THE COMSTOCK LODE. ^ 91 



for a distance of at least 600 feet to the east of the vein, contain their normal 

 equivalents of silicic acid. But after passing the zone of 600 feet to the east 

 of the vein, the country-rock for a mile and a half is filled with seams parallel 

 to the Com stock lode ; is fissured in every direction with a net- work of minor 

 cracks, and has lost its original texture by solfataric decomposition. Here 

 we find the silica contents almost gone. The greater part of this wide zone 

 lying east of the Comstock has been reduced to a more or less ochreous, 

 earthy rock, from which almost the last traces of silica have been taken. 

 Supposing the Comstock to continue downward, along the inclined west wall, 

 at no great depth, the solfatarized zone would be entered. It seems most 

 probable that the whole mineralogical contents of the lode were sent upward 

 from that region. In the immense withdrawal of silica from the rocks of that 

 zone is a sufficient supply for the Comstock fissures. 



Pakagenesis of Mateeials. — The only facts beside those already cited, 

 which throw additional light upon the origin and mode of occurrence of the 

 Comstock, are the paragenetic relations of the various mineral materials. 

 In a large way, of course, the horses are the earliest included materials. 

 Next to them the fissure chambers were filled with quartz. After the 

 quartz the j)ercolating of waters, the attrition of rolled pebbles along their 

 sides, and the thermal decomposition of horse and wall produced those 

 sheets of clay which, in remarkable persistence, line every surface of quartz, 

 and define every line of fissure. That they are later than the quartz is 

 proven by their containing pebbles of that mineral, by their cutting it in 

 certain instances, and by their surrounding it in every direction. The 

 following series of minerals has been observed. The main ore-mass of 

 the bonanzas is composed of, first, quartz ; secondly, an assemblage of 

 crystalline combinations of gold, silver, silver glance, blende, galena, and 

 copper pyrites, the latter two ordinarily in small proportion ; thirdly, un- 

 important, secondary introductions of quartz, which occur as coverings and 

 casts of earlier quartz crystals; fourthly, polybasite and stephanite, which 

 throughout the whole length of the lode occur sparingly in well defined 

 crystals ; fifthly, carbonate of lime ; sixthly, a third occurrence of quartz 

 covering the carbonate of lime, and in some instances remaining in the form 

 of a shell, after that mineral has been entirely dissolved away. Iron pyrites 



