174 DESCRIPTIVE GEOLOGY. 



occasional grains of rounded quartz, with white, decomposed feldspars, and 

 considerable amounts of black mica and hornblende, in a grayish felsitic 

 groundmass, and mineralogically belongs rather to the basic group of 

 trachytes of Camel Peak. Singularly enough, however, the very summit 

 of the peak is made up of a white porous rock, which has all the character- 

 istics of a rhyolite, consisting mainly of grains of free quartz and crystals of 

 sanidin-feldspar in a white, porous, felsitic groundmass. In it the micro- 

 scope detects no plagioclase, hornblende, or biotite. Some of the quartz 

 crystals of this rock are seen to contain very perfect dihexahedral fluid-inclu- 

 sions containing a moving bubble. Fluid-inclusions occur also in the feld- 

 spars. As this is the only occurrence of a rhyolite found in this region, and 

 its external habit is not essentially different from that of the trachytes around 

 it, it has been considered merely a local deviation, and not designated by a 

 special color. 



The prominence of this peak and its peculiar shape have rendered 

 it a point of attraction for the summer thunder-storms, which collect 

 in these hills from the open country to the west, and the loose rock, 

 which forms its top, shows shallow trench-like gullies, radiating out from 

 the cairn on the summit, made by the passage of the electric fluid. A sin- 

 gular result of the action of lightning was observed in a tin can, which had 

 been placed on the end of a pole at the very highest point of the peak by 

 some of the early explorers. When found by us, this can, which had been 

 thrown, to the ground, was found to be perforated with twenty or thirty 

 holes, some as much as a quarter of an inch in diameter, whose rounded 

 edges showed that the iron had been completely melted by the heat gen- 

 erated by the passage of the electric fluid. 



At the eastern base of Hantz Peak is an open mountain-valley, having 

 a considerable extent of meadow-land, to the east of which, in contact with 

 the Archaean rocks, was a small development of bright-red sandstones rest- 

 ing directly on the Archaean schists and gneisses, which have been referred 

 to the Triassic, though it was impossible to detect any outcrops of the 

 overlying Jurassic limestones. 



The Little Snake River, which rises in the hills bordering these 

 meadows, runs for a distance of about 15 miles in a northwesterly direction, 



