INTRODUCTION.

"Geology, in the magnitude and sublimity of the objects of which it treats, ranks next toAstronomyin the scale of the Sciences."—Sir J. F. W. Herschel.

Geology, a term signifying a discourse on the Earth, (from two Greek words: viz. γἡ,ge, the earth; and λὁγος,logos, a discourse,) is the science which treats of the physical structure of the planet on which we live, and of the nature and causes of the successive changes which have taken place in the organic and inorganic kingdoms, from the remotest period to the present time, and is therefore intimately connected with every department of natural philosophy.

While in common with other scientific pursuits it yields the noblest and purest pleasures of which the human mind is susceptible, it has peculiar claims on our attention, since it offers inexhaustible and varied fields of intellectual research, and its cultivation, beyond that of any other science, is in a great measure independent of external circumstances; forit can be followed in whatever condition of life we maybe placed, and wherever our fortunes may lead us.

The eulogium passed by a distinguished living philosopher on scientific knowledge in general, is strikingly applicable to geological investigations. "The highest worldly-prosperity, so far from being incompatible with them, supplies additional advantages for their pursuit; they may be alike enjoyed in the intervals of the most active business, while the calm and dispassionate interest with which they fill the mind, renders them a most delightful retreat from the agitations and dissensions of the world, and from the conflict of passions, prejudices, and interests, in which the man of business finds himself continually involved."[2]

[2]Sir J. F. W. Herschel, "Discourse on the Study of Natural Philosophy."

From the present advanced state of geological science, particularly of that department which it is the more especial object of these volumes to elucidate, namelyPalæontology,[3]or the study of Organic Remains,—it seems scarcely credible, that but little more than a century ago it was a matter of serious question with naturalists, whether the petrified shells imbedded in the rocks and strata were indeed shells that had been secreted by molluscous animals; or whether these bodies, together with the teeth, bones, leaves, wood, &c. found in a fossil state, were not formed by what was then termed the plastic power of the earth; in like manner as minerals, metals, and crystals.

[3]Palæontology: from παλαιος,palaios, ancient—οντα,onta, beings—λὁγος,logos, a discourse.

In a "Natural History of England," published towards the end of the last century, it is gravely observed that at Bethersden in Kent, a kind of stone is found full of shells, "which is a proof that shells and the animals we find in them living, have no necessary connexion." Another amusing instance of the ignorance on such subjects whichprevailed at no remote period, occurs in a "History of the County of Surrey," in which it is stated that in a search for coal near Guildford the borers broke, and "this was thought by Mr. Peter Lely, the Astrologer, to have been the work of subterranean spirits, who wrenched off the augers of the miners, lest their secret haunts should be invaded."

But in the latter part of the seventeenth century, there were several eminent men in England who were greatly in advance of the age in which they lived, and strenuously exerted themselves to discover and promulgate the true principles of Geology. Among these, Dr.Martin Lister, physician to Queen Anne, was one of the most distinguished. This accomplished naturalist, in his great work on shells, which remains to this day a splendid monument of his labours, and of the talents and filial affection of his two daughters, by whom all the plates were engraved, figures and describes many fossil shells as real animal productions, and carefully compares them with recent species. He also recognised the distinction of strata by the organic remains they contain; and to him the honour is due of having first suggested the construction of geological maps;[4]he was likewise well acquainted with the position and extent of the Chalk and other strata of the South of England.[5]

[4]See Notes on the Progress of Geology in England, by W. H. Fitton, M.D. &c.Philos. Mag.vols. i. and ii. for 1832 and 1833.[5]This celebrated physician and British geologist died in 1712, and was interred in the old church at Clapham; where a tablet to his memory is affixed to the outside of the north wall of St. Paul's Chapel.

[4]See Notes on the Progress of Geology in England, by W. H. Fitton, M.D. &c.Philos. Mag.vols. i. and ii. for 1832 and 1833.

[5]This celebrated physician and British geologist died in 1712, and was interred in the old church at Clapham; where a tablet to his memory is affixed to the outside of the north wall of St. Paul's Chapel.

