CHAPTER IX.

THE MESOZOIC AGES (_continued_).

The waters of the Mesozoic period present features quite as remarkable as the land. In our survey of their teeming multitudes, we indeed scarcely know where to begin or whither to turn. Let us look first at the higher or more noble inhabitants of the waters. And here, just as in the case of the greater animals of the land, the Mesozoic was emphatically an age of reptiles. In the modern world the highest animals the sea are mammals, and these belong to three great and somewhat diverse groups. The first is that of the seals and their allies, the walruses, sea-lions, etc. The second is that of the whales and dolphins and porpoises. The third is that of the manatees, or dugongs. All these creatures breathe air, and bring forth their young alive, and nourish them with milk. Yet they all live habitually or constantly in the water. Between these aquatic mammals and the fishes, we have some aquatic reptiles as the turtles, and a few sea-snakes and sea-lizards, and crocodiles; but the number of these is comparatively small, and in the more temperate latitudes there are scarcely any of them.

All this was different in the Mesozoic. In so far as we know, there were no representatives of the seals and whales and their allies, but there were vast numbers of marine reptiles, and many of these of gigantic size. Britain at present does not possess one large reptile, and no marine reptile whatever. In the Mesozoic, in addition to the great Dinosaurs and Pterodactyls of the land, it had at least fifty or sixty species of aquatic reptiles, besides many turtles. Some of these were comparable in size with our modern whales, and armed with tremendous powers of destruction. America is not relatively rich in remains of Mesozoic Saurians, yet while the existing fauna of the temperate parts of North America is nearly destitute of aquatic reptiles, with the exception of the turtles, it can boast, according to Cope's lists, about fifty Mesozoic species, many of them of gigantic size, and the number of known species is increasing every year When it is taken in connection with these statistics, that while we know all the modern species, we know but a small percentage of the fossils, the discrepancy becomes still more startling. Further, from the number of specimens and fragments found, it is obvious that these great aquatic saurians were by no means rare; and that some of the species at least must have been very abundant. Could we have taken our post on the Mesozoic shore, or sailed over its waters, we should have found ourselves in the midst of swarms of these strange, often hideous, and always grotesque creatures.

Let us consider for a little some of the more conspicuous forms, referring to our illustration for their portraits. Every text-book figures the well-known types of the genera _Ichthyosaurus_ and _Plesiosaurus_; we need scarcely, therefore, dwell on them, except to state that the catalogues of British fossils include eleven species of the former genus and eighteen of the latter, We may, however, notice some of the less familiar points of comparison of the two genera. Both were aquatic, and probably marine. Both swam by means of paddles; both were carnivorous, and probably fed principally upon fishes; both were proper reptiles, and breathed air, and had large and capacious lungs. Yet with these points in common, no two animals could have been more different in detail. The Ichthyosaurus had an enormous head, with powerful jaws, furnished with numerous and strong teeth. Its great eyes, strengthened by a circle of bony plates, exceeded in dimensions, and probably in power of vision under water, those of any other animal, recent or fossil. Its neck was short, its trunk massive, with paddles or swimming limbs of comparatively small size, and a long tail, probably furnished with a caudal fin or paddle for propulsion through the water. The Plesiosaur, on the other hand, had a small and delicate head, with slender teeth and small eyes. Its neck, of great length and with numerous joints, resembled the body of a serpent. Its trunk, short, compact, and inflexible, was furnished with large and strong paddles, and its tail was too short to be of any service except for steering. Compared with the Ichthyosaur, it was what the giraffe is to the rhinoceros, or the swan to the porpoise. Two fishermen so variously and differently fitted for their work it would be difficult to imagine. But these differences were obviously related to corresponding differences in food and habit. The Ichthyosaur was fitted to struggle with the waves of the stormy sea, to roll therein like modern whales and grampuses, to seize and devour great fishes, and to dive for them into the depths; and its great armour-plated eyes must have been well adapted for vision in the deeper waters. The Plesiosaur, on the contrary, was fitted for comparatively still and shallow waters; swimming near the surface with its graceful neck curving aloft, it could dart at the smaller fishes on the surface, or stretch its long neck downward in search of those near the bottom. The Ichthyosaurs rolled like porpoises in the surf of the Liassic coral reefs and the waves beyond; the Plesiosaurs careered gracefully in the quiet waters within. Both had their beginning at the same time in the earlier Mesozoic, and both found a common and final grave in its later sediments. Some of the species were of very moderate size, but there were Ichthyosaurs twenty five feet long, and Plesiosaurs at least eighteen feet in length.

