Flowstone is a very common cave formation. It forms when thin layers of rock build on each other, sometimes becoming rounder as it gets thicker.  Often you will see this formation with another formation such as draperies which are also common.  Flowstone forms when running water, deposits a special mineral called calcite, into the rock. The water "flows" down the rock, getting its name. In the the end you get little rivers in the wall or a water fall shape. The same mineral also forms stalagmites and you will often find the two together.