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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 exists any animal in our waters, not yet known to naturalists, answering to the descriptions of the "Sea - Serpent," it must be closely allied to the PlesiosauThe 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.

rus.

Of all these strange old forms, so singularly uniting features of Fishes and Reptiles, 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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But, notwithstanding this difference, the hand of the Pterodactylus is constructed like that of an aquatic swimming marine Reptile; and I believe, that, if we represent it with its long neck stretched upon the water, its large head furnished with powerful, well-armed jaws, ready to dive after the innumerable smaller animals living in the same ocean, we shall have a more natural picture of its habits than if we consider it as a flying animal, which it is generally supposed to have been. It has not the powerful breast-bone, with the large projecting keel along the middle line, such as exists in all the flying animals. Its breast-bone, on the contrary, is thin and flat, like that of the present Sea-Turtle; and if it moved through the water by the help of its long flappers, as the Sea-Turtle does now, it could well dispense with that powerful construction of the breast-bone so essential to all animals which fly through the air. Again, the powerful teeth, long and conical, placed at considerable intervals in the jaw, constitute a feature common to all predaceous aquatic animals, and would seem to have been utterly useless in a flying animal at that time, since there were no aërial beings of any size to prey upon. The Dragon-Flies found in the same deposits with the Pterodactylus were certainly not a game requiring so powerful a battery of attack.

The Fishes of the Jurassic sea were exceedingly numerous, but were all of the Ganoid and Selachian tribes. It would weary the reader, were I to introduce here any detailed description of them, but they were as numerous and varied as those living in our present waters. There was the Hybodus, with the marked furrows on the spines and the strong hooks along their margin, — the huge Chimera, with its long whip, its curved bone over the back, and its parrot-like bill, the Lepidotus, with its large square scales, its large head, its numerous rows of teeth, one within another, forming a powerful grinding apparatus, the Microdon, with its round, flat body, its jaw paved with small grind

ing teeth, the swift Aspidorhynchus, with its long, slender body and massive tail, enabling it to strike the water powerfully and dart forward with great rapidity. There were also a host of small Fishes, comparing with those above mentioned as our Perch, Herring, Smelts, etc., compare with our larger Fishes; but, whatever their size or form, all the Fishes of those days had the same hard scales fitting to each other by hooks, instead of the thin membranous scales overlapping each other at the edge, like the common Fishes of more modern times. The smaller Fishes, no doubt, afforded food to the larger ones, and to the aquatic Reptiles. Indeed, in parts of the intestines of the Ichthyosauri, and in their petrified excrements, have been found the scales and teeth of these smaller Fishes perfectly preserved. It is amazing that we can learn so much of the habits of life of these past creatures, and know even what was the food of animals existing countless ages before man was created.

There are traces of Mammalia in the Jurassic deposits, but they were of those inferior kinds known now as Marsupials, and no complete specimens have yet been found.

The Articulates were largely represented in this epoch. There were already in the vegetation a number of Gymnosperms, affording more favorable nourishment for Insects than the forests of earlier times; and we accordingly find that class in larger numbers than ever before, though still meagre in comparison with its present representation. Crustacea were numerous, those of the Shrimp and Lobster kinds prevailing, though in some of the Lobsters we have the first advance towards the highest class of Crustacea in the expansion of the transverse diameter now so characteristic of the Crabs. Among Mollusks we have a host of gigantic Ammonites; and the naked Cephalopods, which were in later times to become the prominent representatives of that class, already begin to make their appearance. Among Radiates, some of the higher kinds of Echinoderms, the

Ophiurans and Echinoids, take the place of the Crinoids, and the Acalephian Corals give way to the Astræan and Meandrina-like types, resembling the ReefBuilders of the present time.

