.107 



rt <d above the basin at the foot, the descending 

 glacier easily transports the rock blocks out of the cirque 

 walls. This is the quarrying phase of corrasion as opposed 

 to the abrading phase at the foot of the cirque, where the 

 most rapid change of channel slope occurs. It will thus be 

 seen that the abrasive action is practically negligible at 

 the upper portions of the cirque walls, while it increases 

 with descent of the walls and reaches a maximum at the 



It will thus be evident that the greatest change of slope 

 will occur at the point separating the basin formed by 

 overdeepening action from the upper quarrying action and 

 sapping action. It is easy to see that the basining (or 

 overdeepening) at the cirque foot is due to some heavy 

 stream action, otherwise there could be no marked excava- 

 tion formed below the local base level with reversed grade 



Perhaps the most important point to bear in mind in 

 connection with the formation of the cirque as it is seen 

 to-day, is now to be discussed. Widespread geological 

 observations have proved that no country is to-day passing 

 through its maximum Ice Age. On the contrary, it has 

 been proved that any glaciers which may exist to-day in 

 any country whatsoever, are only the dwarfed representa- 

 tives of ice masses, which latter we may call Ice Floods. 

 Furthermore it has been demonstrated that such Ice Floods 

 have only just departed by reason of some cosmopolitan 

 agency. 



It will now be interesting to understand the mechanical 

 significance of such glacial decadence in the history of 

 cirque formation. It is evident in the first place that ice 

 is not mobile under ordinary conditions of pressure unless 

 in large volumes, and that whenever opportunity offers, it 

 will escape from conditions of pressure and return to the 



