DISTRIBUTION OF THE KEWEENAW SERIES. 25 
there is an extension for a short distance into the west side of the valley of 
the Upper Mississippi. The bottom of the lake itself is, throughout most of 
its extent, composed of these rocks, as are also the immediate shores, for a 
great part of the lake’s circumference. In much of its course around the 
lake basin this group does not reach many miles inland, in some places occu- 
pying only projecting headlands, the older rocks forming the intervening 
shores. Towards the west end of the lake, however, in the stretch across 
the state of Wisconsin, there is a very wide surface-spread, the area in Wis- 
consin alone being about five thousand square miles. 
To convey a more definite idea of their distribution in the circuit about 
Lake Superior, it may be said that, besides underlying the greater part of 
the lake, the Keweenawan rocks form the larger part of Keweenaw 
Point, probably also underlying the horizontal sandstone of the remainder; 
constitute the Michigan shore from Keweenaw Point to the Montreal River, 
extending back into the country 8 to 20 miles; in all probability underlie 
the sandstone country still further away from the lake, since they appear 
again in a few places on its southern edge, which would carry them inland 
from the Michigan shore as much as 30 to 35 miles; underlie all of north- 
ern Wisconsin north of a line from the Montreal River at a point 15 miles 
from Lake Superior to Numakagon Lake, and thence to Saint Croix Falls, 
or the west boundary of the state; stretch in Minnesota over two-thirds of 
the triangular area included between the state boundary, the Saint Croix 
River, and the Saint Paul and Duluth Railway; constitute the entire Minne- 
sota shore of the lake, from Duluth to Grand Portage Bay, running back 
into the interior about midway in the coast as much as 30 miles; make up 
the outer ones of the Lucille group of islands off Pigeon Point, and the 
whole of Isle Royale; form the entire peninsula between Black and Nipi- 
gon bays, with all outlying islands, and also the whole group of islands, 
large and small, south of Nipigon Bay; spread over a very wide area in 
the valleys of Black-Sturgeon and Nipigon rivers, north of Lake Superior; 
after a long interval, during which older rocks only appear on the coast, 
come up again in Michipicoten Island, which they entirely compose ; ap- 
pear again on the east coast of the lake at Cape Choyye, Cape Gargantua, 
Pointe aux Mines, Mamainse, Batchewanung Bay, and Gros Cap—at nearly 
