Laurentia
Interior platform
In eastern and central Canada, much of the stable craton is exposed at the surface as the Canadian Shield; when subsurface extensions are considered, the wider term Laurentian Shield is more common, not least because large parts of the structure extend outside Canada. In the United States, the craton bedrock is covered with sedimentary rocks on the broad interior platform in the Midwest and Great Plains regions and is exposed only in northern Minnesota, Wisconsin, the New York Adirondacks, and the Upper Peninsula of Michigan. The sequence of rocks varies from about 1,000 m to in excess of 6,100 m (3,500–20,000 ft) in thickness. The cratonic rocks are metamorphic or igneous with the overlying sedimentary layers composed mostly of limestones, sandstones, and shales. These sedimentary rocks were largely deposited from 650 to 290 million years ago.
Laurentia-3