Another remarkable group of Reptiles, exclusively confined to the Cretaceous series, is that of the Mosasauroids, so called from the type-genus Mosasaurus. The first species of Mosasaurus known to science was the M. Camperi (fig. 210), the skull of which—six feet in length—was discovered in 1780 in the Maestricht Chalk at Maestricht. As this town stands on the river Meuse, the name of Mosasaurus ("Lizard of the Meuse") was applied to this immense Reptile. Of late years the remains of a large number of Reptiles more or less closely related to Mosasaurus, or absolutely belonging to it, have been discovered in the Cretaceous deposits of North America, and have been described by Professors Cope and Marsh. All the known forms of this group appear to have been of large size—one of them, Mosasaurus princeps, attaining the length of seventy-five or eighty feet, and thus rivalling the largest of existing Whales in its dimensions. The teeth in the "Mosasauroids" are long, pointed, and slightly curved; and instead of being sunk in distinct sockets, they are firmly amalgamated with the jaws, as in modern Lizards. The palate also carried teeth, and the lower jaw was so constructed as to allow of the mouth being opened to an immense width, somewhat as in the living Serpents. The body was long and snake-like, with a very long tail, which is laterally compressed, and must have served as a powerful swimming-apparatus. In addition to this, both pairs of limbs have the bones connecting them with the trunk greatly shortened; whilst the digits were enclosed in the integuments, and constituted paddles, closely resembling in structure the "flippers" of Whales and Dolphins. The neck is sometimes moderately long, but oftener very short, as the great size and weight of the head would have led one to anticipate. Bony plates seem in some species to have formed an at any rate partial covering to the skin; but it is not certain that these integumentary appendages were present in all. Upon the whole, there can be no doubt but that the Mosasauroid Reptiles—the true "Sea-serpents" of the Cretaceous period—were essentially aquatic in their habits, frequenting the sea, and only occasionally coming to the land.



The "Mosasauroids" have generally been regarded as a greatly modified group of the Lizards (Lacertilia). Whether this reference be correct or not—and recent investigations render it dubious—the Cretaceous rocks have yielded the remains of small Lizards not widely removed from existing forms. The recent order of the Chelonians is also represented in the Cretaceous rocks, by forms closely resembling living types. Thus the fresh-water deposits of the Wealden have yielded examples of the "Terrapins" or "Mud-Turtles" (Emys); and the marine Cretaceous strata have been found to contain the remains of various species of Turtles, one of which is here figured (fig. 211). No true Serpents (Ophidia) have as yet been detected in the Cretaceous rocks; and this order does not appear to have come into existence till the Tertiary period. Lastly, true Crocodiles are known to have existed in considerable numbers in the Cretaceous period. The oldest of these occur in the fresh-water deposit of the Wealden; and they differ from the existing forms of the group in the fact that the bodies of the vertebrae, like those of the Jurassic Crocodiles, are bi-concave, or hollowed out at both ends. In the Greensand of North America, however, occur the remains of Crocodiles which agree with all the living species in having the bodies of the vertebrae in the region of the back hollowed out in front and convex behind.



Birds have not hitherto been shown, with certainty, to have existed in Europe during the Cretaceous period, except in a few instances in which fragmentary remains belonging to this class have been discovered. The Cretaceous deposits of North America have, however, been shown by Professor Marsh to contain a considerable number of the remains of Birds, often in a state of excellent preservation. Some of these belong to Swimming or Wading Birds, differing in no point of special interest from modern birds of similar habits. Others, however, exhibit such extraordinary peculiarities that they merit more than a passing notice. One of the forms in question constitutes the genus Ichthyornis of Marsh, the type-species of which (I. Dispar) was about as large as a Pigeon. In two remarkable respects, this singular Bird differs from all known living members of the class. One of these respects concerns the jaws, both of which exhibit the Reptilian character of being armed with numerous small pointed teeth (fig. 212, a), sunk in distinct sockets. No existing bird possesses teeth; and this character forcibly recalls the Bird-like Pterosaurs, with their toothed jaws. Ichthyornis, however, possessed fore-limbs constructed strictly on the type of the "wing" of the living Birds; and it cannot, therefore, be separated from this class. Another extraordinary peculiarity of Ichthyornis is, that the bodies of the vertebrie (fig. 212, c) were bi-concave, as is the case with many extinct Reptiles and almost all Fishes, but as does not occur in any living Bird. There can be little doubt that Ichthyornis was aquatic in its habits, and that it lived principally upon fishes; but its powerful wings at the same time indicate that it was capable of prolonged flight. The tail of Ichthyornis has, unfortunately, not been discovered; and it is at present impossible to say whether this resembled the tail of existing Birds, or whether it was elongated and composed of separate vertebrae, as in the Jurassic Archoeopteryx.

Still more wonderful than Ichthyornis is the marvellous bird described by Marsh under the name of Hesperornis regalis. This presents us with a gigantic diving bird, somewhat resembling the existing "Loons" (Colymbus), but agreeing with Ichthyornis in having the jaws furnished with conical, recurved, pointed teeth (fig. 212, b). Hence these forms are grouped together in a new sub-class, under the name of Odontornithes or "Toothed Birds." The teeth of Hesperornis (fig. 212, d) resemble those of Ichthyornis in their general form; but instead of being sunk in distinct sockets, they are simply implanted in a deep continuous groove in the bony substance of the jaw. The front of the upper jaw does not carry teeth, and was probably encased in a horny beak. The breast-bone is entirely destitute of a central ridge or keel, and the wings are minute and quite rudimentary; so that Hesperornis, unlike Ichthyornis, must have been wholly deprived of the power of flight, in this respect approaching the existing Penguins. The tail consists of about twelve vertebrae, of which the last three or four are amalgamated to form a flat terminal mass, there being at the same time clear indications that the tail was capable of up and down movement in a vertical plane, this probably fitting it to serve as a swimming-paddle or rudder. The legs were powerfully constructed, and the feet were adapted to assist the bird in rapid motion through the water. The known remains of Hesperornis regalis prove it to have been a swimming and diving bird, of larger dimensions than any of the aquatic members of the class of Birds with which we are acquainted at the present day. It appears to have stood between five and six feet high, and its inability to fly is fully compensated for by the numerous adaptations of its structure to a watery life. Its teeth prove it to have been carnivorous in its habits, and it probably lived upon fishes. It is a curious fact that two Birds agreeing with one another in the wholly abnormal character of possessing teeth, and in other respects so entirely different, should, like Ichthyornis and Hesperornis, have lived not only in the same geological period, but also in the same geographical area; and it is equally curious that the area inhabited by these toothed Birds should at the same time have been tenanted by winged and bird-like Reptiles belonging to the toothed genus Pterodactylus and the toothless genus Pteranodon.



No remains of Mammals, finally, have as yet been detected in any sedimentary accumulations of Cretaceous age.

LITERATURE.

The following list comprises some of the more important works and memoirs which may be consulted with reference to the Cretaceous strata and their fossil contents:—

(1) 'Memoirs of the Geological Survey of Great Britain.' (2) 'Geology of England and Wales.' Conybeare and Phillips. (3) 'Geology of Yorkshire,' vol. ii. Phillips. (4) 'Geology of Oxford and the Thames Valley.' Phillips. (5) 'Geological Excursions through the Isle of Wight.' Mantell. (6) 'Geology of Sussex.' Mantell. (7) 'Report on Londonderry,' &c. Portlock. (8) 'Recherches sur le Terrain Cretace Superieur de l'Angleterre et de l'Irlande.' Barrois. (9) "Geological Survey of Canada"—'Report of Progress, 1872-73.' (10) 'Geological Survey of California.' Whitney. (11) 'Geological Survey of Montana, Idaho, Wyoming, and Utah.' Hayden and Meek. (12) 'Report on Geology,' &c. (British North American Boundary Commission). G. M. Dawson. (13) 'Manual of Geology.' Dana. (14) 'Lethaea Rossica.' Eichwald. (15) 'Petrefacta Germaniae.' Goldfuss. (16) 'Fossils of the South Downs.' Mantell. (17) 'Medals of Creation.' Mantell. (18) 'Mineral Conchology.' Sowerby. (19) 'Lethaea Geognostica.' Bronn. (20) 'Malacostracous Crustacea of the British Cretaceous Formation' (Palaeontographical Society). Bell. (21) 'Brachiopoda of the Cretaceous Formation' (Palaeontographical Society). Davidson. (22) 'Corals of the Cretaceous Formation' (Palaeontographical Society). Milne-Edwards and Haime. (23) 'Supplement to the Fossil Corals' (Palaeontographical Society). Martin Duncan. (24) 'Echinodermata or the Cretaceous Formation' (Palaeontographical Society). Wright. (25) 'Monograph of the Belemnitidae' (Palaeontographical Society). Phillips. (26) 'Monograph of the Trigoniae' (Palaeontographical Society). Lycett. (27) 'Fossil Cirripedes' (Palaeontographical Society). Darwin. (28) 'Fossil Mollusca of the Chalk of Britain' (Palaeontographical Society). Sharpe. (29) 'Entomostraca of the Cretaceous Formation' (Palaeontographical Society). Rupert Jones. (30) 'Monograph of the Fossil Reptiles of the Cretaceous Formation' (Palaeontographical Society). Owen. (31) 'Manual of Palaeontology.' Owen. (32) 'Synopsis of Extinct Batrachia and Reptilia.' Cope. (33) "Structure of the Skull and Limbs in Mosasauroid Reptiles"—'American Journ. Sci. and Arts, 1872.' Marsh. (34) "On Odontornithes"—'American Journ. Sci. and Arts, 1875.' Marsh. (35) 'Ossemens Fossiles.' Cuvier. (36) 'Catalogue of Ornithosauria.' Seeley. (37) 'Paleontologie Francaise.' D'Orbigny. (38) 'Synopsis des Echinides fossiles.' Desor. (39) 'Cat. Raisonne des Echinides.' Agassiz and Desor. (40) "Echinoids"—'Decades of the Geol. Survey of Britain.' E. Forbes. (41) 'Paleontologie Francaise.' Cotteau. (42) 'Versteinerungen der Boehmischen Kreide-formation.' Reuss. (43) "Cephalopoda, Gasteropoda, Pelecypoda, Brachiopoda; &c., of the Cretaceous Rocks of India"—'Palaeontologica Indica,' ser. i., iii., v., vi., viii. Stoliczka. (44) "Cretaceous Reptiles of the United States"—'Smithsonian Contributions to Knowledge,' vol. xiv. Leidy. (45) 'Invertebrate Cretaceous, and Tertiary Fossils of the Upper Missouri Country,' 1876. Meek.



