Fig. 96Fig. 96.—Ichthyosaurus platydon.
Fig. 96.—Ichthyosaurus platydon.
The dimensions of the Ichthyosaurus varied with the species, of which five are known and described. These areIchthyosaurus communis,I. platydon,I. intermedius,I. tenuirostris, andI. Cuvierii, the largest being more than thirty feet in length.
Fig. 97Fig. 97.—Lower jaw of Ichthyosaurus. (Dr. Buckland.)
Fig. 97.—Lower jaw of Ichthyosaurus. (Dr. Buckland.)
The short, thick neck of the Ichthyosaurus supported a capacious head, and was continued backwards, from behind the eyes, in a column composed of more than a hundred vertebræ. The animal being adapted, like the whale, for rapid movement through the water, its vertebræ had none of the invariable solidity of those of the Lizard or Crocodile,but rather the structure and lightness of those of Fishes. The section of these vertebræ presents two hollow cones, connected only by their summits to the centre of the vertebræ, which would permit of the utmost flexibility of movement. The ribs extended along the entire length of the vertebral column, from the head to the pelvis. The bones of the sternum, or that part of the frame which supported the paddles, present the same combinations with those of the sternum in the Ornithorhynchus, or Duck-billed Platypus, of New Holland, an animal which presents the singular combination of a mammalian furred quadruped having the bill of a duck and webbed feet; which dived to the bottom of the water in search of its food, and returned to the surface to breathe the air. In this phenomenonof living Nature the Creator seems to have repeated, in our days, the organic arrangements which he had originally provided for the Ichthyosaurus.
In order that the animal should be able to move with rapidity in the water, both its anterior and posterior members were converted into fins or paddles. The anterior fins were half as large again as the posterior. In some species each paddle was made up of nearly a hundred bones, of polygonal form, and disposed in series representing the phalanges of the fingers. This hand, jointed at the arm, bears resemblance, in osteological construction, to the paddles, without distinct fingers, of the Porpoise and the Whale. A specimen of the posterior fin ofI. communis, discovered at Barrow-on-Soar, in Leicestershire, in 1840, by Sir Philip Egerton, exhibited on its posterior margin the remains of cartilaginous rays, which bifurcated as they approached the edge, like those in the fins of a fish. “It had previously been supposed,” says Professor Owen, “that the locomotive organs were enveloped, while living, in a smooth integument, like that of the turtle and porpoise, which has no other support than is afforded by the bones and ligaments within; but it now appears that the fin was much larger, expanding far beyond the osseous frame-work, and deviating widely in its fish-like rays from the ordinary reptilian type.” The Professor believes that, besides the fore-paddles, these stiff-necked Saurians were furnished at the end of the tail with a fin to assist them in turning, not placed horizontally, as in the whale, but vertically, forming a powerful instrument of progression and motion. It is obvious that the Ichthyosaurus was an animal powerfully armed for offence and defence. We cannot say, with certainty, whether the skin was smooth, like that of the whale or lizard, or covered with scales, like the great reptiles of our own age. Nevertheless, as the scales of the Fishes and the cuirass and horny armour of other Reptiles of the Lias are preserved, and as no such defensive scales have been found belonging to the Ichthyosaurus, it is probable that the skin was naked and smooth. The tail, composed of from eighty to eighty-five vertebræ, was provided with large and long paddles, arranged vertically as in the Whale.
Fig. 98Fig. 98.—Skeleton of Ichthyosaurus.Containing teeth and bones of Fishes in a coprolitic form. One-fifteenth natural size.
Fig. 98.—Skeleton of Ichthyosaurus.Containing teeth and bones of Fishes in a coprolitic form. One-fifteenth natural size.
