68 THE GEOLOGY OF CALVERT COUNTY 



rest conformably on the Aquia formation, the basal member of the 

 Eocene in Maryland. 



Next above the Nanjemoy are found the three formations of the Chesa- 

 peake Group, which are Miocene in age. They are, beginning with 

 the oldest, the Calvert, Choptank, and St. Mary's formations. The Cal- 

 vert formation rests unconformably on the jSFanjemoy; the Choptank, 

 in turn, rests unconformably on the Calvert, but passes into the St. 

 Mary's formation without a break. The materials of the formations 

 which compose the Chesapeake Group consist of marls, clays, diato- 

 maceous earths and sands. Each formation is abundantly supplied with 

 fossils. Above the St. Mary's formation rests the members of the 

 Columbia Group, which are Pleistocene in age. These are, beginning 

 with the oldest, Sunderland, Wicomico, and Talbot. They are all un- 

 conformable with whatever lies beneath them and they are also uncon- 

 formable with each other. They are developed in terraces lying one 

 above the other and separated by well defined scarp-lines. (Fig. 1.) 

 The materials which enter into them are clay, peat, sand, gravel, and 

 ice-borne boulders. As a group, they record what took place in Calvert 

 County while the regions to the north were covered by the great ice 

 sheet. 



The Eocene. 



The Pamunkey Group, 

 the nanjemoy formation.^ 



The Nanjemoy formation is the only representative of the Eocene 

 in Calvert County. It is extensively developed in other portions of 

 the Maryland Coastal Plain, where it has been carefully studied, but 

 in Calvert County so little of the formation is present and it dips so 

 rapidly beneath tide that its characteristics are not well defined, so 

 that what is said in this chapter regarding it is based largely on ex- 

 posures which are found in neighboring regions. 



^ For a full discussion of the Nanjemoy, the reader is referred to the 

 Eocene Report by Clark and Martin, published by the Maryland Geological 

 Survey, 1901. 



