414 QUICKSILVER DEPOSITS OF THE rACIFIG SLOPE. 



Formation of fissures at great depths — ^yll^le it iippeai's that eveii veiiis iu firm, 

 htiinogeneoiis rock must tend to irregularity near tlie original surfoce as it 

 existed when the fissure formed, it is evident that at great depths fissures in 

 irregular and weak rocks, such as those whi(di form the greater part of the 

 Coast Ranges, must tend to regularity and simplicity; for at great depths the 

 walls of a fissure are so supported by the overlying masses that even if the 

 country is composed of discrete fragments these will be held in place very 

 much as if the material were continuous. Hence, at considerable depths 

 distinct fissures are to be looked for even in the quicksilver mines ; but it 

 is evident that the mutual support of fragmentary rocks will act only so 

 long as the fissures are very narrow. If considerable openings form, such 

 as are suitable for tlie deposition of ore in large masses, irregular reticulated 

 vein cliambers will result in such material at any dejith. In sueli rock as 

 I have seen in the quicksilver mines of California, wide, simple fissure veins 

 are not to be expected at any level and irregular chambers are not so likely 

 to be met with at great depths as at small ones, though they may occasion- 

 ally be found at any distance from the surface. 



Fissure systems at the various mines. Siuce fisSUre SystCUlS are ahllOSt UCCCSSa- 



rily more simple at considerable depths than near the surface, there is, 

 a priori, a strong probability that veins underlie Sulphur Bank and Steam- 

 boat Springs. As to the extent of such probable veins one can now judge 

 only from the amount of water which seems to have issued from them, and 

 this is but a poor guide. They miglit or might not repay the expense of 

 the explorations necessaiy to discover them. At Steamboat the springs 

 rise in lines approximately parallel to the trend of the Sierra, and this is 

 also the probable direction of the underl^'ing fissures. At Sulphur Bank 

 there is no certain indication of a prevailing strike, the local structure being 

 very complex. 



What seem inevitable conclusions from these very simple principles at 

 these active springs are established certainties at other localities. The Red- 

 ington mine has been shown in the foregoing discussion to be closely anal- 

 ogous to Sulphur 13ank both in the method of genesis indicated and in its 

 structural features. Near the surface lay the irregular bonanza, answering 

 to the lower deposits of Sulphur Bank. A few hundred feet below the sur- 



