IV.—Cordierite in Granite from Dartmoor

Extract

The presence of cordierite does not seem to have been often recorded from the granite of Dartmoor, in spite of the abundance of that mineral amongst the contact-altered sediments surrounding the igneous mass. The recently published Survey memoirs on Dartmoor and Ivybridge cover nearly the whole area of the granite, and I can only find references to two specimens in which cordierite, or rather pinite pseudomorphs representing that mineral, have been detected microscopically. Within the limits of the granite proper the mineral does not appear to have been observed at all in an unaltered condition, at least so I infer from the absence of any record of it in the above-mentioned memoirs, as I must confess to a somewhat scanty knowledge of West of England geological literature. Having recently done a certain amount of geologising along the northern margin of Dartmoor, which has not been investigated by the Survey since the introduction of modern petrographical methods, and having obtained some rather interesting results, of which I hope to publish shortly a detailed account, I was glad to take advantage of an opportunity presented by a visit to the South of Devon to make some comparisons with the contact and other phenomena described by the Survey.