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Newsletter - September 2014

The full, illustrated newsletter is available as a pdf for download. Text extracts are given below.

Editorial

The summer seems to be over although we still have two more trips, including Paul Aplin's trip to Vernon Park and Poise Brook on 4 October. That should be really interesting so make sure you book soon. The joint trip with the OUGS to Formby is now full so if you haven't booked, sorry but you have missed out!

But with the darker nights come the Indoor Meetings and what a brilliant programme Jim Spencer put together before he stepped down as Indoor Meetings Secretary. We start on Wednesday 15 October with Dean Lomax talking on Dinosaur Diversity in the British Isles. We hear lots about dinos abroad so it will be good to hear about the ones who made their home 'around here'!

Saturday 15 November sees the first of our Saturday afternoon lectures. This afternoon is dedicated to the Zechstein Evaporites and this is followed on Saturday 6 December with lectures about Ophiolite Suites. Saturday 17 January 2015 will be The Broadhurst Lectures and more information about them will follow.

So, get your diaries out, put the lectures in and we look forward to meeting you in The Williamson Building, Oxford Road, Manchester.


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From Our Archivist, Derek Brumhead

Many will remember Robin Nicolson, who was a member of the University Geology Department between 1960 and 1994 and was a long-standing member and former President of the MGA. He now lives in Berwick-upon-Tweed. Although unfortunately he is not too well, he asked Judy, his wife, to send me a field notebook, for inclusion in our archives, that came into his possession some years ago. It is of very great interest, being a notebook (c. A6 size) of over 300 pages compiled of field excursions in the years 1910-12 by an amateur geologist, a Mr R W Palmer. The notes include a large number of field sketches. A number of the excursions are with the University of Manchester Geologists' Association (The MGA was not formed until 1925). We have several programmes of this Association in our archives so this notebook fits in very well. Mr Palmer travelled all over the country, often by train (not possible now!), walking or cycling. One week's excursion to Shropshire in July 1910 headed 'Excursion to Shropshire by myself' commences 'started on my cycle from home at 6.00 am', with a list of places he passed through. On the way he makes a visit to 'the great Keuper Marl Plain where there is an outlier of Lias beds'. He arrived at Church Stretton at 4.45 pm. The notebook is labelled 'FNB No 1'. One wonder if there were more? The excursions described are:

1910
25-28 March. Isle of Portland
30 April. Alderley Edge
7 May. Hayfield to Edale
14 May. Edale to Castleton
15 June. Northwich (alone)
9 July. Buxton via Whaley Bridge and then to Small Dale, Peak Forest, Sparrow Pit and Doveholes
13-19 July. To Shropshire by myself
9-16 August. Matlock Caverns, Belper, Peak Cavern, and includes 'an examination of a basalt pillar brought from the Giants Causeway in a garden at Holbrook, near Derby.
5 November. Lymm.
29 December. Snelston Quarry near Norbury, Derbyshire. (Lat 5258'N, 146'W)

1911
12 February. From Lancaster to Clough Pike (with Ruby and Miss Edwards)
14-21 April. Excursions along the coast in the vicinity of St Andrews, and between St Andrews, Arbroath and Dundee. Journeys by train from and back to St Andrews. (The descriptions of these excursions takes up 66 pages)
20 May. Buxton via the Goyt valley to Whaley Bridge
10 June. Llangollen
8 August. Neighbourhood of camp at Windmill Hill, Ludgershall, Andover, Wilts.
12-24 August. Isle of Wight. (21 August. Barton Beds, Christchurch Bay)

1912
4-6 April. Arran excursion.



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Tegg's Nose Rocks!

On a sunny and warm 1 June, 13 members and visitors, including a youngster from Rockwatch, joined leader, Jane Michael, to undertake this year's Fred Broadhurst memorial Field Trip. Jane gave an outline of the regional geological setting.

We were near the top of the Millstone Grit just below the Coal Measures of the Carboniferous, i.e. in the Namurian/Westphalian boundary - about 315Ma ago. We were in the tropics in an area of large braided river systems. A delta top environment was starting to develop, more like the tropical rain forest seen now in the Congo. The tall trees formed the coal seen round the area. Tegg's Nose escarpment is on the Chatsworth Grit and is apparently about 200 ft thick, including shale beds. A little way further west, some small coal seams crop out - evidence of further Westphalian deposition.

As Britain moved further north, the area became desert and the Permo-Triassic deposits of sands and muds were laid down. These could be inferred by the ironstaining seen in places. Subsequent geological history is difficult to decipher until the last glaciation, where there are various lines of evidence to show the presence of ice sheets and the erosion caused by them. We started inside the Visitor Centre, looking at the sandstone walls to find laminations together with 'escape structures'. Jane advised that these were made by the action of 'mussel-type' shells fighting to escape the deposition of sediment. This produced funnel-like structures opening upwards, like ice cream cones. Some stone blocks have, however, been inverted. In the car park, the viewpoint gave a better view of the regional geology. Examples of 'parting lineation' were seen in the four stone steps. At the car park entrance we looked at some glacial erratics. At least one has been identified as Eskdale Granite. They were left behind by the icesheets which approached from the south and west from the Irish Sea.

