As he spoke there came the mutter of thunder, and the mountain vibrated slightly. The men in the cave redoubled their activity. Tom and his friends felt that the secret process they had so long sought was about to be demonstrated before their eyes.



CHAPTER XXI—FLASHING GEMS

Eagerly the adventurers looked through the opening at the end of the passage into the larger cave. The men opened the small oven in which the balls of white chemicals and carbon mixed, had been baked, and a pile of things, that looked like irregularly-shaped marbles, were placed in the steel box.

This box, which was about the size of a trunk, was of massive metal. It was placed in a recess in the solid rock, and all about were layers of asbestos and other substances that were nonconductors of heat.

"That box becomes red hot," exclaimed Mr. Jenks, in a whisper. "When things are in readiness, that lever is pulled and the diamonds are made. I pulled it once, but I did not then know the process involved. I supposed that the lightning had nothing to do with making the diamonds."

"It has—a most important part," said Mr. Parker. The hidden adventurers could talk in perfect safety now, for the men in the large cave were too excited to pay much attention to them. The muttering of the thunder grew louder, and at times a particularly loud crash told that a bolt had struck somewhere in the vicinity of the cave.

"But, bless my watch-charm!" exclaimed Mr. Damon, "I didn't know lightning made diamonds."

"It does not—always," went on the scientist. "But great heat and pressure are necessary to create the gems. In nature this was probably obtained by prehistoric volcanic fires, and by the terrific pressure of immense rocks. It is possible to make diamonds in the laboratory of the chemist, but they are so minute as to be practically valueless.

"However, these men seem to have hit upon a new plan. They utilize the terrific heat of lightning, and the pressure which is instantaneously obtained when the bolt strikes. I am anxious to see how it is done. Look, I think they are getting ready to make the gems."

Indeed there seemed to be an air of expectancy among the diamond makers. The mixing machine had now been stopped, and, as it was more quiet in the cave, our friends, in their hiding-place, had to speak in mere whispers. All the men were now gathered about the great steel box.

This receptacle had been closed by a solid metal door, which was screwed and clamped tight. Then one of the men examined a number of heavily insulated electric wires that extended from the box off into the darkness where Tom and his companions could not discern them.

"That's Folwell—the man I befriended, and who got me into this game," whispered Mr. Jenks. "He was also one of the first to turn against me. I think he's one of the leaders."

Folwell came back, after having gone into a dark part of the cave. He went over to an electrical switch on one of the stone walls.

"It's almost time," Tom heard him say to his confederates. "The storm is coming up rapidly."

"Will it be severe enough?" asked one of the helpers. "We had all our work for nothing last time. The flashes weren't heavy enough."

"These will be," asserted Folwell. "The indicator shows nearly a million volts now, and it's increasing."

"A million volts!" exclaimed Tom. "I hope it doesn't strike anywhere around here."

"Oh, it will probably be harmlessly conducted down on the heavy wires," said Mr. Parker. "We are in no danger, at present, though ultimately I expect to see the whole mountain shattered by a lightning bolt."

"Cheerful prospect," murmured Tom.

There was a terrific crash outside. The rocky floor of the cave trembled.

"Here she comes!" cried Folwell. "Get back, everybody! I'm going to throw over the switch now!"

The men retreated well away from the steel box. Folwell threw over the lever—the same one Mr. Jenks remembered pulling. Then the man ran to the electric switch on the wall, and snapped that into place, establishing a connection.

There was a moment's pause, as Folwell ran to join the others in their place of safety. Then from without there came a most nerve-racking and terrifying crash. It seemed as if the very mountain would be rent into fragments.

Watching with eager eyes, the adventurers saw sparks flash from the steel box. Instantly it became red hot, and then glowed white and incandescent. It was almost at the melting point.

Then came comparative quiet, as the echoes of the thunder died away amid the mountain peaks.

"I guess that did the trick!" cried Folwell. "It was a terrific crash all right!"

He and the others ran forward. The steel box was now a cherry red, for it was cooling. Folwell threw back the lever, and another man disconnected the switch. There was a period of waiting until the box was cool enough to open. Then the heavy door was swung back.

With a long iron rod Folwell drew something from the retort. It was the tray which had held the white balls. But they were white no longer, for they had been turned into diamonds. From their hiding-place Tom and the others could see the flashing gems, for, in spite of the fact that the diamonds were uncut, some of them sparkled most brilliantly, due to the peculiar manner in which they were made.

"We have the secret of the diamonds!" whispered Mr. Jenks. "There must be a quart of the gems there!"

The men gathered about Folwell, uttering exclamations of delight. The diamonds were too hot to handle yet.

"That's going some!" exclaimed the chief of the diamond makers. "We have a small fortune here."

