308 QUICKSILVER DEPOSITS OF TBE PACIFIC SLOPE. 



sodium sulphide, this reagent resuUing from the reduction of sohible sulphates 

 by timber in the old workings. However this may be, the occurrence has 

 a bearing upon the rarity of metacinnabarite in quicksilver mines, as will 

 be shown in a subsequent chapter. Any solution capable of dissolving 

 mercuric sulphide will tend to convert metacinnabarite into the red ore. 



Origin of the deposits. — Had tlic Ncw Idrla mine alone been examined noth- 

 ing could be afHrmed concerning its origin further than that the ore was 

 deposited from solutions which obtained access to the mine through a sys- 

 tem of fissures. There is a sulphur spring in the district, but it is cold and 

 may have nothing to do with volcanism. It is certain, however, that many 

 deposits in California, similar in all essential respects to that of New Idria, 

 have been precipitated from hot, fluid, volcanic emanations. It is also 

 known that, in some cases, very hot sulphurous waters which rise at a 

 distance of several miles from any known lava have deposited cinnabai'. 

 There is thus much reason to suppose that the New Idria deposits were 

 formed by hot volcanic solutions, and no reason with which I am acquainted 

 for suspecting any other origin. 



Combustible gases escaped from the rock in great (puintities during 

 the running of the Bell tunnel and produced a disastrous explosion.' This 

 gas was probably marsh gas, and it may or may not have been generated 

 by volcanic action. In the ^5itna mine also, the ore of which was cer- 

 tainly deposited from volcanic springs, as well as at Sulphur Bank, marsh 

 gas escapes. 



Other cinnabar deposits. — Bcsldcs thc Ncw Idria othcv less iujportant deposits 

 of cinnabar have been found Avithin the limits of the map, though none of 

 them was worked during my visit. The San Carlos mine, near the sum- 

 mit of San Carlos Peak, is in the- rocks of the metamorphic series, consist- 

 ing of thin, indurated shales, which have been whitened either by solfataric 

 action or by leaching consequent upon the decomposition of pyrite. No 

 exposures of special interest were accessible. The ore is said to have been 



■ After tbis explosion Mr. Maxwell employed a very IngenioiKS method of lightiDg the tuuuel with- 

 out the use of fire. A mirror was placed at the mouth of the tunnel and was kept at such an angle as 

 to reflect the sun's rays into it. This illumination, which was repeated for my benefit, was very satis- 

 factory. The cloudless sky of California makes this method entirely practicable. A locomotive head- 

 light might perhaps be used to advantage iu a similar manner underground in certain cases. Possibly 

 this device has been employed before, though I am not aware of it. 



