“let’s go down and investigate,” suggested jack.

“better wait,” counseled the professor. “it will soon be dark, and, though we will have moonlight, we can not see to advantage. i think it will be best to keep the ship in the air to-night, and descend in the morning. then we can look about and decide on what to do.”

they all agreed this was the best plan, and, after making a circle above the deserted village, and noting no signs of life, the mermaid was brought to a halt over the centre of the town, and about three hundred feet above it. there the travelers would be comparatively safe.

it was deemed best to keep watch that night, and so, mark, jack, bill and tom took turns, though there was nothing for them to do, as not a thing happened. with the first appearance of dawn mr. henderson gave orders to have the ship lowered, and it came to rest in the middle of what corresponded to a street in the queer mound village.

“now to see what kind of people have lived here!” cried jack. “they must have been a queer lot. something like the esquimaux, only they probably had more trouble keeping cool than the chaps up at the north pole do.”

now that they were down among the mound houses, they saw that the dwellings were much larger than they had supposed. they towered high above the boys’ heads, and some of them were large enough in area to have accommodated a company of soldiers.

“say, the chaps who lived in these must have been some pumpkins,” said jack. “why the ceilings are about fifteen feet high, and the doors almost the same! talk about giants! i guess we’ve struck where they used to hang out, at any rate.”

the houses were a curious mixture of clay and soft stone. there were doors, with big skins from animals as curtains, and the windows were devoid of glass. instead of stairs there were rude ladders, and the furniture in the mound houses was of the roughest kind.

there were fire-places in some of the houses, and the blackened and smoked walls showed that they must have been used. in one or two of the houses clay dishes, most of them broken, were scattered about, and the size of them, in keeping with everything else, indicated that those who used them were of no small stature.

“some of the bowls would do for bath tubs,” said jack, as he came across one or two large ones.

by this time the professor, bill and tom had joined the boys, and the five went on with the exploring tour, while washington and andy remained in the ship to get breakfast.

“the inhabitants are evidently of a half-civilized race,” the professor said. “their houses, and the manner in which they live, show them to be allied to the aztecs, though of course they are much larger than that race.”

“what’s bothering me,” bill said, “is not so much what race they belong to, as what chance we’d stand in a race with them if they took it into their heads to chase after us. i’ve read that them there azhandled races——”

“you mean the aztecs,” interrupted the professor.

“well the aztecs, then. but i’ve read they used to place their enemies on a stone altar and cut their hearts out. now i’m not hankerin’ after anything like that.”

“don’t be foolish,” spoke mr. henderson. “wait until you meet some of the giants, if that is what they are, and then you can decide what to do.”

“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.