The Blue Lias of south Somerset (Lead author: PJB)
The Blue Lias is a building stone long used in north Dorset, and subsequent to phasing out of quarrying at Lyme Regis, it became the staple high status nineteenth century flooring and replacement option for the whole county. From at least medieval times this stone came from south Somerset parishes between Street and Keinton Mandeville. (See Non-Dorset Quarries, Pits & Limekilns.) Uses included - indoor and outdoor flagstone paving, kerb stone guttering and street pavements, access ways and yard setting to tradesmen made of brick shaped setts placed at 90º to bedding, colour enhanced entrance ways to any building, along with steps and stairways to privately built homes and public houses. Flooring, porch entrances, tombstone/ledgers, tablets and monuments of Blue Lias are frequently found in almost every historic church in the county. Body fossils, trace fossils, burrows and calcite veining are commonly seen in the top face or base of any Blue Lias flagstone, whilst the typical very finely- laminated bedding can be seen along edges of blockwork, if laid "the right way up". Whole villages of Blue Lias block-work buildings are very common across the north Dorset county border and every possible use of Blue Lias can be seen at Somerton.
Use of this stone in Dorset was maximised during the nineteenth century and this is well illustrated from Sherborne, formerly the capital not only of Dorset but also of Cornwall and parts of Devon, it had been used and replaced regularly from medieval times; as was the shared experience of emerging towns across the county. An 1850’s Board of Health report from London, describes the difficult position for Sherborne in relation to safety of public pavements along these lines: “The footways are very unequal, owing to the want of way-wardens to compel flagging. The way-wardens, acting for the parish, will only incur the expense of (Inferior Oolite.) Sherborne flags, a rough and very inferior stone, costing when laid, 4d. a superficial foot. Where the house-owner will bear half the expense, the way-wardens will lay down Keinton flags at a cost of 6 1/2d. a foot, which though very inferior to York paving, are very superior to local flags.” Many good examples of Blue Lias use are found around Sherborne and matching examples will be found across the county. Rainfall or clean water may facilitate identification of this very, very fine grained, muddy iron rich limestone - blue if hard and impervious but buff if at all oxidised. (For historical geology and petrology see Lyme Regis under Building Stone Section, Jurassic, Blue Lias, and more under Quarries, Pits and Limekilns - Non-Dorset.)
1) The early C.16th. hexagonal 'monks’ lavatorium' has had the flooring replaced many times since it was moved into the once market place in 1554, now the Parade. Enormously disfigured, this once elaborately vaulted, castellated and windowed wash-house, is of Ham Hill and local stone. Today called the conduit, it provided lead piped water gratis and roofed over, in addition to the Abbey’s twelfth century stream, via open conduit, for market place use.
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2) Today’s Greenhill 'bus passenger shelter' stands on very mixed sized and re-cycled Blue Lias flagstones. It is also sited on the grounds of another, later and larger market place at the top of town, which with several Inns served the Royal Mail red wheeled stage coach route to London from both Exeter and Bath. Pavements are cement slabbed but today's parking area is laid out in setts of 90º Middle Purbeck stone.
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3) Refurbished Hospital Lane's historic flagged pathway with faced out setts of oxidised buff coloured stone.
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4,5 and 6) Blue Lias kerb stone has a variable lifespan and so despite some Dorset towns being highly rated for conservation, long lasting igneous stone has often been introduced. Mid 1960’s
Highways Dept. improvements reduced the number of Cornish granite setts across Cheap St. and introduced Scottish Whinstone, a hard dolerite, to replace worn Blue Lias kerb stone
throughout the town. Although this stone damages expensive alloy wheels, any stone wins out over concrete for conservation purposes. Setts and kerbstone are recycled county-wide.
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Neo-classical 1840’s Abbey House; originally all Blue Lias entrance way and set-back stone frontage. At that time, the pathway, kerb and gutter would have been all of the same stone. (Ashlar Ham Hill facing stone and porch is from the Sherborne Inferior Oolite beds.)
9. This arched access to George St. behind the George Inn, from Greenhill market place, using setts of Blue Lias would have always been preferred to even the best Sherborne Building Stone to carry iron- heeled carts and carriages. These stones will have been a conservancy matter - yet framed in dolerite!
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8.The Plume of Feathers entranceway has c.19th. ceramic tile improvements and the c.20th. pavement looks to be using resin cemented blockwork. Half Moon St. has always been damp and subject to flooding, so a sloping to gutter surface was important.
10. The once Wilmington Inn yard access shows Parish-sourced hard top face kerb stone behind which are 90º placed setts of a more oxidised Blue lias. As one looks further into the private yard there’s not only cheaper but not load-bearing brick but much harder Forest Marble along with occasional Purbeck setts.
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11. The fireplace and flooring of the Marnhull Royal Oak Inn is the c.17th. original. (Kind thanks to the Crown Inn, Marnhull)
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12. Very intact is the Pope family ledger slab also certainly of the c. 17th. St. Gregory’s, Marnhull.
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13. Preserved only by the wall this ledger near the main St. Mary Cerne Abbas doorway has otherwise, de-laminated.
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14. Outside walkway weathering reveals sparitic calcite fossils, standing proud.
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15. A typical interior flagstone floor with outlines of burrows and fossil shell outlines.
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16. Weathering of muddy matrix might also reveal veins and more trace fossils.
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References and further reading:
1)Exploring Sherborne. Gerald H.D.Pitman 1966
2) Sherborne Observed. Gerald H.D.Pitman 1983
3) For historical geology and petrology see Lyme Regis under Building Stone, Dorset/Jurassic.
4) For more see also Quarries, Pits and Limekilns.
1)Exploring Sherborne. Gerald H.D.Pitman 1966
2) Sherborne Observed. Gerald H.D.Pitman 1983
3) For historical geology and petrology see Lyme Regis under Building Stone, Dorset/Jurassic.
4) For more see also Quarries, Pits and Limekilns.
