Vol. 4] 



Reid.—The Gomstock Lode 



183 



can be accounted for, in the most probable way, by assuming a 

 difference of age. 



Fault in Andes Mine and Central Tunnel. — The Andes mine 

 workings and the Central tunnel show many east-west faults. 

 There is a great complexity of these in the surface workings, as 

 is to be expected in the great lode. The largest one in the Andes 

 cuts off sharply one of the bigger quartz bodies between the horses 

 of diabase. Others, of less extent, but still of some size, cut 

 across the vein proper, and act as channels for mineral solutions, 

 as will be mentioned later. These motions are shown by clay and 

 rolled pebbles of quartz. The east-west movements in all the 

 surface workings are characterized by identical features. A very 

 peculiar action is now taking place along one of these cross frac- 

 tures in the Central tunnel, where there is little circulation of 

 air, characterized by the deposition of pyrite from an acid solu- 

 tion. 



BONANZAS. 



Virginia City. — The formation of the Virginia City bonanzas 

 is peculiar, and has never yet been concisely presented. The 

 present developments in mining work have thrown much light 

 upon this question of genesis. In the Virginia City portion of 

 the lode the ore occurs not in the main fissure, but in openings 

 or "veins" in the hanging wall, which occupy nearly vertical po- 

 sitions (see figure 1). These "veins" are more nearly allied to 

 gash veins than to what are usually called ' ' fissure veins. ' ' The 

 "secondary vein" now so productive in the Ophir ground, has 

 brought to light some valuable and interesting facts. (1) It has 

 been found only in the lower mine levels, either as a mere fault 

 zone or a productive deposit. (2) From the lines of motion pre- 

 served finely in the clay gouge, the relative movement of the 

 walls is seen to have been nearly horizontal, whether north or 

 south the writer is not able to state definitely. From the parts 

 of the "vein" observed, however, chiefly on the 2050 level, it 

 seemed probable that the motion was to the south for the east 

 wall, dipping downward about four degrees in the same direc- 

 tion. This corresponds to the view that the vein itself is due to a 

 pulling apart of the rock mass, causing the greatest openings to 



