50 in 50

His thoughts kept returning to that little crystal that meant his life. It was a thin wafer of what looked like dirty glass, ground and polished to the most exacting tolerances. When subjected to an almost microscopic current, it vibrated at exactly the correct frequency that allowed one mass to slide between the molecules of another. This weak signal in turn controlled the much more powerful circuit that enabled himself and all his equipment to move through the earth. If the crystal failed, the atoms of his body would return to the vibratory plane of the normal world and alloy themselves with the earth atoms through which he was moving. . Pete shook his head as if to clear away the offending thoughts and quickened his pace down the slope.

He had been pushing against the resisting rock for three hours now and his leg muscles felt like hot pokers. In a few minutes he would have to turn back, if he wanted to leave himself a margin of safety. But he had been getting Ytt traces for an hour now, and they seemed to be getting stronger as he followed the probable course of the drift. The mother lode had to be a rich one — if he could only find it!

It was time to start the long uphill return. Pete jerked a rock for a last test. He'd mark the spot and take up the search tomorrow. The test bulb flashed and he held the transparency against it.

His body tensed and his heart began to thud heavily. He blinked and looked again — it was there! The tantalum lines burned through the weaker traces with a harsh brilliance. His hand was shaking as he jerked open his knee pocket. He had a comparison film from the White Owl claim, the richest in the territory. There wasn't the slightest doubt — his was the richer ore!

He took the half-crystals out of their cushioned pouch and gently placed the B crystal in the hole he had made when he removed the sample rock. No one else could ever find this spot without the other half of the same crystal, ground accurately to a single ultrashortwave frequency. If half A were used to key the frequency of a signal generator, side B would bounce back an echo of the same wavelength that would be picked up by a delicate receiver. In this way the crystal both marked the claim and enabled Pete to find his way back to it.

He carefully stowed the A crystal in its cushioned compartment and started the long trek back to the surface. Walking was almost impossible; the old crystal in his walk-through was deviating so far that he could scarcely push through the gluey earth. He could feel the imponderable mass of the half-mile of rock over his head, waiting to imprison him in its eternal grip. The only way to the surface was to follow the long hogback of granite until it finally cleared the surface.

The crystal had been in continuous use now for over five hours. If he could only turn it off for a while, the whole unit would have a chance to cool down. His hand shook as he fumbled with his pack straps — he forced himself to slow down and do the job properly.

He turned the hand neutralizer to full power and held the glowing rod at arm's length before him. Out of the haze there suddenly materialized an eighteen-foot boulder of limestone, adjusted now to his own penetrating frequency. Gravity gripped the gigantic rock and it slowly sank. When it had cleared the level of the granite ledge, he turned off the neutralizer. There was a heavy crunch as the molecules of the boulder welded themselves firmly to those of the surrounding rock. Pete stepped into the artificial bubble he had formed in the rock and turned off his walk-through.

With a suddenness that never ceased to amaze him, his hazy surroundings became solid walls of rock. His helmet light splashed off the sides of the little chamber, a bubble with no exit, one half-mile below the freezing Alaskan wastes.

With a grunt of relief, Pete slipped out of his heavy pack and stretched his aching muscles. He had to conserve oxygen; that was the reason he had picked this particular spot. His artificial cave cut through a vein of RbO, rubidium oxide. It was a cheap and plentiful mineral, not worth mining this far north, but still the rock diver's best friend.

Pete rummaged in the pack for the airmaker and fastened its power pack to his belt. He thumbed the unit on and plunged the contact points into the RbO vein. The silent flash illuminating the chamber glinted on the white snow that was beginning to fall. The flakes of oxygen released by the airmaker melted before they touched the floor. The underground room was getting a life-giving atmosphere of its own. With air around him, he could open his faceplate and get some chow out of his pack.

He cautiously cracked the helmet valve and sniffed. The air was good, although pressure was low — around twelve pounds. The oxygen concentration was a little too high; he giggled happily with a mild oxygen jag. Pete hummed tunelessly as he tore the cardboard wrapper from a ration pack.