is a combined mechawal chemical process, in which a body becomes enveloped ani * tiftUy penetrated by mineral matter which is deposited uj 1 just as crystals of alum or of sugar are formed round a < or stick when plungedinto a saturated solution. Theaiib« usually concerned in this operation are carbonate of lin silica, more particularly the former, which is soluble in containing carbonic acid, as all spring water does. The D ill which such incrustation is effected may he readily c^ in fountains and springs which are highly charged with, bouic acid, sa the excess of acid escapes on coming into c with the air, and the calcareous matter incnista the moss, or other bodies exposed to its action. When this is long tinned, a mass of calcareous tufa is formed ; and in a si manner, in fossils, a crust might hare been formed suffid thick to retain the form of the body aStei its substuici been removed by decomposition. As the deposition of n proceeds, it will fill up the cavity, and thus become a ci the organic body r here, therefore, similar results may b tained as in the preceding cases. Sulphuret of iron ai copper, peroxide of iron, and some other substances, sionally occur as incmsting bodies j and in the tertiary concretionary incrustations are frequently found envell organic bodies, which, though altered, have not been enj replaced by mineral matter.

Budihentary Geology. 113

Petr^acttOK hy the mechanical introduction of »edimentary matter. — Where the organic body presents a large and easily accessible cavity, mineral matter gradually fills it up. This matter is sometimes very coarse, and it is in tliis manner that petrifactions in sandstones have been principally formed. Enveloped in and filled nith sand which has become cemented perhaps by matter proceeding from part of its own substance, the organic body, whether a bone or a shell, may be entirely destroyed, and thus at once leave a mould of its exterior and a cast of its interior, or it may be only modified by changes irhieh will be now described.

Petrifaction by inr/lecular penetration and hy subilitulion. — WheD an organic body has been partly disoi^anized, it may become so porous as to allow even fine matter held in soBpension, and slill more so matter in solution, to penetrate tfarough its tissues, or, in other words, solid matter may be thus filtrated through the organic body. In this manner a body may be permeated by mineral matter long before the total removal of its organic constituents, and whilst the more acces-able cayities have been filled by coarse materials introduced through distinct openings, the internal cavities may be also either filled with very fine matter which has passed through their coatings or walls, or lined with crystids separated from matter in solution. This change is sometimes so complete that it amounts to a substitution of one form of matter for another, and the result, therefore, represents in every minute particular the original body, though in a totally different substance. Vegetable fossils afford many examples of this substitution of mineral for organic matter, and it is often possible to detect in the petrifaction the most delicate vessels of the organic body, and thus to determine with the greatest precision the genera of plants. In plants this substitution is principally efi'ected by the introduction of silica, and in like manner the animal or more purely organic portion of other bodies are also petrified by silicioiis matter ; the ligaments, for example, of gryphites becoming silicions whilst the sheila are calcareous, and the

m

interior of many echinidse, or sea-urchins, being filled with silex whilst the thin crust or shell remains calcareous, there being apparently an elective affinity between organic matter and silex.

Petrifaction by chemical change and by transformation,'^ In these cases there is no mechanical introduction of mioeral matter into an organic body, but a chemical action by which either the original component parts of the body are brought into new combinations, as in the change of organic structures into bitumen, or the elements of the body are made to comhine with external substances, and thus to procure a metamorphosis of the fossil, as regards its composition. In the case of tram-formation, there is actually no change in the substance, but merely an alteration in the molecular arrangement of its particles. This change of physical condition might be illustrated by reference to the changes which are effected in sulphur and phosphorus by heat, and it is abundantly exhibited in fossil shells, which, though when recent they are compact, or rarely fibrous, become in the fossil state lamellar, crystalline, and finely fibrous, or undergo other physical changes, such as that from opacity to translucence, &c. In ancient petrifaction, carbonate of lime was the principal agent, and the fossilizationwas complete in proportion to the abundance of that salt present In gypseous, argillaceous, and even sandy deposits, petrifaction is imperfect and the shells of mollusca are only in part preserved.

Water dissolves carbonate of lime when an excess of carbonic acid is present, as is always the case in nature ; and in consequence, an appreciable quantity of bicarbonate of lime exists in sea water, and is one of the many examples of a bahmoe between the formative and destro3ring causes constantly in action. Innumerable springs charged with carbonic acid dissolve the carbonate of lime of ancient formations, and carry it to the ocean, whilst the mollusca, &c. again withdraw it, and liberate the carbonic acid to return to the atmosphere. The shells of the mollusca again pass into new mineral deposits, either whole

Rtdimentary Geology. 115

or triturated into powder ; and the same may be said of the corals and other zoophytes. In regard to silica^ which is the next most important petrifying substance, and even exceeds carbonate of Hme in the extreme delicacy and fidelity of the restoration it produces, it has already been stated that the water of almost all mineral and thermal springs contains a portion of it, that it occurs in most rivers or streams, and that it abotmds in the stems and membranes of many vegetables. Combined heat and pressure favour its solution, — as is shown by the great quantity deposited at the foot of the boihng €reysers of Iceland, — and it is greatly promoted by the presence of an alkali which is usually afforded by the decomposition of rocks ; and further, in the gelatinous or nascent state, in which it always occurs on the decomposition of a mineral, it is readily soluble. Silica, therefore, must have been in solution prior to the formation of rock crystal, and, probably, in a gelatinous state when forming chalcedony, opals, and some of the flints and cherts of various geological formations. Oxide of iron, anhydrous or hydrated, and bisulphuret of iron, have also entered into the formation of fossils : in respect to the latter, the change, as in sihca, is principally produced on the animal substance; for example, the ammonites in shale exhibit a mere film of shining iron pyrites, which has replaced the animal membrane.

From the processes of petrifaction, it is necessary to turn to the consideration of the mineral beds in which petrifaction occurs, and to determine the exact relations of the beds to the fossils they contain. On studying the still passing operations of Nature, it becomes evident that many forms of mineral deposit are in course of production, such as the sand dune or hiU, which though removed from the action of the sea is still shifted and modified by the action of winds, and in which land and marine shells and fragments of bones are enveloped by the drifting sand, and the various deposits of mud, sand, gravel, or shingle, forming in the bays and estuaries, or on the coast of the ocean, in all of which relics of organic bodies may have

Dc Rudihbntakt Gkoloct.

heea entomb^, u llie Mine force 'which opemteil in m

mud or gravel was equally eflicieat for trnnspartiogf orgniiic bodies. But in the^e cases there may not hin

original connection between the fossils and the m beds in which they are found, the inhabitant of a miif' bottom being hurried, when no longer possessed of 1 4 force of resistance, by the currents and deposited a

muddy sediment of an estuary. Many such cQiiiM '^ assemblages must doubtless have been formed, hot the e« observations of modem Zoologists afford s clue ti of the real inhabitants of the several deposits, and to thefl ration from them of eKtraneous bodies ; for examplt, ! been determined by Professor Edward Forbes that theTfl range of marine mollusca is restricted to definite limits, H

le are specially httoral or shore inhabitants,

the rocks or on the gravel or sand which is v left dry alternately by the tidal wave, whilst others U successive and increasing depths below the surface a ocean. And further, it is known that some moUol sLcU-lish Uve buried in the sand or mud, whilst ] rest on the bottom, either adhering to stones c kept in their place by their weight alone ; so that a m comparison of a cluster of such fossils will greatly at skilful Geologist in determining which should be b the particular bed as its natural inhabitants, and which ■ Ijo considered extraneous bodies derived from drift, i to recognize the influence exercised by the petrographio i ilitution of the bed itself on its fossils. Organic beings art, indeed, not only restrained to a particular medium in whiA they can alone Uve, but require also a peculiar collocation d I'ircunivtnnccs suited to their mdividual existence : thus om flail may ho marine, another fresh-water,— one may live in open Niid deep suns, another frequent rocky coasts and clear water, » third delight in the muddy shallows of estuaries; and in n tlitillnr tnaiiiier mollusca are regulated in their habitats la

iUHviiiNry roquiremeuts of their organization; — a lil^d

hed to a rock, aud able to sustain the beatin^^^^l L of the wave,- — the cockle inhabiting the gently-sJopiug

shore in shallow baya,— the myacea burying themaelveB lilar strands, — the pinnre frequenting the muddy bottoms (per waters, — whilst many genera with strong sheila can ;lie force of currents, and rest uninjured on shingle banks iky holtoms. As the Naturalist, therefore, does not look e animal suited to a muddy bottata on a shingle hank, or le thin-shelled spatangus at the bottom of a rocky cliif ed to the violent action of the tidal current, so the gist must exercise a hke caution in hia research, and nber that — 1st, A pecuhar petrographic constitution in a ,m will he accompanied by a pecuhar palEeontological bkge of fossils ; and 2ndly, That such a palieontological iblage does not naturally include genera and species '. to strata of a different petrographic constitution : and ore, when genera or species peculiar to one form of al stratum be found in another, they may be expected to •e, much less developed, and less distinctly characterized in the stratum to which they properly belong. nbiuing the actual mineral structure of the stratum, . is a result of certain necessary conditions, with the ying circumstances of position, deposits may be coo- d as shore or littoral deposits, shaiiow-sea deposits, lea deposits, coral-hank deposits, &c. ; and the probable ■ence of organic bodies must depend on their adaptation ise circumstances, so that it may be assumed, as a very tant character, that in organisms of the coralline type of it, the shell or crust is massive, and marked by ribs,

spines, knobs, aud other peculiarities, which, whilst doubtless added to their fitness foe opposing the contin- 'B of their peculiar location, now afford so many valuable ;ters for studying them as inhabitants of an ocean long passed away. Shingle deposits produced by the more wear of the waves, though often intimately connected wnl hanks, accompany and hnk together all the pEtro^^^^J

graphic forms of deposit. They possess few zoological pecDf liarities, horrowing, as it were, the characters of the seven deposits with which they are connected, bj receiving from them the i^agments of their Tarious organisms, which angradnally, as they are carried along, worn down, pasang* through an oolitic state into an impalpable paste. Muddy deposits, such as marls, compact and sub-compact limestoneif together with sands and sandstones, constitute another im* portant class, and exhibit a totally different zoological blage : the corals are of spongy and incrusting genera, generally without apparent base ; crinoids are rare, seal about, and generally of unattached genera ; the echinida oi less rare, particularly the true echini and their congeners, ani the spatangi abound in muddy and sub-sandy deposits. Of the asterida, the genera asterias and ophiocoma are characteristic of muddy deposits, and of fine sands and gravel. Oftfai acephalous mollusca, the genera which abound are, soleo^ pholadomya, myopsis, pinna, tellina, mytilus, modiolus, ca^ hula, isocardium, cucullea, and amongst the ostracea, gryphoi and exogyra. In the gasteropoda may be noted, rostellani» pterocera, natica, turritella, fasciolaria; and amongst the cephalopoda, the genera nautilus, ammonites, belenmitea^ being either rare or abundant, according to the variations in the form of the deposit. Fish with pavement-like teetli are very characteristic of these mud deposits; and reptiki are especially abundant in the Jurasic beds, though they aie locally rather than generally distributed, occurring in yfhA may be deemed muddy shore deposits. A general and ooostant character of all zoological assemblages in muddy deposita^ is that the prevailing genera and species are provided inth shells or coverings not fitted to withstand the wear of trans* port, being smooth and thin; and in those genera whidi possess a thick shell, the tissue is nearly non-elastic and easily disintegrates. It may be also stated, as distinctive of muddy bottoms, that the genera are more heqaeaiij free than attached, even the stems of pentacrini not exhibit-

Rudimentary Geology. 119

stroDg roots, haying been probably fixed by fibrillfle or ply immersed at their base in the mud.

The snb-pelagic and pelagic forms of muddy deposits, loc^h corresponding to the littoral form in their petrojrttphic conditions, are distingoished from it by zoological bcoliarities.

The deep-sea or pelagic deposits are very uniformly con- ^itated^ homogeneous, regularly stratified in continuous and ften massive beds, except where modified or disturbed by the btion either of currents or of elevating forces. In these ieposits, large spaces are often deficient in organic bodies, or ontain only their d^ris, together with those spongy and [brous corals which are supposed to inhabit the waters of ireat depths; and where cephalopoda abound, the species [iffer ^m those which inhabit muddy shore deposits. li. Gressly arrived at these important deductions from the ■receding facts, having thus as it were adopted views very tmilar to those which have been so ably set forth by Pro-essor Forbes :

1 . Each class or form of deposit presents characters, petropraphic, geognostic, and zoological, peculiar to itself, and disinct from those of any other class or form of deposit, although if the same geological epoch.

2. That the same class or form of deposit, as regards its »etrographic and geognostic condition, exhibits very analogous oological characters in each successive geological formation in rhich it occurs. These two laws are of great interest, and dghly important in the application of zoological characters to he determining of geological formations ; though it is necesary to take intq account, as already pointed out, every disturb-ttg or modifying influence, in order to separate, in any tratum, those organisms which are peculiar to and must have bund a fitting habitus in it, from those which have only been »rought into it from other situations by currents, storms, &c. n the muddy sub-pelagic bottom of the channel of Corfu, in he Ionian Islands, many of the thin-crusted and silky-spined

spatangidse are found, together with nncolse^ tellinee, corbnla^ and other organisms fitted for such a habitus ; but these aie combined with abundant exuvise of other orgamsms foieigD to such a habitus, — ^as the valves of strongly-ribbed caidk, pectens, &c. In the one case, the shells, &c. are genanQj perfect or alive ; in the other, more frequently separated and injured ; and in bivalves though still connected, thej are aftoi found open and the valves twisted round ; and the Greolo||;i§t wiU find many similar cases in the deposits of andent worlds. 3. In every petrographic dass of deposits, two sets of organisms may be expected to occur : the one suited to tbe habitus afforded by its geognostic position, and therefore die truly characteristic organisms of that class of deposit, or thoM which should be used in any comparisons between distant deposits of the same or of any other formation ; the other, extraneous organisms, the absence of which at some other locality would not be evidence of a geological difference, but simply of freedom from the modifying influences which hid affected the first locality. There are many other geological facts on which much light is thrown, if they are not folly explained, by the method of comparing the conditions of zoo* logical existence at ancient epochs with those of the present, such as the abrupt terminations of peculiar petrographie deposits, the local distribution of fossils, &c., cases which cm be observed wherever a mud or other bank is cut off by a current, or where a local deposit is formed under the lea of projecting rocks, or the shelter of a coral reef; but it would be vain to attempt to note them all, and enough has been said to guide the observer to a right mode of geological inquiiy in tracing out the lateral extension of any particular formation. When the inquiry is made in a vertical direction, or by the aid of natural and artificial sections, the observer will find the same classes of deposit recurring at different intervals, and will discover a similar analogy in the assemblage of organisms connected with them ; an analogy, such as similar conditions of existence must produce, — not an identity, which could

alone spring froin identity in tlie OTgaiiiains of the two pmod*. Re is thus led to another geological rale or principle.

4. Similar vsrintions in the conditions of organic exiatmn must produL'e similar modifications in the nssemblage of o^atiic beings which esist in various places nt the same epoch. Want of identity, therefore, in the organisms of ihe same petrographic cUsH of deposit in sucoessive portions of a section of any part of the earth's crust, camiot he explained by a variation of the conditions of existence ; the petrographic and geognistic identity combine with the zoological analogy to show that the eonditioua were really the same, and the change muat be ■scribed to a difference in the aggregate fauna and 6ora of the epoch : or, in other words, it proves that the organisms of successive strata were connected with distinct acts of creation, or formed parts of distinct organic systems or worlds.

As a relation exists between the shell or covering of the animal and the petrographic canditi<»i of the deposit in which it is found, it must be assumed that the animal itself was formed to exist under the physical forces which gave rise to that deposit, and that its general organization was suited to all the circumstances of its destined habitat. Temperature and pressure are the two forces which most materially affect marine organic existence, and restrain or promote tiie distribution of marine organic bodies; but it maybe asked in what manner the stream of oi^anic life commenced ? The earliest historical record of the human race describes a local creation ; and though the learned 4ispute as to the precise time involved in the events noted, the Mosaic account is in favour of the theory of a centre of creation ; and if the past worlds of former geological cpodis he also taken into consideration, the more general principle of centres of creation may be Sftfely adopted as more conformable to the simplicity of nature, than a contemporaneouB or even a succpssive creation of the Bsme species at various and distant localities.

A group of animals being created with organizations suited to certain conditions, such as the breathing of air or water, and

the capability of supporting a certain degree of heat oi of pressure, when the mandate was pronounced that they ahwjl multiply, their lateral progression on the earth would be a. trolled by the laws implied by those conditions. In this n the course of the marine mollnsca might be traced li along the coast at the depth suited to their structure and habits But life is not the only active force i the tidal vi great marine currents are in motion ; the sea 1 the shore, and the detrital matter of the rocks is carried foi ward and deposited in new strata, by which the shallow w is made dry land, the deep water shallow, and the advandg mollusc is thus impelled, by the necessity of keeping at definite depth, to pass from the surface of one bed to that ( another ; and if the general conditions remained the a species may have thus lived over a apace of time duriog whil a long aeries of deposits were formed, and in cousequeni their fossil relics might be found through an extensive n of strata. This combined lateral and vertical extension leqi time, and it may be therefore assumed, as demonstrated I Professor Forbes, that fossils which have the greatest w range, or have existed for the longest time, have also had d greatest cst^Qsion in space.

