This is now the most straightforward way to acquire Ósanwe-kenta, a rare publication that has been on my to-get list.
Part of the answer to this question is:
As discussed in Vol. X, JRRT considered, then rejected a heliocentric creation for Middle Earth.
There is a large collection of writing which never became part of any major text dealing with the problems this caused.
And the related problems of Elvish aging. Certain characters have to be born in certain places and married in certain places, and if the Elvish aging rate is inappropriate for that then things fall apart.
There's a lot of ink spent answering this problem.
I heard a great cry, as if thousands of fanfic writers cried out simultaneously.
I'm too lazy to actually _write_ fanfic, but the fanfic idea I had is now 100x more canon-compatible.
If Tolkien had had access to a spreadsheet program, large parts of this book would never have been written.
Well, maybe not.
Elvish languages were not gendered grammatically, but did distinguish between animate and inanimate.
That is they did not distinguish between "he" and "she", but did between "he/she" and "it".
People may say that Elves in middle earth are psychic. This is not correct.
All thinking minds in middle earth may directly examine each other. The rise of language makes this a less practiced skill.
Anyone who does not wish to be read psychically may close their mind at will.
Middle earth is confirmed to have atoms and isotopes.
The Valar told the elves about them, but didn't explain what they are for, so elvish nuclear engineering is canon-compatible, but not implied by canon.
Middle earth is confirmed to contain evolution (though no word of natural selection) and possibly DNA.
Radioactive decay is also confirmed.
Middle Earth does not have a single tree of common descent, but multiple acts of special creation, each of which then speciates further.
Souls are directly created by Eru for all sentient races (elves, men, dwarves, ents) and sent directly from outside creation.
Felagund means badger and was given to him as a mocking nickname by his cousins.
I reached the bit about the dancing bears.
Rabbits and chickens were not native to Beleriand. (Another point for the European theory.)
Elves do not eat mushrooms, apparently.
I have reached the end of the main text.
The nature of this book is that large portions of it are false starts or abandoned approaches, which is why they were not included in the History.
Despite that, it gives a lovely insight into Tolkien's thought process.
The Appendix: just enough Catholic metaphysics that you can see it when Tolkien uses them.
The big question for this one is: how was the content here not published as part of _The History of Middle Earth_?
I thought Christopher Tolkien had published every grocery list his father wrote. Where did this stuff come from?
(I kid, but only slightly.)