“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.