SECT. 2] 



ABYSSAL PLAINS 



339 



Surveyed Portions 

 Unsurveyed Portions, Certain Connections 

 Approximate Position of Probable Extension 

 Diagrammatic Possible Tributaries 

 Submarine Cable Breaks 



Fig. 20. Northwest Atlantic Mid-Ocean Canyon. (After Heezen et al., 1959.) 



width from 3 to 5 mi and in depth below the adjacent sea floor from 10 to 

 100 fm. There is a consistent asymmetry about the canyon, the west wall being 

 10-15 fm higher than the east wall (Fig. 22). The canyon has been mapped by 

 more than 80 echo-sounding profiles. Surprisingly, the canyon does not follow 

 the axis of greatest depth in the ocean basin but tends to the western side. The 

 average slope of the sea floor at right angles to the axis of the canyon in most 



