In the days before a Priestley had caught and bottled that demon which exists in the shape of carbonic acid gas, when the miner was smitten dead by an invisible foe in the deep bowels of the earth it was natural his awestruck companions should ascribe the mysterious blow to a supernatural enemy. When the workman was assailed suddenly by what we now call fire-damp, which hurled him and his companions right and left upon the dark rocks, scorching, burning, and killing, those who survived were not likely to question the existence of the mine fiend. Hence arose the superstition--now probably quite extinct--of basilisks in the mines, which destroyed with their terrible gaze. When the explanation came, that the thing which killed the miner was what he breathed, not what he saw; and when chemistry took the fire-damp from the domain of faerie, the basilisk and the fire fiend had not a leg to stand on. The explanation of the Knockers is more recent, and less palpable and convincing.