and relict land forms would eventually become 

 completely adjusted to present sea level (Stetson, 

 1938b, 1939; Moore and Curray, 1964). 



A distinction must be made between gross land 

 forms and surficial sediments. All of the relict sur- 

 face sediments above the late Wisconsin low stand 

 of the sea (about 66 or 70 fm.) have been modi- 

 fied during the last 20,000 years or so by the ac- 

 tive surf-zone, as this zone migrated shoreward 

 across the shelf with the latest postglacial (or 

 Holocene) rise of sea level. Thus, the surface sedi- 

 ment layer is a direct product of the Holocene 

 marine transgression. Large terrain features, how- 

 ever, are not likely to have been obliterated by the 

 Holocene rise; hence, much of the present gross 

 morphology on the shelf is probably related to 

 pre-Holocene events. 



Between the nearshore surf-zone and the land 

 a complex of barrier beaches, lagoons, and coastal 

 marshes has developed along most of the Middle 

 Atlantic Coast. This complex traps much of the 

 sediment load now brought to the ocean by rivers 

 and other runoff. A large volume of recent sedi- 

 ment is also deposited in bays or sounds, and the 

 small amount of suspended fine material that 

 escapes is often removed from the shelf by cur- 

 rents or deposited in such depressions as the Hud- 

 son and Block Channels (Stetson, 1955; Curray, 

 1964). 



As changes have occurred in sea level, the shore- 

 line (along with a complex of barrier beaches, 

 lagoons, coastal marshes, and estuaries) has mi- 

 grated scores of miles back and forth across what 

 is now the shelf and the emerged coastal plain 

 (Emery, 1967). As early as 1881 Shaler suggested 

 that the net effect of this repeated migration, 

 combined with a slow subsidence of the conti- 

 nental margin, has been the deposition of the series 

 of layers that now form the thick sedimentary 

 wedge of the Continental Shelf. 



REGIONAL PHYSIOGRAPHY 



The physiographic regions and features on the 

 Middle Atlantic Shelf are described in terms of 

 their topography and sediments in the following 

 paragraphs. The major regions and features dis- 

 cussed are (1) nearshore terrains, (2) terrains 

 southwest of the Hudson Channel, (3) the Hudson 

 Channel, (4) terrains northeast and east of the 

 Hudson Channel, and (5) terraces and ancient 

 shore features on both the inner and outer shelf. 



52 



The baithymetric maps of Stearns and Garrison 

 (1967) serve as illustrations for this section and 

 should be available ; features mentioned in the text 

 are keyed to these maps by chart number. The loca- 

 tions of some of the larger features are also shown 

 in figure 1. 



Nearshore Terrains 



Nearshore terrains are easily accessible and have 

 been much studied (see, for example, Shaler, 1893, 

 1895; Johnson, 1919, 1925; Shepard, 1948; and 

 Guilcher, 1958). In the mapped area they may be 

 divided into three types. 



Tlie s\i,rf-2on£. — Parallel to the shoreline is a 

 relatively smooth concave slope, in some places 

 interriipted by one or more offshore bars, extend- 

 ing from the beach to a dei>th of 5 or 10 fm. The 

 width of the surf-zone rarely exceeds 2 nautical 

 miles (its average width is about one-half mile) 

 and it appears to be deepest off New Jersey and 

 eastern Long Island. The sediments of the surf- 

 zone are mostly clean, coarse to fine sand, with a 

 few patches of gravel and rock. Some black mud 

 that lies between 4 and 11 fm. off New Jersey and 

 Long Island may indicate places where the surf- 

 zone has exposed old coastal marsh deposits 

 such as underlie the present barrier beaches (see 

 Fischer, 1961). 



The harrier heach-lagoon complex. — Shoreward 

 of and parallel to the surf-zone, throughout most 

 of the mapped area, are extensive linear barrier 

 beaches forming the seaward margin of shallow 

 bays, lagoons, and coasital marshes. This terrain 

 is especially well develofjed along the whole of the 

 Maryland, Delaware, New Jersey, and southern 

 Long Island Coasts. The width of the lagoon- 

 coastal marsh terrain usually varies from 1 to 6 

 nautical miles. Except for tidal cliannels, the depth  

 of lagoons seldom exceeds 2 fm. and is generally | 

 less than 1 fm. The marshes are at sea level, be- 

 tween the high- and low-tide marks; and sediments 

 there are mud and organic plant debris. Tidal- 

 delta sands are aromid inlets. Barrier beaches are 

 clean sand often fonned into sand dunes by the 

 wind (see Lucke, 1934a, 1934b; and Fischer, 1961) . 

 Glacial jnoraines. — Running across the north- 

 ern part of the mapped area is a zone of low hills 

 separated from the southern New England sliore 

 by a series of bays and sounds. This region of old 

 glacial moraines forms numerous submerged fea- 

 tures as well as the backbones of Long Island, 



U.S. FISH AND WILDLIFE SERVICE 