It is curious to see to what a degree of perfection has been carried, in our days, the knowledge of the antediluvian animals, their habits, and their economy.Fig. 98represents the skeleton of an Ichthyosaurus found in the Lias of Lyme Regis, which still retains in its abdominal cavity coprolites, that is to say, the residue of digestion. The soft parts of the intestinal canal have disappeared, but thefæcesthemselves are preserved, and their examination informs us as to thealimentary regimen of this animal which has perished from the earth many thousands, perhaps millions, of years. Mary Anning, to whom we owe many of the discoveries made in the neighbourhood of Lyme Regis, her native place, had in her collection an enormous coprolite of the Ichthyosaurus. This coprolite (Fig. 99) contained some bones and scales of Fishes, and of divers Reptiles, well enough preserved to have their species identified. It only remains to be added that, among the bones, those of the Ichthyosaurus were often found, especially those of young individuals. The presence of the undigested remains of vertebræ and other bones of animals of its own species in the coprolites of the Ichthyosaurus proves, as we have already had occasion to remark, that this great Saurian must have been a most voracious monster, since it habitually devoured not only fish, but individuals of its own race—the smaller becoming the prey of the larger. The structure of the jaw of the Ichthyosaurus leads us to believe that the animal swallowed its prey without dividing it. Its stomach and intestines must, then, have formed a sort of pouch of great volume, filling entirely the abdominal cavity, and corresponding in extent to the great development of the teeth and jaws.
Fig. 99Fig. 99.—Coprolite, enclosing bones of small Ichthyosaurus.
Fig. 99.—Coprolite, enclosing bones of small Ichthyosaurus.
The perfection with which its contents have been preserved in the fossilised coprolites, furnishes indirect proofs that the intestinal canal of the Ichthyosaurus resembled closely that of the shark and the dog-fish—fishes essentially voracious and destructive, which have the intestinal canal spirally convoluted, an arrangement which is exactly that indicated in some of the coprolitesof the Ichthyosaurus, as is evident from the impressions which the folds of the intestine have left on the coprolite, of whichFig. 100is a representation. In the cliffs near Lyme Regis coprolites are abundant in the Liassic formation, and have been found disseminated through the shales and limestones along many miles of that coast.
Fig. 100Fig. 100.—Coprolite of Ichthyosaurus.
Fig. 100.—Coprolite of Ichthyosaurus.
What an admirable privilege of science, which is able, by an examination of the simplest parts in the organisation of beings which lived ages ago, to give to our minds such solid teachings and such true enjoyments! “When we discover,” says Dr. Buckland, “in the body of an Ichthyosaurus the food which it has engulfed an instant before its death, when the intervals between its sides present themselves still filled with the remains of fishes which it had swallowed some ten thousand years ago, or a time even twice as great, all these immense intervals vanish, time disappears, and we find ourselves, so to speak, thrown into immediate contact with events which took place in epochs immeasurably distant, as if we occupied ourselves with the affairs of the previous day.”
Fig. 101Fig. 101.—Skull of Plesiosaurus restored. (Conybeare.)a, profile;b, seen from above.
Fig. 101.—Skull of Plesiosaurus restored. (Conybeare.)a, profile;b, seen from above.
The name ofPlesiosaurus(from the Greek words πλησιος,near, and σαυρος,lizard) reminds us that this animal, though presenting many peculiarities of general structure, is allied by its organisation to the Saurian or Lizard family, and, consequently, to the Ichthyosaurus.
The Plesiosaurus presents, in its organic structure, the most curiousassemblage we have met with among the organic vestiges of the ancient world. The Plesiosaurus was a marine, air-breathing, carnivorous reptile, combining the characters of the head of a Lizard, the teeth of a Crocodile, a neck of excessive length resembling that of a Swan, the ribs of a Chameleon, a body of moderate size, and a very short tail, and, finally, four paddles resembling those of a Whale. Let us bestow a glance upon the remains of this strange animal which the earth has revealed, and which science has restored to us.
The head of the Plesiosaurus presents a combination of the characters belonging to the Ichthyosaurus, the Crocodile, and the Lizard. Its enormously long neck comprises a greater number of vertebræ than the neck of either the Camel, the Giraffe, or even the Swan, which of all the feathered race has the longest neck in comparison to the rest of the body. And it is to be remarked, that, contrary to what obtains in the Mammals, where the vertebræ of the neck are always seven, the vertebræ in birds increase in number with the length of the neck.
Fig. 102Fig. 102.—Skeleton of Plesiosaurus dolichodeirus restored. (Conybeare principally.)
Fig. 102.—Skeleton of Plesiosaurus dolichodeirus restored. (Conybeare principally.)
