Back to the Stone Age the fifth in the Edgar Rice Burroughs Pellucidar series. It recounts the adventures of Lieutenant von Horst, a member of the original crew that sailed to Pellucidar with Jason Gridley and Tarzan. He ends up wandering alone among the Stone Age people, huge reptiles and animals that have been extinct on the serface for thousands of years. Edgar Rice Burroughs was an American author, best known for his creation of the jungle hero Tarzan, Lost worlds and the heroic Mars adventurer John Carter.