310 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
dip, and strong cross-columnar structure. All along here the rock tends to be 
very rich in diallage and consequently dark in color. The diallage is always 
very much coarser than any other ingredient of the rock, inclosing a 
number of the feldspars, which, according to measurement, are always at 
the anorthite end of the series. Some of the diallages are two to three 
inches across, and show a brilliant brassy luster on the cleavage. This was 
noticed in a number of places, but at one point on the N. E. 4 of See. 6 
it was especially noticeable. Here one can walk across a pavement hun- 
dreds of square feet in area, made of the ends of the basaltic columns. .The 
surface is weathered to a general brown hue, but in every direction flashes 
back the sunlight to the eye from the brilliant brassy diallages. 
At several points in this vicinity the black rock was observed to include 
masses of coarse anorthite-rock. The latter did not appear to occur here 
in bowlder-like masses, but rather in large, 
irregularly outlined areas. At one point on 
the shore of See. 6, directly west of the island 
above referred to, the nearly white anorthite- 
rock rises like a dome in the black gabbro 
which is seen above and on both sides of it. 
The southern point of the island is formed of 
anorthite-rock; and due north from this point, 
on the mainland, is another area of white rock, 
OTTO apparently trending north and south. 
aa ch J ert, Ya PI yi g 
SAK wR heat wy 
apn eerie Ee On the shore of Sec. 32, T. 56, R. 7 W., 
ures, Minnesota coast, Sec. 32, T. 56,R. the columnar black rock bows down suddenly 
7 Ww. in the direction of the general trend and disap- 
pears under a mass of a pink granite-like rock which forms a bold point 
much like that of the south side of Beaver Bay. This point projects 
into the lake in a nearly due east direction. On its north side is a bay, 
which is bounded on the north by another wall of red rock, while behind 
and on the beach are exposures as indicated in the following figure. The 
point A forms a vertical wall on the south side of the bay; the red rock of 
which it is composed looks much like that of the south point of Beaver Bay, 
but differs in having a large amount of quite coarse quartz. The thin section 
