1914] Sumner, et al.: Physical Conditions in San Francisco Bay 85 
TABLE 22 
SALINITY OF THE WATER AT TwO BEDS OF THE MORGAN OYSTER COMPANY, 
DuRING A NUMBER OF CONSECUTIVE MONTHS 
Month Millbrae Dumbarton 
November, 1912 __......... 31.20 
December 900 eee 31.07 
January, 1913... 30.50 
February 25.86 27.48 
March 26.76 27.29 
April 26.29 27.22 
May 25.17 27.43 
June 24.38 27.27 
July 28.23 28.37 
August 29.78 30.32 
September 30.73 31.49 
An interesting fact which appears from this table is the consider- 
ably higher salinity which is uniformly shown by the Dumbarton 
water, taken near the extreme southern end of the bay, in comparison 
with that from Millbrae, nearer by many miles to the Golden Gate, 
and in much freer communication with the great reservoir of pure 
ocean water. Since no considerable source of fresh water is known 
to occur near the Millbrae beds, we are inclined to attribute the higher 
salinity at Dumbarton to the extensive evaporation which must oceur 
throughout such a large area of very shoal water. It will be recalled 
(p. 66) that an appreciable rise in salinity was commonly found in 
passing from the region below San Francisco to the southernmost of 
our hydrographie stations (5001). 
We are likewise indebted to Messrs. Eaton and Moraghan, of the 
Darbee and Immel and M. B. Moraghan oyster companies respectively, 
for the opportunity of testing twenty-four water samples, taken in 
November and December, 1912, at their beds near Point San Mateo. 
The mean salinity for the November samples is 31.05, that for the 
December ones being 30.01. These figures indicate a salinity of the 
same general magnitude as has been recorded for the other beds during 
these months. 
It is regrettable that a satisfactory series of salinity determinations, 
made in earlier years, is not available for comparison with these of 
ours, particularly in view of the recent steady decline in the oyster- 
raising industry of San Francisco Bay. Unfortunately, the only 
figures of which we are aware, based upon the analysis of water from 
