There was no disputing the fact.

The sounds which came to Frank’s hearing were plain and unmistakable.

The ring of pickaxes was quite audible, and could not have been twenty feet distant through the wall of earth.

The young inventor was dazed with the force of this realization.

Barney had heard the sounds also, and both sat silently gazing at each other.

What did it mean?

Startling queries and theories flashed through the minds of each.

Was some one coming to their rescue through the earth? Or was it all a delusion?

The former theory was at once dispelled. If any friends knew of their presence there they would scarcely go to the trouble of rescuing them by means of digging through a thousand feet of earth.

A few moments’ pulling at the mouth of the shaft would have brought them both out of their difficulty.

As for the latter possibility it was at once dismissed.

“Begorra, Misther Frank,” said Barney, in a mystified way, “phwativer do yez call that?”

“Somebody is digging their way toward us,” said Frank.

“Shure yez don’t suppose it is fairies?” whispered the superstitious Celt.

“Nonsense!”

Frank had hit upon what he believed to be the truth in his own mind.

It had occurred to him that the greasers were conducting mining operations in these hills.

Might it not be that in their shaft sinking they had followed a vein dangerously near the old shaft?

In fact, it was not impossible that in a few hours they might not dig their way actually through into the old mine.

The thought gave Frank a deep thrill of hope.

“Barney,” he said, earnestly, “upon my soul, I believe that we are bound to make our escape.”

“Shure, Misther Frank, phwat do yez mean?” cried Barney, in surprise.

“Hush! let us wait and watch.”

For some time the two prisoners listened to the sounds of the pickaxes, and the voices of the workmen could almost be distinguished.

Suddenly, however, the sounds ceased.

All was quiet beyond the wall of earth.

What did it mean?

Without doubt the miners had ceased work.

Then Frank recollected the hour, and that without doubt they had retired for the purpose of gaining sleep.

With an inspiration the young inventor sprang up.

“Barney!” he cried. “Our time has come!”

The Celt was astonished.

“Shure, phwat do yez mean, Misther Frank?”

“I mean that we must dig our way through and meet that passage. It will be deserted, and though it will lead us into the camp of the greasers, we will stand a chance to escape.”

Barney caught the inspiration.

“Bejabers, ye’re right!” he cried. “But how will we do it? Shure, we ’aven’t any pick nor shovel.”

“Somewhere in this mine there must be some old ones!” cried Frank. “Let us search.”

“It will likely be in the ould mine below, sor.”

“All right.”

“Shall we go down, sor?”

“Yes.”

Barney quickly adjusted the rope and slid down into the old shaft.

Frank followed him.

Then with the pocket lantern they began an exploration of the place, and with most gratifying results.

In one corner they found part of an old spade and an iron bar.

The bar could be used in lieu of a pickaxe. They quickly returned to the upper level.

First making sure that they were not likely to be heard, work was begun.

Frank wielded the bar and Barney the shovel.

For hours they kept at work in a lively manner.

A deep hole had been excavated.

They had made a distance of full fifteen feet into the solid earth.

Frank guessed from the hollow sounds that they were now not many feet from the inner mine.

His theory proved correct.

In less than twenty minutes later his bar went through the wall of earth and he lost it.

But, fortunately, with the shovel they were able to enlarge the aperture sufficiently to enable him to pass through.

Barney followed quickly.

They were now in the new mine.

All was darkness, but Frank cautiously opened the slide of his lantern.

The tools of the miners lay about, but none of the latter were in sight.

The coast was clear apparently, and they moved forward, not, however, without great caution.

The passage seemed to extend a great ways through the earth. They followed it for what seemed a good while and yet there was presented no sign of the main shaft.

“That is curious!” exclaimed Frank, in surprise. “There certainly is a main shaft somewhere. We must soon find it.”

“Begorra, maybe there’s none at all,” said Barney, logically. “Perhaps it leads into some koind av a cave or the loikes.”

There was more in Barney’s remark of a pertinent sort than seemed at the moment likely.

Suddenly Frank came to a stop.

“Goodness gracious!” he exclaimed. “What does that mean?”

“Pwhat?” asked Barney.

“Why, don’t you see?”

“Begorra, it’s a loight.”

“Certainly.”

Far down the passage the faint gleam of light was seen.

It was not daylight as the prisoners well knew at that hour.

They paused and watched it intently for some time.

At first Frank had been inclined to believe it a lantern carried by some of the greasers, who were coming back into the mine to work.

But a few moments’ study convinced him that this was not so.

“That is at the end of this passage,” he declared. “Come on, Barney. Let’s get out of here as quickly as possible.”

They pressed forward at a rapid pace.

Every moment the light grew larger and plainer.

Then Frank saw that it occupied the whole size of the passage and at once understood that it was a chamber beyond illuminated.

This theory was borne out perfectly well, when, a few moments later, they came to the mouth of the passage.

A wonderful scene was spread before them.

They came out upon a sort of circular gallery about a deep amphitheater which lay below them.

The passage was only one of many leading into this gallery, and there were other galleries of similar sort.

It was far from being a new mine, as Frank saw at a glance.

Indeed, it might have been older than the mine they had just escaped from.

The light which illuminated the amphitheater, which was of large dimensions, was created by a large pitchwood fire burning in the center of the mine floor below.

Frank looked up and saw patches of the night sky through apertures in the roof of the mine, which was not far above their heads.

The fact was, a cave had originally occupied the spot and the galleries and passages had been added by man.

It was certainly a wonderful spectacle. The floor was full fifty feet below, and as our adventurers looked down from the gallery they saw a large number of the greasers lounging about the place.

Many were rolled in blankets and sound asleep.

Others were playing dice or talking and smoking their cheroots, and the hum of conversation came upon the air.

“By Jove!” exclaimed Frank, with a thrill, “I tell you, Barney, we have found the den of Costello and his gang.”

“Begorra, that’s thrue,” agreed Barney.

“It is certainly a place well suited for the purpose.”

“I should say so, sor. But however will we get out of here?”

“That is a question.”

“Shure, sor, I think we’d betther get out as soon as possible.”

“Right you are, Barney. If those miners return and discover our escape from the shaft they will be quickly after us.”

“Shure enough, sor.”

“Let us move cautiously along and see where this gallery goes to.”

Frank led the way along the gallery.

It terminated in a flight of steps cut in solid rock.

There were none of the greasers, apparently, in any of the galleries or passages above the floor.

So Frank felt safe in descending these steps.

He went down them until a gallery below was reached.

They were now quite near to the floor. Frank and Barney here paused.

It was, of course, decidedly unsafe to venture down within the circle of the firelight.

“If they would only all go to sleep,” said the young inventor, “then we could be sure of slipping by them.”

But the greasers seemed to have no such idea in view.

There was no doubt but that many of them would remain up all night. What was to be done?

Frank pondered the question seriously and long.

He saw what he believed was the passage which led out of the mine.

But men were constantly passing in and out, and it would be utterly impossible to escape in that direction.

Meanwhile, the risk was great in staying where they were.

At any moment some one of the greasers might come upon them. It was clear that desperate action had got to be taken at once.

Frank considered every daring move which he could think of.

He even thought of a break for liberty through the outer passage. But second thought showed that this was suicidal.

But he noted that there was a line of shadow under the galleries.

Perhaps by keeping in this he could find another outward passage.

It was a terrible risk to take, but Frank did not hesitate.

“Come, Barney!” he said, “let us go down below.”

The Celt, without a word, followed Frank. But they had not descended three steps when the young inventor came to a startled halt.

A thrilled exclamation escaped his lips.