VII. Coal.—The numerous fossil plants from the carboniferous strata that are figured in this work, render it necessary to put the general reader in possession of a concise view of the nature and mode of formation of those ancient accumulations of vegetable matter, which now constitute the beds of mineral fuel termed coal.

Although at the present time no one at all conversant with geology doubts the vegetable origin of Coal, the period is not distant when many eminent philosophers were sceptical on this point; and the truth in this, as in most other questions In natural philosophy, was established with difficulty. The experiments and observations of the late Dr. Macculloch mainly contributed to solve the problem as to the vegetable origin of this substance; and that eminent geologist successfully traced the transition of vegetable matter from peat-wood, brown coal, lignite, and jet, to coal, anthracite, graphite, and plumbago. Nor must the important labours of Mr. Parkinson in this field of research be forgotten. The first volume of the "Organic Remains of a former World," which treats of vegetable fossils, contains much original and valuable information on the transmutation of vegetable matter, by bituminous fermentation, into the various mineral substances in which its original nature and structure are altogether changed and obliterated; and that work may still be consulted with advantage by the student.

But though the vegetable origin of all coal will not admit of question, yet evidence of the original structure of the plants or trees whence it was derived is not always attainable. The most perfect coal seems to have undergone a complete liquefaction, and if any portions of the vegetable tissue remain, they appear as if imbedded in a pure bituminous mass. The slaty coal generally preserves traces of cellular or vascular tissue, and the spiral vessels and dotted cells of coniferous trees may often be detected by the microscope. In many instances the cells are filled with an amber-coloured resinous substance; in others the organization is so well preserved, that on the surface of a block of coal cracked by heat, the vascular tissue, and the dotted glands, may be observed. Some beds of coal appear to be wholly composed of minute leaves or disintegrated foliage; for if a mass recently extracted from the mine be split asunder, the exposed surfaces are found covered with delicate laminæ of carbonized leaves and fibres matted together; and flake after flake may be peeled off through a thickness of many inches, and the same structure be apparent. Rarely are any large trunks or branches observable in the beds of coal; but the general appearance of the carboniferous mass is that of an immense deposit of delicate foliage shed and accumulated in a forest, and consolidated by great pressure while undergoing that peculiar process by which vegetable matter is converted into carbon.

The essential conditions for the transmutation of vegetable substances into coal, appear to be the imbedding of large quantities of recent vegetables beneath deposits which shall exclude the air, and prevent the escape of the gaseous elements when released by decomposition from their organic combination; hence, according as these conditions have been more or less perfectly fulfilled, coal, jet, lignite, brown-coal, peat-wood, &c. will be the result.

VIII. Fossil Corals.—The real nature even of recent Corals is in general so imperfectly understood by the intelligent reader who has not paid especial attention to the department of natural history which treats of the class of animated nature termed Zoophytes, that in describing the Fossil Corals In my Wonders of Geology, I felt it necessary to devote one Lecture to the consideration of Corals and Crinoidea, in order to afford a popular exposition of the structure and economy of these highly Interesting tribes of animal existence.[105]

A very prevalent error regarding their nature Is, that the beautiful stony substances generally called corals, are fabricated by the animalcules which inhabit the cells when living, in the same manner as is the honeycomb of the bee and wasp. This opinion is utterly erroneous: the coral is secreted by the integuments or membranes with which when recent it was invested and permeated; in like manner as are the bones of the skeleton in the higher orders of animals by the tissues designed for that especial purpose, and wholly without the cognisance or control of the creature of which they constitute the internal support.

