242 On Mineral Veins. 
of fluor and cale spar had been removed from a whole series 
of veins, and replaced by an equal quantity of quartz. 
The deposit of metallic ores and metals in the veins has — 
been ascribed to various causes, of which the principal are— 
lst. Injection of the ore or metal into the vein in a molten 
state. 
2nd. Deposition in the veins by the sublimation of sub- 
stances driven by heat from beneath upwards. 
ord. Deposition of ores from solutions in water, brought 
from below. 
Ath. Deposition or rather aggregation in the veins of ores 
or metals derived from the bounding rocks. 
The three first theories are founded on the opinion that 
the metallic ores and metals found in the veins are derived 
from some deposit situate at an unknown depth below the 
surface of the earth. The fourth that they have been derived 
from the rocks bounding or immediately contiguous to the 
vein, and have been aggregated in the latter in the same 
way and by the same power which has collected the other 
mineral constituents of the vein. 
The first supposition assumes that the ores and metals have 
formed a portion of some molten mass, and have been 
injected into the veins. It is hardly necessary to dwell on 
this theory, the conditions under which the sulphides, car- 
bonates and oxides of the different metals are found render- 
ing it impossible that they can have been deposited in a 
melted state, while the peculiar arborescent and crystalline 
form of the native metals in veins—so completely different 
from the rounded figure which melted metals assume— and 
their frequent presence as fine flakes like gilding in the 
cleavage planes of the rock adjoining the veins, afford sufii- 
cient proof that they have not been deposited in this 
state. 
The second theory is more probable, inasmuch as some of 
the metallic ores can be formed by sublimation—a_ fact 
proved by their occasional presence in the flues of smelting 
furnaces—yet to render this theory possible it must be 
assumed that molten masses of ore exist in the interior of 
the earth; or rather, as there are several metals usually 
found in each vein, there must be a corresponding number of 
melted parcels of the different ores, and these must each 
have communication with the vein. But there are many — 
productive veins which do not penetrate far from the surface, 
and the flat veins of the diorite dykes and the mountain 
