Most people think of water as a very “soft” substance: you can plunge your hand into a tub filled with water, and it won’t really hurt (On the other hand, if you try the same thing with a tubful of rocks, it will hurt)! But as soft as water seems, its motion and movement – no matter how slow – can have a powerful effect on even very hard rocks over a long period of time.
Because the limestone beds laid down by the sea creatures were softer than many rock formations (such as marble or granite), the rain water trickling down from the ground above soon began to erode the top layers. Small cracks opened up to the layers below, and the rain water dissolved its way through them, too.
In time, the small cracks grew to be large cracks through which underground streams flowed. And that is how the great cave formations and winding passageways of Howe Caverns were formed: over the course of millions of years, underground brooks and streams gently carved them out of the solid limestone deposits left behind by sea creatures eons before.