From the foreign writers, who at an early period had obtained some correct notions of the structure of our planet, and of the nature of the revolutions it had undergone, I select the following beautiful and philosophical illustration of the physical mutations to which the surface of the earth is perpetuallysubjected. It is from an Arabic manuscript of the thirteenth century;[6]the narrative is supposed to be related by Rhidhz, an allegorical personage.

[6]Quoted by Sir C. Lyell in his "Principles of Geology."

"I passed one day by a very ancient and populous city, and I asked one of its inhabitants how long it had been founded? 'It is, indeed, a mighty city,' replied he; 'we know not how long it has existed, and our ancestors were on this subject as ignorant as ourselves.' Some centuries afterwards I passed by the same place, but I could not perceive the slightest vestige of the city; and I demanded of a peasant, who was gathering herbs upon its former site, how long it had been destroyed? 'In sooth, a strange question,' replied he, 'the ground here has never been different from what you now behold it.' 'Was there not,' said I, 'of old a splendid city here?' 'Never,' answered he, 'so far as we know, and never did our fathers speak to us of any such.'

"On revisiting the spot, after the lapse of other centuries, I found the sea in the same place, and on its shores were a party of fishermen, of whom I asked how long the land had been covered by the waters? 'Is this a question,' said they, 'for a man like you? this spot has always been what it is now.'

"I again returned ages afterwards, and the sea had disappeared. I inquired of a man who stood alone upon the ground, how long ago the change had taken place, and he gave me the same answer that I had received before.

"Lastly, on coming back again, after an equal lapse of time, I found there a flourishing city, more populous and more rich in buildings than the city I had seen the first time; and when I fain would have informed myself regarding its origin, the inhabitants answered me, 'Its rise is lost in remote antiquity—we are ignorant how long it has existed, and our fathers were on this subject no wiser than ourselves.'"

We may smile at the ignorance of the inhabitants of the fabled cities, but are we in a condition to give a more satisfactory reply should it be inquired of us, "What are the physical changes which the country you inhabit has undergone?"—and yet cautious observation, and patient and unprejudiced investigation, are alone necessary to enable us to answer the interrogation.

Dismissing from his mind all preconceived opinions, the student must be prepared to learn that the earth's surface has been, and still is, subject to perpetual mutation,—that the sea and land are continually changing place,—that what is now dry land was once the bottom of the deep, and that the bed of the present ocean will, in its turn, be elevated above the water and become land,—that all the solid materials of the globe have been in a softened, fluid, or gaseous state,—that the relics of countless myriads of animals and plants are entombed in the rocks and strata,—and that vast mountain-chains, and extensive regions, are wholly composed of the petrified remains of beings that lived and died in periods long antecedent to the creation of the human race. Astounding as are these propositions, they rest upon evidence so clear and incontrovertible, that they cannot fail to be admitted by every intelligent and unprejudiced reader, who will bestow but a moderate share of attention to the examination of the phenomena, of which the following pages present a familiar exposition.

I cannot conclude these introductory observations, without adverting to the incalculable benefits which result from scientific pursuits in general, and of Geology in particular. An able modern writer has justly remarked:—"It is fearfully true, that nine-tenths of the immorality which pervades the better classes of society, originate from the want of an interesting occupation to fill up the vacant time; and as the study of the natural sciences is as attractive as it is beneficial, it must necessarily exert a moral and even religious influence upon the young and inquiring mind. The youth who is fond of scientific pursuits will not enter into revelry, for frivolous or vicious excitements will have no fascination for him. The overflowing cup, the unmeaning or dishonest game, will not entice him. If any one doubts the beneficial influence of these studies on the morals and character, I would ask him to point out the immoral youngman who is devotedly attached to any branch of natural science: I never knew such an one. There may be such individuals—for religion only can change the heart—but if there be, they are very rare exceptions; and the loud clamours which are always raised against the man of science who errs, prove how rarely the study of the works of the Creator fails to exert an ennobling effect upon a well-regulated mind. Fortunate, indeed, are the youth of either sex, who early imbibe a taste for natural knowledge, and whose predilections are not thwarted by injudicious friends."

And while Geology exerts this hallowing influence on the character, it possesses the great advantage of presenting subjects adapted to every capacity; on some of its investigations the highest intellectual powers and the most profound acquirements in exact science are required; while many of its problems may be solved by any one who has eyes and will use them; and innumerable facts illustrative of the ancient condition of our planet, and of its inhabitants, may be gathered by any diligent and intelligent observer.

