MARYLAND GEOLOGICAL SURVEY 69 



The name of the formation was suggested by Nanjemoy Creek, in 

 Charles County, where it was found to be typically developed. In 

 Calvert County the Nanjemoy formation is exposed only in the extreme 

 northwestern section, in Lyons Creek Valley, and southward along the 

 Patuxent Eiver to a point about a mile below the mouth of Hall 

 Creek. Throughout this region it forms the basement rock of the 

 county, on which the Calvert formation and the terraces of the Columbia 

 Group rest. It is so completely buried by these over-lying deposits 

 and their talus slopes that it is seldom exposed except in the valleys 

 of streams where erosion is sufficiently rapid to strip the banks of 

 debris. The base of the Xanjemoy formation is not visible within 

 the borders of Calvert County, but if the same relations hold here 

 as have been observed elsewhere, the Nanjemoy lies conformably on 

 the Aquia formation, which is the basal member of the Eocene in 

 Maryland. 



The materials which make up the deposits consist of marls, sands 

 and greensands, which latter frequently become highly arenaceous. Gyp- 

 sum crystals are also found scattered throughout tlie deposits. 



The exposure where the ISTanjemoy formation can be seen in its 

 most typical development is in the cliff at Lyons Creek Wharf. The fol- 

 lowing is a section made at this locality by Dr. G. C. Martin.^ 



Section on bank of Patuxent River one-quarter mile below viouth of Lyons Creek, 



Calvert County. 



Feet. Inches. 



Pleistocene. Sand and gravel fi 



Dlatomaceous clay 



Neocene. Miocene. Siliclous indurated stratum with Miocene fossils.... 10 



Brown prritty clay, with abundant casts of Miocene 



fossils 4 



.Vrsfillaceous jrreensand, with abundant casts of Nan- 

 jemoy fossils 10 



Line of concretions 2 



Eocene. Nanjemoy. Argillaceous greensand and talus 20 



Total 50 



The thickness of the Nanjemoy formation as calculated from neigh- 

 boring regions is about 125 feet. The dip is 12 to 15 feet per mile 

 to the southeast and the strike is from northeast to southwest. 



° The Eocene, Maryland Geological Survey, 1901, p. 72. 



