ON THE ROCKS Newsletter of the Yorkshire Branch of the Open University Geological Society September 2018

The Honister Slate Mine – starting point for the field trip described on page 12

Branch Organiser’s Musings CONTENTS 1. Rick’s musings Welcome to the third newsletter of the year. So far, we have had five absolutely 2. Tina in Norway amazing field trips, and have now been to Ingleton, Knaresborough, Bowland, 4. AGM Date 5. Castleton field trip Castleton and Settle. Over the next few newsletters you will see many of the write 10. Free beer in Spain ups for these trips. 12. Blencathra – day 4 16. Editor’s piece In the last newsletter both and Ann and myself spoke of the need to charge a small 16. Field trips etc fee of £2 for each field trip. So far this year we have collected in £104.10. This, to be honest, confuses me as someone has given me 10p extra, do we treat it as a charitable donation? Or would you like a refund? Either way the £104.00 will be a valuable contribution to help run the branch.

Our next trip is to Norber and Crummackdale, which was the first trip I ever attended with the OUGS. It rained torrentially all day during which I can remember both Geoff and Peter using lots of new words none of which I understood! I had to ask what a syncline was, anticline, erratic and unconformity, the list was endless, but it will always hold a special place in my heart. The forthcoming trip in September will be self-led and follow the walk based on the Ramblings of Alan Stollery.

continued overleaf….. [Type here]

The Yorkshire Branch of the OUGS September 2018

From this last local trip until next year it is a bit quiet, so I am trying to arrange a possible indoor trip to the Hull area in mid-November. I’ll let you have details when I have arranged it.

Although Blencathra 2018 was fully booked we have had a cancellation so there is one last space remaining if anyone is interested. I have recently made the decision that this year’s Blencathra will be the last, but I believe running the trip has given me the confidence to organise trips further afield.

Next year, we will still be in the Lakes, but we will be learning how to complete independent mapping, which is one of the most important skills a geologist can have. We will be based at YMCA Lakeside and our mapping area will be around the area of Coniston, and our leader will be Dr Simon Drake of Birkbeck. Why not look on our website for details of the Mapping in the Lake trip.

Can I remind all members to keep their details up to date and to keep the membership secretary informed of any changes? Can I also remind you that we also have a Facebook group and are also on Twitter. @openunigeolsoc & @YorkshireOUGS

Best wishes

Ricky Savage Yorkshire OUGS Branch Organiser 07761 409807

Quest for the crinkly edges - Norway 2018 Several years ago, when on a Fossil Festival weekend walk at Staithes, I found an interesting bluish sparkling rock (Fig. 1) that was clearly not local. A fellow walker asked if I knew what it was. He explained it was a nice piece of Norwegian larvikite, an igneous stone with feldspar crystals which is more attractive when found in situ before any weathering or erosion has taken place (Fig. 2). I learned these stones could have arrived here in several ways, including glacial transport or less interestingly as ship ballast or for local Whitby sea defences, but my stone seemed far too well rounded to simply be a fragment of local sea wall.

Fig. 2 A clean-surface larvikite specimen Fig. 1 My original larvikite rock

More recently on an East Midlands OUGS trip we visited some of the local glacial-formed geology. Seeing moraines, till, and preserved bogs started a story in my head... a journey connecting how the ice carved both sides of the North Sea. I learned that my rock may have arrived via another means of transport: first carried by icebergs and then later picked up from the sea floor by glacier. What started with the larvikite became an art and geology-inspired trip to Norway to sort of 'trace' the journey. 2

The Yorkshire Branch of the OUGS September 2018

With a photography student in tow, I went searching for geology on a Hurtigruten cruise from Bergen to Kirkenes in December. I prepared for the trip by reading "The Making of a Land: Geology of Norway" by Ivar B. Ramberg, which I highly recommend. Onboard, the ship’s ‘expedition team’ staff were always helpful and though they weren’t geology experts they gave talks in English each day about local topics including some geology in layman’s terms. They even had a copy of "The Making of a Land." Perfect! Though the light and weather (blizzards!) were against us at this time of year, observing structural geology and simply finding rocks to take home were my main goals. Plus, there was plenty of time onboard to read up on topics and view passing landscapes from the open decks, not to mention sketching in the warm lounge.

