536 POPULAR SCIENCE MONTHLY 



great agent in the formation of ore deposits, geologists are not agreed 

 as to the source of this water, the conditions under which it is most 

 effective, nor the relative importance of its work in ascending and 

 descending movements. 



Eegarding its source, we have those who believe with John Wood- 

 ward, Franz Posepny and C. E. Van Hise that the water in the upper- 

 most layers or outer zone of the earth, including the waters on the 

 surface and in the atmosphere, accomplish the formation of ore by 

 means of a perpetual circulation. From the air it falls on the earth 

 as rain; through crevices and fractures it enters the rocks by reason 

 of its head or the weight of more water on top of it, and finds its way 

 deeper and deeper to the very lowest point where the density of the 

 rocks will permit it to penetrate. Down to this depth, which is 

 theoretically not more than five or six miles, the temperature has been 

 constantly increasing, and the water by reason of this higher tempera- 

 ture has been gaining strength as a solvent and picking up alkalies 

 or acids that enable it to hold even the most difficultly soluble sub- 

 stances in solution. Finding no escape downward, and urged on by 

 cooler and heavier waters above, these saturated solutions begin to 

 move laterally and upward, expanding and becoming of lower specific 

 gravity because of the forced deposition of dissolved material as they 

 become supersaturated. Following the directions of least resistance, 

 these metal carriers reach the surface as hot springs or geysers through 

 fractures caused by earth movements. Gradually the walls of these 

 fractures become coated with vein minerals and ores, until the waters 

 stop flowing or the fracture is healed and a vein is formed. 



Then there are those like Vogt, Spurr, Weed and Kemp, who 

 maintain that the chief source of underground waters is the uncon- 

 solidated magma of molten lava within the earth. These authorities 

 point to the immense volumes of steam emitted from volcanoes; they 

 call attention to the conclusions of European scientists who have 

 decided that many of the hot springs can not be derived from meteoric 

 waters heated and returned to the surface; they remind us that there 

 is so much watery vapor derived from lavas that possibly the oceans 

 themselves were formed from volcanic emissions. They point out the 

 ease with which such waters, thus derived and so heated, could gather 

 metallic substances at great depths and bring them to the places where 

 they are now found. They mention the fact that there is a very general 

 association between the more important mining regions and eruptive 

 rocks; and they raise several serious objections to the premises of the 

 disciples of the meteoric water school. 



On this particular point we shall not dwell further; it is quite 

 probable that both theories contain elements of truth; and that ore 

 deposits have been formed by both magmatic and meteoric reascending 



