Origin of Quartz and Metalliferous Veins. 225 



come so altered that what had previously produced the stripes 

 occurring next the walls had been wanting in the subse- 

 quently introduced vein-mass. Such an idea in regard to a 

 separation into stripes and layers cannot, however, be enter- 

 tained. At all events, we never find such an arrangement 

 in veins composed of crystalline mountain rocks ; for the 

 constituent parts, as for example, the quartz, felspar, and 

 mica in granite veins, always occur in more or less uniform 

 mixtures. 



Lastly, We cannot at all explain, by means of the penetra- 

 tion of the vein-masses in a melted condition, the entire de- 

 struction of many substances which had been introduced at 

 an earlier period, a fact which is proved by empty spaces left 

 behind. Brown-spar, calcareous-spar, fluor-spar, and heavy- 

 spar, which had once been formed in the veins, would be fused 

 again by means of the newly introduced vein-mass, but could 

 never disappear ; and they must necessarily again present 

 themselves mixed with the newly formed substances. 



Many objections which stand in opposition to the hypo- 

 thesis now under consideration, have less applicability with 

 regard to the sublimation-hypothesis. According to the 

 latter, we can imagine a filling going on simultaneously with 

 the gradual widening of the fissures, a deposition of the 

 sublimed substances in the form of stripes and layers, an 

 enveloping of separate fragments of the adjoining rockj and 

 a disturbance of the regular sequence of the various portions 

 of the vein, without there being any essential alteration of 

 the latter, &c. As, however, it will hardly be attempted 

 to adopt a different mode of formation for the non-metallic 

 vein-masses from that for the metallic vein-masses, and as 

 the substances which off*er the greatest resistance to heat 

 are amongst the number of the former, we already find a 

 great difficulty in reference to this hypothesis. Even if we 

 assign importance to non-volatility only in regard to the 

 earth's surface, and not in respect to those depths where 

 the highest temperatures prevail ; 'yet, nevertheless, it is a 

 well-established law, that it is only the most volatile sub- 

 stances, such^asjwater, which can retain their gaseous form 

 much under^the point of vaporization. Heavy-spar, fluor- 



