I moved you over to this thread, so the discussion doesn't get split any further. I think the answer is way up top in a message from Tim Jaques, but his wording is a little unclear:

"Caidil Gu La" or "Caidil Gu Law (Latha)" is the title of a fiddle tune in the Simon Fraser Collection. One translation given to this Scottish Gaelic phrase is "sleep on to day." Leslie had composed his own melody for "Lullaby," but the melody to which Cape Breton Lullaby is now sung is the old Scottish air at half speed.

I didn't see a date for the tune.
-Joe-