CHAPTER XVIII.

THE EOCENE PERIOD.

Before commencing the study of the subdivisions of the Kainozoic series, there are some general considerations to be noted. In the first place, there is in the Old World a complete and entire physical break between the rocks of the Mesozoic and Kainozoic periods. In no instance in Europe are Tertiary strata to be found resting conformably upon any Secondary rock. The Chalk has invariably suffered much erosion and denudation before the lowest Tertiary strata were deposited upon it. This is shown by the fact that the actually eroded surface of the Chalk can often be seen; or, failing this, that we can point to the presence of the chalk-flints in the Tertiary strata. This last, of course, affords unquestionable proof that the Chalk must have been subjected to enormous denudation prior to the formation of the Tertiary beds, all the chalk itself having been removed, and nothing left but the flints, while these are all rolled and rounded. In the continent of North America, on the other hand, the lowest Tertiary strata have been shown to graduate downwards conformably with the highest Cretaceous beds, it being a matter of difficulty to draw a precise line of demarcation between the two formations.

In the second place, there is a marked break in the life of the Mesozoic and Kainozoic periods. With the exception of a few Foraminifera, and one Brachiopod (the latter doubtful), no Cretaceous species is known to have survived the Cretaceous period; while several characteristic families, such as the Ammonitidoe, Belemnitidoe, and Hippuritidoe, died out entirely with the close of the Cretaceous rocks. In the Tertiary rocks, on the other hand, not only are all the animals and plants more or less like existing types, but we meet with a constantly-increasing number of living species as we pass from the bottom of the Kainozoic series to the top. Upon this last fact is founded the modern classification of the Kainozoic rocks, propounded by Sil Charles Lyell.

The absence in strata of Tertiary age of the chambered Cephalopods, the Belemnites, the Hippurites, the Inocerami, and the diversified types of Reptiles which form such conspicuous features in the Cretaceous fauna, render the palaeontological break between the Chalk and the Eocene one far too serious to be overlooked. At the same time, it is to be remembered that the evidence afforded by the explorations carried out of late years as to the animal life of the deep sea, renders it certain that the extinction of marine forms of life at the close of the Cretaceous period was far less extensive than had been previously assumed. It is tolerably certain, in fact, that we may look upon some of the inhabitants of the depths of our existing oceans as the direct, if modified, descendants of animals which were in existence when the Chalk was deposited.

It follows from the general want of conformity between the Cretaceous and Tertiary rocks, and still more from the great difference in life, that the Cretaceous and Tertiary periods are separated, in the Old World at any rate, by an enormous lapse of unrepresented time. How long this interval may have been, we have no means of judging exactly, but it very possibly was as long as the whole Kainozoic epoch itself. Some day we shall doubtless find, at some part of the earth's surface, marine strata which were deposited during this period, and which will contain fossils intermediate in character between the organic remains which respectively characterise the Secondary and Tertiary periods. At present, we have only slight traces of such deposits—as, for instance, the Maestricht beds, the Faxoee Limestone, and the Pisolitic Limestone of France.

CLASSIFICATION OF THE TERTIARY ROCKS.—The classification of the Tertiary rocks is a matter of unusual difficulty, in consequence of their occurring in disconnected basins, forming a series of detached areas, which hold no relations of superposition to one another. The order, therefore, of the Tertiaries in point of time, can only be determined by an appeal to fossils; and in such determination Sir Charles Lyell proposed to take as the basis of classification the proportion of living or existing species of Mollusca which occurs in each stratum or group of strata. Acting upon this principle, Sir Charles Lyell divides the Tertiary series into four groups:—

I. The Eocene formation (Gr. eos, dawn; kainos, new), containing the smallest proportion of existing species, and being, therefore, the oldest division. In this classification, only the Mollusca are taken into account; and it was found that of these about three and a half per cent were identical with existing species.

II. The Miocene formation (Gr. meion, less; kainos, new), with more recent species than the Eocene, but less than the succeeding formation, and less than one-half the total number in the formation. As before, only the Mollusca are taken into account, and about 17 per cent of these agree with existing species.

III. The Pliocene formation (Gr. pleion, more; kainos, new), with generally more than half the species of shells identical with existing species—the proportion of these varying from 35 to 50 per cent in the lower beds of this division, up to 90 or 95 per cent in its higher portion.

IV. The Post-Tertiary Formations, in which all the shells belong to existing species. This, in turn, is divided into two minor groups—the Post-Pliocene and Recent Formations. In the Post-Pliocene formations, while all the Mollusca belong to existing species, most of the Mammals belong to extinct species. In the Recent period, the quadrupeds, as well as the shells, belong to living species.

The above, with some modifications, was the original classification proposed by Sir Charles Lyell for the Tertiary rocks, and now universally accepted. More recent researches, it is true, have somewhat altered the proportions of existing species to extinct, as stated above. The general principle, however, of an increase in the number of living species, still holds good; and this is as yet the only satisfactory basis upon which it has been proposed to arrange the Tertiary deposits.

EOCENE FORMATION.

The Eocene rocks are the lowest of the Tertiary series, and comprise all those Tertiary deposits in which there is only a small proportion of existing Mollusca—from three and a half to five per cent. The Eocene rocks occur in several basins in Britain, France, the Netherlands, and other parts of Europe, and in the United States. The subdivisions which have been established are extremely numerous, and it is often impossible to parallel those of one basin with those of another. It will be sufficient, therefore, to accept the division of the Eocene formation into three great groups—Lower, Middle, and Upper Eocene—and to consider some of the more important beds comprised under these heads in Europe and in North America.

I. EOCENE OF BRITAIN. (1.) LOWER EOCENE.—The base of the Eocene series in Britain is constituted by about 90 feet of light-coloured, sometimes argillaceous sands (Thanet Sands), which are of marine origin. Above these, or forming the base of the formation where these are wanting, come mottled clays and sands with lignite (Woolwich and Reading series), which are estuarine or fluvio-marine in origin. The highest member of the Lower Eocene of Britain is the "London Clay," consisting of a great mass of dark-brown or blue clay, sometimes with sandy beds, or with layers of "septaria," the whole attaining a thickness of from 200 to as much as 500 feet. The London Clay is a purely marine deposit, containing many marine fossils, with the remains of terrestrial animals and plants; all of which indicate a high temperature of the sea and tropical or sub-tropical conditions of the land.

(2.) MIDDLE EOCENE.—The inferior portion of the Middle Eocene of Britain consists of marine beds, chiefly consisting of sand, clays, and gravels, and attaining a very considerable thickness (Bag-shot and Bracklesham beds). The superior portion of the Middle Eocene of Britain, on the other hand, consists of deposits which are almost exclusively fresh-water or brackish-water in origin (Headon and Osborne series).

The chief Continental formations of Middle Eocene age are the "Calcaire grossier" of the Paris basin, and the "Nummulitic Limestone" of the Alps.

(3.) UPPER EOCENE.—If the Headon and Osborne beds of the Isle of Wight be placed in the Middle Eocene, the only British representatives of the Upper Eocene are the Bembridge beds. These strata consist of limestones, clays, and marls, which have for the most part been deposited in fresh or brackish water.

II. EOCENE BEDS OF THE PARIS BASIN.—The Eocene strata are very well developed in the neighbourhood of Paris, where they occupy a large area or basin scooped out of the Chalk. The beds of this area are partly marine, partly freshwater in origin; and the following table (after Sir Charles Lyell) shows their subdivisions and their parallelism with the English series:—

GENERAL TABLE OF FRENCH EOCENE STRATA.

UPPER EOCENE.

French Subdivisions. English Equivalents. A. 1. Gypseous series of Mont 1. Bembridge series. Montmartre. A. 2. Calcaire silicieux, or 2. Osborne and Headon series. Travertin Inferieur. A. 3. Gres de Beauchamp, or 3. White sand and clay of Sables Moyens. Barton Cliff, Hants.

MIDDLE EOCENE.

B. 1. Calcaire Grossier. 1. Bagshot and Bracklesham beds. B. 2. Soissonnais Sands, or 2. Wanting. Lits Coquilliers.

LOWER EOCENE.

C. 1. Argile de Londres at base 1. London clay. of Hill of Cassel, near Dunkirk. C. 2. Argile plastique and 2. Plastic clay and sand with lignite. lignite (Woolwich and Reading series). C. 3. Stables de Bracheux. 3. Thanet sands.

III. EOCENE STRATA OF THE UNITED STATES.—The lowest member of the Eocene deposits of North America is the so-called "Lignitic Formation," which is largely developed in Mississippi, Tennessee, Arkansas, Wyoming, Utah, Colorado, and California, and sometimes attains a thickness of several thousand feet. Stratigraphically, this formation exhibits the interesting point that it graduates downwards insensibly and conformably into the Cretaceous, whilst it is succeeded uncomformably by strata of Middle Eocene age. Lithologically, the series consists principally of sands and clays, with beds of lignite and coal, and its organic remains show that it is principally of fresh-water origin with a partial intermixture of marine beds. These marine strata of the "Lignitic formation" are of special interest, as showing such a commingling of Cretaceous and Tertiary types of life, that it is impossible to draw any rigid line in this region between the Mesozoic and Kainozoic systems. Thus the marine beds of the Lignitic series contain such characteristic Cretaceous forms as Inoceramus and Ammonites, along with a great number of Univalves of a distinctly Tertiary type (Cones, Cowries, &c.) Upon the whole, therefore, we must regard this series of deposits as affording a kind of transition between the Cretaceous and the Eocene, holding in some respects a position which may be compared with that held by the Purbeck beds in Britain as regards the Jurassic and Cretaceous.

