end some of the others ashore armed if there came a signal
of distress.

"We have enemies on this isle," said Captain Barforth. "And they may
try to do us harm."

"I'll watch out," answered the mate, shortly. And then he turned away
with a thoughtful look on his sour countenance. That there was
something on his mind was evident.

The small boat was brought ashore at the point where the path led
directly to the sunken cave. Although there was a lively breeze
blowing, those landing did so without mishap. They had with them some
tools for digging, and also a rock drill and some powder.

"It will do no harm to blast one or two of the rocks and see what is
underneath," said Anderson Rover. "We may possibly be lucky enough to
find some entrance into the cave, although I must confess I doubt it."

When they got to the vicinity of the shattered cave they found
everything as they had left it. Even a pick Tom had forgotten remained
undisturbed.

"Evidently the Merrick crowd has not yet found its way here," said
Dick.

"We shall have to be on our guard when we go to blasting," answered his
parent. "For the noise may bring that rascal and his gang here in a
hurry."

And then all set to work with vigor to see if by some means they could
not get down under the rocks and to the spot where the precious
treasure had been deposited so many years before.

CHAPTER XXVII

WHAT HAPPENED ON THE STEAM YACHT

About an hour after the Rovers and Captain Barforth had left the steam
yacht Dora came from the forward deck looking much disturbed.

"What is the trouble?" asked her mother.

"Oh, not very much," she answered, for she did not wish to worry her
parent. "Where is Fred?"

"I think he is at the stern, fishing with Hans and John."

"I want to see them," continued Dora, and hurried off.

She found the three chums at the stern. They had been fishing for some
time and several fish lay on the deck near them.

"Hullo, Dora, want to try your luck?" asked Fred, pleasantly. "I'll fix
you a line--and fix lines for Nellie and Grace, too, if they want
them."

"I want to tell you boys something," said the girl, in almost a
whisper, and not noticing what Fred had proposed. "I--I am afraid
something is going to happen."

"What's that?" asked Songbird, and all three youths looked at Dora
anxiously.

"I was just up near the bow of the boat, and I overheard Mr. Carey, the
mate, talking to Mr. Bossermann, the assistant engine