"That should be a great book," she said simply. "Some day let me
see THAT."

"The third detaches for study one small planet of that system--our
earth--and reviews our latest knowledge of that: as to how it has
been evolved into its present stage of existence through other
stages requiring unknown millions and millions and millions of
years. Once I thought it was created in six days. So it is written.
Do you believe that? "

There was silence.

"What is the next book?" she asked.

"The fourth," said David, with a twinkle in his eye at her refusal
to answer his question, "takes up the history of the earth's
surface--its crust--the layers of this--as one might study the skin
of an apple as large as the globe. In the course of an almost
infinite time, as we measure things, it discovers the appearance of
Life on this crust, and then tries to follow the progress of Life
from the lowest forms upward, always upward, to Man: another time
infinitely vast, according to our standards."

He looked over for some comment but she made none, and he
continued, his interest deepening, his face kindling:--

"The fifth takes up the subject of Man, as a single one of the
myriads of forms of Life that have grown on the earth's crust, and
gives the best of what we know of him viewed as a species of
animal. Does this tire you? "