Hello Martin , The stone that is to be left alone is not St Fillans' Seat , which is at the top of Dundurn , but a big boulder that may cover plague burials . There was a housing development planned but they pulled out because of the stone. I have no idea of the age of the fairy story or for that matter the plague story . I think it may be more about local politics than archaeology/folklore . I can't believe a building developer would stop developing because of fairies .