The was a sudden commotion at one end of the cave. A man rushed in. At the sight of him Tom stared and uttered an exclamation.

"Munson—the stowaway!" he whispered.

"Hello!" cried Folwell, as he saw his confederate. "I thought you were East, keeping Jenks away from here."

"He got the best of me!" cried Munson, "he and that Tom Swift! I stowed away on their airship, but they found me out by a wireless message, and marooned me in the woods. I've been trying to get here ever since! Didn't you get my messages of warning?"

"No—what warnings?" cried Folwell.

"About Jenks, Tom Swift and the others. They're here—they must be on Phantom Mountain now. In fact, I shouldn't be surprised if they were in this cave. I traced them to their camp, but they're gone. They may be among us now—in some of the secret recesses!"

For an instant Folwell stared at the bearer of these tidings. Then he cried out:

"Scatter men, and find these fellows! We must get them before they discover our secret!"

"It's too late—we know it!" exulted Tom Swift. Then he whispered to the others to hurry to the part of the cave where Bill Renshaw had first hidden them.



CHAPTER XXII—PRISONERS

"Do you think there is any danger of them finding us?" asked Mr. Damon, as he hurried along beside Tom.

"I'm afraid so," was the answer. "I've been worried ever since we saw Munson heading this way. But we couldn't do any differently."

"Perhaps Bill Renshaw may be able to conceal us," suggested Mr. Jenks. "Very likely he knows that Munson is on hand. Perhaps we will be safe for a while. I want to make a few more observations as to how they manufacture the diamonds, and then, with what I already know, I'll have the secret."

"And I'd like to make some scientific tests of the sides and bottom rocks of the cave," spoke Mr. Parker. "I think it will bear out my theory that the mountain will soon be destroyed."

"Well, you were right about Earthquake Island, and you may be right about this mountain," said Tom, "but if it is going to be annihilated I hope we get far enough away from it."

"We can keep our presence here a secret for a few more days, I think that will be long enough," proceeded Mr. Jenks. "Then we will leave."

"And, in the meanwhile, they'll be searching for us," objected Mr. Damon. "I wish that ghost-chap would come back and tell us what to do. Bless my liver-pin, but we are going to be in considerable danger, I'm afraid! Those men may capture us, and decide to make diamond dust from us."

"Come on—hurry to the little cave," urged Tom. "Then we'll get ready to defend ourselves."

"The main cave is a large one," said Mr. Jenks, "and there are many hiding places in it. In fact, it is so large that it will take those fellows several days to complete a circuit of it. By that time Bill Renshaw may come back, and take us to some place in which they have already searched for us. Then we'll be comparatively safe."

This thought was some consolation to them, as they made their way through the dark passage, dimly illuminated by the lantern they had rekindled, to the place where Bill had hidden them. They found things as they had left them, and proceeded to get a meal, though Tom said it would be best not to cook anything, or even to make coffee, for fear the odors would enable the searchers to trail them.

So they ate cold food, glad to get that. Silently they sat about the dimly-lighted cavern, and discussed the situation. True they might even now retreat, going out of the entrance Bill had showed them, and so escape. But Mr. Jenks felt that his mission was not completed yet, and they all agreed to stay with him.

"For there are several points about making diamonds that are not quite clear to me," he said. "I need to know how that steel box is constructed, how the electrical switches are arranged, what kind of lightning rods they use, and how they regulate the pressure. The other things, and how to mix the ingredients, I already know."

"Then we'll do our best to help you," promised Tom. "But now I think we had better see what sort of a defense we can put up. We have our guns and revolvers, and with these chairs and tables we can build a sort of barricade behind which we can take refuge if those fellows do discover our hiding place."

This was conceded to be a good idea, and soon a rude sort of fort was made, behind which the adventurers could take their stand and fight, if necessary, though they hoped this would not come to pass.

They remained quietly in the cave the remainder of that day, and, when it was night, as they could tell by their timepieces—there was no daylight—they divided the hours into watches, taking turns standing guard.

Morning, at least in point of time, came without any disturbance, and they made a cold breakfast. They hoped that Bill Renshaw would come, but he did not appear.

After sitting in the dark cave until afternoon, Tom said:

"I think we might as well go and take another observation of the big cave. We can tell what the men are doing, then, for they don't seem to have been near us. Maybe they have given up the search for us, and we can see them at work, and Mr. Jenks can gain what further knowledge he needs."

"That will be a good plan," agreed the diamond man. "It's maddening to sit here, doing nothing."

"And it will be comparatively safe to go from here to our former post of observation," added Tom, "for there doesn't seem to be any opening along the tunnel, into the larger cave, except the place where we were."

Accordingly they started off. Cautiously they looked through the opening into the apartment where they had seen the diamonds made.

