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:
“Men expect too much, do too little,
Put the contraption before the accomplishment,
Lack skill of the interior mind
To fashion dignity with shapes of air.
Luxury, yes but not elegance!”
—Allen Tate (1899–1979)
“Do you know I believe that [William Jennings] Bryan will force his nomination on the Democrats again. I believe he will either do this by advocating Prohibition, or else he will run on a Prohibition platform independent of the Democrats. But you will see that the year before the election he will organize a mammoth lecture tour and will make Prohibition the leading note of every address.”
—William Howard Taft (1857–1930)