Such a
condition of things could not, however, have generally prevailed for any
length of time in the earlier periods of the world, since subterranean
forces must have striven in all epochs to exert a counteracting influence.
Sedimentary strta have been either precipitated or deposited from liquids,
according as the materials entering into their composition are supposed,
whether as limestone or argillaceous slate, to be either chemically
dissolved or suspended and commingled. But earth, when dissolved in fluids
impregnated with carbonic acid, must be regarded as undergoing a mechanical
process while they are being precipitated, deposited, and accumulated into
strata. This view is of some importance with respect to the envelopment of
organic bodies in petrifying calcareous beds. The most ancient sediments of
the transition and secondary formations have probably been formed from water
at a more or less high temperature, and at a time when the heat of the upper
surface of the earth was still very considerable. Considered in this point
of view, a Plutonic action seems to a certain extent also to have taken
place in the sedimentary strata, especially the more ancient; but these
strata appear to have been hardened into a schistose structure, and under
great pressure, and not to have been solidified by cooling, like the rocks
that have issued from the interior, as, for instance, granite, porphyry, and
basalt.
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