No, the danger does not lie there!"

Cyrus Harding advanced towards the enormous causeway whose prolongation enclosed the narrow Shark Gulf. He could now sufficiently examine on this side the ancient channels of the lava. There was no doubt in his mind that the most recent eruption had occurred at a far-distant epoch.

He then returned by the same way, listening attentively to the subterranean mutterings which rolled like long-continued thunder, interrupted by deafening explosions. At nine in the morning he reached the corral.

Ayrton awaited him.

"The animals are cared for, Captain Harding," said Ayrton.

"Good, Ayrton."

"They seem uneasy, Captain Harding."

"Yes, instinct speaks through them, and instinct is never deceived."

"Are you ready?"

"Take a lamp, Ayrton," answered the engineer; "we will start at once."

Ayrton did as desired. The onagas, unharnessed, roamed in the corral.

The gate was secured on the outside, and Cyrus Harding, preceding Ayrton, took the narrow path which led westward to the sh.o.r.e.

The soil they walked upon was choked with the pulverised matter fallen from the cloud. No quadruped appeared in the woods. Even the birds had fled. Sometimes a pa.s.sing breeze raised the covering of ashes, and the two colonists, enveloped in a whirlwind of dust, lost sight of each other. They were then careful to cover their eyes and mouths with handkerchiefs, for they ran the risk of being blinded and suffocated.

It was impossible for Cyrus Harding and Ayrton, with these impediments, to make rapid progress. Moreover, the atmosphere was close, as if the oxygen had been partly burnt up, and had become unfit for respiration.

At every hundred paces they were obliged to stop to take breath. It was therefore past ten o'clock when the engineer and his companion reached the crest of the enormous ma.s.s of rocks of basalt and porphyry which composed the north-west coast of the island.

Ayrton and Cyrus Harding commenced the descent of this abrupt declivity, following almost step for step the difficult path which, during that stormy night, had led them to Dakkar Grotto. In open day the descent was less perilous, and, besides, the bed of ashes which covered the polished surface of the rock enabled them to make their footing more secure.

The ridge at the end of the sh.o.r.e, about forty feet in height, was soon reached. Cyrus Harding recollected that this elevation gradually sloped towards the level of the sea. Although the tide was at present low, no beach could be seen, and the waves, thickened by the volcanic dust, beat upon the basaltic rocks.

Cyrus Harding and Ayrton found without difficulty the entrance to Dakkar Grotto, and paused for a moment at the last rock before it.

"The iron boat should be there," said the engineer.

"It is here, Captain Harding," replied Ayrton, drawing towards him the fragile craft, which was protected by the arch of a vault.

"On board, Ayrton!"

The two colonists stepped into the boat. A slight undulation of the waves carried it farther under the low arch of the crypt, and there Ayrton, with the aid of flint and steel, lighted the lamp. He then took the oars, and the lamp having been placed in the bow of the boat, so that its rays fell before them, Cyrus Harding took the helm and steered through the shades of the grotto.

The _Nautilus_ was there no longer to illuminate the cavern with its electric light. Possibly it might not yet be extinguished, but no ray escaped from the depths of the abyss in which reposed all that was mortal of Captain Nemo.

The light afforded by the lamp, although feeble, nevertheless enabled the engineer to advance slowly, following the wall of the cavern. A deathlike silence reigned under the vaulted roof, or at least in the anterior portion, for soon Cyrus Harding distinctly heard the rumbling which proceeded from the bowels of the mountain.

"That comes from the volcano," he said.

Besides these sounds, the presence of chemical combinations was soon betrayed by their powerful odour, and the engineer and his companion were almost suffocated by sulphureous vapours.

"This is what Captain Nemo feared," murmured Cyrus Harding, changing countenance. "We must go to the end, notwithstanding."

"Forward!" replied Ayrton, bending to his oars and directing the boat towards the head of the cavern.

Twenty-five minutes after entering the mouth of the grotto the boat reached the extreme end.

Cyrus Harding then, standing up, cast the light of the 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 s.p.a.ce. 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 pa.s.sed 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 cognisant 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 sulphureous gases generated in the interior of the volcano to escape."