The same question occurred to Burke. The atmosphere of the brightly lighted halls was ominous and secretive. A man alone in a vast empty building would feel queer even in broad daylight with sunshine and other humans to be seen out of any window. But in this monstrous complex of tunnels and rooms carved out of solid stone, with uncountable millions of miles of pure emptiness without, the feeling of loneliness was incredible. He reflected wryly that a dog would be a comforting companion to have on such a journey as his. He went down the long gallery with doors on either side. Past the room with the piled metal ingots. Past the door through which one saw hundreds of ten-foot metal globes. Up a ramp. Past the rooms where something like bunks must once have stood against the walls. A long way along this corridor. Emptiness, emptiness, emptiness. Innumerable echoings of his footsteps on the stone. Three times he stopped at doors that had swung shut, but none was fully closed. All yielded readily. Then he came to the door Sandy had spoken about. He worked the handle repeatedly. It was firmly shut. He kicked the door and with a loud click it swung open. There were lights inside this room, as everywhere else they had explored. But it was nearly impossible to see any distance. This was an extremely long room, and it contained racks of metal which reached from floor to ceiling. Each rack was a series of shallow metal troughs, and in each trough there was a row of crumbly black metal cubes, very systematically arranged. Each side was about three inches square, and they were dull black, not glistening at all. They filled the racks completely. There were narrow aisles between the rows of racks, through which Burke could make his way easily enough, but which a more portly man might have found inconvenient. He stared at a trough, and was stunned. He picked up one of the cubes, and immediately recognized the object in his hand. It was a dull-black, smudgy cube exactly like the one his uncle had brought back from the Cro-Magnon cave in France. He knew that if he dropped this object--found two hundred seventy million miles from the other one--it would split into thousands of tissue-thin, shiny pieces. He did drop it. Deliberately. And it shattered into layers which lay like films of mica on the floor. For no clearly understandable reason, Burke found that his flesh crawled. He had to force himself to stay in this room with so many thousands of the enigmatic cubes. There had been a cube of this kind on Earth. The one he'd known as a child had belonged to a Cro-Magnon tribesman ten thousand, twenty thousand, how many years ago? And it could only have come from this asteroid. Which meant-- Presently he made his way back to the spaceship. He carried one of the cubes, rather gingerly. He meant to show it to Sandy. But the implications were startling.