"No. Hand me that light, will you?"

Scotty carried the light to where Rick waited. Rick took it and shone it upward to where the slide had come from. He whistled. There was solid ceiling, but it was a yard higher than the rest of the tunnel ceiling.

He calculated quickly. "If this is typical, we have rock three feet thick, ten feet wide, and twenty feet long piled up in front of us. That makes six hundred cubic feet of rock."

"But it can't be typical," Scotty disagreed. "If three feet had fallen uniformly, it wouldn't have filled the tunnel. It must be much thicker right over the broken timbers."

"Not a very cheerful prospect, is it?" Rick had a vision of yards of rock ahead.

"I've seen happier prospects. But what can we do? Keep plugging is all, and hope it doesn't take long for Dr. Miller to locate us."

Rick looked at his watch. "No chance of that yet. It isn't even suppertime. It may be morning before Dr. Miller gets really worried."

Scotty chuckled grimly. "Our own reputation for being able to take care of ourselves is not helping us, either."

"I'll never go into a place without two entrances again," Rick promised.

There was a moment's shocked silence while the boys stared at each other. They spoke simultaneously.

"How do you know this has only one entrance?"

"How do we know this hasn't two entrances?"

They had never reached the end of the mine. For all they knew, it might only be necessary to walk out!

"We'll go see," Rick stated. "Right now."

"Didn't we ever ask about another entrance?" Scotty demanded.

"No, now that I think of it, and no one ever said anything about it."

"Maybe they never said anything because there isn't anything to say."

"No more a.s.sumptions," Rick said. "We can find out for ourselves. Get your shirt on and let's go."

They quickly dressed and hiked down the long tunnel to the point they had reached when the cave-in occurred. Rick paid more attention to the formation than before, and found it was easy to trace the ore vein.

Pockets in the walls showed where offshoots of the main ore vein had been located and dug out, but mostly the mine bored through the hill in one continuous tunnel.

"Funny they didn't take more ore out of the top," Scotty commented.

"Looks like fairly decent stuff overhead and to the left."

"Not good enough, I guess. Refining was pretty primitive in those days.

Techniques are better now, but there probably isn't enough good ore here to make new operations worth the expense of getting it out."

"Look ahead," Scotty said.

Rick had been examining the wall of the tunnel. He turned and looked to where Scotty pointed, and his heart sank. It was another rockslide.

"Funny," Scotty commented. "The tunnel goes uphill to the slide."

Rick saw that his pal was right. But the change in elevation of the tunnel didn't seem important compared to the prospect that now faced them. They simply had to go back and resume their rock hauling. There was no way of knowing whether the tunnel continued beyond the slide, or whether the slide itself was the reason the Civil War miners had gone no farther.

"I need a rest," Rick said, discouraged. "Let's sit down and take a breather before we start back."

"Okay. Douse the light?"

"Might as well. Your battery's getting low."

Scotty switched the light off and they sat down on the hard rock floor.

Rick closed his eyes and breathed deeply. Plenty of hard work ahead. He might as well rest while he could.

Scotty spoke suddenly. "Plenty of good fresh air down here. Isn't that a little odd?"

Rick stirred. "Is it? I hadn't thought much about it. But I suppose the air ought to be stale and smelly."

"Wet your finger."

"Huh? Oh, okay." It was the ancient trick of using the cooling caused by evaporation of moisture from a damp finger to show the movement of air currents. Rick let out an exclamation. The air in the tunnel was in motion!

Scotty said with suppressed excitement, "Close your eyes. I'm going to light a match."

Rick did so, and saw the light even through closed eyelids because his pupils were fully dilated. He opened his eyes cautiously, squinting against the glare of the match. As the pupils contracted he saw that the paper match burned brightly, and that the flame flickered!

Scotty jumped to his feet, switching on the flashlight. "The breeze is coming from the slide!"

With one accord they rushed to the slide and began pulling rocks away.

Clearly, the tunnel sloped upward at this point. The question was, did it emerge in a real opening, or only in a hole driven through for ventilation?

There was only one way to find out: move rock!

They sought for key rocks, those that would allow other rocks to tumble down and out of the way.

Rick thought it was at least to their credit that they learned from experience. Then, as he jumped frantically to escape a sliding boulder, he had to grin at his own thought. They had learned, but not enough.

There was no doubt about it, a current of air came through the slide.

They could feel it, cool and fresh, and redoubled their efforts.

Finally they had to slow down from sheer exhaustion.

"Take a break," Rick said huskily. "We'd be foolish to wear ourselves out."

"You're right." Scotty slumped down where he was and wiped his face.

"That air current is getting stronger. We're making progress."

"Wish I knew toward what," Rick said.

"Air, anyway. And where there's a source of air is also daylight."

"I'd feel better if I could see some."