The body is cylindrical and rounded, like that of the great marine Turtles. It was, doubtless, naked,i.e., not protected with the scales or carapace with which some authors have invested it; for no traces of such coverings have been found near any of the skeletons which have been hitherto discovered. The dorsal vertebræ are attached to each other by nearly plane surfaces like those of terrestrial quadrupeds, a mode of arrangement which must have deprived the whole of its vertebralcolumn of much of its flexibility. Each pair of ribs surrounded the body with a complete girdle, formed of five pieces, as in the Chameleon and Iguana; whence, no doubt, as with the Chameleon, great facilities existed for the contraction and dilatation of the lungs.
Fig. 103Fig. 103.—Sternum and pelvis of Plesiosaurus. Pub., pubis; Isch., ischium; Il., ilium.
Fig. 103.—Sternum and pelvis of Plesiosaurus. Pub., pubis; Isch., ischium; Il., ilium.
The breast, the pelvis, and the bones of the anterior and posterior extremities furnished an apparatus which permitted the Plesiosaurus, like the Ichthyosaurus and existing Cetaceans, to sink in the water and return to the surface at pleasure (Fig. 103). Prof. Owen, in his “Report on British Reptiles,” characterises them as air-breathing and cold-blooded animals; the proof that they respired atmospheric air immediately, being found in the position and structure of the nasal passages, and the bony mechanism of the thoracic duct and abdominal cavity. In the first, the size and position of the external nostrils (Fig. 102), combined with the structure of the paddles, indicate a striking analogy between the extinct Saurians and the Cetaceans, offering, as the Professor observes, “a beautiful example of the adaptation of structure to the peculiar exigencies of species.” While the evidence that they were cold-blooded animals is found in the flexible or unanchylosed condition of the osseous pieces of the occiput and other cranial bones of the lower jaw, and of the vertebral column; from which the Professor draws the conclusion that the heart was adapted for transmitting a part only of the blood through the respiratory organs; the absence of the ball-and-socket articulations of the bones of the vertebræ, the position of the nostrils near the summit of the head, the numerous short and flat digital bones, which must have been enveloped in a simple undivided integumentary sheath, forming in both fore and hind extremities a paddle closely resembling that of the living Cetacea. The paddles are larger and more powerful than those of the Ichthyosaurus, to compensate for the slight assistance the animal derived from the tail. The latter—shorter, as compared with the length of the rest of the body, than in the Ichthyosaurus—was more calculated to act the part of a rudder,in directing the course of the animal through the water, than as a powerful organ of propulsion.
Such were the strange combinations of form and structure in the Plesiosaurus and Ichthyosaurus—genera of animals whose remains have, after an interment extending to unknown thousands of years, been revealed to light and submitted to examination; nay, rebuilt, bone by bone, until we have the complete skeletons before us, and the habits of the animals described, as if they had been observed in life. Conybeare thus speaks of the supposed habits of these extinct forms, which he had built up from scanty materials: “That the Plesiosaurus was aquatic is evident from the form of its paddles; that itwas marine is equally so, from the remains with which it is universally associated; that it may have occasionally visited the shore, the resemblance of its extremities to the turtle may lead us to conjecture; its motion, however, must have been very awkward on land; its long neck must have impeded its progress through the water, presenting a striking contrast to the organisation which so admirably fits the Ichthyosaurus for cutting through the waves. May it not, therefore, be concluded that it swam on or near the surface, arching back its long neck like the swan, and occasionally darting it down at the fish which happened to float within its reach? It may, perhaps, have lurked in shallow water along the coasts, concealed among the sea-weeds, and, raising its nostrils to the surface from a considerable depth, may have found a secure retreat from the assaults of dangerous enemies, while the length and flexibility of its neck may have compensated for the want of strength in its jaws, and incapacity for swift motion through the water, by the suddenness and agility of the attack they enabled it to make on every animal fitted to become its prey.”
Fig. 104Fig. 104.—Remains of Plesiosaurus macrocephalus. One-twelfth natural size.
Fig. 104.—Remains of Plesiosaurus macrocephalus. One-twelfth natural size.
