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J. W. SPENCER ON 



times flat, sometimes sloping steeply — they adhered by frictiou, aud by the pressure of the 

 superincumbent weight. Although held in the ice on four sides, with a force pushing 

 downward, the viscosity of the ice, or the resistance of its molecules in disengaging 

 themselves from each other in order to flow, was less than that of the friction between 

 the loose stones aud the rock ; consequently the ice flowed around and over the stones 

 leaving long grooves upon the under-surfaces of the glacier. The first observation made 

 was at Fondalsbrœen (fig. 1), where an angular stone (fig. Id) whose section was ten by 

 eighteen inches, rested upon the sloping face of smooth rock (a). For twenty feet below 

 the stone, the under-surface of the glacier was grooved (/) by the moulding of the ice 

 about the obstacle. This distance shewed the advance of the glacier after the stone had 

 come in contact with the rock, for it had evidently been completely buried at the lower 

 end of the groove, before the ice had begun to flow about it. As the ice between the 

 stone and the rock gradually disappears, the embedded stone does not suddenly cease to 

 move, but drags, until enough of the surface rests iipon the rock to allow of friction 

 between the two granitoid surfaces to overcome the viscosity of the ice, when the latter 

 flows around the obstacle. Elsewhere, an example was seen of this action. The knife 

 edge of a wedg-shaped piece of gneiss was protruding* beneath the ice and resting upon 

 the rock. The front end of this stone had moved beyond the subjacent surface, while the 

 posterior end was still upon it. Yet the sharpness of the edge had scarcely been blunted 

 Abundant examples were found to shew that the flowing of the ice about loose, 

 obstacles was cjuite the rule. Both large aud small (even an inch in length), angular and 

 rounded masses, lying either upon the rock, or upon morainic matter, were sufficient to 

 channel the bottom of an advancing glacier. No blocks of rock were seen in the act of 

 being torn loose from the floor or sides of the valley, and certainly there were no loose 

 or solid masses being picked up by the advancing glacier. 



Fig. 2. — Section of Tunsbergdalsbrœen, a, bed rock ; c, cavern under ico b ; d, boulder ; 

 ce, moulding in ice of the form of d. 



At Tunsbergdalsbrseeu (fig. 2), whose lower end is 1,600 feet above the sea, a modifi- 

 cation of the above described phenomena was seen. A roughly rounded boulder (fig. 2 d) 

 of thirty inches diameter was enclosed in the convex side of the glacier, which rose above 

 it from thirty to forty feet in height. It was resting upon a surface, sloping at a high 

 angle, and was held in place by the ice itself As the surface of the stone, bearing upon 

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



