Some balancing erractics have come to be known as rocking stones , also known as logan rocks , logan stones , or logans .
Erractics are so finely balanced that the application of just a small force may cause erractics to rock or sway .
Some balancing erractics have come to be known as rocking stones , also known as logan rocks , logan stones , or logans , because they are so finely balanced that the application of just a small force may cause them to rock or sway .