\viii.iams.' THE APPALACHIAN BEGION. 



'273 



Washington and Point of Rocks mil illustrate the general character 

 of the Piedmont plateau about the latitude of Washington. 



In the absence of all paleontological data, it is impossible to assign 

 a definite age to cither of these series. In the light of what has been 

 discovered elsewhere, however, it is not improbable that the western 

 and semicrystalline areas represent the older Paleozoic horizons, meta- 

 morphosed by more intense dynamic action than has affected them 

 farther west, while the holocrystalline rocks on the east are a remnant 

 Ofthepre-Oambrian continent, from which the Paleozoic sediments were 



derived. 



The apparent conformity between the two legions may he explained 

 by supposing that the highly crystalline rocks also formed the floor 

 upon which the now semicrystalline schists were deposited as sedi- 

 ments. These older rocks, already greatly altered and folded, under 

 went at the time of the Appalachian uplilt one more final folding, 

 which gave them their now prevailing trend, and carried the overlying 

 Paleozoic sediments with them. This supposition is also in accord with 

 the fact that several closed synclinals of slate and semicrystalline 

 schists arc found pinched into the gneisses, far to the east of the main 

 contact. 



451 GB 18 



