282 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
The rock in Sec. 26, T. 53, R. 11 W., forms a ridge which presents a bold 
cliff to the northwest and a gradual slope to the southeast. Macroscopic- 
ally it is somewhat different from any of the foregoing, presenting a very 
light-gray color, mottled with darker shades, but the thin section shows 
that it is essentially the same rock, and that the differences are due to 
smaller amounts of augite and to the great freshness of the rock. Even 
the very large olivines are unusually fresh, being traversed only by a few 
rifts bordered by a greenish alteration-product. Coarse-grained, rough- 
textured black olivine-gabbro belonging to the Lester River Group forms 
the barrier rock of the falls of Encampment River in the N. E. 4 of See. 10, 
ALI 5 Sy kul OB Ws 
Another kind of coarse-grained rock is presented in the ledges on the 
west line of Sec. 28, T. 54, R.13 W. This is an orthoclase-gabbro, carry- 
ing orthoclase, oligoclase, diallage, augite in long-twinned blades, apatite 
and a good deal of secondary quartz. Externally it is brownish-black and 
resinous-looking from alteration, and peculiar for its long-bladed augite 
crystals. The thin section of this rock is pictured in Figs. 1 and 2 of Plate V. 
The red porphyries of the Lester River Group can be best seen on the 
lake shore both above and below Lester River. The importance of the place 
not being realized at the time, sufficient attention was not given to it to 
determine the relation of these red rocks to those adjoining them. Some 
of the specimens brought away show a medium-grained, highly crystalline 
rock, which in the thin section looks as if it might be a very greatly altered 
orthoclase-gabbro. Quite a little augite, much of which is fresh, is con- 
tained, and the reddened feldspars are filled with secondary quartz. Other 
specimens show a rock more like the granitic porphyry of Duluth, and 
others again are distinctly felsitic porphyries. Even the latter kinds are 
saturated with secondary quartz, and all kinds so much altered that the 
original condition of the matrix is not easy to determine. At one point 
below the mouth of Lester River a coarse, black olivine-gabbro includes 
patches and vein-like bands of the red rock, in this case one of the more 
distinctly crystalline and augite-bearing kinds, while a few rods farther 
along the shore the same red rock forms the whole face of the exposure. 
Some of the bands of red in the black gabbro are only a few inches wide 
