This is indicated by the
occurrence of Arctic shells in the superficial deposits of this
period, whilst the Musk-ox and the Reindeer roamed far south of
their present limits.
Lastly, it was from the study of fossils that geologists learnt
originally to comprehend a fact which may be regarded as of cardinal
importance in all modern geological theories and
speculations--namely, that the crust of the earth is liable to
local elevations and subsidences. For long after the remains of
shells and other marine animals were for the first time observed
in the solid rocks forming the dry land, and at great heights
above the sea-level, attempts were made to explain this almost
unintelligible phenomenon upon the hypothesis that the fossils
in question were not really the objects they represented, but
were in truth mere _lusus naturoe_, due to some "plastic virtue
latent in the earth." The common-sense of scientific men, however,
soon rejected this idea, and it was agreed by universal consent
that these bodies really were remains of animals which formerly
lived in the sea. When once this was admitted, the further steps
were comparatively easy, and at the present day no geological
doctrine stands on a firmer basis than that which teaches us
that our present continents and islands, fixed and immovable as
they appear, have been repeatedly sunk beneath the ocean.
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