"There's not a soul here!" exclaimed Tom, in a whisper. The others looked. The place was deserted—the machinery silent. Mr. Jenks peered in for a moment, and then exclaimed:

"I'm going in! Now's my chance to find out all that I wish to know! It may never come again, and then we can soon leave Phantom Mountain!"

It was a daring plan, but it seemed to be the best one to follow. They were all tired of inactivity. Mr. Jenks managed to get through the opening, and dropped into the big cave. The others followed. Mr. Jenks hurried over to the steel box, and began an examination of it. Tom Swift was looking at the electrical switch. He saw how it was constructed. Mr. Damon and Mr. Parker were peering interestedly about.

Suddenly the sound of voices was heard, and the echo of footsteps. Mr. Jenks started.

"They're coming back!" he whispered hoarsely. "Run!"

They all turned and sped toward their hiding place. But they were too late. An instant later Folwell, Munson and the other diamond makers confronted them. Our friends made a bold rush, but were caught before they could go ten feet.

"We have them!" cried Munson. "They walked right into our hands!"

It was true. Tom Swift and the others were the prisoners of the diamond makers.



CHAPTER XXIII—BROKEN BONDS

"Well," remarked Tom Swift, in mournful tones, "this looks as if we were up against it; doesn't it?"

"Bless my umbrella, it certainly does," agreed Mr. Damon.

"And it's all my fault," said Mr. Jenks. "I shouldn't have gone into the big cave. I might have known those men would come back any time."

The above conversation took place as our friends lay securely bound in a small cave, or recess, opening from the larger cavern, where, about an hour before, they had been captured and made prisoners by the diamond makers. Despite their struggles they had been overpowered and bound, being carried to the cave, where they were laid in a row on some old bags.

"It certainly is a most unpleasant situation, to say the least," observed Mr. Parker.

"And all my fault," repeated Mr. Jenks.

"Oh, no it isn't," declared Tom Swift, quickly. "We were just as ready to follow you into that cave as you were to go. No one could tell that the men would return so soon. It's nobody's fault. It's just our bad luck."

From where he lay, tied hand and foot, the young inventor could look out into the cave where he and the others had been caught. The diamond makers were busily engaged, apparently in getting ready to manufacture another batch of the precious stones. They paid little attention to their captives, save to warn them, when they had first been taken into the little cave, that it was useless to try to escape.

"They needn't have told us that," observed Tom, as he and the others were talking over their situation in low voices. "I don't believe any one could loosen these ropes."

"They certainly are pretty tight," agreed Mr. Damon. "I've been tugging and straining at mine for the last half hour, and all I've succeeded in doing is to make the cords cut into my flesh."

"Better give it up," advised Mr. Jenks.

"We'll just have to wait."

"For what?" the scientist wanted to know.

"To see what they'll do with us. They can't keep us here forever. They'll have to let us go some time." Following their capture, Folwell and Munson, the latter the stowaway of the airship, had been in earnest conversation regarding our friends, but what conclusion they had reached the adventurers could only guess.

"And we didn't have time to examine the diamond-making machinery close enough so that we could duplicate it if necessary," complained Tom, a little later.

"No," agreed Mr. Jenks. "There are certain things about it that are not clear to me. Well, I don't believe I'll have another chance to inspect it. They'll take good care of that, though they seem to be getting ready to make more diamonds."

"Perhaps they're going to manufacture a big batch, and then leave this place," suggested Mr. Damon. "They will probably go to some other secret cave, and leave us here."

"I hope they untie us before they leave, and give us something to eat," remarked the young inventor.

For two hours longer the captives lay there, in most uncomfortable positions. Then Folwell and Munson, leaving the group of diamond makers who were grouped about the machinery, approached the captives.

"Well," remarked Munson, "we got ahead of you after all; didn't we. You thought you had our secret, but it will be a long while before you ever make diamonds."

"What are you going to do with us?" asked Tom.

"Never mind. You came where you had no right to, and you must take the consequences."

"We did have a right to come here!" exclaimed Mr. Jenks. "I am entitled to know how the diamonds are made. I paid for the information, and you tricked me. If ever it's possible I'll have the whole gang arrested for swindling."

"You'll never get the chance!" declared Folwell. "You were given some diamonds for the money you invested, and that makes us square."

"No, it doesn't!" declared Mr. Jenks. "I invested the money to learn how to make diamonds, and you know it! You tricked me, and I had a right to try to discover your secret! I nearly have it, too, and I'll get it completely before I'm done with you!"

"No, you won't!" boasted Folwell. "But we didn't come here to tell you that. We came to give you something to eat. We're not savages and we'll treat you as well as we can in spite of the fact that you are trespassers. We're going to give you some grub, but I warn you that any attempt to escape will mean that some of you will get hurt."

