280 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Original magnetite and rare and small porphyritic oligoclases complete 
the list of constituents. The rock belongs to Pumpelly’s ashbed type. 
The southeast dip, at 10°, can be plainly made out in this rock at the mouth 
of the river. Ascending Lester River, lower layers come to view. Near 
the middle of the west line of the N. W. 4 of Sec. 4, T. 50, R. 13 W., the 
rock is very fine-grained, of a dark brownish-gray color, and under the 
microscope presents the typical appearance of Pumpelly’s melaphyrs, 
namely, large augites, including numerous tabular plagioclases (oligoclase), 
and with numerous olivines, altered to greenish and brownish substances, 
magnetite, and much red ferrite in the spaces between the augites. Near 
the northwest corner of the section a coarse band is crossed. Next, through 
the greater part of Sec. 33, where the river makes four falls, whose 
height aggregates some 80 feet, the rocks are very dense, dark brownish- 
gray diabases, alternating with red- and dark-green-mottled varieties. These 
are seen in the thin section to be the usual pseud-amygdaloidal diabase, 
holding augite, often fresh, but often altered to a dark-green substance, 
much reddened plagioclase, magnetite, pseud-amygdaloidal chlorite, and 
occasional porphyritic oligoclases. 
In Sees 6 and 7 of T. 51, R. 12 W., French River makes nine falls 
over the rocks of this group, the individual falls running from 6 to 70 feet 
in height. Between these falls the river rushes down an inclined plane 
nearly on the slope of the S. E. dip. The rocks in sight are largely 
fine-grained, rough-textured, luster-mottled kinds, ranging from black to 
bright red in color, according to the amount of secondary peroxide of iron 
present. They are very highly augitic, with much magnetite and olivine 
in minute particles, wholly altered to a green substance, between the augite 
grains. All specimens show rare and small porphyritic oligoclase, and 
there is often pseud-amygdaloidal chlorite. The rock at the falls in the N. 
W. 4 of Sec. 6, beyond which the river was not ascended, is very dense, 
with conchoidal fracture and of a dark-brown to nearly black color. Its 
thin section shows the common characters of this variety, viz, predominant 
plagioclase (oligoclase) in small tabular crystals, and the augite in minute 
rounded particles. One amygdaloid was noticed on French River, near 
the north line of Sec. 7, and 730 steps west from the northeast corner of 
