They lurched across a small gulch and onto a silty flat, winding to avoid the thorn bushes that were scattered across it. The morning air was still and the dust they raised followed them in a dense cloud, coating their faces and clothing an iridescent gray, gritting harshly wherever two parts of metal moved together, such as the driving controls.

They had traveled an hour, enclosed in the cloud of destructive dust, when Blake said, "I wonder-"

"You wonder what?" Cooke asked, his black eyes made blacker by the gray dust that covered his face.

"I wonder if this diamond dust hasn't got us behind an eight-ball-a big, shiny eight- ball named Aurora."

They worked their way along the southern foot of the mountain, toward the high plateau to the east where the creek might have its headwaters. They prospected the canyons one by one, both by carrying back samples of the bedrock gravels to the truck, to pan for particles of the heavy uranium and cadmium ores they sought, and by use of the Geiger counters they each carried. Cooke ran the gauntlet from his first feeling of carefree adventure to a condition of sore, aching legs and blistered hands. Their picks and shovels wore away with amazing rapidity, even from digging in the comparatively loose gravels of the canyon beds, and they found nothing.

They reached the eastern end of the range, a high, bleak plateau where the creek had its headwaters and where the nights were chilly with the breezes from the slowly melting s...o...b..nks. There was nothing there but barren flow rocks and the inevitable diamond so they turned and worked their way back down the northern side of the range. Cooke's soft muscles hardened and his habitual optimism returned, undaunted by the lack of heavy- metal concentrates in the samples they panned or by the Geiger counters that remained silent but for the intermittent clicking of the natural background count.

Twice they found veins of soft iron oxide and once they found a narrow vein of low- grade copper ore but the mountain seemed devoid of any uranium or of any lead-zinc ore that might contain the cadmium they needed.

Blake cared for the little truck with painstaking attention, doing everything possible to keep the diamond dust out of its moving parts. But no way could be devised to keep the dust out of such moving parts as the brake drums, the ball and socket of the front- wheel drive, the control-lever linkage, the winch they were forced to use so many times, and many other moving parts. The air filter caused him more worry than anything else. He knew a certain amount of the fine dust was getting past the filter and into the motor, and there was nothing he could do about it. It was a good filter, made to protect an engine against silica dust; any silica dust fine enough to get past the filter would be too fine to cause any damage before it was reduced to an impalpable powder. But the diamond dust it admitted was six times harder than silica, as well as tougher-the diamond dust would refuse to be reduced to a harmless, impalpable powder.

They rounded the west end of the range early on the thirtieth day and saw the green line of the creek a mile away. The truck labored noisily as Blake turned it up a gentle grade toward the mouth of a narrow canyon and he shifted into a lower gear.

"It's a good thing we're only five miles from camp," Cooke said. "You're about three gears lower than you would be if this truck was in the same condition it was in when we left camp thirty days ago."

"I'm afraid this will be its last trip-I've tried to baby it along and keep the dust out of it, but you just can't enclose a machine in a dust-proof wrapper."

They left the truck on the smooth alluvial fan just outside the canyon's narrow portal and began the by now repet.i.tious process of prospecting the canyon. It was late in the afternoon when they found their first cadmium; a thin gray seam of metallic sulfide in a rock washed down from higher on the canyon's wall.

"The gray sulfide is lead and zinc," Blake said. "Those little yellowish-orange spots in it are cadmium sulfide."

Cooke shook his head. "The percentage of cadmium is so slight-and the lead and zinc is only a thin seam."

"It might have wider portions where it's in place," Blake said, looking up the steeply sloping canyon's side. "It shouldn't be hard to find."

They located it in place an hour later, halfway up the canyon's side, but it was only a short, narrow seam. Blake tried unsuccessfully to dig into it with his prospector's pick, the point of which had long since been worn to a blunt stub. Cooke, pounding vainly at the tight-grained formation beside him, stopped to light a cigarette and wipe the sweat from his face.

"We have acids and glycerin," he said. "If we only had a few holes drilled in this rock, we could fill them with nitroglycerine."

"There's a chance in a thousand that it might get wider at a greater depth," Blake said, ceasing his own futile pounding. "But how do we drill holes in it?"

"The diamond drill-" Cooke began, then his voice trailed off.

"Exactly," Blake said, seeing what was suddenly in Cooke's mind. "How do we drill diamond-bearing rock with a diamond drill?"

