On Mineral Veins. 243 
limestone formation, could not have obtained their ores in 
this way, for there is no passage or communication to 
connect them with the hypothetical deep storehouse. Most 
veins are also saturated with water, the quantity increasing 
with the depth, and it is difficult to see how the sublimed 
ores could penetrate this water for many thousand feet, 
instead of being deposited as soon as it reached the water, 
which we know always is the case in smelting works. 
Again, in the Derbyshire and north of ‘England mining 
fields, where the veins traverse horizontal beds of limestone, 
sandstone, shale, and basalt, if the ores were deposited by 
sublimation, they would be distributed indifferently through- 
out these beds ; but it is found that the veins only carry ore 
while traversing a certain number of these rocks, while in 
the remainder they are invariably barren. In the mines of 
the silurian formation the same phenomena may be observed. 
A change in the character of the bounding rocks usually 
affects the ore-bearing qualities of the vein, and where the 
latter pass from the schist into the granite there is fre- 
quently a change in the metals aggregated, as from copper 
to tin, or the contrary. 
Similar difficulties have to be overcome in endeavouring 
to apply the third theory. As regards the vertical veins it 
has been suggested that the magnetic condition of some of 
the rocks influences the deposition on them of the ores 
brought from below, and held in solution in the water cir- 
culating in the vein. In the mountain limestone the pro- 
ductive character of many of the beds varies within short 
distances, although constant in a certain area, while no 
perceptible difference can be detected in the character of the 
rock. This is not a convincing refutation, for there may be 
a change in the magnetic condition of the rock without any 
visible alteration in its appearance ; but the difficult 
task still remains of accounting on this hypothesis for the 
filling of the flat and wedge-shaped veins, the deposit of 
minerals in the detached strings of quartz, or for the metallic 
ores intimately incorporated with the rocks. In driving 
levels in the mountain limestone, I have met with small 
cavities in the solid compact rock not connected with any 
fissure or joint, and yet these cavities were filled with galena. 
Copper ores are found disseminated through some of the 
old red sandstone beds in Ireland, and in the so-called capper 
slates of Germany. 
Tin ore is also found so intermixed with the granite 
