Suddenly a thought struck him. Perhaps by joining his belt and Nat’s together and then leaning over the edge of the pit he could haul his unfortunate chum up to safety. It was worth trying, anyway.

Going to the edge of the pit and leaning over, Joe communicated his idea to Nat. By this time the sun was streaming dazzlingly into the pit and only by crouching in one corner could Nat escape its ardent rays. Acting on Joe’s instructions, Nat took off his belt and threw it upward. After one or two trials Joe managed to catch it. Then, taking off his own, he joined the two together. Then he extended himself at the edge of the well, and, reaching out his arm to the utmost, lowered the two joined belts down to Nat. They were about a foot too short for Nat to reach them even with the utmost endeavor of which Joe was capable!

Things began to look black, indeed. Momentarily the sun was nearing the zenith, and the place into which Nat had fallen was so designed that when the luminary reached its highest point in the skies the excavation would be filled with its rays, magnified many times by the crystal lens. The lens, in fact, was nothing more nor less than an immense burning-glass designed to shrivel up the victims of the ancient priesthood. How little those who invented such a cruelly ingenious device could have imagined that a boy of the twentieth century would ever be in danger of losing his life by it! Yet such was the case and neither Nat nor Joe could conceal the fact from themselves an instant longer.

“Can’t you think of anything? Don’t you think you could climb up just a foot or two?” asked Joe, despairingly.

“The walls are smooth as glass. I don’t believe a fly could get a hold on them,” was the rejoinder. “Joe, the heat is getting awful!” gasped out poor Nat in conclusion.

“Gracious! What am I to do?” cried Joe to himself. He rose to his feet and gazed about him. Suddenly a thought struck him. If the priests, as seemed only too probable, really roasted people to death in that well, they must have had some means of getting the bodies out. How did they do it? It must have been by a chain or rope, or something of the sort, was the thought that struck Joe after a minute’s reflection. In that case the chain, or whatever they used for the purpose of extricating their victims, must be somewhere in the chamber.

“I’ll find it, if it’s anywhere within reach,” determined Joe.

Then he hailed Nat in as cheerful a voice as he could muster. He told him what he was going to do and begged him to keep up his courage. Nat replied bravely that he could hold out a while longer; but the weakness of his voice made it painfully evident that if help was to be furnished him it would have to come quickly or be too late.

Joe noticed, now that his sight was quickened by the need of hasty action, that off at one side of the chamber was a recess cut in the rocks. He hastened over to it and found that within it was an ancient chest of some sort of sweet-smelling wood. This was so dry-rotted with the ages that a vigorous kick of the lad’s foot smashed the moldering lock off and Joe hastily threw the lid open.

He could not refrain from uttering a cry of joy as his eyes noted its contents, some spears, axes, of stone or flint—whose former purpose seemed only too evident—and, best of all, a coil of chain, forged of the same peculiar greenish metal as the ring had been.

“Hurray!” shouted Joe as he dragged out the chain, “this is what we wanted. Now I’ll have Nat out in no time.”

Hastening back to the lip of the well with the chain, he dangled its end, which terminated in a hook, over the edge. As he did so he gasped at the hot fumes which arose from the cylindrical pit. Joe was only just in time. Nat had barely strength enough to fasten the chain under his armpits and begin scrambling up as Joe hauled with all his might.

But if the hole had not been small enough in circumference for Nat to brace his legs against one side of it and help work himself up in this way, Joe would never have got him out. As it was, the task almost exhausted the strength of both boys, and when it was completed they lay gasping at the edge of the well for some moments, utterly unable to command their limbs.

Joe was the first to recover. The sun had now reached the zenith, and through the mammoth burning-glass was pouring hotly into the well. A sudden idea struck Joe. He tore a bit of paper off an old envelope he happened to have in his pocket and let it flutter into the pit.

As it dropped waveringly the paper turned brown, then black, and as it struck the bottom of the sun-heated pit it dissolved altogether into shrivelled cinder.

Joe turned away from the pit with a shudder. The thought of the fearfully narrow escape Nat had had almost unnerved him. But for Nat’s sake he did not let the other lad see how shaken he was. Shortly after Nat, though still weak, was sufficiently recovered to get shakily to his feet. Then the two lads set about to find a way out of the sacrificial cave. First, however, they armed themselves with a stone-axe apiece.

