It was during one of these rests that Pelton noticed crystals of a bluish, semi-opaque mineral clinging to the rocks about him. These crystals appeared to become more and more plentiful as they neared the summit of the volcano. Pelton knew something of mineralogy, but never in his considerable experience had he encountered such a substance. Curious to know its nature, he thrust several pieces into his pack; hoping that some day, if luck was with him, he might analyze them. Just as the two Americans were starting on the last hundred feet of climbing that lay between them and their goal a large cloud came over the declining sun and an ominous gloom settled over the world. And now the youths peered eagerly over the rim of the crater into "The Devil's Nest." Five minutes later they had descended fifty feet to its floor. They found themselves in a small, circular valley about a thousand feet across. Everywhere, topping the walls of multi-colored stone that surrounded it, were pinnacles of the strange blue mineral, pointing toward the sky like the thin minarets of a city of goblins. On the summit of the rocky barrier at the western side of the crater was a huge mass of the crystal that gleamed darkly under the shadow of the obscuring cloud which hung persistently before the sun. "This place has more weird beauty than 'The Island of Death'," said Calhoun. "It would make a fine painting. Somehow, there's something about it that gives me a creepy feeling." There were a few patches of hardy grass and several bushes scattered here and there over the floor of the crater. Suddenly Pelton's searching eyes fell upon a circular spot of bleached earth, not more than ten feet across, lying thirty paces away at the center of the valley. For a moment he scrutinized it intently and then he grasped his companion violently by the arm. "Look, George!" he cried. A moment later the two youths were bending over a pair of human skeletons whitened by years of exposure. With them there lay several coins, two tarnished brass buckles and the rusted remnants of a few metal buttons. The owners of those bones had obviously been dead for a very long time. "These are evidently the men that Diaz spoke of," said Pelton, "but what in the name of Heaven could have killed them, George?" There was a look almost expressive of fear in his face. "Volcanic gases, probably," essayed Calhoun. "Impossible, man!" returned Pelton; "This volcano has certainly been extinct for ages." Calhoun knelt down beside the skeletons and began to examine them. "Let's see if there are any marks of violence, fractured skulls, broken ribs, or anything," he said. Pelton stepped back from the ghastly patch of earth. Never afterward was he able to tell exactly why.