Foundered strata is a term used by the

British Geological Survey The British Geological Survey (BGS) is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS hea ...

in its maps and geological memoirs, and indeed by other authors, to describe

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

which have collapsed due, for example, to the dissolution of underlying strata. Foundered strata may retain original bedding more or less intact or they may assume a chaotic structure in the process of collapse or some intermediate state of disruption. Examples of foundered strata are found along the northern margin of the outcrop of the

Twrch Sandstone The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous Period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geograph ...

(the former Basal Grit of the Millstone Grit) in the

Brecon Beacons National Park The Brecon Beacons National Park ( cy, Parc Cenedlaethol Bannau Brycheiniog) is one of three national parks in Wales, and is centred on the Brecon Beacons range of hills in southern Wales. It includes the Black Mountain ( cy, Y Mynydd Du) i ...

of South

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. The immediately underlying Carboniferous Limestone has dissolved away in numerous locations such as at Pwll Byfre and resulted in the wholesale collapse of the sandstone beds above it. It is thought that the sandstone has been let down several hundred feet in places due to the removal by solution of limestone strata.British Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' and accompanying memoir

References

External links

images of Pwll Byfre and surrounding area on Geograph website
Structural geology Stratigraphy Geology of the United Kingdom {{geology-stub