Heat is the other great regulating cause which confines fl progrcssiou of land animals to narrow limits. If fitted t temperate climate, they must as they advance southward si it on higher gromid ; and as the mountains of the earth ■ comparatively small, the range is limited and the eztei soon stopped. In marine animals the case is varied, < be miderstood by referring to the conditions of temperature the ocean. It has been stated that the temperature of i earth increases in proportion to the depth below its s in the sea it is the reverse, as the temperature decreatet n the depth, even at the tropics, until it has arrived at a T little above 32°. This to many will appear a contradictio hut it is not so : the outer crust of the earth is cooled on A land by radiation or by radiation and trouBmiAsion on ll

Rx1Dimentary Geology. 123

d by sea; but the passage of heat is slow through the earthy materialB of the upper crust, whilst it is rapid through the aqueous covering; and it is therefore quite accordant with the laws of nature that the earth at the bottom of a sea many miles deep should be icy cold, whilst at a similar depth tu the solid matter of the earth the beat would be sufficient to melt iron. Even in the tropics, as the sun's rays act but feebly on the water, and can have very little heating effect on the ground at great depths, the temperature would not exceed the mean temperature of the place, even if no interchange of water took place, except from below upwards, and pice vertd : but this is not the case, as water of a meau lower temperature will gradually more from north to south, until a gener^ mean temperature has been attained by the ocean except in that merely superficial portion which is subject to the local influences of heated land, a portion which is deeper as it is nearer to the tropical or more heated regions. The very careful esperimenta of M. Ch . Martins in the corvette La Recherche are perhaps the most interesting on record. They were made in the Polar Seas, in the months of July and August of the years 1838-9, and extended to the depth of 870 metres (2784 feet), giving a uniform decrease of 1^° Fah. for 320 feet, or "69 cent, for 1 00 mfitres, the final temperature arrived at being Tcry nearly 32°. Parry and James Ross found the temperature lower, as it mas only 281° at the depth of 2304 feet in July, 1827. The equalization of temperature is further asosted by the flow of the heated equatorial waters towards the Pole, as is seen in the Gulf Stream, which, notwithstand- ■ ing the doubts entertained by some on the subject, is traceable, according to M. Martina, to the North Cape. This uniformly low temperature of the depths of the ocean materially restrains the dispersion of animals suited to a high, and favours that of animals suited to a low temperature ; and therefore explains many of those anomalies which occur in the habitats both of recent and fossil species. But the bottom of the ocean is not only altered by the deposition of freah mineral matter ; it is subject

to all the disturbances of eleyating forces, and it is therefore highly probable that the progression of animal life is stopped at one point by an elevation of the bottom which brings it within the influence of a temperature destructive of the organisms then Uviug upon it, and at another promoted by a depression of the bottom, or vice versd; and in this way various modifications of the groups of organic beings, and many abrupt terminations of them, must have been effected at all periods of the earth's history. These principles serve as a guide in investigating the topography of the ancient world ; and, as pressure, independent of temperature, acts as a limiting force, it cannot be supposed that even the mollusca could be distributed without the aid of banks or shoals to preserve a suitable depth; or that the mammalia could have spread over the earth without a continuity of land, as air . is essential to the preservation of their life. The development of the earlier fossiUferous strata implies therefore a continuity of the ancient shoals of those epochs, and it hence appears that Australia was, to a certain extent, connected with Europe at the epoch of the carboniferous deposits ; or, ascending to newer deposits, analogies between the past and present creations are found in the oolites of Europe in the relics of marsupial animals, in the remains of fishes analogous to the Port Jackson cestracion, and in the remarkable genus trigonia, which still exists in Australia. This recurrence ( in Australia of a zoological type characteristic of the OoUtie period renders it probable that Australia and Europe were then connected by dry land, as in the carboniferous period they were by shoals ; or may it not be possible that some of the mollusca and plants of the carboniferous epoch, which are associated with oolitic plants in the Australian coal field, arrived there by combined lateral and vertical extension at a geological epoch posterior to that of the coal formation of Europe ? In the tertiary periods, or those immediately antecedent to the present, many examples may be traced of jcoutinuity of land now no longer existing; and Geology and Palaeontology become guides to interpret the great changes

1

Iiudiiikmtaby Okoloot.

which have taken place at successive epochs, and to represent, as it were, the various phases of the glohe amidst all its changes ; clearing away those clouds of uncertainty and that confusion which had before baffled the student of nature, and interfered with his perception of truth.

Chapter Vi.

General and Practical Remarks on Geological Formations.

In studying a geological formation, by which term is understood a representation of the mineral and organic conditions of the earth at some former epoch, the observer will meet with evidences of each description of formative process, the natural history of the earth implying an investigation of the changes both mineral and organic of each successive epoch. To express the relation between eruptive, metamorphic, and sedimentary rocks, a compound nomenclature, representing at once the epoch of original deposition and that of raetamorphism, &c., has been proposed by Sir C. Lyell, as Ante- Cambrian carboniferous metamorphic strata, triasic oolitic metamorphic strata, &c., by which is meant that the strata were respectively deposited prior to the Cambrian, and during the triasic, but reduced to their metamorphic condition by forces acting during the carboniferous epoch in the first place, and the oolitic in the second; and in like manner there may be Ante-Cambrian plutonic, Silurian plutonic, carboniferous plutonic, triasic, oolitic, cretaceous plutonic, &c. ; or Silurian volcanic, carboniferous volcanic, triasic, &c., up to the volcanic rocks still forming; and though it is difficult in very many cases to determine with certainty the actual epoch of the original condition, or of the metamorphic change, of the crystalline schists, and also of the upheaving and apparent partial eruptions of the phi tonic rocks, or even of the eruptions of volcanic rocks, it must be admitted that the proposed nomenclatiure is correct in principle.

From a curdbl eompantife stod^ of tiie loologjend jkj- uAogy ci soeoeashre epochs (^ the etfth's YaaXotj^ as duplayed hj (M^anic leHcs fonned in the mineral depositaiy Ger^ogists haTe established a certain number of distinct formatimis, eidi of which is characterized bj its own animafa and plants, and which are exhUnted in a descending order in the aoeompanying Table.

Table cf Com p arat i ve Tkieinen ofFotriSfermu Strata or Furmatum. ^

I

Order.

R C C lCDt»

Post-Flioeene, or GlacuL

Group*

Marine.

Miocene. Eoeene.

CreUceoiu, ezdu- ^&nf; Wealden, wmeh bekmn to the next orMr.

Wealden.

Oolita, indnding Jura Limestone.

lias.

Trias, or new Bed Sandstone.

Permian, including MagnMianLime* stone and red Conglomerate.

Carboniferous, without old Bed Sandstone.

Devonian, or old Bed Sandstone.

Silurian. Cambrian.

I deratmg.

I Marine. >Marine.

Mked marine and

I Marine.

Marine.

Freaii-water.

Associated

with Fresh-water.

Fresh-water.

Fresh-water.

Fresh-water deposits recently

discovered.

Gciiuany, bj Cotta.

Feet,

no

M 900

Total ... 380

Westphalia 600 Saxony so

aoo

Ftom 150 to

Cotta unites these

in one formation.

Total .... 6000

Isc

lOM

to

Variable

many

thousaiid.

Mny thoasnl I iect.

According therefore to Cotta, the total thickness of stratified fossiliferous deposits is 22,750 feet, or about 4j- miles, exclasive of the yariable and micertain deposits of the existing

Rudimentary Geology. 127

period ; but such estimates are only very rough approximationa, aa the (hicknesa of each deposit ma; be expected to vary in CTcry locality, and to undergo very material modifications both in the character and proportions of its several parts.

In the remarks ou these formations, the ascending order will be followed, the lowest recognized strata being first noticed, and each successive formation, growing as it were one out of the other, will be considered in the order of its occnrrence.

Caubrian, The Earliest Known Fossil

This term has been applied by Professor Sedgwick to stratified rocks which occur in Cumberland, North Wales, and other places, under the decidedly Silurian strata, and are for the most part slaty and without fossils. They contain but a small proportion of hme, and their fossils being local and rare, Bttfiicient evidence has not been obtained for placing them in a ioDl<^cal order distinct from that of the Silunan. The apparent thickness of the slaty and gritty beds is cau^iderable, but this is due to contortions, by which the came beds are made to appear several times successively in the same section. The prevalence of the slaty character shows that the progress of formation has not been varied by much original disturbance, and the thickness of its beds indicates the probabiiity of some portion having been a deep-sea, or rather semi-pelagic deposit. The Cambrian is now considered a marked group in the Silurian, and as the Cambrian group placed at the base of that system.

This formation, since the publication of the splendid work of Murchison, has attracted the attention of all Geologists ; and as it exhibits the relics of organic beings in great abundance, and of very peculiar forms, has been rescued from the formerly obscure regions of the grauwacke, and reduced to light and order by the discoveries and research of Sir R.

J

F

:art gkology.

Murehison and bis folloners. The lower group of ihia otJi includes the Llandeila flags, or micaceous slaty grka, u above them the Cnradoc sandstone. The neit in ordersscu ing is the Wenlock group, consisting of a deep bed of ihl surmounted by a bed of limestone ; and the third or om the Ludlow, comjirising the lower Ludlow shale, the Aymcri limestone, and the upper Ludlow, a calcareous grit or m stone. In England these groups follow each other in td sequence of superposition, and are distinct in order of til but in other regions the sequence may be varied in confotn to the laws of geological deposit : whilst, therefore, m S way and Sweden there is a partial similarity in litholop character, and the conditions of deposit have been neariyi same, limestone has been much more developed in many w of North America, and ihe conditions of deposit have hi different.

In the combined Cambrian and Silurian formation the eatd first exhibits traces of life, and we find the remains of Gshl strange in form, but high in organisation, such a onclnis and plectrod^s, many moUusca, including peculiarfet) of the brachiopoda and cephalopoda ; very characteristic a tacea, belonging to the extensive family of trilobites, whw beginning to exist at this early epoch, flourished in uimd both of species and individuals, and then rapidly passed awi the family being traced no fiirther than the cartoniferooa orA radiata, rare ; zoophyta, less abundant than ii orders, but exhibiting some peculiar forms. In respect to d conditions of deposit, it may be observed, that though tbee tensive limestone strata of this epoch, adjacent to the gn Iftlies of America, were probably pelagic (the large orthoca and many brachiopoda having been well suited for deep seal and formed, like the mountain limestone of the carbonifbra system, and even like some deposits of the recent epoch, by || accumulation of the remains of teatacea, or, on the tempt cessation of the influx of mud, by the growth of corals sitited I 4|D<^ habitats, the evideuce afforded by the fossils of Engln

ftVDIMBNtARY GBOLOGY. 129

tnd Ireland, particularly hj the trilobites, the many species of nucula, and even it may be added by the fishes which were probably fitted to grovel in the mud, indicates local deposits of mud and sand in moderate and sometimes shallow depths.

The invertebrate fossils which have not hitherto been discovered in any more recent deposit, excepting in some instances in .the Devonian, are graptolites, which are zoophytes delated to the pennatula ; chain coral, catenipora escharoides ; many genera of trilobites, such as remopleurides, phacops, calymene, asaphus, ampyx, trinucleus, harpes, brontes, and several others; of brachiopoda, the genus pentamerus ; of cephalopoda, the genera phragmoceras and lituites, &c., the great development of the nautiloid type of mollusca being a remarkable fact in this early portion of the earth's history ; but it is impossible to notice here all the peculiarities of the many remarkable fossils of this formation without entering largely into their natural history ; nor is it necessary to state what fossils characterize the subdivisions or groups of the formation, as it is enough, in a practical point of view, to be able to recognize the existence of the formation itself; which is of much importance, as it lies below the great carboniferous system on the one hand, and on the other overlies a series of metamorphic rocks, embracing the useful deposits of various descriptions of slate and other building stones.

In the classification of M. D'Orbigny the Silurian system is

divided thus : —

Q., . r B. Murchisonian, or upper, oiiunan ^ . /^., . «

L A. Silurian, or lower :

and he enumerates 356 species of mollusca and 61 of radiata in

the upper, and 375 species of mollusca and 52 of radiata in

the lower division.

Many of the schistose beds yield good flags and slates.

Besides the various localities of Europe and America, the formation has been noticed at the Falkland Islands, and in South America. In Russia and in North America this formation is frequently exhibited in the actual state of its original

F 5

deposition, occurring in widely - extended horizontal beds abounding in fossils.

Devonian, Or Old Red Sandstone.

This order, so long known under the name old red sandstone — a term nearly as obscure as that of grauwacke — has, bj the researches of Professor Sec^wick, Sir R. J. MurchisoD, Sir H. De la Beche, and Messrs. Phillips and Lonsdale, been raised to the rank of a distinct fossiliferous formation. Viewed as sandstone and conglomerate in the light of drift, it appeared difficult to connect it with the limestones of Devonshire ; but when similar limestones were found on the Continent in similv positions, the limestone of the Eifel being thus placed, tbis difEculty was removed, and tbe formation was found to embrace the usual assemblage of argillaceous, sandy, and calcareoos strata. In Scotland, and on the borders of Wales, it occurs in the form of a red sandstone and conglomerate, associated with shale and marl ; the conglomerate and sandstone at the top, tbe vari^ated marls and impure concretionary limestone (com-stone) in the centre, and variegated micaceous or quartzose sandstone spUtting into tiles (milestone) below. In the North of Scotland many peculiar forms of fishes have been found in the lower division, whilst in the upper, comprising the belt of yellow sandstone, appears the genus holoptychus, which extends into the carboniferous order. Were this portion alone of the system studied, it would appear to be connected with the carboniferous rather than with the Silurian, and it is so placed by Cotta ; but when the Devonshire and Cornwall strata are examined, and compared with those of the Eifel, the presence of species common to the Devonian and Silurian on the one hand, and to the Devonian and carboniferous on the other, impress upon them a different diaracter. In consequence of this mixed distribution of fossils. Professor PbilUps has proposed to embrace under the general term palaeozoic, the Cambrian and Silurian as the lower palaeozoic, the Devonian as the middle palaeozoic, and the carboniferous as the upper palaeozoic, to

Rudimentary Geology. 131

which Sir R. Murchison has added the pennian, including the magnesian limestone. Of 275 species in the Devonian strata of Devon and Cornwall, Professor Phillips states that 25 have heen found in the lower division in England, 51 in the upper division in England, and 57 in the Eifel and Bensberg.

The very dilapidated condition of many of the fossils of this formation shows that they have been drifted into the deposit; the trilobites and many other fossils of the Silurian epoch described by Professor Phillips being generally in a shattered state : if then these fossils, and many of the zoophytes, &c., were brought in by drift, it is very possible that they were living elsewhere at the time of the deposition of the Devonian strata, and that the actual zoological relations between the Silurian and the lower Devonian are closer than would be inferred from such fragments alone. Professor Phillips seems to adopt this opinion, that there is a considerable analogy between the lower Devonian and the Silurian on the one hand, and on the other between the upper Devonian and the carboniferous. Cotta classes the Eifel beds with the Silurian ; but if Silurian, they occupy a higher posi« tion in the series than any of our English or Irish beds, and must therefore be parallel, as shown by our English authors, with the lower Devonian. M. D'Orbigny states the number of mollusca at 1054, and of radiata at 146, — ^numbers so great when compared to the more decided formations below and above, as to strengthen the belief that many of them are extrandous.

In referring to the use of fossil evidence it should therefore be remembered, that as any fossil species of an early epoch may be continued upwards, or drifted into more recent formations, the appearance of a small number of such fossils cannot be considered sufficient evidence to place the strata containing them in the older formation, unless supported by the general grouping and arrangement, under the same petrographic characters ; whilst on the contrary, the appearance, in any bed, of fossils characteristic of a more recent formation^ must always be

Strong presamptive ernfence against its antiquity. Dr. Mantell and Capt. Brickenden have announced the discovery in the Elgin sandstone (considered a portion of this system) of a new reptile, in which the characters of lizards and frogs are blended together, and Dr. Mantell has named it Tderpeton Elginense, Professor Forbes has also announced the discovery of freshwater shells and plants in the old red sandstone of Knocktopher, county Kilkenny, Ireland ; and these two facts of the existence of air-breathing reptiles and of fresh-water animals and plants at so remote an epoch, are singularly confirmatory of the analogies between the past and present states of the world. •

Practically, many beds of this formation, especially of tbe yellow sandstone, are excellent building stones; whilst the decomposition of its marly beds produces a rich productive soil. The limestones are Tahiable both for building stone and lime. In Russia, south of Petersburg, a large area, formerly supposed to belong to the new red sandstone, is of this geological age, though abounding in saliferous and gypseous beds; — being another proof that salt deposits have, in very similar circumstances, been formed at various geological epochs. The determination of this formation is important, as it generally underlies the coal, whilst in Spain coal-bearing strata are associated with it.

Carboniferous.

This formation,, so important in its economic bearings, is a vast assemblage of calcareous, arenaceous, and argillaceous strata. Of these the great masses of limestone were probably formed in deep seas, and the coal shales either in estuaries or lakes, so that where the limestone division prevails, the shales may be expected to diminish, and the estuary character being lost, the coal will become less abundant, as in Ireland, where it is comparatively scarce.

The great limestone deposit which forms the basis of this system has been called the mountain limestone, and is diarac-

Rudimentary Geology. 133

terized bj many peculiar fossils : in the Southrwest of England* in Somersetshire and South Wales, it is strongly marked, and is separated from the coal measures above by a thick deposit of arenaceous strata ; but in the North of England the coal descends into the millstone grit, and even alternates with the upper beds of the mountain limestone ; and in Scotland, this mixture of marine strata with those containing coal is still more marked. In Ireland, many of the masses of the mountain limestone are separated into distinct beds by shale, not associated with coal, which was probably also deposited in tolerably deep water, as in the Mediterranean, where the coral living at the bottom of its waters is frequently covered over by mud moved along by the currents.

