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Cliffs of the Black Cows, Auberville, Calvados, France

   Located on France's northwestern coast, in the Normandy region, the Cliffs of the Black Cows (Falaises des Vaches Noires) got their name from sailors who saw the algae covered rocks along the shore and thought they were cows grazing on the beach.  Rather, they are blocks of soft Cretaceous chalk that eroded from the seaside cliff.  Under the chalk lies Jurassic marl that is prone to landslides.  Both rock formations are famous for the Jurassic and Cretaceous age fossils: ammonites, sea  urchins, belemnites, shark teeth, corals, plus plenty of gastropods and bivalves.

   Also on the cliff is a rich deposit of glauconite, the dark green grains in this sample.  This iron mineral formed on the seafloor in a oxygen-starved environment (otherwise it would be red); today it is found below the chalk layer.  It erodes from the cliffs and accumulates on the beach along with fragments of the chalk, and in this sample, a triangular shell fragment.

Base map Eric Gaba  CC BY-SA 4.0

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