heir tunneling.

The Quabos against the Zyobites! Fish against man! Two diametrically
opposed species of life in a struggle to the death! Which of us would
survive?

* * * * *

The hour of the struggle approached. Every soul in Zyobor moved in a
daze, with strained face and fear haunted eyes. Their proficiency in
mental telepathy was a curse to them now: every one carried constantly,
transmitted from the brains of the servant-fish outposts, a thought
picture of that outer cavern in the murky depths of which writhed the
thousands of crowding Quabos. Each mind in Zyobor was in continual
torment.

Spared that trouble, at least, Stanley and the Professor and I walked
down to the fortification we had so hastily contrived. It was finished.
And none too soon: the vibration indicator in the palace vault told us
that only two feet of rock separated us from the burrowing monsters!

The Professor's scheme had been to cut a long slot down through the rock
floor of the city to the roof of the vast, mysterious body of water
below.

This slot was placed directly in front of the spot in the city wall
where the Quabos were about to emerge. As they forced through the last
shell of rock, the deluge of water, instead of drowning the city, was
supposed to drain down the oblong vent. Any Quabos that were too near
the tunnel entrance would be swept down too.

* * * * *

In silence we approached the edge of the great trough and stared down.

There was a stratum of black granite, fortunately only about thirty feet
thick at this point, and then--the depths! A low roar reached our ears
from far, far beneath us. A steady blast of ice cold air fanned up
against us.

The Professor threw down a large fragment of rock. Seconds elapsed and
we heard no splash. The unseen surface was too far below for the noise
of the rock's fall to carry on up to us.

"The mystery of this ball of earth on which we live!" murmured the
Professor. "Here is this enormous underground body of water. We are far
below sea level. Where, then, is it flowing? What does it empty into?
Can it be that our planet is honeycombed with such hollows as this we
are in? And is each inhabited by some form of life?"

He sighed and shook his head.

"The thought is too big! For, if that were true, wouldn't the seas be
drained from the surface of the earth should an accidental passage be
formed from the ocean bed down