Roberto, your mention of Jeannie Robertson's 'Mary Hamilton' neatly illustrates just how complex the chain of transmission can be. Jeannie recalled learning the ballad as a child from old people in Blairgowrie, Perthshire who used to recite it. However the tune she sang when she recorded the song for Alan Lomax in 1953 is clearly an American tune. I think Mike Yates has researched this and Jeannie's source for the tune may have been Jean Ritchie or Sandy Paton, or perhaps Alan Lomax himself.

Anyway there is a fascinating article just published on the Musical Traditions website by Mike Yates about American commercial recordings of Child Ballads in the 1920's and 1930's: When Cecil Left the Mountains.

Matthew