them which has recently been published by Professors Martins and Gastaldi leaves nothing to be desired either in accuracy or completeness.[1] It is not my purpose, therefore, to enter into a description of them, but only to discuss some considerations arising out of the facts which have been already mentioned.
It has been proved beyond doubt that these gigantic mounds around Ivrea are actually the moraines of a glacier (now extinct) which occupied the valley of Aosta; and it is indisputable that there are boulders from Mont Blanc amongst them. The former facts certify that the glacier was of enormous size, and the latter that it must have existed for a prodigious length of time.
The height of la Serra indicates the depth of the glacier. It does not fix the depth absolutely, inasmuch as its crest must have been degraded during the thousands of years which have elapsed since the retreat of the ice; and, further, it is possible that some portions of the surface of the glacier may have been considerably elevated above the moraine when it was at its maximum altitude. Anyhow, at the mouth of the valley of Aosta, the thickness of the glacier must have been at least 2000 feet, and its width, at that part, five miles and a quarter.
The boulders from Mont Blanc, upon the plain below Ivrea, assure us that the glacier which transported them existed for a prodigious length of time. Their present distance from the cliffs from which they were derived is about 420,000 feet, and if we assume that they travelled at the rate of 400 feet per annum, their journey must have occupied them no less than 1055 years! In all probability they did not travel so fast. But even if they were to be credited with a quicker rate of motion, the length of time which their journey must have taken will be sufficient for my purposes.[2]
- ↑ Essai sur les terrains superficiels de la Vallee du Po, extrait du Bulletin de la Société Géologique de France, 1850.
- ↑ See Forbes' Occasional Papers on the Theory of Glaciers, pp. 193-95, and Travels through the Alps of Savoy, 2d ed. pp. 86-7, for information bearing upon the mean annual motion of existing Alpine glaciers. In the former work an account is given of the discovery of the remains of a knapsack ten years after it had been
