"No, no ghosts," laughed Mr. Wilder, "just the _ignis fatuus_, or
will-o'-the-wisps. All cowboys are very superstitious, you must
remember. The land round the pool is swampy and at night you can
sometimes see the lights dancing about. I suppose some one saw
them, and, finding no person there, immediately decided the pool
was a gathering place for witches."

"Pete says it's the bodies of the men who have died of thirst on
the plains searching for water," declared Horace in an awed tone.

"That's an ingenious explanation, but it is not the truth, my boy.
The lights are caused by certain gases that come from the marshy
ground and glow when the atmosphere is in a certain condition.
Over in Scotland, on the peat bogs, they call them 'friars'
lanterns.'"

"My, but I'd like to see one," sighed Tom.

"Then I'm afraid you'll be obliged to camp by the pool. You might
go there a hundred nights and never see a sign of one," returned
the ranchman. And then, as the shadows cast by the mountains were
reaching farther and farther out onto the prairie, he thought it
best to turn the minds of the boys into other channels.

"Shall we camp in the open or would you rather push on to the
foothills?" he asked. "It'll be dark by the time we get there."

"I vote to keep going," answered Larry.