"As closely as we can tell, the bottom one is right above the discontinuity, which is about six miles below us at this point. The upper one is about a mile below the top of El Viejo. This puts it about a quarter of a mile below the floor of the ocean."

"Too close," Scotty muttered. "What now?"

"We keep shooting, to try and keep track of the upper front. Also, we will place instruments called tiltometers on the mountain slope. These are devices that really measure tilt. You see, if the lens of magma is increasing, El Viejo will swell up slightly. The tiltometers will show it, and we will then have further proof of what is coming."

"But what can we do about it?" Rick demanded.

Balgos shrugged. "_Quien sabe?_ The Spanish phrase is a good one, because it does not only ask 'who knows,' it also carries the meaning of a kind of resignation. There does not seem to be anything we can do."

Rick stared across the dining room, eyes unseeing. It was hard to imagine that molten rock was gathering below them in sufficient quant.i.ty to make a mountain move; but once you succeeded in imagining it, the picture was terrifying.

Motion attracted his glance and his eyes focused in time to see Brad Connel rise from the table and excuse himself. He watched the geologist walk out of the room and turned to Scotty. His pal nodded. He had seen Connel leave, too.

Rick quickly counted noses. All others were present. Connel was the first to leave. He wondered where the geologist was going, and his eyes narrowed.

Connel had been very anxious about his and Scotty's condition, once the hotel was reached. Rick was sure his anxiety was strictly phony. Both boys had been stiff and sore, but a medical examination showed nothing seriously wrong, thanks to Scotty's fast action. Hartson Brant had been reluctant to accept Rick's opinion that Connel had stolen the dynamite and b.o.o.by-trapped them. He pointed out that the geologist had no motive; he had never even been on San Luz before.

Rick had to agree. There was no apparent motive, but that didn't mean Connel was innocent. He might have a motive that no one suspected.

Scotty c.o.c.ked an eyebrow at Rick and made a slight motion of his head toward the door where Connel had vanished. Rick got the signal. He nodded.

The boys thanked Dr. Balgos for his explanation, then excused themselves. They wandered casually from the dining room.

Once outside, Rick grinned at Scotty. "So you're wondering where Connel has gone?"

"Aren't you?"

"Sure. But why not ask the others what he said when he excused himself?"

Scotty shook his head. "They didn't think much of our theory about Connel causing our troubles, did they? If we asked, they'd think we were pushing the same point too hard."

Rick agreed. "Where did he go?"

"I don't know. But if he leaves the hotel, it will be by jeep. There's nothing within walking distance. If we get out back of the pump shed we'll see him if he comes out."

"Aye, aye. And if he jeeps out of here, we'll be on his tail. Roger?"

"You said a Brantish mouthful. Let's go."

A quick reconnaissance disclosed no sign of the geologist outside, and the boys hurried across the dark parking lot to the shadow of the pump shed. A police officer materialized from the darkness and greeted them courteously. "Good evening, senores. _A sus ordenes._"

By placing himself at their orders, the officer was politely asking their business, Rick knew. He replied, "We came out to see if anyone had made another try for the dynamite, Senor _Teniente_." Calling the officer "lieutenant" was a form of flattery.

"_Sargento, muchas gracias_," the officer replied. White teeth flashed in a grin. "But who can tell the future? If I capture the thief, it may soon be lieutenant instead of sergeant."

"We hope so," Scotty said politely.

Rick noted that the three were hidden from the parking lot by the pump house. The position was satisfactory. If Connel was going to take a jeep, he probably would do so right away. Otherwise, why should he be the first to leave the dining room?

"Why would anyone steal dynamite?" Rick asked the police officer. He wanted only to keep a quiet conversation going behind the pump house.

The officer had theories. Perhaps revolutionaries had stolen it. Also, although it was against the law and brought severe punishment, fishermen were known to dynamite fish. This also was a possibility. But the explosion of the dynamite on the mountainside was certainly a puzzle.

Rick didn't think so, but he agreed politely. It was bewildering, he said. Why steal explosives and then use it on a harmless scientific group?

Perhaps fear of discovery caused the thief to set a trap, the officer guessed. He admitted it wasn't a good guess.

A jeep roared into life and the boys stiffened. The officer strolled out of the shadow for a look. "One of your a.s.sociates is going for a ride,"

he said.

Rick waited until the jeep lights cut across the parking lot and moved down the western road, then he said, "It's a nice night for a ride, Scotty. What say we take a jeep and look over the country, too?"

"Good idea," Scotty agreed readily.

They bade the officer good night and started to where Zircon's jeep was parked. It was a temptation to hurry, but they suppressed it and sauntered to the jeep. Fortunately, no keys were needed. The jeep ignition was turned on by a simple switch. Rick got into the driver's seat and started up. He waited, the motor idling, until he was sure Connel was out of sight around the mountain, then he drove slowly across the parking lot and followed.

Fortunately, there was enough moonlight to see the road. Once out of sight of the hotel, Rick stopped and switched off the lights. As his eyes adjusted to the dimness he started off again as fast as vision allowed.

Once he sighted Connel's lights. They were ahead and higher on the mountain. He lost sight of them again as foliage blocked the view.

"Suppose he's heading for the shot station?" he asked.

Scotty shrugged. "We'll soon know."

They reached the pumice works without seeing the geologist's lights again, and Rick stopped at the turnoff. "Now what?" he asked. "Did he go up the trail or not?"

Scotty sniffed the air. "Smell anything?"

Rick breathed deeply. There was the odor of rank vegetation, and, very faintly, the odor of sulfur from the hot springs. But there was another smell, too. After a moment he identified it. "Dust!"

"Seems so," Scotty agreed. "Which means he didn't take the trail to the stations. No dust on those tracks. He must have taken the dirt road to San Souci."

"But why?" Rick was already moving ahead to where the pavement ended.

"What's in San Souci?"

Scotty chuckled. "Ask Connel. Don't ask me."

"I thought Marines knew everything," Rick gibed.

"Almost everything," Scotty corrected.

The jeep moved onto the dirt road and in a moment their own cloud of dust obscured any slight haze that Connel's pa.s.sing might have left.

They were in strange territory now, and Rick slowed down somewhat.

Connel had the advantage of lights. They wouldn't be able to gain on him.

"He can't get far," Scotty said rea.s.suringly. "The road goes to San Souci and nowhere else. It can't be much of a town, so we'll find him."

Scotty was right. San Souci wasn't much of a town. There were a handful of fishermen's huts, a dock with a number of fishing boats, racks for drying fish, a single store, and nothing else. There was a paved road leading from the town to the main city of Calor, but Connel hadn't taken it. Nor was the jeep in San Souci.