SALMON — ON THE FORMATION OF ORE-VEINS 
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 ourselve to them, since they 
challenge fiii'ther 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 gi'ounds 
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 gi'auwacke 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 occiuTence is equally rare 
in ti'achji:ic, 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 Foumet 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 
