The BGS Lexicon of Named Rock Units — Result Details

Mylor Slate Formation

Computer Code: MRSL Preferred Map Code: notEntered
Status Code: Full, without ratification
Age range: Frasnian Age (DR) — Famennian Age (DA)
Lithological Description: Dark grey, locally green-grey slates, interbedded with thin bands and laminae of sandstone, graded and locally cross-bedded siltstone, basic lavas and sedimentary breccias. Sedimentary breccias are particularly significant in the upper 500 m of the formation where derived sandstone detritus occurs as contituent grains in coarse sandstone, as clasts in breccias (both matrix and clast-supported) with grey slate matrix and as large blocks of interbedded sandstone and mudstone up to several tens of metres across.
Definition of Lower Boundary: The Mylor Slate is present within the parautochthon in south Cornwall; it has a conformable lower boundary with the Porthtowan Formation of Gramscatho Group. In the field, the contact between the two Formations would be identified by a change from the grey/geen slates with sandstone, siltstone and lava to the grey and green slaty mudstones with subordinate greywacke sandstone of the Porthtowan Formation.
Definition of Upper Boundary: The upper boundary of the Mylor Slate Formation, is the Carrick thrust; this structure places the green and grey slates of the Mylor Slate Formation in abrupt contact with the Portscatho Formation of the Gramscatho Group. In the field this contact would be identified by a change from the dark grey, locally green-grey slates with interbedded sandstone, siltstone, lavas and breccias (Mylor Slate Formation) to the sandstone turbidites with interbedded grey slate of the Portscatho Formation at the base of the Carrick Nappe.
Thickness: 2000 m.
Geographical Limits: South Cornwall; west from Falmouth to Mount's Bay.
Parent Unit: Not Applicable (-)
Previous Name(s): Mylor Series (MRSR)
Mylor Beds [Obsolete Name And Code: See MRSL] (MLB)
Mylor Slates (-407)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Mylor Creek. Hill and MacAlister, 1906. 
Reference(s):
Leveridge, B E, Holder, M T and Goode, A J J, 1990. Geology of the country around Falmouth. Memoir of the British Geological Survey, Sheet 352 (England and Wales). 
Holder, M T and Leveridge, B E, 1986. A model for the tectonic evolution of south Cornwall. Journal of the Geological Society, London, Vol.143, 125-134. 
Hendriks, E M L, 1931. The stratigraphy of South Cornwall Report of the British Association for 1930, 332 et seq. 
Hendriks, E M L, 1937. Rock Succession and structure in South Cornwall, a revision. With notes on the central European facies and Variscan folding there present. Quarterly Journal of the Geological Society, London, Vol.93, 322-360. 
Hill, J B and MacCallister, D A. 1906. The geology of Falmouth and Truro and of the mining district of Camborne and Redruth. Memoirs of the Geological Survey. Explanation of Sheet 352 (England and Wales). 
Shail, R. 1989. Gramscatho-Mylor facies relationships, Hayle, south Cornwall. Proceedings of the Ussher Society, 7, 125-130. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable