"When the worm has gone, one may try to walk out," Kynes said. "You must walk softly, avoid drum sands, tidal dust basins - head for the nearest rock zone. There are many such zones. You might make it."

"Drum sand?" Halleck asked.

"A comdition of sand compaction," Kynes said. "The slightest step sets it drumming. Worms always come to that.

"And a tidal dust basin?" the Duke asked.

"Certain depressions in the dessert have filled with dust over the centuries. Some are so vast they have currents and tides. All will swallow the unwary who step into them."