The Middle Eocene of the United States is represented by the Claiborne and Jackson beds. The Claiborne series is extensively developed at Claiborne, Alabama, and consists of sands, clays, lignites, marls, and impure limestones, containing marine fossils along with numerous plant-remains. The Jackson series is represented by lignitic clays and marls which occur at Jackson, Mississippi. Amongst the more remarkable fossils of this series are the teeth and bones of Cetaceans of the genus Zeuglodon.

Strata of Upper Eocene age occur in North America at Vicksburg, Mississippi, and are known as the Vicksburg series. They consist of lignites, clays, marls, and limestones. Freshwater deposits of Eocene age are also largely developed in parts of the Rocky Mountain region. The most remarkable fossils of these beds are Mammals, of which a large number of species have been already determined.

LIFE OF THE EOCENE PERIOD.

The fossils of the Eocene deposits are so numerous that nothing more can be attempted here than to give a brief and general sketch of the life of the period, special attention being directed to some of the more prominent and interesting types, amongst which—as throughout the Tertiary series—the Mammals hold the first place. It is not uncommon, indeed, to speak of the Tertiary period as a whole under the name of the "Age of Mammals," a title at least as well deserved as that of "Age of Reptiles" applied to the Mesozoic, or "Age of Molluscs" applied to the Palaeozoic epoch.

As regards the plants of the Eocene, the chief point to be noticed is, that the conditions which had already set in with the commencement of the Upper Cretaceous, are here continued, and still further enforced. The Cycads of the Secondary period, if they have not totally disappeared, are exceedingly rare; and the Conifers, losing the predominance which they enjoyed in the Mesozoic, are now relegated to a subordinate though well-defined place in the terrestrial vegetation. The great majority of the Eocene plants are referable to the groups of the Angiospermous Exogens and the Monocotyledons; and the vegetation of the period, upon the whole, approximates closely to that now existing upon the earth. The plants of the European Eocene are, however, in the main most closely allied to forms which are now characteristic of tropical or sub-tropical regions. Thus, in the London Clay are found numerous fruits of Palms (Napdites, fig. 213), along with various other plants, most of which indicate a warm climate as prevailing in the south of England at the commencement of the Eocene period. In the Eocene strata of North America occur numerous plants belonging to existing types—such as Palms, Conifers, the Magnolia, Cinnamon, Fig. Dog-wood, Maple, Hickory, Poplar, Plane, &c. Taken as a whole, the Eocene flora of North America is nearly related to that of the Miocene strata of Europe, as well as to that now existing in the American area. We conclude, therefore, that "the forests of the American Eocene resembled those of the European Miocene, and even of modern America" (Dana).



As regards the animals of the Eocene period, the Protozoans are represented by numerous Foraminifera, which reach here their maximum of development, both as regards the size of individuals and the number of generic types. Many of the Eocene Foraminifers are of small size; but even these not uncommonly form whole rock-masses. Thus, the so-called "Miliolite Limestone" of the Paris basin, largely used as a building-stone, is almost wholly composed of the shells of a small species of Miliola. The most remarkable, however, of the many members of this group of animals which flourished in Eocene times, are the "Nummulites" (Nummulina), so called from their resemblance in shape to coins (Lat. nummus, a coin). The Nummulites are amongst the largest of all known Foraminifera, sometimes attaining a size of three inches in circumference; and their internal structure is very complex (fig. 214). Many species are known, and they are particularly characteristic of the Middle and Upper of these periods—their place being sometimes taken by Orbitoides, a form very similar to the Nummulite in external appearance, but differing in its internal details. In the Middle Eocene, the remains of Nummulites are found in vast numbers in a very widely-spread and easily-recognised formation known as the "Nummulitic Limestone" (fig. 10). According to Sir Charles Lyell, "the Nummulitic Limestone of the Swiss Alps rises to more than 10,000 feet above the level of the sea, and attains here and in other mountain-chains a thickness of several thousand feet. It may be said to play a far more conspicuous part than any other Tertiary group in the solid framework of the earth's crust, whether in Europe, Asia, or Africa. It occurs in Algeria and Morocco, and has been traced from Egypt, where it was largely quarried of old for the building of the Pyramids, into Asia Minor, and across Persia by Bagdad to the mouths of the Indus. It has been observed not only in Cutch, but in the mountain-ranges which separate Scinde from Persia, and which form the passes leading to Cabul; and it has been followed still further eastward into India, as far as Eastern Bengal and the frontiers of China." The shells of Nummulites have been found at an elevation of 16,500 feet above the level of the sea in Western Thibet; and the distinguished and philosophical geologist just quoted, further remarks, that "when we have once arrived at the conviction that the Nummulitic formation occupies a middle and upper place in the Eocene series, we are struck with the comparatively modern date to which some of the greatest revolutions in the physical geography of Europe, Asia, and Northern Africa must be referred. All the mountain-chains—such as the Alps, Pyrenees, Carpathians, and Himalayas—into the composition of whose central and loftiest parts the Nummulitic strata enter bodily, could have had no existence till after the Middle Eocene period. During that period, the sea prevailed where these chains now rise; for Nummulites and their accompanying Testacea were unquestionably inhabitants of salt water."



The Coelenterates of the Eocene are represented principally by Corals, mostly of types identical with or nearly allied to those now in existence. Perhaps the most characteristic group of these is that of the Turbinolidoe, comprising a number of simple "cup-corals," which probably lived in moderately deep water. One of the forms belonging to this family is here figured (fig. 215). Besides true Corals, the Eocene deposits have yielded the remains of the "Sea-pens" (Pennatulidoe) and the branched skeletons of the "Sea-shrubs" (Gorgontidoe).

The Echinoderms are represented principally by Sea-urchins, and demand nothing more than mention. It is to be observed, however, that the great group of the Sea-lilies (Crinoids) is now verging on extinction, and is but very feebly represented.

Amongst the Mollusca, the Polyzoans and Brachiopods also require no special mention, beyond the fact that the latter are greatly reduced in numbers, and belong principally to the existing genera Terebratula and Rhynchonella. The Bivalves (Lamellibranchs) and the Univalves (Gasteropods) are exceedingly numerous, and almost all the principal existing genera are now represented; though less than five percent of the Eocene species are identical with those now living. It is difficult to make any selection from the many Bivalves which are known in deposits of this age; but species of Cardita, Crassatella, Leda, Cyrena, Mactra, Cardium, Psammobia, &c., may be mentioned as very characteristic. The Caradita planicosta here figured (fig. 216) is not only very abundant in the Middle Eocene, but is very widely distributed, ranging from Europe to the Pacific coast of North America. The Univalves of the Eocene are extremely numerous, and generally beautifully preserved. The majority of them belong to that great section of the Gasteropods in which the mouth of the shell is notched or produced into a canal (when the shell is said to be "siphonostomatous")—this section including the carnivorous and most highly-organized groups of the class. Not only is this the case, but a large number of the Eocene Univalves belong to types which now attain their maximum of development in the warmer regions of the globe. Thus we find numerous species of Cones (Conus), Volutes (Voluta), Cowries (Cyproea, fig. 218), Olives and Rice-shells (Oliva), Mitre-shells (Mitra), Trumpet-shells (Triton), Auger-shells (Terebra), and Fig-shells (Pyrula). Along with these are many forms of Pleurotoma, Rostellaria, Spindle-shells (Fusus), Dog-whelks (Nassa), Murices, and many round-mouthed ("holostomatous") species, belonging to such genera as Turritella, Nerita, Natica, Scalaria, &c. The genus Cerithium (fig. 219), most of the living forms of which are found in warm regions, inhabiting fresh or brackish waters, undergoes a vast development in the Eocene period, where it is represented by an immense number of specific forms, some of which attain very large dimensions. In the Eocene strata of the Paris basin alone, nearly one hundred and fifty species of this genus have been detected. The more strictly fresh-water deposits of the Eocene period have also yielded numerous remains of Univalves such as are now proper to rivers and lakes, together with the shells of true Land-snails. Amongst these may be mentioned numerous species of Limnoea (fig. 220), Physa (fig. 221), Melania, Paludina, Planorbis, Helix, Bulimus, and Cyclostoma (fig. 222).



With regard to the Cephalopods, the chief point to be noticed is, that all the beautiful and complex forms which peculiarly characterised the Cretaceous period have here disappeared. We no longer meet with a single example of the Turrilite, the Baculite, the Hamite, the Scaphite, or the Ammonite. The only exception to this statement is the occurrence of one species of Ammonite in the so-called "Lignitic Formation" of North America; but the beds containing this may possibly be rather referable to the Cretaceous—and this exception does not affect the fact that the Ammonitidoe, as a family, had become extinct before the Eocene strata were deposited. The ancient genus Nautilus still survives, the sole representative of the once mighty order of the Tetrabranchiate Cephalopods. In the order of the Dibranchiates, we have a like phenomenon to observe in the total extinction of the great family of the "Belemnites." No form referable to this group has hitherto been found in any Tertiary stratum; but the internal skeletons of Cuttle-fishes (such as Belosepia) are not unknown.



Remains of Fishes are very abundant in strata of Eocene age, especially in certain localities. The most famous depot for the fossil fishes of this period is the limestone of Monte Bolca, near Verona, which is interstratified with beds of volcanic ashes, the whole being referable to the Middle Eocene. The fishes here seem to have been suddenly destroyed by a volcanic eruption, and are found in vast numbers. Agassiz has described over one hundred and thirty species of Fishes from this locality, belonging to seventy-seven genera. All the species are extinct; but about one-half of the genera are represented by living forms. The great majority of the Eocene Fishes belong to the order of the "Bony Fishes" (Teleosteans), so that in the main the forms of Fishes characterising the Eocene are similar to those which predominate in existing seas. In addition to the above, a few Ganoids and a large number of Placoids are known to occur in the Eocene rocks. Amongst the latter are found numerous teeth of true Sharks, such as Otodus (fig. 224) and Carcharodon. The pointed and serrated teeth of the latter sometimes attain a length of over half a foot, indicating that these predaceous fishes attained gigantic dimensions; and it is interesting to note that teeth, in external appearance very similar to those of the early Tertiary genus Carcharodon, have been dredged from great depths during the recent expedition of the Challenger. There also occur not uncommonly the flattened teeth of Rays (fig. 225), consisting of flat bony pieces placed close together, and forming "a kind of mosaic pavement on both the upper and lower jaws" (Owen).



