There, through scarcely visible clefts and joinings, escaped a pungent vapor, 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 19

The next day, the 8th day 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 service! You will see that though he is dead he will render us others yet!"

"But what did the captain say?" inquired the reporter.

"I will tell you, my friends," said the engineer. "Lincoln Island does not resemble the other islands of the Pacific, and a fact of which Captain Nemo has made me cognizant must sooner or later bring about the subversion of its foundation."

"Nonsense! Lincoln Island, it can't be!" cried Pencroft, who, in spite of the respect he felt for Cyrus Harding, could not prevent a gesture of incredulity.

"Listen, Pencroft," resumed the engineer, "I will tell you what Captain Nemo communicated to me, and which I myself confirmed yesterday, during the exploration of Dakkar Grotto.

"This cavern stretches under the island as far as the volcano, and is only separated from its central shaft by the wall which terminates it. Now, this wall is seamed with fissures and clefts which already allow the sulphurous gases generated in the interior of the volcano to escape."

"Well?" said Pencroft, his brow suddenly contracting.

"Well, then, I saw that these fissures widen under the internal pressure from within, that the wall of basalt is gradually giving way and that after a longer or shorter period it will afford a passage to the waters of the lake which fill the cavern."

"Good!" replied Pencroft, with an attempt at pleasantry. "The sea will extinguish the volcano, and there will be an end of the matter!"

"Not so!" said Cyrus Harding, "should a day arrive when the sea, rushing through the wall of the cavern, penetrates by the central shaft into the interior of the island to the boiling lava, Lincoln Island will that day be blown into the air--just as would happen to the island of Sicily were the Mediterranean to precipitate itself into Mount Etna."

The colonists made no answer to these significant words of the engineer. They now understood the danger by which they were menaced.

It may be added that Cyrus Harding had in no way exaggerated the danger to be apprehended. Many persons have formed an idea that it would be possible to extinguish volcanoes, which are almost always situated on the shores of a sea or lake, by opening a passage for the admission of the water. But they are not aware that this would be to incur the risk of blowing up a portion of the globe, like a boiler whose steam is suddenly expanded by intense heat.