extended to Ivrea, but have been covered by it in quite recent times. Glacier moved over them, probably, ages before the great glacier filled the valley; and, for aught we know to the contrary, it has done the same almost ever since. Yet, to all appearance, ice has never touched the lee-sides, or, if it has done so, it has been done so tenderly, that the marks have been subsequently obliterated.
Now, whilst it may readily be admitted that atmospheric action is capable of completely effacing feeble traces of glacier-erosion,[1] we cannot in the present instances admit any more. The contiguous surfaces to the lee-sides which are highly polished and bearing fine striations, show that sun, frost, and water, have done very little upon them since the ice departed. It would be absurd to suppose that these powers have been able to rub out all traces of ice-action (if the traces were other than very feeble) in one square yard, when in the next, upon the same rock, they have been unable even to roughen the surface, or get rid of fine scratches. It is doubly impossible to suppose that the rock-surfaces were uniformly ground down by ice, and that all the inequalities seen at the present time are the result of subsequent decomposition. I do not think any one will have the hardihood to assert the contrary.
It is stated, therefore—1. That the glacier-eroded rocks in the Valley of Aosta are chiefly characterised by convexity, and principally belong to the class termed moutonnées. 2. That there are examples of roches nivelées in the valley; that they are rare in comparison with the roches moutonnées; and that they are mostly found upon the floor of the valley, or in places where it is narrowest, or where unusual obstructions have occurred. 3. That there are innumerable angular rock-surfaces intermingled with these glaciated surfaces upon the floor and on the sides of the valley) which cannot have been produced since glacier covered the rocks. For the bearing of these facts upon Dr. Tyndall's theory, I must now recapitulate from Chapter VI.
In the preliminary remarks at pp. 142-3, after appealing to
- ↑ Or, given sufficient time, of destroying highly-glaciated surfaces.
