322 HEEZEN AND LAUGHTON [CHAP. 1 4 



somewliat narrower. Given a longer period of time and a source of detrital 

 material, it can be inferred from the bathymetric configuration of the Argentine 

 Basin that plains quite analogous to the Nares and Hatteras could eventually 

 develop. 



East of the Mid- Atlantic Ridge, in the Angola Basin, the large (140,000 mi^) 

 Angola Abyssal Plain spreads out from the seaward edge of the giant Congo 

 Cone, which forms a distributory system of channels and fans leading from the 

 Congo Canyon. The Angola Abyssal Plain is the largest of the abyssal plains of 

 the South Atlantic which lie in temperate latitudes. A narrow abyssal plain lies 

 along the base of the continental rise in the Cape Basin but its width probably 

 does not exceed 100 mi. No detailed sounding surveys have been made in the 

 Guinea Basin, but judging from the form of the gross bathymetric contours off 

 the mouth of the Niger River, it is reasonable to suppose that a large abyssal 

 cone lies seaward of the Niger Delta and that, seaward of this cone, a fairly 

 extensive abyssal plain will be found. 



A few minute abyssal plains have been found in the Scotia Sea. One of the 

 largest abyssal plains discovered to date forms the floor of the Weddell Basin. 

 For obvious reasons, the western extremities of the Weddell Basin have not been 

 well explored, but the Weddell Abyssal Plain has been traced as far east as 

 20°E longitude, and in 20°W longitude it is over 200 mi wide from north to 

 south. 



D. Pacific Ocean 



The flat zones of the Pacific Ocean can be divided into two distinct types, 

 formed by somewhat different mechanisms. On the eastern boundaries in the 

 north and extreme south, there are abyssal plains of the ty^Q described in the 

 Atlantic. The other ty]3e includes large areas of the western and central Pacific 

 which surround the chains of islands found there. These areas have been called 

 archipelagic plains and are described in Section 4, page 336. 



The flat areas of the Pacific, including the archipelagic plains, cover a greater 

 area than those of the Atlantic, but the proportion of the ocean covered by 

 abyssal plains is considerably less and reflects the lower influx of sediments per 

 "iniit area owing to the higher ratio of area to circumference and the prevalence of 

 sediment-trapping marginal trenches, which nearly surround the Pacific basin. 

 The abyssal plains of the Pacific are associated with gaps in the circum-Pacific 

 belt of trenches. The largest abyssal plains of the Pacific are found be- 

 tween the eastern end of the Aleutian Trench and the northern end of the 

 Middle-America Trench. The other major area of abyssal plains in the Pacific 

 lies off the northern shore of Antarctica. The only abyssal plain known at 

 present in the northwestern Pacific is a small one south of Honshu. 



a. Northeast Pacific Abyssal Plains 



The most extensive abyssal plains of the Pacific are found between the 

 eastern part of the Aleutian Trench and the Mendocino Escarpment, which 



