Andy,
Firstly, "Mountains of Mourne" is a song by Percy French of Cavan, Ireland and set to a tune called, "Bendermeer's Stream". French was incredibly prolific and wrote many songs that are presumed to be folksongs but are closer akin to musichall.
My top five:
" Tramps and Hawkers", "St. Clairs Defeat", "Jock O' Hazeldean" " Spainish is the Lovin' Tongue", " Red River Valley." and about forty or fifty others that are equally as important to me.
Don Meixner