[0.42.01] I've embarked in what I thought was a single biome savage, completely flat, deadlands. However, my fortress was wiped out by undead ravens late spring. Save scumming...
Later, towards the end of the first winter, I built a watch post above the trade entrance tunnel (only entrance so far), with the recessed courtyard and original entrance floored over. Since I started building one level above the ground, I've gotten reports of rain of dwarven blood. The strange thing here is that I've gotten blood in the building (before the roof was put up) and on top of the building, but nothing on the ground anywhere, including the floor covering my courtyard?!
I know I have evil areas nearby, so the undead could possibly have migrated, but not the weather, presumably.
Do I have some kind of vertical biome separation shear? I recall encountering an oddity way back with 0.40.09(?) where I could farm properly at ground level, but not a couple of z levels directly above (on a muddied floor) close to the boundary to a mountain biome.
Edit: Looking in the air I can find invisible pools of dwarven blood 1, 2, and 3 levels above the ground. (Invisible = nothing seen graphically, but randomly moving the cursor about in the 'l'ook mode reveals them). The don't seem to fall either...