1874.] Copper Mines of Lake Superior. 165 ° 
greatest lateral.development, and beds of conglomerate, 
melephyre, and compact sandstone, with the same dip and 
strike, stretch from shore to shore. ‘Thence, as they curve 
round in a south-westerly direction, the range diminishes in 
width. Some of the first mines opened were on the west 
coast of the promontory, where, for nearly 30 miles, members 
of the copper-bearing series form the shore wall. 
Here the most productive group of mines is on a system 
of fissure veins, which cut the rocks of the northern range 
at right angles to their strike. The Cliff Mine, the first of 
the lake mines to pay a dividend, and which, from first to 
last, has distributed nearly 2,280,000 dols. among its share- 
holders, is on a vein which, though not generally wide, was 
often filled with mass copper. The copper was associated 
with quartz, calc spar, and other vein stones. ‘The contents 
of the fissure exhibited a banded structure, and was 
influenced markedly by the country rock. In this district, 
likewise, copper was mined from a bed of amygdaloidal trap, 
here known as the ash bed, and work was also done on con- 
glomerate beds; but, if we except Copper Falls and the 
_ Phenix Mines, the operations on the fissure veins alone have 
been financially successful. 
While the Cliff Mine near the point of the promontory 
was the first to prove that the native copper is more than a 
mineralogical curiosity, the Minnesota, near the south- 
western end of the range in the Ontanogan district, became 
even more famous from the enormous masses of copper it 
produced. Here, likewise, the copper occurs in veins which, 
though running with the strata, are palpably subsequent 
formations consisting chiefly of quartz, calc spar, and 
laumonite. The vein stone is different from the enclosing 
rock, the walls are well-defined and often grooved. Inthe 
Minnesota, the masses were not only large, but frequently 
threw off branches into the enclosing rock, which interfered 
with their being detached in the usual manner by removing 
the country rock adjacent. The prosperity of the mine 
ceased after the extraction of a mass of go per cent copper, 
weighing 525 tons, in 1857. No mines here are flourishing 
at present, nor does there seem to be a like revival of 
mining industry to what is taking place in the Keweenah 
Point distriét on the ash bed, under the infection of the 
successful development of certain beds near Portage Lake. 
Portage Lake and River extend so nearly across the 
promontory at about 60 miles from its point that a canal 
less than three miles long suffices to give water communica- 
tion between the east and west shores. The lake is 
VOL. V. (N.S.) Y 
