The BGS Lexicon of Named Rock Units — Result Details

Cheshire - North Wales Catchments Subgroup

Computer Code: CNWCA Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Holocene Epoch (QH)
Lithological Description: Alluvial silt, sand, clay and gravel with some peat. Associated River Terraces are dominated by sand and gravel, gravelly sand or sandy gravel with rare clay and silt. The Subgroup also includes coastal and inland basin peat and a variety of mass movement deposits.
Definition of Lower Boundary: Probably unconformable and in places strongly incised into highly variable sediments of the Caledonia or Albion Glacigenic groups and bedrock.
Definition of Upper Boundary: Ground surface or unconformable below artificial deposits.
Thickness: Highly variable depending on the relative stratigraphical positions of each of the component units. In the major river valleys the thickness may vary between 2 and 5m, but probably does not exceed 10m. For deposits flanking the major river valleys, the thickness probably ranges between 1 and 3m.
Geographical Limits: Catchments of Cheshire and North Wales including the valleys and tributaries of the rivers Mersey, Weaver, Dee, Clwyd and Conway.
Parent Unit: Britannia Catchments Group (BCAT)
Previous Name(s): Swettenham Formation (-4546)
Lytham Formation (LTHM)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Catchments of the rivers Mersey, Weaver, Dee, Clwyd and Conway. Thomas, in Bowen (1999). 95pp. 
Reference(s):
Harvey, A M. 1985. The river systems of northwest England. 122-139 in Johnson, J R (Editor), The Geomorphology of northwest England. [Manchester: Manchester University Press.] 
Thomas, G S P. 1999. Northern England. 91-98 in Bowen, D Q (Editor), A revised correlation of Quaternary and Neogene deposits in the British Isles. Geological Society Special Report No.23. 
McMillan, A A, Hamblin, R J O and Merritt, J W. 2005. An overview of the lithostratigraphical framework for the Quarternary and Neogene deposits of Great Britain (onshore). British Geological Survey Research Report RR/04/04. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable