"I don't understand--"

"I mean that this material that has fallen in here did not all come out of the solid rock."

"What does that mean?" asked Ned.

"Perhaps nothing so far as we are concerned. I was thinking that if they could not blast through the drift, they might as a last resort, drill down through the surface from above and pierce this chamber."

"How could they locate our position close enough to do that?" asked Tad.

"That would not be difficult. From the maps of the mine Mr. Munson could work out our position as closely as a captain does that of his ship at sea."

It was a ray of hope which the boys grasped eagerly. They tried to forget that they were practically entombed many feet underground, and that days might elapse before they were rescued.

"I'll bet Chunky will hug himself with delight when he finds out what's happened," suggested Walter.

"Yes, he'll probably think it's very funny, our being bottled up or rather down in a corner underground," said Ned somewhat dolefully.

"I didn't mean that. He'll be glad he went hunting instead of coming along with us," corrected Walter.

"Yes, I guess he will," agreed Tad. "He'll have a right to congratulate himself that he has missed an opportunity to fall in."

The lads forgot their predicament for the moment in the laugh that followed.

"I wish we had a light," said one.

"We might build a fire. What's the matter with burning up our hats?"

suggested Ned.

"No, we should be suffocated. Don't you know we are sealed up,"

objected Tad. "We don't want to make any additional trouble for ourselves."

"Yes," agreed the guide. "But it is peculiar that there is so much fresh air here. Now and then I can almost imagine I feel a draft, though I know that is not the case."

"Could we not get a draft through that large crack in the rocks up there?"

"I don't see how, Tad. There is nothing but solid rocks above it."

The lad stepped under the opening, holding up a finger which he had wet between his lips. For a full moment he stood poised like a statue while the other two boys lighted matches that they might the better see what he was doing.

"I don't care what you say, there is air coming from somewhere. There can be no doubt of it. I feel it plainly. Try it and see if you don't agree with me, Mr. Phipps."

The engineer stepped up and went through the same process that the boy had gone through. He repeated the experiment twice more.

"You're right," he exclaimed, letting his hand drop to his side.

"Your good sense is worth more than all my technical knowledge and training."

"The next question is to find out where the draft comes from. It must be from the outside somewhere," said Tad hopefully.

"Not necessarily, my boy. Of course it may be drawn down through crevices covering many feet of solid rock before reaching us. Then again, the air may come from some subterranean water course. As you know the mountains are full of them, channel upon channel, some high and broad enough to drive a coach and four through."

"Oh. I hoped--"

"Never mind regrets, boys. Wherever the air comes from makes little difference so long as it really is air. It is saving our lives."

"From what?" demanded Walter.

"From eventual suffocation. Were it not for that we would stand a good chance of dying before they were able to reach us."

The boys were thoughtful for a few moments.

"Hungry?" questioned the engineer.

"Somewhat," admitted Tad.

"We might be more so if we had a chance to think about it," added Ned.

"I've got a package of chewing gum here. Help yourself," offered Mr. Phipps.

The lads were not slow to do so, and in a moment were chewing industriously, laughing and talking at the same time.

"Beats all what a little thing will make a fellow forget his troubles," said Ned. "Now, I remember--"

"h.e.l.lo, boy!"

"Who said that?" demanded Tad Butler springing up from the pile of rocks on which he had been sitting for some time.

"Said what?" snapped Ned. "I was talking when you interrupted me."

"I thought I heard somebody say 'h.e.l.lo,'" confirmed Mr. Phipps.

"So did I," added Walter.

"And I know they did," said Tad emphatically.

"h.e.l.lo, boy!"

This time all sprang up, startled.

"Who's playing tricks?" shouted Ned.

"Heard it that time, did you?" asked Walter. "It wasn't I."

"Nor I," chorused Tad.

"Then it must have been Ned or myself," said Phipps. "I'm sure that I am no ventriloquist."

For the moment Phipps wondered if they were all losing their senses.

He had heard of men, imprisoned under similar circ.u.mstances, imagining they heard voices.