A fascinating look at some of the influence on Middle Earth.
I'm particularly fond of the portion where he discusses how philology works to trace words, and how a hapax legomenon in Anglo-Saxon can have its meaning eludicated by tracing what would be the equivalent word in German, and discovering it had something to do with sworn oaths, and so probably means "sworn band."
But it has other interesting stuff: the contrasting of hobbit views vs. dwarven in The Hobbit. The double level of fate vs chance in his works. I think he doesn't quite understand Boethius's views on evil: he quotes him on how all fortune is unquestionably good, but uses it to describe evil as merely privation. But evil fortune is what happens to you (or doesn't, if you accept Boethius's view). It does not necessarily mean that you can't do evil, and so it contrasts less with Manichaeism that he seems to think. Tolkien's massive revisions and how so many things that seem to be the heart of the stories they appeared in were so often late additions.