The information about the Treak Cavern and bluejohn deposits was given to me by the guide who showed me round the Peak Cavern (Devil's Arse). There are still interconnections being discovered between the various caverns. Just checked on my original post and realised I should have said that the Treak Cavern was the only bluejohn deposit being mined at the moment - and that in limited quantities. Most of the caverns were lead mines - Speedwell being a case in point - and the Arse was not mined but used as a commercial ropewalk for hundreds of years. The rope produced was used in the lead mines.