Depositional Contact: Angular Unconformity at Siccar Point, Scotland

Besides the fact that this is the spot where, in 1788, James Hutton figured out that Earth is mind-bogglingly old, this photo demonstrates a key feature about depositional contacts. All of them, with the exception of buttress unconformities, are surfaces that are parallel to the younger rocks. The younger rocks are deposited on the surface, so they are parallel. Parallel. Parallel.

But notice the small buttress unconformity between the prominent sandstone rib on the left and the overlying rock.

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