Once at sea, even in the 'blue light', or civil twilight, north of the Arctic Circle it's easy to observe large scale features (Fig. 3). Being unfamiliar and half-hidden in snow, the details unfortunately eluded me, so I focused on sketching the wider field of view and then hunting for actual rock samples. Each time I went ashore on an excursion I'd look for an accessible area of rock to find a surface and take close up photos. Asking excursion leaders about local geology usually resulted in answers like "it's regular rock", so I carried on doing my own research on the ship afterwards. For samples to take home, finding pieces of rock in situ was a priority, though loose rocks I could clearly link to in situ were the next option.

Fig. 3 Civil twilight (“blue light”) Fig. 4 A coastal U-shaped valley

Early on I realised that a nice clean surface could be found by peeling away heavy moss on large rocks that had trees on them - like one from an outcrop west of Flesnes on the Lofoten islands Fig. 2).

After rocks the next quest was spotting U-shaped valleys, and the coast did not disappoint (Fig. 4). As an artist the "big picture" viewpoint from out on the water was ideal. Along with plenty of coastal U’s around Bodø and Trondheim a few unexpected observations emerged. Some areas had what appeared to be incline/syncline curves, some peaks showed lee and stoss side patterns, and there were even odd flat horizontal beddings - or so I thought I saw in the snow. With snow sitting on superficial structures, I questioned exactly what it was I was really seeing. I felt like a student again and jotted down my ideas in my sketchbook (Fig. 5). Back in the studio after the trip I returned to the big book to check it out.

While I couldn't confirm specific outcrops with incline curves, the areas were metamorphic so that hypothesis wasn't out of the question. The lee and stoss patterns also made some sense since much of the top structure of the mountains has been formed by wind, erosion, avalanches and falls (mud or snow). But the horizontal patterns remained a mystery. The best explanation I can find, if they were true structures and not just superficial, is that meltwater created progressive isomasses - new rising or falling shorelines of glacial lakes.

3

The Yorkshire Branch of the OUGS September 2018

Fig. 5 Sketchbook notes

In the end I brought home a full sketchbook and a wonderful collection of hand samples: whole piece of quartz vein from the top of Bergen, schist surfaces, marble from Bergtatt mine, granites, gneiss from the famous Ocean Road (Fig. 6), and the find of the trip a piece of limestone from WWII excavated caves at Brønnøysund (Fig. 7).

Fig. 6 A fine specimen of gneiss from Ocean Road Fig. 7 Limestone for caves at Brønnøysund

At the end of a great trip I'd trained the crew to give me the same patient yet glazed look my friends have when I excitedly show them random rocks. I even cheated and found some eclogite and a great samples box at a lovely little rock shop called Living Stone in Brygge (Bergen). All in all, I learned a lot even from a non-geology-based trip.

Report and all photos by Tina Mammoser

The AGM date for your diary The AGM, incorporating a day of talks, will be held at 10.30am on Saturday 26th January 2019 at the Swarthmore Education Centre, 2-7 Woodhouse Square, Leeds, LS3 1AD. Entry to the AGM and the first lecture is free, but to cover the afternoon speakers’ expenses a small charge will be made. It is anticipated the last talk will finish at approximately 3.45pm, and full details of the day will be given in the next newsletter. 4

The Yorkshire Branch of the OUGS September 2018

Field trip to Castleton on 9th June 2018 The field study day, led by Paul Hildreth, was attended by six members who met at 10.30 in the Peak District National Park at Castleton on a warm and sunny late Spring day.

Geology overview

Castleton sits in a dramatic landscape in an area of classical geology where Carboniferous stratigraphy dominates. Castleton is at the boundary of the White Peak country in the south (mainly limestone) forming rolling hills and farmland, and the Dark Peak in the north (mainly shales, sandstones and the Millstone Grits) forming more rugged terrain.

At Castleton there is a clear unconformity between the Mam Tor beds and the Edale/Bowland shales of the upper carboniferous (Namurian) and the lower carboniferous (Dinantian) limestone.

