[AD]This last group is very complex, and might perhaps admit of sub division, locally at least, into subordinate cycles.
[AD]This last group is very complex, and might perhaps admit of sub division, locally at least, into subordinate cycles.
These rocks occupy a large space in England, asthe names above given will serve to show; and they are also largely distributed over the continent of Europe and Asia which had evidently three great and long-continued dips under water, indicated by the three great limestones. In America the case was different. The Jurassic has not been distinctly recognised in any part of the eastern coast of that continent, which then perhaps extended farther into the Atlantic than it does at present; so that no marine beds were formed on its eastern border. But in the west, along the base of the Rocky Mountains and also in the Arctic area, there were Jurassic seas of large extent, swarming with characteristic animals. At the close of the Jurassic period our continents seem to have been even more extensive than at present. In England and the neighbouring parts of the continent of Europe, according to Lyell, the fresh-water and estuarine beds known as the Wealden have been traced 320 miles from west to east, and 200 miles from north-west to south-east, and their thickness in one part of this area is estimated at no less than 2,000 feet. Such a deposit is comparable in extent with the deltas of such great rivers as the Niger or even the Mississippi, and implies the existence of a continent much more extensive and more uniform in drainage than Europe as it at present exists. Lyell even speculates on the possible existence of an Atlantic continent west of Europe. America also at this time had, as already stated, attained to even more than its present extensioneastwards. Thus this later Jurassic period was the culmination of the Mesozoic, the period of its most perfect continental development, corresponding in this to the Carboniferous in the Palæozoic.
The next or closing period of this great Mesozoic time brought a wondrous change. In the Cretaceous period, so called from the vast deposits of chalk by which it is characterized, the continents sunk as they had never sunk before, so that vast spaces of the great continental plateaus were brought down, for the first time since the Laurentian, to the condition of abyssal depths, tenanted by such creatures as live in the deepest recesses of our modern oceans. This great depression affected Europe more severely than America; the depression of the latter being not only less, but somewhat later in date. In Europe, at the period of greatest submergence, the hills of Scandinavia and of Britain, and the Urals, perhaps alone stood out of the sea. The Alps and their related mountains, and even the Himalayas, were not yet born, for they have on their high summits deep-sea beds of the Cretaceous and even of later date. In America, the Appalachians and the old Laurentian ranges remained above water; but the Rocky Mountains and the Andes were in great part submerged, and a great Cretaceous sea extended from the Appalachians westward to the Pacific, and southward to the Gulf of Mexico, opening probably to the North into the Arctic Ocean.
This great depression must have been of very long continuance, since in Western Europe it sufficed forthe production of nearly 1,000 feet in thickness of chalk, a rock which, being composed almost entirely of microscopic shells, is, as we shall see in the sequel, necessarily of extremely slow growth. If we regard the Cretaceous group as one of our great ages or cycles, it seems to be incomplete. The sandstones and clays known as the Greensand and Gault constitute its lower or shallow-water member. The chalk is its middle or deep-sea member, but the upper shallow-water member is missing, or only very locally and imperfectly developed. And the oldest of the succeeding Tertiary deposits, which indicate much less continuous marine conditions, rest on the chalk, as if the great and deep sea of the Cretaceous age had been suddenly upheaved into land. This abrupt termination of the last cycle of the Mesozoic is obviously the reason of the otherwise inexplicable fact that the prevalent life of the period ceases at the top of the chalk, and is exchanged immediately and without any transition for the very different fauna of the Tertiary. This further accords with the fact that the Cretaceous subsidence ended in another great crumpling of the crust, like that which distinguished the Permian. By this the Mesozoic time was terminated and the Cainozoic inaugurated; while the Rocky Mountains, the Andes, the Alps, and the Himalayas, rose to importance as great mountain ranges, and the continents were again braced up to retain a condition of comparative equilibrium during that later period of the earth’s chronology to which we ourselves belong.
LIFE ON LAND IN THE MESOZOIC PERIOD.In the foreground are a Pine, Cycads, and a Pandanus; also small Mammals, an herbivorous Dinosaur, and a Labyrinthodont. In the distance are other Dinosaurs and Crocodiles. In the air are birds (Archæopterux) and Pterodactyls.
LIFE ON LAND IN THE MESOZOIC PERIOD.
In the foreground are a Pine, Cycads, and a Pandanus; also small Mammals, an herbivorous Dinosaur, and a Labyrinthodont. In the distance are other Dinosaurs and Crocodiles. In the air are birds (Archæopterux) and Pterodactyls.
Was the length of the Mesozoic time equal to that of the Palæozoic? Measured by recurring cycles it was. In the latter period we find five great cycles, from the Lower Silurian to the Permian inclusive. So in the Mesozoic we have five also, from the Trias to the Cretaceous inclusive. We have a right to reckon these cycles as ages or great years of the earth; and so reckoning them, the Mesozoic time may have been as long as the Palæozoic. But if we take another criterion the result will be different. The thickness of the deposits in the Palæozoic as compared with the Mesozoic, where these are severally best developed, may be estimated as at least four or five to one; so that if we suppose the beds to have been formed with equal rapidity in the two great periods, then the older of the two was between four and five times as long as the latter, which would indeed be only a little greater than one of the separate ages of the Palæozoic. Either, therefore, the deposits took place with greater rapidity in the Palæozoic, or that period was by much the longer of the two. This it will be observed, is only another aspect of the great laws of geological sequence referred to in our last paper.
Let us look into this question a little more minutely. If the several pulsations of our continents depended upon any regularly recurring astronomical or terrestrial change, then they must represent, at least approximately, equal portions of time, and this, if proved, would settle the question in favour of anequal duration of these two great eras of the earth’s history. But as we cannot yet prove this, we may consider what light we can derive from the nature of the rocks produced. These may be roughly classified as of two kinds: First, the beds of sediment, sand, clay, etc., accumulated by the slow chemical decay of rocks and the mechanical agency of water. Secondly, the beds formed by accumulation of the harder and less perishable parts of living beings, of which the limestones are the chief. With reference to the first of these kinds of deposit, the action of the atmosphere and rains on rocks in the earlier times might have been somewhat more powerful if there was more carbonic acid in the atmosphere, that substance being the most efficient agent in the chemical decay of rocks. It might have been somewhat more powerful if there was a greater rainfall. It must, on the other hand, have been lessened by the apparently more equable temperature which then prevailed. These differences might perhaps nearly balance one another. Then the rocks of the older time were quite as intractable as those of the newer, and they were probably neither so high nor so extensive. Further, the dips and emergences of the great continental plateaus were equally numerous in the two great periods, though they were probably, with the exception of the latest one of each, more complete in the older period. In so far, then, as deposition of sediment is concerned, these considerations would scarcely lead us to infer that it was more rapid in the Palæozoic. But the Palæozoic sedimentsmay be estimated in the aggregate at about 50,000 feet in thickness, while those of the Mesozoic scarcely reach 8,000. We might, therefore, infer that the Palæozoic period was perhaps five or six times as long as the Mesozoic.
If we take the second class of rocks, the limestones, and suppose these to have been accumulated by the slow growth of corals, shells, etc., in the sea, we might, at first sight, suppose that Palæozoic animals would not grow or accumulate limestone faster than their Mesozoic successors. We must, however, consider here the probability that the older oceans contained more lime in solution than those which now exist, and that the equable temperature and extensive submerged plateaus gave very favourable conditions for the lower animals of the sea, so that it would perhaps be fair to allow a somewhat more rapid rate of growth of limestone for the Palæozoic. Now the actual proportions of limestone may be roughly stated at 13,000 feet in the Palæozoic, and 3,000 feet in the Mesozoic, which would give a proportion of about four and a quarter to one; and as a foot of limestone may be supposed on the average to require five times as long for its formation as a foot of sediment, this would give an even greater absolute excess in favour of the Palæozoic on the evidence of the limestones an excess probably far too great to be accounted for by any more favourable conditions for the secretion of carbonate of lime by marine animals.
The data for such calculations are very uncertain, and three elements of additional uncertainty closely related to each other must also be noticed. The first is the unknown length of the intervals in which no deposition whatever may have been taking place over the areas open to our investigation. The second is the varying amounts in which material once deposited may have been swept away by water. The third is the amount of difference that may have resulted from the progressive change of the geographical features of our continents. These uncertainties would all tend to diminish our estimate of the relative length of the Mesozoic. Lastly, the changes that have taken place in living beings, though a good measure of the lapse of time, cannot be taken as a criterion here, since there is much reason to believe that more rapid changes of physical conditions act as an inducing cause of rapid changes of life.
