At this gruesome sight Royce felt that he had had enough for the moment. The air was stifling, rendered still worse by the smoky candle. He retraced his steps, stood firmly on the staple in the slab, and this time pushing at the other staple, caused the stone to revolve on its pivot and set flush with the wall. "What does it all mean?" he thought, as he sat in his room above, eating the frugal dinner which Kulana brought him. He remembered what the old chief had told him about Goruba--that he had been lieutenant of Rabeh, the extraordinary negro who had risen from the position of a slave to the lordship of a great territory in the Sahara, tyrannised over the natives, and long defied the efforts of the French to put him down. Was this secret hoard of wealth Rabeh's? Had he stored it in this cavern in the side of the hill, hoping some day, when he had defeated the French, to dispose of it? "That must be the explanation," Royce concluded. "I don't know anything about the ivory trade, but those tusks must be of immense value, and must have represented a vast fortune even to a potentate like Rabeh. I suppose he let Goruba into the secret. When he was killed and his empire broken up, Goruba was for years a fugitive, the old man said. But he was ambitious, like his master. He always meant to get hold of this treasure. What Rabeh had done, he thought he could do. No doubt he joined the Tubus because their country is near this fort, and has gradually made himself a power with them. That's why he comes on his lonely visits--to see that Rabeh's hoard is safe. I don't suppose the Tubus know anything about it. It wouldn't suit his plans to inform them until he has made himself their absolute master." Then his thoughts turned in another direction. "How many villages were sacked, how many thousands of poor wretches were killed or enslaved in the gathering of this hoard? And Goruba is like his master in that, too--he is the same blood-thirsty tyrant and oppressor. But, please God, Tom will give him a shake. "Ah! those skeletons--how did they come there?" He pondered for a time without arriving at a conclusion. "I see!" he said to himself at last. "They are the skeletons of the poor slaves who dug the passage Rabeh killed them to preserve his secret. Horrible! ... But I haven't discovered everything yet. Where is the entrance at the other end, by which Goruba reaches the cavern? I must go again--but not to-day. I can't face those skeletons again to-day; to-morrow, perhaps." CHAPTER XXIII GORUBA IS CAUGHT On the morning after his discovery of Rabeh's hoard, Royce made a second visit to the cave to search for the exit which he felt sure must lead to the outer air. Carrying a lighted candle, he walked slowly round the walls, examining them carefully. They appeared to be in their natural state--rough, irregular, knobby, but with no hole or gap large enough to admit a man.