The Plesiosaurus was first described by the Rev. W. D. Conybeare and Sir Henry De la Beche, in the “Geological Society’s Transactions” for 1821, and a restoration ofP. dolichodeirus, the most common of these fossils, appeared in the same work for 1824. The first specimen was discovered, as the Ichthyosaurus had been previously, in the Lias of Lyme Regis; since then other individuals and species have been found in the same geological formation in various parts of England, Ireland, France, and Germany, and with such variations of structure that Professor Owen has felt himself justified in recording sixteen distinct species, of which we have representedP. dolichodeirus(Fig. 102), as restored by Conybeare, andP. macrocephalus(Fig. 104), with its skeleton, as moulded from the limestone of Lyme Regis, which has been placed in the Palæontological Gallery of the British Museum.
Plate XVXV.—Ideal scene of the Lias with Ichthyosaurus and Plesiosaurus.
XV.—Ideal scene of the Lias with Ichthyosaurus and Plesiosaurus.
The Plesiosaurus was scarcely so large as the Ichthyosaurus. The specimen ofI. platydonin the British Museum probably belonged to an animal four-and-twenty feet long, and some are said to indicate thirty feet, while there are species of Plesiosauri measuring eighteen and twenty, the largest known specimen ofPlesiosaurus Cramptonifound in the lias of Yorkshire, and now in the Museum of the Royal Society of Dublin, being twenty-two feet four inches in length. On the opposite page (Plate XV.) an attempt is made to represent these grand reptiles of the Lias in their native element, and as they lived.
Cuvier says of the Plesiosaurus, “that it presents the most monstrous assemblage of characteristics that has been met with among the races of the ancient world.” This expression should not be understood in a literal sense; there are no monsters in Nature; in no living creature are the laws of organisation ever positively infringed; and it is more in accordance with the general perfection of creation to see in an organisation so special, in a structure which differs so notably from that of the animals of our own days, the simple development of a type, and sometimes also the introduction of beings, and successive changes in their structure. We shall see, in examining the curious series of animals of the ancient world, that the organisation and physiological functions go on improving unceasingly, and that each of the extinct genera which preceded the appearance of man, present, for each organ, modifications which always tend towards greater perfection. The fins of the fishes of Devonian seas become the paddles of the Ichthyosauri and of the Plesiosauri; these, in their turn, become the membranous foot of the Pterodactyle, and, finally, the wing of the bird. Afterwards comes the articulated fore-foot of the terrestrial mammalia, which, after attaining remarkable perfection in the hand of the ape, becomes, finally, the arm and hand of man, an instrument of wonderful delicacy and power, belonging to an enlightened being gifted with the divine attribute of reason! Let us, then, dismiss any idea of monstrosity with regard to these antediluvian animals; let us learn, on the contrary, to recognise, with admiration, the divine proofs of design which they display, and in their organisation to see only the handiwork of the Creator.
Another strange inhabitant of the ancient world, thePterodactylus(from πτερον,a wing, and δακτυλος,a finger), discovered in 1828, made Cuvier pronounce it to be incontestably the most extraordinary of all the extinct animals which had come under his consideration; and such as, if we saw them restored to life, would appear most strange and dissimilar to anything that now exists. In size and general form, and in the disposition and character of its wings, this fossil genus, according to Cuvier, somewhat resembled our modern bats and vampyres, but had its beak elongated like the bill of a woodcock, and armed with teeth like the snout of a crocodile; its vertebræ, ribs, pelvis, legs, and feet resembled those of a lizard; its three anterior fingers terminated in long hooked claws like that on the fore-finger of the bat; and over its body was a covering, neither composed of feathers as in the bird, nor of hair as in the bat, but probably a naked skin; in short, it was a monster resembling nothing that has ever been heard of upon earth, except the dragons of romance and heraldry. Moreover,it was probably noctivagous and insectivorous, and in both these points resembled the bat; but differed from it in having the most important bones in its body constructed after the manner of those of reptiles.
Fig. 105Fig. 105.—Pterodactylus crassirostris.
Fig. 105.—Pterodactylus crassirostris.
“Thus, like Milton’s fiend, all-qualified for all services and all elements, the creature was a fit companion for the kindred reptiles that swarmed in the seas, or crawled on the shores, of a turbulent planet:
“The Fiend,O’er bog, or steep, through strait, rough, dense, or rare,With head, hands, wings, or feet, pursues his way,And sinks, or swims, or wades, or creeps, or flies.
