Porthmelgan Beach Photo

Erratic boulder

Resting at the side of the stream descending into Porthmelgan is a massive erratic boulder of gabbro. It is probable that it has been transported from the vicinity of Carn Llidi, or one of the other prominent peaks nearby, which belong to the same intrusive mass or rock type. Part of the boulder is rounded and speaks of abrasion, but the opposite side is rough and angular, suggesting that it was a smoothed section of outcrop broken away by frost action and carried no great distance. My Geograph assistant is posing patiently for scale.

© Jonathan Wilkins and licensed for reuse under this Creative Commons Licence