ey doing?" murmured Captain Barforth.

"They are shooting off something, but it is not a gun or a cannon,"
answered Mr. Rover.

"Hurrah! I know what it is!" cried Tom "Good for Fred and Hans! Those
are my fireworks--those I had left from the Fourth of July
celebration. They are giving them a dose of rockets and Roman
candles!"

This news was true, and as the rockets and Roman candles hit the
rowboats and the occupants the latter stopped rowing and then began to
back water in confusion. Soon the rowboats turned back and hastened to
the side of the _Josephine_.

"That's what I call repelling boarders!" said Captain Barforth,
grimly. "I only hope the fireworks hold out."

"It is now to be a race between the _Rainbow_ and that other craft,"
observed Mr. Rover, and he was right. Inside of fifteen minutes both
vessels were headed out to sea, and running at about the same rate of
speed. Soon the haze over the water hid both craft from view.

"Well, one thing is certain," said Mr. Rover. "Our friends are alive
to their danger and are going to do their best to get away from the
enemy."

"And another thing is that we are left marooned on this isle," said
the captain.

The party remained in the tree a while longer, and then, as there
seemed nothing else to do, they descended to the ground.

"Well, we have one thing in our favor," was Dick's comment. "Sid
Merrick and his crowd must be on the _Josephine_, or they wouldn't chase
the _Rainbow_, and that being so they can't interrupt our treasure hunt,
at least for the present."

"But if they capture our steam yacht how are we to get away from here,
even if we do uncover the treasure?" said Sam.

"We'll get away somehow--and make it good and hot for them in the
bargain," answered Tom, and his father nodded in approval.

With their thoughts on the _Rainbow_ and those on board, the treasure
hunters went back to the vicinity of the shattered cave. Nobody felt
much like working, yet to remain idle made the time hang heavily on
their hands.

"There is no use of our going to work in a haphazard fashion," were
Mr. Rover's words. "We must first go over the ground carefully and
plan out just what is best to do. Otherwise a good portion of our
energies will be wasted."

This was sound advice and was followed out. They surveyed the whole
vicinity with care, poking in among the rocks with long sticks, and
turning over such as were loose and easily moved.

"This looks as if it