'sombre trees like dark clouds on the hillside'
Is amazingly evocative. I can see that clearly in my mind. It's perhaps no coincidence why so many people, after seeing the movies remarked at how similar the movies were to what they had imagined when reading the books -- the imagery was just that good.
I wonder how many books had Appendices before LOTR (fiction works obviously). I remember I couldn't wait to finish the main novel so I could investigate the Appendix!