1058 A TREATISE ON METAMORPHISM. 



level of ground water is only a hypothesis. If such deposits exist, I know 

 of no criteria which have been worked out by which they may be dis- 

 criminated from deposits of aqueous solutions. 



The hypothesis that the vapors of the metals rise with the vapors of 

 water from an unknown source and deposit ore in the openings of the rocks 

 is exceedingly attractive, but it has been seen that where opening's occur in 

 rocks below the level of ground water, the rocks are saturated with aqueous 

 solutions, therefore the locus of the deposition of ores from vapors would be 

 in the belt of weathering. The view that fumarolic and solfataric vapors 

 have deposited ores has been especially prevalent in reference to cinnabar 

 and such easily sublimed deposits. Daubrde has maintained that tin ores are 

 formed by the sublimation of stannic chloride and stannic fluoride and their 

 reaction upon water." For the production of any ore deposit by sublimation 

 in this sense I know no scrap of evidence. 6 In Chapter VI, on "The belt of 

 weathering," it has been seen that where there is fumarolic or solfataric action 

 the rocks are rapidly carbonated, hydrated, and oxidized, the mechanical 

 result being softening' and disintegration. The products are colored yellow 

 or brown by oxide of iron. That metallic ore deposits have been produced 

 in connection with such action remains to be proved. 



It has already been seen that in various recent classifications of ore 

 deposits, which are made mainly upon the basis of agent, there are also 

 introduced contact action and eruptive after-action. In so far as deposits 

 are precipitated from gaseous solutions, whether the solutions be derived 

 jDartly from the intruded and partly from the intrusive rock, or partly 

 from both, they belong in this class rather than in an independent class 

 erected on an entirely different basis and therefore an incongruous element 

 in a scientific classification. 



GROUP B. ORES DEPOSITED BY AQUEOUS SOLUTIONS. 



It has been stated that ores deposited by aqueous solutions are believed 

 to be more important than all others combined. The evidence in favor of 

 this view will not be presented in detail, but a few of the more salient points 

 bearing upon it will be summarized. 



"Daubree, A., Memoir sur le gisement, la constitution, et l'origine des arnas de minerai d'etain: 

 Ann. des Mines, 3d series, vol. 20, 1841, p. 65. 



&This statement is restricted to the metallic ore deposits; it does not apply to deposits of sulphur 

 and similar compounds made in connection with volcanic action, in reference to which I express no 

 opinion. 



