A small group of intellectuals from a primitive culture of modified monkey-like humans are banished from the treetops for heresy. In their exile on the ground they have to adapt to vastly different circumstances, fight monsters resembling dinosaurs, and finally happen upon the godly giants, whose existence they had questioned.(Goodreads)

James Benjamin Blish (23 May 1921 30 July 1975) was an American science fiction and fantasy writer. He is best known for his Cities in Flight novels, and his series of Star Trek novelizations written with his wife, J. A. Lawrence. He is credited with creating the term gas giant to refer to large planetary bodies. Blish was a member of the Futurians. His first published stories appeared in Super Science Stories and Amazing Stories. (Wikipedia)