In The Shaping of Middle-earth the gradual transition from the "primitive" legendarium of The Book of Lost Tales to what would become The Silmarillion is described, and it contains a text which could be seen as the first "Silmarillion": the "Sketch of the Mythology".Three other parts are the Ambarkanta or "Shape of the World", a collection of maps and diagrams of the world described by Tolkien; and the Annals of Valinor and Beleriand, chronological works which started out as timelines but gradually turned into full narratives.
If you like this book please peruse the rest of my listings asI have a variety of similar items.