MARYLAND GEOLOGICAL SURVEY 



TOPOGRAPHIC HISTORY. 



79 



The history of the development of the topography as it exists today 

 is not complicated. The topographic features were formed at sev- 

 eral different periods, during all of which the conditions must have 

 been very similar. The physiographic record is merely the history 

 of the development of the four plains already described as occupying 

 different levels, and of the present drainage channels. The plains 

 of Prince George's County are primarily plains of deposition which, 

 since their formation, have been more or less modified by the agencies 

 of erosion. Their deposition and subsequent elevation to the heights 



LAFAVCTTE 





OLDER FORMATIONS 



Fig. 1. — Diagram showing ideal arrangement of the various terrace forma- 

 tions in the Maryland Coastal Plain. 



at which they are now found indicate merely successive periods of 

 depression and uplift. The drainage channels have throughout 

 most of their courses undergone many changes; periods of cutting 

 have been followed by periods of filling, and the present valleys and 

 basins are the results of these opposing forces. 



The Lafayette Stage. — Within the borders of the County there are 

 evidences of frequent changes during Cretaceous and early Tertiary 

 time which resulted in the deposition of a succession of formations 

 composed of heterogeneous materials. These changes, however, were 

 to only a very slight extent influential in producing the present 

 topography, so that in beginning the discussion of the physiographic 

 history of the region they may be omitted. Toward the close of the 

 Tertiary, however, a change in conditions occurred which is clearly 

 shown in the existing topography. A layer of gravels, sands, and 

 clays was spread over the entire Coastal Plain and along the borders 

 of the Piedmont Plateau during the Lafayette submergence. These 

 deposits, which, as already stated, must have been laid down on a 



