They furnish us with a record, the general nature of which
cannot be misinterpreted, of the kinds of things that have lived upon
the surface of the earth during the time that is registered by this
great thickness of stratified rocks. But even a superficial study of
these fossils shows us that the animals and plants which live at the
present time have had only a temporary duration; for the remains of such
modern forms of life are met with, for the most part, only in the
uppermost or latest tertiaries, and their number rapidly diminishes in
the lower deposits of that epoch. In the older tertiaries, the places of
existing animals and plants are taken by other forms, as numerous and
diversified as those which live now in the same localities, but more or
less different from them; in the mesozoic rocks, these are replaced by
others yet more divergent from modern types; and in the palaeozoic
formations the contrast is still more marked. Thus the circumstantial
evidence absolutely negatives the conception of the eternity of the
present condition of things. We can say with certainty that the present
condition of things has existed for a comparatively short period; and
that, so far as animal and vegetable nature are concerned, it has been
preceded by a different condition.
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