The early tropical marine carboniferous (350mya) formed flat and apron reefs, and had some deep water and also volcanics, this environment lasting 40 million years and produced 3km depth of limestone. The limestone lithography varies and is dependent on reef topography.

Subsequent uplift and erosion were followed by the deposition of shales and sandstones of the late carboniferous. Later the folding and uplift caused by the Variscan Orogeny generated a huge anticline dome, the associated hydro-thermals providing the local legacy of important minerals such as galena, fluorite, calcite and baryte. The early carboniferous seas had life in abundance and fossil finds include coral, algae, brachiopods, bivalves, crinoids, goniatites and plants.

The Pleistocene left its mark in the present landscape, and in the recent Holocene the Mam Tor landslide, which remains the largest active landslip in the British Isles.

Location 1 Winnats Pass (Fig. 1)

This is a steeply incised gorge which dissects a reef complex, the origin of which could either be submarine inter-reef channeling or of glacial origin.

Location 2. Odin Mine

Odin’s Mine, a disused lead mine near the village of Castleton in the Peak District National Park, is thought that the mine is the oldest in Derbyshire and to be one of the oldest lead mines in England. It was worked from Roman times until the late 19th century. Unfortunately, while we could see Odin’s Mine from the road it is now closed to visitors because of health and safety concerns and is fenced off. Fig. 1 Winnats Pass The veins that are found in the area of Castleton formed 280mya were due to faulting in the Carboniferous-aged limestones, which allowed mineral rich fluids which were heated from the basalt beneath to enter voids and fissure in the rock. Lead and sulphate combined to form the lead ore galena. Galena (PbS), the main ore of lead, has been used since ancient times and its low melting point made it easy to liberate by smelting. It typically forms in low-temperature sedimentary deposits, such as those commonly found in the Peak District.

5

The Yorkshire Branch of the OUGS September 2018

In the UK the blue, banded, fluorite known as Blue John is found only under the hill known as Treak Cliff. Today the veins are mined only in Blue John Cavern and the nearby Treak Cliff Cavern, and although the abandoned Odin’s Mine is close to both, there is no evidence of Blue John being found there.

A gritstone crushing wheel which was used to crush the ore on-site can still be seen at Odin’s Mine (Fig. 2). It is approximately 1.75m in diameter and had an iron tyre and circular iron track.

Location 3. Mam Tor

Mam Tor (Fig. 3), is a 517m hill near Castleton in the High Peak. Its name means "mother hill", so called because frequent landslips have resulted in a multitude of mini-hills beneath it. These landslips, which are caused by unstable lower layers of shale, also give the hill its alternative name of “Shivering Mountain”.

The rate of slippage depends on fluctuating ground water levels. The former A625 Manchester to Sheffield road was finally closed in 1979, after valiant efforts to repair it over decades had failed. Local people claim they can still feel the mountain shiver!

Fig. 2 The Gritstone Crushing Wheel, which cost £40 in 1823.

Mam Tor is made of rocks of Carboniferous age, approximately 320mya. The base of Mam Tor is composed of black shales of the Bowland Shale Formation overlain by turbiditic sandstone of the Mam Tor Sandstone Formation.

Mam Tor is most well-known for its active landslide. This rotational landslide began roughly 4,000 years ago, with its toe being a debris flow. The landslide is due to weak shales underlying sandstones, and this is common all around the Dark Peak area and on the north side of Mam Tor.

Fig. 3 Mam Tor Evidence for the continued movement of

the slide mass is demonstrated graphically by the severe damage to the old Mam Tor road that traversed this flow. The road was built at the beginning of the 1800s and was subsequently re-laid until local authorities closed it in 1979. Layers of tarmac and gravel are up to 2 metres thick in places, demonstrating the numerous efforts to keep the road open (Fig. 4).

Fig. 4 Evidence of slope instability and numerous attempts to repair the road.

6

The Yorkshire Branch of the OUGS September 2018

This is one of the most extreme cases of geological problems affecting main transport systems in Britain, comparable with the railway at Dawlish. Waltham & Dixon (2000) states that current mean annual movement is "up to 0.25m which increases greatly when winter rainfalls exceed thresholds of both 210 mm/month and 750mm in the preceding six months". Waltham & Dixon also suggest that deep drainage may be the most effective means of stabilizing the flow, though this may not completely stop movement.

