Shales at a coast. Shale is a sedimentary rock formed by the compression of deposits of clay and mud. It forms in horizontal beds. These beds have been uplifted by powerful geological forces, resulting in their steep angle. These shales were laid down in the Ordovician period, which lasted from 488 to 443 million years ago. Photographed at Clarach, Aberystwyth, Wales, UK.
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