296 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
on the west line of See. 28, T. 51, R. 13 W. Itshows labradorite, orthoclase, 
pale-greenish-brown augite—often in twinned blades—titaniferous mag- 
netite, apatite and a good deal of secondary quartz. The next rock noted 
was half a mile up stream at the 40-foot fall, which is somewhere near the 
southern part of Sec. 11, T. 62, R. 2 W. These falls are over a very fine- 
grained, grayish-brown rock, resembling the predominant gray diabases of 
the Duluth Group. There are strong appearances here of a southern dip at 
an angle between 10° and 15°. Above these falls for three-fourths of a 
mile the river is expanded into a lake; then comes another fall over the 
same compact, gray rock, which is exposed also above the falls on a large 
scale. The thin section of a specimen taken from the bed of the river above 
the falls bears out completely the external resemblance to the Duluth gray 
diabases. For a mile above this fall the river is again a lake, at whose 
upper end are again exposures of a fine-grained, gray to black rock, with 
luster-mottlings one-eighth inch across. 
The prevalence among the rocks of the upper Cascade of fine-grained 
diabases closely resembling those near Duluth and Lester River; the occur- 
rence among them also of quartz-porphyry, coarse-grained black gabbro, 
and of the peculiar orthoclase-gabbro with augite twins; the nearly com- 
plete absence, so far as observed, of amygdaloids; the geographical posi- 
tions of the exposures with regard to the older rocks about Brulé Lake and 
Eagle Mountain, and the newer ones on the lake coast—all combine to 
render it highly probable that we have here to do with the eastern exten- 
sions of the Lester River and Duluth groups. 
The exposures at the eastern end of the Minnesota coast between the 
base of the Beaver Bay Group and the Animikie slates are unfortunately 
not continuous, having between them long beaches. The base of the 
Beaver Bay Group intersects the shore about six miles above Portage Bay 
Island. Below here for about a mile were observed numerous exposures of 
a very dense brown, conchoidally fracturing rock, which is plainly bedded, 
and dips 8° to 10° south, with a due east and west trend, the rock appear- 
ing in a series of eastward projecting points, which make an angle with the 
lake shore of about 45°. The layers are distinctly columnar, and are often 
much shattered by close jointing, which in places is almost like a slaty 