On the whole, then, taking such facts as we have, and making large deductions for the several causes tending to exaggerate our conception of Palæozoic time, we can scarcely doubt that the Palæozoic may have been three times as long as the Mesozoic. If so, the continental pulsations, and the changes in animal and vegetable life, must have gone on with accelerated rapidity in the later period,—a conclusion to which we shall again have occasion to refer when we arrive at the consideration of the Tertiary or Neozoic time, and the age of man, and the probable duration of the order of things under which we live.
I have given this preliminary sketch of the whole Mesozoic time, because we cannot here, as in the Palæozoic, take up each age separately; and now we must try to picture to ourselves the life and action of these ages. In doing so we may look at, first, the plant life of this period; second, animal life on the land; and third, animal life in the waters and in the ocean depths.
The Mesozoic shores were clothed with an abundant flora, which changed considerably in its form during the lapse of this long time; but yet it has a character of its own distinct from that of the previous Palæozoic and the succeeding Tertiary. Perhaps no feature of this period is more characteristic than the great abundance of those singular plants, the cycads, which in the modern flora are placed near to the pines, but in their appearance and habit more resemble palms, and which in the modern world are chiefly found in the tropical and warm temperate zones of Asia and America. No plants certainly of this order occur in the Carboniferous, where their nearest allies are perhaps some of the Sigillarise; and in the modern time the cycads are not so abundant, nor do they occur at all in climates where their predecessors appear to have abounded. In the quarries of the island of Portland, we have a remarkable evidence of this in beds with numerous stems of cycads stillin situin the soil in which they grew, and associated with stumps of pines which seem to have flourished along with them. In further illustrationof this point, I may refer to the fact that Carruthers, in a recent paper, catalogues twenty-five British species belonging to eight genera—a fact which markedly characterizes the British flora of the Mesozoic period. These plants will therefore occupy a prominent place in our restoration of the Mesozoic landscape, and we should give especial prominence to the beautiful speciesWilliamsonia gigas, discovered by the eminent botanist whose name it bears, and restored in his paper on the plant in the “Linnæan Transactions.” These plants, with pines and gigantic equisetums, prevailed greatly in the earlier Mesozoic flora, but as the time wore on, various kinds of endogens, resembling the palms and the screw-pines of the tropical islands, were introduced, and toward its close some representatives of the exogens very like our ordinary trees. Among these we find for the first time in our upward progress in the history of the earth, species of our familiar oaks, figs, and walnut, along with some trees now confined to Australia and the Cape of Good Hope, as the banksias and “silver-trees,” and their allies. In America a large number of the genera of the modern trees are present, and even some of those now peculiar to America, as the tulip-trees and sweet-gums. These forests of the later Mesozoic must therefore have been as gay with flowers and as beautiful in foliage as those of the modern world, and there is evidence that they swarmed with insect life. Further, the Mesozoic plants produced in some places beds of coalcomparable in value and thickness to those of the old coal formation. Of this kind are the coal beds of Brora in Sutherlandshire, those of Richmond in Virginia, and Deep River in N. Carolina, those of Vancouver’s Island, and a large part of those of China. To the same age have been referred some at least of the coal beds of Australia and India. So important are these beds in China, that had geology originated in that country, the Mesozoic might have been our age of coal.
