Geology of the Builth Wells district : a brief explanation of the geological map sheet 196 Builth Wells

This Sheet Explanation provides a summary of the district covered by the geological 1:50 000 Series Sheet 196 Builth Wells. The map is published in two editions, Solid, and Solid and Drift, in 2005. The district lies mainly in the county of Powys but also includes parts of Ceredigion and Carmarthenshire. The sparse population is concentrated in Builth Wells, Llangammarch Wells and Llanwrtyd Wells, situated in the broad belt of undulating low ground, that divides the district from north-east to south-west along the course of the River Irfon. To the north-west of this tract, lies the dissected upland plateau of the Cambrian Mountains. To the south-east is the steep escarpment of Mynydd Eppynt, which is cut at the eastern margin of the district by the deeply incised valley of the River Wye. Today, the local economy is based on agriculture and tourism. Major hard rock resources are currently worked for aggregate at Cribarth and Llanelwedd. The geology of the district has a long history of research and was a key area in the development of Lower Palaeozoic stratigraphy. Influential British geologists who contributed to the early understanding of the area include Murchison (1839), who discussed the geology around Builth and Aberedw in The Silurian System. Measured sections were produced by De la Beche (1846), and advances in understanding the stratigraphy were made by Charles Lapworth (1880).