EARLIER TERTIARY (EOCENE AND OLIGOCENE.) 747 



maximum thickness of the Nanjemoy formation is 125 feet. It has been divided into the 

 Potapaco and Woodstock members. It contains an extensive fauna of middle Eocene age. 

 It is not known to occur on the eastern shore of Chesapeake Bay. 



The Calvert formation, which overHes the Eocene formations unconformably, consists of 

 sands, clays, marls, and diatomaceous earth. These deposits have a thickness of about 200 feet. 

 The formation has been divided into the Fairhaven diatomaceous earth member and the Plum 

 Point marl member. It contains an extensive marine fauna. 



The Choptank formation consists of sands, clays, and marls and has a total thickness of 

 125 feet. An extensive marine fauna characterizes these deposits. 



The St. Marys formation consists of clays, sands, and sandy clays, the last typically greenish 

 blue and bearing large quantities of fossils. The formation has a thickness of 150 feet. It 

 carries a distinctive marine fauna. 



The Lafayette formation consists of clays, loams, sands, and gravels which are in many places 

 highly ferruginous. The thickness is variable but in few places exceeds 50 feet. No character- 

 istic fossils have been found in these deposits and there is much doubt as to whether they are 

 of late Pliocene or early Pleistocene age. The formation covers a wide area on the southern 

 peninsula of Maryland and is represented to the north, on the western shore of Chesapeake 

 Bay, by many small outliers. It overlies the Miocene and earlier formations unconformably. 



Virginia. — The Tertiary deposits of Virginia comprise strata of Eocene, of Miocene, and 

 probably of Pliocene age. The Eocene and Miocene formations are highly fossiliferous. The 

 geology and paleontology of the region have been studied by many investigators, among them 

 Rogers,^'" Conrad,"' Clark,'*"- 1^" Miller, ="=-=" Berry,'' and Gardner. 



The following scheme of classification has been adopted for the Tertiary deposits of Virginia : 



Pliocene (?) Lafayette formation. 



Miocene Chesapeake group : 



Yorktown formation. 



St. Marys formation. 



Choptank formation, probably present but does not outcrop. 



Calvert formation. 



Eocene Pamunkey group : 



Nanjemoy formation: 



Woodstock greensand marl member. 

 Potapaco clay member. 

 Aquia formation: 



Paspotansa greensand marl member. 

 Piscataway indurated marl member. 



The Aquia and Nanjemoy formations of Virginia are similar in their lithologic and faunal 

 characters to the same formations in Maryland, the deposits being less highly calcareous in 

 central and southern Virginia than in the valley of the Potomac. 



The Calvert formation in Virginia is similar in character to the same formation in Maryland. 

 It disappears at the outcrop in south-central Virginia, owing to the transgression of the St. 

 Marys formation. 



The St. Marys formation overlaps the Choptank formation near the Maryland-Virginia 

 line and in Virginia directly overlies the Calvert formation unconformably. 



The Yorktown formation consists of sands, sandy clays, and marls. In many places the 

 marls are highly calcareous and fragmental in character. The deposits have a thickness of 150 

 feet and contain an extensive fauna of marine animal remains. The formation overlies the St. 

 Marys formation unconformably. 



The Lafayette formation in Virginia is similar in character to the same formation in Mary- 

 land, the strata being found along the western margin of the Coastal Plain in outliers of various 

 extent. 



North Carolina. — The Tertiary deposits of North Carolina comprise representatives of the 

 Eocene, Miocene, and Pliocene. The extent and character of the deposits have not been known 

 until within recent years. Among those who have studied the region may be mentioned Dall,^'^° 



