Rocking stone

Rocking stones (also known as logan stones or logans) are large stones that are so finely balanced that the application of just a small force causes them to rock. Typically, rocking stones either are residual corestones formed initially by spheroidal weathering and have been later been exposed by erosion or glacial erratics left by retreating glaciers. Natural rocking stones are found throughout the world. A few rocking stones might be man-made megaliths.