32 



University of California Publications. 



[Geology 



grown. This is comparable to the allotriomorphic structure in 

 granitic rocks. The bands may not show successively any regu- 

 larity of chemical phase ; one may be more acid than the next, 

 or may be capriciously either, thus not possessing the regularity 

 of the Rosenbusch order of crystallization. The writer was 

 enabled to exemplify these propositions at the Steamboat 

 Springs, which are near. This occurrence, as is well known, is 

 often cited as an instance of vein filling now in actual progress, 

 and consequently is one from which many of the ideas in regard 

 to vein tilling, including those on the crystallization of vein min- 

 erals, were derived. Another very good instance also occurs at 

 Bridgeport, Mono County, California, near the source of the 

 East Walker. It appears to have passed so far unnoticed. In- 

 stead of quartz being the filling material, a variegated travertine 

 is filling the fissures. It is shown at this place, in addition to 

 what is shown at the Steamboat Springs, how a portion of a vein 

 may be formed without being directly attached to a previous 

 surface. Hence idiomorphism has been taken in the sense just 

 described in the study of the ores. 



An Occurrence of Native Copper. — One occurrence of native 

 copper has been discovered. It is not extensive enough to have 

 sufficient economic value to make the mining of it profitable, but 

 a study of its origin was found to be of an economic worth. 

 While the ore bodies themselves have been produced by aqueous 

 solutions, this occurrence of native copper was produced by 

 reduction due to the heat generated by subsequent dynamic 

 action, and a close parallelism was thus found to smelting pro- 

 cesses, and by chemical and microscopical investigation of the 

 ore and rocks adjacent to the native metal many of the steps that 

 have been taken in the reduction are revealed, with the result that 

 several suggestions were obtained for the actual treatment of 

 the ores, and thus an opportunity was offered for an improve- 

 ment in the smelting formulas and some troublesome irregulari- 

 ties lessened. 



University of California, 

 December, 1904. 



