GRANITE RANGE. 797 



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The Forman Mountains, as represented on the map, are tlie southern 

 point of a range of mountains, in which both these and the Black Rock 

 Mountains are probably merged to the north. They were only examined 

 opposite the Cold Spring, a large spring of fresh cold water on the edge of 

 the desert, near their southern point. Here they were found to consist 

 exclusively of rhyolitic rocks, in which, as at Black Eock, the breccias play 

 the most important role. Of the specimens of rhyolite obtained, one is a 

 pure white felsitic mass, of conchoidal fracture, containing only white, half- 

 kaolinized feldspars, with no other crystalline ingredients. Another variety 

 is a reddish porphyritic rhyolite, with rough fracture, containing well-defined 

 glassy sanidins, sometimes in Calsbad twins, and free quartz in a compact 

 felsitic groundmass. With these occur breccias, which closely resemble 

 the parent rock, being in no way distinguishable from it except from the fact 

 that it shows a combination of angular fragments, all of the same composi- 

 tion and color, which is also that of the material which binds them together. » 

 Another white porous breccia is seen, however, to contain strange frag- 

 ments of dark slate color, apparently of some older rock, which are too 

 homogeneous, however, to offer definite characteristics. 



Granite Range. — In the northwest corner of the map, the Granite 

 Range appears as the first mountain uplift in Nevada east of the State of 

 California, its western base lying about 25 miles east of the 120th meridian, 

 the boundary between the two States. The range rises abruptly above the 

 Mud Lake Desert in about latitude 40°45', but projects in a low, narrow 

 tongue of granite 3 or 4 miles still farther to the southward, toward the plain. 

 To the northward, the range stretches far beyond the limits of the Fortieth 

 Parallel Survey, and has never been thoroughly examined or mapped. 



Within the limit of the map, the range extends in a north and south 

 direction for 25 miles in bold, rugged mountains, which rise grandly for 

 4,000 feet above. the level, floor-like plain of Lower Quaternary beds, 

 the highest peaks attaining an altitude of 10,000 feet above sea-level. 

 Only the southern portion of the mountains was visited, but, as far as 

 examined, they appear to consist entirely of granite, with the later Tertiary 

 volcanic rocks breaking out along the base. This granite, in its physical 

 habit, presents all the marked features which characterize the neighboring 



