256 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
‘Near the southeast corner of Sec. 32, T. 48, R. 12 W., is the most southern ex- 
posure in the banks of the Aminicon river. There are several between here and the 
crossing of the Superior and Bayfield post-road, a half mile below. The rock is a 
coarse-grained gabbro, composed of red-stained plagioclase, a gray plagioclase, and a 
soft greenish altered (chloritic) diabase, with bright, shining grains of magnetite. 
Below the bridge, a dark-colored, coarse-grained variety occurs, in which the several 
minerals show much less alteration. 
* * * * * * * ¥* * 
‘Near the east and west line, running between Secs. 20 and 29, is the junction of 
the reddish sandstones with the crystalline rocks. For 25 feet only have the sand- 
stones been disturbed. In this distance they are broken into short lengths, and dip 
northwest from the crystalline strata at angles varying from 60° to 20°, after which 
they become horizontal and show two well-marked systems of vertical joints. The 
direction of one system is N. 60° E., and of the other N. and 8S. At the immediate 
line of junction, or where the sandstone is removed from the crystalline rocks but a 
very few inches, the layers of sandstone have a facing of fine conglomerate, from a 
few inches to a foot or more in thickness. The pebbles consist of quartz and melaphyr 
or diabase, and are cemented by sand. The sandstone layers at some distance from 
the junction also contain small pebbles of the adjacent crystalline rocks. The sand- 
stone layers are much softer than usual, uniformly reddish in color, and in thickness - 
vary from 1 to 24 inches. 
Between the Aminicon and Middle rivers there are very few exposures of the 
copper-bearing rocks, and none in Sees. 33 and 34, where we would expect to find 
them. The country is somewhat lower than the remainder of the range, and covered 
with drift. Near the center of See. 4, T. 47, R. 12 W., there are two small exposures 
of fine-grained, blackish diabase, separated by a few rods of drift. Similar rocks are 
again visible in Sec. 3, and along the banks of Middle river, for about a mile in sec- 
tions 2and 35. They are all small exposures. In Sec. 35 the rock is often porphyritic. 
A perfect network of minute laumontite veins occurs at one or two localities. 
* * *¥ * * * * * * 
*Near the south line of Sec. 24, T. 48, R. 12 W., Middle river cuts through the 
northern face of the range, leaving a large surface of the rock exposed. On the south, 
the stream has exposed between 300 and 400 feet of a dark-brown diabase, being in 
places somewhat amygdaloidal. This outcrop is nowhere more than 25 feet in height. 
A hundred yards northwest of it, in the left bank of the stream, is an exposure of 
soft, dark-reddish, much altered and decomposed diabase-amygdaloid, carrying numer- 
ous small veins or “strings” of laumontite and calcite. This rock weathers easily, and 
is rapidly crumbling away. It is very similar to that described as occurring at the 
forks of Copper creek. Some of the small veins of calcite were noticed stained with 
copper carbonate. This rock is found along the stream for 200 feet, is about 50 feet in 
height, and is very indistinctly bedded. On the north it is separated from a south- 
ward-dipping and shaly rock by a gully 30 feet across. 
* * * * * * * * * 
* Near the crystalline rock, the bedding has been entirely obliterated, and the out- 
crop presents the appearance of a bed of shale dipping 79° to the 8. 20° E. The 
layers are from one-sixteenth of an inch to an inch in thickness. All of them contain 
flakes of mica, and the most of the layers are reddish-colored. But thin, hard, light- 
1Geology of Wisconsin, Vol. III, p. 346. 2Do., p. 347. 
