From a historical note are you aware that Tavistock became one of four Stannary towns on the fringes of Dartmoor, whose granite bore the tin.
The other 3 were Chagford , Ashburton and Plympton St Maurice - designated in 1328. The latin word for tin is stannum.
Tin mining was extremely important to the economy of Dartmoor , and several of my ancesters were involved in the 19th century.