The deposits of the useful minerals & rocks; their origin, form, and content . states, among them being those in andesite at theApollo mine. Montana.—A considerable portion of the silver productionof Montana comes from the copper district of Butte, where during theperiod 1892-1900 copper to the value of 331 million dollars, silver to86 million, and gold to 14-5 million dollars, were produced. THE COMSTOCK LODE The outcrop of this lode in the Washoe district of Nevada, near theCahfornian boundary, is situated about 1970 m. above sea-level on theeast slope of the Virginia Mountains, one of the n
The deposits of the useful minerals & rocks; their origin, form, and content . states, among them being those in andesite at theApollo mine. Montana.—A considerable portion of the silver productionof Montana comes from the copper district of Butte, where during theperiod 1892-1900 copper to the value of 331 million dollars, silver to86 million, and gold to 14-5 million dollars, were produced. THE COMSTOCK LODE The outcrop of this lode in the Washoe district of Nevada, near theCahfornian boundary, is situated about 1970 m. above sea-level on theeast slope of the Virginia Mountains, one of the north-eastern spurs of theSierra Nevada, in latitude N. 39° 20; the distance from Steamboat THE YOUNG GOLD-SILVER LODES 559 Springs, where the interesting recent deposits of quicksilver occur, is but9-10 The lode itself occurs within a large Tertiary eruptive massconsisting in greater part of andesite. Investigation of the more de-tailed geological position of this occurrence was considerably faciHtatedby the rock exposures in the Sutro Tunnel, made during the period. Shaft. Fig. 299.—Plan of the Comstock Lode (black), showing the extension of the extremepropylitization. Becker. 1868-1878, which reached the deposit at a depth of 500 m. after havingbeen driven 64 kilometres. Becker,^ in addition to granite occurring some httle distance away,differentiated the following eruptive sequence beginning at the oldest:granular diorite, porphyritic diorite, quartz-porphyry, older diabase,younger diabase—the so-called black dyke—older hornblende-andesite,augite-andesite, younger hornblende-andesite, and finally basalt, theyoungest rock in the sequence. According to later investigation by1 Atite, pp. 461, 467. a Loc. cit., 1882. 560 ORE-DEPOSITS Hague and Iddings,^ many of these chemically so closely related rocksmerge gradually into one another, the textural difierences depending uponthe less or greater depth at which they became consohdated. Rockswhich consohdated near the s
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