Then suddenly, a sheet of open water appeared ahead, and at the sight a simultaneous cry of relief went up. Another moment and the vessel would have been out of the gorge, and safe from the perils of the crumbling cliff; but in the very instant of her escape, like the crack of doom, a thunderous explosion volleyed through the canyon. With the sound, the tottering wall of rock bent and swayed, then crashed downward with a deafening roar. Almost, the _Seal_ was clear of the falling _debris_--almost, but not quite. A colossal boulder caught her stern, ripping the whirling propellers from their sockets, and smashing her steering gear to a mass of scrap-iron. “Done!” Garth gasped, staggering under the shock; “the beastly thing’s snapped the propellers, and they were the only ones I had.” The others did not take in the significance of this remark for some moments. They were too occupied in a scrutiny of the curious place the _Seal_ had entered. It was a great circular basin or funnel, enclosed on every side by towering cliffs, and around it the water was sweeping in a giant eddy. Into this the vessel was instantly drawn, being helpless as any log in the whirling water. Turning, the adventurers gazed towards the gorge through which they had come. It had ceased to be. The fall of the cliff had completely choked the passage, _and the basin was now without outlet!_ “I guess the old _Seal’s_ fairly trapped,” remarked Silas gloomily; “it would ha’ been better if the plaguey cliff had buried us all, ’stead of shuttin’ us up in this hole.” As he spoke, Wilson came upstairs. “You’d better come down, Garth,” the engineer said; “there’s a bad smash astern, and I can’t manage it myself.” Glad of aught to relieve the awful depression which had succeeded the excitement of the race through the gorge, the inventor followed his friend below, to do what he could towards patching up the damage. “It’s a terrible outlook,” Mervyn muttered, “to be fastened up here until our provisions give out, and then--death by starvation.” “A terrible outlook indeed,” granted Seymour. “It’s maddening to think that we have escaped all the perils of the underworld, only to be hopelessly imprisoned in this rocky basin.” “Say, what’s this steam mean?” asked Haverly, who stood with face pressed to the glass. A mist-like vapour had commenced to rise from the surface of the gyrating water, growing denser in volume each moment, until the walls of the basin were almost hidden. “Trouble again, I reckon,” the American continued; “I guess we’ve struck little else this trip, so far.” “Some volcanic disturbance,” exclaimed Mervyn. “I----” The words died on his lips in a gasp, as a fresh development forced itself upon his notice. The water in the basin was rising! “Wal, that licks all!” cried Silas, as he too became aware of this new movement; “not content with pluggin’ us up here, it’s goin’ to jam us up against the roof.”