The mine was first worked above the water table at relatively shallow depth. The adit was driven through marl or softer rock presumably by a cut and cover process. The adit then entered harder rock before it reached the mine. The engine houses were used to pump water from lower sections of the mine. As far as I can tell the shafts to the surface were capped and still remain though their location is hard to place as the mine survey does not relate accurately to the surface.Many years ago the capping collapsed on one shaft revealing it to be intact. I dont know how this was remedied.All the mine appears to be on the estate belonging to Lady Gass and the adit is under a field belonging to a tenant farmer. Considering this to be a mothballed mine from the 1830's with extensive natural caves we have made several attempts to open up the adit. As the manhole is by a footpath we took it on ourselves to start work from there some years ago. Gradually we replaced the roof lintels until the tenant farmer asked us to stop pending evidence of third party insurance. ( which most cavers have ). Sadly we never got around to presenting this and the farmer died.The project has since stalled but the simple solution ( with permission )would be to excavate a shaft above the shallow adit at a point beyond the collapse. A new manhole could then be constructed.Things are complicated as water from the adit was being piped to a covered reservoir down the road. If this still happens I do not know.Some day everything will change as Lady Gass is getting on a bit.The project has been with us for nearly 40 years and no doubt will coninue. If only in our thoughts.
This is copyright from The Somerset Heritage Centre but I think I am OK in posting it here.It shows the mine in section plus three of the shafts and what I take to be the natural caverns.