286 GTJILCHER [chap. 13 



In East Antarctica, Jivago and Lissitzin (1958) describe series of sharp, cuesta- 

 like ridges in the Davis Sea and off Queen Maud's Land, whereas they report 

 groups of smooth mounds from the surroundings of Drygalski Island. On the 

 west coast of Brittany, long ridges of submarine rocks rise from a sea-bottom 

 smoothed by sedimentation. These ridges are extensions of the flattened crests 

 of Ordovician sandstone which run across the Crozon Peninsula (Guilcher, 

 1958, p. 206; see also Fig. 1). 



Such resemblances between the shelf and the continental morphology 

 suggest that both belong to the same structural units, and were shaped by the 

 same erosional factors. The Californian borderland is a submerged continuation 

 of California, and the topography on the Norwegian and Scottish shelves calls 

 to mind the pattern of glaciated valleys in Norway and Scotland. On the other 

 hand, the width of the shelf reflects the character of the continental topography : 

 wide platforms face the plains of North-west Europe, Argentina and eastern North 

 America, whereas narrow platforms are found off mountainous areas such as 

 West America or Algeria. OccasionaUy, there is no shelf at all, and mountains 

 are known which j)lunge directly into the deep sea as at Nice in South-east 

 France (Bourcart, 1959, map) ; the Gibraltar area is another area where no 

 shelf is found (Heezen, Tharp and Ewing, 1959). But it must be noticed that 

 this is quite infrequent, since the elements of a platform occur generally in 

 regions of vigorous continental relief, for example in most parts of the Algerian 

 coast (Rosfelder, 1955). 



3. Topography of the Continental Slope 



The main topographical features of the slope are the submarine canj^ons, 

 wliich dissect it deeply in many areas (see Fig. 7 for example). Some of these 

 even encroach on the shelf itself. Since, however, canyons are described in 

 Chapter 20, they will be left out here. 



The continental slope is far from being uniform even if canyons are not 

 considered. Thus Day (1959) has pubhshed British echo-sounding jirofiles from 

 the slope in the south-western Celtic Sea, showing its great irregularity. In 

 this area, a consisicuous terrace, for which the name Meriadzek Terrace has 

 been proposed, breaks the slope at 47° 30'N, 8° 30' W ; it hes at a depth of 1100- 

 1200 fm. Farther to the north-west, the slope consists, on the contrary, of the 

 high and steep Pendragon Scarj), while it becomes much smoother and more 

 gentle in the Porcuj)ine Seabight, which forms a wide re-entrant between 

 Pendragon Scarp and Porcupine Bank. French echo-soundings by Berthois 

 confirm these findings (Guilcher, 1958a; Berthois and Brenot, 1962) and show 

 other variations in profiles, hitherto unknown, between the Celtic Sea and the 

 inner part of the Bay of Biscay. 



In the Gulf of Mexico, Ewing, Ericson and Heezen (1 95S) ])oint to a particular 

 profile of the continental slope over several areas. Oft' West Florida, West 

 Louisiana and Texas, and the Yucatan or Camx^eche Peninsula, "the continental 

 slope is made up of two segments : a wide upper rugged portion with a gentle 



