Edgar Rice Burroughs

Tarzan at the Earth's Core is a novel written by Edgar Rice Burroughs, published in 1930. the thirteenth in his series of books about the title character Tarzan and the fourth in his series set in the interior world of Pellucidar.

Tarzan the Invincible is a novel written by Edgar Rice Burroughs, the fourteenth in his series of books about the title character Tarzan. The novel was originally serialized in the magazine Blue Book from October, 1930 through April, 1931 as "Tarzan, Guard of the Jungle."