The area around Knighton, which also includes NW Herefordshire, is one of only three areas in the country for which there is not a British Geological Survey printed geological map.  Original surveying in the area was done in 1850, by the Royal Engineers, and published by the Tower of London!  Since then, various independent researchers have surveyed small parts of the area but BGS never did survey the area at all due to policy constraints.

In 2013 Dr Arthur Tingley organised a project to fully survey the area and the resulting map has just been printed.  The survey work was carried out by volunteer members of the Teme Valley Geological Society (TVGS), Herefordshire and Worcestershire Earth Heritage Trust and the Woolhope Naturalists’ Field Club, in consultation with academic specialist geologists, and all published and unpublished sources concerning the area.  He was also allowed full access to tunnelling work which was being carried out to improve the transport of water supply for Birmingham from the Elan Valley reservoirs.

EVA tunnel boring machine exposing Wern Quarry Formation 50 metres below Frydd Wood Knighton

 

 

 

 

 

 

 

 

 

The surveyors who were allocated areas to map were Paul Bate, Mike Brooks, Sue Chester, Ingrid Darnley, Kirsten Hunter, Alan Hughes, John Moseley, Neil Raha, Arthur Tingley, Adrian Wyatt.  The entire area was thoroughly checked by Arthur and the team.

Progress was reported through the TVGS web site, and John Nicklin has recently edited those to provide an informative and illustrated history of the project, which can be seen at  https://geo-village.eu/knightonmapping/

Some of the surveyors at an initial planning meeting followed by a lithology familiarisation session given by Professor Mike Rosenbaum at the Ludlow Resources Centre

A total of 30 volunteers, organised by Moira Jenkins, made 15 visits over 3 years to a variety of selected sites to look for fossils, with a special emphasis on graptolites which were used to date the rocks.

Palaeontological volunteers fossil hunting

Volunteers resting

The Geologists’ Association Curry Fund made a grant which allowed printing of a limited edition of 100 maps.  This is a fine result following the format of BGS maps including cross sections, keys, and stating references.  Forty of the maps have been made available to specific researchers, the surveyors and the Libraries of BGS, The Geological Society of London, the Geologists’ Association and six local geological societies, along with relevant museums.  The rest of the maps will be used for education and supporting the work of the Herefordshire and Worcestershire Earth Heritage Trust who are managing the distribution.

The printed map is a folded A0 sheet containing the geological map, sections and columns along with a concise explanation, along with a structural interpretation and geophysical maps (see below).  Although the publication marks a benchmark, we shall maintain a watch for new exposures and continue to record new data, and make corrections and revisions of interpretation as needed.

A postcard of the published Knighton Sheet (2022).

This area of the Welsh Borders is crossed by major lines of faulting such as the Church Stretton Fault System and Pontesford-Linley Disturbance.  In brief, much of the area has a Neoproterozoic basement, and integrates the geological sequences of the Welsh Basin with those of the Ludlovian Shelf successions.  The area illustrates the evolution of facies on a clastic slope during the Ordovician to Silurian, in an era of local and eustatic sea level variation accompanied by environmental change.

View from the Whimble [Radnor Forest] looking east towards the Church Stretton Fault Line – Brampton Bryan on the left, Dolyhir to the right, in the far distance Malvern Hills.

Graptolites were used to date horizons which were similar in appearance.

The graptolite Saetograptus leintwardensis, the earliest occurrence of which is at the Gorstian–Ludfordian boundary.

One of many trays of rocks which support the observations

Water Break its Neck waterfall, the head of one of the dingles cut into the rounded hills of the Radnor Forest.

Andrew Barrington of Barrington Print, working on the Knighton Sheet. 

 

 

 

 

 

This was a major challenge for a small printer to convert a hand-drawn, and then water-coloured map into an A0 sheet in the style of a BGS sheet layout.  It is the first such map produced privately.  Production meetings between Arthur Tingley and Andrew Barrington took place every 2 weeks for 2 years during the COVID epidemic.

Having completed the survey and cartography the next stage is to work on the sheet explanation, based upon the abundant amount of data and observations that our surveyors and associates have made.  New work will provide a stimulus to new ideas, along with a reinterpretation of the wide variety of published and unpublished sources.

The objective of this survey was to fill the gap left in the BGS mapping program in 2013, and to provide a basis for further research.  Some collaborative research has already followed on [Ray et al 2021], and we should anticipate more to come.  It started from a clean sheet to test the state of existing knowledge, and hence we have not been bound by convention.  Thus we provide a view of the geology which mostly confirms previous work, but challenges other aspects.  So, it is now up to others to either prove our interpretation wrong, refine or reinterpret these observations.  Such is the process of science.

Reference:

Ray D.C., Jarochowska E., Hughes H.E., Claussen A.L., Tingley A.C., Moseley J., and Bremer O. 2021

The Silurian Transgression of a Palaeoshoreline: The Area between Old Radnor and Presteigne, Welsh Borderlands. Lithosphere Article ID 7866176, 24 pages. https://doi.org/10.2113/2021/7866176