Then, when their hunger was satisfied, they resumed their places in the turret, wondering what would be the end of their marvellous and terrible journey. Now the roof of the passage would sink, until a few inches only separated the rock from the top of the turret; anon it would rise and become lost to sight as the _Seal_ swept into some vast subterranean chamber, whose midnight darkness the light of the great arc-light seemed but to render more intense, as it trembled through it for a brief moment, then vanished as the vessel swept on. Where would it end? The fateful question hammered at the watchers’ brains as they stood through the long hours, silently awaiting the end. “For Heaven’s sake, speak, some of you!” Seymour cried at last, after a long interval, during which no word had been spoken, “this silence is enough to drive one mad!” “Of what should we speak, my friend?” the scientist asked gravely. “The while our fate is trembling in the balance, our lives hanging, as it were, upon a thread, there seems but little attraction in conversation, however interesting in the ordinary course of events the subject may be.” “I hold there’s no call to despair yet awhile,” Silas interrupted sharply; “the old _Seal’s_ a stayer, an’ so long as she keeps her end up, we’ll pull through.” “Good old Silas!” Seymour cried, clapping his friend on the back. “Wal, it’s this way,” Haverly went on, “I’ve come out of so many tight corners with a whole skin, that one more or less makes no difference. You Britishers pride yourselves on your ‘never say die’ motto. I guess this is a suitable time to apply the same. Say, William, you recollect that little bit of a scrap on the Amazon, six years back?” “Rather,” Seymour returned. “Wal, I reckon as that was considerable tighter than the present situation. You see, professor, it----” He broke off abruptly, as from somewhere far ahead came a murmuring drone, like the first low note of some giant organ. “What is it?” Mervyn asked. The millionaire flung open the door. A cool, damp wind, laden with spray, whistled up the tunnel, and the drone grew in volume as the submarine swept on. A puzzled expression passed over Haverly’s features as he stood listening for some moments. Then his brow cleared and he slammed to the door. “I guess we’re nearing the end,” he said; “it’s the sound of a waterfall.” His comrades gazed despairingly into each other’s faces. What they had feared for so long was about to happen. Somewhere, not far ahead, the river thundered into space over the brink of some subterranean precipice, and towards this spot the _Seal_ was racing. The water hissed and foamed about her stern, and long lines of bubbles, gleaming like pearls beneath the searchlight’s glare, danced far ahead, to lose themselves in the darkness of the tunnel.