The Open University Geological Society Wessex Branch Newsletter Website http://ougs.org/wessex May 2016 Branch Organiser’s Letter CONTENTS Dear All Branch Organiser’s Letter Page 1 I hope you have all been enjoying your geology. Down Farm, Dorset, 13 March 2016 Pages 2-5 Local landslides are in the news at the moment Tedbury Camp & Vallis Vale, 28 Feb 2016 Pages 5-6 and you will find some photos of Bournemouth Bowleaze Cove, Dorset, 29 Nov 2015 Page 7 and Redcliff (above Bowleaze Cove) on pages 7 2016 AGM highlights Page 8 and 9 of this newsletter. As we point out at the A geological mystery Page 8 beginning of every field trip, we should all be Minerals guide no. 19 – Rhodochrosite Page 9 doing our own risk assessments wherever we are and highlight hazards to anyone around. Other organisations’ events Page 10 I’m certainly not going to walk along the beach Forthcoming Wessex Branch events Page 11 at Burton Bradstock or below Redcliff, and will OUGS events listing Page 12 be wary on Bournemouth prom! Wessex Branch committee Page 12 I attended Jeremy’s partner Jenny’s funeral recently. Jenny sadly lost her battle with cancer having been cared for and nursed for the and Seaton Hole on Tuesday 12th July and to past six months by Jeremy. She had a lovely see Lyme Regis coastal defences on Wednesday tribute and farewell at a woodland burial site at 13th July. For the full list, go to http://ougs.org the edge of the New Forest. Jeremy was and click on “All events”. pleased that so many of us from OUGS as well We are fortunate to have been offered a trip to as many others were able to attend. Our Moons Hill in the Mendip Hills near Shepton thoughts are with you Jeremy. Mallet on Wednesday 17th August. Numbers are I apologise I was not able to attend the OUGS limited so contact Jeremy in good time. AGM at Scarborough in April. The main news is As well as other trips in between we also have a that Associate Members now have full voting fairly recently arranged visit to Kimmeridge and rights. Also, a small increase in membership Wytch Farm in Dorset on Friday 7th October. fees was agreed, to take effect next year. The numbers are also limited for this. The There will be full details of these changes in the charge is more than usual as we have to hire a next OUGS Newsletter but in the meantime small coach to enter Wytch Farm, the cost of there’s a summary on page 8 of this newsletter. which will have to be divided amongst us so in Some of us are off to Mull in May on the the region of £15 to £20. We have been trying Wessex trip with Ian Williamson. The geology to gain access to Wytch Farm for a number of sounds fantastic. years and would like to thank our leader Giles Watts for this opportunity. Our next day trip is now confirmed for Saturday 11th June to a Ball Clay quarry in Purbeck, For all the Wessex trips contact Jeremy Cranmer Dorset. It is likely to be muddy so be prepared! on [email protected] The July Symposium on 8th to 10th July is now Good luck to those of you who are doing OU fully booked for residential places but day courses and are about to get into exam time. trippers are still very welcome – local You will soon have more time to join us on trips accommodation can be self-booked. There is a so you can consolidate your learning! full programme of field trips (open to all Best Wishes members) both before and after the Symposium weekend. South West Branch have Sheila Alderman, Branch Organiser Wessex organised five events in the Torbay GeoPark xxxxxxxxxxxxxxx from 3rd to 7th July. And there are two trips run Tel. xxxxxxxxxxxxxxxxx by Wessex after the Symposium: to Beer Head E-mail: [email protected] Wessex Footnotes May 2016 Page 1 WESSEX OUGS FIELD TRIP TO DOWN FARM, DORSET, 13 MARCH 2016 Leader: Martin Green Report by Mike Bowler and Anna Pinguey Down Farm is situated in a broad downland valley at the head of the river Allen. It forms part of Cranborne Chase, rising from Wimborne to the North Dorset escarpment. The group was led on a fascinating tour of the farm by the land owner, Martin Green, a renowned archaeologist and conservationist, on a chilly but sunny day in mid-March. Having been introduced to the group, Martin summarised the history of Down Farm and its unique position in the landscape. A relatively small farm, conventional arable farming became virtually non- viable in the late 20th century. Much of the land is now used for sheep grazing, the remainder used for conservation and educational purposes. Martin is restoring the flora and associated fauna once typical of chalk downland. The whole farm is organic but nitrate levels are still