384 
which we call a metalliferous lode, is filled with ore, or the 
contrary, according to the character of the rock through 
which it passes. Thus, a vein passing through a silicious 
rock will be small, and will contain but little lead ore ; perhaps 
none will occur as it passes through the argillaceous beds, 
but it will be found to have formed in great abundance in the 
limestones. See Fig. 4. 
a a and b b represent respectively the sandstone and 
argillaceous strata, and c the limestone, in which the metal- 
liferous ore is always found in the greatest abundance ; v v 
showing the course and character of the vein. 
My experience does not enable me to speak with any 
certainty upon the effect of an alteration in the line of 
direction of the lead lodes of the north of England ; but, as 
far as the copper lodes of Cornwall are concerned, I have 
positive evidence of chemical changes being produced by an 
alteration in the direction of the lode after it has been 
formed. I have examined several mineral veins which were 
originally filled with the ordinary copper pyrites, a sulphuret 
of copper, combined with a sulphuret of iron ; these have, 
by a shifting of the ground, beeft moved more or less from 
their first direction. 
The portion moved invariably undergoes a change. The 
main original direction of a lode is indicated by the line a 
and b in Fig. 5 ; but by a disturbance or movement of the 
ground to the left of the line d d, the direction of that portion 
of the lode has been changed from N.E. and S.W. to E. and 
W. nearly. Now the E. and W. portion of the lode will be 
found to be converted into the grey sulphuret of copper, and 
to be surrounded by masses of the peroxide of iron, arising 
from the decomposition of the iron pyrites. 
The electricity developed by mineral veins has been 
investigated by Mr. R. W. Fox, Mr. William Jery Henwood, 
Mr. J. A. Phillips, and myself. The results, in all cases, 
