"Stay close to Thamon," he warned, and started off down the valley, the rest of the party following him. Lightened as they were to keep from sinking deep into the treacherous powdery sand, the humans made fast progress, accelerated by the strong breeze that blew at their backs down the valley. At that, Dynamon realized that the lofty mountains on either side provided protection against immeasurably stronger winds higher up. From the saw-toothed peaks on the left, dark streamers of sand stood out for yards, indicating constant winds of gale proportions up there. * * * * * The valley itself, as far as Dynamon could see in the dim half-light, was barren of any kind of life. There was no sign of a creeping, crawling, or flying creature; nor was there any vegetation, trees or grass. Dynamon led his column nearly a mile down the unchanging gray of the valley and then called a halt. "Thamon," he said, beckoning the scientist to him, "can you see any possibility of human habitation in this valley?" "Off-hand, I don't, not on the surface," the scientist replied. "I would have to test the atmosphere for oxygen, but I doubt if there is a large enough proportion. My guess is that there is nothing but nitrogen in this air. That won't support human life, or any other kind of life except possibly certain kinds of plants." "What about tridium?" said Dynamon. "How do you go about looking for it?" "Electrophysiological tests of all kinds," said Thamon. "I must say this valley doesn't look very encouraging. It looks like burned out volcanic ash. Say! What's that up the valley?" Dynamon gazed back in the direction of the Cosmos Carrier, and felt an uneasy prickling along his spine. The desert valley floor behind them seemed suddenly to have sprouted some tall bushes. There were possibly a dozen of them standing at intervals of twenty yards. They were too far away--perhaps one eighth of a mile--for Dynamon to see them very well, but they appeared to consist of a score of leafless branches radiating outward in all directions from a small core. It was as if a basket ball was bristling with ten-foot javelins. "Where did they come from?" Dynamon gasped. "I didn't see them when we walked over that ground a few minutes ago." "Nor I," agreed Thamon. "I can't imagine where they came from." Just then one of the bushes apparently moved a few feet as if blown by the wind. "Good Lord!" exclaimed Thamon. "Did you see that? One of those things rolled forward!" Then another of the fantastic bushes started to roll, and another, and another. In a moment all twelve of the extraordinary apparitions were rolling rapidly down the wind toward the humans. Dynamon felt the hair on the back of his neck stiffen, and he sprang into action, commanding his soldiers to converge around him. "Thamon, what _are_ those things!" Dynamon cried.