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320 it were, unwillingly and by compulsion, instead of finding its way onwards more or less by virtue of gravity. Indeed the idea is forced on the mind, that the sluggish ice would have a tendency to heap itself up just outside the mouth of the valley, and there attain an unusual thickness, thus exercising, after its descent, an extra erosive power." —Phil. Mag., April 1865, p. 287.

Professor Tyndall does not appear to have found the reply convincing. He is reported to have said at the last Birmingham meeting of the British Association, "that he was convinced that the glaciers of the Alps were competent to scoop out the valleys of the Alps," and I am unaware that his opinions have undergone any alteration since that time. In 1869 he gave a hard side-blow to Professor Ramsay, in Macmillan's Magazine, by proving that some existing Alpine glaciers exercise little or no erosion upon their beds near and at their terminations (snouts), because at such places they are almost stationary.

It is impossible to criticise these two theories at the same moment. Both of them agree in attributing enormous powers of excavation to glaciers, but they disagree totally and completely as to the modus operandi by which the effects were produced. They differ even in their general conclusions. One asserts that the greatest effects were produced upon the plains, and that very little was done amongst the mountains; whilst the other declares that the mountains owe their actual forms to the carving of glaciers, and that the plains did not suffer at all! There is no wonder that the unenlightened public enquired, "Who shall decide between the disagreements of these doctors?" But it is surprising to find numerous persons accepting as gospel truth the contradictory dicta of these eminent men, and speaking and writing as if it were