"There's been irrigation," said Hardwick patiently. "The soil here was all ocean-bottom, once--it used to be what is called globigerinous ooze. There's no sand. There are no stones. There's only bedrock and formerly abyssal mud. And--some of it underneath is no longer former. It's globigerinous ooze again." He waved his hand at the landscape. It had been remarkably tidy, once. Every square foot of ground had been cultivated. The highways were of limited width, and the houses were neat and trim. It was, perhaps, the most completely civilized landscape in the galaxy. But Hardwick added: "You said the stuff felt like soap. In a way it's acting like soap. It lies on slightly slanting, effectively smooth rock, like a soap-cake on a slightly slanting sheet of metal. And that's the trouble. So long as a cake of soap is dry on the bottom it doesn't move. Even if you pour water on top, like rain, the top will wet, and the water will flow off, but the bottom won't wet until all the soap is dissolved away. While that was the process here, everything was all right. But they've been irrigating." They passed a row of neat cottages facing the road. One had collapsed completely. The others looked absolutely normal. The bolster-truck went on. Hardwick said, frowning: "They wanted the water to go into the soil. So they arranged it. A little of that did no harm. Plants growing dried it out again. One tree evaporates thousands of gallons a day in a good trade wind. There were some landslides in the early days, especially when storm-swells pounded the cliffs, but on the whole the ground was more firmly anchored when first cultivated than it had been before the colonists came." "But--irrigation? The sea's not fresh, is it?" "Water-freshening plants," said Hardwick dryly. "Ion-exchange systems. They installed them and had all the fresh water they could wish for. And they wished for a lot. They deep-plowed, so the water would sink in. They dammed the water-courses--and it sank in. What they did amounted to something like boring holes in the 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 wet ... and slide! As if it were greased!" "Not greased," corrected Hardwick. "Soaped. Soap is viscous. That is different--and a lucky difference! But the least vibration would encourage movement. And it does. It has. 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 bedrock. And so there's a slow, and gentle, and gradual sliding."