ket for it?" Scotty asked.

"Not as much as there was years ago," Zircon replied. "Pumice, as you
probably know, is volcanic rock. But not an ordinary one. It's a kind of
foamy lava honeycombed with gas bubbles. It's used as an abrasive.
Modern industrial products have replaced it in general use, but
apparently there's still enough demand so that the San Luzians are able
to export a little. Our firing station is about a mile from here."

Rick looked at the rough terrain. "Think we can get through?"

"Easily. According to the map, we have an unpaved road part of the way."

The unpaved road turned out to be a pair of wagon tracks. But at least
there were no trees in the way. Rick held on tight as Zircon shifted
into four-wheel drive and forged ahead.

The big scientist kept an eye on his odometer, or mileage counter, while
the boys watched for a clearing. It was slightly over a mile before they
found one, and Zircon pulled off the road to let Brad Connel and Ruiz go
by.

The jeep stopped as the two came abreast and the geologist called, "Want
to trade stations?"

"We like this one," Zircon replied with a grin.

"Don't blame you. I have another three miles through this stuff. Well,
so long."

The jeep started off and was soon lost as the path curved slightly.

Zircon looked at his watch. "Plenty of time, but we might as well get
ready."

A few minutes search disclosed a spot far enough away from the clearing
for safety, with no trees to be uprooted by the blast. Zircon took two
of the dynamite sticks Rick carried and one of the caps. He placed the
cap over one stick and used a special tool, like a jar opener, to crimp
it into place.

"This is the only really delicate part of the operation," he said. "If
the crimpers slip, they could set off the cap and the dynamite. So be
careful when you do it. Keep the crimpers low on the flange of the cap."

He found a rubber band in his pocket and used it to hold the two sticks
together. A coil of wire was produced next, and the connection made to
the dynamite cap. Zircon dug a shallow hole with his heel and put the
dynamite sticks in, then backed off unwinding wire as he went.

The detonator had been left in the jeep. Rick got it and carried it to
where Zircon waited with the pair of wires.

"How does this thing work?" Scotty asked.

"It's a dynamo," Zircon replied. "When the handle is pushed down it
engages gears that spin a flywheel, which operates the dynamo long