The “Lost World” section, (a rather small part of this plan, I may add) more or less matches the rough plan I made when I visited recently, and also provides many fascinating insights to what may now be lost forever. The plan seems to suggest that this area of workings actually seems to split into 3 sections rather than the 2 I originally identified. Firstly there is the section where one can proceed through 3 chambers (Z6, Z5 and Z4) in an eastward direction, and view a selection of artefacts. Notably chamber Z4 has a collection of big regular slate blocks scattered on the floor. The first collapse encountered in this direction, appears to be in chamber Z3 which is a shame,as the plan shows this chamber to be the first one to be worked up to the floors above. Miles's trip report mentions a run in level at the top of ( I think) chamber Z4, but this doesn't appear to be indicated. It looks now as if these series of chambers may be south of the drop fault. The cross cut is clearly marked and the rather isolated section of smaller workings, which we explored, and Miles also mentioned, are clearly shown, although I still can't work out if these are actually part of the back vein or not. There is collapse eastwards here too I think, but the plan indicates that there is not much beyond. Of particular interest is the extensive area of chambering in the “central section” also accessed at one time by the cross cut. Maybe these are the main back vein workings north of the fault. If so they were sadly inaccessible. I think I remember seeing yet another fall in the level possibly indicating the position of chamber Z4 in north of fault section. But the annotations “tops down, signs of pressure” isn't an encouraging sign, if that was the state of these workings even when the plan was drawn up.
I still wonder if beyond these collapses, there are entire sections which have managed to stay relatively intact. I was surprised that the “lost World” itself is in such reasonably good condition, considering that it is indicated as lying roughly below Llyn Bach and the cracks, as well as being split by the fault. So who knows?
Many thanks for uploading, Graham;D
'I wonder how many breakfasts, and other meals we have missed inside that nasty clockless, timeless hole?'
'The Hobbit'
J R R Tolkien.