who after 1034 had his hands full with his war with King Duncan, and
had always wars with the Hebrides and the Irish, agreed, and the
two joined forces, and sailed on Viking raids to the Hebrides and
England.[16]

About 1044 Thorfinn married Ingibjorg,[17] Finn Arnason's daughter,
and it is interesting to find that in the _Saga Book of the Viking
Club_, Vol. IV, page 171, Mr. Collingwood suggests that the King of
Catanesse, who fought for years to gain possession of Gratiana, the
lost wife of William the Wanderer, was Thorfinn. If this story be
founded on fact, as it probably is, this may account for his somewhat
late marriage with Ingibjorg.

Thorfinn next claimed two trithings of Orkney from his nephew
Ragnvald, who demurred to giving up what the Norse king had conferred
on him, but, finding he could not cope with Thorfinn's Orkney,
Caithness and Scottish forces, Ragnvald fled to King Magnus, who gave
him a force of picked men, and bade Kalf Arnason also to help him,
although Kalf was Thorfinn's friend, and near connection by marriage.

The two jarls met in battle in the Pentland Firth, off Rautharbiorg or
Rattar Brough in Caithness, east of Dunnet Head, Kalf Arnason with
his six ships standing out of the fight. Thorfinn had sixty ships,
smaller, and, save Thorfinn's own, lower in the waist than those of
his enemy, who thus easily boarded them, and then attacked Thorfinn.
Surrounded and boarded on both sides, Thorfinn cut his ship free and
rowed to land. Arrived there, he removed his seventy dead, and all
his wounded. Next he persuaded Kalf Arnason to join him with his six
ships, and renewed and won the fight, though Ragnvald himself escaped
to Norway.[18]