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ROCKS OF THE NORTH AND EAST SHORES. 261 
scenic characteristics. Except over short distances between Marquette and 
Keweenaw Bay, on the north shore of Béte Grise Bay, and on the north 
side of Keweenaw Point, the south coast of Lake Superior shows only 
sandstone or conglomerate as the shore rock, while even these rocks are 
absent for fully 200 miles of the distance between Duluth and the Sault, 
counting only those interruptions to rock exposures which are more than 
two or three miles in length. Low cliffs of sandstone are met with at 
several points on the South Shore, but the largest do not exceed 75 feet in 
height. Moreover, except on the eastern part of Keweenaw Point, and in 
the Huron and Porcupine Mountains, there is either no high ground or it is 
so far inland as to have little influence on the scenery of the shore. 
From the head of the lake to Grand Portage Bay, or nearly to the 
national boundary line, a distance of about 150 miles, typical Keweenawan 
strata form the coast. At Grand Portage, slates, with interbedded and 
intersecting diabases and gabbros, rise from beneath the Keweenawan beds. 
These rocks make up the so-called Animikie Group or ‘Lower Division of 
the Copper-Bearing Series,” which I take, however, to be undoubtedly 
Huronian. These slates form Pigeon Point, the north and west sides of 
Thunder Bay, and the islands at its mouth, including Thunder Cape. Isle 
Royale is composed of Keweenawan strata, undoubtedly in part the con- 
tinuation of beds seen on the Minnesota coast. The peninsula between 
Black and Nipigon Bays is composed chiefly of sandstones belonging at the 
base of the Keweenaw Series, while typical Keweenawan diabases, amyg- 
daloids and interbedded sandstones and porphyry-conglomerates, with the 
usual massive porphyries, form the coast and its numerous flanking islands 
from Black Bay to the east end of the Battle Islands, a distance of some 
75 miles. Beyond the Battle Islands the north and east coast is formed 
chiefly of ancient gneisses and crystalline schists, part of which possibly 
belong with the Huronian, although, as indicated in a subsequent chapter, 
this still remains a matter of some doubt. Along the eastern coast, how- 
ever, as far as the Sault, Keweenawan beds form now and then projecting 
headlands—in the case of the Cape of Mamainse reaching a very consid- 
erable development. Michipicoten Island is also made up of the same 
formation. 
