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Belgium and the Bohemian island. Thus the land slowly gained upon the Triassic ocean, shutting it within ever-narrowing limits, and preparing the large inland seas so characteristic of the later Secondary times. The character of the organic world still retained a general resemblance to that of the Carboniferous epoch. Among Radiates, the Corals were more nearly allied to those of the earlier ages than to those of modern times, and Crinoids abounded still, though some of the higher Echinoderm types were already introduced. Among Mollusks, the lower Bivalves, that is, the Brachiopods and Bryozoa, still prevailed, while Ammonites continued to be very numerous, differing from the earlier ones chiefly in the everincreasing complications of their inner partitions, which become so deeply involuted and cut upon their margins, before the type disappears, as to make an intricate tracery of very various patterns on the surface of these shells. The most conspicuous type of Articulates continues as before to be that of Crustacea; but Trilobites have finished their career, and the Lobster-like Crustacea make their appearance for the first time. It does not seem that the class of Insects has greatly increased since the Carboniferous epoch; and Worms are still as difficult to trace as ever, being chiefly known by the cases in which they sheltered themselves. Among Vertebrates, the Fishes still resemble those of the Carboniferous epoch, belonging principally to the Sclachians and Ganoids. They have, however, approached somewhat toward a modern pattern, the lobes of the tail being more evenly cut, and their general outline more like that of common fishes. The gigantic marsh Reptiles have become far more numerous and various. They continue through several epochs, but may be said to reach their culminating point in the Jurassic and Cretaceous deposits.

I cannot pass over the Triassic epoch without some allusion to the so-called bird-tracks, so generally believed to mark the introduction of Birds at this time. It is true that in the deposits of the Trias

there have been found many traces of footsteps, indicating a vast number of animals which, except for these footprints, remain unknown to us. In the sandstone of the Connecticut Valley they are found in extraordinary numbers, as if these animals, whatever they were, had been in the habit of frequenting that shore. They appear to have been very diversified; for some of the tracks are very large, others quite small, while some would seem, from the way in which the footsteps follow each other, to have been quadrupedal, and others bipedal. We can even measure the length of their strides, following the impressions which, from their succession in a continuous line, mark the walk of a single animal. The fact that we find these footprints without any bones or other remains to indicate the animals by which they were made is accounted for by the mode of deposition of the sandstone. It is very unfavorable for the preservation of bones; but, being composed of minute sand mixed with mud, it affords an admirable substance for the reception of these impressions, which have been thus cast in a mould, as it were, and preserved through ages.

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These animals must have been large, when full-grown, for we find strides measuring six feet between, evidently belonging to the same animal. In the quadrupedal tracks, the front feet seem to have been smaller than the hind ones. Some of the tracks show four toes all turned forward, while in others three toes are turned forward and one backward. happened that the first tracks found belonged to the latter class; and they very naturally gave rise to the idea that these impressions were made by birds, on account of this formation of the foot. This, however, is a mere inference; and since the inductive method is the only true one in science, it seems to me that we should turn to the facts we have in our possession for the explanation of these mysterious footprints, rather than endeavor to supply

For all details respecting these tracks see Hitchcock's Ichnology of New England. Boston, 1858. 4to.

by assumption those which we have not. As there are no bones found in connection with these tracks, the only way to arrive at their true character, in the present state of our knowledge, is by comparing them with bones found in other localities in the deposits of the same period in the world's history. Now there have never been found in the Trias any remains of Birds, while it contains innumerable bones of Reptiles; and therefore I think that it is in the latter class that we shall eventually find the solution of this mystery.

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It is true that the bones of the Triassic Reptiles are scattered and disconnected; no complete skeleton has yet been discovered, nor has any foot been found; so that no direct comparison can be made with the steps. It is, however, my belief, from all we know of the character of the Animal Kingdom in those days, that these animals were reptilian, but combined, like so many of the early types, characters of their own class with those of higher animals yet to come. It seems to me probable, that, in those tracks where one toe is turned backward, the impression is made not by a toe, but by a heel, or by a long sole projecting backward; for it is not pointed, like those of the front toes, but is blunt. It is true that there is a division of joints in the toes, which seems in favor of the idea that they were those of Birds; for when the three toes are turned forward, there are two joints on the inner one, three on the middle, and four on the outer one, as in Birds. But this feature is not peculiar to Birds; it is found in Turtles also. The correspondence of these footprints with each other leaves no doubt that they were all by one kind of animal; for both the bipedal and the quadrupedal tracks have the same character. The only quadrupedal animals now known to us which walk on two legs are the Kangaroos. They raise themselves on their hind legs, using the front ones to bring their food to their mouth. They leap with the hind legs, sometimes bringing down their front feet

