Old Glaciers of Switzerland. 44 1 



that valley when the glacier attained its greatest size viz., 

 at least 5, 200 feet above the present bottom of the valley 

 at Viesch, and more than 3,700 feet at Morcles, not far 

 above the southern end of the delta of the Ehone, whiclr 

 once formed part of the lake. If we may suppose that 

 this latter thickness continued approximately as far as 

 the deepest part of the lake between Evian and Cully, 

 the glacier may have been nearly 4,700 feet thick, if we 

 add to the above thickness at Morcles the depth of the 

 water. 1 By similar observations on the Jura, it is 

 clear that where the ice abutted on that range, it still 

 maintained a thickness of something like 2,200 feet 

 where thickest, swelled as it was by the vast tributary 

 masses of glacier-ice that progressed down the valley of 

 the lakes of Thun and Brienz, and also by that of the 

 Arve and of Chamouni, and by others of smaller size 

 that flowed down the valleys south of the lake. 



Consider the effect of this gigantic glacier flowing 

 over the Miocene rocks, which in this part of Switzer- 

 land are comparatively soft, and yet of unequal hard- 

 ness ! That mass, working slowly and steadily for a 

 period of untold duration, must have exerted a pro- 

 digious grinding effect on the rocks below. Where 

 the glacier-ice was thickest, there the grinding power 

 was greatest, especially on the softer Miocene strata, 

 and the underlying rock was consequently to a corre- 

 sponding extent worn away. No one can doubt that the 

 ice-flow that pressed down the upper valley of the 

 Rhone exercised a great amount of eroding power, 

 representing as it did the snow-drainage of all the 



1 For details on this question, see ' Notice sur la conservation 

 des Blocs Erratlques et sur les Anciens Glaciers du Revers Septen- 

 trionale des Alpes,' par M. Alphonse Favre, Archives des Sciences de 

 la Bibliotheque Universelle, November 1876. 



