Det här låter som Hawksbill Station av Robert Silverberg. Det är en roman från 1970 där politiska fångar skickas till prekambianska perioden via en envägs resebyrå.
Hawksbill Station is a penal colony in the pre-Cambrian era created by the authoritarian United States government, using time travel as a means to exile rebels and political dissidents into the past. The colony houses only male exiles (a female settlement supposedly exists later in the Silurian era), who are sent there as a "humane" alternative to execution. The machine only works one way, so the prisoners are hopelessly marooned in the past.