In the class of the Reptiles, the disappearance of the characteristic Mesozoic types is as marked a phenomenon as the introduction of new forms. The Ichthyosaurs, the Plesiosaurs, the Pterosaurs, and the Mosasaurs of the Mesozoic, find no representatives in the Eocene Tertiary; and the same is true of the Deinosaurs, if we except a few remains from the doubtfully-situated "Lignitic formation" of the United States, On the other hand, all the modern orders of Reptiles are known to have existed during the Eocene period. The Chelonians are represented by true marine Turtles, by "Terrapins" (Emydidoe), and by "Soft Tortoises" (Trionycidoe). The order of the Snakes and Serpents (Ophidia) makes its appearance here, for the first time under several forms—all of which, however, are referable to the non-venomous group of the "Constricting Serpents" (Boidoe). The oldest of these is the Paloeophis toliapicus of the London Clay of Sheppey, first made known to science by the researches of Professor Owen. The nearly-allied Paloeophis typhoeus of the Eocene beds of Bracklesham appears to have been a Boa-constrictor-like Snake of about twenty feet in length. Similar Python-like Snakes (Paloeophis, Dinophis, &c.) have been described from the Eocene deposits of the United States. True Lizards (Lacertilians) are found in some abundance in the Eocene deposits,—some being small terrestrial forms, like the common European lizards of the present day; whilst others equal or exceed the living Monitors in size. Lastly, the modern order of the Crocodilia is largely represented in Eocene times, by species belonging to all the existing genera, together with others referable to extinct types. As pointed out by Owen, it is an interesting fact that in the Eocene rocks of the south-west of England, there occur fossil remains of all the three living types of Crocodilians—namely, the Gavials, the true Crocodiles, and the Alligators (fig. 226)—though at the present day these forms are all geographically restricted in their range, and are never associated together.



Almost all the existing orders of Birds, if not all, are represented in the Eocene deposits by remains often very closely allied to existing types. Thus, amongst the Swimming Birds (Natatores) we find examples of forms allied to the living Pelicans and Mergansers; amongst the Waders (Grallatores) we have birds resembling the Ibis (the Numenius gypsorum of the Paris basin); amongst the Running Birds (Cursores) we meet with the great Gastornis Parisiensis, which equalled the African Ostrich in height, and the still more gigantic Dasornis Londinensis; remains of a Partridge represent the Scratching Birds (Rasores); the American Eocene has yielded the bones of one of the Climbing Birds (Scansores), apparently referable to the Woodpeckers; the Protornis Glarisiensis of the Eocene Schists of Glaris is the oldest known example of the Perching Birds (Insessores); and the Birds of Prey (Raptores) are represented by Vultures, Owls, and Hawks. The toothed Birds of the Upper Cretaceous are no longer known to exist; but Professor Owen has recently described from the London Clay the skull of a very remarkable Bird, in which there is, at any rate, an approximation to the structure of Ichthyornis and Hesperornis. The bird in question has been named the Odontopteryx totiapicus, its generic title being derived from the very remarkable characters of its jaws. In this singular form (fig. 227) the margins of both jaws are furnished with tooth-like denticulations, which differ from true teeth in being actually portions of the bony substance of the jaw itself, with which they are continuous, and which were probably encased by extensions of the horny sheath of the bill. These tooth-like processes are of two sizes, the larger ones being comparable to canines; and they are all directed forwards, and have a triangular or compressed conical form. From a careful consideration of all the discovered remains of this bird, Professor Owen concludes that "Odontopteryx was a warm-blooded feathered biped, with wings; and further, that it was web-footed and a fish-eater, and that in the catching of its slippery prey it was assisted by this Pterosauroid armature of its jaws." Upon the whole, Odontopteryx would appear to be most nearly related to the family of the Geese (Anserinoe) or Ducks (Anatidoe); but the extension of the bony substance of the jaws into tooth-like processes is an entirely unique character, in which it stands quite alone.



The known Mammals of the Mesozoic period, as we have seen, are all of small size; and with one not unequivocal exception, they appear to be referable to the order of the Pouched Quadrupeds (Marsupials), almost the lowest group of the whole class of the Mammalia. In the Eocene rocks, on the other hand, numerous remains of Quadrupeds have been brought to light, representing most of the great Mammalian orders now in existence upon the earth, and in many cases indicating animals of very considerable dimensions. We are, in fact, in a position to assert that the majority of the great groups of Quadrupeds with which we are familiar at the present day were already in existence in the Eocene period, and that their ancient root-stocks were even in this early time separated by most of the fundamental differences of structure which distinguish their living representatives. At the same time, there are some amongst the Eocene quadrupeds which have a "generalised" character, and which may be regarded as structural types standing midway between groups now sharply separated from one another.

The order of the Marsupials—including the existing Kangaroos, Wombats, Opossums, Phalangers, &c.—is poorly represented in deposits of Eocene age. The most celebrated example of this group is the Didelphys gypsorum of the Gypseous beds of Montmartre, near Paris, an Opossum very nearly allied to the living Opossums of North and South America.

No member of the _Edenates_ (Sloths, Ant-eaters, and Armadillos) has hitherto been detected in any Eocene deposit. The aquatic order of the _Sirenians_ (Dugongs and Manatees), with their fish-like bodies and tails, paddle-shaped forelimbs, and wholly deficient hind-limbs, are represented in strata of this age by remains of the ancient "Sea-Cows," to which the name of _Halitherium_ has been applied. Nearly allied to the preceding is the likewise aquatic order of the Whales and Dolphins (_Cetaceans_), in which the body is also fish-like, the hind-limbs are wanting, the fore-limbs are converted into powerful "flippers" or swimming-paddles, and the terminal extremity of the body is furnished with a horizontal, tail-fin. Many existing Cetaceans (such as the Whalebone Whales) have no true teeth; but others (Dolphins, Porpoises, Sperm Whales) possess simple conical teeth. In strata of Eocene age, however, we find a singular group of Whales, constituting the genus _Zeuglodon (fig. 228), in which the teeth differed from those of all existing forms in being of two kinds,—the front ones being conical incisors, whilst the back teeth or molars have serrated triangular crowns, and are inserted in the jaw by two roots. Each molar (fig. 228, A) looks as if it were composed of two separate teeth united on one side by their crowns; and it is this peculiarity which is expressed by the generic name (Gr. _zeugle_, a yoke; _odous_, tooth). The best-known species of the genus is the _Zeuglodon cetoides_ of Owen, which attained a length of seventy feet. Remains of these gigantic Whales are very common in the "Jackson Beds" of the Southern United States. So common are they that, according to Dana, "the large vertebrae, some of them a foot and a half long and a foot in diameter, were formerly so abundant over the country, in Alabama, that they were used for making walls, or were burned to rid the fields of them."



The great and important order of the Hoofed Quadrupeds (Ungulata) is represented in the Eocene by examples of both of its two principal sections—namely, those with an uneven number of toes (one or three) on the foot (Perissodactyle Ungulates), and those with an even number of toes (two or four) to each foot (Artiodactyle Ungulates). Amongst the Odd-toed Ungulates, the living family of the Tapirs (Tapirdoe) is represented by the genus Coryphodon of Owen. Nearly related to the preceding are the species of Paloeotherium, which have a historical interest as being amongst the first of the Tertiary Mammals investigated by the illustrious Cuvier. Several species of Paloeothere are known, varying greatly in size, the smallest being little bigger than a hare, whilst the largest must have equalled a good-sized horse in its dimensions. The species of Paloeotherium appear to have agreed with the existing Tapirs in possessing a lengthened and flexible nose, which formed a short proboscis or trunk (fig. 229), suitable as an instrument for stripping off the foliage of trees—the characters of the molar teeth showing them to have been strictly herbivorous in their habits. They differ, however, from the Tapirs, amongst other characters, in the fact that both the fore and the hind feet possessed three toes each; whereas in the latter there are four toes on each fore-foot, and the hind-feet alone are three-toed. The remains of Paloeotheria have been found in such abundance in certain localities as to show that these animals roamed in great herds over the fertile plains of France and the south of England during the later portion of the Eocene period. The accompanying illustration (fig. 229) represents the notion which the great Cuvier was induced by his researches to form as to the outward appearance of Paloeotherium magnum. Recent discoveries, however, have rendered it probable that this restoration is in some important respects inaccurate. Instead of being bulky, massive, and more or less resembling the living Tapirs in form, it would rather appear that Paloeotherium magnum was in reality a slender, graceful, and long-necked animal, more closely resembling in general figure a Llama, or certain of the Antelopes.



The singular genus Anchitherium forms a kind of transition between the Paloeotheria and the true Horses (Equidoe). The Horse (fig. 230, D) possesses but one fully-developed toe to each foot, this being terminated by a single broad hoof, and representing the middle toe—the third of the typical five-fingered or five-toed limb of Quadrupeds in general. In addition, however, to this fully-developed toe, each foot in the horse carries two rudimentary toes which are concealed beneath the skin, and are known as the "splint-bones." These are respectively the second and fourth toes, in an aborted condition; and the first and fifth toes are wholly wanting. In Hipparion (fig. 230, C), the foot is essentially like that of the modern Horses, except that the second and fourth toes no longer are mere "splint-bones," hidden beneath the skin; but have now little hoofs, and hang freely, but uselessly, by the side of the great middle toe, not being sufficiently developed to reach the ground. In Anchitherium, again (fig. 230, B), the foot is three-toed, like that of Hipparion; but the two lateral toes (the second and fourth) are so far developed that they now reach the ground. The first digit (thumb or great toe) is still wanting; as also is the fifth digit (little finger or little toe). Lastly, the Eocene rocks have yielded in North America the remains of a small Equine quadruped, to which Marsh has given the name of Orohippus. In this singular form—which was not larger than a fox—the foot (fig. 230, A) carries four toes, all of which are hoofed and touch the ground, but of which the third toe is still the largest. The first toe (thumb or great toe) is still wanting; but in this ancient representative of the Horses, the fifth or "little" toe appears for the first time. As all the above-mentioned forms succeed one another in point of time, it may be regarded as probable that we shall yet be able to point, with some certainty, to some still older example of the Equidoe, in which the first digit is developed, and the foot assumes its typical five-fingered condition.