“The Fiend,O’er bog, or steep, through strait, rough, dense, or rare,With head, hands, wings, or feet, pursues his way,And sinks, or swims, or wades, or creeps, or flies.
Paradise Lost, Book II., line 947.
“With flocks of such-like creatures flying in the air, and shoals of Ichthyosauri and Plesiosauri swarming in the ocean, and gigantic Crocodiles and Tortoises crawling on the shores of primæval lakes and rivers—air, sea, and land must have been strangely tenanted in these early periods of our infant world.”[64]
The strange structure of this animal gave rise to most contradictory opinions from the earlier naturalists. One supposed it to be a bird, another a bat, and others a flying reptile. Cuvier was the first to detect the truth, and to prove, from its organisation, that the animal was a Saurian. “Behold,” he says, “an animal which in its osteology, from its teeth to the end of its claws, presents all the characters of the Saurians; nor can we doubt that their characteristics existed in its integuments and softer parts, in its scales, its circulation, its generative organs: it was at the same time provided with the means of flight; but when stationary it could not have made much use of its anterior extremities, even if it did not keep them always foldedas birds fold their wings. It might, it is true, use its small anterior fingers to suspend itself from the branches of trees; but when at rest it must have been generally on its hind feet, like the birds again, and like them it must have carried its neck half-erect and curved backwards, so that its enormous head should not disturb its equilibrium.” This diversity of opinion need not very much surprise us after all, for, with the body and tail of an ordinary mammal, it had the form of a bird in its head and the length of its neck, of the bat in the structure and proportion of its wings, and of a reptile in the smallness of its head and in its beak, armed with at least sixty equal sharp-pointed teeth, differing little in form and size.
Fig. 106Fig. 106.—Pterodactylus brevirostris.
Fig. 106.—Pterodactylus brevirostris.
Dr. Buckland describes eight distinct species, varying in size from a snipe to a cormorant. Of these,P. crassirostris(Fig. 105) andP. brevirostris(Fig. 106), were both discovered in the Lias of Solenhofen.P. macronyxbelongs to the Lias of Lyme Regis.
The Pterodactyle was, then, a reptile provided with wings somewhat resembling those of Bats, and formed, as in that Mammal, of a membrane which connected the body with the excessively elongated phalanges of the fourth finger, which served to expand the membrane that answered the purposes of a wing. The Pterodactyle of the Liassic period was, as we have seen, an animal of small size; the largest species in the older Lias beds did not exceed ten or twelve inches in length, or the size of a raven, while the later forms found fossil in the Greensand and Wealden beds must have measured more than sixteen feet between the tips of the expanded wings. On the other hand, its head was of enormous dimensions compared with the rest of the body. We cannot admit, therefore, that this animal could really fly, and, like a bird, beat the air. The membranous appendage which connected its long finger with its body was rather a parachute than a wing. It served to moderate the velocity of its descent when it dropped on its prey from a height. Essentially a climber, it could only raise itself by climbing up tall trees or rocks, after the manner of lizards, and throw itself thence to the ground, or upon the lower branches, by making use of its natural parachute.
The ordinary position of the Pterodactyle was probably upon its two hind feet, the lower extremities being adapted for standing and moving on the ground, after the manner of birds. Habitually, perhaps, it perched on trees; it could creep, or climb along rocks and cliffs, or suspend itself from trees, with the assistance of its claws and feet, after the manner of existing Bats. It is even probable, Dr. Buckland thought, that it had the power of swimming and diving, socommon to reptiles, and possessed by the Vampyre Bat of the island of Bonin. It is believed that the smaller species lived upon insects, and the larger preyed upon fishes, upon which it could throw itself like the sea-gull.
The most startling feature in the organisation of this animal is the strange combination of two powerful wings attached to the body of a reptile. The imagination of the poets long dwelt on such a combination; theDragonwas a creation of their fancy, and it played a great part in fable and in pagan mythology. The Dragon, or flying reptile, breathing fire and poisoning the air with his fiery breath, had, according to the fable, disputed with man the possession of the earth. Gods and demigods claimed, among their most famous exploits, the glory of having vanquished this powerful and redoubtable monster.
