20 SEVENTEENTH REPORT. 



glacier, tliere is a typical gaping crevasse (bergschrimd) next to 

 the walls of the cirque, which widens with the advancing summer 

 as the glacier melts and i)ulls away from the cliffs and suowtields 

 above. The bergschrund is shown in plates I and IIB. 



When viewed from across the lake the glacier exhibits a banded 

 structure, and these bands look as though they had been folded 

 like rock strata. These dark bands are due to greater accumula- 

 tion of rock debris in the glacial ice; this was probably caused 

 chiefly by gi'eater melting in the summer, thus concentrating the 

 rocky material and making a dark band that contrasts with the 

 bluish ice formed by pressure in the winter when the amount of 

 melting is small. If the layers were formed in this way, they might 

 be compared with the annual rings of growth of trees. Another 

 possibility is that much of the material in these belts was picked up 

 by the glacier from its bed and chiefly accumulated in more or less 

 horizontal openings or shear zones. The folding of these bands 

 probably is chiefly the result of shearing, that is the slipping of 

 some of the ice past adjacent portions, as a result of the pressure 

 above combined with the forward movement of the glacier and the 

 resistance to this motion offered by its bed. The rate of movement 

 of the glacier was not measured but it must be quite small. 



The glacier rises abruptly from Iceberg Lake to a height of thirty 

 or forty feet; large fields of floe ice are usually' frozen to its front. 

 From time to time large blocks of glacial ice break off, forming true 

 bergs, which frequently nearly cover the surface of the lake. (Plate 

 IIB). Near the outlet of Iceberg Lake is a series of falls, but the 

 water is so shallow that none of the larger pieces of ice can float 

 out. The result is that they can disappear only by melting, which 

 is snch a slow process due to the lake's location that even in August 

 bergs are very abundant on the lake; most of these bergs are flat 

 topped cakes, but they often also assume various fantastic shapes. 

 Due to the current of water flowing toward the outlet and winds in 

 the opposite directions the bergs frequently move back and forth 

 and often grind against each other in a manner suggestive of the 

 ])olar zones. 



The photographs accompanying this article were taken early in 

 July and open water had been visible only a short time, the lake of 

 course being frozen over solid most of the year. The water, where 

 not ice covered, is deep blue in color; and since it is all derived from 

 melting snow and ice is close to the freezing temperature. The lake 

 is not large, covering probably less than a square mile of surface, 

 much of that being ice covered; it is about one hundred and fifty 

 feet deep in the middle. Rock debris is so constantly falling into 



