They saw that the temple consisted of two parts, or two circular buildings, one within the other. Around the outer part were many rooms, which had evidently formed the living apartments of the priests. There were galleries, chambers, halls and a.s.sembly rooms.

Then the whole of the interior of the temple, under a great dome that had mostly fallen in, consisted of a vast room, which was probably where the wors.h.i.+p went on. For, even without going farther than to the edge of it, the youths could see stone altars, and many strangely-carved figures and statues. Some had fallen over and lay in ruins on the floor. The whole scene was one of desolation.

"Come on," invited Tom, "it's healthier and more pleasant outside.

Let's look for that tunnel."

But the lads soon realized that it was not going to be as easy to locate this as they had hoped. They were looking for some sort of slanting opening, going down into the earth--the entrance to the underground city--but though they both made a complete circuit of the temple, each at a varying distance from the outer walls, no tunnel entrance showed.

"Breakfust! Breakfust!" called Eradicate, when Tom was about to start on a second round.

"Let's eat," suggested Ned, "and then we four can circle around together." Tom agreed that this would be a good plan. A little later then, with Tom nearest the temple walls, the four began their march around them.

Four times that morning they made the circuit, and the same number in the afternoon, until they were nearly half a mile away from the ruin, but no tunnel showed.

"Well, we'll have to keep at it to-morrow," suggested Tom. "It's too soon to give up."

But the morrow brought no better success, nor did the following two days. In fact for a week they kept up the search for the tunnel, but did not come upon it, and they had now pretty well covered the big plain. They found a few ruins of the ancient city of Poltec.

"Well, what about it?" asked Ned one night as they sat in the balloon, talking it over. "What next, Tom?"

"We've got to keep at it, that's all. I think we'll go up in the balloon, circle around over the plain at just a little elevation, and maybe we can spot it that way."

"All right, I'm with you."

But they did not try that plan. For in the middle of the night Ned suddenly awakened. Something had come to him in his sleep.

"Tom! Tom!" he cried. "I have it! What chumps we were!"

"What's the matter, old man?" asked Tom anxiously. "Are you sick--talking in your sleep?"

"Sleep nothing! I've just thought of it. That tunnel entrance is INSIDE the temple. That's the most natural place in the world for it. I'll bet it's right in the middle of the big inner chamber, where the priests could control it. Why didn't we look there before?"

"That's right; why didn't we?" agreed Tom. "I believe you're right, Ned! We'll look the first thing in the morning."

They did not wait for breakfast before trying the experiment, and Mr. Damon and Eradicate went with Tom and Ned. It was no easy work to make their way over the ruins to the inner auditorium. Wreckage and ruin was all around, and they had to avoid the yawning holes on every side. But when they got to the main, or sacrificial chamber, as Ned insisted on calling it, they found the floor there solid. In the centre was a great altar, but to their chagrin there was not a sign of a tunnel opening.

"Fooled again!" said Tom bitterly.

"Maybe some of those holes outside is the entrance," suggested Mr.

Damon.

"I don't believe so," objected Tom. "They seemed to go only to the cellar, if a temple has such a thing."

Bitterly disappointed, Tom strolled over and stood in front of the big stone altar. It seemed that he must give up the search. Idly he looked at the sacrificial stone. Projecting from it was a sort of a bundle.

Tom took hold of it, and to his surprise he found that it could be moved. Hardly knowing what he was doing, he pulled it toward him.

The next instant he uttered a cry of horror, for the immense stone altar, with a dull rumbling, rolled back as though on wheels, and there, over where it had stood was a hole of yawning blackness, with a flight of stone steps leading down into it. And Tom stood so near the edge that he almost toppled in.

"Look! Look!" he cried when he could get his gasping breath, and step back out of danger.

"The tunnel entrance!" cried Ned. "That's what it is! You've found it, Tom! The entrance to the city of gold at last!"

CHAPTER XIX

THE UNDERGROUND RIVER

They gathered around the opening so unexpectedly disclosed to them, and stared down into the black depths. Beyond the first few steps of the flight that led to they knew not where, nothing could be seen.

In his impatience Tom was about to go down.

"Bless my match box!" cried Mr. Damon. "What are you going to do, Tom, my boy?"

"Go down there, of course! What else? I want to get to the underground city."

"Don't!" quickly advised the odd man. "You don't know what's there.

It may be a trap, where the old Aztecs used to throw their victims.

There may be worse things than bats there. You'll need torches--lights--and you'd better wait until the air clears. It may have been centuries since that place was opened."

"I believe that's right," agreed Ned. "Whew; Smell it! It's as musty as time!"

An unpleasant odor came up the tunnel entrance, and it was stifling to stand too close. Tom lighted a match and threw it down. Almost instantly the flame was snuffed out.

"We couldn't live down there a minute," said the young inventor.

"We've got to wait for it to clear. We'll go back to the balloon and get some electric flash lamps. I brought along a lot of 'em, with extra strong batteries. I thought we'd need some if we did find the city of gold, and it looks as if we were almost there now."

Tom's plan was voted good so they hurried out of the temple, their feet echoing and re-echoing over the stone floor. The place, ruined and desolate as it was, had no terrors for them now. In fact they were glad of the very loneliness, and Tom and Ned actually looked about apprehensively as they emerged, fearing they might see a sign of the Mexicans or the Fogers.

"Guess they can't pick up our trail," said Tom, when, he saw of what Ned was thinking.

"No, we've got the place to ourselves. I wonder how long it will take for the air to get fresh?"

"Not so very long, I guess. There was a good draught. There must be some opening in the underground city by which the air is sucked in.

They'd never have only one opening to it. But we don't need to look for the other. Come on, we'll get out the torches."

These electrical contrivances are familiar to all boys. A small electric lamp is set in the end of a hollow tube of tin, and about the lamp is a reflector. Dry electrical batteries are put in the tin tube, and by means of a push b.u.t.ton the circuit is closed, illuminating the lamp, which gives a brilliant glow. Tom had a special kind of lamp, with tungsten filaments, which gave a very powerful light, and with batteries designed to last a long time. A clip on the spring controlling the push b.u.t.ton made it so that the lamp could be made to give a steady glow. Thus they were well prepared for exploring the tunnel.

It took some little time to get the flash lamps ready, and when they were all charged and they had eaten, they went back to the opening to see if the air had cleared. Tom tested it by dropping a match down, and, to his delight it burned with a clear flame.

"It's all right!" he exclaimed. "The air is pure. Now to see where we will bring up. Come on, everybody."

"Jest one minute, Ma.s.sa Tom," begged Eradicate, as the young inventor was about to descend the steps, which even the brightness of his lamp did not disclose the end. "Is yo' gwine down dar, Ma.s.sa Tom?"

"Certainly, Rad."

"An' is yo'--'scuse me--but is yo' expectin' me fo' t' follow yo'?"