THE WORK OF RUNNING WATER. 



157 



the anticline plunged both ways, the valley enclosed by the hard-layer 

 ridge would be canoe-shaped at both ends (Fig. 147). In such a case 

 there would be Hkely to be a low gap (water-gap) in the rim of the 

 valley through which the drainage which degraded the surface escaped, 

 but there would be likely to be but one, for if two or more streams had 

 drained the area of the valley at an early stage of erosion, one would 



Fig. 145, — A natural bridge in development. Two Medicine River, Mont. Corresponds 

 to the stage represented b}^ Fig, 142, and the view corresponds to that shown dia- 

 grammatically at the right-hand end of the figure. (Whitney.) 



be Hkely to have captured the others (see p. 138) before late maturity. 

 A succession of doubly-plunging antichnes and synchnes might give rise 

 to a very complex series of ridges and valleys. Illustrations of the 

 above phenomena are found at various points in the Appalachian 

 Mountains, especially in eastern Pennsylvania.^ 



' See Willis. The Northern Appalachians, in Physiography of the United States. 



