356 G. F. Becker — Metamorphic rocks of California. 



The direct conversion of quartz to serpentine is a very general 

 and very important process in the Coast Ranges. 



Apatite is also converted to serpentine in the rocks under 

 discussion,* while mica and garnet occur under conditions 

 which suggest but do not prove their transformation to serpen- 

 tine. Pseudomorphs of serpentine after these minerals are 

 known to occur elsewhere. Zoisite is probably but not certainly 

 serpentinized. 



The lithological and mineralogical results reached for the un- 

 altered and metamorphosed rocks of the Coast Eanges having 

 been briefly sketched, a few notes on the geperal geological and 

 ckemico-physical relations of the process of transformation 

 remain to be stated. In the present state of opinion it is not 

 superfluous to insist upon the derivative character of the holo- 

 crj^stalline metamorphic rocks and the serpentine of the quick- 

 silver belt. It appears that at least one mineral of nearly 

 universal distribution in the granular and the schistose rocks, 

 and in the phthanites is especially significant in this respect, 

 and that a sound argument may be based upon its presence in- 

 dependently of other evidence. Zoisite is not known to occur 

 as an original component of eruptive rocks nor, considering 

 that it is essentially a hydrous mineral, is it easy to conceive 

 that it should so occur. That it may be met with in such rocks, 

 like epidote, as a product of decomposition is not improbable, 

 but when it is found imbedded in clear continuous minerals 

 evidently formed in place and showing no decomposition, as is 

 the case in these rocks, there can hardly be a question that 

 these minerals have been formed at a comparatively low 

 temperature, probably below the boiling point and certainly 

 below a red heat. The proof of the metamorphic character of 

 the rocks is wholly independent of zoisite, however, and would 

 be abundantly convincing if zoisite were a common constituent 

 of lavas. 



The depth at which the rocks now exposed were buried at 

 the epoch of metamorphism, soon after the close of the 

 Neocomian, was probably a moderate one, perhaps 2,000 or 

 3,000 feet. At a sufficient pressure rocks appear to be moulded 

 by dynamical action rather than crushed, and Dr. Lehmann has 

 shown that under such conditions even crystals may be bent. 

 In the Coast Ranges no such phenomenon has been observed. 

 On the contrary, the amount of fracturing is really astonishing. 



Both the Coast Ranges and the Gold Belt are underlain by 

 granite, which probably also forms the bed rock in the great 

 valley of California. It is impossible to conceive of any force 

 which should have produced intense lateral compression in the 

 sedimentary rocks overlying the granite without disturbing the 



* Prof. J. D. Dana observed pseudomorphs of serpentine after apatite, this 

 Journal, vol. viii. 1874, p. 371. 



