Skene, William. “On the Authenticity of the Letters Patent Said to Have Been Granted by King William the Lion to the Earl of Marr in 1171”. Proceedings of the Society of Antiquaries of Scotland 12 (November 30, 1877): 603-609. Accessed November 18, 2019. http://journals.socantscot.org/index.php/psas/article/view/5840.