Karla looked at where Schroeder was pointing. The herding animals had squeezed into a street as if suddenly inspired by a common purpose. Other mammoths began to follow, and soon the whole group was moving toward the same part of the square. With Karla helping him, Schroeder climbed off the pyramid and hobbled after the departing herd.

By the time they got to the corner, the entire herd had vanished from the square and was moving slowly along a narrow street that led back to the main boulevard. They tried not to startle the animals, although that didn't seem to be a danger. The mammoths seemed to have accepted the newcomers as part of the herd.

After about ten minutes, they began to see a change in the character of the city. Some of the houses on both sides were damaged. Their walls were knocked in as if hit by a rogue bulldozer. Eventually, they came to an area that looked as if it had been bombed. There were no freestanding buildings, only glowing piles of rubble intermingled with huge boulders made of a different, nonluminous mineral.

The sight revived unpleasant memories for Schroeder. He stopped to give his ankle a rest and looked around at the ruined landscape. “This reminds me of Berlin at the end of World War Two. Come. We must hurry or we'll lose them.”

Karla dodged a pile of manure. “I don't think we'll have to worry about that with the trail they're leaving.”

Schroeder's deep laughter echoed off the walls of rubble that now arose high on both sides. Karla joined in despite her weariness and fears, but they picked up the pace more in eagerness to find a way out than concern at losing the herd.

More of the rock they were seeing was composed of nonglowing material. Then all trace of the luminescent rock disappeared and the path in front of them darkened. Karla turned the flashlight on, and its dim beam caught the tails of the mammoths. The creatures had no trouble navigating the darkness. Karla guessed that their eyes must have adjusted to the lack of light in the same way their bodies had shrunk to accommodate a diminishing supply of food.

Then the flashlight went dead. They followed the herd by listening to the scuffle of the many feet, and the chorus of grunts and snorts. The complete blackness assumed a bluer cast that slowly changed to dark gray. They could see the furry rumps about fifty feet ahead. The animals seemed to have picked up their pace. The grayness turned to white. The path made a right, then a left-hand turn, and they were out in the open, blinking their eyes against the sunlight.