Corn Du the last ice age by ice scouring out hollows below the peaks, the water being partly dammed by moraines of rock debris carried down by ice action subsequent to plucking and frost shattering. Corn Du Corn Du is a mountain immediately to the southwest of Pen y Fan and the second highest peak in South Wales at 873 m (2,864 ft), situated in the Brecon Beacons National Park. The summit itself is marked by a well structured Bronze Age cairn with a central burial cist like that on nearby Pen y Fan. The two summits are visible from great distances
Pen y Boncyn Trefeilw Y Groes Fagl. Pen y Boncyn Trefeilw Pen y Boncyn Trefeilw is a subsidiary summit of Cyrniau Nod in north east Wales. It forms a part of the Berwyn range called the Hirnantau. It has two tops: Stac Rhos and Pen y Cerrig Duon. Pen y Cerrig Duon is now listed as a deleted Nuttall due to re-surveying. The views from the summit are extensive, if unremarkable due to the featureless, flat moorland surroundings. The summit is marked by a small cairn, is which located only a few metres from a track road that continues on to the pass between