This is an incredibly late reply, and probably has been answered by now. But there are a couple ways that I can think of off the top of my head. Depending on how you are storing your map data you can check the spots above and below in a check before falling or going up another spot. You could also have your sprites have a constant spot that is either taken or not, depending if it is a "solid" block or not that you check. Same concept though. Anyways...ya.
