THEORIES OF ORE DTSPOSTTTON HTSTORrCALLY OOXSTDKKED. 315 



considered that the material of veins. ori<i"inally the same a^- the 

 inclosing rock, had been altered by some saline solution and thus pre- 

 pared for its final transformation into metallic minerals. The above. 

 Avhich might be called conversion theories, do not necessarily assume 

 that veins are mechanically formed cracks, and hence of more recent 

 formation than the inclosing rocks. 



Von Trebra. a director of mines who was seeking for facts to aid in 

 their exploitation, thought the changes observed in mountains took 

 phxw slowly -under the influence of heat and humidity, and expressed 

 his idea of conversion as applied to veins more distinctly as the taking 

 awa}' of one constituent of a rock and replacing it by another. The 

 agent of the transformation he called putrefaction or fermentation, 

 by which names he wished to designate some unknown force which 

 produced the chemical changes obserA'ed in the rocks. 



Lehmann, a mineralogist and also a director of mines, supposed that 

 the veins found in mines are only the branches and twigs of an 

 immense trunk that extends to a great depth in the bowels of the 

 earth, where nautre is carrying on the manufacture of the metals, and 

 Avhence they travel toward the surface through rents in the rocks in 

 the form of vapors and exhalations, as the saj:) rises and circulates 

 through plants and trees. This general view is po})nla!' among 

 practical miners e^'en at the present day. probably because it appeals 

 almost exclusively to the imagination. 



Delius, Gerhard, and T^asius had the general idea that \eins were 

 fissures formed hiter than the inclosing rocks, which had been filled 

 by materials l)rought in by circulating waters. The last went so far 

 as to suppose that these waters contained carl)onic acid and other 

 solvents which enabled them to gather up metallic materials in their 

 passage through the rocks. In this respect he approached closely to 

 modern views, but he was in doubt whether the metals were contained 

 in the rocks as such, or whether the solvents ])ossessed the })ower of 

 turning the sul)stances they encountered in one })lace into lead and in 

 another into silver or some other metal. 



Of more permanent value were the works of Von ()p})el ( 17H») and 

 de Charpentier (177.S), who were successively directors of the Saxon 

 mines previous to Werner. 



Von Oppel was the fii'st to distinguish bedded deposits (lager- 

 giinge). or those which lie parallel with the stratification, from true 

 veins. He also gave to the small l)ranches from a main vein the name 

 of "stringers'' (triinnner). and noted that veins sometimes shift or 

 fault the strata they cross, in which case he calls them " shifters " 

 (wechsel). He laid stress on the importance of the causes which have 

 produced rents or fissui'es in the earth, and shows how in the foi'uia- 

 tion of mountains the rocks, being exj)osed to great desiccation and 

 violent shocks, might split one from another, thus producing rents 



