88 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIX PROVINCE. 



CENOZOIC 



TERTIARY. 



The Tertiary deposits of Virginia form part of a complex series of 

 formations that extend interruptedly from iSTew Jersey southward to the 

 Gulf of Mexico. At no point in the region is tlie series more complete 

 or better exposed than in the Chesapeake Bay drainage basin, the bluffs 

 along the Maryland and Virginia streams having long been classic ground 

 for the study of American Tertiary strata. These Tertiary beds overlie 

 unconformably the Cretaceous deposits which they gradually transgress 

 landward. The Tertiary of Virginia is represented by deposits of Eocene, 

 Miocene, and Pliocene (?). 



EOCENE. 



THE PAMUNKEY GROUP. 



The Eocene strata of the Middle Atlantic Coastal Plain form a belt of 

 varying width, extending from northeast to southwest, somewhat to the 

 west of the center of the Coastal Plain. This belt has been traced almost 

 continuously from the Maryland-Delaware line to the valley of the Notto- 

 way Eiver in southern Virginia. Although in places buried beneath later 

 deposits, tine exposures of Eocene strata occur along all the leading stream- 

 channels, while not infrequently broad outcrops of the beds appear at the 

 surface in the intervening country. 



The Eocene deposits overlie the Cretaceous formations unconformably 

 and consist largely of greensaud 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. In certain places, notably in southern Maryland and 

 Virginia, the strata become highly argillaceous, the glauconitic elements 

 largely or entirely disappearing. Infrequently coarse sands and even gravels 

 are found, the latter chiefly toward the base of the deposits and near the 

 ancient shore-line. Very commonly the shells of organisms are so numerous 

 as to form the chief constituent of certain beds, which occasionally become 

 cemented by calcium carbonate to form impure limestones. 



Notwithstanding the fact that several different kinds of materials are 

 found composing the Eocene l)eds, the deposits on the whole are remarkably 



