Hi David
Thanks for your reply. I have a passing interest in the South Wales mines as my Paternal Grandfather was a 'minor' from leaving school, about 1895 until the late 1920s when he moved, with the family to near Kidderminster. However he never went underground. His job was a groundsman. It included hedging, fencing, ditching, drainage, tracks & roads and all the work necessary to keep the entire site working.
I do not know for sure but think he was towards the Eastern end of the valleys.
Regards
Allen Morgan