Grandma's Postcards
Onyx Colonnade in the Mammoth Cave of Kentucky -- Frozen Niagara Entrance
Stalactites grow from the ceiling.  The drip of water passes through the center.  Stalagmites grow or build up from the floor and are the surplus deposit from stalactites.  All the section of cave around Frozen Niagara abounds in both stalactites and stalagmites and is brilliantly lighted with electricity.