Green alone remained unmoved. He knew what was happening, but he couldn't blame the rest for their behavior. They had never heard of an electronic eye, so they couldn't be expected to maintain coolness. The only thing that Green feared at that moment was that the outcries would be heard by the savages outside the cave. So he hastened to assure the women that this phenomenon was nothing to be frightened about. It was common in his home country. A mere matter of white magic that anyone could practice. They quieted down but were still uneasy. Wide-eyed, they bunched up about him. "The natives themselves aren't scared of this," he said. "They must come here at times. See? There's an altar built against that dirt wall. And from the bones piled beneath it I'd say that sacrifices were held here." He looked for another door. There seemed to be none. He found it hard to believe that there couldn't be. Somehow he'd had the feeling that great things lay ahead of him. These rooms, and this lighting, were evidences of an earlier civilization that quite possibly had been on a level with his own. He'd known that the island itself must be powered with an automatically working anti-gravity plant, fueled either atomically or from the planet's magneto-gravitic field. Why the whole unit should be covered with rocks and soil and trees he didn't know. But he had been sure that somewhere in the bowels of this mass of land was just such a place as this. And more. Where was the power plant? Was it sealed up so that no one could get to it? Or, as was likely, was there a door to the plant which could not be opened unless one had a key of some sort? First he had to find the door. He examined the altar, which was made of iron. It was a platform about three feet high and ten feet square. Upon it stood a chair, fashioned from pieces of iron. From its back rose a steel rod about half an inch in diameter and ten feet long, its lower end held secure between two uprights by a thick iron fork. Once the fork was withdrawn, the rod would obviously fall over against the earth wall behind it, though the lower end would still remain on the uprights and would, in fact, stick against whoever was sitting in the chair at the moment. "Odd," said Green. "If it weren't for those catheaded idols on the ends of the platform, and the bones at its foot, I'd not know this _was_ an altar. Bones! They're black, burned black." He looked again at the rod. "Now," he said, half to himself, "if I were to withdraw the fork, and the rod fell, it would strike the wall. That is evident. But what is it all about?" Amra brought him some long pieces of rope. "These were stacked against the wall," she said.