These stones that I brought back from a trip to Nova Scotia have been polished by the actions of water and time.
The fact that something as soft as the flow of water can soften the edges of something as hard as stone seems at first glance rather odd. These stones remind me of something I recently read from the teachings of Lao Tzu:
"Nothing wears away hard strong rocks as well as soft, weak water. From this anyone can see that softness is harder than hardness, and weakness is stronger than strength."
From: Tao by Timothy Freke. N.Y.: Stewart, Tabori and Chang, 2002.