73 
+ 8 e masses 
of black oxyd of copper brought from the mine at Copper Har- 
: bor, Mr. J. E: Teschemacher discovered regular cubic crystals of 
“some have supposed. A pure specimen analyzed in my labora- 
_ tory yielded 79-86 per cent. of copper. 
_ or hydrous green silicate of copper, and the black silicate, whigh 
contains a less proportion of water. These ores, we can easil 
conceive, might be produced by the decomposition of a solution 
of copper by the action of a hot solution of lime. The black 
oxyd may have been derived either from a solution, or from igne- 
ous sublimation. We know that black oxyd of copper is sub- 
limed from the crater of Vesuvius, and is deposited in fine splend- 
ent scales like specular iron ore in the lavas. 
Chlorid of copper is very volatile, and is sublimed in the crater 
of Vesuvius. It is also known to be volatilized in the blast fur- 
nace. The experiments of Mr. Frederick W. Davis, at the Point 
Shirley copper works, have fully demonstrated the fact that a 
considerable proportion of copper is lost by sublimation from cop- 
per ore, containing the chlorid of that metal. 
These facts may at some future day serve to explain some of 
the phenomena relating to the formation of metallic veins. At 
_ present there is no part of geological science so little understood 
as the theory of veins, and on this account I am desifous of call- 
ing the attention of the Section to this subject. 
With respect to the age of the red sandstone of Lake Superior, 
I would remark that there have been and still are differences of 
opinion. No distinct fossils having been found in it, the usual 
_ index for fixing the geological age of stratified rocks is wanting. 
_ #rom the mineralogical character and the geological associa- 
tions of the rocks, their parallelism to those of Nova Scotia, an 
their mineral contents, I was led in 1844, to suggest the identity 
of the two formations, as contemporaneous, and regarded the 
e Superior sandstone as the new red, or at least as of the same 
. age with that of Nova Scotia, New Jersey and Connecticut. This 
} idea I still favor. 
: _ During the last year the linear surveyors, who were engaged 
F In subdividing townships on the southern portion of Keweenaw 
Point, discovered a large protruding mass of Silurian limestone, 
aro which the sandstone strata are horizontal. y assist- 
ant was sent to examine this limestone, and states that its 
Strata lines dip about 30°. .A fragment of a fossil, probably a 
Pen rus, was also found in the limestone. *’ These facts would 
Seconp Serres, Vol. X, No. 28.—July, 1850. 10 
* 
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* 
be 29 
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hae ie es i : te z ae 
There are also found at the Copper Harbor mine, chrysocolla, : 
i ihe 
