The Seal of the Caspian (_Phoca caspica_) is closely allied to the Arctic Seal, and its presence alone in that sea indicates that at no very distant date--at any rate since pliocene times--a closer connection with the Arctic Ocean existed than at present. I am sure it will be readily granted that there is zoological evidence for the belief of such a connection or union between the two great seas. However, it may be urged that owing to the presence of an ice-sheet in Northern Europe during the Glacial period, such a connection must either have been pre-glacial or have existed after that period. But the connection must have occurred at a time when the Caspian extended far to the north--when indeed the so-called post-tertiary Caspian deposits were laid down (Fig. 17). Since the boulder-clay which covers the plain of Northern Russia is assumed to be the ground-moraine of the great northern ice-sheet, we might expect to find that the Caspian deposits were not contemporaneous with it. Curiously enough, it has been shown by Mr. Sjögren that all observations have pointed to the fact that these two deposits do not overlie one another, but occur side by side, and are therefore contemporaneous. This seems to warrant our belief, that while the boulder-clay was being laid down in Northern Europe, the Aralo-Caspian Sea had some communication with the White Sea. [Illustration: Fig. 17.--Map of European Russia (after Karpinski). The faintly dotted parts indicate the areas covered by boulder-clay, the strongly dotted ones those exhibiting Aralo-Caspian and other post-pliocene deposits.]