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Part 1: Porth Ceiriad
From volcano’s and glaciers, to body board’s and surfing!

A short walk along Porth Ceiriad beach gives the observer a fascinating insight into the formation of this part of the Llŷn Peninsula. Look away from the sea for a moment and back towards land and you will see millions of years of geological evolution in front of you.

Porth Ceiriad

Most visitors to Porth Ceiriad descend the steps to gain access to the sandy beach and the sea for brilliant body boarding and surfing conditions that occur at many times during the year. Some however visit for the superb views of the geology that has been uncovered by erosion and weathering. Here is a short walk through some of what you can see with just a little time away from the usual beach activities.

It starts before you even reach the beach. During the descent you are walking down a 25m raised beach platform which has been cut into the boulder clay deposits. Once on the beach walk away from the steps and turn back to look at the boulders packed within the cliff face. The boulders vary in size from pebbles to large rocks. These were deposited by glaciers.

Moving west, and past the steps, the rocks change to a striped black/green colour. These are shale’s with thin sandstone layers. The presence of fossils have been reported but they are not common in these rocks. Moving further west thicker sandstone beds averaging 200mm are seen. These show superb examples of convolute bedding, cross bedding and load casts. The lower sections of this area have sedimentary layers of up to 1000mm thick.

As you walk along take note of the angle of the rock layers. They are not horizontal. Millions of years of forces have ‘folded’ these rocks and tilted them into the shapes and angles we see today. These forces continue today but very rarely do we see or feel the effects.

Porth Ceiriad

Volcano’s on the Llŷn Peninsula? The thin white bands you will now see separating the black/blue mudstone is volcanic material. Look close and, on a bright day, you may even see the glint of gold! Don’t dig it, it’s ‘Fools Gold’ (Pyrite).

A large landslip is obvious due to the mainly large sandstone blocks on the beach. This is as far as you will get unless it is low water, and this is where this short walk ends.

We all appreciate the beach and the sea, but just take an hour out of your day to walk along this stunning area and see what you can see in the walls that enclose this popular bay. This is a very brief description of what you can expect to find, but there are a number of publications which will give you detailed information on Porth Ceiriad and other areas of geological interest on the Llŷn Peninsula.

Please note that examples of geology should not be removed or damaged. Not trying to frighten you, but care must be taken as rocks can be dangerous underfoot (slipping) and overhead (falling). I have been caught in a landslip on Porth Ceiriad beach but luckily it involved small rocks. Believe me, it is not a pleasant experience.

Llyn.info Geology

Part 1: Porth Ceiriad

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