109 



ones for this region. It is known, however, that rocks of 

 Miocene age are on the outer shelf, and there is evidence 

 that most of Santa Monica Bay was formed in relatively recent 

 geologic time. 



Character and Origin of Nondepositional Surfaces 



From a theoretical point of view, there should be an even 

 gradation from coarse to fine sediment when moving from the 

 shore seaward. Numerous investigators, however, have noted 

 the common occurrence of coarse sediments near the outer edge 

 of shelves (Fairbridge, 1947). In addition, there are any 

 number of places where bedrock crops out on a sea floor which, 

 according to theory, should be covered by sediment. Many of 

 these areas of nondeposition are known off the coast of southern 

 California, so that surfaces of non^or slight deposition in 

 Santa Monica Bay are not unique. However, even though many 

 such submarine surfaces are known in many parts of the world, 

 little is known of their origin. There can be no question 

 that in most cases, sediments are transported at least as far 

 as the nondepositional surfaces, but then either by-pass the 

 surface or are deposited and later resuspended and carried 

 away. 



The following criteria are used as evidences of non- 

 deposition: (1) rock outcrops exposed on the sea floor; 

 (2) gravel at considerable distances from shore. Gravel intro- 

 duced by streams cannot be carried far beyond the littoral 

 zone. In fact, gravel frequently migrates shoreward if it is 

 in the zone effected by wave action. Therefore, gravel in 