Among the animals of our epoch, only a single reptile is found provided with wings, or digital appendages analogous to the membranous wings of the bats, and which can be compared to the Pterodactyle. This is called theDragon, one of the Draconidæ, a family of Saurians, which has been described by Daudin, as distinguished by the first six ribs, instead of hooping round the abdomen, extending in nearly a straight line, and sustaining a prolongation of skin which forms a sort of wing analogous to that of the Pterodactyle. Independent of the four feet, this wing sustains the animal, like a parachute, as it leaps from branch to branch; but the creature has no power to beat the air with it as birds do when flying. This reptile lives in the forests of the hottest parts of Africa, and in some isles of the Indian Ocean, especially in Sumatra and Java. The only known species is that figured at page 238 (Fig. 107), which comes from the East Indies.
What a strange population was that which occupied the earth at this stage of its history, when the waters were filled with creatures so extraordinary as those whose history we have traced! Plesiosauri and Ichthyosauri filled the seas, upon the surface of which floated innumerable Ammonites in light skiffs, some of them as large as a good-sized cart-wheel, while gigantic Turtles and Crocodiles crawled on the banks of the rivers and lakes. Only one genus of Mammals had yet appeared, but no birds; nothing broke the silence of the air, if we except the breathing of the terrestrial reptiles and the flight of winged insects.
The earth cooled progressively up to the Jurassic period, the rains lost their continuity and abundance, and the pressure of the atmosphere sensibly diminished. All these circumstances favouredthe appearance and the multiplication of innumerable species of animals, whose singular forms then showed themselves on the earth. We can scarcely imagine the prodigious quantity of Molluscs and Zoophytes whose remains lie buried in the Jurassic rocks, forming entire strata of immense thickness and extent.
Fig. 107Fig. 107.—Draco volans.
Fig. 107.—Draco volans.
The same circumstances concurred to favour the production of plants. If the shores and seas of the period received such a terrible aspect from the formidable animals we have described, the vegetation which covered the land had also its peculiar character and appearance. Nothing that we know of in the existing scenery of the globe surpasses the rich vegetation which decorated the continents of the Jurassic period. A temperature still of great elevation, ahumid atmosphere, and, we have no reason to doubt, a brilliant sun, promoted the growth of a luxuriant vegetation, such as some of the tropical islands, with their burning temperature and maritime climate, can only give us an idea of, while it recalls some of the Jurassic types of vegetation. The elegant Voltzias of the Trias had disappeared, but the Horse-tails (Equiseta) remained, whose slender and delicate stems rose erect in the air with their graceful panicles; the gigantic rushes also remained; and though the tree-ferns had lost their enormous dimensions of the Carboniferous age, they still preserved their fine and delicately-cut leaves.
Alongside these vegetable families, which passed upwards from the preceding age, an entire family—the Cycads (Fig. 72, p. 168)—appear for the first time. They soon became numerous in genera, such as Zamites, Pterophyllum (Williamsonia), and Nilssonia. Among the species which characterise this age, we may cite the following, arranging them in families:—
TheZamitesseem to be forerunners of the Palms, which make their appearance in the following epoch; they were trees of elegant appearance, closely resembling the existing Zamias, which are trees of tropical America, and especially of the West India Islands; they were so numerous in species and in individuals that they seem to have formed, of themselves alone, one half of the forests during the period which engages our attention. The number of their fossilised species exceeds that of the living species. The trunk of the Zamites, simple and covered with scars left by the old leaves, supports a thick crown of leaves more than six feet in length, disposed in fan-like shape, arising from a common centre.
ThePterophyllum(Williamsonia), formed great trees, of considerable elevation, and covered with large pinnated leaves from top to bottom. Their leaves, thin and membranous, were furnished with leaflets truncated at the summit and traversed by fine nervures, not convergent, but abutting on the terminal truncated edge.
TheNilssonia, finally, were Cycadeaceæ resembling the Pterophyllum,but with thick and coriaceous leaves, and short leaflets contiguous to, and in part attached to the base; they were obtuse or nearly truncated at the summit, and would present nervures arched or confluent towards that summit.
Fig. 108Fig. 108.—Millepora alcicornis.(Recent Coral.)
Fig. 108.—Millepora alcicornis.(Recent Coral.)
