te ee od 
SOURCE AND DISTRIBUTION OF THE GOLD. 300 
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 cona- 
temporaneous with their impregnation with their associated metals; and, 
lastly, the epoch of volcanic action, during which the flanks 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 
* See ante, pp. 330, 331. 
+ This axis need not be one continuous mass, but may consist of several disconnected portions, as in the case 
of the Alps. 
£ In several of the most important European languages, “‘ mine” and ‘‘ mountain” are synonomous terms. A 
*“mountain man” is a miner, a “ mountain work” a mine. 
