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.
Read more about this topic: Laurentia
Famous quotes containing the words interior and/or platform:
“Those who sit in a glass house do wrong to throw stones about them; besides, the American glass house is rather thin, it will break easily, and the interior is anything but a gainly sight.”
—Emma Goldman (1869–1940)
“I have rather a strange objection to talking from the back platform of a train.... It changes too often. It moves around and shifts its ground too often. I like a platform that stays put.”
—Woodrow Wilson (1856–1924)