The Cymru Terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes are the , , Wrekin Terrane and the . In this article the definition of terrane is that implying rocks associated with the composition of the Precambrian basement. The Cymru Terrane is bounded to the northwest by the and to the southeast by the . The geological terrane to the west is the Monian Composite Terrane and to the east is Wrekin Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.