heard a shout:

“Haul away!”

It was quite a pull for the two boys, for, though the professor was a small man, he was no lightweight. Hand over hand the cable was hauled until, at last, the shining bald head of the naturalist was observed emerging from the black hole of the abandoned mine.

“Easy, easy, boys!” he cautioned, as soon as his chin was above the surface. “I’ve got two rare specimens with me, and I don’t want them harmed.”

When Jerry and Bob had pulled Professor Snodgrass up as far as possible, by means of the rope, the naturalist rested his elbows on the edge of the shaft and wiggled the rest of the way out by his own efforts. In one hand was a big lizard, struggling to escape, and in the other was a large bat, flapping its uncanny wings.

“Ah, I have you safe, my beauties!” exclaimed the collector. “You can’t get away from me now!” He placed the reptile and bat in his green specimen-box, which was on the ground a short distance away, his face beaming with pride over his achievement, though in queer contrast to his disordered appearance, for he had fallen in the mud of the mine, his clothes were all dirt, his hat was gone and he looked as ruffled as a wet hen.

“Much obliged to you, boys,” he said, coming over to Bob and Jerry. “I might have stayed there forever if you hadn’t come along. Seems as though I am always getting into trouble. Do you remember the day I fell over the cliff with Broswick and Nestor, and you pulled us up with the auto?”

“I would say we did,” replied Jerry. “But now we must pull Ned up.”

Once more the rope was lowered down the shaft and in a few minutes Ned was hauled up safely.

“It’s almost as deep as our mine shaft,” he said, as he brushed the dirt from his clothes, “but I didn’t see any gold there, for it’s as dark as a pocket. How did you come to go down, professor?”

“I suspected I might get some specimens in such a place,” replied the naturalist, “so I just went down, and I had excellent luck, most excellent!”

“It’s a good thing you think so,” put in Jerry. “Most people would call it bad to get caught at the bottom of a mine shaft.”

“Oh, it wasn’t so bad,” went on the professor, casting his eyes over the ground in search of any stray specimens of snakes or bugs. “I had my candle with me until I lost it, just after I caught the lizard and bat. I could have come up all right if the ladder hadn’t broken. It was quite a hole, for a fact. It reminds me of another big hole I once heard about.”

“What hole is that?” asked Ned.

“Oh, that’s quite a story, all about mysteries, buried cities and all that.”

“Tell us about it,” suggested Jerry.

“To-night, maybe,” answered the naturalist. “I want to get back to camp now and attend to my specimens.”

The boys and the professor, the latter carrying his box of curiosities, were soon in the auto and speeding back to the gold mine.

That night, sitting around the camp-fire, which blazed cheerfully, the boys asked Professor Snodgrass to tell them the story he had hinted at when they hauled him from the mine shaft.

“Let me listen, too,” said Jim Nestor, filling his pipe and stretching out on the grass.

Then, in the silence of the early night, broken only by the crackle of the flames and the distantly heard hoot of owls or howl of foxes, the naturalist told what he knew of a buried city of ancient Mexico.

“It was some years ago,” he began, “that a friend of mine, a young college professor, was traveling in Mexico. He visited all the big places and then, getting tired of seeing the things that travelers usually see, he struck out into the wilds, accompanied only by an old Mexican guide.

“He traveled for nearly a week, getting farther and farther away from civilization, until one night he found himself on a big level plain, at the extreme end of which there was a curiously shaped mountain.

“He proposed to his guide that they camp for the night and proceed to the mountain the next day. The guide assented, but he acted so queerly that my friend wondered what the matter was. He questioned his companion, but all he could get out of him was that the mountain was considered a sort of unlucky place, and no one went there who could avoid it.

“This made my friend all the more anxious to see what might be there, and he announced his intention of making the journey in the morning. He did so, but he had to go alone, for, during the night, his guide deserted him.”

“And what did he find at the mountain?” asked Bob. “A gold mine?”

“Not exactly,” replied the professor.

“Maybe it was a silver lode,” suggested Nestor. “There’s plenty of silver in Mexico.”

“It wasn’t a silver mine, either,” went on the professor. “All he found was a big hole in the side of the mountain. He went inside and walked for nearly a mile, his only light being a candle. Then he came to a wall of rock. He was about to turn back, when he noticed an opening in the wall. It was high up, but he built a platform of stones up and peered through the opening.”

“What did he see?” asked Jerry.

“The remains of an ancient, buried city,” replied Professor Snodgrass. “The mountain was nothing more than a big mound of earth, with an opening in the top, through which daylight entered. The shaft through the side led to the edge of the city. My friend gazed in on the remains of a place thousands of years old. The buildings were mostly in ruins, but they showed they had once been of great size and beauty. There were wide streets with what had been fountains in them. There was not a vestige of a living creature. It was as if some pestilence had fallen on the place and the people had all left.”

“Did he crawl through the hole in the wall and go into the deserted city?” asked Nestor, with keen interest.

“He wanted to,” answered the naturalist, “but he thought it would be risky, alone as he was. So he made a rough map of as much of the place as he could see, including his route in traveling to the mountain. Then he retraced his steps, intending to organize a searching party of scientists and examine the buried city.”

“Did he do it?” came from Bob, who was listening eagerly.

“No. Unfortunately, he was taken ill with a fever as soon as he got back to civilization, and he died shortly afterward.”

“Too bad,” murmured Jerry. “It would have been a great thing to have given to the world news of such a place in Mexico. It’s all lost now.”

“Not all,” said the professor, in a queer voice.

“Why not? Didn’t you say your friend died?”

“Yes; but before he expired he told me the story and gave me the map.”

“Where is it?” asked Nestor, sitting up and dropping his pipe in his excitement.

“There!” exclaimed the professor, extending a piece of paper, which he had brought forth from his possessions.

Eagerly, they all bent forward to examine the map in the light of the camp-fire. The drawing was crude enough, and showed that the buried city lay to the east of the chain of Sierra Madre Mountains, and about five hundred miles to the north of the City of Mexico.

“There’s the place,” said the professor, pointing with his finger to the buried city. “How I wish I could go there! It has always been my desire to follow the footsteps of my unfortunate friend. Perhaps I might discover the buried city. I could investigate it, make discoveries and write a book about it. That would be the height of my ambition. But I’m afraid I’ll never be able