Ballard made the sign of comprehension. Here was one of the mysteries very naturally accounted for. The bulkhead and iron-bound door of the zirconium mine were, indeed, fortifications; but the enemy to be repulsed was nature—not man.
"And the electric signal service system in the upper canyon is a part of the defence for the mine?" he predicated.
"Yes. It has served on two or three occasions to give timely warning so that the miners could come up and seal the door in the bulkhead. But it has been a long time since a cloud-burst flood has risen high enough in the Elbow to threaten the mine."
Silence supervened; the silence of the flooding moonlight, the stark hills and the gently lapping waters. Ballard's brain was busy with the newly developed responsibilities. There was a little space for action, but what could be done? In all probability the newly completed dam was about to be subjected to the supreme test, violently and suddenly applied. The alternative was to open the spillway gate, using the cut-off tunnel as a sort of safety-valve when the coming flood water should reach the Elbow.
But there were an objection and an obstacle. Now that he knew the condition of the honeycombed tunnel, Ballard hesitated to make it the raceway for the tremendously augmented torrent. And for the obstacle there was a mechanical difficulty: with the weight of the deepening lake upon it, the stop-gate could be raised only by the power-screws; and the fires were out in the engine that must furnish the power.
The Kentuckian was afoot and alert when he said: "You know the probabilities better than any of us: how much time have we before these flood tides will come down?"
She had risen to stand with him, steadying herself by the hook of the derrick-fall. "I don't know," she began; and at that instant a great slice of the zirconium mine dump slid off and settled into the eddying depths with a splash.
"It is nothing but a few more cubic yards of the waste," he said, when she started and caught her breath with a little gasp.
"Not that—but the door!" she faltered, pointing across the chasm. "It was shut when we came out here—I am positive!"
The heavy, iron-studded door in the bulkhead was open now, at all events, as they could both plainly see; and presently she went on in a frightened whisper: "Look! there is something moving—this side of the door—among the loose timbers!"