1916] McEweii: Hiidrographic Ohscrvations of Scripps Institution 261 



cold areas north of Point Uuiiu' (pi. 6) are close to two submerged 

 valleys, as shown (pi. 1) by the one hundred and the five hundred 

 meter contours. Again, the cold area between Point Fermin and 

 Point Vicente (pi. 6) occurs where the five hundred meter line bends 

 to within a mile of the coast (pi. 2 ) . Likewise the areas of cold water 

 sliown by plate 9 occur wliere the five hundred meter contour run.s 

 close to the coast (pi. 3), while wann water occurs in the region of 

 shallow water between Cerros Island and the mainland. Finally, the 

 cold water southwest of San Clemente Island shown in plate 5 is 

 associated with a rapid increase in depth from a few meters over the 

 Cortes Bank (pi. 2) to 1.500 meters at a distance of less than fifteen 

 miles to the southwest. 



However, since the relation thus revealed between the presence of 

 areas of cold water and the bottom topography does not always hold, 

 there must be other factors (see p. 277) that have an important 

 influence on upwelling. 



(d) Isohalines. — The southward dip of the isohalines southeast of 

 Santa Catalina Island (pi. 10). southeast of San Clemente Island 

 (pi. 11 and pi. 12, fig. 14), and off San Diego (pi. 11 and pi. 12. fig. 15) 

 reveals a southward flow of water having a low salinity. In plate 10 

 the southward dip of the lines nearer the mainland shows a second but 

 narrower southward current, while a flow to the southeast is indicated 

 by plates 13 and 14, figure 19. 



The prevailing southerly drift so clearly revealed by both temper- 

 atures and salinities is sometimes accompanied by a northward flow 

 of water having a high salinity and restricted to a narrow belt bor- 

 dering the mainland. Such a northward flow is revealed by the north- 

 ward dip of the isohalines (pi. 12, figs. 14 and 16) and agrees with that 

 already shown by the isotherms (see p. 260). 



In contrast with this translation of water in some definite direction, 

 the circumscribed areas of water having a high salinity northeast of 

 San Clemente Island shown by plates 11 and 13 suggest a whirling 

 motion. Since the island probably deflects the general soutlierly drift 

 to the east and thus gives rise to a flow to the southeast bordering its 

 coast, there would be a tendency to generate a whirling motion in a 

 counter-clockwise direction. On the other hand, a current flowing 

 southwest past the east point of the island would tend to generate a 

 clockwise whirl. A whirling motion tends to separate the water near 

 its center from the surrounding water and, by thus interfering with 

 the convection currents, permits an increase in both salinity and tem- 



