I don't know about written. I'd believed it was assembled by the two of them, out of the many many layers of drafts and versions of myth that Tolkien spent forever writing and re-writing.

To me it reads much like, oh, _Bullfinch's Mythology_ or something like that. It took me a while to appreciate, but it's definitely grown on me.

(I used to read the first couple of sections to relax and go to sleep, so don't be surprised if they aren't really exciting. => )