Tolkien Prediction #10 That the discord introduced by Melkor in the Music of the Ainur would be described in terms of water.
“Then the discord of Melkor spread ever wider, and the melodies which had been heard before foundered in a sea of turbulent sound” (Silmarillion)
Note at that point I had not read the Silmarillion for about twenty years. I have only ever read it once..to my shame! But, after the rewrites of the last twenty years of his life, post TLoTR, I’m fairly certain that Tolkien incorporated into the Silmarillion the ideas and devices he fully developed in TLoTR.