340 



MINING IKDUSTEY. 



crystals, hexagonal prisms about a sixteenth of an inch in diameter, with per- 

 fect hexagonal pointraent; the rock has, moreover, a brownish-gray color, 

 which seems due to the qliartz, which is of a smoky brown. It contains very 

 little mica or hornblende. 



In the slates of San Juan Canon above the forks are several veins of ar- 

 gentiferous galena. The remains of a rude furnace, constructed for the reduc- 

 tion of their ores, are still visible at the now deserted mining camp of San Juan. 

 In the construction of this furnace, blocks of a yellowish, earthy, rhyolitic tufa, 

 or breccia, which is found at this point on the south side of the canon, were 

 used. 



The lower part of the spur south of San Juan Canon is of rhyolite, which 

 probably forms the low hills south of this on the western extremities of the 

 spurs, which inclose the interior basins at the head of Cross's and the suc- 

 ceeding canon. To return to the eastern slopes of the range, at the southern 

 edge of the mouth of Kingston Canon is a curious local occurrence of a rhy- 

 olitic breccia-like rock, forming the extreme point of the spur, and having, so 

 fer as known, no connection with any other body of eruptive rock ; it is mainly 

 an amorphous paste inclosing small, dark, flinty fragments, probably of altered 

 slate, but in places a compact feldspathic matrix having a somewhat ribboned 

 structure, and inclosing a large amount of free quartz in rounded grains. 



The Bunker Hill slate series, with its dike of syenite, extends to the 

 south of Kingston Caiion, forming a rounded mass of hills on the high eastern 

 spurs of the main ridge, whose crest topographically bends round the head of 

 this canon. 



In Brassfield Canon, the second south from Kingston, is the first appear- 

 ance of the great central granite body, which extends from here south nearly 

 to Summit Canon. The syenite dike here near the mouth of the canon is al- 

 most identical in appearance and composition with that of Kingston, and like- 

 wise impregnated with iron pyrites. The granite is characterized by a very 

 large proportion of quartz ; it is a fine-grained white rock, containing a little 

 white potash mica, and white, easily-decomposed feldspar. In contact with the 

 slates which form the lower ends of the spurs, and rest upon it, it passes into 

 a granulite carrying little or no mica, and in which the whole mass assumes a 

 somewhat homogeneous texture. This granite body rapidly widens out as one 



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