Location 4. Edale/Bowland Shales

Shale itself is a fine-grained, sedimentary rock composed of mud that is a mix of particles of clay minerals and tiny silt-sized fragments of other minerals, especially quartz and calcite. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. It is one of the most common sedimentary rocks.

Shale typically exhibits varying degrees of fissility, breaking into thin layers, often splintery and usually parallel to the otherwise indistinguishable bedding plane because of the parallel orientation of clay mineral flakes. Non-fissile rocks of similar composition but made of particles smaller than 0.06mm are described as mudstones.

The process in the rock cycle which forms shale is called compaction. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. Shales are typically deposited in very slow-moving water and are often found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands. They can also be deposited in sedimentary basins and on the continental shelf, in relatively deep, quiet water. So, this shows the paleogeography of where the shales were formed. While walking up and over the Mam Tor landslip we found a fissile dark- grey laminated shale which yielded an interesting ancient plant fossil, Stigmaria, which represents rooting structures of swamp coal trees such as Lycopsids, which reached up to 50m in height. (Figs. 5 & 6).

Fig. 5 Shale from Mam Tor Land slip Fig.6 Stigmaria close up view with 1cm scale. with Stigmaria.

Location 5. Windy Knoll (Fig. 7)

Having left the Edale/Bowland Shales at location 4 we made our way to Windy Knoll, and a small cave exposed in a reef apron, which in the 19th century revealed over 6000 Pleistocene animal fossils. Nearby is a Neptunian Dyke of black crinoidal limestone.

The curious and rare yellow-brown, sticky Elaterite with its hydrocarbon odour oozes from the ground. Elaterite is also found in Utah and South Australia (Fig. 2). Elaterite is a brown hydrocarbon varying somewhat in consistency, being sometimes soft, elastic and sticky, like India rubber, and occasionally hard 7

The Yorkshire Branch of the OUGS September 2018

and brittle. It is usually dark brown in color and slightly translucent. Bromehead (1923) stated that “Elaterite is yellow but on exposure the colour changes to a deep brown, and the texture to an elastic solid forming the mineral known as Elaterite, or Elastic Bitumen” (Fig. 8).

Fig. 7 Windy Knoll Cave. Fig. 8 Elaterite that is easily found on the surface

Two specimens of Elaterite from Windy Knoll analysed by Macadam in 1917 had the following results:

Carbon 83.62% 82.80% Hydrogen 11.19% 11.92% Oxygen 4.78% 4.92% Nitrogen 0.17% 0.11% Sulphur 0.24% 0.25%

Location 6. The Rakes

While walking from Windy Knoll in an easterly direction multiple rakes (Fig. 9) were observed, marking the epigenetic mineral veins which have been worked by local people over generations. These were orientated at 278° and there were at least four or five that the group counted on the walk from Windy Knoll to Cave Dale. . These rakes have been mined by both surface and underground extractions mainly for lead, fluorite, baryte and calcite

Fig. 9 Photo of one of the numerous rakes

Location 6. Cave Dale Gorge

This is a classical dry valley of glacial origin, incised during post-Wolstonian melt water run-off.

Cave Dale, located at the eastern part of Castleton village, is a classic dry valley. It is a gorge that many visitors come to climb up and well known amongst walker who like a challenge. This has been incised through the limestone and it grades into the head of the Hope Valley. This was incised by run-off across frozen ground in largely post-Wolstonian times. 8

The Yorkshire Branch of the OUGS September 2018

The gorge provides an opportunity to examine in cross section the back-reef facies. A small quarry at the entrance Cave Dale and a number of abandoned adits in the sides of the gorge have been left by 17th and 18th Century miners who attempted to explore the valley sides for galena, elaterite, baryte, fluorite.

Location 7. Basalt Lava Flow (Fig. 10)

Half way down Cave Dale is an out crop of columnar basalt. From time to time volcanoes pushed up hot magma into the limestone, sometimes flowing out over the sea bed. The lava cooled to become basalt. This is the same basalt that can be seen at Dove Holes, Ox Low, Grin Low, Tideswell Dale.

