I9I0.] COAST RANGES OF CALIFORNIA. 337 



Age of the Serpentines. 



The similarity mineralogically and chemically of the serpentines 

 makes it reasonable to suppose that the intrusion of its parent rock 

 took place simultaneously throughout the coast ranges of California. 



In the preceding pages, under areal description, it has been 

 shown that in the Sulphur Creek and Knoxville districts, beds carry- 

 ing Aucella Piochii are strongly metamorphosed by serpentine intru- 

 sion. The evidence points to a time of intrusion following the 

 deposition of the Knoxville beds. This agrees with evidence 

 obtained by H. W. Turner at Mount Diablo and with that of Fair- 

 banks.^® 



Fairbanks reports Knoxville beds in which he found Aucella 

 Piochii to be upturned and broken by serpentine masses. He puts 

 on record other instances showing a shattering and metamorphosing 

 of the Knoxville sandstone by the serpentine, and speaks of the 

 finding of fragments of Knoxville shale in the serpentine and of 

 serpentine in the Knoxville shale and sandstone. It is his opinion 

 that the intrusion of the peridotite masses was at least partly re- 

 sponsible for the unconformity between the Chico and Knoxville 

 beds. 



The serpentines of the southern areas under discussion are 

 usually associated with the Franciscan series of rocks, cherts and 

 sandstones. Evidence which points to the time of intrusion of these 

 dikes has to the writer's knowledge not been found up to the pres- 

 ent time. This is to some extent caused by the lack of the Knox- 

 ville formation where the serpentine occurs. 



Quicksilver in Connection with the Serpentine. 



It is hardly possible to discuss the serpentines of the Coast 

 Ranges without also bringing in quicksilver, and the relation which 

 exists between its deposits and the serpentine. 



The well known name "quicksilver rock" implies that decompo- 

 sition product of the serpentine, which is a mixture of carbonates, 

 compounds of iron and the three forms of silica quartz, chalcedony 

 and opal. This rock occurs as dike-like masses in the body of the 



^"American Geologist, IX., 161-166, 1892. 



