Excerpt from the book's "Introduction from the Encyclopedia of Science Fiction". "Burrough's third major series, the Pellucidar novels, takes its inspiration from the early nineteenth-century Hollow-Earth theory espoused by John Cleves Symmes and first dramatized by the pseudonymous Adam Seaborn as 'Symzonia' (1820). To modern eyes, this may well be the most congenial of Burrough's locales: a secret world without time, where Dinosaurs and beast-men, hidden in their mazes and vast canyons, roam inside our planet. It is perhaps the perfect setting for a Planetary Romance. The first three volumes, here presented, are 'At the Earth's Core' (1922), 'Pellucidar' (1923) and 'Tanar of Pellucidar' (1930); they capture the essence of the concept."