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318 the Alps had been (entirely?) excavated by glaciers! His summing up was as follows:—

"That such an agent was competent to plough out the Alpine valleys cannot, I think, be doubted; while the fact that during the ages which have elapsed since its disappearance the ordinary denuding action of the atmosphere has been unable, in most cases, to obliterate even the superficial traces of the glaciers, suggests the incompetence of that action to produce the same effect. That the glaciers have been the real excavators seems to me far more probable than the supposition that they merely filled valleys which had been previously formed by water denudation. Indeed the choice lies between these two suppositions: shall we assume that glaciers filled valleys which were previously formed by what would undoubtedly be a weaker agent? or shall we conclude that they have been the excavators which have furrowed the uplifted land with the valleys which now intersect it? I do not hesitate to accept the latter view."—Phil. Mag., Sept. 1862, p. 172.

Except for the character of the magazine in which Dr. Tyndall's paper appeared, it might have been supposed that he was poking fun at his readers and at Professor Ramsay. For although to some persons he might have seemed to be supporting the views of the Professor, he was, in reality, advancing opinions which were directly opposed to them. Professor Ramsay promptly repudiated this doubtful extension of his theory. Indeed, he could hardly do otherwise, after having spoken of "the well-ascertained fact, that previous to the Tertiary glacial epoch, most of the grander contours of hill and valley were in Britain (and elsewhere in Europe and America), nearly the same as now." He now repeated the same statement in slightly different words. "The evidence is imperfect; but such as it is, it gives much more than a hint that the large valleys were in their main features approximately as deep as now, before they were filled with ice;" and, further, he produced in evidence a potent reason for declining to believe that the Valley of Aosta had been excavated by glaciers. This latter passage will presently be quoted at length, on account of its importance.

For a time Dr. Tyndall made no sign in reply, but, in October