way below, we find a difference. Some are still the same, and others,
if not quite the same, are very much like what we have now; but here
and there a creature of a different form appears.

Go deeper still, and the kinds of animals change further. Fewer and
fewer resemble those which now range the earth; more and more belong
to other species.

Descend through layer after layer till we come to rocks built in
earliest ages and not one fossil shall we find precisely the same as
one animal living now.

So not only are the rocks built in successive order, stratum after
stratum belonging to age after age in the past, but fossil-remains
also are found in successive order, kind after kind belonging to past
age after age.

Although in the first instance the succession of fossils was
understood by means of the succession of rock-layers, yet in the
second place the arrangement of rock-layers is made more clear by the
means of these very fossils.

A geologist, looking at the rocks in America, can say which there were
first-formed, which second-formed, which third-formed. Also, looking
at the rocks in England, he can say which there were first-formed,
second-formed, third-formed. He would, however, find it very
difficult, if not impossible, to say which among any of the American
rocks was formed at about the same time as any particular one among
the English rocks, were it not for the help afforded him by these
fossils.