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University of California. 



[Vol. i. 



raulated to the same extent. The great volume of water, flowing 

 in powerful currents through the Golden Gate with every incoming 

 and outgoing tide, has been more effective for the transport of sedi- 

 ment than anywhere in the bay, or out beyond the heads; and as a 

 consequence we have here the deepest water. The maximum depth 

 of the Golden Gate is 63 fathoms, or 378 feet,* at its narrowest 

 part, and if we assume this to represent the depth of the bedrock 

 of the submerged Sacramento River, we have a direct measure of 

 the subsidence. It may be argued that if the Golden Gate currents 

 are powerful enough to transport sediments, they should be effective 

 for corrasion, and that the deep trough in the Golden Gate may be 

 due to removal of the bedrock by scouring. The fact, however, 

 that the Coast Survey soundings show the presence of gravel and 

 shells in the trough would indicate that such corrasion is not in 

 progress. The question then arises as to how deep this layer of 

 gravel and shells may be. In reply to this we have only conjecture. 

 Hut from the nature of the material it is improbable that it is suffi- 

 cientlv thick to seriously affect the estimate of subsidence based 

 upon the depth of the channel. 



Within the Bay of San Francisco the deepest water is in the 

 Raccoon Straits, where the lead shows 39 fathoms, or 234 feet, of 

 water. This passage appears to be the landward prolongation of 

 the Golden Gate, and may with great probability be accepted as 

 portion of the ancient river trench. The region around the Bay of 

 San Francisco abounds in minor but very significant evidences of 

 submergence. A view of the bay in clear weather from the univer- 

 sity buildings, looking towards San Rafael, is an ideal picture of a 

 sunken tract, the islands of the bay being very clearly the summits 

 and crests of a hilly portion of the former valley. Richardson's 

 Bay is clearly a flooded valley. The various marshy embayments 

 of the shore between Tiburon Point and the Carquinez Straits are 

 also flooded valleys, which have become more or less completely 

 silted up to the level of high tide. The tide extends far up Peta- 

 luma and Napa Creeks. 



Outside of the entrance to the Golden Gate there is evidence of 



*U. S. C. and G. Survey 



