248 



GEOLOGY. 



tially separated and may be easily seen. Fig. 223 shows quantities of 

 them which have been washed down from the surface, and disposed as 

 cones at its base. While a given mass of snow in a great snow- and ice- 

 field cannot be followed consecutively through its whole history, yet 

 since (1) the granular texture is pronounced in the neve stage where the 

 granules show evidences of growth, and since (2) the same texture is 

 also pronounced in the last stages of the ice when it is undergoing dis- 

 solution, as well as at all observed intermediate stages, and since (3) the 

 crystals are, on the average, larger in proportion to the lateness of the 

 stage of their history, while (4) experiment has shown that granules 

 grow under the conditions Vvhich exist in snow -fields, and (5) that they 

 persist under very considerable pressure, it is legitimate to assume 



Fig. 223. — Figure showing cones of granules of ice which have been washed down the 

 front of the glacier by streamlets, and accumulated after the manner of talus or 

 alluvial cones. North Greenland. 



that a granular crystalline condition persists throughout all stages, 

 and is a feature of progressive growth. 



Inauguration of movement. — Eventually the increase in depth of 

 snow and ice in a snow-field gives rise to motion. The exact nature 

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

 investigators. Brittle and resistant as ice seems, it exhibits, under 

 proper conditions, some of the outward characteristics of a plastic sub- 

 stance. Thus it may be made to change its form, and may even be 