The lava is vesicular, poorly columnar and known locally as “toadstone”. Vesicular basalt has a vesicular texture and is a volcanic rock texture characterized by a rock being pitted with many cavities known as vesicles. As a magma rises to the surface the pressure on it decreases. When this occurs, gasses dissolved in the magma can come out of solution, forming gas bubbles inside it. When the magma reaches the surface and the lava cools, the rock solidifies around the gas bubbles and traps them, preserving them as vesicles.

This outcrop can also be loosely described as a “Columnar Basalt”.

During the cooling of a thick lava flow, contractional joints or fractures form. These structures are predominantly hexagonal in cross-section. The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small columns, while slow cooling is more likely to produce large columns.

Fig. 10 Vesicular Columnar Basalt outcrop in Cave Dale Gorge.

Conclusion

The group returned to a bustling Castleton village in the late afternoon, having been blessed by good weather throughout the day. The group thanked Paul Hildreth for giving his time and expert leadership to the OUGS, and to Ricky Savage for organising an excellent day.

Joint report by Earl Haworth (who took all the photos) and Ricky Savage

References

1. Waltham & Dixon (2000), Movement of the Mam Tor landslide, Derbyshire, UK, The Quarterly Journal of Engineering Geology and Hydrogeology, Volume 33, Number 2, May 2000, pp. 105–123

2. Bromehead, C. E. N. (1923) “The Oil Horizons of England.,” Geological Magazine, Cambridge University Press, 60(7), pp. 297–307.

9

The Yorkshire Branch of the OUGS September 2018

Almeria - winter sun, hot rock and free beer. Are you dreading another Yorkshire winter? Are you fed up with living in a shoebox in the middle of the road watching the icicles grow? Then why not go to Almeria. It’s warm, it’s got great geology and most importantly there is a recent geology guidebook with colour photos (Harvey and Mather, 2015). Almeria is in the SE corner of Spain (Fig 1) and has very low rainfall which combined with the diverse geology produces some very unusual scenery and excellent exposure (Fig 2). Most of the rocks are under 20- million-year-old (Neogene or Quaternary), and are associated with the closing of the Tethys Ocean when North Africa collided with Southern Europe. So nearly all the geological history you learned is no use in this area.

Fig 1. (left) Major geological structures of the Almeria area

Fig 2. (above) The barranco (gorge) of the optimistically named Rio Aguas - illustrating the typical high level of exposure. Ironically, even in January, the river wasn’t carrying any agua.

Here is a quick summary of the most interesting geology. The Gypsum The Tethys has been closing for tens of millions of years and the Mediterranean Sea is all that remains of this once mighty ocean. Or so I thought. In fact, the Tethys/Mediterranean completely dried up about six million years ago. Shortly afterwards, the Atlantic Ocean broke through but the seawater dried up again - this happened several times - producing great thicknesses of evaporite deposits (Woodcock 2017). Although gypsum is a civil engineering disaster zone in the UK, it surprisingly forms a resistant rock here (Fig 3) because the high rates of evaporation have a case-hardening effect. In the Sorbas Basin, it forms a unique landscape known as gypsum-karst which Fig 3 Cliff top houses at Sorbas built on cliffs with gypsum beds. Presumably, the locals have never produces unusual topographic features, and there are visited Sunderland to admire the collapse-breccias even cave systems in gypsum which you can visit. formed when gypsum dissolve in water.

10

The Yorkshire Branch of the OUGS September 2018

The Volcanics Volcanic rocks form attractive scenery in the unspoilt Cabo de Gata coastal national park (Fig 4). These Miocene volcanic lavas and pyroclastics were formed undersea in the westernmost Mediterranean Sea and have been shunted onto the Spanish mainland by strike-slip faulting.

Fig 4. Sunset on sea stacks formed by andesitic volcanic Fig 5. The El Hoyazo Crater- is it an uplifted undersea rocks at Cabo de Gata volcano with a fringing coral reef?

