SALMON ON THE KoRMA'l'ION DP ORE-VEINS. 
3G3 
ouicr edges and upper crusts. In consequence of which the heavier 
and more fusible particles (in comparison to the rest of the mass) 
which were not chemically combined, had time to sink to the 
bottom, somewhat as in our blast-farnaces ; and this may be the 
reason why the great masses of the eruptive rocks contain rich 
metallic mixtures in the highest degTee at their 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 having 
time to sink down, 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 gTanulit 
oftener contain metallic particles, particularly magnetic-iron ore and 
pyrites, than those great 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 their cooling may have supervened more quicldy. 
The smaller masses, or stocks, of granitic rocks are particularly 
distinguished by containing tin-ore. This ore, as well as its usual 
companion, wolfram, lies partly finely distributed in the mass of the 
rock (granite, gTcisen, porphyiy,) and partly crystallized out into 
fine reticulated contraction-fissures, wliich were probably generated 
by cooling before the constituents were all solidified. Quartz, 
chlorite, mica, and tourmaline are crystallized out vdth 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 eraptive or injective, that is, penetrated into the fissures of the 
former solidified or of the neighbouring rock, they could then form 
