Mainland Shelf 



199 



Figure 175. Map showing distribution of median diameter of 1660 surface sediment samples off San Diego. In some 

 areas consisting chiefly of rock or boulder bottom the sand that is represented is only interstitial. From Emery, Butcher, 

 Gould, and Shepard (1952, Fig. 8). 



are equally well sorted. Sorting coefficients 

 can be presented by another separate map, 

 and comparison of the two maps provides 

 new information. Still another map, of 



skewness, is required for a relatively full 

 presentation of the grain-size distribution 

 data. Moreover, the series of maps con- 

 siders only the middle 50 per cent of the 