Passing on to the Even-toed or Artiodactyle Ungulates, no representative of the Hippotamus seems yet to have existed, but there are several forms (Choeropotamus, Hyopotamus, &c.) more or less closely allied to the Pigs (Suida); and the singular group of the Anoplotheridoe may be regarded as forming a kind of transition between the Swine and the Ruminants. The Anoplotheria (fig. 231) were slender in form, the largest not exceeding a donkey in size, with long tails, and having the feet terminated by two hoofed toes each, sometimes with a pair of small accessory hoofs as well. The teeth exhibit the peculiarity that they are arranged in a continuous series, without any gap or interval between the molars and the canines; and the back teeth, like those of all the Ungulates, are adapted for grinding vegetable food, their crowns resembling in form those of the true Ruminants. The genera Dichobune and Xiphodon, of the Middle and Upper Eocene, are closely related to Anoplotherium, but are more slender and deer-like in form. No example of the great Ruminant group of the Ungulate Quadrupeds has as yet been detected in deposits of Eocene age.



Whilst true Ruminants appear to be unknown, the Eocene strata of North America have yielded to the researches of Professor Marsh examples of an extraordinary group (Dinocerata), which may be considered as in some respects intermediate between the Ungulates and the Proboscideans. In Dinoceras itself (fig. 232) we have a large animal, equal in dimensions to the living Elephants, which it further resembles in the structure of the massive limbs, except that there are only four toes to each foot. The upper jaw was devoid of front teeth, but there were two very large canine teeth, in the form of tusks directed perpendicularly downwards; and there was also a series of six small molars on each. Each upper jaw-bone carried a bony projection, which was probably of the nature of a "horn-core," and was originally sheathed in horn. Two similar, but smaller, horn-cores are carried on the nasal bones; and two much larger projections, also probably of the nature of horn-cores, were carried upon the forehead. We may thus infer that Dinoceras possessed three pairs of horns, all of which resembled the horns of the Sheep and Oxen in consisting of a central bony "core," surrounded by a horny sheath. The nose was not prolonged into a proboscis or "trunk," as in the existing Elephants; and the tail was short and slender. Many forms of the Dinocerata are known; but all these singular and gigantic quadrupeds appear to have been confined to the North American continent, and to be restricted to the Eocene period.



The important order of the Elephants (Proboscidea) is also not known to have come into existence during the Eocene period. On the other hand, the great order of the Beasts of Prey (Carnivora) is represented in Eocene strata by several forms belonging to different types. Thus the Ardocyon presents us with an Eocene Carnivore more or less closely allied to the existing Racoons; the Paloeonyctis appears to be related to the recent Civet-cats; the genus Hyoenodon is in some respects comparable to the living Hyaenas; and the Canis Parisiensis of the gypsum-bearing beds of Montmartre may perhaps be allied to the Foxes.



The order of the Bats (Cheiroptera) is represented in Eocene strata of the Paris basin (Gypseous series of Montmartre) by the Vespertilio Parisiensis (fig. 233), an insect-eating Bat very similar to some of the existing European forms. Lastly, the Eocene deposits have yielded more or less satisfactory evidence of the existence in Europe at this period of examples of the orders of the Gnawing Mammals (Rodentia), the Insect-eating Mammals (Insectivora), and the Monkeys (Quadrumana).[24]

[Footnote 24: A short list of the more important works relating to the Eocene rocks and fossils will be given after all the Tertiary deposits have been treated of.]



CHAPTER XIX.

THE MIOCENE PERIOD.

The Miocene rocks comprise those Tertiary deposits which contain less than about 35 per cent of existing species of shells (Mollusca), and more than 5 per cent—or those deposits in which the proportion of living shells is less than of extinct species. They are divisible into a Lower Miocene (Oligocene) and an Upper Miocene series.

In Britain, the Miocene rocks are very poorly developed, one of their leading developments being at Bovey Tracy in Devonshire, where there occur sands, clays, and beds of lignite or imperfect coal. These strata contain numerous plants, amongst which are Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially those belonging to the genus Sequoia (the "Red-Foods"). These Bovey Tracy lignites are of Lower Miocene age, and they are lacustrine in origin. Also of Lower Miocene age are the so-called "Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a thickness of less than 200 feet, and are shown by their numerous fossils to be principally a true marine formation. Lastly, the Duke of Argyll, in 1851, showed that there existed at Ardtun, in the island of Mull, certain Tertiary strata containing numerous remains of plants; and these also are now regarded as belonging to the Lower Miocene.

In France, the Lower Miocene is represented in Auvergne, Cantal, and Velay, by a great thickness of nearly horizontal strata of sands, sandstone, clays, marls, and limestones, the whole of fresh-water origin. The principal fossils of these lacustrine deposits are Mammalia, of which the remains occur in great abundance. In the valley of the Loire occur the typical European deposits of Upper Miocene age. These are known as the "Faluns," from a provincial term applied to shelly sands, employed to spread upon soils which are deficient in lime; and the Upper Miocene is hence sometimes spoken of as the "Falunian" formation. The Faluns occur in scattered patches, which are rarely more than 50 feet in thickness, and consist of sands and marls. The fossils are chiefly marine; but there occur also land and fresh-water shells, together with the remains of numerous Mammals. About 25 per cent of the shells of the Faluns are identical with existing species. The sands, limestones, and marls of the Department of Gers, near the base of the Pyrenees, rendered famous by the number or Mammalian remains exhumed from them by M. Lartet, also belong to the age of the Faluns.

In Switzerland, between the Alps and the Jura, there occurs a great series of Miocene deposits, known collectively as the "Molasse," from the soft nature of a greenish sandstone, which constitutes one of its chief members. It attains a thickness of many thousands of feet, and rises into lofty mountains, some of which—as the Rigi—are more than 6000 feet in height. The middle portion of the Molasse is of marine origin, and is shown by its fossils to be of the age of the Faluns; but the lower and upper portions of the formation are mainly or entirely of fresh-water origin. The Lower Molasse (of Lower Miocene age) has yielded about 500 species of plants, mostly of tropical or sub-tropical forms. The Upper Molasse has yielded about the same number of plants, with about 900 species of Insects, such as wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c.

In Belgium, strata of both Lower and Upper Miocene age are known,—the former (Rupelian Clays) containing numerous marine fossils; whilst the latter (Bolderberg Sands) have yielded numerous shells corresponding with those of the Faluns.

In Austria, Miocene strata are largely developed, marine beds belonging to both the Lower and Upper division of the formation occurring extensively in the Vienna basin. The well-known Brown Coals of Radaboj, in Croatia, with numerous plants and insects, are also of Lower Miocene age.

In Germany, deposits belonging to both the Lower and Upper division of the Miocene formation are extensively developed. To the former belong the marine strata of the Mayence basin, and the marine Rupelian Clay near Berlin; whilst a celebrated group of strata belonging to the Upper Miocene occurs near Epplesheim, in Hesse-Darmstadt, and is well known for the number of its Mammalian remains.

In Greece, at Pikerme, near Athens, there occurs a celebrated deposit of Upper Miocene age, well known to palaeontologists through the researches of M. M. Wagner, Roth, and Gaudry upon the numerous Mammalia which it contains. In Italy, also, strata of both Lower and Upper Miocene age are well developed in the neighbourhood of Turin.

In the Siwalik Hills, in India, at the southern foot of the Himalayas, occurs a series of Upper Miocene strata, which have become widely celebrated through the researches of Dr Falconer and Sir Proby Cautley upon the numerous remains of Mammals and Reptiles which they contain. Beds of corresponding age, with similar fossils, are known to occur in the island of Perim in the Gulf of Cambay.

Lastly, Miocene deposits are found in North America, in New Jersey, Maryland, Virginia, Missouri, California, Oregon, &c., attaining a thickness of 1500 feet or more. They consist principally of clays, sands, and sandstones, sometimes of marine and sometimes of fresh-water origin. Near Richmond, in Virginia, there occurs a remarkable stratum, wrongly called "Infusorial Earth," which is occasionally 30 feet in thickness, and consists almost wholly of the siliceous envelopes of certain low forms of plants (Diatoms), along with the spicules of Sponges and other siliceous organisms (see fig. 16). The White River Group of Hayden occurs in the Upper Missouri region, and is largely exposed over the barren and desolate district known as the "Mauvaises Terres." They have a thickness of 1000 feet or more, and contain numerous remains of Mammals. They are of lacustrine origin, and are believed to be of the age of the Lower Miocene. Upon the whole, about from 15 to 30 per cent of the Mollusca of the American Miocene are identical with existing species.

In addition to the regions previously enumerated, Miocene strata are known to be developed in Greenland, Iceland, Spitzbergen, and in other areas of less importance.

The life of the Miocene period is extremely abundant, and, from the nature of the deposits of this age, also extremely varied in its character. The marine beds of the formation have yielded numerous remains of both Vertebrate and Invertebrate sea-animals; whilst the fresh-water deposits contain the skeletons of such shells, fishes, &c., as now inhabit rivers or lakes. Both the marine and the lacustrine beds have been shown to contain an enormous number of plants, the latter more particularly; whilst the Brown Coals of the formation are made up of vegetable matter little altered from its original condition. The remains of air-breathing animals, such as Insects, Reptiles, Birds, and Mammals, are also abundantly found, more especially in the fresh-water beds.

