458 QnCKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Under the microscope it can be shown, as I think beyond question, 

 that all of the principal components of the sandstones and granular meta- 

 morphic rocks are subject to sei-pentinization. Not only are the augite and 

 hornblende subject to this kind of decomposition, but feldspar, quartz, apa- 

 tite, and probably other minerals ai'e also converted into serpentine. 



In the present state of opinion it is not superfluous to insist upon tlie 

 derivative character of the holocrvstalline metamorphic rocks and the sei'- 

 pentine of the quicksilver belt. Thei'e are in fact two independent lines of 

 evidence leading to this conclusion, for the known occurrences of zoisite 

 and its composition indicate that rocks containing it otherwi.se than as a 

 product of decomposition are metamorphic, while, even if zoisite were a 

 connnon constituent of undecomposed lavas, the proof of the metamorphic 

 character of these rocks would still be ample. 



The depth at which the rocks now exposed were buried at the epoch 

 of metamcrphism, soon after the close of the Neocomian, was probably a 

 moderate one, perhaps two thousand or three thousand feet. At a sufficient 

 pressure rocks appear to be molded by dynamic action rather than crushed, 

 and Dr. Lehuiann has shown that under such conditions even crystals may 

 be bent. In the Coast Ranges no such phenomenon has been observed. 

 On the contrar}', the amount of fracturing is realh' astonishing. The re- 

 crystallization of the sandstones and the serpentinization and silicification 

 are regarded as due to the action of solutions rising from the underlying 

 granite ; and these solutions were heated, charged with mineral matter, 

 and driven to the surface as a result of the same dynamical causes which 

 produced the uplift. 



In conclusion it mav be noted that all the more important minerals of 

 the Archaean schists are found in the metamorphosed rocks of the Coast 

 Ranges The quantitative relations indeed are different, especially those of 

 the feldspai-s; for, while orthoclase predominates in the Archaean, plagio- 

 clase is much more common in the Coast Ranges; but it is evident that, 

 under conditions not greatly dissimilar to those which prevailed in Califor- 

 nia at the close of the Neocomian, rocks not distinguishable from those of 

 Archaean areas miorht have been formed. 



