256 DISCUSSIONS IN CLIMATOLOGY. 



become, of course, separated from their neighbours by 

 fresh interstices, which new interstices become filled 

 by fluid particles which, in turn, crystallize, anew 

 forming interstices, and so on. The ice at the bottom 

 of the valley, so long as this process continues, is 

 constantly receiving additions from above. The ice 

 must therefore expand laterally to make room for 

 these additions, which it must do unless the resistance 

 to lateral expansion be greater than the force exerted 

 by the fluid particles in crystallizing. But a resistance 

 sufficient to do this must be enormous. The ice at the 

 bottom of the valley cannot expand laterally without 

 passing up the sloping sides. In expanding it will 

 take the path of least resistance, but the path of least 

 resistance will always be on the side of the valley 

 towards which the general mass of the ice above is 

 flowing. | 



We can from these conditions understand how the 

 softer portions of the rocky surface over which the 

 ice moved should have been excavated into hollow 

 basins. We have also an explanation of the transport 

 of boulders from a lower to a higher level, for if ice 

 can move from a lower to a higher level, it of course 

 can carry boulders along with it. 



Heat Transformed into Glacial Motion. — From 

 what has been stated regarding the cause of glacial 

 motion, it will now be obvious that a considerable 

 portion of the sun's heat entering the ice must be 

 transformed into work in the motion of the glacier. 

 When a particle of ice is melted and then re-solidified, 

 the amount of heat evolved during solidification is 

 equal to that which had been expended in melting the 

 particle. The particle in solidifying expands, and if, 

 in expanding, work is performed by the expanding par- 

 ticle, the amount of heat evolved during solidification 



