168 Pro/! J. W. Spencer — Glacier-erosion in Noricay. 



2. Many of the Norwegian glaciers are rapidly advancing. In 

 their progress they do not conform to the surfaces over which they 

 are passing, but are apt to arch over from rock to rock and point to 

 point, especially as they are descending the icefalls. Thus are pro- 

 duced great caverns into which the explorer can often wind his way 

 for long distances. 



3. Beneath the glaciers of Fondal, Tunsbergdal, and Buardal, in 

 the northern, north central, and south central snowfields of Norway, 

 as well as under other glaciers, I observed many stones enclosed in 

 ice, resting upon the rocks, to whose surfaces — sometimes flat and 

 sometimes sloping steeply — they adhered by friction, and 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 and the rock, consequently the ice flowed around 

 and over the stones, leaving long grooves upon the under surfaces 

 of the glaciers. (The use here of the word ' viscosity ' is in the sense 

 of ice moving like a viscous body, irrespective of the cause.) The 

 first observation made was at Fondalbrse, where an angular stone, 

 whose section was 10 by 18 inches, rested upon the sloping face of 

 smooth rock. For 20 feet below the stone, the under surface of the 

 glacier was grooved by the moulding of the ice about the obstacle. 

 This distance showed 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 its surface rests upon 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 of this action was seen. The knife edge of 

 a wedge-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, whilst the posterior end was still upon 

 it. Yet the sharpness of the edge had scarcely been blunted. 



4. Abundant examples were found showing that the flowing of 

 the ice about loose obstacles was quite the rule. Both large and 

 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. 



6. 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. 



6. At Tunsbergdalbr^, whose lower end is 1600 feet above the 

 sea, a modification of the above-described phenomenon was seen. A 

 roughly rounded boulder of 30 inches diameter was enclosed in the 

 convex side of the glacier, which rose above it from 30 to 50 feet in 

 height. It was resting upon a surface, sloping at 45°, and was held 

 in place by the ice itself. As the surface of the stone, bearing upon 



