it ranges from less than 15 km off Florida to 

 500 km in tlie Gulf of Maine. The total area is 

 about 510,000 sq km, of which nearly half is in 

 the Gulf of Maine (for simplicity considered here 

 as Continental Shelf). The surface of the Con- 

 tinental Shelf is a plain made somewhat irregular 

 by glacial features in the Gulf of Maine by nu- 

 merous submarine valleys, most of which only 

 indent the shelf-break, by submerged wave-cut 

 cliffs along most of its length, and by sand waves 

 on Georges Bank and elsewhere (fig. 1). 



Beyond the shelf break is a complex array of 

 of continental slope, marginal plateau, and con- 

 tinental rise. The continental slope is steep 

 (averaging 5°), and it descends to between 900 

 and 3,000 m. The average width is about 50 km 

 and the area is about 1 50,000 sq km. Along most 

 of its length, the continental slope is cut by sub- 

 marine canyons. Benches, believed to have been 

 produced by outcrops of resistant strata, occur 

 along part of its length. 



At the base of the continental slope is a broad 

 apron, the continental rise. Much of the shal- 

 lower part may be of structural origin, but the 

 deeper part is probably a fan of debris deposited 

 by turbidity currents. At its toe is an abyssal 

 plain 5,000 to 5,500 m deep. The average width 

 of the continental slope, marginal plateau, and 

 continental rise between the shelf-break and the 

 5,000-m contour is 550 km, and the total area 

 is about 1,400,000 sq km. 



Contour charts of the Continental Shelf and 

 slope are being prepared from most existing 

 soundings; the charts will be contoured at 10-m 

 intervals on the shelf and at 200-m intervals 

 on the slope. The results of new surveys by 

 the Coast and Geodetic Survey will be incor- 

 porated as they become available. In addition, 

 sounding lines will be run about 18 km apart 

 with the Precision Depth Recorder (which re- 

 cords in meters) aboard Gosnold during the 

 course of sampling operations and in certain 

 small areas where detailed studies of topography 

 are desired. The contour charts will serve as 

 base maps for other studies. Profiles obtained 

 aboard Gosnold will supplement contours in pro- 

 viding a basis for Physiographic studies which 

 should include delineation of areas shaped by 

 different erosion and depositional agents, the 

 positions of ancient shorelines of glacially low- 

 ered sea levels, and the extent of postglacial 

 warping, as well as the perennial inferences 

 about submarine canyons. 



Sediments 



Sediments of the Continental Shelf have been 

 studied over a long period of time. Stetson 



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