10 



How toward the Atlantic. The Virginia, Delaware, Maryland, and New 

 Jersey section of the Coastal Plain is one of great estuaries in which tide 

 waters reach across the plain to the Piedmont. These are regarded as 

 drowned river valleys. 



The Coastal Plain as a geologic unit extends out into the Atlantic Ocean 

 and forms the broad and well-known continental shelf there. Off Cap< 

 Hatteras, the shelf is only 30 miles wide, but both northeastward and 

 southwestward from the cape it broadens. Off New England, it is over 

 250 miles wide. See the Tectonic Map of the United States and Fig. 7.1 of 

 this book. 



The Atlantic Coastal Plain is continuous with the Gulf Coastal Plain, 

 which is described in Chapter 41. Florida has been included in the Gulf 

 Coastal Plain, so will not be treated here. 



ATLANTIC COASTAL PLAIN 

 AND ADJACENT OCEAN BASIN 



EXTENT AND CHARACTER OF SEDIMENTS 



The Atlantic Coastal Plain is underlain by poorly consolidated Quater- 

 nary, Tertiary, and Cretaceous sediments that dip gently seaward. The 

 Cretaceous sediments form a narrow inland belt of outcrop, and the Ceno- 

 zoic sediments a broad outer belt. In places, the Cenozoic sediments over- 

 lap the Cretaceous entirely and rest on the crystalline rocks of the Pied- 

 mont. See the Geologic and Tectonic maps of the United States. The 

 surface is nearly a plain, as the term coastal plain implies. The interrup- 

 tions to the plain are low, inland-facing questas and, in places, slightly 

 intrenched streams that cross the Cretaceous and Tertiary rocks as they 



STRATIGRAPHY 



The stratigraphy of the Atlantic Coastal Plain is illustrated by a chart, 

 Fig. 10.1 and five cross sections, viz., numbers 32, 33, 34, 35, and 36 of 

 Figs. 10.2, 10.3, and 10.4. Refer to the index map, Fig. 7.1, for the position 

 of the sections. Three of the sections across the Coastal Plain and two of 

 them run lengthwise of it. 



The chief elements of the stratigraphy are the Upper Cretaceous, Eo- 

 cene, and Miocene. Lower Cretaceous beds have been noted in the north- 

 ern half of the Coastal Plain, and Oligocene beds in the southern part 

 (South Carolina and Georgia). A thin Quaternary cover is fairly extensive 

 in the area between Chesapeake and Delaware bays and in North Caro- 

 lina. For details of the stratigraphy, see Richards (1945, 1947). 



A well in Maryland penetrated 169 feet of dark red, argillaceous sand- 

 stone, apparently of Triassic age. See section 36, Fig. 10.4. 



STRUCTURE 



Coastal Plain 



Regional Dip. With few exceptions, the beds dip gently toward the 

 Atlantic. The crystalline floor upon which the sediments rest dips the 



135 



