“A good idea,” Garth cried, and snatching up a magazine rifle, discharged it to the last cartridge. “That ought to fetch ’em,” remarked Haverly cheerfully. Boom! Once more that muffled explosion shook the underworld, succeeded this time by a continuous roar as of a mighty cataract. Thoroughly alarmed, the explorers gazed in the direction whence came the sound. Far away down the coast, its towering crest gleaming through the twilight, appeared a wall of water. With fearful rapidity it roared down upon the helpless vessel. “Great Heaven!” Mervyn burst out, “a tidal wave! We are lost!” Even while the words trembled on his lips, a shout rang high above the boom of the approaching wave, and down the beach at a furious gallop came Muswani. The Ayuti evidently fully realised the peril of the situation. Straight for the motionless _Seal_ he steered his magnificent steed. A few yards from the rail a word of command pealed from his lips, and at that the mighty elk hurled himself into the air. Clearing the rail by a couple of feet, he landed with a crash upon the deck, the hounds following like shadows at his heels. Quick as thought the two men leaped from his back, and raced for the turret. Then, as the door crashed to behind them and the hounds, and before ever Muswani could leap ashore, the watery wall struck the _Seal._ For one brief instant it seemed as though the ill-fated craft would be overwhelmed. The water foamed and surged, boiled and eddied around her; but by some fortunate chance she was lifted high upon the crest of the giant wave, and was swept forward like a feather. “Try your engines,” Garth bawled to his friend, and instantly Wilson darted below again. But the engines with all their power were as toys in the grip of the waters. No power on earth could have forced the vessel forward against that foaming torrent. Lucky, indeed, had Seymour and the Ayuti been to arrive at the moment they did. A few seconds later, and they had been left ashore, separated by many miles of raging water from the vessel and their friends. Their position they knew was perilous in the extreme. At any instant the submarine might be hurled against some iron cliff and shattered like matchwood; yet dangers faced together lost half their terror. United the little band felt equal to anything; so keeping a cheerful courage, they awaited with what patience they could muster the time when the force of the wave should expend itself. But the time sped by, and still the waters roared onward; still the _Seal_ danced and whirled amid the foam-capped waves. Outside, motionless as a statue, keeping his balance upon the slippery deck with wonderful skill, stood Muswani. Not all the violent lurches of the submarine could shake the great elk from his footing. He was immovable as though he were part of the vessel itself.