The Blue Lias (Lead author: WGT)
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The oldest of the Jurassic building stones are limestones from the Blue Lias Formation, exposed in the cliffs and foreshore east and west of Lyme Regis. These were quarried from the cliffs up to 1914 and inland, at nearby Uplyme (just in Devon), to 1920. This geological formation consists of many thin alternations of oil shale, marl and fine-grained limestones, reflecting cyclic variation in sea floor conditions, 200 million years ago, from stagnant to oxygenated. When stagnant any animal corpses which fell to the sea floor were not scavenged, so fish and reptiles are well-preserved (as found by Mary Anning in the 1820s). Anaerobic bacterial decomposition created hydrogen sulphide and, with burial, the lime muds and clays hardened into limestones and oil shales. Pyrite was formed from the sulphur and iron - the blue-grey colour of the limestone beds is due to finely disseminated pyrite.
Most of the stone used for building came from quarries in Uplyme. 
View of Blue Lias cliffs at Lyme Regis looking south-east. Photo: AH
Recent use of Blue Lias limestone. Photo: AH.
Weathered Blue Lias, garden wall Lyme Regis. Photo: WGT
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Rear of the mill in Lyme Regis. Photo: JT
Blue Lias limestones are fine-grained blue-grey lime mudstones. Bed thicknesses vary, but typically 10-45 centimetres. The stronger beds were used as worked blocks of about brick size, but the stone does not weather well, and the buildings were often rendered or hung with imported slate. Many rough walls are built of large Blue Lias cobbles from the beach. These limestones were also used for making lime mortar. In a wide area of West Dorset Blue Lias limestones were used for curbstones and large paving slabs (particularly in churches).
Ammonite and honeycomb weathering. Photo: AH
Typical Blue Lias wall in a building in Lyme Regis. (between Baptist Church and Sherborne Lane). Photo: WGT
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Slate hung wall near Lyme Regis Museum showing the original blocks of Blue Lias that had weathered. Photo: JT
Blue Lias limestones used in Lyme Regis in recent years are sourced from quarries in south Somerset (Somerton - Langport area). There is a new quarry in the Blue Lias at Keinton Mandeville, Somerset.The grey stone used in Gun Cliff Walk (the sea wall east of the river), chosen to match the colour of Blue Lias, is a very durable granite from Portugal.
Blue Lias wall with ammonites. Photo: AH
Blue Lias slab in porch of Whitchurch Canonicorum church (qv)
See also:
Industrial Lyme: Paper 5 - Stone quarrying Fowler, Harris, Osborn & England, Haycraft, Harvey, Porter, Hutchinson & Frean, Walker, Gollop, Shore, Philpot, Spoor and others. © Richard Bull & Lyme Regis Museum 2010 Revised April 2015 Quarrying the Lias at Lyme Draper J; 2001 Dorset Proceedings vol 123 (Proc. Dorset Nat. Hist. & Archaeol. Soc) WGT 22 Jan 201 |
