flow may be taking place simultaneously. Of course, if 

 pressure be applied to such a mass hut no escape he present 

 for the material so acted upon, then the problem is one of 

 statics and not of dynamics. But if sullicieiit pressure he 

 applied and an avenue of escape from the pressure be pre- 

 sented to the material then such a mass will move away 

 from the zone of pressure along the lines of least resistance 

 open to it. These principles are applicable to glaciers. 

 Under pressure the textural units of the ice will lose their 

 coherence and flow, or relative motion between these units, 

 will be set up. When the pressure is the weight of the 

 body itself the variable motion thus set up away from the 

 zone of pressure is called stream flow and the lines of least 

 resistance always taken are those of quickest descent. 

 And this is true for all substances, whether solid or liquid. 

 Of course in the ease of liquids under ordinary conditions 

 of pressure and temperature the effect of their own weights 

 is to produce great relative movement between the textural 

 units, but in the case of solids it is easily seen that the 

 flowage caused by the weight of a body itself may possibly 

 be of local occurrence only, and as opportunity oilers such 

 a mass will revert to its solid or inert conditions. As 

 already pointed out by the writer 1 these peculiar conditions 

 of inertness, partial rigidity, and plasticity, appear to exist 

 simultaneously in any glacier of medium size. Thus on a 

 declivity and in a decided constriction the flowage may be 

 relatively perfect, whereas, in a broad valley, or at the 

 bottom of a deep basin the motion may be relatively 

 negligible, while in a piedmont glacier or in a glacial 

 'slack" generally the ice may appear to be quite inert. 

 In brief, under the ordinary atmospheric cover only, one 

 cannot expect ice to form a perfect stream. It may be 

 mentioned in passing that during the recent Ice Age 



1 " Corrasion by Gravity Streams," pp. 212 and 273. 



