The Carneddau Range

The North-western Edge of the Snowdon Syncline

August - The Carneddau Range

August – The Carneddau Range

The Carneddau Mountains lie at the north-eastern end of the Snowdonia Mountains (and at the north-eastern end of the Snowdon Syncline) and are oriented roughly south-west to north-east, as is most of the range. This is because all of the rocks which form these mountains were squeezed into a series of large folds (i.e. the Snowdon Syncline) and smaller folds by the mid-Devonian Caledonian Orogeny, which was probably caused by the collision of the Avalonian micro-continent with the Laurentian Continent, and also probably by later collision of fragments of Gondwana from the southeast in the Hercynian Orogeny. Here we can see the eastern faces of the mountains of Carnedd Llewelyn (3484ft/1064m, far right skyline) Carnedd Dafydd, and Pen yr Helgi Du (further left on the skyline) with the slightly nearer broad dome of Pen Llithrig y Wrach to their left and lower, near ridge of Creigiau Gleision at the far left. The paler blue peaks of the Glyders and Tryfan peep over these peaks, on the left-hand skyline. Most of the rocks of the main skyline ridge and steep eastern faces of the Carneddau Mountains are composed of volcanic rocks and igneous intrusions of the lower (and therefore older) parts of the Llewelyn Volcanic Group (which we also saw in the previous page) all of which dip steeply eastwards towards us, and therefore now form the uplifted and exposed ‘north-western rim’ of the northern end of the Snowdon Syncline. However, the rocks in the lower slopes of these mountains, nearer to us (the Crafnant Volcanic Formation) are more tightly folded, as they are located within the more compressed central ‘core’ of the Snowdon Syncline. These rocks form part of a second, later, and therefore younger, sequence of volcanic rocks erupted in north-western Snowdonia (the Snowdon Volcanic Group) which we will see more of later. The Crafnant Volcanic Formation is probably the northern equivalent of the main body of the Snowdon Volcanic Group, which forms the more impressive Snowdon and Moel Hebog Mountains further to the south-west, in the southern end of the Snowdon Syncline. We will visit this youngest, and probably final, sequence of volcanic rocks in the next few pages.

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