CORRASION BY GRAVITY STREAMS. 205 



(b) On channel slopes. 



Location of maximum stream strength. Tendency 

 to basin formation — details of form. 



B. Subsequent history of basins (for streams of constant volume). 



(i) Along channel constrictions. 



(ii) At constrictions determined by channel confluences, 

 (iii) On channel slopes. 



(iv) In regions of variable structural strength. Channel 

 recession and consequent enlargement of channel 

 "cross-section." 



C. History of the same channel basins and grades upon reduction 



of stream volume. 

 (i) Slight reduction in stream volume. 



(ii) Great reduction in stream volume. Decrease of energy 

 is not related in a simple ratio to decrease of stream 

 velocity. Channel grade readjustment with aggrada- 

 tion [at the points of greatest stream strength during 

 the flood stages] marks the early steps in this later 

 phase 



D. Action at "broads" and around obstacles. 



Summary. 



Part II. 



Glaciers are Streams. 



Evidence of Sherzer, Chamberlin and Salisbury, Davis and 

 others. Writer's observations in the Californian Sierras. 



Action of a crystalline solid forced to flow under influence of gravity. 



(a) Greatest volume (Flood) stage. 



(b) Much reduced volume (Drought) stage. 



(c) Terms "Flood" and "Drought" as used in writer's earlier 



reports. 

 Summary. 



Special application of stream principles to the case of ice streams 

 in the formation of : — 

 (a) Rock basins (fiord and Alpine Lakes). 



