Philippa-- Your choice of the word "odd" seems quite apt. Here is what I found in the commentary of the booklet which accompanied the "The Folk Box," Elektra, 1964.

Jean Ritchie calls it "[a] strange combination of nonsense words and ethereal tune." It is her opinion that its origin is in the Mummers' Plays of England. It almost has the feel of a 60s psychedelic trip!

Incidentally, the air was used by Bob Dylan for his words, "Masters of War".

Hope this gets you on the road to its origins.---John