Doctor Who: 13 Cool Details Revealed In Steven Moffat's Time Of Angels Commentary
6. There Was Almost A Subplot About The Writer Of The Weeping Angel Fact Book
Speaking of that base camp, this is where the Doctor examines a book that contains lots of information about the Weeping Angel species.
The episode never tells us where this book came from, and that's because Moffat chose to remove an entire subplot about its origins, simply because he was running out of story space.
He intended to reveal that the book had been written by one of Octavian's clerics. This cleric came on the mission we see in the episode, encountered an Angel, got zapped back in time, and then wrote the book, allowing the Doctor to access it in the future.
Moffat also states that he really wanted an Angel to zap someone back in time (something that never actually occurs in this episode, despite it being the Angels' most prominent power), which was another reason why he wanted to include this subplot.
But then again, he also wanted the Angels to be more "vicious" than they were in Blink, which explains all the neck-snapping we see in The Time Of Angels.