body again, and said 'rock,' and I
got up nerve enough to take a look myself.

"Tweel was right again. The creature was rock, and it didn't breathe!"

"How you know?" snapped Leroy, his black eyes blazing interest.

"Because I'm a chemist. The beast was made of silica! There must have
been pure silicon in the sand, and it lived on that. Get it? We, and
Tweel, and those plants out there, and even the biopods are _carbon_
life; this thing lived by a different set of chemical reactions. It was
silicon life!"

"_La vie silicieuse!_" shouted Leroy. "I have suspect, and now it is
proof! I must go see! _Il faut que je--_"

"All right! All right!" said Jarvis. "You can go see. Anyhow, there the
thing was, alive and yet not alive, moving every ten minutes, and then
only to remove a brick. Those bricks were its waste matter. See,
Frenchy? We're carbon, and our waste is carbon dioxide, and this thing
is silicon, and _its_ waste is silicon dioxide--silica. But silica is a
solid, hence the bricks. And it builds itself in, and when it is
covered, it moves over to a fresh place to start over. No wonder it
creaked! A living creature half a million years old!"

"How you know how old?" Leroy was frantic.

"We trailed its pyramids from the beginning, didn't we? If this weren't
the original pyramid builder, the series would have ended somewhere
before we found him, wouldn't it?--ended and started over with the small
ones. That's simple enough, isn't it?

"But he reproduces, or tries to. Before the third brick came out, there
was a little rustle and out popped a whole stream of those little
crystal balls. They're his spores, or eggs, or seeds--call 'em what you
want. They went bouncing by across Xanthus just as they'd bounced by us
back in the Mare Chronium. I've a hunch how they work, too--this is for
your information, Leroy. I think the crystal shell of silica is no more
than a protective covering, like an eggshell, and that the active
principle is the smell inside. It's some sort of gas that attacks
silicon, and if the shell is broken near a supply of that element, some
reaction starts that ultimately develops into a beast like that one."

"You should try!" exclaimed the little Frenchman. "We must break one to
see!"

"Yeah? Well, I did. I smashed a couple against the sand. Would you like
to come back in about ten thousand years to see if I planted some
pyramid monsters? You'd most likely be able to tell by that time!"
Jarvis