272 E. C. ANDREWS. 



flood, in areas of greatly reduced cross-section, particularly 

 where the canons are of great depth, that from frictional 

 considerations, differential velocity would be correspond- 

 ingly marked. This would give rise to very pronounced 

 varying movement of the upper layers. Yet evidence of 

 internal work as this is, and consequent loss to corrasion, 

 nevertheless, no one would consider for an instant that the 

 energy had actually decreased. On the contrary, despite 

 the loss thus sustained, the energy as a whole would rise 

 enormously. It is simply the algebraic sum of two sets of 

 actions in which the result is gain to the stream. Every 

 day one sees analogies to this in ordinary streams, in 

 "rivers gone mad," or in the great "waves of translation" 

 determined by onshore gales. 



(b) Reduction in glacial volume (Drought) stage. — 

 Several factors here all conspire to reduce the efficiency of 

 the stream as a corrader. 



1. The reduction of volume will give the stream material 

 opportunity frequently to return to its solid state in part 

 or almost as a whole. The observer who has had oppor- 

 tunity to watch the same class of stream material making 

 its channel profile during highest flood, may have difficulty 

 in recognising the flood and drought phases of such a stream 

 as belonging to similar types of stream material. 



2. A much greater amount of the topography now 

 dominates it. Its volume is definitely lessened ; the hills 

 now stand high above it and shower their debris upon it. 

 In proportion as the former action has been fierce, so will 

 the decrease in volume in the early drought stages be 

 correspondingly noted for its incapacity for work. 



3. Then comes the greater factor of decreased velocity. 

 The glacier has undergone great reduction in volume this 

 means great loss of speed, and this, in turn, indicates rela- 

 tive stagnation of corrasive action. [This is exactly the 

 case with present day glaciers ; they are drought glaciers.] 



