524 T. L. WATSON LITHOLOGICAL CHARACTERS OF VA. GRANITES 



standing this fact no published account of the geology of these rocks has 

 been made, so far as the writer is aware. A part of two seasons has been 

 devoted by the writer to a study of the Virginia granites in the field and 

 in the laboratory, and it is with the hope of contributing to the knowl- 

 edge of the geology of these rocks that prompted the preparation of this 

 paper. 



The Virginia Piedmont Eegion 



geology 



The Piedmont province in Virginia forms a part of the eastern crys- 

 talline area which extends south-westward from New York to northern 

 central Alabama. It extends eastward from the Blue ridge to the western 

 margin of the Coastal plain, and it widens southward. Lack of system- 

 atic study of the Virginia Piedmont region forbids more than a general 

 description of its geology at this time. The rocks composing the region 

 are the oldest in the state, and, excepting the areas of Jura-Trias, they 

 are all crystalline. Eogers mapped the crystalline rocks of the region as 

 Archean, but more recent studies reveal the fact that a part of them are 

 as late as Ordovician in age. 



The rocks comprise sedimentary and igneous masses so greatly altered 

 from metamorphism that many of them bear but slight resemblance to 

 the original masses. The region is made up of a complex of schists, 

 gneisses, and granites, with, in places, minor interfoliations of slates, 

 quartzites, and limestones. This complex is further intersected by intru- 

 sions of basic eruptive rocks belonging, so far as they have been studied, 

 to the diabasic, dioritic, and gabbroic types. To the east of Danville, in 

 the extreme southern part of the region, is an area of altered andesite 

 which extends into North Carolina and is regarded as pre-Cambrian 

 in age. 



Over the eastern, northern, central, and southern parts of the Pied- 

 mont are areas of Jura-Trias shale, sandstone, and conglomerate. The 

 northern and eastern areas of these rocks are quite extensive. 



DISTRIBUTION OF THE GRANITES 



The granites are limited to the crystalline area described above and 

 comprise both massive and schistose types. The schistose granites or 

 gneisses have very wide distribution throughout the Virginia Piedmont, 

 forming one of the dominant rock types. The principal areas of pro- 

 ducing massive granites are distributed in a north-south direction near 

 the eastern border of the Piedmont plain. They include (1) the Peters- 

 burg area, (2) the Eichmond area, and (3) the Fredericksburg area. 



