302 University of California Publications in Geology [Vol.13 



the greatest force of crystallization, or with the largest volume 

 change in crystallizing from solution, would be precipitated where the 

 wall pressure is least, and vice versa. This would account for the 

 preference of precipitating dolomite, which has a small atomic volume, 

 for the marginal region of the fissure where the wall pressure is great- 

 est. In the above reaction AgS is shown as the substance precipitated 

 as a silver salt. The reaction, however, like the whole picture here 

 presented, is intended merely as a similitude — a means of indicating 

 the general sort of thing which may be presumed to have occurred. 

 In view of the conditions of high temperature and pressure, it seems 

 more likely that a large complex molecule was deposited as the ore 

 molecule, containing silver, cobalt, nickel, arsenic and sulphur — a mole- 

 cule stable only under those peculiar conditions, and unstable under 

 conditions of less pressure. 



Subsequent molecular rearrangement. — The most complex mole- 

 cules to be found in the present ores are occasional sulpho-salts of 

 silver, such as proustite, etc. The metals usually occur native or in 

 binary compounds. In the mineral mixtures which constitute the 

 present ores evidence was sought by Miller and Knight for paragenic 

 sequences, but the evidence of the veins of many mines seems to show 

 contradictory sequences. My conclusion is that no uniform set of 

 sequences exists. Miller indicates his belief in a period of calcite and 

 silver deposition subsequent to that of the arsenides ; but I find silver 

 in wire form lying within massive unfractured smaltite and niccolite, 

 as if not having come after the arsenides but with them. Another and 

 perhaps more common phenomenon is the occurrence of spherical 

 pellets of silver, perhaps two millimeters in diameter, in the center 

 of pellets of niccolite, which are themselves the cores of pellets of 

 smaltite. The arsenides are never found replacing silver, nor is 

 dolomite or calcite found replacing either silver or arsenide. The 

 relationships are always the reverse; but this may be accounted for 

 much better on the basis of relative forces of crystallization than of 

 absolute time sequence. 



The disorderly mineral relations obtaining in these ores seem to 

 find a more consistent explanation in the rearrangement of vein con- 

 stituents due to the breaking down of the original complex carbonate 

 and sulpho molecules as the pressure was reduced by the approach 

 of the surface due to erosion. A good line of evidence bearing upon 

 this point is found in the fact that in wall fractures uncemented by 

 typical vein matter, severing the veins, and obviously of later origin, 



