Subway Stalactite 

n. A build up of organic material on the ceiling of an underground subway composed mostly of run off from broken or corroded sewer carrying pipes. It's generally black, white, or brown in color with spotting of one or more of the other colors. It resembles a underwater volcanic plume of carbonic material hanging in cave-like stalactite formations. Often beneath subway stalactite there is also subway stalagmite, with different properties than the supplementary subway stalactite.

Subway Stalactite may be a black, brown or white deposit of sewage or run-off forming plume-like organic spikes.

Subway Stalactite by Srztanjur October 5, 2009

Subway Stalagmite

n. Contrary to subway stalactite, subway stalagmite does not form on the ceiling. Subway stalagmite is a deposit left by dripping sewer water or run-off that comes from the stalactite deposits on subway ceilings. Usually it is a lighter color, though it ranges from white to brown, and gives off a foul odor. This can be attributed to the fact that it’s on the floor, below your nose, where air can circulate up to your nose. These are generally flat, and do not develop as tall or as quickly as subway stalactite.

A white to brown flat deposit below a dripping sewer pipe that gives off a foul odor can be considered subway stalagmite.

Subway Stalagmite by Srztanjur October 5, 2009