When opened one or more old instructional scrolls or Tattered Map's may fall out. After the old instructional scrolls have been removed the journal still remains in the players inventory, but attempts at reading it will return the message "The book contained nothing of note".
In other instances, the book will reveal a small journal entry from people who were on the island before you. These entries can contain story lore or hints about the game. Sadly, if the book contains these small entries there are usually no scrolls inside the book when read. Happily, you can tuck the book away in a chest for some light reading later on in the game.