SALMON ON THE FORMATION OF ORE-YEINS 



361 



Assuming, consequently, this mode of development, I shall now 

 endeavour to throw a passing glance at the peculiar processes of 

 vein-formation in general. In the present state of science of course 

 such an assumption is to a great extent a mere matter of belief; 

 but, believing it, we cannot, although it may be incapable of absolute 

 proof, wholly banish it from science. If we take it only so far as it 

 is supported by facts, and always bear steadily in mind that beyond 

 that it is merely hypothetical, the assumption cannot be productive 

 of disadvantage. On the other hand hypotheses have their use, if 

 we do not absolutely and blindly resign om'selve to them, since they 

 challenge further confirmation, and thereby lead to investigations in 

 definite directions. 



I shall consequently here endeavour to give a general geological 

 explanation of ore-veins, without particularly specifying the grounds 

 upon which it is based. These I shall pre-suppose as generally 

 known and recognized, and shall only in some cases, where I deem 

 it necessary, go into a nearer examination. 



With the exception of some, consisting almost wholly of iron- 

 stone, we find ore-veins pre-eminently in the older rocks. Most 

 frequently in the crystalline schists (gneiss, mica-slate, &c.) ; in 

 ancient eruptive formations, as granite, syenite, greenstone, por- 

 phyry, &c. ; in grauwacke formations ; and as far as the Magnesian- 

 limestone (Zechstein). Rarely, on the other hand, in the newer 

 sedimentary formations ; in such they occur in the Muschelkalk and 

 Lias at Milhau, in the south of France, and in Chili and Algiers in 

 members of the chalk-formation. Their occurrence is equally rare 

 in trachytic, basaltic, or phonolitic rocks. 



Like the old crystalline rock-masses, the veins are in general 

 found in mountain districts, not in plains, and very usually in con- 

 nection with these rocks — granite, greenstone, porphyry, &c., which 

 for the most part are penetrated by them. 



These general facts point to a certain connection between the 

 older eruptive rocks and ore-veins, to which Fournet also, in a trea- 

 tise translated by me, specially directs attention. But the proba- 

 bility of such a co-ordination is much increased by the circumstance 

 that, at least in Germany, the relative age of these eruptive rocks is 

 almost the same as that of the ore-veins, that is, they both belong to 



