THEORIES OF ORE DISPOSITION HISTORICALLY CONSIDERED. 323 



nature as then known. His conchisions are. bi'ieflv : That the metal- 

 lic minerals in veins of incrustation (since called crustification) find 

 their ultimate source in eruptive rocks, from which they emanate at 

 first in gaseous form. As they pass through long canals or fissures, 

 at greater distances from the center of eruption, they must condense 

 and thus form deposits analogous to those of springs at their point 

 of exit. The metals in veins are found united less frequently with 

 oxygen than with certain elements to which the name " mineralizers " 

 has been given, and which are not only volatile themselves, l)ut possess 

 the property of rendering volatile many substances with which they 

 combine. These are sulphur, selenium, arsenic, antimony, ])hos- 

 phorus, tellurium, chlorine, bromine, iodine, etc. 



Mineral sj)rings he divides into principal or hottest thermals, which 

 are fed by gases emanating directly from eruptive masses which reach 

 the surface in a liuid state, and, second, less heated springs, which 

 often accompany the former. The latter are fed by meteoric waters, 

 which descend until they come in contact with hot rocks and, wdien 

 heated, ascend again, in which journey they may be charged with 

 mineral substances. 



Vein deposits may be formed by either class of thermals; the sec- 

 ond class would form deposits not only in ordinary fissures, but also 

 in those already charged by direct emanations. It is difficult to 

 account for the gangue minerals as direct emanations, since the}^ are 

 not volatile except such as are combined with fluorine. Certain 

 deposits without gangue in eruptive rocks and deposits in limestone 

 in contact with eruptive rocks, associated with garnet, ilvaite, and 

 similar minerals, may have been deposited by sublimation, but these 

 are exceptional. P"or most veins he admits, in accord with Bischof, 

 that the earthy minerals must have come from the decom})osition of 

 the country rocks. The greater proportion of true veins (veins of 

 incrustation) he considers to have been formed l)y deposition from 

 AVaters circulating in cracks in the earth's crust. In this, his theory 

 resembles Werner's, but difters from it in assuming that the solutions 

 were ascending rather than descending. Werner's argument in favor 

 of descending waters, namely, that veins beconie poorer in depth, he 

 considers not well fouiuied, the facts of nature rather going to prove 

 that the solutions became weaker as they approached the surface. 



Stanniferous veins, which contain a great number of the rarer ele- 

 ments and are associated with acid rocks, are the type of the first 

 class, while ordinary or ]:)lumbiferous veins, which are characterized 

 by the important role of mineralizers and the absence of anhydrous 

 silicates, are usually associated with basic rocks. 



His reasoning is evidently based largely on his observations iu 

 Cornwall, and on an assumed difference in the origin of granite and 

 of volcanic rocks in general. Granite, he assumes, owes its crystal- 



