the Alpine Lakes and Valleys. 211 



and that it has passed over Mont Sion and the defile of Fort 

 de FEcluse. But about a kilometre below Geneva (at the wood 

 of La Batie) th older drift is visible, as I have stated, covered 

 by the glacial deposit over a very large area. At this point 

 one is compelled to conclude that the glacier has not had the 

 power to remove this older drift, and that it has spread itself 

 over it. Is it not evident that the glacier has been supposed 

 to possess immense power above Geneva, and that there is a 

 clear proof that it did not possess that force below the city in 

 question ? I believe, then, that the truth lies in the fact that a 

 glacier can slide over a deposit of rolled pebbles without 

 cutting a way through them. Consequently the ancient 

 glaciers have not had the power to remove, near Geneva, the 

 older drift on which they have left their traces, and, for a still 

 greater reason, they have not had the power to remove the 

 rolled pebbles from the bottom of the lake. 



The rolled pebbles which constitute the older drift below 

 Geneva, and which are placed beneath the glacial drift, seem to 

 me to have been transported by the torrents which were given 

 out by the glaciers of the Rhone and Arve when they reached 

 the neighbourhood of our city. They have been rounded after 

 leaving the glaciers. 



This is perceptible below existing glaciers when they reach 

 a plain. In such cases there is nearly always a certain area 

 of deposit occupied by rolled pebbles, which are fashioned, 

 sorted, and levelled by the torrent. The pebbles which form 

 part of the older drift, and which are evidently derived from the 

 Valais, have traversed the depression of the lake when it was 

 filled with ice. They have made the journey in question in the 

 form of erratic blocks or gravel, and were rolled only when 

 they reached the torrent at the base of the glacier. 



Subsequently, when this deposit was formed and levelled, the 

 advancing glacier has passed over it ; and, on retiring, it has 

 left on its surface the glacial mud, the scratched pebbles and 

 the erratic blocks which we see there even at the present day. 



I have endeavoured to show that the theory of excavation 

 was insufficient to account for the accumulation of the glacial 

 deposits, and I ground my opinion on the weakness of the ex- 

 cavating power of the glacier, as is proved by the presence of 

 the glacial drift reposing on a light deposit formed of rounded 

 pebbles ; for a still stronger reason I cannot believe that a 

 glacier has ever excavated the basin of the lake or a valley. 

 If these depressions had been formed by the glaciers, how shall 

 I explain why there is no lake in the Valley of the Arve, in the 

 valley of Chamouny, or in the Val d'Aoste ? The glaciers have, 

 nevertheless, remained for a longer period in those higher 



