Thanks for all the info, Methos. The information on the colors is good - gives me an idea of the range I have to be creative. I had gathered some pictures myself, but it's very helpful to know what someone who has actually been there finds typical. Overall, the scenario is a blend of Verne's underworld with that described in some other Victorian literature such as Bulwar-Lytton's "Coming Race". There will even be a bit of Pellucidar at the center. So the caves will have streams and pools. Even some mushroom "forests". You sparked another idea with your mention of iron contaminants. I may include a partially embedded sprocket in one tile, or even some kind of a "lost device" resource. I'll pm you to let you know when I have some more work done & posted.