A general idea of the nature of the compound coral-zoophytes may be obtained by the examination of the common Flustra or Sea-mat. This form of polyparia, when taken out of the water, appears to the naked eye like a patch of fine varnished net-work, adhering to a piece of sea-weed or stone; when viewed with a magnifying lens of moderate power, the surface is found beset with pores regularly disposed: and if the Flustra be examined while immersed in sea-water, its surface is seen to be invested by a gelatinous substance, and every pore is the aperture of a cell, whence issues a tube fringed at the extremity with long tentacula or feelers. These expand, then suddenly contract, withdraw into the cell, and again issue forth: the whole surface of the Flustra being studded with the hydra-like animalcules; each enjoying a distinct existence, the entire group being united by one common integument or calcareous frame-work. When the Flustra is exposed to the air, the polypes soon perish, the animal matter rapidly decomposes, and the calcareous lace-like skeleton alone remains. In the larger and more compact corals the phenomena are similar, differing only in degree. In a fossil state, the durable remains of the corals consist for the most part of the calcareous frame-work (or polyparium, as it is termed), which often possesses a crystalline structure; and in some instances is completely transmuted into silex, as in specimens from Antigua, the Falls of the Ohio, and from Tisbury in Wiltshire. (See Plate XXXVIII. figs. 12, 13.)

I must refer to the Wonders of Geology for a more extended notice of fossil corals, and other zoophytes, and will only add that the calcareous and siliceous spines or spicula, not only of sponges, but also of Gorgoniæ, and other corals, are often met with in a fossil state.[106]

IX. Cuvier's Discoveries. The Fossil Quadrupeds of Montmartre. (Plate LXXII.)—The Palæotheria, Anoplotheria, and other genera of extinct quadrupeds related to the Tapir, whose remains were first noticed in the gypseous limestone of Montmartre, near Paris, and which have since been found in many other localities of the same strata, are familiar to every one, from the just celebrity attached to the labours of the illustrious Cuvier, who restored as it were these lost denizens of an earlier world, in their native character and forms, and distinguished them by names long since become classical in the sciences which treat of the ancient history of the earth and its inhabitants.

The gypsum quarries spread over the flanks of Montmartre were many years since known to contain fossil bones of extinct quadrupeds, and some of these had been figured and described in 1768 by Guettard, and afterwards by Pralon, Lamanon, and Parumot: but it was not till the attention of M. Cuvier was directed to the subject by some specimens put into his hands by M. Vuarin, that the interest and importance of these fossils were understood. The curiosity of Baron Cuvier was so much excited by an inspection of a large collection of these bones, soon after he had been successfully engaged in the investigation of the remains of fossil Elephants and Mastodons, that he immediately began to obtain specimens from the quarries, and by liberally rewarding the workmen, and by unremitting personal research, he soon accumulated an immense quantity of bones of all sorts, belonging to numerous individuals. He now perceived that a new world was open to his view: and to use his own expressive language, he found himself in an ancient charnel-house, surrounded by a confused multitude of mangled skeletons of a great variety of unknown beings. To arrange each fragment in its proper place, and restore order to these heterogeneous materials, seemed at first a hopeless task: but a knowledge of the immutable laws by which the organization of animal existence is governed, soon enabled him to assign to each bone, and even fragment, its proper place in the skeleton; and the forms of beings hitherto unseen by mortal eye appeared before him. "I cannot," he exclaims, "express my delight in finding how the application of one principle was instantly followed by the most triumphant results. The essential character of a tooth and its relation to the skull being determined, all the other elements of the fabric immediately fell into their proper places; and the vertebra, ribs, bones of the legs, thigh, and feet, seemed to arrange themselves even without my bidding, and in the very manner I had predicted." The principles of the correlation of structure which his profound researches in comparative anatomy had enabled him to establish, conducted to these important results, and laid the foundation of that science which has since received the name of Palæontology.[107] The mode of induction adopted by this illustrious philosopher, has been the mighty instrument by which subsequent labourers in this department of science have so largely contributed to our knowledge of the ancient condition of the earth, and of the structure and economy of the tribes of beings which have successively dwelt upon it. The examination of the fossil teeth (in Plate LXXII. figs. 4-9) showed that the animals were herbivorous; and the crown of the tooth being composed of two or three simple crescents, as in certain pachydermata, proved that they differed from the ruminants, which have double crescents, and each four bands of enamel. The two principal genera first established were the Palæotherium and Anoplotherium. The first approximates to the Tapirs in the number and disposition of the teeth; the second is remarkable in having no projecting canines, and in all the teeth forming a continued series, as in the human race. Remains of both these genera have been found in the eocene tertiary strata of the Isle of Wight,[108] and on the coast of Hampshire.

