Mendips header
 Overview maps
 Locality areas
  Cheddar Gorge
 Burrington Combe
 Shipham & Rowberrow
 Crook Peak & Axbridge
 Banwell to Churchill
 Harptree & Smitham Hill
 Draycott & Westbury-sub
 Wookey Hole & Ebbor
 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
 Rocks of Mendips
 Geological timescale
 Ancient environments
 Geological structure
 Minerals and mines
  Minerals and mines
 Industrial archaeology
  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
  Flora and fauna
 Typical Mendip habitats
 Special Mendip habitats
 Horseshoe bats
 Appendix of names
 Biodiversity of western
 Biodiversity of eastern
 External links
 Detailed site information
  Coal mining
  Mendip quarry companies
  East Mendip quarries
 Biodiversity of eastern
  West Mendip quarries
 Biodiversity of western
 Site map

The rocks of Mendip

Silurian | Devonian | Lower Carboniferous | Upper Carboniferous | Triassic | Lower to Middle Jurassic

Upper Carboniferous rocks (327 to 299 million years ago)

At the beginning of the late Carboniferous the growth of the carbonate ramp that developed during the lower Carboniferous in the Mendip region was terminated by the southward spread of deltaic sandstones. Lush vegetation, comprising forests of giant tree ferns, club mosses and horsetails, colonised the delta, the rotted remains of which formed thick peat layers that were eventually transformed into coal. These events are reflected in the late Carboniferous rocks of the Mendips, which comprise the Quartzitic Sandstone Formation overlain by the Coal Measures.

Quartzitic Sandstone   Quartzitic Sandstone Formation
The Quartzitic Sandstone Formation, 45–65 m thick across the Mendip area, comprises quartz-dominated sandstone, with thin bands of sandy fissile mudstone, fossil soils (palaeosols) and very thin coals. The succession reflects a major environmental change, as deltas built by southward flowing rivers from a landmass further north covered the formerly shallow marine shelf of the Carboniferous Limestone. Fossils are rare, but the brachiopod Lingula mytilloides and the gastropod Bacunopsis have locally been recorded from a mudstone horizon.
Coal Measures
Only small areas of the Coal Measures are exposed at the surface in the Mendips, but information from nearby outcrops and boreholes shows that the succession can generally be subdivided into three broad intervals. The upper and lower intervals comprise dark non-marine mudstones with coal seams. The middle part of the succession comprises thick sandstones with few coal seams and small amounts of mudstone. These sandstones were deposited following a brief period of earth movements that marked an early stage in the uplift of a mountain chain to the south of the British Isles. Occasional thin marine mudstones with distinctive fossil assemblages ('marine bands') also occur sporadically through parts of the Coal Measures, representing periodic interruptions to the fresh-water coal swamp environment.

Fossil plant (Crossotheca sp)

  Fossil plant remains are locally abundant in the upper part of the Coal Measures, as well as rarer insect remains, the exquisitely preserved remains of which can be found amongst the spoil from old mine workings at Kilmersdon and Writhlington, near Radstock.


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