The Swansea Valley Disturbance runs from Swansea Bay to Herefordshire up the Swansea Valley into the park, through the NE-SW aligned ridge of Cribarth and on towards Brecon. It is responsible for the WSW-ENE alignment of a portion of the Wye Valley. At Cribarth, Variscan movement on this Caledonoid feature has given rise to a couple of folds in the limestone and overlying Twrch Sandstone from which the present landform has subsequently been carved, in part by glacial action. The southernmost lineament is the Neath Disturbance which runs ENE from Swansea Bay up the Vale of Neath and into the park at Pontneddfechan. The limestone is tightly folded here at Bwa Maen (Welsh: 'stone bow') and again at Moel Penderyn, through which it next passes. It passes beneath Pontsticill Reservoir, across the top of Dyffryn Crawnon and then down the shallow Onneu valley to Crickhowell. The erosion of the faulted rocks further ENE on this alignment has led to the valley which separates Sugar Loaf from the main Black Mountains massif and also for a WSW-ENE aligned section of the Monnow valley.