Not until two days had elapsed were the victims of the "accident" able to leave their rooms, and then they met Sam and Mr. Wright at Mrs. Byram's home.

"We'll be ready for work in the morning," Bill said in reply to the superintendent's inquiries. "What troubles me is that I've lost the plan of the old mine. It was in my blouse when the timber fell, an'——"

"How that joist could have got away without some one to help it is what worries me," Joe interrupted. "I set it, an' know the weight from above could not have any effect."

"There is no chance of foul play. The level has been guarded night and day, therefore, unless our trusted men are at fault, it was purely an accident."

"I'm not sayin' it wasn't; but yet the whole business looks queer," and with this remark Joe dismissed the subject from his mind.

Mr. Wright had come to learn when the guardians of the level would be ready to return to duty, and Bill's answer sufficed.

"The men who have been there during the past twenty-four hours shall be given other work in the morning, and once more I can rely on you. Thus far nothing suspicious has been seen or heard," he said, "and I begin to believe Billings has given up his thoughts of revenge. The only strange thing is that Miller's boy has disappeared, and his father can think of no reason why he should run away."

"Farley's won't be the loser if he never comes back," Joe replied. "That boy is a bad one, an' it wouldn't take much to make me believe he an' Billings are firm friends."

"There is no necessity of talking about him; we are not afraid of boys. The question is whether we are warranted in guarding the lower level much longer."

"That's for you to say, sir. We had rather be at our regular work."

"Well, we'll try it a day or two more. Perhaps you'd better break through into the old drift, and then we shall know whether it is possible for evil-disposed persons to find a hiding place there."

This closed the interview so far as Mr. Wright was concerned, and on his leaving the house the others discussed the work to be done the following day; but Skip Miller's disappearance had little place in the conversation.

Bill mourned the loss of the plan, which was supposed to be the only guide to the old mine, but Joe did not think it was of such very great importance.

"All we care to know is whether the air's foul, an', of course, the best way is to finish the tunnel which came so near finishin' us. That work can be done without any guide."

"But we may want to follow up the drift, which will be a long job if we have to go on blindly."

"There's no use fussin' over what can't be helped. The paper got trampled into the dirt, most likely, otherwise them as have been lookin' would 'a found it before this."

"I don't feel like givin' over the search so easy; s'pose we four have a reg'lar hunt in the morning?"

"Sam and I will go now," Fred said. "We shall feel better for a little exercise after being cooped up in the house so long."

"Very well. Take a turn at it this afternoon, an' if you don't succeed Joe an' I'll try to-night."

The boys set off without delay, but they were a long while reaching the slope, for every person on the street thought it necessary to congratulate them upon having escaped a terrible death, and at the breaker Donovan delayed the search by making minute inquiries as to the condition of affairs in the drift just prior to the accident.

"Any one would think from all these questions that you believed somebody was responsible for the trouble," Sam said with a laugh.

"P'rhaps I do. Billings an' Skip Miller disappeared on the same day, an' that looks suspicious to me, though Mr. Wright won't listen to anything of the kind."

"It's a big satisfaction to know they have left," Fred added, "and we have gotten rid of them cheaply. Do you know where they went?"

"Out of the village somewhere; Harvey saw them walking up the track."

"Then we can reckon that there'll be no more mischief done for a while. Come on, Fred, let's get down the slope."

The boys left the breaker without noticing that Chunky was trying to attract their attention, and were soon in the lower level making a systematic search.

Shoveling over the loose dirt along the track, they continued on until the cutting which had so nearly been a grave for Fred was passed, and then Sam said as he halted:

"It's no use to hunt here. It couldn't have got up this way."

"The draught may have carried it quite a distance."

"There isn't air enough stirrin' to move it a foot; but it won't do much harm to look."

They were nearly at the chamber where Sam was taken prisoner before Fred abandoned the hunt, and as he turned to retrace his steps both came to a sudden halt.

As if from beneath their feet arose a muffled cry of distress.

The boys looked at each other in alarm, and as they stood motionless the mysterious sound was repeated.

"What can it mean?" Fred asked in a whisper.

"That's more'n I can tell. There's no drift below this."

"That was surely a human being, and in trouble of some kind."

"Perhaps the cry comes from the end of the drift which has been closed."

"It sounds under the ground right here," and Fred stamped with his foot just as the noise was heard for the third time.

"There's no question about it's being a man. Come on; let's bring some of the miners to help find him."

The boys ran down the drift at full speed, and half an hour later returned with two of the miners.

