UNCONFORMITY OF THE SOUTH RANGE. 203 
sition are present also. Some of the feldspars show no banding, and may 
be orthoclase. The red porphyritic and pseud-amygdaloidal feldspars are 
orthoclase. The rock appears to be a uralitic diabase, somewhat allied to 
the rock found in sections 26 and 27 of T. 37, R. 17 W., and sections 23 and 
28 of T. 37, R. 16 W., in the Saint Croix River district of Wisconsin, though 
without the epidote. It should probably be placed with the uralitic ortho- 
clase-bearing gabbros. It cannot be regarded as certain that the Silver 
Mountain rock is Keweenawan. It may possibly be Huronian, though the 
probabilities are greatly in favor of the former supposition. 
In the 8. E. 4 of Sec. 1, T. 46, R. 39 W., the Ontonagon River makes 
heavy falls—90 feet in six leaps—over diabase and diabase-amygdaloid, 
which rocks appear also largely in a low ridge east and west of the stream. 
Both in the hand specimen and under the microscope these rocks are 
indistinguishable from many of the finer-grained diabases and amygdaloids 
of Keweenaw Point. The massive portions are dark-gray and minutely 
crystalline; the amygdaloids have a brownish matrix, and in the specimens 
brought away show epidote, orthoclase, prehnite and chlorite in the amyg- 
dules. 
The exposures on the west branch of the Ontonagon, in the northwest 
part of T. 46, R. 41 W., are of especial interest on account of the evidence 
they offer in proof of unconformity between the Eastern Sandstone and 
the Keweenawan. The exposures at this place are shown in the accompany- 
ing figure (Fig. 3.) The sandstone is horizontally bedded, showing in a 
south-facing cliff 60 feet high and 350 feet long. It is reddish, very coarse, 
and composed almost entirely of rounded grains of quartz. One hundred 
paces from the foot of this cliff are reddish schists, trending northeast and 
dipping 45° to 60° SE. Seven hundred paces northeast, near the south- 
east corner of section 11, is a small ledge of a dark-brown, weathered, 
medium-grained diabase, of a Keweenawan type, while beginning in the 
northeast part of the same section, and running thence westward through 
sections 9 and 10, and terminating in the 8. E. 4, Sec. 5, is a series of exposures 
of a fine-grained, greenish-gray diabase pseud-amygdaloid, with chlorite 
pseud-amygdules. 
The relation of the rocks of the South Range to those of the Ke- 