The plants of the Miocene period are extraordinarily numerous, and only some of the general features of the vegetation of this epoch can be indicated here. Our chief sources of information as to the Miocene plants are the Brown Coals of Germany and Austria, the Lower and Upper Molasse of Switzerland, and the Miocene strata of the Arctic regions. The lignites of Austria have yielded very numerous plants, chiefly of a tropical character—one of the most noticeable forms being a Palm of the genus Sabal (fig. 234, B), now found in America. The plants of the Lower Miocene of Switzerland are also mostly of a tropical character, but include several forms now found in North America, such as a Tulip-tree (Liriodendron) and a Cypress (Taxodium). Amongst the more remarkable forms from these beds may be mentioned Fan-Palms (Chamoerops, fig 234, A), numerous tropical ferns, and two species of Cinnamon. The plant-remains of the Upper Molasse of Switzerland indicate an extraordinarily rank and luxuriant vegetation, composed mainly of plants which now live in warm countries. Among the commoner plants of this formation may be enumerated many species of Maple (Acer), Plane-trees (Platanus fig. 235), Cinnamon-trees (fig. 236), and other members of the Lauraceoe, many species of Proteaccoe (Banksia, Grevillea, &c.), several species of Sarsaparilla (Smilax), Palms, Cypresses, &c.



In Britain, the Lower Miocene strata of Bovey Tracy have yielded remains of Ferns, Vines, Fig, Cinnamon, Proteaccoe, &c., along with numerous Conifers. The most abundant of these last is a gigantic pine—the Sequoia Couttsioe—which is very nearly allied to the huge Sequoia (Wellingtonia) gigantea of California. A nearly-allied form (Sequoia Langsdorffi) has been detected in the leaf-bed of Ardtun, in the Hebrides.

In Greenland, as well as in other parts of the Arctic regions, Miocene strata have been discovered which have yielded a great number of plants, many of which are identical with species found in the European Miocene. Amongst these plants are found many trees, such as Conifers, Beeches, Oaks, Maples, Plane-trees, Walnuts, Magnolias, &c., with numerous shrubs, ferns, and other smaller plants. With regard to the Miocene flora of the Arctic regions, Sir Charles Lyell remarks that "more than thirty species of Coniferae have been found, including several Sequoias (allied to the gigantic Wellingtonia of California), with species of Thujopsis and Salisburia, now peculiar to Japan. There are also beeches, oaks, planes, poplars, maples, walnuts, limes, and even a magnolia, two cones of which have recently been obtained, proving that this splendid evergreen not only lived but ripened its fruit within the Arctic circle. Many of the limes, planes, and oaks were large-leaved species; and both flowers and fruits, besides immense quantities of leaves, are in many cases preserved. Among the shrubs are many evergreens, as Andromeda, and two extinct genera, Daphnogene and M'Clintockia, with fine leathery leaves, together with hazel, blackthorn, holly, logwood, and hawthorn. A species of Zamia (Zimites) grew in the swamps, with Potamogeton, Sparganium, and Menyanthes; while ivy and villes twined around the forest-trees, and broad-leaved ferns grew beneath their shade. Even in Spitzbergen, as far north as lat. 78 deg. 56', no less than ninety-five species of fossil plants have been obtained, including Taxodium of two species, hazel, poplar, alder, beech, plane-tree, and lime. Such a vigorous growth of trees within 12 deg. of the pole, where now a dwarf willow and a few herbaceous plants form the only vegetation, and where the ground is covered with almost perpetual snow and ice, is truly remarkable."

Taking the Miocene flora as a whole, Dr Heer concludes from his study of about 3000 plants contained in the European Miocene alone, that the Miocene plants indicate tropical or sub-tropical conditions, but that there is a striking inter-mixture of forms which are at present found in countries widely removed from one another. It is impossible to state with certainty how many of the Miocene plants belong to existing species, but it appears that the larger number are extinct. According to Heer, the American types of plants are most largely represented in the Miocene flora, next those of Europe and Asia, next those of Africa, and lastly those of Australia. Upon the whole, however, the Miocene flora of Europe is mostly nearly allied to the plants which we now find inhabiting the warmer parts of the United States; and this has led to the suggestion that in Miocene times the Atlantic Ocean was dry land, and that a migration of American plants to Europe was thus permitted. This view is borne out by the fact that the Miocene plants of Europe are most nearly allied to the living plants of the eastern or Atlantic seaboard of the United States, and also by the occurrence of a rich Miocene flora in Greenland. As regards Greenland, Dr Heer has determined that the Miocene plants indicate a temperate climate in that country, with a mean annual temperature at least 30 deg. warmer than it is at present.

The present limit of trees is the isothermal which gives the mean temperature of 500 Fahr. in July, or about the parallel of 67 deg. N. latitude. In Miocene times, however, the Limes, Cypresses, and Plane-trees reach the 79th degree of latitude, and the Pines and Poplars must have ranged even further north than this.

The Invertebrate Animals of the Miocene period are very numerous, but they belong for the most part to existing types, and they can only receive scanty consideration here. The little shells of Foraminifera are extremely abundant in some beds, the genera being in many cases such as now flourish abundantly in our seas. The principal forms belong to the genera Textularia (fig. 237), Robulina, Glandulina, Polystomella, Amplistegina, &c. Corals are very abundant, in many instances forming regular "reefs;" but all the more important groups are in existence at the present day. The Red Coral (Corallium), so largely sought after as an ornamental material, appears for the first time in deposits of this age. Amongst the Echinoderms, we meet with Heart-Urchins (Spatangus), Cake-Urchins (Scutella; fig. 238), and various other forms, the majority of which are closely allied to forms now in existence.



Numerous Crabs and Lobsters represent the Crustacea; but the most important of the Miocene Articulate Animals are the Insects. Of these, more than thirteen hundred species have been determined by Dr Heer from the Miocene strata of Switzerland alone. They include almost all the existing orders of insects, such as numerous and varied forms of Beetles (Coleoptera), Forest-bugs (Hemiptera), Ants (Hymenoptera), Flies (Diptera), Termites and Dragon-flies (Neuroptera), Grasshoppers (Orthoptera), and Butterflies (Lepidoptera). One of the latter, the well-known Vanessa Pluto of the Brown Coals of Croatia, even exhibits the pattern of the wing, and to some extent its original coloration; whilst the more durably-constructed insects are often in a state of exquisite preservation.



The Mollusca of the Miocene period are very numerous, but call for little special comment. Upon the whole, they are generically very similar to the Shell-fish of the present day; whilst, as before stated, from fifteen to thirty per cent of the species are identical with those now in existence. So far as the European area is concerned, the Molluscs indicate a decidedly hotter climate than the present one, though they have not such a distinctly tropical character as is the case with the Eocene shells. Thus we meet with many Cones, Volutes, Cowries, Olive-shells, Fig-shells, and the like, which are decidedly indicative of a high temperature of the sea. Polyzoans are abundant, and often attain considerable dimensions; whilst Brachiopods, on the other hand, are few in number. Bivalves and Univalves are extremely plentiful; and we meet here with the shells of Winged-Snails (Pteropods), belonging to such existing genera as Hyalea (fig. 239) and Cleodora. Lastly, the Cephalopods are represented both by the chambered shells of Nautili and by the internal skeletons of Cuttle-fishes (Spirulirostra.)



The Fishes of the Miocene Period are very abundant but of little special importance. Besides the remains of Bony Fishes, we meet in the marine deposits of this age with numerous pointed teeth belonging to different kinds of Sharks. Some of the genera of these—such as Carcharodon (fig. 241), Oxyrhina (fig. 240), Lamna, and Galeocerdo—are very widely distributed, ranging through both the Old and New Worlds; and some of the species attain gigantic dimensions.

Amongst the Amphibians we meet with distinctly modern types, such as Frogs (Rana) and Newts or Salamanders. The most celebrated of the latter is the famous Andrias Scheuchzeri (fig. 242), discovered in the year 1725 in the fresh-water Miocene deposits of OEningen, in Switzerland. The skeleton indicates an animal nearly five feet in length; and it was originally described by Scheuchzer, a Swiss physician, in a dissertation published in 1731, as the remains of one of the human beings who were in existence at the time of the Noachian Deluge. Hence he applied to it the name of Homo diluvii testis. In reality, however, as shown by Cuvier, we have here the skeleton of a huge Newt, very closely allied to the Giant Salamander (Menopoma maxima) of Java.



The remains of Reptiles are far from uncommon in the Miocene rocks, consisting principally of Chelonians and Crocodilians. The Land-tortoises (Testudinidoe) make their first appearance during this period. The most remarkable form of this group is the huge Colossochelys Atlas of the Upper Miocene deposits of the Siwalik Hills in India, described by Dr Falconer and Sir Proby Cautley. Far exceeding any living Tortoise in its dimensions, this enormous animal is estimated as having had a length of about twenty feet, measured from the tip of the snout to the extremity of the tail, and to have stood upwards of seven feet high. All the details of its organisation, however, prove that it must have been "strictly a land animal, with herbivorous habits, and probably of the most inoffensive nature." The accomplished palaeontologist just quoted, shows further that some of the traditions of the Hindoos would render it not improbable that this colossal Tortoise had survived into the earlier portion of the human period.

Of the Birds of the Miocene period it is sufficient to remark that though specifically distinct, they belong, so far as known, wholly to existing groups, and therefore present no points of special palaeontological interest.

The Mammals of the Miocene are very numerous, and only the more important forms can be here alluded to. Amongst the Marsupials, the Old World still continued to possess species of Opossum (Didephys), allied to the existing American forms. The Edentates (Sloths, Armadillos, and Ant-eaters), at the present day mainly South American, are represented by two large European forms. One of these is the large Macrotherium giganteum of the Upper Miocene of Gers in Southern France, which appears to hare been in many respects allied to the existing Scaly Ant-eaters or Pangolins, at the same time that the disproportionately long fore-limbs would indicate that it possessed the climbing habits of the Sloths. The other is the still more gigantic Ancylotherium Pentelici of the Upper Miocene of Pikerme, which seems to have been as large as, or larger than, the Rhinoceros, and which must have been terrestrial in its habits. This conclusion is further borne out by the comparative equality of length which subsists between the fore and hind limbs, and is not affected by the curvature and crookedness of the claws, this latter feature being well marked in such existing terrestrial Edentates as the Great Ant-eater.



