THEORY OF METALLIFEROUS VEINS. 249 



iron sulphide reduced from solution in a similar way. Now, both in 

 this petrifying and in this cementing sulphide of iron is found (by so- 

 lution in nitric acid) gold : sometimes in rounded grains, and there- 

 fore simply inclosed drift-gold ; but also sometimes in minute crystals 

 and threads, exactly as in the sulphide of the undecomposed quartz- 

 vein. Evidently, this gold has been deposited from a solution of sul- 

 phate of iron at the moment of the reduction of the latter to a sul- 

 phide. The process was probably as follows : Percolating water oxi- 

 dized iron sulphide and took it into solution as sulphate. This solu- 

 tion coming in contact with drift-gold dissolved it, but, subsequently, 

 coming in contact with decaying organic matter, was again deoxidized 

 and deposited as sulphide ; and the gold crystallizing at the same mo- 

 ment is inclosed.* Or following out the process on the second suppo- 

 sition, gold sulphide in solution in alkaline sulphide, coming in contact 

 with decaying wood, would be deposited by neutralization of the alkali 

 along with other metallic sulphides present and be entangled with them. 

 But, on account of its feeble affinities, the gold would give up its sul- 

 phur either to the alkaline sulphide or to the sulphide of iron and be 

 deposited in a metallic form. Now, a similar reaction would take place 

 in a fissure, and form a gold-bearing vein. In fact, the sub-lava gravels 

 may be regarded as a horizontal water-way or fissure with its walls 

 through which water circulates and deposits. 



Suppose, then, we have hot water containing alkaline carbonate and 

 alkaline sulphide, holding in solution silica and metallic sulphides, 

 among them gold sulphide, and coming upward through a fissure. By 

 any of the reactions on page 245, e. g., by cooling, silica would deposit 

 as quartz vein-stuff and the gold would deposit with other metallic 

 sulphides, giving up, however, its sulphur in the act of deposition, as 

 before explained. If the alkaline waters contained no other metallic 

 sulphide but gold sulphide, then the gold, giving up its sulphur to the 

 alkaline sulphide, would be found in form of metallic gold inclosed in 

 the quartz vein- stuff. 



Illustrations of the Law of Circulation. — We have said that the 

 iron sulphate comes from oxidation of sulphide, but also the sulphide 

 from the deoxidation of the sulphate. This is only another example 

 of a perpetual cycle of changes. Again, the gold in the veins is leached 

 from the strata ; the strata doubtless received it from the sea, for small 

 quantities of gold have been detected in sea- water ; but, again, doubt- 

 less the sea received it from the rocks, and this brings us to another 

 perpetual cycle of changes. 



But in the midst of all these changes there has evidently been an 

 increasing concentration and availability of gold and other metals. In 



* Arthur Phillips, ibid. 



