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:
“The monk in hiding himself from the world becomes not less than himself, not less of a person, but more of a person, more truly and perfectly himself: for his personality and individuality are perfected in their true order, the spiritual, interior order, of union with God, the principle of all perfection.”
—Thomas Merton (1915–1968)
“The use of literature is to afford us a platform whence we may command a view of our present life, a purchase by which we may move it.”
—Ralph Waldo Emerson (1803–1882)