↑ 1.01.1 Paul, Sir James Balfour, The Scots peerage : founded on Wood's ed. of Sir Robert Douglas's Peerage of Scotland; containing an historical and genealogical account of the nobility of that kingdom, (Edinburgh: David Douglas, 1905), vol. III, citing, "a daughter, mother of Moddan, titular Earl of Caithness, who was slain at Thurso in 1040."240.
↑ 2.02.1 Dunbar, Sir Archibald H. Scottish Kings: A Revised Chronology of Scottish History 1005-1625. Edinburgh: D. Douglas (1899), 6.
Wikipedia - information about the role of Mormaer of Caithness: Mormaer of Caithness