The GeoMôn Global Geopark us of international significance because of the rare Precambrian blueschists of southern Anglesey, the stromatolitic limestones (860 Ma) of northern Anglesey, that are the oldest fossils in England or Wales and the largest and most important copper mine in the world between 1780 and 1860, Parys Mountain in Amlwch. It has great geological diversity in its solid rock foundation and glacially deposited cover. The rocks crop out as mainly north-east to south-west fault-bounded slices of mostly Precambrian and Cambrian age metamorphic, igneous and sedimentary assemblages with unprecedented exposure along its coast. The lowland area of ancient rocks owes its origin to the earliest formation of the Earth's crust and its development during 1.8 billion years. It is a tectonic island, displaying rocks from every type of tectonic plate boundary, that in places is injected by mantle material.
Isle of Anglesey