's the sort of thing
the world is supposed to revolve about. I know, for I read it in my
geography."

The boys groaned. The suspicion of a smile played about the corners of
Professor Zepplin's mouth.

"You had better go back to school rather than be traveling with real
men," advised Ned.

"Isn't that an axiom, Professor?" called Stacy indignantly.

"It is not."

"Then what is one?"

"You are a living example of one yourself," was the whimsical reply.
Stacy pondered over the Professor's retort all the rest of that day. But
when noon came and passed and no stop was made for a noonday meal, the
fat boy began to grow restive.

"Don't we stop for something to eat?" he demanded.

"I should like to know where?" answered Tad.

"Isn't there a place wide enough for us, Tad?"

"There is not."

"But when are we going to find one?"

"You know as much about that as I do. Remember none of us ever has been
over this trail. For aught I know we may have to sleep standing up
to-night."

"Well, I reckon I'd just as soon fall off before dark as after. Anyhow,
I don't propose to sleep on this trail as it looks to me now--"

"Hark!"

Tad's voice was sharp and incisive. He was holding up one hand to impose
silence on his companions. Walter Perkins' face grew pale, the fat boy's
eyes were large and frightened. Professor Zepplin halted his pony
sharply and turning in his saddle glanced anxiously back toward his
charges.

"What is it?" stammered Rector.

"I don't know," answered Tad Butler. "It's something awful, whatever it
is."

"Have no fear, young men. I know what that sound is. There is no danger
here where we are, for--"

The Professor did not complete his sentence. The distant rumbling that
had at first attracted their attention suddenly merged into a deafening
roar, and the trail quivered under their feet. The ponies snorted and
threw up their heads, chafing at the bits.

"Hold fast to your horses!" shouted Tad. His voice was lost in the great
roar that now overwhelmed them, sending terror to the hearts of every
Pony Rider Boy on that narrow ledge of rock known as the Yakutat trail.

CHAPTER VI

CAUGHT IN A GIANT SLIDE

Tad knew the meaning of that rushing, roaring sound now. A few particles
chipped from the rocks far above them had struck him sharply in the
face. He knew that a landslide was sweeping down.

His first impulse was to urge his companions forward, but upon second
thought he realized