Righty...
I'm 99.9% certain Barney's adit is on Floor 5 and I
think it is in the north vein. And that's where the confusion starts! The back vein at Cwmorthin was originally referred to as the 'north' vein, although the north vein is the vein to the, er, north of the back vein in the same way that the old vein is to the south of the back vein - and indeed was referred to as the south vein.
The series of chambers that is accessed bu this adit is in totoally the wrong place to be the back vein - it's about 100 yards too far north for a start and it's a long way away from the Floor 4 north adit, which is in the back vein - and given the dip of the veins, it's even further away from the where the Floor 5 back vein adit would have been.
So, this adit does not lead to the back vein and this it leaves the north vein as the only alternative. There appear to be a couple of manways up to floor 6, but we didn't try them as freeclimbing sloping wet slate is never sensible, especially if you want to get back down again.
Having checked the map rather closely, I'll also confirm the location of the Floor 4 adit, which is what we were looking for: good new is we found it, bad news is that it's blocked. It's the adit that's very much hidden behind the floor 5 tip, at the right hand side of the depression as you look at the mountain.
Someone has removed part of the brick wall that originally dammed the adit and the water level has dropped to just over critical wellie depth, which resulted in a slightly wet SimonRL. However, the layout of the tunnels corresponds pretty much exactly to the 1884 survey, albeit the right hand fork is blocked by a fall in the first chamber it reaches; that's a bit of a shame, as floor 4 was massive - albeit that subsequent untopping work has probably destroyed most of it anyway.
I suppose the only answer now is to see whether there are any connections up to floor 4 inside...
Hello again darkness, my old friend...