The Cob

The A4080 road runs for 24½ miles along the southwestern side of Anglesey. It starts on the A5 at Llanfair Pwllgwyngyll and passes through several villages before terminating on the A5 between Bryngwran and Gwalchmai.

Near Ty Mawr

Looking over an outcrop of the Gwna Melange, a metamorphosed sedimentary rock of Cambrian age to the contemporary sediments of the Malltraeth Sands. The Afon Cefni channel can be seen in the middle distance, at approximately low tide. The sea-washed rock outcrop has a thick growth of lichens.

A party of geologists walking along the Malltraeth shore on an organised excursion.

Variable cementing of the sandstone, Carboniferous in age, by carbonates has resulted in irregular weathering and the appearance of large, dark-coloured nodules on the eroded surfaces. The presence of bedding planes passing straight through some nodules is indicative of the structure being secondary in nature. The dark colour is largely due to the slow ablation of the surface compared to less heavily-cemented areas, and the surface is stable enough to be colonised by lichens (yellow Caloplaca is prominent).

Beds of a pebble conglomerate dip steadily to the right in this image. It is widely regarded as being a basal formation to the local Carboniferous outcrop, but here its position in the stratigraphy is rather obscure. Similar beds can be found at the side of Lligwy Bay SH5087 where limestone is also in evidence.

At the left of this image rocks belonging to the Gwna Melange can be seen. These are of Pre-Cambrian age and significantly metamorphosed. Falling down and spreading over the ancient topography, a rough cliff-like feature, are much younger rocks comprising a scree of angular debris obviously derived from the Gwna Melange. Higher up the succession, to the top right of the image the sediments are more obviously bedded and fine-grained in nature. The younger sediments are widely regarded to be of Devonian age, but may be Carboniferous as there is a lack of diagnostic fossils. A walking stick is stuck into a small thrust fault in the Gwna Melange for scale.

Followed by the Anglesey Coastal Path.

Associated with RAF Bodorgan (defunct).

- Pillbox (unclassified): DoB ID: S0003168 An unusual structure, although similar in many respects to the previous pillbox at Trefri. This is a single storey hexagonal plan pillbox with attached rectangular shelter, and semi-circular plan LAAMG post. The curious square structure on the roof with brick pillars at each corner has access to it from inside by means of a circular aperture in the roof. Its purpose remains unexplained by various authorities although one can only surmise it may have been an observation post. The pillbox along with others similar in the locality were part of the airfield defences of the former RAF Bodorgan. SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (2)

- Pillbox (unclassified): DoB ID: S0003168 Unlike the attached LAAMG post at Trefri, this one retains its central concrete pillar whose conical top allowed the mounted weapon to traverse upwards when engaging aircraft. SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (3)

- Pillbox (unclassified): DoB ID: S0003168 View inside showing the circular aperture cut into the ceiling giving access to the curious brick-built structure on the roof. SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (4)

- Pillbox (unclassified): DoB ID: S0003168 View inside looking directly at the floor area below the aperture in the roof. I can only surmise that the concrete object provided a firm base for a ladder through the roof aperture to the structure above. Another thought crossed my mind (and almost dismissed as ridiculous!) that the concrete might also have been the piece removed from the roof during the construction of the roof aperture. SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (5)

- Pillbox (unclassified): DoB ID: S0003168 SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (6)

- Pillbox (unclassified): DoB ID: S0003168 SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (7)

- Pillbox (unclassified): DoB ID: S0003168 SH3968 : North Wales WWII defences: RAF Bodorgan, Anglesey - Hermon pillbox (8)

The junction ahead is a cross-roads. The A4080 approaches the camera, and turns sharp right (i.e., to the left as seen here) to Hermon and Aberffraw. On the right there is a cul-de-sac towards Malltraeth. Behind the camera is a minor road crossing Tywyn Aberffraw, and also (though more slowly) reaching the village of Aberffraw itself.