ISBN 0-7524-2517-X* Laing, Lloyd Robert (2006) "The Archaeology of Celtic Britain and Ireland: C. AD 400–1200" Cambridge University Press ISBN 0-521-83862-2* Nicolson, James R. (1972) "Shetland".
ISBN 075242517X* Laing, Lloyd Robert (2006) "The Archaeology of Celtic Britain and Ireland: C. AD 400—1200" Cambridge University Press ISBN 0521838622* Nicolson, James R. (1972) "Shetland".