Edgar Rice Burroughs 
The Eternal Savage 

While visiting Tarzan in his African jungle home, an American girl falls into the most astonishing science-fiction adventure of all. By a quirk in Time, a white-skinned savage from the Stone Age is thrust forward to modern days long enough to meet her and bring her back to his own world of cave people, saber-tooth tigers, and prehistorical wilderness! THE ETERNAL SAVAGE is the story of Nu of the Niocene and Victoria Custer of Nebraska, U.S.A. – two human beings pitted against the world of the primeval past.