The largest known deposits are those in the Lake Superior region, near Keweenaw Point, Michigan, where masses upwards of 400 tons in weight have been discovered.
South and south-east of Keweenaw Bay, in the Marquette iron district, is an irregular area of mountains, hills, swamps and lakes, some of the mountain peaks of the Huron Mountains (in Marquette county) rising to an elevation of 1400 ft.
Extending in a general north-east and south-west direction through Keweenaw peninsula to the Wisconsin border and beyond is the middle of three approximately parallel ranges, separated from each other by flat lands, with here and there an isolated peak (in the Porcupine Mountains) having an elevation of from 900 to 1400 ft.
Next in value among the mineral products is copper; there are about twenty copper mines in Keweenaw peninsula and its vicinity.
Long; Michipicoten Island in the eastern part; St Ignace, in the northern part, off the mouth of the Nipigon River; Grand Island between Pictured Rocks and Marquette; Manitou Island, east of Keweenaw Point, and the Apostle Group, to the north of Chequamegon Bay.
Lake Superior lies in a deep rift in rocks principally of Archean and Cambrian age, of the Laurentian, Huronian and Keweenaw formations, rich in minerals that have been extensively worked.
From the Apostle Islands to the eastward of Keweenaw point this current has great width, and towards the eastern end of the lake spreads out in the shape of a fan, a branch passing to the northward and westward reaching the north coast.