“That’s it,” confirmed the savant.  “If you will notice it extends back in the direction of the cave from which we were driven.  Now if there is a buried city beneath all this jungle, this mountain of earth and stones, the accumulation of centuries, it is probably on the bottom of some vast cavern.  It is my opinion that we were only in one end of that cavern, and this may be the entrance to another end of it.”

“Then,” asked Mr. Damon, “do you mean that we can enter here, get into the cave that contains the buried city, or part of it, and find there Beecher and his friends?”

“That’s it.  It is possible, and if we could it would save an immense lot of work, and probably be a surer way to save their lives than by digging a tunnel through the landslide to find the mouth of the cave where we first entered.”

“It’s a chance worth taking,” said Mr. Damon.  “Of course it is a chance.  But then everything connected with this expedition is; so one is no worse than another.  As you say, we may find the entombed men more easily this way than any other.”

“I wonder,” said Tom slowly, “if, by any chance, we shall find, through this passage, the lost city we are looking for.”

“And the idol of gold,” added Ned.

“Goosal, do you know anything about this?” asked Professor Bumper.  “Did you ever hear of another passage leading to the cave where you saw the ancient city?”

“No, Learned One, though I have heard stories about there being many cities, or parts of a big one, beneath the mountain, and when it was above ground there were many entrances to it.”

“That settles it!” cried the professor in English, having talked to Goosal in Spanish.  “We’ll try this and see where it leads.”

They entered the stone-lined passage.  In spite of the fact that it had probably been buried and concealed from light and air for centuries, as evidenced by the growth of the giant trees above it, the air was fresh.

“And this is one reason,” said Tom, in commenting on this fact, “why I believe it leads to some vast cavern which is connected in some fashion with the outer air.  Well, perhaps we shall soon make a discovery.”

Eagerly and anxiously the little party pressed forward by the light of the pocket electric lamps.  They were obsessed by two thoughts—­what they might find and the necessity for aiding in the rescue of their rivals.

On and on they went, the darkness illuminated only by the torches they carried.  But they noticed that the air was still fresh, and that a gentle wind blew toward them.  The passage was undoubtedly artificial, a tunnel made by the hands of men now long crumbled into dust.  It had a slightly upward slope, and this, Professor Bumper said, indicated that it was bored upward and perhaps into the very heart of the mountain somewhere in the interior of which was the Beecher party.

Just how far they went they did not know, but it must have been more than two miles.  Yet they did not tire, for the way was smooth.