And now the section was opening ahead of them, and the flat, ruddy sands of Mars glittered in the sun's feeble light. There was a yell in unison from eight farmboy throats as the section lifted.

"Sand awa-a-a-ay!" and the first cars in line began to move.

It was the traditional farmboy cry, made thin and almost soprano in the thin air of Mars.

David let in the resistor and crawled across the line that marked the boundary between dome metal and Martian soil.

And it hit him!

The sudden gravity change was like a sharp fall of a thousand feet. One hundred and twenty pounds of Ms two hundred disappeared as he crossed the line, and it left him by way of the pit of his stomach. He clutched at the wheel as the sensation of fall, fall, fall persisted. The sand-car veered wildly.

There was the sound of Griswold's voice, which maintained its hoarseness even in the incongruous hollowness forced upon it by the thin air which carried sound waves so poorly. "Number seven! Back in line!"

David fought with the wheel, fought with his own sensations, fought to make himself see clearly. He dragged at the oxygen through his nosepiece and slowly the worst passed.

He could see Bigman looking anxiously in Ms direction. He took one hand away from the wheel momentarily to wave, then concentrated on the road.

The Martian desert was almost flat, flat and bare. Not even a scrub of vegetation existed here. This particular area had been dead and deserted for who knew how many thousands or millions of years. The thought suddenly struck him that perhaps he was wrong. Perhaps the desert sands had been coated with blue-green microorganisms until Earthmen had come and burned them away to make room for their farms.

The cars ahead trailed faint dust that rose slowly, as if it were part of a motion-picture film that had been slowed down. It settled as slowly.

David's car was trailing badly. He added speed and still more speed, and found that something was going wrong. The others, ahead of him, were hugging the ground but he, himself, was bounding like a jackrabbit. At every trifling imperfection in the ground surface, at every projecting line of rock, his car took off. It drifted lazily up into the air, inches high, its wheels whining against nothing. It came down as gently, then lurched forward with a jerk as the straining wheels caught hold.

It caused him to lose ground, and when he poured the juice in to gain again, the jumping grew worse. It was the low gravity that did it, of course, but the others managed to compensate for it. He wondered how.

It was getting cold. Even at Martian summer, he guessed the temperature to be barely above freezing. He could look directly at the sun in the sky. It was a dwarfed sun in a purple sky in which he could make out three or four stars. The air was too thin to blank them out or to scatter light in such a manner as to form the sky-blue of Earth.

Griswold's voice was sounding again: "Cars one, four, and seven to the left. Cars two, five, and eight to the center. Cars three, six, and nine to the right Cars two and three will be in charge of their subsections."

Griswold's car, number, one, was beginning to curl to the left, and David, following it with his eyes, noticed the dark line on the leftward horizon. Number four was following one, and David turned his wheel sharply left to match the angle of veer.

What followed caught him by surprise. His car went into a rapid skid, scarcely allowing him time to realize it. He yanked desperately at the wheel, spinning it in the direction of skid. He shut off all power and felt the wheels rasp as the car whirled onward. The desert circled before him, so that only its redness could make any impression.

And then there was Bigman's thin cry through the receiver, "Stamp on the emergency traction. It's just to the right of the resistors."

David probed desperately for the emergency traction, whatever it was, but Ms aching feet found nothing. The dark line on the horizon appeared before him and then vanished. It was much sharper now, and broader. Even in that rapid flash, its nature became appallingly evident. It was one of the fissures of Mars, long and straight. Like the far more numerous ones on Earth's Moon, they were cracks in the planetary surface, made as the world dried through millions of years. They were up to a hundred feet across and no man had plumbed their depth.

"It's a pink, stubby button,". yelled Bigman. "Stamp everywhere."

David did so, and there was a sudden slight yielding beneath his toes. The: swift motion of his sand-car became a rebellious grinding that tore at him. The dust came up in clouds, choking him and obscuring everything.

He bent over the wheel and waited. The car was definitely slowing. And then, finally, it stopped.

He sat back and breathed quietly for a moment Then he withdrew his nosepiece, wiped the inner surfaces while the cold air stung at nose and eyes, and replaced it. His clothes were ruddy gray with dust and his chin was caked with it. He could feel its dry-ness upon his lips, and the interior of his car was filthy with it.

The two other cars of his sub-section had pulled up next to him. Griswold was climbing out of one, his stubbled face made monstrously ugly by the nose-piece. David was suddenly aware of the reason for the popularity of beards and stubble among the farmboys. They were protection against the cold, thin wind of Mars.

Griswold was snarling, showing yellowed and broken teeth. He said, "Earthman, the repairs for this sand-car will come right out of your wages. You had Hennes's warning."

David opened the door and climbed out. From outside, the car was a worse wreck still, if that were possible. The tires were torn and from them projected the huge teeth which were obviously the "emergency traction."

He said, "Not one cent comes out of my wages, Griswold. There was something wrong with the car."

"That's for sure. The driver. A stupid, dumb-lug driver, that's what's wrong with the car."

Another car came squealing up, and Griswold turned to it.

His stubble seemed to bristle. "Get the blast out of here, you cinch-bug. Get on with your job."

Bigman jumped out of his car. "Not till I take a look at the Earthman's car."

Bigman weighed less than fifty pounds on Mars, and in one long, flat leap he was at David's side. He bent for a moment, then straightened. He said, "Where are the weight-rods, Griswold?"

David said, "What are the weight-rods, Bigman?"

The little fellow spoke rapidly. "When you take these sand-cars out into low gravity, you put foot-thick beams over each of the axles. You take them out when you're on high grav. I'm sorry, fella, but I never once thought that this might be what____________________ "

David stopped him. His lips drew back. It would explain why his car had floated upward at each bump while the others were glued to the soil. He turned to Griswold. "Did you know they were gone?"

Griswold swore. "Each man is responsible for his own car. If you didn't notice they were gone, that's your negligence."

All the cars were now on the scene. A circle of hairy men were forming around the three, quiet, attentive, not interfering.

Bigman stormed. "You big hunk of silica, the man's a tenderfoot. He can't be expected to- "

"Quiet, Bigman," said David. "This is my job. I ask you again, Griswold. Did you know about this in advance?"

"And I told you, Earthie. In the desert a man has to watch himself. I'm not going to mother you."

"All right. In that case I'll watch myself right now." David looked about. They were almost at the edge of the fissure. Another ten feet and he would have been a dead man. "However, you'll have to watch yourself, too, because I'm taking your car. You can drive mine back to the farm dome or you can stay here for all I care."