Basins and Troughs 



51 



lowest point on its rim is termed the sill; 

 higher parts may be shallow banks or even 

 islands. Curiously, each of four basins off 

 southern California has two sills whose 

 depths are within 200 feet of each other and 

 another basin (West Cortes) has five sills 

 within a vertical range of about 120 feet. 

 No mechanism is known that can have 

 caused these similarities, but it hardly seems 

 possible that mere coincidence is involved. 

 As shown by Table 5, the sills of the basins 

 range in depth from 1560 to 6240 feet below 

 sea level and the basin floors are 496 to 2892 

 feet deeper than the sills, or 2056 to 8436 feet 

 below sea level. 



Within the area of Chart I are twelve com- 

 plete basins. A deep-area cut by the south- 

 ern border was discovered to be the northern 

 two-thirds of another basin (Fig. 49) by 

 sounding and water sampling during 1952; 

 because the work was done aboard R/V 

 Velero IV, this basin was named Velero Basin 

 (Emery, 1953). Two other relatively deep 

 areas at the border of the chart south of San 



Figure 49. Outlines of present and former marine basins. 

 Wherever possible the outline is at sill depth. Full names 

 are given on Chart I. 



Clemente Basin may be the northern ends 

 of another basin, but this one has not yet 

 been explored. In addition to these thirteen 

 known basins, there is a fairly flat area un- 



Table 5 



Basin Statistics 



3 ^ 



Q m 



OJ O "U 



d -i a 



=3 O. 



C C cS ^ 



p <!-> ^ E 



(U ^ -^ O 



Q .S Q ca cia 



O _ u 



< ^ s^ 



> o 



'Z^ o 



-Eg 

 oi .S -^ 



^ ^ c« 



^^ ^ 



c s 



n3 <u 



<U 'c/2 g 

 S ^ O 



