480 BOUNDARIES OF THE SEA 



are urgent requirements, because sand grains are known to occur 

 in deep-water deposits and must be accounted for in some way. 



When the action of currents along the ocean bed is considered, 

 there is the same failure on the part of the physical oceanographers 

 to provide information. Current charts of the sea floor with as 

 much detail as shown for the surface on navigational charts are 

 needed. Obviously that need cannot be met until the future, but a 

 few data to keep the geologists going in the meantime would be ap- 

 preciated. Probably geologists are too vague when demanding in- 

 formation on bottom currents, but dynamic oceanographers should 

 realize that data are needed to relate them with the sedimentation 

 of clay or sand, current ripples, and nondeposition. It is knowledge 

 of the speed and turbulence of the water actually in contact with 

 the bottom that is required. Maximum velocities due to the com- 

 bination of steady and oscillatory currents are also of the greatest 

 importance. 



Where is this need for bottom data most urgently felt? In the 

 first place on the shelf, particularly near its outer margin where 

 deposition is almost absent. What is the part played by long 

 waves and tidal currents in this problem? Is the cause of clay sedi- 

 mentation close to the shore due partly to a greater supply or 

 only to less transport power? In shallow water even slight de- 

 pressions tend to accumulate finer sediment than the surroundings. 

 Is the protection thus proved more against wave action or against 

 currents? Then there is a strong suspicion that in areas where 

 Glohigerina ooze is accumulating, clay sedimentation is being 

 counteracted. This winnowing may go so far as to leave almost 

 pure foraminiferal sand, whereas clay is accumulating in the more 

 sheltered areas in the surroundings. 



The "non-depositional" condition on guyots is another difficulty, 

 and no explanation is yet available for Tertiary sediment lying 

 bare or only slightly buried even on flat stretches of the deep-sea 

 floor. Fishes and other animals brushing the bottom may be 

 responsible in part. These questions, however, do not belong to 

 this symposium. 



Another geological problem connected with currents is that of 

 the solution of lime and the elimination of organic matter in basins. 



