established that lake-basins and mountain-valleys have been excavated by glaciers.
It is not requisite to decide between all the differences contained in these two theories, in order to arrive at a tolerably correct judgment upon the general conclusions. Professor Ramsay, for example, attributes the production of the greatest effects to the weight of glaciers. Professor Tyndall, on the other hand, assigns most power to the motion. I shall ignore these points, because I have no data from which to arrive at a satisfactory decision, and because it is not necessary for them to be mixed up with a discussion of the question, Were the valleys of the Alps excavated by glaciers? For the consideration of this subject, let us now return to the Valley of Aosta.
The town of Ivrea is placed at the mouth of, but not actually within the valley, and several miles of flat, dusty road have to be traversed before it is entered. Upon this portion of the country civilisation is doing its best to efface the traces of the glacial period. Cultivation of the soil disturbs all deposits, and the hammers of the masons destroy the erratics. After quitting Ivrea, almost the first object of interest is the castle of Montalto, perched on a commanding crag, nearly in the centre of the valley. Thence, from Settimo Vittone up to the foot of the existing glaciers of the range of Mont Blanc, there are traces of glacier-action upon each hand. The road need not be quitted to seek for them;—they are everywhere. I refer especially to the rocks in situ. The rockforms called roches moutonnées are universally distributed, and it is needless, at the present moment, to point to any in particular. Although of varying degrees of resistancy, they have, upon the whole, stood the weathering remarkably well of the thousands of years which have elapsed since the glacier covered them. The floor of the valley, generally speaking, has not been lowered since that time, by the combined agencies of sun, frost, and water, to any appreciable extent. The forms which the roches moutonnées present to-day, are the forms which they presented, perhaps, ten thousand
