716 THE ORIGIN OF SOME HANGING [ Nov. 1902, 
Puate XXXIX, 
Hig. 1. The river-gorge below Airolo, with relics of the older benches. 
2. View of the mouth of the Albigna Valley and waterfall, from the 
Maloggia. 
Puatrse XL. 
Fig. 1. The upper cascade of La Foos, draining Lago Ritom, Val Piora. 
2. The end of an Arctic glacier, Hornsund (Spitsbergen), showing a 
hanging valley protected by ice, with water-cut gorge and subglacial 
water-channel, into which ice has moulded itself. This illustration 
shows clearly the superior erosive power of water over ice, when both 
occupy the same valley. 
Discussion [ON THE TWO FOREGOING PAPERS |, 
The PrestpENnt congratulated the Fellows upon the lucid manner 
in which the whole subject had been presented and discussed by 
Prof. Bonney, and upon the fine series of illustrative lantern-views 
exhibited and described by Prof. Garwood. The subject was one 
of such conspicuous interest from several aspects, and the pheno- 
mena apparently admitted of so many interpretations, that it was 
little to be wondered at that scientific cpinion was so divided upon 
the question. It was very pleasant, however, to find that lifelong 
workers in the Alps like Prof. Bonney and Prof. Heim, who had 
so many years ago described the classic examples of the Maloja, 
were still fully agreed in ascribing the differential denudation which 
had originated the Alpine examples almost wholly to the action of 
running water; and at the same time to find that Prof. Garwood 
concurred with Dr. Reusch in ascribing many of the Norwegian 
examples of hanging valleys to the preservative action of ice and 
snow. While he himself fully agreed with Prof. Bonney that the 
differences in level between the main valley and these lateral valleys 
was a matter of differential denudation by water-action, he could 
hardly follow him when he carried back the date of the main 
valleys in which they occur to the Middle Tertiary age. The 
suggestion made by Prof. Garwood, that the main valley had been 
subsequently deepened owing to increase in erosive power due to 
regional tilt was, he thought, novel and very plausible. The 
examples of associated main and lateral ‘ hanging valleys’ which he 
had himself seen both in the Alps and in Norway, had led him to 
the opinion, that while running water had probably accomplished 
the erosion of both, yet the distinction between them was in some 
way connected with the physical conditions of the Ice-Age. The ice 
possibly aided in bringing about the differential denudation, not 
perhaps as an eroding agent, but, as in the case of the Matterhorn, 
as a transporting agent—the local conditions enabling it to act here 
as a local remover, and there as 2 local preserver of disintegrated 
material. 
Mr. Marr considered that he had hardly a right to speak upon 
these papers, as he knew nothing of the district described ; but he had 
long been interested in ‘ hanging valleys’ in the Lake District. He 
would like to know how Prof. Davis, in the case of certain valleys 
