CORRASION BY GRAVITY STREAMS. 



225 



power. That is to say, an excavation will here be made 

 below the associated base levels ; or, stated more correctly, 

 the stream will here produce a local (temporary) base level 

 occupying a lower vertical position than the local base 

 levels associated with it. 



3. 

 (*,) 



Fig. 



(a) PF= direction of stream. 



= assumed location of increased stream velocity caused 

 in various ways. 



(b) AOB = basin of corrasion formed during local increase of 



stream velocity. 

 Z = vertical measure of the corrasi ve strength of the stream. 



(c) Various dimensions of rock-basins determined by variable 



increase of stream volume (velocity). 



