We met at the Talbot, Knightwick, had a look at the large stone apple press, (HERE for Building Stones database information) its quartz conglomerate wheel, past the now converted church (HERE) with its varieties of building stones then tackled the steep road to join the Worcestershire Way going North. En-route lying on the grassy verge to stop cars parking, we discovered a triplet of foreigners, rocks that definitely do not come from this neck of the woods (see pics). Later investigation was conclusive in that the two obviously igneous rocks were granites from Shap in NW England and the black rock with quartz vein seems to be Greywacke, probably from Scotland, a very mixed, sedimentary rock formed by underwater turbidity currents (the third picture on the above web page is very similar to the rock we saw by the roadside in Knightwick in my opinion). Thanks to Prof. Donny Hutton and Moira Jenkins for the detective work. Moira showed us a beautiful polished piece of Shap granite that she has on a shelf at home.
Cross the road, watch the traffic, carry on up the Worcestershire Way, through the dense, mixed woodland that now cloaks the hills. Closer examination and explorative walks show a hillside pock marked all over with the remains of old quarries and of long-left buildings. There must be a fascinating social history waiting to be discovered.
According to the geological map, along the road and at the top of the hill, we were in Wyche Formation, Silurian, no lime content (verified with acid afterwards), fine silt and sandstones (Sandstone, Micaceous. Sedimentary Bedrock formed approximately 428 to 436 million years ago in the Silurian Period. Local environment previously dominated by shallow seas. Generally grey, brown and pale green mudstones and siltstones with thin tabular green sandstones. Setting: shallow seas. These rocks were formed in shallow seas with mainly siliciclastic sediments (comprising of fragments or clasts of silicate minerals) deposited as mud, silt, sand and gravel).
Wyche Formation from Top of Ankerdine
The Wyche is older than the more familiar Much Wenlock limestone of the area, which according to the map, we traversed on our way uphill. One can only presume that the limestones were used for rubble building and for lime burning to put on fields or to make lime mortar, as happened all along this ridge. On the other hand the Wyche is quite blocky in nature, see pics, and probably lends itself quite well to more regular building. At any rate at the top of the hill, yards before the East Malvern Fault completely transforms the geological content, lie the remains of quarries, with old entrance ways, ancient yew trees and some small exposures. In short order, a group could easily make this more visible and accessible but doubt the County Council would appreciate that as it is one of their managed areas and previous proposals of ours have been dismissed, well, dismissively.
From there we strolled along the Worc. Way to the picnic and car park areas where a board explained something about the Common. Good views over towards Bromyard and its plateau of Devonian St Maughans. In not too unseemly haste we tripped downhill into the comfort of the Talbot’s lounge and the health giving properties of its home brewed ales. Very pleasant.
HERE is a geological map of the area followed below the evening’s pictures.
During the week I have come across two topics worth noting. The first is a critique of Tolkien’s map of Middle Earth from Lord of the Rings (map). The second is a fascinating article on minerals that have yet to be discovered (+-5000 known +-1500 to go) HERE
Stacks on the latter on the web, we even brought home samples from the plentiful deposits found on Crete. Stromatoporoids not so well known but if anyone DOES know about the subject then surely it is Dr Stephen Kershaw (Bio). Stephen has been working for years, gradually building up his research knowledge on the subject and now, towards the end of that jigsaw puzzle he needed to see if any of the missing pieces were to be found in the Much Wenlock formations in Martley. Via our mutual contact and friend Dr David Ray, himself studying the bentonites in the same formations, arrangements were made for a visit to Martley on 25th November.
Three of us (Ingrid, Ian and self) were able to join Stephen, his wife Dr Li Guo (PhD on Quatenary hot spring carbonates (travertines) in Tuscany, from Cardiff University. Li is from Sichuan Province in central China), and Dr Simon Schneider (PhD on Mesozioc Molluscs, from Erlangen University in Southern Germany). Both Li and Simon work for CASP (Cambridge Arctic Shelf Programme) based in Cambridge. On hearing this, I mentioned that Hilary (Harland) is our society librarian, news greeted with surprise and joy by Li. After all it was Hilary’s father WB (Brian) Harland who established the organisation in 1948, known then as the Cambridge Spitsbergen Expeditions, that later in 1975, became CASP. We hope that Li and Hil will meet up!
Back to the little beasties. Stephen has created a very readable and quite light-hearted website, its main aims the explanation of ‘Earth surface environments and processes’ to the general public and to ‘provide information to geo-science researchers’. It is within these fully illustrated pages that you can read how the two stromatos from over 400 million years ago (at Martley sites) can be differentiated.
