“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.  The water, rushing into a cavity whose temperature might be estimated at thousands of degrees, would be converted into steam with a sudden energy which no enclosure could resist.

It was not therefore doubtful that the island, menaced by a frightful and approaching convulsion, would endure only so long as the wall of Dakkar Grotto itself should endure.  It was not even a question of months, nor of weeks, but of days; it might be of hours.

The first sentiment which the colonists felt was that of profound sorrow.  They thought not so much of the peril which menaced themselves personally, but of the destruction of the island which had sheltered them, which they had cultivated, which they loved so well, and had hoped to render so flourishing.  So much effort ineffectually expended, so much labor lost.