186 



HISTORICAL GEOLOGY 



This tremendous deformation took place very slowly, though 

 during a short time as compared with the length of the Paleozoic 

 era. As soon as the folds appeared well above sea-level, irregu- 













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Fig. 112 



Highly generalized structure sections across the Appala- 

 chian Mountains and adjoining districts to illustrate 

 certain important features in the history of the region. 



Upper figure: A, Appalachia; B, marginal sea-bottom 

 (Appalachian geosyncline) mostly filled with sediments 

 derived from Appalachia during Paleozoic time. 



Middle figure: The same region with the strata folded 

 into mountains as they would have appeared, if un- 

 affected by erosion, toward the close of the Paleozoic 

 era. A, Appalachia; B, Triassic basin or downwarp; 

 C, Appalachian Mountains. 



Lower figure: The same region as it now appears after 

 much erosion, the submergence of Appalachia, and the 

 deposition of the Coastal Plain beds. A, Coastal Plain; 

 B, Piedmont Plateau; C, Appalachian Mountains. 

 (By W. J. Miller.) 



larities began to be carved out by the work of erosion so that even 

 from early youth the mountains presented a rugged surface. 

 Mountains now in process of growth, like the Coast Ranges of 



