A day and a night on burro-back brought the treasure-seekers through the mountains to Yuca, the loveliest valley in the world, where nine thousand feet above the sea it is always spring. There, half a thousand years ago, the Incas built their country houses, as of old the kings of Israel built in the mountain-valley of Jezreel, and among the ruins of stone buildings, beautiful as Ahab's house of ivory, several hundred whites and half-breed Indians had made their homes. In Yuca Professor Ditson found many old friends and acquaintances, and the party rested there for a week and, thanks to Jim Donegan's generous letter of credit, which had survived the shipwreck, thoroughly equipped themselves for the last lap of the dash to Eldorado.

One morning, before the dawn of what felt like a mid-May day, the expedition headed back along the trail mounted on mules, the best and surest-footed animals for mountain work. In order to prevent any unwelcome followers, the professor allowed it to be supposed that they were going back for a further exploration of the sacred city of Machu Pichu. When at last they were clear of the valley, with no one in sight, he called a halt, and carefully consulted his map at a point where the trail led in and out among slopes and hillocks of wind-driven sand.

"Here is where we turn off," he said finally.

Jud suddenly produced two large, supple ox-hides which he had carried rolled up back of his saddle.

"So long as we're goin' treasure-huntin'," he remarked "an' Scar Dawson is still above ground, I calculate to tangle our trail before we start."

Under his direction, the whole party rode on for a mile farther, and then doubled back and turned off at right angles from the trail, Jud spreading rawhides for each mule to step on. Their progress was slow, but at the end of half a mile they were out of sight of the original trail and had left no tracks behind except hollows in the sand, which the wind through the day would cover and level.

For the next three days Professor Ditson guided them by the map among a tangle of wild mountains and through caÑons so deep that they were dark at midday. At night their camp-fire showed at times like a beacon on the top of unvisited peaks, and again like a lantern in the depths of a well, as they camped at the bottom of some gorge. Here and there they came upon traces of an old trail half-effaced by the centuries which had passed since it had been used in the far-away days when the Incas and their followers would journey once a year to the sacred lake with their annual offerings. Even although Professor Ditson had been to Eldorado before, yet he found it necessary continually to refer to the map, so concealed and winding was the way.

On the third day they reached a wide plateau which ranged just above the tropical jungles of the eastern lowlands. At first they crossed bare, burned slopes of rock, with here and there patches of scanty vegetation; but as they came to the lower levels they found themselves in a forest of vast cacti which seemed to stretch away for an immeasurable distance. Some of the larger specimens towered like immense candelabras sixty and seventy feet high, and there were clumps of prickly-pears as big as barrels and covered with long, dark-red fruit which tasted like pomegranates. Underfoot were trailing varieties which hugged the earth and through which the mules had to pick their way warily because of the fierce spines with which they were covered. Some of the club-cacti were covered with downy, round, red fruit fully two inches in diameter, luscious, sweet and tasting much like huge strawberries. Jud, who firmly believed that eating was one of the most important duties and pleasures of life, nearly foundered before they reached the pampas beyond the thorny forest. There they had another adventure in South American foods. As they were crossing a stretch of level plain, suddenly a grotesque long-legged bird started up from the tangled grass and, with long bare neck stretched out horizontally and outspread wings, charged the little troop, hissing like a goose as he came.

"Don't shoot!" called out Professor Ditson to the startled Jud, who was the nearest one to the charging bird. "It's only a rhea, the South American ostrich. He'll run in a minute."

Sure enough, the old cock rhea, finding that he could not frighten away the intruders by his tactics, suddenly turned and shot away across the level plain, his powerful legs working like piston-rods and carrying him toward the horizon at a rate of speed that few horses could have equaled. In the deep grass they found the nest, a wide circular depression containing thirty great cream-colored eggs, the contents of each one being equal to about a dozen hen's eggs. The Professor explained that the female rheas of each flock take turns laying eggs in the nest, which, as a fair division of labor, the cock bird broods and guards. After incubation starts the shell turns a pale ashy gray. The party levied on the rhea's treasure-horde to the extent of a dozen glossy, thick-shelled eggs, and for two days thereafter they had them boiled, fried, roasted, and made into omlets, until Jud declared that he would be ashamed ever to look a rhea in the face again.

At last, about noon of the fifth day after leaving Yuca, the trail seemed to end in a great wall of rock high up among the mountains. When they reached the face of this cliff it appeared again, zigzagging up a great precipice, and so narrow that the party had to ride in single file. On one side of the path the mountain dropped off into a chasm so deep that the great trees which grew along its floor seemed as small as ferns. Finally the trail ended in a long, dark tunnel, larger and higher than the one through which they had passed on the way to Yuca. For nearly a hundred feet they rode through its echoing depths, and came out on the shore of an inky little lake not a quarter of a mile across, and so hidden in the very heart of the mountain that it was a mystery how any one had ever discovered it. Although it sloped off sharply from its bare white beach, Professor Ditson told them that it was only about twenty feet deep in the center. A cloud of steam drifting lazily from the opposite shore betokened the presence of a boiling spring, and the water, in spite of the latitude, was as warm as the sun-heated surface of the Amazon itself.

