J. Anderson, “Notice of the Excavation of the Brochs of Yarhouse, Brounaben, Old Stirkoke, Bowermadden, and Dunbeath, in Caithness; with Remarks on the Period of the Brochs; and an Appendix, containing a List of Brochs in Scotland, and Early Notices of many of them”, PSAS, vol. 9, p. 292, Nov. 1872.