86 Copper and Silver of Kewenaw Point, Lake Superior. 
cime and Prehnite also abound, and were formed, without doubt, 
through the igneous agency of the trap on the contents of the 
vein and the ingredients of the wall rock. The spar veins are 
sometimes six feet wide, but their ordinary width is from a few 
inches to three feet. 'They generally traverse the strata at right 
angles to the line of strike, and resemble veins of igneous injec- 
tion. The calc spar is highly crystalline in its structure, and the 
veins are too wide to have been formed by infiltration. If they 
were formed by the washing in of limestone, we would ask where 
the carbonate of lime came from, no limestone being found in 
this region. If the carbonate of lime was deposited as a tufa 
from mineral springs, then it has been since fused into calcareous 
spar by heat under pressure. If injected, then the walls of the 
veins should be silicate of lime, and should bear strong marks of 
fusion, which does not obviously appear. Iam, therefore, still in 
doubt as to the origin of these veins. 
Among the accidental ingredients in the conglomerate, the most 
remarkable is the green hydrous silicate of copper, which has 
long been known to the voyageurs on the lake as the green rock. 
This occurs at Hayes’ Point, at Copper Harbor, and has recently 
been wrought by miners, who have extracted a considerable quan- 
tity of it.* The brown and black siliceous oxides also occur there, 
and are evidently the results of igneous action on the chrysocolla.t 
Black oxide of copper has lately been discovered in the conglo- 
merate at Copper Harbor, at the military post called Fort Wilkins. 
The ore is a vein in the conglomerate, and is fourteen inches wide, 
and has been traced to the distance of fifty feet in length by the 
miners under the direction of Lieut. Ruggles.t Dr. Houghton 
has, I believe, found other veins of this ore in a similar rock, but 
has not yet given an account of the localities. 
* The chrysocolla when free from rock yields from 25 to 30 per cent. of coppery 
but the average of the ore extracted from the mine, when picked as well as it cam 
be for the fatuace, gives but 9 or J0 per cent. 
s brown siliceous oxide contains,— 
Copper, : i é é . 51-08 per cent. 
Silica , ; ; ; 20:00 & 
Oxide of j Oe ; ; ; Lt >, | id 
Oxygen and Water, > ; i 28:12 * 
100-00 
¢ This black we of a yields from 68 to 70 per cent. of copper, wart isa 
very valuable 
