4 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 27 



tide diameter of the sediments. One may compare the scatter diagram 

 of median diameters for the coastal shelf shown in Graph 2. 



Graph 2. Scatter diagram of sediments from samples proportionally 

 distributed by depth and area on the coastal shelf of southern Cali- 

 fornia, 10-183 m. 



Emery, Hiilsemann and Rodolfo (1962) believe that the net result 

 of turbidity flows is of benefit to benthic populations, especially on the 

 aprons at the seaward ends of the canyons and below sill depths of the 

 basins. There, of course, the muddy suspensions bring down water with 

 higher than normal oxygen content, as well as quantities of organic 

 matter. Water of high oxygen tension can be detected as long as two 

 years later, and this may be of some influence on canyon populations 

 above sill depths in or near the oxygen-minimum layer of the sea. The 

 concept that canyons, through frequent sedimentary movements, provide 

 more organic matter for bathyal biota than do continental slopes at the 

 same depths may have a relationship to the survival of refugees from a 

 pre-cooled abyssal realm. The enormous variability of canyon sediments 

 also would provide a diversity of niches for an ancient fauna possibly 

 compressed into bathyal depths (see Bruun, 1957; Madsen, 1961 ; Men- 

 zies and Imbrie, 1957; Zenkevitch and Birstein, 1960; and J. L. Bar- 

 nard, 1961b, 1962d, for notes on the bathyal theory). If 84% of the 

 ocean floor known as abyssal once supported a warm-water fauna of 



