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."

They rested in silence for five minutes by Rick's watch, then resumed,
working as close to the top of the pile as they could get.

Scotty suddenly let out a yell, and Rick dodged to escape another rock,
then leaped down as the whole pile crumbled. The rocks didn't fall far.

"Look," Scotty said breath