126 WORK OF SNOW AND ICE 



retain their individuality. Thus the snow of one season may have 

 been considerably changed before the next season. Again, the sur- 

 face of the snow-field at the end of the melting season is generally 

 soiled by a little earthy matter, some of which was blown up on the 

 surface during the melting season, and some of which was concen- 

 trated at the surface by the melting of the snow in which it was 

 originally imbedded. In many places this earthy matter is sufficient 

 to define snows of successive years, giving the ice a somewhat 

 stratified appearance. 



In addition to its stratification, the ice of the deeper portions 

 may take on a stratiform structure which may be called foliation, 

 to distinguish it from the stratification which arises from deposition. 

 Foliation appears to be akin to slaty or schistose cleavage, and to 

 result largely from the shearing of one part of ice over another, as 

 it moves forward. 



Texture. Ice formed from snow is composed of interlocking 

 crystals. The crystalline character is assumed by the snow-flakes 

 when they form, and the subsequent changes which the snow under- 

 goes seem 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 interlocked that they are not 

 seen readily by the eye; but when the ice has been honeycombed 

 by partial melting, the granules become partially separated and may 

 be seen easily. It is therefore legitimate to assume that a granu- 

 lar crystalline condition persists throughout all stages of the history 

 of ice formed from snow. 



Inauguration of movement. When the ice beneath a snow-field 

 becomes 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 substance. A 

 piece of ice may be made to change its form, and may even be mould- 

 ed into almost any desired shape if subjected to sufficient pressure, 

 applied steadily through long intervals of time. 1 These changes 

 may be brought about without visible fracture, and have been 



