Brecon Beacons Research Articles

Late-Glacial history of the Brecon Beacons, South Wales

In the uplands of the Brecon Beacons, Black Mountains, Fforest Fawr area of South Wales, small arcuate moraines and/or protalus ramparts are found below steep escarpments and in glacial cirques1–3. The freshness and distinctive morphology of many of these features have led to the suggestion that they are not a product of the late Devensian ice sheet, but may have been formed during the Loch Lomond Stadial of the Late-Glacial period (Fig. 1), the last occasion when glaciers existed in the British Isles. I present here pollen-stratigraphic evidence and radiocarbon dates which form the basis for the first Late-Glacial chronology for this area of South Wales, and which prove that the features described above developed during the Loch Lomond Stadial (approximately equivalent with the Younger Dryas of Scandinavia4–6).

Landform and structure in the terrain of the Tawe and Neath Disturbances in South Wales

The geomorphic effects of geologically recent (late-Neogene) movements along the Tawe Disturbance are, in a recently proposed hypothesis, to be seen in fault downthrow of several hundred metres between Mynydd Epynt and the Brecon Beacons and in sinistral strike—slip of perhaps sixteen kilometres in the Wye valley along the foot of the Black Mountains, identified in a disruption of the local river systems. A revised and extended analysis of the courses and the long profiles of some of the tributaries of the Tawe, Usk and Wye rivers shows, however, that where they cut across the outcrop of the disturbance they give no sign of disruption of the integrated drainage pattern: rather, integration is extended by such analysis to incorporate further elements, linked by piracy, with the well established Nant Stalwyn, Fanog and Talley base-levels of erosion. There is analogous indifference to structural control in terrain where the sub-parallel Neath disturbance is transected by the super-imposed Neath, Cynon and Tâf rivers and the rivers of the Black Mountains, with concordant evidence of stages of rejuvenation. There is no justifiable correlation of fault-stepped summit levels and profiles between Mynydd Epynt and the Brecon Beacons; and the Beacons scarp is not to be regarded as the degraded residual of a revived fracture face. The rivers of the Black Mountains cannot be made to match the rivers of Mynydd Epynt, either in alinement or in long profile, by strike-slip along the fault traced by the River Wye at the foot of the Black Mountains; and where they give evidence of links with the Usk and the Wye, and where they cross the Neath disturbance to debouch onto the plain of Gwent, they do so in ways affected by piracy but unaffected by recent faulting. It is concluded that any appearance of late-Neogene fracture along the Tawe and Neath Disturbances is deceptive, and that any tectonism discernible in present-day elements of landscape is limited to simple ‘eustatic’ uplift seen in pulsed rejuvenation of the rivers.

Studies on lower devonian petrifactions from Britain. 1. Pyritised axes of Hostinella from the brecon beacons quarry, Powys, South Wales

A new species, Hostinella heardii, is based on compression and petrifaction fossils from the Senni Beds of the Brecon Beacons, Powys, South Wales. Incident light and scanning electron microscopy (SEM) studies on the iron sulphite (pyrites) petrifactions have provided anatomical details of the xylem and outer cortical region; the former consisting of close-set annular tracheids. An analysis of the composition of individual cells provides some insight into the sequence of events occurring during the petrifaction process. The affinites of the sterile axes are discussed, particularly in relation to Krithodeophyton croftii Edwards also found at the locality.

The aquatic vegetation of Llangorse lake, Wales

A survey was undertaken to assess the present status of submerged, emergent and marginal vegetation in and around Llangorse lake in the Brecon Beacons National Park in Wales. The results of this survey were compared with those of previous surveys of the lake. The most profound change observed was the decline of a relatively diverse submerged macrophytic flora dominated by Potamogeton pectinatus L. and Zannichellia palustris L., from at least eigth species in 1973 to monospecific stands of Z. palustris by 1977. Although cultural eutrophication processes partly accounted for the macrophytic decline they did not adequately explain the survival of Z. palustris alone; it was considered that a combination of cultural eutrophication and mechanical disturbance was the prime causal factor for the occurrence of this unusual situation. A hydrographic survey of the lake was also undertaken and a map showing the submerged contours was produced.

