Heathstone, Carstone, Ironstone (Lead author JT)
The dark brown sandstones, sometimes pebbly, used for buildings in a wide area of south and east Dorset are colloquially known as Heathstone, Carstone or Ironstone - they are cemented into a strong building stone by their iron mineral content. They all come from local sand and clay sequences that were deposited on top of the eroded surface of the Chalk.
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Basal Pebble Beds: The earliest Reading Beds and London Clay Formations contain pebble beds at their bases, deposited during a marine transgression, inundating river-flat and near-shore environments.
Outliers of these rounded pebbles in a matrix of loose sand are scattered over the Chalk Downland. The loose pebbles, reminiscent of the pebbles on Chesil Beach and between 5 and 10 cm on the long axis, have been used for roadstone. On the Edmondsham Estate the crest of Castle Hill has a deep pit in the pebble bed that contains patches of iron-cemented sand creating a conglomerate with the pebbles. Some of these conglomerate blocks are used as boundary markers, or in old rubble walls. |
London Clay Heathstone in the 12th century north wall of Canford Church. Photo: JT.
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West Park Farm Member: Large boulders are found at the base of the sand, often with pebbles and gastropod fossils on the top surface.
Warmwell Farm Sand: Within the Parish of Lytchett Matravers this has yielded small blocks of sharp-grained sandstone used for cottages in Quarr Lane, but no quarries are now visible. Three quarries were recorded in a Tudor Survey of the manor made for the landowner. [Three Tudor Surveys, 1584-1585 - The Manors of Okeford Fitzpaine, Durweston cum Knighton and Lytchett Minster. June Palmer (Ed), Dorset Record Society Vol.18, Nov. 2015].
Lytchett Matravers Sandstone: This is a very fine to medium grained (‹0.5 mm), well-sorted and rounded, ferruginous-cemented sandstone which, when used as ashlar, can be seen to be current bedded.
Warmwell Farm Sand: Within the Parish of Lytchett Matravers this has yielded small blocks of sharp-grained sandstone used for cottages in Quarr Lane, but no quarries are now visible. Three quarries were recorded in a Tudor Survey of the manor made for the landowner. [Three Tudor Surveys, 1584-1585 - The Manors of Okeford Fitzpaine, Durweston cum Knighton and Lytchett Minster. June Palmer (Ed), Dorset Record Society Vol.18, Nov. 2015].
Lytchett Matravers Sandstone: This is a very fine to medium grained (‹0.5 mm), well-sorted and rounded, ferruginous-cemented sandstone which, when used as ashlar, can be seen to be current bedded.
Current bedded Heathstone block in Corfe Mullen church
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The rounded grains of sand in Almer church are <3mm diam, coated in iron oxide. Photos: JT
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London Clay Heathstone in the 12th century north wall of Canford Church. Photo: JT.
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See Thomas, J. 2016: Note on the use of Tertiary Heathstone in buildings over the area of outcrop of the Palaeogene in the Isle of Purbeck, South-central and East Dorset. Proceedings of the Dorset Natural History & Archaeological Society. Vol. 137.
Poole Formation: This is a series of sands and clays that formed in river systems or estuaries. The sandstone from this Formation tends to be iron-cemented ‘sharp sand’ (angular grains). The sandstone used for buildings occurs as concretions, often very large, within the Broadstone Sand. I have not identified any buildings using the Branksome Sand, though there is a question about some ‘sharp sand’ sandstone in Christchurch, which could just as likely be Poole Formation. In a building they are indistinguishable. The Poole Formation Heathstones are variable, these are examples from Studland.
Poole Formation Redend Sandstone Studland, Broadstone Sand. Photo: JT
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Poole Formation on Goathorn, sand below the Oakdale Clay. Photo: JT
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All the Heathstones are found in lenses, or small patches, rather than in beds which can be followed across country. For this reason, there are few excavations or quarries specifically for Heathstone. This stone was collected for building from isolated boulders, from exposures in sand or clay pits, or occasionally from small ‘delves’ (delph or delve = a small excavation). This is in sharp contrast to the building sandstones in other parts of England, where continuous beds of well-cemented sandstone have been extensively quarried from thick deposits. The Normans used Heathstone locally, when they could find it. The early Kingston Lacy Manor house was built of Heathstone, and that was Norman. It never was easy to find.
Barton Beds: Hengistbury Head Ironstone
A marine, micrite cemented, sandy concretion. Image: PJB
There are two iron-rich sandstones in the Barton Beds, the Hengistbury Ironstone nodules and the smaller nodules from Bed G of the Barton Beds at Barton Cliff. Both of these are very fine-grained iron-rich calcareous sand. The Hengistbury nodules are large concretions. Bed G at Barton contains many small white gastropod and bivalve fossils.
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In Higher magnification: oxidised siderite (red/orange/brown ferrous carbonate) with sub-rounded/sub-angular, well-sorted fine quartz sand . In XPL birefringence: white, grey & some black grains of sand. Occasional brown-green (rusted/oxidised) glauconite pellets, many larger than in the Shaftesbury Sandstone (Upper Greensand) Image: PJB
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Barton Bed G
The images below show different views of Stone Bed G from the Barton Beds
The images below show different views of Stone Bed G from the Barton Beds
A micrite-cemented mudstone with finely comminuted shell, siderite & rare silt. Photo: PJB
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Crossed polar XPL thin section view. Comminuted shell - pink, yellow, green & blue speckles. Occasional white finest 0.005mm silt. Fine orange siderite known present. Image: PJB
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Weakly micritic cemented mudstone with articulate - (whole) - gastropod fossil shells. Photo: PJB
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Revised Jan 2020 JT/WG