X. Fossil Edentata. Megatherium, and Megalonyx. (Plates LXXII. and LXXIII.)—The remains of these and other allied forms of the extinct gigantic Edentata, which once inhabited South America, occur in immense quantities throughout the Pampas—those vast plains which present a sea of waving grass for 900 miles. These plains consist of alluvial loam and sand, containing fresh-water and marine shells of existing species; they were evidently once, like Lewes Levels, a gulf or arm of the sea. Since the publication of Mr. Parkinson's work, vast numbers of bones have been exhumed, and many most interesting specimens sent to England by Sir Woodbine Parish, and Charles Darwin, Esq., in whose charming "Journal of Researches into the Natural History and Geology of the Countries visited during the Voyage of H.M.S. Beagle round the World," will be found many highly graphic notices of the discovery of these remains.[109] Mr. Darwin, under the head of Bahia Blanca,[110] describes the remains of no less than nine great quadrupeds found imbedded within the space of 200 square yards. They consisted of three heads and other bones of the Megatherium, of enormous dimensions; and bones of the Megalonyx. Of the Scelidotherium, an allied animal, Mr. Darwin obtained an almost perfect skeleton; it must have been as large as a rhinoceros; in the structure of the head, it approaches nearest the Cape ant-eater, in other respects it is related to the armadilloes. Remains of a different species of Mylodon, of another gigantic edental quadruped, and of a large animal with an osseous dermal coat in compartments, very like that of the Armadillo. Of this last, which has been named Glyptodon, there is a very fine specimen in the Hunterian Museum. Teeth and bones of an extinct species of horse, and of an unknown pachyderm, a huge beast with a long neck like the camel. Lastly the Toxodon (so named from the remarkable curvature of the teeth); this is perhaps one of the strangest animals ever discovered. In size it equals the elephant or megatherium, but the structure of its teeth shows it to have been intimately related to the gnawers—the order which at the present day includes the smallest quadrupeds. In many details it approaches to the pachydermata; judging from the position of its eyes, it was probably aquatic, like the Dugong and Manatee, to which it is also allied.

The beds containing the above fossil remains, consist of stratified gravel and reddish mud, and stand only from fifteen to twenty feet above the level of high water; hence the elevation of the land has been small since the great quadrupeds wandered over the surrounding plains; and the external features of the country must then have been very nearly the same as now.

In another place, Mr. Darwin observes,—"The number of the remains of these large quadrupeds imbedded in the grand estuary deposit which forms the Pampas and covers the granitic rocks of Banda Oriental, must be extraordinarily great. I believe, a straight line drawn in any direction through the Pampas, would cut through some skeleton or bones. Besides those which I found during my short excursions, I heard of many others; and the origin of such names as, 'the stream of the animal,' 'the hill of the giant,' is obvious. At other times, I heard of the marvellous property of certain rivers, which had the power of changing small bones into large; or as some maintained, the bones themselves grew. As far as I am aware, not one of these animals perished, as was formerly supposed, in the marshes or muddy river-beds of the present land, but their bones have been exposed by the streams intersecting the subaqueous deposit, in which they were originally imbedded. We may conclude that the whole area of the Pampas is one wide sepulchre of these extinct gigantic quadrupeds."[111]

