120 QUICKSILVER DEPOSITS OP THE PACIFIC SLOPE. 



That it is common leads to the belief that these conditions are not narrowly 

 restricted, and this is confirmad by the fact that it forms in the olivines of 

 decomposing- basalts and also in limestone beds. It is no more surprising- 

 that serpentine slionld form from many and different Uiiiierals or nnder dif- 

 ferent circnmstances than that ferric oxide slionld do the same. 



Bischof held a similar opinion, calling- attention to the fact that serpen- 

 tine is among the last products of alteration and that in it the series of 

 processes of mineral formation and alteration have nearly reached the limit 

 of possibility. Indeed few geological chemists would be inclined to dispute 

 a proposition of this kind. Dr. Hunt, for instance, who points out the anal- 

 ogy between the modes of occurrence of serpentine and pinite, says of the 

 latter that its constancy of composition and wide distribution show it to be a 

 compound readily formed and of great stability. Such being its character, 

 he continues, it might l)e expected to occur as a frequent product of the 

 aqueous changes of other and less stable silicates, and "its frequent occur- 

 rence as an epigenic product is one of the many examples to be met with 

 in the mineral kingdom of the law of the ' survival of the fittest.'"^ That 

 the same statement applies to serpentine is manifestly true. 



It would seem to follo'.v that the origin of serpentine in each naturally 

 defined geological area requires independent investigation and that the 

 results obtained in one such area are not necessarily applical)le to others. 

 It will be seen in the following pages that the observations ai-e not recon- 

 cilable either with the supposition that the serpentines of the Coast Ranges 

 are derivable from a single mineral or that they are unaltered sediments. 

 They seem to be in this region the most stable compound which could 

 result under a certain set of phj-sical conditions from the mutual reaction 

 of siliceous and magnesian substances. 



Structural evidence as to origin. — Serpentine is fouud througliout tlic uietamor- 

 phic areas of the Coast Ranges in very irregular patches, both near quick- 

 silver deposits and at long distances from the mineS. In some metamorphic 

 regions — for example in the immediate neighborhood of Clear Lake — it is 

 found only in small quantities, while at Knoxville and at New Idria large 

 areas are almost exclusively conqwsed of more or less pure serpentine. 



' Origin of the Crystalline Kocks, 1884, p. 53. 



