Edward Greenly came to Anglesey in the late 1890s and spent twenty years walking the coast. The geological complexity baffled the categories then available, so he invented a new one. Melange - from the French for 'mixture' - describes a jumbled rock body in which blocks of one kind are caught chaotically inside a matrix of another, formed where tectonic plates collide and grind. Greenly's Gwna Melange, exposed along the north coast, became the first named example anywhere; geologists now use the term worldwide. Anglesey contains rocks from the Precambrian through the Neogene, with Miocene marine sediments and extensive Pleistocene glacial features from the most recent Ice Age. The 125-mile Anglesey Coastal Path passes through nearly all of it. The First 100 IUGS Geological Heritage Sites list, published in 2022, names this small island a place of international scientific significance.

On the west coast, Llanddwyn Island reads like an exhibition card for plate tectonics. Pillow lavas - bulbous, billowy formations that form only when basalt erupts underwater and chills against the sea - lie at its eastern tip. These were created at a constructive plate margin some six hundred million years ago, when an ocean called Iapetus was beginning to open between landmasses that would eventually become Europe and North America. Anglesey was on the leading edge of one of those plates. To the north, the mudstones and sandstones contain dropstones - pebbles released from melting icebergs that fell to the seafloor far from any shore - relics of the Gaskiers glaciation that froze much of the planet at the end of Precambrian time. Schools and university field trips come here every year. Few places in Britain demonstrate the deep mechanics of the Earth so clearly.

GeoMôn publishes a series of geological trails for visitors. The Beaumaris trail starts among the dressed stones of the thirteenth-century castle - built by Edward I, the article notes plainly, to 'tame' the local Welsh people - and reads the building as a quarry catalogue: the limestone from quarries near the castle itself, the marble columns from across the Menai Strait, the schist from the inland hills. At Llanddwyn, in the churchyard, lies the grave of Sir Andrew Ramsay, second Director General of the British Geological Survey and one of the founders of Welsh geology. His headstone is a glacial erratic of Shap Granite, dragged here from Cumbria by Pleistocene ice and left, fittingly, to mark the death of a man who spent his life reading such stones. His great-nephew Kyffin Williams, the painter, was the Geopark's first patron.

The Watch House at Porth Amlwch serves as the Geopark visitor centre, open every day except Monday between ten and four. Inside are leaflets for self-guided trails covering the most accessible sites - South Stack's screaming kittiwakes above folded quartzite, the copper-coloured spoil tips of Parys Mountain, the white-quartzite cliffs at Carmel Head. Oriel Ynys Mon, the island's art gallery near Llangefni, holds rooms dedicated to both Kyffin Williams and the wildlife artist Charles Tunnicliffe, whose Anglesey paintings remain the standard visual record of the island's birds. GeoMon-Anglesey Geopark Limited, a registered charity, runs the whole enterprise. Anglesey - Ynys Mon in Welsh, with around sixty per cent of the population speaking Welsh as their first language - wears its science lightly. The rocks are simply the bedrock, in every sense.