L-shaped valley, surrounded by low hills.

"That's the most likely place, outside of the twilight zone, for life to
be found," remarked the doctor. "Neither mountainous nor dead level."

He added: "The spectroscope has plainly shown that there's water vapor
in what little air there is. Must be precious little. If the air was as
humid as the earth's, we couldn't see the surface at all from this
height."

The inviting-looking valley was now less than a hundred miles below.
Inviting, however, only in outline; in color it was a grayish buff,
scorched and forbidding. The hills were yellower, and an alkali white on
their summits.

"Do either of you fellows see anything GREEN?" demanded the engineer, a
little later. They were silent; each had noticed long before, that not
even near the poles was there the slightest sign of vegetation.

"No chance unless there's foliage," muttered the doctor, half to
himself. The builder asked what he meant. He explained: "So far as we
know, all animal life depends upon vegetation for its oxygen. Not only
the oxygen in the air, but that stored in the plants which animals eat.
Unless there's greenery--"

He paused at a low exclamation from Smith. The engineer's eyes were
fixed, in wonder and excitement, upon that part of the valley which lay
at the joint of the "L" below them. It was perhaps six miles across; and
all over the comparatively smooth surface jutted dark projections.
Viewed through the glasses, they had a regular, uniform appearance.