SABRINA TIMES JULY 2011 OPEN UNIVERSITY GEOLOGICAL SOCIETY SEVERNSIDE BRANCH

In this issue: Branch Organiser’s Report

Ireland—Dingle & Portmagee 2 Hello Severnside

Cwm Cerrig-gleisiad 11 We have had a good start to the year with some very successful trips. We looked at Brecon Beacons the remnants of glaciers in Cwm Cerrig Gleisiad with Duncan Hawley. It was a steep climb to the rim of the back wall and even steeper on the way back down but well Henllys Vale 12 worth the effort. We also explored Henllys Vale with Adrian Humpage where the day took 2 different styles. In the morning we followed the river in the valley and looked Branch Officer’s 13 at remnants of industrial heritage, all based around the local geology of iron, coal Meeting and lime stone. In the afternoon we climbed up to the hills above and followed the old tram way to look at the old quarries in the limestone. Although the day of our Events 14 visit was fine, the effects of recent rain on the terrain was obvious and made the going very boggy in places. Brilliant views though. Contacts 16 The next day trip is on 11th September when we are visiting the Abberley Hills with Branch Committee 17 Paul Olver. Here he will be showing us a variety of rocks ranging through pre Cambrian basement, Cambrian quartzites, Silurian, Carboniferous and Triassic exposures! Quite a variety.

Jan is organising some longer trips as well. In the spring 2012 a trip is going to Fuerteventura and Lanzarote and in September 2012 Brian Williams is leading a trip for us to Canada. More details are available on the website.

The Annual Society’s Symposium is taking place in Stirling this year. The theme is ‘North of the Suture’ and as usual there is a interesting programme of lectures plus field trips to look forward to. I think many delegates are planning to extend their visit and travel on to other parts of Scotland.

As happens every so often, the traditional pattern of the Symposium is being considered to see if it still offers what members want. Traditionally, all events are charged for as part of the weekend package (except possibly any field trips on the Monday). Should this change? Should the field trip be separated from the lecture programme so that delegates have a choice about which they attend and pay for? Should there not be any field trips at all? If you have any views or ideas on this, I would be pleased to receive them to feed back to the various national committees who guide organisers on these matters. Your views are important because for these events to continue to run successfully they need to offer what members want.

I believe we are still looking for a National Information Officer. If you think you could do this, please let me know.

We have several new books donated to the library by Philip Clarke. These include a Geol. Soc. publication on James Hutton, lecture notes on ‘Samuel Pepys at the Rhenish wine-house’, and a geological map and explanatory book on the Looking for striations Volcanology of the Chaine des Puys. All of them are available should you wish to at Cwm Cerrig –gleisiad borrow them. (See Page 11) Photo: Philip Clark Best wishes Janet

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Ireland - Dingle and Portmagee April - May 2011 OUGS Severnside Field Trip to South West Ireland 2011. The aim of the trip was to study lower Palaeozoic rocks seen at outcrop on the Dingle Peninsula and on Valentia Island at the west of the Iveragh Peninsula. The group first stayed in Dingle, then moved to Portmagee.

The Dingle Peninsula is the northernmost of three peninsulas, which effectively make up County Kerry. The peninsula is a mountainous finger of land about 40Km long with a maximum width of 24Km. The rocks preserve a unique Ordovician to Carboniferous succession including the most complete Old Red Sandstone magnafacies in SW Ireland. The oldest part of the ORS was deposited in Dingle Basin which formed in a transgressive regime during the convergence of Avalonia and Laurentia. Younger ORS sequences were deposited in basins on the northern margin of the Middle to Late Devonian Munster Basin of South Kerry and Cork. Several researchers have studied the geology of the area since the 1970s, but their findings remain controversial. The visit was intended to view a selection of outcrops but not to form definite conclusions about the geological history.

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Thursday 28th April 2011

The Silurian was visited at the Dunquin Inlier in Ferriter Bay where the group spent time examining the outcrop of sub vertical beds on the beach. The rocks form part of the Dunquin Group which outcrops as a series of inliers along the Dingle Peninsula and in the nearby Blasket Islands. These rocks represent parasequences which are stacked offshore to nearshore regressive phases. 5 repetitions are seen over 250 metres of section.

Two members were seen. An older, resistant muddy limestone, with the tabulate coral favosites, trilobites and graptolites suggest formation in an open marine environment, possibly close to shore in a shallow marine shelf. The other different lithology had cross bedded fine sandstone interbedded with coarse grained cross bedded sandstone that View from the north side of Clogher Head towards contained channels and syn-sedimentary deformation. This high energy Clogher Strand and Silurian rocks of the Dunquin environment was free of fossils and some of the coarse beds contained Group mm scale volcanic clasts. The sequence was topped by a 2metre thick bed of pale felsic volcanic deposit. The pumice in coarse sandstone suggests a nearby volcano with intermittent activity which was a precursor for a big eruption that produced the felsic unit The sequence was overlain by a pinstripe laminated siltstone, dominantly parallel bedded, with desiccation cracks but no burrows. This unit is a tidalite and followed by sandstone with coral fossil cast.

