December 2020 Newsletter
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OUGS East Anglian Branch Newsletter December 2020 From the Branch Organiser Dear All, Welcome to the last newsletter of this unbelievable year. I hope you have at least been able to take part in some of the online events detailed in the national OUGS website and bulletins. Don’t forget that any member can visit any branch activity, but you may have to contact the organiser beforehand to receive a link. The latest bulletin also contains a report of the national AGM which finally took place in October. Things are not likely to return to normal for some time and reluctantly the OUGS Committee has decided the next national AGM, that was to have been held in Glasgow on 17th April, will now be a virtual event online. Similarly, next year’s Symposium has been cancelled to avoid the possibility of unrecoverable fees. All branch AGM’s in the New Year will take place virtually. Our own branch AGM will be zoomed on 30th January, and the agenda, and minutes of the previous AGM, are included in this newsletter. I hope as many of you as possible will take part. If you’re not familiar with Zoom meetings please contact me and I will try to help, or at least point you in the right direction. You don’t have to take part on camera or even speak; just have online access to a smartphone, tablet or computer. Those of you who have elected not to receive OUGS notifications by email will need to send me your email address so we can forward you the appropriate Zoom meeting link in due course. One point to note is that, if voting, only one vote per device is possible. You can of course join and leave whenever you wish and, as I say, switch the video/mic on and off at will. We can continue to socialize post meeting if people would like, though you have to supply your own delectable buffet this year. Unfortunately I have not had any response to my requests in previous newsletters for ideas on how to move forward either while the pandemic is still with us, or suggestions for the future. I have put down an AGM agenda item for us to discuss again the future of the branch. In anticipation of trips restarting in the summer do let me have any suggestions or we can discuss them at the AGM, either in the context of the meeting or informally afterwards. I hope everyone has a Happy Christmas and it would be great to see you on 30th Jan. Phil Ridley From the Newsletter Editor As Phil says this is the last newsletter for 2020, and again we are indebted to Philip Findlay who has thankfully written another really interesting article to offset the newsletter’s otherwise mundane administrative content. This does, however, exhaust my bank of pending articles and so, apart from an initial newsletter in 2021 to circulate the minutes of the upcoming AGM, I am not sure when I will be in a position to edit a second. I am in your hands. Come on all you budding authors – your Branch needs you! Chalk (Clunch) Marks across Cambridgeshire. (by Philip Findlay) Is there chalk in Kent? Yes, there are the white cliffs of Dover. Is there chalk in Sussex? Yes, there are the white cliffs of the Seven Sisters. Is there chalk in Cambridgeshire? Yes, there are the white fields of Cambridgeshire as shown in Fig. 1. However, this view is from a satellite during that short time period when the produce has been harvested and the fields freshly prepared for the next crops. Viewed from ground level the presence of chalk in Cambridgeshire is not as immediately eye-catching as in some other counties. Fig. 1. Fields near Burwell.i This article does not contain detailed information about research concerning the geology of south Cambridgeshire; it is a summary about places visited where chalk, and in particular clunch, have left their marks in the southern parts of the county. The places visited are described in sequence travelling from east to west, from near the Suffolk border to the outskirts of Cambridge and then on to Steeple Morden near the neighbouring counties of Bedfordshire and Hertfordshire. The bedrock succession in south Cambridgeshire is shown in Fig. 2. Towards the border with Suffolk the chalk ridge rises out of the fens and the younger Cretaceous beds then dip gently towards the south-east. Compared with rises of 200m along the limestone ridge of the Cotswolds this 20m ridge is tiny but it still appears significant. Perhaps it is partly an illusion prompted in the east by the constant presence of the flat fens that stretch out to and then along the horizon. The chalk from south Cambridgeshire has long been the raw material for the production of lime for mortar and for agricultural use. Chalk is typically soft. Although chalk’s main mineral component, calcite, has a Mohs Scale hardness of 3, owing to its structure chalk itself has a hardness of only 1.ii It is permeable. When absorbed, moisture near the surface freezes, and then the chalk’s outer layers flake off. In spite of these inherent disadvantages chalk remains an important substance for modern buildings and construction works through its use as a raw material in the production of cement. Fig. 2. Bedrock succession across the Cambridgeshire chalk ridge.iii Clunch, a harder and stronger chalk than most, has been used unprocessed as a building stone. Totternhoe Stone, in a bed typically 1 to 2 metres thick but in Cambridgeshire reaching a maximum of about 7m in the Swaffham Prior area, is probably the most well-known clunch (Fig 2). It is a fine-grained calcarenite with a high proportion of small shell fragments. The location of Totternhoe Stone across South Cambridgeshire is shown in Fig. 3 with younger Cretaceous beds at the surface to the south-east and older ones to the north-west. Fig.3 Map of Totternhoe Stone bedrock across South Cambridgeshire.iv If the map shown in Fig. 3 was extended to the south-west then the Totternhoe Stone bedrock trace would be seen to run just to the north of Luton and Dunstable before passing through the Bedfordshire village of Totternhoe that gives its name to the stone. In Isleham near the Suffolk border, at the other end of the map shown in Fig.3, the Priory Church, built early in the 12th century, has lots of clunch in its walls.v In places, thin blocks have been laid in herringbone patterns, (Fig 4a). Larger blocks in the walls show the fine-grained texture and grey-white colour of the clunch, (Fig 4b). Fig. 4a Priory Church, herringbone pattern. Fig. 4b Priory Church, clunch block. There is evidence that clunch was already being quarried in Isleham from the eleventh to twelfth centuries, so the clunch in the Priory Church walls may not have travelled very far.vi In later years, the softer chalk was converted to lime in lime kilns built within the Isleham quarries. One set of lime kilns (TL 64389 74202), in use from 1860 until 1935, is still standing on the quarry floor (Fig. 5a).vii The quarry itself has also stopped working and bats have taken up residence inside the lime kilns. A public notice appeals for the bats to be left undisturbed. In fact, the whole of the old quarry has become a residential area, as it is now filled with houses making up what is now named Limestone Close. White chalk quarry walls, further reminders of the area’s past identity, are on show at the bottom of the gardens, (Fig. 5b). Fig. 5a Old quarry floor lime kilns, Isleham. Fig. 5b White chalk quarry wall behind houses in Limestone Close in the old quarry, Isleham To help make the clunch used in external walls more weather resistant the surface is often painted with lime wash but this needs to be re-applied periodically. A clunch wall alongside Mill Street, the main street in Isleham, shows both the lacelike remnants of a white lime wash coating, and also the grey-white clunch blocks weathered and crumbled where the lime wash coating has deteriorated, (Fig. 6). Fig. 6 Clunch wall with residual traces of a lime wash coating. Totternhoe Stone and the younger chalk above it are permeable but the West Melbury Marly Chalk below the Totternhoe Stone is not. In places along the chalk ridge, water that has accumulated in the chalk above emerges as springs at the bottom of the Totternhoe Stone. The existence of these springs, as well as the access to clunch that could be used for buildings, may have been important factors in the early establishment of the communities that have grown up along the Totternhoe Stone bedrock line, (Fig. 3). Burwell is one of these communities. The earliest known record of “Burwell” used as a place name is from the year 1060.viii The name means fort or fortified village by the spring.ix The name was already in use before 1143, when under the orders of King Stephen of England, the building of a castle next to the springs was started but never finished. Today the ruins of that building site lie over a wide area and these castle ruins themselves in turn sit on top of the ruins of a Roman building.x The springs and the castle ruins are in a field along the side of which runs the appropriately named “Spring Close”.