The geological place of the extinct Palaeotherium seems to have been in the first great fresh-water formation of the Eocene period, where it is chiefly found with its allies, of which several species have been found and identified by Cuvier. Dr. Buckland is not singular in thinking that they lived and died on the margins of lakes and rivers, as the Rhinoceros and Tapir do now. He is also of opinion that some retired into the water to die, and that the dead carcases of others may have been drifted into the deeper parts in seasons of flood.

The _Palaeotherium_ varied greatly in size, some species being as large as the Rhinoceros, while others ranged between the size of the Horse and that of a Hog or a Roe. The smaller Palaeotherium resembled the Tapir.

Less in size than a Goat, with slim and light legs, it must have been very common in the north of France, where it would browse on the gra.s.s of the wild prairies. Another species, the _P. minimum_, scarcely exceeded the Hare in size, and it probably had all the lightness and agility of that animal. It lived among the bushy thickets of the environs of Paris, in Auvergne, and elsewhere.

All these animals lived upon seeds and fruits, on the green twigs, or subterranean stems, and the succulent roots of the plants of the period.

They generally frequented the neighbourhood of fresh water.

[Ill.u.s.tration: Fig. 154.--Anoplotherium commune. One-twentieth natural size.]

The _Anoplotherium_ (from a??p???, _defenceless_, ??????, _animal_), had the posterior molar teeth a.n.a.logous to those of the Rhinoceros, the feet terminating in two great toes, forming an equally divided hoof, like that of the Ox and other Ruminants, and the tarsus of the toes nearly like those of the Camel. It was about the size of the a.s.s; its head was light; but what would distinguish it most must have been an enormous tail of at least three feet in length, and very thick at its junction with the body. This tail evidently served it as a rudder and propeller when swimming in the lakes or rivers, which it frequented, not to seize fish (for it was strictly herbivorous), but in search of roots and stems of succulent aquatic plants. "Judging from its habits of swimming and diving," says Cuvier, "the Anoplotherium would have the hair smooth, like the otter; perhaps its skin was even half naked. It is not likely either that it had long ears, which would be inconvenient in its aquatic kind of life; and I am inclined to think that, in this respect, it resembled the Hippopotamus and other quadrupeds which frequent the water much." To this description Cuvier had nothing more to add. His memoir upon the _pachydermatous fossils_ of Montmartre is accompanied by a design in outline of _Anoplotherium commune_, which has been closely followed in Fig. 154.

There were species of Anoplotherium of very small size. _A. leporinum_ (or the Hare-Anoplotherium), whose feet are evidently adapted for speed; _A. minimum_ and _A. obliquum_ were of still smaller dimensions; the last, especially, scarcely exceeded the size of a rat. Like the Water-rats, this species inhabited the banks of brooks and small rivers.

[Ill.u.s.tration: Fig. 155.--Xiphodon gracile.]

The _Xiphodon_ was about three feet in height at the withers, and generally about the size of the Chamois, but lighter in form, and with a smaller head. In proportion as the appearance of the _Anoplotherium commune_ was heavy and sluggish, so was that of _Xiphodon gracile_ graceful and active; light and agile as the Gazelle or the Goat, it would rapidly run round the marshes and ponds, depasturing on the aromatic herbs of the dry lands, or browsing on the sprouts of the young shrubs. "Its course," says Cuvier, in the memoir already quoted, "was not embarra.s.sed by a long tail; but, like all active herbivorous animals, it was probably timid, and with large and very mobile ears, like those of the stag, announcing the slightest approach of danger.

Neither is there any doubt that its body was covered with short smooth hair; and consequently we only require to know its colour in order to paint it as it formerly existed in this country, where it has been dug up after so many ages." Fig. 155 is a reproduction from the design in outline with which Cuvier accompanied the description of this animal, which he cla.s.ses with the Anoplotherium, and which has received in our days the name of _Xiphodon gracile_.

