Pen Allt-mawr is a high subsidiary summit of

Waun Fach Waun Fach is, with a summit height of , the highest mountain in the Black Mountains in south-eastern Wales. It is one of the three Marilyns over 600 m that make up the range, the others being Black Mountain and Mynydd Troed. To ...

and the third highest peak in the Black Mountains in south-eastern

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 ...

. A very recognisable and prominent peak of the Black Mountains, it lies near the end of the more westerly of

's two broad southern ridges. Its top Pen Twyn Glas is to the north, while its close neighbour

Pen Cerrig-calch Pen Cerrig-calch is a subsidiary summit of Waun Fach in the Black Mountains in the Brecon Beacons National Park in southern Powys, Wales. Its summit, at a height of 701 m (2,300 ft), is marked by a trig point. The peak sits high abov ...

is to the south. A prominent spur 1 km to the SSW of the summit is known as Pen Gloch-y-pibwr. The stepped Bryniog ridge curves southward from this point. Its summit is stony and has damaged

Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...

cairns and a large shelter cairn together with a

trig point A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The nomenclature varies regionally: they a ...

. Further Bronze Age cairns are found along the western edge of the plateau to the south.

Geology

The summit of Pen Allt-mawr is at the northern tip of a broadly triangular summit surface formed from a slab of southerly tilting upper

Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also exte ...

traditionally known as the Quartz Conglomerate. These rocks which date from the Late Devonian Epoch are continuous with those of Pen Cerrig-calch but other than a tiny outlier forming the summit of Sugar Loaf, are found nowhere else within the Black Mountains. Beneath the Quartz Conglomerate are the

Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s of the Brownstones Formation which form the upper slopes and summits of Pen Twyn Glas and Mynydd Llysiau to the north (though are barely seen). More readily eroded mudstone bands within this formation give rise to the stepped appearance of this hill and many of its neighbours. Sandstones of the Senni Formation (traditionally the 'Senni Beds') form the lower slopes of the mountain.

References

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External links

www.geograph.co.uk : photos of Waun Fach and surrounding area
Hewitts of Wales Nuttalls Mountains and hills of Powys Black Mountains, Wales