chunk: Tyler leaves the other survivors to seek and rescue Lys. A series of adventures ensues among various bands of near-human primitives, each representing a different stage of human advancement, as represented by their weaponry. Tyler rescues Lys from a group of Sto-lu ("hatchet men"), and later aids the escape of a woman of the Band-lu (spearmen) to the Kro-lu (bowmen). Lys is lost again, and chance discoveries of the graves of two men associated with Bradley’s expedition leaves Tyler in despair of that party’s fate. Unable to find his way back to Fort Dinosaur, he retreats to the barrier cliffs ringing Caspak in a vain hope of attracting rescue from some passing ship. Improbably reunited with Lys, he sets up house with her, completes the account of his adventures which he has been writing, and casts it out to sea in his thermos.