Whether Ireland had much coal or not is insignificant. There were many Irish emigrants, along with other ethnic groups, working in the coal mines in America at that time, who would have sung or played their songs/tunes which could have influenced Merle's melody. In 1970 Tony Wales published "Songs of Soldiers, Sailors and Labouring Lads" for the EFDSS and included "Billy the Pit Horse", set to Merle's tune "Dark as A Dungeon". "Billy" was collected by a Geoff Drake in Manmouthshire, Wales, about 1960. It was finally presented to a Professor John O' Donnell in Canada as "an old traditional Welsh song "for publication in "And Now the Fields are Green" (1992), a collection of Canadian mining songs ! Alan Lomax sang the praises of Merle and his song "Dark as a Dungeon at a reception in 1947, yet Granpa Jones did a cover version for King records in 1950 and credited the song to Jones. In 1951, on a Folkways L/P, Cisco Houston retitled it "Down in the Mines" and gave no credit to Merle Travis. So thank God he got the royalties for "16 Tons"