The engineer, calculating the time employed in its fall, was able to calculate the depth of the well, which was found to be about ninety feet.

The floor of the cavern must thus be situated ninety feet above the level of the sea.

“Here is our dwelling,” said Cyrus Harding.

“But it was occupied by some creature,” replied Gideon Spilett, whose curiosity was not yet satisfied.

“Well, the creature, amphibious or otherwise, has made off through this opening,” replied the engineer, “and has left the place for us.”

“Never mind,” added the sailor, “I should like very much to be Top just for a quarter of an hour, for he doesn’t bark for nothing!”

Cyrus Harding looked at his dog, and those of his companions who were near him might have heard him murmur these words,—­

“Yes, I believe that Top knows more than we do about a great many things.”

However, the wishes of the settlers were for the most part satisfied.  Chance, aided by the marvelous sagacity of their leader, had done them great service.  They had now at their disposal a vast cavern, the size of which could not be properly calculated by the feeble light of their torches, but it would certainly be easy to divide it into rooms, by means of brick partitions, or to use it, if not as a house, at least as a spacious apartment.  The water which had left it could not return.  The place was free.

Two difficulties remained; firstly, the possibility of lighting this excavation in the midst of solid rock; secondly, the necessity of rendering the means of access more easy.  It was useless to think of lighting it from above, because of the enormous thickness of the granite which composed the ceiling; but perhaps the outer wall next the sea might be pierced.  Cyrus Harding, during the descent, had roughly calculated its obliqueness, and consequently the length of the passage, and was therefore led to believe that the outer wall could not be very thick.  If light was thus obtained, so would a means of access, for it would be as easy to pierce a door as windows, and to establish an exterior ladder.

Harding made known his ideas to his companions.

“Then, captain, let us set to work!” replied Pencroft.  “I have my pickaxe, and I shall soon make my way through this wall.  Where shall I strike?”

“Here,” replied the engineer, showing the sturdy sailor a considerable recess in the side, which would much diminish the thickness.

Pencroft attacked the granite, and for half an hour, by the light of the torches, he made the splinters fly around him.  Neb relieved him, then Spilett took Neb’s place.

This work had lasted two hours, and they began to fear that at this spot the wall would not yield to the pickaxe, when at a last blow given by Gideon Spilett, the instrument, passing through the rock, fell outside.

“Hurrah! hurrah!” cried Pencroft.