2Q MINESG rSTDFSTEY. 



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defines itself, at times, very well. Its angles are generally quite imperfect, but 

 in the less altered portions of the formation, especially near the summit of the 

 range, the orthoclase is well crystallized. Here it possesses a purely vitreous 

 luster, and is intersected by numerous cracks like the sanidines of the trachyte 

 lavas. The ordinary variety of hornblende is a pale green crystallization, 

 formed of clusters of fibers. Although apparently loosely put together, they 

 are often strangely coherent, and give to the rock its unusual toughness. The 

 prevailing dull green is given to the formation by the hornblende. As occa- 

 sional, although unimportant, minerals occur black and dark-brown, bladed 

 crystals of hornblende, showing on many of their lateral planes an evident 

 striation. These are very brilliant in contrast with the dull earthy luster of 

 the green hornblende. In general, oligoclase takes precedence in perfecting 

 its crystalline form. The specific gravity of the rock is 2.66. The general 

 texture is rough, like that of the trachyte family. The rock is extremely 

 coherent, so that, like the syenites, it breaks with very great difficulty. An 

 unusual variety of texture, and even mineralogical constitution, is embraced 

 within the family which Baron Richthofen has grouped under the name of 

 propylite. In the ordinary nomenclature this Washoe variety would be 

 classed as an oligoclase-hornblende-trachyte. It has an important connection 

 with silver veins, as will be seen by the geographical distribution indicated by 

 Richthofen. 



The prominent silver districts of the Carpathian, and some of those of 

 Mexico occur, either inclosed, or associated with it. In this country we have 

 the Comstock Lode, several of the veins in the Aurora District, some of those 

 in Silver Mountain, and the Moss Lode of Arizona. It is interesting to observe 

 this wide range of association, although it seems improbable that the rock 

 itself is a factor in the production of silver deposits. An analysis of the 

 Washoe propylite shows no trace of silver. 



Its occurrence in the Virginia region is characterized by great varieties 

 of surface form; varieties which depend partly upon differences of origin, and 

 are largely due to the solfataric action which has so generally decomposed it 

 and facilitated aqueous erosion. Back of Middle Hill, just north of Virginia, 

 on an intermediate spur between it and the Ophir Hill, are bold castellated 

 outcrops of hornblendic propylite, very dense, tough, and of ragged, roundish 



