Peter Jackson mentions a Roughside Level in his 1969 NCMRS memoirs (p 2 and 9 of 11) (giving a GR as NY781425) This is at NY784453 (approx). Mike Luff say it was prospected by Angus Oliver but he's not sure what for. It links to the Brownley Hill complex. Mine plans in WCMRG paper of 2007 show the connection(p 11 of 56)
Location Update: I think both mines referenced above are the same location. I get OS of NY 78122 45342 via Bing Maps, and maybe a transposition of cords? Not aware of any other levels apart from this one in this location. The Slate Sills Level is on the Southern end of Moss Cross Vein, in Brownley Hill, and an old plan does 'possibly' show a connection to Brownley into the Quarry Hazle also coinciding with a surface shaft. Mr Mike.