There are two contrasting theories for the deposition environment for these units: 1. A lagoon with abnormal saline conditions. 2. Open marine with sea level changed riven by a magma chamber inflating and deflating.

Our visit to the Silurian Dunquin Group continued in the afternoon at the east side of Clogher Head at the boundary between fossiliferous sandstone of the Ferriter formation and the Lower Clogher Head volcanic formation. We walked south along the clifftop to study several locations. The boundary between the formations is a dextral strike-slip fault with about 300 metres displacement. The volcanics form a unit about 200 m thick, though it is about 900 metres thick at the eruption centre. The Silurian sub vertical beds of the Dunquin inlier northern part of the volcanic deposits consists of ignimbrites. To the south there are lavas. This suggests a Plinian eruption that delivered several layers of material containing welded tuff, fiamme, pumice and ash. These rocks were examined.

Trilobite fossil cast in siltstone

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Thursday 28th April 2011 (contd.)

The Group on the Lower Clogher Head volcanic formation

This inlet was formed by erosion of a palaeosol after volcan- ism had stopped. Soil formed on top of the volcanic rocks and was itself overlain by sediments. The rocks were turned dur- ing mountain building and the soft palaeosol was exposed and eroded.

Further along the cliff we saw the Millcove formation which contains distinctive red sandstone about 1.5metres thick. Research has defined this as a groundwater ferricrete with the red colour controlled by the oxidation state of iron. It was possibly formed in an alluvial plane that underwent cyclical drying. The sandstone was deposited during seasonal sheet flow on floodplains. Also seen within the sandstone are signs of volcanic activity in the form of volcanic bombs - mafic material up to 80 cm diameter.

The top of the Millcove formation was seen at Drom Point and is a major transgressive surface.This unit was best seen on the beach at Clogher Strand where the marine deposits show hummocky cross stratification indicative of storm conditions, followed upwards by finer sediments with extensive trace fossils Chondrites. Shelly fossils broken in the storms have accumulated in decalcified lenses. The deposition environment was a shore face which is shallow marine typical of the Silurian.

Report and Photographs by Phillip Robinson

The trace fossil Chondrites seen at Clogher Strand in the Drom Point formation

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Friday 29 April 2011

Today’s objective was to examine the oldest rocks exposed on the Dingle Peninsula before studying the Lower Devonian rocks of the Dingle Group. First, we drove east of Dingle to Bealacoon Cove in Minard Bay to examine two members of the Annascaul Formation exposed in the Annascaul lnlier. These rocks are the oldest in the Dingle Peninsula and have been dated, using microfossil marine phytoplanktonic cysts called acritarchs, to the early Ordovician Period.

The Illaunglass Member is exposed on the western side of the cove and consists of highly deformed, thinly bedded sandstones and laminated grey/green siltstones. Parts of the exposure are red and purple in colour from haematisation but this is secondary in nature as the colour often changes to green shales along the direction of strike. The sandstones are mainly fine-grained and show tight isoclinal folds, often with two cleavages (Fig.1). This deformation occurred early in the Caledonian deformation event. Laboratory analysis of the acritarchs samples taken from the site show they come in all shapes, including square, knobbly and spine, and vary in size between 30 — 40 microns. These microfossils have survived because the temperature and depth of burial was insufficient to destroy them or allow conversion to oil. Fig. 1 Deformation in laminated sand and siltstones On the eastem side the Bealacoon Member is exposed as a melange. This is a sedimentary deposit of a dark mud matrix supported conglomerate with some brecciation, mainly with angular to sub-rounded and boulders of greywacke sandstone, some of which range from 2 — 10 metres in size. Clasts of shale, dolomite and andesite were also found. All the clasts were aligned and there were large shadow casts around some of them (Fig.2). This member is interpreted as having slumped down slope into deep water.

Clearly visible in the cliff face on this side is the Minard Head Fault (Fig.3). The massive throw places the Ordovician Annascaul Formation unconformably against the Early Fig. 2 Shadow cast Devonian Dingle Group. The bluff above the beach contained a periglacial deposit of glacial till above which were layers of peat, pebbly sand and another finer peat layer. Rootlets could be seen in the peat layers and the pebbly sand contained small angular clasts and larger boulders which is probably a raised beach from when sea levels were higher. This buff has not been mapped or dated but is probably of early Holocene age. Thus the oldest and youngest deposits on the Fig. 3 The Minard Head fault—Ordovician Peninsula are found in the same place. Returning to Dingle we stopped for coffee rocks on left, Devonian rocks on far right and were in time to see the royal newlyweds leave Westminster Abbey for the trip to Buckingham Palace.

Driving west along the coast we reached the panoramic viewing point at Slea Head from where we could see Silurian rocks to the left and Devonian to the right. It was near Slea Head in 1856 that Patrick Ganley of the Geological Survey of Ireland first used truncated cross bedding to prove the way up of strata. Slea Head is Lower Devonian in age with deposits up to 2000m thick of Old Red Sandstone of the Dingle Group. This represents a transition from the shallow marine environments of the Silurian Dunquin Group to continental sedimentation following the Caledonian event and occurred in the inland Dingle Basin due to strike-slip tectonics associated with the lapetus suture zone. The resulting lake was gradually filled with silt and sand sediment, then followed by an axial braided river drainage system, of one or more rivers, with gradual coarser deposition. Drainage from both the south and north sides of the Basin created alluvial fans with different conglomerates which we were to see later in the day.

