THEORIES OF ORE DISPOSITION HISTORICALLY (JONSIDKRED. 333 



deposits. This Mas in, one sense a revival of de Beaiiinoiit's theories, 

 l)nt the moileni stan(l|)()int difTei-ed in that the existence of a liquid, 

 molten interioi' of the earth had ))een dis|)r(>ved hy teri'estrial physi- 

 cists. Vo^t held that as no connnnnication conld be established 

 between ore deposits and a heavy interior, they ninst have been 

 deri\'ed from a crust, say. 10. -J;'), or 50 kilometers in thickness, and in 

 great measure the r(>snlt of ei-iiptive ])i'ocesses within that crust. 



Ennnons (in 181)8) acknowledged the importance of the magmatic 

 concentrations of metals in eruptive rock, but thought that in most 

 cases such accumuhitions must have l)een further concentrated in 

 order to produce economically valuable ore deposits. 



During the second decade the influence of Posepny's paper was 

 felt in an increased adherence among outside geologists and mining 

 engineers to the ascension theorv. Vogt's views received less atten- 

 tion in this country, because for a long time no ore deposits were 

 studied to Avhich they were found to be applical)le. The first case 

 was that of the titaniferous magnetites of the Adirondacks studied 

 by Kemp, who published his results in 1898. 



The year 1900 Avas rendered important in the progi-ess of theo- 

 retical views on ore deposition by the simultaneous appearance of 

 Principles Controlling Deposition of Ores, by Van Hise; Secondary 

 Enrichment, by Emmons and Weed, and Metasomatic Processes, by 

 Lindgren, and by the discussions Avhich they prompted. 



Van Rise's article was a broad, philosophic treatment, based on 

 experimental data, of the whole question of underground circulation 

 as bearing on ore deposition. It wx:)uld be impracticable to give here 

 any complete abstract of his paper, which is probably familiar to 

 most of you. and onlv a brief statement of such points as bear on the 

 general processes heretofore alluded to Avill be attempted. His dis- 

 cussion is practically confined to ore bodies deposited from aqueous 

 solutions, which, he considers, embrace the larger proportion of 

 workable deposits, and he holds that the waters from which these 

 deposits have been made are chiefly of meteoric origin. Their circu- 

 lation is in part descending, in part lateral moving, and in part 

 ascending, and during each of these movements they may take up 

 or deposit metallic minerals according as conditions favor either 

 action. This circulation takes place in openings in rocks, mostly pro- 

 duced by fracture, and hence is confined to the outer portion of the 

 crust, which he has defined as a zone of fracture as distinguished 

 from a deeper zone, that of flowage, where, under accunndated 

 pressure, deformation produces no macroscopic openings. Its gen- 

 eral tendency is to concentrate from the small openings into larger or 

 trunk channels. The deposits from these waters are distinguished- 

 as concentrations (1) from ascending waters alone; (2) from de- 

 scending waters alone, and (3) first from ascending and second from 



