“No doubt of it, from what I heard that fellow Mudd say,” replied Dick. “But let’s think what we had better do.” Doctor Dan gave one of his short laughs. “If you want to find her I can tell you how,” he said. “Tell it, then, for gracious sake!” cried Charley. “Mount that horse, turn his head toward the canyon and give him free rein. I’ll bet you what you like he’ll take you straight to the place where they halted. If you knew these mustangs of ours as well as I do you would say the same thing.” “It’s a splendid idea and we’ll try it right now!” cried Dick. “Shall we pack the canoe on behind the saddle?” “I think we had better. It may hold three but it will never hold four in case we find the girl. I can work my way back to camp through the canyons all right, don’t you be afraid of that.” Doctor Dan then caught the horse, which Dick mounted, after the canoe had been folded up and placed behind the saddle. He then started, Charley and Doctor Dan following behind. Dick threw the bridle down on the horse’s neck and the sure-footed little mustang walked straight toward the entrance of the canyon, but instead of turning into it, kept on under the cliffs. “Hello! It seems they didn’t come the way you thought they did after all!” exclaimed Doctor Dan; “probably there is another canyon just beyond here and----” “Gee! There it comes again!” broke out Charley, pointing off on the lake. The water had begun a furious commotion close to the shore. Dick stopped the horse and all remained staring at it for a minute or more, but as yet nothing appeared. CHAPTER X. EXPLORING AROUND THE LAKE. If Dick and Doctor Dan expected to see a new monster come up out of the lake that was the time they got left. Charley said from the first that nothing was coming and he was right. “It’s not old P. D.,” he declared; “that isn’t the way he boils the pot.” Doctor Dan looked a bit puzzled. “Might I inquire,” he asked in his stately way, “what you mean by old P. D.?” “Why, certainly,” replied Charley. “Life is altogether too short to say Plesiosaurus Dolichodeirus every time and even Plesiosaurus without the doli-what’s-its-name takes too long, so from this time on I shall speak of our rubber-necked friend as old P. D.” “Exactly,” said Doctor Dan. “Now that I know I shall remember. I am not familiar with the scientific names of these monsters. I expect to see something. Watch! It will come. On this very spot Ike Izard and I saw the water boil like this.” “And nothing came of it?” asked Charley. “Nothing then. The monster did not rise.” “No, nor no monster will rise this time,” said Charley, emphatically. “You’ll see.” “I think I know what you are driving at,” said Dick. “You are thinking of the underground lake we talked about.” Charley nodded. Doctor Dan looked puzzled, not understanding what that had to do with the boiling of the water which still continued. They watched the troubled surface of the lake for several minutes.