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.
On Thursday February 14th, having opened all our cards and under grey skies, Ian, Mike and self, continued our foray into the Teme Valley and you know, sounds daft, but it really does feel like exploration when for us, checking out the rocks is a novel experience. Anyway, we headed first to St Marys, Stanford, to see if we could find on the ground evidence of the mapped Raglan Sandstones in the land above the church. At the spot under a spreading chestnut tree we did indeed find sandstone rocks but these were scattered about and could possibly have been from local building works although at the time we preferred not to see them that way. To us they seemed similar to the church and to local walls of the old rectory just across the road.
Sandstone from West of St Mary’s
Sandstone from West of St Mary’s
Travelling up the road by car, we entered Busk Coppice to show Mike the large quarry found on our last visit—did this supply the stone to St Marys’ Stanford, but where is the lime kiln that Mr Churchill the farmer had told us about?
Lime Kiln in Busk Coppice
Lime Kiln Busk Coppice
We wandered about down into gullies keeping in mind that it would not be far from the Bishops Frome layer, here underlying the quarried rock, St Maughans sandstone. We gave up and called the farmer who directed us back up the track to a shooting platform and
Conical Kiln in the Undergrowth
Sketch of Lime Kiln, Busk Coppice
goodness, there, not 3 metres from the trail, was a deep conical brick lined pit, a danger to anyone not seeing it, set in a levelled off terrace. On the terrace below was a substantial brick built arched construction leading into the terrace and under the cone. A magnificent example of an ancient kiln, a little the worse for wear and needing attention to remove trees and soil but other than that looked like it could be relit straight away. This would have been used to make lime for mortar for building and for the fields and was slap bang into the Bishops Frome limestone, the calcrete (fossilised soil) referred to in other posts. According to Mr Churchill, a farm worker by the name of Tommy Tucker used to live in the arched kiln. A little archaeological investigation sounds in order. Read Nils Wilkes fascinating study of Lime Kilns in Worcestershire HERE
So you burn limestone at 900C thus converting it from Calcium Carbonate to Quicklime and Carbon Dioxide, then you slake it with water making Calcium Hydroxide, known as lime putty, used as the base for a slow setting, traditional mortar still used in renovation work today.
That accomplished we went by car along the charming, twisty, switchback lane to just beyond Orleton until we reached the foot of Quarry Hill—the clue being in the name.
Valley Geological Map from BGS, click to enlarge
This is an outlier from the main escarpment. The geological maps show the limestone outcropping around the whole of the Bromyard plateau, with an island of it on top of Quarry Hill.
According to the maps the limestone was set in a sea of (Silurian) Raglan Mudstone only, and as we struggled up the wooded precipitous hillside littered with fallen trees, the redness of the soil seemed to indicate that this was the case. There were occasional obvious trackways contouring the slopes, signs of forestry work or perhaps quarrying, who knows? In the red roots of fallen trees we searched for stone as tell-tale of underlying rock and these at first were typical of Raglan sandstone. Continuing to force our way upwards to the very top we discovered a substantial area clearly shaped by human endeavour. There were no rock faces but the humps and bumps seemed to show that much of the top layer of limestone had been removed. We did uncover large stones set in a semi-circle, perhaps the foundation of a kiln?
Conglomerate, both ruddy and grey with bedrock behind
Just down the slope, we chanced upon exposed bedrock and took samples. To our surprise these mirrored an earlier finding some way down the slope (that we had tried to ignore), of a coarse conglomerate, not what we expected at all. One was ruddy, the other light grey, found 3-400mm above one another in clear layers. The map shows (Devonian) St Maughans conglomerate in a number of places, but nowhere near this spot, and certainly none below the limestone. So how to explain this? We retrieved our samples, cleaned them and will set them before the oracle as soon as we can.
Martley has three geological trails, none to the South. Ian proposed that a walking route written in the 90s by Keith and Audrey Trumper (who started the Path-or-Nones footpath maintenance group, still going) would form the basis of a geology trail that crossed formations with excellent views useful for interpretation.
On Saturday 22nd March, four of us had a close look at the area; Natalie Watkins provided the professional input, the rest of us tagged along, making what we thought were useful comments.
