16 GEOLOGY OF THE GOMSTOCK LODE. 



place is taken to some extent by propylite, but in greater part by meta- 

 morphic rocks. Nowhere have syenite and metamorphic rocks been found 

 occurring on the eastern side. 



The formation of the fissure was only in so far dependent on the con- 

 tact between propylite and syenite, as it follows the same accidentally in 

 part of its course, probably because the resistance along it was inferior to 

 that offered by the solid masses of rock on either side. It is characteristic 

 of fissure veins in general, not only that the country rock on one side has 

 moved downw'ard on the other, but also that within the space formed by the 

 opening of the fissure powerful dynamic action has taken place. Few veins 

 present these phenomena so distinctly as the Comstock, the eastern side of 

 which has apjjareutly moved downward on the western; and the action 

 within the vein is amply evinced by the brecciation of the vein mattei', the 

 presence of masses and seams of clay, the crushed condition of the quartz, etc. 



There is a marked difference between the western and the eastern crop- 

 pings. Those of the western branches of the vein carry principally crys- 

 talhzed quartz of a very glassy appearance, light color, and comparatively 

 of a pure quality. Large angular fragments of the country rock are em- 

 bedded in the quartz and form centers of its crystallization. Metalliferous 

 minerals are scarce, though nowhere entirely wanting Nothing indicates 

 underground wealth, nor indeed has such been found by subsequent mining. 

 The only exception is Cedar Hill, where native gold was found abundantly 

 in places, but its scarce distribution never justified great expectations. In 

 the eastern outcrop particles of country rock, together with those of clayey 

 matter and metallic substances, occur finely disseminated through the quartz, 

 Avhich is reddened by metallic oxides. 



Contents of the Lode. — Tho veln uiattcr is composed of fragments of country 

 rock, clay, quartz, and ores. Near the surface about five-sixths of the mass 

 of the Comstock vein consists of horses, the shape and size of which vary 

 with the different nature of the rock of which they consist. Those of pro- 

 pylite are confined throughout Virginia City to the east side, and they are, 

 as a rule, longer and thinner than those of syenite. From the large horses 

 every variety occurs down to the smallest fragments. The quartz is often 

 so thickly filled with angular pieces as to have a brecciated appearance. 



