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208 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. "Well 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."