This fact alone, from its generality, seems to have shaken
Professor Pictet in his belief in the immutability of species. He who is
acquainted with the distribution of existing species over the globe, will
not attempt to account for the close resemblance of distinct species in
closely consecutive formations, by the physical conditions of the ancient
areas having remained nearly the same. Let it be remembered that the forms
of life, at least those inhabiting the sea, have changed almost
simultaneously throughout the world, and therefore under the most different
climates and conditions. Consider the prodigious vicissitudes of climate
during the pleistocene period, which includes the whole glacial epoch, and
note how little the specific forms of the inhabitants of the sea have been
affected.
On the theory of descent, the full meaning of the fossil remains from
closely consecutive formations, being closely related, though ranked as
distinct species, is obvious. As the accumulation of each formation has
often been interrupted, and as long blank intervals have intervened between
successive formations, we ought not to expect to find, as I attempted to
show in the last chapter, in any one or in any two formations, all the
intermediate varieties between the species which appeared at the
commencement and close of these periods: but we ought to find after
intervals, very long as measured by years, but only moderately long as
measured geologically, closely allied forms, or, as they have been called
by some authors, representative species; and these assuredly we do find.
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