A Building Stone Atlas of Hertfordshire
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Strategic Stone Study A Building Stone Atlas of Hertfordshire Published August 2018 Contents The Church of St Ippolyts (page 25) Introduction ...................................................................................................................................................... 1 Hertfordshire Bedrock Geology Map ................................................................................................................2 Hertfordshire Superficial Geology Map ............................................................................................................3 Stratigraphic Table ............................................................................................................................................4 The use of stone in Hertfordshire’s buildings ............................................................................................. 5-17 Background and historical context ........................................................................................................................................................................... 5 Chiltern Hills .................................................................................................................................................................................................................. 7 East Anglian Chalk ........................................................................................................................................................................................................ 8 Thames Valley .............................................................................................................................................................................................................. 10 Northern Thames Basin ............................................................................................................................................................................................. 11 South Suffolk and North Essex Clayland ................................................................................................................................................................ 12 Bedfordshire and Cambridgeshire Claylands ........................................................................................................................................................ 14 Stones in walls ........................................................................................................................................................................................................ 15-17 Hertfordshire’s indigenous building stones ............................................................................................. 18-25 Lower Cretaceous ........................................................................................................................................................................................................ 18 Upper Cretaceous........................................................................................................................................................................................................ 19 Palaeogene .................................................................................................................................................................................................................. 22 Quaternary ................................................................................................................................................................................................................... 23 Imported building stones ......................................................................................................................... 26-33 Glossary .......................................................................................................................................................... 34 Acknowledgements and References ........................................................................................................... 36 Introduction Hertfordshire lies to the north of London and is bordered by Hempstead. The limited availability of indigenous building Bedfordshire to the north, Cambridgeshire to the north-east, stone in Hertfordshire has resulted in the extensive use of Essex to the east, Buckinghamshire to the west and Greater imported stones across the county. London to the south. Hertfordshire has had a relatively stable history from the point of view of government and administra- The stratigraphy and distribution of these rocks and the tive boundary changes since the mid-1960s when Barnet Urban building stones that are sourced from them are summarised in districts were transferred to form part of the present-day the maps and stratigraphic chart that follow. The building London Borough of Barnet and the former Potters Bar Urban stones themselves are described under the headings ‘Indige- District of Middlesex was transferred to Hertfordshire. For nous’ and ‘Imported’ types and are treated in stratigraphic clarity, Hertfordshire is regarded here as the county area order. To assist the reader in navigating around the Atlas, comprising the ten districts of: Broxbourne, Dacorum, East entries in the stratigraphic table and the corresponding Hertfordshire, Hertsmere, North Hertfordshire, St Albans, descriptions are interactively linked (by means of small Stevenage, Three Rivers, Watford, and Welwyn Hatfield. Despite coloured triangles located in the upper right corner of the the spread of built-up areas, much of Hertfordshire is still given relevant pages). over to agriculture. The section of this Atlas summarising the use of stone in The rocks of Hertfordshire form part of the large shallow Hertfordshire is based on the relevant National Character Areas syncline known as the London Basin and they dip in a (NCAs), the boundaries of which are very relevant to the south-easterly direction becoming progressively younger as vernacular built heritage and are defined by a combination of one heads in that direction across the county. The oldest strata local landscape, history, cultural and economic activity, exposed at the surface in Hertfordshire occur in the north of the geodiversity and biodiversity. Six NCAs fall wholly or in part county at the foot of the chalk Chiltern Hills near Tring and within Hertfordshire: the Chilterns (NCA 110), the East Anglian Ashwell where there is a small strip of Lower Greensand, Gault Chalk (NCA 87), the Thames Valley (NCA 115), the Northern Clay and Upper Greensand sediments. South of this strip, the Thames Basin (NCA 111), the South Suffolk & North Essex Upper Cretaceous Chalk Group is present. Chalk dominates Clayland (NCA 86) and Bedfordshire and Cambridgeshire much of the bedrock geology of Hertfordshire and forms the Claylands (NCA 88). Chiltern Hills. The southern part of the county exposes younger Palaeogene sands and clays belonging mainly to the Upnor, Reading and London Clay formations. During the past 2 million years much of the bedrock geology of Hertfordshire has become covered by the accumulation of fluvial sands, gravels and silts (‘superficial deposits’); the eastern half of the county was affected by glaciers during the last Ice Age which created a thick layer of glacial boulder clays. Overall, the Cretaceous and Palaeogene successions of Hert- fordshire have yielded a limited number of stones suitable for building purposes. Both Chalk Block and Quarry Flint nodules from the Upper Cretaceous have been extensively used in the past for local building purposes. Quartz-cemented sandstones (Sarsen Stones) and Palaeogene conglomeratic beds (Hertford- shire Puddingstone) were also worked for building material and are commonly found in older buildings in the county. Tufa was very locally sourced and employed as an occasional building stone. There are no building stone quarries currently operating in Hertfordshire. Some quarrying of sand and gravel occurs in the St Albans area and in the past clay has supplied a local brick-making industry which continues today near Hemel Hertfordshire Strategic Stone Study 1 Hertfordshire Bedrock Geology Map N Ashwell N Hitchin AshwellBuntingford St Ippolyts Stevenage Bishop's Stortford Hitchin Buntingford Wilstone Wheathampstead St Ippolyts Hertford Stevenage Ashridge St Albans Bishop's Hatfield Stortford Cheshunt Wilstone Sarratt WheathampsteadWatford Hertford Borehamwood AshridgeChorleywood St Albans Bushey Heath Hatfield 0 10 20 Km Cheshunt Sarratt Watford Borehamwood Chorleywood Bushey Heath 0 10 20 Km Hertfordshire Bedrock Geology BUILDING STONE SOURCES LONDON CLAY FORMATION - CLAY, SILT AND SAND LAMBETH GROUP - CLAY, SILT AND SAND THANET FORMATION AND LAMBETH GROUP (UNDIFFERENTIATED) - CLAY, SILT AND SAND WHITE CHALK SUBGROUP - CHALK MELBOURN ROCK MEMBER - CHALK AND LIMESTONE HertfordshireGREY CHALK SUBGROU BedrockP - CHALK Geology BUILDINGTOTTERNHOE STONE STONE SOURCES MEMBER - CHALK AND CALCARENITE GAULT FORMATION AND UPPER GREENSAND FORMATION (UNDIFFERENTIATED) LONDON- MUDST ONE,CLAY SI FORMLTSTONEATION AND - SANDS CLAY, SITONELT AND SAND SELBORNE GROUP LAMBETHGAULT FORM GROUATIONP - -CL MUDSAY, SITONELT AND SAND THANEWOBURNT FORM SANDSATION FORM ANDATION LAMBETH - SANDST ONEGROUP (UNDIFFERENTIATED) - CLAY, SILT AND SAND Derived fromWHITE BGS digitalCHALK geological SUBGROU mappingP -at CHALK 1:50,000 scale, British Geological Survey © NERC. All rights reserved MELBOURN ROCK MEMBER - CHALK AND LIMESTONE Hertfordshire Strategic