MAKYLA^'D GEOLOGICAL SUKVEY V i 



formity between the Magothy and the Matawan is not so ph^inly 

 marked ; at many places these beds seem to be conformable. Indica- 

 tions of an erosion interval may be seen in some good exposures, 

 however, and in the area of this county between Patuxent and 

 Potomac rivers there is a marked unconformity of overlap. A short 

 distance northeast of the District of Columbia line tlie Magothy is 

 entirely lacking, its absence being due to an overlap of the Matawan, 

 which rests upon the Earitan. Farther soutli it again makes its 

 appearance. In the region of its outcrop the formation is in many 

 places overlain by Pleistocene deposits. 



The Maiaivan Formation. 



The formation has received its name from Matawan Creek, a 

 tributary of Raritan Bay, Xew Jersey, in the vicinity of which the 

 deposits of this horizon are extensively and typically developed. The 

 name was proposed by W. B. Clark^ in 189-i and replaced the term 

 Clay marls, previously used by the IS'ew Jersey geologists. The 

 fossils of the Matawan formation furnish evidence of its Upper 

 Cretaceous age. 



Areal Distribution. — In Prince George's County the Matawan 

 formation is found in a sinuous line extending from the Patuxent 

 Biver valley near Priest Bridge southwestward to Fort Washington. 

 Throughout this area it is exposed along the margins of the streams, 

 but is covered by younger materials as it passes under the divides. 

 The Matawan reseml)les the other Cretaceous formations in having 

 a dip to the southeast which carries it beneath later deposits. It 

 undoubtedly underlies the entire county to the southeast of the line 

 of outcrop. In its broader distribution through the Coastal Plain, 

 the Matawan formation extends as a continuous series of outcropping 

 deposits from Raritan Bay to Potomac Tliver. 



Character of Materials. — The Matawan consists chiefly of glau- 



conitic sand intimately mixed with dark-colored clay, while all 



through the material small flakes of mica are commonly found. In 



some places the deposits consist almost entirely of black clay ; in 



iClark, Jour. Geol., vol. II, 1894, pp. 161-177. 



