A fantastic notice in front of the great pit

Atop Parys mountain above  Amlwch depicting the great pit in the early 1900s showing the method of extraction, the pit has been expensively dynamited to remove the many unsafe overhangs and steep cliffs since then.
It was once the biggest source of copper in the world and a new 300 metre deep shaft has discovered  a load of 6 million tons of copper below the old workings