The essential characters of the vegetation during the Liassic sub-period were:—1. The great predominance of the Cycadeaceæ, thus continuing the development which commenced in the previous period, expanding into numerous genera belonging both to this family and that of theZamitesandNilssonia; 2. The existence among the Ferns of many genera with reticulated veins or nervures, and under forms of little variation, which scarcely show themselves in the more ancient formations.
Plate XVIXVI.—Ideal Landscape of the Liassic Period.
XVI.—Ideal Landscape of the Liassic Period.
On the opposite page (Plate XVI.) is an ideal landscape of the Liassic period; the trees and shrubs characteristic of the age are the elegant Pterophyllum, which appears in the extreme left of the picture, and the Zamites, which are recognisable by their thick and low trunk and fan-like tuft of foliage. The large horsetail, or Equisetum of this epoch, mingles with the great Tree-ferns and the Cypress, a Conifer allied to those of our own age. Among animals, we see the Pterodactyle specially represented. One of these reptilesis seen in a state of repose, resting on its hind feet. The other is represented, not flying, after the manner of a bird, but throwing itself from a rock in order to seize upon a winged insect, the dragon-fly (Libellula), the remains of which have been discovered, associated with the bones of the Pterodactyle, in the lithographic limestone of Pappenheim and Solenhofen.
This period is so named because many of the limestones entering into the composition of the formations it comprises, consist almost entirely of an aggregation of rounded concretionary grains resembling, in outward appearance, the roe or eggs of fishes, and each of which contains a nucleus of sand, around which concentric layers of calcareous matter have accumulated; whence the name, from ωον,egg, and λιθος,stone.
The Oolite series is usually subdivided into three sections, theLower,Middle, andUpper Oolite. These rocks form in England a band some thirty miles broad, ranging across the country from Yorkshire, in the north-east, to Dorset, in the south-west, but with a great diversity of mineral character, which has led to a further subdivision of the series, founded on the existence of particular strata in the central and south-western counties:—
The alternations of clay and masses of limestone in the Liassic and Oolite formations impart some marked features to the outline of the scenery both of France and England: forming broad valleys, separated from each other by ranges of limestone hills of more or less elevation. In France, the Jura mountains are composed of the latter; in England, the slopes of this formation are more gentle—the valleys are intersected by brooks, and clothed with a rich vegetation; it forms what is called a tame landscape, as compared with the wilder grandeur of the Primary rocks—it pleases more than it surprises. It yields materials also, more useful than some of the older formations, numerous quarries being met with which furnish excellent building-materials, especially around Bath, where the stone, whenfirst quarried, is soft and easily worked, but becomes harder on exposure to the air.
The annexed section (Fig. 109) will give some idea of the configuration which the stratification assumes, such as may be observed in proceeding from the north-west to the south-east, from Caermarthenshire to the banks of the Ouse.
Fig. 109Fig. 109.—General view of the succession of British strata, with the elevations they reach above the level of the sea.G, Granitic rocks;a, Gneiss;b, Mica-schist;c, Skiddaw or Cumbrian Slates;d, Snowdon rocks;e, Plynlymmon rocks;f, Silurian rocks;g, Old Red Sandstone;h, Carboniferous Limestone;i, Millstone Grit;k, Coal-measures;l, Magnesian Limestone;m, New Red Sandstone;n, Lias;o, Lower, Middle, and Upper Oolites;p, Greensand;q, Chalk;r, Tertiary strata.
Fig. 109.—General view of the succession of British strata, with the elevations they reach above the level of the sea.G, Granitic rocks;a, Gneiss;b, Mica-schist;c, Skiddaw or Cumbrian Slates;d, Snowdon rocks;e, Plynlymmon rocks;f, Silurian rocks;g, Old Red Sandstone;h, Carboniferous Limestone;i, Millstone Grit;k, Coal-measures;l, Magnesian Limestone;m, New Red Sandstone;n, Lias;o, Lower, Middle, and Upper Oolites;p, Greensand;q, Chalk;r, Tertiary strata.