He signalled to some of his confederates. These men unbound the captives' arms, and stood over them while they ate some coarse food that was brought into the small cave. They were given coffee to drink, and then, when the simple meal was over, they were securely bound again, and left to themselves, while the diamond makers went back to their machinery.

It was evident that they were going to attempt a big operation, for an unusually large quantity of the white stuff was prepared. The prisoners watched them idly. They could see some but not all of the operations. In this way several hours passed.

Gloom possessed the hearts of Tom and his friends. Not only had their expedition been almost a failure so far, but the young inventor was worried lest the gang might discover and wreck his airship. This would prove a serious loss. Lying there in the semi-darkness the lad imagined all sorts of unpleasant happenings.

At times he dozed off, as did the others. They had become somewhat used to the pain caused by the bonds, for their nerves were numb from the strain and pressure.

Once, as he was lightly sleeping, Tom was awakened by hearing loud voices in the main cave. He looked out, rolling over slightly to get a better view. He saw the man who, once before had run in to give news of an approaching electrical storm.

"Are you fellows all ready?" asked this same man again.

"Yes. Is there another storm coming?"

"Yes, and it's going to be a corker!" was the reply. "It's one of the worst I've ever seen. It's sweeping right up the valley. It'll be here in an hour."

"That's good. We need a big flash to make all the material we have prepared into diamonds. It's the biggest batch we ever tried. I hope it succeeds, for we're going to leave—" The rest was in so low a tone that Tom could not catch it.

The storm messenger departed. Folwell and Munson busied themselves about the machinery. Tom dozed off again, dimly wondering what had become of Bill Renshaw, and whether the former ghost knew of their plight. The others were asleep, as the young inventor saw by the dim light of a lantern in the cave. Then, he too, shut his eyes.

Tom was suddenly awakened by feeling some one's hands moving about his clothing. At first he thought it was one of the diamond-making gang, who had sneaked in to rob him. "Here! What are you up to?" exclaimed Tom.

"Quiet!" cautioned a voice. "Are you all here?"

"All of us—yes. But who are you?"

"Easy—keep quiet, Tom Swift! I'm Bill Renshaw! I've been searching all over for you, since I got back to your cave and found it empty. Now I'm going to free you. I got in here by a secret entrance. Wait, I'll cut your ropes." There was a slight sound, and an instant later Tom was freed from his bonds.



CHAPTER XXIV—IN GREAT PERIL

The young inventor could scarcely believe the good luck that had so unexpectedly come to him and his companions. No sooner was Tom able to move freely about than Bill Renshaw performed the same service for Mr. Jenks and the others, cautioning them to be quiet as he awakened them, and cut the ropes.

"Bless my circulation!" exclaimed Mr. Damon, in a hoarse whisper. "How did you ever get here. I'd given ourselves up for lost."

"Oh, I came in off the mountain, as there's a big storm due," explained the man. "There was no need of me playing the haunt in daytime, anyhow. I went to the cave, found you and your things gone, and I surmised that you might have walked into some trap."

"We did," admitted Mr. Jenks, grimly.

"Well, I hunted around until I found you," went on Bill. "This mountain is honeycombed with caves, all opening from the large one, I know them better than these fellows do, so I could explore freely, and keep out of their sight. They didn't know that there was a second entrance to this place, but I did, and I made for it, when I couldn't find you in some of the other caves where I looked. And, sure enough, here you were."

"Well, we can't thank you enough," said Mr. Parker. "But you say there is a big storm coming?"

"One of the biggest that's been around these parts in some time," replied Bill.

"Then perhaps the mountain will be destroyed," went on the scientist, as calmly as if he had remarked that it might rain.

"I hope nothing like that happens until we get away," spoke Mr. Damon, fervently.

"What had we better do?" inquired Tom.

"Get away, unless you want to discover some more of their secrets," advised Bill. "Those fellows are planning something, but I can't find out what it is. They are suspicious of me, I think. But they are up to something, and I believe, it would be best for you to leave while you have the chance. It may not be healthy to stay. That's why I did my best to untie you."

"We appreciate what you have done," declared Mr. Jenks, "but I want my rights. I must learn a few more facts about how to make diamonds from lightning flashes, and then I will have the same secret they cheated me out of. I think if we wait a while we may be able to see the parts of the process that are not quite clear to us. What do you say, Tom Swift?"

"Well, I would like to learn the secret," replied the lad, "and if Bill thinks it's safe to stay here a while longer—"

"Oh, I guess it will be safe enough," was the reply. "Those fellows won't bother about you now that they are about to make some more diamonds. Besides, they think you're all tied up. Yes, you can stay here and watch, I reckon. I've got a couple of guns, and—"

"Then we'll stay," decided Tom. "We can put up a better fight now."

