On Sheet 339 of the One Inch (New Series) Map of the Geological Survey there is marked at Woolley, within the metamorphic aureole of the Dartmoor granite, between Bovey Tracey and Lust-leigh, a patch of “Permian” rocks. Upon inquiry the Director of the Geological Survey, Sir John Flett, informed me that this was an error and should have been marked as “Felsite”. As the rock constituting the outcrop presents unusual features and is very different from an ordinary felsite I feel that a description of it should be placed on record. Moreover, it appears to be a good example of a rather uncommon rock type.