The roadside cliffs expose the Slea Head Formation in the upper part of the Dingle Group. The formation consists of coarse pebbly sandstone, dipping SE, with some quartz clasts though most clasts are exotic and shows trough cross- bedding which is the right way up. The grey/green colour of the sandstone indicates that the river was perennial and fast flowing, whilst the direction of the palaeocurrents show that deposition occurred as the rivers flowed SW to NE along the axis of the Dingle Basin. In fact, studies have shown the the river eventually turned east and is linked to Pembrokeshire.

Slow moving water in river meanders allowed finer grained material to be deposited and in these purple and grey mudstones and siltstones trace fossils of Fig. 4 Top of a Beaconite burrow

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Ireland - Dingle and Portmagee 26 April - 2 May 2011 (contd.)

Friday 29 April 2011 (contd.)

Beaconite burrows are clearly visible (Fig.4). The animals that made the burrows back-filled them as they moved up and down and could have been large invertebrates, lungfish or possibly an arthropod called Euarthropleurids which could grow up to 2m in length and became more common in the Carboniferous. Burrowing was probably to avoid dessication. Microfossils of trilete plant spores, from early plants just forming on land, have been found in the mudstones and have been dated to 4ll — 409 Ma (the mid Lower Devonian).

Travelling north to Dunquin Harbour we observed the contact between the Drum Point Formation of the Upper Silurian Dunquin Group and the younger Bulls Head Formation of the Lower Devonian Dingle Group. Looking into Yellow Cove from the cliff top, this contact is clearly faulted and forms a controversial unconformity. There are seven sites in Dunquin where this contact is visible but the uppermost Silurian Croaghmahrin Formation is always absent whether through erosion, faulting or non deposition. Those geologists who insist the contact is conformable place the base of the Lower Devonian Bulls Head Formation in the late Silurian.

The Lower Bulls Head Formation consists of purple mudstones with fine sand infill and contains dessication cracks, whereas the upper part of the formation (Helerolithic and Trabane Members) which we examined on descending the path to Dunquin Pier consists of a coarse-grained sandstone conglomerate with large mud flakes. The yellow coloured Trabane Member forms a junction with the red/lime-green Eask Formation (Fig.5). Both formations are brittle sandstone units which have been stretched and cracked leading to quartz tension veins and boudinage. These formations of the early Dingle Groups represent deposition in the Dingle Basin Lake (Bulls Head Formation) and a fluvial terminal field deposition (Eask Formation).

At Wine Strand a cliff top walk brought us to a cove with exposed sections of the Lower Devonian Glashabeg Formation (Upper Dingle Group), which dip 30° to Fig. 5 Junction of Top of Bulls Head (Yellow) the SE and represent lateral drainage from the north of the basin. The and Eask ( Red/Lime Green) Formation exposures consist of fluvial fining-up cycles each starting with a base layer of coarse conglomerates with pebbles deposited by floods and showing signs of erosion. This layer fines up into cross-bedded sandstones with examples of trough cross-bedding and flame load structures (Fig.6). Siltstones and mudstones complete the cycle. The mudstones are purple in colour and contain calcrete nodules and dessication cracks. The direction of the palaeocurrent and exotic volcanic and red jasper clasts indicate flow from a northern volcanic region. The cycles have been intruded by the most southerly Tertiary dolerite dyke in Ireland composed of feldspar, olivine and pyroxene and containing zeolites and vesicles.

The final stop of the day took us back through Dingle to Trabeg where we observed from the cliff top the fining up Trabeg Formation conglomerate consisting of sand and gravel sediments which originated to the south of deposition. This is in contrast to Wine Strand (Glashabeg Formation) though both formed as alluvial fans either side of the braided river system of Slea Head Formation. The cliffs at the eastern end of the bay consist of vertical Lower Devonian rocks (Bulls Head Formation) overlain by dipping Upper Devonian rocks of the Slieve Mish Group (Fig.7) Mapping of these cliffs has found inverted trough cross-bedding, thus they form the inverted limb (ageing to the north) of a synclinal fold, the right way up limb of which we investigated earlier at Slea Head.

Fig. 6 Loading structures (flames) in sandstone

Report and Photographs by Gillian Toney

Fig. 7 Inverted limb of synclinal fold at Trabeg

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Saturday 30th April 2011

The field trip continued by studying Devonian outcrops near to Dingle. At Kilmurry Bay the mid Devonian Caherbla Group is seen positioned the Acadian unconformity. It consists of 2 formations which are laterally equivalent and interfinger. These are the Kilmurry Sandstone and the Inch Conglomerate. The Kilmurry Sandstone consists of frosted grains of uniform size with no pebbles, with a banded appearance and wind ripple lamination showing segregation of grains into coarse and fine layers. The dunes are cut by fluvial units. The beds in these fossil sand dunes dip to the south, which suggests that the palaeowind direction was from the north. However, most Devonian dunes were driven from the south. There was extensive jointing in two orientations, N-S and E-W, and this accounts for the large boulders on the beach.