See the Investigations of Hermann von Meyer on Triassic Reptiles.

to steady themselves after the spring, and making use also of their tails, to balance the body after leaping. In these tracks we find traces of a tail between the feet. I do not bring this forward as any evidence that these animals were allied to Kangaroos, since I believe that nothing is more injurious in science than assumptions which do not rest on a broad basis of facts; but I wish only to show that these tracks recall other animals besides Birds, with which they have been universally associated. And seeing, as we do, that so many of the early types prophesy future forms, it seems not improbable that they may have belonged to animals which combined with reptilian characters some birdlike features, and also some features of the earliest and lowest group of Mammalia, the Marsupials. To sum up my opinion respecting these footmarks, I believe that they were made by animals of a prophetic type, belonging to the class of Reptiles, and exhibiting many synthetic characters.

The more closely we study past creations, the more impressive and significant do the synthetic types, presenting features of the higher classes under the guise of the lower ones, become. They hold the promise of the future. As the opening overture of an opera contains all the musical elements to be therein developed, so this living prelude of the Creative work comprises all the organic elements to be successively developed in the course of time. When Cuvier first saw the teeth of a Wealden Reptile, he pronounced them to be those of a Rhinoceros, so mammalian were they in their character. So, when Sommering first saw the remains of a Jurassic Pterodactyl, he pronounced them to be those of a Bird. These mistakes were not due to a superficial judgment in men who knew Nature so well, but to this prophetic character in the early types themselves, in which features were united never known to exist together in our days.

The Jurassic epoch, next in succession, was a very important one in the history

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of Europe. It completed the junction of several of the larger islands, filling the channel between the central plateau of France and the Belgian island, as well as that between the former and the island of Bretagne, so that France was now a sort of crescent of land holding a Jurassic sea in its centre, Bretagne and Belgium forming the two horns. This Jurassic basin or inland sea united England and France, and it may not be amiss to say a word here of its subsequent transformations. During the long succession of Jurassic periods, the deposits of that epoch, chiefly limestone and clays, with here and there a bed of sand, were accumulated at its bottom. Upon these followed the chalk deposits of the Cretaceous epoch, until the basin was gradually filled, and partially, at least, turned to dry land. But at the close of the Cretaceous epoch a fissure was formed, allowing the entrance of the sea at the western end, so that the constant washing of the tides and storms wore away the lower, softer deposits, leaving the overhanging chalk cliffs unsupported. These latter, as their supports were undermined, crumbled down, thus widening the channel gradually. This process must, of course, have gone on more rapidly at the western end, where the sea rushed on with most force, till the channel was worn through to the German Ocean on the other side, and the sea then began to act with like power at both ends of the channel. explains its form, wider at the western end, narrower between Dover and Calais, and widening again at the eastern extremity. This ancient basin, extending from the centre of France into England, is rich in the remains of a number of successive epochs. Around its margin we find the Jurassic deposits, showing that there must have been some changes of level which raised the shores and prevented later accumulations from covering them, while in the centre the Jurassic deposits are concealed by those of the Cretaceous epoch above them, these being also partially hidden under

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the later Tertiary beds. Let us see, then, what this inland sea has to tell us of the organic world in the Jurassic epoch.

