COMPOSITION OF VEIN MATERIALS. 561 



what unexpected. Of the others, III is perhaps the most abnormal. In the 

 mine it was a pure white, extremely plastic mass, which could be molded 

 like plaster or potter's clay, and became quite hard on exposure to the air. 

 Sulphuric acid is a very common constituent of these substances, having 

 been found qualitatively in each one of five other specimens taken from 

 widely separated parts of the district. Where the substance occurs in the 

 immediate vicinity of an ore body this acid may be readily conceived to 

 have come from the oxidation of the metallic sulphides ; but in the case 

 of those occurring on barren contacts, far away from any known body of 

 metallic minerals, as is the case with V, it would seem that their formation 

 might date back to the passage of the sulphurous waters which brought in 

 the original ore deposits. 



Lime and magnesia salts. Although lime and magnesia are found in small 

 quantities in both ores and gangue materials, it is rath:?r remarkable, when 

 one reflects that the country rock is a dolomitic limestone, that their minerals 

 are so uncommon. Calcite occurs as incrustation on crevices and lining 

 cavities or druses in the iron, but never in any large amount. Gypsum is 

 rarely found, although it seems evident that it must have been one of the 

 most important products of alteration. It must therefore be assumed that, 

 owing to its ready solubility, it has been entirely carried away. 



Barite. Barite, or heavy spar, is a not uncommon constituent of the 

 gangue, but it is very irregularly distributed. It generally occurs in aggre- 

 gations of tabular crystals, frequently concentrated in considerable masses, 

 and more or less stained by iron oxide. Chloride of silver is generally 

 found associated with it. This association of barite and chloride of silver 

 is noteworthy. Among the miners the presence of the former mineral is 

 considered a sure indication of rich chloride ore. In this connection it is 

 interesting to recall Miller's experiments, mentioned by Sandberger, 1 show- 

 ing that sulphide of barium dissolves pyrargyrite, or ruby silver, without 

 decomposition. The frequent presence of antimony in the ores and vein 

 materials renders it probable that a part of the silver may have originally 

 existed as ruby silver. Moreover, although there are no experimental proofs, 

 it is probable that waters containing sulphide of barium would dissolve the 



1 Neues Jalirbuch fur Miuerulogie, 1869, p. 309. 

 MON XII 36 



