Anglesey

Anglesey (Welsh: Ynys Môn, pronounced {{IPA|/?ɐnɪs'mo:n/}} (IPA), unniss mawn), is an island and county at the north western extremity of North Wales. It is separated from the mainland by a narrow stretch of water known as the Menai Strait. It is connected to the mainland by two bridges, the original Menai Suspension Bridge (carrying the A5), built by Thomas Telford in 1826 as a road link, and the newer, twice reconstructed Britannia Bridge, carrying the A55 and the North Wales Coast Railway line.

Geology

The geology of Anglesey is famously complex and is frequently used for geology field trips by schools and colleges. Younger strata in Anglesey rest upon a foundation of very old pre-Cambrian rocks which appear at the surface in four areas:

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• a western region including Holyhead and Llanfaethlu,
• a central area about Aberffraw and Trefdraeth,
• an eastern region which includes Newborough, Caerwen and Pentraeth and
• a coastal region at Glyn Garth between Menai Bridge and Beaumaris

These pre-Cambrian rocks are schists and slates, often much contorted and disturbed. The general line of strike of the formations in the island is from north-east to south-west. A belt of granitic rocks lies immediately north-west of the central pre-Cambrian mass, reaching from Llanfaelog near the coast to the vicinity of Llanerchymedd. Between this granite and the pre-Cambrian of Holyhead is a narrow tract of Ordovician slates and grits with Llandovery beds in places; this tract spreads out in the north of the island between Dulas Bay and Carmel Point. A small patch of Ordovician strata lies on the northern side of Beaumaris. In parts, these Ordovician rocks are much folded, crushed and metamorphosed, and they are associated with schists and altered volcanic rocks which are probably pre-Cambrian. Between the eastern and central pre-Cambrian masses carboniferous rocks are found. The carboniferous limestone occupies a broad area south of Llugwy Bay and Pentraeth, and sends a narrow spur in a south-westerly direction by Llangefni to Malltraeth sands. The limestone is underlain on the north-west by a red basement conglomerate and yellow sandstone (sometimes considered to be of Old Red Sandstone age). Limestone occurs again on the north coast about Llanfihangel and Llangoed; and in the south-west round Llanidan on the border of the Menai Strait. Puffin Island is made of carboniferous limestone. Malltraeth marsh is occupied by coal measures, and a small patch of the same formation appears near Tall-y-foel Ferry on the Menai Strait. A patch of granitic and felsitic rocks form Parys Mountain, where copper and iron ochre have been worked. Serpentine (Mona Marble) is found near Llanfaerynneubwll and upon the opposite shore in Holyhead. There are abundant evidences of glaciation, and much boulder clay and drift sand covers the older rocks. Patches of brown sand occur on the south-west coast.

Related Topics:
Pre-Cambrian - Schist - Slate - Granitic rocks - Llanfaelog - Llanerchymedd - Ordovician - Dulas Bay - Carboniferous - Limestone - Llugwy Bay - Llangefni - Malltraeth sands - Sandstone - Llanfihangel - Llangoed - Menai Strait - Malltraeth marsh - Tall-y-foel - Parys Mountain - Serpentine - Llanfaerynneubwll - Holyhead

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