484 On Mineral and Metallic Veins. 



wire; how they became alternately barren and productive, and 

 why their contents are always found in these tissures, and never 

 on the general surface, where, under such an origin we might 

 have expected to find them, no man has yet ventured to say. 



As to the theory of the igneous origin of the contents of many 

 metallic veins, we see much to recommend in it, and we should 

 have been surprised at the assertion of Mr. McCulloch, in his 

 late work called a System of Geology,* that " the argument from 

 the analogy of trap and granite veins is one of those superficial 

 resemblances, consisting in words, rather than ideas, which it is 

 painful to find in the writings of those who have been philoso- 

 phers in other things," if we had not reason to suppose, from a 

 rapid perusal we have now for the first time had an opportunity 

 of giving that work, that the author was really and truly de- 

 mented, run a muck, we may say, and at war with good sense, 

 decency, and honesty, when he wrote it. We shall take an early 

 opportunity of making good what we say. — That the contents 

 of veins have been brought into their places by the agency of 

 more than one cause, is very probable ; but we know of no 

 agency that recommends itself so plausibly as that of the igneous 

 theory, for the origin of all compact metallic masses. We refer 

 for striking instances of this, to the compact iron ore of Danne- 

 mora, in Sweden, which is one hundred and eighty feet thick, 

 and to those extraordinary, and hitherto little known masses W 

 crystalline iron, found in immense fissures, in the primary rocks 

 of Franklin county, New York, and in some parts of New 

 Jersey, all of which clearly indicate a subterranean and igneous 

 origin. If masses of pure metallic iron can be thus produced 

 from below, we know not why metals should not be brought, in 

 like manner, into smaller fissures, or veins. Gold and silver are 

 occasionally found in porphyry and sienite, which are volcanic 

 rocks. Native copper is found in trap and porphvry. Lead 

 and zinc have also been found in it. The elvan courses of Corn- 

 wall are porphyritic felspar, in which tin is diffused. It is true 

 that earthy minerals are sometimes found associated with me- 

 tallic njasses having this origin ; but infiltration takes place in 

 all rocks, and especially in vesicular traps and amygdaloids. 

 Those botroidal chalcedonies found in the copper lodes of Corn- 

 wall, are the produce of infiltration, from silicum in solution. 

 Vol. I. p. 391. 



