Part 24

These alternations now appear to me to form the problem in geology that it is of most importance to solve, or rather to define and circumscribe within due limits; for, in order to resolve it satisfactorily, it would be necessary to discover the cause of these events,--an undertaking which presents a difficulty of quite a different kind.

I repeat it, we see pretty clearly what is going on at the surface of the continents in their present state; we have formed a tolerable conception of the uniform progress and regular succession of the primitive formations, but the study of the secondary formations has been little more than merely commenced. That wonderful series of unknown zoophytes and marine mollusca, succeeded by reptiles and fresh-water fishes equally unknown; and these again replaced, in their turn, by other zoophytes and mollusca, more nearly related to those of the present day; those land animals, and those equally unknown fresh water mollusca and other animals which next occupied the surface, to be again displaced but by mollusca and other animals similar to those of our present seas; the relations of these diversified beings to the plants the remains of which accompany theirs, the connection of these two kingdoms with the mineral strata in which they are deposited; the greater or less uniformity existing between these different orders of beings in the different basins;--these are phenomena which appear to me imperiously to demand the attention of philosophers.

Rendered interesting by the variety of the products of the partial or general revolutions of this epoch, and by the abundance of the various species that figure alternately on the stage, this study is divested of the dryness of that of the primordial formations, and does not, like it, almost necessarily launch into hypotheses. The facts are so direct, so curious, and so evident, that they are sufficient, so to speak, to satisfy the most ardent imagination; and the conclusions to which they lead from time to time, however scrupulous the observer may be, having nothing vague in them, are equally free of any thing arbitrary. In fine, it is in those events that approach nearer to our own times, that we may hope to find some traces of more ancient events, and of their causes; if, indeed, after so many fruitless attempts as have been already made, one may be permitted to flatter himself with such a hope.

These ideas have haunted, I may almost say have tormented me, during my researches among fossil bones, the results of which I have lately presented to the public; researches which embrace but a very small part of those phenomena of the age preceding the last general revolution of the globe, and which are yet intimately connected with all the others. It was almost impossible that the desire should not arise of investigating the general mass of these phenomena, at least as they occur in a limited space around us. My excellent friend, M. Brongniart, in whose mind other studies excited the same desire, had the complaisance to associate me with himself in the task; and it is thus that we have laid the first foundations of our labours upon the environs of Paris. But this work, while it still bears my name, has become almost entirely that of my friend, from the infinite attention which he has bestowed, since the first conception of our plan, and since our journeys, upon the profound investigation of the objects, and the perfecting and arranging of the whole. I have placed it, with M. Brongniart’s consent, in the second part of my “Recherches,” in that in which I treat of the fossil bones of our neighbourhood. Although apparently relating only to a rather limited extent of country, it affords numerous results, which are applicable to geology in general, and, in this point of view, it may be considered as intimately connected with the present discourse; at the same time, that it is, without a doubt, one of the best ornaments of my work.

In it there is presented the history of the most recent changes that have taken place in a particular basin, and it descends so far as the Chalk formation, the extent of which over the globe is vastly more considerable than that of the materials of the basin of Paris. The chalk, which has been considered so modern, is thus found to be advanced in antiquity among the ages of the great period preceding the last catastrophe. It forms a sort of limit between the most recent formations, those to which the name of Tertiary may be reserved, and the formations which are named Secondary, which have been deposited before the Chalk, but after the Primitive and Transition formations.

Recapitulation of the Observations upon the Succession of the Tertiary Formations.

The most superficial strata, those deposits of mud and clayey sand, mixed with rolled pebbles, that have been transported from distant countries, and filled with bones of land animals, the species of which are for the most part unknown, or at least foreign to the country in which they are found, seem especially to have covered all the plains, filled the bottom of all the caverns, and choked up all the fissures of rocks that have come in their way. Described with particular care by Mr Buckland, under the name of diluvium, and very different from those other beds equally consisting of transported matters, continually deposited by torrents and rivers, which contain only bones of animals that still live in the country, and distinguished by the name of alluvium, the former are now considered by all geologists as exhibiting the most obvious proof of the immense inundation which has been the last of the catastrophes of our globe.

