"But Tizoc was clever, the way he slipped out of sight," returned Mike. "That's the kind of thing Ra-monez does. Posing as a mariachi player is smart business, too."

"The next time we meet Tizoc, let's hold on to him," Biff said. "Then we could see the face behind the mask."

"If we live long enough to get a look at him. I am afraid we must find some other way, Biff."

The next day brought interesting developments. Dr. La Vega was resting nicely, but was still in no condition to talk. Chaco, however, was up from the 98 .

village with much to tell. El Cielo was in a furore. Tizoc himself had stalked the streets and had been seen by dozens of the natives.

"They have declared a holiday," stated Chaco. "A great fiesta will be held in Tizoc's honor. They are telling stories now, of the great things Tizoc did when he lived here many years ago and fought whole armies single-handed."

"Kirby's work," declared Professor Bortha, between gritted teeth. "There will be no excavating done now."

"But there will be," Chaco a.s.sured him. "Things are very good now, professor. It will take time to plan for the fiesta. n.o.body will leave town until then. So they will work for us instead of going to the mines."

"But aren't they afraid to work for us after the cave-in?"

"Why should they be?" Chaco was puzzled. "None of the workers was hurt, because Tizoc warned us. They say that if there is new danger, Tizoc will warn us again."

As soon as Chaco had gone, Professor Bortha was triumphant.

"We've caught Kirby now!" he gloated. "If he tries to stop our work by coming there as Tizoc, we can trap him. If he never shows up, our work will proceed without interruption. Either way, we win!"

"Kirby knows these workers," objected Mr. Brew-ster. "I should think he would have guessed what their reaction would be."

DANGER BELOW! 99.

"You are right," Bortha admitted. His face became solemn. Then, brightening, he added: "But if we are dealing with Ramonez, it will work out the same. Do you still think that Ramonez is behind this Tizoc business?"

"I have met Ramonez," replied Mr. Brewster, "and I feel that he could be. Until I meet Kirby, I cannot be sure. So I would like to meet Kirby."

Mr. Brewster did, the very next day.

A big man riding a little mule stopped in front of the Hotel Pico, swung from his saddle, and strode into the patio where Mr. Brewster was winning from the twins in their favorite word game. The big man grinned as he swept aside his ranchero hat and mopped his forehead with a blue bandana handkerchief. He asked: "You're Thomas Brewster?"

Mr. Brewster nodded.

"I'm Justin Kirby," returned the newcomer. "I guess you've heard of me. First, tell me: How is Dr. La Vega?"

"He is doing nicely," said Mr. Brewster, as he rose to accept Kirby's hearty handshake. "The doctor was just here-"

"You mean the village medico" interrupted Kirby. "Maybe he isn't the right man. I have a doctor down at the big mine who takes care of such injuries. Maybe I should send him up here."

"When are you going down to the big mine?"

100 .

Kirby turned to look at the sun, which was just coming over the roof on the east side of the patio.

"Today," he replied, "if I can get started within the next hour. Would you like to ride along? I have plenty of mules. Too many. We are sending out a lot of silver, but not bringing in enough machinery."

"Do you have three spare mules?"

"Why, yes." Kirby looked at the twins. "They are coming with you?"

"No, I have two other customers." Mr. Brewster turned to Ted and Monica. "Run out to the corral, please," he said. "Tell Biff and Mike I want to see them."

By the time they reached the corral, the twins were breathless, not just from their run, but because of the news that they brought.

"He's here!" Monica said emphatically. "The man with the red face and the big hat. The one I saw in Mexico City. He looked at me like this."

Monica gave her head a tilt, and Ted nodded.

"Now I can believe you, sis," he said. "He looked just the way you said he did."

"Justin Kirby!" exclaimed Biff. "What does he want?"

"He wants to lend you a couple of mules to ride down to the valley," said Ted. "Dad talked him into it. He will tell you all about it."

Amazed, Biff turned to Mike. "Let's go," he said.

DANGER BELOW! 101.

When they reached the patio and saw Kirby seated there, Mike whispered: "Uno tortuga grande."

Biff smiled. Mike was referring to Kirby as "one big turtle" and Kirby looked the part. But despite his careless way, Kirby had a keen eye. He studied Biff sharply, the moment they were introduced. Then Kirby appeared to relax, but Biff doubted that he really did. He was sure that the big man had appraised him and had decided that he was not the youthful visitor who had made the inquiry at the village inn.

