The shape of the batholith and the relationship between the individual plutons and the main mass of the granite remained entirely speculative until gravity data began to be used to constrain the thickness and shape of the batholith by modelling.
From gravity and magnetic geophysical data, the batholith is interpreted to extend from about 8°W, more than 100 km southwest of the Isles of Scilly, to the eastern edge of Dartmoor.
The negative gravity anomaly, caused by the relatively low density of the granites compared to average continental crust, is linear and trends WSW-ENE, parallel with that associated with the Haig Fras granite.
You can see some wonderful glacial polish and striations on fluted granite along the highway between the Chief and the town of Squamish.
Map showing the main granite outcrops of the Cornubian batholith in southwest England and the location of Haig Fras – the 20 m Gal Bouguer anomaly is also shown as this indicates the location of the negative anomalies associated with these intrusions due to their relatively low density compared to average continental crust The Cornubian batholith is the group of associated granite intrusions which underlie the south-western peninsula of Great Britain.
The granites are classified as S-type, interpreted to be derived from the partial melting of a sedimentary protolith.The intrusions are associated with significant mineralization, particularly tin, for which the area has been famous since about 2000 BC.