line a e b. This would account for the hollowing out of rock-basins across their shorter axes. I do not merely think that this
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is what might happen, but that it is what must happen in course of time; and saying as much is practically admitting the power of glaciers to produce concavities in large areas of rock. It may seem now as if all were conceded that is required by Professor Ramsay. It is not so. His principle appears to me to be sound, but his conclusions entirely unwarrantable. There is not the least doubt that rocks underneath the thicker parts of the existing glaciers are being eroded to a greater extent than those which are covered by a small amount of ice. The same must have happened during the glacial period. But these differences in the depth of the erosion may, I think, be disregarded, because the difference between the maximum and the minimum in any given area would not amount to more than a very few feet; as the evidence which has already been recounted tends to show that glacier-erosion has been insignificant at any and every part of the valleys; and the valleys, it must always be remembered, were occupied by the glaciers for more time than the plains out of which Professor Ramsay would have us believe that his great lake-basins were excavated.
To the foregoing remarks the Professor has two answers. First, he has the idea that the retardation which a glacier would experience upon its arrival on a plain would tend to "heap-up" the ice (see p. 320). This is no doubt correct. He considers that the glacier would in consequence "attain an unusual thickness, thus exercising, after its descent, an extra erosive power." Here we get into the region of surmises. To this we may demur. For he overlooks, or, at least, does not notice, that the glacier would be melting at a rapid rate, at or near its end, and that, in all probability, the extra ablation would counterbalance whatever thick-