After the visit to Kilmurry Bay the group started its journey to Portmagee. On the way further stops were made at the road side to examine the Caherbla Formation. A southerly-inclined avalanche face of Kilmurry sandstone was examined for delicate trace fossils formed by arthropods. Geologist Lance Morrisey had studied the section and found fossil traces similar to traces he had observed being made by living arthropods in Oman. It was not clear if any were on view in this section as the ambient light (and time of day) is an important factor in seeing them. The next stop gave us a view of the Inch sand bar to the east and a cutting which revealed the Inch Conglomerate. This unit is a very coarse breccio-conglomerate containing a large quantity of high grade metamorphic clasts set in a red-purple sandstone matrix. Three distinctive sedimentary facies were seen in two road South dipping beds in the fossil sand cuttings. dunes in the Kilmurry Sandstone The most common facies contains disorganised boulder and cobble grade clasts with a crude stratification, with imbrication that indicates a southerly source in high density stream floods. Another facies contains conglomerate and pebbly sandstones with sub-vertical burrows of trace fossil Beaconites . Other features suggest a low energy sheet flood depositional environment. A third facies consists of red cross-bedded medium grained sandstone of Aeolian origin. They represent small transverse dunes that migrated into the alluvial fans of the other two facies. An unconformity between the Inch Conglomerate and the younger Upper Devonian Lough Slat Conglomerate was seen with white vein quartz and red jasper in the Lough Slat Conglomerate.

For the afternoon session the group was joined by Dr. Pat Meere of UCC who took us to Dunloe pass. He explained the geology in this glaciated valley that lies in the Munster Basin, an area of research at UCC. Devonian crustal extension created the Munster Basin which was infilled by two tongues of coarse sediment that thin southwards: the Chloritic sandstone and the purple Ballenskellig sandstone. Current research is aimed at finding out the true source of sediment as it is possible that the Upper Devonian was derived from recycled Lower Devonian rocks. In the valley wall a major thrust fault could be seen. This is a high angle reactivated normal fault with fluid inclusions that indicate high pressure reactivation. Other similar features are seen towards the basin margin to the north. Outcrops of coarse sediment with good cleavage give a shortening of 20 -30%. An outcrop of purple conglomerate at the road side is repeated at an Tension gashes in the Dunloe Gap elevate location nearby, suggesting another major fault is between the locations. This demonstrates large scale imbrication in the Devonian basin which was subjected to severe compression in the Caledonian orogeny.

Report and Photographs by Phillip Robinson

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Sunday 1st May 2011

Upper Devonian Rocks of Valencia Island With Prof. Ken Higgs On the Sunday, we crossed the bridge to Valencia Island to examine the oldest formation on the peninsula, the Middle Devonian Valencia Slate Formation which is exposed on the northern limb of the Portmagee Anticline. All the locations lie on, or overlook, a 2km stretch of coast just east of the Valencia radio station. The slate is composed of purple siltstone, with subsidiary sandstone and mudstone, which has taken a good axial planar cleavage.

The first location was the "Grotto" quarry entrance, situated on the rise just south east of the radio station. The slate here was suitable for billiard tables as well as roofing slates and working has been revived recently by the Valencia Slate Co. Although these workings are really mines, they were referred to as quarries because of preferential tax treatment at the time. The mine entrance is most unusual, being Fig 2 Slate offcuts outside the Grotto embellished with a somewhat Quarry Fig 1 Quarry entrance showing sub- incongruous grotto. Just inside the horizontal bedding and steep slaty cleavage. entrance, bedding and slaty cleavage were well displayed (Fig 1) and within another entrance we could make out a toy-like "Hymac" within the massive workings. Samples of product lay around the entrance in the form of offcuts, some as big as billiard tables (Fig 2). The second location was the "piece de resistance" of the trip, the Tetrapod Trackway at Dohilla. This is on the cliffs just below the radio station, in the same Valentia Slate Formation and is a national geological monument. It was discovered by Iwan Stossel, a Swiss student doing a mapping project in 1992. It is exposed on a bedding plane near high tide level(Fig 3). During clearance of encumbering boulders, more significant tracks were exposed. The main trackway shows about 150 prints (Fig 4) which are distinct, but the individual digits are not clear. As is often the case, the surviving prints may be from the squashed subsurface layers. The bedding surface is slightly rippled, indicating an original shallow water environment, perhaps a playa lakeside. There are two types of impression, alternating, the smaller probably representing 'hands' or forelimbs (manus) and the larger ones feet (pes) Fig 3 Tetrapod trackway site

The original rocks have been foreshortened by the same Variscan deformation as produced the slaty cleavage and Stossel has used strain analysis to calculate the original stride length and body size. The evidence is that the animal was crocodile or salamander-like with a body length of about one metre of which a third was tail. One section shows an indication of body drag and another some tail marks. Dating of associated volcanic rocks shows an age of 385 million years, making it, arguably, the earliest trace of four limbed vertebrate life entering the terrestrial environment. That is, the first amphibian.