But it is surely unnecessary to dwell on the interest and importance of a study, which instructs us that every pebble we tread upon bears the impress of the Almighty's hand, and affords evidence of Creative wisdom; that every grain of sand, every particle of dust scattered by the wind, may be composed of the aggregated skeletons of beings, so minute as to elude our unassisted vision, but which possessed an organization as marvellous as our own;—a science whose discoveries have realized the wildest imaginings of the poet,—whose realities far surpass in grandeur and sublimity the most imposing fictions of romance;—a science, whose empire is the earth, the ocean, the atmosphere, the heavens;—whose speculations embrace all elements, all space, all time;—objects the most minute, objects the most colossal;—carrying its researches into the smallest atom which themicroscope can render accessible to our visual organs,—and comprehending all the phenomena in the boundless Universe, which the powers of the telescope can reveal.

And as no branch of natural philosophy can more strongly impress the mind with that deep sense of humility and dependence, which the contemplation of the works of the Eternal is calculated to inspire, so none can more powerfully encourage our aspirations after truth and wisdom. Every walk we take offers subjects for profound meditation,—every pebble that attracts our notice, matter for serious reflection; and contemplating the incessant dissolution and renovation which are taking place around us in the organic and inorganic kingdoms of nature, we are struck with the force and beauty of the exclamation of the poet—

"My heart is awed within me, when I thinkOf the great miracle which still goes onIn silence round me—the perpetual workOfThyCreation, finished, yet renewedFor ever!

ON THE PLAN OF THE WORK, AND THE ARRANGEMENT AND SUBDIVISION OF THE SUBJECTS IT EMBRACES.

Withthe view of economizing space, I would refer the reader to the following volumes for figures and descriptions of such fossils as are illustrated therein: by this arrangement I hope to afford the student a comprehensive view of Palæontology, and yet restrict this work within the limits which as a manual it would be inconvenient to exceed; at the same time it will be complete in itself, and afford all the information required by the amateur collector and general reader.

I.Dr. Buckland'sBridgewater Treatise: 2 vols. 8vo.—These volumes contain numerous excellent figures of organic remains; and as the work is, or ought to be, found in every good public or private library in the kingdom, it will be accessible to most of my readers.

II.The Wonders of Geology, or a Familiar Exposition of Geological Phenomena;sixthedition, in two vols, with coloured plates, and numerous figures; by theAuthor. Price 18s.—This work is designed to afford a general view of Geological phenomena, divested as much as possible of scientific language: it is illustrated by numerous figures of organic remains.

III.Geological Excursions round the Isle of Wight and along the adjacent Coasts of Hampshire and Dorsetshire.One volume, richly illustrated. By theAuthor. Price 12s.

IV.Petrifactions and their Teachings; or a Hand-book to the Gallery of Organic Remains in the British Museum.One vol. with many original figures of the most interesting objects. By theAuthor.[7]Price 5s.

[7]The three works above named consist of four volumes uniform with the present edition of the "Medals of Creation:" this series of six volumes comprises the popular geological works of theAuthor.

V.A Pictorial Atlas of Fossil Remains;consisting of Coloured Illustrations selected from "Parkinson's Organic Remains of a Former World," and Artis' "Antediluvian Phytology." 1 vol. 4to. with seventy-four coloured plates, and several lignographs, containing nearly 900 figures of fossils. By theAuthor. Price 2l.2s.

To the above may be addedDana'sMineralogy, which treats of the various mineral substances that enter into the composition of the rocks and strata in which the fossil remains are imbedded.

A good geological map of Great Britain is indispensable. The small map published by the Society for the Diffusion of Useful Knowledge, edited by Sir R. Murchison, price 5s., is an excellent compendium; but Mr. Knipe's large "Geological Map of the British Isles" is the most complete and convenient for the traveller: price 3l.3s.By reference to the map, the geological structure, and the prevailing fossils of a district, may be ascertained.

The above works are referred to as follows: viz.

Bd.Dr. Buckland's Treatise.Wond.The Wonders of Geology.Geol. I. of W.Geology of the Isle of Wight.Petrifactions.Petrifactions and their Teachings.Pict. Atlas.Pictorial Atlas of Organic Remains.

