J. R. Allen, “Report on the Photography of the Sculptured Stones earlier than A.D. 1100, in the District of Scotland south of the river Dee; obtained under the Jubilee Gift of His Excellency Dr. R. H. Gunning, LL.D., F.S.A. Scot”, PSAS, vol. 31, pp. 147–152, Nov. 1897.