(Johnson and Stolfus, 1924; Shepavd, Trefethen, 

 and Cohee, 1934; Emery and Uchupi, 1965; and 

 Uchupi, 1966a, 1966b). 



Terraces and Shore Features 

 on the Outer Shelf 



Below about 40 fm. tlie outer shelf is character- 

 ized by (1) an alternation of discontinuous scarps 

 and relatively flat terraces, some with superim- 

 posed linear ridges of coarse sands and gravels (es- 

 pecially well developed off New Jersey and Dela- 

 ware) and (2) by ancient river deltas (especially 

 south of New England) . Most authors describe the 

 scarps and terraces as old shoreline features, de- 

 veloped during lower Pleistocene sea levels (Tay- 

 lor, 1872; Newberry, 1878; Lindenkohl, 1891; 

 Shepard, 1932; Stetson, 1938b; Veatch and Smith, 

 1939; Dietz, 1952; and Emery, 1961). 



OU shore lines. — Three sets of terraces with bars 

 and spits are observable throughout the area. The 

 deepest set is between 82 and 90 fm. and averages 

 about 85 fm. Remnants of this set may be seen be- 

 tween Veatch Canyon and Atlantis Canyon (86- 

 90 fm. on chart. 0708N-53), just to the east of the 

 head of Block Canyon (82-84 fm. on chart 0807N- 

 51), and to the northeast of Hudson Canyon (82- 

 86 fm. on chart 0807N-52). In addition, Ewing et 

 al. (1963) discovered an 80- to 90-fm. buried ero- 

 sion surface near the Hudson Canyon (their 165- 

 m. terrace) . 



A shallower set, from 73 to 81 fm. and averag- 

 ing about 77 fm., may be seen between Veatch 

 Canyon and Atlantis Canyon (a double set at 78- 

 81 and 73-76 fm. on chart 0708N-53), and to the 

 northeast of Toms Canyon (73-78 fm. on chart 

 0807N-53). The 85- and 77-fm. sets of terraces 

 south of New England have been combined by 

 Garrison and McMaster (1966) into what they call 

 the 80-fm. terrace. 



These terraces are backed by a discontinuous 

 scarp, whose foot is at an average depth of about 

 77 fm. ; this scarp is the NichoUs Shore of Veatch 

 and Smith (1939). It is well defined in the subsur- 

 face (Ewing et al., 1963) and, for the most part, 

 appears to be a constructional escarpment formed 

 by younger sediments deposited on an older sur- 

 face. A more poorly developed deeper scarp, with 

 its foot at about 86 fm., can be seen between Veatch 

 Canyon and Atlantis Canyon (chart 0708N-53), 

 and just to the west of Atlantis Canyon where it 



merges with the higher Nicholls Shore (chart 

 0807N-51). 



The next set of terraces is between 56 and 71 

 fm. and averages about 64 fm.; it may be seen 

 between Hydrographer Canyon and Veatch Can- 

 yon (59-62 fm. on chart 0708N-53), as well as to 

 the west of Atlantis Canyon (64-70 fm. on chart 

 0807N-51), and to the northeast of Hudson Can- 

 yon (59-62 and 62-70 fm. on chart 0807N-52), 

 Toms Canyon (64-71 fm. on charts 0807N-52 and 

 -53), Wilmington Canyon (56-59 and 63-65 fm. 

 on chart 0807N-56), and Baltimore Canyon (62- 

 66 fm. on chart 0807N-56). Referring to the re- 

 gion south of New England, Garrison and Mc- 

 Master (1966) called this set the 65-fm. terrace. 

 It is backed by a poorly developed scarp whose 

 foot is at an average depth of about 64 fm. Called 

 the Franklin Shore by Veatch and Smith (1939), 

 this scarp appears to be partly constructional and 

 partly destructional in origin. Ewing et al. (1963) 

 could not find a clear subsurface indication of the 

 Franklin Shore near the Hudson Canyon. 



Although these three sets of terraces and scarps 

 were certainly formed when the sea v»'as at various 

 lower levels than at present, it is not easy to deter- 

 mine the exact levels. The difficulty was made 

 plain by Johnson (1910, 1932), Johnson and Win- 

 ter (1927), and Miller (1939) in discussions of the 

 problems involved in correlating old shorelines 

 now above sea level. These authors concluded that 

 at a given sea-level shoreline features can be de- 

 veloped at different elevations ajid that determina- 

 tion of former sea levels by physiographic meth- 

 ods alone is, consequently, very inaccurate. 

 Johnson (1932) has also pointed out that a dis- 

 tinction must be made between the elevations of 

 erosional and depositional features formed at the 

 same sea level. All of these conclusions are also 

 applicable to submerged features 



Numerous estimates of former sea levels on the 

 outer shelf have been based on appraisals of the 

 eustatic lowering of sea level during the forma- 

 tion of the Pleistocene ice-sheets (e.g., Maclaren, 

 1842 ; Taylor, 1872 ; Shaler, 1875 ; Daly, 1925 ; Fair- 

 bridge, 1960; Curray, 1961; and Shepard, 1961). 

 Donn, Farrand, and Ewing (1962) give double es- 

 timates for this eustatic lowering which correspond 

 with two different estimates of the present thick- 

 ness of the Antarctic ice-cap. These, combined with 

 dates taken from Emiliani (1961, 1964, 1966) and 



58 



U.S. FISH AND WILDLIFE SERVICE 



