230 Professor Gustav Bischof on tJie Origin of Veins. 



This supposed process has its analogous one at the pre- 

 sent day in the Suffioni of Tuscany. In this case, so large 

 a quantity of the fixed boracic acid is brought up by watery 

 vapour, that it has become an article of commercial im- 

 portance.* Other fixed substances, such as sulphate of lime, 

 alumina, and protoxide of iron, are also detached by means 

 of vapour. 



Although the elucidation of the phenomena of metalli- 

 ferous veins leads us back to Werner's theory of veins, in so 

 far as we are obliged to assume the formation of vein-masses 

 in the moist way, yet there is this essential diff^erence, that, 

 according to Werner, all true veins were almost entirely 

 filled from above downwards, whereas, according to the pre- 

 sent state of the subject, this filling can only be supposed to 

 have taken place from beneath upwards. How^ever, there 

 is no doubt that many fillings of clefts have taken place from 

 above 'downwards or sideways from the adjoining rock. 

 The veins of calcareous-spar in limestone, and most of the 

 small qu£«*tz veins in clay-slate, are certainly of this de- 

 scription. The water charged with lime or silica which 

 penetrated, partly from above, and partly from the sides, into 

 these fissures, and which slowly flowed down the walls of 

 the fissures, precipitated those substances so much the more 

 easily, because the water, during its slow progress, had time 

 enough to evaporate.f 



* According to Payen {Ann, de Chim. et de Phys,, Ser. iii. vol. v. 

 p. 247), 750,000 kilogrammes of crystallized boracic acid are yearly 

 obtained. 



t From Lconhard and Bronn^s Jahrhuch. Jahrgang 1844. Heft Z, 

 p. 257. 



