358 HEEZEN AM) LAUGHTON [CHAP. 14 



aiul became submerged during a catastrophe of seismic volcanic character a few 

 liundred thousand years ago, material like that found in the Albatross cores 

 might have become di.stributed over the adjacent sea bottom." 



C. jSubaerial Erosion Surfaces 



The subaerial erosion hypothesis for abyssal plains was invoked to explain 

 apparently widespread ])eaches and terraces found on the continental rise, 

 continental slope, the Mid- Atlantic Ridge and on seamounts (Tolstoy, 1951). 

 'I'lie abyssal })lains were taken as the lowest of a great series of eustatic terraces. 

 Evidence now available against subaerial erosion at great depths below present 

 sea-level is very conclusive. One of the important arguments in favor of the 

 subaerial erosion hypothesis was the existence of striking streamlike charac- 

 teristics in the submarine canyons which reached the bottom of the ocean 

 basins in 2500 to 3000 fm, 200-600 nautical miles from shore. The sediments in 

 these canyons, however, demanded a submarine origin for the canyons. It was 

 found that the canyon floors are covered by gravel and sand containing a 

 cold shallow-water (glacial) fauna: Tertiary sediments crop out on the canyon 

 walls. On the inter-canyon portions of the continental rise, normal, Recent and 

 \\'isconsin fine sediment (blue mud) was found. These findings give clear 

 evidence that during the last glacial stage, some process of erosion and trans- 

 portation was active in the canyons but not on intervening areas of the con- 

 tinental rise. This evidence clearly demands a submarine erosion process. 

 Considering the great difficulties encountered by the subaerial erosion hypothesis 

 even in connection with submarine canyons, the subaerial erosion of abyssal 

 plains becomes comj)letely impossible. 



D. Lava Plains 



The suggestion was made by Pettersson in 1953 that the abyssal plains were 

 formed by vast outpourings of lava. This interpretation was based on two 

 facts: (1) the existence of nearly level plains, and (2) the fact that the coring 

 tube came up bent and empty after encounter with the abyssal plains. Damage 

 to the coring tube was interpreted as being the result of an encounter with solid 

 rock. The only plausible way to explain solid rock on the flat floor of the ocean 

 basin was to appeal to lava flows. Pettersson believed that the apparent high 

 thermal gradients in the deep-sea sediments might support the idea that wide- 

 spread lava flows in the deep-.sea basins were not uncommon. HoAvever, heat- 

 flow values observed in the oceans are generally similar to those of non-volcanic 

 regions of the continents. According to the experience of Heezen, Ewing 

 and Ericson (1955), coring tubes are often bent and empty after encounters 

 with beds of sand or gravel. Three serious difficulties of the lava plain hypo- 

 thesis are: (1) the high fluidity of lava required to produce slopes as gentle 

 as the typical I :3000; (2) the high speed of flow recjuired for lava to retain 



