Part 14

Chapter 143,421 wordsPublic domain

This fresh water formation, the oldest which has been distinguished in our neighbourhood, and which supports all the formations which we have just enumerated, is itself supported and embraced on all sides by the chalk, an immense formation, both as to thickness and extent, which shews itself in very distant countries, such as Pomerania and Poland; but which, in our vicinity, reigns with a sort of continuity in Berri, Champagne, Picardy, Upper Normandy, and a part of England, and thus forms a great circle, or rather a great basin, in which the deposits of which we have been speaking are contained, but of which they also cover the edges in the places where they were less elevated.

In fact, it is not in our basin only that these various formations have been deposited. In the other countries where the surface of the chalk presented similar cavities for them; in those even where there was no chalk, and where the older formations alone presented themselves as supports, circumstances often led to the formation of deposits more or less similar to ours, and containing the same organic bodies.

Our formations containing fresh-water shells, have been seen in England, in Spain, and even so far as the confines of Poland.

The marine shells interposed between them, have been found along the whole course of the Appenines.

Some of the quadrupeds of our gypsum deposits, our palæotheria, for example, have also left their bones in certain gypseous formations of the Velai, and in the molasse quarries of the south of France.

Thus the partial revolutions which have taken place in our neighbourhood, between the period of the chalk and that of the great inundation, and during which the sea threw itself upon our districts or retired from them, had also taken place in a multitude of other countries. It seems as if the globe had undergone a long series of changes by which variations were produced, probably in close succession, as the deposits which they have left nowhere shew much thickness or solidity. The chalk has been produced by a more tranquil and more continuous sea; it contains only marine productions, among which there are, however, some very remarkable vertebrate animals, but all of the class of reptiles and fishes; large tortoises, vast lizards, and other similar animals.

The formations anterior to the chalk, and in the hollows of which the chalk is itself deposited, as the formations of our neighbourhood are in its hollows, form a great part of Germany and England; and the efforts which the naturalists of these two countries have recently made according with ours, and proceeding upon the same principles, combined with those which had been previously tried by the school of Werner, will soon leave nothing to be desired with respect to our knowledge of them. Messrs de Humboldt and de Bonnard in France and Germany, and Messrs Buckland and Conybeare in England, have furnished the most complete and most instructive accounts of them.

* * * * *

The subjoined table, in which not only the secondary formations have been arranged, but the whole series of strata, from the oldest known to the most modern and most superficial, has been politely furnished me by M. de Humboldt, to adorn my work. It may be considered as an epitome of the labours of geologists up to the present period[246].

_TABLE of Geological Formations in the order of their superposition._ By M. Al. de Humboldt.

Under the chalk are found deposits of green sand, of which its lower strata contains some organic remains. Beneath this are ferruginous sands. In many countries both of these deposits are agglutinated into beds of sandstone, in which lignites, amber, and remains of reptiles, are also observed.

Under this, we find the great mass of strata which compose the Jura chain, and that of the mountains by which it is continued into Suabia and Franconia, the principal ridges of the Apennines, and multitudes of beds in France and England. It consists of limestone-schists, rich in fishes and crustacea; vast beds of oolites, or of a granular limestone; grey marly limestones, with pyrites, characterised by the presence of ammonites, of oysters with recurvate valves, named Gryphææ, and of reptiles, which are remarkable on account of their forms and structures.

Large beds of sand and sandstone, often presenting vegetable impressions, support all these Jura deposits, and are themselves supported by a limestone, the innumerable shells and zoophytes contained in which induced Werner to give it the much too general name of _Shell-limestone_, and which is separated by other beds of sandstone, of the kind denominated _variegated_ sandstone, from a still older limestone, which has been not less improperly called _Alpine limestone_, because it composes the High Alps of the Tyrol; but which also shews itself at the surface in the eastern provinces of France, and in the whole southern part of Germany.

