Paul, I can't claim the glory for this new stuff ;-), a certain Mr Feather I believe, its in Boughey & Vickermans book around ref 501. The walling must also be known about its in a clearing, so I'm sure someone of importance will have spotted it. We'll have a look next time we're up there, its only 200ft away or so from that flat bit you had a feeling about (which is where the cairns are).