At the next locality, we looked west over the Cheshire Plain. Jane pointed out line of Red Rock Fault and how much flatter it was across the Cheshire Plain. The softer Cheshire Plain rocks of Permo-Triassic age (280Ma) are downthrown against the Tegg's Nose side. This faulting was probably part of a rifting system which formed the Cheshire Basin at that time. As we know, the RRF is still occasionally active - the Manchester Swarm of several years ago. What the total 'throw' was is not clear. However the Cheshire Basin is more than 2500m deep in its centre and underneath are Carboniferous rocks. At the edge near us, it is just over 500m to the base of the Permo-Triassic succession. And we were 200m higher than Macclesfield which is the other side of the fault. We turned to look back towards the Visitor Centre and noticed a gentle slope: a dip slope.

Before continuing to investigate the geology, we were able to take time to have a look at the old machinery, which is displayed near the old quarry. There are display boards explaining about the Rock Crusher, the Swing Saw and the area of paving produced with different types of setts.

We looked at the rock face: this Chatsworth Grit showed layers of well-jointed gritstone in the lower half, immediately above which was a section of tabular cross bedding. This indicated that the sand was deposited in a river channel flowing from left to right. The layers of muds and shales which "interrupt" the sandstone could represent 'splays' - flooding events The face perpendicular to the climbing wall is a fault plane. Evidence can be found to bringing a different type of material to this low-sinuosity braided river system, which was, it is thought, flowing across a delta top.

We viewed the disused quarry from several places. We climbed up to look down into the quarry and its sloping faces. The large face is a huge joint plane and the quarry men exploited this line of weakness when removing the rock. These are beds of 'massive' sandstone which dip approximately 20 to the west. The crags to the right of the path are more thinly bedded and have been used for roofing slabs and pavements. Along the path we found some blocks which showed extremely good fossil ripple marks. Facing the quarry clearly shows two faces perpendicular to one another. The wall to the left hand side (the joint plane) is now used by climbers, who were on it. In both faces it is easy to see large 'holes' in the rock: round or ovate and quite deep. Because of the climbers we did not go down into the quarry. Instead Jane pointed out what we should be able to see if we were closer.

Firstly, the 'holes' we noted from above are very crumbly. The cement holding the grains of quartz together has been attacked and it is weathering away. The holes are the result of carbonate concretions: quartz originally cemented by iron-bearing calcite, a carbonate mineral known as siderite (FeCO3) rather than silica. Groundwater removed the calcite by solution, leaving iron-stained sand which weathers very easily and a cavity remains in the rock face.

The face perpendicular to the climbing wall is a fault plane. Evidence can be found to confirm this by way of slickensides - characteristic polishing and scoring features. Jane said it was possible to find the occasional fossil of tree bark, probably from Calamites, horsetail, which forms the basis of the coal that can be found further over towards Macclesfield.

Using a map and the information board at the viewpoint, we were able to name most of the hills. In particular Bosley Minn and Mow Cop are made of Millstone Grit. Jane also pointed out that the piles of rocks behind us stretching up the hill were spoil heaps from the quarry. Nature has taken over since the demise of quarrying and it does look very natural.

As we made our way round in front of the spoil heaps, Jane stopped to look at the view and point out again the Red Rock Fault. After a short climb we reached the Tegg's Nose Summit, with a wonderful 360 panorama - the views were good all day although hazy in the very far distance so we couldn't see The Wrekin!

On our way back to the Visitor Centre we passed through a wonderful wall sculpture which had viewing holes in (based on a pin-hole camera) - despite its distance, you could see Mow Cop clearly. Although we had seen no fossils, the trip had been interesting and enjoyed by the group. Penny Heyworth, the new Outdoor Events Officer, thanked Jane on behalf of everyone.


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Macclesfield

Two weeks after the outing to Tegg's Nose, the MGA was back in Macclesfield. This time, a group of 12 met for a tour of building stones in the town, again led by Jane Michael. This trip was based on "A Geological Trail around Macclesfield' by Cheshire RIGS.

Much of the building stone seen, not surprisingly, is Carboniferous sandstone, taking advantage of local abundance coupled with lower transport costs. Typically the local sandstone is used for "everyday" purposes such as cobbles, paving, walls, and even the roofs of buildings. However, we also saw building stones from other parts of the UK, Scandinavia, even as far away as Brazil and India. The age of the building stones stretched back to 1.5 billion years.

