etching for
thousands of miles over different parts of Europe, has become visible to
us by the effect, not of one, but of many distinct series of
subterranean movements. Time has been required, and a succession of
geological periods, to raise it above the waves in so many regions; and
if calcareous rocks of the middle and upper tertiary periods have been
formed, as homogeneous in mineral composition throughout equally
extensive regions, it may require convulsions as numerous as all those
which have occurred since the origin of the Chalk to bring them up
within the sphere of human observation. Hence the rocks of more modern
periods may appear partial, as compared to those of remoter eras, not
because of any original inferiority in their extent, but because there
has not been sufficient time since their origin for the development of a
great series of elevatory movements.

In regard, however, to one of the most important characteristics of
sedimentary rocks, their organic remains, many naturalists of high
authority have maintained that the same species of fossils are more
uniformly distributed through formations of high antiquity than in those
of more modern date, and that distinct zoological and botanical
provinces, as they are called, which form so striking a feature in the
living creation, were not established at remote eras. Thus the plants of
the Coal, the shells, the trilobites of the Silurian rocks, and the
ammonites of the Oolite, have been supposed to have a wider geographical
range than any living species of plants, crustaceans, or mollusks. This
opinion seems in certain cases to be well founded, especially in
relation to the plants of the Carboniferous epoch, owing probably to the
more uniform temperature of the globe, at a time when the position of
sea and land was less favorable to variations in climate, according to
principles already explained in the seventh and eighth chapters. But a
recent comparison of the fossils of North American rocks with those of
corresponding ages in the European series, has proved that the
terrestrial vegetation of the Carboniferous epoch is an exception to the
general rule, and that the fauna and flora of the earth at successive
periods, from the oldest Silurian to the newest Tertiary was as
diversified as now. The shells, corals, and other classes of organic
remains demonstrate the fact that the earth might then have been divided
into separate zoological provinces, in a manner an