GeoMôn

Index to Anglesey's Geosites

This is the index page from which you may navigate to pages giving details of some of Anglesey's geosites. They are classified according to the period of geological time they represent. Click on a category to view a site listing, from which you may pick a particular site if you want to find out more about it.

There are numerous points along the coast and inland that merit inclusion here, but only some of the most interesting or accessible have been included. A more detailed foray into the Geopark can be found in the GeoTrails section produced by the Geopark.

Did you know that you can enter the 'grid reference' co-ordinates - straight into most car SatNavs to take you to the destination! The co-ordinates (beginning with SH) can be found below each site heading.

Please note that the inclusion of sites in the listings above in no way allows access to the sites described. The information is merely a scientific description. Many of the sites are Sites of Special Scientific Interest (SSSI), and/or on private land where permission to visit could be denied, or the site is unsuitable for safety or other reasons. Access to any site which is not in the public domain is entirely at the discretion of site owners. In no case is the collection and removal of specimens allowed from any site. Bona fide researchers require a permit from CCW to collect any specimens from GCR sites (SSSI) and these are generally allowed only under supervision. Queries regarding any of these sites should be directed to COFNOD, Parc Menai, Bangor. They will be able to answer any queries in the near future when all the relevant information is in their hands.

Carmel Head is the site of both Precambrian Gwna age rocks of more than 550 million years old and younger, less than 500 million year old, rocks (Ordovician) lying beneath them. The younger beds lie at a different angle to the older rocks above. The older rocks were moved by great Earth movements and slid on top of the younger rocks below in what is called a thrust fault.

This area is the world 'type' site for a rock called melange, a great mixture of rock types all jumbled together, which originated at a destructive plate margin, where the sea bed and mantle, descended down a deep ocean trench, which was eventually filled by rocks from the descending plate and its surface deposits. Anglesey's Precambrian rocks were dated from ancient microscopic fossils found in this deposit. The oldest ones are 650 to 700 million years old. Many of the rocks were injected by lava dykes during disturbances caused by the splitting of the Earth's crust at the birth of the Atlantic ocean 65 million years ago and in previous orogenies.

Smokers, rising from under the sea bed disseminated copper and other metals into the Silurian-age mudstones on the sea floor. During the 19th century, Parys Mountain was the largest copper producer in the world. The ore was exported from Amlwch Port, where today, the Loft Museum is dedicated to this industry. When copper prices rise, the mines are to reopen. Mining has taken place sporodically from Bronze-age to present times.

At Beaumaris although Ordovician sediments occur, they are masked by clay, sand, shingle and boulders (till) which in places form small dome-shaped hills (drumlins). A dissected drumlin forms the cliff between Beaumaris and Fryars Bay. The till was left as the ice age melted at the end of the last Ice Age some 18,000 years ago. The castle walls are constructed, in the main, from sandstones and conglomerates which occur between the limestone beds along the coast. From Gallows Point westwards, the coastal rocks are injected by numerous dykes running inland from the coast.

From Moelfre to Red Wharf Bay, for cycles of coral and brachiopod-rich limestone formed in reefs in warm, shallow, tropical seas. Intervening sandstones and shales demonstrate changes in sea level at those times.

The limestone coast around Penmon has been quarried as a superb building stone and used in many Anglesey buildings and as far as Liverpool and other north-West towns.The light house, monastry, Dovecote and hermit cell are all constructed of this rock.

LlanfairPG is famous for the rare blue schist best seen beneath the Marquess of Anglesey's Column. Many large boulders (erratics) of this rock have been carried by the ice deposited on the shores of the Menai Strait. This rock, originally a pillow lava, was carried down in the earth's crust to great depths at a plate margin. Under great pressure, but little heat, it was converted to the blue schist. Eventually it resurfaced during great fault movements.

The carboniferous Limestone on this part of the coast has become reddened, indicating that rocks originally formed under marine conditions were slowly becoming terrestrial. The red colour is iron which oxidised as the limey muds which formed the limestones were exposed to air.

Newbourough and Llanddwyn Island Forest are famous for Precambrian pillow lavas which were extruded as pulses of lava onto the sea bed where they quickly cooled. They are stacked one on top of another and resemble pillows. Spectacular melange can be seen in Pilots Cove at the far end of the Island.

The Aberfffraw side of the Malltraeth Estuary provides the only extensive beds of Namurian (middle Carboniferous) grits and sandstones which are full of sedimentary structures and iron-rich nodules. At the seaward end of the estuary, these sediments and earlier Devonian conglomerates abut against an ancient Precambrian sea cliff (unconformity).

Famous for its folded sedimentary rocks which have suffered only minor metamorphic change (meta-sediments). This coast is one of the most visited by students for mapping excercises. Inland outcrops of serpentine and mantle-derived rocks make the sea area fascinating for academic research.

South Stack exhibits the most spectacular folded schists and quartzites and it is considered to be world class. It is also famous for the sea birds which nest there. Breakwater Park provides a contrasting walk with arches,stacks and thrust vaults, just a few of its treasures. It also boasts some spectacular maritime heathland.