[Illustration: Fig. 20.--Scratched stone from the till of Boston. Natural size about one foot and a half long by ten inches wide. (From photograph.)] [Illustration: Fig. 21.--Typical section of till in Seattle. Washington State, about two hundred feet above Puget Sound. This is on the height between the sound and Lake Washington.] [Illustration: Fig. 22.--Ideal section, showing how the till overlies the stratified rocks.] [Illustration: Fig. 23.--Vessel Rock, a glacial boulder in Gilsum. N. H. (C. H. Hitchcock.)] 3. Transported boulders. Where there is a current of water deep enough to float large masses of ice, there is scarcely any limit to the size of boulders which may be transported upon them, or to the distance to which the boulders may be carried and dropped upon the bottom. The icebergs which break off from the glaciers of Greenland may bear their burdens of rock far down into the Atlantic, depositing them finally amidst the calcareous ooze and the fine sediment from the Gulf Stream which is slowly covering the area between Northern America and Europe. Northern streams like the St. Lawrence, which are deeply frozen over with ice in the winter, and are heavily flooded as the ice breaks up in the spring, afford opportunity for much transportation of boulders in the direction of their current. In attributing the transportation of a boulder to glacial ice, it is necessary, therefore, to examine the contour of the country, so as to eliminate from the problem the possibility of the effects having been produced by floating ice.