Rhaetic Beds

Rhaetic Beds, the name given to the uppermost division of the Trias (q.v.) from its development in the Rhaitic Alps, where it forms a massive group of marine limestones and dolomite, with bands of shale. In Germany they are represented by sandy clays, sandstones, and thin seams of coal, containing ferns, horse-tails (Equisetites), and cycads (Pterophyllum and Zamiies), in addition to the typical marine pelecypods, Avicula contorta, Cardium rhcetieum, Pecten valoniensis, and Puilastra arenicola, the crustacean Estheria, fish, such as Ceratodus, saurians, and the oldest European mammal, Microlestes antiquus. In England these beds form a narrow band'from Lyme Regis to the Yorkshire coast and Carlisle, with an average thickness not exceeding 50 feet, though sometimes 150 feet, and consisting of thin beds of black paper-shales with Avicula contorta, white limestone (White Lias), u, bone-bed containing pyrites, fish bones, coprolites, etc., and grey marls and clays. From their exposure near Cardiff, as also on other Severn cliffs, they are also known as Penarth beds.