2 5 6 



HISTORY OF PROPYLITE. 



Relation of Propylite to Silver. Propylite is frequently as- 

 sociated with veins of silver, as in the Carpathian mountains, and 

 more strikingly in North America. It forms one of the walls of the 

 famous Comstock lode. It is connected with silver veins in the 

 Aurora district, with some of those in Silver Mountain, with 

 the Moss lode of Arizona, and with the silver veins of some parts 

 of Mexico. 



Propylite of the Virginia Mountains. Propylite is a widely 

 distributed rock in the United States, and is met with in the form of 

 tuffs as well as in solid rock. The most important outburst de- 

 scribed by Clarence King occurs in the higher part of the Virginia 

 range, and extends from Pyramid Lake on the south to the Sierra 

 Nevada. Before the propylite was erupted the Virginia mountains 

 consisted of slates, limestones, schists and quartzites, disturbed by 

 intrusive granite. Great masses of diorite had already burst through 

 these, and formed the highest peaks, such as Mount Davidson. Then 

 the propylite was thrown out from fissures, which run in the direction 

 of the range, and extend from the summit of the range to its base 

 on both sides. On the south and east the propylite flood ran to 

 Carson Plain, and on the west to Steamboat Valley ; and only the 

 highest portions of the diorite peaks were lifted above the products 

 of this outburst. The eruption was intermittent, and the material 

 was ejected in a viscous condition. The first outbursts were of 

 olive-green propylite, crystalline and porphyritic. The second, on 

 the north and south of Mount Davidson in Washoe, is a propylitic 

 breccia enclosed in an ordinary propylitic matrix. The third out- 



1 U. S. Geol. Surv., Fortieth Parallel, vol. i. p. 560 ; Table VIII. 



