ball of fire seemed to roll toward them along the earth at terrific
speed, growing larger and more lurid. And now, beside it, wafting from
it, like the tail to a comet, they could discern a swirling cloud, black
in the moonlight.

"It's a fire!" Bruce gasped through his mouthpiece.

"But what?--" began Barney.

Just at that moment he caught the faint white line that marked the shore
of Great Bear Lake. They were, then, nearing their destination. Tilting
the plane upward, that they might get a better panorama of the region,
and so direct their course, Barney gave the great engine more gas. On
they swept. Presently the outlines of bays and frozen streams, of scrub
forests and barren lands were plainly visible. A map under glass was just
before him. Brushing the frost from it, Barney examined it by the light
of a small electric bulb. Then he looked away at the fire which was now
clearly visible. His heart sank. The trading post was, indeed, a reality,
or had been. At the present moment it was a ball of fire.

"It's the trading post!" He barked to the Major.

"'Fraid so," grumbled the Major, hoarsely.

"And the gasoline for our return--"

"There it goes," sang Bruce, with a note of despair.

At that instant the whole ball of fire seemed to rise in air to burst
like some gigantic rocket. There was no question in the boys' minds but