A stalagmite is a type of speleothem formed by the deposit of calcium carbonate which rises from the floor of a limestone cave due to the dripping of mineralized solutions. The corresponding formation on the ceiling above a stalagmite is known as a stalactite. Should both these formations grow together, meeting in the middle, the resultant formation is known as a column or pillar. The term "stalagmite" is derived from the Greek meaning that which drops; "stalactite," from the Greek meaning to fall in drops.
To remember which hangs from the ceiling (stalactite) and which comes up from the floor (stalagmite) think of: