quoted below, there is not, I think, any reason to doubt the literal accuracy of the particular point to which attention has just been drawn; and hence it would appear that the effects produced on rocks by glacier ice in rapid motion may be identical with those caused by it after a great lapse of time, when it is working at its ordinary rate.
3. These results are not surprising when we remember that glaciers are always endeavouring to work in right lines. This is proved by the marks they leave, which Agassiz has well pointed out (see note to p. 146) are always more or less rectilinear.
This disposition to work in right lines, combined with inability to operate upon depressions (except to the limited extent already shown), points to the reason why it is that 'ultimately all angles, and almost all curves, are obliterated, and large areas of flat surfaces are produced' (p. 141).
It should be observed that glaciated rocks, of the forms termed moutonnées, cannot possibly have been eroded to any great depth by glaciers during the modern [1] glacial period.
The degree of flatness of glaciated rocks bears a direct relation to the amount of power which has been employed. In the earlier stages (§§ 2-7) the forms are round; in the more advanced ones, they are flat. The rotundity of the form of roches moutonnées is proof that no great amount of destruction has taken place; and their lee-sides are additional and equally strong evidence.
4. For, unless it can be shown to have been produced subsequently to the retreat of the ice, even a single lee-side to a glaciated rock informs us that we see a surface which was exposed to the atmosphere before the glaciers began to work; while many lee-sides, found together, one after another, within an area of a few yards (and they are often so found in localities where enormous depth of excavation has been presumed to have taken place through glacier
- ↑ Geologists begin to speak of glacial periods of a much more remote date than that to which I am referring.
