years ago. Many of those which are freely exposed to the atmosphere retain a high polish and fine striations. If the soil were to be removed that covers the natter portions of the valley we, should doubtless find higher polish, and still finer striations. Nevertheless, those which are visible remain so perfect, that it is certain weathering has done exceedingly little to alter their contours, and we may argue regarding them as if their icy covering had been but just removed. This point is of no small importance; and, it seems to me, it may be demonstrated from the very contours of these glaciated rocks, that the valley was not excavated by glaciers, and indeed, that it was eroded by glaciers only to a very limited extent.
For the forms which are called moutonnées preponderate very largely. The rocks which I have ventured to term roches nivelées, are comparatively rare,[1] although they are sufficiently numerous to show that the valley was subjected to severe grinding for a great length of time. They are found upon the floor of the valley, or in places where it narrows, or upon the lower sides of little ravines (now watercourses) which the glacier had to cross, into which it was forced down when in the act of crossing, and out of which it escaped by mounting the opposite bank. In brief, they are found precisely where they should be found. In those places where the thickness of the ice was greatest, and where the motion was (probably) quickest; where the glacier was compressed laterally, so that its power was distributed over a smaller area of rock-surface; and where erosion had produced ruts into which the glacier was pressed down, and out of which it could only extricate itself by a severe struggle.
Throughout the valley, in conjunction with the roches moutonnées, there are innumerable angular rock-surfaces which seem never to have been abraded by glacier. These lee-sides[2] are found right up to the bases of the existing glaciers. That is to say, they are found in spots which were not only covered by ice during the whole of the period in which the ancient glacier of Aosta
