Folded Rock Strata and Volcanic eruptions already on list.
Quicksand came up before (I think) as was dismissed as "not underground" (I think). However, I'm adding a new entry to the water section for new mud flows, which by nature can simulate quicksand.
I'll also amend the fossil entry to express potential uses for the fossils.
Bottomless maps were already in (Deeper and Deeper) but was already commented upon as highly unlikely by Toady. Magma aquifers comes close to the idea of a mantle (a volcanic rock layer that generates magma instead of water). I thought of making an explicit "bottom most layers" note, but decided not to. I think it would be freaking awesome to discover that I had 2 z levels
under the magma aquifer to turn into a noble "
dying living complex".
On a personal note:
In a recent thread that included some nice discussion on variations of items on this list:
Those are good ideas for the underground diversity megathread: http://www.bay12games.com/forum/index.php?topic=22308.0
Ohh my goodness... You know what... why don't I make a thread called "Dwarf Fortress Diversity thread" that way I can go on EVERYONE'S suggestions and tell them to put it there
Whoa... I have no Idea where that came from... especially since you didn't say "You should have posted it in the underground diversity thread" like some people have done...
Which somehow suggests
I go around telling people they
SHOULD have posted their ideas here in
MY thread.
And just 33 hours earlier in the 195,623th Magic Thread:
Yeah this is kinda the suggestion boards... Toady doesn't have to pick one person's suggestion and ignore all others...
Toady can pick and chose, as well as not pick and chose, elements out of suggestions that he likes or even dislikes but feel is nessisary.
We don't need another magic thread because we would just be repeating.
So in conclusion, thank you
Footkerchief for very politely advertising our great endeavor.