CENTEAL Am) EASTEEN NEVADA. 343 



Opliir Canon presents a very interesting section through a synclinal 

 fold in the slates inclosed between two bodies of granite. The lower end of 

 the canon is a narrow gorge cut through the granite body, on which rest met- 

 amorphic slates, having a north and south strike and dipping west. Near the 

 contact of the slates and granite is the large vein which gives its name to the 

 canon, a dike-like body of quartz about 40 feet thick, dipping westward with 

 the formation, at an angle of 50°. Above the Murphy ledge, which is near 

 the axis of the synclinal, the slates di]3 about 45° to the east with the same 

 north and south strike. At the upper forks of the canon is found a green 

 hornblende slate similar to that in Ophir Canon, These slates rest on the 

 granite, which at this point forms the crest of the ridge. 



The faults found in the Murphy ledge on the north, and the fact that the 

 Ophir vein, which is regular and unbroken on the south side of the canon, is 

 represented on the northern spur by broken masses of quartz lower down, 

 seem to indicate a general faulting and movement to the eastward of the rocks 

 in this spur ; such a movement, more extended, might perhaps account for the 

 non-appearance of the quartzites in Wisconsin Canon. The upper granite 

 body of Ophir Canon forms the saddle at its head and the main crest for a 

 short distance to the north; and, to the south, extends across the head of 

 Last Chance Canon, its eastern limit seeming to have the same general 

 direction with that of the propylite, by which it is replaced in the Twin 

 River Canons. 



The first peak on the main ridge, south of Ophir Canon — Mount Beseler — 

 is of rhyolite, which rock covers the whole western slope of the range, from 

 the granite crest to the Reese River Valley. The granite of this upper body 

 is a compact, fine-grained variety, of dark color, due to the large proportion of 

 dark, magnesian mica, in very perfect hexagonal crystals, entering into its 

 composition ; it contains, besides, quartz and white orthoclase feldspar ; on the 

 contact surfaces the mica seems somewhat decomposed and chloritic. 



The rock of the lower body is a protogine-granite, coarse-grained though 

 coherent, a white mass of quartz and feldspar, which are so intermingled as to 

 render their crystallization very indistinct, inclosing foliated masses of dark- 

 green chlorite or talc; this body extends along the eastern edge of the range, 

 as far south as the North Twin River Canon. 



