SOURCE AND DISTRIBUTION OF THE GOLD. 



353 



The epoch of the formation of the quartz veins — that is, of their segre- 

 gation and impregnation with gold — is a point of much interest, which has 

 already been up for consideration,* and in regard to which a few words may 

 here be added. There are four all-important occurrences in connection with 

 the geological history of the bed-rock series, the co-ordination of which is 

 particularly desirable ; these are the upheaval of the chain of the Sierra ; 

 the metamorphism of the sedimentary rocks of which the range is composed ; 

 the formation of the quartz veins, which may be assumed to have been con- 

 temporaneous with their impregnation with their associated metals; and, 

 lastly, the epoch of volcanic action, during which the Hanks of the chain were 

 so extensively covered with ejected materials. 



With the upheaval of the range is most closely associated the appearance 

 of its granitic axis, which, it is impossible, in view of all the facts, not to 



* 



regard as an intrusive mass, raised from beneath, and uplifting with itself 

 the overlying sedimentary beds. That this took place at or soon after the 

 close of the Jurassic epoch appears, as already stated, to be beyond doubt. 

 But the granite itself is not the metalliferous rock of the Sierra; for, although 

 it cannot be said to be entirely destitute of veins, yet, on the whole, as has 

 been quite clearly shown in the preceding pages, when we pass above the 

 slate belt, and enter the granite region, we leave the truly auriferous gravels 

 behind. 



If, however, the granite itself is not metalliferous, its appearance seems to 

 be closely associated with the metamorphism of the adjacent sedimentary 

 rocks; while this latter condition is, as a general rule, the concomitant of 

 the occurrence of mineral or metalliferous veins. It may be stated with 

 truth, that most great mountain ranges have an axisf of granitic rock, that 

 this is flanked by metamorphic strata, and that these chemically altered 

 masses are the home of the metalliferous ores.t Indeed, it has been said, 

 and with truth, that mineral veins are only special forms of metamorphism : 

 this is especially true of the rarer and more valuable metals, and particularly 

 of those styled precious. Ores of iron are universally diffused through the 

 formations; the ores of lead, zinc, and, to some extent, those of copper, are 

 frequently found occurring in unaltered strata; but in such cases they are 



* Sec ante, pp. 330, 331. 



t Tli is axis need not be one continuous mass, but may consist of several disconnected portions, as in the case 

 of the Alps. 



t In several of the most important European languages, "mine" and "mountain are synonomons terms. A 



4 



"mountain man " is a miner, a "mountain work " a mine. 



