s so
extensive, so thick, in part so solid, and filled with the exuviae 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 i