XI. Flint.—Animal Remains in siliceous nodules.—So many beautiful specimens of siliceous petrifactions—that is, animal and vegetable remains transmuted into silex or flint—are figured in the subjoined plates, that it may be useful to offer a few remarks on this subject.[112] In many instances the organic remains in chalk-flints are simply incrusted by the silex; such is the state of numerous sponges which are as it were invested by the flint, and have all their pores and tubes filled up by the same material, the original tissue appearing as a brown calcareous substance. In other examples, the sponge has been enveloped in a mass of liquid flint, and has subsequently perished and decomposed; in this manner have been formed those hollow nodules, which on being broken present a cavity containing only a little white powder, or some fragments of silicified sponge; in many instances the cavity is lined with quartz crystals, or mammillated chalcedony. Frequently but part of the zoophyte is permeated by the silex, and the other portion is in the state of a friable calcareous earth imbedded in the chalk. Sponges and other zoophytes often form the nuclei of the flint nodules; the original substance of the organic body being in general silicified, and the most delicate internal structure preserved. Shells, corals, and the minute cases of foraminifera, are often immersed as it were in pure flint, appearing as if preserved in a semi-transparent medium.

But there are innumerable flint nodules in which no traces of spongeous tissue are apparent, and veins, dikes, and sheets of tabular flint, that are in a great measure free from organic remains; containing only such as may be supposed to have become imbedded in a stream of fluid silex that flowed over a sea-bottom. Wood perforated by lithodomi and silicified, is occasionally met with; and fuci or algæ are sometimes found, appearing as if floating in the liquid flint.

For the most part, the minute shells in the chalk and flint are filled with amorphous mineral matter; but in many examples, (as I have ascertained by direct experiment,) the soft parts of foraminifera remain in the shell.

XII. Foraminifera.—Plate LXII. contains figures of several species belonging to various genera of those minute fossil shells, the discoidal involute forms of which were once considered to belong to the Cephalopoda, and to be related to the Nautilus, Spirula, &c., but which are now grouped in one family, under the name of Foraminifera; a term derived from the foramina or perforations with which their shells are traversed, and which have relation to the peculiar organization of the animals.

Since microscopic observations have become so general, thanks to the genius and enthusiasm of Ehrenberg, these fossil bodies have acquired a degree of interest and importance, unsurpassed by more obvious organic remains. Whole mountain chains and extensive tracts of country are now known to be almost entirely composed of the aggregated shells of a few genera of these microzoa.[113] In other deposits their remains are associated with those of Infusoria,[114] (both animal and vegetable,) still more infinitesimal. As much error prevails among collectors as to the real nature of the fossil foraminifera, I am induced to annex the following remarks.[115]

The foraminifera are marine animals of low organization, and, with but few exceptions, extremely minute: in an ounce of sea-sand between three and four millions have been distinctly enumerated. When living, they are not aggregated, but always individually distinct; they are composed of a body (or vital mass) of a gelatinous consistence, which is either entire, and round, or divided into segments, placed either on a simple or alternate line, or coiled spirally, or involuted round an axis. This body is covered with an envelope or shell, which is generally testaceous, rarely cartilaginous, and is modelled on the segments, and follows all the modifications of form and contour of the body. From the extremity of the last segment, there issue, sometimes from one, sometimes from several openings of the shell, or through numerous pores or foramina, very elongated, slender, contractile, colourless filaments, more or less divided and ramified, serving for prehension, and capable of entirely investing the shell. The body varies in colour, but is always identical in individuals of the same species,—it is yellow, fawn-coloured, red, violet, blue, &c. Its consistence is variable; it is composed of minute globules, the aggregation of which determines the general tint. It is sometimes entire, round, and without segments, as in Gromia, Orbulina, &c., which represent, at all ages, the embryonic state of all the other genera. They increase, without doubt, by the entire circumference. When the body is divided by lobes or segments, the primary lobe, as in the permanent condition of the Gromia, is at first round or oval, according to the genus; once formed it never enlarges, but is enveloped externally by testaceous matter; it may be compared to a ball on which is applied a second larger one, then a third still larger, and so on during the life of the animal.

The annexed figure of the animal of Nummulina (as given by MM. Joly and Leymerie) will serve to convey a general idea of the living Foraminifera.

