540 DESCRIPTIVE GEOLOGY. 



proportion of rounded granules of quartz of an amber color, which are 

 fissured into a perfect net-work by minute cracks. Both plagioclase and 

 orthoclase occur, which, according to Zirkel, contain an enormous quantity 

 of half-glassy inclusions. The quartz, on the other hand, contains no inclu- 

 sions at all. It is remarkable that the rock also contains grass-green 

 undichroitic augite and thick magnetite, but no biotite or hornblende. The 

 groundmass is a brownish glass densely filled with both feldspar and augite 

 microlites. This is another interesting instance of the remarkable associa- 

 tion in one rock of free quartz, orthoclase, and augite, and especially so 

 that they are found in. an acid glass. 



Pliocene and Quaternary Formations. — Throughout its whole length, 

 the East Humboldt Range is skirted on the west by Pliocene strata^ extend- 

 ing from the southern limit of the map northward to the Humboldt River. 

 In Huntington Valley, they form a belt varying from one to two miles wide; 

 but from the South Fork of the Humboldt to Trout Creek, the entire valley 

 is filled with these strata, which, in the middle of the valley, are always 

 horizontal, but have a slight dip of deposition along the foot-hills, away from 

 the range, rarely amounting to more than 4° or 5°. These strata doubtless 

 represent a lake-basin which filled the whole Huntington Valley,. and the 

 valley of the South Fork down to the gap, where the latter stream breaks 

 through the Carboniferous limestones of the Elko Range. • 



The Quaternary plain that occupies the depression east of the Hum- 

 boldt Range is divided into two valleys, known as Antelope and Ruby 

 Valleys, separated by a low cross-ridge of limestones and basalts, extending 

 from Spruce Mountain in a northwest direction to the Archaean body of the 

 Humboldt Range. Its highest summit in the region of Spruce Mountain 

 barely rises 600 feet above the valley, while' its western end falls away in 

 low, rounded hills. No fossils were found in the limestone, but there can 

 be little doubt that it belongs to the Wahsatch limestone. The basalts, fine- 

 grained, black rocks, occur, breaking through the limestones in a number of 

 places, and forming the summit for a considerable distance. In the south- 

 west corner of Antelope Valley, between Eagle Lake and the main range, 

 is found a large hot spring, so completely surrounded by the Quaternary 

 deposits that it is difficult to recognize the formation through which it 



