804 DESCRIPTIVE GEOLOGY. 



and Kumiva Peak to the north, are the principal summits, rising from 2,500 

 to 3,000 feet above the plain. 



Highly crystalline quartzitic schists and hornblendic rocks, with both 

 the older and later types of granites, are found in the Truckee Eange. The 

 intrusive granites and metamorphic schists, which have been referred with 

 but little hesitation to the Archaean series, occupj^ but a small area in the 

 range, outcropping at widely separated localities, yet are, from a geological 

 point of view, of considerable interest. The later granites, however, form by 

 far the greater part of the range, occurring probably in an unbroken line for 

 50 to 55 miles. So far as the limited observations in the range extended, 

 the older granites were found only at the southern end, in the region south- 

 east from Winnemucca Lake, where they occur in subordinate masses along 

 the foot-hills, rarely rising to form the more elevated ridges. The time 

 allotted for the examination of this portion of the range would not permit 

 of accurately mapping the granitic outcrops, and, indeed, it would require a 

 very considerable amount of labor to do so, as the formations have been very 

 much disturbed by the outbreaks of diorites and diabase, and still later 

 nearly concealed beneath immense flows of rhyolite and basalt. 



Three or four miles southeast from the mouth of the Truckee River, 

 at the extreme southern end of the lake, occurs a large body of the older 

 granites, which is well exposed by a deep canon cutting through the hills. 

 One variety of this granite, an exceedingly dense, tough rock, is made up 

 almost exclusively of quartz and feldspar, with but little mica, and may be 

 classed as an aplitic granite. The quartz appears in small translucent 

 grains. Flesh-red orthoclase is the prevailing feldspar, while the observed 

 plagioclase crystals are usually very minute. Mica occurs, somewhat 

 segregated in thin laminae, as muscovite. Another variety of granite 

 from the same region is of some special interest, as it belongs to that 

 class of rocks which have been designated as Archaean, yet in many points 

 differs lithologically from the granite just described. It is a medium- 

 grained rock, with a decidedly crumbling textxire, breaking with a rough 

 uneven surface in irregular-shaped pieces. The constituent minerals 

 develop no observable law in their mode of arrangement, while the rock 

 is made up of quartz, feldspar, and mica in the proportions usually found 



