Ballard's square jaw was out-thrust. "We did not build for any such brutal tests as this," he muttered. "Another surge like that----"
"It is coming!" cried Elsa. "The power dam in the upper canyon is gone!" and the sharer of the single Cantrell Christian name shrieked and took shelter under Bigelow's arm.
Far up the moon-silvered expanse of the lake a black line was advancing at railway speed. It was like the ominous flattening of the sea before a hurricane; but the chief terror of it lay in the peaceful surroundings. No cloud flecked the sky; no breath of air was stirring; the calm of the matchless summer night was unbroken, save by the surf-like murmur of the great wave as it rose high and still higher in the narrowing raceway. Instinctively Ballard put his arm about Elsa and drew her back from the cliff's edge. There could be no chance of danger for the group looking on from the top of the high mesa; yet the commanding roar of the menace was irresistible.
When the wave entered the wedge-shaped upper end of the Elbow it was a foam-crested wall ten feet high, advancing with the black-arched front of a tidal billow, mighty, terrifying, the cold breath of it blowing like a chill wind from the underworld upon the group of watchers. In its onrush the remains of the mine dump melted and vanished, and the heavy bulkhead timbering at the mouth of the workings was torn away, to be hurled, with other tons of floating débris, 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.