Out from the Red Cloud piled Tom and the others. They made a rush for the irregular mass of rock which bore so strong a resemblance to the head of some gigantic man.

"That's the one! That's the thing I saw when they were taking me along here blindfolded!" exclaimed Mr. Jenks. "I'm sure we're on the right trail, now!"

"But what gets me, though," remarked Mr. Damon, "is why we couldn't see that landmark when we were up in the air. We had a fine view, and ought to have been able to pick it out with the telescopes."

The adventurers saw the reason a few seconds later. The image was visible only from one place, and that was directly looking up the valley. If one went too far to the right or left the head disappeared from view behind jutting crags, and it was impossible to see it from overhead, because the head was almost under a great spur of a mighty mountain.

"We might have hunted for it a week in the airship, and been directly over it," said Tom, "and yet we would never have seen it."

"Yes, but we never would have gotten here in such good shape if it hadn't been for your wonderful craft," declared Mr. Jenks. "It brought us here safely and quickly, and enabled us to elude the men who tried to keep us back. We're here in spite of them. If we had traveled by train they might have interfered with us in a dozen ways."

"That's so," agreed Mr. Damon. "Well, now we're here, what's to be done? Which way do we start to reach the cave where the diamonds are manufactured, Mr. Jenks?"

"That I can't say. As you know, I only had a momentary glimpse of this stone head as they wore taking me along the trail. Then one the men noticed that the bandage had slipped and he pulled it into place. So I really can't say which direction to take now, in order to discover the secret."

"How long after you saw the head before you reached the cave?" asked Tom. "In that way we may be able to tell how far away it is."

"Well, I should say it was about two or three hours after I saw the head, before we got to the halting place, and I was carried into the cave. That would make it several miles from here, for we went in a wagon."

"Yes, and they might have driven in a round-about way, in order to deceive you," suggested Mr. Damon. "At best we have but a faint idea where the diamond cave is, but we must search for it; eh, Tom?"

"Certainly. We'll start right in. And as the airship will be of but little service to us now, I suggest that we leave it in this valley. It is very much secluded, and no one will harm it, I think. We can then start off prospecting, for I have a large portable tent, and we can carry enough food with us, with what game we can shoot, to enable us to live. I have a regular camping outfit on board."

"Fine!" cried Mr. Parker, "and that will give me a chance to make some observations among the mountains, and perhaps I can predict when a landslide, or an eruption of some dormant volcano, may occur."

"Bless my stars!" cried Mr. Damon. "I don't wish you any bad luck, Mr. Parker, but I sincerely hope nothing of the sort happens! We had enough of that on Earthquake Island!"

"One can not halt the forces of nature," said the scientist, solemnly. "There are many towering peaks around here which may contain old volcanoes. And I notice the presence of iron ore all about. This must be a wonderful place in a thunder and lightning storm."

"Why?" asked Tom, curiously.

"Because lightning would be powerfully attracted here by the presence of the metal. In fact there is evidence that many of the peaks have been struck by lightning," and the scientist showed curious, livid scars on the stone faces of the peaks within sight.

"Then this is a good place to stay away from in a storm," observed Mr. Damon. "However, we won't worry about that now. If this is the landmark Mr. Jenks was searching for, then we must be in the vicinity of Phantom Mountain."

"I think we are," declared the diamond seeker. "Probably it is within sight now, but there are so many peaks, and this is such a wild and desolate part of the country that we may have trouble in locating it."

"We've got to make a beginning, anyhow," decided Tom, "and the sooner the better. Come, we'll make up our camping kits, and start out."

It was something to know that they were on the right trail, and it was a relief to be able to busy oneself, and not be aimlessly searching for a mysterious landmark. They all felt this, and soon the airship was taken to a secluded part of the valley, where it was well hidden from sight in a grove of trees.

Tom and Mr. Damon then served a good meal, and preparations were made to start on their search among the mountains--a search which they hoped would lead them to Phantom Mountain, and the cave of the diamond makers.

