"All the caves discovered so far in Kentucky have fresh pure air.

I do not undertake to account for it." That night they cut long torches of resinous wood, and early the next morning all except two, who were left to guard the horses, entered the cave, led by Hart, who was a fearless man with an inquiring mind.
Everyone carried a torch, burning with little smoke, and after they had passed the cave mouth, which was slightly damp, they came to a perfectly dry passage, all the time breathing a delightfully cool and fresh air, full of vigor and stimulus.
Paul and Henry looked back.

They had come so far now that the light of day from the cave mouth could not reach them, and behind them was only thick impervious blackness.

Before them, where the light of the torches died was the same black wall, and they themselves were only a little island of light.

But they could see that the cave ran on before them, as if it were a subterranean, vaulted gallery, hewed out of the stone by hands of many Titans! Henry held up his torch, and from the roof twenty feet above his head the stone flashed back multicolored and glittering lights.