or two, one of
which the Professor has, had a big bullet in the skull, which we took
out and can show you."

"Where did you find these?"

"Right in front of the place where the treasure was found."

"Well, did they have a fight, do you think, for the possession of the
treasure?"

"Undoubtedly."

"Now, let us go around to the other side of the cave."

It will be remembered that in the other portion of the cave the
skeletons and the treasure, as well as the weapons, were left just as
they were found by the boys, because they had never informed the
Professor of their secret visit to the cave, when they discovered the
chained captives and the skeletons about them.

The party passed around the first projecting wall which separated the
two large chambers, and as they were moving along something sounded in
the second chamber ahead. The boys stopped suddenly. In a moment more
the same peculiar dull and ominous sound was continued, and it seemed to
be very near.

The boys looked at each other in amazement. During all of the previous
visits there had never been the slightest sound within the cavern.

"Possibly," said Harry, "it may be running water."

"It doesn't sound like water to me. I will--" but Harry did not have an
opportunity to say anything more, as a terrific roar, like a cannon
shot, rang out, and the boys were simply petrified.

"What do you think that was?" whispered George. They drew close
together, and spoke in whispers.

"This will never do," declared Harry. "If there is anything in this
place we might as well know it now as later. Will you join me in the
hunt?"

And the boys responded with one assent. "Let us go to the second
chamber. Come on, boys." And they bravely stalked down the corridor.

When the chamber was reached a hollow laugh greeted them, followed by
two hearty laughs. The Professor and John had entered the opening at the
sea end, and hurriedly made their way to the second chamber, where they
awaited the coming of the boys.

The boys were intensely relieved, and the Professor was so happy to see
the determined and resolute spirit they manifested, that he complimented
them highly.

John was no less profuse in his commendations. "I want to say, that men
can be brave when they know what they have to fight, and who their
enemies are; but it takes the stoutest heart to go forth and defend
yourself, or assume the offensive against an unseen and an unknown
enemy."

CHAPTER XVII