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The BGS Lexicon of Named Rock Units — Result Details

Midlands Minor Intrusive Suite

Computer Code: MMI Preferred Map Code: MMI
Status Code: Full
Age range: Ashgill Series (OA) — Ashgill Series (OA)
Lithological Description: Numerous thin sills of grey-green spessarite, lamprophyre and thicker composite sills of hornblende diorite, commonly melanocratic at the base, intruded into strata ranging from Precambrian to Ordovician (Tremadoc) age.
Definition of Lower Boundary: Not seen; no information on depth extent of the intrusive complex.
Definition of Upper Boundary: Taken at the unconformity between the sills and their host rocks and overlying strata of Devonian, Carboniferous and Triassic age.
Thickness: The individual sills range from c. 1m (lamprophyre), to about 60m (diorite). An aggregate thickness of 100 - 150m is probable
Geographical Limits: Most westerly occurrences are at the Wrekin, Shropshire. Easterly surface limit is the Nuneaton inlier, between Bedworth (SP 369 875) and Atherstone (SP 300 976).
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): 'Syenite' Or 'Diorite Intrusions'
Stratotypes:
Type Section  Griff No. 4 Quarry. 
Reference(s):
Carney, J N, Glover, B W and Pharaoh, T C. 1992. Pre-conference field excursion: Precambrian and Lower Paleozoic rocks of the English Midlands. British Geological Survey Technical Report, WA/92/72. 
Bridge, D McC, Carney, J N, Lawley, R S and Rushton, A W A. 1998. Geology of the country around Coventry and Nuneaton. Memoir of the British Geological Survey, Sheet 169 (England and Wales). 
Eastwood, T, Gibson, W, Cantrill, T C and Whitehead, T H. 1923. The geology of country around Coventry, including an account of the Carboniferous rocks of the Warwickshire Coalfield. Memoir of the Geological Survey of Great Britain, Sheet 169. (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E169