356 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



siilpliides, cassiterite, and such fluor-b earing silicates as topaz 

 will be deposited. Furthermore, if boron and oxide of iron are 

 also present, as is almost universally the case, we shall have 

 schorl in addition.*' 



It may, however, be remarked here that neither high 

 temperatures nor great pressure seem to be absolutely necessary 

 in all cases for the solution, transference, and re-deposition of 

 tin oxide, for there is reason to believe that slightly alkaline 

 waters under ordinary conditions of temperature and pressure 

 are capable of slowly dissolving oxide of tin. In this way in 

 recent times deer's horns appear to have been impregnated 

 by circulating stanniferous solutions with oxide of tin.f 

 Again, admitting the necessary dissolving power in the 

 circulating solutions, we are still confronted with a difficulty in 

 the existence of immense masses of sulphide ores, so characteristic 

 of several of our mining districts, as was recently pointed out 

 by Sir Warington Smyth. The solutions would by hypothesis 

 dissolve such sulphides as actually existed in the country rock 

 at the sides of the deposits. Bu.t this does not meet all the 

 conditions. Sandberger urges that the ores are derived from 

 original silicates contained in the country rocks, |' and especially 

 in granite, gneiss, and eruptive rocks generally. § Granting all 

 that he says for this wide-spread source of the metallic 

 components, the question very naturally arises "whence comes 

 the sulphur if not from deep-seated sources or (deep-seated) 

 thermal waters ?" Von Sandberger appears to admit, at least 

 tacitly, a deep-seated source for sulphur, arsenic, &c , and if 

 so, there seems no reason to deny a similar possible origin for 

 much of the metallic substance found in the veins, even 

 though portions of similar substance may have been derived 

 from the country rocks. Our former Vice-president goes 



* The part played by fluorine in kaolinization and in the formation of tin 

 deposits have been particularly studied by Von Buch {Min. Tasch., 1824), Daubree 

 {Ann. des Mines, 181-1), Collins {Cornish Tinstones, S(c, Min. Ma§., 1878). 



fSee Trans. Roy. Geol. Soc. Corn., x, p. 98, Cornish Tin-stones and Tin 

 Ca'pels, PI. xii, fig. 4. 



JStelzner's contention that the silver, &c. found by Sandberger did not really 

 exist in the silicates, but in disseminated pyrites, has been met by Sandberger in 

 his later essays. But this does not affect our present discussion. 



§ In Cornwall, generally, only in acidic rocks of the granite type, scarcely at 

 fill in the basic eruptive rocks. 



