Hi, especially minerals, the area is full of bituminous shale mines, an organic material used in the production of talcum powder and ointments, but already exploited at the end of the 19th century to obtain lighting oil for lamps
That reminds me of my visit to the Big Nickel mine in Sudbury, Ontario. There were some galleries dating back to the 19th century, dug by hand with picks. I could see the pick marks on the stone, like scratch marks from some movie mutant, it was easy to imagine the men down there hacking away at the hard rock in near darkness, just some faint candlelight illuminating their work space. Your tunnel there looks just like the one I visited.
