If a stalactite and a stalagmite joined it would form a column.
Calcium Carbonate
stalagmite
Well, where limestone is on the ceiling of a cave, it drips. This forms stalactites. The stalactites drip the calcium bicarbonate in water to the floor of the cave into a plie. That forms...
The evaporation of mineral-laden groundwater, with the concurrent deposition of the formerly dissolved minerals.