ar that the mysterious hole-maker might still be lurking around.

Well, the evidence was all for it, as Gonzales had reminded us--that
cactus had been oozing.

We cruised at twenty thousand feet and thought it over.

Janus, whose only training was in photography, said, "Some kind of
omnivorous animal? Or bird? Eats rocks and everything?"

"I will not totally discount the notion of such an animal," Randolph
said. "But I will resist to the death the suggestion that it forages
with geometric precision."

After a while, Allenby said, "Land, Burton. By that 'canal.' Lots of
plant life--fauna, too. We'll do a little collecting."

Burton set us down feather-light at the very edge of the sprawling flat
expanse of vegetation, commenting that the scene reminded him of his
native Texas pear-flats.

We wandered in the chilly air, each of us except Burton pursuing his
specialty. Randolph relentlessly stalked another of the rabbity
creatures. Gonzales was carefully digging up plants and stowing them in
jars. Janus was busy with his cameras, recording every aspect of Mars
transferable to film. Allenby walked around, helping anybody who needed
it. An astronomer, he'd done half his work on the way to Mars and would
do the other half on the return trip. Burton lounged in the Sun, his
back against a ship's fin, and played chess with Allenby, who was
calling out his moves in a bull roar. I grubbed for rocks.

My search took me farther and farther away from the others--all I could
find around the 'canal' was gravel, and I wanted to chip at some big
stuff. I walked toward a long rise a half-mile or so away, beyond which
rose an enticing array of house-sized boulders.

As I moved out of earshot, I heard Randolph snarl, "Burton, _will_ you
stop yelling, 'Kt to B-2 and check?' Every time you open your yap, this
critter takes off on me."

Then I saw the groove.

* * * * *

It started right where the ground began to rise--a thin, shallow,
curve-bottomed groove in the dirt at my feet, about half an inch across,
running off straight toward higher ground.

With my eyes glued to it, I walked. The ground slowly rose. The groove
deepened, widened--now it was about three inches across, about one and a
half deep.

I walked on, holding my breath. Four inches wide. Two inches deep.

The ground rose some more. Four and three-eighths inches wide. I didn't
have to measure it--I _knew_.

Now, as the ground ros