1873.] GASTALDI — GLACIER-EROSION IN ALPINE VALLEYS. 399 



the narrow opening fissure in the serpentine, has greatly raised its 

 level, and has formed the magnificent cone of dejection which 

 extends from Lanzo to the Po. (I have described and figured it 

 in the ' Memoria sulla riescavazione dei bacini lacustri : ' Milan, 

 1865.) Thus, the absence of great lacustrine basins at the debouche 

 of the Baltea and the Riparia from the Alps proves that glaciers, as 

 well as running water, only wear away with great difficulty am- 

 phibolite, euphotide, and serpentines. The presence of great basins 

 at the debouche of the valleys of the Ticino, the Adda, and the Adige 

 proves that glaciers easily erode and excavate other rocks. 



In Switzerland, at the foot of the Alps, the glaciers of the Rhone 

 and the Rhine met with rocks still less able to resist erosion ; and 

 thus, independently of the greater extent of the valleys, they have 

 been able to scoop out more extended and deeper basins. 



I do not know the environs of Zurich ; but I think that the lignites 

 of Diirnten and Utznach are the remains of preglacial vegetation. 



I have given you summarily the reasons which have converted me 

 to Mr. Ramsay's theory, and you will judge them for yourself. I 

 wish I could have given them to you more in detail. 



Discission. 



Mr. Drew illustrated the subject by a comparison with the Hima- 

 layas, where similar cirques to those in the Alps exist, and are still 

 occupied by glaciers. The arena of the ampitheatres only is occupied 

 by the ice ; and the almost vertical slopes are covered with an accu- 

 mulation of snow, which belps to feed the glaciers. He was not 

 acquainted with any cirque in the Himalayas in which glacial 

 markings are entirely absent. The bottoms of the cirques were 

 not unfrequently lake-basins. 



Mr. Blanford instanced a small lake beneath Schneehatten, in 

 Norway, in which a glacier terminated. At the other end the lake 

 was bounded by a hard ridge of rock. 



Mr. Koch had studied the effects of glaciers in Switzerland, but 

 had been unable to ascertain the extent of their excavating-power. 

 Where the planing effect of glaciers in ancient times was visible, it 

 appeared to him to have acted in straight, and not in curved lines. 

 He disputed the fact of diorites and serpentines resisting the action 

 of the weather. He had made some experiments on the powers of 

 different rocks to resist the influence of frost and weather, and had 

 been surprised to find how different were the effects under different 

 conditions. 



Prof. Ramsay stated that he had not heard any objections now 

 raised to his theories which he had not already answered, or at- 

 tempted to answer, in print, in the ' Philosophical Magazine ' and 

 elsewhere. The strictures of both Sir Roderick Murchison and Sir 

 Charles Lyell were, so far as he remembered, nearly similar to those 

 to which he now had to reply. He pointed out that at the time 

 when Scandinavia and the greater part of the north of Europe, as 

 well as the Alps, were covered with ice, the circumstances were 

 entirely different from what they were at a later time, when there 



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