Jack struggled and strained at his bonds, as, in fact, all the rest of the party were doing. To his delight, after a brief period of struggling, he managed to loosen them considerably. The work of tying up the party had been done hastily, and, consequently, the knots were not very hard to loosen. In fact, all that Herrera had wanted, was to keep them quiet till he had looted the treasure of the gems.

When Jack had worked his hands free he pulled the gag out of his mouth, and then, after undoing his ankle bonds, he drew out his knife and rapidly liberated his companions.

“Well, a fine mess I’ve made of it,” grumbled out Captain Andrews, as soon as he was free.

“I don’t see that you were any worse than the rest of us,” said Professor Chadwick; “in fact, it was you who had a keen enough mind to guess that our message might have been received and answered by another craft than the Sea King.”

“Which it was,” put in Mr. Jesson.

“Yes; but I kept watch for a while,” contritely said the captain, “and—I’m bitterly ashamed to say it,—I fell asleep at my post of duty.”

“For which we don’t attach a bit of blame to you,” said Professor Chadwick; “what we had passed through was enough to exhaust a giant. To tell you the truth, I almost feel relieved now that the gems are gone.”

“The natives had a legend that they brought bad luck,” said Mr. Jesson, “and indeed they seemed to.”

“I hope they bring evil fortune to that greaser who has them now,” struck in Abner Jennings.

The two sailors added their growling assent to this wish, nor could any of the party refrain from echoing it.

[Illustration: Jack liberated Captain Andrews.]

“I suppose he’s got clear away,” hazarded Ned presently.

“Of course he has,” grunted Captain Andrews. “I’ll bet there’s twenty miles between him and this island right now. And, incidentally, I’m ready to bet as to his future.”

“What will it be?” asked Jack, with some curiosity.

“Why, he’ll throw up his governorship,—the Diaz government is on its last legs, anyhow,—and skip out to Paris. He’ll sell those gems over there and—live happy ever afterward.”

“Why Paris?” asked Mr. Jesson.

“Oh, all those scallywags go over there when they’ve made their graft,” laughed Ned; “they won’t tolerate them any other place, I guess. When I was over there with my folks two years ago we saw more princes and exiled presidents from South America than you could shake a stick at. You couldn’t have thrown a brick on the main boulevards without hitting some ruler who had left his country for his country’s good.”

“All of which disquisition,” said Professor Chadwick dryly, “doesn’t solve our problem.”

“No, indeed,” said Mr. Jesson; “we are as badly off as before.”

“Worse,” exclaimed Jack.

“How’s that?” asked Tom.

“Well, haven’t we lost those gems?”

“Oh, bother the old gems,” said Tom, “we’ve got the box, haven’t we? If any one in the States doesn’t believe we ever had the three gems we can show them the casket as proof that we really did have them once.”

As he spoke he picked up the box from the sand where Herrera had flung it, and handed it to the Professor.

“It will make a handsome relic of our trip at all events,” said that gentleman, with half a sigh. “I guess I’ll present it to some institute interested in such things.”

“Pity those bumps on the cover aren’t precious stones,” said Ned, indicating the three dull-colored knobs on the cover. “Wonder what they are there for?”

“To make the box look nobby,” ventured Tom, a pun which almost cost him a clip on the side of the head.

But they were soon recalled to the seriousness of their situation. In the east the day was beginning to dawn, and a return to sleep was out of the question after all that had occurred.

“I guess I’ll get to work with the wireless,” said Jack, “it’s our only hope.”

“Unless we could swim ashore,” said Captain Andrews. “It isn’t more than five miles off.”

“True. But from what we could see yesterday it is a rugged, inhospitable shore,” said Mr. Jesson.

“Most anything would be better than this, though, so long as it was the mainland,” said Ned.

“Yes, if only the old Flying Road Racer would have kept in the air half an hour longer,” groaned Tom, “we might have used her as an auto to reach some civilized spot.”

“We could easily have done that,” struck in Jack. “The engine and running gear are in perfect order. So far as that is concerned, she is ready for a road trip of a thousand miles right now.”

“You ought to have fixed it so she could swim, while you were about it,” said Ned.

He meant the remark as a joke; but Jack answered quite seriously.

“I’ve been thinking over such a plan,” he said; “maybe some day I’ll get to work and invent something that will make the good old craft as capable in the water as she is on land and in the air.”

“Wish you could invent it right now,” began Ned with a laugh. “I——”

He stopped short with a puzzled look, which, oddly enough, was reflected on all their races the next moment.

“My legs are wobbly!” cried Tom.

“By the trident of Neptune,” roared Captain Andrews, “so are mine!”

“It’s not our legs!” cried Mr. Jesson, “it’s the ground that’s moving!”

“The whole island is quivering like jelly!” cried Ned.

“Good land, what ails de place? It’s done got chills and feber!” shouted Jupe from his pots and pans, which were now rolling in every direction.

