a
nearly perfect chain of the intermediate links.

It is just possible, by the theory, that one of two living forms might
have descended from the other; for instance, a horse from a tapir; and
in this case DIRECT intermediate links will have existed between them.
But such a case would imply that one form had remained for a very long
period unaltered, whilst its descendants had undergone a vast amount of
change; and the principle of competition between organism and organism,
between child and parent, will render this a very rare event; for in all
cases the new and improved forms of life tend to supplant the old and
unimproved forms.

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 natural and domestic 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
forms; 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 the earth.

ON THE LAPSE OF TIME, AS INFERRED FROM THE RATE OF DEPOSITION AND EXTENT
OF DENUDATION.

Independently of our not finding fossil remains of such infinitely
numerous connecting links, it may be objected that time cannot have
sufficed for so great an amount of organic change, all changes having
been effected slowly. It is hardly possible for me to recall to the
reader who is not 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, and yet does not admit how 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
of each stratum. We can best gain some idea of past time by knowing the
agencies at work; and learning how deeply the surface of the land has
been denuded, and how much sediment has been deposit