r start. This was done with a
will, and about two o'clock in the afternoon the outfit set off over
the stage road, headed for the Grand Canyon.

It was a happy party, full of song and jest and joy for that which was
before them. The way led through the Coconino Park. Some three miles
out they halted at the edge of a dry lake basin, in the centre of which
was a great gaping hole. The Professor pointed to it inquiringly.

"There was a lake here up to a few years ago," explained Jim. "Bottom
fell out and the water fell in. Ain't no bottom to it now at all"

"Then---then the water must have leaked out on the other side of the
world," stammered Chunky, his eyes big with wonder.

"I reckon it must have soused a heathen Chinee," answered Nance, with
a grin.

"Pity it didn't fall out the other way and souse a few guides, eh?"
questioned the fat boy, with a good-natured grimace at which Nance
laughed inwardly, his shaking whiskers being the only evidence of
any emotion whatever.

"Up there is Walnut Canyon," explained Jim. "Cliff dwellers lived up
there some time ago."

"Yes, we met some of them down south," nodded Chunky.

"You mean we saw where they once lived long, long ago," corrected
Professor Zepplin.

"Yes, we saw where they lived," agreed Stacy.

The way led on through a forest of pines, the trail underfoot being of
lava, as hard and smooth as a road could be. They were gradually
drawing nearer to Sunset Mountain. After a time they turned off to
the right, heading straight for the mountain.

Tad rode back to the Professor to find out where they were going.

"I thought you boys might like to explore the mountain. You will find
some things there well worth scientific consideration."

"Yes, sir; that will be fine."

"You know the mountain was once a great volcano."

"How long ago?" interrupted Stacy.

"A few million years or so."

"Mr. Nance must have been a boy in short trousers then," returned Stacy
quizzically. The guide's whiskers bristled and stood out straight.

The road by this time had lost its hardness. The ponies' hoofs sank
deep into the cinders, making progress slow for the party. They
managed to get to the base of the mountain, but the mustangs were
pretty well fagged. The animals were turned out for the night after
having been hobbled so that they could not stray far away.

"Now each of you will have to carry a pack," announced the guide.
"I will tell you what to take."