"How did we intend to drill holes for mining when we started out thirty days ago? I won't argue about the diamond drill-I can't see how it could drill through diamond- bearing rock-but why didn't we think of all that before?"

"We didn't know for sure that all formations carried the same high percentage of diamond," Blake pointed out. "We hoped such wouldn't be the case, remember?"

"What a world to live on!" Cooke sighed. "Everything we try to do is foiled by diamonds. How can a superabundance of just one element manage to cause so much grief?"

"Well"-Blake shook his empty canteen and glanced to the west where the sun had disappeared behind the canyon wall-"we can't do any more here, now, so we might as well get on back to the truck and have something to eat before dark."

Cooke led the way to the bed of the canyon, his blithe spirits returned sufficiently for him to be whistling by the time they reached it. They were halfway to the canyon's portal when it became suddenly darker, as though a heavy cloud had covered the sun. It grew darker, although Blake's watch said the sun was not quite ready to set, and when they were almost to the portal's cliffs, where the canyon suddenly opened out upon the desert, he became aware of a low roar above the crunching of his footsteps in the diamond sand.

It came from the desert beyond the portal; a sound like a distant waterfall.

Cooke, two hundred feet ahead of him, was still whistling cheerily and had obviously not heard it. Blake increased his pace and was almost up with him when Cooke stepped beyond the cliffs that still hid the desert from Blake.

Cooke stopped, then, a look of amazement on his face, staring in the direction of their truck and the desert beyond. Then he wheeled to shout back at Blake, "What is it?"

Blake was beside him a few seconds later and he saw the source of the sound he had heard.

It was a mile away; a great, high black wall rushing toward them, its towering crest lost in the atmospheric haze. It was racing toward them at perhaps fifty miles an hour, roaring with a deep, sustained roar and the sheer front of it seething and boiling.

"What-?" Cooke began, but Blake cut him off with a terse, "Come on!" He ran toward the truck, estimating the distance they must cover before the black wall reached them. The truck was not far-but the wall was traveling at least fifty miles an hour.

"Is it-" Cooke began again, then gave up as a gust of wind whipped sand in his mouth and devoted his full attention to keeping up with the fleet Blake.

They reached the truck with the black wall looming almost upon them and jumped inside, slamming the doors. "Sandstorm," Blake said, as Cooke started to ask again. A harder gust of wind lashed at the truck, stinging their faces with sand. "Close your window," Blake said as he cranked up his own. "Those baby zephyrs are the advance guard. I think we're in for a real one."

The black wall struck a moment later with a thunderous roaring and screaming, smashing at the little truck with savage blows and enveloping them in darkness. Sand and gravel slashed against the windows with a sharp, dry hiss and, above the roar of the wind, Blake could hear a violent thumping as the wind found an empty and unfastened water can in the bed of the truck and slammed it back and forth. The pounding ceased abruptly and Blake had a mental vision of their water can going in kangaroo leaps across the mountainside.

" . . . long do you think?" Cooke shouted through the darkness.

"What?" Blake asked, shouting, himself, to be heard above the howl and roar of the storm.

"How long do you think this will last?" "Don't know. Sometimes a sandstorm will last an hour, sometimes ten hours."

He felt inside the utility box under the dash and found a flashlight. Its beam had the appearance of a three-dimensional cone in the dust-filled air of the cab.

"How did that get in here so quick?" Cooke demanded.

"It comes in every little crack and crevice," Blake answered, flashing the light through the windshield. The light revealed the dust and sand flowing past them with incredible speed. There were bright gleams in the torrent of air and sand as larger pieces of diamond reflected the light for a microsecond and bits of dead vegetation were being carried along.

Blake shut off the light and made himself as comfortable as possible in his half of the small cab. "You might as well try to make your mind a contented blank for an indefinite number of hours," he advised.

Cooke followed his advice, grumbling at the lack of leg room. He was asleep within fifteen minutes; a fact Blake confirmed by a quick flash of the light. Blake sighed enviously and composed himself for the hours of futile thinking and worrying that would be his own lot until sleep came. There was, in the genial Cooke's philosophy, a blithe unconcern for "Unborn Tomorrow and Dead Yesterday." But, while he envied Cooke for his carefree att.i.tude, he wondered if it would be of sufficient stability to survive the eventual recognition of a not-so-remote possibility-that all their efforts to leave their shining prison might prove to be futile.

