[Illustration: Fig. 49.--Map showing the glaciated area of Europe according to J. Geikie, and the moraines in Britain and Germany according to Lewis and Salisbury.] The physical geography of Europe is so different from that of America, that there was a marked difference in the secondary or incidental effects of the Glacial period upon the two regions. In America the continental area over which the glaciers spread is comparatively simple in its outlines. East of the Rocky Mountains, as we have seen, the drainage of the Glacial period was, for a time, nearly all concentrated in the Mississippi basin, and the streams had a free course southward. But in Europe there was no free drainage to the south, except over a small portion of the glaciated area in central Russia, about the head-waters of the Dnieper, the Don, and the Volga; though the Danube and the Rhône afforded free course for the waters of a portion of the great Alpine glaciers. But all the great rivers of northern Europe flow to the northward, and, with the exception of the Seine, they all for a time encountered the front of the continental ice-sheet. This circumstance makes it difficult to distinguish closely between the direct glacial deposits in Europe and those which are more or less modified by water-action. At first sight it would seem also somewhat hazardous to attempt to correlate with any portion of the Glacial period the deposition of the gravelly and loamy deposits in valleys, which, like those of the Seine and Somme, lie entirely outside of the glaciated area. Upon close examination, however, the elements of doubt more and more disappear. The Glacial period was one of great precipitation, and it is natural to suppose that the area of excessive snow-fall extended considerably beyond the limit of the ice-front. During that period therefore, the rivers of central France must have been annually flooded to an extent far beyond anything which is known at the present time. Since these rivers flowed to the northward, at a period when, during the long and severe winters, the annual accumulation of ice near their mouths was excessive, ice-gorges of immense extent, such as now form about the mouths of the Siberian rivers, would regularly occur. We are not surprised, therefore, to find, even in these streams, abundant indications of the indirect influence of the great northern ice-sheet.