Again: if these drift-deposits, these vast accumulations of sand, clay, gravel, and bowlders, were caused by a great continental ice-sheet scraping and tearing the rocks on which it rested, and constantly moving toward the sun, then not only would we find, as I have suggested in the case of glaciers, the accumulated masses of rubbish piled up in great windrows or ridges along the lines where the face of the ice-sheet melted, but we would naturally expect that the farther north we went the less we would find of these materials; in other words, that the ice, advancing southwardly, would sweep the north clear of _débris_ to pile it up in the more southern regions. But this is far from being the case. On the contrary, the great masses of the Drift extend as far north as the land itself. In the remote, barren grounds of North America, we are told by various travelers who have visited those regions, "sand-hills and erratics appear to be as common as in the countries farther south."[5] Captain Bach tells us[6] that he saw great chains of sand-hills, stretching [1. "A Short American Tramp," pp. 68, 107. 2. Ibid., p. 68. 3. Ibid., p. 72. 4. Ibid., p. 76. 5. "The Great Ice Age," p. 391. 6. "Narrative of Arctic Land Expedition to the Mouth of the Great Fish River," pp. 140, 346.] {p. 37} away from each side of the valley of the Great Fish River, in north latitude 66°, of great height, and crowned with gigantic bowlders. Why did not the advancing ice-sheet drive these deposits southward over the plains of the United States? Can we conceive of a force that was powerful enough to grind up the solid rocks, and yet was not able to remove its own _débris_? But there is still another reason which ought to satisfy us, once for all, that the drift-deposits were not due to the pressure of a great continental ice-sheet. It is this: If the presence of the Drift proves that the country in which it is found was once covered with a body of ice thick and heavy enough by its pressure and weight to grind up the surface-rocks into clay, sand, gravel, and bowlders, then the tropical regions of the world must have been covered with such a great ice-sheet, upon the very equator; for Agassiz found in Brazil a vast sheet of "ferruginous clay with pebbles," which covers the whole country, "a sheet of drift," says Agassiz, "consisting of the same homogeneous, unstratified paste, and containing loose materials of all sorts and sizes," deep red in color, and distributed, as in the north, in uneven hills, while sometimes it is reduced to a thin deposit. It is recent in time, although overlying rocks ancient geologically. Agassiz had no doubt whatever that it was of glacial origin.