[Illustration: Fig. 13.--Map of Europe, indicating approximately the distribution of land and water during the earlier stages of the Glacial period--shortly after the period represented in Fig. 12, p. 156. The darkly shaded parts indicate the areas covered by water, and the white portions what was land at the time.]
That this ancient Arctic land-connection existed almost throughout the Glacial period appears to me probable. It has often been suggested that such a land-barrier was one of the principal causes of the production of the glacial phenomena in Europe, and as such it must have existed intact certainly during the earlier stages of the Glacial period. The barrier must then have gradually subsided in one or two places; and once a breach was formed, the complete union between the Atlantic and the Arctic Oceans could not have been long delayed.
The terrestrial fauna and flora, as we have seen, lend strong support to the view of the former connection between Scandinavia and Greenland, but many other facts point in the same direction. It was Edward Forbes who first drew attention to the presence of a number of species of littoral molluscs on the coast of Finmark which also occur on the coast of Greenland, and he expressed the firm conviction that they indicated by their existence on both sides of the Atlantic some ancient continuity of the coast-line. He held that the line of migration of these mollusca was probably from west to east, and that it must have taken place during physical conditions entirely different from those prevailing at present. If Forbes's view is correct, a current must have existed from the north coast of North America along the northern shore of the ancient land which stretched east as far as Europe. We have also some palæontological evidence bearing on the existence of such a current (p. 173).
As we shall learn presently, the early stages of the Glacial period were accompanied by a marine transgression over Northern Russia and Germany--an overflow, as it were, of the waters of the Arctic Ocean covering a great part of Northern Europe, with the exception of Norway. One continuous ocean ultimately extended from the east coast of England across Holland, Northern Germany, and Russia to the White Sea (Fig. 12, p. 156). The south of England being at that time joined to France, and Scotland to Scandinavia, there was no direct communication between this large North European Sea and the Atlantic. The glaciers which took their origin in the Scandinavian Mountains discharged icebergs into this sea, and many of them no doubt were stranded on the east coast of England. The boulders of Scandinavian origin which have been discovered in recent geological deposits on that coast have generally been traced to the action of land-ice, but the supposition that they have been carried by icebergs--the older theory--appears to me the more probable one. Such boulders begin to make their first appearance in the Red Crag, a deposit which is now looked upon as belonging to the newer pliocene series. But whether we call it pliocene or pleistocene really matters little. The important fact is, that glacial phenomena, consisting of the appearance of boulders foreign to the country together with an invasion of Arctic shells, are now ushered in upon a coast which shortly before teemed with the southern life of a Mediterranean character. Among the new arrivals in these English crags there are no less than eighteen species of North American marine mollusca. Since the German Ocean had then no direct communication with the Atlantic, these mollusca could only have come from the White Sea, and Forbes's _Arctic current_ would offer an explanation of the manner in which they were enabled to migrate there from their original home.