The Dalradian Supergroup, comprising the Grampian (oldest), Appin, Argyll and Southern Highland (youngest) groups (Fig. 13) consists of lithologically diverse metasediments and typically mafic metavolcanic rocks. The supergroup is probably entirely late Precambrian in age and underlies an area of about 48000 km² in north and west Ireland, Scotland and Shetland. Neither the base nor the top of the Dalradian is seen but, taking the maximum thickness preserved for every group and making no allowance for tectonic thickening, it is calculated to have a total cumulative thickness of c. 25.5 km.