“Wouldn’t it have been wise to make two copies?” asked Tom.

“It would have only increased the risk.  With one copy, and that constantly in my possession, I can be sure of my ground.  Otherwise not.  That is why I am so careful of this.  Now I will show you why I believe we are about over the ancient city of Kurzon.”

“Over it!” cried Mr. Damon.  “Bless my gunpowder!  What do you mean?” and he looked down at the earthen floor of the tent as though expecting it to open and swallow him.

“I mean that the city, like many others of Central and South America, is buried below the refuse of centuries,” went on the professor.  “Very soon, if we are fortunate, we shall be looking on the civilization of hundreds of years ago—­how long no one knows.

“Considerable excavation has been done in Central America,” went on Professor Bumper, “and certain ruins have been brought to light.  Near us are those of Copan, while toward the frontier are those of Quirigua, which are even better preserved than the former.  We may visit them if we have time.  But I have reason to believe that in this section of Copan is a large city, the existence of which has not been made certain of by any one save myself—­and, perhaps, Professor Beecher.

“Certainly no part of it has seen the light of day for many centuries.  It shall be our pleasure to uncover it, if possible, and secure the idol of gold.”

“How long ago do you think the city was buried?” asked Tom.

“It would be hard to say.  From the carvings and hieroglyphics I have studied it would seem that the Mayan civilization lasted about five hundred years, and that it began perhaps in the year A. D. five hundred.”

“That would mean,” said Mr. Damon, “that the ancient cities were in ruins, buried, perhaps, long before Columbus discovered the new world.”

“Yes,” assented the professor.  “Probably Kurzon, which we now seek, was buried deep for nearly five hundred years before Columbus landed at San Salvadore.  The specimens of writing and architecture heretofore disclosed indicate that.  But, as a matter of fact, it is very hard to decipher the Mayan pictographs.  So far, little but the ability to read their calendars and numerical system is possessed by us, though we are gradually making headway.

“Now this is the map of the district, and by the markings you can see where I hope to find what I seek.  We shall begin digging here,” and he made a small mark with a pencil on the map.

“Of course,” the professor explained, “I may be wrong, and it will take some time to discover the error if we make one.  When a city is buried thirty or forty feet deep beneath earth and great trees have grown over it, it is not easy to dig down to it.”

“How do you ever expect to find it?” asked Ned.

“Well, we will sink shafts here and there.  If we find carved stones, the remains of ancient pottery and weapons, parts of buildings or building stones, we shall know we are on the right track,” was the answer.  “And now that I have shown you the map, and explained how valuable it is, I will put it away again.  We shall begin our excavations in the morning.”