The following works, to which reference will often be made, are thus denoted:—

Foss. Flor.The Fossil Flora of Great Britain, by Dr. Lindley, and W. Hutton, Esq. 3 vols. 8vo.

Vég. Foss.Histoire des Végétans: Fossiles, par M. Adolphe Brongniart. 1 vol. 4 to.

Geol. Trans.Transactions of the Geological Society of London. 5 vols. 4to.; and New Series, in 5 vols.

Geol. Proc.Geological Proceedings.

—— Journ.————— Quarterly Journal.

Sil. Syst.The Silurian System, by Sir R. I. Murchison. 2 vols. 4to. with plates and map.

Org. Rem.Parkinson's Organic Remains of a Former World. 3 vols. 4to.

Oss. Foss.Ossemens Fossiles, par Baron Cuvier. 5 vols. 4to. 5me.edit.

Min. Conch.Sowerby's Mineral Conchology. 6 vols. 8vo.

Odont.Odontography; a Treatise on the Comparative Anatomy of the Teeth, by Professor Owen. 2 vols. 8vo.

Brit. Mam.British Fossil Mammalia; by the same Author. 1 vol. 8vo.

Brit. Rep.Reports on British Fossil Reptiles in the British Association Transactions for 1839, and 1841; by the same Author.

Phil. York.Geology of Yorkshire, by Professor John Phillips. 2 vols. 4to.

South. D.Fossils of the South Downs, 1 vol. 4to. 42 plates by the Author. 1822.

Geol. S. E.Geology of the South-east of England. 1 vol. 8vo. by the same.

Tilg. For.Fossils of Tilgate Forest. 1 vol. 4to. 20 plates; by the same. 1827.

Poiss. Foss.Recherches sur les Poissons Fossiles, par M. Agassiz. 4 vols. 4to, and 2 vols, folio.

Man. Geol.Manual or Elements of Geology, by Sir C. Lyell. 1 vol. 8vo. Edit. 1852.

The following abbreviations are also employed:—

§ 1.Relative to the Rocks or Strata.

Drift.Alluvial deposits, or Drift.Tert.Tertiary.Lond. C.London clay.Cret.Cretaceous formation.U. Ch.Upper chalk.L. Ch.Lower chalk.Trias.New Red Sandstone, or Triassic deposits.Carb.Carboniferous or Coal formation.Mt. L.Mountain or Carboniferous limestone.Devon.Devonian or Old Red Sandstone formation.Sil. Syst.Silurian System, or formation.

Drift.Alluvial deposits, or Drift.

Tert.Tertiary.Lond. C.London clay.

Cret.Cretaceous formation.U. Ch.Upper chalk.L. Ch.Lower chalk.

Trias.New Red Sandstone, or Triassic deposits.

Carb.Carboniferous or Coal formation.

Mt. L.Mountain or Carboniferous limestone.

Devon.Devonian or Old Red Sandstone formation.

Sil. Syst.Silurian System, or formation.

§ 2.Relative to Organic Remains.

nat.Natural size.× Magnified in diameter:e.g.× 8, magnified eight diameters, &c.× × Highly magnified; the degree not accurately determined.inv.Invisible to the naked eye.— Less than natural:e.g.—2/3, reduced to two-thirds the diameter of the original.Lign.Lignograph or woodcut.

nat.Natural size.

× Magnified in diameter:e.g.× 8, magnified eight diameters, &c.

× × Highly magnified; the degree not accurately determined.

inv.Invisible to the naked eye.

— Less than natural:e.g.—2/3, reduced to two-thirds the diameter of the original.

Lign.Lignograph or woodcut.

Explanation of Terms.—Upon the occurrence of a scientific word apparently requiring explanation, themeaning, where practicable, is for the most part given in a parenthesis; for example, Caulopteris (fern-stem); Phascotherium (pouch-animal); carboniferous (coal-bearing); except in the case of arbitrary names, and of those whose derivation cannot be concisely expressed.[8]With the view of rendering these volumes more generally useful, English terminology is in many instances made use of, though involving inelegance of expression.

[8]Upwards of 300 scientific terms are explained in the Glossary, "Wonders," vol. ii. p. 915-921.