The gypsum-quarries of the environs of Paris include, moreover, the remains of other Pachyderms: the _Chaeropotamus_, or River-hog (from ?????? p?ta??), which has some a.n.a.logy with the living Pecari, though much larger; the _Adapis_, which reminds us, in its form, of the Hedgehog, of which, however, it was three times the size. It seems to have been a link between the Pachyderms and the Insectivorous Carnivora.

The _Lophiodon_, the size of which varied with the species, from that of the Rabbit to that of the Rhinoceros, was still more closely allied to the Tapir than to the Anoplotherium; it is found in the lower beds of the gypseous formation, that is to say in the "Calcaire Grossier."

A Parisian geologist, M. Desnoyers, librarian of the Museum of Natural History there, has discovered in the gypseous beds of the valley of Montmorency, and elsewhere in the neighbourhood of Paris, as at Pantin, Clichy, and Dammartin, the imprints of the footsteps of some Mammals, of which there seems to be some question, especially with regard to the Anoplotherium and Palaeotherium. Footprints of Turtles, Birds, and even of Carnivora, sometimes accompany these curious traces, which have a sort of almond-shape more or less lobed, according to the divisions of the hoof of the animal, and which recall to mind completely, in their mode of production and preservation, those imprints of the steps of the Labyrinthodon which have been mentioned as occurring in rocks of the Tria.s.sic period. This discovery is interesting, as it furnishes a means of comparison between the imprints and the animals which have produced them. It brings into view, as it were, the material traces left in their walks upon the soil by animals now annihilated, but who once occupied the mysterious sites of an earlier world. (See Fig. 1, p. 12.)

It is interesting to picture in imagination the vast pasturages of the Tertiary period swarming with Herbivora of all sizes. The country now surrounding the city of Paris belongs to the period in question, and not far from its gates, the woods and plains were crowded with "game" of which the Parisian sportsman little dreams, but which would nevertheless singularly animate the earth at this distant epoch. The absence of great Carnivora explains the rapid increase of the agile and graceful denizens of the wood, whose race seems to have been so multiplied then, but which was ultimately annihilated by the ferocious beasts of prey which afterwards made their appearance.

The same novelty, riches, and variety which distinguished the Mammals of the Tertiary period extended to other cla.s.ses of animals. The cla.s.s of Birds, of which we can only name the most remarkable, was represented by the curious fossil known as the "_Bird of Montmartre_." The bones of other birds have been obtained from Hordwell, as well as the remains of quadrupeds. Among the latter the _Hyaenodon_, supposed to be the oldest known example of a true carnivorous animal in the series of British fossils, and the fossil Bat known as the _Vespertilio Parisiensis_.

Among Reptiles the Crocodile, which bears the name of Isle of Wight Alligator, _Crocodilus Toliapicus_. Among the Turtles the _Trionyx_, of which there is a fine specimen in the Museum of Natural History in Paris (Fig. 156).

[Ill.u.s.tration: Fig. 156.--Trionyx, or Turtle, of the Tertiary period.]

In the cla.s.s Fishes we now see the _Pleuronectes_, or flat-fish, of which _Platax altissimus_ and _Rhombus minimus_ are well-known examples.

Among the Crustaceans we see the earliest crabs. At the same time mult.i.tudes of new Mollusca make their appearance: _Oliva_, _Triton_, _Ca.s.sis_, _Harpa_, _Crepidula_, &c.

[Ill.u.s.tration: XXIII.--Ideal Landscape of the Eocene Period.]

The hitherto unknown forms of _Schizaster_ are remarkable among Echinoderms; the Zoophytes are also abundant, especially the _Foraminifera_, which seem to make up by their numbers for their deficiency in size. It was in this period, in the bosom of its seas, and far from sh.o.r.e, that the _Nummulites_ existed, whose calcareous envelopes play such a considerable part as the elements of some of the Tertiary formations. The sh.e.l.ly agglomerates of these Protozoan Rhizopods const.i.tute now very important rocks. The Nummulitic limestone forms, in the chain of the Pyrenees, entire mountains of great height; in Egypt it forms strata of considerable extent, and it is of these rocks that the ancient pyramids were built. What an enormous time must have been necessary to convert the remains of these little sh.e.l.ls into beds many hundreds of feet thick! The _Miliola_ were also so abundant in the Eocene seas as to const.i.tute the greater part of calcareous rocks[83] out of which Paris has been built. Agglomerated in this manner, these little sh.e.l.ls form the continuous beds of limestone which are quarried for building purposes in the environs of Paris, at Gentilly, Vaugirard, and Chatillon.

