going on in the direction
they had started after leaving the stranded airship. They followed a
half-defined path, and were rewarded by getting occasional glimpses on
bare ground of the odd tire marks.

Through a devious winding way, now hidden amid a lane of trees, and
again cutting across an open space, the path led. They saw the marks
often enough to make sure they were on the right trail, and in one
place they saw several different patches of the odd marks.

They went on perhaps half a mile more, when they came to a lonely road
and saw where the car had turned from that into the wood-lot, as Tom
called the place where his craft had settled down.

"Look!" cried the young inventor to Jackson. "They've been here more
than once, and have gone along the road in both directions. They seem
to have used this turning into the lot as a sort of stopping place."

This was plain enough from an examination of the marks in the sandy
soil of the road, which was one not often used. The automobile with the
queer, square marks on the tires had turned into the lot, coming and
going in both directions.

"This settles it!" cried Tom, when he finished making an examination.
"There's something farther back in this lot that we've got to see. This
auto has been coming and going, and we should have followed the tracks
the other way from the point where we first saw them, instead of coming
this way."

"Except that we've learned the place of departure," suggested Jackson.
"Evidently the wood-lot is a blind alley. The car goes in, but it can
come out only just at this point, or, at least, it does."

"That's right!" agreed Tom. "Now the thing to do is to follow our track
back to where we started. There must be some place where the car went
to--some headquarters, or meeting place with some one, farther back in
the lot. If we can only follow the trail back as well as we did coming,
we may find out something."

"Well, let's try, anyhow," suggested Jackson.

They had no difficulty in making their way back to the spot where they
had first seen the queer marks. But from then on their task was not so
easy. For sandy or bare patches of earth were not frequent, and they
had to depend on these to give them direction, for the road was
overgrown and not well defined.

Often they would search about for some time after leaving one patch of
the marks before they found another that would justify them in keeping
on.

"They have headquarters, or a