Another strange and monstrous group of creatures, the Elasmosaurs and their allies, combined the long neck of Plesiosaurs with the swimming tail of Ichthyosaurs, the latter enormously elongated, so that these Creatures were sometimes fifty feet in length, and whale-like in the dimensions of their bodies. It is curious that these composite creatures belong to a later period of the Mesozoic then the typical Ichthyosaurs and Plesiosaurs, as if the characters at one time separated in these genera had united in their successors.

One of the relatives of the Plesiosaurs, the Pliosaur, of which genus several species of great size are known perhaps realized in the highest degree possible the idea of a huge marine predaceous reptile. The head in some of the species was eight feet in length, armed with conical teeth a foot long. The neck was not only long, but massive and powerful, the paddles, four in number, were six or seven feet in length and must have urged the vast bulk of the animal, perhaps forty feet in extent, through the water with prodigious speed. The capacious chest and great ribs show a powerful heart and lungs. Imagine such a creature raising its huge head twelve feet or more out of water, and rushing after its prey, impelled with perhaps the most powerful oars ever possessed by any animal. We may be thankful that such monsters, more terrible then even the fabled sea-serpent, are unknown in our days. Buckland, I think, at one time indulged in the _jeu d'esprit_ of supposing an Ichthyosaur lecturing on the human skull. "You will at once perceive," said the lecturer, "that the skull before us belonged to one of the lower orders of animals. The teeth are very insignificant, the power of the jaws trifling, and altogether it seems wonderful how the creature could have procured food." We cannot retort on the Ichthyosaur and his contemporaries, for we can see that they were admirably fitted for the work they had in hand; but we can see that had man been so unfortunate as to have lived in their days, he might have been anything but the lord of creation.

But there were sea-serpents as well as other monsters in the Mesozoic seas. Many years ago the Lower Cretaceous beds of St. Peter's Mount, near Maestricht, afforded a skull three feet in length, of massive proportions, and furnished with strong conical teeth, to which the name _Mosasaurus Camperi_ was given. The skull and other parts of the skeleton found with it, were held to indicate a large aquatic reptile, but its precise position in its class was long a subject of dispute. Faujas held it to be a crocodile; Camper, Cuvier, and Owen regarded it as a gigantic lizard. More recently, additional specimens, especially those found in the Cretaceous formations of North America, have thrown new light upon its structure, and have shown it to present a singular combination of the character of serpents, lizards, and of the great sea saurians already referred to. Some parts of the head and the articulation of the jaws, in important points resemble those of serpents, while in other respects the head is that of a gigantic lizard. The body and tail are greatly lengthened out, having more then a hundred vertebral joints, and in one of the larger species attaining the length of eighty feet. The trunk itself is much elongated, and with ribs like those of a snake. There are no walking feet, but a pair of fins or paddles like those of Ichthyosaurus. Cope, who has described these great creatures as they occur in the Cretaceous of the United States, thus sketches the Mosasaur: "It was a long and slender reptile, with a pair of powerful paddles in front, a moderately long neck, and flat pointed head. The very long tail was flat and deep, like that of a great eel, forming a powerful propeller. The arches of the vertebral column were more extensively interlocked then in any other reptiles except the snakes. In the related genus _Clidastes_ this structure is as fully developed as in the serpents, so that we can picture to ourselves its well-known consequences; their rapid progress through the water by lateral undulations, their lithe motions on the land, the rapid stroke, the ready coil, or the elevation of the head and vertebral column, literally a living pillar, towering above the waves or the thickets of the shore swamps." As in serpents, the mouth was wide in its gape, and the lower jaw capable of a certain separation from the skull to admit of swallowing large prey. Besides this the lower jaw had an additional peculiarity, seen in some snakes, namely, a joint in the middle of the jaw enabling its sides to expand, so that the food might be swallowed "between the branches of the jaw." Perhaps no creatures more fully realize in their enormous length and terrible powers the great Tanninim (the stretched-out or extended reptiles) of the fifth day of the Mosaic record, then the Mosasaurus and Elasmosaurus. When Mr. Cope showed me, a few years ago, a nearly complete skeleton of Elasmosaurus, which for want of space he had stretched on a gallery along two sides of a large room, I could not help suggesting to him that the name of the creature should be _Teinosaurus_[AF] instead of that which he had given. Marsh has recently ascertained that the Mosasaurs were covered in part at least with bony scales.

