284 Geological Society of London. 



drift ; and that, while in a region so suhject to slight disturhances as the Alps, posi- 

 tive evidence for his theory would be almost impossible to obtain, no lake offered 

 any against it, and one, the Konigsee, was very favourable to it. 



2. " On the Effects of Glacier-erosion in Alpine Valleys." By Signer B. Gastaldi. 

 The author described the occurrence in the valley of the Lanzo and other Alpine 

 valleys, at heights between 2000 and 3000 metres (6500 and 9700 feet), of large 

 cirques, in two of which, in the valley Sauze de Oesanne, the bottom was occupied in 

 the autumn by glaciers reduced to their smallest dimensions. The author noticed the 

 various rocks in which these cirques were cut, and expressed his opinion that they are 

 the beds formerly occupied by glaciers, the power of wliich to excavate even compara- 

 tively hard rocks, such as felspathie, amphibolite-, and chlorite-schists, he considered 

 to be proved. The author then referred to the mouths of the Alpine valleys opening 

 upon the plain, which he described as being generally very narrow in proportion lo 

 their length, width, and orographical importance ; and he pointed out that in the case 

 of the valley of the Stura, at any rate, the outlet of the valley has been cut out by 

 the river. This peculiarity he accounts for by the fact that whilst the calcareous and 

 felspathie rocks are easily disintegrated by atmospheric action, certain other rocks, 

 Buch as the amphibolites, diorites, syenites, amphibolite-schists, euphotides, serpen- 

 tines, etc., resist atmospheric denudation ; and he indicated the peculiar distribution 

 of these rocks in the region under consideration, by reason of which portions of them 

 occupied the points which are now the mouths of the valleys. 



Dismission. — 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 amphitheatres only is occupied b-y the ice, and the almost 

 vertical slopes are covered with an accumulation of snow, which helps 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 cirque beneath Schneehatten, in Norway, in which a 

 glacier terminated. At the other end the lake was bounded by a hard ridge of rock. 

 The rocks around were moutonneed, and glaciated. 



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 attempted to answer iu print, in the Philoso- 

 phical 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 circum- 

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

 merely a few local ice-centres, from which glacier-erosion might radiate. "When 

 there was any thing approaching to a general ice-coating, the erosion must have been 

 enormous, especially at spots where there were already pre-existing valleys, in which, 

 of course, the ice would have been thicker than elsewhere, and where, co-nsequently, 

 its grinding powers would have been far greater, and have added much to the work of 

 the more ancient rivers. He inquired of Mr. Bonney what must take place at the 

 termination of any glacier. There. could be no erosion by the glacier anywhere 

 beyond the point to which it extended ; but where it existed some erosion must take 

 place, and a basin of greater or less depth thus be ground out by the alternating 

 advance and retreat of the glacier. A river flowing out might, it is true, m some 

 cases cut a gorge so as to drain the basin, but this would uot prevent a basin being 

 formed. In the western Alps, where the height was greatest, there also were the 

 largest and, in some instances, the deepest lakes ; though the depth was connected to 

 a great extent with the nature of the rock. Some lakes, however, had been partly 

 filled by detritus. As to the cliffs, he perfectly agreed with Mr. Bonney in attributing 

 them to meteoric causes : and in many cases he thought they were to some extent of 

 preglacial origin, though subsequently much modified. He repudiated any idea of 



