8 University of California Publications in Geology. [Vol. 7 



secondary and the better crystallized masses in the gangue vugs 

 are probably largely secondary. The common reticulated and 

 arborescent shapes occasionally show the octahedron or cubo- 

 oetahedron, very must distorted. 



Galena. — Rich sulphide ore containing a high percentage of 

 gold often has galena disseminated through it accompanied by 

 pyrite and chalcopyrite. Galena is found at all depths, and in 

 the lower workings of some of the barren or low-grade veins it 

 is associated with sphalerite and chalcopyrite. 



Cinnabar. — Minute patches and thin streaks of the red mer- 

 cury sulphide are visible in some of the gangue of the West End 

 mine. The mineral is very scarce in the veins and has only been 

 observed in this mine. 



Pyrite. — The country rock and wall rock of the deposits con- 

 tain much pyrite, but its scarcity in the vein-matter has been 

 commented upon by Spurr. It is held to be largely secondary, 

 but some of that is undoubtedly primary which is so intimately 

 associated with the fine granular black silver bands. Many of 

 the crystals of polybasite when broken show small particles of 

 pyrite and chalcopyrite as inclusions. 



Chalcopyrite. — Limited amounts of chalcopyrite are seen in 

 all parts of the veins, usually in very fine grains, and it is a 

 common inclusion in the polybasite crystals. It is the source of 

 the few secondary copper salts in the oxide zone. 



Sphalerite. — Brown sphalerite is very limited in its occur- 

 rence in the veins. It is found with galena, chalcopyrite, and 

 traces of silver, below the 900-foot level of the Mizpah shaft. 



SlTLPHANTIMONITES : POLYBASITE, STEPHANITE ?, PYRARGYRITE, 

 AND TETRAHEDRITE 



Polybasite. — The brittle black sulphantimonite of silver, 

 accompanying the argentite as one of the primary minerals of 

 the veins, is chiefly polybasite. Platy crystals occur in the quartz 

 cavities and seams, some of them with very brilliant faces. When 

 broken they show a characteristic cherry-red color like pyrar- 

 gyrite. The crystals are thin basal plates with their edge-faces 

 horizontally striated, and they consist mainly of a broad base 

 with narrow faces of the pyramid p (111), the prism m (110), 



