Not sure if this qualifies as a bug, but I've been trying your Caves and Cliffs experimental and have unable to find much coal and iron.  I've sunk probably going on a thousand cubes of mine shaft and have found less than a hundred of each, mostly single pockets in a shaft., and not every shaft. I'm digging on Y12

It reminds me of the diamond shortage right after you launched C &C. If wasn't for surface caves and the occasional cavern I would be using stone tools and having to make charcoal to try and mine.

I realize I may of just gotten a really stinky spawn, but I thought you should be aware.