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,
