I was carried into the cave, I managed to raise one corner of
the bandage. I caught a glimpse of a very peculiarly shaped cliff--it
is like a great head, standing out in bold relief against the moonlight,
when I saw it. That head of rock is near the cave. It may be the
landmark by which we can locate Phantom Mountain."

"Perhaps," admitted the young inventor.

"What I want to know is this," went on Mr. Jenks. "Will you go with me
on this quest--go in your airship to discover the secret of the diamond
makers? If you will, I will share with you whatever diamonds we can
discover, or make; besides paying all expenses. Will you go, Tom Swift?"

The young inventor did not know what to answer. How far was Mr. Jenks
to be trusted? Were the stones he had real diamonds? Was his story,
fantastical as it sounded--true? Would it be safe for Tom to go?

The lad asked himself these questions. Mr. Jenks saw his hesitation.

"Here," said the strange man, "I will prove what I say. Take this
diamond. I intended it for you, anyhow, for what you did for me on
Earthquake Island. Take it, and--and give it to the person for whom you
were about to purchase a diamond to-night. But, first of all, take it to
a gem expert, and get his opinion. That will prove the truth of what
I say, Tom Swift, and I feel sure that you will cast your lot in with
mine, and help me to discover the secret of Phantom Mountain, and aid me
to get my rights from the diamond makers!"

CHAPTER IV--ANDY FOGER GETS A FRIGHT

Tom Swift considered a few minutes. On the face of it, the proposition
appealed to him. He had been home some time now after his adventures on
Earthquake Island, and he was beginning to long for more excitement. The
search for the mysterious mountain, and the cave of the diamond makers,
might offer a new field for him. But there came to him a certain
distrust of Mr. Jenks.

"I don't like to doubt your word," began Tom, slowly, "but you know,
Mr. Jenks, that some of the greatest chemists have tried in vain to make
diamonds; or, at best, they have made only tiny ones. To think that any
man, or set of men, made real diamonds as large as the ones you have,
doesn't seem--well--" and Tom hesitated.

"You mean you can hardly believe me?" asked Mr. Jenks.

"I guess that's it," assented Tom.

"I don't blame you a bit!" exclaimed the odd man. "In fact, I didn't
believe it when they told me they could make diamonds. But they proved
it to me. I'm