In a perfect competition, there are many buyers and sellers of homogeneous /identical products, and there is no barriers of entry and exit the market.
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On the north american continent, 6 cratonic sequences have been recognized.
More about cratonic sequences:
A complete cycle of marine transgression and regression on a craton (block of continental crust) over geologic time is represented by a cratonic sequence, a very large-scale lithostratigraphic sequence in the rock record. Megasequences, stratigraphic sequences, Sloss sequences, supersequences, or just "sequences" are other names for cratonic sequences.
They are geologic proof that the relative sea level has been transgressing and regressing, depositing different sediment layers onto the craton, which are now expressed as sedimentary rock. The differences between the strata that were deposited throughout time as the ancient environment changed are seen in places like the Grand Canyon as a good visual representation of this process.
Learn more about cratonic sequences here:
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I believe it was called Newfoundland.