The work is divided into four parts: the first is anIntroduction to the Study of Organic Remains; the second treats ofFossil Botany; the third embracesFossil Zoology; and the fourth, under the head ofGeological Excursions, illustrates the principles enunciated in the course of the work, by practical observations on a few instructive British localities.

PART I.

PART II.

FOSSIL BOTANY.

Classification of Fossil Vegetables.

Retrospect.

British Localities of Fossil Plants.

PART III.

FOSSIL ZOOLOGY.

On the Fossil Remains of the Animal Kingdom.

Retrospect.

PART IV.

CHAPTER I.

ON THE NATURE AND ARRANGEMENT OF THE BRITISH STRATA, AND THEIR FOSSILS.

"To discover order and intelligence in scenes of apparent wildness and confusion is the pleasing task of the geological inquirer."—Dr. Paris.

Thesolid materials of which the earth is composed, from the surface to the greatest depths within the reach of human observation, consist of minerals and fossils.

Mineralsare inorganic substances formed by natural operations, and are the product of chemical or electro-chemical action.

Fossilsare the durable remains of animals and vegetables which have been imbedded in the strata by natural causes in remote periods, and subsequently more or less altered in structure and composition by mechanical and chemical agencies.

The soft and delicate parts of animal and vegetable organisms rapidly decompose after death; but the firmer and denser structures, such as the bones and teeth of the former, and the woody fibre of the latter, possess considerable durability, and under certain conditions will resist decay formany years, or even centuries; and when deeply imbedded in the earth, protected from atmospheric influences, and subjected to the conservative effects of various mineral solutions, the most perishable tissues often resist decomposition, and becoming transformed into stone, may endure for incalculable periods of time. The calcareous and siliceous cases or frustules of numerous microscopic plants are so indestructible, and occur in such inconceivable quantities, that the belief of some eminent naturalists of the last century, that every grain of flint and lime in certain rocks, may have been elaborated by the energies of vitality, can no longer be regarded as an extravagant hypothesis. Some idea may be formed of the large proportion of the solid materials of the globe that has unquestionably originated from this source, by a reference to the list of strata which are wholly, or in great part, composed of animal and vegetable structures, given in the "Wonders of Geology," p. 888.

There are also immense tracts of country that consist in a great measure of the remains of plants in the state of anthracite, coal, lignite, &c.; and districts covered with peat-bogs and subterranean forests.

Although these relics of animal and vegetable organisms are found in almost every sedimentary deposit, yet they occur far more abundantly, and in a better state of preservation, in some strata than in others: nor are they equally distributed throughout the same bed, but are heaped together in particular localities, and occur but sparingly, or are altogether absent, in other layers of the same rock. Neither are the remains of the same kinds of animals and plants found indiscriminately in strata of different ages: on the contrary, many species are restricted to the most ancient, others to the most recent formations; while some genera range through the entire series of deposits, and also appear as denizens of the existing seas. Hence organic remainsacquire a high degree of importance, not only from the intrinsic interest they possess as objects of natural history, but also for the light they shed on the physical condition of our planet in the remotest ages, and for the data they afford as to the successive physical revolutions which the surface of the earth has undergone.

Fossils have been eloquently and appropriately termedMedals of Creation; for as an accomplished numismatist, even when the inscription of an ancient and unknown coin is illegible, can from the half-obliterated effigy, and from the style of art, determine with precision the people by whom, and the period when, it was struck; in like manner the geologist can decipher these natural memorials, interpret the hieroglyphics with which they are inscribed, and from apparently the most insignificant relics, trace the history of beings of whom no other records are extant, and ascertain the forms and habits of unknown types of organization whose races were swept from the face of the earth, ere the creation of man and the creatures which are his contemporaries. Well might the illustrious Bergman exclaim, "Sunt instar nummorum memorialium, quæ de præteritis globi nostri fatis testantur, ubi omnia silent monumenta historica."

To derive from these Medals of Creation all the information they are capable of affording, regard therefore must be had not only to their peculiar characters, but also to the geological relations of the strata in which they are imbedded. Data may be thus obtained by which the relative age of a formation or group of strata can be determined, as well as the mode of deposition, and the agency by which it was effected; whether in the bed of an ocean, or of a lake, or estuary,—by the action of the sea, or of rivers, or running streams,—by the effects of icebergs or glaciers,—by slow processes through long periods of time, or by sudden inundations or deluges,—or by the agency of volcanoes and earthquakes.

