"Nuts!" observed Harrison. "Let's hear you explain the reason for that big empty city, then."
"Sure. Tweel's civilization is decadent, that's the reason. It's a dying race, and out of all the millions that must once have lived there, Tweel's couple of hundred companions are the remnant. They're an outpost, left to tend the source of the water at the polar cap; probably there are still a few respectable cities left somewhere on the canal system, most likely near the tropics. It's the last gasp of a race—and a race that reached a higher peak of culture than Man!"
"Huh?" said Harrison. "Then why are they dying? Lack of water?"
"I don't think so," responded the chemist. "If my guess at the city's age is right, fifteen thousand years wouldn't make enough difference in the water supply—nor a
