The BGS Lexicon of Named Rock Units — Result Details

Forth Catchments Subgroup

Computer Code: FORCA Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Holocene Epoch (QH)
Lithological Description: A suite of fluvial (river terrace sand and gravel and alluvium) and related lacustrine (clay, silt) and organic (peat) deposits. The fluvial sand and gravels are derived from bedrock and glacigenic sediments. Clasts are composed of mainly Palaeozoic rocks cropping out in the Midland Valley of Scotland and southern Grampian Highlands. Rock types are principally of Carboniferous and Devonian strata (sandstone, siltstone) with volcanic (basalt) and intrusive igneous rocks (microdiorite) of Midland Valley provenance. Variable but generally minor components of Dalradian metasedimentary and Caledonian intrusive igneous rocks derived from the Grampian Highlands are present.
Definition of Lower Boundary: Unconformable contact with units of the Midland Valley, Mearns and Central Grampian Glacigenic subgroups and bedrock.
Definition of Upper Boundary: Generally the ground surface, but units of the subgroup may be overlain locally by mass movement deposits or may locally interfinger with units of the British Coastal Deposits Group.
Thickness: To 25m
Geographical Limits: The present physical catchments of the River Forth and the Firth of Forth. The catchments extend across Stirlingshire, Clackmannanshire, south Fife and the Lothians.
Parent Unit: Britannia Catchments Group (BCAT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  A suite of fluvial (river terrace sand and gravel and alluvium) and related lacustrine (silt and clay) and organic (peat) deposits. The fluvial sands and gravels are derived from bedrock and glacigenic sediments. Clast rock types of the fluvial deposits include Palaeozoic rocks (sandstones, siltstones, basalt) and Dalradian metasedimentary rocks and intrusive igneous rocks cropping out in the catchments of the River Forth and other rivers flowing directly to the Firth of Forth, including the rivers Teith, Almond, Carron, Allan Water, and the rivers Esk and Tyne of the Lothians. 
Reference(s):
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