Silently, in their prison, but which they could now leave whenever they pleased, the adventurers watched the diamond makers once more. The same process they had witnessed before was gone through with. The white balls were put inside the steel box and sealed up. Then they waited for the storm to reach its height.

That this would not be long was evidenced by the mutterings of thunder which every moment grew louder. The outburst of electrical fury was likely to take place momentarily, and that it would be unusually severe was shown by the precautions taken by the diamond makers. They attached a number of extra wires, and brought out some insulated, hard rubber platforms, on which they themselves stood. Tom and Mr. Jenks were much interested in watching this detail of the work, and sought to learn how each part of the process was done.

"I almost think we can make diamonds, Tom, when we get back to civilization," whispered Mr. Jenks.

"I hope we can," answered Tom, "and we can't get back any too soon to suit me. I want to be in my airship again."

"I don't blame you. But look, they are getting ready to adjust the switch."

The adventurers ceased their whispered talk, and eagerly watched the diamond makers. Folwell and Munson were hurrying to and fro in the big cave, attending to the adjustments of the machinery.

"On your insulated plates—all of you," Folwell gave the order. "This is going to be a terrific storm. The gage shows twice the power we have ever used, and it's creeping up every minute! We'll have more diamonds than ever had before!"

"Yes, if the mountain isn't destroyed," added Mr. Parker, in a low voice. "I predict that it will be split from top to bottom!"

"Comforting," thought Tom, grimly.

"I guess we're all ready," said Folwell, in a low tone to Munson. "We'd better get insulated ourselves. I'm going to throw the switch."

He did so. A moment later the man who had before given warning of the storm came dashing in. He was very much excited.

"It's awful!" he cried. "The lightning is striking all over! Big rocks are being split like logs of wood!"

"Well, it can't do any damage in here," said Munson. "We are well protected. Get on one of the plates," and he motioned to one of the hard-rubber platforms that was not occupied. The roar and rumble of the storm outside had given place to short terrific crashes. In their small cave the adventurers could feel the solid ground shake.

A bluish light began dancing about the electrical wires. There was a smell of sulphur in the air. Crash after crash resounded outside. A flash of flame lit up the whole interior of the cave. It came from the copper switch.

"Something's wrong with the insulation!" cried Munson.

"Don't go near it!" yelled Folwell. "If you value your life, stand still!"

Hardly had he spoken than inside the cavern there sounded a report like that of a small cannon. A big ball of fire danced about the middle of the cave and then leaped on top of the steel box.

"This is a fearful storm," cried Munson.

The adventurers in the cave did not know what to say or do. They were in deadly peril.

Suddenly there came a crash louder than any that had preceded it. The whole side of the cave where the switches were was a mass of bluish flame. Then came a ripping, tearing sound, and a tangle of wires and copper connections were thrown to the floor. At the same time the steel box, containing the materials from which diamonds were made, turned blue, and flames shot from it.

"It's all up with us!" cried Munson. "Run for it, everybody! The wires are down, and this place will be an electric furnace in another minute!"

He leaped toward the exit from the cave.

"What about those fellows?" asked Folwell, indicating the place where Tom and the others had been tied.

"They'll have to do the best they can! It's every man for himself, now!" yelled Munson. There was a wild scramble from the cavern.

"Come on!" cried Tom. "We must escape! It's our only chance!"

He leaped into the big cave, followed by the others. Already long tongues of electrical fire were shooting out from the walls and roof as Tom Swift and his companions, evading them as best they could, sought safety in flight.



CHAPTER XXV—THE MOUNTAIN SHATTERED—CONCLUSION

"Can't we get some of the diamonds?" cried Mr. Damon, as he raced along behind Tom. "Now's our chance. Those fellows have all gone!" The odd man made a grab for something as he ran.

"It's as much as our lives are worth," declared the young inventor. "We dare not stop! Come on!"

"I'd like to investigate some of the machinery," spoke Mr. Jenks, "but I wouldn't stop, even for that."

"The storm is too dangerous," called Bill Renshaw. "I can show you a shorter way out than the one those fellows have taken. Follow me."

"No way can be too short," said Mr. Parker, solemnly. "This mountain will go to pieces shortly, I think!"

Tom shuddered. He remembered how narrow had been their escape when Earthquake Island sank into the sea. And that some terrific upheaval was now imminent might be judged from the awful reports that sounded more plainly as the adventurers raced toward the opening of the cave. It was like the bombardment of some doomed city.

Mr. Jenks and Tom cast one longing look behind at the complicated and expensive machinery that had been installed in the cave by the diamond makers. They had abandoned it, and in it lay the secret of making precious gems. But there was no time to stop now, and investigate.

"This way," urged Bill Renshaw. "We'll soon be out."

"But won't it be dangerous to go outside?" asked Mr. Damon. "Shan't we be struck by lightning? There is some protection in here."

