SALMON — ON THE FORMATION OF ORE-VEINS. 



363 



onter edges and upper crusts. In consequence of wliicli tlie hea^der 

 and more fusible particles (in comparison to the rest of tlie mass) 

 whicli were not chemically combined, bad time to sink to tbe 

 bottom, somewhat as in our blast-famaces ; and this may be the 

 reason why the great masses of the eruptive rocks contain rich 

 raetalUc mixtm-es in the highest degTee at theu' rapidly-cooled con- 

 tact-edges and upper crust. Similarly, in the small stock- or vein- 

 formed ramifications of great masses the cooling supervened more 

 quickly, so that the metallic particles in them frequently not ha\nng 

 time to sink do^^^l, solidified simultaneously with the mass ; and 

 the same holds good also, in a certain degree, for many of these 

 massive rock-veins which are to be considered as the pressings-up of 

 the still fluid under-regions into the already consolidated upper- 

 parts. In fact, veins of granite in granite, syenite, and granulit 

 oftener contain metalhc particles, particularly magTietic-u'on ore and 

 pyrites, than those gTeat rock-tracts themselves ; so that it is tolerably 

 equal whether they penetrate merely the solidified crust of their 

 mother-rock, or that of the neighbouring rock, only that in the latter 

 case then* cooling may have supervened more quickly. 



The smaller masses, or stocks, of gTanitic rocks are particularly 

 disting-uished by containing tin-ore. This ore, as well as its usual 

 companion, wolfram, lies partly finely distributed in the mass of the 

 rock (granite, greisen, porphyiy,) and partly crj^stallized out into 

 fine reticulated contraction-fissures, which were probably generated 

 by cooling before the constituents were all solidified. Quartz, 

 chlorite, mica, and tourmaline are crystallized out with these ores ; 

 and if these small ore-veins contain, at the same time, here and 

 there, galena, apatite, blende, or asphalt, fluor-spar, iron-spar, arra- 

 gonite, or a second quartz deposition, and stolzite or lead-salts, then 

 these were evidently not formed until afterwards, by sublimation or 

 infiltration, or generated by a partial change of existing constituents. 

 But when the deeper regions of these particularly rich metallic 

 stocks, in which, in spite of the rapid cooling of the surface, still 

 more metallic particles had accumulated than on the superficies, and 

 remained longer fluid on account of their easier fusibility, became 

 again eruptive or injective, that is, penetrated into the fissures of the 

 former solidified or of the neighbouring rock, they could then forai 