[AF] Heb. _Tanan_; Gr. _Teino_, _Tanuo_; Sansc. _Tanu_; Lat. _Tendo_.--Ges. Lex.

These animals may serve as specimens of the reptilian giants of the Mesozoic seas; but before leaving them we must at least invite attention to the remarkable fact that they were contemporary with species which represent the more common aquatic reptiles of the modern world. In other words, the monsters which we have described existed over and above a far more abundant population of crocodiles and turtles then the modern waters can boast. The crocodiles were represented both in Europe and America by numerous and large species, most of them with long snouts like the modern Gavials, a few with broad heads like those of the alligators. The turtles again presented not only many species, but most of the aquatic subdivisions of the group known in modern times, as for instance the Emydes or ordinary fresh-water forms, the snapping turtles, and the soft-shelled turtles. Cope says that the Cretaceous of New Jersey alone affords twenty species, one of them a snapping turtle six feet in length. Owen records above a dozen large species from the Upper Mesozoic of England, and dates the first appearance of the turtles in England about the time of the Portland stone, or in the upper half of the Mesozoic; but footprints supposed to be those of turtles are found as far back as the Trias. Perhaps no type of modern reptiles is more curiously specialized then these animals, yet we thus find them contemporaneous with many generalized types, and entering into existence perhaps as soon as they. The turtles did not culminate in the Mesozoic, but go on to be represented by more numerous and larger species in the Tertiary and Modern. In the case of the crocodiles, while they attained perhaps a maximum toward the end of the Mesozoic, it was in a peculiar form. The crocodiles of this old time had vertebrae with a hollow at each end like the fishes, or with a projection in the front. At the end of the Mesozoic this was changed, and they assumed a better-knit back, with joints having a ball behind and a socket in front. In the Cretaceous age, species having these two kinds of backbone were contemporaneous. Perhaps this improvement in the crocodilian back had something to do with the persistence of this type after so many others of the sea-lizards of the Mesozoic had passed away.

Of the fishes of the Mesozoic we need only say that they were very abundant, and consisted of sharks and ganoids of various types, until near the close of the period, when the ordinary horny-scaled fishes, such as abound in our present seas, appear to have been introduced. One curious point of difference is that the unequally lobed tail of the Palæozoic fishes is dropped in the case of the greater part of the ganoids, and replaced by the squarely-cut tail prevalent in modern times.

