Slow water fell drop by drop from the point of the stalactite upon the point of the stalagmite.
"That has been going on for ages," said the schoolmaster, "and the same drop of water that leaves some of its substance to form the stalactite, hanging from the roof, goes to form the stalagmite jutting up from the floor.

Come, Paul, here's a seat for you.

You must rest a bit." They beheld a rock formation almost like a chair, and, Paul sitting down in it, found it quite comfortable.

But they paused only a moment, and then passed on, devoting their attention now to the cave dust, which was growing thicker under their feet.

The master scooped up handfuls of it and regarded it attentively by the close light of his torch.
"It's the genuine peter dust!" he exclaimed exultantly.