Then he tried the floor. It consisted of slabs of stone. He tapped them here and there, but they gave no hollow ring; apparently they were solid. The ivory tusks were ranged in such orderly rows that it seemed hardly likely the entrance was beneath them. Puzzling over what to do next, he suddenly thought of testing the place with the candle flame. If there were an opening, there must be a current of air. He returned to the slab in the wall of the well and closed it as tightly as was possible from the inside; then placed the candle at several spots on the floor of the cave, one after another, and, retiring to a distance, watched the flame for signs of flickering. But he had no success; the flame only flickered in the current caused by his own movements. "Where can the entrance be?" he said to himself. "The air is stuffy, but not foul. I'll try the passage." He tapped the wall on each side; no sound rewarded him. Then he placed the candle on the floor near the threshold of the cave, and ejaculated "Got it!" when he saw the flame flicker gently. Hastening to the spot, he knelt down and passed his hand slowly over the slabs, and felt a distinct though slight draught at the seam between two of them. He pushed at each of the slabs. They did not move. He got up, and jumped on them as forcibly as the low roof allowed, still without effect. Then, lifting the candle, he examined the walls. At his left hand, near the roof, was a single staple, like those in the wall of the well. It could not be intended for climbing--what, then, was the use of it? Standing under it, he grasped it and pulled. It did not yield. Then he pushed, more and more forcibly. The staple did not move, but he fancied that the slab on which he was standing sank a little. Looking down, he saw, just below the floor, a narrow jutting ledge of rock. With his left foot on this, he pushed at the slab with his right, still shoving at the staple with his hand. The stone began to revolve, slowly, with a slight grinding sound. Presently it stood upright in the middle of the passage, and moved no more. Royce now saw beneath him half a dozen steep steps leading down into gloom. He descended carefully, lighting his way with the candle, and found himself in a passage, narrower than the upper one, but much cooler and less stuffy. From the direction of the cave there was a steady draught.