s are far more closely related to each other, than
are the fossils from two remote formations. Pictet gives as a well-known
instance, the general resemblance of the organic remains from the
several stages of the chalk formation, though the species are distinct
in each stage. This fact alone, from its generality, seems to have
shaken Professor Pictet in his firm 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
the 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 period, 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 fact of fossil remains
from closely consecutive formations, though ranked as distinct species,
being closely related, 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 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 we assuredly
do find. We find, in short, such evidence of the slow and scarcely
sensible mutation of specific forms, as we have a just right to expect
to find.

ON THE STATE OF DEVELOPMENT OF ANCIENT FORMS.

There has been much discussion whether recent forms are more highly
developed than ancient. I will not here enter on this subject, for
naturalists have not as yet defined to each other's satisfaction what is
meant by high and low forms. But in one particular sense the more recent
forms must, on my theory, be higher than the more ancient; for each new
species is formed by having had some advantage in