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The amazing rocks on this small beach were first described as a 'melange' by the geologist Edward Greenly, who published a geological survey of Anglesey in 1919. The rich variety of rocks here include rose pink quartzites, greenish lavas, pale limestones, dark coloured intrusive dykes, and purple manganese rich shales, all in a colourful mix within a small area. It appears that these rocks were once on an ocean floor and were dragged deep into a trench [subduction zone] at the point where two plates collided. Subsequent earth movements have seen the rocks shifted further and have allowed the intrusion of dykes. This is a geological site of world importance.