The presence of Palm-trees
upon the land, and of numerous large Cowries, Cones, and other
shells of warm regions in the sea, sufficiently proves this. In
the Older Pliocene deposits, on the other hand, northern forms
predominate amongst the Shells, though some of the types of hotter
regions still survive. In the Newer Pliocene, again, the Molluscs
are such as almost exclusively inhabit the seas of temperate
or even cold regions; whilst if we regard deposits like the
"Bridlington Crag" and "Chillesford beds" as truly referable to
this period, we meet at the close of this period with shells such
as nowadays are distinctively characteristic of high latitudes. It
might be thought that the occurrence of Quadrupeds such as the
Elephant, Rhinoceros, and Hippopotamus, would militate against
this generalisation, and would rather support the view that the
climate of Europe and the United States must have been a hot
one during the later portion of the Pliocene period. We have,
however, reason to believe that many of these extinct Mammals
were more abundantly furnished with hair, and more adapted to
withstand a cool temperature, than any of their living congeners.
We have also to recollect that many of these large herbivorous
quadrupeds may have been, and indeed probably were, more or less
migratory in their habits; and that whilst the winters of the
later portion of the Pliocene period were cold, the summers might
have been very hot.
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