G. Gordon and A. Mitchell, “Notice of Incised Sculpturings on the Steatite Rock at Feideland, the Extreme North of the Mainland of Shetland, and of a Cluster of Ruined Structures Styled Picts’ Houses, on the Kaim of Isbister, Shetland”., PSAS, vol. 12, pp. 202–206, Nov. 1877.