Stalagmites are formations that appear on the floor of a cave.  The groundwater seeping into a cave chamber contains carbon dioxide which is absorbed from the atmosphere or the soil.  The carbon dioxide will unite with the limestone to form the calcium which also be dissolved and held in the water through the cave.  When the water carrying the calcium evaporates, it releases the carbon dioxide and the remaining molecules are usually deposited as the crystals of calcium.  This great formation of the stalagmites (bottom) in a cave of Clamouse in Southern France was made from minerals that were deposited by the dripping water.  This room was named "The Cemetery" because the stalagmites resemble in rows of gravestones.   

Image courtesy of http://www.dgl.microsoft.com