As soon as our little party got back to camp, Charley called together the Spaniards not yet assigned to duty, and had the Captain select the three men he wanted for graders. Although both Walter and Charley could speak and understand a little Spanish, the old sailor could not speak a word of it, and he was careful to pick out three men who understood a few words of English. Out of the remainder Charley selected two to go ahead of the machine, to clear its path of trees and to dynamite the larger stumps. Two men were assigned as bridge builders, for at every thousand feet a gap must be left in the road for the back water to pass through during the rainy season. A big, strapping fellow, over six feet tall, was named as assistant for the teamster, and the remaining two Spaniards were named as night guards. All but the night guards were to go to work next morning. To each one Charley explained that they must not permit any strangers to come near either camp or machine. If they saw any strangers, except Indians, they were to report it to him at once, or, if he was not in camp, they must report it to Walter.

"That ought to protect us pretty well," he remarked to his chums, after the Spaniards had dispersed, chattering over the jobs that had been assigned to them. "In the day time, the bridge builders will guard our rear, and the right-of-way men will be the same as scouts in front, while you will be watching all around generally. There will always be a crew on the machine, and the teamster and his helpers will be of some use as scouts in their work. That ought to prevent any chance of our being taken by surprise."

"You talk as though you were preparing for war," Walter remarked.

"It does sound that way," his chum admitted. "I've got a hunch that we are going to see trouble as soon as those convicts get word to their boss that the machine is running again. Judging from what has been attempted already, our mysterious enemies will stop at nothing to accomplish their purpose."

"It's like fighting in the dark," Walter commented. "If we only knew just what we are up against, we would know better what to expect. This mystery business is something I don't fancy."

"It's up to us to solve it," said his chum; "and I'm going to have a try at the job to-morrow. It's comforting, anyway, to hear that machine working so steadily. That Bratton is sure doing some digging. Hear how regular that bucket is dumped. I wonder what those two long and two short whistles mean."

"That's the signal to move track and back up," said Walter, proud of his newly acquired knowledge. "One short whistle means go ahead, three long ones are for the teamster; four long ones are the distress signal, and five long ones is the signal for everyone to come to the machine."

"The men must all be told what that last signal means," said Charley thoughtfully. "It may come handy some time."

As night drew near, the resting crews emerged, yawning, from their tents, and began to prepare for their night's work. Lanterns were filled and cleaned and working clothes donned. Chris, with his assistant's help, filled up a large basket with food, which, at sundown, was sent out to the workers on the machine.

Supper was eaten, and all the Americans gathered around the campfire and told stories and jokes in its genial glow. The Spaniards built another fire, in front of their own tents, and sang Spanish songs to the accompaniment of a couple of mandolins, while Chris and Sam, his new assistant, lounging in the cook tent, talked lovingly about their own country, the poverty-stricken Bahama Islands.

"This is a mighty different camp from what it was four days ago," remarked McCarty. "There was no music or laughing going on then. All you could hear was grumbling and cursing. Believe me, I like this new order better."

When 8 o'clock came, Kitchner called his crew and left for the machine, from which soon came Bratton with his tired crew. "Digging's good," he said, in answer to McCarty's questions. "She's hitting a little rock, but it's soft and digs easy. I struck one dead head, but got it out without much trouble."

"What's a dead head?" Walter asked.

"Submerged stumps or trees," McCarty explained. "We often come upon them in our digging. They are generally big, hard as iron, and mean to get out. One does not see them until the bucket hits them, and then the machine is too close to use dynamite."

"Queer," the other commented.

"Yes," McCarty agreed. "There are forests buried below us, I suppose. The process of building up and tearing down goes on all the time. In the centuries to come, likely, these trees around us will be buried in turn, and another forest rise above them."

"The Lord moves in a mysterious way His wonders to perform," quoted the Captain reverently.

While this conversation was going on, Charley had slipped away from the little circle unnoticed, and stepped softly out into the darkness. He had not gone far before he was halted by an abrupt challenge and a leveled rifle.

"It's the boss," he said, in answer to the challenge. "Where's Gomez?"

"Gomez is on the other side of the camp," answered the sentinel in Spanish. "Each of us make a half circle of camp, meet, and turn back again. No one can go or come unnoticed."

"Esto bueno. Bueno nosche, hombre." (It is good. Good night, man.)

"Bueno nosche, seÑor," replied the Spaniard politely, and Charley strolled back to the fire, satisfied that the night guards were doing their duty.

"Jim," he said, to the teamster, "I want to use one of the mules to-morrow. You've got enough wood hauled to last a couple of days. You can keep right on chopping while I'm gone. Take Juan out with you. He is to be your regular helper. Now, which mule had I better take?"

"Going to ride?" inquired the teamster.

"Yes."

"Waal," he said thoughtfully, "Violet will throw you the furthest, but Pansy might kick you while you're down."

"I'll take Violet," decided the lad, with a grin. "I object to being kicked when I'm down."

"I'm going to take a ride ahead to-morrow," he told his chum, when the rest had retired. "I am in hopes that I may hit on some clew to this mystery. At any rate I will look over the route we have to take, and see what we have got to encounter. I ought to have done that before we bought Murphy out. Well, here goes for bed. I am going to get an early start in the morning."

His intentions were sincere, but he slept so soundly that he did not awaken until the general call for breakfast. While he was eating Chris put up a lunch for him, and, when he was through, Jim, the teamster, accompanied him out to the corral. "I'll put the bridle on Violet for you," he offered. "She sorter objects to strangers fooling around her mouth."

"All right," Charley agreed, but it was with some little secret dismay that he viewed the towering, powerful mule, as Jim bridled it, and, throwing a sack over its back, led it out of the corral.

It was too late to back out without chaffing, for the whole camp had paused on its way to work, to watch the proceedings.

"Lead it out on the grade and give me a hand up," he ordered, and Jim meekly obeyed. Charley placed his foot in the teamster's hand and swung himself lightly astride of the mule, while the teamster jumped hurriedly back.

"Get up," Charley said, as he gathered up the reins. Down went the mule's head, and up and down went its hind part, in a series of jolting, jarring bucks.

"Give it the whip," howled Walter in delight.

But Charley was too busy to heed advice. He grasped desperately at the mule's mane to save himself, but it was too short for a hand-hold, and over the mule's head he went, to land ten feet away in the soft sand with a thud that made his teeth ache.

Slowly he picked himself up, and, rubbing the sand out of his eyes, looked back. The mule was nibbling placidly at a bit of grass, and behind it the whole camp was howling with laughter.

"I really think," remarked the teamster critically, "that you could do better with a saddle on."

"Saddle," exclaimed Charley wrathfully, "have you got a saddle?"

"Got a good one over in my tent. I 'lowed you preferred to ride bare back. Some do, you know."

Charley glared at him with suspicion, but the Missourian's pale-blue eyes met his with a look of entire innocence.

"I guess I could do better with a saddle," agreed the lad dryly. "Go and get it, if you please."

Even with the saddle on, it was all he could do to retain his seat as the mule bucked up and down. But the teamster at last gave it a whack with a stick over the hind quarters and started it off on a run. For one fleeting second Charley glanced back at the grinning faces behind, then he settled down in the saddle and strove to master the vicious brute.