References for John (Haraldson) Jarl, Earl of Orkney * of Caithness
Sir B.Burke:
Burke's Peerage and Baronetage.
London, 1999
D.Schwennicke:
Europäische Stammtafeln, Vol. II, Tafel 89.
Marburg, 1984
A.M.Stokvis:
Manuel d'histoire.
Amsterdam, 1966