Sie COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
ing N. 60° E. The following are the results of the examination of some: 
thin sections of the rocks from some of these larger dikes. 
The coarse-grained, dark-gray, rough-textured rock from the island in 
the mouth of the south arm of Pigeon Bay shows fresh diallage predomi- 
nating, labradorite, a little titanic magnetite, and a few grains of olivine 
altered to a brownish substance. The rock from the island in the mouth 
of Big Trout Bay is dark-gray, medium-grained to coarse-grained, and 
marked by very large-sized and noticeable luster-mottlings, due to the 
large augites. The thin section shows exceedingly fresh diallage, in rela- 
tively great areas; very fresh anorthite, numbers of crystals of which min- 
eral are often inclosed within the diallages; olivine, often quite fresh, and 
not abundant magnetite. The rock is an exceedingly fresh one, and is very 
close to that of the Greenstone of Keweenaw Point. 
Other dikes, nearly as large as these, are of an orthoclase-bearing gab- 
bro, allied to that occurring in the Keweenaw Series as flows, as, for instance, 
the rock of a broad dike on the north side of Big Trout Bay, in which the 
constituents are orthoclase and oligoclase much reddened and clouded, 
and now and then replaced by secondary quartz; diallage partly fresh and 
partly altered to a greenish substance, and titanic magnetite. Apatite is 
also present, and the whole aspect is much like that of the finer-grained 
Keweenawan orthoclase-gabbro, as, for instance, that of the ledges just 
west of Lester River, and especially that of the Bohemian Mountain, just 
north of Lae la Belle, Keweenaw Point. 
The coarse-grained, light-gray rock from just north of the mouth of 
Pigeon River is another orthoclase-bearing gabbro, in a much fresher con- 
dition and with relatively less orthoclase. Abundant and rather fresh dial- 
lage, labradorite, orthoclase, magnetite, a little secondary quartz, and apa- 
tite are the constituents. This rock is much like the Duluth orthoclase- 
gabbro, except that it is finer in grain. It is a kind nearer than usual to 
the non-orthoclastic gabbros. A pink- and black-mottled rock from Victoria 
Island, which is part of a dike continuing to the northeast through Spar 
and Thompson islands, is at the other extreme. The diallage is relatively 
sparse and wholly altered to uralite. The feldspars are very profoundly 
altered, and largely replaced by secondary quartz, which also is present in 
