te climate, such as might have been produced by the proximity of
a cold sea on one side and of a warm one at the other, than by invoking
an arctic climate with enormous glaciers. Most of the living animals and
plants would have been exterminated under the latter conditions.
Palaeontological evidence in Great Britain clearly indicates that
southern species migrated first to these islands, that Arctic species
were then driven south from their native lands,--probably owing
insufficient food-supply and climatic changes in the north,--that
finally eastern species invaded the country--all this without the annual
temperature of Europe being apparently much affected. For we find in the
British pleistocene deposits--and Mr. Lydekker draws particular
attention to this remarkable fact--a curious intermingling of southern
and northern mammals, which undoubtedly lived side by side. Everybody
knows that northern and Arctic species can live perfectly well in a
temperate climate, but that it is almost impossible to acclimatise
southern animals in an Arctic or even temperate one. We have in this
circumstance almost a proof, therefore, that the climate cannot have
been very cold. Though a cold sea bathed the shores of Eastern England,
and even eventually invaded a portion of Northern England, the warm
ocean on the west must have effectually prevented any great lowering of
temperature.

At the time when the North European Sea flooded a portion of England,
Scandinavia was still connected with Scotland, and the latter with
Ireland (Fig. 6, p. 126). There is no doubt that the food-supply in the
Arctic Regions was decreasing with an increase of snowfall and with the
gradual lowering of the land, which reduced also the habitable area.
Arctic species therefore were driven south in search of fresh pastures.
But it need not be supposed that anything like a vast destruction of the
fauna of the Arctic Regions took place. Only fewer mammals were able to
find food in a given space than heretofore. This southward migration may
have commenced, in the case of plants and the invertebrates, at a much
earlier time,--during the Miocene or Pliocene Epochs,--but it is
doubtful whether the mammals and birds which we find in our pleistocene
and recent deposits began to travel south much before the commencement
of the Glacial period. The beginning of the Glacial period in England, I
think, is indicated by the deposition of the Red Crag, though the latter
is gene