The wind was shaking the truck and roaring with undiminished fury when he finally went to sleep, still worrying about the diamond dust that was being driven into every tiny crack about the truck wherever two parts of metal moved against each other. Silica, over a period of time, would ruin machinery. This was diamond, not silica; this had a hardness of forty-two, not seven- He awoke at dawn, stiff and cramped, with Cooke's snoring loud in the silence that had replaced the storm. He jabbed an ungentle elbow into Cooke's ribs. "Wake up-the storm is over."

"Huh?" Cooke blinked and straightened with a moan. "My leg's been asleep so long it-Hey! What happened to our windows?"

"We now have frosted gla.s.s all around," Blake said, rolling down the opaque window on his own side. "Diamond sand is really tough on gla.s.s."

He stepped out of the truck into the calm morning air and looked at the damage.

Cooke came around from the other side and stared open-mouthed at the bright, gleaming metal side of the truck where, before, there had been a thick coat of hard red enamel.

"It looks like we need a new paint job," he said at last. "And we'll have to knock a hole in the windshield to see how to drive to camp."

Blake lifted the motor cover and ran a finger through the blanket of diamond dust that covered every part of the motor. It was heaped on more thickly where there had been grease or oil to hold it.

"What do we do about that?" Cooke asked.

"Nothing. If we should try to wipe it off, it would cause it to work in deeper. We can only let it stay and hope the grease will keep most of it from getting any deeper into the moving parts."

"I wonder how they made out at camp?" Cooke asked as Blake lowered the motor cover.

"I was wondering the same thing. We'd better let the canyons to be prospected between here and camp wait for the time being. They're all near enough to camp that we can walk out to look at them, anyway."

They removed the opaque windshield and got under way, the steering wheel and gearshift lever grating harshly. They saw something shining metallically a half mile farther on and it proved to be their errant water can; lodged beneath a thorn bush, stripped of its enamel and polished to a high l.u.s.ter.

Taylor and Lenson were waiting outside the ship when they drove up. The question and hope was plain to be seen on Lenson's face but there seemed an almost imperceptible anxiety tingeing the questioning look on Taylor's face.

Blake shut off the motor and climbed out. "Nothing," he said. "Not a sign of uranium."

Lenson's face reflected a natural disappointment but Taylor seemed to have something on his mind more serious than simple disappointment. "Then there's no hope of finding uranium in this range?" he asked.

"There was no indication whatever that there is any such thing anywhere along the range," Blake answered. He looked toward the ship. "Where's Wilfred?"

"He left early to spend the day prospecting. We have the ship pretty well fixed up inside and there hasn't been much to do the past few days. Now-how about other minerals? Did you find anything at all?"

"A thin seam of lead-zinc ore that carries a small percentage of cadmium. But I don't think the diamond drill could ever drill through the rock it's in."

Lenson grinned sourly. "I know it can't," he said. "We no longer have a diamond drill.

While you were gone I got to looking around and found a formation that carried zircons.

Since we'll need zirconium, we all three agreed it would be a good idea to set up the drill, put down some holes and blast out some zirconium-bearing ore. We set the drill up yesterday morning. By mid-afternoon we had worn out six of our eight diamond bits and were down four inches. I came back to the ship late in the afternoon to get some more oil for the drill's motor-we've been using it and it was getting worn-and the storm hit before I could get back to the drill. I had left the drill running; its progress was so slow that it didn't need any attention. I got lost in the darkness of the storm and finally had to hole up behind an outcropping until morning. Then I saw where I was and went on to the drill. I found the sand blowing into it while it was running had ruined it. Not only the motor, but the gears of the drill, itself."

"It was no loss, I'm afraid," Blake said. "All the formations Cooke and I saw carried the same high percentage of diamond."

"But suppose we should find some ore-how do we drill it without a drill?" Cooke asked. "That is, suppose we find some ore that isn't so hard and filled with diamonds as to make drilling impossible."

"In that case, we'd probably find we could fix up the old drill after all," Blake said. He turned to Lenson. "You said you had been using the drill's motor for something else- what was that?"

"Water pump," Lenson said. "It seemed like a foolish waste of effort and time to carry water to the ship's tanks in buckets so we took the little high-speed water pump that we had brought along for the very purpose of filling the ship's tanks, took the motor off the drill-we weren't using the drill then-stripped enough tubing out of the ship's air circulating system to reach to the creek and set up our pump." He grinned again. "It lasted long enough to fill one tank, then the bearings went out. We fixed it and a week later, when we used it again, the bearings went out again. Finally, the last time we used it, the impellers were half abraded away as well as the bearings and shafting cut out."

