If you're up here, find it. It's strange, weathered boulder with a depression and notch eroded/carved? Right at the top of the northern peak of Rough Tor, just along from the war memorial plaque with the dragon on it.
How to Become a Witch
Touch a Logan stone nine times at midnight, and any woman will become a witch.
Source: Robert Hunt, Popular Romances of the West of England; or, The Drolls, Traditions, and Superstitions of Old Cornwall (London: John Camden Hotten, 1871), p. 321.