Scotty chuckled, but didn't reply.

Rick said, "Suppose we can't get out?"

"We will. Dr. Miller will be hunting for us sooner or later. He couldn't miss the mine, especially with the boards off the entrance."

"Then all we need is patience and a tight belt."

"That's it."

The boys fell silent. Rick was cheered by Scotty's estimate of the situation. He closed his eyes, and for perhaps the hundredth time started mulling over the chain of events, searching for a clue to the two things they needed to know: how and why the ghost was produced.

But as he thought about it he wondered if perhaps they didn't know why.

The ghost was a means of keeping people out of the area. It had succeeded to a considerable degree. There were no more night family picnics and swimming parties. There were only occasional long-scheduled events.

He explored the idea. The mine area was private property. To keep people out one would need only to post "No Trespa.s.sing" signs. But in all probability that wouldn't be suitable, because it would raise too many questions, and Dr. Miller would have to be let in on the secret of the ghosts that walked the fields.

But why keep people out of the area? To be sure, privacy for the conduct of secret operations was an obvious reason, only what were the secret operations, and why did they have to be kept secret?

He gave up finally. There simply weren't enough data on which to hang a conclusion.

"Think the dust has settled?" he asked.

"Could be. Suppose we go take a look. I'll use my light. Save yours."

They followed the yellow beam of Scotty's flashlight through the dark tunnel to the rockfall. There was still plenty of dust in the air, but it was bearable.

Scotty flashed his light on the timbers, then on the rockslide. One pair of uprights arose from the sloping pile of rock to a sound crosspiece.

Both boys knew what that meant. Rick put it into words. "If that's the set of timbers nearest to the ones that were bad, it means at least ten feet of rock on this side, and probably the same or even more on the other. A total of twenty feet of rock."

Scotty grunted. "One thing is for sure. We won't dig our own way out for a few days. I'm not even sure we can. We might collapse from lack of water if we try working real hard."

"But we can't wait for help from the outside," Rick pointed out. "We can at least work while we still have our health."

"Can you work in the darkness?"

"I suppose we'll have to. The lights won't last long."

"Then let's get to it."

They retreated to an alcove and put their shirts in a safe place, then went to work in their T shirts. Lugging rocks would work up a sweat, and it was chilly underground. The shirts were for use during rest periods.

"Let's see how it goes," Scotty invited, and turned off his light.

Rick groped for a rock and found a good-sized one. He carried it back and promptly b.u.mped into a wall and dropped it. Keeping a straight line was going to be a problem. He groped for the rock and found it again, but this time he tucked it under one arm, using the opposite hand to guide him along the wall.

"I'm on the right-hand wall," he told Scotty. "I'll return along the left-hand wall."

"Good system," Scotty approved.

It was, too. They pa.s.sed each other in the dark and Rick was pleased, until he tripped on a rock and stumbled into the pile.

"We're going to have to count paces," he said ruefully as he nursed a bruised knee. "Say twenty paces up and twenty paces back."

"Better make it twice that," Scotty replied. "We can't pile all the rocks in one place. We'll have to spread them out."

"Forty it is," Rick agreed, and found another rock.

The work went on, gradually a.s.suming the proportions of a dream--or a nightmare. Pick up a rock, tote it forty paces, drop it. Then thirty-five paces as the pa.s.sageway got cluttered. Now and then they had to join forces to lug a particularly big piece.

Rick's watch showed him that two hours had gone by. "Let's take a break," he suggested.

"Okay."

Scotty turned on his light. They found their shirts, then went back to survey what they had accomplished.

One glance told them it wasn't much. They had cleaned out the pa.s.sage up to the main slide, and that was all.

They looked at each other in the flashlight's glow.

"Got any earth-moving equipment in your pocket?" Rick asked wryly.

"Not a dragline or a clamsh.e.l.l," Scotty said. "We certainly didn't make much of a dent, did we?"

"At this rate we'll be here until Christmas," Rick said.

"Not that we'll need a Christmas tree."

"We could use the lights," Rick commented. "Let's keep plugging. I'm not so sure I need a rest after all."

"Might as well."

"Just sitting on the rocks will sap our strength, anyway," Rick pointed out. "We might as well work while we're still fresh. We can take five-minute breaks when we begin to tire."

"I'm with you. Tote those rocks."

"Let's use one light, too. No point in just clearing the tunnel. We want to break through in as short a time as possible. If we use the light we can pull rocks from nearer the top of the slide."

"Sensible as usual. I'll prop my light so it shines on the slide."

Scotty did so, then both boys shed their shirts once more.

The rock hauling went faster even with the rays of the single flashlight. They took turns climbing the slide and throwing rocks down.

The boy taking a turn at the bottom moved them out of the way.

"Watch it!" Rick yelled suddenly, and jumped away from a slide of rock.

Scotty, who was back in the tunnel disposing of a big rock, asked anxiously, "Are you hurt?"