338 



MINING INDUSTET. 



ores found in the slates of the south fork of the canon. From here to the 

 Point of Rocks extends a body of limestone, resting in general on the slates, 

 with a westerly dip. In appearance it does not differ from the other lime- 

 stones of the range, being somewhat granular in texture, of a dark-blue color, 

 and largely intersected by narrow seams of white crystalline calcspar. 



The extreme western angle of this western ridge, called, from its bare, 

 craggy appearance. Point of Rocks, is composed of propylite, whose eruption 

 has been accompanied by a very considerable modification of structure in the 

 surrounding rocks; the limestones and slates are found to be dipping away 

 from it on either side, and somewhat altered at the contact. The main cen- 

 tral mass is a hornblendic propylite, having a greenish -white feldspathic matrix, 

 inclosing crystals of opaque, white feldspar and dark green hornblende; along 

 the summit of the ridge this rock has a distinctly columnar structure; at the 

 head of the western fork of Kingston Canon it is found in large lava-like 

 blocks, having a dark, somewhat glazed surface; here it has a felsitic texture, 

 the feldspar is semi-translucent, of a flesh color, and the hornblende appears 

 in green spots, without any distinguishable crystalline structure. It is trav- 

 ersed here by a dike of compact, dark rock, resembling andesite, but carrying 

 large, rounded grains of limpid quartz, apparently filling vesicular cavities 

 through the mass. This central mass of hornblendic propylite is inclosed on 

 the west and south by a body of quartz-propylite, which covers its flanks, 

 forming the foot-hills on the edge of Reese River Valley, and to the south a 

 portion of the crest of the ridge adjoining the limestone shales. This quartz- 

 propylite is a later phase of the eruption, being separated from the main body 

 on its southern edge by a tufa-like breccia, carrying flinty fragments; it con- 

 tains more or less free quartz, and apparently no hornblende, while the central 

 mass has hornblende and no quartz; that on the crest of the ridge has a yel- 

 lowish paste, inclosing small crystals of white, opaque feldspar, probably oli- 

 goclase, which assumes a reddish color on the weathered surfaces of the west- 

 ern foot-hills, and is sometimes an entirely homogeneous, white mass, with 

 free quartz. 



A ravine marks the line of contact of the propylite with the limestone 

 on the north, but on the ridge, where found adjoining the propylite, the lime- 

 stone is grayish-white and granular, and dips to the northeast. On the south, 



I 



