THE COMSTOCK LODE. 37 



SECTION II. 



STEUCTUEE or THE COMSTOCK LODE Iff PET ATT.. 



The Comstock lode lies at the base of the Mount Davidson group and 

 occupies, during the middle of its course, aline of contact between the syenite 

 mass and the propylites which have overflowed it. North of Ophir ravine it 

 is walled upon both sides by propylite ; south of the Gold Hill Divide, at a 

 point somewhere in the Exchequer claim, it also leaves the syenite and is 

 carried southward chiefly in propylite, but touching indistinctly the older 

 metamorphic rocks upon its west side. Its course is about north 25° east, or 

 a little east of the magnetic meridian. In Seven-Mile Canon, near the base 

 of Cedar Hill, is the most northern known portion of the lode. From that 

 point it continues south in a nearly direct line, underneath Virginia City, 

 across the divide, past Gold Hill to American Flat, where the wide-depressed 

 area has produced conditions unfavorable to further development. Upon this 

 entire length are located a series of mining claims occupying the lode for 

 22,000 feet. 



In point of geological time, the system of fissures which constitutes the 

 Comstock lode are subsequent to the propylite outflow, and belong, in all pro- 

 bability, to the dynamical disturbance connected with the eruptions of ande- 

 site. It is considered certain that the whole series of volcanic outbursts are 

 since the Miocene epoch, and we may safely call the Comstock a Tertiary lode. 

 (For evidence of the Post-Miocene age of the volcanic family the reader is 

 referred to Baron Richthofen's memoir on volcanic rocks, and to the chapter on 

 the Tertiary period in the first volume of this series.) It is by no means a 

 single crack which has been subsequently filled with mineral material, but 

 forms a connected group of fissures whose structural outlines are quite simple, 

 but whose details produce a complexity almost unknown in metal veins. 



Extensive explorations, reaching to a depth of 1,200 feet, have facilitated 

 to a wonderful degree the study of this immense lode ; and although certain 

 minor conditions are even yet obscure, there are data for intelligent compre- 



