“It may be too late then,” remarked Bill in a low tone, and the boys were somewhat inclined to agree with him.

However, there seemed to be no immediate danger, as there was no sign of any of the big people about the village.  The adventurers walked about for some time, but made no discoveries that would throw any light on the reason for the place being left uninhabited.  It seemed as if there had been a sudden departure from the place, for in a number of the houses the remains of half-cooked meals were seen.

“Well, I think we have noted enough for the time being,” the professor remarked, after they had traversed almost half the length of what seemed to be the principal street.  “Let’s go back to the ship and have something to eat.  Washington may have become alarmed at our absence.”

They made a circle in order to take in another part of the town on their way back.  While passing through a sort of alley, though it was only narrow by comparison with the other thoroughfares that were very wide, Mark came to a place where there was a circular slab of stone, resting on the ground.  In the centre was a big iron ring.

“Hello!  Here’s something new!” he exclaimed.  “Maybe it leads to a secret passage, or covers some hidden treasure.”

“I guess it will have to continue to cover it then,” Jack spoke.  “That probably weighs several tons.  None of us could move it.”

They made their way back to the ship, where they found Washington and Andy discussing the advisability of going off in search of them.

“Breakfast is mighty near spoiled,” said the colored man with an injured air.

But the travelers did full justice to the meal, notwithstanding this.  Deciding there was nothing to be gained by staying in that vicinity, the professor started the ship off again.

They traveled several hundred miles in the air, and, as the afternoon was coming to a close, Jack, who was in charge of the conning tower, spied, just ahead of them, another village.

“We will descend there for the night,” the professor said.  “Does there seem to be any sign of life about?”

“None,” replied Mark, who was observing through a telescope the town they were approaching.  “It’s as dead as the other one.”

The airship settled down in a field back of some of the mound houses.

“Now for supper!” cried Jack.  “I’m as hungry as——­”

He stopped short, for, seeming to rise from the very ground, all about the ship, there appeared a throng of men.  And such men as they were!  For not one was less than ten feet tall, and some were nearly fifteen!

“The giants have us!” cried Bill, as he saw the horde of creatures surrounding the ship.

CHAPTER XXV

 Held by the enemy

“Keep the doors closed!” cried the professor.  “It is our only hope!  I will send the ship up again!”