What was Geoffrey famous book?

Please provide more context! There are many famous people named Geoffrey, and it's impossible to know which one you are referring to without more information.

For example, you could be thinking of:

* Geoffrey Chaucer, author of "The Canterbury Tales"

* Geoffrey of Monmouth, author of "Historia Regum Britanniae"

* Geoffrey Rush, a famous actor, who has starred in many films but hasn't written a book.

Please tell me more about the Geoffrey you are asking about!