changes which the earth's surface has undergone in the course of the
millions of years of its existence. Turn back a square foot of the
thin turf, and the solid foundation of the land, exposed in cliffs of
chalk five hundred feet high on the adjacent shore, yields full
assurance of a time when the sea covered the site of the "everlasting
hills"; and when the vegetation of what land lay nearest, was as
different from the present Flora of the Sussex downs, as that of
Central Africa now is.* No less certain is it that, between the time
during which the chalk was formed and that at which the original turf
came into existence, thousands of centuries elapsed, in the course of
which, the state of nature of the ages during which the chalk was
deposited, passed into that which now is, by changes so slow that, in
the coming and going of the generations of men, had such witnessed
them, the contemporary, conditions would have seemed to be unchanging
and unchangeable.

* See "On a piece of Chalk" in the preceding volume of these
Essays (vol. viii. p. 1).

But it is also certain that, before the deposition of the chalk, a
vastly longer period had elapsed; throughout which it is easy to
follow the traces of the same process of ceaseless modification and of
the internecine struggle for existence of living things; and that even
when we can get no further [4] back, it is not because there is any
reason to think we have reached the beginning, but because the trail
of the most ancient life remains hidden, or has become obliterated.

Thus that state of nature of the world of plants which we began by
considering, is far from possessing the attribute of permanence. Rather
its very essence is impermanence. It may have lasted twenty or thirty