a 
< 
NIPIGON LAKE ROOKS. 339 
Bell has shown, northward from the last two of these bays, in a broad belt, 
spreading from the Nipigon River to some twenty miles west of the Black 
Sturgeon River. According to Bell’ the rocks of this belt are chiefly the 
red sandstones and marls above referred to, with an overlying mass of ‘black 
trap,” similar to the olivine-gabbro already described as overlying red marl 
at the mouth of Nipigon River. Still farther north the western half of the 
basin of Lake Nipigon is described by the same geologist as occupied by 
rocks which he assigns to the Keweenaw Series, and which he regards as a 
direct continuation northward of those of the valley of the Black Sturgeon 
River. The rocks thus assigned by Bell are stated to be chiefly “black trap,” 
at times coarse, and again fine; but also to include “ brick-red porphyry,” 
sandstone, “argillites,” “ felsite,” and green and gray limestones. 
The ‘“ black trap” is nearly everywhere the only rock seen. Much of 
it is evidently coarse olivine-gabbro. It is described as only occasionally 
showing distinct bedding, but when it does so as lying sometimes at high 
angles to the east or west, though often as more nearly horizontal. It was 
seen both plainly interbedded with sandstone, and then generally standing 
at a high angle, and also apparently overlying all the rocks of the region. 
The red porphyry is described as presenting itself in one principal exposure 
on the east side of Lake Nipigon, where 
the lake shore and the islands from the Hudson Bay Company’s farm at Nipigon House 
to English Bay, a distance of three miles, are occupied by a brick-red porphyry, com- 
posed of crystalline red orthoclase feldspar, with grains of translucent quartz, inclos- 
ing finer stratified patches of the same color, and others of white quartz. It also holds 
spots of a soft green earthy mineral, and small cavities lined with crystals of feldspar.? 
This porphyry evidently belongs to my group of augite-syenites and 
granitic porphyries. 
The sandstone is met with at several points on the east side of Lake 
Nipigon, where it is ‘‘rather fine-grained, hard, and quartzose,” and flanks 
the granite, and strikes northward with the shore, dipping eastward at an 
angle of 15° at one place, and at another westward into the lake at an 
angle of 80°. Trap, either in the form of beds or great dykes, is asso- 
ciated with it. 
1 Report of the Geological Survey of Canada, for 1867-69, p. 338. 
2Op. cit., p. 348. 
