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.)