Bruce is correct, it is an old song. There are two variants of the tune, one of which is from Skye. I haven't heard specifically about the origins, but perhaps Rosemary McCormack at B&R Heritage Enterprises. They have e-mail at the web-site.

Yes, the Rankins did a couple of the verses (there are 4 that I have at my site), as part of a medley. It is certainly a beautiful song.