There's this from
The Silmarillion:
"But of those unhappy ones who were ensnared by Melkor little is known for a certainty. For who of the living has descended into the pits of Utumno, or has explored the darkness of the counsels of Melkor?"
I'd quote more
but someone's put a line through the following passage in my book
I don't think it need be destroyed.
"But it is known that Melkor had become aware of the Quendi before the Valar began their war against him, and the joy of the Elves in Middle-earth had already been darkened by shadows of fear. Dreadful shapes had begun to haunt the borders of their dwellings, and some of their people vanished into the darkness and were heard of no more."
"Some of these things may have been phantoms and delusions; but some were, no doubt, shapes taken by the servants of Melkor, mocking and degrading the very forms of the Children. For Melkor had in his service great numbers of the Maiar, who had the power, as had their Master, of taking visible and tangible shape in Arda."
This hails from Appendix C to
Tolkien's
Quendi And Eldar, part of which leads Tolkien to write
"
Orc text X", wherein it's said that the idea of the main "stock" [of Orcs] being
Men:
" . . . accords with all that is known of Melkor, and of the nature and behaviour of orcs"
I broke the second passage above for easier reading here, but anyway, it's from the "intro" to
Myths Transformed text 10,
Morgoth's Ring, and thus not repeated in Appendix C to
Quendi And Eldar, published in
The War of the Jewels.
🐾