184 GEOLOGY OF THE COMSTOCK LODE. 



known to flow in such a manner, and these only under exceptional condi- 

 tions, for even basalt commonly accumulates in large masses around the 

 orifices from which it issues; nor am I aware of any distinct evidence that 

 the granitoid rocks have ever flowed like a lava, or reached a higher degree 

 of fluidity than the plastic state. 



Energy displayed in the fault on the Comstock. We liaVC nO meaUS of reduclug tO 



known units the pressure and resultant friction which accompanied the 

 faulting action on the Comstock, but the imagination at least may be 

 brought to bear upon the subject by considering the amount of disloca- 

 tion. If the west country is supposed to have revolved about a distant 

 fixed fulcrum, through a sufficient angle to account for its present relative 

 elevation, then the east country must have been pushed bodily eastward for 

 a distance of 2,150 feet. The maps and sections show that certainly not 

 less than a cubic mile of rock must have been thus driven out of place in 

 spite of all opposition, and the amount of horizontal dislocation involved is 

 not lessened by supposing the west country to have moved instead of the 

 east. Compared with the energy necessary to produce such a movement, 

 that requisite merely to raise each of the sheets composing the mass, in 

 opposition to friction through a mean distance of about 150 feet, certainly 

 seems small. 



Dynamical theory of sheets. — I havc showu that the tcudeucy of the faulting 

 movement is to separate sheets of rock, and that sheets thus separated will 

 arrange themselves along the logarithmic curve when divided from the 

 mass. The possibility thus presented does not conflict with my observa- 

 tions, and I am led to the belief that the sheeted structure of the east and 

 west country is due to the formation of fi'actures parallel to the faulting 

 surface, and that these fractures are the result of faidting under intense 

 lateral pressure. 



Inferences from the fault as to the age of the Lode. SomC light is thrOWn UpOU the age 



of the Comstock as an ore vein by the relations of the fault to the ore, and 

 to the erosion. The " east vein," being a secondary fissure, cannot have 

 formed till faulting had made considerable progress, while the crushed con- 

 dition of the quartz^ and the phenomena attending it show that faulting 



' The evideuce that the "sugary quartz" is really crushed will be given later. 



