St. Germoe's Chair

Tricia's Prah Sands coven met today and so I had an hour pottering around and went down to find this site. No-one quite seems to know what it is 
John Leland, the great antiquarian, visited Cornwall in the reign of Henry VIII and he mentioned St. Germoe’s chair. Accoring to the Cornish Bird 'The most likely explanation then is it is a detached sedilia probably dating from the 13th century. A sedilia is a set of seats used by clergy. There are usually three, with a canopy above and some decoration. They are very rare. Why this one is where it is is a mystery.'