He stood erect and held his hand up; the roof was six inches above his head.

He was in a room of some sort.

Wishing, if possible, to learn the extent of this subterranean chamber, which he did not doubt had at one time been used as a cave and storehouse of smugglers, Cleggett began to sidle around walls, feeling his way with his hands.
He dislodged a pebble.

It rolled to the ground with what was really a slight sound.
But to Cleggett, who had been getting more and more excited, it was loud as an avalanche.

He stopped and held his breath; he fancied that he had heard another noise besides the one which his pebble made.