The Canon

[Birdland]

When The Hobbit was being written Tolkien wasn't sure that he wanted it to be a part of his mythologies, and so it includes much that otherwise shouldn't be in Middle-earth, such as giants in the Misty Mountains throwing rocks down the mountainside...

If one of the laity can pipe up here, I'm still not convinced that Tolkien didn't make a veiled reference to the Stone Giants in LoTR as well.