A very interesting feature is the El Hoyazo Crater (Fig 5) - see Woodcock (2018). This looks like a volcanic crater but is actually an eroded volcanic neck with a coral reef forming the rim. The lavas in the crater unusually contain abundant garnets (a metamorphic mineral) which were absorbed from the host rock. These erode out easily and I managed to pick up handfuls of garnet crystals for use as Christmas presents for many years to come. The Badlands

Fig 6. Badlands topography near Tabernas. This is the Alfaro hill – a film location for Indiana Jones and the Last Crusade

Around Tabernas, the climate is even drier allowing spectacular badlands topography to develop -reminiscent of parts of the Wild West (fig 6). The area was used for filming “spaghetti” westerns in 1960s and 70s and some of the film sets can be visited. Badlands are formed when weak rocks (such as marls) become desiccated and can’t absorb rainfall so only sparse vegetation grows. When it rains heavily, the water runs off and concentrates in gullies which cut deeper into the weak rocks causing slope failure and removing the tenuous vegetation. Interestingly, the NE facing slopes are less steep and more vegetated, because there is less sunshine and less desiccation. Other features Following closure of the Tethys, the compressional regime changed to one of extensional shear which led to the development of basin and range topography. The basins contain varied types of marine and terrestrial deposits, and show interesting erosional features. There are also many topographic features such as raised beaches, river terraces, alluvial fans, and river capture evidence which can be easily interpreted without the cover deposits that we have in the UK.

11

The Yorkshire Branch of the OUGS September 2018

Logistics In winter, flights from local UK airports to Malaga, Alicante, Granada, Murcia or Almeria may be available from around £50 return. Car hire and accommodation is quite cheap in the winter. If you are travelling with non-geo companions, they may enjoy the beaches and the scenery, the birds and the flowers, and the old film sets. The towns of Almeria, Majocar and Tabernas are worth seeing and Granada can be reached in a long-day trip. References

Harvey A.K. and Mather A.E. (2015). Almeria. Classic geology in Europe 12. Dunedin Academic Press Woodcock D. (2017). Miocene-Pliocene sedimentation in the Sorbas Basin Almeria, South East Spain, and its relationship to the Messinian salinity crisis. Proceedings of the OUGS 3 p123-131 Woodcock D. (2018). A short note on the El Hoyazo crater, Almeria, South East Spain. Proceedings of the OUGS 4 p105-108 Disclaimer Other destinations are available and the beer isn’t really free!

Report and all photos by Peter Vallely

***********************************

OUGS Blencathra Field Trip 2017 – Day 4 Honister.

We parked at the Honister Slate mine car park, located at the summit of Honister Pass. Green slate is still quarried here and it is possible to buy everything from coasters to worktops in the shop. The photo on page 1 gives our starting location.

Honister is on the Birker Fell formation, which in turn is part of the Borrowdale Volcanic Group. The Birker Fell formation consists of repeated lava flows erupted from numerous low- profile volcanoes. The lava is andesitic and the eruptions were effusive.

Our steep climb towards Hopper Quarry was punctuated by several huge boulders which have been discarded as unsuitable for use as slate due to their texture. The quarry owner’s loss, however, is our gain as the boulders are rich in information for us geologists. Fig. 1 shows a large block of green slate which serves as a memorial to the reopening of the mine. The block shows a fine-grained rock with slaty cleavage, caused by metamorphism when the lava was squashed and folded. Because metamorphism was low grade, a lot of detail remains.

Fig. 1 Large block of green slate

12

The Yorkshire Branch of the OUGS September 2018

Fig. 2 Fine-grained laminations

Fig. 2 shows fine grained formed from volcanic sediments derived from fall deposits and shows embedded rip-up clasts, whilst Fig. 3 illustrates a flame structure formed when water- saturated sediment was squashed. Fig. 3 Flame structure

Fig.4 depicts a slickenside where crystals have grown on a fault plane. The chaotic relationship between the andesitic lava (dark-coloured) and wet sediment (paler-coloured) is indicated in Fig. 5. The heat of the lava turned water from the sediment to steam, causing vesicles within the lava and also fracturing the rock and leaving space for other minerals to grow.

Fig. 4 Slickenside Fig. 5 Chaotic relationship between andesitic lava and wet sediment

13

The Yorkshire Branch of the OUGS September 2018

Fig. 7 is a view of the side wall of Hopper Quarry, showing spectacular in situ examples of the features we had previously only observed in loose boulders, namely slickensides and a mix of metamorphosed andesitic lava and rock sediment.

