MARYLAND GEOLOGICAL SUKVEY 121 



well records and observations which show that the snrface of the 

 underlying formations rises in passing from the stream valleys to 

 the divides. Consequently, the thickness of the Snnderland can not 

 be determined by the elevation of the deposits, but the evidence fur- 

 nished by the excavations and well records on the stream divides 

 shows that the formation pi'obal)ly has an average thickness of about 

 35 feet. 



Stratlgvaphic licladons. — Thronghout the Coastal Plain the Sun- 

 derland overlies unconfonnably various formations of Cretaceous, 

 and Tertiary age. In Prince George's County it lies unconformably 

 upon the Aquia, JSTanjemoy, Calvert, and Choptank formations. It 

 is not imj^robable that the edges of the Lafayette formation extend 

 beneath part of the Sunderland deposits, although this can not be 

 determined because of the absence of any definite; line denoting a 

 stratigraphic break and because of the similarity of tlie materials of 

 the two formations. 



The Wiconiico Formation. 



This formation receives its name from Wicomico River, in south- 

 ern Maryland. The name was proposed by G. B. Shattuck in May, 

 1901.^ The Wicomico represents the upper part of the Later Colum- 

 bia of McGee and Darton and a part of the Pensauken of Salisbury. 

 The presence of ice-borne boulders furnishes evidence for its con- 

 temporaneity with the ice invasion, although the particular drift 

 sheet with which the formation should be correlated has not yet been 

 determined. 



Areal Disl rihiil Ion. — The next yduiigcr foi'iiiat ioii of Pleisto- 

 cene age is the Wicomico. Like the Sunderland, it was deposited 

 on a terrace or plain. It lies topographically lower than the Sun- 

 derland, wraps around it like a border, and extends \\\) the 

 principal stream estuaries which ]ienetrate it. In Prince George's 

 County the Wicomico formation is distributed in the stream valleys 

 through the entire area, and is especially well developed in the basin 

 of Patuxent River. 



^Johns Hopkins Univ. Circ. No. 1.52. 



