My latest fortress happens to also be my most successful one. I've lasted longer in the old 2d version, but I can't say I accomplished as much as I have in this fortress. Unfortunately the game crashed and I lost the last couple seasons of my 3 year old fortress.
Anyway, I've been trying to dig deeper, but my dwarves refuse to. I'm not really deep, yet. I'm in the fourth level of the igneous intrusive layer and the next layer seems to have more olivine (which indicates more gabro, an igneous intrusive layer rock). Of course, I have one level that has a combination of sedimentary and igneous intrusive rocks, so that next level might be a transition zone.
Is it a coincidence that my dwarves refuse to dig into the next geological layer or is there some other reason? I know it's not that there's other work. They've completed all other dig jobs and sit around idling until I designate something above that level. If it helps, the deepest level in which my dwarves have actually inhabited (sorta. . . it's my tombs) is six levels above the problem level.
EDIT: Here's my region:
[ January 01, 2008: Message edited by: Ostsol ]