After finding lunches in Knightstown, we diverted to investigate the Altazamuth (stet!) Walk. Here, a stone commemorates the measurement of the longitude of Valentia in 1862, a key date in the long running longitude problem which beset sailors of the time. The Heritage Centre was our next port of call, where copies of Matthew Parkes' excellent booklet "The Valentia Tetrapod Trackway" flew off the shelves.

Fig 4 The main trackway showing manus and pes prints)

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

Sunday 1st May 2011 (contd.)

At the next location, we investigated a dolerite dyke which intrudes the Valentia Slate. This cuts east-west across Trawaginnaun Bay and was best seen on the opposite shore (Fig 5) The dyke is the black rock just below the wooden shed. The white slightly anticlinal bed just to the right of it is a volcanic tuff which could give a useful date. At the state of the tide, the dyke was not well exposed nearby, but we found a number of specimens showing coarse plagioclase with big pyroxene? crystals and a chilled margin with smaller crystals. The dyke width was around 20 metres

We carried on along the coast towards the Cromwell Lighthouse at Fort Point, just west of which the slate was gently folded and had a slightly nacreous sheen, Fig 5 Trawaginnaun Bay, the dyke is the showing up a number of myriapod trackways probably produced by a large black rock in the cliff below the wooden millipede-like animal with about ten legs and assignable to Diplichnites (Fig 6)

Appropriately, we finished the day, and the trip, at land's extremity, the monument at Telegraph Field, from where the first message from Europe to America was sent. Thanks and farewells wound up a memorable trip.

Report and Photographs by Tony Thorp

Fig 6 Myriapod trackway assignable to Diplichnites

Historical Dingle Three of us arrived a day earlier than the main group and spent the day exploring some of the historical aspects of the Dingle Peninsular. The whole area is dotted with ancient sites, ringforts, Ogham stones. Man has lived here for many thousands of years! Armed with a guide leaflet, we headed northwest out of Dingle Town and navigated through the narrow lanes beneath Brandon mountain looking for Cnoc Bhreanainn. We parked by a small grotto at the beginning of a footpath up the mountain and explored the scarcely visible ruins of a building . A mile of so inland this site has a commanding view over the coastal plain and out to sea. A couple of miles away, we explored Kilmalkedar Church which is a 12th Century ruined church with Romanesque elements. An Ogham stone, a large stone cross and a sundial can be seen in the Churchyard. Another footpath marked as a pilgrims way leads off towards the mountain. The nearby Gallarus Oratory is a remarkable building. Constructed entirely in dry stones over 1200 years ago. It is shaped like an upturned boat and looks as though it was built yesterday. Traces of mortar indicates it may have been plastered in the past. Driving on towards Ballyferritter, we found the Riasc Monastic settlement where the outline of stone walls was visible plus 2 upright stones carved with celtic designs. The settlement possibly also included another Oratory. Beehive huts - We only glimpsed these from the main road on our way back to Dingle. There are 2 sites on the road heading east towards Ventry and the buildings are reputed to have been build over 4000 years ago. Janet Hiscott

Kilmalkedar Church Sundial Gallarus Oratory Riasc Monastic Settlement

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Ireland - Dingle and Portmagee April - May 2011 (contd.)

A few more photos by Mary Howie

The way to the Tetrapod Trackway Looking for a dyke after the tide has come in !

Valentia Longitude—Altazimuth plaque Wave cut platform

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Cwm Cerrig - gleisiad, Brecon Beacons 15th May 2011

Leader Duncan Hawley, Swansea Metropolitan University A dozen enthusiasts met at the lay-by on the A470 for an enjoyable day examining the apparent cirque and associated “Lumps, Bumps, Hollows and Humps” of Cwm-Cerrig-gleisiad a Fran Frynych National Nature Reserve. We began at the lower end of the reserve and spent the morning investigating the various ridges and features and under Duncan’s guidance, attempting to derive their origins. After lunch everybody successfully made the climb to the top of the backwall which enabled a much better appreciation of the layout and orientation of the ridges in the Cwm below which we had spent the morning studying. After looking at what Duncan explained were the results of an arrested landslip at the north west corner of the Cwm we gathered together to hear that there have been at least three scenarios proposed by various authors for the creation of the landforms, each proposing different phases and extent of glaciation. Duncan distributed a comprehensive handout (copy in Branch Library) which included summaries and we were invited to reach our own conclusions. The principal evidence for glaciation seemed to depend on the presence and distribution of striations on rocks found within topographic features on the Cwm floor. We then completed a circuit of the backwall passing the tops of the deep gullies and descended down the steep path at the eastern end of the backwall to return to the lay-by.

