Back to the Stone Age is a novel by American writer Edgar Rice Burroughs, the fifth in his series set in the lost world of Pellucidar. It first appeared as a six-part serial in Argosy Weekly from January 9 to February 13, 1937, under the title Seven Worlds to Conquer. It was first published in book form in hardcover by Edgar Rice Burroughs, Inc. in September, 1937 under the present title, and has been reissued a number of times since by various publishers. Source: Wikipedia (en)