South Wales Caves

The Llangattock escarpment is distinctive due to the quarrying that has been carried out around its upper flanks. The old tramroad follows the Oolitic beds of limestone that were once quarried and allows an interesting traverse of the mountain. The Oolitic beds that were quarried are in fact the main cave bearing rocks of the mountain, so by virtue of this intervention several entrances to the major caves of this mountain have been revealed. These caves, Daren Cilau, Agen Allwedd, Eglwys Faen and Ogof Pen Eryr all form in the Oolitic beds and have entrances just above the abandoned tram road. These beds of limestone dip gently to the South West through the mountain, emerging in the Clydach Gorge, where the water from the mountain's caves resurges. Caves do not form exclusively in the Oolitic beds, there are several caves such as Pwll Pasg and Pwll Y Gwynt that form in the Upper Limestones. These systems tend to be of a more vertical nature and have very little horizontal development. The top of Mynydd Llangattwg is covered with Millstone Grits, so all caves are found at the boundary with the Upper Limestones or where the Oolitic beds have been exposed by quarrying. The upper layer of Millstone Grit is known locally as Farewell Rock. This name was coined by the local miners as the South Wales coal measures sit above this rock bed and when the miners reached this bed of rock in the pits they knew the coal was over and so became affectionately known as Farewell Rock.

The above diagram is based on an illustration by David Leitch in 'Ogof Agen Allwedd in relation to the Mynydd Llangattawg' published by the Cave Research Group of Great Britain and a subsequent diagram in the Chelsea Speleological Society Newsletter.