Leading the way, Professor Ditson showed them, hidden around a bend, a raft which he and his party had built on their earlier visit, from logs hauled up from the lower slopes with infinite pains. Apparently no one had visited the lost lake since he had been there, and a few minutes later the whole party were paddling their way to the center of Eldorado, where lay hidden the untold wealth of centuries of offerings.

"If I could have dived myself, or if any of the Indians who were with me could have done so," remarked the professor regretfully, "we need not have wasted a year's time."

"Well," returned Jud, already much excited over the prospect of hidden treasure, "I used to do over forty feet in my twenties, when I was pearl-divin', an' now, though I'm gettin' toward fifty, I certainly ought to be able to get down twenty feet."

"Fifty!" exclaimed Will.

"Fifty!" echoed Joe.

"Fifty!" chimed in Professor Ditson.

"That's what I said," returned Jud, looking defiantly at his grinning friends, "fifty or thereabouts. I'll show you," he went on grimly, stripping off his clothes as they reached the very center of the little lake, and poising his lean, wiry body on the edge of the raft. Suddenly he turned to Professor Ditson. "There ain't nothin' hostile livin' here in this lake, is there?" he questioned.

"I don't think so," returned the professor, reassuringly. "Piranhas are never found at this height, and we saw no traces of any other dangerous fish or reptiles when we were here last year."

"Here goes then, for a fortune!" exclaimed Jud, throwing his hands over his head and leaping high into the air with a beautiful jack-knife dive. His slim body shot down out of sight in the dim, tepid water.

The seconds went by, with no sign of him, until he had been under fully three minutes. Just as they all began to be alarmed for his safety, his gray head suddenly shot two feet out of the water near where he had gone down. Puffing like a porpoise, with a few quick strokes he reached the edge of the raft and tossed on its surface something which clinked as it struck the logs.

There, gleaming in the sunlight, was a bird of solid gold, which looked like a crow, with outspread wings, and which was set thickly with rough emeralds as large as an ordinary marble.

With a cheer, Joe and Will gripped Jud's shoulders and pulled him over the side of the raft, where he lay panting in the sunlight, while the treasure was passed from hand to hand.

It was nearly a foot long, and so heavy that it must have handicapped the old man considerably in his dash for the surface.

"Pretty good for a start," puffed Jud happily, as he too examined the gleaming bird. "Unless I miss my guess," he went on earnestly, "the great emerald that old Jim has got his heart set on is down there, too. The bottom is pretty well silted over, but I scrabbled through the mud with my hands, an' when I struck this I figured out that I had just enough breath left to reach the top; but just as I was leavin', my fingers touched somethin' oval an' big as a hen's egg. It was pretty deep in the mud, and I didn't dare wait another second, but I'm sure I can bring it up next time."

For half an hour Jud rested while Professor Ditson told them treasure-stories which he had heard in his wanderings among the Indian tribes or remembered from his studies of Spanish archives. He told them the story of the galleon Santa Maria, which was sunk off the Fortune Islands, loaded down with a great altar of solid gold incrusted with precious stones; and of the buccaneer Sir Henry Morgan, who sacked Panama and burned and sank in the harbor what he thought were empty vessels, but which held millions of dollars in gold and jewels in double bulkheads and false bottoms, and which lie to this day in the mud of Panama harbor. Then, there was the story of the two great treasure-chests which Drake of Devon captured from the great galleon Cacafuego. As they were being transshipped into Drake's vessel, the Golden Hind, both of the chests broke loose and sank off CaÑo Island on the coast of Costa Rica. Still at the bottom of that tiny harbor, thousands of pounds of gold bars and nuggets and a treasure of pearls and emeralds and diamonds lie waiting for some diver to recover them. Then Professor Ditson launched into the story of Pizarro's pilot, who, when the temple of Pachacainac, twenty miles from Lima, was looted, asked as his share of the spoils only the nails that fastened the silver plates which lined the walls of the temple. Pizarro granted him what he thought was a trifling request, and the pilot received for his share over two thousand pounds of solid silver.

"That's enough," said Jud, starting to his feet. "Here goes for the biggest treasure of all."

Down and down through the dim water he dived straight and true. Hardly had he disappeared from sight before great air-bubbles came up and broke on the surface, and a few seconds later wavering up from the depths came what seemed to be his lifeless body with staring, horrified eyes and open mouth.

