Deep within Mammoth Cave, Kentucky. How these shapes are formed: When rainwater falls where limestone is the bedrock it is capable of dissolving the calcium carbonate that makes up the limestone. As it seeps through layers of broken rock and decayed vegetable matter it picks up a considerable amount of carbon dioxide from the "soil air". The amount of calcium carbonate that can be dissolved in water increases with the amount of carbon dioxide (CO2) dissolved in the water. It seeps through tiny fissures in the underlying bedrock becoming chemically saturated with calcium carbonate. Eventually the water droplets make their way through seams in the bedrock to the interior of a cave and find themselves hanging from the roof surrounded by the atmosphere of the cave. Cave air is very like normal air - with little carbon dioxide content. So the droplets, heavily laden with this gas, diffuse their excess CO2 into the air. Then the water is unable to carry as much calcium carbonate and so it too is released and collects as stalactites hanging from the ceiling. The droplets fall, releasing more CO2 and, where they hit, releasing still more calcium carbonate forming the stalagmites that build up from the floor. Sometimes the hanging stalactites meet with jutting stalagmites and together they form columns. When the water simply runs down the wall rather than dripping it forms what is called flow stone and sometimes "draperies". They are all very beautiful and very difficult to photograph without a tripod (not allowed in the cave). Thanks for Looking! Ken