Theory on Trolls, Olog-hai, and their [I]fear[/I].

After reading the essays on the origin of Orks in Morgoth's Ring (HoMe X), the origin of Trolls is left in doubt. First, we must remember that "Melkor could not 'create' living 'creatures' of independant wills" (HoMe X).
In a letter of 1954, Tolkien calls the Trolls "counterfeits", which is why they turn to stone, but immediately adds that anything that speaks must have a "soul". He also muses over whether they may have been humanoid animals twisted by Morgoth, but never reaches a conclusion. However, in HoMe XII, Tolkien states that (when discussing the Olog-hai) "there was no kinship from the beginning between the stone-trolls and the Orcs so that they might breed together". This would mean that they were definately corrupted not Men (and as HoMe X shows, Tolkien decided that Elves and Dwarves were too "resistant" to be turned into Orks).
Which leaves animals and counterfeits, and the matter of their speaking. However, in the Hobbit it says:

"…Trolls, as you probably know, must be underground before dawn, or they go back to the stuff of the mountains they are made of, and never move again."

Although in Letters Tolkien says that a few details were exagerrated or 'fairy-story-ised' by Bilbo, due to his small range of experience when it came to the Wide World, I think that unless the author was absolutely certain that Trolls were in fact made from stone, he would have simply said that they turned into stone and not mentioned that they were from it. Add to this the fact that there seems no good reason for beasts to turn into stone when Orks and Nazgul don't, and the only origin for Trolls seems to be that they were indeed counterfeits. But this still does not solve the matter of whether they posses a soul.
In HoMe X Tolkien toys with the idea of Orks not actually having souls, but merely reeling off "records" set in them by Morgoth, being full of hate. He discards this idea however, but could it not apply to Trolls? Tolkien mentions the example of Aule's mindless Dwarves, ans, after again saying how Morgoth dispersed his power among his agents:

"Aule...of course had no thought of dispersing his power. Only Eru can give love and independance."

[Italics are Tolkien's]. This would seem to say that if Morgoth put his power into these stones, that they could have 'minds' of their own: not proper minds, but a kind of 'artificial intelligance', enough to carry out their task of killing. It would also explain their lack of intelligence, though of course many things can explain that, the most obvious being that they are made out of stone, hardly renowned for its brains.
However, Tolkien later says (again in HoMe X) that such "'Puppets' would simply cease to move or 'live' at all, when not set in motion by the direct will of their maker." And yet we see that Trolls continue to live and act with minds of their own after Morgoth's defeat. Therefore, it seems that they must posses a fea, somehow.
Which brings me to my final theory: Could the Dark Powers 'transplant' a creature's fea into a new hroa? Certainly this happened in Elven reincarnation, although Tolkien states in the Athrabeth (HoMe X) that "The Valar are now given authority to reincarnate the fear of Elves who have died in hroar identical to those they have lost [becuase each fear remembers its old body, so if it is born anew its memories are so potent that its body becomes as that form. This effect that the fea has on the appearence of the hroa is very important, as Tolkien also says in HoMe that the fear of the Men Morgoth corrurpted to become Orks became so debased that it warped their hroar into a reflection of their debasement]". This summarises a debate between Manwe and Eru over what to do with houseless fear: Manwe asks Eru's authority to "meddle with Thy Children", as he does not wish to upset Eru, and Eru grants it, but adds that "The skills [of reincarnating fear] ye have already, if ye will take heed". Thus, so would Melkor, mightiest of the Ainur.
Tolkien also states in HoMe that each housless fea (dead person's soul) is summoned to the Halls of Mados - but that they can ignore those summons if they wish (or as the usual case, have been decieved by the Dark Powers). It is then stated that they are "Unbodied", because "Re-birth is a grace", and "does not lie in the power of any fea in itself". So those who refuse the Summons cannot be reincarnated because the Valar are not there to do it for them. Tolkien also makes it clear that refusing the Summons is "a sign of taint", and that the Unbodied have fallen under Evil's influence, and that "Some were enslaved by the Dark Lord and do his work still, though he himself is gone." Ghosts or poltergeists? Evil spirits at the least, capapble of possesion and killing:

"The wicked among them will take bodies, if they can, unlawfully...[the evil fea] may seek to eject the fea from its body...[or] seek to enslave its host and use both his will and his body for its own purposes. It is said that Sauron did these things, and taught his followers how to achieve them."

Thus Sauron taught his followers to reject the Summons, and then to linger and attempt to posses people and/or harm or kill them.
It seems clear therefore that if Morgoth (and maybe Sauron, as the most powerful Maia) could 'reincarnate', though they had no authority to. Maybe they were not aware of their powers, just as Manwe was not, but certainly they were aware of the power of the fear, and the "hungry Houseless['s]" burning desire for new bodies. Is it then a far stretch of the imagination to think that the Dark Powers could have taken fear of their followers and placed them into bodies of stone? Even if they could not do this with all fear, and I do not think that they could, as Tolkien frequently repeats how the fea cannot be forced to do anything against its will when unhoused, I think that it would have been possible for them to thus place fear into stone. And as the fear shapes its house, so the stone would twist into a grim reflection of these fear's debasement, but as the fear held memories of their old forms, would have 'flesh' and would appear to be a large humanoid. When sunlight hits the Troll, as they were created in the Great Darkness and so "cannot abide the sun", yet their bodies are not of flesh but of stone, it would make sense for them to revert to stone. And so when the Troll is slain, and the fea escapes it, it would thus also logically revert to its original stone.
But what about the Olog-hai? Appendix F of LotR states that "Unlike the older race of the Twilight they could endure the Sun, so long as the will of Sauron held sway over them." In HoMe X it is frequently stated that Morgoth dreams up his evil schemes, but it is Sauron, with his "cooler" head (at least before he imitated Morgoth's nihilistic madness), who carries out the ideas. Such was the case with the Orcs, and above it says that Sauron taught followers how to posses. Would it not therefore make sense that Sauron had at last by the Third Age perfected his technique of transeferring fear; that these Olog-hai and their fear could maintain their living forms in the sun as long as Sauron aided them? I think so.
I am obviously not saying that this is the only origin, or the 'correct' origin, of the Troll-races, but I do think that it is certainly an intriguing (and disturbing) possibility. Please share your thoughts on this.