The Chronicle of The Kings of Norway
Part 37 - Of King Magnus, And Thorfin And Ragnvald, Earls Of Orkney
While King Magnus the Good, a son of King Olaf the Saint, ruled over Norway, as before related, the Earl Ragnvald Brusason lived with him. Earl Thorfin Sigurdson, the uncle of Ragnvald, ruled then over Orkney. King Magnus sent Ragnvald west to Orkney, and ordered that Thorfin should let him have his father's heritage. Thorfin let Ragnvald have a third part of the land along with him; for so had Erase, the father of Ragnvald, had it at his dying day.
Earl Thorfin was married to Ingebjorg, the earl- mother, who was a daughter of Fin Arnason. Earl Ragnvald thought he should have two-thirds of the land, as Olaf the Saint had promised to his father Bruse, and as Bruse had enjoyed as long as Olaf lived. This was the origin of a great strife between these relations, concerning which we have a long saga. They had a great battle in Pentland Firth, in which Kalf Arnason was with Earl Thorfin.
So says Bjarne Gullbrarskald: —
"Thy cutters, dashing through the tide,
Brought aid to Earl Thorfin's side,
Fin's son-in-law, and people say
Thy aid made Bruse's son give way.
Kalf, thou art fond of warlike toil,
Gay in the strife and bloody broil;
But here 'twas hate made thee contend
Against Earl Ragnvald, the king's friend."