Drops of water fell from the vault, but that did not prove that they oozed through the rock.

They were simply the last traces left by the torrent which had so long thundered through this cavity, and the air there was pure though slightly damp, but producing no mephitic exhalation.
"Well, my dear Cyrus," said Gideon Spilett, "here is a very secure retreat, well hid in the depths of the rock, but it is, however, uninhabitable." "Why uninhabitable ?" asked the sailor.
"Because it is too small and too dark." "Couldn't we enlarge it, hollow it out, make openings to let in light and air ?" replied Pencroft, who now thought nothing impossible.
"Let us go on with our exploration," said Cyrus Harding.

"Perhaps lower down, nature will have spared us this labor." "We have only gone a third of the way," observed Herbert.
"Nearly a third," replied Harding, "for we have descended a hundred feet from the opening, and it is not impossible that a hundred feet farther down--" "Where is Top ?" asked Neb, interrupting his master.
They searched the cavern, but the dog was not there.
"Most likely he has gone on," said Pencroft.
"Let us join him," replied Harding.
The descent was continued.

The engineer carefully observed all the deviations of the passage, and notwithstanding so many detours, he could easily have given an account of its general direction, which went towards the sea.
The settlers had gone some fifty feet farther, when their attention was attracted by distant sounds which came up from the depths.

They stopped and listened.