My only attempt to film something ended up like muffled rummaging at the bottom of a sack of coal without a torch during a power cut. You've got so much light, lovely video.
I've never been to this, or any of the neighbouring black-slate but must have driven past a few times. Also I'd like to look-see because I'm told the geology is very different and you can get copper and other inclusions and in some places sedimentary adjoining slate????
However -- Air quality... for non divers (ignoring sumps and pockets) what's air quality like in Cambrian, in your experience