[83] Similar beds of Miliolite limestone are found in the Middle Bagshot beds on the coast of Suss.e.x, off Selsey--the only instance in England of the occurrence of such calcareous deposits of Middle Eocene age.--H. W. B.

On the opposite page we present, in PLATE XXIII., an imaginary landscape of the Eocene period. We remark amongst its vegetation a mixture of fossil species with others belonging to the present time. The Alders, the Wych-elms, and the Cypresses, mingle with _Flabellaria_; the Palms of extinct species. A great Bird--a wader, the _Tantalus_--occupies the projecting point of a rock on the right; the Turtle (_Trionyx_), floats on the river, in the midst of Nymphaeas, Nenuphars, and other aquatic plants; whilst a herd of Palaeotheria, Anoplotheria, and Xiphodon peacefully browse the gra.s.s of the natural meadows of this peaceful oasis.

With a general resemblance in their fossils, nothing can be more dissimilar, on the whole, than the lithological or mineral characters of the Eocene deposits of France and England; "those of our own island,"

says Lyell,[84] "being almost exclusively of mechanical origin--acc.u.mulations of mud, sand, and pebbles; while in the neighbourhood of Paris we find a great succession of strata composed of limestones, some of them siliceous, and of crystalline gypsum and siliceous sandstone, and sometimes of pure flint used for millstones.

Hence it is by no means an easy task to inst.i.tute an exact comparison between the various members of the English and French series. It is clear that, on the sites both of Paris and London, a continual change was going on in the fauna and flora by the coming in of new species and the dying out of others; and contemporaneous changes of geographical conditions were also in progress in consequence of the rising and sinking of the land and bottom of the sea. A particular subdivision, therefore, of time was occasionally represented in one area by land, in another by an estuary, in a third by sea; and even where the conditions were in both areas of a marine character, there was often shallow water in one, and deep sea in another, producing a want of agreement in the state of animal life." The Eocene rocks, as developed in France and England, may be tabulated as follows, in descending order:--

[84] "Elements of Geology," p. 292.

English. French.

/ / Calcaire de la Beauce.

Hempstead beds.

Gres de Fontainebleau.

Upper Eocene. < calcaire="" silicieux="" or="" bembridge="" beds.="">Fluvio-marine< calcaire="" lacustre="" series.="" moyen.="" gypseous="" series="" of="">

/ Osborne beds.

/ Gres de Beauchamp

Headon beds. / and Calcaire Marin.

Upper Bagshot sand. Upper Sables Moyens.

Middle Eocene.< lower="" sables="" moyens,="" barton="" clay.="" middle="">< lower="" calcaire="" bracklesham="" beds.="" bagshot.="" grossier,="" and="" glauconie="">

Lower Bagshot / Lits coquillieres.

beds. Glauconie Moyenne.

/ London clay. Wanting.

Woolwich and / Argile Plastique.

Reading beds, or > Glauconie Inferieure.

Lower Eocene. < plastic="" clay.="" oldhaven="">

Thanet sands. Sables Inferieurs.

The Woolwich and Reading Beds, or the Plastic Clay of older writers, consists of extensive beds of sand with occasional beds of potter's clay, which lie at the base of the Tertiary formation in both England and France. Generally variegated, sometimes grey or white, it is employed as a potter's earth in the manufacture of delf-ware.

In England the red-mottled clay of the Woolwich and Reading Beds in Hampshire and the Isle of Wight is often seen in contact with the chalk; but in the south-eastern part of the London basin, Mr. Prestwich shows that the Thanet Sand (consisting of a base of fine, light-coloured sand, mixed with more or less argillaceous matter) intervenes between the Chalk and the Oldhaven Beds, or in their absence the Woolwich and Reading beds, which lie below the London Clay. The Thanet Sands derive their name from their occurrence in the Isle of Thanet, in Kent, in the eastern part of which county they attain their greatest development.

