warrantable to assert, in the face of a well-ascertained fact like this, that the pools and small tarns lying in rock-basins (which are numerous in almost all mountainous countries) owe their existence to the excavating power of glacier, merely because glacier has passed over the spots which they occupy; and, to say the least, to be injudicious to apply terms like "scooping out" to the rounding and polishing-up of the beds of such pools, because those terms convey an impression that is entirely erroneous. The hollows in which such pools are found would necessarily have been obliterated, not deepened, if the glaciers had worked for a greater length of time.[1]
Professor Ramsay holds the directly contrary opinion. Unless I am entirely mistaken in regard to his ideas, he supposes that the beds of almost all pools, tarns, and lakes, which lie in true rock-basins, have been scooped out or excavated by glaciers. As a rule he does not consider that these lakes occupy hollows which were formed either entirely or in part through upheaval or subsidence, (either or both), or antecedent erosion, but that the lake-basins are simply holes which glaciers have dug out. How or in what way the glaciers did the work, I have not the most remote idea. I turn the Professor's pages over and over without gaining the slightest clue.[2] But I gather from the Proceedings of the Geological Society,
- ↑ Sir Charles Lyell remarks with much force, in the 6th ed. of his Elements, p. 170, "Where opportunities are enjoyed of seeing part of a valley from which a glacier has retreated in historical times, no basin-shaped hollows are conspicuous. Dome-shaped protuberances, the roches moutonnées before described, are frequent; but the converse of them, or cup-and-saucer-shaped cavities, are wanting." The justness of these observations is undeniable. The perusal of Professor Ramsay's papers would lead any one personally unacquainted with glacier-eroded rocks to conclude that the reverse was the case—that saucer-shaped hollows were abundant, or, in other words, that concavities predominated.
- ↑ I cannot find anything more explicit than this:—"The greater number lie in rock-basins formed by the grinding of glacier-ice." This is simple assertion; now for the proof. "Sometimes in the convolutions of the strata (conjoined with preglacial denudation subsequent to the contortion of the beds) softer parts of the country may have been scooped out; but perhaps more generally they were formed by the greater thickness and weight of glacier-ice on particular areas, due to accidents to which it is now often difficult or impossible to find the clue."—Proc. Geol. Soc., 1862, p. 188.
