For half an hour the horses toiled up the steep slope, first to the right, then to the left, but always rising until at last they came suddenly out upon a level plain, entirely surrounded by towering cliffs, except for the narrow break through which they entered. “The crater of an old volcano!” cried Dick. “That’s what this place is sure.” “So I have been informed,” replied Doctor Dan, with his usual gravity. “Where’s the lake?” asked Charley. “Just around that bend in the cliffs,” was the reply. “This sink is double, as you may say. The wall runs pretty near through the middle of it. One half is dry and the lake fills the other half. We shall see it in a minute now.” They rode on and soon turned the corner of the dividing cliff. A broad stretch of water now lay before them. The lake was many times longer than the dry half of the old crater. Its surface was perfectly placid and the water seemed to give out a strange, sulphurous odor. The shores were broken by projecting points of rocks, which cut up the lake into many small coves. “Now, where’s your Plesiosaurus?” exclaimed Charley. “Let him show himself. He’s got an audience that will appreciate him, you bet.” “It was right over there abreast that little island that I first saw him,” said Doctor Dan, gravely. “His body reached almost to that point of rocks on the opposite shore. I hope you don’t think it is all a fake, boys, but I suppose you will never believe it until you see for yourselves.” “That’s what we are here for,” replied Dick, “and it is no reflection on you, doctor, if we find it hard work to believe what we have not seen, but where do we make our camp?” Doctor Dan pointed out the spot where he and Ike Izard had camped and there, sure enough, the boys found traces of a fire and other things which seemed to prove his story true. The horses were now hobbled and the tents pitched. Dr. Dan cooked supper in his usual fine style and everything was arranged for the night. When the supper was over, as it was not yet dark, Dick proposed a walk, and all three, shouldering their rifles, for there was no telling what might happen, started along the lake shore, winding in and out around the projecting cliffs until they had gone at least a mile. It was now getting toward dusk and Dick, in spite of his hopes, began to abandon all idea of seeing anything of the monster of the lake that day. “I suppose we might wait around here for days and not see him,” he said. “Wonder how long a Plesiosaurus can stay down under the water, anyhow?” “Is it known?” asked Doctor Dan. “Certainly not, since only their bones have been found,” replied Charley, “but it must be an air breathing animal or it couldn’t have swum round with its head above the water the way you saw it.” “If that’s the case he must come up every little while,” said Dick.