Glacier ice consists of irregular, rounded grains of various sizes, each of which represents 

 a crystal with a special optic orientation. These grains are sometimes the size of a pigeon's egg, 

 and the deeper they lie, the larger they are. Crystals weighing up to 700 g have been found in the 

 Alps . It is considered that the growth of these grains is due to melted water circulating in the 

 spaces between the crystals or due to the absorption by the larger grains of the adjacent smaller 

 grains, which had the same optic orientation. It is characteristic that every accumulation of ice in 

 time assumes a rough, granular structure, and glacier ice, especially at the ends of the glaciers, 

 is always very old. 



Aside from its granular structure, glacier ice is also characterized by its laminar structure 

 and streaking; along the edges of the hanging walls of the glaciers and icebergs it can be seen that 

 the mass of the ice consists of more or less dense, alternating white and blue streaks. 



This phenomenon is explained differently. Some consider that these streaks are connected to 

 the periodic precipitation. This is proven by the fact that in southern glaciers the separate layers 

 are divided one from the other by summer deposits of dust. Others say that the striations of 

 glacier ice are formed as a result of slipping of the different layers of the ice over each other. 

 Blue ice is formed along the point of contact of these layers due to melting and pressure, whereas 

 the slipping parts, consisting of firn ice, remain white. A third group admits that both factors 

 participate in the formation of striated glacier ice. The noted peculiarities make it possible to con- 

 sider glacier ice as "pressure ice," as distinct from ice formed from sea water and being "ther- 

 mic" ice. 



Naturally, glacier ice differs sharply in its composition from sea ice. Experimenters have 

 shown that water obtained through melting of glacier ice hardly differs from distilled water. 



After a given depression is completely filled vwth ice and snow, glacier ice begins to stream 

 out of the area of its accumulation down one or several beds, depending on the contour of the locale, 

 analogous to the fact that one or more rivers can flow from one and the same lake. 



This property of ice, to flow along valleys as a result of its plasticity, represents in itself the 

 most noteworthy property of glaciers. The velocity of glacier motion, according to Vall's data, is 

 10, 000 times slower than the velocity of the flow of water, having the same angle of drop. During 

 its descent, the glacier, like a river, goes around separate elevated areas, sometimes dividing 

 into arms and often again uniting.* With each turn and narrowing of the bed, additional compres- 

 sions and tensions arise in the mass of the glacier, causing the phenomenon of "coalescence, " con- 

 sisting of the fact that with each compression, the ice melts somewhat and during the next decrease 

 in pressure it again freezes together. 



In the low and middle latitudes, the "basins" of snow and ice nourishing the glaciers ordinar- 

 ily occupy high valleys located between mountain ridges and separate elevations. The glaciers 



*As is well knovm, rivers flowing through soft formations lay out a bed having, in cross sec- 

 tion, a triangular form v^dth its peak down. The bed laid out by glaciers, for the most part, has a 

 flat bottom and very steep side inclines. Aside from the cross section, the beds of glaciers are 

 also characterized by their longitudinal profiles. Thus, in valleys which had been covered by gla- 

 ciers, the bottom of the valley is often deep due to the eroding action of the glaciers. In the 

 Spitsbergen, Novaya Zemlya fjords, we ordinarily find the greatest depths at the very wall of the 

 glacier, and the fjords themselves are separated from the sea by a shelf which had formed from 

 moraine materials. 



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