OF METALLIFEROUS VEINS IN THE MINES OF CORNWALL. 
403 
All the conductors of galvanic electricity were so likewise of common elec- 
tricity ; to which may be added the oxide of tin, and, in a less degree, the sul- 
phurets of bismuth and silver, the phosphate of manganese, and a few of the 
oxides. Sulphuret of zinc appeared to be a more perfect non-conductor of 
common electricity as well as the sulphuret of antimony, than the red oxides 
of those metals. 
Amongst the rocks prevalent in Cornwall, clay-slate or “ killas” seemed to 
possess the property of conducting common electricity in a slight degree, but 
only in the direction of its cleavage, perhaps owing to the moisture it retained. 
I mention these facts in some detail, because it is curious to observe that the 
conducting power of metallic ores appears to have no reference to any of the 
electrical or other properties of the metals in a pure state, or to the proportion 
of them in combination. Silver and mercury, for example, are combined with, 
comparatively, very small quantities of sulphur ; — and zinc, which seems to 
hold an opposite place to silver in the electrical scale, is also found in combi- 
nation with a much less proportion of sulphur than is contained in copper 
pyrites, though the latter is one of the best mineral conductors of electricity. 
There are many other analogous examples, which prove that no conclusion 
can be drawn a priori, from the nature or chemical arrangements of minerals, 
as to their relative electrical properties. 
Much time and attention have been bestowed by geologists on the conside- 
ration of the origin and comparative ages of veins, and but little, I apprehend, 
on the purposes for which they are designed. 
It appears to me that it will prove a vain attempt to reconcile a multitude 
of facts observable in our mines with any known natural causes. 
I may refer to a few of them : — 
1st. The very oblique descent of a large proportion of the veins into the 
earth, in some cases in very hard rock, and in others in ground so soft that 
it would immediately fall in, however small the excavation, without being 
completely supported by timber. Were it possible to conceive fissures to exist 
under such circumstances, it is not reasonable to suppose that they would not 
take the direction in which the resistance would be least, that is, either the 
vertical, or the line of the cleavage of the rocks. 
2nd. Veins are often divided into branches, which unite again at a consider- 
