This from Mark Shea's website. Regardless of what you think of source criticism (I think Mark's poking a little fun), it's excellently done and a good read!
Hilarious! What makes it extremely funny is Tolkien's "conceit" that he is deriving the stories in The Hobbit and The Lord of the Rings from "The Red Book of Westmarch" -- originally written by Bilbo and Frodo, with emendations by Sam, and preserved by Sam's daughter's descendants who became the Wardens of Westmarch. And, of course, the material in The Silmarillion is supposedly derived from the work of Rumil, Pengolod, and other Elvish chroniclers and bards.
I personally take a fairly conservative view towards source criticism -- there is definitely something to it, but the multiplication of hypothetical documents and traditions otherwise not preserved is probably erroneous.