If the trail IS to come to fruition then funding will be required for art and design, printing and so on; David is looking into this. The route veers from the original walking route (No 9 if you are interested, see it HERE on the PONS web site) and is not yet settled but will be around 6 miles and is hilly. The formations crossed, or nearby, are Bromsgrove Sandstone and Sidmouth Mudstone (Triassic), Haffield Breccia (Permian), Highley Fmn (Carboniferous), Wyche Fmn, Wenlock, Raglan Mudstone (Silurian) and good views through the Teme gap by Osebury Rock and of the Bromyard Plateau (Devonian). We spent time scrabbling about in some of the many quarries on Ankerdine, now deep in a mixed woodland, and from which several local buildings have been made. These include most of the old church, though there are other materials from whence we know not where. Incidentally the church is undergoing conversion to a dwelling and we were kindly allowed to look around by the builder. Capturing our attention too, the wheel of the apple press by the Talbot (see pic) is a coarse version of, we concluded, the local Wyche Fmn. In our travels we collected samples of Wyche and the variation was instructive in itself, from fine silty material to coarse, gravelly, proving the existence of different environments all those years ago (+-420Ma) in the early Silurian.
Finally we were kindly entertained to tea and sweet things by always welcoming Nigel and Sarah in their delightful cottage, uniquely placed on the East Malvern Fault, with Silurian, Permian and Triassic in their back garden.
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.
We stayed with our plans to hold a field trip in May, on 26th and so pleased we did—a very special time together, led by Donnie (Prof. Donnie Hutton), around three local (to Martley) geology sites. The weather was wonderful (seems long time ago as I write this; actually, it IS a long time ago) and for a number of us the day was made extra special by the sight of a beautiful red kite floating along the Nubbins outcrop for 15 or 20 minutes whilst we gathered at Martley Hall in the morning. I have said elsewhere that for twenty years I have scanned the skies in vain and never seen a kite here (other have) until 26th May.
Here is Ian’s contribution (thanks Ian)
Penny Hill, Martley–first, the group drove to examine the Silurian ‘Wenlock’ limestone ridge which forms Penny Hill just north of the village. Accompanied by the landowner, Trevor Nott, and family, we were able to see how the stone which forms the hill is sheared off to the East along the East Malvern Fault. To the east, the wide rift valley of the Worcester Basin, later backfilled with riverine Triassic Bromsgrove sandstone and overlying marl deposits in a dramatic demonstration of the borderline between “old” and “young” Britain and the power of erosion.
The Wenlock limestone is rich in fossils (bioclastic) and formed in shallow coastal waters 423-428 million years ago south of the equator. At this time, most of proto-Britain was part of the micro continent Avalonia, drifting towards the modern day North American landmass of Laurentia through the closing of the Iapetus Ocean.
Iapetus Ocean and Avalonia
The resulting collision attached a piece of Laurentia to the north of us, forming the northern half of Scotland, and may have produced the Malvern fault system during the Caledonian orogeny (mountain building period), setting off the formation of the rift valley of the Severn.
The fossils – no dinosaurs of course, they came hundreds of millions of years later–are predominantly small seabed dwelling creatures; corals, brachiopods (shellfish),
stromatoporoids, crinoids and trilobites, although none of the latter were seen. They are embedded in a grey-blue flaggy limestone with alternating stone, thin mudstone interbed layers and evidence of volcanic eruptions in the form of weathered ash (bentonite) layers. Currently these layers throughout the whole of the country’s Wenlock distribution, are being microscopically investigated by Dr David Ray. We hope he will become a visiting speaker to TVGS.
Fast forwarding 125 million years to the echoes of the mountain building caused by the distant collision of Africa and Eurasia (the Variscan orogeny), our land mass was now drifting through the lush green equatorial region during the carboniferous era, laying down coal deposits across the Midlands, including small patches in Martley. It was probably these tectonic forces which pushed up the previously flat Welsh Marches limestone of which Penny and Abberley Hills are an important part, to form the folded landscape we see today. Note: the profile of Penny Hill has now been recreated following quarrying and refuse landfill. The refuse was capped with clay, extracted mainly from Cob House Fisheries to leave behind many new fishing pools, allowing the controlled capture of biogenic methane. This is used as a fuel for electrical generators on site at Penny Hill to produce electricity for the National Grid, enough for a significant proportion of the energy demand of Martley Parish. Here a few pictures from Penny Hill [easyrotator]erc_56_1340727442[/easyrotator]
After a thorough look around Penny Hill, completing the circuit from the north, around the west, then east and back to our start, we drive over to Brockhill Court where we made our acquaintance with Sir Anthony Winnington, who was doing a bit of gardening, and who most graciously allowed us to see the fascinating geology that exists on his land, adjacent to the house.
