Coba jelasin Daftar pustaka dari Petroglif dong

Beckensall, Stan and Laurie, Tim, Prehistoric Rock Art of County Durham, Swaledale and Wensleydale, County Durham Books, 1998 ISBN 1-897585-45-4

Beckensall, Stan, Prehistoric Rock Art in Northumberland, Tempus Publishing, 2001 ISBN 0-7524-1945-5