The four islands off the west coast of Pembrokeshire have long been renowned for their wildlife. Ramsey (265ha), with its twin hills rising to 136m off St David's Peninsula, and lonely Grassholm (8ha) 17km to the south-west are owned by the Royal Society for the Protection of Birds. Beyond the Marloes Peninsula, southern bastion of St Bride's Bay, lies the tableland of Skomer (291ha), while 3.5km across Broad Sound in Skokholm (98ha), its cliffs of Old Red Sandstone a pleasant contrast to the darker rocks, often of volcanic origin, of which the other islands are composed.