PEEVIOUS mVESTIGATIONS. 17 



Propylite is much more common than syenite. Few large veins are so abun- 

 dant in clay and clayey matter as the Comstock. It forms the western and 

 eastern selvages from north to south in continuous sheets sometimes of from 

 10 to 20 feet in thickness. Other sheets divide horses from quartz, or different 

 bodies of the latter from one another. Most horses terminate at the lower 

 end in clayey substances. The differences mentioned before as prevailing 

 in the quartz of the outcrops continue downward, but are not so conspicuous 

 in depth on account of the general white color of the quartz. Finely dis- 

 seminated particles of wall rock are always abundant where the quartz con- 

 tains ore. The quartz is generally fractured, and at numerous places the 

 effects of dynamical action on it are such as to give it the appearance of 

 crushed sugar. The principal silver ores of the Comstock are stephanite, 

 vitreous silver ore, native silver, and very rich galena. Quartz is the only 

 gangue, though carbonate of lime and gypsum occur in places. Zeolites are 

 limited to the northern portion of the vein, where chabasite and stilbite fill 

 small fissures and cavities in propylitic breccia within the body of the vein. 



The ore is distributed in a different way in the northern and southern 

 parts of the vein. The passage between the two modes of occurrence is 

 gradual. In the northern part the ore is concentrated in elongated lenticular 

 masses, of which the greatest axis is not far from the vertical. The different 

 ore bodies often adjoin each other in such a way as to make a nearly con- 

 tinuous line, as was the case in the Gould d Curry and the Savage mines. 

 The ore has been exceedingly rich in the center of the different bodies, 

 where, at the same time, it was soft and could be easily removed, while the 

 outer parts were hard, and consisted of second-class and low-grade ore. 



Near the center of the Lode, at the Bullion mine, quartz fills the entire 

 width of the vein from the western to the eastern wall, though it is too poor 

 for extraction. The occurrence of ore in chimneys and in barren portions 

 between them ceases in this neighborhood. To the south the ore is concen- 

 trated in continuous sheets, the principal one of which is very near and 

 parallel to the eastern wall. The second sheet occurred farther to the west, 

 extending from the outcroppings to a couple of hundred feet in depth. This 

 sheet dipped to the west at an angle of about 60°, flattening in depth and 

 terminating in horizontal layers of clay. It was particularly rich in gold. 



2 L 



