It was noon of the next day when Captain Andrews announced that they were still some two hundred miles from their destination. But, as the boys were all three of them busy over the aero-auto, adjusting and examining every part of the queer craft, the time flew swiftly. The dawn of the third day found them anchored off the jungle-clad coast, while not a mile from them the waves were breaking on the bar that marked the mouth of the shallow river, which, they subsequently learned, was called the Apak.

It would be two hours, so Captain Andrews calculated, before the tide turned and made the passage of the bar possible. In the meantime. Jack brought on deck the silver chest, which he had, of course, taken possession of, pending the time when he could deliver it to his father. The adventurers spread the three blazing gems it contained out on the deck, and revelled in the glow of light and wonderful inward fires the precious stones revealed as the bright sunlight played upon them.

The Vagrant had once been used as a passenger craft at Galveston, and her former owners had installed an iron safe in the cabin for the protection of valuables. In this receptacle Jack replaced the silver casket after they had examined the gems to their hearts content.

By this time Captain Andrews was ready to pronounce the crossing of the bar at the river mouth feasible. The tide had risen till the tempestuous breakers had subsided into long swells, with a narrow passage of smooth water marking the channel. Carefully following this, the skipper of the Sea King piloted the Vagrant through into the calm water of the estuary beyond.

The boys, grouped forward, gazing at the surroundings with eager eyes, beheld a scene full of wild, tropic beauty. The white beach, blazingly radiant in the strong light, was bordered by a dense jungle of dark, melancholy looking mangroves. Beyond these came a tangle of brilliantly green jungle, in which the broad fronds of the banana plant predominated, while here and there a tall palm reared its feathery head.

Further back still the foliage changed again. Lordly groves of mahogany trees, rosewood, and giant royal palms raised their crests. In the distant background, far withdrawn, the misty blue outlines of a range of majestic, rugged-looking mountains showed against the steely blue sky. They looked as if they were hundreds of miles off at least; but Captain Andrews explained that the distance from the shore to the foothills was not so considerable, by a great deal, as it looked. The condition of the atmosphere, laden with the moisture of the lowlands, lent them this appearance of tremendous remoteness.

“It is in those mountains,” said Captain Andrews, “that the remnants of the most ancient of the Maya tribes still live. They tell stories up the coast, in the civilized portions of Yucatan, about vast ruins and remains of splendid cities to be found back there.”

The boys gazed up at him as he stood at the wheel. A magic world of romance and adventure seemed suddenly opened before them by his words.

“I recall reading once,” said Tom, the studious, “that the Mayas were civilized long before the Aztecs or Toltecs, and that their knowledge of the building arts exceeded that of either of those races.”

“Sort of pioneer real-estate men,” chuckled Ned Bangs, who in moments when he was not oppressed by trouble, as he had been recently, possessed a whimsical vein of humor.

“Ho! ho! ho! ah reckon dat’s right, Marse Ned,” roared Jupe, opening his big lips and exposing his ivories.

“Has any one ever penetrated into their country?” went on Tom, addressing Captain Andrews.

“I guess your father went as far as anybody,” was the response, “and you know how far he got. I have heard that the remnants of the ancient tribes have a law, making it death for the man who dares to advance into their territory.”

“But the natives that caught you didn’t seem disposed to kill you,” objected Jack.

“Oh, those fellows; they are of the inferior coast tribes,” was the rejoinder. “The ancient races regarded them as dirt under their feet. I guess they don’t know any more about the interior of those mountains than we do.”

The current of the river, discolored and yellow from the recent earthquake back in the foothills, was so swift as they ascended that Captain Andrews found no opportunity for further talk. It required all his attention to keep the Vagrant’s bow pointed upstream. The river narrowed considerably after passing its mouth. Its turbid current rolled seaward between two low and densely wooded banks, not more than sixty feet apart.

“How far is it to the spot where that craft of Herrera’s was moored?” asked Jack, when he found an opportunity.

“Fully fifteen or twenty miles, I should say,” was the response, “and if we are making two miles an hour against this current we are doing well. This river runs mighty near as fast as the Lachine Rapids back home.”

“You’re not far out on that, Cap,” remarked the volatile Ned Bang’s, who had quite recovered his usual flow of spirits.

The lad had not as much at stake as Jack and Tom, and, moreover, he did not quite realize the seriousness of the undertaking before them to the same extent that they did.

Hour after hour they fought their way up the coffee-colored river. The character of the vegetation on the banks had begun to change by this time. Here and there stood a majestic clump of mahogany trees; but logwood, a valuable article of commerce in the dyeing industry, formed the major part of the growth. Once, as they rounded a bend, the flash of a lithe body was seen among the trees, as a beautifully spotted jaguar slunk away from the overhanging limb where it had been lying.

“Let’s try the gas-guns on the next one we see,” suggested Tom, and the lads hastened below and returned armed with the odd weapons.

An opportunity to use them soon presented itself. From a thick mass of brake there came a mighty squealing and grunting, as the Vagrant came slowly around one of the numerous bends in the stream. All at once several small, bristly animals, like miniature pigs, dashed out with a mighty commotion.

Three gas-guns flashed to three shoulders simultaneously. It was an odd and rather uncanny sight to behold an instant later, six little wild piggies lying with their toes turned up, “dead to the world,” as the slangy Ned Bangs put it.

The boys were keen for going ashore and gathering in the victims of the ammonium nitrate compound. But Captain Andrews vetoed the proposal as impossible.

“There’s hardly a foot of water in shore there,” he said, “it’s a case of ‘keep in de middle ob de road’ in this river.”

Dinner was eaten at one o’clock. Jack “spelling” Captain Andrews at the wheel while the skipper partook of a hearty meal, after which he indulged in a nap while Tom, in his turn, relieved Jack.

The latter was still below enjoying Jupe’s cookery, when there came a sudden hail from above:

“Say, Jack, hurry up on deck, won’t you? There’s something odd about the water just ahead of us.”

Ned it was who uttered the summons, poking his head down the companion way.

Jack finished his meal in a jiffy, and was on deck in another two seconds. He found the Vagrant’s nose still pointed up stream, but Tom, using the bridge controls, had slowed down the engines till the craft was almost stationary in the swift current.

Right ahead of them lay the cause of Jack’s abrupt summons to the deck.

A chain, composed of huge iron links, was stretched from bank to bank of the river, effectually barring further progress.