Alan of Australia -- Percy's Song was written by Bob Dylan and was also covered by Fairport Convention in the late 60s. It's an entirely different song, albeit exceptionally beautiful.
The refrain is actually
"Turn, turn, turn again
(snippet of verse goes here)
Turn, turn, to the rain and the wind."
But who's to say that Bobby didn't get his inspiration from the Twa Sisters or the Cruel Mother?