EASTERN PIEDMONT OF MARYLAND 345 



which evidently extends southward into Albemarle county; (2) the 

 southward continuation of the Sykesville- Washington granite area, 

 which apparently is more or less continuously developed from Washing- 

 ton to Fredericksburg, and possibly includes the granitic masses at 

 Columbia, on the James river, which is approximately on the strike, 

 according to the general trend of the formations ; (3) the granitic mass 

 in the area about Richmond, which conforms in position to the more 

 easterly granite of the Maryland area. 



When an attempt is made to decipher from the remarks and lithologic 

 descriptions a general clue regarding the structure of the Virginia Pied- 

 mont one may be led to the following suggestions : On the west is a well 

 denned anticline of the Blue Ridge with Cambrian and Ordovician rocks 

 on the west and the rocks of the Piedmont on the east. Throughout 

 most of the distance from the Potomac to the James the analogues of the 

 Blue Ridge and Catoctin mountains of Maryland may be traced as com- 

 panion topographic features. It is, however, to be noted that in passing 

 southward these parallel ridges become separated and the easternmost 

 less prominent and broken up, suggesting the southward dying out of the 

 eastern part of the double-topped anticline exhibited in the Maryland 

 area. With the Blue Ridge on the west and a southward continuation of 

 Catoctin mountain, represented by Bull Run, Southwest, Carters, Green, 

 and Finley mountains, on the east are associated amygdaloidal chloritic 

 rocks representing surface flows, which have been termed by Mr Keith 

 11 Catoctin schist " and occasional meta-rhyolites. East of the more 

 mountainous part of the Piedmont little is known of the structure in the 

 northern part of Virginia south of the Washington sheet, but it seems 

 reasonably probable that we have here a broad synclinal area compara- 

 ble to that of the western Piedmont in Maryland. The rocks are in large 

 degree similar and the areal distribution and position of the region with 

 respect to the Maryland territory support this assumption. 



South of the James river, if one may judge at all from the meager de- 

 scriptions published, including the sections of the Virginia survey, there 

 are a series of more sharply compressed folds, which bring to the surface 

 more crystalline gneisses comparable in character to the Baltimore 

 gneisses of Maryland. Associated with these are less crystalline schists 

 similar to the Wissahickon formation of Pennsylvania and Maryland, but 

 differing apparently by a somewhat less pronounced degree of metamor- 

 phism. It is in this area that Darton * found fossils indicating the Pale- 

 ozoic age of these deposits. Southward from Amelia court-house is the 

 suggestion of a large synclinorium plunging to the southward along a 

 line from Amelia, Virginia, to Warrington, North Carolina, which would 



* Amer. Jour. Sci., 3d ser., vol. xlir, 1892, pp. 50-52. 

 XLVI-Bum.. Ctf.oi.. Sop. Am., Vol. 16, 1904 



