Chenobi gazed with pride upon his giant steed. It would mean no slight wrench when the time came for him to part with the magnificent brute; but that had not to be considered yet. Time enough to think of that when they got out of the grip of the tidal wave, which foamed forward relentless as ever. The shore had long since faded from view. Nought was visible on either hand but a waste of waters, tumbling and foaming in mad confusion. And ever and anon a thunderous explosion would burst out, echoing across the water like the firing of great guns. Once, close alongside, the mighty body of an ichthyosaurus was flung up, rent and torn in ghastly fashion by some giant natural force. Suddenly a cry came from Seymour. “Great Scott! Look there!” The others turned quickly. To starboard a beetling line of cliffs loomed into view, threatening and terrible. Next moment an exclamation from the American announced the appearance of a similar barrier upon the port side. Through the canyon or gorge thus formed, the waters swept in a maddened torrent, the _Seal_ lurching and rolling in a fashion which bade fair to capsize her. A hundred times--ay, more--she seemed likely to be dashed against one or other of the rocky walls, but by a miracle she escaped destruction in this manner. So for perhaps an hour she was swept forward; then a terrible fact became apparent to the adventurers. Silas was the first to notice it. “Say!” he remarked, “I guess these yer cliffs are closing in on us.” “What do you mean?” asked the scientist; “how closing in?” “Just cast your eye to the top of this starboard wall,” was the reply; “if the hull outfit ain’t leaning outward, call me a darn nigger.” An instant’s scrutiny showed Mervyn that the thing was true. Shaken to its foundations by the force of the explosions, which moment by moment were becoming more frequent, the whole cliff was tottering to its fall. How long it would be ere it thundered down upon the hapless submarine none could tell. “Full speed ahead!” Silas snapped, his voice recovering its strength under the excitement of the moment; “we must get out of this or we’re done.” All saw the force of his words, and within two minutes the _Seal_ was leaping forward like a flash of light, her whole hull quivering with the throb of the engines. Her pace was tremendous. The cliffs dashed past in a dazzling line on either side, and still the tottering mass to starboard hung poised, as though loth to crush the gallant vessel and her crew. The moments seemed to crawl by, and each was laden with the suspense of a century. How long till this gorge shall end? was the cry of each of the comrades. How long till these rocky walls shall cease?