The segments, as the body increases, are agglomerated in six different ways, and these modifications are the basis of M. D'Orbigny's classification. The discoidal forms, as the Rotalia, Rosalina, Cristellaria, &c. are involuted like the nautilus, and divided by septa or partitions, the different lobes of the body occupying contemporaneously every chamber, and being connected by a tube or canal that extends through the entire series. In the spiral forms, the Textilaria, &c. the same structure is apparent. These two groups are the most abundant in the cretaceous strata; many beds of the white chalk consist almost wholly of the aggregated shells of the Rosalinæ, Rotaliæ, and Textilariæ.[116] Whatever the form of the body, the filaments always consist of a colourless matter as transparent as glass; they elongate from the base to six times the diameter of the shell. They often divide and subdivide, so as to appear branched. Though alike in form in the different genera, they vary much in their position. In some they form a bundle which issues from a single opening, and is withdrawn into the same by contraction; in others the filaments project only through each of the pores in the shell which covers the last segment; in others they issue from both the large aperture and the foramina. In fine, these filaments or pseudopodia fulfil in the foraminifera the functions of the numerous tentacula in the Asteriadæ, or Star-fishes, serving as instruments of locomotion and attachment.

Neither organs of nutriment nor of reproduction have been detected. In the genera having one large aperture from which the filaments issue and retract, we can conceive nutriment to be absorbed by that opening; but this cannot be the case in the species which have the last cell closed up; in these the filaments issuing through the foramina are probably also organs of nutrition. M. D'Orbigny considers the Foraminifera as constituting a distinct class in zoology; less complicated than the Echinoderms and the Polypiaria in their internal organization, they have by their filaments the mode of locomotion of the first, and by their free, individual existence—not aggregated and immovably fixed—they are more advanced in the scale of being than the latter. To me they appear to be merely hydra-form polypes of the most simple structure, protected by shells;[117] those composed of different segments, I conceive to be a single aggregated individual, and not a successive series of beings.

The white chalk is well known to be largely composed of a few kinds of foraminifera, but the occurrence of the soft bodies of these animalcules in a fossil state was first discovered by me, in 1845, in chalk-flints, and was announced in a paper, read before the Geological Society, entitled, "Notes of a Microscopical Examination of Chalk and Flint."[118] This statement was regarded by some eminent palæontologists as so "startling and unsatisfactory," that I resumed the investigation, and communicated the result to the Royal Society, in a memoir "On the Fossil Remains of the Soft Parts of Foraminifera discovered in the Chalk and Flint of the South-East of England;"[119] and with the kind assistance of that able chemist and microscopist, Mr. Henry Deane, of Clapham Common, I obtained, by immersing chalk in dilute hydrochloric acid, and mounting the residue in Canada balsam, several specimens of the entire integuments of the bodies of Rotaliæ, as distinct as if recent! This fact is now admitted; and the experiment has been successfully repeated in India, by Mr. Carter, on the limestones of that country;[120] and in America, by Dr. Bailey, &c.[121] In some limestone recently collected by my eldest son, Mr. Walter Mantell, in the Middle Island of New Zealand, and which, like our cretaceous strata, is almost entirely made up of foraminifera, I have detected the soft parts of the bodies of Rotaliæ in the cells of the fossil shells, as distinctly as in the chalk of England; and two of the species appear to be identical with European forms.

M. D'Orbigny gives the following summary of the distribution of the known fossil species of Foraminifera:—

There are 228 species in the Tertiary deposits of Vienna alone, of which twenty-seven species are known living in the Adriatic and the Mediterranean.

Foraminifera are unknown in the Silurian and Devonian formations.

One species only is known in the Carboniferous system of Russia, the Fusulina cylindrica.

Jurassic or Oolitic formation Genera 5 Species 20
Cretaceous " 34 " 280
Tertiary " 56 " 450
Living in the present seas " 68 " 1,000

Of these last, 575 species inhabit tropical seas, 350 the seas of temperate, and 75 the seas of cold climates.

