SECT. 2] 



ABYSSAL, PLAINS 



331 



elevation which occur in the plain (Ewing and Ewing, 1962) have been found 

 by reflection studies to lie above deeper conical structures. The deeper struc- 

 tures have been interpreted as salt domes by Ewing, Worzel and Ewing (1962). 

 Assuming that the plain was perfectly flat at the close of the Wisconsin, a 

 diff'erential movement of 1 m/1000 years is indicated. This distortion may 

 indicate differential compaction or vertical migration of the sub-bottom 

 structures. 



c. Caribbean Sea 



The southern Caribbean Sea is divided into the Colombia and the Venezuela 

 Basins (Fig. 14). The Colombia Basin is floored by the well developed Colombia 



Cuba 



1000 



2000 



3000 



100 



200 300 



Nautical miles 



400 



500 



Fig. 14. Caribbean abyssal plains. 



Abyssal Plain, which spreads out from the foot of the Magdalena Cone. This 

 abyssal plain is primarily fed from the south by the Magdalena River (Heezen, 

 1955, 1956a) and to a lesser extent from the west via the submarine canyons of 

 Costa Rica and possibly Panama. Seismic-refraction studies off the northern 

 coast of Colombia indicate that the sedimentary beds thin from approximately 

 3 km at the base of the continental slope to less than 2 km on the northern 

 part of the Colombia Abyssal Plain (Ewing, Antoine and Ewing, 1960). The 

 Colombia Abyssal Plain is separated from the Venezuela Basin by the Beata 

 Ridge, which extends in a southerly direction from Cape Beata on the island 

 of Hispaniola. However, north of Aruba there is an abyssal gap between the 

 southern end of the Beata Ridge and the continental slope of South America. 

 The Aruba Gap provides a narrow connection between the Colombia Abyssal 



