"Just you take it easy, Uncle Barney. You mustn't excite yourself now," said Jack kindly. "We'll do what we can toward getting the box back."
The boys had brought some food along, and they insisted upon it that the old man eat and drink something. This seemed to strengthen Uncle Barney greatly, and he arose to his feet.
"Now we'll get after those rascals," he said, with something of the old-time fire in his eyes. "I'm not going to allow 'em to rob me in this fashion!"
While the old lumberman had been eating, the Rover boys had glanced around the cave curiously. It was a place partly natural and partly artificial. On one side it looked as if a little mining had been done, and Jack, who had studied geology, gazed at the surface of rocks and dirt with much interest.
"Why, Uncle Barney, this looks to me as if it was zinc ore!" he cried presently.
"Hush, hush, boy! I don't want anybody to know about that!" answered the old man quickly.
"Then it is zinc ore, is it?" queried Randy, who had also been inspecting a side of the cave.
"Yes, if you must know," was the surprising reply. "Right here, in the middle of this island, is one of the most valuable zinc ore beds to be found anywhere."