CHAPTERS 
EXTENT AND GENERAL NATURE OF THE KEWEENAW 
SERIES. 
General statement as to the scope of the term Keweenawan.—General statement as to the geographical 
extent of the series.—More detailed description of its extent.—Extent of the series underneath 
the waters of Lake Superior.—Its entire geographical extent in square miles.—Constancy of its 
general characteristics.—Basie crystalline rocks.—Detrital rocks. —Porphyry-conglomerates.— 
Other conglomerates.—Sandstones.—Source of the pebbles of the porphyry-conglomerates now 
found in the original acid rocks of the series itself.—General characteristics of these original acid 
rocks.—Recapitulation. 
That my statements as to the geographical extent of the Keweenawan 
rocks may be understood, it is necessary to say at the outset that I exclude 
from the Keweenaw Series the slaty rocks of the region of Thunder Bay 
and Pigeon River—the so-called ‘‘Lower Group” of Logan, and Animikie 
Group of Hunt. The nature and general relations of these slates are dis- 
cussed on a subsequent page. It should also be stated that I include in the 
Keweenaw Series the white and red dolomitic sandstones with accom- 
panying crystalline rocks, which are so largely developed in the peninsula 
between Black and Thunder bays, and stretch thence a long distance north- 
ward in the valleys of the Black-Sturgeon and Nipigon rivers, and occupy 
a large area about Lake Nipigon. Again, I exclude the horizontal sand- 
stones which form the South Shore east of Béte Grise Bay, on Keweenaw 
Point, and westward from Clinton Point, in Wisconsin, to Fond du Lae, in 
Minnesota. The Keweenaw or copper-bearing series, then, as considered 
in the following pages, is made to include only the succession of interbedded 
“traps,” amygdaloids, felsitic porphyries, porphyry-conglomerates, and sand- 
stones, and the conformably overlying thick sandstone, as typically devel- 
oped in the region of Keweenaw Point and Portage Lake on the south shore 
of Lake Superior. 
The series of rocks under consideration is almost entirely restricted to 
the Lake Superior basin, whose limits it passes only at the southwest, where 
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