Under London and its southern suburbs the Thanet sand is from thirteen to forty-four feet thick, but it becomes thinner in a westerly direction, and does not occur beyond Ealing.[85]

[85] "Memoir of the Geological Survey of Great Britain. The Geology of Middles.e.x, &c.;" by W. Whitaker, p. 9.

The Woolwich and Reading beds in the Hampshire basin rest immediately on the Chalk, and separate it from the overlying London Clay, as may be seen in the fine exposure of the Tertiary strata in Alum Bay, at the western extremity of the Isle of Wight, and in Studland Bay, on the western side of the Isle of Purbeck, in Dorsetshire.

In the London basin the Woolwich and Reading beds also rest on the Chalk, where the Thanet Sands are absent, as is the case, for the most part, over the area west of Ealing and Leatherhead.

The beds in question are very variable in character, but may be generally described as irregular alternations of clays and sands--the former mostly red, mottled with white, and from their plastic nature suitable for the purposes of the potter; the latter also of various colours, but sometimes pure white, and sometimes containing pebbles of flint.

The Woolwich and Reading beds are called after the localities of the same names; they are fifty feet thick at Woolwich, and from sixty to seventy feet at Reading.

The Oldhaven beds (so termed by Mr. W. Whitaker from their development at the place of the same name in Kent) are a local deposit, occurring beneath the London Clay on the south side of the London basin, from Croydon eastward, at the most eastern part of Surrey, and through Kent--in the north-western corner of which county they form some comparatively broad tracts. The beds consist of rounded flint pebbles, in a fine sandy base, or of fine light-coloured sand, and are from eighty to ninety feet thick under London.

The London Clay, which has a breadth of twenty miles or more about London, consists of tenacious brown and bluish-grey clay, with layers of the nodular concretions, called Septaria, which are well known on the Ess.e.x and Hampshire coasts, where they are collected for making Roman cement. The London Clay has a maximum thickness of nearly 500 feet. The fossils of the London Clay are of marine genera, and very plentiful in some districts. Taken altogether they seem to indicate a moderate, rather than a tropical climate, although the Flora is, as far as can be judged, certainly tropical in its affinities.[86] The number of species of extinct Turtles obtained from the Isle of Sheppey alone, is stated by Prof. Aga.s.siz to exceed that of all the species of Chelone now known to exist throughout the globe. Above this great bed lie the Bracklesham and Bagshot beds, which consist of light-yellow sand with an intermediate layer of dark-green and brown clay, over which lie the Barton Clay (in the Hampshire basin) and the white Upper Bagshot Sands, which are succeeded by the Fluvio-marine series comprising the Headon, Bembridge, and Hempstead series, and consisting of limestones, clays, and marls, of marine, brackish, and fresh-water origin.[87] For fuller accounts of the Tertiary strata of England, the reader is recommended to the numerous excellent memoirs of Mr. Prestwich, to the memoir "On the Tertiary Fluvio-marine Formations of the Isle of Wight," by Professor Edward Forbes, and to the memoir "On the Geology of the London Basin," by Mr.

W. Whitaker.

[86] Prestwich. _Quart. Jour. Geol. Soc._, vol. x., p. 448.

[87] Detailed sections of the whole of the Tertiary strata of the Isle of Wight have been constructed by Mr. H. W. Bristow from actual measurement of the beds in their regular order of succession, as displayed at Hempstead, Whitecliff Bay, Colwell and Tolland's Bays, Headon Hill, and Alum Bay. These sections, published by the Geological Survey of Great Britain, show the thickness, mineral character, and organic remains found in each stratum, and are accompanied by a pamphlet in explanation.

