"It must have been because of the disturbance of the equilibrium, or due to a change of weight. Probably this pedestal rests on a platform, like the platform of a large scale. Its weight, with that of the statue, rested on certain concealed levers, and held the stone up out of sight in the roof of the tunnel. When I yanked down the statue I made the weight uneven, and the stone fell, and there doesn't seem to be any way of putting the weight back again."

"No, we never could get the statue back on the pedestal," said Ned.

"But maybe there's some mechanism at the stone gate, or near it, like the black k.n.o.b which turned off the water. We may be able to work that and raise the big stone slab."

"It's the only thing to try, as long as we haven't dynamite to blast it," agreed Tom. "Come on, we'll take a look."

They went back to where the rock closed the tunnel, but a long and frantic search failed to show the least projection, lever, handle or any other thing, that could be moved.

"What in the world do you suppose those ancients made such a terrible contrivance for?" Ned wanted to know.

"Well, if we could read the warning on the statue we might know,"

replied Mr. Damon. "That probably says that whoever disturbs the status will close up the golden city forever."

"Maybe there's another way out--or in," suggested Tom hopefully. "We didn't look for that. It must be our next move. We must not let a single chance go by. We'll look for some way of getting out, at the far end of this underground city."

Filled with gloomy and foreboding thoughts, they walked away from the stone barrier. To search for another means of egress would take some time, and the same fear came to all of them--could they live that long?

"It was a queer thing, to make that statue hollow," mused Ned as he walked between Mr. Damon and Tom. "I wonder why it was done, when all the others are solid gold?"

"Maybe they found they couldn't melt up, and cast in a mould, enough gold to make a solid statue that size," suggested Mr. Damon. "Then, too, there may have been no means of getting it on the pedestal if they made it too heavy."

They discussed these and other matters as they hurried on to seek for some way of escape. In fact to talk seemed to make them less gloomy and sad, and they tried to keep up their spirits.

For several hours they searched eagerly for some means of getting out of the underground city. They went to the farthest limits of it, and found it to be several miles in diameter, but eventually they came to solid walls of stone which reached from roof to ceiling, and there was no way out.

They found that the underground city was exactly like an overturned bowl, or an Esquimo ice hut, hollow within, and with a tunnel leading to it--but all below the surface of the earth. The city had been hollowed out of solid rock, and there was but one way in or out, and that was closed by the seamless stone.

"There's no use hunting any longer," declared Tom, when, weary and footsore, they had completed a circuit of the outer circ.u.mference of the city, "the rock pa.s.sage is our only hope."

"And that's no hope at all!" declared Ned.

"Yes, we must try to raise that stone slab, or--break it!" cried Tom desperately. "Come on."

"Wait a bit," advised Mr. Damon. "Bless my dinner plate! but I'm hungry. We brought some food along, and my advice to you is to eat and keep up our strength. We'll need it."

"By golly gracious, that's so!" declared Eradicate. "I'll git de eatin's."

Fortunately there was a goodly supply, and, going in one the houses they ate off a table of solid gold, and off dishes of the precious, yellow metal. Yet they would have given it all--yes, even the gold in their dirigible balloon--for a chance for freedom.

"I wonder what became of the chaps who used to live here?" mused Ned as he finished the rather frugal meal.

"Oh, they probably died--from a plague maybe, or there may have been a war, or the people may have risen in revolt and killed them off,"

suggested Tom grimly.

"But then there ought to be some remains--some mummies or skeletons or something."

"I guess every one left this underground city--every soul."

suggested Mr. Damon, "and then they turned on the river and left it.

I shouldn't be surprised but what we are the first persons to set foot here in thousands of years."

"And WE may stay here for a thousand years," predicted Tom.

"Oh, good land a' ma.s.sy; doan't say dat!" cried Eradicate. "Why we'll all be dead ob starvation in dat time."

"Before then, I guess," muttered Tom. "I wonder if there's any water in this hole?"

"We'll need it--soon," remarked Ned, looking at the scanty supply they had brought in with them. "Let's have a hunt for it."

"Let Rad do that, while we work on the stone gate," proposed the young inventor. "Rad, chase off and see if you can find some water."

While the colored man was gone, Tom, Ned and Mr. Damon went back to the stone gate. To attack it without tools, or some powerful blasting powder seemed useless, but their case was desperate and they knew they must do something.

"We'll try chipping away the stone at the base," suggested Tom. "It isn't a very hard rock, in fact it's a sort of soft marble, or white sand stone, and we may be able to cut out a way under the slab door with our knifes."

Fortunately they had knives with big, strong blades, and as Tom had said, the stone was comparatively soft. But, after several hours'

work they only had a small depression under the stone door.

"At this rate it will take a month," sighed Ned.

"Say!" cried Tom, "we're foolish. We should try to cut through the stone slab itself. It can't be so very thick. And another thing. I'm going to play the flames from the gas torches on the stone. The fires will make it brittle and it will chip off easier."

This was so, but even with that advantage they had only made a slight impression on the solid stone door after more than four hours of work, and Eradicate came back, with a hopeless look on his face, to report that he had been unable to find water.

"Then we've got to save every drop of what we've got," declared Tom.

"Short rations for everybody."

"And our lights, too," added Mr. Damon. "We must save them."

"All out but one!" cried Tom quickly. "If we're careful we can make them gas torches last a week, and the electric flashes are good for several days yet."

Then they laid out a plan of procedure, and divided the food into as small rations as would support life. It was grim work, but it had to be done. They found, with care, that they might live for four days on the food and water and then--

Well--no one liked to think about it.

"We must take turns chipping away at the stone door," decided Tom.

"Some of us will work and some will sleep--two and two, I guess."

This plan was also carried out, and Tom and Eradicate took the first trick of hacking away at the door.

How they managed to live in the days that followed they could never tell clearly afterward. It was like some horrible nightmare, composed of hours of hacking away at the stone, and then of eating sparingly, drinking more sparingly, and resting, to get up, and do it all over again.

Their water was the first to give out, for it made them thirsty to cut at the stone, and parched mouths and swollen tongues demanded moisture. They did manage to find a place where a few drops of water trickled through the rocky roof, and without this they would have died before five days had pa.s.sed.

They even searched, at times for another way out of the city of gold, for Tom had insisted there must be a way, as the air in the underground cave remained so fresh. But there must have been a secret way of ventilating the place, as no opening was found, and they went back to hacking at the stone.

Just how many days they spent in their horrible golden prison they never really knew. Tom said it was over a week, Ned insisted it was a month, Mr. Damon two months, and Eradicate pitifully said "it seem mos' laik a yeah, suah!"

It must have been about eight days, and at the end of that time there was not a sc.r.a.p of food left, and only a little water. They were barely alive, and could hardly wield the knives against the stone slab. They had dug a hole about a foot deep in it, but it would have to be made much larger before any one could crawl through, even when it penetrated to the other side. And how soon this would be they did not know.