He noticed how living in this new cliff had slowed his pulse, slowed everything. A mineral result, protection against the solar radiations. Life was still swift, but not as swift as before. "Now, Sim!" cried Lyte, testing the valley air. They ran. Between the hot death and the cold one. Together, away from the cliffs, out toward the distant, beckoning ship. Never had they run this way in their lives. The sound of their feet running was a hard, insistent clatter over vast oblongs of rock, down into ravines, up the sides, and on again. They raked the air in and out their lungs. Behind them the cliffs faded away into things they could never turn back to now. They did not eat as they ran. They had eaten to the bursting point in the cave, to save time. Now it was only running, a lifting of legs, a balancing of bent elbows, a convulsion of muscles, a slaking in of air that had been fiery and was now cooling. "Are they watching us?" Lyte's breathless voice snatched at his ears, above the pound of his heart. Who? But he knew the answer. The cliff peoples, of course. How long had it been since a race like this one? A thousand days? Ten thousand? How long since someone had taken the chance and sprinted with an entire civilization's eyes upon their backs, into gullies, across cooling plain. Were there lovers pausing in their laughter back there, gazing at the two tiny dots that were a man and woman running toward destiny? Were children eating of new fruits and stopping in their play to see the two people racing against time? Was Dienc still living, narrowing hairy eyebrows down over fading eyes, shouting them on in a feeble, rasping voice, shaking a twisted hand? Were there jeers? Were they being called fools, idiots? And in the midst of the name calling, were people praying them on, hoping they would reach the ship? Yes, under all the cynicism and pessimism, some of them, all of them, must be praying. Sim took a quick glance at the sky, which was beginning to bruise with the coming night. Out of nowhere clouds materialized and a light shower trailed across a gully two hundred yards ahead of them. Lightning beat upon distant mountains and there was a strong scent of ozone on the disturbed air. "The halfway mark," panted Sim, and he saw Lyte's face half turn, longingly looking back at the life she was leaving. "Now's the time, if we want to turn back, we still have time. Another minute--" * * * * * Thunder snarled in the mountains. An avalanche started out small and ended up huge and monstrous in a deep fissure. Light rain dotted Lyte's smooth white skin. In a minute her hair was glistening and soggy with rain. "Too late now," she shouted over the patting rhythm of her own naked feet. "We've got to go ahead!" And it was too late. Sim knew, judging the distances, that there was no turning back now.