"None at all," said Mr. Parker, quickly. "This mountain is a natural lightning rod. To stay here in this cave will be sure death when the storm gets directly over it. And that will be very soon. We must get on insulated ground. Is there any part of this mountain that does not contain iron ore?" the scientist asked of the former spirit.

"Yes; the way out by which we are going lands on a dirt hill."

"That's good; then we may be saved."

On they ran. They had no lanterns, but the blue light of the electricity, as it leaped from point to point inside the cave, where there were outcroppings of iron ore, made the place bright enough to see.

"Here we are!" cried Bill Renshaw at length. "Here's the way out!"

Making a sudden turn in the winding passage he showed the adventurers a small opening in the side of the crag. In an instant they had passed through, and found themselves in daylight once more. The sudden glare almost blinded them, for, though the sky was overcast by clouds, from which jagged tongues of lightning played, the outside was much lighter than the dark cave.

"I should say it was a storm!" cried Tom Swift. "See, it is striking every minute, and all around us!"

In fact, lightning bolts were falling on every side of the adventurers. Every time the balls of fire struck, they burst open great stones, or seared a livid scar on the face of some cliff. As for Tom and the others, they stood on a dry dirt hill, in which, fortunately, there was no iron ore. To this fact they undoubtedly owed their lives, though had there been rain, to moisten the ground and make the earth a good conductor of electricity, they probably would have been badly shocked. But the electrical outburst was not accompanied by rain.

Tom looked up. He saw a compact mass of cloud moving toward the summit of the mountain on the slope of which they stood. From this cloud there played shafts of reddish-green fire.

"Look!" called the young inventor to Mr. Parker. The instant the latter saw the cloud, he cried:

"We must get away from here by all means! That is the center of the storm. As soon as it gets over the mountain, where that lightning rod is, all the electrical fluid will be discharged in one bolt at the mountain, and it will be destroyed! We must run, but keep on the dirt places! Run for your lives!"

They needed no second warning. Turning, they fled down the steep side of the mountain, slipping and stumbling, but taking care not to step on any iron ore. Behind them flashed the lightning bolts.

Suddenly there was a most awful crash. It seemed as if the end of the world had come, and the ear drums of Tom and his companion almost burst with the fearful report. The concussion knocked them down, and they lay stunned for a moment.

Following the terrible report there was a low, rumbling sound. Hardly knowing whether he was dead or alive, Tom opened his eyes and looked about him. What he saw caused him to cry out in terror.

The whole mountain seemed bathed in fire. Great blue, red and green flashes played around it. Then the towering cliff seemed to melt and crumble up, and the great peak, the top of it containing the diamond makers' cave, from which they had fled but a few minutes before, the entire summit was toppled over into the valley on the other side, and in the direction opposite to that where the adventurers stood.

Then came a profound silence, and the lightning ceased. The storm was over, and only the rattle of stones and boulders, as they came to rest in the valley below, reached the ears of our friends.

"Phantom Mountain has been destroyed, just as I said it would be," spoke Mr. Parker, solemnly. Once more he had prophesied correctly.

For a few minutes the adventurers hardly knew what to say. They arose awkwardly from the ground where the shock had tossed them. Then Tom remarked, as calmly as possible:

"Well, it's all over. I guess we may as well get back to our airship."

"What became of Munson and the others?" asked Mr. Damon.

Mr. Jenks pointed to the trail, far below. The figures of some men, running madly, could be seen.

"There they go," he said; "I fancy we have seen the last of them." And they had, for some time at least.

There was little use lingering any longer on Phantom Mountain—indeed little of it was left on which to remain. Looking back toward the place where the cave had been, Tom and the others started forward again. The diamond-making machinery had all been destroyed. So, also, had the finished diamonds stored in the cavern and the large supply which had probably been made by the last terrific crash. No one would ever have them now. Tom and Mr. Jenks felt a sense of disappointment, but they were glad to have escaped with their lives. They sought their former camp, but the tent and all their food was buried under tons of earth and rocks.

Three days later, after rather severe hardships, they were near the place where they had left the Red Cloud. They had suffered cold and hunger, for they had no food supplies, and, had it not been that Bill Renshaw knew the haunts of some game, of which they managed to snare some, they would have fared badly, for they had left their guns in the cave.

"Well, there are the trees behind which I hope my airship is hidden," announced Tom, as they came to the spot. "Good old Red Cloud! Maybe we won't do some eating when we get aboard, eh?"

"Bless my appetite! but we certainly will!" cried Mr. Damon.

"There's somebody walking around the place," spoke Mr. Jenks.

"I hope it's no one who has damaged the ship," came from Tom, apprehensively. He broke into a run, and soon confronted an aged miner, who seemed to have established a rude sort of camp near the airship.

