204 



Sediments 



SANTA 

 MONICA 



Figure 1 80. Sediments off San Diego, San Pedro, and Santa Monica classified according to origin. Note that the term 

 "mud" is used here as a noncommital designation for various mixtures of silt and clay. Dotted line is shelf-break. 

 Revised from Emery (1952Z)). 



of 2.5-1 off San Diego and 1.05-1 off Santa 

 Monica. Plagioclase is 4 to 100 times as 

 abundant as orthoclase. Heavy minerals 

 are dominated by hornblende off San Diego 

 (67 per cent) and off San Pedro (65 per 

 cent), but off Santa Monica hornblende 

 takes second place to augite (29 versus 30 

 per cent), and off Santa Barbara both horn- 

 blende and augite are present only in traces 

 whereas epidote averages 34 per cent and 

 ilmenite 22 per cent. Thus, the heavy min- 

 erals in the detrital sediments of the main- 



land shelf correspond closely with those of 

 the adjacent beaches. 



Detrital sediments in the nearshore parts 

 of the mainland shelf also resemble the 

 beaches in their mobility. This movement 

 was first recognized when measurements 

 made along the pier at Scripps Institution 

 of Oceanography showed that seasonal and 

 tidal cycle cutting and filling of the beach 

 were reflected in simultaneous filling and 

 cutting of the submerged areas to a water 

 depth of at least 6 meters (Shepard and 



