SANDSTONES OF THUNDER BAY. 333 
equivalents of the horizontal sandstones of the South Shore and therefore as 
newer than the Keweenawan, while the latter separates them from the under- 
lying slates, but considers both groups as newer than the Keweenawan. 
The underlying slates, however, I refer, as indicated in the next 
chapter, to the Huronian, while I can have little hesitation in following 
Bell and Logan as to the inferior position of these sandstones to the great 
thickness of unmistakably Keweenawan rocks which constitute Isle Royale, 
the peninsula between Black and Nipigon bays, and the line of islands in 
front of Nipigon Bay. This relation is indicated by the existence of a 
southeasterly dip of from 3° to 10° throughout the peninsula between 
Thunder and Black bays—the higher angle being reached on the Black 
Bay shore—and of the same southeasterly dip along the southeast shore of 
Black Bay, where reddish sandstone and conglomerate may be seen pass- 
ing under typically Keweenawan diabases and amygdaloids. This sand- 
stone and conglomerate seem to be the upward continuation of those on 
the west side of Black Bay. Further evidence is found in the occurrence 
of heavy calcite seams and veins in the sandstone, and of dikes intersecting 
it towards the southeast end of the peninsula west of Black Bay, both 
things unknown in the horizontal sandstone of the South Shore. Yet more 
conclusive than any of these points is the fact, that along the Black Stur- 
geon River and thence westward to the northeast corner of Nipigon Bay, 
red sandstones and marls, which are beyond question the coutinuation of 
those of the west side of Black Bay, are found to be overlain by heavy 
beds of olivine-gabbro. 
According to Bell, the belt of level sandy country which runs from 
the northwest corner of Nipigon Bay westward to the Black Sturgeon River 
is bounded both north and south by “hills of columnar trap” resting upon 
the “indurated red marls and associated rocks.”* 
coarse gabbro to red marl may be beautifully seen on the northwest shore 
of Nipigon Bay, and on both sides of Nipigon Harbor near the Red Rock 
Post of the Hudson’s Bay Company. The overlying rock is medium- 
grained to coarse-grained, white- and black-mottled olivine-gabbro. A sec- 
tion of a specimen from the cliff on the northwest shore of Nipigon Bay, 
just outside of the mouth of Nipigon Harbor, shows under the microscope 
This superposition of 
10p. cit., p. 338. 
