Mists of Dawn by Chad Oliver (1952)
Chad Oliver (1928-1993) was a Texas-raised science fiction fan who peppered the letter columns of the SF magazines when he was a teen, signing his missives "The Mad Lad." He went on to become an anthropologist and a a professor of anthropology at the University of Texas. Oliver's fiction often combined his two loves -- anthropology and the American Southwest -- producing a distinquished stream of novels and stories.
Mists of Dawn, his first novel was written when he was a doctoral student and rigorously used the latest anthropological knowledge to build a fast-paced, entertaining story about a youth trapped in the Neandethal world of 50,000 B.C. 17-year old Mark Nye is accidently thrown against the controls of his uncle's experimental space-time machine and finds himself in the distant past. Stalked by Neandethals, Mark finds refuge with a group of Cro-Magnons. The basic problems remains, though: How can Mark bridge the 52 millenia that separates him from his home?
George Kelly's recent 'Time Travel Week" on his (always excellent) blog brought back memories of some of the time travel novels I read as a kid. most notably those featured in the Winston Adventures in Science Fiction series -- books such as Evan Hunter's Find the Feathered Serpent and Danger: Dinosaurs, Poul Anderson's Vault of the Ages, as well as Mists of Dawn.
Mists of Dawn was exciting when I read it as a kid. It's still a darned good read.