138 QUICKSILVER DEPOSITS OF TUE PACIFIC SLOPE. 



trated by quartz veins excapting in the mines, but this rock is too soft and 

 trtuo-h to be readilv tissured. While serpentinization and siHcification are 

 nsiialK- so associated as to lead to the belief that the latter followed the 

 former, it is anything- but improbable that exposures may hereafter be 

 discovered from wliich it will appear that at least in some cases silica 

 was thrown down verv near areas of serpentinization and simultaneously 

 with the progress of the latter process. 



To sum up the results in a few words, it appears reasonably certain 

 that the conversion of sandstones and shales to holoiM-ystalline rocks took 

 place at the period of the Post-Neocomian upheaval at temperatures some- 

 what above those now prevalent, at considerable but not at enormous 

 pressure, and at the expense of basic solutions rising from the underlying 

 shattered granite; further, that serpentinization of holocrystalline, metamor- 

 phic rocks and slightly altered sandstones took place at somewhat lower 

 temperatures, also at the expense of rising solutions. It is probable, but 

 not absolutely certain, that the regional siHcification was subsequent to ser* 

 pentinizatiou and mainly produced in a similar manner. The formation of 

 ore deposits was not contemporaneous with the metamorphism. Impregna- 

 tion of the rocks with calcite and gypsum went on at ordinary temperatures 

 and is still in progress. Chloritization was effected at least mainly at ordi- 

 nary temperatures. In no case which has been examined are the holo- 

 crvstalline rocks of the metamorphic series injected eruptives or original 

 sediments, nor are anv of the serpentines studied original sediments. Xo 

 considerable portion of the serpentines can have been derived from olivine 

 and in no case has any occurrence of serpentine been traced to an olivinitic 

 rock. 



Comparison between Neocomian metamorphics and the Archaean. \\ lietllCr tllC Arch;\?an 



rocks are metamorphosed sediments or crystalline precipitates or of igneous 

 orio-in is a question upon which eminent authorities differ, and one upon 

 which neither evidence nor argument will be offered here. It is a matter of 

 interest, however, to compare the altered strata of the Knoxville group with 

 the crystalline Pre-Paleozoic rocks, since they appear to have much in com- 

 mon. That there is no slight similarity between the metamorphic rocks of 

 the Coast Ranires and the strata of Arcluran areas is evident from the fact 



