358 



PHYSICAL GEOLOGY 



It is evident that a series of strata, subjected to forces sufficient 

 to produce the intense folding shown in the Alps and in the southern 



Fig. 346. — Diagram showing a cross section of the Alps along the Simplon tunnel. 

 The complicated structure and former extension of the strata are shown. (After 

 Schmidt.) 



Appalachians (Fig. 347), will often break and fault instead of fold- 

 ing. It is, consequently, seldom that folded strata are free from 

 dislocations over a distance of even a few miles. The strata of folded 

 mountains have often been so compressed that cleavage planes parallel 



Sea Levi 



Fig. 347. — J, section across the southern Appalachians where extreme faulting has oc- 

 curred (U. S. Geol. Surv.) ; B, section in the vicinity of Chattanooga, Tennessee. 



to the folds have been induced. Metamorphism is in proportion 

 to the intensity of the compression. 



Origin and Development of Folded Mountains 



Four points have been established with reference to folded moun- 

 tains : (1) they were formed from thick sediments that had accumu- 

 lated in geosynclines ; (2) they were folded as a result of lateral 

 pressure; (3) the rate of folding was slow; and (4) their outlines, 

 after prolonged erosion, are determined largely by the character of 

 the rocks and the arrangement of the strata. A discussion of these 

 points follows. 



1 here is also reason to believe that mountains of this class are situ- 