If the forests of the Mesozoic present a great advance over those of the Palæozoic, so do the animals of the land, which now embrace all the great types of vertebrate life. Some of these creatures have left strange evidence of their existence in their footprints on the sand and clay, now cemented into beds of hard rock excavated by the quarryman. If we had landed on some wide muddy Mesozoic shore, we might have found it marked in all directions with animal footprints. Some of these are shaped much like a human hand. The creature that made this mark was a gigantic successor of the crocodilian newts or labyrinthodonts of the Carboniferous, and this type seems to have attained its maximum in this period, where one species,Labyrinthodon giganteus, had great teeth three or four inches in length, and presenting in their cross section the most complicated foldings of enamel imaginable. But we may see on the shores still more remarkable footprints. They indicate biped and three-toed animals of giganticsize, with a stride perhaps six feet in length. Were they enormous birds? If so, the birds of this age must have been giants which would dwarf even our ostriches. But as we walk along the shore we see many other impressions, some of them much smaller and different in form. Some, again, very similar in other respects, have four toes; and, more wonderful still, in tracing up some of the tracks, we find that here and there the creature has put down on the ground a sort of four-fingered hand, while some of these animals seem to have trailed long tails behind them. What were these portentous creatures—bird, beast, or reptile? The answer has been given to us by their bones, as studied by Yon Meyer and Owen, and more recently by Huxley and Cope. We thus have brought before us theDinosaurs—the terrible Saurians—of the Mesozoic age, the noblest of the Tanninim of old. These creatures constitute numerous genera and species, some of gigantic size, others comparatively small;—some harmless browsers on plants, others terrible renders of living flesh; but all remarkable for presenting a higher type of reptile organization than any now existing, and approaching in some respects to the birds and in others to the mammalia. Let us take one example of each of the principal groups. And first marches before us theIguanodonor his relationHadrosaurus—a gigantic biped, twenty feet or more in height, with enormous legs shaped like those of an ostrich, but of elephantine thickness. It strides along, not by leaps like akangaroo, but with slow and stately tread, occasionally resting, and supporting itself on the tripod formed by its hind limbs and a huge tail, like the inverted trunk of a tree. The upper part of its body becomes small and slender, and its head, of diminutive size and mild aspect, is furnished with teeth for munching the leaves and fruits of trees, which it can easily reach with its small fore-limbs, or hands, as it walks through the woods. The outward appearance of these creatures we do not certainly know. It is not likely that they had bony plates like crocodiles, but they may have shone resplendent in horny scale armour of varied hues. But another and more dreadful form rises before us. It isMegalosaurusor perhapsLælaps. Here we have a creature of equally gigantic size and biped habits; but it is much more agile, and runs with great swiftness or advances by huge leaps, and its feet and hands are armed with strong curved claws; while its mouth has a formidable armature of sharp-edged and pointed teeth. It is a type of a group of biped bird-like lizards, the most terrible and formidable of rapacious animals that the earth has ever seen. Some of these creatures, in their short deep jaws and heads, resembled the great carnivorous mammals of modern times, while all in the structure of their limbs had a strange and grotesque resemblance to the birds. Nearly all naturalists regard them as reptiles; but in their circulation and respiration they must have approached to the mammalia, and their general habit of body recalls that ofthe kangaroos. They were no doubt oviparous; and this, with their biped habit, seems to explain the strong resemblance of their hind quarters to those of birds. Had we seen the eagle-clawed Lælaps rushing on his prey; throwing his huge bulk perhaps thirty feet through the air, and crushing to the earth under his gigantic talons some feebler Hadrosaur, we should have shudderingly preferred the companionship of modern wolves and tigers to that of those savage and gigantic monsters of the Mesozoic.
We must not leave the great land-lizards of the reptilian age, without some notice of that Goliath of the race which, by a singular misnomer, has received the appellation ofCeteosaurusor “Whale-Saurian.” It was first introduced to naturalists by the discovery of a few enormous vertebrae in the English Oolite; and as these in size and form seemed best to fit an aquatic creature, it was named in accordance with this view. But subsequent discoveries have shown that, incredible though this at first appeared, the animal had limbs fitted for walking on the land. Professor Phillips has been most successful in collecting and restoring the remains of Ceteosaurus, and devotes to its history a long and interesting section of his “Geology of Oxford.” The size of the animal may be estimated, from the fact that its thigh-bone is sixty-four inches long, and thick in proportion. From this and other fragments of the skeleton, we learn that this huge monster must have stood ten feet high when on all fours, and that itslength, could not have been less than fifty feet; perhaps much more. From a single tooth, which has been found, it seems to have been herbivorous; and it was probably a sort of reptilian Hippopotamus, living on the rich herbage by the sides of streams and marshes, and perhaps sometimes taking to the water, where the strokes of its powerful tail would enable it to move more rapidly than on the land. In structure, it seems to have been a composite creature, resembling in many points the contemporary Dinosaurs; but in others, approaching to the crocodiles and the lizards.
