MARYLAND GEOLOGICAL SURVEY 89 



Stratigrapiiic Eelations. — The Sunderland formation is built as a 

 terrace lying irregularly and unconformably on older rocks which range 

 in age from pre-Cambrian down to the later members of the Miocene. 

 (Plate XI, Fig. 1). In certain localities in southern Maryland it 

 is believed to rest unconformably on the basal portions of the Lafayette, 

 and in other localities there may be remnants of the Lafayette 

 lying concealed beneath its base. It also lies at a distinctly lower level 

 than this formation, wraps about it like a border, and is separated from it 

 by a scarp which is at times abrupt and very well defined. The most 

 typical of these scarps can be seen near Congress Heights and amounts to 

 about 60 feet. Others occur at Bryantown, Aquasco, and Charlotte Hall. 



A word may be added regarding the scarp at Charlotte Hall as it seems 

 to have been overlooked by former geologists. The height of the scarp 

 is about 20 feet and separates the flat surface of the Lafayette above from 

 the plain surface of the Sunderland below. The Lafayette surface 

 stretches away in an unbroken plain, gently rising toward the Piedmont 

 and the Sunderland extends southward toward the ocean. Just be} r ond 

 the main scarp-line there are in the vicinity of Charlotte Hall a number 

 of outliers of Lafayette which rise above the general level of the Sunder- 

 land. These bear the same relation to the main Lafayette deposit as the 

 outliers of the Talbot formation, which now rise above the surface of 

 Chesapeake Bay, bear to the mainland close by. This topography at 

 Charlotte Hall might be easily overlooked by one making a hurried 

 reconnaissance and might be entirely misunderstood by one unaccustomed 

 to the geology of the Coastal Plain. The narrow flat reentrants which 

 separate the main body of the Lafayette from the outliers might be 

 looked upon as a valley cut by stream erosion and the presence of opposing 

 scarps where the outliers face the main body of the Lafayette formation 

 might be considered as indicative of river banks. On the southeast side 

 of these outliers, where they faced toward the Sunderland sea, there is 

 no opposing bank, but they drop away similarily to the Sunderland 

 surface which is unobstructed by other prominences toward the southeast. 

 It is evident that these outliers were once portions of the mainland and 

 that the narrow flats which ramify among them were formerly stream 



