Contact Metamorphism in South-Eastern Dartmoor

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Abstract
I. H istorical I ntroduction T he area mapped and described comprises Sheets CXIV S.W., CXIX N.E. and S.W., CXX N.W., and CXXV N.W. and N.E. of the six-inch Ordnance Survey series, Devon. The history of research in the area may be considered to show three phases : (i) the pioneer observations, extending up to 1811; (ii) the investigation of the sequence and structure of the rocks outside the metamorphic aureole; and (iii) the investigation of the petrogenesis and structure of the rocks comprising the granite intrusion and its metamorphic aureole. The previous work (see list of references, pp. 604-7) deals with the second phase in some detail, but the third has received less attention. This paper will treat of the petrogenesis and structure of the thermo- and dynamo-metamorphosed rocks. The earliest observations on the area which are of geological interest are found in the two early ‘surveys ’of the county of Devon by Risdon (1610) and Westcote (1630) respectively; they refer to the Brent lodestones. An account of a large Devon magnet, probably from Brent, is given in volume 2 of he Philosophical Transactions. Chapple (1785) gives further details of the Brent magnets. Following these come some notices of the occurrence of various rocks in the ‘agricultural surveys ’ of Fraser (1794) and Vancouver (1808), the general county histories of Polwhele (1797) andand Lysons (1822), and the ‘Natural History’ of Bellamy (1839). The earliest petrographical observations are due to Maton, a keen observer, who thus described the Dartmoor granite in 1797: ‘The