148 



GEOLOGY. 



Adjustment has been carried to a high degree of perfection in most 

 parts of the Appalachian system. Here, as in all other mountains 



X 





\ 



\ 







b 

 d 



Fig. 133. — Diagram showing the outcrops of hard layers on the flanks of a truncated 

 fold, cd represents the present surface; dotted lines above, earlier surfaces. 



81*10' ^ Sf OO' 



sncy 



hroa 



Fig. 134. — Example of adjusted drainage in a region of folded rocks, Va.-W. Va. 



of similar structure, strata of unequal hardness were folded into ridges. 

 In this case, the folds have been truncated by erosion, exposing the 

 more and the less resistant beds {E and & respectively) in alternate 



