Lastly, it has been shown upon physical as well as palaeontological evidence, that the greater part of the North Temperate Zone, at a comparatively recent geological period, has been visited with all the rigours of an Arctic climate, resembling that of Greenland at the present day.

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..