The aquatic Sirenians and Cetaceans are represented in Miocene times by various forms of no special importance. Amongst the former, the previously existing genus Halitherium continued to survive, and amongst the latter we meet with remains of Dolphins and of Whales of the "Zeuglodont" family. We may also note here the first appearance of true "Whalebone Whales," two species of which, resembling the living "Right Whale" of Arctic seas, and belonging to the same genus (Baloena), have been detected in the Miocene beds of North America.

The great order of the Ungulates or Hoofed Quadrupeds is very largely developed in strata of Miocene age, various new types of this group making their appearance here for the first time, whilst some of the characteristic genera of the preceding period are still represented under new shapes. Amongst the Odd-toed or "Perissodactyle" Ungulates, we meet for the first time with representatives of the family Rhinoceridoe comprising only the existing Rhinoceroses. In India in the Upper Miocene beds of the Siwalik Hills, and in North America, several species of Rhinoceros have been detected, agreeing with the existing forms in possessing three toes to each foot, and in having one or two solid fibrous "horns" carried upon the front of the head. On the other hand, the forms of this group which distinguish the Miocene deposits of Europe appear to have been for the most part hornless, and to have resembled the Tapirs in having three-toed hind-feet, but four-toed fore-feet.

The family of the Tapirs is represented, both in the Old and New Worlds, by species of the genus Lophiodon, some of which were quite diminutive in point of size, whilst others attained the dimensions of a horse. Nearly allied to this family, also, is the singular group of quadrupeds which Marsh has described from the Miocene strata of the United States under the name of Brontotheridoe. These extraordinary animals, typified by Brontotherium (fig. 243) itself, agree with the existing Tapirs of South America and the Indian Archipelago in having the fore-feet four-toed, whilst the hind-feet are three-toed; and a further point of resemblance is found in the fact (as shown by the form of the nasal bones) that the nose was long and flexible, forming a short movable proboscis or trunk, by means of which the animal was enabled to browse on shrubs or trees. They differ, however, from the Tapirs, not only in the apparent presence of a long tail, but also in the possession of a pair of very large "horn-cores," carried upon the nasal bones, indicating that the animal possessed horns of a similar structure to those of the "Hollow-horned" Ruminants (e.g., Sheep and Oxen). Brontotherium gigas is said to be nearly as large as an Elephant, whilst B. Ingens appears to have attained dimensions still more gigantic. The well-known genus Titanotherium of the American Miocene would also appear to belong to this group.



The family of the Horses (Equidoe) appears under various forms in the Miocene, but the most important and best known of these is Hipparion. In this genus the general conformation of the skeleton is extremely similar to that of the existing Horses, and the external appearance of the animal must have been very much the same. The foot of Hipparion, however, as has been previously mentioned, differed from that of the Horse in the fact that whilst both possess the middle toe greatly developed and enclosed in a broad hoof, the former, in addition, possessed two lateral toes, which were sufficiently developed to carry hoofs, but were so far rudimentary that they hung idly by the side of the central toe without touching the ground (see fig. 230). In the Horse, on the other hand, these lateral toes, though present, are not only functionally useless, but are concealed beneath the skin. Remains of the Hipparion have been found in various regions in Europe and in India; and from the immense quantities of their bones found in certain localities, it may be safely inferred that these Middle Tertiary ancestors of the Horses lived, like their modern representatives, in great herds, and in open grassy plains or prairies.

Amongst the Even-toed or Artiodactyle Ungulates, we for the first time meet with examples of the Hippopotamus, with its four-toed feet, its massive body, and huge tusk-like lower canine teeth. The Miocene deposits of Europe have not hitherto yielded any remains of Hippopotamus; but several species have been detected in the Upper Miocene of the Siwalik Hills by Dr Falconer and Sir Proby Cautley. These ancient Indian forms, however, differ from the existing Hippopotamus amphibius of Africa in the fact that they possessed six incisor teeth in each jaw (fig. 244), whereas the latter has only four.



Amongst the other Even-toed Ungulates, the family of the Pigs (Suida) is represented by true Swine (Sus Erymanthius), Peccaries (Dicotyles antiquus), and by forms which, like the great Elotherium of the American Miocene, have no representative at the present day. The Upper Miocene of India has yielded examples of the Camels. Small Musk-deer (Amphitragulus and Dremotherium) are known to have existed in France and Greece; and the true Deer (Cervidoe), with their solid bony antlers, appear for the first time here in the person of species allied to the living Stags (Cervus), accompanied by the extinct genus Dorcatherium. The Giraffes (Camelopardalidoe), now confined to Africa, are known to have lived in India and Greece; and the allied Helladotherium, in some respects intermediate between the Giraffes and the Antelopes, ranged over Southern Europe from Attica to France. The great group of the "Hollow-horned" Ruminants (Cavicornia), lastly, came into existence in the Miocene period; and though the typical families of the Sheep and Oxen are apparently wanting, there are true Antelopes, together with forms which, if systematically referable to the Antilopidoe, nevertheless are more or less clearly transitional between this and the family of the Sheep and Goats. Thus the Paloeoreas of the Upper Miocene of Greece may be regarded as a genuine Antelope; but the Tragoceras of the same deposit is intermediate in its characters between the typical Antelopes and the Goats. Perhaps the most remarkable, however, of these Miocene Ruminants is the Sivatherium giganteum (fig. 245) of the Siwalik Hills, in India. In this extraordinary animal there were two pairs of horns, supported by bony "horn-cores," so that there can be no hesitation in referring Sivatherium to the Cavicorn Ruminants. If all these horns had been simple, there would have been no difficulty in considering Sivatherium as simply a gigantic four-horned Antelope, essentially similar to the living Antilope (Tetraceros) quadricornis of India. The hinder pair of horns, however, is not only much larger than the front pair, but each possesses two branches or snags—a peculiarity not to be paralleled amongst any existing Antelope, save the abnormal Prongbuck (Antilocapra) of North America. Dr Murie, however, in an admirable memoir on the structure and relationships of Sivatherium, has drawn attention to the fact that the Prongbuck sheds the sheath of its horns annually, and has suggested that this may also have been the case with the extinct form. This conjecture is rendered probable, amongst other reasons, by the fact that no traces of a horny sheath surrounding the horn-cores of the Indian fossil have been as yet detected. Upon the whole, therefore, we may regard the elephantine Sivatherium as being most nearly allied to the Prongbuck of Western America, and thus as belonging to the family of the Antelopes.



It is to the Miocene period, again, to which we must refer the first appearance of the important order of the Elephants and their allies (Proboscideans), all of which are characterised by their elongated trunk-like noses, the possession of five toes to the foot, the absence of canine teeth, the development of two or more of the incisor teeth into long tusks, and the adaptation of the molar teeth to a vegetable diet. Only three generic groups of this order are known-namely, the extinct Deinotherium, the equally extinct Mastodons, and the Elephants; and all these three types are known to have been in existence as early as the Miocene period, the first of them being exclusively confined to deposits of this age. Of the three, the genus Deinotherium is much the most abnormal in its characters; so much so, that good authorities regard it as really being one of the Sea-cows (Sirenia)—though this view has been rendered untenable by the discovery of limb-bones which can hardly belong to any other animal, and which are distinctly Proboscidean in type. The most celebrated skull of the Deinothere (fig. 246) is one which was exhumed from the Upper Miocene deposits of Epplesheim, in Hesse-Darmstadt, in the year 1836. This skull was four and a half feet in length, and indicated an animal larger than any existing species of Elephant. The upper jaw is destitute of incisor or canine teeth, but is furnished on each side with five molars, which are opposed to a corresponding series of grinding teeth in the lower jaw. No canines are present in the lower jaw; but the front portion of the jaw is abruptly bent downwards, and carries two huge tusk-like incisor teeth, which are curved downwards and backwards, and the use of which is rather problematical. Not only does the Deinothere occur in Europe, but remains belonging to this genus have also been detected in the Siwalik Hills, in India.



The true Elephants (Elephas) do not appear to have existed during the Miocene period in Europe, but several species have been detected in the Upper Miocene deposits of the Siwalik Hills, in India. The fossil forms, though in all cases specifically, and in some cases even sub-generically, distinct, agree with those now in existence in the general conformation of their skeleton, and in the principal characters of their dentition. In all, the canine teeth are wanting in both jaws; and there are no incisor teeth in the lower jaw, whilst there are two incisors in the front of the upper jaw, which are developed into two huge "tusks." There are six molar teeth on each side of both the upper and lower jaw, but only one, or at most a part of two, is in actual use at any given time; and as this becomes worn away, it is pushed forward and replaced by its successor behind it. The molars are of very large size, and are each composed of a number of transverse plates of enamel united together by ivory; and by the process of mastication, the teeth become worn down to a flat surface, crossed by the enamel-ridges in varying patterns; These patterns are different in the different species of Elephants, though constant for each; and they constitute one of the most readily available means of separating the fossil forms from one another. Of the seven Miocene Elephants of India, as judged by the characters of the molar, teeth, two are allied to the existing Indian Elephant, one is related to the living African Elephant, and the remaining four are in some respects intermediate between the true Elephants and the Mastodons.



The Mastodons, lastly, though quite elephantine in their general characters, possess molar teeth which have their crowns furnished with conical eminences or tubercles placed in pairs (fig. 247, B), instead of having the approximately flat surface characteristic of the grinders of the Elephants. As in the latter, there are two upper incisor teeth, which grow permanently during the life of the animal, and which constitute great tusks; but the Mastodons, in addition, often possess two lower incisors, which in some cases likewise grow into small tusks. Three species of Mastodon are known to occur in the Upper Miocene of the Siwalik Hills of India; and the Miocene deposits of the European area have yielded the remains of four species, of which the best known are the M. Longirostris and the M. Angustidens.

