s of floating debris, against the back-wall of the
dam.

Knowing all the conditions, Ballard thought the masonry would never
withstand the hammer-blow impact of the wreck-laden billow. Yet it
stood, apparently undamaged, even after the splintered mass of wreckage,
tossed high on the crest of the wave, had leaped the coping course to
plunge thundering into the ravine below. The great wall was like some
massive fortification reared to endure such shocks; and Elsa, facing the
terrific spectacle beside her lover, like a reincarnation of one of the
battle-maidens, gave him his rightful meed of praise.

"You builded well--you and the others!" she cried. "It will not break!"

But even as she spoke, the forces that sap and destroy were at work.
There was a hoarse groaning from the underground caverns of the
zirconium mine--sounds as of a volcano in travail. The wave retreated
for a little space, and the white line of the coping showed bare and
unbroken in the moonlight. Silence, the deafening silence which follows
the thunderclap, succeeded to the clamour of the waters, and this in
turn gave place to a curious gurgling roar as of some gigantic vessel
emptying itself through an orifice in its bottom.

The white-haired king was nearest to the brink of peril. At the gurgling
roar he turned with arms outspread and swept the onlooking group,
augmented now by the men from Garou's cook camp, back and away from the
dam-head. Out of the torrent-worn pit in the lower ravine a great jet of
water was spurting intermittently, like the blood from a severed artery.

"That is the end!" groaned Ballard, turning away from the death grapple
between his work and the blind giant of the Boiling Water; and just then
Blacklock shouted, snatched, wrestled for an instant with a writhing
captive--and was left with a torn mackintosh in his hands for his only
trophy.

They all saw the Mexican when he slipped out of the rain-coat, eluded
Blacklock, and broke away, to dart across the chasm on the white pathway
of the dam's coping course. He was half-way over to the shore of escape
when his nerve failed. To the spouting fountain in the gulch below and
the sucking whirlpool in the Elbow above was added a second tidal wave
from the cloud-burst sources; a mere ripple compared with the first, but
yet great enough to make a maelstrom of the gurgling whirlpool, and to
send its crest of spray flying over the narrow causeway. When the
barrier was bared again th