Wherry Mine, Mount's Bay, Penzance, Cornwall, England. Wooden trestle bridge carrying the horizontal rods from the steam engine, left, to pump in the coffer dam at the end of the trestle which protected the shaft of the mine which was only uncovered at low water. Opened in 1781 to exploit a vein of quartz-feldspar porphyry, the mine was destroyed in 1798 when a ship in a storm destroyed the trestles and the coffer. Engraving from Transactions of the Royal Geological Society of Cornwall, 1818.