Verse 3, line 3: "bord and pillar" - a method of mining that involved digging out an area of coal and leaving pillars of coal to hold up the roof (I think - open to correction).

Verse 4, Line 2: "flows"

Verse 6, Line 2: "Crawled in the seams"

Verse 7, Line 1: "the Plessey, the Brockwell Seam"

Picky, picky.

Reference:"Ewan MacColl Peggy Seeger Songbook," Oak Publications, New York, 1963