Narsilion is the "Song of the Sun and Moon", telling of their creation: After the Two Trees of Valinor were poisoned, Manwë commanded Yavanna and Nienna to attempt to heal the Trees. Yavanna sang and Nienna wept, but to little avail until at last Telperion bore one silver flower and Laurelin a single golden fruit. These Yavanna took and gave to Aulë. Manwë hallowed them and Aulë and his people made vessels to hold them and preserve their radiance. Varda then took the vessels and gave them the power to traverse the lower regions of Ilmen.
Of the song, only its name is known, briefly mentioned in The Silmarillion. Christopher Tolkien was unsure whether his father ever wrote any "Song of the Sun and Moon". While editing his father's works, he didn't find any excerpt with that title, and noted that if it ever existed, it had disappeared.