"That's what happened, nonsense or not," Rick said curtly.

Scotty added, "And what were you doing here?"

"Came to get my wallet," the geologist answered readily. "I missed it and figured I must have dropped it up here. It wasn't anywhere else I'd been. Better get in and let me take you back. If you were close enough to get nosebleeds you must be shaken up quite a bit."

"We're shaken," Rick agreed. "Our jeep is down at our shot station. We decided to leave it there and take a hike."

They climbed into the back of Connel's jeep. The nosebleeds had stopped now, but their faces were smeared with blood. Neither felt like talking, nor, apparently, did Connel. He stopped at their third station and asked, "Can you make it? Or do you want to ride back with me?"

"We can make it," Rick said. "Thanks for the lift."

"I'd better stay behind you to make sure," Connel stated.

The boys headed straight back to the hotel, Connel a hundred yards to their rear. In the parking lot they thanked him again for the lift, then hurried in to let warm water wash away the traces of their experience.

Later, stretched out on their beds, they talked it over.

"You saved our bacon," Rick stated. "But what really happened?"

"I'm not sure," Scotty replied. "There are two possibilities. One, we sprung a b.o.o.by trap. I don't really credit that one much, because we were rolling away when the stuff let go. If we'd hit a trip wire or something similar, the dynamite would have gone off right then. So, second possibility, someone was waiting for us. We jumped back just as he pushed the plunger. Or, maybe he saw we had spotted the trap and tried to get us, anyway."

"Who's he?" Rick asked.

"Persons unknown," Scotty answered. "Or maybe one person not unknown."

"Meaning Connel? He could have done it. Suppose he set the trap, then took his jeep up the hill out of sight. Then he could have walked back, fired the shot, hurried back for his jeep, and driven down."

"Could be," Scotty agreed. "Only, did he know we were coming?"

Rick shrugged. "How can we know that? For all we know, from his third shot station he might be able to look right down on the trail. He sees us, hurries into position, fires the charge, and hurries back. We can't really tell until we get to that third station. Personally, I vote for Connel."

"Not proven," Scotty warned.

Rick knew it. "It may never be proven, on account of no witnesses. But suppose it was some unknown party? Why wouldn't that party try for Connel? Why wait until he's pa.s.sed, and we're coming into position?

Would an unknown thief be that interested in us?"

"Too many questions," Scotty objected. "I haven't any answers. But you make a good case for its being Connel. Also, did you notice how he jumped on us for stealing the dynamite? That probably would have been his story if we'd been killed. Now tell me what his motive is. Why should he try to delay the project?"

Rick had no answer to that. "Makes no sense," he agreed. "Unless there's something he doesn't want us to see. That dynamite sure discouraged our trip to his third station!"

CHAPTER VII

Casa Guevara

The scientific party lost only one day because of the dynamite theft.

Governor Montoya supplied more explosives and the firing schedule continued. Now, however, the dynamite was guarded by police supplied by His Excellency. Police also were in evidence around the Hot Springs Hotel. No more chances were being taken.

After three days, the scientists began to have a better idea of what was going on in the earth beneath them, but Rick and Scotty could make little sense of the ma.s.s of data. Even the picture being filled in by Dr. Williams was confusing. Now, two magma areas were showing where only one had shown before.

Esteben Balgos answered Rick's plea for an explanation. Over an excellent dinner of roast suckling pig and bananas steamed with lemon juice, the volcanologist took time to answer their questions.

"There is much we do not know about volcanoes," the Peruvian scientist began. "For example, we do not know exactly what causes magma to form.

Magma is, in simplest terms, molten rock. Some event takes place far below, where the earth's crust ends and the mantle begins, and the rock melts."

"How far below?" Rick asked.

"The distance varies. Under the ocean trenches, for example, the mantle may begin only four miles down. Under some of the mountainous land ma.s.ses it may be closer to forty miles."

Scotty whistled. "That's a whale of a distance. How can you tell how far down it is?"

"By the seismic traces from earthquakes, or from explosive shots like the ones we are shooting. When the shock waves have reached the zone between the earth's crust and the mantle, we see the results on our tracings."

"Is it really a sharp line?" Rick queried.

"Probably not. No one is sure yet. It may be a kind of transitional zone, from one kind of material to another, or it may be a distinct layer. We call it the Mohorovicic Discontinuity, after the Yugoslav scientist who discovered it by a.n.a.lysis of seismic tracings. At any rate, it is somewhat above this discontinuity that magma is formed. We don't know how."

"Then it rises?" Scotty asked.

"It forces its way up, by expansion. Sometimes the magma strikes water and there is an explosion--a steam explosion. But generally the magma rises through a fairly small channel. It forms a pool under the volcano.

The pool is actually a reservoir of molten rock. Generally it is shaped like a lens. The magma gathers. Eventually it forces its way to the surface, again through channels."

"What kind of channels?" Rick asked.

"It depends on the kind of volcano. Sometimes the channels are weaknesses in the whole surrounding earth structure, and the magma flows through cracks and emerges as sheets of lava. Sometimes there is a central channel through which the magma can rise."

"Which do we have?" Scotty wanted to know.

"Probably neither or perhaps both. There was once a central channel in El Viejo. It is closed now, and we do not know if it is weaker than the rest of the mountain. There is a weak fissure under the hot springs. So, El Viejo can vent either way."

Rick shook his head. He had learned enough of natural forces to know there are often no definite answers to questions, but this was critical.

"So the volcano could blow off on top or side, and we can't guess which?"

"That is correct. However, explosive action in a volcano usually comes when the magma meets enough water to create steam. Now, our closest magma front is still far below the floor of the surrounding ocean. You follow me? Good. When the magma rises to the level of the ocean floor, what do you think will happen?"

Rick could see the picture in his mind. He said slowly, "It will probably meet water. Plenty of it, from seepage of the ocean downward through cracks in the ocean floor. Maybe there are cracks like the one in the parking lot, caused by earthquakes."

"Precisely. And when the magma meets the water, then what?"

"The water turns to steam instantly." Scotty answered grimly. "The steam expands instantly--and boom!"

"Boom," Balgos agreed solemnly. "But how big a boom we do not know. It may blow the top off El Viejo. It may blow a gap along one of the cracks. We don't know."

Rick digested this information in silence. The picture was certainly not a cheerful one. "How far down are the magma fronts?" he asked.