368 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
On Hat Point again, at the east side of Portage Bay, the slates are 
finely exposed on both sides of the point, where they are gray to black 
argillaceous quartz-slates, marked by thin lines of lamination, and strongly 
jointed by cross-joints. Cutting the slate on the east side of the point, 
where the dip is nearer 15° than 10° 8. E., are several east and west dikes. 
One of these, twenty feet wide, is of a black rock, which under the micro- 
scope resembles the rock of the dike back of Grand Portage village, but is 
coarser in grain. It is distinctly an orthoclase-gabbro. The body of Hat 
Point, however, is formed by what may be a great dike, though it seems to 
be an immense overlying mass, upwards of 300 feet thick, of a medium- 
grained to coarse-grained, very highly crystalline, light-gray olivine-gabbro. 
Thin sections of this rock show very abundant olivines of large size—up 
to two-tenths of an inch across—and extraordinarily fresh, they being only 
here and there crossed by brown ocherous bands. The other ingredients 
are greatly predominant and very fresh anorthite, the usual titaniferous 
magnetite, and sparse diallage. _In the gabbro are included irregular 
blotches of darker-colored rock, which in the thin section are seen to be 
almost or quite without the olivine, and to have the diallage relatively very 
abundant. The Hat Point gabbro is not to be distinguished in the thin 
section from the similar olivinitic rocks of the Bad River region of Wis- 
consin and of the Cloquet River of Minnesota. I have already suggested 
the possibility of the two belonging to a corresponding horizon, or rather 
to the same general time of outflow. At the end of Hat Point the over- 
lying gabbro mass sinks to the water’s edge, and the whole appearance is 
that of slight discordance to the underlying slate. 
Hat Point forms the west side of Wauswaugoning Bay. All around 
the head of the bay are bold cliffs of slate, and of the gabbro of a great 
dike. At the east side of Wauswaugoning Bay are immense exposures of 
slate and cutting dike masses. Here the slates are often hard, dense, sharp- 
edged, ringing quartzites, in layers one inch to six and even eight inches in 
thickness. These hard kinds are interbedded with more slaty kinds, some 
of which are lustrous, dark-gray to black clay-slates, and others quartz- 
schists, in which the quartzose and argillaceous portions are mingled in 
various proportions. Some of these slaty layers are indistinguishable from 
