Holyhead Historic RIGS site

NRW RIGS no. 127 [SH 24726 82619]

GeoMôn Global Geopark original webpage

RIGS Statement of Interest:

Holyhead Historic RIGS site demonstrates the use of local rocks in ancient buildings around the town.

Holyhead Roman Fort walls and enclosed later churches have been selected as a RIGS to exemplify the earliest surviving use of Precambrian (Monian) New Harbour Group schist in a mortared construction, together with adjacent medieval 14th and 15th century ecclesiastical buildings in the same material. This beautiful metamorphic crystalline schist forms one of the largest surface exposures of Precambrian rock in North-.West and North Anglesey. Here, the rock is termed ‘Soldier’s Point’ schist from Greenly’s type-location and exhibits gritty bands interleaved with satin-like mica layers often only millimetres thick (foliation). Any building constructed from this schist is likely to be over 150 years old and shows superbly etched and weathered examples of folding on various scales in its foliation. The rectangular enclosure now forming the upper churchyard is bounded to the North, South and West by 4th century Roman walls, showing stone courses in typical Roman herring-bone pattern. Drum towers at the corners are medieval, on Roman foundations. A former sea-cliff edge with modern parapet wall bounds the site to the East. Further interest accrues from the presence of red brick dust and fragments in the Roman cement, probably brought from the Cheshire area by the builders. Within the walled area, the larger church is St. Cybi’s, while the much-altered Eglwys y Bedd (Church of the Grave) stands near the South entrance on the line of the original Roman gate. The site shows the former, long-continued use of what might now be considered an attractive but difficult and inappropriate building material.

Geological setting/context: There are three main categories of RIGS selected for their historical importance: 1. Historical constructions (arbitrarily up to 2,000 years old) and/or archaeological constructions and sites of extraction (arbitrarily more than 2,000 years old) where rock has been used or removed and where the relevance of geology can be demonstrated. The construction type of RIGS can include castles, churches, ruins, lanes, walls, cromlechs, standing stones and extraction sites may include disused mines and quarries. 2. Sites or features related to the development of geological thought and geology as a science, such as sites where certain concepts or theories were developed or types of feature first explained (e.g. Hutton’s Unconformity). 3. RIGS commemorating the work and contributions of important geologists. These usually take the form of a monument (such as a grave) or memorial.

Network context of the site: Holyhead Roman Fort and Medieval Churches are Historical constructions, of RIGS Category 1 which typify the sustained use of an attractive but refractory country rock, the Precambrian New Harbour Group of schists, over many centuries up to the C19th. The chosen site exemplifies other local vernacular architecture such as the early C19th Market Hall and the important complex of Port Buildings.

References:

WHEELER, R.M. (1920). Segontium and the Roman Occupation of Wales. Y Cymmrodor, 98–101.

ROYAL COMMISSION ON ANCIENT & HISTORICAL MONUMENTS IN WALES AND MONMOUTHSHIRE (1937 &1960). An Inventory of the Ancient Monuments in Anglesey. HMSO, London, 31–34.

CREW, P. (1980, 1981) Beacon Watchtower on Mynydd Twr, Holyhead. Archaeology in Wales.

GREENLY, E. (1919). Geology of Anglesey. Memoirs of the Geological Survey of Great Britain. HMSO, London, 980pp. (2 vols)