the knots of denser matter
on the two-armed luminous spiral which began circling the sun. There were
smaller particles which were attracted to the earth by earth gravity and
which increased the size of the earth till it was far larger than it is
now. Ever since, the earth has been shrinking periodically, and when it
shrinks, its surface becomes wrinkled, and these wrinkles we call
mountain ranges."

"Of course," interpolated Ace, shining eyed, "the crust of the earth got
cooled, while the inside was still a mass of molten metal and gas, which
kept boiling over on to the crust,--couldn't you say, Mr. Norris?"

"You've got the idea."

"I s'pose that's _the hot place!_" chuckled the old man.

"Probably where they got the idea. In time the metals and heavier
substances sank, while the lighter ones rose as granite rocks, till there
was an outer shell miles thick.

"The Valley of Ten Thousand Smokes, in Alaska, is a volcanic region where
the ground is hot and breaks through with one even now,--I was there
several years ago,--but generally speaking, this earth has a crust 150
miles thick.

"As I was saying, the continents are built of the lighter granite,
chiefly, while the oceans lie on the heavier basalt."

"But I thought you said we were on a chunk of basalt now," said Ted.

"We are. You know the Pacific has flowed where now you see these peaks,
as the high lands have been worn down between successive upbuildings."

"But--where did the water in the ocean come from in the first place?"
marveled the old prospector.

"Out of the earth," smiled Norris. "Up through hot springs, geysers and
volcanoes. The water vapor was always here, you know,--mixed with the
molten rock and gases."

"I swan!" ejaculated the old guide. "I thought I knew something about
rocks, but--this beats anything in my kid's fairy books."

"You bet!" Ace agreed. "You just wait till you hear----"

"I expect we'd better start on now," Norris rose. "Do you chaps realize
what a predicament we are in?" and shading his eyes with a lowered hat
brim, he peered off across the hummocky granite slopes, which shone
mirror-like in places under the noon-day sun.

A moving speck in the sky to the North drew an exclamation from him. In
another moment a sound that increased to a hum like that of a giant
motor-boat descended from the skies, and the speck disclosed itself as a
mammoth aeroplane.

"Signal them!" cried Norris. "What can we signal them with? Get