ORE DEPOSIT THEORIES. 249 
investigator, entitled “The Origin of Certain Auriferous 
Lodes,” and also to the extraordinarily destructive criticism 
of Sandberger’s theories by A. W. Stelzner.* 
On the other hand, it must be admitted that the absence 
of the metals in the wall-rock, although constituting a dis- 
proof of the old lateral secretion theory, does not amount 
to a disproof of the modern meteoric theory, for the latter 
does not rely exclusively on the rocks in the immediate 
vicinity of the deposit to furnish the metallic contents. If 
the meteoric theory has an extended application in the case 
of ore-bearing fissure veins, it follows, from the nature of the 
case, that direct evidence must be wanting in many indi- 
vidual cases. 
The definite proof of either the plutonic or thé meteoric 
theory in the case of some fissure-veins being impossible, it 
remains for us to decide which is the most probable. Per- 
sonally, I think there can be no doubt that the plutonic 
theory has by far the more general application. For, in the 
case of the plutonic theory, there are certain fissure-veins 
of which there is definite proof of a plutonic origin; and 
these deposits in numerous cases have been shown to pass 
over into other types, of which there is no direct evidence of 
a plutonic origin. Moreover, the causes of variation, which 
have been proved to be real causes in the case of fissure 
veins of known plutonic origin, are sufficient to account for 
most of the variations which we meet with in veins for 
which we have no direct proof of plutonic origin. 
In the case of the meteoric theory, on the other hand, 
with the exception of a few highly-specialised types, like the 
hydrosiliceous nickel veins of New Caledonia and the zeo- 
litic copper deposits (including fissure-veins) of the Lake 
Superior district, we know of no deep-seated ore bearing 
fissure-veins which have certainly obtained their metallic 
contents through the leaching action of meteoric waters. 
It is true that we are compelled to theoretically admit 
that circulation of meteoric waters must take place 
through all rocks which are not in a condition of “ flowage.”’ 
But this need not by any means amount to an admission 
that this circulation is effective in leaching out the minute 
metallic contents of rocks. 
It is here, I think, that the weak point lies in the general 
application of the meteoric theory. All experience in deep 
mines goes to prove the practical impermeability of rocks 
Ye (2) Die Lateralsecretionstheorie u. ihre Bedeutung fiir das. 
Pribramer Gebiet. B.u. H. Jahrbuch der K. K. Bergakademie, 
Xxxvu. Bd., 1889. Beitrage zur Entstehung der Freiberger 
Bleierze und der Erzgebirgischen La a Y Aiea 8 Ca 
1896, p. 377-412. 