The presence not merely of a vast variety of terrestrial plants in the coal shales and grits, but in some cases of fresh-water fossils, has led to the beUef that some of these deposits were lacustrine; but whether formed in actual lakes, or at the mouths of rivers which, when occasionally dammed up, became for the time lakes, cannot be determined. The fossils of this formation are very characteristic: in the plants, so rich in forms which resemble the tree ferns of the tropics, there is evidence of a climate Uke that of our most Southern regions, and the analogy is supported by a great abundance of sauroid fishes, and of cartilaginous fishes of the families of squalidae and raiidse. The crinoids, or Uly-shaped animals, are largely iQfeveloped ; as are the corals, many of which are lamelliferous, as in coral reefs now forming : and in investigating this portion of the zoology of the formation, it is desirable to study the habitats of corals, many of which are confined to reefs whilst others live in shallow water on the coast and are frequently enveloped in mud, and thus to trace out the peculiar condition of the sea-bottom of that epoch. Of brachiopodous molluscs, the genera productus and spirifer abound.

Coal is the product of ancient vegetation entombed in mud and sand, and in the course of ages reduced to its present state by chemical change ; but consistently with this conclusion it

might be assnmed either that the plants grew where the coal now exists, or that they were washed down into estuaries, and there accumulated, or that coal is the product of ancient bog or peat moss, — an opinion supported bj microscopic inyestigatioD. It is highly probable that each of these theories is correct in certain locaUties, and the alternations which must have taken place in either case are very remarkable: for example, in the North of England the total thickness of the coal-bearing strata may be estimated at 3000 feet, whereas the coal itself is arranged in many layers or seams, the total thickness of which does not exceed 60', whilst the thickness of the seams varies from a few inches to 6' or 7'. In the Newcastle district, counting the minute seams, there are forty layers. At Dudley there are eleven, of which one is 30' thick. In South Wales there are twenty-three beds exceeding 1' 6" in thickness, besides many others, the total thickness of workable coal being 95', equal in mass to many hundred million tons of coal. At Mons there are 115 workable seams, few of which exceed 3' thick. Besides the Irish and Scotch coal fields, England and Wales possess the following coal basins : Northumberland and Durham, Yorkshire, Staffordshire, Lancashire, Whitehaven, Warwickshire, Shropshire including Coalbrook Dale, North Wales, South Wales, some of which may be subdivided into other basins.

These masses of vegetable matter, composed of the remains of plants which have long since passed from the living world, the greater proportion belonging to the order of ferns and others being giant mosses and cellular plants, exhibit peculiar conditions of organic Ufe. Some of these conditions have been repeated, though in a fainter degree, at subsequent epochs, and given rise to Umited carbonaceous deposits ; but as the various changes, physical and organic, effected on the earth's crost, advance towards the present state of things, an approximation to the conditions now observable, or a recession from those which once so greatly promoted the growth of succulent plants, is in accordance with the laws of nature. As the effect of a diminution of central heat became locally perceptible, sac-

I

JtVDIMKNTABY 6K0L06T. 135.

cessire portioiis of the earth were fitted, though in a yarying degree, for the support of such plants, and partial deposits therefore appear at various epochs ; and it may he added, that when the Polar regions were thus hrought to a proper temperature, they were, from the deficiency of solar heat, hetter fitted for such vegetation, the climate being more equahle and less affected hy the scorching efifects of the sun*s rays than in Southern regions. The seams are sometimes extended over a wide space, but the general character of a coal deposit is that of a basin in which the phenomenon of faults is strikingly exhibited, the seams being sometimes thrown up or down several hundred feet; some faults being accompanied or caused by dykes, whilst in others the cause of dislocation and of vertical slips is not visible on the surface. The knowledge of the various forms of faults, and of the direction in which a suddenly lost seam should be sought, constitutes one of the most difficult points in mining science.

The following Table from Dr. Ure gives the quantities of coal shipped from the several ports in England, Wales, Scotland, and Ireland, in 1836 and 1837, and there has since been a vast increase, as it appears in Taylor's Tables (' Statistics of Coal,' p. 260) that 11,254,750 tons were shipped in 1845.

Tons. Tons.

England and Wales 6,757,937 7,570,254 812,317 or 1202 per cent.

Scotland .... 624,308 626,532 2,224 (Mr 0*36 „

Ireland .... 7,027 7,515 488 or 6*94 „

Total. . . 7,389,272 8,204,301 815,029 or 11*03 per cent.

In Fuller's time (1661), 200,000 chaldrons were imported annuallyinto London, but now the consumption is nearly 3,500,000 tons, which is brought into port in about 9700 ships. The annual quantity raised was estimated at 15,500,000 tons by Mr. Taylor, and Durham and Northumberland, he considered, could have met that demand for 1700 years. Mr. R. C. Taylor estimates the whole British production in 1845 at nearly 35,000,000 tons per annum. The area of the coal measures of

Rudimkntaby Obology.

Great Britain and Ireland is 1 1,859 square mfles, or 7>58 acres, or about one-tenth of the total area ; and there are 51 coal fields. The French Mining Reports state that < raised in thirty departments of France, in which 258 mis in operation, and 21,913 workmen employed. In 181' quantity raised was 665,000 tons; in 1825, the quantit doubled; in 1832, the produce was 1,600,000 tons; in it amounted to 2,500,000, and it is now more than 4,00 tons.

Cotta gave in 1839 a statement of the coal produced i several coal districts of Europe, which is useful for compa though requiring much correction, as the produce of Be was in 1845 about 5,000,000 tons.

In England Belgium France Prussia Russia

Tons.

Austria w*^ Bohemia 184,616 Bavaria . . . 32,308

Saxony . . . 28,616

Carried forward 30,753,233

Tc Brought forward 30,71 In Sweden and Norway ! Hanover . Spain . . Both Hesse Sardinia . Weimar . Portugal .

Total

Mr. R. C. Taylor states the production of the United S as about 4,500,000 tons, but this affords an imperfect me of the power of production, as the area of the Alleghany field is 65,300 square miles, or nearly one-fifth of the tota of the States in which it is situated. Dumas gave, in j the following values of the coal produced :

England 90,000,000 » 3,562,

Low Countries, including Rhenish Pro- "1 07 aaq aaa __ | 454 vinces and Luxemburg .... J

France 12,000,000 » 475,

Russia, Silesia 3,600,000 « 135,

Hanover and German Confederation . . 3,600,000 » 135,

Total 5,772,

; coal produced by the British coal fields more than doubles thequanCityraisedin the collieries of the rest of Europe; and the gross value of the collieries of Great Britain sod Ireland cannot be estimated at leas than ^9,000,000 sterling.

Bat this u not the only valuable product of the formation. Beds of argillaceous carbonate of iron, or clay ironstone, which is the iron ore principally used in the British Isles, are associated with the coal shales, thus putting in contact nith each other the mineral ore and the fuel for smelting it. In 1826, the quantity of pig or cast iron produced nas between eOO,000 and 700,000 tons; and in 1846, 2,214,000, bemg equivaleut in value to £8,856,000, at £4 per ton sterling. In France, the number of establishment a in 1836 was 894, and of workmen 15,738, the product being 303,739 tons of pig iron; and in 1845, 448,900 tons of pig or cast metal were produced and manufactured into 342,200 tons of bar iron, which, at about £6 per Con, would be worth two millions sterling; and as the manufacture of pig into bar iron is so closely connected with the first process of smelting, that the higher value of this product may be assumed instead of that of pig iron in estimating the importance of the iron manufacture, — how great must be the wealth produced by this homely but most essential metal, even in this early stage. In France, that beautiful association of the iron ore with coal, which distinguishfs the British coal fields, exists only very imperfectly, so that a large portion of the iron is smelted by wood or charcoal.

Blelgium, which as a coal country ranks in Europe next to lagd, 150,000 tons of iron were produced in 1845, and t snmmer travellers know the busy aclirity of the iron I works of Liege, where 4200 men are employed night and day, and are aided by eleven steam engines with an aggregate force of 500 horse-power.

Nor are these the only resources of the formation. In England the mountain limestone, which exhibits in its layers of silicious or chert concretions a strong analogy to the subsequent pelagic deposit of the chalk, is the source of much mineral

I

138 y K CD I KB NT AST 6KOLOGT.

wultb, and produces more than one-hmlf of its letul. proportion dae to this formation mav be assumed as toos, equivalent to about j£5{)0,OI>0 sterling ; so tlud, this fonnatioD alone, mineral weaith is annuaUy pi in Great Britain to the amount of nearly £ 1 9,000,000 whilst, in addition to this dirert production, ita indirect anceaaafTordiiig the means of smelting the ores of othen ■nch as copper and nnc, is foiciblj illustrated by the works of Swansea, to which copper ores are brought trfm ill qnarters of the globe, and the value of the lime, and mKbles or other budding stones, produced from the limestone, and of the excellent building stone which is obtained from many of itt grits, as in the neighbourhood of Glasgow, the beauty of thit dty being due to the prosimity of such excellent materials, b Teiy great. If the mind passing from the simple value oftlie materials themselves can realize the vast results proceeding from coal and iron in the use of machinery in manufactonM and railways, it discovers in the possession of such large tod. productive coal formations, the source and foundation oftbe commercial, and, as its consequence, the political greatness of Great Britain.

Great Britain has in her colonial possessions of New Hollaild Knother coal formation, which has been supposed to belong lo a more recent epoch, though it is highly probable that tte peculiarity of some of the plants onlyimpUes a commencemeal of that isolation of type which now distinguishes that couatrj; and the coal of the East Indies is also supposed to he more recent than the true coal formation. China and Japan Me supposed to possess extensive deposits, and coal occurs is Borneo and Lab uan. In America a formation both of blindand bituminous cool, within the limits of the United States, greallv exceeds in extent our British coal fields ; and in our own colonin of New Brunswick, Nova Scotia, Cape Breton, Prince Edward's Island, and Newfoundland, there is an extensive coal formatkn. In New Zealand coal of good quality has also been found; ID^ there is reason to believe that in our South African posseaaioM

^^Roal romintioa of cousiderable extent exists in Port Natal. The preceding ia but a faint and imperfect sketch of the lateral diBtribntioQ of this most valuable mineral formation, as it has been impossible in eo brief a apace even to notice some of its deposits, such, for example, as the Spanish cool district of Aaturias ; bat enough has been said to show how large a portion of the earth's surface had been at this epoch clothed with ft tropical vegetation. The disturbances which have affected the crust of the earth either during or subsequent to the formation are not only exhibited in the great faults of the coal beds, but in the remarkable difference of position in which each beds occur, many of the seams at Newcastle being worked under the sea, whilst at Chipo, which rises above the Plain of Santa Fc de Bogota, coat is found at 8000 feet above the sea, and at Huaaoco at 12,800 feet, orat the limits of eternal snow. It was supposed only recently that reptiles first existed at this epoch, exhibiting in the Archegosaurus a monstrous form between the toad and lizard, the body of the former being combined with the JBWB and teeth of a saurian, and it was further asanmed from the discovery of carboniferous reptiles that the future discovery of the remains of birds and mammals in that formation would not be impossible ; but it does not appear that the one diacotery renders the other more probable, as the peculiar blending of the saurian and batrachian types in one indicates a more than usual development of reptiUan organization calculated to combine in one great class the functions spread over many classes in the more balanced and perfect organic system of the existing world. The discovery of three species of the genus Archegosaurus and of the genus Apateou ■carried back the origin of reptile life from the pcrmiau to the carboniferoua epoch, but it has now been pushed still further back to the Devonian by Capt, Brickenden and Dr. Mantell, thus proving the existence of dry land and of air-breathing animals of a similarly mixed type between the lizard and the frog anterior to the coal deposits.

J

PKKMIAN, INCLUDING MAGNXSIAN UMXflTOHK.

This fomiatioii, including its andnljiiig icd ooiig^oHiento» landstones, and marb, is imporUnt, u it Ofcrlies the cuboniferous. In the South-west of En^and its strata are nnooafonnable to those of the carboniferous sjstcm, whilst in the North-east they are confonnable to and seem to form part rf them ; but as in all formations, cases of this partial eonfomap bilit J between the upper and lower will ooeiir, acoordii^ is the disturbing movements are more or less extensire or loatl^ it is necessary to determine great geological diTiaions fiom a general and not from a local examination. Though ths sandstones strongly resemble the new red sandstone^ the fomk of this formation closely approximate to the carboniferons, the genera productus and spirifer of the brachiopoda occurring k both ; as well as the genus palseoniscus of fishes, a remarkible genus, which howeTer extended upwards into the new red sandstone, where the palaeoniscus catopterus occurs in profoiiaif associated with posidonomya minuta, in a small patch <Nr pool of the sandstone and marls of Rhone Hill, county Tyrone. In the op))Osite direction, spirifer undulatus (Sow.), supposed a characteristic species of the magnesian limestone, occurs k Ireland in beds which are overlaid by apparently well-marked carboniferous limestone. On the Continent, the name 'rothee todtliegendes * has been given to the lower red con^omente^ to distinguish it from the white grits which immediate underlie the kupferschiefer or copper slate and aometiiiMi contain copper ore, which the red-^e»l-lyer does not. h England, there is neither the copper slate nor the white grit» and the lower red sandstone and conglomerate are placed hf Cotta in the carboniferous system which immediately unde^ lies the magnesian limestone. In the South-west of Ea|^ land, drift or conglomerate beds prevail which possess tl» peculiarity of a dolomitic or magnesian limestone paste; M the North-east, a yellow magnesian limestone, passing upwards and downwards into marl slate and marl with gypsum. Ob

Rudimsmtaby Geology. 141

the Continent, tlie zechstein is a dense though sometimes porous, grey, generally fetid magnesian limestone, connected upwards with marls containing many extraneous suhstances, such as ironstone, gypsum, and rode salt, thus approaching to the character of the true new red. The copper slate of Mansfield has a thickness varying from 1^ ft. to 2 feet, and is worked in numerous establishments by a most difficult process, called there krummholzerarbeit, or crooked-stick work, the miners crawling and working in low cavities, only 18 or 20 inches high, lying upon their sides, and being supported by pieces of bent timber or crooked sticks. In England, the ^finrmation is practically important from the excellent building atone which some of the magnesian beds afford, the tint being q>ecia]ly favourable for Grothic buildings. York and Beverley Minsters are favourable examples of the stone, but its durability varies according as the more purely magnesian limestone or the gritty beds have been used. This stone has been sdected for the New Palace of Westminster as the best building stone of England.

It was long thought that nothing but deteriorated coal would be found under the magnesian Umestone; but this error, doubtless proceeding from a belief that the magnesian lime- Stone, Uke crystalline dolomites, had been formed from meter morphic action, has now been dispelled, and the magnificent odilieries of Hetton in South Durham have laid open the coal seams by piercing through the magnesian limestone. Mr. W. Sling has illustrated the formation by his recent monograph of permian fossils. This monograph exhibits some cases of approximation to the subsequent trias, but more of a close resemblance to the carboniferous ; and it may also be stated that the flora of the permian approximates more closely to that of the carboniferous than of the trias, though M. Adolphe Brongniart has pointed out great differences in its several divisions. In Russia, the permian system is fully developed, and combining all forms of deposit, is manifestly entitled to the rank of a distinct formation. Mr. Kinghas described 277 species

I

of planta and animals, and very recently tvfo remarkable from the Rjissian strata have been described by Fisdiet, Ommotolampes Eichwaldi, nhleh is 3 feet long, and en by bony Bhields, which were at fitat mistaken for tin shell, and Trachelocanthus Stschesrovskii, which baa a sp its throat turned backwards, — both of which, from nities, were probably fresh-water fishes.

New Red 8Akd8Tone, Or Tkias.

This formation, from the prevalence of a Tari^ ractcr id its sandstones and marls, has been » ' poikilitic.' On the Continent, where its several mei are better developed than in England, it has received the of 'trias,' aa divisible into three great sections. The I of these is the ' bmiter sandatein,' or variegated s which is distinguished by greenish stripes and spots, a tains clay galls ; it is associated both above and below variegated red and green marls, containing both laminate fibrous gypsum. Mid rock salt. The muschelkalk, or O division, is deficient in England, and as gypsum and R occur on the Continent in marls, both of the upper and '. division, it is difficult to dedde geaeraUy whether oar ^^ bearing strata do or do not belong to the more decided ^K stones and conglomerates which underlie them. The ' ^H sandstone of the Vosges, supposed to belong to the ! ^f or variegated division, is placed by Sir R. Murehison ii permian : it is a valuable building stone.

