sentences:  The majority lie on or close to the margins of terranes, blocks of the Earth's crust which have had differing geological histories before assuming their present configuration.However, in recent years there has been a progressive elucidation of the way in which Wales’ many terranes came together during the late Precambrian and the Palaeozoic era.The Stanner-Hanter Complex on the English border comprises volcanic rocks around 700 million years old which puts them within the Cryogenian period.