The discovery that particular fossils are confined to certain deposits, was soon productive of important results, which greatly tended to the advancement of modern Geology; for although Dr. Lister, more than a century before, had obtained a glimpse of this law, its principles were neither understood nor regarded in this country until the late Dr. William Smith, by his own unaided exertions, proved by numerous observations on the British strata, its value and applicability for the identification of a deposit, in districts remote from each other.

This phenomenon did not escape the notice of the distinguished French philosophers, MM. Cuvier and Brongniart, who in their admirable work, "Géographie Minéralogique des Environs de Paris," enunciated the same principle:—

"Le moyen que nous avons employé pour reconnoitre au milieu d'un si grand nombre de lits calcaires, un lit déjà, observé, dans un canton très-éloigné, est pris de la nature des fossiles renfermés dans chaque couche; ces fossiles sont toujours généralement les mêmes dans les couches correspondantes, et présentent d'un système de couche à un autre système, des différences d'espèces assez notables. C'est un signe de reconnoissance qui jusqu'à présent ne nous a pas trompés."[9]

[9]Géog. Min. Oss. Foss. tom. ii. p. 266.

Now, though recent discoveries have shown that this rule has many exceptions, and that its too stringent adoption has been productive of some erroneous generalizations, yet if employed with due caution it is fraught with the most interesting results, and is the only certain basis of our knowledge respecting the appearance, continuance, and extinction, of the lost races of animals and plants, which were once denizens of our planet.

ROCKS AND STRATA.

In the "Wonders of Geology" will be found a comprehensive sketch of the composition and arrangement of the several formations or groups of strata; and a reference to that work will afford the student the necessary informationon this branch of Geology. For the convenience of the general reader I subjoin a synoptical view of the characters and relations of the British fossiliferous deposits.

The total thickness of the entire series of rocks within the scope of human examination, is estimated at from fifteen to twenty miles, reckoning from the summits of the highest mountains to the greatest depths hitherto penetrated; and as this vertical section scarcely amounts to1/400th of the diameter of the globe, it is familiarly termed the Earth's crust. The substances of which the sedimentary strata are composed have been deposited by the action of water, and subsequently more or less modified in structure and composition by heat, and by electro-chemical forces. The superficial accumulations of water-worn detritus, consisting of gravel, boulders, sand, clay, &c. are termedDrift, orAlluvialdeposits. When the successive layers in which the sediments subsided are obvious, the deposits are said to bestratified; when the nature of the materials has been altered by igneous action or high temperature, but the lines of stratification are not wholly effaced, the rocks are denominatedmetamorphic(transformed). When all traces of organic remains and of sedimentary deposition are lost, and the mass is crystalline, and composed of known products of igneous action, such rocks are namedplutonic, as granite, sienite, trap, basalt, porphyry, and the like. Lastly, rocks resembling the lavas, scoria, and other substances emitted by burning mountains still in activity, are calledvolcanic.

The sedimentary origin ascribed to ancient crystalline rocks is, of course, hypothetical, since all evidence of aqueous deposition is wanting, and the minerals (mica,quartz, andfelspar) of which they are so largely constituted, are not readily soluble in water under ordinary circumstances. But rocks unquestionably deposited by water, when exposed to intense heat under great pressure, acquire a crystalline structure (Wond.p. 864); and a series of changes, from aloose earthy deposit, to compact volcanic lava, may be traced in numerous instances, so as to leave but little doubt that the rocks called primitive or primary,mayhave originally been either argillaceous, siliceous, or calcareous strata, abounding in organic remains (Wond.p. 873). These crystalline masses have been formed at successive periods; for granite is found of all ages, occurring in the most ancient, as well as in comparatively modern epochs. The difference between the composition and aspect of these rocks, and those of recent volcanoes, is with much probability ascribed to the fact that the latter are of sub-aerial origin; that is, were erupted on the surface, and the gaseous products in consequence escaped; while the former were ejected at great depths, either beneath the sea, or under immense accumulations of other deposits, and being thus subjected to great pressure, the volatile elements were confined, and formed new combinations: in like manner as chalk when burnt in the open air is converted into lime, the carbonic acid gas escaping; but when exposed to the same degree of heat in a closed iron tube, is transformed into granular marble (Wond.p. 104).