XIII. Fossil Elk of Ireland, or Cervus megaloceros. (Plate LXXI.)—The shell-marls of Ireland contain in abundance the bones of an animal, which like the Dodo, was once contemporary with the human species, but has long been extinct: the last individuals of the race were, in all probability, exterminated by the early Celtic tribes. The remains of this noble creature generally occur in the deposits of marl that underlie the peat-bogs, which are apparently, like those of Scotland, the sites of ancient lakes or bays. In Curragh immense quantities of these bones lie within a small area; the skeletons appear to be entire, and are found with the skull elevated, and the antlers thrown back on the shoulders, as if a small herd of these Elks had sought refuge in the marshes, and had been engulfed in the morass, in the same manner as the Mastodons of America. (See description of Plate LXXIV., ante, p. 167.)

This creature far exceeded in magnitude any living species of elk or deer. The skeleton is upwards often feet in height to the top of the skull, and the antlers are from ten to fourteen feet from one extremity to the other. The fine perfect skeletons in the British Museum, College of Surgeons, and in the Museum at Edinburgh, render a particular description unnecessary. The bones are generally well preserved, of a dark brown colour, with patches of blue phosphate of iron. In some instances they are in so fresh a condition, that the hollows of the long bones contain marrow having the appearance of fresh suet. Remains of this majestic animal have been found collocated with ancient sepulchral urns, stone implements, and rude canoes, in such manner, as to leave no doubt that this now extinct deer was coeval with the early human inhabitants of these Islands. Its bones and antlers have been found at Walton, in Essex, associated with the remains of the Mammoth, or fossil elephant.[122]

XIV. Fossil Infusoria—Infusorial Earths.—In the note on Foraminifera some account is given of various rocks composed of the fossil remains of those minute animals; but the durable relics of the yet more infinitesimal organisms designated by the terms Infusoria, or Infusorial animalcules, form deposits of equal interest and importance. Strata of great extent and thickness are wholly, or in great part, made up of innumerable layers, consisting of the aggregated siliceous cases or shields of Infusoria: and similar structures are found to be the chief constituents of the white earthy deposits of lakes, rivers, and basins of brackish water, in every part of the world.

Slowly, imperceptibly, but incessantly, are the vital energies of the feeblest and minutest animal and vegetable existences separating from the element in which they live, the most enduring of mineral substances, silex—fabricating it into structures of the most exquisite forms and sculpturing, and thus adding to the accumulations of countless ages, which make up the sedimentary strata of the crust of the globe.

In the "Medals of Creation"[123] will be found a summary of what was then known as to the formation and composition of many tertiary deposits which the indefatigable Ehrenberg, Dr. Bailey, and other eminent observers, had carefully investigated and described. The five years that have since elapsed have been fruitful in results of the most important and interesting character; from every quarter of the world, from the loftiest mountain peaks, and from the deepest recesses of the ocean which the plummet can reach, from the ashes of volcanoes and from the snow of the glaciers, the durable remains of Infusoria have been obtained. That excellent scientific periodical, Silliman's American Journal, contains numerous interesting communications on this subject from the eminent chemical professor of the Military College at West Point, Dr. J. W. Bailey; and the labours of Mr. Bowerbank, Williamson, and other active members of the Microscopical Society of London, have yielded much interesting information on the infusorial deposits of our own country.