The arched entrance of another passage than the one by which they came opened off on one side of the cavern, and as they peered into it they could feel a sharp puff of delightfully cool air. “That means that this passage leads out into the open,” cried Nat gleefully. “Come on, Joe, we’ll soon be out of this mess.”

Joe, rejoicing as much as Nat, followed the young leader of the Motor Rangers. As they advanced the air blew upon them cleaner and sweeter every instant. Both lads inhaled it in great lungfuls. It seemed as if they could never get enough of it after that oven-like chamber of the sun.

“I wonder what part of the city we’ll come out in,” said Nat presently.

“Near the camp, I hope. How astonished the others will be when we tell them of what has happened to us! I’ll bet they’ve had a tame time compared to ours.”

“I hope so for their sakes,” said Nat with a laugh, “but I guess we are out of the woods now.”

But were they? It seemed to the two young Motor Rangers, a moment later, that they were not by any means “out of the woods,” as Nat had phrased it.

Instead, they soon found themselves at the mouth of the passage; but as far from finding their friends as ever. For the tunnel emerged in the face of a precipitous cliff, below which glittered the waters of the lake. It was a cruel disappointment.

While they still stood there, almost crushed by the sense that after all they were still prisoners—and apparently hopeless ones—a startling thing happened.

In the passage behind them distant voices sounded!

Human voices they were beyond a doubt. They were borne to the ears of our two young friends with the booming sound produced by the tunnel, which formed, as it were, a giant speaking-tube.

The boys exchanged alarmed glances. Who could these denizens of the subterranean world of the island be? Survivors of the cruel race of whose practices they had just had a terrible revelation? Robbers, or worse, who had made the Lost City their rendezvous? Or was it, after all, a trick of the imagination?

Determined to test this last idea, Nat slipped a short distance into the tunnel and listened intently.

A few seconds satisfied him that their imaginations had played them no pranks. Voices, far off, but apparently coming nearer, could be distinctly heard. Nat turned faint and sick for an instant, and a glance at Joe’s face showed him that his companion, too, was badly shaken. Nat did not blame him. The knowledge that mysterious beings of some sort were within the tunnel and coming toward them—perhaps on their track—gave him a most uncomfortable thrill.

He glanced down from the ledge on which they stood. The cliff face was smooth, although some metal rings showed that a ladder must once have existed by which the lake might be reached. Above the mouth of the tunnel the precipice was sheer also.

They were fairly trapped. As they realized this each lad instinctively grasped his stone-axe tighter. Nat crouched behind a boulder and Joe squeezed in close beside him.

“Who do you think they are?” he quivered, “survivors of the Lost Race, or—or——”

“I don’t know,” rejoined Nat, with what composure he could summon, “but this I do know, that they are not likely to be friendly if they find us.”

“Then there is a chance——”

“Yes, a chance that they may not come as far as this, or may not see us. They may be crossing some intersecting passage from a higher level.”

But a few minutes later the voices grew louder. The perspiration broke out on Joe’s forehead. He gripped his axe more tightly, but the sense of the mystery surrounding the beings who were approaching made him catch his breath in agitation. He felt as if he were in some nightmare.

“Mind! Don’t make a hostile move unless they attack us first,” warned Nat in an impressive whisper.

The next instant a high-pitched voice came booming down the tunnel.

“S-s-s-s-say this bub-bub-beats the Sub-ub-ub-ubway!”

“Jumping hop-toads! That’s Ding-dong Bell!” cried Joe, dashing down his hammer.

“And the professor!” cried Nat as another familiar voice came toward them.

“And Mr. Tubbs! What on earth!”

With wild whoops of joy the two boys who an instant before had been expecting to face, they knew not what, peril, rushed to meet their friends. They were in such a hurry that they narrowly escaped being shot, the other party being as much alarmed at their approach as they had been at the advance of the professor and his companions.

Matters were soon explained. The professor and his comrades had found the mouth of a tunnel in an old temple. Entering this, it had brought them underground. Some distance above the lake end of the tunnel which the boys had traversed, the passage by which the professor had travelled joined it. The hurry of Nat and Joe to reach the fresh air explained why they had not noticed the branch passage. Had they done so and followed it they would have come out not far from camp.