sequent formations: but the mere fact of writing in England should not make us postpone to that place an order of beings. which we find earlier in another portion of what, geologically, may be regarded as but one great zoological province. These animals, called collectively Enaliosauria, or Marine Saurians, abounded throughout a long period of the earth's history, while mammalian life was yet hardly developed; but they disappeared in what we shall have to speak of as the Cretaceous Era. The Ichthyosaur, of which ten species have been distinguished, was an

FIG. 42.

Skeleton of Ichthyosaurus.

animal of marine habits and great bulk (reaching about thirty feet in length), in which to the form of the fish there were united, in a remarkable way, characters of animals higher in the scale. A body, framed upon a purely piscine vertebral column, containing a huge voracious stomach, and terminating in a vertically expanded tail, in which respect it also preserved the fish character, was furnished with the head of a crocodile, and four fins approximating to the character of the paddles of the whale, but composed of a greater number of bones, and thus showing an affinity to the fins of fishes. Over all was a skin resembling that of the cetaceous animals. Nor should it be omitted that the sternum or breastbone presents a structure resembling that of the ornithorhynchus or duck-rat of Australia. The vast jaws of this animal having a stretch of seven feet; its eye resting in a socket eighteen inches in diameter, and defended by an apparatus of bony plates, like that of a bird of prey; the powerful range of teeth, and the position of the breathing apertures near the extremity of the snout; all speak to the naturalist of ferocious habits like those of the modern crocodile, to which the Ichthyosaur may be con

sidered as a link from the predaceous fish. A curious light has been thrown upon these habits by the pellets voided by the animal, which have been found in great quantities in a fossilized state (coprolites). In these we find fragments not only of fish, but of reptiles, arguing that the animal must have been a destructive creature both to its own class and to that below it.

The genus next in importance is the Plesiosaurus, so called as being nearer to the Saurian character. This animal was under eighteen feet long, and altogether a feebler creature than the

Ichthyosaur, which seems to have made it a prey. Yet it was itself one of the destructive potentates of the early seas. A body, generally fish-like, though framed on vertebræ presenting less concave ends, and which terminated in a short tail, serving only

as a rudder, was furnished with a long neck and small head, together with four slender paddles, more cetacean than those of the Ichthyosaur. Moving, like that animal, quickly in the water, by means of the special organs designed for the purpose, the Plesiosaur would have a further advantage in its long, flexible, serpent-like neck; but the small size of the head, though there we find the same superior arrangement of teeth seen in the thecodonts, must have rendered it a much less formidable creature than that last described. Professor Owen regards it as fitted to live near shores and to ascend estuaries.

The attention of the geologists of the United States has been called to certain footmarks in the sandstone of the valleys of Connecticut (Fig. 32), indicative, as they think, of birds of the orders Grallatores (waders) and Rasores (scrapers). "The footsteps appear in regular succession on the continuous track of an animal, in the act of walking or running, with the right and left

foot always in their relative places. The distance of the intervals between each footstep on the same track is occasionally varied, but to no greater amount than may be explained by the bird having

altered its pace. Many tracks of different individuals and different species are often found crossing each other, and crowded, like impressions of feet upon the shores of a muddy stream, where ducks and geese resort. Some of these prints indicate small animals, but others denote birds of what would now be an unusually large size, one having a foot fifteen inches in length, and a stride of from four to six feet. There are anomalies in the forms of some of the feet; but their being the vestiges of birds has for some years been generally admitted. There is, however, some uncertainty regarding the date of the rocks which present these memorials, for the phenomena of superposition only denote their being between the carboniferous and cretaceous formations, and an exact place is assigned them, merely upon the strength of the discovery that they present fish of certain genera never found above the Triassic series. Along with distinctly ornithic footmarks are those of the Labyrinthodont. Altogether, above thirty species of Triassic birds are made out from these tracings by American geologists."

OOLITE.

The chronicles of this period consist of a series of beds, mostly calcareous, taking their general name (Oolite system) from a conspicuous member of them—the oolite-a limestone composed of an aggregation of small round grains or spherules, and so called from its fancied resemblance to a cluster of eggs or the roe of a fish. This texture of stone is novel and striking. It is of chemical origin, each spherule being an aggregation of particles round a central nucleus. The oolite system is largely developed in England, France, Westphalia, and Northern Italy; it appears

1 Dr. Buckland (Bridgwater Treatise), quoting an article by Professor Hitchcock in the American Journal of Science, 1836.

* In 1847, Professor Pleininger, of Stuttgard, published a description of two fossil molar teeth, referred by him to a warm-blooded quadruped, which he obtained from a bone breccia in Würtemburg, occurring between the lias and keuper. He regarded them as the teeth of a predacious mammal. Professor Owen has been unable to recognise the "affinity with any mammalian type, recent or extinct, known to him."

in Northern India and Africa, and patches of it exist in Scotland, and in the vale of the Mississippi. It may of course be yet discovered in many other parts of the world.

The series, as shown in the neighbourhood of Bath, is (beginning with the lowest) as follows: 1. Lias, a set of strata variously composed of limestone, clay, marl, and shale, clay being predominant; 2. Lower oolitic formation, including, besides the great oolitic bed of central England, Fullers'-earth beds, Forest marble, and Cornbrash; 3. Middle oolitic formation, composed of two sub-groups, the Oxford Clay and Coral Rag, the latter being a mere layer of the works of the coral polype; 4. Upper oolitic formation, including what are called Kimmeridge clay and Portland oolite. In Yorkshire there is an additional group above the lias, and in Sutherlandshire there is another group above that again. In the wealds (moorlands) of Kent and Sussex, there is, in like manner, above the fourth of the Bath series, another additional group, to which the name of the Wealden has been given, from its topographical situation, and which, composed of sandstones and clays, is subdivided into Purbeck beds, Hastings sand, and Weald clay.

There are no particular appearances of disturbance between the close of the Trias and the beginning of the Lias and Oolite system, as far as has been observed in England. Yet there is a great change in the materials of the rocks of the two formations, showing that, while the bottoms of the seas of the one period had been chiefly arenaceous, those of the other were chiefly clayey and limy. And there is an equal difference between the two periods in respect of both botany and zoology. While the Permian and Triassic systems, with the single exception of the Muschelkalk, show comparatively scanty traces of life, those in the lias and oolite are extremely abundant, particularly in the department of animals, and more particularly still of sea mollusca. The distinguishing characters of the zoology appear to be uniform over a great space. "In the equivalent deposits in the Himalayan Mountains, at Fernando Po, in the region north of the Cape of Good Hope, and in the Run of Cutch, and other