Since I last posted, someone was good enough to give me a cassette dub of that album, which I hadn't heard in over a decade, but rediscovered with much pleasure (isn't that a great set of jigs on the second band?) I found that "Willie O" is essentially identical to songs discussed previously on this forum under the titles The Ghost of Willie-O or Bay of Biscay.

I'm afraid I have to disagree that "Willie-O" is derived from "Sweet William's Ghost" (Child 77). The versions of the latter I have found -- including Irish ones from Paddy Tunney (on The Voice of the People, Vol. 3) and Len Graham (on Ye Lovers All, credited to Sandy McConnell of Bellanaleck, Co. Fermagh) -- have nothing specific in common with "Willie-O". The mere theme of the lover's ghostly return is present in many sources, such as "The Grey Cock" (Child 248) and broadsides like "The Nightingale". The broadside that Malcolm posted might have been inspired by any of this (my opinion, but I'll defer to those with more experience).

However, there does seem to be a connection between the later development of this song and Irish versions of "The Grey Cock". (TGC has been a lot more widely known than "Sweet William's Ghost", in any case.) Maud Karpeles prints "The Lover's Ghost (The Grey Cock)" from Matthew Aylward of Bonavista Bay, Newfoundland, with the following verse:

    O when will I see you, my love, she cries,
    And when will I see you again?
    When the little fishes fly and the seas they do run dry
    And the hard rocks they melt with the sun.

Len Graham (on Ye Lovers All again) gives "True Lover John" which he got from Joe Holmes of Ballymoney, Co. Antrim. This is a non-ghostly night visiting song containing (perhaps slightly incongruously) the verses about the cock from the ghost song, and the following:

    This fair maid she arose and she quickly followed after,
    Saying "When will you come to see me?"
    "When the fishes they do fly and the seas they all run dry,
    And seven moons shine brightly o'er yon lea."

Now, on The Voice of the People, Vol. 3, there's a recording of "Willie-O" by Nora Cleary, which follows the broadside pretty closely, but adds a verse which isn't in that source:

    "Oh Willie dear, when will we meet again?"
    "When the fishes they will fly and the sea it will run dry
    And the rocks they will melt with the sun."

So, it seems that material from "The Grey Cock" (not "Sweet William's Ghost") could be freely added to any song with the appropriate context.

Levana