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):
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). 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E169