significantly above the natural state due to earlier fertiliser application, and it will take many decades before the vegetation returns to its previous state. The farm contains a rich diversity of archaeological evidence resulting from human occupation after the last Ice Age, with Mesolithic, Neolithic, Bronze Age, Roman and modern features and artefacts in abundance. Martin explained how periglacial conditions 10-20,000 years ago influenced the local geomorphology. Drainage from the north Dorset escarpment led to rivers cutting through the chalk to form an undulating landscape. Clay with flints gradually washed out. Streams (locally known as winterbournes) still appear as the water table rises in wet periods. The land to the north is peppered with springs and, for seven years out of ten, large ponds form in the lower lying areas. Martin invited the group to his museum, which features many of the artefacts found during excavations on the farm and from other locations, to provide context for the various stages of human activity over 10,000 years, including an exhibit of human remains excavated from a Bronze Age barrow in Fir Tree Field. There is also an interesting geological section with rock and fossils collected by Martin and donated by contacts. Martin then led the group on a circuit of Fir Tree Field, a rectangular field close to the farmstead. Meltwater from the last Ice Age resulted in a number of collapse features Martin Green in his museum at Down Farm caused by dissolution through fissures in the Photo by Mike Bowler underlying rock. Subsequently these features have been infilled by natural and human activity creating a unique chronological stratification. One such feature was excavated by Martin in the 1980s; the stratification and radio carbon dating techniques have established the sequence of various natural and archaeological artefacts, giving a rich and unique record of evidence. One theory is that such natural features attracted humans to deposit artefacts as offerings, perhaps seeing the pit as an entrance to the "underworld". The excavation was abandoned when the water table made further digging impossible at a Fir Tree Field shaft Photo by Mike Bowler depth of 13m, but subsequent auguring allowed an estimate of a total depth of 25m. The excavated shaft (10m in diameter) is fenced off but access was granted and viewing enhanced by a pier allowing us to gaze into the shaft from above. Wessex Footnotes May 2016 Page 2 The group paused to observe some mad March hares in an adjacent field. They seemed unperturbed by the group, possibly even curious. It felt like a privilege to witness such behaviour, as most such farmland is normally inaccessible to the public. Martin then showed us an excavated Bronze Age pond barrow where human remains had been cremated and buried in inverted pots, along with a cow burial. Three post holes were found from the entrance to the barrow aligned with nearby Pembury Knoll, which may have had some significance, and following the excavation Martin had erected new posts in situ to demonstrate the alignment. Smaller post holes within the barrow enclosure were also marked by new poles. Part of the pond barrow was covered by sheet flint, a natural flint layer which at the time of excavation was thought to be a man-made floor. Fir Tree Field pond barrow Across one corner of the field runs the Dorset Cursus, a Photo by Mike Bowler Neolithic monument which was constructed in two phases, running for almost 10km from Thickthorn Down in the south west to Martin Down in the north east. The Cursus consisted of two parallel chalk banks approximately 90m apart. This is the largest English Neolithic construction currently known. There are several theories about the purpose of the Cursus, and further reading is recommended. Most of the Cursus has been ploughed out, but a small ridge of the bank is still visible in this field, which a trench excavation in 1982 confirmed. At the top of a natural undulation in the same field, earlier excavations had discovered a Bronze Age barrow with a group of three crouch burials, two adults and a child. The burial sites have been marked and the remains retained in the museum. Before taking a break for lunch Martin showed the group a training dig site in an adjacent field, used annually by Southampton University. He also summarised some of the other activity hosted at Down Farm, including smelting and pottery workshops. In the afternoon, Martin entertained us with a very interesting demonstration of flint-knapping. He explained how black flint is more workable than 'chert' with its grey inclusions.