117 



Relation of Bottom Character to Surface Currents 



Shepard and MacDonald (in Revelle and Shepard, 1939, 

 p. 278) report that during a period of calm weather near the 

 head of Santa Monica Canyon, they observed a surface current 

 set to the southeast during the flood tide, whereas there was 

 no appreciable ctirrent during the ebb. The same phenomenon 

 was observed during the present survey, but the currents were 

 always weak, Shepard ajid Revelle state that if the south- 

 east current also exists on the bottom it might carry material 

 to the canyon from the northwest, dumping its load in the 

 canyon so that the water would be relatively free of sediment 

 when it approached the shelf on the south. If such a net 

 current flow exists, there is no reason to believe that the 

 current would drop its load when it reached the canyon. Also, 

 the nondepositional surface extends a considerable distance 

 landward of the Santa Monica Canyon so that if such a current 

 were carrying sediment, it would not cross a depression before 

 reaching the rock and gravel area. Furthermore, the net current 

 flow along the bottom varies through the entire east quadrant 

 and may at times have a seaward set. 



Conclusions 



The presence of rock outcrops, abundance of phosphorite 

 smd gravel, the great number of borings made by pholads and 

 echinoids, and abundance of CaCo3 are indicative of nondepo- 

 sition. However, the presence of some fine-grained material 

 indicates that there is some deposition, although it may not 

 be permanently deposited. The origin of non or slight '* 