Kirby's expression showed a sudden change as he tilted his head toward Mike. Instantly, Biff knew that Kirby had tabbed the Mexican youth as the one that the innkeeper had mentioned. Almost as quickly, Kirby was all smiles again as he shook hands with Mike and learned that this was Miguel Arista, nephew of one of Mexico's most famous judges.

Professor Bortha came from his room just then. He stared at Kirby in brief surprise, then came over and shook hands in an easy, gracious manner. Kirby's round face formed a grin.

"Good digging, professor," he said. "If you need more men to help you, I can send some up from the valley."

"But I thought," returned Bortha rather coldly, "that you were hiring all you could get."

"Not now," declared Kirby. "It takes money as 102 .

well as men to mine silver. Things have been getting slack lately."

Two hours later, Biff and Mike were riding patient mules down a corkscrew trail that made Biff feel shaky when he found one foot dangling "a mile above nothing" as Mike had put it. At one spot, they were forced over to the very edge so that other mules could trudge up past them on the inner side of the trail, bringing oranges, bananas, and other tropical products to El Cielo.

Biff turned his head away from the huge gulf that yawned below and looked back at Mike, who was on the next burro.

"I was wrong about Kirby," confided Biff. "He seems to be a pretty good sort. You must be right; Ramonez is probably behind this Tizoc game."

"No, I have changed my mind too," returned Mike. "I now feel that Kirby is much smarter than Ramonez. So Kirby is probably Tizoc. If he is, there's no telling what he may try next."

"He can't very well knife us." Biff forced a laugh. "Not here in broad daylight on a mountain trail."

"He wouldn't have to do that," declared Mike coolly. "Just one little nudge the wrong way and your burro might let you slip-down there."

Mike gestured toward the abyss where Biff did not care to look. A moment later, the nudge came. A fat mule lumbering up the trail with a few extra bunches of bananas brushed Biff's mount too forcibly.

DANGER BELOW! 103.

A sudden shift, and Biff could almost feel the edge of the trail melt away under his mule's hind foot. The animal lurched and stumbled. Over its neck, Biff was watching chunks of stone that plummeted downward, striking bigger rocks below and bouncing off into s.p.a.ce as though inviting him to follow.

There was only one slim chance that Biff could see. That was to spring for safety and grab one jutting stone that projected like a rough cornice from trail edge, just beyond the stumbling burro's nose.

It was like jumping out into s.p.a.ce and back to earth again, but it was worth the try. Then, as Biff shifted in the saddle to launch himself in the grim leap, he heard a shout from behind him: "Hang on, Biff! Don't jump. Hang on!"

CHAPTER XII.

Chaco Makes a Find BIFF hung on. Just why he did, he wasn't entirely-sure, except that it was because of Mike's shout. In the adventures that they had so far encountered, team play had become second nature with the two boys.

Now, Mike's advice proved its worth. The saddle was still the safest place, for the burro was clambering back on to the trail. Momentarily, Biff thought he was going overboard in a back somersault to nowhere. Then the mule's front hoofs found solid ground and the animal no longer reared.

This was almost at the projecting stone that Biff had hoped to grab. Biff's eyes went wide as that very stone slid loose, dislodged by the tramp of the burro's hoofs. Lazily, it went over the brink and was gone. If Biff had grabbed it, his weight would have carried it away and he would have gone with it. 104 CHACO MAKES A FIND 105.

Instead, Biff was still on his burro and the surefooted beast had found its way to safety. From farther down the trail, Mr. Brewster and Kirby had heard the shouting and the clatter. They had sprung from their mules and were starting back, but their help would have come too late. Biff's adventure had ended happily before they were halfway there.

Kirby stormed at the natives in charge of the fruit-laden mule train, berating them for being so careless. They merely shrugged and pretended not to understand.

During the rest of the trip, Biff felt occasional shivers when he thought back to his near-disaster. But he had gained a new confidence and was ready now to rely on his pack mule, should any further emergency occur.

When they reached the valley and Biff was riding side by side with Mike, Biff had his first chance to thank his friend for the timely advice that he had given.

"Don't thank me, Biff," said Mike, with a slight smile. "Blame Kirby. Now you know why I don't trust him. He should have been watching those other mule drivers from the time we started to pa.s.s them. At least he could have warned us."

"But what would he gain by getting rid of us?" Biff asked.

"Plenty," replied Mike. "Your father would have

CHACO MAKES A FIND 107.

returned to Mexico City with your family. The excavation work at El Cielo probably would have been abandoned, what with the accident to Dr. La Vega and another one on the mountain trail."

