THE WORK OF SNOW AND ICE. 



315 



are obviously just those whose yielding most promotes motion, and a 

 successive yielding of the points that come in succession to oppose 

 motion most (and thus to receive the greatest stresses) permits con- 

 tinuous motion. It is merely necessary to assume that the gravity 

 of the accumulated mass is sufficient to produce the minute temporary 

 liquefaction at the points of greatest stress, the result being accom- 

 plished not so much by the lowering of the melting-point as by the 

 development of heat by pressure. 



Fig. 292. — Portion of the east face of Bowdoin glacier, North Greenland, 

 showing oblique upward thrust, with shear. 



This conception of glacial '^flowage" involves only the momentary 

 ^liquefaction of minute portions of the mass, while the ice as a whole remains 

 rigid, as its crystalline nature requires. Instead of assigning a slow 

 viscous fluidity like that of asphalt to the whole mass, which seems incon- 

 sistent with its crystaUine character, it assigns a free fluidity to a suc- 

 cession of particles that form only a minute fraction of the whole at any 

 instant. 



"^ This conception is consistent with the retention of the granular 

 condition of the ice, with the heterogeneous (in the main) orientation 



