SUMMARY. 469 



of carbonates, and in one portion (at the mine) the deposits of sinter are 

 insignificant in extent, the chief effect liaving been decomposition of granite 

 and the precipitation of suliduu- and cinnabar. In this part of tlie area also 

 steam and gas still issne in small cpiantities. 



The amount of cinnabar is considerable. Tlie ore was mined and 

 reduced a few years since, but mining would not pay at present prices. 



Quicksilver in very small amounts is being deposited by the springs 

 now active, together with gold and several other metals. They are dis- 

 solved as alkaline sulphosalts, as will l)e explained in a subsequent para- 

 graph. The waters and gases are similar to those of Sulphur Bank, except- 

 ing that ammonia and organic compounds are absent. 



The four metals most abundant in the present spring deposits, anti- 

 mony, arsenic, lead, and copper, exist in the granite, but I was unable to 

 detect quicksilver. This may be due to the small quantity of (piicksilver 

 in the average granite or, as I think more probable, to irregularity in the 

 composition of that rock. The granite is the probable source of the mercury. 



The Oathill, Great Eastern, and Great Western districts. The Ueigllborhood of OathiU 



is a most interesting one and contains many quicksilver deposits within a 

 small area. The underlying rock is of the Knoxville series, identified by 

 the presence of Aiurlla. It is in part metamorphosed and serpentinized and 

 in part unaltered. Andesite and basalt have broken through it. 



The basalt eruption gave rise to hot springs, onff of which still ex- 

 ists at Lidell, issuing from the workings of a now abandoned quicksilver 

 mine. In two cases also cinnabar deposits occur at the contact between 

 basalt dikes and the adjoining rock, forming veins. Irregular stockworks 

 of the more usual type also occur. 



The Oathill mine is the principal one of the mines belonging to the 

 Napa Consolidated Company. It is in unaltered sandstone, the strata of 

 which are nearly horizontal. The deposits are true veins, cutting the strata 

 at an angle of 45°. From these veins ore bodies sometimes make out into 

 the country, following the stratification. These are impregnations. The 

 ore is the usual mixture of cinnabar, pyrite, silica, and calcite, and bitumen 

 also occurs. Small quantities of barite are also found, and this is the only 

 case in which this mineral is known to accompany cinnaliar in California. 

 It is also found at Almadcn. 



