I recently recorded it and played it at a Friend's funeral on a walnut low "G" open-holed flute, on which it is particularly haunting and evocative.
As I recall it is one of those really old ones that nobody seems to agree on where or when it originated - English trad, Negro/Slave Spiritual, Scottish pipe tune, or what.
Like "Morning Has Broken", "The Parting Glass", and a few others that seem to go back to a time before anybody remembers, or at least took the time to write them down.
There is something primal and mystical about them, isn't here?