The present note will be restricted to remarks on the nature of the organisms which enter so largely into the composition of certain tertiary deposits; since the opinion once entertained of the animal nature of many infusoria, now regarded as true vegetables, materially affects the geological conclusions respecting the persistence of certain species of organisms through long periods of time, during which the mollusca, zoophytes, &c. underwent repeated mutations both in the species and genera. Thus, for example, the polierschiefer, or polishing-slate of Bilin, and the berghmehl of Tuscany, are described by Ehrenberg as masses of the siliceous shells of animalcules of such extreme minuteness, that a cubic inch of the stone contains upwards of forty millions; the infusorial earth of Richmond, in Virginia, in like manner, is stated to be made up of the siliceous skeletons of animalcules of infinitesimal minuteness. But later investigations have (I conceive) satisfactorily established, that the greater part of these fossil organisms belongs to the vegetable and not to the animal kingdom.[124] The whole of the figures in Plate IV. of the "Medals of Creation," described as living Infusoria, on the authority of Ehrenberg, are undoubted vegetables, belonging to the great botanical groups called Diatomaceæ (from the angular segments into which they separate by partial division), and Desmidiaceæ.[125] The entire family of Bacillaria belongs to this group. These simplest forms of vegetable structures abound in every lake or stream of fresh and brackish water, in every pool, or bay, and throughout the ocean, from the equator to the poles; they secrete siliceous envelopes, which present an endless variety of form and structure, and after the death and decomposition of the perishable tissues of the plants, remain as perfectly transparent colourless shields of pure silica; such are the Gaillonellæ, Euastra, Closteria, Naviculæ, Synhedræ, Podospheniæ, Xanthidia, &c., which constitute so large a proportion of the infusorial earths described by Ehrenberg and other authors.[126]

The extent of this infinitesimal flora throughout regions where no other forms of vegetation are known, is strikingly demonstrated by the observations of the eminent botanist and traveller. Dr. Hooker, in his account of the Antarctic regions.

"Everywhere," he states, "the waters and the ice alike abound in these microscopic vegetables. Though too small to be visible to the unassisted eye, their aggregated masses stained the iceberg and pack-ice wherever they were washed by the sea, and imparted a pale ochreous colour to the ice. From the south of the belt of ice which encircles the globe, to the highest latitudes reached by man, this vegetation is everywhere conspicuous, from the contrast between its colour and that of the white snow and ice in which it is imbedded. In the eightieth degree of south latitude all the surface ice carried along by currents, and the sides of every berg, and the base of the great Victoria barrier itself—a perpendicular wall of ice, from one to two hundred feet above the sea-level—were tinged brown from this cause, as if the waters were charged with oxide of iron. The majority of these plants consist of simple vegetable cells, enclosed in indestructible silex (as other Algæ are in carbonate of lime); and it is obvious that the death of such multitudes must form sedimentary deposits of immense extent.

"The universal existence of such an invisible vegetation as that of the Antarctic ocean, is u truly wonderful fact, and the more so, from its being unaccompanied by plants of a high order. This ocean swarms with mollusca, and entomostracous crustaceans, small whales, and porpoises; and the sea with penguins and seals, and the air with birds: the animal kingdom is everywhere present, the larger creatures preying on the smaller, and these again on those more minute; all living nature seems to be carnivorous. This microscopic vegetation is the sole nutrition of the herbivorous animals; and it may likewise serve to purify the atmosphere, and thus execute in the antarctic latitudes the office of the trees and grasses of the temperate regions, and the broad foliage of the palms of the tropics."[127]

Dr. Hooker also observes, that the siliceous cases of the same kind of Diatomaceæ now living in the waters of the South Polar Ocean, have contributed in past ages to the formation of European strata; for the tripoli and the phonolite stones of the Rhine contain the siliceous shields of identical species. Such are the comments of one of our most eminent botanists on the phenomena under review. The reader will probably ask,—What, then, are the essential characters which separate the animal from the vegetable kingdom? To this question it is impossible to give a satisfactory reply: perhaps the only distinction that will be generally admitted by zoologists and botanists is the following:—animals require organic substances for their support; vegetables derive their sustenance from inorganic matter.

The facts thus cursorily reviewed throw much doubt on many of M. Ehrenberg's statements as to the identity of species of animalcules now living, with those whose remains occur in the eocene, and in the secondary strata. The so-called Xanthidia of the chalk, are certainly altogether distinct from the recent diatomæ to which the name was first applied; the chalk organisms are probably the gemmules of sponges or other zoophytes.[128]