South wall of the Cwm with gullies and The ridges in the bottom of the Cwm debris cone Pen-Y-Fan (886m) and Corn Ddu in the background

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A geologist has to use every clue ! The climb up the backwall Beacons Way signpost

View from the top of the backwall Backwall of Cwm with landslip blocks in Duncan pointing out the features within foreground the Cwm

Photographs by the Editor 11

Henllys Vale 19th June 2011

A most enjoyable and interesting journey descending a Westphalian sequence within the Lower Coal Measures of the Carboniferous, enthusiastically led by Adrian Humpage and Co. of the B.G.S. Our group met in Ystradowen and followed the rather vigorous Afron Twrch to the north-east, Adrian explained that the area was renowned for the best exposure in the S.Wales coalfield of the (310Ma old) Amman (or) Vanderbeckei Marine Band (a stratigraphic marker with diagnostic fossil assemblage, important for correlation due to its lateral extensiveness and close proximity to the coal seams that immediately follow in older strata below), perhaps unsurprisingly we never got to see even a hint of this notable band, possibly due to vegetation and it’s puny 20cm width!

We walked on up river and onto progressively older rocks (the strata dips gently southwards); on the far bank a fresh adit exploiting the coal was spotted by our beady eyed BGS man, indicating that the seams still had some (locally) economic potential. As we continued, an exposed face of interbedded sandstone with carbonaceous shales and sideritic beds marked our first official stop. Adrian explained that the coal bearing rocks originated from plants such as Calamites (species of Horsetail tree) growing, dying and accumulating in an anoxic swampy environment (those same conditions promoting the precipitation of the Ironstone too). Rather conveniently this outcrop was ornamented with a carpet of Calamites’ modern relative Equisetum said to have been used to polish metal on account of its cellular structure containing Silica spicules (Gold content within Fig. 1 the plants cells was also mentioned to many a pricked ear!) Shales and 30cm high Equisetum A few minutes walk up-stream the channel widened and (further on) a tributary entered the main channel revealing Quaternary Glacial-Fluvial features: – Large Erratic boulders (too large to have been transported by present day fluvial bedload) found in the river and within the thick strata of till on the river banks that were unconformably sat on Carboniferous bedrock (the unconformity represents some 300Ma!). The river was soon crossed via an iron bridge giving us a superb viewpoint of a cleanly washed gully wall made up of thin shales and iron sand beds.

Another ~5Mtr high exposure was found on the west bank with lenticular sand body representing a fluvial channel, shales with abundant plant impressions representing floodplains, thin sands representing channel overspill, thin coals representing swamp and Fig. 2 Erratic Boulder thin shale with Goniatite fossils representing a marine transgression. This was by far the best example of the day for understanding the Deltaic palaeo-environment that has been inferred from the area’s lithology. It was also explained that the delta's high sediment input originated from weathering of the high Caledonian mountain range to the north.

Iron Pyrites found in a small coal seam nearby demonstrated why the name ‘Brass Vein Coal’ has been assigned and why the seams were poor quality (and therefore currently uneconomical).

At this point we lunched at the old colliery engine-house and lime kiln before our route broke from the river and headed uphill. Adrian explained that mineral extraction in the area probably started 100’s of years ago with the exploitation of the Iron Ore (seen as individual nodules or beds within the shale’s) and Limestone (initially used agriculturally before being put to use in the iron production process), followed by Silcaceous Sand (along with the Limestone transported from strata further up the hill) before the Coal was mined till the late 1940’s (whilst the sand was still being mined into the 1950’s).

Lunch now a distant memory we trudged and squelched through boggy terrain up through a gap (marking an ancient fault plane) and onwards up the dip slope of the ‘Farewell Rock’ a unit of sandstone marking the end of coal (or is it ironstone!). Further climbing, lots more Erratics and Till, wet feet, wild ponies, glorious skylarks and a face- off with a bull of huge proportions (brought to a safe conclusion by our brave retreat and wide berth diversion tactics!) brought us to the top of the ‘John Hayes Incline’ (that is the tramway Fig. 3 Colliery Chimney and remnants we had been following since the engine house), and to a change in lithology to Lime Kiln quartzite (source of the silica sand used for refractory brick making). Adrian made the point that much of the quarried quartzite was probably collected naturally pulverised as a result of fault dip-slip movement in the locality.

Journey’s end (at least one way) was marked by an interesting discussion as to quartzite’s lithological history: – potentially a misnomer when considering its origin, i.e. crystalline texture resulting from pressure dissolution and quartz overgrowth during compaction and lithification. Report and Photographs by Howard Fowkes

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Branch Officer’s Meeting 11 June 2011

Following is an extract from Janet’s report of the recent Branch Officer’s meeting:

Symposium We were asked to discuss amongst committees and membership the format of the Symposium. Ours last year was traditional in that we had a field trip in the middle of the weekend and the price for the weekend included this. However, there are older members who enjoy the academic side but can no longer manage the field trip. Conversely there are also many people who would not come if there were no field trips. So should the field trip element be costed separately; dropped all together; be there but arranged as a follow on to the academic portion so that delegates can choose either or both elements and the costs charged could reflect this. Or another variation on this theme?

Comments are asked for. I am sure that this will be an ongoing discussion over the coming months so plenty of opportunity to think about it and to discuss with others on field days etc. Let me have your views anytime, please. I will also email the membership for their views.

