266 



E. C. ANDREWS. 



obliquely round the cliff face, as offering lines of least 

 resistance to flow. At the same time the main glacial flow 

 over the opposing ridge summit formed grooves following 

 the general direction of this higher mass, Fig. 11 (b). 



Fig. 11. 



J=* 





-_.=-- 



:-■. 



m 





; 



n 



- 1 ! 



i-j- 



r 



~J 



.' H - 



T ' 





Directions fol- 

 lowed by ice in 

 passing over a 

 rock mass in the 

 San Joaquin 

 Valley, Cali- 

 fornia. 



(b) Ideal sketch illus- 

 trating action of 

 ice in traversing 

 two high ridges 

 in the San Joa- 

 quin Valley. 

 The ridges rise 

 1000 feet above 

 the valley base. 



4. On the San Joaquin cliffs where the rock faces are 

 formed of dense structures and where the valley cross- 

 sections in their lower portions are relatively small, the 

 great walls are literally covered with huge and closely set 

 horizontal grooves, giving rise to the appearance of the 

 parallel grooves on a circular galvanised iron tank. Some 

 of the grooves are as much as ten feet in depth. In each 

 case their disposition is such as strikingly to suggest that 

 here the glacier locally took the lines of least resistance 

 and moulded the stream to the wall. In other cases a 

 slight upward motion of the ice grooves was observed on 



