"What caused it?"
"That crowbar had evidently been left there to prop up a weak place in the side of the shaft, and when I moved it, the whole thing gave way. Some of the rocks came tumbling out, and then the side of the shaft caved in. If I hadn't jumped back in the nick of time my goose would have been cooked. There must be a couple of tons of rock in the shaft now."
"We couldn't dig our way through?"
Joe shook his head. "We'd be wasting time trying. I guess the only thing we can hope for is that somebody heard the crash and comes to see what happened."
"But they don't know we're down here."
"That's true, too. And they won't be very likely to start clearing away the shaft unless they know we're here. This mine was abandoned a long time ago, by the looks of things."
"They might see our footprints up to the side of the shaft."
"It was snowing when we came here. They may be covered over by now."
The boys were silent. They realized that their plight was almost hopeless. In the cold, dark depths of the earth, with their air supply cut off, they were facing suffocation, exposure and starvation, and there seemed not the slightest possibility of escape.
"The only thing to do," said Frank, at last, "is to keep on following this tunnel. There's no use going back into the mine itself."