The life cycle and larval growth of Drusus annulatus Stephens (Trichoptera: Limnephilidae) in a mountain stream

SYNOPSISThe life cycle of Drusus annulatus in a stream in the Brecon Beacons is described, and compared with its life cycle in watercress beds, with particular reference to larval growth.

Uptake of lead by two populations ofGrimmia doniana

AbstractAnalyses of populations of Grimmia doniana from Old Red Sandstone walls (Brecon Beacons, Breconshire) and vitrified lead slag (Charterhouse, Somerset) showed the former to have a low and the latter a high lead content. Lead in material from the field was shown to be ionically bound to an extracellular site. Uptake of lead from solutions of lead nitrate was by a passive physical process, without penetration of the cytoplasm. No difference in lead uptake capacity was detected between the two populations. The results are discussed in terms of a natural non-specific lead tolerance mechanism occurring in Grimmia doniana.

THE ALTITUDINAL ZONING OF GRASSLAND AND SOILS ON THE BRECON BEACONS IN SOUTH WALES

The altitudinal sequence of soils occurs lower on the north than on the south face of the Brecon Beacons where the highest slopes of the north face are occupied by shallow, strongly leached rankers. Except on lower slopes, Vacciniun, Calluna and Nardus dominate the flora associated with each soil type. Unlike their distribution elsewhere, Rhytidiadelphus and Hypnum are associated with gleyed soils. It is suggested that exposure and inaccessibility have limited hill grazing. The vegetation on the peaty gleyed soils is associated elsewhere with drier soils, formerly extensive on the Beacons, and is preserved despite a changing edaphic environment. Some potentially nutritious pastures on the north face are too exposed to be grazed by sheep during winter, but Vaccinium pastures on some lower slopes supply useful winter protein.

Shiels in the Brecon Beacons

AbstractThe writer has for some time taken an interest in the many shielings of the Scottish Highlands and has compared these with similar summer pastures and their huts in various other parts of Europe. Apart from one well-preserved but roofless hut in the Berwyns, close to the B4391 road and just north of the county boundary, and two or three doubtful sites in the valley north-west of Llangynog, no field observations had been made in Wales. Last summer, however, an opportunity offered to examine the Brecon Beacon and several shiels (Lluestau or Hafodau) were found.

Shiels in the Brecon Beacons

Shiels in the Brecon Beacons

HILL SOILS AND GRASSLANDS IN BRECKNOCKSHIRE: A STUDY OF POTENTIAL LAND USE

The present and potential land use of rough hill pastures in Brecknockshire has been investigated. The interests of the Brecon Beacons National Park, reservoir, Forestry Commission and commonland need not compete, but could be complementary. Areas containing a high proportion of the podzolized soils carry the most nutritious pastures, rich in Agrostis and Vaccinium, and agreement amongst the commoners could ensure they are grazed to the limit of their productivity. In the absence of afforestation, the grazing of superior pastures around the peaks of the Fforest Fawr‐Brecon Beacons range is consistent with the interests of both the National Park and reservoir authorities, although the erosion hazard is greater. The S. and E. directed spurs of Drygarn, the N. E. plateau of Mynydd Eppynt and the S. W. flanks of the Black Mountains have similarly productive hill pastures. Areas such as the long back‐slopes of the Fforest Fawr‐Brecon Beacons range and higher land of Drygarn contain a high proportion of peaty gleyed soils under Molinetum, They provide inferior grazing but support the most productive forests, chiefly of Sitka spruce. By agreement amongst the commoners, where they are known, these areas could be leased to the Forestry Commission for afforestation. However, because common rights are so obscure, prior legislation would probably be necessary. Until their recent destruction, the uplands supported woodland and afforestation of selected areas need not be regarded as incongruous. It would also open up otherwise inaccessible places.