Fig. 7 The side wall of Hopper Quarry Fig. 8 Crates of roofing slates, with Little Round How on the left

The adjacent Honister quarry enabled us to get closer to similar outcrops and see crates of roofing slates, without fear of rock falls. Tantalizing glimpses of Little Round How (¾ of the way up on the left side of Fig. 8) tempted some of the group to continue after lunch, whilst others opted for an informative and enjoyable half day at Threlkeld Quarry and Mining Museum. After getting an introduction to Little Round How we set off to explore and try to puzzle out its story.

Fig. 9 shows a debris flow of volcanic ash, containing clasts of andesitic lava. Below this are layers of sediment which have been depressed and deformed into a V shape. At bottom right of the photo are fingernail sized lumps. In cross section in Fig. 10, we can tell these lumps are ash aggregate balls (accretionary papillae).

Figure 12. Cross section of figure 11

Fig. 9 A debris flow of volcanic ash

Fig. 10 Ash aggregate balls (accretionary papillae)

14

The Yorkshire Branch of the OUGS September 2018

Everywhere we looked were laminations, some combined with accretionary papillae (Fig. 11), and several examples of block and ash (Fig. 12).

Figure 14. Laminations

Fig. 11 Accretionary papillae and laminations

Fig. 13 shows our final puzzle - rounded volcanic bombs (upper left) combined with angular lava blocks (right), indicative of a block and ash flow caused by a collapsing dome, for example.

A top day ended with us returning to the mine cafe with a sense of achievement and of having learnt a lot about volcanics in general and the Birk Fell Formation in particular. Fig. 12 (right) Block and ash

Fig. 13 Our final puzzle

Report and all photos by Heather Cuffe 15

The Yorkshire Branch of the OUGS September 2018

Editor’s piece

I hope you have enjoyed reading this latest issue of your magazine, and I’d like to thank those of you who have switched to receiving it via email. A number of members are still receiving it via post and are therefore not able to enjoy the photos in full colour. There are also some members receiving it by post because they have still not returned the completed GDPR form to the national membership secretary. They are also missing out on the emails which Rick and I send about forthcoming field trips or other items we think might be of interest. The form can be downloaded from the OUGS website at https://ougs.org/files/ouc/general/Data_Protection_2018.pdf.

As usual I am always looking for articles, photos or interesting snippets from members to include in future issues, and am still hoping to continue with the series of biographies of members and their time with the OU, but currently don’t have any to publish. So, why not share your experiences with fellow members. It doesn’t have to be long and don’t worry about the formatting as I can sort that out.

Peter Ellenger

OUGS Yorkshire Branch 2018 field trips

September - Saturday 15th Norber Erratics led by Rick Savage A walk covering 10-12 km, starting from Austwick and going to see the Norber Erratics, limestone pavement, Horton Whetstone Hole and Crummackdale Anticline – full details here October - Monday 29th - 3rd November Five-night stay at Blencathra led by James, George and Rick Savage One space remaining - full details here

If you have any queries about any of the above trips please contact Rick Savage on 07761 409807 or email him at [email protected]

Field Trip Insurance Each person attending field meetings does so on the understanding that they attend at their own risk. The OUGS has Public Liability insurance cover for field and indoor meetings, but Personal Accident cover and Personal Liability cover remain the responsibility and personal choice of participants. There may be an element of appropriate cover included in Members’ own household or travel insurance. Members should also note that they will be required to take out appropriate travel insurance for any overseas events; annual travel insurance may be the best form of cover for any member who regularly attends field events.

Other excursion and meeting opportunities There are many geology trips/lectures in Yorkshire, and elsewhere, which could be of interest. Details of these can be found on the various society websites, below: OUGS https://ougs.org/events/ LGA http://www.leedsga.org.uk/ YGS www.yorksgeolsoc.org.uk/ Down to Earth https://www.geosupplies.co.uk/ HGS www.hullgeolsoc.org.uk/ Mid-week Geology Group http://mwggyorkshire.org.uk/ Friends of Settle Carlisle Line https://www.foscl.org.uk/

16