MOVEMENTS AND DEFORMATIONS 



355 



folded mountains usually embrace a series of roughly parallel folds, 

 the whole forming an anticlinorium (Fig. 286). 



Distribution of folded mountain systems. The location of folded 

 mountains is so often near the borders of the continents that the 

 relation is probably significant, but there are very notable excep- 



Fig. 286. Anticlinorium: diagrammatic. (Van Hise, U. S. Geol. Surv.) 



tions. Among these are the Urals, the complex series that stretches 

 from the Pyrenees to the Hindu Kush, the Central Asian chain 

 which embraces the Sayan, the Altai, and the Tien Shan, and many 

 minor ranges. 



Folding movements had extraordinary prevalence in the early 

 ages. The Archean rocks are almost universally crumpled, often 

 in the most intricate fashion, and the proterozoic formations are 

 much folded. After the inauguration of the well-known sedi- 



Fig. 287. Ranges of the Great Basin. Length of section, 120 miles. (Gil- 

 bert.) 



mentary eras, folding appears to have taken place chiefly at long 

 intervals, and for any given period to have been concentrated 

 along certain tracts. The Appalachians and the Juras are types. 



2. Plateau-forming movements. An important phase of mass- 

 ive movement was the relative settling or raising of great blocks or 

 segments as though by vertical rather than horizontal forces. The 

 great plateaus are examples of the protrusive phase of this action; 

 perhaps the great "deeps" of the ocean bottom, and some of the 

 basins or troughs (Graben) on the continents, are examples of the 

 depressional phase. The plateaus usually embrace numerous 



