Maxwell Journal was the journal of Ethan Maxwell, dating back to 1790. It recounted many of Ethan's encounters, including a section on killing Arcadius. However, the journal has since been destroyed by the aforementioned.
In You Made a Choice to Be Good, Dorian and Matt read some passages using a cardan grille (a cipher device used for code-breaking), an object found during the Time Capsule Day. Dorian manages to decrypt some of the passages but the messages are meaningless.