Anderson, J. (1880) “Notice of a Fragment of a Silver Penannular Brooch, ornamented with Gold Filigree Work and Amber Settings, found at Achavrole, Dunbeath, Caithness, in 1860”, Proceedings of the Society of Antiquaries of Scotland, 14, pp. 445-452. doi: 10.9750/PSAS.014.445.452.