In this shell-limestone are deposited great masses of gypsum and rich beds of salt; and under it are found the thin beds of copper-slates so rich in fishes, among which there are also fresh-water reptiles. The copper-slate rests upon a red sandstone, to the epoch of which belong those famous deposits of coal, which supply the present inhabitants of the civilized countries of Europe with fuel, and are the remains of the first vegetable productions with which the face of the globe was adorned. We learn from the trunks of ferns, whose impressions they have preserved, how different these ancient forests have been from ours.

We then quickly come to those transition formations, in which primeval nature, nature dead and purely mineral, seems to have disputed the empire with organising nature. Black limestones, and schists which present only crustacea and shells of kinds now extinct, alternate with remains of primitive formations, and announce our having arrived at those formations, the oldest with which we are acquainted, those ancient foundations of the present envelop of the globe, the marbles and primitive slates, the gneisses, and, lastly, the granites.

Such is the precise enumeration of the successive masses with which nature has enveloped the globe. The positive geological information presented by it, has been obtained, by combining the knowledge furnished by mineralogy with that presented by the sciences connected with organic existence. This order, so new and so interesting in facts, has only been acquired by geology, since it preferred positive knowledge, furnished by observation, to fanciful systems, contradictory conjectures regarding the first origin of the globe, and all those phenomena, which, having no resemblance to what actually takes place in nature, could neither find in it, for their explanation, materials nor touchstone. A few years ago, the greater number of geologists might have been compared to historians, who, in writing the history of France, should have interested themselves only about the events which had taken place among the Gauls before the time of Julius Cesar. In composing their romances, however, these historians would have taken advantage of their knowledge of posterior facts; and the geologists of whom I speak, absolutely neglected the posterior facts, which could alone have reflected some light upon the darkness of preceding times.

_Enumeration of the Fossil Animals recognised by the Author._

In concluding this discourse, there only remains for me now to present the result of my own researches, or, in other words, a general account of my great work. I shall enumerate the animals which I have discovered, in the inverse order of that which I have followed in my enumeration of the formations. By proceeding deeper and deeper into the series of strata, I there rose in the series of epochs. I shall now take the oldest formations,--make known the animals which they contain,--and, passing from one epoch to another, point out those which successively make their appearance in proportion as we approach the present time.

We have seen that zoophytes, mollusca, and certain crustacea, begin to appear in the Transition formations; perhaps there may even at that period be bones and skeletons of fishes; but we do not by any means observe at so early a period remains of animals which live on land, and respire air in its ordinary state.

The great beds of coal, and the trunks of palms and ferns of which they preserve the impressions, although they afford evidence of the existence of dry land, and of a vegetation no longer confined to the waters, do not yet shew bones of quadrupeds, not even of oviparous quadrupeds.

It is only a little above this, in the bituminous copper-slates, that we see the first traces of them; and, what is very remarkable, the first quadrupeds are reptiles of the family of lizards, very much resembling the large monitors which live at the present day in the torrid zone. Several individuals of this kind have been found in the mines of Thuringia[247], among innumerable fishes of a genus now unknown, but which, from its relations to the genera of our days, appears to have lived in fresh water. Every body knows that the monitors are also fresh water animals.

A little higher is the limestone called Alpine, and resting upon it the shell-limestone, so rich in entrochites and encrinites, which forms the basis of a great part of Germany and Lorraine.

In it have been found skeletons of a very large sea-tortoise, the shells of which might have been from six to eight feet in length; and those of another oviparous quadruped of the family of lizards, of a large size, and with a very sharp muzzle[248].

Rising still through sandstones, which present only vegetable impressions of large arundinaceæ, bamboos, palms, and other monocotyledonous plants, we come to the different strata of the deposit which has been named the Jura limestone, on account of its forming the principal nucleus of that chain of mountains.

It is here that the class of Reptiles assumes its full development, and shews itself under the most varied forms and gigantic sizes.

The middle part, which is composed of oolites and lias, or of grey sandstone containing gryphites, contains the remains of two genera, the most extraordinary of all, which have combined the characters of the class of oviparous quadrupeds with organs of motion similar to those of the cetacea.

