Bartram's Dirge, as Bruce pointed out, was a 19th century fake written by Robert Surtees and passed off as "collected from oral tradition", largely on the strength of the equally fake (but expertly shammed) "scholarly notes" attached to it, which took in Walter Scott among others. The Heidless Cross was written relatively recently by George Weir, who evidently based on it Surtees' pastiche. The Weir song, as recorded by the Corries, was never represented as being traditional, though a lot of people have assumed without thinking that it "must" have been.