114 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



w. 



ALLEGHENY PLATEAU 



Fr °si^urg J Md^' coa / measures " 



ALLEGHENY 

 FRONT 



\3I 



Corriganville 



DEVILS 

 BACKBONE 

 0/ ~! WILLS 

 JO' MOUNTAIN 



IRON ORE 

 RIDGE 



Flintstone 



RAGGED 

 MOUNTAIN 

 POLISH 

 MOUNTAIN 



SIDELING 

 HILL 



•pg j Roconoss. 

 "***■ "" "rboniferou s) 



CACAPON 

 _-.,-,.,.,... MOUNTAIN F 



RIDGE ANTICLINE t " 



oei C/osely folded Hanco ^ 



U. MILES 



Fig. 8.20. Section from Allegheny plateau to Cacapon Mountain anticline at Hancock, Md. Reproduced 

 from Butts et a/., 1933. Section 21 of index map, Fig. 7.1. 



granitic or clastic rocks. One of the windows, such as that containing 

 Grandfather Mountain, North Carolina, lies 35 miles southeast of the 

 northwest boundary of the Rlue Ridge province (King, 1951). 



PIEDMONT PROVINCE 



Principal Foliate Rocks 



The most voluminous rocks in the crystalline Piedmont of Penn- 

 sylvania, Maryland, and Virginia is a great schist series which exhibits 

 in part high-grade metamorphism (Jonas, 1932). It contains in places 

 various metavolcanics. In Cecil and Harford counties, Maryland, a 

 volcanic sequence well described by Marshall (1937) shows considerable 

 variation, grading from massive amygdaloids and even-textured volcanics 



through schistose amygdaloids to fine-grained hornblende schists which 

 in places are indistinguishable from sheared gabbro except by micro- 

 scopic examination. Several bodies of mylonitized granite in the schist 

 series have been recognized. 



The most troublesome and yet unsolved problem is the age of the 

 schist. It has been correlated with the Glenarm series of Pennsylvania 

 and Maryland, and to this most authorities agree; but the age of the 

 Glenarm is not yet known. It is generally believed to be late Precambrian 

 or early Paleozoic. 



A few anticlines and domes of older rocks, the Raltimore gneiss, are 

 found within the schist series, in Maryland and Pennsylvania, and pre- 

 sumably others occur in Virginia. 



The Piedmont and eastern part of the Blue Ridge in North and South 