The _ichthyosaurus_[249], discovered by Sir Everard Home, has the head of a lizard, but prolonged into an attenuated muzzle, armed with conical and pointed teeth; enormous eyes, the sclerotica of which is strengthened by a frame consisting of bony pieces; a spine composed of flat vertebræ, of a depressed circular form, and concave on both surfaces like those of fishes; slender ribs; a sternum and clavicles like those of lizards and ornithorynchi; a small and weak pelvis; and four limbs, of which the humeri and femurs are short and thick, while the other bones are flattened, and closely set like the stones in a pavement, so as to form, when enveloped with the skin, fins of a single piece, almost incapable of bending; analogous, in short, both as to use and organization, to those of cetacea. These reptiles have lived in the sea; on shore, they could only at most have crept in the hobbling manner of seals; at the same time after they have respired elastic air.

The remains of four species have been found:

The most extensively distributed (_I. communis_) has blunt conical teeth; its length sometimes exceeds twenty feet.

The second (_I. platyodon_), which is at least as large as the former, has compressed teeth, with round and bulging roots.

The third (_I. tenuirostris_), has slender and pointed teeth, and the muzzle thin and elongated.

The fourth (_I. intermedius_), is, as its name implies, intermediate between the last species and the common, with respect to the form of its teeth. The two latter species do not attain half the size of the two first.

The _plesiosaurus_, discovered by Mr Conybeare, must have appeared still more monstrous than the ichthyosaurus. It had the same limbs, but somewhat more elongated and more flexible; its shoulder and pelvis were more robust; its vertebræ had more of the forms and articulations of the lizards; but what distinguished it from all oviparous and viviparous quadrupeds, was a slender neck as long as its body, composed of thirty and odd vertebræ, a number greater than that of the neck of any other animal, rising from the trunk like the body of a serpent, and terminating in a very small head, in which all the essential characters of that of the lizard family are observed.

If any thing could justify those hydras and other monsters, the figures of which are so often presented in the monuments of the middle ages, it would incontestibly be this plesiosaurus.[250]

Five species are already known, of which the most generally distributed (_P. dolichodeirus_) attains a length of more than twenty feet.

A second species (_P. recentior_), found in more modern strata, has the vertebræ flatter.

A third (_P. carinatus_) shews a ridge on the under surface of its vertebræ.

A fourth, and lastly a fifth (_P. pentagonus_ and _P. trigonus_), have the ribs marked with five and three ridges.[251]

These two genera are found everywhere in the lias: they were discovered in England, where this rock is exposed in cliffs of great extent; but they have also been found since in France and Germany.

Along with these had lived two species of Crocodiles, the bones of which are also found deposited in the lias, among ammonites, terebratulæ, and other shells of that ancient sea. We have skeletons of them in our cliffs at Honfleur, where the remains are found, from which I have drawn up their characters.[252]

One of these species, the _Long-beaked Gavial_, has the muzzle longer, and the head more narrow, than the gavial or long-beaked crocodile of the Ganges; the bodies of its vertebræ are convex before, while in our crocodiles of the present day they are so behind. It has been found in the lias deposits of Franconia, as well as in those of France.

A second species, the _Short-beaked Gavial_, has the muzzle of ordinary length, less attenuated than the gavial of the Ganges, but more so than our crocodiles of St Domingo. Its vertebræ are slightly concave at each of their extremities.

But these crocodiles are not the only ones which have been deposited in the strata of these secondary limestones.

The beautiful oolite quarries of Caen have presented a very remarkable one, the muzzle of which is as long and more pointed than that of the long-beaked gavial, and its head more dilated behind, with wider temporal fossæ. Its stony scales, marked with small round cavities, must have rendered it the best defended of all the crocodiles.[253] Its lower teeth are alternately longer and shorter.

