Essay on the Theory of the Earth

by baron Georges Cuvier

What has just been said does not entitle us to admit that the various parts of the earth have been, from time to time, overflowed with water. Yet are there other appearances which completely indicate such a change, namely, beds of coal, and the fossil remains of land animals. The carbonisation of roots of trees in clefts of rocks, and of marsh plants in peat-bogs, which takes place, as it were, under our own immediate observation; the transitions of bituminous wood into pitch-coal, the frequent presence of vegetables partly converted into coal, in the neighbourhood of beds of coal, and which are more abundant the nearer they are to these beds; and, finally, the chemical nature of coal, which is similar to that of vegetables, go to prove the vegetable origin of the older and independent coal formation.

Though some fossil vegetables might derive their origin, by being floated to quarters more or less remote from their native soil, as we find to be the case in many islands of the South Sea, and on other shores; on the other hand, neither the breadth and extent of beds of coal, nor the erect position in which fossil trees and reed plants are not unfrequently found in their neighbourhood, coincide with such an explanation. The plants, from which these beds were formed, once stood and grew in the place where they were buried; and, from these remains, we infer that they were entirely land plants, tree-ferns, Lycopodia, and other cryptogamia. It also appears undeniable, that the land, being once dry, was, during a longer or shorter time, covered with luxuriant vegetation; that it was afterwards overflowed with water, and then became dry land again. But, was this overflow of water produced by a sudden, violent, and universal catastrophe, such as we consider the deluge? Many circumstances leave room for opposite conjecture. If it is probable that the older or black coal is of vegetable origin, the plants from which it has originated, must have suffered an incomparably greater change than those of more recent coal formations. Their composition and their texture, afford evidence of a long operation of the fluid in which the changes were produced; and their situation, proves that the substance of the plants, though not entirely dissolved, was yet much comminuted, and was kept floating and swimming, and then precipitated. How can we, in any other way, account for the layers of sandstone and slate-clay, with which coal regularly alternates, so that from one to sixty alternate beds have been enumerated? How can we explain the combination of mineral coal with slate-clay, or account for the appearance of bituminous shale, flinty slate, of iron-pyrites and iron-ore, in the midst of mineral coal itself? We do not, however, admit of a repeated uncovering and covering of the land with water, and of a renewal of vegetation for every particular bed of coal; far from it, for violent inundations exhibit very different phenomena. These formations, like pure mineral formations, bear the evident impress of a lengthened operation, and of gentle precipitations; and whoever still entertains doubts regarding this, may have them completely removed by the condition in which vegetable remains are frequently found in the coal formations, by the perfect preservation of the most delicately shaped fern leaves, by the upright position of stems, and by other appearances of a similar character. It is also an important objection against the universality of the cover of water, notwithstanding the wide extent of beds of coal, that they are sometimes accompanied with fossil remains of fresh-water shells, from which we are entitled to draw the conclusion, that they must have been deposited in inclosed basins of inland waters.

From the beds of coal found in various situations among Alpine limestone, as well as in other secondary formations, under similar circumstances, we are at liberty to maintain that they are not indebted for their origin to any universal and sudden revolution.

When we proceed to the second division of coal formations, to brown coal, or to lignite, the principal difference we discover is, that the change which the vegetables have undergone, having taken place at a time when the chemical power had lost much of its energy, was incomplete; and besides, we observe in the different brown coal formations the same repetition of single beds alternating with other beds of rocks, the mixture of different minerals, and not unfrequently of upright stems. Some appear to be derived from sea plants, and others from fresh-water plants; but the greater proportion from land plants. They, equally with the beds of black coal, give evidence of a new overflow of water, and the water plants themselves, which never thrive at a great depth, and which frequently appear under prodigious beds of rocks, must have experienced such a change. But that change was scarcely of the kind which we understand by a deluge, and the frequent repetition of deluges indicated, according to some, by the repeated beds of coal from the transition to the newest tertiary periods, is hardly credible. It may be maintained, with more certainty, of brown coal than of black coal, that they have been formed in land water, and hence in limited and isolated basins of water, since fresh-water animals are their constant attendants.

Although the beds of coal of our secondary formations appear to have originated in a similar way with other mineral formations, and not by violent catastrophes, it is otherwise with a part of those vegetable remains which are met with in alluvial land. Subterranean forests, whose circumference, in some instances, extends about 70 square leagues, partly in a state of good preservation, and partly more or less decomposed, afford satisfactory proof of deluges, and have undoubtedly been covered up with earth by a violent eruption of standing or running water. But these are local effects, similar to what take place in our own day, but on a larger scale.

