Found the following information (I think on this forum a while back and saved it pending a possible explore of this area.)
If I remember rightly, think it was Speedy's posting so I hope he dosn't mind me posting it here again.
If I understand correctly the original plan contains only a conjectural lay out of the eastern workings, so the following information builds on this. (The original can be found in the Rhosydd documents section on this forum)
There may have been some limited extraction of slate from this area after the fall, but i'm not sure.
"Floor 8 had been extended by 1 chamber (Ch. H)
- Floor 7 had been extended by 2 chambers (Ch. H and I)
- The remains of an incline winding drum and gear can be found at Fl. 7 where chambers G & H
have been opened into each other.
- An incline with an fully intact winding drum and breaking system had been built between Fl. 7 &
6 in Ch. I.
- Floor 6 had been extended by 1 chamber (Ch. N)
- Floor 5 had been extended by 1 chamber (Ch. P)
- Chambers K, L, M, N, & O had been opened up to Floor 4 but no further."
'I wonder how many breakfasts, and other meals we have missed inside that nasty clockless, timeless hole?'
'The Hobbit'
J R R Tolkien.