Brecon Beacons National Park

Brecon Beacons National Park

The Glaciation of Clun Forest, Radnor Forest, and some Adjoining Districts

The district described, which comprises the county of Radnor and parts of Montgomeryshire, Shropshire, Brecknockshire, Herefordshire, and Worcestershire, is some 1000 square miles in area, and is included in Sheets 151, 164, 165, 166, 179, 180, 181, 196, 197, and 198 of the 1-inch map of the Ordnance Survey of England & Wales. To be more precise, the area is bounded on the north by the River Severn from Newtown to below Welshpool; on the east by a line from Welshpool by Forden, Chirbury, and Church Stoke, to Craven Arms and Ludlow, thence by Woofferton and Tenbury to the neighbourhood of Bromyard, and so to Hereford; on the south by tho scarp of the Brecon Beacons and the Black Mountains; and on the west by the River Wye from Builth Wells to its junction with the Ithon, thence along that stream to its head, and so northwards to Newtown. The country is somewhat complicated topographically, and the drainage-system has been rendered more intricate by the efforts of ice during the glaciation. The two principal elevated areas within the district are Clun Forest (1666 feet above O.D.) and Radnor Forest (2166 feet O.D.), the former consisting of Ludlow rocks and Old lied Sandstone, and the latter of Wenlock and Ludlow Beds. South-east of Radnor Forest lies a somewhat faulted belt of country consisting of Silurian rocks, in which the escarpments of the Aymestry and Wenlock limestones are prominent features. South and east of the Silurian country lies an extensive area of

Societies and Academies

LONDON. Geological Society, Jan. 23.—J. K. Charlesworth: The South Wales end-moraine. The Irish Sea ice stood over Cardigan Bay at the period of the maximum advance of the Newer Drift period, and ponded back the natural drainage of northern Pembrokeshire and southern Cardiganshire to form a chain of extra-glacial lakes connected by marginal streams. The end-moraine of the Newer Drift passes across eastern and southern Wales. In northern Pembrokeshire and southern Cardiganshire it was laid down along the edge of the Irish Sea ice. Farther east, the moraine is practically continuous, and represents the marginal product of the local Welsh ice, which was centred in the mountains of Central Wales, the Carmarthenshire Vans, the Brecon Beacons, the Black Mountains, and the mountains of Radnor Forest. This ice flowed beyond the outlets of the great valleys of the east to form the valley-glaciers of the Severn and other rivers, and extended southwards on to the coastal plain of Glamorgan. The Newer Drift is of early Magdalenian age.—A. Jowett and J. K. Charlesworth: The glacial geology of the Derbyshire dome and the western slopes of the Southern Pennines. The Derbyshire Dome of the Southern Pennines was overridden at the period of maximum glaciation by ice from the north and north-west. This is shown by the occurrence of patches of true boulder clay, by the wide distribution of erratics of Lake District and Galloway rocks over the dome and along its valleys, and other evidence. The upper limit of the erratics from the north follows the outer flanks of the southwestern Pennines at about 1250 feet above sea-level. The ice-recession from this position was associated with a copious marginal drainage, which eroded a well-developed suite of channels linking a number of big extra-glacial lakes in the valleys of the western Pennines.

The Upper Towy Drainage-System

The most remarkable feature in the physical geography of Wales is undoubtedly the great plateau which extends almost without interruption from near the coast of Denbighshire in North Wales through Central and South Wales, where it occupies a large area of the counties of Cardigan, Carmarthen, Radnor, and probably also of Brecon. It truncates alike the highly folded Lower Palæozoic rocks of North and Central Wales and the gently inclined Old Red Sandstone marls of Breconshire. Its surface is apparently little influenced, either by the attitude of the rocks or by their lithological characters. It abuts against the mountains of North Wales between Cader Idris and Snowdonia, which in places rise abruptly above its level, while southwards it extends to the foot of the great Upper Old Red Sandstone escarpment of Breconshire and Carmarthenshire, which overlooks it as a line of high cliffs overlooks a level foreshore. Sir Andrew Ramsay attributed the formation of the plateau to marine denudation, and at one time regarded the escarpment of the Brecon Beacons as an ancient line of cliff. Occasional references to the plateau occur in later publications. I have given reasons for distinguishing in Central Wales two distinct plateaux: namely, the Higher Plateau described above, and the Coastal Plateau which lies south of the Dovey Estuary and, extending inland from the coast of Cardigan Bay for a distance of 3 to 15 miles, is sharply marked off from the High Plateau on the east. The Coastal Plateau was attributed to marine erosion