SALMON — ON THE roUMATION OP ORE-VEINS. 
391 
III. Baryto and Fluor-spar Avitli Galena, and some other ores, dis- 
posed in very regular layers. Predominates north of Freiberg. 
The order in which these combinations are given is also, at the same 
time, that of their relative age, and from this we can easily under- 
stand how the oldest combination is characterized by quartz and 
fragments of the neighboming rocks, while the newest is marked by 
a particularly regular layer-like form. 
According to our theory, the Freiberger ore-veins are due to the 
porpliyry-eruptions. The eruptive force opened fissures from time 
to time, during a long period ; and through these fissures water, 
perhaps sea-water, penetrating to a great depth, found in the still- 
heated deeply -lying porphyry-masses (which at Freiberg only pene- 
trate to the surface in isolated dykes) those earths and metals which 
are soluble under a high pressui-e at a high temperature and with the 
co-operation of alcalies ; and which it (the ^^'atcl•) then subsequently 
deposited in its circulation through the upper and colder regions of 
the fissures. Of the earths, silicic acid, when dissolved in great 
quantities, crystalhzed again at a very high temperature. For this 
reason, it fills principally the oldest fissm'es, or foi'ms the oldest por- 
tions in newer ones, or in those which, occupying a medium position 
in the whole vein-region, preserved longest a very high temperature. 
The other minerals followed it more or less periodically, according to 
their capacities for reduction or solidification, which certainly cannot 
as yet be specially authenticated, although G. Bischofi" has already 
done much with reference to it. The depositions in the fissures en- 
sued at first very energetically and under continued distui-bances, 
whence arises their breccia-foim and the massiveness of their con- 
tents ; while later, with a decreasing temperatm-e and less dis- 
turbances, and with slower deposition, the layer-like form gradually 
made its appearance. Vapour- and gas-streams may have occurred 
later, in place of the slow continuous circulation of water, and accu- 
mulated in drusy cavities or more recent sublimation-clefts, or, by a 
change in existing contents, have introduced metamorpliism and 
translocation. But as, according to this theoiy, the deep-lying 
poi-phyry-masses are the original bearers of the contents of the Frei- 
berg ore-veins, it should incite us to a further investigation, which 
might besides be important in a practical point of view. 
