A large rock transported by a glacier and set down by the melting ice is known as an erratic (from the Latin “errare” meaning to wander). On the north coast of Tiree is an erratic, made of granite, an alien amongst an indigeneous geology of gneiss.
The ringing stone has an ancient history. The cupmarks pitting its surface mark the spots where humans have hit the large stone with a smaller stone striker. With your ear against the stone as it is struck you can hear an extraordinarily resonant spatial sound, with a metallic ring.
The effect is due to the density of the rock and absence of flaws or fissures. Some think that the void or cleft underneath the stone also contributes to the sound produced.
It is well worth walking off the track to experience it first hand.