Pollexfen, John H, and George Sim. “Notice of Coins of David I. of Scotland, and Henry I. of England, Found, With Gold Ornaments, &C., at Plan, in the Island of Bute, in June 1863”. Proceedings of the Society of Antiquaries of Scotland, vol. 5, Nov. 1865, pp. 372-84, doi:10.9750/PSAS.005.372.384.