And then, while the others hung back for a moment, and Nort thus dashed ahead alone, his companions saw him quickly disappear. The wall of water suddenly rushed forward, but it never came quite to the place where the party of five now stood in nameless terror--five, for Nort had disappeared into the depths of the stream that had so mysteriously appeared again out of the blackness. From whence it came, and whither it was rushing, not to foam entirely over that startled group, none in it could say. But it had engulfed Nort--that they had seen. CHAPTER XXI THE FIGURE ON THE ROCK Horror and surprise held the five speechless for a moment. Then, as they heard the noise of the rushing water, and saw, by the light of their lanterns, that it came almost to them, but suddenly turned to the right, they came to their senses. "Nort! Nort!" yelled Dick, his voice being flung back at him in echoes from the rocky, vaulted roof of the tunnel. "What in th' world happened?" asked Old Billee in trembling accents. "Nort fell into the stream, and was carried away," answered Bud, his voice choking. "But why doesn't the water reach us?" asked Snake. "That's what we'll have to find out," asserted Bud, bravely. "Come on!" "But be careful," cautioned Billee. "Something may happen t' us, an' then we can't help Nort! Go easy!" He spoke only in time, for the next moment, with an exclamation of horror, Bud and Dick, who had forged ahead, recoiled back. "Look out!" shouted Bud, and he made such a lurch backward to recover his balance that the lantern was flung from his hand. It dropped, as they all could see, into the midst of black, swirling waters, white foam-capped on top. And it was into this stream that Nort had fallen and been carried away, and into this stream that Bud and Dick had been nearly precipitated as they dashed forward. Bud's lantern was extinguished with a hiss as the waters penetrated it and covered the wick. It sank from sight, but not before it had, in a flash, illuminated the surface of the water. "It's a good thing we took the right-hand side," said Billee, as he and the others saw what it was that had caused the water to rush almost to their feet and then branch off. "I mean it's a good thing, for it may help us to solve the mystery. But as for poor Nort----" He did not finish, but Dick sent up a despairing cry: "Nort! Oh, Nort! Where are you?" And only the vaulty echoes answered. "What are we going to do?" asked Snake, who seemed unable to suggest anything. "Everybody come here with their lanterns," directed Bud. "And light that spare one, Billee." Thus was replaced the one he had dropped in the effort to save himself from falling into the same torrent that had engulfed his cousin.