In Thuring^a and Swabia the muschelkalk division is developed ; the limestone (which is occasionally i occurring under several forms or varieties which alternate marls and clays sometimes containing gypsum and rock e In the upper division or keuper, marls and clays pr though still associated \rith sandstones. Gypsum and salt still occur, and £ometinie= an impure coal. As fossils m extremely rare in the sandstone divisions, it was scarcely ^_ possible to allocate to their proper place in this triple ayaUik

Hudimentart Geology. 143

English beds -, but the fossils of a dark marly stratum d the ' bone-bed,' which occm's at Asmouth, and on the ,s of the Sevt^iu in Gloucestershire, are characteristic either ae keuper or muschelkalk ; they are, Hybodua jilicatilis, ichthys apicalis, Gyrolepis tenuis triatus, G. Albertii, — of h it is very remarkable that Ssuricbtliys apicalis, Gyro- Alhertii, G- tenuiatriatus, hare been also fouod in a seam ilcareous grit connected with black shale in an equally deposit on the face of Ben Evenagh, at Lisnagrib, county terry, the Acrodus minimus, another mnschelkalk fossil, J there added to the list. It may therefore be reasonably red that though the muschelkalk is not fully dcTeloped in Sritish Islands, two members of the series, with a trace of ttber, are certainly present.

le remarkable foot-prints of an animal, to which the name itherium was given, should be here noticed. Various con-ies as to their nature were hazarded, but Mr. Owen has ed that they were formed by the animal which he had ionsly named labyrinthodon from the nature of its teeth, irbich belongs to the batrachian order, or is a gigantic frog, ill be observed that in respect to this organic form an igy of type continues through the Devonian, the carbo- Dus, the permian, and the triasic formations. The genus onites of the cephalopodous molluscs first appears here ; in the flora as well aa fauna there is a striking difference the underlying strata, the species of forty-seven geiiera i by Professor Bronn being quite distinct. The type of podous Crustacea, to which our crab and lobster belong, appears, and footsteps of supposed wading birds have observed iu America. It was announced some years ago the remains of mammals had been discovered in this ation in Wurtembei^, and thia discovery has been con- !d by the detailed description of the fossil bones by M. er, who considers them to belong to an animal of the npiaJ type, alUed to the didelphis ; and if this be a correct

detCTUimstion, it is Bnotlier example of the tcry Mdj uice of this now almiffit isolated type on the nnh,

Id England, this fomiation is tlie depositor; of nAfl In Cheshire, the nltemHtiog beds of red and greninartfl gypsum and rock salt sometimes exceed COO feet in ' and at Northwich, the two beds of salt are at least 61! fill ihirkness, and extend laterally fur l| mile. I prevails more than salt ; but even there, on the line be Uelfast and CHTrickfergiis, (here is reason to beliert iWB may he found. And generally the eurious connection ('ifl phflte of lime with chloride of sodium deserves ittm affording a probable indication of the occurrence of sill i|i formations, and some clue to the laws which r deposition. The averse quantily of salt mamifertiiCT Cheshire may be stated at about 250,000 Ions annually. 1 celebrated salt mines of Wieliczka, in Galicia, belong ts s formation.

In this formation argillaeeoua matter or clay prepond being associated with argillaceous limestone, marl, sandjjl and sandstone, and it is remarkable as having been tll^ of marine reptilia ; for although the genus ichthyosaurti appeared in more ancient deposits, it seems lo haV attained its full development, and was accompanied 1 equally curious genus plesiosaurus. The exist marine enuriaii amidst the Gallapi^os Islands, by Dr. Dam'in, exemplifies the probable mode of exiilcB of these vast animals, and the confommbilily of their h»i with those of the crocodile. A eurious genus of ce]ihalopoie molluscs, the belemnite, nrst appears here, and the gryphxl genusof the family of oysters, is abundant, establishing by tfi presence the marine origin of the deposit, and confirining I fact that marine saurians were, at that early period, swimmi in multitudes around the muddy shores of the then east

J

Rudihentaiiv Geology. 145

laud. The characteristic colour ot'tlie limestone, which ! times in a. section exhibits a riband-like HrraDgemeut amongst the argillaceoiia beds, ia blue, but there is occasionally a white VEnetf, whilst in aome instances aitnilstone prevnila over the limestone in the lower members ; as for example, in Wiirtemberg, where sandstones of browniah and yeliowiah hues ars asaotiated with marls and Umeatonea in the lower lias, the upper being composed of dark lias shale and limestone. The has shale of Wiirtemberg is so rich in a species of the genua posidonomya, the P. Bronnii, that it has been called the poaidorian shale; and the similar occnrrence of that genus in shales of the carboniferous period, as well as in maris of the new red, is illustrative of the analogous character of all such deposita. Some thin beds of coal occur also in the shales, which, as well as the hmestonea, are strongly impregnated with bitumen, the product, most probably, of decomposing animal substances, such

fishes, &c., which aboiinded at the epoch of their deposition. Ily the sandstones, though iiable to become ironshot

detained, are occasionally sufficiently firm to be used for The limestone ia occasionally hydraulic, and the soil IB gencTslly fertile.

Oolite Or Jura Formation.

The clays of the lias form the basis of the oolitic system, and in ascencSng into it, other argillaceous hands mark those changes in the conditions of deposit which are to be expected in every great formation, representing, as it must do, thevi tioDB of drift consequent on the changing direction of currents. These hands hate, in England, led to a division of the ooUtes mto lower oolite resting on the lias ; the middle oolite resting on the Oxford clay, which separates it from the lower oolite ; and the upper oolite resting on the Kimmeridge clay, which is between it and the middle oolite ; but it muat be evident IhaC nich day bands, being merely the residt of local causes, c not be expected to occur onivcrsaHy, or ^o jiroduce a similar dimioD in all countries. On the Continent, the funn

1

been diTided into the upper and lower Jura, the upper being characterized by a light-coloured, whitish or yellowish limestone, which forms the great mass of the Jura Mountains, from which it has derived its name, and the lower consisting of roe-stone and dolomite, the latter penetrated by holes or cavities, and of sandstone, marl, and clay. The hornstone partings of the Jura limestone strongly resemble the flints of the chalk, and its surfaces exhibit very beautiful dendritic markings ai oxide of manganese like those of the chalk of Ireland. The Bavarian Jura formation is remarkable for the numerous bone caverns of its dolomites, and for the celebrated lithographic stone of Solenhofen. The wooded hills of Pappenheim are composed of a regularly stratified hme-stone, arranged in thin horizontal beds. The stone is extraordinarily pure and dense, yellow or grey in colour, and, from the thinness and regularity of its layers, peculiarly fitted for lithography. The hills themselves are distinguished by their broken aspect and wall-like character, which makes them look like so many fortresses ; and on entering the valleys, the ringing sound of the true lithographic stone, as it is broken up for use, is heard on all sides. The layers used for this purpose are from 1 to 4 inches thick, and when still thinner, or unfit by containing fossils for lithography, they become useful as ■] roofing tiles, as door and window linings, as tables, &c., to which purposes they had been extensively applied long before the invention of lithography. These peculiarities of the physical features of the country, and of the mechanical characters of the stone, deserve to be remembered in looking out for good hthographic stone in other countries. The presence of large fossils is a great defect in lithographic stones, and veins also . should be carefully avoided, as in printing they mark the drawing, * however fine they may be, with white lines, and increase greatty the difficulty of reducing the surface to a uniform state. Of the English oolites the Stonesfield slate, lying at the base of the great oolite, a member of the lower division, is the most remarkable : it is a sHghtly oolitic limestone, and though only 6 feet

■t

Rudimentary Geology. 147

thick, abounds in fossils. With impressions of ferns and other terrestrial plants, the elytra of beetles, and the remains of saurian genera already noticed, occur those of the pterodactyl or flying lizard ; and what is still more remarkable, the jaws of at least three species of mammiferous quadrupeds of the marsupial order, — ^partly allied to the opossum, and partly to the marsupial genus myrmecobius of Australia, — a singular analogy, at this early epoch, to a region still so widely distinct in its fauna from other parts of the worlds In the lower division also occurs the Bath oolite, which is an excellent stone for the dehcate mouldings of Oothic architecture, and is represented in France by the Caen stone, which was imported for the purpose by our early architects, as may be seen in the beautiful Temple Church. In the middle ooUte is the ' coral rag,' so called from the continuous beds of corals of which it is composed, and which still retain the position in which they originally grew. In the upper oohte is the celebrated Portland stone, so well known for its beauty as a building stone.

Many parts of this system are distinguished by a profusion of some particular fossil, a fact which is always characteristic of a regular deposit, as distinguished from a drift : such, for example, were the great oolite, the surface of which is studded over with pear-encrinites, which were afterwards buried by the irruption of the Bradford clay, the clays of the upper oolite, vdth their oysters and gryphites (ostrea deltoidea and gryphsea virgula), the nerinsean limestone of the Jura, distinguished by the peculiar univalve genus nerinsea and the diceras hmestone of the Alps, so called from the abundance of specimens of the very curious bivalve genus diceras.

In this formation the fossils generally mark a marine origin, but the frequent occurrence of fragments of wood, the coal beds and bituminous shale which enter into the system, the many impressions of plants and of insects, as in the calcareous slates of Stonesfleld and Solenhofen, the abundance of saurians and of encrinites which may be considered more fitted ibr

shallow than for deep waters, and, above all, the actoal discovery of land animals, which it is now known existed even in the trias, all concur in proving that the deposits were formed in the vicinity of land ; and it is therefore a fitting precursor of the next formation, in which evidences of land and fresh water in connection with it are more decisive.

Wealden Formation.

This formation, remarkable for its fresh-water origin, is not entirely destitute of marine fossils, and it has therefore the . character rather of an estuary than of an inland lake. On the Continent, it has been associated with the cretaceous system, and considered the equivalent of the Neocomien of the French. In England, the oolitic beds were first raised up quietly without any great disturbance, as is shown by the celebrated 'dirt-bed' of Portland, with its upright roots, which rests horizontally upon them, the roots even penetrating into the subjacent oolite; and then portions of the compound deposit were thrown out of the horizontal position, as appears in the section at Lulworth Cove. If the principal basin, in which these beds have been traced, extending at each end from France into England, be really continuous, the deposit, whether lacustrine or estuary, was very extensive, though much interrupted, formations of a different character being contemporaneously deposited within its area: but these are problems very difficult of solution, as it is almost impossible to represent to the mind the actual condition of the earth's surface in respect to land, sea, and river, at each successive epoch of its history, obscured as it must have been by the effects of reiterated changes and unceasing wear.

This vast lake or estuary being exposed to the action of the sea, the dry land bordering it, and islands within its precincts, . were covered by the marine deposits of the cretaceous epoch, an operation which was aided by a depression of the land sufficient to permit deep sea deposits. Such wonderful oscillations are strongly contrasted with the comparative quiet which now

3Logv. H9

reigns ou the earth ; but they are Icamt from geological Jn- Tcat^tions, just as the facts, the habits and opinions of past ages are from historic records ; and we owe therefore to this science the knowledge we now possess of changes which must without it have been unknown to us. In England, where this formation is more extensively developed than in anv other country, the well-known Purheck limestone, distinguished by a profusion of fresh-water shells, forms its base. The beds of limestone are separated by marls, and the conjoint thickness is about 250 feet, a great depth for a fresh-water deposit. The Eastings sands with clays and calcareous grits succeed, and are about 400 feet thick, being equally extraordiitary as & fresh-water drift ; and the whole ta covered by the Weald clay, with its thin beds of sand and shelly limestone, about 200 feet thick. This formation implies the existence for a long time of vast areas of fresh water, resembling those of North America, in which at this moment, from the continued wear of their banks, and depth of their bottom, which in some cases is below the level of the sea, estensive deposits must be forming. Mr. Robertson has proved the existence of Wealden beds at Brora, in Sutberlandshirt-, nnil advanced reasons for associating the Yorkshire oolitic coal also with this formation. The Neocomien beds, which French Geologists consider the equivalent of the Wealden, are marine dejposils consisting of variously coloured sands, and of marls and clays characterized by peculiar fossils, amongst which especially Holaster complanatua, one of the Echinidsc, abounds. These beds are separated from the overlying greensand by French, and associated with them by English Geolt^ists.

Similar fresh-water deposits can be traced in other countries; and it is evident therefore tliat a very large portion of Europe was once covered with fresh water. In Westphalia the Wealden is represented by a deposit 800 feet thick, consisting of sandstone and bituminous marl, with layers of coal and of ironstone and beds of limestone, the whole being characterised by freshwater fossils. In Saxony, at Niederschone, it is reduced to a

deposit 40 feet thick, of dark-coloured sandy ahale and marl, which is sometimes bitmniDoiis, and contains traces of coal, with an abundaiu^ of vegetable remains. Amongst these ibssil plants only one shell has hitherto been discovered, but that is a most characteristic one, belonging to the fresh-wat^ genus anodonta, which is confined exclusivd|y to muddy lakes and pools. The quadersandstein, or green-sand, overlies this deposit, and Cotta thinks it probable that the beds of that fimnition in Silesia, which contain coal and the remains of plants, should also be allotted to the Wealden. Amongst the numerous reptiles of this epoch appear tort(»ses of genera whidi now occur in the fresh water of tropical regions. The igvanodon, so called by its discoverer. Dr. Mantell, from its analogy with the living iguana, was a herbivorous reptile about 30 fe^t long, and appears to have abounded at this epoch, associated with the hylseosaurus, another gigantic saurian. The nature of the fossil plants, and the number and magnitude of the reptiles, show that the climate still continued tropical. The Purbeck limestone is well known as lumachella nuurble, the designatioD lumachella being derived from the Italian word himaca» a snsO, and applied to those varieties of limestone which, with a granular or marble structure, abound in fossils. Caution is required in the selection of this stone, as some of its beds ei^sily diantegrate ; and in all specifications for its supply a si^nple should be referred to, in order to insure the delivery of the pn^ kind ; a remark which is applicable in various degrees to dbnost every building stone. The sandstones, whidi are not durable, wear into very picturesque scenery, as about Tunbridge. The clays produce a strong soil, as in the rich district of the Weald of Kent.

Before quitting this last member of the oolitic series it it right to make a few general observations on the facta which it exhibits. The sera of the oolites was one in which the reptile type was most highly developed ; and reptiles^ fiom the first appearance of the type in the old red sandstone or pit^ bably in the l^iprian, to its condition of highest develepment

«Kcdimentary Geology. 151

flie oolites, appenr to have been designed to fulfil the functions of other classes of animals. Hence there is it Tarintion in the anatomical structnre calculated to embrace forma anrj functions now appropriated to other animals. In Australia this eiteoaon of one type so as to represent several classes of animals is found in the marsupials, some of which are herbiTOrous, some camivorotis, and when it is considered that the saurians of this epoch peopled at once the seas, the land, and the air, wc may reasonably believe that they represented in great measure other classes, and that there is little rcasoo to believe that anv great,, number of other mammals or of birds then existed. The asaocitttioti with them of the mareupial type, which exists isolated in Australia, is rather confirmatory of this view than otherwise; and the occnrrence of coal in the Yorkshire oolites, as well as in the East Indies and elsewhere, is another proof that the general conditions of the earth were still fitted for the rank and loxuriant vegetation of those early ejiochs, and for the existence of multitudes of huge reptiles, against which Man in his primitive state must have contended in vain. The earth was, in fact, progressing towards a fit state fcr Man's residence, and the animals which lived at each stage were perfect in their kind, and suited to the conditions of the epoch.

Cretaceous.

Succeeding to the extensive fresh-water formation of the "Wealden, is a still more estensive, and generally more widely diffused marine formation — the cretaceous. This change similar to that which will take place if, after the long-con tinned deposit of fresh-water detritus in the depths of the lakes of North America, the sea shall be admitted by a depression of the surface, and the bottom of Ihe lakes now actually below the sea level shall become a sea bottom. Even a moderate depression would cause such an irruption of the sea over a large portion of the country, and marine deposits would immediately commence. If, again, after an accumulation of such deposits,

livalent in thickness to the cretaceous, the whole mass were

iiptin«d bj the action of subterranean forces, the fresh-wi deposits might be brought to viev by the fracture and remi of part of the marine covering, of which the remaimng ] iTOiild continue m a murai bouadarv surrounding them, and result would be analogotis to the Wealden and chalk. Co* nenciog at its base, the cretaceous system is sandy, and th» division has been named the greensand formation in Englanjt.' the quadersand stein formation in Germany, — names derinfi from the principal peculiarity of the sandstone in each locaB^ik In each it admits of further subdivision info upper and the ttto being separated in England by a deposit of mari i day called gault ; in Germany by one of marl, marly sandst< and limestone (the planerkalk). But though tliese divis* exhibit a striking conformity nheo viewed at particular loc Idea (if, for example, the green-sand of England be comparM with the quadersaiidatein of Stutony and Bohemia), conaideraM modifications appear in other localities. In Westphalia oi North Germany, a conglomerate and a clay which Cotta m killers the equivalent of the Specton clay occur below the low quadcr : the planer is replaced by a blue clay with cryatali t gypsum, corresponding slill more closely with the Englil gautt ; the upper qnader is represented by a green-sand, wlu) is surmounted by bright and red marl. The sandstone of tl Carpathian Moimtains is also referrible to this epoch. On d Continent, the upper limit of the green-sand is nut alwayadi tinrt, as the same lithological character, in sandy loarla Ul sandstones, extends in 'Westphalia aod North Germany high up into the upper aection of the cretaceous system ; but these are only natural variations, being the necessary result of those local peculiarities which have already been so frequently adverted te. In England, the upper section of the cretaceous formation can be divided into the lower chalk without flints, and the upper chalk with flints, the whole reposing on the chalk mnrl, — a subdivision which is purely local. In Saxony and Bohemia, the whole section is reduced to beds of flints ; in Westphalia North Germany, the upper member is feebly representeil.