As his white face showed above the surface, Will and Joe leaped in together, and in an instant had him out and on the raft again. In another minute the two boys were making good use of their knowledge of first aid, which they had learned as Boy Scouts. Working as they had never worked for merit badges, they laid Jud on the raft face down, with his arms above his head and his face turned a little to one side. Then, while Joe pulled his tongue out, Will, kneeling astride his body, pressed his open hands into the spaces on either side of his ribs. Then, alternately pressing and relaxing his weight as the water ran out of Jud's mouth and nose, Will began the artificial breathing at the rate of fifteen times a minute, while Joe rubbed with all his might the old trapper's legs and body toward the heart. At the end of a couple of minutes of this strenuous treatment Jud gave a gasp and at last opened his eyes. Half an hour later he was able to tell what had happened.

"I didn't get more than half-way down," he said weakly, "when a great greenish-yellow eel, five feet long an' big as my arm, came gliding toward me. I tried to pass it but in a second I felt its cold, clammy body pressin' against mine. Then came a flash, an' somethin' broke in my head, an' the next thing I knew I was up here with you chaps workin' over me."

Professor Ditson brought his hands together with a loud clap.

"That is what Dawson meant by saying the lake was guarded," he said. "What attacked Jud here was a gymnotus."

"A Jim-what?" queried Jud.

"An electric eel," explained the Professor. "The old priests must have brought them up from the lowlands, and they have thrived here in this warm water ever since. It carries an electric battery in the back of its head, and a big one can give a shock which will stun a strong man. Wait a moment," he went on, "and I'll show you every electric eel within a radius of fifty yards."

As he spoke he fumbled in his knapsack and pulled out a cylinder two feet long, wrapped in waxed paper, with a curious little clockwork attachment at one end.

"I brought along two or three sticks of dynamite equipped with detonators," explained the professor. "They are really small depth-bombs. I thought," he went on, "that if the mud were too deep at the bottom of the lake, a stick or so of dynamite exploded there might stir things up. I'll set this one to go off half-way down, and the shock will stun every living thing in the water for a couple of hundred feet around."

Winding and setting the automatic mechanism so as to explode the bomb at a ten foot depth, the scientist carefully threw one into the water some distance from the raft. Two seconds later there was a dull, heavy plop, and the water shouldered itself up in a great wave which nearly swamped the raft. As it went down, scores of fish of different kinds floated stunned on the surface. Among them were a dozen great green-gold electric eels. As they floated by, Hen slashed each one in two with his machete.

As he finished the last one, Will began to strip off his clothes.

"I can dive twenty feet," he said, "and I'm going to have the next chance at the Inca Emerald."

"No," objected Professor Ditson, "Let Hen try it. He's a great swimmer."

Jud also protested weakly that he wanted to go down again; but Will cut short all further argument by diving deep into the center of the still heaving circle of widening ripples in front of the raft. Even as he did so, Hen, who had stood up to take his place, gave a cry of warning; but it was too late to reach the boy's ears, already deep under the water. Just beyond the circle of the ripples drifted what seemed to be the end of a floating snag; yet the quick eyes of the negro had caught the glint of a pair of green, catlike eyes showing below the tip of a pointed snout which looked like a bit of driftwood.

"It's a big 'gator," he murmured to Professor Ditson, who stood beside him.

The latter took one look at the great pointed head and olive-colored body, now showing plainly in the water.

"It's worse than that," he whispered, as if afraid of attracting the saurian's attention. "It's an American crocodile. The explosion and the sight of the dead fish have brought it over from the farther shore."

Without paying any attention to the raft or the men, the great crocodile suddenly sank through the water, so close to them that they could see its triangular head, with the large tooth showing on each side of its closed lower jaw, which is one of the features that distinguishes a crocodile from an alligator. Even as they watched, wavering up through the smoky water came the white figure of the boy from the depths below, swimming strongly toward the surface, his right hand clasped tightly around some large object. Even as they glimpsed the ascending body, a gasp of horror went up from the little group on the raft. Before their very eyes, with a scythe-like flirt of its long, flattened tail, the great reptile shot its fifteen-foot body down toward the swimming boy.

Not until fairly overshadowed by the rushing bulk of the crocodile did Will realize his danger. Then he tried frantically to swerve out of the line of the rush of this terrible guardian of the treasure-horde. It was too late. Even as he swung away, the cruel jaws of the great saurian opened with a flash of curved keen teeth and closed with a death-grip on Will's bare thigh.

