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POPULAR SCIENCE MONTHLY 





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H'ig. 5. Raised Beach near Lubetus, Quaternary overlying Merced Strata. 



about San Francisco, and double that farther down the coast. These last 

 movements were differential, and it is quite possible that in some cases 

 the two took place together. In the same way, it is quite possible that 

 while in parts of the area the evidence suggests elevation continuing 

 at present, elsewhere subsidence is in progress, though not so evident. 

 The point of special interest in this connection is the fact that this 

 differential movement about San Francisco is clearly a movement of the 

 fault blocks and reveals slipping along these planes of faulting of 

 hundreds of feet in times so recent as to suggest that much of it may 

 have taken place since the human occupation. 



Considering first the evidence of movement, a good example is 

 furnished by the San Andreas fault, where it reaches the ocean at 

 Mussel Rock. At the foot of the parallel San Bruno fault a few miles 

 to the northeast the recent marine deposits are about at sea-level. 

 Coming south along the sea-cliff or southwest, these deposits are clearly 

 seen rising, making distinct benches in the little stream valleys where 

 they overlie the wind and wash deposits of the preceding stage, these 

 wash deposits in places being full of half exposed spruce logs, which the 

 neighboring inhabitants use for firewood. Before the San Andreas 

 fault is reached, these deposits have risen to over 700 feet above sea- 

 level, lying on the truncated upturned edges of the Merced strata. As 

 soon as the trace of the San Andreas fault has been crossed, the top 

 of these sediments is found at only 220 feet above sea-level, whence 

 it descends until within a short distance it reaches the level of the 

 beach. Here is therefore clear evidence of movement along the fault 

 plane of several hundred feet since this last submergence. The ques- 

 tion of most interest then becomes: How recent was this last uplift? 



