Llanelli Naturalists Newsletter - Winter 1992/1993
Richard H. Davies

{rokbox align=|right|}images/stories/newsletters/1992_11/01.jpg{/rokbox}Pwll Edrychiad is a large karat depression lying to the south west of the village of Carmel (NGR SN584162). It lies on the narrow band of Carboniferous limestone which encircles the South Wales coalfield. The cause of this abrupt slump in the limestone is not known but may be partly connected with the Carreg Cennen Disturbance.

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The elliptical depression is approximately 700m, long on its major (east-west) axis between the western end of Carn farm and the limestone outcrop occupied by the Llwynyfran quarry near Maesybont. The depression is about 350m. wide on its minor (north-south) axis and the area totally enclosed amounts to over 20 hectares. The lowest part of the floor lies at a height just below 200m. O.D. whilst the complete depression would be enclosed by a contour line at 223m. O.D. The lowest part of the surrounding high ground is on the north east side of the hollow, near the village of Carmel (see appendix 1).

The northern flank of the depression consists of rocks of the Old Red Sandstone, which outcrop naturally at 225m. O.D. The sides of the hollow are steep, whilst the floor is uneven and contains a number of swallow holes.

Glacial action has no doubt played a part in widening and deepening this depression. It is probable that Pwll Edrychiad once contained a lake. Near the end of the last Ice Age, the depression would have held summer melt waters whilst the fissures within the limestone would have remained frozen by permafrost which would have prevented drainage. With the gradual warming of the climate, the lake would have drained away through the swallow holes. Similar periglacial lake sites have been identified by W.H. Stanton 91992) on the Mendips.

The etymology of the name "Pwll Edrychiad" is not straightforward. The earliest reference to the area was by Edward Lhwyd (ca.1690) and cited by Fenton (1817):-

"Gwenlaish river runs underground from Pyllau Drychiad in Llaufihangel parish to Ffynnon Gwenlais".

This may be one of the earliest descriptions of an underground river in Wales. Recent hydrological studies on the Gwenlais has shown that a significant input comes from this area (Hardwick 6 Gunn 1991).

By the nineteenth century, the hollow was being described on maps and documents as "Pwll Edrychiad", though the latest 1:50,000 O.S. sheet of the area shows a further change to "Pulla" - an attempt at Pyllau?

The problem is to decide whether the first element of the name is "Pwll" (pool or pit) or "pyllau" (the plural). The uncertainty is whether the second syllable should be attached to the third or first syllable. It is most probably the latter with the "Pyllau" referring to the swallow holes in the floor of the depression. There is a large group of swallow holes on the Mynydd Du known as "Pyllau'r Fai" (the pits of the plain).

"Drychiad" can be translated as "manifestation" or "appearance". It is possible that pools would appear if the swallow holes became periodically water-filled.

The eastern end of the depression was enclosed and became part of Garn farm at an early but unknown date. Murphy (1992) has shown that this farm was in existence by 1543. An estate plan of the farm clearly shows a quarry in operation on the eastern slope of the depression in 1782. (Appendix 2).

An Ordnance Survey map of ca.1810 shows a track crossing the depression outside the Garn boundary. It is likely that the line of the track determined the limit of the Garn enclosure. The 1810 map is very useful in showing that the remainder of the depression was common land and remained as such until the 1820's. This part of the depression formed an isthmus between the Mynydd Mawr common of the Coal Measures and Millstone Grit and the lower elevations of the Mynydd bath common to the north on the Old Red Sandstone. 

After the Act of Enclosure, the area was divided between a number of cottages and the smallholding of Pwll Edrychiad was created. Analysis of the Tithe map and schedule for the parish of Llanfihangel Aberbythwch, (ca 1840) shows the patchwork of allocations made in the area.

The trackway across the depression was lost and a new road built from near Garn towards Maesybont which runs along the flank of the silica ridge. In time, this road became known as "Heol Each y Lord". It is not clear who the lord referred to was, as both Lords Cawdor and Dynevor held large estates locally.

The state of agriculture can be assessed from the O.S. surveys of 1880 and 1907. It is clear from these maps that the eastern part of the depression was rough pasture.

A visit to this area in the summer of 1990 showed that the grassland contains a large population of Yellow Rattle Rhinanthus minor, a species parasitic on grass roots, together with Ladies Mantle Alchemilla filicaulis subsp. vestita and Salad Burnet Poterium sanguisorba. Thyme Thymus drucei and Carline Thistle Carlina vulgaris were associated with old lime heaps. On a later yisit, an extensive colony of Greater Butterfly Orchid Platanthera chlorantha was found which contained 200-300 individual spikes.

These species are indicative of an old grassland community which has never been ploughed. The steep slopes of the depression and the uneven floor have provided a strong disincentive against arable agriculture. It is doubtful if the smallholding of Pwll Edrychiad could ever have been solely reliant on farming. The 1891 census shows that the occupier, Rees Thomas, was listed as a shoemaker with his eldest son as a collier. In such cases, agriculture was viewed as a supplement to the income. As a consequence of this, the land would have been managed at a low level of intensity and would not have been subject to the pressures for higher productivity which faced the larger farms.

It may be significant that part of this are of old pasture lies within the boundaries of Garn. It may be that this area was protected by its topography and by its position at the furthest extent of the farm. it would haye been less likely to be ploughed as there were far easier alternatives. Although the size of Garn would have made it a viable agricultural holding, the occupiers had, until about 1900 a significant additional source of income from limeburning. The 1891 census shows Mary Morris and her second eldest son listed as farmers, whilst Mary's eldest son, David, was listed as a limeburner.

The evidence suggests that a significant portion of Pwll Edrychiad probably retains an undisturbed soil. This soil is base rich and such soils are scarce in Dyfed. It is widely recognised that only a tiny remnant of the traditional grasslands existing during the Second World War have survived the agricultural practices of the last 50 years. Studies of the grasslands surrounding the Coedydd Carmel SSSI indicate that agricultural "improvements" have all but obliterated the original plant communities.

The Pwll Edrychiad depression is an unusual geomorphological feature of the karst of Dyfed. The diverse grassland flora has suryived because of the unamenable topography coupled with a tradition of low level pastoral agriculture.

The limestone outcrop to the east of the depression is a mixture of pasture and small woodlands which is separated from the Coedydd Carmel SSSI by the A476 road. The cartographical constancy of these woodlands over 200 years strongly suggests that they should be regarded as being of ancient origin, although their flora has not been investigated by the author. Active consideration should be perhsps given as to whether Pwll Edrychiad and the woodlands of Garn west of the A476 should be designated as SSSI.

References

Stanton, W.H. 1992. There was I, surveying this hole. New Scientist. 30.5.1992

Fenton, R. 1817. Tours in Wales. page 337.

Hardwick, P. & Gunn, J. 1991. The hydrogeology of the Gwenlais Valley, South

Wales. A report produced for the Campaign for the Protection of the Gwenlais Valley by the Limestone Research Group.

Murphy, X. 1992. Past land use at Carmel Woods, near Llandybie, Dyfed: an historical and archaeological survey. A report produced for the Countryside Council for Wales by Dyfed Archaeological Trust.