The Origin of the Diamond Dogs
From Equestripedia, the Archives of Equestria!
The Origin of the Diamond Dogs was a book written in either the Age of Heroes or Era of Princess Celestia, though given that it's not written in Olde Equestrianne, it's most likely the latter. The book was supposedly about the history of the Diamond Dogs race that live underground. The book itself was located in the Dark Magic wing of the Royal Library of Canterlot.
