Laing, Samuel. “On the Age of the Burgs or ’Brochs,’ and Some Other Pre-Historic Remains, of Orkney and Caithness”. Proceedings of the Society of Antiquaries of Scotland 7 (November 30, 1869): 56–100. Accessed November 24, 2024. https://journals.socantscot.org/index.php/psas/article/view/5313.