maryland geological survey xxix 



Eocene 



The Eocene is represented in the Middle Atlantic Slope by a group of 

 deposits stretching along the eastern margin of the Cretaceous for- 

 mations, and overlying them unconformably. They have been dis- 

 cussed in much detail in an earlier volume/ where they were described 

 under the names of Aquia and Nanjemoy formations, which together 

 constitute the Pamunkey group. 



The deposits of both formations consist largely of greensand marls, 

 which may, however, by weathering lose their characteristic green color 

 and by the deposition of a greater or less amount of hydrous iron oxide 

 become firm red or brown sandstones or incoherent red sands. At 

 times, notably in Southern ^Maryland and Virginia, the strata become 

 highly argillaceous, the giaueonitic elem.ents largely or quite disappear- 

 ing. Infrequently coarse sands and even gravels are found, the latter 

 chiefly toAvard the base of the Aquia formation and near the ancient 

 shore line, especially toward the northeast in central and eastern Mary- 

 land. 



Very commonly the shells of organisms are so numerous as to. form 

 the chief constituents of certain beds. jSTotwithstanding these facts, 

 the deposits are remarkably homogeneous, although the recent investi- 

 gations of the Survey have shown the necessity of dividing them into 

 two formations on both lithologic and faunal grounds. The lower or 

 Aquia formation is much more arenaceous than the upper or Kanjemoy 

 formation, which, particularly in its lower part, is generally highly 

 argillaceous. The Aquia formation is also much more calcareous than 

 the Nanjemoy formation, indurated layers frequently appearing in the 

 former. 



Miocene 



The Miocene deposits occupy the region to the southeast of and overlie 

 those of the Eocene. They have long been known as the Chesapeake 

 group, from the superb sections found exposed on the shores of Chesa- 

 peake Bay, and have been recently divided by the State Survey into three 

 well-defined formations — the Calvert, Choptank, and St. Mary's for- 



1 Maryland Geological Survey, Eoceue, 1901. 



