On the vast lapse of time, as inferred from the rate of deposition and
of denudation.
On the poorness of our palaeontological collections.
On the intermittence of geological formations.
On the absence of intermediate varieties in any one formation.
On the sudden appearance of groups of species.
On their sudden appearance in the lowest known fossiliferous strata.
In the sixth chapter I enumerated the chief objections which might be
justly urged against the views maintained in this volume. Most of them
have now been discussed. One, namely the distinctness of specific
forms, and their not being blended together by innumerable
transitional links, is a very obvious difficulty. I assigned reasons
why such links do not commonly occur at the present day, under the
circumstances apparently most favourable for their presence, namely on
an extensive and continuous area with graduated physical conditions. I
endeavoured to show, that the life of each species depends in a more
important manner on the presence of other already defined organic
forms, than on climate; and, therefore, that the really governing
conditions of life do not graduate away quite insensibly like heat or
moisture. I endeavoured, also, to show that intermediate varieties,
from existing in lesser numbers than the forms which they connect,
will generally be beaten out and exterminated during the course of
further modification and improvement. The main cause, however, of
innumerable intermediate links not now occurring everywhere throughout
nature depends on the very process of natural selection, through which
new varieties continually take the places of and exterminate their
parent-forms.
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