328 MINING INDFSTEY. 



No. 3, on a line drawn tlirougli San Juan, east 27° south, shows a section 

 of the central granite body, the slates and quartzite resting upon it, and the 

 rhyolite on their flanks. 



No. 4, on a line, north 2^° south, drawn through the northern spur of 

 Ophir Canon, shows the two granite bodies, the synclinal fold in the slates, 

 and the rhyolite flow from Prometheus which covers the western slopes. 



To what extent the present configuration of the range is due to glacial 

 action is not easy to determine, since the decomposable nature of some of the 

 rocks, and the position of the strata of others, are not adapted to preserve the 

 traces of such action. 



From the fact, however, of glacier polishings having been found on the 

 face of a spur, at the mouth of Santa F^ Canon, in such a position as to ne- 

 cessitate the supposition of the existence of a glacier in that canon, whose 

 lower extremity, covering the end of this spur, extended out into Smoky 

 Valley, it may be inferred that the basin-shaped heads of most of the large 

 canons were formerly filled by glaciers, which, flowing over the inclosing 

 ridges at their lowest points, by their abrasion, followed the course of the 

 present canons; the subsequent action of water having cut the narrow gorges 

 which now exist in their lower portions. 



The great accumulations of debris at the mouths of the larger canons, 

 whose slope is frequently more than 6°, through which the waters have cut 

 channels from 50 to 100 feet deep, and of more than double the width, favor 

 this supposition, while the narrowness and steepness of the range, and the 

 probable existence of lakes which filled the adjoining valleys, might account 

 for the absence of any well-defined moraines. 



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 comparatively low, for five miles south of Tele- 

 graph 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 feldspar of two varieties, a semi-translucent orthoclase, 

 and an opaque white variety, probabl}^ oligoclase ; the mica a dark magne- 

 sian variety ; hornblende is found as an accessory ingredient, sometimes con- 



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