Cusop History Group

Many thanks to Roddy for the following information, posted on our Facebook page:

The geology of Cusop seems to be a mystery to many people. The rocks are of the red beds of the Upper Silurian and the Lower Old Red Sandstone ( Devonian) over 400 million years old. This sequence of rocks can be found from the Clee Hills and as far as the tip of S W Wales. It underlies the coal measures the so called Carboniferous to the south.This great arc of deposited material once lay close to sea level and and tropical seas, it was also a coastal region lying south of the Equator which has since broken up and drifted northwards. From the Clee Hiils to S W Wales, throughout Herefordshire, parts of Gwent, the Welsh Coal valleys and the Forest of Dean which it also underlies there are within these area two major levels or horizons. The so called Townsend Tuff Beds and higher up the (old named) Psammosteous Limestone. The TTB and the PL. These names have been changed in the very modern literature for no good reason as far as I can see but none other than to confuse the reader. Most books will use these older terms, two others are the Downtonian and the Dittononian, Downton and Ditton are closely linked with places in the Clee Hills. The change of names has been strongly objected to. During Sir Roderick Murchisons time he suggested to place the base of the Devonian system at the Ludlow Bone Bed at Ludford Corner in Ludlow. Much study in those Victorian days of the area around Ludlow by geologists was done and little was then understood what actually they were they looking at. Murchison took on the job of sorting it out, he made a few mistakes but he was a pioneer and many followed him as time went on. He even visited Cusop himself on his tour of Wales in 1831 and mentions the search for coal. Enough of geological the history which would fill a book of it's own. The TTB was noticed as an outcrop of rock in Merbach Hill where it is particularly interesting, it is three layers of tuff, a volcanic air fall tuff from by it's nature an explosive Plinian type eruption. The rock is a green grey and very sharp, hard and brittle. This can be seen at Cusop in the brook upstream from the old brickyard but it actually can be found in the lower bank on the left side of the track in the brickyards before you get to the woodland. It may be somewhat grassed over but is not much above the level of the trackway. It is not easy to see any layering due to the soil cover. The TTB has been traced south to Llanigon Brook and there are two outcrops at Talgarth but one may now be covered. There is a geological anomaly at Talgarth which may be down to a fault in the rock, British Geological were going to investigate this but money, time and manpower being a problem it may never be sorted out now. The other horizon is the P.L. approximately 100 meters above the TTB. The P.L. is a calcrete or a paleosol formed under desert conditions with very low rainfall. These can be found in modern deserts. Normally just one layer some two meters thick but there are claims for three near Dorstone, Scar Quarry lane but I have seen two layers ar Hay Forest Velindre and in the area of the Park Woods Talgarth. These limestones were burnt in kilns for lime and Cusop still has the ruins of a lime kiln in Cusop Dingle. The layers of limestones can be thin they are not uniform everywhere. The rocks below the P.L have often been referred to as Downtonian and above the P.L. as the Dittonian.
The Downtonian rocks are mud dominated and the Dittonian sand dominated. The whole area had been affected by tectonic earth movements throughout it's formation, possible tsunamis affected the coastlines in Downtonian times and seasonal heavy rainfall from a high mountain mass to the north. This accounts for the great mass of sediment spreading out on a coastal plain which at the same time was sinking under it's own weight. This has been suggested as the basin the later coal swamps of the Carboniferous in South Wales formed in. Borings have been sunk through the Carboniferous into the Devonian and Silurian which suggests this is in fact the case. The Silurian and the Devonian ( Torquay) marine limestones have shown that there was a very lively ocean containing many creatures. The dry land 'continental' red beds of the Silurian and the Devonian and this goes for Cusop has shown primitive fishes lived in this arid climate in rivers and perhaps playa lakes some of very temporary origin. From the Clee Hill to S W Wales fossil plants, arthropods and fishes are found but usually in pockets which can be rich in fish fossil material. Looking like tadpoles with an armoured plate. There is still much to be discovered, there is still much to learn. Many fish had scales that were like sharks scales and were likely to have been ancestors of the modern shark. Fish with teeth, some with no teeth, long bony external fin spines. Strange plants and sea scorpions some as big as a man ( found in Germany) they are all there to be discovered?