There was a series of bumps, and the armor-tender, weightless on contragravity, shook as the handling-machine came aboard.

"You ever see any nuclear bombing, Miss Quinton?" the young man with the hairy legs asked, offering her his candybag.

"Only by telecast, back Solside," Paula Quinton replied, helping herself. "Test-shots at the Federation Navy proving-ground on Mars. I never even heard of nuclear bombs being used for mining till I came here, though."

"It'll be something to see," he promised. "These volcanoes have been dormant for, oh, maybe as long as a thousand years; there ought to be a pretty good head of gas down there. The 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.