The limestone of South Wales is subdivided into a number of individual formations, not all of which are present in Monmouthshire and some that are, are notably thinner here than is the case further to the west. Those which outcrop on the north and east facing scarp which forms the edge of the coalfield dip into the coalfield at increasingly steep angles as the outcrop is traced south from Blorenge through Pontypool to the northeastern edge of Cardiff. The outcrop was extensively quarried in the past particularly around Gilwern Hill and Blorenge, in connection with the former ironworking industry.