no purpose. Their water was all but gone, and of their food only enough
remained for a day longer, though their life-torches still gave forth
plenty of vapor.

"Well, what's to be done?" asked Jack, as they sat about, looking
helplessly at one another.

"Might as well give up," suggested Mark bitterly.

"Give up? Not a bit of it!" cried Andy, as cheerfully as he could.
"Let's keep on. We'll find the projectile sooner or later."

So they kept on. It was while making their way between two great
mountain peaks that towered above their heads on either side, thousands
of feet up, making a sort of natural gateway, that Jack, who was in the
lead, cried out in astonishment at the sight that met his gaze when he
had passed the pinnacles.

"Look!" he shouted, pointing forward.

What he indicated was a great crater--larger and deeper than any they
had yet met with. It seemed a mile across, and, if gloom and darkness
were any indications, it was a hundred miles deep.

But it was not the size of the great hole in the ground, not its
fearful gloom, that attracted their attention. What did was a great
natural or artificial bridge of stone that was thrown across the middle
of it from edge to edge. A bridge of stone that spanned the abyss; a
roadway, fifty feet wide, which reached into some unknown land,
connecting it with the desolate country in which our friends had been