The light from the young miner's lamp, thrown on the wall, revealed no trace of any recent work with pick or crowbar.

Harry would then ask himself if it was not the effect of some acoustic illusion, or some strange and fantastic echo.

At other times, on suddenly throwing a bright light into a suspicious-looking cleft in the rock, he thought he saw a shadow.

He rushed forward.

Nothing, and there was no opening to permit a human being to evade his pursuit! Twice in one month, Harry, whilst visiting the west end of the pit, distinctly heard distant reports, as if some miner had exploded a charge of dynamite.