230 GEOLOGY 



often acquires a stratiform structure which may perhaps best !>< 

 called foliation, to distinguish it from the stratification which 

 arises from deposition. The foliation appears to be akin to slat v 

 cleavage or to schistosity, and to result largely from the shearing 

 of one part over another in the course of the movements to which 

 the ice is subjected, as will be illustrated presently. 



Texture. The ice derived from the snow is formed of inter- 

 locking crystalline grains. The crystalline character is assumed 

 by the snow-flakes when they form, and the subsequent changes 

 which the snow undergoes seem only to modify the original crystals 

 by building up some and destroying others. By the time the snow 

 is converted into neve, the granules have become coarse, and 

 wherever the ice derived from the neve has been examined, the 

 granular crystalline texture is present. The individual crystals 

 in the ice are usually larger than those of the neve, and more closely 

 grown together. In compact ice the crystals are so intimately inter- 

 locked that they are not readily seen by the eye; but when the 

 ice has been honeycombed by partial melting, the granules become 

 partially separated and may be easily seen. While a given mas- 

 of snow in a great snow-and-ice-field cannot be followed uninter- 

 ruptedly through its whole history, yet since the granular textun- 

 is pronounced in the neve stage where the granules show evidei 

 of growth, and since the same texture is also pronounced in thr 

 last stages of the ice when it is undergoing dissolution, as well as 

 at all observed intermediate stages, it is legitimate to assume that 

 a granular crystalline condition persists throughout all stages of 

 the history of the ice, and that it is a feature of progressive 

 growth. 



Inauguration of movement. When the snow and ice in a snow- 

 field become very deep, motion is developed. The exact nature 

 of the motion has not been demonstrated to the satisfaction of all 

 who have studied the problem, though much is known about it. 

 Brittle and resistant as ice seems, it may, under proper conditions, 

 be made to exhibit some of the characteristics of a plastic subst am-c. 

 A piece of ice may be made to change its form, and may even le 

 moulded into almost any desired shape if carefully subjected to 

 sufficient pressure, steadily applied through long intervals of 



