16 THE OCEAN FLOOR 



One characteristic ascribed by Kuenen to turbidity 

 currents is their capacity of leaving behind so-called 

 graded bedding, in which the size of the particles 

 regularly decreases upward, owing to the settling of 

 coarser particles at a quicker rate. Cases of graded 

 bedding have in fact been found by mineralogists work- 

 ing on cores from the "Albatross," especially in a long 

 core from the center of the Tyrrhenian Sea studied by 

 E. Norin of Uppsala. On the other hand Otto Mellis 

 of Stockholm, who has made an extensive study of other 

 cores from the Mediterranean, has declared graded 

 bedding there to be rather the exception than the rule. 



Leaving an open question the prevalence of turbidity 

 currents in particular areas of the sea, one seems justified 

 in asserting that the theory that they are the dominant, 

 still less the only, cause of bottom currents in great 

 ocean depths is not borne out by our present knowledge 

 of deep-sea sediments. Still less does it appear well 

 founded to state that all cases of extensive flat bottom 

 in great depths are due to turbidity currents. According 

 to this view it would be useless to collect and investigate 

 long sediment cores, since one would suspect their layers 

 of having been reshuffled by turbidity currents. 