I have spoken especially of the inhabitants of the Jurassic sea lying between England and France, because it was there that were first found the remains of some of the most remarkable and largest Jurassic animals. But wherever these deposits have been investigated, the remains contained in them reveal the same organic character, though, of course, we find the land Reptiles only where there happen to have been marshes, the aquatic Saurians wherever large estuaries or bays gave them an opportunity of coming in near shore, so that their bones were preserved in the accumulations of mud or clay constantly collecting in such localities, the Crustacea, Shells, or SeaUrchins on the old sea-beaches, the Corals in the neighborhood of coral reefs, and so on. In short, the distribution of animals then as now was in accordance with their nature and habits, and we shall seek vainly for them in the localities where they did not belong.

But when I say that the character of the Jurassic animals is the same, I mean, that, wherever a Jurassic sea-shore occurs, be it in France, Germany, England, or elsewhere throughout the world, the Shells, Crustacea, or other animals found upon it have a special character, and are not to be confounded by any one thoroughly acquainted with these fossils with the Shells or Crustacea of any preceding or subsequent time,-that, where a Jurassic marsh exists, the land Reptiles inhabiting it are Jurassic, and neither Triassic nor Cretaceous, that a Jurassic coral reef is built of Corals belonging as distinctly to the Jurassic creation as the Corals on the Florida reefs belong to the present creation, that, where some Jurassic bay or inlet is disclosed to us with the Fishes anciently inhabiting it, they are as characteristic of their time as are the Fishes of Massachusetts Bay now.

And not only so, but, while this unity of creation prevails throughout the entire epoch as a whole, there is the same variety of geographical distribution, the same circumscription of fauna within distinct zoological provinces, as at the present time. The Fishes of Massachusetts Bay are not the same as those of Chesapeake Bay, nor those of Chesapeake Bay the same as those of Pamlico Sound, nor those of Pamlico Sound the same as those of the Florida coast. This division of the surface of the earth into given areas within which certain combinations of animals and plants are confined is not peculiar to the present creation, but has prevailed in all times, though with ever-increasing diversity, as the surface of the earth itself assumed a greater variety of climatic conditions. D'Orbigny and others were mistaken in assuming that faunal differences have been introduced only in the last geological epochs. Besides these adjoining zoological faunæ, each epoch is divided, as we have seen, into a number of periods, occupying successive levels one above another, and differing specifically from each other in time as zoological provinces differ from each other in space. In short, every epoch is to be looked upon from two points of view: as a unit, complete in itself, having one character throughout, and as a stage in the progressive history of the world, forming part of an organic whole.

As the Jurassic epoch was ushered in by the upheaval of the Jura, so its close was marked by the upheaval of that system of mountains called the Côte d'Or. With this latter upheaval began the Cretaceous epoch, which we will examine with special reference to its subdivision into periods, since the periods in this epoch have been clearly distinguished, and investigated with especial care. I have alluded in the preceding article to the immediate contact of the Jurassic and Cretaceous epochs in Switzerland, affording peculiar facilities for the direct comparison of their organic remains. But

the Cretaceous deposits are well known, not only in this inland sea of ancient Switzerland, but in a number of European basins, in France, in the Pyrenees, on the Mediterranean shores, and also in Syria, Egypt, India, and Southern Africa, as well as on our own continent. In all these localities, the Cretaceous remains, like those of the Jurassic epoch, have one organic character, distinct and unique. This fact is especially significant, because the contact of their respective deposits is in many localities so immediate and continuous that it affords an admirable test for the development-theory. If this is the true mode of origin of animals, those of the later Jurassic beds must be the progenitors of those of the earlier Cretaceous deposits. Let us see now how far this agrees with our knowledge of the physiological laws of development.

Take first the class of Fishes. We have seen that in the Jurassic periods there were none of our common Fishes, none corresponding to our Herring, Pickerel, Mackerel, and the like,no Fishes, in short, with thin membranous scales, but that the class was represented exclusively by those with hard, flint-like scales. In the Cretaceous epoch, however, we come suddenly upon a horde of Fishes corresponding to our smaller common Fishes of the Pickerel and Herring tribes, but principally of the kinds found now in tropical waters; there are none like our Cods, Haddocks, etc., such as are found at present in the colder seas. The Fishes of the Jurassic epoch corresponding to our Sharks and Skates and Gar-Pikes still exist, but in much smaller proportion, while these more modern kinds are very numerous. Indeed, a classification of the Cretaceous Fishes would correspond very nearly to one founded on those now living. Shall we, then, suppose that the large reptilian Fishes of the Jurassic time began suddenly to lay numerous broods of these smaller, more modern, scaly Fishes? And shall we account for the diminution of the previous forms by supposing that in order to give a fair chance to the new kinds they brought

