no time with such thoughts. They ran, all three, into
the dark tunnel.

Quade caught up with them quickly. Personal enmity was suspended
before this common peril. They could not run at full speed, for a
multitude of obstacles hindered them. Tortuous ridges of rock lay
directly across their path, formations that had been whipped in some
mad, eon-old convulsion and then, through the ages, remained frozen
into their present distortion; black pits gaped suddenly before them;
half-seen stalagmites, whose crystalline edges were razor-sharp, tore
through to their flesh. Haste was perilous where every moment they
might stumble into an unseen cleft and go pitching into awful depths
below. They were staking everything on the draft that blew steadily
in their faces; Phil told himself desperately that it must lead to
some opening--it must!

But what if the opening were a vertical, impassable tunnel? He would
not think of that....

Old David Guinness tired fast, and was already lagging in the rear
when Quade gasped hoarsely:

"Hurry! It's close behind!"

* * * * *

Surging rapidly at a constant distance behind them, it came on. It was
as fast as they were, and evidently untiring. It was in its own
element; obstacles meant nothing to it. It oozed over the jagged
ridges that took the humans precious moments to scramble past, and the
speed of its weird progress seemed to increase as theirs faltered. It
was a heartless mass driven inexorably by primal instinct towards the
food that lay ahead. The dim phosphorescent illumination tinged its
flabby tissues a weird white.

The passage they stumbled through narrowed. Long irregular spears of
stalactites hung from the unseen ceiling; others, the drippings of
ages, pronged up from the floor, shredding their clothes as they
jarred into them. One moment they were clambering up-hill, slipping on
the damp rock; the next they were sliding down into unprobed darkness,
reckless of where they would land. They were aware only that the
water-odorous draft was still in their faces, and the hungry mound of
flesh behind....

"I can't last much longer!" old Guinness's winded voice gasped. "Best
leave me behind. I--I might delay it!"

For answer, Phil went back, grabbed him by the arm and dragged his
tired body forward. He was snatching a glance behind to see how close
the monster was, when Sue's frightened voice reached him from ahead.

"There's a wall here, Phil