158 



GEOLOGY. 



In the structural adjustment which goes with the erosion of folds, 

 it often happens that the valleys come to be located on the anticHnes, 



Fig. 146. — A canoe-shaped valley bordered by a ridge formed by the outcrop of a 

 hard layer in a plunging syncline. The ridge bounding the canoe-valley is separated 

 from an outer ridge by a curved valley underlain by relatively weak rock. (After 

 Willis.) 



Fig. 147. — A diagram to illustrate the effects of erosion on a doubly-plunging anticline 

 made up of beds of unequal hardness. 



while the outcrops of the hard layers on the flanks of the anticlines, 

 or even in the original synclines, become the mountains. The ad- 



