628 DESCRIPTIVE GEOLOGY. 



mining developments centred there, a geological description of the most 

 characteristic portion, extending from the town of Austin southward for 

 60 miles, was prepared, accompanied "bj a geological map, for " Mming 

 Industry ". 



From Austin northward, the range extends about 25 miles, with a trend 

 nearly north and south true. In the extreme southeastern corner of the 

 map are found the northern outlying portions of the granitic bodies, which 

 play so important a part in the structure of the range to the south. North 

 of the granitic bodies, the r-ange is made up of quartzites, slates, and lime- 

 stones, which have been refen'ed to the Carboniferous age, represented by 

 the Weber Quartzites, and the overlying Upper Coal-Measure series, while 

 flanking the Palaeozoic formations on the east side are broad accumulations 

 of rhyolite, through which, in the deep canons and open basins, may be 

 recognized the soft, friable beds of the uplifted Truckee Miocene. 



The following description of the Austin body of granite is taken from 

 the "Geology of the Toyabe Range 'V "The Austin body of granite, which 

 is particularly interesting as being the principal ore-bearing body of the 

 range, forms the core of the main ridge of the Toyabe, which is here com- 

 paratively low for 5 .miles south of Telegraph Pass. It is exposed mainly 

 on the western slope of this ridge, where it is worn into the rounded spurs 

 and open, shallow ravines, characteristic of an easily decomposed granite. 

 This is a normal granite, consisting of quartz, feldspar, and mica; the 

 feldspars of two varieties, a semi-translucent orthoclase, and an opaque, 

 white variety, probably oligoclase ; the mica, a dark magnesian variety ; . 

 hornblende is found as an accessory ingredient, sometimes concentrated in 

 bands or bunches. It forms the southern foot-hills of Telegraph Peak, 

 underlying the metamorphic rocks, which are dark-blue siliceous limestone 

 shales, dipping to the north and east at a low angle. At Telegraph Pass, 

 it is exposed on the eastern slope of the ridge, where it is traversed by a 

 dike, about 15 feet wide, of white granulitic rock, containing sparse crys- 

 tals of mica, and black crystalline grains of tourmaline, concentrated in 

 bunches throughout the mass. This dike has a northwest strike, which is 

 in the direction of the principal veins of this neighborhood." 



^Mining Industry, vol. iii, 328. 