_4nd

Bcdimentarv Geology. 153

^!rall bi'low it consists of chalk marls and sandstones, far more in character with the green-sand than with the clialk, of which it ia proved to be equivaient by fossils. In France, the Maestricht beds resting on the white chalk with flints are at the summitj and from their pecnharities have been considered by some Geoli^sts an upper member, approximating the chalk to tbr tertiary strata, though their fossils are those of the white chalk, and the chalky character is carried downwards into the greensand. All theae modifications of lithological character must bt anticipated by the Geologist, and his skill alone can dispersi: the obscurity which they occasion as he traces out the boundaries of sea and land, of bay and ocean, at each successive epoch. Sometimes indeed the mineral conditions remain unaltered from one geological epoch to another, as is the case in the Mediterranean, where the Scaglia or white limestone with its flints has beeu in part deposited during the oolitic, in part during the cretaceous, and probably in part during the tertiary epoch, unless there be a transition member between the chalk and tertiary formations.

Few phenomena are more striking, or h attention, and excited more speculation, than the o long lines of flints in chalk ; the marked contrast between the dark hue of the flint and the pure white of the English chalk having attracted special attention to chalk flints. The occurrence of silicioua nodules similarly arranged is not confined to the chalk, but is observed both in the mountain limestone and in the oolite ; nor is the arrangement by nodules always the prevailing one, as in the chalk of Ireland extensive layers or beds are very common, and again in the oolitic and cretaceous portions of the white limestone of the Mediterranenn, The origin of flints has excited much speculation, though from the preceding observations it is evident that tlie question does not refer to the chalk alone. A microscopic examination having shown that they contain numerous infusorial remains, Ehrenberg was disposed to consider that they bad beeu

t almost exclusively of such animals ; whilst the disco

Tery of the texture of sponge in flints has led 1^. Boirerbank to aseribe tbem ezdunyely to a spongeooa origin ; nd again, others are more indined to beheve that the siHcSyhsnng been held in solution by thermal waters, was dqxMited in a gelatinous state and enveloped the spmiges and other bodies it contains. It i& highly probable that all these causes hue contributed to produce the result ; and considering the pecnliir affinity of silica lor organic substances, there can be little doubt that sponges have materially, though not exdoaiTeljr, contnbuted to the production of chalk flints. As yet, the compsrifloo of flints and (^erts in various formations has not becB Mj carried out, but it may be assumed that they will exhibit a isaterial and characteristic di£Perence in their zoological femains. The cretaceous system is peculiarly rich in fossils^ the whole mass even of the white chalk, as has been shown l^ Profeaor Ehrenberg, swarming with infusoria and other microscopic animals, in addition to the multitude of those of larger dimensions, as echinida, cephalopoda, &c. The spongiadss and alcyonidse are abundant : of the crinoidee there is the pecuKar genus marsupites ; of the echinida» the genus ananehytes^ sod a profusion of species of many other genera ; g£ the molkacs generally, the remarkable genera hippurites and radiolides, which with caprina, &c. Ibrmed extensive banks or reeh m the cretacean sea, deserve special attention, as their true nature is still doubtfuh the genus spondylus (plagiostoms and podopsis) has a very characteristic species in plagiostoins spinosum ; the genus pecten affords in P. quadricostatus and P. quinquecostatus the t3rpe c^ a new genus» rl^mchondls : the genus inoceramus abounds; whilst of the e^halopodous division there are many most characteristic genera and spedes, such for example as the genus turrilkes, a chambered shell with an external turreted form,, the beautiful genus baculites^ which unites a straight form with the skia« ous septa ci the ammonites, the hook-shaped hwEmtes, and a great number of ammonites and nautili, producing in this one order an assemblage so strangely different from tW r of our

Budihkktaky Gkoloot. 155

tut tropical seas, where the aingle genus nautilus alone remains, as justly to escite our admiration and surprise. Id fiah there is a nearer approach to the existing epoch, as the gcDera si|ualu3, galeus, and lanina occur ; of reptiles, there is the peculiar genus mosoaaurus, as nell as the pterodactyl or flying lizard. In the flora the cretaceoua approiimates more closely to the existing epoch, as lifty-one species of dicotyledonous plants have been discorered in the quadersandstein of Silesia, some of trhich are nearly allied to the very common genera willow and maple.

Practically, the chalk hills are well known for their smooth outline and surface, and for the short herbage of their downs, so fitted for sheep pasture, whilst the marly heds of the lower portion of the system have long been known for their fertility, as noted hy White of Setbome. In countries where the chalk is more indurated, and resembles the oolites, as in Greece, the tame character of its hills is changed tB a far more bold and striking outline, resembling that of mountains of quartz rock. Chalk is valuable for lime, being easily worked and burnt, and, though soft, can be used as a building stone ; but the white limestone of the Mediterranean, which belongs partly to the chalk, is an excellent building stone, tiinugh, being hard and brittle, dangerous in mihtary buildings exposed to cannonade. Flints, made up into a species of concrete, and strengthened by stone quoins, were extensively used in the walla of ancient churches, and are still so appUed ; they are also used as a road stone, but being extremely brittle, and breaking into fragments with sharp cutting edges, cannot be considered well fitted for such a purpose. Of the lower part of the system, the green-saud or quaders nd-stein is more practically useful on the Continent tlian it is in England, though the soil proceeding from it is much less fertile. In Saxony, the quadersandstein — so called from its breaking into quadrangular portions — is celebrated as a budding stone, the colour being pure and good ; aud as the planer (or gault) ia, there mostly deli cient, the upper and lower quaders are almost

JIDDlMKirTABT GKOLOGT.

'h contact, ud each yields its TAluable bed of building sbn lu other localitin the position of the pliiner is marked b; line of water springs which it throws ap, and taking an luns development, it stretches up into and occupies the place of I upper quader, which is there wanting. The boiindarj' hiU* i the bottom of the valley of the Elbe at Mebsen are ofgnoitl and sj'enite ; and at Dresden a depth of 856 feet was bore through without arriving at the granite. If this accumulatit of qnadersandstein and planerkalk could be removed, and tl basin containing it liud bsi^ and then filled with water, d bottom of the iidand sea thus formed would be more than 5C feet below the present sea level, and the surface of its wate about 300 feet above; bnt as the sandstones and liraCBtoa were a marine d^osit, it appears that after an qmch when i not very distant countries land plants were growing, and I extensive fresh-water deposit forming, this basin must halt been depressed more than 300 feet below its present len Hud have been a deep hollow in the sea ; anotiier of the sot prising results, like that of the Wealden, which geotogia research ha^ made known.

In America the upper chnlk is represented by beds of and clay totailv unlike this portion of our English cretaceos system. The fossils, or in otherwords the zoology of the bed is however a sufficient proof of contemporariety in epoch ; here, as in the existing epoch, local mineral vnriatioQ is f< connected with a general fauna. One of the most rem able zoological facts of this formation is the great developmes of the ammoaidar, which appears the result of some great ]gt of nature. In the Silurian epoch the nautilidx appear to hat arrived at their stage of highest development, exhibiting evn variation of form, as the straight in the orthoceratites, the ob lique, the open, &c., and then suddenly diminished, though tb type is continued in our present fauna. The ammonidse, i contrary, commenced with the muschelkalk of the trias genus ceratitcs, or perhaps with the goniatites of the car) ferooa, flouriahed in the oolites, and finally attained their

.&amp;1Jdimxnta&amp;T Gxolooy* 157

development in ererj possible yamtion of fonn in the cretaceoas. Inhere they appear for the last time ; the straight ammonites or baculites, the crooked or hamites, the open whorled or crioceratites, the obliquely whorled or toxaceratites, the tnrrilites, and many others, passing away from the organic world for ever.

This history of the ammonites, when compared with that of the nautiUdse, induces a behef that the type of nautilus must Lave commenced at still earher epochs, of which as yet no zoological evidence has been attained.

Tertiary Class Of Formations.

At this period of geological history, the present order of creation may be said to begin, as the remains of animal species which still exist are blended with the relics of the extinct. Sir C. Lyell has adopted this combination as the groundwork of his classification, and invented terms to signify, as it were, the dawning and gradual precession of the existing creation ; His subdivisions depending on the proportional number of existing species in each, a principle of classification which, though beautiful, requires to be applied with much caution.

Co-operating with M. Deshayes, the well-known French conchologist

. Sir C. Lyell matured his plan from an examination

of about 3000 species of fossil shells, and their comparison with

about 5000 hving species by M. Deshayes, and exhibited the

KiumbeTs of recent species in each division, as below : —

Newer Pliocene of Sicily . . 90 to 95 per cent.

Older Pliocene, or Sub-Apennine . 35 to 50 „ Miocene of the Loire and Gironde . 17 „

Eocene of London and Paris . 3i „

the distribution of the fossils submitted to examination having

Pliooene, older and newer .... 777

Miocene 1021

Eocene 1238

3036 I^C. LyeD, in the drd edition of his Manual (1851), further

PlS8

Kudimkntast Okolooy.

remarks, that since the epoch of compurison, the species b of the fossil and existing fauDK have heeii greatly inc the uunibeT of recent known species having been raised fi 601)0 to 10,000.

In studying these formations it mnst be remembered A the existence of species identical with those now living o be explained hy a growing approximation to the present ji ncal conditions of the earth ; and in consequence that thoK variations which are now observed in local fauns must be u- pectedalso in those of the tertiary epochs. The existing fauna is in fact composed of a number of local faanee, of which many of the species are quite peculiar, and as distinct as the species nf niccessive tertiary formations, but which are bound together i by other species which have, if not an universal range, a di biition at least as wide as the species of more ancient epo And in a similar manner the several tertiary deposits of wi separated regions must be expected to exhibit an of local species connected together by other species of a extended range. In determining, therefore, the exact pltu A deposit in the series of tertiary formations, the fossils si be compared with the recent species of the neighbouring ci and seas. On this principle, so well explained by Sir C. L the contemporaneous fossils in deposits of each tertiary e| and specially in the more recent, may, at Tarious parts 01 earth's surface, have scarcely any resemblance to each o although in each locality conforming to the general mle d growing approach to the recent types ; and it is thereforesa times very difficult to determine the exact mutual relada^ such local deposits to eachother. To the true tertjaries have U subsequently added the post-tertiary, post-pliocene or qnaten strata, in which the organic distinction vanishes, althongfa a their position and other circumstances it is impossible tofl sociate them with strata still in course of deposition j as,9 example, beds of clay or sand containing shells identical il those now existing, which occur inland at an elevation p . bably 200 feet above the level of the sea, and by their pi

HtlDIMENTABY G£OLOCT. 139

I in inlets or indentations of more ancient rocks mark out the muddy bottom or tlie sandy shore of an ocean ouder very different conditions to the present. Thoi^h comparatively recent, the tertiary formations exhibit acciunulationa of detritjc matter which rival in magnitude those oftbnner epochs, as, for example, in the London clay of the eocene epot^ which has been found 500 feet thick, in the nummulilic limestcmea of the Itledit£rmnean which appear a repetition of the cretaceous beds, in the similarly remarkable tertiary limestones of North America, in the immense deposit of molasse or soft sandstone of Switzerland, and even in the vast lacustrine deposits of sands and marls of Auvei^ne.

The marine andfresb water beds appear to have been deposited in extensive basins, and it is remarkable that the great cities of London aud Paris have been founded on such ancient basins, whilst in the brovm coal which is spread over a large portion of Germany, and abounds in land plants, though not apparently connected with a basin sufficiently marked by any depression of its surface to explain so great an accumulation of vegetable matter as that at Zittou in Saiony, where it affords the elements of a coal formation. In genera), the tertiary deposits of - England do not attain any great terrestrial height, no elevating force having been exerted beyond what was necessary to raise them partially above the sea level ; but along the axis of greatest moTement, both in Europe and America, the case is different, the Nagelflue of Switzerland with its brown coal and limestone, skirting the Alps in a chain of mountains GOOO feet high, the thickness of the deposits being 2000 feet, and the nummulitic limestone occurring in the Swiss Alps at an elevation of 10,000 feet. These deposits are very widely spread, occurring in North and South France, in the South of England, as also, in the uppermembers, in Scotland and Ireland, in North German;^ and along the Shine in Middle and South Germany, on both slopes of the Alps and Apennines, in Sicily, or^the coast of AlHca, and specially on the shores of the Mediterranean, in Poland, in North and South Russia, in North and South Asia,

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as, for example, in the Bsj of BengRl, in the East of Nord' America, and in Equatorial America, &c.i so that in almost every part of the globe Iracps hate been found of that graduil approximatiou to the present physical and xoological conditions of the earth's surface which is learnt from the study of tertiiirj deposits. In a few Northern localities, it is snpposed thai a tendency towards a colder climate can he traced within the Utpr tertiary epoch ; but generally the cUmate appears to have continued nearly tropical.

The English tertiary deposits are very local, and only in tant in the lower members. The basins of London and E shire arc the lowest geolt^daily, and belong to tliis | They are bounded and underlaid by the chalk, and their si consist of sands, clays, and grsTels. Compariaoa betweenl French and English tertiaries haa shown that the eocene d aits may be subdivided, and that the upper portion is de6 in Great Britain, whilst the middle subdivision include! £| fresh-water beds of Hampshire, and the upper sand o sand, and the lower the London clay, and the plastic which consists of alternating beds of day, sand, peculiarities which, though local and not accompanied by ■ important zoological diiferences, are within these distiit great practical use, as will be seen in treating of the snbjee ' Springs.' There are several shells, such as nautili, &c., 9 tropical type, and many plants also, more than ae of which have been discriminated; and a^ain in the teeth and hones of many crocodiles and turtles, and r the bones of a large serpent, have been found. The renwini' i of a bird, of various cjuadrupeda, and of a monkey of the geuM inacacus, hear also testimony to a warm climate.

The deposits of the Paris basin are very difFerenl in mineral character from those of the London basin, though connected with them by zoological evidence. Tlie London and Bognot clay beds, which are so remarkable in the London basin,-

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«*Tebee

RUDIMENTARY GEOLOGr. Ifil

ii.v6 been asaociatcd by Mr. Prcstwich nitli marine sbelly beds of tbe lower portion of the Paris basin, and the English plastic clay and sands with tbe sanda, plastic clay, and lignite, of the base of tbe French system ; whiUt the Bagshot and Brachleahant aanda, the Boston beds, and the fresh-water and fluyiomarine beds of the Isle of Wight, Hordwell, &,c. correspond to the sihcious and fresh-water limestone, the marine calcairc grossier, the marine sands and sandstones, and the freah-water limestone, marl, and gypsum of the middle portion of the Paris basin ; the Fontainbleau sandstone and the upper fresh-water limestone, marl, and sihcious millstone having, as it is supposed, no equivalents in the London basin. The celebrated Montmartre gypsum quarries were the classic ground of the grCB^ Cuvier's wonderful researches and discoveries. The range of the London clay has been extended through a large portion of the N.E. of Europe, by Dr. Girard, of Berlin. In other countries tbe variation of mineral character is even more striking, indicating a still greater variation of tbe conditions of deposit. In the Mediterranean Islands the white limestone ranges without any marked physical diiference from the oolite epoch up to the lower tertiary inclusive, and in the United States the eocene beds are in part represented by soft chalky limestones, exhibiting even the external physical characters of our chalk downs. A gigantic cetacean, called by Owen zeuglodon, occurs in the upper beds, and multitudes of orbitoidea, a fosail resembling nummulitea in form, in the

The great mineral difference in these deposits in the two faasina leads to similar differences of practical application. The London clay beds sometimes abound in calcareous nodules. Used for making Roman cement, which often contain marine Bhella, the remains of turtles and fruita ; and when traversed by cracks and veins dividing the mass into parts, as by septa, are called septaria. Uarnich and the Isle of Sheppy are well-known localities of these nodules. In the Paris basin, the ctdcaire grossier fiimisbea, in some of its varieties, very good

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■ P Wm Ektabv Gkoexmit.

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tnUdiiig ■tone, wtd the dicioiia freah-wBtcr dtpont jitldi ii ocUeot milUiDMC.

The tniocene epoch a represented in EngUnd hj the ItMB portion of the Suffolk crag, which is sabdirided into the tnd- Itoe erag below luid the red crag above. Tbe coralliue cragii rery local, and is generallj calcareous and marly, being s di1» of shells and small corals, whilst the red crag is a highly fnnginoiia grit. Although the thickness of both raeicben of tUi deposit is very small, not Ii^thcr exceeding 60 or '0 feet,tli( numberoffossils is very great. Mr. Searles Wood has Dbtaintd 230 species of sholk from the red crag, aad 34o from '&» MraUine, 150 of which were common to both. There b a cwi' riderable diiference in the proportion of recent shdls in the in divisions ; and as the lower had been disturbed before ih> depoBition of the upper, they exhibit a. striking conseifiient oo the chnngc from a coral reef to a shingle botlPA an example which shows that coral reefs are not necessarily of great thickness, the product of almost infinite ages, thpy rest on the peaka of submarine Tolcnnoes ; since in the aneient epochs, a growth of coral may have conn iin a snn<l or mud hank, have been interrupted by a new At nfn similar kind, and then again renewed, such allematieMJ helng fmpienlly observable in the carboniferous period, AiluiiB nfToiiraine, the Bordeaui beds, the sands, marls, ami ruiiglnrneratc of Piedmont, and part, at least, of the molasHtf BwilRprlanil, belong to this epoch.

