That's a lot of hammers considering I didn't even chop anything that turn around that city.

http://forums.civfanatics.com/uploads/119660/Civ4ScreenShot0005.JPG

I've attached a save for bug confirmation, I have no idea what's going on there.

did you "produce" research, wealth or culture the turns before?

^^I can see a forge in the city... I suppose that the game is in Marathon ( turn 492 = 960 AD ) .... it is feasible that some chops in research, wealth or culture could have produced that overflow

did you "produce" research, wealth or culture the turns before?

Can't recall. How does that affect chopping? Why wouldn't the hammers immediately convert to whatever was being produced? Do they get stored somehow and only get used when you actually start to build something? That could explain the huge overflow from chopping but I haven't heard of that feature before.

So did I understand correctly? Is this how it works?

^^Yup... If you chop during wealth/research/culture, the chops will be stored until you start building something in the city ( they don't decay as well, a thing that can be useful for storing :hammers: for a not-yet-avaliable wonder). With the forge ( and possibly Organized religion ) it is feasible that a few chops could produce 268 :hammers: of chopping overflow while in wealth/research/culture.