From these ancient crystalline rocks generally underlying the sedimentary deposits, and never appearing as if they had been ejected from a crater, the termhypogene[10](nether-formed) is employed by Sir C. Lyell to designate the whole class; and they are subdivided into, 1.plutonic, those in which all traces of sedimentary origin are lost, as granite; and 2.metamorphic, those which still manifest traces of stratification, as mica-schist, &c.

[10]Nether-formed, from ιπο,hypo, under; and γἱνομαι, ginomai, to be formed.

The fossiliferous rocks are, for the convenience of study, separated into three grand divisions.

1. TheTertiary; comprising the deposits between the Chalk and the superficial Drift and modern Alluvium.

2. TheSecondary; from theChalkto theTrias or New Red, inclusive.

3. ThePalæozoic; from thePermianto theSilurian; including the vast series of unfossiliferous slate rocks termed theCambrian, in which all traces of organic remains are lost.

In the following arrangement the strata are enumerated as if lying in regular sequence, one beneath the other; but in nature such an unbroken series has never been observed. A few groups only occur in a serial order, and these but rarely in their original position. The beds are for the most part disrupted, and lie in various angles of inclination; sometimes they are completely retroverted, the newer strata underlying those upon which they were originally deposited. The order of succession has been ascertained by careful observation of the relative superposition of the respective members of the series in different countries; and from an immense number of facts collected by able observers in every part of the globe.

This synopsis presents a chronological arrangement of the rocks according to the present state of geological knowledge, but it must not be supposed that these rigid distinctions, these hard lines, which are necessary to facilitate the acquisition of a general idea of the phenomena attempted to be explained, exist in nature. By whatever names we designate geological periods, there appear to be no clearly defined boundaries between them in reference to the whole earth: such well marked lines may be seen in particular localities, but daily experience teaches us that there is a blending, and a gradual and insensible passage, from the lowest to the highest sedimentary strata, particularly in respect of fossil remains. The terms employed to designate formations can only be considered as expressing thepredominance of certain characters, to be used provisionally, as a convenient mode of classifying and generalizing the facts collected, whilst that knowledge is accumulating which in after times will reveal the nature and order of succession of the principal events in the earth's physical history.[11]

[11]"Wonders of Geology," p. 892.

Dr. Buckland's "Bridgewater Treatise" (Vol. II.frontispiece) contains a comprehensive Diagram of the rocks and strata of which the crust of the earth is composed; it was drawn by the late Mr. Thomas Webster.

SYNOPSIS OF THE BRITISH STRATA.

"Hard lines are admissible in Science, whose object is not to imitate Nature, but to interpret her works."—Greenough.

The classification of the stratified rocks is based on three principal characters; namely, 1, the mineral structure; 2, the order of superposition; and 3, the nature of the organic remains; the following synopsis has been drawn up in accordance with these principles.[12]

[12]See "Wonders of Geology," vol. i. pp. 200-207, for a Synoptical Table of the principal rocks.

CHRONOLOGICAL ARRANGEMENT OF THE BRITISH FORMATIONS.

COMMENCING WITH THE UPPERMOST OR NEWEST DEPOSITS.

Modern or Human Epoch.

Alluvial Deposits: remains of Man and existing species of mammalia.

Post-Pliocene.

Drift; Boulder clay; Till; &c. comprising the superficial irregular accumulations of transported materials, consisting of gravel, boulders, sand, clay, &c.

Observations.—These beds have been formed by a variety of causes; by land-floods and inundations, by irruptions of the sea, and by theagency of glaciers and icebergs. They are the catacombs of the extinct colossal mammalia—of the mastodon, mammoth, rhinoceros, hippopotamus, elk, horse, ox, whale, &c. They cannot be definitively separated from those of the Modern or Human epoch, for the gravel beds near Geneva, which closely resemble the newest tertiary drift in materials and position, abound in bones of animals, almost all of which belong to existing species.[13]

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