All the phenomena of distribution of the British fauna and flora are, as we have seen, much more easily explained by the supposition of a damp, temperate 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. Palæontological 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.