First stop on 25th, was the main quarry face at Penny Hill, a fossiliferous location with plenty of corals, a sign that there might also be stromatoporoids, and there were! Not many but they were there. Patient explanation and demonstration by the three doctors, led Ing, Ian and self to believe that we too could go off and find them on our own but now I am not so sure, hmm. They are layered as are their near namesakes, closer examination revealing what Stephen calls a ‘Kremlin wall’ design, and his site illustrates exactly what he means:
Having used his picture without permission I hope the KGB do not visit Martley soon.
Stromatoporoids layers showing brick like segmentation
After Penny Hill, a rare visit to one of Martley’s finest exposures (in the Coalbrookdale formation)-that behind Quarry Farm. The welcome by Val and Peter Wedell-Hall has to be noted and appreciated. They were both keenly interested in the subject that Stephen and team were researching. Their quarry face has a coral reef and again provided samples for the team. An outstanding visit was capped by the offer of a glass of champagne. Lo and behold, a bottle of Moet was produced, opened and enjoyed, by myself certainly, others too. I hesitate to tell you that one philistine tipped half his glass away as he was driving, though not at the time. Never has geology been so enjoyable.
Later visits to the Canyon and to the new face that we have cleared near the canyon did not bear fruit. We all parted at Callow farm drive, beautiful sunshine, lovely day, a most enjoyable and educational experience–thanks Stephen, Li and Simon, hope to see you again soon.
TVGS would like to thank Graham Worton for his excellent, clear and comprehensive guide to this unique and totally essential to visit area—thank you Graham—we hope to see you again!
Thank you too to Ingrid Darnley for contributing this report on the field trip.
A small and enthusiastic group of TVGS members met up at the Dudley Canals Trust car park. On a baking hot day the prospect of spending an hour in the cool Dudley canal tunnels was certainly an inviting one and we weren’t disappointed. This trip had been long in the planning and we were all very much looking forward to it, especially as we had as a guide Graham Worton, Borough Geologist and Keeper of Geology at Dudley Musuem & Art Gallery.
The Dudley Canal trust is run completely by volunteers and what a grand bunch they were, the Black Country humour providing a great accompaniment to the stunning trip through the tunnels. As someone who lived in Dudley for more than 35 years I was ashamed to admit I had never been in the canal tunnel or to Wrens Nest before.
425 million years ago rich limestone and coal seams were created beneath the West Midlands. These valuable deposits laid the foundations for the Industrial Revolution with the Black Country at its heart., the exploitation of these resources resulted in the spectacular network of underground canal tunnels carved beneath the region to mine the raw materials that powered industrial growth.
The trip gave us an underground view of what we were to see at Wrens Nest as the tunnel underpins both Wrens Nest and Castle Hill. The insides of the hills were extensively exploited and became a maze of mines, tunnels, steps and railways.
Our boat entered the underground tunnels via the ‘Tipton Portal’ entrance. The Dudley canal tunnel was very important during Industrial Revolution and beyond as the mining companies used it to bring limestone out from the galleries where it was being dug out. The boats were loaded up and then the cargo was transported to ironworks in the Black Country, Birmingham and beyond. We had a trip of 45 minutes where we saw several disused caverns, some of the trip taking place in the dark with excellent multi-media and tableaux to re-create some of the scenes from long ago. The ‘Introduction to Geology’ film was excellent, the best I have seen in its class. Fortunately our way out was illuminated by the twinkling of John Nicklin’s (and friend’s) white legs walking along the tunnel walls, ‘legging’ the boat in the old traditional way. Seriously John, good on you for volunteering!
Graham Worton supplemented the boat captain’s commentary adding to the interest of the boat trip as a taster for what was to come at Wrens Nest. Leaving the boat, we drove a short distance to the Wrens Nest nature reserve, parking in the unlikely surroundings of the old Mons Hill Dudley Technology College.
The Wren’s Nest is a disused Victorian quarry and derives its name from the Old English word Wrosne, meaning “the link”. This may relate to its topographical position on the boundary between the Severn and Trent watersheds.
Wren’s Nest National Nature Reserve is a geological site of exceptional importance and is one of the most notable geological locations in the British Isles. It is internationally famous for its large numbers of beautifully preserved Silurian limestone fossils. In recognition of its geological significance, Wren’s Nest was declared a National Nature Reserve in 1956, the first National Nature Reserve for geology, and also a Site of Special Scientific Interest in 1990 because of its exceptional geological and paleontological features of Silurian age.
The folded layers of the Much Wenlock Limestone Formation (formerly the Dudley Limestone) that form the hills have been quarried above and below ground for hundreds of years. The rocks of Castle Hill, Wren’s Nest and their surrounds provided the raw materials to establish Dudley as the centre of what became known as the ‘Black Country’ owing to the juxtaposition of materials for the manufacture of iron:- coal, ironstone and limestone together with fireclay, a unique assemblage.