Prnrl.irnlly, the formation varies in importance in difTwtiil ilUirii'lu. In Suffolk, the coralline crag yields a soft buildi^f ' Btiilli'. «ind tlio marls are useful as manure. In the StyiioM Alpii Uitiestotiri of a coralline and of an oolitic structure u* Iftff If ili'vptiiped, and the molasae. from the ease with It ti tilllt 1* h1<i> valuable.

rUUCKNE FORMATIONS.

pliiiot'iiu includes in England the cerebral

1

Rddimentary Geology. 163

crag of Suffolk, 30 remarkable for a great quantity of coprolites and liighl; phosphotized bonca. Muuh difference of opinion still exists as to the true age of this deposit, which, Irom its physical character, must be considered an ancient drift of beds. Although many eocene fossils occur, the association with them of recent forms makes it difficult to con* ceive that this is not comparatively a recent formation. The red crag of Norfolk belongs to the newer pliocene, being more recent than that of Suffolk, and it is unnecessary to dwell longer on the upper or newer pliocene formations, which are very feebly represented in the British Islands, being confined to minor deposits of sand, gravel, and clay. On the Continent, however, they are very largely developed, extending in Sicily over nearly half the island, and attaining an elevation of 3000 feet, being composed partly of calcareous and partly of argillo- cAus strata, and exhibiting by the occurrence of recent species of shells amidst such a mass of stratified matter, a striking proof of the accuracy of geological reasoning as regards the older fonnations. In Italy, the Sub-Apennines range from the miocenc up to the newest pliocene, affording astrikin^ pxempli6-cation of the great development of these comparatively recent strata, and the blue clay of the Mediterranean, rising sometimes to the height of 1000 feet above the sea, is also of this epoch. The thickness of the Norwich crag, consisting of sand and loam, and considered an estuary deposit, is small, about 40 feet, and the Suffolk crag belonging to the older pliocene is also insigniaficant in its vertical extension. In Sicily, the newer pliocene is a TBst marine deposit, but in Russia there is aa equal extension of fresh-water deposits, a vast mass of argillaceous litncstone found the Caspian, which Sir R. Murchison calls tlie Aralo- Caspian, or Steppe limestone, containing univalve shells of fresh-water origin associated with bivalves, which are common to partially saline or brackish water, but without corals. The thickness of this supposed member of the pliocene is in some places between 200 and 300 feet, and it attains elevations of 700 feet above the present level of the Caspian. In like man*

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ner the tertiary strata of Vienna correspond t at the base, but merging at the top into the plii eludes a t'resh-water deposit of limestone ; these beds passing into the more northern or Russian deposits. It ia remMkahle thut whilst the species of testacea of the newer phocene fornialioii were nearly identical with those of the enisting period, there should still have been so marked a distinction iu the animals of a higher class, as is proved bj the bones of the Tarious celebrated bone cares and ossiferous breccias of all parts of the globe, a difference which continued even beyond the limits of the pliocene. It is also remarkable, that whilst in the Uld World (though animals of a high order now coufinnl to warm climates extended far northward of their present limits) the general type of estinct organisms conforms Cn that of animals still existing, the type in Australia now peculiar to itself, though European iu the oohtic period, assume^iti distinctiveness in the tertiary period, that vast region even then been isolated from the rest of the world.

The connection of the ancient lava currents of Auverf the tertiary strata requires a few additional remarks, of the stratified deposits of the country is considered by Lyell to be generally eocene, although some portii sihiy extend upwards to the miocene, whilst the base system is granite, and therefore either eruptive or metamorjihic of a more ancient date. Sir C. Lyell describes successin gravel beds, the alluvions of different ages, covered by lavu, and points out that the lava current of the Puy de Tartimt has passed over B red sandy clay, rich in the hones of mimr mala, which are associated with those of reptiles and of bird^ and with several recent land shells. The bones, though clos^ allied to those of recent species, are considered distinct, ttA include the fossil horse of Owen. Sir C. Lyell, from the BuperpositioLi of the lava, is enabled to affirm that the bCM beds, in whatever way the animals were destroyed and tbrir relics so imbedded, belonged to the alluvial formations of the -river bed and river plain at the time of the flowing of the U"

of Tartaret; whilst he shows from an ancient R^man bridge, not more recent though probably older than the fifth century, which spans with its two arches the rirer Couze and abuts on both banks against the lava which had thus been cut through and formed into the present existing marine fourteen centuries ago, that the lava of the Fuy de Tartaret was, as respects the eveots of human history, of great antiquity, and referrible either to the close of the newer pliocene or to the post-pliocene period, a period when "the mollusca were identical with those now living, although a great maoy of the mammalia belonged to species uow extinct," This recurrence of alluvions and even of ossiferous beds, with overlying streams of lava, deserves especial attention, as it is utterly impossible to reconcile such repeated volcanic eruptions to any one catastrophe.

The beds of sand and gravel spread over so large a portioa of tlie earth have always attracted attention, and for a long time were ascribed to the passage of diluvial waters over its BQrface ; but a rigid examination of the peculiar characters of these deposits has shown that such an opinion is untenable : for example, they sometimes consist of deep beds of sand, separated by fine clay partings into a multitude of beds; sometimea they are composed of alternating layers of sand and gravel, Which exhibit cross lamination ; sometimes they consist of clay *itli imbedded boulders of various rocks and of various sizes, the term boulder being properly applied to rolled or rounded iiiasses i sometimes they contain marine shells, sometimes bones, «tid sometimes they extend over large spaces and occur at great .altitudes and of g;reat thickness, without any trace of organic l^odies. Many marls and clays or silt, with laud and fresh- ■^^ter shells, belong to this division. Wlien the various eircuni- '*tances attending such deposits are considered, it is evident , 'tbat they cannot be ascribed either to one great wave or to the *Tish of tumultuous waters, continued only through a eery limited time. The substances of which these deposits consist having been broItEo up, triturated, and moved by water, the term drift has been appUed to them ; but though all these snb- ,

1

hare bera more or ks drilled, their distrilnitioii hu beea zi-oiiSed bj tsmbx locd pecolmrities, giving rise to deep i^poK^s c-lT sasi in one phce, tnd to long eontinnoas banks or shoals :* others, just as in leeent drift the sounding leadtetd- £m tha: siich zxiincackins are now taking place. The grat ' emiics.' or those Uree anamlar masses of rock which ofta r»c OG thf STir^ce of sand or graTel, are rightlr separKtedfion :h« beds 02 which they lie and distinguished from the roondei boalien connected with these beds^ or with the day which hM 3«x-Jziz!A:ed in hollows of the earth's surface : they are nov seaenllj belicred to hare been transported by ioe, as £n^ me:::$ c: r.xk an? now drifted along on icebergs. In Nortbem Svvdea the phenomenon of drift is strikingly exhibited in loDg :r!Li:i:VKw whilst the rocks are vom down in midulating surfiM^ 12.1 so=>?:i=es exhibit rounded northern and abrupt soathen ^df^ ccrtes?>?r:dinz to the wearing actum of such loose mlt^ rjds in ?r?€Tes*iTe modon.

W::hoc: e:::e!i:i§: into details, it maybe generally remained, :'".«: zhi s'.:rer^o:il detritus, so long called diluTium, exhibiti ■.:s.".:' ::: <i'tral .v.>:ir.c:iTe phases. 1. As deep beds of sand, :.:: "-.^iie.: v.v :". oue ir.ass. but mauifestly deposited in SM- ^-cfs^iv: "..IV-ri, i.::i wiiioh tboush doubtless triturated bv the .i,*::o-.-. -.":' w^?.:er. :■.::. I even moved along bv currents, are com- I dr.i::v ; '.y : r:i:: ^ v.ii .mi iv^uiar deposits. 2. As lines of gravel u^'..: V.*: cri\ey.v ^lav. with rounded boulders which sometimes s a r ::•.'••.!": :r.e ir.orv v|i:io: deposits, and by their definite direc-li.'ii ill sv.v*h :r.i'Utx's for even hundreds of miles, indicate the ao::o:i of oi:rrv:i:s :::oWn^: in Northern Europe, in a slightk vl-vcr^iit d:rx.v:ioii fro'^n the Scandinavian Mountains to the so'.::h ou the one haiui. and from the south to the north on the o:r.<.T ; ii'.iioatiiii: thai the transport was not effected simply hy the us'.:.il submarine currents dowins from north to south, bat pdrdy» at least, by undulations of the bottom, which caused power'ul waves of translation in all directions from the axis of disturban^v. *^ As 'erratics,' cr large ang:ular blocks, which are not immersed in beds of sand, mud, or gravel, but .rest

surface, or on ridges of rock wliere there is no supercohering ; «nd it has been hitJierto considered that moving Ihe only sufficiently satisfactory cause of the translation

ses, which, having preserved their angles, cannot been exposed to the rolling action of water. 4. In the

ises, tiie detritus is supposed to have travelled from .

but it ia very often partly local, and then is profdnced by the wear of the adjacent rocks, either by the direct action of the sea against them, or by the attrition of fragments "when moved by the tidal wave along a coast or a bank. Where both forms of detritus occur, it ia difficult to discriminate be~ tween them, or to determine which is the miderlying or overlying bed. 5. The connection of the boulder formation, and tlie phenomena of erratics with ice as a motive agent, aeems ■fiirtlier supported by the fact that both in the old and new Vortds they are observed only in regions where the effects of extreme cold might be looked for, the boulder formation having in Europe been traced southward to the 52° of latitude, and in America to the 38 J°, where it is occaaionally more than 200 ieet thick and bears on its surface 'erratics,' rivalling in size those of Europe, a block of greenstone 100 feet in circumference having been noticed by Sir C. Lyell, whilst the largest £european erratic on the Island Fohnen measures 44 feet across ; and further, that having ceased within the tropics, Buch appearances are again observed on approaching the antarctic zone. The surfaces of roclts, when laid bare, are in America as in Europe striated, furrowed, or smoothed; and as these phenomena estend from the northern elevated districts towards the south, they required a general force, such AS that which now effects the transmission of the Polar "waters to the Equator, and caimot be explained by the waves «f pulsation consequent on elevating forces alone ; for though to the north of the Scandinavian chain the ' erratics' have moved to the northward, their extension in that direction Jibs possibly not been traced sufficiently fat to remove them ttouh the possible action of glaciers, which it is reasonable to

1

Entarv Qkoi.O

'usumc Tniist have co-eciistcd with (lie flonliug sheet lud'

of icp, and co-operated with tliein and with marine uid

currents in transportiug fragments of rocks by Und tsd

C. On examining the scratches and grooves on rocks ii

Mwly poaaible to doubt that many of them hftTe

y pebbles moring with and immersed in t1

■ boulder ciay which once covered the rocks. Various

rliave been assigned for this movement, such for

viand-slips, the saturation of masses of detritus and their

I SB Bcmi-fluid mud down the slopes of mountains and aloagl

[ leys, and lately coast-slips of matter below ihe tidal line,

I suggested by Mr. R. Midlett, who considers it sufficient

n for the movement of erratics ; but whilst to

these causes some peculiar local effects may be ascribed,

can be considered sufficient to account for the more general!

noniena. The mud, sand, and gravel along the t

ofUn put into motion, sometimes by the tidal ware prodi

wear, polishing and grooving in lines parallel to the shi

sometimes in consequence of the sudden removal of its

iu deep water by the excavation of its bed by currents

the shore detritus sinks in and moves perpendicularly Wit

wards ; but iu these cases the moving matter is in a semifldd

state, and can neither be expected to carry on its surface Iai|<

bodies, nor hold fa,st in its grasp the angular fragments irtitdi,

scratch and groove. The only condition in which such eStff*-

1 may be ascribed to the movement of a solid bed of clay and ill

imbedded angular fragments, is when the mass is retained in I

compressed and firm state by superincumbent pressure ; ivi

there can be little doubt that the accumulations of mud and

other detritus which have been formed in tbe deep recesses of

the ocean, and so consolidated by pressure as to support th*

heaviest fragments, ore ot1:en broken up by tbe convTilsirt

elevation of the sea bottom, and by a change of its level are

put into motion and gradually slide along the inclined plane

thus formed, carrj'ing forcibly with tliem the sharp pebbki,,

which groove and scratch the rocks below. And fiirthi

iu2

J

&amp;Cdimentary Geologv. 169

1 be Temembereil that vhen the surface of a rock, 1 K by the removal of clay or other matter, is examined, the tSia of screral successive actions may be manifest, as, tuple, the rocks may have been pohshed by tbe attrition of ~1 carried along by ordinary currents, and Bubsequeatly iced and grooved by the movement of consolidated mas Say and the sharp stones imbedded in them, a countries where the tertiary strata are fully deretoped,

s deep sea or as great lacustrine deposits, they supply t ibtc building materials both in limestone and in sandstone. Tie fossil bitumen so extensively used in asphalte pavements, namely, that of Bastenuc, a small village of the South of France, 15 miles north of Orthez, is tertiary, Tbe formation in which the bitumen is found rests on a sandy limestone, which ha been allocated b> the cretaceous system, and it consists o beda of variously coloured sands and clays, which are 50 or 6' feat deep, and covered by gravel and sand, which extend many miles in every direction. These beds are usually borizontn!, tbongh sometimes much disturbed by the intrusion of igneous rocks. Under aljout 45 feet of variegated sands and clays there is a small quantity of bitumen in a bed of blackish ec 4 feet thick ; from 5 to 15 feet of bitumen are then observed, the upper part of which is mixed with louse and coarse sand, the lower being more compact, and mixed with finer sand. In some places there are 10 to 15 feet of saud without bitumen, whilst in others the bituminous sand is thicker, and rests directly on tbe secondary sandy limestone. In tno locabties marine shells have been foimd in tbe bituminous sand, and referred by Mr. Pratt to the raioeene period. Tbe shells arranged in layers, and are quite perfect, the valves not being separated from each other ; and tbe bitumen, when in a soft liquid state, was, in Mr. Pratt's opinion, forced into the shells, after their deposition in the sands iu which the animals hved, filling even their smallest cavities. The eruption of tbe bitumen is supposed to have been connected with the appearance o ophite, an igneous rock which has produced such great changes

in the Pyrenees. The bitumen is easQj cat when first exp bnt in a few days it hardens so mnch as to become incn^bk, of pnrification : the purification is effected bj boiling the ifh!^ mixture in a large quantity of water two or three times, wheOt by continued and careful stirring, the sand gradually setdis ^ai the bottom, while the pure bitumen rises to the surface auu "j is taken off. A small portion of bitumen occurs in the tertiary rocks of Anti-Paxo, and again in a larger quantity a! Zante. The existence of gypsum and salt in the terii^

strata has been already noticed. •• j

jt J '

Before quitting the remarkable geological epoch emV^nuflf : by the tertiaries, it is desirable again to bring before the iflid \ ' the zoological history it has unfolded. Approximated as iC is to the existing world by many still existing species, th^i^.vt .. sufficient peculiarities to stamp upon it individuality, wbeCher .' the lower or the higher portion of the organic creation be m:ule ; the basis of comparison. The tertiary world is as distingiii:>hsl from the existing by its corals as it is by its mammals ; and whilst it rejects any decided union with either the past or the present, it manifests numerous affinities to both. In the mollusca, the nautiloid type which flourished in its most extended development of form in the Silurian epoch, was still lepnsented by two genera, — aturia (clymene) and nautilus, and. seven species. In the reptilia which swarmed in the oolitic, epoch, and appeared so early as the Devonian, the t^tiaries were rich, the London clay alone having furnished in the three families of marine, fluviatile, and marsh turtles, relics of no less than 27 species, and in the marine genus chelone 1 1 ^leeds, whilst in the whole extent of our present world only five species have as yet been discovered ; — in the crocodilia, three crocodiles, one alligator, and one gavial, some of which exhibit that mixture of types which has been noticed in reference to the combination of the lizard and batrachian types, in the early reptiles of the old red and carboniferous epochs ; in the lacertilia, one true lizard; and in serpents, six species, some of which were ^gantic and probably marine. In mftminiJui,

If more recent deposits, including bone caves, estdbit some toes which are yet existing, such as the red deer, the rein- Br, the goBt, the wolf, and the fox ) others closely allied to 6 existing species of ox, horse, hyaena, rhinoeeros, hippopotamus, and elephtint, associated with extinct forms; and here, as in preceding cases, particular orders seem tu have attained a peculiar deTcIopment, namely, the edcntata or toothless and the pachydermata or thick-skinned animals, including the gigantic fossil sloth or mylodon robustum, the mighty dinotherium equalling the elephant in size and with tusks turned downwards as if to tear up the ground, the hyrBcotherium, antbracotherium, the lophiodon and palseotherium, resembling the American tapirs, the anaplotherium, which seems to connect together the genera rhinoceros, horse, hippopotamus, hog, and camel, — and many other extinct genera, besides the cetaceous genus leuglodon, which may he considered the marine representative of this type. But amidst all these strange forms, iucluding the glyptodon or giant armadillo, there appear representatives of that order, the quadruraana, which at least suggests, even if it caricatures, the form and actions of man, in extinct species of apes, and even of the ourang. Tlie bat also had begun to flit about in the dim twi- l^ht of a world which as yet hod not been tenanted by Man ; and on every side it appeared that the Creator had nearly established that balance in the numbers, powers, and fonctions of other animals which would render the world fit for the reception of the greatest work of creative power — a being endowed with reason, or with the power of investigating and studying his own structure, and comprehending the relations which connect him at once with the great Creator, and with all the works of creative power.

