"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[p. 233] 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.