Symposium 2012 This event will be held in Northampton and the theme will be that OUGS is 40 years old. The organisers would like to hear from founder members and wonder if anyone has photos from the early years that they would be willing to lend to form part of an exhibition?

Geofest There will be a Geofest in the National Museum, Cardiff on 22-23 October 2011 For details go to...... www.swga.org.uk

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Severnside Branch Events

DATE EVENT LEADER DETAILS

2011

The “Suture on a Shoestring” goes to the Norwegian Arctic. A

spectacular follow-up to the 2002 trip to Norway which was led by Mark. We will examine the geology and geomorphology in a transect from Western Sweden (Abisko) to the Lofoten- July 23rd Vesterålen Archipelago along the Norwegian coast. We will fly to to Arctic Norway Mark Anderson Narvik, hire self-drive cars and be based in three or four August 6th different centres: (1) Abisko, (2) ? Ballangen, (3) Salangen and (4) Harstad, probably in huts on campsites or hostels.

Further details are being arranged by Jan AJ.

Meet in the carpark of the Crown pub in the centre of Martley village at the southern end of the Abberley Hills at 10 am- the village is best reached off the main A44 at Knightwick where there is a road signposted to Martley. We would be looking at brand new exposures of the Precambrian basement and Cambrian quartzites within the September Abberley Hills Paul Olver village itself, some Triassic Bromsgrove Sandstone in a local 11th village quarry as well as in the Church - these will both be in the morning. Bring sandwiches but we will call in at the Crown for a drink. In the afternoon we would look at the Much Wenlock Limestone of the Abberley Hills at the Penny Hill Quarry and a Carboniferous teschenite dyke intruded into Late Silurian (Pridoli) rocks near Shelsley Beauchamp

Joint event with London branch- mid week visit- names to Jenny Parry please

Meet at 11 am. It will take about 3 hours which includes October Bath Stone Mines dressing everyone up and H & S stuff. 19th The address is Stoke Hill Mine/Midford Lane, Limpley stoke. Nr Bath BA2 7GP.

Numbers limited. Able bodied only See advert on last page December Volunteers are sought to give short presentations. Day of Lectures 4th

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DATE EVENT LEADER DETAILS

2012

A weekend in the laboraties at Aberystwyth University Aberystwyth Charlie Bendall and February Sediments and Fossils Bill Perkins

See advert on last page February Fuerteventura and 25th to Lanzarote March 7th

See advert on last page September 10th to Gaspe, Canada Prof. Brian Williams 19th

National Events

August19th to 21st 2011 OUGS Symposium Stirling “North of the Suture—Stitches in Time” Contact: Jacqueline Wiles 01786 820127 [email protected]

Event Notes Note: EVENT DETAILS CAN CHANGE Any last-minute changes of times or arrangements are on the OUGS website.... www.ougs.org Or...... Contact Jan Ashton-Jones Tel: 01432 870827 Email: [email protected] If you are not receiving email reminders from Janet regarding forthcoming events or if you get a new email address please let her know so that she can keep in touch.

Transport If you are able to offer a lift to any event or if you have local knowledge regarding bus or train services etc. that might help those without their own transport to attend an event please let Janet know. Updates Why not try the following link to a service for keeping an eye on changes in the events list. http://www.changedetection.com

THERE IS A NOMINAL FEE OF £2 ON DAY TRIPS (UNLESS OTHERWISE STATED) TO COVER LEADERS EXPENSES. ALWAYS WEAR APPROPRIATE GEAR...WARM CLOTHING AND HIKING BOOTS. BEAR IN MIND THAT MANY SITES, ESPECIALLY QUARRIES, REQUIRE THE WEARING OF HARD HATS. ACTIVE QUARRIES REQUIRE HARD HATS AND YELLOW JACKETS. IMPORTANT Each person attending a field meeting does so on the understanding that he/she attends at his/her own risk. The OUGS has Public Liability Insurance cover for field and indoor meetings but Personal Accident and Personal Liability cover remain the responsibility and personal choice of the participant. There may be an element of appropriate cover included in house or travel insurance. Although OUGS activities are not par- ticularly dangerous members are advised to check whether exclusions apply to activities in which they propose to partici- pate in case they wish to arrange further cover. An annual travel insurance may be the best solution for any member who regularly attends field events. This is again a matter of personal choice. All members participating in overseas events will be required to have travel insurance for the duration of the event. Partici- pants should be covered for Medical, Repatriation and Personal Liability expenses. The Personal Accident element remains the personal choice of the member who should exclusions so that they can make an informed decision about the cover they require. Disclaimer None of the information in any of the advertisements for field trips or other events in this newsletter constitutes a brochure under the Package and Travel Regulations (1992) 15

OUGS Neighbours It’s worthwhile taking a look at what the other branches are doing. Many of their events could be convenient to attend.

