SHOSHONE RANGE. 631 



before becoming perfectly free from sediment. The beds are very soft and 

 friable, split easily into thin fissile plates, and emit a strong odor of clay. 

 Much of the rock, however, shows no trace of bedding through thicknesses 

 of 20 or 30 feet. The material of some of the coarser beds, examined under 

 the microscope, reveals the volcanic nature of the beds, exhibiting particles 

 of qum^tz, fragments of glassy feldspar, and black grains of hornblende or 

 magnetic iron. A number of specimens treated with dilute acid gave no 

 reaction, indicating the absence of soluble carbonates. 



In the beds are frequent bands, seams, or irregular aggregations of 

 chalcedonic material of variegated and beautiful colors, which, withstand- 

 ing atmospheric agencies much better than the friable material, protrude 

 in a marked manner beyond the face of the bluffs. That these beds are of 

 the nature of lacustrine deposits would seem evident, not only from their 

 general appearance, but from the presence of vertebrate remains found 

 exposed in the bluffs. The bones collected were of too fragmentary a 

 nature to admit of specific deteruiination or to throw any light upon the 

 age of the beds. 



As already mentioned, the beds have been referred, like many other 

 similar outcrops, to the Miocene Tertiary. It is evident that the beds are 

 older than the great accumulations of rhyolite which have poured out and 

 concealed them over wide areas. That they have been disturbed and up- 

 turned since their deposition, probably by the intrusion of volcanic rocks, is 

 shown in many localities, and that they underlie unconformably Pliocene 

 strata which are later than the rhyolite masses is equally evident. 



In the extreme northern end of the quartzite body, near the head of 

 Boone Creek, occur one or two local outbursts of propylite. In one instance, 

 near the contact of propylite with the quartzite, a small dike of black vesic- 

 ular basalt was observed, which forlned a limited outflow, superimposed 

 upon both the quartzites and propylites. 



Shoshone Range. — The Shoshone Range, which trends about north 

 25° east, or south 25° west, lies for the greater part within the limit of 

 Map V. The meridian of 114° 55', which forms the eastern boundary of 

 the map, cuts the range at the northern end through the great quartzitic 

 series in the region of Shoshone Peak. This formation, referred to the hori- 



