glacier progresses; and until this stratum, interposed by the glacier itself, is ground away, the bed-rock (or whatever may happen to be over the bed-rock) is not assailed. The evidence is that the stratum of glacial drift which was deposited in this way at the mouth of the Valley of Aosta was able to resist the grinding of the glacier during the whole of its prolonged operations around Ivrea, and this fact gives, perhaps, a clearer idea of the extremely limited power of glaciers for excavation than any other which can be brought forward.
The weight of evidence seems to me to bear heavily against Professor Ramsay's theory. In support of it, he has literally nothing more than the facts that glaciers abrade rocks over which they pass, and that there are numerous rock-basins (occupied or not occupied by lakes) lying within areas which were formerly covered by glacier. Here certainty ends. There are nothing but conjectures left, most of which have not even probability on their side. The idea that all petty pools and small tarns (which lie in rock-basins) occupy areas which have been subjected to special grinding, seems to me to be fully as absurd as the notion that each one lies in an area of special subsidence; and if all the geologists in the world were to swear that it was a solemn verity, I could not believe it, after what I have seen of the behaviour of glaciers upon rocks. The notion that the great lake-basins occupy areas that were filled with especially soft strata, which were subjected to exceptional grinding, seems to me not to be warranted. It is doubtful if the soft strata had any existence; it is doubtful if there was exceptional grinding; and it is highly improbable that the glaciers would have worked upon those basins at a rate ten, fifty, or a hundred times faster than they did in other places, even if the basins were filled with soft strata. More evidence is wanted upon this head; but it will be surprising if fresh facts upset those which have been already observed. Looking at all this doubt and conjecture on one side, and the numerous facts upon the other which prove that very small glacier-erosion has occurred throughout the Alps generally, and the extremely limited capacity of glaciers for
