228 Professor Gustav Bischof on the 



may be deduced, because there is no want of time in geology. 

 The Carlsbad springs, for example, notwithstanding the very 

 small amount of fluor-spar they contain, nevertheless yield 

 the by no means inconsiderable quantity of 247 German cwt. 

 in the course of the year. If a vein having 1000 feet in 

 length, 1000 feet in depth, and 1 foot in thickness, were to 

 be filled with fluor-spar by means of the hot mineral waters 

 of Carlsbad, then a period of 819,562 years would be re- 

 quisite.* As, however, according to my calculations, founded 

 on the law of the cooling of our earth, about nine millions of 

 years must have elapsed since the formation of the carbonifer- 

 ous series, a million of years will not be thought too much to 

 allow for the filling of a vein of fluor-spar of the supposed 

 dimensions. 



Lastly, as to the manner in which the circulation of watery 

 solutions may be conceived to have taken place in vein- 

 fissures, we are naturally, first of all, led to think of the 

 analogy with our springs rising from beneath. Just as our 

 mineral waters bring to the surface enormous quantities of 

 salts, so could they at earlier periods have carried along with 

 them substances of a diff'erent description.! We do not 



* The mean quantity of silver in the Mexican ores amounts, accord- 

 ing to Garces (von Humboldt, in Karsten's Archiv,, vol. xvii. p. 328), to 

 2l oz. per cwt., therefore ^^y. If we leave out of consideration the other 

 component parts of the metalliferous mass, and assume that the silver is 

 simply disseminated in the principal vein-stone, the quartz, then the 

 relative quantities of the quartz and the silver would be 666 : 1. The 

 springs which are richest in silica (the hot springs of Iceland excepted) 

 contain of it about txs^tj^ > these 666 parts of silica would therefore re- 

 quire 6660000 parts of water for their solution. It is only necessary 

 for us therefore to find a watery solution capable of dissolving ^ibb^^ ot^tj of 

 silver, perhaps in the state of sulphuret ; and the possibility would then 

 be shewn of supposing that the silver of the Mexican ores was intro- 

 duced along with silica in the moist way into the vein-fissures. Such a 

 degree of difficulty in dissolving a substance, as it is beyond the bounds 

 of the reaction of our most delicate tests, would be regarded as insolu- 

 bility in our laboratories. 



t There is also another analogous case presented by the fact, that just 

 as we find calc-sinter and iron ochre in the form of deposits from springs, 

 so in many districts not yet opened up by mining operations, rich ores 

 are met with on the surface of the soil. Thus the mines of Gualgoya 



