The History of Dufton Village A useful short history of the Lakeland area from prehistoric times to the late 14th century, Contains references to Jarl Buthar and the Cumbrian resistance movement.
Robert Ferguson "The Northmen in Cumberland and Westmoreland", pub. 1866, a scholarly etymology which comprehensively examines the influence of the Old Norse language and personal names on the place-names of the Cumbrian area.