American geography

Geography of the Interior United States

1. The Superior Upland

An outlying upland of the Laurentian highlands of Canada projects into the United States west and south of Lake Superior. This upland, part of the Canadian Shield along with the Adirondacks, is a greatly deformed structure and is composed primarily of igneous and metamorphic crystalline rocks commonly associated with a rugged landscape.

At some ancient period, this had a strong relief, but today the upland as a whole is gently rolling with the inter-streams surfaces being plateau-like in their evenness. Here they have altitudes of 1,400 to 1,600 feet in their higher areas.

The erosion of the region must have been far advanced in ancient times, even practically completed, because the even peneplain surface is overlapped by fossiliferous marine strata from an early geological date, Cambrian. This shows that the depression of the region beneath an ancient sea took place after a long existence as dry land.

Glaciation has strongly scoured away the deeply-weathered soils that presumably existed here in preglacial time. It left behand firm and rugged ledges in the low hills and swells of the ground and spread an irregular drift cover over the lower parts, whereby the drainage is generally disordered being deposited in lakes and swamps and elsewhere rushing down rocky rapids.