British Cave Research Association Field Guide to the Bath Stone Quarries, Box, Wiltshire Geology and Regional Geophysics Internal Report IR/16/031
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British Cave Research Association Field Guide to the Bath Stone quarries, Box, Wiltshire Geology and Regional Geophysics Internal Report IR/16/031 1 BRITISH GEOLOGICAL SURVEY GEOLOGY AND REGIONAL GEOPHYSICS INTERNAL REPORT British Cave Research The National Grid and other Ordnance Survey data © Crown Copyright and database rights Association Field Guide to the 2015. Ordnance Survey Licence No. 100021290 EUL. Bath Stone quarries, Box, Keywords Bath Stone Mines, Corsham, Wiltshire. Gull Caves, Chalfield oolite., Great Oolite Group, Bath oolite, cambering. National Grid Reference Andrew R Farrant, and Charlie Self NW corner 383000,170000 SE corner, 385000, 168000 Map 265, 1:50 000 scale, Bath Front cover Charlie Self examining a gull fissure backfilled with spoil in the Box quarries (Jack’s workings). Bibliographical reference A R FARRANT, C A SELF. 2016. British Cave Research Association Field Guide to the Bath Stone quarries, Box, Wiltshire. British Geological Survey Internal Report, IR/16/031. 19pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2016. All rights reserved Keyworth, Nottingham British Geological Survey 2016 3 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com BGS Central Enquiries Desk Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference collection of BGS publications, including maps, for consultation. email [email protected] We publish an annual catalogue of our maps and other publications; this catalogue is available online or from any of the BGS shops. 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Natural History Museum, Cromwell Road, London SW7 5BD Tel 020 7589 4090 Fax 020 7584 8270 Tel 020 7942 5344/45 email [email protected] Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE Tel 029 2052 1962 Fax 029 2052 1963 Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB Tel 01491 838800 Fax 01491 692345 Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Belfast BT9 5BF Tel 028 9038 8462 Fax 028 9038 8461 www.bgs.ac.uk/gsni/ Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon SN2 1EU Tel 01793 411500 Fax 01793 411501 www.nerc.ac.uk Website www.bgs.ac.uk Shop online at www.geologyshop.com 2 Contents Contents .......................................................................................................................................... 5 Figures ............................................................................................................................................ 5 1 Introduction ............................................................................................................................ 6 2 The geology of the Box area. ................................................................................................. 7 3 The formation of cambers, gulls and gull caves .................................................................. 9 4 Age of the gull caves ............................................................................................................. 17 References .................................................................................................................................... 19 Figures Figure 1. Location of underground quarry workings in the Corsham area (from Forster et al., 1985). ........................................................................................................................................ 6 Figure 2. Location of the Box quarries. .......................................................................................... 7 Figure 3. Map of the Avon valley around Bath. .............................................................................. 8 Figure 4. North-south section though the Great Oolite Group (from Forster et al., 1985) ............. 9 Figure 5. Example of camber and gull formation. ........................................................................ 10 Figure 6 Camber and gull formation in the Bath area. ChO is the Chalfield Oolite Fm; Fe - Fullers Earth Fm; FmB - Forest Marble; and InO - Inferior Oolite. ...................................... 10 Figure 7. The Gully Wood gull-caves, including Sally’s Rift. ..................................................... 12 Figure 8. Charlie Self next to a gull used for the storage of waste stone, Jack’s workings. ......... 13 Figure 9. Gulls in the Jack’s Entrance area of the Box Freestone Mine. ...................................... 14 Figure 10. Transects through Box Freestone Mine: 1. Owen Bishop Road close to Jack’s Entrance and the hillside (Jack’s Entrance to the west); and 2. Delta Rectangle Passage in the interior of the mine beneath the interfluve. Two zones of extension are apparent on Owen Bishop Road in the Jack’s Entrance area. ............................................................................... 15 Figure 11. Gulls in the Delta rectangle area of the Box Freestone Mine. ..................................... 15 Figure 12. NW-SE trending water worn gull, showing cross-bedding in the oolitic limestone picked out by dissolution. ....................................................................................................... 16 Figure 13. Smooth sided NE-SW trending gull, Delta Rectangle series. ...................................... 17 Figure 14. Phreatic half tube preserved in the roof of the passage, AO route, near the Cliftworks entrance ................................................................................................................................... 17 Figure 15. Geological map of western England. Known gulls and caves are shown as circles, whilst dated gull caves are shown as stars. Geology is based on BGS 1:625,000 scale digital data. Topography is NEXTMap Britain elevation data from Intermap Technologies. .......... 18 Figure 16. U-series data for sites in the Cotswolds (from Farrant et al., 2015). ........................... 18 5 1 Introduction The venue for the 2016 British Cave Research Association Cave Science Symposium Field Trip is the underground ‘Bath Stone’ quarries around Box, near Corsham, Wiltshire (Figure 1). The aim of the field trip is to examine the cambering and gulling, gull caves and karstic features observed in the quarries. The underground quarries at Box lie at the southern end of the Cotswold Hills, on the southern side of the By Brook valley, a tributary if the River Avon. This valley has incised though the Great Oolite Group, a sequence of Middle Jurassic (Bathonian) limestones and mudstones. The underground quarries are developed within the Chalfield Oolite Formation. This is an excellent building stone, as it can be sawn by hand in any direction as a ‘freestone’ which then hardens on exposure to air, rather than having a distinct cleavage like slate. The field trip will focus on the accessible part of the quarry complex, entered via Jack’s Entrance (Figure 2). Surveys of the quarries are available from the Shepton Mallet Caving Club. CORSHAM M5 Cardiff SPRING AND M4 TUNNEL QUARRIES Bristol Bath Box Mine Box railway tunnel Figure 1. Location of underground quarry workings in the Corsham area (from Forster et al., 1985). 6 Quarryman’s A4 Corsham Arms Cliftworks Cathedral Back Door Four Ways Box crossroads 200 m Jack’s Entrance Figure 2. Location of the Box quarries. Stone extraction in the Box area began during Roman times, initially as separate surface quarries, but then extending underground and eventually amalgamating into a single large underground network. The construction of the Box railway tunnel in 1841 led to the exploitation of stone reserves further down dip (Spring and Tunnel quarries), accessed via a railway siding from the main line. This part of the quarry is connected to the accessible workings at Box via the Wind Tunnel and Brewer’s Drift, but is sealed by the MOD. Quarrying continued until just before the Second World War when part of the site was requisitioned by the War Office in around 1935 although the older parts of the quarry were abandoned much earlier. Many mining artefacts can still be seen including old cranes, saw-sharpening benches, miners’ graffiti and old wells.