326 HEEZEN AND LAUGHTON [CHAP. 14 



b. California Abyssal Plain 



The abyssal plain off California, bounded by the Mendocino Escarpment on 

 the north and the Murray Escarpment to the south, covers an area of 130,000 

 mi2. The large submarine canyons of central California have built many deep- 

 sea fans and abyssal cones which dominate the continental rise. These deep-sea 

 distribntory channels lead toward the abyssal plain. The abyssal plain oflF 

 California was originally described by Menard in 1955 and was simply referred 

 to as the "Deep Plain". The main part of the California Abyssal Plain has a 

 slope of about 1 : 1000 to the WSW and abuts a more irregular and deeper 

 region approximately 450 mi from the coast. The plain is not a filling sedi- 

 mentary basin but a region across which transport of sedimentary material by 

 turbidity currents takes place. The slope may, therefore, be one of equilibrium 

 between deposition and erosion by passing turbidity currents. 



c. Bellinghausen Abyssal Plain 



An abyssal plain of uncertain extent lies parallel to the continental rise in 

 the Bellinghausen Sea area of the southeast Pacific. The area has only been 

 crossed twice by a ship employing a P.D.R., hence we cannot give details as to 

 the extent or nature of this abyssal plain. It would seem likely, however, 

 that the plain slopes south to north and is related to the continental rise 

 of Antarctica. 



d. Mornington Abyssal Plain 



A small plain of about 10,000 mi 2 lies west of Mornington Island, Chile, 

 between about 48° and 52° S. A prominent canyon was found at about 

 49°S. 



E. Indian Ocean 



The northern Indian Ocean is divided into two triangular bights by the 

 peninsula of India. To the east of India lies the Bay of Bengal, which widens 

 from north to south. The Ganges and Brahmaputra Rivers empty into the 

 northern apex of the bay. Soundings made southeast of Ceylon have revealed 

 the existence of an abyssal plain at the base of the continental slope near 

 Ceylon, occujiying much of the northeast part of the Indian Ocean. In this 

 plain mid-ocean canyons were discovered by the Swedish Albatross Expedition 

 (Dietz, 1953). It is reasonable to suspect that this abyssal plain is related to 

 the abyssal cone of the Ganges-Brahmaputra, which dominates the entire 

 floor of the Bay of Bengal. The southern limit of this plain is poorly known but 

 the plain reaches at least to 8° South latitude. The area of the Ceylon Abyssal 

 Plain probably exceeds 200,000 mi^. 



West of the Indian peninsula, the Indus River empties into the Arabian Sea. 

 A deep submarine canyon has been discovered off the mouth of the Indus and 

 an abyssal cone and associated abyssal plain occupy much of the northeast 



