34 MINING INDUSTRY. 



ling, rendering it very difficult to get a specimen Like the Graveyard spur 

 outcrop, it is wholly surrounded by propylite, and from its thinness seems 

 to be rather the fragment of an old overflow than the outpouring of a local 

 dike. 



About a half mile east of the Virginia divide is a third but exceedingly 

 small locality of the trachyte. It consists of a mere accumulation of blocks, 

 dispersed about the surface, and indicates probably the limit of the trachyte 

 flow in that direction. It is a sanidin-mica-trachyte. The study of this 

 third out-crop reveals no traces of subterranean connection ; it is difficult to 

 conceive of its having burst out through a local chimney, and it is probably a 

 part of a sheeted overflow. 



Two miles to the east of this zone occurs the main ejection of trachytic 

 rock. It occupies a broad zone from the Washoe foot-hills to Pyramid Lake, 

 a distance of forty miles. In a nearly meridional direction it is poured out 

 along the heights of the range, and nearly all of the prominent eroded sum- 

 mits and elevated table lands are formed of it. This formation enters the 

 map at the northeast corner and occupies a broad belt quite across it. 



A series of bold h ills continue from the Truckee River, almost without a 

 depression, until they reach the pass north of the Gould and Curry mill. Here 

 they descend steeply about 800 feet ; ascending to the south of the pass to an 

 almost equal height. The pass itself is wholly of propylite, except a narrow 

 dike of trachyte less than 100 feet wide ; through this small aperture the 

 whole mass of the formation has come. Continuing southward, the area of the 

 trachyte widens rapidly until it has overflowed the width of two miles. Across 

 this has been eroded the Six-Mile Canon, opening up the internal structure of 

 the mass to a great depth. A prominent conical hill seen from Virginia City, 

 and known as the Sugar Loaf, is of this formation, as are also the series of 

 hills which continue thence southward to the Dayton road. Whenever it 

 is eroded to any great depth there may be seen traces of an earlier flow 

 of the oligoclase-hornblende variety of the trachyte. This is especially 

 observable in the most northern part of the map, and again at the base of 

 Mount Rose, where the oligoclase-hornblende trachyte occurs, having a fissile, 

 slaty structure given to it by the parallel arrangement of both oligoclase and 

 hornblende. It is of a steel-gray color, with dull brown parallel planes. There 



