Answer:
When underground in a cave, you may find cone-like limestone structures on the ceiling and the floor. On the ceiling are stalactites. (They hold on tite.). On the floor are stalagmites. Where they meet, the combined structure is called a column.
Formation of Stalactites and Stalagmites
Where limestone is present above a cave, it can be dissolved by water as calcium bicarbonate. When it drips down into a cave, it reverts to particles of calcium carbonate in the air. If the water carries to the floor of the cave, stalagmites (limestone pinnacles) are formed. If the calcium precipitates before it can drip, an "icicle" of limestone, a stalactite, hangs from the ceiling. Usually these forms are created simultaneously, and may merge to form columns or sheets of columns.
Unlike their icy counterparts, stalactites and stalagmites take hundreds to thousands of years to form, at an average of 5/1000ths of an inch (.13 mm) a year. A stalagmite in an Oregon cave has grown less than 1/4 of an inch since it was broken off 100 years ago!