Indeed! Not sure I quite agree with that bit, it's not a nice feeling when those same floors form the ceiling... I've now revisited...

I was with you on said digging trip when the shale dropped ;) The issue which has been highlighted above is with something put in by...

Joe, that comment on a public forum is unhelpful if you want access to remain for the long term. The mine was already off limits for 10...

I can vouch for this. Decades ago I used to work in a lab and I acquired fluorescein. As a party trick I used to drink it, twas...

Where there's also some interesting natural rifts...one with a hell of a draught coming out. Assume it would connect back to surface...

If you contact petzl directly they’ll send you a rubber stopper to put on the end of drill bit to avoid injury.