MARYLAND GEOLOGICAL SURVEY 63 



material, which forms the Coastal Plain, to the erosive effect of rain and 

 rivers, with the result that rapid denudation toward the head waters of 

 streams has been accompanied by rapid sedimentation along the lower 

 courses. Many of the larger estuaries, such as the Patuxent, Eappahan- 

 nock, and Pamunkey rivers, have been filled in toward their heads while 

 shorter estuaries have been transformed to meandering streams. The 

 most extensive beach and dune deposits are found along the ocean front 

 extending from Sandy Hook southward. Here the waves have thrown up 

 extensive barrier beaches, and the winds have caught up the loose sand and 

 piled it into dunes. Behind this obstruction, which separates the ocean 

 waters from an ancient irregular shore line, lie many brackish-water 

 lagoons which have already been considerably filled up with mud since 

 they were separated from the ocean. Chief among these may be men- 

 tioned Barnegat Bay in New Jersey, Chincoteague Bay in Maryland, and 

 Albemarle and Pamlico sounds in North Carolina. 



Physiography of the Region. 



The Atlantic Coastal Plain is the name applied to a low and partially 

 submerged surface of varying width extending from Cape Cod southward 

 through Florida and confined between the Piedmont Plateau on the west 

 and the margin of the continental shelf on the east. The line of demarca- 

 tion between the Coastal Plain and the Piedmont Plateau is sinuous and 

 ill-defined, for the one passes over into the other oftentimes with insensi- 

 ble topographic gradations, although the origin of the two districts is quite 

 different. A convenient, although somewhat arbitrary, boundary between 

 the two regions is furnished in Maryland by the Baltimore and Ohio 

 Railroad in its extension from Wilmington southwestward through 

 Baltimore to Washington. The eastern limit of the Coastal Plain is at 

 the edge of the continental shelf. In this region it is located about 100 

 miles off shore at a depth of 100 fathoms beneath the surface of the 

 Atlantic Ocean. It is in reality the submerged border of the North 

 American continent which extends out with a gently-sloping surface to 

 the 100-fathom line. At this point there is a rapid descent to a depth of 

 3,000 fathoms where the continental rise gives place to the oceanic abyss. 