But the wonders of Mesozoic reptiles are not yet exhausted. While noticing numerous crocodiles and lizard: like creatures, and several kinds of tortoises, we are startled by what seems a flight of great bats, wheeling and screaming overhead, pouncing on smaller creatures of their own kind, as hawks seize sparrows and partridges, and perhaps diving into the sea for fish. These were the Pterodactyles, the reptile bats of the Mesozoic. They fly by means of a membrane stretched on a monstrously enlarged little finger, while the other fingers of the fore limb are left free to be used as hands or feet. To move these wings, they had large breast-muscles like those of birds. In their general structure, they were lizards, but no doubt of far higher organization than any animals of this order now living; and in accordance with this, the interior of their skull shows that they must have had a brain comparable withthat of birds, which, they rivalled in energy and intelligence. Some of them were larger than the largest modern birds of prey, others were like pigeons and snipes in size. Specimens in the Cambridge Museum indicate one species twenty feet in the expanse of its wings. Cope has recently described an equally gigantic species from the Mesozoic of Western America, and fragments of much larger species are said to exist.[AE]Imagine such a creature, a flying dragon, with vast skinny wings, its body, perhaps, covered with scales, both wings and feet armed with strong claws, and with long jaws furnished with sharp teeth. Nothing can be conceived more strange and frightful. Some of them had the hind limbs long, like wading birds. Some had short, legs, adapted perhaps for perching. They could probably fold up their wings, and walk on all fours. Their skeleton, like that of birds, was very light, yet strong; and the hollow bones have pores, which show that, as in birds, air could be introduced into them from the lungs. This proves a circulation resembling that of birds, and warm blood. Indeed, in many respects, these creatures bridge over the space between the birds and the reptiles. “That they lived,” says Seeley, "exclusively upon land or in the air is improbable, considering the circumstances under which their remains are found. It is likely that they haunted the sea-shores; and while sometimes rowing themselves over the water with their powerful wings,used the wing membrane, as does the bat, to encloses the prey and bring it to the mouth. The large Pterodactyles probably pursued a more substantial prey than dragon-flies. Their teeth were well suited for fish; but probably fowl and small mammal, and even fruits, made a variety in their food. As the lord of the cliff, it may be supposed to have taken toll of all animals that could be conquered with tooth and nail. From its brain, it might be regarded as an intelligent animal. The jaws present indications of having been sheathed with a horny covering, and some species show a rugose anterior termination of the snout, suggestive of fleshy lips like those of the bat, and which may have been similarly used to stretch and clean the wing-membrane."
[AE]Seeley: “Ornithosauria.”
[AE]Seeley: “Ornithosauria.”
Here, however, perched on the trees, we see true birds. At least they have beaks, and are clothed with feathers. But they have very strange wings, the feathers all secondaries, without any large quills, and several fingers with claws at the angle of the wing, so that though less useful as wings, they served the double purpose of wing and hand. More strange still, the tail was long and flexible, like that of a lizard, with the feathers arranged in rows along its sides. If the lizards of this strange and uncertain time had wings like bats, the birds had tails and hands like lizards. This was in short the special age of reptiles, when animals of that class usurped the powers which rightfully belonged to creatures yet in their nonage, the true birds and mammals ofour modern days, while the birds were compelled to assume some reptilian traits.
Yet, strange to say, representatives of the higher creatures destined to inherit the earth at a later date actually existed. Toward the close of the Mesozoic we find birds approaching to those of our own day, and almost at the beginning of the time there were small mammals, remains of which are found both in the earlier and later formations of the Mesozoic, but which never seem to have thriven; at least so far as the introduction of large and important species is concerned. Traversing the Mesozoic woods, we might see here and there little hairy creatures, which would strike a naturalist as allies of the modern bandicoots, kangaroo rats, and myrmecobius of Australia; and closer study would confirm this impression, though showing differences of detail. In their teeth, their size, and general form, and probably in their pouched or marsupial reproduction, these animals were early representatives of the smaller quadrupeds of the Austral continent, creatures which are not only small but of low organisation in their class.
One of these mammals, known to us only by its teeth, and well namedMicrolestes, the “little thief” sneaks into existence, so to speak, in the Trias of Europe, while another very similar,Dromatherium, appears in rocks of similar age in America; and this is the small beginning of the great class Mammalia, destined in its quadrupedal forms to culminate in the elephants and their contemporaries in the Tertiaryperiod. Who that saw them trodden under foot lay the reptile aristocracy of the Mesozoic could have divined their destiny? But, notwithstanding the struggle for existence, the weakest does not always “go to the wall.” The weak things of this world are often chosen to confound those that are mighty; and the little quadrupeds of the Mesozoic are an allegory. They may typify the true, the good, and the hopeful, mildly and humbly asserting themselves in the world that now is, in the presence of the dragon monsters of pride and violence, which in the days to come they will overthrow. Physically the Mesozoic has passed away, but still exists morally in an age of evil reptiles, whose end is as certain as that of the great Dinosaurs of the old world.
