This is a summary of The Magician's Nephew:
Digory and Polly discover a secret passage that links their houses, and are tricked into vanishing out of this world and into the World of Charn, where they wake up the evil Queen Jadis. There, they witness the creation of the Land of Narnia, as it is sung into being by the Great Lion, Aslan.
http://www.narnia.com/chronicles/books/index.htm Sounds to me alot like the creation story from the Silmarillion. Hmmm.