Rock Succession and Structure in South Cornwall: a Revision. With Notes on the Central European Facies and Variscan Folding there present

Abstract

The area dealt with in this paper is the coast of South Cornwall from Porthleven in Mount's Bay to Pentewan in Mevagissey Bay. It is separated by the Carrick Roads and tributary creeks into two parts, Meneage and the Roseland-Gorran country. The similarity of the rocks and problems in the two areas is recognized in the memoirs of H.M. Geological Survey (Flett and Hill 1912; Hill and MacAlister 1906; Reid 1907; Reid and Scrivenor 1906), but no detailed correlation based on local developments has been made, and the stratigraphical terms in use (“Mylor,” “Falmouth,” “Portscatho,” “Veryan,” “Manaccan” and “Grampound”) have never been satisfactorily defined, so that the geological history of Cornwall is still unexplained. The rock succession of South Cornwall begins with the altered rocks of two peninsulas (the Lizard and Dodman), of unknown age, related to one another and to the Start in South Devon by their rock types and by certain peculiar features in their boundary lines. The Lizard differs from the other two in the presence of an intrusive complex, also of unknown age, of serpentine-gabbro and granite-gneiss, described in 1912 by Sir John Flett, who regarded the serpentine as injection-foliated, and the Lizard boundary features as compatible with both dislocation and intrusion (Flett and Hill 1912, pp. 213–6, 242). In 1896, Professor Bonney had pointed to Kiberick valley, near Veryan, as a locality likely to afford crucial evidence of the age of the Lizard serpentine (1896, p. 48), and he had previously (1877)