GLACIAL EEOSION. 



91 



along. But it was being rolled, as shewn by the moulding (e e ) of its form in the glacier 

 which was advancing faster than the stone was rolling down the steep slope. The 

 pressure upon this stone could not have been merely that of the superincvimbent ice, a 

 few ieet thick, but also that of a powerful component of the weight of a glacier from 

 1,500 to 2,000 feet high descending more or less like a fluid. The energy upon the boulder 

 was sufficient to crush it into one large and two smaller masses, together with stone dust. 

 "When seen, the three fragments had hardly begun to part company. 



The abrasion of the solid rock by the fall of stones, and detached masses of ice and 

 stones, was illustrated at the locality just named. The two guides and myself succeeded 

 in detaching a large boulder of about five tons weight, adjacent to the edge of the glacier. 

 It went rolling and sliding down a hundred feet or more, tearing away great blocks of ice 

 which held a considerable amount of debris, and in its wake, the rock was more or less 

 crushed or scratched. 



Fk; 



3. — At Tunsbergdalsbrœen, d, a loose boulder, resting on rock a, in cavern c, against 



which a tongue 7, of tlie moving glacies b, impiges and is bent backward. 



A further example of the ability of the ice to flow like a plastic body was shewn in a 

 cavern (fig. 3 c) 400 feet higher than the end of the glacier, where the temperature was 4° C, 

 while that outside was 13° C. Upon the debris of the floor rested a rounded boulder (d) 

 whose longer diameter measured thirty inches. A tongue of ice (q), in size more than a 

 cubic yard, was hanging from the roof, and pressing against the stone. In place of 

 pushing the stone along or flowing around it, the lower layer of ice above the tongue had 

 yielded, and was bent backward as easily and gracefully as if it had been a thin sheet of 

 lead, instead of one of ice a foot thick. 



According to the experiments of Herr PfafF, ' the temperature of ice has a great deal 

 to do with its flow about obstacles. Below freezing-point, the movement is scarcely more 

 than appreciable, while above that point, but not below, it may reach twenty-eight inches 

 a day, or more. The conditions arising from the temperature beneath the glaciers are 

 more or less favorable for the movement of the ice, as the lower surfaces are never 

 entirely below freezing-point, even in winter. Prof. S. A. Sexe " found that the water 

 flowing from a Folgefond glacier, in February, 1861, had a temperature of 1° R., whilst 

 that of the air was *7° R. below freezing-point. 



' Nature, Aug. 19, 1875. 



Om Sneebni^eu Folgefon, af S. A. Sexe. 