Here is Bryan’s report (thanks Bryan)
Brockhill Dyke, Shelsley Beauchamp, where a teschenite dyke is exposed in an old pit. Little remains of the dyke except high up in the eastern end of the pit. However, good fresh specimens of the rock were obtained after a stiff scramble halfway up the face. Sodium rich, it belongs to the syeno-gabbro suite of rocks. It’s mineral composition is very similar to gabbro but the inclusion of an alkaline mineral, (either nepheline or analcite – in this case analcite) distinguishes it from gabbro. Plagioclase feldspar, clinopyroxene, analacite (easily distinguishable), minor amphibolites and biotite make up this medium- grained basic rock. The dyke extends east-west for about 1200 metres and is exposed in small pits on the western side of the Teme. The river itself runs along the line of the dyke until it finds a way through, just below Brockhill Court. Emplaced in the Downton Series of red marls and sandstones it is about ten metres wide and dips almost vertically. No in situ examination of the margins was possible but the Droitwich Memoire has it that narrow doleritic edges to the dyke can be seen. Loose specimens were found of what may have been a fine grained rock from the chilled margin of the dyke. Excellent examples of spheroidal (onion) weathering can be found in the debris of the pit and on the exposed face.
The country rock, marls, silts and sandstones, were ‘baked’ by the hot (1600 degrees C?) magma. The sandstones and are now hornfels, a very hard, metamorphic rock. During the baking some layers of the purple marls were sufficiently plastic to allow the escape of volatile gases and the development of vesicles and tubes which were later lined with calcite, chlorite and analcite. Extreme baking produced vitrified black specimens with conchoidal fracturing. Good examples of all of these rocks can be found in the garden walls of the nearby Brockhill Court.
An explanation of the cause of the Brockhill dyke was given by our very knowledgeable guide, Prof Donny Hutton. The dyke is one of a suite of dykes emplaced in late Carboniferous times (300 Ma) during the Variscan Orogeny. Similar dykes with similar E-W orientation can be found inNorthern Englandand the Midland Valley of Scotland. Variscan subduction with consequent loading and downbending of the lithosphere induced ‘flexural bulging’ with uplift and tensional fracturing of the crust. Low degrees of adiabatic melting produced buoyant syeno-gabbros which rose and pushed into the fractures. Some pictures:
Donny also gave us a very useful rule of thumb for distinguishing between sandstones, siltstones and mudstones. If we can, with the naked eye, see individual crystals and can feel them, then it’s a sandstone; if we can’t see the crystals but can feel them, then it’s a siltstone; and if we can neither see nor feel the crystals, then it’s a mudstone or shale.
Southstone Rock, Teme Valley–to round off the day, a sensational walk up the western slope of the Teme valley to see what is reputed to be the largest tufa deposit in the country, known as Southstone Rock and still, visibly, growing. Originally the site of a hermitage and a homestead, there is no habitation there now (to see an aerial photo before trees, check out Cliff Barnards book, A Tale of Two Villages, ISBN: 0952657503), but the sacred spring keeps working, gushing fulsomely out of the base of the Bishops Frome limestone, laden with calcium carbonate that precipitates in the cooler air. The moss, Palustriella Commutata, seems to enjoy ‘taking the water’ and grows abundantly, being petrified in the process thus creating an easy to work, warm, light but durable building material. This has been quarried for centuries, witness Shelsley Walsh church and nearby cottage, the Lion at Clifton and many other premises, but peculiarly it is difficult to see evidence of this at the site itself. EHT have produced an excellent leaflet ‘Southstone Rock’ Geology and Landscape Trail Guide and these are freely available from EHT (01905 885184).
Here is Ingrid’s report on this part of the day (thanks Ingrid)
On Saturday 26th May (one of the last days of summer 2012) TVGS arrived at the final stop of the Teme Valley Tour. Several of us had never been here and, as promised by those in the know, it certainly proved to be one of the best kept secret places in the area.
After some manoeuvring we somehow managed to fit all the cars safely into a lay by at the side of the road opposite the track up to Southstone Rock. A short trek along a lush and overgrown path and a steep climb steeply upwards. Round a bend and across a rickety bridge and there it was! Best described as a cross between Gormenghast, pumice stone and Lord of the Rings this great white edifice towered above us. The newbies amongst us sunk onto the nearest rock in the shade underneath to catch our breath. We rapidly moved when Donny informed us that it was a little fragile with a tendency to move chunks of itself downwards into the stream below, and no, not pumice at all but the miraculous Tufa rock. Literally a ‘living rock’ and this is one of the best examples in the country. Moving smartly from under the overhang in case of falling boulders, we climbed upwards through a series of secret paths and labyrinthine ways to reach the top.
