VIRGINIA EANGE. 825 



northward for 150 miles to about latitude 40° 15', where it falls away in 

 low volcanic hills bordering upon the Mud Lake Desert. Only the northern 

 half of the range, lying north of the Carson River, comes within the limit of 

 this exploration, and the following observations therefore are restricted to 

 this area. Immediately beyond the southern boundary of the map occurs 

 an elevated and distinct group, lying between the broad valley of the Car- 

 son Eiver and the deep narrow canon of the Truckee, with Mount Davidson, 

 a mass of diorite, as the centre, having an elevation of 7,827 feet above sea- 

 level, and as the celebrated Comstock Lode occurs along the eastern slope 

 of the mountain, the surrounding region has become one of great scientific 

 and economical interest. In "Mining Industry", Vol. Ill of this series, 

 wall be found a detailed geological description of the Washoe Mining Dis- 

 trict, with a careful study of its typical volcanic rocks by Mr. Clarence 

 King, accompanied by an elaborate account of the Comstock Mines by Mr. 

 James D. Hague. 



That portion of the range included within the map is built up, so far as 

 known, with the exception of some Pliocene beds in the Truckee Canon, 

 exclusively of crystalline intrusive masses, and of these pre-Tertiary rocks 

 occupy a very limited area. Granite, although reaching the surface in large 

 masses in the Pine Nut Eegion to the south, and in obscure outcrops at the 

 base of Mount Davidson, has ncA^er been observed north of the Truckee Canon, 

 and, if ever seen, will probably be found in some deeply eroded canon. 



The range has been pre-eminently one of great activity throughout 

 the volcanic period, as nearly all varieties of Tertiary intrusive rocks known 

 in Nevada have been recognized here, many of them affording typical 

 specimens. Propylites, quartz-propylites, andesites, dacites, hornblende- 

 trachytes, augite-trachytes, rhyolites, and basalts have all been poured out 

 along this line of upheaval, and, as might be expected, the more recent 

 rocks, breaking through the earlier bodies, occupy the largest areas, capping 

 the elevated ridges and concealing the older flows. 



Steamboat Springs are situated a short distance to the south of the limit of 

 the map, on the western side of the range, and near the base of a volcanic hill. 

 They cover an area about one-quarter or one-third of a mile in length by 800 

 to 1 ,000 feet in width. The surface of the ground is covered by a deep accu- 