There are abundant fossil remains of land animals, resembling those of water animals, found in such a state of preservation, that we cannot suppose them to have been brought hither from distant places, and by means of currents. Their appearing in beds of rocks, or generally in aqueous precipitates, proves that the soil they first inhabited, must have been dry land, afterwards overflowed with water.

The appearance of what are called fresh water shells, in alternate beds with marine animals, being sometimes observed in newer flœtz rocks in great abundance, seems to indicate a reiterated retreat and return of the sea. But however meritorious the labours of naturalists, through whom attention has been directed to the subject, may be in other respects, we are nevertheless disposed to entertain doubts concerning their conclusions. In our own seas and ponds upon the coasts, we observe the same testaceous animals growing equally well in salt water, and in water nearly fresh; and, again, fresh water animals living in salt water[402]. By artificial means the inhabitants of the sea may be changed into inhabitants of fresh water; as fresh-water animals are, in their turn, converted into marine animals, so that, to decide concerning the proper element of each individual species is often matter of difficulty. Therefore, other circumstances besides that of containing salt must be taken into account. The occasional plenty, scarcity, or absolute want of food; the soil being sometimes sandy, slimy, or rocky; the depth, extent, agitation or tranquillity of the water; and, finally, the quality of the air contained in it, may be as instrumental in determining the habitation of these animals, as the materials which the water holds in solution. An excellent observer has indeed very lately shewn in a treatise, which supports the idea of fresh-water formations, that we possess no unerring character for distinguishing sea shell-fish from those of fresh water; but admitted, notwithstanding the transition above stated, we can draw a line of distinction between them, we must not forget that this investigation is neither regarding sea shell-fish now existing, nor of our present waters. We indeed draw our conclusion, and not without reason, from similar conformation, similar modes of existence. But one of two things must be; either that the shell-fish, whose remains are found in beds of rocks, lived in the water out of which these beds were precipitated, or the water in which they lived, was dislodged by other water containing the materials of the precipitations. In the first and more generally admitted case, the water was so different from the present water, whether salt or fresh, that we cannot infer from the inhabitants of the latter any thing concerning the inhabitants of the former; but we can confidently maintain, that a greater resemblance prevails between our sea and land water, than between either the one or the other, and that fluid which was inhabited by the shell-fish. In other respects, there remains no other difference between fresh and salt water formations, but that the bottom upon which the former is placed once contained land water; a fact worthy of observation: but the notion of enclosed basins, and of isolated formations originating in them, the way in which fresh water formations are supposed to have taken place, remained a long time unsatisfactory. Finally, we may be permitted to ask, upon what grounds they considered themselves entitled to ascribe to the former sea the continual possession of a portion of salt, while the salt precipitates appear only at particular intervals, and after long interruptions? If the sea occasionally contained a great, and sometimes a very small, quantity of salt, it might equally be at times altogether without it. And yet it deserves to be remembered, that the beds of rock, to which the salt formations are most nearly related, contain no petrifactions; that, therefore, the so-called marine animals are wanting in those periods during which we have any direct evidence of the presence of salt water.

