One fun thing about the new york subways is that they do have fully formed stalactites growing from the ceiling. And thats cool, geologically, and visually, but its less cool when you're waiting for the train and a horrible wet germy sploop of concentrated yuck plops onto your head.
So there's stalactites, right, and you know how caves work so you must be thinking: Well, aren't there corresponding stalagmites growing out of the floor? No! Because enough people walk over every part of the floor consistently enough, they have no chance to build up, because they are constantly getting worn down. Instead what happens is a disgusting puddle of muck and minerals builds up, gets polished by footsteps, and then gets another layer of city goop distributed over and compressed down by feet again. What this results in most resembles a pile of snot, sadly.