The tent which would afford them shelter was in sections, and could be laced together. They carried food, compressed into small packages, coffee, a few cooking utensils; and each one had a gun, Tom carrying a combination rifle and shotgun, for game.

"We can't live very high while we're on the trail," said the young inventor, "but it won't be much worse than it was on Earthquake Island. Are we all ready?"

"I guess so," answered Mr. Damon. "How long are we going to be away?"

"Until we find the diamond makers!" declared Tom, firmly.

Shouldering their packs, the adventurers started off. Tom turned for a last look at his airship, dimly seen amid the trees. Would he ever come back to the Red Cloud? Would she be there when he did return? Would their quest be successful? These questions the lad asked himself, as he followed his companions along the rocky trail.

"Perhaps we can find the road by which these men go in and out of the cave," suggested Mr. Damon, when they had gone on for several miles.

"I fancy not," replied Mr. Jenks. "They probably take great pains to hide it. I think though, that our best plan will be to go here and there, looking for the entrance to the cave. I believe I would remember the place."

"But why can't you follow the directions given by the miner who told you about Phantom Mountain?" asked Mr. Damon.

"Because his talk was too indefinite," answered Mr. Jenks. "He was so frightened by seeing what he believed to be a ghost, that he didn't take much notice of the location of the place. All he knows is that Phantom Mountain is somewhere around here."

"And we've got to hunt until we find it; is that the idea?" asked Mr. Parker.

"Or until we see the phantom" added Tom, in a low voice.

"Bless my topknot!" exclaimed Mr. Damon. "You don't mean to say you expect to see that ghost; do you Tom?"

"Perhaps," answered the young inventor, and he did not add something else of which he was thinking. For Tom had a curious theory regarding the phantom.

They tramped about the remainder of that day. Toward evening Tom shot some birds, which made a welcome addition to their supper. Then the tent was put together, some spruce and hemlock boughs were cut to make a soft bed, and on these, while the light of a campfire gleamed in on them, the adventurers slept.

Their experience the following day was similar to the first. They saw no evidence of a large cave such as Mr. Jenks had described, nor were there any traces of men having gone back and forth among the mountains, as might have been expected of the diamond makers, for, as Mr. Jenks had said, they made frequent journeys to the settlement for food, and other supplies.

"Well, I haven't begun to give up yet," announced Tom, on the third day, when their quest was still unsuccessful. "But I think we are making one mistake."

"What is that?" inquired Mr. Jenks.

"I think we should go up higher. In my opinion the cave is near the top of some peak; isn't it, Mr. Jenks?"

"I have that impression, though, as you know, I never saw the outside of it. Still, it might not be a bad idea to ascend some of these peaks."

Following this suggestion, they laid their trail more toward the sky, and that night found them encamped several thousand feet above the sea-level. It was quite cool, and the campfire was a big one about which they sat after supper, talking of many things.

Tom did not sleep well that night. He tossed from side to side on the bed of boughs, and once or twice got up to replenish the fire, which had burned low. His companions were in deep slumber.

"I wonder what time it is?" mused Tom, when he had been up the third time to throw wood on the blaze. "Must be near morning." He looked at his watch, and was somewhat startled to see that it was only a little after twelve. Somehow it seemed much later.

As he was putting the timepiece back into his pocket the lad looked around at the dark and gloomy mountains, amid which they were encamped. As his gaze wandered toward the peak of the one on the side of which the tent was pitched, he gave a start of surprise.

For, coming down a place where, that afternoon, Tom had noticed a sort of indefinite trail. was a figure in white. A tall, waving figure, which swayed this way and that--a figure which halted and then came on again.

"I wonder--I wonder if that can be a wisp of fog?" mused the young inventor. He rubbed his eyes, thinking it might be a swirling of the night mist or a defect of vision. Then, as he saw more plainly, he noticed the thing in white rushing toward him.

"It's the phantom--the phantom!" cried Tom, aloud. "It's the thing the miner saw! We're on Phantom Mountain now!"