THE ORDOVICIAN ROCKS IN THE CAUTLEY AND DENT DISTRICTS OF WESTMORLAND AND YORKSHIRE

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Abstract
Summary: The Ordovician inliers of the Cautley and Dent districts (Westmorland and NW. Yorkshire) expose an almost complete sequence of Ashgill beds—which form a better type sequence than that in Ash Gill, Coniston—underlain by the Pusgillian and part of the Onnian Stage of the Caradoc Series. Eight zones are recognized in the Ashgill Series, characterized by distinctive trilobite and brachiopod assemblages; faunal lists are appended. The term “Cautley Mud-stones” is introduced for strata from the Onnian Stage to the top of Zone 7. Marr’s “contemporaneous volcanic group” and “ mucronatus band of the Staurocephalus group” are renamed the “Cautley Volcanic Group” and “Cystoid Limestone” respectively. The term “Wilsey Beck Sandstone” is proposed for a rock unit that forms a useful marker horizon in Zone 2 of the Dent district. The approximate maximum thickness of Ordovician beds exposed is 2,100 feet (640 metres). Tentative correlations are made with Ashgill successions in Great Britain and abroad.

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