100 THE GEOLOGY OF I'RIXCE GEOlUiE S COUNTY 



PaleontoJogic Character. — The Monmouth formation is generally 

 very fossiliferous and the forms are usually well preserved. They 

 consist of foraminifers, pelecypods, gastropods, and cephalopods. 

 Among the most abundant are Exogijra cosfafa Say, (Jryphaea vesicu- 

 laris Lamarck, Idonearca vulgaris Morton, Cardium perelongatum 

 Whitney, and Belemnitdla americana Morton. They are typical 

 Upper Cretaceous species. 



Strike. Dip and Thickness. — The strike of the Monmouth forma- 

 tion is from northeast to southwest, and the dip is toward the south- 

 east at the rate of about 25 feet to the mile. The maximum thickness 

 of the Monmouth formation along its outcrop in the area of Prince 

 George's County is from 40 to 50 feet. In northern Kew Jersey it 

 is about 200 feet thick, but it steadily decreases in thickness along 

 the strike southwestward, until it finally disappears as an outcropping 

 formation in the north-central part of this county. 



Stratigraphic Belations. — The Monmouth is conformable with the 

 underlying Matawan and with the Eancocas, which overlies it on the 

 Eastern Shore of Maryland and in Delaware and N"ew Jersey. 

 Within Prince George's County it is overlain unconformably by 

 Eocene and Pleistocene deposits. The Monmouth is readily distin- 

 guished from the ]\Iatawan, as it lacks the darker colored micaceous 

 sands and marls of that fonnation. Erom the Eancocas it is distin- 

 guished by the great predominance of reddish-brown sand. 



The Eocexe Eor:\[ations. 

 the pamunkey group. 



The Aquia Formation. 



The formation receives its name from Aquia Creek, a tributary of 

 Potomac River in Virginia, where deposits belonging to this horizon 

 are characteristically developed. This name was proposed by W. B 

 Clark' in 1895. 



^Clark, Johns Hopkins Univ. Circ, 1895, p. 3. 