In the sub-kingdom of the Mollusca many important revolutions occurred. Among the lamp-shells a little _Leptaena_, no bigger then a pea, is the last and depauperated representative of a great Palæozoic family. Another, that of the Spirifers, still shows a few species in the Lower Mesozoic. Others, like Rhynchonella, and Terebratula, continue through the period, and extend into the Modern. Passing over the ordinary bivalves and sea-snails, which in the main conform to those of our own time, we find perhaps the most wonderful changes among the relatives of the cuttle-fishes and Nautili. As far back as the Silurian we find the giant Orthoceratites contemporary with Nautili, very like those of the present ocean. With the close of the Palæozoic, however, the Orthoceratites and their allies disappear, while the Nautili continue, and are reinforced by multitudes of new forms of spiral chambered shells, some of them more wonderful and beautiful then any of those which either preceded or followed them. Supreme among these is the great group of the _Ammonites_,--beautifully spiral shells, thin and pearly like the Nautilus, and chambered like it, so as to serve as a float, but far more elaborately constructed, inasmuch as the chambers were not simply curved, but crimped and convoluted, so as to give the outer wall much more effectual support. This outer wall, too, was worked into ornamental ribs and bands, which not only gave it exquisite beauty, but contributed to combine strength to resist pressure with the lightness necessary to a float. In some of these points it is true the Gyroceras and Goniatites of the Palæozoic partially anticipated them, but much less perfectly. The animals which inhabited these shells must have been similar to that of Nautilus, but somewhat different in the proportion of parts. They must have had the same power of rising and sinking in the water, but the mechanical construction of their shells was so much more perfect relatively to this end, that they were probably more active and locomotive then the Nautili. They must have swarmed in the Mesozoic seas, some beds of limestone and shale being filled with them; and as many as eight hundred species of this family are believed to be known, including, however, such forms as the _Baculites_ or straight Ammonites, bearing to them perhaps a relation similar to that of Orthoceras to Nautilus. Further, some of the Ammonites are of gigantic size, one species being three feet in diameter, while others are very minute. The whole family of Ammonitids, which begins to be in force in the Trias, disappears at the end of the Mesozoic, so that this may be called the special age of Ammonites as well as of reptiles.

Further, this time was likewise distinguished by the introduction of true cuttle-fishes, the most remarkable of which were those furnished with the internal supports or "bones," known as _Belemnites_, from a fancied resemblance to javelins or thunder-bolts, a comparison at least as baseless as that often made in England of the Ammonites to fossil snakes. The shell of the Belemnite is a most curious structure. Its usual general shape is a pointed cylinder or elongated cone. At top it has a deep cavity for the reception of certain of the viscera of the animal. Below this is a conical series of chambers, the Phragmacone; and the lower half of the shell is composed of a solid shelly mass or guard, which, in its structure of radiating fibres and concentric layers, resembles a stalactite, or a petrified piece of exogenous wood. This structure was an internal shell or support like those of the modern cuttle-fishes; but it is difficult to account for its peculiarities, so much more complex then in any existing species. The most rational supposition seems to be that it was intended to serve the triple purpose of a support, a float, and a sinker. Unlike the shell of a Nautilus, if thrown into the water it would no doubt have, sunk, and with the pointed end first. Consequently, it was not a float simply, but a float and sinker combined, and its effect must have been to keep the animal at the bottom, with its head upward. The Belemnite was therefore an exceptional cuttle-fish, intended to stand erect on the sea-bottom and probably to dart upward in search of its prey; for the suckers and hooks with which its arms were furnished show that, like other cuttle-fishes, it was carnivorous and predaceous. The guard may have been less ponderous when recent then in the fossil specimens, and in some species it was of small size or slender, and in others it was hollow. Possibly, also, the soft tissues of the animal were not dense, and it may have had swimming fins at the sides. In any case they must have been active creatures, and no doubt could dart backward by expelling water from their gill chamber, while we know that they had ink-bags, provided with that wonderfully divided pigment, inimitable by art, with which the modern Sepia darkens the water to shelter itself from its enemies. The Belemnites must have swarmed in the Mesozoic seas; and as squids and cuttles now afford choice morsels to the larger fishes, so did the Belemnites in their day. There is evidence that even the great sea-lizards did not disdain to feed on them. We can imagine a great shoal of these creatures darting up and down, seizing with their ten hooked arms their finny or crustacean prey. In an instant a great fish or saurian darts down among them; they blacken the water with a thick cloud of inky secretion and disperse on all sides, while their enemy, blindly seizing a few mouthfuls, returns sullenly to the surface. A great number of species of Belemnites and allied animals have been described; but it is probable that in naming them too little regard has been paid to distinctions of age and sex. The Belemnites were for the most part small creatures; but there is evidence that there existed with them some larger and more formidable cuttles; and it is worthy of note that, in several of these, the arms, as in the Belemnites, were furnished with hooks as well as suckers, an exceptional arrangement in their modern allies. It is probable that while the four-gilled or shell-bearing cuttles culminated in size and perfection in the Ammonitids of the Mesozoic, the modern cuttles of the two-gilled and shell-less type are grander in dimensions then their Mesozoic predecessors. It is, however, not a little singular that a group so peculiar and apparently so well provided with means, both of offence and defence, as the Belemnites, should come in and go out with the Mesozoic, and that the Nautiloid group, after attaining to the magnitude and complexity of the great Ammonites, should retreat to a few species of diminutive and simply-constructed Nautili; and in doing so should return to one of the old types dating as far back as the older Palæozoic, and continuing unchanged through all the intervening time.

