Update of what i've finished so far.
Imperialjester wrote:that would be cool to make the grass grow.
as far as i can tell it shouldn't be too hard to implement, just need to do some checks to see which tile is on top, and if it is when exposed ie the tile above is destroyed it checks if ontop and if it is it'll trigger a timed event on activation it'd just swap the tile graphic, i'd write an example in code but i suck, and i'm not sure how easy it is to add to your current system, but anyway hope one of you guys can, i adjusted the tiles just in case, i'll probably add a few more stones.
Btw have you guys even thought about trees yet? You going to scatter pre defined trees during generation, or generate trees with l-forms or some algorithm. The tree trunk tiles are seamless so you can generate wide trees ie. 2 tiles wide, also can you just walk past trees? It'd be painful if every tree had to be chopped down to explore the terrain