Syme stopped the car abruptly as a deep, winding channel appeared across their path. "Gully," he announced. "Shall we cross it, or follow it?" Tate peered through the steelite nose of the car. "Follow, I guess," he offered. "It seems to go more or less where we're going, and if we cross it we'll only come to a couple dozen more." Syme nodded and moved the sand car up to the edge of the gully. Then he pressed a stud on the control board; a metal arm extruded from the tail of the car and a heavy spike slowly unscrewed from it, driving deep into the sand. A light on the board flashed, indicating that the spike was in and would bear the car's weight, and Syme started the car over the edge. As the little car nosed down into the gully, the metal arm left behind revealed itself to be attached to a length of thick, very strong wire cable, with a control cord inside. They inched down the almost vertical incline, unreeling the cable behind them, and starting minor landslides as they descended. Finally they touched bottom. Syme pressed another stud, and above, the metal spike that had supported them screwed itself out of the ground again and the cable reeled in. Tate had been watching with interest. "Very ingenious," he said. "But how do we get up again?" "Most of these gullies peter out gradually," said Syme, "but if we want or have to climb out where it's deep, we have a little harpoon gun that shoots the anchor up on top." "Good. I shouldn't like to stay down here for the rest of my natural life. Depressing view." He looked up at the narrow strip of almost-black sky visible from the floor of the gully, and shook his head. Neither Syme nor Tate ever had a chance to test the efficiency of their harpoon gun. They had traveled no more than five hundred meters, and the gully was as deep as ever, when Tate, looking up, saw a deeper blackness blot out part of the black sky directly overhead. He shouted, "Look out!" and grabbed for the nearest steering lever. The car wheeled around in a half circle and ran into the wall of the gully. Syme was saying, "What--?" when there was a thunderous crash that shook the sturdy walls of the car, as a huge boulder smashed into the ground immediately to their left. When the smoky red dust had cleared away, they saw that the left tread of the sand car was crushed beyond all recognition. Syme was cursing slowly and steadily with a deep, seething anger. Tate said, "I guess we walk from here on." Then he looked up again and caught a glimpse of the horde of beasts that were rushing up the gully toward them. "My God!" he said. "What are those?" Syme looked. "Those," he said bitterly, "are Martians."