THE NANJEMOY FORMATION, 103 



SECTIONS ALONG NOTTOWAY RIVER. 



The most southerly exposures of Eocene strata in Virginia occur near 

 Boiling's Bridge on the Xottoway Eiver where McGee" first reported the 

 presence of three or four feet of dark-colored clay containing Eocene fossils. 

 Tn the absence of any characteristic species this material is referred to the 

 Aquia formation. It occurs in immediate contact with Potomac strata. 



The Nanjemoy Formation. 



Name and areal distribution. — This formation has been so named because 

 of the excellent exposures of beds of this age along the Nanjemoy 

 Creek, a stream flowing into the Potomac River from the Maryland side. 

 The name was proposed by Clark and Martin in 1901.^ 



Stratigraphic relations. — The stratigraphic relations of the Kanjemoy 

 formation are very simple. The formation rests conformably upon the 

 Aquia, while it is covered by the deposits of the Calvert formation with 

 which it is unconformable. The Calvert transgresses the Nanjemoy alto- 

 gether in northeastern Maryland and probably also in southern Virginia, 

 so that it comes to rest directly upon the Aquia, the Nanjemoy not appear- 

 ing at the surface. It probably underlies the Calvert, however, throughout 

 the entire eastern portion of the State. In certain places near the outcrop 

 of the formation the Nanjemoy deposits are unconformably overlain by the 

 unconsolidated materials of the Pleistocene. 



Lithulogic cliaracter. — The Nanjemoy formation is composed of green- 

 sand, often highly argillaceous and less frequently calcareous than the 

 Aquia deposits, and with here and there layers containing abundant crystals 

 and crystalline masses of gypsum. The base of the Nanjemoy is usually 

 marked by a bed of compact white and pink clay resting directly upon the 

 greensand of the Aquia. This clay bed forms a very persistent layer which 

 has received the name of Marlboro clay from Marlboro, Maryland, where it 

 is well exposed. 



Strike, dip, and thichness. — The strike of the Nanjemoy is almost due 

 north and south, while the beds dip to the east at the rate of from 12 

 to 15 feet to the mile. In the deep wells in the vicinity of Norfolk the 

 Nanjemoy is reached at the depth of about 600 feet. The thickness where 

 all the beds are developed is about 125 feet. It generally thins somewhat 

 to the westward, as in the case of most of the Coastal Plain formations. 



aAmer. Jour. Sci., vol. xxxv, 1888, p. 126. 

 ^Eocene, Maryland Geological Survey, p. 64. 



