By the theory of natural selection all living species have been
connected with the parent-species of each genus, by differences not
greater than we see between the varieties of the same species at the
present day; and these parent-species, now generally extinct, have in
their turn been similarly connected with more ancient species; and so
on backwards, always converging to the common ancestor of each great
class. So that the number of intermediate and transitional links,
between all living and extinct species, must have been inconceivably
great. But assuredly, if this theory be true, such have lived upon
this earth.
ON THE LAPSE OF TIME.
Independently of our not finding fossil remains of such infinitely
numerous connecting links, it may be objected, that time will not have
sufficed for so great an amount of organic change, all changes having
been effected very slowly through natural selection. It is hardly
possible for me even to recall to the reader, who may not be a
practical geologist, the facts leading the mind feebly to comprehend
the lapse of time. He who can read Sir Charles Lyell's grand work on
the Principles of Geology, which the future historian will recognise
as having produced a revolution in natural science, yet does not admit
how incomprehensibly vast have been the past periods of time, may at
once close this volume. Not that it suffices to study the Principles
of Geology, or to read special treatises by different observers on
separate formations, and to mark how each author attempts to give an
inadequate idea of the duration of each formation or even each
stratum.
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