"Is anything the matter?" asked Tom, breathlessly. "Is my airship all right?"

"I guess she's all right, stranger," was the reply. "I don't know much about these contraptions, but I haven't touched her. I knowed she was an airship, for I've seen pictures of 'em, and I've been waiting until the owner came along."

"Why?" asked Tom, wonderingly.

"Because I've got a proposition to make to you," went on the miner, who said his name was Abe Abercrombie. "I've been a miner for a good many years, and I'm just back from Alaska, prospecting around here. I haven't had any luck, but I know of a gold mine in Alaska that will make us all rich. Only it needs an airship to get to it, and I've been figuring how to hire one. Then I comes along, and I sees this big one, and I makes up my mind to stay here until the owners come back. That's what I've done. Now, if I prove that I'm telling the truth, will you go to Alaska—to the valley of gold with me?"

"I don't know," answered Tom, to whom the proposition was rather sudden. "We've just had some pretty startling adventures, and we're almost starved. Wait until we get something to eat, and we'll talk. Come aboard the Red Cloud," and the lad led the way to his craft which was in as good condition as when he left it to go to the diamond cave. Later he listened to the miner's story.

Tom Swift did go to the valley of gold in Alaska, and what happened to him and his companions there will be told of in the next volume of this series, to be called "Tom Swift in the Caves of Ice; or, the Wreck of the Airship."

It did not take our friends long, after they had eaten a hearty meal, to generate some fresh gas, and start the Red Cloud oh her homeward way. Tom wanted to take Bill Renshaw with him, but the old man said he would rather remain among the mountains where he had been born. So, after paying him well for his services, they said good-by to him. Abercrombie, the miner, also remained behind, but promised to call and see Tom in a few months.

"Well, we didn't make any money out of this trip," observed Mr. Jenks, rather dubiously, as they were nearing Shopton, after an uneventful trip. "I guess I owe you considerable, Tom Swift. I promised to get you a lot of diamonds, but all I have are those I had from my first visit to the cave."

"Oh, that's all right," spoke Tom, easily. "The experience was worth all the trip cost."

"Speaking of diamonds, look here!" exclaimed Mr. Damon, suddenly, and he pulled out a double handful.

"Where did you get them?" cried the others in astonishment.

"I grabbed them up, as we ran from the cave," said the eccentric man; "but, bless my gaiters! I forgot all about them until you spoke. We'll share them."

These diamonds, some of which were large, proved very valuable, though the total sum was far below what Mr. Jenks hoped to make when he started on the remarkable trip. Tom gave Mary Nestor a very fine stone, and it was set in a ring, instead of a pin, this time.

On their arrival in Shopton, where Mr. Swift, the housekeeper, Mr. Jackson and Eradicate Sampson were much alarmed for Tom's safety, an attempt was made to manufacture diamonds, using a powerful electric current instead of lightning. But it was not a success, and so Mr. Jenks concluded to give up his search for the secret which was lost on Phantom Mountain.

And now we will take leave of Tom Swift, to meet him again soon in other adventures he is destined to have in the caves of ice and the valley of gold.



THE END



THE TOM SWIFT SERIES

By VICTOR APPLETON

TOM SWIFT AND HIS MOTOR CYCLE Or Fun and Adventure on the Road TOM SWIFT AND HIS MOTOR BOAT Or The Rivals of Lake Carlopa TOM SWIFT AND HIS AIRSHIP Or The Stirring Cruise of the Red Cloud TOM SWIFT AND HIS SUBMARINE BOAT Or Under the Ocean for Sunken Treasure TOM SWIFT AND HIS ELECTRIC RUNABOUT Or The Speediest Car on the Road TOM SWIFT AND HIS WIRELESS MESSAGE Or The Castaways of Earthquake Island TOM SWIFT AMONG THE DIAMOND MAKERS Or The Secret of Phantom Mountain TOM SWIFT IN THE CAVES OF ICE Or The wreck of the Airship TOM SWIFT AND HIS SKY RACER Or The Quickest Flight on Record TOM SWIFT AND HIS ELECTRIC RIFLE Or Daring Adventures In Elephant Land TOM SWIFT IN THE CITY OF GOLD Or Marvelous Adventures Underground TOM SWIFT AND HIS AIR GLIDER Or seeking the Platinum Treasure TOM SWIFT IN CAPTIVITY Or A Daring Escape by Airship TOM SWIFT AND HIS WIZARD CAMERA Or The Perils of Moving Picture Taking TOM SWIFT AND HIS GREAT SEARCHLIGHT Or On the Border for Uncle Sam TOM SWIFT AND HIS GIANT CANNON Or The Longest Shots on Record TOM SWIFT AND HIS PHOTO TELEPHONE Or The Picture that Saved a Fortune TOM SWIFT AND HIS AERIAL WARSHIP Or The Naval Terror of the Seas TOM SWIFT AND HIS BIG TUNNEL Or The Hidden City of the Andes



THE MOTION PICTURE CHUMS SERIES

By VICTOR APPLETON

In these stories we follow the adventures of three boys, who, after purchasing at auction the contents of a moving picture house, open a theatre of their own. Their many trials and tribulations, leading up to the final success of their venture, make very entertaining stories.

