"Listen," exclaimed Bob breathlessly, "wasn't that a cry?"
Another moment and the sound came again.
"Elmer!" exclaimed the two air ship boys together.
The Cibola swung instantly at Alan's quick touch. Again the light flashed. Sand and rock and brush. The brilliant circle of light shot here and there, but the anxious watchers saw sign of neither friend nor foe. Then like a flash the level plain dropped into the sudden slope of a coulee and the darker shadow of water blotted out the glare of sand.
"The river," whispered Ned. "Now watch sharp."
As the light was blotted out this time Alan swung the wheel again. He knew instantly that they were on the wrong track, as they were going east and crossing the Chusco. Elmer and Buck would not cross the river. The camp was to be on the west side.
"Follow the river," ordered Ned quickly; "the west shore."
In order that the Cibola might be laid on the new course Ned threw on the light switch again. As he did so and the light flashed there was the sharp crack of a rifle and the light was gone.
"Turn her on," exclaimed Alan; "I want to get a line on the river bed."
Ned laughed. "I'll need a new bulb first. Some one down below turned it off."