Geological Society of London. 381 



certain changes, — a great glacial period, a period of submergence, and a second 

 minor glacial period. 



Mr. Prestwich maintained that temperature was a most important question in 

 connexion with the subject of Mr. Jamieson's paper. The glacial deposits were 

 not formed in a deep sea, but in shallow water with shore temperatures. He 

 thought that the paper was very speculative, and remarked that the evidence upon 

 which the opinions expressed were founded was not always given. 



2. " Notes on the Upper Engadine and the Italian Valleys of 

 Monte Eosa, and their relation to the Glacier-erosion Theory of 

 Lake-basins." By the Eev. T. G. Bonney, M.A., F.G.S. 



The author stated that he had examined (1) the small lakes on 

 the summit of the Bernina Pass. These were situated in a position 

 very favourable to glacier-erosion, and he thought might be attributed 

 to tliat cause. (2) The lakes on the upper part of the Maloya Pass, 

 These lay in three rock-basins, and at first sight seemed favourable 

 to the glacier-erosion theory ; but further examination showed that 

 they were in no way connected with the glacial system of the neigh- 

 bourhood, and were probably preglacial. (3) The Val Bregaglia to 

 the Lake of Como. The presence of barriers in the valley, its fre- 

 quent V-like form, and the signs of glacial action to near the 

 present level of the stream, seemed to indicate that the glacier had 

 had but slight erosive power. (4) The Oomo arm of the lake. It 

 was shown that the glacier, which was supj)osed to have excavated 

 the lake, had passed over the ridge of Nagelfluhe and Molasse that 

 incloses it, and had not been able to grind away its remarkably 

 sharp crest. (5) Similar evidence was produced with regard to tlie 

 Lake of Orta. (6) The Italian Valleys E. of Monte Eosa. These 

 were shown to offer difficulties precisely similar to those of the Val 

 Bregaglia. The author therefore argued that these cases showed how 

 superficial the action of the glaciers had been ; and that they must 

 have been wholly inadequate to excavate the greater lake-basins, 

 since no approach to this form, no U-like trough, was found in the 

 valleys down which the glaciers had flowed on their way to the 

 lakes. As then the principal features of the district appeared to be 

 preglacial, he contended that disturbances of the beds of the valleys 

 along lines transverse to their direction were more likely to have 

 produced the lakes. 



Discussion. — Mr. Drew differed from the author, and thought that glaciers 

 coming from different directions might have produced single results at certain points. 



Prof. Ramsay was glad to find that the author was gradually coming round 

 towards his own views, as he now admitted that glaciers may have excavated some 

 lake-basins. He argued that the valleys originated before they were covered with 

 a thick coating of ice, but he maintained that at its origin the ice would have great 

 weight and excavating power. 



Rev. J. F. Blake thought that if the slope of the bottom of the glacier changed, 

 its excavating power would be increased. 



Mr. Koch had sounded many lakes, and found great circular cavities, which he 

 thought could hardly be due to ice-action. In winter glaciers move very slightly, 

 and would be able to perform very little work. 



The Author, in reply, remarked that ice-denudation is different from aqueous 

 denudation. A glacier planes and could not cut out a notch. He said that he 

 could only admit the smaller lakelets in special positions as the result of glacier- 

 action. He did not think there was satisfactory evidence of the existence of an 

 ice-sheet all over Switzerland. He urged that it is not always safe to argue from 

 small phenomena to large ones. 



