Grosset & Dunlap - Pellucidar Series
J. Allen St. John illustration for Pellucidar, first edition 1918 - The
first of several sequels to
At the Earth's Core was Pellucidar
serialized in All-Story beginning May 1, 1915, not having book
publication until 1923 from A. C. McClurg. Besides the dust
wrapper, St John provided four sepia plates within.
While not published as often as the Martian or Tarzan stories,
the Pellucidar series has remained popular even though no one
today believes that such a hollow-earth is even possible.  The
first book in the series,
At the Earth's Core, was begun in 1913.  
The last book in the series,
Savage Pellucidar, would be
published posthumously fifty years later in 1963.
At the Earth's Core - Version 2  G&D c. 1924  - $10.99
AT THE EARTH'S CORE - G&D - c.1932 -  $10.99
Tarzan at the Earth's Core - G&D c. 1937 - $11.99
Edgar Rice Burroughs circa 1925.
(RIGHT) Bradbury has made this hyperbolic statement (right
caption in picture) many times in many forums, but the most
succinct and explanatory version is this excerpt from Sam
Weller's recently published book,
Listen To The Echoes: The Ray
Bradbury Interviews,
Bradbury talks about Burroughs, creator of
Tarzan. . .

"I love to say it because it upsets everyone terribly—Burroughs
is probably the most influential writer in the entire history of the
world," . . .

"By giving romance and adventure to a whole generation of
boys, Burroughs caused them to go out and decide to become
special. That's what we have to do for everyone, give the gift of
life with our books. Say to a girl or boy at age ten: Hey, life is fun!
Grow tall! I've talked to more biochemists and more astronomers
and technologists in various fields, who, when they were ten
years old, fell in love with John Carter and Tarzan and decided to
become something romantic. Burroughs put us on the moon. All
the technologists read Burroughs."
Tanar of Pellucidar  - G&D C. 1931 - $11.99
Pellucidar - G&D edition c. 1929 -  $10.99
PELLUCIDAR - G&D c. 1926  V2 -  $10.99
At the Earth's Core - antiqued G&D c.1924  - $10.99