Quateknary, Post-Tertiarv, Or Post-Pmockne —

1

Our inquiry haa now come to that point where, though we (till see in the recent results of geological phenomena eridenco

of the fonxiatiye processes of nature, — coral ree& still rising from the depths of the Pacific, — conglomerates being still formed in the Mediterranean, — ^beds of marl being still degosited in kkes, — travertin being deposited from mineral spring;8^ —and peat being observed to have formed over fresh-water shells, the bones of land animals, and even the works of hnmsn art, — ^we are still kept at a distance from the recent epoch; for although organic relics are all of recent species, they are generally arranged in positions and associated with detritic matter of such a description that their appearance indicates the action of forces prior to the present order of things. These masses, the true post-pliocene, though now exposed to view and frequently found at high elevations and of great depth, have evidently been, like the antecedent formations, under the level of the waters either of lakes or of seas, whilst true recent strata are, in most cases, still in the position from which the former have emerged. To this obscure region must be ascribed raised beaches or those remarkable accumulations of gravel which though far above the present level seem to mark the former position of the sea boundary or shore, or which bordering the sides of lakes show in like manner a depression of the surface of their waters. Raised beaches, as well as the pleistoc^e deposits, have been ably examined by Mr. Smith, of Jordan Hill, who has noticed 150 species of shells in those of £a- rppean origin; but it must be manifest that at this point, where the ancient strata are blended with the recent, ancient beaches whether marine or lacustrine must be studied in direct reference to adjacent localities, as the changes of position ot * altitude do not imply an alteration in zoological conditions.

Recent or Alluvial, — The natural phenomena which can be now studied are valuable guides in estimating those of past epochs ; and by many analogies of alluvial deposits may be k learnt the mode in which more ancient deposits have been formed. The action of rivers may be estimated by the exten- ^< sion of the deltas at their mouths, and that of the sea observed *' in all its phases. The processes of destruction and of formatioii

i

nUDIMENTARY GEOLOGY. 1?3

connected with these actions extend over the whole earth, though, being necessarily modified by many local pecuHarities, they produce pfirallel, not identical formations, the contempo' raneity of which it will be difficult at more remote ages to determine. These formations may be divided into mechanical, chemical, and organic, and also into land and sea formatioDs, volcanic products being connected with each.

Meehamcal Depimts. — Torrents and rivers, in their course through mountain regions, carry along with them a mixture of large and small fragments torn from the boundary rocks, and deposit their load in the lower and more tranquil portion of their course, as gravel, sand, or mud, — the nature of the deposit and the distance to which it is carried being proportioned to the strength of the current ; and this simple and constantly occurring natural event exemplifiea the removal of portions o( rocks from their native bed and their subsequent deposition, and the formation of alternating beds of clay, sand, and gravel. When a river passes through roclis rich in ores or in predoua stones, its waters often separate from their matrix those substances which from their superior weight remain behind, whilst the finer matter is hurried onwards. Deposits of this kind are valuable from the quantity of ore and of gems which they sometimes contain, and which are separated by repeating the natural process or washing away the remaining fine matter. Particles of gold, platinum, iridium, rhodinm, palladium, osmium, chrome, and magnetic iron, are obtained in 'Wicklow, in the Ural chain of Russia, in lirazil, in Cahfomia, Austraha, and elsewhere ; the term stream gold or stream tin, &c. being applied to such products. As yet, platinum has only been obtained in this secondary manner, and the greater proportion of gold is similarly procured, as well as a considerable part of the tin, as also the zircon of Bohemia, the chrysoberyb and hyacinths of Ceylon, the diamonds of Brazil and of the East Indies. In Borneo, gold has been found mixed with alluvial matter in limestone caves. The gravel of the Rhine is estimated by M. D'Aubrde to contain an

1

J

amount of gold equivalent in value to 165.828,000 franca, or je6,564,025.

J^e//a*.— Where rivers discharge their suspended mud into the sea, and where the coast is shelving, and there is uo powerful marine current, a delta is often formed by the depositioa of mud at the point nhere the waters have lost their transporting puver. It usually commences at the centre of the river's mouth, an island being first fanned, nbich goes on extending and widening till a triangular space is occupied liy the deposit, the apes being directed upwards, and the base &cing the sea; and this form having been first noticed in thr mouth of the Nile, the name Delta was applied to it from the Greek letter of that name. Sometimes, as in the Nile and the Rhine, aeveral islands are simultaneously formed, so thsi the delta is finally a compound one, and is separated by various channels. The delta of the Ganges is still more remarkable than those of the Nile and Rhine, its perpendicular depth frOB* the apex to the base being about ISO miles, and therefore ~ hibiting a formation comparable iu extent to many of of past geological epochs.

PFrom the action of the Sea. — The sea effects a change in ibrm and position of the land with which it is in contact; ■whilst at one point its waters encroach upon and carry a the land, at another they deposit new matter, and increase i and as they contain from three to four per cent. mineral salts (aa chloride of sodium, chloride of magnnto sulphate and carbonate of magnesia, sulphate and carbonate i lime), the formations produced are often more fixed and than those of fresh water. This is specially the case in wi chmales ; and as the fragments of shells as well as comminuted portions of calcareous rocks are often mixed with the deposits, sandstones are sometimes formed, sometimes limestones, sometimes conglomerates. In a formation of this kind at the Island Grande Terre, near Guadaloupe, human remaiiu have been imbedded, and many such are in prepress of de- ^H pontioa below the waters of the sea, and will b« brought ton

Budihkntabt Gkologt. 175

^t by such npheaTiIs of the cout and sea bottom as that strikinglj' affected the coast of Chili.

I

Calc Tuff and Calc Sinter, or Travertin. — All spring waters are charged with mineral matter, which, coming to the surface, they, in their course, deposit by the influence of liglit, air, evaporatioQ, loss of temperature, ahsorptioD, and escape of carbonic acid. Cold springs charged with lime yield in this manner calc tuff, or sinter iu the form of calc spar, and hot springs in that of arragonite. Calc tuff is usually a poroua mass, but sometimes its layers are sufficiently firm to be used in building, and are then valuable from their lightness. The moat remarkable example of such 'travertin' formations is to be found iu Italy, and bo rapid is the progress of deposition, that at the Baths of San Fihppo, a mass, 30 feet thick, has been formed in twenty years. These springs are made use of to procure stone casts, the lime bein^ deposited in a firm and soUd state on models immersed in the water.

Silieiout Tuff, or Sinter. — Thermal eprings deposit much nlex on cooling. Tlie hot springs of Iceland, and especially the Geyser, are of this description. At intervals of a few minutes, a lofty column of hot water is thrown up, and then t dense fog overspreads the surrounding ground, and from this condensed spray the siles is deposited in the porous form of tuff, or sinter, whilst, in the interior of the basin, a species of opal is formed. In the Azores several springs deposit silex ; and it is very probable that semi-opal and hyalite, which are frequently found in the crevices of basalt, and, in short, most of the sihcious minerals which are so abundant and so beautiful in that rock, have been formed in a similar manner by the filtration or absorption of the water by which the mineral matter had been originally dissolved.

Bog Iron {lAnumite). — Ferru^oua springs or waters depodt a brownish red scum of peroxide of iron on their banks, or at the bottom of bogs and marshes masses of iron on^.,

which has heen called from such lcx»lities hog or marsh iron; and as sand or graTel maj be mixed ap with and consolidated bj the mineral matter, a variety of ironstone is formed, which has been called sand ore. In Sweden, bog ironstone has been fished up from under the sea, where, according to Hausmann, \ it is still produced, and it would be interesting to compare tbe microscopic structure of this ore with that of fresh water. The presence of phosphoric acid in bog iron ore, so imfavourable for smelting, is probably due to the decay of organic bodies in the water during its formation.

Deposition of Saline Bodies, — ^The saline deposits thrown down by springs, streams, and lakes are not extensive. From the mineral springs of the Baths at Vienna is precipitated a fine powder, consisting of gypsum and muriate of lime. In the South of Russia, several lakes annually overflow their banks and deposit a saline crust ; a phenomenon which is much more common in the lakes and in the very low grounds of the warmer zones. In Egypt, soda has in this manner been deposited in large quantity. The extensive turf moors at Franzensbad, near Eger, are partly coated with a white saline crust of sulphate of soda (Glauber salt) and sulphate of iron. Some salts exude out of rocks, as saltpetre (nitrate of potash or nitre), in the limestone caverns of Brazil and of Ceylon.

Mineral Oil, or Pitch. — In several parts of the earth there are springs of a mineral oil which on drying becomes either asphalte or a species of coaly mass. The Carpathians and the vicinity of the Dead Sea are rich in these springs, and in the island of Trinidad they almost form a sea of asphalte.

Organic Formations,

Turf, — ^This vegetable -formation is sometimes covered by more modem mineral deposits of little extent, and sometimes exhibits a passage into brown coal. Turf consists principally of an accumulation of marsh and water plants, especially of various species of moss, the lower layers of which have in succession died, and through the action of humic acid been

Rudimentary Geology. 177

^changed into a peculiar brown, felted, slimy, and combustible mass. In some layers of turf, the remains of plants are so decayed and changed that their original condition can only be inferred, but in others the actual species of the moss can yet be determined. In some bogs, the growth appears to have ceased, whilst in others vegetation is still vigorous on the upper surface. In Alt-Warmbnicher moor, near Hanover, cutting for the second time, the turf has been re-formed, according to Leonhard, in fifty years, a layer from 4 feet to 6 feet thick having been in course of formation during the last thirty years. At Franzensbad, near Eger, a similar fact has been observed, the exhausted turf hollows having been again filled with new turf plants in from ten to twenty years, which are formed into useful turf in from fifty to one hundred years. The great bogs of Ireland are amongst the finest examples of this kind of formation, both as regards their extent and depth ; and although no very detailed or satisfactory observations have been made on the new growth of bog in old exhausted hollows, where drainage and 'cultivation have not so modified the conditions as to stop it, a very slight observation is sufficient to show that the first step of the accumulation of moss plants can yet be traced. Keferstein has remarked that turf formations are rare on calcareous and frequent on silicious bottoms, but Ireland is at least an exception to this rule, as turf is abundant in some of the limestone districts, and has in several cases grown over lacustrine deposits of shell-marl. Thick beds of turf occur on the summits of some high hills in Ireland and other countries, where a clay bottom retains the moisture. On the banks of the North Sea, a species of turf , is formed from accumulations of sea weed. Large masses of bog have sometimes been detached, and become floating islands, one of which, on the Gordauer lake, in Prussia, was so large as to support a hundred head of cattle, until, in 1707, it was broken into three parts by a severe storm. Sometimes turf is found below the high-water level of the sea, as at Greifswalde and Geageland, on the East Sea, and on the north

H 5

PWfB RCDtMENTABV GEOLOGY.

MMSt of Ireland, neM Portnish, where tbe elytra of b (still fresh and bright) occut between Injers of turf. Turf ( also tbrmed in the wann zones, as at San Paulo in the Bradll In the Irish bogs, tlie roots, trunks, and fragments of branches of large trees, both oak and fir, are abundant, i m seTernl instances, two or three successive sets of the ri stand upright one above the other. Turf affords a connecthi Unk between the esistiug epoch end the next preceding it. Il sometimes very compact and full of iron pyrites which f quentty induces spontaneous combustion and the formation ( sulphates, often contains fresh-water shells and is covered b layers of sand and clay, and aa it passes into brown coal i more nearly connected with the diluvial than the allurii section of the post-tertiaries. A bed of turf with stems t trees has been found under o covering of 12 feet of s and 7 feet of earth ; and at Wittgendorf also, near Sprot tau, in Silesia, turf rests on fresh-water marl, and : covered with sand and gravel. A wooden bridge, made t Germanicus in his German war, was found under a hog} and in Galway, a hut and paved passage was found ) 30 feet of bog by the late Capt. Wm. Mudge, H.N., botl being interesting examples of the manner in which sa formations, when unrestrained by cultivation, spread over aJ deform the surface of the earth. The growth of sphagnum fl hog moss being most rapid in the centre of a hollow, whe the moisture is greatest, bogs are generally much swollen i the middle, and go on increasing in height and thickness n the slope is sufficient to discharge the waters and hmit tfa growth. Examples are cited where towns once visible fi each other, are now shut out from view by the elevation of turf moss between them.

Stibmarine Forests. — On various parts of the coast of G Britain and of the North of France the r growths of trees and plants are found in positions below tl level of the sea, though belonging to species still living, are sometimes exposed by the encroachment of the sea m tl

Rudihintary Gsology. 179

;, and at other times simply by the ebb of the tide, and

probably owe their present position to a partial depression of the land : Genernl Lewia has noted a fine example of such forests on the western coast of Jersey.

Coral Reefs and Jgianrf*.— They prevail in the Pacific and Indian Oceans and in the Red and Mediterranean Seas. Recent researches, especially those of Quoy, Gaimard, and Ehreaberg, have shown that the growth of coral does not continue in great depths, and that coral reefa or isjaoda are generally not more than 20 feet or 30 feet thick, and are only incrustations on the inequalities of the sea bottom, whether formed c mountain masses not yet elevated to view, or on banks of detritic matter. Whilst, then, such formations explain the nature of the true coral reefs of ancient epochs, and account for the deposits of shale with calcareous layers of corals common in the carboniferous system, the formation of the greater masses of limestone cannot he ascribed to the action of coral-polypes alone.

Infusoria. — Some masses of rock consist of little else than infusoria] remains, as tripoli, polishing slate, &c. Sometimes the infusoria which have formed these strata belong to estinct and sometimes to still living species, so that the microscope, guided by Ehrenberg, confirms the reasoning on successive ' creations which had been founded on the contemplation of higher organisms. The silicious skeletons of these minute beings are accumulated at the bottoms of marshes and stagnant waters, as in the turf moor near Eger, and thick beds of a white silicious powder are thus formed, consisting of the unmixed silicious portions of still existing infusoria. Some of these infusorial substances, such as tripoli, polishing slate, &c., have been classed with metals, from their general appearance, but their true character has now been revealed by the microscope. Most infusorial deposits probably belong to antecedent epochs, but that of Eger is evidently recent, and in all Co tries where waters flow over much decomposing silicious roii sorial formations may be expected.

Land-alips are also phenomena of the rec«ut, although w out doubt they have occurred tJso at ancient epochs. ever a soft stratum is liable to be removed \>y the action d percolating water, slips in the harder superjacent rock a common, as in the Isle of Wight, &c. They are finely a hibited in Ireland, where the sofl liasic and oolitic beds b removed or squeezed out from below the basaltic cap whid coTors the cretaceous and subjacent strata, the top e and slides down, as in fig. 18, which is a poitiou of the bas^d| escarpment of the North of Ireland. Pig. IB.

Rttdimentart 6E0L06T* 181

Chapter Vii.

Theory of Springs.

As water is the most important substance in nature, being the solvent by which nutrition is conveyed both to the plant and to the animal, as well as the chief agent by which the mineral kingdom has been again and again both abraded and restored, it is desirable to consider that constant change and movement by which its purity and fitness for performing its several functions are insured. The ocean is the great recipient of the larger portion of rivers and streams which flow over the earth's surface, and its waters are in constant motion, the warm currents proceeding from the Equator to the Pole, and the cold from the Pole to the Equator; whilst evaporation causes a perpetual movement of vapour upwards, which, being condensed, falls in rain upon the earth, and again returns to the sea. These simple processes bring within the reach of organic action a constant supply of this vital fluid in a pure and efficient conditi(m, as springs, rivers, or lakes. The useM distribution of water is promoted by the physical inequalities of the earth ; for had its surface been uniformly level, the falHng rain woidd have soaked and saturated the upper strata so as to produce a swampy condition, not probably very dissimilar to that it actually possessed, over large tracts, in the earlier geological epochs. The conjoint actions of elevating and denuding forces have, on the contrary, produced chains of mountains, valleys, basins, and all the minor modifications of these three great forms. In the vicinity of mountains, the effect of this arrangement is readily observed in the river which one day struggles with its riband-like stream through

a wide bed of stones and grayel, and the next ashes forward an oyerflowing and turbulent stream, baying been swollen bj sadden rains wbieb, falling witbin tbe area of its connected Tallejs, bad been collected into one great liquid mass witbin its bed. Tbe more numerous tbe feeders and tbe more doselj connected witb mountain masses, on tbe summits of which a very large portion of moisture is always deposited over a comparatively small space* tbe more sudden will be tbe rise of the discbarging or recipient river. A large portion of water is tbus carried off directly by running over tbe surface, bat anotber large portion percolates tbrougb tbe sur&ce to a greater or less depth, in proportion to its porosity. In clayey soils, this passage of the water is very slow, the surface in wet weather becoming moist and clammy, whilst in dry, it forms a crust fissured by cracks. In sandy or grarelly soils, the passage is very quick, and the surface remains comparatively diy ; but where the soil is not very deep, and part of the water is retained by a more retentive substratum, tbe moisture is readily restored by a continued evaporation and an injurious aridity is prevented, this condition of the surface being more generally favourable for vegetation than an impervious soil. W]uT( , on th** contrary, the sand or gravel is very deep, and restb on an incli^M: 1 surface, It acts as a filter, and a general nrirlitv of suri'ace is produced .by the rapid removal of the water. TIksc considerations naturally lead to the following theory of Springs.

1 . Whilst part of the rain which falls on tbe surface runs off as on an inclined plane, another part filt^ through it, and when collected together in any cavity of a less pervious substratum, forms a reservoir of water. Even on the sides of mountains, especially in damp climates, this process may be observed, for, whilst the general surface becomes wet and boggy, wherever an inequality has led to an aocumulation '* '"'ter, numerous springs are seen issuing as scareely perrills, which gradually increase as they join with and finally emerge in the greater valley as con*

KDIHIfZKTAftY BKOLOST.

sidenble atreuns. Sach ii tlie most simple and ordinsiy form of BpringB, from which ma)' be deriTed enij other, by taking into consideTa^ii the peculiar modifieatioii in each case of the earth's aor&ce ; and spiii^ are therefore superficial, ■mall, numerous, and very temporary, where the previous atratom is very ^allow, and the iaequaUticB of the sub- Btratnin slight.