The limestone deposits were an important source of building stone, then for lime mortar and agricultural fertiliser. During the height of the industrial revolution up to 20,000 tons of rock were removed annually from Wren’s Nest and used in the many local blast furnaces. Mining and quarrying ceased in 1924, leaving the hills honeycombed with a network of underground workings and caverns. However, without the industrial revolution, the rocks at Wren’s Nest might never have been exposed or the fossils discovered. It was during the mid-1840s that many of the best fossils were found, including the ‘Dudley Bug’ trilobite, which became an important local symbol and was featured on the town’s coat of arms until 1974.
Limestone mining has in particular left a spectacular legacy of quarries and caverns, including Dark Cavern, Britain’s largest man-made limestone cavern, that, according to our guide could accommodate the Houses of Parliament and St Paul’s cathedral (twice!). There are ambitious plans to re-open it, old wharves and a defunct canal and to hold shows and entertainment in them as once was. The caverns were linked to the national canal system by the Dudley Tunnel, the earliest narrowboat canal tunnel in the world. Built in 1785 at just over a mile long, it cuts the English watershed and when first built was the longest canal tunnel in England.
Wren’s Nest and Castle Hill contain excellent exposures of middle Silurian (Wenlock and lower Ludlow series) rocks, including a definitive section through the Much Wenlock Limestone Formation. The Wenlock Limestone of Dudley contains the most diverse and abundant fossil fauna in the British Isles: over 600 species of marine invertebrate, representing some 29 major taxonomic groups. The site is the type locality for 186 species (more than any other British site); 63 of these recorded nowhere else. In general the majority of the limestones were deposited in shallow tropical or sub-tropical waters which were quiet or intermittently agitated, although there were periods of higher energy. At times the conditions were conducive to the development of patch reefs, with sub-tidal and lagoonal or similarly protected waters allowing reef growth just below wave-base.
The Wenlock Limestone of Dudley is a fossil lagerstatten, containing rare and important life assemblages, in the form of beds of articulated crinoids (sea lilies) superbly preserved under deposits of terrigenous mud and volcanic clay. Rare annelid (worm) and early plant remains have been found, containing soft tissue. Other features of the site include bioherms (fossil ‘patch’ reefs preserved ‘in situ’), and expansive ripple beds, which provide evidence of littoral zone conditions.
The famous geologist Sir Roderick Murchison visited Dudley Murchison visited Dudley around 1837. In 1839 he published an illustrated catalogue of Silurian fossils, ‘The Silurian System’, of which 65% were from the Wrens Nest limestone quarries. These original fossils including crinoids can still be seen on display in Dudley Museum and Art Gallery today.
In 1839 he was at Dudley (at around the time he documented our own Martley Rock gravel pit) and again in 1849 to address members of the British Association, inside Dark Cavern – by gaslight. An estimated 15,000 people attended each event, with Murchison being acclaimed ‘King of Siluria’ at Wren’s Nest, and carried out on the shoulders of the quarry workers for whom he had become a great friend and favourite.
Graham has recorded a 3 minute YouTube recording about this at awww.youtube.com/watch?v=eIAMy-BmWmc
THE GEOLOGICAL TRAIL
Graham took us along the Wrens Nest Trail which is a walk of about 3 km.
In a description of this type it is impossible to do justice to the descriptions Graham gave throughout the trip which, whilst focusing on the geology, explained this within the context of the social and economic history of the area which was fascinating. What I have done is to try and give a brief overview.
Quarry trench, Mons Hill
This is where our tour started with a general introduction looking at the southern face of the quarry.
This man-made trench was excavated in the 18th century. Three distinct lithological units can be seen here. The oldest of these is the Nodular Member, the top of which forms the large bedding plane. This unit passes up, eastwards, into the Upper Quarried Limestone Member which comprises a sequence of alternating flaggy limestones and thin shales, overlain by a massive 4.2 metre thick bed of coarse grained blue-grey limestone. Above this is a 1.2 metre thick bed of nodular limestone with shale partings. Continuing eastwards, the sequence passes up through silty shales with thin nodular limestone bands into pale grey shales. The latter has two bands of green bentonite clay (formed from water-lain volcanic ash) several metres above the base. The entire sequence dips eastwards at an angle of about 60 degrees. Limestone was extracted along the strike of the beds, hence the linear shape of the workings.
The Nature Conservancy Council (N.C.C.) Cutting.
This is a narrow cutting, about 35 metres long, which was excavated by the NCC in 1977 to provide a dip section through the Nodular Member. The eastern end of this cutting corresponds with the top of the Member. It passes through a sequence of progressively older beds, comprising nodules and lenses of limestone, separated by silty shales and mudstones.
