lamp upon the
walls of the cavern which separated it from the central shaft of the
volcano. What was the thickness of this wall? It might be ten feet or
a hundred feet--it was impossible to say. But the subterranean sounds
were too perceptible to allow of the supposition that it was of any
great thickness.

The engineer, after having explored the wall at a certain height
horizontally, fastened the lamp to the end of an oar, and again surveyed
the basaltic wall at a greater elevation.

There, through scarcely visible clefts and joinings, escaped a pungent
vapour, which infected the atmosphere of the cavern. The wall was
broken by large cracks, some of which extended to within two or three
feet of the water's edge.

Cyrus Harding thought for a brief space. Then he said in a low voice--

"Yes! the captain was right! The danger lies there, and a terrible
danger!"

Ayrton said not a word, but, upon a sign from Cyrus Harding, resumed the
oars, and half an hour later the engineer and he reached the entrance of
Dakkar Grotto.

CHAPTER NINETEEN.

CYRUS HARDING GIVES AN ACCOUNT OF HIS EXPLORATION--THE CONSTRUCTION OF
THE SHIP PUSHED FORWARD--A LAST VISIT TO THE CORRAL--THE BATTLE BETWEEN
FIRE AND WATER--ALL THAT REMAINS OF THE ISLAND--IT IS DECIDED TO LAUNCH
THE VESSEL--THE NIGHT OF THE 8TH OF MARCH.

The next day, the 8th of January, after a day and night passed at the
corral, where they left all in order, Cyrus Harding and Ayrton arrived
at Granite House.

The engineer immediately called his companions together, and informed
them of the imminent danger which threatened Lincoln Island, and from
which no human power could deliver them.

"My friends," he said, and his voice betrayed the depth of his emotion,
"our island is not among those which will endure while this earth
endures. It is doomed to more or less speedy destruction, the cause of
which it bears within itself, and from which nothing can save it."

The colonists looked at each other, then at the engineer. They did not
clearly comprehend him.

"Explain yourself, Cyrus!" said Gideon Spilett.

"I will do so," replied Cyrus Harding, "or rather I will simply afford
you the explanation which, during our few minutes of private
conversation, was given me by Captain Nemo."

"Captain Nemo!" exclaimed the colonists.

"Yes, and it was the last service he desired to render us before his
death!"

"The last service!" exclaimed Pencroft, "the last serv