Leighton had seen figures of like character and workmanship in Bogota, where they were exhibited as ornaments worn by the ancient Chibchas. Usually they were said to have been brought up by divers from the bottom of Lake Guatavita. Hence, there was little doubt as to the origin and antiquity of the disc presented to them by the Black Magnet. But how this disc came to be at the bottom of a well in this vast subterranean labyrinth was not so easily answered. If this disc was the much talked of clew to the lost treasure of the Chibchas, and to all the other mysteries that seemed to crop up at every step the further they went into this cave, it was not an easy one to run down. And then, Miranda, who had insisted all along that by following the direction in which they had been going they were bound to reach the lake, blundered upon the answer to the whole question. "It is Guatavita!" he said. Of course, that was it! Herran and Leighton gasped for a moment as they took in the idea, and then they agreed that Miranda was right. Raoul smiled enigmatically as they discussed the problem in detail. "Well, do you understand it now?" he asked. "Have you discovered Guatavita's secret? I wish I had known it three years ago!" he added bitterly. "Ah! I see--I see!" shouted the doctor excitedly. "There is the well that come out at the bottom of the lake. Here is the magnet that go down there just when the people throw in all the gold. And then it come back here--and no one know except the king and his family. So, every year, they take all the gold of the country. Ah! they are very wise leetle fellows, those kings!" "Then, if this is true," said Leighton meditatively; "if this well has its outlet at the bottom of the lake, and was made and used secretly to collect, by means of the Black Magnet, the treasure offered by the people in the Feast of El Dorado, to-day there is no gold left in Guatavita." "If it were drained of all its waters," remarked Raoul, "I believe that the emptied basin would be found to contain nothing more than a few stray gold ornaments--like the one you fished up just now--that failed to reach the Black Magnet when they were flung into the lake centuries ago." "Your plans to empty the lake, then, are useless?" "After what I have learned to-day, added to what I have long suspected, I should say--quite useless." "But the fabulous amount of treasure those deluded people threw into the lake for centuries----?" "Has all come up here, where we are standing now, caught by the Black Magnet." "He fish very well, this leetle stone," said Miranda, caressing it fondly. "He catch more, better fish than the whole world." "Where is all that gold to-day?" demanded Leighton. "Ah! Where!" "Good heavens! What is that?"