172 Prof. Tyndall on the Conformation of the Alps. 



different places, and found them coincident : they all pointed 

 to Mont Blanc*, which was the place where the ancient gla- 

 ciers had received their load, carrying with them across the 

 Canton-de-Vaud, occupying the bed of what is now the Lake 

 of Neuchatel, and depositing them on the slopes of the Jura. 

 The railroad between Neuchatel and Brienne has disclosed several 

 well-scarred rocks; the evidence of glacier- action is here just as 

 conclusive as in the other parts of the Alps ; and the fact of ice 

 moving thus across the country from Mont Blanc to the Jura 

 fortifies the conception previously formed of the magnitude of 

 the phenomenon. 



It is, then, perfectly certain that all this mountain region was 

 held by ice, enormous as to mass and in incessant motion. That 

 such an agent was competent to plough out the Alpine valleys 

 cannot, I think, be doubted ; while the fact that during the ages 

 which must have elapsed since its disappearance the ordinary de- 

 nuding action of the atmosphere has been unable, in most cases, 

 to obliterate even the superficial traces of the glaciers, suggests the 

 incompetence of that action to produce the same effect. That the 

 glaciers have been the real excavators, seems to me far more pro- 

 bable than the supposition that they merely filled valleys which 

 had been previously formed by water denudation. Indeed the 

 choice lies between these two suppositions : shall we assume 

 that the glaciers filled valleys which were previously formed by 

 what would undoubtedly be a weaker agent ? or shall we conclude 

 that they have been the excavators which have furrowed the 

 uplifted land with the valleys which now intersect it ? I do not 

 hesitate to accept the latter view ; and this view will carry us 

 still further. According to it the glacier is essentially self- 

 destructive. The more deeply it ploughs the surface of the 

 earth, the more must it retreat. Let the present Alpine valleys 

 be filled to the level of the adjacent ridges, and vast glaciers 

 would again start into existence ; but every one of these valleys 

 is a kind of furnace which sends draughts of hot air up 

 to the heights, and thus effectually prevents the formation of 

 ice. While standing on the summit of the Grauhaupt a week 

 or two ago, I was perfectly astonished at the force with which 

 these gusts of heated air rose vertically from the Val du Lys. 

 Marked by the precipitated vapours which chanced to be afloat 

 at the time, the vertical gusts were often as violent as the 

 draught from a factory chimney. Thus, given the uplifted 

 land, and we have a glacial epoch ; let the ice work down the 

 earth, every foot it sinks necessitates its own diminution ; the 

 glaciers shrink as the valleys deepen ; and finally we have a 



* That is, in the direction which a local guide pointed out as that of 

 Mont Blanc. The mountain itself was not seen. 



