a wide corridor that they followed, where the walls came
together high above their heads; he could hardly see where they met by
the light of Loah's torch. Now and then there were lateral passages,
but they were narrow, hardly more than cracks; and Rawson, looking
into them, nodded his head with satisfaction.

Occasionally his footsteps rang hollowly on the stone, and he knew
that the floor was thin between this and other caverns below. "What an
old honeycomb it is!" he exclaimed. "And we had it all figured as
being solid. The weight is all here, of course, but it's concentrated
in that red stuff down near the neutral zone. But anyway, Loah has
shown me just what I wanted."

He had gathered a handful of little fragments, and, keeping count of
his steps, had shifted a bit of rock to his left hand for every
hundred paces. By this he knew they must have gone five or six miles
when he reached the tunnel's high point. Many times it had widened.
Here, too, was a cave more than a hundred feet across.

From the farther side the tunnel continued, pitching sharply downward,
but Rawson did not explore farther. "I can seal that off with a
flame-thrower," he said. "I've seen how they use them." Then he took
Loah's light and looked with every evidence of approval at the rocky
walls and the roof that seemed heavy with dew.

He had wondered about the air, but he found that it seeped through
from that central shaft, although Loah told him that in some deeper
passages the air was bad. Here, although it was moving gently, it
seemed wet as if charged with moisture. Rawson, staring upward, felt a
drop strike him in the face, dripping from the rocks above.

"It's a gamble," he said, "just a gamble. But the stakes are worth
while. And now, Loah-San, we will return."

* * * * *

He made crude work with the flame-throwers at first but finally he got
the knack, and the mouth of the tunnel beyond the big room was sealed.
Then, with the help of Loah and some few of the others, he brought in
more and more weapons of the Reds. He was curious as to their
construction, but his curiosity had to go unsatisfied. They were only
cylinders, so far as he could see, cylinders a foot long and six
inches through, of some metal with the dull lustre of aluminum. But
they were sealed, and he dared not cut one open with another
flame-thrower for fear of what might come forth.

On the top of each cylinder a tube was connected t