"And the motor was wearing out, too?"

Lenson nodded. "The bank was dry and sandy where we set the pump and breezes were always stirring up little clouds of dust. The motor was in pretty bad shape before it soaked through our thick skulls that the dust was pure diamond dust and not at all as harmless as it looked."

"So now you're back to carrying water in buckets?" Cooke observed. "And Red and I are going to be back to walking. This is a cruel world to anyone accustomed to mechanized a.s.sistance."

"About finding uranium-" Taylor said, the aura of worry still about him. "What would you suggest next?"

"We can hike across the desert to the nearest range and see what we can find," Blake said. "It will be slow, doing it all on foot, but we have a boundless supply of two things on this world-time and diamonds."

"No." Taylor shook his head. "Time is the very thing we don't have. I haven't said anything to Len or Wilfred about it yet. I wanted to wait until all five of us were here to talk over what we-"

"h.e.l.lo." Wilfred's hail interrupted Taylor and he came hurrying toward them. "I saw your truck pull in so I turned around and came back. Any luck?"

"None," Blake said. "It just wasn't there to be found."

"What was this about not having time, and something you hadn't told us yet?" Lenson asked Taylor, his eyes on Taylor's face.

The others turned their attention to Taylor as he spoke.

"I've been making daily observations with the transit, as you know," he said. "I've observed the apparent motion of our sun, the yellow sun, and the Thousand Suns cl.u.s.ter.

I found that this is spring-whether late or early I don't know-but that's of no importance. I thought, at first, the yellow sun was swinging in its...o...b..t around our blue- white sun. You can see the yellow sun-like a very bright yellow star-in advance of our own sun each morning. According to my observations, the yellow sun is making an apparent advance of approximately one degree every five days in front of our own sun.

This happens to be what its apparent advance should be as we swing out in our orbit, so I became suspicious and made other observations. I discovered we are approaching the Thousand Suns at a speed of one hundred miles a second."

"That's what you didn't tell us?" Lenson asked. "I don't understand-we'll either be long since gone from here, or long since dust, before our wandering binary reaches the nearest star of the Thousand Suns."

"I said the apparent advance of the yellow sun is accounted for by our own orbital movement," Taylor said. "There is no orbital movement of the yellow sun observable.

This isn't a binary-the yellow sun is a member of the Thousand Suns."

"You mean-" Blake began.

"In approximately seven and a half months the two suns will collide."

"And our position in our orbit at that time?"

"We'll go into the yellow sun the radius of our orbit-four hundred million miles-in advance of the collision."

Tall Lenson barely changed expression and the surprise on Wilfred's face hardened into quick stubbornness, as though he had already decided he would refuse to accept such a fate. Cooke leaned one hip on the fender of the truck, his black eyes flickering over the others as he a.n.a.lyzed their reactions. But for once, Blake felt, Cooke was finding nothing to amuse him.

"You're sure your observations were accurate-that there's no hope we might have already swung past the yellow sun by then?" Blake asked.

"I've made my observations as accurate as possible, and checked for errors. Our sun is moving toward the yellow sun at a hundred miles a second and a distance of slightly more than one and a half billion miles now separates them. Our observation of these suns couldn't indicate that they were not a binary during the brief period we dropped into normal s.p.a.ce-especially with our limited means for taking observations from the ship. It was natural for us to a.s.sume that two suns so close together were a binary. Only very precise observations during the short time we observed them could have revealed the truth and we had neither the proper instruments for such observations nor any reason to think such observations were necessary."

"It wouldn't have changed our circ.u.mstances," Blake pointed out. "With seven or eight months of grace, we would have landed to see what the planet had to offer in the way of mineral wealth, anyway."

"That's true," Taylor said. "The result would have been the same. So here we are and we have, according to my most optimistic calculations, six months to fit our ship with a drive and get away from here as fast as we can."

"Six months?" Cooke demanded. "You said it would be seven and a half."

"We'll have to be a long way from here by then-Aurora carries an exceptionally high percentage of carbon and you know what happens when any nuclear conversion process absorbs an excess of carbon."

"Oh-oh-nova!"

"And they reach out a long, long way," Taylor said.