sedimentary rock
"Sedimentary rocks can be read like a book. Each layer of sedimentary rock is like a chapter in the history of the earth. Remember that sedimentary rocks are always deposited from oldest to youngest, and unless some incredible earth movements (faults and folds) have deformed the sediments, the oldest layer is always going to be on the bottom and the youngest layer is always going to be on the top. "
There are layers of different rock types that are typically deposited vertically over time, like the layers in a cake.
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