It would seem that Iain/John Cameron wrote the words in Gaelic originally. The link George Seto recommends gives Gaelic words for Chi Mi Na Morbheanna, and the Gaelic lyrics are also found on another Mudcat thread. According to Barry Taylor (see correct link posted by Malcolm Douglas), Cameron set his lyrics to "Duil ri Baile Chaolais fhaicinn (Hoping to see Ballachulish). The original tune was based on Johnny stays long at the Fair."

If anyone has words to the Baile Chaolais song, I'd quite like to see them, especially since I have some acquaintances from Ballachulish.