316 University of California Publications in Zoology [Vol. 13 



orange-peel bucket dredge revealed only a few specimens of Mya. 

 East of Point San Quentin the sample shows 12.26 per cent of lime 

 at the surface, decreasing to about 10 per cent at a depth of 70.5 

 centimeters. A large number of specimens of Ostrea lurida were 

 obtained at a near-by station. Again at stations D 5796 and D 5798 

 the lime content is fairly high, but at those stations the water is nine- 

 teen fathoms deep. The stony character of the bottom at station 

 D 5702, which lies within the Golden Gate, would prevent dredging 

 on a commercial scale. 



TABLE 5 



The Lime Content of Some of the Tubular Bottom Samples 



Nearest Depth Depth of 



"Albatross" dredging Percentage of sample water in 



stations station of lime in cm. fathoms 



D 5816 A D 5816 A 20.79 9 



H5301 D5798 15.33 46-56 10 



D 5796 D 5796 16.58 19 



H5129C D5824 10.13 50.5-70.5 2 



H5129D D5824 12.26 0-20 . 3.5 



'D 5702 D 5702 27.81 13 



H5306 D5834 10.38 0-10 10 



H5309 D5839 25.33 70-80 10 



H5310 D5836 21.75 91-108 5 



D 5783 D 5783 86.21 2 



D 5847 A D 5847 A 24.86 125-136 8.5 



H5312 D 5847 A 37.27 123.5-133.5 5 



Large quantities of Ostrea lurida were dredged off the Oakland 

 Harbor Light at D 5832 and D 5833. They were also obtained abund- 

 antly farther south at station D 5835. Besides surface deposits, 

 Sumner et al. (1914, pi. 6) show that a layer of shells from 50 to 80 

 centimeters thick, extending from station H 5306 to H 5312, a distance 

 of about sixteen miles, lies buried in the mud to a depth of about 50 

 centimeters. It is this old layer that contributes to the lime content 

 noted in table 5 at stations D 5847 A, H 5129 C, H 5301, H 5309, 

 H 5310, and H 5312. At all of these stations the water is less than 

 ten fathoms deep, and the bottom is of a type of mud that might 

 easily be dredged and then washed, leaving the concentrated shell. 

 It is probable that the most extensive surface and subsurface deposits 

 occur within a radius of five miles of Hunter's Point. A resurvey 

 of those waters need not be expensive and might lead to the discovery 

 of even greater deposits of shell than are now known. 



