"Water-freshening plants," said Bordman drily. "Ion-exchange systems. They installed them and had all the fresh water they could wish for. And they wished for a lot. They deep-ploughed, so the water would sink in. They dammed the water-courses. What they did amounted to something like boring holes in that cake of soap I used for an illustration just now. Water went right down to the bottom. What would happen then?" Barnes said: "Why the bottom would get wet--and the soap would slide! As if it were greased!" "Not greased," corrected Bordman. "Soaped. Soap is viscous. That's different, and a lucky difference, too. But the least vibration would encourage movement. And it does. So the population is now walking on eggs. Worse, it's walking on the equivalent of a cake of soap which is getting wetter and wetter on the bottom. It's already sliding as a viscous substance does, reluctantly. But in spite of the oil-slick they're trying to keep in place upwind there's still some battering from the sea. There are still some vibrations in the bed-rock. And so there's a slow, gentle, gradual sliding." "And they figure," said Barnes, "that locking onto a ship with the landing-grid might be like an earthquake." He stopped. "An earthquake, now--" "Not much vulcanism on this planet," Bordman told him. "But of course there are tectonic quakes occasionally. They made this island." Barnes said uneasily: "I don't think, sir, that I'd sleep well if I lived here." "You are living here for the moment. But at your age I think you'll sleep." The bolster-truck turned, following the highway. The road was very even, and the motion of the truck along it was infinitely smooth. Its lack of vibration explained why it was permitted to move when all other vehicles were stopped. But Bordman reflected uneasily that this did not account for the orders of the Sector Chief forbidding the rocket-landing of a ship's boat. It was true enough that the living-surface of the island rested upon slanting stone, and that if the bottom were wet enough that it could slide off into the sea. It already had moved. At least one place was moving at four inches per hour. But that was viscous flow. It would be enhanced by vibration, and assuredly the hammering of seas upon the windward cliff should be lessened by any possible means. But it did not mean that the sound of a rocket-landing would be disastrous, nor the straining of a landing-grid as it stopped a space-ship in orbit and drew it to ground should produce a landslide. There was something else, though the situation for the island's civilian population was already serious enough. If any really massive movement of the ground did begin, viscous or any other, if any considerable part of the island's surface did begin to move, all of it would go. And the population would go with it. If there were survivors, they could be numbered in dozens.