Interior Platform
In eastern and central Canada, much of the stable craton is exposed at the surface as the Canadian Shield; when sub-surface 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 of the interior platform except in northern Minnesota, Wisconsin, the Adirondacks of New York and the Upper Peninsula of Michigan. The sequence of rocks varies from approximately 1,000 to in excess of 6,100 metres (3,500–20,000 ft) in thickness. The cratonic rocks are metamorphic and igneous, while the overlying sedimentary rocks are composed mostly of limestones, sandstones, and shales. These sedimentary rocks were deposited from 650 to 290 million years ago.
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