I've got a city with an Old Growth Forest within its zone, in fact nearly abutting my buildings. I've already built two farms on fertile land, and have researched the Civilization tech needed to build lumbermills, but I can't get the "lumbermill" option to come up on my build display. What am I doing wrong, or is this a bug? I've also built a market, a palace, all the improvements you might expect at this level of development. Am I missing a precursor building requirement for a lumbermill?
Failing that, what else can I do to enhance my pathetic materials production?