252 



E. C. ANDREWS. 



variation in the vertical measure of stream strength so the 

 time necessitated for such aggradation was accentuated. 



Fig. 10. 



(cv) 



<t) 





Stages in the action of streams whose volume is decreasing. 



(a) A B represents the rock basin formed by a heavy stream 



volume (flood). Z O represents the deepest point to which 

 such stream can corrade while the point B is stationary. 



(b) Result of volume decreasing in a moderate degree. Z'O' repre- 



sents the new vertical limit of the stream's action and the 

 mass BOA O'B'A' shows the resultant silting following \m 

 such reduction of stream volume. 



