SECT. 2] CONTINENTAL SHELF AND SLOPE 287 



average seaward slope, and a jDrecipitous lower scarp. . . . The Campeche and 

 West Florida escarpments are approximately 1000 fathoms high, whereas the 

 Sigsbee scarp south of Texas is 400-600 fathoms high." The foot of these 

 scarps is extremely sharp and well defined. The West Florida scarp was mapped 

 in detail and described by Jordan (1951), and by Jordan and Stewart (1959) : it 

 runs fairly straight to the north of 27°N, while in the south it is complicated 

 by many small embayments. The southern part of the Campeche escarpment 

 was investigated by Creager (1958), who found that the scarp ends in two 

 parallel walls bordering a comparatively narrow trough. The slope off West 

 Louisiana was mapped by Gealy (1955). On the other hand, no steep scarp is 



w 



C. Race Grand Banks Flemish Cop 



1000 



2000 



NW 

 St. Johns Grond Banks 



NW 



G.of 

 Portlond Maine Georges Bank 



WNW 

 Off C.Henry, Virginia 



W E 



St. Lucie, Florido 



Blake Plateau SSW NNE 



^Tooo^ 



(e) 



100 200 300 400 500 



I I I \ I I 



Nautical miles 



Fig. 5. Five transverse profiles across the shelf and slope of eastern North America. 

 Depths in fathoms, lengths in nautical miles. (After Heezen, Tharp and Ewing, 1959.) 



found off the Mississippi delta, but only a "relatively smooth and fairly con- 

 tinuous slope", which merges very gradually into the abyssal plain of the 

 central part of the Gulf. Another impressive scarj) is the Blake Escarpment, 

 which begins at about 600 fm off the Blake Plateau in front of Georgia and 

 Florida. Here the gradient exceeds 1 in 2 in some profiles (Heezen, Tharp and 

 Ewing, 1959). Off the east coast of the United States, the transverse sections 

 show many benches in the slope which are remarkably persistent in the Cape 

 Hatteras region, and have been correlated from profile to profile (ibid.). 



The Morocco continental margin is another area where accurate echo- 

 soundings have been carried out in recent years by the French Navy as far 



