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Part of Hall of Planet Earth.
AMNH/R. Mickens
The sediments that formed both of the Old Red Sandstones were laid down in the same basin during the Devonian Period, about 400 million years ago. Although both samples were deposited around the same time, their surrounding environments were slightly different. Small differences in grain size and in the composition of the materials that cements the grains together account for the coloration and texture of these two rocks.