2. In additi(» to the water which forms the superficial springs on the mountain side, a portion may pass between the underlying rock and the superficial matter above it, whether the latter be a stratified deposit or ordinary detritus resulting from the umple decomposition of the rock itself; or should the oTerlying deposit be moderately porous, some of the water may pass directly through it to the underlying rock, where reservoirs of water will be formed in its hollows or depressions. This is a case which occurs even in granitic and h^hly metamoiphic rocks ; and as open fissures are rare in granite, whilst saperficial disintegration, especially in hot countries, has proceeded to a great extent, it affords almost the only chance of meeting with deep-seated springs. Colonel Baddely, R. E., has shown its application and explained the principles which regulate the appearance of springs in Ceylon. The under* lying rock is a highly mctamorphic homblendic or syenitic gneiss, the outcrop|nng e^a of which having ondet^ne much original modification, ore supposed to form an undulated surface — thus, in fig. 19,

Pig. 19.

s

the hoQom being filled np l^ a debritns, proceeding, accordiiig to Colonel Baddely, from die ample diahitegratioi) in mto of the more felapathic snr&ce. From the mere in^tectioa of the figure, it is evident that whaterer wxf be the origin of the matter filling up the ineqaalities of the mideriying rock, llic water, dther in part percolating through it, or pawing betweai it and the surface of the sooud rock, must accumulate in the hollows, and that io consequence it woidd be necesuiy to aink -at £ to 80 feet for water, although at a it had been found at 40 ; and further, that should the rock under 6 alone gradoilfy off, and become exposed in a valley, or on the aide of a hiD, the water may all be carried off as quickly as aopplied, and produce therefore no permanent spring, — circumstances whidi render the search for water very precarious. It may be further added in respect to this example, that a rising or projecting spring can only be expected irhere the water passing between the detritus and the rock is pent up by them, and thus alFords a head of water ; as if it merely filters throogh, the pressure can only raise the spring to the height at which the water stands at the time in the reservoir or hollow. The other form of this case is, where the hollows of the crystalline rock are filled by stratified deposits (No. 20) of shale and

Eg. 20.

sand Here, as the shale has been worn away, and the nek denuded at the summit, the water may gam access to tht layer of sand (»'), and produce therefore a spring under flie bore-hole (o), the water being held back by the projectkni of

BVDllIBHTAKT GKOt-OGT. iBS

the rock to tlie left of it. When tlie water hu uturated the whole of this stratum, it will rise OTer the projecting rock; but u the stTatnm is open to the Tallej below, it wiU be rapidly discha^ed, and produce no permanent spring under the bore-hole (A). Again, under bath a and 6, there will be a second siqiply of water due to the sand stratum (^); but as these lower reservoirs fcom thai imperfect connection with the surface mnat require a considerable time to fill, their practical value will be in proportion to their magnitude, or to the quantity of water stored in them.

3. In the preceding instances, the accumulation of water has been considered to arise principiilly from that which flows over the underlying soUd rock, but it may be entirely due to that which enters directly from the stratified deposits, and is merely held back or dammed ap by that rock, asinNo. 21.

Here it is evident that the supply of water will be in pnqKirtion to the extent of sur&ce on which the rain fidla, and from which it is directed to the layers (tf sand

(«> Biid^),thereinaiDijigniui being dther day or somi impemooa stratum. If the supply be abundant, the b will be kept Baturated up to the line of the bore-bole (< a coiutant spring be obtained ; hot if it be only ami casual, there may be a spring during the rainy season, or whilst the wafer I if making its way through the stra- [ tDm,butnoneatftlaterperiod,andtbe I chance ofpermaiwiu^ will be increased „V as the bore-hole is carried nearer to ,' the rocky dam at g; and the same reasoning will apply to the upper stratum of sand (t^), and its bore-hole (i) i and it may be observed also, that a bore-hole (o*) by which a temporaiy spring only had been found in «*, i^ being carried through the intervening clays, would obtain a permanent one in *'.

This case leads to those where the water is received and thrown up entirely by stratified deposits arranged in the form of banns or troughs, which may happen either where thp basin is produced by ao undulation or depression of the underlying strata, or where it occupies the valley produced by the disruption of these strata on elevation ; and as some precaution is necessary m reference to this distinction, each case will be considered separately.

No. 22 is the first case where the strata of sand and clay have been deposited in a basin of undulation, and the water enter ■and stratum («) is prevented from descending by the

Rudimentary Geolooy.

I strata below, and from •flcending by the ckj' eboTe; no that it is pent up iu the sand Btratum itself. An inspection «f the figure is sufGcient to show that the nearer the boreliole b made to the lower point of the valley, the more abundant and secure will be (he supply, and the higher the ji;t from the aperture. If, instead of one layer of sand or gravel, there bad been several, the reasoning would be the same, only it might happen that the upper layers, closed up by the clay passing over them, as in the figure, would be fouad unproductive of water, or that two layers of clay might come into contact with each other, and shut out the sand, cases which have been illustrated by

mt borings at Portsmunth. f Ko. 23 is a basin formed a valley of disruption or 1 of denudation, or which 8 from the preceding only !> Has circumstance, that the nidary walls, as it were, of J Talley may in themselves W partly pervious, and there- B allow the water to escape. If such occur, the water cannot ( above the level of these

; strata, represented in the figure.

Rtjdiiieiitaxt Gbologt.

geconduy denudation maj modify tlie buin deposit, and aSM il^ supply of water, as in No. 24, where it is evident that anj

layers of sand cut through by denudation in the centre of the basin must discbarge the water they receive at once into tbe inner valley of denudation, and that no water can be expected until tbe lower layer, or at least tbe first layer not a&ected by tbe denudation, baa been touched by the borer. Faults m^' also materially affect tbe arrangeinent of springs, as in some cases when filled by impernous matter tbey act as dams, and in others discharge tbe water, — so that in boring in the vicinity of a fault, care mnat be taken to ascertain its conditioii, and if it be supposed open, to place the bore-hole in tbe strata dipping _^om it.

It is conceived that these examples are sufficient to aspliia the application of principles to practice in every case, and to show the great necessity of studying the geological as well U the physical character of a country in which water is sought for. In granite, and in most crystalline rocks, a search for water must be very precarious, as it can only occni in ot connected with fissures. In stratified deposits, not metamorphosed, tbe occurrence of alternating porous and impervious beds brings tbe principle into operation ; and ia pro-porUon as tbe porous beds are looser in teitnre, as in tertiary and post-lertiHry sands and gravel, and the arrangement assumes a basin-like form, will tbe chance of sncceas increase and a correct knowledge of tbe stratification at the oa^ cropping of the strata must therefore be tbe BDrest guide. In boring, tbe strata passed through should be compared with.

anOlMENTARY GEOLOGY. 189

; visible on the surface, in order to judge what specific itr&tnm has been arriTcd at or pnascil through. Should there Lb no basin-like depoiits of looser materials, the piirauit of :eT in more solid strata must be equaJly guided by a know- ^ of their geological and physical peculiarities; as, for mple, in the chalk and even in the oolitic district*, where namerous fissures allow the water to descend, until it is stopped by either a less frnctured bed or by some of the divisional dayey beds of such formations ; and when once such bed or stT&tnm has been discovered in any district, it becomes an index for the operations of the borer.

Although the several methods of boring cannot be here described in detail, it may be well briefly to notice the most remarkable. — 1. The common one, in which an anger is used Sir soft soils, and chisels or jumpers for rocks. In this mode the boiiag tool is connected with the surface by jointed rods, futened firmly together, and which must be frequently raised to dear the hole of the debris ; so that in great depths the wdght to be used and the time lost in separating and refiTing the joints become sources of great expense. — 2. The Chinese mode, by percussion alone ; the borer itself weighing about 180 ft*,, and being suspended by a cord, is alternately raised and allowed to fall, the debris either passing up through grooves in the sides of the tool and being then drawn up when accumulated on the head, or received into a separate cylinder with a valve opening from below upwards. This method is much more economical than the common, and has been used very extensively in Germany, though it is subject to two accidents requiring great precaution, viz. the great difiiculty of drawing up a broken borer, and the danger, from the flexibility of the cord, of the bore-hole taking an oblique direction, and therefore requiring to be abandoned. ^3. The 1 of Fanvelle, in which a hollow borer, either an auger I jumper, is used, the cutting tool being of larger diameter 1 the hollow stem, so that an annular space is formed ind the borer ; and water being forced down this space by

a force-pump, ascends by the tube, bringing witb it d^risy or if forced down the tube, ascends in a similar i by the annulus. As this arrangement renders it mme to bring the boring tools which are constantly kept c to the surface, a vast saying of time and expense is e The cities of London, Paris, Vienna, and Mentz are on basins, and the first two are now supplied with tl wholesome portion of their water by Artesian well borings in the London basin passing through the day, which only yields impure mineral springs, and water either in the sands of the plastic clay, or in the of the upper surface of the chalk.

In tracing out the sequence of strata which have n passed under review, it is scarcely necessary to say 1 Greologist should have his hammer almost const^tly i and will find it often desirable to use some descri] clinometer in unrayelling the intricacies of stratificati is unnecessary to describe the hammer, as geological h can now be readily procured, and the form itself sb varied to suit the nature of the rock ; or to figure any • clinometer, as the observer may attain his object simple contrivances, such as a small wooden quadran plumb-bob and a common pocket compass, — minute i being unnecessary.

Chapter Viii.

Conclading Remarks.

OT76H it is hoped tliat the sketch ^ven in the preceding es of this most interesting Science will haye made its ling principles familiar to the reader's mind^ it may not be less to recapitulate some of thern^ and to suggest that tion which is necessary both for their right perception and ir correct application.

Sedimentary deposits must be studied in their mineral con- Lon, in their organic fossils, and in the order of their stratiition. The mineral condition is an indication of the physical cumstances which regulated the deposit and so affected ;etable and animal life as to produce a peculiar local flora 1 fauna ; but the physical condition of the earth's surface 1 the circumstances connected with it having frequently ried in time and place, the mere mineral condition of a atum is insufficient to determine the epoch of its deposi- n. '

The organic fossils represent the flora and fauna of the och of deposition, but the laws of organic development are t sufficiently known to enable the Naturalist to assume from rely organic considerations that any one generic or specific m must have preceded every other, and hence the fossils >ne are not sufficient to determine a geological epoch. Order of stratification, as it embraces the examination both the mineral and organic conditions of a deposit at its sue-

192 &amp;Udimbmtakt Oboix&gt;Gy.

oessiye stages, or, in other words, of the physical and organk relations of the successive periods of deposition, is the onl^ sure guide to the first determination of geological epochs. In applying it to this purpose, however, care must be taken to avoid those sources of error which have been pointed out ; or to study stratification in districts which have not been thrown into confusion by disturbing forces, as the contortions th^ produce often place, to all appearance, the newer strata bdow the older, and sometimes invert a whole series of deposits. The relative ages of geological epochs being once established by the study of undisturbed districts, a due is obtained by whidi the confusion of contorted strata may be reduced to order.

The natural progression of organic beings in space and' time as represented by their lateral and vertical extension in geological strata has been sometimes violently interrupted by an elevation or depression of the strata by which the physical conditions required by such organisms were suddenly changed ; a fact well exemplified at the junction of unccm/bm* able formations : but this is not always the case, and in districts therefore which have not been disturbed at the interval betweoi two successive formations, and in which the superior formation is conformable to the inferior, the interruption of organic progression is due either to a gradual alteration of physical condition as to depth, or to a change of climate, or to both combined. In the case of violently interrupted progression there will be an abrupt and marked change of zoological characters ; in that of a gradual change of physical condition, an \ equally gradual change of zoological character ; in the one a | sudden alteration of formation, in the other a transition. In ^ the present state of natural operations, a gradual alteraticm ' appears to be the ordinary rule, and abrupt alteration, the local exception ; and the labours of some modem Geologists , have tended to establish the same deduction for the former epochs of the Earth's History.

The conditions of the earth which favour the contmued existence of any specific organic form are now difi^erent in various

RrniMENTARY GEOLOGY. 103

ts surface ; nor cnn it be supposed, a priori, thftt at epoch these conditions were perfectly iinif'ortn over the l^le surface. And further, in the gradunl progress of the a state fitted for the reception of organic beings, it is nn&hle to believe that some portions must have become Intable before others, the progression taking place from to the Equator, which is rendered more probable by the greater development of the earlier fossiliferous formationg ill both high northern and southern latitudes. Where disturbances by elevation had begun to alter the physical conditions of the surface, and to modify the distribution of sea and land, the natural orgnnit? progression must have been interrupted; but wherever such Wolent actions had not cooperated with the gradual change of temperature, it is reasonable to infer that the lateral and vertical extension of many organic bodies may have brought them into new positions on the earth's surface long after the conditions necessary for their continued existence had ceased at the original centre of their creation, and thus the characteristic organisms of one formation may appear at the epoch of another ; but a mixture of characteristic forms of the new with those of the old formation will be usually found to explain the true state of this case. It is not therefore surprising that a carboniferous flora should appear in the Silurian, tlie Devonian, the carboniferous, and even more recent formations, although there can be little doubt that in each case careful observation will discover the new organic types which characterize the change of epoch.

This difficulty of always determining the actual simultaneity of apparently similar formations in no respect affects the practical application of Geology. In limited countries, such as Great Britain and Ireland, the physical conditions catnot have varied bo unequally as materially to protract the existence of organisms in one place more than anotlier; and hence the order of geological formation being once well established in one district, it becomes a certain giiide to the examination of any-other. In more enlarged spaces, though synchronism of

Dudimentabv Geology.

I

formation may not be established, the organic group whici in one couDtry co-exists 'with some definite product being dii-covered in another, it may be assumed as at least probablE that the associated product will also be discoreretl.

Vast masses of strata which were once apparently stratified deposits have been so metamorphosed or changed that tlieir original structure can no longer be recognized. Espcrimi in the laboratory bave proved that similar changes can bt effected on the small scale ; and it is reasonable to conclade that tbe long'Continue«t and intense lieat of the eavtk acting under pressure upon stratified deposits was sufficient to redact them to the condition of the crystalline schists.

Rocks which had been in a state of igneous fusion can be traced from the earlint epocbs, tmd they are found to graduate into the true volcanic rocks of the present time. Tbe effects they have produced on some of the strata fre^ently determiitf the epoch of their appearance, but there is often mnch Culty in determining the relative ages of soch rocks, and stiQ more the depths from which they bave proceeded. It kai been here suggested that specific gravity may pos»Uy the safest method of solving such questions, and with such rule, that graiute has probably proceeded less depth than most of the porphyries and basalts.

The penetration of strata, in the form of dykes, by rocks, the contortions of the strata, and the eteTation mountain chains, are so many proofs of the operation various epocbs of disturbing forces, the results of which still observed in volcanoes and earthquakes. If the primary cause of such disturbances be the pressure of the st^dityiog and contracting crust upon the still Ut)uid nucleus of the earthi it is reaionable to believe that the intensity of the elevating force should increase with the augmenting thickness and pressure of the contracting crust, though the quantity of matter erupted may decrease ; nor is this inconsistent with facts, as some of the greatest mountain chains have been elevated at comparatively recent epochs, whilst the ancient basaltic flow*

Rudimentary Geology. 195

to have been, as a whole, more extensive than tliose of icent Tolcanoes. In respett to contortions, they may be either explained as the result of pressure on the solidifying strata by the wavE-like movement of the disturbed fluid matter, or be considered, according to the theory of Professor Rogers, to represent the wave itself continued into the crust. To Professor Rogers is due the most laborious and accurate amination of the facts of contortions, and a most persjiicv enunciation of his theory founded upon them, bnt it is very doubtful whether any simple ware of translation of a dense liquid 'mass can be made to conform to the varied forms of contortion. Whilst, then, such swells of the comparatively level surface, as have been demonstrated by the pendulum deductinns of M. Rozet may be reasonably considered waves conforming to those of the liquid nucleus, contortions are more probably the effect of pressure on strata, wliich not being sufficiently elastic either to follow the movement of the liquid wave, or to transmit the vibration or quake of a solid medium, are folded together.

In studying many natural phenomena, such for example as denudation, the apparent magnitude of a result should not be allovied to oppress or perplex the mind, as it must be remembered, that though almost immeasurably vast in the limited perceptions uf man, they are atomic when compared to the magnitude of the earth itself j but this is not the case aa regards the estimation of forces in the explanation either of ■wear or of contortions, as the laws of matter are uniform and general, and the fcvce of gravity may be studied as well in the fell of a pebble aa in that of a mountain, or the magnetic force of the earth estimated by the vibrations of a needle. The phe< nomena stand forth as facts to be observed and studied ; but in seeking to explain them, no supposition of unknown forces, immense in proportion to the forces we see acting on the earth I as the earth itself is to the mountain which studs or the valley I which dimples its surface, can be admitted. The density of L the earth, and the laws which regulate its motion, are known,

L Iz J

1

by ■ be ■

I

I

19i>

Rudimentary Geology.

and the general properties of matter, whether at rest or ii motion, are also known ; and it cannot therefore be si4d tl the elements are wanting for the full elucidation of all physical I phenomena, or that anj theory is fully established which | cannot be shown to conform to known physical laws.

The End.

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