"All the islands have caves. If we're going at this thing we've got to do it right; we've got to find the right key, and the right cave, and then there can be no possible doubt when we return and report to Townsend that there's no iron chest."
"You think that's all a yarn for the marines, eh?"
"Nothing else; but Townsend is bound by a promise, and he's the sort of man who doesn't make a promise lightly."
The three chums slept out the night in the car of the air ship. When morning dawned, the barometer indicated fair weather. The wind was north by east, quartering offshore, but it was so light as not to cause Matt much concern.
Matt was the first of the three to be astir. After he had looked at the barometer and taken note of the wind, he awoke Dick and Carl.
"We're off for Turtle Key, pards," cried Matt, "and we're going it alone. Up with you, and let's put to sea."
[CHAPTER X.]
THE AIR SHIP SPRINGS A LEAK.
The Hawk had been moored between two trees. The landing had been easily made, the preceding afternoon, and Matt was confident that the ascent could be made as easily. And such would have been the case, had nothing gone wrong.