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.