They reached a patch of crushed and yellowed growth where Connel obviously had parked his jeep. There were oil stains on some of the broken leaves.

Scotty pointed to a brown-paper cigarette stub. "Ever see Connel smoke one of those?"

Rick hadn't. "He smokes cigars. Where do you suppose that came from?"

Scotty got out of the jeep and bent over the b.u.t.t. "The tip is still damp," he said. "Someone's been here very recently. We'd better keep an eye open."

Trampled vegetation showed them the path to the firing place. Moving cautiously, the boys walked down the path, eyes constantly searching for signs of movement in the heavy growth.

The clearing where Connel had placed his shots was only a short distance down the path. Rick examined it carefully, but it looked like all the others, except for one thing. The broken earth was yellow, and of a different texture than the deep jungle loam at the other stations.

Rick walked into the shattered area and picked up a piece of the yellow ground. It broke in his hands. "Funny-looking stuff," he said.

"Yes," Scotty agreed. "Take a look around while I keep a watch. I have a funny feeling we're not alone here."

There was a fairly deep crater in the middle of the area. Rick stepped into it and kicked yellow earth out of his way. He was puzzled. There was nothing visible in the area except the yellow ground, and there was nothing about that to give him a clue to Connel's determination to keep them away.

His foot dislodged a clump of earth. It rolled to the bottom of the shot crater, exposing two large crystals. Rick picked them up and rubbed the dirt off. They felt rather greasy. He didn't think they were quartz.

His mind ranged over the possibilities. Probably datolite, he decided.

The color was about right, and he knew datolite was found in igneous rocks of volcanic origin. He put the crystals in his pocket.

A trace of blue caught his eye and he knelt, digging with his hands. He uncovered a few more of the datolite crystals and put them in his pocket. They weren't particularly good specimens; he had some in his rock collection that were perfectly formed and clear, but at least they were something to take home.

Digging uncovered a layer of hard blue rock, heavily pockmarked and filled with the yellow ground. He saw one place where the blue actually blended in with yellow and decided that the blue and yellow were probably the same rock. The slaty blue simply turned to yellow when it was exposed to the air for a while.

There were loose pieces of blue, broken by the dynamite blasts. He picked up a couple of smaller pieces, then added a piece of yellow to his collection. He uncovered another crystal, too, a large one nearly the size of a golf ball and put that in his pocket.

Scotty was getting restless. "Let's get going," he said. "I don't like this."

Rick had seen enough, and it had told him nothing. He was just as puzzled over Connel's motive as ever. Obviously, the answer was not here--or, if it was, they couldn't see it.

"Okay," he said. "Move out."

Scotty led the way back to the jeep. Rick got into the driver's seat and started the motor. He backed and turned in the narrow s.p.a.ce Connel's jeep had created, and finally got his wheels straight for the run back.

From somewhere behind them a voice called, "_Parada!_"

"Who's that yelling at us to stop?" Rick asked.

"I can't see anyone," Scotty replied. His eyes were scanning the jungle.

"But I don't know anyone around here we want to talk to. I've got a hunch we should get going."

Rick felt the same. He released the clutch and the jeep moved ahead.

"_Parada!_" the voice yelled again, and on the echo came the clear crash of a rifleshot. A jagged star suddenly appeared on the windshield between them!

Rick reacted instinctively. He shoved the gas pedal to the floor and bent low, the skin of his back crawling with the expectation of a rifle bullet hitting it. The jeep leaped ahead and he steered as best he could. He shifted into second and the vehicle picked up speed. The rifle snapped again and he heard the sound of the slug hitting metal in the rear of the jeep. Then the trail turned and there was heavy jungle growth between them and the unseen sniper.

Not until they reached the second station, a mile away, did Rick slow down. He looked at Scotty, his face grim. "The place was guarded. What else can you make out of it?"

"Just that," Scotty agreed. "The guard must have been making a tour around the shot station. He got back just as we were taking off."

"Funny he didn't hear the jeep when we came," Rick said.

"Not very. Sound gets lost pretty fast in this heavy growth. You couldn't hear us a hundred yards away. Probably there's just the one guard, and he goes around the station in a big circle."

"I'll buy it," Rick agreed. "But why? Why guard a chunk of jungle with nothing in it but some torn up yellow ground?"

"When I find out," Scotty replied, "I'll let you know first thing."

CHAPTER X

The Volcanic Pipe

Hartson Brant and Julius Weiss were still at work in the conference room when Rick and Scotty returned. David Riddle had gone, and the others had evidently not finished placing the tiltometers.

The two listened to Rick's story in silence, then Hartson Brant sighed.

"I don't know how you do it, Rick. But if there's trouble around, you and Scotty will find it. Are you sure the rifleman shot at you?"

"We've got a bullet hole in the windshield and one just under the rear seat," Scotty said. "One might be an accident, but not two."

"I agree." Hartson Brant nodded. "Let's see the samples of earth you brought back, Rick."

He took both the yellow and blue pieces from his pocket and put them on the table. Hartson Brant and Weiss examined them with interest.

"Unusual," Weiss said. "I think you are right in a.s.suming that the yellow is simply an oxidized form of the blue, Rick. But I can't tell you what the material is. I've never seen anything like it before."

"The grain is pretty fine," Hartson Brant added. "It could be igneous or sedimentary in origin. I'm not enough of a rock hound to know. David Riddle can tell us when he returns."

"Connel would know, too," Scotty reminded. "He's a geologist. Wouldn't you think he would have mentioned an unusual formation like this when he found it?"

"Perhaps it's not unusual to a geologist," Weiss pointed out.

"Where is Riddle?" Rick asked.

"He went to his room a few minutes ago. He should be back shortly. Rick, I think you'd better tell us the whole story. Why do you suspect Connel?

Why was it important for you to look at his shot station?"

Rick started at the beginning. "It wasn't any one thing, it was a series of little offbeat things. We thought it was funny he didn't even want company after Ruiz was hurt. Then he reacted so violently when we proposed swapping stations. It just seemed odd. The theft of the tracings bothered us, too. No ordinary thief would steal papers and leave Dr. Williams' wallet in his pocket, or leave his pocket transistor radio and stuff like that."

"But you can't connect Connel with the theft of the papers," Weiss objected.

"No, sir, we can't. But we almost got caught in the stolen dynamite, and he could have set that off. It was while we were on the way to his third station."