OUGS Oxford Branch Organiser: Sally Munnings 01635 821290 [email protected]

OUGS Southwest Branch Organiser: Chris Popham 07971 930431 [email protected]

OUGS Wessex Branch Organiser: Sheila Alderman 01935 825379 (eve) [email protected]

OUGS West Midlands Branch Organiser: Linda Tonkin 01902 846074 [email protected]

Non OUGS Organisations

Many of our members belong to other Earth Science related organizations which also do interesting events.

Welsh Stone Forum http://www.museumwales.ac.uk/en/364/.

Program: Sat 16 July Gwrhyd Quarry, Rhiwfawr, SA9 2SB (major supplier of Pennant Gritstone). Meet 11am at quarry (www.specialiststone.uk.com).

Sat 10 September Building Stones of Old Radnor area. Meet 11 am Harp Inn.

Thurs 20 October: Royal Forest Pennant Quarry, Parkend, GL15 4JS (also major supplier of Pennant, but significantly different). Meet 2 pm Bixslade Stone Works.

Fri 21 October: Identifying Building Stone Seminar, National Museum of Wales 11 am - 3.30 pm. Contact : [email protected]

Geologists Association Secretary: Sarah Stafford 020 7287 0280 [email protected] Affiliated Regions South Wales www.swga.org.uk West of England www.wega.org.uk Bath Geology Society www.bathgeolsoc.org.uk

Central Wales RIGS www.geologywales.co.uk/central-wales-rigs

The Russell Society www.russellsoc.org

Library

The Branch Book and Map Library list is online The library is in the care of Branch Organiser Janet Hiscott Request a catalogue on...... [email protected]

OUGS Sales Is your fieldwork kit lacking a few items? If it is check out OUGS sales! We have all you require...... Hand lenses, Lanyards, Notebooks, Reference Cards and much more! Click on sales on the OUGS website www.ougs.org Editorial You can opt to receive by email the colour version of this newsletter, in .pdf format. Just send an email to [email protected] Why not share your geological experiences with other members ? All contributions for the newsletter will be very welcome. We can read or scan most data formats. For photos please send the images in a separate file, preferably in jpeg (.jpg) or bitmap (.bmp) format. Most branches load their local Newsletters onto their websites so they can be accessed easily by anyone with an interest in that Branch's activities - maybe if they are visiting that area.

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OUGS Severnside Branch Committee

Janet Hiscott - Branch Organiser 01633 781557 (evenings) [email protected] Kath Addison-Scott - Treasurer 01179 538085 [email protected] Jan Ashton-Jones - Events 01432 870827 [email protected] Jan Boddy 01793 762575 [email protected] Anthony Bukowski 02920 300080 [email protected] Philip Clark 01982 560735 [email protected] Elizabeth Edmundson 01792 863119 [email protected] John de Caux - Newsletter 01633 875955 [email protected]

Severnside are going to Gaspe with Prof. Brian Williams Volcanoes on a Shoestring Going Where ? Fuerteventura and Lanzarote 2012 Gaspe, it’s a peninsular, SE Quebec, Leader – Linda Fowler Canada!! 25th February- March 7th 2012 in 2-person bungalows with pool in Caleta de When: September 10th -20th 2012 Fuste, Fuerteventura and including 2 nights on Pre-Camb. metamorphics; Cambro-Ordovician turbidites Lanzarote. (world-famous!!); The deeply eroded shield volcanoes of Silurian marine shelfal clastics and carbonates (full of Fuerteventura are an excellent opportunity to fossils); explore the associated plutonic rocks and dyke Lr - Mid - & Up. Devonian [ORS Facies] clastics with World swarms and the Jurassic and Cretaceous ocean Heritage crust into which they were intruded. In contrast, fish faunas and palaeobotany; Timanfaya National Park on Lanzarote is an active ALL of this is overlain u/c by horizontal Up. Carboniferous post-erosional volcanic area. We explored the F- coarse clastic red beds. island in late 2010 and previously visited Lanzarote in the late 1990s. Cost for 10 days i.r.o £1200 including accommodation, For more details or to express interest, flights, car hire, fuel, leaders expenses. Want to come? contact Jan Ashton-Jones Contact Jan Ashton-Jones 01432870827

Day of Lectures 2011 Venue: Museum of Wales, Cardiff Date: 4th December 2011 Time: doors of museum open at 10 am. Start asap after that. Coffee and tea will be available at start 1st lecture- given by Dr Keith Moseley, Head of Physics ,Monmouth School, Associate Lecturer, S282 Astronomy, The Open University Title: 'Planet Hunting' In 1995 the first exoplanet was discovered orbiting 51 Pegasi. By the time this presentation takes place the number may have passed 1000. Planet hunting is an example of how automation in astronomy has led to a flood of discover- ies. How is it done? What have we found and what does it tell us about the status of our own planet in our own solar system?

2nd lecture given by Lucy McCobb, Museum of Wales, Cardiff A Prehistory of Creepy-Crawlies' (essentially the fossil record of arthropods) Lunch at the Pen & Wig at about 12.45 2pm Presentations by volunteers of their holiday snaps! Please contact Janet Hiscott if you wish to do a presentation. 01633781557 email. [email protected] 3.30ish finish Contact: Jan Ashton-Jones 01432 870827 email [email protected]

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