Abstract
A detailed gravity survey over 1800 km 2 between Dartmoor and Bodmin Moor, with an average station spacing of 3.25 kn −2 is interpreted in terms of the depth to the buried Cornubian granite. Large areas are defined where the granite surface lies within 1 km of sea level; in contrast, the NE edge of the Bodmin granite dips steeply to depths of at least 3 km. A closed minimum Bouger gravity anomaly at Lamerton, NW of Tavistock, has a residual anomaly some 2 mGal larger than the adjacent area. This can be quantitatively interpreted as either a Tertiary basin filled with argillaceous sediments or a small granite cupola extending from the roof-region of the granite at about 2 km depth. Both these solutions are novel. A shallow piston core to a depth of about 15 m together with a resistivity depth sounding supports the sedimentary interpretation of the Lamerton anomaly, and suggests a thickness of about 150 m of Tertiary clays in a fault-bounded basin, elongated to the NW.
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