so THE PHYSIOGRAPHY OF PRINCE GEORGE^S COUNTY 



rather irregular surface, formed a thin mantle of materials, ranging 

 from 25 to 50 feet in thickness. When the uplift which terminated 

 Lafayette deposition occurred, a very even, gently sloping plain 

 extending from the Piedmont Plateau to the ocean, bordered the 

 continent. Across this plain, which was composed of coarse, uncon- 

 solidated materials, streams rising in the Piedmont gradually 

 extended their courses, while new ones confined to the Coastal Plain 

 were also developed. At this time the shore line seems to have been 

 farther east than now, and the present submerged channels of the 

 continental shelf were probably then eroded. The Coastal Plain 

 portions of Delaware River, with its extension Delaware Bay; 

 Chesapeake Bay, which is the continuation of Susquehanna River; 

 and Potomac, Patuxent, Rappahannock, James, and other rivers 

 date from this post-Lafayette uplift. The attitude of the subse- 

 quent deposits makes this evident, for the Sunderland, Wicomico, 

 Talbot, and Recent terrace formations all slope toward these various 

 waterways. The Lafayette formation was cut through by the streams, 

 and valleys were opened in the older deposits. Several of these 

 valleys became many miles wide before the corrasive power of the 

 streams was checked by the Sunderland submergence. 



The Sunderland Stage. — As the Coastal Plain was depressed, in 

 early Pleistocene time, the ocean waters gradually extended up the 

 river valleys and over the lower lying portions of the stream divides. 

 The weaves worked on the Lafayette-covered divides and removed the 

 mantle of loose materials, which were either deposited farther out 

 in the ocean or dropped in the estuaries formed by the drowning 

 of the lower courses of the streams. Sea cliffs produced on points 

 exposed to wave action w^ere gradually pushed back as long as the 

 sea continued to advance. These cliffs are now represented by the 

 escarpment separating the Sunderland from the Lafayette. The 

 materials which the waves gathered from the shore, together with 

 other materials brought in by the streams, were spread out in the 

 estuaries and constitute the Sunderland formation. 



The tendency of the work done was to destroy all irregularities 

 produced during the post-Lafayette erosion interval. In many 

 places old stream courses were undoubtedly obliterated, but the 



