"...This adventurous huntsman married Elizabeth, daughter of Malice Spar, Earl of Orkney and Stratherne, in whose right their son Henry was, in 1379, created Earl of Orkney, by Haco, king of Norway. His title was recognized by the Kings of Scotland, and remained with his successors until it was annexed to the crown, in 1471, by act of Parliament. In exchange for this earldom, the castle and domains of Ravenscraig, or Ravensheuch, were conferred on William Saintclair, Earl of Caithness " (Scott).
From the notes to Scott's "Lay of the Last Minstrel", which contains several St. Clair references.
Not all are convinced that Prince Henry Sinclair's voyage to what later became America occurred, but today, June 2, in 1398, is the date credited with Prince Henry's landing at Chadebucto Bay (now Trin Bay), in Nova Scotia (http://sinclair.quarterman.org/timeline.html).