80 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
between the acidic and basic half-glassy rocks, just as the orthoclase gab- 
bros do between the basic and acid granular rocks. 
As typical localities for the rocks of this class may be mentioned, for 
the more distinctly crystalline kinds, Beds 45, 65 and 66 of Marvine’s Eagle 
River section, Keweenaw Point;* for the kinds highly porphyritic with red 
feldspars, but without much non-polarizing matter in the base, the porphyry 
at the Duluth elevator, Duluth, Minn.; for the black and dark-gray kinds, 
with much non-polarizing matrix, the south shore of Michipicoten Island; 
and for the red aphanitic and brown aphanitic kinds, the north shore of 
Lake Superior, one mile below the mouth of Silver creek, N. E. 4, Sec. 22, 
T. 53, R. 10 W., and the bay above the Great Palisades, on the same coast. 
1Geological Survey of Michigan, Vol. I, Part II, Chapter VIII. 
