324 Mr. J. A. Phillips's Notes on the Chemical Geology 



absolute, since in many instances a vein, besides having a 

 somewhat different direction from that of the bedding of the en- 

 closing rock, throws off branches cutting the slate at consider- 

 able angles. 



One of the most remarkable gold veins in California is that 

 extending from Mount Ophir, in Mariposa county, to Mokelumne 

 Hill in Calaveras, a distance of over seventy miles. This lead*, 

 which frequently crops boldly out above the surface of the ground, 

 and varies in thickness from six to sixty feet, may in some places 

 be traced for many miles across the country, and often presents 

 an outcrop like an immense white wall. Although by no means 

 continuous, this may be considered as an axis with regard to the 

 other veins of the region, which have generally an almost similar 

 direction, and are most frequently grouped at no very consider- 

 able distances from it. 



The gangue of the auriferous veins of California is invariably 

 quartz, which is generally crystalline in its structure, or partially 

 vitreous and semitransparent. In the majority of cases the 

 quartz constituting an auriferous veinstone is ribboned in such 

 a way as to have the appearance of a succession of layers parallel 

 with the walls of the lead; and some one or more of these 

 laminae are not unfrequently far more productive of gold than 

 the others. 



In some instances these parallel bands are separated from 

 each other by a thin layer of quartz, slightly differing, either in 

 colour or structure, from that forming the seams themselves; or 

 they may be only distinguished by a difference of the colour or 

 structure of two adjoining members of the series. 



In many cases, however, laminse of the enclosing slates divide 

 the vein into distinct bands ; and in such instances it will be ob- 

 served that the thickness of the interposed fragments of slate is 

 sometimes not greater than that of a sheet of the thinnest paper. 

 Cavities or druses containing crystals of quartz sometimes occur 

 in all the auriferous veins of the country ; and a certain amount 

 of crystallization may also not unfrequently be remarked along 

 the lines of junction of the several bands of which a vein is com- 

 posed. In such cases crystallization appears to have been set 

 up on the surface of the last-deposited stratum, which has in- 

 duced the formation of a similar crop of crystals on the layer 

 subsequently formed on its surface. Quartz crystals, however, 

 rarely occur in notable quantities in any of the most productive 

 veins; and when the structure of a lead is highly crystal- 

 line, and the quartz more than ordinarily transparent, it is con- 



* In California a quartz vein is called a " lead," and in Australia a 

 " reef." In the gold-regions of the latter country the term lead is applied 

 to the deposits of the " deep placers." 



