Mendips header
 
 Home
 Overview maps
 Locality areas
  Cheddar Gorge
 Charterhouse
 Blackdown
 Burrington Combe
 Shipham & Rowberrow
 Crook Peak & Axbridge
 Banwell to Churchill
 Priddy
 Harptree & Smitham Hill
 Draycott & Westbury-sub
 -Mendip
 Wookey Hole & Ebbor
 Gorge
 Wells
 Great Elm & Vallis Vale
 Mells & the Wadbury Valley
 The Vobster area
 The Whatley area
 Torr Works & Asham Wood
 Beacon Hill
 Stoke St Michael & Oakhill
 Holwell & Nunney
 Shepton Mallet & Maesbury
 Gurney Slade & Emborough
 The Nettlebridge valley
 Geology
 Rocks of Mendips
 Fossils
 Geological timescale
 Ancient environments
 Geological structure
 Minerals and mines
  Minerals and mines
 Industrial archaeology
 Quarrying
  Stone as a resource
 Employment & the economy
 Quarrying & geodiversity
 Quarrying & the environment
 History of quarrying
 Caves and karst
 How caves form
 Dry valleys and gorges
 Dolines and sinkholes
 Mendip caves
 Going caving
 Hydrogeology
 Biodiversity
  Flora and fauna
 Typical Mendip habitats
 Special Mendip habitats
 Horseshoe bats
 Appendix of names
 Biodiversity of western
 Mendip
 Biodiversity of eastern
 Mendip
 External links
 Detailed site information
  Coal mining
  Mendip quarry companies
  East Mendip quarries
 Biodiversity of eastern
 Mendip
  West Mendip quarries
 Biodiversity of western
 Mendip
 Acknowledgements
 Site map
Shepton Mallet and Maesbury
The geological history of the Shepton Mallet area stretches back over 300 million years. Located at the boundary between the young Jurassic rocks and the older, harder Carboniferous strata, there is a huge variety of rocks to be seen within a small area.

The oldest rocks, including the Devonian Portishead Formation, the Avon Group mudstones and the Carboniferous Limestone outcrop on the southern side of the Beacon Hill pericline. The Black Rock Limestone is exposed in several old quarries at Windsor Hill. These quarries were opened by John Wainwright and Co. Ltd. in about 1902. In this quarry the German palaeontologist Walter Kunhe obtained a specimen of Oligokyphus, a mammal-like reptile that resembled a weasel, from a fissure infilled with Jurassic Lias Group sediments. Triassic rocks outcrop around Croscombe.

Most of Shepton Mallet is built on a shelf of Jurassic Downside Stone, a near-shore (littoral) variation of the Blue Lias limestone up to 30 m thick. On the southern side of the town, the Downside Stone rests on Triassic Mercia Mudstone and Dolomitic Conglomerate. However, to the north, it oversteps the Triassic rocks and rests directly on the underlying Carboniferous Limestone between Doulting and Downside. In places erosion has cut through the Downside Stone cover to reveal the older rocks beneath, for example in the Ham Woods valley between Windsor Hill and Croscombe.

  Aerial view of Shepton Mallet and Maesbury (click to enlarge view).

Aerial view of Shepton Mallet and Maesbury (click to enlarge view).

Cross-section cartoon N–S showing relationship of Carboniferous Limestone and Mesozoic sediments (click to enlarge view).

Cross-section cartoon N–S showing relationship of Carboniferous Limestone and Mesozoic sediments (click to enlarge view).

Building stone
Both the Downside and the Doulting Stone have been quarried for building stone. The Downside Stone, and its lateral variant, the Chilcote Stone can be seen in several disused quarries around Downside, most of which are on private land. The largest lies just north-east of the old railway viaduct on the B3136 south of Downside and shows several metres of pale white bioclastic limestone. Another quarry in Downside, now used as a builders' yard displays the striking angular unconformity between the Downside Stone and the underlying Carboniferous Black Rock Limestone.

The rocks are also exposed in Ham Woods and in a small roadside cutting in Bowlish. Here, the interbedded pale grey limestone and thin mudstone indicate a change from a near-shore (littoral) to a more offshore, but still shallow-water setting. Farther south, Downside Stone merges with the more typical deeper water Lias Group sediments.

To the east of Shepton Mallet, the Inferior Oolite or 'Doulting Stone' is still being actively quarried around Doulting. It has been used in Wells Cathedral, Glastonbury Abbey and many local buildings. It is a working quarry so permission is needed for a site visit. However, spectacular examples of the stone can be seen on Chelynch Road by the quarry entrance. The quarries here were connected by a tramway to the East Somerset Railway.
  Downside Stone quarry, Ham Woods

The Doulting 'Freestone' being quarried from St Andrews Quarry, Doulting, 1957.

Hydrogeology
Several small streams draining the sandstone on Beacon Hill sink underground on meeting the Carboniferous Limestone. At Thrupe Lane Swallet, a small stream sinks in an almost vertical cave system 120 m deep. The water from this and the other stream sinks resurges at the St Andrew's Risings in Wells.

Around Doulting are a group of springs that emerge from the base of the permeable Inferior Oolite where it overlies the impermeable Charmouth Mudstone. One of the springs is a holy well, named after St Aldhelm, the Bishop of Sherborne, who died here in 709.

  St Aldhelm's Well, a spring which rises at the base of the Inferior Oolite formation.
goto the British Geological Survey home page