10-i THE GEOLOGY OF PRIXCE GEOKGe's COUNTY 



peake Bay. On the Eastern Shore it does not ontcrop and is so 

 deeply buried by later deposits that it has not yet been recognized 

 with certainty in well borings. 



Character of Materials. — The Xanjenioy formation consists pri- 

 marily of greensand, which is in most places highly argillaceous and 

 locally calcareous, with certain layers carrying abundant crystals 

 and crystalline masses of gypsum. The formation contains consid- 

 erable clay, especially at its base, as shown in the section at Upper 

 Marlboro already given. The following section is fairly typical and 

 characteristic of the glauconite phase : 



Section in ravine 1 mile south of Thrift, Md. 

 Miocene: Ft. In. 



Lead-colored clay with Miocene fossils 40 



EocEXE (Nanjemoy-Potapaco substage) : 



Dark argillaceous greensand 7 



Argillaceous greensand, packed with Venericardia 

 potapacoenis • 



Dark glauconitic clay 



Layer of Yenericardia potapacoenis 



Greensand with many scattered specimens of Veneri- 

 cardia potapacoenis 



Line of concretions 



Glauconitic clay with Venericardia potapacoenis 



Dark greensand 



Layer packed with shells of Venericardia. potapacoenis. 



Argillaceous greensand 



Line of concretions 



Argillaceous greensand 



Greensand with Venericardia potapacoenis 



Dark glauconitic clay 



Layer of shells of Venericardia potapacoenis 



74 6 



Paleontologic Character. — A great many fossils are to be seen in 

 the outcrops of the ISTanjemoy formation along South and Patuxent 

 rivers, along Piscataway, Mattawoman, and ISTanjemoy creeks in 

 Maryland, and along Potomac and Aquia creeks in Virginia. An 

 idea of the abundance of these fossils may be obtained by examining 

 the foregoing section. The fossils of the Nanjemoy formation have 

 been described and illustrated in the report on the Eocene issued by 

 the Maryland Geological Survey. 



