the cold crust was churned into the hot interior, of course it melted
and expanded, and that caused more volcanoes, and so on in a vicious
circle, till finally, by the end of the Formative Era, so called, the
rock that contained more heavy minerals sank to the lower levels, while
the lighter ones rose as granite."

"Gee!" said Ted, "I'd have called granite heavy."

"Not so heavy as the specimens of basic rock we'll find. Well, in this
Formative Era our atmosphere, and the hydrosphere or oceanic areas were
being formed, along with the granite continents. But while we are on the
subject, I hope you boys will some day see The Valley of Ten Thousand
Smokes, in Alaska, where the earth is still boiling so close to the
surface that you have to watch your step or you'll break through into----"

"The Hot Place?" laughed Pedro.

"Literally, yes."

"Oh, tell us about that!"

"Some time!--The interior of the earth is still hot, but the rock crust
allows very little of it to rise to the surface. After the Formative Era
came the Archeozoic Era, when life began in the form of amoebas or some
simple form of protoplasm. For with the formation of the gases of the
earth mass into an envelope of air, to moderate the sun's warmth by day
and retain some of it by night,--life became possible."

"But where did those first creatures come from?" Ted could not restrain
himself from asking.

"According to one theory, the first germs of life flew here from some
other planet, and not necessarily one of those revolving around our own
sun, for space is full of suns and planetary systems. But that theory can
neither be proved nor disproved. When I was a student, Osborn's theory
was the latest. That was in 1916. Without going into it too deeply, it
had to do with the electric energy of the chemical elements that compose
protoplasm, and these always had been latent in the earth mass."

"Then they must have been latent in the sun, too," marveled Ted. "And in
other suns and their planets too."

"Very likely," assented the Geological Survey man. "Now of course the
ocean waters collected in the depressed areas over the heavier rock
bottoms, the basalt. You remember just after we lost the burro we were on
a basalt formation----"

"Then that was formerly a part of the ocean floor?" asked Ted.

"Either that or volcanic lava."

"But how did it----"

"Just a minute. Of course land masses have gone down as well as up, but
the general trend has be