SALMON — ON THE FOUMATION OF ORE-VEINS. 
3G7 
must have exercised an influence upon it. But if, on the extingniish- 
ing of the plutonic activity of the v^^hole district the mean tempera- 
ture of each level continued, in consequence of the cooling, to 
deci'ease gradually while these processes of dissolving and vein- 
depositing still continued, it is evident that the zones of unequal 
deposition must descend deeper, and become mixed together pro- 
miscuously. Since we have found that the original inequality of 
temperatiire and the vai'iations existing in the neighbouring rocks 
might give rise to a zone-like distribution of the materials, so the 
result would necessarily become much more complicated by the 
alteration of one of these conditions — temperature. The same 
materials which were deposited at the beginning in the upper levels, 
next the walls of the fissures, as outer bands, would by the con- 
tinued cooling be repeated in deeper regions, in the middle of the 
vein. But the consequences would become yet more complicated, if 
we must assume that in a vein-district all the fissures were not 
opened at the same time, but by degrees, at successive periods, and 
after the process of filling up had already begun ; and further, that 
of those formed at the same time, some became quite filled up before 
others. As there results from a gradual depression of the tempera- 
ture of the whole vein-region a kind of series and succession of suc- 
cessively deposited minerals, so it would happen from the different 
periods of fissure-formation that certain fissures might only contain 
the earliest mineral-deposits, others only the latest, while some 
would ha^'e a very extended succession. Thus, and no otherwise, 
can the so-called vein-formations of distinct districts have originated. 
They are nothing else than the products of unequal stadii of cooling 
of one and the same eruptive or vein-forming process. The frequent 
parallelism and gTouping together of veins of similar formation is 
very easily explained by the circumstance that earthquakes generally 
open moi-e or less parallel fissure-groups. We need only consider 
such a vein-region as a region in which, in the course of a thousand 
years, many fissure-opening disturbances have followed upon each 
other. 
If these so-called vein-formations sometimes show great analogies 
of mineralogical composition and of successive age in very remote 
regions, we need not after this consider them in any way as contem- 