The tremor grew stronger. Accompanying it was a queer, moaning sort of sound. All at once there came a violent convulsion, and they were all thrown flat. The roaring noise increased till it was almost deafening.

“It’s an earthquake!” called out Professor Chadwick.

“An earthquake?” cried the others in terrified tones as they rolled about.

Suddenly, not far from them, a great ragged fissure yawned in the earth and almost instantly closed again. From that moment, for the ensuing ten minutes, the castaways were in a condition bordering on panic. With the very earth under their feet refusing them support they felt that they were, indeed, in a sorry plight.

At the conclusion of the period of time mentioned, the shocks stopped as suddenly as they had begun.

“Do you think there’ll be any more of them?” asked Tom in rather a quavery voice.

“Impossible to say,” said Mr. Jesson. “I imagine that this is a continuation of the one that caused that cliff to collapse, which resulted in my escape from those Indians.”

“I suspect that is it,” said Professor Chadwick. “The great storm may have also resulted from the generally disturbed conditions. We may have no more shocks and we may have a dozen.”

“I’ve known cases of whole islands being swallowed in the South Seas——” began Abner Jennings gloomily.

But Professor Chadwick stopped him.

“If you can’t talk of something more cheerful, my man, don’t talk at all,” he said.

“And tidal waves, too, that wiped out whole cities like Galveston,” muttered Jennings, in a low tone, however.

“There is no reason to expect that another shock will occur,” resumed the Professor; “the very nature of these seismic disturbances results in——”

“Wow! Glory to Goshen, here comes annudder one!” bellowed Jupe, dropping a frying pan with a clatter and throwing himself flat on his face.

The others followed his example. Indeed, it was impossible to remain on one’s feet. The mighty earth waves undulated like the billows of the sea.

This shock lasted longer than the other, and was more severe. When it was over they arose to their feet considerably unnerved by the convulsion of nature.

“Do——do you think there is any danger of this island sinking. Professor?” asked Ned in a shaky voice.

“I do not,” rejoined the other with a confidence that he was very far from actually feeling, however. “I see no evidence of any volcanic formation hereabouts.”

“Maybe de ole Mudder Earth done got a bad tummy ache,” hazarded Jupe.

“I wish she’d get it in her foot, then,” grumbled Ned. “I don’t—say, Jack,” he broke off suddenly, “am I seeing things or is that beach narrower than it was?”

A worried look passed over Jack’s face.

“I’m afraid your eyesight is all right, Ned,” he said. “The water is closer than it was, beyond a doubt.”

“And that means?” gasped Captain Andrews. “That we are sinking,” calmly said Professor Chadwick. “There is no use deceiving ourselves. Jack, send out a call for aid. There may be a chance of some ship catching the message.”

Jack sent an appeal flashing forth from the wireless. Then he listened as usual for an answer.

It came, but not in the way he had expected. He flung the receivers from his ears with an angry expression.

“It’s that rascal Herrera,” he said. “He intercepted the call.”

“The villain! What did he say?” demanded Mr. Jesson.

“He said that we could stay here till the island sank, for all he cared, and added that Diaz had been driven out of Mexico, and that he was off to Europe with those gems.”

“Dat dere coffee-colored man is de worst no ’count trash I ebber done heard of,” announced Jupe solemnly, while the others stood thunderstruck at such pitiless behavior.

Before they could utter a word of comment, however, another shock struck the island. And this time it caused an amazing thing to happen. The centre of the isolated spot of land had been quite an elevation. During this spasm of the earth, however, an astonishing change took place in the form of the island. The “crown” of the sandy little place sank until it was depressed into a sort of cup. On the outer rim of this odd subsidence of the island, were the adventurers who looked with alarmed eyes on this freak of the earthquake. It mean only one thing, and that was that if another shock occurred and the land sank any further, that the sea must overwhelm it utterly.

While they were still looking over the altered scene. Captain Andrews gave a shout.

“Shiver my timbers,” he cried, “look yonder, will you?”

The subsidence of the centre of the island, of course, gave them a clear view of the distant shore and of the neck of water between it and the island.

An astounding thing had happened, as the adventurers could now see. Although they had not known it, the island had once formed part of the mainland, and a narrow neck still connected it at a depth of only a few feet at low water. It was now low tide, and the earthquake, while it depressed the central part of the island, had performed a still more astonishing freak.

It had raised this narrow neck linking it to the shore till it was quite a few inches above the level of the water, making a causeway of wet sand between the island and the mainland!

Jack was the first to grasp the significance of this. He gave a glad shout as he did so.

“Hurrah! We are saved!” he cried. “The earthquake has saved us!”

“What?” demanded his hearers, not quite so quick-thinking as Jack.

“Don’t you see?” exclaimed the boy. “We can drive the Flying Road Racer ashore over that neck of sand as easily as if we were taking a spin in the park.”

“But suppose another shock causes the neck of sand to subside again?” asked Mr. Jesson skeptically.

“We must take our chances of that,” Tom answered him. “In any case, it means death to remain where we are.”