Heol Senni quarry

This large and obvious disused open quarry on the hillside above the village of Heol Senni was an important source of stone in the early part of the 19th C. It was a dangerous place and it is believed that one quarryman, who lived at Dan-y-Graig Isaf was killed by falling stones in the early part of the 20th C.

The quarry is important now, not for quarrying, but for its significance to geologists, and palaeontologists. It is also often visited by walkers, paragliding groups (see for example one flight report) and others. The quarry is listed in the Geological Conservation Review (GCR) database, where it is part of ".. the British geological record of Earth history from about 417 to 354 million years ago (Ma)..". It contains non-marine rocks called the ‘Old Red Sandstone’ which is described by the GCR in detail. The site is a protected 'Site of Special Geological Interest' and may not be used to collect fossils, stones or other components without a licence. The Countryside Council for Wales is responsible for it and this is their description of it:

National grid reference: SN 914222, Site area: 3.4 hectares
The site is of special geological interest on two scores:
(i) Non-marine Devonian: the site has cliff exposures of the Brownstones (the upper part of the Welsh Lower Old Red Sandstone). The Brownstones here consist of pebbly, cross-bedded sands, which formed in a large braided river system. The cliffs allow reconstruction of bar morphologies and river size, and show the way channels were stacked vertically to build up the sequence. The well developed stream topography between bars and channels that is seen in the deposits here is typical of the eastern outcrops of the Brownstones, and contrasts with the deposits of the western Brownstones in south Wales. This locality is the best of the eastern Brownstone outcrops, showing a distinct form of river alluvium.
(ii) Vertebrate palaeontology: the type and only locality for Althaspis senniensis. Chordates are extremely rare in the Senni Beds and are know only from two other sites. Althaspis senniensis is a typical pteraspid of the ‘Dittonian’ and is very similar to, and might even be conspecific with Althaspis leachi, a form known throughout north-west Europe at the top of the Gedinnian Stage. Another Senni Beds quarry locally yields Rhinopteraspis dunensis, which occurs in the type area of the Siegenian Stage. Taken together these two quarries show that the Gedinnian/Siegenian boundary lies somewhere within the Senni Beds between these two fossil-bearing horizons. At present, work is being concentrated on these two species, and future research potential lies in determining the stratigraphical and facies controls on their distribution in Europe.

It is sometimes a nesting site for peregrine falcons and foxes may be seen on ledges in the upper cliff-face of the quarry. Two fox hounds from the Sennybridge Farmers' Hunt were lost in 2001 when they ventured out onto one of these ledges, while chasing a fox, and fell to their deaths.