Venus Shadow."

Jan whistled softly. He had seen the effects of that disease. Dekker was right.

"Jan, you're the best driver in Oostpoort," said Dekker. "You will have to take a groundcar to Rathole and bring the fellow back."

So now Jan gripped his clay pipe between his teeth and piloted the groundcar into the teeth of the Twilight Gale.

Den Hoorn was a comparatively flat desert sweep that ran along the western side of the Oost Mountains, just over the mountain from Oostpoort. It was a thin fault area of a planet whose crust was peculiarly subject to earthquakes, particularly at the beginning and end of each long day when temperatures of the surface rocks changed. On the other side of it lay Rathole, a little settlement that eked a precarious living from the Venerian vegetation. Jan never had seen it.

He had little difficulty driving up and over the mountain, for the Dutch settlers had carved a rough road through the ravines. But even the 2½-meter wheels of the groundcar had trouble amid the tumbled rocks of Den Hoorn. The wind hit the car in full strength here and, though the body of the groundcar was suspended from the axles, there was constant danger of its being flipped over by a gust if not handled just right.

The three earthshocks that had shaken Den Hoorn since he had been driving made his task no easier, but he was obviously lucky, at that. Often he had to detour far from his course to skirt long, deep cracks in the surface, or steep breaks where the crust had been raised or dropped several meters by past quakes.

The groundcar zig-zagged slowly westward. The tattered violet-and-indigo clouds boiled low above it, but the wind was as dry as the breath of an oven. Despite the heavy cloud cover, the afternoon was as bright as an Earth-day. The thermometer showed the outside temperature to have dropped to 40 degrees Centigrade in the west wind, and it was still going down.

Jan reached the edge of a crack that made further progress seem impossible. A hundred meters wide, of unknown depth, it stretched out of sight in both directions. For the first time he entertained serious doubts that Den Hoorn could be crossed by land.

After a moment's hesitation, he swung the groundcar northward and raced along the edge of the chasm as fast as the car would negotiate the terrain. He looked anxiously at his watch. Nearly three hours had passed since he left Oostpoort. He had seven hours to go and he was still at least 16 kilometers from Rathole. His pipe was out, but he could not take his hands from the wheel to refill it.

He had driven at least eight kilometers before he realized that the crack was narrowing. At least as far again, the two edges came together, but not at the same level. A sheer cliff three meters high now barred his passage. He drove on.

Apparently it was the result of an old quake. He found a spot where rocks had tumbled down, making a steep, rough ramp up the break. He drove up it and turned back southwestward.

He made it just in time. He had driven less than three hundred meters when a quake more severe than any of the others struck. Suddenly behind him the break reversed itself, so that where he had climbed up coming westward he would now have to climb a cliff of equal height returning eastward.

The ground heaved and buckled like a tempestuous sea. Rocks rolled and leaped through the air, several large ones striking the groundcar with ominous force. The car staggered forward on its giant wheels like a drunken man. The quake was so violent that at one time the vehicle was hurled several meters sideways, and almost overturned. And the wind smashed down on it unrelentingly.

The quake lasted for several minutes, during which Jan was able to make no progress at all and struggled only to keep the groundcar upright. Then, in unison, both earthquake and wind died to absolute quiescence.

Jan made use of this calm to step down on the accelerator and send the groundcar speeding