Thirty feet above her hung a dense, poisonous cloud of smoke, blotting out the light of the sun like an immense black curtain, and making the canyon dark as midnight. The rugged walls of the canyon flashed past in a gleaming line as the electric light danced upon them, and around the vessel a shower of ashes began to fall, converting the spotless paint of the deck into a mass of sooty-grey blotches. _Boom!_ A thunderous explosion reverberated down the canyon, shaking the instruments in the turret lockers, and a burst of flame leapt up some distance ahead, its vivid crimson glow paling the beams of the great searchlight. It died away in a moment, “A volcano!” gasped the scientist. Then the _Seal,_ narrowly escaping collision with the rocky wall, swept out of the gorge. Before them, seen dimly through the falling ashes, lay the black and silent waters of a great lake; and, in the midst, its fiery crest glowing like the mouth of the Pit, towered a mighty volcano. CHAPTER IV. TRAPPED! SWIFT as an arrow the submarine swept forward towards the volcano, the foam leaping from her steel nose in two mighty, diverging lines. Without a doubt she was the first vessel to furrow the waters of the lake; yet the explorers would gladly have dispensed with the empty honour of being the discoverers of this barren and desolate region, if, in exchange, they might have retraced their course. But the magnetic power held them too tightly! With a shock which flung the occupants of her turret to the floor, the _Seal_ struck the beach immediately below the crater, burying her prow deep in the yielding sand. As her quivering hull came to a standstill, another booming explosion burst from the volcano, and once more a lurid flash of flame leapt from its glowing mouth, far into the sulphur-laden air above. “Great Heaven!” cried Seymour, “we’re done now for sure!” As the words left his lips Garth entered the turret. “The engines are absolutely useless,” he said gloomily. “Heaven alone knows what’s come to them----” Glancing outside, he paused in the middle of his sentence, stricken dumb by the perilous position of the _Seal._ “Let me introduce you to the North Pole,” Silas said sarcastically; “nice cheerful location, ain’t it?” “And this is the lodestar of the explorers!” Garth exclaimed in disgust, “to reach which so many lives have been sacrificed on the ice-fields of the Arctic Seas.” “It is a terrible disappointment,” muttered Mervyn. “I thought to find here a habitable island, with perhaps men and beasts; but even the sense of disappointment wanes before the peril of the position into which we have been dragged by this magnetic attraction.” “Magnetic attraction!” cried the inventor; “whatever do you mean?”