'At the Earth's Core' is a novel of 1914 by Edgar Rice Burroughs. In 'At
the Earth's Core', David Innes and Parry Abner move in a metal
prospector into the Earth's crust and development into a world they
never imagined with Sun drooping in the heavens. Besides the cave people
and dinosaurs one of the most interesting idea is that time is man's
creation and without the Sun rising and settling one loses track of
time. This world is occupied by prehistoric animals as well as primitive
humans, intelligent gorillas and pterosaurs.