"Forward! cried Tom Swift.  
"Where?" asked Mr Damon, hanging back for an instant. "Bless my compass, Tom! do you know where you're going?"
 
"I haven't the least idea, but it must lead to something, or the ancients who made this revolving stone door wouldn't have taken such care to block the passage."
 
"Ask Goosal if he knows anything about it," suggested Mr. Damon to the professor.
 
"He says he never was here before," translated the savant, "but years ago, when he went into the hidden city by the cave we left yesterday, he saw doors like this which opened this way."
 
"Then we're on the right track!" cried Tom. "If this is the same kind of door, it must lead to the same place. Ho for Kurzon and the idol of gold!"
 
As they passed through the stone door, Tom and Professor Bumper tried to get some idea of the mechanism by which it worked. But they found this impossible, it being hidden within the stone itself or in the adjoining walls. But, in order that it might not close of itself and entomb them, the portal was blocked open with stones found in the passage.
 
"It's always well to have a line of retreat open," said Tom. "There's no telling what may lie beyond us."
 
For a time there seemed to be nothing more than the same passage along which they had come. Then the passage suddenly widened, like the large end of a square funnel. Upward and outward the stone walls swept, and they saw dimly before them, in the light of their torches, a vast cavern, seemingly formed by the falling in of mountains, which, in toppling over, had met overhead in a sort of rough arch, thus protecting, in a great measure, that which lay beneath them.
 
Goosal, who had brought with him some of the fiber bark torches, set a bundle of them aflame. As they flared up, a wondrous sight was revealed to Tom Swift and his friends.
 
Stretching out before them, as though they stood at the end of an elevated street and gazed down on it, was a city—a large city, with streets, houses, open squares, temples, statues, fountains, dry for centuries—a buried and forgotten city—a city in ruins—a city of the dead, now dry as dust, but still a city, or, rather, the strangely preserved remains of one.
 
"Look!" whispered Tom. A louder voice just then, would have seemed a sacrilege. "Look!"
 
"Is it what we are looking for?" asked Ned in a low voice.
 
"I believe it is," replied the professor. "It is the lost city of Kurzon, or one just like it. And now if we can find the idol of gold our search will be ended—at least the major part of it."
 
"Where did you expect to find the idol?" asked Tom.
 
"It should be in the main temple. Come, we will walk in the ancient streets—streets where no feet but ours have trod in many centuries. Come!"
 
In eager silence they pressed on through this newly discovered wonderland. For it was a wonderful city, or had been. Though much of it was in ruins, probably caused by an earthquake or an eruption from a volcano, the central portion, covered as it was by the overtoppling mountains that formed the arching roof, was well preserved.
 
There were rude but beautiful stone buildings. There were archways; temples; public squares; and images, not at all beautiful, for they seemed to be of man-monsters—doubtless ancient gods. There were smoothly paved streets; wondrously carved fountains, some in ruins, all now as dry as bone, but which must have been places of beauty where youths and maidens gathered in the ancient days.
 
Of the ancient population there was not a trace left. Tom and his friends penetrated some of the houses, but not so much as a bone or a heap of mouldering dust showed where the remains of the people were. Either they had fled at the approaching doom of the city and were buried elsewhere, or some strange fire or other force of nature had consumed and obliterated them.
 
"What a wealth of historic information I shall find here!" murmured Professor Bumper, as he caught sight of many inscriptions in strange characters on the walls and buildings. "I shall never get to the end of them."
 
"But what about the idol of gold?" asked Mr. Damon, "Do you think you'll find that?"
 
"We must hurry on to the temple over there," said the scientist, indicating a building further along.
 
"And then we must see about rescuing your rivals, Professor," put in Tom.
 
"Yes, Tom. But fortunately we are on the ground here before them," agreed the professor.
 
Undoubtedly it was the chief temple, or place of worship, of the long-dead race which the explorers now entered. It was a building beautiful in its barbaric style, and yet simple. There were massive walls, and a great inner court, at the end of which seemed to be some sort of altar. And then, as they lighted fresh torches, and pressed forward with them and their electric lights, they saw that which caused a cry of satisfaction to burst from all of them.
 
"The idol of gold!"
 
Yes, there it squatted, an ugly, misshapen, figure, a cross between a toad and a gila monster, half man, half beast, with big red eyes—rubies probably—that gleamed in the repulsive golden face. And the whole figure, weighing many pounds, seemed to be of SOLID GOLD!
 
Eagerly the others followed Professor Bumper up the altar steps to the very throne of the golden idol. The scientist touched it, tried to raise it and make sure of its solidity and material.
 
"This is it!" he cried. "It is the idol of gold! I have found— We have found it, for it belongs to all of us!"
 
"Hurray!" cried Tom Swift, and Ned and Mr. Damon joined in the cry.
 
There was no need for silence or caution now; and yet, as they stood about the squat and ugly figure, which, in spite of its hideousness, was worth a fortune intrinsically and as an antique, they heard from the direction of the stone passage a noise.
 
"What is it?" asked Tom Swift.
 
There was a murmur of voices.
 
"Indians!" cried Professor Bumper, recognizing the language—a mixture of Spanish and Indian.
 
The cave was illuminated by the glare of other torches which seemed to rush forward. A moment later it was seen that they were being carried by a number of Indians.
 
"Friends," murmured Goosal, using the Spanish term, "Amigos."
 
"They are our own Indians!" cried Tom Swift. "I see Tolpec!" and he pointed to the native who had deserted from Jacinto's force to help them.
 
"How did they get here?" asked Professor Bumper.
 
This was quickly told. In their camp, where, under the leadership of Tolpec they had been left to do the excavating, the natives had heard, seen and felt the effects of the storm and the earthquake, though it did little damage in their vicinity. But they became alarmed for the safety of the professor and his party and, at Tolpec's suggestion, set off in search of them.
 
The Indians had seen, passing along the trail, the uprooted trees, and had noted the footsteps of the explorers going down to the stone passage. It was easy for them to determine that Tom and his friends had gone in, since the marks of their boots were plainly in evidence in the soft soil.
 
None of the Indians was as much wrought up over the discovery of Kurzon and the idol as were the white adventurers. The gold, of course, meant something to the natives, but they were indifferent to the wonders of the underground city. Perhaps they had heard too many legends concerning such things to be impressed.
 
"That statue is yours—all yours," said old Goosal when he had talked with his relatives and friends among the natives. "They all say what you find you keep, and we will help you keep it."
 
"That's good," murmured Professor Bumper. "There was some doubt in my mind as to our right to this, but after all, the natives who live in this land are the original owners, and if they pass title to us it is clear. That settles the last difficulty."
 
"Except that of getting the idol out," said Mr. Damon.
 
"Oh, we'll accomplish that!" cried Tom.
 
"I can hardly believe my good luck," declared Professor Bumper. "I shall write a whole book on this idol alone and then——"
 
Once more came an interruption. This time it was from another direction, but it was of the same character—an approaching band of torch-bearers. They were I............