are competent to "root masses (of rock) bodily away."[1] He seems to feel that mere grinding, rasping, and polishing would not be equal to the production of valleys, thousands of feet in depth, in any reasonable length of time, and so invokes this quicker process to get himself out of the difficulty. When and how Dr. Tyndall became possessed of this extraordinary idea I have no means of telling. Comparison of the following passages would lead one to suppose that it was acquired posterior to the publication of his Glaciers of the Alps:—
| "The lighter débris is scattered by the winds far and wide over the glacier, sullying the purity of its surface. Loose shingle rattles at intervals down the sides of the mountains, and falls upon the ice where it touches the rocks. Large rocks are continually let loose, which come jumping from ledge to ledge, the cohesion of some being proof against the shocks which they experience; while others, when they hit the rocks, burst like bomb-shells, and shower their fragments upon the ice. Thus the glacier is incessantly loaded along its borders with the ruins of the mountains which limit it."—Glaciers of the Alps, Chapter on Moraines, p. 263 (1860). | "In the vast quantities of moraine-matter which cumbers many of the valleys we have also suggestions as to the magnitude of the erosion which has taken place. This moraine-matter, moreover, is only in part derived from the falling of rocks from the eminences upon the glacier; it is also in great part derived from the grinding and ploughing-out of the glacier itself. This accounts for the magnitude of many of these ancient moraines, which date from a period when almost all the mountains were covered with ice and snow, and when consequently the quantity of moraine-matter derived from the naked crests cannot have been considerable."[2]—Phil. Mag., Oct. 1864, p. 271. |
It has been already shown (pp. 325-6) that the notion that the mountains were completely covered by glaciers (or anything like completely covered) is erroneous, and the evidence which leads to that conclusion is clearly supported by the fact that a great proportion (I think it may be said the great proportion) of the materials are angular which compose the moraines of the past, as well as of
