"That is strange," said Leighton coldly. "You left us, without a word, at a time when you were needed. The attack that you say was made upon you we should have heard. But--we have heard nothing." "Believe me, or not, as you like; it is true," was the sullen reply. "Why do you say we have the secret of Guatavita?" "Look!" Raoul pointed to the projection in the wall behind which the Black Magnet had disappeared. It was not a shelf, as they had at first supposed, but the opening of a shaft, or well, that slanted downward at an angle that in the course of fifty feet, or less, would reach considerably beyond the vertical line of the cave's wall. In shape this shaft was oblong, slightly larger in length and in breadth than the Black Magnet. It was evidently of artificial origin, its four walls being perfectly smooth and without irregularities of line. Even by one who had not seen the magnet descend into this shaft, its intended use as a sort of runway for raising and lowering heavy bodies would be quickly recognized. But where it led to was another matter. One thing was easily discovered: where it reached a point some twenty feet below the level of the cave's floor the shaft was filled with water. Beyond this, of course, nothing could be made out. It was to the bottom of the pool thus indicated that the magnet had plunged. "It is a well hewn out of the rock by Indians--or perhaps by Spaniards digging for gold," said Leighton. "I believe that we are the first white people who have ever stood in this place," said Raoul; then added, "unless David Meudon was here three years ago." "But what is it about?" demanded Miranda impatiently. "What for is the magnet, and this well, and this machine?" "Pull up the magnet and see for yourself," was the laconic reply. "Caramba! That will be impossible," protested the doctor, not relishing the prospect of another turn at the machine. "It is the logical thing to do," agreed Leighton.