OF METALLIFEROUS VEINS IN THE MINES OF CORNWALL. 
405 
which conduct electricity have generally, in this county at least, non-conduct- 
ing substances interposed in the veins between the ore and the surface. Thus 
a brown iron ochre with quartz, & c. named “ gossan” by the miners, is almost 
invariably found resting on copper. Sulphuret of zinc occurs sometimes in the 
same situation, both with regard to copper and lead ; but tin ore, which is a 
non-conductor, is without either, and is mostly found nearer the surface than 
copper. 
Tin veins are usually intersected by those of copper when they do not coin- 
cide in their horizontal direction or underlie ; thus, in this case, the conducting 
veins traverse the non-conducting ones. And when two veins of copper meet 
at opposite angles in descending, they are, I apprehend, generally found to be 
unproductive at and near the place of junction ; but when they unite, proceeding 
downward in the same direction but at different angles, they are commonly 
observed to be enriched. These facts appear curious when regarded in con- 
nection with the opposite currents of electricity in veins having opposite dips. 
There are some districts in this county in which the ore veins have generally 
a north underlie, and in others the south prevails ; and it often happens that 
when lodes occur which deviate from the prevalent underlie of the others, in 
any district, the former are intersected, and sometimes shifted by the latter. 
This is strikingly the case in numerous mines in the parishes of St. Agnes and 
Perran. 
The usual horizontal bearing of the copper and tin veins in our principal 
mining districts, appears to be nearly E. and W., or rather from E.N.E. to 
W.S.W. ; but in others they deviate materially from these directions, sometimes 
to E.S.E. and W.N.W. : indeed, in some places this is the prevailing course 
of the veins of ore. 
When veins containing the sulphuret of silver occur, (which as I have before 
stated is a non-conductor of electricity,) they are generally found nearly at 
right angles to the copper and tin veins, and seem thus to assume in great 
measure the character of cross veins of quartz, clay, &c. 
With respect to the two latter, it has been observed that when they shift the 
ore veins, there is frequently to be found in them scattered stones of ore, or a 
small vein of it, or “leader” (to use a mining term), between the dislocated 
parts of the lode. This is also the case often with slides ; so that, although 