Local sandstone is used for the wall around the bowling green in Victoria Park, where we looked for cross bedding as way-up indicators; used as sandstone flags for roofing tiles on Buxton Road; and for a relic of cobbled pavement with a decorative, but protective, edging of harder basalt. We admired the detail on the sandstone statue of a nag's head above the door of the Nag's Head (where else?). Then more locally sourced cobbles and paving on the 108 Steps and around Market Square. On the 108 Steps, Jane led the search for de-watering structures and an Ordnance Survey bench mark. We discussed and agreed the bench mark is not in its original orientation probably having re-cycled for the steps.

Red Triassic sandstone is used in the Parish Church, the United Reform Church (URC) and for statues of a rambler and the Cheshire Cat in Victoria Park, more examples of bedding and way up structures and also recent weathering.

Millstone grit has been used for the Town Hall and Costa Coffee. Pebbles are embedded in the pillars of the Town Hall, prompting one of many discussions of depositional environment and the forces required to transport different sized material.

Other examples where stone, apart from locally sourced sandstone flags, has been utilised for roofing material include slates used for the new housing along Buxton Road. Slates are a metamorphic rock formed by pressure, making splitting into thin tiles possible. This property gives slates a great advantage over heavy flags. The traditional source of slates is Wales. Slates became used more widely with easier (and cheaper) transport. Green Borrowdale slates are on the roof of the Cheshire Building Society on Castle Street. Borrowdale slates are formed from volcanic ash (tuff), which is then metamorphosed.

Biotite granite on Mill Street, described as similar to Cornish granite, prompted a discussion of biotite versus the muscovite granite used for a column in the market centre; Jane told us that the two are on a sliding scale and not mutually exclusive.

Portland limestone is used in the Parish Church and the war memorial. It is widely used as a building stone because it can be cut in any direction. We all examined the shells and the recent weathering of the war memorial. The Parish Church has an impressive font of crinoidal limestone. Crinoids are sea lilies, the stems appear as "polo mints" or ladders depending on their orientation.

Granite from Shap (Town Hall) and Ross of Mull (URC) differ in that Ross of Mull has equally sized crystals throughout, compared with Shap which has characteristic large pink feldspars, displaying their attractive twinning property, supported by smaller crystals.

Jane led us round examples of building stones from other countries. These are familiar sights on high streets and were often the "house style" of the original occupants.

Penny Heyworth


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Geo Web Watch

Most of us have access to the web either via our own computer or using our local library. There are many geo-themed websites out there and so your Editor thought it might be useful to highlight some of these each quarter.

If you have any favourite sites which you use, please let me know and I'll be pleased to include them next time.

This month I thought I would turn to some websites which enable us to keep an eye on what is going on both with respect to earthquakes and also volcanoes.

The London Volcanic Ash Advisory Centre (VAAC) is an International Civil Aviation Organization (ICAO) designated centre, responsible for issuing advisories for volcanic eruptions originating in Iceland and the north-eastern corner of the North Atlantic. It is 'hosted' by the Met Office and of course was very busy during the Eyjafjallajokull eruption in 2010.

If you are going on holiday and want to make sure there's not delays, keep your eyes on this site!!

Earthquake Hazard Monitoring. If you want to know whether there has been an earthquake somewhere today (yes, lots), then you need to visit this site. It is part of the USGS, which I mentioned last newsletter. However, this link takes you direct to a list of any and all earthquakes. Then all you need to do is click on a quake and a map and a box with more information comes up. Click on Shake Map in that box and you can find out anything you want to know about the quake: strength, intensity and potential damage.

Further links from the page take you to other earthquake related details. You can register here to receive email or text alerts when there is a quake!


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Greater Manchester RIGS

As many of you will know, Marjorie Mosley has been co-ordinating the work of GM RIGS for several years now.

Regionally Important Geological and Geomorphological Sites (RIGS), designated by locally developed criteria, are currently the most important places for geology and geomorphology outside statutorily protected land, such as Sites of Special Scientific Interest (SSSI). The designation of RIGS is one way of recognising and protecting important Earth science and landscape features for future generations to enjoy.

In this respect Greater Manchester is a bit behind some other areas of the country in assessing and then recommending for acceptance suitable sites locally. This is because there are only a very few people doing the work and Greater Manchester has a database of over 800 possible sites which need to be assessed.

Assessing the sites is not difficult and you do not need to be a professional or very experienced amateur to undertake this. You basically need to 'know the rules' (one of which is easy access - so if you can't get at it, then it probably won't qualify!) and there are various forms to complete which give you the points to look for. There is help available for anyone who is interested and you won't be 'cast adrift' with no guidance. It is also a great excuse for getting out into the countryside of Greater Manchester (yes, there is a lot of countryside, some well hidden away) and seeing new places. You also do find that your geological knowledge improves!

If you are interested, then please could you contact either Marjorie Mosley, Sue Plumb or Jane Michael. We'll then take it from there.


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