It appears, therefore, that a
gradual refrigeration was going on during the Pliocene period,
commencing in the Coralline Crag, becoming intensified in the Red
Crag, being still more severe in the Norwich Crag, and finally
culminating in the Arctic cold of the Glacial period.
Besides the _Mollusca_, the Red Crag contains the ear-bones of
Whales, the teeth of Sharks and Rays, and remains of the Mastodon,
Rhinoceros, and Tapir.
The _Newer Pliocene_ deposits are represented in Britain by the
_Norwich Crag_, a local formation occurring near Norwich. It
consists of incoherent sands, loams, and gravels, resting in
detached patches, from 2 to 20 feet in thickness, upon an eroded
surface of Chalk. The Norwich Crag contains a mixture of marine,
land, and fresh-water shells, with remains of fishes and bones
of mammals; so that it must have been deposited as a local
sea-deposit near the mouth of an ancient river. It contains
altogether more than 100 marine shells, of which 89 per cent
belong to existing species. Of the Mammals, the two most important
are an Elephant (_Elephas meridionalis_), and the characteristic
Pliocene Mastodon (_M. Arvernensis_), which is hitherto the only
Mastodon found in Britain.
According to the most recent views of high authorities, certain
deposits--such as the so-called "Bridlington Crag" of Yorkshire,
and the "Chillesford beds" of Suffolk--are to be also included
in the Newer Pliocene, upon the ground that they contain a small
proportion of extinct shells.
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