The BGS Lexicon of Named Rock Units — Result Details
Lester Slates and Sandstones Member
| Computer Code: | LSS | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full, without ratification | ||
| Age range: | Givetian Age (DV) — Givetian Age (DV) | ||
| Lithological Description: | The succession comprises dark grey to grey slates, brownish-grey sandstones (locally cross-bedded, with beds up to 1.4 m thick), gritty sandstones, siltstones and mudstones (commonly with abundant Chondrites) and thinly bedded crinoidal shelly limestone with nodules. The Holey Limestone is located near the top of the Formation: it is up to 0.8 m thick, dark grey with mudstone partings and contains corals and brachiopods. | ||
| Definition of Lower Boundary: | Obscured by folding and faulting, but likely to be gradational and conformable with the underlying Wild Pear Slates; estimated to be below the lowest thick sandstone of the overlying Lester Slates and Sandstones Member (a sequence of slates, sandstones, gritty sandstones, siltstones and mudstones). | ||
| Definition of Upper Boundary: | 10 m above the top of the Holey Limestone (a lateral equivalent of Holwill's (1964) Rillage Limestone). Below the boundary, rocks assigned to the underlying Lester Slates-and-Sandstones, are sandstones and siltstones with abundant Chondrites; the rocks at the base of the Combe Martin Slates are silvery grey, calcareous slates that are commonly silty, with thin (< 0.3 m) grey fine-grained sandstones. Chondrites are less common in the Combe Martin Slates than in the underlying Lester Slates and Sandstones. | ||
| Thickness: | From 40 to 100 m. | ||
| Geographical Limits: | South-west England. North Devon, near to Ilfracombe. | ||
| Parent Unit: | Ilfracombe Slates Formation (IFS) | ||
| Previous Name(s): | Ilfracombe Group
(ILFG)
Lester Series (LESTS) Lester Beds (LESTB) |
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| Alternative Name(s): | Rillage Limestone |
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| Stratotypes: | |||
| Type Area | Lester Point and Lester Cliff. Edmonds et al., 1985. | ||
| Reference(s): | |||
| Edmonds, E A, Whittaker, A, and Williams, B J. 1985. Geology of the country around Ilfracombe and Barnstaple. Memoir of the British Geological Survey, Sheets 277 and 293 (England and Wales). | |||
| Phillips, J. 1841. Figures and descriptions of the Palaeozoic fossils of Cornwall, Devon and west Somerset. (London: Longman, Brown, Green and Longmans). | |||
| Evans, J W. 1922. The geological structure of the country round Combe Martin. Proceedings of the Geologists' Association, Vol.33, 201-228. | |||
| Evans J W and Stubblefield C J, 1929. Handbook of the geology of Great Britain. (London: Thomas Murby & Co.) | |||
| Holwill F J W, House M R, Lane R, Gauss G A, Hendriks E M L and Dearman W R. 1969. Summer (1966) field meeting in Devon and Cornwall. Proceedings of the Geologists Association, Vol. 80, pp 43-62. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E277 | |||