So the performance of "Song of the Earth" in Glyneath is a stage adaptation of the book? Is the adaptation any good?

yes, it would be good if Siwsan George were still with us. Wasn't "Traditional Songs of Wales" on Saydisk? Heard 9bach do "Can Merthyr" recently- very good version, also sang "Pontypridd". I do wonder about the wisdom of bass and drums though.