STATE AGRICULTURAL SOCIETY. 3G1 



posas rocks in eighteen hundred and sixty-four, but no figures or descrip- 

 tions are given. 



We may thus" regard the secondary age of a part, at least, of the gold 

 bearing rocks of the Sierra Nevada as established, a result of no small 

 importance practicall}', for it destroj^s the dogma, which has been very 

 generally accepted, that the Silurian or Pala)ozoic rocks are the reposi- 

 tories of the gold of the globe. We may now look for gold in regions 

 whei-e, before, it was generally presumed to be absent, because the forma- 

 tions were not Silurian or Pala30zoic. 



The Silurian age of the gold rocks of California has not alwaj^s been 

 assumed. It has been repeatedly questioned. In the preface to the 

 ■writer's "Report of a Geological Eeconuoissance in California" it is stated 

 that a considerable part of the gold bearing slates of California are prob- 

 ably carboniferous. The absence of all evidence of Silurian fossils west 

 of the Eocky Mountains is also distinctly noted — (p. 276.) The opinion 

 of the comparatively modern age of the gold rocks has been steadily 

 gaining strength and support for j'ears past, and has been the subject of 

 discussion in the daily journals. 



The prevalence of gold in the Coast Mountains, in or in close proximity 

 to rocks of tertiary age, leads us to question whether it may not occur in 

 the rocks of this late period also. The fact, recently ascertained, that 

 gold is very generally associated with cinnabar, makes it more than 

 probable that the metal has been deposited in formations as recent even 

 as the Miocene, (or middle tertiary',) for, according to the best evidence 

 we now have, this is the age of a part, at least, of the quicksilver bear- 

 ing rocks. 



Such a result need not surprise us, although so far in opposition to 

 generally existing views of the geological association of gold. The geo- 

 logical age of the rocks has manifestly nothing to do with the deposition 

 of gold; it is only necessaiy that the rocks should have a favorable 

 mineral composition and a suitable degree of raetamorphism. On this 

 general view, we maybe prepared to find gold in rocks of any geological 

 period, from the tertiary to the Laurentian or Huronian rocks, inclusive. 



The lithology of the chief gold bearing zone or belt of rocks of Cali- 

 fornia is interesting. The chief or "Mother Vein" extends through 

 several counties, with occasional breaks or interruptions ; and throughout 

 its course preserves its distinguishing characters. It follows also the 

 same geological horizon, or zone, keeping between well marked geological 

 and geographical boundaries, so that a description of the strata adjoin- 

 ing it at one place will serve to give a general view of them throughout. 

 A cross section in considerable detail was made on the Mariposa estate 

 in eighteen hundred and sixty-four. This estate includes the southern 

 end of the "Great Vein" — thei^e known as the "Pino Tree." . It also 

 includes several veins lying west of the line of the Pine Tree, of which 

 the most important is the "Princeton," noted for its richness and lai'ge 

 production of gold. This group of veins follows a long valley between 

 two high ridges — Bear Mountain on the west, and Mount Bullion on the 

 east. Those ridges are formed of hard rocks; the rocks of the valley 

 are argillaceous and sandy slates and sandstones. The stratification of 

 these slates is remaikably regular and distinct — their thin outcrops 

 standing sharply out at intervals in long lines in the ravines and on the 

 hillsides, mark their trend, and show that they arc nearly vertical, or 

 have a slight inclination northeast or easterly. The general direction of 



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