PEMBROKESHIRE (Sir Benfro, Dyfed), the most west erly county of South Wales, bounded north-east by Cardigan, east by Carmarthen, south by the Bristol Channel, and west and north west by St. Bride's bay and Cardigan bay of St. George's Chan nel. The coastline is much indented and over 140 m. in length. Area (administrative county) 393,003 acres. Pop. (1931) 87,179. Geology.—The region falls naturally into an upland northern section of older rocks, and a lowland southern section of somewhat newer rocks. In the north the rocks range from pre-Cambrian near St. Davids to the Ordovician and Silurian, forming the mass of the Preseli hills which reach 1,76o ft. in Preseli Top. The general strike of the beds is south-west to north-east. From the Carmarthenshire border westward the rocks of the northern sec tion of the county become older and older,—Silurian, Ordovician (Arenig, Llandeilo and Bala beds) Cambrian (Lingula Flags and Treinadoc beds) and finally pre-Cambrian granitic (Dimetian) and volcanic (Pebedian) rocks near St. Davids. As the rocks get older to the west so the elevation of the hills becomes reduced and the Preseli finger out to sea forming numerous headlands, islands and bays. The rocks of the north and west are inter spersed with igneous material such as the gabbros and diabases of Strumble Head, Fishguard, Llanwnda and Preseli; diorites north-west of St. Davids, bostonites and porphyrites about Aber castle and the basaltic laccolite of Pen Caer, besides various con temporaneous acid lavas and tuffs. The Ordovician and Silurian rocks extend southward to the neighbourhood of Narberth and Haverfordwest, where Arenig, Llandeilo, Bala and Llandovery beds are recorded. Silver-bearing lead has been mined at Llan fyrnach. The southern plain is open to the sea and may be looked upon geologically as a continuation westwards of the south Wales coalfield, with associated Lower Carboniferous, Old Red Sandstone and narrow belts of Silurian rocks, the whole having been considerably folded and faulted, producing a general north-west to south-east strike. The coal measures, highly in clined and anthracitic, stretch across from Carmarthen bay to the shore of St. Bride's bay ; they are bordered on the north and south-east by the Millstone Grits, Carboniferous Limestone series and Old Red Sandstone. On account of the folding the limestone appears again farther south at Pembroke, Caldy island and St. Gowan's Head; most of the remaining ground about Milford Haven being occupied by Old Red Sandstone with infolded strips of Silurian. There has been much general subsidence of the coastline and the lower sections of many of the valleys have been drowned. The submerged lower reaches of the eastern and western Cleddan form Milford Haven. There are submerged forests in the vicinity Amroth.
southern slopes of the Preseli hills) is especially rich in Megalithic remains—dolmens, alignments, standing stones and stone circles. There are similar remains in the southern half of the county but they are not nearly so marked, as a group, as in the north-western district. This wealth of Megalithic remains suggests that north west Pembrokeshire had cultural relations with many of the north west coastal promontories of Europe in the days when metal was beginning to be known in the west. The interest of the stone circle culture in Pembrokeshire was increased when it was shown that the stones forming the inner circle at Stonehenge were de rived from rocks in Pembrokeshire (see H. H. Thomas "The Source of the Stones of Stonehenge," Antiquaries Jour. vol. iii., 1923). There are well preserved dolmens at Longhouse near Mattery, Pentre, Evan, Nevern and near Moylgrove. The stone circle known as Parc-y-Marw near Fishguard is well preserved.
The county does not show a wealth of Bronze Age objects though isolated finds fringe, as it were, the megalithic area. The number of hill-top camps, presumably of Romano-British type and date, is important, especially guarding ways in from the coast, though actual Roman influence in the county is very slight. Castell Flemish on the south-west slopes of the Preseli was probably a military site. It is probable that the hill-top camps continued to be occupied through the post-Roman centuries as the county suffered badly from raiders from over the sea. In Pembrokeshire, as in Ireland, the native cultures lived on un interrupted by Roman influences, and Pembrokeshire was appar ently invaded by the Irish Deisi about A.D. 27o. In the early centuries of our era the county maintained its contacts with Ire land and Brittany and became a great centre of Celtic Chris tianity. Memorials of this period remain in the numerous church dedications and in the beautiful Celtic crosses such as those of Carew, Penally and Nevern. Stones with Ogham inscriptions have been found at Caldy, Bridell, St. Dogmells, Cilgerran and other places. The route that had linked Ireland, Pembrokeshire, Cornwall, Brittany and north-west Spain in Megalithic times be came the route of the Celtic saints and, in the middle ages, an important pilgrim's way to the shrine of Santiago da Compo stella (north-west Spain) (see A. Hartwell Jones, Y Cynimrodor, 1912). In a sheltered valley, at a focus of roads from a number of little landing places on the north-west coast of Pembrokeshire, there grew up the great cathedral of St. Davids (q.v.), soon to become itself a centre of pilgrimage, and at the landing places were built chapels for the pilgrims. St. Non's and St. Patrick's are probably very early.