CAUSE OF VERTICALITY OF GLACIAL MARGIN. 203 



rays, touching the surrounding earth's surface at low angles, are reflected 

 at like low angles, and hence often impinge upon the edge of the ice. On 

 a lake, just before sunset, you have doubtless often seen a brilliant illus- 

 tration of the wide space from which rays of low slant are reflected so as 

 to be caught by an object of slight elevation. Prominences about the 

 glaciers catch and absorb the heat on their sides rather than their sum- 

 mits, and in turn radiate this heat in lines chiefly normal to their walls 

 and favorable to reception by the edges of adjacent glaciers. It ai)i)ears, 

 therefore, that a larger proi)ortion of the sun's rays falls on the glacier 

 edges at the north than at the south, and it is the proportion of rays that 

 determines the contour. It is interesting to note in this connection that 

 nunataks are often surrounded, like an ancient castle, by a moat sunk 

 between the foot of the eminence and the mass of the glacier, whose face 

 is usually vertical. It is only when the movement of the ice is notably 

 great that it presses hard against the nunataks. AVe must not, however, 

 fall into the error of supposing that verticality is due simply to reflection 

 from cliff's, because glaciers that end on broad, smooth, gravel-bottomed 

 valleys are as vertical as any. Here it must be the direct rays and the 

 rays reflected from the smooth surface of the valley which j)roduce the 

 eff'ect. 



Stratification. 



General Characteristics. — Next to verticality, the most impressive feature 

 is the pronounced stratification of the ice. The stratification of glaciers 

 is not new, but the extent, definiteness and peculiar characteristics dis- 

 played by its phenomenal exposure in these northern regions are perhaps 

 in some measure a revelation. The ice is almost as distinctly bedded and 

 laminated as sedimentary rock. The vertical face usually i)resents two 

 great divisions — an upper tract of thick, obscurely laminated layers of 

 nearly white ice and a lower laminated tract discolored by debris. At 

 the base there is usually a talus-slope, and sometimes, but only sometimes, 

 a tyi)ical moraine. In the upper portion l)luish solid layers separate the 

 more porous ice into minor divisions, and these are grouped by consolida- 

 tion into more massive layers. Sometimes the whole upper division 

 consists of a single stratum, but more commonly it is divided into several 

 great beds separated hy ([uite distinct planes. (Figures 1 and 2, plate 3, 

 and figure 3, plate 4.) 



Tlie lower discolored division also sometimes consists of one great 

 stratum, but oftener it is divided into several great layers, as in the case 

 of the white ice above. Very numerous partings furtlier divide these 

 beds into minor layers of varying thickness, grading down into dolicate 

 laminations, a do/x'U or a score to an inch. In addition to the bluish 

 bands and the physical partings found abcjve, there are here interstratified 



