Summary of site:
The rocks in this stream section are the varied mudstones thought to be near the top of the Ballinamallard Mudstone Formation bridging the time line separating two of the major divisions of the Carboniferous period, the Visean below and the Namurian above. The section also completes the sedimentary history of a major, land-locked desert basin subsiding and filling on the south eastern side of a prominent upland ridge of Devonian and Tyrone Igneous Complex rocks.
The exposure, in the Makenny townland stream is good but, unfortunately, not complete. The dominant rock types are a greyish-red mudstone and beds consisting of baked, angular mud flakes swept off a desert floor in flood conditions. Thin sandstones part the mudstones at intervals. The top 15 m of the section to the north west show a change to grey and greenish-grey lime-rich mudstones which contain vague, filmy impressions of fossil plants, so far not identified and a flora of microscopic plant spores representing 9 species. One of them, Reticulatisporites carnosus, is restricted in time to a period representing the last stage of the Visean, the Brigantian and the first of the Namurian, the Pendleian, fixing events to 333 million years ago.
The Ballinamallard Mudstone is the last of three formations that make up the Kilskeery Group and it rounds off its history. The first two, the Topped Mountain Formation and the Ballyreagh Conglomerate Formation, record the progressive deepening and filling of the desert basin. The first phase, the Topped Mountain, poured the 1,000 m of mainly sand into the desert lowland south east of the upland ridge. Strong uplift followed, leading to more vigorous and aggressive erosion with desert storms swilling coarse-grained cobble and gravel fans down the flanks of the ridge and onto the earlier sands. These are the rocks of the Ballyreagh Conglomerate Formation. The slowing and eventual stalling of uplift led to the finer sediments from the now diminished ridge, washing over the conglomerates and the 1,000 m of these fine muds are now the Ballinamallard Mudstone.
While all this was happening, conditions further south, preserved in the rocks on Cuilcagh Mountain, were quite different with marine invasion from the south creating deltas, tidal deposits, salt-encrusted coastlines and, within the sea, noxious black shales.
This locality is important because it fixes the age of the final events in the desert basin represented by the Kilskeery Group at the end of the Visean and the start of the Namurian.
There are no threats to the site with the possible exception of overgrowth.