THE COMSTOCK LODE. 35 



is a considerable amount of sanidin in its composition, but far less tlian of 

 oligoclase. Fragments of this earlier trachyte are found embedded in the 

 breccia which immediately succeeded it. These breccias form the majority 

 of the whole outflow. They are of an extremely rough, open texture, fre- 

 quently scoriaceous, like volcanic products, and of unlimited variety of texture 

 and form. They contain angular blocks of both sanidin and oligoclase- 

 trachytes, varying in size from a mere pebble to blocks twenty feet in diameter. 

 These breccias may be seen in the neighborhood of the Gould and Curry 

 mill, and they form the greater part of the abrupt eastern slope from the pass 

 between Mount Rose and Mount Emma. They weather in large cavernous 

 forms, and the heavy included rock-masses which are constantly liberated by 

 the crumbling paste fall to the base of the eastern slope. 



Capping the breccias is a broad, thick overflow of normal sanidin-trachyte, 

 varying in thickness from 100 to 1000 feet. It is of a dull pink color, 

 weathering deep salmon and almost brick-red ; it is composed chiefly of sani- 

 din and brown magnesian mica. The crystals of the former average about 

 the size of a pea; they are not of the most vitreous form of the sanidin but 

 rather unusually opaque, are fissured in every direction, and frequently the 

 disjointed halves of the same crystal appear embedded in the paste, side by 

 side. 



North of the Six-Mile Canon road, and below the Gould and Curry mill, 

 there is a very fine exposure of the hornblende variety. It is a lilac-colored 

 paste, surrounding well-defined needles of hornblende, crystals of oligoclase of 

 minute size, and occasional bits of sanidin. This is the most compact and 

 dense of all the family. The Sugar Loaf is composed of a similar base, in 

 which, however, mica replaces the hornblende, its magnesian contents impart- 

 ing an olive-brown hue to the whole rock. Accidental minerals in this ques- 

 tionable variety are carbonate of lime, rare specimens of glassy quartz, and 

 a zeolitic mineral, which appears to be natrolite. 



On the south slope of the Sugar Loaf were found several considerable 

 masses of granite, rounded boulders of which were embedded in trachyte. 

 This is a frequent occurrence in other parts of the Great Basin, although 

 we never find them in either the propylite or basaltic family. 



Near the Gould and Curry mill is a quarry from which the foundations 



