I ran across this interesting tidbit From http://www.pbm.com/~lindahl/ballads/early_child/#his No sources cited so don't know how accurate a statement it is. (And is Greg Lindahl a Mudcatter? I've run across his name and his website before.)

Most magical and supernatural ballad themes also tend to enter ballads at this time. If a ballad has ghosts, or people returning from the dead, or magicians casting spells, it is most likely (thought not certain) to have come from the eighteenth century or later. In earlier ballads, supernatural influences are largely restricted to the devil and the occasional elf. (The latter tended to be unnatural minions of evil, not Tolkien-type elves.)

Janie