262 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



cooler, were forced, relieving the explosive energies of the subsiding volcanism. 

 The water and other vapors, largely given off by the congealing lava below, 

 carried with them, separated and concentrated from the magma, metals of such 

 kind and of such quantities as are present in the veins, together with silica and 

 other materials. 



The nature of the metallic minerals in the veins in this case is believed to 

 depend largely upon the particular magma whence the emanations proceeded. In 

 the chief Tonopah veins this was the earlier andesite. Other factors, such as 

 relative depth, have evidently an important controlling influence. 