THE MOTION PICTURE CHUMS' FIRST VENTURE

Or Opening a Photo Playhouse in Fairlands.

The adventures of Frank, Randy and Pep in running a Motion Picture show. They had trials and tribulations but finally succeed.

THE MOTION PICTURE CHUMS AT SEASIDE PARK

Or The Rival Photo Theatres of the Boardwalk.

Their success at Fairlands encourages the boys to open their show at Seaside Park, where they have exciting adventures—also a profitable season.

THE MOTION PICTURE CHUMS ON BROADWAY

Or The Mystery of the Missing Cash Box.

Backed by a rich western friend the chums established a photo playhouse in the great metropolis, where new adventures await them.

THE MOTION PICTURE CHUMS' OUTDOOR EXHIBITION

Or The Film that Solved a Mystery.

This time the playhouse was in a big summer park. How a film that was shown gave a clew to an important mystery is interestingly related.

THE MOTION PICTURE CHUMS' NEW IDEA

Or The First Educational Photo Playhouse.

In this book the scene is shifted to Boston, and there is intense rivalry in the establishment of photo playhouses of educational value.

THE MOTION PICTURE CHUMS AT THE FAIR

Or The Greatest Film Ever Exhibited.

The chums go to San Francisco, where they have some trials but finally meet with great success.

THE MOTION PICTURE CHUMS' WAR SPECTACLE

Or The Film that Won the Prize.

Through being of service to the writer of a great scenario, the chums are enabled to produce it and win a prize.



THE BOYS OF COLUMBIA HIGH SERIES

By GRAHAM B. FORBES

Never was there a cleaner, brighter, more manly boy than Frank Allen, the hero of this series of boys tales, and never was there a better crowd of lads to associate with than the students of the School. All boys will read these stories with deep interest. The rivalry between the towns along the river was of the keenest, and plots and counterplots to win the champions, at baseball, at football, at boat racing, at track athletics, and at ice hockey, were without number. Any lad reading one volume of this series will surely want the others.

THE BOYS OF COLUMBIA HIGH Or The All Around Rivals of the School

THE BOYS OF COLUMBIA HIGH ON THE DIAMOND Or Winning Out by Pluck

THE BOYS OF COLUMBIA HIGH ON THE RIVER Or The Boat Race Plot that Failed

THE BOYS OF COLUMBIA HIGH ON THE GRIDIRON Or The Struggle for the Silver Cup

THE BOYS OF COLUMBIA HIGH ON THE ICE Or Out for the Hockey Championship

THE BOYS OF COLUMBIA HIGH IN TRACK ATHLETICS Or A Long Run that Won

THE BOYS OF COLUMBIA HIGH IN WINTER SPORTS Or Stirring Doings on Skates and Iceboats

12mo. Illustrated. Handsomely bound in cloth, with cover design and wrappers in colors.

GROSSET & DUNLAP, PUBLISHERS, NEW YORK



THE OUTDOOR CHUMS SERIES

By CAPTAIN QUINCY ALLEN

The outdoor chums are four wide-awake lads, Sons of wealthy men of a small city located on a lake. The boys love outdoor life, and are greatly interested in hunting, fishing, and picture taking. They have motor cycles, motor boats, canoes, etc., and during their vacations go everywhere and have all sorts of thrilling adventures. The stories give full directions for camping out, how to fish, how to hunt wild animals and prepare the skins for stuffing, how to manage a canoe, how to swim, etc. Full of the spirit of outdoor life.

THE OUTDOOR CHUMS Or The First Tour of the Rod, Gun and Camera Club.

THE OUTDOOR CHUMS ON THE LAKE Or Lively Adventures on Wildcat Island.

THE OUTDOOR CHUMS IN THE FOREST Or Laying the Ghost of Oak Ridge.

THE OUTDOOR CHUMS ON THE GULF Or Rescuing the Lost Balloonists.

THE OUTDOOR CHUMS AFTER BIG GAME Or Perilous Adventures in the Wilderness.

THE OUTDOOR CHUMS ON A HOUSEBOAT Or The Rivals of the Mississippi.

THE OUTDOOR CHUMS IN THE BIG WOODS Or The Rival Hunters at Lumber Run.

THE OUTDOOR CHUMS AT CABIN POINT Or The Golden Cup Mystery.

THE END