Probably "Auld Lang Syne", "Annie Laurie" or "Loch Lomond". For what it's worth, I heard, or read, once (twenty years back, at least) that when the makers of the film "Brigadoon" were getting music composed for this ultra-realistic view of life in bonnie Scotland as it ever was, they only had knowledge of two songs, and apparently musicologists can tell which of the songs/tunes in the film were based on each example. Anyone else heard/read this?