"Then whatever Kirby is after at the excavation would be all his."

"Yes, unless Ramonez is Tizoc, which I doubt more and more."

Biff had his doubts, too, but they began to fade when the party reached the headquarters of Kirby's mining operation. There, even Mr. Brewster was impressed by its size; and Biff put the question to Mike: "When Kirby has something as big as all this, why should he be after something bigger?"

To that, Mike could not find a ready answer.

By "all this" Biff referred to a dozen buildings that spread over half as many acres at the foot of a canyon wall. There were offices, housing projects for the workers, a supply shop, and a corral in which were more than fifty mules.

Other buildings behind high adobe walls contained the mining equipment. Kirby showed his visitors a courtyard where the ore had once been treated by the "patio process" in which mules had dragged big blocks around a stone-floored pit. Next were the stamping mills, where broken ore had been crushed. Other buildings contained more modern machinery, much of it still unpacked from the compact crates and 108 .

boxes that had been brought by mule trains here to Hacienda Arroyo, as Kirby called the mining center.

"Our ores come from dozens of different mines," Kirby told Mr. Brewster. "Years ago, one man owned most of them. He tapped one group of mines by drilling a mile-long tunnel beneath them, so the ore could be dropped down through chutes and brought out more cheaply. We are still using the old tunnel."

Mr. Brewster nodded. As chief engineer for the Ajax Mining Corporation, he was familiar with such methods.

"The mine owner built the new hacienda up by El Cielo," continued Kirby. "He died soon after, and the place became the Hotel Pico. Relatives split up the mine holdings. Political troubles ended mining operations. Many workings were abandoned, some even forgotten. In order to revive them, I have had to buy up stocks in worthless companies, just to make sure I have acquired the good ones."

Apparently, Mr. Brewster understood that, too, though he made no comment.

"My problem," continued Kirby, in a frank tone, "is transportation. You can't afford to pay men and feed mules to carry loads on a three-day trip over the mountains. Not at today's costs. It was all right in the old days but not now.

"Shipping silver is difficult enough. Bringing in supplies and equipment is worse. A lot of machinery has CHACO MAKES A FIND 109.

to be dismantled and a.s.sembled later. A couple of hundred pounds is all a burro can lug over those trails. The more we expand, the more mules we need for extra relays. That means still more costs."

Kirby paused to wave at a cl.u.s.ter of much-used jeeps that were parked in the office yard.

"We drive those on some of the canyon roads," he stated, "but they won't do for long hauls. That's why I went up to El Cielo to see your plane come in. Maybe we can ship silver and supplies in and out from that landing field."

"Why not build your own field down here?" asked Mr. Brewster.

"I hope to, later," replied Kirby. "But I can't raise money for that job until I can prove that it will pay off. If I use planes from El Cielo, I can see how much I save by cutting out the two-day pack trip beyond there."

That evening, the visitors had a wonderful meal of enchiladas de polio, Mexican pancakes stuffed with chicken, as well as frijoles, tasty beans served in native style. This was the fare that the mine workers preferred, but there were few of them around. It was plain that Kirby was cutting expenses by employing very small crews.

At dinner, Kirby introduced the surgeon in charge of the small but well-equipped hospital at Hacienda Arroyo. He said he would gladly ride up to El Cielo 110 .

the next day to discuss Dr. La Vega's condition with the local medico, provided the start was not too early.

That suited Mr. Brewster. At dawn the next day, he woke up Biff and Mike, much to their surprise. Over a hearty breakfast of huevos rancheros, eggs done in Mexican ranch style, Biff said sleepily: "But dad, I thought we were making a late start-"

"Up the trail, yes," interposed Mr. Brewster, "so I decided to take advantage of these early hours to look over some of Kirby's mine workings."

They drove by jeep to the big tunnel and followed the track on foot behind plodding mules that were patiently hauling empty cars up a slight grade to receive the ore that came down through the chorreras, as Kirby termed the chutes from the old workings above. On the trip out, the mules had an easy haul because of the downgrade which also served to drain the tunnel during the rainy season.

There was time for a quick jeep ride to some of the other mines close by. Following that, Mr. Brewster and the boys returned to Hacienda Arroyo and soon were mounted on their mules, ready to start back up the trail to El Cielo. The surgeon was with them, but Kirby did not come along.

"I have a lot to do here at the mines," said Kirby, when they parted. "So I don't know when I'll be in El Cielo again. Sometimes I stay down here for weeks at a time."