Whilst herbivorous Quadrupeds, as we have seen, were extremely abundant during Miocene times, and often attained gigantic dimensions, Beasts of Prey (Carnivora) were by no means wanting, most of the principal existing families of the order being represented in deposits of this age. Thus, we find aquatic Carnivores belonging to both the living groups of the Seals and Walruses; true Bears are wanting, but their place is filled by the closely-allied genus Amphicyon, of which various species are known; Weasels and Otters were not unknown, and the Hyoenictis and Iditherium of the Upper Miocene of Greece are apparently intermediate between the Civet-cats and the Hyaenas; whilst the great Cats of subsequent periods are more than adequately represented by the huge "Sabre-toothed Tiger" (Machairodus), with its immense trenchant and serrated canine teeth.

Amongst the Rodent Mammals, the Miocene rocks have yielded remains of Rabbits, Porcupines (such as the Hystrix primigenius of Greece), Beavers, Mice, Jerboas, Squirrels, and Marmots. All the principal living groups of this order were therefore differentiated in Middle Tertiary times.

The Cheiroptera are represented by small insect-eating Bats; and the order of the Insectivorous Mammals is represented by Moles, Shrew-mice, and Hedgehogs.



Lastly, the Monkeys (Quadrumana) appear to have existed during the Miocene period under a variety of forms, remains of these animals having been found both in Europe and in India; but no member of this order has as yet been detected in the Miocene Tertiary of the North American continent. Amongst the Old World Monkeys of the Miocene, the two most interesting are the Pliopithecus and Dryopithecus of France. The former of these (fig. 248) is supposed to have been most nearly related to the living Semnopitheci of Southern Asia, in which case it must have possessed a long tail. The Mesopithecus of the Upper Miocene of Greece is also one of the lower Monkeys, as it is most closely allied to the existing Macaques. On the other hand, the Dryopithecus of the French Upper Miocene is referable to the group of the "Anthropoid Apes," and is most nearly related to the Gibbons of the present day, in which the tail is rudimentary and there are no cheek-pouches. Dryopithecus was, also, of large size, equalling Man in stature, and apparently living amongst the trees and feeding upon fruits.



CHAPTER XX.

THE PLIOCENE PERIOD.

The highest division of the Tertiary deposits is termed the Pliocene formation, in accordance with the classification proposed by Sir Charles Lyell. The Pliocene formations contain from 40 to 95 per cent of existing species of Mollusca, the remainders belonging to extinct species. They are divided by Sir Charles Lyell into two divisions, the Older Pliocene and Newer Pliocene.

The Pliocene deposits of Britain occur in Suffolk, and are known by the name of "Crags," this being a local term used for certain shelly sands, which are employed in agriculture. Two of these Crags are referable to the Older Pliocene, viz., the White and Red Crags,—and one belongs to the Newer Pliocene, viz., the Norwich Crag.

The White or Coralline Crag of Suffolk is the oldest of the Pliocene deposits of Britain, and is an exceedingly local formation, occurring in but a single small area, and having a maximum thickness of not more than 50 feet. It consists of soft sands, with occasional intercalations of flaggy limestone. Though of small extent and thickness, the Coralline Crag is of importance from the number of fossils which it contains. The name "Coralline" is a misnomer; since there are few true Corals, and the so-called "Corals" of the formation are really Polyzoa, often of very singular forms. The shells of the Coralline Crag are mostly such as inhabit the seas of temperate regions; but there occur some forms usually looked upon as indicating a warm climate.

The Upper or Red Crag of Suffolk—like the Coralline Crag—has a limited geographical extent and a small thickness, rarely exceeding 40 feet. It consists of quartzose sands, usually deep red or brown in colour, and charged with numerous fossils.

Altogether more than 200 species of shells are known from the Red Crag, of which 60 per cent are referable to existing species. The shells indicate, upon the whole, a temperate or even cold climate, decidedly less warm than that indicated by the organic remains of the Coralline Crag. It appears, therefore, that a gradual refrigeration was going on during the Pliocene period, commencing in the Coralline Crag, becoming intensified in the Red Crag, being still more severe in the Norwich Crag, and finally culminating in the Arctic cold of the Glacial period.

Besides the Mollusca, the Red Crag contains the ear-bones of Whales, the teeth of Sharks and Rays, and remains of the Mastodon, Rhinoceros, and Tapir.

The Newer Pliocene deposits are represented in Britain by the Norwich Crag, a local formation occurring near Norwich. It consists of incoherent sands, loams, and gravels, resting in detached patches, from 2 to 20 feet in thickness, upon an eroded surface of Chalk. The Norwich Crag contains a mixture of marine, land, and fresh-water shells, with remains of fishes and bones of mammals; so that it must have been deposited as a local sea-deposit near the mouth of an ancient river. It contains altogether more than 100 marine shells, of which 89 per cent belong to existing species. Of the Mammals, the two most important are an Elephant (Elephas meridionalis), and the characteristic Pliocene Mastodon (M. Arvernensis), which is hitherto the only Mastodon found in Britain.

According to the most recent views of high authorities, certain deposits—such as the so-called "Bridlington Crag" of Yorkshire, and the "Chillesford beds" of Suffolk—are to be also included in the Newer Pliocene, upon the ground that they contain a small proportion of extinct shells. Our knowledge, however, of the existing Molluscan fauna, is still so far incomplete, that it may reasonably be doubted if these supposed extinct forms have actually made their final disappearance, whilst the strata in question have a strong natural connection with the "Glacial deposits," as shown by the number of Arctic Mollusca which they contain. Here, therefore, these beds will be included in the Post-Pliocene series, in spite of the fact that some of their species of shells are not known to exist at the present day.

The following are the more important Pliocene deposits which have been hitherto recognised out of Britain:—

1. In the neighbourhood of Antwerp occur certain "crags," which are the equivalent of the White and Red Crag in part. The lowest of these contains less than 50 per cent, and the highest 60 per cent, of existing species of shells, the remainder being extinct.

2. Bordering the chain of the Apennines, in Italy, on both sides is a series of low hills made up of Tertiary strata, which are known as the Sub-Apennine beds. Part of these is of Miocene age, part is Older Pliocene, and a portion is Newer Pliocene. The Older Pliocene portion of the Sub-Apennines consists of blue or brown marls, which sometimes attain a thickness of 2000 feet.

3. In the valley of the Arno, above Florence, are both Older and Newer Pliocene strata. The former consist of blue clays and lignites, with an abundance of plants. The latter consist of sands and conglomerates, with remains of large Carnivorous Mammals, Mastodon, Elephant, Rhinoceros, Hippopotamus, &c.

4. In Sicily, Newer Pliocene strata are probably more largely developed than anywhere else in the world, rising sometimes to a height of 3000 feet above the sea. The series consists of clays, marls, sands, and conglomerates, capped by a compact limestone, which attains a thickness of from 700 to 800 feet. The fossils of these beds belong almost entirely to living species, one of the commonest being the Great Scallop of the Mediterranean (Pecten Jacoboeus).

5. Occupying an extensive area round the Caspian, Aral, and Azof Seas, are Pliocene deposits known as the "Aralo-Caspian" beds. The fossils in these beds are partly freshwater, partly marine, and partly intermediate in character, and they are in great part identical with species now inhabiting the Caspian. The entire formation appears to indicate the former existence of a great sheet of brackish water, forming an inland sea, like the Caspian, but as large as, or larger than, the Mediterranean.

6. In the United States, strata of Pliocene age are found in North and South Carolina. They consist of sands and clays, with numerous fossils, chiefly Molluscs and Echinoderms. From 40 to 60 per cent of the fossils belong to existing species. On the Loup Fork of the river Platte, in the Upper Missouri region, are strata which are also believed to be referable to the Pliocene period, and probably to its upper division. They are from 300 to 400 feet thick, and contain land-shells, with the bones of numerous Mammals, such as Camels, Rhinoceroses, Mastodons, Elephants, the Horse, Stag, &c.

As regards the life of the Pliocene period, there are only two classes of organisms to which our attention need be directed—namely, the Shell-fish and the Mammals. So far as the former are concerned, we have to note in the first place that the introduction of new species of animals upon the globe went on rapidly during this period. In the Older Pliocene deposits, the number of shells of existing species is only from 40 to 60 per cent; but in the Newer Pliocene the proportion of living forms rises to as much as from 80 to 95 per cent. Whilst the Molluscs thus become rapidly modernised, the Mammals still all belong to extinct species, though modern generic types gradually supersede the more antiquated forms of the Miocene. In the second place, there is good evidence to show that the Pliocene period was one in which the climate of the northern hemisphere underwent a gradual refrigeration. In the Miocene period, there is evidence to show that Europe possessed a climate very similar to that now enjoyed by the Southern United States, and certainly very much warmer than it is at present. The presence of Palm-trees upon the land, and of numerous large Cowries, Cones, and other shells of warm regions in the sea, sufficiently proves this. In the Older Pliocene deposits, on the other hand, northern forms predominate amongst the Shells, though some of the types of hotter regions still survive. In the Newer Pliocene, again, the Molluscs are such as almost exclusively inhabit the seas of temperate or even cold regions; whilst if we regard deposits like the "Bridlington Crag" and "Chillesford beds" as truly referable to this period, we meet at the close of this period with shells such as nowadays are distinctively characteristic of high latitudes. It might be thought that the occurrence of Quadrupeds such as the Elephant, Rhinoceros, and Hippopotamus, would militate against this generalisation, and would rather support the view that the climate of Europe and the United States must have been a hot one during the later portion of the Pliocene period. We have, however, reason to believe that many of these extinct Mammals were more abundantly furnished with hair, and more adapted to withstand a cool temperature, than any of their living congeners. We have also to recollect that many of these large herbivorous quadrupeds may have been, and indeed probably were, more or less migratory in their habits; and that whilst the winters of the later portion of the Pliocene period were cold, the summers might have been very hot. This would allow of a northward migration of such terrestrial animals during the summer-time, when there would be an ample supply of food and a suitably high temperature, and a southward recession towards the approach of winter.