Suddenly, when about three miles to the southwest of the camp, it seemed to pause hesitatingly; and then, as if all at once having descried the little group of tents, started swaying, tottering toward them. As it moved the disturbing roar continued to increase in volume.
Tad Butler heard it now.
He slipped from his tent and stood listening apprehensively.
"I think that means trouble," he said to himself. The hot, oppressive air felt like a blast from an open furnace door. "It's coming this way," he continued.
The lad bounded to the tent of the guide. Slipping inside he laid a hand on Parry's shoulder.
The guide was up like a flash.
"What is it?" he demanded sharply.
"It's I, Tad Butler. I think there is a bad storm coming——"
"I hear it," snapped Parry, springing from his blankets. He was out in the open in a twinkling, with Tad Butler close upon his heels.
For a moment the guide stood with head inclined, listening intently.