Between this diluvium and the chalk, are the formations alternately filled with fresh water and salt water productions, which mark the irruptions and retreatings of the sea, to which this part of the globe has been subjected, since the deposition of the chalk-strata: first, marls and buhrstones, or cavernous quartz, filled with fresh-water shells, similar to those of our marshes and pools; under them marls, sandstones, and limestones, all the shells of which are marine, such as oysters, &c.

At a greater depth are found fresh water formations of an older date, and particularly those famous gypsum deposits of the neighbourhood of Paris, which have afforded so much facility in ornamenting the buildings of that great city, and in which we have discovered whole genera of land-animals, of which no traces had been elsewhere perceived.

They rest upon those not less remarkable beds of limestone, of which our capital is built, in the more or less compact texture of which the patience and sagacity of our naturalists, and of several ardent collectors, have already detected more than 800 species of shells, all of them marine, but the greater part unknown in the presently-existing sea. They also contain only bones of fishes, and of cetacea and other marine mammifera.

Under this marine limestone there is another fresh water deposit, formed of clay, in which there are interposed large beds of lignite (brown coal), or that sort of fossil-coal which is of more recent origin than the common or black coal. Among shells, which are always of fresh water origin, there are also found bones in the deposit; but, what is remarkable, bones of reptiles, and not of mammifera. It is filled with crocodiles and tortoises, but the genera of extinct mammifera which the gypsum contains, are not found in it: they evidently did not exist in the country when these clays and lignites were formed.

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.

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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.

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

+---------------------------------------------+-- | Alluvial Deposits. | +---------------------------------------------+ | Lacustrine Formation with Buhrstones. | +---------------------------------------------+ | Fountainbleau sandstone and sand. | +---------------------------------------------+ | Gypsum with bones. Siliceous Limestone. | Tertiary +---------------------------------------------+ | Coarse Limestone. |Formations. | (London Clay.) | +---------------------------------------------+ | Tertiary sandstone with lignites. | +---------------------------------------------+ | (Plastic clay,--Molasse,--Nagelfluhe.) | +----------+---------------------------------------------+----------+ | white. | | Chalk. tufaceous. Ananchites. | | chloritic. | +-----+--------------------------------------------------+----------+ |Green sand. | |Weald clay. (Secondary Sandstone with lignites.)| Secondary |Iron Sand. | +-----+--------------------------------------------------+----------+ | Ammonites. Jura Limestone. Slaty beds with fishes and | | Planulites. crustacea. | +-----------------------------------------+Coral rag. | | Quadersandstein, or white sandstone, |Dive clay. | | sometimes above the lias. |Oolites and Caen | +-----------------------------------------+ limestone. | | Muschelkalk. |Marly or calcareous lias | | Ammonites nodosus. | with Gryphæa arcuata.| +-----------------------------------------+-------------------------+ | Marls with fibrous gypsum. Saliferous variegated sandstone. | | Arenaceous beds. | +-------------------------------------------------------------------+ | Productus aculeatus. | | Magnesian limestone. Zechstein. (Alpine limestone.) | | Copper slate. | +-------------+-----------------------------------------------------+ |Quartziferous| Co-ordinate formations of porphyry, | |Porphyry. | red sandstone, and coal. | Formations. +-------------+-----------------------------------------------------+ | Transition Formations. | | | | Slates with Lydian-stone, greywacke, diorites, euphotides. | | Limestones with orthoceratis, trilobites and euomphalites. | +-------------------------------------------------------------------+ | Primitive Formations. | | | | Clayslates (Thonschiefer). | | Micaslates. | | Gneiss. | | Granites. | +-------------------------------------------------------------------+

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.