28 MINING INDtlSTEY. 



rock, and it is rare at any point east of the Comstock Lode to find 

 more than an accidental relic of unaltered propylite. The chief product 

 of the thermal action is a soft, yellow, ochreous rock, which easily weathers, 

 and develops near its surface parallel and concentric planes of decomposition. 

 An exceedingly beautiful variety of agate-like banded propylites are found on 

 the divide. The white steam-cracks thread the formation in all directions, 

 and seem to be the centers of decomposition. Not all of the solfataras appear 

 to have been oxydizers. At rare intervals, over the whole outcrop, may be 

 found white, decomposed, chalky masses which may be easily cut with a 

 knife ; but in all these extreme products there is still discernible the crystals 

 of feldspar which originally gave it its porphyritic form. Olive and gray and 

 purple are colors which occur frequently, the earthy crystals of orthoclase 

 being dispersed in white specks throughout the mass. The ochreous pro- 

 duct appears to be chiefly a mixture of silica, clay, and sesquioxide of iron. 

 The white portions are either entirely free from iron, or else contain it in the 

 protoxydized form. West of the Comstock lode and near the Belcher Mine 

 are two parallel lines of solfatarism, which in both cases have produced the 

 white product, the upper one closely resembling certain of the white trachytic 

 tufas. It is difficult to distinguish between hand specimens of both. 



As the range descends toward the Carson Plain, especially in the region 

 of the Daney Mine, the propylite is of subaqueous origin and consists chiefly 

 of an earthy tufa deposit clearly stratified, and containing impressions of 

 leaves and rolled masses of the original propylite. Covering this tufa deposit 

 are beds of yellow clays, which are evidently washed down from the solfatara 

 region. The area of the most intense hot-spring action begins about five hun- 

 dred feet east of the Comstock, and continues for two miles still further to the 

 east. 



In the southwest comer of the map appear irregular masses, colored as 

 quartz-propylite. These rocks overflow the propylite, the metamorphic rocks 

 of American Canon with their accompanying granite, and are in turn capped by 

 basalt. Little can be learned of their origin except that they succeed the 

 propylite, as is evidenced by their cutting it in dikes above the American Flat 

 road. They are of very great variety of texture and constitution, ranging all 

 the way from a propylite, containing here and there an occasional grain of 