With a shout and a splash, the black form of the giant negro shot down into the water. Hen had learned to love the happy-hearted, unselfish boy, and, desperate at the sight of his danger, had gone to his rescue. No man nor any ten men can pull apart the closed jaws of a man-eating crocodile. The plated mail in which he is armored from head to tail can not be pierced by a knife-thrust and will even turn aside a bullet from any except the highest powered rifles. Yet all the crocodilians—alligators, crocodiles, gavials, or caymans—have one vulnerable spot, and Hen, who had hunted alligators in Florida bayous, knew what this was.

Swimming as the onlookers had never seen man swim before, the great negro shot toward the crocodile, which was hampered by the struggling boy, locked his strong legs around the reptile's scaly body, and sank both of his powerful thumbs deep into the sockets of the crocodile's eyes. The great saurian writhed horribly as he felt the rending pain. Inexorably the thumbs of his assailant gouged out the the soft tissues of the eye-sockets until the crocodile reluctantly loosed his grip and sought refuge from the unbearable pain by a rush into the deeps beyond the raft. As the great jaws opened, Hen unwound his legs from the armored body, and, catching Will in his mighty arms, shot up to the surface with him.

In another moment the boy, slashed and torn, but conscious, was stretched on the raft beside Jud, while Joe and the professor bound up the gashes in his thigh, which, although bleeding profusely, were not deep enough to be dangerous. As the last knot of the hasty bandages was tied, Will smiled weakly and opened his right hand. There, in the outstretched palm, gleamed and coruscated the green glory of a great oval emerald, cut and polished by some skilful lapidarist perhaps a thousand years ago. Lost for centuries, the gem which had been worshiped by a great nation had once again come to the earth from which it had disappeared.

Three weeks later, Professor Amandus Ditson lay sleeping in a luxurious bedroom on the ground floor of the rambling house of a Spanish friend whom he was visiting in the beautiful, historic, blood-stained city of Lima. In other rooms of the same house slept Will and Jud and Joe. Two days later the steamer would sail which was to take them all back north. Pinto was already on his way back to his wife and children at Para, and Hen was visiting friends of his own in the city and intended to join the party on the steamer.

The silence of the night was broken abruptly by a grating, creaking noise, and into the room of the sleeping scientist through the veranda window stepped a great masked figure. As the electric lights were switched on. Professor Ditson awoke to find himself looking into the barrel of an automatic revolver.

"Give me the treasure from Eldorado," croaked a voice from behind the mask, "if you want to keep on livin'."

The scientist stared steadily at the speaker for a moment before he spoke.

"If you will take off your mask, Dawson," he said finally, "I am sure you will find it more comfortable. I was positive," he went on, as the other obeyed and showed the scarred, scowling face of the outlaw, "that I made a mistake in sparing your life."

"I'll spare yours, too," retorted Dawson, "unless you make me kill you. I'm goin' to take the treasure an' light out. It would be much safer for me to kill you, but I won't unless I have to—just to show you how grateful I am."

"I appreciate your consideration," returned the scientist, quietly; "but you're too late. The treasure is not here."

"I know better," growled Dawson. "I've had you shadowed ever since you got here. It's locked in that leather bag, which never leaves your sight day or night, an' I'm goin' to take it right now."

Suiting his action to his words, and still keeping his revolver leveled at the professor, the outlaw pulled toward him a big cowskin bag, which, as he said truly, the scientist had kept with him night and day ever since he purchased it at a shop in Lima the morning of his arrival.

"Dawson," returned Professor Ditson, earnestly. "I give you my word as a gentleman that the treasure is now in the safe on the steamer which leaves the day after to-morrow, and I hold the receipt of the steamship company for it. Don't open that bag. There is nothing in it for you but—death."

"I'll see about that," muttered Scar Dawson. "Don't move," he warned, as the scientist started up from his bed. "I'll shoot if you make me."

Even as he spoke, he drew a knife from his belt and slit the leather side of the bag its whole length with a quick slash, and started to thrust in his hand.

As he did so he gave a yell of terror, for out from the opening suddenly appeared, wavering and hissing horribly, the ghastly head of the great bushmaster which the scientist had carried and cared for all the way from the Amazon basin. In another second, half its great length reared threateningly before the terrified outlaw. With one more yell, Dawson threw himself backward. There was a crash of broken glass, and by the time Will and Jud and Joe and their host, aroused by the noise, had reached the room, they found only Professor Ditson, coolly tying up the damaged bag, into which, by some means known only to himself, he had persuaded the bushmaster to return.

To-day, in the world-famous gem collection of Big Jim Donegan, in the place of honor, gleams and glows the great Emerald of the Incas. What he did for those who won the treasure for him, and how that same party of treasure-hunters traveled far to bring back to him that grim, beautiful, and historic stone of the Far East, the Red Diamond—well, that's still another story.