copper box, I have no further reason
to remain silent. I found one of the skulls,--the others I could not
find, one of which I knew must be in the treasure cave. If I had known
you found the one in the cave I should not have tried to get away, as I
hoped, finally, to find the cave. Since coming here I learned that you
had found the third island; I knew of only two, and supposed that the
two skulls were from those two, namely, Wonder and Venture Islands."

"But who placed the skulls there?" queried Harry.

"Ah! No one knows that. The Spaniard Guiterez offers no explanation. All
the so-called _treasure charts_ have been made from the accounts which
he gave, of the vast amount of gold and silver which is hidden in these
natural caches. The place where the copper box was deposited is the
grand mausoleum. Only those who know the secret could ever reach the
vault. All others would perish."

"The carbonic gas!" exclaimed George.

Walter turned to George, as he said this, but did not comprehend what he
meant. It was now evident that Walter had tried to conceal his identity,
and thereby hide the secret which would enable him alone to find the
vast wealth.

"So the letter which we found concealed in the seat of our boat, was
written by one of your companions?" asked Harry.

"Yes."

"This clears up the mysterious things which we have tried to fathom for
over two years," said John. "The meaning of the letters is now clear."

"From the time we landed on the island," rejoined the Professor, "we
found evidences of white people that we could not follow up, and it is
now plain that they were in search for the treasure, so we can now
comprehend what the notes meant."

There is but little more to add to the chapter pertaining to the
experiences of the boys on the islands. Perhaps, at some time in the
future, their work on the new islands will be told. What John and the
boys found in the Copper box, the historical sketches and the locations
of the treasure islands which were pointed out on the parchments found
in the compartment below the skull, were amazing revelations of the days
of piratical adventures, when the southern half of the world was one
vast carnival of crime, in which gold was the only booty and to obtain
which the means were always considered to be justified by the end.

Our young friends, during their experiences in southern waters, did
their part in bringing to the uneducated savages the blessings of
civilizati