"Those side-fins," said Chuka's deep voice pleasantly, "the bottom ones, makes things better for you. The shade overhead cuts off direct sunlight, and they cut off the reflected glare. It would blister your skin even if the sun never touched you directly." Bordman did not answer. The caterwheel car went on. It came to a patch of sand--tawny sand, heavily mineralized. There was a dune here. Not a big one for Xosa II, no more than a hundred feet high. But they went up its leeward, steeply slanting side. All the planet seemed to tilt insanely as the caterwheels spun. They reached the dune's crest, where it tended to curl over and break like a water-comber, and here the wheels struggled with sand precariously ready to fall, and Bordman had a sudden perception of the sands of Xosa II as the oceans that they really were. The dunes were waves which moved with infinite slowness, but the irresistible force of storm-seas. Nothing could resist them. Nothing! They traveled over similar dunes for two miles. Then they began to climb the approaches to the mountains. And Bordman saw for the second time--the first had been through the ports of the landing-boat--where there was a notch in the mountain wall and sand had flowed out of it like a waterfall, making a beautifully symmetrical cone-shaped heap against the lower cliffs. There were many such falls. In one place there was a sand-cascade. Sand had poured over a series of rocky steps, piling up on each in turn to its very edge, and then spilling again to the next. They went up a crazily slanting spur of stone, whose sides were too steep for sand to lodge on, and whose narrow crest had a bare thin coating of powder. The landscape looked like a nightmare. As the car went on, wobbling and lurching and dipping, the heights on either side made Bordman tend to dizziness. The coloring was impossible. The aridness, the dessication, the lifelessness of everything about was somehow shocking. Bordman found himself straining his eyes for the merest, scrubbiest of bushes and for however stunted and isolated a wisp of grass. The journey went on for an hour. Then there came a straining climb up a now-windswept ridge of eroded rock, and then the attainment of its highest point--and then the ground car went onward for a hundred yards and stopped. They had reached the top of the mountain range, and there was doubtlessly another range beyond. But they could not see it. Here, as the place to which they had climbed so effortfully, there were no more rocks. There was no valley. There was no descending slope. There was sand. This was one of the sand-plateaus which were a unique feature of Xosa II. And Bordman knew, now, that the disputed explanation was the true one.