At its western end the cutting joins a trench formed by quarrying of the Lower Quarried Limestone Member, a section of which can be examined in the north face of the workings. It is considerably thicker (16.2 metres) than the Upper Quarried Limestone Member, and comprises thickly bedded blue-grey limestone with shale partings, notably near the top and bottom. At the top is a 26 cm bed of limestone which was usually left to form the roof of underground workings. Colonies of stromatoporoids and corals (Coenites, Favosites) are preserved in position of growth towards the top of the Member.
The lowest, and therefore the oldest beds, are exposed in the north-western corner of the trench. They consist of greenish grey mudstones with limestone nodules and lenses. Below these, friable shales of the Coalbrookdale Formation (formerly Wenlock Shale) are just visible beside the steps.
Watershed Viewpoint (Murchison Point)
After walking across a plateau of wild flowers we looked out at the stunning view across Dudley at this, the watershed point. To the left (East) water drains into rivers which flow into the North Sea. To the right (West), water drains into the Atlantic. From the 1830′s onwards eminent geologist Sir Roderick Murchison made numerous visits to the area and this is said to be Murchison’s favourite spot. He encouraged local miners to establish a collection of Carboniferous Coal Measures and Silurian Limestone fossils. The Collection contained many new species and included the famous Calymene blumenbachii, or ‘Dudley Bug’.
After Murchison published his work on ‘The Silurian System’, in 1839 he encouraged and inspired local mine agents, industrialists, lay people, patrons and luminaries of the day to establish the Dudley and Midland Geological Society. Murchison inaugurated this, the Midland’s first geological society, in 1842. In 1975 the geological society’s third incarnation, the Black Country Geological Society (BCGS), was born.
Since September 2001 Dudley Museum and art Gallery has hosted regular rock and fossil fairs that draw large numbers of people from across the country. The next one in September 2013 will form part of the Dudley Museum Year of Geology celebrations, Graham highly recommends this to TVGS members! http://discover.dudley.gov.uk/events/dudley-rock-fossil-festival-2013/ Saturday 28 and Sunday 29 September at Dudley Town Hall and Dudley Museum and Art Gallery.
The Fossil Trench and Ripple beds
In the “Fossil Trench”, there is a huge rock face covered in ripple marks from the Silurian Much Wenlock Limestone Formation. The surface of the rock preserves ripples as seen on beaches today, in sand laid down around 400 million years ago over a period of three million years. The ripples were created by the wind and waves, layers of sand and mud built up on top, each with its own pattern. Today, as each layer erodes, the ripples underneath are exposed again. Such features can be seen today in the littoral zone (on sandy beaches and in river estuaries) and indicate wave or current action in shallow water. This demonstrates the principle of “uniformitarianism”: the idea that the natural processes we see happening now (e.g. volcanoes, erosion, etc) also happened throughout geological history.
The exposure is fenced off and we viewed it from a platform. Graham explained that a fossil dealer had cut out a 2M square section of a significant and beautiful crinoid formation, leaving a gap at the bottom of the flat rock face, so the rock above eventually slid down into the trench, At the moment, the rock face is unstable. In consultation with local residents it was decided to fence it off until the slope is stable enough to be reopened.
At the base of the limestone exposure bedding plane, the scree is rich in fossils including trilobites, brachiopods, corals, crinoids, bryozoans and cephalopods. There was an opportunity to explore the fossil collecting opportunity at the end of the tour.
Kingswood Chasm Cleared of Trees but not of bits of Metal
Don’t know why it came into my head, but working at Kingswood Chasm (just off Martley Footpath click MT687C to go to the map, choose Martley parish, then MT6876 and use zoom arrow on left of map as required) one of the society’s new sites, was a little like collecting puffins on St Kilda with the cast of Last of the Summer Wine.
Well sort of–precipitous slopes slippy as a skating rink, cliffs, waterfall and old guys having fun, breaking all the health and safety rules (no-one could see us) and doing a good job. What is there here you may ask? Certainly the best exposure of Coalbrookdale limestone in the district, (see here how it fits into the Silurian-Wenlock range, half way down the page), part of the Wenlock sequence of around 423-428 Ma it is characterized by these types of fossils and we have indeed found some there. Thanks to the Bray family for access to this site and for their great assistance in the clearance operations. Nearby we will erect an Interpretation Board that will explain the broad view across the Teme to the Bromyard plateau and the local very noticeable slippage of land downhill towards the river. The stream bed that we have been clearing is a slash in the hillside, draining as it does an area of flatter land, reddish soils, east across the East Malvern Fault towards the Nubbins and the village. The water cuts its way into limestone found more or less continuously from the Abberley Hills, Penny Hill, to Ankerdine and beyond–all Wenlock series with a variety of formations on display at different points. Our aim is to make the exposure more visible and establish a permissive loop path from the right of way, closer to the rocks, so that visitors can enjoy the feature. We need to emphasise that more work is required, including a proper pathway and even then, walkers will have to proceed at their own risk over extremely steep and slippy slopes.