The Crustaceans of the Mesozoic had lost all the antique peculiarities of the older time, and had so much of the aspect of those of the present day, that an ordinary observer, if he could be shown a quantity of Jurassic or Cretaceous crabs, lobsters, and shrimps, would not readily recognise the difference, which did not exceed what occurs in distant geographical regions in the present day. The same remark may be made as to the corals of the Mesozoic; and with some limitations, as to the star-fishes and sea-urchins, which latter are especially numerous and varied in the Cretaceous age. In short, all the invertebrate forms of life, and the fishes and reptiles among the vertebrates, had already attained their maximum elevation in the Mesozoic; and some of them have subsequently sunk considerably in absolute as well as relative importance.

In the course of the Mesozoic, as indicated in the last chapter, there had been several great depressions and re-elevations of the Continental Areas. But these had been of the same quiet and partial character with those of the Palæozoic, and it was not until the close of the Mesozoic time, in the Cretaceous age, that a great and exceptional subsidence involved for a long period the areas of our present continents in a submergence wider and deeper then any that had previously occurred since the dry land first rose out of the waters.

Every one knows the great chalk beds which appear in the south of England, and which have given its name to the latest age of the Mesozoic. This great deposit of light-coloured and usually soft calcareous matter attains in some places to the enormous thickness of 1,000 feet. Nor is it limited in extent. According to Lyell, its European distribution is from Ireland to the Crimea, a distance of 1,140 geographical miles; and from the south of France to Sweden, a distance of 840 geographical miles. Similar rocks, though not in all cases of the precise nature of chalk, occur extensively in Asia and in Africa, and also in North and South America.

But what is chalk? It was, though one of the most familiar, one of the most inscrutable of rocks, until the microscope revealed its structure. The softer varieties, gently grated or kneaded down in water, or the harder varieties cut in thin slices, show a congeries of microscopic chambered shells belonging to the humble and simple group of Protozoa. These shells and their fragments constitute the material of the ordinary chalk. With these are numerous spicules of sponges and silicious cell-walls of the minute one-celled plants called Diatoms. Further, the flinty matter of these organisms has by the law of molecular attraction been collected into concretions, which are the flints of the chalk. Such a rock is necessarily oceanic; but more then this, it is abyssal. Laborious dredging has shown that similar matter is now being formed only in the deep bed of the ocean, whither no sand or mud is drifted from the land, and where the countless hosts of microscopic shell-bearing protozoa continually drop their little skeletons on the bottom, slowly accumulating a chalky mud or slime. that such a rock should occur over vast areas of the continental plateaus, that both in Europe and America it should be found to cover the tops of hills several thousand feet high, and that its thickness should amount to several hundreds of feet, are facts which evidence a revolution more stupendous perhaps then that at the close of the Palæozoic. For the first time since the Laurentian, the great continental plateaus changed places with the abysses of the ocean, and the successors of the Laurentian Eozoon again reigned on surfaces which through the whole lapse of Palæozoic and Mesozoic time had been separated more or less from that deep ocean out of which they rose at first. This great Cretaceous subsidence was different from the disturbances of the Permian age. There was at first no crumpling of the crust, but merely a slow and long-continued sinking of the land areas, followed, however, by crumpling of the most stupendous character, which led at the close of the Cretaceous and in the earlier Tertiary to the formation of what are now the greatest mountain chains in the world. As examples may be mentioned the Himalaya, the Andes, and the Alps, on all which the deep-sea beds of the Cretaceous are seen at great elevations. In Europe this depression was almost universal, only very limited areas remaining out of water. In America a large tract remained above water in the region of the Appalachians. This gives us some clue to the phenomena. The great Permian collapse led to the crumpling-up of the Appalachians and the Urals, and the older hills of Western Europe. The Cretaceous collapse led to the crumpling of the great N.W. and S.E. chain of the Rocky Mountains and Andes, and to that of the east and west chains of the south of Asia and Europe. The cause was probably in both cases the same; but the crust gave way in a different part, and owing to this there was a greater amount of submergence of our familiar continental plateaus in the Cretaceous then in the Permian.

