e volcanoes we shot three
months ago yielded a fine flow of lava with all sorts of
metals--nickel, beryllium, vanadium, chromium, iridium, as well as
copper and iron."

"What sort of gas were you speaking about?" she asked.

"Hydrogen. That's what's going to make the fireworks; it combines
explosively with fluorine. The hydrogen-fluorine combination is what
passes for combustion here: the result is hydrofluoric acid, the local
equivalent of water. The subsurface hydrogen is produced when the acid
filters down through the rock, combines with pure metals underneath."

The door at the rear of the control-cabin opened, and Juan Murillo,
the seismologist, entered, followed by an assistant, who was not
human. He was a biped, vaguely humanoid, but he had four arms and a
face like a lizard's, and, except for some equipment on belt, he was
entirely naked.

He spoke rapidly to Murillo, in a squeaking jabber. Murillo turned.

"Yes, if you wish, Gorkrink," he said, in Lingua Terra. Then he turned
back to Gomes as the Ullran sat down in a chair by the door.

"Well, she's all yours, Lourenco; shoot the works."

Gomes stabbed the radio-detonator button in front of him.

* * * * *

Out on the rolling skyline, fifty miles away, a lancelike ray of
blue-white light shot up into the gathering dusk--a clump of five
rays, really, from five deep shafts in an irregular pentagon half a
mile across, blended into one by the distance. An instant later, there
was a blinding flash, like sheet-lightning, and a huge ball of
varicolored fire belched upward, leaving a series of smoke-rings to
float more slowly after it. The fireball flattened, then spread to
form the mushroom-head of a column of incandescent gas that mounted to
overtake it, engorging the smoke-rings as it rose, twisting, writhing,
changing shape, turning to dark smoke in one moment and belching flame
and crackling with lightning the next.

"In about half an hour," the large young man told Paula Quinton, "the
real fireworks should be starting. What's coming up now is just small
debris from the nuclear blast. When the shock-waves get down far
enough to crack things open, the gas'll come up, and then steam and
ash, and then magma."

"Well, even this was worth staying over for," the girl said, watching
the screen.

"You going on to Ullr on the _City of Canberra_?" Lourenco Gomes
asked. "I wish I were; I have to stay over and make another shot, i