270 University of California Publications in Geology [Vol. 13 



dislocated. Long and careful study of many such occurrences, how- 

 ever, has brought out evidence which seems to prove the contrary, 

 namely, that the veins were formed in dislocated fractures. The fact 

 that the surfaces of dislocation are not themselves mineralized with 

 ore is the outstanding first-glance evidence against this interpretation ; 

 but it is only superficial evidence, and is illusory. By turning again 

 to the diagram (figure 1) illustrating the stress rule of deposition, 

 the true explanation of this condition will be readily seen. A more 

 complete discussion of this matter will be taken up in subsequent 

 paragraphs. In the meantime a study of the accompanying vein 

 photographs will be of service (pis. 15, 16). 



Paragenesis. — In typical cases where calcite or dolomite is the 

 gangue for smaltite, niccolite, breithauptite, and silver, it is found 

 that in different spots in a given vein or in different veins the spacial 

 relations of these minerals vary. It is a common thing to find sheets 

 of silver lying in fractures and cleavages of the calcite or dolomite ; 

 but it is an equally common thing to find masses of smaltite in 

 the midst of carbonate as if of simultaneous origin, with wire silver 

 imbedded in the unfractured smaltite. Smaltite fringes occur on 

 carbonate veins, and carbonate fringes occur on smaltite veins. 

 Breithauptite is commonly associated with silver more intimately than 

 is niccolite, and niccolite more intimately than is smaltite, and both 

 occur in associations with smaltite and silver. It is therefore impos- 

 sible to recognize any consistent sequence in origin. Silver in many 

 cases occurs in fractures in smaltite and niccolite, and yet a very com- 

 mon phenomenon is the occurrence of pellets of smaltite in dolomite, 

 the pellets being from one to five millimeters in diameter, and con- 

 taining a central pellet of niccolite or breithauptite, which in turn 

 contains a core of silver, the metal being perfectly spherical in form. 

 The carbonates vary from pure calcite to dolomite, containing notable 

 percentages of iron or manganese, the latter imparting a strong salmon 

 red color to many of the veins, and being regarded by the miners of 

 the district as a "good sign." The distribution of these various car- 

 bonates makes it difficult to formulate rules that will consistently bear 

 out any idea of regular sequence in origin. A rule embracing 75 

 per cent of the carbonate occurrences will not be sufficient to establish 

 an age relation, for the 25 per cent of exceptions must be explained. 

 The only rule which I have been able to develop is that the gray 

 dolomite is the most usual associate of the rich ores, pink manganif- 

 erous carbonate is next most closely associated with them, and white 