There is still another in the oolite of England; but there have only been found some portions of its cranium, which do not suffice to afford a complete idea of it.[254]

Another very remarkable genus of reptiles, the remains of which, although they are also found beyond the limits of the lias concretion, are especially abundant in the oolite and upper sands, is the _megalosaurus_, justly so named, for, along with the forms of the lizards, and particularly of the monitors, of which it has also the sharp-edged and dentated teeth, it presents so enormous a size, that if we suppose it to have possessed the proportions of the monitors, it must have exceeded seventy feet in length. It was, in fact, a lizard of the size of a whale.[255] It was discovered by Mr Buckland in England; but we have it also in France; and in Germany there are found bones, if not of the same species, at least of a species which can be referred to no other genus. It is to M. Sœmmering that we owe the first description of this last. He discovered the bones in strata lying above the oolite, in those limestone-schists of Franconia, long celebrated for the numerous fossil remains which they furnished to the cabinets of the curious, and which will be still more celebrated for the services which their employment in lithography render to the arts and sciences.

The crocodiles continue to make their appearance in these schists, and always of the long-muzzled or rostrated kind. M. de Sœmmering has described one (the _Crocodilus priscus_), the entire skeleton of a small individual of which was found nearly in as good a state of preservation, as it could have been in our cabinets.[256] It is one of those which most resemble the present gavial of the Ganges; the anterior or united part of its lower jaw, however, is less elongated; its lower teeth are alternately and regularly longer and shorter. It has ten vertebræ in the tail.

But the most remarkable animals which these limestone slates contain, are the flying lizards, which I have named _Pterodactyli_.

They are reptiles whose principal characters are, a very short tail, a very long neck, the muzzle much elongated, and armed with sharp teeth; the legs also long, and one of the toes of the anterior extremity excessively elongated, having probably served for the attachment of a membrane adapted for supporting them in the air, accompanied with four other toes of ordinary size, terminated by hooked claws. One of these strange animals, whose appearance would be frightful did they occur alive at the present day, may have been of the size of a thrush[257], the other of that of a common bat[258]; but it would appear from some fragments that larger species had existed[259].

A little above the limestone slates is found the nearly homogeneous limestone of the Jura ridges. It also contains bones, but always of reptiles, crocodiles, and fresh-water tortoises, of which a vast quantity is found in particular in the neighbourhood of Soleure. They have been very carefully searched for by M. Hugi; and, from the fragments which he has already collected, it is easy to recognise a considerable number of Fresh-water Tortoises, or Emydes, which further discoveries can alone determine, but of which several are already distinguished by their size and peculiar forms, from all the species hitherto known[260].

It is among these innumerable oviparous quadrupeds, of all sizes and forms; in the midst of these crocodiles, tortoises, flying reptiles, huge megalosauri, and monstrous plesiosauri, that some small Mammifera are said to make their appearance for the first time; and the assertion is so far authenticated by the occurrence of jaws, and some other bones discovered in England, which undoubtedly belong to this class of animals, and particularly to the family of Didelphides, or to that of the Insectivora.

It may, however, be supposed, that the stoney matters which encrust these bones, owe their origin to some local recomposition, posterior to the original formation of the strata. However this may be, it is still found for a long time that the class of Reptiles predominates.

The ferruginous sands, placed in England above the chalk, contain abundance of crocodiles, tortoises, megalosauri, and especially a reptile which presents a character quite peculiar, in as much as its teeth appear worn, like those of our herbivorous mammifera.

To Mr Mantell of Lewes, in Sussex, we are indebted for the discovery of this latter animal, as well as of other large reptiles belonging to the sands lying beneath the chalk. He has named it _Iguanodon_[261].

In the chalk itself there are only reptiles to be seen: there are found in it remains of tortoises and crocodiles. The famous tufaceous quarries of the mountain of St Peter, near Maestricht, which belong to the chalk formation, along with very large sea tortoises, and a multitude of marine shells and zoophytes, have afforded a genus of lizards not less gigantic than the megalosaurus, which has become celebrated by the researches of Camper, and the figures which Faujas has given of its bones, in his history of that mountain.