"It was right here that we heard it," Sam said, as he pointed to the shovels they had left behind, in order to mark the spot.

The party listened intently, but no sound save their own breathing could be distinguished.

"I thought you'd been frightened about nothing," one of the miners said with a laugh. "You might as well tell us the mine was haunted as to give out such a yarn. I'll guarantee that nothin' larger'n a mouse could hide here."

"But we surely heard a cry," Fred insisted.

"And it seemed to come from beneath our feet."

"Nonsense. It's foolish to make such talk when we know the thing's impossible," and the men turned away as if angry at having been brought so far on a useless errand.

"We know whether——"

Sam ceased speaking very suddenly, for at that moment the sound of distress came with great distinctness.

The men looked around, each trying to hide his fear, and then a regular search was begun.

The noise could not have come from the old drift, and the level was examined thoroughly, but without success.

"It beats me," one of the miners said at length. "I'm sure there's nothing beneath here but the solid earth."

"Let the boys tell Wright," the other suggested, and his companion assented.

"We'll hang around here till he comes or you get back; but don't stay very long, for I don't like the looks of things."

"Why not?"

"It may be a warnin' for some of us. I've heard tell of such."

Fred laughed heartily, and the man replied impatiently:

"When you've been in a mine as long as I have, you won't think there's any fun to be made of warnin's. Before the explosion of fire damp in the old workings, I've been told the miners heard all kinds of queer noises."

"Go on," the second man said fretfully, "an' don't waste time chinnin' here when p'rhaps we oughter be gettin' out to save our lives."

The boys started, feeling a trifle disturbed because of the unexplainable cries, and arrived at the store as the whistle sounded for the night shift to begin work.

The superintendent was surprised by the information brought, and insisted, as had the miners, that the sounds could not have been made by a human being.

"I will go down the slope at once, however," he said, and the boys accompanied him on what proved to be a useless errand.

Every portion of the lower level was searched. A party descended the old shaft, traversing the abandoned passages to the chamber connecting with the new portion of the workings, but nowhere could be seen any signs of life.

Joe and Bill, alarmed because the boys had not returned, came to look for them in time to join the exploring parties, and the latter was decidedly uneasy when Mr. Wright ordered the useless labor to be stopped.

He, in common with several others, believed the mysterious noises to be warnings, and there was every evidence of a panic until Mr. Wright spoke at considerable length on the subject, intimating that the cries were due to natural causes.

Then those who were off duty went home, and among them were Joe, Bill, and their helpers.

These last discussed the subject without arriving at any definite conclusion when the time to separate arrived.

On the following morning work was resumed in the cutting. The loose earth having been cleared away, a reasonably solid roof was put up, and once more the tunneling operations were pushed forward vigorously.

All hands were on the alert for a repetition of the mysterious cries, but nothing was heard save the noise of the picks and shovels, with now and then a muffled crash as fragments of the vein were detached by blasts.

During the "nooning" lunch was eaten in the cutting, and while they were sitting quiet a singular vibration of the earth could be felt.

"It seems as if some one was digging directly beneath us," Fred said, when the little party ceased eating to gaze at each other in surprise.

"Most likely there's a line of slate just under our feet, an' brings the sound from the other drift," Joe replied promptly.

"That's about the size of it," Bill added; but the boys noticed that both the men listened from time to time as if in great perplexity.

The peculiar tapping continued without interruption, and before the time of rest had more than half expired Joe said, as he arose to his feet:

"Come on, lads. We're close to the old drift, an' after that's been opened we'll have another look around, for I want to find out what these queer noises mean."

Each one worked with the utmost rapidity, and when another hour had been spent Bill's pick broke through the barrier of earth.

"That ends the job, an' now to see how the air is."

The miner had hardly ceased speaking when a huge volume of gas burst through the aperture, nearly suffocating the party and extinguishing the lamps instantly.

"Jump to it lively, boys!" Joe cried hoarsely, as he began shoveling back the earth. "When you can't work any longer get a breath of fresh air in the drift."

There was every danger that the lower level might be so filled with the noxious vapor as to cause an explosion, and both men and boys labored manfully.

All were working blindly, but the general direction of the aperture was known, and the greater portion of the earth could be thrown with a fair degree of accuracy.

Ten minutes passed and the flow of foul air was partially checked. Twice had each person been forced to retreat to the main drift, and Fred was about to go for the third time when it seemed as if the flooring of dirt gave way beneath his feet.

Half suffocated by the gas, and overwhelmed by the falling fragments, he hardly realized what had occurred until finding himself in what was unmistakably another and yet lower tunnel or drift.