THEOllIES OF OUE DISPOSITION II ISTOKICALLV CONSIDERED. 328 



iiadii'c as llioii known. His conclusions sire, briefly: That the metal- 

 lic Miincrals in veins of incrustation (since called crust ilicat ion) find 

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

 first in gaseous form. As they pass thi'ouirh long canals or fissures, 

 at greater distances from the center of eru|)tion, 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 fre([uently with 

 oxygen than with certain elements to which the name '' miueralizers '' 

 has heeii gi\en. and which are not only volatile themselves, but possess 

 the property of rendering vohitile many substances with which they 

 combine. These are sidphur, selenium, arsenic, antimony, phos- 

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



Mineral springs he divides into principal or hottest tliermals, which 

 are fed by gases emanating directl}' from eruptive masses which reach 

 the surface in a fluid 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, Avhen 

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

 mineral substances. 



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

 ond class would form deposits not onlj^ 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 they are 

 not volatile except such as are combined watli 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. For most veins he admits, in accord Avith Bischof, 

 that the earthy minerals must have come from the decomposition of 

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

 incrustation) he considers to have been formed by deposition from 

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

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

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

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

 considers not well founded, 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 plumbiferous veins, which are characterized 

 by the important role of miueralizers and the absence of anhydrous 

 silicates, are usually associated with basic rocks. 



His reasoning is evidently based largely on his observations in 

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

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



