l.AWSON.J 



Coast of Northern California. 



267 



a similar order. Rodeo Lagoon is an incipient fiord, flooded only 

 in its lower portion. Lake Merced is a flooded stream valley, the 

 bottom of which is 10 feet below the tide. Half-moon Bay belongs 

 to the same category of things. South of this point the tide invades 

 the mouths of the streams to a small extent, and the subsidence is 

 insignificant. It probably tapers out to a feather-edge before 

 reaching Pigeon Point. 



As regards the nature of the curve which delimits this sunken 

 tract about the Bay of San Francisco, very little information is to 

 hand. It is doubtless a synclinal sag, but it is not yet ascertained 

 whether the synclinal axis lies approximately parallel to the coast 

 or approximately normal to it, one or the other position being much 

 more probable than any intermediate position. The rate of defor- 

 mation in the direction parallel to the coast may be roughly ascer- 

 tained as follows: The sag appears to extend a little beyond Bodega 

 Head on the north but does not materially affect the Russian River. 

 We may safely suppose it to feather out at the latter point. This 

 is about 54 miles from the Golden Gate. The total sag at the 

 Golden Gate being assumed to be 378 feet, this gives us a gradient 

 for the tilted plane of 7 feet to the mile. This tilt should be recogniz- 

 able in the terraces of the coast in the interval between these two 

 points, but, unfortunately, for this particular portion of the coast, the 

 terraces do not lend themselves to such a check. To the south- 

 ward we have the bedrock of the ancient valley bottom exposed at 

 Coyote, in the Santa Clara Valley, about 70 miles through the center 

 of the valley in the probable course of a stream. Coyote is 630 

 feet above the bottom of the Golden Gate, which gives us a gradient 

 of 9 feet to the mile. But to this a correction must be applied for 

 the grade of the ancient stream bed, which may perhaps be placed 

 at one foot to the mile. This would reduce the grade due to de- 

 formation to 8 feet to the mile; but a part of this is due not simply 

 to the sag but also to a correlative buckling which is apparent in 

 the arched form of the Santa Clara Valley, to which the writer has 

 on a former occasion called attention,* but has not since farther 

 investigated. It is safe to predict that the grade due to deformation 



*This Bulletin, Vol. 1, No. 4. 



