1132 A TREATISE ON METAMORPHISM. 



descending waters upon a sulphide of nickel, the latter being- deposited by 

 the deep circulation. 



In conclusion, it appears that the silicates deposited by ascending 

 waters, like the carbonates, are essentially gangue minerals. The only sili- 

 cates deposited by ascending waters which may be ores are those of zinc, 

 manganese, and nickel. It yet remains to be shown that any of these 

 compounds are sufficiently abundant as first concentrates by ascending 

 waters to serve as important ores. 



CRITERIA FOR DISCRIMINATING DEPOSITS OF THE DEEP CIRCULATION. 



The ascending waters depositing ores are necessarily those of the deep 

 circulation. The criteria by which ores may be determined to have been 

 deposited by ascending waters from a deep circulation have not yet been 

 fully worked out, but certain suggestions may be made. 



The first and most conclusive criterion discriminating ores produced by 

 deep waters is that at the present time the waters are observed to be ascend- 

 ing. Locally, as in the Comstock lode, great volumes of hot water are rising, 

 and doubtless ores are still being deposited. In such cases the evidence in 

 favor of deposition from ascending waters is complete. A characteristic of 

 ascending streams of the deep circulation is their independence of rainfall 

 and other local conditions. The volume and the temperature of the water 

 remains nearly constant from one year's end to the other. The best illustra- 

 tion of such an occurrence known to me is that furnished by the Comstock 

 lode, already mentioned. An almost equally good case is that in the Smug- 

 gler Union mine at Telluride, Colo., where, about 600 meters below the sur- 

 face, in the Pennsylvania shaft, a stream of water at a definite temperature 

 rises with uniform flow entirely unaffected by the seasons. The regularity 

 of the temperature and volume of this water have led to the use of the stream 

 for mine purposes. Equally good instances of an extended rising circulation 

 independent of local precipitation are found in the Joplin district of Mis- 

 souri. Here in practically all of the sulphide mines below a very moderate 

 depth there is unanimous agreement among the miners that the volume of 

 water which rises is not influenced in the slightest degree by precipitation. 

 Whether the season be dry or wet the steady flow of rising water must be 

 handled. Where for some reason the process of concentration of the ores 

 has ceased, as is doubtless the case in many regions, we do not find 



