400 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
rocks have been more satisfactorily worked out, though there are many doubt- 
ful minor points, and probably some schistose rocks have been called Huron- 
ian that are not certainly so. However, it seems certain that here we have 
genuine schists interbedded with the older gneiss in such a way as to admit 
of no doubt of their being subordinate to it. Brooks has observed this in 
the Menominee region, and I have found it so in the Penokee region and the 
region of the Wisconsin Valley. In the Wisconsin Valley, in the neighbor- 
hood of Wausau, is found a southwestward extension of the Menominee 
Huronian in the shape of siliceous schist, chert-schist, siliceous lime- 
stone, mica-schist, quartzite, quartz-porphyry and greenstone (including 
diabase, gabbro and peridotite). Genuine hornblendic schists are un- 
known in this region in the Huronian, while they are frequently associated 
with the gneiss. Hornblende-rocks have been heretofore regarded as char- 
acteristic of the Huronian Series. But I have already shown good reason 
for suspecting that all of the so-called diorites, syenites and hornblende- 
rocks of the Marquette and Menominee regions are in all probability but 
uralitic diabases, while the hornblende-schists may be, in part at least, 
altered augitic schists. So far as our present knowledge of the microscopic 
characters of the rocks of the two systems goes, hornblende is very much 
more characteristic of the older gneisses than of the Huronian. 
On the east shore of Lake Superior, Murray, Logan, and Bell have 
described rocks which they refer to the Huronian. To the south of Batch- 
ewanung Bay, for instance, is a large development of rocks which have a 
typical Huronian aspect, and are composed chiefly, according to Macfar- 
lane,’ of pyroxenic greenstones, slates, slate-conglomerates, quartzites, 
and jaspery iron-ores. The rocks are much folded. 
Further north, according to Logan, Huronian rocks are “spread over 
what appears to be a triangular area, extending along the shore from eight to 
nine miles on each side of Michipicoten River, at the mouth, and about the 
same distance up the stream. A little further west it presents a very narrow 
strip running about twelve miles along the coast, and another one of eight 
miles about five miles south from Otter Head.”? 
‘Geological Survey of Canada, Report of Progress, 1863-1866, p. 123. 
? Geology of Canada, 1863, p. 63. See general geological map of the Lake Superior region, accom- 
panying this memoir. 
