Cursiter, James W. “Note on a Stone Bearing an Incised Cross, from the Site of St Colm’s Chapel, Walls, Orkney”. Proceedings of the Society of Antiquaries of Scotland 32 (November 30, 1898): 50–52. Accessed April 19, 2024. https://journals.socantscot.org/index.php/psas/article/view/6690.