Anglesey's rocks provide a detailed record of the events leading to the formation of southern Britain. Formed between 650 & 300 Ma, they include high grade gneisses, a granite pluton, metasediments, sandstones, mudstones and the famous Anglesey Blueschists. There are also Paleogene dykes, abundant glacial features, a number of NE–SW faults and large sandstones blocks possibly marking the location of an ancient subduction zone.