Richard, Lakes of Pontchartrain is not the usual tune. Paddy Moloney tells how it came to be used on 'The Long Black Veil':
[1995:] Mark Knopfler [...] when he was recording 'The Lily of the West' used the air of 'The Lakes of Pontchartrain'. "He didn't so much use it as I suggested it. Perhaps the original tune is the minor version of 'Lily of the West'. I thought it would be a good song for him, and while we were doing it I happened to mention that it reminds me of this air 'The Lakes of Pontchartrain' which Paul Brady had done. I'd say the 'Pontchartrain' air came from the 'Lily of the West' which is hundreds of years old - even the English will claim 'The Lily of the West' as their own, but it's written in some of the old Irish books and the Colm O'Loughlin book as well as in old manuscripts [...]." (Paddy Moloney of The Chieftains, interviewed by John O'Regan, Rock 'n' Reel 21, p 36)