From Bill Reese:

"It seems from a conversation with the author of the book, that the TUNE Merle Travis used for "Dark as a dungeon" was a Welsh melody.

Geoff Drake is a Welsh immigrant to Canada who learned this song when he was visiting Idris Griffith's son, Elwyn, in his native Wales. Noting the similarity to Merle Travis' "Dark As A Dungeon" (page 55), he says the words are obviously not those of a poet like Travis, whose miners "lust for the lure of the mine." 2 This man knows the coal and hates it while respecting it.
Verse 3 refers to the Davy Lamp, which has a naked flame to denote firedamp gas and superceded the taking of canaries down to the coal face: when the canary fell off its perch, the men ran!"