324 MINING INDUSTRT. 



Slates. — In the slates are comprised the more highly metamorphosed 

 beds, which include fissile limestone shales, more or less siliceous clay-slates, 

 and, locally, schistose and somewhat crystalline rocks, resembling mica and 

 hornblende schists, and, in one instance, a marbleized limestone. As these 

 rocks form a gradation into the limestone, their line of division cannot always 

 be definitely located. These beds have been so much disturbed and con- 

 torted, and their character so frequently changed by local metamorphism, 

 that it has been impossible for the writer to form a satisfactory estimate of 

 their thickness; probably 7,000 feet would cover that of the slates and lime- 

 stones combined. 



Quartzites. — The quartzite series, found only in the southern portion of 

 the range, form beds of compact white quartz rock, colored reddish-brown 

 on the weathered surface, between which are intercalated thin beds of white 

 granular limestone. These are found underlying the slates, with no appa- 

 rent nonconformity ; they represent a thickness of several thousand feet, and 

 may belong to the Devonian series; this point will probably be elucidated by 

 the future work of this survey, when the character and thickness of the strata 

 which make up the carboniferous and lower formations in this region will 

 be definitely determined. 



Granites. — The only considerable bodies of the older eruptive rocks in 

 the range are the granites, which form intrusive masses, upon which rest 

 the sedimentary rocks. They vary in texture and composition, to a certain 

 degree, in the different bodies, but are generally characterized by a large 

 proportion of quartz and an almost entire absence of hornblende; the pro- 

 portion of mica entering into their composition is generally small, and, in 

 one body, replaced by chlorite, forming a protogine-granite. 



A series of syenite and greenstone dikes, often so fine-grained and com- 

 pact that their composition could not be determined, which occur with 

 remarkable frequency and regularity along the eastern slopes of the range, 

 cutting through the granite as well as the various sedimentary formations, 

 may be considered to form a second phase of the granitic eruption; these 

 dikes, though from 20 to 50 feet wide, were too small to be. represented on 

 the map. 



A body of dioritic rock, occurring at the Twin Rivers, supposed to be 



