William Morris wrote a number of early fantasy (a generation before Tolkien's Lord Of The Rings) that are characterized by a rich, archaic prose. His books are heavily influenced by medieval romances, and fall much closer to such than to the modern post-Tolkien fantasy (or the swords-and-sorcery genre that dominated the mid-20th century). The Roots of the Mountains takes place in an early north-European setting - reminiscent of Viking Scandinavia, or pre-Christian Britain or Germany. As the subtitle of this edition implies, this book kind of reminds one of the human parts of the Lord of the Rings (maybe a Rohan without elves, hobbits, or orcs involved) - indeed, Tolkien admitted Morris as an influence.
The language is a little difficult, although therein lies much of Morris's charm - unlike modern fantasy authors (and, worse, Sci-Fi channel programs), Morris does not use modern language and "feel" in his fantasy, but creates a medieval/fantasy atmosphere with his very choice of words (using many words that went out of fashion with Chaucer).
The story itself is an engaging adventure involving love, battle, and a more pastoral setting of people who live closer to the land than most of us do today.