Another remarkable indication of the nature of the Cretaceous subsidence, is the occurrence of beds filled with grains of the mineral Glauconite or "green-sand." These grains are not properly sand, but little concretions, which form in the bottom of the deep sea, often filling and taking casts of the interior and fine tubes of Foraminiferal shells. Now this Glauconite, a hydrous silicate of iron and potash, is akin to similar materials found filling the pores of fossils in Silurian beds. It is also akin to the Serpentine filling the pores of Eozoon in the Laurentian. Such materials are formed only in the deeper parts of the ocean, and apparently most abundantly where currents of warm water are flowing at the surface, as in the area of the Gulf Stream. Thus, not only in the prevalence of Foraminifera, but in the formation of hydrous silicates, does the Cretaceous recall the Laurentian. Such materials had no doubt been forming, and such animals living in the ocean depths, all through the intervening ages, but with the exception of a few and merely local instances, we know nothing of them, till the great subsidence and re-elevation of the Cretaceous again allows them to ascend to the continental plateaus, and again introduces us to this branch of the world-making process.

The attention recently drawn to these facts by the researches of Dr. Carpenter and others, and especially the similarity in mineral character and organic remains of some of the deposits now forming in the Atlantic and those of the chalk, have caused it to be affirmed that in the bed of the Atlantic these conditions of life and deposit have continued from the Cretaceous up to the present time, or as it has been expressed, that "we are still living in the Cretaceous epoch." Now, this is true or false just as we apply the statement. We have seen that the distinction between abyssal areas, continental oceanic plateaus, and land surfaces has extended through the whole lapse of geological time. In this broad sense we may be said to be still living in the Laurentian epoch. In other words, the whole plan of the earth's development is one and the same, and each class of general condition once introduced is permanent somewhere. But in another important sense we are not living in the Cretaceous epoch; otherwise the present site of London would be a thousand fathoms deep in the ocean; the Ichthyosaurs and Ammonites would be disporting themselves in the water, and the huge Dinosaurs and strange Pterodactyls living on the land. The Italian peasant is still in many important points living in the period of the old Roman Empire. The Arab of the desert remains in the Patriarchal period, and there are some tribes not yet beyond the primitive age of stone. But the world moves, nevertheless, and the era of Victoria is not that of the Plantagenets or of Julius Cæsar. So while we may admit that certain of the conditions of the Cretaceous seas still prevail in the bed of the present ocean, we must maintain that nearly all else is changed, and that the very existence of the partial similarity is of itself the most conclusive proof of the general want of resemblance, and of the thorough character of the changes which have occurred.

