Smith.] 



Islands of Southern California. 



203 



It may be objected that such submarine features as are here 

 described might normally be developed by wave action and coastal 

 currents along any coast line, with sea level nearly stationary for a 

 considerable period. It is to be noted, however, that where cliff 

 cutting is taking place the general features as described are best 

 developed; and where deposition, not cutting, is in progress, as in 

 the embayments, and along those parts of the main coast where 

 wave- and current-built features are forming, the submarine fea- 

 tures depart most widely from the general type. Where shore 

 drift is furnished in comparative abundance, the off-shore depths 

 may be built up rapidly to those normal to the present sea-level 

 Where drift is rapidly removed by waves and currents from a 

 region of active cutting, and in particular along the rugged coasts 

 where cutting is slow and the amount of shore drift inconsiderable, 

 the features in general conform most closely to the description of 

 the whole. It is for these reasons, in addition to the fact of the 

 drowning of the lower parts of the broader valleys, along parts 

 of the island coasts, that the submarine features are believed to 

 indicate a comparatively recent coastal depression. 



Well-developed beaches are uncommon on the California coast. 

 We should expect them to be more numerous, considering the 

 width of the submarine platform, if the land had stood at or near 

 the same level throughout the time of its formation. If, however, 

 a recent depression of the coast is postulated, the scarcity of 

 beaches is easily accounted for. 



Since the general characteristics of the upper platform are sim- 

 ilar about all the islands considered here, and along the main coast 

 of this part of the state, it is concluded that the latest recorded 

 movements have been uniform for all of this part of the California 

 coast. 



Notching the upper platform and its outer escarpment, along 

 the Pacific Coast between San Diego and the Columbia River, are 

 a number of submarine valleys, which have been described in con- 

 siderable detail by Professor Davidson.* Some nine of those de- 



*The Submerged Valleys of the Coast of California, U. S. A., and of Lower 

 California, Mexico. Proc. Calif. Acad. Sci., Third Series, Geol. Voi. I, No. 

 2, 1897. 



