contribution by Dr. Brian John.
The main features of the Newport area are the wide sweep of Newport Bay, the estuary and valley of the Afon Nyfer, and the dominating craggy hill summit of Carningli. There is also a fine cliffed coast, with abundant small coves and creeks and caves carved out by wave action over many thousands of years. The bay itself is bounded by the twin headlands of Pen Dinas to the west and Pen Morfa to the north-east, on the high coastline which runs towards Ceibwr and Pen Cemaes near the mouth of the River Teifi. There are other prominent features too, including the "cwm" of Cilgwyn, the spur dominated by the tors called Carnedd Meibion Owen, and the upland ridge which runs from Carningli summit westward towards Dinas and Fishguard. On that ridge there are more tors, including Carnffoi, Carn Enoch and Garn Fawr. It would not be exaggerating to say that wherever you are in the Newport area your eye is drawn to rocky outcrops of one type or another.
To explain the origins of this landscape we need to go back around 450 million years to the Ordovician Period. At that time there was a shallow ocean here -- although because of the process of continental drift "here" was not actually here at all. There was a great deal of volcanic activity, with molten lava intruded into softer rocks formed out of sea-floor sediments and with many violent eruptions at the surface. Carningli was almost certainly formed as a volcanic island in the sea, like the island of Surtsey off the coast of Iceland. It still looks like a volcano from certain viewpoints, but what we see today is just the stump or the core of a mountain that must at one time have been many thousands of feet high. The mountain is made of the igneous rocks called dolerite and rhyolite -- and these rock types coincide with almost all of the high points in the landscape, where there may at one time also have been smaller eruptions going on. Because these rocks are harder than granite they have resisted erosion very well; but in comparison the shales, mudstones and sandstones made of sea-floor and river sediments are much softer, and have been eroded away to form the valleys and depressions in the undulating landscape. Later on, around 400 million years ago, there was a great period of mountain-building referred to as the "Caledonian Orogeny." The earth's crust at the time was subject to enormous pressures as mountains were built and destroyed; and this "earthstorm" was also characterized by incredible contortions in the layers of rock beneath the land surface.
The cliffs which run westwards and northwards from the mouth of the Nevern River and Traeth Mawr (Newport Sands or "Big Beach") reveal for us in fascinating detail what happens when mountains are built.
Look for the spectacular "Caledonian" folds in the layered rocks, and you will also see faults galore and areas where movement has been so severe that rock shattering has occurred. (Faulting is essentially the sliding of rock layers along a crack, with more movement on one side than the other.) In the cliffs you can see blackish mudstones and flaky and friable shales -- called "rab" by the locals -- and also volcanic rocks including ash which at one time settled out on the old sea floor. There are some spectacular layers of white or grey volcanic ash exposed in the cliffs between Newport and Cwm-yr- Eglwys.
There have been many changes in sea-level and in the appearance of the landscape since the Caledonian mountain-building episode, including the laying down of layers of rock that have been entirely stripped away. Naturally enough, the shape of the land as we see it today owes most of its details to the most recent geological period, the Quaternary or Pleistocene which has lasted (thus far) for about 2 million years. For most of this time Planet Earth has been affected by substantial quantities of ice on land and sea, and this is why we refer to the Quaternary as "The Ice Age." That term is misleading, since there have been many ice ages before.
What traces of the Ice Age can we see in the Newport area today?
Well, Newport Bay is itself a product of the Ice Age, since it is at the mouth of a wide river valley which has a rock floor at least 30m beneath present sea-level; that means it was eroded at a time when sea-level was very low, probably coinciding with one of the powerful glacial episodes which affected the northern hemisphere. The course of the river has been changed many times by the presence of glacier ice in the neighbourhood, or because of sands, gravels and other glacial deposits blocking or "plugging" old river routes. The sand dunes of the Bennet formed at the end of the last glacial episode.
Many of the scars or landslides on the cliffs between Newport and Ceibwr formed because of pressure release when glacier ice which had pressed against the cliff faces melted away. On the top of Carningli there are beautiful smoothed slabs of rock fashioned by over-riding glacier ice maybe 20,000 years ago. The great scree slopes on the south and east sides of Carningli were created by frost action, again at the end of the last glacial episode. And in Cwm Gwaun we see one of the world's most famous sub-glacial meltwater channels, pictured in many textbooks and scientific publications as a classic of its type and indeed designated as an SSSI precisely for that reason. It was formed maybe 200,000 years ago when the Irish Sea Glacier from an older glaciation was melting away and when huge volumes of meltwater flowed westwards under pressure, beneath maybe 1,000m of ice. In effect, the Gwaun Valley at the time was a gigantic cold-water pipe, with its bottom part made of rock and its top part made of glacier ice.
And has geology slowed down, or ceased to be relevant today? Not a bit of it. Every time it pours with rain and sediment-rich water floods down into the River Nevern, parts of the landscape are lowered by a few centimetres. Every time a cave collapses (as happened when the Witches Cauldron at Ceibwr was created) or a section of cliff falls into the sea, the sea gains at the expense of the land. And the precarious rocks on the flanks of Carningli are still on the move, as anybody who has climbed on them will attest. The world is changing around us, just as fast is it did the the boisterous days of the Ordovician or the Caledonian Mountains.
A little postscript. Not many people know that two of the bluestones at Stonehenge were picked up from the Newport area by the great Irish Sea Glacier as it flowed across Pembrokeshire on its way to the Bristol Channel and the coasts of Devon and Somerset. Geologists have now matched up the rock type of these bluestones with the tors at Carn Clust-y-ci and Carn Llwyd.