Metalliferous Veins. 167 



been formed* from a consideration of volcanic phenomena alone. 

 Here injected veins are of frequent occurrence, and the fissures 

 and rents are doubtless often lined with crystals which may have 

 been sublimed. But will the generalization which has been thus 

 hastily drawn of the analogy of these phenomena to those of 

 metalliferous districts, honestly hold good in the cases before us ? 

 In the universally recognised volcanic rocks, the veins are of 

 very nearly homogeneous texture, whatever be the containing 

 rocks ; and, supplied from a common source, it is natural to 

 expect that they would be so. In our lodes, on the contrary, the 

 contents of the vein change with a change of rock. Mixed, too, 

 as are the ores of copper, zinc, tin, and lead indiscriminately 

 in our veins, with innumerable earthy minerals ; if they were 

 ever presented to each other in a state of fusion, would they not 

 chemically combine? We find, however, no such compounds in 

 our veins. 



The same objections equally apply to the theory of sublimes 

 tion, for the very idea involves a mode of escape. Why, then, 

 have not the volatile mineralizing substances, sulphur, &c. been 

 dissipated ? One would have expected that they would, and if 

 deposited in the veins that they would have separately occupied 

 one portion, the metals, &c. in a pure state, another, and per- 

 haps different situations would have been filled by silica (quartz) 

 and other substances, with which the veins abound. This is 

 certainly as unlike our lodes as it is possible to imagine any- 

 thing. 



We now approach the segregation of Professor Sedgwick, and 

 witfy this, I rather think, I tolerably coincide, presuming that Mr 

 Burr truly interprets it ; for I believe we shall all subscribe 10 

 the truth of the oxide of tin being deposited on the contempora* 

 neous masses and veins of schorl-rock we find tin-ore very ge- 

 nerally accompanying schorl. Indeed, it appears to me little 

 other than the contemporaneity of the veins and rocks. But the 

 Professor considers that he can draw a line of distinction be- 

 tween veins of segratlon and true veins ; he has not, however, 

 done so, and I must confess I doubt his ability to do so in"a man- 

 ner which shall be unobjectionable ; for I have already said I 

 believe the phenomena of the large and the small veins to be 



