Glyn Tarell includes the villages of Libanus and Tai'r Bull.

The lie of the land

The Community ranges in height from 140m in the Usk valley east of Llansypddid to 886m at Pen y Fan, the highest peak in southern Britain.  Other notable summits include:

• Corn Du at 873m (SO 007213)
• Fan Fawr at 734m (SN 970193)
• Fan Frynych at 629m (SN 957227)

The area is of course drained primarily by the Afon Tarell which meets the River Usk at Llanfaes.  Its two main tributaries are Nant Cwm Llwch and Nant Gwdi.

Old Red Sandstones

The entire community is formed from rocks of the Old Red Sandstone.  Those in the northern, lower-lying half belong to the St Maughan's Formation.  The higher ground, in the south, is formed from sandstones of the Senni Formation (below about 600m) and of the Brownstones Formation above this height.

The very summits of Pen y Fan and Corn Du and the plateau south of Bwlch Duwynt extending south to Cefn Crew is formed from the harder-wearing sandstones of the Plateau Beds Formation.

A number of major geological faults have been identified in the area including the NE-SW trending Cribarth and Swansea Valley Faults

Legacy of the Ice Ages

There are several spectacular glacial cirques including those of Cwm Llwch and Craig Cerrig-gleisiad.  Llyn cwm Llwch occupies a small rock hollow excavated by a glacier beneath the NW spur of Corn Du.  Below Craig Cerrig-gleisiad is an unusual glacial moraine whose origins also involve a major landslip involving the tilted bedrock. 

There is a spectacular glacial moraine in the lonely cwm of Blaen Crew south of Corn Du.  Beneath Craig y Fro is another moraine whose story may also be complicated by an ancient landslip.

Archaeology

One or two earthworks and cairns.  There are the remains of a settlement in Cwm Cerrig-gleisiad.  Sarn Helen, the Roman road cuts through the westernmost corner of the area. 

Maps

Geology

Sheets 213 'Brecon' and 231 'Merthyr Tydfil' of the British Geological Survey’s 1:50,000 map series of England and Wales together give full coverage of both the bedrock geology and superficial deposits of the Community area.  Sheet 231 is published in two editions.  BGS publish a 'memoir' and a 'sheet explanation' to accompany these maps.

General

The following Ordnance Survey maps cover the Community:

• Landranger sheet 160 'Brecon Beacons' (1:50,000 scale)
• Explorer sheet OL12 'Brecon Beacons National Park/Western area' (1:25,000 scale)

Public transport

Bus services operate along the road.

See Traveline Cymru for bus and train services including stops, timetables and route-planning information.