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 give 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insensible degrees, one fauna has been replaced by another, are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.
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