1^1'^] Barrows: Shipivorm in San Francisco Bay 35 



On the other hand, the lowest salinity observed occurred for all 

 stations, with one exception, during the period April 23-May 6, 1912. 

 This, again, corresponds in general, as would be expected, with the 

 period of greatest discharge from these rivers, and precedes by only 

 a few weeks the month of maximum average monthly discharge. 



The lag just observed between the time of observation of greatest 

 salinity at these stations and the month of minimum average discharge 

 and the precedence of the time of observation of the least salinity 

 before the montli of maximum average discharge are probably to be 

 explained by the arbitrary selection of observation periods which 

 happened not to coincide precisely with the actual periods of greatest 

 and least discharge from the rivers. This minor discrepancy, however, 

 does not vitiate the general conclusions to be drawn. 



In the following table (Sumner, et al., 1914, p. 83) the salinity, as 

 observed at ebb tide, i.e., when it might be expected to be at a minimum, 

 on March 5 and 6, 1914, is compared with the salinity observed at a 

 corresponding period in 1912 for station 4975 and for station 4978, 

 which lies in the ship channel about two miles west by south from 

 station 4977, described above, and for station 4974, which lies below 

 San Pablo Strait and is some fourteen miles from station 4975. 



COMPAEISON OF SALINITY AT SELECTED STATIONS AND PEEIODS 



IN 1912 AND 1914 



* "Surface samples from these stations gave chlorine percentages so low that the salinities 

 could not be obtained from Knudsen's Hydrographic Tables. These samples have therefore 

 been regarded as nearly pure river water." (Sumner, et al., 1913, p. 83.) 



A difference of from 9 to 15 parts, per 1000 is to be noted in the 

 salinity of this part of the bay between observations during the flood 

 seasons of these two years for which, as has been noted, the discharge 

 of fresh water from the Sacramento-San Joaquin system differed so 

 markedly. A point of greater significance, however, is the reduction 

 of the salinity at station 4975 to practically nil at the surface and to 

 3.77 at the bottom during the flood season of the "wet" year 1914, 

 whereas during the corresponding flood season of the "dry" year 1912 

 the surface salinity remained fairly high, 13.91. 



Though we have but the single observation for these stations in 

 1914, it is presumable that the low salinity indicated on this occasion 



