Most of what we know as present-day North America was underwater during the Precambrian. Later, limestones, sandstones, and shales were deposited on top of the Precambrian deposits, as North America was periodically covered by shallow seas or received sediments from higher ground. Several continental collisions pushed Precambrian basement rocks up, exposing them in mountainous regions like the Rockies and the Appalachians, as well as in the Canadian Shield (throughout Wisconsin, Minnesota, Michigan, New York, and East Central Canada). However, Precambrian rocks underlie the majority of North America today.
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