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 exterior must be joined to the interior to obtain anything from God, that is to say, we must kneel, pray with the lips, and so on, in order that proud man, who would not submit himself to God, may be now subject to the creature.”
—Blaise Pascal (1623–1662)
“I marched in with the men afoot; a gallant show they made as they marched up High Street to the depot. Lucy and Mother Webb remained several hours until we left. I saw them watching me as I stood on the platform at the rear of the last car as long as they could see me. Their eyes swam. I kept my emotion under control enough not to melt into tears.”
—Rutherford Birchard Hayes (1822–1893)