Copper and Silver of Kewenaw Point, Lake Superior. 87 
The most interesting rock on Kewenaw Point is the greenstone 
trap, which is there observed in immense dykes or ranges of hills, 
running in an EK. N. KE. and W.S. W. direction, or nearly parallel 
with the northwestern shore of the peninsula, with a slight cur- 
vature or convexity to the northwest. These trap dykes are 
equalled in extent only by those of Nova Scotia and the eastern 
part of Maine. They pursue the same course as those in Nova 
Scotia and are probably of the same age, and agree with them in 
most of their characters and in many of the included minerals, 
as also in their geological position. The trap rocks of Lake 
Superior pass through the red sandstone and conglomerate rocks, 
and are interfused with them, producing at and near their junction 
avery porous amygdaloid, which is always found at the lower side 
of the dyke where it is next to the sandstone, as is the case also 
in Nova Scotia. 
On Kewenaw Point there are found in this rock very handsome 
agates, which at a place called Agate Harbor, form the pebbly 
beach. Stilbite, Laumonite, analcime, datholite, Prehnite and cal- 
¢areous spar, are among the minerals frequently found in the 
geodes in the amygdaloid. 
Prehnite and datholite also form veins in the trap, which are 
sometimes three or four feet in width, and of considerable extent. 
These veins also include native copper, and not unfrequently the 
individual crystals contain within them delicate leaves of the 
bright metal, not thicker than gold foil, while the whole mass of 
the vein is strung together by filaments of pure copper. The 
principal vein of datholite is situated in the rocks on the westerly 
point of Eagle Harbor, where it has been opened by the miners in 
search for copper. The finest specimens of Prehnite are obtained 
at the company’s vein No. 5, three miles south of Cat Harbor. 
Analcime crystals are — in most of these veins, associated with 
calcareous spar. 
Stilbite and Laumonite occur in the small geodes in the amyg- 
daloid, and although generally disseminated are rarely obtained in 
handsome specimens. Heulandite, which is so abundant in Nova 
Scotia, was not observed in this region. Calcareous spar occurs 
in the form of the dog-tooth variety, and has a great number of 
planes on the angles and edges of the scalene dodecahedron, the 
erystals being the most complicated of any I have seen of the 
same species. Associated with this mineral, crystals of analcime 
