Lacaille, A.D. 1924. Some Antiquities in Strathfillan, Perthshire. Cupped Boulder near Helensburgh, and Cross-slabs in Glen Fruin, Dumbartonshire. Proceedings of the Society of Antiquaries of Scotland. 58, (Nov. 1924), 124–130. DOI:https://doi.org/10.9750/PSAS.058.124.130.