Mynachdy RIGS Site

NRW RIGS no. 572 [SH 31339 92644]

GeoMôn Global Geopark original webpage

RIGS Statement of Interest:

Mynachdy RIGS Site, a disused pit to the NW of Mynachdy Farmhouse, is important for rare minerals,rocks and history.

Mynachdy RIGS Site is a disused, overgrown pit, a short distance to the NW of Mynachdy Farmhouse is of regional geological importance because: a) it was quarried for unusual and rare minerals which are no longer visible; b) the geological origin of the sliver of deep sea-derived rocks in an otherwise more usual suite of New Harbour Group schists is controversial; c) its importance in early writings is emphasised by the number of eminent scientists who referred to the ‘marble’. These include Pliny writing about the ancient people who put asbestos cloth in the fire to remove stains and used it for shrouds around the hearts of their princes to preserve the ashes from those of the wood pyre. The Mynachdy serpentine and asbestos acquired great fame when the first two curators of the Ashmolian Museum in Oxford, Robert Plot and then Edward Lyuyd described the manufacture of an incombustible paper cloth from minerals found there. Thomas Pennant (1770) visited the quarry and noted the silky and elegant white asbestos. Although the quarry has not been worked in the last two centuries, Greenly (1919) noted bundles of asbestos in the complex of serpentine, ophicalcite, amphibole and dolerite. Today, no asbestos is visible, however, if the vegetation were removed there may be some small amounts remaining. Mynachdy has been considered to be of great importance for more than a thousand years and despite the lack of visible evidence today its rarity and former glory deserve to be recognised as an important historical RIGS.

Geological setting/context: There are three main categories of RIGS selected for their historical importance: 1. Historical constructions and sites of extraction (arbitrarily up to 2,000 years old) and/or archaeological constructions (arbitrarily more than 2,000 years old) where rock has been used or removed and where the relevance of geology can be demonstrated. This type of RIGS can include castles, churches, ruins, lanes, walls, cromlechs and standing stones as well as ancient 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: Mynachdy has been selected as an historical RIGS as part of category 1 (see above). Although the site was undoubtedly used by Ancient British people, it appears to have been used, at least spasmodically, for many centuries. Mynachdy is referred to in many early pioneering geological works, and the site has generated much interest and debate. The selection of the site as an historical RIGS reflects both the unusual geological occurrence and the importance put on it by many early writers.

References:

GREENLY, E. (1919). The geology of Anglesey. Memoirs of the Geological Survey of Great Britain. HMSO, London, 980pp, 102 & 320. (2 vols)

GREENLY, E. (1920). 1:50,000 (and 1 inch to 1 mile) Geological Map of Anglesey. Geological Survey of Great Britain, Special Sheet No. 92 and (93 with parts of 94, 105 and 106).

LHUYD, E. (1684). Lithophyllacii Britannici Ichnographia.

MORRIS, L. (1748). Plans of Harbours in St George’s Channel.

THOMAS, J. (1775). History of Anglesey.

PENNANT, T. (1770). Tour of Wales.

PLINY. Natural History. xix, c.1.