Geograph - photograph every grid square

The Afon Hepste meets the Afon Mellte within this square, both rivers having cut deeply down through a succession of rock layers in the last few hundreds of thousands of years as the Vale of Neath to which they are heading was excavated deeper and deeper by glacial ice during the last and earlier ice ages. The steep valley sides are thickly mantled in what has been described as Wales’ rainforest, providing a habitat for a large variety of lower plants which enjoy the damp conditions that the shade and tumbling rivers provide. Almost all of the land in the square is owned and managed by Natural Resources Wales who are charged with overseeing the SAC designation enjoyed by the native woodland and with managing the softwood plantations on the flatter higher ground.

The abandoned farmsteads of Cilhepste-cerig and Cilhepste-fach by which a popular visitors’ path passes, bear witness to the agricultural way of life which was ended in the middle of the C20th when the area was afforested. Also abandoned are some of the steep, twisting tracks which were used to move between river and plateau in the past; only those accessing Sgwd yr Eira are still frequented.

There are five waterfalls marked within the square on the 25K Ordnance Survey map, one of which Sgwd yr Eira (translated as fall of snow’), gets 99.9% of the attention. Celebrated as the fall behind which you can walk, the constantly wet ledges of sandstone and mudstone behind the falling curtain carry a public footpath across the border between Powys and Rhondda Cynon Taf. The cap-rock is Twrch Sandstone (a.k.a. Basal Grit). The immediate approaches to the fall on either side are very rough, in contrast to the paths down the valleys sides which have been improved in recent times. A NW-SE aligned geological fault crosses the Hepste valley west of the falls and it is thought that the falls were initiated at that spot and have retreated upstream over an unknown period. The fault is also responsible for the gullies either side of the valley; the larger one on the south side provides a convenient route down which the recently realigned path twists.

Another fault runs parallel to the first some 200m downstream and gives rise to the Lower Cilhepste Falls, rather more difficult of access and less visited than their more famous neighbour. A small block of limestone bedrock (an ‘inlier’ in geologists’ terms) is exposed within the heart of these multi-tier falls – otherwise everything else in this square is gritstone (sandstone) or mudstone (shale).

Creeping into the southwest corner of the square is the furthest outpost of the former ‘Glyn-neath Gunpowder Works’; the rest of this extended site is stretched out along either side of the Mellte river down to the outskirts of Pontneddfechan. More on this in the discussion on square SN 9108.