Trof. J. W. Spencer — Glacier-erosion in Norivay. 169 



the rock, was small compared with that held in the ice, it should 

 have been dragged along. But it was being rolled, as shown by the 

 moulding 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 superincumbent ice, 

 but a powerful component of the energy of a glacier descending 

 1500 — 2000 feet, as if the ice were moving more or less as a fluid. 

 The energy upon our boulder was sufficient to crush it into one large 

 and two smaller masses, together with stone dust. When seen these 

 fragments had hardly begun to part company. 



7. 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 and 

 scratched. 



8. A further example of the ability of the ice to flow like a plastic 

 body was shown in a cavern 400 feet higher than the end of the 

 glacier, where the temperature was 4° C, whilst that outside was 

 13° C. Upon the debris of the floor rested a rounded boulder whose 

 longer diameter was 30 inches. It could have been rolled over by 

 one man. A tongue of ice, 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 lov/er layer of ice 

 above the tongue had yielded, and was bent backward at right angles, 

 as easily and gracefully as if it had been a thin sheet of lead, in 

 place of one of ice a foot thick. 



9. According to tbe experiments of 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, whilst above 

 that point, but not below, it may reach 28 inches a day or more. The 

 conditions arising from the temperature beneath a glacier are more 

 or less favourable to 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° E., whilst that of the air 

 was 7° R. 



10. The movement or flow of the ice about detached stones has 

 been observed by Prof. Sexe beneath the Buarbree, and by Prof. J. 

 W. Niles ■'' beneath the Aletsch glacier. Prof. Sexe illustrates the 

 sliding of the ice over a loose stone, which was wedged beneath the 

 glacier by a projection of the rock. My observations were upon 

 masses not held ujd by wedges, but upon surfaces often sloping down- 

 ward. Although Prof. Niles did not record observations showing 

 that there was definite movement of the stone, yet he concluded that 



1 Nature, Aug. 19th, 1875. 



2 " Om Sneebrseen Folgefon," af S. A. Sexe. 



3 Am. Jour. Sc, Nov. 1878. 



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