The most salient and characteristic feature of this age is, undoubtedly, the appearance of animals belonging to the class of Mammals. But the organisation, quite special, of the first of the Mammalia will certainly be a matter of astonishment to the reader, and must satisfy him that Nature proceeded in the creation of animals by successive steps, by transitions which, in an almost imperceptible manner, connect the beings of one age with others more complicated in their organisation. The first Mammals which appeared upon the earth, for example, did not enjoy all the organic attributes belonging to the more recent creations of the class. In the latter the young are brought forth living, and not from eggs, like Birds, Reptiles, and Fishes. But the former belonged to that order of animals quite special, and never numerous, the young of which are transferred in a half-developed state, from the body of the mother to an external pouch in which they remain until they become perfected; in short, to marsupial animals. The mother nurses her young during a certain time in a sort of pouch external to the body, in the neighbourhood of the abdomen, and provided with teats to which the young adhere. After a more or less prolonged sojourn in this pouch, the young animal, when sufficientlymatured and strong enough to battle with the world, emerges from its warm retreat, and enters fully into life and light; the process being a sort of middle course between oviparous generation, in which the animals are hatched from eggs after exclusion from the mother’s body, like Birds; and viviparous, in which the animals are brought forth alive, as in the ordinary Mammals.
In standard works on natural history the animals under consideration are classed asmammiferous Didelphæ. They are brought forth in an imperfect state, and during their transitional condition are suckled in a pouch supported by bones calledmarsupial, which are attached by their extremities to the pelvis, and serve to support the marsupium, whence the animals provided with these provisions for bringing up their progeny are calledMarsupial Mammals. The Opossum, Kangaroo, and Ornithorhynchus are existing representatives of this group.
Fig. 110Fig. 110.—Jaw of Thylacotherium Prevostii.
Fig. 110.—Jaw of Thylacotherium Prevostii.
Fig. 111Fig. 111.—Jaw of Phascolotherium.
Fig. 111.—Jaw of Phascolotherium.
The name ofThylacotherium, orAmphitherium, orPhascolotherium, is given to the first of these marsupial Mammals which made their appearance, whose remains have been discovered in the Lower Oolite, and in one of its higher stages, namely, that called theGreat Oolite.Fig. 110represents the jaw of the first of these animals, andFig. 111the other—both of the natural size. These jaw-bones represent all that has been found belonging to these early marsupial animals; and Baron Cuvier and Professor Owen have both decided as to their origin. The first was found in the Stonesfield quarries. The Phascolotherium, also a Stonesfield fossil, was the ornament of Mr. Broderip’s collection. The animals which lived on the land during the Lower Oolitic period would be nearly the same with those of the Liassic. The insects were, perhaps, more numerous.
Fig. 112Fig. 112.—Ammonites Herveyii.
Fig. 112.—Ammonites Herveyii.
Fig. 113Fig. 113.—Terebratula digona.
Fig. 113.—Terebratula digona.
The marine fauna included Reptiles, Fishes, Molluscs, and Zoophytes. Among the first were the Pterodactyle, and a great Saurian, the Teleosaurus, belonging to a family which made its appearance in this age, and which reappears in the following epoch.Among the Fishes, the Ganoids and Ophiopsis predominate. Among the Ammonites,Ammonites Humphriesianus,A. Herveyii(Fig. 112),A. Brongniarti,Nautilus lineatus, and many other representatives of the cephalopodous Mollusca. Among the Brachiopods areTerebratula digona(Fig. 113) andT. spinosa. Among the Gasteropoda thePleurotomaria conoideais remarkable from its elegant shape and markings, and very unlike any of the livingPleurotomaas represented byP. Babylonia(Fig. 114).Ostrea MarshiiandLima proboscidea, which belong to the Acephala, are fossil Mollusca of this epoch, to which also belongEntalophora cellarioides,Eschara Ranviliana,Bidiastopora cervicornis; elegant and characteristic molluscous Polyzoa. We give a representation of two living species, as exhibiting the form of these curious beings. (Figs. 115and116.)
Fig. 114Fig. 114.—Pleurotoma Babylonia. (Recent.)
Fig. 114.—Pleurotoma Babylonia. (Recent.)
The Echinoderms and Polyps appear in great numbers in the deposits of the Lower Oolite:Apiocrinus elegans,Hyboclypus gibberulus,Dysaster Endesiirepresent the first;Montlivaltia caryophyllata,Anabacia orbulites,Cryptocœnia bacciformis, andEunomia radiatarepresent the second.