them forth in large numbers, while they reproduced their own kind less abundantly? According to very careful estimates, if we accept this view, the progeny of the Jurassic Fishes must have borne a proportion of about ninety per cent. of entirely new types to some ten per cent. of those resembling the parents. One would like a fact or two on which to rest so very extraordinary a reversal of all known physiological laws of reproduction, but, unhappily, there is not one.

Still more unaccountable, upon any theory of development according to ordinary laws of reproduction, are those unique, isolated types limited to a single epoch, or sometimes even to a single period. There are some very remarkable instances of this in the Cretaceous deposits. To make my statement clearer, I will say a word of the sequence of these deposits and their division into periods.

These Cretaceous beds were at first divided only into three sets, called the Neocomian, or lower deposits, the GreenSands, or middle deposits, and the Chalk, or upper deposits. The Neocomian, the lower division, was afterwards subdivided into three sets of beds, called the Lower, Middle, and Upper Neocomian by some geologists, the Valengian, Neocomian, and Urgonian by others. These three periods are not only traced in immediate succession, one above another, in the transverse cut before described, across the mountain of Chaumont, near Neufchâtel, but they are also traced almost on one level along the plain at the foot of the Jura. It is evident that by some disturbance of the surface the eastern end of the range was raised slightly, lifting the lower or Valengian deposits out of the water, so that they remain uncovered, and the next set of deposits, the Neocomian, is accumulated along their base, while these in their turn are slightly raised, and the Urgonian beds are accumulated against them a little lower down. They follow each other from east to west in a narrower area, just as the Azoic, Silurian, and Devonian deposits follow each other from north to south in

the northern part of the United States. The Cretaceous deposits have been intimately studied in various localities by different geologists, and are now subdivided into at least ten, or it may be fifteen or sixteen distinct periods, as they stand at present. This is, however, but the beginning of the work; and the recent investigations of the French geologist, Coquand, indicate that several of these periods at least are susceptible of further subdivision. I present here a table enumerating the periods of the Cretaceous epoch best known at present, in their sequence, because I want to show how sharply and in how arbitrary a manner, if I may so express it, new forms are introduced. The names are simply derived from the localities, or from some circumstances connected with the locality where each period has been studied.

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Rudistes are found suddenly in the Urgonian deposits; there are none in the two preceding sets of beds; they disappear in the three following periods, and reappear again in great numbers in the Cenomanian, Turonian, and Senonian periods, and disappear again in the succeeding one. These can hardly be missed from any negligence or oversight in the examination of these deposits, for they are by no means rare. They are found always in great numbers, occupying crowded beds, like Oysters in the present time. So numerous are they, where they occur at all, that the deposits containing them are called by many naturalists the first, second, third, and fourth bank of Rudistes. Which of the ordinary Bivalves, then, gave rise to this very remarkable form in the class, allowed it to die out, and revived it again at various intervals? This is by no means the only instance of the same kind. There are a number of types making their appearance suddenly, lasting during one period or during a succession of periods, and then disappearing forever, while others, like the Rudistes, come in, vanish, and reappear at a later time.

I am well aware that the advocates of the development-theory do not state their views as I have here presented them. On the contrary, they protest against any idea of sudden, violent, abrupt changes, and maintain that by slow and imperceptible modifications during immense periods of time these new types have been introduced without involving any infringement of the ordinary processes of development; and they account for the entire absence of corroborative facts in the past history of animals by what they call the "imperfection of the geological record." Now, while I admit that our knowledge of geology is still very incomplete, I assert that just where the direct sequence of geological deposits is needed for this evidence, we have it. The Jurassic beds, without a single modern scaly Fish, are in immediate contact with the Cretaceous beds, in which the Fishes of that kind are proportionately

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