182 M. Tuomey on a Copper Mine in Tennessee. 
has been dissolved out. This process, the solution of the ore, is 
constantly, though, of course, slowly going on, as may be seen 
at the works, and hence the very variable thickness of the ore b. 
From portions of the bed every trace of copper has disappeared, 
down toc. The copper ore J, is a bluish black altered sulphuret. 
That the alteration is due to heat is rendered highly probable 
by the vesicular structure of the ore itself, as well as by the 
joints with which it is intersected, and which correspond in 
direction with those of the surrounding rocks of the country. 
In every published account of these mines that I have seen, 
the impression is left, that the ore b is derived from the under- 
lying portion of the bed c, by decomposition. Now ¢ has been 
reached in all the mines, and invariably consists of arsenical iron, 
with rarely more than one per cent. of copper in the form of yel- 
low sulphuret, and consequently could not furnish by decompo- 
sition or any other conceivable process, an ore containing 20 per 
cent. of that metal. 
This lower arsenical iron portion ¢, of the bed is found every- 
where immediately underlying the black ore, at no great distance 
below the surface, and is frequently met with even in the levels 
driven in the hill-side. 
he whole of that portion of the bed above ¢, doubtless once 
consisted of yellow sulphuret of copper, and the part below ¢: 
as at present, of arsenical iron. uring the metamorphism of 
the slates the sulphuret was altered to the black ore, and subse- 
quently the soluble salts derived from this ore, were dissolve 
out by the simple process of leaching, the residual gossan, of 
tron hat being left in the upper portion of the bed, and the still 
unbleached ore, resting on the arsenical iron. 
It is remarkable that this same arsenical iron with a little cop- 
per, is found in some of the shafts sunk, in exploring for copper 
in Alabama. ; 
The solution of the question, What is below the arsenical iron ? 
isa most interesting subject in connection with the value and 
future prospects of the mines, At one place a shaft has been 
sunk in the arsenical iron, to a depth of 10 or 12 fathoms with- 
out showing any encouraging change, and at another a shaft 
has been commenced calculated to cut the bed, 50 fathoms below 
the present level of the mine, or, as it is called in the mining Tre- 
ports, for the purpose of “ proving the yellow sulphuret.” These 
experimental shafts, if continued, will be of the utmost import- 
ance to the whole copper region, including portions of Georgia 
and Alabama. Should this arsenical iron terminate, at a moder- 
ate depth, in the yellow sulphuret, then indeed may Tennessee 
t of such mines as are not found in the history of mining 
