370 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
parently bedded just like the slates, and dipping like them, was exposed 
on a large scale. The thin section shows that this rock is the same as that 
from Brick Island, above described. Its relation to the surrounding slates 
is worthy of very careful study. Unfortunately at the time of my visit its 
nature was not realized, and being taken merely as a phase of the slaty 
quartzites around, it was not given any especial attention. It is this red rock 
on Pigeon Point that has caused Foster and Whitney, on Mather’s author- 
ity,' to mark this point as granitic on their large map of the Lake Superior 
region. The Pigeon Point slates maintain a constant lakeward dip at an 
angle of 15° to 20°, and even 25°, the usual trend being more to the north 
than that of the point itself. The high dip along most of the point is note- 
worthy. 
Cutting the slates along the south side of Pigeon Point are a number 
of dikes trending often nearly east and west, and in other cases in a north- 
erly direction. Some of these dikes are composed of the same orthoclase- 
gabbro as that noted in the dikes on Grand Portage and Wauswaugoning 
bays. One dike was observed, however, in which the rock was a fine- 
grained olivine-gabbro, or luster-mottled rock, close to the melaphyrs of 
Pumpelly. It is, in fact, save as to greater fineness of grain, identical with 
the type rock of the Greenstone of Keweenaw Point. On the north side of 
Pigeon Point are clifis of a coarse, light-gray, fresh olivine-gabbro, which 
appear to form a dike of large size through much of the length of the point. 
Following Pigeon River upwards from its mouth, slates and slaty 
quartzites are found all the way to the head of the stream, and beyond to 
Gunflint Lake, on the national boundary line. The general dip of these 
rocks, which have never been examined in detail, is southeast, at an angle 
of some 10°, which would give a thickness of some 10,000 feet for the slate 
series as seen along the national boundary line. Peculiar cherty layers are 
met with at low horizons in the slates, and also banded lean magnetic iron 
ores closely similar to the lean iron ores of the Penokee region of Wisconsin. 
By all the geologists who have traversed this region these slates 
are described as cut by immense numbers of large dikes, which often 
‘Seo large map of Lake Superior, accompanying Foster and Whitney’s Report. 
2Richard Owen, Bell, N. H. Winchell. 