At that time the region where LymeRegis is now situated in modern England was an estuary on the shore of that ancient sea. About forty years ago a discovery of large and curious bones, belonging to some animal unknown to the scientific world, turned the attention of naturalists to this locality, and since then such a quantity and variety of such remains have been found in that neighborhood as to show that the Sharks, Whales, Porpoises, etc., of the present ocean are not more numerous and diversified than were the inhabitants of this old bay or inlet. Among these animals, the Ichthyosauri (Fish-Lizards) form one of the best-known and most prominent groups. They are chiefly found in the Lias, the lowest set of beds of the Jurassic deposits, and seem to have come in with the close of the Triassic epoch. It is greatly to be regretted that all that is known of the Triassic Reptiles antecedent to the Ichthyosauri still remains in the form of original papers, and is not yet embodied in text-books. They are quite as interesting, as curious, and as diversified as those of the Jurassic epoch, which are, however, much more extensively known, on account of the large collections of these animals belonging to the British Museum. It will be more easy to understand the structural relations of the latter, and their true position in the Animal Kingdom, when those which preceded them are better understood. One of the most remarkable and numerous of these Triassic Reptiles seems to have been an animal resembling, in the form of the head, and in the two articulating surfaces at the juncture of the head with the backbone, the Frogs and Salamanders, though its teeth are like those of a Crocodile. As yet nothing has been found of these animals except the head, neither the backbone nor the limbs; so that little is known of their general structure.

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contain a number of conical teeth, of reptilian form and character; the eyeball was very large, as may be seen by the socket, and it was supported by pieces of bone, such as we find now only in the eyes of birds of prey and in the bony fishes. The ribs begin at the neck and continue to the tail, and there is no distinction between head and neck, as in most Reptiles, but a continuous outline, as in Fishes. They had four limbs, not divided into fingers, but forming mere paddles. Yet fingers seem to be hinted at in these paddles, though not developed, for the bones are in parallei rows, as if to mark what might be such a division. The back-bones are short, but very high, and the surfaces of articulation are hollow, conical cavities, as in Fishes, instead of ball-and-socket joints, as in Reptiles. The ribs are more complicated than in Vertebrates generally:

they consist of several pieces, and the breast-bone is formed of a number of bones, making together quite an intricate bony net-work. There is only one living animal, the Crocodile, characterized by this peculiar structure of the breastbone. The Ichthyosaurus is, indeed, one of the most remarkable of the synthetic types: by the shape of its head one would associate it with the Porpoises, while by its paddles and its long tail it reminds one of the whole group of Cetaceans to which the Porpoises belong; by its crocodilian teeth, its ribs, and its breast-bone, it seems allied to Reptiles; and by its uniform neck, not distinguished from the body, and the structure of the back-bone, it recalls the Fishes.

Another most curious na mber of this group is the Plesiosaurus, odd Saurian (Figure 2). By its disproportionately long and flexible neck, and its small, flat

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head, it unquestionably foreshadows the Serpents, while by the structure of the back-bone, the limbs, and the tail, it is closely allied with the Ichthyosaurus. Its flappers are, however, more slender, less clumsy, and were, no doubt, adapted to more rapid motion than the fins of the Ichthyosaurus, while its tail is shorter in proportion to the whole length of the animal. It seems probable, from its general structure, that the Ichthyosaurus moved like a Fish, chiefly by the flapping of the tail, aided by the fins, while in the Plesiosaurus the tail must have been much less efficient as a locomotive organ, and the long, snake-like, flexible neck no doubt rendered the whole body more agile and rapid in its movements. In comparing the two, it may be said, that, as a whole, the Ichthyosaurus, though belonging by

its structure to the class of Reptiles, has a closer external resemblance to the Fishes, while the Plesiosaurus is more decidedly reptilian in character. If there exknown to naturalists, answering to the ists any animal in our waters, not yet descriptions of the "Sea - Serpent," it must be closely allied to the Plesiosaurus. The occurrence in the fresh waters of North America of a Fish, the Lepidosteus, which is closely allied to the fossil Fishes found with the Plesiosaurus in the Jurassic beds, renders such a supposition probable.

gularly uniting features of Fishes and Of all these strange old forms, so sinReptiles, none has given rise to more discussion than the Pterodactylus, (Figure 3,) another of the Saurian tribe, associated, however, with Birds by some nat

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Fig. 3.

uralists, on account of its large winglike appendages. From the extraordinary length of its anterior limbs, they have generally been described as wings, and the animal is usually represented as a flying Reptile. But if we consider its whole structure, this does not seem probable, and I believe it to have been an

VOL. XII.

15

essentially aquatic animal, moving after the fashion of the Sea-Turtle. Its socalled wings resemble in structure the front paddles of the Sea-Turtles far more them, indeed, only by the extraordinary than the wings of a Bird; differing from length of the inner toe, while the outer ones are comparatively much shorter.

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