The Neath Disturbance is a geological structure which stretches across south Wales from Swansea Bay northeastwards as far as Hereford in western England.
[1] The Disturbance gives rise to a lineament crossing the region, that is to say that it is responsible for a number of significant landscape features along its 100 km length.
A part of the Vale of Grwyne north of The Sugarloaf and the northeast-southwest aligned section of the Monnow valley on the English/Welsh border are also excavated along this line of weakness.
[2][3] The Neath Disturbance is possibly the southernmost geological feature within Britain which can be described as following the Caledonoid trend.
The phrase describes a suite of major geological structures associated with the closure of the former Iapetus Ocean in the middle Palaeozoic Era and giving rise to the Caledonian orogeny or mountain-building period.