which have given rise to them, masses of Cretaceous rock which
formed the bottom of the sea before those mountains existed.
It is therefore clear that the elevatory forces which gave rise
to the mountains operated subsequently to the Cretaceous epoch;
and that the mountains themselves are largely made up of the
materials deposited in the sea which once occupied their place.
As we go back in time, we meet with constant alternations of sea
and land, of estuary and open ocean; and, in correspondence with
these alternations, we observe the changes in the fauna and
flora to which I have referred.

But the inspection of these changes gives us no right to believe
that there has been any discontinuity in natural processes.
There is no trace of general cataclysms, of universal deluges,
or sudden destructions of a whole fauna or flora.
The appearances which were formerly interpreted in that way have
all been shown to be delusive, as our knowledge has increased
and as the blanks which formerly appeared to exist between the
different formations have been filled up. That there is no
absolute break between formation and formation, that there has
been no sudden disappearance of all the forms of life and
replacement of them by others, but that changes have gone on
slowly and gradually, that one type has died out and another has
taken its place, and that thus, by insensible degrees, one fauna
has been replaced by another, are conclusions strengthened by
constantly increasing evidence. So that within the whole of the
immense period indicated by the fossiliferous stratified rocks,
there is assuredly not the slightest proof of any break in the
uniformity of Nature's operations, no indication that events
have followed other than a clear and orderly sequence.