There is, however, a geognostic fact, which, in preference to all others, has been cited in evidence of violent revolutions and deluges, that is, the appearance of conglomerates or of reproduced kinds of stone. Indeed, there might still be a wide field for investigation here, and more than one formation, which now passes for sandstone, might be acknowledged as an original and chemical production; without having occasion to go so far as Mr Gerhard does with greywacke,—that is, to consider them as immediate precipitates from the atmosphere. But still conglomerates sufficiently genuine, will remain from the transition period through all the subsequent formations, to serve as acknowledged monuments of destruction, as well as of the renovation of what was destroyed. These are the Codices rescripti, in the archives of the Earth, out of which, the antiquarian will one day decipher the almost obliterated traces of her former condition, as well as the history of her changes. Though these conglomerates deviate so much in their nature, and in the character of their origin, from chemical productions, they have yet among themselves this remarkable and common characteristic, that, with few exceptions, the older are much less varied in character, and more extensive in distribution, than the newer, and that, at length, the newest conglomerates become mere local appearances. But, in reference to the main question which engages our attention, we may conjecture that the beds of rocks from which the sea had never retreated, might be assailed by its floods and currents, and shattered to pieces, as happens even in our own time, and the fragments be again reunited into solid rocks, by means of the still remaining dissolved matter in the water. But of many conglomerates it is evident that they have been deposited on the dry land, in the same way as our gravels. Jupiter, who took counsel with himself, whether he would destroy the sinful world with fire or water, and at length decided for water[403], may not be so justly considered the author of these appearances, as Saturn, who devoured his children. Or, to be less metaphorical in our language, it may perhaps have been with the origin of conglomerates, as it is in our own day with the origin of fragments of rock and boulders, in which the rock being fractured in various places by the alternations of heat and cold, by the influence of air and atmospheric water, falls into pieces of greater or smaller magnitude, which are carried forward by the water, and gradually rounded in their progress, so that they assume a more perfectly globular shape the farther they are removed from their original situation. Therefore, as regards the foregoing enquiry, it is not an unimportant circumstance, that the long but continual rolling of the boulders during their rounding, appears to be much more efficacious than a rapid and violent impetus, and that, in this case, as in many other geognostic appearances, time rather than force is to be taken into account. Another circumstance, perhaps, corresponds with this, that the change produced by the weather, not only by the first disunion, but also by the progressive disintegration of the rocks, by the blunting of the edges and corners, by the diminution of the fragments, and generally in the origin of the boulders and fragments of rocks of every description, has just as much influence as the mechanical operation of the water; and that a great part of the land called Alluvial, generally owes its existence to this cause[404]. But if, upon farther consideration, the conglomerates appear to derive their origin in a similar way with rolled masses of gravel, they afford evidence, nevertheless, of the elevated station of the water in the neighbourhood, from which they had been before removed; for their conglomeration could take place only under water; and, with few exceptions, they occupy an incomparably greater elevation than any of the coal formations, or any of the beds of rocks which enclose the remains of land animals.

Geognosy certainly contains many facts, which cannot be explained, but by a change from dry land to the bottom of the sea, although our knowledge of them is still so imperfect, that we cannot hazard a probable conjecture respecting the numbers of these changes, whether they commence at the same or at different periods in the various quarters of the world, and whether they are local or universal. These changes appear neither sudden nor violent, such as we consider revolutions of the earth, but at all times proceed with silent and regular steps, and depend upon similar causes, concealed it is true from us, such as the universal retreat of the waters from their original height to the present bed of the ocean. We do not belong to those geologists who divert the world from its axis for the purpose of explaining the inequalities of its surface, at whose command the Earth sometimes opens her bosom to engulf the sea, and at other times the floodgates of Heaven are lifted up to pour down another ocean. He who reflects on the devastation caused by earthquakes, inundations and the fall of mountains, even though they are merely local appearances confined to particular quarters, cannot help putting the question to himself, how the order, regularity and connection exhibited by strata of rocks, could in any measure exist, if the same or similar accidents had happened throughout the whole world, and if mechanical power had operated with such energy, and to such an extent? All our knowledge of the structure of the earth, and of the existence of its inhabitants, declares rather a quiet uninterrupted and continually progressive advancement in its formation and development.

In the lapse of geological epochs, we observe a gradation of rock formations following one another, in which the latter, however remotely connected, still appear sufficiently similar to the earlier to indicate a common origin, till they at length terminate in simple formations, resembling those which are presently taking place. When the precipitates were exhausted, and the structure was completed, nay, even earlier, its destruction commenced; not that violent destruction by which lofty mountains are torn asunder and levelled, no uproar of nature, no gigantic struggle of the elements, such as we commonly conceive, but a decomposition of the strata of rocks to a greater or less depth, caused partly by chemical, partly by mechanical, but slow operating powers, what they wanted in intensity being compensated by the endurance of their operation. According to the common law of nature, deficiency of power is supplied by duration of time; for, of all the oracles which have been consulted concerning the formation of the earth, there is no one which can make such important revelations to us as the oracle of the age of mountains. These operations at the earth’s surface generally appear to have produced its present figure, and to have designed it for the habitation of numerous organic beings. This appears as early as a suitable element occurred; first, in water, then in land animals; and, like the formation of rocks, we observe a regular succession of organic formations, the later always descending from the earlier, down to the present inhabitants of the earth, and to the last created being who was to exercise dominion over them. But here occurs this important distinction: the organic world with youthful vigour renews itself daily, and decomposes its materials only to reunite them by fresh combinations in uninterrupted succession; while the powers of the inorganic world appear almost extinguished. Though this course of nature is manifest to our own observation, her resources and progress are, on the contrary, more concealed; and we can hardly lift the veil which conceals her, unless we follow Bacon’s advice, Turn back from rash theories, and follow observation and experience.