PRINCIPLES CONTROLLING ORE DEPOSITS 73 5 



impossible in the deep-seated zone in which there are no con- 

 tinuous cracks and crevices of considerable size ; hence the 

 hypothesis of the derivation of the metals of the ores from the 

 Barysphere is untenable. Valuable ore bodies have been depos- 

 ited in openings and passages of considerable size and by a 

 vigorous underground circulation. Since the magnitude of open- 

 ings and vigorous circulation are correlative with, and exist only 

 in the upper zone, that of fracture, the ores must have been 

 derived from and deposited in this upper part of the crust of the 

 earth. 



If, then, we admit the fundamental premise, that the majority 

 of ore deposits are the work of underground water, it seems to 

 me that the conclusion cannot be escaped that the metals which 

 are in the ore deposits are immediately derived from an upper 

 zone, probably having a maximum depth of 10,000 meters, or 

 seven or eight miles, in which the circulating waters are vigorous 

 and effective. 



However, I do not assert that now, or at any time in the 

 past, metals for ores have not been derived ultimately from a 

 deeper source through the agency of vulcanism, the medium of 

 transfer being the igneous rocks. We do not know how deep 

 down the igneous rocks which are intruded into the zone of 

 fracture or flow out at the surface of the earth are transformed 

 to magma, if they have not always existed as magma. We do 

 not know very well the process by which the igneous rocks 

 make their way up through the solid rocks of the zone of flowage. 

 We do know, however, that they come from a very considerable 

 depth, and take advantage of openings and cracks and crevices as 

 soon as they reach the zone of fracture. For instance, in the 

 Sierra Nevada, where there are various great sets of joints in the 

 granite — vertical, inclined, and horizontal — the lava coming up 

 from below has wedged itself into these joints, producing sets 

 of parallel dikes. As these joints are utilized by the igneous 

 rocks, so are openings of other kinds where igneous rocks 

 intrude the zone of fracture. Igneous rocks in vast quantities 

 as lava are poured out on the surface or as tuff fall upon it. 