At the base of the _Argile Plastique_ of France is a conglomerate of chalk and of divers calcareous substances, in which have been found at Bas-Meudon some remains of Reptiles, Turtles, Crocodiles, Mammals, and, more lately, those of a large Bird, exceeding the Ostrich in size, the _Gastornis_, which Professor Owen cla.s.ses among the wading rather than among aquatic birds. In the Soissonnais there is found, at the same horizon, a great ma.s.s of lignite, enclosing some sh.e.l.ls and bones of the most ancient Pachyderm yet discovered, the _Coryphodon_, which resembles at once both the Anoplotherium and the Pig. The _Sables Inferieurs_, or Bracheux Sands, form a marine bed of great thickness near Beauvais; they are princ.i.p.ally sands, but include beds of calciferous clay and banks of sh.e.l.ly sandstone, and are considered to be older than the plastic clay and lignite, and to correspond with the Thanet Sands of England. They are rich in sh.e.l.ls, including many Nummulites. At La Fere, in the Department of the Aisne, a fossil skull of _Arctocyon primaevus_, supposed to be related both to the Bear and to the Kinkajou, and to be the oldest known Tertiary Mammal, was found in a deposit of this age.

This series seems to have been formed chiefly in fresh water.

The _Calcaire grossier_, consisting of marine limestones of various kinds, and with a coa.r.s.e, sometimes compact, grain, is suitable for mason-work. These deposits, which form the most characteristic member of the Paris basin, naturally divide themselves into three groups of strata, characterised, the first, by _Nummulites_; the second by _Miliolites_; and the third or upper beds by _Cerithia_. The beds are also sometimes named Nummulite limestone, Miliolite limestone, and Cerithium limestone. Above these a great ma.s.s, generally sandy, is developed. It is marine at the base, and there are indications of brackish water in its upper parts; it is called Beauchamp Sandstone, or Sables Moyens (_Gres de Beauchamp_). These sands are very rich in sh.e.l.ls. The _siliceous limestone_, or lower travertin, is a compact siliceous limestone extending over a wide area, and resembles a precipitate from mineral waters. The _gypseous_ formation consists of a long series of marly and argillaceous beds, of a greyish, green, or white colour, in the intervals between which a thick deposit of gypsum, or sulphate of lime, is intercalated. This gypsum bed is found in its greatest thickness in France at Montmartre and Pantin near Paris. The formation of this gypsum is probably due to the action of free sulphuric acid upon the carbonate of lime of the formation; the sulphuric acid itself being produced by the transformation of the gaseous ma.s.ses of sulphuretted hydrogen emanating from volcanic vents, into that acid, by the action of air and water. It was, as we have already said, in the gypsum-quarries of Montmartre that the numerous bones of Palaeotherium and Anoplotherium were found. It is exclusively at this horizon that we find the remains of these animals, which seem to have been preceded by the _Coryphodon_, and afterwards by the _Lophiodon_; the order of succession in the appearance of these animals is now perfectly established. It may be added that round Paris the Eocene formation, from its lowest beds to the highest, is composed of beds of plastic clay, of the _Calcaire grossier_ with its _Nummulites_, _Miliolites_, and _Alveolites_, followed by the gypseous formation; the series terminating in the Fontainebleau Sandstone, remarkable for its thickness and also for its fine scenery, as well as for its usefulness in furnishing paving-stone for the capital. In Provence the same series of rocks are continued, and attain an enormous thickness. This upper part of the Eocene deposit is entirely of lacustrine formation. Grignon has procured from a single spot, where they were embedded in a calcareous sand, no less than 400 fossils, chiefly formed of comminuted sh.e.l.ls, in which, however, were well-preserved species both of marine, terrestrial, and fresh-water sh.e.l.ls. Of the Paris basin, Sir Charles Lyell says: "Nothing is more striking in this a.s.semblage of fossil testacea than the great proportion of species referable to the genus _Cerithium_. There occur no less than 137 species of this genus in the Paris basin, and almost all of them in the _Calcaire grossier_. Most of the living _Cerithia_ (Figs.

157 and 168) inhabit the sea near the mouths of rivers, where the waters are brackish; so that their abundance in the marine strata now under consideration is in harmony with the hypothesis that the Paris basin formed a gulf into which several rivers flowed."[88]

[88] "Elements of Geology," p. 300.