Pencroft and Neb, waving their torches, threw the light into every crevice; and at the same time, Harding, Gideon Spilett, and Herbert, their spears raised, were ready for any emergency which might arise.

The enormous cavern was empty.

The settlers explored it in every direction.

There was nothing there, not an animal, not a human being; and yet Top continued to bark.

Neither caresses nor threats could make him be silent.
"There must be a place somewhere, by which the waters of the lake reached the sea," said the engineer.
"Of course," replied Pencroft, "and we must take care not to tumble into a hole." "Go, Top, go!" cried Harding.
The dog, excited by his master's words, ran towards the extremity of the cavern, and there redoubled his barking.
They followed him, and by the light of the torches, perceived the mouth of a regular well in the granite.