656 RECORD OF MEETINGS OF THE 



the pressure were insufficient to restrain them and would, were 

 their chemical powers sufficient, have opportunity to take up 

 even sparsely distributed metals. 



On the other hand if their emission, as seems more probable, 

 is in largest part a function of the stage of solidification and 

 takes place gradually while the mass is congealing, or soon 

 thereafter, then they must depart along crevices and openings 

 whose ratio to the entire mass would be similar to those given 

 above. They might have, and probably do have, an enhanced 

 ability to dissolve out in a searching and thorough manner the 

 finely distributed metallic particles as compared with relatively 

 cold meteoric waters which might later permeate the rock; but 

 as regards the problem of leaching, the general relations of 

 crevices to mass are much the same for both, and it holds also 

 true that the discovery of the metals by assay of igneous rocks 

 proves that all the original contents have not been taken, by 

 either process. 



We may, however, consider an igneous mass of rock as the 

 source of the water even if not of the ores and gangue, and 

 then we have a well-established reservoir for this solvent in a 

 highly heated condition and at the necessary depths within the 

 earth. Both from its parent mass and from the overlying rocks 

 traversed by it, it may take the metals and gangue. 



In the upward and especially in the closing journey, meteoric 

 waters may mingle with the magmatic, and as temperatures 

 and pressures fall, the precipitation of dissolved burdens takes 

 place and our ore-bodies are believed to result. Gradually the 

 source of water and its store of energy become exhausted; 

 circulations die out and the period of vein-formation, com- 

 paratively brief, geologically speaking, closes. Secondary en- 

 richment through the agency of the meteoric waters alone 

 remains to influence the character of the deposit of ore. In 

 brief, and so far as the process of formation of our veins in the 

 Western mining districts is concerned, this is the conception 

 which has been gaining adherents year by year and which, on 

 the whole, most fully accords with our observed geologic rela- 

 tions. It accords with them, I may add, in several other im- 

 portant particulars upon which I have not time to dwell. 



