THE COMSTOCK LODE. 75 



observed. The epochs of trachytic and basaltic eruption are in themselves 

 quite enough to account for the movements which have crushed the Comstock 

 quartz-bodies. To open a fissure of sufficient width to permit the immense 

 volumes of trachyte-lava, which lie east of the vein, to outflow, would 

 probably communicate sufficient pressure to the Comstock itself to produce all 

 the effects of fracture and grinding which are shown by the fragmentary 

 condition of the quartz, and the manner in which the east wall-material 

 is crowded in among those fragments. The fact that the quartz is arranged 

 in zones, which are parallel to the direction of the lode, and that the main 

 fissure-lines traversing the horses are also parallel, shows a coincidence of 

 direction in all the disturbing forces of the neighborhood. Such movements 

 will indeed only account for the degrees of fineness into which the various 

 zones of a given body are crushed. For the varied conditions of color and 

 minerahzation we must look to the varieties of chemical activity which sub- 

 sequently occupied the vein. Quartz forms the only ore-gangue in the whole 

 Comstock. 



Minerals. — The catalogue of Comstock minerals, both those which com- 

 bine to form the silver bonanzas, and those unimportant accompanying species, 

 is remarkably meager. Those of value are native gold, native silver, argentite, 

 (silver glance) polybasite, and stephanite, with some very rich galena and occa- 

 sional specimens of pyrargyrite. Besides these, occur in the quartz, iron pyrites, 

 copper pyrites, oxide of iron, manganese, sulphates of lime and magnesia, and 

 carbonates of magnesia, lime, lead, and copper. The line of oxidation, or 

 rather of those minerals in the form of oxides, is confined to the upper 500 

 feet of the lode. Here a large proportion of the iron pyrites, and all of the 

 carbonates of lead and manganese, are changed into the oxides of those metals 

 which produce the prevailing red hue. A zone of manganese oxide occupies 

 the entire length of the lode from the outcrop 200 feet down. Below this, 

 there is only a very small percentage of manganese, which is found in two 

 forms, as the carbonates on the second level of the Savage, and in the general 

 mass of the silver ore, probably as a part of the polybasite. It is difficult to 

 assign the true lower limits of the "Colorado" or "Iron Hat." The quartz is 

 reddened and the iron minerals more or less oxidized to a depth of 500 feet, 

 but it is probable that the lower 100 feet are chiefly colored by the percolation 