The Mesozoic mammals are among the most interesting fossils known to us. In a recent memoir by Professor Owen, thirty-three species are indicated—all, or nearly all, Marsupial—all small—all closely allied to modern Australian animals; some herbivorous, some probably carnivorous. Owen informs us that these animals are not merely marsupials, but marsupials of low grade, a point in which, however, Huxley differs somewhat in opinion. They are at least not lower than some that still exist, and not so low as those lowest of mammals in Modern Australia, the duck-billed platypus and the echidna. Owen further supposes that they were possibly the first mammals, and not only the predecessors but the progenitors of the modern marsupials. If so, we havethe singular fact that they not only did not improve throughout the vast Mesozoic time, but that they have been in the progress of subsequent geological ages expelled out of the great eastern continent, and, with the exception of the American opossums, banished, like convicts, to Australia. Yet, notwithstanding their multiplied travels and long experiences, they have made little advance. It thus seems that the Mesozoic mammals were, from the evolutionist point of view, a decided failure, and the work of introducing mammals had to be done over again in the Tertiary; and then, as we shall find, in a very different way. If nothing more, however, the Mesozoic mammals were a mute prophecy of a better time, a protest that the age of reptiles was an imperfect age, and that better things were in store for the world. Moses seems to have been more hopeful of them than Owen or even Huxley would have been. He says that God “created” the great Tanninim, the Dinosaurs and their allies, but only “made” the mammals of the following creative day; so that when Microlestes and his companions quietly and unnoticed presented themselves in the Mesozoic, they would appear in some way to have obviated, in the case of the tertiary mammals, the necessity of a repetition of the greater intervention implied in the word “create.” How that was effected none of us know; but, perhaps, we may know hereafter.
CHAPTER IX.
THE MESOZOIC AGES (continued).
Thewaters 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 sealsand 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 theirportraits. Every text-book figures the well-known types of the generaIchthyosaurusandPlesiosaurus; 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 therhinoceros, 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 iscurious that these composite creatures belong to a later period of the Mesozoic than 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 than even the fabled sea-serpent, are unknown in our days. Buckland, I think, at one time indulged in thejeu d’espritof 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 theIchthyosaur 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 nameMosasaurus Camperiwas 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 than 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 paddleslike 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 than in any other reptiles except the snakes. In the related genusClidastesthis 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, than the Mosasaurus and Elasmosaurus. When Mr. Cope showed me, a few years ago, a nearly complete skeletonof 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 beTeinosaurus[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.
[AF]Heb.Tanan; Gr.Teino,Tanuo; Sansc.Tanu; Lat.Tendo.—Ges. Lex.
LIFE IN THE MESOZOIC PERIOD.Aquatic Reptiles and Cephalopods.Reptiles.—Plesiosaur and Osteopygis, Ichthyosaur, Teliosaur, Plesiosaur, Elasmosaur, Mosasaur (in order of the heads from left to right).—Cephalopods.—Ammonite, Crioceras, Belemnites, Baculites, and Ammonites (in order from left to right). The Reptiles after Hawkins and Cope’s Restorations.
LIFE IN THE MESOZOIC PERIOD.
Aquatic Reptiles and Cephalopods.Reptiles.—Plesiosaur and Osteopygis, Ichthyosaur, Teliosaur, Plesiosaur, Elasmosaur, Mosasaur (in order of the heads from left to right).—Cephalopods.—Ammonite, Crioceras, Belemnites, Baculites, and Ammonites (in order from left to right). The Reptiles after Hawkins and Cope’s Restorations.
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 than 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 than 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 nearthe 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 littleLeptaena, no bigger than 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 than any of those which either preceded or followed them. Supreme among these is the great group of theAmmonites,—beautifully spiral shells, thin and pearly like the Nautilus, andchambered 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 than 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 theBaculitesor 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 ofthe 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 asBelemnites, 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 than 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 thebottom, 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 than 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, blindlyseizing 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 than 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 somuch 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 than 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 greatdeposit 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 than 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 than 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 thecrumpling-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 than 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 merelylocal 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 livingin 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 bestowedonly 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.