The duration of the Cretaceous subsidence must have been very great. We do not know the rate at which the Foraminifera accumulate calcareous mud. In some places, where currents heap up their shells, they may be gathered rapidly; but on the average of the ocean bed, afoot of such material must indicate the lapse of ages very long when compared with those of modern history. We need not wonder, therefore, that while some forms of deep-sea Cretaceous life, especially of the lower grades, seem to have continued to our time, the inhabitants of the shallow waters and the land have perished; and that the Neozoic or Tertiary period introduces us to a new world of living beings. I say we need not wonder; yet there is no reason why we should expect this as a necessary consequence. As the Cretaceous deluge rose over the continents of the Mesozoic, the great sea saurians might have followed. Those of the land might have retreated to the tracts still remaining out of water, and when the dry land again appeared in the earlier Tertiary, they might again have replenished the earth, and we might thus have truly been living in the Reptilian age up to this day. But it was not so. The old world again perished, and the dawn of the Tertiary shows to us at once the dynasties of the Mammalian age, which was to culminate in the introduction of man. With the great Cretaceous subsidence the curtain falls upon the age of reptiles, and when it rises again, after the vast interval occupied in the deposition of the green-sand and chalk, the scene has entirely changed. There are new mountains and new plains, forests of different type, and animals such as no previous age had seen.

How strange and inexplicable is this perishing of types in the geological ages! Some we could well spare. We would not wish to have our coasts infested by terrible sea saurians, or our forests by carnivorous Dinosaurs. Yet why should these tyrants of creation so utterly disappear without waiting for us to make war on them? Other types we mourn. How glorious would the hundreds of species of Ammonites have shone in the cases of our museums, had they still lived! What images of beauty would they have afforded to the poets who have made so much of the comparatively humble Nautilus! How perfectly, too, were they furnished with all those mechanical appliances for their ocean life, which are bestowed only with a niggardly hand on their successors! Nature gives us no explanation of the mystery.

"From scarped cliff and quarried stone, She cries--'A thousand types are gone.'"

But why or how one was taken and another left she is silent, and I believe must continue to be so, because the causes, whether efficient or final, are beyond her sphere. If we wish for a full explanation, we must leave Nature, and ascend to the higher domain of the Spiritual.

CONDENSED TABULAR VIEW OF THE AGES AND PERIODS OF THE MESOZOIC.

Key to Symbols

### Duration of Ammonites and Belemnites. === Ages of Cycads and Pines. --- Beginning of Age of Angiospermous Exogens. +++ "And God created great reptiles, and every living moving thing which the waters brought forth abundantly, and every flying creature after its kind."

Time. Ages. Periods. Animals and Plants.

MESOZOIC.

Cretaceous {Newer.{Maestricht beds; Fox Hill # - + { {and Pierre Groups of # - + { {Western America; Greensand # - + { {of New Jersey. # - + { # - + {Middle.{Chalk; Benton and Dakota # Close of - + { {Groups of Western America. # Reptilian - + { # Ages. - + {Older.{Lower Greensand and Gault; # - + { {Lower Clays of New Jersey # + { {and Alabama. # + # + Upper {N. Purbeck Beds. }Jurassic # Culmination + Jurassic {M. Portland Limestone. } Beds of # of + {O. Portland Sandstone. }Nebraska # Reptilian + } and # Ages. + Middle {N. Kimmeridge Clay, etc.}Colorado.# = + Jurassic {M. Coralline Limestone. } # = + {O. Calcareous Grit & } # = + { Oxford Clay. } # = + # = + Lower {N. Cornbrash & Forest } Lower # = + Jurassic { Marble. }Jurassic # = + {M. Great & Inferior } of # = + { Oolites., etc. } Utah, # = + {O. Lias Clay and }Nevada, # = + { Limestone. } etc. = + = + {N. Keuper {Upper Triassic Appearance of = + { Sandstone, {Sandstones of Mammals = + { etc. {Prince Edward I., and = + {M. Muschelkalk.{Connecticut, etc. Birds. + Triassic { + {O. Bunter {Lower Triassic Beginning of + { Sandstone. {Sandstones of Reptilian + { {Prince Edward I., Ages. + { {Connecticut, etc. +