He at the outset affirms that nature has, like mankind, also had her intestine wars, and that “the surface of the globe has been much convulsed by successive revolutions and various catastrophes.”
As first proof of the revolutions on the surface of the earth he instances fossil shells, which in the lowest and most level parts of the earth are “almost everywhere in such a perfect state of preservation that even the smallest of them retain their most delicate parts, their sharpest ridges, and their finest and tenderest processes.”
“We are therefore forcibly led to believe not only that the sea has at one period or another covered all our plains, but that it must have remained there for a long time and in a state of tranquillity, which circumstance was necessary for the formation of deposits so extensive, so thick, in part so solid, and filled with the exuviæ of aquatic animals.”
But the traces of revolutions become still more marked when we ascend a little higher and approach nearer to the foot of the great mountain chains. Hence the strata are variously inclined, and at times vertical, contain shells differing specifically from those of beds on the plains below, and are covered by horizontal later beds. Thus the sea, previous to the formation of the horizontal strata, had formed others, which by some means have been broken, lifted up, and overturned in a thousand ways. There had therefore been also at least one change in the basin of that sea which preceded ours; it had also experienced at least one revolution.
He then gives proofs that such revolutions have been numerous.
“Thus the great catastrophes which have produced revolutions in the basins of the sea were preceded, accompanied, and followed by changes in the nature of the fluid and of the substances which it held in solution, and when the surface of the seas came to be divided by islands and projecting ridges, different changes took place in every separate basin.”
We now come to the Cuvierian doctrine par excellence, one in which he radically differs from Lamarck’s views as to the genetic relations between the organisms of successive strata.
“Amid these changes of the general fluid it must have been almost impossible for the same kind of animals to continue to live, nor did they do so in fact. Their species, and even their genera, change with the strata, and although the same species occasionally recur at small distances, it is generally the case that the shells of the ancient strata have forms peculiar to themselves; that they gradually disappear till they are not to be seen at all in the recent strata, still less in the existing seas, in which, indeed, we never discover their corresponding species, and where several even of their genera are not to be found; that, on the contrary, the shells of the recent strata resemble, as regards the genus, those which still exist in the sea, and that in the last formed and loosest of these strata there are some species which the eye of the most expert naturalists cannot distinguish from those which at present inhabit the ocean.
“In animal nature, therefore, there has been a succession of changes corresponding to those which have taken place in the chemical nature of the fluid; and when the sea last receded from our continent its inhabitants were not very different from those which it still continues to support.”
He then refers to successive irruptions and retreats of the sea, “the final result of which, however, has been a universal depression of the level of the sea.”
“These repeated irruptions and retreats of the sea have neither been slow nor gradual; most of the catastrophes which have occasioned them have been sudden.”