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 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.