ry him through the open door. Two others went
ahead, the green jets of flame from their weapons lighting the
passage.

The system of communicating tunnels seemed at first only the vents and
blow-holes from some previous volcanic activity. And yet, at times
they gave place to more regular arrangement that plainly was
artificial. The air in them was pure, though odorous with a pungent
tang which Dean could not identify. Through some of the passages it
blew gently with uncomfortable warmth.

The guard of wild red figures hurried him along through a vast world
of caverns and winding passages which seemed one great mine. The
richness of it was amazing. Dean Rawson was a man, a human being,
facing death in some form which he could not yet know, and, so fast
had his wild experiences crowded in upon him, he seemed numbed to all
normal emotions; yet through it all the mind of the engineer was at
work, and Dean's eyes were flashing from side to side, trying to see
and understand the ever-changing panorama of a subterranean world.

* * * * *

Mole-men, both red and yellow, were everywhere. But it was apparent at
a glance that the yellow giants were a race of toilers--slaves, driven
by the reds.

Their great bodies glowed orange-colored with the reflected heat of
the blasts of flame used to melt the metals from their ores. Gold and
silver, other metals that Rawson could not distinguish in the half
light--the glow of the molten stuff came from every distant cave that
the passages opened up.

The sheer marvel of it overwhelmed him. His own danger, even the death
that waited for him, were forgotten.

A world within a world--and who knew how far it extended? Mole-men, by
scores and hundreds, the denizens of a great subterranean world, of
which his own world had been in ignorance. Here was civilization of a
sort, and now the barriers that had separated this world from the
world above had been broken down; the two were united. Suddenly there
came to Rawson's mind a flashing comprehension of a menace wild and
terrible that had come with the breaking of those barriers.

They were passing through a wider hall when the whistling chatter of
Dean's escort ceased. They were looking to one side where a cloud of
smoke had rolled from a slope beyond. One of the red figures
staggered, choking, from the cloud. Two yellow mole-men followed
closely after.

The red mole-man was unarmed; each yellow one had a f