vexity, and this affords evidence that the Alps have been subjected to less abrading power than the district in Greenland to the east of Clanshavn. Now, if there is any truth in the assumption that glaciers dig away into soft rocks with much greater rapidity than into hard ones, there is, of course, greater opportunity for the exercise of this discriminative excavation when great power is exerted and when great erosion occurs, than when less power is exercised and less matter is removed. In Greenland, although enormous power has been exerted, and a considerable depth of rock has been undoubtedly removed, we find no appreciable distinction made in the treatment of two materials of very different degrees of hardness. How, then, is it possible to suppose that the prodigious amount of distinction could have been made which is assumed by Professor Ramsay in the less eroded Alps?
These are by no means the only obstacles which stand in the way of acceptance of his theory.[1] The difficulty is great of explaining how the glaciers excavated the rock-basins which exist, but it is still more troublesome to account for the non-existence of those which ought to have been made. The Professor explained at considerable length why they would not be formed upon steep ground (§ 9, p. 316), and I cordially agree with the first part of his remarks; but he went on to say that when a glacier descended into a "flat valley the case was different. There, to use homely phrases, the ice had time to select soft places for excavation." "Why, then," asked several eminent persons—Mr. John Ball and Professor Favre amongst the number—"are there not lakes in the Valley of Aosta?" The valley is precisely the kind of one in which they should have been formed. Its inclination, as I have shown (p. 313), is very moderate, and several parts of it (the site of the city of Aosta, for example) are almost plains. The glacier which occupied it, one would have thought, was thick enough to have ground out basins in
- ↑ For some of the more important objections, see Sir R. Murchison's Address to the Royal Geog. Soc. 1864; Sir C. Lyell's Antiquity of Man and Elements of Geology; Prof. Studer's Origine des Lacs Suisses; Prof. Favre in Phil. Mag. March 1865; and Mr. John Ball in Phil. Mag. Feb. 1863.
