Page:A Treatise on Geology, volume 1.djvu/313

 CHAP. VI. stream, or rather the general flow of warmed water to the north, is variable by slight causes in the present system of nature, and may be admitted to be displaceable by a great disturbance of the sea-bed. Such disturbance must have happened. But further, the northward warm flow of the sea is balanced by a return cold current. It is conceivable that this return of cold water may have passed through the area where erratic blocks occur in Europe, and thus we should have abundantly the elements of cold required for glaciers on the land which stood above the waves in Britain and Scandinavia, It is no small confirmation of this view that we find in the gravel and clay, associated with erratic blocks, and clearly forming the sea-bed of their era, shells which, upon the whole, indicate an arctic character of the marine fauna of the period. It is further important that we find in the valleys of Scandinavia, and the Irish Cumbrian and Grampian Highlands, marks of radiating glaciers, rocks worn and striated for hundreds of feet below the summits; in fact, almost or quite down to the actual sea level, and much below the probable level of the ancient sea which floated the icebergs. Spitzbergen, according to Dr. Martins, gives us at present examples of glaciers which pass to some distance from land, and to some depth below the sea.

Striation and broader grooving of hard rocks on the line of glacier movement are found extensively round the Scandinavian mountains. But it occurs also in low ground in Russia, as on Lake Onega, where the configuration of land to the north forbids the belief that glaciers could be formed. From these and other instances, we must admit with Murchison, that ice dragged on the stony bed of the sea might become a powerful agent. for scratching the rocks, the stones which covered them being also scratched, a circumstance which has caught the attention of Mr. Miller, in his examination of the boulder clay. It does not occur on sea beaches,