This was a significant area of pilgrimage in years gone and was said to be inhabited by a hermit. Latterly a cottage was built at the top, but little remains of this and this quiet wooded area was sadly decimated by developers a few years ago, who clear felled leaving all manner of brash and rubbish that nature is slowly healing. The densely wooded hill rose steeply above us but we headed to the shady outlet of a strong fresh water spring – very refreshing on a hot afternoon. From there we followed the narrow stream a little way downhill to see a miracle-tufa rock in production-as the clear water flowed over mosses, slowly petrifying them as it tumbled over a most picturesque water fall to the valley below.
It wouldn’t be a TVGS field trip if we didn’t have a bit of scrambling, duly paying homage in the time honoured way of all pilgrims, we wetted our feet climbing up the stream bed from the bottom to see this more closely. Down below us Donny diverted some of the party by finding playdoh, sorry volcanic clays, apparently top quality potting clays, in the base of the stream near the rickety bridge. It was time to make our way soggily down the hill through the heat of an English summer day, a perfect end to a thoroughly interesting day.
Finally, especial thanks to Donny for his time and the notes that he distributed, we all enjoyed our outing.
7th April TVGS’s first work party descended on Martley Rock. Armed to the teeth something like a bunch of brigands, the foot soldiers, rakes and shovels on shoulders, led into battle by Skinny’s trusty old Merry Tiller. Old it might be but it did the job wonderfully. Hardened soil softened under its caress as Skinny manfully wrestled the bronco so that the rakers and trampers could follow on behind, levelling and firming prior to seeding. A group of agriculturists had stayed at The Chandlery during the week, up to meet with Dave Richards at Ridgend Farm to advise on better production from cattle and field. Not knowing what hit him, the expert in grass seed gave up the struggle quickly and was soon on the phone requesting a free sack of ‘the right stuff’ to seed this scenic corner of Worcestershire. Thanks LIMAGRAIN of Market Rasen (http://www.limagrain.co.uk/index.php), your generosity and expertise is very much appreciated by TVGS. Apart from preparing the ground for seeding, we attended to the whole of the long trench, cleaning up the lips by rounding them off, and removing spoil from the east, Triassic, end. By the time we had finished after a couple off hours we were really pleased with our efforts. Just shows what can be done with a small group in a short time. Mike Install brought along some bean poles and we erected a temporary fence to stop traffic on seeded areas by the road. Andy cleared overhanging branches and during the week Mike (Dunnet) had sprayed the nettles and dogs mercury so that by the time we arrived on site it looked pretty ill. I think its the nub of why we do it when you can draw in people with different skills to get the job done–Mike D is from a gardening background, many of you know him from the Hort Soc and his wonderful open gardens up on Ankerdine. Everyone knows Skinny, don’t you? It seems that way to me–whether in the Teme Valley or downtown Martley, Skinny is well known as tree surgeon, grafter and keen to assist with community projects. The rest of us have all done a bit of raking and tramping in our time so played our part in the exercise. Good job–thanks Ian, Mike, Skinny, Alan, Andy.
Ian Spreading Seed
Sunday 8th–Ian and I managed to get up to the site and seed the whole area, afterwards raking it in.
With some spare time we also managed to clean out the east end of the exposed quarry, down to solid rock, using spoil from there to fill in the depression on the next level.
We aim to clean out all of the this pit, in order to expose solid rock and any features that it might exhibit.
Yellowstone–On Monday 26th March, Dr Ian Sutton presented ‘Yellowstone’ to a mid thirties audience (number not age). Those who had been to Yellowstone had their enthusiasm for this unique and varied park rekindled; those who have never been, myself included, renewed their vows to go there asap. How long do you need? There is so much to see, and though we focus on geology in our group, Ian, in a beautifully illustrated talk, showed that it’s not only steam and hisses, but wild life, scenic wonder and just wide open spaces–with the threat of doom through mega explosion not far down in one’s consciousness. Actually Ian discounted that and latest research suggests that the magma chambers underneath are not so large as to pose an ‘end of the world’ threat to North America. Thanks Ian!
Mapping Course–One more reminder for the Mapping Course starting 15th May, call Nat at EHT 01905 855184
The Martley Geology Project–the team is considering the way forward, i.e. the current project has some months to run and a number of milestones to achieve but can we now start to think of more? The audit of Martley geology lists over 40 sites in the parish and a handful of these meet the criteria of accessibility, interest and relevance. Given our aim of making Martley a European Geo Village, with trails and representative sites, we need to keep this in mind. Anyone reading this and interested in taking part in anyway whatsoever in our future projects, please speak up!