6 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 27 



mains whether a turbidity flow scatters organic material so widely that 

 no accumulation as dense as that in Monterey Canyon would result 

 after settling. The grassy material appeared remarkably fresh, although 

 it was greenish-black. Pockets full of debris in areas of high repose may 

 have been accumulated through mechanisms other than movement of sed- 

 iments. Perhaps gradients are sufScient in some canyon axes to permit 

 cascading and saltation of debris, but continuing impulsion by water 

 movement would have to be presumed. Descending currents in canyons 

 have not been demonstrated, although they might be predicted, especially 

 where canyons intersect lagoons. Because of evaporation and winter 

 cooling of water in shallow lagoons, density currents might be estab- 

 lished that flow slowly part way down the canyon axis. Indeed, Mon- 

 terey Canyon impinges upon the mouth of Elkhorn Slough (hydrographic 

 conditions poorly known). The only other canyon with evidence of 

 high accumulation of organic material is Newport Canyon, from which 

 came several samples composed of black sulfide ooze. Coincidentally, 

 that canyon lies near the mouth of Newport Bay, another lagoon sup- 

 porting eel-grass (but not as densely as at Elkhorn Slough, because of 

 human influences). Another conjecture is that canyon topography in- 

 fluences formation of surface-water eddies in which organic material is 

 trapped, becomes waterlogged and sinks to the canyon floor. 



Ofi the Congo River {Vema samples, information from Dr. R. J. 

 Menzies) one may presume that debris accumulates in the canyon simply 

 from waterlogging of enormous supplies that are present. But the can- 

 yons of California are not served by large rivers, hence their source of 

 organic matter has to lie elsewhere. 



Biological 



STANDING crop 



Individually, the several canyons with their distinct profiles and dif- 

 ferent distances from shore are difificult to compare. The small number 

 of samples per canyon adds to this difficulty, because patchiness of sedi- 

 ments and therefore patchiness of biological distributions occur. This is 

 well demonstrated in the erratic recovery of brissopsid urchins. Even the 

 levels of polychaete standing crop differ enormously and inconsistently 

 at similar depths in each canyon, although consistency with sediment- 

 type is apparent, the finer sediments supporting larger crops. By group- 

 ing all of the canyon samples, regardless of the artificiality so incurred, a 

 significant impression of the trend of decreasing crop with depth is seen 



